Distribution of biogenic silica and quartz in recent deep-sea sediments

NASA Astrophysics Data System (ADS)

Leinen, Margaret; Cwienk, Douglas; Heath, G. Ross; Biscaye, Pierre E.; Kolla, V.; Thiede, Jørn; Dauphin, J. Paul

1986-03-01

All available quartz and biogenic silica concentrations from deep-sea surface sediments were intercalibrated, plotted, and contoured on a calcium-carbonate-free basis. The maps show highest concentrations of biogenic silica (opal) along the west African coast, along equatorial divergences in all oceans, and at the Polar Front in the southern Indian Ocean. These are all areas where upwelling is strong and there is high biological productivity. Quartz in pelagic sediments deposited far from land is generally eolian in origin. Its distribution reflects dominant wind systems in the Pacific, but in much of the Atlantic and Indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes.

Spatial variability of surface-sediment porewater pH and related water-column characteristics in deep waters of the northern South China Sea

NASA Astrophysics Data System (ADS)

Shao, Changgao; Sui, Yi; Tang, Danling; Legendre, Louis

2016-12-01

This study analyzes the pH of surface-sediment porewater (i.e. 2-3 cm below the water-sediment interface), and concentrations of CaCO3 and organic carbon (OC) in 1192 sediment cores from the northern South China Sea, in water depths ranging from 137 to 3702 m. This is the first study in the literature to analyze the large-scale spatial variability of deep-water surface-sediment pH over a large ocean basin. The data showed strong spatial variations in pH. The lowest pH values (<7.3) were observed south of Hainan Island, an area that is affected by summer upwelling and freshwater runoff from the Pearl and Red Rivers. Moderately low pH values (generally 7.3-7.5) occurred in two other areas: a submarine canyon, where sediments originated partly from the Pearl River and correspond to a paleo-delta front during the last glacial period; and southwest of Taiwan Island, where waters are affected by the northern branch of the Kuroshio intrusion current (KIC) and runoff from Taiwan rivers. The surface sediments with the highest pH (⩾7.5, and up to 8.3) were located in a fourth area, which corresponded to the western branch of the KIC where sediments have been intensively eroded by bottom currents. The pH of surface-sediment porewater was significantly linearly related to water depth, bottom-water temperature, and CaCO3 concentration (p < 0.05 for the whole sampling area). This study shows that the pH of surface-sediment porewater can be sensitive to characteristics of the overlying water column, and suggests that it will respond to global warming as changes in surface-ocean temperature and pH progressively reach deeper waters.

Constraints on the sources of branched GDGTs in open ocean sediments: dust transport or in situ production?

NASA Astrophysics Data System (ADS)

Weijers, J.; Schefuss, E.; Kim, J.; Sinninghe Damsté, J. S.; Schouten, S.

2012-12-01

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids synthesized by soil bacteria that, upon soil erosion, are transported by rivers to the ocean where they accumulate in the near shore sedimentary archive. The degrees of cyclisation (CBT) and methylation (MBT) of these compounds have been shown to relate to soil pH and annual mean air temperature [1]. Therefore, brGDGTs in near shore sedimentary archives can be used to estimate past continental air temperatures and enable a direct comparison of these to marine sea surface temperature estimates obtained from the same samples. In addition, brGDGT abundance relative to crenarchaeol, an isoprenoid GDGT synthesized by marine pelagic Thaumarchaeota, quantified in the branched vs. isoprenoid tetraether (BIT) index, is an indicator of the relative input of soil organic matter in near shore sediments [2]. High BIT values near river outflows testify of relative strong soil organic matter input and generally the BIT index will decrease off shore to values near 0, the marine end-member value. Even in remote open ocean sediments, however, the BIT index will rarely reach 0 as small amounts of brGDGTs are often present. The occurrence of these brGDGTs in open marine settings might be a result of i) dust input, ii) sediment dispersion from near coastal areas, or iii) in situ production in marine sediments. In order to constrain the origin of branched GDGTs in open marine sediments we analyzed i) atmospheric dust samples taken along an equatorial African coastal transect, ii) marine surface waters near and away of the Congo river outflow, iii) a series of surface sediments at and around the Congo deep sea fan, and iv) a series of open marine surface sediments from different oceans with BIT values < 0.08. Our results show that brGDGTs are present, though in relative low amounts, in dust. Their distribution resembles that of soil input as also found in the Congo deep sea fan, with MBT and CBT values that could be representative of tropical African soils. Strikingly, BIT indices are much lower than expected for soils (0.15-0.42), likely as a result of sea spray on the dust filters. Open ocean sediments, on the contrary, are typically characterized by relative high amounts of cyclopentane containing brGDGTs resulting in low CBT values ranging from -0.4 - 0.8. These values are similarly low as reported earlier in marine sediments near Svalbard [3] and in the East China Sea [4], for which in situ production was invoked. Thus, brGDGT transport by dust does seem possible, though quantities are low. Since open ocean brGDGT distributions are markedly different from those in soils and dust, the latter is most likely not a significant source. Our results indicate that production of brGDGTs in ocean sediments, though in relative low amounts, is much more widespread than previously thought. This emphasizes that the MBT-CBT proxy for continental air temperature should only be used at locations where soil organic matter input is significant as evidenced by high BIT indices. References: [1] Weijers J.W.H. et al. (2007) Geochmim. Cosmochim. Acta 71, 703-713. [2] Hopmans E.C. et al. (2004) Earth Planet. Sci. Lett. 224, 107-116. [3] Peterse F. et al. (2009) Org. Geochem. 40, 692-699. [4] Zhu C. Et al. (2011) Org. Geochem. 42, 376-386.

Distribution of benthic foraminifers (>125 um) in the surface sediments of the Arctic Ocean

USGS Publications Warehouse

Osterman, Lisa E.; Poore, Richard Z.; Foley, Kevin M.

1999-01-01

Census data on benthic foraminifers (>125 ?m) in surface sediment samples from 49 box cores are used to define four depth-controlled biofacies, which will aid in the paleoceanographic reconstruction of the Arctic Ocean. The shelf biofacies contains a mix of shallow-water calcareous and agglutinated species from the continental shelves of the Beaufort and Chukchi Seas and reflects the variable sedimentologic and oceanic conditions of the Arctic shelves. The intermediate-depth calcareous biofacies, found between 500 and 1,100 meters water depth (mwd), contains abundant Cassidulina teretis , presumably indicating the influence of Atlantic-derived water at this depth. In water depths between 1,100 and 3,500 m, a deepwater calcareous biofacies contains abundant Oridorsalis umbonatus . Below 3,500 mwd, the deepwater mixed calcareous/agglutinated biofacies of the Canada, Makarov, and Eurasian Basins reflects a combination of low productivity, dissolution, and sediment transport. Two other benthic foraminiferal species show specific environmental preferences. Fontbotia wuellerstorfi has a depth distribution between 900 and 3,500 mwd, but maximum abundance occurs in the region of the Mendeleyev Ridge. The elevated abundance of F. wuellerstorfi may be related to increased food supply carried by a branch of Atlantic water that crosses the Lomonosov Ridge near the Russian Continental Shelf. Triloculina frigida is recognized to be a species preferring lower slope sediments commonly disturbed by turbidites and bottom currents. INTRODUCTION At present, our understanding of the Arctic Ocean lags behind our understanding of other oceans, and fundamental questions still exist about its role in and response to global climate change. The Arctic Ocean is particularly sensitive to climatic fluctuations because small changes in the amounts of sea-ice cover can alter global albedo and thermohaline circulation (Aagaard and Carmack, 1994). Numerous questions still exist regarding the nature and timing of paleoclimatic events in the Arctic Ocean. In order to attempt to answer some of these questions, baseline studies are imperative. This report discusses the distribution of benthic foraminifers in surface sediment samples from 49 box cores (figs. 1 and 2, table 1) collected by the U.S. Geological Survey (USGS) with the assistance of the U.S. Coast Guard (USCG). A modern data set of benthic foraminiferal distribution is necessary for interpreting the paleoclimatic and oceanographic history of the Arctic Ocean.

Investigation of hurricane Ivan using the coupled ocean-atmosphere-wave-sediment transport (COAWST) model

USGS Publications Warehouse

Zambon, Joseph B.; He, Ruoying; Warner, John C.

2014-01-01

The coupled ocean–atmosphere–wave–sediment transport (COAWST) model is used to hindcast Hurricane Ivan (2004), an extremely intense tropical cyclone (TC) translating through the Gulf of Mexico. Sensitivity experiments with increasing complexity in ocean–atmosphere–wave coupled exchange processes are performed to assess the impacts of coupling on the predictions of the atmosphere, ocean, and wave environments during the occurrence of a TC. Modest improvement in track but significant improvement in intensity are found when using the fully atmosphere–ocean-wave coupled configuration versus uncoupled (e.g., standalone atmosphere, ocean, or wave) model simulations. Surface wave fields generated in the fully coupled configuration also demonstrates good agreement with in situ buoy measurements. Coupled and uncoupled model-simulated sea surface temperature (SST) fields are compared with both in situ and remote observations. Detailed heat budget analysis reveals that the mixed layer temperature cooling in the deep ocean (on the shelf) is caused primarily by advection (equally by advection and diffusion).

Hydrocarbon gas in sediment of the Southern Pacific Ocean

USGS Publications Warehouse

Kvenvolden, K.A.

1988-01-01

Methane, ethane, ethene, propane, and propene are common hydrocarbon gases in near-surface sediment from offshore areas in the southern Pacific Ocean near Papua New Guinea, the Solomon Islands, Vanuatu, Tonga, New Zealand, and Antarctica. Sea floor sites for sampling of sediment were selected on the basis of anomalies in marine seismic records, and the samples were intentionally biased toward finding possible thermogenic hydrocarbon gases. In none of the areas, however, were thermogenic hydrocarbons clearly identified. The hydrocarbon gases that were found appear to be mainly the products of in situ microbial processes. ?? 1988 Springer-Verlag New York Inc.

Meltwater input to the southern ocean during the last glacial maximum

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

Shemesh, A.; Burckle, L.H.; Hays, J.D.

1994-12-02

Three records of oxygen isotopes in biogenic silica from deep-sea sediment cores from the Atlantic and Indian sectors of the Southern Ocean reveal the presence of isotopically depleted diatomaceous opal in sediment from the last glacial maximum. This depletion is attributed to the presence of lids of meltwater that mixed with surface water along certain trajectories in the Southern Ocean. An increase in the drainage from Antarctica or extensive northward transport of icebergs are among the main mechanisms that could have produced the increase in meltwater input to the glacial Southern Ocean. Similar isotopic trends were observed in older climaticmore » cycles at the same cores.« less

Microplastics in the Antarctic marine system: An emerging area of research.

PubMed

Waller, Catherine L; Griffiths, Huw J; Waluda, Claire M; Thorpe, Sally E; Loaiza, Iván; Moreno, Bernabé; Pacherres, Cesar O; Hughes, Kevin A

2017-11-15

It was thought that the Southern Ocean was relatively free of microplastic contamination; however, recent studies and citizen science projects in the Southern Ocean have reported microplastics in deep-sea sediments and surface waters. Here we reviewed available information on microplastics (including macroplastics as a source of microplastics) in the Southern Ocean. We estimated primary microplastic concentrations from personal care products and laundry, and identified potential sources and routes of transmission into the region. Estimates showed the levels of microplastic pollution released into the region from ships and scientific research stations were likely to be negligible at the scale of the Southern Ocean, but may be significant on a local scale. This was demonstrated by the detection of the first microplastics in shallow benthic sediments close to a number of research stations on King George Island. Furthermore, our predictions of primary microplastic concentrations from local sources were five orders of magnitude lower than levels reported in published sampling surveys (assuming an even dispersal at the ocean surface). Sea surface transfer from lower latitudes may contribute, at an as yet unknown level, to Southern Ocean plastic concentrations. Acknowledging the lack of data describing microplastic origins, concentrations, distribution and impacts in the Southern Ocean, we highlight the urgent need for research, and call for routine, standardised monitoring in the Antarctic marine system. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Cadmium and zinc isotopes of organic-rich marine sediments during Oceanic Anoxic Event 2

NASA Astrophysics Data System (ADS)

Sweere, T.; Dickson, A. J.; Jenkyns, H. C.; Porcelli, D.; Henderson, G. M.; van den Boorn, S.

2017-12-01

Mesozoic Oceanic Anoxic Events (OAEs) are characterized by widespread deposition of organic-rich sediments and the spread of low-oxygen marine environments. To drive and sustain unusually efficient carbon-burial during these events requires high export productivity rates, which has to be supported by an abundance of nutrients in the surface ocean. The presence of redox-sensitive bio-essential micronutrients may be particularly important, and potentially bio-limiting, during such events as they may be drawn down into sediment under low-oxygen conditions. Cadmium and zinc isotopes have potential as tracers for past (micro)nutrient dynamics considering their nutrient-like distribution in the modern ocean and isotope fractionation with uptake by primary producers. The modern deep ocean is generally well mixed for Cd and Zn while short-term cycling of these elements in the surface ocean imposes regional variation. Additional regional variation may be caused by sulfide formation and associated isotope fractionation in euxinic environments. The impact of such regional environmental conditions on the Cd- and Zn-isotope composition of the sediment therefore needs to be addressed in order to explore the use of these elements as a proxy for past nutrient conditions. Here we present an extensive dataset of cadmium- and zinc-isotope compositions of organic-rich marine sediments from different basins deposited during OAE 2 (Late Cretaceous). This comparison highlights regional differences in Cd- and Zn-isotope compositions. However, despite regional environmental controls, a correlation between δ114Cd and δ66Zn across the different sites is observed, which implies a largely similar control on the two isotope systems. When regional environmental controls are accounted for, the data may provide insight in the δ66Zn and δ114Cd evolution of global seawater during OAE 2 as well as information on the global cycling of redox-sensitive micronutrients during the event

Sediments in Arctic sea ice: Implications for entrainment, transport and release

USGS Publications Warehouse

Nurnberg, D.; Wollenburg, I.; Dethleff, D.; Eicken, H.; Kassens, H.; Letzig, T.; Reimnitz, E.; Thiede, Jorn

1994-01-01

Despite the Arctic sea ice cover's recognized sensitivity to environmental change, the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood. Sea ice sediment inclusions were studied in the central Arctic Ocean during the Arctic 91 expedition and in the Laptev Sea (East Siberian Arctic Region Expedition 1992). Results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central Arctic Ocean. This study documents the regional distribution and composition of particle-laden ice, investigates and evaluates processes by which sediment is incorporated into the ice cover, and identifies transport paths and probable depositional centers for the released sediment. In April 1992, sea ice in the Laptev Sea was relatively clean. The sediment occasionally observed was distributed diffusely over the entire ice column, forming turbid ice. Observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment. In the central Arctic Ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes. The surface sediment accumulation in central Arctic multi-year sea ice exceeds by far the amounts observed in first-year ice from the Laptev Sea in April 1992. Sea ice sediments are generally fine grained, although coarse sediments and stones up to 5 cm in diameter are observed. Component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles. The biogenous components, namely shells of pelecypods and benthic foraminiferal tests, point to a shallow, benthic, marine source area. Apparently, sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing. Clay mineralogy of ice-rafted sediments provides information on potential source areas. A smectite maximum in sea ice sediment samples repeatedly occurred between 81??N and 83??N along the Arctic 91 transect, indicating a rather stable and narrow smectite rich ice drift stream of the Transpolar Drift. The smectite concentrations are comparable to those found in both Laptev Sea shelf sediments and anchor ice sediments, pointing to this sea as a potential source area for sea ice sediments. In the central Arctic Ocean sea ice clay mineralogy is significantly different from deep-sea clay mineral distribution patterns. The contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms. ?? 1994.

Why Do Organisms in the Atlantic Ocean Produce So Much CaCO3?

NASA Astrophysics Data System (ADS)

Toggweiler, J. R.

2010-12-01

Sediments in the Atlantic are richer in CaCO3 than sediments in the other oceans. Sediment trap observations show that sinking particles in the Atlantic also tend to have more CaCO3 in relation to organic carbon than sinking particles elsewhere. The reason for the extra production of CaCO3 has never been very clear. The Atlantic is unusual because it receives much more than its share of the global input of river water. River water adds alkalinity to the surface ocean while the production of CaCO3 takes it away. In this presentation a new tracer, called Alk*, is derived from the surface alkalinity distribution to highlight the impact of river inputs and the production of CaCO3. If the production of CaCO3 were evenly distributed across the ocean one would expect the Atlantic to have a higher level of Alk* becaused of its river inputs. We find instead that Alk* is lower in the middle of the Atlantic than almost any place else. This, of course, is consistent with the fact that organisms in the Atlantic produce a lot of CaCO3. Comparison with other areas with especially low values of Alk* (Red Sea and northern Arabian Sea) shows that the production of CaCO3 is highly correlated across the ocean with the surface salinity. Hence, we argue that organisms in the Atlantic produce a lot of CaCO3 simply because the Atlantic is so salty. Salty waters, by definition, have more CO3= ions, which increase the supersaturation with respect to calcite and aragonite. This finding, while extremely simple, has major implifications for the impact of ocean acidification on calcifying organisms.

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.

A palaeotemperature curve for the Precambrian oceans based on silicon isotopes in cherts.

PubMed

Robert, François; Chaussidon, Marc

2006-10-26

The terrestrial sediment record indicates that the Earth's climate varied drastically in the Precambrian era (before 550 million years ago), ranging from surface temperatures similar to or higher than today's to global glaciation events. The most continuous record of sea surface temperatures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments), but the long-term cooling of the oceans inferred from those data has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments. Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence, a model of the silicon cycle in the Precambrian era shows that the observed silicon isotope variations imply seawater temperature changes from about 70 degrees C 3,500 million years ago to about 20 degrees C 800 million years ago.

Marine ferromanganese encrustations: Archives of changing oceans

USGS Publications Warehouse

Koschinsky, Andrea; Hein, James

2017-01-01

Marine iron–manganese oxide coatings occur in many shallow and deep-water areas of the global ocean and can form in three ways: 1) Fe–Mn crusts can precipitate from seawater onto rocks on seamounts; 2) Fe–Mn nodules can form on the sediment surface around a nucleus by diagenetic processes in sediment pore water; 3) encrustations can precipitate from hydrothermal fluids. These oxide coatings have been growing for thousands to tens of millions of years. They represent a vast archive of how oceans have changed, including variations of climate, ocean currents, geological activity, erosion processes on land, and even anthropogenic impact. A growing toolbox of age-dating methods and element and isotopic signatures are being used to exploit these archives.

Continental sedimentary processes decouple Nd and Hf isotopes

NASA Astrophysics Data System (ADS)

Garçon, Marion; Chauvel, Catherine; France-Lanord, Christian; Huyghe, Pascale; Lavé, Jérôme

2013-11-01

The neodymium and hafnium isotopic compositions of most crustal and mantle rocks correlate to form the "Terrestrial Array". However, it is now well established that whereas coarse detrital sediments follow this trend, fine-grained oceanic sediments have high Hf ratios relative to their Nd isotopic ratios. It remains uncertain whether this "decoupling" of the two isotopic systems only occurs in the oceanic environment or if it is induced by sedimentary processes in continental settings. In this study, the hafnium and neodymium isotopic compositions of sediments in large rivers is expressly used to constrain the behavior of the two isotopic systems during erosion and sediment transport from continent to ocean. We report major and trace element concentrations together with Nd and Hf isotopic compositions of bedloads, suspended loads and river banks from the Ganges River and its tributaries draining the Himalayan Range i.e. the Karnali, the Narayani, the Kosi and the Marsyandi Rivers. The sample set includes sediments sampled within the Himalayan Range in Nepal, at the Himalayan mountain front, and also downstream on the floodplain and at the outflow of the Ganges in Bangladesh. Results show that hydrodynamic sorting of minerals explains the entire Hf isotopic range, i.e. more than 10 εHf units, observed in the river sediments but does not affect the Nd isotopic composition. Bedloads and bank sediments have systematically lower εHf values than suspended loads sampled at the same location. Coarse-grained sediments lie below or on the Terrestrial Array in an εHf vs. εNd diagram. In contrast, fine-grained sediments, including most of the suspended loads, deviate from the Terrestrial Array toward higher εHf relative to their εNd, as is the case for oceanic terrigenous clays. The observed Nd-Hf decoupling is explained by mineralogical sorting processes that enrich bottom sediments in coarse and dense minerals, including unradiogenic zircons, while surface sediments are enriched in fine material with radiogenic Hf signatures. The data also show that Nd-Hf isotopic decoupling increases with sediment transport in the floodplain to reach its maximum at the river mouth. This implies that the Nd-Hf isotopic decoupling observed in worldwide oceanic clays and river sediments is likely to have the same origin. Finally, we estimated the Nd-Hf isotopic composition of the present-day mantle if oceanic sediments had never been subducted and conclude that the addition of oceanic sediments with their anomalous Nd-Hf isotopic compositions has slowly shifted the composition of the Earth's mantle towards more radiogenic Hf values through time.

Recent sediment dynamics in hadal trenches: Evidence for the influence of higher-frequency (tidal, near-inertial) fluid dynamics

NASA Astrophysics Data System (ADS)

Turnewitsch, Robert; Falahat, Saeed; Stehlikova, Jirina; Oguri, Kazumasa; Glud, Ronnie N.; Middelboe, Mathias; Kitazato, Hiroshi; Wenzhöfer, Frank; Ando, Kojiro; Fujio, Shinzou; Yanagimoto, Daigo

2014-08-01

In addition to high hydrostatic pressure, scarcity of food is viewed as a factor that limits the abundance and activity of heterotrophic organisms at great ocean depths, including hadal trenches. Supply of nutritious food largely relies on the flux of organic-rich particulate matter from the surface ocean. It has been speculated that the shape of hadal trenches helps to ‘funnel' particulate matter into the deeper parts of the trench, leading to sediment ‘focussing' and improved benthic food supply. Here we investigate for five Northwest Pacific trenches the efficiency of sediment focussing by evaluating ratios of measured (sediment-derived) and expected (water-column-derived) sedimentary inventories of the naturally occurring and radioactive particulate-matter tracer 210Pbxs. The sites comprise a broad range of surface-ocean productivity and physical-oceanographic regimes. Across the five trench-axis settings the inventory ratio varies between 0.5 and 4.1, with four trench-axis settings having ratios>1 (sediment focussing) and one trench-axis setting a ratio<1 (sediment winnowing). Although the fluid- and sediment-dynamical forcing behind sediment focussing remains unclear, this study finds evidence for another mechanism that is superimposed on, and counteracts, the focussing mechanism. This superimposed mechanism is related to higher-frequency (tidal, near-inertial) fluid dynamics. In particular, there is evidence for a strong and negative relation between the intensity of propagating internal tides and the extent of sediment focussing in the trench-axis. The relation can be approximated by a power function and the most intense drop in sediment focussing already occurs at moderate internal-tide intensities. This suggests that propagating internal tides may have a subtle but significant influence on particulate-matter dynamics and food supply in hadal trenches in particular, but possibly also in the deep seas in general. A mechanism for the influence of internal tides on sediment dynamics is proposed.

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.

Evidence of strong ocean heating during glacial periods

NASA Astrophysics Data System (ADS)

Zimov, S. A.; Zimov, N.

2013-12-01

Numerous hypotheses have addressed glacial-interglacial climatic dynamics, but none of them explain the sharp 25C temperature increase in Greenland in the last deglaciation (Cuffey et al. 1995; Dahl-Jensen et al. 1998). These robust data were obtained through analyzing the temperature profile in the Greenland ice sheet where cold from the last glaciation is preserved in the depth of the glacial sheet. We suggest that during glaciations the ocean accumulated energy: interior ocean water heated up to ~20-30C and during deglaciation this energy is released. In the analogy with reconstructing the ice sheet temperature profiles, the most reliable proof of ocean interior warming during the last glaciation is the heat flux profiles in the bottom sediments. In the final reports based on temperature measurements conducted during the DSDP (Deep Sea Drilling Project) it is stated that heat flux in the bottom sediments doesn't vary with depth and consequently there were no substantial temperature changes in the ocean interior during the last glacial cycle, and heat flux on the surface of the ocean bottom is the geothermal heat flux (Erickson et al., 1975, Hyndman et al., 1987). However, we have critically investigated data in all initial reports of all deep sea drilling projects and have noticed that all temperature data show that heat flow decreases strongly with depth (a minimum of 40 mW/m2), i.e. most of the heat flux detected on the surface of the ocean floor is not the geothermal heat flux but remaining heat that bottom sediments release. Sharp shifts in heat flow are seen within boreholes at depths crossing gas hydrate bottom. All this means that during the last glacial period interior water temperature was on 25-30C degrees warmer. Conversely, in isolated seas heat flow in the sediments shows little change with depth.

Sea, ice and surface water circulation, Alaskan Continental Shelf

NASA Technical Reports Server (NTRS)

Wright, F. F. (Principal Investigator); Sharma, G. D.

1972-01-01

The author has identified the following significant results. Two cruises were conducted in Cook Inlet to obtain ground truth. Forty-seven stations during 22-23 August and 68 stations during 25-29 September 1972 were occupied and temperature, salinity, percent light transmission, and suspended load of surface waters obtained. Similar data at various depths was also obtained at selected stations. Cook Inlet is an estuary with complex mixing of river discharges and ocean water. The Upper Cook Inlet shows a gradual and systematic decrease in salinity, however, west of Kenai the mixing of waters is complex. The sediments in suspension originating at the head of the inlet generally settle out east of Kenai and Drift River. Sediment load in suspension decreased gradually from 1700 mg/1 near Anchorage to about 50 mg/1 in the Narrows. In the Lower Cook Inlet the suspended load varied between 1-10 mg/1. Surface waters with sediments in suspension and ocean water with relatively lower sediment concentration are clearly discernible in ERTS-1 images obtained during September 18, 1972 pass over Cook Inlet. The movement and mixing of these waters can also be delineated in the images.

The relation between the age of the subconducting slab and the recycling of sediments into the mantle

NASA Technical Reports Server (NTRS)

Abbott, D.; Hoffman, S.

1985-01-01

The recycling of sediments into the mantle has become an important issue because recent papers have suggested that the geochemical inverse models of the evolution of radiogenic isotope abundances over the history of the Earth have nonunique solutions. Both the recycling of continent-derived sediments into the mantle and mixing in the mantle could produce similar geochemical effects in the mean isotopic ratios of new igneous material emplaced in continents. Recent models of Archaean heat flow and of plate tectonics during early Earth history have demonstrated that higher internal heat production of the early Earth was mainly dissipated through a higher creation rate of oceanic lithosphere. If the seafloor creation rate was higher on the early Earth, then the residence time of any one piece of oceanic lithosphere on the surface would have been shorter. It is possible that a higher rate of recycling of oceanic lithosphere into the mantle could have resulted in some transport of sediment into the mantle.

Suspension freezing of bottom sediment and biota in the Northwest Passage and implications for Arctic Ocean sedimentation

USGS Publications Warehouse

Reimnitz, E.; Marincovich, L.; McCormick, M.; Briggs, W.M.

1992-01-01

No evidence was seen for entrainment by bottom adfreezing, bluff slumping, river flooding, dragging ice keels, or significant eolian transport from land to sea. Muddy sediment with pebbles and cobbles, algae with holdfasts, ostracodes with appendages, and well-preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice. These materials indicate that suspension freezing reaching to a water depth of 25-30 m during the previous fall was responsible for entrainment. This mechanism requires rapid ice formation in open, shallow water during a freezing storm, when the ocean becomes supercooled, and frazil and anchor ice attach to and ultimately lift sediment and living organisms to the sea surface. -from Authors

Microbial community composition and function in the Tonga Trench: from 400m below the sea surface to 9100m water depth and from 0 to 2 m below the seafloor.

NASA Astrophysics Data System (ADS)

Leon Zayas, R. I.; Bartlett, D.; Biddle, J.

2016-12-01

Exploration of the deep ocean has expanded our understanding of oceanic ecosystems including continental margins and mid-ocean ridges, but little is known about the deepest sites on Earth, oceanic trenches. In this study, sediment and water samples were collected from the Tonga Trench at 9100m below sea level. These include four water column samples at depths of 400m, 3000m, 5000m and 9100m, and sediment samples at 0, 1, and 2 meter below the seafloor (mbsf). DNA was extracted and sequencing was performed for the recovery of metagenomic data for all samples. The analysis of the sediment samples from Tonga Trench has provided a new perspective of life in the deep ocean. The data for microbial community composition and metabolic profiles at the surface sediments, 0 mbsf, suggest that the microbes are present and taxonomically similar to the water column microbes, and perform an array of aerobic as well as anaerobic metabolisms, including degradation of organic carbon, oxidative phosphorylation, fermentation, nitrate reduction and sulfur oxidation among others. On the other hand, at 1 and 2 mbsf, the microbial community has diminished richness and diversity when compared to 0 mbsf and is potentially environmentally degraded due to the lack of quality data recoverable. Tonga Trench water column metagenomes are compared to other deep and hadal environments to better understand how different geographical locations, water masses and depth affect microbial community composition, distribution and metabolic potential. To our knowledge, this is the deepest metagenome analyzed to date (9100m), presenting an unprecedented look at one of the deepest environments on our planet.

Transport and deposition of the fire biomarker levoglucosan across the tropical North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Schreuder, Laura T.; Hopmans, Ellen C.; Stuut, Jan-Berend W.; Sinninghe Damsté, Jaap S.; Schouten, Stefan

2018-04-01

Biomass burning impacts biogeochemical cycling, vegetation dynamics and climate. However, interactions between fire, climate and vegetation are not well understood and therefore studies have attempted to reconstruct fire and vegetation history under different climatic conditions using sedimentary archives. Here we focus on levoglucosan, a thermal by-product of cellulose generated during biomass burning, and, therefore, a potential fire biomarker in the marine sedimentary archive. However, before levoglucosan can be applied as a biomass burning proxy in marine sediments, there is a need for studies on how levoglucosan is transported to the marine environment, how it is reflecting biomass burning on continents, as well as the fate of levoglucosan in the marine water column and during deposition in marine sediments. Here we present analyses of levoglucosan, using an improved Ultra High Pressure Liquid Chromatography-Electro Spray Ionization/High Resolution Mass Spectrometry (UHPLC-ESI/HRMS) method, in atmospheric particles, in particulate matter settling through the water column and in marine surface sediments on a longitudinal transect crossing the tropical North Atlantic Ocean at 12°N. Levoglucosan was detected in the atmosphere, although in low concentration, possibly due to the sampled particle size, the source area of the aerosols, or the short time interval of sampling by which large burning events may have been missed. In sinking particles in the tropical North Atlantic Ocean we find that levoglucosan deposition is influenced by a mineral ballast effect associated with marine biogenic particles, and that levoglucosan is not transported in association with mineral dust particles. Highest levoglucosan concentrations and seasonal differences in sinking particles were found close to continents and low concentrations and seasonal differences were found in the open ocean. Close to Africa, levoglucosan concentration is higher during winter, reflecting seasonal burning in northwestern Africa. However, close to South America levoglucosan concentrations appear to be affected by riverine transport from the Amazon River. In surface sediments close to South America, levoglucosan concentration is higher than in the middle of the Atlantic Ocean, implying that here the influence from the South American continent is important and perennial. Our study provides evidence that degradation of levoglucosan during settling in the marine water column is not substantial, but is substantial at the sediment-water interface. Nevertheless, levoglucosan was detected in all surface sediments throughout the tropical North Atlantic, indicating its presence in the marine sedimentary record, which reveals the potential for levoglucosan as a biomass burning proxy in marine sediments.

Organophosphate Ester Flame Retardants and Plasticizers in Ocean Sediments from the North Pacific to the Arctic Ocean.

PubMed

Ma, Yuxin; Xie, Zhiyong; Lohmann, Rainer; Mi, Wenying; Gao, Guoping

2017-04-04

The presence of organophosphate ester (OPE) flame retardants and plasticizers in surface sediment from the North Pacific to Arctic Ocean was observed for the first time during the fourth National Arctic Research Expedition of China in the summer of 2010. The samples were analyzed for three halogenated OPEs [tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCPP), and tris(dichloroisopropyl) phosphate], three alkylated OPEs [triisobutyl phosphate (TiBP), tri-n-butyl phosphate, and tripentyl phosphate], and triphenyl phosphate. Σ 7 OPEs (total concentration of the observed OPEs) was in the range of 159-4658 pg/g of dry weight. Halogenated OPEs were generally more abundant than the nonhalogenated OPEs; TCEP and TiBP dominated the overall concentrations. Except for that of the Bering Sea, Σ 7 OPEs values increased with increasing latitudes from Bering Strait to the Central Arctic Ocean, while the contributions of halogenated OPEs (typically TCEP and TCPP) to the total OPE profile also increased from the Bering Strait to the Central Arctic Ocean, indicating they are more likely to be transported to the remote Arctic. The median budget of 52 (range of 17-292) tons for Σ 7 OPEs in sediment from the Central Arctic Ocean represents only a very small amount of their total production volume, yet the amount of OPEs in Arctic Ocean sediment was significantly larger than the sum of polybrominated diphenyl ethers (PBDEs) in the sediment, indicating they are equally prone to long-range transport away from source regions. Given the increasing level of production and usage of OPEs as substitutes of PBDEs, OPEs will continue to accumulate in the remote Arctic.

Metabolic Potential of Microbial Genomes Reconstructed from a Deep-Sea Oligotrophic Sediment Metagenome

NASA Astrophysics Data System (ADS)

Tully, B. J.; Huber, J. A.; Heidelberg, J. F.

2016-02-01

The South Pacific Gyre (SPG) possesses the lowest rates of sedimentation, surface chlorophyll concentration and primary productivity in the global oceans, making it one of the most oligotrophic environments on earth. As a direct result of the low-standing biomass in surface waters, deep-sea sediments are thin and contain small amount of labile organic carbon. It was recently shown that the sediment column within the SPG is fully oxic through to the underlying basalt basement and may be representative of 9-37% of the global marine environment. In addition, it appears that approximately 50% of the total organic carbon is removed from the oligotrophic sediments within the first 20 centimeters beneath the sea floor (cmbsf). To understand the microbial processes that contribute to the removal of the labile organic matter, metagenomic sequencing and analysis was carried out on a sample of sediment collected from 0-5 cmbsf from SPG site 10 (U1369). Analysis of 9 partially reconstructed environmental genomes revealed that the members of the SPG surface sediment microbial community are phylogenetically distinct from surface/upper ocean organisms, with deep branches within the Alpha- and Gammaproteobacteria, Nitrospirae, Nitrospina, the phylum NC10, and several unique phylogenetic groups. Within these partially complete genomes there is evidence for microbially mediated metal (iron/manganese) oxidation and carbon fixation linked to the nitrification. Additionally, despite low sedimentation and hypothesized energy-limitation, members of the SPG microbial community had motility and chemotactic genes and possessed mechanisms for the utilization of high molecular weight organic matter, including exoproteases and peptide specific membrane transporters. Simultaneously, the SPG genomes showed a limited potential for the degradation of recalcitrant carbon compounds. Finally, the presence of putative genes with functions involved with denitrification and the consumption of C1 compounds suggest that there may be microenvironments in the surface sediments were microbes can deplete oxygen concentrations to hypoxic/anoxic levels. This study represents an important first analysis in understanding how microorganisms in oligotrophic sediments impact deep-sea carbon transformations.

Distribution of short chain chlorinated paraffins in marine sediments of the East China Sea: influencing factors, transport and implications.

PubMed

Zeng, Lixi; Zhao, Zongshan; Li, Huijuan; Wang, Thanh; Liu, Qian; Xiao, Ke; Du, Yuguo; Wang, Yawei; Jiang, Guibin

2012-09-18

Short chain chlorinated paraffins (SCCPs) are high production volume chemicals in China and found to be widely present in the environment. In this study, fifty-one surface sediments and two sediment cores were collected from the East China Sea to study their occurrence, distribution patterns and potential transport in the marginal sea. SCCPs were found in all surface sediments and ranged from 5.8 to 64.8 ng/g (dry weight, d.w.) with an average value of 25.9 ng/g d.w. A general decreasing trend with distance from the coast was observed, but the highest value was found in a distal mud area far away from the land. The C10 homologue was the most predominant carbon chain group, followed by C11, C12, and C13 homologue groups. Significant linear relationship was found between total organic carbon (TOC) and total SCCP concentrations (R(2) = 0.51, p < 0.05). Spatial distributions and correlation analysis indicated that TOC, riverine input, ocean current, and atmospheric deposition played an important role in controlling SCCP accumulation in marine sediments. Vertical profiles of sediment cores showed that SCCP concentrations decreased from surface to the depth of 36 cm, and then slightly increased again with depth, which showed a significant positive correlation with TOC and chlorine contents (Cl%). The results suggest that SCCPs are being regionally or globally distributed by long-range atmospheric or ocean current transport.

Morphology of methane hydrate host sediments

USGS Publications Warehouse

Jones, K.W.; Feng, H.; Tomov, S.; Winters, W.J.; Eaton, M.; Mahajan, D.

2005-01-01

The morphological features including porosity and grains of methane hydrate host sediments were investigated using synchrotron computed microtomography (CMT) technique. The sediment sample was obtained during Ocean Drilling Program Leg 164 on the Blake Ridge at water depth of 2278.5 m. The CMT experiment was performed at the Brookhaven National Synchrotron Light Source facility. The analysis gave ample porosity, specific surface area, mean particle size, and tortuosity. The method was found to be highly effective for the study of methane hydrate host sediments.

Hydrocarbons in surface sediments from the Sfax coastal zone, (Tunisia) Mediterranean Sea.

PubMed

Zaghden, Hatem; Kallel, Monem; Louati, Afifa; Elleuch, Boubaker; Oudot, Jean; Saliot, Alain

2005-11-01

The Semi-enclosed Mediterranean Sea records various signals of high anthropic pressures from surrounding countries and the industrialized European countries. This is particularly true for oil pollution. Although accounting for 1% of the world's ocean surface, it receives about 25% of the petroleum inputs to the ocean. To achieve a global budget we need to collect information from different parts of the Mediterranean. Particularly, we focus in this paper on the Southern Mediterranean, where data are presently very scarce. In this context, the University of Sfax has undertaken an estimation of hydrocarbon pollution along the coasts of Sfax and Gabès Gulf. Non-aromatic hydrocarbons were analysed in 8 surface sediments by FT/IR and GC/MS. Non-aromatic hydrocarbon concentrations vary in the range 310-1406 microg g(-1) sediments dry weight, which is high, compared to other Mediterranean sites. GC/MS data indicate a large group of unresolved compounds suggesting a petroleum contamination, confirmed by the identification of hopanes with predominant C29 and C30alpha,beta compounds and steranes with predominance of C27 over C28) and C29 compounds.

An Ocean Basin of Dirt? Using Molecular Biomarkers and Radiocarbon to Identify Organic Carbon Sources and their Preservation in the Arctic Ocean

NASA Astrophysics Data System (ADS)

Harvey, H.; Belicka, L. L.

2005-12-01

In the modern Arctic Ocean, primary production in waters over the broad continental shelves and under ice contributes an estimated 250 Mt/yr of POC to Arctic waters. The delivery of terrestrial material from large rivers, ice transport and through coastal erosion adds at least an additional 12 Mt/yr of POC. Although the marine organic carbon signal in Arctic Ocean exceeds that of terrestrial carbon by an order or magnitude or more, recent evidence suggests that this balance is not maintained and significant fractions of terrestrial carbon is preserved in sediments. Using an integrated approach combining lipid biomarkers and radiocarbon dating in particles and sediments, the process of organic carbon recycling and historical changes in its sources and preservation has been examined. A suite of lipid biomarkers in particles and sediments of western Arctic shelves and basins were measured and principle components analysis (PCA) used to allow a robust comparison among the 120+ individual compounds to assign organic sources and relative inputs. Offshore particles from the chlorophyll maximum contained abundant algal markers (e.g. 20:5 and 22:6 FAMEs), low concentrations of terrestrial markers (amyrins and 24-ethylcholest-5-en-3b-ol), and reflected modern 14C values. Particles present in deeper halocline waters also reflect marine production, but a portion of older, terrestrial carbon accompanies the sinking of the spring bloom. Surface and deeper sediments of basins contain older organic carbon and low concentrations of algal biomarkers, suggesting that marine carbon produced in surface waters is rapidly recycled. Taken together, these observations suggest that marine derived organic matter produced in shallow waters fuels carbon cycling, but relatively small amounts are preserved in sediments. As a result, the organic carbon preserved in sediments contrasts sharply to that typically observed in lower latitudes, with an increasing terrestrial signature with distance from land and potential for significant changes under a changing climate.

Microbial diversity and stratification of South Pacific abyssal marine sediments.

PubMed

Durbin, Alan M; Teske, Andreas

2011-12-01

Abyssal marine sediments cover a large proportion of the ocean floor, but linkages between their microbial community structure and redox stratification have remained poorly constrained. This study compares the downcore gradients in microbial community composition to porewater oxygen and nitrate concentration profiles in an abyssal marine sediment column in the South Pacific Ocean. Archaeal 16S rRNA clone libraries showed a stratified archaeal community that changed from Marine Group I Archaea in the aerobic and nitrate-reducing upper sediment column towards deeply branching, uncultured crenarchaeotal and euryarchaeotal lineages in nitrate-depleted, anaerobic sediment horizons. Bacterial 16S rRNA clone libraries revealed a similar shift on the phylum and subphylum level within the bacteria, from a complex community of Alpha-, Gamma- and Deltaproteobacteria, Actinobacteria and Gemmatimonadetes in oxic surface sediments towards uncultured Chloroflexi and Planctomycetes in the anaerobic sediment column. The distinct stratification of largely uncultured bacterial and archaeal groups within the oxic and nitrate-reducing marine sediment column provides initial constraints for their microbial habitat preferences. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.

Assessing modern rates of river sediment discharge to the ocean using satellite gravimetry

NASA Astrophysics Data System (ADS)

Mouyen, Maxime; Longuevergne, Laurent; Steer, Philippe; Crave, Alain; Lemoine, Jean-Michel; Save, Himanshu; Robin, Cécile

2017-04-01

Worldwide rivers annually export about 19 Gigatons of sediments to the ocean that mostly accumulate in the coastal zones and on the continental shelves. This sediment discharge testifies of the intensity of continental erosion and records changes in climate, tectonics and human activity. However, natural and instrumental uncertainties inherent to the in-situ measurements of sediment discharge prevent from conclusive estimates to better understand these linkages. Here we develop a new method, using the Gravity Recovery and Climate Experiment (GRACE) satellite data, to infer mass-integrative estimates of sediment discharge of large rivers to the ocean. GRACE satellite provides global gravity time series that have proven useful for quantifying mass transport, including continental water redistribution at the Earth surface (ice sheets and glaciers melting, groundwater storage variations) but has been seldom used for monitoring sediment mass transfers so far. Here we pair the analysis of regularized GRACE solutions at high spatial resolution corrected from all known contributions (hydrology, ocean, atmosphere) to a particle tracking model that predicts the location of the sediment sinks for 13 rivers with the highest sediments loads in the world. We find that the resulting GRACE-derived sediment discharges off the mouth of the Amazon, Ganges-Brahmaputra, Changjiang (Yangtze), Indus, Magdalena, Godavari and Mekong rivers are consistent with in-situ measurements. Our results suggest that the lack of time continuity and of global coverage in terrestrial sediment discharge measurements could be reduced by using GRACE, which provides global and continuous data since 2002. GRACE solutions are regularly improved and new satellite gravity missions are being prepared hence making our approach even more relevant in a near future. The accumulation of sediments over time will keep increasing the signal to noise ratio of the gravity time series, which will improve the precision of the GRACE-derived sediment discharges values.

Diffusive Transfer of Oxygen From Seamount Basaltic Crust Into Overlying Sediments: an Example From the Clarion-Clipperton Fracture Zone, Equatorial Pacific Ocean

NASA Astrophysics Data System (ADS)

Kasten, S.; Mewes, K.; Mogollón, J.; Picard, A.; Rühlemann, C.; Eisenhauer, A.; Kuhn, T.; Ziebis, W.

2015-12-01

Within the Clarion-Clipperton Fracture Zone (CCFZ) located in the equatorial Pacific Ocean numerous seamounts, with diameters ranging from 3 to 30 km and varying heights above the surrounding seafloor of up to 2500 m, occur throughout the deep-sea plain. There is evidence that these may serve as conduits for low-temperature hydrothermal circulation of seawater through the oceanic crust. During RV SONNE cruise SO205 in April/May 2010 and BIONOD cruise with RV ĹATALANTE in spring 2012 we took piston and gravity cores for geochemical analyses, as well as for high-resolution pore-water oxygen and nutrient measurements. Specifically, we took cores along a transect at three sites, located 400, 700 and 1000 m away from the foot of a 240 m high seamount, called 'Teddy Bare'. At all 3 sites oxygen penetrates the entire sediment column of the organic carbon-poor sediment. More importantly, oxygen concentrations initially decrease with sediment depth but increase again at depths of 3 m and 7 m above the basaltic basement, suggesting an upward diffusion of oxygen from seawater circulating within the seamount crust into the overlying basal sediments. This is the first time this has been shown for the deep subsurface in the Pacific Ocean. Mirroring the oxygen concentrations nitrate concentrations accumulate with sediment depth but decrease towards the basement. Transport-reaction modeling revealed that (1) the diffusive flux of oxygen from the basaltic basement exceeds the oxygen consumption through organic matter oxidation and nitrification in the basal sediments and (2) the nutrient exchange between the sediment and the underlying basaltic crust occurs at orders-of-magnitude lower rates than between the sediment surface and the overlying bottom water. We furthermore show that the upward diffusion of oxygen from the basaltic basement affects the preservation of organic compounds within the oxic sediment column at all 3 sites. Our investigations indicate that an upward diffusion of oxygen from the basalt into the overlying sediment may be a widespread phenomenon in this area of the Pacific Ocean that is characterized by numerous seamounts.

Exploring Metabolic Activities of Deeply Buried Microbial Communities in Oxic Sediments Underlying Oligotrophic Open Ocean Gyres

NASA Astrophysics Data System (ADS)

Ziebis, W.; Patel, A.; Krupke, A.; Ferdelman, T. G.

2012-12-01

The vast majority of scientific drilling expeditions have focused on continental margins where oxygen is depleted within the surface (1 m) layer of the sediment and buried organic carbon sustains anaerobic microbial communities. IODP expeditions 329 (South Pacific Gyre) and 336 (Mid-Atlantic Ridge - North Pond) took place in oligotrophic open ocean regions, which constitute 48% of the world ocean. These expeditions have revealed that unlike continental margins the seafloor underneath oligotrophic ocean gyres is oxic. Within the South Pacific Gyre (SPG) dissolved oxygen persists throughout the sediment cover and reaches the basement even at the sites with thickest sediment cover (62 and 75 mbsf). North Pond is a sedimented pond (< 300 m sediment cover) located on the flank of the Mid-Atlantic Ridge underlying the oligotrophic central Atlantic. Here, oxygen diffuses upward from the basaltic aquifer underlying the sediment package in addition to deep oxygen penetration from the overlying water. Oxygen is the main electron acceptor available for sub-seafloor microbial activity in these vast oligotrophic open ocean regions. Microbial cells are present and active in the organic poor sediments, albeit numbers are near or below the detection limit (<103 cm-3 sediment) in the extremely organic-poor sediment of the SPG (below 2 -15 m sediment depth, depending on the location). However, we have very limited knowledge on the microbial community compositions and metabolic activities. Even the dominance of bacteria or archaea remains largely elusive. It has been suggested that while archaea dominate in the anoxic sediments of continental margins bacteria might be more abundant in the oxic seafloor underlying oligotrophic ocean gyres where aerobic respiration prevails. Experiments were conducted with sediment samples from the SPG and North Pond to explore the pattern of microbial diversity and metabolic activity using a suite of radio and stable isotopes in combination with single cell analyses. Our goal was to track the uptake and turnover of metabolically important elements (C, N, P) and to compare metabolic activities (heterotrophy / autotrophy) between sites and with depth. Labeling of cells using fluorescent oligonucleotide probes (HISH and CARD-FISH) in combination with nanoSIMS has thus far revealed a clear dominance of bacteria in SPG sub-seafloor sediments, which showed a high uptake of nitrogen (ammonium). Current experiments using cell extractions and cell encapsulations followed by incubations with radiotracers will further reveal carbon turnover pathways of specific microorganisms.

Bioturbation determines the response of benthic ammonia-oxidizing microorganisms to ocean acidification

PubMed Central

Laverock, B.; Kitidis, V.; Tait, K.; Gilbert, J. A.; Osborn, A. M.; Widdicombe, S.

2013-01-01

Ocean acidification (OA), caused by the dissolution of increasing concentrations of atmospheric carbon dioxide (CO2) in seawater, is projected to cause significant changes to marine ecology and biogeochemistry. Potential impacts on the microbially driven cycling of nitrogen are of particular concern. Specifically, under seawater pH levels approximating future OA scenarios, rates of ammonia oxidation (the rate-limiting first step of the nitrification pathway) have been shown to dramatically decrease in seawater, but not in underlying sediments. However, no prior study has considered the interactive effects of microbial ammonia oxidation and macrofaunal bioturbation activity, which can enhance nitrogen transformation rates. Using experimental mesocosms, we investigated the responses to OA of ammonia oxidizing microorganisms inhabiting surface sediments and sediments within burrow walls of the mud shrimp Upogebia deltaura. Seawater was acidified to one of four target pH values (pHT 7.90, 7.70, 7.35 and 6.80) in comparison with a control (pHT 8.10). At pHT 8.10, ammonia oxidation rates in burrow wall sediments were, on average, fivefold greater than in surface sediments. However, at all acidified pH values (pH ≤ 7.90), ammonia oxidation rates in burrow sediments were significantly inhibited (by 79–97%; p < 0.01), whereas rates in surface sediments were unaffected. Both bacterial and archaeal abundances increased significantly as pHT declined; by contrast, relative abundances of bacterial and archaeal ammonia oxidation (amoA) genes did not vary. This research suggests that OA could cause substantial reductions in total benthic ammonia oxidation rates in coastal bioturbated sediments, leading to corresponding changes in coupled nitrogen cycling between the benthic and pelagic realms. PMID:23980243

A History of Warming Sea Surface Temperature and Ocean Acidification Recorded by Planktonic Foraminifera Geochemistry from the Santa Barbara Basin, California

NASA Astrophysics Data System (ADS)

Osborne, E.; Thunell, R.; Bizimis, M.; Buckley, W. P., Jr.; benitez-Nelson, C. R.; Chartier, C. J.

2015-12-01

The geochemistry of foraminiferal shells has been widely used to reconstruct past conditions of the ocean and climate. Since the onset of the Industrial Revolution, anthropogenically produced CO2 has resulted in an increase in global temperatures and a decline in the mean pH of the world's oceans. The California Current System is a particularly susceptible region to ocean acidification due to natural upwelling processes that also cause a reduction in seawater pH. The trace element concentration of magnesium and boron in planktonic foraminiferal shells are used here as proxies for temperature and carbonate ion concentration ([CO32-]), respectively. Newly developed calibrations relating Mg/Ca ratios to temperature (R2 0.91) and B/Ca ratios to [CO32-] (R2 0.84) for the surface-mixed layer species Globogerina bulloides were generated using material collected in the Santa Barbara Basin sediment trap time-series. Using these empirical relationships, temperature and [CO32-] are reconstructed using a 0.5 meter long multi-core collected within the basin. 210Pb activities were used to determine a sedimentation rate for the core to estimate ages for core samples (sedimentation rate: 0.341 cm/yr). A spike in 137Cs activity is used as a tie-point to the year 1965 coinciding with the peak of nuclear bomb testing. Our down-core record extends through the mid-19th century to create a history of rising sea surface temperatures and declining [CO32-] as a result of anthropogenic CO2 emissions.

Occurrence and Risk Assessment of PAHs in Surface Sediments from Western Arctic and Subarctic Oceans

PubMed Central

Lin, Yan; Cai, Minggang; Zhang, Jingjing; Zhang, Yuanbiao; Kuang, Weiming; Liu, Lin; Huang, Peng; Ke, Hongwei

2018-01-01

In the fourth Chinese National Arctic Research Expedition (from July to September, 2010), 14 surface sediment samples were collected from the Bering Sea, Chukchi Sea, and Canadian Basin to examine the spatial distributions, potential sources, as well as ecological and health risk assessment of polycyclic aromatic hydrocarbons (PAHs). The ∑PAH (refers to the sum of 16 priority PAHs) concentration range from 27.66 ng/g to 167.48 ng/g (dry weight, d.w.). Additionally, the concentrations of ∑PAH were highest in the margin edges of the Canadian Basin, which may originate from coal combustion with an accumulation of Canadian point sources and river runoff due to the surface ocean currents. The lowest levels occurred in the northern of Canadian Basin, and the levels of ∑PAH in the Chukchi Sea were slightly higher than those in the Being Sea. Three isomer ratios of PAHs (Phenanthrene/Anthracene, BaA/(BaA+Chy), and LMW/HMW) were used to investigate the potential sources of PAHs, which showed the main source of combustion combined with weaker petroleum contribution. Compared with four sediment quality guidelines, the concentrations of PAH are much lower, indicating a low potential ecological risk. All TEQPAH also showed a low risk to human health. Our study revealed the important role of the ocean current on the redistribution of PAHs in the Arctic. PMID:29649142

Surface Ocean Radiocarbon Reservoir Ages From Land-Sea Tephra Correlation Constrains Deglacial Chronology and Ocean Circulation in the Southeast Bering Sea

NASA Astrophysics Data System (ADS)

Cook, M. S.; Miller, R.; White-Nockleby, C.; Chapman, A.; Mix, A. C.

2017-12-01

Radiocarbon estimates of the past ocean are valuable because unlike passive tracers, radiocarbon has the potential to trace both the distribution and rate of transport of water masses. Most studies using paired radiocarbon measurements on planktonic and benthic foraminifera assume that the surface reservoir age was constant at the preindustrial value, which if incorrect, can strongly bias radiocarbon reconstructions. The subarctic Pacific is ringed by volcanic arcs, and there is great potential to use tephrochronology as a stratigraphic tool in sediments from the last glacial and deglaciation, and assign calendar ages to the marine sediment without relying on calibrated planktonic radiocarbon ages. In this study, we use major and trace element analysis of volcanic glass to match tephras between radiocarbon-dated lake cores from Sanak Island in the eastern Aleutians to marine cores from Umnak Plateau in the southeast Bering Sea. There are numerous thin tephras preserved in laminated sediments from the Bolling-Allerod and early Holocene in marine cores from depths (1000-1500 m) within the modern oxygen minimum zone. We find that trace elements are crucial in distinguishing tephras from individual eruptions. Our preliminary radiocarbon measurements suggest that the benthic-atmosphere radiocarbon differences and marine surface reservoir ages in the Bolling-Allerod are similar to pre-industrial values, supporting previously published radiocarbon reconstructions from the region.

Exploring Arctic history through scientific drilling

NASA Astrophysics Data System (ADS)

ODP Leg 151 Shipboard Scientific Party

During the brief Arctic summer of 1993, the Ocean Drilling Program's research vessel JOIDES Resolution recovered the first scientific drill cores from the eastern Arctic Ocean. Dodging rafts of pack ice shed from the Arctic ice cap, the science party sampled sediments north of 80°N latitude from the Yermak Plateau, as well as from sites in Fram Strait, the northeastern Greenland margin, and the Iceland Plateau (Figure 1).The sediments collected reveal the earliest history of the connection between the North Atlantic and Arctic Oceans through the Nordic Seas. The region between Greenland and Norway first formed a series of isolated basins, sometimes with restricted deep circulation, that eventually joined and allowed deep and surface Arctic Ocean water to invade the region. A record was also retrieved that shows major glaciation in the region began about 2.5 m.y.a.

Comparison of solid-phase and pore-water approaches for assessing the quality of marine and estuarine sediments

USGS Publications Warehouse

Carr, Robert Scott; Chapman, Duane C.

1992-01-01

As part of our continuing evaluation of the pore-water approach for assessing sediment quality, we made a series of side-by-side comparisons between the standard 10-day amphipod whole sediment test with the corophiid Grandidierella japonica and a suite of tests using pore water extracted from the same sediments. the pore-water tests evaluated were the sea urchin (Arbacia punctulata) sperm cell test and morphological development assay, the life-cycle test with the polychaete Dinophilus gyrociliatus, and acute exposures of red drum (Sciaenops ocellatus) embryo-larval stages. Sediment and surface microlayer samples were collected from contaminated sites. Whole-sediment, pore-water, and surface microlayer toxicity tests were performed. Pore-water toxicity tests were considerably more sensitive than the whole-sediment amphipod test, which is currently the most sensitive toxicity test now recommended for determining the acceptability of dredged material for open ocean disposal.

Open ocean pelago-benthic coupling: cyanobacteria as tracers of sedimenting salp faeces

NASA Astrophysics Data System (ADS)

Pfannkuche, Olaf; Lochte, Karin

1993-04-01

Coupling between surface water plankton and abyssal benthos was investigated during a mass development of salps ( Salpa fusiformis) in the Northeast Atlantic. Cyanobacteria numbers and composition of photosynthetic pigments were determined in faeces of captured salps from surface waters, sediment trap material, detritus from plankton hauls, surface sediments from 4500-4800 m depth and Holothurian gut contents. Cyanobacteria were found in all samples containing salp faeces and also in the guts of deep-sea Holothuria. The ratio between zeaxanthin (typical of cyanobacteria) and sum of chlorophyll a pigments was higher in samples from the deep sea when compared to fresh salp faeces, indicating that this carotenoid persisted longer in the sedimenting material than total chlorophyll a pigments. The microscopic and chemical observations allowed us to trace sedimenting salp faeces from the epipelagial to the abyssal benthos, and demonstrated their role as a fast and direct link between both systems. Cyanobacteria may provide a simple tracer for sedimenting phytodetritus.

A photoautotrophic source for lycopane in marine water columns

NASA Technical Reports Server (NTRS)

Wakeham, Stuart G.; Freeman, Katherine H.; Pease, Tamara K.; Hayes, J. M.

1993-01-01

Suspended particulate matter and recent sediments from diverse oceanic sites have been investigated for their contents of lycopane. Lycopane was present in all samples, including both oxic and anoxic water column and sediments. The highest concentrations in the water column were found in surface waters of the central Pacific gyre (1.5 ng/L) and in the anoxic waters of the Cariaco Trench (1.1 ng/L) and the Black Sea (0.3 ng/L). Vertical concentration profiles suggest that lycopane is probably algal in origin. Moreover, biogeochemical conditions in anoxic zones apparently result in a secondary production of lycopane from an as yet unidentified precursor. Compound-specific carbon isotopic analyses have been carried out on lycopane from water column and sediment samples. Isotopic compositions of lycopane range between -23.6 and -32.9 percent and are consistent with a photoautotrophic origin. We postulate that some lycopane is produced in surface waters of the ocean, while additional lycopane is produced in anoxic zones by anaerobic microbial action on an algal precursor.

Tracer constraints on organic particle transfer efficiency to the deep ocean

NASA Astrophysics Data System (ADS)

Weber, T. S.; Cram, J. A.; Deutsch, C. A.

2016-02-01

The "transfer efficiency" of sinking organic particles through the mesopelagic zone is a critical determinant of ocean carbon sequestration timescales, and the atmosphere-ocean partition of CO2. Our ability to detect large-scale variations in transfer efficiency is limited by the paucity of particle flux data from the deep ocean, and the potential biases of bottom-moored sediment traps used to collect it. Here we show that deep-ocean particle fluxes can be reconstructed by diagnosing the rate of phosphate accumulation and oxygen disappearance along deep circulation pathways in an observationally constrained Ocean General Circulation Model (OGCM). Combined with satellite and model estimates of carbon export from the surface ocean, these diagnosed fluxes reveal a global pattern of transfer efficiency to 1000m and 2000m that is high ( 20%) at high latitudes and negligible (<5%) throughout subtropical gyres, with intermediate values in the tropics. This pattern is at odds with previous estimates of deep transfer efficiency derived from bottom-moored sediment traps, but is consistent with upper-ocean flux profiles measured by neutrally buoyant sediment traps, which show strong attenuation of low latitude particle fluxes over the top 500m. Mechanistically, the pattern can be explained by spatial variations in particle size distributions, and the temperature-dependence of remineralization. We demonstrate the biogeochemical significance of our findings by comparing estimates of deep-ocean carbon sequestration in a scenario with spatially varying transfer efficiency to one with a globally uniform "Martin-curve" particle flux profile.

Distributions of microbial activities in deep subseafloor sediments

NASA Technical Reports Server (NTRS)

D'Hondt, Steven; Jorgensen, Bo Barker; Miller, D. Jay; Batzke, Anja; Blake, Ruth; Cragg, Barry A.; Cypionka, Heribert; Dickens, Gerald R.; Ferdelman, Timothy; Hinrichs, Kai-Uwe;

A deep oxic ecosystem in the subseafloor South Pacific Gyre

NASA Astrophysics Data System (ADS)

D'Hondt, S. L.; Inagaki, F.; Alvarez Zarikian, C. A.; Integrated Ocean Drilling Program Expedition 329 Shipboard Scientific Party

2011-12-01

Scientific ocean drilling has demonstrated the occurrence of rich microbial communities, abundant active cells and diverse anaerobic activities in anoxic subseafloor sediment. Buried organic matter from the surface photosynthetic world sustains anaerobic heterotrophs in anoxic sediment as deeply buried as 1.6 km below the seafloor. However, these studies have been mostly restricted to the organic-rich sediment of continental margins and biologically productive regions. IODP Expedition 329 discovered that subseafloor habitat and life are fundamentally different in the vast expanse of organic-poor sediment that underlies Earth's largest oceanic province, the South Pacific Gyre (SPG). Dissolved O2 and dissolved major nutrients (C, N, P) are present throughout the entire sediment sequence and the upper basaltic basement of the SPG. The drilled sediment is up to 75 m thick. Although heterotrophic O2 reduction (aerobic respiration) persists for millions of years in SPG sediment (which accumulates very slowly), it falls below minimum detection just a few meters to tens of meters beneath the SPG seafloor. Cell concentrations approach minimum detection at similar depths, but are intermittently detectable throughout the entire sediment sequence. In situ radiolysis of water may be a significant source of energy for the microbes that inhabit the deepest (oldest) sediment.

Shell preservation of Limacina inflata (Pteropoda) in surface sediments from the Central and South Atlantic Ocean: a new proxy to determine the aragonite saturation state of water masses

NASA Astrophysics Data System (ADS)

Gerhardt, Sabine; Henrich, Rüdiger

2001-08-01

Over 300 surface sediment samples from the Central and South Atlantic Ocean and the Caribbean Sea were investigated for the preservation state of the aragonitic test of Limacina inflata. Results are displayed in spatial distribution maps and are plotted against cross-sections of vertical water mass configurations, illustrating the relationship between preservation state, saturation state of the overlying waters, and overall water mass distribution. The microscopic investigation of L. inflata (adults) yielded the Limacina dissolution index (LDX), and revealed three regional dissolution patterns. In the western Atlantic Ocean, sedimentary preservation states correspond to saturation states in the overlying waters. Poor preservation is found within intermediate water masses of southern origin (i.e. Antarctic intermediate water (AAIW), upper circumpolar water (UCDW)), which are distinctly aragonite-corrosive, whereas good preservation is observed within the surface waters above and within the upper North Atlantic deep water (UNADW) beneath the AAIW. In the eastern Atlantic Ocean, in particular along the African continental margin, the LDX fails in most cases (i.e. less than 10 tests of L. inflata per sample were found). This is most probably due to extensive "metabolic" aragonite dissolution at the sediment-water interface combined with a reduced abundance of L. inflata in the surface waters. In the Caribbean Sea, a more complex preservation pattern is observed because of the interaction between different water masses, which invade the Caribbean basins through several channels, and varying input of bank-derived fine aragonite and magnesian calcite material. The solubility of aragonite increases with increasing pressure, but aragonite dissolution in the sediments does not simply increase with water depth. Worse preservation is found in intermediate water depths following an S-shaped curve. As a result, two aragonite lysoclines are observed, one above the other. In four depth transects, we show that the western Atlantic and Caribbean LDX records resemble surficial calcium carbonate data and δ13C and carbonate ion concentration profiles in the water column. Moreover, preservation of L. inflata within AAIW and UCDW improves significantly to the north, whereas carbonate corrosiveness diminishes due to increased mixing of AAIW and UNADW. The close relationship between LDX values and aragonite contents in the sediments shows much promise for the quantification of the aragonite loss under the influence of different water masses. LDX failure and uncertainties may be attributed to (1) aragonite dissolution due to bottom water corrosiveness, (2) aragonite dissolution due to additional CO 2 release into the bottom water by the degradation of organic matter based on an enhanced supply of organic matter into the sediment, (3) variations in the distribution of L. inflata and hence a lack of supply into the sediment, (4) dilution of the sediments and hence a lack of tests of L. inflata, or (5) redeposition of sediment particles.

Are the Element Budget and the Occurrence of Polymetallic Nodules influenced by Fluids Circulating through the Oceanic Crust or/and Sediments?

NASA Astrophysics Data System (ADS)

Heller, C.; Kuhn, T.

2016-12-01

Hydrothermal fluids can extract significant amounts of heat from oceanic lithosphere by lateral fluid flow through permeable basaltic crust of an age of up to 65 Ma. Fluid recharge and discharge occur at basement outcrops in between impermeable pelagic sediments. Recharge of oxic seawater causes upward oxygen diffusion into sediments overlying the permeable basalt in areas proximal to recharge sites. It is suggested that this oxygen have a strong impact on sediments and Mn nodules during fluid exposure time. The aim of this study is to investigate if and how fluid flow through oceanic crust influence the distribution and element budget of the Mn nodules. For that purpose, Mn nodules were examined which were collected during the research cruise SO240 in the equatorial NE Pacific at sites with and without faults in the upper basement and overlying sediments. Faults are thought to be preferred fluid pathways. Nodules were found on the sediment surface as well as in the sediment and consist of different nm- to µm-thick, dense and porous layers. The geochemical composition of bulk nodules and single nodule layers were determined by XRF, ICP-MS/OES and by high resolution analyses with EMPA and LA-ICP-MS. Dense layers have low Mn/Fe ratios (<4) and high concentrations of Co, Zr and REY, while porous layers are characterized by high Mn/Fe ratios (> 10) and high Ni+Cu and Li concentrations (Koschinsky et al., 2010; Kuhn et al., 2010). The different compositions depends on different formation processes of the layers. Dense layers are formed by element precipitation from oxygen rich seawater and/or pore water and are called hydrogenetic, while porous layers were formed by precipitation from almost oxygen-free (suboxic) pore water (Burns & Burns, 1978; Glasby, 2006) and are called diagenetic (Halbach et al., 1988). Preliminary results show that there are significant differences between the geochemical composition of nodules grown at sediment surface and those found within sediments. Compared to surface nodules, buried nodules are enriched in Co and W, but has lower concentration of Mo, Ba, Zn, Li. Distribution of Rare Earth Elements (REY) are also different. Especially, the element distribution in the bulk samples and the single layers of the buried nodules could be used to find a possible influence of circulating fluids on nodule formation.

Fertilisation of the Southern Atlantic: Ephemeral River Valleys as a replenishing source of nutrient-enriched mineral aerosols

NASA Astrophysics Data System (ADS)

Dansie, Andrew; Wiggs, Giles; Thomas, David

2016-04-01

Oceanic dust deposition provides biologically important iron and macronutrients (Phosphorus (P) and Nitrogen-based (N) compounds) that contribute to phytoplankton growth, marine productivity and oceanic atmospheric CO2 uptake. Research on dust emission sources to date has largely focused on the northern hemisphere and on ephemeral lakes and pans. Our work considers the ephemeral river valleys of the west coast of Namibia as an important yet overlooked source of ocean-fertilizing dust. Dust plumes are frequently emitted from the river valleys by strong easterly winds during the Southern Hemisphere winter, when the upwelling of the Benguela Current is at its weakest. We present field data from dust emission source areas along the main river channels near the coastal termini of the Huab, Kuiseb and Tsauchab river valleys. Collected data include erodible surface sediment, wind-blown flux, and associated meteorological data. Extensive surface sediment sampling was also undertaken throughout the combined 34,250 km2 extent of each river valley catchment with samples collected from within the main river channels, the main branches of each river system, selected tributaries, and into the upper watersheds. Geochemical data show valley sediment and wind-blown flux material have high concentrations of bioavailable Fe, P and N, exceeding that measured at the major dry lake basin dust sources in southern Africa. The contribution of fertilising deposition material is enhanced by both the spatial proximity of the source areas to the ocean and enrichment of source material by ephemeral fluvial accumulation and desiccation. Results show that geographical factors within each watershed play a key role in the nutrient composition of the emitting fluvial deposits in the river valleys. Analysis explores potential relationships between land use, geology, climate and precipitation in the upper watersheds and their influence on bioavailability of Fe, P and N compounds in wind-erodible valley sediments. MODIS data for dust plume identification and chlorophyll concentration in the southern Atlantic is utilised to investigate associations between recorded dust emission events and phytoplankton growth in the ocean surface waters.

Three decades of TBT contamination in sediments around a large scale shipyard.

PubMed

Kim, Nam Sook; Shim, Won Joon; Yim, Un Hyuk; Ha, Sung Yong; An, Joon Geon; Shin, Kyung Hoon

2011-08-30

Tributyltin (TBT) contamination in sediments was investigated in the vicinity of a large-scale shipyard in the years after the implementation of a total ban on the use of TBT based antifouling paints in Korea. Extremely high level of TBT (36,292ng Sn/g) in surface sediment was found at a station in front of a drydock and near surface runoff outfall of the shipyard. TBT concentration in surface sediments of Gohyeon Bay, where the shipyard is located, showed an apparent decreased TBT concentration gradient from the shipyard towards the outer bay. The vertical distribution of TBT contamination derived from a sediment core analysis demonstrated a significant positive correlation (r(2)=0.88; p<0.001) with the annual tonnage of ship-construction in the shipyard within the past three decades. TBT concentrations at six stations surveyed before (2003) and seven years after (2010) the total ban showed no significant differences (p>0.05). Despite the ban on the use of TBT, including ocean going vessels, surface sediments are still being heavily contaminated with TBT, and its levels well exceeded the sediment quality guideline or screening values. Copyright © 2011 Elsevier B.V. All rights reserved.

Is Ice-Rafted Sediment in a North Pole Marine Record Evidence for Perennial Sea-ice Cover?

NASA Technical Reports Server (NTRS)

Tremblay, L.B.; Schmidt, G.A.; Pfirman, S.; Newton, R.; DeRepentigny, P.

2015-01-01

Ice-rafted sediments of Eurasian and North American origin are found consistently in the upper part (13 Ma BP to present) of the Arctic Coring Expedition (ACEX) ocean core from the Lomonosov Ridge, near the North Pole (approximately 88 degrees N). Based on modern sea-ice drift trajectories and speeds, this has been taken as evidence of the presence of a perennial sea-ice cover in the Arctic Ocean from the middle Miocene onwards. However, other high latitude land and marine records indicate a long-term trend towards cooling broken by periods of extensive warming suggestive of a seasonally ice-free Arctic between the Miocene and the present. We use a coupled sea-ice slab-ocean model including sediment transport tracers to map the spatial distribution of ice-rafted deposits in the Arctic Ocean. We use 6 hourly wind forcing and surface heat fluxes for two different climates: one with a perennial sea-ice cover similar to that of the present day and one with seasonally ice-free conditions, similar to that simulated in future projections. Model results confirm that in the present-day climate, sea ice takes more than 1 year to transport sediment from all its peripheral seas to the North Pole. However, in a warmer climate, sea-ice speeds are significantly faster (for the same wind forcing) and can deposit sediments of Laptev, East Siberian and perhaps also Beaufort Sea origin at the North Pole. This is primarily because of the fact that sea-ice interactions are much weaker with a thinner ice cover and there is less resistance to drift. We conclude that the presence of ice-rafted sediment of Eurasian and North American origin at the North Pole does not imply a perennial sea-ice cover in the Arctic Ocean, reconciling the ACEX ocean core data with other land and marine records.

ACEX: A First Look at Arctic Ocean Cenozoic History

NASA Astrophysics Data System (ADS)

Moran, K.; Backman, J.

2004-12-01

The first Integrated Ocean Drilling Program mission specificplatform expedition (ACEX - Arctic Coring Expedition) drilled and recovered core from five holes at four sites through Cenozoic sediments draping the crest of the Lomonosov Ridge in the central Arctic Ocean. Coring continued into the underlying Cretaceous sedimentary bedrock. Sites are located only a few nautical miles apart along a single seismic line (AWI-91090), showing an identical and coherent Cenozoic seismostratigraphy. Preliminary results from shipboard investigations of core-catcher-based bio- and lithostratigraphy, pore water analyses and core logger data describe a thick (~160 m) middle Miocene through Pleistocene sequence that shows large amplitude, cyclic variability in the density, magnetic susceptibility and acoustic velocity of the sediments. Sediments are largely carbonate free. Pleistocene sedimentation rates are close to 3 cm/ka, whereas Pliocene sediments are by-and-large missing. A sharp change in physical properties at ~200 m defines the transition into a 200+ m thick Paleogene sequence that is initially dominated by large numbers of dinoflagellate cysts. The early Miocene, Oligocene and late Eocene appear to be largely missing in a hiatus. However, a 32 m thick interval separates the overlying middle Miocene from the underlying middle Eocene and presumably preserves some of the early Neogene and late Paleogene sections. Dinoflagellate cysts, diatoms, ebridians and silicoflagellates are common to abundant in the middle Eocene section, which bottoms in a spectacular layer showing massive occurrences of glochidia and massulae (megaspores) of the freshwater hydropterid fern Azolla (duckweed) at the early/middle Eocene boundary (~306 m), suggesting strongly reduced surface water salinity or perhaps even a brief episode of fresh water conditions at the surface. Biosilica is not present prior to the late early Eocene (~320 m). The (sub-) tropical dinoflagellate species Apectodinium augustum occurs abundantly at around 380m in pyrite-rich mudstones, indicating that the Paleocene/Eocene boundary and the associated Carbon Isotope Excursion (CIE) interval were recovered, and that the Arctic Ocean experienced surface temperatures on the order of 20°C during the Paleocene Eocene Thermal Maximum (PETM). Benthic foraminifers indicate that the early Eocene through latest Paleocene sediments were deposited in shallow-marine, neritic to inner neritic, environments. The mudstone of late Paleocene age rests unconformably on Campanian marine sands, sandstone and mudstone.

Clay mineral continental amplifier for marine carbon sequestration in a greenhouse ocean.

PubMed

Kennedy, Martin J; Wagner, Thomas

2011-06-14

The majority of carbon sequestration at the Earth's surface occurs in marine continental margin settings within fine-grained sediments whose mineral properties are a function of continental climatic conditions. We report very high mineral surface area (MSA) values of 300 and 570 m(2) g in Late Cretaceous black shales from Ocean Drilling Program site 959 of the Deep Ivorian Basin that vary on subcentennial time scales corresponding with abrupt increases from approximately 3 to approximately 18% total organic carbon (TOC). The observed MSA changes with TOC across multiple scales of variability and on a sample-by-sample basis (centimeter scale), provides a rigorous test of a hypothesized influence on organic carbon burial by detrital clay mineral controlled MSA. Changes in TOC also correspond with geochemical and sedimentological evidence for water column anoxia. Bioturbated intervals show a lower organic carbon loading on mineral surface area of 0.1 mg-OC m(-2) when compared to 0.4 mg-OC m(-2) for laminated and sulfidic sediments. Although either anoxia or mineral surface protection may be capable of producing TOC of < 5%, when brought together they produced the very high TOC (10-18%) apparent in these sediments. This nonlinear response in carbon burial resulted from minor precession-driven changes of continental climate influencing clay mineral properties and runoff from the African continent. This study identifies a previously unrecognized land-sea connection among continental weathering, clay mineral production, and anoxia and a nonlinear effect on marine carbon sequestration during the Coniacian-Santonian Oceanic Anoxic Event 3 in the tropical eastern Atlantic.

Quantitative estimation of surface ocean productivity and bottom water oxygen concentration using benthic foraminifera

NASA Astrophysics Data System (ADS)

Loubere, Paul

1994-10-01

An electronic supplement of this material may be obtained on adiskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN toAGU's FTP account using ANONYMOUS as the usemame andGUEST as the password. Go to the right directory by typing CDAPEND. Type LS to see what files are available. Type GET and thename of the file to get it. Finally, type EXIT to leave the system.)(Paper 94PA01624, Quantitative estimation of surface oceanproductivity and bottom water concentration using benthicforaminifera, by P. Loubere). Diskette may be ordered from AmericanGeophysical Union, 2000 Florida Avenue, N.W., Washington, DC20009; $15.00. Payment must accompany order.Quantitative estimation of surface ocean productivity and bottom water oxygen concentration with benthic foraminifera was attempted using 70 samples from equatorial and North Pacific surface sediments. These samples come from a well defined depth range in the ocean, between 2200 and 3200 m, so that depth related factors do not interfere with the estimation. Samples were selected so that foraminifera were well preserved in the sediments and temperature and salinity were nearly uniform (T = 1.5° C; S = 34.6‰). The sample set was also assembled so as to minimize the correlation often seen between surface ocean productivity and bottom water oxygen values (r² = 0.23 for prediction purposes in this case). This procedure reduced the chances of spurious results due to correlations between the environmental variables. The samples encompass a range of productivities from about 25 to >300 gC m-2 yr-1, and a bottom water oxygen range from 1.8 to 3.5 ml/L. Benthic foraminiferal assemblages were quantified using the >62 µm fraction of the sediments and 46 taxon categories. MANOVA multivariate regression was used to project the faunal matrix onto the two environmental dimensions using published values for productivity and bottom water oxygen to calibrate this operation. The success of this regression was measured with the multivariate r² which was 0.98 for the productivity dimension and 0.96 for the oxygen dimension. These high coefficients indicate that both environmental variables are strongly imbedded in the faunal data matrix. Analysis of the beta regression coefficients shows that the environmental signals are carried by groups of taxa which are consistent with previous work characterizing benthic foraminiferal responses to productivity and bottom water oxygen. The results of this study suggest that benthic foraminiferal assemblages can be used for quantitative reconstruction of surface ocean productivity and bottom water oxygen concentrations if suitable surface sediment calibration data sets are developed and appropriate means for detecting no-analog samples are found.

Mercury Concentrations in Coastal Sediment from Younger Lagoon, Central California

NASA Astrophysics Data System (ADS)

Hohn, R. A.; Ganguli, P. M.; Swarzenski, P. W.; Richardson, C. M.; Merckling, J.; Johnson, C.; Flegal, A. R.

2013-12-01

Younger Lagoon Reserve, located in northern Monterey Bay, is one of the few relatively undisturbed wetlands that remain along the Central Coast of California. This lagoon system provides protected habitat for more than 100 bird species and for populations of fish, mammals, and invertebrates. Total mercury (HgT) concentrations in water within Younger Lagoon appear to vary with rainfall conditions and range from about 5-15 pM. These concentrations are similar to HgT in water from six nearby lagoon systems. However, Younger Lagoon contains elevated concentrations of dissolved organic carbon (~1 mM) and monomethylmercury (MMHg, ~1 pM) relative to our comparison lagoon sites (DOC < 0.5 mM and MMHg < 0.5 pM). We attribute Younger Lagoon's high DOC and MMHg to its restricted connection to the ocean and minor riverine contribution. Coastal lagoons in this region typically form at the mouth of streams. They behave as small estuaries during the wet season when surface water discharge keeps the mouth of the stream open to the ocean, and then transition into lagoons in the dry season when a sand berm develops and effectively cuts off surface water exchange. At Younger Lagoon, the sand berm remains intact throughout the year, breaching only during particularly high tides or intense rain events. Therefore, the lagoon's connection to nearshore seawater is primarily via surface water - groundwater interaction through the sand berm. Because Younger Lagoon is largely isolated from a surface water connection with the ocean, runoff from upgradient urban and agricultural land has an enhanced impact on water (and presumably sediment) quality. As a result, the lagoon is eutrophic and experiences annual algal blooms. Groundwater surveys suggest surface water, groundwater, and coastal seawater are hydraulically connected at Younger Lagoon, and mixing among these water masses appears to influence water geochemistry. To date, no chemical analyses have been conducted on sediment from Younger Lagoon. To address this data gap we collected sediment samples during a February 2013 field campaign. One set of sediment samples is from the bottom of the lagoon along a transect perpendicular to the shoreline and another set is from an approximately 1 m depth profile on the lagoon side of the sand berm (depth of the groundwater table at the time of collection). These samples are being analyzed for HgT, MMHg, and total organic carbon (TOC) and will provide a first glimpse into the distribution of mercury species and organic carbon in sediments from the Younger Lagoon Reserve. We will also collect and analyze sediment samples from another lagoon site with comparable watershed characteristics.

Where the oil from surface and subsurface plumes deposited during/after Deepwater Horizon oil spill?

NASA Astrophysics Data System (ADS)

Yan, B.

2016-02-01

The Deepwater Horizon (DwH) oil spill released an estimated 4.9 million barrels (about 200 million gallons) of crude oil into the Gulf of Mexico between April 20, 2010 and July 15, 2010. Though Valentine et al. has linked the elevated oil components in some sediments with the subsurface plume, the sites with fallout from the ocean surface plume has not been identified. This piece of information is critical not only for a comprehensive scientific understanding of the ecosystem response and fate of spill-related pollutants, but also for litigation purposes and future spill response and restoration planning. In this study we focus on testing the hypothesis that marine snow from the surface plume were deposited on the sea floor over a broad area. To do so, we use publicly available data generated as part of the ongoing Natural Resource Damage Assessment (NRDA) process to assess the spatial distribution of petroleum hydrocarbons in the water column and deep-ocean sediments of the Gulf of Mexico. Sensitive hydrocarbon markers are used to differentiate hydrocarbons from surface plume, deep subsurface plume, and in-situ burning. Preliminary results suggest the overlapping but different falling sites of these plumes and the sedimentation process was controlled by various biological, chemical, and physical factors.

Variations of oxygen-minimum and primary productivity recorded in sediments of the Arabian Sea

NASA Astrophysics Data System (ADS)

Schulte, Sonja; Rostek, Frauke; Bard, Edouard; Rullkötter, Jürgen; Marchal, Olivier

1999-11-01

Two deep-sea sediment cores from the northeastern and the southeastern Arabian Sea were studied in order to reconstruct the palaeoenvironments of the past glacial cycles. Core 136KL was recovered from the high-productivity area off Pakistan within the modern oxygen-minimum zone (OMZ). By contrast, modern primary productivity at the site of MD900963 close to Maldives is moderate and bottom waters are today well oxygenated. For both cores, we reconstructed the changes in palaeoproductivity using a set of biomarkers (alkenones, dinosterol and brassicasterol); the main result is that primary productivity is enhanced during glacial stages and lowered during interstadials. The proxies associated with productivity show a 23 kyr cyclicity corresponding to the precession-related insolation cycle. Palaeoredox conditions were studied in both cores using a new organic geochemical parameter (C 35/C 31- n-alkane ratio) developed by analysing surface sediments from a transect across the OMZ off Pakistan. The value of this ratio in core 136KL shows many variations during the last 65 kyr, indicating that the OMZ was not stable during this time: it disappeared completely during Heinrich- and the Younger Dryas events, pointing to a connection between global oceanic circulation and the stability of the OMZ. The C 35/C 31 ratio determined in sediments of core MD900963 shows that bottom waters remained rather well oxygenated over the last 330 kyr, which is confirmed by comparison with authigenic metal concentrations in the same sediments. A zonally averaged, circulation-biogeochemical ocean model was used to explore how the intermediate Indian Ocean responds to a freshwater flux anomaly at the surface of the North Atlantic. As suggested by the geochemical time series, both the abundance of Southern Ocean Water and the oxygen concentration are significantly increased in response to this freshwater perturbation.

Late Pliocene Depositional History and Paleoclimate Reconstructions of the Southwest Pacific

NASA Astrophysics Data System (ADS)

Royce, B.; Patterson, M. O.; Pietras, J.

2017-12-01

Drift deposits off the eastern margin of New Zealand are important archives for the paleoclimate and paleoceanographic history of the southwest Pacific. Ocean Drilling Program (ODP) Site 1123 is located on the North Chatham rise drift just North of the westerly wind driven Subtropical Front (STF) and provides a record of near continuous sediment deposition since the Miocene along the southwest Pacific deep western boundary current (DWBC). While the Miocene and Late Pleistocene portion of this record have been well studied, the Late Pliocene record is less well developed. Southern Ocean geological records demonstrate that Late Pliocene cooling is the transient time bracketing the warmer than present Early Pliocene and bipolar glaciation at 2.7 Ma. A newly developed, robust, and astronomically tuned long-term record of benthic δ13C from ODP Site 1123 spanning the Early to Late Pliocene implies a reduction in Southern Ocean ventilation and lowering of preformed values from waters sourced along the Antarctic margin during the Late Pliocene. Thus, Late Pliocene Southern Hemisphere cooling and sea ice expansion may have drastically reduced outgassing and increased the burial of heat into the deep ocean. South Atlantic records off the west coast of Africa demonstrate an increase in the flux of iron to the open ocean during this time potentially enhancing surface ocean productivity and providing an additional cooling mechanism. Currently, atmospheric transport of dust to the Southern Ocean is dominated by persistent mid-latitude circumpolar westerly winds; this is particularly relevant for dust sourced from New Zealand. The Late Pliocene to Early Pleistocene uplift of the North Island axial ranges and South Island southern alps potentially provided a greater amount of not only sediment to the deep ocean, but also wind blow dust to the Pacific sector of the Southern Ocean. We will present a detailed high-resolution sedimentological study on the development of the Chatham Rise drift during the Late Pliocene in order to understand both the terrigenous flux rate of sediment into the southwest Pacific and changes in surface ocean productivity. Time series analysis on proxy data demonstrates a close coupling between orbital driven perturbations in climate and the depositional history of the Chatham Rise drift.

Vertical mercury distributions in the oceans

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

Gill, G.A.; Fitzgerald, W.F.

1988-06-01

The vertical distribution of mercury (Hg) was determined at coastal and open ocean sites in the northwest Atlantic and Pacific Oceans. Reliable and diagnostic Hg distribution were obtained, permitting major processes governing the marine biogeochemistry of Hg to be identified. The northwest Atlantic near Bermuda showed surface water Hg concentrations near 4 pM, a maximum of 10 pM within the main thermocline, and concentrations less than or equal to surface water values below the depth of the maximum. The maximum appears to result from lateral transport of Hg enriched waters from higher latitudes. In the central North Pacific, surface watersmore » (to 940 m) were slightly elevated (1.9 {plus minus} 0.7 pM) compared to deeper waters (1.4 {plus minus} 0.4 pM), but on thermocline Hg maximum was observed. At similar depths, Hg concentrations near Bermuda were elevated compared to the central North Pacific Ocean. The authors hypothesize that the source of this Hg comes from diagenetic reactions in oxic margin sediments, releasing dissolved Hg to overlying water. Geochemical steady-state box modeling arguments predict a relatively short ({approximately}350 years) mean residence time for Hg in the oceans, demonstrating the reactive nature of Hg in seawater and precluding significant involvement in nutrient-type recycling. Mercury's distributional features and reactive nature suggest that interaction of Hg with settling particulate matter and margin sediments play important roles in regulating oceanic Hg concentrations. Oceanic Hg distributions are governed by an external cycling process, in which water column distributions reflect a rapid competition between the magnitude of the input source and the intensity of the (water column) removal process.« less

Lithium isotopes in large rivers reveal the cannibalistic nature of modern continental weathering and erosion

NASA Astrophysics Data System (ADS)

Dellinger, Mathieu; Gaillardet, Jérôme; Bouchez, Julien; Calmels, Damien; Galy, Valier; Hilton, Robert G.; Louvat, Pascale; France-Lanord, Christian

2014-09-01

The erosion of major mountain ranges is thought to be largely cannibalistic, recycling sediments that were deposited in the ocean or on the continents prior to mountain uplift. Despite this recognition, it has not yet been possible to quantify the amount of recycled material that is presently transported by rivers to the ocean. Here, we have analyzed the Li content and isotope composition (δLi7) of suspended sediments sampled along river depth profiles and bed sands in three of the largest Earth's river systems (Amazon, Mackenzie and Ganga-Brahmaputra rivers). The δLi7 values of river-sediments transported by these rivers range from +5.3 to -3.6‰ and decrease with sediment grain size. We interpret these variations as reflecting a mixture of unweathered rock fragments (preferentially transported at depth in the coarse fraction) and present-day weathering products (preferentially transported at the surface in the finest fraction). Only the finest surface sediments contain the complementary reservoir of Li solubilized by water-rock interactions within the watersheds. Li isotopes also show that river bed sands can be interpreted as a mixture between unweathered fragments of igneous and sedimentary rocks. A mass budget approach, based on Li isotopes, Li/Al and Na/Al ratios, solved by an inverse method allows us to estimate that, for the large rivers analyzed here, the part of solid weathering products formed by present-day weathering reactions and transported to the ocean do not exceed 35%. Li isotopes also show that the sediments transported by the Amazon, Mackenzie and Ganga-Brahmaputra river systems are mostly sourced from sedimentary rocks (>60%) rather than igneous rocks. This study shows that Li isotopes in the river particulate load are a good proxy for quantifying both the erosional rock sources and the fingerprint of present-day weathering processes. Overall, Li isotopes in river sediments confirm the cannibalistic nature of erosion and weathering.

IODP workshop: developing scientific drilling proposals for the Argentina Passive Volcanic Continental Margin (APVCM) - basin evolution, deep biosphere, hydrates, sediment dynamics and ocean evolution

NASA Astrophysics Data System (ADS)

Flood, Roger D.; Violante, Roberto A.; Gorgas, Thomas; Schwarz, Ernesto; Grützner, Jens; Uenzelmann-Neben, Gabriele; Hernández-Molina, F. Javier; Biddle, Jennifer; St-Onge, Guillaume; Workshop Participants, Apvcm

2017-05-01

The Argentine margin contains important sedimentological, paleontological and chemical records of regional and local tectonic evolution, sea level, climate evolution and ocean circulation since the opening of the South Atlantic in the Late Jurassic-Early Cretaceous as well as the present-day results of post-depositional chemical and biological alteration. Despite its important location, which underlies the exchange of southern- and northern-sourced water masses, the Argentine margin has not been investigated in detail using scientific drilling techniques, perhaps because the margin has the reputation of being erosional. However, a number of papers published since 2009 have reported new high-resolution and/or multichannel seismic surveys, often combined with multi-beam bathymetric data, which show the common occurrence of layered sediments and prominent sediment drifts on the Argentine and adjacent Uruguayan margins. There has also been significant progress in studying the climatic records in surficial and near-surface sediments recovered in sediment cores from the Argentine margin. Encouraged by these recent results, our 3.5-day IODP (International Ocean Discovery Program) workshop in Buenos Aires (8-11 September 2015) focused on opportunities for scientific drilling on the Atlantic margin of Argentina, which lies beneath a key portion of the global ocean conveyor belt of thermohaline circulation. Significant opportunities exist to study the tectonic evolution, paleoceanography and stratigraphy, sedimentology, and biosphere and geochemistry of this margin.

Ocean acidification: Towards a better understanding of calcite dissolution

NASA Astrophysics Data System (ADS)

Wilhelmus, Monica M.; Adkins, Jess; Menemenlis, Dimitris

2016-11-01

The drastic increase of anthropogenic CO2 emissions over the past two centuries has altered the chemical structure of the ocean, acidifying upper ocean waters. The net impact of this pH decrease on marine ecosystems is still unclear, given the unprecedented rate at which CO2 is being released into the atmosphere. As part of the carbon cycle, calcium carbonate dissolution in sediments neutralizes CO2: phytoplankton at the surface produce carbonate minerals, which sink and reach the seafloor after the organisms die. On time scales of thousands of years, the calcium carbonate in these shells ultimately reacts with CO2 in seawater. Research in this field has been extensive; nevertheless, the dissolution rate law, the impact of boundary layer transport, and the feedback with the global ocean carbon cycle remain controversial. Here, we (i) develop a comprehensive numerical framework via 1D modeling of carbonate dissolution in sediments, (ii) approximate its impact on water column properties by implementing a polynomial approximation to the system's response into a global ocean biogeochemistry general circulation model (OBGCM), and (iii) examine the OBGCM sensitivity response to different formulations of sediment boundary layer properties. We find that, even though the burial equilibration time scales of calcium carbonate are in the order of thousands of years, the formulation of a bottom sediment model along with an improved description of the dissolution rate law can have consequences on multi-year to decadal time scales.

Warm ocean surface led to ice margin retreat in central-eastern Baffin Bay during the Younger Dryas

NASA Astrophysics Data System (ADS)

Oksman, Mimmi; Weckström, Kaarina; Miettinen, Arto; Juggins, Stephen; Divine, Dmitry; Jackson, Rebecca; Korsgaard, Niels J.; Telford, Richard; Kucera, Michal

2017-04-01

The Greenland ice sheet stability is linked to fast-flowing ice streams that are influenced by sea surface temperatures (SSTs) at their front. One of the largest ice streams in West Greenland is the Jakobshavn Isbræ, which has been shown to have collapsed at ca. 12.2 kyr BP in the middle of the Younger Dryas (YD) cold period (12.9-11.7 kyr BP). The cause for this collapse is still unknown yet hypotheses, such as warm Atlantic water inflow, have been put forward to explain it. Here we present the first diatom-based high-resolution reconstruction of sea surface conditions in the central-eastern Baffin Bay between 14.0 and 10.2 kyr BP. The sea surface temperatures reveal warmer conditions beginning at ca. 13.4 kyr BP and leading to intensive calving and iceberg discharge from Jakobshavn Isbræ visible as increased sedimentation rates and deposition of coarse-grained material in our sediment stratigraphy. The warm YD ocean surface conditions in Baffin Bay are out of phase with the δ18O record from the North Greenland Ice Core Project (NGRIP) and other SST records from northern North-Atlantic. We show that the ocean has had significant interactions with the Greenland ice sheet in the past and emphasize its importance under the current warming of the North Atlantic.

Interglacial/glacial changes in coccolith-rich deposition in the SW Pacific Ocean: An analogue for a warmer world?

NASA Astrophysics Data System (ADS)

Duncan, Bella; Carter, Lionel; Dunbar, Gavin; Bostock, Helen; Neil, Helen; Scott, George; Hayward, Bruce W.; Sabaa, Ashwaq

2016-09-01

Satellite observations of middle to high latitudes show that modern ocean warming is accompanied by increased frequency and poleward expansion of coccolithophore blooms. However, the outcomes of such events and their causal processes are unclear. In this study, marine sediment cores are used to investigate past coccolithophore production north and south of the Subtropical Front. Calcareous pelagites from subtropical waters off northernmost New Zealand (site P71) and from subantarctic waters on Campbell Plateau (Ocean Drilling Program [ODP] site 1120C) record marked changes in pelagite deposition. At both locations, foraminiferal-rich sediments dominate glacial periods whereas coccolith-rich sediments characterise specific interglacial periods. Sediment grain size has been used to determine relative abundances of coccoliths and foraminifers. Results show coccoliths prevailed around certain Marine Isotope Stage (MIS) transitions, at MIS 7b/a and MIS 2/1 at P71, and at MIS 6/5e at ODP 1120C. Palaeo-environmental proxies suggest that coccolithophore production and deposition at P71 reflect enhanced nutrient availability associated with intense winter mixing in the subtropical Tasman Sea. An increased inflow of that warm, micronutrient-bearing subtropical water in concert with upper ocean thermal stratification in late spring/summer, led to peak phytoplankton production. At ODP 1120C during MIS 6/5e, an increased inflow of subtropical water, warm sea surface temperatures and a thermally stratified upper ocean also favoured coccolithophore production. These palaeo-environmental reconstructions together with model simulations suggest that (i) future subtropical coccolithophore production at P71 is unlikely to reach abundances recorded during MIS 7b/a but (ii) future subantarctic production is likely to dominate sedimentation over Campbell Plateau as modern conditions trend towards those prevalent during MIS 5e.

Is the Core Top Really Modern? A Story of Chemical Erosion, Bioturbation, and Lateral Sediment Redistribution from the Eastern Equatorial Pacific

NASA Astrophysics Data System (ADS)

Mekik, F.

2016-12-01

Paleoceanographic work is based on calibrating paleo-environmental proxies using well-preserved core top sediments which represent the last one thousand years or less. However, core top sediments may be in places as old as 9000 years due to various sedimentary and diagenetic processes, such as chemical erosion, bioturbation and lateral sediment redistribution. We hypothesize that in regions with high surface ocean productivity, high organic carbon to calcite ratios reaching the seabed promote calcite dissolution in sediments, even in regions above the lysocline. This process may lead to chemical erosion of core tops which in turn may result in core top aging. The eastern equatorial Pacific (EEP), a popular site for calibration of paleoceanographic proxies, is such a place. Better understanding the relationship between core top age and dissolution will help correct biases inherent in proxy calibration because dissolution of foraminifers alters shell chemistry, and wholesale dissolution of sediments leads to core top aging and loss. We present both new and literature-based core top data of radiocarbon ages from the EEP. We created regional maps of both core top radiocarbon age and calcite preservation measured with the Globorotalia menardii Fragmentation Index (MFI; over 100 core tops). Our maps show a clear pattern of deep sea sedimentary calcite dissolution mimicking the pattern of surface ocean productivity observed from satellites and sediment traps in the EEP. Core top radiocarbon ages generally parallel the dissolution patterns observed in the region. Where this relationship does not hold true, bioturbation and/or lateral sediment redistribution may play a role. Down core radiocarbon and 230Th-normalized sediment accumulation rate data from several cores in the EEP support this hypothesis. Better understanding the role of diagenesis promotes the development of more reliable paleo-environmental proxies.

Fossilized glycolipids reveal past oceanic N2 fixation by heterocystous cyanobacteria

PubMed Central

Bauersachs, Thorsten; Speelman, Eveline N.; Hopmans, Ellen C.; Reichart, Gert-Jan; Schouten, Stefan; Damsté, Jaap S. Sinninghe

2010-01-01

N2-fixing cyanobacteria play an essential role in sustaining primary productivity in contemporary oceans and freshwater systems. However, the significance of N2-fixing cyanobacteria in past nitrogen cycling is difficult to establish as their preservation potential is relatively poor and specific biological markers are presently lacking. Heterocystous N2-fixing cyanobacteria synthesize unique long-chain glycolipids in the cell envelope covering the heterocyst cell to protect the oxygen-sensitive nitrogenase enzyme. We found that these heterocyst glycolipids are remarkably well preserved in (ancient) lacustrine and marine sediments, unambiguously indicating the (past) presence of N2-fixing heterocystous cyanobacteria. Analysis of Pleistocene sediments of the eastern Mediterranean Sea showed that heterocystous cyanobacteria, likely as epiphytes in symbiosis with planktonic diatoms, were particularly abundant during deposition of sapropels. Eocene Arctic Ocean sediments deposited at a time of large Azolla blooms contained glycolipids typical for heterocystous cyanobacteria presently living in symbiosis with the freshwater fern Azolla, indicating that this symbiosis already existed in that time. Our study thus suggests that heterocystous cyanobacteria played a major role in adding “new” fixed nitrogen to surface waters in past stratified oceans. PMID:20966349

Ciliate diversity and distribution patterns in the sediments of a seamount and adjacent abyssal plains in the tropical Western Pacific Ocean.

PubMed

Zhao, Feng; Filker, Sabine; Stoeck, Thorsten; Xu, Kuidong

2017-09-12

Benthic ciliates and the environmental factors shaping their distribution are far from being completely understood. Likewise, deep-sea systems are amongst the least understood ecosystems on Earth. In this study, using high-throughput DNA sequencing, we investigated the diversity and community composition of benthic ciliates in different sediment layers of a seamount and an adjacent abyssal plain in the tropical Western Pacific Ocean with water depths ranging between 813 m and 4566 m. Statistical analyses were used to assess shifts in ciliate communities across vertical sediment gradients and water depth. Nine out of 12 ciliate classes were detected in the different sediment samples, with Litostomatea accounting for the most diverse group, followed by Plagiopylea and Oligohymenophorea. The novelty of ciliate genetic diversity was extremely high, with a mean similarity of 93.25% to previously described sequences. On a sediment depth gradient, ciliate community structure was more similar within the upper sediment layers (0-1 and 9-10 cm) compared to the lower sediment layers (19-20 and 29-30 cm) at each site. Some unknown ciliate taxa which were absent from the surface sediments were found in deeper sediments layers. On a water depth gradient, the proportion of unique OTUs was between 42.2% and 54.3%, and that of OTUs shared by all sites around 14%. However, alpha diversity of the different ciliate communities was relatively stable in the surface layers along the water depth gradient, and about 78% of the ciliate OTUs retrieved from the surface layer of the shallowest site were shared with the surface layers of sites deeper than 3800 m. Correlation analyses did not reveal any significant effects of measured environmental factors on ciliate community composition and structure. We revealed an obvious variation in ciliate community along a sediment depth gradient in the seamount and the adjacent abyssal plain and showed that water depth is a less important factor shaping ciliate distribution in deep-sea sediments unlike observed for benthic ciliates in shallow seafloors. Additionally, an extremely high genetic novelty of ciliate diversity was found in these habitats, which points to a hot spot for the discovery of new ciliate species.

Potential Mechanisms for Microbial Energy Acquisition in Oxic Deep-Sea Sediments

PubMed Central

Heidelberg, John F.

2016-01-01

ABSTRACT The South Pacific Gyre (SPG) possesses the lowest rates of sedimentation, surface chlorophyll concentration, and primary productivity in the global oceans. As a direct result, deep-sea sediments are thin and contain small amounts of labile organic carbon. It was recently shown that the entire SPG sediment column is oxygenated and may be representative of up to a third of the global marine environment. To understand the microbial processes that contribute to the removal of the labile organic matter at the water-sediment interface, a sediment sample was collected and subjected to metagenomic sequencing and analyses. Analysis of nine partially reconstructed environmental genomes, which represent approximately one-third of the microbial community, revealed that the members of the SPG surface sediment microbial community are phylogenetically distinct from surface/upper-ocean organisms. These genomes represent a wide distribution of novel organisms, including deep-branching Alphaproteobacteria, two novel organisms within the Proteobacteria, and new members of the Nitrospirae, Nitrospinae, and candidate phylum NC10. These genomes contain evidence for microbially mediated metal (iron/manganese) oxidation and carbon fixation linked to nitrification. Additionally, despite hypothesized energy limitation, members of the SPG microbial community had motility and chemotaxis genes and possessed mechanisms for the degradation of high-molecular-weight organic matter. This study contributes to our understanding of the metabolic potential of microorganisms in deep-sea oligotrophic sediments and their impact on local carbon geochemistry. IMPORTANCE This research provides insight into the microbial metabolic potential of organisms inhabiting oxygenated deep-sea marine sediments. Current estimates suggest that these environments account for up to a third of the global marine sediment habitat. Nine novel deep-sea microbial genomes were reconstructed from a metagenomic data set and expand the limited number of environmental genomes from deep-sea sediment environments. This research provides phylogeny-linked insight into critical metabolisms, including carbon fixation associated with nitrification, which is assignable to members of the marine group 1 Thaumarchaeota, Nitrospinae, and Nitrospirae and neutrophilic metal (iron/manganese) oxidation assignable to a novel proteobacterium. PMID:27208118

Potential Mechanisms for Microbial Energy Acquisition in Oxic Deep-Sea Sediments.

PubMed

Tully, Benjamin J; Heidelberg, John F

2016-07-15

The South Pacific Gyre (SPG) possesses the lowest rates of sedimentation, surface chlorophyll concentration, and primary productivity in the global oceans. As a direct result, deep-sea sediments are thin and contain small amounts of labile organic carbon. It was recently shown that the entire SPG sediment column is oxygenated and may be representative of up to a third of the global marine environment. To understand the microbial processes that contribute to the removal of the labile organic matter at the water-sediment interface, a sediment sample was collected and subjected to metagenomic sequencing and analyses. Analysis of nine partially reconstructed environmental genomes, which represent approximately one-third of the microbial community, revealed that the members of the SPG surface sediment microbial community are phylogenetically distinct from surface/upper-ocean organisms. These genomes represent a wide distribution of novel organisms, including deep-branching Alphaproteobacteria, two novel organisms within the Proteobacteria, and new members of the Nitrospirae, Nitrospinae, and candidate phylum NC10. These genomes contain evidence for microbially mediated metal (iron/manganese) oxidation and carbon fixation linked to nitrification. Additionally, despite hypothesized energy limitation, members of the SPG microbial community had motility and chemotaxis genes and possessed mechanisms for the degradation of high-molecular-weight organic matter. This study contributes to our understanding of the metabolic potential of microorganisms in deep-sea oligotrophic sediments and their impact on local carbon geochemistry. This research provides insight into the microbial metabolic potential of organisms inhabiting oxygenated deep-sea marine sediments. Current estimates suggest that these environments account for up to a third of the global marine sediment habitat. Nine novel deep-sea microbial genomes were reconstructed from a metagenomic data set and expand the limited number of environmental genomes from deep-sea sediment environments. This research provides phylogeny-linked insight into critical metabolisms, including carbon fixation associated with nitrification, which is assignable to members of the marine group 1 Thaumarchaeota, Nitrospinae, and Nitrospirae and neutrophilic metal (iron/manganese) oxidation assignable to a novel proteobacterium. Copyright © 2016 Tully and Heidelberg.

Submarine groundwater discharge is an important source of REEs to the coastal ocean

NASA Astrophysics Data System (ADS)

Johannesson, K. H.; Chevis, D. A.; Palmore, C. D.; Telfeyan, K.; Burdige, D.; Cable, J. E.; Hemming, S. R.; Rasbury, T.; Moran, S. B.; Prouty, N.; Swarzenski, P. W.

2014-12-01

Rare earth element (REE) concentrations of submarine groundwater discharge (SGD) were measured in three subterranean estuaries (i.e., Indian River Lagoon, Florida; Pettaquamscutt estuary, Rhode Island; Kona Coast, Hawaii). Using site-specific SGD estimates previously obtained by a variety of techniques (e.g., seepage meters, Ra, and Rn), we estimated SGD-derived fluxes of REEs to the coastal ocean using simple, one-dimensional modeling techniques. Our results indicate that the SGD fluxes of REEs are either of the same magnitude as riverine REE fluxes (Indian River Lagoon; Pettaquamscutt estuary), or far exceed surface runoff sources of REEs to the coastal ocean (Kona Coast). At each site important biogeochemical reactions occurring in the subterranean estuary, such as redox reactions, sediment bioirrigation, mineral dissolution and re-precipitation, and salt-induced mobilization from "nano-colloids", appear to facilitate release of REEs into solution, which are then advected to the coastal ocean via SGD. Neodymium isotope analysis of SGD and aquifer sediment are consistent with sediment diagenesis and redox transformations of Fe(III) oxides/oxyhydroxides, as well as preferential weathering of REE-bearing minerals like apatite, as being important sources of REEs to coastal seawater. Our investigations demonstrate that geochemical reactions occurring in the studied subterranean estuaries represent a net source of light and middle REEs to coastal seawater, whereas the heavy REEs appear to be sequestered in the subterranean estuary sediment.

Rare earth elements and neodymium isotopes in sedimentary organic matter

NASA Astrophysics Data System (ADS)

Freslon, Nicolas; Bayon, Germain; Toucanne, Samuel; Bermell, Sylvain; Bollinger, Claire; Chéron, Sandrine; Etoubleau, Joel; Germain, Yoan; Khripounoff, Alexis; Ponzevera, Emmanuel; Rouget, Marie-Laure

2014-09-01

We report rare earth element (REE) and neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n = 25), estuaries (n = 18), open-ocean settings (n = 15), and cold seeps (n = 12). Sedimentary organic matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2-0.02 M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25 M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H2O2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases. The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with ΣREE = 109 ± 86 ppm (mean ± s; n = 58). The organic fractions leached from cold seep sediments display even higher concentration levels (285 ± 150 ppm; mean ± s; n = 12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea-water). The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display εNd values that typically range between the εNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit εNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition. Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation.

Swept Away: Resuspension of Bacterial Mats Regulates Benthic-Pelagic Exchange of Sulfur

NASA Astrophysics Data System (ADS)

Grant, Jonathan; Bathmann, Ulrich V.

1987-06-01

Filaments and extracellular material from colorless sulfur bacteria (Beggiatoa spp.) form extensive white sulfur mats on surface sediments of coastal, oceanic, and even deep-sea environments. These chemoautotrophic bacteria oxidize soluble reduced sulfur compounds and deposit elemental sulfur, enriching the sulfur content of surface sediment fivefold over that of deeper sediments. Laboratory flume experiments with Beggiatoa mats from an intertidal sandflat (Nova Scotia) demonstrated that even slight erosion of sediment causes a flux of 160 millimoles of sulfur per square meter per hour, two orders of magnitude greater than the flux produced by sulfur transformations involving either sulfate reduction or sulfide oxidation by benthic bacteria. These experiments indicate that resuspension of sulfur bacterial mats by waves and currents is a rapid mechanism by which sediment sulfur is recycled to the water column. Benthic communities thus lose an important storage intermediate for reduced sulfur as well as a high-quality bacterial food source for benthic grazers.

Nitrogen isotopic composition of nitrate in the South China Sea: A clue to the origin of nitrogen

NASA Astrophysics Data System (ADS)

Yang, Z.; Chen, J.; Chen, M.; Ran, L.; Li, H.; Zhu, Y.; Wang, C.; Ji, Z.; Zhang, J.; Zhang, D.

2016-02-01

Nitrogen isotopic composition of water column nitrate was measured in the South China Sea to clarify the sources of nitrogen. The δ15NNO3 value in deep water (5.4±0.2‰) was higher than the average deep oceanic δ15NNO3 ( 5‰), and a weak δ15NNO3 maximum (5.9±0.2‰) was observed at 500 m depth, matching the salinity minimum. These indicated the intrusion of the North Pacific Water which carried nitrate with a high δ15NNO3 and showed a similar δ15NNO3 distribution profile with the South China Sea. The high N* (1.74±0.23 μmol/L) combined with the low δ15NNO3 (4.7±0.2‰) at 100 m depth indicated that N2 fixation (and possibly Atmospheric Deposition) introduces new N to the surface ocean. The distribution of δ15N values of nitrate, sinking particles and surface sediment suggest that laterally-advected sediments may be a source of nitrogen to the deep ocean.

The Rusty Sink: Iron Promotes the Preservation of Organic Matter in Sediments

NASA Astrophysics Data System (ADS)

Lalonde, K. M.; Mucci, A.; Moritz, A.; Ouellet, A.; Gelinas, Y.

2011-12-01

The biogeochemical cycles of iron (Fe) and organic carbon (OC) are strongly interlinked. In oceanic waters, organic ligands have been shown to control the concentration of dissolved Fe [1], whereas in soils, solid Fe phases provide a sheltering and preservative effect for organic matter [2]. Until now however, the role of iron in the preservation of OC in sediments has not been clearly established. Here we show that 21.5 ± 8.6% of the OC in sediments is directly bound to reactive iron phases, which promote the preservation of OC in sediments. Iron-bound OC represents a global mass of 19 to 45 × 10^15 g of OC in surface marine sediments. This pool of OC is different from the rest of sedimentary OC, with 13C and nitrogen-enriched organic matter preferentially bound to Fe which suggests that biochemical fractionation occurs with OC-Fe binding. Preferential binding also affects the recovery of high molecular weight lipid biomarkers and acidic lignin oxidation products, changing the environmental message of proxies derived from these biomarkers. [1] Johnson, K. S., Gordon, R. M. & Coale, K. H. What controls dissolved iron in the world ocean? Marine Chemistry 57, 137-161 (1997). [2] Kaiser, K. & Guggenberger, G. The role of DOM sorption to mineral surfaces in the preservation of organic matter in soils. Organic Geochemistry 31, 711-725 (2000).

Microbial control of the dark end of the biological pump

PubMed Central

2014-01-01

A fraction of the carbon captured by phytoplankton in the sunlit surface ocean sinks to depth as dead organic matter and faecal material. The microbial breakdown of this material in the subsurface ocean generates carbon dioxide. Collectively, this microbially mediated flux of carbon from the atmosphere to the ocean interior is termed the biological pump. In recent decades it has become clear that the composition of the phytoplankton community in the surface ocean largely determines the quantity and quality of organic matter that sinks to depth. This settling organic matter, however, is not sufficient to meet the energy demands of microbes in the dark ocean. Two additional sources of organic matter have been identified: non-sinking organic particles of debated origin that escape capture by sediment traps and exhibit stable concentrations throughout the dark ocean, and microbes that convert inorganic carbon into organic matter. Whether these two sources can together account for the significant mismatch between organic matter consumption and supply in the dark ocean remains to be seen. It is clear, however, that the microbial community of the deep ocean works in a fundamentally different way from surface water communities. PMID:24707320

Clay mineral continental amplifier for marine carbon sequestration in a greenhouse ocean

PubMed Central

Kennedy, Martin J.; Wagner, Thomas

2011-01-01

The majority of carbon sequestration at the Earth’s surface occurs in marine continental margin settings within fine-grained sediments whose mineral properties are a function of continental climatic conditions. We report very high mineral surface area (MSA) values of 300 and 570 m2 g in Late Cretaceous black shales from Ocean Drilling Program site 959 of the Deep Ivorian Basin that vary on subcentennial time scales corresponding with abrupt increases from approximately 3 to approximately 18% total organic carbon (TOC). The observed MSA changes with TOC across multiple scales of variability and on a sample-by-sample basis (centimeter scale), provides a rigorous test of a hypothesized influence on organic carbon burial by detrital clay mineral controlled MSA. Changes in TOC also correspond with geochemical and sedimentological evidence for water column anoxia. Bioturbated intervals show a lower organic carbon loading on mineral surface area of 0.1 mg-OC m-2 when compared to 0.4 mg-OC m-2 for laminated and sulfidic sediments. Although either anoxia or mineral surface protection may be capable of producing TOC of < 5%, when brought together they produced the very high TOC (10–18%) apparent in these sediments. This nonlinear response in carbon burial resulted from minor precession-driven changes of continental climate influencing clay mineral properties and runoff from the African continent. This study identifies a previously unrecognized land–sea connection among continental weathering, clay mineral production, and anoxia and a nonlinear effect on marine carbon sequestration during the Coniacian-Santonian Oceanic Anoxic Event 3 in the tropical eastern Atlantic. PMID:21576498

Transport and transportation pathways of hazardous chemicals from solid waste disposal.

PubMed Central

Van Hook, R I

1978-01-01

To evaluate the impact of hazardous chemicals in solid wastes on man and other organisms, it is necessary to have information about amounts of chemical present, extent of exposure, and chemical toxicity. This paper addresses the question of organism exposure by considering the major physical and biological transport pathways and the physicochemical and biochemical transformations that may occur in sediments, soils, and water. Disposal of solid wastes in both terrestrial and oceanic environments is considered. Atmospheric transport is considered for emissions from incineration of solid wastes and for wind resuspension of particulates from surface waste deposits. Solid wastes deposited in terrestrial environments are subject to leaching by surface and ground waters. Leachates may then be transported to other surface waters and drinking water aquifers through hydrologic transport. Leachates also interact with natural organic matter, clays, and microorganisms in soils and sediments. These interactions may render chemical constituents in leachates more or less mobile, possibly change chemical and physical forms, and alter their biological activity. Oceanic waste disposal practices result in migration through diffusion and ocean currents. Surface area-to-volume ratios play a major role in the initial distributions of chemicals in the aquatic environment. Sediments serve as major sources and sinks of chemical contaminants. Food chain transport in both aquatic and terrestrial environments results in the movement of hazardous chemicals from lower to higher positions in the food web. Bioconcentration is observed in both terrestrial and aquatic food chains with certain elements and synthetic organics. Bioconcentration factors tend to be higher for synthetic organics, and higher in aquatic than in terrestrial systems. Biodilution is not atypical in terrestrial environments. Synergistic and antagonistic actions are common occurrences among chemical contaminants and can be particularly important toxicity considerations in aquatic environments receiving runoff from several terrestrial sources. PMID:367772

Global Paleobathymetry Reconstruction with Realistic Shelf-Slope and Sediment Wedge

NASA Astrophysics Data System (ADS)

Goswami, A.; Hinnov, L. A.; Gnanadesikan, A.; Olson, P.

2013-12-01

We present paleo-ocean bathymetry reconstructions in a 0.1°x0.1° resolution, using simple geophysical models (Plate Model Equation for oceanic lithosphere), published ages of the ocean floor (Müller et al. 2008), and modern world sediment thickness data (Divins 2003). The motivation is to create realistic paleobathymetry to understand the effect of ocean floor roughness on tides and heat transport in paleoclimate simulations. The values for the parameters in the Plate Model Equation are deduced from Crosby et al. (2006) and are used together with ocean floor age to model Depth to Basement. On top of the Depth to Basement, we added an isostatically adjusted multilayer sediment layer, as indicated from sediment thickness data of the modern oceans and marginal seas (Divins 2003). We also created another version of the sediment layer from the Müller et al. dataset. The Depth to Basement with the appropriate sediment layer together represent a realistic paleobathymetry. A Sediment Wedge was modeled to complement the reconstructed paleobathymetry by extending it to the coastlines. In this process we added a modeled Continental Shelf and Continental Slope to match the extent of the reconstructed paleobathymetry. The Sediment Wedge was prepared by studying the modern ocean where a complete history of seafloor spreading is preserved (north, south and central Atlantic Ocean, Southern Ocean between Australia-Antarctica, and the Pacific Ocean off the west coast of South America). The model takes into account the modern continental shelf-slope structure (as evident from ETOPO1/ETOPO5), tectonic margin type (active vs. passive margin) and age of the latest tectonic activity (USGS & CGMW). Once the complete ocean bathymetry is modeled, we combine it with PALEOMAP (Scotese, 2011) continental reconstructions to produce global paleoworld elevation-bathymetry maps. Modern time (00 Ma) was assumed as a test case. Using the above-described methodology we reconstructed modern ocean bathymetry, starting with age of the oceanic crust. We then reconstructed paleobathymetry for PETM (55 Ma) and Cenomanian-Turonian (90 Ma) times. For each case, the final products are: a) a global depth to basement measurement map based on plate model and EarthByte published age of the ocean crust for modern world; b) global oceanic crust bathymetry maps with a multilayer sediment layer (two versions with two types of sediment layers based on: i) observed total sediment thickness of the modern oceans and marginal seas, and ii) EarthByte-estimated global sediment data for 00 Ma); c) global oceanic bathymetry maps (two versions with two types of sediment layers) with reconstructed shelf and slope; and d) global elevation-bathymetry maps (two versions with two types of sediment layers) with continental elevations (PALEOMAP) and ocean bathymetry. Similar maps for other geological times can be produced using this method provided that ocean crustal age is known.

The biological carbon pump in the ocean: Reviewing model representations and its feedbacks on climate perturbations.

NASA Astrophysics Data System (ADS)

Hülse, Dominik; Arndt, Sandra; Ridgwell, Andy; Wilson, Jamie

2016-04-01

The ocean-sediment system, as the biggest carbon reservoir in the Earth's carbon cycle, plays a crucial role in regulating atmospheric carbon dioxide concentrations and climate. Therefore, it is essential to constrain the importance of marine carbon cycle feedbacks on global warming and ocean acidification. Arguably, the most important single component of the ocean's carbon cycle is the so-called "biological carbon pump". It transports carbon that is fixed in the light-flooded surface layer of the ocean to the deep ocean and the surface sediment, where it is degraded/dissolved or finally buried in the deep sediments. Over the past decade, progress has been made in understanding different factors that control the efficiency of the biological carbon pump and their feedbacks on the global carbon cycle and climate (i.e. ballasting = ocean acidification feedback; temperature dependant organic matter degradation = global warming feedback; organic matter sulphurisation = anoxia/euxinia feedback). Nevertheless, many uncertainties concerning the interplay of these processes and/or their relative significance remain. In addition, current Earth System Models tend to employ empirical and static parameterisations of the biological pump. As these parametric representations are derived from a limited set of present-day observations, their ability to represent carbon cycle feedbacks under changing climate conditions is limited. The aim of my research is to combine past carbon cycling information with a spatially resolved global biogeochemical model to constrain the functioning of the biological pump and to base its mathematical representation on a more mechanistic approach. Here, I will discuss important aspects that control the efficiency of the ocean's biological carbon pump, review how these processes of first order importance are mathematically represented in existing Earth system Models of Intermediate Complexity (EMIC) and distinguish different approaches to approximate biogeochemical processes in the sediments. The performance of the respective mathematical representations in constraining the importance of carbon pump feedbacks on marine biogeochemical dynamics is then compared and evaluated under different extreme climate scenarios (e.g. OAE2, Eocene) using the Earth system model 'GENIE' and proxy records. The compiled mathematical descriptions and the model results underline the lack of a complete and mechanistic framework to represent the short-term carbon cycle in most EMICs which seriously limits the ability of these models to constrain the response of the ocean's carbon cycle to past and in particular future climate change. In conclusion, this presentation will critically evaluate the approaches currently used in marine biogeochemical modelling and outline key research directions concerning model development in the future.

Inferring Source Regions and Supply Mechanisms of Iron in the Southern Ocean from Satellite Data

NASA Astrophysics Data System (ADS)

Graham, R. M.

2016-02-01

In many biogeochemical models a large shelf sediment iron flux is prescribed through the seafloor over all areas of bathymetry shallower than 1000 m. Here we infer the likely location of shelf sediment iron sources by identifying where mean annual satellite chlorophyll concentrations are enhanced over shallow bathymetry ( < 1000 m). We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry located more than 500 km from a coastline. Chlorophyll concentrations > 2 mg m-3are only found within 50 km of a continental or island coastline. These results suggest that large sedimentary iron fluxes only exist on continental or island shelves. Large sedimentary iron fluxes are unlikely to be found on isolated seamounts and submerged plateaus. We further compare satellite chlorophyll concentrations to the position of ocean fronts to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. Sharp gradients in chlorophyll concentrations are observed across western boundary currents. Large chlorophyll blooms develop where western boundary currents detach from the continental shelves and turn eastwards into the Southern Ocean. Chlorophyll concentrations are enhanced along contours of sea surface height extending off continental and island shelves. These observations support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Likewise, iron from island shelves is entrained into nearby fronts and advected downstream. Mean annual chlorophyll concentrations are very low in open ocean regions with large modelled upwelling velocities, where fronts cross over topographic ridges. These results suggests that open ocean upwelling is unlikely to deliver iron to the surface from deep sources such as hydrothermal vents.

Modern and ancient geochemical constraints on Proterozoic atmosphere-ocean redox evolution

NASA Astrophysics Data System (ADS)

Hardisty, D. S.; Horner, T. J.; Wankel, S. D.; Lu, Z.; Lyons, T.; Nielsen, S.

2017-12-01

A detailed understanding of the spatiotemporal oxygenation of Earth's atmosphere-ocean system through the Precambrian has important implications for the environments capable of sustaining early eukaryotic life and the evolving oxidant budget of subducted sediments. Proxy records suggest an anoxic Fe-rich deep ocean through much of the Precambrian and atmospheric and surface-ocean oxygenation that started in earnest at the Paleoproterozoic Great Oxidation Event (GOE). The marine photic zone represented the initial site of oxygen production and accumulation via cyanobacteria, yet our understanding of surface-ocean oxygen contents and the extent and timing of oxygen propagation and exchange between the atmosphere and deeper ocean are limited. Here, we present an updated perspective of the constraints on atmospheric, surface-ocean, and deep-ocean oxygen contents starting at the GOE. Our research uses the iodine content of Proterozoic carbonates as a tracer of dissolved iodate in the shallow ocean, a redox-sensitive species quantitatively reduced in modern oxygen minimum zones. We supplement our understanding of the ancient record with novel experiments examining the rates of iodate production from oxygenated marine environments based on seawater incubations. Combining new data from iodine with published shallow marine (Ce anomaly, N isotopes) and atmospheric redox proxies, we provide an integrated view of the vertical redox structure of the atmosphere and ocean across the Proterozoic.

Sedimentation Deposition Patterns on the Chukchi Shelf Using Radionuclide Inventories

NASA Astrophysics Data System (ADS)

Cooper, L. W.; Grebmeier, J. M.

2016-02-01

Sediment core collections and assays of the anthropogenic and natural radioisotopes, 137Cs and 210Pb, respectively, are providing long-term indications of sedimentation and current flow processes on the Chukchi and East Siberian sea continental shelf. This work, which has been integrated into interdisciplinary studies of the Chukchi Sea supported by both the US Bureau of Ocean Energy Management (COMIDA Hanna Shoal Project) and the National Oceanic and Atmospheric Administration (Russian-US Long Term Census of the Arctic, RUSALCA) includes studies of total radiocesium inventories, sedimentation rate determinations, where practical, and depths of maxima in radionuclide deposition. Shallow maxima in the activities of the anthropogenic radionuclide in sediment cores reflect areas with higher current flow (Barrow Canyon and Herald Canyon; 3-6 cm) or low sedimentation (Hanna Shoal; 1-3 cm). The first sedimentation studies from Long Strait are consistent with quiescent current conditions and steady recent sedimentation of clay particles. Elsewhere, higher and more deeply buried radionuclide inventories (> 2 mBq cm-2 at 15-17 cm depth) in the sediments correspond to areas of high particle deposition north of Bering Strait where bioturbation in productive sediments is also clearly an important influence. Radiocesium activities from bomb fallout dating to 1964 are now present at low levels (<1 mBq cm-2) at the sediment surface, but burial of the bomb era radionuclide in sediments is observed to >20 cm. Independent sedimentation rate measurements with the natural radionuclide 210Pb are largely consistent with the radiocesium measurements.

High sedimentation rates and thrust fault modulation: Insights from ocean drilling offshore the St. Elias Mountains, southern Alaska

NASA Astrophysics Data System (ADS)

Worthington, Lindsay L.; Daigle, Hugh; Clary, Wesley A.; Gulick, Sean P. S.; Montelli, Aleksandr

2018-02-01

The southern Alaskan margin offshore the St. Elias Mountains has experienced the highest recorded offshore sediment accumulation rates globally. Combined with high uplift rates, active convergence and extensive temperate glaciation, the margin provides a superb setting for evaluating competing influences of tectonic and surface processes on orogen development. We correlate results from Integrated Ocean Drilling Program (IODP) Expedition 341 Sites U1420 and U1421 with regional seismic data to determine the spatial and temporal evolution of the Pamplona Zone fold-thrust belt that forms the offshore St. Elias deformation front on the continental shelf. Our mapping shows that the pattern of active faulting changed from distributed across the shelf to localized away from the primary glacial depocenter over ∼300-780 kyrs, following an order-of-magnitude increase in sediment accumulation rates. Simple Coulomb stress calculations show that the suppression of faulting is partially controlled by the change in sediment accumulation rates which created a differential pore pressure regime between the underlying, faulted strata and the overlying, undeformed sediments.

Physical characteristics of summer sea ice across the Arctic Ocean

USGS Publications Warehouse

Tucker, W. B.; Gow, A.J.; Meese, D.A.; Bosworth, H.W.; Reimnitz, E.

1999-01-01

Sea ice characteristics were investigated during July and August on the 1994 transect across the Arctic Ocean. Properties examined from ice cores included salinity, temperature, and ice structure. Salinities measured near zero at the surface, increasing to 3-4??? at the ice-water interface. Ice crystal texture was dominated by columnar ice, comprising 90% of the ice sampled. Surface albedos of various ice types, measured with radiometers, showed integrated shortwave albedos of 0.1 to 0.3 for melt ponds, 0.5 for bare, discolored ice, and 0.6 to 0.8 for a deteriorated surface or snow-covered ice. Aerial photography was utilized to document the distribution of open melt ponds, which decreased from 12% coverage of the ice surface in late July at 76??N to almost none in mid-August at 88??N. Most melt ponds were shallow, and depth bore no relationship to size. Sediment was pervasive from the southern Chukchi Sea to the north pole, occurring in bands or patches. It was absent in the Eurasian Arctic, where it had been observed on earlier expeditions. Calculations of reverse trajectories of the sediment-bearing floes suggest that the southernmost sediment was entrained during ice formation in the Beaufort Sea while more northerly samples probably originated in the East Siberian Sea, some as far west as the New Siberian Islands.

Planktic foraminifera form their shells by attachment of metastable carbonate particles

NASA Astrophysics Data System (ADS)

Wirth, R.; Jacob, D. E.; Eggins, S.

2016-12-01

Planktic foraminifera shells contribute up to half the inorganic carbon exported from the surface ocean to the seafloor. Their tiny calcium carbonate shells are preserved in sediments as calcite, and provide our most valuable geochemical archive of changes surface ocean conditions and climate spanning the last 100 million years. Here we show the shells of living planktic foraminifers Orbulina universa and Neogloboquadrina dutertrei consist of nano-particulate vaterite and amorphous calcium carbonate. This indicates formation via a non-classical crystallization pathway involving metastable carbonate intermediate phases before transforming to calcite, and requires a new perspective on how geochemical proxies are incorporated into planktic foraminifer shells. Our findings indicate planktic foraminifer shells could be far more susceptible to dissolution and ocean acidification than previously thought, and account for unexpected shell dissolution above the calcite saturation horizon in the ocean, which is a major uncertainty in modelling oceanic carbon fluxes.

Characterizing Cretaceous Glaciation Events: K-Ar Ages of Southern Ocean Sediments

NASA Astrophysics Data System (ADS)

Wright, M. A.; Hemming, S. R.; Barbeau, D. L.; Torfstein, A.; Pierce, E. L.; Williams, T.; McManus, J. F.; Gombiner, J.

2012-12-01

Evidence from paleosols and carbonate weathering models suggest that the Late Cretaceous had a supergreenhouse climate due to atmospheric CO2 concentrations two to four times greater than modern levels, tropical sea surface temperatures exceeding 35°C, and high-latitude temperatures exceeding 20°C. Despite this warmth, the Late Cretaceous was apparently punctuated by large (>25 m) and rapid (<<1 million year) sea-level changes, as recorded by marginal marine stratigraphic architectures and pelagic stable isotope compositions. The magnitude and tempo of these changes suggest a glacio-eustatic control, presumably from the growth and decay of continental ice sheets on Antarctica. Because continental glaciation tends to increase the weathering of bedrock and production of sediment delivered to the oceans, circum-Antarctic marine sediment flux would be expected to increase during periods of glaciation. In order to identify a Late Cretaceous glaciation signal from such marine records, we must first constrain the compositional signal of continental detritus in marine sediments. Here we report the results of downcore K-Ar analysis of the terrigenous sediments of Quaternary Weddell Sea cores PS1170-1 and PS1388-3 in order to identify the compositional signature of continent-derived detritus deposited in the Weddell Sea during a known glacial period. Further, we use our K-Ar analyses of circum-Antarctic Quaternary sediment cores to pinpoint potential sediment source areas. Having constrained this glaciation signal, we also present preliminary K-Ar and Sm-Nd analysis of the Campanian-Maastrictian boundary event (69 Ma) at Ocean Drilling Project site 690C to assess the controversial hypothesis of Late Cretaceous glaciation of Antarctica.

A depocenter of organic matter at 7800 m depth in the SE Pacific Ocean

NASA Astrophysics Data System (ADS)

Danovaro, R.; Della Croce, N.; Dell'Anno, A.; Pusceddu, A.

2003-12-01

The Atacama trench, the deepest ecosystem of the southern Pacific Ocean (ca. 8000 m depth) was investigated during the Atacama Trench International Expedition. Sediments, collected at three bathyal stations (1040-1355 m depth) and at a hadal site (7800 m) were analyzed for organic matter quantity and biochemical composition (in terms of phytopigments, proteins, carbohydrates and lipids), bacterial abundance, biomass and carbon production and extracellular enzymatic activities. Functional chlorophyll- a (18.0±0.10 mg m -2), phytodetritus (322.2 mg m -2) and labile organic carbon (16.9±4.3 g C m -2) deposited on surface sediments at hadal depth (7800 m) reached concentrations similar to those encountered in highly productive shallow coastal areas. High values of bacterial C production and aminopeptidase activity were also measured (at in situ temperature and 1 atm). The chemical analyses of the Atacama hadal sediments indicate that this trench behaves as a deep oceanic trap for organic material. We hypothesize that, despite the extreme physical conditions, benthic microbial processes might be accelerated as a result of the organic enrichment.

Uranium Stable Isotopes: A Proxy For Productivity Or Ocean Oxygenation?

NASA Astrophysics Data System (ADS)

Severmann, S.

2015-12-01

Uranium elemental abundances in sediments have traditionally been used to reconstruct primary productivity and carbon flux in the ocean. 238U/235U isotope compositions, in contrast, are currently understood to reflect the extent of bottom water anoxia in the ocean. A review of our current understanding of authigenic U enrichment mechanism into reducing sediments suggests that a revision of this interpretation is warranted. Specifically, the current interpretation of U isotope effects in suboxic vs. anoxic deposits has not taken into account the well-documented linear relationship with organic C burial rates. Although organic C rain rates (i.e., surface productivity) and bottom water oxygenation are clearly related, distinction between these two environmental controls is conceptually important as it relates to the mechanism of enhanced C burial and ultimately the strength of the biological pump. Here we will review new and existing data to test the hypothesis that the isotope composition of authigenic U in reducing sediments are best described by their relationship with parameters related to organic carbon delivery and burial, rather than bottom water oxygen concentration.

Underwater microscope for measuring spatial and temporal changes in bed-sediment grain size

USGS Publications Warehouse

Rubin, David M.; Chezar, Henry; Harney, Jodi N.; Topping, David J.; Melis, Theodore S.; Sherwood, Christopher R.

2007-01-01

For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the laboratory for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches.

Underwater Microscope for Measuring Spatial and Temporal Changes in Bed-Sediment Grain Size

USGS Publications Warehouse

Rubin, David M.; Chezar, Henry; Harney, Jodi N.; Topping, David J.; Melis, Theodore S.; Sherwood, Christopher R.

2006-01-01

For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the lab for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in-situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches.

Recent changes of sediment flux to the western Pacific Ocean from major rivers in East and Southeast Asia

NASA Astrophysics Data System (ADS)

Wang, Houjie; Saito, Yoshiki; Zhang, Yong; Bi, Naishuang; Sun, Xiaoxiao; Yang, Zuosheng

2011-09-01

The five largest rivers in East and Southeast Asia (Yellow, Yangtze, Pearl, Red and Mekong) are important contributors of terrigenous sediment to the western Pacific Ocean. Although they have annually delivered ~ 2000 × 10 9 kg of sediment to the ocean since 1000 yr BP, they presently contribute only ~ 600 × 10 9 kg/yr, which is reverting to a level typical of the relatively undisturbed watersheds before the rise in human activities in East and Southeast Asia at 2000 yr BP. During the most recent decades flow regulation by dams and sediment entrapment by reservoirs, as well as human-influenced soil erosion in the river basins, have sharply reduced the sediment delivered from the large river basins to the ocean. We constructed a time series of data on annual water discharges and sediment fluxes from these large rivers to the western Pacific Ocean covering the period 1950-2008. These data indicate that the short-term (interannual scale) variation of sediment flux is dominated by natural climatic oscillations such as the El Niño/La Niña cycle and that anthropogenic causes involving dams and land use control the long-term (decadal scale) decrease in sediment flux to the ocean. In contrast to the relatively slow historical increase in sediment flux during the period 2000-1000 yr BP, the recent sediment flux has been decreased at an accelerating rate over centennial scales. The alterations of these large river systems by both natural and anthropogenic forcing present severe environmental challenges in the coastal ocean, including the sinking of deltas and declines in coastal wetland areas due to the decreasing sediment supply. Our work thus provides a regional perspective on the large river-derived sediment flux to the ocean over millennial and decadal scales, which will be important for understanding and managing the present and future trends of delivery of terrigenous sediment to the ocean in the context of global change.

Prokaryotic responses to hydrostatic pressure in the ocean--a review.

PubMed

Tamburini, Christian; Boutrif, Mehdi; Garel, Marc; Colwell, Rita R; Deming, Jody W

2013-05-01

Effects of hydrostatic pressure on pure cultures of prokaryotes have been studied extensively but impacts at the community level in the ocean are less well defined. Here we consider hydrostatic pressure effects on natural communities containing both unadapted (piezosensitive) prokaryotes originating from surface water and adapted (including piezophilic) prokaryotes from the deep sea. Results from experiments mimicking pressure changes experienced by particle-associated prokaryotes during their descent through the water column show that rates of degradation of organic matter (OM) by surface-originating microorganisms decrease with sinking. Analysis of a much larger data set shows that, under stratified conditions, deep-sea communities adapt to in situ conditions of high pressure, low temperature and low OM. Measurements made using decompressed samples and atmospheric pressure thus underestimate in situ activity. Exceptions leading to overestimates can be attributed to deep mixing events, large influxes of surface particles, or provision of excessive OM during experimentation. The sediment-water interface, where sinking particles accumulate, will be populated by a mixture of piezosensitive, piezotolerant and piezophilic prokaryotes, with piezophilic activity prevailing deeper within sediment. A schematic representation of how pressure shapes prokaryotic communities in the ocean is provided, allowing a reasonably accurate interpretation of the available activity measurements. © 2013 Society for Applied Microbiology and Blackwell Publishing Ltd.

Phosphorus in the ocean and marine sediments: similarities between present and past processes

NASA Astrophysics Data System (ADS)

Tamburini, F.

2004-12-01

Because phosphorus (P) is an essential nutrient, geochemical research has focused over the years on understanding the different aspects of the P cycle in the oceans, from the global to microbial scale. In the last 40 years, giant phosphorite deposits were largely studied, and their episodic occurrence in the geological record was alternatively interpreted as the product of shallow water environments, high productivity, low-sedimentation rates, and/or changes in sea level. Although research has focused more recently on the oceanic burial fluxes and residence time of P, there is still a general agreement on the need for more data. Thanks to new analytical techniques, allowing the detection of small quantities of phosphate (on the order of ?mol/g), and to the increased availability of sediment cores, P-bearing sediments have been found everywhere beneath the ocean floor. This finding has changed our understanding of P behavior in the ocean, and is redefining the role of P as an important nutrient, for example, over glacial-interglacial time scales. I will present glacial-interglacial reconstructions of burial and benthic fluxes of P, with the goal of understanding to which extent the P cycle is linked to global processes. The data, averaged to the whole ocean, indicate that burial fluxes of reactive P during glacial times are not considerably lower than during interglacials. This observation could lead to the conclusion that no changes occurred in P cycle on glacial-interglacial timescales and, therefore, that C cycle and climate variations were independent of P cycle. However, when the benthic flux estimates are taken into account, a different picture arises. During low sea level periods, the redistribution of sediments from shallow to deep waters, due to the reduction of the continental margin surface, fostered P regeneration during settling of organic matter. Even if P burial fluxes remain fairly constant, the oceanic phosphate inventory of glacial bottom waters was probably higher. On a different time scale, the shift in P behavior between glacial and interglacial periods could have been promoted by conditions similar to those that led to the formation of phosphorite deposits, which are abundant in the geological past but rare today.

Preliminary study on detection sediment contamination in soil affected by the Indian Ocean giant tsunami 2004 in Aceh, Indonesia using laser-induced breakdown spectroscopy (LIBS)

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

Idris, Nasrullah, E-mail: nasrullah.idris@unsyiah.ac.id; Ramli, Muliadi; Hedwig, Rinda

This work is intended to asses the capability of LIBS for the detection of the tsunami sediment contamination in soil. LIBS apparatus used in this work consist of a laser system and an optical multichannel analyzer (OMA) system. The soil sample was collected from in Banda Aceh City, Aceh, Indonesia, the most affected region by the giant Indian Ocean tsunami 2004. The laser beam was focused onto surface of the soil pellet using a focusing lens to produce luminous plasma. The experiment was conducted under air as surrounding gas at 1 atmosphere. The emission spectral lines from the plasma weremore » detected by the OMA system. It was found that metal including heavy metals can surely be detected, thus implying the potent of LIBS technique as a fast screening tools of tsunami sediment contamination.« less

A 600-ka Arctic sea-ice record from Mendeleev Ridge based on ostracodes

USGS Publications Warehouse

Cronin, Thomas M.; Polyak, L.V.; Reed, D.; Kandiano, E. S.; Marzen, R. E.; Council, E. A.

2013-01-01

Arctic paleoceanography and sea-ice history were reconstructed from epipelagic and benthic ostracodes from a sediment core (HLY0503-06JPC, 800 m water depth) located on the Mendeleev Ridge, Western Arctic Ocean. The calcareous microfaunal record (ostracodes and foraminifers) covers several glacial/interglacial cycles back to estimated Marine Isotope Stage 13 (MIS 13, ∼500 ka) with an average sedimentation rate of ∼0.5 cm/ka for most of the stratigraphy (MIS 5–13). Results based on ostracode assemblages and an unusual planktic foraminiferal assemblage in MIS 11 dominated by a temperate-water species Turborotalita egelida show that extreme interglacial warmth, high surface ocean productivity, and possibly open ocean convection characterized MIS 11 and MIS 13 (∼400 and 500 ka, respectively). A major shift in western Arctic Ocean environments toward perennial sea ice occurred after MIS 11 based on the distribution of an ice-dwelling ostracode Acetabulastoma arcticum. Spectral analyses of the ostracode assemblages indicate sea ice and mid-depth ocean circulation in western Arctic Ocean varied primarily at precessional (∼22 ka) and obliquity (∼40 ka) frequencies.

Global Ocean Sedimentation Patterns: Plate Tectonic History Versus Climate Change

NASA Astrophysics Data System (ADS)

Goswami, A.; Reynolds, E.; Olson, P.; Hinnov, L. A.; Gnanadesikan, A.

2014-12-01

Global sediment data (Whittaker et al., 2013) and carbonate content data (Archer, 1996) allows examination of ocean sedimentation evolution with respect to age of the underlying ocean crust (Müller et al., 2008). From these data, we construct time series of ocean sediment thickness and carbonate deposition rate for the Atlantic, Pacific, and Indian ocean basins for the past 120 Ma. These time series are unique to each basin and reflect an integrated response to plate tectonics and climate change. The goal is to parameterize ocean sedimentation tied to crustal age for paleoclimate studies. For each basin, total sediment thickness and carbonate deposition rate from 0.1 x 0.1 degree cells are binned according to basement crustal age; area-corrected moments (mean, variance, etc.) are calculated for each bin. Segmented linear fits identify trends in present-day carbonate deposition rates and changes in ocean sedimentation from 0 to 120 Ma. In the North and South Atlantic and Indian oceans, mean sediment thickness versus crustal age is well represented by three linear segments, with the slope of each segment increasing with increasing crustal age. However, the transition age between linear segments varies among the three basins. In contrast, mean sediment thickness in the North and South Pacific oceans are numerically smaller and well represented by two linear segments with slopes that decrease with increasing crustal age. These opposing trends are more consistent with the plate tectonic history of each basin being the controlling factor in sedimentation rates, rather than climate change. Unlike total sediment thickness, carbonate deposition rates decrease smoothly with crustal age in all basins, with the primary controls being ocean chemistry and water column depth.References: Archer, D., 1996, Global Biogeochem. Cycles 10, 159-174.Müller, R.D., et al., 2008, Science, 319, 1357-1362.Whittaker, J., et al., 2013, Geochem., Geophys., Geosyst. DOI: 10.1002/ggge.20181

Ocean color imagery: Coastal zone color scanner

NASA Technical Reports Server (NTRS)

Hovis, W. A.

1975-01-01

Investigations into the feasibility of sensing ocean color from high altitude for determination of chlorophyll and sediment distributions were carried out using sensors on NASA aircraft, coordinated with surface measurements carried out by oceanographic vessels. Spectrometer measurements in 1971 and 1972 led to development of an imaging sensor now flying on a NASA U-2 and the Coastal Zone Color Scanner to fly on Nimbus G in 1978. Results of the U-2 effort show the imaging sensor to be of great value in sensing pollutants in the ocean.

An alternative model for CaCO3 over-shooting during the PETM: Biological carbonate compensation

NASA Astrophysics Data System (ADS)

Luo, Yiming; Boudreau, Bernard P.; Dickens, Gerald R.; Sluijs, Appy; Middelburg, Jack J.

2016-11-01

Decreased CaCO3 content of deep-sea sediments argues for rapid and massive acidification of the oceans during the Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma BP). In the course of the subsequent recovery from this acidification, sediment CaCO3 content came to exceed pre-PETM levels, known as over-shooting. Past studies have largely attributed the latter to increased alkalinity input to the oceans via enhanced weathering, but this ignores potentially important biological factors. We successfully reproduce the CaCO3 records from Walvis Ridge in the Atlantic Ocean, including over-shooting, using a biogeochemical box model. Replication of the CaCO3 records required: 1) introduction of a maximum of ∼6500 GtC of CO2 directly into deep-ocean waters or ∼8000 GtC into the atmosphere, 2) limited deep-water exchange between the Indo-Atlantic and Pacific oceans, 3) the disappearance of sediment bioturbation during a portion of the PETM, and 4) most central to this study, a ∼50% reduction in net CaCO3 production, during acidification. In our simulations, over-shooting is an emergent property, generated at constant alkalinity input (no weathering feedback) as a consequence of attenuated CaCO3 productivity. This occurs because lower net CaCO3 production from surface waters allows alkalinity to build-up in the deep oceans (alkalinization), thus promoting deep-water super-saturation. Restoration of CaCO3 productivity later in the PETM, particularly in the Indo-Atlantic Ocean, leads to greater accumulation of CaCO3, ergo over-shooting, which returns the ocean to pre-PETM conditions over a time scale greater than 200 ka.

Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age

NASA Astrophysics Data System (ADS)

Wang, Xingchen Tony; Sigman, Daniel M.; Prokopenko, Maria G.; Adkins, Jess F.; Robinson, Laura F.; Hines, Sophia K.; Chai, Junyi; Studer, Anja S.; Martínez-García, Alfredo; Chen, Tianyu; Haug, Gerald H.

2017-03-01

The Southern Ocean regulates the ocean’s biological sequestration of CO2 and is widely suspected to underpin much of the ice age decline in atmospheric CO2 concentration, but the specific changes in the region are debated. Although more complete drawdown of surface nutrients by phytoplankton during the ice ages is supported by some sediment core-based measurements, the use of different proxies in different regions has precluded a unified view of Southern Ocean biogeochemical change. Here, we report measurements of the 15N/14N of fossil-bound organic matter in the stony deep-sea coral Desmophyllum dianthus, a tool for reconstructing surface ocean nutrient conditions. The central robust observation is of higher 15N/14N across the Southern Ocean during the Last Glacial Maximum (LGM), 18-25 thousand years ago. These data suggest a reduced summer surface nitrate concentration in both the Antarctic and Subantarctic Zones during the LGM, with little surface nitrate transport between them. After the ice age, the increase in Antarctic surface nitrate occurred through the deglaciation and continued in the Holocene. The rise in Subantarctic surface nitrate appears to have had both early deglacial and late deglacial/Holocene components, preliminarily attributed to the end of Subantarctic iron fertilization and increasing nitrate input from the surface Antarctic Zone, respectively.

Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age

PubMed Central

Sigman, Daniel M.; Prokopenko, Maria G.; Adkins, Jess F.; Robinson, Laura F.; Hines, Sophia K.; Chai, Junyi; Studer, Anja S.; Martínez-García, Alfredo; Chen, Tianyu; Haug, Gerald H.

2017-01-01

The Southern Ocean regulates the ocean’s biological sequestration of CO2 and is widely suspected to underpin much of the ice age decline in atmospheric CO2 concentration, but the specific changes in the region are debated. Although more complete drawdown of surface nutrients by phytoplankton during the ice ages is supported by some sediment core-based measurements, the use of different proxies in different regions has precluded a unified view of Southern Ocean biogeochemical change. Here, we report measurements of the 15N/14N of fossil-bound organic matter in the stony deep-sea coral Desmophyllum dianthus, a tool for reconstructing surface ocean nutrient conditions. The central robust observation is of higher 15N/14N across the Southern Ocean during the Last Glacial Maximum (LGM), 18–25 thousand years ago. These data suggest a reduced summer surface nitrate concentration in both the Antarctic and Subantarctic Zones during the LGM, with little surface nitrate transport between them. After the ice age, the increase in Antarctic surface nitrate occurred through the deglaciation and continued in the Holocene. The rise in Subantarctic surface nitrate appears to have had both early deglacial and late deglacial/Holocene components, preliminarily attributed to the end of Subantarctic iron fertilization and increasing nitrate input from the surface Antarctic Zone, respectively. PMID:28298529

A Non-Equilibrium Sediment Transport Model for Coastal Inlets and Navigation Channels

DTIC Science & Technology

2011-01-01

exchange of water , sediment, and nutrients between estuaries and the ocean. Because of the multiple interacting forces (waves, wind, tide, river...in parallel using OpenMP. The CMS takes advantage of the Surface- water Modeling System (SMS) interface for grid generation and model setup, as well...as for plotting and post- processing (Zundel, 2000). The circulation model in the CMS (called CMS-Flow) computes the unsteady water level and

Predicting Sediment Thickness on Vanished Ocean Crust Since 200 Ma

NASA Astrophysics Data System (ADS)

Dutkiewicz, A.; Müller, R. D.; Wang, X.; O'Callaghan, S.; Cannon, J.; Wright, N. M.

2017-12-01

Tracing sedimentation through time on existing and vanished seafloor is imperative for constraining long-term eustasy and for calculating volumes of subducted deep-sea sediments that contribute to global geochemical cycles. We present regression algorithms that incorporate the age of the ocean crust and the mean distance to the nearest passive margin to predict sediment thicknesses and long-term decompacted sedimentation rates since 200 Ma. The mean sediment thickness decreases from ˜220 m at 200 Ma to a minimum of ˜140 m at 130 Ma, reflecting the replacement of old Panthalassic ocean floor with young sediment-poor mid-ocean ridges, followed by an increase to ˜365 m at present-day. This increase reflects the accumulation of sediments on ageing abyssal plains proximal to passive margins, coupled with a decrease in the mean distance of any parcel of ocean crust to the nearest passive margin by over 700 km, and a doubling of the total passive margin length at present-day. Mean long-term sedimentation rates increase from ˜0.5 cm/ky at 160 Ma to over 0.8 cm/ky today, caused by enhanced terrigenous sediment influx along lengthened passive margins, superimposed by the onset of ocean-wide carbonate sedimentation. Our predictive algorithms, coupled to a plate tectonic model, provide a framework for constraining the seafloor sediment-driven eustatic sea-level component, which has grown from ˜80 to 210 m since 120 Ma. This implies a long-term sea-level rise component of 130 m, partly counteracting the contemporaneous increase in ocean basin depth due to progressive crustal ageing.

An operation manual for a time-series, storm-activated suspended sediment sampler deployed in the coastal ocean: function, maintenance, and testing procedures

USGS Publications Warehouse

Rendigs, Richard R.; Bothner, Michael H.

2004-01-01

This manual describes the operation and testing procedures for two models of a multi-port suspended sediment sampler that are moored in the coastal ocean and that collect samples on a programmable time schedule that can be interrupted to collect during a storm. The ability to sense and collect samples before, during, and after the height of a storm is a unique feature of these instruments because it provides samples during conditions when it is difficult or impossible to sample from a surface ship. The sensors used to trigger storm sampling are a transmissometer or a pressure sensor. The purpose of such samples is to assess composition and concentration of sediment resuspended from the seafloor during storms and subsequently transported within the coastal system. Both light transmission and the standard deviation of pressure from surface waves correlate with the passage of major storms. The instruments successfully identified the onset of storms and collected samples before, during, and after the storm maximum as programmed. The accuracy of determining suspended matter concentrations collected by the sediment sampler has not been fully evaluated. Preliminary laboratory tests using a suspension of muddy sediment collected in a near-bottom sediment trap yielded excellent results. However in laboratory tests with different sediment types, the suspended matter concentrations determined with these samplers became less accurate with increasing average grain size. Future calibration work is necessary and should be conducted in a facility that ideally has a water depth of at least 30 feet to prevent cavitation of the pump that draws sea water through the filters. The test facility should also have the capability for adding suspended matter of known composition and concentration to a fixed volume of seawater that is well mixed.

What governs the enrichment of Pb in the continental crust? An answer from the Mexican Volcanic Belt

NASA Astrophysics Data System (ADS)

Goldstein, S. L.; Lagatta, A.; Langmuir, C. H.; Straub, S. M.; Martin-Del-Pozzo, A.

2009-12-01

One of Al Hofmann’s many important contributions to our understanding of geochemical cycling in the Earth is the observation that Pb behaves like the light rare earth elements Ce and Nd during melting to form oceanic basalts, but is enriched in the continental crust compared to the LREE by nearly an order of magnitude (Hofmann et al. 1986). This is unusual behavior, and has been called one of the Pb paradoxes, since in most cases, the ratios of elements are effectively the same in the continental crust and oceanic basalts if they show similar mantle melting behavior. One of several mechanisms suggested to mediate this special enrichment is hydrothermal circulation at ocean ridges, which preferentially transports Pb compared to the REE from the interior of the ocean crust to the surface. We confirm the importance of hydrothermal processes at the East Pacific to mediate Pb enrichment at the Trans-Mexican Volcanic Belt (TMVB, through comparison of Pb isotope and Ce/Pb ratios of TMVB lavas with sediments from DSDP Site 487 near the Middle America trench. The lavas of the Trans-Mexican Volcanic Belt include “high Nb” alkali basalts (HNAB), whose trace element patterns lack subduction signatures. The HNAB basalts and hydrothermally affected sediments from DSDP 487, form end-members that bound calcalkaline lavas from volcanoes Colima, Toluca, Popocatépetl, and Malinche in Ce/Pb versus Pb isotope space. The HNAB represent the high Ce/Pb and high Pb-isotope end-member. The hydrothermal sediments have Pb isotopes like Pacific MORB but Ce/Pb ratios typical of the arcs and the continental crust, and an order of magnitude lower than MORB. No analyzed calcalkaline lavas are have compositions outside of the bounds formed by the HNAB and the hydrothermal sediments. The Ce/Pb and Pb isotope ratios show that the calcalkaline lava compositions are inconsistent with contributions from HNAB and EPR MORB, rather the contributions are from HNAB upper mantle and subducted hydrothermal sediments. The Trans-Mexican Volcanic Belt data confirm the two-step process of Pb enrichment in the arc lavas (and more generally in the continental crust). In the first step, hydrothermal processes at the East Pacific Rise preferentially transport Pb from the basaltic oceanic crust to surface sediments. In the second step, during subduction, these sediments are the main source of asthenospheric mantle-derived Pb to the lavas. Our data also confirm the importance of subduction contributions to the Quaternary Mexican arc, despite the >40 km thick continental crust. Ref: Hofmann et al. (1986) EPSL 79 p. 33-45.

Chromium isotopes in siliciclastic sediments and sedimentary rocks as a proxy for Earth surface redox

NASA Astrophysics Data System (ADS)

Reinhard, C. T.; Planavsky, N. J.; Wang, X.; Owens, J. D.; Johnson, T. M.; Fischer, W. W.; Lyons, T. W.

2013-12-01

Chromium (Cr) isotopes are an emerging and potentially promising proxy for tracking redox processes at Earth's surface. However, recent efforts to reconstruct the Cr isotope record through time have primarily focused on sporadically deposited iron-rich chemical sediments, with large temporal gaps and limited capacity to explore the Cr isotope record relative to modern and recent marine processes. However, the basic inorganic chemistry of Cr suggests that anoxic marine basins factor prominently in the global Cr cycle, and that likewise sediments deposited within anoxic basins may offer an unexplored Cr isotope archive throughout Earth's history. We present authigenic δ53Cr data from sediments of the Cariaco Basin, Venezuela--a ';type' environment on the modern Earth for large, perennially anoxic basins with relatively strong hydrological connections to the global ocean. Combined with currently available constraints on the δ53Cr composition of modern Atlantic seawater, these data are consistent with the hypothesis that anoxic marine basins can serve as a chemical archive of the first-order features of seawater δ53Cr variation. We employ a simple quantitative model to explore the implications of this hypothesis for global Cr isotope mass balance and the possible utility of authigenic δ53Cr in anoxically deposited siliciclastic sediments and sedimentary rocks as a global paleoredox proxy. Our focus is a basic analysis of the primary controls on seawater δ53Cr as related to both the marine redox landscape and the processes involved in the weathering and aqueous-particulate transport of Cr at Earth's surface. As a case study, we provide analysis of new bulk δ53Cr data through a Cretaceous Oceanic Anoxic Event (OAE-2), which shows a well-defined ~1.0‰ negative excursion during the event coupled with evidence for a drawdown of the marine Cr reservoir. We present a conceptual model to explain these observations, and interpret this shift to suggest a shutdown of internal oceanic Cr isotope fractionation associated with a perturbation to benthic marine redox.

Internal Waves, Western Indian Ocean

NASA Image and Video Library

1991-12-01

STS044-79-077 (24 Nov.-1 Dec. 1991) --- This photograph, captured from the Earth-orbiting Space Shuttle Atlantis, shows sunglint pattern in the western tropical Indian Ocean. Several large internal waves reflect around a shallow area on the sea floor. NASA scientists studying the STS-44 photography believe the shallow area to be a sediment (a submerged mountain) on top of the Mascarene Plateau, located northeast of Madagascar at approximately 5.6 degrees south latitude and 55.7 degrees east longitude. Internal waves are similar to surface ocean waves, except that they travel inside the water column along the boundary between water layers of different density. At the surface, their passage is marked on the sea surface by bands of smooth and rough water. These bands appear in the sunglint pattern as areas of brighter or darker water. NASA scientists point out that, when the waves encounter an obstacle, such as a near-surface seamount, they bend or refract around the obstacle in the same manner as surface waves bend around an island or headland.

Exploring Microbial Life in Oxic Sediments Underlying Oligotrophic Ocean Gyres

NASA Astrophysics Data System (ADS)

Ziebis, W.; Orcutt, B.; Wankel, S. D.; D'Hondt, S.; Szubin, R.; Kim, J. N.; Zengler, K.

2015-12-01

Oxygen, carbon and nutrient availability are defining parameters for microbial life. In contrast to organic-rich sediments of the continental margins, where high respiration rates lead to a depletion of O2 within a thin layer at the sediment surface, it was discovered that O2 penetrates several tens of meters into organic-poor sediments underlying oligotrophic ocean gyres. In addition, nitrate, another important oxidant, which usually disappears rapidly with depth in anoxic sediments, tends to accumulate above seawater concentrations in the oxic subsurface, reflecting the importance of nitrogen cycling processes, including both nitrification and denitrification. Two IODP drilling expeditions were vital for exploring the nature of the deep subsurface beneath oligotrophic ocean gyres, expedition 329 to the South Pacific Gyre (SPG) and expedition 336 to North Pond, located on the western flank of the Mid-Atlantic ridge beneath the North Atlantic Gyre. Within the ultra-oligotrophic SPG O2 penetrates the entire sediment column from the sediment-water interface to the underlying basement to depths of > 75 m. At North Pond, a topographic depression filled with sediment and surrounded by steep basaltic outcrops, O2 penetrates deeply into the sediment (~ 30 m) until it eventually becomes depleted. O2 also diffuses upward into the sediment from seawater circulating within the young crust underlying the sediment, resulting in a deep oxic layer several meters above the basalt. Despite low organic carbon contents microbial cells persist throughout the entire sediment column within the SPG (> 75 m) and at North Pond, albeit at low abundances. We explored the nature of the subsurface microbial communities by extracting intact cells from large volumes of sediment obtained from drill cores of the two expeditions. By using CARD-FiSH, amplicon (16s rRNA) and metagenome sequencing we shed light on the phylogenetic and functional diversity of the elusive communities residing in the deep oxic sediments of these two different areas. Given the global extent of this oxic subsurface studies of the diversity and metabolic potential of its biome, together with the analyses of porewater geochemical and isotopic composition, are beginning to reveal its role in global biogeochemical cycles.

Cenozoic marine geochemistry of thallium deduced from isotopic studies of ferromanganese crusts and pelagic sediments

USGS Publications Warehouse

Rehkamper, M.; Frank, M.; Hein, J.R.; Halliday, A.

2004-01-01

Cenozoic records of Tl isotope compositions recorded by ferromanganese (Fe-Mn) crusts have been obtained. Such records are of interest because recent growth surfaces of Fe-Mn crusts display a nearly constant Tl isotope fractionation relative to seawater. The time-series data are complemented by results for bulk samples and leachates of various marine sediments. Oxic pelagic sediments and anoxic marine deposits can be distinguished by their Tl isotope compositions. Both pelagic clays and biogenic oozes are typically characterized by ??205Tl greater than +2.5, whereas anoxic sediments have ??205Tl of less than -1.5 (??205Tl is the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). Leaching experiments indicate that the high ??205Tl values of oxic sediments probably reflect authigenic Fe-Mn oxyhydroxides. Time-resolved Tl isotope compositions were obtained from six Fe-Mn crusts from the Atlantic, Indian, and Pacific oceans and a number of observations indicate that these records were not biased by diagenetic alteration. Over the last 25 Myr, the data do not show isotopic variations that significantly exceed the range of Tl isotope compositions observed for surface layers of Fe-Mn crusts distributed globally (??205 Tl=+12.8??1.2). This indicates that variations in deep-ocean temperature were not recorded by Tl isotopes. The results most likely reflect a constant Tl isotope composition for seawater. The growth layers of three Fe-Mn crusts that are older than 25 Ma show a systematic increase of ??205Tl with decreasing age, from about +6 at 60-50 Ma to about +12 at 25 Ma. These trends are thought to be due to variations in the Tl isotope composition of seawater, which requires that the oceans of the early Cenozoic either had smaller output fluxes or received larger input fluxes of Tl with low ??205Tl. Larger inputs of isotopically light Tl may have been supplied by benthic fluxes from reducing sediments, rivers, and/or volcanic emanations. Alternatively, the Tl isotope trends may reflect the increasing importance of Tl fluxes to altered ocean crust through time. ?? 2004 Elsevier B.V. All rights reserved.

The observation of underwater frazil ice formation and upward sediment transport in an Arctic polynya in the Chukchi Sea

NASA Astrophysics Data System (ADS)

Ito, M.; Ohshima, K. I.; Fukamachi, Y.; Simizu, D.; Mahoney, A. R.; Eicken, H.

2016-12-01

Sea ice is a great contributor to energy- and salt-budget, dense water formation and bio-related material cycle in the polar ocean. In coastal polynya, the ice production becomes maximum when open water is maintained owing to underwater frazil ice formation associated with supercooling. In addition, an interaction between frazil ice and re-suspended sediment can be a major process of sediment incorporation into sea ice. Although these process have been reported from laboratory experiments and numerical simulations, in-situ observations have been limited because the under-ice observation is logistically challenging and detection methods of frazil ice and sedimentary particles have not been well established. Since 2009, mooring observations with ADCPs, Ice-Profiling Sonars and C-T recorders have been continuously carried out off Barrow in the Chukchi Sea, through a collaboration between Hokkaido University and University of Alaska Fairbanks. Recently, some in-situ measurements reported the possibility that an ADCP can detect frazil ice and re-suspended sediment using acoustic backscatter strength data. Thus, we analyzed the ADCP data in the Chukchi Sea, focusing on underwater frazil ice formation and upward sediment transport. In winter, polynyas were formed episodically around the observational sites several times by offshore-ward strong winds of > 10 m/s. During these polynya events, surface-intensified signals were detected throughout the water column at two sites with water depths of 40 - 50 m simultaneously. In these cases, potential supercooling occurred and signals were particularly enhanced at timings of in-situ supercooling. Thus, we interpreted these signals as those of frazil ice. On the other hand, bottom-intensified signals originating from re-suspended sediment were detected throughout the water column just after frazil ice was detected. These signals were associated with strong ocean currents of 1 m/s. Thus, sedimentary particles are likely dispersed from the ocean bottom by the strong currents and subsequently brought up to the ocean surface under turbulent mixing conditions. We estimated the fall velocity of sedimentary particles as 0.4 mm/s based on the vertical profiles of the ADCP backscatter strength. This fall velocity corresponds to that of the particle diameter of 20 μm.

Patterns and Controls of Nutrient Concentrations in a Southeastern United States Tidal Creek

DTIC Science & Technology

2013-09-01

which the Duplm’s salinity was controlled solely by mixing between Altamaha River and Atlantic Ocean water . Marine end-membei composition was...ix’iiirrint; within the water - shed must hove been responsible. SEDIMENT AND WATER COLUMN MICROBIAL PROCESSES There was a great deal ot...subsequent processes transform these nutrients in the land-ocean transition zone. Here, we describe spatial and temporal patterns in surface water

Evolution of biogeochemical cycling of phosphorus during 45~50 Ma revealed by sequential extraction analysis of IODP Expedition 302 cores from the Arctic Ocean

NASA Astrophysics Data System (ADS)

Hashimoto, S.; Yamaguchi, K. E.; Takahashi, K.

2012-12-01

The modern Arctic Ocean plays crucial roles in controlling global climate system with the driving force of global thermohaline circulation through the formation of dense deep water and high albedo due to the presence of perennial sea-ice. However, the Arctic sea-ice has not always existed in the past. Integrated Ocean Drilling Program (IODP) Expedition 302 Arctic Coring Expedition (ACEX) has clarified that global warming (water temperature: ca. 14~16○C) during 48~49 Ma Azolla Event induced the loss of sea-ice and desalination of surface ocean, and that sea-ice formed again some million years later (45 Ma). In the Arctic Ocean, warming and cooling events repeated over and over (e.g., Brinkhuis et al., 2006; Moran et al., 2006; März et al., 2010). Large variations in the extent of thermohaline circulation through time often caused stagnation of seawater and appearance of anaerobic environment where hydrogen sulfide was produced by bacterial sulfate reduction. Ogawa et al. (2009) confirmed occurrence of framboidal pyrite in the ACEX sediments, and suggested that the Arctic Ocean at the time was anoxic, analogous to the modern Black Sea, mainly based on sulfur isotope analysis. To further clarify the variations in the nutrient status of the Arctic Ocean, we focus on the geochemical cycle of phosphorus. We performed sequential extraction analysis of sedimentary phosphorus in the ACEX sediments, using the method that we improvped based on the original SEDEX method by Ruttenberg (1992) and Schenau et al. (2000). In our method, phosphorus fractions are divided into five forms; (1) absorbed P, (2) Feoxide-P, (4) carbonate fluorapatite (CFAP) + CaCO3-P + hydroxylapatite (HAP), (4) detrital P, and (5) organic P. Schenau et al. (2000) divided the (3) fraction into non-biological CFAP and biological HAP and CaCO3-P. When the Arctic Ocean was closed and in its warming period, the water mass was most likely stratified and an anaerobic condition would have prevailed where bacterial sulfate reduction was active. In this case, most of the phosphorus in sediment was stored as organic P, which was originally derived as sinking particles of detrital plankton from the surface ocean. Increased rainfalls during such a warming period would have enhanced continental weathering and delivery of phosphorus to the surface ocean, and biological activity using increased amounts of phosphorus supply would also have increased. Feoxide-P is considered to be less important as a sink for phosphorus because of the likely formation of pyrite through the reductive dissolution of Fe oxide. CFAP could be a sink for phosphorus, because the formation of CFAP tends to increase with increasing age and depth.

The Carbon Isotopic Record of The C37:2 Alkenone In Sediments From The Equatorial and South Atlantic: Last Glacial Maximum (lgm) Vs. Holocene

NASA Astrophysics Data System (ADS)

Benthien, A.; Schulte, S.; Andersen, N.; Müller, P. J.; Schneider, R. R.

The carbon isotopic signal of the C37-alkenone, a taxon-specific biomarker for hap- tophyte algae, has been used in various paleoceanographic studies as a proxy for an- cient surface water CO2 concentration ([CO2aq]). However, a number of recent cul- ture, field and sediment studies imply that the carbon isotopic fractionation (ep) of alkenones is controlled predominantly by physiological processes and environmental factors other than the ambient CO2 concentration (i.e., growth rate, nutrient availabil- ity, light intensity, active carbon uptake, bicarbonate utilisation). The environmental conditions controlling phytoplankton growth are likely to vary strongly with oceano- graphic setting. Culture experiments can not perfectly recreate natural growth con- ditions and physical processes which affect the carbon isotopic signal in the field and its preservation in the sediment. Consequently, the use of the carbon isotopic record of alkenones as a reliable paleoceonographic proxy also requires sediment- based studies covering a broad range of different oceanic regimes for the past and modern ocean. Here, we present the first basin-wide comparison of alkenone ep val- ues from sediments of the Last Glacial Maximum (LGM) and the latest Holocene. Different oceanographic regions from the equatorial and South Atlantic Ocean were examined. Generally, alkenone ep is lower during the LGM compared to the Holocene. Considering present understanding of LGM-Holocene changes in surface water condi- tions, the observed glacial/interglacial difference in ep indicates that different effects controlled the isotopic fractionation in alkenone-producing algae depending on the regional setting. In upwelling regions, the variations in ep probably reflect a glacial increase in haptophyte productivity controlled by the availability of surface water nu- trient concentrations. By contrast, in oligotrophic areas slightly lower nutrient content was available during LGM. Here, the observed ep difference can be explained partly with an assumed glacial decrease in surface water [CO2aq]. However, it can not be ruled out that changes in haptophyte productivity also affected the ep signal to some extent. This study clearly demonstrates that a reliable reconstruction of [CO2aq] on the basis of the isotopic composition of alkenones is not feasible without a detailed 1 knowledge of ancient haptophyte growth conditions. 2

Limited contribution of ancient methane to surface waters of the U.S. Beaufort Sea shelf

PubMed Central

Sparrow, Katy J.; Kessler, John D.; Southon, John R.; Garcia-Tigreros, Fenix; Schreiner, Kathryn M.; Ruppel, Carolyn D.; Miller, John B.; Lehman, Scott J.; Xu, Xiaomei

2018-01-01

In response to warming climate, methane can be released to Arctic Ocean sediment and waters from thawing subsea permafrost and decomposing methane hydrates. However, it is unknown whether methane derived from this sediment storehouse of frozen ancient carbon reaches the atmosphere. We quantified the fraction of methane derived from ancient sources in shelf waters of the U.S. Beaufort Sea, a region that has both permafrost and methane hydrates and is experiencing significant warming. Although the radiocarbon-methane analyses indicate that ancient carbon is being mobilized and emitted as methane into shelf bottom waters, surprisingly, we find that methane in surface waters is principally derived from modern-aged carbon. We report that at and beyond approximately the 30-m isobath, ancient sources that dominate in deep waters contribute, at most, 10 ± 3% of the surface water methane. These results suggest that even if there is a heightened liberation of ancient carbon–sourced methane as climate change proceeds, oceanic oxidation and dispersion processes can strongly limit its emission to the atmosphere. PMID:29349299

Limited contribution of ancient methane to surface waters of the U.S. Beaufort Sea shelf

USGS Publications Warehouse

Sparrow, Katy J.; Kessler, John D.; Southon, John R.; Garcia-Tigreros, Fenix; Schreiner, Kathryn M.; Ruppel, Carolyn D.; Miller, John B.; Lehman, Scott J.; Xu, Xiaomei

2018-01-01

In response to warming climate, methane can be released to Arctic Ocean sediment and waters from thawing subsea permafrost and decomposing methane hydrates. However, it is unknown whether methane derived from this sediment storehouse of frozen ancient carbon reaches the atmosphere. We quantified the fraction of methane derived from ancient sources in shelf waters of the U.S. Beaufort Sea, a region that has both permafrost and methane hydrates and is experiencing significant warming. Although the radiocarbon-methane analyses indicate that ancient carbon is being mobilized and emitted as methane into shelf bottom waters, surprisingly, we find that methane in surface waters is principally derived from modern-aged carbon. We report that at and beyond approximately the 30-m isobath, ancient sources that dominate in deep waters contribute, at most, 10 ± 3% of the surface water methane. These results suggest that even if there is a heightened liberation of ancient carbon–sourced methane as climate change proceeds, oceanic oxidation and dispersion processes can strongly limit its emission to the atmosphere.

Cohesive and mixed sediment in the Regional Ocean Modeling System (ROMS v3.6) implemented in the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST r1234)

NASA Astrophysics Data System (ADS)

Sherwood, Christopher R.; Aretxabaleta, Alfredo L.; Harris, Courtney K.; Rinehimer, J. Paul; Verney, Romaric; Ferré, Bénédicte

2018-05-01

We describe and demonstrate algorithms for treating cohesive and mixed sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of cohesive and mixed (combination of cohesive and non-cohesive) sediment; and biodiffusive mixing of bed sediment. These routines supplement existing non-cohesive sediment modules, thereby increasing our ability to model fine-grained and mixed-sediment environments. Additionally, we describe changes to the sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application.

A new look at the multi-G model for organic carbon degradation in surface marine sediments for coupled benthic-pelagic simulations of the global ocean

NASA Astrophysics Data System (ADS)

Stolpovsky, Konstantin; Dale, Andrew W.; Wallmann, Klaus

2018-06-01

The kinetics of particulate organic carbon (POC) mineralization in marine surface sediments is not well constrained. This creates considerable uncertainties when benthic processes are considered in global biogeochemical or Earth system circulation models to simulate climate-ocean interactions and biogeochemical tracer distributions in the ocean. In an attempt to improve our understanding of the rate and depth distribution of organic carbon mineralization in bioturbated (0-20 cm) sediments at the global scale, we parameterized a 1-D diagenetic model that simulates the mineralization of three discrete POC pools (a multi-G model). The rate constants of the three reactive classes (highly reactive, reactive, refractory) are fixed and determined to be 70, 0.5 and ˜ 0.001 yr-1, respectively, based on the Martin curve model for pelagic POC degradation. In contrast to previous approaches, however, the reactivity of the organic material degraded in the seafloor is continuous with, and set by, the apparent reactivity of material sinking through the water column. Despite the simplifications of describing POC remineralization using G-type approaches, the model is able to simulate a global database (185 stations) of benthic oxygen and nitrate fluxes across the sediment-water interface in addition to porewater oxygen and nitrate distributions and organic carbon burial efficiencies. It is further consistent with degradation experiments using fresh phytoplankton reported in a previous study. We propose that an important yet mostly overlooked consideration in upscaling approaches is the proportion of the reactive POC classes reaching the seafloor in addition to their reactivity. The approach presented is applicable to both steady-state and non-steady state scenarios, and links POC degradation kinetics in sedimentary environments to water depth and the POC rain rate to the seafloor.

Ocean-atmosphere dynamics during Hurricane Ida and Nor'Ida: An application of the coupled ocean-;atmosphere–wave–sediment transport (COAWST) modeling system

USGS Publications Warehouse

Olabarrieta, Maitane; Warner, John C.; Armstrong, Brandy N.; Zambon, Joseph B.; He, Ruoying

2012-01-01

The coupled ocean–atmosphere–wave–sediment transport (COAWST) modeling system was used to investigate atmosphere–ocean–wave interactions in November 2009 during Hurricane Ida and its subsequent evolution to Nor'Ida, which was one of the most costly storm systems of the past two decades. One interesting aspect of this event is that it included two unique atmospheric extreme conditions, a hurricane and a nor'easter storm, which developed in regions with different oceanographic characteristics. Our modeled results were compared with several data sources, including GOES satellite infrared data, JASON-1 and JASON-2 altimeter data, CODAR measurements, and wave and tidal information from the National Data Buoy Center (NDBC) and the National Tidal Database. By performing a series of numerical runs, we were able to isolate the effect of the interaction terms between the atmosphere (modeled with Weather Research and Forecasting, the WRF model), the ocean (modeled with Regional Ocean Modeling System (ROMS)), and the wave propagation and generation model (modeled with Simulating Waves Nearshore (SWAN)). Special attention was given to the role of the ocean surface roughness. Three different ocean roughness closure models were analyzed: DGHQ (which is based on wave age), TY2001 (which is based on wave steepness), and OOST (which considers both the effects of wave age and steepness). Including the ocean roughness in the atmospheric module improved the wind intensity estimation and therefore also the wind waves, surface currents, and storm surge amplitude. For example, during the passage of Hurricane Ida through the Gulf of Mexico, the wind speeds were reduced due to wave-induced ocean roughness, resulting in better agreement with the measured winds. During Nor'Ida, including the wave-induced surface roughness changed the form and dimension of the main low pressure cell, affecting the intensity and direction of the winds. The combined wave age- and wave steepness-based parameterization (OOST) provided the best results for wind and wave growth prediction. However, the best agreement between the measured (CODAR) and computed surface currents and storm surge values was obtained with the wave steepness-based roughness parameterization (TY2001), although the differences obtained with respect to DGHQ were not significant. The influence of sea surface temperature (SST) fields on the atmospheric boundary layer dynamics was examined; in particular, we evaluated how the SST affects wind wave generation, surface currents and storm surges. The integrated hydrograph and integrated wave height, parameters that are highly correlated with the storm damage potential, were found to be highly sensitive to the ocean surface roughness parameterization.

Ocean-atmosphere dynamics during Hurricane Ida and Nor'Ida: An application of the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system

USGS Publications Warehouse

Olabarrieta, Maitane; Warner, John C.; Armstrong, Brandy N.; Zambon, Joseph B.; He, Ruoying

2012-01-01

The coupled ocean–atmosphere–wave–sediment transport (COAWST) modeling system was used to investigate atmosphere–ocean–wave interactions in November 2009 during Hurricane Ida and its subsequent evolution to Nor’Ida, which was one of the most costly storm systems of the past two decades. One interesting aspect of this event is that it included two unique atmospheric extreme conditions, a hurricane and a nor’easter storm, which developed in regions with different oceanographic characteristics. Our modeled results were compared with several data sources, including GOES satellite infrared data, JASON-1 and JASON-2 altimeter data, CODAR measurements, and wave and tidal information from the National Data Buoy Center (NDBC) and the National Tidal Database. By performing a series of numerical runs, we were able to isolate the effect of the interaction terms between the atmosphere (modeled with Weather Research and Forecasting, the WRF model), the ocean (modeled with Regional Ocean Modeling System (ROMS)), and the wave propagation and generation model (modeled with Simulating Waves Nearshore (SWAN)). Special attention was given to the role of the ocean surface roughness. Three different ocean roughness closure models were analyzed: DGHQ (which is based on wave age), TY2001 (which is based on wave steepness), and OOST (which considers both the effects of wave age and steepness). Including the ocean roughness in the atmospheric module improved the wind intensity estimation and therefore also the wind waves, surface currents, and storm surge amplitude. For example, during the passage of Hurricane Ida through the Gulf of Mexico, the wind speeds were reduced due to wave-induced ocean roughness, resulting in better agreement with the measured winds. During Nor’Ida, including the wave-induced surface roughness changed the form and dimension of the main low pressure cell, affecting the intensity and direction of the winds. The combined wave age- and wave steepness-based parameterization (OOST) provided the best results for wind and wave growth prediction. However, the best agreement between the measured (CODAR) and computed surface currents and storm surge values was obtained with the wave steepness-based roughness parameterization (TY2001), although the differences obtained with respect to DGHQ were not significant. The influence of sea surface temperature (SST) fields on the atmospheric boundary layer dynamics was examined; in particular, we evaluated how the SST affects wind wave generation, surface currents and storm surges. The integrated hydrograph and integrated wave height, parameters that are highly correlated with the storm damage potential, were found to be highly sensitive to the ocean surface roughness parameterization.

Emergence of burrowing urchins from California continental shelf sediments-A response to alongshore current reversals?

USGS Publications Warehouse

Nichols, F.H.; Cacchione, D.A.; Drake, D.E.; Thompson, J.K.

1989-01-01

Two sequences of bottom photographs taken every two or four hours for two months during the Coastal Ocean Dynamics Experiment (CODE) off the Russian River, California, reveal the dynamic nature of interations between the water column, the sediments, and benthic organisms in the mid-shelf silt deposit. Time-lapse photographs taken between late spring and early summer in 1981 and 1982 show that the subsurface-dwelling urchin Brisaster latifrons (one of the largest invertebrates found in shelf-depth fine sediment off the U.S. Pacific coast) occasionally emerged from the sediment, plowed the sediment surface during the course of a few hours to several days, then buried themselves again. Frame-by-frame study of the film sequences shows that the urchins typically emerged following relaxation of coastal upwelling, periods characterized by current direction reversals and increases in bottom water turbidity. Among the possible causes of the emergence of urchins and the consequent bioturbation of the upper few cm of sediment, a response to an enhanced food supply seems most plausible. Circumstantial evidence suggests the possibility that phytoplankton sedimentation during periods of upwelling relaxation could provide a new source of food at the sediment surface. ?? 1989.

Glacial flour dust storms in the Gulf of Alaska: hydrologic and meteorological controls and their importance as a source of bioavailable iron

USGS Publications Warehouse

Crusius, John; Schroth, A.W.; Gasso, S.; Moy, C.M.; Levy, R.C.; Gatica, M.

2011-01-01

Iron is an essential micronutrient that limits primary productivity in much of the ocean, including the Gulf of Alaska (GoA). However, the processes that transport iron to the ocean surface are poorly quantified. We combine satellite and meteorological data to provide the first description of widespread dust transport from coastal Alaska into the GoA. Dust is frequently transported from glacially-derived sediment at the mouths of several rivers, the most prominent of which is the Copper River. These dust events occur most frequently in autumn, when coastal river levels are low and riverbed sediments are exposed. The dust plumes are transported several hundred kilometers beyond the continental shelf into iron-limited waters. We estimate the mass of dust transported from the Copper River valley during one 2006 dust event to be between 25–80 ktons. Based on conservative estimates, this equates to a soluble iron loading of 30–200 tons. We suggest the soluble Fe flux from dust originating in glaciofluvial sediment deposits from the entire GoA coastline is two to three times larger, and is comparable to the annual Fe flux to GoA surface waters from eddies of coastal origin. Given that glaciers are retreating in the coastal GoA region and in other locations, it is important to examine whether fluxes of dust are increasing from glacierized landscapes to the ocean, and to assess the impact of associated Fe on marine ecosystems.

Surface Nutrient Utilisation and Productivity During Glacial-Interglacial Periods from the Equatorial Indian Ocean

NASA Astrophysics Data System (ADS)

R, C. K.; Bhushan, R.; Agnihotri, R.; Sawlani, R.; Jull, A. J. T.

2016-12-01

Seawaters and underlying sediments off Sri Lanka provide a unique marine realm affected by both branches of Northern Indian Ocean i.e. Arabian Sea (AS) and Bay of Bengal (BOB). AS and BOB are known for their distinct response to southwest monsoon. AS experiencing mainly winds and upwelling while BOB receives precipitation driven surface runoff from the Indian sub-continent. Multiple proxies were measured on a radiocarbon dated sediment core raised off Sri Lanka; their down core variations were used to understand oceanic history (nutrient utilisation, surface productivity, nature of organic matter) spanning last glacial-interglacial cycle ( 26 to 2.5 ka BP). Variations in CaCO3, biogenic silica (BSi) and δ15N from 26 ka to 12.5 ka BP indicate the region was experiencing high surface productivity with probably reduced surface nutrient utilisation efficiency. Sedimentary δ15N depth profile is decoupled from down core variations of major productivity indices (e.g. CaCO3, OC), hinting plausibly partial utilization of nutrients in the mixed layer (photic zone). δ13C of OC and C/N (wt. ratio) clearly reveal the terrestrial origin of organic matter at 15 ka BP, a period known for witnessing onset of deglaciation in northern hemisphere. δ13C minimum at 9 ka BP indicates intense monsoonal activity during this time coinciding well with solar insolation (June) maximum of the northern hemisphere. With the onset of Holocene ( 11 ka BP), δ15N variations appear to correlate with BSi and Ba/Ti indicating enhanced utilization of available nutrients at surface. Suggesting surface productivity over the region was probably micro-nutrient limited. The increased inventory of terrestrial runoff in Holocene probably demonstrates enhanced carbon sequestration capability of the region.

Annual net community production and the biological carbon flux in the ocean

NASA Astrophysics Data System (ADS)

Emerson, Steven

2014-01-01

The flux of biologically produced organic matter from the surface ocean (the biological pump), over an annual cycle, is equal to the annual net community production (ANCP). Experimental determinations of ANCP at ocean time series sites using a variety of different metabolite mass balances have made it possible to evaluate the accuracy of sediment trap fluxes and satellite-determined ocean carbon export. ANCP values at the Hawaii Ocean Time-series (HOT), the Bermuda Atlantic Time-series Study (BATS), Ocean Station Papa (OSP) are 3 ± 1 mol C m-2 yr-1—much less variable than presently suggested by satellite remote sensing measurements and global circulation models. ANCP determined from mass balances at these locations are 3-4 times particulate organic carbon fluxes measured in sediment traps. When the roles of dissolved organic carbon (DOC) flux, zooplankton migration, and depth-dependent respiration are considered these differences are reconciled at HOT and OSP but not at BATS, where measured particulate fluxes are about 3 times lower than expected. Even in the cases where sediment trap fluxes are accurate, it is not possible to "scale up" these measurements to determine ANCP without independent determinations of geographically variable DOC flux and zooplankton migration. Estimates of ANCP from satellite remote sensing using net primary production determined by the carbon-based productivity model suggests less geographic variability than its predecessor (the vertically generalized productivity model) and brings predictions at HOT and OSP closer to measurements; however, satellite-predicted ANCP at BATS is still 3 times too low.

Highlighting patterns of fungal diversity and composition shaped by ocean currents using the East China Sea as a model.

PubMed

Li, Wei; Wang, Mengmeng; Pan, Haoqin; Burgaud, Gaëtan; Liang, Shengkang; Guo, Jiajia; Luo, Tian; Li, Zhaoxia; Zhang, Shoumei; Cai, Lei

2018-01-01

How ocean currents shape fungal transport, dispersal and more broadly fungal biogeography remains poorly understood. The East China Sea (ECS) is a complex and dynamic habitat with different water masses blending microbial communities. The internal transcribed spacer 2 region of fungal rDNA was analysed in water and sediment samples directly collected from the coastal (CWM), Kuroshio (KSWM), Taiwan warm (TWM) and the shelf mixed water mass (MWM), coupled with hydrographic properties measurements, to determine how ocean currents impact the fungal community composition. Almost 9k fungal operational taxonomic units (OTUs) spanning six phyla, 25 known classes, 102 orders and 694 genera were obtained. The typical terrestrial and freshwater fungal genus, Byssochlamys, was dominant in the CWM, while increasing abundance of a specific OTU affiliated with Aspergillus was revealed from coastal to open ocean water masses (TWM and KSWM). Compared with water samples, sediment harboured an increased diversity with distinct fungal communities. The proximity of the Yangtze and Qiantang estuaries homogenizes the surface water and sediment communities. A significant influence of ocean currents on community structure was found, which is believed to reduce proportionally the variation explained by environmental parameters at the scale of the total water masses. Dissolved oxygen and depth were identified as the major parameters structuring the fungal community. Our results indicate that passive fungal dispersal driven by ocean currents and river run-off, in conjunction with the distinct hydrographic conditions of individual water masses, shapes the fungal community composition and distribution pattern in the ECS. © 2017 John Wiley & Sons Ltd.

In-situ measurements of rare earth elements in deep sea sediments using nuclear methods.

PubMed

Obhođaš, Jasmina; Sudac, Davorin; Meric, Ilker; Pettersen, Helge E S; Uroić, Milivoj; Nađ, Karlo; Valković, Vlado

2018-03-21

The prospecting activities for finding new rare earth elements (REE) sources have increased greatly in recent years. One of the main discoveries was announced in 2011 by Japanese researchers who found large quantities of REE on the ocean seafloor at the sea depths greater than 4,000 m. The classic approach to investigate REE in deep sea sediments is to obtain sediment samples by drilling that is followed by laborious laboratory analysis. This is very expensive, time consuming and not appropriate for exploring vast areas. In order to efficiently explore the ocean floor for REE deposits, the further development of affordable sensors is needed. Here, we propose two nuclear techniques for exploring REE in surface deep sea sediments: i) Passive measurement of lutetium-176 radioactivity, appropriate if long-term in-situ measurements are possible, and ii) The use of the neutron sensor attached to a remotely operated vehicle for rapid in-situ measurement of gadolinium by thermal neutron-capture. Since concentrations of lutetium and gadolinium show strong linear correlation to the total REE concentrations in deep sea sediments, it is possible to deduce the total REE content by measuring Lu or Gd concentrations only.

Biogeochemistry of Dissolved Free Amino Acids in Marine Sediments.

DTIC Science & Technology

1980-09-01

Oceans , the Black Sea , and the Sea of Azov. Interstitial water of surface sediments | _ A Irom these regions, including even Pacific red clays and...Awapara, 1962; de Zwaan, 1977). Serine has been reported as the major constituent of the ceolomic fluid of a sea urchin (Giordano et al., 1950). The...Harper, and F. P. Filice (1950) The amino acids ot a starfish and a sea urchin (Asteroidea and Echinoidea). Wasmann J. Biol. 8, 129-132. Goldberg, E

Persistence of deeply sourced iron in the Pacific Ocean

PubMed Central

Horner, Tristan J.; Williams, Helen M.; Hein, James R.; Saito, Mak A.; Burton, Kevin W.; Halliday, Alex N.; Nielsen, Sune G.

2015-01-01

Biological carbon fixation is limited by the supply of Fe in vast regions of the global ocean. Dissolved Fe in seawater is primarily sourced from continental mineral dust, submarine hydrothermalism, and sediment dissolution along continental margins. However, the relative contributions of these three sources to the Fe budget of the open ocean remains contentious. By exploiting the Fe stable isotopic fingerprints of these sources, it is possible to trace distinct Fe pools through marine environments, and through time using sedimentary records. We present a reconstruction of deep-sea Fe isotopic compositions from a Pacific Fe−Mn crust spanning the past 76 My. We find that there have been large and systematic changes in the Fe isotopic composition of seawater over the Cenozoic that reflect the influence of several, distinct Fe sources to the central Pacific Ocean. Given that deeply sourced Fe from hydrothermalism and marginal sediment dissolution exhibit the largest Fe isotopic variations in modern oceanic settings, the record requires that these deep Fe sources have exerted a major control over the Fe inventory of the Pacific for the past 76 My. The persistence of deeply sourced Fe in the Pacific Ocean illustrates that multiple sources contribute to the total Fe budget of the ocean and highlights the importance of oceanic circulation in determining if deeply sourced Fe is ever ventilated at the surface. PMID:25605900

Persistence of deeply sourced iron in the Pacific Ocean.

PubMed

Horner, Tristan J; Williams, Helen M; Hein, James R; Saito, Mak A; Burton, Kevin W; Halliday, Alex N; Nielsen, Sune G

2015-02-03

Biological carbon fixation is limited by the supply of Fe in vast regions of the global ocean. Dissolved Fe in seawater is primarily sourced from continental mineral dust, submarine hydrothermalism, and sediment dissolution along continental margins. However, the relative contributions of these three sources to the Fe budget of the open ocean remains contentious. By exploiting the Fe stable isotopic fingerprints of these sources, it is possible to trace distinct Fe pools through marine environments, and through time using sedimentary records. We present a reconstruction of deep-sea Fe isotopic compositions from a Pacific Fe-Mn crust spanning the past 76 My. We find that there have been large and systematic changes in the Fe isotopic composition of seawater over the Cenozoic that reflect the influence of several, distinct Fe sources to the central Pacific Ocean. Given that deeply sourced Fe from hydrothermalism and marginal sediment dissolution exhibit the largest Fe isotopic variations in modern oceanic settings, the record requires that these deep Fe sources have exerted a major control over the Fe inventory of the Pacific for the past 76 My. The persistence of deeply sourced Fe in the Pacific Ocean illustrates that multiple sources contribute to the total Fe budget of the ocean and highlights the importance of oceanic circulation in determining if deeply sourced Fe is ever ventilated at the surface.

Increased fluxes of shelf-derived materials to the central Arctic Ocean

PubMed Central

Kipp, Lauren E.; Charette, Matthew A.; Moore, Willard S.; Henderson, Paul B.; Rigor, Ignatius G.

2018-01-01

Rising temperatures in the Arctic Ocean region are responsible for changes such as reduced ice cover, permafrost thawing, and increased river discharge, which, together, alter nutrient and carbon cycles over the vast Arctic continental shelf. We show that the concentration of radium-228, sourced to seawater through sediment-water exchange processes, has increased substantially in surface waters of the central Arctic Ocean over the past decade. A mass balance model for 228Ra suggests that this increase is due to an intensification of shelf-derived material inputs to the central basin, a source that would also carry elevated concentrations of dissolved organic carbon and nutrients. Therefore, we suggest that significant changes in the nutrient, carbon, and trace metal balances of the Arctic Ocean are underway, with the potential to affect biological productivity and species assemblages in Arctic surface waters. PMID:29326980

How does ice sheet loading affect ocean flow around Antarctica?

NASA Astrophysics Data System (ADS)

Dijkstra, H. A.; Rugenstein, M. A.; Stocchi, P.; von der Heydt, A. S.

2012-12-01

Interactions and dynamical feedbacks between ocean circulation, heat and atmospheric moisture transport, ice sheet evolution, and Glacial Isostatic Adjustment (GIA) are overlooked issues in paleoclimatology. Here we will present first results on how ocean flows were possibly affected by the glaciation of Antarctica across the Eocene-Oligocene Transition (~ 34 Ma) through GIA and bathymetry variations. GIA-induced gravitationally self-consistent bathymetry variations are determined by solving the Sea Level Equation (SLE), which describes the time dependent shape of (i) the solid Earth and (ii) the equipotential surface of gravity. Since the ocean circulation equations are defined relative to the equipotential surface of gravity, only bathymetry variations can influence ocean flows, although the sea surface slope will also change through time due to gravitational attraction. We use the Hallberg Isopycnal Model under late Eocene conditions to calculate equilibrium ocean flows in a domain in which the bathymetry evolves under ice loading according to the SLE. The bathymetric effects of the glaciation of Antarctica lead to substantial spatial changes in ocean flows, and close to the coast, the flow even reverses direction. Volume transports through the Drake Passage and Tasman Seaway adjust to the new bathymetry. The results indicate that GIA-induced ocean flow variations alone may have had an impact on sedimentation and erosion patterns, the repositioning of fronts, ocean heat transport and grounding line and ice sheet stability.

Tracking the Hercules 265 marine gas well blowout in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Romero, Isabel C.; Özgökmen, Tamay; Snyder, Susan; Schwing, Patrick; O'Malley, Bryan J.; Beron-Vera, Francisco J.; Olascoaga, Maria J.; Zhu, Ping; Ryan, Edward; Chen, Shuyi S.; Wetzel, Dana L.; Hollander, David; Murawski, Steven A.

2016-01-01

On 23 July 2013, a marine gas rig (Hercules 265) ignited in the northern Gulf of Mexico. The rig burned out of control for 2 days before being extinguished. We conducted a rapid-response sampling campaign near Hercules 265 after the fire to ascertain if sediments and fishes were polluted above earlier baseline levels. A surface drifter study confirmed that surface ocean water flowed to the southeast of the Hercules site, while the atmospheric plume generated by the blowout was in eastward direction. Sediment cores were collected to the SE of the rig at a distance of ˜0.2, 8, and 18 km using a multicorer, and demersal fishes were collected from ˜0.2 to 8 km SE of the rig using a longline (508 hooks). Recently deposited sediments document that only high molecular weight (HMW) polycyclic aromatic hydrocarbon (PAH) concentrations decreased with increasing distance from the rig suggesting higher pyrogenic inputs associated with the blowout. A similar trend was observed in the foraminifera Haynesina germanica, an indicator species of pollution. In red snapper bile, only HMW PAH metabolites increased in 2013 nearly double those from 2012. Both surface sediments and fish bile analyses suggest that, in the aftermath of the blowout, increased concentration of pyrogenically derived hydrocarbons was transported and deposited in the environment. This study further emphasizes the need for an ocean observing system and coordinated rapid-response efforts from an array of scientific disciplines to effectively assess environmental impacts resulting from accidental releases of oil contaminants.

Can we constrain postglacial sedimentation in the western Arctic Ocean by ramped pyrolysis 14C? A case study from the Chukchi-Alaskan margin.

NASA Astrophysics Data System (ADS)

Suzuki, K.; Yamamoto, M.; Rosenheim, B. E.; Omori, T.; Polyak, L.; Nam, S. I.

2017-12-01

The Arctic Ocean underwent dramatic climate changes in the past. Variations in sea-ice extent and ocean current system in the Arctic cause changes in surface albedo and deep water formation, which have global climatic implications. However, Arctic paleoceanographic studies are lagging behind the other oceans due largely to chronostratigraphic difficulties. One of the reasons for this is a scant presence of material suitable for 14C dating in large areas of the Arctic seafloor. To enable improved age constraints for sediments impoverished in datable material, we apply ramped pyrolysis 14C method (Ramped PyrOx 14C, Rosenheim et al., 2008) to sedimentary records from the Chukchi-Alaska margin recovering Holocene to late-glacial deposits. Samples were divided into five fraction products by gradual heating sedimentary organic carbon from ambient laboratory temperature to 1000°C. The thermographs show a trimodal pattern of organic matter decomposition over temperature, and we consider that CO2 generated at the lowest temperature range was derived from autochthonous organic carbon contemporaneous with sediment deposition, similar to studies in the Antarctic margin and elsewhere. For verification of results, some of the samples treated for ramped pyrolysis 14C were taken from intervals dated earlier by AMS 14C using bivalve mollusks. Ultimately, our results allow a new appraisal of deglacial to Holocene deposition at the Chukchi-Alaska margin with potential to be applied to other regions of the Arctic Ocean.

Electrokinetic Transduction of Acoustic Waves In Ocean Sediments

DTIC Science & Technology

2002-09-30

acoustic —motion in ocean sediments. The Biot theory of poroelastic media captures much of the sediment physics left out by other models [2]. It fits...in subsurface acoustical imaging, Mine Counter- Measures, and Anti-Submarine Warfare. To obtain essential experimental data to support the modeling ...Electrokinetic Transduction of Acoustic Waves In Ocean Sediments Gareth I. Block Applied Research Laboratories, U.T. Austin P.O. Box 8029

The origin of Cretaceous black shales: a change in the surface ocean ecosystem and its triggers

PubMed Central

OHKOUCHI, Naohiko; KURODA, Junichiro; TAIRA, Asahiko

2015-01-01

Black shale is dark-colored, organic-rich sediment, and there have been many episodes of black shale deposition over the history of the Earth. Black shales are source rocks for petroleum and natural gas, and thus are both geologically and economically important. Here, we review our recent progress in understanding of the surface ocean ecosystem during periods of carbonaceous sediment deposition, and the factors triggering black shale deposition. The stable nitrogen isotopic composition of geoporphyrins (geological derivatives of chlorophylls) strongly suggests that N2-fixation was a major process for nourishing the photoautotrophs. A symbiotic association between diatoms and cyanobacteria may have been a major primary producer during episodes of black shale deposition. The timing of black shale formation in the Cretaceous is strongly correlated with the emplacement of large igneous provinces such as the Ontong Java Plateau, suggesting that black shale deposition was ultimately induced by massive volcanic events. However, the process that connects these events remains to be solved. PMID:26194853

Monitoring of hourly variations in coastal water turbidity using the geostationary ocean color imager (GOCI)

NASA Astrophysics Data System (ADS)

Choi, J.; Ryu, J.

2011-12-01

Temporal variations of suspended sediment concentration (SSC) in coastal water are the key to understanding the pattern of sediment movement within coastal area, in particular, such as in the west coast of the Korean Peninsula which is influenced by semi-diurnal tides. Remote sensing techniques can effectively monitor the distribution and dynamic changes in seawater properties across wide areas. Thus, SSC on the sea surface has been investigated using various types of satellite-based sensors. An advantage of Geostationary Ocean Color Imager (GOCI), the world's first geostationary ocean color observation satellite, over other ocean color satellite images is that it can obtain data every hour during the day and makes it possible to monitor the ocean in real time. In this study, hourly variations in turbidity on the coastal waters were estimated quantitatively using GOCI. Thirty three water samples were obtained on the coastal water surface in southern Gyeonggi Bay, located on the west coast of Korea. Water samples were filtered using 25-mm glass fiber filters (GF/F) for the estimation of SSC. The radiometric characteristics of the surface water, such as the total water-leaving radiance (LwT, W/m2/nm/sr), the sky radiance (Lsky, W/m2/nm/sr) and the downwelling irradiance, were also measured at each sampling location. In situ optical properties of the surface water were converted into remote sensing reflectance (Rrs) and then were used to develop an algorithm to generate SSC images in the study area. GOCI images acquired on the same day as the samples acquisition were used to generate the map of turbidity and to estimate the difference in SSC displayed in each image. The estimation of the time-series variation in SSC in a coastal, shallow-water area affected by tides was successfully achieved using GOCI data that had been acquired at hourly intervals during the daytime.

The deep sea is a major sink for microplastic debris

PubMed Central

Woodall, Lucy C.; Sanchez-Vidal, Anna; Canals, Miquel; Paterson, Gordon L.J.; Coppock, Rachel; Sleight, Victoria; Calafat, Antonio; Rogers, Alex D.; Narayanaswamy, Bhavani E.; Thompson, Richard C.

2014-01-01

Marine debris, mostly consisting of plastic, is a global problem, negatively impacting wildlife, tourism and shipping. However, despite the durability of plastic, and the exponential increase in its production, monitoring data show limited evidence of concomitant increasing concentrations in marine habitats. There appears to be a considerable proportion of the manufactured plastic that is unaccounted for in surveys tracking the fate of environmental plastics. Even the discovery of widespread accumulation of microscopic fragments (microplastics) in oceanic gyres and shallow water sediments is unable to explain the missing fraction. Here, we show that deep-sea sediments are a likely sink for microplastics. Microplastic, in the form of fibres, was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in contaminated sea-surface waters. Our results show evidence for a large and hitherto unknown repository of microplastics. The dominance of microfibres points to a previously underreported and unsampled plastic fraction. Given the vastness of the deep sea and the prevalence of microplastics at all sites we investigated, the deep-sea floor appears to provide an answer to the question—where is all the plastic? PMID:26064573

The deep sea is a major sink for microplastic debris.

PubMed

Woodall, Lucy C; Sanchez-Vidal, Anna; Canals, Miquel; Paterson, Gordon L J; Coppock, Rachel; Sleight, Victoria; Calafat, Antonio; Rogers, Alex D; Narayanaswamy, Bhavani E; Thompson, Richard C

2014-12-01

Marine debris, mostly consisting of plastic, is a global problem, negatively impacting wildlife, tourism and shipping. However, despite the durability of plastic, and the exponential increase in its production, monitoring data show limited evidence of concomitant increasing concentrations in marine habitats. There appears to be a considerable proportion of the manufactured plastic that is unaccounted for in surveys tracking the fate of environmental plastics. Even the discovery of widespread accumulation of microscopic fragments (microplastics) in oceanic gyres and shallow water sediments is unable to explain the missing fraction. Here, we show that deep-sea sediments are a likely sink for microplastics. Microplastic, in the form of fibres, was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in contaminated sea-surface waters. Our results show evidence for a large and hitherto unknown repository of microplastics. The dominance of microfibres points to a previously underreported and unsampled plastic fraction. Given the vastness of the deep sea and the prevalence of microplastics at all sites we investigated, the deep-sea floor appears to provide an answer to the question-where is all the plastic?

Is ice-rafted sediment in a North Pole marine record evidence for perennial sea-ice cover?

PubMed

Tremblay, L B; Schmidt, G A; Pfirman, S; Newton, R; DeRepentigny, P

2015-10-13

Ice-rafted sediments of Eurasian and North American origin are found consistently in the upper part (13 Ma BP to present) of the Arctic Coring Expedition (ACEX) ocean core from the Lomonosov Ridge, near the North Pole (≈88° N). Based on modern sea-ice drift trajectories and speeds, this has been taken as evidence of the presence of a perennial sea-ice cover in the Arctic Ocean from the middle Miocene onwards (Krylov et al. 2008 Paleoceanography 23, PA1S06. (doi:10.1029/2007PA001497); Darby 2008 Paleoceanography 23, PA1S07. (doi:10.1029/2007PA001479)). However, other high latitude land and marine records indicate a long-term trend towards cooling broken by periods of extensive warming suggestive of a seasonally ice-free Arctic between the Miocene and the present (Polyak et al. 2010 Quaternary Science Reviews 29, 1757-1778. (doi:10.1016/j.quascirev.2010.02.010)). We use a coupled sea-ice slab-ocean model including sediment transport tracers to map the spatial distribution of ice-rafted deposits in the Arctic Ocean. We use 6 hourly wind forcing and surface heat fluxes for two different climates: one with a perennial sea-ice cover similar to that of the present day and one with seasonally ice-free conditions, similar to that simulated in future projections. Model results confirm that in the present-day climate, sea ice takes more than 1 year to transport sediment from all its peripheral seas to the North Pole. However, in a warmer climate, sea-ice speeds are significantly faster (for the same wind forcing) and can deposit sediments of Laptev, East Siberian and perhaps also Beaufort Sea origin at the North Pole. This is primarily because of the fact that sea-ice interactions are much weaker with a thinner ice cover and there is less resistance to drift. We conclude that the presence of ice-rafted sediment of Eurasian and North American origin at the North Pole does not imply a perennial sea-ice cover in the Arctic Ocean, reconciling the ACEX ocean core data with other land and marine records. © 2015 The Author(s).

The Impact of Ocean Acidification on the Functional Morphology of Foraminifera

PubMed Central

Khanna, Nikki; Godbold, Jasmin A.; Austin, William E. N.; Paterson, David M.

2013-01-01

Culturing experiments were performed on sediment samples from the Ythan Estuary, N. E. Scotland, to assess the impacts of ocean acidification on test surface ornamentation in the benthic foraminifer Haynesina germanica. Specimens were cultured for 36 weeks at either 380, 750 or 1000 ppm atmospheric CO2. Analysis of the test surface using SEM imaging reveals sensitivity of functionally important ornamentation associated with feeding to changing seawater CO2 levels. Specimens incubated at high CO2 levels displayed evidence of shell dissolution, a significant reduction and deformation of ornamentation. It is clear that these calcifying organisms are likely to be vulnerable to ocean acidification. A reduction in functionally important ornamentation could lead to a reduction in feeding efficiency with consequent impacts on this organism's survival and fitness. PMID:24358253

The geomicrobiology of the Greenland Ice Sheet: impact on DOC export (Invited)

NASA Astrophysics Data System (ADS)

Wadham, J. L.; Stibal, M.; Lawson, E. C.; Barnett, M. J.; Hasan, F.; Telling, J.; Anesio, A.; Lis, G.; Cullen, D.; Butler, C.; Tranter, M.; Nienow, P. W.

2010-12-01

The Greenland Ice Sheet (GrIS) is the largest mass of ice in the northern hemisphere, and contributes ~370 km3 in runoff annually to the Arctic Ocean. While recent work has highlighted runoff increases of up to 100% from the GrIS over the next century, very little is known about the associated impacts upon rates of sediment-bound and dissolved organic carbon export from the ice sheet to the coastal ocean. This is relevant given recent work that has suggested that the high proportion of labile dissolved organic carbon (DOC) present in glacial runoff may be important in sustaining the productivity of ecosystems downstream. Here we report the phylogenetic and functional diversity of micro-organisms inhabiting the surface and basal regions of the Greenland Ice Sheet (at Leverett Glacier, SW Greenland), and whose activity influences the biogeochemical composition of runoff. Real time PCR data on runoff, together with 16S-rRNA bacterial clone libraries on sediments, demonstrate a subglacial microbial community that contrasts phylogenetically and functionally with the ice sheet surface ecosystem. We envisage that large sectors of the subglacial environment are microbially active, with overridden paleosols and in-washed surface organic matter providing a carbon substrate for a range of metabolic pathways. This includes methanogenesis which proceeds at rates similar to deep ocean sediments and via a CO2/H2 pathway. These subglacial microbial communities serve to chemically modify the DOC composition of meltwater inputs from the ice sheet surface and modulate the reactivity of bulk DOC exported in runoff. Evidence for subglacial microbial influences on DOC in runoff includes elevated concentrations of dissolved carbohydrates (e.g. glucose and fructose of up to 1 μmol/L), which are preferentially exported during subglacial outburst events. We examine the temporal changes in DOC export in runoff from the ice sheet over a full melt season, and consider how changes in total runoff over the coming century may perturb this contribution.

Rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments

NASA Astrophysics Data System (ADS)

Elderfield, H.; Hawkesworth, C. J.; Greaves, M. J.; Calvert, S. E.

1981-04-01

Analyses have been made of REE contents of a well-characterized suite of deep-sea (> 4000 m.) principally todorokite-bearing ferromanganese nodules and associated sediments from the Pacific Ocean. REE in nodules and their sediments are closely related: nodules with the largest positive Ce anomalies are found on sediments with the smallest negative Ce anomalies; in contrast, nodules with the highest contents of other rare earths (3 + REE) are found on sediments with the lowest 3 + REE contents and vice versa. 143Nd /144Nd ratios in the nodules (˜0.51244) point to an original seawater source but an identical ratio for sediments in combination with the REE patterns suggests that diagenetic reactions may transfer elements into the nodules. Analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to REE contents of nodules and sediments is negligible. Inter-element relationships and leaching tests suggest that REE contents are controlled by a P-rich phase with a REE pattern similar to that for biogenous apatite and an Fe-rich phase with a pattern the mirror image of that for sea water. It is proposed that 3 + REE concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate. Processes which favour the enrichment of transition metals in equatorial Pacific nodules favour the depletion of 3 + REE in nodules and enrichment of 3 + REE in associated sediments. In contrast, Ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions.

The Yellow Sea [high res

NASA Image and Video Library

2015-02-27

Remote sensing of ocean color in the Yellow Sea can be a challenge. Phytoplankton, suspended sediments, and dissolved organic matter color the water while various types of aerosols modify those colors before they are "seen" by orbiting radiometers. The Aqua-MODIS data used to create the above image were collected on February 24, 2015. NASA's OceanColor Web is supported by the Ocean Biology Processing Group (OBPG) at NASA's Goddard Space Flight Center. Our responsibilities include the collection, processing, calibration, validation, archive and distribution of ocean-related products from a large number of operational, satellite-based remote-sensing missions providing ocean color, sea surface temperature and sea surface salinity data to the international research community since 1996. Credit: NASA/Goddard/Ocean Color NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Sea-level responses to sediment transport over the last ice age cycle

NASA Astrophysics Data System (ADS)

Ferrier, K.; Mitrovica, J. X.

2013-12-01

Sea-level changes over the last ice age cycle were instrumental in steering Earth's topographic evolution. These sea-level variations were driven by changes in surface mass loads, including not only ice and ocean mass variations but also the transfer of rock from eroding mountains to sedimentary deposits. Here we use an extended numerical model of ice age sea level (Dalca et al., 2013) to explore how sediment erosion and deposition affected global sea-level variations over the last ice age cycle. The model takes histories of ice and sediment loads as inputs, and it computes gravitationally self-consistent sea level responses by accounting for the deformational, gravitational, and rotational perturbations in the Earth's viscoelastic form. In these model simulations, we use published estimates of erosion rates, sedimentation rates, and ice sheet variations to constrain sediment and ice loading since the Last Interglacial. We explore sea-level responses to several erosional and depositional scenarios, and in each we quantify the relative contributions of crustal deformation and gravitational perturbation to the computed sea-level change. We also present a case study to illustrate the effects that sediment transfer can have on sea level at the regional scale. In particular, we focus on the region surrounding the Indus River, where fluvial sediment fluxes are among the highest on Earth. Preliminary model results suggest that sediment fluxes from Asia to the ocean are large enough to produce a significant response in sea level along the northeastern coast of the Arabian Sea. Moreover, they suggest that modeled sea-level histories are sensitive to the timing and spatial distribution of sediment erosion and deposition. For instance, sediment deposition along the continental shelf - which may have been the primary site of Indus River sediment deposition during the Holocene - produces a different sea-level response than sediment deposition on the deep-sea Indus Fan, where most of the Indus sediment may have been deposited during the glacial period preceding the Holocene. These simulations highlight the role that massive continent-to-ocean sediment fluxes can play in driving sea-level patterns over thousands of years. References: Dalca A.V., Ferrier K.L., Mitrovica J.X., Perron J.T., Milne G.A., Creveling J.R., 2013. On postglacial sea level - III: Incorporating sediment redistribution. Geophys. J. Int., doi: 10.1093/gji/ggt089.

Fate of copper complexes in hydrothermally altered deep-sea sediments from the Central Indian Ocean Basin.

PubMed

Chakraborty, Parthasarathi; Sander, Sylvia G; Jayachandran, Saranya; Nath, B Nagender; Nagaraju, G; Chennuri, Kartheek; Vudamala, Krushna; Lathika, N; Mascarenhas-Pereira, Maria Brenda L

2014-11-01

The current study aims to understand the speciation and fate of Cu complexes in hydrothermally altered sediments from the Central Indian Ocean Basin and assess the probable impacts of deep-sea mining on speciation of Cu complexes and assess the Cu flux from this sediment to the water column in this area. This study suggests that most of the Cu was strongly associated with different binding sites in Fe-oxide phases of the hydrothermally altered sediments with stabilities higher than that of Cu-EDTA complexes. The speciation of Cu indicates that hydrothermally influenced deep-sea sediments from Central Indian Ocean Basin may not significantly contribute to the global Cu flux. However, increasing lability of Cu-sediment complexes with increasing depth of sediment may increase bioavailability and Cu flux to the global ocean during deep-sea mining. Copyright © 2014 Elsevier Ltd. All rights reserved.

Assessment of Density Variations of Marine Sediments with Ocean and Sediment Depths

PubMed Central

Tenzer, R.; Gladkikh, V.

2014-01-01

We analyze the density distribution of marine sediments using density samples taken from 716 drill sites of the Deep Sea Drilling Project (DSDP). The samples taken within the upper stratigraphic layer exhibit a prevailing trend of the decreasing density with the increasing ocean depth (at a rate of −0.05 g/cm3 per 1 km). Our results confirm findings of published studies that the density nonlinearly increases with the increasing sediment depth due to compaction. We further establish a 3D density model of marine sediments and propose theoretical models of the ocean-sediment and sediment-bedrock density contrasts. The sediment density-depth equation approximates density samples with an average uncertainty of about 10% and better represents the density distribution especially at deeper sections of basin sediments than a uniform density model. The analysis of DSDP density data also reveals that the average density of marine sediments is 1.70 g/cm3 and the average density of the ocean bedrock is 2.9 g/cm3. PMID:24744686

Google Earth-Based Grand Tours of the World's Ocean Basins and Marine Sediments

NASA Astrophysics Data System (ADS)

St John, K. K.; De Paor, D. G.; Suranovic, B.; Robinson, C.; Firth, J. V.; Rand, C.

2016-12-01

The GEODE project has produced a collection of Google Earth-based marine geology teaching resources that offer grand tours of the world's ocean basins and marine sediments. We use a map of oceanic crustal ages from Müller et al (2008; doi:10.1029/2007GC001743), and a set of emergent COLLADA models of IODP drill core data as a basis for a Google Earth tour introducing students to the world's ocean basins. Most students are familiar with basic seafloor spreading patterns but teaching experience suggests that few students have an appreciation of the number of abandoned ocean basins on Earth. Students also lack a valid visualization of the west Pacific where the oldest crust forms an isolated triangular patch and the ocean floor becomes younger towards the subduction zones. Our tour links geographic locations to mechanical models of rifting, seafloor spreading, subduction, and transform faulting. Google Earth's built-in earthquake and volcano data are related to ocean floor patterns. Marine sediments are explored in a Google Earth tour that draws on exemplary IODP core samples of a range of sediment types (e.g., turbidites, diatom ooze). Information and links are used to connect location to sediment type. This tour compliments a physical core kit of core catcher sections that can be employed for classroom instruction (geode.net/marine-core-kit/). At a larger scale, we use data from IMLGS to explore the distribution of the marine sediments types in the modern global ocean. More than 2,500 sites are plotted with access to original data. Students are guided to compare modern "type sections" of primary marine sediment lithologies, as well as examine site transects to address questions of bathymetric setting, ocean circulation, chemistry (e.g., CCD), and bioproductivity as influences on modern seafloor sedimentation. KMZ files, student exercises, and tips for instructors are available at geode.net/exploring-marine-sediments-using-google-earth.

Different Planctomycetes diversity patterns in latitudinal surface seawater of the open sea and in sediment.

PubMed

Shu, Qinglong; Jiao, Nianzhi

2008-04-01

The 16S rRNA gene approach was applied to investigate the diversity of Planctomycetes in latitudinal surface seawater of the Western Pacific Ocean. The results revealed that the Pirellula-Rhodopirellula-Blastopirellula clade dominated the Planctomycetes community at all surface seawater sites while the minority genera Gemmata and Planctomyces were only found at sites H5 and H2 respectively. Although the clone frequency of the PRB clade seemed stable (between 83.3% and 94.1%) for all surface seawater sites, the retrieved Pirellula-Rhodopirellula-Blastopirellula clade presented unexpected diversity. Interestingly, low latitude seawater appeared to have higher diversity than mid-latitudes. integral-LIBSHUFF software analysis revealed significantly different diversity patterns between in latitudinal surface seawater and in the sediment of South China Sea station M2896. Our data suggested that different hydrological and geographic features contributed to the shift of Planctomycetes diversity in marine environments. This is, to our knowledge, the first systematic assessment of Planctomycetes in latitudinal surface seawater of the open sea and the first comparison of diversity pattern between surface seawater and sediments and has broadened our understanding of Planctomycetes diversity in marine environments.

Testing a laser-induced breakdown spectroscopy technique on the Arctic sediments

NASA Astrophysics Data System (ADS)

Han, D.; Nam, S. I.

2017-12-01

Physical and geochemical investigations coupled with the Laser-induced Breakdown Spectroscopy (LIBS) were performed on three surface sediment cores (ARA03B/24BOX, ARA02B/01(A)MUC, ARA02B/02MUC and ARA02B/03(A)MUC) recovered from the western Arctic Ocean (Chukchi Sea) during IBRV ARON expeditions in 2012. The LIBS technique was applied to carry out elemental chemical analysis of the Arctic sediments and compared with that measured by ITRAX X-ray fuorescence (XRF) core scanning. LIBS and XRF have shown similar elemental composition within each sediment core. In this study, mineral composition (XRD), grain size distribution and organic carbon content as well as elemental composition (LIBS) were all considered to understand paleoenvironmental changes (ocean circulation, sea-ice drift, iceberg discharge, and etc.) recorded in the Arctic Holocene sediment. Quantitative LIBS analysis shows a gradually varying distribution of the elements along the sampled core and clear separation between the cores. The cores are geochemically characterized by elevated Mn profile. The gradient of mineral composition and grain sizes among the cores shows regional distribution and variation in sedimentary condition due to geological distance between East Siberian and North America. The present study reveals that a LIBS technique can be employed for in-situ sediment analyses for the Arctic Ocean. Furthermore, LIBS does not require costly equipment, trained operators, and complicated sample pre-treatment processes compared to Atomic absorption spectroscopy (AAS) and inductively coupled plasma emission spectroscopy (ICP), and also known to show relatively high levels of sensitivity, precision, and distinction than XRF analysis, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), and electron probe X-ray microanalysis (EPMA).

Antarctic and Southern Ocean influences on Late Pliocene global cooling

USGS Publications Warehouse

McKay, Robert; Naish, Tim; Carter, Lionel; Riesselman, Christina; Dunbar, Robert; Sjunneskog, Charlotte; Winter, Diane; Sangiorgi, Francesca; Warren, Courtney; Pagani, Mark; Schouten, Stefan; Willmott, Veronica; Levy, Richard; DeConto, Robert; Powell, Ross D.

2012-01-01

The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ~3.3 Ma, followed by a coastal sea surface temperature cooling of ~2.5 °C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world.

Antarctic and Southern Ocean influences on Late Pliocene global cooling

PubMed Central

McKay, Robert; Naish, Tim; Carter, Lionel; Riesselman, Christina; Dunbar, Robert; Sjunneskog, Charlotte; Winter, Diane; Sangiorgi, Francesca; Warren, Courtney; Pagani, Mark; Schouten, Stefan; Willmott, Veronica; Levy, Richard; DeConto, Robert; Powell, Ross D.

2012-01-01

The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ∼3.3 Ma, followed by a coastal sea surface temperature cooling of ∼2.5 °C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world. PMID:22496594

Evidence for ice-free summers in the late Miocene central Arctic Ocean

PubMed Central

Stein, Ruediger; Fahl, Kirsten; Schreck, Michael; Knorr, Gregor; Niessen, Frank; Forwick, Matthias; Gebhardt, Catalina; Jensen, Laura; Kaminski, Michael; Kopf, Achim; Matthiessen, Jens; Jokat, Wilfried; Lohmann, Gerrit

2016-01-01

Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014, we discovered multiple submarine landslides along Lomonosov Ridge. Removal of younger sediments from steep headwalls has led to exhumation of Miocene sediments close to the seafloor. Here we document the presence of IP25 as a proxy for spring sea-ice cover and alkenone-based summer sea-surface temperatures >4 °C that support a seasonal sea-ice cover with an ice-free summer season being predominant during the late Miocene in the central Arctic Ocean. A comparison of our proxy data with Miocene climate simulations seems to favour either relatively high late Miocene atmospheric CO2 concentrations and/or a weak sensitivity of the model to simulate the magnitude of high-latitude warming in a warmer than modern climate. PMID:27041737

Seagrass impact on sediment exchange between tidal flats and salt Marsh, and the sediment budget of shallow bays

USGS Publications Warehouse

Donatelli, Carmine; Ganju, Neil Kamal; Fagherazzi, Sergio; Leonardi, Nicoletta

2018-01-01

surroundings and are therefore frequently referred to as ecological engineers. The effect of seagrasses on coastal bay resilience and sediment transport dynamics is understudied. Here we use six historical maps of seagrass distribution in Barnegat Bay, USA, to investigate the role of these vegetated surfaces on the sediment storage capacity of shallow bays. Analyses are carried out by means of the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) numerical modeling framework. Results show that a decline in the extent of seagrass meadows reduces the sediment mass potentially stored within bay systems. The presence of seagrass reduces shear stress values across the entire bay, including unvegetated areas, and promotes sediment deposition on tidal flats. On the other hand, the presence of seagrasses decreases suspended sediment concentrations, which in turn reduces the delivery of sediment to marsh platforms. Results highlight the relevance of seagrasses for the long-term survival of coastal ecosystems, and the complex dynamics regulating the interaction between subtidal and intertidal landscapes.

Alkenone Paleotemperature Determinations

NASA Astrophysics Data System (ADS)

Herbert, T. D.

2003-12-01

The organic biomarker proxy for past sea surface temperatures ("U37k") came to paleoceanography from an unexpected direction. Nearly all paleoceanographic tools rely on some aspect of the fossilized hard parts of marine organisms. Thus, assemblages of calcareous microplankton such as foraminifera and coccoliths, or of siliceous plankton such as radiolaria and diatoms, provided the basis for the CLIMAP reconstruction of the Ice Age ocean (CLIMAP, 1976, 1981). Additionally, a host of chemical methods relies on the same hard parts to furnish isotopic and trace element signatures, and generally requires that skeletal material be well preserved. The alkenone method differs in several important ways. Individual molecules, extracted and separated from a matrix of hundreds to thousands of other organic compounds, are the targets. In most cases, the remnant alkenones and alkenoates that are the subject of this review constitute no more, and often considerably less, than a few percent of their initial flux that left the surface layer of the ocean and fell toward the sediments. Good preservation is thus not a major issue for use of the proxy. In addition, while many geochemical techniques assume that skeletal material is a passive recorder of isotopic and trace element composition of seawater, and that incorporation of paleo-environmental signals follows thermodynamic laws that can be modeled using nonbiogenic phases in the laboratory, the alkenone method assumes that the ratios of biomarkers measured were actively regulated by the producing organisms in life according to the temperature of the water in which they grew.Alkenone paleothermometry promises a direct estimate of near-surface ocean temperatures. Alkenones and the related alkenoates come exclusively from a few species of haptophyte algae. These organisms require sunlight, and they generally prefer the upper photic zone. The environmental information contained in their molecular fossils therefore is quite specific, although, as will be discussed at length in a later section, ambiguities still exist on the depth and seasonal variations of alkenone-producing species in the ocean. In contrast, many assemblages of planktonic organisms such as foraminifera and radiolaria contain many species known to live well below the surface mixed layer. The link between microfossil assemblages and sea surface temperature and salinity is therefore indirect and statistical, rather than mechanistic.As originally defined by the Bristol organic geochemistry group (Brassell, 1986a, b), the U37k index reflected the proportions of the di-(C37:2), tri-(C37:3), and tetra-(C37:4) unsaturated ketones. Subsequent work showed that there was no empirical benefit to including the C37:4 ketone in a paleotemperature equation. The currently accepted U37k' index (Prahl and Wakeham, 1987) varies positively with temperature, and is defined as C37:2/(C37:2+C37:3), where C37:2 represents the quantity of the di-unsaturated ketone and C37:3 the quantity of the tri-unsaturated form. The alkenone paleotemperature proxy thus depends only on the relative proportions of the common C37 ketones and not on their absolute amounts. Furthermore, although the alkenones are produced by calcareous algae, they survive in sediments where carbonate has dissolved, as first recognized by Marlowe et al. (1984a, b) and Brassell et al. (1986a). The above expression for the index shows that it can vary between 0 and 1.0; thus, it may saturate at either extremely cold or warm temperatures.Alkenones appear recalcitrant to diagenesis in the water column and within sediments relative to other large macromolecules. Indeed, the first reported occurrence of alkenones came not from recent material, but from Miocene age sediments of the Walvis Ridge (Boon et al., 1978). Shortly thereafter, these compounds were linked to modern haptophyte algae, principally Emiliania huxleyi (de Leeuw et al., 1980; Volkman et al., 1980a, b; Marlowe et al., 1984a, b). Reviews of lipid analyses of Deep Sea Drilling Project sediments revealed that most sediments of Pleistocene through mid-Eocene age appeared to contain measurable quantities of alkenones and alkenoates ( Marlowe et al., 1984a, 1990; Brassell, 1993). Brassell et al. (1986a) provided the seminal study linking alkenone unsaturation to paleotemperature fluctuations in the Late Pleistocene. After noting that modern surface sediments differed in their unsaturation ratios depending on latitude, Brassell et al. (1986a, b) reconstructed alkenone unsaturation in conjunction with benthic and planktonic foraminiferal δ18O over the last 8×105 yr in a core from the subtropical North Atlantic. The unsaturation index declined during glacial periods, suggesting cooler surface ocean temperatures during ice age conditions. The authors further demonstrated that the alkenone index gave a continuous paleoclimatic curve, even in intervals barren of foraminifera due to dissolution. Prahl and Wakeham (1987) and Prahl et al. (1988) proposed the first quantitative calibration of alkenone unsaturation to growth temperature. Unsaturation parameters measured on a strain of E.huxleyi grown in the laboratory at known temperatures were compared to the unsaturation index on particulate material collected from the near-surface ocean in the northeast Pacific. Prahl and Wakeham (1987) showed that the laboratory calibration appeared to apply well to the field observations of unsaturation and the water temperature in which the alkenones apparently were synthesized. The calibration of alkenone unsaturation to temperatures expanded with the first systematic study of core-top sediments by Sikes et al. (1991). That study produced two important results: (i) the unsaturation index in recent sediments followed a relation to overlying sea surface temperatures (SSTs) very similar to the Prahl et al. (1988) calibration, and (ii) there appeared to be no ill effects on the unsaturation index over the time of core storage. Pristine or frozen samples were therefore not needed to produce good estimates of the U37k' index for paleoceanographic studies.As with any paleoceanographic proxy, a number of uncertainties must be evaluated that could affect the accuracy measurement as an estimate of past SSTs. The principal caveats raised can be broadly categorized as ecological, physiological, genetic, and diagenetic. All describe factors, which could cause the U37k' index to deviate from a unique relation to SSTs. Ecological concerns come from observations that alkenone-producing species do not inhabit precisely the same depth throughout the ocean, and that they vary in abundance seasonally. The alkenone unsaturation parameter recorded by sediments could therefore measure past temperatures very precisely, but at which depths, and with what seasonal bias? It is also possible that the proportions of alkenones synthesized by haptophyte algae vary with growth rate, independent of temperature. Our present state of ignorance dictates that we do not know the growth phase of haptophyte material exported out of the photic zone - whether the products represent the initial exponential growth phase observed in culture or stationary growth. Natural populations also differ in their genetic composition. Alkenone-producing species are notable for their wide range of environmental tolerances. The consequences for the U37k' index of genetic variations within strains of the same producing species and between the different alkenone-synthesizing species are still debated. In addition, alkenones measured in sediments represent the surviving molecules of a series of degradational pathways that begin in the water column, proceed to the sediment/water interface, and may continue into the sediment. Should there be a bias in the relative lability of the C37:2 and C37:3 ketones, this would be imparted to paleoceanographic reconstructions of temperature.As should become clear, the U37k' index appears nevertheless to provide a remarkably faithful estimate of paleotemperatures near the sea surface. At the same time, difficulties in matching the space and timescales of modern process studies to the information contained in sediments mean that the caveats raised above remain significant. Field studies provide only snapshots of haptophyte abundance and alkenone unsaturation parameters, sediment traps provide only a few years of data at only a few locations in the global ocean, and it is unclear how well laboratory cultures replicate the natural environment. I have endeavored to treat different lines of evidence systematically, but I have found it difficult to discuss each aspect in a purely serial way. The reader will therefore be asked to digest a review in which very diverse measurements and paradigms are woven together to answer the central question of how to reconstruct past ocean surface temperatures with the U37k' proxy.

The metal oxide fraction of pelagic sediment in the equatorial North Pacific Ocean: A source of metals in ferromanganese nodules

USGS Publications Warehouse

Piper, D.Z.

1988-01-01

Pelagic sediment recovered at DOMES Site A in the equatorial North Pacific (151??W, 9?? 15???N) consists of a surface homogeneous layer, approximately 10 cm thick, overlying a strongly mottled layer that is lighter in color. The radiolarian composition of both units is Quaternary. In areas where this sediment was only a few centimeters thick, the underlying sediment was early Tertiary. Clay mineralogy and major oxide composition of the two Quaternary sediments are uniform. Their similarity to continental shale suggests that the sediment has a terrigenous source. Clay mineralogy and major oxide composition of the Tertiary sediment also are uniform, although they differ markedly from the Quarternary sediment. In contrast to the major oxides, concentrations of Mn, Co, Cu, and Ni soluble in hydroxylamine hydrochlorideacetic acid are strongly different in the surface and subsurface Quaternary sediment. Mn and Ni exhibit pronounced depletions in the subsurface sediment, Ni slightly more than Mn. Cu is also depleted in the subsurface sediment, but less than Mn. It is also depleted in the subsurface Tertiary sediment, whereas the Mn concentration remains high. Concentration of Co relative to Mn increases into the subsurface Quaternary sediment to a constant Co:Mn ratio of 3 ?? 10-2. The trivalent REE (the REE exclusive of Ce) and Fe exhibit little down-core variation. Distribution of elements in these sediments is closely related to their concentration in associated surface ferromanganese nodules. The nodules are of two distinct types: those from the area where the Quaternary sediment is relatively thick have ??-MnO2 as the dominant manganese mineral. The ratios of Ni:Mn, Cu:Mn, and Fe:Mn in these nodules approximate the corresponding ratios of the soluble fraction of surface sediment. Todorokite is the dominant mineral of nodules recovered from areas where the Quaternary sediment is thin. Relatively high Cu/Mn, Ni/Mn, and low Fe/Mn ratios of these nodules mirror differences between the soluble fraction of surface and subsurface Quaternary sediment. These compositional trends of sediment and nodules at DOMES Site A reflect a diagenetic origin for the todorokite nodules and a predominantly hydrogenous origin for the ??-MnO2 nodules. ?? 1988.

Residual β activity of particulate (234)Th as a novel proxy for tracking sediment resuspension in the ocean.

PubMed

Lin, Wuhui; Chen, Liqi; Zeng, Shi; Li, Tao; Wang, Yinghui; Yu, Kefu

2016-06-02

Sediment resuspension occurs in the global ocean, which greatly affects material exchange between the sediment and the overlying seawater. The behaviours of carbon, nutrients, heavy metals, and other pollutants at the sediment-seawater boundary will further link to climate change, eutrophication, and marine pollution. Residual β activity of particulate (234)Th (RAP234) is used as a novel proxy to track sediment resuspension in different marine environments, including the western Arctic Ocean, the South China Sea, and the Southern Ocean. Sediment resuspension identified by high activity of RAP234 is supported by different lines of evidence including seawater turbidity, residence time of total (234)Th, Goldschmidt's classification, and ratio of RAP234 to particulate organic carbon. A conceptual model is proposed to elucidate the mechanism for RAP234 with dominant contributions from (234)Th-(238)U and (212)Bi-(228)Th. The 'slope assumption' for RAP234 indicated increasing intensity of sediment resuspension from spring to autumn under the influence of the East Asian monsoon system. RAP234 can shed new light on (234)Th-based particle dynamics and should benefit the interpretation of historical (234)Th-(238)U database. RAP234 resembles lithophile elements and has broad implications for investigating particle dynamics in the estuary-shelf-slope-ocean continuum and linkage of the atmosphere-ocean-sediment system.

Residual β activity of particulate 234Th as a novel proxy for tracking sediment resuspension in the ocean

PubMed Central

Lin, Wuhui; Chen, Liqi; Zeng, Shi; Li, Tao; Wang, Yinghui; Yu, Kefu

2016-01-01

Sediment resuspension occurs in the global ocean, which greatly affects material exchange between the sediment and the overlying seawater. The behaviours of carbon, nutrients, heavy metals, and other pollutants at the sediment-seawater boundary will further link to climate change, eutrophication, and marine pollution. Residual β activity of particulate 234Th (RAP234) is used as a novel proxy to track sediment resuspension in different marine environments, including the western Arctic Ocean, the South China Sea, and the Southern Ocean. Sediment resuspension identified by high activity of RAP234 is supported by different lines of evidence including seawater turbidity, residence time of total 234Th, Goldschmidt’s classification, and ratio of RAP234 to particulate organic carbon. A conceptual model is proposed to elucidate the mechanism for RAP234 with dominant contributions from 234Th-238U and 212Bi-228Th. The ‘slope assumption’ for RAP234 indicated increasing intensity of sediment resuspension from spring to autumn under the influence of the East Asian monsoon system. RAP234 can shed new light on 234Th-based particle dynamics and should benefit the interpretation of historical 234Th-238U database. RAP234 resembles lithophile elements and has broad implications for investigating particle dynamics in the estuary-shelf-slope-ocean continuum and linkage of the atmosphere-ocean-sediment system. PMID:27252085

Evolution of organic carbon burial in the Global Ocean during the Neogene

NASA Astrophysics Data System (ADS)

LI, Z.; Zhang, Y.

2017-12-01

Although only a small fraction of the organic carbon (OC) that rains from surface waters is eventually buried in the sediments, it is a process that controls the organic sub-cycle of the long-term carbon cycle, and the key for atmospheric O2, CO2 and nutrient cycling. Here we constrain the spatiotemporal variability of OC burial by quantifying the total organic carbon (TOC) mass accumulation rate (MAR) over the Neogene (23.0-2.6 Ma) by compiling the TOC, age model and sediment density data from sites retrieved by the Deep Sea Drilling Program, Ocean Drilling Program, and Integrated Ocean Drilling Program. We screened all available sites which yielded 80 sites with adequate data quality, covering all major ocean basins and sedimentary depositional environments. All age models are updated to the GTS 2012 timescale so the TOC MAR records from different sites are comparable. Preliminary results show a clear early Miocene peak of OC burial in many sites related to high sediment flux which might reflect the orogenic uplift and/or glacier erosion. Places that receive high influx of terrigenous inputs become "hotspots" for Neogene burial of OC. At "open ocean" sites, OC burial seems to be more impacted by marine productivity changes, with a pronounced increase during the middle Miocene "Monterey Formation" and late Miocene - early Pliocene "Biogenic Bloom". Upon the completion of the data collection, we will further explore the regional and global OC burial in the context of tectonic uplift, climate change and the evolution of primary producers and consumers during the last 23 million years of Earth history.

Validation of a continuous flow method for the determination of soluble iron in atmospheric dust and volcanic ash.

PubMed

Simonella, Lucio E; Gaiero, Diego M; Palomeque, Miriam E

2014-10-01

Iron is an essential micronutrient for phytoplankton growth and is supplied to the remote areas of the ocean mainly through atmospheric dust/ash. The amount of soluble Fe in dust/ash is a major source of uncertainty in modeling-Fe dissolution and deposition to the surface ocean. Currently in the literature, there exist almost as many different methods to estimate fractional solubility as researchers in the field, making it difficult to compare results between research groups. Also, an important constraint to evaluate Fe solubility in atmospheric dust is the limited mass of sample which is usually only available in micrograms to milligrams amounts. A continuous flow (CF) method that can be run with low mass of sediments (<10mg) was tested against a standard method which require about 1g of sediments (BCR of the European Union). For validation of the CF experiment, we run both methods using South American surface sediment and deposited volcanic ash. Both materials tested are easy eroded by wind and are representative of atmospheric dust/ash exported from this region. The uncertainty of the CF method was obtained from seven replicates of one surface sediment sample, and shows very good reproducibility. The replication was conducted on different days in a span of two years and ranged between 8 and 22% (i.e., the uncertainty for the standard method was 6-19%). Compared to other standardized methods, the CF method allows studies of dissolution kinetic of metals and consumes less reagents and time (<3h). The method validated here is suggested to be used as a standardized method for Fe solubility studies on dust/ash. Copyright © 2014 Elsevier B.V. All rights reserved.

Geology, geohydrology, and soils of NASA, Kennedy Space Center: A review

NASA Technical Reports Server (NTRS)

Schmalzer, Paul A.; Hinkle, C. Ross

1990-01-01

Sediments underlying Kennedy Space Center (KSC) have accumulated in alternating periods of deposition and erosion since the Eocene. Surface sediments are of Pleistocene and Recent ages. Fluctuating sea levels with the alternating glacial-interglacial cycles have shaped the formation of the barrier island. Merritt Island is an older landscape whose formation may have begun as much as 240,000 years ago, although most of the surface sediments are not that old. Cape Canaveral probably dates from less than 7,000 years B.P. (before present) as does the barrier strip separating Mosquito Lagoon from the Atlantic Ocean. Merritt Island and Cape Canaveral have been shaped by progradational processes but not continuously so, while the Mosquito Lagoon barrier has been migrating landward. Deep acquifers beneath KSC are recharged inland but are highly mineralized in the coastal region and interact little with surface vegetation. The Surficial acquifer has formed in the Pleistocene and Recent deposits and is recharged by local rainfall. Sand ridges in the center of Merritt Island are important to its recharge.

Changes in Ocean Circulation with an Ice-Free Arctic: Reconstructing Early Holocene Arctic Ocean Circulation Using Geochemical Signals from Individual Neogloboquadrina pachyderma (sinistral) Shells

NASA Astrophysics Data System (ADS)

Livsey, C.; Spero, H. J.; Kozdon, R.

2016-12-01

The impacts of sea ice decrease and consequent hydrologic changes in the Arctic Ocean will be experienced globally as ocean and atmospheric temperatures continue to rise, though it is not evident to what extent. Understanding the structure of the Arctic water column during the early/mid Holocene sea ice minimum ( 6-10 kya), a post-glacial analogue of a seasonally ice-free Arctic, will help us to predict what the changes we can expect as the Earth warms over the next century. Neogloboquadrina pachyderma (sinistral; Nps) is a species of planktonic foraminifera that dominates assemblages in the polar oceans. This species grows its chambers (ontogenetic calcite) in the surface waters and subsequently descends through the water column to below the mixed layer where it quickly adds a thick crust of calcite (Kohfeld et al., 1996). Therefore, geochemical signals from both the surface waters and sub-mixed layer depths are captured within single Nps shells. We were able to target <5 μm - sized domains for δ18O using secondary ion mass spectrometry (SIMS), therefore capturing signals from both the ontogenetic and crust calcite in single Nps shells. This data was combined with laser ablation- inductively coupled mass spectrometry (LA-ICPMS) Mg/Ca profiles of trace metals through the two layers of calcite of the same shells, to determine the thermal structure of the water column. Combining δ18O, temperature, and salinity gradients from locations across the Arctic basin allow us to reconstruct the hydrography of the early Holocene Arctic sea ice minimum. These results will be compared with modern Arctic water column characteristics in order to develop a conceptual model of Arctic Ocean oceanographic change due to global warming. Kohfeld, K.E., Fairbanks, R.G., Smith, S.L., Walsh, I.D., 1996. Neogloboquadrina pachyderma(sinistral coiling) as paleoceanographic tracers in polar oceans: Evidence from northeast water polynya plankton tows, sediment traps, and surface sediments. Paleoceanography 11, 679-699.

Modeling transport and deposition of the Mekong River sediment

USGS Publications Warehouse

Xue, Zuo; He, Ruoying; Liu, J. Paul; Warner, John C.

2012-01-01

A Coupled Wave–Ocean–SedimentTransport Model was used to hindcast coastal circulation and fine sedimenttransport on the Mekong shelf in southeastern Asian in 2005. Comparisons with limited observations showed that the model simulation captured the regional patterns and temporal variability of surface wave, sea level, and suspended sediment concentration reasonably well. Significant seasonality in sedimenttransport was revealed. In summer, a large amount of fluvial sediments was delivered and deposited near the MekongRiver mouth. In the following winter, strong ocean mixing, and coastal current lead to resuspension and southwestward dispersal of a small fraction of previously deposited sediments. Model sensitivity experiments (with reduced physics) were performed to investigate the impact of tides, waves, and remotely forced ambient currents on the transport and dispersal of the fluvial sediment. Strong wave mixing and downwelling-favorable coastal current associated with the more energetic northeast monsoon in the winter season are the main factors controlling the southwestward along-shelf transport.

Episodic fresh surface waters in the Eocene Arctic Ocean

NASA Astrophysics Data System (ADS)

Brinkhuis, Henk; Schouten, Stefan; Collinson, Margaret E.; Sluijs, Appy; Damsté, Jaap S. Sinninghe; Dickens, Gerald R.; Huber, Matthew; Cronin, Thomas M.; Onodera, Jonaotaro; Takahashi, Kozo; Bujak, Jonathan P.; Stein, Ruediger; van der Burgh, Johan; Eldrett, James S.; Harding, Ian C.; Lotter, André F.; Sangiorgi, Francesca; Cittert, Han Van Konijnenburg-Van; de Leeuw, Jan W.; Matthiessen, Jens; Backman, Jan; Moran, Kathryn; Expedition 302 Scientists

2006-06-01

It has been suggested, on the basis of modern hydrology and fully coupled palaeoclimate simulations, that the warm greenhouse conditions that characterized the early Palaeogene period (55-45Myr ago) probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes. Little field evidence, however, has been available to constrain oceanic conditions in the Arctic during this period. Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition, showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch (~50Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an ~800,000-year interval. The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea. The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from ~10°C to 13°C, pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans. We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas.

Episodic fresh surface waters in the Eocene Arctic Ocean

USGS Publications Warehouse

Brinkhuis, H.; Schouten, S.; Collinson, M.E.; Sluijs, A.; Damste, J.S.S.; Dickens, G.R.; Huber, M.; Cronin, T. M.; Onodera, J.; Takahashi, K.; Bujak, J.P.; Stein, R.; Van Der Burgh, J.; Eldrett, J.S.; Harding, I.C.; Lotter, A.F.; Sangiorgi, F.; Cittert, H.V.K.V.; De Leeuw, J. W.; Matthiessen, J.; Backman, J.; Moran, K.

2006-01-01

It has been suggested, on the basis of modern hydrology and fully coupled palaeoclimate simulations, that the warm greenhouse conditions that characterized the early Palaeogene period (55-45 Myr ago) probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes. Little field evidence, however, has been available to constrain oceanic conditions in the Arctic during this period. Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition, showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch (???50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an ???800,000-year interval. The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea. The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from ???10??C to 13??C, pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans. We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas. ?? 2006 Nature Publishing Group.

Foraminifer- and diatom-based paleoceanographic study of Holocene sediments from the Sabrina Coast, East Antarctica

NASA Astrophysics Data System (ADS)

Vadman, K. J.; Shevenell, A.; Leventer, A.; Domack, E. W.; Huber, B. A.; Orsi, A. H.; Gulick, S. P. S.

2015-12-01

Cruise NBP14-02 conducted the first interdisciplinary oceanographic survey of the continental shelf adjacent to the Totten Glacier-Moscow University Ice Shelf system on the Sabrina Coast, East Antarctica. Hydrographic data indicate that this system is presently influenced by subsurface (>350 m) intrusion of relatively warm (>0°C) modified Circumpolar Deep Water (mCDW) via a cross-shelf trough. To assess the late Quaternary influence of mCDW, we collected marine sediment cores at two locations, each of which recovered a complete 10-13 m sequence of glacial diamict and Holocene laminated diatom ooze/mud. Chronology is constrained by 210Pb and species-specific foraminifer-based AMS 14C dates. Foraminifer CaCO3 is most abundant in surface sediments (0-0.2 mcd) and from 1.5 to 5 mcd. Planktic foraminifer, Neogloboquadrina pachyderma(s), dominates surface sediments and diatom muds downcore, but is less abundant in diatom oozes. Benthic foraminifer species, Bulimina aculeata, which prefers hemipelagic environments and bottom waters >0°C, dominates the living benthic assemblage. The fossil benthic assemblage is characterized by Trifarina angulosa, associated with oxygenated bottom waters and strong bottom currents, suggesting that this assemblage may record past changes in the shoreward flow of ocean currents and the location of oceanic frontal zones. T. angulosa presence in oozes of mat-forming diatom species associated with oceanic fronts, supports this interpretation. Modern benthic and planktic δ18O suggest a well-mixed water column. Below 1.5 mcd, foraminifer isotopes and diatom assemblages indicate surface stratification and increased biogenic productivity, suggesting that modern environmental conditions, including mCDW inflow, existed episodically during the Holocene. Paired T. angulosa δ18O and Mg/Ca analyses will provide additional information on past mCDW influence on this climatically sensitive region at the outlet of the extensive (287,000 km2) Aurora Subglacial Basin, which holds a 2-4.5 km thick volume of ice equivalent to >5 m of eustatic sea level rise.

Dissolved organic matter (DOM) in pore water of Arctic Ocean sediments: linking DOM molecular composition with microbial community structure

NASA Astrophysics Data System (ADS)

Rossel, P. E.; Bienhold, C.; Boetius, A.; Dittmar, T.

2016-02-01

Marine organic matter (OM) that sinks from surface waters to the seafloor is the energy and carbon source for benthic communities. These communities produce dissolved organic matter (DOM) in the process of remineralization, enriching the sediment porewater with fresh DOM compounds. In the Arctic Ocean, primary production is limited by nutrients and light and is thus strongly influenced by sea ice cover. Ice cover is expected to further decrease due to global warming, which may have important consequences for primary production and the quantity and quality of OM exported to the seafloor. This study focused on: 1) the molecular composition of the DOM in sediment pore waters of the deep Eurasian Arctic basins, 2) whether there is any relation between Arctic Ocean ice cover and DOM composition and 3) whether the DOM composition correlates with microbial community structure. Molecular data, obtained via 15 Tesla Fourier transform ion cyclotron resonance mass spectrometry, were statistically correlated with environmental parameters. The productive ice margin stations showed higher abundances of molecular formulae of peptides, unsaturated aliphatics and saturated fatty acids. This molecular trend is indicative of fresh OM and phytodetritus deposition, compared to the northernmost, ice-covered stations which had stronger aromatic signals. Benthic bacterial community structure, as assessed with the fingerprinting method ARISA, was significantly correlated with DOM molecular composition. Further analyses using Illumina next-generation sequencing will enable the taxonomic identification of specific bacterial groups and their interdependence with DOM compounds. This study contributes to the understanding of the coupling between Arctic Ocean productivity and its depositional regime, and provides first insights into potential links between microbial community structure and DOM molecular composition in Arctic sediments

Quantifying trace element and isotope fluxes at the ocean-sediment boundary: a review.

PubMed

Homoky, William B; Weber, Thomas; Berelson, William M; Conway, Tim M; Henderson, Gideon M; van Hulten, Marco; Jeandel, Catherine; Severmann, Silke; Tagliabue, Alessandro

2016-11-28

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment-water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment-water boundary on many TEI cycles, and underline the fact that our knowledge of the source-sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment-water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'. © 2015 The Authors.

Quantifying trace element and isotope fluxes at the ocean-sediment boundary: a review

NASA Astrophysics Data System (ADS)

Homoky, William B.; Weber, Thomas; Berelson, William M.; Conway, Tim M.; Henderson, Gideon M.; van Hulten, Marco; Jeandel, Catherine; Severmann, Silke; Tagliabue, Alessandro

2016-11-01

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment-water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment-water boundary on many TEI cycles, and underline the fact that our knowledge of the source-sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment-water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory. This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

Sediment failures within the Peach Slide (Barra Fan, NE Atlantic Ocean) and relation to the history of the British-Irish Ice Sheet

NASA Astrophysics Data System (ADS)

Owen, Matthew J.; Maslin, Mark A.; Day, Simon J.; Long, David

2018-05-01

The Peach Slide is the largest known submarine mass movement on the British continental margin and is situated on the northern flank of the glacigenic Barra Fan. The Barra Fan is located on the northwest British continental margin and is subject to cyclonic ocean circulation, with distinct differences between the circulation during stadial and inter-stadial periods. The fan has experienced growth since continental uplift during the mid-Pliocene, with the majority of sediments deposited during the Pleistocene when the fan was a major depocentre for the British-Irish Ice Sheet (BIIS). Surface and shallow sub-surface morphology of the fan has been mapped using newly digitised archival paper pinger and deep towed boomer sub-bottom profile records, side scan sonar and multibeam echosounder data. This process has allowed the interpretation and mapping of a number of different seismic facies, including: contourites, hemipelagites and debrites. Development of a radiocarbon based age model for the seismic stratigraphy constrains the occurrence of two periods of slope failure: the first at circa 21 ka cal BP, shortly after the BIIS's maximum advance during the deglaciation of the Hebrides Ice Stream; and the second between 12 and 11 ka cal BP at the termination of the Younger Dryas stadial. Comparison with other mass movement events, which have similar geological and oceanographic settings, suggests that important roles are played by contouritic and glacigenic sedimentation, deposited in inter-stadial and stadial periods respectively when different thermohaline regimes and sediment sources dominate. The effect of this switch in sedimentation is to rapidly deposit thick, low permeability, glacigenic layers above contourite and hemipelagite units. This process potentially produced excess pore pressure in the fan sediments and would have increased the likelihood of sediment failure via reduced shear strength and potential liquefaction.

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.

Indicators of sewage contamination in sediments beneath a deep-ocean dump site off New York

USGS Publications Warehouse

Bothner, Michael H.; Takada, H.; Knight, I.T.; Hill, R.T.; Butman, B.; Farrington, J.W.; Colwell, R.R.; Grassle, J. F.

1994-01-01

The world's largest discharge of municipal sewage sludge to surface waters of the deep sea has caused measurable changes in the concentration of sludge indicators in sea-floor sediments, in a spatial pattern which agrees with the predictions of a recent sludge deposition model. Silver, linear alkylbenzenes, coprostanol, and spores of the bacterium Clostridium perfringens, in bottom sediments and in near-bottom suspended sediment, provide evidence for rapid settling of a portion of discharged solids, accumulation on the sea floor, and biological mixing beneath the water sediment interface. Biological effects include an increase in 1989 of two species of benthic polychaete worm not abundant at the dump site before sludge dumping began in 1986. These changes in benthic ecology are attributed to the increased deposition of utilizable food in the form of sludge-derived organic matter.

Do manganese nodules grow or dissolve after burial? Results from the Central Indian Ocean Basin

NASA Astrophysics Data System (ADS)

Pattan, J. N.; Parthiban, G.

2007-07-01

Fifty buried manganese nodules at different depth intervals were recovered in 12 sediment cores from the Central Indian Ocean Basin (CIOB). A maximum of 15 buried nodules were encountered in one sediment core (AAS-22/GC-07) and the deepest nodule was recovered at 5.50 m below seafloor in core AAS-04/GC-5A. Approximately 80% of the buried nodules are small in size (˜2 cm diameter) in contrast to the Atlantic Ocean and Peru Basin (Pacific Ocean) where the majority of the buried nodules are large, ˜8 cm and >6 cm, respectively. Buried nodule size decreases with core depth and this distribution appears to be similar to the phenomenon of "Brazil Nut Effect". Buried nodules exhibit both smooth and rough surface textures and are ellipsoidal, elongated, rounded, sub rounded, irregular and polynucleated. Buried nodules from siliceous ooze are enriched in Mn, Cu, Ni, Zn, Mo, Ga, V and Rb whereas those from red clay are enriched in Fe, Co, Ti, U, Th, Y, Cr, Nb and Rare Earth Elements (REE). Buried nodules from siliceous ooze suggest their formation under hydrogenetic, early digenetic and diagenetic processes whereas those from red clay are of hydrogenetic origin. REE are enriched more than 1.5 times in buried nodules from red clay compared to siliceous ooze. However, the mode of incorporation of REE into buried nodules from both sedimentary environments is by a single authigenic phase consisting of Fe-Ti-P. Shale-normalized REE patterns and Ce anomalies suggest that nodules from siliceous ooze formed under more oxidizing conditions than those from red clay. Nodules buried at depths between 1.5 and 2.5 m are diagenetic (Mn/Fe ratio 10-15), formed in highly oxic environments (large positive Ce anomalies) and record aeolian dust (high Eu anomalies). Chemical composition, surface texture and morphology of buried nodules are similar to those of surface nodules from the same basin. Furthermore, buried nodule compositions do not exhibit any distinct patterns within the core depth, suggesting that buried nodules neither grow nor dissolve after their burial in the sediment column.

Meteoric 10Be/9Be ratios in marine sedimentary records: Deciphering the mixing between their marine and terrestrial sources and influence of costal trace metal fluxes

NASA Astrophysics Data System (ADS)

Wittmann, H.; von Blanckenburg, F.; Mohtadi, M.; Christl, M.; Bernhardt, A.

2017-12-01

Meteoric 10Be to stable 9Be ratios combine a cosmogenic nuclide produced in the atmosphere at a rate known from reconstructions of magnetic field strength with a stable isotope that records the present and past continental weathering and erosion flux. In seawater, the 10Be/9Be ratio provides important information on metal release from bottom sediments, called boundary exchange, and the oceanic mixing of reactive trace metals due to the inherently different sources of the two isotopes. When measured in the authigenic phase of marine sediments, the 10Be/9Be ratio allows deriving the feedbacks between erosion, weathering, and climate in the geologic past. At an ocean margin site 37°S offshore Chile, we use the 10Be/9Be ratio to trace changes in terrestrial particulate composition due to exchange with seawater. We analyzed the reactive (sequentially extracted) phase of marine surface sediments along a coast-perpendicular transect, and compared to samples from their riverine source. We find evidence for growth of authigenic rims through co-precipitation, not via reversible adsorption, that incorporate an open ocean 10Be/9Be signature from a deep water source only 30 km from the coast, thereby overprinting terrestrial riverine 10Be/9Be signatures. We show that the measured 10Be/9Be ratios in marine sediments comprise a mixture between seawater-derived and riverine-sourced phases. As 10Be/9Be ratios increase due to exchange with seawater, particulate-bound Fe concentrations increase, which we attribute to release of Fe-rich pore waters during boundary exchange in the sediment. The implications for the use of 10Be/9Be in sedimentary records for paleo-denudation flux reconstructions are that in coast-proximal sites that are neither affected by deeper water nor by narrow boundary currents, the authigenic record will be a direct recorder of terrigenous denudation of the adjacent river catchments. Hence archive location and past oceanic circulation have to be accounted for when reconstructing continental erosion and weathering, and only at open ocean sites that are fully reset by seawater global signals can be reconstructed.

Strangelove ocean at era boundaries, terrestrial or extraterrestrial cause

NASA Astrophysics Data System (ADS)

Hsue, Kenneth J.

Negative perturbations in carbon-isotope value of calcite in pelagic sediments were found at times of biotic crisis, marking horizons which are, or were proposed as era boundaries: Cretaceous/Tertiary (K/T), Permian/Triassic (P/T), and Precambrian/Cambrian (PreC/C). The anomaly was also found at several other mass-extinction horizons, such as terminal Ordovician, Frasnian-Famenian, etc. Studies of K/T boundary indicate that only the planktic fraction of the sediments has the negative isotope anomaly, whereas the benthic fraction has the same value across the boundary. This geochemical signal is thus considered a record of strangelove ocean, or an ocean where isotope fractionation of dissolved carbonate ions in surface waters (by biotic function of planktic organisms) has been significantly reduced because of the drastic reduction of the biomass in the oceans. The reduction of marine biomass at each of the era boundaries was related to chemical pollution of the oceans as a consequence of a catastrophic event; a pH decrease of 0.5 could inhibit the fertility of planktons. Studies of earthquakes, volcanic eruptions, and meteorite-impact occurrences have indicated a linearly inverse log/log relationship between the magnitude and frequency of events. The frequency of era boundaries in geologic history supports the postulate that the rare events causing those biotic crises were large bolide-impacts.

Strangelove ocean at era boundaries, terrestrial or extraterrestrial cause

NASA Technical Reports Server (NTRS)

Hsue, Kenneth J.

1988-01-01

Negative perturbations in carbon-isotope value of calcite in pelagic sediments were found at times of biotic crisis, marking horizons which are, or were proposed as era boundaries: Cretaceous/Tertiary (K/T), Permian/Triassic (P/T), and Precambrian/Cambrian (PreC/C). The anomaly was also found at several other mass-extinction horizons, such as terminal Ordovician, Frasnian-Famenian, etc. Studies of K/T boundary indicate that only the planktic fraction of the sediments has the negative isotope anomaly, whereas the benthic fraction has the same value across the boundary. This geochemical signal is thus considered a record of strangelove ocean, or an ocean where isotope fractionation of dissolved carbonate ions in surface waters (by biotic function of planktic organisms) has been significantly reduced because of the drastic reduction of the biomass in the oceans. The reduction of marine biomass at each of the era boundaries was related to chemical pollution of the oceans as a consequence of a catastrophic event; a pH decrease of 0.5 could inhibit the fertility of planktons. Studies of earthquakes, volcanic eruptions, and meteorite-impact occurrences have indicated a linearly inverse log/log relationship between the magnitude and frequency of events. The frequency of era boundaries in geologic history supports the postulate that the rare events causing those biotic crises were large bolide-impacts.

"Recent" macrofossil remains from the Lomonosov Ridge, central Arctic Ocean

NASA Astrophysics Data System (ADS)

Le Duc, Cynthia; de Vernal, Anne; Archambault, Philippe; Brice, Camille; Roberge, Philippe

2016-04-01

The examination of surface sediment samples collected from 17 sites along the Lomonosov Ridge at water depths ranging from 737 to 3339 meters during Polarstern Expedition PS87 in 2014 (Stein, 2015), indicates a rich biogenic content almost exclusively dominated by calcareous remains. Amongst biogenic remains, microfossils (planktic and benthic foraminifers, pteropods, ostracods, etc.) dominate but millimetric to centrimetric macrofossils occurred frequently at the surface of the sediment. The macrofossil remains consist of a large variety of taxa, including gastropods, bivalvia, polychaete tubes, scaphopods, echinoderm plates and spines, and fish otoliths. Among the Bivalvia, the most abundant taxa are Portlandia arctica, Hyalopecten frigidus, Cuspidaria glacilis, Policordia densicostata, Bathyarca spp., and Yoldiella spp. Whereas a few specimens are well preserved and apparently pristine, most mollusk shells displayed extensive alteration features. Moreover, most shells were covered by millimeter scale tubes of the serpulid polychaete Spirorbis sp. suggesting transport from low intertidal or subtidal zone. Both the ecological affinity and known geographic distribution of identified bivalvia as named above support the hypothesis of transportation rather than local development. In addition to mollusk shells, more than a hundred fish otoliths were recovered in surface sediments. The otoliths mostly belong to the Gadidae family. Most of them are well preserved and without serpulid tubes attached to their surface, suggesting a local/regional origin, unlike the shell remains. Although recovered at the surface, the macrofaunal assemblages of the Lomonosov Ridge do not necessarily represent the "modern" environments as they may result from reworking and because their occurrence at the surface of the sediment may also be due to winnowing of finer particles. Although the shells were not dated, we suspect that their actual ages may range from modern to several thousands of years as suggested by the radiocarbon dating of the upper centimeter of the sediment in PS87/030-2 (7792 ± 59 14C years BP), PS87/055-1 (3897 ± 41 14C years BP), and PS87/099-4 (1421 ± 66 14C years BP). Reference Stein, R. (Ed.), 2015. The Expedition PS87 of the Research Vessel Polarstern to the Arctic Ocean in 2014, Reports on Polar and Marine Research 688, Bremerhaven, Alfred Wegener Institute for Polar and Marine Research, 273 pp (http://epic.awi.de/37728/1/BzPM_0688_2015.pdf).

Production of giant marine diatoms and their export at oceanic frontal zones: Implications for Si and C flux from stratified oceans

NASA Astrophysics Data System (ADS)

Kemp, A. E. S.; Pearce, R. B.; Grigorov, I.; Rance, J.; Lange, C. B.; Quilty, P.; Salter, I.

2006-12-01

From a synthesis of recent oceanic observations and paleo-data it is evident that certain species of giant diatoms including Rhizosolenia spp. Thalassiothrix spp. and Ethmodiscus rex may become concentrated at oceanic frontal zones and subsequently form episodes of mass flux to the sediment. Within the nutrient bearing waters advecting towards frontal boundaries, these species are generally not dominant, but they appear selectively segregated at fronts, and thus may dominate the export flux. Ancient Thalassiothrix diatom mat deposits in the eastern equatorial Pacific and beneath the Polar Front in the Southern Ocean record the highest open ocean sedimentation rates ever documented and represent vast sinks of silica and carbon. Several of the species involved are adapted to a stratified water column and may thrive in Deep Chlorophyll Maxima. Thus in oceanic regions and/or at times prone to enhanced surface water stratification (e.g., during meltwater pulses) they provide a mechanism for generating substantial biomass at depth and its subsequent export with concomitant implications for Si export and C drawdown. This ecology has important implications for ocean biogeochemical models suggesting that more than one diatom "functional type" should be used. In spite of the importance of these giant diatoms for biogeochemical cycling, their large size coupled with the constraints of conventional oceanographic survey schemes and techniques means that they are undersampled. An improved insight into these key species will be an important prerequisite for enhancing our understanding of marine biogeochemical cycling and for assessing the impacts of climate change on ocean export production.

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle.

PubMed

Ren, Haojia; Sigman, Daniel M; Martínez-García, Alfredo; Anderson, Robert F; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T F; Haug, Gerald H

2017-08-15

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N 2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen ("fixed N") from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N 2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N 2 fixation covaried with sea level. The N 2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N-a "sluggish" ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems.

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle

NASA Astrophysics Data System (ADS)

Ren, Haojia; Sigman, Daniel M.; Martínez-García, Alfredo; Anderson, Robert F.; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T. F.; Haug, Gerald H.

2017-08-01

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen (“fixed N”) from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N2 fixation covaried with sea level. The N2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N—a “sluggish” ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems.

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle

PubMed Central

Ren, Haojia; Sigman, Daniel M.; Martínez-García, Alfredo; Anderson, Robert F.; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T. F.; Haug, Gerald H.

2017-01-01

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen (“fixed N”) from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N2 fixation covaried with sea level. The N2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N—a “sluggish” ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems. PMID:28760968

Cenozoic Circulation History of the North Atlantic Ocean From Seismic Stratigraphy of the Newfoundland Ridge Drift Complex

NASA Astrophysics Data System (ADS)

Boyle, P. R.; Romans, B.; Norris, R. D.; Tucholke, B. E.; Swift, S. A.; Sexton, P. F.

2014-12-01

In the North Atlantic Ocean, contour-following bottom currents have eroded regional unconformities and deposited contourite drifts that exceed two km in thickness and extend for 100s of km. The character of deep-water masses that are conveyed through ocean basins by such currents influence global heat transfer and ocean-atmosphere partitioning of CO2. The Newfoundland Ridge Drift Complex lies directly under the modern Deep Western Boundary Current southeast of Newfoundland, close to the site of overturning in the northwest Atlantic Ocean and at the intersection of the warm Gulf Stream and cool Labrador surface currents. To the south are regions of the western North Atlantic basin that are influenced by southern- as well as northern-sourced bottom waters. Here, we document the evolution of North Atlantic deep-water circulation by seismic-stratigraphic analysis of the long-lived and areally extensive Newfoundland Ridge Drift Complex. IODP Expedition 342 boreholes provide age control on seismic units, allowing sedimentation patterns to be placed in a temporal framework. We find three major phases of sedimentation: pre-contourite drift (~115-50 Ma), active contourite drift (~50-2.6 Ma), and late-contourite drift (~2.6-0 Ma). Bottom-current-controlled deposition of terrigenous-rich sediment began at ~50 Ma, which correlates to the onset of a long-term global cooling trend. A further change in deep circulation near the Eocene-Oligocene transition (~30 Ma) is indicated by more focused drift sedimentation with greatly increased accumulation rates and stratal architecture dominated by mud waves. At ~2.6 Ma to present the axis of drift accumulation shifted markedly towards shallower water depths, corresponding with the onset of Northern Hemisphere ice sheets. We discuss how these reorganizations of deep circulation correlate with results of other North Atlantic seismic stratigraphic studies to the north and south.

Biogeography of Radiolaria Polycystina (Protista) in the World Ocean

NASA Astrophysics Data System (ADS)

Boltovskoy, Demetrio; Correa, Nancy

2016-12-01

Analysis of 307 species of Radiolaria Polycystina in a worldwide dataset of 4774 plankton, sediment trap, and surface sediment samples allows recognizing six major biogeographic Domains. Five of them are circumglobal (Polar North, Polar South, Bi-Subpolar, Transitional and Tropical-Subtropical), and one is restricted to the Eastern Equatorial Pacific. Each Domain is characterized by a particular suite of species, all of which, however, occur widely, albeit sparsely, in one or more other Domains. Of the eight environmental variables evaluated, temperature correlates best with the partitions established. Species distributions in the water column and in the sediments are generally in agreement, but in the sediments cold water forms extend farther towards the equator than do warm water radiolarians towards the poles. In the Recent sedimentary record of planktonic Foraminifera the same phenomenon is magnified by the higher dissolution rates of warm water species, as compared with the cold water ones. Of the three major oceans, the Pacific was the most speciose, but estimates based on data corrected for sample-size show much smaller inter-oceanic differences, with ∼10 radiolarians probably being absent from either basin. The radiolarian biogeographic pattern is generally similar to those based on other planktonic and nektonic open-ocean organisms, but the degree of uniqueness of the Domains, as well as the position of the intervening boundaries, are variable, which reflects methodological differences, as well as taxon-specific traits. Partitions of the World Ocean defined on the basis of species ranges resemble the major divisions (presumably functionally homogeneous units) established on the basis of physical traits and chlorophyll fields, but secondary divisions nested within the latter are not reflected by any of the biogeographic schemes based on species distribution ranges. This conflict raises questions about the importance of several physical mechanisms for structuring pelagic communities, and/or on the coupling of structure and function in the pelagic realm.

Quantification of Surface Suspended Sediments along a River Dominated Coast with NOAA AVHRR and SeaWiFS Measurements: Louisiana, USA

NASA Technical Reports Server (NTRS)

Myint, S. W.; Walker, N. D.

2002-01-01

The ability to quantify suspended sediment concentrations accurately over both time and space using satellite data has been a goal of many environmental researchers over the past few decades This study utilizes data acquired by the NOAA Advanced Very High Resolution Radiometer (AVHRR) and the Orbview-2 Sea-viewing wide field-of-view (SeaWiFS) ocean colour sensor, coupled with field measurements to develop statistical models for the estimation of near-surface suspended sediment and suspended solids "Ground truth" water samples were obtained via helicopter, small boat and automatic water sampler within a few hours of satellite overpasses The NOAA AVHRR atmospheric correction was modified for the high levels of turbidity along the Louisiana coast. Models were developed based on the field measurements and reflectance/radiance measurements in the visible and near infrared Channels of NOAA-14 and Orbview-2 SeaWiFS. The best models for predicting surface suspended sediment concentrations were obtained with a NOAA AVHRR Channel 1 (580-680nm) cubic model, Channel 2 (725-1100 nm) linear mod$ and SeaWiFs Channel 6 (660-68Onm) power modeL The suspended sediment models developed using SeaWiFS Channel 5 (545-565 nm) were inferior, a result that we attribute mainly to the atmospheric correction technique, the shallow depth of the water samples and absorption effects from non-sediment water constituents.

Impacts of Ocean Acidification on Sediment Processes in Shallow Waters of the Arctic Ocean

PubMed Central

Gazeau, Frédéric; van Rijswijk, Pieter; Pozzato, Lara; Middelburg, Jack J.

2014-01-01

Despite the important roles of shallow-water sediments in global biogeochemical cycling, the effects of ocean acidification on sedimentary processes have received relatively little attention. As high-latitude cold waters can absorb more CO2 and usually have a lower buffering capacity than warmer waters, acidification rates in these areas are faster than those in sub-tropical regions. The present study investigates the effects of ocean acidification on sediment composition, processes and sediment-water fluxes in an Arctic coastal system. Undisturbed sediment cores, exempt of large dwelling organisms, were collected, incubated for a period of 14 days, and subject to a gradient of pCO2 covering the range of values projected for the end of the century. On five occasions during the experimental period, the sediment cores were isolated for flux measurements (oxygen, alkalinity, dissolved inorganic carbon, ammonium, nitrate, nitrite, phosphate and silicate). At the end of the experimental period, denitrification rates were measured and sediment samples were taken at several depth intervals for solid-phase analyses. Most of the parameters and processes (i.e. mineralization, denitrification) investigated showed no relationship with the overlying seawater pH, suggesting that ocean acidification will have limited impacts on the microbial activity and associated sediment-water fluxes on Arctic shelves, in the absence of active bio-irrigating organisms. Only following a pH decrease of 1 pH unit, not foreseen in the coming 300 years, significant enhancements of calcium carbonate dissolution and anammox rates were observed. Longer-term experiments on different sediment types are still required to confirm the limited impact of ocean acidification on shallow Arctic sediment processes as observed in this study. PMID:24718610

Impacts of ocean acidification on sediment processes in shallow waters of the Arctic Ocean.

PubMed

Gazeau, Frédéric; van Rijswijk, Pieter; Pozzato, Lara; Middelburg, Jack J

2014-01-01

Despite the important roles of shallow-water sediments in global biogeochemical cycling, the effects of ocean acidification on sedimentary processes have received relatively little attention. As high-latitude cold waters can absorb more CO2 and usually have a lower buffering capacity than warmer waters, acidification rates in these areas are faster than those in sub-tropical regions. The present study investigates the effects of ocean acidification on sediment composition, processes and sediment-water fluxes in an Arctic coastal system. Undisturbed sediment cores, exempt of large dwelling organisms, were collected, incubated for a period of 14 days, and subject to a gradient of pCO2 covering the range of values projected for the end of the century. On five occasions during the experimental period, the sediment cores were isolated for flux measurements (oxygen, alkalinity, dissolved inorganic carbon, ammonium, nitrate, nitrite, phosphate and silicate). At the end of the experimental period, denitrification rates were measured and sediment samples were taken at several depth intervals for solid-phase analyses. Most of the parameters and processes (i.e. mineralization, denitrification) investigated showed no relationship with the overlying seawater pH, suggesting that ocean acidification will have limited impacts on the microbial activity and associated sediment-water fluxes on Arctic shelves, in the absence of active bio-irrigating organisms. Only following a pH decrease of 1 pH unit, not foreseen in the coming 300 years, significant enhancements of calcium carbonate dissolution and anammox rates were observed. Longer-term experiments on different sediment types are still required to confirm the limited impact of ocean acidification on shallow Arctic sediment processes as observed in this study.

Arctic Sediment Transport from Land to Sea - An Integrated Study of Coastal - Marine Processes and Deposits in Dicksonfjorden, Svalbard

NASA Astrophysics Data System (ADS)

Jensen, M.; Choi, K.; Forwick, M.; Howe, J. A.; Husum, K.; Korsun, S.; Maat, D.; Nam, S. I.

2016-12-01

Valleys and fjords are the key transport and storage systems for sediments and biogeochemical elements from high arctic landscapes to the ocean. Sediment and nutrient fluxes are important for the biochemical cycle in the fjords and eventually in the ocean, and are important input data to earth system models. At present, high latitude systems are underrepresented in such models (Russell, 2014). Dicksonfjorden is a fjord in the larger Isfjorden system, Central Spitsbergen, Svalbard. It has no direct glacial input, in contrast to fjords affected by tidewater glaciers. The sediment supply is very high and the inner fjord receives sediment from a tide-influenced delta. This study is part of a multidisciplinary project aiming at mapping and quantifying sediment types and dispersal patterns in present Arctic valley - fjord systems and is the first comprehensive study of the depositional system in Dicksonfjorden. The first field campaign took place in summer 2016, when detailed mapping of the tidal delta and the sea floor in the inner fjord, coring onshore and offshore and sampling for foraminifera, nutrients and microbial abundances were performed. The surface mapping is based on high-resolution drone images, which will be processed to a high-resolution digital elevation model, and the bathymetry and sediment distribution data from the sea floor has been collected with a Gavia Offshore Surveyor AUV, providing high-resolution bathymetry and backscatter data of the seabed. Core transects from the delta surface will be described and compared to marine cores from the fjord basin retrieved from R/V Helmer Hanssen. Sediment accumulation rates will be assessed from 210Pb and 137Cs radionuclides. Preliminary results on the physical and chemical characteristics of the sedimentation system in inner Dicksonfjorden will be presented and implications for the fjord ecosystem will be discussed. References Russell , J.L., 2014. Control on the Latitudinal distribution of climate processes: Results from Earth System Model simulations. AAPG/SEPM Hedberg Research Conference "Latitudinal controls on stratigraphic models and sedimentary concepts, Banff, Alberta, Canada, September 28 - October 1, 2014, Abstract volume, 10-11.

Ocean acidification: One potential driver of phosphorus eutrophication.

PubMed

Ge, Changzi; Chai, Yanchao; Wang, Haiqing; Kan, Manman

2017-02-15

Harmful algal blooms which may be limited by phosphorus outbreak increases currently and ocean acidification worsens presently, which implies that ocean acidification might lead to phosphorus eutrophication. To verify the hypothesis, oxic sediments were exposed to seawater with different pH 30days. If pH was 8.1 and 7.7, the total phosphorus (TP) content in sediments was 1.52±0.50 and 1.29±0.40mg/g. The inorganic phosphorus (IP) content in sediments exposed to seawater with pH8.1 and 7.7 was 1.39±0.10 and 1.06±0.20mg/g, respectively. The exchangeable phosphorus (Ex-P) content in sediments was 4.40±0.45 and 2.82±0.15μg/g, if seawater pH was 8.1 and 7.7. Ex-P and IP contents in oxic sediments were reduced by ocean acidification significantly (p<5%). The reduced phosphorus in sediments diffused into water, which implied that ocean acidification was one potential facilitator of phosphorus eutrophication in oxic conditions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Forereef and backreef corals exhibit different responses to anthropogenic stressors in Belize

NASA Astrophysics Data System (ADS)

Fowell, S.; Foster, G. L.; Castillo, K.; Ries, J. B.; Tyrrell, T.

2016-02-01

The health of coral reefs is threatened by simultaneous anthropogenic impacts, namely ocean acidification, ocean warming, elevated nutrients (nutrification) and sedimentation. These processes have been shown to reduce the ability of corals to grow, but culturing experiments have previously demonstrated this response to vary across different reef environments and between different taxa. The absence of in-situ pH data, records of nutrient evolution and limited sea surface temperature (SST) measurements prior to the 1980s, has prevented the extent of either ocean acidification, nutrification or ocean warming to be quantified in Belize. Here, we have applied a multi-proxy approach (Li/Mg, Sr/Ca, Ba/Ca, δ11B, δ13C) to reconstruct these variables in corals from across the southern Mesoamerican Barrier Reef System over the last 100 years. We find that although the warming signal is spatially coherent, significant spatial variability exists in the extent of acidification and sediment input. Further investigations into the impact of such variability, and possible changes in net primary production must be conducted before we can conclude which anthropogenic stressor is responsible for the decline in forereef coral extension rates.

Large-Scale Distribution and Activity of Prokaryotes in Deep-Sea Surface Sediments of the Mediterranean Sea and the Adjacent Atlantic Ocean

PubMed Central

Giovannelli, Donato; Molari, Massimiliano; d’Errico, Giuseppe; Baldrighi, Elisa; Pala, Claudia; Manini, Elena

2013-01-01

The deep-sea represents a substantial portion of the biosphere and has a major influence on carbon cycling and global biogeochemistry. Benthic deep-sea prokaryotes have crucial roles in this ecosystem, with their recycling of organic matter from the photic zone. Despite this, little is known about the large-scale distribution of prokaryotes in the surface deep-sea sediments. To assess the influence of environmental and trophic variables on the large-scale distribution of prokaryotes, we investigated the prokaryotic assemblage composition (Bacteria to Archaea and Euryarchaeota to Crenarchaeota ratio) and activity in the surface deep-sea sediments of the Mediterranean Sea and the adjacent North Atlantic Ocean. Prokaryotic abundance and biomass did not vary significantly across the Mediterranean Sea; however, there were depth-related trends in all areas. The abundance of prokaryotes was positively correlated with the sedimentary concentration of protein, an indicator of the quality and bioavailability of organic matter. Moving eastwards, the Bacteria contribution to the total prokaryotes decreased, which appears to be linked to the more oligotrophic conditions of the Eastern Mediterranean basins. Despite the increased importance of Archaea, the contributions of Crenarchaeota Marine Group I to the total pool was relatively constant across the investigated stations, with the exception of Matapan-Vavilov Deep, in which Euryarchaeota Marine Group II dominated. Overall, our data suggest that deeper areas of the Mediterranean Sea share more similar communities with each other than with shallower sites. Freshness and quality of sedimentary organic matter were identified through Generalized Additive Model analysis as the major factors for describing the variation in the prokaryotic community structure and activity in the surface deep-sea sediments. Longitude was also important in explaining the observed variability, which suggests that the overlying water masses might have a critical role in shaping the benthic communities. PMID:24039667

210Po/210Pb Activity Ratios as a Possible `Dating Tool' of Ice Cores and Ice-rafted Sediments from the Western Arctic Ocean - Preliminary Results

NASA Astrophysics Data System (ADS)

Krupp, K.; Baskaran, M. M.

2016-02-01

We have collected and analyzed a suite of surface snow samples, ice cores, ice-rafted sediments (IRS) and aerosol samples from the Western Arctic for Po-210 and Pb-210 to examine the extent of disequilibrium between this pair to possibly use 210Po/210Pb activity ratio to date different layers of ice cores and time of incorporation of ice-rafted sediments into the sea ice. We have earlier reported that the activity concentrations of 210Pb in IRS vary over an order of magnitude and it is 1-2 orders of magnitude higher than that of the benthic sediments (1-2 dpm/g in benthic sediments compared to 25 to 300 dpm/g in IRS). In this study, we have measured 210Po/210Pb activity ratios in aerosols from the Arctic Ocean to constrain the initial 210Po/210Pb ratio at the time of deposition during precipitation. The 210Po activity concentration in recent snow is compared to surface ice samples. The `age' of IRS incorporation can be calculated as follows: [210Po]measured = [210Po]initial + [210Pb] (1 - exp(-λt)) (1) where λ is the decay constant of 210Po, 138.4 days, and `t' is the in-growth time period. From this equation, `t' can be calculated as follows: t = (-1/λ) [ln (1- ((210Po/210Pb)measured - (210Po/210Pb)initial)] (2) The assumption involved in this approach are: i) there is no preferential uptake of 210Po (highly biogenic - S group); and iii) both 210Po and 210Pb remain as closed system. The calculated age using equation (2) will be discussed and presented.

Chernobyl radioactivity found in mid-water sediment interceptors in the N. Pacific and Bering Sea

NASA Astrophysics Data System (ADS)

Kusakabe, M.; Ku, T.-L.; Harada, K.; Taguchi, K.; Tsunogai, S.

1988-01-01

Fission-product nuclides 134Cs, 137Cs and 103Ru originated from the Chernobyl accident have been detected in sediment traps deployed at mid-water depths ranging from 110 to 780 m in the N. Pacific and the Bering Sea. The detected radioactivities, originally associated with fine airborne particles, have apparently been incorporated into much larger aggregates of predominantly biogenic material formed in the surface ocean, and transferred downward through the water column with velocities of the order of 100 m/day.

Organic carbon sources across salinity gradients in Chilean Fjords: Reloncaví Fjord ( 41°S) and Southern Patagonian ice fields area ( 48°S)

NASA Astrophysics Data System (ADS)

Placencia, Juan; Llanos, Gustavo; Contreras, Sergio

2017-04-01

The organic matter preserved in marine sediments contains contributions of allochthonous and autochthonous and variable source inputs. Allochthonous sources are terrestrial erosion (including anthropogenic material) of relatively labile and refractory material, while autochthonous sources including marine phytoplankton. In order to establish the sources of the organic matter (allochthonous/autochthonous) and how organic carbon is distributed along a salinity gradient, on this study we examined of organic Carbon/Nitrogen molar ratios (C:N), isotopic composition (δ13C) and n-alkanes (n-C24 to n-C34) in surface sediments from two continuous systems: river-fjord-ocean in Northern Patagonia (41°S-43°S), and glacier-fjord-ocean in central Patagonia (47°S-50°S). The continental inner fjord areas are characterized with sediment enriched in allochthonous organic carbon and high C:N (8-12) and low δ13C values (-23‰ to -26‰). Towards the Pacific Ocean, low C:N (6-7) and high δ13C values (-20‰ to -22‰) suggest prevalent autochthonous marine sources. Estuarine waters with salinity between 2 psu and 30 psu were associated with high C:N and low δ13C values together with odd over even long-chain n-alkane predominance (n-C31, n-C29 and n-C27) in surface sediments. All geochemical proxies suggest a great contribution of terrigenous input by glacier origin rivers, mainly from terrestrial plants in both areas. Our study provides a framework to guide future researches on environmental and climate change on these systems. This study was supported by the Chilean Navy's Hydrographic and Oceanographic Service, the Chilean National Oceanographic Committee through the Grants CONA C19F1308 and C20F1404, and the Research Office at Universidad Católica de la Ssma. Concepción.

Regional-scale drivers of marine nematode distribution in Southern Ocean continental shelf sediments

NASA Astrophysics Data System (ADS)

Hauquier, Freija; Verleyen, Elie; Tytgat, Bjorn; Vanreusel, Ann

2018-07-01

Many marine meiofauna taxa seem to possess cosmopolitan species distributions, despite their endobenthic lifestyle and restricted long-distance dispersal capacities. In light of this paradox we used a metacommunity framework to study spatial turnover in free-living nematode distribution and assess the importance of local environmental conditions in explaining differences between communities in surface and subsurface sediments of the Southern Ocean continental shelf. We analysed nematode community structure in two sediment layers (0-3 cm and 3-5 cm) of locations maximum 2400 km apart. We first focused on a subset of locations to evaluate whether the genus level is sufficiently taxonomically fine-grained to study large-scale patterns in nematode community structure. We subsequently used redundancy and variation partitioning analyses to quantify the unique and combined effects of local environmental conditions and spatial descriptors on genus-level community composition. Macroecological patterns in community structure were highly congruent at the genus and species level. Nematode community composition was highly divergent between both depth strata, likely as a result of local abiotic conditions. Variation in community structure between the different regions largely stemmed from turnover (i.e. genus/species replacement) rather than nestedness (i.e. genus/species loss). The level of turnover among communities increased with geographic distance and was more pronounced in subsurface layers compared to surface sediments. Variation partitioning analysis revealed that both environmental and spatial predictors significantly explained variation in community structure. Moreover, the shared fraction of both sets of variables was high, which suggested a substantial amount of spatially structured environmental variation. Additionally, the effect of space independent of environment was much higher than the effect of environment independent of space, which shows the importance of including spatial descriptors in meiofauna and nematode community ecology. Large-scale assessment of free-living nematode diversity and abundance in the Southern Ocean shelf zone revealed strong horizontal and vertical spatial structuring in response to local environmental conditions, in combination with (most likely) dispersal limitation.

Sediment studies at Bikini Atoll part 3. Inventories of some long-lived gamma-emitting radionuclides associated with lagoon surface sediments

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

Noshkin, V.E.

1997-12-01

Surface sediment samples were collected during 1979 from 87 locations in the lagoon at Bikini Atoll. The collections were made to better define the concentrations and distribution of long-lived radionuclides associated with the bottom material and to show what modifications occurred to the composition of the surface sediment from the nuclear testing program conducted by the United States at the Atoll between 1946 and 1958. This is the last of three reports on Bikini sediment studies. In this report, we discuss the concentrations and inventories of the residual long-lived gamma-emitting radionuclides in sediments from the lagoon. The gamma-emitting radionuclides detectedmore » most frequently in sediments collected in 1979, in addition to Americium-241 ({sup 241}Am) (discussed in the second report of this series), included Cesium-137 ({sup 137}Cs), Bismuth-207 ({sup 207}Bi), Europium-155 ({sup 155}Eu), and Cobalt-60 ({sup 60}Co). Other man-made, gamma-emitting radionuclides such as Europium-152,154 ({sup 152,154}Eu), Antimony-125 ({sup 125}Sb), and Rhodium-101,102m ({sup 101,102m}Rh) were occasionally measured above detection limits in sediments near test site locations. The mean inventories for {sup 137}Cs, {sup 207}Ei, {sup 155}Eu, and {sup 60}Co in the surface 4 cm of the lagoon sediment to be 1.7, 0.56, 7.76, and 0.74 TBq, respectively. By June 1997, radioactive decay would reduce these values to 1.1, 0.38, 0.62, and 0.07 TBq, respectively. Some additional loss results from a combination of different processes that continuously mobilize and return some amount of the radionuclides to the water column. The water and dissolved constituents are removed from the lagoon through channels and exchange with the surface waters of the north equatorial Pacific Ocean. Highest levels of these radionuclides are found in surface deposits lagoonward of the Bravo Crater. Lowest concentrations and inventories are associated with sediment lagoonward of the eastern reef. The quantities in the 0-4 cm surface layer are estimated to be less than 35% of the total inventory to depth in the sediment column.« less

Quantitative estimation of global patterns of surface ocean biological productivity and its seasonal variation on timescales from centuries to millennia

NASA Astrophysics Data System (ADS)

Loubere, Paul; Fariduddin, Mohammad

1999-03-01

We present a quantitative method, based on the relative abundances of benthic foraminifera in deep-sea sediments, for estimating surface ocean biological productivity over the timescale of centuries to millennia. We calibrate the method using a global data set composed of 207 samples from the Atlantic, Pacific, and Indian Oceans from a water depth range between 2300 and 3600 m. The sample set was developed so that other, potentially significant, environmental variables would be uncorrelated to overlying surface ocean productivity. A regression of assemblages against productivity yielded an r2 = 0.89 demonstrating a strong productivity signal in the faunal data. In addition, we examined assemblage response to annual variability in biological productivity (seasonality). Our data set included a range of seasonalities which we quantified into a seasonality index using the pigment color bands from the coastal zone color scanner (CZCS). The response of benthic foraminiferal assemblage composition to our seasonality index was tested with regression analysis. We obtained a statistically highly significant r2 = 0.75. Further, discriminant function analysis revealed a clear separation among sample groups based on surface ocean productivity and our seasonality index. Finally, we tested the response of benthic foraminiferal assemblages to three different modes of seasonality. We observed a distinct separation of our samples into groups representing low seasonal variability, strong seasonality with a single main productivity event in the year, and strong seasonality with multiple productivity events in the year. Reconstructing surface ocean biological productivity with benthic foraminifera will aid in modeling marine biogeochemical cycles. Also, estimating mode and range of annual seasonality will provide insight to changing oceanic processes, allowing the examination of the mechanisms causing changes in the marine biotic system over time. This article contains supplementary material.

Biogeographical distribution and diversity of bacterial communities in surface sediments of the South China Sea.

PubMed

Li, Tao; Wang, Peng

2013-05-01

This paper aims at an investigation of the features of bacterial communities in surface sediments of the South China Sea (SCS). In particular, biogeographical distribution patterns and the phylogenetic diversity of bacteria found in sediments collected from a coral reef platform, a continental slope, and a deep-sea basin were determined. Bacterial diversity was measured by an observation of 16S rRNA genes, and 18 phylogenetic groups were identified in the bacterial clone library. Planctomycetes, Deltaproteobacteria, candidate division OP11, and Alphaproteobacteria made up the majority of the bacteria in the samples, with their mean bacterial clones being 16%, 15%, 12%, and 9%, respectively. By comparison, the bacterial communities found in the SCS surface sediments were significantly different from other previously observed deep-sea bacterial communities. This research also emphasizes the fact that geographical factors have an impact on the biogeographical distribution patterns of bacterial communities. For instance, canonical correspondence analyses illustrated that the percentage of sand weight and water depth are important factors affecting the bacterial community composition. Therefore, this study highlights the importance of adequately determining the relationship between geographical factors and the distribution of bacteria in the world's seas and oceans.

Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions

NASA Astrophysics Data System (ADS)

Prahl, Fredrick G.; Muehlhausen, Laurel A.; Zahnle, Debra L.

1988-09-01

Cultures of the marine coccolithophorid, Emiliania huxleyi, were grown in the laboratory at five temperatures (8°, 10°, 15°, 20°, 25°C) and monitored by capillary gas chromatography for their long-chain, unsaturated lipid compositions. The long-chain lipids of this plant comprise a series of C 37, C 38 and C 39 di-, tri- and, in cells grown below 15°C, tetra-unsaturated methyl and ethyl ketones and a methyl and ethyl ester of a di-unsaturated C 36 fatty acid. Systematic changes in the degree of unsaturation and in the overall carbon chain length distribution of the alkenones and in the proportion of fatty acid esters relative to alkenones are noted as a function of growth temperature. We present temperature calibrations for these changes in the lipid composition of laboratory cultures and compare these results with the compositions of this biomarker series measured in a variety of sediments accumulating beneath warm (⩾25°C) and cold (⩽12°C) surface waters in the tropical and temperate North Pacific Ocean, respectively. The comparisons demonstrate 1) this series of biomarkers is deposited in these oceanic sediments with minimal evidence of alteration to its original composition and 2) the strain of E. huxleyi used in this laboratory calibration is representative of the "average" marine phytoplankton supplying this novel series of biomarkers to contemporary sediments in these two environments and a wide variety of other oceanic environments. The long-chain alkenones constitute a major component (8.0 ± 2.9%) of the total organic carbon content of living cells of E. huxleyi. The high cellular abundance of these compounds appears to be relatively constant and independent of the growth temperature of the plant. These biomarkers provide a well-designed and useful geochemical tool for assessing variations not only in surface water temperatures but potentially also in the productivity of an important group of marine phytoplankton in oceans of the recent and distant past.

Sediment flux measurements at the oceanic boundary of a large estuary

NASA Astrophysics Data System (ADS)

Downing-Kunz, M.; Work, P. A.; Schoellhamer, D. H.

2016-12-01

Sediment is an important resource for San Francisco Bay (SFB), in the context of wetland restoration projects, dredging operations, ecosystem health, and contaminant transport and fate. One way to help manage sediment (and sediment-associated contaminants) in SFB is by developing a quantitative sediment budget to account for sources, sinks, and storage of sediment. Previously developed sediment budgets have shown that sediment exchange at the oceanic boundary of SFB (Golden Gate) is the most poorly understood element of the SFB sediment budget, owing to logistical challenges that inhibit routine field observations. In this study, field observations of suspended-sediment flux at the Golden Gate were conducted on ebb and flood tides during two distinct periods of the 2016 hydrograph: peak (4,000 m3/s) and low (200 m3/s) rates of freshwater inflow to SFB. Suspended-sediment flux was estimated from a boat-mounted acoustic Doppler current profiler that provided measurements of discharge and acoustic backscatter (ABS) at a cross-section near the oceanic boundary. Discrete water samples were analyzed for suspended-sediment concentration (SSC) and related to ABS. During the period of peak freshwater inflow, maximum discharge observed at Golden Gate reached 130,000 m3/s during ebb tide; observed SSC (20-40 mg/L) were lower than expected compared to upstream conditions. A network of five SSC monitoring stations extending 5-80 km upstream demonstrated a watershed-sourced sediment pulse (SSC reaching 200 mg/L) moved downstream to within 20 km of the oceanic boundary, an observation corroborated by concurrent satellite imagery. This finding, combined with lower SSC near the Golden Gate, suggests the sediment pulse was trapped within SFB, indicating a freshwater inflow threshold exceeding 4,000 m3/s for sediment export at the oceanic boundary. Such trapping could provide additional sediment to benefit wetland restoration efforts.

Transfer of radionuclides from high polluted bottom sediments to marine organisms through benthic food chain in post Fukushima period

NASA Astrophysics Data System (ADS)

Bezhenar, Roman; Jung, Kyung Tae; Maderich, Vladimir; Willemsen, Stefan; de With, Govert; Qiao, Fangli

2015-04-01

A catastrophic earthquake and tsunami occurred on March 11, 2011 and severely damaged the Fukushima Daiichi Nuclear Power Plant (FDNPP) that resulted in an uncontrolled release of radioactivity into air and ocean. Around 80% of the radioactivity released due to the FDNPP accident in March-April 2011 was either directly discharged into the ocean or deposited onto the ocean surface from the atmosphere. A large amount of long-lived radionuclides (mainly Cs-137) were released into the environment. The concentration of radionuclides in the ocean reached a maximum in mid-April of 2011, and then gradually decreased. From 2011 the concentration of Cs-137 in water essentially fell except the area around the FDNPP where leaks of contaminated water are continued. However, in the bottom sediment high concentrations of Cs-137 were found in the first months after the accident and slowly decreased with time. Therefore, it should be expected that a time delay is found of sediment-bound radionuclides in marine organisms. For the modeling of radionuclide transfer from highly polluted bottom sediments to marine organisms the dynamical food chain model BURN-POSEIDON (Heling et al, 2002; Maderich et al., 2014) was extended. In this model marine organisms are grouped into a limited number of classes based on their trophic level and type of species. These include: phytoplankton, zooplankton, fishes (two types: piscivorous and non-piscivorous), crustaceans, and molluscs for pelagic food chain and bottom sediment invertebrates, demersal fishes and bottom predators for benthic food chain and whole water column predators feeding by pelagial and benthic fishes. Bottom invertebrates consume organic parts of bottom sediments with adsorbed radionuclides which then migrate through the food chain. All organisms take radionuclides directly from water as well as via food. In fishes where radioactivity is not homogeneously distributed over all tissues of the organism, it is assumed that radionuclide accumulates in a specific tissue called target tissue. This tissue (bone, flesh, stomach, and organs) controls the overall elimination rate of the nuclide in the organism. The model prediction for the coastal area around the FDNPP agree well with observations. In addition the effects from the Chernobyl accident on the Baltic Sea are modelled and these results also are in good agreement with available data. These results demonstrate the importance of the benthic food chain in long-term transfer of radionuclides from high polluted bottom sediments to the marine organisms. The developed model can be applied for different regions of the World Ocean.

California coast nearshore processes study. [nearshore currents, sediment transport, estuaries, and river discharge

NASA Technical Reports Server (NTRS)

Pirie, D. M.; Steller, D. D. (Principal Investigator)

1973-01-01

The author has identified the following significant results. Large scale sediment plumes from intermittent streams and rivers form detectable seasonal patterns on ERTS-1 imagery. The ocean current systems, as plotted from three California coast ERTS mosaics, were identified. Offshore patterns of sediment in areas such as the Santa Barbara Channel are traceable. These patterns extend offshore to heretofore unanticipated ranges as shown on the ERTS-1 imagery. Flying spot scanner enhancements of NASA tapes resulted in details of subtle and often invisible (to the eye) nearshore features. The suspended sediments off San Francisco and in Monterey Bay are emphasized in detail. These are areas of extremely changeable offshore sediment transport patterns. Computer generated contouring of radiance levels resulted in maps that can be used in determining surface and nearsurface suspended sediment distribution. Tentative calibrations of ERTS-1 spectral brightness against sediment load have been made using shipboard measurements. Information from the combined enhancement and interpretation techniques is applicable to operational coastal engineering programs.

Research highlights: impacts of microplastics on plankton.

PubMed

Lin, Vivian S

2016-02-01

Each year, millions of metric tons of the plastic produced for food packaging, personal care products, fishing gear, and other human activities end up in lakes, rivers, and the ocean. The breakdown of these primary plastics in the environment results in microplastics, small fragments of plastic typically less than 1-5 mm in size. These synthetic particles have been detected in all of the world's oceans and also in many freshwater systems, accumulating in sediment, on shorelines, suspended in surface waters, and being ingested by plankton, fish, birds, and marine mammals. While the occurrence of plastics in surface waters has been surveyed in a number of studies, the impacts of microplastics on marine organisms are still being elucidated. This highlight features three recent publications that explore the interactions of microplastics with planktonic organisms to clarify the effects of these pollutants on some of the ocean's smallest and most important inhabitants.

The CARIACO Ocean Time-Series: two decades of oceanographic observations to understand linkages between biogeochemistry, ecology, and long-term environmental variability.

NASA Astrophysics Data System (ADS)

Lorenzoni, L.; Muller-Karger, F. E.; Rueda-Roa, D. T.; Thunell, R.; Scranton, M. I.; Taylor, G. T.; benitez-Nelson, C. R.; Montes, E.; Astor, Y. M.; Rojas, J.

2016-02-01

The CARIACO Ocean Time-Series project, located in the Cariaco Basin off the coast of Venezuela, seeks to understand relationships between hydrography, primary production, community composition, microbial activity, particle fluxes, and element cycling in the water column, and how variations in these processes are preserved in sediments accumulating in this anoxic basin. CARIACO uses autonomous and shipboard measurements to understand ecological and biogeochemical changes and how these relate to regional and global climatic/ocean variability. CARIACO is a model for national ocean observing programs in Central/South America, and has been developed as a community facility platform with open access to all data (http://imars.marine.usf.edu/cariaco). Research resulting from this program has contributed to knowledge about the decomposition and cycling of particles, the biological pump, and to our understanding of the ecology and oceanography of oxygen minimum zones. Despite this basin being anoxic below 250m, remineralization rates of organic matter are comparable to those in well oxygenated waters. A dynamic microbial community significantly influences carbon and nutrient biogeochemical cycling throughout the water column. Since 1995, declining particulate organic carbon fluxes have been measured throughout the water column using sediment traps, likely in response to declining Chl-a concentrations and smaller phytoplankton which have replaced the larger taxa over the past decade. This community shift appears to be caused by regional changes in the physical regime. CARIACO also recorded marked long-term changes in surface and deep DIC in response to a combination of factors including surface water warming. The observations of CARIACO highlight the importance of a sustained, holistic approach to studying biodiversity, ecology and the marine carbon cycle to predict potential impacts of climate change on the ocean's ecosystem services and carbon sequestration efficiency.

A smoothed particle hydrodynamics (SPH) study on polydisperse sediment from technical activities on seabed

NASA Astrophysics Data System (ADS)

Tran-Duc, Thien; Phan-Thien, Nhan; Khoo, Boo Cheong

2018-02-01

Technical activities to collect poly-metallic nodules on a seabed are likely to disturb the top-layer sediment and re-suspend it into the ambient ocean water. The transport of the re-suspended polydisperse-sized sediment is a process in which particles' size variation leads to a difference in their settling velocities; and thus the polydispersity in sizes of sediment has to be taken into account in the modeling process. The sediment transport within a window of 12 km is simulated and analyzed numerically in this study. The sediment characteristic and the ocean current data taken from the Peru Basin, Pacific Ocean, are used in the simulations. More than 50% of the re-suspended sediment are found to return to the bottom after 24 h. The sediment concentration in the ambient ocean water does not exceed 3.5 kg/m3 during the observed period. The deposition rate steadily increases and reaches 70% of the sediment re-suspension rate after 24 h. The sediment plume created by the activities comprises mainly very fine sediment particles (clays and silts), whereas coarser particles (sands) are found in abundance in the deposited sediment within 1 km from the source location. It is also found that the deposition process of the re-suspended sediment is changed remarkably as the current velocity increases from 0.05 m/s (medium current) to 0.1 m/s (strong current). The strong sediment deposition trend is also observed as the sediment source moves continuously over a region due to the sediment scattering effect.

A Giant Arctic Freshwater Pond at the end of the Early Eocene; Implications for Ocean Heat Transport and Carbon Cycling

NASA Astrophysics Data System (ADS)

Brinkhuis, H.; Schouten, S.; Collinson, M. E.; Sluijs, A.; Sinninghe-Damste, J. S.; Dickens, G. R.; Huber, M.; Cronin, T. M.; Bujak, J. P.; Stein, R.; Eldrett, J. S.; Harding, I. C.; Sangiorgi, F.

2005-12-01

In the last decades remains of the free-floating, fresh water fern Azolla have been found in unusually high abundances in basal middle Eocene (~48.5 Ma) marine sediments deposited in all Nordic seas. While generally taken to signal some `freshwater input', their source and significance were not determined. Through palynological and organic geochemical analyses of unique cores obtained from unprecedented Arctic Ocean drilling (IODP 302 - ACEX) we show that the brackish surface conditions that prevailed in the Arctic Ocean through the late Paleocene and early Eocene culminated in the deposition of laminated organic rich deposits yielding huge amounts of remains of Azolla. This, plus e.g., low diversity dinoflagellate assemblages, and concomitant low BIT values, indicates in-situ Azolla growth, and that the surface of the Arctic Ocean episodically resembled a giant fresh water pond over an interval altogether lasting ~800,000 years. The Arctic Basin thus constituted the main source of the freshwater pulses found elsewhere, reaching as far south as the southern North Sea.TEX86-derived surface temperatures were 13-14°C before and after the Azolla interval and only 10°C during the event, which may be related to obstruction of pole ward ocean heat transport and/or increased carbon burial.

Nature and tectonic implications of uneven sedimentary filling of the South China Sea oceanic basin

NASA Astrophysics Data System (ADS)

Yin, Shaoru; Li, Jiabiao; Ding, Weiwei; Fang, Yinxia

2017-04-01

The IODP Expedition 349 in 2014, for the first time, illustrated significant differences of sediment rate and lithology in the central South China Sea (SCS) oceanic basin. Based on seismic reflection profiles tied to IODP349 drilling data, we investigated characteristics of sedimentary filling of the whole SCS oceanic basin, and examined their implications for tectonics. Results show that sediments fill the SCS oceanic basin mainly in three depositional patterns. Firstly, during the Oligocene to middle Miocene, sediments amassed almost solely and then connected like a band parallel to the continent in a low average sediment rate (<10 m/Myr) in the northern oceanic basin. These sediments were deposited mainly in the form of submarine fans and mass transport deposits. Sediments were predominately supplied by the Red and Pearl Rivers and the Dongsha Islands. The sedimentary characteristics likely reflect the latest early Miocene end of seafloor spreading of the SCS and the first-phase rapid uplift of the Tibetan Plateau. Secondly, during the late Miocene, deposition mainly occurred in the Northwest Sub-basin and extended southeastward with a middle average sediment rate ( 30 m/Myr). Sediments were mostly transported by the Red River and Xisha Trough and deposited in the form of submarine fans. The abnormal increase of sediment rate in the Northwest Sub-basin reflects late Miocene slip reversal of the Red River Fault. Finally, since the Pliocene, sediments gradually propagated northeastward in the Southwestern Sub-basin, and accumulated rapidly in the southeastern and northeastern basin, especially in the northern Manila Trench during the Quaternary, in an average sediment rate about 60-80 m/Myr. These sediments were transported mainly by submarine canyons and settled in the form of submarine fans and canyon-overbank deposition. Sediments came from four major sources, including Taiwan, Dongsha Islands, Mekong River, and northern Palawan. The Pliocene to Quaternary explosion of uneven sedimentary filling in the SCS oceanic basin points to the combined action of local and regional tectonics, including the two-phase rapid uplift of the Tibetan Plateau, the Pliocene to Quaternary increased northwestward movement of the Philippine Sea plate and Dongsha event. This study exhibits hitherto most completed observation of sedimentary filling of the SCS oceanic basin and provides new geophysical evidences for the local and regional important tectonics.

Underwater MASW to evaluate stiffness of water-bottom sediments

USGS Publications Warehouse

Park, C.B.; Miller, R.D.; Xia, J.; Ivanov, J.; Sonnichsen, G.V.; Hunter, J.A.; Good, R.L.; Burns, R.A.; Christian, H.

2005-01-01

The multichannel analysis of surface waves (MASW) is initially intended as a land survey method to investigate the near-surface materials for their elastic properties. The acquired data are first analyzed for dispersion characteristics and, from these the shear-wave velocity is estimated using an inversion technique. Land applications show the potential of the MASW method to map 2D bedrock surface, zones of low strength, Poisson's ratio, voids, as well as to generate shear-wave profiles for various othe geotechnical problems. An overview is given of several underwater applications of the MASW method to characterize stiffness distribution of water-bottom sediments. The first application details the survey under shallow-water (1-6 m) in the Fraser River (Canada). The second application is an innovative experimental marine seismic survey in the North Atlantic Ocean near oil fields in Grand Bank offshore Newfoundland.

Migration of As, Hg, Pb, and Zn in arroyo sediments from a semiarid coastal system influenced by the abandoned gold mining district at El Triunfo, Baja California Sur, Mexico.

PubMed

Marmolejo-Rodríguez, Ana Judith; Sánchez-Martínez, Martha Alicia; Romero-Guadarrama, Juan Armando; Sánchez-González, Alberto; Magallanes-Ordóñez, Víctor René

2011-08-01

Extensive waste deposits (tailings) and ash from the ignition oven of the abandoned gold mine of mining district El Triunfo (MD-ET) in Baja California Sur, Mexico have released trace elements into the sediments of the Hondo-Las Gallinas-El Carrizal arroyo, which connects to the Pacific Ocean through an evaporitic basin. Migration of these elements through the arroyo is mainly caused by winds or tropical hurricanes that occur sporadically during the summer and cause the otherwise dry arroyo to overflow. To evaluate the concentration and distribution of the elements As, Hg, Pb, and Zn along the 48 km arroyo, surface sediments were collected from 26 sites, ranging from close to the MD-ET to the mouth of the arroyo at the Pacific Ocean. Concentrations in tailings and ash were for As 8890 and 505 000 mg kg(-1); for Hg 0.336 and 54.9 mg kg(-1); for Pb 92,700 and 19,300 mg kg(-1); and for Zn 49,600 and 1380 mg kg(-1). The average of the Normalized Enrichment Factor (Av-NEF) in surface sediments, calculated using background levels, indicates that the sediments are severely contaminated with As and Zn (Av-NEF = 22), Pb (Av-NEF = 24) and with a moderate contamination of Hg (Av-NEF = 7.5). The anthropogenic influence of those elements is reflected in the arroyo sediments as far as 18 km away from the MD-ET, whereas the samples closest to the discharge into the Pacific Ocean show a natural to moderate enrichment for As and Zn and low or no enrichment for Hg and Pb. A principal components analysis identified four principal components that explained 90% of the total variance. Factor 1 was characterized by a high positive contribution of the anthropogenic source elements, especially As, Pb, and Zn (37%), whereas Factor 2 was strongly correlated with the oxy-hydroxides of Fe and Mn (27%). Factor 3 was correlated with Li (16%) and Factor 4 with Al (10%), which indicates more than one source of lithogenic composition, though they played a minor role in the distribution of the elements.

Distribution of Ra isotopes and the 210Pb and 210Po balance in surface seawaters of the mid Northern Hemisphere

NASA Astrophysics Data System (ADS)

Nozaki, Yoshiyuki; Dobashi, Fumi; Kato, Yoshihisa; Yamamoto, Yoshiyuki

1998-08-01

210Po, 210Pb, 228Ra, and 226Ra were measured in surface sea waters along the 1989-1990 global traverse of the oceans using the new R.V. Hakuho-Maru. Where the traverse intersects other expedition routes, the data are generally confirmatory. In the high-productivity regimes like the Red Sea, and the Arabian Sea 210Po is removed from the mixed layer at much faster rates than 210Pb. This fractionation occurs during scavenging presumably because 210Po is strongly sorbed by organic particles, whereas 210Pb is more likely associated with inorganic detritus. The 210Po/ 210Pb activity ratios leaving the mixed layer by particulate transport can be estimated from the steady state balance of 210Pb and 210Po in the surface waters for different oceanic regions, and are compared with those in the literature obtained by sediment-trap experiments. Although this comparison appears to merge, there exist some inconsistencies, which may be attributable to one of the following possibilities: (1) the model-derived atmospheric 210Pb flux is overestimated for the North Pacific and the North Atlantic, or (2) the sediment-trap data do not represent the real 210Po/ 210Pb ratio in the vertical particulate flux due to some experimental artifacts, such as incomplete trapping and size fractionation. Further careful studies of sediment trapping including seasonal variation are needed to resolve this issue. Our Ra data confirmed that strong sources for 228Ra exist in the Bay of Bengal and the Southeast Asian continental shelf zone, whereas the Mediterranean and the Red Sea, though they are surrounded by land, are not effective sources of 228Ra in the surface water.

Anthropogenic radioactivity in the Arctic Ocean--review of the results from the joint German project.

PubMed

Nies, H; Harms, I H; Karcher, M J; Dethleff, D; Bahe, C

1999-09-30

The paper presents the results of the joint project carried out in Germany in order to assess the consequences in the marine environment from the dumping of nuclear wastes in the Kara and Barents Seas. The project consisted of experimental work on measurements of radionuclides in samples from the Arctic marine environment and numerical modelling of the potential pathways and dispersion of contaminants in the Arctic Ocean. Water and sediment samples were collected for determination of radionuclide such as 137Cs, 90Sr, 239 + 240Pu, 238Pu, and 241Am and various organic micropollutants. In addition, a few water and numerous surface sediment samples collected in the Kara Sea and from the Kola peninsula were taken by Russian colleagues and analysed for artificial radionuclide by the BSH laboratory. The role of transport by sea ice from the Kara Sea into the Arctic Ocean was assessed by a small subgroup at GEOMAR. This transport process might be considered as a rapid contribution due to entrainment of contaminated sediments into sea ice, following export from the Kara Sea into the transpolar ice drift and subsequent release in the Atlantic Ocean in the area of the East Greenland Current. Numerical modelling of dispersion of pollutants from the Kara and Barents Seas was carried out both on a local scale for the Barents and Kara Seas and for long range dispersion into the Arctic and Atlantic Oceans. Three-dimensional baroclinic circulation models were applied to trace the transport of pollutants. Experimental results were used to validate the model results such as the discharges from the nuclear reprocessing plant at Sellafield and subsequent contamination of the North Sea up the Arctic Seas.

Seagrass Impact on Sediment Exchange Between Tidal Flats and Salt Marsh, and The Sediment Budget of Shallow Bays

NASA Astrophysics Data System (ADS)

Donatelli, Carmine; Ganju, Neil Kamal; Fagherazzi, Sergio; Leonardi, Nicoletta

2018-05-01

Seagrasses are marine flowering plants that strongly impact their physical and biological surroundings and are therefore frequently referred to as ecological engineers. The effect of seagrasses on coastal bay resilience and sediment transport dynamics is understudied. Here we use six historical maps of seagrass distribution in Barnegat Bay, USA, to investigate the role of these vegetated surfaces on the sediment storage capacity of shallow bays. Analyses are carried out by means of the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) numerical modeling framework. Results show that a decline in the extent of seagrass meadows reduces the sediment mass potentially stored within bay systems. The presence of seagrass reduces shear stress values across the entire bay, including unvegetated areas, and promotes sediment deposition on tidal flats. On the other hand, the presence of seagrasses decreases suspended sediment concentrations, which in turn reduces the delivery of sediment to marsh platforms. Results highlight the relevance of seagrasses for the long-term survival of coastal ecosystems, and the complex dynamics regulating the interaction between subtidal and intertidal landscapes.

Screening-level risk assessment applied to dredging of polluted sediments from Guanabara Bay, Rio de Janeiro, Brazil.

PubMed

Silveira, Ana Elisa F; Nascimento, Juliana R; Sabadini-Santos, Elisamara; Bidone, Edison D

2017-05-15

Guanabara Bay is characterized by predominant eutrophication and anoxic sediments with a mixture of pollutants. The risk prognosis associated with the dumping of its dredged sediments into the open ocean was addressed by our algorithm. Our algorithm could prioritize areas, characterize major processes related to dredging, measure the potential risk of sediments, and predict the effects of sediment mixing. The estimated risk of dredged sediment was >10-fold than that of ocean sediments. Among metals, mercury represented 50-90% of the total risk. The transfer of dredged material into the ocean or internal dumping in the bay requires a 1:10 dilution to mitigate the risk and bring the risk levels close to that in the EPA criteria, below which there is less likelihood of adverse effects to the biota, and a 1:100 dilution to maintain the original characteristics of the ocean disposal control area. Our algorithm indicator can be used in the design of both aquatic and continental disposal of dredged materials and their management. Copyright © 2017. Published by Elsevier Ltd.

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

Bishop, James K.B.; Wood, Todd

Three Carbon Explorer (CE) floats profiling to kilometer depths in the Southern Ocean tracked dawn-dusk variations of mixing/stratification, particulate organic carbon (POC), and light scattering and sedimentation at 100, 250, and 800 m continuously from January 2002 to April 2003. Data were analyzed in conjunction with contemporaneous satellite winds and chlorophyll and derived subsurface light fields. The CE deployed at 66{sup o}S 172{sup o}W operated in the ice edge zone in absence of light. Two CEs deployed at 55{sup o}S 172{sup o}W recorded wintertime mixing to {approx}400 m, yet observed very different bloom dynamics and sedimentation the following spring. Fourmore » hypotheses are explored. The strongest is that shallow transient stratification of the deep winter mixed layer to shallower than photosynthetic critical depth occurred more frequently in the non-bloom/higher sedimentation case. The lower particle export to 800 m under the bloom was hypothesized to be due to higher interception of sinking carbon by a relatively starved over wintering zooplankton population. In the Southern Ocean surface phytoplankton biomass may counter indicate particle flux at kilometer depths.« less

Remote Sensing of Ocean Color

NASA Astrophysics Data System (ADS)

Dierssen, Heidi M.; Randolph, Kaylan

The oceans cover over 70% of the earth's surface and the life inhabiting the oceans play an important role in shaping the earth's climate. Phytoplankton, the microscopic organisms in the surface ocean, are responsible for half of the photosynthesis on the planet. These organisms at the base of the food web take up light and carbon dioxide and fix carbon into biological structures releasing oxygen. Estimating the amount of microscopic phytoplankton and their associated primary productivity over the vast expanses of the ocean is extremely challenging from ships. However, as phytoplankton take up light for photosynthesis, they change the color of the surface ocean from blue to green. Such shifts in ocean color can be measured from sensors placed high above the sea on satellites or aircraft and is called "ocean color remote sensing." In open ocean waters, the ocean color is predominantly driven by the phytoplankton concentration and ocean color remote sensing has been used to estimate the amount of chlorophyll a, the primary light-absorbing pigment in all phytoplankton. For the last few decades, satellite data have been used to estimate large-scale patterns of chlorophyll and to model primary productivity across the global ocean from daily to interannual timescales. Such global estimates of chlorophyll and primary productivity have been integrated into climate models and illustrate the important feedbacks between ocean life and global climate processes. In coastal and estuarine systems, ocean color is significantly influenced by other light-absorbing and light-scattering components besides phytoplankton. New approaches have been developed to evaluate the ocean color in relationship to colored dissolved organic matter, suspended sediments, and even to characterize the bathymetry and composition of the seafloor in optically shallow waters. Ocean color measurements are increasingly being used for environmental monitoring of harmful algal blooms, critical coastal habitats (e.g., seagrasses, kelps), eutrophication processes, oil spills, and a variety of hazards in the coastal zone.

Spatial variations in geochemical characteristics of the modern Mackenzie Delta sedimentary system

NASA Astrophysics Data System (ADS)

Vonk, Jorien E.; Giosan, Liviu; Blusztajn, Jerzy; Montlucon, Daniel; Graf Pannatier, Elisabeth; McIntyre, Cameron; Wacker, Lukas; Macdonald, Robie W.; Yunker, Mark B.; Eglinton, Timothy I.

2015-12-01

The Mackenzie River in Canada is by far the largest riverine source of sediment and organic carbon (OC) to the Arctic Ocean. Therefore the transport, degradation and burial of OC along the land-to-ocean continuum for this riverine system is important to study both regionally and as a dominant representative of Arctic rivers. Here, we apply sedimentological (grain size, mineral surface area), and organic and inorganic geochemical techniques (%OC, δ13C-OC and Δ14C-OC, 143Nd/144Nd, δ2H and δ18O, major and trace elements) on particulate, bank, channel and lake surface sediments from the Mackenzie Delta, as well as on surface sediments from the Mackenzie shelf in the Beaufort Sea. Our data show a hydrodynamic sorting effect resulting in the accumulation of finer-grained sediments in lake and shelf deposits. A general decrease in organic carbon (OC) to mineral surface area ratios from river-to-sea furthermore suggests a loss of mineral-bound terrestrial OC during transport through the delta and deposition on the shelf. The net isotopic value of the terrestrial OC that is lost en route, derived from relationships between δ13C, OC and surface area, is -28.5‰ for δ13C and -417‰ for Δ14C. We calculated that OC burial efficiencies are around 55%, which are higher (∼20%) than other large river systems such as the Amazon. Old sedimentary OC ages, up to 12 14C-ky, suggest the delivery of both a petrogenic OC source (with an estimated contribution of 19 ± 9%) as well as a pre-aged terrestrial OC source. We calculated the 14C-age of this pre-aged, biogenic, component to be about 6100 yrs, or -501‰, which illustrates that terrestrial OC in the watershed can reside for millennia in soils before being released into the river. Surface sediments in lakes across the delta (n = 20) showed large variability in %OC (0.92-5.7%) and δ13C (-30.7‰ to -23.5‰). High-closure lakes, flooding only at exceptionally high water levels, hold high sedimentary OC contents (>2.5%) and young biogenic OC with a terrestrial or an autochthonous source whereas no-closure lakes, permanently connected to a river channel, hold sediments with pre-aged, terrestrial OC. The intermediate low-closure lakes, flooding every year during peak discharge, display the largest variability in OC content, age and source, likely reflecting variability in for example the length of river-lake connections, the distance to sediment source and the number of intermediate settling basins. Bank, channel and suspended sediment show variable 143Nd/144Nd values, yet there is a gradual but distinct spatial transition in 143Nd/144Nd (nearly three ε units; from -11.4 to -13.9) in the detrital fraction of lake surface sediments from the western to the eastern delta. This reflects the input of younger Peel River catchment material in the west and input of older geological source material in the east, and suggests that lake sediments can be used to assess variability in source watershed patterns across the delta.

Influence of sediment recycling on the trace element composition of primitive arc lavas

NASA Astrophysics Data System (ADS)

Collinet, M.; Jagoutz, O. E.

2017-12-01

Primitive calc-alkaline lavas from continental arcs are, on average, enriched in incompatible elements compared to those from intra-oceanic arcs. This relative enrichment is observed in different groups of trace elements: LILE (e.g. K, Rb), LREE to MREE (La-Dy) and HFSE (e.g.Zr, Nb) and is thought to result from (1) a transfer of material from the subducting slab to the mantle wedge at higher temperature than in intra-oceanic margins and/or (2) lower average degrees of melting in the mantle wedge, as a consequence of thicker overlying crusts and higher average pressures of melting. In addition to thicker overlying crusts and generally higher slab temperatures, continental margins are characterized by larger volumes of rock exposed above sea level and enhanced erosion rates compared to intra-oceanic arcs. As several geochemical signatures of arc lavas attest to the importance of sediment recycling in subduction zones, we explore the possibility that the high concentrations of incompatible elements in primitive lavas from continental arcs directly reflect a larger input of sediment to the subduction system. Previous efforts to quantify the sediment flux to oceanic trenches focused on the thickness of pelagic and hemipelagic sediments on top of the plate entering the subduction zone (Plank and Langmuir, 1993, Nature). These estimates primarily relied on the sediment layer drilled outboard from the subduction system and likely underestimate the volume of sediment derived from the arc itself. Accordingly, we find that such estimates of sediment flux do not correlate with the concentration of incompatible elements in primitive arc lavas. To account for regional contributions of coarser detrital sediments, usually delivered to oceanic trenches by turbidity currents, we apply to arc segments a model that quantifies the sediment load of rivers based on the average relief, area, temperature and runoff of their respective drainage areas (Syvitski et al., 2003, Sediment. Geol.). Our new estimates of sediment fluxes correlate positively with incompatible element concentrations in primitive arc lavas. We conclude that a large fraction of the local terrigenous sediments is subducted and contributes to the observed dichotomy in the trace element budget between primitive lavas from continental and oceanic margins.

Increased thermohaline stratification as a possible cause for an ocean anoxic event in the Cretaceous period.

PubMed

Erbacher, J; Huber, B T; Norris, R D; Markey, M

2001-01-18

Ocean anoxic events were periods of high carbon burial that led to drawdown of atmospheric carbon dioxide, lowering of bottom-water oxygen concentrations and, in many cases, significant biological extinction. Most ocean anoxic events are thought to be caused by high productivity and export of carbon from surface waters which is then preserved in organic-rich sediments, known as black shales. But the factors that triggered some of these events remain uncertain. Here we present stable isotope data from a mid-Cretaceous ocean anoxic event that occurred 112 Myr ago, and that point to increased thermohaline stratification as the probable cause. Ocean anoxic event 1b is associated with an increase in surface-water temperatures and runoff that led to decreased bottom-water formation and elevated carbon burial in the restricted basins of the western Tethys and North Atlantic. This event is in many ways similar to that which led to the more recent Plio-Pleistocene Mediterranean sapropels, but the greater geographical extent and longer duration (approximately 46 kyr) of ocean anoxic event 1b suggest that processes leading to such ocean anoxic events in the North Atlantic and western Tethys were able to act over a much larger region, and sequester far more carbon, than any of the Quaternary sapropels.

Warm tropical ocean surface and global anoxia during the mid-Cretaceous period.

PubMed

Wilson, P A; Norris, R D

2001-07-26

The middle of the Cretaceous period (about 120 to 80 Myr ago) was a time of unusually warm polar temperatures, repeated reef-drowning in the tropics and a series of oceanic anoxic events (OAEs) that promoted both the widespread deposition of organic-carbon-rich marine sediments and high biological turnover. The cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide. In contrast, there is no consensus on the climatic causes and effects of the OAEs, with both high biological productivity and ocean 'stagnation' being invoked as the cause of ocean anoxia. Here we show, using stable isotope records from multiple species of well-preserved foraminifera, that the thermal structure of surface waters in the western tropical Atlantic Ocean underwent pronounced variability about 100 Myr ago, with maximum sea surface temperatures 3-5 degrees C warmer than today. This variability culminated in a collapse of upper-ocean stratification during OAE-1d (the 'Breistroffer' event), a globally significant period of organic-carbon burial that we show to have fundamental, stratigraphically valuable, geochemical similarities to the main OAEs of the Mesozoic era. Our records are consistent with greenhouse forcing being responsible for the warm temperatures, but are inconsistent both with explanations for OAEs based on ocean stagnation, and with the traditional view (reviewed in ref. 12) that past warm periods were more stable than today's climate.

Trace metal cycling and 238U/235U in New Zealand's fjords: Implications for reconstructing global paleoredox conditions in organic-rich sediments

NASA Astrophysics Data System (ADS)

Hinojosa, Jessica L.; Stirling, Claudine H.; Reid, Malcolm R.; Moy, Christopher M.; Wilson, Gary S.

2016-04-01

Reconstructing the history of ocean oxygenation provides insight into links between ocean anoxia, biogeochemical cycles, and climate. Certain redox-sensitive elements respond to changes in marine oxygen content through phase shifts and concomitant isotopic fractionation, providing new diagnostic proxies of past ocean hypoxia. Here we explore the behavior and inter-dependence of a suite of commonly utilized redox-sensitive trace metals (U, Mo, Fe, and Mn) and the emerging ;stable; isotope system of U (238U/235U, or δ238U) in New Zealand fjords. These semi-restricted basins have chemical conditions spanning the complete redox spectrum from fully oxygenated to suboxic to intermittently anoxic/euxinic. In the anoxic water column, U and Mo concentrations decrease, while Fe and Mn concentrations increase. Similarly, signals of past euxinic conditions can be found by U, Mo, Fe, and Mn enrichment in the underlying sediments. The expected U isotopic shift toward a lower δ238U in the anoxic water column due to U(VI)-U(IV) reduction is not observed; instead, water column δ238U profiles are consistent in fjords of all oxygen content, falling within previously reported ranges for open ocean seawater (δ238U = -0.42 ± 0.07‰). Additionally, surface sediment δ238U results show evidence for competing U isotope fractionation processes. One site indicates increased export of 238U from seawater to the underlying sediments (fractionation between aqueous seawater U and particulate sediment U, or ΔU(aq)-U(solid) = -0.25‰), consistent with redox-driven fractionation. Another site suggests potential U(VI) adsorption-driven fractionation, reflecting increased export of 235U from seawater to sediments (ΔU(aq)-U(solid) = 0.25‰). We discuss several potential factors that could alter δ238U in waters and sediments beyond redox-driven shifts, including adsorption to organic matter in waters of high primary productivity, reaction rates for competing processes of U adsorption and release, and isotopic constraints of U coming into the system from terrestrial environments. These potential complications should be understood and constrained through observations, experiments, and models before future application of δ238U as a global paleoredox tracer can achieve its full potential.

Recent Trends in Suspended Sediment Load & Water Quality in the Upper Chesapeake Bay

NASA Astrophysics Data System (ADS)

Freeman, L. A.; Ackleson, S. G.

2016-02-01

The Chesapeake Bay spans several major cities on the US east coast and drains a large watershed (164,200 km2) to the Atlantic Ocean. Upstream deforestation and agriculture have led to a major decline in water quality (increased sediment and nutrient load) of the Bay over the past century. Sediment flux into the Chesapeake Bay is a natural process, but has become an environmental concern as land use changes have exacerbated natural suspended sediment loads and saturated the capacity of the estuary to filter and remove sediments. In situ measurements of suspended sediments and surface reflectance from the Potomac, Patapsco, and Severn River were used to develop algorithms that convert surface reflectance from Landsat (1-3, 4-5, 7, 8) imagery to suspended sediment concentration for the entire Chesapeake Bay. A unique time series of suspended sediment load in the Chesapeake Bay was compiled from Landsat imagery dating from 1977-2015. Particular focus is given to the upper Chesapeake Bay near Washington, DC and Baltimore, MD to understand urban effects. In particular, the Potomac, Patapsco, and Severn River are examined from both remote sensing and in situ measurements. Landsat imagery combined with in situ monitoring provides environmental scientists and resource managers with detailed trends in sediment distribution and concentration, a key measure of water quality. Trends of suspended sediment load in several rivers and the upper Chesapeake Bay will be presented, along with a discussion of suspended sediment algorithms for Landsat imagery. Advantages of Landsat 8 (improved signal-to-noise performance and more bands) versus previous sensors will be examined for suspended sediment applications.

Late Eocene to present isotopic (Sr-Nd-Pb) and geochemical evolution of sediments from the Lomonosov Ridge, Arctic Ocean: Implications for continental sources and linkage with the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Stevenson, Ross; Poirier, André; Véron, Alain; Carignan, Jean; Hillaire-Marcel, Claude

2015-09-01

New geochemical and isotopic (Sr, Nd, Pb) data are presented for a composite sedimentary record encompassing the past 50 Ma of history of sedimentation on the Lomonosov Ridge in the Arctic Ocean. The sampled sediments encompass the transition of the Arctic basin from an enclosed anoxic basin to an open and ventilated oxidized ocean basin. The transition from anoxic basin to open ventilated ocean is accompanied by at least three geochemical and isotopic shifts and an increase in elements (e.g., K/Al) controlled by detrital minerals highlighting significant changes in sediment types and sources. The isotopic compositions of the sediments prior to ventilation are more variable but indicate a predominance of older crustal contributions consistent with sources from the Canadian Shield. Following ventilation, the isotopic compositions are more stable and indicate an increased contribution from younger material consistent with Eurasian and Pan-African crustal sources. The waxing and waning of these sources in conjunction with the passage of water through Fram Strait underlines the importance of the exchange of water mass between the Arctic and North Atlantic Oceans.

Late Quaternary changes in intermediate water oxygenation and oxygen minimum zone, northern Japan: A benthic foraminiferal perspective

NASA Astrophysics Data System (ADS)

Shibahara, Akihiko; Ohkushi, Ken'ichi; Kennett, James P.; Ikehara, Ken

2007-09-01

A strong oxygen minimum zone (OMZ) currently exists at upper intermediate water depths on the northern Japanese margin, NW Pacific. The OMZ results largely from a combination of high surface water productivity and poor ventilation of upper intermediate waters. We investigated late Quaternary history (last 34 kyr) of ocean floor oxygenation and the OMZ using quantitative changes in benthic foraminiferal assemblages in three sediment cores taken from the continental slope off Shimokita Peninsula and Tokachi, northern Japan, at water depths between 975 and 1363 m. These cores are well located within the present-day OMZ, a region of high surface water productivity, and in close proximity to the source region of North Pacific Intermediate Water. Late Quaternary benthic foraminiferal assemblages experienced major changes in response to changes in dissolved oxygen concentration in ocean floor sediments. Foraminiferal assemblages are interpreted to represent three main groups representing oxic, suboxic, and dysoxic conditions. Assemblage changes in all three cores and hence in bottom water oxygenation coincided with late Quaternary climatic episodes, similar to that known for the southern California margin. These episodes, in turn, are correlated with orbital and millennial climate episodes in the Greenland ice core including the last glacial episode, Bølling-Ållerød (B/A), Younger Dryas, Preboreal (earliest Holocene), early Holocene, and late Holocene. The lowest oxygen conditions, marked by dysoxic taxa and laminated sediments in one core, occurred during the B/A and the Preboreal intervals. Suboxic taxa dominated mainly during the last glacial, the Younger Dryas, and most of the Holocene. Dysoxic conditions during the B/A and Preboreal intervals in this region were possibly caused by high surface water productivity at times of reduced intermediate ventilation in the northwestern Pacific. Remarkable similarities are evident in the late Quaternary sequence of benthic foraminiferal assemblage change between the two very distant continental margins of northern Japan and southern California. The oscillations in OMZ strength, reflected by these faunal changes, were widespread and apparently synchronous over wide areas of the North Pacific, reflecting broad changes in intermediate water ventilation and surface ocean productivity closely linked with late Quaternary climate change on millennial and orbital timescales.

The Cenozoic palaeoenvironment of the Arctic Ocean

USGS Publications Warehouse

Moran, K.; Backman, J.; Brinkhuis, H.; Clemens, S.C.; Cronin, T.; Dickens, G.R.; Eynaud, F.; Gattacceca, J.; Jakobsson, M.; Jordan, R.W.; Kaminski, M.; King, J.; Koc, N.; Krylov, A.; Martinez, N.; Matthiessen, J.; McInroy, D.; Moore, T.C.; Onodera, J.; O'Regan, M.; Palike, H.; Rea, B.; Rio, D.; Sakamoto, T.; Smith, D.C.; Stein, R.; St, John K.; Suto, I.; Suzuki, N.; Takahashi, K.; Watanabe, M. E.; Yamamoto, M.; Farrell, J.; Frank, M.; Kubik, P.; Jokat, W.; Kristoffersen, Y.

2006-01-01

The history of the Arctic Ocean during the Cenozoic era (0-65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ???14 Myr, we find sedimentation rates of 1-2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (???3.2 Myr ago) and East Antarctic ice (???14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (???45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ???49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (???55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change. ?? 2006 Nature Publishing Group.

Extensive survey of terrestrial organic carbon in surface sediments of the East Siberian Sea

NASA Astrophysics Data System (ADS)

Vonk, Jorien; Gustafsson, Örjan; Alling, Vanja; Sánchez-García, Laura; van Dongen, Bart; Andersson, Per; Dudarev, Oleg; Semiletov, Igor; Eglinton, Tim

2010-05-01

The East Siberian Sea (ESS) is the largest and shallowest continental shelf sea of the Arctic Ocean, yet it is the least explored. The perenially frozen tundra and taiga of the circum-Arctic coastal area holds approximately half of the global belowground carbon pool. Significant amounts of terrestrial organic carbon (terrOC) are exported with the Great Siberian Arctic rivers to the shelf seas. In addition, the carbon-rich, ice-bound Yedoma coasts in East Siberia release significant amounts of Pleistocene carbon through thermal degradation and coastal erosion. The fate of these large-scale releases of terrOC in the East Siberian Shelf Sea is still poorly understood. The urgency of this research is accentuated by the fact that the East-Siberian Arctic landmass is experiencing the strongest climate warming on Earth, with a great potential for various carbon-climate feedback links. During the International Siberian Shelf Study 2008 (ISSS-08), a 50-day research expedition onboard the Russian vessel Yakob Smirnitskiy in late summer 2008, we obtained surface sediments from over 60 ESS locations. The data obtained after bulk analyses of these sediments are combined with results obtained from previous ESS campaigns in 2003 and 2004 to facilitate a comprehensive investigation of the ESS surface sediment composition. Sedimentary OC contents were between 0.13 and 3.7% (median 1.02%, interquartile range 0.563) with the highest values near the Indigirka and Kolyma river mouths and in the Long Strait. Stable carbon isotope values were in the range of -27.4 to -21.2 per mill (median -25.3 per mill, interquartile range 2.04), with more depleted values close to the coast. A clear transition was observed east of 170° E with more enriched values, signalling a regime shift with stronger influence of the Pacific Ocean. The terrOC fraction in the surface sediments was estimated from the 13C data to be on average 70% for ESS as a whole, with maximal values of 90-100% (along most of the coastline and in Sannikov and Dmitry Laptev Strait) and minimal values of 10-35% (outer shelf and Long Strait). An extensive set of bulk organic 14C data of the sedimentary OC in the ESS will also be interpreted with respect to relative contributions of coastal Yedoma erosion versus river input. Based on published and calculated (calculated from ISSS08 sediment cores) sedimentation velocities, we estimated terrOC burial sink on the East Siberian Shelf Sea.

Three-Dimensional Acoustic Propagation Through Shallow Water Internal, Surface Gravity and Bottom Sediment Waves

DTIC Science & Technology

2011-09-01

energy never ends. I am also very pleased to have Dr. William M. Carey, Dr. Henrik Schmidt, Dr. Glen G. Gawarkiewicz and Dr. Pierre Lermusiaux on my...Internal Waves for Multi- Megameter Acoustic Propagation in the Ocean, J. Acoust. Soc. Amer., Vol. 100, P. 3607-3620, 1996. [6] J.R. Apel , M. Badiey

Millennial Variability of Eastern Equatorial Bottom Water Oxygenation and Atmospheric CO2 over the past 100 kyr

NASA Astrophysics Data System (ADS)

Marcantonio, F.; Loveley, M.; Wisler, M.; Hostak, R.; Hertzberg, J. E.; Schmidt, M. W.; Lyle, M. W.

2017-12-01

Storage of respired carbon in the deep ocean may play a significant role in lowering atmospheric CO2 concentrations by about 80 ppm during the last glacial maximum compared to pre-industrial times. The cause of this sequestration and the subsequent release of the deep respired carbon pool at the last termination remains elusive. Within the last glacial period, on millennial timescales, the relationship between the CO2 cycle and any waxing and waning of a deep respired pool also remains unclear. To further our understanding of the millennial variability in the storage of a deep-ocean respired carbon pool during the last glacial, we measure authigenic uranium and 230Th-derived non-lithogenic barium fluxes (xsBa flux) in two high-sedimentation-rate cores from the Panama Basin of the Eastern Equatorial Pacific (EEP) (8JC, 6° 14.0' N, 86° 02.6' W; 1993 m water depth; 17JC 00° 10.8' S, 85° 52.0' W; 2846 m water depth). Sediment authigenic U concentrations are controlled by the redox state of sediments which, in turn, is a function of the rain of organic material from the surface ocean and the oxygen content of bottom waters. At both 8JC and 17JC, the mismatch between xsBa fluxes, a proxy for the reconstruction of oceanic productivity, and authigenic uranium concentrations suggests that the primary control of the latter values is changes in bottom water oxygenation. Peak authigenic uranium concentrations occur during glacial periods MIS 2, 3, and 4, respectively, and are two to three times higher than those during interglacial periods, MIS 1 and 5. EEP bottom waters were likely suboxic during times of the last glacial period when atmospheric CO2 concentrations were at their lowest concentrations. In addition, the pattern of increased deep-water oxygenation during times of higher CO2 during the last glacial is similar to that reported in a study of authigenic U in sediments from the Antarctic Zone of the Southern Ocean (Jaccard et al., 2016). We suggest that a respired carbon pool existed within a large swath of the abyssal Southern and Pacific Oceans throughout the entire last glacial cycle, and that this respired carbon was periodically released through increased ventilation of deep ocean waters. Jaccard et al. (2016) Nature 530, 207-210.

TRACE ELEMENT DISTRIBUTION IN SEDIMENTS OF THE MID-ATLANTIC RIDGE.

DTIC Science & Technology

MARINE GEOLOGY, ATLANTIC OCEAN), (*OCEAN BOTTOM, MINERALS), SEDIMENTATION, IRON, COBALT, MANGANESE, STRONTIUM, CHLORITES, NEUTRON ACTIVATION, GEOCHEMISTRY, CALCITE , CARBONATES, X RAY DIFFRACTION, CLAY MINERALS, THESES

Influence of Initial Geometry and Boundary Conditions on Flat Subduction Models and Resulting Topography

NASA Astrophysics Data System (ADS)

Nelson, P.; Moucha, R.

2014-12-01

Numerical investigations of surface deformation in response to flat slab subduction began with seminal papers by Bird (1988) and Mitrovica et al. (1989). Recently, a number of numerical studies have begun to explore the complexity in the dynamics of flat-slab subduction initiation and continuation, but did not address the corresponding surface deformation (English et al., 2003; Pérez-Campos et al., 2008; Liu et al., 2010; Jones et al., 2011; Arrial and Billen, 2013; Vogt and Gerya, 2014). Herein, we explore the conditions that lead to flat-slab subduction and characterize the resulting surface deformation using a 2D finite-difference marker-in-cell method. We specifically explore how initial model geometry and boundary conditions affect the evolution of the angle at which a slab subducts in the presence/absence of a buoyant oceanic plateau and the resulting surface topography. In our simulations, the surface is tracked through time as an internal erosion/sedimentation surface. The top boundary of the crust is overlaid by a "sticky" (viscous 10^17 Pa.s) water/air layer with correspondingly stratified densities. We apply a coupled surface processes model that solves the sediment transport/diffusion erosion equation at each time step to account for the corresponding crustal mass flux and its effect on crustal deformation. Model results show the initial angle of subduction has a substantial impact on the subduction angle of the slab and hence the evolution of topography. The results also indicate plate velocity and the presence of an oceanic plateau in a forced subduction only have a moderate effect on the angle of subduction.

High-Frequency Sound Interaction with Ocean Sediments and with Objects in the Vicinity of the Water/Sediment Interface and Mid-Frequency Shallow Water Propagation and Scattering

DTIC Science & Technology

2007-09-30

combined with measured sediment properties, to test the validity of sediment acoustic models , and in particular the poroelastic (Biot) model . Addressing...TERM GOALS 1. Development of accurate models for acoustic scattering from, penetration into, and propagation within shallow water ocean sediments...2. Development of reliable methods for modeling acoustic detection of buried objects at subcritical grazing angles. 3. Improving our

Trace element concentrations in surface estuarine and marine sediments along the Mississippi Gulf Coast following Hurricane Katrina.

PubMed

Warren, Crystal; Duzgoren-Aydin, Nurdan S; Weston, James; Willett, Kristine L

2012-01-01

Hurricanes are relatively frequent ecological disturbances that may cause potentially long-term impacts to the coastal environment. Hurricane Katrina hit the Mississippi Gulf Coast in August 2005, and caused a storm surge with the potential to change the trace element content of coastal surface sediments. In this study, surface estuarine and marine sediments were collected monthly following the storm from ten sites along the Mississippi Gulf Coast (Mobile Bay, Grand Bay Bayous Heron and Cumbest, Pascagoula, Ocean Springs, Biloxi Gulf, Back Biloxi Bay, Gulfport Gulf, Gulfport Courthouse Rd, and Gulfport Marina). Concentrations of V, Cr, Mn, Fe, Co, Ni, Zn, As, Cd, and Pb were measured by inductively coupled plasma-mass spectrometry to evaluate their temporal and spatial variations in the year following Hurricane Katrina. Sediments were characterized by pH, particle size distribution and total carbon and nitrogen content. Trace element contents of the sediments were determined in both <2 mm and <63 μm grain size fractions. Results revealed no significant temporal and spatial variability in trace element concentrations, in either size fraction. Potential ecological risk of the sediments was assessed by using NOAA SQuiRTs' guideline values; most concentrations remained below probable adverse effects guidelines to marine organisms suggesting that trace elements redistributed by Hurricane Katrina would not cause an adverse impact on resident organisms. Instead, the concentrations of trace elements were site-dependent, with specific contaminants relating to the use of the area prior to Hurricane Katrina.

Aragonite saturation states and nutrient fluxes in coral reef sediments in Biscayne National Park, FL, USA

USGS Publications Warehouse

Lisle, John T.; Reich, Christopher D.; Halley, Robert B.

2014-01-01

Some coral reefs, such as patch reefs along the Florida Keys reef tract, are not showing significant reductions in calcification rates in response to ocean acidification. It has been hypothesized that this recalcitrance is due to local buffering effects from biogeochemical processes driven by seagrasses. We investigated the influence that pore water nutrients, dissolved inorganic carbon (DIC) and total alkalinity (TA) have on aragonite saturation states (Ωaragonite) in the sediments and waters overlying the sediment surfaces of sand halos and seagrass beds that encircle Alinas and Anniversary reefs in Biscayne National Park. Throughout the sampling period, sediment pore waters from both bottom types had lower oxidation/reduction potentials (ORP), with lower pH relative to the sediment surface waters. The majority (86.5%) of flux rates (n = 96) for ΣNOx–, PO43–, NH4+, SiO2, DIC and TA were positive, sometimes contributing significant concentrations of the respective constituents to the sediment surface waters. The Ωaragonite values in the pore waters (range: 0.18 to 4.78) were always lower than those in the overlying waters (2.40 to 4.46), and 52% (n = 48) of the values were aragonite in 75% (n = 16) of the samples, but increased it in the remainder. The elevated fluxes of nutrients, DIC and TA into the sediment–water interface layer negatively alters the suitability of this zone for the settlement and development of calcifying larvae, while enhancing the establishment of algal communities.

Export fluxes in a naturally iron-fertilized area of the Southern Ocean - Part 1: Seasonal dynamics of particulate organic carbon export from a moored sediment trap

NASA Astrophysics Data System (ADS)

Rembauville, M.; Salter, I.; Leblond, N.; Gueneugues, A.; Blain, S.

2015-06-01

A sediment trap moored in the naturally iron-fertilized Kerguelen Plateau in the Southern Ocean provided an annual record of particulate organic carbon and nitrogen fluxes at 289 m. At the trap deployment depth, current speeds were typically low (~ 10 cm s-1) and primarily tidal-driven (M2 tidal component). Although advection was weak, the sediment trap may have been subject to hydrodynamical and biological (swimmer feeding on trap funnel) biases. Particulate organic carbon (POC) flux was generally low (< 0.5 mmol m-2 d-1), although two episodic export events (< 14 days) of 1.5 mmol m-2 d-1 were recorded. These increases in flux occurred with a 1-month time lag from peaks in surface chlorophyll and together accounted for approximately 40% of the annual flux budget. The annual POC flux of 98.2 ± 4.4 mmol m-2 yr-1 was low considering the shallow deployment depth but comparable to independent estimates made at similar depths (~ 300 m) over the plateau, and to deep-ocean (> 2 km) fluxes measured from similarly productive iron-fertilized blooms. Although undertrapping cannot be excluded in shallow moored sediment trap deployment, we hypothesize that grazing pressure, including mesozooplankton and mesopelagic fishes, may be responsible for the low POC flux beneath the base of the winter mixed layer. The importance of plankton community structure in controlling the temporal variability of export fluxes is addressed in a companion paper.

Investigating the fate of microplastics in the San Diego Bay area: A paleoenvironmental approach

NASA Astrophysics Data System (ADS)

Fontaine, R. M.; Hangsterfer, A.; Bhattacharya, A.

2017-12-01

Microplastics in marine waste surveys compare the observed amount of microplastic debris in the ocean with constructed models to determine availability of microplastics in the ocean. However, most of these studies have been constrained in the surface ocean and the surveys have found a substantial difference between estimated and observed amount of microplastic in the ocean. One possible reason could be that microplastics are settling along continental shelves or the ocean bottom. Via this research we have collected samples to study marine sediments (collected from increasing depth along the continental shelf around San Diego) for microplastics. Our goal is to determine the relationship between density and microplastic distribution. The main objective is to investigate sinks of microplastic (plastic products sizes less than 1 mm) along continental shelves; more specifically, this small study aims to investigate (a) what are the dominant types of microplastics (for example, heavy plastic or light plastic), (b) shapes of microplastics derived from commonly used heavy and light plastics, (c) is there specific locations (for example floating in water column vs. settling ocean floor along the continental shelves, which would be the first places where one might expect microplastics (that are delivered via river systems or from beaches) typically and finally, (d) is there any marine environmental preference between light and heavy microplastics. In this study, we provide observational evidence about the poorly understood fate of microplastics in the ocean as well as lend itself to the question: if and how long microplastics remain bioavailable. We have targeted four marine environments along San Diego that encompass several important connections between land and the ocean:Bays, river mouth, upwelling region and shelf. At each site listed above, we take four sets of 1-2ft cores: 20ft , 40ft, 60ft, 80ft. We combine traditional measurements (pH, salinity, density, DOC, N, P for water samples and grain size, mineralogy, chemistry, TOC and XRF for sediment samples) with microscopy to identify plastic types and amount. The comprehensive method allows us to understand water and sediment controls on microplastic distribution.

Impact of the Agulhas Return Current on the glacial Subantarctic region in the South Indian Ocean

NASA Astrophysics Data System (ADS)

Ikehara, M.; Crosta, X.; Manoj, M. C.

2017-12-01

The Southern Ocean has played an important role in the evolution of the global climate system. The Southern Ocean circulation is dominated by the Antarctic Circumpolar Current (ACC), the world's longest and largest current system. Sea ice coverage on sea surface strongly affects the climate of the Southern Hemisphere through its impacts on the energy and gas budget, on the atmospheric circulation, on the hydrological cycle, and on the biological productivity. The Agulhas Return Current (ARC) originates from the Agulhas Current, the major western boundary current in the Indian Ocean, and transports heat from subtropical to subantarctic region. It's thought that the Agulhas leakage from the Indian Ocean to the Atlantic was reduced for the last glacial due to a northward shift of the westerlies and ACC, however, there are still unknown yet how the ARC was responded to the reduced Agulhas leakage. A piston core DCR-1PC was collected from the Del Caño Rise (46°S, 44°E, 2632m), Indian sector of the Southern Ocean. Core site located in the Subantarctic region between the Subtropical Front (STF) and Subantarctic Front (SAF). Age model of the core was established by radiocarbon dating of planktic foraminifer Globorotalia bulloides and oxygen isotope stratigraphy of benthic foraminifers Cibicidoides wuellerstorfi and Melonis bareelanus. Sediment of DCR-1PC show the cyclic changes of diatom/carbonate ooze sedimentation corresponding to Southern Ocean fronts' migrations on glacial-interglacial timescales. Records of ice-rafted debris (IRD) and oxygen isotope in planktic foraminfer G. bulloides suggest that the melting of sea ice was significantly increased during the last glacial maximum (LGM) in the Subantarctic surface water. Diatom assemblage based summer SST also shows the relative warmer condition in the Subantarctic during the LGM. These results might be explained by the strong influence of the Agulhas Return Current during the LGM in the Subantarctic. The reduced Agulhas leakage due to a northward shift of the westerlies and ACC impacted significantly on sea ice melting in the glacial Subantarctic region in the South Indian Ocean.

Diversity and Biogeography of Bathyal and Abyssal Seafloor Bacteria

PubMed Central

Bienhold, Christina; Zinger, Lucie; Boetius, Antje; Ramette, Alban

2016-01-01

The deep ocean floor covers more than 60% of the Earth’s surface, and hosts diverse bacterial communities with important functions in carbon and nutrient cycles. The identification of key bacterial members remains a challenge and their patterns of distribution in seafloor sediment yet remain poorly described. Previous studies were either regionally restricted or included few deep-sea sediments, and did not specifically test biogeographic patterns across the vast oligotrophic bathyal and abyssal seafloor. Here we define the composition of this deep seafloor microbiome by describing those bacterial operational taxonomic units (OTU) that are specifically associated with deep-sea surface sediments at water depths ranging from 1000–5300 m. We show that the microbiome of the surface seafloor is distinct from the subsurface seafloor. The cosmopolitan bacterial OTU were affiliated with the clades JTB255 (class Gammaproteobacteria, order Xanthomonadales) and OM1 (Actinobacteria, order Acidimicrobiales), comprising 21% and 7% of their respective clades, and about 1% of all sequences in the study. Overall, few sequence-abundant bacterial types were globally dispersed and displayed positive range-abundance relationships. Most bacterial populations were rare and exhibited a high degree of endemism, explaining the substantial differences in community composition observed over large spatial scales. Despite the relative physicochemical uniformity of deep-sea sediments, we identified indicators of productivity regimes, especially sediment organic matter content, as factors significantly associated with changes in bacterial community structure across the globe. PMID:26814838

Geochemical evidence for enhanced preservation of organic matter in the oxygen minimum zone of the continental margin of northern California during the Late Pleistocene

USGS Publications Warehouse

Dean, Walter E.; Gardner, James V.; Anderson, Roger Y.

1994-01-01

The present upper water mass of the northeastern Pacific Ocean off California has a well-developed oxygen minimum zone between 600 and 1200 m wherein concentrations of dissolved oxygen are less than 0.5 mL/L. Even at such low concentrations of dissolved oxygen, benthic burrowing organisms are abundant enough to thoroughly bioturbate the surface and near-surface sediments. These macro organisms, together with micro organisms, also consume large quantities of organic carbon produced by large seasonal stocks of plankton in the overlying surface waters, which are supported by high concentrations of nutrients within the California Current upwelling system. In contrast to modern conditions of bioturbation, laminated sediments are preserved in upper Pleistocene sections of cores collected on the continental slope at water depths within the present oxygen minimum zone from at least as far north as the California-Oregon border and as far south as Point Conception. Comparison of sediment components in the laminae with those delivered to sediment traps as pelagic marine “snow” demonstrates that the dark-light lamination couplets are indeed annual (varves). These upper Pleistocene varved sediments contain more abundant lipid-rich “sapropelic” (type II) organic matter than the overlying bioturbated, oxidized Holocene sediments. The baseline of stable carbon isotopic composition of the organic matter in these slope cores does not change with time, indicating that the higher concentrations of type II organic matter in the varved sediments represent better preservation of organic matter rather than any change in the source of organic matter.

Redox-controlled carbon and phosphorus burial: A mechanism for enhanced organic carbon sequestration during the PETM

NASA Astrophysics Data System (ADS)

Komar, Nemanja; Zeebe, Richard E.

2017-12-01

Geological records reveal a major perturbation in carbon cycling during the Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma), marked by global warming of more than 5 °C and a prominent negative carbon isotope excursion of at least 2.5‰ within the marine realm. The entire event lasted about 200,000 yr and was associated with a massive release of light carbon into the ocean-atmosphere system over several thousands of years. Here we focus on the terminal stage of the PETM, during which the ocean-atmosphere system rapidly recovered from the carbon cycle perturbation. We employ a carbon-cycle box model to examine the feedbacks between surface ocean biological production, carbon, oxygen, phosphorus, and carbonate chemistry during massive CO2 release events, such as the PETM. The model results indicate that the redox-controlled carbon-phosphorus feedback is capable of producing enhanced organic carbon sequestration during large carbon emission events. The locale of carbon oxidation (ocean vs. atmosphere) does not affect the amount of carbon sequestered. However, even though the model produces trends consistent with oxygen, excess accumulation rates of organic carbon (∼1700 Pg C during the recovery stage), export production and δ13 C data, it fails to reproduce the magnitude of change of sediment carbonate content and the CCD over-deepening during the recovery stage. The CCD and sediment carbonate content overshoot during the recovery stage is muted by a predicted increase in CaCO3 rain. Nonetheless, there are indications that the CaCO3 export remained relatively constant during the PETM. If this was indeed true, then an initial pulse of 3,000 Pg C followed by an additional, slow leak of 2,500 Pg C could have triggered an accelerated nutrient supply to the surface ocean instigating enhanced organic carbon export, consequently increasing organic carbon sequestration, resulting in an accelerated restoration of ocean-atmosphere biogeochemistry during the termination phase of the PETM.

Variable reactivity of particulate organic matter in a global ocean biogeochemical model

NASA Astrophysics Data System (ADS)

Aumont, Olivier; van Hulten, Marco; Roy-Barman, Matthieu; Dutay, Jean-Claude; Éthé, Christian; Gehlen, Marion

2017-05-01

The marine biological carbon pump is dominated by the vertical transfer of particulate organic carbon (POC) from the surface ocean to its interior. The efficiency of this transfer plays an important role in controlling the amount of atmospheric carbon that is sequestered in the ocean. Furthermore, the abundance and composition of POC is critical for the removal of numerous trace elements by scavenging, a number of which, such as iron, are essential for the growth of marine organisms, including phytoplankton. Observations and laboratory experiments have shown that POC is composed of numerous organic compounds that can have very different reactivities. However, this variable reactivity of POC has never been extensively considered, especially in modelling studies. Here, we introduced in the global ocean biogeochemical model NEMO-PISCES a description of the variable composition of POC based on the theoretical reactivity continuum model proposed by Boudreau and Ruddick (1991). Our model experiments show that accounting for a variable lability of POC increases POC concentrations in the ocean's interior by 1 to 2 orders of magnitude. This increase is mainly the consequence of a better preservation of small particles that sink slowly from the surface. Comparison with observations is significantly improved both in abundance and in size distribution. Furthermore, the amount of carbon that reaches the sediments is increased by more than a factor of 2, which is in better agreement with global estimates of the sediment oxygen demand. The impact on the major macronutrients (nitrate and phosphate) remains modest. However, iron (Fe) distribution is strongly altered, especially in the upper mesopelagic zone as a result of more intense scavenging: vertical gradients in Fe are milder in the upper ocean, which appears to be closer to observations. Thus, our study shows that the variable lability of POC can play a critical role in the marine biogeochemical cycles which advocates for more dedicated in situ and laboratory experiments.

Nitrate-dependent iron oxidation limits iron transport in anoxic ocean regions

NASA Astrophysics Data System (ADS)

Scholz, Florian; Löscher, Carolin R.; Fiskal, Annika; Sommer, Stefan; Hensen, Christian; Lomnitz, Ulrike; Wuttig, Kathrin; Göttlicher, Jörg; Kossel, Elke; Steininger, Ralph; Canfield, Donald E.

2016-11-01

Iron is an essential element for life on Earth and limits primary production in large parts of the ocean. Oxygen-free continental margin sediments represent an important source of bioavailable iron to the ocean, yet little of the iron released from the seabed reaches the productive sea surface. Even in the anoxic water of oxygen minimum zones, where iron solubility should be enhanced, most of the iron is rapidly re-precipitated. To constrain the mechanism(s) of iron removal in anoxic ocean regions we explored the sediment and water in the oxygen minimum zone off Peru. During our sampling campaign the water column featured two distinct redox boundaries separating oxic from nitrate-reducing (i.e., nitrogenous) water and nitrogenous from weakly sulfidic water. The sulfidic water mass in contact with the shelf sediment contained elevated iron concentrations >300 nM. At the boundary between sulfidic and nitrogenous conditions, iron concentrations dropped sharply to <20 nM coincident with a maximum in particulate iron concentration. Within the iron gradient, we found an increased expression of the key functional marker gene for nitrate reduction (narG). Part of this upregulation was related to the activity of known iron-oxidizing bacteria. Collectively, our data suggest that iron oxidation and removal is induced by nitrate-reducing microbes, either enzymatically through anaerobic iron oxidation or by providing nitrite for an abiotic reaction. Given the important role that iron plays in nitrogen fixation, photosynthesis and respiration, nitrate-dependent iron oxidation likely represents a key-link between the marine biogeochemical cycles of nitrogen, oxygen and carbon.

Black Carbon in Estuarine and Coastal Ocean Dissolved Organic Matter

NASA Technical Reports Server (NTRS)

Mannino, Antonio; Harvey, H. Rodger

2003-01-01

Black carbon (BC) in ultrafiltered high-molecular-weight DOM (UDOM) was measured in surface waters of Delaware Bay, Chesapeake Bay and the adjacent Atlantic Ocean (USA) to ascertain the importance of riverine and estuarine DOM as a source of BC to the ocean. BC comprised 5-72% of UDOM-C (27+/-l7%) and on average 8.9+/-6.5% of dissolved organic carbon (DOC) with higher values in the turbid region of the Delaware Estuary and lower yields in the river and coastal ocean. The spatial and seasonal distributions of BC along the salinity gradient of Delaware Bay suggest that the higher levels of BC in surface water UDOM originated from localized sources, possibly from atmospheric deposition or released from resuspended sediments. Black carbon comprised 4 to 7% of the DOC in the coastal Atlantic Ocean, revealing that river-estuary systems are important exporters of colloidal BC to the ocean. The annual flux of BC from Delaware Bay UDOM to the Atlantic Ocean was estimated at 2.4x10(exp 10) g BC yr(exp -1). The global river flux of BC through DOM to the ocean could be on the order of 5.5x1O(exp 12)g BC yr (exp -1). These results support the hypothesis that the DOC pool is the intermediate reservoir in which BC ages prior to sedimentary deposition.

Upper oceanic response to tropical cyclone Phailin in the Bay of Bengal using a coupled atmosphere-ocean model

NASA Astrophysics Data System (ADS)

Prakash, Kumar Ravi; Pant, Vimlesh

2017-01-01

A numerical simulation of very severe cyclonic storm `Phailin', which originated in southeastern Bay of Bengal (BoB) and propagated northwestward during 10-15 October 2013, was carried out using a coupled atmosphere-ocean model. A Model Coupling Toolkit (MCT) was used to make exchanges of fluxes consistent between the atmospheric model `Weather Research and Forecasting' (WRF) and ocean circulation model `Regional Ocean Modelling System' (ROMS) components of the `Coupled Ocean-Atmosphere-Wave-Sediment Transport' (COAWST) modelling system. The track and intensity of tropical cyclone (TC) Phailin simulated by the WRF component of the coupled model agrees well with the best-track estimates reported by the India Meteorological Department (IMD). Ocean model component (ROMS) was configured over the BoB domain; it utilized the wind stress and net surface heat fluxes from the WRF model to investigate upper oceanic response to the passage of TC Phailin. The coupled model shows pronounced sea surface cooling (2-2.5 °C) and an increase in sea surface salinity (SSS) (2-3 psu) after 06 GMT on 12 October 2013 over the northwestern BoB. Signature of this surface cooling was also observed in satellite data and buoy measurements. The oceanic mixed layer heat budget analysis reveals relative roles of different oceanic processes in controlling the mixed layer temperature over the region of observed cooling. The heat budget highlighted major contributions from horizontal advection and vertical entrainment processes in governing the mixed layer cooling (up to -0.1 °C h-1) and, thereby, reduction in sea surface temperature (SST) in the northwestern BoB during 11-12 October 2013. During the post-cyclone period, the net heat flux at surface regained its diurnal variations with a noontime peak that provided a warming tendency up to 0.05 °C h-1 in the mixed layer. Clear signatures of TC-induced upwelling are seen in vertical velocity (about 2.5 × 10-3 m s-1), rise in isotherms and isohalines along 85-88° E longitudes in the northwestern BoB. The study demonstrates that a coupled atmosphere-ocean model (WRF + ROMS) serves as a useful tool to investigate oceanic response to the passage of cyclones.

OESbathy version 1.0: a method for reconstructing ocean bathymetry with generalized continental shelf-slope-rise structures

NASA Astrophysics Data System (ADS)

Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.

2015-09-01

We present a method for reconstructing global ocean bathymetry that combines a standard plate cooling model for the oceanic lithosphere based on the age of the oceanic crust, global oceanic sediment thicknesses, plus generalized shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to develop a methodology for reconstructing ocean bathymetry in the geologic past that includes heterogeneous continental margins in addition to abyssal ocean floor. First, the plate cooling model is applied to maps of ocean crustal age to calculate depth to basement. To the depth to basement we add an isostatically adjusted, multicomponent sediment layer constrained by sediment thickness in the modern oceans and marginal seas. A three-parameter continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Parameters of the shelf-slope-rise structures at active and passive margins are determined from modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and central Atlantic, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth to basement, ocean bathymetry with an isostatically adjusted multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

Faulting of gas-hydrate-bearing marine sediments - contribution to permeability

USGS Publications Warehouse

Dillon, William P.; Holbrook, W.S.; Drury, Rebecca; Gettrust, Joseph; Hutchinson, Deborah; Booth, James; Taylor, Michael

1997-01-01

Extensive faulting is observed in sediments containing high concentrations of methane hydrate off the southeastern coast of the United States. Faults that break the sea floor show evidence of both extension and shortening; mud diapirs are also present. The zone of recent faulting apparently extends from the ocean floor down to the base of gas-hydrate stability. We infer that the faulting resulted from excess pore pressure in gas trapped beneath the gas hydrate-beating layer and/or weakening and mobilization of sediments in the region just below the gas-hydrate stability zone. In addition to the zone of surface faults, we identified two buried zones of faulting, that may have similar origins. Subsurface faulted zones appear to act as gas traps.

Manganese cycles in Arctic marine sediments - Climate signals or diagenesis?

NASA Astrophysics Data System (ADS)

März, C.; Stratmann, A.; Eckert, S.; Schnetger, B.; Brumsack, H.-J.

2009-04-01

In comparison to sediments from other parts of the world ocean, the inorganic geochemistry of Arctic Ocean sediments is poorly investigated. However, marked light to dark brown layers are well-known features of Quaternary Arctic sediments, and have been related to variable Mn contents. Brown layers represent intervals relatively rich in Mn (often > 1 wt.%), while yellowish-greyish intervals contain less Mn. As these brown layers are widespread in pelagic Quaternary deposits of the Arctic Ocean, there are attempts to use them as stratigraphic, age-equivalent marker horizons that are genetically related to global climate changes (e.g. Jakobsson et al., 2000; Löwemark et al., 2008). In the Arctic Ocean, other conventional stratigraphic methods often fail, therefore the use of Mn-rich layers as a chemostratigraphic tool seems to be a promising approach. However, several inorganic-geochemical and modelling studies of Mn cycles in the Arctic as well as in other parts of the world ocean have shown that multiple Mn layers in marine sediments can be created by non-steady state diagenetic processes, i.e. secondary Mn redistribution in the sediment due to microbially mediated dissolution-reprecipitation reactions (e.g. Li et al., 1969; Gobeil et al., 1997; Burdige, 2006; Katsev et al., 2006). Such biogeochemical processes can lead to rapid migration or fixation of redox boundaries in the sediment, resulting in the formation or (partial) destruction of metal-rich layers several thousands of years after sediment deposition. As this clearly would alter primary paleoenvironmental signals recorded in the sediments, we see an urgent need to unravel the real stratigraphic potential of Arctic Mn cycles before they are readily established as standard tools. For this purpose, we are studying Mn cycles in Arctic Ocean sediments recovered during R/V Polarstern expedition ARK XXIII/3 on the Mendeleev Ridge (East Siberian Sea). First results of pore water and sediment composition (analysed by ICP-OES and WD-XRF) indicate that certain Mn-rich layers are currently dissolving, while others are forming. This internal Mn re-distribution, while being more pronounced in some locations than in others, also has an impact on related trace metal distributions (e.g. Co, Cu, Ni, Mo). As Mn diagenesis obviously occurs in most cores studied so far (pelagic depositional areas unaffected by turbidites), we conclude that caution has to be taken when applying Mn layers as stratigraphic tools. In addition to more sensitive analyses (acid digestions and HR-ICP-MS measurements), we will apply methods like sequential Mn extraction, X-ray diffraction and electron microscopy to study these Mn-rich layers. These data will be put into a broader context by comparing them to parameters like magnetic susceptibility, grain size distribution, sediment colour or porosity. Hopefully, this will result in a better understanding of Mn biogeochemistry in the Arctic Ocean, including its application as paleoenvironmental proxy. Burdige, D.J. (2006) Geochemistry of marine sediments. Princeton University Press, 609 pp. Gobeil, C., Macdonald, R.W., Sundby, B. (1997) Diagenetic separation of cadmium and manganese in suboxic continental margin sediments. Geochim. Cosmochim. Acta 61, 4647-4654. Jakobsson, M., Løvlie, R., Al-Hanbali, H., Arnold, E.M., Backman, J., Mörth, M. (2000) Manganese and color cycles in Artic Ocean sediments constrain Pleistocene chronology. Geology 8, 23-26. Katsev, S., Sundby, B., Mucci, A. (2006) Modeling vertical excursions of the redox boundary in sediments: Application to deep basins of the Arctic Ocean. Limnol. Oceanogr. 51, 1581-1593. Li, Y.-H., Bischoff, J. Mathieu, G. (1969) Migration of manganese in Arctic Basin sediments. Earth Planet. Sci. Lett. 7, 265-270. Löwemark, L., Jakobsson, M., Mörth, M., Backman, J. (2008) Arctic Ocean manganese contents and sediment colour cycles. Polar. Res. 27, 105-113.

The influence of buried nodules on the mobility of metals in deep sea sediments

NASA Astrophysics Data System (ADS)

Heller, Christina; Kuhn, Thomas

2017-04-01

Hydrothermal fluids can extract significant amounts of heat from oceanic lithosphere by lateral fluid flow through permeable basaltic crust of an age of up to 65 Ma. Fluid recharge and discharge occur at basement outcrops in between impermeable pelagic deep sea sediments. Recharge of oxic seawater causes upward oxygen diffusion into sediments overlying the permeable basalt in areas proximal to recharge sites. It is suggested that this oxygen has a strong impact on sediments and Mn-nodules during fluid exposure time. The aim of this study is to investigate if/how fluid flow through oceanic crust influence the distribution and element budget of Mn-nodules. Nodules occur widespread at the seafloor of the Clarion-Clipperton Zone (CCZ) in the equatorial North Pacific and were analyzed in many studies worldwide. Nodules buried in the deep sea sediments could be found only rarely (von Stackelberg, 1997, Geol. Soc. Spec. Publ., 119: 153-176). High resolution side-scan sonar recordings (unpublished Data BGR Hannover) indicate that there exist a coherent layer of nodules buried in the sediments of the working area. During the expedition SO 240/FLUM nodules were found on the sediment surface in 4200 to 4300 m water depth as well as in the sediment down to 985 cm below seafloor. In general, nodules consist of different nm- to µm-thick, dense and porous layers. The geochemical composition of bulk nodules and single nodule layers were determined by XRF, ICP-MS/OES, XRD and by high resolution analyses with electron microprobe and LA-ICP-MS. Dense layers have low Mn/Fe ratios (<4) and high concentrations of Co, Zr and REY, while porous layers are characterized by high Mn/Fe ratios (> 10) and high Ni+Cu and Li concentrations. The different compositions depend on different formation processes of the layers. They were formed by metal precipitation from oxic (hydrogenetic) and suboxic (diagenetic) bottom-near seawater and/or pore water (Wegorzewski and Kuhn, 2014, Mar. Geol. 357, 123-138). Preliminary results show that there are significant differences between the geochemical composition of nodules grown at sediment surface and those found within sediments. Compared to surface nodules, buried nodules are enriched in Co and W, but have lower concentration of Mo, Ba, Zn and Li. The distribution of Rare Earth Elements and Y(REY) is also different. Furthermore, the locations of the buried manganese nodules correlates with increased contents of Mn, Co and other elements in the suboxic pore water. It seems that the hydrogenetic layers of the buried nodules were dissolved and/ or recrystallized due to diagenetic processes in the sediment. As a result, a new Fe-rich layer type was formed, with Mn being released into the pore water and/or being used to form todorokite in the nodules. The mineralogical analyses of surface and buried nodules support this assumption. Until now, it couldńt be proven that the hydrothermal fluid flow in the basalts underneath the sediments has an influence on the nodule geochemistry.

Climate sensitivity to Arctic seaway restriction during the early Paleogene

NASA Astrophysics Data System (ADS)

Roberts, Christopher D.; LeGrande, Allegra N.; Tripati, Aradhna K.

2009-09-01

The opening and closing of ocean gateways affects the global distribution of heat, salt, and moisture, potentially driving climatic change on regional to global scales. Between 65 and 45 million years ago (Ma), during the early Paleogene, exchange between the Arctic and global oceans occurred through two narrow and shallow seaways, the Greenland-Norway seaway and the Turgai Strait. Sediments from the Arctic Ocean suggest that, during this interval, the surface ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions in the Paleogene Arctic remain uncertain. Here we show results from an isotope-enabled, atmosphere-ocean general circulation model, which indicate that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the Arctic seaways. We also present modelled estimates of seawater and calcite δ18O for the Paleogene. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~ 6 psu and warming of sea-surface temperatures by 2 °C in the North Atlantic and 5-10 °C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We propose that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the Paleocene Eocene Thermal Maximum (PETM).

MODIS imagery as a tool for synoptic water quality assessments in the southern California coastal ocean

USGS Publications Warehouse

Nezlin, N.P.; DiGiacomo, P.M.; Jones, B.H.; Reifel, K.M.; Warrick, J.A.; Johnson, S.C.; Mengel, M.J.

2007-01-01

The dynamics of rainstorm plumes in the coastal waters of southern California was studied during the Bight'03 Regional Water Quality Program surveys. Measurements of surface salinity and bacterial counts collected from research vessels were compared to MODIS-Aqua satellite imagery. The spectra of normalized water-leaving radiation (nLw) were different in plumes and ambient ocean waters, enabling plumes discrimination and plume area size assessments from remotely-sensed data. The plume/ocean nLw differences (i.e., plume optical signatures) were most evident during first days after the rainstorm over the San Pedro shelf and in the San Diego region and less evident in Santa Monica Bay, where suspended sediments concentration in discharged water was lower than in other regions. In the Ventura area, plumes contained more suspended sediments than in other regions, but the grid of ship-based stations covered only a small part of the freshwater plume and was insufficient to reveal the differences between the plume and ocean optical signatures. The accuracy of plume area assessments from satellite imagery was not high (77% on average), seemingly because of inexactitude in satellite data processing. Nevertheless, satellite imagery is a useful tool for the estimation of the extent of polluted plumes, which is hardly achievable by contact methods.

In situ Raman-based measurements of high dissolved methane concentrations in hydrate-rich ocean sediments

NASA Astrophysics Data System (ADS)

Zhang, Xin; Hester, Keith C.; Ussler, William; Walz, Peter M.; Peltzer, Edward T.; Brewer, Peter G.

2011-04-01

Ocean sediment dissolved CH4 concentrations are of interest for possible climate-driven venting from sea floor hydrate decomposition, for supporting the large-scale microbial anaerobic oxidation of CH4 that holds the oceanic CH4 budget in balance, and for environmental issues of the oil and gas industry. Analyses of CH4 from recovered cores near vent locations typically show a maximum of ˜1 mM, close to the 1 atmosphere equilibrium value. We show from novel in situ measurement with a Raman-based probe that geochemically coherent profiles of dissolved CH4 occur rising to 30 mM (pCH4 = 3 MPa) or an excess pressure ˜3× greater than CO2 in a bottle of champagne. Normalization of the CH4 Raman ν1 peak to the ubiquitous water ν2 bending peak provides a fundamental internal calibration. Very large losses of CH4 and fractions of other gases (CO2, H2S) must typically occur from recovered cores at gas rich sites. The new data are consistent with observations of microbial biomass and observed CH4 oxidation rates at hydrate rich sites and support estimates of a greatly expanded near surface oceanic pore water CH4 reservoir.

Increased Oxygenation of the Oceans Since the Mid-Cenozoic as Constrained by Cr/Co and Os/Ir Ratios in Oxic Pelagic Sediments

NASA Astrophysics Data System (ADS)

Hu, M.; Lee, C.

2005-12-01

In terms of redox, the marine sediments can be roughly divided into anoxic to suboxic sediments on the margins and oxic sediments in pelagic (open ocean) environments. The relative amounts of anoxic/suboxic sediments being deposited at any given time could be related to biological productivity and/or the efficiency of the ocean circulation system. How the depositional area of anoxic/suboxic deposition has changed through time is thus of concern. One way to track redox conditions is to investigate variations in the concentrations of redox sensitive trace metals. Most studies along these lines have focused on anoxic sediments. However, one problem with using anoxic sediments to study the global oceans is that such sediments are typically deposited in somewhat isolated basins, whose redox conditions may vary from basin to basin. An alternative approach, taken here, is to examine redox-sensitive elemental ratios in oxic pelagic sediments. This is motivated by the fact that pelagic sediments are more likely to reflect average ocean chemistry. In addition, the redox-sensitive metal contents of oxic sediments represent the complement to anoxic sediments. Choosing an appropriate redox-sensitive elemental ratio which eliminates dilution/concentration effects, requires the identification of trace metals that are preferentially precipitated in oxic conditions and those precipitated in more reducing conditions. Overall elemental behaviors were estimated by comparing hydrogenous or authigenic burial fluxes of various trace metals at given pelagic ODP sites to global riverine input fluxes. If the pelagic burial fluxes of a given element are significantly smaller than the riverine input flux, other burial outputs are implied, and it is hypothesized here that this element may precipitate in reducing conditions, such as in oceanic margin. If, on the other hand, the pelagic burial flux is equal to or greater than the riverine input flux, the implication is that oxic pelagic sediments must account for a significant proportion of the burial output of that element. In this case, we assume that this element is oxic-loving. Results of this work reveal that V, Cr, and Co may be particularly redox-sensitive: V and Cr precipitate in reducing environments while Co precipitates in more oxidizing environments. Results of our study, combined with existing data from the literature, show that Cr/Co ratios decrease with depth in DSDP596, 39, 801A, 319, 321, 465A, 577 in the N and S Pacific. After correcting for sedimentation rate, it is shown that the variation of Cr/Co versus time in all of these cores converge, which suggests that the variations in Cr/Co reflect a true variation in seawater composition. This also supported by the lack of sedimentation constrained by Cr/Co and Ce flux. Cr/Co remains low during the Cretaceous but begins to rise at ~25Ma across the entire Pacific. If the Cr/Co and Os/Ir ratio of inputs to the ocean have not changed much, this trend also matches that Os/Ir in the DSDP 596 site in the south Pacific. One interpretation of these results is that there has been a decrease in the area of anoxic/suboxic sedimentation beginning at this time. If correct, the implication is that there was a fundamental change in the redox conditions of the ocean in the mid-Cenozoic. We speculate that this might have been related to mid-Cenozoic global cooling, which may have increased the efficiency of the oceanic circulation system.

Erosion of the Laurentide region of North America by glacial and glaciofluvial processes

USGS Publications Warehouse

Bell, M.; Laine, E.P.

1985-01-01

Collection of seismic reflection data from continental margins and ocean basins surrounding North America makes it possible to estimate the amount of material eroded from the area formerly covered by Laurentide ice sheets since major glaciation began in North America. A minimum estimate is made of 1.62 ?? 106 km3, or an average 120 m of rock physically eroded from the Laurentide region. This figure is an order of magnitude higher than earlier estimates based on the volume of glacial drift, Cenozoic marine sediments, and modern sediment loads of rivers. Most of the sediment produced during Laurentide glaciation has already been transported to the oceans. The importance of continental glaciation as a geomorphic agency in North America may have to be reevaluated. Evidence from sedimentation rates in ocean basins surrounding Greenland and Antarctica suggests that sediment production, sediment transport, and possibly denudation by permanent ice caps may be substantially lower than by periodic ice caps, such as the Laurentide. Low rates of sediment survival from the time of the Permo-Carboniferous and Precambrian glaciations suggest that predominance of marine deposition during some glacial epochs results in shorter lived sediment because of preferential tectonism and cycling of oceanic crust versus continental crust. ?? 1985.

Impact of ice-shelf sediment content on the dynamics of plumes under melting ice shelves

NASA Astrophysics Data System (ADS)

Wells, A.

2015-12-01

When a floating ice shelf melts into an underlying warm salty ocean, the resulting fresh meltwater can rise in a buoyant Ice-Shelf-Water plume under the ice. In certain settings, ice flowing across the grounding line carries a basal layer of debris rich ice, entrained via basal freezing around till in the upstream ice sheet. Melting of this debris-laden ice from floating ice shelves provides a flux of dense sediment to the ocean, in addition to the release of fresh buoyant meltwater. This presentation considers the impact of the resulting suspended sediment on the dynamics of ice shelf water plumes, and identifies two key flow regimes depending on the sediment concentration frozen into the basal ice layer. For large sediment concentration, melting of the debris-laden ice shelf generates dense convectively unstable waters that drive convective overturning into the underlying ocean. For lower sediment concentration, the sediment initially remains suspended in a buoyant meltwater plume rising along the underside of the ice shelf, before slowly depositing into the underlying ocean. A theoretical plume model is used to evaluate the significance of the negatively buoyant sediment on circulation strength and the feedbacks on melting rate, along with the expected depositional patterns under the ice shelf.

Reoxidation of estuarine sediments during simulated resuspension events: Effects on nutrient and trace metal mobilisation

NASA Astrophysics Data System (ADS)

Vidal-Durà, Andrea; Burke, Ian T.; Stewart, Douglas I.; Mortimer, Robert J. G.

2018-07-01

Estuarine environments are considered to be nutrient buffer systems as they regulate the delivery of nutrients from rivers to the ocean. In the Humber Estuary (UK) seawater and freshwater mixing during tidal cycles leads to the mobilisation of oxic surface sediments (0-1 cm). However, less frequent seasonal events can also mobilise anoxic subsurface (5-10 cm) sediments, which may have further implications for the estuarine geochemistry. A series of batch experiments were carried out on surface and subsurface sediments taken from along the salinity gradient of the Humber Estuary. The aim was to investigate the geochemical processes driving major element (N, Fe, S, and Mn) redox cycling and trace metal behaviour during simulated resuspension events. The magnitude of major nutrient and metal release was significantly greater during the resuspension of outer estuarine sediments rather than from inner estuarine sediments. When comparing resuspension of surface versus subsurface sediment, only the outer estuary experiments showed significant differences in major nutrient behaviour with sediment depth. In general, any ammonium, manganese and trace metals (Cu and Zn) released during the resuspension experiments were rapidly removed from solution as new sorption sites (i.e. Fe/Mn oxyhydroxides) formed. Therefore Humber estuary sediments showed a scavenging capacity for these dissolved species and hence may act as an ultimate sink for these elements. Due to the larger aerial extent of the outer estuary intertidal mudflats in comparison with the inner estuary area, the mobilisation of the outer estuary sediments (more reducing and richer in sulphides and iron) may have a greater impact on the transport and cycling of nutrients and trace metals. Climate change-associated sea level rise combined with an increasing frequency of major storm events in temperate zones, which are more likely to mobilise deeper sediment regions, will impact the nutrient and metal inputs to the coastal waters, and therefore enhance the likelihood of eutrophication in this environment.

Anomalous Subsidence at Rifted Continental Margins: Distinguishing Mantle Dynamic Topography from Anomalous Oceanic Crustal Thickness

NASA Astrophysics Data System (ADS)

Cowie, L.; Kusznir, N. J.

2012-12-01

It has been proposed that some continental rifted margins have anomalous subsidence histories and that at breakup they were elevated at shallower bathymetries than the isostatic response of classical rift models (McKenzie 1978) would predict. The existence of anomalous syn or post breakup subsidence of this form would have important implications for our understanding of the geodynamics of continental breakup and rifted continental margin formation, margin subsidence history and the evolution of syn and post breakup depositional systems. We have investigated three rifted continental margins; the Gulf of Aden, Galicia Bank and the Gulf of Lions, to determine whether the oceanic crust in the ocean-continent transition of these margins has present day anomalous subsidence and if so, whether it is caused by mantle dynamic topography or anomalous oceanic crustal thickness. Residual depth anomalies (RDA) corrected for sediment loading, using flexural backstripping and decompaction, have been calculated by comparing observed and age predicted oceanic bathymetries in order to identify anomalous oceanic bathymetry and subsidence at these margins. Age predicted bathymetric anomalies have been calculated using the thermal plate model predictions from Crosby & McKenzie (2009). Non-zero sediment corrected RDAs may result from anomalous oceanic crustal thickness with respect to the global average, or from mantle dynamic uplift. Positive RDAs may result from thicker than average oceanic crust or mantle dynamic uplift; negative RDAs may result from thinner than average oceanic crust or mantle dynamic subsidence. Gravity inversion incorporating a lithosphere thermal gravity anomaly correction and sediment thickness from 2D seismic data has been used to determine Moho depth and oceanic crustal basement thickness. The reference Moho depths used in the gravity inversion have been calibrated against seismic refraction Moho depths. The gravity inversion crustal basement thicknesses together with Airy isostasy have been used to predict a "synthetic" gravity derived RDA. Sediment corrected RDA for oceanic crust in the Gulf of Aden are positive (+750m) indicating anomalous uplift with respect to normal subsidence. Gravity inversion predicts normal thickness oceanic crust and a zero "synthetic" gravity derived RDA in the oceanic domain. The difference between the positive sediment corrected RDA and the zero "synthetic" gravity derived RDA, implies that the anomalous subsidence reported in the Gulf of Aden is the result of mantle dynamic uplift. For the oceanic crust outboard of Galicia Bank both the sediment corrected RDA and the "synthetic" gravity derived RDA are negative (-800m) and of similar magnitude, indicating anomalous subsidence, which is the result of anomalously thin oceanic crust, not mantle dynamic topography. We conclude that there is negligible mantle dynamic topography influencing the Galicia Bank region. In the Gulf of Lions, gravity inversion predicts thinner than average oceanic crust. Both sediment corrected RDA (-1km) and "synthetic" gravity derived RDA (-500m) are negative. The more negative sediment corrected RDA compared with the "synthetic" gravity derived RDA implies that the anomalous subsidence in the Gulf of Lions is the result of mantle dynamic subsidence as well as thinner than average oceanic crust.

Estimates of Eastern Equatorial Pacific Sea Surface Temperatures During the Pliocene From Carbonate 'Clumped Isotope' Thermometry

NASA Astrophysics Data System (ADS)

Thiagarajan, N.; Tripati, A.; Eiler, J.

2007-12-01

The early Pliocene (5 to 3 Ma) was an interval in Earth history that was globally warmer than the present; thus, study of the details of Pliocene climate can provide insights into the dynamics of warm climates. There are two competing models of the temperature structure of the tropical Pacific upper-ocean during the early Pliocene: the dynamical 'ocean thermostat' model [1,2] and the 'El Padre' (or permanent 'El Nino') model [3], each of which predict zonal temperature gradients and mean conditions in the Eastern Equatorial Pacific (EEP), and which differ markedly from one another in these predictions. The dynamical 'ocean thermostat' model predicts an increased temperature contrast between the Western Equatorial Pacific (WEP) and EEP, enhanced thermocline tilt and intensified upwelling under warmer conditions. In contrast, the 'El Padre' model postulates a collapse of the zonal temperature gradient, reduced thermocline tilt and a reduction in upwelling and/or warmer temperatures of upwelled waters. Existing reconstructions of tropical temperatures produce WEP sea surface temperatures which agree with each other, but yield very different results in the EEP [4,5]. We have reconstructed EEP sea surface temperatures at Ocean Drilling Program (ODP) Site 847 using a few samples spanning key intervals of the last 6 million years using carbonate clumped isotope thermometer [6,7,8]. This technique is based on the temperature dependence of the abundances of 13C-18O bonds in carbonate minerals. Initial measurements of planktonic foraminifera and coccoliths from ODP Site 847 indicate cool EEP sea surface temperatures, supporting models of Pliocene climate that have enhanced zonal temperature gradients, relative to modern. Analyses of Globigerinoides sacculifer (with sac) from sediments indicate calcification temperatures of 20.3°C ± 0.1°C and seawater δ18O values of -0.8‰ ± 0.1‰ from ~6.1 to 5.1 million years ago. Measurements of a mixed coccolith assemblage from the fine fraction of 5.6 Ma sediments show calcification temperatures of 20.4°C ± 2.3°C and seawater δ18O values of -1.4‰ ± 0.6‰. G. sacculifer (with sac) and mixed coccoliths from 1.4 Ma sediments yield calcification temperatures of 22.3°C ± 2.5°C and seawater δ18O values of 1.7‰ ± 0.7‰, and 19.4°C ± 1.8°C and seawater δ18O values of 0.4‰ ± 0.5‰, respectively. Our preliminary findings are consistent with the 'dynamical ocean thermostat' model. [1] Clement, A., et al., 1996, An Ocean Dynamical Thermostat, J. of Clim., 9, 2190-2196. [2] Cane, M., et al., 1997, Twentieth-Century Sea Surface Temperature Trends, Science, 957-960. [3] Fedorov, A., et al., 2006, The Pliocene Paradox (Mechanisms for a permanent El Nino), Science, 312, 1437-1443. [4] Rickaby, R. and Halloran, P., 2005, Cool La Nina during the warmth of the Pliocene?, Science, 307, 1948-1953. [5] Wara, M., et al. ,2005, Permanent El Nino-like conditions during the Pliocene Warm Period, Science, 309, 758-761. [6] Ghosh, P., et al., 2006, 13C-18O bonds in carbonate minerals: A new kind of paleothermometer, GCA, 70, 1439-1456. [7] Eiler, J. and Tripati, A., 2007, 'Clumped isotope' thermometry in benthic foraminifera and ostracods: A novel tool for reconstructing deep-ocean temperatures. Fall AGU. [8] Tripati, A., et al. 2007, 'Carbonate `clumped isotope' thermometry in planktonic foraminifera and coccoliths. Fall AGU.

Substantial export of suspended sediment to the global oceans from glacial erosion in Greenland

NASA Astrophysics Data System (ADS)

Overeem, I.; Hudson, B. D.; Syvitski, J. P. M.; Mikkelsen, A. B.; Hasholt, B.; van den Broeke, M. R.; Noël, B. P. Y.; Morlighem, M.

2017-11-01

Limited measurements along Greenland's remote coastline hamper quantification of the sediment and associated nutrients draining the Greenland ice sheet, despite the potential influence of river-transported suspended sediment on phytoplankton blooms and carbon sequestration. Here we calibrate satellite imagery to estimate suspended sediment concentration for 160 proglacial rivers across Greenland. Combining these suspended sediment reconstructions with numerical calculations of meltwater runoff, we quantify the amount and spatial pattern of sediment export from the ice sheet. We find that, although runoff from Greenland represents only 1.1% of the Earth's freshwater flux, the Greenland ice sheet produces approximately 8% of the modern fluvial export of suspended sediment to the global ocean. Sediment loads are highly variable between rivers, consistent with observed differences in ice dynamics and thus with control by glacial erosion. Rivers that originate from deeply incised, fast-moving glacial tongues form distinct sediment-export hotspots: just 15% of Greenland's rivers transport 80% of the total sediment load of the ice sheet. We conclude that future acceleration of melt and ice sheet flow may increase sediment delivery from Greenland to its fjords and the nearby ocean.

Exploring frontiers of the deep biosphere through scientific ocean drilling

NASA Astrophysics Data System (ADS)

Inagaki, F.; D'Hondt, S.; Hinrichs, K. U.

2015-12-01

Since the first deep biosphere-dedicated Ocean Drilling Program (ODP) Leg 201 using the US drill ship JOIDES Resolution in 2002, scientific ocean drilling has offered unique opportunities to expand our knowledge of the nature and extent of the deep biosphere. The latest estimate of the global subseafloor microbial biomass is ~1029cells, accounting for 4 Gt of carbon and ~1% of the Earth's total living biomass. The subseafloor microbial communities are evolutionarily diverse and their metabolic rates are extraordinarily slow. Nevertheless, accumulating activity most likely plays a significant role in elemental cycles over geological time. In 2010, during Integrated Ocean Drilling Program (IODP) Expedition 329, the JOIDES Resolutionexplored the deep biosphere in the open-ocean South Pacific Gyre—the largest oligotrophic province on our planet. During Expedition 329, relatively high concentrations of dissolved oxygen and significantly low biomass of microbial populations were observed in the entire sediment column, indicating that (i) there is no limit to life in open-ocean sediment and (ii) a significant amount of oxygen reaches through the sediment to the upper oceanic crust. This "deep aerobic biosphere" inhabits the sediment throughout up to ~37 percent of the world's oceans. The remaining ~63 percent of the oceans is comprised of higher productivity areas that contain the "deep anaerobic biosphere". In 2012, during IODP Expedition 337, the Japanese drill ship Chikyu explored coal-bearing sediments down to 2,466 meters below the seafloor off the Shimokita Peninsula, Japan. Geochemical and microbiological analyses consistently showed the occurrence of methane-producing communities associated with the coal beds. Cell concentrations in deep sediments were notably lower than those expected from the global regression line, implying that the bottom of the deep biosphere is approached in these beds. Taxonomic composition of the deep coal-bearing communities profoundly differs from those in shallower marine sediments and instead resembles organotrophic communities in forest soils. These findings suggest that the terrigenous microbial ecosystem has been partly retained from the original depositional setting over 20 million years and contributed to deep carbon cycling ever since.

Antarctic ice dynamics and southern ocean surface hydrology during the last glacial maximum

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

Labeyrie, L.D.; Burckle, L.; Labracherie, M.

1985-01-01

Eight high sedimentation rate cores located between 61/sup 0/S and 43/sup 0/S in the Atlantic and Indian sectors of the Southern Ocean have been studied in detail for foraminifera and diatom /sup 18/O//sup 16/O ratios, and changes in radiolarian and diatom specific abundance. Comparison of these different parameters permits a detailed description of the surface water hydrology during the last glacial maximum. The authors demonstrate that from 25 kyr BP to 15 kyr BP a large number of icebergs formed around the Antarctic continent. Melting along the Polar Front decreased surface salinity by approximately 1.5 per thousand between 43/sup 0/Smore » and 50/sup 0/S. They propose that an increase of snow accumulation at the Antarctic periphery and downdraw during maximum ice extension are primary causes for this major discharge of icebergs.« less

Does size and buoyancy affect the long-distance transport of floating debris?

NASA Astrophysics Data System (ADS)

Ryan, Peter G.

2015-08-01

Floating persistent debris, primarily made from plastic, disperses long distances from source areas and accumulates in oceanic gyres. However, biofouling can increase the density of debris items to the point where they sink. Buoyancy is related to item volume, whereas fouling is related to surface area, so small items (which have high surface area to volume ratios) should start to sink sooner than large items. Empirical observations off South Africa support this prediction: moving offshore from coastal source areas there is an increase in the size of floating debris, an increase in the proportion of highly buoyant items (e.g. sealed bottles, floats and foamed plastics), and a decrease in the proportion of thin items such as plastic bags and flexible packaging which have high surface area to volume ratios. Size-specific sedimentation rates may be one reason for the apparent paucity of small plastic items floating in the world’s oceans.

Direct comparison of 210Po, 234Th and POC particle-size distributions and export fluxes at the Bermuda Atlantic Time-series Study (BATS) site.

PubMed

Stewart, Gillian; Moran, S Bradley; Lomas, Michael W; Kelly, Roger P

2011-05-01

Particle-reactive, naturally occurring radionuclides are useful tracers of the sinking flux of organic matter from the surface to the deep ocean. Since the Joint Global Ocean Flux Study (JGOFS) began in 1987, the disequilibrium between (234)Th and its parent (238)U has become widely used as a technique to measure particle export fluxes from surface ocean waters. Another radionuclide pair, (210)Po and (210)Pb, can be used for the same purpose but has not been as widely adopted due to difficulty with accurately constraining the (210)Po/(210)Pb radiochemical balance in the ocean and because of the more time-consuming radiochemical procedures. Direct comparison of particle flux estimated in different ocean regions using these short-lived radionuclides is important in evaluating their utility and accuracy as tracers of particle flux. In this paper, we present paired (234)Th/(238)U and (210)Po/(210)Pb data from oligotrophic surface waters of the subtropical Northwest Atlantic and discuss their advantages and limitations. Vertical profiles of total and particle size-fractionated (210)Po and (234)Th activities, together with particulate organic carbon (POC) concentrations, were measured during three seasons at the Bermuda Atlantic Time-series Study (BATS) site. Both (210)Po and (234)Th reasonably predict sinking POC flux caught in sediment traps, and each tracer provides unique information about the magnitude and efficiency of the ocean's biological pump. Copyright © 2010 Elsevier Ltd. All rights reserved.

Sedimentation processes in a coral reef embayment: Hanalei Bay, Kauai

USGS Publications Warehouse

Storlazzi, C.D.; Field, M.E.; Bothner, Michael H.; Presto, M.K.; Draut, A.E.

2009-01-01

Oceanographic measurements and sediment samples were collected during the summer of 2006 as part of a multi-year study of coastal circulation and the fate of terrigenous sediment on coral reefs in Hanalei Bay, Kauai. The goal of this study was to better understand sediment dynamics in a coral reef-lined embayment where winds, ocean surface waves, and river floods are important processes. During a summer period that was marked by two wave events and one river flood, we documented significant differences in sediment trap collection rates and the composition, grain size, and magnitude of sediment transported in the bay. Sediment trap collection rates were well correlated with combined wave-current near-bed shear stresses during the non-flood periods but were not correlated during the flood. The flood's delivery of fine-grained sediment to the bay initially caused high turbidity and sediment collection rates off the river mouth but the plume dispersed relatively quickly. Over the next month, the flood deposit was reworked by mild waves and currents and the fine-grained terrestrial sediment was advected around the bay and collected in sediment traps away from the river mouth, long after the turbid surface plume was gone. The reworked flood deposits, due to their longer duration of influence and proximity to the seabed, appear to pose a greater long-term impact to benthic coral reef communities than the flood plumes themselves. The results presented here display how spatial and temporal differences in hydrodynamic processes, which result from variations in reef morphology and orientation, cause substantial variations in the deposition, residence time, resuspension, and advection of both reef-derived and fluvial sediment over relatively short spatial scales in a coral reef embayment.

Authigenesis of trace metals in energetic tropical shelf environments

USGS Publications Warehouse

Breckel, E.J.; Emerson, S.; Balistrieri, L.S.

2005-01-01

We evaluated authigenic changes of Fe, Mn, V, U, Mo, Cd and Re in suboxic, periodically remobilized, tropical shelf sediments from the Amazon continental shelf and the Gulf of Papua. The Cd/Al, Mo/Al, and U/Al ratios in Amazon shelf sediments were 82%, 37%, and 16% less than those in Amazon River suspended sediments, respectively. Very large depletions of U previously reported in this environment were not observed. The Cd/Al ratios in Gulf of Papua sediments were 76% lower than measurements made on several Papua New Guinea rivers, whereas U/Al ratios in the shelf sediments were enriched by approximately 20%. Other metal/Al ratios in the Papua New Guinea river suspended sediments and continental shelf sediments were not distinguishably different. Comparison of metal/Al ratios to grain size distributions in Gulf of Papua samples indicates that our observations cannot be attributed to differences in grain size between the river suspended sediments and continental shelf sediments. These two shelves constitute a source of dissolved Cd to the world ocean equal to 29-100% of the dissolved Cd input from rivers, but only 3% of the dissolved Mo input and 4% of the dissolved U input. Release of Cd, Mo, and U in tropical shelf sediments is likely a result of intense Fe and Mn oxide reduction in pore waters and resuspension of the sediments. Since we do not observe depletions of particulate Fe and Mn in the shelf sediments most of these dissolved metals must reoxidize in the overlying waters and reprecipitate. As Cd exhibits the largest losses on these tropical shelves, we examined the ability of newly formed Fe and Mn oxides to adsorb dissolved Cd using a geochemical diffuse double-layer surface complexation model and found the oxide surfaces are relatively ineffective at readsorbing Cd in seawater due to surface-site competition by Mg and Ca. If the remobilization and reoxidation of Fe and Mn occurs frequently enough before sediment is buried significant amounts of Cd may be removed from the oxide surfaces. Because a much greater percentage of Mn than Fe becomes remobilized in these shelf sediments, metals closely associated with Mn oxides (like Cd) are more likely to show losses during deposition. ?? 2005 Elsevier Ltd. All rights reserved.

Stormwater runoff plumes in the Southern California Bight: A comparison study with SAR and MODIS imagery.

PubMed

Holt, Benjamin; Trinh, Rebecca; Gierach, Michelle M

2017-05-15

Stormwater runoff is the largest source of pollution in the Southern California Bight (SCB), resulting from untreated runoff and pollutants from urban watersheds entering the coastal waters after rainstorms. We make use of both satellite SAR and MODIS-Aqua ocean color imagery to examine two different components of runoff plumes, the surface slick and the sediment discharge. We expand on earlier satellite SAR studies by examining an extensive collection of multi-platform SAR imagery, spanning from 1992 to 2014, that provides a more comprehensive view of the plume surface slick characteristics, illustrated with distribution maps of the extent and flow direction of the plumes. The SAR-detected surface plumes are compared with coincident rain and runoff measurements, and with available measured shoreline fecal bacteria loads. We illustrate differences in the detection of SAR surface plumes with the sediment-related discharge plumes derived from MODIS imagery. A conceptual satellite stormwater runoff monitoring approach is presented. Copyright © 2017 Elsevier Ltd. All rights reserved.

Modeling the sediment transport induced by deep sea mining in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Purkiani, Kaveh; Paul, André; Schulz, Michael; Vink, Annemiek; Walter, Maren

2017-04-01

A numerical modeling study is conducted in the German license area in northeastern Pacific Ocean to investigate the sediment dispersal of mining exploitation. A sediment transport module is implemented in a hydrodynamic model. All differently sized particles can aggregate and break up until equilibrium floc sizes are obtained. A nested model approach using the MITgcm (Massachusetts Institute of Technology general circulation model) is applied and validated against hydrographic and hydrodynamic measurements obtained in this region. Two different sediment discharge scenarios have been examined to investigate the effect of flocculation on sediment transport distribution in the deep ocean. The suspended sediment is mainly influenced by a dominant SW current far away from the sediment discharge location. Independent of initial particle size all initial particles larger than 30 μm attain similar floc size equilibrium. In contrast to coastal seas and estuaries where floc size equilibrium can be obtained in a few hours, due to low shear rate (G) the flocculation process at deep ocean is completed within 1˜2 days. Considering temporal evolution of the floc size in the model, an increase in floc sinking velocity consequently enhances the sediment deposition at seafloor. The analysis of different sediment concentration scenarios suggests that floc sinking velocity increases at higher suspended sediment concentration (SSC). The presence of a dominant current in this region induces a fine sediment plume in SW direction. The dispersed SSC plume at 20 km downstream the discharge location is able to form the flocculation process and induces a spatial variation of floc size and floc sinking velocity.

From the Surface to the Deep-Sea: Bacterial Distributions across Polymetallic Nodule Fields in the Clarion-Clipperton Zone of the Pacific Ocean.

PubMed

Lindh, Markus V; Maillot, Brianne M; Shulse, Christine N; Gooday, Andrew J; Amon, Diva J; Smith, Craig R; Church, Matthew J

2017-01-01

Marine bacteria regulate fluxes of matter and energy essential for pelagic and benthic organisms and may also be involved in the formation and maintenance of commercially valuable abyssal polymetallic nodules. Future mining of these nodule fields is predicted to have substantial effects on biodiversity and physicochemical conditions in mined areas. Yet, the identity and distributions of bacterial populations in deep-sea sediments and associated polymetallic nodules has received relatively little attention. We examined bacterial communities using high-throughput sequencing of bacterial 16S rRNA gene fragments from samples collected in the water column, sediment, and polymetallic nodules in the Pacific Ocean (bottom depth ≥4,000 m) in the eastern Clarion-Clipperton Zone. Operational taxonomic units (OTUs; defined at 99% 16S rRNA gene identity) affiliated with JTB255 (Gammaproteobacteria) and Rhodospirillaceae (Alphaproteobacteria) had higher relative abundances in the nodule and sediment habitats compared to the water column. Rhodobiaceae family and Vibrio OTUs had higher relative abundance in nodule samples, but were less abundant in sediment and water column samples. Bacterial communities in sediments and associated with nodules were generally similar; however, 5,861 and 6,827 OTUs found in the water column were retrieved from sediment and nodule habitats, respectively. Cyanobacterial OTUs clustering among Prochlorococcus and Synechococcus were detected in both sediments and nodules, with greater representation among nodule samples. Such results suggest that vertical export of typically abundant photic-zone microbes may be an important process in delivery of water column microorganisms to abyssal habitats, potentially influencing the structure and function of communities in polymetallic nodule fields.

Marine Microbial Gene Abundance and Community Composition in Response to Ocean Acidification and Elevated Temperature in Two Contrasting Coastal Marine Sediments.

PubMed

Currie, Ashleigh R; Tait, Karen; Parry, Helen; de Francisco-Mora, Beatriz; Hicks, Natalie; Osborn, A Mark; Widdicombe, Steve; Stahl, Henrik

2017-01-01

Marine ecosystems are exposed to a range of human-induced climate stressors, in particular changing carbonate chemistry and elevated sea surface temperatures as a consequence of climate change. More research effort is needed to reduce uncertainties about the effects of global-scale warming and acidification for benthic microbial communities, which drive sedimentary biogeochemical cycles. In this research, mesocosm experiments were set up using muddy and sandy coastal sediments to investigate the independent and interactive effects of elevated carbon dioxide concentrations (750 ppm CO 2 ) and elevated temperature (ambient +4°C) on the abundance of taxonomic and functional microbial genes. Specific quantitative PCR primers were used to target archaeal, bacterial, and cyanobacterial/chloroplast 16S rRNA in both sediment types. Nitrogen cycling genes archaeal and bacterial ammonia monooxygenase ( amoA ) and bacterial nitrite reductase ( nirS ) were specifically targeted to identify changes in microbial gene abundance and potential impacts on nitrogen cycling. In muddy sediment, microbial gene abundance, including amoA and nirS genes, increased under elevated temperature and reduced under elevated CO 2 after 28 days, accompanied by shifts in community composition. In contrast, the combined stressor treatment showed a non-additive effect with lower microbial gene abundance throughout the experiment. The response of microbial communities in the sandy sediment was less pronounced, with the most noticeable response seen in the archaeal gene abundances in response to environmental stressors over time. 16S rRNA genes ( amoA and nirS ) were lower in abundance in the combined stressor treatments in sandy sediments. Our results indicated that marine benthic microorganisms, especially in muddy sediments, are susceptible to changes in ocean carbonate chemistry and seawater temperature, which ultimately may have an impact upon key benthic biogeochemical cycles.

Evaluation of Dredged Material Proposed for Ocean Disposal from Federal Projects in New York and New Jersey and the Military Ocean Terminal (MOTBY)

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

Barrows, E.S.; Antrim, L.D.; Pinza, M.R.

1996-08-01

The U.S. Army Corps of Engineers (USACE) is authorized by Section 103 of the Marine Protection, Research, and Sanctuaries Act of 1972 (MPRSA), Public Law 92-532, and by the Clean Water Act of 1972 (CWA) and Amendments of 1977 to permit, evaluate, and regulate the disposal of dredged material in ocean waters to minimize adverse environmental effects. Compliance with the regulations of the MPRSA calls for physical and biological testing of sediment proposed for dredging prior to its disposal in ocean waters. The testing required by the MPRSA criteria is conducted under a testing manual developed by the USACE andmore » the U.S. Environmental Protection Agency (EPA), Evaluation of Dredged Material Proposed for Ocean Disposal (Testing Manual), commonly referred to as the `Green Book.` Testing protocols in the Green Book include bulk sediment analysis, grain size analysis, elutriate testing, and biological testing. The biological testing includes bioassays for acute toxicity as well as analysis to determine bioaccumulation of certain contaminants by marine organisms. The objective of the USACE-NYD Federal Projects Program was to evaluate sediment proposed for dredging and unconfined ocean disposal at the Mud Dump Site. The results of analytical measurements and bioassays performed on the test sediments were compared with analyses of sediment from the Mud Dump Reference Site to determine whether the test sediments were acutely toxic to marine organisms or resulted in statistically significantly greater bioaccumulation of contaminants in marine organisms, relative to the reference sediment. Testing for the federal project areas was performed according to the requirements.« less

Transport processes near coastal ocean outfalls

USGS Publications Warehouse

Noble, M.A.; Sherwood, C.R.; Lee, Hooi-Ling; Xu, Jie; Dartnell, P.; Robertson, G.; Martini, M.

2001-01-01

The central Southern California Bight is an urbanized coastal ocean where complex topography and largescale atmospheric and oceanographic forcing has led to numerous sediment-distribution patterns. Two large embayments, Santa Monica and San Pedro Bays, are connected by the short, very narrow shelf off the Palos Verdes peninsula. Ocean-sewage outfalls are located in the middle of Santa Monica Bay, on the Palos Verdes shelf and at the southeastern edge of San Pedro Bay. In 1992, the US Geological Survey, together with allied agencies, began a series of programs to determine the dominant processes that transport sediment and associated pollutants near the three ocean outfalls. As part of these programs, arrays of instrumented moorings that monitor currents, waves, water clarity, water density and collect resuspended materials were deployed on the continental shelf and slope information was also collected on the sediment and contaminant distributions in the region. The data and models developed for the Palos Verdes shelf suggest that the large reservoir of DDT/DDE in the coastal ocean sediments will continue to be exhumed and transported along the shelf for a long time. On the Santa Monica shelf, very large internal waves, or bores, are generated at the shelf break. The near-bottom currents associated with these waves sweep sediments and the associated contaminants from the shelf onto the continental slope. A new program underway on the San Pedro shelf will determine if water and contaminants from a nearby ocean outfall are transported to the local beaches by coastal ocean processes. The large variety of processes found that transport sediments and contaminants in this small region of the continental margin suggest that in regions with complex topography, local processes change markedly over small spatial scales. One cannot necessarily infer that the dominant transport processes will be similar even in adjacent regions.

Global pulses of organic carbon burial in deep-sea sediments during glacial maxima

PubMed Central

Cartapanis, Olivier; Bianchi, Daniele; Jaccard, Samuel L.; Galbraith, Eric D.

2016-01-01

The burial of organic carbon in marine sediments removes carbon dioxide from the ocean–atmosphere pool, provides energy to the deep biosphere, and on geological timescales drives the oxygenation of the atmosphere. Here we quantify natural variations in the burial of organic carbon in deep-sea sediments over the last glacial cycle. Using a new data compilation of hundreds of sediment cores, we show that the accumulation rate of organic carbon in the deep sea was consistently higher (50%) during glacial maxima than during interglacials. The spatial pattern and temporal progression of the changes suggest that enhanced nutrient supply to parts of the surface ocean contributed to the glacial burial pulses, with likely additional contributions from more efficient transfer of organic matter to the deep sea and better preservation of organic matter due to reduced oxygen exposure. These results demonstrate a pronounced climate sensitivity for this global carbon cycle sink. PMID:26923945

Data report: Permeabilities of eastern equatorial Pacific and Peru margin sediments

USGS Publications Warehouse

Gamage, Kusali; Bekins, Barbara A.; Screaton, Elizabeth; Jørgensen, Bo B.; D'Hondt, Steven L.; Miller, D. Jay

2006-01-01

Constant-flow permeability tests were conducted on core samples from Ocean Drilling Program Leg 201 from the eastern equatorial Pacific and the Peru margin. Eighteen whole-round core samples from Sites 1225, 1226, 1227, 1230, and 1231 were tested for vertical permeabilities. Sites 1225, 1226, and 1231 represent sediments of the open ocean, whereas Sites 1227 and 1230 represent sediments of the ocean margin. Measured vertical permeabilities vary from ~8 x 10–19 m2 to ~1 x 10–16 m2 for a porosity range of 45%–90%.

Physical response of a back-barrier estuary to a post-tropical cyclone

USGS Publications Warehouse

Beudin, Alexis; Ganju, Neil Kamal; Defne, Zafer; Aretxabaleta, Alfredo

2017-01-01

This paper presents a modeling investigation of the hydrodynamic and sediment transport response of Chincoteague Bay (VA/MD, USA) to Hurricane Sandy using the Coupled Ocean-Atmosphere-Wave-Sediment-Transport (COAWST) modeling system. Several simulation scenarios with different combinations of remote and local forces were conducted to identify the dominant physical processes. While 80% of the water level increase in the bay was due to coastal sea level at the peak of the storm, a rich spatial and temporal variability in water surface slope was induced by local winds and waves. Local wind increased vertical mixing, horizontal exchanges, and flushing through the inlets. Remote waves (swell) enhanced southward flow through wave setup gradients between the inlets, and increased locally generated wave heights. Locally generated waves had a negligible effect on water level but reduced the residual flow up to 70% due to enhanced apparent roughness and breaking-induced forces. Locally generated waves dominated bed shear stress and sediment resuspension in the bay. Sediment transport patterns mirrored the interior coastline shape and generated deposition on inundated areas. The bay served as a source of fine sediment to the inner shelf, and the ocean-facing barrier island accumulated sand from landward-directed overwash. Despite the intensity of the storm forcing, the bathymetric changes in the bay were on the order of centimeters. This work demonstrates the spectrum of responses to storm forcing, and highlights the importance of local and remote processes on back-barrier estuarine function.

New deglacial and Holocene micropaleontological and geochemical records from the southern margin of the Svalbard Archipelago (Arctic Ocean)

NASA Astrophysics Data System (ADS)

Rigual-Hernández, Andrés.

2010-05-01

This study is presented in the context of the Spanish research project "The development of an Arctic ice stream-dominated sedimentary system: The southern Svalbard continental margin" (SVAIS), developed within the framework of the International Polar Year (IPY) Activity N. 367 (NICE STREAMS). Its main goal is to understand the evolution of glacial continental margins and their relationship with the changes in ice sheet dynamics induced by natural climatic changes, combining the geophysical data with the sediment record both collected during an oceanographic cruise in the Storfjorden area (SW Svalbard margin) in August 2007. This marine depositional system, dominated by an ice stream during the last glacial period, was selected due to its small size inducing a rapid response to climatic changes, and for the oceanographic relevance of the area for global ocean circulation. The results obtained aim to define the sedimentary architecture and morphology, and to provide more insight into the paleoceanographic and paleoclimatic evolution of the region. We specifically report on new micropaleontological and geochemical data obtained from the sediment cores. A preliminary age model indicates that the sediment sequences cover approximately the Last Deglaciation and the Holocene. Microfossils are generally well preserved, although the abundances of the different groups show marked shifts along the record. Low concentrations of coccolithophores, diatoms, planktic foraminifers and cysts of organic-walled dinoflagellates (dinocysts) are found at the lower half of the sequence (IRD-rich, coarser-grained sediments), and increase towards the Late Holocene (fine-grained bioturbated sediments). The Climatic Optimum is characterized by the warmest sea surface temperatures as estimated from the fossil assemblage, diverse transfer functions and biogeochemical proxies, and by high nutrient contents in the bottom waters shown by light carbon isotope values and high Cd/Ca ratios in benthic foraminifers. Dilution by terrigenous material, related to the retreat of the Barents Sea Ice Sheet in response to changes in the strength of the Atlantic-sourced, warm Western Spitsbergen Current, seems to be important in driving the abundances of microfossils and of organic compounds. The different stages of the Deglaciation and the Holocene and the associated modifications in the surface oceanic environment are documented by changes in the fossil assemblage composition of the different microfossil groups, while synchronous changes in the bottom water masses are registered by stable isotope and trace element analyses of benthic foraminifers.

Coupled atmosphere-ocean-wave simulations of a storm event over the Gulf of Lion and Balearic Sea

USGS Publications Warehouse

Renault, Lionel; Chiggiato, Jacopo; Warner, John C.; Gomez, Marta; Vizoso, Guillermo; Tintore, Joaquin

2012-01-01

The coastal areas of the North-Western Mediterranean Sea are one of the most challenging places for ocean forecasting. This region is exposed to severe storms events that are of short duration. During these events, significant air-sea interactions, strong winds and large sea-state can have catastrophic consequences in the coastal areas. To investigate these air-sea interactions and the oceanic response to such events, we implemented the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System simulating a severe storm in the Mediterranean Sea that occurred in May 2010. During this event, wind speed reached up to 25 m.s-1 inducing significant sea surface cooling (up to 2°C) over the Gulf of Lion (GoL) and along the storm track, and generating surface waves with a significant height of 6 m. It is shown that the event, associated with a cyclogenesis between the Balearic Islands and the GoL, is relatively well reproduced by the coupled system. A surface heat budget analysis showed that ocean vertical mixing was a major contributor to the cooling tendency along the storm track and in the GoL where turbulent heat fluxes also played an important role. Sensitivity experiments on the ocean-atmosphere coupling suggested that the coupled system is sensitive to the momentum flux parameterization as well as air-sea and air-wave coupling. Comparisons with available atmospheric and oceanic observations showed that the use of the fully coupled system provides the most skillful simulation, illustrating the benefit of using a fully coupled ocean-atmosphere-wave model for the assessment of these storm events.

Can sediments at hydrocarbon seep sites represent a source for marine bioavailable iron? — A case study from the South China Sea

NASA Astrophysics Data System (ADS)

Li, N.; Feng, D.; Chen, D.

2017-12-01

Niu Li1, Dong Feng1,2, and Duofu Chen2,31CAS Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China. 2Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China. 3Hadal Science and Technology Research Center, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China. Iron is an essential micronutrient and commonly considered to be one of the key-limiting factors for biological productivity in many ocean regions. Seafloor Fe supply should be most efficient in suboxic conditions. Recent studies shown that widely spread anoxic environments can develop in hydrocarbon seep sediment and local bottom water, owing to the occurrence of aerobic and/or anaerobic methane oxidation. Under this condition, the iron in sediment can be reduced to dissolved Fe2+ in the ocean. However, questions remain about whether the hydrocarbon seep sediment can represent a source for bioavailable iron to the ocean, and the control factor for the transformation of iron in the sediment remains largely unexplored. For a number of hydrocarbon seeps from the northern and southern South China Sea, the iron speciation, pyrite sulfur isotope, and iron isotope, as well as the major and trace elements are used to constrain the intensity of cold seep, and its impact on transformation of iron in sediment. Samples from both areas show sediment iron lost during the high methane flux conditions, owing to the suboxic conditions cause by aerobic methane oxidation. On the other hand, high sediment iron content accompanied by high sulfur content can be seen during the conditions of high methane flux without the occurrence of aerobic methane oxidation, which is possible ascribed to the anaerobic methane oxidation and the release of iron through seep activity. This study reveals the transformation of iron in the sediment is closely related to the methane flux and the hydrocarbon seep sediment can represent a source for bioavailable iron to the ocean. Acknowledgments: Funding was provided by the NSF of China (Grants: 41422602 and 41373085).

High pCO2-induced exopolysaccharide-rich ballasted aggregates of planktonic cyanobacteria could explain Paleoproterozoic carbon burial.

PubMed

Kamennaya, Nina A; Zemla, Marcin; Mahoney, Laura; Chen, Liang; Holman, Elizabeth; Holman, Hoi-Ying; Auer, Manfred; Ajo-Franklin, Caroline M; Jansson, Christer

2018-05-29

The contribution of planktonic cyanobacteria to burial of organic carbon in deep-sea sediments before the emergence of eukaryotic predators ~1.5 Ga has been considered negligible owing to the slow sinking speed of their small cells. However, global, highly positive excursion in carbon isotope values of inorganic carbonates ~2.22-2.06 Ga implies massive organic matter burial that had to be linked to oceanic cyanobacteria. Here to elucidate that link, we experiment with unicellular planktonic cyanobacteria acclimated to high partial CO 2 pressure (pCO 2 ) representative of the early Paleoproterozoic. We find that high pCO 2 boosts generation of acidic extracellular polysaccharides (EPS) that adsorb Ca and Mg cations, support mineralization, and aggregate cells to form ballasted particles. The down flux of such self-assembled cyanobacterial aggregates would decouple the oxygenic photosynthesis from oxidative respiration at the ocean scale, drive export of organic matter from surface to deep ocean and sustain oxygenation of the planetary surface.

Wave-current interaction: Effect on the wave field in a semi-enclosed basin

NASA Astrophysics Data System (ADS)

Benetazzo, A.; Carniel, S.; Sclavo, M.; Bergamasco, A.

2013-10-01

The effect on waves of the Wave-Current Interaction (WCI) process in the semi-enclosed Gulf of Venice (northern region of the Adriatic Sea) was investigated using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system. COAWST relies on the ocean model ROMS (Regional Ocean Modeling System), the wave model SWAN (Simulating WAves Nearshore), and the CSTMS (Community Sediment Transport Modeling System) routines. The two-way data transfer between circulation and wave models was synchronous via MCT (Model Coupling Toolkit), with ROMS providing: current field, free surface elevation, and bathymetry to SWAN. For coupling, the 3-D current profiles were averaged using a formulation which integrated the near-surface velocity over a depth controlled by the spectral mean wavenumber. COAWST system was implemented on a parent grid (with horizontal resolution of 2.0 km) covering the whole Adriatic Sea with one-way nesting to a child grid resolving the northern area (Gulf of Venice) at a resolution of 0.5 km. The meteorological forcings provided by the operational meteorological model COSMO-I7 (a mesoscale model developed in the framework of the COSMO Consortium) were used to drive the modeling system in the period bracketing September 2010-August 2011. The adopted winds and the simulated waves were compared with observations at the CNR-ISMAR Acqua Alta oceanographic tower, located off the Venice littoral. Wave heights and sea surface winds were also compared with satellite-derived data. The analysis of WCI was performed on the child grid over the winter season (January-March 2011) with particular focus on the waves generated by prevailing and dominant winds blowing on the Adriatic Sea: Bora and Sirocco. Due to the variable wind direction with respect to the ocean current direction different effects on WCI were depicted, showing that within the northern Adriatic Sea the ocean-wave interactions are strongly dependent on the wind forcing direction. Further investigations reveal that, when applied to intense storms, the effect of coupling on waves results in variations of significant wave height up to 0.6 m, with some areas experiencing significant increase/decrease of wave spectral energy for opposite/following currents respectively.

Ejecta from Ocean Impacts

NASA Technical Reports Server (NTRS)

Kyte, Frank T.

2003-01-01

Numerical simulations of deep-ocean impact provide some limits on the size of a projectile that will not mix with the ocean floor during a deep-ocean impact. For a vertical impact at asteroidal velocities (approx. 20 km/s), mixing is only likely when the projectile diameter is greater than 112 of the water depth. For oblique impacts, even larger projectiles will not mix with ocean floor silicates. Given the typical water depths of 4 to 5 km in deep-ocean basins, asteroidal projectiles with diameters as large as 2 or 3 km may commonly produce silicate ejecta that is composed only of meteoritic materials and seawater salts. However, the compressed water column beneath the projectile can still disrupt and shock metamorphose the ocean floor. Therefore, production of a separate, terrestrial ejecta component is not ruled out in the most extreme case. With increasing projectile size (or energy) relative to water depths, there must be a gradation between oceanic impacts and more conventional continental impacts. Given that 60% of the Earth's surface is covered by oceanic lithosphere and 500 m projectiles impact the Earth on 10(exp 5) y timescales, there must be hundreds of oceanic impact deposits in the sediment record awaiting discovery.

Climatic teleconnections between the subtropical and polar North Atlantic during the Last Interglacial period (MIS5e)

NASA Astrophysics Data System (ADS)

Bauch, H. A.; Zhuravleva, A.

2017-12-01

Meridional gradients in sea surface temperature (SST) control ocean-atmosphere circulation patterns and, thus, regulate the global climate. Here we reconstruct variability of these gradients in the course of the Last Interglacial (MIS5e), by using sediment records from the low and high latitude North Atlantic which are linked via the Gulf Stream.In the Nordic Seas, i.e., at the northern end of the Gulf Stream extension, strong post-Saalian meltwater discharge reduced northward-directed transport of surface oceanic heat until the mid-MIS5e, resulting in a late and rather weak SST peak. To decipher the corresponding climatic changes in the area of the Gulf Stream origin, we employ stable isotopes data, planktic foraminifera assemblages as well as a new alkenone paleotemperature record from core drilled on the upper northern slope of the Little Bahama Bank. In addition, chemical composition of sediments (XRF data) was used to asses past sea level fluctuations and sedimentation regimes on this shallow-water carbonate bank. Significant variations in Sr/Ca ratios point to a two-fold structure of the Last Interglacial. Stabilized Sr/Ca values were reached only during the second phase of MIS5e, possibly representing the interval of maximum bank-top flooding after the northern hemisphere deglaciation terminated. Faunal-based proxies as well as oxygen isotopic gradients between surface and bottom-dwelling foraminifera corroborate existence of the two major climatic phases within the Last Interglacial, in agreement with the respective development in the polar region. This further suggests a strong climatic coupling between the subtropical and high-latitude North Atlantic with important implications for meridional SST gradients during the Last Interglacial.

Trawling-induced alterations of deep-sea sediment accumulation rates during the Anthropocene

NASA Astrophysics Data System (ADS)

Puig, P.; Paradis, S.; Masque, P.; Martin, J.; Juan, X.; Palanques, A.

2015-12-01

Commercial bottom trawling causes direct physical disturbance of the marine sedimentary environments by scraping and ploughing the seabed, generating periodic resuspension of surface sediments. However, the quantification of the sediment that is removed by trawling and exported across the continental margin remains largely unaddressed, and the preservation of the signal of such impacts in the geological record have been mostly overlooked. The analysis of sediment cores collected along the Catalan margin (NW Mediterranean) has allowed evaluating the contribution of this anthropogenic activity to the present-day sediment dynamics. Sediment cores at intensively trawled sites are characterized by over-consolidated sediments with lower 210Pb surface concentrations and inventories that indicate widespread erosion of recent sedimentary deposits. In turn, combined 210Pb and 137Cs chronologies indicate a significant increase of sediment accumulation rates within submarine canyon environments since the 1970s, coincidently with a strong impulse in the industrialization of the trawling fleets of this region. Two sampling sites that exhibited high sediment accumulation rates (0.6-0.7 cm/y) were reoccupied 1-2 decades after the first studies and revealed a second and even larger increase of sediment accumulation rates (>2 cm/y) occurring at the beginning of the XXI century. This recent change has been attributed to a preferential displacement of the trawling fleet towards fishing grounds surrounding submarine canyons and, also, to technical improvements in trawling vessels, presumably related to financial subsidies provided to the fishing sector. The alteration of sediment accumulation rates described in this continental margin may occur in many regions of the World's oceans given the wide geographical distribution of this human activity, and therefore, it could represent a potential marker of the Anthropocene in deep-sea environments.

Release of Black Carbon From Thawing Permafrost Estimated by Sequestration Fluxes in the East Siberian Arctic Shelf Recipient

NASA Astrophysics Data System (ADS)

Salvadó, Joan A.; Bröder, Lisa; Andersson, August; Semiletov, Igor P.; Gustafsson, Örjan

2017-10-01

Black carbon (BC) plays an important role in carbon burial in marine sediments globally. Yet the sequestration of BC in the Arctic Ocean is poorly understood. Here we assess the concentrations, fluxes, and sources of soot BC (SBC)—the most refractory component of BC—in sediments from the East Siberian Arctic Shelf (ESAS), the World's largest shelf sea system. SBC concentrations in the contemporary shelf sediments range from 0.1 to 2.1 mg g-1 dw, corresponding to 2-12% of total organic carbon. The 210Pb-derived fluxes of SBC (0.42-11 g m-2 yr-1) are higher or in the same range as fluxes reported for marine surface sediments closer to anthropogenic emissions. The total burial flux of SBC in the ESAS ( 4,000 Gg yr-1) illustrates the great importance of this Arctic shelf in marine sequestration of SBC. The radiocarbon signal of the SBC shows more depleted yet also more uniform signatures (-721 to -896‰; average of -774 ± 62‰) than of the non-SBC pool (-304 to -728‰; average of -491 ± 163‰), suggesting that SBC is coming from an, on average, 5,900 ± 300 years older and more specific source than the non-SBC pool. We estimate that the atmospheric BC input to the ESAS is negligible ( 0.6% of the SBC burial flux). Statistical source apportionment modeling suggests that the ESAS sedimentary SBC is remobilized by thawing of two permafrost carbon (PF/C) systems: surface soil permafrost (topsoil/PF; 25 ± 8%) and Pleistocene ice complex deposits (ICD/PF; 75 ± 8%). The SBC contribution to the total mobilized permafrost carbon (PF/C) increases with increasing distance from the coast (from 5 to 14%), indicating that the SBC is more recalcitrant than other forms of translocated PF/C. These results elucidate for the first time the key role of permafrost thaw in the transport of SBC to the Arctic Ocean. With ongoing global warming, these findings have implications for the biogeochemical carbon cycle, increasing the size of this refractory carbon pool in the Arctic Ocean.

OESbathy version 1.0: a method for reconstructing ocean bathymetry with realistic continental shelf-slope-rise structures

NASA Astrophysics Data System (ADS)

Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.

2015-04-01

We present a method for reconstructing global ocean bathymetry that uses a plate cooling model for the oceanic lithosphere, the age distribution of the oceanic crust, global oceanic sediment thicknesses, plus shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to reconstruct realistic ocean bathymetry based on parameterized relationships of present-day variables that can be applied to global oceans in the geologic past, and to isolate locations where anomalous processes such as mantle convection may affect bathymetry. Parameters of the plate cooling model are combined with ocean crustal age to calculate depth-to-basement. To the depth-to-basement we add an isostatically adjusted, multicomponent sediment layer, constrained by sediment thickness in the modern oceans and marginal seas. A continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Shelf-slope-rise structures at active and passive margins are parameterized using modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and Central Atlantic Ocean, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth-to-basement, ocean bathymetry with an isostatically adjusted, multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

A new instrument system to investigate sediment dynamics on continental shelves

USGS Publications Warehouse

Cacchione, D.A.; Drake, D.E.

1979-01-01

A new instrumented tripod, the GEOPROBE system, has been constructed and used to collect time-series data on physical and geological parameters that are important in bottom sediment dynamics on continental shelves. Simultaneous in situ digital recording of pressure, temperature, light scattering, and light transmission, in combination with current velocity profiles measured with a near-bottom vertical array of electromagnetic current meters, is used to correlate bottom shear generated by a variety of oceanic processes (waves, tides, mean flow, etc.) with incipient movement and resuspension of bottom sediment. A bottom camera system that is activated when current speeds exceed preset threshold values provides a unique method to identify initial sediment motion and bed form development. Data from a twenty day deployment of the GEOPROBE system in Norton Sound, Alaska, during the period September 24 - October 14, 1976 show that threshold conditions for sediment movement are commonly exceeded, even in calm weather periods, due to the additive effects of tidal currents, mean circulation, and surface waves. ?? 1979.

Late to middle Pleistocene Arctic glacial history implied from a sedimentary record from the Northwind Ridge

NASA Astrophysics Data System (ADS)

Liu, Y.; Dong, L.; Shi, X.; Zhu, A.

2017-12-01

Abstract: Sediment core ARC6-C21 collected from the Northwind Ridge, western Arctic Ocean, covers the late to middle Quaternary (Marine Isotope Stages (MIS) 1-11), as estimated by correlation to earlier proposed Arctic Ocean stratigraphies and AMS14C dating of the youngest sediments. Detailed examination of the elemental composition of sediment along with grain size in core ARC6-C21 provides important new information about sedimentary environments and provenance. We use increased contents of coarse debris as an indicator of glacier collapse events at the margins of the western Arctic Ocean, and identify the provenance of these events from geochemical composition. Notably, peaks of MgO and CaO, including large dropstones, presumably track the Laurentide Ice Sheet (LIS) discharge events to the Arctic Ocean. Major LIS inputs occurred during the stratigraphic intervals estimated as MIS 3, intra-MIS 5 and 7 events, MIS 8, and MIS 10. Inputs from the East Siberian Ice Sheet (ESIS) and/or Eurasia Ice Sheet (EIS)are inferred from peaks of SiO2, K2O and Na2O associated with coarse sediment. Major ESIS and/or EIS sedimentary events occurred in the intervals estimated as MIS 2, MIS 4, MIS 6, MIS 8 and MIS 10. Keywords: Sediment core, Pleistocene, western Arctic Ocean, geochemistry, grain size, sediment provenance, glaciations

Radioactive Cs in the estuary sediments near Fukushima Daiichi Nuclear Power Plant.

PubMed

Yamasaki, Shinya; Imoto, Junpei; Furuki, Genki; Ochiai, Asumi; Ohnuki, Toshihiko; Sueki, Keisuke; Nanba, Kenji; Ewing, Rodney C; Utsunomiya, Satoshi

2016-05-01

The migration and dispersion of radioactive Cs (mainly (134)Cs and (137)Cs) are of critical concern in the area surrounding the Fukushima Daiichi Nuclear Power Plant (FDNPP). Considerable uncertainty remains in understanding the properties and dynamics of radioactive Cs transport by surface water, particularly during rainfall-induced flood events to the ocean. Physical and chemical properties of unique estuary sediments, collected from the Kuma River, 4.0km south of the FDNPP, were quantified in this study. These were deposited after storm events and now occur as dried platy sediments on beach sand. The platy sediments exhibit median particle sizes ranging from 28 to 32μm. There is increasing radioactivity towards the bottom of the layers deposited; approximately 28 and 38Bqg(-1) in the upper and lower layers, respectively. The difference in the radioactivity is attributed to a larger number of particles associated with radioactive Cs in the lower part of the section, suggesting that radioactive Cs in the suspended soils transported by surface water has decreased over time. Sequential chemical extractions showed that ~90% of (137)Cs was strongly bound to the residual fraction in the estuary samples, whereas 60~80% of (137)Cs was bound to clays in the six paddy soils. This high concentration in the residual fraction facilitates ease of transport of clay and silt size particles through the river system. Estuary sediments consist of particles <100μm. Radioactive Cs desorption experiments using the estuary samples in artificial seawater revealed that 3.4±0.6% of (137)Cs was desorbed within 8h. More than 96% of (137)Cs remained strongly bound to clays. Hence, particle size is a key factor that determines the travel time and distance during the dispersion of (137)Cs in the ocean. Copyright © 2016 Elsevier B.V. All rights reserved.

Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust

USGS Publications Warehouse

von Huene, Roland E.; Scholl, D. W.

1991-01-01

At ocean margins where two plates converge, the oceanic plate sinks or is subducted beneath an upper one topped by a layer of terrestrial crust. This crust is constructed of continental or island arc material. The subduction process either builds juvenile masses of terrestrial crust through arc volcanism or new areas of crust through the piling up of accretionary masses (prisms) of sedimentary deposits and fragments of thicker crustal bodies scraped off the subducting lower plate. At convergent margins, terrestrial material can also bypass the accretionary prism as a result of sediment subduction, and terrestrial matter can be removed from the upper plate by processes of subduction erosion. Sediment subduction occurs where sediment remains attached to the subducting oceanic plate and underthrusts the seaward position of the upper plate's resistive buttress (backstop) of consolidated sediment and rock. Sediment subduction occurs at two types of convergent margins: type 1 margins where accretionary prisms form and type 2 margins where little net accretion takes place. At type 2 margins (???19,000 km in global length), effectively all incoming sediment is subducted beneath the massif of basement or framework rocks forming the landward trench slope. At accreting or type 1 margins, sediment subduction begins at the seaward position of an active buttress of consolidated accretionary material that accumulated in front of a starting or core buttress of framework rocks. Where small-to-mediumsized prisms have formed (???16,300 km), approximately 20% of the incoming sediment is skimmed off a detachment surface or decollement and frontally accreted to the active buttress. The remaining 80% subducts beneath the buttress and may either underplate older parts of the frontal body or bypass the prism entirely and underthrust the leading edge of the margin's rock framework. At margins bordered by large prisms (???8,200 km), roughly 70% of the incoming trench floor section is subducted beneath the frontal accretionary body and its active buttress. In rounded figures the contemporary rate of solid-volume sediment subduction at convergent ocean margins (???43,500 km) is calculated to be 1.5 km3/yr. Correcting type 1 margins for high rates of terrigenous seafloor sedimentation during the past 30 m.y. or so sets the long-term rate of sediment subduction at 1.0 km3/yr. The bulk of the subducted material is derived directly or indirectly from continental denudation. Interstitial water currently expulsed from accreted and deeply subducted sediment and recycled to the ocean basins is estimated at 0.9 km3/yr. The thinning and truncation caused by subduction erosion of the margin's framework rock and overlying sedimentary deposits have been demonstrated at many convergent margins but only off northern Japan, central Peru, and northern Chile has sufficient information been collected to determine average or long-term rates, which range from 25 to 50 km3/m.y. per kilometer of margin. A conservative long-term rate applicable to many sectors of convergent margins is 30 km3/km/m.y. If applied to the length of type 2 margins, subduction erosion removes and transports approximately 0.6 km3/yr of upper plate material to greater depths. At various places, subduction erosion also affects sectors of type 1 margins bordered by small- to medium-sized accretionary prisms (for example, Japan and Peru), thus increasing the global rate by possibly 0.5 km3/yr to a total of 1.1 km3/yr. Little information is available to assess subduction erosion at margins bordered by large accretionary prisms. Mass balance calculations allow assessments to be made of the amount of subducted sediment that bypasses the prism and underthrusts the margin's rock framework. This subcrustally subducted sediment is estimated at 0.7 km3/yr. Combined with the range of terrestrial matter removed from the margin's rock framework by subduction erosion, the global volume of subcrustally subducted materia

Sedimentology of the Argo and Gascoyne abyssal plains, NW Australia: Report on Ocean Drilling Program Leg 123 (Sept. 1–Nov. 1, 1988)

USGS Publications Warehouse

Thurow, Jürgen

1988-01-01

Ocean Drilling Program Leg 123 drilled two sites in the Indian Ocean in order to study the rifting and early spreading of one of the world’s oldest ocean basins.Site 765 was drilled in 5714 meters of water on the Argo Abyssal Plain northwest of Australia. The sedimentary succession records the opening of an ocean basin, from the first sediments deposited atop young oceanic crust, to the present day. The oldest sediments are microlaminated brown silty claystones, locally rich in calcareous bioclasts. Most of the sequence is dominated by turbidites (primarily calcareous) which probably originated within canyons cut into the margin of the drowned platform of the North West Shelf of Australia.Site 766 is located in 3998 meters of water, at the base of the steep western margin of the Exmouth Plateau. The oldest sediments penetrated are glauconitic, volcaniclastic, and bioclastic sandstones and siltstones, which are interbedded with inclined basaltic sills. These sediments were deposited by a prograding submarine fan system which shed shallow marine sediments westward or northwestward off of the western rim of the Exmouth Plateau. Sandstones are succeeded by silty claystones, recording gradual abandonment or redirection of the fan system. An overlying sequence of pelagic and hemipelagic clayey and zeolitic calcareous oozes and chalks is succeeded by featureless and homogeneous pelagic nannofossil oozes.

Tropical Pacific Climate, Carbon, and Ocean Biogeochemical Response to the Central American Seaway in a GFDL Earth System Model

NASA Astrophysics Data System (ADS)

Sentman, L. T.; Dunne, J. P.; Stouffer, R. J.; Krasting, J. P.; Wittenberg, A. T.; Toggweiler, J. R.; Broccoli, A. J.

2017-12-01

To explore the tropical Pacific climate, carbon, and ocean biogeochemical response to the shoaling and closure of the Central American Seaway during the Pliocene (5.3-2.6 Ma), we performed a suite of sensitivity experiments using the Geophysical Fluid Dynamics Laboratory Earth System Model, GFDL-ESM2G, varying only the seaway widths and sill depths. These novel ESM simulations include near-final closure of the seaway with a very narrow, 1º grid cell wide opening. Net mass transport through the seaway into the Caribbean is 20.5-23.1 Sv with a deep seaway, but only 14.1 Sv for the wide/shallow seaway because of the inter-basin bi-directional horizontal mass transport. Seaway transport originates from the Antarctic Circumpolar Current in the Pacific and rejoins it in the South Atlantic, reducing the Indonesian Throughflow and transporting heat and salt southward into the South Atlantic, in contrast to present-day and previous seaway simulations. Tropical Pacific mean climate and interannual variability is sensitive to the seaway shoaling, with the largest response to the wider/deeper seaway. In the tropical Pacific, the top 300-m warms 0.4-0.8°C, the equatorial east-west sea surface temperature gradient increases, the north-south sea surface temperature asymmetry at 110°W decreases, thermocline deepens 5-11 m, and the east-west thermocline gradient increases. In the Niño-3 region, ENSO amplitude increases, skewed toward more cold (La Niña) events, El Niño and La Niña develops earlier ( 3 months), the annual cycle weakens and the semi-annual and interannual cycles strengthen from increased symmetry of the north-south sea surface temperature gradient, and atmospheric global teleconnections strengthen with the seaway. The increase in global ocean overturning with the seaway results in a younger average ocean ideal age, reduced dissolved inorganic carbon inventory and marine net primary productivity, and altered inter-basin patterns of surface sediment carbonate sedimentation and preservation in the Caribbean and eastern equatorial Pacific, consistent with paleoclimate proxy data. The air-sea CO2 flux into the ocean decreases with the narrow seaway, thereby increasing atmospheric pCO2 concentrations by at least 236 ppm compared with present-day, with implications for warming during the Pliocene.

The Present Near-Surface Inventory of Water on Mars: How well does it Constrain the Existence of a Former Ocean?

NASA Astrophysics Data System (ADS)

Clifford, S. M.

2015-12-01

Carr and Head (Geophys. Res. Lett., 42, 726-732, 2015) have estimated that the size of the present-day inventory of near-surface water on Mars (that which exists in climatically exchangeable reservoirs) is equal to a global equivalent layer (GEL) ~34 m deep. Based on this estimate, they have attempted to extrapolate the evolution of this inventory backward in time, taking into account the introduction of new water by volcanism and outflow channel activity and the loss of water by exospheric escape. They conclude that, at the end of the Noachian, Mars had a near-surface water inventory of ~24 m which, they argue, was incompatible with the existence of a former ocean. Here, we argue that the uncertainties associated with Carr and Head analysis are significant and preclude its use as a reliable constraint on the size of the Noachian inventory of water or the presence of an early ocean. Indeed, consideration of the geologic evolution of the northern plains suggest that, if early Mars possessed an inventory of water sufficient to form an early ocean, then a frozen relic of that body may survive at depth to the present day. While sublimation undoubtedly depleted some fraction of the ocean's initial inventory of ice, the subsequent accumulation of ~0.5 - 1.5 km of sediments and volcanics, combined with recurrent episodes of outflow channel activity and obliquity-driven polar ice redistribution, could have led to the development of a complex volatile stratigraphy throughout the northern plains (at depths far below those that can be assessed as part of the present-day near-surface inventory). Thus, even if the present near-surface inventory of ice could be determined with high precision, it would place no constraint on either the past near-surface inventory of H2O or the former presence of a northern ocean.

Eocene climate and Arctic paleobathymetry: A tectonic sensitivity study using GISS ModelE-R

NASA Astrophysics Data System (ADS)

Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

2009-12-01

The early Paleogene (65-45 million years ago, Ma) was a ‘greenhouse’ interval with global temperatures warmer than any other time in the last 65 Ma. This period was characterized by high levels of CO2, warm high-latitudes, warm surface-and-deep oceans, and an intensified hydrological cycle. Sediments from the Arctic suggest that the Eocene surface Arctic Ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions remain uncertain. We present equilibrium climate conditions derived from a fully-coupled, water-isotope enabled, general circulation model (GISS ModelE-R) configured for the early Eocene. We also present model-data comparison plots for key climatic variables (SST and δ18O) and analyses of the leading modes of variability in the tropical Pacific and North Atlantic regions. Our tectonic sensitivity study indicates that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the seaways connecting the Arctic to the Atlantic and Tethys. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~6 psu and warming of sea-surface temperatures by 2°C in the North Atlantic and 5-10°C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We also suggest that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates in the Atlantic.

The Effect of the Leeuwin Current on Offshore Surface Gravity Waves in Southwest Western Australia

NASA Astrophysics Data System (ADS)

Wandres, Moritz; Wijeratne, E. M. S.; Cosoli, Simone; Pattiaratchi, Charitha

2017-11-01

The knowledge of regional wave regimes is critical for coastal zone planning, protection, and management. In this study, the influence of the offshore current regime on surface gravity waves on the southwest Western Australian (SWWA) continental shelf was examined. This was achieved by coupling the three dimensional, free surface, terrain-following hydrodynamic Regional Ocean Modelling System (ROMS) and the third generation wave model Simulating WAves Nearshore (SWAN) using the Coupled Ocean-Atmosphere-WaveSediment Transport (COAWST) model. Different representative states of the Leeuwin Current (LC), a strong pole-ward flowing boundary current with a persistent eddy field along the SWWA shelf edge were simulated and used to investigate their influence on different large wave events. The coupled wave-current simulations were compared to wave only simulations, which represented scenarios in the absence of a background current field. Results showed that the LC and the eddy field significantly impact SWWA waves. Significant wave heights increased (decreased) when currents were opposing (aligning with) the incoming wave directions. During a fully developed LC system significant wave heights were altered by up to ±25% and wave directions by up to ±20°. The change in wave direction indicates that the LC may modify nearshore wave dynamics and consequently alter sediment patterns. Operational regional wave forecasts and hindcasts may give flawed predictions if wave-current interaction is not properly accounted for.

Composition and fate of terrigenous organic matter along the Arctic land-ocean continuum in East Siberia: Insights from biomarkers and carbon isotopes

NASA Astrophysics Data System (ADS)

Tesi, Tommaso; Semiletov, Igor; Hugelius, Gustaf; Dudarev, Oleg; Kuhry, Peter; Gustafsson, Örjan

2014-05-01

Climate warming is predicted to translocate terrigenous organic carbon (TerrOC) to the Arctic Ocean and affect the marine biogeochemistry at high latitudes. The magnitude of this translocation is currently unknown, so is the climate response. The fate of the remobilized TerrOC across the Arctic shelves represents an unconstrained component of this feedback. The present study investigated the fate of permafrost carbon along the land-ocean continuum by characterizing the TerrOC composition in three different terrestrial carbon pools from Siberian permafrost (surface organic rich horizon, mineral soil active layer, and Ice Complex deposit) and marine sediments collected on the extensive East Siberian Arctic Shelf (ESAS). High levels of lignin phenols and cutin acids were measured in all terrestrial samples analyzed indicating that these compounds can be used to trace the heterogeneous terrigenous material entering the Arctic Ocean. In ESAS sediments, comparison of these terrigenous biomarkers with other TerrOC proxies (bulk δ13C/Δ14C and HMW lipid biomarkers) highlighted contrasting across-shelf trends. These differences could indicate that TerrOC in the ESAS is made up of several pools that exhibit contrasting reactivity toward oxidation during the transport. In this reactive spectrum, lignin is the most reactive, decreasing up to three orders of magnitude from the inner- to the outer-shelf while the decrease of HMW wax lipid biomarkers was considerably less pronounced. Alternatively, degradation might be negligible while sediment sorting during the across-shelf transport could be the major physical forcing that redistributes different TerrOC pools characterized by different matrix-association.

Glacial reduction and millennial-scale variations in Drake Passage throughflow.

PubMed

Lamy, Frank; Arz, Helge W; Kilian, Rolf; Lange, Carina B; Lembke-Jene, Lester; Wengler, Marc; Kaiser, Jérôme; Baeza-Urrea, Oscar; Hall, Ian R; Harada, Naomi; Tiedemann, Ralf

2015-11-03

The Drake Passage (DP) is the major geographic constriction for the Antarctic Circumpolar Current (ACC) and exerts a strong control on the exchange of physical, chemical, and biological properties between the Atlantic, Pacific, and Indian Ocean basins. Resolving changes in the flow of circumpolar water masses through this gateway is, therefore, crucial for advancing our understanding of the Southern Ocean's role in global ocean and climate variability. Here, we reconstruct changes in DP throughflow dynamics over the past 65,000 y based on grain size and geochemical properties of sediment records from the southernmost continental margin of South America. Combined with published sediment records from the Scotia Sea, we argue for a considerable total reduction of DP transport and reveal an up to ∼ 40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude, millennial-scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply an enhanced export of northern ACC surface and intermediate waters into the South Pacific Gyre and reduced Pacific-Atlantic exchange through the DP ("cold water route"). We conclude that changes in DP throughflow play a critical role for the global meridional overturning circulation and interbasin exchange in the Southern Ocean, most likely regulated by variations in the westerly wind field and changes in Antarctic sea ice extent.

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

Bishop, James K.B.

Prediction of the substantial biologically mediated carbon flows in a rapidly changing and acidifying ocean requires model simulations informed by observations of key carbon cycle processes on the appropriate space and time scales. From 2000 to 2004, the National Oceanographic Partnership Program (NOPP) supported the development of the first low-cost fully-autonomous ocean profiling Carbon Explorers that demonstrated that year-round real-time observations of particulate organic carbon (POC) concentration and sedimentation could be achieved in the world's ocean. NOPP also initiated the development of a sensor for particulate inorganic carbon (PIC) suitable for operational deployment across all oceanographic platforms. As a result,more » PIC profile characterization that once required shipboard sample collection and shipboard or shore based laboratory analysis, is now possible to full ocean depth in real time using a 0.2W sensor operating at 24 Hz. NOPP developments further spawned US DOE support to develop the Carbon Flux Explorer, a free-vehicle capable of following hourly variations of particulate inorganic and organic carbon sedimentation from near surface to kilometer depths for seasons to years and capable of relaying contemporaneous observations via satellite. We have demonstrated the feasibility of real time - low cost carbon observations which are of fundamental value to carbon prediction and when further developed, will lead to a fully enhanced global carbon observatory capable of real time assessment of the ocean carbon sink, a needed constraint for assessment of carbon management policies on a global scale.« less

Ecology and Physics of Bacterial Chemotaxis in the Ocean

PubMed Central

Seymour, Justin R.

2012-01-01

Summary: Intuitively, it may seem that from the perspective of an individual bacterium the ocean is a vast, dilute, and largely homogeneous environment. Microbial oceanographers have typically considered the ocean from this point of view. In reality, marine bacteria inhabit a chemical seascape that is highly heterogeneous down to the microscale, owing to ubiquitous nutrient patches, plumes, and gradients. Exudation and excretion of dissolved matter by larger organisms, lysis events, particles, animal surfaces, and fluxes from the sediment-water interface all contribute to create strong and pervasive heterogeneity, where chemotaxis may provide a significant fitness advantage to bacteria. The dynamic nature of the ocean imposes strong selective pressures on bacterial foraging strategies, and many marine bacteria indeed display adaptations that characterize their chemotactic motility as “high performance” compared to that of enteric model organisms. Fast swimming speeds, strongly directional responses, and effective turning and steering strategies ensure that marine bacteria can successfully use chemotaxis to very rapidly respond to chemical gradients in the ocean. These fast responses are advantageous in a broad range of ecological processes, including attaching to particles, exploiting particle plumes, retaining position close to phytoplankton cells, colonizing host animals, and hovering at a preferred height above the sediment-water interface. At larger scales, these responses can impact ocean biogeochemistry by increasing the rates of chemical transformation, influencing the flux of sinking material, and potentially altering the balance of biomass incorporation versus respiration. This review highlights the physical and ecological processes underpinning bacterial motility and chemotaxis in the ocean, describes the current state of knowledge of chemotaxis in marine bacteria, and summarizes our understanding of how these microscale dynamics scale up to affect ecosystem-scale processes in the sea. PMID:23204367

Ecology and physics of bacterial chemotaxis in the ocean.

PubMed

Stocker, Roman; Seymour, Justin R

2012-12-01

Intuitively, it may seem that from the perspective of an individual bacterium the ocean is a vast, dilute, and largely homogeneous environment. Microbial oceanographers have typically considered the ocean from this point of view. In reality, marine bacteria inhabit a chemical seascape that is highly heterogeneous down to the microscale, owing to ubiquitous nutrient patches, plumes, and gradients. Exudation and excretion of dissolved matter by larger organisms, lysis events, particles, animal surfaces, and fluxes from the sediment-water interface all contribute to create strong and pervasive heterogeneity, where chemotaxis may provide a significant fitness advantage to bacteria. The dynamic nature of the ocean imposes strong selective pressures on bacterial foraging strategies, and many marine bacteria indeed display adaptations that characterize their chemotactic motility as "high performance" compared to that of enteric model organisms. Fast swimming speeds, strongly directional responses, and effective turning and steering strategies ensure that marine bacteria can successfully use chemotaxis to very rapidly respond to chemical gradients in the ocean. These fast responses are advantageous in a broad range of ecological processes, including attaching to particles, exploiting particle plumes, retaining position close to phytoplankton cells, colonizing host animals, and hovering at a preferred height above the sediment-water interface. At larger scales, these responses can impact ocean biogeochemistry by increasing the rates of chemical transformation, influencing the flux of sinking material, and potentially altering the balance of biomass incorporation versus respiration. This review highlights the physical and ecological processes underpinning bacterial motility and chemotaxis in the ocean, describes the current state of knowledge of chemotaxis in marine bacteria, and summarizes our understanding of how these microscale dynamics scale up to affect ecosystem-scale processes in the sea.

Nd isotopic composition and REE pattern in the surface waters of the eastern Indian Ocean and its adjacent seas

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

Amakawa, Hiroshi; Alibo, D.S.; Nozaki, Yoshiyuki

2000-05-01

The Nd isotopic composition and dissolved rare earth elements (REEs) have been measured in the surface waters along the 1996/97 R.V. Hakuho-Maru Expedition route from Tokyo to the Southern Ocean, southwest of Australia, through the Philippine and Indonesian Archipelago, the eastern Indian Ocean, the Bay of Bengal and the South China Sea. The radiogenic {epsilon}{sub Nd} values of {minus}1.3 and {minus}1.4 were found in the Sulu Sea and near the Lombok Strait, indicating the strong influence of surrounding volcanic islands, whereas non-radiogenic {epsilon}{sub Nd} values of less than {minus}10 were found in the Southern Ocean and the Bay of Bengalmore » suggesting Nd of continental origin. The dissolved Nd concentrations also showed a wide range of variation from 2.8 to 19.6 pmol/kg and the trivalent REE patterns exhibited characteristic features that can be grouped into each different oceanic province. The geographical distribution of dissolved Nd is different from that of atmospherically derived {sup 210}Pb, but generally resembles that of coastally derived {sup 228}Ra. This strongly suggests that fluvial and coastal input predominates over eolian input for dissolved Nd in the surface ocean. However, the riverine dissolved Nd flux appears to be relatively minor, and remobilization of Nd from coastal and shelf sediments may play an important role in the total Nd input to the ocean. By modeling the distributions of the isotopic composition and concentration of Nd together with the activity ratio of {sup 228}Ra/{sup 226}Ra in the southeastern Indian Ocean, the authors estimate a mean residence time of Nd in the surface mixed layer to be 1.5--2.6 years. The short mean residence time is comparable with, or slightly longer than that of {sup 210}Pb suggesting similar chemical reactivity.« less

Particulate matter in pack ice of the Beaufort Gyre

USGS Publications Warehouse

Reimnitz, E.; Barnes, P.W.; Weber, W.S.

1993-01-01

Fine sediment occurred in very small patches of turbid ice, as thin spotty surface layers, in mud pellets or in old snowdrifts. The latter were widespread south of 74??N, containing an estimated 22 tonnes of silt and clay km-2. Average particle concentration in sea ice (40 mg1-1) was much higher than in sea water (0.8 mg 1 -1) or in new snow. Assuming one-third of the load is released each year, the estimated deposition rate would equal the measured Holocene rate (~2cm 1000 year-1). Therefore, modern sea-ice rafting represents a substantial fraction of the total Arctic Ocean sediment budget. -from Authors

Agglutinated Foraminifera indicate a deep bottom current over the Hovgaard Ridge, West of Spitsbergen

NASA Astrophysics Data System (ADS)

Kaminski, Michael; Frank, Niessen

2015-04-01

The Hovgård Ridge is situated in Fram Strait, west of Spitsbergen. The ridge either represents a submerged fragment of continental crust or an upwarped fragmant of ocean crust within the Fram Strait. Its crest rises to a water depth of approx. 1170 m. During Expedition 87 of the Icebreaker POLARSTERN in August 2014, a sediment-echosounding profile was recorded and a boxcore station was collected from the crest of Hovgård Ridge at 1169 m water depth. The surficial sediment at this station consists of dark yellowish brown pebbly-sandy mud with a minor admixture of biogenic components in the coarse fraction. Patches of large tubular foraminifera and isolated pebbles were clearly visible on the sediment surface. The sediment surface of the boxcore was covered with patches of large (>1 mm diameter) large tubular astrorhizids belonging mostly to the species Astrorhiza crassatina Brady, with smaller numbers of Saccorhiza, Hyperammina, and Psammosiphonella. Non-tubular species consist mainly of opportunistic forms such as Psammosphaera and Reophax. The presence of large suspension-feeding tubular genera as well as opportunistic forms, as well as sediment winnowing, point to the presence of a deep current at this locality that is strong enough to disturb the benthic fauna. This is confirmed by data obtained from sediment echosounding, which exhibit lateral variation of relative sedimentation rates within the Pleistocene sedimentary drape covering the ridge indicative of winnowing in a south-easterly direction.

Dynamical excitation of the tropical Pacific Ocean and ENSO variability by Little Ice Age cooling.

PubMed

Rustic, Gerald T; Koutavas, Athanasios; Marchitto, Thomas M; Linsley, Braddock K

2015-12-18

Tropical Pacific Ocean dynamics during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are poorly characterized due to a lack of evidence from the eastern equatorial Pacific. We reconstructed sea surface temperature, El Niño-Southern Oscillation (ENSO) activity, and the tropical Pacific zonal gradient for the past millennium from Galápagos ocean sediments. We document a mid-millennium shift (MMS) in ocean-atmosphere circulation around 1500-1650 CE, from a state with dampened ENSO and strong zonal gradient to one with amplified ENSO and weak gradient. The MMS coincided with the deepest LIA cooling and was probably caused by a southward shift of the intertropical convergence zone. The peak of the MCA (900-1150 CE) was a warm period in the eastern Pacific, contradicting the paradigm of a persistent La Niña pattern. Copyright © 2015, American Association for the Advancement of Science.

Linking geology and microbiology: inactive pockmarks affect sediment microbial community structure.

PubMed

Haverkamp, Thomas H A; Hammer, Øyvind; Jakobsen, Kjetill S

2014-01-01

Pockmarks are geological features that are found on the bottom of lakes and oceans all over the globe. Some are active, seeping oil or methane, while others are inactive. Active pockmarks are well studied since they harbor specialized microbial communities that proliferate on the seeping compounds. Such communities are not found in inactive pockmarks. Interestingly, inactive pockmarks are known to have different macrofaunal communities compared to the surrounding sediments. It is undetermined what the microbial composition of inactive pockmarks is and if it shows a similar pattern as the macrofauna. The Norwegian Oslofjord contains many inactive pockmarks and they are well suited to study the influence of these geological features on the microbial community in the sediment. Here we present a detailed analysis of the microbial communities found in three inactive pockmarks and two control samples at two core depth intervals. The communities were analyzed using high-throughput amplicon sequencing of the 16S rRNA V3 region. Microbial communities of surface pockmark sediments were indistinguishable from communities found in the surrounding seabed. In contrast, pockmark communities at 40 cm sediment depth had a significantly different community structure from normal sediments at the same depth. Statistical analysis of chemical variables indicated significant differences in the concentrations of total carbon and non-particulate organic carbon between 40 cm pockmarks and reference sample sediments. We discuss these results in comparison with the taxonomic classification of the OTUs identified in our samples. Our results indicate that microbial communities at the sediment surface are affected by the water column, while the deeper (40 cm) sediment communities are affected by local conditions within the sediment.

Dispersal of thermophilic Desulfotomaculum endospores into Baltic Sea sediments over thousands of years.

PubMed

de Rezende, Júlia Rosa; Kjeldsen, Kasper Urup; Hubert, Casey R J; Finster, Kai; Loy, Alexander; Jørgensen, Bo Barker

2013-01-01

Patterns of microbial biogeography result from a combination of dispersal, speciation and extinction, yet individual contributions exerted by each of these mechanisms are difficult to isolate and distinguish. The influx of endospores of thermophilic microorganisms to cold marine sediments offers a natural model for investigating passive dispersal in the ocean. We investigated the activity, diversity and abundance of thermophilic endospore-forming sulfate-reducing bacteria (SRB) in Aarhus Bay by incubating pasteurized sediment between 28 and 85 °C, and by subsequent molecular diversity analyses of 16S rRNA and of the dissimilatory (bi)sulfite reductase (dsrAB) genes within the endospore-forming SRB genus Desulfotomaculum. The thermophilic Desulfotomaculum community in Aarhus Bay sediments consisted of at least 23 species-level 16S rRNA sequence phylotypes. In two cases, pairs of identical 16S rRNA and dsrAB sequences in Arctic surface sediment 3000 km away showed that the same phylotypes are present in both locations. Radiotracer-enhanced most probable number analysis revealed that the abundance of endospores of thermophilic SRB in Aarhus Bay sediment was ca. 10(4) per cm(3) at the surface and decreased exponentially to 10(0) per cm(3) at 6.5 m depth, corresponding to 4500 years of sediment age. Thus, a half-life of ca. 300 years was estimated for the thermophilic SRB endospores deposited in Aarhus Bay sediments. These endospores were similarly detected in the overlying water column, indicative of passive dispersal in water masses preceding sedimentation. The sources of these thermophiles remain enigmatic, but at least one source may be common to both Aarhus Bay and Arctic sediments.

Dispersal of thermophilic Desulfotomaculum endospores into Baltic Sea sediments over thousands of years

PubMed Central

de Rezende, Júlia Rosa; Kjeldsen, Kasper Urup; Hubert, Casey R J; Finster, Kai; Loy, Alexander; Jørgensen, Bo Barker

2013-01-01

Patterns of microbial biogeography result from a combination of dispersal, speciation and extinction, yet individual contributions exerted by each of these mechanisms are difficult to isolate and distinguish. The influx of endospores of thermophilic microorganisms to cold marine sediments offers a natural model for investigating passive dispersal in the ocean. We investigated the activity, diversity and abundance of thermophilic endospore-forming sulfate-reducing bacteria (SRB) in Aarhus Bay by incubating pasteurized sediment between 28 and 85 °C, and by subsequent molecular diversity analyses of 16S rRNA and of the dissimilatory (bi)sulfite reductase (dsrAB) genes within the endospore-forming SRB genus Desulfotomaculum. The thermophilic Desulfotomaculum community in Aarhus Bay sediments consisted of at least 23 species-level 16S rRNA sequence phylotypes. In two cases, pairs of identical 16S rRNA and dsrAB sequences in Arctic surface sediment 3000 km away showed that the same phylotypes are present in both locations. Radiotracer-enhanced most probable number analysis revealed that the abundance of endospores of thermophilic SRB in Aarhus Bay sediment was ca. 104 per cm3 at the surface and decreased exponentially to 100 per cm3 at 6.5 m depth, corresponding to 4500 years of sediment age. Thus, a half-life of ca. 300 years was estimated for the thermophilic SRB endospores deposited in Aarhus Bay sediments. These endospores were similarly detected in the overlying water column, indicative of passive dispersal in water masses preceding sedimentation. The sources of these thermophiles remain enigmatic, but at least one source may be common to both Aarhus Bay and Arctic sediments. PMID:22832348

A conduit dilation model of methane venting from lake sediments

USGS Publications Warehouse

Scandella, B.P.; Varadharajan, C.; Hemond, Harold F.; Ruppel, C.; Juanes, R.

2011-01-01

Methane is a potent greenhouse gas, but its effects on Earth's climate remain poorly constrained, in part due to uncertainties in global methane fluxes to the atmosphere. An important source of atmospheric methane is the methane generated in organic-rich sediments underlying surface water bodies, including lakes, wetlands, and the ocean. The fraction of the methane that reaches the atmosphere depends critically on the mode and spatiotemporal characteristics of free-gas venting from the underlying sediments. Here we propose that methane transport in lake sediments is controlled by dynamic conduits, which dilate and release gas as the falling hydrostatic pressure reduces the effective stress below the tensile strength of the sediments. We test our model against a four-month record of hydrostatic load and methane flux in Upper Mystic Lake, Mass., USA, and show that it captures the complex episodicity of methane ebullition. Our quantitative conceptualization opens the door to integrated modeling of methane transport to constrain global methane release from lakes and other shallow-water, organic-rich sediment systems, and to assess its climate feedbacks.

The Application of 238U/235U as a Redox-Proxy for Past Ocean Chemistry

NASA Astrophysics Data System (ADS)

Andersen, M. B.; Westermann, S.; Bahniuk, A.; Vasconcelos, C.; McKenzie, J. A.; Föllmi, K. B.; Vance, D.

2014-12-01

The recent discovery of significant variation in 238U/235U caused by redox change at the surface Earth has led to its use to extract information on the oxygenation state of ancient oceans from marine sediments [e.g. 1]. Recent studies have focused on improving the understanding of the 238U/235U signature in modern marine carbonates [2] and black shales [3] to improve the robustness of this tracer. To further advance its use we have focused on improving our understanding of 238U/235U systematics in modern dolomite, another commonly occurring rock-type in the geological record, before turning to 238U/235U signatures in ancient sediments. The measured dolomite samples, precipitated in modern environments of coastal hypersaline lagoons in Brazil, all exhibit 238U/235U values that deviate from the seawater composition [3]. Observed values are both lighter (ca. 130 ppm; as also observed in dolomite from tidal-ponds on Bahamas [2]) and heavier (50-180 ppm). These distinct 238U/235U values for different dolomite-precipitates likely attest to the particular formation style, as well as early diagenetic processes. We use such modern settings to discuss the utility of 238U/235U in ancient sediments, the singularity of any observed 238U/235U signal, its relation to global ocean chemistry and potential diagenetic overprinting. These constraints are then used to evaluate a well-preserved marine carbonate section [4] and published black shale 238U/235U data [1], both deposited during the Oceanic Anoxic Event 2 (93 Ma). We discuss the capabilities of both the carbonate and black shale section for retaining information on the 238U/235U composition in the ocean during OAE 2. [1] Montoya-Pino et al. (2010) Geology, 38, 315-318 [2] Romaniello et al. (2013) 362, 305-316 [3] Andersen et al. (2014) EPSL, 400, 184-194 [4] Westermann et al. (2010) Cret. Res., 31, 500-514

Source identification and distribution reveals the potential of the geochemical Antarctic sea ice proxy IPSO25

PubMed Central

Belt, S. T.; Smik, L.; Brown, T. A.; Kim, J.-H.; Rowland, S. J.; Allen, C. S.; Gal, J.-K.; Shin, K.-H.; Lee, J. I.; Taylor, K. W. R.

2016-01-01

The presence of a di-unsaturated highly branched isoprenoid (HBI) lipid biomarker (diene II) in Southern Ocean sediments has previously been proposed as a proxy measure of palaeo Antarctic sea ice. Here we show that a source of diene II is the sympagic diatom Berkeleya adeliensis Medlin. Furthermore, the propensity for B. adeliensis to flourish in platelet ice is reflected by an offshore downward gradient in diene II concentration in >100 surface sediments from Antarctic coastal and near-coastal environments. Since platelet ice formation is strongly associated with super-cooled freshwater inflow, we further hypothesize that sedimentary diene II provides a potentially sensitive proxy indicator of landfast sea ice influenced by meltwater discharge from nearby glaciers and ice shelves, and re-examination of some previous diene II downcore records supports this hypothesis. The term IPSO25—Ice Proxy for the Southern Ocean with 25 carbon atoms—is proposed as a proxy name for diene II. PMID:27573030

Microbiota associated with tubes of Escarpia sp. from cold seeps in the southwestern Atlantic Ocean constitutes a community distinct from that of surrounding marine sediment and water.

PubMed

Medina-Silva, Renata; Oliveira, Rafael R; Trindade, Fernanda J; Borges, Luiz G A; Lopes Simão, Taiz L; Augustin, Adolpho H; Valdez, Fernanda P; Constant, Marcelo J; Simundi, Carolina L; Eizirik, Eduardo; Groposo, Claudia; Miller, Dennis J; da Silva, Priscila Reis; Viana, Adriano R; Ketzer, João M M; Giongo, Adriana

2018-04-01

As the depth increases and the light fades in oceanic cold seeps, a variety of chemosynthetic-based benthic communities arise. Previous assessments reported polychaete annelids belonging to the family Siboglinidae as part of the fauna at cold seeps, with the 'Vestimentifera' clade containing specialists that depend on microbial chemosynthetic endosymbionts for nutrition. Little information exists concerning the microbiota of the external portion of the vestimentiferan trunk wall. We employed 16S rDNA-based metabarcoding to describe the external microbiota of the chitin tubes from the vestimentiferan Escarpia collected from a chemosynthetic community in a cold seep area at the southwestern Atlantic Ocean. The most abundant operational taxonomic unit (OTU) belonged to the family Pirellulaceae (phylum Planctomycetes), and the second most abundant OTU belonged to the order Methylococcales (phylum Proteobacteria), composing an average of 21.1 and 15.4% of the total reads on tubes, respectively. These frequencies contrasted with those from the surrounding environment (sediment and water), where they represent no more than 0.1% of the total reads each. Moreover, some taxa with lower abundances were detected only in Escarpia tube walls. These data constitute on the first report of an epibiont microbial community found in close association with external surface of a cold-seep metazoan, Escarpia sp., from a chemosynthetic community in the southwestern Atlantic Ocean.

Attenuation of sinking particulate organic carbon flux through the mesopelagic ocean

PubMed Central

Marsay, Chris M.; Sanders, Richard J.; Henson, Stephanie A.; Pabortsava, Katsiaryna; Achterberg, Eric P.; Lampitt, Richard S.

2015-01-01

The biological carbon pump, which transports particulate organic carbon (POC) from the surface to the deep ocean, plays an important role in regulating atmospheric carbon dioxide (CO2) concentrations. We know very little about geographical variability in the remineralization depth of this sinking material and less about what controls such variability. Here we present previously unpublished profiles of mesopelagic POC flux derived from neutrally buoyant sediment traps deployed in the North Atlantic, from which we calculate the remineralization length scale for each site. Combining these results with corresponding data from the North Pacific, we show that the observed variability in attenuation of vertical POC flux can largely be explained by temperature, with shallower remineralization occurring in warmer waters. This is seemingly inconsistent with conclusions drawn from earlier analyses of deep-sea sediment trap and export flux data, which suggest lowest transfer efficiency at high latitudes. However, the two patterns can be reconciled by considering relatively intense remineralization of a labile fraction of material in warm waters, followed by efficient downward transfer of the remaining refractory fraction, while in cold environments, a larger labile fraction undergoes slower remineralization that continues over a longer length scale. Based on the observed relationship, future increases in ocean temperature will likely lead to shallower remineralization of POC and hence reduced storage of CO2 by the ocean. PMID:25561526

Westerly Winds and the Southern Ocean CO2 Sink Since the Last Glacial-Interglacial Transition

NASA Astrophysics Data System (ADS)

Hodgson, D. A.; Saunders, K. M.; Roberts, S. J.; Perren, B.; Butz, C.; Sime, L. C.; Davies, S. J.; Grosjean, M.

2017-12-01

The capacity of the Southern Ocean carbon sink is partly controlled by the Southern Hemisphere westerly winds (SHW) and sea ice. These regulate the upwelling of dissolved carbon-rich deep water to Antarctic surface waters, determine the surface area for air-sea gas exchange and therefore modulate the net uptake of atmospheric CO2. Some models have proposed that strengthened SHW will result in a weakening of the Southern Ocean CO2 sink. If these models are correct, then one would expect that reconstructions of changes in SHW intensity on centennial to millennial timescales would show clear links with Antarctic ice core and Southern Ocean marine geological records of atmospheric CO2, temperature and sea ice. Here, we present a 12,300 year reconstruction of past wind strength based on three independent proxies that track the changing inputs of sea salt aerosols and minerogenic particles into lake sediments on sub-Antarctic Macquarie Island. The proxies are consistent in showing that periods of high wind intensity corresponded with the increase in CO2 across the late Last Glacial-Interglacial Transition and in the last 7,000 years, suggesting that the winds have contributed to the long term outgassing of CO2 from the ocean during these periods.

Evolution of Plate Tectonics on Earth since the Mid-Mesoarchean was Controlled by Sedimentary Fluxes from Continents to Oceans and Mantle Temperature

NASA Astrophysics Data System (ADS)

Sobolev, S. V.; Brown, M.

2017-12-01

Plate tectonics (PT) is the most important geological process operating on Earth, making it unique among the rocky planets in the Solar System. The question of how PT was initiated and which factors controlled its evolution over Earth's history are widely discussed, but remain controversial. It is broadly accepted that a necessary condition for initiation and stable operation of PT is maintaining low strength along plate boundaries, particularly along the subduction zone interfaces in the subduction channels. Examples from the South American Andes and other convergent margins show that unconsolidated continental sediments in trenches serve as an efficient lubricant for subduction; if these are lacking, friction in the subduction channel and strength of the plate boundary are significantly increased. We suggest that lubrication of subduction by accumulation of continental sediments in trenches played a crucial role during the evolution of PT on Earth since the mid-Mesoarchean. We posit that continental emergence and enhanced surface erosion caused an increasing flux of sediments into the oceans, which in turn lubricated subduction channels and intensified PT. Thus, peaks in orogenesis, as confirmed by several proxies, during periods of supercraton/supercontinent assembly represent periods of vigorous subduction and continental sedimentation in trenches prior to terminal collision. Conversely, a decrease in plate boundary length and a reduction in continental sediment accumulation in trenches during periods of stability after supercraton/supercontinent assembly is the likely reason for periods of lower PT vigor, including the so called `boring billion' between 1.8 and 0.8 Ga. The largest surface erosion and subduction-lubrication event occurred at the end of the `snowball' Earth epoch in the Neoproterozoic and likely accelerated the most recent episode of vigorous PT. Based on analysis of various geological observations, we suggest that the cyclic behavior of PT on Earth since the mid-Mesoarchean (the so-called `supercontinent cycle') can be interpreted in terms of the balance of power between PT, driven by slab pull and controlled by the temperature of the upper mantle, and the efficiency of lubrication in the subduction zones, controlled by accumulation of continental sediment in the trenches.

High Frequency Acoustic Reflection and Transmission in Ocean Sediments

DTIC Science & Technology

2003-09-30

Development of a physical model of high-frequency acoustic interaction with the ocean floor, including penetration through and reflection from smooth and...experiments and additional laboratory measurements in the ARL:UT sand tank, an improved model of sediment acoustics will be developed that is...distinct areas of concentration: development of a broadband the oretical model to describe the acoustic interaction with the ocean floor in littoral

Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

NASA Astrophysics Data System (ADS)

Hahn, Annette; Schefuß, Enno; Andò, Sergio; Cawthra, Hayley C.; Frenzel, Peter; Kugel, Martin; Meschner, Stephanie; Mollenhauer, Gesine; Zabel, Matthias

2017-06-01

Due to the high sensitivity of southern Africa to climate change, a reliable understanding of its hydrological system is crucial. Recent studies of the regional climatic system have revealed a highly complex interplay of forcing factors on precipitation regimes. This includes the influence of the tropical easterlies, the strength of the southern hemispheric westerlies as well as sea surface temperatures along the coast of the subcontinent. However, very few marine records have been available in order to study the coupling of marine and atmospheric circulation systems. Here we present results from a marine sediment core, recovered in shallow waters off the Gouritz River mouth on the south coast of South Africa. Core GeoB18308-1 allows a closer view of the last ˜ 4 kyr. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input, give information on oceanographic and hydrologic changes during the recorded time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflect the variability of the terrigenous input to the core site. The combination of down-core sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age ( ˜ 300-650 cal yr BP) was characterized by climatic conditions favorable to torrential flood events. The Medieval Climate Anomaly ( ˜ 950-650 cal yr BP) is expressed by lower sea surface temperatures in the Mossel Bay area and humid conditions in the Gouritz River catchment. These new results suggest that the coincidence of humid conditions and cooler sea surface temperatures along the south coast of South Africa resulted from a strengthened and more southerly anticyclonic circulation. Most probably, the transport of moisture from the Indian Ocean by strong subtropical easterlies was coupled with Agulhas Bank upwelling pulses, which were initiated by an increase in Agulhas Current strength.

In-life pteropod shell dissolution as an indicator of past ocean carbonate saturation

NASA Astrophysics Data System (ADS)

Wall-Palmer, Deborah; Smart, Christopher W.; Hart, Malcolm B.

2013-12-01

Recent concern over the effects of ocean acidification upon calcifying organisms has highlighted the aragonitic shelled thecosomatous pteropods as being at a high risk. Both in-situ and laboratory studies have shown that an increased dissolved CO2 concentration, leading to decreased water pH and low carbonate concentration, causes reduced calcification rates and enhanced dissolution in the shells of living pteropods. In fossil records unaffected by post-depositional dissolution, this in-life shell dissolution can be detected. Here we present the first evidence of variations of in-life pteropod shell dissolution due to variations in surface water carbonate concentration during the Late Pleistocene by analysing the surface layer of pteropod shells in marine sediment cores from the Caribbean Sea and Indian Ocean. In-life shell dissolution was determined by applying the Limacina Dissolution Index (LDX) to the sub-tropical pteropod Limacina inflata. Average shell size information shows that high in-life dissolution is accompanied by smaller shell sizes in L. inflata, which may indicate a reduction in calcification rate. Comparison of the LDX profile to Late Pleistocene Vostok atmospheric CO2 concentrations, shows that in-life pteropod dissolution is closely associated to variations in past ocean carbonate saturation. This study confirms the findings of laboratory studies, showing enhanced shell dissolution and reduced calcification in living pteropods when surface ocean carbonate concentrations were lower. Results also demonstrate that oceanic pH levels that were less acidic and changing less rapidly than those predicted for the 21st Century, negatively affected pteropods during the Late Pleistocene.

Sea ice and surface water circulation, Alaskan continental shelf

NASA Technical Reports Server (NTRS)

Wright, F. F. (Principal Investigator); Sharma, G. D.; Burns, J. J.

1973-01-01

The author has identified the following significant results. Sediments contributed by the Copper River in the Gulf of Alaska are carried westward along the shore as a distinct plume. Oceanic water relatively poor in suspended material appears to intrude near Montague Island, and turbid water between Middleton Island and Kayak Island is the result of Ekman between transport. An anticlockwise surface water circulation is observed in this region. Ground truth data indicate striking similarity with ERTS-1 imagery obtained on October 12, 1972. Observations of ERTS-1 imagery reveal that various characteristics and distribution of sea ice in the Arctic Ocean can be easily studied. Formation of different types of sea ice and their movement is quite discrenible. Sea ice moves parallel to the cost in near shore areas and to the northerly direction away from the coast.

Major paleoceanographic changes recorded in Upper Albian-Lower Cenomanian sediments in the Western Tethys and in the North Atlantic: possible response to intense tectonic activity

NASA Astrophysics Data System (ADS)

Giorgioni, Martino; Weissert, Helmut; Keller, Christina; Bernasconi, Stefano; Hochuli, Peter; Garcia, Therese; Coccioni, Rodolfo; Petrizzo, Maria Rose

2010-05-01

During the mid-Cretaceous intense and widespread volcanism induced a high atmospheric CO2 concentration and, consequently, a very strong greenhouse effect (Bice & Norris, 2002). Opening and closing of oceanic gateways had an impact on paleoceanography (Poulsen et al, 1998; Poulsen et al, 2001). Global temperature and sea level reached the highest levels in the last 120 million years. (e.g. Pucéat et al, 2003; Hay, 2008). In this study we test if tectonically driven changes in oceanic circulation had an impact on Tethyan oceanography as predicted by models (Poulsen et al, 1998; Poulsen et al., 2001). We trace sedimentological changes during the Albian-Cenomanian across the Western Tethys and into the North Atlantic, integrating litho-, bio-, and isotope stratigraphy to obtain a robust correlation between studied sections, from pelagic to coastal settings. Albian sediments display very different facies from one site to the other. Pelagic marls with several black shales alternated to green, white, or red beds (Marne a Fucoidi/Scaglia Variegata Formation) are observed in the southern Tethys. Silty/sandy nodular limestone and marly limestones, with hiatuses and condensed intervals, (Garschella Formation) were deposited along the northern Tethyan shelf. Black shales and bioturbated marls are present in cycles, with several hiatuses, in the North Atlantic. These heterogeneous sediments became gradually replaced by more homogeneous and carbonate-rich facies between the Late Albian and the Early Cenomanian. These new facies consist of white, sometimes reddish, micritic limestones, rich in planktonic foraminifera. This sedimentation pattern is dominant in Upper Cretaceous successions, both in deep basins and on shelves. This change in sedimentation happened gradually in an East-West extending trend. It is first observed in the southern Tethys, then along the northern Tethys, and finally in the North Atlantic. We interpret the described change in sedimentation as due to a gradual turn of the oceanic circulation happening on the million of year time frame, which is probably related to one or more of the opening and closing of oceanic gateways during the mid-Cretaceous. References: Bice K. L. & Norris R. D. - Possible atmospheric CO2 extremes of the Middle Cretaceous (late Albian-Turonian) - Paleoceanography, vol. 17, n. 4, 2002 Hay W. - Evolving ideas about the Cretaceous climate and ocean circulation - Cretaceous Research, vol. 29, pp. 725-753, 2008 Poulsen C. J., Barron E., Arthur M. A., Peterson W. H. - Response of the mid-Cretaceous global oceanic circulation to tectonic and CO2 forcings - Paleoceanography, vol 16, n. 6, pp. 576-592, December 2001 Poulsen C. J., Seidov D., Barron E. J., Peterson W. H. - The impact of paleogeographic evolution on the surface oceanic circulation and the marine environment within the mid-Cretaceous Tethys - Paleoceanography, vol. 13, n. 5, pp. 546-559, 1998 Pucéat E., Lecuyer C., Sheppard S. M. F., Dromart G., Reboulet S., Grandjean P. - Thermal evolution of Cretaceous Tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels - Paleoceanography, vol. 18, n. 2, 2003

The Scientific and Societal Need for Accurate Global Remote Sensing of Marine Suspended Sediments

NASA Technical Reports Server (NTRS)

Acker, James G.

2006-01-01

Population pressure, commercial development, and climate change are expected to cause continuing alteration of the vital oceanic coastal zone environment. These pressures will influence both the geology and biology of the littoral, nearshore, and continental shelf regions. A pressing need for global observation of coastal change processes is an accurate remotely-sensed data product for marine suspended sediments. The concentration, delivery, transport, and deposition of sediments is strongly relevant to coastal primary production, inland and coastal hydrology, coastal erosion, and loss of fragile wetland and island habitats. Sediment transport and deposition is also related to anthropogenic activities including agriculture, fisheries, aquaculture, harbor and port commerce, and military operations. Because accurate estimation of marine suspended sediment concentrations requires advanced ocean optical analysis, a focused collaborative program of algorithm development and assessment is recommended, following the successful experience of data refinement for remotely-sensed global ocean chlorophyll concentrations.

Transition from continental to oceanic crust on the Wilkes-Adelie margin of Antarctica

NASA Astrophysics Data System (ADS)

Eittreim, Stephen L.

1994-12-01

The Wilkes-Adelie margin of East Antarctica, a passive margin rifted in the Early Cretaceous, has an unusually reflective Moho which can be traced seismically across the continent-ocean transition. Velocity models and depth sections were constructed from a combined set of U.S. and French multichannel seismic reflection lines to investigate the transition from continental to oceanic crust. These data show that the boundary between oldest oceanic crust and transitional continental crust is marked by a minimum in subsediment crustal thickness and, in places, by a shoaling of Moho. The Moho reflection is continuous across the edge of oceanic crust, and gradually deepens landward under the continental edge. A marginal rift basin, some tens of kilometers in width, lies in the transition between continental and oceanic crust, contains an average of about 4 km of synrift sediment that is prograded in places, and has characteristics of a former rift valley, now subsided to about 10 km. Three types of reflections in the seismic data are interpreted as volcanic deposits: (1) high-amplitude reflections that floor the marginal rift basin, (2) irregularly seaward dipping sequences that comprise an anomalously thick edge of oceanic crust, and (3) highly irregular and diffractive reflections from oceanic crustal basins that cap a normal-thickness ocean crust. The present depth to the prefit surface of continental crust is compatible with passive margin subsidence since 95 Ma, corrected for its load of synrift and postrift sediment and mechanically stretched by factors of beta = 1.8 or higher. Comparison of seismic crustal thickness measurements with inferred crustal thinning from subsidence analysis shows agreement for areas where beta less than 4. In areas where beta greater than 4, measured thickness is greater than that inferred from subsidence analysis, a result that could be explained by underplating the crust beneath the marginal rift basin.

Storm-driven sediment transport in Massachusetts Bay

USGS Publications Warehouse

Warner, J.C.; Butman, B.; Dalyander, P.S.

2008-01-01

Massachusetts Bay is a semi-enclosed embayment in the western Gulf of Maine about 50 km wide and 100 km long. Bottom sediment resuspension is controlled predominately by storm-induced surface waves and transport by the tidal- and wind-driven circulation. Because the Bay is open to the northeast, winds from the northeast ('Northeasters') generate the largest surface waves and are thus the most effective in resuspending sediments. The three-dimensional oceanographic circulation model Regional Ocean Modeling System (ROMS) is used to explore the resuspension, transport, and deposition of sediment caused by Northeasters. The model transports multiple sediment classes and tracks the evolution of a multilevel sediment bed. The surficial sediment characteristics of the bed are coupled to one of several bottom-boundary layer modules that calculate enhanced bottom roughness due to wave-current interaction. The wave field is calculated from the model Simulating WAves Nearshore (SWAN). Two idealized simulations were carried out to explore the effects of Northeasters on the transport and fate of sediments. In one simulation, an initially spatially uniform bed of mixed sediments exposed to a series of Northeasters evolved to a pattern similar to the existing surficial sediment distribution. A second set of simulations explored sediment-transport pathways caused by storms with winds from the northeast quadrant by simulating release of sediment at selected locations. Storms with winds from the north cause transport southward along the western shore of Massachusetts Bay, while storms with winds from the east and southeast drive northerly nearshore flow. The simulations show that Northeasters can effectively transport sediments from Boston Harbor and the area offshore of the harbor to the southeast into Cape Cod Bay and offshore into Stellwagen Basin. This transport pattern is consistent with Boston Harbor as the source of silver found in the surficial sediments of Cape Cod Bay and Stellwagen Basin.

Calcareous dinoflagellate cysts as recorder of Late Cretaceous paleo-temperature using Sr/Ca thermometry and δ44/40Caseawater

NASA Astrophysics Data System (ADS)

Gussone, N. C.; Friedrich, O.

2017-12-01

We evaluate the potential of calcareous dinoflagellates as archives for Sr/Ca-based paleo-temperature reconstructions and δ44/40Caseawater fluctuations on sediments from Ocean Drilling Program Expedition 113 (Hole 690C, Weddell Sea, Southern Ocean). Between 73 and 68 Ma, Sr/Ca ratios of two Cretaceous dinoflagellate species, Pirumella krasheninnikovii and Orthopithonella globosa show a pronounced decrease, consistent with a significant drop in sea-surface temperature as reflected by the δ18O of planktic foraminifers. The apparent temperature sensitivity of the dinoflagellate cysts' Sr/Ca is 0.06 and 0.08 mmol/mol °C-1, using δ18O-derived paleo sea-surface temperatures, which is significant and large enough to resolve paleoenvironmental temperature changes at current analytical precision. As the chemical composition of the cyst calcite appears to have a good preservability, the Sr/Ca of calcareous dinoflagellates has a high potential to serve as paleo temperature proxy. The Ca isotope composition of the two dinoflagellate species shows identical trends of increasing δ44/40Ca between 73 and 67 Ma. The planktic foraminifer Archaeoglobigerina australis and the benthic foraminifer Nuttallides truempyi reveal the same increase but are offset relative to the dinoflagellates by about +0.5‰, due to species-specific Ca isotope fractionation. Bulk carbonate sediment shows significant scatter, likely caused by changes in faunal composition and does not satisfyingly reproduce the trend revealed by the dinoflagellate and foraminifer records. These observations demonstrate the importance of taxon-specific records and careful determination of fractionation factors of selected archives and highlight complications arising from utilizing less suitable archives, such as bulk sediments, for δ44/40Caseawater reconstructions. Our records indicate strong changes in the oceanic Ca carbonate chemistry associated with the temperature decrease towards the end of the Cretaceous.

Foraminifer Shell Weight and Fragmentation: A Quantitative Study of the Influence of Temperature, [CO32-] and Dissolution on Proxies of the Marine Carbonate System

NASA Astrophysics Data System (ADS)

Mekik, F.; Pourmand, A.; Ward, B. M.

2015-12-01

Quantifying the various components of the marine carbonate system is important for understanding anthropogenic ocean acidification, and the rates and magnitudes of ocean acidification/ alkalization events in Earth's past. We performed multiple statistical analyses (factor analysis, partial correlations, multiple regression analysis and independent samples t -tests) on core top data using the Globorotalia menardii fragmentation index (MFI) in 89 core tops from across the tropical Pacific, Atlantic and Indian Oceans, the fragmentation trend of four species of foraminifers (Globorotalia truncatulinoides, G. menardii, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata) in the EEP, tropical Atlantic and tropical Indian Ocean core tops, and Globorotalia menardii shell weight in a suite of 25 core tops the EEP in order to isolate the effects of surface ocean parameters such as temperature and [CO32-] from dissolution in sediments. Surface ocean parameters showed no significant effect on the G. menardii fragmentation index. We found no statistically significant influence of habitat water temperature or [CO32-] on foraminifer fragmentation in any of four species. While we found a strong influence of habitat water [CO32-] on the size normalized shell weight proxy in N. dutertrei and Pulleniatina obliquiloculata in our previous work, we found a much reduced influence of [CO32-] on the shell weight of G. menardii, which is most influenced by shell dissolution.

Southern Ocean vertical iron fluxes; the ocean model effect

NASA Astrophysics Data System (ADS)

Schourup-Kristensen, V.; Haucke, J.; Losch, M. J.; Wolf-Gladrow, D.; Voelker, C. D.

2016-02-01

The Southern Ocean plays a key role in the climate system, but commonly used large-scale ocean general circulation biogeochemical models give different estimates of current and future Southern Ocean net primary and export production. The representation of the Southern Ocean iron sources plays an important role for the modeled biogeochemistry. Studies of the iron supply to the surface mixed layer have traditionally focused on the aeolian and sediment contributions, but recent work has highlighted the importance of the vertical supply from below. We have performed a model study in which the biogeochemical model REcoM2 was coupled to two different ocean models, the Finite Element Sea-ice Ocean Model (FESOM) and the MIT general circulation model (MITgcm) and analyzed the magnitude of the iron sources to the surface mixed layer from below in the two models. Our results revealed a remarkable difference in terms of mechanism and magnitude of transport. The mean iron supply from below in the Southern Ocean was on average four times higher in MITgcm than in FESOM and the dominant pathway was entrainment in MITgcm, whereas diffusion dominated in FESOM. Differences in the depth and seasonal amplitude of the mixed layer between the models affect on the vertical iron profile, the relative position of the base of the mixed layer and ferricline and thereby also on the iron fluxes. These differences contribute to differences in the phytoplankton composition in the two models, as well as in the timing of the onset of the spring bloom. The study shows that the choice of ocean model has a significant impact on the iron supply to the Southern Ocean mixed layer and thus on the modeled carbon cycle, with possible implications for model runs predicting the future carbon uptake in the region.

Sources of the transuranic elements plutonium and neptunium in arctic marine sediments.

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

Cooper, L. W.; Kelley, J. M.; Bond, L. A.

2000-01-01

We report here thermal ionization mass spectrometry measurements of {sup 239}Pu, {sup 240}Pu, {sup 241}Pu, {sup 242}Pu, and {sup 237}Np isolated from oceanic, estuarine, and riverine sediments from the Arctic Ocean Basin. {sup 238}Pu/{sup 239+240}Pu activity ratios are also reported for alpha spectrometric analyses undertaken on a subset of these samples. Our results indicate that the Pu in sediments on the Alaskan shelf and slope, as well as that in the deep basins (Amerasian and Eurasian) of the Arctic Ocean, has its origin in stratospheric and tropospheric fallout. Sediments from the Ob and Yenisei Rivers show isotopic Pu signatures thatmore » are distinctly different from those of northern-hemisphere stratospheric fallout and indicate the presence of weapons-grade Pu originating from nuclear fuel reprocessing wastes generated at Russian facilities within these river catchments. Consequently, sediments of the Eurasian Arctic Ocean, particularly those in the Barents and Kara Seas, probably contain a mixture of Pu from stratospheric fallout, tropospheric fallout, and fuel-reprocessing wastes of riverine origin. In particular, the {sup 241}Pu/{sup 239}Pu ratios observed in these sediments are inconsistent with significant contributions of Pu to the arctic sediments studied from western European reprocessing facilities, principally Sellafield in the UK. Several other potential sources of Pu to arctic sediments can also be excluded as significant based upon the transuranic isotope ratios presented.« less

Calibration of Gephyrocapsa Coccolith Abundance in Holocene Sediments for Paleo-temperature Assessment

NASA Astrophysics Data System (ADS)

Bollmann, J.; Brabec, B.

2001-12-01

Abundance and assemblage compositions of microplankton, together with their chemical and stable isotopic composition, have been among the most successful methods in paleoceanography. One of the most frequently applied techniques for reconstruction of paleo-temperature is a transfer function using the relative abundance of planktic foraminifera in sediment samples. Here we present evidence, suggesting that absolute sea surface temperature for a given location can be also calculated from the relative abundance of Gephyrocapsa morphotypes in sediment samples with an accuracy comparable to foraminifera transfer functions. By extrapolating this finding, paleo-enviromental interpretations can be obtained for the Late Pleistocene and discrepancies between the different currently used methods (e.g., foraminifer, alkenone and Ca/Mg derived temperature estimates) might be resolved. Eighty-one Holocene sediment samples were selected from the Pacific, Indian and Atlantic Oceans covering a temperature gradient from 13.4° C to 29.4° C, a salinity gradient from 32.21 to 37.34 and a productivity gradient of 0.045 to 0.492μ g chlorophyll/L. Standard multiple linear regression analyses were applied to this data set, linking the relative abundance of Gephyrocapsa morphotypes to mean sea surface temperature. The best model revealed an r2 of 0.8 with a standard residual error of 1.8° C for calculation of the mean sea surface temperature.

Endocrine disrupting chemicals in New Orleans surface waters and Mississippi Sound sediments.

PubMed

Wang, Guangdi; Ma, Peng; Zhang, Qiang; Lewis, John; Lacey, Michelle; Furukawa, Yoko; O'Reilly, S E; Meaux, Shelley; McLachlan, John; Zhang, Shaoyuan

2012-05-01

Endocrine disrupting compounds (EDCs), represented by steroid hormones, organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and bisphenol A have been determined in four sediment cores from the Gulf of Mexico, from New Orleans surface water (Lake Pontchartrain and Mississippi River), and from the influent and effluent of a New Orleans municipal sewage treatment plant. During the five-month monitoring of selected EDCs in the Mississippi River (MR) and Lake Pontchartrain (LP) in 2008, 21 of 29 OCPs in MR and 17 of 29 OCPs in LP were detected; bisphenol A was detected in all of the samples. Steroid hormones (estrone, 17β-estradiol and 17α-ethinylestradiol) were detected occasionally. Total EDC (OCPs + PCBs + steroid hormones + bisphenol A) concentrations in the two surface water samples were found to vary from 148 to 1112 ng L(-1). Strong correlation of the distribution of total OCPs, total PCBs and total EDCs between solid and water phases was found in LP, while moderate or no correlation existed in MR. OCPs, PCBs, steroid hormones, and bisphenol A were all detected in the ocean sediments, and total EDCs were measured in the range of 77 to 1796 ng g(-1) dry sediment weight. The EDCs were also found in untreated and treated municipal sewage samples with a removal efficiency of 83% for OCPs but no removal efficiency for 17α-ethinylestradiol.

Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean

USGS Publications Warehouse

Polyak, L.; Bischof, J.; Ortiz, J.D.; Darby, D.A.; Channell, J.E.T.; Xuan, C.; Kaufman, D.S.; Lovlie, R.; Schneider, D.A.; Eberl, D.D.; Adler, R.E.; Council, E.A.

2009-01-01

Sediment cores from the western Arctic Ocean obtained on the 2005 HOTRAX and some earlier expeditions have been analyzed to develop a stratigraphic correlation from the Alaskan Chukchi margin to the Northwind and Mendeleev-Alpha ridges. The correlation was primarily based on terrigenous sediment composition that is not affected by diagenetic processes as strongly as the biogenic component, and paleomagnetic inclination records. Chronostratigraphic control was provided by 14C dating and amino-acid racemization ages, as well as correlation to earlier established Arctic Ocean stratigraphies. Distribution of sedimentary units across the western Arctic indicates that sedimentation rates decrease from tens of centimeters per kyr on the Alaskan margin to a few centimeters on the southern ends of Northwind and Mendeleev ridges and just a few millimeters on the ridges in the interior of the Amerasia basin. This sedimentation pattern suggests that Late Quaternary sediment transport and deposition, except for turbidites at the basin bottom, were generally controlled by ice concentration (and thus melt-out rate) and transportation distance from sources, with local variances related to subsurface currents. In the long term, most sediment was probably delivered to the core sites by icebergs during glacial periods, with a significant contribution from sea ice. During glacial maxima very fine-grained sediment was deposited with sedimentation rates greatly reduced away from the margins to a hiatus of several kyr duration as shown for the Last Glacial Maximum. This sedimentary environment was possibly related to a very solid ice cover and reduced melt-out over a large part of the western Arctic Ocean.

Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene.

PubMed

Burls, Natalie J; Fedorov, Alexey V; Sigman, Daniel M; Jaccard, Samuel L; Tiedemann, Ralf; Haug, Gerald H

2017-09-01

An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, the world's largest ocean, where relatively fresh surface waters inhibit North Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400-ppmv (parts per million by volume) CO 2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanying pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redox-sensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming.

Late Holocene sea ice conditions in Herald Canyon, Chukchi Sea

NASA Astrophysics Data System (ADS)

Pearce, C.; O'Regan, M.; Rattray, J. E.; Hutchinson, D. K.; Cronin, T. M.; Gemery, L.; Barrientos, N.; Coxall, H.; Smittenberg, R.; Semiletov, I. P.; Jakobsson, M.

2017-12-01

Sea ice in the Arctic Ocean has been in steady decline in recent decades and, based on satellite data, the retreat is most pronounced in the Chukchi and Beaufort seas. Historical observations suggest that the recent changes were unprecedented during the last 150 years, but for a longer time perspective, we rely on the geological record. For this study, we analyzed sediment samples from two piston cores from Herald Canyon in the Chukchi Sea, collected during the 2014 SWERUS-C3 Arctic Ocean Expedition. The Herald Canyon is a local depression across the Chukchi Shelf, and acts as one of the main pathways for Pacific Water to the Arctic Ocean after entering through the narrow and shallow Bering Strait. The study site lies at the modern-day seasonal sea ice minimum edge, and is thus an ideal location for the reconstruction of past sea ice variability. Both sediment cores contain late Holocene deposits characterized by high sediment accumulation rates (100-300 cm/kyr). Core 2-PC1 from the shallow canyon flank (57 m water depth) is 8 meter long and extends back to 4200 cal yrs BP, while the upper 3 meters of Core 4-PC1 from the central canyon (120 mwd) cover the last 3000 years. The chronologies of the cores are based on radiocarbon dates and the 3.6 ka Aniakchak CFE II tephra, which is used as an absolute age marker to calculate the marine radiocarbon reservoir age. Analysis of biomarkers for sea ice and surface water productivity indicate stable sea ice conditions throughout the entire late Holocene, ending with an abrupt increase of phytoplankton sterols in the very top of both sediment sequences. The shift is accompanied by a sudden increase in coarse sediments (> 125 µm) and a minor change in δ13Corg. We interpret this transition in the top sediments as a community turnover in primary producers from sea ice to open water biota. Most importantly, our results indicate that the ongoing rapid ice retreat in the Chukchi Sea of recent decades was unprecedented during the last 4000 years.

Modern pollen distribution in the northeastern Indian Ocean and its significance.

PubMed

Luo, Chuanxiu; Jiang, Weiming; Chen, Chixin; Peng, Huanhuan; Xiang, Rong; Liu, Jianguo; Lu, Jun; Su, Xiang; Zhang, Qiang; Yang, Mingxi

2018-06-26

In order to provide a reference for reconstructing the paleoclimate of the northeastern Indian Ocean, 36 airborne pollen samples were analyzed using methods for airborne pollen, and 26 surface water samples were analyzed using a lab method for surface water. We found that little pollen is airborne over the Indian Ocean in spring, but airborne pollen types and concentrations can help to deduce paleomonsoon strength and direction. The conclusions included the following: (1) Pollen in the sediment was transported mainly via ocean currents instead of the early summer or spring wind. (2) Airborne pollen types and concentrations are proportional to the wind speed and inversely proportional to the pollen distance transported and depend on whether the wind is from the land or from the sea. If the wind is from the land, the pollen concentration is proportional to the angle between the wind direction and the coastline. (3) The pollen concentration in the sample collected from a water depth of 30-45 m is higher than in the samples collected from a depth of 5 m. The pollen concentration and salinity are higher in the equatorial area than in the Northern Hemisphere.

A modern framework for the interpretation of 238U/235U in studies of ancient ocean redox

NASA Astrophysics Data System (ADS)

Andersen, M. B.; Romaniello, S.; Vance, D.; Little, S. H.; Herdman, R.; Lyons, T. W.

2014-08-01

The abundance and isotope composition of redox sensitive elements in ancient sediments are increasingly used to understand the past ocean's geochemical state and the oxygenation history of the Earth. The redox transition of uranium (U) from soluble U+6 to relatively insoluble U+4 and its subsequent incorporation into reduced sediments has been used to deduce the redox state of the oceans in the past. Furthermore, recent analytical improvements have revealed significant 238U/235U fractionation during this redox transition, offering the potential for U isotopes to act as a redox proxy. However, the development of U isotopes as a geochemical tracer requires that U isotope systematics associated with redox changes, are well-characterized. This study focuses on U isotopes in recent sediments from the two largest modern anoxic ocean basins, the Black Sea and the Cariaco Basin, with the aim of advancing our understanding of the U isotope systematics in reducing marine environments. These anoxic sediments have high U accumulation rates and high 238U/235U ratios relative to seawater, in general agreement with a process that accumulates reduced U with a heavy isotopic composition. Using Al and Ca concentrations to correct for detrital and biogenic carbonate-bound U, we estimate the reduced authigenic U accumulated in the sediments and its 238U/235U. These results highlight the importance of isotopic mass balance constraints during diffusive transport and reaction of U from seawater and through pore-water, affecting the observed 238U/235U in sediments. Using these constraints, the average percentages of U depletion from top to bottom of the water column can be estimated, assuming batch-removal of U into anoxic sediments in a restricted basin. Using this framework, 238U/235U in modern anoxic sediments from the Black Sea imply U depletions in the water column of ∼30%, which is close to the observed ∼40% U depletion in the modern Black Sea water column at these depths. Similar U depletion in the water column is estimated from anoxic sediment samples of the Cariaco Basin. These recent anoxic sediments provide a basis for interpreting authigenic 238U/235U in ancient sediments. In particular, such analyses may offer insights, based on mass balance relationships, into whether particular ancient sediments were deposited in an open ocean or restricted basin. As such, this approach may provide key insight into the controls on local versus ocean-scale redox and, in that light, constraints the capacity of other proxies to capture global signals for anoxia/euxinia.

Organic matter diagenesis within the water column and surface sediments of the northern Sargasso Sea revealed by lipid biomarkers

NASA Astrophysics Data System (ADS)

Conte, M. H.; Pedrosa Pàmies, R.; Weber, J.

2017-12-01

The intensity of particle cycling processes within the mesopelagic and bathypelagic ocean controls the length scale of organic material (OM) remineralization and diagenetic transformations of OM composition through the water column and into the sediments. To elucidate the OM cycling in the oligotrophic North Atlantic gyre, we analyzed lipid biomarkers in the suspended particles (30-4400 m depth, 100 mab), the particle flux (500 m, 1500 m and 3200 m depth), and in the underlying surficial sediments (0-0.5 cm, 4500-4600 m depth) collected at the Oceanic Flux Program (OFP) time series site located 75km SE of Bermuda. Changes in lipid biomarker concentration and composition with depth highlight the rapid remineralization of OM within the upper mesopelagic layer and continuing diagenetic transformations of OM throughout the water column and within surficial sediments. Despite observed similarities in biomarker composition in suspended and sinking particles, results show there are also consistent differences in relative contributions of phytoplankton-, bacterial- and zooplankton-derived sources that are maintained throughout the water column. For example, sinking particles are more depleted in labile biomarkers (e.g. polyunsaturated fatty acids (PUFA)) and more enriched in bacteria-derived biomarkers (e.g. hopanoids and odd/branched fatty acids) and indicators of fecal-derived OM (e.g. saturated fatty acids, FA 18:1w9 and cholesterol) than in the suspended pool. Strong seasonality in deep (3200 m) fluxes of phytoplankton-derived biomarkers reflect the seasonal input of bloom-derived material to underlying sediments. The rapid diagenetic alteration of this bloom-derived input is evidenced by depletion of PUFAs and enrichment of microbial biomarkers (e.g. odd/branched fatty acids) in surficial sediments over a two month period.

500 kyr of Indian Ocean Walker Circulation Variability Using Foraminiferal Mg/Ca and Stable Isotopes

NASA Astrophysics Data System (ADS)

Groeneveld, J.; Mohtadi, M.; Lückge, A.; Pätzold, J.

2017-12-01

The tropical Indian Ocean is a key location for paleoclimate research affected by different oceanographic and atmospheric processes. Annual climate variations are strongly controlled by the Indian and Asian Monsoon characterized by bi-annually reversing trade winds. Inter-annual climate variations in the Walker circulation are caused by the Indian Ocean Dipole and El Niño-Southern Oscillation resulting in either heavy flooding or severe droughts like for example the famine of 2011 in eastern Africa. Oceanographically the tropical western Indian Ocean receives water masses from the Indonesian Gateway area, sub-Antarctic waters that upwell south of the equator, and the outflow waters from the highly saline Red Sea. On the other hand, the tropical western Indian Ocean is a major source for providing water masses to the Agulhas Current system. Although the eastern Indian Ocean has been studied extensively, the tropical western Indian Ocean is still lacking in high quality climate-archives that have the potential to provide important information to understand how the ocean and atmospheric zonal circulation have changed in the past, and possibly will change in the future. Until now there were no long sediment cores available covering several glacial-interglacial cycles in the tropical western Indian Ocean. Core GeoB 12613-1, recovered during RV Meteor Cruise M75/2 east of the island of Pemba off Tanzania, provides an open-ocean core with well-preserved sediments covering the last five glacial-interglacial cycles ( 500 kyr). Mg/Ca and stable isotopes on both surface- and thermocline dwelling foraminifera have been performed to test how changes in sea water temperatures and relative sea water salinity were coupled on orbital time scales. The results are compared with similar records generated for the tropical eastern Indian Ocean in core SO139-74KL off Sumatra. Water column stratification on both sides of the Indian Ocean and the cross-basin gradients in sea water temperature and relative salinity varied both on millennial and orbital time scales implying changes in the Walker circulation.

Potential Increasing Dominance of Heterotrophy in the Global Ocean

NASA Astrophysics Data System (ADS)

Kvale, K.; Meissner, K. J.; Keller, D. P.

2016-02-01

Autotrophs are largely limited by resources in the modern ocean. However, standard metabolic theory suggests continued ocean warming could globally benefit heterotrophs, thereby reducing autotrophic nutrient limitation. The paleo record as well as modern observations offer evidence this has happened in the past and could happen again. Increasing dominance of heterotrophs would result in strong nutrient recycling in the upper ocean and high rates of net primary production (NPP), yet low carbon export to the deep ocean and sediments. We describe the transition towards such a state in the early 22nd century as a response to business-as-usual Representative Concentration Pathway forcing (RCP8.5) in an intermediate complexity Earth system model in three configurations: with and without an explicit calcifier phytoplankton class and calcite ballast model. In all models nutrient regeneration in the near surface becomes an increasingly important driver of primary production. The near-linear relationship between changes in NPP and global sea surface temperature (SST) found over the 21st century becomes exponential above a 2-4 °C global mean SST change. This transition to a more heterotrophic ocean agrees roughly with metabolic theory. Inclusion of small phytoplankton and calcifiers increase the model NPP:SST sensitivity because of their relatively higher nutrient affinity than general phytoplankton. Accounting for organic carbon "protected" from remineralization by carbonate ballast mitigates the exponential increase in NPP and provides an increasingly important pathway for deep carbon export with higher SST changes, despite simultaneous increasing carbonate dissolution rates due to ocean acidification.

Lasting Impact of a Tsunami Event on Sediment-Organism Interactions in the Ocean

NASA Astrophysics Data System (ADS)

Seike, Koji; Sassa, Shinji; Shirai, Kotaro; Kubota, Kaoru

2018-02-01

Although tsunami sedimentation is a short-term phenomenon, it may control the long-term benthic environment by altering seafloor surface characteristics such as topography and grain-size composition. By analyzing sediment cores, we investigated the long-term effect of the 2011 tsunami generated by the Tohoku Earthquake off the Pacific coast of Japan on sediment mixing (bioturbation) by an important ecosystem engineer, the heart urchin Echinocardium cordatum. Recent tsunami deposits allow accurate estimation of the depth of current bioturbation by E. cordatum, because there are no preexisting burrows in the sediments. The in situ hardness of the substrate decreased significantly with increasing abundance of E. cordatum, suggesting that echinoid bioturbation softens the seafloor sediment. Sediment-core analysis revealed that this echinoid rarely burrows into the coarser-grained (medium-grained to coarse-grained) sandy layer deposited by the 2011 tsunami; thus, the vertical grain-size distribution resulting from tsunami sedimentation controls the depth of E. cordatum bioturbation. As sandy tsunami layers are preserved in the seafloor substrate, their restriction on bioturbation continues for an extended period. The results demonstrate that understanding the effects on seafloor processes of extreme natural events that occur on geological timescales, including tsunami events, is important in revealing continuing interactions between seafloor sediments and marine benthic invertebrates.

Impact of volcanic ash on anammox communities in deep sea sediments.

PubMed

Song, Bongkeun; Buckner, Caroline T; Hembury, Deborah J; Mills, Rachel A; Palmer, Martin R

2014-04-01

Subaerial explosive volcanism contributes substantial amounts of material to the oceans, but little is known about the impact of volcanic ash on sedimentary microbial activity. We have studied anammox communities in deep sea sediments near the volcanically active island of Montserrat, Lesser Antilles. The rates of anammox and denitrification in the sediments were measured using (15)N isotope pairing incubation experiments, while 16S rRNA genes were used to examine anammox community structures. The higher anammox rates were measured in sediment containing the lower accumulation of volcanic ash in the surface sediments, while the lowest activities were found in sediments with the highest ash deposit. 16S rRNA gene analysis revealed the presence of 'Candidatus Scalindua spp.' in the sediments. The lowest diversity of anammox bacteria was observed in the sediments with the highest ash deposit. Overall, this study demonstrates that the deposition of volcanic material in deep sea sediments has negative impacts on activity and diversity of the anammox community. Since anammox may account for up to 79% of N2 production in marine ecosystems, periods of extensive explosive volcanism in Earth history may have had a hitherto unrecognized negative impact on the sedimentary nitrogen removal processes. © 2013 Society for Applied Microbiology and John Wiley & Sons Ltd.

The rare earth element geochemistry on surface sediments, shallow cores and lithological units of Lake Acıgöl basin, Denizli, Turkey

NASA Astrophysics Data System (ADS)

Budakoglu, Murat; Abdelnasser, Amr; Karaman, Muhittin; Kumral, Mustafa

2015-11-01

The sediments in Lake Acıgöl, located in SW Anatolia, Turkey, were formed under tectono-sedimentary events. REE geochemical investigations of the Lake Acıgöl sediments, from surface and shallow core sediments at different depths (0-10 cm, 10-20 cm and 20-30 cm) are presented to clarify the characteristics of REE and the nature of source rocks in the lake sediments' and to deduce their paleoenvironmental proxies. The chondrite-normalized REE patterns of these sediments are shown as light enrichment in LREE and flat HREE with a negative Eu anomaly that is close to the continental collision basin (CCB) in its profile; this is not comparable with PAAS and UCC. Inorganic detrital materials control the REE characteristics of the Lake Acıgöl sediments and these sediments were accumulated in oxic and dysoxic depositional conditions and/or at passive margins derived from oceanic island arc rocks. They were affected by low chemical weathering, either at the original source or during transport, before deposition under arid or subtropical humid climatic conditions. In addition, we used GIS techniques (such as Inverse Distance Weighted (IDW) and Geographically Weighted Regression (GWR)) to investigate the spatial interpolation and spatial correlation of the REEs from the lake surface sediments in Lake Acıgöl and its surrounding lithological units. GIS techniques showed that the lithological units (e.g., Hayrettin Formation) north of Lake Acıgöl have high REE contents; however, Eu/Eu∗ values were higher in some lake surface sediments than in lithological units, and that refers to a negative Eu-anomaly. Therefore, Lake Acıgöl sediments are derived from the weathered products, mainly from local, highly basic bedrock around the lake from the Archean crust. The chronology of Lake Acıgöl sediment was conducted using the Constant Rate of Supply (CRS) model. Using the CRS methods for the calculation of sedimentation rate, we obtained a 0.012 g/cm2/year value which is an average value for the first 20 cm depth of this lake. The core activity profiles of 210Pb and 137Cs were measured to estimate the age of the sediments; we observed activities of 8.08 ± 5.5 Bq/kg for 210Pb and 0.86 ± 0.6 Bq/kg for 137Cs.

Slush Fund: Modeling the Multiphase Physics of Oceanic Ices

NASA Astrophysics Data System (ADS)

Buffo, J.; Schmidt, B. E.

2016-12-01

The prevalence of ice interacting with an ocean, both on Earth and throughout the solar system, and its crucial role as the mediator of exchange between the hydrosphere below and atmosphere above, have made quantifying the thermodynamic, chemical, and physical properties of the ice highly desirable. While direct observations of these quantities exist, their scarcity increases with the difficulty of obtainment; the basal surfaces of terrestrial ice shelves remain largely unexplored and the icy interiors of moons like Europa and Enceladus have never been directly observed. Our understanding of these entities thus relies on numerical simulation, and the efficacy of their incorporation into larger systems models is dependent on the accuracy of these initial simulations. One characteristic of seawater, likely shared by the oceans of icy moons, is that it is a solution. As such, when it is frozen a majority of the solute is rejected from the forming ice, concentrating in interstitial pockets and channels, producing a two-component reactive porous media known as a mushy layer. The multiphase nature of this layer affects the evolution and dynamics of the overlying ice mass. Additionally ice can form in the water column and accrete onto the basal surface of these ice masses via buoyancy driven sedimentation as frazil or platelet ice. Numerical models hoping to accurately represent ice-ocean interactions should include the multiphase behavior of these two phenomena. While models of sea ice have begun to incorporate multiphase physics into their capabilities, no models of ice shelves/shells explicitly account for the two-phase behavior of the ice-ocean interface. Here we present a 1D multiphase model of floating oceanic ice that includes parameterizations of both density driven advection within the `mushy layer' and buoyancy driven sedimentation. The model is validated against contemporary sea ice models and observational data. Environmental stresses such as supercooling and melting events will be discussed for terrestrial ice. The impact of fluid motion within the mushy layer on nutrient transport and habitability will be discussed. Results from the model's application to icy moon environments will be presented, highlighting ice shell composition, thickness, thermodynamics, and role in potential habitability.

Coral reefs will transition to net dissolving before end of century.

PubMed

Eyre, Bradley D; Cyronak, Tyler; Drupp, Patrick; De Carlo, Eric Heinen; Sachs, Julian P; Andersson, Andreas J

2018-02-23

Ocean acidification refers to the lowering of the ocean's pH due to the uptake of anthropogenic CO 2 from the atmosphere. Coral reef calcification is expected to decrease as the oceans become more acidic. Dissolving calcium carbonate (CaCO 3 ) sands could greatly exacerbate reef loss associated with reduced calcification but is presently poorly constrained. Here we show that CaCO 3 dissolution in reef sediments across five globally distributed sites is negatively correlated with the aragonite saturation state (Ω ar ) of overlying seawater and that CaCO 3 sediment dissolution is 10-fold more sensitive to ocean acidification than coral calcification. Consequently, reef sediments globally will transition from net precipitation to net dissolution when seawater Ω ar reaches 2.92 ± 0.16 (expected circa 2050 CE). Notably, some reefs are already experiencing net sediment dissolution. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

The growth of continents and some consequences since 1.5 Ga

NASA Technical Reports Server (NTRS)

Howell, David G.

1988-01-01

The budget of Earth's oceanic sediment masses was discussed in terms of crustal growth and recycling. Based on estimates of the volume of oceanic sediments and the average age of oceanic crust, a continental denudation rate of 1.65 cu km/yr was computed. This crudely balances estimated crustal production rates of about 1 cu km/yr, but the efficiency of sediment loss via subduction, for example, must be considered. It was argued, on the basis of earthquake focal solutions, imagery of subduction zones, and plate kinematic reconstructions that little, if any, sediment was lost in this way. This yields a present day crustal growth rate of about 1 cu km/yr. The volume of continents to 1.5 Ga ago was discussed, assuming constant continental thickness and freeboard, and a constant hydrosphere volume. It was concluded that ocean ridge length was a factor of about 1.75 greater 1.5 Ga ago, but a major uncertainty is the average spreading rate in the past.

Searching for signatures across microbial communities: Metagenomic analysis of soil samples from mangrove and other ecosystems.

PubMed

Imchen, Madangchanok; Kumavath, Ranjith; Barh, Debmalya; Azevedo, Vasco; Ghosh, Preetam; Viana, Marcus; Wattam, Alice R

2017-08-18

In this study, we categorize the microbial community in mangrove sediment samples from four different locations within a vast mangrove system in Kerala, India. We compared this data to other samples taken from the other known mangrove data, a tropical rainforest, and ocean sediment. An examination of the microbial communities from a large mangrove forest that stretches across southwestern India showed strong similarities across the higher taxonomic levels. When ocean sediment and a single isolate from a tropical rain forest were included in the analysis, a strong pattern emerged with Bacteria from the phylum Proteobacteria being the prominent taxon among the forest samples. The ocean samples were predominantly Archaea, with Euryarchaeota as the dominant phylum. Principal component and functional analyses grouped the samples isolated from forests, including those from disparate mangrove forests and the tropical rain forest, from the ocean. Our findings show similar patterns in samples were isolated from forests, and these were distinct from the ocean sediment isolates. The taxonomic structure was maintained to the level of class, and functional analysis of the genes present also displayed these similarities. Our report for the first time shows the richness of microbial diversity in the Kerala coast and its differences with tropical rain forest and ocean microbiome.

Undergraduate Research Experience in Ocean/Marine Science (URE-OMS) with African Student Component

DTIC Science & Technology

2008-01-01

Intergovernmental Panel on Climate Change (IPCC). RESULTS Temporal and Spatial Variations of Sea Surface Temperature and Chlorophyll a in Coastal Waters of...Duck, North Carolina [4] Climate change has affected the North Carolina coastal environments and coastal hazards have already taken place in the area...from geological materials (sands, dead and/or bleached corals ...etc) shifted by waves, tides, and currents moving sediments and eroding shorelines

Coast and river mouths, Columbia, South America

NASA Technical Reports Server (NTRS)

1982-01-01

Numerous rivers in Ecuador and Columbia stand out in this South American Pacific coastal scene (1.5N, 79.0W). This region has one of the highest rainfalls in the world with the consequent heavy cloud cover and it is rare to be able to photograph the surface. The Pacific mountain drainage area is small but produces a large volume of runoff and sediment flow into the ocean.

Terminal Proterozoic reorganization of biogeochemical cycles

NASA Technical Reports Server (NTRS)

Logan, G. A.; Hayes, J. M.; Hieshima, G. B.; Summons, R. E.

1995-01-01

The Proterozoic aeon (2,500-540 million years ago) saw episodic increases in atmospheric oxygen content, the evolution of multicellular life and, at its close, an enormous radiation of animal diversity. These profound biological and environmental changes must have been linked, but the underlying mechanisms have been obscure. Here we show that hydrocarbons extracted from Proterozoic sediments in several locations worldwide are derived mainly from bacteria or other heterotrophs rather than from photosynthetic organisms. Biodegradation of algal products in sedimenting matter was therefore unusually complete, indicating that organic material was extensively reworked as it sank slowly through the water column. We propose that a significant proportion of this reworking will have been mediated by sulphate-reducing bacteria, forming sulphide. The production of sulphide and consumption of oxygen near the ocean surface will have inhibited transport of O2 to the deep ocean. We find that preservation of algal-lipid skeletons improves at the beginning of the Cambrian, reflecting the increase in transport by rapidly sinking faecal pellets. We suggest that this rapid removal of organic matter will have increased oxygenation of surface waters, leading to a descent of the O2-sulphide interface to the sea floor and to marked changes in the marine environment, ultimately contributing to the Cambrian radiation.

The isotopic composition of authigenic chromium in anoxic marine sediments: A case study from the Cariaco Basin

NASA Astrophysics Data System (ADS)

Reinhard, Christopher T.; Planavsky, Noah J.; Wang, Xiangli; Fischer, Woodward W.; Johnson, Thomas M.; Lyons, Timothy W.

2014-12-01

Chromium (Cr) isotopes are an emerging proxy for tracking redox processes at the Earth's surface. However, there has been limited exploration of the Cr isotope record of modern and recent marine sediments. The basic inorganic chemistry of Cr suggests that anoxic marine basins should factor prominently in the global Cr cycle and that sediments deposited within anoxic basins may offer a valuable Cr isotope archive throughout Earth's history. Here, we present δ53Cr data from sediments of the Cariaco Basin, Venezuela-a 'type' environment for large, perennially anoxic basins with a relatively strong hydrological connection to the global oceans. We document a marked positive shift in bulk δ53Cr values following the termination of the Last Glacial Maximum, followed by relative stasis. Based on a suite of independent redox proxies, this transition marks a switch from oxic to persistently anoxic and sulfidic (euxinic) depositional conditions within the basin. We find good agreement between two independent approaches toward estimating the δ53Cr composition of authigenic Cr in euxinic Cariaco Basin sediments and that these estimates are very similar to the δ53Cr composition of modern open Atlantic Ocean seawater. These data, together with considerations of reaction kinetics and mass balance within the Cariaco Basin, are consistent with the hypothesis that anoxic marine settings can serve as a chemical archive of first-order trends in seawater δ53Cr composition. Additionally, the Cariaco Basin data suggest that there has been secular stability in the average δ53Cr value of Atlantic seawater over the last ∼15 kyr.

Quantifying trace element and isotope fluxes at the ocean–sediment boundary: a review

PubMed Central

Berelson, William M.; Severmann, Silke

2016-01-01

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment–water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment–water boundary on many TEI cycles, and underline the fact that our knowledge of the source–sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment–water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’. PMID:29035270

A Detailed Record of Changing Surface Water Conditions From Sediments Deposited During Marine Isotope Stage 11, ODP Site 980, Northeast Atlantic Ocean

NASA Astrophysics Data System (ADS)

Arvin, T. A.; Cullen, J. L.; Oppo, D. W.; McManus, J. F.

2004-05-01

Many recent paleoceanographic studies have focused on using high sedimentation rate deep-sea sediment sections that have produced records of abrupt climate variability operating at sub-orbital time scales. This is particularly true in the North Atlantic where proxies of changing surface water conditions from high quality sediment records have repeatedly demonstrated that millennial-scale climate change has been the rule rather than the exception over the past 500 kyr, during both glacial and interglacial intervals. Abrupt climate change during warm interglacials is an area of special interest as it may relate more directly to an understanding of recent and future climate change. With this in mind we have focused our efforts on documenting millennial-scale climate change from sediments deposited at ODP Site 980, northeast Atlantic Ocean during Marine Isotope Stage (MIS) 11. We have used unsplit, whole sample >150 micron size fractions from over 200 sediment samples to record changes in the number lithic grains per gram sediment to measure changes in the input of Ice-Rafted Debris (IRD). We then compare our new IRD record to previously generated records of changing surface water conditions during MIS11: variations in oxygen isotopic composition of the surface dwelling planktic foraminifer species N. pachyderma, right coiling and changes in the relative abundance of the polar species N. pachyderma, left coiling. Our MIS11 results are then compared to compatible records from MIS5e and the Holocene. Our detailed IRD record from around 418 kya to 382 kya reveals a remarkable lack of even trace amounts IRD input into sediments at ODP Site 980. IRD concentration abruptly drops and remains 0 to trace amounts per gram as soon as benthic delta O-18 values fall to and remain at < 3.5 per mil at the onset of MIS11. Only three very small amplitude IRD events are observed over the entire 35 kyr interval. The earliest 8 kyr of MIS11 is completely devoid of any IRD, despite the fact that the relative abundance of the polar species N. pachyderma, left coiling, after dropping from near 90% to below 10% at 418 kya, rises to as high as 30% during this early MIS11 time interval. This seems to indicate the influx of non-ice bearing colder polar waters to the region above Site 980 that don't seem to be influencing he N. pachyderma, right coiling isotope record in a simple way. The MIS11 IRD record significantly differs from our records from MIS5e and the Holocene, particularly when we focus on the earliest 12 kyr of MIS11. Both the approximately 10 kyr long MIS5e interval and the last 11 kyr of the Holocene exhibit a series of between 6 and 9 discrete small amplitude increases in IRD against a background of little or no IRD. At the same time relative abundances of N. pachyderma, left coiling are considerably less during both MIS5e and the Holocene when compared to the first 10 kyr of MIS11. The evidence presented here suggests that MIS11 surface water conditions above Site 980 were somewhat different from conditions recorded in sediments from two other warm interglacial intervals, MIS5e and the Holocene and that its use as an ancient analog to modern and future climate may be less straightforward than previously thought.

Badlands as a major source of petrogenic particulate Organic Carbon and sediments to the Gulf of Lion (NW Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Copard, Y.; Eyrolle-Boyer, F.; Radakovitch, O.; Poirel, A.; Raimbault, P.; Gairoard, S.; Di-Giovanni, C.

2017-12-01

Rivers feed the marine environments both in term of sediments and nutrients and consequently, the characterization of their nature, sources and changes over a different spatial and time ranges is a critical for many scientific (e.g. biogeochemical cycles, contaminants transfer, geomorphology, ecology) and societal issues (e.g. food security, catastrophic floods). Specifically, continental sources showing some high erosion rates deserve to be studied since their fingerprint can be significant for the rivers fluxes. These included some sedimentary rocks (e.g. marls) forming badlands and containing a significant amount of petrogenic particulate organic carbon (pPOC) for which its contribution to the Rivers still remains evasive. Our study focuses on the Mediterranean area considered as very sensitive to the Global Change and particularly the Gulf of Lion mainly fed by the Rhône River, one of the major conveyors of sediments to this Sea. Based on radiocarbon data performed on a set of riverine samples and time series analyses from monitoring stations from French CZOs, we (i) update the POC flux of the Rhône River, (ii) determine the pPOC content and flux in suspended sediments and (iii) estimate the badlands contribution from the Durance catchment (a major tributary of the Rhône River) to the pPOC flux and to sediment discharge. Sediment discharge by the Rhône River to the Sea is 6.5 ± 4.3 Tg yr-1 (period 1990-2014) , its POC discharge reaches 0.145 ± 0.095 Tg yr-1 (period 2007-2014) while pPOC (0.44 wt. %) contributes to 30 % of this POC flux. Despite their insignificant surfaces (0.2 %) regarding the Rhône catchment area, badlands presently in erosion from the Durance catchment provide respectively, 16, 5 and 20 % of the pPOC, POC and sediment fluxes to the Rhône River. Consequently, badlands can be considered as a major source of sediments and pPOC for the NW Mediterranean Sea. We suggest that river-dominated ocean margins, such as the Rhône River, with badlands in erosion in their catchment could export a significant amount of sediments and pPOC to the oceans. According to the natural climate variability and more recently to the anthropogenic (LULUCF) disorders occurring in continental surfaces, such contributions had to and will strongly vary with times (from the geological times to the next decades scales).

How well suited are maar lakes of Madagascar for palaeoenvironmental multi-proxy reconstructions? - First results from shallow seismic, sedimentological and hydrological investigations in Central and Northwest Madagascar.

NASA Astrophysics Data System (ADS)

Daut, Gerhard; Jasmin Krahn, Kim; Rabhobisoa, Jean-Jacques; Ornella Moanazafy, Sergénie; Haberzettl, Torsten; Kasper, Thomas; Mäusbacher, Roland; Schwalb, Antje

2017-04-01

Madagascar is well known for its unique flora and fauna which are frequently in the focus of scientific investigations. However, studies on environmental changes in Madagascar linked to Quaternary climatic and/or anthropogenic impact are scarce. The aim of this initial study is to evaluate the potential of maar lakes, situated in different climatic zones of Madagascar, for paleoenvironmental studies and to identify promising coring sites with continuous sediment sequences reaching far back in time. Therefore, in November 2016, a shallow seismic profiling campaign, combined with surface sediment, short gravity core (max. 1.8 m), water and plankton sampling was performed on three target sites. These were two deep maar lakes, i.e., Andraikiba (Central Madagascar, 50m waterdepth) as well as Amparahibe (46,5m waterdepth) and Andampy Ambatoloaka, a shallow (5m waterdepth during low tide) former maar lake now connected to the Ocean (both NW-Madagascar. Vertical water parameter measurements in Lake Amparahibe confirm anoxic bottom conditions, while dissolved oxygen values at the water surface are about 7.9 mg/L (103%). Temperature decreases with depth from 29.3 °C to 27.2 °C, and the lake is slightly alkaline with an electrical conductivity of around 245 µS/cm. Since Andampy Ambatoloaka is connected to the ocean, it shows slightly alkaline conditions as well, electrical conductivity is high ( 57.8 mS/cm) and dissolved oxygen and temperature values are relatively stable at about 8.2 mg/L (104%) and 28.1 °C, respectively. The shallow seismic survey shows an infill with layered sediments of >50 m thickness in Lake Andraikiba. In Lake Amparahibe natural gas in the sediment prevented deeper penetration, however the record shows 10 m of undisturbed, layered sediments in the uppermost part. Sediment cores obtained from both lakes consist of dark brownish to blackish, clayey to silty and partly laminated sediments. High values of magnetic susceptibilities (>1800*10-6 SI) and high contents in organic matter, indicate a mixed signal of terrestrial input and intra-lake productivity, with sedimentation most probably under anoxic conditions. The marine site, in contrast, is influenced by tides, and characterized by coral debris in the shallow parts of the maar and grey silty sediments in the central part with a water depth of 5 m during low tide. However, initial results indicate that a combination of these maar lakes along climatic gradients hold a high potential for paleoenvironmental reconstructions even on long timescales.

Germanium Isotopes - the Global Budget and Paleoceanographic Potential

NASA Astrophysics Data System (ADS)

Baronas, J. J.; Hammond, D. E.; Rouxel, O. J.

2017-12-01

The distribution of element isotope ratios in rocks, sediments, rivers, and seawater can provide key insights about the operation and coupling of various biogeochemical cycles that are directly or indirectly responsible for the climate and habitability of the Earth surface environment. Germanium (Ge) is a trace element that shares many chemical similarities with silicon (Si), in addition to some siderophilic, chalcophilic, and organophilic properties. As a result, Ge stable isotope ratios (δ74Ge) and Ge/Si ratios can be used to trace various biogeochemical processes. These include silicate rock weathering, which modulates atmospheric pCO2 and supplies nutrients to ecosystems, biogenic silica formation, which is coupled to ocean productivity, and marine sediment diagenesis, which ultimately controls the removal of material from the Earth's surface. I will present an overview of my dissertation research concerning the global Ge isotope cycle, with insights into Ge isotope fractionation during secondary mineral precipitation during weathering on continents and during authigenesis in marine sediments. I will also discuss the potential for the δ74Ge sedimentary record to be used as a paleoceanographic proxy, given the constraints on the global Ge isotope budget.

The “White Ocean” Hypothesis: A Late Pleistocene Southern Ocean Governed by Coccolithophores and Driven by Phosphorus

PubMed Central

Flores, José-Abel; Filippelli, Gabriel M.; Sierro, Francisco J.; Latimer, Jennifer

2012-01-01

Paleoproductivity is a critical component in past ocean biogeochemistry, but accurate reconstructions of productivity are often hindered by limited integration of proxies. Here, we integrate geochemical (phosphorus) and micropaleontological proxies at millennial timescales, revealing that the coccolithophore record in the Subantarctic zone of the South Atlantic Ocean is driven largely by variations in marine phosphorus availability. A quantitative micropaleontological and geochemical analysis carried out in sediments retrieved from Ocean Drilling Program Site 1089 (Subantarctic Zone) reveals that most of the export productivity in this region over the last 0.5 my was due to coccolithophores. Glacial periods were generally intervals of high productivity, with productivity reaching a peak at terminations. Particularly high productivity was observed at Termination V and Termination IV, events that are characterized by high abundance of coccolithophores and maxima in the phosphorus/titanium and strontium/titanium records. We link the increase in productivity both to regional oceanographic phenomena, i.e., the northward displacement of the upwelling cell of the Antarctic divergence when the ice-sheet expanded, and to the increase in the inventory of phosphorus in the ocean due to enhanced transfer of this nutrient from continental margins during glacial lowstands in sea level. The Mid-Brunhes interval stands out from the rest of the record, being dominated by the small and highly calcified species Gephyrocapsa caribbeanica that provides most of the carbonate in these sediments. This likely represents higher availability of phosphorus in the surface ocean, especially in mesotrophic and oligotrophic zones. Under these condition, some coccolithophore species developed an r-strategy (opportunistic species; growth rate maximized) resulting in the bloom of G. caribbeanica. These seasonal blooms of may have induced “white tides” similar to those observed today in Emiliania huxleyi. PMID:22783242

Paleoenvironments of the Jurassic and Cretaceous Oceans: Selected Highlights

NASA Astrophysics Data System (ADS)

Ogg, J. G.

2007-12-01

There are many themes contributing to the sedimentation history of the Mesozoic oceans. This overview briefly examines the roles of the carbonate compensation depth (CCD) and the associated levels of atmospheric carbon dioxide, of the evolution of marine calcareous microplankton, of major transgressive and regressive trends, and of super-plume eruptions. Initiation of Atlantic seafloor spreading in the Middle Jurassic coincided with an elevated carbonate compensation depth (CCD) in the Pacific-Tethys mega-ocean. Organic-rich sediments that would become the oil wealth of regions from Saudi Arabia to the North Sea were deposited during a continued rise in CCD during the Oxfordian-early Kimmeridgian, which suggests a possible increase in carbon dioxide release by oceanic volcanic activity. Deep-sea deposits in near-equatorial settings are dominated by siliceous shales or cherts, which reflect the productivity of siliceous microfossils in the tropical surface waters. The end-Jurassic explosion in productivity by calcareous microplankton contributed to the lowering of the CCD and onset of the chalk ("creta") deposits that characterize the Tithonian and lower Cretaceous in all ocean basins. During the mid-Cretaceous, the eruption of enormous Pacific igneous provinces (Ontong Java Plateau and coeval edifices) increased carbon dioxide levels. The resulting rise in CCD terminated chalk deposition in the deep sea. The excess carbon was progressively removed in widespread black-shale deposits in the Atlantic basins and other regions - another major episode of oil source rock. A major long-term transgression during middle and late Cretaceous was accompanied by extensive chalk deposition on continental shelves and seaways while the oceanic CCD remained elevated. Pacific guyots document major oscillations (sequences) of global sea level superimposed on this broad highstand. The Cretaceous closed with a progressive sea-level regression and lowering of the CCD that again enabled widespread carbonate deposition in the deep sea.

Wave-driven sediment mobilization on a storm-controlled continental shelf (Northwest Iberia)

USGS Publications Warehouse

Oberle, Ferdinand; Storlazzi, Curt D.; Hanebuth, Till

2014-01-01

Seafloor sediment mobilization on the inner Northwest Iberian continental shelf is caused largely by ocean surface waves. The temporal and spatial variability in the wave height, wave period, and wave direction has a profound effect on local sediment mobilization, leading to distinct sediment mobilization scenarios. Six grain-size specific sediment mobilization scenarios, representing seasonal average and storm conditions, were simulated with a physics-based numerical model. Model inputs included meteorological and oceanographic data in conjunction with seafloor grain-size and the shelf bathymetric data. The results show distinct seasonal variations, most importantly in wave height, leading to sediment mobilization, specifically on the inner shelf shallower than 30 m water depth where up to 49% of the shelf area is mobilized. Medium to severe storm events are modeled to mobilize up to 89% of the shelf area above 150 m water depth. The frequency of each of these seasonal and storm-related sediment mobilization scenarios is addressed using a decade of meteorological and oceanographic data. The temporal and spatial patterns of the modeled sediment mobilization scenarios are discussed in the context of existing geological and environmental processes and conditions to assist scientific, industrial and environmental efforts that are directly affected by sediment mobilization. Examples, where sediment mobilization plays a vital role, include seafloor nutrient advection, recurrent arrival of oil from oil-spill-laden seafloor sediment, and bottom trawling impacts.

An atmosphere-ocean GCM modelling study of the climate response to changing Arctic seaways in the early Cenozoic.

NASA Astrophysics Data System (ADS)

Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

2008-12-01

The report of fossil Azolla (a freshwater aquatic fern) in sediments from the Lomonosov Ridge suggests low salinity conditions occurred in the Arctic Ocean in the early Eocene. Restricted passages between the Arctic Ocean and the surrounding oceans are hypothesized to have caused this Arctic freshening. We investigate this scenario using a water-isotope enabled atmosphere-ocean general circulation model with Eocene boundary conditions including 4xCO2, 7xCH4, altered bathymetry and topography, and an estimated distribution of Eocene vegetational types. In one experiment, oceanic exchange between the Arctic Ocean and other ocean basins was restricted to two shallow (~250 m) seaways, one in the North Atlantic, the Greenland-Norwegian seaway, and the second connecting the Arctic Ocean with the Tethys Ocean, the Turgai Straits. In the restricted configuration, the Greenland-Norwegian seaway was closed and exchange through the Turgai Straits was limited to a depth of ~60 m. The simulations suggest that the severe restriction of Arctic seaways in the early Eocene may have been sufficient to freshen Arctic Ocean surface waters, conducive to Azolla blooms. When exchange with the Arctic Ocean is limited, salinities in the upper several hundred meters of the water column decrease by ~10 psu. In some regions, surface salinity is within 2-3 psu of the reported maximum modern conditions tolerated by Azolla (~5 psu). In the restricted scenario, salt is stored preferentially in the North Atlantic and Tethys oceans, resulting in enhanced meridional overturning, increased poleward heat transport in the North Atlantic western boundary current, and warming of surface and intermediate waters in the North Atlantic by several degrees. Increased sensible and latent heat fluxes from the North Atlantic Ocean, combined with a reduction in cloud albedo, also lead to an increase in surface air temperature of over much of North America, Greenland and Eurasia. Our work is consistent with previous findings on the potential influence of Arctic gateways on ocean overturning and also suggests that Northern Hemisphere climate, particularly in the North Atlantic, was very sensitive to changes in Arctic seaways. This result is of particular significance when considered in the context of the Paleocene Eocene Thermal Maximum (PETM). Volcanic activity prior to the PETM may have been responsible for the formation of a sub-aerial barrier in the North Atlantic, and consequently may have driven warming of intermediate waters sufficient to destabilize methane clathrates. Evidence for freshening of Arctic ocean waters prior to the PETM would support this hypothesis.

Shallow methylmercury production in the marginal sea ice zone of the central Arctic Ocean.

PubMed

Heimbürger, Lars-Eric; Sonke, Jeroen E; Cossa, Daniel; Point, David; Lagane, Christelle; Laffont, Laure; Galfond, Benjamin T; Nicolaus, Marcel; Rabe, Benjamin; van der Loeff, Michiel Rutgers

2015-05-20

Methylmercury (MeHg) is a neurotoxic compound that threatens wildlife and human health across the Arctic region. Though much is known about the source and dynamics of its inorganic mercury (Hg) precursor, the exact origin of the high MeHg concentrations in Arctic biota remains uncertain. Arctic coastal sediments, coastal marine waters and surface snow are known sites for MeHg production. Observations on marine Hg dynamics, however, have been restricted to the Canadian Archipelago and the Beaufort Sea (<79 °N). Here we present the first central Arctic Ocean (79-90 °N) profiles for total mercury (tHg) and MeHg. We find elevated tHg and MeHg concentrations in the marginal sea ice zone (81-85 °N). Similar to other open ocean basins, Arctic MeHg concentration maxima also occur in the pycnocline waters, but at much shallower depths (150-200 m). The shallow MeHg maxima just below the productive surface layer possibly result in enhanced biological uptake at the base of the Arctic marine food web and may explain the elevated MeHg concentrations in Arctic biota. We suggest that Arctic warming, through thinning sea ice, extension of the seasonal sea ice zone, intensified surface ocean stratification and shifts in plankton ecodynamics, will likely lead to higher marine MeHg production.

Shallow methylmercury production in the marginal sea ice zone of the central Arctic Ocean

PubMed Central

Heimbürger, Lars-Eric; Sonke, Jeroen E.; Cossa, Daniel; Point, David; Lagane, Christelle; Laffont, Laure; Galfond, Benjamin T.; Nicolaus, Marcel; Rabe, Benjamin; van der Loeff, Michiel Rutgers

2015-01-01

Methylmercury (MeHg) is a neurotoxic compound that threatens wildlife and human health across the Arctic region. Though much is known about the source and dynamics of its inorganic mercury (Hg) precursor, the exact origin of the high MeHg concentrations in Arctic biota remains uncertain. Arctic coastal sediments, coastal marine waters and surface snow are known sites for MeHg production. Observations on marine Hg dynamics, however, have been restricted to the Canadian Archipelago and the Beaufort Sea (<79°N). Here we present the first central Arctic Ocean (79–90°N) profiles for total mercury (tHg) and MeHg. We find elevated tHg and MeHg concentrations in the marginal sea ice zone (81–85°N). Similar to other open ocean basins, Arctic MeHg concentration maxima also occur in the pycnocline waters, but at much shallower depths (150–200 m). The shallow MeHg maxima just below the productive surface layer possibly result in enhanced biological uptake at the base of the Arctic marine food web and may explain the elevated MeHg concentrations in Arctic biota. We suggest that Arctic warming, through thinning sea ice, extension of the seasonal sea ice zone, intensified surface ocean stratification and shifts in plankton ecodynamics, will likely lead to higher marine MeHg production. PMID:25993348

A biogeographic network reveals evolutionary links between deep-sea hydrothermal vent and methane seep faunas

PubMed Central

2016-01-01

Deep-sea hydrothermal vents and methane seeps are inhabited by members of the same higher taxa but share few species, thus scientists have long sought habitats or regions of intermediate character that would facilitate connectivity among these habitats. Here, a network analysis of 79 vent, seep, and whale-fall communities with 121 genus-level taxa identified sedimented vents as a main intermediate link between the two types of ecosystems. Sedimented vents share hot, metal-rich fluids with mid-ocean ridge-type vents and soft sediment with seeps. Such sites are common along the active continental margins of the Pacific Ocean, facilitating connectivity among vent/seep faunas in this region. By contrast, sedimented vents are rare in the Atlantic Ocean, offering an explanation for the greater distinction between its vent and seep faunas compared with those of the Pacific Ocean. The distribution of subduction zones and associated back-arc basins, where sedimented vents are common, likely plays a major role in the evolutionary and biogeographic connectivity of vent and seep faunas. The hypothesis that decaying whale carcasses are dispersal stepping stones linking these environments is not supported. PMID:27974524

Carbonate counter pump stimulated by natural iron fertilization in the Polar Frontal Zone

NASA Astrophysics Data System (ADS)

Salter, Ian; Schiebel, Ralf; Ziveri, Patrizia; Movellan, Aurore; Lampitt, Richard; Wolff, George A.

2014-12-01

The production of organic carbon in the ocean's surface and its subsequent downward export transfers carbon dioxide to the deep ocean. This CO2 drawdown is countered by the biological precipitation of carbonate, followed by sinking of particulate inorganic carbon, which is a source of carbon dioxide to the surface ocean, and hence the atmosphere over 100-1,000 year timescales. The net transfer of CO2 to the deep ocean is therefore dependent on the relative amount of organic and inorganic carbon in sinking particles. In the Southern Ocean, iron fertilization has been shown to increase the export of organic carbon, but it is unclear to what degree this effect is compensated by the export of inorganic carbon. Here we assess the composition of sinking particles collected from sediment traps located in the Polar Frontal Zone of the Southern Ocean. We find that in high-nutrient, low-chlorophyll regions that are characterized by naturally high iron concentrations, fluxes of both organic and inorganic carbon are higher than in regions with no iron fertilization. However, the excess flux of inorganic carbon is greater than that of organic carbon. We estimate that the production and flux of carbonate in naturally iron-fertilized waters reduces the overall amount of CO2 transferred to the deep ocean by 6-32%, compared to 1-4% at the non-fertilized site. We suggest that an increased export of organic carbon, stimulated by iron availability in the glacial sub-Antarctic oceans, may have been accompanied by a strengthened carbonate counter pump.

Validation of Spectral Unmixing Results from Informed Non-Negative Matrix Factorization (INMF) of Hyperspectral Imagery

NASA Astrophysics Data System (ADS)

Wright, L.; Coddington, O.; Pilewskie, P.

2017-12-01

Hyperspectral instruments are a growing class of Earth observing sensors designed to improve remote sensing capabilities beyond discrete multi-band sensors by providing tens to hundreds of continuous spectral channels. Improved spectral resolution, range and radiometric accuracy allow the collection of large amounts of spectral data, facilitating thorough characterization of both atmospheric and surface properties. We describe the development of an Informed Non-Negative Matrix Factorization (INMF) spectral unmixing method to exploit this spectral information and separate atmospheric and surface signals based on their physical sources. INMF offers marked benefits over other commonly employed techniques including non-negativity, which avoids physically impossible results; and adaptability, which tailors the method to hyperspectral source separation. The INMF algorithm is adapted to separate contributions from physically distinct sources using constraints on spectral and spatial variability, and library spectra to improve the initial guess. Using this INMF algorithm we decompose hyperspectral imagery from the NASA Hyperspectral Imager for the Coastal Ocean (HICO), with a focus on separating surface and atmospheric signal contributions. HICO's coastal ocean focus provides a dataset with a wide range of atmospheric and surface conditions. These include atmospheres with varying aerosol optical thicknesses and cloud cover. HICO images also provide a range of surface conditions including deep ocean regions, with only minor contributions from the ocean surfaces; and more complex shallow coastal regions with contributions from the seafloor or suspended sediments. We provide extensive comparison of INMF decomposition results against independent measurements of physical properties. These include comparison against traditional model-based retrievals of water-leaving, aerosol, and molecular scattering radiances and other satellite products, such as aerosol optical thickness from the Moderate Resolution Imaging Spectroradiometer (MODIS).

Earthquakes drive large-scale submarine canyon development and sediment supply to deep-ocean basins.

PubMed

Mountjoy, Joshu J; Howarth, Jamie D; Orpin, Alan R; Barnes, Philip M; Bowden, David A; Rowden, Ashley A; Schimel, Alexandre C G; Holden, Caroline; Horgan, Huw J; Nodder, Scott D; Patton, Jason R; Lamarche, Geoffroy; Gerstenberger, Matthew; Micallef, Aaron; Pallentin, Arne; Kane, Tim

2018-03-01

Although the global flux of sediment and carbon from land to the coastal ocean is well known, the volume of material that reaches the deep ocean-the ultimate sink-and the mechanisms by which it is transferred are poorly documented. Using a globally unique data set of repeat seafloor measurements and samples, we show that the moment magnitude ( M w ) 7.8 November 2016 Kaikōura earthquake (New Zealand) triggered widespread landslides in a submarine canyon, causing a powerful "canyon flushing" event and turbidity current that traveled >680 km along one of the world's longest deep-sea channels. These observations provide the first quantification of seafloor landscape change and large-scale sediment transport associated with an earthquake-triggered full canyon flushing event. The calculated interevent time of ~140 years indicates a canyon incision rate of 40 mm year -1 , substantially higher than that of most terrestrial rivers, while synchronously transferring large volumes of sediment [850 metric megatons (Mt)] and organic carbon (7 Mt) to the deep ocean. These observations demonstrate that earthquake-triggered canyon flushing is a primary driver of submarine canyon development and material transfer from active continental margins to the deep ocean.

Paleoproductivity in the northwestern Pacific Ocean during the Pliocene-Pleistocene climate transition (3.0-1.8 Ma)

NASA Astrophysics Data System (ADS)

Venti, Nicholas L.; Billups, Katharina; Herbert, Timothy D.

2017-02-01

Alkenone mass accumulation rates (MARs) provide a proxy for export productivity in the northwestern Pacific (Ocean Drilling Program Site 1208) spanning the late Pliocene through early Pleistocene (3.0-1.8 Ma). We investigate changes in productivity associated with global cooling during the onset and expansion of Northern Hemisphere glaciation (NHG). Alkenone MARs vary on obliquity timescales throughout, but the amplitude increases at 2.75 Ma concurrent with the intensification of NHG and cooling of the sea surface by 3°C. The obliquity-scale variations in alkenone MARs parallel shipboard measurements of sediment color reflectance (%) with higher MARs significantly correlated (>95%) with darker (opal-rich) intervals. Variations in both lead benthic foraminiferal δ18O values by 1.5-2 kyr suggesting that export productivity may be a contributing factor, rather than a response, to the extent of continental glaciation. The biological pump is therefore a plausible mechanism for transferring atmospheric CO2 into the deep ocean during the onset of NHG and the ensuing obliquity-dominated climate regime. Obliquity-scale correlation between productivity and magnetic susceptibility is consistent with a link via westerly winds delivering terrigenous sediments and mixing the upper water column. Alkenone MARs also contain a 400 kyr modulation. Because this periodicity is a multiple of the residence time of carbon in the ocean, it may reflect inputs of new nutrients associated with eccentricity-forced changes in the terrestrial biosphere and weathering. We ascribe these findings to interactions between the East Asian winter monsoon and productivity in the North Pacific Ocean, perhaps contributing to Plio-Pleistocene climate change.

Antarctic Ocean Nutrient Conditions During the Last Two Glacial Cycles

NASA Astrophysics Data System (ADS)

Studer, A.; Sigman, D. M.; Martinez-Garcia, A.; Benz, V.; Winckler, G.; Kuhn, G.; Esper, O.; Lamy, F.; Jaccard, S.; Wacker, L.; Oleynik, S.; Gersonde, R.; Haug, G. H.

2014-12-01

The high concentration of the major nutrients nitrate and phosphate in the Antarctic Zone of the Southern Ocean dictates the nature of Southern Ocean ecosystems and permits these nutrients to be carried from the deep ocean into the nutrient-limited low latitudes. Incomplete nutrient consumption in the Antarctic also allows the leakage of deeply sequestered carbon dioxide (CO2) back to the atmosphere, and changes in this leakage may have driven glacial/interglacial cycles in atmospheric CO2. In a sediment core from the Pacific sector of the Antarctic Ocean, we report diatom-bound N isotope (δ15Ndb) records for total recoverable diatoms and two assemblages of diatom species. These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ15Ndb (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Measurements in the same sediment core indicate that export production was reduced during ice ages, pointing to an ice age reduction in the supply of deep ocean-sourced nitrate to the Antarctic Ocean surface. The reduced export production of peak ice ages also implies a weaker winter-to-summer decline (i.e. reduced seasonality) in mixed layer nitrate concentration, providing a plausible explanation for an observed reduction in the inter-assemblage δ15Ndb difference during these coldest times. Despite the weak summertime productivity, the reduction in wintertime nitrate supply from deep waters left the Antarctic mixed layer with a low nitrate concentration, and this wintertime change also would have reduced the outgassing of CO2. Relief of light limitation fails to explain the intermediate degree of nitrate consumption that characterizes early glacial conditions, as improved light limitation coincident with reduced nitrate supply would drive nitrate consumption to completion. Thus, the data favor iron availability as the dominant control on annual Antarctic Ocean export production over glacial cycles.

Morphology of Shatsky Rise oceanic plateau from high resolution bathymetry

NASA Astrophysics Data System (ADS)

Zhang, Jinchang; Sager, William W.; Durkin, William J.

2017-06-01

Newly collected, high resolution multi-beam sonar data are combined with previous bathymetry data to produce an improved bathymetric map of Shatsky Rise oceanic plateau. Bathymetry data show that two massifs within Shatsky Rise are immense central volcanoes with gentle flank slopes declining from a central summit. Tamu Massif is a slightly elongated, dome-like volcanic edifice; Ori Massif is square shaped and smaller in area. Several down-to-basin normal faults are observed on the western flank of the massifs but they do not parallel the magnetic lineations, indicating that these faults are probably not related to spreading ridge faulting. Moreover, the faults are observed only on one side of the massifs, which is contrary to expectations from a mechanism of differential subsidence around the massif center. Multi-beam data show many small secondary cones with different shapes and sizes that are widely-distributed on Shatsky Rise massifs, which imply small late-stage magma sources scattered across the surface of the volcanoes in the form of lava flows or explosive volcanism. Erosional channels occur on the flanks of Shatsky Rise volcanoes due to mass wasting and display evidence of down-slope sediment movement. These channels are likely formed by sediments spalling off the edges of summit sediment cap.

NW Pacific mid-depth ventilation changes during the Holocene

NASA Astrophysics Data System (ADS)

Rella, S.; Uchida, M.

2010-12-01

During the last 50 years the oxygen content of North Pacific Intermediate Water primarily originating in the Okhotsk Sea has declined suggesting decreased mid-depth water circulation, likely leading to changes in biological productivity in the NW Pacific realm and a decrease in CO2 drawdown. It is therefore of high interest to elucidate the climate-oceanic interconnections of the present interglacial period (Holocene) in the NW Pacific, in order to predict possible future climate and surface productivity changes associated with a decrease in mid-depth ventilation in this ecologically sensitive region. However, such efforts have been hampered so far by the lack of appropriate sediment cores with fast sedimentation rates during the Holocene. Core CK05-04 that was recovered in 2005 from off Shimokita peninsula, Japan, at ~1000 m depth shows sedimentation rates of ~80 cm/kyr during the Holocene and therefore presents an ideal opportunity to reconstruct for the first time the Holocene ventilation history of the NW Pacific Ocean. We employ Accelerator Mass Spectroscopy (NIES-TERRA, Tsukuba) radiocarbon analysis of co-existing benthic and planktonic foraminifera to conclude on the ventilation age of the mid-depth water using benthic-planktonic radiocarbon age differences. At the conference we would like to present the results.

Polycyclic aromatic hydrocarbons in ocean sediments from the North Pacific to the Arctic Ocean.

PubMed

Ma, Yuxin; Halsall, Crispin J; Xie, Zhiyong; Koetke, Danijela; Mi, Wenying; Ebinghaus, Ralf; Gao, Guoping

2017-08-01

Eighteen polycyclic aromatic hydrocarbons (PAHs) were measured in surficial sediments along a marine transect from the North Pacific into the Arctic Ocean. The highest average Σ 18 PAHs concentrations were observed along the continental slope of the Canada Basin in the Arctic (68.3 ± 8.5 ng g -1 dw), followed by sediments in the Chukchi Sea shelf (49.7 ± 21.2 ng g -1 dw) and Bering Sea (39.5 ± 11.3 ng g -1 dw), while the Bering Strait (16.8 ± 7.1 ng g -1 dw) and Central Arctic Ocean sediments (13.1 ± 9.6 ng g -1 dw) had relatively lower average concentrations. The use of principal components analysis with multiple linear regression (PCA/MLR) indicated that on average oil related or petrogenic sources contributed ∼42% of the measured PAHs in the sediments and marked by higher concentrations of two methylnaphthalenes over the non-alkylated parent PAH, naphthalene. Wood and coal combustion contributed ∼32%, and high temperature pyrogenic sources contributing ∼26%. Petrogenic sources, such as oil seeps, allochthonous coal and coastally eroded material such as terrigenous sediments particularly affected the Chukchi Sea shelf and slope of the Canada Basin, while biomass and coal combustion sources appeared to have greater influence in the central Arctic Ocean, possibly due to the effects of episodic summertime forest fires. Copyright © 2017 Elsevier Ltd. All rights reserved.

Paleobathymetric grids of the Cenozoic Southern Ocean - Opening the door towards improved reconstructions of the Southern Ocean's past

NASA Astrophysics Data System (ADS)

Hochmuth, K.; Gohl, K.; Leitchenkov, G. L.; Sauermilch, I.; Whittaker, J. M.; De Santis, L.; Olivo, E.; Uenzelmann-Neben, G.; Davy, B. W.

2017-12-01

Although the Southern Ocean plays a fundamental role in the global climate and ocean current system, paleo-ocean circulation models of the Southern Ocean suffer from missing boundary conditions. A more accurate representation of the geometry of the seafloor and their dynamics over long time-scales are key for enabling more precise reconstructions of the development of the paleo-currents, the paleo-environment and the Antarctic ice sheets. The accurate parameterisation of these models controls the meaning and implications of regional and global paleo-climate models. The dynamics of ocean currents in proximity of the continental margins is also controlled by the development of the regional seafloor morphology of the conjugate continental shelves, slopes and rises. The reassessment of all available reflection seismic and borehole data from Antarctica as well as its conjugate margins of Australia, New Zealand, South Africa and South America, allows us to create paleobathymetric grids for various time slices during the Cenozoic. Those grids inform us about sediment distribution and volume as well a local sedimentation rates. The earliest targeted time slice of the Eocene/Oligocene Boundary marks a significant turning point towards an icehouse climate. From latest Eocene to earliest Oligocene the Southern Ocean changes fundamentally from a post greenhouse to an icehouse environment with the establishment of a vast continental ice sheet on the Antarctic continent. With the calculated sediment distribution maps, we can evaluate the dynamics of the sedimentary cover as well as the development of structural obstacles such as oceanic plateaus and ridges. The ultimate aim of this project is - as a community based effort - to create paleobathymetric grids at various time slices such as the Mid-Miocene Climatic Optimum and the Pliocene/Pleistocene, and eventually mimic the time steps used within the modelling community. The observation of sediment distribution and local sediment volumes open the door towards more sophisticated paleo-topograpy studies of the Antarctic continent and more detailed studies of the paleo-circulation. Local paleo - water depths at the oceanic gateways or the position of paleo-shelf edges highly influence the regional circulation patterns supporting more elaborated climate models.

Characteristics of storm runoff and sediment dispersal in the San Pedro Channel, southern California.

PubMed

Ahn, J H; Grant, S B

2007-01-01

In-site measurements of particle size spectra were obtained from three offshore cruises to evaluate the physical consequences of increased sediment transport and deposition offshore which was caused by episodic storm runoff water from the Santa Ana River watershed, a highly urbanised coastal watershed in southern California. Of the total annual runoff discharge to the coastal ocean, 89.2% occurred in the 2003/2004 winter season, and 0.22 Mt of sediment mass was transported during the storm events. The runoff plume at surface taken offshore by cross-shore currents progressed rapid aggregation and sedimentation, while the initially high concentration of suspended sediment discharged from the river outlet was dominated by small particles. Vertical profiles of particle size spectra revealed two separated plumes near the river outlet and turbidity plume along the bottom consisted of an abundance of very fine and dense particles. It would appear to support the theory that even if the storm runoff does not carry a high concentration of sediment being capable of generating negative buoyancy, sediment deposition on the shelf might mobilise in dense, fluid mud transported offshore by gravity. In a coastal pollution context, sediment particle size spectra information may offer potentially useful means of characterising particle-associated pollutants for purposes of source tracking and environmental interpretation.

High pCO 2-induced exopolysaccharide-rich ballasted aggregates of planktonic cyanobacteria could explain Paleoproterozoic carbon burial

DOE PAGES

Kamennaya, Nina A.; Zemla, Marcin; Mahoney, Laura; ...

2018-05-29

Here, the contribution of planktonic cyanobacteria to burial of organic carbon in deep-sea sediments before the emergence of eukaryotic predators ~1.5 Ga has been considered negligible owing to the slow sinking speed of their small cells. However, global, highly positive excursion in carbon isotope values of inorganic carbonates ~2.22–2.06 Ga implies massive organic matter burial that had to be linked to oceanic cyanobacteria. Here to elucidate that link, we experiment with unicellular planktonic cyanobacteria acclimated to high partial CO 2 pressure ( pCO 2) representative of the early Paleoproterozoic. We find that high pCO 2 boosts generation of acidic extracellularmore » polysaccharides (EPS) that adsorb Ca and Mg cations, support mineralization, and aggregate cells to form ballasted particles. The down flux of such self-assembled cyanobacterial aggregates would decouple the oxygenic photosynthesis from oxidative respiration at the ocean scale, drive export of organic matter from surface to deep ocean and sustain oxygenation of the planetary surface.« less

High pCO 2-induced exopolysaccharide-rich ballasted aggregates of planktonic cyanobacteria could explain Paleoproterozoic carbon burial

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

Kamennaya, Nina A.; Zemla, Marcin; Mahoney, Laura

Here, the contribution of planktonic cyanobacteria to burial of organic carbon in deep-sea sediments before the emergence of eukaryotic predators ~1.5 Ga has been considered negligible owing to the slow sinking speed of their small cells. However, global, highly positive excursion in carbon isotope values of inorganic carbonates ~2.22–2.06 Ga implies massive organic matter burial that had to be linked to oceanic cyanobacteria. Here to elucidate that link, we experiment with unicellular planktonic cyanobacteria acclimated to high partial CO 2 pressure ( pCO 2) representative of the early Paleoproterozoic. We find that high pCO 2 boosts generation of acidic extracellularmore » polysaccharides (EPS) that adsorb Ca and Mg cations, support mineralization, and aggregate cells to form ballasted particles. The down flux of such self-assembled cyanobacterial aggregates would decouple the oxygenic photosynthesis from oxidative respiration at the ocean scale, drive export of organic matter from surface to deep ocean and sustain oxygenation of the planetary surface.« less

The radiocarbon reservoir age of the Chukchi Sea, Arctic Ocean

NASA Astrophysics Data System (ADS)

Pearce, C.; Gyllencreutz, R.; West, G.; O'Regan, M.; Jakobsson, M.

2017-12-01

Radiocarbon (14C) dating is the standard method for obtaining the age of marine sediments of Holocene and late Pleistocene age. For accurate calibrations, however, this tool relies on precise knowledge of the local radiocarbon reservoir age of the surface ocean, i.e. the regional difference (ΔR) from the average global marine calibration dataset. This parameter has become impossible to measure from modern mollusk samples because of 14C contamination from extensive testing of thermo-nuclear bombs in the second half of the twentieth century. The local reservoir age can thus only be calculated from the radiocarbon age of samples collected before AD 1950 or from sediment records containing absolute age markers, derived from e.g. tephrochronology or paleomagnetism. Knowledge of the marine reservoir age in the Arctic Ocean is extremely sparse, and relies on work by only a few studies. No information exists for the entire East Siberian Sea, and the Chukchi Sea is represented solely by sites along the Alaskan coast. Here we present new radiocarbon measurements on historical mollusk collections from the East Siberian and Chukchi margins. Our results show a clear and consistent signal of "old" Pacific Water in the Chukchi Sea with ΔR values around 450 years. Towards the East Siberian Sea the values drop as Pacific Water has decreased influence further away from the Bering Strait. Complementing the modern data, we also provide constraints on the reservoir age during the late Holocene. These are based on tephrochronology and high resolution analyses of paleomagnetic secular variation from a sediment archive from Herald Canyon, Chukchi Sea.

Coral reefs will transition to net dissolving before end of century

NASA Astrophysics Data System (ADS)

Eyre, Bradley D.; Cyronak, Tyler; Drupp, Patrick; De Carlo, Eric Heinen; Sachs, Julian P.; Andersson, Andreas J.

2018-02-01

Ocean acidification refers to the lowering of the ocean’s pH due to the uptake of anthropogenic CO2 from the atmosphere. Coral reef calcification is expected to decrease as the oceans become more acidic. Dissolving calcium carbonate (CaCO3) sands could greatly exacerbate reef loss associated with reduced calcification but is presently poorly constrained. Here we show that CaCO3 dissolution in reef sediments across five globally distributed sites is negatively correlated with the aragonite saturation state (Ωar) of overlying seawater and that CaCO3 sediment dissolution is 10-fold more sensitive to ocean acidification than coral calcification. Consequently, reef sediments globally will transition from net precipitation to net dissolution when seawater Ωar reaches 2.92 ± 0.16 (expected circa 2050 CE). Notably, some reefs are already experiencing net sediment dissolution.

Sediments and fossiliferous rocks from the eastern side of the Tongue of the Ocean, Bahamas

USGS Publications Warehouse

Gibson, T.G.; Schlee, J.

1967-01-01

In August 1966, two dives were made with the deep-diving submersible Alvin along the eastern side of the Tongue of the Ocean to sample the rock and sediment. Physiographically, the area is marked by steep slopes of silty carbonate sediment and precipitous rock cliffs dusted by carbonate debris. Three rocks, obtained from the lower and middle side of the canyon (914-1676 m depth), are late Miocene-early Pliocene to late Pleistocene-Recent in age; all are deep-water pelagic limestones. They show (i) that the Tongue of the Ocean has been a deep-water area at least back into the Miocene, and (ii) that much shallow-water detritus has been swept off neighbouring banks to be incorporated with the deep-water fauna in the sediment. ?? 1967 Pergamon Press Ltd.

Particle Fluxes in the Marginal Seas of Antarctica: A 20-year Synthesis in Honor of Jack Dymond

NASA Astrophysics Data System (ADS)

Dunbar, R. B.; Langone, L.

2004-12-01

One of Jack Dymond's long-standing scientific passions was the study of particles moving through the ocean water column. Jack's pioneering work in this area in the 1970's and generous mentoring of others throughout his career lead directly to the first authors involvement in sediment trap studies. Here we present a synthesis of 20 years of particle flux studies in coastal Antarctic (including the work of Collier and Dymond et al.) and highlight some of the important features and unresolved issues related to integrating particle trap interceptor data with other measures of production, transport, and deposition. The first sediment trap arrays were deployed on the Antarctic shelf in 1981 and 1982 in the Antarctic Peninsula. Simple instruments were also deployed in 1984 and 1986 in the Ross Sea. Since then, several nations (US, Italy, New Zealand) have recovered time series sediment trap data on moorings in both of these areas. This current synthesis makes use of data from approximately 22 sites, the majority of which are in the Ross Sea, and includes about 900 discrete samples of particles in vertical transit through the water column. We now have many complete time series that extend through the winter, allowing several important generalizations to be made. For example, annual particle-mediated organic C fluxes to below 200 meters in the Ross Sea average 4.4±3.3 g C m-2 yr-1. These values are significantly less than export fluxes calculated using short-term surface water mass balance approaches or Th isotope techniques yet are higher than seabed sediment accumulation rates. Intriguingly, seasonal seabed arrival rates of organic C estimated from in-situ summertime benthic respirometry studies yield C flux values similar in magnitude to those from sediment traps deployed at the same time, lending strong support to trap data. The cause of current disagreements between various methods of flux estimation may in fact not be solved until process studies are accomplished that extend through the austral autumn into winter and/or the biogeochemistry of Th is better understood in coastal area of the Southern Ocean. Nearly all Ross Sea particle flux time series show relative low sedimentation during the periods of highest primary production in surface waters followed by either events or periods of enhanced sedimentation during the latest austral summer and/or autumn. This high degree of decoupling between production and sedimentation is unusual and may well represent low grazing rates. It is likely that purely physical phenomena associated with the return of winter sea ice are responsible for enhanced autumn sedimentation in the Ross Sea. Compared to the Ross Sea region, biogenic fluxes in the Palmer Basin area of the Antarctic Peninsula are higher, but are more tightly coupled to productivity in surface waters. We conclude our synthesis by presenting a general model for particle production and deposition in several end-member environments of the Antarctic Margin.

Principal sources and dispersal patterns of suspended particulate matter in nearshore surface waters of the northeast Pacific Ocean and the Hawaiian Islands

NASA Technical Reports Server (NTRS)

Carlson, P. R. (Principal Investigator); Conomos, T. J.; Janda, R. J.; Peterson, D. H.

1973-01-01

The author has identified the following significant results. ERTS-1 multispectral scanner imagery of the nearshore surface waters of the Northeast Pacific Ocean is proving to be a useful tool for determining source and dispersal of suspended particulate matter. The principal sources of the turbid water, seen best on the green and red bands, are river and stream effluents and actively eroding coastlines; secondary sources are waste effluents and production of planktonic organisms, but these may sometimes be masked by the very turbid plumes of suspended sediment being discharged into the nearshore zone during times of high river discharge. The configuration and distribution of the plumes of turbid water also can be used to infer near-surface current directions. Comparison of imagery of the nearshore water off the northern California coast from October 1972 and January 1973 shows a reversal of the near-surface currents, from predominantly south-setting in the fall (California Current) to north-setting in the winter (Davidson Current).

Rock magnetic and geochemical analyses of surface sediment characteristics in deep ocean environments: A case study across the Ryukyu Trench

NASA Astrophysics Data System (ADS)

Kawamura, N.; Kawamura, K.; Ishikawa, N.

2008-03-01

Magnetic minerals in marine sediments are often dissolved or formed with burial depth, thereby masking the primary natural remanent magnetization and paleoclimate signals. In order to clarify the present sedimentary environment and the progressive changes with burial depth in the magnetic properties, we studied seven cores collected from the Ryukyu Trench, southwest Japan. Magnetic properties, organic geochemistry, and interstitial water chemistry of seven cores are described. Bottom water conditions at the landward slope, trench floor, and seaward slope are relatively suboxic, anoxic, and oxic, respectively. The grain size of the sediments become gradually finer with the distance from Okinawa Island and finer with increasing water depth. The magnetic carriers in the sediments are predominantly magnetite and maghemized magnetite, with minor amounts of hematite. In the topmost sediments from the landward slope, magnetic minerals are diluted by terrigenous materials and microfossils. The downcore variations in magnetic properties and geochemical data provided evidence for the dissolution of fine-grained magnetite with burial depth under an anoxic condition.

Acoustic measurement of sediment dynamics in the coastal zones using wireless sensor networks

NASA Astrophysics Data System (ADS)

Sudhakaran, A., II; Paramasivam, A.; Seshachalam, S.; A, C.

2014-12-01

Analyzing of the impact of constructive or low energy waves and deconstructive or high energy waves in the ocean are very much significant since they deform the geometry of seashore. The deformation may lead to productive result and also to the end of deteriorate damage. Constructive waves results deposition of sediment which widens the beach where as deconstructive waves results erosion which narrows the beach. Validation of historic sediment transportation and prediction of the direction of movement of seashore is essential to prevent unrecoverable damages by incorporating precautionary measurements to identify the factors that influence sediment transportation if feasible. The objective of this study is to propose a more reliable and energy efficient Information and communication system to model the Coastal Sediment Dynamics. Various factors influencing the sediment drift at a particular region is identified. Consequence of source depth and frequency dependencies of spread pattern in the presence of sediments is modeled. Property of source depth and frequency on sensitivity to values of model parameters are determined. Fundamental physical reasons for these sediment interaction effects are given. Shallow to deep water and internal and external wave model of ocean is obtained intended to get acoustic data assimilation (ADA). Signal processing algorithms are used over the observed data to form a full field acoustic propagation model and construct sound speed profile (SSP). The inversions of data due to uncertainties at various depths are compared. The impact of sediment drift over acoustic data is identified. An energy efficient multipath routing scheme Wireless sensor networks (WSN) is deployed for the well-organized communication of data. The WSN is designed considering increased life time, decreased power consumption, free of threats and attacks. The practical data obtained from the efficient system to model the ocean sediment dynamics are evaluated with remote sensing data and the reasons of deviations and uncertainties are unbiased. The probability of changes and impact of sediment drift over ocean dynamic model over the long running of years is estimated.

Black Carbon in Estuarine (Coastal) High-molecular-weight Dissolved Organic Matter

NASA Technical Reports Server (NTRS)

Mannino, Antonio; Harvey, H. Rodger

2003-01-01

Dissolved organic matter (DOM) in the ocean constitutes one of the largest pools of organic carbon in the biosphere, yet much of its composition is uncharacterized. Observations of black carbon (BC) particles (by-products of fossil fuel combustion and biomass burning) in the atmosphere, ice, rivers, soils and marine sediments suggest that this material is ubiquitous, yet the contribution of BC to the ocean s DOM pool remains unknown. Analysis of high-molecular-weight DOM isolated from surface waters of two estuaries in the northwest Atlantic Ocean finds that BC is a significant component of DOM, suggesting that river-estuary systems are important exporters of BC to the ocean through DOM. We show that BC comprises 4-7% of the dissolved organic carbon (DOC) at coastal ocean sites, which supports the hypothesis that the DOC pool is the intermediate reservoir in which BC ages prior to sedimentary deposition. Flux calculations suggest that BC could be as important as vascular plant-derived lignin in terms of carbon inputs to the ocean. Production of BC sequesters fossil fuel- and biomass-derived carbon into a refractory carbon pool. Hence, BC may represent a significant sink for carbon to the ocean.

The impact of sedimentary coatings on the diagenetic Nd flux

NASA Astrophysics Data System (ADS)

Abbott, April N.; Haley, Brian A.; McManus, James

2016-09-01

Because ocean circulation impacts global heat transport, understanding the relationship between deep ocean circulation and climate is important for predicting the ocean's role in climate change. A common approach to reconstruct ocean circulation patterns employs the neodymium isotope compositions of authigenic phases recovered from marine sediments. In this approach, mild chemical extractions of these phases is thought to yield information regarding the εNd of the bottom waters that are in contact with the underlying sediment package. However, recent pore fluid studies present evidence for neodymium cycling within the upper portions of the marine sediment package that drives a significant benthic flux of neodymium to the ocean. This internal sedimentary cycling has the potential to obfuscate any relationship between the neodymium signature recovered from the authigenic coating and the overlying neodymium signature of the seawater. For this manuscript, we present sedimentary leach results from three sites on the Oregon margin in the northeast Pacific Ocean. Our goal is to examine the potential mechanisms controlling the exchange of Nd between the sedimentary package and the overlying water column, as well as the relationship between the εNd composition of authigenic sedimentary coatings and that of the pore fluid. In our comparison of the neodymium concentrations and isotope compositions from the total sediment, sediment leachates, and pore fluid we find that the leachable components account for about half of the total solid-phase Nd, therefore representing a significant reservoir of reactive Nd within the sediment package. Based on these and other data, we propose that sediment diagenesis determines the εNd of the pore fluid, which in turn controls the εNd of the bottom water. Consistent with this notion, despite having 1 to 2 orders of magnitude greater Nd concentration than the bottom water, the pore fluid is still <0.001% of the total Nd reservoir in the upper sediment column. Therefore, the pore fluid reservoir is too small to maintain a unique signature, and instead must be controlled by the larger reservoir of Nd in the reactive coatings. In addition, to achieve mass balance, we find it necessary to invoke a cryptic radiogenic (εNd of +10) trace mineral source of neodymium within the upper sediment column at our sites. When present, this cryptic trace metal results in more radiogenic pore fluid.

An Unaccounted Fraction of Marine Biogenic CaCO3 Particles

PubMed Central

Heldal, Mikal; Norland, Svein; Erichsen, Egil S.; Thingstad, T. Frede; Bratbak, Gunnar

2012-01-01

Biogenic production and sedimentation of calcium carbonate in the ocean, referred to as the carbonate pump, has profound implications for the ocean carbon cycle, and relate both to global climate, ocean acidification and the geological past. In marine pelagic environments coccolithophores, foraminifera and pteropods have been considered the main calcifying organisms. Here, we document the presence of an abundant, previously unaccounted fraction of marine calcium carbonate particles in seawater, presumably formed by bacteria or in relation to extracellular polymeric substances. The particles occur in a variety of different morphologies, in a size range from <1 to >100 µm, and in a typical concentration of 104–105 particles L−1 (size range counted 1–100 µm). Quantitative estimates of annual averages suggests that the pure calcium particles we counted in the 1–100 µm size range account for 2–4 times more CaCO3 than the dominating coccolithophoride Emiliania huxleyi and for 21% of the total concentration of particulate calcium. Due to their high density, we hypothesize that the particles sediment rapidly, and therefore contribute significantly to the export of carbon and alkalinity from surface waters. The biological and environmental factors affecting the formation of these particles and possible impact of this process on global atmospheric CO2 remains to be investigated. PMID:23110119

Limited contribution of ancient methane to surface waters of the U.S. Beaufort Sea shelf

NASA Astrophysics Data System (ADS)

Sparrow, K. J.; Kessler, J. D.

2017-12-01

In response to climate change, methane can be released to ocean sediments and waters from thawing subsea permafrost and decomposing methane hydrates. However, it is unknown if methane derived from these massive stores of frozen, ancient carbon reaches the atmosphere. We quantified the fraction of methane sourced from ancient carbon in shelf waters of the U.S. Beaufort Sea, a region that has both permafrost and methane hydrates and is experiencing significant warming. While the radiocarbon-methane analyses indicate that ancient carbon is being mobilized and emitted as methane into shelf bottom waters, surprisingly, we find that modern sources of methane predominate in surface waters of relatively shallow mid-outer shelf stations. These results suggest that even if there is a heightened liberation of ancient methane as climate change proceeds, oceanic dispersion and oxidation processes can strongly limit its emission to the atmosphere.

The reduction in the biomass of cyanobacterial N2 fixer and the biological pump in the Northwestern Pacific Ocean

PubMed Central

Kim, Dongseon; Jeong, Jin-Hyun; Kim, Tae-Wook; Noh, Jae Hoon; Kim, Hyung Jeek; Choi, Dong Han; Kim, Eung; Jeon, Dongchull

2017-01-01

The comparison of sediment trap data with physical and biogeochemical variables in the surface water column of the Tropical Northwestern Pacific Ocean (TNWPO) indicated that the magnitude of the springtime biological pump has reduced with time due to a corresponding decrease in the biomass of cyanobacterial N2 fixer. The decrease in the biomass of N2 fixer likely resulted from a reduction in phosphate concentrations in response to surface water warming and consequent shoaling of the mixed layer depth during the study period (2009−2014). The same reduction in biological pump was also observed during summer. However, the cause of the summer reduction remains uncertain and is worth assessing in future studies. Our findings have major implications for predicting future trends of the biological pump in the TNWPO, where significant warming has occurred. PMID:28155909

Carbon release by off-axis magmatism in a young sedimented spreading centre

NASA Astrophysics Data System (ADS)

Lizarralde, Daniel; Soule, S. Adam; Seewald, Jeff S.; Proskurowski, Giora

2011-01-01

Continental rifting creates narrow ocean basins, where coastal ocean upwelling results in high biological productivity and organic-rich sedimentation. In addition, topographic gradients promote silicate weathering, which consumes atmospheric CO2 (ref. 1). The carbon flux associated with these processes has led to the suggestion that rifting may cool the atmosphere, leading in some cases to glaciation and even a snowball Earth scenario. Guaymas basin, within the Gulf of California, is a young spreading system where new igneous crust is formed beneath a layer of organic-rich sediment that is 1-2kmthick. Here we present seismic data from Guaymas basin that image recent, basin-wide magmatic intrusions into sediments; sonar backscatter and seafloor photographs that indicate numerous, broadly distributed chemosynthetic seafloor biological communities, and geochemical analyses of water samples suggesting that the methane that supports these communities is derived from magma-driven thermogenic alteration of sediments. Our results suggest that active shallow magmatism releases carbon from sediments up to 50km away from the plate boundary. This is a much larger area than the less than 5km found at unsedimented mid-ocean ridges, and than previously recognized. We conclude that thick sediments may promote broad magmatism, reducing the efficiency of natural carbon sequestration within young sedimented rifts.

The geologic records of dust in the Quaternary

USGS Publications Warehouse

Muhs, Daniel R.

2013-01-01

Study of geologic records of dust composition, sources and deposition rates is important for understanding the role of dust in the overall planetary radiation balance, fertilization of organisms in the world’s oceans, nutrient additions to the terrestrial biosphere and soils, and for paleoclimatic reconstructions. Both glacial and non-glacial processes produce fine-grained particles that can be transported by the wind. Geologic records of dust flux occur in a number of depositional archives for sediments: (1) loess deposits; (2) lake sediments; (3) soils; (4) deep-ocean basins; and (5) ice sheets and smaller glaciers. These archives have several characteristics that make them highly suitable for understanding the dynamics of dust entrainment, transport, and deposition. First, they are often distributed over wide geographic areas, which permits reconstruction of spatial variation of dust flux. Second, a number of dating methods can be applied to sediment archives, which allows identification of specific periods of greater or lesser dust flux. Third, aeolian sediment particle size and composition can be determined so that dust source areas can be ascertained and dust transport pathways can be reconstructed. Over much of the Earth’s surface, dust deposition rates were greater during the last glacial period than during the present interglacial period. A dustier Earth during glacial periods is likely due to increased source areas, greater aridity, less vegetation, lower soil moisture, possibly stronger winds, a decreased intensity of the hydrologic cycle, and greater production of dust-sized particles from expanded ice sheets and glaciers.

Hazard potential of widespread but hidden historic offshore heavy metal (Pb, Zn) contamination (Gulf of Cadiz, Spain).

PubMed

Hanebuth, Till J J; King, Mary Lee; Mendes, Isabel; Lebreiro, Susana; Lobo, Francisco J; Oberle, Ferdinand K; Antón, Laura; Ferreira, Paulo Alves; Reguera, Maria Isabel

2018-05-10

Natural and human-induced seabed sediment disturbances affect wide areas of the global coastal ocean. These recurrent to chronic disturbances mobilize significant amounts of material, including substances that have the potential to significantly harm the environment once re-released. This very challenging issue is difficult to deal with if sub-surface contaminant concentrations are unknown. Based on the analysis of 11 new, up to 5-m long sediment cores taken offshore in the Gulf of Cadiz, the contamination history (using the trace elements lead and zinc) is well documented over major parts of the gulf. Ore mining and metal processing industries on the southwestern Iberian Peninsula started five thousand years ago and experienced a first peak during the Roman Period, which can be detected over the entire gulf. The Industrial Era added a massive, shelf-wide heavy metal excursion of unprecedented dimension. This metal contamination to the coastal ocean decreased in the 1990s and appears to be today limited to larger areas off the Tinto/Odiel and Guadiana River mouths. The unforeseen, significant finding of this study is that the gulf-wide, peak heavy metal concentration, stemming from the Industrial Era, is widely overlain by a modern sediment veneer just thick enough to cover the contaminant horizon, but thin enough to have this layer within the reach of natural or human-induced sediment mobilization events. Published by Elsevier B.V.

Lithospheric thickness jumps at the S-Atlantic continental margins from satellite gravity data and modelled isostatic anomalies

NASA Astrophysics Data System (ADS)

Shahraki, Meysam; Schmeling, Harro; Haas, Peter

2018-01-01

Isostatic equilibrium is a good approximation for passive continental margins. In these regions, geoid anomalies are proportional to the local dipole moment of density-depth distributions, which can be used to constrain the amount of oceanic to continental lithospheric thickening (lithospheric jumps). We consider a five- or three-layer 1D model for the oceanic and continental lithosphere, respectively, composed of water, a sediment layer (both for the oceanic case), the crust, the mantle lithosphere and the asthenosphere. The mantle lithosphere is defined by a mantle density, which is a function of temperature and composition, due to melt depletion. In addition, a depth-dependent sediment density associated with compaction and ocean floor variation is adopted. We analyzed satellite derived geoid data and, after filtering, extracted typical averaged profiles across the Western and Eastern passive margins of the South Atlantic. They show geoid jumps of 8.1 m and 7.0 m for the Argentinian and African sides, respectively. Together with topography data and an averaged crustal density at the conjugate margins these jumps are interpreted as isostatic geoid anomalies and yield best-fitting crustal and lithospheric thicknesses. In a grid search approach five parameters are systematically varied, namely the thicknesses of the sediment layer, the oceanic and continental crusts and the oceanic and the continental mantle lithosphere. The set of successful models reveals a clear asymmetry between the South Africa and Argentine lithospheres by 15 km. Preferred models predict a sediment layer at the Argentine margin of 3-6 km and at the South Africa margin of 1-2.5 km. Moreover, we derived a linear relationship between, oceanic lithosphere, sediment thickness and lithospheric jumps at the South Atlantic margins. It suggests that the continental lithospheres on the western and eastern South Atlantic are thicker by 45-70 and 60-80 km than the oceanic lithospheres, respectively.

Discriminating between natural and anthropogenic features of the sedimentary record in the coastal Beaufort Sea

NASA Astrophysics Data System (ADS)

Trefry, J. H.; Trocine, R. P.; Fox, A. L.; Fox, S. L.; Durell, G.; Kasper, J.

2016-02-01

The coastal Beaufort Sea is at a crossroads with respect to the impacts of human activities. Accurate discrimination of regional and global anthropogenic impacts, versus those due to natural physical and biogeochemical processes, is an important tool for managing environmental issues in the Arctic. We have investigated several natural and anthropogenic features in age-dated sediment cores from the coastal Beaufort Sea. For example, Hg enrichment (by 20 to >50% or +20 to 40 ng/g) was identified in some surface sediments using Hg/Al ratios in cores from nearshore, outer shelf and slope environments. Nearshore Hg anomalies, although quite limited in number, have been linked to drilling fluids deposited during oil and gas exploration in the 1980s. In contrast, similar offshore Hg anomalies are likely due to natural sediment diagenesis as previously noted by others in the deeper Arctic Ocean. We also found Ba enrichment in surface sediments that can be best explained by the deposition of natural, Ba-rich suspended particles from the Colville River; yet, Ba enrichment can sometimes be explained by the presence of drilling fluids in sediments near historic drilling sites. Human induced diagenetic changes are likely to follow current increases in river runoff and coastal erosion. Higher deposition rates for sediment and organic carbon in the coastal Beaufort Sea may create future anomalies for As, Cd and other metals. For example, metal anomalies can presently be found in older subsurface sediments where a layer of carbon-rich sediment was previously deposited. Correct identification of natural versus anthropogenic forcing factors that lead to distinct diagenetic features in the sedimentary record will help us to identify problem areas and make informed regulatory decisions.

An Inverse Method for Obtaining the Attenuation Profile and Small Variations in the Sound Speed and Density Profiles of the Ocean Bottom.

DTIC Science & Technology

1985-05-01

Source level in decibels SBL Sub-bottom loss TL Transmission loss of signal going through the water/sediment interface -- 4 - • .’ I.. zL...explained in the legend to figure 3-1. ’-4 RLb - S-BL-2Oog2D-2aD (3.1) RL8b S- TLb- SBL -TLW-2az-2Olog(D+z)-2aD (3.2) jZ h𔃾 -57- OCEAN SURFACE...RLb -RLab= SBL + [TL,+TL,-BL-201og2D" + 2az + 20log(D+z). (3.3) Assuming that the term within the bracket remains constant for the entire wedge, we

Atlantic Ocean Circulation and Climate: The Current View From the Geological Record

NASA Astrophysics Data System (ADS)

Curry, W.

2006-12-01

Several recent advances in our understanding of past ocean circulation come from geological reconstructions using deep sea sediment proxies of water mass structure and flow. Put together, the observations suggest that the Atlantic Ocean during the last glacial period (21,000 years ago) was very different from today. Geochemical tracers document a shoaling of North Atlantic Deep Water and a much greater volume of deep waters with an Antarctic origin. Sedimentary pore water profiles have detected a reversal in the salinity gradient between northern and southern deep water sources. Uranium-series decay products in North Atlantic sediments indicate that the southward transport of North Atlantic Deep Water was as much as 30-40% reduced from today's transport. Ocean-margin density reconstructions are consistent with a one third reduction in transport through the Florida Straits. A reversed cross-basin density gradient in the South Atlantic calls for a different intermediate water circulation in the South Atlantic. The glacial Atlantic circulation appears to be best explained by a reduced influence of North Atlantic deep water sources and much greater influence of Antarctic deep water sources. More recent changes in Atlantic circulation have been much more modest. During the Little Ice Age (LIA - a much smaller cooling event about 200 to 600 years ago), transport of the Florida Current was reduced by about 10%, significant but a much smaller reduction than observed during the glacial period. There is little evidence for a change in the distribution or geochemistry of the water masses during the LIA. For both climate events (the glacial and the LIA) reduced Florida Current transport was accompanied by increased salinity of its surface waters, linking changes in ocean circulation to large scale changes in surface water hydrology. A feedback between the circulation of the Atlantic Ocean and the climate of the tropics has been proposed before and also seen in some coupled climate models: variations in the temperature gradients in the Atlantic basin affect the position of the Intertropical Convergence Zone and alter evaporation and precipitation patterns in the tropics. The salinity anomalies caused by these atmospheric shifts eventually are transported back to high latitudes by ocean circulation (Vellinga and Wu, 2004). Several recent geological reconstructions appear to observe such a coupling on centennial and millennial time scales.

Warming and surface ocean acidification over the last deglaciation: implications for foraminiferal assemblages

NASA Astrophysics Data System (ADS)

Dyez, K. A.; Hoenisch, B.; deMenocal, P. B.

2017-12-01

Although plankton drift with ocean currents, their presence and relative abundance varies across latitudes and environmental seawater conditions (e.g. temperature, pH, salinity). While earlier studies have focused on temperature as the primary factor for determining the regional species composition of planktic foraminiferal communities, evidence has recently been presented that foraminiferal shell thickness varies with ocean pH, and it remains unclear whether ongoing ocean acidification will cause ecological shifts within this plankton group. The transition from the last glacial maximum (LGM; 19,000-23,000 years B.P.) to the late Holocene (0-5,000 years B.P.) was characterized by both warming and acidification of the surface ocean, and thus provides an opportunity to study ecosystem shifts in response to these environmental changes. Here we provide new δ11B, Mg/Ca, and δ18O measurements from a suite of global sediment cores spanning this time range. We use these geochemical data to reconstruct ocean temperature, pH and salinity and pair the new data with previously published analyses of planktic foraminifera assemblages to study the respective effects of ocean warming and acidification on the foraminiferal habitat. At most open-ocean sample locations, our proxies indicate warming and acidification similar to previously published estimates, but in some marginal seas and coastal locations pH changes little between over the glacial termination. At face value, these observations suggest that warming is generally more important for ecosystem changes than acidification, at least over the slow rates of warming and ocean acidification in this time period. While geochemical data collection is being completed, we aim to include these data in an ecological model of foraminiferal habitat preferences.

Connectivity of microbial populations in coral reef environments: microbiomes of sediment, fish and water

NASA Astrophysics Data System (ADS)

Biddle, J.; Leon, Z. R.; McCargar, M.; Drew, J.

2016-12-01

The benthic environments of coral reefs are heavily shaped by physiochemical factors, but also the ecological interactions of the animals and plants in the reef ecosystem. Microbial populations may be shared between the ecosystem of sediments, seagrasses and reef fish, however it is unknown to what degree. We investigated the potential connections between the microbiomes of sediments, seagrass blades and roots (Syringodium isoetifolium), Surgeonfish (A. nigricauda, Acanthurinae sp. unknown, C. striatus) and Parrotfish (C. spinidens) guts in reef areas of Fiji. We contrasted these with sediment samples from the Florida Keys and ocean water microbiomes from the Atlantic, Pacific and Indian Oceans. In general, we see a higher diversity of sediment microbial communities in Fiji compared to the Florida Keys. However, many of the same taxa are shared in these chemically similar environments, whereas the ocean water environments are completely distinct with few overlapping groups. We were able to show connectivity of a core microbiome between seagrass, fish and sediments in Fiji, including identifying a potential environmental reservoir of a surgeonfish symbiont, Epulopiscum. Finally, we show that fish guts have different microbial populations from crop to hindgut, and that microbial populations differ based on food source. The connection of these ecosystems suggest that the total microbiome of these environments may vary as their animal inhabitants shift in a changing ocean.

Arctic Ocean circulation during the anoxic Eocene Azolla event

NASA Astrophysics Data System (ADS)

Speelman, Eveline; Sinninghe Damsté, Jaap; März, Christian; Brumsack, Hans; Reichart, Gert-Jan

2010-05-01

The Azolla interval, as encountered in Eocene sediments from the Arctic Ocean, is characterized by organic rich sediments ( 4wt% Corg). In general, high levels of organic matter may be caused by increased productivity, i.e. extensive growth of Azolla, and/or enhanced preservation of organic matter, or a combination of both. Anoxic (bottom) water conditions, expanded oxygen minimum zones, or increased sedimentation rates all potentially increase organic matter preservation. According to plate tectonic, bathymetric, and paleogeographic reconstructions, the Arctic Ocean was a virtually isolated shallow basin, with one possible deeper connection to the Nordic Seas represented by a still shallow Fram Strait (Jakobsson et al., 2007), hampering ventilation of the Arctic Basin. During the Azolla interval surface waters freshened, while at the same time bottom waters appear to have remained saline, indicating that the Arctic was highly stratified. The restricted ventilation and stratification in concert with ongoing export of organic matter most likely resulted in the development of anoxic conditions in the lower part of the water column. Whereas the excess precipitation over evaporation maintained the freshwater lid, sustained input of Nordic Sea water is needed to keep the deeper waters saline. To which degree the Arctic Ocean exchanged with the Nordic Seas is, however, still largely unknown. Here we present a high-resolution trace metal record (ICP-MS and ICP-OES) for the expanded Early/Middle Eocene section capturing the Azolla interval from Integrated Ocean Drilling Program (IODP) Expedition 302 (ACEX) drilled on the Lomonosov Ridge, central Arctic Ocean. Euxinic conditions throughout the interval resulted in the efficient removal of redox sensitive trace metals from the water column. Using the sedimentary trace metal record we also constrained circulation in the Arctic Ocean by assessing the relative importance of trace metal input sources (i.e. fluvial, eolian, and through seawater inflow). Excess vanadium accumulation during the Azolla event (80 ppm), basin volume and surface area, average vanadium sea (1.8 ppb) and river water (1.0 ppb) concentrations, together indicate that an inflow of Nordic Sea water of 0.2 Sv is needed to sustain vanadium levels. The same calculation using molybdenum gives an inflow of only 0.02 Sv. These low inflow rates imply Arctic Ocean (deep) water residence times of 2000 - 20000 years, respectively. Based on climate modeling we calculated a summed net amount of precipitation for the Eocene Arctic Basin (Precipitation - Evaporation + Runoff) of 0.46 Sv. Together these notions indicate that a compensating inflow of saline North Atlantic water occurred, accompanied by an outflow of more fresh waters, resulting in a bi-directional, two-layer flow through the (proto-) Fram Strait. Consequently, the limited exchange of water through the Fram Strait implies that a relatively low export productivity would have been sufficient to render Arctic bottom waters anoxic. Jakobsson, M., Backman, J., Rudels, B., Nycander, J., Frank, M., Mayer, L., Jokat, W., Sangiorgi, F., O'Regan, M., Brinkhuis, H., King, J., Moran, K. (2007). The early Miocene onset of a ventilated circulation regimen in the Arctic Ocean. Nature 447, 986-990.

Influence of the hydrodynamic conditions on the accessibility of the demersal species to the deep water trawl fishery off the Balearic Islands (western Mediterranean)

NASA Astrophysics Data System (ADS)

Amores, A.; Rueda, L.; Monserrat, S.; Guijarro, B.; Pasqual, C.; Massutí, E.

2013-12-01

Ocean mean surface vorticity from gridded multi-mission satellite altimetry data was explored in the Western Mediterranean basin for the period 2000-2010, with the aim of comparing its variability with several species of the deep water fishery in the area. Monthly catches per unit of effort (CPUE) of adult red shrimp (Aristeus antennatus), reported in the deep water bottom trawl fishery developed off northern Mallorca Island displayed a good correlation with surface vorticity. This correlation could be explained by assuming that most of the surface vorticity episodes could reach the bottom, increasing the seabed velocities and producing sediment resuspensions, which could affect the near bottom water turbidity. A. antennatus would respond to this increased turbidity by moving downwards to the deeper waters. This massive displacement of red shrimp specimens away from the fishing grounds would consequently decrease their accesibility to fishing exploitation. This relationship between vorticity and catches also holds for other species , considered as by-catch of the deep water fishery in the area. Results appear to support the suggestion that the water turbidity generated by the vorticy episodes is significant enough to affect the dynamics of the demersal species. The way the surface vorticity observed can affect the bottom sediments is also investigated using a year-long moored near-bottom currentmeter and a sediment trap sited in the fishing grounds.

Amino acid epimerization implies rapid sedimentation rates in Arctic Ocean cores

USGS Publications Warehouse

Sejrup, H.P.; Miller, G.H.; Brigham-Grette, J.; Lovlie, R.; Hopkins, D.

1984-01-01

The palaeooceanography of the Arctic Ocean is less well known than any other ocean basin, due to difficulties in obtaining cores and in providing a secure chronological framework for those cores that have been raised. Most recent investigators have suggested that low sedimentation rates (0.05-0.1 cm kyr-1) have characterized the deep basins over the past 5 Myr (refs 1,2) despite the glacial-marine character of the sediment and proximity to major centres of shelf glaciation. These calculations have been primarily based on the down-core pattern in the inclination of magnetic minerals, supported by uranium-series, 14C and micropalaeontological evidence. Here we analyse amino acid diagnesis in foraminifera from two gravity cores raised from the floor of the Arctic Ocean, our results suggest that these cores span <200 kyr., conflicting with the earlier estimate of 3 Myr based on palaeomagnetic data. The chronology of other Arctic Ocean cores and previous palaeoenvironmental interpretations need re-evaluation. ?? 1984 Nature Publishing Group.

The Effects of Sediment Properties on Low Frequency Acoustic Propagation

DTIC Science & Technology

2014-09-30

identified in task (a). c. Understanding the effect of ocean acidification on acoustic propagation. The PIs (Miller and Potty) are trying to get funding...the half-space. The properties of the sediment used in the model calculation are shown in the top panel. b. Effect of Ocean Acidification on...Acoustic Propagation: One of the consequences of increasing atmospheric CO2 is ocean acidification . The reduction in pH is a direct result of increased

Pu isotopes in the western North Pacific Ocean before the accident at Fukushima Dai-ichi Nuclear Power Station

NASA Astrophysics Data System (ADS)

Yamada, M.; Zheng, J.; Aono, T.

2011-12-01

Anthropogenic radionuclides such as Pu-239 (half-life: 24100 yr), Pu-240 (half-life: 6560 yr) and Pu-241 (half-life: 14.325 yr) mainly have been released into the environment as the result of atmospheric nuclear weapons testing. In the North Pacific Ocean, two distinct sources of Pu isotopes can be identified; i.e., the global stratospheric fallout and close-in tropospheric fallout from nuclear weapons testing at the Pacific Proving Grounds in the Marshall Islands. The atom ratio of Pu-240/Pu-239 is a powerful fingerprint to identify the sources of Pu in the ocean. The Pu-240/Pu-239 atom ratios in seawater and marine sediment samples collected in the western North Pacific before the accident at Fukushima Dai-ichi Nuclear Power Station will provide useful background data for understanding the process controlling Pu transport and for distinguishing future Pu sources. The atom ratios of Pu-240/Pu-239 in water columns from the Yamato and Tsushima Basins in the Japan Sea were significantly higher than the mean global fallout ratio of 0.18; however, there were no temporal variation of atom ratios during the period from 1984 to 1993 in the Japan Sea. The total Pu-239+240 inventories in the whole water columns were approximately doubled during the period from 1984 to 1993 in the two basins. The atom ratio of Pu-240/Pu-239 in surface water from Sagami Bay, western North Pacific Ocean, was 0.224 and showed no notable variation from the surface to the bottom with the mean atom ratio being 0.234. The atom ratios for the Pacific coast, near the Rokkasho nuclear fuel reprocessing plant, were approximately the same as the 0.224 ratio obtained from Sagami Bay, western North Pacific margin. The atom ratios in the surficial sediments from Sagami Bay ranged from 0.229 to 0.247. The mean atom ratio in the sediment columns in the East China Sea ranged from 0.248 for the Changjiang estuary to 0.268 for the shelf edge. The observed atom ratios were significantly higher than the mean global fallout ratio of 0.180, proving the existence of close-in fallout Pu originating from the Pacific Proving Grounds. The North Equatorial Current and Kuroshio Current were proposed as pathways for transporting Pacific Proving Grounds-origin Pu to the western North Pacific Ocean.

Glacial reduction and millennial-scale variations in Drake Passage throughflow

PubMed Central

Lamy, Frank; Arz, Helge W.; Kilian, Rolf; Lange, Carina B.; Lembke-Jene, Lester; Wengler, Marc; Kaiser, Jérôme; Baeza-Urrea, Oscar; Hall, Ian R.; Harada, Naomi; Tiedemann, Ralf

2015-01-01

The Drake Passage (DP) is the major geographic constriction for the Antarctic Circumpolar Current (ACC) and exerts a strong control on the exchange of physical, chemical, and biological properties between the Atlantic, Pacific, and Indian Ocean basins. Resolving changes in the flow of circumpolar water masses through this gateway is, therefore, crucial for advancing our understanding of the Southern Ocean’s role in global ocean and climate variability. Here, we reconstruct changes in DP throughflow dynamics over the past 65,000 y based on grain size and geochemical properties of sediment records from the southernmost continental margin of South America. Combined with published sediment records from the Scotia Sea, we argue for a considerable total reduction of DP transport and reveal an up to ∼40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude, millennial-scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply an enhanced export of northern ACC surface and intermediate waters into the South Pacific Gyre and reduced Pacific–Atlantic exchange through the DP (“cold water route”). We conclude that changes in DP throughflow play a critical role for the global meridional overturning circulation and interbasin exchange in the Southern Ocean, most likely regulated by variations in the westerly wind field and changes in Antarctic sea ice extent. PMID:26417070

Basin-scale estimates of pelagic and coral reef calcification in the Red Sea and Western Indian Ocean.

PubMed

Steiner, Zvi; Erez, Jonathan; Shemesh, Aldo; Yam, Ruth; Katz, Amitai; Lazar, Boaz

2014-11-18

Basin-scale calcification rates are highly important in assessments of the global oceanic carbon cycle. Traditionally, such estimates were based on rates of sedimentation measured with sediment traps or in deep sea cores. Here we estimated CaCO3 precipitation rates in the surface water of the Red Sea from total alkalinity depletion along their axial flow using the water flux in the straits of Bab el Mandeb. The relative contribution of coral reefs and open sea plankton were calculated by fitting a Rayleigh distillation model to the increase in the strontium to calcium ratio. We estimate the net amount of CaCO3 precipitated in the Red Sea to be 7.3 ± 0.4·10(10) kg·y(-1) of which 80 ± 5% is by pelagic calcareous plankton and 20 ± 5% is by the flourishing coastal coral reefs. This estimate for pelagic calcification rate is up to 40% higher than published sedimentary CaCO3 accumulation rates for the region. The calcification rate of the Gulf of Aden was estimated by the Rayleigh model to be ∼1/2 of the Red Sea, and in the northwestern Indian Ocean, it was smaller than our detection limit. The results of this study suggest that variations of major ions on a basin scale may potentially help in assessing long-term effects of ocean acidification on carbonate deposition by marine organisms.

Toward explaining the Holocene carbon dioxide and carbon isotope records: Results from transient ocean carbon cycle-climate simulations

NASA Astrophysics Data System (ADS)

Menviel, L.; Joos, F.

2012-03-01

The Bern3D model was applied to quantify the mechanisms of carbon cycle changes during the Holocene (last 11,000 years). We rely on scenarios from the literature to prescribe the evolution of shallow water carbonate deposition and of land carbon inventory changes over the glacial termination (18,000 to 11,000 years ago) and the Holocene and modify these scenarios within uncertainties. Model results are consistent with Holocene records of atmospheric CO2 and δ13C as well as the spatiotemporal evolution of δ13C and carbonate ion concentration in the deep sea. Deposition of shallow water carbonate, carbonate compensation of land uptake during the glacial termination, land carbon uptake and release during the Holocene, and the response of the ocean-sediment system to marine changes during the termination contribute roughly equally to the reconstructed late Holocene pCO2 rise of 20 ppmv. The 5 ppmv early Holocene pCO2 decrease reflects terrestrial uptake largely compensated by carbonate deposition and ocean sediment responses. Additional small contributions arise from Holocene changes in sea surface temperature, ocean circulation, and export productivity. The Holocene pCO2 variations result from the subtle balance of forcings and processes acting on different timescales and partly in opposite direction as well as from memory effects associated with changes occurring during the termination. Different interglacial periods with different forcing histories are thus expected to yield different pCO2 evolutions as documented by ice cores.

Basin-scale estimates of pelagic and coral reef calcification in the Red Sea and Western Indian Ocean

PubMed Central

Steiner, Zvi; Erez, Jonathan; Shemesh, Aldo; Yam, Ruth; Katz, Amitai; Lazar, Boaz

2014-01-01

Basin-scale calcification rates are highly important in assessments of the global oceanic carbon cycle. Traditionally, such estimates were based on rates of sedimentation measured with sediment traps or in deep sea cores. Here we estimated CaCO3 precipitation rates in the surface water of the Red Sea from total alkalinity depletion along their axial flow using the water flux in the straits of Bab el Mandeb. The relative contribution of coral reefs and open sea plankton were calculated by fitting a Rayleigh distillation model to the increase in the strontium to calcium ratio. We estimate the net amount of CaCO3 precipitated in the Red Sea to be 7.3 ± 0.4·1010 kg·y−1 of which 80 ± 5% is by pelagic calcareous plankton and 20 ± 5% is by the flourishing coastal coral reefs. This estimate for pelagic calcification rate is up to 40% higher than published sedimentary CaCO3 accumulation rates for the region. The calcification rate of the Gulf of Aden was estimated by the Rayleigh model to be ∼1/2 of the Red Sea, and in the northwestern Indian Ocean, it was smaller than our detection limit. The results of this study suggest that variations of major ions on a basin scale may potentially help in assessing long-term effects of ocean acidification on carbonate deposition by marine organisms. PMID:25368148

Combined simulation of carbon and water isotopes in a global ocean model

NASA Astrophysics Data System (ADS)

Paul, André; Krandick, Annegret; Gebbie, Jake; Marchal, Olivier; Dutkiewicz, Stephanie; Losch, Martin; Kurahashi-Nakamura, Takasumi; Tharammal, Thejna

2013-04-01

Carbon and water isotopes are included as passive tracers in the MIT general circulation model (MITgcm). The implementation of the carbon isotopes is based on the existing MITgcm carbon cycle component and involves the fractionation processes during photosynthesis and air-sea gas exchange. Special care is given to the use of a real freshwater flux boundary condition in conjunction with the nonlinear free surface of the ocean model. The isotopic content of precipitation and water vapor is obtained from an atmospheric GCM (the NCAR CAM3) and mapped onto the MITgcm grid system, but the kinetic fractionation during evaporation is treated explicitly in the ocean model. In a number of simulations, we test the sensitivity of the carbon isotope distributions to the formulation of fractionation during photosynthesis and compare the results to modern observations of δ13C and Δ14C from GEOSECS, WOCE and CLIVAR. Similarly, we compare the resulting distribution of oxygen isotopes to modern δ18O data from the NASA GISS Global Seawater Oxygen-18 Database. The overall agreement is good, but there are discrepancies in the carbon isotope composition of the surface water and the oxygen isotope composition of the intermediate and deep waters. The combined simulation of carbon and water isotopes in a global ocean model will provide a framework for studying present and past states of ocean circulation such as postulated from deep-sea sediment records.

Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene

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

Burls, Natalie J.; Fedorov, Alexey V.; Sigman, Daniel M.

An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, theworld’s largest ocean,where relatively fresh surface waters inhibitNorth Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400–ppmv (parts per million by volume) CO 2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanyingmore » pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redoxsensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming.« less

Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene

PubMed Central

Burls, Natalie J.; Fedorov, Alexey V.; Sigman, Daniel M.; Jaccard, Samuel L.; Tiedemann, Ralf; Haug, Gerald H.

2017-01-01

An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, the world’s largest ocean, where relatively fresh surface waters inhibit North Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400–ppmv (parts per million by volume) CO2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanying pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redox-sensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming. PMID:28924606

Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene

DOE PAGES

Burls, Natalie J.; Fedorov, Alexey V.; Sigman, Daniel M.; ...

2017-09-13

An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, theworld’s largest ocean,where relatively fresh surface waters inhibitNorth Pacific deep convection. We present complementary measurement and modeling evidence that the warm, ~400–ppmv (parts per million by volume) CO 2 world of the Pliocene supported subarctic North Pacific deep-water formation and a Pacific meridional overturning circulation (PMOC) cell. In Pliocene subarctic North Pacific sediments, we report orbitally paced maxima in calcium carbonate accumulation rate, with accompanyingmore » pigment and total organic carbon measurements supporting deep-ocean ventilation-driven preservation as their cause. Together with high accumulation rates of biogenic opal, these findings require vigorous bidirectional communication between surface waters and interior waters down to ~3 km in the western subarctic North Pacific, implying deep convection. Redoxsensitive trace metal data provide further evidence of higher Pliocene deep-ocean ventilation before the 2.73-Ma (million years) transition. This observational analysis is supported by climate modeling results, demonstrating that atmospheric moisture transport changes, in response to the reduced meridional sea surface temperature gradients of the Pliocene, were capable of eroding the halocline, leading to deep-water formation in the western subarctic Pacific and a strong PMOC. This second Northern Hemisphere overturning cell has important implications for heat transport, the ocean/atmosphere cycle of carbon, and potentially the equilibrium response of the Pacific to global warming.« less

Late Quaternary Paleoceanographic Settings in the Central Arctic Ocean as Revealed from the Composition of Coarse Grains on the Alpha-Mendeleev and Lomonosov Ridges

NASA Astrophysics Data System (ADS)

Bazhenova, E.; Spielhagen, R. F.; Kudryavtseva, A.; Voronovich, E.; Stein, R. H.; Krylov, A.

2017-12-01

In the central Arctic Ocean, circulation of surface oceanic currents and trajectories of sea-ice drift generally follow the two main systems, the Beaufort Gyre and the Transpolar Drift. The boundary between the two systems is located above the Lomonosov Ridge but might have been shifted over the Quaternary glacial/interglacial cycles due to changing water masses, sea-ice cover, and wind patterns. Changes in sediment core composition can provide information about the different source areas of material reaching the central part of the Arctic basin, and hence, about the driving paleaoceanographic settings. We will summarize results of completed and ongoing investigations performed on several sediment cores recovered by the German RV "Polarstern" in 2007, 2008, and 2014: PS72/340-5, and PS72/344-3 - on the Mendeleev Ridge; PS70/330-1, and PS70/342-1 - on the Alpha Ridge; PS87/023-1, PS87/030-1, PS87/056-1, and PS2185 - on the Lomonosov Ridge. We focused on the petrographic classification of coarse grains (>0.5 mm) isolated from the sediments. Identification of grain composition was done using an optical binocular. Additionally, grain surface was treated with HCL 10%-solution to check for the presence of detrital carbonates. Clast types were classified following published studies from the Mendeleev and Lomonosov ridges which utilized the same size fractions. The studied cores span the last two glacial/interglacial cycles (ca. 200 kyrs). On the Mendeleev Ridge, total grain counts decrease towards the East Siberian margin (from core PS72/340 to core PS72/344), similar to the bulk dolomite content and the amount of larger dropstones. Sediments are generally very fine-grained throughout the cores. Peaks of all clast types in these two cores are synchronous, probably indicating events of abrupt iceberg discharge. Morphometry of larger dropstones (>2 cm) in these cores clearly indicates iceberg transportation. In cores PS87/056-1 and PS87/070-1 (central Lomonosov Ridge), quartz and carbonate peaks are not observed simultaneously, which can be indicative of two different source areas supplying IRD to these core sites. Morphometry of larger dropstones (>2 cm) indicates both iceberg and sea-ice transport; some material holds evidence of riverine transportation.

Sedimentary regimes at Potter Cove, King George Island, maritime Antarctica - from source to sink

NASA Astrophysics Data System (ADS)

Monien, Donata; Monien, Patrick; Brünjes, Robert M.; Widmer, Tatjana; Schnetger, Bernhard; Brumsack, Hans-Jürgen

2013-04-01

Increased particle run-off due to recently retreated ice masses along the Antarctic margins may play an important role in fertilizing the high-nutrient-low-chlorophyll regions of the Southern Ocean. At Potter Cove, King George Island, maritime Antarctica, small melt water streams at the south-eastern shoreline (Potter Peninsula) discharge up to 1,500 mg L-1 (av. 110 mg L-1) of suspended particle matter (SPM) per day into the coastal water body during the summer seasons. Apart from potential light limitation of plankton growth by the suspension load, the particle run-off affects benthic feeders, possibly changes the depositional regime and the preservation of chemical proxies in the outlet zones, and exports trace elements offshore. In Potter Cove's water column, the average particle size is low, and extreme turbidity events are restricted to the upper five to seven meters. High particle loads are often associated with low salinities, most probably induced by increased onshore precipitation. Sediment traps installed in the inner and outer cove at 5 and 20 m water depth suggest mass accumulation rates of 0.83 and 0.58 g cm-2 yr-1, and 0.13 and 0.11 g cm-2 yr-1 (considering 183 days of sedimentation), respectively. 210Pb measurements of short sediment cores reveal recent sediment accumulation rates of approximately 0.1 to 0.6 g cm-2 yr-1. The SPM sampled in the melt water streams and plumes is chemically different to surface sediments deposited in Potter Cove. Chemical characteristics suggest a significant impact of particle sorting: SPM and outer cove sediments are more clayey, whereas inner cove sediments contain more heavy minerals. Generally, sediment deposits in Potter Cove exhibit coarser grain sizes and are mainly derived from Barton Peninsula (northern shoreline), whereas the SPM consists of more fine-grained material originating from Potter Peninsula eluviations. Sequential leaching of the SPM by ascorbic acid showed that approximately 0.5 to 2% of the total iron (5.9 wt.% Fe) is easily dissolvable, which in turn can be translated into an additional load of approximately 5 to 21 mmol L-1 dissolved Fe2+. In consequence, the results of our three-summer study highlight that the major part of the particle load from the melt water streams are exported to the Southern Ocean rather than being deposited near shore in Potter Cove. These exported particles are rich in easily leachable Fe acting as a natural fertilization to the Fe-limited Southern Ocean.

Sources, degradation and transport of terrigenous organic carbon on the East Siberian Arctic Shelf Seas

NASA Astrophysics Data System (ADS)

Tesi, Tommaso; Semiletov, Igor; Dudarev, Oleg; Gustafsson, Örjan

2013-04-01

Recent studies suggest that the present hydrological regime increase observed in the Arctic rivers is mainly the consequence of the changes in permafrost conditions as a result of climate warming. Given the enormous amount of carbon stored in coastal and terrestrial permafrost the potentially increased supply from this large carbon pool to the coastal Arctic Ocean, possibly associated with a translocated release to the atmosphere as CO2, is considered a plausible scenario in a warming climate. However, there is not sufficient information regarding the reactivity of terrigenous material once supplied to the Arctic Ocean. In this study, we address this critical issue by examining the organic composition of surface sediments collected over extensive scales on the East Siberian Arctic Shelf (ESAS) as part of the International Siberian Shelf Study (ISSS). The ESAS represents by far the largest shelf of the Arctic Ocean. Samples were collected from the inner- to the outer-shelf following the sediment transport pathway in a region between the Lena and the Kolyma rivers. The analytical approach includes the characterization of marine and land-derived carbon using a large number of molecular biomarkers obtained by alkaline CuO oxidation such as lignin-phenols, cutin-derived products, p-hydroxy benzenes, benzoic acids, fatty acids, and dicarboxylic acids. Our results indicated high concentrations of terrigenous material in shallow sediments and a marked decrease of terrestrial biomarkers with increasing distance from the coastline. In parallel, lignin-based degradation proxies suggested highly altered terrigenous carbon in mid- and outer-shelf sediments compared to coastal sediments. Furthermore, the ratio of cutin-derived products over lignin significantly increased along the sediment transport pathway. Considering that cutin is considered to be intrinsically more reactive compared to lignin, high values of this ratio off the coastal region were interpreted as selective transport of fine sediments relatively rich in cutin. Finally, in addition to degradation and sorting processes, our results indicated dilution of land-derived material with marine phytodetritus with increasing distance from the shore. Results from our study indicate that the benthic sediment transport system in the ESAS is quite dynamic and acts as an efficient incinerator of terrigenous material as observed in mid-latitude settings. Therefore, considering the mega-pool of terrigenous carbon susceptible to remobilization because of climate-induced changes, our results suggest future limited burial of this material in mid- and outer-shelf deposits.

Fluvial sediments a summary of source, transportation, deposition, and measurement of sediment discharge

USGS Publications Warehouse

Colby, B.R.

1963-01-01

This paper presents a broad but undetailed picture of fluvial sediments in streams, reservoirs, and lakes and includes a discussion of the processes involved in the movement of sediment by flowing water. Sediment is fragmental material that originates from the chemical or physical disintegration of rocks. The disintegration products may have many different shapes and may range in size from large boulders to colloidal particles. In general, they retain about the same mineral composition as the parent rocks. Rock fragments become fluvial sediment when they are entrained in a stream of water. The entrainment may occur as sheet erosion from land surfaces, particularly for the fine particles, or as channel erosion after the surface runoff has accumulated in streams. Fluvial sediments move in streams as bedload (particles moving within a few particle diameters of the streambed) or as suspended sediment in the turbulent flow. The discharge of bedload varies with several factors, which may include particle size and a type of effective shear on the surface of the streambed. The discharge of suspended sediment depends partly on concentration of moving sediment near the streambed and hence on discharge of bedload. However, the concentration of fine sediment near the streambed varies widely, even for equal flows, and, therefore, the discharge of fine sediment normally cannot be computed theoretically. The discharge of suspended sediment also depends on velocity, turbulence, depth of flow, and fall velocity of the particles. In general, the coarse sediment transported by a stream moves intermittently and is discharged at a rate that depends on properties of the flow and of the sediment. If an ample supply of coarse sediment is available at the surface of the streambed, the discharge of the coarse sediment, such as sand, can be roughly computed from properties of the available sediment and of the flow. On the other hand, much of the fine sediment in a stream usually moves nearly continuously at about the velocity of the flow, and even low flows can transport large amounts of fine sediment. Hence, the discharge of fine sediments, being largely dependent on the availability of fine sediment upstream rather than on the properties of the sediment and of the flow at a cross section, can seldom be computed from properties, other than concentrations based directly on samples, that can be observed at the cross section. Sediment particles continually change their positions in the flow; some fall to the streambed, and others are removed from the bed. Sediment deposits form locally or over large areas if the volume rate at which particles settle to the bed exceeds the volume rate at which particles are removed from the bed. In general, large particles are deposited more readily than small particles, whether the point of deposition is behind a rock, on a flood plain, within a stream channel, or at the entrance to a reservoir, a lake, or the ocean. Most samplers used for sediment observations collect a water-sediment mixture from the water surface to within a few tenths of a foot of the streambed. They thus sample most of the suspended sediment, especially if the flow is deep or if the sediment is mostly fine; but they exclude the bedload and some of the suspended sediment in a layer near the streambed where the suspended-sediment concentrations are highest. Measured sediment discharges are usually based on concentrations that are averages of several individual sediment samples for a cross section. If enough average concentrations for a cross section have been determined, the measured sediment discharge can be computed by interpolating sediment concentrations between sampling times. If only occasional samples were collected, an average relation between sediment discharge and flow can be used with a flow-duration curve to compute roughly the average or the total sediment discharges for any periods of time for which the flow-duration c

The Interior Lowland Plains Unit of Mars: Evidence for a Possible Mud Ocean and Induced Tectonic Deformation

NASA Technical Reports Server (NTRS)

Tanaka, K. L.; Banerdt, W. B.

2000-01-01

We conclude from MOC and MOLA data that the northern plains of Mars were infilled by a sediment-rich, mud ocean. Evidence for subsidence within the north polar basin and reversed channel-floor gradients are consistent with tectonic deformation due to the sediment load.

Biogeochemical flux and phytoplankton succession: A year-long sediment trap record in the Australian sector of the Subantarctic Zone

NASA Astrophysics Data System (ADS)

Wilks, Jessica V.; Rigual-Hernández, Andrés S.; Trull, Thomas W.; Bray, Stephen G.; Flores, José-Abel; Armand, Leanne K.

2017-03-01

The Subantarctic Zone (SAZ) plays a crucial role in global carbon cycling as a significant sink for atmospheric CO2. In the Australian sector, the SAZ exports large quantities of organic carbon from the surface ocean, despite lower algal biomass accumulation in surface waters than other Southern Ocean sectors. We present the first analysis of diatom and coccolithophore assemblages and seasonality, as well as the first annual quantification of bulk organic components of captured material at the base of the mixed layer (500 m depth) in the SAZ. Sediment traps were moored in the SAZ southwest of Tasmania as part of the long-term SAZ Project for one year (September 2003 to September 2004). Annual mass flux at 500 m and 2000 m was composed mainly of calcium carbonate, while biogenic silica made up on average <10% of material captured in the traps. Organic carbon flux was estimated at 1.1 g m-2 y-1 at 500 m, close to the estimated global mean carbon flux. Low diatom fluxes and high fluxes of coccoliths were consistent with low biogenic silica and high calcium carbonate fluxes, respectively. Diatoms and coccoliths were identified to species level. Diatom and coccolithophore sinking assemblages reflected some seasonal ecological succession. A theoretical scheme of diatom succession in live assemblages is compared to successional patterns presented in sediment traps. This study provides a unique, direct measurement of the biogeochemical fluxes and their main biological carbon vectors just below the winter mixed layer depth at which effective sequestration of carbon occurs. Comparison of these results with previous sediment trap deployments at the same site at deeper depths (i.e. 1000, 2000 and 3800 m) documents the changes particle fluxes experience in the lower "twilight zone" where biological processes and remineralisation of carbon reduce the efficiency of carbon sequestration.

Biogeochemical and Microbial Variation across 5500 km of Antarctic Surface Sediment Implicates Organic Matter as a Driver of Benthic Community Structure

PubMed Central

Learman, Deric R.; Henson, Michael W.; Thrash, J. Cameron; Temperton, Ben; Brannock, Pamela M.; Santos, Scott R.; Mahon, Andrew R.; Halanych, Kenneth M.

2016-01-01

Western Antarctica, one of the fastest warming locations on Earth, is a unique environment that is underexplored with regards to biodiversity. Although pelagic microbial communities in the Southern Ocean and coastal Antarctic waters have been well-studied, there are fewer investigations of benthic communities and most have a focused geographic range. We sampled surface sediment from 24 sites across a 5500 km region of Western Antarctica (covering the Ross Sea to the Weddell Sea) to examine relationships between microbial communities and sediment geochemistry. Sequencing of the 16S and 18S rRNA genes showed microbial communities in sediments from the Antarctic Peninsula (AP) and Western Antarctica (WA), including the Ross, Amundsen, and Bellingshausen Seas, could be distinguished by correlations with organic matter concentrations and stable isotope fractionation (total organic carbon; TOC, total nitrogen; TN, and δ13C). Overall, samples from the AP were higher in nutrient content (TOC, TN, and NH4+) and communities in these samples had higher relative abundances of operational taxonomic units (OTUs) classified as the diatom, Chaetoceros, a marine cercozoan, and four OTUs classified as Flammeovirgaceae or Flavobacteria. As these OTUs were strongly correlated with TOC, the data suggests the diatoms could be a source of organic matter and the Bacteroidetes and cercozoan are grazers that consume the organic matter. Additionally, samples from WA have lower nutrients and were dominated by Thaumarchaeota, which could be related to their known ability to thrive as lithotrophs. This study documents the largest analysis of benthic microbial communities to date in the Southern Ocean, representing almost half the continental shoreline of Antarctica, and documents trophic interactions and coupling of pelagic and benthic communities. Our results indicate potential modifications in carbon sequestration processes related to change in community composition, identifying a prospective mechanism that links climate change to carbon availability. PMID:27047451

The fate of river organic carbon in coastal areas: A study in the Rhône River delta using multiple isotopic (δ13C, Δ14C) and organic tracers

NASA Astrophysics Data System (ADS)

Cathalot, C.; Rabouille, C.; Tisnérat-Laborde, N.; Toussaint, F.; Kerhervé, P.; Buscail, R.; Loftis, K.; Sun, M.-Y.; Tronczynski, J.; Azoury, S.; Lansard, B.; Treignier, C.; Pastor, L.; Tesi, T.

2013-10-01

A significant fraction of the global carbon flux to the ocean occurs in River-dominated Ocean Margins (RiOMar) although large uncertainties remain in the cycle of organic matter (OM) in these systems. In particular, the OM sources and residence time have not been well clarified. Surface (0-1 cm) and sub-surface (3-4 cm) sediments and water column particles (bottom and intermediate depth) from the Rhône River delta system were collected in June 2005 and in April 2007 for a multi-proxy study. Lignin phenols, black carbon (BC), proto-kerogen/BC mixture, polycyclic aromatic hydrocarbons (PAHs), carbon stable isotope (δ13COC), and radiocarbon measurements (Δ14COC) were carried out to characterize the source of sedimentary organic material and to address degradation and transport processes. The bulk OM in the prodelta sediment appears to have a predominantly modern terrigenous origin with a significant contribution of modern vascular C3 plant detritus (Δ14COC = 27.9‰, δ13COC = -27.4‰). In contrast, the adjacent continental shelf, below the river plume, seems to be dominated by aged OM (Δ14COC = -400‰, δ13COC = -24.2‰), and shows no evidence of dilution and/or replacement by freshly produced marine carbon. Our data suggest an important contribution of black carbon (50% of OC) in the continental shelf sediments. Selective degradation processes occur along the main dispersal sediment system, promoting the loss of a modern terrestrial OM but also proto-kerogen-like OM. In addition, we hypothesize that during the transport across the shelf, a long term resuspension/deposition loop induces efficient long term degradation processes able to rework such refractory-like material until the OC is protected by the mineral matrix of particles.

Distinct genetic differentiation and species diversification within two marine nematodes with different habitat preference in Antarctic sediments.

PubMed

Hauquier, Freija; Leliaert, Frederik; Rigaux, Annelien; Derycke, Sofie; Vanreusel, Ann

2017-05-30

Dispersal ability, population genetic structure and species divergence in marine nematodes are still poorly understood, especially in remote areas such as the Southern Ocean. We investigated genetic differentiation of species and populations of the free-living endobenthic nematode genera Sabatieria and Desmodora using nuclear 18S rDNA, internal transcribed spacer (ITS) rDNA, and mitochondrial cytochrome oxidase I (COI) gene sequences. Specimens were collected at continental shelf depths (200-500 m) near the Antarctic Peninsula, Scotia Arc and eastern side of the Weddell Sea. The two nematode genera co-occurred at all sampled locations, but with different vertical distribution in the sediment. A combination of phylogenetic (GMYC, Bayesian Inference, Maximum Likelihood) and population genetic (AMOVA) analyses were used for species delimitation and assessment of gene flow between sampling locations. Sequence analyses resulted in the delimitation of four divergent species lineages in Sabatieria, two of which could not be discriminated morphologically and most likely constitute cryptic species. Two species were recognised in Desmodora, one of which showed large intraspecific morphological variation. Both genera comprised species that were restricted to one side of the Weddell Sea and species that were widely spread across it. Population genetic structuring was highly significant and more pronounced in the deeper sediment-dwelling Sabatieria species, which are generally less prone to resuspension and passive dispersal in the water column than surface Desmodora species. Our results indicate that gene flow is restricted at large geographic distance in the Southern Ocean, which casts doubt on the efficiency of the Weddell gyre and Antarctic Circumpolar Current in facilitating circum-Antarctic nematode species distributions. We also show that genetic structuring and cryptic speciation can be very different in nematode species isolated from the same geographic area, but with different habitat preferences (surface versus deeper sediment layers).

Global Distribution of Net Electron Acceptance in Subseafloor Sediment

NASA Astrophysics Data System (ADS)

Fulfer, V. M.; Pockalny, R. A.; D'Hondt, S.

2017-12-01

We quantified the global distribution of net electron acceptance rates (e-/m2/year) in subseafloor sediment (>1.5 meters below seafloor [mbsf]) using (i) a modified version of the chemical-reaction-rate algorithm by Wang et al. (2008), (ii) physical properties and dissolved oxygen and sulfate data from interstitial waters of sediment cores collected by the Ocean Drilling Program, Integrated Ocean Drilling Program, International Ocean Discovery Program, and U.S. coring expeditions, and (iii) correlation of net electron acceptance rates to global oceanographic properties. Calculated net rates vary from 4.8 x 1019 e-/m2/year for slowly accumulating abyssal clay to 1.2 x 1023 e-/m2/year for regions of high sedimentation rate. Net electron acceptance rate correlates strongly with mean sedimentation rate. Where sedimentation rate is very low (e.g., 1 m/Myr), dissolved oxygen penetrates more than 70 mbsf and is the primary terminal electron acceptor. Where sedimentation rate is moderate (e.g., 3 to 60 m/Myr), dissolved sulfate penetrates as far as 700 mbsf and is the principal terminal electron acceptor. Where sedimentation rate is high (e.g., > 60 m/Myr), dissolved sulfate penetrates only meters, but is the principal terminal electron acceptor in subseafloor sediment to the depth of sulfate penetration. Because microbial metabolism continues at greater depths than the depth of sulfate penetration in fast-accumulating sediment, complete quantification of subseafloor metabolic rates will require consideration of other chemical species.

Spatio-temporal variation of water flow and sediment discharge in the Mahanadi River, India

NASA Astrophysics Data System (ADS)

Bastia, Fakira; Equeenuddin, Sk. Md.

2016-09-01

The transport of sediments by rivers to the oceans represents an important link between the terrestrial and marine ecosystem. Therefore, this work aims to study spatio-temporal variation of the sediment discharge and erosion rate in the Mahanadi river, one of the biggest rivers in India, over past three decades vis-à-vis their controlling factors. To understand the sediment load variation, the trend analysis in the time series data of rainfall, water and sediment discharge of the Mahanadi river were also attempted. The non-parametric Mann-Kendall and Sen's methods were used to determine whether there was a positive or negative trend in the time series data with their statistical significance. The occurrence of abrupt changes was detected using Pettitt test. The trend test result represents that sediment load delivered from the Mahanadi river to the global ocean has decreased sharply at the rate of 0.515 × 106 tons/year between 1980 and 2010. Water discharge and rainfall in the basin showed no significant decreasing trend except at only one tributary. The decline in sediment discharge from the basin to the Bay of Bengal is mainly due to the increase in the number of dams, which has recorded the increase from 70 to 253 during the period of 1980 to 2010. Over the past 30 years the Mahanadi river has discharged about 49.0 ± 20.5 km3 of water and 17.4 ± 12.7 × 106 tons of sediment annually to the Bay of Bengal whereas the mean erosional rate is 265 ± 125 tons/km2/year over the period of 30 years in the basin. Based on the current data (2000-2001 to 2009-2010), sediment flux and water discharge to the ocean are 12 ± 5 × 106 tons/year and 49 ± 16 km3/year respectively; and ranking Mahanadi river second in terms of water discharge and sediment flux to the ocean among the peninsular rivers in India.

Diatom species abundance and morphologically-based dissolution proxies in coastal Southern Ocean assemblages

NASA Astrophysics Data System (ADS)

Warnock, Jonathan P.; Scherer, Reed P.

2015-07-01

Taphonomic processes alter diatom assemblages in sediments, thus potentially negatively impacting paleoclimate records at various rates across space, time, and taxa. However, quantitative taphonomic data is rarely included in diatom-based paleoenvironmental reconstructions and no objective standard exists for comparing diatom dissolution in sediments recovered from marine depositional settings, including the Southern Ocean's opal belt. Furthermore, identifying changes to diatom dissolution through time can provide insight into the efficiency of both upper water column nutrient recycling and the biological pump. This is significant in that reactive metal proxies (e.g. Al, Ti) in the sediments only account for post-depositional dissolution, not the water column where the majority of dissolution occurs. In order to assess the range of variability of responses to dissolution in a typical Southern Ocean diatom community and provide a quantitative guideline for assessing taphonomic variability in diatoms recovered from core material, a sediment trap sample was subjected to controlled, serial dissolution. By evaluating dissolution-induced changes to diatom species' relative abundance, three preservational categories of diatoms have been identified: gracile, intermediate, and robust. The relative abundances of these categories can be used to establish a preservation grade for diatom assemblages. However, changes to the relative abundances of diatom species in sediment samples may reflect taphonomic or ecological factors. In order to address this complication, relative abundance changes have been tied to dissolution-induced morphological change to the areolae of Fragilariopsis curta, a significant sea-ice indicator in Southern Ocean sediments. This correlation allows differentiation between gracile species loss to dissolution versus ecological factors or sediment winnowing. These results mirror a similar morphological dissolution index from a parallel study utilizing Fragilariopsis kerguelensis, suggesting that results are applicable to a broad spectrum of diatoms typically preserved in the sediments.

The impact of wind energy turbine piles on ocean dynamics

NASA Astrophysics Data System (ADS)

Grashorn, Sebastian; Stanev, Emil V.

2016-04-01

The small- and meso-scale ocean response to wind parks has not been investigated in the southern North Sea until now with the help of high-resolution numerical modelling. Obstacles such as e.g. wind turbine piles may influence the ocean current system and produce turbulent kinetic energy which could affect sediment dynamics in the surrounding area. Two setups of the unstructured-grid model SCHISM (Semi-implicit Cross-scale Hydroscience Integrated System Model) have been developed for an idealized channel including a surface piercing cylindrical obstacle representing the pile and a more realistic test case including four exemplary piles. Experiments using a constant flow around the obstacles and a rotating M2 tidal wave are carried out. The resulting current and turbulence patterns are investigated to estimate the influence of the obstacles on the surrounding ocean dynamics. We demonstrate that using an unstructured ocean model provides the opportunity to embed a high-resolution representation of a wind park turbine pile system into a coarser North Sea setup, which is needed in order to perform a seamless investigation of the resulting geophysical processes.

Hydrological Process of Martian Surface in Hesperian epoch

NASA Astrophysics Data System (ADS)

Yamashiki, Y. A.; Sato, H.; Kuroki, R.; Miyamoto, H.; Hemmi, R.

2017-12-01

It is considered that the Mars in Noachian ecoch was much warmer temperature than current condition, with atmosphere and ocean supported by its magnetic actiity. Several valley which seems to be developed by ancient hydrological processes are obsered in Martian surface, is being considered to be built long time before. Some fluvial fun was formed during the following Hesperian epoch, which is considered as much cooler and drier than Noachian epoch. In this study, we applied Hydro-debris 2D model into Martian surface in Hesperian epoch in order to try develping surface vallay formation throughout hydrological processes. Sediment transport and associated small-scale debris-flow occurrence may be the key for valley formation, where might be the micro-habitable zone.

Modeling radiocesium transport from a river catchment based on a physically-based distributed hydrological and sediment erosion model.

PubMed

Kinouchi, Tsuyoshi; Yoshimura, Kazuya; Omata, Teppei

2015-01-01

The accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in March 2011 resulted in the deposition of large quantities of radionuclides, such as (134)Cs and (137)Cs, over parts of eastern Japan. Since then high levels of radioactive contamination have been detected in large areas, including forests, agricultural land, and residential areas. Due to the strong adsorption capability of radiocesium to soil particles, radiocesium migrates with eroded sediments, follows the surface flow paths, and is delivered to more populated downstream regions and eventually to the Pacific Ocean. It is therefore important to understand the transport of contaminated sediments in the hydrological system and to predict changes in the spatial distribution of radiocesium concentrations by taking the land-surface processes related to sediment migration into consideration. In this study, we developed a distributed model to simulate the transport of water and contaminated sediment in a watershed hydrological system, and applied this model to a partially forested mountain catchment located in an area highly contaminated by the radioactive fallout. Observed discharge, sediment concentration, and cesium concentration measured from June 2011 until December 2012 were used for calibration of model parameters. The simulated discharge and sediment concentration both agreed well with observed values, while the cesium concentration was underestimated in the initial period following the accident. This result suggests that the leaching of radiocesium from the forest canopy, which was not considered in the model, played a significant role in its transport from the catchment. Based on the simulation results, we quantified the long-term fate of radiocesium over the study area and estimated that the effective half-life of (137)Cs deposited in the study area will be approximately 22 y due to the export of contaminated sediment by land-surface processes, and the amount of (137)Cs remaining in the catchment will be reduced to 39% of the initial total within 30 y after contamination. This study provides a perspective on the transport of suspended sediments and radiocesium in catchments with similar land use and radiocesium contamination. Copyright © 2014 Elsevier Ltd. All rights reserved.

Insights into Deep-Sea Sediment Fungal Communities from the East Indian Ocean Using Targeted Environmental Sequencing Combined with Traditional Cultivation

PubMed Central

Zhang, Xiao-yong; Tang, Gui-ling; Xu, Xin-ya; Nong, Xu-hua; Qi, Shu-Hua

2014-01-01

The fungal diversity in deep-sea environments has recently gained an increasing amount attention. Our knowledge and understanding of the true fungal diversity and the role it plays in deep-sea environments, however, is still limited. We investigated the fungal community structure in five sediments from a depth of ∼4000 m in the East India Ocean using a combination of targeted environmental sequencing and traditional cultivation. This approach resulted in the recovery of a total of 45 fungal operational taxonomic units (OTUs) and 20 culturable fungal phylotypes. This finding indicates that there is a great amount of fungal diversity in the deep-sea sediments collected in the East Indian Ocean. Three fungal OTUs and one culturable phylotype demonstrated high divergence (89%–97%) from the existing sequences in the GenBank. Moreover, 44.4% fungal OTUs and 30% culturable fungal phylotypes are new reports for deep-sea sediments. These results suggest that the deep-sea sediments from the East India Ocean can serve as habitats for new fungal communities compared with other deep-sea environments. In addition, different fungal community could be detected when using targeted environmental sequencing compared with traditional cultivation in this study, which suggests that a combination of targeted environmental sequencing and traditional cultivation will generate a more diverse fungal community in deep-sea environments than using either targeted environmental sequencing or traditional cultivation alone. This study is the first to report new insights into the fungal communities in deep-sea sediments from the East Indian Ocean, which increases our knowledge and understanding of the fungal diversity in deep-sea environments. PMID:25272044

The role of ocean currents for carbonate platform stratigraphy (Invited)

NASA Astrophysics Data System (ADS)

Betzler, C.; Lindhorst, S.; Luedmann, T.; Eberli, G. P.; Reijmer, J.; Huebscher, C. P.

2013-12-01

Breaks and turnovers in carbonate bank growth and development record fluctuations in sea-level and environmental changes. For the carbonate banks of the Bahamas, the Maldives, the Queensland, and the Marion Plateau, sea-level changes and synchronous oceanographic and atmospheric circulation events were recorded through compositional and architectural changes. Most of these major carbonate edifices contain drift deposits, indicating that oceanic currents were a major driver of carbonate-bank evolution. It is proposed that such currents have a larger imprint on the growth patterns and the stratigraphic packaging of carbonates than previously thought. In the Bahamas, slope facies of carbonate banks exposed to deep oceanic currents are not arranged into sediment-texture controlled and depth-dependant strike-continuous facies belts. Facies patterns are controlled by the interplay of shallow-water input, succeeding sediment sorting as well as redistribution and erosion processes. This complements the classical windward - leeward classification of carbonate platform slopes and accounts for the significant and potentially dominant process of alongslope sediment transport and dispersal. Deep oceanic currents also have the potential to steepen the carbonate bank slopes, through sediment winnowing at the distal slope, such as for example in the Maldives. This process can be enhanced as the bank grows and expands in size which may accelerate currents. Oceanic current onset or amplification, however, may also account for slope steepening as an externally, i.e. climate-driven agent, thus forcing the banks into an aggradation mode of growth which is not a response to sea-level fluctuations or a result of the windward / leeward exposure of the bank edge. Ignorance of the impact of currents on platforms and platform slopes may lead to an erroneous conclusion that changes in sediment production, distribution, and morphologies of sediment bodies are features solely related to sea-level changes.

LOSCAR: Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir Model

NASA Astrophysics Data System (ADS)

Zeebe, R. E.

2011-06-01

The LOSCAR model is designed to efficiently compute the partitioning of carbon between ocean, atmosphere, and sediments on time scales ranging from centuries to millions of years. While a variety of computationally inexpensive carbon cycle models are already available, many are missing a critical sediment component, which is indispensable for long-term integrations. One of LOSCAR's strengths is the coupling of ocean-atmosphere routines to a computationally efficient sediment module. This allows, for instance, adequate computation of CaCO3 dissolution, calcite compensation, and long-term carbon cycle fluxes, including weathering of carbonate and silicate rocks. The ocean component includes various biogeochemical tracers such as total carbon, alkalinity, phosphate, oxygen, and stable carbon isotopes. We have previously published applications of the model tackling future projections of ocean chemistry and weathering, pCO2 sensitivity to carbon cycle perturbations throughout the Cenozoic, and carbon/calcium cycling during the Paleocene-Eocene Thermal Maximum. The focus of the present contribution is the detailed description of the model including numerical architecture, processes and parameterizations, tuning, and examples of input and output. Typical CPU integration times of LOSCAR are of order seconds for several thousand model years on current standard desktop machines. The LOSCAR source code in C can be obtained from the author by sending a request to loscar.model@gmail.com.

Measurement of sediment and crustal thickness corrected RDA for 2D profiles at rifted continental margins: Applications to the Iberian, Gulf of Aden and S Angolan margins

NASA Astrophysics Data System (ADS)

Cowie, Leanne; Kusznir, Nick

2014-05-01

Subsidence analysis of sedimentary basins and rifted continental margins requires a correction for the anomalous uplift or subsidence arising from mantle dynamic topography. Whilst different global model predictions of mantle dynamic topography may give a broadly similar pattern at long wavelengths, they differ substantially in the predicted amplitude and at shorter wavelengths. As a consequence the accuracy of predicted mantle dynamic topography is not sufficiently good to provide corrections for subsidence analysis. Measurements of present day anomalous subsidence, which we attribute to mantle dynamic topography, have been made for three rifted continental margins; offshore Iberia, the Gulf of Aden and southern Angola. We determine residual depth anomaly (RDA), corrected for sediment loading and crustal thickness variation for 2D profiles running from unequivocal oceanic crust across the continental ocean boundary onto thinned continental crust. Residual depth anomalies (RDA), corrected for sediment loading using flexural backstripping and decompaction, have been calculated by comparing observed and age predicted oceanic bathymetries at these margins. Age predicted bathymetric anomalies have been calculated using the thermal plate model predictions from Crosby & McKenzie (2009). Non-zero sediment corrected RDAs may result from anomalous oceanic crustal thickness with respect to the global average or from anomalous uplift or subsidence. Gravity anomaly inversion incorporating a lithosphere thermal gravity anomaly correction and sediment thickness from 2D seismic reflection data has been used to determine Moho depth, calibrated using seismic refraction, and oceanic crustal basement thickness. Crustal basement thicknesses derived from gravity inversion together with Airy isostasy have been used to correct for variations of crustal thickness from a standard oceanic thickness of 7km. The 2D profiles of RDA corrected for both sediment loading and non-standard crustal thickness provide a measurement of anomalous uplift or subsidence which we attribute to mantle dynamic topography. We compare our sediment and crustal thickness corrected RDA analysis results with published predictions of mantle dynamic topography from global models.

Iron Biogeochemistry in the High Latitude North Atlantic Ocean.

PubMed

Achterberg, Eric P; Steigenberger, Sebastian; Marsay, Chris M; LeMoigne, Frédéric A C; Painter, Stuart C; Baker, Alex R; Connelly, Douglas P; Moore, C Mark; Tagliabue, Alessandro; Tanhua, Toste

2018-01-19

Iron (Fe) is an essential micronutrient for marine microbial organisms, and low supply controls productivity in large parts of the world's ocean. The high latitude North Atlantic is seasonally Fe limited, but Fe distributions and source strengths are poorly constrained. Surface ocean dissolved Fe (DFe) concentrations were low in the study region (<0.1 nM) in summer 2010, with significant perturbations during spring 2010 in the Iceland Basin as a result of an eruption of the Eyjafjallajökull volcano (up to 2.5 nM DFe near Iceland) with biogeochemical consequences. Deep water concentrations in the vicinity of the Reykjanes Ridge system were influenced by pronounced sediment resuspension, with indications for additional inputs by hydrothermal vents, with subsequent lateral transport of Fe and manganese plumes of up to 250-300 km. Particulate Fe formed the dominant pool, as evidenced by 4-17 fold higher total dissolvable Fe compared with DFe concentrations, and a dynamic exchange between the fractions appeared to buffer deep water DFe. Here we show that Fe supply associated with deep winter mixing (up to 103 nmol m -2 d -1 ) was at least ca. 4-10 times higher than atmospheric deposition, diffusive fluxes at the base of the summer mixed layer, and horizontal surface ocean fluxes.

Evolutionary and geologic consequences of organic carbon fixing in the primitive anoxic ocean

NASA Astrophysics Data System (ADS)

Berry, W. B. N.; Wilde, P.

1983-03-01

Steps leading to development of the modern photic-based marine food web are postulated as the result of modifications of the environment, enhanced by the activity of Archean sulfur chemoautotrophs. Such organisms (Anoxium) evolved in an anoxic ocean prior to 3.9 × 109 yr ago at Archean analogs of modern oceanic hydrothermal vents. At this time geothermal energy was more readily available to organisms than photic energy, given atmospheric conditions at the surface similar to Venus, where intensity is low and only middle and red visible wavelengths penetrate the cloudy CO2-rich atmosphere. Competition for the reduced sulfur developed due to oxidation and loss of sulfur to sediments. Consequently, evolutionary advantage shifted to Anoxium isolates that could use alternate energy sources such as light to supplement the diminished supplies of reduced sulfur. Initially, photo-sulfur organisms evolved similar to modern purple bacteria that absorb in the red visible spectra. Subsequent carbon fixing and oxidation improved both the quantity and range of light reaching the ocean surface. This permitted absorption in the blue visible range so that water splitting was now feasible, releasing free oxygen and accelerating oxidation. Eventually, reducing environments became restricted, completing the shift in the principal marine carbon-fixing activity from anoxic chemoautotrophic to aerobic photosynthetic organisms.

Dense water plumes modulate richness and productivity of deep sea microbes.

PubMed

Luna, Gian Marco; Chiggiato, Jacopo; Quero, Grazia Marina; Schroeder, Katrin; Bongiorni, Lucia; Kalenitchenko, Dimitri; Galand, Pierre E

2016-12-01

Growing evidence indicates that dense water formation and flow over the continental shelf is a globally relevant oceanographic process, potentially affecting microbial assemblages down to the deep ocean. However, the extent and consequences of this influence have yet to be investigated. Here it is shown that dense water propagation to the deep ocean increases the abundance of prokaryotic plankton, and stimulates carbon production and organic matter degradation rates. Dense waters spilling off the shelf modifies community composition of deep sea microbial assemblages, leading to the increased relevance of taxa likely originating from the sea surface and the seafloor. This phenomenon can be explained by a combination of factors that interplay during the dense waters propagation, such as the transport of surface microbes to the ocean floor (delivering in our site 0.1 megatons of C), the stimulation of microbial metabolism due to increased ventilation and nutrients availability, the sediment re-suspension, and the mixing with ambient waters along the path. Thus, these results highlight a hitherto unidentified role for dense currents flowing over continental shelves in influencing deep sea microbes. In light of climate projections, this process will affect significantly the microbial functioning and biogeochemical cycling of large sectors of the ocean interior. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Numerical investigation of fluid mud motion using a three-dimensional hydrodynamic and two-dimensional fluid mud coupling model

NASA Astrophysics Data System (ADS)

Yang, Xiaochen; Zhang, Qinghe; Hao, Linnan

2015-03-01

A water-fluid mud coupling model is developed based on the unstructured grid finite volume coastal ocean model (FVCOM) to investigate the fluid mud motion. The hydrodynamics and sediment transport of the overlying water column are solved using the original three-dimensional ocean model. A horizontal two-dimensional fluid mud model is integrated into the FVCOM model to simulate the underlying fluid mud flow. The fluid mud interacts with the water column through the sediment flux, current, and shear stress. The friction factor between the fluid mud and the bed, which is traditionally determined empirically, is derived with the assumption that the vertical distribution of shear stress below the yield surface of fluid mud is identical to that of uniform laminar flow of Newtonian fluid in the open channel. The model is validated by experimental data and reasonable agreement is found. Compared with numerical cases with fixed friction factors, the results simulated with the derived friction factor exhibit the best agreement with the experiment, which demonstrates the necessity of the derivation of the friction factor.

The effects of post-accretion sedimentation on the magnetization of oceanic crust

NASA Astrophysics Data System (ADS)

Dyment, J.; Granot, R.

2016-12-01

The presence of marine magnetic anomalies related to seafloor spreading is often considered a key evidence to locate the continent-ocean boundary (COB) at passive margins. Conversely, thermal demagnetization is also advocated to explain the poor shape of such oceanic anomalies under thick sedimentary cover. To investigate the effects of post-accretion sedimentation on marine magnetic anomalies, we focus our study on two conjugate regions of the southern South Atlantic Ocean (Anomalies M4 to M0) that, although formed at the same time and along the same spreading segments, reveal contrasting characters. The anomalies exhibit strong amplitudes (>400 nT) and a well-marked shape off South Africa, where the sediments are less than 3 km-thick, but become weaker ( 200 nT) and much smoother off northern Argentina, where the sedimentary cover is thicker than 5 km. We interpret this observation as reflecting thermal demagnetization of the extrusive layer and its low Curie temperature titanomagnetite. We perform a series of thermo-magnetic models (Dyment and Arkani-Hamed, Geophys. J. Int., 1995, modified to include the sedimentary cover) to simulate the acquisition and loss of remanent magnetization in the oceanic lithosphere. We assume that most of the sediments accumulated shortly after crustal accretion. We investigate a range of possible thermal demagnetization temperatures for the extrusive layer and find that 200°C to 280ºC best explains the observations, in reasonable agreement with Curie temperatures of titanomagnetite, suggesting that most of the extrusive layer may be demagnetized under sediments thicker than 5 km. Thermal demagnetization should therefore be considered while interpreting marine magnetic anomalies for the age and nature of the crust (i.e., continental versus oceanic) in regions with thick sedimentary cover.

231Pa and 230Th in the ocean model of the Community Earth System Model (CESM1.3)

NASA Astrophysics Data System (ADS)

Gu, Sifan; Liu, Zhengyu

2017-12-01

The sediment 231Pa / 230Th activity ratio is emerging as an important proxy for deep ocean circulation in the past. In order to allow for a direct model-data comparison and to improve our understanding of the sediment 231Pa / 230Th activity ratio, we implement 231Pa and 230Th in the ocean component of the Community Earth System Model (CESM). In addition to the fully coupled implementation of the scavenging behavior of 231Pa and 230Th with the active marine ecosystem module (particle-coupled: hereafter p-coupled), another form of 231Pa and 230Th have also been implemented with prescribed particle flux fields of the present climate (particle-fixed: hereafter p-fixed). The comparison of the two forms of 231Pa and 230Th helps to isolate the influence of the particle fluxes from that of ocean circulation. Under present-day climate forcing, our model is able to simulate water column 231Pa and 230Th activity and the sediment 231Pa / 230Th activity ratio in good agreement with available observations. In addition, in response to freshwater forcing, the p-coupled and p-fixed sediment 231Pa / 230Th activity ratios behave similarly over large areas of low productivity on long timescales, but can differ substantially in some regions of high productivity and on short timescales, indicating the importance of biological productivity in addition to ocean transport. Therefore, our model provides a potentially powerful tool to help the interpretation of sediment 231Pa / 230Th reconstructions and to improve our understanding of past ocean circulation and climate changes.

The Cooling Oceanic Lithosphere as Constrained by Surface Wave Dispersion Data

NASA Astrophysics Data System (ADS)

Hogg, C.; Laske, G.

2003-12-01

The tremendous improvement in resolution capabilities of global surface wave phase velocity maps now encourage us to search for anomalies that are caused by mantle plumes. On the other hand, the implications of even large--scale anomalies in such maps are still not well understood. One such anomaly is caused by the cooling oceanic lithosphere. Some studies investigate the cooling effects by fitting thermal models to the 3--dimensional mantle models resulting from tomographic inversions. The inversion of surface wave data for structure at depth is nonunique and the model often depends on the techniques applied. We prefer to compare the dispersion data directly with predictions from thermal models. Simple cooling models produce a signal that is roughly proportional to the square root of age. This signal is typically much smaller than the one caused by other lateral heterogeneity within the Earth's crust and upper mantle. In a careful analysis we are able to extract clear, roughly linear trends, in all major oceans. We explore the parameter space by fitting cooling half space as well as cooling plate models to the data. In the Pacific ocean, our data are inconsistent with standard parameters that are used to fit the observed bathymetry, and perhaps surface heat flux data. Instead of an initial temperature of 1350~deg C in the cooling half space model our data require a lower temperature (around 1200~deg C) to be well fit, especially the Love wave data. Regarding the cooling plate model, our data seem to require a thicker lithosphere to be well fit (135~km instead of the 'standard' 100 ~m). We observe similar trends for the other oceans investigated: the Indian ocean, the South and the North Atlantic oceans. For the Indian ocean in particular, a crust correction (removing the predictions caused by crustal structure including water depth and sediment thickness) is crucial to obtain an internally consistent dataset. For the Atlantic ocean, a large signal remains unexplained. An age--dependent signal is also apparent in the SS-S and PP-P body wave datasets. However, a comprehensive analysis is somewhat hampered for two reasons: 1) the uneven sampling of the data does not allow us to analyze trends in some oceans (e.g. South Atlantic Ocean); 2) the signal in the oldest parts of the oceans appear ''too fast''. We suspect that we observe effects that are deeper--rooted than the lithosphere--asthenosphere system (e.g. subducting slabs). The surface wave dispersion maps contain an intriguing oscillating signal that is particularly strong for Rayleigh waves in the Pacific ocean. This signal is symmetric to the EPR and we speculate that this is caused by current convective processes or by processes at the time when the plates were formed.

Preserved Organic Matter in the Alpine Tethyan Ocean Continental Transition (Totalp unit, Eastern Swiss Alps)

NASA Astrophysics Data System (ADS)

Mateeva, T.; Wolff, G. A.; Kusznir, N.; Wheeler, J.; Manatschal, G.

2015-12-01

Observations at hydrothermal systems in modern ocean settings suggest that methane produced by serpentinization can support methanotrophic bio-systems. An important question is whether such bio-systems are localised or are more pervasive in their association with serpentinized mantle in the subsurface. This has implications for the global importance of the hidden sub-surface bio-systems, the fate of methane and the carbon cycle. The Totalp unit, a remnant of a former Ocean Continent Transition (OCT) exposed in Alps of Eastern Switzerland, has been chosen to investigate the presence or absence of methanotrophic biosystems within serpentinized exhumed mantle in the Alpine Tethyan margin. The Totalp unit is made of serpentinized mantle and ophicalcites overlain by Upper Jurassic to Lower Cretaceous post-rift sediments. The Totalp unit has undergone little Alpine deformation and only a low-grade metamorphic overprint (<200°C). Totalp samples are characterized by total carbon contents of 0.02% to 12.90% and organic carbon contents of 1x10-4 % to 8%. This large range of values reflects the large lithological diversity of this area. The serpentinized peridotite, ophicalcite and post-rift sediments contain hydrocarbons in the form of n-alkanes in the range C20 - C40; isoprenoids, for example pristane and phytane are present in sediments. The organic biological marker distribution is consistent with the temperature history of the OCT (i.e.lower maximum temperature than 200°C). First results from Totalp show evidence for preservation of marine organic matter in the serpentinized mantle and overlying sediments, although there is no evidence that any organic matter is generated from methanotrophic bio-systems. Nevertheless, focussing on Tethyan hydrothermal systems and preserved hydrocarbons will be critical in understanding whether methanotrophic biomarkers can be preserved and if so whether the methane originated from serpentenization.

High-velocity basal sediment package atop oceanic crust, offshore Cascadia: Impacts on plate boundary processes and fluid migration

NASA Astrophysics Data System (ADS)

Peterson, D. E.; Keranen, K. M.

2017-12-01

Differences in fluid pressure and mechanical properties at megathrust boundaries in subduction zones have been proposed to create varying seismogenic behavior. In Cascadia, where large ruptures are possible but little seismicity occurs presently, new seismic transects across the deformation front (COAST cruise; Holbrook et al., 2012) image an unusually high-wavespeed sedimentary unit directly overlying oceanic crust. Wavespeed increases before sediments reach the deformation front, and the well-laminated unit, consistently of 1 km thickness, can be traced for 50 km beneath the accretionary prism before imaging quality declines. Wavespeed is modeled via iterative prestack time migration (PSTM) imaging and increases from 3.5 km/sec on the seaward end of the profile to >5.0 km/s near the deformation front. Landward of the deformation front, wavespeed is low along seaward-dipping thrust faults in the Quaternary accretionary prism, indicative of rapid dewatering along faults. The observed wavespeed of 5.5 km/sec just above subducting crust is consistent with porosity <5% (Erickson and Jarrard, 1998), possibly reflecting enhanced consolidation, cementation, and diagenesis as the sediments encounter the deformation front. Beneath the sediment, the compressional wavespeed of uppermost oceanic crust is 3-4 km/sec, likely reduced by alteration and/or fluids, lowest within a propagator wake. The propagator wake intersects the plate boundary at an oblique angle and changes the degree of hydration of the oceanic plate as it subducts within our area. Fluid flow out of oceanic crust is likely impeded by the low-porosity basal sediment package except along the focused thrust faults. Decollements are present at the top of oceanic basement, at the top of the high-wavespeed basal unit, and within sedimentary strata at higher levels; the decollement at the top of oceanic crust is active at the toe of the deformation front. The basal sedimentary unit appears to be mechanically strong, similar to observations from offshore Sumatra, where strongly consolidated sediments at the deformation front are interpreted to facilitate megathrust rupture to the trench (Hupers et al., 2017). A uniformly strong plate interface at Cascadia may inhibit microseismicity while building stress that is released in great earthquakes.

Glacial-interglacial vegetation dynamics in South Eastern Africa coupled to sea surface temperature variations in the Western Indian Ocean

NASA Astrophysics Data System (ADS)

Dupont, L. M.; Caley, T.; Kim, J.-H.; Castañeda, I.; Malaizé, B.; Giraudeau, J.

2011-11-01

Glacial-interglacial fluctuations in the vegetation of South Africa might elucidate the climate system at the edge of the tropics between the Indian and Atlantic Oceans. However, vegetation records covering a full glacial cycle have only been published from the eastern South Atlantic. We present a pollen record of the marine core MD96-2048 retrieved by the Marion Dufresne from the Indian Ocean ∼120 km south of the Limpopo River mouth. The sedimentation at the site is slow and continuous. The upper 6 m (spanning the past 342 Ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials, the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests. During glacials open mountainous scrubland dominated. Montane forest with Podocarpus extended during humid periods was favoured by strong local insolation. Correlation with the sea surface temperature record of the same core indicates that the extension of mountainous scrubland primarily depends on sea surface temperatures of the Agulhas Current. Our record corroborates terrestrial evidence of the extension of open mountainous scrubland (including fynbos-like species of the high-altitude Grassland biome) for the last glacial as well as for other glacial periods of the past 300 Ka.

Carbon Cycle Model of a Hawaiian Barrier Reef under Rising Ocean Acidification and Temperature Conditions of the Anthropocene

NASA Astrophysics Data System (ADS)

Drupp, P. S.; Mackenzie, F. T.; De Carlo, E. H.; Guidry, M.

2015-12-01

A CO2-carbonic acid system biogeochemical box model (CRESCAM, Coral Reef and Sediment Carbonate Model) of the barrier reef flat in Kaneohe Bay, Hawai'i was developed to determine how increasing temperature and dissolved inorganic carbon (DIC) content of open ocean source waters, resulting from rising anthropogenic CO2 emissions and ocean acidification, affect the CaCO3budget of coral reef ecosystems. CRESCAM consists of 17 reservoirs and 59 fluxes, including a surface water column domain, a two-layer permeable sediment domain, and a coral framework domain. Physical, chemical, and biological processes such as advection, carbonate precipitation/dissolution, and net ecosystem production and calcification were modeled. The initial model parameters were constrained by experimental and field data from previous coral reef studies, mostly in Kaneohe Bay over the past 50 years. The field studies include data collected by our research group for both the water column and sediment-porewater system.The model system, initially in a quasi-steady state condition estimated for the early 21st century, was perturbed using future projections to the year 2100 of the Anthropocene of atmospheric CO2 ­concentrations, temperature, and source water DIC. These perturbations were derived from the most recent (2013) IPCC's Representative Concentration Pathway (RCP) scenarios, which predict CO2 atmospheric concentrations and temperature anomalies out to 2100. A series of model case studies were also performed whereby one or more parameters (e.g., coral calcification response to declining surface water pH) were altered to investigate potential future outcomes. Our model simulations predict that although the Kaneohe Bay barrier reef will likely see a significant decline in NEC over the coming century, it is unlikely to reach a state of net erosion - a result contrary to several global coral reef model projections. In addition, we show that depending on the future response of NEP and NEC to OA and rising temperatures, the surface waters could switch from being a present-day source of CO2 to the atmosphere to a future sink. This ecosystem specific model can be applied to any reef system where data are available to constrain the initial model state and is a powerful tool for examining future changes in coral reef carbon budgets.

Surface area and the seabed area, volume, depth, slope, and topographic variation for the world's seas, oceans, and countries.

PubMed

Costello, Mark John; Cheung, Alan; De Hauwere, Nathalie

2010-12-01

Depth and topography directly and indirectly influence most ocean environmental conditions, including light penetration and photosynthesis, sedimentation, current movements and stratification, and thus temperature and oxygen gradients. These parameters are thus likely to influence species distribution patterns and productivity in the oceans. They may be considered the foundation for any standardized classification of ocean ecosystems and important correlates of metrics of biodiversity (e.g., species richness and composition, fisheries). While statistics on ocean depth and topography are often quoted, how they were derived is rarely cited, and unless calculated using the same spatial resolution the resulting statistics will not be strictly comparable. We provide such statistics using the best available resolution (1-min) global bathymetry, and open source digital maps of the world's seas and oceans and countries' Exclusive Economic Zones, using a standardized methodology. We created a terrain map and calculated sea surface and seabed area, volume, and mean, standard deviation, maximum, and minimum, of both depth and slope. All the source data and our database are freely available online. We found that although the ocean is flat, and up to 71% of the area has a < 1 degree slope. It had over 1 million approximately circular features that may be seamounts or sea-hills as well as prominent mountain ranges or ridges. However, currently available global data significantly underestimate seabed slopes. The 1-min data set used here predicts there are 68,669 seamounts compared to the 30,314 previously predicted using the same method but lower spatial resolution data. The ocean volume exceeds 1.3 billion km(3) (or 1.3 sextillion liters), and sea surface and seabed areas over 354 million km(2). We propose the coefficient of variation of slope as an index of topographic heterogeneity. Future studies may improve on this database, for example by using a more detailed bathymetry, and in situ measured data. The database could be used to classify ocean features, such as abyssal plains, ridges, and slopes, and thus provide the basis for a standards based classification of ocean topography.

Suspended-sediment and fresh-water discharges in the Ob and Yenisey rivers, 1960-1988

USGS Publications Warehouse

Meade, R.H.; Bobrovitskaya, N.N.; Babkin, V.I.

2000-01-01

Of the world's great rivers, the Ob and Yenisey rank among the largest suppliers of fresh water and among the smallest suppliers of suspended sediment to the coastal ocean. Sediment in the middle reaches of the rivers is mobilized from bordering terraces and exchanged between channels and flood plains. Sediment in the lower reaches of these great rivers is deposited and stored (permanently, on a millennial time scale) in flood plains. Sediment discharges, already small under natural conditions, are diminished further by large manmade reservoirs that trap significant proportions of the moving solids. The long winter freeze and sudden spring breakup impose a peakedness in seasonal water runoff and sediment discharge that contrasts markedly with that in rivers of the tropics and more temperate climates. Very little sediment from the Ob and Yenisey rivers is being transported to the open waters of the Arctic Ocean under present conditions.

Sediment chemoautotrophy in the coastal ocean

NASA Astrophysics Data System (ADS)

Vasquez-Cardenas, Diana; Meysman, Filip J. R.; van Breugel, Peter; Boschker, Henricus T. S.

2016-04-01

A key process in the biogeochemistry of coastal sediments is the reoxidation of reduced intermediates formed during anaerobic mineralization which in part is performed by chemoautotrophic micro-organisms. These microbes fix inorganic carbon using the energy derived from reoxidation reactions and in doing so can fix up to 32% of the CO2 released by mineralization. However the importance and distribution of chemoautotrophy has not been systematically investigated in these environments. To address these issues we surveyed nine coastal sediments by means of bacterial biomarker analysis (phospholipid derived fatty acids) combined with stable isotope probing (13C-bicarbonate) which resulted in an almost doubling of the number of observations on coastal sedimentary chemoautotrophy. Firstly, sediment chemoautotrophy rates from this study and rates compiled from literature (0.07 to 36 mmol C m-2 d-1) showed a power-law relation with benthic oxygen uptake (3.4 to 192 mmol O2 m-2 d-1). Benthic oxygen uptake was used as a proxy for carbon mineralization to calculate the ratio of the CO2 fixed by chemoautotrophy over the total CO2 released through mineralization. This CO2 efficiency was 3% in continental shelf, 9% in nearshore and 21% in salt marsh sediments. These results suggest that chemoautotrophy plays an important role in C-cycling in reactive intertidal sediments such as salt marshes rather than in the organic-poor, permeable continental shelf sediments. Globally in the coastal ocean our empirical results show that chemoautotrophy contributes ˜0.05 Pg C y-1 which is four times less than previous estimates. Secondly, five coastal sediment regimes were linked to the depth-distribution of chemoautotrophy: 1) permeable sediments dominated by advective porewater transport, 2) bioturbated sediments, and cohesive sediments dominated by diffusive porewater transport characterized by either 3) canonical sulfur oxidation, 4) nitrate-storing Beggiatoa, or 5) electrogenic sulfur oxidation. Sediments with an O2-H2S interface exhibited highest chemoautotrophy activity in the top centimeter via canonical sulfur oxidation, whereas in the presence of electrogenic sulfur oxidation a uniform distribution of chemoautotrophy throughout the top centimeters of the sediment was evidenced. Lowest dark carbon fixation was found in permeable advective-driven sediments with deep oxygen penetration resulting in higher subsurface than surface activity. Hence, the depth-distribution of chemoautotrophy in coastal sediments varies due to several biogeochemical characteristics such as grain size, organic carbon content, presence of filamentous sulfur oxidizing bacteria, and macrofaunal activity.

Benthic Oxygen Uptake in the Arctic Ocean Margins - A Case Study at the Deep-Sea Observatory HAUSGARTEN (Fram Strait)

PubMed Central

Cathalot, Cecile; Rabouille, Christophe; Sauter, Eberhard; Schewe, Ingo; Soltwedel, Thomas

2015-01-01

The past decades have seen remarkable changes in the Arctic, a hotspot for climate change. Nevertheless, impacts of such changes on the biogeochemical cycles and Arctic marine ecosystems are still largely unknown. During cruises to the deep-sea observatory HAUSGARTEN in July 2007 and 2008, we investigated the biogeochemical recycling of organic matter in Arctic margin sediments by performing shipboard measurements of oxygen profiles, bacterial activities and biogenic sediment compounds (pigment, protein, organic carbon, and phospholipid contents). Additional in situ oxygen profiles were performed at two sites. This study aims at characterizing benthic mineralization activity along local bathymetric and latitudinal transects. The spatial coverage of this study is unique since it focuses on the transition from shelf to Deep Ocean, and from close to the ice edge to more open waters. Biogeochemical recycling across the continental margin showed a classical bathymetric pattern with overall low fluxes except for the deepest station located in the Molloy Hole (5500 m), a seafloor depression acting as an organic matter depot center. A gradient in benthic mineralization rates arises along the latitudinal transect with clearly higher values at the southern stations (average diffusive oxygen uptake of 0.49 ± 0.18 mmol O2 m-2 d-1) compared to the northern sites (0.22 ± 0.09 mmol O2 m-2 d-1). The benthic mineralization activity at the HAUSGARTEN observatory thus increases southward and appears to reflect the amount of organic matter reaching the seafloor rather than its lability. Although organic matter content and potential bacterial activity clearly follow this gradient, sediment pigments and phospholipids exhibit no increase with latitude whereas satellite images of surface ocean chlorophyll a indicate local seasonal patterns of primary production. Our results suggest that predicted increases in primary production in the Arctic Ocean could induce a larger export of more refractory organic matter due to the longer production season and the extension of the ice-free zone. PMID:26465885

The Importance of Subsurface Production for Carbon Export - Evidence from Past Oceans

NASA Astrophysics Data System (ADS)

Kemp, A. E. S.

2016-02-01

The maxim of the geological concept of uniformitarianism is "the present is the key to the past", but in the context of our temporally and spatially minimal observational record of modern ocean biogeochemical processes, ancient ocean sediments may provide critical evidence of the key species involved in carbon flux. Specifically, laminated marine sediments that preserve the seasonal flux cycle represent "palaeo-sediment traps" that vastly expand our knowledge of the operations of the marine biological carbon pump. Several key subsurface-dwelling diatom taxa, hitherto thought to be biogeochemically insignificant, are dominant components of ancient marine sediments. For example, the sapropels and equivalent horizons that have accumulated in the Mediterranean over the past 5 million years, contain abundant rhizosolenid and hemiaulid diatoms. These deposits contain the highest concentrations of organic carbon and there is extensive evidence that this was produced by subsurface production in a deep chlorophyll maximum. The highly stratified conditions that led to this subsurface production and carbon flux are in contrast to prevailing views that have held upwelling systems as those with the highest potential for export in the global ocean. Similarly, studies of ancient "greenhouse" periods such as the Cretaceous, with highly stratified oceans and which are potential analogues for future climate change, show evidence for extensive subsurface production. Together with emerging evidence from stratified regions of the modern ocean, such as the subtropical gyres, insights from these ancient oceans suggest that a reappraisal is required of current views on key phytoplankton producers and their role the operation of the marine biological carbon pump.

Effects of Dynamic Topography on the Cenozoic Carbonate Compensation Depth

NASA Astrophysics Data System (ADS)

Campbell, Siobhan M.; Moucha, Robert; Derry, Louis A.; Raymo, Maureen E.

2018-04-01

Reconstructions of the carbonate compensation depth (CCD) in the past have been used to inform hypotheses about the nature of weathering, tectonics, climate change, and the major ion content of the world's oceans over the Cenozoic. These reconstructions are sensitive to uncertainties in the input data, in particular, the paleodepth estimates of sediment cores. Here we propose that a significant, previously unconsidered contributor to uncertainties in paleodepth estimates is from dynamic topography produced by radial stresses exerted on the Earth's surface by the convecting mantle; these stresses can warp the ocean floor by hundreds of meters over broad regions and also vary significantly over millions of years. We present new reconstructions of the equatorial Pacific and Indian Ocean CCDs over the last 30 and 23 Myr, respectively, which demonstrate an overall deepening trend since the Miocene, and illustrate the possible effect of long-term changes in dynamic topography on these reconstructions.

The Indian Ocean gravity low - Evidence for an isostatically uncompensated depression in the upper mantle

NASA Technical Reports Server (NTRS)

Ihnen, S. M.; Whitcomb, J. H.

1983-01-01

The broad gravity low in the equatorial Indian Ocean south of Sri Lanka is the largest and most striking feature in the gravitational field of the earth. The most negative long-wavelength free-air gravity anomalies are found there and the sea surface (geoid) lies more than 100 meters below the best fitting ellipsoid. A model of the lithosphere and upper mantle is proposed which accurately predicts the observed free-air gravity and geoid elevation. This model is consistent with bathymetry and sediment thickness data and suggests that the crust south of India currently floats as much as 600 meters lower than would be expected if the region were isostatically compensated. This residual depression of the crust is apparently confirmed by observations of ocean depth. An uncompensated depression is consistent with the presence of a mechanical wake left in the upper mantle behind India as it traveled toward Asia.

Evolution of biomolecular loadings along a major river system

NASA Astrophysics Data System (ADS)

Freymond, Chantal V.; Kündig, Nicole; Stark, Courcelle; Peterse, Francien; Buggle, Björn; Lupker, Maarten; Plötze, Michael; Blattmann, Thomas M.; Filip, Florin; Giosan, Liviu; Eglinton, Timothy I.

2018-02-01

Understanding the transport history and fate of organic carbon (OC) within river systems is crucial in order to constrain the dynamics and significance of land-ocean interactions as a component of the global carbon cycle. Fluvial export and burial of terrestrial OC in marine sediments influences atmospheric CO2 over a range of timescales, while river-dominated sedimentary sequences can provide valuable archives of paleoenvironmental information. While there is abundant evidence that the association of organic matter (OM) with minerals exerts an important influence on its stability as well as hydrodynamic behavior in aquatic systems, there is a paucity of information on where such associations form and how they evolve during fluvial transport. Here, we track total organic carbon (TOC) and terrestrial biomarker concentrations (plant wax-derived long-chain fatty acids (FA), branched glycerol dialkyl glycerol tetraethers (brGDGTs) and lignin-derived phenols) in sediments collected along the entire course of the Danube River system in the context of sedimentological parameters. Mineral-specific surface area-normalized biomarker and TOC concentrations show a systematic decrease from the upper to the lower Danube basin. Changes in OM loading of the available mineral phase correspond to a net decrease of 70-80% of different biomolecular components. Ranges for biomarker loadings on Danube River sediments, corresponding to 0.4-1.5 μgFA/m2 for long-chain (n-C24-32) fatty acids and 17-71 ngbrGDGT/m2 for brGDGTs, are proposed as a benchmark for comparison with other systems. We propose that normalizing TOC as well as biomarker concentrations to mineral surface area provides valuable quantitative constraints on OM dynamics and organo-mineral interactions during fluvial transport from terrigenous source to oceanic sink.

Cadmium-isotopic evidence for increasing primary productivity during the Late Permian anoxic event

NASA Astrophysics Data System (ADS)

Georgiev, Svetoslav V.; Horner, Tristan J.; Stein, Holly J.; Hannah, Judith L.; Bingen, Bernard; Rehkämper, Mark

2015-01-01

Earth's most extreme extinction event near the end of the Late Permian decimated more than 90% of all extant marine species. Widespread and intensive oceanic anoxia almost certainly contributed to the catastrophe, though the driving mechanisms that sustained such conditions are still debated. Of particular interest is whether water column anoxia was a consequence of a 'stagnant ocean', or if it was controlled by increases in nutrient supply, primary productivity, and subsequent heterotrophic respiration. Testing these competing hypotheses requires deconvolving sedimentary/bottom water redox conditions from changes in surface water productivity in marine sediments. We address this issue by studying marine shales from East Greenland and the mid-Norwegian shelf and combining sedimentary redox proxies with cadmium-isotopic analyses. Sedimentary nitrogen-isotopic data, pyrite framboid analyses, and organic and inorganic shale geochemistry reveal sulfidic conditions with vigorous upwelling, and increasingly anoxic conditions with a strengthening upwelling in the Greenland and Norwegian sections, respectively. Detailed analysis of sedimentary metal budgets illustrates that Cd is primarily associated with organic carbon and records primary geochemical signatures, thus enabling reconstruction of surface water nutrient utilization. Cadmium-isotopic analyses of the authigenic shale fraction released by inverse aqua regia digestion yield an average δ114Cd110 of + 0.15 ± 0.01 ‰ (2 SE, n = 12; rel. NIST SRM 3108), indicative of incomplete surface water nutrient utilization up-section. The constant degree of nutrient utilization combined with strong upwelling requires increasing primary productivity - and not oceanic stagnation - to balance the larger nutrient fluxes to both study sites during the development of the Late Permian water column anoxia. Overall, our data illustrate that if bottom water redox and upwelling can be adequately constrained, Cd-isotopic analyses of organic-rich sediments can be used to provide valuable information on nutrient utilization and therefore past productivity.

Bacterial Production and Enzymatic Activities in Deep-Sea Sediments of the Pacific Ocean: Biogeochemical Implications of Different Temperature Constraints

NASA Astrophysics Data System (ADS)

Danovaro, R.; Corinaldesi, C.; dell'Anno, A.

2002-12-01

The deep-sea bed, acting as the ultimate sink for organic material derived from the upper oceans primary production, is now assumed to play a key role in biogeochemical cycling of organic matter on global scale. Early diagenesis of organic matter in marine sediments is dependent upon biological processes (largely mediated by bacterial activity) and by molecular diffusion. Organic matter reaching the sea floor by sedimentation is subjected to complex biogeochemical transformations that make organic matter largely unsuitable for direct utilization by benthic heterotrophs. Extracellular enzymatic activities in the sediment is generally recognized as the key step in the degradation and utilization of organic polymers by bacteria and a key role in biopolymeric carbon mobilization is played by aminopeptidase, alkaline phosphatase and glucosidase activities. In the present study we investigated bacterial density, bacterial C production and exo-enzymatic activities (aminopeptidase, glucosidase and phosphatase activity) in deep-sea sediments of the Pacific Ocean in relation with the biochemical composition of sediment organic matter (proteins, carbohydrates and lipids), in order to gather information on organic matter cycling and diagenesis. Benthic viral abundance was also measured to investigate the potential role of viruses on microbial loop functioning. Sediment samples were collected at eight stations (depth ranging from 2070-3100 m) along two transects located at the opposite side (north and south) of ocean seismic ridge Juan Fernandez (along latitudes 33° 20' - 33° 40'), constituted by the submerged vulcanoes, which connects the Chilean coasts to Rapa Nui Island. Since the northern and southern sides of this ridge apparently displayed small but significant differences in deep-sea temperature (related to the general ocean circulation), this sampling strategy allowed also investigating the role of different temperature constraints on bacterial activity and biogeochemical processes and to define possible scenarios dealing with climate induced changes in deep-sea conditions.

Paleoceanographic Inferences from Carbon and Nitrogen Isotopic Compositions of Cenomanian Black Shales from DSDP/ODP Sites 367, 530, 603, 641, 1257-1261, and 1276 in the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Yum, J.; Meyers, P. A.; Bernasconi, S. M.; Arnaboldi, M.

2005-12-01

The mid-Cretaceous (Cenomanian- Turonian) was characterized as a peak global greenhouse period with highest sea level, highest CO2 concentration in atmosphere and low thermal gradients from the poles to the equator. The depositional environment of the organic-carbon-rich black shales that typify this period remains an open question. A total of 180 Cenomanian- Turonian core samples were selected from multiple ODP and DSDP sites in the Atlantic Ocean: 530 (Cape Basin), 603 (Hatteras Rise), 641 (Galicia Bank), 1257-1261 (Demerara Rise), 1276 (Newfoundland Basin). Total organic carbon and nitrogen concentrations and isotopic compositions were measured to investigate variations in the proto-Atlantic Ocean paleoceanographic conditions that contributed to the origin of the black shales for this period. These new data were combined with existing data from Sites 367 (Senegal Rise), 530, and 603. Both the black shales and the organic-carbon-poor background sediments (less than 1 percent) have carbon isotope values between -29 to -22 permil. The C/N ratios of the background sediments are low (less than 20) compared to those of the black shales (20-40). Nitrogen isotope values range from 0 to 4 permil in the background samples. All black shales have similarly low nitrogen isotope values that range between -4 to 0 permil. These exceptionally low values are inferred to reflect the productivity of blue green algae and cyanobacteria under strongly surface stratified oceanic conditions. Although carbon isotope and C/N values of black shales show almost similar patterns at each location, there are site-specific shifts in these data that could be related to the amount of continental run off and/or the effect of latitude. Our multi-site comparison suggests that specially stratified depositional environments that could produce and accumulate the abnormally high carbon concentrations in sediments occurred throughout the proto-Atlantic ocean during the mid-Cretaceous. However, regional factors affected the amount and origin of organic matter delivered to each location.

Salinity of the Early and Middle Eocene Arctic Ocean From Oxygen Isotope Analysis of Fish Bone Carbonate

NASA Astrophysics Data System (ADS)

Waddell, L. M.; Moore, T. C.

2006-12-01

Plate tectonic reconstructions indicate that the Arctic was largely isolated from the world ocean during the early and middle Eocene, with exchange limited to shallow, and possibly intermittent, connections to the North Atlantic and Tethys (via the Turgay Strait). Relative isolation, combined with an intensification of the hydrologic cycle under an Eocene greenhouse climate, is suspected to have led to the development of a low- salinity surface water layer in the Arctic that could have affected deep and intermediate convection in the North Atlantic. Sediment cores recently recovered from the Lomonosov Ridge by the IODP 302 Arctic Coring Expedition (ACEX) allow for the first assessment of the salinity of the Arctic Ocean during the early and middle Eocene. Stable isotope analysis performed on the structural carbonate of fish bone apatite from ~30 samples between the ages of ~55 and ~44 myr yielded δ18O values between -6.84‰ and -2.96‰ VPDB, with a mean value of -4.89‰. From the δ18O values we calculate that the Arctic Ocean was probably brackish during most of the early and middle Eocene, with an average salinity of 19 to 24‰. Negative excursions in the δ18O record (<-6‰) indicate three events during which the salinity of the Arctic surface waters was severely lowered: the Paleocene Eocene Thermal Maximum (PETM), the Azolla event at ~49 Ma, and a third previously unidentified event at ~46 Ma. During the PETM, low salinities developed under conditions of increased regional precipitation and runoff associated with extreme high latitude warmth and possible tectonic uplift in the North Atlantic. During the other two low-salinity events, sea level was lowered by ~20-30 m, implying a possible severing of Arctic connections to the world ocean. The most positive δ18O value (-2.96‰) occurs at ~45 Ma, the age of the youngest dropstone discovered in the ACEX sediments, and may therefore correspond to a climatic cooling rather than a high salinity event.

Reconstructing Holocene Summer Sea-Ice Conditions in the Central and Western Arctic Ocean: Morphological Variations and Stable Isotope Composition of Neogloboquadrina pachyderma

NASA Astrophysics Data System (ADS)

Asahi, H.; Nam, S. I.; Stein, R. H.; Mackensen, A.; Son, Y. J.

2017-12-01

The usability of planktic foraminiferal census data in Arctic paleoceanography is limited by the predominance of Neogloboquadrina pachyderma (sinistral). Though a potential usability of their morphological variation has been suggested by recent studies, its application is restricted to the central part of the Arctic Ocean. Here we present their regional distribution, using 80 surface sediment samples from the central and the western Arctic Ocean. Among seven morphological variations encountered, distinct presence of "large-sized" N. pachyderma morphotypes at the summer sea-ice edge in the western Arctic demonstrates its strong potential as sea-ice distribution indicator. Based on their regional patterns, we further developed planktic foraminifer (PF)-based transfer functions (TFs) to reconstruct summer surface-water temperature, salinity and sea-ice concentration in the western and central Arctic. The comparison of sea-ice reconstructions by PF-based TF to other pre-existed approaches showed their recognizable advantages/disadvantages: the PF-based approach in the nearby/within heavily ice-covered region, the dinocyst-based approach in the extensively seasonal ice retreat region, and the IP25-based approach with overall reflection over a wide range of sea-ice coverage, which is likely attributed to their (a) taphonomical information-loss, (b) different seasonal production patterns or combination of both. The application of these TFs on a sediment core from Northwind Ridge suggests general warming, freshening, and sea-ice reduction after 6.0 ka. This generally agrees with PF stable isotope records and sea-ice reconstructions from dinocyst-based TF at proximal locations, indicating that the sea-ice behavior at the Northwind Ridge is notably different from the IP25-based sea-ice reconstructions reported from elsewhere in the Arctic Ocean. Lack of regional coverage of PF-based reconstructions hampers further discussion whether the observed inconsistency is simply caused by different regional coverage of data and/or their different sensitivity yet. Thus, additional PF-census data with their isotope signatures from other cores from different ice regimes in the Arctic Ocean (e.g., Lomonosov Ridge and Mendeelev Ridge) will provide further discussion for such inconsisntency.

Biogeochemical cycling of zinc and its isotopes in the Southern Ocean

NASA Astrophysics Data System (ADS)

Zhao, Y.; Vance, D.; Abouchami, W.; de Baar, H. J. W.

2014-01-01

We report Zn concentration and isotope data for seawater samples from the Atlantic sector of the Southern Ocean, collected during the IPY/GEOTRACES ANT-XXIV/III cruise along the Greenwich Zero Meridian. Data are reported for the full depth range of the water column at three stations, as well as a transect of surface samples, using a new analytical approach that is presented in detail here. Zn concentrations increase with depth, though due to proximity to upwelling sites, surface concentrations are not as low as in some parts of the ocean such as further northward into the Sub-Antarctic Zone. For two depth profiles south of the Polar Front Zone, the physical stratification of the upper water column is reflected in sudden near-surface changes in Zn concentration with depth. In contrast, beneath 100-300 m Zn concentrations barely change with depth. Zn isotopic data beneath 1000 m, for the Southern Ocean data presented here as well as published data from the North Atlantic and North Pacific, are strikingly homogeneous, with an average δ66Zn = +0.53 ± 0.14‰ (2SD, 2SE = 0.03, n = 21). The surface Southern Ocean is more variable, with δ66Zn ranging from 0.07‰ to 0.80‰. Between the two is a thin horizon at 40-80 m which, in the Southern Ocean as well as the North Atlantic and North Pacific, is characterised by distinctly light isotopic signatures, with δ66Zn about 0.3‰ lower than surface waters. Strong correlations between Si and Zn concentrations seen here and elsewhere, coupled to the lack of any systematic relationship between Si and Zn isotopes in the Southern Ocean, suggest that the removal of Zn associated with diatom opal involves little or no isotopic fractionation. Regeneration of this Zn also explains the homogeneous Zn isotopic composition of the global deep ocean so far sampled. However, the low Zn content of opal requires that deep ocean Zn does not directly come from the opal phase itself, but rather from associated organic material external to the diatom frustule during growth. Experimental data are consistent with little or no fractionation during incorporation of Zn into this material. On the other hand, the light zinc at 40-80 m is most consistent with the regeneration of an intra-cellular pool that both culturing experiments and field data suggest will be isotopically light. The data thus imply two processes by which Zn is taken up in the surface ocean, that these pools have very different regeneration lengthscales, and that physical mixing of the oceans cannot eradicate their isotopic signatures. Finally, the deep δ66Zn ocean value is significantly higher than the current best estimate of the input to the oceans. The most obvious candidate for the required light sink is the survival of some of the cellular Zn to be buried in sediment.

Porosity-depth trends of carbonate deposits along the northwest shelf of Australia (IODP Expedition 356)

NASA Astrophysics Data System (ADS)

Lee, Eun Young; Kominz, Michelle; Reuning, Lars; Takayanagi, Hideko; Knierzinger, Wolfgang; Wagreich, Michael; Expedition 356 shipboard scientists, IODP

2017-04-01

The northwest shelf (NWS) of Australia extends from northern tropical to southern temperate latitudes situated offshore from the low-moderate-relief and semi-arid Australian continent. The shelf environment is dominated throughout by carbonate sedimentation with warm-water and tropical carbonate deposits, connected to the long-term northward drift of Australia bringing the NWS into tropical latitudes. IODP expedition 356 cored seven sites (U1458-U1464) covering a latitudinal range of 29°S-18°S off the NWS. This study focuses on porosity-depth trends of the Miocene - Pleistocene carbonate sediment on the NWS. The NWS is an ideal area to study regional (and furthermore general) carbonate porosity-depth relationships, because it contains a nearly continuous sequence of carbonate sediment ranging in depth from the surface to about 1,100m and in age from Pleistocene to Miocene. Porosity-depth trends of sedimentary rocks are generally controlled by a variety of factors which govern the rates of porosity loss due to mechanical compaction and of porosity loss (or gain) due to chemical processes during diagenesis. This study derives porosity data from Moisture and Density (MAD) technique conducted during IODP Expedition 356. MAD samples were collected from packstone (44%), wackestone (27%), mudstone (15%) and grainstone (7%), with the rest from floatstone, rudstone, dolostone, sandstone and other subordinate lithologies. To understand porosity-depth trends, the porosity data are arranged both exponentially and linearly, and correlated with age models and lithologic descriptions provided by IODP shipboard scientists. Porosity(%)-depth(m) trends of all the porosity data are Porosity=52e-0.0008/Depth (exponential) and Porosity=-0.03Depth+52 (linear). Porosities near surface and in the deepest parts of each well are least well represented by these trend lines. Porosity values of Pleistocene sediment are generally higher than those of Miocene - Pliocene sediment. The initial porosity in porosity-depth trends increases from 52% to 57% with increasing mud content from grainstone to packstone, wackestone, and mudstone. Carbonate sediment that includes non-skeletal grains usually has lower porosity values than the trend lines. *This research was a part of the project titled 'International Ocean Discovery Program', funded by the Ministry of Oceans and Fisheries, Korea.

A 26 million year gap in the central Arctic record at the greenhouse-icehouse transition: Looking for clues

USGS Publications Warehouse

Sangiorgi, F.; Brumsack, H.-J.; Willard, D.A.; Schouten, S.; Stickley, C.E.; O'Regan, M.; Reichart, G.-J.; Sinninghe, Damste J.S.; Brinkhuis, H.

2008-01-01

The Cenozoic record of the Lomonosov Ridge (central Arctic Ocean) recovered during Integrated Ocean Drilling Program (IODP) Expedition 302 revealed an unexpected 26 Ma hiatus, separating middle Eocene (???44.4 Ma) from lower Miocene sediments (???18.2 Ma). To elucidate the nature of this unconformity, we performed a multiproxy palynological (dinoflagellate cysts, pollen, and spores), micropaleontological (siliceous microfossils), inorganic, and organic (Tetra Ether Index of lipids with 86 carbon atoms (TEX86) and Branched and Isoprenoid Tetraether (BIT)) geochemical analysis of the sediments from ???5 m below to ???7 m above the hiatus. Four main paleoenvironmental. phases (A-D) are recognized in the sediments encompassing the unconformity, two below (A-B) and two above (C-D): (A) Below the hiatus, proxies show relatively warm temperatures, with Sea Surface Temperatures (TEX86-derived SSTs) of about 8??C and high fresh to brackish water influence. (B) Approaching the hiatus, proxies indicate a cooling trend (TEX86-derived SSTs of ???5??C), increased freshwater influence, and progressive shoaling of the Lomonosov Ridge drilling site, located close to or at sea level. (C) The interval directly above the unconformity contains sparse reworked Cretaceous to Oligocene dinoflagellate cysts. Sediments were deposited in a relatively shallow, restricted marine environment. Proxies show the simultaneous influence of both fresh and marine waters, with alternating oxic and anoxic conditions. Pollen indicates a relatively cold climate. Intriguingly, TEX86-derived SSTs are unexpectedly high, ???15-19??C. Such warm surface waters may be partially explained by the ingression of warmer North Atlantic waters after the opening of the Fram Strait during the early Miocene. (D) Sediments of the uppermost interval indicate a phase of extreme oxic conditions, and a well-ventilated environment, which occurred after the complete opening of the Fram Strait. Importantly, and in contrast with classical postrifting thermal subsidence models for passive margins, our data suggest that sediment erosion and/or nondeposition that generated the hiatus was likely due to a progressive shoaling of the Lomonosov Ridge. A shallow water setting both before and after the hiatus suggests that the Lomonosov Ridge remained at or near sea level for the duration of the gap in the sedimentary record. Interacting sea level changes and/ or tectonic activity (possibly uplift) must be invoked as possible causes for such a long hiatus. Copyright 2008 by the American Geophysical Union.

Spatial distribution of polycyclic aromatic hydrocarbon and polychlorinated biphenyl sources in the Nakdong River Estuary, South Korea.

PubMed

Lee, Jun H; Woo, Han J; Jeong, Kap S; Kang, Jeong W; Choi, Jae U; Jeong, Eun J; Park, Kap S; Lee, Dong H

2017-10-15

Our research team investigated the elemental composition and the presence of various toxic organic compounds, such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), in estuary surface sediments to trace the spatial distribution of the sources of pollution deposited in Nakdong River, Busan, South Korea. The spatial patterns of elemental composition and toxic organic compounds were determined from the measurements of total organic carbon (TOC), total nitrogen, total sulfur, PAHs, and PCBs. The sediments had TOC contents of between 0.02 and 1.80 wt% (avg. 0.34 wt%), depending on the amount of clay-sized particles. The concentrations of PAHs and PCBs (10.8-167.7 ng g -1 dry wt and 197.0-754.0 pg g -1 dry wt, respectively) in surface sediments revealed different spatial patterns for these compounds, suggesting that they partially originated from the combustion of fossil fuels and from the use of commercial PCB products at adjacent industrial complexes. Although these concentrations were far below the Sediment Quality Guideline (SQG) of the National Oceanic and Atmospheric Administration (NOAA), the sediments at one site contained PCBs at concentrations close to the response level (754.0 pg g -1 dry wt), and were dominated by low-molecular-weight PAHs. The PAHs and PCBs in Nakdong River Estuary sediments were likely to have originated from the combustion of fossil fuels and biomass at the adjacent industrial complexes. The primarily analyzed results determined that PAHs originated from the combustion of fossil fuels and biomass, and overall concentrations were related to the contributions of individual PAHs in most sediment samples. Based on the SQG of the NOAA, our results indicate that the anthropogenic activity should be considered on the future-sustainable management of this estuary system.

Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model

USGS Publications Warehouse

Warner, J.C.; Sherwood, C.R.; Signell, R.P.; Harris, C.K.; Arango, H.G.

2008-01-01

We are developing a three-dimensional numerical model that implements algorithms for sediment transport and evolution of bottom morphology in the coastal-circulation model Regional Ocean Modeling System (ROMS v3.0), and provides a two-way link between ROMS and the wave model Simulating Waves in the Nearshore (SWAN) via the Model-Coupling Toolkit. The coupled model is applicable for fluvial, estuarine, shelf, and nearshore (surfzone) environments. Three-dimensional radiation-stress terms have been included in the momentum equations, along with effects of a surface wave roller model. The sediment-transport algorithms are implemented for an unlimited number of user-defined non-cohesive sediment classes. Each class has attributes of grain diameter, density, settling velocity, critical stress threshold for erosion, and erodibility constant. Suspended-sediment transport in the water column is computed with the same advection-diffusion algorithm used for all passive tracers and an additional algorithm for vertical settling that is not limited by the CFL criterion. Erosion and deposition are based on flux formulations. A multi-level bed framework tracks the distribution of every size class in each layer and stores bulk properties including layer thickness, porosity, and mass, allowing computation of bed morphology and stratigraphy. Also tracked are bed-surface properties including active-layer thickness, ripple geometry, and bed roughness. Bedload transport is calculated for mobile sediment classes in the top layer. Bottom-boundary layer submodels parameterize wave-current interactions that enhance bottom stresses and thereby facilitate sediment transport and increase bottom drag, creating a feedback to the circulation. The model is demonstrated in a series of simple test cases and a realistic application in Massachusetts Bay. 

Enhanced transfer of organic matter to higher trophic levels caused by ocean acidification and its implications for export production: A mass balance approach.

PubMed

Boxhammer, Tim; Taucher, Jan; Bach, Lennart T; Achterberg, Eric P; Algueró-Muñiz, María; Bellworthy, Jessica; Czerny, Jan; Esposito, Mario; Haunost, Mathias; Hellemann, Dana; Ludwig, Andrea; Yong, Jaw C; Zark, Maren; Riebesell, Ulf; Anderson, Leif G

2018-01-01

Ongoing acidification of the ocean through uptake of anthropogenic CO2 is known to affect marine biota and ecosystems with largely unknown consequences for marine food webs. Changes in food web structure have the potential to alter trophic transfer, partitioning, and biogeochemical cycling of elements in the ocean. Here we investigated the impact of realistic end-of-the-century CO2 concentrations on the development and partitioning of the carbon, nitrogen, phosphorus, and silica pools in a coastal pelagic ecosystem (Gullmar Fjord, Sweden). We covered the entire winter-to-summer plankton succession (100 days) in two sets of five pelagic mesocosms, with one set being CO2 enriched (~760 μatm pCO2) and the other one left at ambient CO2 concentrations. Elemental mass balances were calculated and we highlight important challenges and uncertainties we have faced in the closed mesocosm system. Our key observations under high CO2 were: (1) A significantly amplified transfer of carbon, nitrogen, and phosphorus from primary producers to higher trophic levels, during times of regenerated primary production. (2) A prolonged retention of all three elements in the pelagic food web that significantly reduced nitrogen and phosphorus sedimentation by about 11 and 9%, respectively. (3) A positive trend in carbon fixation (relative to nitrogen) that appeared in the particulate matter pool as well as the downward particle flux. This excess carbon counteracted a potential reduction in carbon sedimentation that could have been expected from patterns of nitrogen and phosphorus fluxes. Our findings highlight the potential for ocean acidification to alter partitioning and cycling of carbon and nutrients in the surface ocean but also show that impacts are temporarily variable and likely depending upon the structure of the plankton food web.

Annual cycles of deep-ocean biogeochemical export fluxes in subtropical and subantarctic waters, southwest Pacific Ocean

NASA Astrophysics Data System (ADS)

Nodder, Scott D.; Chiswell, Stephen M.; Northcote, Lisa C.

2016-04-01

The annual cycles of particle fluxes derived from moored sediment trap data collected during 2000-2012 in subtropical (STW) and subantarctic waters (SAW) east of New Zealand are presented. These observations are the most comprehensive export flux time series from temperate Southern Hemisphere latitudes to date. With high levels of variability, fluxes in SAW were markedly lower than in STW, reflecting the picophytoplankton-dominated communities in the iron-limited, high nutrient-low chlorophyll SAW. Austral spring chlorophyll blooms in surface STW were near synchronous with elevated fluxes of bio-siliceous, carbonate, and organic carbon-rich materials to the deep ocean, probably facilitated by diatom and/or coccolithophorid sedimentation. Lithogenic fluxes were also high in STW, compared to SAW, reflecting proximity to the New Zealand landmass. In contrast, the highest biogenic fluxes in SAW occurred in spring when surface chlorophyll concentrations were low, while highest annual chlorophyll concentrations were in summer with no associated flux increase. We hypothesize that the high spring export in SAW results from subsurface chlorophyll accumulation that is not evident from remote-sensing satellites. This material was also rich in biogenic silica, perhaps related to the preferential export of diatoms and other silica-producing organisms, such as silicoflagellates and radiolarians. Organic carbon fluxes in STW are similar to that of other mesotrophic to oligotrophic waters (˜6-7 mg C m-2 d-1), whereas export from SAW is below the global average (˜3 mg C m-2 d-1). Regional differences in flux across the SW Pacific and Tasman region reflect variations in physical processes and ecosystem structure and function.

Annual Cycles of Deep-ocean, Biogeochemical Export Fluxes and Biological Pump Processes in Subtropical and Subantarctic Waters, Southwest Pacific Ocean

NASA Astrophysics Data System (ADS)

Nodder, S.; Chiswell, S.; Northcote, L.

2016-02-01

One of the key aspects of the global carbon cycle is the efficiency and spatio-temporal variability of the biological pump. In this paper, the annual cycles of particle fluxes, derived from moored sediment trap data collected from 2000-12 in subtropical (STW) and subantarctic waters (SAW), east of New Zealand, are presented. These observations are the most comprehensive export flux time-series from temperate Southern Hemisphere latitudes to date. With high levels of variability, fluxes in SAW were markedly lower than in STW, reflecting the picophytoplankton-dominated communities in the iron-limited, high nutrient-low chlorophyll SAW. Austral spring chlorophyll blooms in surface STW were near-synchronous with elevated fluxes of bio-siliceous, carbonate and organic carbon-rich materials to the deep ocean, probably facilitated by diatom sedimentation. Lithogenic fluxes were also high in STW, compared to SAW, reflecting proximity to the New Zealand landmass. In contrast, the highest biogenic fluxes in SAW occurred in spring when surface chlorophyll concentrations were low, while highest annual chlorophyll concentrations were in summer with no associated flux increase. We hypothesize that the high spring export in SAW occurs from subsurface chlorophyll accumulations that are not evident from remote-sensing satellites. This material was also rich in biogenic silica, perhaps related to the preferential export of diatoms and other silica-producing organisms, such as silicoflagellates and radiolarians. Particle fluxes in STW are similar to that of other mesotrophic to oligotrophic waters ( 6-7 mgC m-2 d-1), whereas export from SAW is below global averages ( 3 mgC m-2 d-1), and is characterized by carbonate-dominated and prominent bio-siliceous deposition.

Diazotrophic bacterioplankton in a coral reef lagoon: phylogeny, diel nitrogenase expression and response to phosphate enrichment.

PubMed

Hewson, Ian; Moisander, Pia H; Morrison, Amanda E; Zehr, Jonathan P

2007-05-01

We investigated diazotrophic bacterioplankton assemblage composition in the Heron Reef lagoon (Great Barrier Reef, Australia) using culture-independent techniques targeting the nifH fragment of the nitrogenase gene. Seawater was collected at 3 h intervals over a period of 72 h (i.e. over diel as well as tidal cycles). An incubation experiment was also conducted to assess the impact of phosphate (PO(4)3*) availability on nifH expression patterns. DNA-based nifH libraries contained primarily sequences that were most similar to nifH from sediment, microbial mat and surface-associated microorganisms, with a few sequences that clustered with typical open ocean phylotypes. In contrast to genomic DNA sequences, libraries prepared from gene transcripts (mRNA amplified by reverse transcription-polymerase chain reaction) were entirely cyanobacterial and contained phylotypes similar to those observed in open ocean plankton. The abundance of Trichodesmium and two uncultured cyanobacterial phylotypes from previous studies (group A and group B) were studied by quantitative-polymerase chain reaction in the lagoon samples. These were detected as transcripts, but were not detected in genomic DNA. The gene transcript abundance of these phylotypes demonstrated variability over several diel cycles. The PO(4)3* enrichment experiment had a clearer pattern of gene expression over diel cycles than the lagoon sampling, however PO(4)3* additions did not result in enhanced transcript abundance relative to control incubations. The results suggest that a number of diazotrophs in bacterioplankton of the reef lagoon may originate from sediment, coral or beachrock surfaces, sloughing into plankton with the flooding tide. The presence of typical open ocean phylotype transcripts in lagoon bacterioplankton may indicate that they are an important component of the N cycle of the coral reef.

LOSCAR: Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir Model v2.0.4

NASA Astrophysics Data System (ADS)

Zeebe, R. E.

2012-01-01

The LOSCAR model is designed to efficiently compute the partitioning of carbon between ocean, atmosphere, and sediments on time scales ranging from centuries to millions of years. While a variety of computationally inexpensive carbon cycle models are already available, many are missing a critical sediment component, which is indispensable for long-term integrations. One of LOSCAR's strengths is the coupling of ocean-atmosphere routines to a computationally efficient sediment module. This allows, for instance, adequate computation of CaCO3 dissolution, calcite compensation, and long-term carbon cycle fluxes, including weathering of carbonate and silicate rocks. The ocean component includes various biogeochemical tracers such as total carbon, alkalinity, phosphate, oxygen, and stable carbon isotopes. LOSCAR's configuration of ocean geometry is flexible and allows for easy switching between modern and paleo-versions. We have previously published applications of the model tackling future projections of ocean chemistry and weathering, pCO2 sensitivity to carbon cycle perturbations throughout the Cenozoic, and carbon/calcium cycling during the Paleocene-Eocene Thermal Maximum. The focus of the present contribution is the detailed description of the model including numerical architecture, processes and parameterizations, tuning, and examples of input and output. Typical CPU integration times of LOSCAR are of order seconds for several thousand model years on current standard desktop machines. The LOSCAR source code in C can be obtained from the author by sending a request to loscar.model@gmail.com.

Sediment tracing by `customised' magnetic fingerprinting: from the sub-catchment to the ocean scale

NASA Astrophysics Data System (ADS)

Maher, B.

2009-04-01

Robust identification of catchment suspended sediment sources is a prerequisite both for understanding sediment delivery processes and targeting of effective mitigation measures. Fine sediment delivery can pose management problems, especially with regard to nutrient run-off and siltation of water courses and bodies. Suspended sediment load constitutes the dominant mode of particulate material loss from catchments but its transport is highly episodic. Identification of suspended sediment sources and fluxes is therefore a prerequisite both for understanding of fluvial geomorphic process and systems and for designing strategies to reduce sediment transport, delivery and yields. Here will be discussed sediment ‘fingerprinting', using the magnetic properties of soils and sediments to characterise sediment sources and transport pathways over a very wide variety of spatial scales, from Lake Bassenthwaite in the English Lake District to the Burdekin River in Queensland and even the North Atlantic Ocean during the last glacial maximum. The applicability of magnetic ‘fingerprinting' to such a range of scales and environments has been significantly improved recently through use of new and site-appropriate magnetic measurement techniques, statistical processing and sample treatment options.

Sedimentary processes in modern and ancient oceanic arc settings: evidence from the Jurassic Talkeetna Formation of Alaska and the Mariana and Tonga Arcs, western Pacific

USGS Publications Warehouse

Draut, Amy E.; Clift, Peter D.

2006-01-01

Sediment deposited around oceanic volcanic ares potentially provides the most complete record of the tectonic and geochemical evolution of active margins. The use of such tectonic and geochemical records requires an accurate understanding of sedimentary dynamics in an arc setting: processes of deposition and reworking that affect the degree to which sediments represent the contemporaneous volcanism at the time of their deposition. We review evidence from the modern Mariana and Tonga arcs and the ancient arc crustal section in the Lower Jurassic Talkeetna Formation of south-central Alaska, and introduce new data from the Mariana Arc, to produce a conceptual model of volcaniclastic sedimentation processes in oceanic arc settings. All three arcs are interpreted to have formed in tectonically erosive margin settings, resulting in long-term extension and subsidence. Debris aprons composed of turbidites and debris flow deposits occur in the immediate vicinity of arc volcanoes, forming relatively continuous mass-wasted volcaniclastic records in abundant accommodation space. There is little erosion or reworking of old volcanic materials near the arc volcanic front. Tectonically generated topography in the forearc effectively blocks sediment flow from the volcanic front to the trench; although some canyons deliver sediment to the trench slope, most volcaniclastic sedimentation is limited to the area immediately around volcanic centers. Arc sedimentary sections in erosive plate margins can provide comprehensive records of volcanism and tectonism spanning < 10 My. The chemical evolution of a limited section of an oceanic arc may be best reconstructed from sediments of the debris aprons for intervals up to ~ 20 My but no longer, because subduction erosion causes migration of the forearc basin crust and its sedimentary cover toward the trench, where there is little volcaniclastic sedimentation and where older sediments are dissected and reworked along the trench slope.

The application of microtextural and heavy mineral analysis to discriminate between storm and tsunami deposits

USGS Publications Warehouse

Costa, Pedro J.M.; Gelfenbaum, Guy R.; Dawson, Sue; La selle, Seanpaul; Milne, F; Cascalho, J.; Ponte Lira, C.; Andrade, C.; Freitas, M. C.; Jaffe, Bruce E.

2017-01-01

Recent work has applied microtextural and heavy mineral analyses to sandy storm and tsunami deposits from Portugal, Scotland, Indonesia and the USA. We looked at the interpretation of microtextural imagery (scanning electron microscopy) of quartz grains and heavy mineral compositions. We consider inundation events of different chronologies and sources (the AD 1755 Lisbon and 2004 Indian Ocean tsunamis, the Great Storm of 11 January 2005 in Scotland, and Hurricane Sandy in 2012) that affected contrasting coastal and hinterland settings with different regional oceanographic conditions. Storm and tsunami deposits were examined along with potential source sediments (alluvial, beach, dune and nearshore sediments) to determine provenance.Results suggest that tsunami deposits typically exhibit a significant spatial variation in grain sizes, microtextures and heavy minerals. Storm deposits show less variability, especially in vertical profiles. Tsunami and storm quartz grains had more percussion marks and fresh surfaces compared to potential source material. Moreover, in the studied cases, tsunami samples had fewer fresh surfaces than storm deposits.Heavy mineral assemblages are typically site-specific. The concentration of heavy minerals decreases upwards in tsunamigenic units, whereas storm sediments show cyclic concentrations of heavy minerals, reflected in the laminations observed macroscopically in the deposits.

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.

Sulphide-sulphate stability and melting in subducted sediment and its role in arc mantle redox and chalcophile cycling in space and time

NASA Astrophysics Data System (ADS)

Canil, Dante; Fellows, Steven A.

2017-07-01

The redox budget during subduction is tied to the evolution of oxygen and biogeochemical cycles on Earth's surface over time. The sulphide-sulphate couple in subducted crust has significant potential for redox and control on extraction of chalcophile metals from the arc mantle. We derive oxygen buffers for sulphide-sulphate stability ('SSO buffers') using mineral assemblages in subducted crust within the eclogite facies, and examine their disposition relative to the fO2 in the arc mantle along various P-T trajectories for subduction. The fO2 required for sulphide stability in subducted crust passing beneath an arc is shifted by variations in the bulk Ca/(Ca + Mg + Fe) of the subducting crust alone. Hotter slabs and more Fe-rich sediments stabilize sulphide and favour chalcophile sequestration deep into the mantle, whereas colder slabs and calcic sediment will stabilize anhydrite, in some cases at depths of melt generation in the arc mantle (<130 km). The released sulphate on melting potentially increases the fO2 of the arc mantle. We performed melting experiments on three subducted sediment compositions varying in bulk Ca/(Ca + Mg + Fe) from 0.3 to 0.6 at 2.5 GPa and 900-1100 °C to confirm how anhydrite stability can change by orders of magnitude the S, Cu, As, Zn, Mo, Pb, and Sb contents of sediment melts, and their subsequent liberation to the arc mantle. Using Cu/Sc as a proxy for the behaviour of S, the effect of variable subducted sediment composition on sulphide-sulphate stability and release of chalcophiles to the arc mantle is recognizable in volcanic suites from several subduction zones in space and time. The fO2 of the SSO buffers in subducted sediment relative to the arc mantle may have changed with time by shifts in the nature of pelagic sedimentation in the oceans over earth history. Oxidation of arc mantle and the proliferation of porphyry Cu deposits may be latter-day advents in earth history partly due to the rise of planktic calcifiers in the oceans in only the past 250 million years.

Stereo Refractive Imaging of Breaking Free-Surface Waves in the Surf Zone

NASA Astrophysics Data System (ADS)

Mandel, Tracy; Weitzman, Joel; Koseff, Jeffrey; Environmental Fluid Mechanics Laboratory Team

2014-11-01

Ocean waves drive the evolution of coastlines across the globe. Wave breaking suspends sediments, while wave run-up, run-down, and the undertow transport this sediment across the shore. Complex bathymetric features and natural biotic communities can influence all of these dynamics, and provide protection against erosion and flooding. However, our knowledge of the exact mechanisms by which this occurs, and how they can be modeled and parameterized, is limited. We have conducted a series of controlled laboratory experiments with the goal of elucidating these details. These have focused on quantifying the spatially-varying characteristics of breaking waves and developing more accurate techniques for measuring and predicting wave setup, setdown, and run-up. Using dynamic refraction stereo imaging, data on free-surface slope and height can be obtained over an entire plane. Wave evolution is thus obtained with high spatial precision. These surface features are compared with measures of instantaneous turbulence and mean currents within the water column. We then use this newly-developed ability to resolve three-dimensional surface features over a canopy of seagrass mimics, in order to validate theoretical formulations of wave-vegetation interactions in the surf zone.

What sediment plumes at tide water glaciers can tell us about fjord circulation and subglacial hydrology

NASA Astrophysics Data System (ADS)

Schild, K. M.; Hawley, R. L.

2013-12-01

Marine-terminating outlet glaciers discharge most of Greenland's mass, but the subglacial transport of meltwater is not well understood. The coincident rise in both ice velocity and surface melt during the last decade points to a possible link between the amount of surface melt, glacier velocities, and discharge rates through processes including basal lubrication and/or an increase in melt at the terminus due to discharge plume enhanced entrainment of warm ocean waters. Characterizing the response of the Greenland Ice Sheet to increasing melt is limited in part by the lack of direct observation of the subglacial system. We use ground-based observations (time lapse cameras, DMI weather stations) and satellite remote sensing (MODIS) to infer the subglacial hydrological evolution of a tidewater glacier by identifying the lag between meltwater availability, inferred from warm temperatures and supraglacial lake drainage, and the appearance of a sediment plume at the terminus. The detection of sediment plumes is constrained by melange presence in the spring and decreasing solar illumination in the fall. At Rink Isbræ, West Greenland, we find the appearance of sediment plumes lagging the onset of positive temperatures from 2007-2011 by approximately 44 days, but the plumes are present as the melange clears suggesting this lag may be much shorter but is undetectable. We also observe an abundance of sediment plumes each season (11-25 individual events), which indicates supraglacial drainage events are not the sole source for all sediment plumes. These findings suggest multiple passageways exist from the surface to the subglacial system and the presence of a well-established drainage network early in the melt season. In this poster, we will discuss potential mechanisms for the episodic nature of the recorded plume events; whether they are the product of variable subglacial water supply (suggesting the presence of pulse drainages from subglacial storage basins), highly variable fjord circulation (only allowing subglacial sediment plumes to appear at the surface under specific fjord and plume conditions), or a combination. A clearer understanding of sediment plumes are important for understanding the subglacial hydrological system of tidewater glaciers, as well as gauging the impact of rapid fresh water delivery to melange/sea ice extent in the fjord, terminus stability, submarine melting and fjord circulation.

Freshwater sediments and sludges: two important terrestrial sinks for emissions from damaged NPPs

NASA Astrophysics Data System (ADS)

Fischer, Helmut W.; Evangelia Souti, Maria; Ulbrich, Susanne; Hormann, Volker

2013-04-01

Surface deposition of radionuclides released from the damaged Fukushima NPPs is well documented and emissions to the Pacific Ocean and their distribution with time and space are also subject to monitoring and research. In both cases, solid matter (soil and sea sediment, respectively) acts as a sink for radioisotopes after their transport through air and water. The possible hazards from direct irradiation of workers and public and from entry of radionuclides into food chains are well recognized. Apart from direct deposition onto soil, plants, building roofs etc., aerosols and contaminated rainwater will reach surface waters, leading to long-term deposition in freshwater sediments (and possibly to interim contamination of drinking water). In populated and industrial areas, drained rainwater will enter the wastewater collection and treatment chain if a combined rain and wastewater sewer is used. Depending on the processes in the wastewater treatment plant and chemical element and speciation, the isotopes will either concentrate in treatment sludge or be released with the effluent to rivers and lakes and their sediments. The mentioned media may act as long-term storage for radioisotopes when disposed of properly, but can also contribute to direct irradiation of workers or public, lead to continuous releases to the environment and possibly enter the food chain in the same way as soil and sea sediments. It appears therefore essential to monitor these environmental compartments as well. However, very few data on Fukushima-related radioisotope concentration in sludges and freshwater sediments have been published to date. We will therefore compare data for regional surface deposition and related concentrations in surface water, river sediments and sewage sludge obtained in Europe during 1986 to published data from Japan in 2011 for the most important common short-lived (I-131, half-life = 8.02 d) and long-lived (Cs-137, half-life = 30.17 yr) isotopes. As in central Europe the Chernobyl fallout was not accompanied by other catastrophic events, well documented time series of data exist. It might become possible to estimate sludge and sediment isotope concentrations in Japan by proportionality considerations and by application of transport models when no or insufficient current data exist. Additional insight into transport processes can be obtained from ongoing investigations of medically used I-131 in wastewater and rivers. The results might help in identification and remediation of possibly emerging hazards.

Observations of large-amplitude cross-shore internal bores near the shelf break, Santa Monica Bay, CA

USGS Publications Warehouse

Noble, M.A.; Xu, J. P.

2003-01-01

Two sets of moorings were deployed along a cross-shelf transect in central Santa Monica bay for four months in the winter of 1998-1999. Both sites had an array of instruments attached to tripods set on the seafloor to monitor currents over the entire water column, surface waves, near-bed temperature, water clarity and suspended sediment. A companion mooring had temperature sensors spaced approximately 10 m apart to measure temperature profiles between the surface and the seafloor. One array was deployed in 70 m of water at a site adjacent to the shelf break, just northwest of a major ocean outfall. The other was deployed on the mid shelf in 35 m of water approximately 6 km from the shelf break site. The subtidal currents in the region flowed parallel to the isobaths with fluctuating time scales around 10 days, a typical coastal-ocean pattern. However, during the falling phase of the barotropic spring tide, sets of large-amplitude, sheared cross-shore current pulses with a duration of 2-5 h were observed at the shelf break site. Currents in these pulses flowed exclusively offshore in a thin layer near the bed with amplitudes reaching 30-40 cm/s. Simultaneously, currents with amplitudes around 15-20 cm/s flowed exclusively onshore in the thicker layer between the offshore flow layer and the sea surface. The net offshore transport was about half the onshore transport. Near-surface isotherms were depressed 30-40 m. These pulses were likely internal bores generated by tidal currents. Bed stresses associated with these events exceeded 3 dynes/cm2. These amplitudes are large enough to resuspend and transport not only fine-grained material, but also medium to coarse sands from the shelf toward the slope. Consequently, the seafloor over the shelf break was swept clear of fine sediments. The data suggest that the internal bores dissipate and are reduced in amplitude as they propagate across this relatively narrow shelf. There is evidence that they reach the 35 m site, but other coastal ocean processes obscure their distinctive characteristics.

Hydrodynamic Controls on Archaeal Tetraether Lipid Compositions in Washington Margin Sediments: Insights From Compound-Specific Radiocarbon Measurements

NASA Astrophysics Data System (ADS)

Uchida, M.; Eglinton, T. I.; Montlucon, D. B.; Pearson, A.; Hayes, J. M.

2008-12-01

Continental margin sediments represent a large sink of organic carbon derived from marine and terrestrial sources. Archaeal glycerol dibiphytanyl glycerol tetraether lipids (GDGTs) are derived from both marine and terrestrial sources and have been used both for reconstruction of paleo sea surface temperatures and as an index of terrestrial carbon input to the marine sediments. However, the sources and modes of supply as well as the preservation of GDGTs in marginal sediments are poorly understood. The distribution and deposition of GDGTs is further complicated by hydrodynamic processes. We have analyzed a suite of surface sediment samples collected along a transect from the mouth of the Columbia River, across the Washington Margin, to the Cascadia Basin in the northeast Pacific Ocean. Sediments were separated according to their grain size and hydrodynamic properties, and the organic matter characterized in terms of its bulk elemental, isotopic, and molecular properties. Here we present radiocarbon measurements on individual GDGTs, alkenones, and fatty acids from size-fractionated sediments from shelf and slope sediments, and discuss the results in the context of previous studies of the molecular abundances and isotopic compositions of sedimentary organic matter for in this region. Systematic variations in elemental, isotopic and molecular-level composition are observed across the different particle classes. Moreover, these variations are manifested in the isotopic composition of different molecular markers of both marine and terrestrial sources organic matter. Both marine-derived lipids, including alkenones and marine archaeal tetraethers, and soil microbe-derived tetraether lipids show strong distributional and isotopic variations among the size-fractionated sediments. These variations in terrestrial and marine biomarker properties inform on the sources, particle dynamics, and transport history of organic matter buried on river-influenced continental margins. The implications of these findings for the application of molecular markers as proxies of organic matter input, and on the interpretation of past marine and continental environmental conditions from sedimentary records will also be discussed.

Abyssal ostracods from the South and Equatorial Atlantic Ocean: Biological and paleoceanographic implications

USGS Publications Warehouse

Yasuhara, Moriaki; Cronin, T. M.; Martinez, Arbizu P.

2008-01-01

We report the distribution of ostracods from ???5000 m depth from the Southeast and Equatorial Atlantic Ocean recovered from the uppermost 10 cm of minimally disturbed sediments taken by multiple-corer during the R/V Meteor DIVA2 expedition M63.2. Five cores yielded the following major deep-sea genera: Krithe, Henryhowella, Poseidonamicus, Legitimocythere, Pseudobosquetina, and Pennyella. All genera are widely distributed in abyssal depths in the world's oceans and common in Cenozoic deep-sea sediments. The total number of ostracod specimens is higher and ostracod shell preservation is better near the sediment-water interface, especially at the 0-1 cm core depths. Core slices from ???5 to 10 cm were barren or yielded a few poorly preserved specimens. The DIVA2 cores show that deep-sea ostracod species inhabit corrosive bottom water near the carbonate compensation depth (CCD) even though their calcareous valves are rarely preserved as fossils in sediment cores due to postmortem dissolution. Their occurrence at great water depths may partially explain the well-known global distributions of major deep-sea taxa in the world's oceans, although further expeditions using minimal-disturbance sampling devices are needed to fill geographic gaps. ?? 2008 Elsevier Ltd. All rights reserved.

Earthquakes drive large-scale submarine canyon development and sediment supply to deep-ocean basins

PubMed Central

Mountjoy, Joshu J.; Howarth, Jamie D.; Orpin, Alan R.; Barnes, Philip M.; Bowden, David A.; Rowden, Ashley A.; Schimel, Alexandre C. G.; Holden, Caroline; Horgan, Huw J.; Nodder, Scott D.; Patton, Jason R.; Lamarche, Geoffroy; Gerstenberger, Matthew; Micallef, Aaron; Pallentin, Arne; Kane, Tim

2018-01-01

Although the global flux of sediment and carbon from land to the coastal ocean is well known, the volume of material that reaches the deep ocean—the ultimate sink—and the mechanisms by which it is transferred are poorly documented. Using a globally unique data set of repeat seafloor measurements and samples, we show that the moment magnitude (Mw) 7.8 November 2016 Kaikōura earthquake (New Zealand) triggered widespread landslides in a submarine canyon, causing a powerful “canyon flushing” event and turbidity current that traveled >680 km along one of the world’s longest deep-sea channels. These observations provide the first quantification of seafloor landscape change and large-scale sediment transport associated with an earthquake-triggered full canyon flushing event. The calculated interevent time of ~140 years indicates a canyon incision rate of 40 mm year−1, substantially higher than that of most terrestrial rivers, while synchronously transferring large volumes of sediment [850 metric megatons (Mt)] and organic carbon (7 Mt) to the deep ocean. These observations demonstrate that earthquake-triggered canyon flushing is a primary driver of submarine canyon development and material transfer from active continental margins to the deep ocean. PMID:29546245

Size and Carbon Content of Sub-seafloor Microbial Cells at Landsort Deep, Baltic Sea

PubMed Central

Braun, Stefan; Morono, Yuki; Littmann, Sten; Kuypers, Marcel; Aslan, Hüsnü; Dong, Mingdong; Jørgensen, Bo B.; Lomstein, Bente Aa.

2016-01-01

The discovery of a microbial ecosystem in ocean sediments has evoked interest in life under extreme energy limitation and its role in global element cycling. However, fundamental parameters such as the size and the amount of biomass of sub-seafloor microbial cells are poorly constrained. Here we determined the volume and the carbon content of microbial cells from a marine sediment drill core retrieved by the Integrated Ocean Drilling Program (IODP), Expedition 347, at Landsort Deep, Baltic Sea. To determine their shape and volume, cells were separated from the sediment matrix by multi-layer density centrifugation and visualized via epifluorescence microscopy (FM) and scanning electron microscopy (SEM). Total cell-carbon was calculated from amino acid-carbon, which was analyzed by high-performance liquid chromatography (HPLC) after cells had been purified by fluorescence-activated cell sorting (FACS). The majority of microbial cells in the sediment have coccoid or slightly elongated morphology. From the sediment surface to the deepest investigated sample (~60 m below the seafloor), the cell volume of both coccoid and elongated cells decreased by an order of magnitude from ~0.05 to 0.005 μm3. The cell-specific carbon content was 19–31 fg C cell−1, which is at the lower end of previous estimates that were used for global estimates of microbial biomass. The cell-specific carbon density increased with sediment depth from about 200 to 1000 fg C μm−3, suggesting that cells decrease their water content and grow small cell sizes as adaptation to the long-term subsistence at very low energy availability in the deep biosphere. We present for the first time depth-related data on the cell volume and carbon content of sedimentary microbial cells buried down to 60 m below the seafloor. Our data enable estimates of volume- and biomass-specific cellular rates of energy metabolism in the deep biosphere and will improve global estimates of microbial biomass. PMID:27630628

Millennial-Scale Variability in the Indian Monsoon and Links to Ocean Circulation

NASA Astrophysics Data System (ADS)

DeLong, K. A.; Came, R. E.; Johnson, J. E.; Giosan, L.

2014-12-01

Millennial-scale variability in the Indian monsoon was temporally linked to changes in global ocean circulation during the last glacial period, as evidenced by planktic-benthic foraminiferal stable isotope and trace element results from an intermediate depth sediment core from the northwestern Bay of Bengal. Paired planktic foraminiferal Mg/Ca and δ18Oc constrain sea surface temperatures and isolate millennial-scale variations in the δ18O of surface waters (δ18Osw), which resulted from changes in river runoff in the northwestern Bay. Concurrently with low δ18Osw events, benthic foraminiferal δ13C decreased, suggesting an increased influence of an aged water mass at this intermediate depth site during the low salinity events. Benthic foraminiferal Cd/Ca results support the identification of this water mass as aged Glacial Antarctic Intermediate Water (GAAIW). Lagged correlation analysis (r= 0.41) indicates that changes in subsurface properties led changes in surface properties by an average of 380 years. The implication is that Southern Hemisphere climate exerted a controlling influence on the Indian monsoon during the last glacial period.

Driving forces and their contribution to the recent decrease in sediment flux to ocean of major rivers in China.

PubMed

Li, Tong; Wang, Shuai; Liu, Yanxu; Fu, Bojie; Zhao, Wenwu

2018-09-01

Understanding the mechanisms behind land-ocean sediment transport processes is crucial, due to the resulting impacts on the sustainable management of water and soil resources. This study investigated temporal trends and historical phases of sediment flux delivered to the sea by nine major rivers in China, while also quantifying the contribution of key anthropogenic and natural driving forces. During the past six decades, sediment flux from these nine major rivers exhibited a statistically significant negative trend, decreasing from 1.92Gtyr -1 during 1954-1968 to 1.39Gtyr -1 , 0.861Gtyr -1 and 0.335Gtyr -1 during 1969-1985, 1986-1999 and 2000-2016, respectively. We used a recently developed Sediment Identity approach and found that the sharp decrease in sediment load observed across China was mainly (~95%) caused by a reduction in sediment concentration. Reservoir construction exerted the strongest influence on land-ocean sediment fluxes, while soil conservation measures represented a secondary driver. Before 1999, soil erosion was not controlled effectively in China and reservoirs, especially large ones, played a dominant role in reducing riverine sediments. After 1999, soil erosion has gradually been brought under control across China, so that conservation measures directly accounted for ~40% of the observed decrease in riverine sediments. With intensifying human activities, it is predicted that the total sediment flux delivered to the sea by the nine major rivers will continue to decrease in the coming decades, although at a slower rate, resulting in severe challenges for the sustainable management of drainage basins and river deltas. Copyright © 2018 Elsevier B.V. All rights reserved.

Non-destructive X-ray Computed Tomography (XCT) Analysis of Sediment Variance in Marine Cores

NASA Astrophysics Data System (ADS)

Oti, E.; Polyak, L. V.; Dipre, G.; Sawyer, D.; Cook, A.

2015-12-01

Benthic activity within marine sediments can alter the physical properties of the sediment as well as indicate nutrient flux and ocean temperatures. We examine burrowing features in sediment cores from the western Arctic Ocean collected during the 2005 Healy-Oden TransArctic Expedition (HOTRAX) and from the Gulf of Mexico Integrated Ocean Drilling Program (IODP) Expedition 308. While traditional methods for studying bioturbation require physical dissection of the cores, we assess burrowing using an X-ray computed tomography (XCT) scanner. XCT noninvasively images the sediment cores in three dimensions and produces density sensitive images suitable for quantitative analysis. XCT units are recorded as Hounsfield Units (HU), where -999 is air, 0 is water, and 4000-5000 would be a higher density mineral, such as pyrite. We rely on the fundamental assumption that sediments are deposited horizontally, and we analyze the variance over each flat-lying slice. The variance describes the spread of pixel values over a slice. When sediments are reworked, drawing higher and lower density matrix into a layer, the variance increases. Examples of this can be seen in two slices in core 19H-3A from Site U1324 of IODP Expedition 308. The first slice, located 165.6 meters below sea floor consists of relatively undisturbed sediment. Because of this, the majority of the sediment values fall between 1406 and 1497 HU, thus giving the slice a comparatively small variance of 819.7. The second slice, located 166.1 meters below sea floor, features a lower density sediment matrix disturbed by burrow tubes and the inclusion of a high density mineral. As a result, the Hounsfield Units have a larger variance of 1,197.5, which is a result of sediment matrix values that range from 1220 to 1260 HU, the high-density mineral value of 1920 HU and the burrow tubes that range from 1300 to 1410 HU. Analyzing this variance allows us to observe changes in the sediment matrix and more specifically capture where, and to what extent, the burrow tubes deviate from the sediment matrix. Future research will correlate changes in variance due to bioturbation to other features indicating ocean temperatures and nutrient flux, such as foraminifera counts and oxygen isotope data.

The oceanic budgets of nickel and zinc isotopes: the importance of sulfidic environments as illustrated by the Black Sea

PubMed Central

Little, Susan H.; Archer, Corey; Cameron, Vyllinniskii; Andersen, Morten B.; Rijkenberg, Micha J. A.; Lyons, Timothy W.

2016-01-01

Isotopic data collected to date as part of the GEOTRACES and other programmes show that the oceanic dissolved pool is isotopically heavy relative to the inputs for zinc (Zn) and nickel (Ni). All Zn sinks measured until recently, and the only output yet measured for Ni, are isotopically heavier than the dissolved pool. This would require either a non-steady-state ocean or other unidentified sinks. Recently, isotopically light Zn has been measured in organic carbon-rich sediments from productive upwelling margins, providing a potential resolution of this issue, at least for Zn. However, the origin of the isotopically light sedimentary Zn signal is uncertain. Cellular uptake of isotopically light Zn followed by transfer to sediment does not appear to be a quantitatively important process. Here, we present Zn and Ni isotope data for the water column and sediments of the Black Sea. These data demonstrate that isotopically light Zn and Ni are extracted from the water column, probably through an equilibrium fractionation between different dissolved species followed by sequestration of light Zn and Ni in sulfide species to particulates and the sediment. We suggest that a similar, non-quantitative, process, operating in porewaters, explains the Zn data from organic carbon-rich sediments. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’. PMID:29035259

High fungal diversity and abundance recovered in the deep-sea sediments of the Pacific Ocean.

PubMed

Xu, Wei; Pang, Ka-Lai; Luo, Zhu-Hua

2014-11-01

Knowledge about the presence and ecological significance of bacteria and archaea in the deep-sea environments has been well recognized, but the eukaryotic microorganisms, such as fungi, have rarely been reported. The present study investigated the composition and abundance of fungal community in the deep-sea sediments of the Pacific Ocean. In this study, a total of 1,947 internal transcribed spacer (ITS) regions of fungal rRNA gene clones were recovered from five sediment samples at the Pacific Ocean (water depths ranging from 5,017 to 6,986 m) using three different PCR primer sets. There were 16, 17, and 15 different operational taxonomic units (OTUs) identified from fungal-universal, Ascomycota-, and Basidiomycota-specific clone libraries, respectively. Majority of the recovered sequences belonged to diverse phylotypes of Ascomycota (25 phylotypes) and Basidiomycota (18 phylotypes). The multiple primer approach totally recovered 27 phylotypes which showed low similarities (≤97 %) with available fungal sequences in the GenBank, suggesting possible new fungal taxa occurring in the deep-sea environments or belonging to taxa not represented in the GenBank. Our results also recovered high fungal LSU rRNA gene copy numbers (3.52 × 10(6) to 5.23 × 10(7)copies/g wet sediment) from the Pacific Ocean sediment samples, suggesting that the fungi might be involved in important ecological functions in the deep-sea environments.

Black Carbon in Sedimentary Organic Carbon in the Northeast Pacific using the Benzene Polycarboxylic Acid Method

NASA Astrophysics Data System (ADS)

Coppola, A. I.; Ziolkowski, L. A.; Druffel, E. R.

2010-12-01

Black carbon (BC) in the Northeast Pacific ultrafiltered dissolved organic matter (UDOM) was found to be surprisingly old with a 14C age of 18,000 +/-3,000 14C years (Ziolkowski and Druffel, 2010) using the Benzene Polycarboxylic Acid (BPCA) method, while BC in sedimentary organic carbon (SOC) was found to be 2,400-12,900 14C years older than non-BC SOC (Masiello and Druffel, 1998) with a different method. Using the dichromate-sulfuric acid oxidation method (Wolbach and Anders, 1989), Masiello and Druffel (1998) estimated that 12-31% of SOC in the Northeast Pacific and the Southern Ocean surface sediments was black carbon (BC). However, the dichromate-sulfuric acid oxidation may over-estimate the concentration of BC, because this method is more biased toward modern (char) material (Currie et al., 2002). Alternatively, the BPCA method isolates aromatic components of BC as benzene rings substituted with carboxylic acid groups, and provides structural information about the BC. Recent modifications to the BPCA method by Ziolkowski and Druffel (2009) involve few biases in quantifying BC in the continuum between char and soot in UDOM. Here we use the BPCA method to determine the concentrations and 14C values of BC in sediments from three sites in the Northeast Pacific Ocean. Constraining the difference between non-BC SOC and BC-SOC using the BPCA method allows for a more precise estimate of how much BC is present in the sediments and its 14C age. Presumably, the intermediate reservoir of BC is oceanic dissolved organic carbon (DOC) and is, in part, responsible for DOC’s great 14C age. These results can be utilized to better constrain the oceanic carbon budget as a possible sink of BC. References: Currie, L. A., Benner Jr., B. A., Kessler, J.D., et al (2002), A critical evaluation of interlaboratory data on total, elemental, and isotopic carbon in the carbonaceous particle reference material, nist srm 1649a, J. Res. Natl. Inst. Stand. Technol., 107, 279-298. Masiello, C., and E. R. Druffel (1988), Black carbon in deep-sea sediments, Science, 280, 1911-1913. Wolbach, W., and E. Anders (1989), Elemental carbon in sediments: Determination and isotopic analysis in presence of kerogen, Geochim. Cosmochim. Acta, 53, 1637-1647. Ziolkowski, L. A., and E. R. Druffel (2010), Aged black carbon identified in marine dissolved organic carbon, J. Geophys. Res., 37, L16601, doi: 10.1029/2010GL043963.

Sulfur Upwelling off the African Coast

NASA Technical Reports Server (NTRS)

2002-01-01

Though these aquamarine clouds in the waters off the coast of northern Namibia may look like algae blooms, they are in fact clouds of sulfur produced by anaerobic bacteria on the ocean's floor. This image of the sulfur-filled water was taken on April 24, 2002, by the Sea-viewing Wide Field-of-View Sensor (SeaWiFS), flying aboard the Orbview-2 satellite. The anaerobic bacteria (bacteria that can live without oxygen) feed upon algae carcasses that exist in abundance on the ocean's floor off of Namibia. As the bacteria ingest the algae husks, they produce hydrogen sulfide, which slowly builds up in the sea-floor sediments. Eventually, the hydrogen sulfide reaches the point where the sediment can no longer contain it, and it bubbles forth. When this poisonous chemical reaches the surface, it combines with the oxygen in the upper layers of the ocean to create clouds of pure sulfur. The sulfur causes the Namibian coast to smell like rotten eggs, and the hydrogen sulfide will often kill fish and drive lobsters away. For more information, read: A Bloom By Any Other Name A high-resolution (250 meters per pixel) image earlier on the 24th taken from the Moderate-Resolution Imaging Spectroradiometer (MODIS) shows additional detail in the plumes. Image courtesy the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE. MODIS image courtesy Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC

Chemical gradients in sediment cores from an EPA reference site off the Farallon Islands - Assessing chemical indicators of dredged material disposal in the deep sea

USGS Publications Warehouse

Bothner, Michael H.; Gill, P.W.; Boothman, W.S.; Taylor, B.B.; Karl, Herman A.

1998-01-01

Heavy metal and organic contaminants have been determined in undisturbed sediment cores from the US Environmental Protection Agency reference site for dredged material on the continental slope off San Francisco. As expected, the concentrations are significantly lower than toxic effects guidelines, but concentrations of PCBs, PAHs, Hg, Pb, and Clostridium perfringens (a bacterium spore found in sewage) were nearly two or more times greater in the surface sediments than in intervals deeper in the cores. These observations indicate the usefulness of measuring concentration gradients in sediments at the San Francisco deep ocean disposal site (SF-DODS) where a thin (0.5 cm thick) layer of dredged material has been observed beyond the boundary. This thin layer has not been chemically characterized by the common practice of homogenizing over the top 10 cm. An estimated 300 million cubic yards of dredged material from San Francisco Bay are expected to be discharged at the SF-DODS site during the next 50 years. Detailed depth analysis of sediment cores would add significant new information about the fate and effects of dredged material in the deep sea.

Sediment Accretion During Horst and Graben Subduction associated with the Tohoku Oki M9 Earthquake, Northern Japan

NASA Astrophysics Data System (ADS)

Moore, J. C.; Chester, F. M.

2015-12-01

The stratigraphic sequence within the frontal accretionary prism of the Japan Trench, the site of large slip during the Tohoku earthquake, is unique due to horst and graben subduction. Boreholes at IODP Site C0019, penetrating the toe of the Tohoku accretionary prism, document a younger over older intraprism thrust contact with a 9 Ma age gap across the basal plate boundary fault. The anomalously young (Quaternary to Pliocene), fault-bounded sediment package is 130 m thick, of a total of 820 m of sediment above the plate boundary fault. In contrast, typical accretionary prism structure consists of stacked sediment packages on imbricate faults above the basal decollement resulting in an overall increase in age downward. Site C0019 penetrates the prism directly above a horst of the subducting Pacific oceanic crust. Here the plate-boundary fault consists of a thin, weak smectitic pelagic clay that is probably the principal slip surface of ~50 m offset in the 2011 Tohoku earthquake. The fault continues seaward deepening off the seaward edge of the horst and beneath the sediment fill of the adjacent graben, dying out at the landward base of the next incoming horst. The plate boundary fault and its splays in the graben form a narrow-taper protoprism and a small sedimentary basin of trench fill marking the seaward edge of the upper plate. The modern fault and sediment distributions within the graben are used to motivate a viable model for the presence of anomalously young sediments directly above the plate boundary fault. In this model sediments in the trench are thrust over the incoming horst by propagation of the plate boundary thrust up the landward-dipping fault of the incoming horst and along the smectitic clay layer to emplace Quaternary and Pliocene trench deposits directly on top of the incoming horst. These young deposits are in turn overlain by sediments 9 Ma or older that have been transported out of the graben along imbricate faults associated with the necessary increase in the taper of the prism above the graben. The Quaternary to Pliocene units thicken due to internal deformation accounting for the 130 m thickness now observed over the plate boundary fault at Site C0019. Conversely emplacement of very young sediment directly above a basal detachment would be unexpected in accretionary prisms subducting smoother oceanic crust.

The geochemistry of redox sensitive trace metals in sediments

NASA Astrophysics Data System (ADS)

Morford, Jennifer L.; Emerson, Steven

1999-06-01

We analyzed the redox sensitive elements V, Mo, U, Re and Cd in surface sediments from the Northwest African margin, the U.S. Northwest margin and the Arabian Sea to determine their response under a range of redox conditions. Where oxygen penetrates 1 cm or less into the sediments, Mo and V diffuse to the overlying water as Mn is reduced and remobilized. Authigenic enrichments of U, Re and Cd are evident under these redox conditions. With the onset of sulfate reduction, all of the metals accumulate authigenically with Re being by far the most enriched. General trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes: oxic, reducing where oxygen penetrates ≤1 cm, and anoxic conditions. Using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations, we calculate the area of sediments below 1000 m water depth in which oxygen penetration is ≤1 cm to be 4% of the ocean floor. We conclude that sediments where oxygen penetrates ≤1 cm release Mn, V and Mo to seawater at rates of 140%-260%, 60%-150% and 5%-10% of their respective riverine fluxes, using the authigenic metal concentrations and accumulation rates from this work and other literature. These sediments are sinks for Re, Cd and U, with burial fluxes of 70%-140%, 30%-80% and 20%-40%, respectively, of their dissolved riverine inputs. We modeled the sensitivity of the response of seawater Re, Cd and V concentrations to changes in the area of reducing sediments where oxygen penetrates ≤1 cm. Our analysis suggests a negligible change in seawater Re concentration, whereas seawater concentrations of Cd and V could have decreased and increased, respectively, by 5%-10% over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10%-20% if the area increased by a factor of 3. The concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of Cd/Ca and V/Ca ratios observed in foraminifera shells over the last 40 kyr. This implies that the area of reducing sediments in the ocean deeper than 1000 m (4%) has not been greater than twice the present value in the recent past.

Seawater as the source of minor elements in black shales, phosphorites and other sedimentary rocks

USGS Publications Warehouse

Piper, D.Z.

1994-01-01

Many of the minor elements in seawater today have a concentration-depth profile similar to that of the biologically essential nutrients, NO-3 and PO3-4. They show a relative depletion in the photic zone and enrichment in the deep ocean. The difference between their surface- and deep-ocean values, normalized to the change in PO3-4, approaches the average of measured minor-element: P ratios in marine plankton, although individual analyses of the latter show extreme scatter for a variety of reasons. Despite this scatter in the minor-element analyses of plankton, agreement between the two sets of data shows unequivocally that an important marine flux of many minor elements through the ocean is in the form of biogenic matter, with a composition approaching that of plankton. This interpretation is further supported by sediment studies, particularly of sediments which accumulate in shelf-slope environments where biological productivity in the photic zone is exceptionally high and organic carbon contents of the underlying sediment elevated. The interelement relations observed for some of these sediments approach the average values of plankton. These same interelement relations are observed in many marine sedimentary rocks such as metalliferous black shales and phosphorites, rocks which have a high content of marine fractions (e.g., organic matter, apatite, biogenic silica and carbonates). Many previous studies of the geochemistry of these rocks have concluded that local hydrothermal activity, and/or seawater with an elemental content different from that of the modern ocean, was required to account for their minor-element contents. However, the similarity in several of the minor-element ratios in many of these formations to minor-element ratios in modern plankton demonstrates that these sedimentary rocks accumulated in environments whose marine chemistry was virtually identical to that seen on continental shelf-slopes, or in marginal seas, of the ocean today. The accumulation of the marine fraction of minor elements on these ancient sea floors was determined largely by the accumulation of organic matter, settling from the photic zone and with a composition of average plankton. A second marine fraction of minor elements in these rocks accumulated through precipitation and adsorption from seawater. The suite of elements in this fraction reflects redox conditions in the bottom water, as determined by bacterial respiration. For example, high Mn, high Cr+V and high Mo concentrations, above those which can be attributed to the accumulation of planktonic matter, characterize accumulation under bottom-water oxidizing, denitrifying and sulfate-reducing conditions, respectively. ?? 1994.

Molybdenum Cycling in Upwelling Sediments: An Example from Namibian Margin Sediments

NASA Astrophysics Data System (ADS)

Arnold, G. L.; Goldhammer, T.; Formolo, M.; Brunner, B.; Ferdelman, T.

2008-12-01

The paleo-redox application of molybdenum (Mo) isotopes is strongly tied to our knowledge of the modern marine Mo cycle. Elemental mass balance indicates that ~47% of the Mo supplied to the oceans is removed to deep sea sediments, leaving the remaining Mo to "near-shore" reducing sediments (1). The Black Sea is likely the best studied reducing environment with regards to Mo isotopes, yet accounts for only a small fraction of the Mo mass balance. The accumulation of Mo in continental margin sediments has been recently re-assessed and may account for a larger fraction of the marine Mo reservoir than previously thought (2). In the presence of sulfide, the molybdate anion is transformed, by the replacement of oxygen with sulfur, to particle reactive oxy-thiomolybdates (3). This is often cited as the mechanism by which Mo removal proceeds in the Black Sea where sulfide concentrations in the water are high. In contrast, in continental margin settings, the removal mechanism is poorly understood, and the extent to which sulfur cycling plays a role remains un-quantified. To better understand removal/cycling processes in a continental margin setting, where sulfide may only be present in the pore waters and not in the water column, Mo was studied in an array of marine settings off the Namibian coast. Surface sediments were collected across a transect from near-shore/high productivity to deep water/low productivity sediments. These sediments were incubated in bag experiments to study the relationship between sulfur and Mo cycling. Molybdenum concentrations in the Namibian sediments range from detrital values at the lowest productivity site to 25 ppm in surface sediments with high productivity. Preliminary results allude to a correlation between sulfate reduction rates and Mo accumulation in these sediments. Detailed studies of Mo, Mo isotopes, other trace metals, and sulfur investigations from both sediment cores and bag experiments will be presented. (1)Bertine and Turekian (1973), Geochim. Cosmochim. Acta 87, 1415. (2)McManus et al. (2006), Geochim. Cosmochim. Acta 70, 4643. (3)Erickson and Helz (2000) Geochim. Cosmochim. Acta 64, 1149.

The Toba Volcanic Event and Interstadial/Stadial Climates at the Marine Isotopic Stage 5 to 4 Transition in the Northern Indian Ocean

NASA Astrophysics Data System (ADS)

Schulz, Hartmut; Emeis, Kay-Christian; Erlenkeuser, Helmut; von Rad, Ulrich; Rolf, Christian

2002-01-01

The Toba volcanic event, one of the largest eruptions during the Quaternary, is documented in marine sediment cores from the northeastern Arabian Sea. On the crest of the Murray Ridge and along the western Indian continental margin, we detected distinct concentration spikes and ash layers of rhyolithic volcanic shards near the marine isotope stage 5-4 boundary with the chemical composition of the "Youngest Toba Tuff." Time series of the U k'37-alkenone index, planktic foraminiferal species, magnetic susceptibility, and sediment accumulation rates from this interval show that the Toba event occurred between two warm periods lasting a few millennia. Using Toba as an instantaneous stratigraphic marker for correlation between the marine- and ice-core chronostratigraphies, these two Arabian Sea climatic events correspond to Greenland interstadials 20 and 19, respectively. Our data sets thus depict substantial interstadial/stadial fluctuations in sea-surface temperature and surface-water productivity. We show that variable terrigenous (eolian) sediment supply played a crucial role in transferring and preserving the productivity signal in the sediment record. Within the provided stratigraphic resolution of several decades to centennials, none of these proxies shows a particular impact of the Toba eruption. However, our results are additional support that Toba, despite its exceptional magnitude, had only a minor impact on the evolution of low-latitude monsoonal climate on centennial to millennial time scales.

Early Paleogene variations in the calcite compensation depth: new constraints using old borehole sediments from across Ninetyeast Ridge, central Indian Ocean

NASA Astrophysics Data System (ADS)

Slotnick, B. S.; Lauretano, V.; Backman, J.; Dickens, G. R.; Sluijs, A.; Lourens, L.

2015-03-01

Major variations in global carbon cycling occurred between 62 and 48 Ma, and these very likely related to changes in the total carbon inventory of the ocean-atmosphere system. Based on carbon cycle theory, variations in the mass of the ocean carbon should be reflected in contemporaneous global ocean carbonate accumulation on the seafloor and, thereby, the depth of the calcite compensation depth (CCD). To better constrain the cause and magnitude of these changes, the community needs early Paleogene carbon isotope and carbonate accumulation records from widely separated deep-sea sediment sections, especially including the Indian Ocean. Several CCD reconstructions for this time interval have been generated using scientific drill sites in the Atlantic and Pacific oceans; however, corresponding information from the Indian Ocean has been extremely limited. To assess the depth of the CCD and the potential for renewed scientific drilling of Paleogene sequences in the Indian Ocean, we examine lithologic, nannofossil, carbon isotope, and carbonate content records for late Paleocene - early Eocene sediments recovered at three sites spanning Ninetyeast Ridge: Deep Sea Drilling Project (DSDP) Sites 213 (deep, east), 214 (shallow, central), and 215 (deep, west). The disturbed, discontinuous sediment sections are not ideal, because they were recovered in single holes using rotary coring methods, but remain the best Paleogene sediments available from the central Indian Ocean. The δ13C records at Sites 213 and 215 are similar to those generated at several locations in the Atlantic and Pacific, including the prominent high in δ13C across the Paleocene carbon isotope maximum (PCIM) at Site 215, and the prominent low in δ13C across the early Eocene Climatic Optimum (EECO) at both Site 213 and Site 215. The Paleocene-Eocene thermal maximum (PETM) and the K/X event are found at Site 213 but not at Site 215, presumably because of coring gaps. Carbonate content at both Sites 213 and 215 drops to <5% shortly after the first occurrence of Discoaster lodoensis and the early Eocene rise in δ13C (~52 Ma). This reflects a rapid shoaling of the CCD, and likely a major decrease in the net flux of 13C-depleted carbon to the ocean. Our results support ideas that major changes in net fluxes of organic carbon to and from the exogenic carbon cycle occurred during the early Paleogene. Moreover, we conclude that excellent early Paleogene carbonate accumulation records might be recovered from the central Indian Ocean with future scientific drilling.

Let's Bet on Sediments! Hudson Canyon Cruise--Grades 9-12. Focus: Sediments of Hudson Canyon.

ERIC Educational Resources Information Center

National Oceanic and Atmospheric Administration (DOC), Rockville, MD.

These activities are designed to teach about the sediments of Hudson Canyon. Students investigate and analyze the patterns of sedimentation in the Hudson Canyon, observe how heavier particles sink faster than finer particles, and learn that submarine landslides are avalanches of sediment in deep ocean canyons. The activity provides learning…

The relationship between Arabian Sea upwelling and Indian Monsoon revisited in a high resolution ocean simulation

NASA Astrophysics Data System (ADS)

Yi, Xing; Hünicke, Birgit; Tim, Nele; Zorita, Eduardo

2018-01-01

Studies based on sediment records, sea-surface temperature and wind suggest that upwelling along the western coast of Arabian Sea is strongly affected by the Indian summer Monsoon. We examine this relationship directly in an eddy-resolving global ocean simulation STORM driven by atmospheric reanalysis over the last 61 years. With its very high spatial resolution (10 km), STORM allows us to identify characteristics of the upwelling system. We analyse the co-variability between upwelling and meteorological and oceanic variables from 1950 to 2010. The analysis reveals high interannual correlations between coastal upwelling and along-shore wind-stress (r = 0.73) as well as with sea-surface temperature (r = -0.83). However, the correlation between the upwelling and the Monsoon is small. We find an atmospheric circulation pattern different from the one that drives the Monsoon as the main modulator of the upwelling variability. In spite of this, the patterns of temperature anomalies that are either linked to Arabian Sea upwelling or to the Monsoon are spatially quite similar, although the physical mechanisms of these links are different. In addition, no long-term trend is detected in our modelled upwelling in the Arabian Sea.

Iron Resources and Oceanic Nutrients - Advancement of Global Environment Simulations (ironages)

NASA Astrophysics Data System (ADS)

de Baar, H. J. W.; Ironages Team

Iron limits productivity in 40 percent of the oceans, and is a co-limitation in the re- maining 60 percent of surface waters. Moreover the paradigm of a single factor limit- ing plankton blooms, is presently giving way to co-limitation by light, and the nutri- ents N, P, Si, and Fe. Primary production, export into the deep sea, and CO2 uptake from the atmosphere together form the 'biological pump' in Ocean Biogeochemi- cal Climate Models (OBCM's). Thus far OBCM's assume just one limiting nutrient (P) and one universal phytoplankton species, for deriving C budgets and CO2 ex- change with the atmosphere. New realistic OBCM's are being developed in IRON- AGES for budgeting and air/sea exchanges of both CO2 and DMS, implementing (1) co-limitation by 4 nutrients of 5 major taxonomic classes of phytoplankton in a nested plankton ecosystem model, (ii) DMS(P) pathways, (iii) global iron cycling, (iv) chem- ical forms of iron and (v) iron supply in surface waters from above by aerosols and from below out of reducing margin sediments. IRONAGES is a consortium of 12 Eu- ropean institutes coordinated by the Royal NIOZ.

Stability of Gas Hydrates on Continental Margins: Implications of Subsurface Fluid Flow

NASA Astrophysics Data System (ADS)

Nunn, J. A.

2008-12-01

Gas hydrates are found at or just below the sediment-ocean interface in continental margins settings throughout the world. They are also found on land in high latitude regions such as the north slope of Alaska. While gas hydrate occurrence is common, gas hydrates are stable under a fairly restricted range of temperatures and pressures. In a purely conductive thermal regime, near surface temperatures depend on basal heat flow, thermal conductivity of sediments, and temperature at the sediment-water or sediment-air interface. Thermal conductivity depends on porosity and sediment composition. Gas hydrates are most stable in areas of low heat flow and high thermal conductivity which produce low temperature gradients. Older margins with thin continental crust and coarse grained sediments would tend to be colder. Another potentially important control on subsurface temperatures is advective heat transport by recharge/discharge of groundwater. Upward fluid flow depresses temperature gradients over a purely conductive regime with the same heat flow which would make gas hydrates more stable. Downward fluid flow would have the opposite effect. However, regional scale fluid flow may substantially increase heat flow in discharge areas which would destabilize gas hydrates. For example, discharge of topographically driven groundwater along the coast in the Central North Slope of Alaska has increased surface heat flow in some areas by more than 50% over a purely conductive thermal regime. Fluid flow also alters the pressure regime which can affect gas hydrate stability. Modeling results suggest a positive feedback between gas hydrate formation/disassociation and fluid flow. Disassociation of gas hydrates or permafrost due to global warming could increase permeability. This could enhance fluid flow and associated heat transport causing a more rapid and/or more spatially extensive gas hydrate disassociation than predicted solely from conductive propagation of temporal changes in surface or water bottom temperature. Model results from both the North Slope of Alaska and the Gulf of Mexico are compared.

On a grain of sand - a microhabitat for the opportunistic agglutinated foraminifera Hemisphaerammina apta n. sp., from the early Eocene Arctic Ocean

NASA Astrophysics Data System (ADS)

McNeil, David H.; Neville, Lisa A.

2018-02-01

Hemisphaerammina apta n. sp. is an attached monothalamous agglutinated foraminifera discovered in shelf sediments of the early Eocene Arctic Ocean. It is a simple yet distinctive component of the endemic agglutinated foraminiferal assemblage that colonized the Arctic Ocean after the microfaunal turnover caused by the Paleocene-Eocene Thermal Maximum. Associated foraminifera are characterized by a high percentage of monothalamous species (up to 60 %) and are entirely agglutinated indicating a brackish (mesohaline) early Eocene Arctic Ocean. Hemisphaerammina apta occurs exclusively as individuals attached to fine detrital grains (0.2 to 1.8 mm) of sediment. It is a small species (0.06 to 0.2 mm in diameter), fine-grained, with a low hemispherical profile, no floor across the attachment area, no substantive marginal flange, no internal structures, and no aperture. Lacking an aperture, it apparently propagated and fed through minute (micrometre-sized) interstitial pores in the test wall. Attachment surfaces vary from concave to convex and rough to smooth. Grains for attachment are diverse in shape and type but are predominantly of quartz and chert. The presence of H. apta in the early Eocene was an opportunistic response to an environment with an active hydrological system (storm events). Attachment to grains of sand would provide a more stable base on a sea floor winnowed by storm-generated currents. Active transport is indicated by the relative abundance of reworked foraminifera mixed with in situ species. Contemporaneous reworking and colonization by H. apta is suggested by its attachment to a reworked specimen of Cretaceous foraminifera.

Possible Climatic Signal Recorded by Alkenone Distributions in Sediments from Freshwater and Saline Lakes on the Skarvsnes and Skallen Areas, Antarctica

NASA Astrophysics Data System (ADS)

Sawada, K.; Takeda, M.; Takano, Y.

2014-12-01

The distribution of long-chain (C37 - C39) alkenones in marine sediment has been well documented to record paleo-sea surface temperatures. The alkenones were also found in sediments of terrestrial saline lakes, and recently the calibrations of alkenone unsaturation indices - temperature have been established in continental areas. Furthermore, these biomarkers have been identified in lacustrine sediments on high-latitudinal terrestrial areas such as Greenland and Antarctica. In the present study, the alkenones were identified in the lacustrine sediment cores in freshwater (Lake Naga-ike) and saline lakes (Lake Suribati and Lake Funazoko) on the Skarvsnes, and a saline lake (Lake Skallen Oh-ike) on the Skallen, Antarctica. Here, we report that the alkenone distribution in the Antarctic lakes was examined as paleotemperature proxy. C37-C38 Tetra- and tri-unsaturated alkenones and C37 tetra- and tri-unsaturated alkenoates are identified in all sediment samples. The C37 di-unsaturated (C37:2) alkenones can be identified in sediments of surface layers (0-15 cm) of Lake Naga-ike and layers of 160-190 cm depth, in which age is ca. 3000 years BP by 14C dating, in Lake Skallen Ohike, and alkenone unsaturation index (UK37) is analyzed from these sediments. By using a calibration obtained from a culture strain Chrysotila lamellosa as reported by Nakamura et al. (2014), paleotemperatures are calculated to be 9.2-15ºC in surface sediments of Lake Naga-ike and 6.8-8.6ºC in Lake Skallen Oh-ike, respectively. The estimated temperatures are concordant with summer temperature of lake waters observed in Lake Naga-ike. Also, the highest concentrations of the alkenones and alkenoates are observed in deeper (older) sediment layers from Lake Naga-ikes, which has not been connected the ocean and intruded sea water. This implies that the alkenones are originated from indigenous biological organism(s) in Antarctic lake water. The class distributions (unsaturation ratios) of alkenones varied with core depths in Lake Naga-ike and Lake Suribati, whereas these are nearly constant with core depths in Lake Funazoko. These variations presumably depended on changes of climatic and environmental conditions in lake water. Thus, it is suggested that the alkenone proxies can be applicable for Antarctic climate changes.