Light attenuation in a shallow, turbid reservoir, Lake Houston, Texas

USGS Publications Warehouse

Lee, Roger W.; Rast, Walter

1997-01-01

with an average error of the computed coefficient to measured value of ±13 percent. The model can be useful in computing the thickness of the euphotic zone to determine primary productivity in the reservoir.

The plumbing of the global biological pump: Efficiency control through leaks, pathways, and time scales

NASA Astrophysics Data System (ADS)

Pasquier, Benoît; Holzer, Mark

2016-08-01

We systematically quantify the pathways and time scales that set the efficiency, Ebio, of the global biological pump by applying Green-function-based diagnostics to a data-assimilated phosphorus cycle embedded in a jointly assimilated ocean circulation. We consider "bio pipes" that consist of phosphorus paths that connect specified regions of last biological utilization with regions where regenerated phosphate first reemerges into the euphotic zone. The bio pipes that contribute most to Ebio connect the Eastern Equatorial Pacific (EEqP) and Equatorial Atlantic to the Southern Ocean ((21 ± 3)% of Ebio), as well as the Southern Ocean to itself ((15 ± 3)% of Ebio). The bio pipes with the largest phosphorus flow rates connect the EEqP to itself and the subantarctic Southern Ocean to itself. The global mean sequestration time of the biological pump is 130 ± 70 years, while the sequestration time of the bio pipe from anywhere to the Antarctic region of the Southern Ocean is 430 ± 30 years. The distribution of phosphorus flowing within a given bio pipe is quantified by its transit-time partitioned path density. For the largest bio pipes, ˜1/7 of their phosphorus is carried by thermocline paths with transit times less than ˜300-400 years, while ˜4/7 of their phosphorus is carried by abyssal paths with transit times exceeding ˜700 years. The path density reveals that Antarctic Intermediate Water carries about a third of the regenerated phosphate last utilized in the EEqP that is destined for the Southern Ocean euphotic zone. The Southern Ocean is where (62 ± 2)% of the regenerated inventory and (69 ± 1)% of the preformed inventory first reemerge into the euphotic zone.

The sensitivity of primary productivity to intra-seasonal mixed layer variability in the sub-Antarctic Zone of the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Joubert, W. R.; Swart, S.; Tagliabue, A.; Thomalla, S. J.; Monteiro, P. M. S.

2014-03-01

The seasonal cycle of primary productivity is impacted by seasonal and intra-seasonal dynamics of the mixed layer through the changing balance between mixing and buoyancy forcing, which regulates nutrient supply and light availability. Of particular recent interest is the role of synoptic scale events in supplying nutrients, particularly iron, to the euphotic zone in the Sub Antarctic Zone (SAZ), where phytoplankton blooms occur throughout summer. In this study, we present high resolution measurements of net community production (NCP) constrained by ΔO2/Ar ratios, and mixed layer depth (MLD) in the Atlantic SAZ. We found a non-linear relationship between NCP and MLD, with the highest and most variable NCP observed in shallow MLDs (< 45 m). We propose that NCP variability in the SAZ may be driven by alternating states of synoptic-scale deepening of the mixed layer, leading to the entrainment of iron (dFe), followed by restratification, allowing rapid growth in an iron replete, high light environment. Synoptic iron fluxes into the euphotic zone based on water column dFe profiles and high resolution glider MLD data, reveal a potentially significant contribution of "new iron" which could sustain NCP throughout summer. Future process studies will help elaborate these findings further.

BENTHIC-PELAGIC PROCESSES IN PENSACOLA BAY, FL: EFFECTS OF LIGHT ON OXYGEN FLUXES

EPA Science Inventory

Eutrophication caused by excess nutrients can exacerbate hypoxia by increasing bottom water and sediment respiration. However, in shallow sub-tropical estuaries, the euphotic zone often extends below the pycnocline allowing oxygen fluxes in Pensacola Bay, FL, USA. Measurements we...

A Novel Anoxic Pathway for Urea and Cyanate in Marine Oxygen Deficient Zones Revealed by Combined Microbiological and Biogeochemical Tools

NASA Astrophysics Data System (ADS)

Widner, B.; Fuchsman, C. A.; Babbin, A. R.; Ji, Q.; Mulholland, M. R.

2016-02-01

Urea and cyanate are reduced nitrogen compounds that can serve as nitrogen and carbon sources for marine microbes, and cyanate forms from decomposition of urea. Some marine bacteria, including cyanobacteria, possess genes encoding an ABC-type cyanate transporter and an intracellular cyanate hydratase, and genes for urea uptake and assimilation are widespread. To investigate cyanate distribution and availability in the ocean, we recently developed a nanomolar cyanate assay specific to seawater. In an oxygenated water column, urea and cyanate concentrations are generally low in surface waters and exhibit a concentration maximum near the base of the euphotic zone likely due to production from organic matter degradation. Below the euphotic zone, urea and cyanate concentrations decrease, likely due to oxidation reactions. It has been suggested that simple organic nitrogen compounds may support anaerobic ammonium oxidation (anammox) in oxygen deficient zones (ODZs). We mapped urea and cyanate distributions and used stable isotope-labeled urea and cyanate to measure their potential support of anammox and their uptake within the Eastern Tropical North and South Pacific ODZs. We also employed metagenomic techniques to determine the abundance and distribution of genes for the uptake and assimilation of urea and cyanate. The combined data indicate that, in ODZs, urea is used primarily as a nitrogen source while cyanate is used as both a nitrogen source and to generate energy.

Importance of salt fingering for new nitrogen supply in the oligotrophic ocean.

PubMed

Fernández-Castro, B; Mouriño-Carballido, B; Marañón, E; Chouciño, P; Gago, J; Ramírez, T; Vidal, M; Bode, A; Blasco, D; Royer, S-J; Estrada, M; Simó, R

2015-09-09

The input of new nitrogen into the euphotic zone constrains the export of organic carbon to the deep ocean and thereby the biologically mediated long-term CO2 exchange between the ocean and atmosphere. In low-latitude open-ocean regions, turbulence-driven nitrate diffusion from the ocean's interior and biological fixation of atmospheric N2 are the main sources of new nitrogen for phytoplankton productivity. With measurements across the tropical and subtropical Atlantic, Pacific and Indian oceans, we show that nitrate diffusion (171±190 μmol m(-2) d(-1)) dominates over N2 fixation (9.0±9.4 μmol m(-2) d(-1)) at the time of sampling. Nitrate diffusion mediated by salt fingers is responsible for ca. 20% of the new nitrogen supply in several provinces of the Atlantic and Indian Oceans. Our results indicate that salt finger diffusion should be considered in present and future ocean nitrogen budgets, as it could supply globally 0.23-1.00 Tmol N yr(-1) to the euphotic zone.

Primary production in the northern Red Sea

NASA Astrophysics Data System (ADS)

Qurban, Mohammed Ali; Balala, Arvin C.; Kumar, Sanjeev; Bhavya, P. S.; Wafar, Mohideen

2014-04-01

Rates of uptake of carbon and nitrogen (ammonium, nitrate and urea) by phytoplankton, along with concentrations of nutrients and chlorophyll a, in the Saudi Arabian waters of the northern Red Sea (23 °N-28 °N) were measured in autumn, 2012. Concentrations of nitrate, nitrite and phosphate within the euphotic zone were in trace amounts while those of silicon were in excess of 0.5 μmol L- 1. Concentrations of chlorophyll (Chl a) were very low within the euphotic zone (0.01-0.6 μg L- 1 at discrete depths and 1.53-21.5 mg m- 2 as column-integrated values). A deep chlorophyll maximum and a nitrite maximum were present between 60 and 80 m at almost all of the stations occupied. Rates of carbon uptake at discrete depths ranged from 0.02 to 3 μg C L- 1 h- 1. Chl-normalized carbon uptake rates related with ambient light in a Michaelis-Menten kinetic pattern. About 80% of the carbon uptake was attributable to the < 20 μm fraction. Ammonium and urea were the nitrogen compounds taken up in preference by phytoplankton and accounted for close to 90% of the total N uptake. Considered together, these results indicate that the waters of the northern Red Sea are oligotrophic and that the primary production is strongly N-controlled. Analyses of the data and interpretation of the results led to the following speculations: (1) the perceived north-south gradient in Chl a (and possibly in primary production) in the Red Sea is maintained by circulation of Chl- and nutrient-rich waters through a series of gyres, (2) there is a greater role for heterotrophy and microbial loop in the trophic dynamics, and (3) in situ nitrification in the euphotic zone is an important source of N for phytoplankton and consequently export of carbon to deep sea could be lesser than that indicated by f-ratios.

Organic Matter Composition, Recycling Susceptibility, and the Effectiveness of the Biological Pump – An Evaluation Using NMR Spectra of Marine Plankton

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paytan, Adina

Carbon (C) sequestration through fertilization of phytoplankton with micronutrients and enhancement of the absorption and retention of atmospheric C by ocean biota heavily depends on the efficiency of the “biological pump”. The long-term effectiveness of this strategy depends on a net transfer of C from the upper ocean-atmosphere system to the deep ocean where the C is removed from contact with the atmosphere for an extended period of time. This C removal can be equated to the amount of C fixation by phytoplankton minus the C cycling and regeneration in the euphotic zone. If the regeneration efficiency is increased, thenmore » despite increased C fixation, no net loss (sequestration) of C will result. A reduction in cycling efficiency in the euphotic zone, on the other hand, will increase the effectiveness of the “biological pump” and thus C sequestration. The degree of organic matter biodegradation and recycling depends on the “reactivity” of compounds synthesized by the biota, which in turn, is controlled by the structural characteristic of these compounds. There is considerable evidence that different phytoplankton taxa differ substantially in their biogeochemical characteristics and it is likely that the relative abundance of different compounds synthesized by these distinct taxa, and even within each group at different growth conditions, will differ too. This variability in biosynthesis and thus abundance of a wide range of organic compounds in the water column would lend itself to different susceptibility for biodegradation and regeneration. Knowledge of the distribution of various organic matter structural groups synthesized by distinct taxa, the dependence of the organic matter compound classes on different growth conditions (temperature, light, nutrients) and the selective susceptibility of these compound to regeneration is crucial for estimating the potential for rapid regeneration in the euphotic zone, and thus the effectiveness of the “biological pump”.« less

Bacterial Diversity in the South Adriatic Sea during a Strong, Deep Winter Convection Year

PubMed Central

Korlević, M.; Pop Ristova, P.; Garić, R.; Amann, R.

2014-01-01

The South Adriatic Sea is the deepest part of the Adriatic Sea and represents a key area for both the Adriatic Sea and the deep eastern Mediterranean. It has a role in dense water formation for the eastern Mediterranean deep circulation cell, and it represents an entry point for water masses originating from the Ionian Sea. The biodiversity and seasonality of bacterial picoplankton before, during, and after deep winter convection in the oligotrophic South Adriatic waters were assessed by combining comparative 16S rRNA sequence analysis and catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). The picoplankton communities reached their maximum abundance in the spring euphotic zone when the maximum value of the chlorophyll a in response to deep winter convection was recorded. The communities were dominated by Bacteria, while Archaea were a minor constituent. A seasonality of bacterial richness and diversity was observed, with minimum values occurring during the winter convection and spring postconvection periods and maximum values occurring under summer stratified conditions. The SAR11 clade was the main constituent of the bacterial communities and reached the maximum abundance in the euphotic zone in spring after the convection episode. Cyanobacteria were the second most abundant group, and their abundance strongly depended on the convection event, when minimal cyanobacterial abundance was observed. In spring and autumn, the euphotic zone was characterized by Bacteroidetes and Gammaproteobacteria. Bacteroidetes clades NS2b, NS4, and NS5 and the gammaproteobacterial SAR86 clade were detected to co-occur with phytoplankton blooms. The SAR324, SAR202, and SAR406 clades were present in the deep layer, exhibiting different seasonal variations in abundance. Overall, our data demonstrate that the abundances of particular bacterial clades and the overall bacterial richness and diversity are greatly impacted by strong winter convection. PMID:25548042

Impact of a cyclonic eddy on phytoplankton community structure and photosynthetic competency in the subtropical North Pacific Ocean

NASA Astrophysics Data System (ADS)

Vaillancourt, Robert D.; Marra, John; Seki, Michael P.; Parsons, Michael L.; Bidigare, Robert R.

2003-07-01

A synoptic spatial examination of the eddy Haulani (17-20 November 2000) revealed a structure typical of Hawaiian cyclonic eddies with divergent surface flow forcing the upward displacement of deep waters. Hydrographic surveys revealed that surface water in the eddy center was ca. 3.5°C cooler, 0.5 saltier, and 1.4 kg m -3 denser than surface waters outside the eddy. Vertically integrated concentrations of nitrate+nitrite, phosphate and silicate were enhanced over out-eddy values by about 2-fold, and nitrate+nitrite concentrations were ca. 8× greater within the euphotic zone inside the eddy than outside. Si:N ratios were lower within the upper mixed layer of the eddy, indicating an enhanced Si uptake relative to nitrate+nitrite. Chlorophyll a concentrations were higher within the eddy compared to control stations outside, when integrated over the upper 150 m, but were not significantly different when integrated over the depth of the euphotic zone. Photosynthetic competency, assessed using fast repetition-rate fluorometry, varied with the doming of the isopycnals and the supply of macro-nutrients to the euphotic zone. The physical and chemical environment of the eddy selected for the accumulation of larger phytoplankton species. Photosynthetic bacteria ( Prochlorococcus and Synechococcus) and small (<3 μm diameter) photosynthetic eukaryotes were 3.6-fold more numerically abundant outside the eddy as compared to inside. Large photosynthetic eukaryotes (>3 μm diameter) were more abundant inside the eddy than outside. Diatoms of the genera Rhizosolenia and Hemiaulus outside the eddy contained diazotrophic endosymbiontic cyanobacteria, but these endosymbionts were absent from the cells of these species inside the eddy. The increase in cell numbers of large photosynthetic eukaryotes with hard silica or calcite cell walls is likely to have a profound impact on the proportion of the organic carbon production that is exported to deep water by sinking of senescent cells and cells grazed by herbivorous zooplankton and repackaged as large fecal pellets.

Counterintuitive effect of fall mixed layer deepening on eukaryotic new production in the Sargasso Sea

NASA Astrophysics Data System (ADS)

Fawcett, S. E.; Lomas, M. W.; Ward, B. B.; Sigman, D. M.

2012-12-01

The Sargasso Sea is characterized by a short period of deep vertical mixing in the late winter and early spring, followed by strong thermal stratification during the summer. Stratification persists into the fall, impeding the upward flux of nitrate from depth so that recycled forms of nitrogen (N) such as ammonium are thought to support most primary production. We collected particles from surface waters during March, July, October, and December, used flow cytometry to separate the prokaryotic and eukaryotic phytoplankton, and analyzed their respective 15N/14N. In all months, the 15N/14N of the prokaryotic genera, Prochlorococcus and Synechococcus, was low, indicative of reliance on recycled N throughout the year. In July, the 15N/14N of eukaryotic phytoplankton was variable but consistently higher than that of the prokaryotes, reflecting eukaryotic consumption of subsurface nitrate. Two eukaryotic profiles from October and December were similar to those from July. In three other fall profiles, the eukaryotes had a 15N/14N similar to that of the prokaryotes, suggesting a switch toward greater reliance on recycled N. This change in the dominant N source supporting eukaryotic production appears to be driven by the density structure of the upper water column. The very shallow low-density surface "mixed layer" (≤20 m) that develops in early-to-mid summer does not contribute to stratification at the base of the euphotic zone, and subsurface nitrate can mix up into the lower euphotic zone, facilitating continued production. The deepening of the mixed layer into the fall, typically taken as an indication of weaker overall stratification, actually strengthens the isolation of the euphotic zone as a whole, reducing the upward supply of nitrate to the photosynthetically active layer. The same counterintuitive dynamic explains the latitudinal patterns in a set of three October depth profiles. Two northern stations (32°N and 27°N) were characterized by a thick, low-density surface layer, and the 15N/14N of all phytoplankton was low, consistent with assimilation of recycled N. The southernmost station (23°N) had a shallower mixed layer, and eukaryote 15N/14N reflects growth on nitrate. In the subtropics, evidence for the direct supply of nitrate into surface waters in the face of the strong upper ocean stratification has long been sought. Our N isotope results suggest a mechanism by which subsurface nitrate is imported into shallow waters. This interpretation offers a new perspective on the relationship between euphotic zone stratification and nitrate assimilation, implying that significant new production occurs under conditions previously assumed to drive oligotrophy.

STABLE ISOTOPE VARIATIONS IN SUSPENDED PARTICLES IN A TEMPERATE NORTH PACIFIC ESTUARY, OREGON, USA

EPA Science Inventory

Spatial distributions of 13C and 15N in suspended particles were examined monthly over an annual cycle in the euphotic zone (0.5m) of the Yaquina River and Estuary, Oregon. Suspended organic matter in estuaries is a mixture of land-derived and oceanic carbon and nitrogen. In a...

Quantification of multiple simultaneously occurring nitrogen flows in the euphotic ocean

NASA Astrophysics Data System (ADS)

Xu, Min Nina; Wu, Yanhua; Zheng, Li Wei; Zheng, Zhenzhen; Zhao, Huade; Laws, Edward A.; Kao, Shuh-Ji

2017-03-01

The general features of the N cycle in the sunlit region of the ocean are well known, but methodological difficulties have previously confounded simultaneous quantification of transformation rates among the many different forms of N, e.g., ammonium (NH4+), nitrite (NO2-), nitrate (NO3-), and particulate/dissolved organic nitrogen (PN/DON). However, recent advances in analytical methodology have made it possible to employ a convenient isotope labeling technique to quantify in situ fluxes among oft-measured nitrogen species within the euphotic zone. Addition of a single 15N-labeled NH4+ tracer and monitoring of the changes in the concentrations and isotopic compositions of the total dissolved nitrogen (TDN), PN, NH4+, NO2-, and NO3- pools allowed us to quantify the 15N and 14N fluxes simultaneously. Constraints expressing the balance of 15N and 14N fluxes between the different N pools were expressed in the form of simultaneous equations, the unique solution of which via matrix inversion yielded the relevant N fluxes, including rates of NH4+, NO2-, and NO3- uptake; ammonia oxidation; nitrite oxidation; DON release; and NH4+ uptake by bacteria. The matrix inversion methodology that we used was designed specifically to analyze the results of incubations under simulated in situ conditions in the euphotic zone. By taking into consideration simultaneous fluxes among multiple N pools, we minimized potential artifacts caused by non-targeted processes in traditional source-product methods. The proposed isotope matrix method facilitates post hoc analysis of data from on-deck incubation experiments and can be used to probe effects of environmental factors (e.g., pH, temperature, and light) on multiple processes under controlled conditions.

An overview of mesoscales distribution of ocean color in the North Atlantic

NASA Technical Reports Server (NTRS)

Yentsch, C. S.

1989-01-01

The spatial changes in phytoplankton abundance is the result of regional differences in the amount of nutrient fluxed into the euphotic zone. The energy contributing to this flux is derived from ocean currents. A close coupling between physics and biology of the system accounts for mesoscale features associated with fluid dynamics being reflected by changes in ocean color.

STABLE ISOTOPIC INDICATORS FOR THE BIOGEOCHEMICAL CYCLING OF ORGANIC MATTER IN A TEMPERATE NORTH PACIFIC ESTUARY, OREGON, USA

EPA Science Inventory

The distributions of 13C and 15N in suspended particles were examined monthly over a two year period at ten stations along a 60 km transect in the euphotic zone (0.5m) of the Yaquina River and Estuary, Oregon. Organic material in estuaries is a mixture of land-derived and ocean...

Global assessment of ocean carbon export by combining satellite observations and food-web models

NASA Astrophysics Data System (ADS)

Siegel, D. A.; Buesseler, K. O.; Doney, S. C.; Sailley, S. F.; Behrenfeld, M. J.; Boyd, P. W.

2014-03-01

The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of 6 Pg C yr-1. Global export estimates show small variation (typically < 10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean's biological pump.

Global evaluation of particulate organic carbon flux parameterizations and implications for atmospheric pCO2

NASA Astrophysics Data System (ADS)

Gloege, Lucas; McKinley, Galen A.; Mouw, Colleen B.; Ciochetto, Audrey B.

2017-07-01

The shunt of photosynthetically derived particulate organic carbon (POC) from the euphotic zone and deep remineralization comprises the basic mechanism of the "biological carbon pump." POC raining through the "twilight zone" (euphotic depth to 1 km) and "midnight zone" (1 km to 4 km) is remineralized back to inorganic form through respiration. Accurately modeling POC flux is critical for understanding the "biological pump" and its impacts on air-sea CO2 exchange and, ultimately, long-term ocean carbon sequestration. Yet commonly used parameterizations have not been tested quantitatively against global data sets using identical modeling frameworks. Here we use a single one-dimensional physical-biogeochemical modeling framework to assess three common POC flux parameterizations in capturing POC flux observations from moored sediment traps and thorium-234 depletion. The exponential decay, Martin curve, and ballast model are compared to data from 11 biogeochemical provinces distributed across the globe. In each province, the model captures satellite-based estimates of surface primary production within uncertainties. Goodness of fit is measured by how well the simulation captures the observations, quantified by bias and the root-mean-square error and displayed using "target diagrams." Comparisons are presented separately for the twilight zone and midnight zone. We find that the ballast hypothesis shows no improvement over a globally or regionally parameterized Martin curve. For all provinces taken together, Martin's b that best fits the data is [0.70, 0.98]; this finding reduces by at least a factor of 3 previous estimates of potential impacts on atmospheric pCO2 of uncertainty in POC export to a more modest range [-16 ppm, +12 ppm].

Annual and interannual variations of phytoplankton pigment concentration and upwelling along the Pacific equator

NASA Technical Reports Server (NTRS)

Halpern, David; Feldman, Gene C.

1994-01-01

The following variables along the Pacific equator from 145 deg E to 95 deg W were employed: surface layer phytoplankton pigment concentrations derived from Nimbus 7 coastal zone color scanner (CZCS) measurements of ocean color radiances; vertical velocities simulated at the 90-m bottom of the euphotic layer from a wind-driven ocean general circulation model; and nitrate concentrations estimated from model-simulated temperature. The upward flux of nitrate into the euphotic layer was calculated from the simulated vertical motion and nitrate concentration. The CZCS-derived phytoplankton pigment concentration was uniform from 175 deg to 95 deg W. Longitudinal profiles of upwelling, phytoplankton biomass, and 90-m nitrate flux were of different shapes. The small annual cycles of the phytoplankton pigment and nitrate flux were in phase: increased phytoplankton biomass was associated with increased upward nitrate flux, but the phase was not consistent with the annual cycles of the easterly wind or of the upwelling intensity. Variation of phytoplankton pigment concentration was greater during El Nino than during the annual cycle. The substantially reduced phytoplankton pigment concentration observed during El Nino was associated with smaller upward nitrate flux. Phytoplankton biomass during non-El Nino conditions was not related to nitrate flux into the euphotic layer.

Annual Nutrient Loadings, Primary Productivity, and Trophic State of Lake Koocanusa, Montana and British Columbia, 1972-80

USGS Publications Warehouse

Woods, Paul F.

1982-01-01

Limnological data collected at Lake Koocanusa were used to investigate the relationship of nutrient loadings, primary productivity, and trophic state of the reservoir during 1972-80. The reservoir, on the Kootenai River, was impounded by Libby Dam on March 21, 1972. Manipulation of the 7.16-cubic-kilometer reservoir for flood control, its primary function, created large fluctuations in reservoir volume and produced annual lake-filling times that ranged from 0.14 to 0.66 year. Loadings of nitrogen and phosphorus prior to and following impoundment of Lake Koocanusa were found to be large enough to predict eutrophic conditions. Beginning in 1976, total phosphorus loadings, but not total nitrogen loadings, were substantially reduced following improvements in waste-water treatment at a fertilizer plant located upstream from the reservoir. The closure of Libby Dam substantially reduced loadings of nitrogen and phosphorus downstream from Lake Koocanusa. On the average, the reservoir retained 63 percent of its influent loading of total phosphorus and 25 percent of its influent loading of total nitrogen. Daily areal and volumetric primary productivity varied widely in each year at four sampled limnological stations. During the 9 years studied, daily areal primary productivity, in milligrams of carbon fixed per square meter, ranged from 0.4 to 420.0; the mean of the 313 sampled days was 128.5. Annual areal primary productivity ranged from 23.2 to 38.5 grams of carbon fixed per square meter and thereby categorized Lake Koocanusa as oligotrophic. The relationship of annual areal primary productivity and 12 selected environmental variables was determined by multiple regression analysis. One of the models that was derived used two variables-annual euphotic zone depth and annual areal phosphorus loading-and accounted for 62.0 percent of the variation in annual areal primary productivity. The distribution of chlorophyll a within the water column indicated that, on the average, more than one-half of the phytoplankton in the reservoir was beneath the euphotic zone. These results support the hypothesis that the reservoir's weak thermal structure had allowed circulation of phytoplankton out of the euphotic zone. The trophic state of Lake Koocanusa was categorized as eutrophic when based on the relationship of the nutrient loadings and the reservoir's ratio of mean depth to hydraulic-residence time. This result conflicted with the oligotrophic ranking the reservoir received based on its areal primary productivity. The discrepancy in trophic state was attributed mainly to the failure of nutrient loading models to adequately account for physical processes within reservoirs. Part of the nutrient loading that entered Lake Koocanusa was unavailable to phytoplankton because the nutrients were carried beneath the euphotic zone by large volumes of interflow and underflow. Another part of the nutrient loading was adsorbed to suspended sediment and removed from the water column. Thus, phytoplankton primary productivity was controlled not only by nutrients, but also by other limno logical processes.

The inhibition of marine nitrification by ocean disposal of carbon dioxide.

PubMed

Huesemann, Michael H; Skillman, Ann D; Crecelius, Eric A

2002-02-01

In an attempt to reduce the threat of global warming, it has been proposed that the rise of atmospheric carbon dioxide concentrations be reduced by the ocean disposal of CO2 from the flue gases of fossil fuel-fired power plants. The release of large amounts of CO2 into mid or deep ocean waters will result in large plumes of acidified seawater with pH values ranging from 6 to 8. In an effort to determine whether these CO2-induced pH changes have any effect on marine nitrification processes, surficial (euphotic zone) and deep (aphotic zone) seawater samples were sparged with CO2 for varying time durations to achieve a specified pH reduction, and the rate of microbial ammonia oxidation was measured spectrophotometrically as a function of pH using an inhibitor technique. For both seawater samples taken from either the euphotic or aphotic zone, the nitrification rates dropped drastically with decreasing pH. Relative to nitrification rates in the original seawater at pH 8, nitrification rates were reduced by ca. 50% at pH 7 and more than 90% at pH 6.5. Nitrification was essentially completely inhibited at pH 6. These findings suggest that the disposal of CO2 into mid or deep oceans will most likely result in a drastic reduction of ammonia oxidation rates within the pH plume and the concomitant accumulation of ammonia instead of nitrate. It is unlikely that ammonia will reach the high concentration levels at which marine aquatic organisms are known to be negatively affected. However, if the ammonia-rich seawater from inside the pH plume is upwelled into the euphotic zone, it is likely that changes in phytoplankton abundance and community structure will occur. Finally, the large-scale inhibition of nitrification and the subsequent reduction of nitrite and nitrate concentrations could also result in a decrease of denitrification rates which, in turn, could lead to the buildup of nitrogen and unpredictable eutrophication phenomena. Clearly, more research on the environmental effects of ocean disposal of CO2 is needed to determine whether the potential costs related to marine ecosystem disturbance and disruption can be justified in terms of the perceived benefits that may be achieved by temporarily delaying global warming.

Plankton Production Biology

DTIC Science & Technology

2012-09-30

understanding of the dynamics of the euphotic zone and the flux of particulate organic carbon (POC) into the mesopelagic (“twilight”) domain below. On p. 13...handicap of satellite-based estimates of the dynamics of primary production”. Moreover, at present we have little hope for predicting accurately from...will permit the study of stage-specific population dynamics (growth rate, production, mortality) of copepod larvae (nauplii) in mixed populations in the

Dynamics and controls of heterotrophic prokaryotic production in the western tropical South Pacific Ocean: links with diazotrophic and photosynthetic activity

NASA Astrophysics Data System (ADS)

Van Wambeke, France; Gimenez, Audrey; Duhamel, Solange; Dupouy, Cécile; Lefevre, Dominique; Pujo-Pay, Mireille; Moutin, Thierry

2018-05-01

Heterotrophic prokaryotic production (BP) was studied in the western tropical South Pacific (WTSP) using the leucine technique, revealing spatial and temporal variability within the region. Integrated over the euphotic zone, BP ranged from 58 to 120 mg C m-2 d-1 within the Melanesian Archipelago, and from 31 to 50 mg C m-2 d-1 within the western subtropical gyre. The collapse of a bloom was followed during 6 days in the south of Vanuatu using a Lagrangian sampling strategy. During this period, rapid evolution was observed in the three main parameters influencing the metabolic state: BP, primary production (PP) and bacterial growth efficiency. With N2 fixation being one of the most important fluxes fueling new production, we explored relationships between BP, PP and N2 fixation rates over the WTSP. The contribution of N2 fixation rates to bacterial nitrogen demand ranged from 3 to 81 %. BP variability was better explained by the variability of N2 fixation rates than by that of PP in surface waters of the Melanesian Archipelago, which were characterized by N-depleted layers and low DIP turnover times (TDIP < 100 h). This is consistent with the fact that nitrogen was often one of the main factors controlling BP on short timescales, as shown using enrichment experiments, followed by dissolved inorganic phosphate (DIP) near the surface and labile organic carbon deeper in the euphotic zone. However, BP was more significantly correlated with PP, but not with N2 fixation rates where DIP was more available (TDIP > 100 h), deeper in the Melanesian Archipelago, or within the entire euphotic zone in the subtropical gyre. The bacterial carbon demand to gross primary production ratio ranged from 0.75 to 3.1. These values are discussed in the framework of various assumptions and conversion factors used to estimate this ratio, including the methodological errors, the daily variability of BP, the bacterial growth efficiency and one bias so far not considered: the ability for Prochlorococcus to assimilate leucine in the dark.

The spatial distribution of particulate organic carbon and microorganisms on seamounts of the South West Indian Ridge

NASA Astrophysics Data System (ADS)

Djurhuus, A.; Read, J. F.; Rogers, A. D.

2017-02-01

We used elemental analysis, to measure particulate organic carbon (POC), and flow cytometry, to estimate abundance of microorganisms from above four seamounts (Coral, Melville, Middle of What and Atlantis) along the Southwest Indian Ridge (SWIR) from latitude 32.6°S to 41.3°S, longitude 57.1°E to 42.7°E. Samples were collected from the surface to the bottom using a CTD fitted with optical sensors. POC was predicted from models created from in-situ transmission (optical) data (cp). The high resolution predicted POC in the euphotic zone showed a heterogeneous distribution both above individual and between seamounts. The shallow penetration of two of the seamounts displayed an effect on the POC concentration in the euphotic zone depleting the layer around the summit. The transmission data showed higher concentrations of particles towards the surface, caused by primary production, and near to the seabed, probably resulting from re-suspension of sediments. The POC concentrations and microbial abundance were positively correlated to cp and fluctuated with particle abundance, with microorganisms accounting for 50% of the observed POC. Based on non-metric multidimensional scaling it is clear that the microbial clusters strongly indicate three separate biological regimes associated with northeastern, central and southwestern zones of the section of the SWIR that was sampled. This biological zonation is associated with physical oceanographic boundaries represented by the Subtropical and Subantarctic Fronts, forming three distinct "biogeographical" regions.

Novel pyropheophorbide steryl esters in Black Sea sediments

NASA Astrophysics Data System (ADS)

King, Linda L.; Repeta, Daniel J.

1991-07-01

A series of non-polar chlorophyll degradation products (NPCs) with greater than 10 components has been isolated from Black Sea sediment and identified as pyropheophorbide steryl esters by visible and mass spectrometry. These compounds have been previously observed in seawater and sediment trap samples, and may be formed during grazing of phytoplankton by zooplanktonic herbivores. In Black Sea sediments, NPCs constitute 14% of the total phorbins determined spectroscopically at 660 nm, and 39% of the total chlorophyll degradation products measured by high pressure liquid chromatography. NPCs therefore constitute a significant sedimentary sink for chlorophyll. The distribution of sterols released by hydrolysis of NPCs most closely resembles sterols in suspended particulate matter collected from the euphotic zone and is quite different from the distribution of solvent-extractable sterols in sediments. Sterols extracted from sediments have high concentrations of 4-methylsterols and high stanol/stenol ratios. NPC-derived sterols have very low concentrations of 4-methylsterols and low stanol/stenol ratios. We suggest that these differences reflect an enhanced preservation of NPCs in sediments relative to free sterols and phorbins. As a result, the original production of sterols in the euphotic zone may be more closely approximated by the distribution of NPC-derived sterols than by the distribution of free sterols in sediments.

Novel pyropheophorbide steryl esters in Black Sea sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, L.L.; Repeta, D.J.

1991-07-01

A series of non-polar chlorophyll degradation products (NPCs) with greater than 10 components has been isolated from Black Sea sediment and identified as pyropheophorbide steryl esters by visible and mass spectrometry. These compounds have been previously observed in seawater and sediment trap samples, and may be formed during grazing of phytoplankton by zooplanktonic herbivores. In Black Sea sediments, NPCs constitute 14% of the total phorbins determined spectroscopically at 660 nm, and 39% of the total chlorophyll degradation products measured by high pressure liquid chromatography. NPCs therefore constitute a significant sedimentary sink for chlorophyll. The distribution of sterols released by hydrolysismore » of NPCs most closely resembles sterols in suspended particulate matter collected from the euphotic zone and is quite different from the distribution of solvent-extractable sterols in sediments. Sterols extracted from sediemtns have high concentrations of 4-methylsterols and high stanol/stenol ratios. BNPC-derived sterols have very low concentrations of 4-methylsterols and low stanol/stenol ratios. The authors suggest that these differences reflect an enhanced preservation of HPCs in sediments relative to free sterols and phorbins. As a result, the original production of sterols in the euphotic zone may be more closely approximated by the distribution of NPC-derived sterols than by the distribution of free sterols in sediments.« less

Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California

USGS Publications Warehouse

Wankel, Scott D.; Kendall, C.; Pennington, J.T.; Chavez, F.P.; Paytan, A.

2007-01-01

Coupled measurements of nitrate (NO3-), nitrogen (N), and oxygen (O) isotopic composition (??15NNO3 and ??18ONO3) were made in surface waters of Monterey Bay to investigate multiple N cycling processes occurring within surface waters. Profiles collected throughout the year at three sites exhibit a wide range of values, suggesting simultaneous and variable influence of both phytoplankton NO3- assimilation and nitrification within the euphotic zone. Specifically, increases ??18ONO3 were consistently greater than those in ??15NN03. A coupled isotope steady state box model was used to estimate the amount of NO3- supplied by nitrification in surface waters relative to that supplied from deeper water. The model highlights the importance of the branching reaction during ammonium (NH4+) consumption, in which NH4+ either serves as a substrate for regenerated production or for nitrification. Our observations indicate that a previously unrecognized proportion of nitrate-based productivity, on average 15 to 27%, is supported by nitrification in surface waters and should not be considered new production. This work also highlights the need for a better understanding of isotope effects of NH4+ oxidation, NH4+ assimilation, and NO4+ assimilation in marine environments.

Modelling Biogenic Carbon Cycling and Remineralization In The Mesopelagic. 2. Rates and Patterns.

NASA Astrophysics Data System (ADS)

Rivkin, R. B.; Legendre, L.; Nagata, T.; Bussey, H.; Matthews, P.; Churchill, D.

Both dissolved (DOC) and particulate organic carbon (POC) are exported from the surface ocean into the mesopelagic layer (i.e. twilight zone; ~100 to 1000 m). Rela- tively little is known about processes controlling the fate and loss rates of this biogenic carbon (BC). Trap studies suggest that about 90% of the POC that is exported from the euphotic zone is remineralized between 100 and 1000m, however the remineral- ization of DOC is largely uncharacterized. The BC that is transferred or buried below the permanent pycnocline (i.e. sequestration, S) is isolated from the atmosphere for long periods (from hundred to million years) and is therefore of significance to global climate. The sequestration of BC can be computed from euphotic zone export (E) and the subsequent remineralization (R) of BC in the mesopelagic layer. Since both POC and DOC are respired, sequestration can be estimated as S = E - R. Unfortunately there are very few direct measurements of R in the mesopelagic layer. We therefore estimated this property, at the global scale, from a meta-analysis of the distributions of physical, chemical and bacterial properties in the mesopelagic layer. We computed heterotrophic respiration from empirical relationships among temperature, DOC, and bacterial biomass, production and growth efficiency. Preliminary estimates of R are 11 to 35 (mean = 22) Gt C/year for the World Ocean. These values are 28 to 88% of the computed upper ocean respiration of ~40 Gt C/y. These data suggest that global dissolved and particulate primary production may be >75 Gt/y.

Temporal dynamics of phytoplankton and heterotrophic protists at station ALOHA

NASA Astrophysics Data System (ADS)

Pasulka, Alexis L.; Landry, Michael R.; Taniguchi, Darcy A. A.; Taylor, Andrew G.; Church, Matthew J.

2013-09-01

Pico- and nano-sized autotrophic and heterotrophic unicellular eukaryotes (protists) are an important component of open-ocean food webs. To date, however, no direct measurements of cell abundance and biomass of these organisms have been incorporated into our understanding of temporal variability in the North Pacific Subtropical Gyre (NPSG). Based primarily on epifluoresence microscopy augmented with flow cytometry, we assessed the abundance and biomass of autotrophs and heterotrophic protists at Station ALOHA between June 2004 and January 2009. Autotrophic eukaryotes (A-EUKS) were more abundant in both the upper euphotic zone and deep chlorophyll maximum layer (DCML) during winter months, driven mostly by small flagellates. A higher ratio of A-EUKS to heterotrophic protists (A:H ratio) and a structural shift in A-EUKS to smaller cells during the winter suggests a seasonal minimum in grazing pressure. Although Prochlococcus spp. comprised between 30% and 50% of autotrophic biomass in both the upper and lower euphotic zone for most of the year, the community structure and seasonality of nano- and micro-phytoplankon differed between the two layers. In the upper layer, Trichodesmium spp. was an important contributor to total biomass (20-50%) in the late summer and early fall. Among A-EUKS, prymnesiophytes and other small flagellates were the dominant contributors to total biomass in both layers regardless of season (10-20% and 13-39%, respectively). Based on our biomass estimates, community composition was less seasonally variable in the DCML relative to the upper euphotic zone. In surface waters, mean estimates of C:Chl a varied with season—highest in the summer and lowest in the winter (means=156±157 and 89±32, respectively); however, there was little seasonal variability of C:Chl a in the DCML (100 m mean=29.9±9.8). Biomass of heterotrophic protists peaked in the summer and generally declined monotonically with depth without a deep maximum. Anomalous patterns of A:H variability during summer 2006 (low mesozooplankton, high A-EUKS and H-dinoflagellates) suggest that top-down forcing is strong enough to impact lower trophic levels in the NPSG. Continued studies of community abundance and biomass relationships are needed for adequate representations of plankton dynamics in ecosystem models and for developing a predictive understanding of both intra- and inter-lower trophic level responses to climate variability in the NPSG.

Post-obduction carbonate system development in New Caledonia (Népoui, Lower Miocene)

NASA Astrophysics Data System (ADS)

Maurizot, Pierre; Cabioch, Guy; Fournier, François; Leonide, Philippe; Sebih, Salim; Rouillard, Pierrick; Montaggioni, Lucien; Collot, Julien; Martin-Garin, Bertrand; Chaproniere, George; Braga, Juan C.; Sevin, Brice

2016-01-01

For the first time, depositional models of Lower Miocene carbonate systems from New Caledonia (Southwest Pacific) are proposed, on the basis of a sedimentological and paleoenvironmental study of both cores and outcrops. In the Népoui area, two distinct stages of carbonate ramp development (Aquitanian Lower Népoui and Burdigalian Upper Népoui carbonate systems), separated by a phase of siliciclastic deltaic deposition, are evidenced. The post-obduction marine transgression of the Western New Caledonian margin occurred at approximately 24 Ma and is characterized by the development of an aggrading foraminiferal-coralline algal-scleractinian ramp system ("Chapeau Chinois Limestone") during the early Aquitanian (24-23 Ma). A retrogradational event is evidenced at approximately 23 Ma followed by the development of a shallowing upward carbonate unit (Operculina "Green Sands" and Xuudhen Limestone) during the late Aquitanian. This unit is topped by a major erosional unconformity overlain by conglomeratic deposits ("Pindaï conglomerates"), and interpreted to record a significant uplift at around 21-19 Ma. During the Burdigalian, a marine transgression occurred at around 19 Ma, followed by the development of a low-angle carbonate ramp or open platform ("Népü Limestone") up to the late Burdigalian (19-17 Ma). In both Aquitanian and Burdigalian carbonate ramps, extensive sea-grass meadows are shown to have colonized the proximal ramp environments within the euphotic zone. In the Aquitanian carbonate ramp (Lower Népoui Formation), carbonate production within sea-grass meadows is dominated by large benthic foraminifera, together with red algae and sparse scleractinians. Mesophotic environments are characterized by large and flat lepidocyclinids, rhodoliths and platy corals whereas in deeper oligophotic settings significant carbonate producers consist mainly of large and flat benthic foraminifera. In the Burdigalian carbonate ramp (Upper Népoui Formation), porcellaneous foraminifera thriving in sea-grass meadows together with red algae and scattered coral colonies characterize the carbonate production in the euphotic zone. Antecedent topography is regarded as a major factor controlling the extension of carbonate systems at regional and local scale. The thickness and development pattern of Lower Miocene deposits from Népoui are dominantly controlled by tectonic subsidence. Finally, extensive sea-grass development promoted the dominance of foralgal carbonate production within the euphotic zone.

Spatial Distribution, Structure, Biomass, and Physiology of Microbial Assemblages across the Southern Ocean Frontal Zones during the Late Austral Winter

PubMed Central

Hanson, Roger B.; Lowery, H. Kenneth

1985-01-01

We examined the spatial distributions of picoplankton, nanoplankton, and microplankton biomass and physiological state relative to the hydrography of the Southern Ocean along 90° W longitude and across the Drake Passage in the late austral winter. The eastern South Pacific Ocean showed some large-scale biogeographical differences and size class variability. Microbial ATP biomass was greatest in euphotic surface waters. The horizontal distributions of microbial biomass and physiological state (adenylate energy charge ratio) coincided with internal currents (fronts) of the Antarctic Circumpolar Current. In the Drake Passage, the biological scales in the euphotic and aphotic zones were complex, and ATP, total adenylate, and adenylate energy charge ratio isopleths were compressed due to the extension of the sea ice from Antarctica and constriction of the Circumpolar Current through the narrow passage. The physiological state of microbial assemblages and biomass were much higher in the Drake Passage than in the eastern South Pacific Ocean. The temperature of Antarctic waters, not dissolved organic carbon, was the major variable controlling picoplankton growth. Estimates of picoplankton production based on ATP increments with time suggest that production under reduced predation pressure was 1 to 10 μg of carbon per liter per day. Our results demonstrate the influence of large-scale hydrographic processes on the distribution and structure of microplankton, nanoplankton, and picoplankton across the Southern Ocean. PMID:16346777

Fertilization Potention of Volcanic Dust in the Low-Nutrient Low-Chlorophyll Western North Pacific Subtropical Gyre: Satellite Evidence and Laboratory Study

DTIC Science & Technology

2011-02-08

emphasize the supply of the macronutrients combined nitrogen and phosphate to the euphotic zone, atmospheric deposition can provide not only these two... macronutrients but also the micronutrient iron [Wu et ai, 2001; Jickells et ai, 2005; Duarte et ai, 2006], which can stimulate nitrate uptake in... macronutrients . The effect of this one single event could account for about a tenth of the annual new production in the receiving water. Thus, on a local or

Relationship between diversity and the vertical structure of the upper ocean

NASA Astrophysics Data System (ADS)

Longhurst, Alan R.

1985-12-01

The sources of diversity in the plankton ecosystem of the upper 250 m in the eastern tropical Pacific Ocean are explored in the data from LHPR plankton profiles. Though there is good evidence for resource partitioning among feeding guilds of congeners, and for specialization in predation—both known to create diversity in simple aquatic ecosystems—the existence of a stable vertical structure, including a thermocline, may be one of the more important causes of variation in regional plankton diversity in the euphotic zone.

A numerical analysis of shipboard and coastal zone color scanner time series of new production within Gulf Stream cyclonic eddies in the South Atlantic Bight

NASA Technical Reports Server (NTRS)

Pribble, J. Raymond; Walsh, John J.; Dieterle, Dwight A.; Mueller-Karger, Frank E.

1994-01-01

Eddy-induced upwelling occurs along the western edge of the Gulf Stream between Cape Canaveral, Florida, and Cape Hatteras, North Carolina, in the South Atlantic Bight (SAB). Coastal zone color scanner images of 1-km resolution spanning the period April 13-21, 1979, were processed to examine these eddy features in relation to concurrent shipboard and current/temperature measurements at moored arrays. A quasi-one-dimensional (z), time dependent biological model, using only nitrate as a nutrient source, has been combined with a three-dimensional physical model in an attempt to replicate the observed phytoplankton field at the northward edge of an eddy. The model is applicable only to the SAB south of the Charleston Bump, at approximately 31.5 deg N, since no feature analogous to the bump exists in the model bathymetry. The modeled chlorophyll, nitrate, and primary production fields of the euphotic zone are very similar to those obtained from the satellite and shipboard data at the leading edges of the observed eddies south of the Charleston Bump. The horizontal and vertical simulated fluxes of nitrate and chlorophyll show that only approximately 10% of the upwelled nitrate is utilized by the phytoplankton of the modeled grid box on the northern edge of the cyclone, while approximately 75% is lost horizontally, with the remainder still in the euphotic zone after the 10-day period of the model. Loss of chlorophyll due to sinking is very small in this strong upwelling region of the cyclone. The model is relatively insensitive to variations in the sinking parameterization and the external nitrate and chlorophyll fields but is very sensitive to a reduction of the maximum potential growth rate to half that measured. Given the success of this model in simulating the new production of the selcted upwelling region, other upwelling regions for which measurements or successful models of physical and biological quantities and rates exist could be modeled similarly.

Upward nitrate transport by phytoplankton in oceanic waters: balancing nutrient budgets in oligotrophic seas.

PubMed

Villareal, Tracy A; Pilskaln, Cynthia H; Montoya, Joseph P; Dennett, Mark

2014-01-01

In oceanic subtropical gyres, primary producers are numerically dominated by small (1-5 µm diameter) pro- and eukaryotic cells that primarily utilize recycled nutrients produced by rapid grazing turnover in a highly efficient microbial loop. Continuous losses of nitrogen (N) to depth by sinking, either as single cells, aggregates or fecal pellets, are balanced by both nitrate inputs at the base of the euphotic zone and N2-fixation. This input of new N to balance export losses (the biological pump) is a fundamental aspect of N cycling and central to understanding carbon fluxes in the ocean. In the Pacific Ocean, detailed N budgets at the time-series station HOT require upward transport of nitrate from the nutricline (80-100 m) into the surface layer (∼0-40 m) to balance productivity and export needs. However, concentration gradients are negligible and cannot support the fluxes. Physical processes can inject nitrate into the base of the euphotic zone, but the mechanisms for transporting this nitrate into the surface layer across many 10s of m in highly stratified systems are unknown. In these seas, vertical migration by the very largest (10(2)-10(3) µm diameter) phytoplankton is common as a survival strategy to obtain N from sub-euphotic zone depths. This vertical migration is driven by buoyancy changes rather than by flagellated movement and can provide upward N transport as nitrate (mM concentrations) in the cells. However, the contribution of vertical migration to nitrate transport has been difficult to quantify over the required basin scales. In this study, we use towed optical systems and isotopic tracers to show that migrating diatom (Rhizosolenia) mats are widespread in the N. Pacific Ocean from 140°W to 175°E and together with other migrating phytoplankton (Ethmodiscus, Halosphaera, Pyrocystis, and solitary Rhizosolenia) can mediate time-averaged transport of N (235 µmol N m(-2) d(-1)) equivalent to eddy nitrate injections (242 µmol NO3 (-) m(-2) d(-1)). This upward biotic transport can close N budgets in the upper 250 m of the central Pacific Ocean and together with diazotrophy creates a surface zone where biological nutrient inputs rather than physical processes dominate the new N flux. In addition to these numerically rare large migrators, there is evidence in the literature of ascending behavior in small phytoplankton that could contribute to upward flux as well. Although passive downward movement has dominated models of phytoplankton flux, there is now sufficient evidence to require a rethinking of this paradigm. Quantifying these fluxes is a challenge for the future and requires a reexamination of individual phytoplankton sinking rates as well as methods for capturing and enumerating ascending phytoplankton in the sea.

Upward nitrate transport by phytoplankton in oceanic waters: balancing nutrient budgets in oligotrophic seas

PubMed Central

Pilskaln, Cynthia H.; Montoya, Joseph P.; Dennett, Mark

2014-01-01

In oceanic subtropical gyres, primary producers are numerically dominated by small (1–5 µm diameter) pro- and eukaryotic cells that primarily utilize recycled nutrients produced by rapid grazing turnover in a highly efficient microbial loop. Continuous losses of nitrogen (N) to depth by sinking, either as single cells, aggregates or fecal pellets, are balanced by both nitrate inputs at the base of the euphotic zone and N2-fixation. This input of new N to balance export losses (the biological pump) is a fundamental aspect of N cycling and central to understanding carbon fluxes in the ocean. In the Pacific Ocean, detailed N budgets at the time-series station HOT require upward transport of nitrate from the nutricline (80–100 m) into the surface layer (∼0–40 m) to balance productivity and export needs. However, concentration gradients are negligible and cannot support the fluxes. Physical processes can inject nitrate into the base of the euphotic zone, but the mechanisms for transporting this nitrate into the surface layer across many 10s of m in highly stratified systems are unknown. In these seas, vertical migration by the very largest (102–103 µm diameter) phytoplankton is common as a survival strategy to obtain N from sub-euphotic zone depths. This vertical migration is driven by buoyancy changes rather than by flagellated movement and can provide upward N transport as nitrate (mM concentrations) in the cells. However, the contribution of vertical migration to nitrate transport has been difficult to quantify over the required basin scales. In this study, we use towed optical systems and isotopic tracers to show that migrating diatom (Rhizosolenia) mats are widespread in the N. Pacific Ocean from 140°W to 175°E and together with other migrating phytoplankton (Ethmodiscus, Halosphaera, Pyrocystis, and solitary Rhizosolenia) can mediate time-averaged transport of N (235 µmol N m-2 d-1) equivalent to eddy nitrate injections (242 µmol NO3− m-2 d-1). This upward biotic transport can close N budgets in the upper 250 m of the central Pacific Ocean and together with diazotrophy creates a surface zone where biological nutrient inputs rather than physical processes dominate the new N flux. In addition to these numerically rare large migrators, there is evidence in the literature of ascending behavior in small phytoplankton that could contribute to upward flux as well. Although passive downward movement has dominated models of phytoplankton flux, there is now sufficient evidence to require a rethinking of this paradigm. Quantifying these fluxes is a challenge for the future and requires a reexamination of individual phytoplankton sinking rates as well as methods for capturing and enumerating ascending phytoplankton in the sea. PMID:24688877

Control of the phytoplankton distribution in the Strait of Gibraltar by wind and fortnightly tides

NASA Astrophysics Data System (ADS)

Gómez, F.; Gorsky, G.; García-Górriz, E.; Picheral, M.

2004-03-01

CTD-fluorescence-turbidity profiles from two surveys conducted in June and September 1997 were examined in order to evaluate the influence of the predictable fortnightly (spring/neap) tidal cycle and the less predictable wind on the phytoplankton distribution in the Strait of Gibraltar. The injection of the nutrient-rich North Atlantic Water (NACW) in the Atlantic inflowing current is associated with initial phytoplankton blooming conditions (high fluorescence, low turbidity). In September, a thick layer of NACW was recorded in the euphotic zone of the Atlantic side of the Strait, but biological variables showed post-bloom conditions. This is interpreted as the previous development of a phytoplankton bloom favoured by the ascent of NACW into the euphotic zone during the neap tide period. The passage of NACW through the Strait into the Mediterranean Sea was initially hindered by easterly winds and later by the spring tide. The neap tide period favoured the injection and passage of nutrient-rich North Atlantic Water (NACW) into the Atlantic inflowing current, enhanced during the westerly winds regime. During the spring tides, the injection and passage of NACW is hindered, especially when the easterlies blow. The contribution of the NACW to the primary production was estimated as 100-150 kg carbon s -1 (enhanced during the neap tides). The influence of the wind-driven upwelling along the NW Alborán Sea on the northeastern side of the Strait is discussed.

Variability in productivity controlled by haline stratification over 300ky in the Bay of Bengal.

NASA Astrophysics Data System (ADS)

Da Silva, R.; Mazumdar, A.; Peketi, A.; Joshi, R.; Shaji, A.; Naik, B. G.; Carvalho, M.; Molleti, S.

2017-12-01

The unique hydrographic setting of the Bay of Bengal (BoB) makes it an ideal tropical marine system to study the influence of regional and global forcings on productivity and [CO2aq] through the late quaternary. Enormous fresh water flux into the BoB and consequent haline stratification significantly weakens the convective mixing and wind driven processes which are commonly responsible for transport of nutrients to the euphotic zone driving primary productivity. Here, we present a high resolution organic carbon-Calcium carbonate burial flux and δ13CTOC records for the last 300 ky. A giant Calypso piston corer was used on board ORV Marion Dufresne (MD-161) for the retrieval of the sediment core MD161-19 (core length: 39 m) off Mahanadi Basin (Lat.:18º59.1020"; Long.:85º41.1669") in western BoB at a water depth of 1480m. The results show significant productivity variation at marine isotope sub-stages and millennial timescales. Colder sub-stages and stadials (Dansgard-Oeschger cycle) show boost in productivity which may be attributed to thinning of low salinity water cap, thereby facilitating efficient nutrient transport across the euphotic zone by the combination of wind driven processes (entrainment and upwelling), convective mixing and cold core eddies. Our long term high resolution data indicates a possibility of marked changes in productivity/ biogeochemistry of BOB in the future due to global warming, in turn affecting coastal economy.

Distribution and Magnitude of Dinitrogen Fixation in the Eastern Tropical North Pacific Oxygen Deficient Zone.

NASA Astrophysics Data System (ADS)

Selden, C.; Mulholland, M. R.; Widner, B.; Bernhardt, P. W.; Macías Tapia, A.; Jayakumar, A.

2016-12-01

The Eastern Tropical North Pacific Ocean (ETNP) hosts one of the world's three major open ocean oxygen deficient zones (ODZs). Hotspots for fixed nitrogen (N) loss processes, ODZs have classically been discounted as areas of significant dinitrogen (N2) fixation, the microbe-mediated reduction of N2 to ammonium (NH4+), which has historically been ascribed primarily to euphotic, nutrient-deplete tropical waters. Challenging this paradigm, active expression of nifH (the dinitrogen reductase structural gene) has recently been documented in the ETNP, Eastern Tropical South Pacific, and Arabian Sea ODZs, implying a closer coupling of fixed nitrogen input and loss processes than previously thought. Here, we report rates of N­2 fixation measured in the ETNP ODZ along vertical gradients of oxygen, light, and dissolved N concentrations. Detailed vertical profiles of N2 fixation rates and dissolved N concentrations made within the ODZ were compared with similar profiles from oxic waters outside the ODZ. In addition, different organic carbon sources were investigated as potential rate-limiting factors for N2 fixation in sub-euphotic waters. By establishing the magnitude and distribution of N­2 fixation in the ETNP ODZ, this study contributes to current understanding of N cycling in anoxic and aphotic waters, and serves to elucidate nuances in the global N budget, enabling more accurate biogeochemical modeling. Understanding these processes in present day ODZs is crucial for predicting how ongoing anthropogenic intensification of coastal ODZs will alter biogeochemical cycles in the future.

Chemically and geographically distinct solid-phase iron pools in the Southern Ocean.

PubMed

von der Heyden, B P; Roychoudhury, A N; Mtshali, T N; Tyliszczak, T; Myneni, S C B

2012-11-30

Iron is a limiting nutrient in many parts of the oceans, including the unproductive regions of the Southern Ocean. Although the dominant fraction of the marine iron pool occurs in the form of solid-phase particles, its chemical speciation and mineralogy are challenging to characterize on a regional scale. We describe a diverse array of iron particles, ranging from 20 to 700 nanometers in diameter, in the waters of the Southern Ocean euphotic zone. Distinct variations in the oxidation state and composition of these iron particles exist between the coasts of South Africa and Antarctica, with different iron pools occurring in different frontal zones. These speciation variations can result in solubility differences that may affect the production of bioavailable dissolved iron.

Hot-spots of primary productivity: An Alternative interpretation to Conventional upwelling models

NASA Astrophysics Data System (ADS)

van Ruth, Paul D.; Ganf, George G.; Ward, Tim M.

2010-12-01

The eastern Great Australian Bight (EGAB) forms part of the Southern and Indian Oceans and is an area of high ecological and economic importance. Although it supports a commercial fishery, quantitative estimates of the primary productivity underlying this industry are open to debate. Estimates range from <100 mg C m -2 day -1 to > 500 mg C m -2 day -1. Part of this variation may be due to the unique upwelling circulation of shelf waters in summer/autumn (November-April), which shares some similarities with highly productive eastern boundary current upwelling systems, but differs due to the influence of a northern boundary current, the Flinders current, and a wide continental shelf. This study examines spatial variations in primary productivity in the EGAB during the upwelling seasons of 2005 and 2006. Daily integral productivity calculated using the vertically generalised production model (VGPM) showed a high degree of spatial variation. Productivity was low (<800 mg C m -2 day -1) in offshore central and western regions of the EGAB. High productivities (1600-3900 mg C m -2 day -1) were restricted to hotspots in the east that were influenced by the upwelled water mass. There was a strong correlation between the depth of the euphotic zone and the depth of the mixed layer that suggested that ˜50% of the euphotic zone lay below the mixed layer depth. As a result, high rates of primary productivity did not require upwelled water to reach the surface. A significant proportion of total productivity in the euphotic zone (57% in 2005 and 65% in 2006) occurred in the upwelled water mass below the surface mixed layer. This result has implications for daily integral productivities modelled with the VGPM, which uses surface measures of phytoplankton biomass to calculate productivity. Macro-nutrient concentrations could not be used to explain the difference in the low and high productivities (silica > 1 μmol L -1, nitrate/nitrite > 0.4 μmol L -1, phosphate > 0.1 μmol L -1). Mixing patterns or micro-nutrient concentrations are possible explanations for spatial variations in primary productivity in the EGAB. On a global scale, daily rates of primary productivity of the EGAB lie between the highly productive eastern boundary current upwelling systems, and less productive coastal regions of western and south eastern Australia, and the oligotrophic ocean. However, daily productivity rates in the upwelling hotspots of the EGAB rival productivities in Benguela and Humboldt currents.

Constraints on nitrogen cycling at the subtropical North Pacific Station ALOHA from isotopic measurements of nitrate and particulate nitrogen

NASA Astrophysics Data System (ADS)

Casciotti, K. L.; Trull, T. W.; Glover, D. M.; Davies, D.

2008-07-01

Nitrogen supply to surface waters can play an important role in the productivity and ecology of subtropical ecosystems. As part of the Vertical Transport in the Global Ocean (VERTIGO) program, we examined the fluxes of nitrogen into and out of the euphotic zone at station ALOHA in the North Pacific Subtropical Gyre using natural abundance stable isotopic measurements of nitrate ( δN and δO), as well as sinking and suspended particulate nitrogen (δ 15N PN). Paralleling the steep gradient in nitrate concentration in the upper thermocline at ALOHA, we observed a steep gradient in δN, decreasing from a maximum of +7.1‰ at 500 meters (m) to +1.5-2.4‰ at 150 m. δO values also decreased from +3.0‰ at 300 m to +0.7-0.9‰ at 150 m. The decreases in both δN and δO require inputs of isotopically "light" nitrate to balance the upward flux of nitrate with high δN (and δO). We conclude that both nitrogen fixation and diagenetic alteration of the sinking flux contribute to the decrease in δN and δO in the upper thermocline at station ALOHA. While nitrogen fixation is required to explain the nitrogen isotope patterns, the rates of nitrogen fixation may be lower than previously estimated. By including high-resolution nitrate isotope measurements in the nitrogen isotope budget for the euphotic zone at ALOHA, we estimate that approximately 25%, rather than 50%, of export production was fueled by N 2 fixation during our study. On the other hand, this input of N 2-derived production accumulates in the upper thermocline over time, playing a significant role in subtropical nutrient cycling through maintenance of the subsurface nitrate pool. An increase in sinking δ 15N PN between 150 and 300 m, also suggests that fractionation during remineralization contributed to the low δN values observed in this depth range by introducing a subsurface nitrate source that is 0.5‰ lower in δ 15N than the particle flux exported from the euphotic zone. While the time scale of these observations are currently limited, they highlight the need for inclusion of δN measurements in a time series program to allow a broader assessment of the variations in subsurface δN values and the links between subsurface nitrate and export flux at station ALOHA.

Scientific investigations in the Gulf of Mexico and Caribbean Sea during the 1974-1975 Calypso cruise, parts 1 and 2

NASA Technical Reports Server (NTRS)

Elsayed, S. Z.; Reheim, H. A.; Fryxell, G. A.; Harlan, J. C.; Hill, J. M.; Babai, P.; Whitney, P.

1975-01-01

The distribution and concentrations of the standing crop of phytoplankton and nutrient salts in the Gulf of Mexico and the Caribbean Sea were investigated to provide ground truth for correlating temperature and chlorophyll-a measurements with observations from NASA U-2 aircraft equipped with specially designed sensors for measuring ocean color phenomena. The physical, chemical, and biological data obtained is summarized. Sampling procedures and methods used for determining plant pigments, species composition of phytoplankton, nutrient salt analysis, and the euphotic zones are described.

Influence of a Decaying Cyclonic Eddy on Biogenic Silica and Particulate Organic Carbon in the Tropical South China Sea Based on 234Th-238U Disequilibrium.

PubMed

Yang, Weifeng; Chen, Min; Zheng, Minfang; He, Zhigang; Zhang, Xinxing; Qiu, Yusheng; Xu, Wangbin; Ma, Lili; Lin, Zhiyu; Hu, Wangjiang; Zeng, Jian

2015-01-01

Eddies play a critical role in regulating the biological pump by pumping new nutrients to the euphotic zone. However, the effects of cyclonic eddies on particle export are not well understood. Here, biogenic silica (BSi) and particulate organic carbon (POC) exports were examined inside and outside a decaying cyclonic eddy using 234Th-238U disequilibria in the tropical South China Sea. For the eddy and outside stations, the average concentrations of BSi in the euphotic zone were 0.17±0.09 μmol L-1 (mean±sd, n = 20) and 0.21±0.06 μmol L-1 (n = 34). The POC concentrations were 1.42±0.56 μmol L-1 (n = 34) and 1.30±0.46 μmol L-1 (n = 51). Both BSi and POC abundances did not show change at the 95% confidence level. Based on the 234Th-238U model, BSi export fluxes in the eddy averaged 0.18±0.15 mmol Si m-2 d-1, which was comparable with the 0.40±0.20 mmol Si m-2 d-1 outside the eddy. Similarly, the average POC export fluxes were 1.5±1.4 mmol C m-2 d-1 and 1.9±1.3 mmol C m-2 d-1 for the eddy and outside stations. From these results we concluded that cyclonic eddies in their decaying phase have little effect on the abundance and export of biogenic particles.

Influence of a Decaying Cyclonic Eddy on Biogenic Silica and Particulate Organic Carbon in the Tropical South China Sea Based on 234Th-238U Disequilibrium

PubMed Central

Yang, Weifeng; Chen, Min; Zheng, Minfang; He, Zhigang; Zhang, Xinxing; Qiu, Yusheng; Xu, Wangbin; Ma, Lili; Lin, Zhiyu; Hu, Wangjiang; Zeng, Jian

2015-01-01

Eddies play a critical role in regulating the biological pump by pumping new nutrients to the euphotic zone. However, the effects of cyclonic eddies on particle export are not well understood. Here, biogenic silica (BSi) and particulate organic carbon (POC) exports were examined inside and outside a decaying cyclonic eddy using 234Th-238U disequilibria in the tropical South China Sea. For the eddy and outside stations, the average concentrations of BSi in the euphotic zone were 0.17±0.09 μmol L-1 (mean±sd, n = 20) and 0.21±0.06 μmol L-1 (n = 34). The POC concentrations were 1.42±0.56 μmol L-1 (n = 34) and 1.30±0.46 μmol L-1 (n = 51). Both BSi and POC abundances did not show change at the 95% confidence level. Based on the 234Th-238U model, BSi export fluxes in the eddy averaged 0.18±0.15 mmol Si m-2 d-1, which was comparable with the 0.40±0.20 mmol Si m-2 d-1 outside the eddy. Similarly, the average POC export fluxes were 1.5±1.4 mmol C m-2 d-1 and 1.9±1.3 mmol C m-2 d-1 for the eddy and outside stations. From these results we concluded that cyclonic eddies in their decaying phase have little effect on the abundance and export of biogenic particles. PMID:26317555

Light absorption coefficients by phytoplankton pigments, suspended particles and colored dissolved organic matter in the Crimea coastal water (the Black sea) in June 2016

NASA Astrophysics Data System (ADS)

Moiseeva, N.; Churilova, T.; Efimova, T.; Krivenko, O.; Latushkin, A.

2017-11-01

Variability of the bio-optical properties of the Crimean coastal waters in June 2016 has been analyzed. The type of vertical distribution chlorophyll a concentration and phytoplankton light absorption coefficients and spectra shape differed between shallow and deeper water. In the deeper water seasonal stratification divided euphotic zone into layers with different environmental conditions. In the deeper part of the euphotic zone (below the thermocline) phytoplankton absorption spectra had local maximum at 550 nm, which was likely to be associated with high abundance of cyanobacteria (Synechococcus sps.) in the phytoplankton community. The concentration of chlorophyll a specific light absorption coefficient of phytoplankton decreased with depth (especially pronounced in the blue domain of the spectrum). In the shallow water the vertical distributions of all absorption properties were relatively homogeneous due to vertical water mixing. In the shallow water non-algal particles light absorption coefficient and its contribution to total particulate absorption were higher than those in the deeper water. The non-algal particles (NAP) and colored dissolved organic matter (CDOM) light absorption spectra were well described by an exponential function with a slope averaging 0.010 nm-1 (SD = 0.001 nm-1) and 0.022 nm-1 (SD = 0.0060 nm-1), correspondingly. The CDOM absorption at 440 nm and slope coefficient varied significantly across the investigated area, which was possibly associated with the terrestrial influences. The assessment of the contribution of phytoplankton, NAP and CDOM to total light absorption showed that CDOM dominated in the absorption at 440 nm.

Nitrification and its influence on biogeochemical cycles from the equatorial Pacific to the Arctic Ocean

PubMed Central

Shiozaki, Takuhei; Ijichi, Minoru; Isobe, Kazuo; Hashihama, Fuminori; Nakamura, Ken-ichi; Ehama, Makoto; Hayashizaki, Ken-ichi; Takahashi, Kazutaka; Hamasaki, Koji; Furuya, Ken

2016-01-01

We examined nitrification in the euphotic zone, its impact on the nitrogen cycles, and the controlling factors along a 7500 km transect from the equatorial Pacific Ocean to the Arctic Ocean. Ammonia oxidation occurred in the euphotic zone at most of the stations. The gene and transcript abundances for ammonia oxidation indicated that the shallow clade archaea were the major ammonia oxidizers throughout the study regions. Ammonia oxidation accounted for up to 87.4% (average 55.6%) of the rate of nitrate assimilation in the subtropical oligotrophic region. However, in the shallow Bering and Chukchi sea shelves (bottom ⩽67 m), the percentage was small (0–4.74%) because ammonia oxidation and the abundance of ammonia oxidizers were low, the light environment being one possible explanation for the low activity. With the exception of the shallow bottom stations, depth-integrated ammonia oxidation was positively correlated with depth-integrated primary production. Ammonia oxidation was low in the high-nutrient low-chlorophyll subarctic region and high in the Bering Sea Green Belt, and primary production in both was influenced by micronutrient supply. An ammonium kinetics experiment demonstrated that ammonia oxidation did not increase significantly with the addition of 31–1560 nm ammonium at most stations except in the Bering Sea Green Belt. Thus, the relationship between ammonia oxidation and primary production does not simply indicate that ammonia oxidation increased with ammonium supply through decomposition of organic matter produced by primary production but that ammonia oxidation might also be controlled by micronutrient availability as with primary production. PMID:26918664

Further Examination of Biogeochemical Consequences of Mesoscale Eddies in the Sargasso Sea

NASA Astrophysics Data System (ADS)

Marquez, I. A., Jr.; Krause, J. W.; Lomas, M. W.

2016-02-01

The Bermuda Atlantic Time Series (BATS) is an ongoing 25-year biogeochemical record in the North Atlantic subtropical gyre. Contemporaneous data on the particulate phases of four major bioreactive elements, C, N, P, and Si only exist during two years and also for a companion project (Trophic BATS, i.e. TBATS). A combined dataset from BATS and TBATS was used to better understand the coupling of C, N, P, and Si in the Sargasso Sea by analyzing particulate phases of each element in the water column and exported material. Three conclusions are inferred: first, the effect of mesoscale eddies on standing stocks, export rates, and elemental coupling of C, N, P, and Si displays strong seasonality. Statistically significant differences between particulate water column and export ratios using internal and between site comparisons were robust in the summer only. Second, N, Si and particularly P were more efficiently recycled within the euphotic zones of eddies as elemental ratios in export material were greater than the corresponding ratios in the water column. This suggests that P may have a more critical biogeochemical role and its supply rate to the euphotic zone may control primary production in these closed systems. Third, the trends seen in these eddies do not support that export production was enhanced, instead these features had more efficient recycling of N, P, and Si relative to the BATS site. This decrease in export efficiency suggests a stimulation of export production above 'normal' BATS conditions within eddies would require significantly higher autotrophic standing stock and correspondingly high rates of organic matter production.

Transparent Exopolymer Particles (TEP) in the NE Aegean Sea frontal area: Seasonal dynamics under the influence of Black Sea water

NASA Astrophysics Data System (ADS)

Parinos, C.; Gogou, A.; Krasakopoulou, E.; Lagaria, A.; Giannakourou, A.; Karageorgis, A. P.; Psarra, S.

2017-10-01

The abundance of Transparent Exopolymer Particles (TEP) was determined on a seasonal basis (autumn, spring and summer) along a north-south transect in the NE Aegean Sea and the vicinity of the Dardanelles Straits. Their distribution patterns were studied in respect to hydrographic conditions and water mass characteristics in the area, as well as particulate organic carbon (POC) concentrations, changes in standing stocks of chlorophyll-α and bacterial production. TEP concentrations ranged from 15.4 to 188 μg GX eq L-1. Their spatial distribution patterns within the euphotic zone displayed significant seasonal variability, which appears to closely reflect the temporal variation of the water column structure, resulting from the encounter and interplay of the Black Sea and Levantine Water masses, and the associated biogeochemical processes. Minimum TEP concentrations during autumn could be likely attributed to a minor quantity of TEP and/or its dissolved precursors exuded by phytoplankton and their enhanced degradation due to their long residence time in the water column. During spring, high TEP production was mediated by actively growing phytoplankton, while during summer a positive link to the intense stratification of the water column and the enhanced bacterial growth within the Black Sea Water layer was observed. The results reported in this study highlight the fact that TEP carbon represents a significant fraction of the POC pool. Moreover, TEP production is critical in promoting particle coagulation rates, playing an important role in carbon cycling/transportation out of the euphotic zone.

Examining Lake Michigan Spring Euphotic Depth (Zeu) Anomalies: Utilizing 10 Years of MODIS-Aqua Data at 4 Kilometer Resolution

NASA Technical Reports Server (NTRS)

Acker, James G.

2013-01-01

Examination of ten years of euphotic depth anomalies in Lake Michigan during the months of March-June indicates the following: The well-known and frequently observed occurrence of a turbidity feature in the southern part of Lake Michigan during the spring season has become less common during the period 2003-2012. Overall, the clarity of Lake Michigan water in the southern end of the lake appears to have increased spring season over the period 2003-2012. Euphotic depth can be used as a primary indicator of changes in Lake Michigan lacustrine optics, and for other large lakes. Unique events, such as the heavy rains in June 2008, can have a distinct signature in the euphotic depth anomaly distribution in Lake Michigan.

Methyl mercury distributions in relation to the presence of nano- and picophytoplankton in an oceanic water column (Ligurian Sea, North-western Mediterranean)

NASA Astrophysics Data System (ADS)

Heimbürger, Lars-Eric; Cossa, Daniel; Marty, Jean-Claude; Migon, Christophe; Averty, Bernard; Dufour, Aurélie; Ras, Josephine

2010-10-01

Recent findings on the distribution of methylated mercury (MeHg T) in waters have highlighted the importance of organic carbon remineralization on the production of these compounds in the open ocean. Here, we present the first time-series (20 monthly samplings between July 2007 and May 2009) of high-resolution vertical profiles (10-12 depths in a 2350 m water column) of MeHg T distributions in an open ocean environment, the Ligurian Sea (North-western Mediterranean Sea). Concentrations varied within the sub-picomolar range (general mean: 0.30 ± 0.17 pmol L -1, n = 214) with the lowest values at the surface, increasing with depth up to the oxygen minimum zone, and decreasing slowly at greater depth. Concentrations in the surface waters never exceeded 0.15 pmol L -1, while the highest concentrations (up to 0.82 pmol L -1) were associated to the hypoxycline during the autumn bloom. A detailed vertical MeHg T profile reveals a "double-peak" pattern, coincidental with the two microbial layers described by Tanaka and Rassoulzadegan (2002), the so-called "microbial food web" in the euphotic zone (<100 m) and the "microbial loop" in the aphotic zone (>100 m). Temporal variations in the MeHg T abundance and distribution in the water column were linked to seasonality. The highest MeHg T concentrations were found in the oxygen minimum zone during the period of stratification, and coincide with the greatest abundance of nano- and picophytoplankton (cyanobacteria, nanoflagellates, etc.) in the euphotic layer. None of our deep MeHg T measurements (˜100 m above the sea bottom) revealed a significant sedimentary source of MeHg T. We explored the correlation between MeHg T concentrations and the apparent oxygen utilization, a proxy of organic matter remineralization, over the study period. Results of this study strengthen the hypothesis that net mercury methylation in the open ocean occurs in the water column, is linked to organic matter regeneration, and is promoted by the presence of small-sized nano- and picophytoplankton, that dominate under oligotrophic conditions.

Vertical distribution of pigmented and non-pigmented nanoflagellates in the East China Sea

NASA Astrophysics Data System (ADS)

Tsai, Sheng-Fang; Lin, Fan-Wei; Chan, Ya-Fan; Chiang, Kuo-Ping

2016-08-01

Nanoflagellates can be separated into two groups according to their trophic mode, i.e. pigmented nanoflagellates (PNF) and heterotrophic nanoflagellates (HNF). However, a newly identified group, mixotrophic nanoflagellates (MNF), are pigmented and show the ability of prey on bacteria. To examine the vertical variations in PNF and HNF abundances, as well as their relationships and the nutritional strategies that they might use, two summer cruises were undertaken in the East China Sea in July 2011 (OR1 966) and July 2012 (OR1 1004). The results show that both HNF and PNF abundances decline with increasing water depth. Vertical variations of abundances are believed to be influenced by prey and light, for HNF and PNF respectively. Over a large part of the sampling area, the ratio of PNF to HNF abundances is about 1:1 in the disphotic and euphotic zones, but exceeds 1.5 in the nutrient-depleted environment along the margin of the continental shelf. The correlation between PNF abundance and bacteria/Synechococcus abundance is positive where PNF/HNF >1.5. However, there is no significant correlation between PNF/HNF abundance when PNF/HNF >1.5 and light/nutrients, indicating that vertical distributions are influenced mainly by prey (bacteria and Synechococcus) in the nutrient-depleted environment. This study assumes that PNF consists mostly of MNF. In the euphotic zone they receive energy from photosynthesis, which is stimulated by the available nutrients from grazing. Their abundance is thus higher than that of HNF. However, in the disphotic zone, both PNF and HNF satisfy their nutrient demands by grazing, and PNF/HNF is close to 1. In other words, mixotrophy might be the main trophic mode for PNF in the nutrient-depleted, oligotrophic environment. Meanwhile, in deeper water (300 m), the much lower prey density means that MNF cannot satisfy the basic energy demands of metabolism and photosynthesis, and thus HNF abundance exceeds that of PNF.

Effects of Water Depth, Seasonal Exposure, and Substrate Orientation on Microbial Bioerosion in the Ionian Sea (Eastern Mediterranean)

PubMed Central

Färber, Claudia; Wisshak, Max; Pyko, Ines; Bellou, Nikoleta; Freiwald, André

2015-01-01

The effects of water depth, seasonal exposure, and substrate orientation on microbioerosion were studied by means of a settlement experiment deployed in 15, 50, 100, and 250 m water depth south-west of the Peloponnese Peninsula (Greece). At each depth, an experimental platform was exposed for a summer period, a winter period, and about an entire year. On the up- and down-facing side of each platform, substrates were fixed to document the succession of bioerosion traces, and to measure variations in bioerosion and accretion rates. In total, 29 different bioerosion traces were recorded revealing a dominance of microborings produced by phototrophic and organotrophic microendoliths, complemented by few macroborings, attachment scars, and grazing traces. The highest bioerosion activity was recorded in 15 m up-facing substrates in the shallow euphotic zone, largely driven by phototrophic cyanobacteria. Towards the chlorophyte-dominated deep euphotic to dysphotic zones and the organotroph-dominated aphotic zone the intensity of bioerosion and the diversity of bioerosion traces strongly decreased. During summer the activity of phototrophs was higher than during winter, which was likely stimulated by enhanced light availability due to more hours of daylight and increased irradiance angles. Stable water column stratification and a resulting nutrient depletion in shallow water led to lower turbidity levels and caused a shift in the photic zonation that was reflected by more phototrophs being active at greater depth. With respect to the subordinate bioerosion activity of organotrophs, fluctuations in temperature and the trophic regime were assumed to be the main seasonal controls. The observed patterns in overall bioeroder distribution and abundance were mirrored by the calculated carbonate budget with bioerosion rates exceeding carbonate accretion rates in shallow water and distinctly higher bioerosion rates at all depths during summer. These findings highlight the relevance of bioerosion and accretion for the carbonate budget of the Ionian Sea. PMID:25893244

State of Climate 2011 - Global Ocean Phytoplankton

NASA Technical Reports Server (NTRS)

Siegel, D. A.; Antoine, D.; Behrenfeld, M. J.; d'Andon, O. H. Fanton; Fields, E.; Franz, B. A.; Goryl, P.; Maritorena, S.; McClain, C. R.; Wang, M.;

Coccolithophore ecology in the tropical and subtropical Atlantic Ocean: New perspectives from the Atlantic meridional transect (AMT) programme

NASA Astrophysics Data System (ADS)

Poulton, Alex J.; Holligan, Patrick M.; Charalampopoulou, Anastasia; Adey, Tim R.

2017-11-01

Coccolithophore species composition was determined in 199 samples collected from the upper 300 m of the Atlantic Ocean, spanning temperate, tropical and subtropical waters in both hemispheres during four Atlantic Meridional Transect (AMT) cruises over the period 2003-2005. Of the 171 taxa observed, 140 consistently represented <5% of total cell numbers, and were classed as rare. Multivariate statistical techniques were used on the common taxa to assess variability in community composition vertically in the water column, horizontally across hydrographic provinces (subtropical gyres, equatorial waters, temperate waters), and temporally between cruises. Sharper gradients of statistical dissimilarity in species composition occurred vertically over a few tens of metres than horizontally over hundreds of kilometres. Three floral groups were identified from analysis of the depth of normalised abundance maxima in the subtropical gyres and equatorial waters: the upper euphotic zone (UEZ, >10% surface irradiance); the lower euphotic zone (LEZ, 10-1% surface irradiance); and the sub-euphotic zone (SEZ, <1% surface irradiance). The LEZ includes the deep chlorophyll maximum (DCM) and nutricline, and was characterised by species such as Emiliania huxleyi and Gephyrocapsa ericsonii which were also abundant at higher latitudes. It is suggested that this pattern reflects similarities in the light (and inorganic nutrient) conditions between the LEZ and temperate waters. The SEZ is below the depth where light is thought to be sufficient to support photosynthesis, suggesting that deep-dwelling species such as Florisphaera profunda and Gladiolithus spp. may be mixotrophic or phagotrophic, although conclusive proof will need to be gained experimentally. Mixotrophy could also be an important nutritional strategy for species abundant (Umbellosphaera spp., holococcolithophores) in the UEZ where inorganic nutrient concentrations are depleted and limiting to growth, although other nutritional strategies, such as the use of organic nutrients, are also possible. Statistical differences were also found in the species composition between the different cruises, with high levels of similarity for similar timed cruises (May or September-October). Few individual taxa showed significant variability in abundance over the time-span of sampling, except species such as E. huxleyi and G. ericsonii at higher latitudes. In subtropical and equatorial waters, high levels of species richness and low levels of species dominance remained throughout the sampling period indicating that seasonal fluctuations reflected differences in the whole coccolithophore community rather than in just one or a few species. Multivariate analyses of the taxa classified as rare also indicated some level of temporal, as well as vertical, zonation. Such insights into coccolithophore ecology and community composition provide important new perspectives that require innovative research to fully understand their impact on ocean biogeochemistry.

Numerical experiments based on a coupled physical-biochemical ocean model to study the Kuroshio-induced nutrient supply on the shelf-slope region off the southwestern coast of Japan

NASA Astrophysics Data System (ADS)

Kuroda, Hiroshi; Takasuka, Akinori; Hirota, Yuichi; Kodama, Taketoshi; Ichikawa, Tadafumi; Takahashi, Daisuke; Aoki, Kazuhiro; Setou, Takashi

2018-03-01

We developed a triply nested 1/50° ocean model coupled with a NPZD-type lower trophic level ecosystem model and used it to conduct numerical experiments to identify the major processes that supply nutrients on the shelf-slope region north of the Kuroshio. Tosa Bay, an open-type bay facing the Kuroshio, was selected for our experiment. Comparisons of numerical simulations using different grid sizes revealed that a grid size no larger than 1/50° was essential to reproduce a time-independent density structure related to the Kuroshio jet that uplifted nitrate from subsurface waters into the euphotic zone north of the Kuroshio front. The monthly mean budget of nitrate within the euphotic zone on the shelf showed that primary production was nearly balanced by physical advection and the biochemical supply of nitrate via mechanisms such as remineralization of detritus. Eddy advection of nitrate based on Reynolds decomposition, attributable primarily to submesoscale variations, had both positive and negative values within the bay, the indication being that eddy advection functioned regionally to supply or remove nitrate. Lagrangian particle-tracking experiments were performed to examine the major pathways of the nitrate used for primary production in Tosa Bay during the summer, when subsurface maxima of primary production typically appeared. The experiments revealed that when the Kuroshio took a stable nearshore path, nitrate was frequently uplifted around the Kuroshio front and horizontally transported along the front and into the bay via the counterclockwise circulation within the bay; it was sometimes further uplifted onto the shelf.

Optofluidic Single-Cell Genome Amplification of Sub-micron Bacteria in the Ocean Subsurface

PubMed Central

Landry, Zachary C.; Vergin, Kevin; Mannenbach, Christopher; Block, Stephen; Yang, Qiao; Blainey, Paul; Carlson, Craig; Giovannoni, Stephen

2018-01-01

Optofluidic single-cell genome amplification was used to obtain genome sequences from sub-micron cells collected from the euphotic and mesopelagic zones of the northwestern Sargasso Sea. Plankton cells were visually selected and manually sorted with an optical trap, yielding 20 partial genome sequences representing seven bacterial phyla. Two organisms, E01-9C-26 (Gammaproteobacteria), represented by four single cell genomes, and Opi.OSU.00C, an uncharacterized Verrucomicrobia, were the first of their types retrieved by single cell genome sequencing and were studied in detail. Metagenomic data showed that E01-9C-26 is found throughout the dark ocean, while Opi.OSU.00C was observed to bloom transiently in the nutrient-depleted euphotic zone of the late spring and early summer. The E01-9C-26 genomes had an estimated size of 4.76–5.05 Mbps, and contained “O” and “W”-type monooxygenase genes related to methane and ammonium monooxygenases that were previously reported from ocean metagenomes. Metabolic reconstruction indicated E01-9C-26 are likely versatile methylotrophs capable of scavenging C1 compounds, methylated compounds, reduced sulfur compounds, and a wide range of amines, including D-amino acids. The genome sequences identified E01-9C-26 as a source of “O” and “W”-type monooxygenase genes related to methane and ammonium monooxygenases that were previously reported from ocean metagenomes, but are of unknown function. In contrast, Opi.OSU.00C genomes encode genes for catabolizing carbohydrate compounds normally associated with eukaryotic phytoplankton. This exploration of optofluidics showed that it was effective for retrieving diverse single-cell bacterioplankton genomes and has potential advantages in microbiology applications that require working with small sample volumes or targeting cells by their morphology.

Pigments, size and distribution of Synechococcus spp. in the Black Sea

NASA Astrophysics Data System (ADS)

Uysal, Zahit

2000-03-01

Pigments, size and distribution of Phycoerythrin-containing unicellular cyanobacteria Synechococcus spp. within the euphotic zone were studied for the first time in April-May 1994 in the western and southwestern Black Sea by epifluorescence microscopy and flow-cytometry. Synechococcus was present in varying quantities at every station and depth studied. Surface spatial distribution of Synechococcus revealed that cells were much more abundant in offshore waters than near coastal regions under the direct influence of the Danube river. Minimum and maximum cell concentrations ranged between 9×10 2 and 1.45×10 5 cells/ml at the surface, between 2×10 3 and 1.23×10 5 cells/ml at the chlorophyll sub-maximum layer, and between 1.3×10 2 and 3.5×10 2 at the nitrite maximum layer. Cells at the chlorophyll sub-maximum layer (based on in-situ fluorometer readings) fluoresce brighter and longer than the ones at the surface and lower depths. Spectral properties of chromophore pigment types of total 64 clonal isolates from different depths down to the lower layer of the euphotic zone (˜60 m) in the southern Black Sea coast revealed that all have type 2 phycoerythrobilin in common, lacking in phycourobilin. In vivo fluorescence emission maxima for the phycoerythrobilin were about the same (˜578 nm) for all isolates. All isolates examined showed in vivo absorption maxima at between 435 and 442 nm and at about 681 nm due to chlorophyll- a. Based on the flow cytometer mean forward light scatter data for size distribution, it could be concluded that cells at the surface mixed layer (0-10 m) were larger in cell size than the cells at lower depths (20-60 m).

Bacterioplankton activity in the surface waters of the Arabian Sea during and after the 1994 SW monsoon

NASA Astrophysics Data System (ADS)

Pomroy, Alan; Joint, Ian

1999-03-01

Bacterial biomass and production were measured on two cruises to the northwestern Arabian Sea in 1994; the first cruise took place towards the end of the SW monsoon in September, and the second cruise during the inter-monsoon period in November and December. Although phytoplankton production was significantly higher during the monsoon, bacterial numbers showed little difference. Bacteria were most abundant in the euphotic zone and highest bacterial numbers were measured during the monsoon period in the Gulf of Oman and the shelf waters off southern Oman; in these regions, numbers ranged from 0.9 to 1.6×10 9 bacteria l -1. On both cruises, bacteria were less abundant in the euphotic zone of the central Arabian Sea and typically ca 0.8×10 9 cells l -1 were present. The majority of bacteria (80-95%) were small cocci that were larger (median diameter 0.40 μm) during the monsoon period than the inter-monsoon, when the cells had a diameter of 0.36 μm; there was no comparable change in cell dimensions of bacteria present as rods. Bacterial production was measured by the incorporation of 3H-thymidine and 3H-leucine. On both cruises, uptake rates were highest on the Omani shelf and decreased offshore. In the central Arabian Sea, thymidine incorporation rates were similar in the monsoon and inter-monsoon periods, but higher rates of leucine incorporation were measured during the monsoon period. Bacterial production was a relatively small proportion of phytoplankton production in both periods sampled; bacterial production was equivalent to between 10 and 30% of the daily primary production in the Arabian Sea.

Middle-Upper Permian carbon isotope stratigraphy at Chaotian, South China: Pre-extinction multiple upwelling of oxygen-depleted water onto continental shelf

NASA Astrophysics Data System (ADS)

Saitoh, Masafumi; Isozaki, Yukio; Ueno, Yuichiro; Yoshida, Naohiro; Yao, Jianxin; Ji, Zhansheng

2013-05-01

In order to examine the causal relationships between the carbon cycle in a shallow euphotic zone and the environmental changes in a relatively deep disphotic zone at the end-Guadalupian (Middle Permian), isotopic compositions of carbonate carbon (δ13Ccarb) of the Guadalupian-Lopingian (Upper Permian) rocks were analyzed in the Chaotian section in northern Sichuan, South China. By analyzing exceptionally fresh drill core samples, a continuous chemostratigraphic record was newly obtained. The ca. 65 m-thick analyzed carbonate rocks at Chaotian comprise three stratigraphic units, i.e., the Limestone Unit of the Guadalupian Maokou Formation, the Mudstone Unit of the Maokou Formation, and the lower part of the Wuchiapingian (Lower Lopingian) Wujiaping Formation, in ascending order. The Limestone Unit of the Maokou Formation is characterized by almost constant δ13Ccarb values of ca. +4‰ followed by an abrupt drop for 7‰ to -3‰ in the topmost part of the unit. In the Mudstone Unit of the Maokou Formation, the δ13Ccarb values are rather constant around +2‰, although distinct three isotopic negative excursions for 3‰ from ca. +2 to -1‰ occurred in the upper part of the unit. In the lower part of the Wujiaping Formation, the δ13Ccarb values monotonously increase for 5‰ from ca. 0 to +5‰. The present data newly demonstrated four isotopic negative excursions in the topmost part of the Maokou Formation in the Capitanian (Late Guadalupian) at Chaotian. It is noteworthy that these negative excursions are in accordance with the emergence of an oxygen-depleted condition on the relatively deep disphotic slope/basin on the basis of litho- and bio-facies characteristics. They suggest multiple upwelling of oxygen-depleted waters with dissolved inorganic carbon of relatively low carbon isotope values along the continental margin, from the deeper disphotic slope/basin to the shallower euphotic shelf, slightly before the end-Guadalupian extinction. Although the negative excursions at Chaotian are apparently correlated with the previously proposed large negative excursion in the middle Capitanian in South China, the age difference according to the biostratigraphic constraints clearly exclude this interpretation. The isotopic negative excursions at Chaotian are unique and no similar isotopic signal in the same period has been reported elsewhere. The multiple upwelling of oxygen-depleted waters onto the euphotic shelf may have represented local phenomena that occurred solely around northwestern South China.

The 3D Distribution of Dissolved and Colloidal Fe, Mn, Zn, Cu, Ni, Cd and Pb in the Western Antarctic Peninsula Shelf Region; Implications for Natural Fe Fertilization

NASA Astrophysics Data System (ADS)

Sherrell, R. M.; Fitzsimmons, J. N.; Roccanova, J.; Schofield, O.; Meredith, M. P.

2016-02-01

The Western Antarctic Peninsula (WAP) shelf region is is a natural Fe fertilization zone where primary production exceeds that of the adjacent open Southern Ocean. Until recently, however, distributions of Fe and of other bioactive metals were completely lacking for the WAP, and the sources and delivery mechanisms of Fe to the euphotic zone were only speculated upon. We have previously presented surface water (2m) dissolved (dTM, <0.2µm) and particulate (pTM, >0.45µm) distributions for Fe and a suite of other bioactive metals over the WAP shelf, covering the Palmer LTER sampling grid for Jan. 2010, 2011 and 2012. We now report the first complete 3D distribution of dissolved and colloidal Fe (and Mn, Zn, Cu, Ni, Cd and Pb) over the LTER grid in Jan. 2015, allowing assessment of dFe size speciation, sources and transport pathways in this dynamic shelf system. Dissolved metals were analyzed by automated offline preconcentration (seaFAST-pico, ESI) followed by sector-field ICP-MS. We confirm previous findings of low ( 0.1nM) dFe in surface waters on the mid-outer shelf in the northern portion of the grid, and now find that concentrations at this level or below persist through the euphotic zone. However, dFe increases rapidly with depth, with low surface values underlain by substantially higher concentrations even at 50m. Inner shelf surface waters are generally substantially > 0.1nM, suggesting Fe replete conditions in this region. Vertical profiles reveal that dFe generally increases with depth, much moreso in the inner shelf (dFe up to 5.0nM) than the outer shelf. A general N-S gradient in dFe is also evident, with concentrations higher in the southern WAP, especially in Marguerite Bay. In addition, shelf stations often show a dFe maximum suggesting remineralization from sinking biogenic particles. These findings for dFe and for the other metals, will be used to help unravel the biogeochemical workings of natural Fe fertilization in this region.

Wind-induced upwelling in the Kerguelen Plateau region

NASA Astrophysics Data System (ADS)

Gille, S. T.; Carranza, M. M.; Cambra, R.

2014-11-01

In contrast to most of the Southern Ocean, the Kerguelen Plateau supports an unusually strong spring chlorophyll (Chl a) bloom, likely because the euphotic zone in the region is supplied with higher iron concentrations. This study uses satellite wind, sea surface temperature (SST), and ocean color data to explore the impact of wind-driven processes on upwelling of cold (presumably iron-rich) water to the euphotic zone. Results show that, in the Kerguelen region, cold SSTs correlate with high wind speeds, implying that wind-mixing leads to enhanced vertical mixing. Cold SSTs also correlate with negative wind-stress curl, implying that Ekman pumping can further enhance upwelling. In the moderate to high eddy kinetic energy (EKE) regions surrounding Kerguelen, we find evidence of coupling between winds and SST gradients associated with mesoscale eddies, which can locally modulate the wind-stress curl. This coupling introduces persistent wind-stress curl patterns and Ekman pumping around these long-lived eddies, which may modulate the evolution of Chl a in the downstream plume far offshore. Close to the plateau, this eddy coupling breaks down. Kerguelen has a significant wind shadow on its downwind side, which changes position depending on the prevailing wind and which generates a wind-stress curl dipole that shifts location depending on wind direction. This leads to locally enhanced Ekman pumping for a few hundred kilometers downstream from the Kerguelen Plateau; Chl a values tend to be more elevated in places where wind-stress curl induces Ekman upwelling than in locations of downwelling, although the estimated upwelling rates are too small for this relationship to derive from direct effects on upward iron supply, and thus other processes, which remain to be determined, must also be involved in the establishment of these correlations. During the October and November (2011) KErguelen Ocean and Plateau compared Study (KEOPS-2) field program, wind conditions were fairly typical for the region, with enhanced Ekman upwelling expected to the north of the Kerguelen Islands.

Sensitivity of Last Glacial Maximum climate to uncertainties in tropical and subtropical ocean temperatures

USGS Publications Warehouse

Hostetler, S.; Pisias, N.; Mix, A.

2006-01-01

The faunal and floral gradients that underlie the CLIMAP (1981) sea-surface temperature (SST) reconstructions for the Last Glacial Maximum (LGM) reflect ocean temperature gradients and frontal positions. The transfer functions used to reconstruct SSTs from biologic gradients are biased, however, because at the warmest sites they display inherently low sensitivity in translating fauna to SST and they underestimate SST within the euphotic zones where the pycnocline is strong. Here we assemble available data and apply a statistical approach to adjust for hypothetical biases in the faunal-based SST estimates of LGM temperature. The largest bias adjustments are distributed in the tropics (to address low sensitivity) and subtropics (to address underestimation in the euphotic zones). The resulting SSTs are generally in better agreement than CLIMAP with recent geochemical estimates of glacial-interglacial temperature changes. We conducted a series of model experiments using the GENESIS general atmospheric circulation model to assess the sensitivity of the climate system to our bias-adjusted SSTs. Globally, the new SST field results in a modeled LGM surface-air cooling relative to present of 6.4 ??C (1.9 ??C cooler than that of CLIMAP). Relative to the simulation with CLIMAP SSTs, modeled precipitation over the oceans is reduced by 0.4 mm d-1 (an anomaly -0.4 versus 0.0 mm d-1 for CLIMAP) and increased over land (an anomaly -0.2 versus -0.5 mm d-1 for CLIMAP). Regionally strong responses are induced by changes in SST gradients. Data-model comparisons indicate improvement in agreement relative to CLIMAP, but differences among terrestrial data inferences and simulated moisture and temperature remain. Our SSTs result in positive mass balance over the northern hemisphere ice sheets (primarily through reduced summer ablation), supporting the hypothesis that tropical and subtropical ocean temperatures may have played a role in triggering glacial changes at higher latitudes.

Temporal and spatial variability of biological nitrogen fixation off the upwelling system of central Chile (35-38.5°S)

NASA Astrophysics Data System (ADS)

Fernandez, Camila; González, Maria Lorena; Muñoz, Claudia; Molina, Veronica; Farias, Laura

2015-05-01

Although N2 fixation could represent a supplementary source of bioavailable nitrogen in coastal upwelling areas and underlying oxygen minimum zones (OMZs), the limited data available prevent assessing its variability and biogeochemical significance. Here we report the most extensive N2 fixation data set gathered to date in the upwelling area off central Chile (36°S). It covers interannual to high frequency time scales in an area of about 82,500 km2 in the eastern South Pacific (ESP). Because heterotrophic N2 fixation may be regulated by DOM availability in the ESP, we conducted experiments at different oxygen conditions and included DOM amendments in order to test diazotrophic activity. Rates in the euphotic zone showed strong temporal variability which resulted in values reaching 0.5 nmol L-1 d-1 in 2006 (average 0.32 ± 0.17 nmol L-1 d-1) and up to 126.8 nmol L-1 d-1 (average 24.75 ± 37.9 nmol L-1 d-1) in 2011. N2 fixation in subsurface suboxic conditions (1.5 ± 1.16 nmol L-1 d-1) also occurred mainly during late summer and autumn while virtually absent in winter. The diversity of diazotrophs was dominated by heterotrophs, with higher richness in surface compared to OMZ waters. Rates in oxygen depleted conditions could exceed values obtained in the euphotic layer, but rates were not dependent on the availability of dissolved organic matter. N2 fixation also showed a positive correlation with total chlorophyll and the C:N ratio of phytoplankton, but not to the P excess compared to N. We conclude that the diazotrophic community responds to the composition of phytoplankton rather than the extent of N deficiency and the availability of bulk DOM in this system.

Patterns of chlorophyll-a distribution linked to mesoscale structures in two contrasting areas Campeche Canyon and Bank, Southern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Durán-Campos, Elizabeth; Salas-de-León, David Alberto; Monreal-Gómez, María Adela; Coria-Monter, Erik

2017-05-01

The chlorophyll-a (Chl-a) distribution in Campeche Canyon and Campeche Bank, at the Southern Gulf of Mexico, as well as its relationship with hydrographic structure were analyzed. The results show the existence of the Gulf Common Water (GCW), the Caribbean Tropical Surface Water (CTSW) and the Caribbean Subtropical Underwater (CSUW) in the 120 m upper layer at the Campeche Canyon. While at the Campeche Bank only the Caribbean Tropical Surface Water (CTSW) was found. The 15 °C and 18.5 °C isotherms topography depict the presence of a mesoscale anticyclone-cyclone dipole. The nutrient pumping mechanism fertilizes the eutrophic zone promoted by the cyclonic eddy. Submesoscale processes in the border of an anticyclone and a cyclone results in maximum of nitrate concentration and vertically integrated Chl-a at the frontal zone. Two Chl-a vertical distribution patterns were found, a deep maximum at the base of the euphotic layer not associated to the thermocline over the Campeche Canyon and a peak associated to the thermocline related to the shallow bottom at the Campeche Bank. Oligotrophic conditions were observed in the 50 m upper layer and mesotrophic conditions were found below this layer. The differences between the Campeche Bank and Campeche Canyon are that: in the canyon, the nutrient and Chl-a peaks were linked with the cyclone, and the submesoscale processes in the border of an anticyclone and a cyclone, respectively. In the vertical the maximum Chl-a was associated to the base of the euphotic layer and dominated by coccolithophores. In the Campeche Bank the nutrient and Chl-a peaks were influenced by the shelf break in the vertical the maximum Chl-a was associated with the thermocline and the silicoflagellate was identified as the dominant species.

A Coupled Epipelagic-Meso/Bathypelagic Particle Flux Model for the Bermuda Atlantic Time-series Station (BATS)/Oceanic Flux Program (OFP) Site

NASA Astrophysics Data System (ADS)

Glover, D. M.; Conte, M.

2002-12-01

Of considerable scientific interest is the role remineralization plays in the global carbon cycle. It is the ``biological pump'' that fixes carbon in the upper water column and exports it for long time periods to the deep ocean. From a global carbon cycle point-of-view, it is the processes that govern remineralization in the mid- to deep-ocean waters that provide the feedback to the biogeochemical carbon cycle. In this study we construct an ecosystem model that serves as a mechanistic link between euphotic processes and mesopelagic and bathypelagic processes. We then use this prognostic model to further our understanding of the unparalleled time-series of deep-water sediment traps (21+ years) at the Oceanic Flux Program (OFP) and the euphotic zone measurements (10+ years) at the Bermuda Atlantic Time-series Site (BATS). At the core of this mechanistic ecosystem model of the mesopelagic zone is a model that consists of an active feeding habit zooplankton, a passive feeding habit zooplankton, large detritus (sinks), small detritus (non-sinking), and a nutrient pool. As the detritus, the primary source of food, moves through the water column it is fed upon by the active/passive zooplankton pair and undergoes bacterially mediated remineralization into nutrients. The large detritus pool at depth gains material from the formation of fecal pellets from the passive and active zooplankton. Sloppy feeding habits of the active zooplankton contribute to the small detrital pool. Zooplankton mortality (both classes) also contribute directly to the large detritus pool. Aggregation and disaggregation transform detrital particles from one pool to the other and back again. The nutrients at each depth will gain from detrital remineralization and zooplankton excretion. The equations that model the active zooplankton, passive zooplankton, large detritus, small detritus, and nutrients will be reviewed, results shown and future model modifications discussed.

The fate of nitrogen fixed by diazotrophs in the ocean

NASA Astrophysics Data System (ADS)

Mulholland, M. R.

2007-01-01

While we now know that N2 fixation is a significant source of new nitrogen (N) in the marine environment, little is known about the fate of this N (and associated C), despite the importance of diazotrophs to global carbon and nutrient cycles. Specifically, does N fixed during N2 fixation fuel autotrophic or heterotrophic growth and thus facilitate carbon (C) export from the euphotic zone, or does it contribute primarily to bacterial productivity and respiration in the euphotic zone? For Trichodesmium, the diazotroph we know the most about, the transfer of recently fixed N2 (and C) appears to be primarily through dissolved pools. The release of N varies among and within populations and as a result of the changing physiological state of cells and populations. The net result of trophic transfers appears to depend on the co-occurring organisms and the complexity of the colonizing community. In order to understand the impact of diazotrophy on carbon flow and export in marine systems, we need a better understanding of the trophic flow of elements in Trichodesmium-dominated communities and other diazotrophic communities under various defined physiological states. Nitrogen and carbon fixation rates themselves vary by orders of magnitude within and among studies of Trichodesmium, highlighting the difficulty in extrapolating global rates of N2 fixation from direct measurements. Because the stoichiometry of N2 and C fixation does not appear to be in balance with that of particles, and the relationship between C and N2 fixation rates is also variable, it is equally difficult to derive global rates of one from the other. This paper seeks to synthesize what is known about the fate of diazotrophic production in the environment. A better understanding of the physiology and physiological ecology of Trichodesmium and other marine diazotrophs is necessary to quantify and predict the effects of increased or decreased diazotrophy in the context of the carbon cycle and global change.

Response of phytoplankton and enhanced biogeochemical activity to an episodic typhoon event in the coastal waters of Japan

NASA Astrophysics Data System (ADS)

Tsuchiya, Kenji; Kuwahara, Victor S.; Yoshiki, Tomoko M.; Nakajima, Ryota; Shimode, Shinji; Kikuchi, Tomohiko; Toda, Tatsuki

2017-07-01

Daily field surveys were conducted at a coastal-shelf station in Sagami Bay, Japan after the passage of typhoon Malou in 2010 to evaluate the after-effect of a typhoon passage on the physical-chemical environment, phytoplankton bloom formation and microbial processes within and below the euphotic layer. The passage of Malou induced an abrupt decrease in salinity and increased loading of nutrients to the euphotic layer. Dinoflagellates dominated the phytoplankton community at the surface, whereas diatoms dominated below the surface just after the passage of Malou. Four days later, the dominant dinoflagellate taxa at the surface changed from Protoperidinium spp. to Prorocentrum spp. and Ceratium spp., indicating a dinoflagellate community succession from heterotrophic to autotrophic functional groups. Five days after passage, the dominant phytoplankton taxa shifted from dinoflagellates to diatom groups of Chaetoceros spp. and Cerataulina spp. throughout the water column. Below the euphotic layer, there were increases in diatom frustules, mainly composed of Chaetoceros spp. and Cerataulina spp., bacterial abundance and NH4+ concentrations. Diatom carbon biomass contributed to approximately half of particulate organic carbon (POC) below the euphotic layer, suggesting a significant contribution of diatoms to POC sinking flux after the passage of a typhoon. Bacterial abundance was positively correlated to both phaeopigment concentrations (p < 0.01) and NH4+ concentrations (p < 0.01), suggesting bacterial growth was associated with zooplankton grazing and remineralization of NH4+. The results suggest that the passage of a typhoon could significantly affect biogeochemical activities within and below the euphotic layer in temperate coastal waters.

Radon and radium in the ice-covered Arctic Ocean, and what they reveal about gas exchange in the sea ice zone.

NASA Astrophysics Data System (ADS)

Loose, B.; Kelly, R. P.; Bigdeli, A.; Moran, S. B.

2014-12-01

The polar sea ice zones are regions of high primary productivity and interior water mass formation. Consequently, the seasonal sea ice cycle appears important to both the solubility and biological carbon pumps. To estimate net CO2 transfer in the sea ice zone, we require accurate estimates of the air-sea gas transfer velocity. In the open ocean, the gas transfer velocity is driven by wind, waves and bubbles - all of which are strongly altered by the presence of sea ice, making it difficult to translate open ocean estimates of gas transfer to the ice zone. In this study, we present profiles of 222Rn and 226Ra throughout the mixed-layer and euphotic zone. Profiles were collected spanning a range of sea ice cover conditions from 40 to 100%. The profiles of Rn/Ra can be used to estimate the gas transfer velocity, but the 3.8 day half-life of 222Rn implies that mixed layer radon will have a memory of the past ~20 days of gas exchange forcing, which may include a range of sea ice cover conditions. Here, we compare individual estimates of the gas transfer velocity to the turbulent forcing conditions constrained from shipboard and regional reanalysis data to more appropriately capture the time history upper ocean Rn/Ra.

Microbial gardening in the ocean's twilight zone: detritivorous metazoans benefit from fragmenting, rather than ingesting, sinking detritus: fragmentation of refractory detritus by zooplankton beneath the euphotic zone stimulates the harvestable production of labile and nutritious microbial biomass.

PubMed

Mayor, Daniel J; Sanders, Richard; Giering, Sarah L C; Anderson, Thomas R

2014-12-01

Sinking organic particles transfer ∼10 gigatonnes of carbon into the deep ocean each year, keeping the atmospheric CO2 concentration significantly lower than would otherwise be the case. The exact size of this effect is strongly influenced by biological activity in the ocean's twilight zone (∼50-1,000 m beneath the surface). Recent work suggests that the resident zooplankton fragment, rather than ingest, the majority of encountered organic particles, thereby stimulating bacterial proliferation and the deep-ocean microbial food web. Here we speculate that this apparently counterintuitive behaviour is an example of 'microbial gardening', a strategy that exploits the enzymatic and biosynthetic capabilities of microorganisms to facilitate the 'gardener's' access to a suite of otherwise unavailable compounds that are essential for metazoan life. We demonstrate the potential gains that zooplankton stand to make from microbial gardening using a simple steady state model, and we suggest avenues for future research. © 2014 The Authors. Bioessays published by WILEY Periodicals, Inc.

Seasonality of coastal zone scanner phytoplankton pigment in the offshore oceans

NASA Technical Reports Server (NTRS)

Banse, K.; English, D. C.

1994-01-01

The NASA Global Ocean Data Set of plant pigment concentrations in the upper euphotic zone is evaluated for diserning geographical and temporal patterns of seasonality in the open sea. Monthly medians of pigment concentrations for all available years are generated for fields of approximately 77,000 sq km. For the climatological year, highest and lowest medians, month of occurence of the highest median, ratio of highest to lowest medians, and absolute range between the highest and lowest medians are mapped ocean-wide between 62.5 deg N and 62.5 deg S. Seasonal cycles are depicted for 48 sites. In much of the offshore ocean, seasonality of pigment is inferred to be driven almost equally by the interaction of the abiotic environment with phytoplankton physiology and the loss of cells from grazing. Special emphasis among natural domains or provinces is given to the Subantarctic water ring, with no seasonality in its low chlorophyll concentrations in spite of strong environmental forcing, and the narrow Transition Zones, a few degrees of latitude on the equatorial sides of the Subtropical Convergences of the southern hemisphere and their homologs in the northern hemisphere, which have late winter blooms caused by nutrient injection into the upper layers.

Bio-Optical Properties of the Arabian Sea as Determined by In-Situ and SeaWifs Data

NASA Technical Reports Server (NTRS)

Trees, Charles C.

1998-01-01

The overall objective of this work was to characterize optical and fluorescence properties in the euphotic zone during two British Ocean Flux Study (BOFS) Arabian Sea cruises. This was later expanded in 1995 to include three U.S. Joint Global Ocean Flux Study (JGOFS) Arabian Sea Cruises. The region was to be divided into one or more "bio-optical provinces", within each of which a single set of regression models was to be developed to relate the vertical distribution of irradiance attenuation and normalized fluorescence (SF and NF) to remote sensing reflectance and diffuse attenuation coefficient [K(490)]. The working hypothesis was that over relatively large spatial and temporal scales, the vertical profiles of bio-optical properties were predictable.

Predicting improved optical water quality in rivers resulting from soil conservation actions on land.

PubMed

Dymond, J R; Davies-Colley, R J; Hughes, A O; Matthaei, C D

2017-12-15

Deforestation in New Zealand has led to increased soil erosion and sediment loads in rivers. Increased suspended fine sediment in water reduces visual clarity for humans and aquatic animals and reduces penetration of photosynthetically available radiation to aquatic plants. To mitigate fine-sediment impacts in rivers, catchment-wide approaches to reducing soil erosion are required. Targeting soil conservation for reducing sediment loads in rivers is possible through existing models; however, relationships between sediment loads and sediment-related attributes of water that affect both ecology and human uses of water are poorly understood. We present methods for relating sediment loads to sediment concentration, visual clarity, and euphotic depth. The methods require upwards of twenty concurrent samples of sediment concentration, visual clarity, and euphotic depth at a river site where discharge is measured continuously. The sediment-related attributes are related to sediment concentration through regressions. When sediment loads are reduced by soil conservation action, percentiles of sediment concentration are necessarily reduced, and the corresponding percentiles of visual clarity and euphotic depth are increased. The approach is demonstrated on the Wairua River in the Northland region of New Zealand. For this river we show that visual clarity would increase relatively by approximately 1.4 times the relative reduction of sediment load. Median visual clarity would increase from 0.75m to 1.25m (making the river more often suitable for swimming) after a sediment load reduction of 50% associated with widespread soil conservation on pastoral land. Likewise euphotic depth would increase relatively by approximately 0.7 times the relative reduction of sediment load, and the median euphotic depth would increase from 1.5m to 2.0m with a 50% sediment load reduction. Copyright © 2017 Elsevier B.V. All rights reserved.

Chemical and physical microenvironments at the Viking landing sites

NASA Technical Reports Server (NTRS)

Clark, B. C.

1979-01-01

Physical and chemical considerations permit the division of the near-surface regolith on Mars into at least six zones of distinct microenvironments. The zones are euphotic, duricrust/peds, tempofrost, permafrost, endolithic, and interfacial/transitional. Microenvironments vary significantly in temperature extremes, mean temperature, salt content, relative pressure of water vapor, UV and visible light irradiance, and exposure to ionizing radiation events (100 Mrad) and oxidative molecular species. From what is known of the chemistry of the atmosphere and regolith fines (soil), limits upon the aqueous chemistry of soil pastes may be estimated. Heat of wetting could reach 45 cal/g dry soil; initial pH is indeterminate between 1 and 10; ionic strength and salinity are predicted to be extremely high; freezing point depression is inadequate to provide quantities of liquid water except in special cases. The prospects for biotic survival are grim by terrestrial standards, but the extremes of biological resiliency are inaccessible to evaluation. Second-generation in situ experiments which will better define Martian microenvironments are clearly possible. Antarctic dry valleys are approximations to Martian conditions, but deviate significantly by at least half-a-dozen criteria.

Chemical and physical microenvironments at the Viking landing sites.

PubMed

Clark, B C

1979-12-01

Physical and chemical considerations permit the division of the near-surface regolith on Mars into at least six zones of distinct microenvironments. The zones are euphotic, duricrust/peds, tempofrost, permafrost, endolithic, and interfacial/transitional. Microenvironments vary significantly in temperature extremes, mean temperature, salt content, relative pressure of water vapor, UV and visible light irradiance, and exposure to ionizing radiation events (100 Mrad) and oxidative molecular species. From what is known of the chemistry of the atmosphere and regolith fines (soil), limits upon the aqueous chemistry of soil pastes may be estimated. Heat of wetting could reach 45 cal/g dry soil; initial pH is indeterminate between 1 and 10; ionic strength and salinity are predicted to be extremely high; freezing point depression is inadequate to provide quantities of liquid water except in special cases. The prospects for biotic survival are grim by terrestrial standards, but the extremes of biological resiliency are inaccessible to evaluation. Second-generation in situ experiments which will better define Martian microenvironments are clearly possible. Antarctic dry valleys are approximations to Martian conditions, but deviate significantly by at least half-a-dozen criteria.

The distribution and metabolism of urea in the eastern Canadian Arctic

NASA Astrophysics Data System (ADS)

Harrison, W. G.; Head, E. J. H.; Conover, R. J.; Longhurst, A. R.; Sameoto, D. D.

1985-01-01

Urea concentrations, uptake, and excretion were measured at various locations in northern Baffin Bay and surrounding waters during the summer of 1980. Concentrations were variable (<0.03 to > 2.00 mg-at. N m -3) but followed patterns of decreasing concentration with depth in the euphotic zone and with distance from land. Urea accounted for > 50% of the total dissolved nitrogen in the upper mixed layer at most stations. Urea uptake rates showed generally the same distributional patterns as did concentrations and on the average accounted for 32% of the total nitrogen (NO 3- + NH 4+ + urea) productivity in the eupholic zone. Ammonium, and frequently NO 3-, were utilized in preference to urea. Dual isotope ( 14C and 15N-urea) labelling experiments suggested that most urea-C was respired as CO 2 while 50 to 80% of the urea-N was incorporated by the phytoplankton. Excretion measurements suggested that the four dominant macrozooplankton species ( Calanus hyperboreus, C. finmarchicus, C. glacialis, and Metridia sp.) supplied only -3% of the urea-N but -40% of the NH 4+-N requirements of the primary producers.

Variable viral and grazer control of prokaryotic growth efficiency in temperate freshwater lakes (French Massif Central).

PubMed

Ram, A S Pradeep; Palesse, S; Colombet, J; Sabart, M; Perriere, F; Sime-Ngando, T

2013-11-01

The effects of viral lysis and heterotrophic nanoflagellate grazing (top down forces) on prokaryotic mortality and their subsequent impact on their metabolism were estimated in the upper euphotic and deeper aphotic depth of 11 freshwater lakes located in the French Massif Central. The standing stocks of viruses (VA) and heterotrophic nanoflagellate (HNF) varied significantly (p < 0.05) with sampled depth. VA was substantially (twofold on an average) and significantly higher (p < 0.03) at the aphotic compared to euphotic depth, whereas the reverse was true (p < 0.02) for HNF. Among the prokaryote subgroup, high nucleic acid content prokaryotes explained for significant variability in the total VA and served as principle host target for viral proliferation. Like standing stocks, flagellate grazing and viral infection rates also followed similar patterns. In the investigated lakes, the mechanism for regulating prokaryotic production varied with sampled depth from grazing control in the euphotic to control due to viral lysis in the aphotic. We also tested the hypothesis of top down control on prokaryotic growth efficiency (PGE, which we used as an index of prokaryotic physiological and energetic status at the community level) at both depths. Overall, among the studied lakes, PGE varied widely (4-51 %) with significantly (p < 0.05) lower values in the aphotic (mean = 18 ± 4 %) than euphotic depth (mean = 32 ± 9 %). Contrasting observations on the top down control of PGE between sampled depths were observed. The presence of grazers was found to stimulate PGE at the euphotic, whereas viruses through their lytic infection had a strong negative impact on PGE at the aphotic depth. Such observed differences in PGE and the mechanism controlling prokaryotic production with depth could eventually have strong implication on carbon and nutrient flux patterns in the studied lakes.

Organic matter processing by microbial communities throughout the Atlantic water column as revealed by metaproteomics.

PubMed

Bergauer, Kristin; Fernandez-Guerra, Antonio; Garcia, Juan A L; Sprenger, Richard R; Stepanauskas, Ramunas; Pachiadaki, Maria G; Jensen, Ole N; Herndl, Gerhard J

2018-01-16

The phylogenetic composition of the heterotrophic microbial community is depth stratified in the oceanic water column down to abyssopelagic layers. In the layers below the euphotic zone, it has been suggested that heterotrophic microbes rely largely on solubilized particulate organic matter as a carbon and energy source rather than on dissolved organic matter. To decipher whether changes in the phylogenetic composition with depth are reflected in changes in the bacterial and archaeal transporter proteins, we generated an extensive metaproteomic and metagenomic dataset of microbial communities collected from 100- to 5,000-m depth in the Atlantic Ocean. By identifying which compounds of the organic matter pool are absorbed, transported, and incorporated into microbial cells, intriguing insights into organic matter transformation in the deep ocean emerged. On average, solute transporters accounted for 23% of identified protein sequences in the lower euphotic and ∼39% in the bathypelagic layer, indicating the central role of heterotrophy in the dark ocean. In the bathypelagic layer, substrate affinities of expressed transporters suggest that, in addition to amino acids, peptides and carbohydrates, carboxylic acids and compatible solutes may be essential substrates for the microbial community. Key players with highest expression of solute transporters were Alphaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria, accounting for 40%, 11%, and 10%, respectively, of relative protein abundances. The in situ expression of solute transporters indicates that the heterotrophic prokaryotic community is geared toward the utilization of similar organic compounds throughout the water column, with yet higher abundances of transporters targeting aromatic compounds in the bathypelagic realm. Copyright © 2018 the Author(s). Published by PNAS.

Organic matter processing by microbial communities throughout the Atlantic water column as revealed by metaproteomics

PubMed Central

Bergauer, Kristin; Fernandez-Guerra, Antonio; Garcia, Juan A. L.; Sprenger, Richard R.; Stepanauskas, Ramunas; Pachiadaki, Maria G.; Herndl, Gerhard J.

2018-01-01

The phylogenetic composition of the heterotrophic microbial community is depth stratified in the oceanic water column down to abyssopelagic layers. In the layers below the euphotic zone, it has been suggested that heterotrophic microbes rely largely on solubilized particulate organic matter as a carbon and energy source rather than on dissolved organic matter. To decipher whether changes in the phylogenetic composition with depth are reflected in changes in the bacterial and archaeal transporter proteins, we generated an extensive metaproteomic and metagenomic dataset of microbial communities collected from 100- to 5,000-m depth in the Atlantic Ocean. By identifying which compounds of the organic matter pool are absorbed, transported, and incorporated into microbial cells, intriguing insights into organic matter transformation in the deep ocean emerged. On average, solute transporters accounted for 23% of identified protein sequences in the lower euphotic and ∼39% in the bathypelagic layer, indicating the central role of heterotrophy in the dark ocean. In the bathypelagic layer, substrate affinities of expressed transporters suggest that, in addition to amino acids, peptides and carbohydrates, carboxylic acids and compatible solutes may be essential substrates for the microbial community. Key players with highest expression of solute transporters were Alphaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria, accounting for 40%, 11%, and 10%, respectively, of relative protein abundances. The in situ expression of solute transporters indicates that the heterotrophic prokaryotic community is geared toward the utilization of similar organic compounds throughout the water column, with yet higher abundances of transporters targeting aromatic compounds in the bathypelagic realm. PMID:29255014

Cycling of Dissolved Organic Phosphorus and Alkaline Phosphatase Activity in Euphotic Zone of the Western North Pacific

NASA Astrophysics Data System (ADS)

Suzumura, M.

2010-12-01

Phosphorus is an essential nutrient for marine organisms. In oligotrophic environments, concentrations of dissolved inorganic phosphate (SRP), the most bioavailable form of phosphorus, are low and have been hypothesized to constrain the primary productivity. Evidence has been found that dissolved organic phosphorus (DOP) supports a significant fraction of primary production through hydrolytic remineralization of DOP to SRP by alkaline phosphatase (APA). In this study, DOP biogeochemistry was investigated at three locations of the open-ocean environment in the Kuroshio region and at a semi-eutrophic coastal site of the western North Pacific. Concentrations of SRP, DOP and hydrolyzable ester-P were measured in the euphotic zone. Kinetic parameters of APA were determined using a fluorogenic substrate, including potential maximum velocity (Vmax), apparent Michaelis-Menten half-saturation constant (Km), and turnover time (TA) of APA hydrolyzable DOP. SRP concentrations were quite low (≤ 10 nM) in the surface seawater and rapidly increased below the chlorophyll a maximum layer (CML). DOP concentration ranged from 29 to 223 nM. Above the CML, DOP composed a major fraction accounting for 60-100% of dissolved total P. A significant linear relationship was found between the concentrations of SRP and hydrolyzable ester-P (R2 = 0.83, P < 0.01). This suggests active utilization of ester-P under phosphate-depleted conditions. In the Kuroshio region, Vmax of APA exhibited the highest value at the surface water (0 m) and decreased rapidly with depth, while at the coastal site the peak value was found at CML. TA of hydrolyzable DOP was quite variable among the locations and increased with depth especially below CML. The estimated values of in situ hydrolysis rate were much lower (2-34%) than the potential Vmax which was determined with the addition of an excess amount of the substrate. The results suggest that marine microbes can efficiently and rapidly utilize hydrolyzable DOP under phosphate-depleted conditions and that there is still room in the in situ APA activity. Utilization of DOP, however, is likely regulated by the ambient concentrations of hydrolyzable ester-P lower than the apparent Km.

The trophic role of mesozooplankton at 47°N, 20°W during the North Atlantic Bloom Experiment

NASA Astrophysics Data System (ADS)

Dam, Hans G.; Miller, Carolyn A.; Jonasdottir, Sigrun H.

The biomass and grazing rates of three size classes of mesozooplankton—0.2-0.5 mm (small), 0.5-1.0 mm (medium) and 1.0-2.0 mm (large)—were quantified in the vicinity of 47°N, 20°W, from 25 April to 7 May (leg 4) and from 18 to 31 May 1989 (leg 5) as part of the North Atlantic Bloom Experiment (NABE) of the Joint Global Ocean Flux Study (JGOFS). Biomass was inversely related to body size, with the small size fraction accounting for > 50% of the entire mesozooplankton biomass. Diel differences in biomass, however, were directly related to body size, indicating that vertical migration became more pronounced as the size of the animals increased. Total zooplankton biomass increased by almost a factor of 3 from the beginning to the end of the study. The average carbon-weight of individuals increased six-fold from leg 4 to leg 5 of the study. Carbon-specific rates of phytoplankton ingestion were (1) inversely related to body size; (2) greater at night for all size fractions; and (3) generally greater on leg 4 than on leg 5, particularly for the small size fraction. Grazing was dominated by the small size fraction (66% of the total grazing) on leg 4 and by the medium size fraction (44% of the total grazing) on leg 5. The removal of the daily primary production by mesozooplankton was not different from leg 4 to leg 5, averaging 2.7% day -1 (range 0.6-5.2% day -1). Comparisons of (1) estimated metabolic rates and (2) measured nitrogen excretion rates with daily rations of carbon and nitrogen, respectively, for zooplankton suggest that a phytoplankton diet only contributed about 50% of the daily carbon and nitrogen rations of animals. We hypothesize that mesozooplankton fecal pellets contributed < 5% of the POC flux out of the euphotic zone measured with particle traps. However, we estimate that during leg 5, the active flux of dissolved nitrogen out of the euphotic zone due to mesozooplankton diel vertical migration was 26% of the passive PON flux.

Differential Assimilation of Inorganic Carbon and Leucine by Prochlorococcus in the Oligotrophic North Pacific Subtropical Gyre

PubMed Central

Björkman, Karin M.; Church, Matthew J.; Doggett, Joseph K.; Karl, David M.

2015-01-01

The light effect on photoheterotrophic processes in Prochlorococcus, and primary and bacterial productivity in the oligotrophic North Pacific Subtropical Gyre was investigated using 14C-bicarbonate and 3H-leucine. Light and dark incubation experiments were conducted in situ throughout the euphotic zone (0–175 m) on nine expeditions to Station ALOHA over a 3-year period. Photosynthetrons were also used to elucidate rate responses in leucine and inorganic carbon assimilation as a function of light intensity. Taxonomic group and cell-specific rates were assessed using flow cytometric sorting. The light:dark assimilation rate ratios of leucine in the top 150 m were ∼7:1 for Prochlorococcus, whereas the light:dark ratios for the non-pigmented bacteria (NPB) were not significant different from 1:1. Prochlorococcus assimilated leucine in the dark at per cell rates similar to the NPB, with a contribution to the total community bacterial production, integrated over the euphotic zone, of approximately 20% in the dark and 60% in the light. Depth-resolved primary productivity and leucine incorporation showed that the ratio of Prochlorococcus leucine:primary production peaked at 100 m then declined steeply below the deep chlorophyll maximum (DCM). The photosynthetron experiments revealed that, for Prochlorococcus at the DCM, the saturating irradiance (Ek) for leucine incorporation was reached at approximately half the light intensity required for light saturation of 14C-bicarbonate assimilation. Additionally, high and low red fluorescing Prochlorococcus populations (HRF and LRF), co-occurring at the DCM, had similar Ek values for their respective substrates, however, maximum assimilation rates, for both leucine and inorganic carbon, were two times greater for HRF cells. Our results show that Prochlorococcus contributes significantly to bacterial production estimates using 3H-leucine, whether or not the incubations are conducted in the dark or light, and this should be considered when making assessments of bacterial production in marine environments where Prochlorococcus is present. Furthermore, Prochlorococcus primary productivity showed rate to light-flux patterns that were different from its light enhanced leucine incorporation. This decoupling from autotrophic growth may indicate a separate light stimulated mechanism for leucine acquisition. PMID:26733953

Open ocean dead zones in the tropical North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Karstensen, J.; Fiedler, B.; Schütte, F.; Brandt, P.; Körtzinger, A.; Fischer, G.; Zantopp, R.; Hahn, J.; Visbeck, M.; Wallace, D.

2015-04-01

Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg-1) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg-1. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day-1, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

High biomass, low export regimes in the Southern Ocean

NASA Astrophysics Data System (ADS)

Lam, Phoebe J.; Bishop, James K. B.

2007-03-01

This paper investigates ballasting and remineralization controls of carbon sedimentation in the Twilight Zone (100-1000 m) of the Southern Ocean. Size-fractionated (<1 μm, 1-51 μm, >51 μm) suspended particulate matter was collected by large-volume in-situ filtration from the upper 1000 m in the Subantarctic (55°S, 172°W) and Antarctic (66°S, 172°W) zones of the Southern Ocean during the Southern Ocean Iron Experiment (SOFeX) in January-February 2002. Particles were analyzed for major chemical constituents (POC, P, biogenic Si, CaCO 3), and digital and SEM image analyses of particles were used to aid in the interpretation of the chemical profiles. Twilight Zone waters at 66°S in the Antarctic had a steeper decrease in POC with depth than at 55°S in the Subantarctic, with lower POC concentrations in all size fractions at 66°S than at 55°S, despite up to an-order-of magnitude higher POC in surface waters at 66°S. The decay length scale of >51-μm POC was significantly shorter in the upper Twilight Zone at 66°S ( δe=26 m) compared to 55°S ( δe=81 m). Particles in the carbonate-producing 55°S did not have higher excess densities than particles from the diatom-dominated 66°S, indicating that there was no direct ballast effect that accounted for deeper POC penetration at 55°S. An indirect ballast effect due to differences in particle packaging and porosities cannot be ruled out, however, as aggregate porosities were high (˜97%) and variable. Image analyses point to the importance of particle loss rates from zooplankton grazing and remineralization as determining factors for the difference in Twilight Zone POC concentrations at 55°S and 66°S, with stronger and more focused shallow remineralization at 66°S. At 66°S, an abundance of large (several mm long) fecal pellets from the surface to 150 m, and almost total removal of large aggregates by 200 m, reflected the actions of a single or few zooplankton species capable of grazing diatoms in the euphotic zone, coupled with a more diverse particle-feeding zooplankton community immediately below. Surface waters with high biomass levels and high proportion of biomass in the large-size fraction were associated with low particle loading at depth, with all indications implying conditions of low export. The 66°S region exhibits this "high biomass, low export" (HBLE) condition, with very high >51-μm POC concentrations at the surface (˜2.1 μM POC), but low concentrations below 200 m (<0.07 μM POC). The 66°S region remained HBLE after iron fertilization. Iron addition at 55°S caused a 10 fold increase in >51-μm biomass concentrations in the euphotic zone, bringing surface POC concentrations to levels found at 66°S (˜3.8 μM), and a concurrent decrease in POC concentrations below 200 m. The 55°S region, which began with moderate levels of biomass and stronger particle export, transitioned to being HBLE after iron fertilization. We propose that iron addition to already HBLE waters will not cause mass sedimentation events. The stability of an iron-induced HBLE condition is unknown. Better understanding of biological pump processes in non-HBLE Subantarctic waters is needed.

Upper Ocean Response to Hurricanes Katrina and Rita (2005) from Multi-sensor Satellites

NASA Astrophysics Data System (ADS)

Gierach, M. M.; Bulusu, S.

2006-12-01

Analysis of satellite observations and model simulations of the mixed layer provided an opportunity to assess the biological and physical effects of hurricanes Katrina and Rita (2005) in the Gulf of Mexico. Oceanic cyclonic circulation was intensified by the hurricanes' wind field, maximizing upwelling, surface cooling, and deepening the mixed layer. Two areas of maximum surface chlorophyll-a concentration and sea surface cooling were detected with peak intensities ranging from 2-3 mg m-3 and 4-6°C, along the tracks of Katrina and Rita. The temperature of the mixed layer cooled approximately 2°C and the depth of the mixed layer deepened by approximately 33-52 m. The forced deepening of the mixed layer injected nutrients into the euphotic zone, generating phytoplankton blooms 3-5 days after the passage of Katrina and Rita (2005).

A dissolved cobalt plume in the oxygen minimum zone of the eastern tropical South Pacific

NASA Astrophysics Data System (ADS)

Hawco, Nicholas J.; Ohnemus, Daniel C.; Resing, Joseph A.; Twining, Benjamin S.; Saito, Mak A.

2016-10-01

Cobalt is a nutrient to phytoplankton, but knowledge about its biogeochemical cycling is limited, especially in the Pacific Ocean. Here, we report sections of dissolved cobalt and labile dissolved cobalt from the US GEOTRACES GP16 transect in the South Pacific. The cobalt distribution is closely tied to the extent and intensity of the oxygen minimum zone in the eastern South Pacific with highest concentrations measured at the oxycline near the Peru margin. Below 200 m, remineralization and circulation produce an inverse relationship between cobalt and dissolved oxygen that extends throughout the basin. Within the oxygen minimum zone, elevated concentrations of labile cobalt are generated by input from coastal sources and reduced scavenging at low O2. As these high cobalt waters are upwelled and advected offshore, phytoplankton export returns cobalt to low-oxygen water masses underneath. West of the Peru upwelling region, dissolved cobalt is less than 10 pM in the euphotic zone and strongly bound by organic ligands. Because the cobalt nutricline within the South Pacific gyre is deeper than in oligotrophic regions in the North and South Atlantic, cobalt involved in sustaining phytoplankton productivity in the gyre is heavily recycled and ultimately arrives from lateral transport of upwelled waters from the eastern margin. In contrast to large coastal inputs, atmospheric deposition and hydrothermal vents along the East Pacific Rise appear to be minor sources of cobalt. Overall, these results demonstrate that oxygen biogeochemistry exerts a strong influence on cobalt cycling.

Vertical stratification of bacterial communities driven by multiple environmental factors in the waters (0-5000 m) off the Galician coast (NW Iberian margin)

NASA Astrophysics Data System (ADS)

Dobal-Amador, Vladimir; Nieto-Cid, Mar; Guerrero-Feijoo, Elisa; Hernando-Morales, Victor; Teira, Eva; Varela-Rozados, Marta M.

2016-08-01

The processes mediated by microbial planktonic communities occur along the entire water column, yet the microbial activity and composition have been studied mainly in surface waters. This research examined the vertical variation in bacterial abundance, activity and community composition and structure from surface down to 5000 m depth following a longitudinal transect off the Galician coast (NW Iberian margin, from 43°N, 9°W to 43°N, 15°W). Community activity and composition changed with depth. The leucine incorporation rates decreased from the euphotic layer to the bathypelagic waters by three orders of magnitude, whereas prokaryotic abundance decreased only by one order of magnitude. The relative abundance of SAR11 and Alteromonas, determined by catalyzed reported deposition fluorescence in situ hybridization (CARD-FISH), decreased with depth. Meanwhile, the contribution of SAR 202 and SAR324 was significantly higher in the deeper layers (i.e. NEADW, North East Atlantic Deep Water and LDW, Lower Deep Water) than in the euphotic zone. Bacterial community structure, assessed by Automated Ribosomal Intergenic Spacer Analysis (ARISA), was depth-specific. A distance based linear model (DistLM) revealed that the variability found in bacterial community structure was mainly explained by temperature nitrate, phosphate, dissolved organic matter (DOM) fluorescence, prokaryotic abundance, leucine incorporation and to a lesser extent salinity, oxygen, CDOM absorbance and dissolved organic carbon concentration. Our results displayed a bacterial community structure shaped not only by depth-related physicochemical features but also by DOM quality, indicating that different prokaryotic taxa have the potential to metabolize particular DOM sources.

New Chemical, Bio-Optical and Physical Observations of Upper Ocean Response to the Passage of a Mesoscale Eddy Off Bermuda

NASA Technical Reports Server (NTRS)

McNeil, J. D.; Jannasch, H. W.; Dickey, T.; McGillicuddy, Dennis J., Jr.; Brzezinski, M.; Sakamoto, C. M.

1999-01-01

A mesoscale eddy advected across the Bermuda Testbed Mooring site over a 30-day period centered on July 14, 1995. Temperature and current measurements along with biogeochemical measurements were used to characterize the biological response of the upper ocean associated with the introduction of nitrate into the euphotic layer due to the doming of isotherms associated with the eddy. Complementary shipboard data showed an anomalous water mass, which extended from a depth of approximately 50 to 1000 m, manifesting as a cold surface expression and warm anomaly at depth. Although mesoscale eddies are frequently observed in the Sargasso Sea, the present observations are particularly unique because of the high-temporal-resolution measurements of the new instrumentation deployed on the mooring. Analyzers that measure nitrate plus nitrite were placed at depths of 80 and 200 m and bio-optical sensors were located at depths of 20, 35, 45, 71, and 86 m. Peak nitrate values of nearly 3.0 micro-M at 80 m and chlorophyll a values of 1.4 mg/cubic m at 71 m were observed, a well as a 25- to 30-meter shoaling of the 1% light level depth. A Doppler shift from the inertial period (22.8 hours) to 25.2 hours was observed in several time series records due to the movement of the eddy across the mooring. Inertial pumping brought cold, nutrient-rich waters farther into the euphotic zone than would occur solely by isothermal lifting. Silicic acid was depleted to undetectable levels owing to the growth of diatoms within the eddy. The chlorophyll a values associated with the eddy appear to be the largest recorded during the eight years of the ongoing US JGOFS Bermuda Atlantic Time Series Study program.

A bio-optical model for integration into ecosystem models for the Ligurian Sea

NASA Astrophysics Data System (ADS)

Bengil, Fethi; McKee, David; Beşiktepe, Sükrü T.; Sanjuan Calzado, Violeta; Trees, Charles

2016-12-01

A bio-optical model has been developed for the Ligurian Sea which encompasses both deep, oceanic Case 1 waters and shallow, coastal Case 2 waters. The model builds on earlier Case 1 models for the region and uses field data collected on the BP09 research cruise to establish new relationships for non-biogenic particles and CDOM. The bio-optical model reproduces in situ IOPs accurately and is used to parameterize radiative transfer simulations which demonstrate its utility for modeling underwater light levels and above surface remote sensing reflectance. Prediction of euphotic depth is found to be accurate to within ∼3.2 m (RMSE). Previously published light field models work well for deep oceanic parts of the Ligurian Sea that fit the Case 1 classification. However, they are found to significantly over-estimate euphotic depth in optically complex coastal waters where the influence of non-biogenic materials is strongest. For these coastal waters, the combination of the bio-optical model proposed here and full radiative transfer simulations provides significantly more accurate predictions of euphotic depth.

Enhanced export of carbon by salps during the northeast monsoon period in the northern Arabian Sea

NASA Astrophysics Data System (ADS)

Ramaswamy, V.; Sarin, M. M.; Rengarajan, R.

2005-07-01

A drifting sediment trap was deployed and 234Th activity in the water column was measured to calculate export flux of carbon at a time-series station in the northern Arabian Sea (lat. 21°30' N; long. 64°00' E) during the winter monsoon, 10-23 February 1997. The sampling period was characterised by an extensive salp swarm, and salp faecal pellets were the dominant contributors to the particulate matter in the sediment traps. Average 234Th flux out of the photic zone was 2300 dpm m -2 d -1 and average POC/ 234Th ratio in trap-derived particles was 0.14 mg/dpm. Average 234Th-derived export flux of carbon was about 332 mg m -2 d -1, representing 36% of the daily primary production (PP) (925 mg C m -2 d -1). Export of about one-third of the daily PP during the end of the winter monsoon could be due to the episodic nature of salp swarms. Salp swarms are frequently observed in the Arabian Sea and may be a significant pathway for rapid export of carbon from the euphotic zone.

Primary production and microbial activity in the euphotic zone of Lake Baikal (Southern Basin) during late winter

NASA Astrophysics Data System (ADS)

Straškrábová, V.; Izmest'yeva, L. R.; Maksimova, E. A.; Fietz, S.; Nedoma, J.; Borovec, J.; Kobanova, G. I.; Shchetinina, E. V.; Pislegina, E. V.

2005-04-01

Three years of regular weekly/biweekly monitoring of seasonal changes in temperature, transparency, chlorophyll a (CHL) and bacteria [erythrosine-stained microscopic counts and cultivable colony forming units (CFUs)] at the vertical profile in the South basin of Lake Baikal (51°54'195″N, 105°04'235″E, depth 800 m) were evaluated. In more detail, the structure and function of phytoplankton and the microbial loop in the euphotic layer at the same site were investigated during the late-winter-early-spring period under the ice. The depth of euphotic zone (up to 1% of surface irradiation) was 35 to 40 m. Primary production was measured three times a week with the 14C method in 2, 10, 20, 30 and 40 m. Maximum production was found in 10 m, with lower values towards the surface (light inhibition) and towards the lower layers. The total production in cells larger than 1 μm in the column (0-40 m) was 204-240 mg C d -1 m -2, 30-40% of it being in cells 1-3 μm (mostly picocyanobacteria), which represented roughly 9% of the total chlorophyll a (estimated from pigment analyses). A major part of phytoplankton biomass was formed by diatoms ( Synedra acus Hust., Asterionella formosa Hass. and Stephanodiscus meyerii Genkal & Popovskaya). Total production (including extracellular, dissolved organic matter) was 235-387 mg C day -1 m -2, and the exudates were readily used by bacteria (particles 0.2-1 μm). This part amounted to 1-5% of cellular production in 2 to 20 m and 11-77% of cellular production in 20-40 m, i.e., in light-limited layers. From 0 to 30 m, chlorophyll a concentration was 0.8 to 1.3 μg l -1, wherefrom it decreased rapidly to 0.1 μg l -1 towards the depth of 40 m. Bacteria (DAPI-stained microscopic counts) reached 0.5-1.4×10 6 ml -1; their cell volumes measured via image analysis were small (average 0.05 μm -3), often not well countable when erythrosine stain was used. Bacterial biomasses were in the range of 6-21 μg C l -1. Numbers of colony forming units (CFUs) on nutrient fish-agar were c. 3-4 orders lower than DAPI counts. The amounts of heterotrophic protists were low, whereby flagellates reached 6 to 87 ml -1 and ciliates, 0.2-1.2 ml -1 (mostly Oligotrichida). Bacterial production was measured in the same depths as primary production using 3H-thymidine (Thy) and 14C-leucine (Leu) uptake. Consistently, bacterial abundances, biomasses, thymidine and leucine production were higher by 30-50% in layers 2, 10 and 20 m compared with that in the deeper 30 and 40 m, where cellular primary production was negligible. Leucine uptake in the deeper layers was even three times lower than in the upper ones. From the comparison of primary and bacterial production, bacteria roughly use 20-40% of primary production during 24 h in the layers 2 to 20 m.

Chlorophyll a reconstruction from in situ measurements: 1. Method description

NASA Astrophysics Data System (ADS)

Fründt, B.; Dippner, J. W.; Waniek, J. J.

2015-02-01

Understanding the development of primary production is essential for projections of the global carbon cycle in the context of climate change. A chlorophyll a hindcast that serves as a primary production indicator was obtained by fitting in situ measurements of nitrate, chlorophyll a, and temperature. The resulting fitting functions were adapted to a modeled temperature field. The method was applied to observations from the Madeira Basin, in the northeastern part of the oligotrophic North Atlantic Subtropical Gyre and yielded a chlorophyll a field from 1989 to 2008 with a monthly resolution validated with remotely measured surface chlorophyll a data by SeaWiFS. The chlorophyll a hindcast determined with our method resolved the seasonal and interannual variability in the phytoplankton biomass of the euphotic zone as well as the deep chlorophyll maximum. Moreover, it will allow estimation of carbon uptake over long time scales.

Chemical whitings and chlorophyll distributions in the Great Lakes as viewed by Landsat

NASA Technical Reports Server (NTRS)

Strong, A. E.

1978-01-01

A chemical precipitation of calcium carbonate, or whiting, was first observed by satellite in Lake Michigan during August 1973. Since that initial observation similar events have been noted in Lakes Michigan, Erie, and Ontario with imagery from Landsat, Skylab, and NOAA satellites. By the use of Landsat multispectral data together with NOAA thermal infrared data, it has been observed that whitings occur several meters below the lake surface in relatively warm water. They are most vividly displayed during and after periods of upwelling. As the epilimnetic waters become supersaturated with Ca(+2) ions during summer, a triggering mechanism (presumably biological or physical) initiates the whiting, which may continue for several months. The effects on the biota of the euphotic zone when this milky cloud is present in the upper layers are poorly understood. However, Great Lakes circulation studies are taking advantage of these natural dye tracers.

Potential impacts of the Deepwater Horizon oil spill on large pelagic fishes

NASA Astrophysics Data System (ADS)

Frias-Torres, Sarrah; Bostater, Charles R., Jr.

2011-11-01

Biogeographical analyses provide insights on how the Deepwater Horizon oil spill impacted large pelagic fishes. We georeferenced historical ichthyoplankton surveys and published literature to map the spawning and larval areas of bluefin tuna, swordfish, blue marlin and whale shark sightings in the Gulf of Mexico with daily satellite-derived images detecting surface oil. The oil spill covered critical areas used by large pelagic fishes. Surface oil was detected in 100% of the northernmost whale shark sightings, in 32.8 % of the bluefin tuna spawning area and 38 % of the blue marlin larval area. No surface oil was detected in the swordfish spawning and larval area. Our study likely underestimates the extend of the oil spill due to satellite sensors detecting only the upper euphotic zone and the use of dispersants altering crude oil density, but provides a previously unknown spatio-temporal analysis.

The whale pump: marine mammals enhance primary productivity in a coastal basin.

PubMed

Roman, Joe; McCarthy, James J

2010-10-11

It is well known that microbes, zooplankton, and fish are important sources of recycled nitrogen in coastal waters, yet marine mammals have largely been ignored or dismissed in this cycle. Using field measurements and population data, we find that marine mammals can enhance primary productivity in their feeding areas by concentrating nitrogen near the surface through the release of flocculent fecal plumes. Whales and seals may be responsible for replenishing 2.3×10(4) metric tons of N per year in the Gulf of Maine's euphotic zone, more than the input of all rivers combined. This upward "whale pump" played a much larger role before commercial harvest, when marine mammal recycling of nitrogen was likely more than three times atmospheric N input. Even with reduced populations, marine mammals provide an important ecosystem service by sustaining productivity in regions where they occur in high densities.

The Whale Pump: Marine Mammals Enhance Primary Productivity in a Coastal Basin

PubMed Central

Roman, Joe; McCarthy, James J.

2010-01-01

It is well known that microbes, zooplankton, and fish are important sources of recycled nitrogen in coastal waters, yet marine mammals have largely been ignored or dismissed in this cycle. Using field measurements and population data, we find that marine mammals can enhance primary productivity in their feeding areas by concentrating nitrogen near the surface through the release of flocculent fecal plumes. Whales and seals may be responsible for replenishing 2.3×104 metric tons of N per year in the Gulf of Maine's euphotic zone, more than the input of all rivers combined. This upward “whale pump” played a much larger role before commercial harvest, when marine mammal recycling of nitrogen was likely more than three times atmospheric N input. Even with reduced populations, marine mammals provide an important ecosystem service by sustaining productivity in regions where they occur in high densities. PMID:20949007

Enhanced POC export in the oligotrophic northwest Pacific Ocean after extreme weather events

NASA Astrophysics Data System (ADS)

Chen, Kuo-Shu; Hung, Chin-Chang; Gong, Gwo-Ching; Chou, Wen-Chen; Chung, Chih-Ching; Shih, Yung-Yen; Wang, Chau-Chang

2013-11-01

study effects of extreme weather events (EWEs, e.g., dust storm and typhoon) on the export of particulate organic carbon (POC) measured by a floating sediment trap in the oligotrophic ocean, eight sea-going expeditions were conducted in the oligotrophic northwest Pacific (NWP) in 2007 and 2008, covering all four seasons and the passage of several EWEs. Results of year-round field observations demonstrate that the POC export fluxes in the oligotrophic NWP did not exhibit apparent seasonal variations yielding an average flux of 36.9 ± 5.8 mg-C m-2 d-1 without EWE effects. With EWE effects, however, the POC export flux (51.7 ± 13.2 mg-C m-2 d-1) showed an approximately 40% increase compared to the average flux measured without EWE effects. These results suggest that EWEs can trigger elevated POC export from the euphotic zone in the oligotrophic ocean.

Quantifying the time lag between organic matter production and export in the surface ocean: Implications for estimates of export efficiency

NASA Astrophysics Data System (ADS)

Stange, P.; Bach, L. T.; Le Moigne, F. A. C.; Taucher, J.; Boxhammer, T.; Riebesell, U.

2017-01-01

The ocean's potential to export carbon to depth partly depends on the fraction of primary production (PP) sinking out of the euphotic zone (i.e., the e-ratio). Measurements of PP and export flux are often performed simultaneously in the field, although there is a temporal delay between those parameters. Thus, resulting e-ratio estimates often incorrectly assume an instantaneous downward export of PP to export flux. Evaluating results from four mesocosm studies, we find that peaks in organic matter sedimentation lag chlorophyll a peaks by 2 to 15 days. We discuss the implications of these time lags (TLs) for current e-ratio estimates and evaluate potential controls of TL. Our analysis reveals a strong correlation between TL and the duration of chlorophyll a buildup, indicating a dependency of TL on plankton food web dynamics. This study is one step further toward time-corrected e-ratio estimates.

Ecosystem responses to biogeochemical fronts in the South Brazil Bight

NASA Astrophysics Data System (ADS)

Brandini, Frederico P.; Tura, Pedro M.; Santos, Pedro P. G. M.

2018-05-01

Here we described the general hydrography in the South Brazil Bight (23-28°S) with emphasis on frontal processes and their role in the structure and functioning of the regional shelf ecosystem. One of the key roles of fronts for ecosystem dynamics is the injection of nutrients into the euphotic zone increasing primary production. Frontal systems also affect plankton biodiversity and fisheries. Physical mechanisms behind frontogenesis in this region are similar in the analogous western side of oceanic basins; their magnitude and seasonal dynamics, however, may differ due to peculiarities in shelf morphology, wind field, tidal circulation and continental drainage. Here we provide a reassessment of earlier and recent ecological and hydrographic studies for a better evaluation of the spatial and temporal dynamics of fronts and their regional ecological implications. Albeit in a fragmented manner, we give a more detailed conceptual framework about the ecosystem responses to the complex frontal system in the South Brazil Bight.

The phytoplankton bloom in the northwestern Arabian Sea during the southwest monsoon of 1979

NASA Technical Reports Server (NTRS)

Brock, John C.; Mcclain, Charles R.; Luther, Mark E.; Hay, William W.

1991-01-01

The present study investigates the biological variability of the northwestern Arabian Sea during the 1979 southwest monsoon by the synthesis of satellite ocean color remote sensing with an analysis of in situ hydrographic and meteorological data sets and the results of wind-driven modeling of upper-ocean circulation. The phytoplankton bloom peaked during August-September, extended from the Oman coast to about 65 deg E, and lagged behind the development of open-sea upwelling by at least 1 mo. The pigment distributions, hydrographic data, and model results all suggest that the boom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore Ekman pumping. Coastal upwelling was evident from May through September, yielded the most extreme concentrations of phytoplankton biomass, and, along the Arabian coast, was limited to the continental shelf in the promotion of high concentrations of phytoplankton.

Distribution and structure of pranktonic Archaea in the Arctic Ocean using 2008 - 2010 R/V Mirai cruise samples

NASA Astrophysics Data System (ADS)

Amano (Sato), C.; Akiyama, S.; Uchida, M.; Utsumi, M.

2011-12-01

Recent molecular biological techniques indicate that there is widely spreading marine planktonic Archaea in the world's ocean under euphotic zone, and those microbial metabolisms are now recognized the drive forces of the world ocean geochemical cycling. In addition, after the discovery of large amount of marine Archaea, it is pointed out to an accurate calculation of the ocean carbon cycling that the grasp of the Archaea quantitive distribution and their methabolism are indispensable. Remarkably, part of marine Archaea (Crenarchaeota) certainly has carbon fixing ability, thus there is currently great interest in the marine Archaea for getting to understand the carbon cycling. In this study, we evaluated the Archaeal spatial distribution and their biomass in the Pacific sector of the Arctic Ocean, where is the Archaeal quantitative data was less and strongly needed to reveal the marine bacterial carbon cycling due to resent changing the Arctic region such as extensive melting ice. The Arctic Ocean cruise by R/V MIRAI was done from August to October in 2008 - 2010 in the Chukchi Sea, Canada Basin and East Siberian Sea. In these cruises, vertical seawater samples were collected with 12 L Niskin bottles with CTD system at total 30 stations to investigate the distributions of bacterial population density. The Catalyzed Reporter Deposition Fluorescence in situ hybridization (CARD-FISH) technique targeting Crenarchaeal, Euryarchaeal and Eubacterial rRNA was used for identifying and enumerating marine microbial cells under florescent microscope. These cells were counted and measured the size, and calculated the biomass. From the results, in the Pacific sector of the Arctic Ocean, it was determined that the fraction of Archaea was abundant under euphotic zone like as other oceans, and the vertical distribution of planktonic Archaea were obviously different by each sea area. Especially in East Siberian Sea, the fraction of Crenarchaeota was relatively high near bottom reaching 40% of total detected bacteria. And it was found that Crenarchaeota was less dominant in the fresh surface layer contrasted to Euryarchaeota. This Archaeal distribution characteristic founded out in the Pacific sector of the Arctic Ocean would be come from obvious water mass structure and environmental factors. This result should connect to understand whole Arhcaeal quantitative knowledge in the world ocean.

C : N : P stoichiometry at the Bermuda Atlantic Time-series Study station in the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Singh, A.; Baer, S. E.; Riebesell, U.; Martiny, A. C.; Lomas, M. W.

2015-06-01

Nitrogen (N) and phosphorus (P) availability determine the strength of the ocean's carbon (C) uptake, and variation in the N : P ratio in inorganic nutrients is key to phytoplankton growth. A similarity between C : N : P ratios in the plankton biomass and deep-water nutrients was observed by Alfred C. Redfield around 80 years ago and suggested that biological processes in the surface ocean controlled deep ocean chemistry. Recent studies have emphasized the role of inorganic N : P ratios in governing biogeochemical processes, particularly the C : N : P ratio in suspended particulate organic matter (POM), with somewhat less attention given to exported POM and dissolved organic matter (DOM). Herein, we extend the discussion on ecosystem C : N : P stoichiometry but also examine temporal variation of stoichiometric relationships. We have analysed elemental stoichiometry in the suspended POM and total (POM + DOM) organic matter (TOM) pools in the upper 100 m, and in the exported POM and sub-euphotic zone (100-500 m) inorganic nutrient pools from the monthly data collected at the Bermuda Atlantic Time-series Study (BATS) site located in the western part of the North Atlantic Ocean. C : N : P ratios in the TOM pool were more than twice that in the POM pool. Observed C : N ratios in suspended POM were approximately equal to the canonical Redfield Ratio (C : N : P = 106 : 16 : 1), while N : P and C : P ratios in the same pool were more than twice the Redfield Ratio. Average N : P ratios in the subsurface inorganic nutrient pool were ~ 26 : 1, squarely between the suspended POM ratio and the Redfield ratio. We have further linked variation in elemental stoichiometry with that of phytoplankton cell abundance observed at the BATS site. Findings from this study suggest that the variation elemental ratios with depth in the euphotic zone was mainly due to different growth rates of cyanobacterial cells. These time-series data have also allowed us to examine the potential role of climate variability on C : N : P stoichiometry. This study strengthens our understanding of elemental stoichiometry in different organic matter pools and should improve biogeochemical models by constraining the range of non-Redfield stoichiometry.

Black Sea spectral bio-optical models based on satellite data and their applications for assessment of spatial and temporal variability in waters transparency, chlorophyll a content and primary production

NASA Astrophysics Data System (ADS)

Churilova, T.; Suslin, V.

2012-04-01

Satellite observations of ocean color provide a unique opportunity in oceanography to assess productivity of the sea on different spatial and temporal scales. However it has been shown that the standard SeaWiFS algorithm generally overestimates summer chlorophyll concentration and underestimates pigment content during spring phytoplankton bloom in comparison with in situ measurements. It is required to develop regional algorithms which are based on biooptical characteristics typical for the Sea and consequently could be used for correct transformation of spectral features of water-leaving radiance to chlorophyll a concentrations (Chl), light absorption features of suspended and dissolved organic matter (CDM), downwelling light attenuation coefficient/euphotic zone depth (PAR1%) and rate of primary synthesis of organic substances (PP). The numerous measurements of light absorption spectra of phytoplankton, non-algal particles and coloured dissolved organic matter carried out since 1996 in different seasons and regions of the Black Sea allowed to make a parameterization of the light absorption by all optically active components. Taking into account regional peculiarities of the biooptical parameters, their difference between seasons, shallow and deep-waters, their depth-dependent variability within photosynthetic zone regional spectral models for estimation of chlorophyll a concentration (Chl Model), colored dissolved and suspended organic matter absorption (CDM Model), downwelling irradiance (PAR Model) and primary production (PP Model) have been developed based on satellite data. Test of validation of models showed appropriate accuracy of the models. The developed models have been applied for estimation of spatial/temporal variability of chlorophyll a, dissolved organic matter concentrations, waters transparency, euphotic zone depth and primary production based on SeaWiFS data. Two weeks averaged maps of spatial distribution of these parameters have been composed for period from 1998 to 2009 (most of them presented on site http://blackseacolor.com/browser3.html). Comparative analysis of long-term series (since 1998) of these parameters with subsurface water temperature (SST) and solar radiance of the sea surface (PAR-0m) revealed the key factors determining the seasonal and inter-annual variations of Chl, PAR1%, CDM, PP. The seasonal dynamics of these parameters were more pronounced compared with inter-annual variability. The later was related to climate effect. In deep-waters region relatively lower SST during cold winters were forcing more intensive winter-spring phytoplankton bloom. In north-western shelf inter-annual variability in river (Danube) run off, which was related to climate change as well, determined year-to-year changing in Chl, CDM, PAR1%, and PP.

Modelling Ecosystem Dynamics of the Oxygen Minimum Zones in the Angola Gyre and the Northern Benguela Upwelling System.

NASA Astrophysics Data System (ADS)

Schmidt, M.; Eggert, A.

2016-02-01

The Angola Gyre and the Northern Benguela Upwelling System are two major oxygen minimum zones (OMZ) of different kind connected by the system of African Eastern Boundary Currents. We discuss results from a 3-dimensional coupled biogeochemical model covering both oxygen-deficient systems. The biogeochemical model component comprises trophic levels up to zooplankton. Physiological properties of organisms are parameterized from field data gained mainly in the course of the project "Geochemistry and Ecology of the Namibian Upwelling System" (GENUS). The challenge of the modelling effort is the different nature of both systems. The Angola Gyre, located in a "shadow zone" of the tropical Atlantic, has a low productivity and little ventilation, hence a long residence time of water masses. In the northern Benguela Upwelling System, trade winds drive an intermittent, but permanent nutrient supply into the euphotic zone which fuels a high coastal productivity, large particle export and high oxygen consumption from dissimilatory processes. In addition to the local processes, oxygen-deficient water formed in the Angola Gyre is one of the source water masses of the poleward undercurrent, which feeds oxygen depleted water into the Benguela system. In order to simulate the oxygen distribution in the Benguela system, both physical transport as well as local biological processes need to be carefully adjusted in the model. The focus of the analysis is on the time scale and the relative contribution of the different oxygen related processes to the oxygen budgets in both the oxygen minimum zones. Although these are very different in both the OMZ, the model is found as suitable to produce oxygen minimum zones comparable with observations in the Benguela and the Angola Gyre as well. Variability of the oxygen concentration in the Angola Gyre depends strongly on organismic oxygen consumption, whereas the variability of the oxygen concentration on the Namibian shelf is governed mostly by pole-ward advection of tropical water masses.

Plankton dynamics and biogeochemical fluxes in the Costa Rica Dome: introduction to the CRD Flux and Zinc Experiments.

PubMed

Landry, Michael R; De Verneil, Alain; Goes, Joaquim I; Moffett, James W

2016-03-01

The Costa Rica Dome (CRD) is an open-ocean upwelling system in the Eastern Tropical Pacific that overlies the ocean's largest oxygen minimum zone (OMZ). The region has unique characteristics, biomass dominance by picophytoplankton, suppressed diatoms, high biomass of higher consumers and presumptive trace metal limitation, but is poorly understood in terms of pelagic stock and process relationships, including productivity and production controls. Here, we describe the goals, project design, physical context and major findings of the Flux and Zinc Experiments cruise conducted in June-July 2010 to assess trophic flux relationships and elemental controls on phytoplankton in the CRD. Despite sampling during a year of suppressed summertime surface chlorophyll, cruise results show high productivity (∼1 g C m -2 day -1 ), high new production relative to export, balanced production and grazing, disproportionate biomass-specific productivity of large phytoplankton and high zooplankton stocks. Zinc concentrations are low in surface waters relative to phosphorous and silicate in other regions, providing conditions conducive to picophytoplankton, like Synechococcus , with low Zn requirements. Experiments nonetheless highlight phytoplankton limitation or co-limitation by silicic acid, driven by a strong silica pump that is linked to low dissolution of biogenic silica in the cold shallow thermocline of the lower euphotic zone.

In situ grazing experiments apply new technology to gain insights into deep-sea microbial food webs

NASA Astrophysics Data System (ADS)

Pachiadaki, Maria G.; Taylor, Craig; Oikonomou, Andreas; Yakimov, Michail M.; Stoeck, Thorsten; Edgcomb, Virginia

2016-07-01

Predation by grazing protists in aquatic habitats can influence prokaryotic community structure and provides a source of new, labile organic matter. Due to methodological difficulties associated with studies of deep-sea (below photic zone) microbiota, trophic interactions between eukaryotes and prokaryotes in mesopelagic and bathypelagic realms are largely obscured. Further complicating matters, examinations of trophic interactions using water samples that have been exposed to upwards of hundreds of atmospheres of pressure change prior to initiating experiments can potentially introduce significant artifacts. Here we present results of the first study of protistan grazing in water layers ranging from the euphotic zone to the bathypelagic, utilizing the Microbial Sampler-Submersible Incubation Device (MS-SID) that makes possible in situ studies of microbial activities. Protistan grazing in the mesopelagic and bathypelagic realm of the East Mediterranean Sea was quantified using fluorescently labeled prokaryotes (FLP) prepared from the naturally-occurring prokaryotic assemblages. These studies reveal daily prokaryotic removal due to grazing ranging from 31.3±5.9% at 40 m depth to 0.5±0.3% at 950 m. At 3540 m depth, where a chemocline habitat exists with abundant and active prokaryotes above Urania basin, the daily consumption of prokaryotes by protists was 19.9±6.6% of the in situ abundance.

Late summer metalimnetic oxygen minimum zone in the northern Baltic Sea

NASA Astrophysics Data System (ADS)

Raateoja, M.; Kuosa, H.; Flinkman, J.; Pääkkönen, J.-P.; Perttilä, M.

2010-02-01

The frequently observed, but commonly ignored hydrographic characteristic of the Baltic Sea, the oxygen minimum zone (OMiZ) above and within the summertime thermocline, was studied during the 6-yr monitoring programme encompassing the Gulfs of Bothnia and Finland in the northern Baltic Sea. A temperature-anomaly-driven density gradient was found to be a prerequisite for the existence of the OMiZ. We determined the magnitude of the apparently utilized O 2 in the OMiZ by combining graphical analysis and empirical modelling. A sound criterion for distinguishing the cases in which the OMiZ had a biological origin, and not only a hydrodynamic one, was the accompanying ammonium maximum zone (AMaZ). Of a total of 46 stations visited, a density gradient was found at every station, an accompanying OMiZ at 37 stations, and an accompanying AMaZ at 20 stations. This suggests that biological activity is an essential factor in forming the OMiZ. We investigated to what extent the OMiZ was a manifestation of microbial decomposition of autochthonous organic matter, as zooplankton respiration was also a factor. As a study average, ~ 80% of the apparently utilized O 2 was consumed by the microbial decomposition process and ~ 20% of it by mesozooplankton respiration. According to the O 2 quota consumed in the process, the microbial community in the OMiZ of the Gulf of Finland decomposed, on average, 14% of all the organic matter settling from the euphotic zone in the time frame of mid-June to early August. A pronounced allochthonous organic carbon pool in the Gulf of Bothnia hinders a prompt estimation of a corresponding share for that basin.

Warm Anomaly Effects on California Current Phytoplankton

NASA Astrophysics Data System (ADS)

Gomez Ocampo, E.; Gaxiola-Castro, G.; Beier, E.; Durazo, R.

2016-02-01

Positive temperature anomalies were reported in the NE Pacific Ocean since the boreal winter of 2013-2014. Previous studies showed that these anomalies were caused by lower than normal rates of heat loss from the ocean to the atmosphere and by relatively weak cold water advection to the upper ocean. Anomalous Sea Surface Temperature (SST), Absolute Dynamic Topography (ADT), and Chlorophyll (CHL) obtained from monthly remote sensing data were registered in the California Current region during August 2014. Anomalies appeared around the coastal and oceanic zones, particularly in the onshore zone between Monterey Bay, California and Magdalena Bay, Baja California. High positive SST anomalous values up to 4ºC above the long-term mean, 20 cm in ADT, and less of 4.5 mg m-3 of CHL were registered. Changes of 20 cm in ADT above the average are equivalent to 50 m thermocline deepening considering typical values of stratification for the area, which in turn influenced the availability of nutrients and light for phytoplankton growth in the euphotic zone. To examine the influence of the warm anomaly on phytoplankton production, we fitted with Generalized Additive Models the relationship between monthly primary production satellite data and ADT. Primary production inferred from the model, showed during August 2014 high negative anomalies (up to 0.5 gC m-2 d1) in the coastal zone. The first empirical orthogonal function of ADT and PP revealed that the highest ADT anomalies and the lowest primary production occurred off the Baja California Peninsula, between Punta Eugenia and Cabo San Lucas. Preliminary conclusions showed that warm anomaly affected negatively to phytoplankton organisms during August 2014, being this evident by low biomass and negative primary production anomalies as result of pycnocline deepens.

Multilayer Approach for Characterization of Bacterial Diversity in a Marginal Sea: From Surface to Seabed

NASA Technical Reports Server (NTRS)

Ivana, Babic; Maja, Mucko; Ivica, Vilibic; Hrvoje, Mihanovic; Reffaella, Casotti; Zrinka, Ljubesic; Ivona, Cetinic; Cecilia, Balestra; Ines, Petric; Suncica, Bosak;

Wind driven nutrient and subsurface chlorophyll-a enhancement in the Bay of La Paz, Gulf of California

NASA Astrophysics Data System (ADS)

Coria-Monter, Erik; Monreal-Gómez, María Adela; Salas de León, David Alberto; Durán-Campos, Elizabeth; Merino-Ibarra, Martín

2017-09-01

Nutrient and chlorophyll-a distributions in the Bay of La Paz, Gulf of California, Mexico were analyzed during the late spring of 2004 to assess their relations to hydrography and circulation patterns. The results show the presence of both Gulf of California Water and Subtropical Subsurface Water. Water circulation was dominated by wind stress driven cyclonic circulation along f / H contours (f is planetary vorticity and H is depth), and upwelling resulting from the divergence shows a vertical velocity of ∼0.4 m d-1. Nutrient concentrations were higher in the center of the cyclonic pattern, where a rise in the nutricline contributed nutrients to the euphotic layer as a result of Ekman pumping. The vertical section showed the presence of a chlorophyll-a maximum at the thermocline shoaling to a depth of only 12 m. Along the surface, two peaks of chlorophyll-a were observed, one at Boca Grande and another off San Juan de la Costa, associated with upwelling and mixing derived from current interactions with abrupt topographies. The chlorophyll-a maximum increased from 0.8 mg m-3 in the external part of the cyclonic pattern to 2.0 mg m-3 in its center. The vertically integrated chlorophyll-a concentrations followed a similar pattern, rising from 10 to 20 mg m-2 and reaching their highest values in the center of the cyclonic circulation pattern. A schematic model was developed to describe processes that occur in late spring: the wind stress driven cyclonic structure promotes upward nutrient flux, which in turn drives an enhancement of chlorophyll-a. Upwelling was found to be the main mechanism of fertilization responsible for the enhancement of productivity levels by means of nutrient transport into the euphotic zone during spring. Other chlorophyll enhancement areas point to the occurrence of additional fertilization processes that may derive from interactions between cyclonic circulation patterns and the topography off of San Juan de la Costa, where phosphate mining occurs.

Oceanography of Glacier Bay, Alaska: Implications for biological patterns in a glacial fjord estuary

USGS Publications Warehouse

Etherington, L.L.; Hooge, P.N.; Hooge, Elizabeth Ross; Hill, D.F.

2007-01-01

Alaska, U.S.A, is one of the few remaining locations in the world that has fjords that contain temperate idewater glaciers. Studying such estuarine systems provides vital information on how deglaciation affects oceanographic onditions of fjords and surrounding coastal waters. The oceanographic system of Glacier Bay, Alaska, is of particular interest ue to the rapid deglaciation of the Bay and the resulting changes in the estuarine environment, the relatively high oncentrations of marine mammals, seabirds, fishes, and invertebrates, and the Bay’s status as a national park, where ommercial fisheries are being phased out. We describe the first comprehensive broad-scale analysis of physical and iological oceanographic conditions within Glacier Bay based on CTD measurements at 24 stations from 1993 to 2002. easonal patterns of near-surface salinity, temperature, stratification, turbidity, and euphotic depth suggest that freshwater nput was highest in summer, emphasizing the critical role of glacier and snowmelt to this system. Strong and persistent tratification of surface waters driven by freshwater input occurred from spring through fall. After accounting for seasonal nd spatial variation, several of the external physical factors (i.e., air temperature, precipitation, day length) explained a large mount of variation in the physical properties of the surface waters. Spatial patterns of phytoplankton biomass varied hroughout the year and were related to stratification levels, euphotic depth, and day length. We observed hydrographic atterns indicative of strong competing forces influencing water column stability within Glacier Bay: high levels of freshwater ischarge promoted stratification in the upper fjord, while strong tidal currents over the Bay’s shallow entrance sill enhanced ertical mixing. Where these two processes met in the central deep basins there were optimal conditions of intermediate tratification, higher light levels, and potential nutrient renewal. These conditions were associated with high and sustained hlorophylla levels observed from spring through fall in these zones of the Bay and provide a framework for understanding he abundance patterns of higher trophic levels within this estuarine system.

Simulation of annual plankton productivity cycle in the Black Sea by a one-dimensional physical-biological model

NASA Astrophysics Data System (ADS)

Oguz, Temel; Ducklow, Hugh; Malanotte-Rizzoli, Paola; Tugrul, Suleyman; Nezlin, Nikolai P.; Unluata, Umit

1996-07-01

The annual cycle of the plankton dynamics in the central Black Sea is studied by a one-dimensional vertically resolved physical-biological upper ocean model, coupled with the Mellor-Yamada level 2.5 turbulence closure scheme. The biological model involves interactions between the inorganic nitrogen (nitrate, ammonium), phytoplankton and herbivorous zooplankton biomasses, and detritus. Given a knowledge of physical forcing, the model simulates main observed seasonal and vertical characteristic features, in particular, formation of the cold intermediate water mass and yearly evolution of the upper layer stratification, the annual cycle of production with the fall and the spring blooms, and the subsurface phytoplankton maximum layer in summer, as well as realistic patterns of particulate organic carbon and nitrogen. The computed seasonal cycles of the chlorophyll and primary production distributions over the euphotic layer compare reasonably well with the data. Initiation of the spring bloom is shown to be critically dependent on the water column stability. It commences as soon as the convective mixing process weakens and before the seasonal stratification of surface waters begins to develop. It is followed by a weaker phytoplankton production at the time of establishment of the seasonal thermocline in April. While summer nutrient concentrations in the mixed layer are low enough to limit production, the layer between the thermocline and the base of the euphotic zone provides sufficient light and nutrient to support subsurface phytoplankton development. The autumn bloom takes place sometime between October and December depending on environmental conditions. In the case of weaker grazing pressure to control the growth rate, the autumn bloom shifts to December-January and emerges as the winter bloom, or, in some cases, is connected with the spring bloom to form one unified continuous bloom structure during the January-March period. These bloom structures are similar to the year-to-year variabilities present in the data.

Reconnaissance of marine resources

NASA Technical Reports Server (NTRS)

Szekielda, K.-H.; Suszkowski, D. J.; Tabor, P. S.

1975-01-01

A test area along the NW Coast of Africa was used during the Skylab mission to study the distribution of temperature and plankton. The S190B Earth Terrain Camera with a spectral film response of 0.4-0.7 micrometers allowed qualitative estimates of the distribution patterns of suspended material. Differentiation between inorganic particles and phytoplankton could be made by comparing the green band and the red band of the S190A Camera System. The pictorial display of data obtained from the S191 scanning radiometer in the 10-11 micrometer atmospheric window allowed a detailed interpretation of the temperature distribution in the area where cold upwelled water reaches the euphotic zone. The comparison between infrared data and the imageries taken simultaneously indicated the origin of the cold water as well as the pathway within the Canary current. A fish survey carried out almost simultaneously in the area, by echosounding, showed high correlation between the position of good fishing grounds and the distribution of plankton as detected by remote sensing detectors on Skylab.

Massive outbreaks of Noctiluca scintillans blooms in the Arabian Sea due to spread of hypoxia.

PubMed

do Rosário Gomes, Helga; Goes, Joaquim I; Matondkar, S G P; Buskey, Edward J; Basu, Subhajit; Parab, Sushma; Thoppil, Prasad

2014-09-09

In the last decade, the northern Arabian Sea has witnessed a radical shift in the composition of winter phytoplankton blooms, which previously comprised mainly of diatoms, the unicellular, siliceous photosynthetic organisms favoured by nutrient-enriched waters from convective mixing. These trophically important diatom blooms have been replaced by widespread blooms of a large, green dinoflagellate, Noctiluca scintillans, which combines carbon fixation from its chlorophyll-containing endosymbiont with ingestion of prey. Here, we report that these massive outbreaks of N. scintillans during winter are being facilitated by an unprecedented influx of oxygen deficient waters into the euphotic zone and by the extraordinary ability of its endosymbiont Pedinomonas noctilucae to fix carbon more efficiently than other phytoplankton under hypoxic conditions. We contend that N. scintillans blooms could disrupt the traditional diatom-sustained food chain to the detriment of regional fisheries and long-term health of an ecosystem supporting a coastal population of nearly 120 million people.

How Choice of Depth Horizon Influences the Estimated Spatial Patterns and Global Magnitude of Ocean Carbon Export Flux

NASA Astrophysics Data System (ADS)

Palevsky, Hilary I.; Doney, Scott C.

2018-05-01

Estimated rates and efficiency of ocean carbon export flux are sensitive to differences in the depth horizons used to define export, which often vary across methodological approaches. We evaluate sinking particulate organic carbon (POC) flux rates and efficiency (e-ratios) in a global earth system model, using a range of commonly used depth horizons: the seasonal mixed layer depth, the particle compensation depth, the base of the euphotic zone, a fixed depth horizon of 100 m, and the maximum annual mixed layer depth. Within this single dynamically consistent model framework, global POC flux rates vary by 30% and global e-ratios by 21% across different depth horizon choices. Zonal variability in POC flux and e-ratio also depends on the export depth horizon due to pronounced influence of deep winter mixing in subpolar regions. Efforts to reconcile conflicting estimates of export need to account for these systematic discrepancies created by differing depth horizon choices.

El Niño-related offshore phytoplankton bloom events around the Spratley Islands in the South China Sea

NASA Astrophysics Data System (ADS)

Isoguchi, Osamu; Kawamura, Hiroshi; Ku-Kassim, Ku-Yaacob

2005-11-01

Satellite chlorophyll-a (Chl-a) observations reveal offshore phytoplankton bloom events with high Chl-a (>1 mg m-3) spreading over 300 km off the coasts around the Spratley Islands in the South China Sea (SCS) during the spring of 1998. The bloom entails anomalous wind jet and sea surface temperature (SST) cooling, suggesting that the wind jet-induced mixing and/or offshore upwelling bring about the cooling and the bloom through the supply of nutrient-rich waters into the euphotic zone. The strong wind jet is orographically formed responding to shifts in wind direction over the eastern SCS. The wind shift is connected with the Philippine Sea anomalous anticyclone that is established during El Niño, indicating the El Niño-related offshore bloom. The long-term reanalysis winds over the eastern SCS demonstrates that wind jet formation and associated offshore cooling/bloom are expected to occur in most cases of the subsequent El Niño years.

Ice sheets as a significant source of highly reactive nanoparticulate iron to the oceans.

PubMed

Hawkings, Jon R; Wadham, Jemma L; Tranter, Martyn; Raiswell, Rob; Benning, Liane G; Statham, Peter J; Tedstone, Andrew; Nienow, Peter; Lee, Katherine; Telling, Jon

2014-05-21

The Greenland and Antarctic Ice Sheets cover ~ 10% of global land surface, but are rarely considered as active components of the global iron cycle. The ocean waters around both ice sheets harbour highly productive coastal ecosystems, many of which are iron limited. Measurements of iron concentrations in subglacial runoff from a large Greenland Ice Sheet catchment reveal the potential for globally significant export of labile iron fractions to the near-coastal euphotic zone. We estimate that the flux of bioavailable iron associated with glacial runoff is 0.40-2.54 Tg per year in Greenland and 0.06-0.17 Tg per year in Antarctica. Iron fluxes are dominated by a highly reactive and potentially bioavailable nanoparticulate suspended sediment fraction, similar to that identified in Antarctic icebergs. Estimates of labile iron fluxes in meltwater are comparable with aeolian dust fluxes to the oceans surrounding Greenland and Antarctica, and are similarly expected to increase in a warming climate with enhanced melting.

Basin-wide N2 fixation in the deep waters of the Mediterranean Sea

NASA Astrophysics Data System (ADS)

Benavides, Mar; Bonnet, Sophie; Hernández, Nauzet; Martínez-Pérez, Alba María.; Nieto-Cid, Mar; Álvarez-Salgado, Xosé Antón; Baños, Isabel; Montero, María. F.; Mazuecos, Ignacio P.; Gasol, Josep M.; Osterholz, Helena; Dittmar, Thorsten; Berman-Frank, Ilana; Arístegui, Javier

2016-06-01

Recent findings indicate that N2 fixation is significant in aphotic waters, presumably due to heterotrophic diazotrophs depending on organic matter for their nutrition. However, the relationship between organic matter and heterotrophic N2 fixation remains unknown. Here we explore N2 fixation in the deep chlorophyll maximum and underneath deep waters across the whole Mediterranean Sea and relate it to organic matter composition, characterized by optical and molecular methods. Our N2 fixation rates were in the range of those previously reported for the euphotic zone of the Mediterranean Sea (up to 0.43 nmol N L-1 d-1) and were significantly correlated to the presence of relatively labile organic matter with fluorescence and molecular formula properties representative for peptides and unsaturated aliphatics and associated with the presence of more oxygenated ventilated water masses. Finally, and despite that the aphotic N2 fixation contributes largely to total water column diazotrophic activity (>50%), its contribution to overall nitrogen inputs to the basin is negligible (<0.5%).

Phenotypic Variability in the Coccolithophore Emiliania huxleyi.

PubMed

Blanco-Ameijeiras, Sonia; Lebrato, Mario; Stoll, Heather M; Iglesias-Rodriguez, Debora; Müller, Marius N; Méndez-Vicente, Ana; Oschlies, Andreas

2016-01-01

Coccolithophores are a vital part of oceanic phytoplankton assemblages that produce organic matter and calcium carbonate (CaCO3) containing traces of other elements (i.e. Sr and Mg). Their associated carbon export from the euphotic zone to the oceans' interior plays a crucial role in CO2 feedback mechanisms and biogeochemical cycles. The coccolithophore Emiliania huxleyi has been widely studied as a model organism to understand physiological, biogeochemical, and ecological processes in marine sciences. Here, we show the inter-strain variability in physiological and biogeochemical traits in 13 strains of E. huxleyi from various biogeographical provinces obtained from culture collections commonly used in the literature. Our results demonstrate that inter-strain genetic variability has greater potential to induce larger phenotypic differences than the phenotypic plasticity of single strains cultured under a broad range of variable environmental conditions. The range of variation found in physiological parameters and calcite Sr:Ca highlights the need to reconsider phenotypic variability in paleoproxy calibrations and model parameterizations to adequately translate findings from single strain laboratory experiments to the real ocean.

Chromophoric and fluorescent dissolved organic matter in and above the oxygen minimum zone off Peru

NASA Astrophysics Data System (ADS)

Loginova, A. N.; Thomsen, S.; Engel, A.

2016-11-01

As a result of nutrient upwelling, the Peruvian coastal system is one of the most productive regions in the ocean. Sluggish ventilation of intermediate waters, characteristic for the Eastern Tropical South Pacific (ETSP) and microbial degradation of a high organic matter load promotes deoxygenation at depth. Dissolved organic matter (DOM) plays a key role in microbial respiration and carbon cycling, but little is known on DOM distribution and cycling in the ETSP. DOM optical properties give important insights on DOM sources, structure and biogeochemical reactivity. Here, we present data and a conceptual view on distribution and cycling of chromophoric (CDOM) and fluorescent (FDOM) DOM in and above the oxygen minimum zone (OMZ) off Peru. Five fluorescent components were identified during PARAFAC analysis. Highest intensities of CDOM and of the amino acid-like fluorescent component (C3) occurred above the OMZ and coincided with maximum chl a concentrations, suggesting phytoplankton productivity as major source. High intensities of a marine humic-like fluorescent component (C1), observed in subsurface waters, indicated in situ microbial reworking of DOM. FDOM release from inner shelf sediment was determined by seawater analysis and continuous glider sensor measurement and included a humic-like component (C2) with a signature typical for terrestrially derived humic acids. Upwelling supplied humic-like substances to the euphotic zone. Photo-reactions were likely involved in the production of a humic-like fluorescent component (C5). Our data show that variable biological and physical processes need to be considered for understanding DOM cycling in a highly dynamic coastal upwelling system like the ETSP off Peru.

Water quality of Calero Reservoir, Santa Clara County, California, 1981-83

USGS Publications Warehouse

Clifton, D.G.; Gloege, I.S.

1987-01-01

Data were collected from December 1980 to September 1983 to describe water quality conditions of Calero Reservoir and the Almaden-Calero canal, Santa Clara County, California. Results show that water in Calero Reservoir and the canal generally met water quality criteria, as identified by the California Regional Water Quality Control Board San Francisco Bay Region, for municipal and domestic supply, water contact and non-contact recreation, warm water fish habitat, wildlife habitat, and fish spawning. Water temperature profiles show that Calero Reservoir can be classified as a warm monomictic reservoir. Water transparency profiles showed rapid attenuation of light with depth in the water column. The depth of the euphotic zone ranged from .5 m to 5.0 m. In winter and spring, light-extinction values generally were high throughout the water column; in summer and fall, values generally were high near the reservoir bottom. Dissolved oxygen concentrations were < 5.0 mg/L in about 22% of the measurements. Median pH values were 7.9 in the reservoir and 8.4 in the canal. Mean specific conductance values were 299 microsiemens/cm at 25 C in the reservoir and 326 in the canal. Calcium and magnesium were the dominant cations and bicarbonate the dominant anion in Calero Reservoir. Concentrations of total recoverable mercury in the bottom sediments in Calero Reservoir ranged from 0.06 to 0.85 mg/kg, but concentrations in the water column were was generally < 1 mg/L. Mean total nitrogen concentration in the Reservoir was 1.00 mg/L, much of it in dissolved form (mean concentration was 0.85 mg/L). Mean total organic nitrogen concentration in Calero Reservoir was 0.65 mg/L, and mean total nitrate concentration was 0.21 mg/L. Mean total phosphorus and dissolved orthophosphorous concentrations were 0.05 and 0.019 mg/L, respectively. Net primary productivity in the euphotic zone ranged from -2,000 to 10,000 mg of oxygen/sq m/day; the median value was 930. Carlson 's trophic-state index, calculated using water transparency, total phosphorus, and chlorophyll-a values, indicated that the reservoir was eutrophic. Fecal coliform bacteria concentrations were < 20 colonies/100 ml in the reservoir and < 200 colonies/100 ml in the canal. Fecal streptococcal bacteria concentrations were generally < 45 colonies/100 ml in the reservoir and up to 260 colonies/100 ml in the canal. (Author 's abstract)

The optical and physiological properties of phytoplankton - base of model for estimation of primary production in the sea from satellite data.

NASA Astrophysics Data System (ADS)

Finenko, Z. Z.; Churilova, T. Ya.

An assessment of the spatial and temporal variation in the photo physiological parameters and chlorophyll-specific absorption coefficients of marine phytoplankton is essential for estimate of global primary production by satellite data. Relationships of photosynthesis rate on light intensity have been used for estimation of two photosynthetic parameters of phytoplankton in the Black Sea: light saturated photosynthesis intensity (Pb/max, mgC mg Chl-1 h-1) and photosynthesis efficiency (alpha/b mgC mg Chl -1 h-1/ W m-2). The results have shown that variability of photosynthetic parameters of surface phytoplankton during the year varied by one order of values: Pb/max - from 1 to 11 mg C mg Chl-1 h-1 and (alpha/b - from 0.04 to 0.35 mg C mg Chl-1 h-1/Wm-2. Temporal dynamics was characterised by increasing of the values from winter to summer and decreasing to the end of the year. The vertical profiles of Pb/max and alpha/b had opposite character of change: values of Pb/max decreased with depth, alpha/b - increased. Photosynthetic parameters changed with depth more significantly at time of stratification, than - without stratification. The influence of temperature, nitrate concentration and light intensity on Pb/max rather evidence, but temperature and optical depth effect on Pb/max more significantly. Depth-dependent variability of photosynthesis efficiency is generally effected of nutrient concentration. Vertical uniformity of maximum quantum yield of photosynthesis (Fm) and spectral mean absorption coefficient of phytoplankton (aph) in euphotic zone were obtained for cold period of year. In summer - Fm increased from surface to bottom of euphotic zone, aph - decrease. Fm and aph values of surface phytoplankton depended on chlorophyll concentration but their changes had opposite direction: Fm - increased and aph - decreased when chlorophyll concentration grew. As a result Pb/max = Z Fm aph Ik T and alpha/b = Z Fm aph T (where Z - a dimensional constant equal to the atomic mass of carbon, Ik - the photon flux density at which photosynthesis rate becomes light saturated, (mol photons m-2 s-1; T - a constant value for transition from seconds by one hour) change in 2-3 times for the range of chlorophyll concentration (0.05-10.0 mg m-3 ). Pb/max and alpha/b have been approximated by one-peaked curve with maximum at 3 mg m -3 Chl a concentration. These relationships could be used for modeling of Pb/max and alpha/b based on surface chlorophyll concentrations from satellite colour images.

Microenvironments and microscale productivity of cyanobacterial desert crusts

USGS Publications Warehouse

Garcia-Pichel, F.; Belnap, Jayne

1996-01-01

We used microsensors to characterize physicochemical microenvironments and photosynthesis occurring immediately after water saturation in two desert soil crusts from southeastern Utah, which were formed by the cyanobacteria Microcoleus vaginatus Gomont, Nostoc spp., and Scytonema sp. The light fields within the crusts presented steep vertical gradients in magnitude and spectral composition. Near-surface light-trapping zones were formed due to the scattering nature of the sand particles, but strong light attenuation resulted in euphotic zones only ca. 1 mm deep, which were progressively enriched in longer wavelengths with depth. Rates of gross photosynthesis (3.4a??9.4 mmol O2A?ma??2A?ha??1) and dark respiration (0.81a??3.1 mmol Oa??2A?ma??2A?ha??1) occurring within 1 to several mm from the surface were high enough to drive the formation of marked oxygen microenvironments that ranged from oxygen supersaturation to anoxia. The photosynthetic activity also resulted in localized pH values in excess of 10, 2a??3 units above the soil pH. Differences in metabolic parameters and community structure between two types of crusts were consistent with a successional pattern, which could be partially explained on the basis of the microenvironments. We discuss the significance of high metabolic rates and the formation of microenvironments for the ecology of desert crusts, as well as the advantages and limitations of microsensor-based methods for crust investigation.

Possible impacts of ozone depletion on trophic interactions and biogenic vertical carbon flux in the Southern Ocean

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marchant, H.J.; Davidson, A.

1992-03-01

Among the most productive region of the Southern Ocean is the marginal ice edge zone that trails the retreating ice edge in spring and early summer. The timing of this near-surface phytoplankton bloom coincides with seasonal stratospheric ozone depletion when UV irradiance is reportedly as high as in mid-summer. Recent investigations indicate that antarctic marine phytoplankton are presently UV stressed. The extent to which increasing UV radiation diminishes the ability of phytoplankton to fix C02 and/or leads to changes in their species composition is equivocal. The colonial stage in the life cycle of the alga Phaeocystis pouchetii is one ofmore » the major components of the bloom. The authors have found that this alga produces extracellular products which are strongly UV-B absorbing. When exposed to increasing levels of UV-B radiation, survival of antarctic colonial Phaeocystis was significantly greater than colonies of this species from temperate waters and of the single-celled stage of its life cycle which produces no UV-B-absorbing compounds. Phaeocystis is apparently a minor dietary component of Antarctic krill, Euphausia superba, and its nutritional value to crustacea is reportedly low. Phytoplankton, principally diatoms, together with fecal pellets and molted exoskeletons of grazers contribute most of the particulate carbon flux from the euphotic zone to deep water.« less

The Use of Chlorophyll Fluorescence Lifetime to Assess Phytoplankton Physiology within a River-Dominated Environment

NASA Technical Reports Server (NTRS)

Hall, Callie M.; Miller, Richard L.; Redalje, Donald G.; Fernandez, Salvador M.

2002-01-01

Chlorophyll a fluorescence lifetime was measured for phytoplankton populations inhabiting the three physical zones surrounding the Mississippi River's terminus in the Gulf of Mexico. Observations of river discharge volume, nitrate + nitrite, silicate, phosphate, PAR (Photosynthetically Active Radiation) diffuse attenuation within the water column, salinity, temperature, SPM, and chl a concentration were used to characterize the distribution of chl fluorescence lifetime within a given region within restricted periods of time. 33 stations extending from the Mississippi River plume to the shelf break of the Louisiana coast were surveyed for analysis of chlorophyll fluorescence lifetime during two cruises conducted March 31 - April 6, 2000, and October 24 - November 1, 2000. At each station, two to three depths were chosen for fluorescence lifetime measurement to represent the vertical characteristics of the water column. Where possible, samples were taken from just below the surface and from just above and below the pycnocline. All samples collected were within the 1% light level of the water column (the euphotic zone). Upon collection, samples were transferred to amber Nalgene bottles and left in the dark for at least 15 minutes to reduce the effects of non-photochemical quenching and to insure that photosynthetic reaction centers were open. Before measurements within the phase fluorometer were begun, the instrument was allowed to warm up for no less than one hour.

Insights on the marine microbial nitrogen cycle from isotopic approaches to nitrification

PubMed Central

Casciotti, Karen L.; Buchwald, Carolyn

2012-01-01

The microbial nitrogen (N) cycle involves a variety of redox processes that control the availability and speciation of N in the environment and that are involved with the production of nitrous oxide (N2O), a climatically important greenhouse gas. Isotopic measurements of ammonium (NH+4), nitrite (NO−2), nitrate (NO−3), and N2O can now be used to track the cycling of these compounds and to infer their sources and sinks, which has lead to new and exciting discoveries. For example, dual isotope measurements of NO−3 and NO−2 have shown that there is NO−3 regeneration in the ocean's euphotic zone, as well as in and around oxygen deficient zones (ODZs), indicating that nitrification may play more roles in the ocean's N cycle than generally thought. Likewise, the inverse isotope effect associated with NO−2 oxidation yields unique information about the role of this process in NO−2 cycling in the primary and secondary NO−2 maxima. Finally, isotopic measurements of N2O in the ocean are indicative of an important role for nitrification in its production. These interpretations rely on knowledge of the isotope effects for the underlying microbial processes, in particular ammonia oxidation and nitrite oxidation. Here we review the isotope effects involved with the nitrification process and the insights provided by this information, then provide a prospectus for future work in this area. PMID:23091468

Insights on the marine microbial nitrogen cycle from isotopic approaches to nitrification.

PubMed

Casciotti, Karen L; Buchwald, Carolyn

2012-01-01

The microbial nitrogen (N) cycle involves a variety of redox processes that control the availability and speciation of N in the environment and that are involved with the production of nitrous oxide (N(2)O), a climatically important greenhouse gas. Isotopic measurements of ammonium (NH(+) (4)), nitrite (NO(-) (2)), nitrate (NO(-) (3)), and N(2)O can now be used to track the cycling of these compounds and to infer their sources and sinks, which has lead to new and exciting discoveries. For example, dual isotope measurements of NO(-) (3) and NO(-) (2) have shown that there is NO(-) (3) regeneration in the ocean's euphotic zone, as well as in and around oxygen deficient zones (ODZs), indicating that nitrification may play more roles in the ocean's N cycle than generally thought. Likewise, the inverse isotope effect associated with NO(-) (2) oxidation yields unique information about the role of this process in NO(-) (2) cycling in the primary and secondary NO(-) (2) maxima. Finally, isotopic measurements of N(2)O in the ocean are indicative of an important role for nitrification in its production. These interpretations rely on knowledge of the isotope effects for the underlying microbial processes, in particular ammonia oxidation and nitrite oxidation. Here we review the isotope effects involved with the nitrification process and the insights provided by this information, then provide a prospectus for future work in this area.

Evidence for anoxygenic photosynthesis from the distribution of bacteriochlorophylls in the Black Sea.

PubMed

Repeta, D J; Simpson, D J; Jorgensen, B B; Jannasch, H W

1989-11-02

The contribution of anoxygenic photosynthesis to carbon cycling in the Black Sea, the world's largest body of anoxic marine water, has been vigorously investigated and debated for over four decades. Penetration of light into the sulphide-containing deep water may result in a zone of anaerobic primary production by photosynthetic bacteria. We report here the results of analyses of photosynthetic pigments in samples of suspended particulate matter collected from two stations in the western basin of the Black Sea. Our data demonstrate high concentrations of a bacterio-chlorophyll at the chemocline, and thus the potential for anoxygenic photosynthesis as a component of primary production in the carbon cycle of the Black Sea. More than 95% of the pigments in the bacteriochlorophyll-maximum are accounted for by a series of aromatic carotenoids and bacteriochlorophylls-e, including a previously unreported geranyl ester of 4-i-butyl bacteriochlorophyll-e. The distribution of pigments is characteristic of the obligate phototrophs Chlorobium phaeobacteroides and C. phaeovibriodes. Total depth-integrated bacteriochlorophyll at one station exceeded total chlorophyll-a in the overlying oxygenated portion of the euphotic zone. We suggest that anoxygenic photosynthesis is a relatively recent phenomenon in the Black Sea initiated by shallowing of the chemocline over the past decade and development of an anoxic layer devoid of O2 and H2S.

Bio-optical characterization of offshore NW Mediterranean waters: CDOM contribution to the absorption budget and diffuse attenuation of downwelling irradiance

NASA Astrophysics Data System (ADS)

Pérez, Gonzalo L.; Galí, Martí; Royer, Sarah-Jeanne; Sarmento, Hugo; Gasol, Josep M.; Marrasé, Cèlia; Simó, Rafel

2016-08-01

We investigated the peculiar bio-optical characteristics of the Mediterranean Sea focusing on the spectral diffuse attenuation coefficient [Kd (λ)] and its relationship with chlorophyll a concentration (Chl a), complemented with measurements of light absorption by chromophoric dissolved organic matter (CDOM) and the optical properties of particulate material. The non-water absorption budget showed that CDOM was the largest contributor in the 300-600 nm range (>60% of the absorption at 443 nm in the euphotic layer), increasing to 80% within the first optical depth (FOD). This translated into CDOM accounting for >50% of KdBio (λ) (the irradiance attenuation coefficient caused by all non-water absorptions) between 320 and 555 nm and throughout both layers (FOD and euphotic). Indeed, we tested three Chl a-based bio-optical models and all three underestimated Kd (λ), evidencing the importance of CDOM beside Chl a to fully account for light attenuation. The Morel & Maritorena (2001) model (M&M 01) underestimated Kd (λ) in the UV and blue spectral regions within the FOD layer, showing lower differences with increasing wavelengths. The Morel et al. (2007a) model (BGS 07) also underestimated Kd (λ) in the FOD layer, yet it performed much better in the 380-555 nm range. In the euphotic layer, the Morel (1988) model (JGR 88) underestimated Kd (λ) showing higher differences at 412 and 443 nm and also performed better at higher wavelengths. Observed euphotic layer depths (Z1%) were 28 m shallower than those predicted with the M&M 01 empirical relationship, further highlighting the role of CDOM in the bio-optical peculiarity of Mediterranean Sea. In situ measurements of the CDOM index (Φ), an indicator of the deviation of the CDOM-Chl a average relationship for Case 1 waters, gave a mean of 5.9 in the FOD, consistent with simultaneous estimates from MODIS (4.8±0.4). The implications of the bio-optical anomaly for ecological and biogeochemical inferences in the Mediterranean Sea are discussed.

Particle Fluxes and Bulk Geochemical Characterization of the Cabo Frio Upwelling System in Southeastern Brazil: Sediment Trap Experiments between Spring 2010 and Summer 2012.

PubMed

Albuquerque, Ana Luiza S; Belém, André L; Zuluaga, Francisco J B; Cordeiro, Livia G M; Mendoza, Ursula; Knoppers, Bastiaan A; Gurgel, Marcio H C; Meyers, Philip A; Capilla, Ramsés

2014-05-14

Physical and biogeochemical processes in continental shelves act synergistically in both transporting and transforming suspended material, and ocean dynamics control the dispersion of particles by the coastal zone and their subsequent mixing and dilution within the shelf area constrained by oceanic boundary currents, followed by their gradual settling in a complex sedimentary scenario. One of these regions is the Cabo Frio Upwelling System located in a significantly productive area of Southeastern Brazil, under the control of the nutrient-poor western boundary Brazil Current but also with a wind-driven coastal upwelling zone, inducing cold-water intrusions of South Atlantic Central Water on the shelf. To understand these synergic interactions among physical and biogeochemical processes in the Cabo Frio shelf, a series of four experiments with a total of 98 discrete samples using sediment traps was performed from November 2010 to March 2012, located on the 145 m isobath on the edge of the continental shelf. The results showed that lateral transport might be relevant in some cases, especially in deep layers, although no clear seasonal cycle was detected. Two main physical-geochemical coupling scenarios were identified: singular downwelling events that can enhance particles fluxes and are potentially related to the Brazil Current oscillations; and events of significant fluxes related to the intrusion of the 18°C isotherm in the euphotic zone. The particulate matter settling in the Cabo Frio shelf area seems to belong to multiple marine and terrestrial sources, in which both Paraiba do Sul River and Guanabara Bay could be potential land-sources, although the particulate material might subject intense transformation (diagenesis) during its trajectory to the shelf edge.

Uranium biogeochemistry across the redox transition zone of a permanently stratified fjord: Framvaren, Norway

USGS Publications Warehouse

Swarzenski, P.W.; McKee, B.A.; Skei, J.M.; Todd, J.F.

1999-01-01

During August 1995, the vertical concentration profile of dissolved and particulate uranium exhibited strong non-conservative characteristics in the upper 30 m of Framvaren Fjord. There was a pronounced peak in both particulate (> 0.2 ??m; 1.09 nM) and dissolved (< 0.2 ??m; 17.06 nM) uranium in the finely stratified waters at the O2/H2S interface which is positioned well within the euphotic zone at about 20-21 m. Such concentration maxima at the redox boundary are also observed for dissolved organic carbon (DEC), Sr and Ba. Dissolved U levels seen in the water column from 18 m down to 30 m exceeded the high salinity (salinity = 35) U concentrations (13.63 ?? 0.84 nM; Chen, J.H., Edwards, R.L., Wasserburg, G.L., 1986. 238U, 234U and 232Th in seawater. Earth Planet Sci. Lett. 80, 241-251.) observed uniformly in the open ocean. A prolific population of S microbes (e.g., Chromatium, Chlorobium sp.) flourishes at the O2/H2S interface. The source of elevated U at the redox boundary must be due to microbial uptake and subsequent release processes rather than dilution from oceanic uranium. Uranium oxidation state determinations in waters from 1, 22 and 30 m depth reveal that reduced U(IV) is not present in significant abundance, and that the chemical and/or biological reduction of hexavalent uranium is largely inhibited. Our results suggest that U and other trace constituents such as DOC, Sr, Ba, Fe(II), Mn(II) are greatly modified by direct and indirect microbial transformation reactions which are most concentrated across the redox transition zone in Framvaren Fjord.

Monitoring and Predicting the Export and Fate of Global Ocean Net Primary Production: The EXPORTS Field Program

NASA Astrophysics Data System (ADS)

Exports Science Definition Team

2016-04-01

Ocean ecosystems play a critical role in the Earth's carbon cycle and its quantification on global scales remains one of the greatest challenges in global ocean biogeochemistry. The goal of the EXport Processes in the Ocean from Remote Sensing (EXPORTS) science plan is to develop a predictive understanding of the export and fate of global ocean primary production and its implications for the Earth's carbon cycle in present and future climates. NASA's satellite ocean-color data record has revolutionized our understanding of global marine systems. EXPORTS is designed to advance the utility of NASA ocean color assets to predict how changes in ocean primary production will impact the global carbon cycle. EXPORTS will create a predictive understanding of both the export of organic carbon from the euphotic zone and its fate in the underlying "twilight zone" (depths of 500 m or more) where variable fractions of exported organic carbon are respired back to CO2. Ultimately, it is the sequestration of deep organic carbon transport that defines the impact of ocean biota on atmospheric CO2 levels and hence climate. EXPORTS will generate a new, detailed understanding of ocean carbon transport processes and pathways linking upper ocean phytoplankton processes to the export and fate of organic matter in the underlying twilight zone using a combination of field campaigns, remote sensing and numerical modeling. The overarching objective for EXPORTS is to ensure the success of future satellite missions by establishing mechanistic relationships between remotely sensed signals and carbon cycle processes. Through a process-oriented approach, EXPORTS will foster new insights on ocean carbon cycling that will maximize its societal relevance and be a key component in the U.S. investment to understand Earth as an integrated system.

Mesopelagic microplankton of the Arabian Sea

NASA Astrophysics Data System (ADS)

Gowing, Marcia M.; Garrison, David L.; Wishner, Karen F.; Gelfman, Celia

2003-10-01

The Arabian Sea is notable for its dramatic monsoonal effects on euphotic zone biogeochemical processes and the large spatial extent of its mesopelagic oxygen minimum zone. As part of the US Joint Global Ocean Flux Study Arabian Sea project, we sampled microplankton (organisms 20-200 μm including diatoms, dinoflagellates, ciliates, sarcodines and nauplii) at five depths from 250 to 1000 or 1100 m at six stations during four seasonal cruises in 1995. Abundances of groups of organisms at discrete depths averaged 1-2 l -1 seasonally. Mean seasonal integrated biomass of the assemblage was 29 mg C m -2 during the late Northeast Monsoon, 37 mg C m -2 during the Spring Intermonsoon, 47 mg C m -2 during the late Southwest Monsoon and 49 mg C m -2 during the early Northeast Monsoon. Overall, protozoans dominated the mesopelagic microplankton assemblage. Integrated biomass peaked during the late SW Monsoon at two stations as expected if microplankton responded to surface productivity and mesopelagic organic carbon fluxes. At three stations, microplankton biomass peaked during the early NE Monsoon; this may reflect a continuing response to SW Monsoon productivity signals by these larger, slow-growing organisms. Protozooplankton abundance did not appear to be negatively affected by low (<0.1 ml dissolved O 2 l -1) oxygen, whereas naupliar abundance and biomass were higher where oxygen concentration was higher. Total microplankton biomass was highest where oxygen concentrations and also mesozooplankton biomass were lowest, suggesting that predation also played a role in microplankton distributions. Calculations based on allometric relationships indicated that the mesopelagic heterotrophic microplankton assemblage could, on average, respire 9-38% of the particulate carbon flux that entered the system at 100 m and possibly 18-76% of the flux remaining at 250 m. Microplankton may therefore be significant carbon cyclers in the ocean's vast "twilight zone".

Assimilation of Sea Color Data Into A Three Dimensional Biogeochemical Model: Sensitivity Experiments

NASA Astrophysics Data System (ADS)

Echevin, V.; Levy, M.; Memery, L.

The assimilation of two dimensional sea color data fields into a 3 dimensional coupled dynamical-biogeochemical model is performed using a 4DVAR algorithm. The biogeochemical model includes description of nitrates, ammonium, phytoplancton, zooplancton, detritus and dissolved organic matter. A subset of the biogeochemical model poorly known parameters (for example,phytoplancton growth, mortality,grazing) are optimized by minimizing a cost function measuring misfit between the observations and the model trajectory. Twin experiments are performed with an eddy resolving model of 5 km resolution in an academic configuration. Starting from oligotrophic conditions, an initially unstable baroclinic anticyclone splits into several eddies. Strong vertical velocities advect nitrates into the euphotic zone and generate a phytoplancton bloom. Biogeochemical parameters are perturbed to generate surface pseudo-observations of chlorophyll,which are assimilated in the model in order to retrieve the correct parameter perturbations. The impact of the type of measurement (quasi-instantaneous, daily mean, weekly mean) onto the retrieved set of parameters is analysed. Impacts of additional subsurface measurements and of errors in the circulation are also presented.

Ocean Color Measurements from Landsat-8 OLI using SeaDAS

NASA Technical Reports Server (NTRS)

Franz, Bryan Alden; Bailey, Sean W.; Kuring, Norman; Werdell, P. Jeremy

2014-01-01

The Operational Land Imager (OLI) is a multi-spectral radiometer hosted on the recently launched Landsat-8 satellite. OLI includes a suite of relatively narrow spectral bands at 30-meter spatial resolution in the visible to shortwave infrared that make it a potential tool for ocean color radiometry: measurement of the reflected spectral radiance upwelling from beneath the ocean surface that carries information on the biogeochemical constituents of the upper ocean euphotic zone. To evaluate the potential of OLI to measure ocean color, processing support was implemented in SeaDAS, which is an open-source software package distributed by NASA for processing, analysis, and display of ocean remote sensing measurements from a variety of satellite-based multi-spectral radiometers. Here we describe the implementation of OLI processing capabilities within SeaDAS, including support for various methods of atmospheric correction to remove the effects of atmospheric scattering and absorption and retrieve the spectral remote-sensing reflectance (Rrs; sr exp 1). The quality of the retrieved Rrs imagery will be assessed, as will the derived water column constituents such as the concentration of the phytoplankton pigment chlorophyll a.

On some physical and dynamical properties of microplastic particles in marine environment.

PubMed

Chubarenko, I; Bagaev, A; Zobkov, M; Esiukova, E

2016-07-15

Simplified physical models and geometrical considerations reveal general physical and dynamical properties of microplastic particles (0.5-5mm) of different density, shape and size in marine environment. Windage of extremely light foamed particles, surface area and fouling rate of slightly positively buoyant microplastic spheres, films and fibres and settling velocities of negatively buoyant particles are analysed. For the Baltic Sea dimensions and under the considered idealised external conditions, (i) only one day is required for a foamed polystyrene particle to cross the sea (ca. 250km); (ii) polyethylene fibres should spend about 6-8months in the euphotic zone before sinking due to bio-fouling, whilst spherical particles can be retained on the surface up to 10-15years; (iii) for heavy microplastic particles, the time of settling through the water column in the central Gotland basin (ca. 250m) is less than 18h. Proper physical setting of the problem of microplastics transport and developing of physically-based parameterisations are seen as applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

Satellite-observed variability of phytoplankton size classes associated with a cold eddy in the South China Sea.

PubMed

Lin, Junfang; Cao, Wenxi; Wang, Guifen; Hu, Shuibo

2014-06-15

Ocean-color remote sensing has been used as a tool to detect phytoplankton size classes (PSCs). In this study, a three-component model of PSC was reparameterized using seven years of pigment measurements acquired in the South China Sea (SCS). The model was then used to infer PSC in a cyclonic eddy which was observed west of Luzon Island from SeaWiFS chlorophyll-a (chla) and sea-surface height anomaly (SSHA) products. Enhanced productivity and a shift in the PSC were observed, which were likely due to upwelling of nutrient-rich water into the euphotic zone. The supply of nutrients promoted the growth of larger cells (micro- and nanoplankton), and the PSC shifted to greater sizes. However, the picoplankton were still important and contributed ∼48% to total chla concentration. In addition, PSC time series revealed a lag period of about three weeks between maximum eddy intensity and maximum chlorophyll, which may have been related to phytoplankton growth rate and duration of eddy intensity. Copyright © 2014 Elsevier Ltd. All rights reserved.

Climate Influence on Deep Sea Populations

PubMed Central

Company, Joan B.; Puig, Pere; Sardà, Francesc; Palanques, Albert; Latasa, Mikel; Scharek, Renate

2008-01-01

Dynamics of biological processes on the deep-sea floor are traditionally thought to be controlled by vertical sinking of particles from the euphotic zone at a seasonal scale. However, little is known about the influence of lateral particle transport from continental margins to deep-sea ecosystems. To address this question, we report here how the formation of dense shelf waters and their subsequent downslope cascade, a climate induced phenomenon, affects the population of the deep-sea shrimp Aristeus antennatus. We found evidence that strong currents associated with intense cascading events correlates with the disappearance of this species from its fishing grounds, producing a temporary fishery collapse. Despite this initial negative effect, landings increase between 3 and 5 years after these major events, preceded by an increase of juveniles. The transport of particulate organic matter associated with cascading appears to enhance the recruitment of this deep-sea living resource, apparently mitigating the general trend of overexploitation. Because cascade of dense water from continental shelves is a global phenomenon, we anticipate that its influence on deep-sea ecosystems and fisheries worldwide should be larger than previously thought. PMID:18197243

Spatial Patterns in the Efficiency of the Biological Pump: What Controls Export Ratios at the Global Scale?

NASA Astrophysics Data System (ADS)

Moore, J. K.

2016-02-01

The efficiency of the biological pump is influenced by complex interactions between chemical, biological, and physical processes. The efficiency of export out of surface waters and down through the water column to the deep ocean has been linked to a number of factors including biota community composition, production of mineral ballast components, physical aggregation and disaggregation processes, and ocean oxygen concentrations. I will examine spatial patterns in the export ratio and the efficiency of the biological pump at the global scale using the Community Earth System Model (CESM). There are strong spatial variations in the export efficiency as simulated by the CESM, which are strongly correlated with new nutrient inputs to the euphotic zone and their impacts on phytoplankton community structure. I will compare CESM simulations that include dynamic, variable export ratios driven by the phytoplankton community structure, with simulations that impose a near-constant export ratio to examine the effects of export efficiency on nutrient and surface chlorophyll distributions. The model predicted export ratios will also be compared with recent satellite-based estimates.

Paleoproterozoic snowball earth: extreme climatic and geochemical global change and its biological consequences

NASA Technical Reports Server (NTRS)

Kirschvink, J. L.; Gaidos, E. J.; Bertani, L. E.; Beukes, N. J.; Gutzmer, J.; Maepa, L. N.; Steinberger, R. E.

2000-01-01

Geological, geophysical, and geochemical data support a theory that Earth experienced several intervals of intense, global glaciation ("snowball Earth" conditions) during Precambrian time. This snowball model predicts that postglacial, greenhouse-induced warming would lead to the deposition of banded iron formations and cap carbonates. Although global glaciation would have drastically curtailed biological productivity, melting of the oceanic ice would also have induced a cyanobacterial bloom, leading to an oxygen spike in the euphotic zone and to the oxidative precipitation of iron and manganese. A Paleoproterozoic snowball Earth at 2.4 Giga-annum before present (Ga) immediately precedes the Kalahari Manganese Field in southern Africa, suggesting that this rapid and massive change in global climate was responsible for its deposition. As large quantities of O(2) are needed to precipitate this Mn, photosystem II and oxygen radical protection mechanisms must have evolved before 2.4 Ga. This geochemical event may have triggered a compensatory evolutionary branching in the Fe/Mn superoxide dismutase enzyme, providing a Paleoproterozoic calibration point for studies of molecular evolution.

Dinitrogen Fixation Within and Adjacent to Oxygen Deficient Waters of the Eastern Tropical South Pacific Ocean

NASA Astrophysics Data System (ADS)

Widner, B.; Mulholland, M. R.; Bernhardt, P. W.; Chang, B. X.; Jayakumar, A.

2016-02-01

Recent work suggests that planktonic diazotrophs are geographically more widely distributed than previously thought including relatively warm (14-23oC) aphotic oxygenated pelagic waters and in aphotic waters within oxygen deficient zones. Because the volume of aphotic water in the ocean is large and may increase in the future, if dinitrogen (N2) fixation is widely occurring at sub-euphotic depths, this could result in a dramatic upward revision of global nitrogen (N) inputs via this process. N2 fixation rates were measured during a cruise in the Eastern Tropical South Pacific using stable isotope tracer techniques that account for slow gas dissolution. Results are compared with light, nutrient, and oxygen gradients (and necessarily temperature gradients). In addition, rates of N2 fixation made in vertical profiles within and above oxygen deficient waters are compared with those measured in vertical profiles adjacent to oxygen deficient waters. Results suggest that while rates of N2 fixation were measurable in deeper anoxic waters, volumetric N2 fixation rates were higher in surface waters.

Modelling Biogenic Carbon Cycling and Remineralization In The Mesopelagic Layer 1. Conceptual Development

NASA Astrophysics Data System (ADS)

Legendre, L.; Rivkin, R. B.; Nagata, T.

Most of the biogenic carbon (BC) that is exported (E) from the euphotic zone to the mesopelagic layer (i.e. 100 to 1000 m) is remineralized to CO2 (i.e. respiration, R). A significant part of this remineralized CO2 is ventilated back to the surface layer on decadal time scales, where it equilibrates with the atmosphere. Only the BC that is remineralized or buried (i.e.. sequestration, S) below the permanent pycnocline, typi- cally ca. 1000 m, is isolated from the atmosphere long enough to be of significance to the global climate. Current estimates of E and S for the World Ocean are ca. 7 to 12 and 1 to 2 Gt C/year, respectively. The main biological mechanisms that control R in the mesopelagic layer are the size structure, sinking velocity and chemical composi- tion of E. The interactions among these factors are non-linear. Because the changing climate will modify both R and the downward propagation of characteristics of the surface ocean (e.g. heat, storm mixing), these factors will influence S, which will in turn feedback to climate.

Phenotypic Variability in the Coccolithophore Emiliania huxleyi

PubMed Central

Lebrato, Mario; Stoll, Heather M.; Iglesias-Rodriguez, Debora; Müller, Marius N.; Méndez-Vicente, Ana; Oschlies, Andreas

2016-01-01

Coccolithophores are a vital part of oceanic phytoplankton assemblages that produce organic matter and calcium carbonate (CaCO3) containing traces of other elements (i.e. Sr and Mg). Their associated carbon export from the euphotic zone to the oceans' interior plays a crucial role in CO2 feedback mechanisms and biogeochemical cycles. The coccolithophore Emiliania huxleyi has been widely studied as a model organism to understand physiological, biogeochemical, and ecological processes in marine sciences. Here, we show the inter-strain variability in physiological and biogeochemical traits in 13 strains of E. huxleyi from various biogeographical provinces obtained from culture collections commonly used in the literature. Our results demonstrate that inter-strain genetic variability has greater potential to induce larger phenotypic differences than the phenotypic plasticity of single strains cultured under a broad range of variable environmental conditions. The range of variation found in physiological parameters and calcite Sr:Ca highlights the need to reconsider phenotypic variability in paleoproxy calibrations and model parameterizations to adequately translate findings from single strain laboratory experiments to the real ocean. PMID:27348427

The deep chlorophyll layer in Lake Ontario: Extent, mechanisms of formation, and abiotic predictors

USGS Publications Warehouse

Scofield, Anne E.; Watkins, James M.; Weidel, Brian C.; Luckey, Frederick J.; Rudstam, Lars G.

2017-01-01

Epilimnetic production has declined in Lake Ontario, but increased production in metalimnetic deep chlorophyll layers (DCLs) may compensate for these losses. We investigated the spatial and temporal extent of DCLs, the mechanisms driving DCL formation, and the use of physical variables for predicting the depth and concentration of the deep chlorophyll maximum (DCM) during April–September 2013. A DCL with DCM concentrations 2 to 3 times greater than those in the epilimnion was present when the euphotic depth extended below the epilimnion, which occurred primarily from late June through mid-August. In situ growth was important for DCL formation in June and July, but settling and photoadaptation likely also contributed to the later-season DCL. Supporting evidence includes: phytoplankton biovolume was 2.4 × greater in the DCL than in the epilimnion during July, the DCL phytoplankton community of July was different from that of May and the July epilimnion (p = 0.004), and there were concurrences of DCM with maxima in fine particle concentration and dissolved oxygen saturation. Higher nutrient levels in the metalimnion may also be a necessary condition for DCL formation because July metalimnetic concentrations were 1.5 × (nitrate) and 3.5 × (silica) greater than in the epilimnion. Thermal structure variables including epilimnion depth, thermocline depth, and thermocline steepness were useful for predicting DCM depth; the inclusion of euphotic depth only marginally improved these predictions. However, euphotic depth was critical for predicting DCM concentrations. The DCL is a productive and predictable feature of the Lake Ontario ecosystem during the stratified period.

Phytoplankton characteristics and hydrological conditions in the western part of the Sea of Okhotsk in the spring of 1999 and 2000 based on expeditionary and satellite data

NASA Astrophysics Data System (ADS)

Zakharkov, S. P.; Selina, M. S.; Vanin, N. S.; Shtraikhert, E. A.; Biebov, N.

2007-08-01

Using the data obtained in 1999 2000 during the spring bloom of phytoplankton (late May early June), the variability of the pigment concentrations, the phytoplankton biomass and species compositions, and the hydrological conditions on the eastern shelf of Sakhalin Island was studied. The study resulted in revealing 135 microalgae species belonging to eight divisions. The most diversely presented were the Dinophyta dinoflagellates and Bacillariophyta diatoms (70 and 53 species, respectively). The concentration of chlorophyll a in the euphotic zone amounted, on average, to 3.8 mg/m3 in 1999 and 2.4 mg/m3 in 2000. It was shown that, in the northern and southern parts of the coastal zone, the concentration of chlorophyll a and the phytoplankton density in the spring were considerably different and depended on the hydrological conditions. In the north, their maximum values were found in the area of the depth break and were determined by the tidal mixing. The increased algae concentrations and temperature inversions at depths of 400 600 m confirm the downslope sliding of the near-bottom shelf waters. In the southern part, the high phytoplankton concentrations in the surface layer in 1999 confirmed by the monthly averaged estimates from the SeaWiFS satellite color scanner were caused by the abnormal northward propagation of the Soya Current waters and by intense tidal mixing.

Re-assessing the nitrogen signal in continental margin sediments: New insights from the high northern latitudes

NASA Astrophysics Data System (ADS)

Knies, Jochen; Brookes, Steven; Schubert, Carsten J.

2007-01-01

Organic and inorganic nitrogen and their isotopic signatures were studied in continental margin sediments off Spitsbergen. We present evidence that land-derived inorganic nitrogen strongly dilutes the particulate organic signal in coastal and fjord settings and accounts for up to 70% of the total nitrogen content. Spatial heterogeneity in inorganic nitrogen along the coast is less likely to be influenced by clay mineral assemblages or various substrates than by the supply of terrestrial organic matter (TOM) within eroded soil material into selected fjords and onto the shelf. The δ15N signal of the inorganic nitrogen ( δ15N inorg) in sediments off Spitsbergen seems to be appropriate to trace TOM supply from various climate- and ecosystem zones and elucidates the dominant transport media of terrigenous sediments to the marine realm. Moreover, we postulate that with the study of sedimentary δ15N inorg in the Atlantic-Arctic gateway, climatically induced changes in catchment's vegetations in high northern latitudes may be reconstructed. The δ15N org signal is primarily controlled by the availability of nitrate in the dominating ocean current systems and the corresponding degree of utilization of the nitrate pool in the euphotic zone. Not only does this new approach allow for a detailed view into the nitrogen cycle for settings with purely primary-produced organic matter supply, it also provides new insights into both the deposition of marine and terrestrial nitrogen and its ecosystem response to (paleo-) climate changes.

Calcite production by Coccolithophores in the South East Pacific Ocean: from desert to jungle

NASA Astrophysics Data System (ADS)

Beaufort, L.; Couapel, M.; Buchet, N.; Claustre, H.

2007-09-01

BIOSOPE cruise achieved an oceanographic transect from the Marquise Islands to the Peru-Chili upwelling (PCU) via the centre of the South Pacific Gyre (SPG). Water samples from 6 depths in the euphotic zone were collected at 20 stations. The concentrations of suspended calcite particles, coccolithophores cells and detached coccoliths were estimated together with size and weight using an automatic polarizing microscope, a digital camera, and a collection of softwares performing morphometry and pattern recognition. Some of these softwares are new and described here for the first time. The coccolithophores standing stocks are usually low and reach maxima west of the PCU. The coccoliths of Emiliania huxleyi, Gephyrocapsa spp. and Crenalithus spp. (Order Isochrysidales) represent 50% of all the suspended calcite particles detected in the size range 0.1-46 μm (21% of PIC in term of the calcite weight). The latter species are found to grow preferentially in the Chlorophyll maximum zone. In the SPG their maximum concentrations was found to occur between 150 and 200 m, which is very deep for these taxa. The weight and size of coccoliths and coccospheres are correlated. Large and heavy coccoliths and coccospheres are found in the regions with relative higher fertility in the Marquises Island and in the PCU. Small and light coccoliths and coccospheres are found west of the PCU. This distribution may correspond to that of the concentration of calcium and carbonate ions.

Isotopic and enzymatic analyses of planktonic nitrogen utilisation in the vicinity of Cape Sines (Portugal) during weak upwelling activity

NASA Astrophysics Data System (ADS)

Slawyk, Gerd; Coste, Bernard; Collos, Yves; Rodier, Martine

1997-01-01

Using measurements of 15N uptake and activities of nitrate reductase and glutamine synthetase, the utilization of nitrogenous nutrients by microplankton in the Portuguese upwelling area was investigated. During this cruise the euphotic zone of coastal waters was in most cases bisected by a nitracline forming two layers. Total inorganic nitrogen uptake rates (NH 4+ + NO 3-) in the upper mixed and nitrate-impoverished layer ranged from 0.1 to 0.8 nM h -1 and were primarily supported by regenerated (ammonium) nitrogen (62-97%), whereas they varied between 0.9 and 10.4 nM h -1 in the deep nitrate-rich layer and were mainly driven by new (nitrate) nitrogen (52-82%). Depth profiles of Chl a-specific uptake rates for ammonium and nitrate paralleled those of absolute uptake rates, i.e. values of VNH 4+Chl were highest (up to 16.1 nmol μg -1 h -1) in nitrate-poor surface waters while values of VNO 3-Chl were maximum (up to 8.4 nmol μg -1 h -1)within the nitracline. This latter vertical ordering of planktonic nitrogen nutrition was consistent with an aged upwelling situation. However, applying several indices of cell metabolism and nutritional status, such as 15N uptake/enzyme activity, surge uptake internally controlled uptake, and V maxChl/K t ratios, we were able to demonstrate that the phytoplankton assemblages inhabiting the nutrient-impoverished upper layer still bore the signature of physically mediated nitrogen (nitrate) supply generated by active upwelling that had occurred during the week before our visit to the area. This signature was the most evident in samples from the station furthest inshore and faded with distance from shore as a result of the deepening of the nitrate isopleths (weakening of upwelling activity), which showed the same offshore trend. The appearance of nitrate-rich waters at the surface, after a strong pulse of upwelling favourable winds just before the end of the cruise, led to a five-fold increase in average (over the euphotic zone) absolute and Chl a-specific nitrate uptake rates (10.4 nM h -1, 7.5 nmol μ -1 h -1) compared to the mean rates during weak upwelling (1.7 nM h -1, 1.5 nmol μ -1 h -1). From a comparison with the neighbouring Moroccan upwelling, it is assumed that new production in the Portuguese upwelling averages 50 nM h -1. Thus, this upwelling would rank with the northwest African upwelling system off Cape Blanc or with the Californian upwelling at Point Conception for the capacity of new production, but seems to be much less efficient (seven-fold) than the highly permanent Peru upwelling.

Impacts of the Changjiang diluted water on sinking processes of particulate organic matters in the East China Sea

NASA Astrophysics Data System (ADS)

Sukigara, Chiho; Mino, Yoshihisa; Tripathy, Sarat Chandra; Ishizaka, Joji; Matsuno, Takeshi

2017-12-01

Intensive surveys with repeated CTD and microstructure turbulent observations, water and sediments sampling as well as onboard incubation and sediment trap experiments were conducted to reveal the nitrogen budget in the center of the East China Sea (ECS) during July 2010 and 2011. Low salinity water (Changjiang Diluted Water, CDW) covered the study area in 2010, but not in 2011. Higher chlorophyll a (chl. a) concentration, primary productivity, and downward particle flux in the upper layer were observed in 2010 than those in 2011. Existence of the CDW resulted in a steep pycnocline and an associated subsurface chl. a maximum (SCM) layer directly beneath the CDW. From chemical analyses of particulate carbon and nitrogen contents and isotope ratios, it became apparent that the particles sunk out the euphotic zone in 2010 was primarily originated in the CDW layer and secondly in the SCM layer. Whereas, in 2011, sinking particles were originated in the surface layer but a part of them were decomposed in the bottom of pycnocline. Our findings indicate that the CDW would supply particles into the deep layer and contribute to the downward transport of materials and the efficiency of biological pump in the ECS.

Sensitive monitoring of iodine species in sea water using capillary electrophoresis: vertical profiles of dissolved iodine in the Pacific Ocean.

PubMed

Huang, Zhuo; Ito, Kazuaki; Morita, Isamu; Yokota, Kuriko; Fukushi, Keiichi; Timerbaev, Andrei R; Watanabe, Shuichi; Hirokawa, Takeshi

2005-08-01

Using a novel high-sensitivity capillary electrophoretic method, vertical distributions of iodate, iodide, total inorganic iodine, dissolved organic iodine and total iodine in the North Pacific Ocean (0-5500 m) were determined without any sample pre-treatment other than UV irradiation before total iodine analysis. An extensive set of data demonstrated that the iodine behaviour in the ocean water collected during a cruise in the North Pacific Ocean in February-March 2003 was not conservative but correlated with variations in concentrations of dissolved oxygen and nutrient elements such as silicon, nitrogen and phosphorus. This suggests that the vertical distribution of iodine is associated with biological activities. The dissolved organic iodine was found in the euphotic zone in accord with observations elsewhere in the oceans. The vertical profile of dissolved organic iodine also appears to be related to biogeochemical activity. The concentrations of all measured iodine species vary noticeably above 1000 m but only minor latitudinal changes occur below 1000 m and slight vertical alterations can be observed below 2400 m. These findings are thought to reflect the stratification of nutrients and iodine species with different biological activities in the water column.

Protistan Bacterivory in an Oligomesotrophic Lake: Importance of Attached Ciliates and Flagellates

PubMed

Carrias; Amblard; Bourdier

1996-05-01

Seasonal and depth variations of the abundance, biomass, and bacterivory of protozoa (heterotrophic and mixotrophic flagellates and ciliates) were determined during thermal stratification in an oligomesotrophic lake (Lake Pavin, France). Maximal densities of heterotrophic flagellates (1.9x10(3) cells ml-1) and ciliates (6.1 cells ml-1) were found in the metalimnion. Pigmented flagellates dominated the flagellate biomass in the euphotic zone. Community composition of ciliated protists varied greatly with depth, and both the abundance and biomass of ciliates was dominated by oligotrichs. Heterotrophic flagellates dominated grazing, accounting for 84% of total protistan bacterivory. Maximal grazing impact of heterotrophic flagellates was 18.9x10(6) bacteria 1(-1)h-1. On average, 62% of nonpigmented flagellates were found to ingest particles. Ciliates and mixotrophic flagellates averaged 13% and 3% of protistan bacterivory, respectively. Attached protozoa (ciliates and flagellates) were found to colonize the diatom Asterionella formosa. Attached bacterivores had higher ingestion rates than free bacterivorous protozoa and may account for 66% of total protozoa bacterivory. Our results indicated that even in low numbers, epibiotic protozoa may have a major grazing impact on free bacteria.

Nutrient characteristics of the water masses and their seasonal variability in the eastern equatorial Indian Ocean.

PubMed

Sardessai, S; Shetye, Suhas; Maya, M V; Mangala, K R; Prasanna Kumar, S

2010-01-01

Nutrient characteristics of four water masses in the light of their thermohaline properties are examined in the eastern Equatorial Indian Ocean during winter, spring and summer monsoon. The presence of low salinity water mass with "Surface enrichments" of inorganic nutrients was observed relative to 20 m in the mixed layer. Lowest oxygen levels of 19 microM at 3 degrees N in the euphotic zone indicate mixing of low oxygen high salinity Arabian Sea waters with the equatorial Indian Ocean. The seasonal variability of nutrients was regulated by seasonally varying physical processes like thermocline elevation, meridional and zonal transport, the equatorial undercurrent and biological processes of uptake and remineralization. Circulation of Arabian Sea high salinity waters with nitrate deficit could also be seen from low N/P ratio with a minimum of 8.9 in spring and a maximum of 13.6 in winter. This large deviation from Redfield N/P ratio indicates the presence of denitrified high salinity waters with a seasonal nitrate deficit ranging from -4.85 to 1.52 in the Eastern Equatorial Indian Ocean. 2010 Elsevier Ltd. All rights reserved.

High Nutrient Transport and Cycling Potential Revealed in the Microbial Metagenome of Australian Sea Lion (Neophoca cinerea) Faeces

PubMed Central

Lavery, Trish J.; Roudnew, Ben; Seymour, Justin; Mitchell, James G.; Jeffries, Thomas

2012-01-01

Metagenomic analysis was used to examine the taxonomic diversity and metabolic potential of an Australian sea lion (Neophoca cinerea) gut microbiome. Bacteria comprised 98% of classifiable sequences and of these matches to Firmicutes (80%) were dominant, with Proteobacteria and Actinobacteria representing 8% and 2% of matches respectively. The relative proportion of Firmicutes (80%) to Bacteriodetes (2%) is similar to that in previous studies of obese humans and obese mice, suggesting the gut microbiome may confer a predisposition towards the excess body fat that is needed for thermoregulation within the cold oceanic habitats foraged by Australian sea lions. Core metabolic functions, including carbohydrate utilisation (14%), protein metabolism (9%) and DNA metabolism (7%) dominated the metagenome, but in comparison to human and fish gut microbiomes there was a significantly higher proportion of genes involved in phosphorus metabolism (2.4%) and iron scavenging mechanisms (1%). When sea lions defecate at sea, the relatively high nutrient metabolism potential of bacteria in their faeces may accelerate the dissolution of nutrients from faecal particles, enhancing their persistence in the euphotic zone where they are available to stimulate marine production. PMID:22606263

High nutrient transport and cycling potential revealed in the microbial metagenome of Australian sea lion (Neophoca cinerea) faeces.

PubMed

Lavery, Trish J; Roudnew, Ben; Seymour, Justin; Mitchell, James G; Jeffries, Thomas

2012-01-01

Metagenomic analysis was used to examine the taxonomic diversity and metabolic potential of an Australian sea lion (Neophoca cinerea) gut microbiome. Bacteria comprised 98% of classifiable sequences and of these matches to Firmicutes (80%) were dominant, with Proteobacteria and Actinobacteria representing 8% and 2% of matches respectively. The relative proportion of Firmicutes (80%) to Bacteriodetes (2%) is similar to that in previous studies of obese humans and obese mice, suggesting the gut microbiome may confer a predisposition towards the excess body fat that is needed for thermoregulation within the cold oceanic habitats foraged by Australian sea lions. Core metabolic functions, including carbohydrate utilisation (14%), protein metabolism (9%) and DNA metabolism (7%) dominated the metagenome, but in comparison to human and fish gut microbiomes there was a significantly higher proportion of genes involved in phosphorus metabolism (2.4%) and iron scavenging mechanisms (1%). When sea lions defecate at sea, the relatively high nutrient metabolism potential of bacteria in their faeces may accelerate the dissolution of nutrients from faecal particles, enhancing their persistence in the euphotic zone where they are available to stimulate marine production.

A coupled physical-biological pelagic model of a shallow sill fjord

NASA Astrophysics Data System (ADS)

Aksnes, Dag L.; Lie, Ulf

1990-10-01

A vertically resolved model for the land-locked fjord Lindåspollene, western Norway is presented. Salinity, temperature, oxygen, nitrogen-nutrients, silicate, and two groups of phytoplankton and herbivores are represented as dynamic variables. From 'below' the model is driven by solar radiation, precipitation, wind and tidal exchange and from 'above' by herbivore mortality. Simulation results are presented and discussed together with actual observations from Lindåspollene. The main seasonal and vertical characteristics of the phytoplankton and herbivore dynamics seem to be well reflected by the model, and realistic seasonal patterns may be produced for several successive years. The most characteristic vertical features are the formation of a summer surface production maximum and a deep chlorophyll maximum. Furthermore, a herbivore biomass which develops in the surface layer divides into a shallow and a deep component during summer and becomes concentrated in the surface layer again in the autumn. The nutricline and the pycnocline develop independently of one another, with consequences for the supply of nutrients to the upper euphotic zone. The bottom-up control exerted by the meteorological forcing, especially the freshwater runoff, seems to be of paramount significance for the observed vertical structure and seasonality of the present fjord system.

The effects of temporal variability of mixed layer depth on primary productivity around Bermuda

NASA Technical Reports Server (NTRS)

Bissett, W. Paul; Meyers, Mark B.; Walsh, John J.; Mueller-Karger, Frank E.

1994-01-01

Temporal variations in primary production and surface chlorophyll concentrations, as measured by ship and satellite around Bermuda, were simulated with a numerical model. In the upper 450 m of the water column, population dynamics of a size-fractionated phytoplankton community were forced by daily changes of wind, light, grazing stress, and nutrient availability. The temporal variations of production and chlorophyll were driven by changes in nutrient introduction to the euphotic zone due to both high- and low-frequency changes of the mixed layer depth within 32 deg-34 deg N, 62 deg-64 deg W between 1979 and 1984. Results from the model derived from high-frequency (case 1) changes in the mixed layer depth showed variations in primary production and peak chlorophyll concentrations when compared with results from the model derived from low-frequency (case 2) mixed layer depth changes. Incorporation of size-fractionated plankton state variables in the model led to greater seasonal resolution of measured primary production and vertical chlorophyll profiles. The findings of this study highlight the possible inadequacy of estimating primary production in the sea from data of low-frequency temporal resolution and oversimplified biological simulations.

Photosynthetic microbial mats in the 3,416-Myr-old ocean.

PubMed

Tice, Michael M; Lowe, Donald R

2004-09-30

Recent re-evaluations of the geological record of the earliest life on Earth have led to the suggestion that some of the oldest putative microfossils and carbonaceous matter were formed through abiotic hydrothermal processes. Similarly, many early Archaean (more than 3,400-Myr-old) cherts have been reinterpreted as hydrothermal deposits rather than products of normal marine sedimentary processes. Here we present the results of a field, petrographic and geochemical study testing these hypotheses for the 3,416-Myr-old Buck Reef Chert, South Africa. From sedimentary structures and distributions of sand and mud, we infer that deposition occurred in normal open shallow to deep marine environments. The siderite enrichment that we observe in deep-water sediments is consistent with a stratified early ocean. We show that most carbonaceous matter was formed by photosynthetic mats within the euphotic zone and distributed as detrital matter by waves and currents to surrounding environments. We find no evidence that hydrothermal processes had any direct role in the deposition of either the carbonaceous matter or the enclosing sediments. Instead, we conclude that photosynthetic organisms had evolved and were living in a stratified ocean supersaturated in dissolved silica 3,416 Myr ago.

Potential new production in two upwelling regions of the western Arabian Sea: Estimation and comparison

NASA Astrophysics Data System (ADS)

Liao, Xiaomei; Zhan, Haigang; Du, Yan

2016-07-01

Using satellite-derived and in situ data, the wind-driven potential new production (nitrate supply) for the 300 km wide coastal band in two upwelling regions of the western Arabian Sea (AS) during the southwest monsoon is estimated. The upward nitrate flux to the euphotic zone is generally based on the physical processes of coastal transport (Ekman transport and geostrophic transport) and offshore Ekman pumping. The coastal geostrophic current in the western AS influences the upwelling intensity and latitudinal distributions of nitrate supply. The Oman and Somalia upwelling regions have similar level of potential new production (nitrate supply) during the summer monsoon, while the satellite estimates of primary production off Oman are 2 times greater than those off Somalia. The much higher potential f-ratio in the Somalia upwelling region indicates that the primary production could be limited by availability of other macronutrients (e.g., silicate). The correlation analysis of the primary production and the aerosol optical thickness shows that the Oman upwelling region displays a stronger coupling between the atmospheric deposition and the phytoplankton abundance. The high summertime dust levels in the atmosphere are suggested to contribute to the high primary production in the Oman upwelling region.

[Design and experimentation of marine optical buoy].

PubMed

Yang, Yue-Zhong; Sun, Zhao-Hua; Cao, Wen-Xi; Li, Cai; Zhao, Jun; Zhou, Wen; Lu, Gui-Xin; Ke, Tian-Cun; Guo, Chao-Ying

2009-02-01

Marine optical buoy is of important value in terms of calibration and validation of ocean color remote sensing, scientific observation, coastal environment monitoring, etc. A marine optical buoy system was designed which consists of a main and a slave buoy. The system can measure the distribution of irradiance and radiance over the sea surface, in the layer near sea surface and in the euphotic zone synchronously, during which some other parameters are also acquired such as spectral absorption and scattering coefficients of the water column, the velocity and direction of the wind, and so on. The buoy was positioned by GPS. The low-power integrated PC104 computer was used as the control core to collect data automatically. The data and commands were real-timely transmitted by CDMA/GPRS wireless networks or by the maritime satellite. The coastal marine experimentation demonstrated that the buoy has small pitch and roll rates in high sea state conditions and thus can meet the needs of underwater radiometric measurements, the data collection and remote transmission are reliable, and the auto-operated anti-biofouling devices can ensure that the optical sensors work effectively for a period of several months.

The Modulation of Biological Production by Oceanic Mesoscale Turbulence

NASA Astrophysics Data System (ADS)

Lévy, Marina

This chapter reviews the current state of knowledge on bio-physical interactions at mesoscale and at sub-mesoscale. It is focused on the mid-latitudes open ocean. From examples taken from my own studies or selected in the literature, I show how high-resolution process-oriented model studies have helped to improve our understanding. I follow a process oriented approach; I first discuss the role of mesoscale eddies in moderating the nutrient flux into the well-lit euphotic zone. Then I address the impact on biogeochemistry of transport occurring on a horizontal scale smaller than the scale of an eddy. I show that submesoscale processes modulate biogeochemical budgets in a number of ways, through intense upwelling of nutrients, subduction of phytoplankton, and horizontal stirring. Finally, I emphasize that mesoscale and submesoscale dynamics have a strong impact on productivity through their influence on the stratification of the surface of the ocean. These processes have in common that they concern the short-term, local effect of oceanic turbulence on biogeochemistry. Efforts are still needed before we can get a complete picture, which would also include the far-field long-term effect of the eddies.

Photosynthetic microbial mats in the 3,416-Myr-old ocean

NASA Astrophysics Data System (ADS)

Tice, Michael M.; Lowe, Donald R.

2004-09-01

Recent re-evaluations of the geological record of the earliest life on Earth have led to the suggestion that some of the oldest putative microfossils and carbonaceous matter were formed through abiotic hydrothermal processes. Similarly, many early Archaean (more than 3,400-Myr-old) cherts have been reinterpreted as hydrothermal deposits rather than products of normal marine sedimentary processes. Here we present the results of a field, petrographic and geochemical study testing these hypotheses for the 3,416-Myr-old Buck Reef Chert, South Africa. From sedimentary structures and distributions of sand and mud, we infer that deposition occurred in normal open shallow to deep marine environments. The siderite enrichment that we observe in deep-water sediments is consistent with a stratified early ocean. We show that most carbonaceous matter was formed by photosynthetic mats within the euphotic zone and distributed as detrital matter by waves and currents to surrounding environments. We find no evidence that hydrothermal processes had any direct role in the deposition of either the carbonaceous matter or the enclosing sediments. Instead, we conclude that photosynthetic organisms had evolved and were living in a stratified ocean supersaturated in dissolved silica 3,416Myr ago.

Hydrographic and acoustic evidence for enhanced plankton stocks in a small cyclone in the northeastern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Ressler, Patrick H.; Jochens, Ann E.

2003-01-01

Mesoscale eddies (diameters of hundreds of km) have been shown to influence plankton production as well as the distribution of seabirds and marine mammals in the Gulf of Mexico. Smaller circulation features (eddies with diameters of tens of km) may have similar effects. We show that a small, sub-mesoscale cyclone located on the continental shelf and slope in the northeastern Gulf of Mexico during November 1997 was an area of enhanced nutrients, chlorophyll, and acoustic volume backscattering strength ( Sv). Nitrate concentrations at mid-depth in the euphotic zone were as high as 2 μM, surface chlorophyll exceeded 1 μg l -1, and Sv was as much as 15 dB referenced to 1 m -1 4 π-1 greater within this feature than in surrounding waters. Since Sv at 153 kHz is a proxy for the abundance of sound-scattering mesozooplankton and micronekton, we infer that this cyclone was locally enriched in biomass of these organisms. As with mesoscale eddies, smaller cyclones could also function as patches of favorable habitat for higher-trophic-level organisms and their prey.

Convection and the seeding of the North Atlantic bloom

NASA Astrophysics Data System (ADS)

D'Asaro, Eric A.

Observations of vertical velocities in deep wintertime mixed layers using neutrally buoyant floats show that the convectively driven vertical velocities, roughly 1000 m per day, greatly exceed the sinking velocities of phytoplankton, 10 m or less per day. These velocities mix plankton effectively and uniformly across the convective layer and are therefore capable of returning those that have sunk to depth back into the euphotic zone. This mechanism cycles cells through the surface layer during the winter and provides a seed population for the spring bloom. A simple model of this mechanism applied to immortal phytoplankton in the subpolar Labrador Sea predicts that the seed population in early spring will be a few percent of the fall concentration if the plankton sink more slowly than the mean rate at which the surface well-mixed layer grows over the winter. Plankton that sink faster than this will mostly sink into the abyss with only a minute fraction remaining by spring. The shallower mixed layers of mid-latitudes are predicted to be much less effective at maintaining a seed population over the winter, limiting the ability of rapidly sinking cells to survive the winter.

Distribution and diversity of Prochlorococcus ecotypes in the Red Sea.

PubMed

Shibl, Ahmed A; Thompson, Luke R; Ngugi, David K; Stingl, Ulrich

2014-07-01

Photosynthetic prokaryotes of the genus Prochlorococcus play a major role in global primary production in the world's oligotrophic oceans. A recent study on pelagic bacterioplankton communities in the northern and central Red Sea indicated that the predominant cyanobacterial 16S rRNA gene sequence types were from Prochlorococcus cells belonging to a high-light-adapted ecotype (HL II). In this study, we analyzed microdiversity of Prochlorococcus sp. at multiple depths within and below the euphotic zone in the northern, central, and southern regions of the Red Sea, as well as in surface waters in the same locations, but in a different season. Prochlorococcus dominated the communities in clone libraries of the amplified 16S-23S rRNA internal transcribed spacer (ITS) region. Almost no differences were found between samples from coastal or open-water sites, but a high diversity of Prochlorococcus ecotypes was detected at 100-meter depth in the water column. In addition, an unusual dominance of HL II-related sequences was observed in deeper waters. Our results indicate that the Red Sea harbors diverse Prochlorococcus lineages, but no novel ecotypes, despite its unusual physicochemical properties. © 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

Assimilation of seasonal chlorophyll and nutrient data into an adjoint three-dimensional ocean carbon cycle model: Sensitivity analysis and ecosystem parameter optimization

NASA Astrophysics Data System (ADS)

Tjiputra, Jerry F.; Polzin, Dierk; Winguth, Arne M. E.

2007-03-01

An adjoint method is applied to a three-dimensional global ocean biogeochemical cycle model to optimize the ecosystem parameters on the basis of SeaWiFS surface chlorophyll observation. We showed with identical twin experiments that the model simulated chlorophyll concentration is sensitive to perturbation of phytoplankton and zooplankton exudation, herbivore egestion as fecal pellets, zooplankton grazing, and the assimilation efficiency parameters. The assimilation of SeaWiFS chlorophyll data significantly improved the prediction of chlorophyll concentration, especially in the high-latitude regions. Experiments that considered regional variations of parameters yielded a high seasonal variance of ecosystem parameters in the high latitudes, but a low variance in the tropical regions. These experiments indicate that the adjoint model is, despite the many uncertainties, generally capable to optimize sensitive parameters and carbon fluxes in the euphotic zone. The best fit regional parameters predict a global net primary production of 36 Pg C yr-1, which lies within the range suggested by Antoine et al. (1996). Additional constraints of nutrient data from the World Ocean Atlas showed further reduction in the model-data misfit and that assimilation with extensive data sets is necessary.

A dynamic box model of bioactive elements in the southern Taiwan Strait

NASA Astrophysics Data System (ADS)

Hua-Sheng, Hong; Shao-Ling, Shang

1994-06-01

A dynamic box model was applied to study the characteristics of biogeochemical cycling of PO4-P, NO3-N, AOU, POC and PON in the southern Taiwan Strait region based on the field data of the “Minnan Taiwan Bank Fishing Ground Upwelling Ecosystem Study” during the period of Dec. 1987-Nov. 1988. According to the unique hydrological and topographical features of the region, six boxes and three layers were considered in the model. The variation rates and fluxes of elements induced by horizontal current, upwelling, by diffusion, sinking of particles and biogeochemical processes were estimated respectively. Results further confirmed that upwellings had important effects in this region. The nearshore upwelling areas had net input fluxes of nutrients brought by upwelling water, also had high depletion rates of nutrients and production rates of particulate organic matter and dissolved oxygen. The abnormal net production of nutrients in the middle layer, (10-30 m) indicated the important role of bacteria in this high production region. The phytoplankton POC contributed about 28% of the total POC. POC settling out from the euphotic zone was estimated to be 2×10-6 g/(m2·s) which was about 35% of the primary production.

Protistan diversity and activity inferred from RNA and DNA at a coastal ocean site in the eastern North Pacific.

PubMed

Hu, Sarah K; Campbell, Victoria; Connell, Paige; Gellene, Alyssa G; Liu, Zhenfeng; Terrado, Ramon; Caron, David A

2016-04-01

Microbial eukaryotes fulfill key ecological positions in marine food webs. Molecular approaches that connect protistan diversity and biogeography to their diverse metabolisms will greatly improve our understanding of marine ecosystem function. The majority of molecular-based studies to date use 18S rRNA gene sequencing to characterize natural microbial assemblages, but this approach does not necessarily discriminate between active and non-active cells. We incorporated RNA sequencing into standard 18S rRNA gene sequence surveys with the purpose of assessing those members of the protistan community contributing to biogeochemical cycling (active organisms), using the ratio of cDNA (reverse transcribed from total RNA) to 18S rRNA gene sequences within major protistan taxonomic groups. Trophically important phytoplankton, such as diatoms and chlorophytes exhibited seasonal trends in relative activity. Additionally, both radiolaria and ciliates displayed previously unreported high relative activities below the euphotic zone. This study sheds new light on the relative metabolic activity of specific protistan groups and how microbial communities respond to changing environmental conditions. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Diversity of Arctic pelagic Bacteria with an emphasis on photoheterotrophs: a review

NASA Astrophysics Data System (ADS)

Boeuf, D.; Humily, F.; Jeanthon, C.

2014-06-01

The Arctic Ocean is a unique marine environment with respect to seasonality of light, temperature, perennial ice cover, and strong stratification. Other important distinctive features are the influence of extensive continental shelves and its interactions with Atlantic and Pacific water masses and freshwater from sea ice melt and rivers. These characteristics have major influence on the biological and biogeochemical processes occurring in this complex natural system. Heterotrophic bacteria are crucial components of marine food webs and have key roles in controlling carbon fluxes in the oceans. Although it was previously thought that these organisms relied on the organic carbon in seawater for all of their energy needs, several recent discoveries now suggest that pelagic bacteria can depart from a strictly heterotrophic lifestyle by obtaining energy through unconventional mechanisms that are linked to the penetration of sunlight into surface waters. These photoheterotrophic mechanisms may play a significant role in the energy budget in the euphotic zone of marine environments. Modifications of light and carbon availability triggered by climate change may favor the photoheterotrophic lifestyle. Here we review advances in our knowledge of the diversity of marine photoheterotrophic bacteria and discuss their significance in the Arctic Ocean gained in the framework of the Malina cruise.

Physical and Biological Drivers of Biogeochemical Tracers Within the Seasonal Sea Ice Zone of the Southern Ocean From Profiling Floats

NASA Astrophysics Data System (ADS)

Briggs, Ellen M.; Martz, Todd R.; Talley, Lynne D.; Mazloff, Matthew R.; Johnson, Kenneth S.

2018-02-01

Here we present initial findings from nine profiling floats equipped with pH, O2, NO3-, and other biogeochemical sensors that were deployed in the seasonal ice zone (SIZ) of the Southern Ocean in 2014 and 2015 through the Southern Ocean Carbon and Climate Observations and Modelling (SOCCOM) project. A large springtime phytoplankton bloom was observed that coincided with sea ice melt for all nine floats. We argue this bloom results from a shoaling of the mixed layer depth, increased vertical stability, and enhanced nutrient and light availability as the sea ice melts. This interpretation is supported by the absence of a springtime bloom when one of the floats left the SIZ in the second year of observations. During the sea ice covered period, net heterotrophic conditions were observed. The rate of uptake of O2 and release of dissolved inorganic carbon (derived from pH and estimated total alkalinity) and NO3- is reminiscent of biological respiration and is nearly Redfieldian for the nine floats. A simple model of mixed layer physics was developed to separate the physical and biological components of the signal in pH and O2 over one annual cycle for a float in the Ross Sea SIZ. The resulting annual net community production suggests that seasonal respiration during the ice covered period of the year nearly balances the production in the euphotic layer of up to 5 mol C m-2 during the ice free period leading to a net of near zero carbon exported to depth for this one float.

Surface and mid-water sources of organic carbon by photoautotrophic and chemoautotrophic production in the Black Sea

NASA Astrophysics Data System (ADS)

Yılmaz, Ayşen; Çoban-Yıldız, Yeşim; Telli-Karakoç, Fatma; Bologa, Alexandru

2006-08-01

The multilayered surface waters of the Black Sea contain aerobic, suboxic and anoxic layers that support both photoautotrophic (PP) and chemoautotrophic (ChP) biological production. During the R/V Knorr cruise in May-June 2001, phytoplankton biomass (represented as chlorophyll- a), photoautotrophic and chemoautotrophic production (ChP) rates were determined in the western Black Sea. Integrated chlorophyll- a concentrations in the euphotic zone were as low as 2.2 mg m -2 in the central gyre, while they were as high as 19.9 mg m -2 in the NW shelf region. Integrated photoautotrophic production rates ranged from 112 to 355 mg C m -2 d -1. The lowest values were determined in the central gyre and the highest values were found at the shelf-break station near the Bosphorus, the NW shelf/shelf-break area and in the Sevastopol eddy. Primary production and chlorophyll- a data revealed that post-bloom conditions existed during this sampling period. Bioassay experiments showed that under optimum light conditions, photoautotrophic production was nitrogen-limited. ChP increased in the redox transition zone and coincided with the lower boundary of the fine particle layer. The maximum values were shallower (at σθ=16.25) in the central gyre and deeper (at σθ=16.5) in the shelf-break region near Sakarya Canyon. Integrated ChP rates were 63 and 1930 mg C m -2 d -1, which were equivalent to 30% and 89% of the overall water-column production for the central gyre and Sakarya Canyon regions, respectively.

Unusual bacterioplankton community structure in ultra-oligotrophic Crater Lake

USGS Publications Warehouse

Urbach, Ena; Vergin, Kevin L.; Morse, Ariel

2001-01-01

The bacterioplankton assemblage in Crater Lake, Oregon (U.S.A.), is different from communities found in other oxygenated lakes, as demonstrated by four small subunit ribosomal ribonucleic acid (SSU rRNA) gene clone libraries and oligonucleotide probe hybridization to RNA from lake water. Populations in the euphotic zone of this deep (589 m), oligotrophic caldera lake are dominated by two phylogenetic clusters of currently uncultivated bacteria: CL120-10, a newly identified cluster in the verrucomicrobiales, and ACK4 actinomycetes, known as a minor constituent of bacterioplankton in other lakes. Deep-water populations at 300 and 500 m are dominated by a different pair of uncultivated taxa: CL500-11, a novel cluster in the green nonsulfur bacteria, and group I marine crenarchaeota. b-Proteobacteria, dominant in most other freshwater environments, are relatively rare in Crater Lake (<=16% of nonchloroplast bacterial rRNA at all depths). Other taxa identified in Crater Lake libraries include a newly identified candidate bacterial division, ABY1, and a newly identified subcluster, CL0-1, within candidate division OP10. Probe analyses confirmed vertical stratification of several microbial groups, similar to patterns observed in open-ocean systems. Additional similarities between Crater Lake and ocean microbial populations include aphotic zone dominance of group I marine crenarchaeota and green nonsulfur bacteria. Comparison of Crater Lake to other lakes studied by rRNA methods suggests that selective factors structuring Crater Lake bacterioplankton populations may include low concentrations of available trace metals and dissolved organic matter, chemistry of infiltrating hydrothermal waters, and irradiation by high levels of ultraviolet light.

Physical-Biological Coupling in the Western South China Sea: The Response of Phytoplankton Community to a Mesoscale Cyclonic Eddy.

PubMed

Wang, Lei; Huang, Bangqin; Chiang, Kuo-Ping; Liu, Xin; Chen, Bingzhang; Xie, Yuyuan; Xu, Yanping; Hu, Jianyu; Dai, Minhan

2016-01-01

It is widely recognized that the mesoscale eddies play an important part in the biogeochemical cycle in ocean ecosystem, especially in the oligotrophic tropical zones. So here a heterogeneous cyclonic eddy in its flourishing stage was detected using remote sensing and in situ biogeochemical observation in the western South China Sea (SCS) in early September, 2007. The high-performance liquid chromatography method was used to identify the photosynthetic pigments. And the CHEMical TAXonomy (CHEMTAX) was applied to calculate the contribution of nine phytoplankton groups to the total chlorophyll a (TChl a) biomass. The deep chlorophyll a maximum layer (DCML) was raised to form a dome structure in the eddy center while there was no distinct enhancement for TChl a biomass. The integrated TChl a concentration in the upper 100 m water column was also constant from the eddy center to the surrounding water outside the eddy. However the TChl a biomass in the surface layer (at 5 m) in the eddy center was promoted 2.6-fold compared to the biomass outside the eddy (p < 0.001). Thus, the slight enhancement of TChl a biomass of euphotic zone integration within the eddy was mainly from the phytoplankton in the upper mixed zone rather than the DCML. The phytoplankton community was primarily contributed by diatoms, prasinophytes, and Synechococcus at the DCML within the eddy, while less was contributed by haptophytes_8 and Prochlorococcus. The TChl a biomass for most of the phytoplankton groups increased at the surface layer in the eddy center under the effect of nutrient pumping. The doming isopycnal within the eddy supplied nutrients gently into the upper mixing layer, and there was remarkable enhancement in phytoplankton biomass at the surface layer with 10.5% TChl a biomass of water column in eddy center and 3.7% at reference stations. So the slight increasing in the water column integrated phytoplankton biomass might be attributed to the stimulated phytoplankton biomass at the surface layer.

Selected physical, biological and biogeochemical implications of a rapidly changing Arctic Marginal Ice Zone

NASA Astrophysics Data System (ADS)

Barber, David G.; Hop, Haakon; Mundy, Christopher J.; Else, Brent; Dmitrenko, Igor A.; Tremblay, Jean-Eric; Ehn, Jens K.; Assmy, Philipp; Daase, Malin; Candlish, Lauren M.; Rysgaard, Søren

2015-12-01

The Marginal Ice Zone (MIZ) of the Arctic Ocean is changing rapidly due to a warming Arctic climate with commensurate reductions in sea ice extent and thickness. This Pan-Arctic review summarizes the main changes in the Arctic ocean-sea ice-atmosphere (OSA) interface, with implications for primary- and secondary producers in the ice and the underlying water column. Changes in the Arctic MIZ were interpreted for the period 1979-2010, based on best-fit regressions for each month. Trends of increasingly open water were statistically significant for each month, with quadratic fit for August-November, illustrating particularly strong seasonal feedbacks in sea-ice formation and decay. Geographic interpretations of physical and biological changes were based on comparison of regions with significant changes in sea ice: (1) The Pacific Sector of the Arctic Ocean including the Canada Basin and the Beaufort, Chukchi and East Siberian seas; (2) The Canadian Arctic Archipelago; (3) Baffin Bay and Hudson Bay; and (4) the Barents and Kara seas. Changes in ice conditions in the Barents sea/Kara sea region appear to be primarily forced by ocean heat fluxes during winter, whereas changes in the other sectors appear to be more summer-autumn related and primarily atmospherically forced. Effects of seasonal and regional changes in OSA-system with regard to increased open water were summarized for photosynthetically available radiation, nutrient delivery to the euphotic zone, primary production of ice algae and phytoplankton, ice-associated fauna and zooplankton, and gas exchange of CO2. Changes in the physical factors varied amongst regions, and showed direct effects on organisms linked to sea ice. Zooplankton species appear to be more flexible and likely able to adapt to variability in the onset of primary production. The major changes identified for the ice-associated ecosystem are with regard to production timing and abundance or biomass of ice flora and fauna, which are related to regional changes in sea-ice conditions.

Nitrite oxidation in the upper water column and oxygen minimum zone of the eastern tropical North Pacific Ocean

PubMed Central

Beman, J Michael; Leilei Shih, Joy; Popp, Brian N

2013-01-01

Nitrogen (N) is an essential nutrient in the sea and its distribution is controlled by microorganisms. Within the N cycle, nitrite (NO2−) has a central role because its intermediate redox state allows both oxidation and reduction, and so it may be used by several coupled and/or competing microbial processes. In the upper water column and oxygen minimum zone (OMZ) of the eastern tropical North Pacific Ocean (ETNP), we investigated aerobic NO2− oxidation, and its relationship to ammonia (NH3) oxidation, using rate measurements, quantification of NO2−-oxidizing bacteria via quantitative PCR (QPCR), and pyrosequencing. 15NO2− oxidation rates typically exhibited two subsurface maxima at six stations sampled: one located below the euphotic zone and beneath NH3 oxidation rate maxima, and another within the OMZ. 15NO2− oxidation rates were highest where dissolved oxygen concentrations were <5 μM, where NO2− accumulated, and when nitrate (NO3−) reductase genes were expressed; they are likely sustained by NO3− reduction at these depths. QPCR and pyrosequencing data were strongly correlated (r2=0.79), and indicated that Nitrospina bacteria numbered up to 9.25% of bacterial communities. Different Nitrospina groups were distributed across different depth ranges, suggesting significant ecological diversity within Nitrospina as a whole. Across the data set, 15NO2− oxidation rates were decoupled from 15NH4+ oxidation rates, but correlated with Nitrospina (r2=0.246, P<0.05) and NO2− concentrations (r2=0.276, P<0.05). Our findings suggest that Nitrospina have a quantitatively important role in NO2− oxidation and N cycling in the ETNP, and provide new insight into their ecology and interactions with other N-cycling processes in this biogeochemically important region of the ocean. PMID:23804152

Low Oxygen and Ocean Acidification on the Vancouver Island Shelf

NASA Astrophysics Data System (ADS)

Bianucci, L.; Denman, K.

2008-12-01

In the recent years hypoxic events have been observed along the west coast of North America (off Oregon and California). Although a common cause of coastal hypoxia is usually anthropogenic eutrophication, in these upwelling regions the advection of oxygen-depleted waters from offshore is a key mechanism. Moreover, the high productivity typical of these margins generates a large flux of sinking particular organic matter. The remineralization of this matter below the euphotic zone produces an elevated consumption of oxygen. When concentrations become lower than certain threshold, hypoxia leads to a major change in the ecosystem and the affected areas are called 'dead zones'. Furthermore, the two processes that drive oxygen levels down (physical upwelling and biological demand) also increase dissolved inorganic carbon in the shelf, which leads to a pH reduction. Ocean acidification and hypoxia can severely affect ecosystems, and the links between these phenomena have not been explored. This presentation will discuss a model study of the carbon and oxygen coupling on the Vancouver Island shelf, with focus on the connection between acidification and hypoxia. Moreover, the role of biology versus physics will be investigated. This region comprises the northern end of the wind-driven upwelling margin off western North America, where low oxygen events have not been extensively studied. However, the proximity to an Oxygen Minimum Zone offshore and the observed decline of oxygen in the Northeast Pacific turns this shelf into a potential candidate to suffer from low-oxygen events. The model used is the Regional Ocean Modeling System (ROMS) in a quasi-2D configuration of the shelf (across-shore section with uniform properties alongshore). The biogeochemical model has carbon, oxygen, and nitrogen as state variables, and includes cycling of dissolved organic matter. Carbon and oxygen cycles are coupled through ecosystem processes such as photosynthesis and remineralization, while they are decoupled by other processes (e.g., nitrification and denitrification).

Sinking fluxes of minor and trace elements in the North Pacific Ocean measured during the VERTIGO program

NASA Astrophysics Data System (ADS)

Lamborg, C. H.; Buesseler, K. O.; Lam, P. J.

2008-07-01

As part of the Vertical Transport in the Global Ocean (VERTIGO) program, we collected and analyzed sinking particles using sediment traps at three depths in the oceanic mesopelagic zone and at two biogeochemically contrasting sites (N. Central Pacific at ALOHA; N. Pacific Western Subarctic Gyre at K2). In this paper, we present the results of minor and trace element determinations made on these samples. Minor and trace elements in the sinking material showed 2 trends in flux with depth: increasing and constant. The sinking particulate phase of some elements (Al, Fe, Mn) was dominated by material of lithogenic origin and exhibited flux that was constant with depth and consistent with eolian dust inputs (ALOHA), or increasing in flux with depth as a result of lateral inputs from a shelf (K2). This shelf-derived material also appears to have been confined to very small particles, whose inherent sinking rates are slow, and residence time within the mesopelagic "twilight zone" would be consequently long. Furthermore, the flux of this material did not change with substantial changes in the rain of biogenic material from the surface (K2), suggesting mechanistic decoupling from the flux of organic carbon and macronutrients. Micronutrient (Fe, Co, Zn and Cu) fluxes examined in a 1-D mass balance suggest widely differing sources and sinks in the water column as well as impacts from biological uptake and regeneration. For example, total Fe fluxes into and out of the euphotic zone appeared to be dominated by lithogenic material and far exceed biological requirements. The export flux of Fe, however, appeared to be balanced by the eolian input of soluble Fe. For Zn and Cu, the situation is reversed, with atmospheric inputs insufficient to support fluxes, and the cycling therefore dominated by the draw down of an internal pool. For Co, the situation lies in between, with important, but ultimately insufficient atmospheric inputs.

Upwelling and isolation in oxygen-depleted anticyclonic modewater eddies and implications for nitrate cycling

NASA Astrophysics Data System (ADS)

Karstensen, Johannes; Schütte, Florian; Pietri, Alice; Krahmann, Gerd; Fiedler, Björn; Grundle, Damian; Hauss, Helena; Körtzinger, Arne; Löscher, Carolin R.; Testor, Pierre; Vieira, Nuno; Visbeck, Martin

2017-04-01

The temporal evolution of the physical and biogeochemical structure of an oxygen-depleted anticyclonic modewater eddy is investigated over a 2-month period using high-resolution glider and ship data. A weakly stratified eddy core (squared buoyancy frequency N2 ˜ 0.1 × 10-4 s-2) at shallow depth is identified with a horizontal extent of about 70 km and bounded by maxima in N2. The upper N2 maximum (3-5 × 10-4 s-2) coincides with the mixed layer base and the lower N2 maximum (0.4 × 10-4 s-2) is found at about 200 m depth in the eddy centre. The eddy core shows a constant slope in temperature/salinity (T/S) characteristic over the 2 months, but an erosion of the core progressively narrows down the T/S range. The eddy minimal oxygen concentrations decreased by about 5 µmol kg-1 in 2 months, confirming earlier estimates of oxygen consumption rates in these eddies. Separating the mesoscale and perturbation flow components reveals oscillating velocity finestructure ( ˜ 0.1 m s-1) underneath the eddy and at its flanks. The velocity finestructure is organized in layers that align with layers in properties (salinity, temperature) but mostly cross through surfaces of constant density. The largest magnitude in velocity finestructure is seen between the surface and 140 m just outside the maximum mesoscale flow but also in a layer underneath the eddy centre, between 250 and 450 m. For both regions a cyclonic rotation of the velocity finestructure with depth suggests the vertical propagation of near-inertial wave (NIW) energy. Modification of the planetary vorticity by anticyclonic (eddy core) and cyclonic (eddy periphery) relative vorticity is most likely impacting the NIW energy propagation. Below the low oxygen core salt-finger type double diffusive layers are found that align with the velocity finestructure. Apparent oxygen utilization (AOU) versus dissolved inorganic nitrate (NO3-) ratios are about twice as high (16) in the eddy core compared to surrounding waters (8.1). A large NO3- deficit of 4 to 6 µmol kg-1 is determined, rendering denitrification an unlikely explanation. Here it is hypothesized that the differences in local recycling of nitrogen and oxygen, as a result of the eddy dynamics, cause the shift in the AOU : NO3- ratio. High NO3- and low oxygen waters are eroded by mixing from the eddy core and entrain into the mixed layer. The nitrogen is reintroduced into the core by gravitational settling of particulate matter out of the euphotic zone. The low oxygen water equilibrates in the mixed layer by air-sea gas exchange and does not participate in the gravitational sinking. Finally we propose a mesoscale-submesoscale interaction concept where wind energy, mediated via NIWs, drives nutrient supply to the euphotic zone and drives extraordinary blooms in anticyclonic mode-water eddies.

Feeding ecology of the copepod Lucicutia aff. L. grandis near the lower interface of the Arabian Sea oxygen minimum zone

NASA Astrophysics Data System (ADS)

Gowing, Marcia M.; Wishner, Karen F.

Feeding ecology of the calanoid copepod Lucicutia aff. L. grandis collected in the Arabian Sea at one station during the Spring Intermonsoon and during the Southwest Monsoon of 1995 was studied with transmission electron microscopy of gut-contents. Highest abundances of these animals occurred from ˜400 to 1100 m, near the lower interface of the oxygen minimum zone and at the inflection point where oxygen starts to increase. We expected that their gut-contents would include particles and cells that had sunk relatively undegraded from surface waters as well as those from within the oxygen minimum zone, and that gut-contents would differ between the Spring Intermonsoon and the more productive SW Monsoon. Overall, in both seasons Lucicutia aff. L. grandis was omnivorous, and consumed a variety of detrital particles, prokaryotic and eukaryotic autotrophs, gram-negative bacteria including metal-precipitating bacteria, aggregates of probable gram-positive bacteria, microheterotrophs, virus-like particles and large virus-like particles, as well as cuticle and cnidarian tissue. Few significant differences in types of food consumed were seen among life stages within or among various depth zones. Amorphous, unidentifiable material was significantly more abundant in guts during the Spring Intermonsoon than during the late SW Monsoon, and recognizable cells made up a significantly higher portion of gut-contents during the late SW Monsoon. This is consistent with the Intermonsoon as a time when organic material is considerably re-worked by the surface water microbial loop before leaving the euphotic zone. In both seasons Lucicutia aff. L. grandis had consumed what appeared to be aggregates of probable gram-positive bacteria, similar to those we had previously found in gut-contents of several species of zooplankton from the oxygen minimum zone in the eastern tropical Pacific. By intercepting sinking material, populations of Lucicutia aff. L. grandis act as a filter for carbon sinking to the sea floor. They also modify sinking carbon in several ways: enhancing pelagic-abyssal coupling of carbon from cyanobacteria, eliminating part of the deep-sea microbial loop by direct consumption of bacterial aggregates, and redistributing particulate manganese and iron from association with suspended cells or aggregates to containment in rapidly sinking fecal pellets. Lucicutia aff. L. grandis can be viewed as representative of deep-dwelling detritivorous mesozooplankton. Assessing the magnitude of the effects of such organisms on carbon flux in the Arabian Sea will require data on feeding rates.

Calculating Irradiance For Photosynthesis In The Ocean

NASA Technical Reports Server (NTRS)

Collins, Donald J.; Davis, Curtiss O.; Booth, C. Rockwell; Kiefer, Dale A.; Stallings, Casson

1990-01-01

Mathematical model predicts available and usable irradiances. Yields estimates of irradiance available for photosynthesis (Epar) and irradiance usable for photosynthesis (Epur) as functions of depth in ocean. Describes Epur and Epar in terms of spectral parameters measured remotely (from satellites or airplanes). These irradiances useful in studies of photosynthetic productivity of phytoplankton in euphotic layer.

Assessment of satellite derived diffuse attenuation coefficients and euphotic depths in south Florida coastal waters

EPA Science Inventory

Optical data collected in coastal waters off South Florida and in the Caribbean Sea between January 2009 and December 2010 were used to evaluate products derived with three bio-optical inversion algorithms applied to MOIDS/Aqua, MODIS/Terra, and SeaWiFS satellite observations. Th...

Iron from a submarine source impacts the productive layer of the Western Tropical South Pacific (WTSP).

PubMed

Guieu, Cécile; Bonnet, Sophie; Petrenko, Anne; Menkes, Christophe; Chavagnac, Valérie; Desboeufs, Karine; Maes, Christophe; Moutin, Thierry

2018-06-13

In the Western Tropical South Pacific, patches of high chlorophyll concentrations linked to the occurrence of N 2 -fixing organisms are found in the vicinity of volcanic islands. The survival of these organisms relies on a high bioavailable iron supply whose origin and fluxes remain unknown. Here, we measured high dissolved iron (DFe) concentrations (up to 66 nM) in the euphotic layer, extending zonally over 10 degrees longitude (174 E-175 W) at ∼20°S latitude. DFe atmospheric fluxes were at the lower end of reported values of the remote ocean and could not explain the high DFe concentrations measured in the water column in the vicinity of Tonga. We argue that the high DFe concentrations may be sustained by a submarine source, also characterized by freshwater input and recorded as salinity anomalies by Argo float in situ measurements and atlas data. The observed negative salinity anomalies are reproduced by simulations from a general ocean circulation model. Submarine iron sources reaching the euphotic layer may impact nitrogen fixation across the whole region.

Repeated invasions into the twilight zone: evolutionary origins of a novel assemblage of fishes from deep Caribbean reefs.

PubMed

Tornabene, Luke; Van Tassell, James L; Robertson, D Ross; Baldwin, Carole C

2016-08-01

Mesophotic and deeper reefs of the tropics are poorly known and underexplored ecosystems worldwide. Collectively referred to as the 'twilight zone', depths below ~30-50 m are home to many species of reef fishes that are absent from shallower depths, including many undescribed and endemic species. We currently lack even a basic understanding of the diversity and evolutionary origins of fishes on tropical mesophotic reefs. Recent submersible collections in the Caribbean have provided new specimens that are enabling phylogenetic reconstructions that incorporate deep-reef representatives of tropical fish genera. Here, we investigate evolutionary depth transitions in the family Gobiidae (gobies), the most diverse group of tropical marine fishes. Using divergence-time estimation coupled with stochastic character mapping to infer the timing of shallow-to-deep habitat transitions in gobies, we demonstrate at least four transitions from shallow to mesophotic depths. Habitat transitions occurred in two broad time periods (Miocene, Pliocene-Pleistocene), and may have been linked to the availability of underutilized niches, as well as the evolution of morphological/behavioural adaptations for life on deep reefs. Further, our analysis shows that at least three evolutionary lineages that invaded deep habitats subsequently underwent speciation, reflecting another unique mode of radiation within the Gobiidae. Lastly, we synthesize depth distributions for 95 species of Caribbean gobies, which reveal major bathymetric faunal breaks at the boundary between euphotic and mesophotic reefs. Ultimately, our study is the first rigorous investigation into the origin of Caribbean deep-reef fishes and provides a framework for future studies that utilize rare, deep-reef specimens. © 2016 John Wiley & Sons Ltd.

Depositional paleoenvironments of the Lower Permian (upper Cisuralian) carbonate succession of Paso Hondo Formation in Chiapas State, southeastern Mexico

NASA Astrophysics Data System (ADS)

Torres-Martínez, Miguel A.; Barragán, Ricardo; Sour-Tovar, Francisco; González-Mora, Sergio

2017-11-01

The Paso Hondo Formation outcrops around of the Chicomuselo region, Chiapas State, Mexico. It is a Permian lithostratigraphic unit mainly composed of massive limestone which has been dated for the Artinskian-Kungurian (late Cisuralian). A microfacies analysis carried out on the carbonate rocks of a stratigraphic section, allowed for the first time the recognition of the depositional conditions that prevailed in the Chicomuselo region at the end of the Cisuralian. The facies associations studied allowed identifying different marine paleoenvironments related with a homoclinal carbonate ramp. The presence of anhydrite nodules, a mud-dominated carbonate production in euphotic zone (precursor of mudstones and packstones) and the presence of a diverse fauna mainly composed of photic-independent biota (mollusks, bryozoans, brachiopods and crinoids), indicate that the studied section was deposited in a relatively uniform low angle ramp. Thus, facies of different environments of inner ramp were detected, including those of a lagoon close to a peritidal area, with periodical restricted or open circulation, and open waters deposits influenced by the storm zone. In addition, mid-ramp facies were also observed. Facies associations of the basal levels on the studied section were mainly correlated with lagoonal shallow marine environments, being ostracods, calcispheres and peloids the dominant allochems. In contrast, there is a shift upwards to facies of open waters and mid-ramp environments, characterized by abundant skeletal grains of bryozoans, brachiopods and crinoids. The paleoenvironments recorded through the stratigraphic section were related with specific bathymetries, having a general tend towards the sea level rise. This record coincides with the global transgression event occurred during the Early Permian which have also been described for coeval localities of Texas and New Mexico in the United States and western Venezuela.

What if the Diatoms of the Deep Chlorophyll Maximum Can Ascend?

NASA Astrophysics Data System (ADS)

Villareal, T. A.

2016-02-01

Buoyancy regulation is an integral part of diatom ecology via its role in sinking rates and is fundamental to understanding their distribution and abundance. Numerous studies have documented the effects of size and nutrition on sinking rates. Many pelagic diatoms have low intrinsic sinking rates when healthy and nutrient-replete (< 1-2 meters per day). Physiological control of buoyancy via ion regulation and osmolyte control can easily result in cell sap densities less than seawater, resulting in near-zero sinking rates across a large size spectrum of diatoms as well as positive buoyancy in giant diatoms with their low surface:volume ratio. Ascent by smaller diatoms is much less described although predicted in cells as small as 200 cubic microns. Decreased sedimentation rates have long been linked to formation of layers in the water column, particularly at the low light and nutricline conditions of the deep chlorophyll maximum. The potential for ascending behavior adds an additional layer of complexity by allowing both active depth regulation similar to that observed in flagellated taxa and upward transport by some fraction of deep euphotic zone diatom blooms supported by nutrient injection. In this talk, I review the data documenting positive buoyancy in small diatoms, offer direct visual evidence of ascending behavior in common diatoms typical of both oceanic and coastal zones, and note the characteristics of sinking rate distributions within a single species. Buoyancy control leads to bidirectional movement at similar rates across a wide size spectrum of diatoms although the frequency of ascending behavior may be only a small portion of the individual species' abundance. While much remains to be learned, the paradigm of unidirectional downward movement by diatoms is both inaccurate and an oversimplification.

Spatial and Temporal Patterns of Chlorophyll Concentration in the Southern California Bight

NASA Astrophysics Data System (ADS)

Nezlin, Nikolay P.; McLaughlin, Karen; Booth, J. Ashley T.; Cash, Curtis L.; Diehl, Dario W.; Davis, Kristen A.; Feit, Adriano; Goericke, Ralf; Gully, Joseph R.; Howard, Meredith D. A.; Johnson, Scott; Latker, Ami; Mengel, Michael J.; Robertson, George L.; Steele, Alex; Terriquez, Laura; Washburn, Libe; Weisberg, Stephen B.

2018-01-01

Distinguishing between local, anthropogenic nutrient inputs and large-scale climatic forcing as drivers of coastal phytoplankton biomass is critical to developing effective nutrient management strategies. Here we assess the relative importance of these two drivers by comparing trends in chlorophyll-a between shallow coastal (0.1-16.5 km) and deep offshore (17-700 km) areas, hypothesizing that coastal regions influenced by anthropogenic nutrient inputs may have different spatial and temporal patterns in chlorophyll-a concentration from offshore regions where coastal inputs are less influential. Quarterly conductivity-temperature-depth (CTD) fluorescence measurements collected from three southern California continental shelf regions since 1998 were compared to chlorophyll-a data from the more offshore California Cooperative Fisheries Investigations (CalCOFI) program. The trends in the coastal zone were similar to those offshore, with a gradual increase of chlorophyll-a biomass and shallowing of its maximum layer since the beginning of observations, followed by chlorophyll-a declining and deepening from 2010 to present. An exception was the northern coastal part of SCB, where chlorophyll-a continued increasing after 2010. The long-term increase in chlorophyll-a prior to 2010 was correlated with increased nitrate concentrations in deep waters, while the recent decline was associated with deepening of the upper mixed layer, both linked to the low-frequency climatic cycles of the Pacific Decadal Oscillation and North Pacific Gyre Oscillation. These large-scale factors affecting the physical structure of the water column may also influence the delivery of nutrients from deep ocean outfalls to the euphotic zone, making it difficult to distinguish the effects of anthropogenic inputs on chlorophyll along the coast.

Temporal and spatial changes in plankton respiration and biomass in the Canary Islands region: the effect of mesoscale variability

NASA Astrophysics Data System (ADS)

Arístegui, Javier; Montero, María F.

2005-02-01

The temporal and spatial variabilities in the abundance and respiratory activity of plankton communities (<200 μm) were studied during three seasonal cruises around Gran Canaria Island (Canary Islands), a region of high mesoscale variability. Marked seasonal changes in respiratory activity, plankton community structure, and the ratio of heterotrophic to autotrophic biomass can be largely explained by hydrographic changes at the mesoscale level. Wind/current shearing at the flanks of the island enhances plankton respiration, presumably as the consequence of an increase in turbulence. Counter-paired cyclonic and anticyclonic eddies generated downstream of the island act as a two-way biological pump, increasing plankton production by nutrient pumping into the euphotic zone and accelerating the transport of organic matter into the aphotic zone, respectively. Coastal upwelling waters invading the Canary region in the form of filaments can transport either water with low plankton respiration and large phytoplankton cells or water with high respiratory rates associated with small cells. Plankton respiration was closely related to the abundance of Synechococcus type cyanobacteria and heterotrophic nanoflagellates during the three periods, but was only correlated with chlorophyll during the most fertile season, suggesting that respiration was mainly linked to microbial food web processes. Size-fractionated studies showed that 51-67% of the respiratory activity was due to picoplankton cells (<2 μm). Respiration rates (average values: 113±18 to 187±87 mmol C m -2 d -1) matched primary production rates during the fertile period, but were up to one order of magnitude higher during the rest of the year. Substantial inputs of organic matter from the coastal upwelling would be necessary to balance the large annual heterotrophic deficit in the region of study.

Operational Monitoring and Forecasting in Regional Seas: the Aegean Sea example

NASA Astrophysics Data System (ADS)

Nittis, K.; Perivoliotis, L.; Zervakis, V.; Papadopoulos, A.; Tziavos, C.

2003-04-01

The increasing economic activities in the coastal zone and the associated pressure on the marine environment have raised the interest on monitoring systems able to provide supporting information for its effective management and protection. Such an integrated monitoring, forecasting and information system is being developed during the past years in the Aegean Sea. Its main component is the POSEIDON network that provides real-time data for meteorological and surface oceanographic parameters (waves, currents, hydrological and biochemical data) from 11 fixed oceanographic buoys. The numerical forecasting system is composed by an ETA atmospheric model, a WAM wave model and a POM hydrodynamic model that provide every day 72 hours forecasts. The system is operational since May 2000 and its products are published through Internet while a sub-set is also available through cellular telephony. New type of observing platforms will be available in the near future through a number of EU funded research projects. The Mediterranean Moored Multi-sensor Array (M3A) that was developed for the needs of the Mediterranean Forecasting System and was tested during 2000-2001 will be operational in 2004 during the MFSTEP project. The M3A system incorporates sensors for optical and chemical measurements (Oxygen, Turbidity, Chlorophyll-a, Nutrients and PAR) in the euphotic zone (0-100m) together with sensors for physical parameters (Temperature, Salinity, Current speed and direction) at the 0-500m layer. A Ferry-Box system will also operate during 2004 in the southern Aegean Sea, providing surface data for physical and bio-chemical properties. The ongoing modeling efforts include coupling with larger scale circulation models of the Mediterranean, high-resolution downscaling to coastal areas of the Aegean Sea and development of multi-variate data assimilation methods.

Hidden biosphere in an oxygen-deficient Atlantic open ocean eddy: future implications of ocean deoxygenation on primary production in the eastern tropical North Atlantic

NASA Astrophysics Data System (ADS)

Loescher, Carolin; Fischer, Martin; Neulinger, Sven; Fiedler, Björn; Philippi, Miriam; Schütte, Florian; Singh, Arvind; Hauss, Helena; Karstensen, Johannes; Körtzinger, Arne; Schmitz, Ruth

2016-04-01

The eastern tropical North Atlantic (ETNA) is characterized by a highly productive coastal upwelling system and a moderate oxygen minimum zone with lowest open ocean oxygen (O2) concentrations of approximately 40 μmol kg-1. The recent discovery of re-occurring mesoscale eddies with close to anoxic O2 concentrations (<1 μmol kg-1) located just below the mixed layer has challenged our understanding of O2 distribution and biogeochemical processes in this area. Here, we present the first microbial community study from a deoxygenated anticyclonic modewater eddy in the open waters of the ETNA. In the eddy, we observed significantly lower bacterial diversity compared to surrounding waters, along with a significant community shift. We detected enhanced primary productivity in the surface layer of the eddy indicated by elevated chlorophyll concentrations and carbon uptake rates of up to three times as high as in surrounding waters. Carbon uptake rates below the euphotic zone correlated to the presence of a specific high-light ecotype of Prochlorococcus, which is usually underrepresented in the ETNA. Our data indicate that high primary production in the eddy fuels export production and supports enhanced respiration in a specific microbial community at shallow depths, below the mixed layer base. The O2-depleted core waters eddy promoted transcription of the key gene for denitrification, nirS. This process is usually absent from the open ETNA waters. In light of future projected ocean deoxygenation, our results show that even distinct events of anoxia have the potential to alter microbial community structure with critical impacts on primary productivity and biogeochemical processes of oceanic water bodies.

Hidden biosphere in an oxygen-deficient Atlantic open ocean eddy: future implications of ocean deoxygenation on primary production in the eastern tropical North Atlantic

NASA Astrophysics Data System (ADS)

Löscher, C. R.; Fischer, M. A.; Neulinger, S. C.; Fiedler, B.; Philippi, M.; Schütte, F.; Singh, A.; Hauss, H.; Karstensen, J.; Körtzinger, A.; Künzel, S.; Schmitz, R. A.

2015-08-01

The eastern tropical North Atlantic (ETNA) is characterized by a highly productive coastal upwelling system and a moderate oxygen minimum zone with lowest open ocean oxygen (O2) concentrations of around 40 μmol kg-1. Only recently, the discovery of re-occurring mesoscale eddies with sometimes close to anoxic O2 concentrations (<1 μmol kg-1) and located just below the mixed layer challenged our understanding of O2 distribution and biogeochemical processes in this area. Here, we present the first metagenomic dataset from a deoxygenated anticyclonic modewater eddy in the open waters of the ETNA. In the eddy, we observed a significantly lower bacterial diversity compared to surrounding waters, along with a significant community shift. We detected enhanced primary productivity in the surface layer of the eddy indicated by elevated chlorophyll concentrations and increased carbon uptake rates up to three times as high as in surrounding waters. Carbon uptake below the euphotic zone correlated to the presence of a specific high-light ecotype of Prochlorococcus, which is usually underrepresented in the ETNA. Our combined data indicate that high primary production in the eddy fuels export production and the presence of a specific microbial community responsible for enhanced respiration at shallow depths, below the mixed layer base. Progressively decreasing O2 concentrations in the eddy were found to promote transcription of the key gene for denitrification, nirS, in the O2-depleted core waters. This process is usually absent from the open ETNA waters. In the light of future ocean deoxygenation our results show exemplarily that even distinct events of anoxia have the potential to alter microbial community structures and with that critically impact primary productivity and biogeochemical processes of oceanic water bodies.

Hidden biosphere in an oxygen-deficient Atlantic open-ocean eddy: future implications of ocean deoxygenation on primary production in the eastern tropical North Atlantic

NASA Astrophysics Data System (ADS)

Löscher, C. R.; Fischer, M. A.; Neulinger, S. C.; Fiedler, B.; Philippi, M.; Schütte, F.; Singh, A.; Hauss, H.; Karstensen, J.; Körtzinger, A.; Künzel, S.; Schmitz, R. A.

2015-12-01

The eastern tropical North Atlantic (ETNA) is characterized by a highly productive coastal upwelling system and a moderate oxygen minimum zone with lowest open-ocean oxygen (O2) concentrations of approximately 40 μmol kg-1. The recent discovery of re-occurring mesoscale eddies with close to anoxic O2 concentrations (< 1 μmol kg-1) located just below the mixed layer has challenged our understanding of O2 distribution and biogeochemical processes in this area. Here, we present the first microbial community study from a deoxygenated anticyclonic modewater eddy in the open waters of the ETNA. In the eddy, we observed significantly lower bacterial diversity compared to surrounding waters, along with a significant community shift. We detected enhanced primary productivity in the surface layer of the eddy indicated by elevated chlorophyll concentrations and carbon uptake rates of up to three times as high as in surrounding waters. Carbon uptake rates below the euphotic zone correlated to the presence of a specific high-light ecotype of Prochlorococcus, which is usually underrepresented in the ETNA. Our data indicate that high primary production in the eddy fuels export production and supports enhanced respiration in a specific microbial community at shallow depths, below the mixed-layer base. The transcription of the key functional marker gene for dentrification, nirS, further indicated a potential for nitrogen loss processes in O2-depleted core waters of the eddy. Dentrification is usually absent from the open ETNA waters. In light of future projected ocean deoxygenation, our results show that even distinct events of anoxia have the potential to alter microbial community structure with critical impacts on primary productivity and biogeochemical processes of oceanic water bodies.

Annual Net Community Production in the Western Subtropical North Pacific Determined from Argo-O2 Measurements

NASA Astrophysics Data System (ADS)

Yang, B.; Emerson, S. R.; Bushinsky, S. M.

2016-02-01

Export of organic carbon from the surface ocean to depth (the biological pump) helps maintain the pCO2 of the atmosphere and the O2 content of the oxygen minimum zones of the ocean. In the upper ocean, at steady state over a seasonal cycle the net organic carbon export is equal to the Annual Net Community Production (ANCP). The geographic distribution of this quantity determined by satellite-predicted Net Primary Production (NPP) and the recycling efficiency in the euphotic zone is more heterogeneous than the limited experimental estimates of ANCP. We evaluate the relationship between these two estimates of ANCP in the subtropical Western North Pacific Ocean ( 165o E and 20o N) using oxygen measurements on Argo Floats. In January of 2015 we deployed four floats with Anderaa oxygen sensors attached to a 60 cm stick on top of the float end cap, which can be readily calibrated against atmospheric pO2. We present data from these floats and air-sea oxygen flux calculations. The degree of oxygen supersaturation in summer is 1-2 percent, and in winter it fluctuates between being over and undersaturated. Evaluating the role of bubbles in winter is critical to an accurate determination of the annual flux. While there is not a full year of data at the time of writing this abstract, there will be when the Ocean Science meeting is held. So far, after nine months of measurements, there is a net flux of oxygen to the atmosphere, indicating that photosynthesis exceeds respiration. In February we will present a full annual cycle of air-sea oxygen flux and an estimate of ANCP in this very rarely studied region of the ocean.

3D-Analysis of a non-planispiral ammonoid from the Hunsrück Slate: natural or pathological variation?

PubMed Central

Stilkerich, Julia; Smrecak, Trisha A.

2017-01-01

We herein examine the only known non-planispirally coiled early Devonian ammonoid, the holotype specimen of Ivoites opitzi, to investigate if the host was encrusted in vivo and if these sclerobionts were responsible for the trochospiral coiling observed in this unique specimen. To test if the presence of runner-like sclerobionts infested the historically collected specimen of Ivoites opitzi during its life, we used microCT to produce a three-dimensional model of the surface of the specimen. Our results indicate that sclerobionts grew across the outer rim (venter) on both sides of the ammonoid conch at exactly the location where the deviation from the planispiral was recognized, and where subsequent ammonoid growth would likely preclude encrustation. This indicates in vivo encrustation of the I. opitzi specimen, and represents the earliest documentation of the phenomenon. Further, this suggests that non-planispiral coiling in I. opitzi was likely pathologically induced and does not represent natural morphological variation in the species. Despite the observed anomalies in coiling, the specimen reached adulthood and retains important identifying morphological features, suggesting the ammonoid was minimally impacted by encrustation in life. As such, appointing a new type specimen—as suggested by some authors—for the species is not necessary. In addition, we identify the sclerobionts responsible for modifying the coiling of this specimen as hederelloids, a peculiar group of sclerobionts likely related to phoronids. Hederelloids in the Devonian are commonly found encrusting on fossils collected in moderately deep environments within the photic zone and are rarely documented in dysphotic and aphotic samples. This indicates that when the ammonoid was encrusted it lived within the euphotic zone and supports the latest interpretations of the Hunsrück Slate depositional environment in the Bundenbach-Gemünden area. PMID:28674668

Revisiting nitrification in the Eastern Tropical South Pacific: A focus on controls

NASA Astrophysics Data System (ADS)

Peng, Xuefeng; Fuchsman, Clara A.; Jayakumar, Amal; Warner, Mark J.; Devol, Allan H.; Ward, Bess B.

2016-03-01

Nitrification, the oxidation of ammonium (NH4+) to nitrite (NO2-) and to nitrate (NO3-), is a component of the nitrogen (N) cycle internal to the fixed N pool. In oxygen minimum zones (OMZs), which are hotspots for oceanic fixed N loss, nitrification plays a key role because it directly supplies substrates for denitrification and anaerobic ammonia oxidation (anammox), and may compete for substrates with these same processes. However, the control of oxygen and substrate concentrations on nitrification are not well understood. We performed onboard incubations with 15N-labeled substrates to measure rates of NH4+ and NO2- oxidation in the eastern tropical South Pacific (ETSP). The spatial and depth distributions of NH4+ and NO2- oxidation rates were primarily controlled by NH4+ and NO2- availability, oxygen concentration, and light. In the euphotic zone, nitrification was partially photoinhibited. In the anoxic layer, NH4+ oxidation was negligible or below detection, but high rates of NO2- oxidation were observed. NH4+ oxidation displayed extremely high affinity for both NH4+ and oxygen. The positive linear correlations between NH4+ oxidation rates and in situ NH4+ concentrations and ammonia monooxygenase subunit A (amoA) gene abundances in the upper oxycline indicate that the natural assemblage of ammonia oxidizers responds to in situNH4+ concentrations or supply by adjusting their population size, which determines the NH4+ oxidation potential. The depth distribution of archaeal and bacterial amoA gene abundances and N2O concentration, along with independently reported simultaneous direct N2O production rate measurements, suggests that AOA were predominantly responsible for NH4+ oxidation, which was a major source of N2O production at oxygen concentrations > 5 µM.

Application of the Coastal and Marine Ecological Classification Standard using Satellite-derived and Modeled Data Products for Pelagic Habitats in the Northern Gulf of Mexico

EPA Science Inventory

Satellite-derived data for sea surface temperature, salinity, chlorophyll; euphotic depth; and modeled bottom to surface temperature differences (Delta t) were evaluated to assess the utility of these products as proxies for in situ measurements. The data were used to classify su...

Chlorophyll a reconstruction from in situ measurements: 2. Marked carbon uptake decrease in the last century

NASA Astrophysics Data System (ADS)

Fründt, B.; Dippner, J. W.; Schulz-Bull, D. E.; Waniek, J. J.

2015-02-01

A chlorophyll a hindcast in the Madeira Basin from 1871 to 2008 was used to analyze the long-term variability in the oligotrophic, subtropical gyres in relation to the climate change of the last century. The deep chlorophyll maximum (DCM), as dominant pattern of the chlorophyll a field, showed a fast decrease in its strength in the 1940s. An absolute minimum was reached between 1967 and 1973 when no DCM established with a recovering to the end of the time series. Long-term variability of the DCM was related to the North Atlantic Oscillation with a time delay of 9 years. The marked decrease in the 1940s was correlated to the drop of the solar radiation in transition from early brightening to global dimming. Caused by the influence of the solar radiation and maybe related to increasing global temperatures in the last century, the integrated chlorophyll a concentration decreased by about 0.7 mg m-2 in 2008 compared to 1871. The high-resolved chlorophyll a hindcast allowed an estimation of the carbon uptake by the ocean due to primary production in the euphotic zone. A rough calculation over the area of the global subtropical oceans showed 700 megaton less carbon uptake in 2008.

DeepPIV: Particle image velocimetry measurements using deep-sea, remotely operated vehicles

NASA Astrophysics Data System (ADS)

Katija, Kakani; Sherman, Alana; Graves, Dale; Klimov, Denis; Kecy, Chad; Robison, Bruce

2015-11-01

The midwater region of the ocean (below the euphotic zone and above the benthos) is one of the largest ecosystems on our planet, yet remains one of the least explored. Little-known marine organisms that inhabit midwater have developed life strategies that contribute to their evolutionary success, and may inspire engineering solutions for societally relevant challenges. Although significant advances in underwater vehicle technologies have improved access to midwater, small-scale, in situ fluid mechanics measurement methods that seek to quantify the interactions that midwater organisms have with their physical environment are lacking. Here we present DeepPIV, an instrumentation package affixed to remotely operated vehicles that quantifies fluid motions from the surface of the ocean down to 4000 m depths. Utilizing ambient suspended particulate, fluid-structure interactions are evaluated on a range of marine organisms in midwater. Initial science targets include larvaceans, biological equivalents of flapping flexible foils, that create mucus houses to filter food. Little is known about the structure of these mucus houses and the function they play in selectively filtering particles, and these dynamics can serve as particle-mucus models for human health. Using DeepPIV, we reveal the complex structures and flows generated within larvacean mucus houses, and elucidate how these structures function. Funding is gratefully acknowledged from the Packard Foundation.

Seasonal variation of absorption by particles and colored dissolved organic matter (CDOM) in Funka Bay, southwestern Hokkaido, Japan

NASA Astrophysics Data System (ADS)

Sasaki, Hiroaki; Miyamura, Tsuyoshi; Saitoh, Sei-ichi; Ishizaka, Joji

2005-08-01

Between November 2000 and October 2001, the seasonal variation in absorption by particles (phytoplankton and detritus) and colored dissolved organic matter (CDOM) was measured in Funka Bay (a subarctic coastal region of Japan). In autumn-winter, chlorophyll a concentration (Chl a) near the euphotic zone remained very low (<1.0 mg m -3) but markedly increased in spring (16.8 mg m -3). Chlorophyll-specific absorption coefficient for phytoplankton ( a∗ph( λ)) was high during summer and low during the spring bloom. This is because the package effect was greater during the spring bloom due to the presence of large diatoms, while small phytoplankton dominated during summer. Absorption at 440 nm by CDOM was higher than that of phytoplankton and detritus, except during the spring bloom, and the relative contribution of CDOM absorption to the total absorption coefficient was >50%. CDOM and detritus absorption did not increase with increasing Chl a, but it showed a time lag between the spring bloom. It is suggested that phytoplankton degradation started after the spring bloom; detritus absorption increased and, then, CDOM absorption increased. River runoff was not a significant influence in Funka Bay, therefore, CDOM production may be mainly related to microbial activity.

Larvae from deep-sea methane seeps disperse in surface waters.

PubMed

Arellano, Shawn M; Van Gaest, Ahna L; Johnson, Shannon B; Vrijenhoek, Robert C; Young, Craig M

2014-07-07

Many species endemic to deep-sea methane seeps have broad geographical distributions, suggesting that they produce larvae with at least episodic long-distance dispersal. Cold-seep communities on both sides of the Atlantic share species or species complexes, yet larval dispersal across the Atlantic is expected to take prohibitively long at adult depths. Here, we provide direct evidence that the long-lived larvae of two cold-seep molluscs migrate hundreds of metres above the ocean floor, allowing them to take advantage of faster surface currents that may facilitate long-distance dispersal. We collected larvae of the ubiquitous seep mussel "Bathymodiolus" childressi and an associated gastropod, Bathynerita naticoidea, using remote-control plankton nets towed in the euphotic zone of the Gulf of Mexico. The timing of collections suggested that the larvae might disperse in the water column for more than a year, where they feed and grow to more than triple their original sizes. Ontogenetic vertical migration during a long larval life suggests teleplanic dispersal, a plausible explanation for the amphi-Atlantic distribution of "B." mauritanicus and the broad western Atlantic distribution of B. naticoidea. These are the first empirical data to demonstrate a biological mechanism that might explain the genetic similarities between eastern and western Atlantic seep fauna. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Forecasting of cyanobacterial density in Torrão reservoir using artificial neural networks.

PubMed

Torres, Rita; Pereira, Elisa; Vasconcelos, Vítor; Teles, Luís Oliva

2011-06-01

The ability of general regression neural networks (GRNN) to forecast the density of cyanobacteria in the Torrão reservoir (Tâmega river, Portugal), in a period of 15 days, based on three years of collected physical and chemical data, was assessed. Several models were developed and 176 were selected based on their correlation values for the verification series. A time lag of 11 was used, equivalent to one sample (periods of 15 days in the summer and 30 days in the winter). Several combinations of the series were used. Input and output data collected from three depths of the reservoir were applied (surface, euphotic zone limit and bottom). The model that presented a higher average correlation value presented the correlations 0.991; 0.843; 0.978 for training, verification and test series. This model had the three series independent in time: first test series, then verification series and, finally, training series. Only six input variables were considered significant to the performance of this model: ammonia, phosphates, dissolved oxygen, water temperature, pH and water evaporation, physical and chemical parameters referring to the three depths of the reservoir. These variables are common to the next four best models produced and, although these included other input variables, their performance was not better than the selected best model.

Impacts of Mesoscale Eddies on the Vertical Nitrate Flux in the Gulf Stream Region

NASA Astrophysics Data System (ADS)

Zhang, Shuwen; Curchitser, Enrique N.; Kang, Dujuan; Stock, Charles A.; Dussin, Raphael

2018-01-01

The Gulf Stream (GS) region has intense mesoscale variability that can affect the supply of nutrients to the euphotic zone (Zeu). In this study, a recently developed high-resolution coupled physical-biological model is used to conduct a 25-year simulation in the Northwest Atlantic. The Reynolds decomposition method is applied to quantify the nitrate budget and shows that the mesoscale variability is important to the vertical nitrate supply over the GS region. The decomposition, however, cannot isolate eddy effects from those arising from other mesoscale phenomena. This limitation is addressed by analyzing a large sample of eddies detected and tracked from the 25-year simulation. The eddy composite structures indicate that positive nitrate anomalies within Zeu exist in both cyclonic eddies (CEs) and anticyclonic eddies (ACEs) over the GS region, and are even more pronounced in the ACEs. Our analysis further indicates that positive nitrate anomalies mostly originate from enhanced vertical advective flux rather than vertical turbulent diffusion. The eddy-wind interaction-induced Ekman pumping is very likely the mechanism driving the enhanced vertical motions and vertical nitrate transport within ACEs. This study suggests that the ACEs in GS region may play an important role in modulating the oceanic biogeochemical properties by fueling local biomass production through the persistent supply of nitrate.

Panspermia Survival Scenarios for Organisms that Survive Typical Hypervelocity Solar System Impact Events.

NASA Astrophysics Data System (ADS)

Pasini, D.

2014-04-01

Previous experimental studies have demonstrated the survivability of living cells during hypervelocity impact events, testing the panspermia and litho-panspermia hypotheses [1]. It has been demonstrated by the authors that Nannochloropsis Oculata Phytoplankton, a eukaryotic photosynthesizing autotroph found in the 'euphotic zone' (sunlit surface layers of oceans [2]), survive impacts up to 6.93 km s-1 (approx. shock pressure 40 GPa) [3, 4]. Also shown to survive impacts up to 5.49 km s-1 is the tardigrade species Hypsibius dujardini (a complex micro-animal consisting of 40,000 cells) [5, 6]. It has also been shown that they can survive sustained pressures up to 600 MPa using a water filled pressure capsule [7]. Additionally bacteria can survive impacts up to 5.4 km s-1 (~30 GPa) - albeit with a low probability of survival [1], and the survivability of yeast spores in impacts up to 7.4 km s-1 (~30 GPa) has also recently been demonstrated [8]. Other groups have also reported that the lichen Xanthoria elegans is able to survive shocks in similar pressure ranges (~40 GPa) [9]. Here we present various simulated impact regimes to show which scenarios are condusive to the panspermia hypothesis of the natural transfer of life (via an icy body) through space to an extraterrestrial environment.

Diffuse attenuation coefficient for downwelling irradiance at 490 nm and its spectral characteristics in the Black Sea upper layer: modeling, in situ measurements and ocean color data

NASA Astrophysics Data System (ADS)

Suslin, V. V.; Slabakova, V. K.; Churilova, T. Ya.

2017-11-01

Vertical diffuse attenuation coefficient, Kd(490), is one of the key parameter required for water quality modeling, hydrodynamic and biological processes in the sea. We showed that standard level-2 product of Kd(490) was underestimated in comparison with Kd(490) values simulated by the regional model during the diatom bloom in the Black Sea. Using data of SeaWiFS, MERIS and MODIS color scanners, a regional relationship between the model value of Kd(490) and the ratio of remote sensing reflectances has been obtained. Based on the bulgarian argo-bio-buoy dataset, the relationship between the attenuation coefficient of photosynthetically active radiation and attenuation coefficient at a wavelength of 490 nm is obtained. The simplified model, below as the S-model, of the diffuse attenuation coefficient spectrum for downwelling irradiance in the Black Sea upper layer is described. As a consequence of the S-model, the link between the depth of the euphotic zone and Kd(490) has been obtained. It is shown that the Kd(490) values, retrieved from ocean color data with using the regional link and from argo-bio-buoy measurements at depths between 6-20 m, are close to each other.

Changes in Microbial Plankton Assemblages Induced by Mesoscale Oceanographic Features in the Northern Gulf of Mexico.

PubMed

Williams, Alicia K; McInnes, Allison S; Rooker, Jay R; Quigg, Antonietta

2015-01-01

Mesoscale circulation generated by the Loop Current in the Northern Gulf of Mexico (NGOM) delivers growth-limiting nutrients to the microbial plankton of the euphotic zone. Consequences of physicochemically driven community shifts on higher order consumers and subsequent impacts on the biological carbon pump remain poorly understood. This study evaluates microbial plankton <10 μm abundance and community structure across both cyclonic and anti-cyclonic circulation features in the NGOM using flow cytometry (SYBR Green I and autofluorescence parameters). Non-parametric multivariate hierarchical cluster analyses indicated that significant spatial variability in community structure exists such that stations that clustered together were defined as having a specific 'microbial signature' (i.e. statistically homogeneous community structure profiles based on relative abundance of microbial groups). Salinity and a combination of sea surface height anomaly and sea surface temperature were determined by distance based linear modeling to be abiotic predictor variables significantly correlated to changes in microbial signatures. Correlations between increased microbial abundance and availability of nitrogen suggest nitrogen-limitation of microbial plankton in this open ocean area. Regions of combined coastal water entrainment and mesoscale convergence corresponded to increased heterotrophic prokaryote abundance relative to autotrophic plankton. The results provide an initial assessment of how mesoscale circulation potentially influences microbial plankton abundance and community structure in the NGOM.

Rapid removal of Chernobyl fallout from Mediterranean surface waters by biological activity

NASA Astrophysics Data System (ADS)

Fowler, Scott W.; Buat-Menard, Patrick; Yokoyama, Yuji; Ballestra, Serge; Holm, Elis; Nguyen, Huu Van

1987-09-01

The sinking of participate organic matter from the euphotic zone is an important pathway for the vertical transport of many elements and organic compounds in the sea1-3. Many natural4-5 and artificial5-7 radionuclides in surface waters are readily adsorbed onto suspended particles and are presumably scavenged and removed to depth on time scales commensurate with both particle sinking rate and retention time of the radionuclide on the particle. Previously, abyssal benthic organisms from the northeast Pacific were found to contain short-lived fission products which entered the sea surface as fallout from nuclear testing8. The presence of these radionuclides at great depth could not be explained by Stokesian settling of small fallout particles and it was hypothesized8 that zooplankton grazing in the surface layers packaged these particle-reactive radionuclides into large, relatively dense faecal pellets which rapidly sank to depth. We report here data from a time-series sediment trap experiment and concomitant zooplankton collections which show conclusively that Chernobyl radioactivity, in particular the rare earth nuclides 141Ce and 144Ce, entering the Mediterranean as a single pulse, was rapidly removed from surface waters and transported to 200m in a few days primarily by zooplankton grazing.

Future changes in coastal upwelling ecosystems with global warming: The case of the California Current System.

PubMed

Xiu, Peng; Chai, Fei; Curchitser, Enrique N; Castruccio, Frederic S

2018-02-12

Coastal upwelling ecosystems are among the most productive ecosystems in the world, meaning that their response to climate change is of critical importance. Our understanding of climate change impacts on marine ecosystems is largely limited to the open ocean, mainly because coastal upwelling is poorly reproduced by current earth system models. Here, a high-resolution model is used to examine the response of nutrients and plankton dynamics to future climate change in the California Current System (CCS). The results show increased upwelling intensity associated with stronger alongshore winds in the coastal region, and enhanced upper-ocean stratification in both the CCS and open ocean. Warming of the open ocean forces isotherms downwards, where they make contact with water masses with higher nutrient concentrations, thereby enhancing the nutrient flux to the deep source waters of the CCS. Increased winds and eddy activity further facilitate upward nutrient transport to the euphotic zone. However, the plankton community exhibits a complex and nonlinear response to increased nutrient input, as the food web dynamics tend to interact differently. This analysis highlights the difficulty in understanding how the marine ecosystem responds to a future warming climate, given to range of relevant processes operating at different scales.

Water quality of the Lexington Reservoir, Santa Clara County, California, 1978-80

USGS Publications Warehouse

Iwatsubo, R.T.; Sylvester, M.A.; Gloege, I.S.

1988-01-01

Analysis of water samples from Lexington Reservoir and Los Gatos Creek upstream from the reservoir from June 1978 through September 1980 showed that water generally met water-quality objectives identified by California Regional Water Quality Control Board, San Francisco Bay Region. Water-temperature profiles show that Lexington Reservoir is a warm monomictic lake. During summer, dissolved-oxygen concentrations generally were not reduced below 5.0 mg/L in the hyplimnion; only once during the study did bottom waters become anoxic. Water transparency decreased with depth. The euphotic zone ranged from 1.0 to 5.4 m, depending on suspended solids and algae, and was greater in summer than in spring. Calcium and bicarbonate were dominant ions at all stations except during spring, following the rainy season, when waters were a mixed cation bicarbonate type. Nitrogen concentrations were greater in samples from reservoir stations than in those from Los Gatos Creek, with most of the nitrogen in ammonia and organic forms. The amount of dissolved nitrate appeared to be related to phytoplankton abundance. Phosphorus and trace-element concentrations were low at all stations. Estimates of net primary productivity and Carlson 's trophic-state index, based on chlorophyll-a concentrations, indicated that reservoir classification ranges from oligotrophic to mesotrophic. Blue-green algae generally were predominant in reservoir samples. (USGS)

Enhanced Particulate Organic Carbon Export at Eddy Edges in the Oligotrophic Western North Pacific Ocean

PubMed Central

Shih, Yung-Yen; Hung, Chin-Chang; Gong, Gwo-Ching; Chung, Wan-Chen; Wang, Yu-Huai; Lee, I-Huan; Chen, Kuo-Shu; Ho, Chuang-Yi

2015-01-01

Mesoscale eddies in the subtropical oligotrophic ocean are ubiquitous and play an important role in nutrient supply and oceanic primary production. However, it is still unclear whether these mesoscale eddies can efficiently transfer CO2 from the atmosphere to deep waters via biological pump because of the sampling difficulty due to their transient nature. In 2007, particulate organic carbon (POC) fluxes, measured below the euphotic zone at the edge of warm eddy were 136–194 mg-C m−2 d−1 which was greatly elevated over that (POC flux = 26–35 mg-C m−2 d−1) determined in the nutrient-depleted oligotrophic waters in the Western North Pacific (WNP). In 2010, higher POC fluxes (83–115 mg-C m−2 d−1) were also observed at the boundary of mesoscale eddies in the WNP. The enhanced POC flux at the edge of eddies was mainly attributed to both large denuded diatom frustules and zooplankton fecal pellets based on scanning electron microscopy (SEM) examination. The result suggests that mesoscale eddies in the oligotrophic waters in the subtropical WNP can efficiently increase the oceanic carbon export flux and the eddy edge is a crucial conduit in carbon sequestration to deep waters. PMID:26171611

Subsurface phytoplankton layers in the Arctic Ocean

NASA Astrophysics Data System (ADS)

Tremblay, J. E.

2016-02-01

Recent observations underscored the near-ubiquitous presence of subsurface chlorophyll maxima (SCM) and their potential importance for total primary production (PP) and pelagic food webs in perennially stratified waters of the Arctic Ocean. The contribution of SCM layers to annual PP is particularly important in oligotrophic areas, where modest nutrient supply to the upper euphotic zone results in weak or short-lived phytoplankton blooms near the surface. The large amount of nutrients present in the Pacific halocline relative to comparable depths in the Atlantic sector of the Arctic may also foster particularly productive SCM along the path of Pacific water. The association between strongly stratified conditions and the SCM in today's Arctic Ocean has broad relevance in providing a glimpse into the future of other oceans whose vertical stratification progressively rises with water temperature and freshwater content. In this regard, there is much to learn on the photosynthetic and nutritive ecology of SCM layers, whose biogeochemical significance depends on the extent to which they rely on allochthonous nitrogen (new production), their contribution to carbon biomass and their ability to influence air-sea CO2 exchange. Here we report on several years of eco-physiological investigations of SCM across the Arctic Ocean, with an aim to provide a basis of comparison with the ecology of SCM in other ocean areas.

Diversity of Arctic Pelagic Prokaryotes with an emphasis on photoheterotrophic bacteria: a review

NASA Astrophysics Data System (ADS)

Boeuf, D.; Humily, F.; Jeanthon, C.

2014-02-01

The Arctic Ocean is a unique marine environment with respect to seasonality of light, temperature, perennial ice cover and strong stratification. Other important distinctive features are the influence of extensive continental shelves and its interactions with Atlantic and Pacific water masses and freshwater from sea ice melt and rivers. These characteristics have major influence on the biological and biogeochemical processes occurring in this complex natural system. Heterotrophic bacteria are crucial components of marine food webs and have key roles in controlling carbon fluxes in the oceans. Although it was previously thought that these organisms relied on the organic carbon in seawater for all of their energy needs, several recent discoveries now suggest that pelagic bacteria can depart from a strictly heterotrophic lifestyle by obtaining energy through unconventional mechanisms that are linked to the penetration of sunlight into surface waters. These photoheterotrophic mechanisms may play a significant role in the energy budget in the euphotic zone of marine environments. We can suspect that this role could be of greater importance in the Arctic Ocean where environmental changes triggered by climate change could favor the photoheterotrophic lifestyle. Here we review advances in our knowledge of the diversity of marine photoheterotrophic bacteria and discuss their significance in the Arctic Ocean gained in the framework of the Malina cruise.

Feeding ecology of mesopelagic zooplankton of the subtropical and subarctic North Pacific Ocean determined with fatty acid biomarkers

NASA Astrophysics Data System (ADS)

Wilson, S. E.; Steinberg, D. K.; Chu, F.-L. E.; Bishop, J. K. B.

2010-10-01

Mesopelagic zooplankton may meet their nutritional and metabolic requirements in a number of ways including consumption of sinking particles, carnivory, and vertical migration. How these feeding modes change with depth or location, however, is poorly known. We analyzed fatty acid (FA) profiles to characterize zooplankton diet and large particle (>51 μm) composition in the mesopelagic zone (base of euphotic zone -1000 m) at two contrasting time-series sites in the subarctic (station K2) and subtropical (station ALOHA) Pacific Ocean. Total FA concentration was 15.5 times higher in zooplankton tissue at K2, largely due to FA storage by seasonal vertical migrators such as Neocalanus and Eucalanus. FA biomarkers specific to herbivory implied a higher plant-derived food source at mesotrophic K2 than at oligotrophic ALOHA. Zooplankton FA biomarkers specific to dinoflagellates and diatoms indicated that diatoms, and to a lesser extent, dinoflagellates were important food sources at K2. At ALOHA, dinoflagellate FAs were more prominent. Bacteria-specific FA biomarkers in zooplankton tissue were used as an indicator of particle feeding, and peaks were recorded at depths where known particle feeders were present at ALOHA (e.g., ostracods at 100-300 m). In contrast, depth profiles of bacterial FA were relatively constant with depth at K2. Diatom, dinoflagellate, and bacterial biomarkers were found in similar proportions in both zooplankton and particles with depth at both locations, providing additional evidence that mesopelagic zooplankton consume sinking particles. Carnivory indices were higher and increased significantly with depth at ALOHA, and exhibited distinct peaks at K2, representing an increase in dependence on other zooplankton for food in deep waters. Our results indicate that feeding ecology changes with depth as well as by location. These changes in zooplankton feeding ecology from the surface through the mesopelagic zone, and between contrasting environments, have important consequences for the quality and quantity of organic material available to deeper pelagic and benthic food webs, and for organic matter sequestration.

Particle export fluxes to the oxygen minimum zone of the eastern tropical North Atlantic

NASA Astrophysics Data System (ADS)

Engel, Anja; Wagner, Hannes; Le Moigne, Frédéric A. C.; Wilson, Samuel T.

2017-04-01

In the ocean, sinking of particulate organic matter (POM) drives carbon export from the euphotic zone and supplies nutrition to mesopelagic communities, the feeding and degradation activities of which in turn lead to export flux attenuation. Oxygen (O2) minimum zones (OMZs) with suboxic water layers (< 5 µmol O2 kg-1) show a lower carbon flux attenuation compared to well-oxygenated waters (> 100 µmol O2 kg-1), supposedly due to reduced heterotrophic activity. This study focuses on sinking particle fluxes through hypoxic mesopelagic waters (< 60 µmol O2 kg-1); these represent ˜ 100 times more ocean volume globally compared to suboxic waters, but they have less been studied. Particle export fluxes and attenuation coefficients were determined in the eastern tropical North Atlantic (ETNA) using two surface-tethered drifting sediment trap arrays with seven trapping depths located between 100 and 600 m. Data on particulate matter fluxes were fitted to the normalized power function Fz = F100 (z/100)-b, with F100 being the flux at a depth (z) of 100 m and b being the attenuation coefficient. Higher b values suggest stronger flux attenuation and are influenced by factors such as faster degradation at higher temperatures. In this study, b values of organic carbon fluxes varied between 0.74 and 0.80 and were in the intermediate range of previous reports, but lower than expected from seawater temperatures within the upper 500 m. During this study, highest b values were determined for fluxes of particulate hydrolyzable amino acids (PHAA), followed by particulate organic phosphorus (POP), nitrogen (PN), carbon (POC), chlorophyll a (Chl a) and transparent exopolymer particles (TEP), pointing to a sequential degradation of organic matter components during sinking. Our study suggests that in addition to O2 concentration, organic matter composition co-determines transfer efficiency through the mesopelagic. The magnitude of future carbon export fluxes may therefore also depend on how organic matter quality in the surface ocean changes under influence of warming, acidification and enhanced stratification.

Physical-Biological Coupling in the Western South China Sea: The Response of Phytoplankton Community to a Mesoscale Cyclonic Eddy

PubMed Central

Wang, Lei; Huang, Bangqin; Chiang, Kuo-Ping; Liu, Xin; Chen, Bingzhang; Xie, Yuyuan; Xu, Yanping; Hu, Jianyu; Dai, Minhan

2016-01-01

It is widely recognized that the mesoscale eddies play an important part in the biogeochemical cycle in ocean ecosystem, especially in the oligotrophic tropical zones. So here a heterogeneous cyclonic eddy in its flourishing stage was detected using remote sensing and in situ biogeochemical observation in the western South China Sea (SCS) in early September, 2007. The high-performance liquid chromatography method was used to identify the photosynthetic pigments. And the CHEMical TAXonomy (CHEMTAX) was applied to calculate the contribution of nine phytoplankton groups to the total chlorophyll a (TChl a) biomass. The deep chlorophyll a maximum layer (DCML) was raised to form a dome structure in the eddy center while there was no distinct enhancement for TChl a biomass. The integrated TChl a concentration in the upper 100 m water column was also constant from the eddy center to the surrounding water outside the eddy. However the TChl a biomass in the surface layer (at 5 m) in the eddy center was promoted 2.6-fold compared to the biomass outside the eddy (p < 0.001). Thus, the slight enhancement of TChl a biomass of euphotic zone integration within the eddy was mainly from the phytoplankton in the upper mixed zone rather than the DCML. The phytoplankton community was primarily contributed by diatoms, prasinophytes, and Synechococcus at the DCML within the eddy, while less was contributed by haptophytes_8 and Prochlorococcus. The TChl a biomass for most of the phytoplankton groups increased at the surface layer in the eddy center under the effect of nutrient pumping. The doming isopycnal within the eddy supplied nutrients gently into the upper mixing layer, and there was remarkable enhancement in phytoplankton biomass at the surface layer with 10.5% TChl a biomass of water column in eddy center and 3.7% at reference stations. So the slight increasing in the water column integrated phytoplankton biomass might be attributed to the stimulated phytoplankton biomass at the surface layer. PMID:27088991

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buesseler, K.O.; Trull, T.W.; Steinberg, D.K.

The VERtical Transport In the Global Ocean (VERTIGO) study examined particle sources and fluxes through the ocean's 'twilight zone' (defined here as depths below the euphotic zone to 1000 m). Interdisciplinary process studies were conducted at contrasting sites off Hawaii (ALOHA) and in the NW Pacific (K2) during 3 week occupations in 2004 and 2005, respectively. We examine in this overview paper the contrasting physical, chemical and biological settings and how these conditions impact the source characteristics of the sinking material and the transport efficiency through the twilight zone. A major finding in VERTIGO is the considerably lower transfer efficiencymore » (T{sub eff}) of particulate organic carbon (POC), POC flux 500/150 m, at ALOHA (20%) vs. K2 (50%). This efficiency is higher in the diatom-dominated setting at K2 where silica-rich particles dominate the flux at the end of a diatom bloom, and where zooplankton and their pellets are larger. At K2, the drawdown of macronutrients is used to assess export and suggests that shallow remineralization above our 150 m trap is significant, especially for N relative to Si. We explore here also surface export ratios (POC flux/primary production) and possible reasons why this ratio is higher at K2, especially during the first trap deployment. When we compare the 500 m fluxes to deep moored traps, both sites lose about half of the sinking POC by >4000 m, but this comparison is limited in that fluxes at depth may have both a local and distant component. Certainly, the greatest difference in particle flux attenuation is in the mesopelagic, and we highlight other VERTIGO papers that provide a more detailed examination of the particle sources, flux and processes that attenuate the flux of sinking particles. Ultimately, we contend that at least three types of processes need to be considered: heterotrophic degradation of sinking particles, zooplankton migration and surface feeding, and lateral sources of suspended and sinking materials. We have evidence that all of these processes impacted the net attenuation of particle flux vs. depth measured in VERTIGO and would therefore need to be considered and quantified in order to understand the magnitude and efficiency of the ocean's biological pump.« less

Benthic-Pelagic Coupling in Biogeochemical and Climate Models: Existing Approaches, Recent developments and Roadblocks

NASA Astrophysics Data System (ADS)

Arndt, Sandra

2016-04-01

Marine sediments are key components in the Earth System. They host the largest carbon reservoir on Earth, provide the only long term sink for atmospheric CO2, recycle nutrients and represent the most important climate archive. Biogeochemical processes in marine sediments are thus essential for our understanding of the global biogeochemical cycles and climate. They are first and foremost, donor controlled and, thus, driven by the rain of particulate material from the euphotic zone and influenced by the overlying bottom water. Geochemical species may undergo several recycling loops (e.g. authigenic mineral precipitation/dissolution) before they are either buried or diffuse back to the water column. The tightly coupled and complex pelagic and benthic process interplay thus delays recycling flux, significantly modifies the depositional signal and controls the long-term removal of carbon from the ocean-atmosphere system. Despite the importance of this mutual interaction, coupled regional/global biogeochemical models and (paleo)climate models, which are designed to assess and quantify the transformations and fluxes of carbon and nutrients and evaluate their response to past and future perturbations of the climate system either completely neglect marine sediments or incorporate a highly simplified representation of benthic processes. On the other end of the spectrum, coupled, multi-component state-of-the-art early diagenetic models have been successfully developed and applied over the past decades to reproduce observations and quantify sediment-water exchange fluxes, but cannot easily be coupled to pelagic models. The primary constraint here is the high computation cost of simulating all of the essential redox and equilibrium reactions within marine sediments that control carbon burial and benthic recycling fluxes: a barrier that is easily exacerbated if a variety of benthic environments are to be spatially resolved. This presentation provides an integrative overview of the benthic-pelagic coupling that accounts for the complex process interplay from the euphotic ocean to the deep sediment. It explores the intensity of the benthic-pelagic coupling across different environments and from the seasonal to the geological timescale. Different modelling approaches of coupling sediment and water column dynamics in regional/global biogeochemical models and (paleo)climate models are critically evaluated and their most important limitations, as well as the implications for our ability to predict the response of the global carbon cycle to past or future perturbations is discussed. Finally, the presentation identifies major roadblocks to the development of new model approaches and highlights how new techniques, new observational and laboratory data, as well as a close interdisciplinary collaboration can overcome these roadblocks.

Evaluation of the impact of storm event inputs on levels of gross primary production and respiration in a drinking water reservoir

NASA Astrophysics Data System (ADS)

Samal, N. R.; Pierson, D. C.; Staehr, P. A.; Pradhanang, S. M.; Smith, D. G.

2013-12-01

Episodic inputs of dissolved and particulate material during storm events can have important effects on lake and reservoir ecosystem function and also impact reservoir drinking water quality. We evaluate the impacts of storm events using vertical profiles of temperature, dissolved oxygen, turbidity, conductivity and chlorophyll automatically collected at 6 hour intervals in Ashokan Reservoir, which is a part of the New York City drinking water supply. Storm driven inputs to the reservoir periodically result in large input of suspended sediments that result in reservoir turbidity levels exceeding 25 NTU, and substantial reductions in the euphotic depth. Dissolved materials associated with these same storms would be expected to stimulate bacterial production. This study involves the use of a conceptual model to calculate depth specific estimates of gross primary production (GPP) and ecosystem respiration (R) using three years of data that included 777 events that increased reservoir turbidity levels to over 25 NTU. Using data from before, during and after storm events, we examine how the balance between GPP and R is influenced by storm related increases in turbidity and dissolved organic matter, which would in turn influence light attenuation and bacterial production. Key words: metabolism, primary production, GPP, respiration, euphotic depth, storm event, reservoir

Concurrent estimates of carbon export reveal physical biases in ΔO2/Ar-based net community production estimates in the Southern California Bight

NASA Astrophysics Data System (ADS)

Haskell, William Z.; Fleming, John C.

2018-07-01

Net community production (NCP) represents the amount of biologically-produced organic carbon that is available to be exported out of the surface ocean and is typically estimated using measurements of the O2/Ar ratio in the surface mixed layer under the assumption of negligible vertical transport. However, physical processes can significantly bias NCP estimates based on this in-situ tracer. It is actively debated whether discrepancies between O2/Ar-based NCP and carbon export estimates are due to differences in the location of biological production and export, or the result of physical biases. In this study, we calculate export production across the euphotic depth during two months of upwelling in Southern California in 2014, based on an estimate of the consumption rate of dissolved organic carbon (DOC) and the dissolved: total organic carbon consumption ratio below the euphotic depth. This estimate equals the concurrent O2/Ar-based NCP estimates over the same period that are corrected for physical biases, but is significantly different than NCP estimated without a correction for vertical transport. This comparison demonstrates that concurrent physical transport estimates would significantly improve O2/Ar-based estimates of NCP, particularly in settings with vertical advection. Potential approaches to mitigate this bias are discussed.

Effects of Variable Oxygen Concentrations on the Sinking Fluxes and Composition of Organic Matter in The Baltic Sea

NASA Astrophysics Data System (ADS)

Cisternas-Novoa, C.; Le Moigne, F. A. C.; Roa, J.; Wagner, H.; Engel, A.

2016-02-01

The downward flux of organic matter (OM) from the euphotic zone is critical to understand the biogeochemistry cycles in the ocean. Local changes in stratification, nutrient inputs, community structure and oxygen concentrations potentially affect the magnitude of OM flux. The Baltic Sea is a unique environment with strong natural gradients of primary productivity, nutrients and O2 concentrations. The genuine effect of oxygen minimum deficiency on the fate of sinking OM and the efficiency of the biologic carbon pump has yet to be clarified. Previous work suggested that under oxygen deficiency, nitrogen rich amino acids are preferentially utilized causing nitrogen loss from the water column (van Mooy et al., 2002, Kalvelage et al 2013). Here, we investigate how different oxygen conditions and surface productivity affect sinking particles flux and particles composition in the central Baltic Sea. Sinking OM was collected in June 2015 using surface-tethered free-drifting traps in the Gotland and Landsort deeps. Sinking particles were collected for a period of 48 and 24 hours at four depths from below the mixed layer and down to hypoxic deep waters (40, 60, 110 and 180 m). Fluxes of POC, PON, POP and amino acids were estimated. We will discuss the effect of low oxygen levels on the biological carbon pump associated with fluxes of OM and sinking particles.

AUV based study on physical and ecological processes at fronts

NASA Astrophysics Data System (ADS)

Tippenhauer, Sandra; Wulff, Thorben; Von Appen, Wilken-Jon

2017-04-01

Small-scale processes and their effects get more and more attention when it comes to understanding processes and changes in the (Arctic) ocean. Here we present a study on physical processes and ecological responses at submesoscale frontal systems in the Fram Strait investigated using an autonomous underwater vehicle (AUV). The AUV is equipped with physical and biogeochemical sensors such as an acoustic Doppler current profiler, a turbulence probe, a conductivity-temperature-depth probe, and sensors for Oxygen, Nitrate, Chlorophyll a, and photosynthetically active radiation (PAR). The study is designed such that the AUV covers tracks of several kilometers length in cross-frontal direction with the front roughly located in the middle of the track. On its way, the AUV records high-resolution vertical or zigzag profiles of the physical and biogeochemical properties in the upper 50 m which includes the euphotic zone. In both, physical and biogeochemical terms, the measurements revealed a complex structure of the water column. At the fronts the distribution of phytoplankton and nutrients was highly inhomogeneous, possibly due to wind-driven frontogenesis or the growth of mixed layer eddies. To set the observations into a larger context we also examine ship-based and satellite data. We investigate how the observed patterns of the potential vorticity and the biogeochemical properties may be formed and which processes could lead to a smoothing of the observed gradients.

Challenges in integrative approaches to modelling the marine ecosystems of the North Atlantic: Physics to fish and coasts to ocean

NASA Astrophysics Data System (ADS)

Holt, Jason; Icarus Allen, J.; Anderson, Thomas R.; Brewin, Robert; Butenschön, Momme; Harle, James; Huse, Geir; Lehodey, Patrick; Lindemann, Christian; Memery, Laurent; Salihoglu, Baris; Senina, Inna; Yool, Andrew

2014-12-01

It has long been recognised that there are strong interactions and feedbacks between climate, upper ocean biogeochemistry and marine food webs, and also that food web structure and phytoplankton community distribution are important determinants of variability in carbon production and export from the euphotic zone. Numerical models provide a vital tool to explore these interactions, given their capability to investigate multiple connected components of the system and the sensitivity to multiple drivers, including potential future conditions. A major driver for ecosystem model development is the demand for quantitative tools to support ecosystem-based management initiatives. The purpose of this paper is to review approaches to the modelling of marine ecosystems with a focus on the North Atlantic Ocean and its adjacent shelf seas, and to highlight the challenges they face and suggest ways forward. We consider the state of the art in simulating oceans and shelf sea physics, planktonic and higher trophic level ecosystems, and look towards building an integrative approach with these existing tools. We note how the different approaches have evolved historically and that many of the previous obstacles to harmonisation may no longer be present. We illustrate this with examples from the on-going and planned modelling effort in the Integrative Modelling Work Package of the EURO-BASIN programme.

Particle-associated extracellular enzyme activity and bacterial community composition across the Canadian Arctic Ocean.

PubMed

Kellogg, Colleen T E; Deming, Jody W

2014-08-01

Microbial enzymatic hydrolysis of marine-derived particulate organic carbon (POC) can be a dominant mechanism for attenuating carbon flux in cold Arctic waters during spring and summer. Whether this mechanism depends on composition of associated microbial communities and extends into other seasons is not known. Bacterial community composition (BCC) and extracellular enzyme activity (EEA, for leucine aminopeptidases, glucosidases and chitobiases) were measured on small suspended particles and potentially sinking aggregates collected during fall from waters of the biologically productive North Water and river-impacted Beaufort Sea. Although other environmental variables appeared influential, both BCC and EEA varied along a marine productivity gradient in the two regions. Aggregates harbored the most distinctive bacterial communities, with a small number of taxa driving differences between particle-size classes (1.0-60 and > 60 μm) and free-living bacteria (0.2-1.0 μm). Significant relationships between patterns in particle-associated BCC and EEA suggest strong links between these two variables. Calculations indicated that up to 80% of POC in the euphotic zone of the North Water, and 20% in the Beaufort Sea, may be hydrolyzed enzymatically, underscoring the importance of this mechanism in attenuating carbon fluxes in Arctic waters even as winter approaches. © 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

Carbon fluxes in the Arabian Sea: Export versus recycling

NASA Astrophysics Data System (ADS)

Rixen, Tim; Gaye, Birgit; Ramaswamy, Venkitasubramani

2016-04-01

The organic carbon pump strongly influences the exchange of carbon between the ocean and the atmosphere. It is known that it responds to global change but the magnitude and the direction of change are still unpredictable. Sediment trap experiments carried out at various sites in the Arabian Sea between 1986 and 1998 have shown differences in the functioning of the organic carbon pump (OCP). An OCP driven by eukaryotic phytoplankton operated in the upwelling region off Oman and during the spring bloom in the northern Arabian Sea. Cyanobacteria capable of fixing nitrogen seem to dominate the phytoplankton community during all other seasons. The export driven by cyanobacteria was much lower than the export driven by eukaryotic phytoplankton. Productivity and nutrient availability seems to be a main factor controlling fluxes during blooms of eukaryotic phytoplankton. The ballast effect caused by inputs of dust into the ocean and its incorporation into sinking particles seems to be the main factor controlling the export during times when cyanobacteria dominate the phytoplankton community. C/N ratios of organic matter exported from blooms dominated by nitrogen fixing cyanobacteria are enhanced and, furthermore, indicate a more efficient recycling of nutrients at shallower water depth. This implies that the bacterial-driven OCP operates more in a recycling mode that keeps nutrients closer to the euphotic zone whereas the OCP driven by eukaryotic phytoplankton reduces the recycling of nutrients by exporting them into greater water-depth.

Modulation and daily banding of Mg/Ca in Orbulina universa tests by symbiont photosynthesis and respiration: a complication for seawater thermometry?

NASA Astrophysics Data System (ADS)

Eggins, Stephen M.; Sadekov, Aleksey; De Deckker, Patrick

2004-09-01

The Mg/Ca composition of calcium carbonate tests (shells) secreted by planktonic foraminifera is increasingly being employed to estimate past seawater temperatures and reconstruct paleocean and climate records spanning hundreds of thousands of years. We show, using two high-resolution microanalysis techniques, that the final chamber of the planktonic foraminifera Orbulina universa typically comprises between three and six paired, low and high Mg, growth bands. The number and spacing of these bands is consistent with a diurnal origin, modulated by changing pH within the foraminiferal microenvironment due to the day-night, photosynthesis-respiration cycle of algal symbionts. The amplitude of Mg/Ca variation within individual tests and across many daily growth bands cannot be accounted for by seawater temperature in the shallow, euphotic zone habitat of O. universa. Our results indicate the Mg/Ca composition of calcite precipitated by O. universa in nature is strongly influenced by diurnal changes in the biological activity of algal symbionts and the host foraminifer. This brings into question the fundamental premise often made in applying Mg/Ca palaeoseawater thermometry, that the Mg/Ca composition of foraminiferal calcite is determined by seawater temperature, and whether the Mg/Ca composition of other planktonic species that are more widely used for palaeoseawater thermometry are subject to similar influences.

Giant larvaceans: biologically equivalent flapping flexible foils exhibit bending modes that enhance fluid transport

NASA Astrophysics Data System (ADS)

Katija, Kakani; Sherman, Alana; Robison, Bruce

2016-11-01

The midwater region of the ocean (below the euphotic zone and above the benthos) is one of the largest ecosystems on our planet, yet remains one of the least explored. Little-known marine organisms that inhabit midwater have developed life strategies that contribute to their evolutionary success, and may inspire engineering solutions for societally relevant challenges. A group of midwater organisms, known as giant larvaceans (genus Bathochordaeus), beat their tails to drive food and particle-laden water through complex, mucus filtering structures to feed. Giant larvaceans, whose motion and kinematics resemble flapping flexible foils, range in size from 1 to 10 cm in length, and can be found between the surface and 400 m. Using remotely-operated vehicles and DeepPIV, an instrument that enables in situ particle image velocimetry (PIV) measurements, the filtration rates and kinematics of giant larvaceans were investigated. These measurements yielded filtration rates for giant larvaceans as high as 80 L/hr, which exceeds expected filtration rates by a factor of 2 when compared with other larvacean groups. Comparing tail kinematics between Bathochordeaus and smaller larvaceans reveals differences in tail bending modes, where a hinge is present throughout the tail beat in giant larvaceans. Using laboratory PIV measurements with swimming animals and soft-bodied mechanical mimics, we reveal how these differences in tail kinematics can lead to enhanced fluid transport. This work has been supported by the Packard Foundation.

Physical Mechanisms Routing Nutrients in the Central Red Sea

NASA Astrophysics Data System (ADS)

Zarokanellos, Nikolaos D.; Kürten, Benjamin; Churchill, James H.; Roder, Cornelia; Voolstra, Christian R.; Abualnaja, Yasser; Jones, Burton H.

2017-11-01

Mesoscale eddies and boundary currents play a key role in the upper layer circulation of the Red Sea. This study assesses the physical and biochemical characteristics of an eastern boundary current (EBC) and recurrent eddies in the central Red Sea (CRS) using a combination of in situ and satellite observations. Hydrographic surveys in November 2013 (autumn) and in April 2014 (spring) in the CRS (22.15°N-24.1°N) included a total of 39 and 27 CTD stations, respectively. In addition, high-resolution hydrographic data were acquired in spring 2014 with a towed undulating vehicle (ScanFish). In situ measurements of salinity, temperature, chlorophyll fluorescence, colored dissolved organic matter (CDOM), and dissolved nitrate: phosphorous ratios reveal distinct water mass characteristics for the two periods. An EBC, observed in the upper 150 m of the water column during autumn, transported low-salinity and warm water from the south toward the CRS. Patches of the low-salinity water of southern origin tended to contain relatively high concentrations of chlorophyll and CDOM. The prominent dynamic feature observed in spring was a cyclonic/anticyclonic eddy pair. The cyclonic eddy was responsible for an upward nutrient flux into the euphotic zone. Higher chlorophyll and CDOM concentrations, and concomitant lower nitrate:phosphorous ratios indicate the influence of the EBC in the CRS at the end of the stratified summer period.

Enhancement of Non-photochemical Quenching as an Adaptive Strategy under Phosphorus Deprivation in the Dinoflagellate Karlodinium veneficum

PubMed Central

Cui, Yudong; Zhang, Huan; Lin, Senjie

2017-01-01

Intensified water column stratification due to global warming has the potential to decrease nutrient availability while increasing excess light for the photosynthesis of phytoplankton in the euphotic zone, which together will increase the need for photoprotective strategies such as non-photochemical quenching (NPQ). We investigated whether NPQ is enhanced and how it is regulated molecularly under phosphorus (P) deprivation in the dinoflagellate Karlodinium veneficum. We grew K. veneficum under P-replete and P-depleted conditions, monitored their growth rates and chlorophyll fluorescence, and conducted gene expression and comparative proteomic analyses. The results were used to characterize NPQ modulation and associated gene expression dynamics under P deprivation. We found that NPQ in K. veneficum was elevated significantly under P deprivation. Accordingly, the abundances of three light-harvesting complex stress-related proteins increased under P-depleted condition. Besides, many proteins related to genetic information flow were down-regulated while many proteins related to energy production and conversion were up-regulated under P deprivation. Taken together, our results indicate that K. veneficum cells respond to P deprivation by reconfiguring the metabolic landscape and up-tuning NPQ to increase the capacity to dissipate excess light energy and maintain the fluency of energy flow, which provides a new perspective about what adaptive strategy dinoflagellates have evolved to cope with P deprivation. PMID:28360892

Transport Functions Dominate the SAR11 Metaproteome at Low-Nutrient Extremes in the Sargasso Sea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sowell, Sarah M.; Wilhelm, Larry; Norbeck, Angela D.

2009-01-01

The northwestern Sargasso Sea is part of the North Atlantic subtropical oceanic gyre that is characterized as seasonally oligotrophic with pronounced stratification in the summer and autumn. Essentially a marine desert, the biological productivity of this region is reduced during stratified periods as a result of low concentrations of phosphorous and nitrogen in the euphotic zone. To better understand the mechanisms of microbial survival in this oligotrophic environment, we used capillary LC-tandem mass spectrometry to study the composition of microbial proteomes in surface samples collected in September 2005. A total of 2279 peptides that mapped to 236 SAR11 proteins, andmore » 3208 peptides that mapped to 404 Synechococcus proteins, were detected. Mass spectra from SAR11 periplasmic binding proteins accounted for a disproportionately large fraction of the peptides detected, consistent with observations that these extremely small cells devote a large proportion of their volume to periplasm. Abundances were highest for periplasmic substrate-binding proteins for phosphate, amino acids, phosphonate, sugars, and spermidine. Although the data showed that a large fraction of microbial protein synthesis in the Sargasso Sea is devoted to inorganic and organic nutrient acquisition, the proteomes of both SAR11 and Synechococcus also indicated that these populations were actively growing. Our findings support the view that competition for multiple nutrients in oligotrophic systems is extreme but sufficient to sustain microbial community activity.« less

Changes in Microbial Plankton Assemblages Induced by Mesoscale Oceanographic Features in the Northern Gulf of Mexico

PubMed Central

Williams, Alicia K.; McInnes, Allison S.; Rooker, Jay R.; Quigg, Antonietta

2015-01-01

Mesoscale circulation generated by the Loop Current in the Northern Gulf of Mexico (NGOM) delivers growth-limiting nutrients to the microbial plankton of the euphotic zone. Consequences of physicochemically driven community shifts on higher order consumers and subsequent impacts on the biological carbon pump remain poorly understood. This study evaluates microbial plankton <10 μm abundance and community structure across both cyclonic and anti-cyclonic circulation features in the NGOM using flow cytometry (SYBR Green I and autofluorescence parameters). Non-parametric multivariate hierarchical cluster analyses indicated that significant spatial variability in community structure exists such that stations that clustered together were defined as having a specific ‘microbial signature’ (i.e. statistically homogeneous community structure profiles based on relative abundance of microbial groups). Salinity and a combination of sea surface height anomaly and sea surface temperature were determined by distance based linear modeling to be abiotic predictor variables significantly correlated to changes in microbial signatures. Correlations between increased microbial abundance and availability of nitrogen suggest nitrogen-limitation of microbial plankton in this open ocean area. Regions of combined coastal water entrainment and mesoscale convergence corresponded to increased heterotrophic prokaryote abundance relative to autotrophic plankton. The results provide an initial assessment of how mesoscale circulation potentially influences microbial plankton abundance and community structure in the NGOM. PMID:26375709

Raman-activated cell sorting and metagenomic sequencing revealing carbon-fixing bacteria in the ocean.

PubMed

Jing, Xiaoyan; Gou, Honglei; Gong, Yanhai; Su, Xiaolu; Xu, La; Ji, Yuetong; Song, Yizhi; Thompson, Ian P; Xu, Jian; Huang, Wei E

2018-05-04

It is of great significance to understand CO 2 fixation in the oceans. Using single cell Raman spectra (SCRS) as biochemical profiles, Raman activated cell ejection (RACE) was able to link phenotypes and genotypes of cells. Here we show that mini-metagenomic sequences from RACE can be used as a reference to reconstruct nearly complete genomes of key functional bacteria by binning shotgun metagenomic sequencing data. By applying this approach to 13 C-bicarbonate spiked seawater from euphotic zone of the Yellow Sea of China, the dominant bacteria Synechococcus spp. and Pelagibacter spp. were revealed, and both of them contain carotenoid and were able to incorporate 13 C into the cells at the same time. Genetic analysis of the reconstructed genomes suggests that both Synechococcus spp. and Pelagibacter spp. contained all genes necessary for carotenoid synthesis, light energy harvesting and CO 2 fixation. Interestingly, the reconstructed genome indicates that Pelagibacter spp. harbored intact sets of genes for β-carotene (precursor of retional), proteorhodopsin synthesis and anaplerotic CO 2 fixation. This novel approach shines light on the role of marine "microbial dark matter" in global carbon cycling, by linking yet-to-be-cultured Synechococcus spp. and Pelagibacter spp. to carbon fixation and flow activities in situ. This article is protected by copyright. All rights reserved. © 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.

An annual cycle of phytoplankton biomass in the Arabian Sea, 1994 1995, as determined by moored optical sensors

NASA Astrophysics Data System (ADS)

Kinkade, C. S.; Marra, J.; Dickey, T. D.; Weller, R.

A surface-to-bottom mooring in the central Arabian Sea (15.5°N, 61.5°E) deployed from October 1994 to October 1995, included fluorometers, PAR irradiance sensors, Lu 683 sensors, and a spectral radiometer. An annual cycle of phytoplankton biomass was determined by transforming signals from the optical sensors into chlorophyll a (chl a). Half-yearly phytoplankton blooms with water-column stratification were observed near the end of each monsoon, as well as biomass increases in response to mesoscale flow features. During the Northeast Monsoon, the integrate water-column chl a rose from 15 to 25 mg m -2, while during the Southwest Monsoon, chl a increased from 15 to a maximum >40 mg m -2. We present an empirical relationship between the ratio of downwelling Ed443/ Ed550 (blue to green wavelength ratio) and integral euphotic zone chl a determined by moored fluorometers ( r2=0.73). There is a more significant relationship between Ed443/ Ed550 measured at one depth in the water column (65 m) and the average vertical attenuation coefficient for PAR (K PAR) between 0 and 65 m ( r2=0.845). Because biofouling was a significant problem at times, data return from any one sensor was incomplete. However, optical sensor/data intercomparison helped fill gaps while permitting investigation of the temporal variability in observed phytoplankton biomass.

High incorporation of carbon into proteins by the phytoplankton of the Bering Strait and Chukchi Sea

NASA Astrophysics Data System (ADS)

Lee, Sang H.; Kim, Hak-Jun; Whitledge, Terry E.

2009-07-01

High incorporation of carbon into proteins and low incorporation into lipids were a characteristic pattern of the photosynthetic allocations of phytoplankton throughout the euphotic zone in the Bering Strait and Chukchi Sea in 2004. According to earlier studies, this indicates that phytoplankton had no nitrogen limitation and a physiologically healthy condition, at least during the cruise period from mid-August to early September in 2004. This is an interesting result, especially for the phytoplankton in the Alaskan coastal water mass-dominated region in the Chukchi Sea which has been thought to be potentially nitrogen limited. The relatively high ammonium concentration is believed to have supported the nitrogen demand of the phytoplankton in the region where small cells (<5 μm) composed of about 50% of the community, since they prefer to use regenerated nitrogen such as ammonium. In fact, a small cell-size community of phytoplankton incorporated much more carbon into proteins in nitrate-depleted water suggesting that small phytoplankton had less nitrogen stress than large phytoplankton. If the high carbon incorporation into proteins by the phytoplankton in 2004 is a general pattern of the photosynthetic allocations in the Chukchi Sea, they could provide nitrogen-sufficient food for the highest benthic faunal biomass in the Arctic Ocean, sustaining large populations of benthic-feeding marine mammals and seabirds.

Dissipation processes in the Tongue of the Ocean

NASA Astrophysics Data System (ADS)

Hooper V, James A.; Baringer, Molly O.; St. Laurent, Louis C.; Dewar, William K.; Nowacek, Doug

2016-05-01

The Tongue of the Ocean (TOTO) region located within the Bahamas archipelago is a relatively understudied region in terms of both its biological and physical oceanographic characteristics. A prey-field mapping cruise took place in the fall between 15 September 2008 and 1 October 2008, consisting of a series of transects and "clovers" to study the spatial and temporal variability. The region is characterized by a deep scattering layer (DSL), which is preyed on by nekton that serves as the food for beaked whale and other whale species. This study marks the first of its kind where concurrent measurements of acoustic backscatter and turbulence have been conducted for a nekton scattering layer well below the euphotic zone. Turbulence data collected from a Deep Microstructure Profiler are compared to biological and shear data collected by a 38 kHz Simrad EK 60 echo sounder and a hydrographic Doppler sonar system, respectively. From these measurements, the primary processes responsible for the turbulent production in the TOTO region are assessed. The DSL around 500 m and a surface scattering layer (SSL) are investigated for raised ɛ values. Strong correlation between turbulence levels and scattering intensity of prey is generally found in the SSL with dissipation levels as large as ˜10-7 W kg-1, 3 orders of magnitude above background levels. In the DSL and during the diel vertical migration, dissipation levels ˜10-8 W kg-1 were observed.

Viral and grazer regulation of prokaryotic growth efficiency in temperate freshwater pelagic environments.

PubMed

Pradeep Ram, A S; Colombet, Jonathan; Perriere, Fanny; Thouvenot, Antoine; Sime-Ngando, Telesphore

2015-02-01

In aquatic systems, limited data exists on the impact of mortality forces such as viral lysis and flagellate grazing when seeking to explain factors regulating prokaryotic metabolism. We explored the relative influence of top-down factors (viral lysis and heterotrophic nanoflagellate grazing) on prokaryotic mortality and their subsequent impact on their community metabolism in the euphotic zone of 21 temperate freshwater lakes located in the French Massif Central. Prokaryotic growth efficiency (PGE, index of prokaryotic community metabolism) determined from prokaryotic production and respiration measurements varied from 5 to 74% across the lakes. Viral and potential grazer-induced mortality of prokaryotes had contrasting impact on PGE. Potential flagellate grazing was found to enhance PGE whereas viral lysis had antagonistic impacts on PGE. The average PGE value in the grazing and viral lysis dominated lake water samples was 35.4% (±15.2%) and 17.2% (±8.1%), respectively. Selective viral lysis or flagellate grazing on prokaryotes together with the nature of contrasted substrates released through mortality processes can perhaps explain for the observed variation and differences in PGE among the studied lakes. The influences of such specific top-down processes on PGE can have strong implications on the carbon and nutrient fluxes in freshwater pelagic environments. © FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Deep in shadows, deep in time: the oldest mesophotic coral ecosystems from the Devonian of the Holy Cross Mountains (Poland)

NASA Astrophysics Data System (ADS)

Zapalski, Mikołaj K.; Wrzołek, Tomasz; Skompski, Stanisław; Berkowski, Błażej

2017-09-01

Recent mesophotic coral ecosystems (MCE) occur at depths between 30 and 150 m and are characterized by dominance of platy corals. Such morphology is an effect of specific adaptation to efficient light harvesting. Here, we describe and analyze platy coral assemblages from two Middle Devonian localities in the Holy Cross Mountains (Poland) that during this time were located on the southern shelf of Laurussia at tropical latitudes. The Eifelian argillaceous sediments of Skały are dominated by platy and encrusting tabulate corals ( Roseoporella, Platyaxum and Alveolites). Coeval faunas from the shallow-water parts of the Holy Cross Mountains basin display bulbous and branching morphology, thus indicating a Paleozoic coral zonation similar to that known in the Recent. Hence, the Skały site seems to be the oldest known MCE (ca. 390 Ma). A Givetian biostrome from Laskowa Quarry is a second example dominated by platy corals, with abundant branching forms; this site can be recognized as another Devonian MCE. Frondescent Platyaxum, common at both sites, had a growth habit similar to that of Recent Leptoseris, Mycedium or Pavona. Platy morphology is photoadaptive and may evidence photosymbiosis in tabulate ( Alveolites, Roseoporella, Platyaxum) and rugose corals ( Phillipsastrea). Furthermore, it may serve as a tool for recognition of the lower euphotic zone in the fossil record.

Carbonate-sensitive phytotransferrin controls high-affinity iron uptake in diatoms

NASA Astrophysics Data System (ADS)

McQuaid, Jeffrey B.; Kustka, Adam B.; Oborník, Miroslav; Horák, Aleš; McCrow, John P.; Karas, Bogumil J.; Zheng, Hong; Kindeberg, Theodor; Andersson, Andreas J.; Barbeau, Katherine A.; Allen, Andrew E.

2018-03-01

In vast areas of the ocean, the scarcity of iron controls the growth and productivity of phytoplankton. Although most dissolved iron in the marine environment is complexed with organic molecules, picomolar amounts of labile inorganic iron species (labile iron) are maintained within the euphotic zone and serve as an important source of iron for eukaryotic phytoplankton and particularly for diatoms. Genome-enabled studies of labile iron utilization by diatoms have previously revealed novel iron-responsive transcripts, including the ferric iron-concentrating protein ISIP2A, but the mechanism behind the acquisition of picomolar labile iron remains unknown. Here we show that ISIP2A is a phytotransferrin that independently and convergently evolved carbonate ion-coordinated ferric iron binding. Deletion of ISIP2A disrupts high-affinity iron uptake in the diatom Phaeodactylum tricornutum, and uptake is restored by complementation with human transferrin. ISIP2A is internalized by endocytosis, and manipulation of the seawater carbonic acid system reveals a second-order dependence on the concentrations of labile iron and carbonate ions. In P. tricornutum, the synergistic interaction of labile iron and carbonate ions occurs at environmentally relevant concentrations, revealing that carbonate availability co-limits iron uptake. Phytotransferrin sequences have a broad taxonomic distribution and are abundant in marine environmental genomic datasets, suggesting that acidification-driven declines in the concentration of seawater carbonate ions will have a negative effect on this globally important eukaryotic iron acquisition mechanism.

Factors Affecting Mercury Stable Isotopic Distribution in Piscivorous Fish of the Laurentian Great Lakes.

PubMed

Lepak, Ryan F; Janssen, Sarah E; Yin, Runsheng; Krabbenhoft, David P; Ogorek, Jacob M; DeWild, John F; Tate, Michael T; Holsen, Thomas M; Hurley, James P

2018-03-06

Identifying the sources of methylmercury (MeHg) and tracing the transformations of mercury (Hg) in the aquatic food web are important components of effective strategies for managing current and legacy Hg sources. In our previous work, we measured stable isotopes of Hg (δ 202 Hg, Δ 199 Hg, and Δ 200 Hg) in the Laurentian Great Lakes and estimated source contributions of Hg to bottom sediment. Here, we identify isotopically distinct Hg signatures for Great Lakes trout ( Salvelinus namaycush) and walleye ( Sander vitreus), driven by both food-web and water-quality characteristics. Fish contain high values for odd-isotope mass independent fractionation (MIF) with averages ranging from 2.50 (western Lake Erie) to 6.18‰ (Lake Superior) in Δ 199 Hg. The large range in odd-MIF reflects variability in the depth of the euphotic zone, where Hg is most likely incorporated into the food web. Even-isotope MIF (Δ 200 Hg), a potential tracer for Hg from precipitation, appears both disconnected from lake sedimentary sources and comparable in fish among the five lakes. We suggest that similar to the open ocean, water-column methylation also occurs in the Great Lakes, possibly transforming recently deposited atmospheric Hg deposition. We conclude that the degree of photochemical processing of Hg is controlled by phytoplankton uptake rather than by dissolved organic carbon quantity among lakes.

Satellite captures trichodesmium blooms in the southwestern tropical Pacific

NASA Astrophysics Data System (ADS)

Dupouy, Cécile; Neveux, Jacques; Subramaniam, Ajit; Mulholland, Margaret R.; Montoya, Joseph P.; Campbell, Lisa; Carpenter, Edward J.; Capone, Douglas G.

Obtaining a true estimate of nitrogen fixation by cyanobacteria in the oceans, mainly Trichodesmium, is an important step toward understanding the entire nitrogen cycle in the tropical ocean. This strictly anaerobic process, which has a high Fe requirement, could regulate atmospheric CO2 over geological time. For example, during interglacial periods, N2 fixation would be too low (low Fe) to balance denitrification and the ocean would lose its fixed nitrogen [Falkowski, 1997]. Has the level of marine nitrogen fixation been underestimated until now? High N2 fixation rates measured on Trichodesmium spp. communities have led to an upward revision of this marine flux [Capone et al, 1997]. Recent modeling studies and observations predict that N2 fixation could regulate the long-term N:P equilibrium in the oceans and balance denitrification [Tyrell, 1999; J L. Sarmiento and N. Gruber, manuscript in preparation, 1999].The major nitrogen fixer, Trichodesmium spp., which are filamentous, nonheterocystous N2-fixing cyanobacteria, has a nearly ubiquitous distribution in the euphotic zone of tropical and subtropical seas and could play a major role in bringing new N to these oligotrophic systems. Satellite images from Sea-viewing Wide Field-of-view Sensor (SeaWiFs), the recently launched ocean color sensor, and data from a recent cruise, provide further evidence of the importance of Trichodesmium in the southwestern tropical Pacific Ocean.

Deriving depths of deep chlorophyll maximum and water inherent optical properties: A regional model

NASA Astrophysics Data System (ADS)

Xiu, Peng; Liu, Yuguang; Li, Gang; Xu, Qing; Zong, Haibo; Rong, Zengrui; Yin, Xiaobin; Chai, Fei

2009-10-01

The Bohai Sea is a semi-enclosed inland sea with case-2 waters near the coast. A comprehensive set of optical data was collected during three cruises in June, August, and September 2005 in the Bohai Sea. The vertical profile measurements, such as chlorophyll concentration, water turbidity, downwelling irradiance, and diffuse attenuation coefficient, showed that the Bohai Sea was vertically stratified with a relative clear upper layer superimposed on a turbid lower layer. The upper layer was found to correspond to the euphotic zone and the deep chlorophyll maximum (DCM) occurs at the base of this layer. By tuning a semi-analytical model (Lee et al., 1998, 1999) for the Bohai Sea, we developed a method to derive water inherent optical properties and the depth of DCM from above-surface measurements. Assuming a 'fake' bottom in the stratified water, this new method retrieves the 'fake' bottom depth, which is highly correlated with the DCM depth. The average relative error between derived and measured values is 33.9% for phytoplankton absorption at 440 nm, 25.6% for colored detrital matter (detritus plus gelbstoff) absorption at 440 nm, and 24.2% for the DCM depth. This modified method can retrieve water inherent optical properties and monitor the depth of DCM in the Bohai Sea, and the method is also applicable to other stratified waters.

Implications for an Enhanced Biological Pump in the Sea-Ice Reduction Region of the Western Arctic Ocean

NASA Astrophysics Data System (ADS)

Nishino, S.; Shimada, K.; Itoh, M.; Yamamoto-Kawai, M.; Chiba, S.

2009-12-01

Since the late 1990s, catastrophic sea-ice reduction during summer has been observed in the western Arctic Ocean. Regions of decreasing sea ice might be associated with increased biological production compared to ice-covered ocean areas due to light intensification in the water column. The R/V Mirai field experiments in summer 2004 revealed that the algal biomass (chlorophyll a) in the open water region of the western Canada Basin increased from that observed in summer 1994, when the sea ice covered that area. Under the euphotic zone of the increased algal biomass area, evidence of diatom detritus decomposition was found, while such evidence was not observed in 1994, suggesting an enhancement of biological pump (see figure). The increase of algal biomass was not found throughout the sea-ice reduction region; rather, it was observed western Canada Basin where nutrients are effectively supplied from shelf regions. Further west from the Canada Basin, Russian river water with relatively high nutrients may play an important role in the biogeochemical cycles. Monthly sea-ice concentrations (white = 100%, black = 0%) in September of (a) 1994 and (b) 2004 (National Ice Center), and (c) vertical profiles of silicate obtained from the field experiments of Arctic Ocean Section 94 in 1994 (○) and Mirai04 in 2004 (■). The positions where the profiles were obtained are depicted by dots in (a) and (b), respectively.

Photosynthetic pigments as biomarkers oof phytoplankton populations and processes involved in the transformation of particulate organic matter at the Biotrans site (47°N, 20°W)

NASA Astrophysics Data System (ADS)

Williams, R.; Claustre, H.

1991-03-01

Particulate samples were collected throughout the water column (0-4200 m)in June/July 1988 at the Biotrans site and their carotenoids and chlorophylls analysed by HPLC. These photosynthetic pigments were used as biomarkers to characterize the autotropiic pupolations, their utilization by heterotrophs snd sedimentation of particles out the euphotic zone. In the upper 50 m the pico- and nanophytoplankton accounted for 85% of the chlorophyll a biomass. The major pigment of the nanophytoplankton fraction was 19'-hexanolloxyfucoxanthin (prymnesiophytes), whereas the main pigment in the microphytoplankton was peridinin (dinoflagellates). The peaks in the distributions of phaeophorbide a and nanophytoplankton pigments (19'- hexanoyloxyfucoxanthin, 19'-butanoyloxyfucoxanthin, chlorophyll b,lutein and/or zeaxanthin) coincided between 75 and 100 m, which pointed to an active grazing of nanophytoplankton by zooplankton. These pigments were detected in particles >20 μm from the Double Longhurst Hardy Plankton Recorder down to 1000 m, probably as a consequence of their incorporation into sedimenting faecal material. In contrast, the vertical distributions of phaeophorbide a and peridinin (microphytoplankton pigment) did not coincide, and this carotenoid was not detected below 400 m in particles > 20μm. A vertical profile (0-4200 m) shows,at 2300 m, the presence of nanophytoplanktonic material similar in its pigment pattern and compositionto that of surface populations, suggesting fast sedimentation of Prymnesiophyte floc.

Changes in zooplankton habitat, behavior, and acoustic scattering characteristics across glider-resolved fronts in the Southern California Current System

NASA Astrophysics Data System (ADS)

Powell, Jesse R.; Ohman, Mark D.

2015-05-01

We report cross-frontal changes in the characteristics of plankton proxy variables measured by autonomous Spray ocean gliders operating within the Southern California Current System (SCCS). A comparison of conditions across the 154 positive frontal gradients (i.e., where density of the surface layer decreased in the offshore direction) identified from six years of continuous measurements showed that waters on the denser side of the fronts typically showed higher Chl-a fluorescence, shallower euphotic zones, and higher acoustic backscatter than waters on the less dense side. Transitions between these regions were relatively abrupt. For positive fronts the amplitude of Diel Vertical Migration (DVM), inferred from a 3-beam 750 kHz acoustic Doppler profiler, increased offshore of fronts and covaried with optical transparency of the water column. Average interbeam variability in acoustic backscatter also changed across many positive fronts within 3 depth strata (0-150 m, 150-400 m, and 400-500 m), revealing a front-related change in the acoustic scattering characteristics of the assemblages. The extent of vertical stratification of distinct scattering assemblages was also more pronounced offshore of positive fronts. Depth-stratified zooplankton samples collected by Mocness nets corroborated the autonomous measurements, showing copepod-dominated assemblages and decreased zooplankton body sizes offshore and euphausiid-dominated assemblages with larger median body sizes inshore of major frontal features.

Anomalous δ13C in POC at the chemoautotrophy maximum in the Cariaco Basin

NASA Astrophysics Data System (ADS)

Scranton, M. I.; Taylor, G. T.; Thunell, R.; Tappa, E.; benitez-Nelson, C. R.; Muller-Karger, F. E.; Lorenzoni, L.; Astor, Y. M.

2016-02-01

The Cariaco Basin is the world's largest truly marine, permanently anoxic basin and is located on the continental shelf of Venezuela which experiences strong seasonal upwelling. The CARIACO program has been studying the hydrography, biogeochemistry and properties of sinking flux of the Cariaco Basin since 1995. One of the major puzzles of CARIACO has been the nature of the chemoautotrophic maximum which is seen at depths just below the appearance of hydrogen sulfide ( 250-300 m). The identity and sources of oxidants and reductants to this active microbial community, and the identity of the chemoautotrophic organisms themselves, are still only partially known. Below about 50m (the euphotic zone), δ13C values of suspended particulates range from -23 to -26‰, typical of marine phytoplankton. However we have observed both enrichments (values of up to -16‰) and depletions (values of -28‰) near the redox interface. We had expected to see isotopically light POC in the chemoautotrophy maximum, since DIC δ13C should decrease with depth as organic carbon is remineralized. However both positive and negative isotopic excursions in POC occur at depths where dark carbon fixation is at a maximum, and at or near the transition from micro-oxic to sulfidic water. We postulate that this signal may help to define carbon fixation pathways (and dominant chemoautotrophic populations) in the oxic/sulfidic transition region.

Ocean Color Products Supporting the Assessment of Good Environmental Status: Development of a Spatial Distribution Model for the Seagrass Posidonia Oceanica (L.) Delille, 1813

NASA Astrophysics Data System (ADS)

Zucchetta, M.; Taji, M. A.; Mangin, A.; Pastres, R.

2015-12-01

Posidonia oceanica (L.) Delile, 1813 is a seagrass species endemic to the Mediterranean Sea, which is considered as one of the key habitats of the coastal areas. This species forms large meadows sensitive to several anthropogenic pressures, that can be regarded as indicators of environment quality in coastal environments and its distributional patterns should be take into account when evaluating the Environmental Status following the Ecosystem approach promoted by the Mediterranean Action Plan of UNEP and the EU Marine Strategy Framework Directive (2008/56/EC). The aim of this study was to develop a Species Distribution Model for P. oceanica, to be applied to the whole Mediterranean North African coast, in order to obtain an estimation of the potential distribution of this species in the region to be considered as an indicator for the assessment of good Environmental Status. As the study area is a data-poor zone with regard to seagrass distribution (i.e. only for some areas detailed distribution maps are available), the Species Distribution Model (SDM) was calibrated using high resolution data from 5 Mediterranean sites, located in Italy and Spain and validated using available data from the North African coast. Usually, when developing SDMs species occupancy data is available at coarser resolution than the information of environmental variables, and thus has to be downscaled at the appropriate grain to be coupled to the environmental conditions. Tackling the case of P. oceanica we had to face the opposite problem: the quality (in terms of resolution) of the information on seagrass distribution is generally very high compared to the environmental data available over large scale in marine domains (e.g. global bathymetry data). The high resolution application and the model transfer (from calibration areas to North African coast) was possible taking advantage of Ocean Color products: the probability of presence of the species in a given area was modelled using a binomial generalized linear model as a function of the bathymetry and some water characteristics mainly obtained from satellite data. Full resolution (c.a. 300m) Medium Resolution Imaging Spectrometer (MERIS) sensor imagery have been processed in order to extract a set of environmental variables to be coupled to seagrass distribution in the areas used to calibrate the model and for the whole North Africa coast (i.e. model application area). For the period 2003-2011 we processed data of: 1) the diffuse attenuation coefficient 2) coloured dissolved organic matter 3) Particle backscatter at 443nm; 4) Euphotic depth, estimated considering the coefficient of extinction of light; 5) Euphotic depth/ depth ratio, combining the estimation of euphotic depth with the bathymetry. Other variables have been resampled at MERIS full resolution, like data obtained from Moderate Resolution Imaging Spectroradiometer (MODIS; Sea Surface Temperature and Photosynthetically Available Radiation) or by model simulation (e.g. water salinity). The fitted model suggests that water transparency plays a major role, but also other variables, such as salinity and photosynthetically available radiation at surface, are important at larger spatial scales in explaining meadows distribution. The availability of high resolution time-series of input data allowed us to apply the validated model to the whole NA coast. Using model predictions to identify areas with suitable conditions for P. oceanica, it was possible to develop an indicator of potential habitat use and to define baseline reference conditions, necessary for the assessment of Good Environmental Status in Mediterranean coastal waters. This work shows how the Ocean and Land Colour Instrument (OLCI) within the Sentinel-3 mission can be exploited - thanks to the way opened by MERIS - to carry out the operational monitoring needed for the implementation of the UNEP MAP and EU MSFD Ecosystem Approach to the integrated management of land, water and living resources.

Impact of Submesoscale Processes on Dynamics of Phytoplankton Filaments

DTIC Science & Technology

2015-02-12

submesoscale processes on the formation of chlorophyll a filaments during late springearlier summer, and late summer time frames. We show that during...the late summer time frame, ASC leads to the development of filaments with high values of chlorophyll a concentration along the edge of the cold jet...in contrast to the earlier summer time, when the ASC mixes phytoplankton much deeper to the area below of the euphotic depth, and chlorophyll a

Spring phytoplankton community response to an episodic windstorm event in oligotrophic waters offshore from the Ulleungdo and Dokdo islands, Korea

NASA Astrophysics Data System (ADS)

Baek, Seung Ho; Lee, Minji; Kim, Yun-Bae

2018-02-01

We investigated the phytoplankton distribution and its relationship to environmental factors at 40 stations in oligotrophic waters offshore from the Ulleungdo and Dokdo islands (hereafter Ulleungdo or Dokdo) in Japan/East Sea, prior to and following an episodic windstorm event. Nutrient addition bioassay experiments (control, + N, + P, and + NP, in both the presence and absence of added Fe) were also conducted to investigate the growth response of the phytoplankton assemblage and its nutrient consumption, using surface seawater collected from stations 36 and 40, which are in the vicinity of the Dokdo. Field measurements showed that the surface water temperature ranged from 13.33 °C to 16.18 °C and the salinity ranged from 34.03 to 34.55. The nitrate + nitrite, phosphate, and silicate concentrations varied from 0.07 to 2.22 μM, 0.01 μM to 0.19 μM and 0.76 to 6.93 μM, respectively. The Chl-a concentration varied from 0.36 to 15.97 μg L- 1 (average 2.66 ± 3.26 μM), but was significantly higher in Zone III-a (Dokdo) than in Zone I-b (between Ulljin and Ulleungdo, prior to the windstorm), Zone I-a (between Ulljin and Ulleungdo, following the windstorm), and Zone II-a (Ulleungdo) (F = 17.438, p < 0.001; ANOVA). Diatoms and Raphidophyta were the dominant phytoplankton types. Following episodic windstorm events the abundance of the raphidophyte Heterosigma akashiwo was maintained at high levels in the offshore oligotrophic area around the Ulleungdo and Dokdo, particularly in Zone III-a (F = 16.889, p < 0.001; ANOVA). In the algal bioassays conducted with and without added Fe, the in vivo fluorescence values in the + N and + NP treatments were higher than in the control and the + P treatments, which suggests that plankton biomass production was stimulated by N availability. In the + N and + NP treatments, H. akashiwo typically dominated in the initial, logarithmic, and stationary growth phases. The growth rate of the phytoplankton community in the presence of added Fe was not statistically different (p > 0.05) from that in the treatments without added Fe. The results suggest that in this area natural phytoplankton communities, including those dominated by H. akashiwo, respond rapidly to pulsed nitrogen loading events. The episodic windstorm event probably resulted in vertical mixing that brought nutrients into the euphotic upper layer. The results suggest that such events are important in triggering spring phytoplankton blooms in potentially oligotrophic waters, such as those in the vicinity of the Dokdo in the Japan/East Sea.

Factors affecting the estimate of primary production from space

NASA Technical Reports Server (NTRS)

Balch, W. M.; Byrne, C. F.

1994-01-01

Remote sensing of primary production in the euphotic zone has been based mostly on visible-band and water-leaving radiance measured with the coastal zone color scanner. There are some robust, simple relationships for calculating integral production based on surface measurements, but they also require knowledge for photoadaptive parameters such as maximum photosynthesis which currently cannot be obtained from spave. A 17,000-station data set is used to show that space-based estimates of maximum photosynthesis could improve predictions of psi, the water column light utiliztion index, which is an important term in many primary productivity models. Temperature is also examined as a factor for predicting hydrographic structure and primary production. A simple model is used to relate temperature and maximum photosynthesis; the model incorporates (1) the positive relationship between maximum photosynthesis and temperature and (2) the strongly negative relationship between temperature and nitrate in the ocean (which directly affects maximum growth rates via nitrogen limitation). Since these two factors relate to carbon and nitrogen, 'balanced carbon/nitrogen assimilation' was calculated using the Redfield ratio, It is expected that the relationship between maximum balanced carbon assimilation versus temperature is concave-down, with the peak dependent on nitrate uptake kinetics, temperature-nitrate relationships,a nd the carbon chlorophyll ration. These predictions were compared with the sea truth data. The minimum turnover time for nitrate was also calculated using this approach. Lastly, sea surface temperature gradients were used to predict the slope of isotherms (a proxy for the slope of isopycnals in many waters). Sea truth data show that at size scales of several hundred kilometers, surface temperature gradients can provide information on the slope of isotherms in the top 200 m of the water column. This is directly relevant to the supply of nutrients into the surface mixed layer, which is useful for predicting integral biomass and primary production.

Contrasting genomic properties of free-living and particle-attached microbial assemblages within a coastal ecosystem

PubMed Central

Smith, Maria W.; Zeigler Allen, Lisa; Allen, Andrew E.; Herfort, Lydie; Simon, Holly M.

2013-01-01

The Columbia River (CR) is a powerful economic and environmental driver in the US Pacific Northwest. Microbial communities in the water column were analyzed from four diverse habitats: (1) an estuarine turbidity maximum (ETM), (2) a chlorophyll maximum of the river plume, (3) an upwelling-associated hypoxic zone, and (4) the deep ocean bottom. Three size fractions, 0.1–0.8, 0.8–3, and 3–200 μm were collected for each habitat in August 2007, and used for DNA isolation and 454 sequencing, resulting in 12 metagenomes of >5 million reads (>1.6 Gbp). To characterize the dominant microorganisms and metabolisms contributing to coastal biogeochemistry, we used predicted peptide and rRNA data. The 3- and 0.8-μm metagenomes, representing particulate fractions, were taxonomically diverse across habitats. The 3-μm size fractions contained a high abundance of eukaryota with diatoms dominating the hypoxic water and plume, while cryptophytes were more abundant in the ETM. The 0.1-μm metagenomes represented mainly free-living bacteria and archaea. The most abundant archaeal hits were observed in the deep ocean and hypoxic water (19% of prokaryotic peptides in the 0.1-μm metagenomes), and were homologous to Nitrosopumilus maritimus (ammonia-oxidizing Thaumarchaeota). Bacteria dominated metagenomes of all samples. In the euphotic zone (estuary, plume and hypoxic ocean), the most abundant bacterial taxa (≥40% of prokaryotic peptides) represented aerobic photoheterotrophs. In contrast, the low-oxygen, deep water metagenome was enriched with sequences for strict and facultative anaerobes. Interestingly, many of the same anaerobic bacterial families were enriched in the 3-μm size fraction of the ETM (2–10X more abundant relative to the 0.1-μm metagenome), indicating possible formation of anoxic microniches within particles. Results from this study provide a metagenome perspective on ecosystem-scale metabolism in an upwelling-influenced river-dominated coastal margin. PMID:23750156

The role of Thaumarchaeota in the Quaternary nitrogen cycle

NASA Astrophysics Data System (ADS)

Dong, L.; Jia, G.; Zhiyang, L.; Wu, Z.

2016-12-01

Paired downcore profiles of sedimentary organic δ15N, and crenarchaeol, a specific biomarker of Thaumarchaeota, the ammonia oxidation archaea, were reported from marine isotope stage (MIS) 6 to MIS2 in core MD05-2897 and from MIS2 to MIS1 in core MD01-2392 to explore the role of Thaumarchaeota in the Quaternary nitrogen biogeochemical cycles. Both cores were retrieved from the southern South China Sea (SCS). The δ15N glacial-interglacial patterns of the two cores were opposite to the existing tropical eastern Pacific records, with decreasing trend during deglacial periods and high values in the glacial times and low values in the interglacial intervals (from 5 to 3.5‰), but were consistent with the foraminiferal bound δ15N record in the northern SCS. Basically, the crenarchaeol abundance paralleled the curve of δ15N record during glacial-interglacial timescale, indicating enhanced archaeal ammonia oxidation occurred during both deglacial and interglacial intervals, which could lower the δ15N value of the remaining NO3- via the release of 15N-enriched N2O. The proposed stronger archaeal ammonia oxidization in the interglacial SCS could reasonably account for the opposite trend of the δ15N record in the denitrification zone of the eastern Pacific. In addition, the paired records of GDGT [2]/[3] ratio, a proxy for evaluating the relative ratio of shallow and deep AOA, was found also coupled with the δ15N record, indicating the increase contribution of nitrification from the shallow AOA in the interglacial periods. Although our findings here are not in conflict with the hypothesis that the nitrogen fixation enhanced during interglacial periods, they can further suggest that organic matter mineralization in the euphotic zone, which could provide ammonia for AOA, likely enhanced more during the interglacials and then ultimately reduced the biological pump efficiency.

Effects of varied nitrate and phosphate supply on polysaccharidic and proteinaceous gel particles production during tropical phytoplankton bloom experiments

NASA Astrophysics Data System (ADS)

Engel, A.; Borchard, C.; Loginova, A.; Meyer, J.; Hauss, H.; Kiko, R.

2015-04-01

It has been suggested that oxygen minimum zones (OMZ) will expand in the tropical oceans as a result of global change with potential consequences for marine element cycling, such as an increase in anaerobic nitrogen loss, resulting in a lower supply of nitrate relative to phosphate to the euphotic zone. So far, the effects of changes in nutrient ratios on organic matter recycling and export fluxes are not well understood. Here, were investigated how different phosphate (Varied P: 0.15-1.58 μmol L-1) or nitrate (Varied N: 1.9-21.9 μmol L-1) concentrations affect the abundance and size distribution of polysaccharidic transparent exopolymer particles (TEP), which are suggested to enhance particle aggregation and export fluxes, and on proteinaceous coomassie stainable particles (CSP), a supposedly good substrate for heterotrophic bacteria. Two series of mesocosm bloom experiments were conducted with natural plankton communities collected from the Eastern Tropical North Atlantic (ETNA) close to Cape Verde in October 2012. Until bloom peak, a positive correlation between gel particle abundance and Chl a concentration was determined, linking the release of dissolved gel precursors and the subsequent formation of gel particles to autotrophic production. After bloom peak, gel particle abundance remained stable or even increased, implying a continued partitioning of dissolved into particulate organic matter after biomass production itself ceased. During both experiments, differences between TEP and CSP dynamics were observed; TEP were generally more abundant than CSP. Changes in size distribution indicated aggregation of TEP during the bloom, while newly formed CSP decomposed. Abundance of gel particles clearly increased with nitrate concentration during the second experiment, suggesting that changes in [DIN]:[DIP] ratios can affect gel particle formation with potential consequences for carbon and nitrogen cycling as well as food web dynamics in tropical ecosystems.

Effects of varied nitrate and phosphate supply on polysaccharidic and proteinaceous gel particle production during tropical phytoplankton bloom experiments

NASA Astrophysics Data System (ADS)

Engel, A.; Borchard, C.; Loginova, A.; Meyer, J.; Hauss, H.; Kiko, R.

2015-10-01

Gel particles such as the polysaccharidic transparent exopolymer particles (TEP) and the proteinaceous Coomassie stainable particles (CSP) play an important role in marine biogeochemical and ecological processes like particle aggregation and export, or microbial nutrition and growth. So far, effects of nutrient availability or of changes in nutrient ratios on gel particle production and fate are not well understood. The tropical ocean includes large oxygen minimum zones, where nitrogen losses due to anaerobic microbial activity result in a lower supply of nitrate relative to phosphate to the euphotic zone. Here, we report of two series of mesocosm experiments that were conducted with natural plankton communities collected from the eastern tropical North Atlantic (ETNA) close to Cape Verde in October 2012. The experiments were performed to investigate how different phosphate (experiment 1, Varied P: 0.15-1.58 μmol L-1) or nitrate (experiment 2, Varied N: 1.9-21.9 μmol L-1) concentrations affect the abundance and size distribution of TEP and CSP. In the days until the bloom peak was reached, a positive correlation between gel particle abundance and Chl a concentration was determined, linking the release of dissolved gel precursors and the subsequent formation of gel particles to autotrophic production. After the bloom peak, gel particle abundance remained stable or even increased, implying a continued partitioning of dissolved into particulate organic matter after biomass production itself ceased. During both experiments, differences between TEP and CSP dynamics were observed; TEP were generally more abundant than CSP. Changes in size distribution indicated aggregation of TEP after the bloom, while newly formed CSP decomposed. Abundance of gel particles clearly increased with nitrate concentration during the second experiment, suggesting that changes in [DIN] : [DIP] ratios can affect gel particle formation with potential consequences for carbon and nitrogen cycling as well as food web dynamics in tropical ecosystems.

Dissolved Gases in Seawater and Sediments (Paper 7R0315)

NASA Astrophysics Data System (ADS)

Key, R. M.

1987-07-01

Certainly the most controversial results derived from the study of any dissolved gas concerned oxygen utilization rates in the North Atlantic. Jenkins (1982) estimated a net oxy-gen utilization rate (OUR) for the Beta triangle region of the North Atlantic (apices 26.5°N x 38.5°W, 32.5°N x 30.0°W, and 22.5°N x 28.5°W) of 5.7 moles of oxygen consumed m-2 yr-1 for the zone below 100m. He assumed that the oxygen distribution below the euphotic zone was stationary and steady state and therfore that the in situ oxygen consumption must be balanced by physical transport of oxygen into the area. His estimates were based on measured distributions of dissolved oxygen and the tracers 3He and 3H and a simple model which assumed lateral advection was small. The derived value or OUR was several times higher that previous estimates based on 14C and 15N incubation techniques. The OUR requires a downward flux of carbon from the photic zone of approximately 50 gCm-2yr-1 , which is again much higher that previous results. Jenkins and Goldman (1985) amplified the arguments in a study of seasonal oxygen cycling and primary production based on a ten year time series of measurements from the Panulirus station near Bermuda. Considering insolation, heat budgets and 3He/3H data they estimated a vertically integrated oxygen production rate of 5 Mm-2yr-1 and a subsequent new production of 50 gCm-2yr-1. The results were supported by calculations based on a second order turbulence closure model (Klein and Coste, 1984). These results have been challenged primarily on the basis of the spatial variability of the phenomenon!. Whatever the final outcome Jenkins has clearly demonstrated that the time has come to take a fresh look at oxygen utilization rates and primary productivity given the tools and modelling capabilities now at hand. The TTO data set will go a long way toward providing the necessary data set for the North Atlantic when the analyses are complete. Other studies have dealt with the photooxidative daylight loss of oxygen from near-surface tropical waters (Gieskes and Kraay, 1982), isotopic fractionation between fresh and seawater and the atmosphere (Benson and Krause, 1984) , edge effects on chemistry in the 02 minimum zone (Mullins et al., 1985), and the relationship between oxygen and other biogeochemical properties (Pak, 1984; Blizard and Pak, 1984; Lewitus and Broenkow, 1985).

VERTIGO (VERtical Transport In the Global Ocean): A study of particle sources and flux attenuation in the North Pacific

NASA Astrophysics Data System (ADS)

Buesseler, K. O.; Trull, T. W.; Steinberg, D. K.; Silver, M. W.; Siegel, D. A.; Saitoh, S.-I.; Lamborg, C. H.; Lam, P. J.; Karl, D. M.; Jiao, N. Z.; Honda, M. C.; Elskens, M.; Dehairs, F.; Brown, S. L.; Boyd, P. W.; Bishop, J. K. B.; Bidigare, R. R.

2008-07-01

The VERtical Transport In the Global Ocean (VERTIGO) study examined particle sources and fluxes through the ocean's "twilight zone" (defined here as depths below the euphotic zone to 1000 m). Interdisciplinary process studies were conducted at contrasting sites off Hawaii (ALOHA) and in the NW Pacific (K2) during 3-week occupations in 2004 and 2005, respectively. We examine in this overview paper the contrasting physical, chemical and biological settings and how these conditions impact the source characteristics of the sinking material and the transport efficiency through the twilight zone. A major finding in VERTIGO is the considerably lower transfer efficiency ( Teff) of particulate organic carbon (POC), POC flux 500/150 m, at ALOHA (20%) vs. K2 (50%). This efficiency is higher in the diatom-dominated setting at K2 where silica-rich particles dominate the flux at the end of a diatom bloom, and where zooplankton and their pellets are larger. At K2, the drawdown of macronutrients is used to assess export and suggests that shallow remineralization above our 150-m trap is significant, especially for N relative to Si. We explore here also surface export ratios (POC flux/primary production) and possible reasons why this ratio is higher at K2, especially during the first trap deployment. When we compare the 500-m fluxes to deep moored traps, both sites lose about half of the sinking POC by >4000 m, but this comparison is limited in that fluxes at depth may have both a local and distant component. Certainly, the greatest difference in particle flux attenuation is in the mesopelagic, and we highlight other VERTIGO papers that provide a more detailed examination of the particle sources, flux and processes that attenuate the flux of sinking particles. Ultimately, we contend that at least three types of processes need to be considered: heterotrophic degradation of sinking particles, zooplankton migration and surface feeding, and lateral sources of suspended and sinking materials. We have evidence that all of these processes impacted the net attenuation of particle flux vs. depth measured in VERTIGO and would therefore need to be considered and quantified in order to understand the magnitude and efficiency of the ocean's biological pump.

Ammonium production off central Chile (36°S) by photodegradation of phytoplankton-derived and marine dissolved organic matter.

PubMed

Rain-Franco, Angel; Muñoz, Claudia; Fernandez, Camila

2014-01-01

We investigated the production of ammonium by the photodegradation of dissolved organic matter (DOM) in the coastal upwelling system off central Chile (36°S). The mean penetration of solar radiation (Z1%) between April 2011 and February 2012 was 9.4 m, 4.4 m and 3.2 m for Photosynthetically Active Radiation (PAR; 400-700 nm), UV-A (320-400 nm) and UV-B (280-320 nm), respectively. Ammonium photoproduction experiments were carried out using exudates of DOM obtained from cultured diatom species (Chaetoceros muelleri and Thalassiosira minuscule) as well as natural marine DOM. Diatom exudates showed net photoproduction of ammonium under exposure to UVR with a mean rate of 0.56±0.4 µmol L(-1) h(-1) and a maximum rate of 1.49 µmol L(-1) h(-1). Results from natural marine DOM showed net photoproduction of ammonium under exposure to PAR+UVR ranging between 0.06 and 0.2 µmol L(-1) h(-1). We estimated the potential contribution of photochemical ammonium production for phytoplankton ammonium demand. Photoammonification of diatom exudates could support between 117 and 453% of spring-summer NH4(+) assimilation, while rates obtained from natural samples could contribute to 50-178% of spring-summer phytoplankton NH4(+) requirements. These results have implications for local N budgets, as photochemical ammonium production can occur year-round in the first meters of the euphotic zone that are impacted by full sunlight.

Heterotrophic bacterioplankton in the Arabian Sea:. Basinwide response to year-round high primary productivity

NASA Astrophysics Data System (ADS)

Ducklow, H. W.; Smith, D. C.; Campbell, L.; Landry, M. R.; Quinby, H. L.; Steward, G. F.; Azam, F.

Heterotrophic bacterial abundance and productivity were measured during five and four cruises, respectively, in the northwest Arabian Sea as part of the US JGOFS Process Study, which provided a new view of seasonal bacterial dynamics in that part of the basin influenced by monsoonal forcing. In this paper, surface layer data are used to address two questions concerning the influence of the monsoon cycle on bacterial dynamics: (1) Is there a bacterial bloom in the SW Monsoon? and (2) Is bacterial production low during the oligotrophic Spring Intermonsoon? An extensive comparison of epifluorescence microscopy and flow cytometry, unprecedented at this scale, detected essentially the same heterotrophic bacterial populations and distributions, with some between-cruise differences. Use of the two methods allowed us to extend our observations in space and time. Bacterial productivity, both in the surface layer and integrated over the euphotic zone, was elevated less than 2-fold during the Southwest Monsoon. Levels of bacterial abundance and production were low during the Northeast Monsoon, then increased in March during the Spring Intermonsoon. There was some stimulation of abundance or production inshore in response to coastal upwelling. In general, the basin was enriched in bacterial biomass >5×10 8 cells l -1 throughout the year, relative to other tropical regimes, presumably in response to overall high PP and DOC levels. Seasonally uniform DOC levels may be regulated in part by intense bacterial utilization rates, but also reflect seasonal consistency in PP.

Elucidating Small-Scale Animal-Fluid Interactions in the Deep Sea

NASA Astrophysics Data System (ADS)

Katija, K.; Sherman, A.; Graves, D.; Kecy, C. D.; Klimov, D.; Robison, B. H.

2016-02-01

The midwater region of the ocean (below the euphotic zone and above the benthos) is one of the largest ecosystems on our planet, yet remains one of the least explored. Little-known marine organisms that inhabit midwater have developed life strategies that contribute to their evolutionary success, and understanding interactions with their physical, fluid environment will shed light on these strategies. Although significant advances in underwater vehicle technologies have improved access to midwater, small-scale, in situ fluid mechanics measurement methods that seek to quantify the interactions that midwater organisms have with their physical environment are lacking. Here we present DeepPIV, an instrumentation package affixed to remotely operated vehicles that quantifies fluid motions from the surface of the ocean down to 4000 m depths. Utilizing ambient suspended particulate, fluid-structure interactions can be evaluated on a range of marine organisms in midwater and on the benthos. As a proof of concept for DeepPIV, we targeted giant larvaceans (Bathochordaeus stygias) in Monterey Bay that create mucus houses to filter food. Once mucus houses become clogged, they are abandoned by the larvacean, and are left to sink to the ocean bottom; in Monterey Bay, sinking mucus houses contribute to nearly a third of the particulate on the ocean bottom. Little is known about the structure of these mucus houses and the function they play in selectively filtering particles. Using DeepPIV, we reveal the complex structures and flows generated within larvacean mucus houses, which are used to ultimately elucidate how these structures function.

Genomic makeup of the marine flavobacterium Nonlabens (Donghaeana) dokdonensis and identification of a novel class of rhodopsins.

PubMed

Kwon, Soon-Kyeong; Kim, Byung Kwon; Song, Ju Yeon; Kwak, Min-Jung; Lee, Choong Hoon; Yoon, Jung-Hoon; Oh, Tae Kwang; Kim, Jihyun F

2013-01-01

Rhodopsin-containing marine microbes such as those in the class Flavobacteriia play a pivotal role in the biogeochemical cycle of the euphotic zone (Fuhrman JA, Schwalbach MS, Stingl U. 2008. Proteorhodopsins: an array of physiological roles? Nat Rev Microbiol. 6:488-494). Deciphering the genome information of flavobacteria and accessing the diversity and ecological impact of microbial rhodopsins are important in understanding and preserving the global ecosystems. The genome sequence of the orange-pigmented marine flavobacterium Nonlabens dokdonensis (basonym: Donghaeana dokdonensis) DSW-6 was determined. As a marine photoheterotroph, DSW-6 has written in its genome physiological features that allow survival in the oligotrophic environments. The sequence analysis also uncovered a gene encoding an unexpected type of microbial rhodopsin containing a unique motif in addition to a proteorhodopsin gene and a number of photolyase or cryptochrome genes. Homologs of the novel rhodopsin gene were found in other flavobacteria, alphaproteobacteria, a species of Cytophagia, a deinococcus, and even a eukaryote diatom. They all contain the characteristic NQ motif and form a phylogenetically distinct group. Expression analysis of this rhodopsin gene in DSW-6 indicated that it is induced at high NaCl concentrations, as well as in the presence of light and the absence of nutrients. Genomic and metagenomic surveys demonstrate the diversity of the NQ rhodopsins in nature and the prevalent occurrence of the encoding genes among microbial communities inhabiting hypersaline niches, suggesting its involvement in sodium metabolism and the sodium-adapted lifestyle.

Ammonium Production off Central Chile (36°S) by Photodegradation of Phytoplankton-Derived and Marine Dissolved Organic Matter

PubMed Central

Rain-Franco, Angel; Muñoz, Claudia; Fernandez, Camila

2014-01-01

We investigated the production of ammonium by the photodegradation of dissolved organic matter (DOM) in the coastal upwelling system off central Chile (36°S). The mean penetration of solar radiation (Z1%) between April 2011 and February 2012 was 9.4 m, 4.4 m and 3.2 m for Photosynthetically Active Radiation (PAR; 400–700 nm), UV-A (320–400 nm) and UV-B (280–320 nm), respectively. Ammonium photoproduction experiments were carried out using exudates of DOM obtained from cultured diatom species (Chaetoceros muelleri and Thalassiosira minuscule) as well as natural marine DOM. Diatom exudates showed net photoproduction of ammonium under exposure to UVR with a mean rate of 0.56±0.4 µmol L−1 h−1 and a maximum rate of 1.49 µmol L−1 h−1. Results from natural marine DOM showed net photoproduction of ammonium under exposure to PAR+UVR ranging between 0.06 and 0.2 µmol L−1 h−1. We estimated the potential contribution of photochemical ammonium production for phytoplankton ammonium demand. Photoammonification of diatom exudates could support between 117 and 453% of spring-summer NH4 + assimilation, while rates obtained from natural samples could contribute to 50–178% of spring-summer phytoplankton NH4 + requirements. These results have implications for local N budgets, as photochemical ammonium production can occur year-round in the first meters of the euphotic zone that are impacted by full sunlight. PMID:24968138

The impact on atmospheric CO2 of iron fertilization induced changes in the ocean's biological pump

NASA Astrophysics Data System (ADS)

Jin, X.; Gruber, N.; Frenzel, H.; Doney, S. C.; McWilliams, J. C.

2007-10-01

Using numerical simulations, we quantify the impact of changes in the ocean's biological pump on the air-sea balance of CO2 by fertilizing a small surface patch in the high-nutrient, low-chlorophyll region of the eastern tropical Pacific with iron. Decade-long fertilization experiments are conducted in a basin-scale, eddy-permitting coupled physical biogeochemical ecological model. In contrast to previous studies, we find that most of the dissolved inorganic carbon (DIC) removed from the euphotic zone by the enhanced biological export is replaced by uptake of CO2 from the atmosphere. Atmospheric uptake efficiencies, the ratio of the perturbation in air-sea CO2 flux to the perturbation in export flux across 100 m, are 0.75 to 0.93 in our patch size-scale experiments. The atmospheric uptake efficiency is insensitive to the duration of the experiment. The primary factor controlling the atmospheric uptake efficiency is the vertical distribution of the enhanced biological production. Iron fertilization at the surface tends to induce production anomalies primarily near the surface, leading to high efficiencies. In contrast, mechanisms that induce deep production anomalies (e.g. altered light availability) tend to have a low uptake efficiency, since most of the removed DIC is replaced by lateral and vertical transport and mixing. Despite high atmospheric uptake efficiencies, patch-scale iron fertilization of the ocean's biological pump tends to remove little CO2 from the atmosphere over the decadal timescale considered here.

Seawater Respiration, Carbon Flux, Nutrient Retention Efficiency and Heterotrophic Energy Production in the Peruvian Upwelling

NASA Astrophysics Data System (ADS)

Packard, T. T.; Osma, N.; Fernández-Urruzola, I.; Codispoti, L. A.; Christensen, J. P.; Gómez, M.

2016-02-01

Oceanic depth profiles of seawater respiration (R) and vertical carbon flux are described by similar power functions and because they are conceptually and mathematically related, they can be calculated from one another. The maximum curvature of the respiration depth profile controls carbon flux. When the curvature is sharp, the carbon flux (FC) from the epipelagic ocean is low and the nutrient retention efficiency (NRE) is high allowing these waters to maintain high productivity. When the curvature is weak, NRE is low, seawater becomes nutrient impoverished, and productivity is reduced. This means that the attenuation of respiration in ocean water columns is critical in understanding and predicting vertical FC, the capacity of epipelagic ecosystems to retain their nutrients, and primary productivity. The new metric, NRE, is the ratio of nutrient regeneration in a seawater layer to the nutrients introduced into it. In other words, NRE = R/FC. A depth profile of FC is the integral of water column R. This relationship facilitates calculating ocean sections of FC. In a FC section across the Peru upwelling system we found a carbon flux maximum extending down to 400 m, 50 km off the Peru coast. Along this same section, by coupling respiratory electron transport system activity to heterotrophic oxidative phosphorylation, we calculated an ocean section of heterotrophic energy production (HEP). In the euphotic zone, HEP ranged from 250 to 500 J d-1 m-3. Below 200m, HEP dropped to less than 5 J d-1 m-3.

15N/14N variations in Cretaceous Atlantic sedimentary sequences: implication for past changes in marine nitrogen biogeochemistry

USGS Publications Warehouse

Rau, G.H.; Arthur, M.A.; Dean, W.E.

1987-01-01

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds ("black shales") were found to have significantly lower ??15N values (lower 15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have ??15N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin. The recurring 15N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N2-fixing blue-green algae, a possible source of this sediment 15N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment. ?? 1987.

The impact on atmospheric CO2 of iron fertilization induced changes in the ocean's biological pump

NASA Astrophysics Data System (ADS)

Jin, X.; Gruber, N.; Frenzel, H.; Doney, S. C.; McWilliams, J. C.

2008-03-01

Using numerical simulations, we quantify the impact of changes in the ocean's biological pump on the air-sea balance of CO2 by fertilizing a small surface patch in the high-nutrient, low-chlorophyll region of the eastern tropical Pacific with iron. Decade-long fertilization experiments are conducted in a basin-scale, eddy-permitting coupled physical/biogeochemical/ecological model. In contrast to previous studies, we find that most of the dissolved inorganic carbon (DIC) removed from the euphotic zone by the enhanced biological export is replaced by uptake of CO2 from the atmosphere. Atmospheric uptake efficiencies, the ratio of the perturbation in air-sea CO2 flux to the perturbation in export flux across 100 m, integrated over 10 years, are 0.75 to 0.93 in our patch size-scale experiments. The atmospheric uptake efficiency is insensitive to the duration of the experiment. The primary factor controlling the atmospheric uptake efficiency is the vertical distribution of the enhanced biological production and export. Iron fertilization at the surface tends to induce production anomalies primarily near the surface, leading to high efficiencies. In contrast, mechanisms that induce deep production anomalies (e.g. altered light availability) tend to have a low uptake efficiency, since most of the removed DIC is replaced by lateral and vertical transport and mixing. Despite high atmospheric uptake efficiencies, patch-scale iron fertilization of the ocean's biological pump tends to remove little CO2 from the atmosphere over the decadal timescale considered here.

Iron Supply and Demand in an Antarctic Shelf Ecosystem

NASA Astrophysics Data System (ADS)

McGillicuddy, D. J., Jr.; Sedwick, P.; Dinniman, M. S.; Arrigo, K. R.; Bibby, T. S.; Greenan, B. J. W.; Hofmann, E. E.; Klinck, J. M., II; Smith, W.; Mack, S. L.; Marsay, C. M.; Sohst, B. M.; van Dijken, G.

2016-02-01

The Ross Sea sustains a rich ecosystem and is the most productive sector of the Southern Ocean. Most of this production occurs within a polynya during the November-February period, when the availability of dissolved iron (dFe) is thought to exert the major control on phytoplankton growth. Here we combine new data on the distribution of dFe, high-resolution model simulations of ice melt and regional circulation, and satellite-based estimates of primary production to quantify iron supply and demand over the Ross Sea continental shelf. Our analysis suggests that the largest sources of dFe to the euphotic zone are wintertime mixing and melting sea ice, with a lesser input from intrusions of Circumpolar Deep Water, and a small amount from melting glacial ice. Together these sources are in approximate balance with the annual biological dFe demand inferred from satellite-based productivity algorithms, although both the supply and demand estimates have large uncertainties. Our findings illustrate the complexities of iron cycling in the Southern Ocean, highlighting the heterogeneity of the underlying processes along the Antarctic continental margin. Explicit representation of these complexities, and the temporal variability in both proximate and ultimate sources of iron, will be necessary to understand how a changing climate will affect this important ecosystem and its influence on biogeochemical cycles. Reduction of the present uncertainties in iron supply and demand will require coupled observational and modeling systems capable of resolving the wide range of physical, biological, and chemical processes involved.

Tabulate Corals after the Frasnian/Famennian Crisis: A Unique Fauna from the Holy Cross Mountains, Poland

PubMed Central

Zapalski, Mikołaj K.; Berkowski, Błażej; Wrzołek, Tomasz

2016-01-01

Famennian tabulate corals were very rare worldwide, and their biodiversity was relatively low. Here we report a unique tabulate fauna from the mid- and late Famennian of the western part of the Holy Cross Mountains (Kowala and Ostrówka), Poland. We describe eight species (four of them new, namely ?Michelinia vinni sp. nov., Thamnoptychia mistiaeni sp. nov., Syringopora kowalensis sp. nov. and Syringopora hilarowiczi sp. nov.); the whole fauna consists of ten species (two others described in previous papers). These corals form two assemblages—the lower, mid-Famennian with Thamnoptychia and the upper, late Famennian with representatives of genera ?Michelinia, Favosites, Syringopora and ?Yavorskia. The Famennian tabulates from Kowala represent the richest Famennian assemblage appearing after the F/F crisis (these faunas appear some 10 Ma after the extinction event). Corals described here most probably inhabited deeper water settings, near the limit between euphotic and disphotic zones or slightly above. At generic level, these faunas show similarities to other Devonian and Carboniferous faunas, which might suggest their ancestry to at least several Carboniferous lineages. Tabulate faunas described here represent new recruits (the basin of the Holy Cross mountains was not a refuge during the F/F crisis) and have no direct evolutionary linkage to Frasnian faunas from Kowala. The colonization of the seafloor took place in two separate steps: first was monospecific assemblage of Thamnoptychia, and later came the diversified Favosites-Syringopora-Michelinia fauna. PMID:27007689

Methods of eutrophication assessment in the context of the water framework directive: Examples from the Eastern Mediterranean coastal areas

NASA Astrophysics Data System (ADS)

Pavlidou, Alexandra; Simboura, Nomiki; Rousselaki, Eleni; Tsapakis, Manolis; Pagou, Kalliopi; Drakopoulou, Paraskevi; Assimakopoulou, Georgia; Kontoyiannis, Harilaos; Panayotidis, Panayotis

2015-10-01

A set of methodological tools were tested in order to assess the eutrophication quality of selected coastal areas in Eastern Mediterranean Sea, Greece, in the context of the Water Framework Directive under various anthropogenic pressures. Three, five-step tools, namely, TRIX, chlorophyll-a (chl-a) biomass classification scheme, and eutrophication index (E.I.) were applied in oligotrophic waters for (a) the whole water column and (b) the euphotic zone. The relationship among the eutrophication assessment indices and the ecological quality status (EcoQ) assessment indices for benthic macroinvertebrates (BENTIX index) and macroalgae (ecological evaluation index-EEIc) was also explored. Agricultural activities and mariculture are the pressures mostly related to the eutrophication assessment of the selected Greek coastal water bodies. Chl-a proved to be the criterion with the best overall correlation with the EcoQ indices, while TRIX with the lowest. Moreover, among the eutrophication indices, E.I. showed better overall agreement with BENTIX showing that probably it reflects the indirect relation of macroinvertebrates with water eutrophication in a better way. Among the eutrophication indices used, TRIX rather overestimated the eutrophication status of the selected coastal areas. The first stage of eutrophication was reflected more efficiently using E.I. than TRIX, but E.I. seems to be a rather sensitive index. A future modification of the high to good boundary of E.I. may be needed in order to demonstrate the high status of the relatively undisturbed Greek coastal sites.

Tabulate Corals after the Frasnian/Famennian Crisis: A Unique Fauna from the Holy Cross Mountains, Poland.

PubMed

Zapalski, Mikołaj K; Berkowski, Błażej; Wrzołek, Tomasz

2016-01-01

Famennian tabulate corals were very rare worldwide, and their biodiversity was relatively low. Here we report a unique tabulate fauna from the mid- and late Famennian of the western part of the Holy Cross Mountains (Kowala and Ostrówka), Poland. We describe eight species (four of them new, namely ?Michelinia vinni sp. nov., Thamnoptychia mistiaeni sp. nov., Syringopora kowalensis sp. nov. and Syringopora hilarowiczi sp. nov.); the whole fauna consists of ten species (two others described in previous papers). These corals form two assemblages-the lower, mid-Famennian with Thamnoptychia and the upper, late Famennian with representatives of genera ?Michelinia, Favosites, Syringopora and ?Yavorskia. The Famennian tabulates from Kowala represent the richest Famennian assemblage appearing after the F/F crisis (these faunas appear some 10 Ma after the extinction event). Corals described here most probably inhabited deeper water settings, near the limit between euphotic and disphotic zones or slightly above. At generic level, these faunas show similarities to other Devonian and Carboniferous faunas, which might suggest their ancestry to at least several Carboniferous lineages. Tabulate faunas described here represent new recruits (the basin of the Holy Cross mountains was not a refuge during the F/F crisis) and have no direct evolutionary linkage to Frasnian faunas from Kowala. The colonization of the seafloor took place in two separate steps: first was monospecific assemblage of Thamnoptychia, and later came the diversified Favosites-Syringopora-Michelinia fauna.

Incorporating a prognostic representation of marine nitrogen fixers into the global ocean biogeochemical model HAMOCC

NASA Astrophysics Data System (ADS)

Paulsen, Hanna; Ilyina, Tatiana; Six, Katharina D.; Stemmler, Irene

2017-03-01

Nitrogen (N2) fixation is a major source of bioavailable nitrogen to the euphotic zone, thereby exerting an important control on ocean biogeochemical cycling. This paper presents the incorporation of prognostic N2 fixers into the HAMburg Ocean Carbon Cycle model (HAMOCC), a component of the Max Planck Institute Earth System Model (MPI-ESM). Growth dynamics of N2 fixers in the model are based on physiological characteristics of the cyanobacterium Trichodesmium. The applied temperature dependency confines diazotrophic growth and N2 fixation to the tropical and subtropical ocean roughly between 40°S and 40°N. Simulated large-scale spatial patterns compare well with observations, and the global N2 fixation rate of 135.6 Tg N yr-1 is within the range of current estimates. The vertical distribution of N2 fixation also matches well the observations, with a major fraction of about 85% occurring in the upper 20 m. The observed seasonal variability at the stations BATS and ALOHA is reasonably reproduced, with highest fixation rates in northern summer/fall. Iron limitation was found to be an important factor in controlling the simulated distribution of N2 fixation, especially in the Pacific Ocean. The new model component considerably improves the representation of present-day N2 fixation in HAMOCC. It provides the basis for further studies on the role of diazotrophs in global biogeochemical cycles, as well as on the response of N2 fixation to changing environmental conditions.

Direct measurements of the light dependence of gross photosynthesis and oxygen consumption in the ocean

NASA Astrophysics Data System (ADS)

Bailleul, B.; Park, J.; Brown, C. M.; Bidle, K. D.; Lee, S.; Falkowski, P. G.

2016-02-01

For decades, a lack of understanding of how respiration is influenced by light has been stymying our ability to quantitatively analyze how phytoplankton allocate carbon in situ and the biological mechanisms that participate to the fate of blooms. Using membrane inlet mass spectrometry (MIMS), the light dependencies of gross photosynthesis and oxygen uptake rates were measured during the bloom demises of two prymnesiophytes, in two open ocean regions. In the North Atlantic, dominated by Emiliania huxleyi, respiration was independent of irradiance and was higher than the gross photosynthetic rate at all irradiances. In the Amundsen Sea (Antarctica), dominated by Phaeocystis antarctica, the situation was very different. Dark respiration was one order of magnitude lower than the maximal gross photosynthetic rate. ut the oxygen uptake rate increased by 10 fold at surface irradiances, where it becomes higher than gross photosynthesis. Our results suggest that the light dependence of oxygen uptake in P. antarctica has two sources: one is independent of photosynthesis, and is possibly associated with the photo-reduction of O2 mediated by dissolved organic matter; the second reflects the activity of an oxidase fueled in the light with photosynthetic electron flow. Interestingly, these dramatic light-dependent changes in oxygen uptake were not reproduced in nutrient-replete P. antarctica cultures, in the laboratory. Our measurements highlight the importance of improving our understanding of oxygen consuming reactions in the euphotic zone, which is critical to investigating the physiology of phytoplankton and tracing the fate of phytoplankton blooms.

The influence of oceanographic features on the foraging behavior of the olive ridley sea turtle Lepidochelys olivacea along the Guiana coast

NASA Astrophysics Data System (ADS)

Chambault, Philippine; de Thoisy, Benoît; Heerah, Karine; Conchon, Anna; Barrioz, Sébastien; Dos Reis, Virginie; Berzins, Rachel; Kelle, Laurent; Picard, Baptiste; Roquet, Fabien; Le Maho, Yvon; Chevallier, Damien

2016-03-01

The circulation in the Western Equatorial Atlantic is characterized by a highly dynamic mesoscale activity that shapes the Guiana continental shelf. Olive ridley sea turtles (Lepidochelys olivacea) nesting in French Guiana cross this turbulent environment during their post-nesting migration. We studied how oceanographic and biological conditions drove the foraging behavior of 18 adult females, using satellite telemetry, remote sensing data (sea surface temperature, sea surface height, current velocity and euphotic depth), simulations of micronekton biomass (pelagic organisms) and in situ records (water temperature and salinity). The occurrence of foraging events throughout migration was located using Residence Time analysis, while an innovative proxy of the hunting time within a dive was used to identify and quantify foraging events during dives. Olive ridleys migrated northwestwards using the Guiana current and remained on the continental shelf at the edge of eddies formed by the North Brazil retroflection, an area characterized by low turbulence and high micronekton biomass. They performed mainly pelagic dives, hunting for an average 77% of their time. Hunting time within a dive increased with shallower euphotic depth and with lower water temperatures, and mean hunting depth increased with deeper thermocline. This is the first study to quantify foraging activity within dives in olive ridleys, and reveals the crucial role played by the thermocline on the foraging behavior of this carnivorous species. This study also provides novel and detailed data describing how turtles actively use oceanographic structures during post-nesting migration.

Large-scale distribution of microbial and viral populations in the South Atlantic Ocean.

PubMed

De Corte, Daniele; Sintes, Eva; Yokokawa, Taichi; Lekunberri, Itziar; Herndl, Gerhard J

2016-04-01

Viruses are abundant, diverse and dynamic components of the marine environments and play a significant role in the ocean biogeochemical cycles. To assess potential variations in the relation between viruses and microbes in different geographic regions and depths, viral and microbial abundance and production were determined throughout the water column along a latitudinal transect in the South Atlantic Ocean. Path analysis was used to examine the relationships between several abiotic and biotic parameters and the different microbial and viral populations distinguished by flow cytometry. The depth-integrated contribution of microbial and viral abundance to the total microbial and viral biomass differed significantly among the different provinces. Additionally, the virus-to-microbe ratio increased with depth and decreased laterally towards the more productive regions. Our data revealed that the abundance of phytoplankton and microbes is the main controlling factor of the viral populations in the euphotic and mesopelagic layers, whereas in the bathypelagic realm, viral abundance was only weakly related to the biotic and abiotic variables. The relative contribution of the three viral populations distinguished by flow cytometry showed a clear geographical pattern throughout the water column, suggesting that these populations are composed of distinct taxa able to infect specific hosts. Overall, our data indicate the presence of distinct microbial patterns along the latitudinal transect. This variability is not limited to the euphotic layer but also detectable in the meso- and bathypelagic layers. © 2016 The Authors. Environmental Microbiology Reports published by Society for Applied Microbiology and John Wiley & Sons Ltd.

Underwater Optics in Sub-Antarctic and Antarctic Coastal Ecosystems

PubMed Central

Huovinen, Pirjo; Ramírez, Jaime; Gómez, Iván

2016-01-01

Understanding underwater optics in natural waters is essential in evaluating aquatic primary production and risk of UV exposure in aquatic habitats. Changing environmental conditions related with global climate change, which imply potential contrasting changes in underwater light climate further emphasize the need to gain insights into patterns related with underwater optics for more accurate future predictions. The present study evaluated penetration of solar radiation in six sub-Antarctic estuaries and fjords in Chilean North Patagonian region (39–44°S) and in an Antarctic bay (62°S). Based on vertical diffuse attenuation coefficients (Kd), derived from measurements with a submersible multichannel radiometer, average summer UV penetration depth (z1%) in these water bodies ranged 2–11 m for UV-B (313 nm), 4–27 m for UV-A (395 nm), and 7–30 m for PAR (euphotic zone). UV attenuation was strongest in the shallow Quempillén estuary, while Fildes Bay (Antarctica) exhibited the highest transparency. Optically non-homogeneous water layers and seasonal variation in transparency (lower in winter) characterized Comau Fjord and Puyuhuapi Channel. In general, multivariate analysis based on Kd values of UV and PAR wavelengths discriminated strongly Quempillén estuary and Puyuhuapi Channel from other study sites. Spatial (horizontal) variation within the estuary of Valdivia river reflected stronger attenuation in zones receiving river impact, while within Fildes Bay a lower spatial variation in water transparency could in general be related to closeness of glaciers, likely due to increased turbidity through ice-driven processes. Higher transparency and deeper UV-B penetration in proportion to UV-A/visible wavelengths observed in Fildes Bay suggests a higher risk for Antarctic ecosystems reflected by e.g. altered UV-B damage vs. photorepair under UV-A/PAR. Considering that damage repair processes often slow down under cool temperatures, adverse UV impact could be further exacerbated by cold temperatures in this location, together with episodes of ozone depletion. Overall, the results emphasize the marked spatial (horizontal and vertical) and temporal heterogeneity of optical characteristics, and challenges that these imply for estimations of underwater optics. PMID:27144454

Pulsed remineralisation in the northwestern Mediterranean Sea: a hypothesis

NASA Astrophysics Data System (ADS)

Denis, Michel; Martin, Valérie; Momzikoff, André; Gondry, Geneviève; Stemmann, Lars; Demers, Serge; Gorsky, Gaby; Andersen, Valérie

2003-02-01

A general study of biogeochemical processes (DYNAPROC cruise) was conducted in May 1995 at a time-series station in the open northwestern Mediterranean Sea where horizontal advection was weak. Short-term variations of the vertical distributions of pico- and nanophytoplankton were investigated over four 36-h cycles, along with parallel determinations of metabolic CO 2 production rates and amino acid-containing colloid (AACC) concentrations at the chlorophyll maximum depth. The vertical (0-1000-m depth) distributions of (i) AACC, (ii) suspended particles and (iii) metabolic CO 2 production rate were documented during the initial and final stages of these 36-h cycles. This study was concerned with diel vertical migration (DVM) of zooplankton, which provided periodic perturbations. Accordingly, the time scale of the experimental work varied from a few hours to a few days. Although all distributions exhibited a periodic behaviour, AACC distributions were generally not linked to diel vertical migrations. In the subsurface layer, Synechococcus made the most abundant population and large variations in concentration were observed both at day and at night. The corresponding integrated (over the upper 90 m) losses of Synechococcus during one night pointed to a potential source of exported organic matter amounting to 534 mg C m -2. This study stresses the potential importance of organic matter export from the euphotic zone through the daily grazing activity of vertically migrating organisms, which would not be accounted for by measurements at longer time scales. The metabolic CO 2 production exhibited a peak of activity below 500 m that was shifted downward, apparently in a recurrent way and independently of the vertical distributions of AACC or of suspended particulate material. To account for this phenomenon, a «sustained wave train» hypothesis is proposed that combines the effect of the diel superficial faecal pellet production by swarming migrators and the repackaging activity of the nonmigrating midwater populations. Our results confirm the recent finding that the particulate compartment is not the major source of the observed instantaneous remineralisation rate and shed a new light on the fate of organic matter in the aphotic zone.

Chemical and biological quality of selected lakes in Ohio, 1976 and 1977

USGS Publications Warehouse

Tobin, Robert L.; Youger, John D.

1979-01-01

Twenty-eight Ohio lakes (14 per year) were sampled by the U.S. Geological Survey and Ohio Environmental Protection Agency for the water-quality characteristics during the spring and summer of 1976 and 1977. Data items included: profiles of temperature, dissolved oxygen, pH, and specific conductance; physical, biological, nutrient, and organic characteristics; major and minor constituents; and physical and chemical data associated with major inflows. Light penetration (secchi disk) was greatest (21 feet) in Mogadore Reservoir and least (0.8 foot) in Stonelick Lake. Seasonal thermal gradients developed in most lakes greater than 17 feet in depth. Dissolved-oxygen saturation ranged from 220 percent in Summit Lake to zero percent in the bottom waters of all lakes having stable thermal gradients. Five-day BOD ranged from 0.3 milligrams per liter im Michael J. Kirwan Reservoir to more than 17 milligrams per liter in Nimisilia Reservoir. Anaerobic zones were frequently characterized by hydrogen sulfide and high concentrations of ammonia. All lakes had moderately hard to very hard waters. Calcium, bicarbonate, and sulfate were the principal constituents. Specific conductance ranged from 130 micromhos (Lake Logan) to 1250 micromhos (Summit Lake). Because of nutrient uptake and recycling, significant chemical and physical differences developed in different thermal strata. Pesticide residues and trace elements were not above the limits recommended by the Ohio Environmental Protection Agency. All counts of fecal colifrom bacteria were within State standards. Blue-green algae (Cyanophyta) dominated the phytoplankton communities of 18 lakes in spring and 26 lakes in summer. Algal counts from euphotic-zone composite samples ranged from 180 cells per milliliter in Killdeer Reservoir to 3,400,000 cells per milliliter in Kiser Lake. Maximum algal counts were greater than 100,000 cells per milliliter in 19 lakes. Streams ate a major source of macronutrients in Ohio lakes. The estimated discharge-weighted mean concentration for nitrite and total phosphorus in 62 inflow samples was 1.22 milligrams per liter as N and 0.12 milligrams per liter as P.

Linking Net Community Production and Hydrography Under La Nina and El Nino conditions in the Eastern Tropical South Pacific (ETSP)

NASA Astrophysics Data System (ADS)

Prokopenko, M. G.

2016-02-01

Presence of the Subantarctic Mode Water (SAMW) in the upper thermocline of the ETSP results in steep vertical gradients in the major nutrient stoichiometry, specifically the silicate to nitrate ratio. Thus, biological export production within the High Nutrient Low Chlorophyll (HNLC) and low-silicate waters of the northern ETSP, the region of high CO2 outgassing, is likely to be particularly sensitive to the variability in the hydrographic conditions that determine the depth of origin for the waters upwelled into the euphotic zone. During two cruises, in spring 2010 (mild El Nino), and in spring 2011 (moderately strong La Nina), we quantified Net Community Production rates (NCP, as Net biological O2 production), based on O2/Ar supersaturation ratios measured along 10S between the coast of Peru and 100W. Biases in the estimates of the net biological O2 production within the mixed layer arising from non-equilibrium O2 fluxes from the Oxygen Minimum Zone below, were quantified with a regional box model of coupled oxygen-nitrate mass balances. Potential export efficiencies along the 10S transect were derived from the comparison between satellite-based Net Primary Production and our field-based NCP estimates. Somewhat predictably, regional NCP rates and potential export efficiency, as well as the degree of the biological nitrate uptake were higher under the La Nina than under the El Nino conditions, likely due to deeper origin of the upwelled waters characterized by the higher silicate to nitrate ratios. A less intuitive implication is that while reducing the CO2 outgassing by the increased biological carbon uptake locally, the La Nina-enhanced export production within the ETSP may transiently diminish basin-scale capacity for the oceanic biological CO2 uptake by enhancing the fixed nitrogen losses, This may occur via expanding the vertical extent of the regional OMZ, as was observed at several stations along the cruise tracks in 2011, which in turn may drive an increase in the magnitude of regional denitrification. Further work would test this hypothesis.

Phytoplankton across Tropical and Subtropical Regions of the Atlantic, Indian and Pacific Oceans

PubMed Central

Estrada, Marta; Delgado, Maximino; Blasco, Dolors; Latasa, Mikel; Cabello, Ana María; Benítez-Barrios, Verónica; Fraile-Nuez, Eugenio; Mozetič, Patricija; Vidal, Montserrat

2016-01-01

We examine the large-scale distribution patterns of the nano- and microphytoplankton collected from 145 oceanic stations, at 3 m depth, the 20% light level and the depth of the subsurface chlorophyll maximum, during the Malaspina-2010 Expedition (December 2010-July 2011), which covered 15 biogeographical provinces across the Atlantic, Indian and Pacific oceans, between 35°N and 40°S. In general, the water column was stratified, the surface layers were nutrient-poor and the nano- and microplankton (hereafter phytoplankton, for simplicity, although it included also heterotrophic protists) community was dominated by dinoflagellates, other flagellates and coccolithophores, while the contribution of diatoms was only important in zones with shallow nutriclines such as the equatorial upwelling regions. We applied a principal component analysis to the correlation matrix among the abundances (after logarithmic transform) of the 76 most frequent taxa to synthesize the information contained in the phytoplankton data set. The main trends of variability identified consisted of: 1) A contrast between the community composition of the upper and the lower parts of the euphotic zone, expressed respectively by positive or negative scores of the first principal component, which was positively correlated with taxa such as the dinoflagellates Oxytoxum minutum and Scrippsiella spp., and the coccolithophores Discosphaera tubifera and Syracosphaera pulchra (HOL and HET), and negatively correlated with taxa like Ophiaster hydroideus (coccolithophore) and several diatoms, 2) a general abundance gradient between phytoplankton-rich regions with high abundances of dinoflagellate, coccolithophore and ciliate taxa, and phytoplankton-poor regions (second principal component), 3) differences in dominant phytoplankton and ciliate taxa among the Atlantic, the Indian and the Pacific oceans (third principal component) and 4) the occurrence of a diatom-dominated assemblage (the fourth principal component assemblage), including several pennate taxa, Planktoniella sol, Hemiaulus hauckii and Pseudo-nitzschia spp., in the divergence regions. Our findings indicate that consistent assemblages of co-occurring phytoplankton taxa can be identified and that their distribution is best explained by a combination in different degrees of both environmental and historical influences. PMID:26982180

Microfacies and biofabric of nummulite accumulations (Bank) from the Eocene deposits of Western Alborz (NW Iran)

NASA Astrophysics Data System (ADS)

Hadi, Mehdi; Mosaddegh, Hossein; Abbassi, Nasrollah

2016-12-01

The nummulite bank from the Eocene Ziarat Formation is described for the first time from Alborz, Iran, enhancing the record of these nummulite-rich accumulations in the Eocene of the circum-Tethyan carbonate platform. Five microfacies types have been defined within the shallow-water carbonate deposits of the Ziarat formation located in the western Alborz zone. Microfacies type 1 contains the most diverse Alveolina species associated with predominance of Nummulites A-forms. Microfacies type 2 is characterized by the presence of bivalve (oysters) fragments. Microfacies type 3 is supported by the high abundance of nummulitids. Microfacies type 4 is dominated by the occurrence of encrusting foraminifera-algal with flat growth forms that are mainly formed within the acervulinids assemblage. Finally, there is the presence of orthophragminids and nummuitids represented by microfacies type 5. Microfacies data obtained from the investigation area show that nummulite banks were formed within the back, core and fore-bank palaeoenvironments. The classification method of this paper is based on use biometric, biofabric, taphonomic and palaeoecological characteristics of larger benthic foraminifera. In addition, the calculated intraskeletal porosity by the use of numerous sections and FE-SEM images of Nummulites tests were displacement of tests in order to achieve a better understanding of paleo-conditions that occurred during sedimentation. We conclude that differences among bank frameworks suggest that small biconvex A-forms of Nummulites tests along with alveolinids were living in shallow, euphotic waters, whereas robust and ovate nummulitid tests thrived and concentrated in the intermediate (40-80 m) water with biofabrics in the min-scales, which indicates the influence of waves and currents in combination with wave-winnowing processes. More distal accumulations, the fore-bank were characterized by orthophragminid and nummulitid tests in the deeper part of the photic zone. The larger benthic foraminifera, as confirmed by Discocyclina javana (VERBEEK), D. cf. dispansa (SOWERBY), Assilina ex. gr. exponens (SOWERBY), Nummulites ex. gr. globulus)SCHAUB(, Alveolina ellipsoidalis (SCHWAGER), A. subpyrenaica (LEYMERIE), A. pisiformis (HOTTINGER), A. tumida (HOTTINGER), A. cemali (SIREL et ACAR), A. laxa (HOTTINGER), A. ex. gr. cremae)CHECCHIA-RISPOLI(, suggest the early Ilerdian-Middle Eocene age of these sediments.

Phytoplankton across Tropical and Subtropical Regions of the Atlantic, Indian and Pacific Oceans.

PubMed

Estrada, Marta; Delgado, Maximino; Blasco, Dolors; Latasa, Mikel; Cabello, Ana María; Benítez-Barrios, Verónica; Fraile-Nuez, Eugenio; Mozetič, Patricija; Vidal, Montserrat

2016-01-01

We examine the large-scale distribution patterns of the nano- and microphytoplankton collected from 145 oceanic stations, at 3 m depth, the 20% light level and the depth of the subsurface chlorophyll maximum, during the Malaspina-2010 Expedition (December 2010-July 2011), which covered 15 biogeographical provinces across the Atlantic, Indian and Pacific oceans, between 35°N and 40°S. In general, the water column was stratified, the surface layers were nutrient-poor and the nano- and microplankton (hereafter phytoplankton, for simplicity, although it included also heterotrophic protists) community was dominated by dinoflagellates, other flagellates and coccolithophores, while the contribution of diatoms was only important in zones with shallow nutriclines such as the equatorial upwelling regions. We applied a principal component analysis to the correlation matrix among the abundances (after logarithmic transform) of the 76 most frequent taxa to synthesize the information contained in the phytoplankton data set. The main trends of variability identified consisted of: 1) A contrast between the community composition of the upper and the lower parts of the euphotic zone, expressed respectively by positive or negative scores of the first principal component, which was positively correlated with taxa such as the dinoflagellates Oxytoxum minutum and Scrippsiella spp., and the coccolithophores Discosphaera tubifera and Syracosphaera pulchra (HOL and HET), and negatively correlated with taxa like Ophiaster hydroideus (coccolithophore) and several diatoms, 2) a general abundance gradient between phytoplankton-rich regions with high abundances of dinoflagellate, coccolithophore and ciliate taxa, and phytoplankton-poor regions (second principal component), 3) differences in dominant phytoplankton and ciliate taxa among the Atlantic, the Indian and the Pacific oceans (third principal component) and 4) the occurrence of a diatom-dominated assemblage (the fourth principal component assemblage), including several pennate taxa, Planktoniella sol, Hemiaulus hauckii and Pseudo-nitzschia spp., in the divergence regions. Our findings indicate that consistent assemblages of co-occurring phytoplankton taxa can be identified and that their distribution is best explained by a combination in different degrees of both environmental and historical influences.

Downward particle flux and carbon export in the Beaufort Sea, Arctic Ocean; the Malina experiment

NASA Astrophysics Data System (ADS)

Miquel, J.-C.; Gasser, B.; Martín, J.; Marec, C.; Babin, M.; Fortier, L.; Forest, A.

2015-01-01

As part of the international, multidisciplinary project Malina, downward particle fluxes were investigated by means of a drifting multi-sediment trap mooring deployed at three sites in the Canadian Beaufort Sea in late summer 2009. Mooring deployments lasted for 28-50 h and targeted the shelf-break and the slope along the Beaufort-Mackenzie continental margin, as well as the edge between the Mackenzie Shelf and the Amundsen Gulf. Besides analyses of C and N, the collected material was investigated for pigments, phyto- and microzooplankton, faecal pellets and swimmers. The measured fluxes were relatively low, in the range of 11-54 mg m-2 d-1 for the total mass, 1-15 mg C m-2 d-1 for organic carbon and 0.2-2.5 mg N m-2 d-1 for nitrogen. Comparison with a long-term trap dataset from the same sampling area showed that the short-term measurements were at the lower end of the high variability characterizing a rather high flux regime during the study period. The sinking material consisted of aggregates and particles that were characterized by the presence of hetero- and autotrophic microzooplankters and diatoms and by the corresponding pigment signatures. Faecal pellets contribution to sinking carbon flux was important, especially at depth where they represented up to 25% of the total carbon flux. The vertical distribution of different morphotypes of pellets showed a marked pattern with cylindrical faeces (produced by calanoid copepods) present mainly within the euphotic zone, whereas elliptical pellets (produced mainly by smaller copepods) were more abundant at mesopelagic depths. These features, together with the density of matter within the pellets, highlighted the role of the zooplankton community in the transformation of carbon issued from the primary production and the transition of that carbon from the productive surface zone to the Arctic Ocean's interior. Our data indicate that sinking carbon flux in this late summer period is primarily the result of a heterotrophic driven ecosystem as compared to the system driven by autotrophy earlier in the year.

Downward particle flux and carbon export in the Beaufort Sea, Arctic Ocean; the role of zooplankton

NASA Astrophysics Data System (ADS)

Miquel, J.-C.; Gasser, B.; Martín, J.; Marec, C.; Babin, M.; Fortier, L.; Forest, A.

2015-08-01

As part of the international, multidisciplinary project Malina, downward particle fluxes were investigated by means of a drifting multi-sediment trap mooring deployed at three sites in the Canadian Beaufort Sea in late summer 2009. Mooring deployments lasted between 28 and 50 h and targeted the shelf-break and the slope along the Beaufort-Mackenzie continental margin, as well as the edge between the Mackenzie Shelf and the Amundsen Gulf. Besides analyses of C and N, the collected material was investigated for pigments, phyto- and microzooplankton, faecal pellets and swimmers. The measured fluxes were relatively low, in the range of 11-54 mg m-2 d-1 for the total mass, 1-15 mg C m-2 d-1 for organic carbon and 0.2-2.5 mg N m-2 d-1 for nitrogen. Comparison with a long-term trap data set from the same sampling area showed that the short-term measurements were at the lower end of the high variability characterizing a rather high flux regime during the study period. The sinking material consisted of aggregates and particles that were characterized by the presence of hetero- and autotrophic microzooplankters and diatoms and by the corresponding pigment signatures. Faecal pellets contribution to sinking carbon flux was important, especially at depths below 100 m, where they represented up to 25 % of the total carbon flux. The vertical distribution of different morphotypes of pellets showed a marked pattern with cylindrical faeces (produced by calanoid copepods) present mainly within the euphotic zone, whereas elliptical pellets (produced mainly by smaller copepods) were more abundant at mesopelagic depths. These features, together with the density of matter within the pellets, highlighted the role of the zooplankton community in the transformation of carbon issued from the primary production and the transition of that carbon from the productive surface zone to the Arctic Ocean's interior. Our data indicate that sinking carbon flux in this late summer period is primarily the result of a heterotrophic-driven ecosystem.

Revealing sources and chemical identity of iron ligands across the California Current System

NASA Astrophysics Data System (ADS)

Boiteau, R.; Repeta, D.; Fitzsimmons, J. N.; Parker, C.; Twining, B. S.; Baines, S.

2016-02-01

The California Current System is one of the most productive regions of the ocean, fueled by the upwelling of nutrient rich water. Differences in the supply of micronutrient iron to surface waters along the coast lead to a mosaic of iron-replete and iron-limited conditions across the region, affecting primary production and community composition. Most of the iron in this region is supplied by upwelling of iron from the benthic boundary layer that is complexed by strong organic ligands. However, the source, identity, and bioavailability of these ligands are unknown. Here, we used novel hyphenated chromatography mass spectrometry approaches to structurally characterize organic ligands across the region. With these methods, iron ligands are detected with liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC-ICPMS), and then their mass and fragmentation spectra are determined by high resolution electrospray ionization mass spectrometry (LC-ESIMS). Iron isotopic exchange was used to compare the relative binding strengths of different ligands. Our survey revealed a broad range of ligands from multiple sources. Benthic boundary layers and anoxic sediments were sources of structurally amorphous weak ligands, likely organic degradation products, as well as siderophores, strong iron binding molecules that facilitate iron acquisition. In the euphotic zone, marine microbes and zooplankton grazing produced a wide distribution of other compounds that included known and novel siderophores. This work demonstrates that the chemical nature of ligands from different sources varies substantially and has important implications for iron biogeochemical cycling and availability to members of the microbial community.

DeepPIV: Measuring in situ Biological-Fluid Interactions from the Surface to Benthos

NASA Astrophysics Data System (ADS)

Katija, K.; Sherman, A.; Graves, D.; Kecy, C. D.; Klimov, D.; Robison, B. H.

2015-12-01

The midwater region of the ocean (below the euphotic zone and above the benthos) is one of the largest ecosystems on our planet, yet it remains one of the least explored. Little known marine organisms that inhabit midwater have developed strategies for swimming and feeding that ultimately contributes to their evolutionary success, and may inspire engineering solutions for societally relevant challenges. Fluid mechanics governs the interactions that midwater organisms have with their physical environment, but limited access to midwater depths and lack of non-invasive methods to measure in situ small-scale fluid motions prevent these interactions from being better understood. Significant advances in underwater vehicle technologies have only recently improved access to midwater. Unfortunately, in situ small-scale fluid mechanics measurement methods are still lacking in the oceanographic community. Here we present DeepPIV, an instrumentation package that can be affixed to remotely operated underwater vehicles that quantifies small-scale fluid motions from the surface of the ocean down to 4000 m depths. Utilizing ambient, suspended particulate in the coastal regions of Monterey Bay, fluid-structure interactions are evaluated on a range of marine organisms in midwater. Initial science targets include larvaceans, biological equivalents of flapping flexible foils, that create mucus houses to filter food. Little is known about the structure of these mucus houses and the function they play in selectively filtering particles, and these dynamics can serve as particle-mucus models for human health. Using DeepPIV, we reveal the complex structures and flows generated within larvacean mucus houses, and elucidate how these structures function.

Peru upwelling plankton respiration: calculations of carbon flux, nutrient retention efficiency and heterotrophic energy production

NASA Astrophysics Data System (ADS)

Packard, T. T.; Osma, N.; Fernández-Urruzola, I.; Codispoti, L. A.; Christensen, J. P.; Gómez, M.

2014-11-01

Oceanic depth profiles of plankton respiration are described by a power function, RCO2 = (RCO2)0(z/z0)b similar to the vertical carbon flux profile. Furthermore, because both ocean processes are closely related, conceptually and mathematically, each can be calculated from the other. The exponent (b), always negative, defines the maximum curvature of the respiration depth-profile and controls the carbon flux. When b is large, the C flux (FC) from the epipelagic ocean is low and the nutrient retention efficiency (NRE) is high allowing these waters to maintain high productivity. The opposite occurs when b is small. This means that the attenuation of respiration in ocean water columns is critical in understanding and predicting both vertical FC as well as the capacity of epipelagic ecosystems to retain their nutrients. The NRE is a new metric defined as the ratio of nutrient regeneration in a seawater layer to the nutrients introduced into that layer via FC. A depth-profile of FC is the integral of water column respiration. This relationship facilitates calculating ocean sections of FC from water column respiration. In a FC section across the Peru upwelling system we found a FC maximum extending down to 400 m, 50 km off the Peru coast. Finally, coupling respiratory electron transport system activity to heterotrophic oxidative phosphorylation promoted the calculation of an ocean section of heterotrophic energy production (HEP). It ranged from 250 to 500 J d-1 m-3 in the euphotic zone, to less than 5 J d-1 m-3 below 200 m on this ocean section.

Biogeography and Photosynthetic Biomass of Arctic Marine Pico-Eukaroytes during Summer of the Record Sea Ice Minimum 2012

PubMed Central

Metfies, Katja; von Appen, Wilken-Jon; Kilias, Estelle; Nicolaus, Anja; Nöthig, Eva-Maria

2016-01-01

Information on recent photosynthetic biomass distribution and biogeography of Arctic marine pico-eukaryotes (0.2–3 μm) is needed to better understand consequences of environmental change for Arctic marine ecosystems. We analysed pico-eukaryote biomass and community composition in Fram Strait and large parts of the Central Arctic Ocean (Nansen Basin, Amundsen Basin) using chlorophyll a (Chl a) measurements, automated ribosomal intergenic spacer analysis (ARISA) and 454-pyrosequencing. Samples were collected during summer 2012, the year with the most recent record sea ice minimum. Chl a concentrations were highest in eastern Fram Strait and pico-plankton accounted for 60–90% of Chl a biomass during the observation period. ARISA-patterns and 454-pyrosequencing revealed that pico-eukaryote distribution is closely related to water mass distribution in the euphotic zone of the Arctic Ocean. Phaeocystaceae, Micromonas sp., Dinophyceae and Syndiniales constitute a high proportion of sequence reads, while sequence abundance of autotrophic Phaeocystaceae and mixotrophic Micromonas sp. was inversely correlated. Highest sequence abundances of Phaeocystaceae were observed in the warm Atlantic Waters in Fram Strait, while Micromonas sp. dominated the abundant biosphere in the arctic halocline. Our results are of particular interest considering existing hypotheses that environmental conditions in Nansen Basin might become more similar to the current conditions in Fram Strait. We propose that in response, biodiversity and biomass of pico-eukaryotes in Nansen Basin could resemble those currently observed in Fram Strait in the future. This would significantly alter biogeochemical cycles in a large part of the Central Arctic Ocean. PMID:26895333

Primary production in the tropical continental shelf seas bordering northern Australia

NASA Astrophysics Data System (ADS)

Furnas, Miles J.; Carpenter, Edward J.

2016-10-01

Pelagic primary production (14C uptake) was measured 81 times between 1990 and 2013 at sites spanning the broad, shallow Northern Australian Shelf (NAS; 120-145°E) which borders the Australian continent. The mean of all areal production measurements was 1048±109 mg C m-2 d-1 (mean±95% CI). Estimates of areal primary production were correlated with integral upper-euphotic zone chlorophyll stocks (above the 50% and 20% light penetration depths) accessible to ocean color remote sensing and total water column chlorophyll standing crop, but not surface (0-2 m) chlorophyll concentrations. While the NAS is subject to a well characterized monsoonal climate regime (austral summer-NW monsoon -wet: austral winter- SE monsoon -dry), most seasonal differences in means of regional-scale chlorophyll standing crop (11-33 mg Chl m-2 for 12 of 15 season-region combinations) and areal primary production (700-1850 mg C m- day-1 for 12 of 15 season-region combinations) fell within a 3-fold range. Apart from the shallow waters of the Torres Strait and northern Great Barrier Reef, picoplankton (<2 μm size fraction) dominated chlorophyll standing crop and primary production with regional means of picoplankton contributions ranging from 45 to >80%. While the range of our post-1990 areal production estimates overlaps the range of production estimates made in NAS waters during 1960-62, the mean of post-1990 estimates is over 2-fold greater. We regard the difference to be due to improvements in production measurement techniques, particularly regarding the reduction of potential metal toxicity and incubations in more realistic light regimes.

Effects of the Relaxation of Upwelling-Favorable Winds on the Diurnal and Semidiurnal Water Temperature Fluctuations in the Santa Barbara Channel, California

NASA Astrophysics Data System (ADS)

Aristizábal, María. F.; Fewings, Melanie R.; Washburn, Libe

2017-10-01

In the Santa Barbara Channel, California, and around the Northern Channel Islands, water temperature fluctuations in the diurnal and semidiurnal frequency bands are intermittent, with amplitudes that vary on time scales of days to weeks. The cause of this intermittency is not well understood. We studied the effects of the barotropic tide, vertical stratification, propagation of coastal-trapped waves, regional wind relaxations, and diurnal-band winds on the intermittency of the temperature fluctuations during 1992-2015. We used temperature data from 43 moorings in 10-200 m water depth and wind data from two buoys and one land station. Subtidal-frequency changes in vertical stratification explain 20-40% of the intermittency in diurnal and semidiurnal temperature fluctuations at time scales of days to weeks. Along the mainland north of Point Conception and at the Northern Channel Islands, the relaxation of upwelling-favorable winds substantially increases vertical stratification, accounting for up to 55% of the subtidal-frequency variability in stratification. As a result of the enhanced stratification, wind relaxations enhance the diurnal and semidiurnal temperature fluctuations at those sites, even though the diurnal-band wind forcing decreases during wind relaxation. A linear model where the background stratification is advected vertically explains a substantial fraction of the temperature fluctuations at most sites. The increase of vertical stratification and subsequent increase in diurnal and semidiurnal temperature fluctuations during wind relaxation is a mechanism that can supply nutrients to the euphotic zone and kelp forests in the Channel in summer when upwelling is weak.

Modest net autotrophy in the oligotrophic ocean

NASA Astrophysics Data System (ADS)

Letscher, Robert T.; Moore, J. Keith

2017-04-01

The metabolic state of the oligotrophic subtropical ocean has long been debated. Net community production (NCP) represents the balance of autotrophic carbon fixation with heterotrophic respiration. Many in vitro NCP estimates based on oxygen incubation methods and the corresponding scaling relationships used to predict the ecosystem metabolic balance have suggested the ocean gyres to be net heterotrophic; however, all in situ NCP methods find net autotrophy. Reconciling net heterotrophy requires significant allochthonous inputs of organic carbon to the oligotrophic gyres to sustain a preponderance of respiration over in situ production. Here we use the first global ecosystem-ocean circulation model that contains representation of the three allochthonous carbon sources to the open ocean, to show that the five oligotrophic gyres exhibit modest net autotrophy throughout the seasonal cycle. Annually integrated rates of NCP vary in the range 1.5-2.2 mol O2 m-2 yr-1 across the five gyre systems; however, seasonal NCP rates are as low as 1 ± 0.5 mmol O2 m-2 d-1 for the North Atlantic. Volumetric NCP rates are heterotrophic below the 10% light level; however, they become net autotrophic when integrated over the euphotic zone. Observational uncertainties when measuring these modest autotrophic NCP rates as well as the metabolic diversity encountered across space and time complicate the scaling up of in vitro measurements to the ecosystem scale and may partially explain the previous reports of net heterotrophy. The oligotrophic ocean is autotrophic at present; however, it could shift toward seasonal heterotrophy in the future as rising temperatures stimulate respiration.

Seasonality and vertical structure of microbial communities in an ocean gyre.

PubMed

Treusch, Alexander H; Vergin, Kevin L; Finlay, Liam A; Donatz, Michael G; Burton, Robert M; Carlson, Craig A; Giovannoni, Stephen J

2009-10-01

Vertical, seasonal and geographical patterns in ocean microbial communities have been observed in many studies, but the resolution of community dynamics has been limited by the scope of data sets, which are seldom up to the task of illuminating the highly structured and rhythmic patterns of change found in ocean ecosystems. We studied vertical and temporal patterns in the microbial community composition in a set of 412 samples collected from the upper 300 m of the water column in the northwestern Sargasso Sea, on cruises between 1991 and 2004. The region sampled spans the extent of deep winter mixing and the transition between the euphotic and the upper mesopelagic zones, where most carbon fixation and reoxidation occurs. A bioinformatic pipeline was developed to de-noise, normalize and align terminal restriction fragment length polymorphism (T-RFLP) data from three restriction enzymes and link T-RFLP peaks to microbial clades. Non-metric multidimensional scaling statistics resolved three microbial communities with distinctive composition during seasonal stratification: a surface community in the region of lowest nutrients, a deep chlorophyll maximum community and an upper mesopelagic community. A fourth microbial community was associated with annual spring blooms of eukaryotic phytoplankton that occur in the northwestern Sargasso Sea as a consequence of winter convective mixing that entrains nutrients to the surface. Many bacterial clades bloomed in seasonal patterns that shifted with the progression of stratification. These richly detailed patterns of community change suggest that highly specialized adaptations and interactions govern the success of microbial populations in the oligotrophic ocean.

A role of vertical mixing on nutrient supply into the subsurface chlorophyll maximum in the shelf region of the East China Sea

NASA Astrophysics Data System (ADS)

Lee, Keunjong; Matsuno, Takeshi; Endoh, Takahiro; Ishizaka, Joji; Zhu, Yuanli; Takeda, Shigenobu; Sukigara, Chiho

2017-07-01

In summer, Changjiang Diluted Water (CDW) expands over the shelf region of the northern East China Sea. Dilution of the low salinity water could be caused by vertical mixing through the halocline. Vertical mixing through the pycnocline can transport not only saline water, but also high nutrient water from deeper layers to the surface euphotic zone. It is therefore very important to quantitatively evaluate the vertical mixing to understand the process of primary production in the CDW region. We conducted extensive measurements in the region during the period 2009-2011. Detailed investigations of the relative relationship between the subsurface chlorophyll maximum (SCM) and the nitracline suggested that there were two patterns relating to the N/P ratio. Comparing the depths of the nitracline and SCM, it was found that the SCM was usually located from 20 to 40 m and just above the nitracline, where the N/P ratio within the nitracline was below 15, whereas it was located from 10 to 30 m and within the nitracline, where the N/P ratio was above 20. The large value of the N/P ratio in the latter case suggests the influence of CDW. Turbulence measurements showed that the vertical flux of nutrients with vertical mixing was large (small) where the N/P ratio was small (large). A comparison with a time series of primary production revealed a consistency with the pattern of snapshot measurements, suggesting that the nutrient supply from the lower layer contributes considerably to the maintenance of SCM.

A multitrophic model to quantify the effects of marine viruses on microbial food webs and ecosystem processes

PubMed Central

Weitz, Joshua S; Stock, Charles A; Wilhelm, Steven W; Bourouiba, Lydia; Coleman, Maureen L; Buchan, Alison; Follows, Michael J; Fuhrman, Jed A; Jover, Luis F; Lennon, Jay T; Middelboe, Mathias; Sonderegger, Derek L; Suttle, Curtis A; Taylor, Bradford P; Frede Thingstad, T; Wilson, William H; Eric Wommack, K

2015-01-01

Viral lysis of microbial hosts releases organic matter that can then be assimilated by nontargeted microorganisms. Quantitative estimates of virus-mediated recycling of carbon in marine waters, first established in the late 1990s, were originally extrapolated from marine host and virus densities, host carbon content and inferred viral lysis rates. Yet, these estimates did not explicitly incorporate the cascade of complex feedbacks associated with virus-mediated lysis. To evaluate the role of viruses in shaping community structure and ecosystem functioning, we extend dynamic multitrophic ecosystem models to include a virus component, specifically parameterized for processes taking place in the ocean euphotic zone. Crucially, we are able to solve this model analytically, facilitating evaluation of model behavior under many alternative parameterizations. Analyses reveal that the addition of a virus component promotes the emergence of complex communities. In addition, biomass partitioning of the emergent multitrophic community is consistent with well-established empirical norms in the surface oceans. At steady state, ecosystem fluxes can be probed to characterize the effects that viruses have when compared with putative marine surface ecosystems without viruses. The model suggests that ecosystems with viruses will have (1) increased organic matter recycling, (2) reduced transfer to higher trophic levels and (3) increased net primary productivity. These model findings support hypotheses that viruses can have significant stimulatory effects across whole-ecosystem scales. We suggest that existing efforts to predict carbon and nutrient cycling without considering virus effects are likely to miss essential features of marine food webs that regulate global biogeochemical cycles. PMID:25635642

Nitrate Sources, Supply, and Phytoplankton Growth in the Great Australian Bight: An Eulerian-Lagrangian Modeling Approach

NASA Astrophysics Data System (ADS)

Cetina-Heredia, Paulina; van Sebille, Erik; Matear, Richard J.; Roughan, Moninya

2018-02-01

The Great Australian Bight (GAB), a coastal sea bordered by the Pacific, Southern, and Indian Oceans, sustains one of the largest fisheries in Australia but the geographical origin of nutrients that maintain its productivity is not fully known. We use 12 years of modeled data from a coupled hydrodynamic and biogeochemical model and an Eulerian-Lagrangian approach to quantify nitrate supply to the GAB and the region between the GAB and the Subantarctic Australian Front (GAB-SAFn), identify phytoplankton growth within the GAB, and ascertain the source of nitrate that fuels it. We find that nitrate concentrations have a decorrelation timescale of ˜60 days; since most of the water from surrounding oceans takes longer than 60 days to reach the GAB, 23% and 75% of nitrate used by phytoplankton to grow are sourced within the GAB and from the GAB-SAFn, respectively. Thus, most of the nitrate is recycled locally. Although nitrate concentrations and fluxes into the GAB are greater below 100 m than above, 79% of the nitrate fueling phytoplankton growth is sourced from above 100 m. Our findings suggest that topographical uplift and stratification erosion are key mechanisms delivering nutrients from below the nutricline into the euphotic zone and triggering large phytoplankton growth. We find annual and semiannual periodicities in phytoplankton growth, peaking in the austral spring and autumn when the mixed layer deepens leading to a subsurface maximum of phytoplankton growth. This study highlights the importance of examining phytoplankton growth at depth and the utility of Lagrangian approaches.

Penetration of UV-visible solar radiation in the global oceans: Insights from ocean color remote sensing

NASA Astrophysics Data System (ADS)

Lee, Zhongping; Hu, Chuanmin; Shang, Shaoling; Du, Keping; Lewis, Marlon; Arnone, Robert; Brewin, Robert

2013-09-01

Penetration of solar radiation in the ocean is determined by the attenuation coefficient (Kd(λ)). Following radiative transfer theory, Kd is a function of angular distribution of incident light and water's absorption and backscattering coefficients. Because these optical products are now generated routinely from satellite measurements, it is logical to evolve the empirical Kd to a semianalytical Kd that is not only spectrally flexible, but also the sun-angle effect is accounted for explicitly. Here, the semianalytical model developed in Lee et al. (2005b) is revised to account for the shift of phase function between molecular and particulate scattering from the short to long wavelengths. Further, using field data collected independently from oligotrophic ocean to coastal waters covering >99% of the Kd range for the global oceans, the semianalytically derived Kd was evaluated and found to agree with measured data within ˜7-26%. The updated processing system was applied to MODIS measurements to reveal the penetration of UVA-visible radiation in the global oceans, where an empirical procedure to correct Raman effect was also included. The results indicated that the penetration of the blue-green radiation for most oceanic waters is ˜30-40% deeper than the commonly used euphotic zone depth; and confirmed that at a depth of 50-70 m there is still ˜10% of the surface UVA radiation (at 360 nm) in most oligotrophic waters. The results suggest a necessity to modify or expand the light attenuation product from satellite ocean-color measurements in order to be more applicable for studies of ocean physics and biogeochemistry.

Production and flux of carbohydrate species in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Hung, Chin-Chang; Guo, Laodong; Schultz, Gary E.; Pinckney, James L.; Santschi, Peter H.

2003-06-01

Carbohydrates are an important organic compound class in seawater and play an active role in the biogeochemical cycling of organic carbon and trace elements in the ocean, but are poorly characterized. To better understand the sources and role of carbohydrate species in marine environments, the concentrations and fluxes of particulate carbohydrates (CHO), total acid polysaccharides (APS), uronic acids (URA), phytoplankton composition and bacterial production were measured in the Gulf of Mexico in 2000 and 2001. A strong positive correlation between APS concentration and cyanobacteria abundance was found in 2000. In 2001, prymnesiophyte abundance correlated well with both concentrations of APS and URA. Bacterial production data, measured simultaneously in 2001, showed significant positive relationships with particulate organic carbon (POC), CHO, APS and URA concentrations, respectively. The average fluxes out of the euphotic zone of CHO, APS and URA in 2000 were 8.1, 1.3, and 0.7 mg C m-2 d-1, respectively. In 2001, the average fluxes of CHO, APS and URA were about 3 times higher than those in 2000, which was a time of lower nutrient concentrations, indicating that the fluxes of carbohydrate species are related to the nutrient status and phytoplankton composition. The results suggest that APS in the upper water column can be produced by cyanobacteria, prymnesiophytes, and heterotrophic bacteria. Most importantly, our data indicate that APS and CHO compounds are more resistant to biological degradation than other organic compounds, suggesting that the role of CHO compounds in carbon cycling in the ocean is more complex than previously thought.

A multitrophic model to quantify the effects of marine viruses on microbial food webs and ecosystem processes.

PubMed

Weitz, Joshua S; Stock, Charles A; Wilhelm, Steven W; Bourouiba, Lydia; Coleman, Maureen L; Buchan, Alison; Follows, Michael J; Fuhrman, Jed A; Jover, Luis F; Lennon, Jay T; Middelboe, Mathias; Sonderegger, Derek L; Suttle, Curtis A; Taylor, Bradford P; Frede Thingstad, T; Wilson, William H; Eric Wommack, K

2015-06-01

Viral lysis of microbial hosts releases organic matter that can then be assimilated by nontargeted microorganisms. Quantitative estimates of virus-mediated recycling of carbon in marine waters, first established in the late 1990s, were originally extrapolated from marine host and virus densities, host carbon content and inferred viral lysis rates. Yet, these estimates did not explicitly incorporate the cascade of complex feedbacks associated with virus-mediated lysis. To evaluate the role of viruses in shaping community structure and ecosystem functioning, we extend dynamic multitrophic ecosystem models to include a virus component, specifically parameterized for processes taking place in the ocean euphotic zone. Crucially, we are able to solve this model analytically, facilitating evaluation of model behavior under many alternative parameterizations. Analyses reveal that the addition of a virus component promotes the emergence of complex communities. In addition, biomass partitioning of the emergent multitrophic community is consistent with well-established empirical norms in the surface oceans. At steady state, ecosystem fluxes can be probed to characterize the effects that viruses have when compared with putative marine surface ecosystems without viruses. The model suggests that ecosystems with viruses will have (1) increased organic matter recycling, (2) reduced transfer to higher trophic levels and (3) increased net primary productivity. These model findings support hypotheses that viruses can have significant stimulatory effects across whole-ecosystem scales. We suggest that existing efforts to predict carbon and nutrient cycling without considering virus effects are likely to miss essential features of marine food webs that regulate global biogeochemical cycles.

Phenology of particle size distributions and primary productivity in the North Pacific subtropical gyre (Station ALOHA)

PubMed Central

Letelier, Ricardo M.; Whitmire, Amanda L.; Barone, Benedetto; Bidigare, Robert R.; Church, Matthew J.; Karl, David M.

2015-01-01

Abstract The particle size distribution (PSD) is a critical aspect of the oceanic ecosystem. Local variability in the PSD can be indicative of shifts in microbial community structure and reveal patterns in cell growth and loss. The PSD also plays a central role in particle export by influencing settling speed. Satellite‐based models of primary productivity (PP) often rely on aspects of photophysiology that are directly related to community size structure. In an effort to better understand how variability in particle size relates to PP in an oligotrophic ecosystem, we collected laser diffraction‐based depth profiles of the PSD and pigment‐based classifications of phytoplankton functional types (PFTs) on an approximately monthly basis at the Hawaii Ocean Time‐series Station ALOHA, in the North Pacific subtropical gyre. We found a relatively stable PSD in the upper water column. However, clear seasonality is apparent in the vertical distribution of distinct particle size classes. Neither laser diffraction‐based estimations of relative particle size nor pigment‐based PFTs was found to be significantly related to the rate of 14C‐based PP in the light‐saturated upper euphotic zone. This finding indicates that satellite retrievals of particle size, based on particle scattering or ocean color would not improve parameterizations of present‐day bio‐optical PP models for this region. However, at depths of 100–125 m where irradiance exerts strong control on PP, we do observe a significant linear relationship between PP and the estimated carbon content of 2–20 μm particles. PMID:27812434

Analysis of Seasonal Chlorophyll-a Using An Adjoint Three-Dimensional Ocean Carbon Cycle Model

NASA Astrophysics Data System (ADS)

Tjiputra, J.; Winguth, A.; Polzin, D.

2004-12-01

The misfit between numerical ocean model and observations can be reduced using data assimilation. This can be achieved by optimizing the model parameter values using adjoint model. The adjoint model minimizes the model-data misfit by estimating the sensitivity or gradient of the cost function with respect to initial condition, boundary condition, or parameters. The adjoint technique was used to assimilate seasonal chlorophyll-a data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite to a marine biogeochemical model HAMOCC5.1. An Identical Twin Experiment (ITE) was conducted to test the robustness of the model and the non-linearity level of the forward model. The ITE experiment successfully recovered most of the perturbed parameter to their initial values, and identified the most sensitive ecosystem parameters, which contribute significantly to model-data bias. The regional assimilations of SeaWiFS chlorophyll-a data into the model were able to reduce the model-data misfit (i.e. the cost function) significantly. The cost function reduction mostly occurred in the high latitudes (e.g. the model-data misfit in the northern region during summer season was reduced by 54%). On the other hand, the equatorial regions appear to be relatively stable with no strong reduction in cost function. The optimized parameter set is used to forecast the carbon fluxes between marine ecosystem compartments (e.g. Phytoplankton, Zooplankton, Nutrients, Particulate Organic Carbon, and Dissolved Organic Carbon). The a posteriori model run using the regional best-fit parameterization yields approximately 36 PgC/yr of global net primary productions in the euphotic zone.

The study of deep-sea cephalopods.

PubMed

Hoving, Henk-Jan T; Perez, Jose Angel A; Bolstad, Kathrin S R; Braid, Heather E; Evans, Aaron B; Fuchs, Dirk; Judkins, Heather; Kelly, Jesse T; Marian, José E A R; Nakajima, Ryuta; Piatkowski, Uwe; Reid, Amanda; Vecchione, Michael; Xavier, José C C

2014-01-01

"Deep-sea" cephalopods are here defined as cephalopods that spend a significant part of their life cycles outside the euphotic zone. In this chapter, the state of knowledge in several aspects of deep-sea cephalopod research are summarized, including information sources for these animals, diversity and general biogeography and life cycles, including reproduction. Recommendations are made for addressing some of the remaining knowledge deficiencies using a variety of traditional and more recently developed methods. The types of oceanic gear that are suitable for collecting cephalopod specimens and images are reviewed. Many groups of deep-sea cephalopods require taxonomic reviews, ideally based on both morphological and molecular characters. Museum collections play a vital role in these revisions, and novel (molecular) techniques may facilitate new use of old museum specimens. Fundamental life-cycle parameters remain unknown for many species; techniques developed for neritic species that could potentially be applied to deep-sea cephalopods are discussed. Reproductive tactics and strategies in deep-sea cephalopods are very diverse and call for comparative evolutionary and experimental studies, but even in the twenty-first century, mature individuals are still unknown for many species. New insights into diet and trophic position have begun to reveal a more diverse range of feeding strategies than the typically voracious predatory lifestyle known for many cephalopods. Regular standardized deep-sea cephalopod surveys are necessary to provide insight into temporal changes in oceanic cephalopod populations and to forecast, verify and monitor the impacts of global marine changes and human impacts on these populations. © 2014 Elsevier Ltd All rights reserved.

Controls on the distributions of organic carbon and nitrogen in the eastern Pacific Ocean

NASA Astrophysics Data System (ADS)

Hansell, Dennis A.; Waterhouse, Tye Y.

1997-05-01

Measurements of total organic carbon (TOC) and nitrogen (TON) were made on the WOCE P18 line (from 67°S to 23°N along 103°/110°W). There was an accumulation of TOC on the equator and in the oligotrophic waters north and south of the equator. The concentrations of TOC were well correlated with temperature, indicating an important physical control on its distribution. The boundary separating shallow, TOC-rich water from deep, TOC-poor water overlaid the main thermocline. This observation suggests that water column stability or residence time imparted by the main thermocline is a primary determinant of TOC accumulation. Elevated TON concentrations were found in all surface waters, with the lowest values found in the region of 20-35°S. Net TON drawdown in the South Pacific subtropical gyre, likely due to biological utilization and vertical export of the nitrogen, was initiated with depletion of equatorially upwelled nitrate. The degree to which inorganic nitrogen was limiting in the surface layer south of the equator served to control the concentrations of TON. Such controls were not exerted on organic carbon, as reflected by increasing C:N ratios of organic matter as TON was removed. Unlike the findings in the South Pacific, TON concentrations in oligotrophic waters north of the equator were frequently higher than on the equator. Such accumulations are hypothesized to be maintained from nitrogen fixation, nitrogen input due to vertical migration of autotrophs or diffusive flux of inorganic nitrogen into the euphotic zone across the relatively shallow nitracline.

Insights into global diatom distribution and diversity in the world's ocean.

PubMed

Malviya, Shruti; Scalco, Eleonora; Audic, Stéphane; Vincent, Flora; Veluchamy, Alaguraj; Poulain, Julie; Wincker, Patrick; Iudicone, Daniele; de Vargas, Colomban; Bittner, Lucie; Zingone, Adriana; Bowler, Chris

2016-03-15

Diatoms (Bacillariophyta) constitute one of the most diverse and ecologically important groups of phytoplankton. They are considered to be particularly important in nutrient-rich coastal ecosystems and at high latitudes, but considerably less so in the oligotrophic open ocean. The Tara Oceans circumnavigation collected samples from a wide range of oceanic regions using a standardized sampling procedure. Here, a total of ∼12 million diatom V9-18S ribosomal DNA (rDNA) ribotypes, derived from 293 size-fractionated plankton communities collected at 46 sampling sites across the global ocean euphotic zone, have been analyzed to explore diatom global diversity and community composition. We provide a new estimate of diversity of marine planktonic diatoms at 4,748 operational taxonomic units (OTUs). Based on the total assigned ribotypes, Chaetoceros was the most abundant and diverse genus, followed by Fragilariopsis, Thalassiosira, and Corethron We found only a few cosmopolitan ribotypes displaying an even distribution across stations and high abundance, many of which could not be assigned with confidence to any known genus. Three distinct communities from South Pacific, Mediterranean, and Southern Ocean waters were identified that share a substantial percentage of ribotypes within them. Sudden drops in diversity were observed at Cape Agulhas, which separates the Indian and Atlantic Oceans, and across the Drake Passage between the Atlantic and Southern Oceans, indicating the importance of these ocean circulation choke points in constraining diatom distribution and diversity. We also observed high diatom diversity in the open ocean, suggesting that diatoms may be more relevant in these oceanic systems than generally considered.

Phenology of particle size distributions and primary productivity in the North Pacific subtropical gyre (Station ALOHA).

PubMed

White, Angelicque E; Letelier, Ricardo M; Whitmire, Amanda L; Barone, Benedetto; Bidigare, Robert R; Church, Matthew J; Karl, David M

2015-11-01

The particle size distribution (PSD) is a critical aspect of the oceanic ecosystem. Local variability in the PSD can be indicative of shifts in microbial community structure and reveal patterns in cell growth and loss. The PSD also plays a central role in particle export by influencing settling speed. Satellite-based models of primary productivity (PP) often rely on aspects of photophysiology that are directly related to community size structure. In an effort to better understand how variability in particle size relates to PP in an oligotrophic ecosystem, we collected laser diffraction-based depth profiles of the PSD and pigment-based classifications of phytoplankton functional types (PFTs) on an approximately monthly basis at the Hawaii Ocean Time-series Station ALOHA, in the North Pacific subtropical gyre. We found a relatively stable PSD in the upper water column. However, clear seasonality is apparent in the vertical distribution of distinct particle size classes. Neither laser diffraction-based estimations of relative particle size nor pigment-based PFTs was found to be significantly related to the rate of 14 C-based PP in the light-saturated upper euphotic zone. This finding indicates that satellite retrievals of particle size, based on particle scattering or ocean color would not improve parameterizations of present-day bio-optical PP models for this region. However, at depths of 100-125 m where irradiance exerts strong control on PP, we do observe a significant linear relationship between PP and the estimated carbon content of 2-20 μm particles.

Insights into global diatom distribution and diversity in the world’s ocean

PubMed Central

Malviya, Shruti; Scalco, Eleonora; Audic, Stéphane; Vincent, Flora; Veluchamy, Alaguraj; Poulain, Julie; Wincker, Patrick; Iudicone, Daniele; de Vargas, Colomban; Bittner, Lucie; Zingone, Adriana; Bowler, Chris

2016-01-01

Diatoms (Bacillariophyta) constitute one of the most diverse and ecologically important groups of phytoplankton. They are considered to be particularly important in nutrient-rich coastal ecosystems and at high latitudes, but considerably less so in the oligotrophic open ocean. The Tara Oceans circumnavigation collected samples from a wide range of oceanic regions using a standardized sampling procedure. Here, a total of ∼12 million diatom V9-18S ribosomal DNA (rDNA) ribotypes, derived from 293 size-fractionated plankton communities collected at 46 sampling sites across the global ocean euphotic zone, have been analyzed to explore diatom global diversity and community composition. We provide a new estimate of diversity of marine planktonic diatoms at 4,748 operational taxonomic units (OTUs). Based on the total assigned ribotypes, Chaetoceros was the most abundant and diverse genus, followed by Fragilariopsis, Thalassiosira, and Corethron. We found only a few cosmopolitan ribotypes displaying an even distribution across stations and high abundance, many of which could not be assigned with confidence to any known genus. Three distinct communities from South Pacific, Mediterranean, and Southern Ocean waters were identified that share a substantial percentage of ribotypes within them. Sudden drops in diversity were observed at Cape Agulhas, which separates the Indian and Atlantic Oceans, and across the Drake Passage between the Atlantic and Southern Oceans, indicating the importance of these ocean circulation choke points in constraining diatom distribution and diversity. We also observed high diatom diversity in the open ocean, suggesting that diatoms may be more relevant in these oceanic systems than generally considered. PMID:26929361

Seasonal changes on microbial metabolism and biomass in the euphotic layer of Sicilian Channel.

PubMed

Zaccone, R; Caruso, G; Leonardi, M; Maimone, G; Monticelli, L S; Azzaro, M; Cuttitta, A; Patti, B; La Ferla, R

2015-12-01

As a part of a wider project on fisheries ecology, several biological and environmental parameters were monitored during two oceanographic cruises (BANSIC 2012 and NOVESAR 2013) in the Sicily Channel, which connects the Western and Eastern Mediterranean basins. The prokaryotic abundances and biomass as well as hydrolysis rates on organic matter were investigated in the euphotic layer of a retention area for fish larval stages including anchovy (Engraulis encrasicolus, Linnaeus, 1758) with the aim to investigate the different biogeochemical signatures in two seasonal conditions. The environmental parameters, particulate organic carbon and nitrogen together with heterotrophic production were also measured. Results showed significant increases for most of the studied parameters with increasing temperature during summer. This had effects on the Carbon cycle and recycling of nutrients; in fact total prokaryotic abundance and biomass, as well as carbon hydrolyzed by two enzymes (Leucine aminopeptidase and β-glucosidase), increased significantly during summer. Conversely Alkaline phosphatase activity, Chlorophyll concentration and Oxygen increased during winter. The same environmental parameters affected also the presence of fish eggs. Moreover high percentages of free enzymes (i.e., enzymes not associated with cells) were measured, accounting for percentages variable from 12 to 95 % of the total enzymatic activity, with values generally higher in summer than in winter. In this oligotrophic environment, the prokaryotic biomass was supported by the C hydrolyzed by enzymatic activities. The ratio between the hydrolyzed C and prokaryotic biomass was higher in winter than in summer, indicating that alkaline phosphatase activity contribute to an efficient incorporation of C into biomass in winter. Copyright © 2015 Elsevier Ltd. All rights reserved.

Coupling of the spatial-temporal distributions of nutrients and physical conditions in the southern Yellow Sea

NASA Astrophysics Data System (ADS)

Wei, Qin-Sheng; Yu, Zhi-Gang; Wang, Bao-Dong; Fu, Ming-Zhu; Xia, Chang-Shui; Liu, Lu; Ge, Ren-Feng; Wang, Hui-Wu; Zhan, Run

2016-04-01

This study investigated the coupling of the spatial-temporal variations in nutrient distributions and physical conditions in the southern Yellow Sea (SYS) using data compiled from annual-cycle surveys conducted in 2006-2007 as well as satellite-derived sea-surface temperature (SST) images. The influence of physical dynamics on the distribution and transport of nutrients varied spatially and seasonally in the SYS. The Changjiang Diluted Water (CDW) plume (in summertime), the Subei Coastal Water (SCW) (year-round), and the Lubei Coastal Current (LCC) (in wintertime) served as important sources of nutrients in the inshore area in a dynamic environment. The saline Taiwan Warm Current (TWC) might transport nutrients to the northeast region of the Changjiang Estuary in the summer, and this nutrient source began to increase from spring to summer and decrease when autumn arrived. Three types of nutrient fronts, i.e., estuarine, offshore, and coastal, were identified. A circular nutrient front caused by cross-shelf transport of SCW in the southeast shelf bank area in the winter and spring was observed. The southeastward flow of western coastal cold water in the SYS might be an important conduit for cross-shelf nutrient exchange between the SYS and the East China Sea (ECS). The tongue-shaped low-nutrient region in the western study area in the wintertime was driven by the interaction of the southward Yellow Sea Western Coastal Current (YSWCC) and the biological activity. The vertically variable SCM (subsurface Chl-a maximum) in the central SYS was controlled by coupled physical-chemical processes that involved stratification and associated nutricline. The average nutrient fluxes into the euphotic zone due to upwelling near the frontal zone of the Yellow Sea Cold Water Mass (YSCWM) in the summer are estimated here for the first time: 1.4 ± 0.9 × 103 μmol/m2/d, 0.1 ± 0.1 × 103 μmol/m2/d, and 2.0 ± 1.3 × 103 μmol/m2/d for DIN, PO4-P, and SiO3-Si, respectively. The depletion of nutrients in the central SYS and the upwelled transport in the boundary of the YSCWM resulted in a spatial transfer of the high Chl-a zone, varying generally from the central SYS to the boundary of the YSCWM from spring to summer, and the nutrient flux associated with this upwelling could contribute significantly to local primary production. This study deepens our understanding of the mechanisms influencing the distribution and transport of nutrients in the SYS.

The flux of bio- and lithogenic material associated with sinking particles in the mesopelagic “twilight zone” of the northwest and North Central Pacific Ocean

NASA Astrophysics Data System (ADS)

Lamborg, C. H.; Buesseler, K. O.; Valdes, J.; Bertrand, C. H.; Bidigare, R.; Manganini, S.; Pike, S.; Steinberg, D.; Trull, T.; Wilson, S.

2008-07-01

As part of the VERTIGO program, we collected and analyzed sinking particles using tethered and neutrally buoyant sediment traps at three depths in the oceanic mesopelagic zone and at two biogeochemically contrasting sites (N. Central Pacific at ALOHA; N. Pacific Western Subarctic Gyre at K2). This effort represented the first large-scale use of neutrally buoyant traps and represents a significant step forward in the study of the marine biological pump. In this paper, we present the results of mass, macronutrient, biominerals and phytoplankton pigment determinations made on these samples. The impact of a variety of potential collection biases were examined, including those from in-trap particle degradation, zooplankton swimmers and poisons. Though these factors have been observed to affect results in other programs, we found them to have relatively little impact on measured fluxes in this study. There was evidence, however, that the neutrally buoyant traps performed better than the tethered traps in terms of flux accuracy during one deployment, possibly because of improved large particle collection efficiency. Fluxes of material exhibited three different patterns through the mesopelagic: increasing, decreasing and constant with depth. Decreasing fluxes with depth were observed for all biogenic material formed in the euphotic zone. The attenuation of flux with depth was not the same for all components, however, with phytoplankton pigments exhibiting the greatest degradation with depth and particulate inorganic carbon the least. Organic carbon and nitrogen showed a very high correlation in these samples, with little evidence of different attenuation length scales. Increasing fluxes with depth were observed for particulate Ba at both sites and Al at K2. The increases in Ba are attributed to the formation of barite in degrading particles, while increasing Al at K2 was the result of lateral inputs from a continental shelf/slope. Constant fluxes with depth were observed for Al at ALOHA, where fluxes appeared to be in steady state with atmospheric dust deposition. The mesopelagic zone at K2 was observed to attenuate particle flux less than at ALOHA, and with a higher POC/PIC ("rain") ratio. These two factors combine to imply that the Subarctic province had a much more efficient biological pump than had the subtropical gyre during our occupations. This could be the result of either faster sinking particles, generated from grazing by large zooplankton, or inherently slower particle degradation rates.

Temporal patterns of phytoplankton abundance in the North Atlantic

NASA Technical Reports Server (NTRS)

Campbell, Janet W.

1989-01-01

A time series of CZCS images is being developed to study phytoplankton distribution patterns in the North Atlantic. The goal of this study is to observe temporal variability in phytoplankton pigments and other organic particulates, and to infer from these patterns the potential flux of biogenic materials from the euphotic layer to the deep ocean. Early results of this project are presented in this paper. Specifically, the satellite data used were 13 monthly composited images of CZCS data for the North Atlantic from January 1979 to January 1980. Results are presented for seasonal patterns along the 20 deg W meridian.

Biological oceanography of the red oceanic system

NASA Astrophysics Data System (ADS)

Theil, Hjalmar; Weikert, Horst

1. In 1977, 1979 and 1980-81, investigations were carried out which aimed at evaluating the potential risks from mining metalliferous muds precipating in the Atlantis II Deep of the central Red Sea. This environmental research was initiated by the Saudi Sudanese Red Sea Joint Commission in order to avoid any danger for the Red Sea ecosystem. The broad environmental research programme coherent studies in physical, chemical, biological, and geological oceanography as well as toxicological investigations in the oceanic and in reef zones. We summarise the results from our biological fiels studies in the open sea. 2. The biological investigations were concentrated on the area of the Atlantis II Deep. Benthos was sampled between 700-2000m. For comparison a few samples were also taken further north in the central Red Sea, and to east and west along the flanking deep terraces (500-1000m). Plankton studies covered the total water column above the Deep, and were extended along the axial through to north and south. 3. Benthos sampling was carried out using a heavy closing trawl, a large box grab (box size 50 × 50 cm), Van Veen grabs and traps; photographic surveys were made a phototrap and a photosled. Community respiration was measured with a ship-board method using grab subsamples. Nutrient concentrations, seston and phytoplankton standing stocks as well as in situ primary production were determined from hydrocast samples. Data on zooplankton and micronekton composition and standing stock were obtained from samples collected using different multiple opening-and-closing nets equipped with 100 μm, 300 μm, and 1000 μm mesh sizes. Daily and ontogenetical vertical migration patterns were studied by comparisons of data from midday and midnight tows. 4. Throughout the whole area the sediment is a pteropod ooze containing low contentrations of organic matter; measured organic carbon and nitrogen contents were 0.5 and 0.05% respectively, and chloroplastic pigment equivalents (chlorophyll and degradation products) were mostly at the lower limit of determination with up to 1.2 ng·cm -. Similarly the faunal components were rare. Meiofauna occured at abundances of up to 600 specimens·10 cm -2 (<0.3mg ash free dry weight · 10 cm -2), and macrofauna with up to 960 specimens · m -2. Photosled surveys showed low densities of megafauna of up to 20 specimens ·100m -2 (Thiel, 1979, 1981). The number of species is low compared with other regions, but some species seem to penetrate into greater depths in the Red Sea than in the Indian Ocean, possibly because of the high temperature of the Red Sea deep water. It reveals an interesting adaptation by these species to life in this low energy ecosystem (Thiel, 1979, 1980, in press; Klausewitz and Thiel, 1982). 5. Phytoplankton production was low in the euphotic zone overlying the Atlantis II Deep area and did not exceed 100 mg C · m -2 d -2 most of the year. Similarly, the levels of the standing stocks of seston, phytoplankton and zooplankton were typical of oligotrophic conditions. For all three categories, the average standing stocks were lowest in autum, but the maxima for each occured in different seasons. The seston stock was greatest in spring (March) amounting to 90 g dry weight · m -2 in the upper 75m higher by a factor of 2 than in autum. The phytoplankton stock was greatest in spring, and at the biggining of summer (June) when it reached about 17 mg chl a · m -2 in the euphotic zone, about 1.6 times the minimum autumn level. The zooplankton stock was greatest in winter (February) when it attained 15 g wet weight · m -2 or 51,000 individuals · m -2 in the total 1850m water colunm, values which were a factor of 3 and 1.6 higher respectively than in autum (Weikert, 1980a, 1981). The zooplankton stock which is poor in species exhibits a conspicuous planktocline below 100m, which roughly corresponds to the bottom of the euphotic zone. In winter, the planktocline shifts some tens of metres towards the sea surface. A secondary zooplankton maximum which overlaps with the deep scattering layer, is situated between 300-600m, and is confined to the oxygen minimum layer (Weikert, 1980a,b). Below about 1100m, the planktonic standing crop is extremely low, for example at about 1450m the abundance of the 300 μm net plankton was <0.1 mg wet weight · 100 m -3 with only 0.4 specimens · 100 m -3. The profiles of zooplankton abundance and biomass are paralled by the profile of diversity which is greatly reduced in the subsurface zooplankton communities. These findings were repeated both from different seasons and from other sites along the deep graben (Weikert, 1980a: Beckmann, 1984); all together they depict an extreme example of the peculiar bathymetric distribution of zooplankton typical of other partially land-locked seas (Weikert, 1982). No diel vertical migrations were observed below 1100m. All organic matter must be transported to greater depths and to the bottom in the form of sinking particles. However, the quantities of organic material which sink to such depths will be small, because decomposition rates can be expected much higher than normal because of the high uniform temperatures (21.6°C) of the deep water (Weikert, 1982). 6. Respiration measurements and the determinations of electron transport system activity were conducted on small, undisturbed sediment samples. The data can be evaluated by comparison with results obtained from the Arctic and the Atlantic Oceans employing exactly the same methods. In the Red Sea, respiration and ETS activity were found to be high but standing stocks and biomasses were low; the reverse was observed in the Arctic and the Atlantic. We believe that this difference in the ratio of respiration to biomass is determined by the great contrasts in the temperatures of the environments studied: Arctic -1.5°C, Atlantic 2°C, Red Sea 21.5°C. Independent of the species' adaptations to their environment this temperature influence will apply to all the living components of the ecosystem. Hence for Red Sea organisms maintenance costs are comparatively high, which greatly reduces their production potential. 7. Thus the oceanic ecosystem of the Red Sea can be summarised as follows: Primary production is low throughout most of the year and throughout most of the entire basin, and consequently so is secondary production (zooplankton). In subsurface waters, high maintenance costs reduces energy for investments in growth and reproduction. In addition degradation of organic matter is so fast in the upper layers that the standing stock in the intermediate layers is reduced and particle transport to greater depth in the central graben greatly restricted. The low abundance and biomass of the deep-sea plankton and benthos in the Red Sea is readily explained by the low availability of food and the high metabolic demands created by the unique high in situ temperature.

Interannual variability in phytoplankton blooms observed in the northwestern Arabian Sea during the southwest monsoon

NASA Technical Reports Server (NTRS)

Brock, John C.; Mcclain, Charles R.

1992-01-01

Interannual changes in the strength and seasonal evolution of the 1979 through 1982 surface-level southwest monsoon winds are related to variations in the summer phytoplankton bloom of the northwestern Arabian Sea by synthesis of satellite ocean-color remote sensing with analysis of in-situ hydrographic and meteorological data sets. The 1979-1981 southwest monsoon phytoplankton blooms in the northwest Arabian Sea peaked during August-September, extended from the Omani coast to about 6 E, and appeared to lag the development of open-sea upwelling by at least 1 month. In all 3 years the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore Ekman pumping. Coastal upwelling was evident from May through September, yielded the most extreme concentrations of phytoplankton biomass, and along the Omani coast was limited in its impact on upper ocean biological variability to the continental shelf. Ekman pumping stimulated the development of a broad open-ocean component of the southwest monsoon phytoplankton bloom oceanward of the Omani shelf. Phytoplankton biomass on the Omani continental shelf was increased during both the early and late phases of the 1980 southwest monsoon due to stronger coastal upwelling under the most intense southwesterly winds of the four summers investigated. Diminished coastal upwelling during the early phase of the weak 1982 southwest monsoon resulted in a coastal bloom that reached a mean phytoplankton-pigment concentration that was 28 percent of that seen in 1980. The lack of a strong regional northwestern Arabian Sea bloom in late summer 1982 is attributed to the development of persistent, shallow temperature stratification that rendered Ekman pumping less effective in driving upward nutrient fluxes.

The structure of phytoplankton communities in the eastern part of the Laptev Sea

NASA Astrophysics Data System (ADS)

Sukhanova, I. N.; Flint, M. V.; Georgieva, E. Ju.; Lange, E. K.; Kravchishina, M. D.; Demidov, A. B.; Nedospasov, A. A.; Polukhin, A. A.

2017-01-01

Studies have been performed on a transect along 130°30' E from the Lena River delta (71°60' N) to the continental slope and adjacent deepwater area (78°22' N) of the Laptev Sea in September 2015. The structure of phytoplankton communities has distinct latitudinal zoning. The southern part of the shelf (southward of 73°10' N), the most desalinated by riverine discharge, houses a phytoplankton community with a biomass of 175-840 mg/m2, domination of freshwater Aulacoseira diatoms, and significant contribution of green algae (both in abundance and biomass). The northern border for the distribution range of the southern complex of phytoplankton species lies between the 8 and 18 psu isohalines ( 73°10' N). The continental slope and deepwater areas of the Laptev Sea (north of 77°30' N), with a salinity of >27 psu in the upper mixed layer, are populated by the community prevalently composed of Chaetoceros and Rhizosolenia diatoms, very abundant in the Arctic, and dinoflagellates. The phytoplankton number in this area fall in the range of 430-1100 × 106 cell/m2, and the biomass, in the range of 3600 mg/m2. A moderate desalinating impact of the Lena River discharge is observed in the outer shelf area between 73°20' and 77°30' N; the salinity in the upper mixed layer is 18-24 psu. The phytocenosis in this area has a mosaic spatial structure with between-station variation in the shares of different alga groups in the community, cell number of 117-1200 × 106 cells/m2, and a biomass of 1600-3600 mg/m2. As is shown, local inflow of "fresh" nutrients to the euphotic layer in the fall season leads to mass growth of diatoms.

Peruvian upwelling plankton respiration: calculations of carbon flux, nutrient retention efficiency, and heterotrophic energy production

NASA Astrophysics Data System (ADS)

Packard, T. T.; Osma, N.; Fernández-Urruzola, I.; Codispoti, L. A.; Christensen, J. P.; Gómez, M.

2015-05-01

Oceanic depth profiles of plankton respiration are described by a power function, RCO2 = (RCO2)0 (z/z0)b, similar to the vertical carbon flux profile. Furthermore, because both ocean processes are closely related, conceptually and mathematically, each can be calculated from the other. The exponent b, always negative, defines the maximum curvature of the respiration-depth profile and controls the carbon flux. When |b| is large, the carbon flux (FC) from the epipelagic ocean is low and the nutrient retention efficiency (NRE) is high, allowing these waters to maintain high productivity. The opposite occurs when |b| is small. This means that the attenuation of respiration in ocean water columns is critical in understanding and predicting both vertical FC as well as the capacity of epipelagic ecosystems to retain their nutrients. The ratio of seawater RCO2 to incoming FC is the NRE, a new metric that represents nutrient regeneration in a seawater layer in reference to the nutrients introduced into that layer via FC. A depth profile of FC is the integral of water column respiration. This relationship facilitates calculating ocean sections of FC from water column respiration. In an FC section and in a NRE section across the Peruvian upwelling system we found an FC maximum and a NRE minimum extending down to 400 m, 50 km off the Peruvian coast over the upper part of the continental slope. Finally, considering the coupling between respiratory electron transport system activity and heterotrophic oxidative phosphorylation promoted the calculation of an ocean section of heterotrophic energy production (HEP). It ranged from 250 to 500 J d-1 m-3 in the euphotic zone to less than 5 J d-1 m-3 below 200 m on this ocean section.

Are the spring and fall blooms on the Scotian Shelf related to short-term physical events?

NASA Astrophysics Data System (ADS)

Greenan, B. J. W.; Petrie, B. D.; Harrison, W. G.; Oakey, N. S.

2004-03-01

Physical, chemical and biological data from the Scotian Shelf indicate that short-term physical events affect the dynamics of spring and fall blooms. This is based on results from a three-week mooring deployment measuring currents, temperature, salinity and fluorescence in October 2000, combined with biweekly sampling of temperature, salinity, nutrients and chlorophyll throughout the year at this mooring site. A wind-driven upwelling event in mid-October shows temperature, salinity and density iso-surfaces rising by approximately 20 m. During this event, a bloom with peak chlorophyll concentrations of about 2.5 mg m -3 began as nutrients are brought into the upper part of the water column. Gradient Richardson Numbers ( Ri), a proxy for vertical mixing, are estimated for the mooring period in 2 m vertical bins using SeaHorse CTD data and nearby ADCP current measurements. These data indicate that vertical mixing may have played a complementary role to the upwelling in bringing nutrients into the euphotic zone. A trend of decreasing Ri in the ocean mixed layer with increasing surface wind stress is suggested. It appears that this short-term physical event is a primary factor in initiating the fall bloom on the inner Scotian Shelf in 2000. In April of that year, the termination of the spring bloom coincided with a downwelling event suggesting that it played a role in determining the duration of the bloom. SeaWiFS ocean color satellite provided a spatial context for chlorophyll observations, however, the lack of temporal resolution due to poor atmospheric conditions means that these data provide limited information on short-term chlorophyll variability.

Fronts and eddies: Engines for biogeochemical variability of the Central Red Sea during winter-spring periods

NASA Astrophysics Data System (ADS)

Zarokanellos, Nikolaos; Jones, Burton

2017-04-01

The central Red Sea (CRS) has been shown to be characterized by significant eddy activity throughout the year. In winter, weakened stratification may lead to enhanced vertical exchange contributing to physical and biogeochemical processes. In winter 2014-2015 we began an extended glider time series to monitor a region in the northern CRS where eddy activity is significant. Remote sensing and glider observations that include CTD, oxygen, CDOM and chlorophyll fluorescence, and multi-wavelength optical backscatter, have been used to characterize the effects of winter mixing and eddy activity in this region. During winter, deep mixing driven by surface cooling and strong winds combined with eddy features, can supply nutrients into the upper layer dramatically modifies the environment from its typically stratified conditions. These mixing events disperse the phytoplankton from the deep chlorophyll maximum throughout the upper mixed layer, and increase the chlorophyll signature detected by ocean color imagery. In addition to the mixing, cyclonic eddies in the region can enhance the vertical displacement of deeper, nutrient containing water toward the euphotic zone contributing to increased chlorophyll concentration and biological productivity. Remote sensing analyses indicate that these eddies also contribute to significant horizontal dispersion including the exchange between the open sea and coastal coral reef ecosystems. During the winter mixing periods, diel fluctuations in phytoplankton biomass have been observed indicative of solar driven plankton dynamics. The biogeochemical response to the subsurface physical processes provides a sensitive indicator to the processes that result from the mixing and eddy dynamics - processes that are not necessarily detectable via remote sensing. In order to understand the seasonal responses, but also the interannual influences on these processes, sustained in situ autonomous platform measurements are essential.

Biogeochemistry of Recently Discovered Oxygen-Depleted Mesoscale Eddies in the Open Eastern Tropical North Atlantic

NASA Astrophysics Data System (ADS)

Fiedler, B.; Grundle, D.; Löscher, C. R.; Schütte, F.; Hauss, H.; Karstensen, J.; Silva, P.; Koertzinger, A.

2016-02-01

Severely oxygen-depleted mesoscale features in the open eastern tropical North Atlantic, which are formed in the Mauritanian upwelling region, were discovered only recently. So far, few remote surveys conducted with autonomous platforms such as moorings, underwater gliders and profiling floats have provided a very first insight into these mesoscale eddies. Due to their hydrographic properties such water bodies are well isolated from ambient waters and therefore can develop severe near-surface oxygen deficits. In this presentation we show results from the first-ever biogeochemical survey of one of these anticyclonic mode-water eddies conducted in spring 2014 at the Cape Verde Ocean Observatory (CVOO) off West Africa. Very low oxygen concentrations of 4.5 µmol kg-1 associated with a CO2 partial pressure of 1164 µatm were found close to the core of the eddy (at 100 m depth). Measurements for nitrate and phosphate also show exceptional high values. Findings point to rapid oxygen consumption through remineralization of organic matter along with depressed lateral mixing of this water body. Indeed, rates for oxygen utilization (OUR) were found to be enhanced when compared to known values in the Atlantic. A closer look into the carbonate system inside the eddýs core revealed disadvantageous conditions for calcifying organisms with the pH dropping down to 7.6 and the Aragonite saturation level reaching 1 at the lower boundary of the euphotic zone. Finally, strong indications for a shift in nitrogen cycling in the core of the eddy from nitrification towards denitrification were found based on gene abundance and N2O-isotope analyses. To our knowledge such severe hypoxic and even suboxic near-surface conditions along with active denitrification have never been reported before in the open Atlantic Ocean.

Ocean time-series reveals recurring seasonal patterns of virioplankton dynamics in the northwestern Sargasso Sea.

PubMed

Parsons, Rachel J; Breitbart, Mya; Lomas, Michael W; Carlson, Craig A

2012-02-01

There are an estimated 10(30) virioplankton in the world oceans, the majority of which are phages (viruses that infect bacteria). Marine phages encompass enormous genetic diversity, affect biogeochemical cycling of elements, and partially control aspects of prokaryotic production and diversity. Despite their importance, there is a paucity of data describing virioplankton distributions over time and depth in oceanic systems. A decade of high-resolution time-series data collected from the upper 300 m in the northwestern Sargasso Sea revealed recurring temporal and vertical patterns of virioplankton abundance in unprecedented detail. An annual virioplankton maximum developed between 60 and 100 m during periods of summer stratification and eroded during winter convective mixing. The timing and vertical positioning of this seasonal pattern was related to variability in water column stability and the dynamics of specific picophytoplankton and heterotrophic bacterioplankton lineages. Between 60 and 100 m, virioplankton abundance was negatively correlated to the dominant heterotrophic bacterioplankton lineage SAR11, as well as the less abundant picophytoplankton, Synechococcus. In contrast, virioplankton abundance was positively correlated to the dominant picophytoplankton lineage Prochlorococcus, and the less abundant alpha-proteobacteria, Rhodobacteraceae. Seasonally, virioplankton abundances were highly synchronous with Prochlorococcus distributions and the virioplankton to Prochlorococcus ratio remained remarkably constant during periods of water column stratification. The data suggest that a significant fraction of viruses in the mid-euphotic zone of the subtropical gyres may be cyanophages and patterns in their abundance are largely determined by Prochlorococcus dynamics in response to water column stability. This high-resolution, decadal survey of virioplankton abundance provides insight into the possible controls of virioplankton dynamics in the open ocean.

A shift in the biogenic silica of sediment in the Larsen B continental shelf, off the Eastern Antarctic Peninsula, resulting from climate change.

PubMed

Sañé, Elisabet; Isla, Enrique; Bárcena, María Ángeles; DeMaster, David J

2013-01-01

In 2002, section B of the Larsen ice shelf, off of the Eastern Antarctic Peninsula, collapsed and created the opportunity to study whether the changes at the sea surface left evidence in the sedimentary record. Biogenic silica is major constituent of Antarctic marine sediment, and its presence in the sediment column is associated with diatom production in the euphotic zone. The abundance of diatom valves and the number of sponge spicules in the biogenic silica was analyzed to determine how the origin of the biogenic silica in the upper layers of the sediment column responded to recent environmental changes. Diatom valves were present only in the upper 2 cm of sediment, which roughly corresponds to the period after the collapse of the ice shelf. In contrast, sponge spicules, a more robust form of biogenic silica, were also found below the upper 2 cm layer of the sediment column. Our results indicate that in this region most of the biogenic silica in the sedimentary record originated from sponge spicules rather than diatoms during the time when the sea surface was covered by the Larsen ice shelf. Since the collapse of the ice shelf, the development of phytoplankton blooms and the consequent influx of diatom debris to the seabed have shifted the biogenic silica record to one dominated by diatom debris, as occurs in most of the Antarctic marine sediment. This shift provides further evidence of the anthropogenic changes to the benthic habitats of the Antarctic and will improve the interpretation of the sedimentary record in Polar Regions where these events occur.

New Chemical, Bio-Optical and Physical Observations of Upper Ocean Response to the Passage of a Mesoscale Eddy off Bermuda

NASA Technical Reports Server (NTRS)

McNeil, J. D.; Jannasch, H. W.; Dickey, T.; McGillicuddy, D.; Brzekinski, M.; Sakamoto, C. M.

1999-01-01

A mesoscale eddy advected across the Bermuda Testbed Mooring site over a 30-day period centered on July 14, 1995. Temperature and current measurements along with biogeochemical measurements were used to characterize the biological response of the upper ocean associated with the introduction of nitrate into the euphoric layer due to the doming of isotherms associated with the eddy. Complementary shipboard data showed an anomalous water mass, which extended from a depth of approximately 50 to 1000 m, manifesting as a cold surface expression and warm anomaly at depth. Although mesoscale eddies are frequently observed in the Sargasso Sea, the present observations are particularly unique because of the high-temporal-resolution measurements of the new instrumentation deployed on the mooring. Analyzers that measure nitrate plus nitrite were placed at depths of 80 and 200 m and bio-optical sensors were located at depths of 20, 35, 45, 71, and 86 m. Peak nitrate values of nearly 3.0 microns at 80 m and chlorophyll alpha values of 1.4 mg/cu m at 71 m were observed, as well as a 25- to 30-meter shoaling of the 1% light level depth. A Doppler shift from the inertial period (22.8 hours) to 25.2 hours was observed in several time series records due to the movement of the eddy across the mooring. Inertial pumping brought cold, nutrient-rich waters farther into the euphotic zone than would occur solely by isothermal lifting. Silicic acid was depleted to undetectable levels owing to the growth of diatoms within the eddy. The chlorophyll alpha values associated with the eddy appear to be the largest recorded during the 8 years of the ongoing U.S. JGOFS Bermuda Atlantic Time Series Study (BATS) program.

Picophytoplankton variability: Influence of winter convective mixing and advection in the northeastern Arabian Sea

NASA Astrophysics Data System (ADS)

Bemal, Suchandan; Anil, Arga Chandrashekar; Shankar, D.; Remya, R.; Roy, Rajdeep

2018-04-01

The deepening of mixed layer and ensuing changes in optical and physicochemical properties of euphotic zone can influence phytoplankton community dynamics in the northeastern Arabian Sea during winter monsoon. The response of picophytoplankton community to such changes during winter convective mixing is not well understood. Herein, we have compared variations in the picophytoplankton community structure during early (November-December 2012), peak (end-January 2014) and late (mid-February 2015) winter monsoon from three separate cruises in the southern northeastern Arabian Sea. The higher Synechococcus abundance owing to entrainment of nutrients in mixed layer was observed during peak winter monsoon, while the concomitant changes in nitrate concentration, light and oxygen environment restricted Prochlorococcus growth resulting in lower abundance during the same period. This highlights the diverse responses of picophytoplankton groups to physicochemical changes of water column during winter convective mixing. The divinyl chlorophyll b/a ratio (marker for Prochlorococcus ecotypes) indicated prevalence of one low-light adapted ecotype (sensitive to light shock) in sub-surface water, one high-light adapted ecotype in surface water during early winter monsoon and both disappeared during intense mixing period in peak winter monsoon. Subsequently, a distinct low-light adapted ecotype, capable to tolerate light shock, was noticed during late winter monsoon and we argue that this ecotype is introduced to southern northeastern Arabian Sea through advection from north by sub-surface circulation. The total picophytoplankton biomass available to microbial loop is restored during late winter monsoon, when stratification begins, with a higher abundance of Synechococcus and the re-occurrence of Prochlorococcus population in the region. These inferences indicate that variability in picophytoplankton community structure and their contribution to the microbial loop are driven by convective mixing and advection, which in turn influence ecosystem functioning and trophodynamics of the southern northeastern Arabian Sea.

Phytoplankton Functional Diversity and New Production during Spring and Summer Blooms in the Subarctic Atlantic Ocean

NASA Astrophysics Data System (ADS)

Van Oostende, N.; Fawcett, S. E.; Ji, Q.; Marconi, D.; Lueders-Dumont, J.; Sigman, D. M.; Ward, B. B.

2016-02-01

In the subarctic Atlantic Ocean, strong seasonal cycles in heat flux drive water column stratification, which governs the supply of nutrients to the euphotic zone that fuels the biological pump. The export efficiency of this pump is largely determined by the degree of phytoplankton nitrate (NO3-) assimilation and phytoplankton community size structure. We investigated nitrogen assimilation and phytoplankton community diversity and size structure on spring and summer cruises to 50-60°N, by using a combination of stable isotope tracer incubations, flow cytometry, microscopy, size-fractionated algal pigments, and nitrogen stable isotope measurements. As expected in springtime, the phytoplankton community was dominated by large (>20 µm) cells while in late summer these constituted only a minor fraction of the assemblage. The weaker density stratification of the water column in the spring compared to the summer allowed for surface nutrient concentrations that were not limiting phytoplankton growth (e.g., [NO3-] >5 µM). Despite stronger water column stratification in the summer, partial consumption of subsurface NO3-, which had recently been supplied to surface waters, allowed for total chlorophyll and particulate nitrogen (PN) to attain similar levels during both seasons. High 15N/14N of NO3- and PN in surface waters is consistent with NO3- utilization. In springtime, however, the phytoplankton community consumed NO3- at PN-normalized rates up to fivefold higher than in summer, despite having comparable uptake rates for ammonium and inorganic carbon. This observation implies that the large phytoplankton species that are abundant in spring, mostly diatoms, contribute disproportionally more to new production than summer phytoplankton communities that are devoid of these large species.

Carbon associated nitrate (CAN) in the Ediacaran Johnnie Formation, Death Valley, California and links to the Shuram negative carbon isotope excursion

NASA Astrophysics Data System (ADS)

Dilles, Z. Y. G.; Prokopenko, M. G.; Bergmann, K.; Loyd, S. J.; Corsetti, F. A.; Berelson, W.; Gaines, R. R.

2014-12-01

Nitrogen, a major nutrient of marine primary production whose many redox states are linked through biological processes to O2, may afford better understanding of changes in post-Great Oxidation Event (GOE) environmental redox conditions. Using a novel approach to quantify nitrate content in carbonates, we identified a trend of CAN increase in the late-Proterozoic, including several distinct peaks within a carbonate succession of the Sonora province, Mexico, deposited ~630-500 Ma. The goal of the current study was to investigate CAN variability in the context of the global "Shuram" event, a large negative δ13C excursion expressed in Rainstorm member carbonates of the Johnnie Formation in Death Valley, CA. The lower Rainstorm Member "Johnnie Oolite", a time-transgressive, regionally extensive, shallow dolomitic oolite, was sampled. CAN concentrations ranged from 7.31 to 127.36 nmol/g, with higher values measured toward the base of the bed. This trend held at each sampled locality, along with a tendency towards decreasing CAN with larger magnitude negative δ13C excursions. Modern analog ooids formed in low-latitude marine environments lack CAN, consistent with their formation in low-nitrate waters of the euphotic zone characteristic of the modern ocean nitrogen cycling. In contrast, maximum values within the Johnnie oolite exceed by a factor of five to seven CAN measured in carbonates deposited below the main nitracline in the modern ocean, implying high nitrate content within shallow depositional environments. Johnnie oolite data, broadly consistent with the Sonora sequence findings, may indicate large perturbations in the Ediacaran nitrogen cycle immediately preceding the negative δ13C excursion. The implication of these findings for possible changes in the Ediacaran nitrogen, oxygen and carbon biogeochemical cycling will be further discussed.

Contrasting Impact of Future CO2 Emission Scenarios on the Extent of CaCO3 Mineral Undersaturation in the Humboldt Current System

NASA Astrophysics Data System (ADS)

Franco, A. C.; Gruber, N.; Frölicher, T. L.; Kropuenske Artman, L.

2018-03-01

The eastern boundary upwelling systems are among those regions that are most vulnerable to an ocean acidification-induced transition toward undersaturated conditions with respect to mineral CaCO3, but no assessment exists yet for the Humboldt Current System. Here we use a high-resolution (˜7.5 km) regional ocean model to investigate past and future changes in ocean pH and CaCO3 saturation state in this system. We find that within the next few decades, the nearshore waters off Peru are projected to become corrosive year round with regard to aragonite, the more soluble form of CaCO3. The volume of aragonite undersaturated water off Peru will continue to increase in the future irrespective of the amount of CO2 emitted to the atmosphere. In contrast, the development of the saturation state with regard to calcite, a less soluble form of carbonate, depends strongly on the scenario followed. By 2050, calcite undersaturation appears in the nearshore waters off Peru occasionally, but by 2090 in a high-emission scenario (RCP8.5), ˜60% of the water in the euphotic zone will become permanently calcite undersaturated. Most of this calcite undersaturation off Peru can likely be avoided if a low emission scenario (RCP2.6) consistent with the Paris Agreement is followed. The progression of ocean acidification off Chile follows a similar pattern, except that the saturation states are overall higher. But also here, calcite undersaturated waters will become common in the subsurface waters under the RCP8.5 scenario by the end of this century, while this can be avoided under the RCP2.6 scenario.

Insights on multivariate updates of physical and biogeochemical ocean variables using an Ensemble Kalman Filter and an idealized model of upwelling

NASA Astrophysics Data System (ADS)

Yu, Liuqian; Fennel, Katja; Bertino, Laurent; Gharamti, Mohamad El; Thompson, Keith R.

2018-06-01

Effective data assimilation methods for incorporating observations into marine biogeochemical models are required to improve hindcasts, nowcasts and forecasts of the ocean's biogeochemical state. Recent assimilation efforts have shown that updating model physics alone can degrade biogeochemical fields while only updating biogeochemical variables may not improve a model's predictive skill when the physical fields are inaccurate. Here we systematically investigate whether multivariate updates of physical and biogeochemical model states are superior to only updating either physical or biogeochemical variables. We conducted a series of twin experiments in an idealized ocean channel that experiences wind-driven upwelling. The forecast model was forced with biased wind stress and perturbed biogeochemical model parameters compared to the model run representing the "truth". Taking advantage of the multivariate nature of the deterministic Ensemble Kalman Filter (DEnKF), we assimilated different combinations of synthetic physical (sea surface height, sea surface temperature and temperature profiles) and biogeochemical (surface chlorophyll and nitrate profiles) observations. We show that when biogeochemical and physical properties are highly correlated (e.g., thermocline and nutricline), multivariate updates of both are essential for improving model skill and can be accomplished by assimilating either physical (e.g., temperature profiles) or biogeochemical (e.g., nutrient profiles) observations. In our idealized domain, the improvement is largely due to a better representation of nutrient upwelling, which results in a more accurate nutrient input into the euphotic zone. In contrast, assimilating surface chlorophyll improves the model state only slightly, because surface chlorophyll contains little information about the vertical density structure. We also show that a degradation of the correlation between observed subsurface temperature and nutrient fields, which has been an issue in several previous assimilation studies, can be reduced by multivariate updates of physical and biogeochemical fields.

Nitrogen fixation in denitrified marine waters.

PubMed

Fernandez, Camila; Farías, Laura; Ulloa, Osvaldo

2011-01-01

Nitrogen fixation is an essential process that biologically transforms atmospheric dinitrogen gas to ammonia, therefore compensating for nitrogen losses occurring via denitrification and anammox. Currently, inputs and losses of nitrogen to the ocean resulting from these processes are thought to be spatially separated: nitrogen fixation takes place primarily in open ocean environments (mainly through diazotrophic cyanobacteria), whereas nitrogen losses occur in oxygen-depleted intermediate waters and sediments (mostly via denitrifying and anammox bacteria). Here we report on rates of nitrogen fixation obtained during two oceanographic cruises in 2005 and 2007 in the eastern tropical South Pacific (ETSP), a region characterized by the presence of coastal upwelling and a major permanent oxygen minimum zone (OMZ). Our results show significant rates of nitrogen fixation in the water column; however, integrated rates from the surface down to 120 m varied by ∼30 fold between cruises (7.5±4.6 versus 190±82.3 µmol m(-2) d(-1)). Moreover, rates were measured down to 400 m depth in 2007, indicating that the contribution to the integrated rates of the subsurface oxygen-deficient layer was ∼5 times higher (574±294 µmol m(-2) d(-1)) than the oxic euphotic layer (48±68 µmol m(-2) d(-1)). Concurrent molecular measurements detected the dinitrogenase reductase gene nifH in surface and subsurface waters. Phylogenetic analysis of the nifH sequences showed the presence of a diverse diazotrophic community at the time of the highest measured nitrogen fixation rates. Our results thus demonstrate the occurrence of nitrogen fixation in nutrient-rich coastal upwelling systems and, importantly, within the underlying OMZ. They also suggest that nitrogen fixation is a widespread process that can sporadically provide a supplementary source of fixed nitrogen in these regions.

Physical and Biogeochemical Controls of the Phytoplankton Blooms in North Western Mediterranean Sea: A Multiplatform Approach Over a Complete Annual Cycle (2012-2013 DEWEX Experiment)

NASA Astrophysics Data System (ADS)

Mayot, Nicolas; D'Ortenzio, Fabrizio; Taillandier, Vincent; Prieur, Louis; de Fommervault, Orens Pasqueron; Claustre, Hervé; Bosse, Anthony; Testor, Pierre; Conan, Pascal

2017-12-01

The North Western Mediterranean Sea exhibits recurrent and significant autumnal and spring phytoplankton blooms. The existence of these two blooms coincides with typical temperate dynamics. To determine the potential control of physical and biogeochemical factors on these phytoplankton blooms, data from a multiplatform approach (combining ships, Argo and BGC-Argo floats, and bio-optical gliders) were analyzed in association with satellite observations in 2012-2013. The satellite framework allowed a simultaneous analysis over the whole annual cycle of in situ observations of mixed layer depth, photosynthetical available radiation, particle backscattering, nutrients (nitrate and silicate), and chlorophyll-a concentrations. During the year 2012-2013, satellite ocean color observations, confirmed by in situ data, have revealed the existence of two areas (or bioregions) with comparable autumnal blooms but contrasting spring blooms. In both bioregions, the ratio of the euphotic zone (defined as the isolume 0.415 mol photons m-2 d-1, Z0.415) and the MLD identified the initiation of the autumnal bloom, as well as the maximal annual increase in [Chl-a] in spring. In fact, the autumnal phytoplankton bloom might be initiated by mixing of the summer shallowing deep chlorophyll maximum, while the spring restratification (when Z0.415/MLD ratio became >1) might induce surface phytoplankton production that largely overcomes the losses. Finally, winter deep convection events that took place in one of the bioregions induced higher net accumulation rate of phytoplankton in spring associated with a diatom-dominated phytoplankton community principally. We suggest that very deep winter MLD lead to an increase in surface silicates availability, which favored the development of diatoms.

Phosphogenesis in the 2460 and 2728 million-year-old banded iron formations as evidence for biological cycling of phosphate in the early biosphere

PubMed Central

Li, Yi-Liang; Sun, Si; Chan, Lung S

2013-01-01

The banded iron formation deposited during the first 2 billion years of Earth's history holds the key to understanding the interplay between the geosphere and the early biosphere at large geological timescales. The earliest ore-scale phosphorite depositions formed almost at ∼2.0–2.2 billion years ago bear evidence for the earliest bloom of aerobic life. The cycling of nutrient phosphorus and how it constrained primary productivity in the anaerobic world of Archean–Palaeoproterozoic eons are still open questions. The controversy centers about whether the precipitation of ultrafine ferric oxyhydroxide due to the microbial Fe(II) oxidation in oceans earlier than 1.9 billion years substantially sequestrated phosphate, and whether this process significantly limited the primary productivity of the early biosphere. In this study, we report apatite radial flowers of a few micrometers in the 2728 million-year-old Abitibi banded iron formation and the 2460 million-year-old Kuruman banded iron formation and their similarities to those in the 535 million-year-old Lower Cambrian phosphorite. The lithology of the 535 Million-year-old phosphorite as a biosignature bears abundant biomarkers that reveal the possible similar biogeochemical cycling of phosphorus in the Later Archean and Palaeoproterozoic oceans. These apatite radial flowers represent the primary precipitation of phosphate derived from the phytoplankton blooms in the euphotic zones of Neoarchean and Palaoeproterozoic oceans. The unbiased distributions of the apatite radial flowers within sub-millimeter bands do not support the idea of an Archean Crisis of Phosphate. This is the first report of the microbial mediated mineralization of phosphorus before the Great Oxidation Event when the whole biosphere was still dominated by anaerobic microorganisms. PMID:23404127

Phosphogenesis in the 2460 and 2728 million-year-old banded iron formations as evidence for biological cycling of phosphate in the early biosphere.

PubMed

Li, Yi-Liang; Sun, Si; Chan, Lung S

2012-01-01

The banded iron formation deposited during the first 2 billion years of Earth's history holds the key to understanding the interplay between the geosphere and the early biosphere at large geological timescales. The earliest ore-scale phosphorite depositions formed almost at ∼2.0-2.2 billion years ago bear evidence for the earliest bloom of aerobic life. The cycling of nutrient phosphorus and how it constrained primary productivity in the anaerobic world of Archean-Palaeoproterozoic eons are still open questions. The controversy centers about whether the precipitation of ultrafine ferric oxyhydroxide due to the microbial Fe(II) oxidation in oceans earlier than 1.9 billion years substantially sequestrated phosphate, and whether this process significantly limited the primary productivity of the early biosphere. In this study, we report apatite radial flowers of a few micrometers in the 2728 million-year-old Abitibi banded iron formation and the 2460 million-year-old Kuruman banded iron formation and their similarities to those in the 535 million-year-old Lower Cambrian phosphorite. The lithology of the 535 Million-year-old phosphorite as a biosignature bears abundant biomarkers that reveal the possible similar biogeochemical cycling of phosphorus in the Later Archean and Palaeoproterozoic oceans. These apatite radial flowers represent the primary precipitation of phosphate derived from the phytoplankton blooms in the euphotic zones of Neoarchean and Palaoeproterozoic oceans. The unbiased distributions of the apatite radial flowers within sub-millimeter bands do not support the idea of an Archean Crisis of Phosphate. This is the first report of the microbial mediated mineralization of phosphorus before the Great Oxidation Event when the whole biosphere was still dominated by anaerobic microorganisms.

Bio-Optical Properties of the Arabian Sea as Determined by In Situ and Sea WiFS Data

NASA Technical Reports Server (NTRS)

Trees, Charles C.

1997-01-01

The overall objective of this work was to characterize optical and fluorescence properties in the euphotic zone during two British Ocean Flux Study (BOFS) Arabian Sea cruises. This was later expanded in 1995 to include three U.S. JGOFS Arabian Sea Cruises. The region was to be divided into one or more "bio-optical provinces," within each of which a single set of regression models was to be developed to relate the vertical distribution of irradiance attenuation and normalized fluorescence (SF and NF) to remote sensing reflectance and diffuse attenuation coefficient. The working hypothesis was that over relatively large spatial and temporal scales, the vertical profiles of bio-optical properties were predictable. The specific technical objectives were: (1) To characterize the vertical distribution of the inherent and apparent optical properties by measuring downwelling and upwelling irradiances, upwelling radiances, scalar irradiance of PAR, and beam transmissions at each station - from these data, spectral diffuse attenuation coefficients, irradiance reflectances, remote sensing reflectances, surface-leaving radiances and beam attenuation coefficients were determined; (2) To characterize the spectral absorption of total particulate, detrital, and dissolved organic material at each station from discrete water samples; (3) To describe the vertical distribution of photoadaptive properties in the water column by measuring profiles of stimulated (SF) and natural (NF) fluorescence and examining relationships between SF and NF as a function of diffuse optical depth, pigment biomass and primary productivity; and (4) To establish locally derived, in-water algorithms relating remote sensing reflectance spectra to diffuse attenuation coefficients, phytoplankton pigment concentrations and primary productivity, through intercomparisons with in situ measurements, for application to SeaWiFS data.

Net Community Production in the East Coastal waters of the United States from Oxygen to Argon Ratios

NASA Astrophysics Data System (ADS)

Gao, Y.; Cai, W. J.; Collins, A. L.; Jonsson, B.; Salisbury, J.

2016-02-01

The increase in anthropogenic nutrient input may enhance phytoplankton biomass and their photosynthesis may cause oxygen supersaturation in euphotic zone; while organic matter input from land to sea and decomposition during transportation may lead to oxygen undersaturation. Net community production (NCP) reflects the net outcome between photosynthesis and respiration. Our current understating of NCP mainly relies on bottle incubation and satellite data analysis, which may cause bias in the large area of coastal water. To improve our understanding in the east coast of the United States (25°N to 45 °N) from an integrated perspective, we conducted continuous onboard determination of oxygen (O2) to argon (Ar) ratios in order to separate biological activity from physical mixing effects during June to July 2015 as part of the NOAA East Coast Ocean Acidification (ECOA) investigation. Biological driven O2 supersaturation was derived from difference of O2/Ar in water away from the equilibrium status using equilibrator inlet mass spectrometer. Temperature changed 5°C to 30°C from north to south, and salinity ranged from 20 in the shore region (e.g. inside of Chesapeake Bay) to 36 in offshore water. Photosynthesis (positive NCP) was the dominant process in the Gulf of Maine and in lower Chesapeake Bay due to the re-occurring phytoplankton blooms. In response to large amount of terrestrial organic matter input and quick remineralization at temperature of 20-25°C, respiration (negative NCP) were often observed in the Block Island sound, Delaware Bay mouth and Chesapeake Bay mouth. In the warm subtropics gyre, NCP was slightly negative that may be related to nutrient deficiency and low organic matter input.

Predicting plankton net community production in the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Serret, Pablo; Robinson, Carol; Fernández, Emilio; Teira, Eva; Tilstone, Gavin; Pérez, Valesca

2009-07-01

We present, test and implement two contrasting models to predict euphotic zone net community production (NCP), which are based on 14C primary production (PO 14CP) to NCP relationships over two latitudinal (ca. 30°S-45°N) transects traversing highly productive and oligotrophic provinces of the Atlantic Ocean (NADR, CNRY, BENG, NAST-E, ETRA and SATL, Longhurst et al., 1995 [An estimation of global primary production in the ocean from satellite radiometer data. Journal of Plankton Research 17, 1245-1271]). The two models include similar ranges of PO 14CP and community structure, but differ in the relative influence of allochthonous organic matter in the oligotrophic provinces. Both models were used to predict NCP from PO 14CP measurements obtained during 11 local and three seasonal studies in the Atlantic, Pacific and Indian Oceans, and from satellite-derived estimates of PO 14CP. Comparison of these NCP predictions with concurrent in situ measurements and geochemical estimates of NCP showed that geographic and annual patterns of NCP can only be predicted when the relative trophic importance of local vs. distant processes is similar in both modeled and predicted ecosystems. The system-dependent ability of our models to predict NCP seasonality suggests that trophic-level dynamics are stronger than differences in hydrodynamic regime, taxonomic composition and phytoplankton growth. The regional differences in the predictive power of both models confirm the existence of biogeographic differences in the scale of trophic dynamics, which impede the use of a single generalized equation to estimate global marine plankton NCP. This paper shows the potential of a systematic empirical approach to predict plankton NCP from local and satellite-derived P estimates.

Low rates of nitrogen fixation in eastern tropical South Pacific surface waters

PubMed Central

Knapp, Angela N.; Casciotti, Karen L.; Berelson, William M.; Prokopenko, Maria G.; Capone, Douglas G.

2016-01-01

An extensive region of the Eastern Tropical South Pacific (ETSP) Ocean has surface waters that are nitrate-poor yet phosphate-rich. It has been proposed that this distribution of surface nutrients provides a geochemical niche favorable for N2 fixation, the primary source of nitrogen to the ocean. Here, we present results from two cruises to the ETSP where rates of N2 fixation and its contribution to export production were determined with a suite of geochemical and biological measurements. N2 fixation was only detectable using nitrogen isotopic mass balances at two of six stations, and rates ranged from 0 to 23 µmol N m−2 d−1 based on sediment trap fluxes. Whereas the fractional importance of N2 fixation did not change, the N2-fixation rates at these two stations were several-fold higher when scaled to other productivity metrics. Regardless of the choice of productivity metric these N2-fixation rates are low compared with other oligotrophic locations, and the nitrogen isotope budgets indicate that N2 fixation supports no more than 20% of export production regionally. Although euphotic zone-integrated short-term N2-fixation rates were higher, up to 100 µmol N m−2 d−1, and detected N2 fixation at all six stations, studies of nitrogenase gene abundance and expression from the same cruises align with the geochemical data and together indicate that N2 fixation is a minor source of new nitrogen to surface waters of the ETSP. This finding is consistent with the hypothesis that, despite a relative abundance of phosphate, iron may limit N2 fixation in the ETSP. PMID:26976587

Stirring Up the Biological Pump: Vertical Mixing and Carbon Export in the Southern Ocean

NASA Astrophysics Data System (ADS)

Stukel, Michael R.; Ducklow, Hugh W.

2017-09-01

The biological carbon pump (BCP) transports organic carbon from the surface to the ocean's interior via sinking particles, vertically migrating organisms, and passive transport of organic matter by advection and diffusion. While many studies have quantified sinking particles, the magnitude of passive transport remains poorly constrained. In the Southern Ocean weak thermal stratification, strong vertical gradients in particulate organic matter, and weak vertical nitrate gradients suggest that passive transport from the euphotic zone may be particularly important. We compile data from seasonal time series at a coastal site near Palmer Station, annual regional cruises in the Western Antarctic Peninsula (WAP), cruises throughout the broader Southern Ocean, and SOCCOM (Southern Ocean Carbon and Climate Observations and Modeling) autonomous profiling floats to estimate spatial and temporal patterns in vertical gradients of nitrate, particulate nitrogen (PN), and dissolved organic carbon. Under a steady state approximation, the ratio of ∂PN/∂z to ∂NO3-/∂z suggests that passive transport of PN may be responsible for removing 46% (37%-58%) of the nitrate introduced into the surface ocean of the WAP (with dissolved organic matter contributing an additional 3-6%) and for 23% (19%-28%) of the BCP in the broader Southern Ocean. A simple model parameterized with in situ nitrate, PN, and primary production data suggested that passive transport was responsible for 54% of the magnitude of the BCP in the WAP. Our results highlight the potential importance of passive transport (by advection and diffusion) of organic matter in the Southern Ocean but should only be considered indicative of high passive transport (rather than conclusive evidence) due to our steady state assumptions.

Apparent increase in coccolithophore abundance in the subtropical North Atlantic from 1990 to 2014

NASA Astrophysics Data System (ADS)

Krumhardt, Kristen M.; Lovenduski, Nicole S.; Freeman, Natalie M.; Bates, Nicholas R.

2016-02-01

As environmental conditions evolve with rapidly increasing atmospheric CO2, biological communities will change as species reorient their distributions, adapt, or alter their abundance. In the surface ocean, dissolved inorganic carbon (DIC) has been increasing over the past several decades as anthropogenic CO2 dissolves into seawater, causing acidification (decreases in pH and carbonate ion concentration). Calcifying phytoplankton, such as coccolithophores, are thought to be especially vulnerable to ocean acidification. How coccolithophores will respond to increasing carbon input has been a subject of much speculation and inspired numerous laboratory and mesocosm experiments, but how they are currently responding in situ is less well documented. In this study, we use coccolithophore (haptophyte) pigment data collected at the Bermuda Atlantic Time-series Study (BATS) site together with satellite estimates (1998-2014) of surface chlorophyll and particulate inorganic carbon (PIC) as a proxy for coccolithophore abundance to show that coccolithophore populations in the North Atlantic subtropical gyre have been increasing significantly over the past 2 decades. Over 1990-2012, we observe a 37 % increase in euphotic zone-integrated coccolithophore pigment abundance at BATS, though we note that this is sensitive to the period being analyzed. We further demonstrate that variability in coccolithophore chlorophyll a here is positively correlated with variability in nitrate and DIC (and especially the bicarbonate ion) in the upper 30 m of the water column. Previous studies have suggested that coccolithophore photosynthesis may benefit from increasing CO2, but calcification may eventually be hindered by low pHT (< 7.7). Given that DIC has been increasing at BATS by ˜ 1.4 µmol kg-1 yr-1 over the period of 1991-2012, we speculate that coccolithophore photosynthesis and perhaps calcification may have increased in response to anthropogenic CO2 input.

Ocean time-series reveals recurring seasonal patterns of virioplankton dynamics in the northwestern Sargasso Sea

PubMed Central

Parsons, Rachel J; Breitbart, Mya; Lomas, Michael W; Carlson, Craig A

2012-01-01

There are an estimated 1030 virioplankton in the world oceans, the majority of which are phages (viruses that infect bacteria). Marine phages encompass enormous genetic diversity, affect biogeochemical cycling of elements, and partially control aspects of prokaryotic production and diversity. Despite their importance, there is a paucity of data describing virioplankton distributions over time and depth in oceanic systems. A decade of high-resolution time-series data collected from the upper 300 m in the northwestern Sargasso Sea revealed recurring temporal and vertical patterns of virioplankton abundance in unprecedented detail. An annual virioplankton maximum developed between 60 and 100 m during periods of summer stratification and eroded during winter convective mixing. The timing and vertical positioning of this seasonal pattern was related to variability in water column stability and the dynamics of specific picophytoplankton and heterotrophic bacterioplankton lineages. Between 60 and 100 m, virioplankton abundance was negatively correlated to the dominant heterotrophic bacterioplankton lineage SAR11, as well as the less abundant picophytoplankton, Synechococcus. In contrast, virioplankton abundance was positively correlated to the dominant picophytoplankton lineage Prochlorococcus, and the less abundant alpha-proteobacteria, Rhodobacteraceae. Seasonally, virioplankton abundances were highly synchronous with Prochlorococcus distributions and the virioplankton to Prochlorococcus ratio remained remarkably constant during periods of water column stratification. The data suggest that a significant fraction of viruses in the mid-euphotic zone of the subtropical gyres may be cyanophages and patterns in their abundance are largely determined by Prochlorococcus dynamics in response to water column stability. This high-resolution, decadal survey of virioplankton abundance provides insight into the possible controls of virioplankton dynamics in the open ocean. PMID:21833038

Mercury sources, distribution, and bioavailability in the North Pacific Ocean: Insights from data and models

USGS Publications Warehouse

Sunderland, E.M.; Krabbenhoft, D.P.; Moreau, J.W.; Strode, S.A.; Landing, W.M.

2009-01-01

Fish harvested from the Pacific Ocean are a major contributor to human methylmercury (MeHg) exposure. Limited oceanic mercury (Hg) data, particularly MeHg, has confounded our understanding of linkages between sources, methylation sites, and concentrations in marine food webs. Here we present methylated (MeHg and dimethylmercury (Me2Hg)) and total Hg concentrations from 16 hydrographie stations in the eastern North Pacific Ocean. We use these data in combination with information from previous cruises and coupled atmospheric-oceanic modeling results to better understand controls on Hg concentrations, distribution, and bioavailability. Total Hg concentrations (average 1.14 ?? 0.38 pM) are elevated relative to previous cruises. Modeling results agree with observed increases and suggest that at present atmospheric Hg deposition rates, basin-wide Hg concentrations will double relative to circa 1995 by 2050. Methylated Hg accounts for up to 29% of the total Hg in subsurface waters (average 260 ??114 fM). We observed lower ambient methylated Hg concentrations in the euphotic zone and older, deeper water masses, which likely result from decay of MeHg and Me2Hg when net production is not occurring. We found a significant, positive linear relationship between methylated Hg concentrations and rates of organic carbon remineralization (r2 = 0.66, p < 0.001). These results provide evidence for the importance of particulate organic carbon (POC) transport and remineralization on the production and distribution of methylated Hg species in marine waters. Specifically, settling POC provides a source of inorganic Hg(II) to microbially active subsurface waters and can also provide a substrate for microbial activity facilitating water column methylation. Copyright 2009 by the American Geophysical Union.

Groups without Cultured Representatives Dominate Eukaryotic Picophytoplankton in the Oligotrophic South East Pacific Ocean

PubMed Central

Shi, Xiao Li; Marie, Dominique; Jardillier, Ludwig; Scanlan, David J.; Vaulot, Daniel

2009-01-01

Background Photosynthetic picoeukaryotes (PPE) with a cell size less than 3 µm play a critical role in oceanic primary production. In recent years, the composition of marine picoeukaryote communities has been intensively investigated by molecular approaches, but their photosynthetic fraction remains poorly characterized. This is largely because the classical approach that relies on constructing 18S rRNA gene clone libraries from filtered seawater samples using universal eukaryotic primers is heavily biased toward heterotrophs, especially alveolates and stramenopiles, despite the fact that autotrophic cells in general outnumber heterotrophic ones in the euphotic zone. Methodology/Principal Findings In order to better assess the composition of the eukaryotic picophytoplankton in the South East Pacific Ocean, encompassing the most oligotrophic oceanic regions on earth, we used a novel approach based on flow cytometry sorting followed by construction of 18S rRNA gene clone libraries. This strategy dramatically increased the recovery of sequences from putative autotrophic groups. The composition of the PPE community appeared highly variable both vertically down the water column and horizontally across the South East Pacific Ocean. In the central gyre, uncultivated lineages dominated: a recently discovered clade of Prasinophyceae (IX), clades of marine Chrysophyceae and Haptophyta, the latter division containing a potentially new class besides Prymnesiophyceae and Pavlophyceae. In contrast, on the edge of the gyre and in the coastal Chilean upwelling, groups with cultivated representatives (Prasinophyceae clade VII and Mamiellales) dominated. Conclusions/Significance Our data demonstrate that a very large fraction of the eukaryotic picophytoplankton still escapes cultivation. The use of flow cytometry sorting should prove very useful to better characterize specific plankton populations by molecular approaches such as gene cloning or metagenomics, and also to obtain into culture strains representative of these novel groups. PMID:19893617

El Niño and similar perturbation effects on the benthos of the Humboldt, California, and Benguela Current upwelling ecosystems

NASA Astrophysics Data System (ADS)

Arntz, W. E.; Gallardo, V. A.; Gutiérrez, D.; Isla, E.; Levin, L. A.; Mendo, J.; Neira, C.; Rowe, G. T.; Tarazona, J.; Wolff, M.

2006-03-01

To a certain degree, Eastern Boundary Current (EBC) ecosystems are similar: Cold bottom water from moderate depths, rich in nutrients, is transported to the euphotic zone by a combination of trade winds, Coriolis force and Ekman transport. The resultant high primary production fuels a rich secondary production in the upper pelagic and nearshore zones, but where O2 exchange is restricted, it creates oxygen minimum zones (OMZs) at shelf and upper slope (Humboldt and Benguela Current) or slope depths (California Current). These hypoxic zones host a specifically adapted, small macro- and meiofauna together with giant sulphur bacteria that use nitrate to oxydise H2S. In all EBC, small polychaetes, large nematodes and other opportunistic benthic species have adapted to the hypoxic conditions and co-exist with sulphur bacteria, which seem to be particularly dominant off Peru and Chile. However, a massive reduction of macrobenthos occurs in the core of the OMZ. In the Humboldt Current area the OMZ ranges between <100 and about 600 m, with decreasing thickness in a poleward direction. The OMZ merges into better oxygenated zones towards the deep sea, where large cold-water mega- and macrofauna occupy a dominant role as in the nearshore strip. The Benguela Current OMZ has a similar upper limit but remains shallower. It also hosts giant sulphur bacteria but little is known about the benthic fauna. However, sulphur eruptions and intense hypoxia might preclude the coexistence of significant mega- und macrobenthos. Conversely, off North America the upper limit of the OMZ is considerably deeper (e.g., 500-600 m off California and Oregon), and the lower boundary may exceed 1000m. The properties described are valid for very cold and cold (La Niña and "normal") ENSO conditions with effective upwelling of nutrient-rich bottom water. During warm (El Niño) episodes, warm water masses of low oxygen concentration from oceanic and equatorial regions enter the upwelling zones, bringing a variety of (sub)tropical immigrants. The autochthonous benthic fauna emigrates to deeper water or poleward, or suffers mortality. However, some local macrofaunal species experience important population proliferations, presumably due to improved oxygenation (in the southern hemisphere), higher temperature tolerance, reduced competition or the capability to use different food. Both these negative and positive effects of El Niño influence local artisanal fisheries and the livelihood of coastal populations. In the Humboldt Current system the hypoxic seafloor at outer shelf depths receives important flushing from the equatorial zone, causing havoc on the sulphur bacteria mats and immediate recolonisation of the sediments by mega- and macrofauna. Conversely, off California, the intruding equatorial water masses appear to have lower oxygen than ambient waters, and may cause oxygen deficiency at upper slope depths. Effects of this change have not been studied in detail, although shrimp and other taxa appear to alter their distribution on the continental margin. Other properties and reactions of the two Pacific EBC benthic ecosystems to El Niño seem to differ, too, as does the overall impact of major episodes (e.g., 1982/1983(1984) vs. 1997/1998). The relation of the "Benguela Niño" to ENSO seems unclear although many Pacific-Atlantic ocean and atmosphere teleconnections have been described. Warm, low-oxygen equatorial water seems to be transported into the upwelling area by similar mechanisms as in the Pacific, but most major impacts on the eukaryotic biota obviously come from other, independent perturbations such as an extreme eutrophication of the sediments ensuing in sulphidic eruptions and toxic algal blooms. Similarities and differences of the Humboldt and California Current benthic ecosystems are discussed with particular reference to ENSO impacts since 1972/73. Where there are data available, the authors include the Benguela Current ecosystem as another important, non-Pacific EBC, which also suffers from the effects of hypoxia.

Cycling of nutrient elements in the North Sea

NASA Astrophysics Data System (ADS)

Brockmann, U. H.; Laane, R. W. P. M.; Postma, J.

The cycling of elements of inorganic and organic nutrients (carbon, nitrogen, phosphorus and silicate) in the North Sea is described. The regional effects on nutrient cycling such as thermal and haline stratification, coastal interaction, river discharges, upwelling and frontal zones are discussed. The horizontal and vertical distribution of the inorganic nutrients (nitrate, phosphate, ammonia and silicate) at the surface is given for the whole North Sea during two situations: spring (1986) and winter (1987). In winter, highest nutrient concentrations were found at the northern boundary in the Atlantic inflow, and in the continental coastal waters. During the winter cruise, nutrient minima were detected in the Dogger Bank area. This is an indication that primary production continues during winter. Generally, the surface concentrations during winter were similar to the bottom concentrations. Except for phosphate, highest concentrations were measured just above the bottom. During late spring 1986 the concentrations of nutrients at the surface and below the densicline were generally significantly lower than during winter. Only at the Atlantic boundary in the north and near the estuaries higher concentrations were detected. In stratified parts of the North Sea, the decomposition of sedimented biomass caused the ammonia concentrations in the bottom layer to be significantly higher in spring than in winter. Incidents of frontal upwelling in the central North Sea introduce nutrient-rich bottom water into the euphotic zone, enhancing phytoplankton growth in the central North Sea during summer. The ratios of nitrogen nutrients to phosphate show that in the central North Sea nitrogen is a limiting factor rather than phosphorus, whereas in the continental coastal water and off England the opposite is true. Riverine input and trapping mechanisms in the estuaries and tidal flats cause the concentrations of organic matter (dissolved and particulate) to be highest in the coastal zones and to decrease seaward. During summer the concentration of dissolved organic carbon increases throughout the North Sea. It is calculated that about 60% of the biomass formed by primary production is converted into dissolved organic carbon, 40% directly goes into the foodweb. The biological impact of the plankton is readily apparent from increased surface concentrations of different dissolved organic substances during spring blooms. Examples of eutrophication and effects of nutrient limitation are given, together with other biological repercussions such as coupling of phytoplankton and nutrient succession. Budget calculations for the different nutrient elements show that in the North Sea the biological turnover greatly exceeds the estimated annual inflow and outflow of nutrient elements. Finally, recommendations are given for future research. They include analysing dissolved organic compounds and micronutrients and following multidisciplinary measurements strategies at one location in order to obtain more information for balancing budgets and for the detailed analysis of nutrient cycling in the North Sea.

Pelagic and sympagic contribution of organic matter to zooplankton and vertical export in the Barents Sea marginal ice zone

NASA Astrophysics Data System (ADS)

Tamelander, Tobias; Reigstad, Marit; Hop, Haakon; Carroll, Michael L.; Wassmann, Paul

2008-10-01

The structure and function of the marine food web strongly regulate the cycling of organic matter derived from primary production by phytoplankton and ice algae in Arctic shelf seas. Improved knowledge of trophic relationships and export of organic matter from the surface layer is needed to better understand how the Arctic marine ecosystem may respond to climate-related changes in distribution of sea ice, water masses, and associated primary production regimes. Pelagic and sympagic inputs of organic matter to dominant meso- and macrozooplankton species and vertical export were investigated in the northern Barents Sea by means of stable carbon and nitrogen isotopes (δ 13C and δ 15N). Samples were collected during spring and summer (2003-2005) from a total of 13 stations with different ice conditions, abundances of ice algae, and phytoplankton bloom phases. δ 13C signatures were different in organic matter of phytoplankton (mean -24.3‰) and ice algal origin (mean -20.0‰). Stable carbon isotope compositions showed that most of the energy assimilated by zooplankton originated from pelagic primary production, but at times ice algae also contributed to zooplankton diets. Trophic level (TL) estimates of copepods ( Calanus glacialis and Calanus hyperboreus) and krill ( Thysanoessa inermis and Thysanoessa longicaudata), calculated based on δ 15N values, varied among stations from 1.3 to 2.7 and from 1.5 to 3.1, for respective taxa. TL in C. glacialis was significantly and inversely related to the depth-integrated phytoplankton chlorophyll a concentration. A similar trend, although weaker, also was observed for the other species. This relationship indicates that copepods graze primarily on the abundant autotrophic biomass during the peak bloom phase. At stations with lower chlorophyll a concentration, the TL of Calanus spp. was 1.0 higher, indicating omnivory outside the peak bloom phase in response to changed food availability. The majority of organic matter exported from the euphotic zone was derived from pelagic primary production, but at 3 of 11 stations within the marginal ice zone (MIZ), the ice algal signal dominated the isotope composition of sinking material. The δ 13C of settling organic matter was positively related to the vertical flux of particulate organic carbon, with maximum values around -21‰ during the peak bloom phase. Sedimentation of isotopically light copepod faecal pellets (mean δ 13C -25.4‰) was reflected in a depletion of 13C in the sinking material. The results illustrate tight pelagic-benthic coupling in the Barents Sea MIZ through vertical export of fresh phytodetritus during phytoplankton blooms and episodic export of ice algae.

C : N : P stoichiometry at the Bermuda Atlantic Time-series Study station in the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Singh, A.; Baer, S. E.; Riebesell, U.; Martiny, A. C.; Lomas, M. W.

2015-11-01

Nitrogen (N) and phosphorus (P) availability, in addition to other macro- and micronutrients, determine the strength of the ocean's carbon (C) uptake, and variation in the N : P ratio of inorganic nutrient pools is key to phytoplankton growth. A similarity between C : N : P ratios in the plankton biomass and deep-water nutrients was observed by Alfred C. Redfield around 80 years ago and suggested that biological processes in the surface ocean controlled deep-ocean chemistry. Recent studies have emphasized the role of inorganic N : P ratios in governing biogeochemical processes, particularly the C : N : P ratio in suspended particulate organic matter (POM), with somewhat less attention given to exported POM and dissolved organic matter (DOM). Herein, we extend the discussion on ecosystem C : N : P stoichiometry but also examine temporal variation in stoichiometric relationships. We have analyzed elemental stoichiometry in the suspended POM and total (POM + DOM) organic-matter (TOM) pools in the upper 100 m and in the exported POM and subeuphotic zone (100-500 m) inorganic nutrient pools from the monthly data collected at the Bermuda Atlantic Time-series Study (BATS) site located in the western part of the North Atlantic Ocean. C : N and N : P ratios in TOM were at least twice those in the POM, while C : P ratios were up to 5 times higher in TOM compared to those in the POM. Observed C : N ratios in suspended POM were approximately equal to the canonical Redfield ratio (C : N : P = 106 : 16 : 1), while N : P and C : P ratios in the same pool were more than twice the Redfield ratio. Average N : P ratios in the subsurface inorganic nutrient pool were ~ 26 : 1, squarely between the suspended POM ratio and the Redfield ratio. We have further linked variation in elemental stoichiometry to that of phytoplankton cell abundance observed at the BATS site. Findings from this study suggest that elemental ratios vary with depth in the euphotic zone, mainly due to different growth rates of cyanobacterial cells. We have also examined the role of the Arctic Oscillation on temporal patterns in C : N : P stoichiometry. This study strengthens our understanding of the variability in elemental stoichiometry in different organic-matter pools and should improve biogeochemical models by constraining the range of non-Redfield stoichiometry and the net relative flow of elements between pools.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyd, P.W.; Gall, M.P.; Silver, M.W.

A central question addressed by the VERTIGO (VERtical Transport In the Global Ocean) study was 'What controls the efficiency of particle export between the surface and subsurface ocean'? Here, we present data from sites at ALOHA (N Central Pacific Gyre) and K2 (NW subarctic Pacific) on phytoplankton processes, and relate them via a simple planktonic foodweb model, to subsurface particle export (150-500 m). Three key factors enable quantification of the surface-subsurface coupling: a sampling design to overcome the temporal lag and spatial displacement between surface and subsurface processes; data on the size-partitioning of Net Primary Production (NPP) and subsequent transformationsmore » prior to export; estimates of the ratio of algal- to faecal-mediated vertical export flux. At ALOHA, phytoplankton were characterized by low stocks, NPP, F{sub v}/F{sub m} (N-limited), and were dominated by picoplankton. The HNLC waters at K2 were characterized by both two-fold changes in NPP and floristic shifts (high to low proportion of diatoms) between deployment 1 and 2. Prediction of export exiting the euphotic zone was based on size-partitioning of NPP, a copepod-dominated foodweb and a ratio of 0.2 (ALOHA) and 0.1 (K2) for algal:faecal particle flux. Predicted export was 20-22 mg POC m{sup -2} d{sup -1} at ALOHA (i.e. 10-11% NPP (0-125 m); 1.1-1.2 x export flux at 150 m (E{sub 150}). At K2, export was 111 mg C m{sup -2} d{sup -1} (21% NPP (0-50 m); 1.8 x E{sub 150}) and 33 mg POC m{sup -2} d{sup -1} (11% NPP, 0-55 m); 1.4 x E{sub 150}) for deployments 1 and 2, respectively. This decrease in predicted export at K2 matches the observed trend for E{sub 150}. Also, the low attenuation of export flux from 60 to 150 m is consistent with that between 150 to 500 m. This strong surface-subsurface coupling suggests that phytoplankton productivity and floristics play a key role at K2 in setting export flux, and moreover that pelagic particle transformations by grazers strongly influence to what extent sinking particles are further broken down in the underlying waters of the Twilight Zone.« less

Quantifying the surface subsurface biogeochemical coupling during the VERTIGO ALOHA and K2 studies

NASA Astrophysics Data System (ADS)

Boyd, Philip W.; Gall, Mark P.; Silver, Mary W.; Coale, Susan L.; Bidigare, Robert R.; Bishop, James L. K. B.

2008-07-01

A central question addressed by the VERtical Transport In the Global Ocean (VERTIGO) study was 'What controls the efficiency of particle export between the surface and subsurface ocean'? Here, we present data from sites at ALOHA (N Central Pacific Gyre) and K2 (NW subarctic Pacific) on phytoplankton processes, and relate them via a simple planktonic foodweb model, to subsurface particle export (150-500 m). Three key factors enable quantification of the surface-subsurface coupling: a sampling design to overcome the temporal lag and spatial displacement between surface and subsurface processes; data on the size partitioning of net primary production (NPP) and subsequent transformations prior to export; estimates of the ratio of algal- to faecal-mediated vertical export flux. At ALOHA, phytoplankton were characterized by low stocks, NPP, Fv/ Fm (N-limited), and were dominated by picoplankton. The HNLC waters at K2 were characterized by both two-fold changes in NPP and floristic shifts (high to low proportion of diatoms) between deployment 1 and 2. Prediction of export exiting the euphotic zone was based on size partitioning of NPP, a copepod-dominated foodweb and a ratio of 0.2 (ALOHA) and 0.1 (K2) for algal:faecal particle flux. Predicted export was 20-22 mg POC m -2 d -1 at ALOHA (i.e. 10-11% NPP (0-125 m); 1.1-1.2×export flux at 150 m ( E150). At K2, export was 111 mg C m -2 d -1 (21% NPP (0-50 m); 1.8× E150) and 33 mg POC m -2 d -1 (11% NPP, 0-55 m); 1.4× E150) for deployments 1 and 2, respectively. This decrease in predicted export at K2 matches the observed trend for E150. Also, the low attenuation of export flux from 60 to 150 m is consistent with that between 150 and 500 m. This strong surface-subsurface coupling suggests that phytoplankton productivity and floristics play a key role at K2 in setting export flux, and moreover that pelagic particle transformations by grazers strongly influence to what extent sinking particles are further broken down in the underlying waters of the Twilight Zone.

Interannual control of plankton communities by deep winter mixing and prey/predator interactions in the NW Mediterranean: Results from a 30-year 3D modeling study

NASA Astrophysics Data System (ADS)

Auger, P. A.; Ulses, C.; Estournel, C.; Stemmann, L.; Somot, S.; Diaz, F.

2014-05-01

A realistic modeling approach is designed to address the role of winter mixing on the interannual variability of plankton dynamics in the north-western (NW) Mediterranean basin. For the first time, a high-resolution coupled hydrodynamic-biogeochemical model (Eco3m-S) covering a 30-year period (1976-2005) is validated on available in situ and satellite data for the NW Mediterranean. In this region, cold, dry winds in winter often lead to deep convection and strong upwelling of nutrients into the euphotic layer. High nutrient contents at the end of winter then support the development of a strong spring bloom of phytoplankton. Model results indicate that annual primary production is not affected by winter mixing due to seasonal balance (minimum in winter and maximum in spring). However, the total annual water column-integrated phytoplankton biomass appears to be favored by winter mixing because zooplankton grazing activity is low in winter and early spring. This reduced grazing is explained here by the rarefaction of prey due to both light limitation and the effect of mixing-induced dilution on prey/predator interactions. A negative impact of winter mixing on winter zooplankton biomass is generally simulated except for mesozooplankton. This difference is assumed to stem from the lower parameterized mortality, top trophic position and detritivorous diet of mesozooplankton in the model. Moreover, model suggests that the variability of annual mesozooplankton biomass is principally modulated by the effects of winter mixing on winter biomass. Thus, interannual variability of winter nutrient contents in the euphotic layer, resulting from winter mixing, would control spring primary production and thus annual mesozooplankton biomass. Our results show a bottom-up control of mesozooplankton communities, as observed at a coastal location of the Ligurian Sea.

Supporting NGSS-aligned Study of Authentic Data about Climate

NASA Astrophysics Data System (ADS)

Zalles, D. R.

2013-12-01

The subject of climate change holds tremendous opportunity for students to learn how scientists use data to develop and test theories of how the natural world works and appreciate how climate change instantiates cross-cutting NGSS science themes like stability and change, energy and matter, and cause and effect. To do so, students and teachers need help seeing in authentic Earth system data complex climate interactions and generate plans for building greater understanding of the complexities through further data investigation. With ever-growing repositories of global and regional public data and user friendly tools for their display, K-12 educators are challenged to help students study data independently rather than through the usual pre-filtered didactic presentations of data found in textbooks. The paper will describe strategies for facilitating critical thinking about authentic climate-related data in two climate change education projects funded by NASA and NSF, as well as learning outcomes. Data Enhanced Investigations for Climate Change Education (dicce.sri.com) brings data from NASA satellite missions to classrooms. Studying Topography, Orographic Rainfall, and Ecosystems with Geospatial Information Technology (store.sri.com) provides recent climatological and vegetation data about certain study areas in California and New York plus geospatially distributed projected values of temperature, precipitation, and land cover in 2050 and 2099, derived from NCAR's A2 climate change model. Supportive resources help students move from naïve conceptions of simple linear relationships between variables into critical analysis of what other variables could be mediating those relationships. DICCE contains guides for how to interpret multiyear trends that are evident in the NASA mission data in relation to what we know about current climate change. If a learner plots a line of best fit across multiple months or years of regional data and notices that the line is either sloping up or down, the trend guide suggests what this might mean and suggests what additional types of data to examine for verification. For example, the variable euphotic depth looks at ocean surface water clarity. If students notice that euphotic depth has decreased, the trend guide explains how this could be evidence of increased runoff from coastal lands. Yet, increased runoff may or may not be an effect of regional climate change; an effect if from increasingly severe storms, or not an effect if from increased deforestation in the coastal watershed. Or, perhaps both could be occurring. To investigate further, students are encouraged to study if other data about the region shows trends (e.g., accumulated precipitation, rainfall rate, and air temperature) and to see if the decreased euphotic depth is also occurring further from the coastline. This could indicate decreased phytoplankton, which in turn could result from climate change if the decrease is due to increased sea surface temperatures that mitigate upwelling of nutrients from colder depths. The STORE project also stimulates discovery of complex relationships in data. For example, students seeking confirmation of a linear relationship between increased elevation and increased precipitation study authentic data showing how the relationship is mediated by proximity to large bodies of water and storm paths.

Seasonal mercury levels in phytoplankton and their relationship with algal biomass in two dystrophic shield lakes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirkwood, A.E.; Chow-Fraser, P.; Mierle, G.

1999-03-01

This study focused on the seasonal dynamics of total Hg in the phytoplankton (living and dead) of two dystrophic shield lakes (Mouse and Ranger). Phytoplankton samples were taken from metalimnetic and hypolimnetic depths in the euphotic zone and were collected and analyzed using ultraclean techniques. In both lakes, phytoplankton Hg (PHYTO-Hg) levels (pg/L) in the metalimnion did not significantly change among dates over the season, although Ranger Lake exhibited significant differences between Hg values measured at the beginning and end of the season. In contrast, PHYTO-Hg significantly increased in the hypolimnia of both lakes by the end of the season.more » Combined influences of external Hg inputs, remineralization, phytoplankton sedimentation, and increased methylmercury production in the hypolimnia over the season may have contributed to these trends. A highly significant positive relationship existed between PHYTO-Hg levels and whole-water Hg levels, and the mean bioconcentration factor for Hg between the water column and phytoplankton was significantly higher in the hypolimnion compared to the metalimnion for both lakes. In most cases, parameters associated with algal biomass had significant positive correlations with PHYTO-Hg levels. Weight-specific PHYTO-Hg (pg/mg dry weight) varied significantly over the season, and there were interlake differences with respect to season trends. On the basis of these results, the authors recommend that the future sampling regimes include collection of phytoplankton at different limnetic depths through the season to account for spatial and temporal variations. Weight specific Hg levels in phytoplankton could not be explained well by the parameters tested, and the only significant regressions were with parameters reflecting algal biomass. This study provides in situ evidence of Hg accumulation in lake phytoplankton as a function of algal biomass on a seasonal basis and stresses the need to confirm these trends in other lake systems.« less

Incorporating Prognostic Marine Nitrogen Fixers and Related Bio-Physical Feedbacks in an Earth System Model

NASA Astrophysics Data System (ADS)

Paulsen, H.; Ilyina, T.; Six, K. D.

2016-02-01

Marine nitrogen fixers play a fundamental role in the oceanic nitrogen and carbon cycles by providing a major source of `new' nitrogen to the euphotic zone that supports biological carbon export and sequestration. Furthermore, nitrogen fixers may regionally have a direct impact on ocean physics and hence the climate system as they form extensive surface mats which can increase light absorption and surface albedo and reduce the momentum input by wind. Resulting alterations in temperature and stratification may feed back on nitrogen fixers' growth itself.We incorporate nitrogen fixers as a prognostic 3D tracer in the ocean biogeochemical component (HAMOCC) of the Max Planck Institute Earth system model and assess for the first time the impact of related bio-physical feedbacks on biogeochemistry and the climate system.The model successfully reproduces recent estimates of global nitrogen fixation rates, as well as the observed distribution of nitrogen fixers, covering large parts of the tropical and subtropical oceans. First results indicate that including bio-physical feedbacks has considerable effects on the upper ocean physics in this region. Light absorption by nitrogen fixers leads locally to surface heating, subsurface cooling, and mixed layer depth shoaling in the subtropical gyres. As a result, equatorial upwelling is increased, leading to surface cooling at the equator. This signal is damped by the effect of the reduced wind stress due to the presence of cyanobacteria mats, which causes a reduction in the wind-driven circulation, and hence a reduction in equatorial upwelling. The increase in surface albedo due to nitrogen fixers has only inconsiderable effects. The response of nitrogen fixers' growth to the alterations in temperature and stratification varies regionally. Simulations with the fully coupled Earth system model are in progress to assess the implications of the biologically induced changes in upper ocean physics for the global climate system.

Carbon Cycle in South China Sea: Flux, Controls and Global Implications

NASA Astrophysics Data System (ADS)

Dai, M.; Cao, Z.; Yang, W.; Guo, X.; Yin, Z.; Gan, J.

2016-12-01

The contemporary coastal ocean is generally seen as a significant CO2 sink of 0.2-0.4 Pg C/yr at the global scale. However, mechanistic understanding of the coastal ocean carbon cycle remains limited, leading to the unanswered question of why some coastal systems are sources while others are sinks of atmospheric CO2. As the largest marginal sea of Northern Pacific, the South China Sea (SCS) is a mini-ocean with wide shelves in both its southern and northern parts. Its northern shelf, which receives significant land inputs from the Pearl River, a world major river, can be categorized as a River-Dominated Margin (RioMar) during peak discharges, and is characterized as a CO2 sink to the atmosphere. The SCS basin is identified as an Ocean-Dominated Margin (OceMar) and a CO2 source. OceMar is characterized by exchange with the open ocean via a two-dimensional (at least) process, i.e., the horizontal intrusion of open ocean water and subsequent vertical mixing and upwelling. Depending on the different ratios of dissolved inorganic carbon (DIC) and nutrients from the source waters into the continental margins, the relative consumption or removal bwtween DIC and nutrients, when being transported into the euphotic zones where biogeochemical processes take over, determines the CO2 fluxes. Thus, excess DIC relative to nutrients existing in the upper layer will lead to CO2 degassing. The CO2 fluxes in both RioMars and OceMars can be quantified using a semi-analytical diagnostic approach by coupling the physical dynamics and biogeochemical processes. We extended our mechanistic studies in the SCS to other OceMars including the Caribbean Sea, the Arabian Sea, and the upwelling system off the Oregon-California coast, and RioMars including the East China Sea and Amazon River plume to demonstrate the global implications of our SCS carbon studies.

Using light-dependent scleractinia to define the upper boundary of mesophotic coral ecosystems on the reefs of Utila, Honduras.

PubMed

Laverick, Jack H; Andradi-Brown, Dominic A; Rogers, Alex D

2017-01-01

Shallow water zooxanthellate coral reefs grade into ecologically distinct mesophotic coral ecosystems (MCEs) deeper in the euphotic zone. MCEs are widely considered to start at an absolute depth limit of 30m deep, possibly failing to recognise that these are distinct ecological communities that may shift shallower or deeper depending on local environmental conditions. This study aimed to explore whether MCEs represent distinct biological communities, the upper boundary of which can be defined and whether the depth at which they occur may vary above or below 30m. Mixed-gas diving and closed-circuit rebreathers were used to quantitatively survey benthic communities across shallow to mesophotic reef gradients around the island of Utila, Honduras. Depths of up to 85m were sampled, covering the vertical range of the zooxanthellate corals around Utila. We investigate vertical reef zonation using a variety of ecological metrics to identify community shifts with depth, and the appropriateness of different metrics to define the upper MCE boundary. Patterns observed in scleractinian community composition varied between ordination analyses and approaches utilising biodiversity indices. Indices and richness approaches revealed vertical community transition was a gradation. Ordination approaches suggest the possibility of recognising two scleractinian assemblages. We could detect a mesophotic and shallow community while illustrating that belief in a static depth limit is biologically unjustified. The switch between these two communities occurred across bathymetric gradients as small as 10m and as large as 50m in depth. The difference between communities appears to be a loss of shallow specialists and increase in depth-generalist taxa. Therefore, it may be possible to define MCEs by a loss of shallow specialist species. To support a biological definition of mesophotic reefs, we advocate this analytical framework should be applied around the Caribbean and extended into other ocean basins where MCEs are present.

In situ observations of ocean productivity using the SeaCycler mooring in the central Labrador Sea

NASA Astrophysics Data System (ADS)

Atamanchuk, Dariia; Koelling, Jannes; Devred, Emmanuel; Siddall, Greg; Send, Uwe; Wallace, Douglas

2017-04-01

The Central Labrador Sea is a major deep-convection region in the NW Atlantic which is the most intense sink for anthropogenic carbon in the global ocean (de Vries et al, 2013). CO2 enters the ocean by air-sea exchange and is transported into the ocean's interior mainly though the biological pump (Longhurst et al., 1989). Despite its important role for CO2 uptake and high natural variability, the Labrador Sea is undersampled due to rough conditions and an overall lack of volunteer observing ship (VOS) transits. The SeaCycler moored profiler is currently providing year-round data from the central Labrador Sea and resolves daily changes of inorganic carbon and related properties from the upper 150m of the water column. SeaCycler's sensor float is equipped with 13 physical, chemical and biooptical sensors which measure temperature, salinity, dissolved gases, nutrients and optical properties of seawater. A combination of Pro-CV (Pro-Oceanus Inc, Canada) and CO2 optode (Aanderaa, Norway) sensors in profiling mode provides a detailed description of Dissolved Inorganic Carbon (DIC) dynamics in the upper 150m over the productive season. This allows, for the first time, high-resolution carbon-based estimates of ocean productivity from throughout the euphotic zone over an annual cycle which can be compared to estimates derived from simultaneous oxygen and nitrate (Deep SUNA, Satlantic LP, Canada) profiles. These in situ carbon, nitrogen and oxygen-based estimates of using in-situ data are further compared with remotely-sensed estimates from MODIS satellite data. The SeaCycler data allow estimation of the annual cycle of the air-sea CO2 flux and carbon export. Concurrently recorded in-situ bio-optical data allow direct comparison of optical measurements of biomass change and reveal key patterns in the seasonal succession of phytoplankton groups responsible for carbon drawdown.

An examination of the factors influencing mercury and methylmercury particulate distributions, methylation and demethylation rates in laboratory-generated marine snow.

PubMed

Ortiz, Veronica L; Mason, Robert P; Ward, J Evan

2015-12-20

In the marine environment, settling particulates have been widely studied for their role as effective vertical transporters of nutrients and metals scavenged from the euphotic zone to the benthos. These particulates are composed of transparent exopolymers, plankton and bacterial cells, detritus and organic matter, and form various size fractions from colloids (<0.2μm) to aggregates, and finally marine snow (>300 μm). As marine snow forms in the water column, anoxic layers form around and within the aggregation potentially creating a prime environment for the methylation of mercury (Hg), which occurs primarily in low oxygen environments. To examine this process, marine aggregates were produced from sieved estuarine seawater (100 μm) in 1-L glass bottles spiked with stable isotope enriched methylmercury (CH 3 199 Hg) and inorganic mercury ( 200 Hg(II)) at 18° C using a roller-table. After the rolling period, different particle-size fractions were collected and analyzed, including: visible marine snow (>300μm), particulates 8 to 300 μm, and particulates 0.2 to 8μm. Particulate analysis indicated higher incorporation of both forms of Hg into marine snow compared to unrolled treatments, with greater incorporation of 200 Hg(II) than CH 3 199 Hg. In addition, inorganic Hg was methylated and CH 3 Hg was demethylated in the larger particulate fractions (>8μm). Methylation and demethylation rates were assessed based on changes in isotopic composition of Hg(II) and CH 3 Hg, and found to be comparable to methylation rates found in sediments. These results indicate that net Hg methylation can occur in marine snow and smaller aggregates in oxic coastal waters, and that this net formation of CH 3 Hg may be an important source of CH 3 Hg in both coastal and open ocean surface environments.

Annual, orbital, and enigmatic variations in tropical oceanography recorded by the Equatorial Atlantic amplifier

NASA Technical Reports Server (NTRS)

Mcintyre, Andrew

1992-01-01

Equatorial Atlantic surface waters respond directly to changes in zonal and meridional lower tropospheric winds forced by annual insolation. This mechanism has its maximum effect along the equatorial wave guide centered on 10 deg W. The result is to amplify even subtle tropical climate changes such that they are recorded by marked amplitude changes in the proxy signals. Model realizations, NCAR AGCM and OGCM for 0 Ka and 126 Ka (January and July), and paleoceanographic proxy data show that these winds are also forced by insolation changes at the orbital periods of precession and obliquity. Perhelion in boreal summer produces a strengthened monsoon, e.g., increase meridional and decrease zonal wind stress. This reduces oceanic Ekman divergence and thermocline/nutricline shallowing. The result, in the equatorial Atlantic, is reduced primary productivity and higher euphotic zone temperatures; vice versa for perihelion in boreal winter. Perihelion is controlled by precession. Thus, the dominant period in spectra from a stacked SST record (0-252 Ka BP) at the site of the equatorial Atlantic amplifier is 23 Ky (53 percent of the total variance). This precessional period is coherent (k = 0.920) and in phase with boreal summer insolation. Oscillations of shorter period are present in records from cores sited beneath the amplifier region. These occur between 12.5 and 74.5 Ka BP, when eccentricity modulation of precession is at a minimum. Within this time interval there are 21 cycles with mean periods of 3.0 plus or minus 0.5 Ky. Similar periods have been documented from high latitude regions, e.g., Greenland ice cores from Camp Century. The Camp Century signal in this same time interval contains 21 cycles. A subjective correlation was made between the Camp Century and the equatorial records; the signals were statistically similar, r = 0.722 and k = 0.960.

Results of Sustained Observations from SABSOON

NASA Astrophysics Data System (ADS)

Seim, H.; Nelson, J.

2001-12-01

A variety of meteorological and oceanographic data being collected on the continental shelf off Georgia by the South Atlantic Bight Synoptic Offshore Observational Network (SABSOON) permit an examination of episodic and seasonal phenomena operative on the shelf. Data are collected at offshore platforms and transmitted to shore in near-real time and made available on the project website. Examples of data collected since 1999 are presented that illustrate some of processes being addressed using the network. Maximum winds occur during remarkably energetic downbursts observed in spring and summer, associated with the passage of squalls over the coastal ocean. Peak wind speed at 50 m height exceed 40 ms and air temperature drops by 4 oC or more in less than 6 minutes, often accompanied by large changes in humidity and heavy rainfall, suggesting down draft of air from aloft. These events may play an important role in the offshore transport of continentally-derived material. Continuous ADCP measurements are being used to examine the seasonality of cross-shelf exchange and its relationship to the cross-shelf density gradient. The low-frequency cross-shelf circulation changes sign when the cross-shelf density gradient changes sign. Vertical stratification is surprisingly episodic, and maximum stratification has occurred in the winter and spring associated with appearance of long-salinity surface lens and may be associated with baroclinic instabilities. Strong stratification has also been observed in summer during Gulf Stream-derived intrusions onto the shelf, during which time the upper and lower layers become largely decoupled. Continuous optical measurements of above-water and in-water irradiance (PAR) show the mid-shelf surface sediments are often in the euphotic zone. Chlorophyll fluorescence (stimulated) shows strong light-dependent diurnal variability in near-surface waters and evidence of resuspension of benthic diatoms during storm events, particularly in the early fall. >http://www.skio.peachnet.edu/projects/sabsoon.html

Modeling downward particulate organic nitrogen flux from zooplankton ammonium regeneration in the northern Benguela

NASA Astrophysics Data System (ADS)

Fernández-Urruzola, I.; Osma, N.; Gómez, M.; Pollehne, F.; Postel, L.; Packard, T. T.

2016-12-01

The vertical fluxes of particulate organic matter play a crucial role in the distribution of nutrients throughout the oceans. Although they have been the focus of intensive research, little effort has been made to explore alternative approaches that quantify the particle export at a high spatial resolution. In this study, we assess the minimum nitrogen flux (FN) required to sustain the heterotrophic metabolism in the water column from ocean depth profiles of zooplankton NH4+ excretion (RNH4+). The reduction of RNH4+ as a function of depth was described by a power law fit, RNH4+ = (RNH4+)m (z /zm)b , whereby the b-value determines the net particulate nitrogen loss with increasing depth. Integrating these excretory functions from the base of the euphotic zone to the ocean bottom, we calculated FN at two stations located over the Namibian outer shelf. Estimates of FN (ranging between 0.52 and 1.14 mmol N m-2 d-1) were compared with the sinking fluxes of particles collected in sediment traps (0.15-1.01 mmol N m-2 d-1) 50 m over the seafloor. We found a reasonable agreement between the two approaches when fast-sinking particles dominated the ecosystem, but the FN was somewhat at odds with the measured gravitational flux during a low-sedimentation regime. Applying our conceptual model to the mesozooplankton RNH4+ we further constructed a section of FN along a cross-shelf transect at 20° S, and estimated the efficiency of the epipelagic ecosystem to retain nutrients. Finally, we address the impact of the active flux driven by the migrant mesozooplankton to the total nitrogen export. Depending on the sedimentation regime, the downward active flux (0.86 mmol N m-2 d-1 at 150 m) accounted for between 50 and 307% of the gravitational flux.

Remote Sensing the Phytoplankton Seasonal Succession of the Red Sea

PubMed Central

Brewin, Robert J. W.; Stenchikov, Georgiy; Hoteit, Ibrahim

2013-01-01

The Red Sea holds one of the most diverse marine ecosystems, primarily due to coral reefs. However, knowledge on large-scale phytoplankton dynamics is limited. Analysis of a 10-year high resolution Chlorophyll-a (Chl-a) dataset, along with remotely-sensed sea surface temperature and wind, provided a detailed description of the spatiotemporal seasonal succession of phytoplankton biomass in the Red Sea. Based on MODIS (Moderate-resolution Imaging Spectroradiometer) data, four distinct Red Sea provinces and seasons are suggested, covering the major patterns of surface phytoplankton production. The Red Sea Chl-a depicts a distinct seasonality with maximum concentrations seen during the winter time (attributed to vertical mixing in the north and wind-induced horizontal intrusion of nutrient-rich water in the south), and minimum concentrations during the summer (associated with strong seasonal stratification). The initiation of the seasonal succession occurs in autumn and lasts until early spring. However, weekly Chl-a seasonal succession data revealed that during the month of June, consistent anti-cyclonic eddies transfer nutrients and/or Chl-a to the open waters of the central Red Sea. This phenomenon occurs during the stratified nutrient depleted season, and thus could provide an important source of nutrients to the open waters. Remotely-sensed synoptic observations highlight that Chl-a does not increase regularly from north to south as previously thought. The Northern part of the Central Red Sea province appears to be the most oligotrophic area (opposed to southern and northern domains). This is likely due to the absence of strong mixing, which is apparent at the northern end of the Red Sea, and low nutrient intrusion in comparison with the southern end. Although the Red Sea is considered an oligotrophic sea, sporadic blooms occur that reach mesotrophic levels. The water temperature and the prevailing winds control the nutrient concentrations within the euphotic zone and enable the horizontal transportation of nutrients. PMID:23755161

The influence of nanoflagellates on the spatial variety of picoplankton and the carbon flow of the microbial food web in the oligotrophic subtropical pelagic continental shelf ecosystem

NASA Astrophysics Data System (ADS)

Chiang, Kuo-Ping; Tsai, An-Yi; Tsai, Pei-Jung; Gong, Gwo-Ching; Huang, Bang-Qin; Tsai, Sheng-Fang

2014-06-01

To investigate the mechanism of the spatial dynamics of picoplankton community (bacteria and Synechococcus spp.) and to estimate the carbon flux of the microbial food web in the oligotrophic Taiwan Warm Current Water of the subtropical marine pelagic ecosystem, we conducted size-fractionation experiments during five cruises by the R/V Ocean Research II during the summers of 2010 and 2011 in the southern East China Sea. We carried out culture experiments using surface water, which according to a temperature-salinity (T-S) diagram, is characterized as oligotrophic Taiwan Current Warm Water. We found a negative correlation between bacteria growth rate and temperature, and another negative correlation between nitrate and temperature indicating that the active growth of heterotrophic bacteria might be induced by nutrients lifted from a deep layer by cold upwelling water. This finding suggests that the area we studied was a bottom-up control pelagic ecosystem. Upwelling brings nutrient-rich water to the euphotic zone and promotes bacterial growth, resulting in increased picoplankton biomass, which increases the consumption rate of nanoflagellates. The net growth rate (growth rate-grazing rate) becomes negative when the densities of bacteria and Synechococcus spp. are lower than the threshold values. The interaction between growth and grazing will limit the abundance of bacteria (105-106 cells ml-1) and Synechococcus spp. (104-105 cells ml-1) within a narrow range. Meanwhile, 61% of bacteria production and 54% of Synechococcus spp. production are transported to a higher trophic level (nanoflagellate), though the cascade effect might cause an underestimation of both percentages of transported carbon. Based on the successive size-fractionation experiments, we estimated that the predation values were underestimated and that the diet of nanoflagellates is composed of 64% bacteria and 36% Synechococcus spp.

Evaluation of the sinks and sources of atmospheric CO2 by artificial upwelling.

PubMed

Pan, Yiwen; Fan, Wei; Huang, Ting-Hsuan; Wang, Shu-Lun; Chen, Chen-Tung Arthur

2015-04-01

Artificial upwelling is considered a promising way to reduce the accumulation of anthropogenic carbon dioxide in the atmosphere. This practice could transport nutrient-rich deep water to the euphotic zone, enhance phytoplankton growth and consequently increase organic carbon exportation to the deep ocean via the biological pump. However, only a few studies quantitatively assess changes in oceanic CO2 uptake resulting from artificial upwelling. This article uses a simulation to examine the effect of hypothetical artificial upwelling-induced variations of CO2 fugacity in seawater (fCO2) using observed carbon and nutrient data from 14 stations, ranging from 21 to 43°N, in the West Philippine Sea (WPS), the East China Sea (ECS) and the Sea of Japan. Calculations are based on two basic assumptions: First, a near-field mixing of a nutrient-rich deep-ocean water plume in a stratified ocean environment is assumed to form given the presence of an artificial upwelling devise with appropriate technical parameters. Second, it is assumed that photosynthesis of marine phytoplankton could deplete all available nutrients following the stoichiometry of the modified Redfield ratio C/H/O/N/S/P=103.1/181.7/93.4/11.7/2.1/1. Results suggest artificial upwelling has significant effects on regional changes in sea-air differences (ΔfCO2sea-air) and the carbon sequestration potential (ΔfCO2mixed-amb). Large variations of ΔfCO2sea-air and ΔfCO2mixed-amb are shown to be associated with different regions, seasons and technical parameters of the artificial upwelling device. With proper design, it is possible to reverse the contribution of artificial upwelling from a strong CO2 source to sink. Thus, artificial upwelling has the potential to succeed as a geoengineering technique to sequester anthropogenic CO2, with appropriate technical parameters in the right region and season. Copyright © 2014 Elsevier B.V. All rights reserved.

Aps and Tep Chemical Characterization: Link Between The Dom and Pom Pools

NASA Astrophysics Data System (ADS)

Gogou, A.; Repeta, D. J.

The ocean inventory of dissolved organic carbon (DOC) is approximately 750 GT, comprising one of the Earth's largest carbon reservoirs on Earth. Despite its potential significance, the mechanisms that lead to DOM production and to spatial and temporal variations of DOM concentration in the world ocean are poorly understood. Chemical characterization studies show that up to 50% of HMW DOM is a structurally well-defined class of acylated polysaccharides (APS), which exhibits novel molecular-level characteris tics. Although APS synthesis occurs in the euphotic zone, a large fraction of the marine inventory of APS (appr. 10-30 GT C), resides in the deep ocean, and is approximately equal in mass to the total marine inventory of particulate organic carbon. While radiocarbon dating of deep sea DOC yields very old apparent ages (4000-6000 ybp), radiocarbon measurements made by our group on individual APS sugars shows that APS in the deep ocean has a radiocarbon value of +56 per mil, equivalent to surface water POC and DIC. This is the first clear evidence for the presence of "young" DOC in the deep ocean. One mechanism that could be important for the rapid removal of APS from surface seawater is physical removal by macroaggregates. To investigate the significance of this mechanism, we studied the chemical composition of surface-active POM (TEP) produced naturally on surface waters and in laboratory experiments, after bubbling of HMW DOM isolated from algal cultures. 1H-NMR spectral properties and molecular-level distribution of neutral sugars in natural and artificially produced TEP closely resembled those observed for cultured and oceanic HMW DOM, while they are significantly different from those of suspended particulate matter in the ocean (Gogou and Repeta, 2000). The results of these experiments provide evidence that POM with similar chemical characteristics to HMW DOM can be produced from algal-derived DOM in the surface ocean.

A new stratigraphic model for the deposition of the Dammam Formation

NASA Astrophysics Data System (ADS)

Lokier, Stephen; Fiorini, Flavia; Min, Jina

2017-04-01

In recent years, mixed siliciclastic-carbonate successions have increasingly become targets for hydrocarbon exploration and production activities. Despite the abundance of these successions throughout the Middle East, there have been very few attempts to employ quantitative techniques to interpret their depositional settings and to develop constrained sequence stratigraphic models for their deposition. This study focuses on the Eocene age Dammam Formation that crops out on the flanks of the Jebel Hafeet anticline south of Al Ain in the United Arab Emirates. The Dammam Formation comprises units alternating between poorly-lithified, easily-weathered, siliciclastic and marly horizons and well-lithified limestones. These units were deposited in a foreland basin that formed in association with the Late Cretaceous obduction of the Semail Ophiolite onto the northeastern margin of the Arabian Plate. The Paleogene infilling of this basin is recorded in the shallowing-upward sedimentary sequence of the lithologies of the Pabdeh Group. This succession records the transition from marine carbonate sedimentation, through increasingly evaporitic-dominated units during the late Eocene to early Miocene to a fluvial-alluvial system by mid to late Miocene times. The Dammam Formation was deposited in an open shallow-marine setting strongly influenced by the influx of siliciclastic material sourced from the close-by uplifted massif of the obducted ophiolite. The skeletal assemblage of the Dammam Formation is dominated by Nummulites and Assilina larger benthic foraminifera along with subordinate smaller foraminifera, echinoids, bivalves, corals, bryozoan, gastropods, echinoids and calcareous algae. Previous studies of the Dammam Formation have employed the biotic component in the reconstruction of water depth. However, these studies neglected to consider that turbidity, associated with the abundant siliciclastic component, resulted in a reduction in the depth of the euphotic zone and a consequent response of the benthic biota. We employ a range of quantitative analytical techniques in order to constrain the influence of the siliciclastic component on the lithofacies of the Dammam Formation and present a new sequence stratigraphic model for the deposition of the formation.

Nutrient pumping by submesoscale circulations in the mauritanian upwelling system

NASA Astrophysics Data System (ADS)

Hosegood, P. J.; Nightingale, P. D.; Rees, A. P.; Widdicombe, C. E.; Woodward, E. M. S.; Clark, D. R.; Torres, R. J.

2017-12-01

Observations made within a cold filament in the Mauritanian upwelling system demonstrate that intense submesoscale circulations at the peripheral edges of the filament are likely responsible for anomalously high levels of observed primary productivity by resupplying nutrients to the euphotic zone. Measurements made on the shelf within the recently upwelled water reveal that primary production (PP) of 8.2 gC/m-2 day-1 was supported by nitrate concentrations (NC) of 8 mmol m-3. Towards the front that defined the edge of the filament containing the upwelled water as it was transported offshore, PP dropped to 1.6 gC m-2 day-1 whilst NC dropped to 5.5 mmol m-3. Thus, whilst the observed nutrients on the shelf accounted for 90% of new production, this value dropped to ∼60% near the filament's front after accounting for vertical turbulent fluxes and Ekman pumping. We demonstrate that the N15 was likely to have been supplied at the front by submesoscale circulations that were directly measured as intense vertical velocities ⩾100 m day-1 by a drifting acoustic Doppler current profiler that crossed a submesoscale surface temperature front. At the same time, a recently released tracer was subducted out of the mixed layer within 24 h of release, providing direct evidence that the frontal circulations were capable of accessing the reservoir of nutrients beneath the pycnocline. The susceptibility of the filament edge to submesoscale instabilities was demonstrated by O(1) Rossby numbers at horizontal scales of 1-10 km. The frontal circulations are consistent with instabilities arising from a wind-driven nonlinear Ekman buoyancy flux generated by the persistent northerly wind stress that has a down-front component at the northern edge of the inshore section of the filament. The prevalence of submesoscale instabilities and their associated vertical circulations are proposed to be a key mechanism operating at sub-grid scales and sustaining new production throughout the upwelling system.

Survival of the Tardigrade Hypsibius Dujardini during Hypervelocity Impact Events up to 5.49 km s-1

NASA Astrophysics Data System (ADS)

Pasini, D.

2014-04-01

Studies have previously been conducted to verify the survivability of living cells during hypervelocity impact events to test the panspermia and lithopanspermia hypotheses [1, 2]. It has been demonstrated that bacteria survive impacts up to 5.4 km s-1 (approx. shock pressure 30 GPa) - albeit with a low probability of survival [1], whilst larger, more complex, objects (such as seeds) break up at ~1 km s-1 [2]. The survivability of yeast spores in impacts up to 7.4 km s-1 has also recently been shown [3]. Previous work by the authors demonstrated the survivability of Nannochloropsis Oculata Phytoplankton, a eukaryotic photosynthesizing autotroph found in the 'euphotic zone' (sunlit surface layers of oceans [4]), at impact velocities up to 6.07 km s-1 [5]. Other groups have also reported that lichens are able to survive shocks in similar pressure ranges [6]. However, whilst many simple single celled organisms have now been shown to survive such impacts (and the associated pressures) as those encountered during the migration of material from one planet to another [1, 3, 5], complex multicellular organisms have either largely not been tested or, those that have been, have not survived the process [2]. Hypsibius dujardini, like most species of tardigrade, are complex organisms composed of approximately 40,000 cells [7]. When humidity decreases they enter a highly dehydrated state known as a 'tun' and can survive extreme temperatures (as low as - 253°C or as high as 151°C), as well as exposure to Xrays and the vacuum of space [7]. Here we test the shock survivability of Hypsibius dujardini by firing a nylon projectile onto a frozen sample of water containing frozen tardigrades using a light gas gun (LGG) [8]. The recovered ice and water were then analysed under an optical microscope to check the viability of any remnant organisms that may have survived impact, and the pressures generated.

Suspended marine particulate proteins in coastal and oligotrophic waters

NASA Astrophysics Data System (ADS)

Bridoux, Maxime C.; Neibauer, Jaqui; Ingalls, Anitra E.; Nunn, Brook L.; Keil, Richard G.

2015-03-01

Metaproteomic analyses were performed on suspended sediments collected in one coastal environment (Washington margin, Pacific Ocean, n = 5) and two oligotrophic environments (Atlantic Ocean near BATS, n = 5, and Pacific Ocean near HOTS, n = 5). Using a database of 2.3 million marine proteins developed using the NCBI database, 443 unique peptides were detected from which 363 unique proteins were identified. Samples from the euphotic zone contained on average 2-3x more identifiable proteins than deeper waters (150-1500 m) and these proteins were predominately from photosynthetic organisms. Diatom peptides dominate the spectra of the Washington margin while peptides from cyanobacteria, such as Synechococcus sp. dominated the spectra of both oligotrophic sites. Despite differences in the exact proteins identified at each location, there is good agreement for protein function and cellular location. Proteins in surface waters code for a variety of cellular functions including photosynthesis (24% of detected proteins), energy production (10%), membrane production (9%) and genetic coding and reading (9%), and are split 60-40 between membrane proteins and intracellular cytoplasmic proteins. Sargasso Sea surface waters contain a suite of peptides consistent with proteins involved in circadian rhythms that promote both C and N fixation at night. At depth in the Sargasso Sea, both muscle-derived myosin protein and the muscle-hydrolyzing proteases deseasin MCP-01 and metalloprotease Mcp02 from γ-proteobacteria were observed. Deeper waters contain peptides predominately sourced from γ-proteobacteria (37% of detected proteins) and α-proteobacteria (26%), although peptides from membrane and photosynthetic proteins attributable to phytoplankton were still observed (13%). Relative to surface values, detection frequencies for bacterial membrane proteins and extracellular enzymes rose from 9 to 16 and 2 to 4% respectively below the thermocline and the overall balance between membrane proteins and intracellular proteins grows to an approximate 75-25 split. Unlike the phytoplankton membrane proteins, which are detrital in nature, the bacterial protein suite at depth is consistent with living biomass.

W Photoprotection in Tropical Marine Organisms

NASA Technical Reports Server (NTRS)

Armstrong, Roy A.

1997-01-01

Increasing levels of ultraviolet (UV) radiation reaching the earth's surface which results from stratospheric ozone depletions could have serious implications for terrestrial plants and for aquatic organisms within the euphotic zone. A documented 9% decline in ozone at mid-latitudes is considered to produce a 12% increase in harmful UV radiation. The biologically damaging effects of higher UV levels, particularly W-B (280-320 rim), could manifest earlier in the tropics because of the relative thinness of the earth's equatorial ozone layer. Tropical marine organisms are also living close to their upper tolerance levels of water temperature, However, despite the large potential effects on plants and animals, little is known about UV effects on tropical ecosystems. Long-term ecological studies are needed to quantify the effects of increased UV radiation on terrestrial and marine ecosystems and to produce reliable data for prediction. Plants have developed several mechanisms to protect themselves from harmful UV radiation, one of which is the production of secondary leaf pigments that absorb W-B radiation (screening pigments). A higher concentration of screening pigments (e.g. flavonoids) in leaves may be interpreted as a natural response to increased W radiation. If higher concentrations of flavonoids filter out the excessive W radiation, no damage will occur, as suggested by Caldwell et al. (1989) and Tevini (1993). Failure to screen all W-B may result in deleterious effects on photosynthesis, plant genetic material, and plant and leaf morphology and growth. Eventually this will have an impact on ecosystem processes, structure, species composition, and productivity. This paper describes an ongoing project that is assessing the responses of mangroves, seagrasses and corals to W radiation by studying pigment concentrations, biophysical parameters, and variations in spectral reflectance in the field and in W-reduction experiments. Preliminary results on the distribution of W-absorbing flavonoid compounds in red mangroves (Rhizophora mangle) and the seagrass Thalassia testudinum, are presented. This research also provides, for the first time, a permanent record of daily W irradiance measurements at a tropical -location.

Phosphorus cycling in the red tide incubator region of monterey bay in response to upwelling.

PubMed

Mackey, Katherine R M; Mioni, Cécile E; Ryan, John P; Paytan, Adina

2012-01-01

This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in northeastern Monterey Bay (the Red Tide Incubator region) of coastal California, with particular emphasis on how bacteria and phytoplankton that form harmful algal blooms mediate and respond to changes in P availability. In situ measurements of nutrient concentrations, phytoplankton community composition, and cell-specific alkaline phosphatase (AP) activity (determined via enzyme-labeled fluorescence assay) were measured during three cruises. Upwelling led to a 10-fold increase in dissolved inorganic (DIP) in surface waters, reaching ∼0.5 μmol L(-1). This DIP was drawn down rapidly as upwelling relaxed over a period of 1 week. Ratios of nitrate to DIP drawdown (∼5:1, calculated as the change in nitrate divided by the change in DIP) were lower than the Redfield ratio of 16:1, suggesting that luxury P uptake was occurring as phytoplankton bloomed. Dissolved organic (DOP) remained relatively constant (∼0.3 μmol L(-1)) before and immediately following upwelling, but doubled as upwelling relaxed, likely due to phytoplankton excretion and release during grazing. This transition from a relatively high DIP:DOP ratio to lower DIP:DOP ratio was accompanied by a decline in the abundance of diatoms, which had low AP activity, toward localized, spatially heterogeneous blooms of dinoflagellates in the genera Prorocentrum, Ceratium, Dinophysis, Alexandrium, and Scrippsiella that showed high AP activity regardless of ambient DIP levels. A nutrient addition incubation experiment showed that phytoplankton growth was primarily limited by nitrate, followed by DIP and DOP, suggesting that P regulates phytoplankton physiology and competition, but is not a limiting nutrient in this region. AP activity was observed in bacteria associated with lysed cell debris and aggregates of particulate organic material, where it may serve to facilitate P regeneration, as well as affixed to the surfaces of intact phytoplankton cells, possibly indicative of close, beneficial phytoplankton-bacteria interactions.

Phosphorus Cycling in the Red Tide Incubator Region of Monterey Bay in Response to Upwelling

PubMed Central

Mackey, Katherine R. M.; Mioni, Cécile E.; Ryan, John P.; Paytan, Adina

2012-01-01

This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in northeastern Monterey Bay (the Red Tide Incubator region) of coastal California, with particular emphasis on how bacteria and phytoplankton that form harmful algal blooms mediate and respond to changes in P availability. In situ measurements of nutrient concentrations, phytoplankton community composition, and cell-specific alkaline phosphatase (AP) activity (determined via enzyme-labeled fluorescence assay) were measured during three cruises. Upwelling led to a 10-fold increase in dissolved inorganic (DIP) in surface waters, reaching ∼0.5 μmol L−1. This DIP was drawn down rapidly as upwelling relaxed over a period of 1 week. Ratios of nitrate to DIP drawdown (∼5:1, calculated as the change in nitrate divided by the change in DIP) were lower than the Redfield ratio of 16:1, suggesting that luxury P uptake was occurring as phytoplankton bloomed. Dissolved organic (DOP) remained relatively constant (∼0.3 μmol L−1) before and immediately following upwelling, but doubled as upwelling relaxed, likely due to phytoplankton excretion and release during grazing. This transition from a relatively high DIP:DOP ratio to lower DIP:DOP ratio was accompanied by a decline in the abundance of diatoms, which had low AP activity, toward localized, spatially heterogeneous blooms of dinoflagellates in the genera Prorocentrum, Ceratium, Dinophysis, Alexandrium, and Scrippsiella that showed high AP activity regardless of ambient DIP levels. A nutrient addition incubation experiment showed that phytoplankton growth was primarily limited by nitrate, followed by DIP and DOP, suggesting that P regulates phytoplankton physiology and competition, but is not a limiting nutrient in this region. AP activity was observed in bacteria associated with lysed cell debris and aggregates of particulate organic material, where it may serve to facilitate P regeneration, as well as affixed to the surfaces of intact phytoplankton cells, possibly indicative of close, beneficial phytoplankton–bacteria interactions. PMID:22347222

Spatial and temporal variability of Alexandrium cyst fluxes in the Gulf of Maine: Relationship to seasonal particle export and resuspension.

PubMed

Pilskaln, C H; Anderson, D M; McGillicuddy, D J; Keafer, B A; Hayashi, K; Norton, K

2014-05-01

Quantification of Alexandrium cyst fluxes through the Gulf of Maine water column is central to understanding the linkage between the source and fate of annual Alexandrium blooms in the offshore waters. These blooms often lead to paralytic shellfish poisoning (PSP) and extensive closures of shellfish beds. We report here on time-series sediment trap deployments completed at four offshore locations in the gulf between 2005 and 2010 as components of two ECOHAB-GOM field programs. Data presented documents the substantial spatial and temporal fluctuations in Alexandrium fundyense cyst fluxes in the gulf. Cyst delivery out of the euphotic zone peaked primarily between July and August following annual spring-summer Alexandrium blooms and was greatest in the western gulf. At all sites, cyst flux maxima to the subsurface waters were rarely coincident with seasonal peaks in the total mass export of particulate material indicating that cyst delivery was primarily via individually sinking cysts. Where persistent benthic nepheloid layers (BNLs) exist, significant sediment resuspension input of cysts to the near-bottom water column was evidenced by deep cyst fluxes that were up to several orders of magnitude greater than that measured above the BNL. The largest cyst fluxes in the BNL were observed in the eastern gulf, suggesting greater resuspension energy and BNL cyst inventories in this region. Temporal similarities between peak cyst export out of the upper ocean and peak cyst fluxes in the BNL were observed and document the contribution of seasonal, newly formed cysts to the BNL. The data however also suggest that many Alexandrium cells comprising the massive, short-lived blooms do not transition into cysts. Time-series flow measurements and a simple 1D model demonstrate that the BNL cyst fluxes reflect the combined effects of tidal energy-maintained resuspension, deposition, and input of cysts from the overlying water column.

Spatial and temporal variability of Alexandrium cyst fluxes in the Gulf of Maine: Relationship to seasonal particle export and resuspension

PubMed Central

Pilskaln, C.H.; Anderson, D.M.; McGillicuddy, D.J.; Keafer, B.A.; Hayashi, K.; Norton, K.

2014-01-01

Quantification of Alexandrium cyst fluxes through the Gulf of Maine water column is central to understanding the linkage between the source and fate of annual Alexandrium blooms in the offshore waters. These blooms often lead to paralytic shellfish poisoning (PSP) and extensive closures of shellfish beds. We report here on time-series sediment trap deployments completed at four offshore locations in the gulf between 2005 and 2010 as components of two ECOHAB–GOM field programs. Data presented documents the substantial spatial and temporal fluctuations in Alexandrium fundyense cyst fluxes in the gulf. Cyst delivery out of the euphotic zone peaked primarily between July and August following annual spring–summer Alexandrium blooms and was greatest in the western gulf. At all sites, cyst flux maxima to the subsurface waters were rarely coincident with seasonal peaks in the total mass export of particulate material indicating that cyst delivery was primarily via individually sinking cysts. Where persistent benthic nepheloid layers (BNLs) exist, significant sediment resuspension input of cysts to the near-bottom water column was evidenced by deep cyst fluxes that were up to several orders of magnitude greater than that measured above the BNL. The largest cyst fluxes in the BNL were observed in the eastern gulf, suggesting greater resuspension energy and BNL cyst inventories in this region. Temporal similarities between peak cyst export out of the upper ocean and peak cyst fluxes in the BNL were observed and document the contribution of seasonal, newly formed cysts to the BNL. The data however also suggest that many Alexandrium cells comprising the massive, short-lived blooms do not transition into cysts. Time-series flow measurements and a simple 1D model demonstrate that the BNL cyst fluxes reflect the combined effects of tidal energy-maintained resuspension, deposition, and input of cysts from the overlying water column. PMID:25431527

Changing nutrient stoichiometry affects phytoplankton production, DOP build up and dinitrogen fixation - a mesocosm experiment in the eastern tropical North Atlantic

NASA Astrophysics Data System (ADS)

Meyer, J.; Löscher, C. R.; Neulinger, S. C.; Reichel, A. F.; Loginova, A.; Borchard, C.; Schmitz, R. A.; Hauss, H.; Kiko, R.; Riebesell, U.

2015-07-01

Ocean deoxygenation due to climate change may alter redox-sensitive nutrient cycles in the marine environment. The productive eastern tropical North Atlantic (ETNA) upwelling region may be particularly affected when the relatively moderate oxygen minimum zone (OMZ) deoxygenates further and microbially-driven nitrogen (N) loss processes are promoted. Consequently, water masses with a low N : P ratio could reach the euphotic layer, possibly influencing primary production in those waters. Previous mesocosm studies in the oligotrophic Atlantic Ocean identified N availability as controlling of primary production, while a possible co-limitation of nitrate and phosphate (P) could not be ruled out. To better understand the impact of changing N : P ratios on primary production and on N2 fixation in the ETNA surface ocean, we conducted land-based mesocosm experiments with natural plankton communities and applied a broad range of N : P ratios (2.67-48). Silicate was supplied at 15 μmol L-1 in all mesocosms. We monitored nutrient drawdown, bloom formation, biomass build up and diazotrophic feedback in response to variable nutrient stoichiometry. Our results confirmed N to be limiting to primary production. We found that excess P was channeled through particulate organic matter (POP) into the dissolved organic matter (DOP) pool. In mesocosms with low P availability, DOP was utilized while N2 fixation increased, suggesting a link between those two processes. Interestingly this observation was most pronounced in mesocosms where inorganic N was still available, indicating that bioavailable N does not necessarily has to have a negative impact on N2 fixation. We observed a shift from a mixed cyanobacterial/proteobacterial dominated active diazotrophic community towards diazotrophic diatom symbionts of the Richelia-Rhizosolenia symbiosis. We hypothesize that a potential change in nutrient stoichiometry in the ETNA might lead to a general shift within the diazotrophic community, potentially modifying primary productivity.

Changing nutrient stoichiometry affects phytoplankton production, DOP accumulation and dinitrogen fixation - a mesocosm experiment in the eastern tropical North Atlantic

NASA Astrophysics Data System (ADS)

Meyer, J.; Löscher, C. R.; Neulinger, S. C.; Reichel, A. F.; Loginova, A.; Borchard, C.; Schmitz, R. A.; Hauss, H.; Kiko, R.; Riebesell, U.

2016-02-01

Ocean deoxygenation due to climate change may alter redox-sensitive nutrient cycles in the marine environment. The productive eastern tropical North Atlantic (ETNA) upwelling region may be particularly affected when the relatively moderate oxygen minimum zone (OMZ) deoxygenates further and microbially driven nitrogen (N) loss processes are promoted. Consequently, water masses with a low nitrogen to phosphorus (N : P) ratio could reach the euphotic layer, possibly influencing primary production in those waters. Previous mesocosm studies in the oligotrophic Atlantic Ocean identified nitrate availability as a control of primary production, while a possible co-limitation of nitrate and phosphate could not be ruled out. To better understand the impact of changing N : P ratios on primary production and N2 fixation in the ETNA surface ocean, we conducted land-based mesocosm experiments with natural plankton communities and applied a broad range of N : P ratios (2.67-48). Silicic acid was supplied at 15 µmol L-1 in all mesocosms. We monitored nutrient drawdown, biomass accumulation and nitrogen fixation in response to variable nutrient stoichiometry. Our results confirmed nitrate to be the key factor determining primary production. We found that excess phosphate was channeled through particulate organic matter (POP) into the dissolved organic matter (DOP) pool. In mesocosms with low inorganic phosphate availability, DOP was utilized while N2 fixation increased, suggesting a link between those two processes. Interestingly this observation was most pronounced in mesocosms where nitrate was still available, indicating that bioavailable N does not necessarily suppress N2 fixation. We observed a shift from a mixed cyanobacteria-proteobacteria dominated active diazotrophic community towards a diatom-diazotrophic association of the Richelia-Rhizosolenia symbiosis. We hypothesize that a potential change in nutrient stoichiometry in the ETNA might lead to a general shift within the diazotrophic community, potentially influencing primary productivity and carbon export.

Effect of Interannual Variability on the Ocean Acidification-induced Habitat Restriction of the Humboldt Current System.

NASA Astrophysics Data System (ADS)

Franco, A. C.; Gruber, N.; Munnich, M.

2016-02-01

The Humboldt Current System (HCS) is one of the most productive ecosystems in the world. This high productivity is supported by a large input of nutrients from the subsurface layers to the surface due to year-round upwelling. However, upwelling also supplies waters with low pH and low aragonite saturation state potentially affecting many organisms, especially those that calcify. The influence, extent and source of upwelled water varies substantially on interannual timescales in association with the El Niño/Southern Oscillation (ENSO) phenomenon, accentuating productivity during La Niña events and dampening it during El Niño, altering the dynamics of the whole ecosystem. On top of this natural variability, the continuing acidification of the upper ocean in response to raising atmospheric CO2 may decrease pH further and increase the volume of water corrosive to aragonite in this region, leading to a progressively smaller suitable habitat for sensitive organisms. Here we use an eddy-resolving basin-scale ocean model that covers the whole Pacific Ocean with higher resolution near the coast off South America ( 6 km) to investigate the role of ENSO events on low aragonite saturation episodes and productivity variations. We compare 2 simulations: a hindcast simulation that spans the last 30 years and a future scenario that represents year 2090 (following IPCC's "business-as-usual" scenario). We found that in the region off Peru, the sole effect of increasing atmospheric CO2 to 840 matm shoals the annual average aragonite saturation depth to 30 m, creating a year round presence of aragonite undersaturated water in the euphotic zone. We then contrast the effect on primary productivity and the aragonite saturation state of at least eight El Niño and eight La Niña episodes that have been reported for the past 30 years, in an attempt to answer the question: does habitat availability under future ocean acidification will resemble a pervasive La Niña-like state?

Deep-water sponges (Porifera) from Bonaire and Klein Curaçao, Southern Caribbean.

PubMed

Van Soest, Rob W M; Meesters, Erik H W G; Becking, Leontine E

2014-10-29

Four submersible dives off the coast of Bonaire (Caribbean Netherlands) and Klein Curaçao (Curaçao) to depths of 99.5-242 m, covering lower mesophotic and upper dysphotic zones, yielded 52 sponge specimens belonging to 31 species. Among these we identified 13 species as new to science. These are Plakinastrella stinapa n. sp., Pachastrella pacoi n. sp., Characella pachastrelloides n. sp., Geodia curacaoensis n. sp., Caminus carmabi n. sp., Discodermia adhaerens n. sp., Clathria (Microciona) acarnoides n. sp., Antho (Acarnia) pellita n. sp., Parahigginsia strongylifera n. sp., Calyx magnoculata n. sp., Neopetrosia dutchi n. sp., Neopetrosia ovata n. sp. and Neopetrosia eurystomata n. sp. We also report an euretid hexactinellid, which belongs to the rare genus Verrucocoeloidea, recently described (2014) as V. liberatorii Reiswig & Dohrmann. The remaining 18 already known species are all illustrated by photos of the habit, either in situ or 'on deck', but only briefly characterized in an annotated table to confirm their occurrence in the Southern Caribbean. The habitat investigated-steep limestone rocks, likely representing Pleistocene fossil reefs--is similar to deep-water fossil reefs at Barbados of which the sponges were sampled and studied by Van Soest and Stentoft (1988). A comparison is made between the two localities, showing a high degree of similarity in sponge composition: 53% of the present Bonaire-Klein Curaçao species were also retrieved at Barbados. At the level of higher taxa (genera, families) Bonaire-Klein Curaçao shared approximately 80% of its lower mesophotic and upper dysphotic sponge fauna with Barbados, despite a distance between them of 1000 km, indicating high faunal homogeneity. We also preliminarily compared the shallow-water (euphotic) sponge fauna of Curaçao with the combined data available for the Barbados, Bonaire and Klein Curaçao mesophotic and upper dysphotic sponges, which resulted in the conclusion that the two faunas show only little overlap.

The glacial iron cycle from source to export

NASA Astrophysics Data System (ADS)

Hawkings, J.; Wadham, J. L.; Tranter, M.; Raiswell, R.; Benning, L. G.; Statham, P. J.; Tedstone, A. J.; Nienow, P. W.; Telling, J.; Bagshaw, E.; Simmons, S. L.

2014-12-01

Nutrient availability limits primary production in large sectors of the world's oceans. Iron is the major limiting nutrient in around one third of the oceanic euphotic zone, most significantly in the Southern Ocean proximal to Antarctica. In these areas the availability of bioavailable iron can influence the amount of primary production, and thus the strength of the biological pump and associated carbon drawdown from the atmosphere. Despite experiencing widespread iron limitation, the Polar oceans are among the most productive on Earth. Due to the extreme cold, remoteness and their perceived "stasis", ice sheets have previously been though of as insignificant in global biogeochemical cycles. However, large marine algal blooms have been observed in iron-limited areas where glacial influence is large, and it is possible that these areas are stimulated by glacial bioavailable iron input. Here we discuss the importance of the Greenland and Antarctic ice sheets in the global iron cycle. Using field collected trace element data, bulk meltwater chemistry and mineralogical analysis, including photomicrographs, EELS and XANES, we present, for the first time, a conceptual model of the glacial iron cycle from source to export. Using this data we discuss the sources of iron in glacial meltwater, transportation and alteration through the glacial system, and subsequent export to downstream environments. Data collected in 2012 and 2013 from two different Greenlandic glacial catchments are shown, with the most detailed breakdown of iron speciation and concentrations in glacial areas yet reported. Furthermore, the first data from Greenlandic icebergs is presented, allowing meltwater-derived and iceberg-derived iron export to be compared, and the influence of both in marine productivity to be estimated. Using our conceptual model and flux estimates from our dataset, glacial iron delivery in both the northern and southern hemisphere is discussed. Finally, we compare our flux estimates to other major iron sources to the polar regions such as aeolian dust, and discuss potential implications of increased melting of the ice sheets on the global iron cycle in the future.

Bio-optical signatures and biogeochemistry from intense upwelling and relaxation in coastal California

NASA Astrophysics Data System (ADS)

Kudela, Raphael M.; Garfield, Newell; Bruland, Kenneth W.

2006-12-01

The NSF-sponsored Coastal Ocean Processes Wind Events and Shelf Transport (WEST) experiment investigates the interplay between wind-driven transport and shelf productivity; while eastern boundary shelves are characterized by high productivity due to upward fluxes of nutrients into the euphotic zone, wind forcing also represents negative physical and biological controls via offshore transport and deep (light-limiting) mixing of primary producers. Although this interaction has been well documented for eastern boundary systems generally and for California specifically, one of the primary goals of WEST was to characterize more fully the interplay between positive and negative effects of wind stress, which result in the consistently elevated biological productivity in these shelf regions. During 3 month-long summer cruises (2000-2002) we observed extremes in upwelling/relaxation, using both in situ instrumentation and remotely sensed data. Relationships between optical and physical properties were examined, with emphasis on biogeochemical implications. During 2000, the WEST region was optically dominated by phytoplankton and covarying constituents. During 2001 and 2002, periods of more intense upwelling favorable winds, we observed a transition to optical properties dominated by detrital and inorganic materials. In all years, the continental shelf break provided a natural boundary between optically distinct shelf and open ocean waters. During 2002, we obtained discrete trace-metal measurements of particulate iron and aluminum; we develop a bio-optical proxy for acetic-acid leachable iron from backscatter and fluorescence, and demonstrate that particulate iron is not well correlated to traditional upwelling proxies such as macronutrients, temperature, and salinity. We conclude that the shelf break between ca. 100 and 200 m water depth serves as a natural break point between coastal and oceanic water masses in this region, and that the elevated biomass and productivity associated with this eastern boundary current regime is dominated by these iron rich, shallow shelf waters.

Remote sensing the phytoplankton seasonal succession of the Red Sea.

PubMed

Raitsos, Dionysios E; Pradhan, Yaswant; Brewin, Robert J W; Stenchikov, Georgiy; Hoteit, Ibrahim

2013-01-01

The Red Sea holds one of the most diverse marine ecosystems, primarily due to coral reefs. However, knowledge on large-scale phytoplankton dynamics is limited. Analysis of a 10-year high resolution Chlorophyll-a (Chl-a) dataset, along with remotely-sensed sea surface temperature and wind, provided a detailed description of the spatiotemporal seasonal succession of phytoplankton biomass in the Red Sea. Based on MODIS (Moderate-resolution Imaging Spectroradiometer) data, four distinct Red Sea provinces and seasons are suggested, covering the major patterns of surface phytoplankton production. The Red Sea Chl-a depicts a distinct seasonality with maximum concentrations seen during the winter time (attributed to vertical mixing in the north and wind-induced horizontal intrusion of nutrient-rich water in the south), and minimum concentrations during the summer (associated with strong seasonal stratification). The initiation of the seasonal succession occurs in autumn and lasts until early spring. However, weekly Chl-a seasonal succession data revealed that during the month of June, consistent anti-cyclonic eddies transfer nutrients and/or Chl-a to the open waters of the central Red Sea. This phenomenon occurs during the stratified nutrient depleted season, and thus could provide an important source of nutrients to the open waters. Remotely-sensed synoptic observations highlight that Chl-a does not increase regularly from north to south as previously thought. The Northern part of the Central Red Sea province appears to be the most oligotrophic area (opposed to southern and northern domains). This is likely due to the absence of strong mixing, which is apparent at the northern end of the Red Sea, and low nutrient intrusion in comparison with the southern end. Although the Red Sea is considered an oligotrophic sea, sporadic blooms occur that reach mesotrophic levels. The water temperature and the prevailing winds control the nutrient concentrations within the euphotic zone and enable the horizontal transportation of nutrients.

Ground-truthing the Foraminifera-bound Nitrogen Isotope Paleo-proxy in the Modern Sargasso Sea

NASA Astrophysics Data System (ADS)

Smart, S.; Ren, H. A.; Fawcett, S. E.; Conte, M. H.; Rafter, P. A.; Ellis, K. K.; Weigand, M. A.; Sigman, D. M.

2016-02-01

We present the nitrogen isotope ratios (δ15N) of planktonic foraminifera, a type of calcifying zooplankton, collected from surface ocean net tows, moored sediment traps and core-top sediments at the Bermuda Atlantic Time-series Study site in the Sargasso Sea between 2009 and 2013. Consistent with previous measurements from low-latitude core-top sediments, the annually averaged δ15N of organic matter bound within the shells of euphotic zone-dwelling foraminifera approximates that of thermocline nitrate, the dominant source of new nitrogen to Sargasso Sea surface waters. Based on net tow collections in the upper 200 m of the water column, we observe no systematic difference between the biomass δ15N and shell-bound δ15N of a given foraminifera species. For multiple species, the δ15N of net tow-collected upper ocean shells is lower than shells from sediment traps (by 0.5-2.1‰) and lower than shells from seafloor sediments (by 0.5-1.4‰). We are currently investigating whether these differences reflect actual processes affecting shell-bound δ15N or instead relate to the different time periods over which the three sample types integrate. The foraminiferal biomass δ15N time-series from the surface Sargasso Sea exhibits significant seasonal variations, with the lowest values in fall and the highest values in spring. The roles of hydrography, biogeochemistry, and ecosystem dynamics in driving these seasonal variations will be discussed. These data from the modern subtropical ocean form part of a greater effort to ground-truth the use of foram-bound δ15N to reconstruct past nutrient conditions, not only as a recorder of the isotopic composition of nitrogen supply in oligotrophic environments but also as a recorder of the degree of nitrate consumption in high-latitude regions such as the Southern Ocean.

Increase in Dominance of Eukaryote Over Prokaryote Phytoplankton Biomass Between the Surface and the Deep Chlorophyll Maximum in the Summertime Western North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Vaillancourt, R. D.; Lance, V. P.; Hargreaves, B. R.; Marra, J. F.

2016-02-01

We report a general increase in the dominance of eukaryotes phytoplankton between the surface and the deep chlorophyll maximum (DCM) depths in the western North Atlantic Ocean along a transect between Bermuda (BATS) and the New England continental shelf sea during the summer 2007 & 2008. At each of 40 stations HPLC pigment concentrations were determined from 6 -10 depths from the surface to near or below the base of the euphotic zone. The community composition was determined using CHEMTAX (Mackey et al. 1996) using marker pigment ratios for varying light regimes published in Higgins et al (2011) and from our own monocultures. Cluster analysis was used to partition the dataset into five distinct regional groups to reduce the pigment ratio variability in CHEMTAX runs. Within each regional group the data were again clustered depth-wise into five to seven overlapping optical depth (OD) bins, and each OD bin was analyzed using a pigment ratio matrix ideal for that light depth range. This analysis revealed the likely presence of nine pigment classes: pelagophytes, diatoms, dinoflagellates, Synechococcus sp., Prochlorococcs sp., cryptophytes, chlorophytes, prasinophytes, and haptophytes. Partial verification of CHEMTAX results was obtained using flow cytometry cell counts coincident with samples from the BATS stations that show reasonable (according to published values) Chl a/cell values for surface and deep populations. At most locations and depths, the eukaryote haptophyte group dominated the phytoplankton biomass. In the upper optical depth the proportion of phytoplankton biomass contributed by prokaryotes was 39 (± 23)%. Deeper, between OD 1 and 2, this proportion decreased to 33 (± 17)%, between ODs 2 and 4.6 to 25 (± 15)%, and below OD 4.6, to 21 (± 17)%. Some geographic variation was observed, with the trend most pronounced in oligotrophic ocean waters and weaker in continental shelf waters.

Methane in the South China Sea and the Western Philippine Sea

NASA Astrophysics Data System (ADS)

Tseng, Hsiao-Chun; Chen, Chen-Tung Arthur; Borges, Alberto V.; DelValls, T. Angel; Chang, Yu-Chang

2017-03-01

Approximately 700 water samples from the South China Sea (SCS) and 300 water samples from the western Philippine Sea (wPS) were collected during eight cruises from August 2003 to July 2007 to determine methane (CH4) distributions from the surface to a depth of 4250 m. The surface CH4 concentrations exceeded atmospheric equilibrium, both in the SCS and the wPS, and the concentrations were 4.5±3.6 and 3.0±1.2 nmol L-1, respectively. The sea-to-air fluxes were calculated, and the SCS and the wPS were found to emit CH4 to the atmosphere at 8.6±6.4 μmol m-2 d-1 and 4.9±4.9 μmol m-2 d-1, respectively. In the SCS, CH4 emissions were higher over the continental shelf (11.0±7.4 μmol m-2 d-1) than over the deep ocean (6.1±6.0 μmol m-2 d-1), owing to greater biological productivity and closer coupling with the sediments on the continental shelf. The SCS emitted 30.1×106 mol d-1 CH4 to the atmosphere and exported 1.82×106 mol d-1 CH4 to the wPS. The concentrations of both CH4 and chlorophyll a were high in the 150 m surface layer of the wPS, but were not significantly correlated with each other. CH4 concentrations generally declined with increasing depth below the euphotic zone but remained constant below 1,000 m, both in the SCS and the wPS. Some high CH4 concentrations were observed at mid-depths and bottom waters in the SCS, and were most likely caused by the release of CH4 from gas hydrates or gas seepage.

Coastal sources, sinks and strong organic complexation of dissolved cobalt within the US North Atlantic GEOTRACES transect GA03

NASA Astrophysics Data System (ADS)

Noble, Abigail E.; Ohnemus, Daniel C.; Hawco, Nicholas J.; Lam, Phoebe J.; Saito, Mak A.

2017-06-01

Cobalt is the scarcest of metallic micronutrients and displays a complex biogeochemical cycle. This study examines the distribution, chemical speciation, and biogeochemistry of dissolved cobalt during the US North Atlantic GEOTRACES transect expeditions (GA03/3_e), which took place in the fall of 2010 and 2011. Two major subsurface sources of cobalt to the North Atlantic were identified. The more prominent of the two was a large plume of cobalt emanating from the African coast off the eastern tropical North Atlantic coincident with the oxygen minimum zone (OMZ) likely due to reductive dissolution, biouptake and remineralization, and aeolian dust deposition. The occurrence of this plume in an OMZ with oxygen above suboxic levels implies a high threshold for persistence of dissolved cobalt plumes. The other major subsurface source came from Upper Labrador Seawater, which may carry high cobalt concentrations due to the interaction of this water mass with resuspended sediment at the western margin or from transport further upstream. Minor sources of cobalt came from dust, coastal surface waters and hydrothermal systems along the Mid-Atlantic Ridge. The full depth section of cobalt chemical speciation revealed near-complete complexation in surface waters, even within regions of high dust deposition. However, labile cobalt observed below the euphotic zone demonstrated that strong cobalt-binding ligands were not present in excess of the total cobalt concentration there, implying that mesopelagic labile cobalt was sourced from the remineralization of sinking organic matter. In the upper water column, correlations were observed between total cobalt and phosphate, and between labile cobalt and phosphate, demonstrating a strong biological influence on cobalt cycling. Along the western margin off the North American coast, this correlation with phosphate was no longer observed and instead a relationship between cobalt and salinity was observed, reflecting the importance of coastal input processes on cobalt distributions. In deep waters, both total and labile cobalt concentrations were lower than in intermediate depth waters, demonstrating that scavenging may remove labile cobalt from the water column. Total and labile cobalt distributions were also compared to a previously published South Atlantic GEOTRACES-compliant zonal transect (CoFeMUG, GAc01) to discern regional biogeochemical differences. Together, these Atlantic sectional studies highlight the dynamic ecological stoichiometry of total and labile cobalt. As increasing anthropogenic use and subsequent release of cobalt poses the potential to overpower natural cobalt signals in the oceans, it is more important than ever to establish a baseline understanding of cobalt distributions in the ocean.

Phosphorus dynamics in biogeochemically distinct regions of the southeast subtropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Duhamel, Solange; Björkman, Karin M.; Repeta, Daniel J.; Karl, David M.

2017-02-01

The southeast subtropical Pacific Ocean was sampled along a zonal transect between the coasts of Chile and Easter Island. This remote area of the world's ocean presents strong gradients in physical (e.g., temperature, density and light), chemical (e.g., salinity and nutrient concentrations) and microbiological (e.g., cell abundances, biomass and specific growth rates) properties. The goal of this study was to describe the phosphorus (P) dynamics in three main ecosystems along this transect: the upwelling regime off the northern Chilean coast, the oligotrophic area associated with the southeast subtropical Pacific gyre and the transitional area in between these two biomes. We found that inorganic phosphate (Pi) concentrations were high and turnover times were long (>210 nmol l-1 and >31 d, respectively) in the upper water column, along the entire transect. Pi uptake rates in the gyre were low (euphotic layer integrated rates were 0.26 mmol m-2 d-1 in the gyre and 1.28 mmol m-2 d-1 in the upwelling region), yet not only driven by decreases in particle mass or cell abundance (particulate P- and cell- normalized Pi uptake rates in the euphotic layer were ∼1-4 times and ∼3-15 times lower in the gyre than in the upwelling, respectively). However these Pi uptake rates were at or near the maximum Pi uptake velocity (i.e., uptake rates in Pi amended samples were not significantly different from those at ambient concentration: 1.5 and 23.7 nmol l-1 d-1 at 50% PAR in the gyre and upwelling, respectively). Despite the apparent Pi replete conditions, selected dissolved organic P (DOP) compounds were readily hydrolyzed. Nucleotides were the most bioavailable of the DOP substrates tested. Microbes actively assimilated adenosine-5‧-triphosphate (ATP) leading to Pi and adenosine incorporation as well as Pi release to the environment. The southeast subtropical Pacific Ocean is a Pi-sufficient environment, yet DOP hydrolytic processes are maintained and contribute to P-cycling across the wide range of environmental conditions present in this ecosystem.

The annual cycle of primary productivity in a tropical estuary: the inner regions of the Golfo de Nicoya, Costa Rica.

PubMed

Gocke, K; Cortés, J; Murillo, M M

2001-12-01

A one year cycle of primary productivity (PP) was studied using the "light and dark bottle" technique in the Golfo de Nicoya, located at 10 degrees N and 85 degrees W at the Pacific coast of Costa Rica. Samples were always incubated at 0, 1, 2, 3 and 4 m depth for 5 hrs from 8:30 till 13:30. The measurements were performed twice per month, first around high tide and one week later at low tide to account for tidal influences. This routine study was supplemented by special measurements about regional and short-term variations of primary productivity using the 14C-method, which mainly served to account for the shortcomings of the routinely employed incubation technique. The upper Golfo de Nicoya is an extremely productive, phytoplankton dominated estuarine system with an annual gross PP of 1037, a net PP of 610 and a community respiration of 427 g C m(-2) a(-1). Highest monthly PP values occurred during the dry season and at the beginning of the rainy season. Peaks in primary productivity coincided with massive blooms of red tide forming algae. Internal biological dynamics, estuarine circulation and land run-off are the most important nutrient sources. High water turbidity reduces the euphotic layer to 4-5 m depth, making the underwater light regime the rate limiting factor. On an annual basis, 41% of the organic carbon produced in the system is already consumed in the euphotic layer. Considering the entire water column (mean depth at mean tidal water level is around 7.7 m) 79% is consumed in the pelagial. Taking into account the organic material consumed and stored in the sediments the carbon budget of the upper gulf is probably balanced. Since, however, the system receives a considerable amount of organic material from its terrestrial surroundings (especially from the mangrove forests), a surplus of organic carbon is exported from the upper Golfo de Nicoya, which enhances the overall water productivity of the lower gulf and the adjacent area.

Influence of basin-scale and mesoscale physical processes on biological productivity in the Bay of Bengal during the summer monsoon

NASA Astrophysics Data System (ADS)

Muraleedharan, K. R.; Jasmine, P.; Achuthankutty, C. T.; Revichandran, C.; Dinesh Kumar, P. K.; Anand, P.; Rejomon, G.

2007-03-01

Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July-August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m -3), low surface primary production (2.55 mg C m -3 day -1) and low zooplankton biovolume (0.14 ml m -3). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO 3-N > 8.2 μM, PO 4-P > 0.8 μM, SiO 4-Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a - 0.25 mg m -3, PP - 9.23 mg C m -3 day -1), and mesozooplankton biovolume (1.12 ml m -3) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.

Light response of phytoplankton in the South Atlantic Ocean: Interpretation of observations and application to remote sensing

NASA Technical Reports Server (NTRS)

Hood, Raleigh R.

1995-01-01

A simplified, nonspectral derivation of a classical theory in plant physiology is presented and used to derive an absorption-based primary productivity algorithm. Field observations from a meridional transect (4 deg N to 42 deg S) in the Atlantic Ocean are then described and interpreted in this theoretical context. The observations include photosynthesis-irradiance curve parameters (alpha and P(sub max)), chlorophyll a and phaeopigment concentration, and estimated phytoplankton absorption coefficients at wavelength = 440 nm (a(sub ph)(440)). Observations near the top (50% I(sub 0)) and bottom (6% I(sub 0)) of the euphotic zone are contrasted. At both light levels, alpha, P(sub max), a(sub ph)(440), and pigment concentration varied similarly along the transect: values were highest at the equator and at the southern end of the transect and lowest in the central South Atlantic. It is concluded that this pattern was related to increased nutrient availability due to equatorial upwelling in the north, and increased wind mixing in the south. At the 50% light level, alpha increased relative to a(sub ph) at the southern end of the transect. This result appears to reflect a large-scale meridional (southward) increase in the average quantum efficiency of the photosynthetic units of the phytoplankton. A correlation analysis of the data reveals that at the 50% light level, variations in P(sub max) were more closely related to a(sub ph)(440) than chlorophyll concentration and that phytoplankton absorption explains 90% of the variability in P(sub max). In theory, this shows that the ratio of the average quantum efficiency of the photosynthetic units of the phytoplankton to the product of their average absorption cross section and turnover time is relatively constant. This result is used to simplify the absorption-based primary productivity algorithm derived previously. The feasibility of using this model to estimate production rate from satellite ocean color observations is discussed. It is concluded that an absorption-based algorithm should provide more accurate production rate estimates than one based upon chlorophyll (pigment) concentration.

Acoustic estimates of zooplankton and micronekton biomass in cyclones and anticyclones of the northeastern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Ressler, Patrick Henry

2001-12-01

In the Gulf of Mexico (GOM), coarse to mesoscale eddies can enhance the supply of limiting nutrients into the euphotic zone, elevating primary production. This leads to 'oases' of enriched standing stocks of zooplankton and micronekton in otherwise oligotrophic deepwater (>200 m bottom depth). A combination of acoustic volume backscattering (Sv) measurements with an acoustic Doppler current profiler (ADCP) and concurrent net sampling of zooplankton and micronekton biomass in GOM eddy fields between October 1996 and November 1998 confirmed that cyclones and flow confluences were areas of locally enhanced Sv and standing stock biomass. Net samples were used both to 'sea-truth' the acoustic measurements and to assess the influence of taxonomic composition on measured Sv. During October 1996 and August 1997, a mesoscale (200--300 km diameter) cyclone-anticyclone pair in the northeastern GOM was surveyed as part of a cetacean (whale and dolphin) and seabird habitat, study. Acoustic estimates of biomass in the upper 10--50 m of the water column showed that the cyclone and flow confluence were enriched relative to anticyclonic Loop Current Eddies during both years. Cetacean and seabird survey results reported by other project researchers imply that these eddies provide preferential habitat because they foster locally higher concentrations of higher-trophic-level prey. Sv measurements in November 1997 and 1998 showed that coarse scale eddies (30--150 km diameter) probably enhanced nutrients and S, in the deepwater GOM within 100 km of the Mississippi delta, an area suspected to be important habitat for cetaceans and seabirds. Finally, Sv, data collected during November-December 1997 and October-December 1998 from a mooring at the head of DeSoto Canyon in the northeastern GOM revealed temporal variability at a single location: characteristic temporal decorrelation scales were 1 day (diel vertical migration of zooplankton and micronekton) and 5 days (advective processes). A combination of acoustic and net sampling is a useful way to survey temporal and spatial patterns in zooplankton and micronekton biomass in coarse to mesoscale eddies. Further research should employ such a combination of methods to investigate plankton patterns in eddies and their implications for cetacean and seabird habitat.

A new bio-optical model to estimate phytoplankton primary production: An application in the eastern Mediterranean Sea

NASA Astrophysics Data System (ADS)

Stefanì, Chiara; Bonamano, Simone; Melchiorri, Cristiano; Piermattei, Viviana; Fani, Fabiola; Lazzara, Luigi; Marcelli, Marco

2015-04-01

The estimation of phytoplankton primary production provides basic input for the quantification of carbon flux in the ocean because of the strong relationship between available photosynthetic energy at the ocean surface and energy storage by algal photosynthesis. We used a new version of PhytoVFP (Variable Fluorescence Phytoplankton Production) bio-optical model to calculate phytoplankton primary production (PP) in the euphotic zone. PhytoVFP is classified as a Wavelength- and Depth-resolved (WRDR) model and is based on the implementation of photosynthetic efficiency (Fv / Fmax), measured in-situ by the PrimProd probe. An innovation of the model is the reproduction of the daily photoacclimation process by varying photosynthetic parameters (Ek, alfa and Pbmax ) along the water column as a function of stratification. The PhytoVFP model is structured into three main modules: (1) "PAR estimation ";- (2) "Photo-acclimation of marine phytoplankton"; - (3) "Phytoplankton primary production estimation". The performance of the PhytoVFP model was evaluated using PAR and 14C primary production measures collected during the SAMCA3 and SAMCA4 oceanographic cruises. The comparison between the measured and calculated radiation showed a good correlation, both in the surface and along the water column (R2 = 0.8992 in the presence, and R2 = 0.8747 in the absence, of clouds) Sensitivity tests, carried out on phie (photosynthetic quantum yield) and beta (photoinhibition parameter), allowed us to identify the best model parametrization which minimized the MAE (Mean Absolute Error). The values assigned to these parameters allowed to have a good correlation between the measured and estimated primary production values (R² = 0.808923). The results of PhytoVFP model have been also compared with its older version and the Morel (1991) model showing that the MAE of the new version is lower than the other models. The PhytoVFP model was applied on Primprod data collected during MedGOOS12 cruise in order to analyse the vertical distribution of phytoplankton primary production in the eastern Mediterranean sea.

Meiofaunal abundances and faunal similarity on the continental rise off the coast of California

NASA Astrophysics Data System (ADS)

Rohal, Melissa; Thistle, David; Easton, Erin E.

2014-11-01

Metazoan meiofauna (e.g., nematodes, benthic copepods) play important roles in deep-sea sediment communities, but information as basic as standing stocks is not known for much of the world ocean. We therefore sampled six stations: one near the 2700-m isobath and one near the 3700-m isobath off northern, central, and southern California. We counted benthic copepods, both Desmoscolecidae and nondesmoscolecid nematodes, kinorhynchs, nauplii, and ostracods from multiple-corer samples. Nematodes from our 2700-m and 3700-m stations, and ostracods and nauplii from our 3700-m stations, were unusually abundant compared to those from other stations from comparable depths in the Pacific. Off California, the abundances of benthic copepods, kinorhynchs, and nondesmoscolecids at the 2700-m stations were significantly greater than those at the 3700-m stations. Abundance of benthic copepods was correlated with the percentage of medium sand in the sediment, so sediment texture could be important to them. That of kinorhynchs was correlated with the concentration of chloroplastic-pigment equivalents and percentage nitrogen, so consumable material from the euphotic zone could be important to them. In contrast to the usual pattern of decreasing abundance with depth, Desmoscolecidae abundance in the central region was greater at the 3700-m than at the 2700-m station. The three regions differed significantly in both kinorhynch and ostracod abundances, independently of depth. In the food-poor deep sea, animals are expected to be more abundant where food is plentiful. Unexpectedly, ostracod abundance was negatively correlated with all food variables. A possible explanation is that the natural enemies of ostracods are abundant where food is abundant. Multivariate faunal similarity at 2700 m differed significantly from that at 3700 m, independently of regions. Benthic copepods were most responsible for the difference. Regions also differed in multivariate faunal similarity independently of depth. In general, faunal similarity is expected to decrease as separation distance increases, but unexpectedly, the northern- and southern-region faunas were more similar to each other than to the central-region fauna. Kinorhynchs were most responsible for this pattern.

Biological response to coastal upwelling and dust deposition in the area off Northwest Africa

NASA Astrophysics Data System (ADS)

Ohde, T.; Siegel, H.

2010-05-01

Nutrient supply in the area off Northwest Africa is mainly regulated by two processes, coastal upwelling and deposition of Saharan dust. In the present study, both processes were analyzed and evaluated by different methods, including cross-correlation, multiple correlation, and event statistics, using remotely sensed proxies of the period from 2000 to 2008 to investigate their influence on the marine environment. The remotely sensed chlorophyll- a concentration was used as a proxy for the phytoplankton biomass stimulated by nutrient supply into the euphotic zone from deeper water layers and from the atmosphere. Satellite-derived alongshore wind stress and sea-surface temperature were applied as proxies for the strength and reflection of coastal upwelling processes. The westward wind and the dust component of the aerosol optical depth describe the transport direction of atmospheric dust and the atmospheric dust column load. Alongshore wind stress and induced upwelling processes were most significantly responsible for the surface chlorophyll- a variability, accounting for about 24% of the total variance, mainly in the winter and spring due to the strong north-easterly trade winds. The remotely sensed proxies allowed determination of time lags between biological response and its forcing processes. A delay of up to 16 days in the surface chlorophyll- a concentration due to the alongshore wind stress was determined in the northern winter and spring. Although input of atmospheric iron by dust storms can stimulate new phytoplankton production in the study area, only 5% of the surface chlorophyll- a variability could be ascribed to the dust component in the aerosol optical depth. All strong desert storms were identified by an event statistics in the time period from 2000 to 2008. The 57 strong storms were studied in relation to their biological response. Six events were clearly detected in which an increase of chlorophyll- a was caused by Saharan dust input and not by coastal upwelling processes. Time lags of <8 days, 8 days, and 16 days were determined. An increase in surface chlorophyll- a concentration of up to 2.4 mg m -3 after dust storms in which the dust component of the aerosol optical depth was up to 0.9 was observed.

Coupling of the spatial dynamic of picoplankton and nanoflagellate grazing pressure and carbon flow of the microbial food web in the subtropical pelagic continental shelf ecosystem

NASA Astrophysics Data System (ADS)

Chiang, K.-P.; Tsai, A.-Y.; Tsai, P.-J.; Gong, G.-C.; Tsai, S.-F.

2013-01-01

In order to investigate the mechanism of spatial dynamics of picoplankton community (bacteria and Synechococcus spp.) and estimate the carbon flux of the microbial food web in the oligotrophic Taiwan Warm Current Water of subtropical marine pelagic ecosystem, we conducted size-fractionation experiments in five cruises by the R/V Ocean Research II during the summers of 2010 and 2011 in the southern East China Sea. We carried out culture experiments using surface water which, according to a temperature-salinity (T-S) diagram, is characterized as oligotrophic Taiwan Current Warm Water. We found a negative correlation bettween bacteria growth rate and temperature, indicating that the active growth of heterotrophic bacteria might be induced by nutrients lifted from deep layer by cold upwelling water. This finding suggests that the area we studied was a bottom-up control pelagic ecosystem. We suggest that the microbial food web of an oligotrophic ecosystem may be changed from top-down control to resource supply (bottom-up control) when a physical force brings nutrient into the oligotrophic ecosystem. Upwelling brings nutrient-rich water to euphotic zone and promotes bacteria growth, increasing the picoplankton biomass which increased the consumption rate of nanoflagellate. The net growth rate (growth rate-grazing rate) becomes negative when the densities of bacteria and Synechococcus spp. are lower than the threshold values. The interaction between growth and grazing will limit the abundances of bacteria (105-106 cells mL-1 and Synechococcus spp. (104-105 cells mL-1) within a narrow range, forming a predator-prey eddy. Meanwhile, 62% of bacteria production and 55% of Synechococcus spp. production are transported to higher trophic level (nanoflagellate), though the cascade effect might cause an underestimation of both percentages of transported carbon. Based on the increasing number of sizes we found in the size-fractionation experiments, we estimated that the predation values were underestimated by 28.3% for bacteria and 34.6% for Synechococcus spp. Taking these corrections into consideration, we conclude that picoplankton production is balanced by nonoflagellate grazing and the diet of nanoflagellate is composed of 64% bacteria and 36% Synechococcus spp.

Surface ocean carbon isotope anomalies on glacial terminations: An alternative view

NASA Astrophysics Data System (ADS)

Lund, D. C.; Cote, M.; Schmittner, A.

2016-12-01

Late Pleistocene glacial terminations are characterized by surface ocean carbon isotope minima on a global scale. During the last deglaciation (i.e. Termination 1), planktonic foraminiferal δ13C anomalies occurred in the Atlantic, Indian, Pacific, and Southern Oceans. Despite the apparently ubiquitous nature of δ13C anomalies on glacial terminations, their cause remains a matter of ongoing debate. The prevailing view is that isotopically light carbon from the abyss was upwelled in the Southern Ocean, resulting in outgassing of 13C-depleted carbon to the atmosphere and its advection to lower latitudes via mode and intermediate waters (Spero and Lea, 2002). Alternatively, carbon isotope minima may be driven by weakening of the biological pump related to circulation-driven changes in the oceanic preformed nutrient budget (Schmittner and Lund, 2015). Here we assess the deep upwelling and biological pump hypotheses using a new compilation of 70 globally-distributed planktonic δ13C records from the published literature. We find that 1) the mean deglacial δ13C anomaly is similar in all ocean basins, 2) the eastern tropical Pacific yields smaller mean δ13C anomalies than the western tropical Pacific, and 3) δ13C anomalies in the Southern Ocean decrease with increasing latitude. Our results are generally inconsistent with the deep upwelling hypothesis, which predicts that the δ13C signal should be largest in the Southern Ocean and upwelling regions. Instead, the spatial pattern in δ13C anomalies supports the biological pump hypothesis, which predicts that reduced export of light carbon from the euphotic zone triggers negative carbon isotope anomalies in the surface ocean and positive anomalies at intermediate depths. Upwelling of relatively 13C-enriched intermediate waters tends to moderate carbon isotope minima in upwelling regions. Our results suggest that the initial rise in atmospheric CO2 during Termination 1 was likely due to weakening of the biological pump associated with a reduction in the Atlantic Meridional Overturning Circulation, consistent with model results (Schmittner and Lund, 2015). Spero, H., and D. Lea (2002) Science 296, 522-525. Schmittner, A., and D. Lund (2015) Climate of the Past 11, 135-152.

Identifying organism involved in new and regenerated production using TAG-SIP

NASA Astrophysics Data System (ADS)

Morando, M.; Capone, D. G.

2016-02-01

The coupling of stable isotope probing (SIP) with high throughput sequencing (TAG-SIP), allows examination of DNA from individual taxa for the incorporation of a specific isotopically labeled substrate, facilitating an in-depth investigation of the activity and functional diversity of in situ microbial communities. This approach was applied to the monthly San Pedro Ocean Time-series (SPOT), during April of 2014 in order to characterize the organisms involved in new and regenerated production by investigating the assimilation of 15N-NO3-, 15N-NH4+, and 15N-urea at several light depths throughout the euphotic zone. Overall, very little variation was seen between the DNA banding patterns and density of each discrete OTU compared over multiple control treatments, i.e. unlabeled substrate was added to each control and so any disparity between the DNA banding of these OTU replicates reflects methodological variation. The lack of disparity found here further demonstrates TAG-SIP's high precision, accuracy, and more importantly validates the TAG-SIP's reproducibility in both gradient formation and DNA sedimentation with respect to density. The mean density of these discrete control OTU DNA bands (n=7) were then compared to those of their isotopically treated equivalent OTU after a 24h incubation in order to accurately assess and identify significant shifts in DNA density. Therefore we are confident that differences in density between control and treated sample DNA greater than the variation quantified among the controls themselves, is direct evidence of `heavy' isotope incorporation, i.e. metabolic activity and growth. Direct evidence of activity was found in a broad range of taxa, thought not every treatment yielded positive results. As expected the majority of the organisms identified as assimilators were found within the 15N-NH4+ treatments. Many taxa displayed evidence of uptake in one or more but not all treatments providing evidence on which taxa are metabolizing a broad range of substrates as opposed to those which are specializing. Overall, this dataset provides unique insight into which organisms contribute to new biomass formation and ultimately to carbon export and those that help maintain the population through the recycling of nutrients.

Rethinking CCD's Significance in Estimating Late Neogene Whole Ocean Carbonate Budget

NASA Astrophysics Data System (ADS)

Si, W.; Rosenthal, Y.

2017-12-01

The global averaged calcite compensation depth (CCD) record is conventionally used to reconstruct two correlatable parameters of the carbonate system - the alkalinity budget of the ocean and/or the saturation state of the ocean. Accordingly, the available CCD reconstructions have been interpreted to suggest either relative stable (Pearson and Palmer, 2000) or increased alkalinity of the ocean over the past 15 Ma (Tyrrell and Zeebe, 2004; Pälike et al., 2012). However, CCD alone is insufficient to constrain the carbonate system because the weathering flux of alkalinity into the ocean is not only balanced by CaCO3 dissolution on the seafloor but also by the biologic production in the euphotic zone and, the CCD records cannot be readily interpreted as changes in either process. Here, we present evidence of the co-evolution of surface CaCO3 production and deepsea dissolution through the late Neogene. By examining separately the mass accumulation rates (MAR) of coccoliths, planktonic foraminifera, and quantifying dissolution (using a proxy revised from Broecker et al., 1999) in seventeen deepsea cores from multiple depth-transects, we find that 1) MAR of dissolution-resistant coccoliths was substantially higher in the mid Miocene and declining on a global scale towards the present; 2) unlike coccoliths, MAR of planktonic foraminifera, shows no apparent secular trend through that time; 3) the revised dissolution index, shows significantly improved preservation of planktonic foraminiferal shells over that time, particularly at intermediate water depth and exhibits close association between changes in preservation with key climatic events. Our new records have two immediate implications. First, the substantially weakened pelagic biogenic carbonate production from mid Miocene to present alone could account for the improved preservation of deepsea carbonates without calling for a scenario of increased weathering input. Second, with the constrain of global averaged CCD records, the net accumulation of pelagic carbonate has declined over the course of late Neogene. Hence, the weathering alkalinity input should have decreased since 15 Ma, as oppose to the weathering hypothesis (Raymo et al., 1988).

Recovery of sockeye salmon in the Elwha River, Washington, after dam removal: Dependence of smolt production on the resumption of anadromy by landlocked kokanee

USGS Publications Warehouse

Hansen, Adam G.; Gardner, Jennifer R.; Beauchamp, David A.; Paradis, Rebecca; Quinn, Thomas P.

2016-01-01

Pacific salmon Oncorhynchus spp. are adept at colonizing habitat that has been reopened to anadromous passage. Sockeye Salmon O. nerka are unique in that most populations require lakes to fulfill their life history. Thus, for Sockeye Salmon to colonize a system, projects like dam removals must provide access to lakes. However, if the lakes contain landlocked kokanee (lacustrine Sockeye Salmon), the recovery of Sockeye Salmon could be mediated by interactions between the two life history forms and the processes associated with the resumption of anadromy. Our objective was to evaluate the extent to which estimates of Sockeye Salmon smolt production and recovery are sensitive to the resumption of anadromy by kokanee after dam removal. We informed the analysis based on the abiotic and biotic features of Lake Sutherland, which was recently opened to passage after dam removal on the Elwha River, Washington. We first developed maximum expectations for the smolt-producing capacity of Lake Sutherland by using two predictive models developed from Sockeye Salmon populations in Alaska and British Columbia: one model was based on the mean seasonal biomass of macrozooplankton, and the other was based on the euphotic zone volume of the lake. We then constructed a bioenergetics-based simulation model to evaluate how the capacity of Lake Sutherland to rear yearling smolts could change with varying degrees of anadromy among O. nerka fry. We demonstrated that (1) the smolt-producing capacity of a nursery lake for juvenile Sockeye Salmon changes in nonlinear ways with changes in smolt growth, mortality, and the extent to which kokanee resume anadromy after dam removal; (2) kokanee populations may be robust to changes in abundance after dam removal, particularly if lakes are located higher in the watershed on tributaries separate from where dams were removed; and (3) the productivity of newly establishing Sockeye Salmon can vary considerably depending on whether the population becomes rearing limited or is recruitment limited and depending on how adult escapement is managed.

Oxygen cycling in the northern Benguela Upwelling System: Modelling oxygen sources and sinks

NASA Astrophysics Data System (ADS)

Schmidt, Martin; Eggert, Anja

2016-12-01

This paper elucidates the oxygen dynamics in the northern Benguela Upwelling System by means of process oriented, numerical modelling. Owing to the complex physical-biological interaction in this system, a coupled hydrodynamic-biogeochemical model is required to grasp the various aspects of the oxygen dynamics. We used high-resolution atmospheric fields derived from observations to force our model, available since 1999. The model results represent a 15 years, consistent data set of realistic hydrographic and ecosystem variables, including oxygen distribution patterns. After a concise description of the main aspects of the model, we use the model data to analyse the components contributing to the oxygen dynamics, namely, the ocean circulation, the exchange between ocean and atmosphere as well as the local biogeochemical oxygen cycling in the system. We thoroughly validate the model with available field observations and remote sensing data. The strengths of coastal upwelling, which controls the nutrient supply to the euphotic zone, as well as the poleward undercurrent that carries oxygen and nutrients to the shelf in the northern Benguela Upwelling System are well reproduced in the model. Among the biological oxygen sinks, mineralisation in the sediment, respiration of zooplankton and nitrification in the water column are important. We also found that vertical migration of zooplankton in response to the oxygen conditions provides a regulating feedback, which may prevent a complete deoxygenation of suboxic waters. As long as oxygen or nitrate are available in the bottom waters, the activities of chemolithoautotrophic sulphur bacteria on the sediment surface keep the redoxcline within the sediment and prevent the release of hydrogen sulphide into the water column. By horizontal integration of the simulated ocean-atmosphere oxygen flux, it can be shown that the Kunene upwelling cell between 16 ° S and 18 ° S is a boundary between the equatorial ocean, characterise by weak oxygen release to the atmosphere, and the subtropical Benguela Upwelling System governed by an enhanced and seasonal varying flux. Furthermore, a comparison of oxygen fluxes controlled by physical transport versus biogeochemical processes shows that the physical processes dominate in the northern Benguela Upwelling System.

Are boundary conditions in surface productivity at the Southern Polar Front reflected in benthic activity?

NASA Astrophysics Data System (ADS)

Brandt, Angelika; Vanreusel, Ann; Bracher, Astrid; Jule Marie Hoppe, Clara; Lins, Lidia; Meyer-Löbbecke, Anna; Altenburg Soppa, Mariana; Würzberg, Laura

2014-10-01

In austral summer 2012, during the expedition ANT-XXVIII/3 on board RV Polarstern, two sites were sampled 1600 km apart in the South Polar Front area (52°S) at the boundary of different productivity regimes for meio- and macrobenthos using a multiple-corer and an epibenthic sledge, respectively. Patterns in density and abundance data were compared between different size classes of the benthos and interpreted in relation to surface primary productivity data and sediment oxygen consumption. We tested the hypothesis that long-term satellite-derived surface phytoplankton biomass, in situ real time biomass, and productivity measurements at the surface and throughout the euphotic zone are reflected in abyssal benthos densities, abundances and activity. Specifically, we investigated the effect of boundary conditions for lower and higher surface productivity. Surface and integrated to 100 m depth biomass and primary productivity measurements vary stations, with the lowest values at station 85 (0.083 mg Chl-a m-3 at surface, 9 mg Chl-a m-2 and 161 mg C m-2 d-1- integrated over the first 100 m depth), and the highest values at station 86 (2.231 mg Chl-a m-3 at surface, 180 mg Chl-a m-2 and 2587 mg C m-2 d-1 integrated over first 100 m depth). Total meiofaunal densities varied between 102 and 335 individuals/10 cm². Densities were the highest at station 86-30 (335 individuals) and lowest at station 81-13 (102 individuals). Total macrofaunal densities (individuals/1000 m²) varied between 26 individuals at station 81-17 and 194 individuals at station 86-24. However, three EBS hauls were taken at station 86 with a minimum of 80 and a maximum of 194 individuals. Sediment oxygen consumption did not vary significantly between stations from east to west. Bentho-pelagic coupling of meio- and macrobenthic communities could not be observed in the South Polar Front at the boundary conditions from low to high surface productivity between stations 81 and 86.

Quantifying the biological impact of surface ocean light attenuation by colored detrital matter in an ESM using a new optical parameterization

NASA Astrophysics Data System (ADS)

Kim, G. E.; Pradal, M.-A.; Gnanadesikan, A.

2015-08-01

Light attenuation by colored detrital material (CDM) was included in a fully coupled Earth system model (ESM). This study presents a modified parameterization for shortwave attenuation, which is an empirical relationship between 244 concurrent measurements of the diffuse attenuation coefficient for downwelling irradiance, chlorophyll concentration and light absorption by CDM. Two ESM model runs using this parameterization were conducted, with and without light absorption by CDM. The light absorption coefficient for CDM was prescribed as the average of annual composite MODIS Aqua satellite data from 2002 to 2013. Comparing results from the two model runs shows that changes in light limitation associated with the inclusion of CDM decoupled trends between surface biomass and nutrients. Increases in surface biomass were expected to accompany greater nutrient uptake and therefore diminish surface nutrients. Instead, surface chlorophyll, biomass and nutrients increased together. These changes can be attributed to the different impact of light limitation on surface productivity versus total productivity. Chlorophyll and biomass increased near the surface but decreased at greater depths when CDM was included. The net effect over the euphotic zone was less total biomass leading to higher nutrient concentrations. Similar results were found in a regional analysis of the oceans by biome, investigating the spatial variability of response to changes in light limitation using a single parameterization for the surface ocean. In coastal regions, surface chlorophyll increased by 35 % while total integrated phytoplankton biomass diminished by 18 %. The largest relative increases in modeled surface chlorophyll and biomass in the open ocean were found in the equatorial biomes, while the largest decreases in depth-integrated biomass and chlorophyll were found in the subpolar and polar biomes. This mismatch of surface and subsurface trends and their regional dependence was analyzed by comparing the competing factors of diminished light availability and increased nutrient availability on phytoplankton growth in the upper 200 m. Understanding changes in biological productivity requires both surface and depth-resolved information. Surface trends may be minimal or of the opposite sign than depth-integrated amounts, depending on the vertical structure of phytoplankton abundance.

A high-resolution record of Holocene millennial-scale oscillations of surface water, foraminiferal paleoecology and sediment redox chemistry in the SE Brazilian margin

NASA Astrophysics Data System (ADS)

Dias, B. B.; Barbosa, C. F.; Albuquerque, A. L.; Piotrowski, A. M.

2014-12-01

Holocene millennial-scale oscillations and Bond Events (Bond et al. 1997) are well reported in the North Atlantic as consequence of fresh water input and weaking of the Atlantic Meridional Overturning Circulation (AMOC). It has been hypothesized that the effect of weaking of AMOC would lead to warming in the South Atlantic due to "heat piracy", causing surface waters to warm and a reorganization of surface circulation. There are few reconstructions of AMOC strength in the South Atlantic, and none with a high resolution Holocene record of changes of productivity and the biological pump. We reconstruct past changes in the surface water mass hydrography, productivity, and sediment redox changes in high-resolution in the core KCF10-01B, located 128 mbsl water depth off Cabo Frio, Brazil, a location where upwelling is strongly linked to surface ocean hydrography. We use Benthic Foraminiferal Accumulation Rate (BFAR) to reconstruct productivity, which reveals a 1.3kyr cyclicity during the mid- and late-Holocene. The geochemistry of trace and rare earth elements on foraminiferal Fe-Mn oxide coatings show changes in redox-sensitive elements indicating that during periods of high productivity there were more reducing conditions in sediment porewaters, producing a Ce anomaly and reduction and re-precipitation of Mn oxides. Bond events 1-7 were identified by a productivity increase along with reducing sediment conditions which was likely caused by Brazil Current displacement offshore allowing upwelling of the nutritive bottom water South Atlantic Central Waters (SACW) to the euphotic zone and a stronger local biological pump. In a global context, correlation with other records show that this occurred during weakened AMOC and southward displacement of the ITCZ. We conclude that Bond climatic events and millennial-scale variability of AMOC caused sea surface hydrographic changes off the Brazilian Margin leading to biological and geochemical changes recorded in coastal records. The 8.2kyr climatic event is reported here for the first time in South American coastal sediment records as high productivity conditions and a rapid change in porewater redox chemistry.

Could Aerosol Dust Plume-derived Trace Metals and Inorganic Nutrient be Fueling the Recent Growth and Proliferation of Noctiluca scintillans Blooms in the Arabian Sea?

NASA Astrophysics Data System (ADS)

Tan, Y. S.; Ang, A.; Gomes, H. R.; Goes, J. I.

2016-12-01

Noctiluca scintillans, a species of mixotrophic dinoflagellate, has been proliferating in the Arabian Sea for the past 20 years in winter when convective mixing brings up nutrient-rich waters from deeper depths. It is believed that the unique mixotrophic nature of this organism, where it is able to feed on other phytoplankton, as well as photosynthesize by hosting a large endosymbiotic population of Pedinomonas noctilucae, gives it a greater competitive advantage over other phytoplankton. It is believed that this physiological plasticity of Noctiluca is responsible for the species shift from a diatom dominated ecosystem of the past in the Arabian sea, to the current widespread blooms of Noctiluca. Here we have attempted to examine how Noctiluca are able to sustain themselves over an extended period when nutrients from winter convective mixing are completely exhausted in the euphotic zone. In this study we test the hypotheses, that new inputs of nutrients from anthropogenic sources such as sewage and land-based nutrient runoff as well as from thick aeolian dust storms from the nearby regions such as Oman and Iran allow Noctiluca to survive and grow from winter into the spring inter-monsoon season. A recently cultured strain of Arabian Sea green Noctiluca grown in media amended with dust collected from Oman and Iran, different trace metals (Iron, Selenium and Cobalt) as well as nutrients (Nitrate, Ammonium and Urea) has been used to test our hypotheses. This is the first time such experiments have been conducted in the laboratory as previously no Noctiluca culture survived beyond 6 months. Growth of Noctiluca was measured in terms of cell count and the photosynthetic efficiency of cells using the fluorescence induction and relaxation technique which deduces the quantum efficiency of photochemistry in PSII. Moreover, we also measured the ammonia content in the cells which has long been suspected to provide buoyancy to cells and/or serve as a nitrogenous nutrient to the green endosymbionts that Noctiluca harbors.

Physical properties of the tunic in the pinkish-brown salp Pegea confoederata (Tunicata: Thaliacea).

PubMed

Sakai, Daisuke; Kakiuchida, Hiroshi; Nishikawa, Jun; Hirose, Euichi

2018-01-01

Invisibility in the water column is a crucial strategy for gelatinous zooplanktons in avoiding detection by visual predators, especially for animals distributed in the euphotic zone during the daytime; i.e., surface dwellers that do not undergo diel vertical migration. Salps, a member of the subphylum Tunicata (Urochordata), usually have a transparent body that is entirely covered with a cellulosic matrix, called the tunic. Some non-migrator species are known to exhibit a nano-scale nipple array on the tunic surface. However, the physical properties of the salp tunic has been poorly investigated, except for Thetys vagina , in which the tunic was expected to show low reflectance based on the refractive index of the tunic. Pegea confoederata is a non-vertical migrant salp showing pinkish-brown body. We measured the hardness, water content, absorption spectra, and refractive index of its tunic to evaluate its fragility and visibility. There are nipple-like protuberances about 80 nm high on the surface of the tunic in P. confoederata . The tunic is very soft; the maximum force to pierce the tunic with a steel rod (1 mm diameter) was < 1 N. The water content of the tunic was > 95%. The absorption spectra of the tunic had no prominent peaks in the wavelength range of 280-800 nm, indicating the tunic is nearly transparent. The difference in refractive indices between tunic and seawater was estimated as 0.002-0.015 at 589 nm. Rigorous coupled wave analyses (RCWA) of light reflection based on 3-dimensional models supported an anti-reflective effect of the nipple array on the tunic surface, which was estimated to vary slightly depending on the forms and the arrangement patterns of nipple-like protuberances in an array. The tunic of P. confoederata is very soft and contains more water than those of sessile tunicates (ascidians). Based on the refractive index of the tunic, light reflection is expected to be very low, making this salp's tunic barely visible in water column. Our results suggest that the nipple array may produce an anti-reflective effect.

On the Subsurface Chlorophyll Maximum layer in the Black Sea Romanian shelf waters

NASA Astrophysics Data System (ADS)

Vasiliu, Dan; Gomoiu, Marian-Traian; Secrieru, Dan; Caraus, Ioan; Balan, Sorin

2013-04-01

By analyzing data recorded in 38 sampling stations (bottom depths between 16 and 200 m) covering the entire Romanian shelf, from the Danube's mouths to the southern part of the coast, the authors study Subsurface Chlorophyll Maximum (SCM) from May 2009 to April 2011. Chlorophyll a (Chla), seawater temperature, salinity, sigma T, dissolved oxygen, ph, beam attenuation, were measured over the water column depth with the CTD probe and averaged over 1-db intervals (about 1 m depth). Nutrients and phytoplankton qualitative and quantitative parameters were recorded from different depths according to water masses stratification (inscribed in the research protocol of the cruise). In late winter/early spring, due to strong mixing processes of water masses, SCM was not observed in the Black Sea shelf waters. In spring (May), the Danube's increased discharges, characteristic to that period, strongly affected the vertical distribution of Chla, particularly in the area of the Danube's direct influence, where Chla reached maximum in the surface layer (19.76 - 30.39 µg.l-1). In the deeper sampling stations, a relatively weak SCM (Chla within 0.77 - 1.21 µg.l-1) was observed, mainly at the lower limit of the euphotic zone (between 30 and 40 m depths). Here, the position and magnitude of SCM seemed to be controlled mainly by the light conditions; the seasonal thermocline was not well contoured yet. In the warm season, once the stratification becomes stronger, the magnitude of SCM increased (Chla varies between 1.45 - 2.12 µg.l-1). The SCM was well pronounced below the upper boundary of thermocline, at depths between 20 and 25 m, where the dissolved oxygen concentrations have also reached the highest values (>10 mg.l-1 O2), thus suggesting strong photosynthetic processes, where both nutrient and light conditions are favorable. A particular situation was found in July 2010, when abnormally high discharges from the Danube led to a well pronounced SCM (3.23 - 6.87 µg.l-1 Chla) above thermocline (within 8 - 12 m depths) in the shallow waters, the nutrients being not limitative factors. Keywords Chlorophyll a, Subsurface Chlorophyll Maximum layer, the Black Sea, the Danube

Flux of particulate matter through copepods in the Northeast water polynya

NASA Astrophysics Data System (ADS)

Daly, Kendra L.

1997-01-01

Particulate organic carbon (POC) and nitrogen (PON) production by large calanoid copepods was investigated on the northeast Greenland shelf during August 1992 and May to August 1993. Both Calanus hyperboreus and C. glacialis females, when suspended in seawater collected from the chlorophyll maximum, produced about 40 pellets per day, which contained a carbon and nitrogen content equivalent to 8% and 6% of body carbon, respectively, and 2% of body nitrogen. In experiments, the carbon:nitrogen (C:N) ratio by weight of suspended particulates, C. hyperboreus, and fecal pellets was 6.7, 7.7 and 28.5, respectively. The unusually high C:N ratio for pellets, in part, may be attributed to elevated ratios of > 20μm size fractions of particulate organic matter, the size fraction more common in the diet of these large copepods and the fraction dominated by diatoms according to microscopic and pigment data. The implied elevated C:N ratios of large phytoplankton cells were probably due to nitrogen deficiency, as shown by other studies in this region. In addition, female C. hyperboreus appeared to be more efficient in assimilating nitrogen than carbon, which also would have contributed to high C:N ratios in egested pellets. Unfractionated POC concentrations explained 54% of the variability in carbon egestion and 70% of the variability in nitrogen egestion in copepods, whereas copepod body content accounted for little of the variation on the short time scales of the experiments. Carbon egestion by C. hyperboreus was positively correlated with POC concentrations at the depth of the chlorophyll maximum, while nitrogen egestion was negatively correlated with PON concentrations in the euphotic zone. Estimates of potential community egestion rates for the upper water column indicate that copepods represent a major pathway of organic carbon transformation in this Arctic shelf system. On average, copepods may have ingested 45% of the primary production and egested fecal matter equivalent to 20% of the carbon and 12% of the nitrogen particulate flux sedimenting from the surface layer. However, several lines of evidence suggest that pellets were remineralized in the water column and, hence, may have contributed little organic carbon and nitrogen to the benthos.

Bacterial activity in sea ice and open water of the Weddell Sea, Antarctica: A microautoradiographic study.

PubMed

Grossmann, S

1994-07-01

Metabolic activity of bacteria was investigated in open water, newly forming sea ice, and successive stages of pack ice in the Weddell Sea. Microautoradiography, using [(3)H]leucine as substrate, was compared with incorporation rates of [(3)H]leucine into proteins. Relation of [(3)H]leucine incorporation to the biomass of active bacteria provides information about changes of specific metabolic activity of cells. During a phytoplankton bloom in an ice-free, stratified water column, total numbers of bacteria in the euphotic zone averaged 2.3 × 10(5) ml(-1), but only about 13% showed activity via leucine uptake. Growth rate of the active bacteria was estimated as 0.3-0.4 days(-1). Total cell concentration of bacteria in 400 m depth was 6.6 × 10(4) ml(-1). Nearly 50% of these cells were active, although biomass production and specific growth rate were only about one-tenth that of the surface populations. When sea ice was forming in high concentrations of phytoplankton, bacterial biomass in the newly formed ice was 49.1 ng C ml(-1), exceeding that in open water by about one order of magnitude. Attachment of large bacteria to algal cells seems to cause their enrichment in the new ice, since specific bacterial activity was reduced during ice formation, and enrichment of bacteria was not observed when ice formed at low algal concentration. During growth of pack ice, biomass of bacteria increased within the brine channel system. Specific activity was still reduced at these later stages of ice development, and percentages of active cells were as low as 3-5%. In old, thick pack ice, bacterial activity was high and about 30% of cells were active. However, biomass-specific activity of bacteria remained significantly lower than that in open water. It is concluded that bacterial assemblages different to those of open water developed within the ice and were dominated by bacteria with lower average metabolic activity than those of ice-free water.

The Laurencia Paradox: An Endless Source of Chemodiversity.

PubMed

Harizani, Maria; Ioannou, Efstathia; Roussis, Vassilios

Nature, the most prolific source of biological and chemical diversity, has provided mankind with treatments for health problems since ancient times and continues to be the most promising reservoir of bioactive chemicals for the development of modern drugs. In addition to the terrestrial organisms that still remain a promising source of new bioactive metabolites, the marine environment, covering approximately 70% of the Earth's surface and containing a largely unexplored biodiversity, offers an enormous resource for the discovery of novel compounds. According to the MarinLit database, more than 27,000 metabolites from marine macro- and microorganisms have been isolated to date providing material and key structures for the development of new products in the pharmaceutical, food, cosmeceutical, chemical, and agrochemical sectors. Algae, which thrive in the euphotic zone, were among the first marine organisms that were investigated as sources of food, nutritional supplements, soil fertilizers, and bioactive metabolites.Red algae of the genus Laurencia are accepted unanimously as one of the richest sources of new secondary metabolites. Their cosmopolitan distribution, along with the chemical variation influenced to a significant degree by environmental and genetic factors, have resulted in an endless parade of metabolites, often featuring multiple halogenation sites.The present contribution, covering the literature until August 2015, offers a comprehensive view of the chemical wealth and the taxonomic problems currently impeding chemical and biological investigations of the genus Laurencia. Since mollusks feeding on Laurencia are, in many cases, bioaccumulating, and utilize algal metabolites as chemical weaponry against natural enemies, metabolites of postulated dietary origin of sea hares that feed on Laurencia species are also included in the present review. Altogether, 1047 secondary metabolites, often featuring new carbocyclic skeletons, have been included.The chapter addresses: (1) the "Laurencia complex", the botanical description and the growth and population dynamics of the genus, as well as its chemical diversity and ecological relations; (2) the secondary metabolites, which are organized according to their chemical structures and are classified into sesquiterpenes, diterpenes, triterpenes, acetogenins, indoles, aromatic compounds, steroids, and miscellaneous compounds, as well as their sources of isolation which are depicted in tabulated form, and (3) the biological activity organized according to the biological target and the ecological functions of Laurencia metabolites.

Diversity of picoeukaryotes at an oligotrophic site off the Northeastern Red Sea Coast

PubMed Central

2013-01-01

Background Picoeukaryotes are protists ≤ 3 μm composed of a wide diversity of taxonomic groups. They are an important constituent of the ocean’s microbiota and perform essential ecological roles in marine nutrient and carbon cycles. Despite their importance, the true extent of their diversity has only recently been uncovered by molecular surveys that resulted in the discovery of a substantial number of previously unknown groups. No study on picoeukaryote diversity has been conducted so far in the main Red Sea basin-a unique marine environment characterized by oligotrophic conditions, high levels of irradiance, high salinity and increased water temperature. Results We sampled surface waters off the coast of the northeastern Red Sea and analyzed the picoeukaryotic diversity using Sanger-based clone libraries of the 18S rRNA gene in order to produce high quality, nearly full-length sequences. The community captured by our approach was dominated by three main phyla, the alveolates, stramenopiles and chlorophytes; members of Radiolaria, Cercozoa and Haptophyta were also found, albeit in low abundances. Photosynthetic organisms were especially diverse and abundant in the sample, confirming the importance of picophytoplankton for primary production in the basin as well as indicating the existence of numerous ecological micro-niches for this trophic level in the upper euphotic zone. Heterotrophic organisms were mostly composed of the presumably parasitic Marine Alveolates (MALV) and the presumably bacterivorous Marine Stramenopiles (MAST) groups. A small number of sequences that did not cluster closely with known clades were also found, especially in the MALV-II group, some of which could potentially belong to novel clades. Conclusions This study provides the first snapshot of the picoeukaryotic diversity present in surface waters of the Red Sea, hence setting the stage for large-scale surveying and characterization of the eukaryotic diversity in the entire basin. Our results indicate that the picoeukaryotic community in the northern Red Sea, despite its unique physiochemical conditions (i.e. increased temperatures, increased salinity, and high UV irradiance) does not differ vastly from its counterparts in other oligotrophic marine habitats. PMID:23962380

Diversity of picoeukaryotes at an oligotrophic site off the Northeastern Red Sea Coast.

PubMed

Acosta, Francisco; Ngugi, David Kamanda; Stingl, Ulrich

2013-08-20

Picoeukaryotes are protists ≤ 3 μm composed of a wide diversity of taxonomic groups. They are an important constituent of the ocean's microbiota and perform essential ecological roles in marine nutrient and carbon cycles. Despite their importance, the true extent of their diversity has only recently been uncovered by molecular surveys that resulted in the discovery of a substantial number of previously unknown groups. No study on picoeukaryote diversity has been conducted so far in the main Red Sea basin-a unique marine environment characterized by oligotrophic conditions, high levels of irradiance, high salinity and increased water temperature. We sampled surface waters off the coast of the northeastern Red Sea and analyzed the picoeukaryotic diversity using Sanger-based clone libraries of the 18S rRNA gene in order to produce high quality, nearly full-length sequences. The community captured by our approach was dominated by three main phyla, the alveolates, stramenopiles and chlorophytes; members of Radiolaria, Cercozoa and Haptophyta were also found, albeit in low abundances. Photosynthetic organisms were especially diverse and abundant in the sample, confirming the importance of picophytoplankton for primary production in the basin as well as indicating the existence of numerous ecological micro-niches for this trophic level in the upper euphotic zone. Heterotrophic organisms were mostly composed of the presumably parasitic Marine Alveolates (MALV) and the presumably bacterivorous Marine Stramenopiles (MAST) groups. A small number of sequences that did not cluster closely with known clades were also found, especially in the MALV-II group, some of which could potentially belong to novel clades. This study provides the first snapshot of the picoeukaryotic diversity present in surface waters of the Red Sea, hence setting the stage for large-scale surveying and characterization of the eukaryotic diversity in the entire basin. Our results indicate that the picoeukaryotic community in the northern Red Sea, despite its unique physiochemical conditions (i.e. increased temperatures, increased salinity, and high UV irradiance) does not differ vastly from its counterparts in other oligotrophic marine habitats.

Synthesis of integrated primary production in the Arctic Ocean: II. In situ and remotely sensed estimates

NASA Astrophysics Data System (ADS)

Hill, Victoria J.; Matrai, Patricia A.; Olson, Elise; Suttles, S.; Steele, Mike; Codispoti, L. A.; Zimmerman, Richard C.

2013-03-01

Recent warming of surface waters, accompanied by reduced ice thickness and extent may have significant consequences for climate-driven changes of primary production (PP) in the Arctic Ocean (AO). However, it has been difficult to obtain a robust benchmark estimate of pan-Arctic PP necessary for evaluating change. This paper provides an estimate of pan-Arctic PP prior to significant warming from a synthetic analysis of the ARCSS-PP database of in situ measurements collected from 1954 to 2007 and estimates derived from satellite-based observations from 1998 to 2007. Vertical profiles of in situ chlorophyll a (Chl a) and PP revealed persistent subsurface peaks in biomass and PP throughout the AO during most of the summer period. This was contradictory with the commonly assumed exponential decrease in PP with depth on which prior satellite-derived estimates were based. As remotely sensed Chl a was not a good predictor of integrated water column Chl a, accurate satellite-based modeling of vertically integrated primary production (IPPsat), requires knowledge of the subsurface distribution of phytoplankton, coincident with the remotely sensed ocean color measurements. We developed an alternative approach to modeling PP from satellite observations by incorporating climatological information on the depths of the euphotic zone and the mixed layer that control the distribution of phytoplankton that significantly improved the fidelity of satellite derived PP to in situ observations. The annual IPP of the Arctic Ocean combining both in situ and satellite based estimates was calculated here to be a minimum of 466 ± 94 Tg C yr-1 and a maximum of 993 ± 94 Tg C yr-1, when corrected for subsurface production. Inflow shelf seas account for 75% of annual IPP, while the central basin and Beaufort northern sea were the regions with the lowest annual integrated productivity, due to persistently stratified, oligotrophic and ice-covered conditions. Although the expansion of summertime ice retreat should stimulate photosynthesis by exposing more of the AO to solar irradiance, total PP is ultimately limited by nutrient availability. Therefore, changes in AO PP will be forced by the balance between stratification and mixing, the effects of which are not yet quantified.

Response of O2 and pH to ENSO in the California Current System in a high-resolution global climate model

NASA Astrophysics Data System (ADS)

Turi, Giuliana; Alexander, Michael; Lovenduski, Nicole S.; Capotondi, Antonietta; Scott, James; Stock, Charles; Dunne, John; John, Jasmin; Jacox, Michael

2018-02-01

Coastal upwelling systems, such as the California Current System (CalCS), naturally experience a wide range of O2 concentrations and pH values due to the seasonality of upwelling. Nonetheless, changes in the El Niño-Southern Oscillation (ENSO) have been shown to measurably affect the biogeochemical and physical properties of coastal upwelling regions. In this study, we use a novel, high-resolution global climate model (GFDL-ESM2.6) to investigate the influence of warm and cold ENSO events on variations in the O2 concentration and the pH of the CalCS coastal waters. An assessment of the CalCS response to six El Niño and seven La Niña events in ESM2.6 reveals significant variations in the response between events. However, these variations overlay a consistent physical and biogeochemical (O2 and pH) response in the composite mean. Focusing on the mean response, our results demonstrate that O2 and pH are affected rather differently in the euphotic zone above ˜ 100 m. The strongest O2 response reaches up to several hundreds of kilometers offshore, whereas the pH signal occurs only within a ˜ 100 km wide band along the coast. By splitting the changes in O2 and pH into individual physical and biogeochemical components that are affected by ENSO variability, we found that O2 variability in the surface ocean is primarily driven by changes in surface temperature that affect the O2 solubility. In contrast, surface pH changes are predominantly driven by changes in dissolved inorganic carbon (DIC), which in turn is affected by upwelling, explaining the confined nature of the pH signal close to the coast. Below ˜ 100 m, we find conditions with anomalously low O2 and pH, and by extension also anomalously low aragonite saturation, during La Niña. This result is consistent with findings from previous studies and highlights the stress that the CalCS ecosystem could periodically undergo in addition to impacts due to climate change.

The strengthening East Australian Current, its eddies and biological effects — an introduction and overview

NASA Astrophysics Data System (ADS)

Suthers, Iain M.; Young, Jock W.; Baird, Mark E.; Roughan, Moninya; Everett, Jason D.; Brassington, Gary B.; Byrne, Maria; Condie, Scott A.; Hartog, Jason R.; Hassler, Christel S.; Hobday, Alistair J.; Holbrook, Neil J.; Malcolm, Hamish A.; Oke, Peter R.; Thompson, Peter A.; Ridgway, Ken

2011-03-01

The poleward flowing East Australian Current (EAC) is characterised by its separation from the coast, 100-200 nautical miles north of Sydney, to form the eastward flowing Tasman Front and a southward flowing eddy field. The separation zone greatly influences coastal ecosystems for the relatively narrow continental shelf (only 15-50 km wide), particularly between 32-34°S. In this region the continental shelf has a marked shift in the seasonal temperature-salinity relationship and elevated surface nitrate concentrations. This current parallels the portion of the coast where Australia's population is concentrated and has a long history of scientific research. However, understanding of physical and biological processes driven by the EAC, particularly in linking circulation to ecosystems, is limited. In this special issue of 16 papers on the EAC, we examine the effects of climatic wind-stress forced ocean dynamics on EAC transport variability and coastal sea level, from ENSO to multi-decadal time scales; eddy formation and structure; fine scale connectivity and larval retention. Comparisons with the poleward-flowing Leeuwin Current on Australia's west coast show differences in ecosystem productivity that can be attributed to the underlying physics in each region. On average there is double the chlorophyll a concentration on the east coast than the west. In comparison to the Leeuwin, the EAC may have less local retention of larvae and act as a partial barrier to onshore transport, which may also be related to the local spawning and early life history of small pelagic fish on each coast. Inter-annual variations in the EAC transport produce a detectable sea-level signal in Sydney Harbour, which could provide a useful fisheries index as does the Fremantle sea level and Leeuwin Current relationship. The EAC's eddy structure and formation by the EAC are examined. A particular cold-core eddy is shown to have a "tilt" towards the coast, and that during a rotation the flow of particles may rise up to the euphotic zone and then down beneath. In a warm-core eddy, surface flooding is shown to produce a new shallower surface mixed layer and promote algal growth. An assessment of plankton data from 1938-1942 showed that the local, synoptic conditions had to be incorporated before any comparison with the present. There are useful relationships of water mass characteristics in the Tasman Sea and separation zone with larval fish diversity and abundance, as well as with long-line fisheries. These fisheries-pelagic habitat relationships are invaluable for fisheries management, as well as for climate change assessments. There is further need to examine the EAC influence on rainfall, storm activity, dust deposition, and on the movements by fish, sharks and whales. The Australian Integrated Marine Observing System (IMOS) has provided new infrastructure to determine the changing behaviour of the EAC and its bio-physical interaction with the coasts and estuaries. The forecasting and hindcasting capability developed under the Bluelink project has provided a new tool for data synthesis and dynamical analysis. The impact of a strengthening EAC and how it influences the livelihoods of over half the Australian population, from Brisbane to Sydney, Hobart and Melbourne, is just being realised.

Reflections about chance in my career, and on the top-down regulated world.

PubMed

Banse, Karl

2013-01-01

Paraphrasing Pasteur, in scientific work Fortuna favors only the prepared mind. This is illustrated by my career after an incidental escape from the former German East Prussia just ahead of the Red Army, my switch in Kiel from zoology to oceanography, and my learning of a vacancy in Seattle. Treated here are the accidental discovery of upwelling during the southwest monsoon along India's west coast, studies of benthic polychaetous annelids in the Oregonian zoogeographic province, the discovery of phytoplankton blooms and an absence of upwelling during the northeast monsoon in the northern Arabian Sea, and an ocean-wide description of the seasonality of satellite-derived chlorophyll. My admonition is that grazing rather than cell division rate regulates the abundance and size composition of phytoplankton and affects the dynamics of the understudied zooplankton. I end with a pessimistic view about predicting the vertical flux of particulate organic matter from the euphotic layer with an accuracy useful for deep-sea carbon budgets.

Decadal Comparisons of Particulate Matter in Repeat Transects in the Atlantic, Pacific, and Indian Ocean Basins

NASA Astrophysics Data System (ADS)

Gardner, W. D.; Mishonov, A. V.; Richardson, M. J.

2018-01-01

Basin-wide sections of beam cp (proxy for particle concentration) in ocean basins collected during numerous oceanographic programs over the last four decades record variable concentrations in euphotic surface waters, very low concentrations through most of the water column, and very low to very high concentrations near the seafloor. Sections resampled at decadal intervals show that intense benthic nepheloid layers (BNLs) recur in the same general locations in these repeat sections, most often where eddy kinetic energy (EKE: cm2 s-2) is high in overlying waters. Areas beneath regions of low surface EKE consistently have weak to no BNLs. The decadal persistence of the close connection between surface and benthic EKE and presence or absence of BNLs is clear. Understanding the location and causes of intense versus weak BNLs helps in assessing scavenging of adsorption-prone elements in the deep sea and quantifying the impact of deep ocean sediment dynamics on sediment redistribution.

The remote sensing of ocean primary productivity - Use of a new data compilation to test satellite algorithms

NASA Technical Reports Server (NTRS)

Balch, William; Evans, Robert; Brown, Jim; Feldman, Gene; Mcclain, Charles; Esaias, Wayne

1992-01-01

Global pigment and primary productivity algorithms based on a new data compilation of over 12,000 stations occupied mostly in the Northern Hemisphere, from the late 1950s to 1988, were tested. The results showed high variability of the fraction of total pigment contributed by chlorophyll, which is required for subsequent predictions of primary productivity. Two models, which predict pigment concentration normalized to an attenuation length of euphotic depth, were checked against 2,800 vertical profiles of pigments. Phaeopigments consistently showed maxima at about one optical depth below the chlorophyll maxima. CZCS data coincident with the sea truth data were also checked. A regression of satellite-derived pigment vs ship-derived pigment had a coefficient of determination. The satellite underestimated the true pigment concentration in mesotrophic and oligotrophic waters and overestimated the pigment concentration in eutrophic waters. The error in the satellite estimate showed no trends with time between 1978 and 1986.

Carbon Metabolism of Prochlorococcus sp. Under Nitrogen Limitation

NASA Astrophysics Data System (ADS)

Szul, M.

2016-02-01

Phytoplankton growth rates are limited by nutrient availability in the world's euphotic oligotrophic oceans. In these vast biomes, convergent evolutions of the dominant planktonic populations suggest traits such as small genome and cell size provide selective advantages. While these traits have been shown to improve both thrift and competition for scarce nutrients, how fitness is manifest through reductive evolution on metabolisms remains poorly understood. To develop a better understanding of carbon fate and flux under nutrient limitation, we grew axenic Prochlorococcus under nitrogen-limited and nitrogen-replete conditions and measured metabolite pools, the flux of carbon through these pools as well as photosynthesis, photosystem health and efficiency. Our data show cells under nitrogen limitation reduce rates of both metabolite flux and total carbon fixation while maintaining elevated metabolite pool levels and releasing a larger proportion of total fixed carbon to the environment. Accounting for these observations, potential metabolic mechanisms that contribute to the fitness of Prochlorococcus in the nutrient limited oceans will be discussed.

Flux and stable C and N isotope composition of sinking particles in the Ulleung Basin of the East/Japan Sea

NASA Astrophysics Data System (ADS)

Hyun Kwak, Jung; Han, Eunah; Hwang, Jeomshik; Kim, Young, II; Lee, Chung Il; Kang, Chang-Keun

2017-09-01

Seasonal variability of sinking fluxes of total mass (TMF), particulate organic carbon and nitrogen (POC and PON) was examined using sinking particles collected from sediment traps during July 2011 to December 2011, and December 2012 to June 2013 at an offshore channel site; and from November 2013 to August 2014 at a nearshore slope site of the Ulleung Basin in the East/Japan Sea. δ13C and δ15N values of sinking particles were measured to elucidate the major export processes of POC and PON. Annual TMF (112-638 g m-2 yr-1) and fluxes of POC and PON (9.6-32.1 g C m-2 yr-1 and 1.2-4.5 g N m-2 yr-1, respectively) in the Ulleung Basin corresponded to the upper limit of values reported for other open seas and oceans in the world. No great seasonal variability in both quantitative (TMF, and fluxes and contents of POC and PON) and qualitative (C/N ratios, and δ13C and δ15N values) estimates of vertical fluxes was observed, reflecting a steady standing stock of chlorophyll a in the upper part of water column. Furthermore, high contents of POC and PON and nearly constant δ13C and δ15N values in sinking particles collected in the sediment traps, indicate that primary production in the euphotic zone may be a good predictor of TMF and export flux of organic matter. In this regard, our pilot study points out the importance of high annual primary production and low water temperature (<1 °C) beneath the 200-m water depth, which would enable more sinking particles to be preserved during export process by limiting microbial decomposition activity in the water column, in determining the high annual flux of sinking particles in the Ulleung Basin (UB). A simple stable isotope mixing model of sinking particles indicates that despite a slight seasonal variation, the contribution of intact phytoplankton to sinking organic flux is significant to the POC and PON flux in the UB. Further continuous time series sediment trap experiments are proposed to estimate the contribution of allochthonus sources such as lateral advection through resuspended clay mineral, and aeolian and terrestrial inputs to the sedimentary flux.

The Importance of Kinetics and Redox in the Biogeochemical Cycling of Iron in the Surface Ocean

PubMed Central

Croot, Peter L.; Heller, Maija I.

2012-01-01

It is now well established that Iron (Fe) is a limiting element in many regions of the open ocean. Our current understanding of the key processes which control iron distribution in the open ocean have been largely based on thermodynamic measurements performed under the assumption of equilibrium conditions. Using this equilibrium approach, researchers have been able to detect and quantify organic complexing ligands in seawater and examine their role in increasing the overall solubility of iron. Our current knowledge about iron bioavailability to phytoplankton and bacteria is also based heavily on carefully controlled laboratory studies where it is assumed the chemical species are in equilibrium in line with the free ion association model and/or its successor the biotic ligand model. Similarly most field work on iron biogeochemistry generally consists of a single profile which is in essence a “snap-shot” in time of the system under investigation. However it is well known that the surface ocean is an extremely dynamic environment and it is unlikely if thermodynamic equilibrium between all the iron species present is ever truly achieved. In sunlit waters this is mostly due to the daily passage of the sun across the sky leading to photoredox processes which alter Fe speciation by cycling between redox states and between inorganic and organic species. Episodic deposition events, dry and wet, are also important perturbations to iron cycling as they bring in new iron to the system and alter the equilibrium between iron species and phases. Here we utilize new field data collected in the open ocean on the complexation kinetics of iron in the surface ocean to identify the important role of weak iron binding ligands (i.e., those that cannot maintain iron in solution indefinitely at seawater pH: αFeL < αFe′) in allowing transient increases in iron solubility in response to iron deposition events. Experiments with the thermal O2- source SOTS-1 also indicate the short term impact of this species on iron solubility also with relevance to the euphotic zone. This data highlights the roles of kinetics, redox, and weaker iron binding ligands in the biogeochemical cycling of iron in the ocean. PMID:22723797

Mesoscale and high-frequency variability of macroscopic particles (> 100 μm) in the Ross Sea and its relevance for late-season particulate carbon export

NASA Astrophysics Data System (ADS)

Bochdansky, Alexander B.; Clouse, Melissa A.; Hansell, Dennis A.

2017-02-01

The Ross Sea plays a major role in the transfer of organic carbon from the surface into the deep sea due to the combination of high seasonal productivity and Antarctic bottom water formation. Here we present a particle inventory of the Ross Sea based on a combined deployment of a video particle profiler (VPP) and a high-resolution digital holographic microscope (DIHM). Long-distance (100 s of kilometers) and short-distance (10 s of kilometers) sections showed high variability of particle distributions that co-varied with the density structure of the water column. Particle export was apparent at sites of locally weakened pycnoclines, likely an indirect effect of nutrient mixing into the surface layer and local blooms that lead to export. Particle volume abundances at 200-300 m depth were highly correlated with particle volume abundances in the upper mixed layer (< 60 m), consistent with particles at depth primarily the result of export rather than lateral advection. Phaeocystis antarctica (Haptophyta) colonies that were initially retained in the mixed layer sank below the euphotic zone within a period of two weeks. Fine-scale analysis at a resolution < 1 m revealed a significantly overdispersed (i.e., highly patchy) environment in all casts. Patchiness, as determined by the Lloyd index of patchiness and the Index of Aggregation, increased in and below the pycnocline presumably due to aggregation of particles while accumulating on density gradients. In contrast, particles in the upper mixed layer and in the nepheloid layers were more randomly distributed. In 40 of the 84 VPP depth profiles, a periodicity of particle peaks ranged from 10 to 90 m with a mode of 30 m, which can be regarded as the "relevant scale" or "characteristic patch size" of the vertical distribution of particles. While chlorophyll fluorescence and particle mass determined by VPP were significantly correlated at higher particle abundances, the relationship changed from cast to cast, reflecting changes in the relative contribution of fresh phytoplankton to total particle mass. Particles that sank below the main pycnocline were composed of phytoplankton, marine snow with and without embedded phytoplankton, crustacean plankton, and a surprisingly high percentage of heterotrophic (and perhaps mixotrophic) protists, such as acantharians and tintinnids.

Phytoplankton community structure in relation to hydrographic features along a coast-to-offshore transect on the SW Atlantic Continental Shelf

NASA Astrophysics Data System (ADS)

Islabão, C. A.; Mendes, C. R. B.; Detoni, A. M. S.; Odebrecht, C.

2017-12-01

The continental shelf in Southern Brazil is characterized by high biological productivity associated with horizontal and vertical density gradients due to the mixing of distinct water masses. Phytoplankton biomass and composition were evaluated in summer 2013 along an on-offshore transect off the mouth of the Patos Lagoon (Lat. 32°12S). Photosynthetic active radiation, temperature, salinity and fluorescence vertical profiles were carried out and Brünt-Väisäla frequency was estimated. Three water bodies were identified: the Subtropical Shelf Water along the entire transect, the Plata Plume Water on the middle shelf surface and the Tropical Water farther offshore. The water was sampled (N = 40) for the analyses of dissolved inorganic nutrients, phytoplankton cell density and composition. Phytoplankton present in the water was identified and quantified by the classical microscope sedimentation technique, complemented with CHEMTAX analysis of high-performance liquid chromatography (HPLC) pigment data. From the results obtained, chlorophyll a concentration was higher at both coastal stations (1.6-2.0 mg m-3) where the water column was homogeneous and diatoms dominated the stations. This group was replaced by dinoflagellates in stratified conditions on the shelf and farther offshore. Along the onshore-offshore gradient, two types of dinoflagellates were found: the peridinin-containing dinoflagellates Prorocentrum and Scrippsiella with a small contribution at the coastal stations, and the fucoxantin-containing small Gymnodiniales cells (< 15 μm) with more than 50% of the total chlorophyll a at the stations on the continental shelf, especially associated with the chlorophyll maximum at the base of the euphotic zone. The positive (negative) relationship between the biomass of dinoflagellates (diatoms) with the Brünt-Väisäla frequency, respectively, support the hypothesis that stratification is the most important environmental factor that determines the biomass of phytoplankton communities and distribution on the shelf and in coastal waters off Southern Brazil in summer. Picoplankton cells (Prochlorococcus and Synechococcus), recorded for the first time in the region under study, were predominant in the nutrient-poor and well-lit surface layers along the transect, indicating the importance of their low sedimentation rates (small size) and photo-adaptive strategies to survive on the upper layers of the water column.

A tale of two gyres: Contrasting distributions of dissolved cobalt and iron in the Atlantic Ocean during an Atlantic Meridional Transect (AMT-19)

NASA Astrophysics Data System (ADS)

Shelley, Rachel U.; Wyatt, Neil J.; Tarran, Glenn A.; Rees, Andrew P.; Worsfold, Paul J.; Lohan, Maeve C.

2017-11-01

Cobalt (Co) and iron (Fe) are essential for phytoplankton nutrition, and as such constitute a vital link in the marine biological carbon pump. Atmospheric deposition is an important, and in some places the dominant, source of trace elements (TEs) to the global ocean. Dissolved cobalt (dCo) and iron (dFe) were determined along an Atlantic Meridional Transect (AMT-19; Oct/Nov 2009) between 50°N and 40°S in the upper 150 m in order to investigate the behaviour and distribution of these two essential, bioactive TEs. During AMT-19, large differences in the distributions of dCo and dFe were observed. In the North Atlantic gyre provinces, extremely low mixed layer dCo concentrations (23 ± 9 pM) were observed, which contrasts with the relatively high mixed layer dFe concentrations (up to 1.0 nM) coincident with the band of highest atmospheric deposition (∼5-30°N). In the South Atlantic gyre, the opposite trend was observed, with relatively high dCo (55 ± 18 pM) observed throughout the water column, but low dFe concentrations (0.29 ± 0.08 nM). Given that annual dust supply is an order of magnitude greater in the North than the South Atlantic, the dCo distribution was somewhat unexpected. However, the distribution of dCo shows similarities with the distribution of phosphate (PO43-) in the euphotic zone of the Atlantic Ocean, where the North Atlantic gyre is characterised by chronically low PO4, and higher concentrations are observed in the South Atlantic gyre (Mather et al., 2008), suggesting the potential for a similar biological control of dCo distributions. Inverse correlations between dCo and Prochlorococcus abundance in the North Atlantic gyre provinces, combined with extremely low dCo where nitrogen fixation rates were highest (∼20-28°N), suggests the dominance of biological controls on dCo distributions. The contrasting dCo and dFe distributions in the North and South Atlantic gyres provides insights into the differences between the dominant controls on the distribution of these two bioactive trace metals in the central Atlantic Ocean.

Heterotroph Interactions Alter Prochlorococcus Transcriptome Dynamics during Extended Periods of Darkness

PubMed Central

Coe, Allison; Roggensack, Sara E.

2018-01-01

ABSTRACT Microbes evolve within complex ecological communities where biotic interactions impact both individual cells and the environment as a whole. Here we examine how cellular regulation in the marine cyanobacterium Prochlorococcus is influenced by a heterotrophic bacterium, Alteromonas macleodii, under different light conditions. We monitored the transcriptome of Prochlorococcus, grown either alone or in coculture, across a diel light:dark cycle and under the stress of extended darkness—a condition that cells would experience when mixed below the ocean’s euphotic zone. More Prochlorococcus transcripts exhibited 24-h periodic oscillations in coculture than in pure culture, both over the normal diel cycle and after the shift to extended darkness. This demonstrates that biotic interactions, and not just light, can affect timing mechanisms in Prochlorococcus, which lacks a self-sustaining circadian oscillator. The transcriptomes of replicate pure cultures of Prochlorococcus lost their synchrony within 5 h of extended darkness and reflected changes in stress responses and metabolic functions consistent with growth cessation. In contrast, when grown with Alteromonas, replicate Prochlorococcus transcriptomes tracked each other for at least 13 h in the dark and showed signs of continued biosynthetic and metabolic activity. The transcriptome patterns suggest that the heterotroph may be providing energy or essential biosynthetic substrates to Prochlorococcus in the form of organic compounds, sustaining this autotroph when it is deprived of solar energy. Our findings reveal conditions where mixotrophic metabolism may benefit marine cyanobacteria and highlight new impacts of community interactions on basic Prochlorococcus cellular processes. IMPORTANCE Prochlorococcus is the most abundant photosynthetic organism on the planet. These cells play a central role in the physiology of surrounding heterotrophs by supplying them with fixed organic carbon. It is becoming increasingly clear, however, that interactions with heterotrophs can affect autotrophs as well. Here we show that such interactions have a marked impact on the response of Prochlorococcus to the stress of extended periods of darkness, as reflected in transcriptional dynamics. These data suggest that diel transcriptional rhythms within Prochlorococcus, which are generally considered to be strictly under the control of light quantity, quality, and timing, can also be influenced by biotic interactions. Together, these findings provide new insights into the importance of microbial interactions on Prochlorococcus physiology and reveal conditions where heterotroph-derived compounds may support autotrophs—contrary to the canonical autotroph-to-heterotroph trophic paradigm. PMID:29854954

Tidal influence on particulate organic carbon export fluxes around a tall seamount

NASA Astrophysics Data System (ADS)

Turnewitsch, Robert; Dumont, Matthew; Kiriakoulakis, Kostas; Legg, Sonya; Mohn, Christian; Peine, Florian; Wolff, George

2016-12-01

As tall seamounts may be 'stepping stones' for dispersion and migration of deep open ocean fauna, an improved understanding of the productivity at and food supply to such systems needs to be formed. Here, the 234Th/238U approach for tracing settling particulate matter was applied to Senghor Seamount - a tall sub-marine mountain near the tropical Cape Verde archipelago - in order to elucidate the effects of topographically-influenced physical flow regimes on the export flux of particulate organic carbon (POC) from the near-surface (topmost ⩽ 100 m) into deeper waters. The comparison of a suitable reference site and the seamount sites revealed that POC export at the seamount sites was ∼2-4 times higher than at the reference site. For three out of five seamount sites, the calculated POC export fluxes are likely to be underestimates. If this is taken into account, it can be concluded that POC export fluxes increase while the passing waters are advected around and over the seamount, with the highest export fluxes occurring on the downstream side of the seamount. This supports the view that biogeochemical and biological effects of tall seamounts in surface-ocean waters might be strongest at some downstream distance from, rather than centred around, the seamount summit. Based on measured (vessel-mounted ADCP) and modelled (regional flow field: AVISO; internal tides at Senghor: MITgcm) flow dynamics, it is proposed that tidally generated internal waves result in a 'screen' of increased rates of energy dissipation that runs across the seamount and leads to a combination of two factors that caused the increased POC export above the seamount: (1) sudden increased upward transport of nutrients into the euphotic zone, driving brief pulses of primary production of new particulate matter, followed by the particles' export into deeper waters; and (2) pulses of increased shear-driven aggregation of smaller, slower-settling into larger, faster-settling particles. This study shows that, under certain conditions, there can be an effect of a tall seamount on aspects of surface-ocean biogeochemistry, with tidal dynamics playing a prominent role. It is speculated that these effects can control the spatiotemporal distribution of magnitude and nutritional quality of the flux of food particles to the benthic and benthic-pelagic communities at and near tall seamounts.

Historical And Modern Deep-Sea Transmissometry Data In World Ocean Database - Its Status, Challenges, And Utilization.

NASA Astrophysics Data System (ADS)

Mishonov, A. V.; Richardson, M. J.; Gardner, W. D.; Boyer, T.

2016-12-01

The World Ocean Database (WOD) contains over 13 million profiles of major oceanographic variables (T, S, etc.) with new data added continually, and is available without restriction. A subset of more than 24000 profiles include data from deep-sea transmissometers (Tr), instruments that measure the attenuation of a beam of red light (c) over a fixed path length (typically 25cm). Full water column Tr data collected along with standard hydrographic data can be applied to a variety of important scientific questions, e.g., why and how does primary production biomass change in the euphotic zone on decadal time scales? can sources of natural bottom nepheloid layers of resuspended sediment be differentiated from `industrial' sources due from future deep-sea mining? what is the role of resuspended sediment in the biogeochemical cycles of trace elements in the deep sea? Tr measurements were made over the past four decades during 550 cruises throughout all the world's ocean basins. We present a synopsis of these optical data collected during international, global programs such as the WOCE, JGOFS, and CLIVAR. Some of the transects were repeated two-three times over 10-15 years, purposely to allow an assessment of the variability of hydrographic conditions on decadal time scales. The optical measurements (c due to water and particles) throughout the entire water column made over recent decades along with the hydrographic data allow us to understand how optical conditions might be affected by climate change. Tr data have also been collected in many regional programs, e.g. SAVE in the late 1980's, and AMT beginning in the mid-1990's and continuing to today. Tr data held in WOD has been acquired using different instruments by different research teams and this brings some challenges to data post-processing and comparison. The majority of data now in WOD has been post-processed by our team, but incomplete metadata and methodology documentation have added to the difficulty of mining the historical data. New data collected by ongoing programs such as CLIVAR and GEOTRACES are being post-processed and coming to WOD on a regular basis. We encourage others who are making hydrographic measurements to include Tr measurements and submit data to WOD along with complete metadata / methodology to maximize the use of these valuable measurements.

Late summer distribution and stoichiometry of dissolved N, Si and P in the Southern Ocean near Heard and McDonald Islands on the Kerguelen Plateau

NASA Astrophysics Data System (ADS)

Chase, Z.; Bowie, A. R.; Blain, S.; Holmes, T.; Rayner, M.; Sherrin, K.; Tonnard, M.; Trull, T. W.

2016-12-01

The Kerguelen plateau in the Southern Indian Ocean is a naturally iron-fertilised region surrounded by iron-limited, High Nutrient Low Chlorophyll waters. The Heard Earth Ocean Biosphere Interaction (HEOBI) project sampled waters south of the Polar Front in the vicinity of Heard and McDonald Islands (HIMI) in January and February 2016. Fe fertilised waters over the plateau generally exhibited high phytoplankton biomass and photosynthetic competency (as in previous studies and satellite observations), but interestingly, phytoplankton biomass was low near HIMI, though photosynthetic competency was high. In plateau waters away from HIMI, silicic acid (Si) concentrations were strongly depleted in surface waters, averaging 3 μM, while nitrate concentrations were close to 25 μM. Relative to the remnant winter water, this represents an average seasonal drawdown of 32 μM Si and only 8 μM nitrate. Though absolute drawdown was lower at an HNLC reference site south of Heard Island, the drawdown ratio was similarly high (ΔSi: ΔN 4-5). The average N:P drawdown ratio was 12, typical for a diatom-dominated system (Weber and Deutsch 2010). N:P drawdown was positively correlated with Si drawdown, perhaps indicative of an impact of Fe on both seasonal Si drawdown and diatom N:P uptake (Price 2005). In the well-mixed, shallow waters (< 200 m) around HIMI nutrient concentrations were elevated, with no surface nutrient depletion. Nutrient concentrations near the islands were generally consistent with input from vertical mixing of the regional nutrient profile. However, N* values (N* = N - P*16) near the islands were anomalously low (-5 to -7) relative to the regional nutrient profile (N* 3). Subsurface minima in N* (as low as -6) were observed just below the pycnocline at several plateau stations. If negative N* values here are indicative of intense remineralisation of P-rich organic matter, and possible preferential remineralisation of P (Blain et al. 2015), these observations suggest the existence of strong production and remineralisation of organic matter around Heard and McDonald Islands, despite the apparent lack of nutrient drawdown or biomass accumulation. Mixed layers deeper than the euphotic zone are one mechanism that retains these remineralization signatures and near the islands, tidal mixing also contributes.

Zooplankton fecal pellets, marine snow, phytodetritus and the ocean's biological pump

NASA Astrophysics Data System (ADS)

Turner, Jefferson T.

2015-01-01

The 'biological pump' is the process by which photosynthetically-produced organic matter in the ocean descends from the surface layer to depth by a combination of sinking particles, advection or vertical mixing of dissolved organic matter, and transport by animals. Particulate organic matter that is exported downward from the euphotic zone is composed of combinations of fecal pellets from zooplankton and fish, organic aggregates known as 'marine snow' and phytodetritus from sinking phytoplankton. Previous reviews by Turner and Ferrante (1979) and Turner (2002) focused on publications that appeared through late 2001. Since that time, studies of the biological pump have continued, and there have been >300 papers on vertical export flux using sediment traps, large-volume filtration systems and other techniques from throughout the global ocean. This review will focus primarily on recent studies that have appeared since 2001. Major topics covered in this review are (1) an overview of the biological pump, and its efficiency and variability, and the role of dissolved organic carbon in the biological pump; (2) zooplankton fecal pellets, including the contribution of zooplankton fecal pellets to export flux, epipelagic retention of zooplankton fecal pellets due to zooplankton activities, zooplankton vertical migration and fecal pellet repackaging, microbial ecology of fecal pellets, sinking velocities of fecal pellets and aggregates, ballasting of sinking particles by mineral contents, phytoplankton cysts, intact cells and harmful algae toxins in fecal pellets, importance of fecal pellets from various types of zooplankton, and the role of zooplankton fecal pellets in picoplankton export; (3) marine snow, including the origins, abundance, and distributions of marine snow, particles and organisms associated with marine snow, consumption and fragmentation of marine snow by animals, pathogens associated with marine snow; (4) phytodetritus, including pulsed export of phytodetritus, phytodetritus from Phaeocystis spp., picoplankton in phytodetritus, the summer export pulse (SEP) of phytodetritus in the subtropical North Pacific, benthic community responses to phytodetritus; (5) other components of the biological pump, including fish fecal pellets and fish-mediated export, sinking carcasses of animals and macrophytes, feces from marine mammals, transparent exopolymer particles (TEP); (6) the biological pump and climate, including origins of the biological pump, the biological pump and glacial/interglacial cycles, the biological pump and contemporary climate variations, and the biological pump and anthropogenic climate change. The review concludes with potential future modifications in the biological pump due to climate change.

Using Argo-O2 data to examine the impact of deep-water formation events on oxygen uptake in the Labrador Sea

NASA Astrophysics Data System (ADS)

Wolf, M. K.; Hamme, R. C.; Gilbert, D.; Yashayaev, I.

2016-02-01

Deep-water formation allows the deep ocean to communicate with the atmosphere, facilitating exchanges of heat as well as important gases such as CO2 and oxygen. The Labrador Sea is the most studied location of deep convection in the North Atlantic Ocean and a strong contributor to the global thermohaline circulation. Since there are no internal sources of oxygen below the euphotic zone, deep-water formation is vital for oxygen transport to the deep ocean. Recent studies document large interannual variability in the strength and depth of convection in the Labrador Sea, from mixed layers of 100m to greater than 1000m. A weakening of this deep convection starves the deep ocean of oxygen, disrupting crucial deep sea biological processes, as well as reducing oceanic CO2 uptake and ocean circulation. We used data from the extensive Argo float network to examine these deep-water formation events in the Labrador Sea. The oxygen optodes onboard many Argo floats suffer from biases whose amplitude must be determined; therefore we investigated and applied various optode calibration methods. Using calibrated vertical profiles of oxygen, temperature, and salinity, we observed the timing, magnitude, and location of deep convection, restratification, and spring phytoplankton blooms. In addition, we used surface oxygen values along with NCEP wind speeds to calculate the air-sea oxygen flux using a range of air-sea gas exchange parameterizations. We then compared this oxygen flux to the rate of change of the measured oxygen inventory. Where the inventory and flux did not agree, we identified other oceanic processes such as biological activity or lateral advection of water masses occurring, or advection of the float itself into a new area. The large role that horizontal advection of water or the float has on oxygen uptake and cycling leads us to conclude that this data cannot be easily interpreted as a 1-D system. Oxygen exchanges with the atmosphere at a faster rate than CO2, is more affected by bubble injection, and reacts differently to temperature change. Oxygen is also produced and consumed by photosynthesis and respiration respectively at a specific ratio to CO2. These properties enable us to use oxygen as a separate constraint from carbon to determine the effect these various processes have on gas cycling, and the global ocean circulation.

Thorium-234 as a tracer of spatial, temporal and vertical variability in particle flux in the North Pacific

NASA Astrophysics Data System (ADS)

Buesseler, K. O.; Pike, S.; Maiti, K.; Lamborg, C. H.; Siegel, D. A.; Trull, T. W.

2009-07-01

An extensive 234Th data set was collected at two sites in the North Pacific: ALOHA, an oligotrophic site near Hawaii, and K2, a mesotrophic HNLC site in the NW Pacific as part of the VERTIGO (VERtical Transport In the Global Ocean) study. Total 234Th: 238U activity ratios near 1.0 indicated low particle fluxes at ALOHA, while 234Th: 238U ˜0.6 in the euphotic zone at K2 indicated higher particle export. However, spatial variability was large at both sites—even greater than seasonal variability as reported in prior studies. This variability in space and time confounds the use of single profiles of 234Th for sediment trap calibration purposes. At K2, there was a decrease in export flux and increase in 234Th activities over time associated with the declining phase of a summer diatom bloom, which required the use of non-steady state models for flux predictions. This variability in space and time confounds the use of single profiles of 234Th for sediment trap calibration purposes. High vertical resolution profiles show narrow layers (20-30 m) of excess 234Th below the deep chlorophyll maximum at K2 associated with particle remineralization resulting in a decrease in flux at depth that may be missed with standard sampling for 234Th and/or with sediment traps. Also, the application of 234Th as POC flux tracer relies on accurate sampling of particulate POC/ 234Th ratios and here the ratio is similar on sinking particles and mid-sized particles collected by in-situ filtration (>10-50 μm at ALOHA and >5-350 μm at K2). To further address variability in particle fluxes at K2, a simple model of the drawdown of 234Th and nutrients is used to demonstrate that while coupled during export, their ratios in the water column will vary with time and depth after export. Overall these 234Th data provide a detailed view into particle flux and remineralization in the North Pacific over time and space scales that are varying over days to weeks, and 10's-100's km at a resolution that is difficult to obtain with other methods.

High-nitrogen fixation rates in the particulate and dissolved pools in the Western Tropical Pacific (Solomon and Bismarck Seas)

NASA Astrophysics Data System (ADS)

Berthelot, H.; Benavides, M.; Moisander, P. H.; Grosso, O.; Bonnet, S.

2017-08-01

Dinitrogen (N2) fixation rates were investigated in the euphotic layer of the Bismarck and Solomon Seas using 15N2 incubation assays taking into account both the particulate and the dissolved pools. Average depth-integrated particulate N2 fixation rates were 203 (range 43-399) and 1396 (range 176-3132) μmol N m-2 d-1 in the Bismarck and Solomon Seas, respectively. In both seas, N2 fixation measured in the dissolved pool was similar to particulate N2 fixation, highlighting the potentially substantial underestimation of N2 fixation in oceanic budgets when only particulate N2 fixation is considered. Among the diazotroph phylotypes targeted using quantitative polymerase chain reaction amplification of nifH genes, Trichodesmium was the most abundant. Regression analyses suggest that it accounted for the major proportion of N2 fixation. However, unicellular cyanobacterial and non-cyanobacterial diazotrophs were also occasionally abundant. This study reports high pelagic N2 fixation rates and confirms that the Western Tropical South Pacific is a hot spot for marine N2 fixation.

Biological and physical oceanographic observations pertaining to the trawl fishery in a region of persistent coastal upwelling

NASA Technical Reports Server (NTRS)

Howe, J. T.; Gibson, D. B.; Evans, T. O.; Breaker, L.; Wrigley, R. C.; Broenkow, W. W.

1981-01-01

An upwelling episode in the Point Sal region of the central California coast is examined by using data obtained by a data buoy. The episodes was interrupted by the abrupt abatement of the strong wind which promotes coastal upwelling. The mean hourly upwelling index is calculated to be higher than the 20 year mean monthly value. During 3 days of light wind commercial bottom trawl operations were possible. Shipboard estimates of chlorophyll content in surface waters during trawling show the high concentrations that are indicative of a rich biomass of phytoplankton, a result of the upwelling episode. Satellite imagery shows the extent of the upwelling water to be of the order of 100 km offshore; the result of many upwelling episodes. Shipboard echo sounder data show the presence of various delmersal species and of zooplakton; the latter graze on the phytoplankton in the upper euphotic layers. The fish catch data are recorded according to species for 2 days of trawling, and the catch per trawl hour is recorded.

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

NASA Astrophysics Data System (ADS)

Wankel, S. D.; Buchwald, C.; Ziebis, W.; Wenk, C. B.; Lehmann, M. F.

2015-12-01

Nitrogen (N) is a key component of fundamental biomolecules. Hence, its cycling and availability are central factors governing the extent of ecosystems across the Earth. In the organic-lean sediment porewaters underlying the oligotrophic ocean, where low levels of microbial activity persist despite limited organic matter delivery from overlying water, the extent and modes of nitrogen transformations have not been widely investigated. Here we use the N and oxygen (O) isotopic composition of porewater nitrate (NO3-) from a site in the oligotrophic North Atlantic (Integrated Ocean Drilling Program - IODP) to determine the extent and magnitude of microbial nitrate production (via nitrification) and consumption (via denitrification). We find that NO3- accumulates far above bottom seawater concentrations (~ 21 μM) throughout the sediment column (up to ~ 50 μM) down to the oceanic basement as deep as 90 m b.s.f. (below sea floor), reflecting the predominance of aerobic nitrification/remineralization within the deep marine sediments. Large changes in the δ15N and δ18O of nitrate, however, reveal variable influence of nitrate respiration across the three sites. We use an inverse porewater diffusion-reaction model, constrained by the N and O isotope systematics of nitrification and denitrification and the porewater NO3- isotopic composition, to estimate rates of nitrification and denitrification throughout the sediment column. Results indicate variability of reaction rates across and within the three boreholes that are generally consistent with the differential distribution of dissolved oxygen at this site, though not necessarily with the canonical view of how redox thresholds separate nitrate regeneration from dissimilative consumption spatially. That is, we provide stable isotopic evidence for expanded zones of co-occurring nitrification and denitrification. The isotope biogeochemical modeling also yielded estimates for the δ15N and δ18O of newly produced nitrate (δ15NNTR (NTR, referring to nitrification) and δ18ONTR), as well as the isotope effect for denitrification (15ϵDNF) (DNF, referring to denitrification), parameters with high relevance to global ocean models of N cycling. Estimated values of δ15NNTR were generally lower than previously reported δ15N values for sinking particulate organic nitrogen in this region. We suggest that these values may be, in part, related to sedimentary N2 fixation and remineralization of the newly fixed organic N. Values of δ18ONTR generally ranged between -2.8 and 0.0 ‰, consistent with recent estimates based on lab cultures of nitrifying bacteria. Notably, some δ18ONTR values were elevated, suggesting incorporation of 18O-enriched dissolved oxygen during nitrification, and possibly indicating a tight coupling of NH4+ and NO2- oxidation in this metabolically sluggish environment. Our findings indicate that the production of organic matter by in situ autotrophy (e.g., nitrification, nitrogen fixation) supplies a large fraction of the biomass and organic substrate for heterotrophy in these sediments, supplementing the small organic-matter pool derived from the overlying euphotic zone. This work sheds new light on an active nitrogen cycle operating, despite exceedingly low carbon inputs, in the deep sedimentary biosphere.

Nitrogen cycling in the subsurface biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

NASA Astrophysics Data System (ADS)

Wankel, S. D.; Buchwald, C.; Ziebis, W.; Wenk, C. B.; Lehmann, M. F.

2015-08-01

Nitrogen (N) is a key component of fundamental biomolecules. Hence, the cycling and availability of N is a central factor governing the extent of ecosystems across the Earth. In the organic-lean sediment porewaters underlying the oligotrophic ocean, where low levels of microbial activity persist despite limited organic matter delivery from overlying water, the extent and modes of nitrogen transformations have not been widely investigated. Here we use the N and oxygen (O) isotopic composition of porewater nitrate (NO3-) from a site in the oligotrophic North Atlantic (IODP) to determine the extent and magnitude of microbial nitrate production (via nitrification) and consumption (via denitrification). We find that NO3- accumulates far above bottom seawater concentrations (∼ 21 μM) throughout the sediment column (up to ∼ 50 μM) down to the oceanic basement as deep as 90 mbsf, reflecting the predominance of aerobic nitrification/remineralization within the deep marine sediments. Large changes in the δ15N and δ18O of nitrate, however, reveal variable influence of nitrate respiration across the three sites. We use an inverse porewater diffusion-reaction model, constrained by the N and O isotope systematics of nitrification and denitrification and the porewater NO3- isotopic composition, to estimate rates of nitrification and denitrification throughout the sediment column. Results indicate variability of reaction rates across and within the three boreholes that are generally consistent with the differential distribution of dissolved oxygen at this site, though not necessarily with the canonical view of how redox thresholds separate nitrate regeneration from dissimilative consumption spatially. That is, we provide isotope evidence for expanded zones of co-ocurring nitrification and denitrification. The isotope biogeochemical modeling also yielded estimates for the δ15N and δ18O of newly produced nitrate (δ15NNTR and δ18ONTR), as well as the isotope effect for denitrification (15ϵDNF), parameters with high relevance to global ocean models of N cycling. Estimated values of δ15NNTR were generally lower than previously reported δ15N values for sinking PON in this region. We suggest that these values can be related to sedimentary N-fixation and remineralization of the newly fixed organic N. Values of δ18ONTR generally ranged between -2.8 and 0.0 ‰, consistent with recent estimates based on lab cultures of nitrifying bacteria. Notably, some δ18ONTR values were elevated, suggesting incorporation of 18O-enriched dissolved oxygen during nitrification, and possibly indicating a tight coupling of NH4+ and NO2- oxidation in this metabolically sluggish environment. Our findings indicate that the production of organic matter by in situ autotrophy (e.g., nitrification, nitrogen fixation) supply a large fraction of the biomass and organic substrate for heterotrophy in these sediments, supplementing the small organic matter pool derived from the overlying euphotic zone. This work sheds new light on an active nitrogen cycle operating, despite exceedingly low carbon inputs, in the deep sedimentary biosphere.

Particulate matter chemistry and dynamics in the twilight zone at VERTIGO ALOHA and K2 sites

NASA Astrophysics Data System (ADS)

Bishop, James K. B.; Wood, T. J.

2008-12-01

Understanding particle dynamics in the 'Twilight Zone' is critical to prediction of the ocean's carbon cycle. As part of the VERtical Transport In the Global Ocean (VERTIGO) project, this rarely sampled regime extending from the base of the euphotic layer to 1000 m, was characterized by double-paired day/night Multiple Unit Large Volume in-situ Filtration System (MULVFS) deployments and by ˜100 high-frequency CTD/transmissometer/turbidity sensor profiles. VERTIGO studies lasting 3 weeks, contrasted oligotrophic station ALOHA (22.75°N 158°W), sampled in June-July 2004, with a biologically productive location (47 °N 161°E) near station K2 in the Oyashio, occupied July-August 2005. Profiles of major and minor particulate components (C org, N, P, Ca, Si, Sr, Ba, Mn) in <1, 1-51, and >51 μm size fractions, in-water optics, neutrally buoyant sediment trap (NBST) fluxes, and zooplankton data were intercompared. MULVFS total C org and C-Star particle beam attenuation coefficient ( C P) were consistently related at both sites with a 27 μM m -1 conversion factor. At K2, C P profiles further showed a multitude of transient spikes throughout the water column and spike abundance profiles closely paralleled the double peaked abundance profiles of zooplankton. Also at K2, copepods contributed ˜40% and 10%, night and day, respectively to >51 μm C org of MULVFS samples in the mixed layer, but few copepods were collected in deeper waters; however, non-swimming radiolarians were quantitatively sampled. A recent hypothesis regarding POC differences between pumps and bottles is examined in light of these results. Particulate >51 μm C org, N, and P at both ALOHA and K2 showed strong attenuation with depth at both sites. Notable at ALOHA were unusually high levels of >51 μm Sr (up to 4 nM) in the mixed layer, a reflection of high abundances of SrSO 4 precipitating Acantharia. Notable at K2 were major changes in water column inventories of many particulate components to 700 m over 10 days. Carbon mass balance, with the consideration of particle inventory changes included, indicated that over 98% and 96% of primary produced C org was remineralized shallower than 500 m at ALOHA and K2, respectively. Production of CaCO 3 was estimated to be ˜0.06, 0.89, and 0.02 mmol m -2 d -1 at ALOHA and at K2 during two separate week long study periods, respectively. Similarly, Si production was estimated to be ˜0.08, 10.7, and 4.2 mol m -2 d -1. An estimated 50% and 65% of produced Si was remineralized by 500 m at ALOHA and K2, respectively. Little carbonate dissolution was seen in the upper 500 m at ALOHA, a reflection of 400% super saturation of surface waters and the 700 m deep saturation horizon. Over 92% of produced CaCO 3 was dissolved shallower than 500 m at K2 and biological enhancement of dissolution was readily apparent in waters above the 200 m calcite saturation horizon.

Bathypelagic particle flux signatures from a suboxic eddy in the oligotrophic tropical North Atlantic: production, sedimentation and preservation

NASA Astrophysics Data System (ADS)

Fischer, Gerhard; Karstensen, Johannes; Romero, Oscar; Baumann, Karl-Heinz; Donner, Barbara; Hefter, Jens; Mollenhauer, Gesine; Iversen, Morten; Fiedler, Björn; Monteiro, Ivanice; Körtzinger, Arne

2016-06-01

Particle fluxes at the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic for the period December 2009 until May 2011 are discussed based on bathypelagic sediment trap time-series data collected at 1290 and 3439 m water depth. The typically oligotrophic particle flux pattern with weak seasonality is modified by the appearance of a highly productive and low oxygen (minimum concentration below 2 µmol kg-1 at 40 m depth) anticyclonic modewater eddy (ACME) in winter 2010. The eddy passage was accompanied by unusually high mass fluxes of up to 151 mg m-2 d-1, lasting from December 2009 to May 2010. Distinct biogenic silica (BSi) and organic carbon flux peaks of ˜ 15 and 13.3 mg m-2 d-1, respectively, were observed in February-March 2010 when the eddy approached the CVOO. The flux of the lithogenic component, mostly mineral dust, was well correlated with that of organic carbon, in particular in the deep trap samples, suggesting a tight coupling. The lithogenic ballasting obviously resulted in high particle settling rates and, thus, a fast transfer of epi-/meso-pelagic signatures to the bathypelagic traps. We suspect that the two- to three-fold increase in particle fluxes with depth as well as the tight coupling of mineral dust and organic carbon in the deep trap samples might be explained by particle focusing processes within the deeper part of the eddy. Molar C : N ratios of organic matter during the ACME passage were around 18 and 25 for the upper and lower trap samples, respectively. This suggests that some productivity under nutrient (nitrate) limitation occurred in the euphotic zone of the eddy in the beginning of 2010 or that a local nitrogen recycling took place. The δ15N record showed a decrease from 5.21 to 3.11 ‰ from January to March 2010, while the organic carbon and nitrogen fluxes increased. The causes of enhanced sedimentation from the eddy in February/March 2010 remain elusive, but nutrient depletion and/or an increased availability of dust as a ballast mineral for organic-rich aggregates might have contributed. Rapid remineralisation of sinking organic-rich particles could have contributed to oxygen depletion at shallow depth. Although the eddy formed in the West African coastal area in summer 2009, no indications of coastal flux signatures (e.g. from diatoms) were found in the sediment trap samples, confirming the assumption that the suboxia developed within the eddy en route. However, we could not detect biomarkers indicative of the presence of anammox (anaerobic ammonia oxidation) bacteria or green sulfur bacteria thriving in photic zone suboxia/hypoxia, i.e. ladderane fatty acids and isorenieratene derivatives, respectively. This could indicate that suboxic conditions in the eddy had recently developed and/or the respective bacterial stocks had not yet reached detection thresholds. Another explanation is that the fast-sinking organic-rich particles produced in the surface layer did not interact with bacteria from the suboxic zone below. Carbonate fluxes dropped from ˜ 52 to 21.4 mg m-2 d-1 from January to February 2010, respectively, mainly due to reduced contribution of shallow-dwelling planktonic foraminifera and pteropods. The deep-dwelling foraminifera Globorotalia menardii, however, showed a major flux peak in February 2010, most probably due to the suboxia/hypoxia. The low oxygen conditions forced at least some zooplankton to reduce diel vertical migration. Reduced "flux feeding" by zooplankton in the epipelagic could have contributed to the enhanced fluxes of organic materials to the bathypelagic traps during the eddy passage. Further studies are required on eddy-induced particle production and preservation processes and particle focusing.

Net community production and metabolic balance at the oligotrophic ocean site, station ALOHA

NASA Astrophysics Data System (ADS)

le B. Williams, Peter J.; Morris, Paul J.; Karl, David M.

2004-11-01

To test the hypothesis that in oligotrophic areas of the ocean respiration exceeds production, a 12-month study was undertaken of in vitro-determined net oxygen production and consumption in the top 150 m of the water column at the extreme oligotrophic site, Station ALOHA, in the North Pacific subtropical gyre. Throughout the year the water column was observed to be in metabolic deficit, the calculated cumulative shortfall being 9±1.7 mol O2 m-2 a-1 (approximately 100 g C m-2 a-1), an amount equivalent to 40% of measured production (annual estimated rates of production and consumption were, respectively, 22 and 31 mol O2 m-2 a-1). We consider three possible explanations for the observed deficit: the in vitro oxygen rate measurements, in themselves, are fundamentally flawed and should be discounted, the observations are correct and the observed deficit is a true account of the balance of oxygen (and organic carbon) at Station ALOHA, or the observations are correct as they stand, but need not be interpreted as organic carbon imbalance for that ecosystem. We find no error unique to the oxygen rate measurements themselves. We find also no evidence that the associated organic carbon deficit can be sustained over the long-term by internal organic reserves or by external subsidy. Accordingly we accept the geochemical findings that calculated in situ oxygen flux requires the euphotic zone of the water column at this site to be slightly (circa 2 mol C m-2 a-1) autotrophic, in contrast to the simple analysis of our observations which gives a net heterotrophic water column. We discuss a number of processes that may give rise to the observed discrepancy. In part it may derive from the difficulty of reproducing the variations in the light field experienced by an algal cell due to vertical advection. It may also derive from the intermittency of production. This latter effect would manifest itself in the following manner. Because of its universal distribution in the food web, respiration has greater integrating properties than photosynthesis and so will give a more accurate estimate of the long-term mean in studies with coarse sampling frequencies. If the system is undersampled, then short bursts of photosynthesis are prone to be missed from the integration of the production term but will be seen in the consumption term: hence the apparent deficit. The corollary of this line of reasoning is that, in undersampled systems, respiration has the potential to give a more accurate measurement of integrated system production than photosynthesis.

Prokaryotic dynamics and heterotrophic metabolism in a deep convection site of Eastern Mediterranean Sea (the Southern Adriatic Pit)

NASA Astrophysics Data System (ADS)

Azzaro, M.; La Ferla, R.; Maimone, G.; Monticelli, L. S.; Zaccone, R.; Civitarese, G.

2012-08-01

We report on investigations of prokaryotic abundance, biomass, extracellular enzymatic activity, prokaryotic heterotrophic production and respiration in the full water column (˜1200 m) of a deep convection site (the Southern Adriatic Pit), carried out on six cruises in 2006-2008. Prokaryotic abundance (PA) varied vertically and temporally and ranged from 1.2 to 20.4×105 cell ml-1. Cell volumes, generally increased with depth; the lowest mean cell volume was observed in a period with no active convective process (Feb-07) and the highest in a period of stratification (Jun-08) following the convection process occurred in Feb-08. Prokaryotic biomass decreased with the depth and was related with both seasonal cycles of organic matter and hydrological processes. The picophytoplankton ranged in the upper layer (UL) from 0.089 to 10.71×104 cell ml-1. Cells were also recorded till 500 m depth in Feb-08 and this finding could be linked to water convection occurred in the Southern Adriatic Pit in that month. In UL the variations of enzymatic activities as well as leucine-aminopeptidase/ß-glucosidase ratio showed a seasonal trend probably linked to the productive processes of the photic layer. An inverse relation between alkaline phosphatase activity (APA) and phosphate concentrations was found (APA=0.0003PO4-1.7714, R2=0.333, P<0.05). Generally cell-specific enzymatic activities increased with depth as did cell-specific carbon dioxide production rates, while cell-specific prokaryotic heterotrophic production had an opposite trend. High values of prokaryotic growth efficiency registered in the deep layers in Nov-06 reflected a supply of preformed C transported within the deep water masses. Overall, in 2007 when no convective phenomenon was observed, the variability of prokaryotic metabolism was governed by the seasonal cycle of the organic matter, while in Nov-06 and Jun-08 the dynamics of deep water ventilation influenced the trend along the water column of many microbial parameters. The yearly trophic balance of the study site appeared to move towards autotrophy only in UL, whilst in the whole water column, the prokaryotic carbon demand exceeded POC availability rained down from euphotic zone. This mismatch was balanced by the DOC entrapped in the "younger waters" of new formation that alters the normal flux of the biological pump and fuels the deep marine biota in this area of deep water convection.

Exploring Estimates of Net Community Production and Export Along the Western Antarctic Peninsula (WAP), 1993-2014.

NASA Astrophysics Data System (ADS)

Ducklow, H. W.; Stukel, M. R.; Bowman, J. S.; Kim, H.; Cassar, N.; Eveleth, R.; Li, Z.; Doney, S. C.; Sailley, S. F.; Jickells, T. D.; Baker, A. R.; Chance, R.

2016-12-01

In this presentation, we will compare different estimates of net community production (NCP) and export production (EP), including both traditional (changes in nutrient inventories and biological incubations) and newer measurements (Oxygen-Argon ratio, Thorium-234 disequilibrium, Iodide accumulation). Palmer Long Term Ecological Research (PAL-LTER) has been conducting observations of core biogeochemical (nutrient and carbon inventories, sediment trap flux) and ecological (standing stocks, production and grazing rates) processes along the WAP since 1993. Datasets include both temporally-intensive (semiweekly, Oct-April) observations in two nearshore locations at Palmer Station, and regionally-extensive observations over a 200 x 700 km grid of stations extending across the shelf into deep ocean water (>3000 m) each January. These observations provide a long term temporal and spatial context for more recent and focused measurements of net NCP and EP from the euphotic zone. For example, long-term net drawdown of nitrate averaged 415 mmol N m-2 season-1 (33 gC m-2 Season-1) at Palmer Station and 557 mmol N m-2 Season-1 (45 gC m-2 Season-1) over the regional grid. In comparison, discrete bottle-based O2/Ar estimates of NCP averaged 44 mmol O2 m-2 d-1 (0.37 gC m-2 d-1) regionally in January 2008-11. Th234 export was 684 dpm-2 d-1 (0.15 gC m-2 d-1) in January 2012, sourced from 15NO3 uptake-based new production of 4.1 mmol N m-2 d-1 (0.37 gC m-2 d-1). Intercomparison of these estimates is not straightforward. Measurements are based on several elemental currencies (C, N, O2, Th). We do not fully understand the processes each method claims to address. Is NCP the same as new production? Different processes and their measurements proceed over timescales of hours (new and net PP) to weeks (O2/Ar, 234Th) to months (inventory drawdowns). As implied above, assignment of time duration of net drawdown processes is uncertain for changes in water column inventories. Models provide additional insights, as modeled processes can be exactly defined. Inverse foodweb models of foodwebs in the PAL-WAP region yield NCP and EP estimates ranging 0.14 - 0.48 gC m-2 d-1. NCP and EP are equivalent in these steady-state foodweb models. We will synthesize these and other estimates and placed in emergent objective schemes.

Biological Productivity from an Oxygen Mass Balance in the subarctic North Pacific

NASA Astrophysics Data System (ADS)

Giesbrecht, K. E.; Hamme, R. C.

2008-12-01

Biological productivity is an important process controlling the export of carbon into the deep ocean and thus influencing the earth's climate. An O2 mass balance of the upper ocean can estimate this export of organic carbon if the physical processes affecting the O2 concentrations are accounted for. This can be accomplished by measuring the dissolved O2/Ar ratio, because their similar physical properties allow us to consider Ar an 'abiotic' O2 analogue. Here we present a two-year data set of O2/N2/Ar ratio measurements collected at Station Papa and along Line P in 2007/08. Line P, situated in the subarctic North Pacific, is a series of oceanographic stations running from the southwest tip of Vancouver Island to Station Papa (50°N, 145°W), one of the oldest deep-ocean time series in existence which is located in the High-Nutrient/Low-Chlorophyll (HNLC) region of the subarctic gyre. Current cruises along Line P run three times per year, typically in February, June and August. The dissolved gas ratios are measured using a stable isotope mass spectrometer and oxygen concentrations by titration. In a simple steady state, we equate biological O2 production to diffusive gas exchange, using the O2/Ar ratio to normalize the physical component of the oxygen signal and calculate the net biological oxygen production. Diffusive gas exchange is calculated using a wind speed parameterization. Preliminary estimates of the net biological production in the mixed layer at Station Papa for 2007 are calculated at 30.9 and 14.0 mmol C m-2 d- 1 for June and August respectively, both exhibiting mixed layer O2/Ar supersaturations. The O2/Ar undersaturation in the mixed layer for February 2007 suggests net respiration at that time. The wind speed parameterization of diffusive gas exchange is the major source of error for this method. We plan to refine our productivity calculation to account for vertical mixing and also by measuring rates of production using a number of different methods, so that we may determine if the values obtained converge on a result. Future investigations to obtain a better-constrained estimate of the biological carbon export in this region by measuring Nitrogen and Carbon uptake rates in the euphotic zone using dual, stable isotope tracer 15N/13C incubations in addition to the oxygen mass balance will be discussed.

Linking phytoplankton nitrogen uptake, macronutrients and chlorophyll- a in SW Atlantic waters: The case of the Gulf of San Jorge, Argentina

NASA Astrophysics Data System (ADS)

Paparazzo, Flavio E.; Williams, Gabriela N.; Pisoni, Juan P.; Solís, Miriam; Esteves, José L.; Varela, Diana E.

2017-08-01

We compared biological and chemical parameters in surface waters of the Gulf of San Jorge to better understand carbon export and the factors that control phytoplankton production in an area of the Argentinian Continental Shelf, a vastly under sampled region of the SW Atlantic Ocean. In April of 2012, we estimated new and regenerated primary production in the Gulf by measuring nitrate and ammonium uptake, respectively. We also measured macronutrient, and in situ chlorophyll-a concentrations, which were compared to chlorophyll-a estimates from remote sensing. Although the Gulf of San Jorge presents high levels of chlorophyll-a and primary production, the relationship between these parameters is not straightforward. Previous studies showed that surface chlorophyll-a explains only part of the variance in euphotic-zone integrated primary production, and that satellite-derived chlorophyll-a underestimates in situ primary production. Our results showed large spatial variability in the Gulf, with transitional physico-chemical conditions, such as fronts, that could favor an increase in biological production. In situ chlorophyll-a concentrations were highest at the mid-shelf station (6.0 mg m- 3) and lowest at the northernmost location by an order of magnitude. Remote sensing measurements of chlorophyll-a underestimated our in situ chlorophyll-a concentrations. Total nitrogen (nitrate + ammonium) uptake showed relatively similar rates throughout the study area (≈ 130 nM-N d- 1), except in the northernmost station where it was much lower (53 nM-N d- 1). This north region had a distinct water mass and maximal levels of macronutrients (nitrate ≈ 6 μM, ammonium ≈ 1.2 μM, phosphate ≈ 1.2 μM and silicic acid ≈ 4 μM). For the entire sampling region, chlorophyll-a concentrations strongly correlated with total nitrogen uptake (r = 0.76, n = 8, p < 0.05) and new primary production (r = 0.78, n = 8, p < 0.05). Values of the f-ratio were 0.9 in mid-shelf, and ranged between 0.35 and 0.45 in inner and coastal stations. Our results indicate that highest carbon export may occur in the outer part of the Gulf, closer to the mid-shelf region. Further studies will be necessary to better understand the functioning of this ecosystem, including the impact of fisheries and horizontal transport by currents in the overall CO2 balance.

Analysis of hyper-baric biofilms on engineering surfaces formed in the Deep Sea

NASA Astrophysics Data System (ADS)

Meier, A.; Tsaloglou, N. M.; Connelly, D.; Keevil, B.; Mowlem, M.

2012-04-01

Long-term monitoring of the environment is essential to our understanding of global processes, such as global warming, and their impact. As biofilm formation occurs after only short deployment periods in the marine environment, it is a major problem in long-term operation of environmental sensors. This makes the development of anti-fouling strategies for in situ sensors critical to their function. The effects on sensors can range from measurement drift, which can be compensated, to blockage of channels and material degradation, rendering them inoperative. In general, the longer the deployment period the more severe the effects of the biofouling become. Until now, biofilm research has focused mainly on the eutrophic and euphotic zones of the oceans. Hyper-baric biofilms are poorly understood due to difficulties in experimental setup and the assumption that biofouling in these oligotrophic regions could be regarded as insignificant. Our study shows significant biofilm formation occurs in the deep sea. We deployed a variety of materials, typically used in engineering structures, on a 4500 metre deep mooring during a cruise to the Cayman Trough, for 10 days. The materials were clear plain glass, poly-methyl methacrylate (PMMA), Delrin™, and copper, a known antifouling agent. The biofilms were studied by fluorescence microscopy and molecular analysis. For microscopy the nucleic acid stain, SYTO©9, was used and surface coverage was quantified by using a custom MATLAB™ program. Further molecular analyses, including UV Vis spectrometric quantification of DNA, nucleic acid amplification using Polymerase Chain Reaction (PCR), and Denaturing Gradient Gel Electrophoresis (DGGE), were utilised for the analysis of the microbial community composition of these biofilms. Six 16S/18S universal primer sets representative for the three kingdoms, Archea, Bacteria, and Eukarya were used for the PCR and DGGE. Preliminary results from fluorescence microscopy showed that the biofilm coverage on copper and PMMA was a third of that on Delrin™ and less than half the amount seen on glass surfaces. PCR showed that the microorganisms in these biofilms were predominantly Archea . DGGE conditions were optimised for the separation of PCR products from the three kingdoms. Sequencing data is still being processed. These results show that mitigation strategies are essential for any kind of long-term deployments of remote sensors even in the deep sea. Such strategies could consist for example of chlorine production through the electrolysis of seawater, back-flushing sensor channels with various chemicals, thin films of nickel/copper/zinc alloys in various ratios as surface treatments, quorum-sensing, furanone-treatment and micro-structuring of surfaces.

Changes in the ecosystem structure of the Black Sea under predicted climatological and anthropogenic variations

NASA Astrophysics Data System (ADS)

Akoglu, Ekin; Salihoglu, Baris; Fach Salihoglu, Bettina; Libralato, Simone; Cannaby, Heather; Oguz, Temel; Solidoro, Cosimo

2014-05-01

A dynamic Ecopath with Ecosim higher-trophic-level (HTL) model representation of the Black Sea ecosystem was coupled to the physical (BIMS-CIR) and biogeochemical (BIMS-ECO) models of the Black Sea in order to investigate historical anthropogenic and climatological interactions and feedbacks in the ecosystem. Further, the coupled models were used to assess the likely consequences of these interactions on the ecosystem's structure and functioning under predicted future climate (IPCC A1B) and fishing variability. Therefore, two model scenarios were used; i) a hindcast scenario (1980-1999) to evaluate and understand the impacts of the short-term climate and physical variability and the introduction of invasive species on the Black Sea ecosystem, and ii) a forecast scenario (2080-2099) to investigate the potential implications of climate change and anthropogenic exploitation on living resources of the Black Sea ecosystem by the end of the 21st century. According to the outcomes of the hindcast simulation, fisheries were found to be the main driver in determining the structure and functioning of the Black Sea ecosystem under changing environmental conditions. The coupled physical-biogeochemical forecast simulations predicted a slight but statistically significant basin-wide increase in the Black Sea's primary productivity by the end of the century due to increased stratification induced by basin-wide temperature increase and reduced Cold Intermediate Layer (CIL) formation which increased the residence time of riverine nutrients within the euphotic zone. Despite this increased primary productivity, the HTL model forecast simulation predicted a significant decrease in the commercial fish stocks primarily due to fisheries exploitation if current catch rates are maintained into the future. Results further suggested that some economically important small pelagic fish species are likely to disappear from the ecosystem making the recovery of the already-collapsed piscivorous fish stocks increasingly unlikely. In addition, a further reduction in the proportion of piscivorous fish in the fish community was found to be consequent. From a management perspective, the results of the study suggested that along with managing fishing exploitation levels of the target stocks, monitoring and management of other species in the ecosystem that are tightly coupled with the fish species in terms of food web interactions were found to be the most effective way of applying an ecosystem-based management strategy in the Black Sea. Such an approach will ensure the sustainable utilisation of the fish stocks of the Black Sea by maintaining the ecological integrity of the Black Sea marine food web.

The Carbon Isotopic Composition of Organic Matter in the Microfossils of Planktonic Foraminifera

NASA Astrophysics Data System (ADS)

Swart, K. A.; Oleynik, S.; Sigman, D. M.

2016-12-01

Surface ocean pCO2 is an important measure of the ocean/atmosphere C cycle. Reconstruction of euphotic zone pCO2 over glacial cycles has the potential to indicate the roles of different ocean regions in atmospheric pCO2 changes. Moreover, pCO2 in some surface ocean regions should provide a measure of atmospheric pCO2 change over periods predating the ice core record. The δ13C values of phytoplankton biomass have been used as a proxy for surface ocean pCO2, although carbon fixation rate and other parameters are also important. We have investigated "foraminifera-bound organic matter" (FBOM) as an alternative to bulk sedimentary organic matter for δ13C measurement. One motivation is the ubiquity of foraminifera in unproductive regions where conditions are best for reconstruction of pCO2 but where sedimentary organic matter concentrations are low. We have modified an elemental analyzer so that, interfaced with a stable isotope ratio mass spectrometer, precision for δ13C is 0.2‰ down to 20 nmol C, 1500-fold less C than typically required. This allows for measurements of 10 tests. Cleaning and decalcification protocols have been developed for the analysis of FBOM δ13C (1SD = .4‰). In Holocene sediments from the tropical N. Atlantic, FBOM C content is 65-95 µm C/g CaCO3, with a C/N of 20. For G. ruber, the Holocene δ13C value is -25.0±0.4‰, 2-3‰ lower than surface water suspended POM and expected photosynthate. This difference, along with the high C/N, suggests that FBOM has a substantial lipid component. G. ruber and G. sacculifer, which share similar ecological niches, δ13C values and downcore trends are similar. We do not see systemic differences among species in Holocene sediments that relate to depth of habitat or the presence of endosymbionts. We have examined three tropical N. Atlantic sediment cores back to the last ice age. Given ice core information on pCO2 and reconstruction of local SST, FBOM δ13C values in G. ruber from one core show the expected amplitude of δ13C elevation during the LGM, while 2 other records do not show this shift, with instead a slightly lower FBOM δ13C value during the LGM. Possible explanations for these findings will be offered. Moreover, measurements will be reported on coretop samples from the equatorial Pacific.

Relationship between Chlorophyll a Concentration, Light Attenuation and Diving Depth of the Southern Elephant Seal Mirounga leonina

PubMed Central

Jaud, Thomas; Dragon, Anne-Cécile; Garcia, Jade Vacquie; Guinet, Christophe

2012-01-01

Recently, a number of Antarctic marine environmental studies have used oceanographic parameters collected from instrumented top predators for ecological and physical information. Phytoplankton concentration is generally quantified through active measurement of chlorophyll fluorescence. In this study, light absorption coefficient (K0.75) was used as an indicator of phytoplankton concentration. This measurement, easy to obtain and requiring low electric power, allows for assessing of the fine scale horizontal structuring of phytoplankton. As part of this study, Southern elephant seals (SES) were simultaneously equipped with a fluorometer and a light logger. Along the SES tracks, variations in K0.75 were strongly correlated with chlorophyll, a concentration measured by the fluorometer within the euphotic layer. With regards to SES foraging behaviour, bottom depth of the seal’s dive was highly dependent on light intensity at 150 m, indicating that the vertical distribution of SES’s prey such as myctophids is tightly related to light level. Therefore, change in phytoplankton concentration may not only have a direct effect on SES’s prey abundance but may also determine their vertical accessibility with likely consequences on SES foraging efficiency. PMID:23082166

Dynamic Changes of Photosynthetic Picoeukaryotes Composition in the Northwestern Pacific Ocean Revealed by High-Throughput Tag Sequencing of Plastid 16S rRNA Gene

NASA Astrophysics Data System (ADS)

Choi, D. H.; Noh, J. H.; Selph, K. E.; Lee, C. M.

2016-02-01

Photosynthetic picoeukaryotes (PPEs) are major oceanic primary producers. However, the diversity of such communities remains poorly understood, especially in the northwestern (NW) Pacific. We investigated the abundance and diversity of PPEs, and recorded environmental variables, along a transect from the coast to the open Pacific Ocean. High-throughput tag sequencing (using the MiSeq system) revealed the diversity of plastid 16S rRNA genes. The dominant PPEs changed at the class level along the transect. Prymnesiophyceae were the only dominant PPEs in the warm pool of the NW Pacific, but Mamiellophyceae dominated in coastal waters of the East China Sea. Phylogenetically, most Prymnesiophyceae sequences could not be resolved at lower taxonomic levels because no close relatives have been cultured. Within the Mamiellophyceae, the genera Micromonas and Ostreococcus dominated in marginal coastal areas affected by open water, whereas Bathycoccus dominated in the lower euphotic depths of open oligotrophic waters. Cryptophyceae and Phaeocystis (of the Prymnesiophyceae) dominated in areas affected principally by coastal water. We also defined the biogeographical distributions of Chrysophyceae, Prasinophyceae, Bacillariophyceaea, and Pelagophyceae. These distributions were influenced by temperature, salinity, and chlorophyll a and nutrient concentrations.

Fueling plankton production by a meandering frontal jet: a case study for the Alboran Sea (Western Mediterranean).

PubMed

Oguz, Temel; Macias, Diego; Garcia-Lafuente, Jesus; Pascual, Ananda; Tintore, Joaquin

2014-01-01

A three dimensional biophysical model was employed to illustrate the biological impacts of a meandering frontal jet, in terms of efficiency and persistency of the autotrophic frontal production, in marginal and semi-enclosed seas. We used the Alboran Sea of the Western Mediterranean as a case study. Here, a frontal jet with a width of 15-20 km, characterized by the relatively low density Atlantic water mass, flows eastward within the upper 100 m as a marked meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of a strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates phytoplankton growth along the jet. Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet. The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data. The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive.

Changes in optical characteristics of surface microlayers hint to photochemically and microbially mediated DOM turnover in the upwelling region off the coast of Peru

NASA Astrophysics Data System (ADS)

Galgani, Luisa; Engel, Anja

2016-04-01

The coastal upwelling system off the coast of Peru is characterized by high biological activity and a pronounced subsurface oxygen minimum zone, as well as associated emissions of atmospheric trace gases such as N2O, CH4 and CO2. From 3 to 23 December 2012, R/V Meteor (M91) cruise took place in the Peruvian upwelling system between 4.59 and 15.4° S, and 82.0 to 77.5° W. During M91 we investigated the composition of the sea-surface microlayer (SML), the oceanic uppermost boundary directly subject to high solar radiation, often enriched in specific organic compounds of biological origin like chromophoric dissolved organic matter (CDOM) and marine gels. In the SML, the continuous photochemical and microbial recycling of organic matter may strongly influence gas exchange between marine systems and the atmosphere. We analyzed SML and underlying water (ULW) samples at 38 stations focusing on CDOM spectral characteristics as indicator of photochemical and microbial alteration processes. CDOM composition was characterized by spectral slope (S) values and excitation-emission matrix fluorescence (EEMs), which allow us to track changes in molecular weight (MW) of DOM, and to determine potential DOM sources and sinks. Spectral slope S varied between 0.012 to 0.043 nm-1 and was quite similar between SML and ULW, with no significant differences between the two compartments. Higher S values were observed in the ULW of the southern stations below 15° S. By EEMs, we identified five fluorescent components (F1-5) of the CDOM pool, of which two had excitation/emission characteristics of amino-acid-like fluorophores (F1, F4) and were highly enriched in the SML, with a median ratio SML : ULW of 1.5 for both fluorophores. In the study region, values for CDOM absorption ranged from 0.07 to 1.47 m-1. CDOM was generally highly concentrated in the SML, with a median enrichment with respect to the ULW of 1.2. CDOM composition and changes in spectral slope properties suggested a local microbial release of DOM directly in the SML as a response to light exposure in this extreme environment. In a conceptual model of the sources and modifications of optically active DOM in the SML and underlying seawater (ULW), we describe processes we think may take place (Fig. 1); the production of CDOM of higher MW by microbial release through growth, exudation and lysis in the euphotic zone, includes the identified fluorophores (F1, F2, F3, F4, F5). Specific amino-acid-like fluorophores (F1, F4) accumulate in the SML with respect to the ULW, as photochemistry may enhance microbial CDOM release by (a) photoprotection mechanisms and (b) cell-lysis processes. Microbial and photochemical degradation are potential sinks of the amino-acid-like fluorophores (F1, F4), and potential sources of reworked and more refractory humic-like components (F2, F3, F5). In the highly productive upwelling region along the Peruvian coast, the interplay of microbial and photochemical processes controls the enrichment of amino-acid-like CDOM in the SML. We discuss potential implications for air-sea gas exchange in this area.

Deep winter convection and phytoplankton dynamics in the NW Mediterranean Sea under present climate and future (horizon 2030) scenarios.

PubMed

Macias, Diego; Garcia-Gorriz, Elisa; Stips, Adolf

2018-04-26

Deep water convection (DC) in winter is one of the major processes driving open-ocean primary productivity in the Northwestern Mediterranean Sea. DC is highly variable in time, depending on the specific conditions (stratification, circulation and ocean-atmosphere interactions) of each specific winter. This variability also drives the interannual oscillations of open-ocean primary productivity in this important region for many commercially-important fish species. We use a coupled model system to 1) understand to what extent DC impacts phytoplankton seasonality in the present-day and 2) to explore potential changes in future scenarios (~2030). Our model represents quite accurately the present-day characteristics of DC and its importance for open-ocean phytoplankton blooms. However, for the future scenarios the importance of deep nutrients in fertilizing the euphotic layer of the NW Mediterranean decreases. The model simulates changes in surface density and on the levels of kinetic energy that make mesoscale activity associated with horizontal currents to become a more important fertilization mechanism, inducing subsequently phenological changes in seasonal plankton cycles. Because of our focus on the open-sea, an exact quantification of the impact of those changes on the overall biological production of the NW Mediterranean cannot be made at the moment.

Fueling Plankton Production by a Meandering Frontal Jet: A Case Study for the Alboran Sea (Western Mediterranean)

PubMed Central

Oguz, Temel; Macias, Diego; Garcia-Lafuente, Jesus; Pascual, Ananda; Tintore, Joaquin

2014-01-01

A three dimensional biophysical model was employed to illustrate the biological impacts of a meandering frontal jet, in terms of efficiency and persistency of the autotrophic frontal production, in marginal and semi-enclosed seas. We used the Alboran Sea of the Western Mediterranean as a case study. Here, a frontal jet with a width of 15–20 km, characterized by the relatively low density Atlantic water mass, flows eastward within the upper 100 m as a marked meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of a strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates phytoplankton growth along the jet. Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet. The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data. The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive. PMID:25372789

Dynamic changes in the composition of photosynthetic picoeukaryotes in the northwestern Pacific Ocean revealed by high-throughput tag sequencing of plastid 16S rRNA genes.

PubMed

Choi, Dong H; An, Sung M; Chun, Sungjun; Yang, Eun C; Selph, Karen E; Lee, Charity M; Noh, Jae H

2016-02-01

Photosynthetic picoeukaryotes (PPEs) are major oceanic primary producers. However, the diversity of such communities remains poorly understood, especially in the northwestern (NW) Pacific. We investigated the abundance and diversity of PPEs, and recorded environmental variables, along a transect from the coast to the open Pacific Ocean. High-throughput tag sequencing (using the MiSeq system) revealed the diversity of plastid 16S rRNA genes. The dominant PPEs changed at the class level along the transect. Prymnesiophyceae were the only dominant PPEs in the warm pool of the NW Pacific, but Mamiellophyceae dominated in coastal waters of the East China Sea. Phylogenetically, most Prymnesiophyceae sequences could not be resolved at lower taxonomic levels because no close relatives have been cultured. Within the Mamiellophyceae, the genera Micromonas and Ostreococcus dominated in marginal coastal areas affected by open water, whereas Bathycoccus dominated in the lower euphotic depths of oligotrophic open waters. Cryptophyceae and Phaeocystis (of the Prymnesiophyceae) dominated in areas affected principally by coastal water. We also defined the biogeographical distributions of Chrysophyceae, prasinophytes, Bacillariophyceaea and Pelagophyceae. These distributions were influenced by temperature, salinity and chlorophyll a and nutrient concentrations. © FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Seasonal variations in C:N:Si:Ca:P:Mg:S:K:Fe relationships of seston from Norwegian coastal water: Impact of extreme offshore forcing during winter-spring 2010.

PubMed

Erga, Svein Rune; Haugen, Stig Bjarte; Bratbak, Gunnar; Egge, Jorun Karin; Heldal, Mikal; Mork, Kjell Arne; Norland, Svein

2017-11-20

The aim of this study was to reveal the relative content of C, N, Ca, Si, P, Mg, K, S and Fe in seston particles in Norwegian coastal water (NCW), and how it relates to biological and hydrographic processes during seasonal cycles from October 2009-March 2012. The following over all stoichiometric relationship for the time series was obtained: C 66 N 11 Si 3.4 Ca 2.3 P 1 Mg 0.73 S 0.37 K 0.35 Fe 0.30 , which is novel for marine waters. A record-breaking (187-year record) negative North Atlantic Oscillation (NAO) index caused extreme physical forcing on the Norwegian Coastal Current Water (NCCW) during the winter 2009-2010, and the inflow and upwelling of saline Atlantic water (AW) in the fjord was thus extraordinary during late spring-early summer in 2010. The element concentrations in fjord seston particles responded strongly to this convection, revealed by maximum values of all elements, except Fe, exceeding average values with 10.8 × for Ca, 9.3 for K, 5.3 for S, 5.1 for Mg, 4.6 for Si, 4.0 for P, 3.8 for C, and 3.3 for N and Fe. This indicates that the signature of the Atlantic inflow was roughly two times stronger for Ca and K than for the others, probably connected with peaks in coccolithophorids and diatoms. There is, however, 1.5 × more of Si than Ca contained in the seston, which could be due to a stronger dominance of diatoms than coccolithophorids, confirming their environmental fitness. In total our data do not indicate any severe nutrient limitation with respect to N, P and Fe, but accumulation of iron by Fe-sequestering bacteria might at times reduce the availability of the dissolved Fe-fraction. There is a high correlation between most of the measured elements, except for Ca, which together with Fe only weakly correlated with the other elements. It is to be expected that environmental alterations in NCW related to climate change will influence the seston elemental composition, but the full effect of this will be strongly dependent on the future dominance of the high pressure versus low pressure systems (i.e. NAO index), since they are key regulators for the direction of wind driven vertical convection (i.e. upwelling or downwelling). Changes in stratification, temperature, light, pH (ocean acidification), CaCO 3 concentrations (carbon pump) and availability of nutrients in the euphotic zone (biogeochemical cycling) are essential for the future dominance of coccolithophorids versus diatoms.

Carbon export fluxes in the Southern Ocean: results from inverse modeling and comparison with satellite-based estimates

NASA Astrophysics Data System (ADS)

Schlitzer, Reiner

The use of dissolved nutrients and carbon for photosynthesis in the euphotic zone and the subsequent downward transport of particulate and dissolved organic material strongly affect carbon concentrations in surface water and thus the air-sea exchange of CO 2. Efforts to quantify the downward carbon flux for the whole ocean or on basin-scales are hampered by the sparseness of direct productivity or flux measurements. Here, a global ocean circulation, biogeochemical model is used to determine rates of export production and vertical carbon fluxes in the Southern Ocean. The model exploits the existing large sets of hydrographic, oxygen, nutrient and carbon data that contain information on the underlying biogeochemical processes. The model is fitted to the data by systematically varying circulation, air-sea fluxes, production, and remineralization rates simultaneously. Use of the adjoint method yields model property simulations that are in very good agreement with measurements. In the model, the total integrated export flux of particulate organic matter necessary for the realistic reproduction of nutrient data is significantly larger than export estimates derived from primary productivity maps. Of the 10,000 TgC yr -1(10 GtC yr -1) required globally, the Southern Ocean south of 30°S contributes about 3000 TgC yr -1 (33%), most of it occurring in a zonal belt along the Antarctic Circumpolar Current and in the Peru, Chile and Namibia coastal upwelling regions. The export flux of POC for the area south of 50°S amounts to 1000±210 TgC yr -1, and the particle flux in 1000 m for the same area is 115±20 TgC yr -1. Unlike for the global ocean, the contribution of the downward flux of dissolved organic carbon is significant in the Southern Ocean in the top 500 m of the water column. Comparison with satellite-based productivity estimates (CZCS and SeaWiFS) shows a relatively good agreement over most of the ocean except for the Southern Ocean south of 50°S, where the model fluxes are systematically higher than the satellite-based values by factors between 2 and 5. This discrepancy is significant, and an attempt to reconcile the low satellite-derived productivity values with ocean-interior nutrient budgets failed. Too low productivity estimates from satellite chlorophyll observations in the polar and sub-polar Southern Ocean could arise because of the inability of the satellite sensors to detect frequently occurring sub-surface chlorophyll patches, and to a poor calibration of the conversion algorithms in the Southern Ocean because of the very limited amount of direct measurements.

The fate of dissolved dimethylsulfoniopropionate (DMSP) in seawater: tracer studies using 35S-DMSP

NASA Astrophysics Data System (ADS)

Kiene, Ronald P.; Linn, Laura J.

2000-08-01

The algal osmolyte dimethylsulfoniopropionate (DMSP) is distributed globally in the marine euphotic zone, where it represents a major form of reduced sulfur. Previous investigations of DMSP cycling have focused mainly on its degradation to the volatile sulfur species dimethylsulfide (DMS) and little is known about the other possible fates of the sulfur. In this study 35S-DMSP was used to trace the biogeochemical fate of sulfur in the natural pool of dissolved DMSP in seawater. Dissolved 35S-DMSP added to seawater was degraded within hours, with the 35S partitioning into three major, relatively stable, operational pools: particulates, dissolved non-volatile degradation products (DNVS), and volatiles. The mean values for partitioning of DMSP obtained from 20 different seawater incubations were (in terms of sulfur): particulates (33%; range 6-85%;); DNVS (46%; range 21-74%); and volatiles (9%; range 2-21%). Oceanic water samples had lower incorporation of DMSP-S into particulates and higher incorporation into DNVS as compared with coastal-shelf samples. Transient accumulation of untransformed 35S-DMSP in bacteria accounted for some of the particulate 35S, but most of the cell-associated DMSP was rapidly transformed and the sulfur incorporated into relatively stable macromolecules. 35S-labeled DNVS accumulated steadily during DMSP metabolism and approximately half of this pool was confirmed to be sulfate, implying that oxidation of DMSP-sulfur takes place on time scales of minutes to hours. Volatile products were produced rapidly from 35S-DMSP, but most were consumed within 1-3 h. Experiments showed that methanethiol (MeSH) was the major volatile compound produced from tracer DMSP, with longer-lived DMS formed in lower amounts. Tracer additions of 35S-MeSH to seawater resulted in incorporation of sulfur into cellular macromolecules and DNVS, suggesting MeSH was an intermediate in the conversion of DMSP into these pools. Experiments with 35S-DMS revealed that turnover of DMS was much slower than for DMSP or MeSH, and the retention of the DMS-sulfur in particles was only a minor fraction of the total amount metabolized. The majority of the 35S-DMS was transformed into DNVS including sulfate. Temperature and DMSP concentration significantly affected the partitioning of sulfur during DMSP degradation, with lower temperatures and higher substrate concentrations causing a shift from particulate into volatile and non-volatile dissolved products. Our work demonstrates that natural turnover of dissolved DMSP results in minor net production of sulfur gases, and substantial production of previously unrecognized products (particulate and dissolved non-volatile sulfur). The main fates of DMSP are tied to assimilation and oxidation of the reduced sulfur by microorganisms, both of which may act as important controls on the production of climatically active DMS.

Nutrient availability and the ultimate control of the biological carbon pump in the western tropical South Pacific Ocean

NASA Astrophysics Data System (ADS)

Moutin, Thierry; Wagener, Thibaut; Caffin, Mathieu; Fumenia, Alain; Gimenez, Audrey; Baklouti, Melika; Bouruet-Aubertot, Pascale; Pujo-Pay, Mireille; Leblanc, Karine; Lefevre, Dominique; Helias Nunige, Sandra; Leblond, Nathalie; Grosso, Olivier; de Verneil, Alain

2018-05-01

Surface waters (0-200 m) of the western tropical South Pacific (WTSP) were sampled along a longitudinal 4000 km transect (OUTPACE cruise, DOI: 10.17600/15000900) during the austral summer (stratified) period (18 February to 3 April 2015) between the Melanesian Archipelago (MA) and the western part of the SP gyre (WGY). Two distinct areas were considered for the MA, the western MA (WMA), and the eastern MA (EMA). The main carbon (C), nitrogen (N), and phosphorus (P) pools and fluxes provide a basis for the characterization of the expected trend from oligotrophy to ultra-oligotrophy, and the building of first-order budgets at the daily and seasonal timescales (using climatology). Sea surface chlorophyll a well reflected the expected oligotrophic gradient with higher values obtained at WMA, lower values at WGY, and intermediate values at EMA. As expected, the euphotic zone depth, the deep chlorophyll maximum, and nitracline depth deepen from west to east. Nevertheless, phosphaclines and nitraclines did not match. The decoupling between phosphacline and nitracline depths in the MA allows for excess P to be locally provided in the upper water by winter mixing. We found a significant biological soft tissue carbon pump in the MA sustained almost exclusively by dinitrogen (N2) fixation and essentially controlled by phosphate availability in this iron-rich environment. The MA appears to be a net sink for atmospheric CO2, while the WGY is in quasi-steady state. We suggest that the necessary excess P, allowing the success of nitrogen fixers and subsequent carbon production and export, is mainly brought to the upper surface by local deep winter convection at an annual timescale rather than by surface circulation. While the origin of the decoupling between phosphacline and nitracline remains uncertain, the direct link between local P upper water enrichment, N2 fixation, and organic carbon production and export, offers a possible shorter timescale than previously thought between N input by N2 fixation and carbon export. The low iron availability in the SP gyre and P availability in the MA during the stratified period may appear as the ultimate control of N input by N2 fixation. Because of the huge volume of water to consider, and because the SP Ocean is the place of intense denitrification in the east (N sink) and N2 fixation in the west (N source), precise seasonal C, N, P, and iron (Fe) budgets would be of prime interest to understand the efficiency, at the present time and in the future, of the oceanic biological carbon pump.

Shallow water submarine hydrothermal activity - A case study in the assessment of ocean acidification and fertilization

NASA Astrophysics Data System (ADS)

Zhang, J.; Yoshida, K.; Hagiwara, T.; Nagao, K.; Kusakabe, M.; Wang, B.; Chen, C. A.

2012-12-01

Most natural Shallow Water submarine Hydrothermal activates (SWH) along coastlines are related to hydrothermal eruptions involving heating of groundwater with the volcanic gas. These SWHs supply nutrients such as phosphorus and micro nutrients like iron to the euphotic zone, contributing to the overall natural fertility and primary productivity of coastal waters. However, SWHs also have a negative effect, dispersing toxic materials such as mercury and arsenic, and affecting the acidification of the surrounding waters. In this study, we evaluate the impact of "iron supply" and "ocean acidification" on the primary production in a coastal marine environment, at a SWH area discovered off Gueshandao Island, northeast Taiwan. In the past three years, expeditions were conducted and observations made around this SWH site. Divers, small boats and a research vessel (R/V OR1, Ocean University National Taiwan) were used to survey successively larger areas around the site. Some of the results obtained are as follows. Hydrothermal vents are located in a hilly terrain rich with hot spring water with gas erupting intermittently. There are two types of vents, roughly divided by color, yellow hot spring water with higher temperature >110 degC ejected from sulfur chimneys of various sizes, and colorless water with lower temperature ~80 degC ejected directly from the crevices of the andesitic bedrock. Natural sulfur solidifying in the mouth of a small chimney was captured by a video camera, and explosions were also observed at intervals of a few minutes. Sediment, sand and particles of sulfur were deposited on the sides to a radius of about 50 m condensing around the chimney. The bottom type changes from sand/particles to outcrop/rock away from the vents. Moreover, gas samples were collected from the vents; the ratios of gas concentrations (N2/Ar) and isotopic composition of noble gas (3He/4He) suggest that these volcanic gases are mantle-derived. Hydrothermal fluid with high pH values between 2.1 ~ 3.5 erupts from the vents, and diffuses toward the ocean surface affecting water up to 1 km way. The high pCO2 in the surface seawater is widely distributed, and the low pH value is also observed widely in mid-depth water (5 ~ 15 m). Water samples collected around the SHW site show higher concentrations of nutrients Si and P, and typically higher micro nutrients Mn, and even Fe as compared to normal seawater. Chlorophyll a in particular shows high values of several tens to hundreds times greater than normal subtropical seawater. We find for the first time in the nature, that SHW enhances the growth of phytoplankton, and contributes to primary productivity of the surrounding waters.

Bacterial Chitin Hydrolysis in Two Lakes with Contrasting Trophic Statuses

PubMed Central

Carstens, Dörte; Keller, Esther; Vazquez, Francisco; Schubert, Carsten J.; Zeyer, Josef; Bürgmann, Helmut

2012-01-01

Chitin, which is a biopolymer of the amino sugar glucosamine (GlcN), is highly abundant in aquatic ecosystems, and its degradation is assigned a key role in the recycling of carbon and nitrogen. In order to study the significance of chitin decomposition in two temperate freshwater lakes with contrasting trophic and redox conditions, we measured the turnover rate of the chitin analog methylumbelliferyl-N,N′-diacetylchitobioside (MUF-DC) and the presence of chitinase (chiA) genes in zooplankton, water, and sediment samples. In contrast to the eutrophic and partially anoxic lake, chiA gene fragments were detectable throughout the oligotrophic water column and chiA copy numbers per ml of water were up to 15 times higher than in the eutrophic waters. For both lakes, the highest chiA abundance was found in the euphotic zone—the main habitat of zooplankton, but also the site of production of easily degradable algal chitin. The bulk of chitinase activity was measured in zooplankton samples and the sediments, where recalcitrant chitin is deposited. Both, chiA abundance and chitinase activity correlated well with organic carbon, nitrogen, and concentrations of particulate GlcN. Our findings show that chitin, although its overall contribution to the total organic carbon is small (∼0.01 to 0.1%), constitutes an important microbial growth substrate in these temperate freshwater lakes, particularly where other easily degradable carbon sources are scarce. PMID:22101058

Potential Impact of North Atlantic Climate Variability on Ocean Biogeochemical Processes

NASA Astrophysics Data System (ADS)

Liu, Y.; Muhling, B.; Lee, S. K.; Muller-Karger, F. E.; Enfield, D. B.; Lamkin, J. T.; Roffer, M. A.

2016-02-01

Previous studies have shown that upper ocean circulations largely determine primary production in the euphotic layers, here the global ocean model with biogeochemistry (GFDL's Modular Ocean Model with TOPAZ biogeochemistry) forced with the ERA-Interim is used to simulate the natural variability of biogeochemical processes in global ocean during 1979-present. Preliminary results show that the surface chlorophyll is overall underestimated in MOM-TOPAZ, but its spatial pattern is fairly realistic. Relatively high chlorophyll variability is shown in the subpolar North Atlantic, northeastern tropical Atlantic, and equatorial Atlantic. Further analysis suggests that the chlorophyll variability in the North Atlantic Ocean is affected by long-term climate variability. For the subpolar North Atlantic region, the chlorophyll variability is light-limited and is significantly correlated with North Atlantic Oscillation. A dipole pattern of chlorophyll variability is found between the northeastern tropical Atlantic and equatorial Atlantic. For the northeastern North Atlantic, the chlorophyll variability is significantly correlated with Atlantic Meridional Mode (AMM) and Atlantic Multidecadal Oscillation (AMO). During the negative phase of AMM and AMO, the increased trade wind in the northeast North Atlantic can lead to increased upwelling of nutrients. In the equatorial Atlantic region, the chlorophyll variability is largely link to Atlantic-Niño and associated equatorial upwelling of nutrients. The potential impact of climate variability on the distribution of pelagic fishes (i.e. yellowfin tuna) are discussed.

Physical control of interannual variations of the winter chlorophyll bloom in the northern Arabian Sea

NASA Astrophysics Data System (ADS)

Girijakumari Keerthi, Madhavan; Lengaigne, Matthieu; Levy, Marina; Vialard, Jerome; Parvathi, Vallivattathillam; de Boyer Montégut, Clément; Ethé, Christian; Aumont, Olivier; Suresh, Iyyappan; Parambil Akhil, Valiya; Moolayil Muraleedharan, Pillathu

2017-08-01

The northern Arabian Sea hosts a winter chlorophyll bloom, triggered by convective overturning in response to cold and dry northeasterly monsoon winds. Previous studies of interannual variations of this bloom only relied on a couple of years of data and reached no consensus on the associated processes. The current study aims at identifying these processes using both ˜ 10 years of observations (including remotely sensed chlorophyll data and physical parameters derived from Argo data) and a 20-year-long coupled biophysical ocean model simulation. Despite discrepancies in the estimated bloom amplitude, the six different remotely sensed chlorophyll products analysed in this study display a good phase agreement at seasonal and interannual timescales. The model and observations both indicate that the interannual winter bloom fluctuations are strongly tied to interannual mixed layer depth anomalies ( ˜ 0.6 to 0.7 correlation), which are themselves controlled by the net heat flux at the air-sea interface. Our modelling results suggest that the mixed layer depth control of the bloom amplitude ensues from the modulation of nutrient entrainment into the euphotic layer. In contrast, the model and observations both display insignificant correlations between the bloom amplitude and thermocline depth, which precludes a control of the bloom amplitude by daily dilution down to the thermocline depth, as suggested in a previous study.

The CAFE model: A net production model for global ocean phytoplankton

NASA Astrophysics Data System (ADS)

Silsbe, Greg M.; Behrenfeld, Michael J.; Halsey, Kimberly H.; Milligan, Allen J.; Westberry, Toby K.

2016-12-01

The Carbon, Absorption, and Fluorescence Euphotic-resolving (CAFE) net primary production model is an adaptable framework for advancing global ocean productivity assessments by exploiting state-of-the-art satellite ocean color analyses and addressing key physiological and ecological attributes of phytoplankton. Here we present the first implementation of the CAFE model that incorporates inherent optical properties derived from ocean color measurements into a mechanistic and accurate model of phytoplankton growth rates (μ) and net phytoplankton production (NPP). The CAFE model calculates NPP as the product of energy absorption (QPAR), and the efficiency (ϕμ) by which absorbed energy is converted into carbon biomass (CPhyto), while μ is calculated as NPP normalized to CPhyto. The CAFE model performance is evaluated alongside 21 other NPP models against a spatially robust and globally representative set of direct NPP measurements. This analysis demonstrates that the CAFE model explains the greatest amount of variance and has the lowest model bias relative to other NPP models analyzed with this data set. Global oceanic NPP from the CAFE model (52 Pg C m-2 yr-1) and mean division rates (0.34 day-1) are derived from climatological satellite data (2002-2014). This manuscript discusses and validates individual CAFE model parameters (e.g., QPAR and ϕμ), provides detailed sensitivity analyses, and compares the CAFE model results and parameterization to other widely cited models.

Macronutrient and carbon supply, uptake and cycling across the Antarctic Peninsula shelf during summer

PubMed Central

Jones, Elizabeth M.; Venables, Hugh J.; Firing, Yvonne L.; Dittrich, Ribanna; Heiser, Sabrina; Dougans, Julie

2018-01-01

The West Antarctic Peninsula shelf is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-shelf modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the shelf, contrary to cross-shelf reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially shelf sediment porewaters, as the primary drivers of cross-shelf enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’. PMID:29760112

Macronutrient and carbon supply, uptake and cycling across the Antarctic Peninsula shelf during summer.

PubMed

Henley, Sian F; Jones, Elizabeth M; Venables, Hugh J; Meredith, Michael P; Firing, Yvonne L; Dittrich, Ribanna; Heiser, Sabrina; Stefels, Jacqueline; Dougans, Julie

2018-06-28

The West Antarctic Peninsula shelf is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-shelf modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the shelf, contrary to cross-shelf reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially shelf sediment porewaters, as the primary drivers of cross-shelf enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment.This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'. © 2018 The Authors.

Assessment of satellite derived diffuse attenuation coefficients ...

EPA Pesticide Factsheets

Optical data collected in coastal waters off South Florida and in the Caribbean Sea between January 2009 and December 2010 were used to evaluate products derived with three bio-optical inversion algorithms applied to MOIDS/Aqua, MODIS/Terra, and SeaWiFS satellite observations. The products included the diffuse attenuation coefficient at 490 nm (Kd_490) and for the visible range (Kd_PAR), and euphotic depth (Zeu, corresponding to 1% of the surface incident photosynthetically available radiation or PAR). Above-water hyperspectral reflectance data collected over optically shallow waters of the Florida Keys between June 1997 and August 2011 were used to help understand algorithm performance over optically shallow waters. The in situ data covered a variety of water types in South Florida and the Caribbean Sea, ranging from deep clear waters, turbid coastal waters, and optically shallow waters (Kd_490 range of ~0.03 – 1.29m-1). An algorithm based on Inherent Optical Properties (IOPs) showed the best performance (RMSD < 13% and R2 ~1.0 for MODIS/Aqua and SeaWiFS). Two algorithms based on empirical regressions performed well for offshore clear waters, but underestimated Kd_490 and Kd_PAR in coastal waters due to high turbidity or shallow bottom contamination. Similar results were obtained when only in situ data were used to evaluate algorithm performance. The excellent agreement between satellite-derived remote sensing reflectance (Rrs) and in situ Rrs suggested that

Defining Planktonic Protist Functional Groups on Mechanisms for Energy and Nutrient Acquisition: Incorporation of Diverse Mixotrophic Strategies.

PubMed

Mitra, Aditee; Flynn, Kevin J; Tillmann, Urban; Raven, John A; Caron, David; Stoecker, Diane K; Not, Fabrice; Hansen, Per J; Hallegraeff, Gustaaf; Sanders, Robert; Wilken, Susanne; McManus, George; Johnson, Mathew; Pitta, Paraskevi; Våge, Selina; Berge, Terje; Calbet, Albert; Thingstad, Frede; Jeong, Hae Jin; Burkholder, JoAnn; Glibert, Patricia M; Granéli, Edna; Lundgren, Veronica

2016-04-01

Arranging organisms into functional groups aids ecological research by grouping organisms (irrespective of phylogenetic origin) that interact with environmental factors in similar ways. Planktonic protists traditionally have been split between photoautotrophic "phytoplankton" and phagotrophic "microzooplankton". However, there is a growing recognition of the importance of mixotrophy in euphotic aquatic systems, where many protists often combine photoautotrophic and phagotrophic modes of nutrition. Such organisms do not align with the traditional dichotomy of phytoplankton and microzooplankton. To reflect this understanding, we propose a new functional grouping of planktonic protists in an eco-physiological context: (i) phagoheterotrophs lacking phototrophic capacity, (ii) photoautotrophs lacking phagotrophic capacity, (iii) constitutive mixotrophs (CMs) as phagotrophs with an inherent capacity for phototrophy, and (iv) non-constitutive mixotrophs (NCMs) that acquire their phototrophic capacity by ingesting specific (SNCM) or general non-specific (GNCM) prey. For the first time, we incorporate these functional groups within a foodweb structure and show, using model outputs, that there is scope for significant changes in trophic dynamics depending on the protist functional type description. Accordingly, to better reflect the role of mixotrophy, we recommend that as important tools for explanatory and predictive research, aquatic food-web and biogeochemical models need to redefine the protist groups within their frameworks. Copyright © 2016 The Authors. Published by Elsevier GmbH.. All rights reserved.

A tale of two basins: An integrated physical and biological perspective of the deep Arctic Ocean

NASA Astrophysics Data System (ADS)

Bluhm, B. A.; Kosobokova, K. N.; Carmack, E. C.

2015-12-01

This review paper integrates the current knowledge, based on available literature, on the physical and biological conditions of the Amerasian and Eurasian basins (AB, EB) of the deep Arctic Ocean (AO) in a comparative fashion. The present day (Holocene) AO is a mediterranean sea that is roughly half continental shelf and half basin and ridge complex. Even more recently it is roughly two thirds seasonally and one third perennially ice-covered, thus now exposing a portion of basin waters to sunlight and wind. Basin boundaries and submarine ridges steer circulation pathways in overlying waters and limit free exchange in deeper waters. The AO is made integral to the global ocean by the Northern Hemisphere Thermohaline Circulation (NHTC) which drives Pacific-origin water (PW) through Bering Strait into the Canada Basin, and counter-flowing Atlantic-origin water (AW) through Fram Strait and across the Barents Sea into the Nansen Basin. As a framework for biogeography within the AO, four basic, large-scale circulation systems (with L > 1000 km) are noted; these are: (1) the large scale wind-driven circulation which forces the cyclonic Trans-Polar Drift from Siberia to the Fram Strait and the anticyclonic Beaufort Gyre in the southern Canada Basin; (2) the circulation of waters that comprise the halocline complex, composed largely of waters of Pacific and Atlantic origin that are modified during passage over the Bering/Chukchi and Barents/Siberian shelves, respectively; (3) the topographically-trapped Arctic Circumpolar Boundary Current (ACBC) which carries AW cyclonically around the boundaries of the entire suite of basins, and (4) the very slow exchange of Arctic Ocean Deep Waters. Within the basin domain two basic water mass assemblies are observed, the difference between them being the absence or presence of PW sandwiched between Arctic Surface Waters (ASW) above and the AW complex below; the boundary between these domains is the Atlantic/Pacific halocline front. Both domains have vertical stratification that constrains the transfer of nutrients to the surface layer (euphotic zone), thus leading to their oligotrophic state, particularly in the more strongly stratified Pacific Arctic where, despite high nutrient values in the inflow, convective reset of surface layer nutrients by haline convection in winter is virtually absent. First and multi-year sea ice drastically alters albedo and insulates the underlying water column from extreme winter heat loss while its mechanical properties (thickness, concentration, roughness, etc.) greatly affect the efficiency of momentum transfer from the wind to the underlying water. Biologically, sea ice algal growth in the basins is proportionally almost equal to or exceeding phytoplankton production, and is a habitat and transport platform for sympagic (ice-associated) fauna. Owing to nutrient limitation due to strong stratification and light limitation due to snow and ice cover and extreme sun angle, primary production in the two basin domains is very low compared to the adjacent shelves. Severe nutrient limitation and complete euphotic zone drawdown in the AB favors small phytoplankton, a ubiquitous deep chlorophyll maximum layer, a low f-ratio of new to recycled carbon fixation, and a low energy food web. In contrast, nutrients persist -albeit in low levels- in the western EB, even in summer, suggesting light limitation, heavy grazing or both. The higher stocks of nutrients in the EB are more conducive to marginal ice blooms than in the AB. The large-scale ocean currents (NHTC and ACBC) import substantial expatriate, not locally reproducing zooplankton biomass especially from the adjoining subarctic Atlantic (primarily Calanus finmarchicus), but also from the Pacific (e.g., Pseudocalanus spp., Neocalanus spp. and Metridia pacifica). These advective inputs serve both as source of food to resident pelagic and benthic biota within the basins, and as potential grazers exerting top down control on limited phytoplankton resources. Benthic organisms within the AO basin show previously unappreciated biodiversity and surprising dispersion of species given the isolation of individual basins and low vertical carbon flux and resulting biomass. Larval dispersion is aided by the large-scale flows and perhaps, we hypothesize in the deep benthos by convective updrafts driven by geothermal heating. Zooplankton diversity, in contrast, is low, but again faunal assemblages are equally distributed between the EB and AB. Species pools of both pelagic and benthic communities change more with water depth rather than laterally, with the exception of expatriates and rare species, with close ties to today's North Atlantic biogeographic region. Climate related change in the AO is thus manifest at significantly differing time scales. Throughout ∼90% of the Pleistocene the AO has existed in glacial mode, with narrow continental shelves, greatly restricted river inflow, thicker and perhaps immobile sea ice, and total blockage of exchange with the Pacific Ocean. During the Holocene, on shorter time scales of 1000-100 years, significant changes in high latitude climate are tied to changes in temperature and perhaps moisture delivery patterns. The Arctic also experiences significant multi-decadal variability; however, the pace of change over the past three decades has been without precedent. Within the basin interior the ice is now thinner and less compact, and thus more responsive to wind stress (forcing and mixing). Concurrent with sea ice melt and increased river flow, the accumulation of fresh water and the stratification have increased, thus constraining vertical nutrient flux affecting phytoplankton size distributions, limiting primary production in parts of the basins now and likely in the future, and increasing vulnerability to acidification. In addition, sea ice is now retreating on an annual basis past the shelf break, exposing basin waters directly to sunlight and wind forcing. Thus, upwelling favorable winds (generally from east to west) can now directly and efficiently drive shelf-break upwelling, and draw nutrients from subsurface basin waters onto the shelf; at the same time upwelling favorable winds will also create onshore pressure gradients over the slope and basin which will act to slow or block the flow of waters in the ACBC, and thus alter advective pathways of both abiotic and biotic materials. Given the opening of a new ocean to multiple user groups, we expect that the central AO will play an increasing larger role both in the research and political arenas in the future, and we encourage pan-Arctic international collaboration over focus on territorial boundaries.

Coeur d'Alene Lake, Idaho: Insights Gained From Limnological Studies of 1991-92 and 2004-06

USGS Publications Warehouse

Wood, Molly S.; Beckwith, Michael A.

2008-01-01

More than 100 years of mining and processing of metal-rich ores in northern Idaho's Coeur d'Alene River basin have resulted in widespread metal contamination of the basin's soil, sediment, water, and biota, including Coeur d'Alene Lake. Previous studies reported that about 85 percent of the bottom of Coeur d'Alene Lake is substantially enriched in antimony, arsenic, cadmium, copper, lead, mercury, silver, and zinc. Nutrients in the lake also are a major concern because they can change the lake's trophic status - or level of biological productivity - which could result in secondary releases of metals from contaminated lakebed sediments. This report presents insights into the limnological functioning of Coeur d'Alene Lake based on information gathered during two large-scale limnological studies conducted during calendar years 1991-92 and water years 2004-06. Both limnological studies reported that longitudinal gradients exist from north to south for decreasing water column transparency, loss of dissolved oxygen, and increasing total phosphorus concentrations. Gradients also exist for total lead, total zinc, and hypolimnetic dissolved oxygen concentrations, ranging from high concentrations in the central part of the lake to lower concentrations at the northern and southern ends of the lake. In the southern end of the lake, seasonal anoxia serves as a mechanism to release dissolved constituents such as phosphorus, nitrogen, iron, and manganese from lakebed sediments and from detrital material within the water column. Nonparametric statistical hypothesis tests at a significance level of a=0.05 were used to compare analyte concentrations among stations, between lake zones, and between study periods. The highest dissolved oxygen concentrations were measured in winter in association with minimum water temperatures, and the lowest concentrations were measured in the Coeur d'Alene Lake hypolimnion during late summer or autumn as prolonged thermal stratification restricted mixing of the oxygenated upper water column and the hypolimnion, where oxygen was consumed. Large differences in median concentrations of dissolved inorganic nitrogen were measured between the euphotic zone and hypolimnion in the deep areas of the lake. These differences in nitrogen concentrations were attributable to several limnological processes, including seasonal inflow plume routing, isolation from wind-driven circulation and associated hypolimnetic enrichment, phytoplanktonic assimilation during summer months, and benthic flux. Increased chlorophyll-a and total phosphorus concentrations were measured throughout the lake in the 2004-06 study compared with results from the 1991-92 study. No significant change in hypolimnetic dissolved inorganic nitrogen concentration throughout the lake was noted even though total nitrogen loads into the lake decreased between study periods. Total zinc and total lead decreased throughout the lake from the 1991-92 study to the 2004-06 study except in the southern part of the lake, where concentrations were typically low. Median detected nitrogen-to-phosphorus ratios decreased from the 1991-92 study to the 2004-06 study. Whereas the lake was clearly phosphorus-limited in 1991-92, in 2004-06 the lake may have been much closer to the boundary value of 7.2 that separates nitrogen from phosphorus limitation. However, due to changes in analytical reporting limits in the period between the two studies, the data are insufficiently certain to draw reliable conclusions with regard to limiting nutrients. For both studies, the trophic state of the lake was classified as oligotrophic (less productive) or mesotrophic (moderately productive), depending on the constituent used for classification. Internal circulation from wind-generated waves and changes in the lake's thermocline are important processes for distribution of water-quality constituents throughout Coeur d'Alene Lake. Surficial distribution of trace metals throughout most o

Correlation and zonation of miocene strata along the atlantic margin of North America using diatoms and silicoflagellates

USGS Publications Warehouse

Abbott, W.H.

1978-01-01

Six Atlantic Miocene siliceous microfossil zones are proposed based on onshore and offshore samples from the United States Atlantic Margin. Diatoms and silicoflagellates are used to establish the zones. These zones are from oldest to youngest: 1. Zone I Actinoptychus heliopelta Concurrent Range Zone - Early Miocene 2. Zone II Delphineis ovata Partial Range Zone - late Early to early Middle Miocene 3. Zone III Delphineis ovata/Delphineis penelliptica Concurrent Range Zone - early Middle Miocene 4. Zone IV Delphineis penelliptica Partial Range Zone - Middle Miocene 5. Zone V Delphineis penelliptica/Coscinodiscus plicatus Concurrent Range Zone - Middle Miocene 6. Zone VI Coscinodiscus plicatus Partial Range Zone - Middle Miocene. The six zones are easily traced along the Southern and Middle Atlantic Seaboard, but the older three are found for the most part between Cape Hatteras and New Jersey. There is some suggestion of sea-level change during Zone IV. Using rare planktonic diatoms that are index species from other regions and the zonal markers established in this study, correlation can be made with the Standard Foraminiferal Zones, the North Pacific Diatom Zones and with DSDP core 391A in the Blake-Bahama Basin. ?? 1978.

[Current approach to zoning atomic shipbuilding plants].

PubMed

Blekher, A Ia

2005-01-01

The paper discusses the currently introduced radiation-and-hygienic system for zoning atomic shipbuilding plants, in accordance with which three radiation-and-hygienic zones (a strict regime zone, a controlled approach zone, and a free regime zone) are established at the plant site and two zones (a sanitary-and-protective zone and a follow-up zone) are also established outside the plant site.

Incorporating Conservation Zone Effectiveness for Protecting Biodiversity in Marine Planning

PubMed Central

Makino, Azusa; Klein, Carissa J.; Beger, Maria; Jupiter, Stacy D.; Possingham, Hugh P.

2013-01-01

Establishing different types of conservation zones is becoming commonplace. However, spatial prioritization methods that can accommodate multiple zones are poorly understood in theory and application. It is typically assumed that management regulations across zones have differential levels of effectiveness (“zone effectiveness”) for biodiversity protection, but the influence of zone effectiveness on achieving conservation targets has not yet been explored. Here, we consider the zone effectiveness of three zones: permanent closure, partial protection, and open, for planning for the protection of five different marine habitats in the Vatu-i-Ra Seascape, Fiji. We explore the impact of differential zone effectiveness on the location and costs of conservation priorities. We assume that permanent closure zones are fully effective at protecting all habitats, open zones do not contribute towards the conservation targets and partial protection zones lie between these two extremes. We use four different estimates for zone effectiveness and three different estimates for zone cost of the partial protection zone. To enhance the practical utility of the approach, we also explore how much of each traditional fishing ground can remain open for fishing while still achieving conservation targets. Our results show that all of the high priority areas for permanent closure zones would not be a high priority when the zone effectiveness of the partial protection zone is equal to that of permanent closure zones. When differential zone effectiveness and costs are considered, the resulting marine protected area network consequently increases in size, with more area allocated to permanent closure zones to meet conservation targets. By distributing the loss of fishing opportunity equitably among local communities, we find that 84–88% of each traditional fishing ground can be left open while still meeting conservation targets. Finally, we summarize the steps for developing marine zoning that accounts for zone effectiveness. PMID:24223870

Ecological characteristics of core-use areas used by Bering-Chukchi-Beaufort (BCB) bowhead whales, 2006-2012

NASA Astrophysics Data System (ADS)

Citta, John J.; Quakenbush, Lori T.; Okkonen, Stephen R.; Druckenmiller, Matthew L.; Maslowski, Wieslaw; Clement-Kinney, Jaclyn; George, John C.; Brower, Harry; Small, Robert J.; Ashjian, Carin J.; Harwood, Lois A.; Heide-Jørgensen, Mads Peter

2015-08-01

The Bering-Chukchi-Beaufort (BCB) population of bowhead whales (Balaena mysticetus) ranges across the seasonally ice-covered waters of the Bering, Chukchi, and Beaufort seas. We used locations from 54 bowhead whales, obtained by satellite telemetry between 2006 and 2012, to define areas of concentrated use, termed "core-use areas". We identified six primary core-use areas and describe the timing of use and physical characteristics (oceanography, sea ice, and winds) associated with these areas. In spring, most whales migrated from wintering grounds in the Bering Sea to the Cape Bathurst polynya, Canada (Area 1), and spent the most time in the vicinity of the halocline at depths <75 m, which are within the euphotic zone, where calanoid copepods ascend following winter diapause. Peak use of the polynya occurred between 7 May and 5 July; whales generally left in July, when copepods are expected to descend to deeper depths. Between 12 July and 25 September, most tagged whales were located in shallow shelf waters adjacent to the Tuktoyaktuk Peninsula, Canada (Area 2), where wind-driven upwelling promotes the concentration of calanoid copepods. Between 22 August and 2 November, whales also congregated near Point Barrow, Alaska (Area 3), where east winds promote upwelling that moves zooplankton onto the Beaufort shelf, and subsequent relaxation of these winds promoted zooplankton aggregations. Between 27 October and 8 January, whales congregated along the northern shore of Chukotka, Russia (Area 4), where zooplankton likely concentrated along a coastal front between the southeastward-flowing Siberian Coastal Current and northward-flowing Bering Sea waters. The two remaining core-use areas occurred in the Bering Sea: Anadyr Strait (Area 5), where peak use occurred between 29 November and 20 April, and the Gulf of Anadyr (Area 6), where peak use occurred between 4 December and 1 April; both areas exhibited highly fractured sea ice. Whales near the Gulf of Anadyr spent almost half of their time at depths between 75 and 100 m, usually near the seafloor, where a subsurface front between cold Anadyr Water and warmer Bering Shelf Water presumably aggregates zooplankton. The amount of time whales spent near the seafloor in the Gulf of Anadyr, where copepods (in diapause) and, possibly, euphausiids are expected to aggregate provides strong evidence that bowhead whales are feeding in winter. The timing of bowhead spring migration corresponds with when zooplankton are expected to begin their spring ascent in April. The core-use areas we identified are also generally known from other studies to have high densities of whales and we are confident these areas represent the majority of important feeding areas during the study (2006-2012). Other feeding areas, that we did not detect, likely existed during the study and we expect core-use area boundaries to shift in response to changing hydrographic conditions.

Iron fertilisation of the ocean through major volcanic eruptions. A case study of the Kasatochi eruption 2008

NASA Astrophysics Data System (ADS)

Lindenthal, A.; Langmann, B.; Hort, M.; Hoshyaripour, G.; Paetsch, J.; Lorkowski, I.

2012-04-01

Until recently it was more or less common sense that once volcanic ash enters the ocean it simply deposits into the sediments without any further impact on ocean biochemistry. This view has been notably revised after the eruption of Kasatochi volcano in 2008. During the eruption significant amounts of ash were deposited into oceanic NE Pacific. The NE Pacific is known as a high-nutrient-low-chlorophyll (HNLC) region where algae growth is limited by the bio-available, i.e. soluble iron. These bio-available iron salts residing on the volcanic ash are most likely formed by gas-ash/aerosol interactions inside the volcanic plume. The physico-chemical mechanisms behind the processes contributing to bio-available iron production in volcanic plumes, however, are still poorly constrained. As the eruption occurred in early August, the atmospheric and oceanic conditions were favourable to generate a massive phytoplankton bloom as was observed by satellite instruments and in-situ measurements. Here we investigate this event with the marine biogeochemical model ECOHAM, which is a regional scale three-dimensional ocean biogeochemistry model, coupled to the hydrodynamic model HAMSON. It has been successfully applied mainly over the NW European continental shelf area where iron limitation does not play a role. For applications of this model to the eruption of Kasatochi volcano, an iron cycle model has been implemented, which considers the influence of iron addition to the euphotic zone on diatoms, flagellates, and carbon dioxide concentrations. This model-approach assumes that all dissolved iron in the first meters of seawater is bio-available for phytoplankton uptake. It describes the limitation of phytoplankton growth rates by iron in addition to the limitation by the macro-nutrients nitrogen, phosphate and silicate as well as by light. The surface ocean iron input associated with the eruption of Kasatochi volcano has been determined by an atmospheric-aerosol model to be on the order of 4.5-6x1011kg (ash volume of 0.23-0.3km3). This amount of volcanic ash is consistent with estimates from 1D eruption column models. ECOHAM model results show that volcanic ash can stimulate algae blooms in surface ocean waters in HNLC regions like the NE Pacific. Soluble iron released from volcanic ash acts as a key micro nutrient for phytoplankton growth, especially for diatoms. Model results have been verified with measurements of station Papa (50°N, 145°W). Here a deposition of bio-available iron of 968 micromol Fe/m2 into the surface ocean between Aug. 8-11 lead to an increase in the primary production of chlorophyll in the upper 10m of the ocean of 3.7mg Chl/m3. Following the ash deposition the CO2 partial pressure at station Papa dropped by about 40microatm, which compares well with the 50microatm drop observed in our model calculations.

Visible-infrared remote-sensing model and applications for ocean waters. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Lee, Zhongping

1994-01-01

Remote sensing has become important in the ocean sciences, especially for research involving large spatial scales. To estimate the in-water constituents through remote sensing, whether carried out by satellite or airplane, the signal emitted from beneath the sea surface, the so called water-leaving radiance (L(w)), is of prime importance. The magnitude of L(w) depends on two terms: one is the intensity of the solar input, and the other is the reflectance of the in-water constituents. The ratio of the water-leaving radiance to the downwelling irradiance (E(d)) above the sear surface (remote-sensing reflectance, R(sub rs)) is independent of the intensity of the irradiance input, and is largely a function of the optical properties of the in-water constituents. In this work, a model is developed to interpret r(sub rs) for ocean water in the visible-infrared range. In addition to terms for the radiance scattered from molecules and particles, the model includes terms that describe contributions from bottom reflectance, fluorescence of gelbstoff or colored dissolved organic matter (CDOM), and water Raman scattering. By using this model, the measured R(sub rs) of waters from the West Florida Shelf to the Mississippi River plume, which covered a (concentration of chlorophyll a) range of 0.07 - 50 mg/cu m, were well interpreted. The average percentage difference (a.p.d.) between the measured and modeled R(sub rs) is 3.4%, and, for the shallow waters, the model-required water depth is within 10% of the chart depth. Simple mathematical simulations for the phytoplankton pigment absorption coefficient (a(sub theta)) are suggested for using the R(sub rs) model. The inverse problem of R(sub rs), which is to analytically derive the in-water constituents from R(sub rs) data alone, can be solved using the a(sub theta) functions without prior knowledge of the in-water optical properties. More importantly, this method avoids problems associated with a need for knowledge of the shape and value of the chlorophyll-specific absorption coefficient. The simulation was tested for a wide range of water types, including waters from Monterey Bay, the West Florida Shelf, and the Mississippi River plume. Using the simulation, the R(sub rs)-derived in-water absorption coefficients were consistent with the values from in-water measurements (r(exp 2) greater than 0.94, slope approximately 1.0). In the remote-sensing applications, a new approach is suggested for the estimation of primary production based on remote sensing. Using this approach, the calculated primary production (PP) values based upon remotely sensed data were very close to the measured values for the euphotic zone (r(exp 2) = 0.95, slope 1.26, and 32% average difference), while traditional, pigment-based PP model provided values only one-third the size of the measured data. This indicates a potential to significantly improve the accuracy of the estimation of primary production based upon remote sensing.

Water quality of lakes and streams in Voyageurs National Park, northern Minnesota, 1977-84

USGS Publications Warehouse

Payne, G.A.

1991-01-01

Water-quality investigations in six interconnected lakes that comprise most of the surface area of Voyageurs National Park in northern Minnesota revealed substantial differences in water-quality. Three large lakes; Sand Point, Namakan, and Rainy, near the eastern and northern boundaries of the Park; are oligotrophic to mesotrophic, having low dissolved solids and alkalinity, and dimictic circulation. In contrast, Kabetogama Lake, Black Bay, and Sullivan Bay, near the western and southern boundaries of the Park, were eutrophic, having higher dissolved solids and alkalinity, and polymictic circulation. Chemical characteristics of the three lakes along the eastern and northern boundary were similar to those of the Namakan River--a major source of inflow that drains an extensive area of exposed bedrock and thin noncalcareous drift east of the Park. The lake and embayments along the western and southern boundary receive inflow from two streams that drain an area west and south of the Park that is overlain by calcareous drift. Samples from one of these streams contained dissolved-solids concentrations about five times, and total alkalinity concentrations about eight times concentrations measured in the Namakan River. The nutrient-enriched lakes and embayments had high algal productivity that produced blooms of blue-green algae in some years. Annual patterns in the levels of trophic-state indicators revealed that the shallow, polymictic lakes experienced seasonal increases in totalphosphorus concentrations in their euphotic zones that did not occur in the deeper, dimictic lakes; this indicates a link between the frequent recirculation of these lakes and internal cycling of phosphorus. Secchi-disk transparency was limited by organic color in Sand Point, Namakan, and Rainy Lakes, and resuspended bottom material reduced transparency in Black Bay. Waters in the large lakes and embayments met nearly all U.S. Environmental Protection Agency criteria for protection of freshwater aquatic life, recreation, and drinking water. Some sites exceeded criteria because of oil and grease, phenols, sulfide, and ammonia. Reconnaissance sampling of 19 small lakes in remote areas of the Park indicated that most of them are sharply stratified and had very low dissolved solids and alkalinity concentrations (4.0-29 milligrams per liter total alkalinity). Thirteen of the lakes could be classified as moderately sensitive to acid precipitation, and two could be classified extremely sensitive. About half of the interior lakes had low nutrient concentrations (10-30 micrograms per liter total phosphorus) and low algal productivity (0.1- 2.0 micrograms per liter chlorophyll a). Five of the lakes had a marked reduction in trophic state from spring to summer. The Namakan River is the largest source of inflow to the Park and was found to have better quality than its receiving waters based on dissolved solids and nutrient concentrations, algal productivity, and transparency. The Ash River was found to deliver water that generally was poorer in quality than its receiving waters.

Numerical modeling of benthic processes in the deep Arabian Sea

NASA Astrophysics Data System (ADS)

Luff, Roger; Wallmann, Klaus; Grandel, Sibylle; Schlüter, Michael

Aerobic and anaerobic degradation of particulate organic carbon (POC) and carbonate equilibria in deep-sea surface sediments were studied at five stations located in the western (WAST), northern (NAST), eastern (EAST), central (CAST), and southern (SAST) Arabian Sea. In situ oxygen fluxes, porewater profiles of dissolved oxygen, nitrate, and Mn, pH profiles and solid-phase profiles of particulate organic carbon, Mn, and Fe were measured at each station. An early diagenesis model was applied to simulate the degradation and dissolution processes and to determine the benthic fluxes of POC, oxygen, nitrate, phosphate, CO 2, HCO 3-, and CO 32-. The benthic data sets were evaluated to constrain the POC input and the kinetics of organic matter degradation used in the model. The modeling showed that the POC rain rate to the seafloor is high at the western and northern stations, and decreases towards the southeast. At stations located in the vicinity of continental margins (WAST, NAST, EAST), 5-7% of the primary production sinks to the deep-sea floor. This unusually high POC rain is either caused by dust particles that accelerate and amplify the particle export from the euphotic zone or by rapid lateral transport processes. At the more remote stations (CAST, SAST) that receive lower dust inputs, the rain efficiency decreases to 1-4%. In the model, organic matter was separated into three fractions (3-G-model) that differ considerably in reactivity. At stations WAST, NAST, EAST, and CAST the bulk of organic matter is composed of extremely labile organic matter with a first order degradation constant ( k) of 15-30 yr -1. The moderately labile fraction with a kinetic constant of 0.2-0.6 yr -1 dominates the POC input at the oligotrophic station in the southern Arabian Sea (SAST). The third fraction that has a very low reactivity ( k=2-5×10 -4 yr -1) is only a minor component of the POC rain at all investigated stations. More than 95% of the organic matter is consumed in aerobic degradation processes. Denitrification and metal oxide reduction only contribute 1-2% to the total POC degradation. At the western station (WAST) a non-negligible portion (2%) of organic matter is consumed via sulfate reduction. The modeling demonstrates that carbonate dissolution is a major process in the deep Arabian Sea; 52-83% of the carbonate rain to the seafloor is dissolved within the surface sediments. In the western Arabian Sea, the monsoon systems produce a strong seasonality in the primary production. Non-steady-state modeling indicates that the benthic oxygen, nutrient, and inorganic carbon fluxes closely follow the seasonal dynamics in primary and export production. This very close benthic-pelagic coupling is established by the extremely labile organic matter fraction that dominates the POC rain to the seafloor. The metabolically released CO 2 induces a seasonal change in carbonate dissolution and carbonate alkalinity fluxes.

33 CFR 165.169 - Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 33 Navigation and Navigable Waters 2 2014-07-01 2014-07-01 false Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone. 165.169 Section 165.169 Navigation and... Areas First Coast Guard District § 165.169 Safety and Security Zones: New York Marine Inspection Zone...

33 CFR 165.169 - Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 33 Navigation and Navigable Waters 2 2011-07-01 2011-07-01 false Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone. 165.169 Section 165.169 Navigation and... Areas First Coast Guard District § 165.169 Safety and Security Zones: New York Marine Inspection Zone...

33 CFR 165.169 - Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone. 165.169 Section 165.169 Navigation and... Areas First Coast Guard District § 165.169 Safety and Security Zones: New York Marine Inspection Zone...

33 CFR 165.169 - Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 33 Navigation and Navigable Waters 2 2012-07-01 2012-07-01 false Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone. 165.169 Section 165.169 Navigation and... Areas First Coast Guard District § 165.169 Safety and Security Zones: New York Marine Inspection Zone...

33 CFR 165.169 - Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 33 Navigation and Navigable Waters 2 2013-07-01 2013-07-01 false Safety and Security Zones: New York Marine Inspection Zone and Captain of the Port Zone. 165.169 Section 165.169 Navigation and... Areas First Coast Guard District § 165.169 Safety and Security Zones: New York Marine Inspection Zone...

Medial meniscus anatomy-from basic science to treatment.

PubMed

Śmigielski, Robert; Becker, Roland; Zdanowicz, Urszula; Ciszek, Bogdan

2015-01-01

This paper focuses on the anatomical attachment of the medial meniscus. Detailed anatomical dissections have been performed and illustrated. Five zones can be distinguished in regard to the meniscus attachments anatomy: zone 1 (of the anterior root), zone 2 (anteromedial zone), zone 3 (the medial zone), zone 4 (the posterior zone) and the zone 5 (of the posterior root). The understanding of the meniscal anatomy is especially crucial for meniscus repair but also for correct fixation of the anterior and posterior horn of the medial meniscus.

33 CFR 3.05-35 - Sector Long Island Sound Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2010 CFR

2010-07-01

... Inspection Zone and Captain of the Port Zone. 3.05-35 Section 3.05-35 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES First Coast Guard District § 3.05-35 Sector Long Island Sound Marine Inspection Zone and Captain of the Port Zone. Sector Long Island Sound's office is located in New...

33 CFR 3.05-35 - Sector Long Island Sound Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Inspection Zone and Captain of the Port Zone. 3.05-35 Section 3.05-35 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES First Coast Guard District § 3.05-35 Sector Long Island Sound Marine Inspection Zone and Captain of the Port Zone. Sector Long Island Sound's office is located in New...

33 CFR 3.55-15 - Sector San Diego Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2011 CFR

2011-07-01

... Inspection Zone and Captain of the Port Zone. 3.55-15 Section 3.55-15 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES Eleventh Coast Guard District § 3.55-15 Sector San Diego Marine Inspection Zone and Captain of the Port Zone. Sector San Diego's office is located in San Diego, CA. The...

33 CFR 3.25-20 - Sector North Carolina Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Inspection Zone and Captain of the Port Zone. 3.25-20 Section 3.25-20 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES Fifth Coast Guard District § 3.25-20 Sector North Carolina Marine Inspection Zone and Captain of the Port Zone. Sector North Carolina's office is located in Wilmington, NC...

33 CFR 3.05-35 - Sector Long Island Sound Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Inspection Zone and Captain of the Port Zone. 3.05-35 Section 3.05-35 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES First Coast Guard District § 3.05-35 Sector Long Island Sound Marine Inspection Zone and Captain of the Port Zone. Sector Long Island Sound's office is located in New...

33 CFR 3.55-15 - Sector San Diego Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2010 CFR

2010-07-01

... Inspection Zone and Captain of the Port Zone. 3.55-15 Section 3.55-15 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES Eleventh Coast Guard District § 3.55-15 Sector San Diego Marine Inspection Zone and Captain of the Port Zone. Sector San Diego's office is located in San Diego, CA. The...

33 CFR 3.35-15 - Sector Charleston Marine Inspection Zone and Captain of the Port Zone; Marine Safety Unit Savannah.

Code of Federal Regulations, 2011 CFR

2011-07-01

... Inspection Zone and Captain of the Port Zone; Marine Safety Unit Savannah. 3.35-15 Section 3.35-15 Navigation..., SECTORS, MARINE INSPECTION ZONES, AND CAPTAIN OF THE PORT ZONES Seventh Coast Guard District § 3.35-15 Sector Charleston Marine Inspection Zone and Captain of the Port Zone; Marine Safety Unit Savannah...

33 CFR 3.05-20 - Sector Southeastern New England Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Marine Inspection Zone and Captain of the Port Zone. 3.05-20 Section 3.05-20 Navigation and Navigable... INSPECTION ZONES, AND CAPTAIN OF THE PORT ZONES First Coast Guard District § 3.05-20 Sector Southeastern New England Marine Inspection Zone and Captain of the Port Zone. Sector Southeastern New England's office is...

33 CFR 3.65-15 - Sector Columbia River Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Inspection Zone and Captain of the Port Zone. 3.65-15 Section 3.65-15 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES Thirteenth Coast Guard District § 3.65-15 Sector Columbia River Marine Inspection Zone and Captain of the Port Zone. Sector Columbia River's office is located in Astoria...

33 CFR 3.55-10 - Sector Los Angeles-Long Beach Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2010 CFR

2010-07-01

... Marine Inspection Zone and Captain of the Port Zone. 3.55-10 Section 3.55-10 Navigation and Navigable... INSPECTION ZONES, AND CAPTAIN OF THE PORT ZONES Eleventh Coast Guard District § 3.55-10 Sector Los Angeles-Long Beach Marine Inspection Zone and Captain of the Port Zone. Sector Los Angeles-Long Beach's (LA-LB...

33 CFR 3.05-35 - Sector Long Island Sound Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Inspection Zone and Captain of the Port Zone. 3.05-35 Section 3.05-35 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES First Coast Guard District § 3.05-35 Sector Long Island Sound Marine Inspection Zone and Captain of the Port Zone. Sector Long Island Sound's office is located in New...

33 CFR 3.55-15 - Sector San Diego Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Inspection Zone and Captain of the Port Zone. 3.55-15 Section 3.55-15 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES Eleventh Coast Guard District § 3.55-15 Sector San Diego Marine Inspection Zone and Captain of the Port Zone. Sector San Diego's office is located in San Diego, CA. The...

33 CFR 3.05-20 - Sector Southeastern New England Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Marine Inspection Zone and Captain of the Port Zone. 3.05-20 Section 3.05-20 Navigation and Navigable... INSPECTION ZONES, AND CAPTAIN OF THE PORT ZONES First Coast Guard District § 3.05-20 Sector Southeastern New England Marine Inspection Zone and Captain of the Port Zone. Sector Southeastern New England's office is...

33 CFR 3.55-15 - Sector San Diego Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Inspection Zone and Captain of the Port Zone. 3.55-15 Section 3.55-15 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES Eleventh Coast Guard District § 3.55-15 Sector San Diego Marine Inspection Zone and Captain of the Port Zone. Sector San Diego's office is located in San Diego, CA. The...

33 CFR 3.25-20 - Sector North Carolina Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Inspection Zone and Captain of the Port Zone. 3.25-20 Section 3.25-20 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES Fifth Coast Guard District § 3.25-20 Sector North Carolina Marine Inspection Zone and Captain of the Port Zone. Sector North Carolina's office is located in Wilmington, NC...

33 CFR 3.25-20 - Sector North Carolina Marine Inspection Zone and Captain of the Port Zone.

Code of Federal Regulations, 2011 CFR

2011-07-01

... Inspection Zone and Captain of the Port Zone. 3.25-20 Section 3.25-20 Navigation and Navigable Waters COAST... ZONES, AND CAPTAIN OF THE PORT ZONES Fifth Coast Guard District § 3.25-20 Sector North Carolina Marine Inspection Zone and Captain of the Port Zone. Sector North Carolina's office is located in Wilmington, NC...