Can upwelling signals be detected in intertidal fishes of different trophic levels?

PubMed

Pulgar, J; Poblete, E; Alvarez, M; Morales, J P; Aranda, B; Aldana, M; Pulgar, V M

2013-11-01

For intertidal fishes belonging to three species, the herbivore Scartichthys viridis (Blenniidae), the omnivore Girella laevifrons (Kyphosidae) and the carnivore Graus nigra (Kyphosidae), mass and body size relationships were higher in individuals from an upwelling zone compared with those from a non-upwelling zone. RNA:DNA were higher in the herbivores and omnivores from the upwelling zone. Higher biomass and RNA:DNA in the upwelling intertidal fishes may be a consequence of an increased exposure to higher nutrient availability, suggesting that increased physiological conditioning in vertebrates from upwelling areas can be detected and measured using intertidal fishes of different trophic levels. © 2013 The Fisheries Society of the British Isles.

Has upwelling strengthened along worldwide coasts over 1982-2010?

NASA Astrophysics Data System (ADS)

Varela, R.; Álvarez, I.; Santos, F.; Decastro, M.; Gómez-Gesteira, M.

2015-05-01

Changes in coastal upwelling strength have been widely studied since 1990 when Bakun proposed that global warming can induce the intensification of upwelling in coastal areas. Whether present wind trends support this hypothesis remains controversial, as results of previous studies seem to depend on the study area, the length of the time series, the season, and even the database used. In this study, temporal and spatial trends in the coastal upwelling regime worldwide were investigated during upwelling seasons from 1982 to 2010 using a single wind database (Climate Forecast System Reanalysis) with high spatial resolution (0.3°). Of the major upwelling systems, increasing trends were only observed in the coastal areas of Benguela, Peru, Canary, and northern California. A tendency for an increase in upwelling-favourable winds was also identified along several less studied regions, such as the western Australian and southern Caribbean coasts.

Has upwelling strengthened along worldwide coasts over 1982-2010?

PubMed Central

Varela, R.; Álvarez, I.; Santos, F.;  deCastro, M.; Gómez-Gesteira, M.

2015-01-01

Changes in coastal upwelling strength have been widely studied since 1990 when Bakun proposed that global warming can induce the intensification of upwelling in coastal areas. Whether present wind trends support this hypothesis remains controversial, as results of previous studies seem to depend on the study area, the length of the time series, the season, and even the database used. In this study, temporal and spatial trends in the coastal upwelling regime worldwide were investigated during upwelling seasons from 1982 to 2010 using a single wind database (Climate Forecast System Reanalysis) with high spatial resolution (0.3°). Of the major upwelling systems, increasing trends were only observed in the coastal areas of Benguela, Peru, Canary, and northern California. A tendency for an increase in upwelling-favourable winds was also identified along several less studied regions, such as the western Australian and southern Caribbean coasts. PMID:25952477

Seasonality in planktic foraminifera of the central California coastal upwelling region

NASA Astrophysics Data System (ADS)

Davis, Catherine V.; Hill, Tessa M.; Russell, Ann D.; Gaylord, Brian; Jahncke, Jaime

2016-09-01

The close association between planktic foraminiferal assemblages and local hydrography make foraminifera invaluable proxies for environmental conditions. Modern foraminiferal seasonality is important for interpreting fossil distributions and shell geochemistry as paleoclimate proxies. Understanding this seasonality in an active upwelling area is also critical for anticipating which species may be vulnerable to future changes in upwelling intensity and ocean acidification. Two years (2012-2014) of plankton tows, along with conductivity-temperature-depth profiles and carbonate chemistry measurements taken along the north-central California shelf, offer new insights into the seasonal dynamics of planktic foraminifera in a seasonal coastal upwelling regime. This study finds an upwelling affinity for Neogloboquadrina pachyderma as well as a seasonal and upwelling associated alternation between dominance of N. pachyderma and Neogloboquadrina incompta, consistent with previous observations. Globigerina bulloides, however, shows a strong affinity for non-upwelled waters, in contrast to findings in Southern California where the species is often associated with upwelling. We also find an apparent lunar periodicity in the abundances of all species and document the presence of foraminifera even at very low saturation states of calcite.

Development of upwelling on pathway and freshwater transport of Pearl River plume in northeastern South China Sea

NASA Astrophysics Data System (ADS)

Chen, Zhaoyun; Jiang, Yuwu; Liu, James T.; Gong, Wenping

2017-08-01

In situ observations, satellite images, and numerical modeling results have shown that the Pearl River plume axis extends alongshore and passes through two separate upwelling regions—one off the Guangdong and Fujian coasts (the Yuedong upwelling) and the other in the Taiwan Bank during the initial and medium stages of the Yuedong upwelling, while it is directed offshore when the Yuedong upwelling is strong. Model experiments are conducted to examine the effects of wind strength and baroclinicity on the upwelling and the corresponding pathway and freshwater transport of the Pearl River plume. The baroclinic effect is important to intensifying the horizontal velocity at the upwelling front and freshwater transport in the northeastern South China Sea. The freshwater transport flux is further decomposed into advection, vertical shear, and tidal pumping components, and advection is the dominant contributor. As the Yuedong upwelling develops, the zone with a relatively high-pressure gradient moves offshore due to offshore Ekman transport and the shift in the upwelling front, which is responsible for the offshore transport of the river plume. When the river plume is transported to the outer-shelf, sometimes it can be further entrained into eddies, allowing its export to the open sea.

Spatio-temporal variability of upwelling along the southwest coast of India based on satellite observations

NASA Astrophysics Data System (ADS)

Jayaram, Chiranjivi; Kumar, P. K. Dinesh

2018-03-01

Upwelling phenomenon along the eastern boundaries of global ocean has received greater attention in the recent times due to its environmental and economic significance in the global warming and the scenario of changing climate as opined by IPCC AR5. In this context, the availabile satellite data on sea surface winds, sea surface temperature (SST), sea level anomaly (SLA) and chlorophyll-a concentration (Chl-a), for the period 1981-2016 were analyzed to identify the coastal upwelling pattern in the Southeastern Arabian Sea (SEAS). Synergistic approach, using winds, SST, SLA and Chl-a revealed that strong upwelling was prevailing between 8°N and 12°N. During the study period, geographical differences existed in the peak values of upwelling favorable conditions considered for study. Analysis of the alongshore winds which are conducive for upwelling were observed to be curtailed towards the northern part of the study region between 2005 and 2010. Also, the strength of upwelling reduced during the strong ENSO years of 1997 and 2015. Linear regression based trend analysis of upwelling indices like Ekman transport, SST and chlorophyll along the coast, during the upwelling period, revealed slight increase in the strength towards the southern region while it decreased to the north during the study period.

Long-time observation of annual variation of Taiwan Strait upwelling in summer season

NASA Astrophysics Data System (ADS)

Tang, D. L.; Kawamura, H.; Guan, L.

The Taiwan Strait is between Taiwan Island and Mainland China, where several upwelling zones are well known for good fishing grounds. Earlier studies in the strait have been conducted on detecting upwelling by ship measurements with short-term cruises, but long-term variations of upwelling in this region are not understood. The present paper examines satellite images for a long-time observation of two major upwelling zones in the Taiwan Strait: Taiwan Bank Upwelling (TBU) and Dongshan Upwelling (DSU). Sea surface temperature (SST) and chlorophyll a (Chl-a) images have been analyzed for summer months (June, July, and August) from 1980 to 2002. Results reveal annual variation of two upwelling zones. These two upwelling zones occur every year characterized with distinct low water temperature and high Chl-a concentrations. During the period from 1989 to 1998, SST is found to be 1.15 °C lower in TBU, and 1.42 °C lower in the DSU than the Taiwan Strait. The size of DSU has been found to be larger during summer of 1989, 1990, 1993 and 1995; TBU has been found to be weak during summer of 1994 and 1997. Ocean color images obtained from CZCS, OCI, and SeaWiFS also show high Chl-a concentrations (0.8-2.5 mg m-3) in two upwelling zones, which coincide with low SST in terms of location, shape, and time. These high Chl-a concentrations in TBU and DSU may be related to upwelling waters that bring nutrients from bottom to surface. The present results also show the potential of using satellite data for monitoring of ocean environment for long time period.

Dynamics of Black Band Disease in a Diploria strigosa population subjected to annual upwelling on the northeastern coast of Venezuela

NASA Astrophysics Data System (ADS)

Rodríguez, S.; Cróquer, A.

2008-06-01

Temporal variability of Black Band Disease (BBD) prevalence, incidence, recurrence, recovery and virulence was estimated in a Diploria strigosa population from an upwelling zone of Venezuela, for 1 year between August 2004 and August 2005. The sampling spanned both upwelling and non-upwelling seasons, and included three samplings, roughly 60 days apart, within each season. The negative effects of BBD epizootiology in the sampling population (El Mercado reef) were positively correlated with sea surface temperature (taken as an upwelling estimator). Disease prevalence, incidence and recurrence decreased significantly during upwelling, and the recovery rate increased. Contrary to expectations, tissue mortality did not decrease significantly during the upwelling season, remaining at 1.2 ± 0.7 mm day-1. BBD prevalence, and the ensuing rates of tissue mortality were higher than values previously reported for other Caribbean reefs, even during upwelling episodes, suggesting that nutrient enrichment of the local waters by upwelling counteracts the expected reductions of the disease prevalence and virulence due to the lower temperature. Colonies which had previously been infected with BBD were up to six times more susceptible to new infections than those which were not infected during the preceding 7 months, suggesting that the infected colonies never healed completely. The high variability between tissue mortality values among coral colonies also suggests that overall host health-status may alter susceptibility to BBD infections.

Coupled ice-ocean dynamics in the marginal ice zones Upwelling/downwelling and eddy generation

NASA Technical Reports Server (NTRS)

Hakkinen, S.

1986-01-01

This study is aimed at modeling mesoscale processes such as upwelling/downwelling and ice edge eddies in the marginal ice zones. A two-dimensional coupled ice-ocean model is used for the study. The ice model is coupled to the reduced gravity ocean model through interfacial stresses. The parameters of the ocean model were chosen so that the dynamics would be nonlinear. The model was tested by studying the dynamics of upwelling. Wings parallel to the ice edge with the ice on the right produce upwelling because the air-ice momentum flux is much greater than air-ocean momentum flux; thus the Ekman transport is greater than the ice than in the open water. The stability of the upwelling and downwelling jets is discussed. The downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence. The constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling/downwelling regions, i.e., wind-forced vortices. Steepening and strengthening of vortices are provided by the nonlinear terms. When forcing is time-varying, the advection terms will also redistribute the vorticity. The wind reversals will separate the vortices from the ice edge, so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice.

A study on the seasonal variability of upwelling and its effects on physical parameters in Arabian Sea

NASA Astrophysics Data System (ADS)

Shukla, Rohit Kumar; Shaji, Chithra; Ojha, Satya P.; Kumar, Pankaj

2017-04-01

The upwelling in Arabian Sea is an important phenomenon, mainly occurring along the southwest coast of India during summer monsoon, which increases the biological productivity in the region. The south west coast of Arabian sea region accounts for about 53% of fish yield of the total fish production in Arabian Sea, thus it is imperative to study and understand the process of upwelling in this region. To study the upwelling features in southwest coast of India, monthly Ekman mass transport is estimated using analyzed wind and derived products from Oceansat-II scatterometer data. Seasonal variability of Ekman mass transport has been analyzed to study the occurrences of coastal upwelling in this region. Results show prominent region of upwelling along southwest coast of India is between 7° and 15° N. Transport estimate demonstrate that the strong offshore Ekman mass transport, as high as -2000 kg/m/s, was observed during summer monsoon months due to favorable wind conditions. Very weak offshore transport, as low as -200 kg/m/s, was observed during pre-monsoon months as winds were weak and spatially variable. Moderate offshore transport, up to -750 kg/m/s, was observed during winter monsoon months. The upwelling associated ocean surface features such as Sea-surface temperature (SST, from AVHRR), chlorophyll concentration (AQUA-MODIS), wind stress curl derived from Oceansat-II and sea surface salinity (SSS, from Aquarius) were examined to demonstrate the spatial and temporal evolution of upwelling in this region. With the advancement of the summer monsoon and upwelling, the monthly mean SST range reaches up to 26-27°C (August - September) from about 29-30°C (April - May). The monthly mean Chlorophyll concentration reaches up to 25-30 mg/m3 (August-September) from 0.1-0.2 mg/m3 (January-February). The monthly SSS which was observed to be about 34 psu (December 2102- January 2013) reaches to 36.5 psu (August-September). Analysis of SST from different sources suggests that the occurrence of a mini-cold pool (MCP) off the southern tip of India (STI) is a persistent phenomenon which occurs during both the summer and the winter monsoon seasons. The dynamics which governs the occurrence of MCP during the summer monsoon season is mainly due to upwelling, advection of the cold upwelled water from the western Arabian Sea and the southwest coast of India. Since, Somalia upwelling is an established fact, hence, we estimate upwelling only on southwest coast of India to understand the genesis of MCP. Results show that the genesis of MCP off STI starts by June and peaks in August and the SST attains a value as low as 26.0 °C, essentially due to upwelling and advection of upwelled water from the Somalia region along with upwelled water from southwest coast of India.

Changes in monsoon-driven upwelling in the South China Sea over glacial Terminations I and II: a multi-proxy record

NASA Astrophysics Data System (ADS)

Sadatzki, Henrik; Sarnthein, Michael; Andersen, Nils

2016-06-01

Upwelling intensity in the South China Sea has changed over glacial-interglacial cycles in response to orbital-scale changes in the East Asian Monsoon. Here, we evaluate new multi-proxy records of two sediment cores from the north-eastern South China Sea to uncover millennial-scale changes in winter monsoon-driven upwelling over glacial Terminations I and II. On the basis of U/Th-based speleothem chronology, we compare these changes with sediment records of summer monsoon-driven upwelling east of South Vietnam. Ocean upwelling is traced by reduced (UK'37-based) temperature and increased nutrient and productivity estimates of sea surface waters (δ13C on planktic foraminifera, accumulation rates of alkenones, chlorins, and total organic carbon). Accordingly, strong winter upwelling occurred north-west of Luzon (Philippines) during late Marine Isotope Stage 6.2, Heinrich (HS) and Greenland stadials (GS) HS-11, GS-26, GS-25, HS-1, and the Younger Dryas. During these stadials, summer upwelling decreased off South Vietnam and sea surface salinity reached a maximum suggesting a drop in monsoon rains, concurrent with speleothem records of aridity in China. In harmony with a stadial-to-interstadial see-saw pattern, winter upwelling off Luzon in turn was weak during interstadials, in particular those of glacial Terminations I and II, when summer upwelling culminated east of South Vietnam. Most likely, this upwelling terminated widespread deep-water stratification, coeval with the deglacial rise in atmospheric CO2. Yet, a synchronous maximum in precipitation fostered estuarine overturning circulation in the South China Sea, in particular as long as the Borneo Strait was closed when sea level dropped below -40 m.

Life cycle strategies of copepods in coastal upwelling zones

NASA Astrophysics Data System (ADS)

Peterson, W.

1998-06-01

Life cycles of copepods of coastal upwelling zones are of the multigenerational type—as many as 10 or more generations may be produced each year, depending upon water temperature, food concentration and length of the upwelling season. Abundant food resources and moderate temperature convey advantages to those copepods living in coastal upwelling zones, however, there is a clear disadvantage in that coastal upwelling zones are highly advective environments. Typically, water circulation patterns are such that surface waters are carried offshore, deeper waters carried onshore and most of the water column over the continental shelf is moving equatorward. The challenge to copepod species that inhabit upwelling systems is life cycle closure—how do eggs, nauplii, juveniles and adults avoid being swept out of these ecosystems in the face of persistent transport out of the system? In this review, I first list the species which dominate coastal upwelling ecosystems then discuss three variations on the multigenerational life cycle scheme that are observed in upwelling systems. The latter part of the review is devoted to discussion of how individuals are retained in the productive continental shelf waters within coastal upwelling ecosystems. The suggestion is made that the only copepod species that successfully achieve life cycle closure in such systems are those that are preadapted to upwelling circulation patterns. Our quantitative understanding of the relative importance of physical factors (such as advection) and biological factors (birth, growth, and mortality) on life cycle strategies and population dynamics is quite rudimentary. It would help our understanding if there were more field studies and more computer modeling studies that focused on seasonal cycles of abundance, development times and vertical distribution of life cycle stages, and measurements of water circulation patterns.

Observed impact of upwelling events on water properties and biological activity off the southwest coast of New Caledonia.

PubMed

Ganachaud, Alexandre; Vega, Andrés; Rodier, Martine; Dupouy, Cécile; Maes, Christophe; Marchesiello, Patrick; Eldin, Gerard; Ridgway, Ken; Le Borgne, Robert

2010-01-01

The upwelling events that follow strong trade wind episodes have been described in terms of their remarkable signature in the sea surface temperature southwest off New Caledonia. Upwelling brings deeper, and colder waters to the surface, causing 2-4 degrees C drops in temperature in a few hours, followed by a slower relaxation over several days. Upwelling may sporadically bring nutrients to the surface under certain conditions, and increase the biological productivity. Two multidisciplinary hydrographic cruises allow the impact of upwelling on the chemical and biological properties of the water to be documented. Both cruises took place in austral summer (December 2004 and December 2005), but the first cruise occurred during a strong upwelling event, while the second cruise occurred in calm conditions. The water properties and planktonic composition show important contrasts, with a strong southeastward current (the "ALIS current of New Caledonia") competing with the upwelling system. Our analysis suggests that, while observed productivities are far less than those of typical upwelling systems, some wind events in New Caledonia may contribute to biological activity. A currentmeter mooring, deployed during the second cruise, documents the ocean response to a changing wind field and the local impact of upwelling on currents and temperatures on the water column. The results are discussed, with the help of climatology, Argo float profiler data, satellite data and of a high-resolution numerical simulation. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

Coastal Upwelling Drives Intertidal Assemblage Structure and Trophic Ecology.

PubMed

Reddin, Carl J; Docmac, Felipe; O'Connor, Nessa E; Bothwell, John H; Harrod, Chris

2015-01-01

Similar environmental driving forces can produce similarity among geographically distant ecosystems. Coastal oceanic upwelling, for example, has been associated with elevated biomass and abundance patterns of certain functional groups, e.g., corticated macroalgae. In the upwelling system of Northern Chile, we examined measures of intertidal macrobenthic composition, structure and trophic ecology across eighteen shores varying in their proximity to two coastal upwelling centres, in a hierarchical sampling design (spatial scales of >1 and >10 km). The influence of coastal upwelling on intertidal communities was confirmed by the stable isotope values (δ13C and δ15N) of consumers, including a dominant suspension feeder, grazers, and their putative resources of POM, epilithic biofilm, and macroalgae. We highlight the utility of muscle δ15N from the suspension feeding mussel, Perumytilus purpuratus, as a proxy for upwelling, supported by satellite data and previous studies. Where possible, we used corrections for broader-scale trends, spatial autocorrelation, ontogenetic dietary shifts and spatial baseline isotopic variation prior to analysis. Our results showed macroalgal assemblage composition, and benthic consumer assemblage structure, varied significantly with the intertidal influence of coastal upwelling, especially contrasting bays and coastal headlands. Coastal topography also separated differences in consumer resource use. This suggested that coastal upwelling, itself driven by coastline topography, influences intertidal communities by advecting nearshore phytoplankton populations offshore and cooling coastal water temperatures. We recommend the isotopic values of benthic organisms, specifically long-lived suspension feeders, as in situ alternatives to offshore measurements of upwelling influence.

Coastal Upwelling Drives Intertidal Assemblage Structure and Trophic Ecology

PubMed Central

Reddin, Carl J.; Docmac, Felipe; O’Connor, Nessa E.; Bothwell, John H.; Harrod, Chris

2015-01-01

Similar environmental driving forces can produce similarity among geographically distant ecosystems. Coastal oceanic upwelling, for example, has been associated with elevated biomass and abundance patterns of certain functional groups, e.g., corticated macroalgae. In the upwelling system of Northern Chile, we examined measures of intertidal macrobenthic composition, structure and trophic ecology across eighteen shores varying in their proximity to two coastal upwelling centres, in a hierarchical sampling design (spatial scales of >1 and >10 km). The influence of coastal upwelling on intertidal communities was confirmed by the stable isotope values (δ13C and δ15N) of consumers, including a dominant suspension feeder, grazers, and their putative resources of POM, epilithic biofilm, and macroalgae. We highlight the utility of muscle δ15N from the suspension feeding mussel, Perumytilus purpuratus, as a proxy for upwelling, supported by satellite data and previous studies. Where possible, we used corrections for broader-scale trends, spatial autocorrelation, ontogenetic dietary shifts and spatial baseline isotopic variation prior to analysis. Our results showed macroalgal assemblage composition, and benthic consumer assemblage structure, varied significantly with the intertidal influence of coastal upwelling, especially contrasting bays and coastal headlands. Coastal topography also separated differences in consumer resource use. This suggested that coastal upwelling, itself driven by coastline topography, influences intertidal communities by advecting nearshore phytoplankton populations offshore and cooling coastal water temperatures. We recommend the isotopic values of benthic organisms, specifically long-lived suspension feeders, as in situ alternatives to offshore measurements of upwelling influence. PMID:26214806

(abstract) Seasonal Variability in Coastal Upwelling: A Comparison of Four Coastal Upwelling Sites from Space

NASA Technical Reports Server (NTRS)

Carr, Mary-Elena

1996-01-01

Coastal upwelling of subsurface nutrient-rich water occurs along the eastern boundary of the ocean basins and leads to high primary production and fish catches. In this study satellite observations are used to compare the seasonal cycle in wind forcing and in the oceanic and biological response of the major coastal upwelling regions associated with the Canary, Benguela, California, and Humboldt Currents.

Biological and physical oceanographic observations pertaining to the trawl fishery in a region of persistent coastal upwelling

NASA Technical Reports Server (NTRS)

Howe, J. T.; Gibson, D. B.; Evans, T. O.; Breaker, L.; Wrigley, R. C.; Broenkow, W. W.

1981-01-01

An upwelling episode in the Point Sal region of the central California coast is examined by using data obtained by a data buoy. The episodes was interrupted by the abrupt abatement of the strong wind which promotes coastal upwelling. The mean hourly upwelling index is calculated to be higher than the 20 year mean monthly value. During 3 days of light wind commercial bottom trawl operations were possible. Shipboard estimates of chlorophyll content in surface waters during trawling show the high concentrations that are indicative of a rich biomass of phytoplankton, a result of the upwelling episode. Satellite imagery shows the extent of the upwelling water to be of the order of 100 km offshore; the result of many upwelling episodes. Shipboard echo sounder data show the presence of various delmersal species and of zooplakton; the latter graze on the phytoplankton in the upper euphotic layers. The fish catch data are recorded according to species for 2 days of trawling, and the catch per trawl hour is recorded.

Reconstruction of the Mesoscale Velocity Shear Seaward of Coastal Upwelling Regions from the Refraction of the Surface Wave Field

NASA Technical Reports Server (NTRS)

Flament, Pierre; Graber, Hans C.; Halpern, D.; Holt, B.

1996-01-01

The objective of this project is to study fronts that develop at the boundary between cold water recently upwelled to the surface through Ekman divergence, and warmer surrounding waters. This specific objective was suggested by studying the small scale structure of upwelling fronts (coastal, island, and equatorial) through shipboard surveys and infrared satellite images. Constraints on the shuttle equator crossing imposed by other land sites precluded a coverage of the area targeted in the initial SIR-C proposal, the California Current. The site was then relocated to the Equatorial Pacific upwelling tongue, that can be satisfactorily imaged for a wide range of longitudes of the equator crossing. Some limited data was nevertheless obtained over coastal upwelling off California in 1989, using the JPL AIRSAR in multifrequency mode, and over island upwelling off Hawaii in 1990, using the radar in along-track interferometric mode.

Nutrient supply, surface currents, and plankton dynamics predict zooplankton hotspots in coastal upwelling systems

NASA Astrophysics Data System (ADS)

Messié, Monique; Chavez, Francisco P.

2017-09-01

A simple combination of wind-driven nutrient upwelling, surface currents, and plankton growth/grazing equations generates zooplankton patchiness and hotspots in coastal upwelling regions. Starting with an initial input of nitrate from coastal upwelling, growth and grazing equations evolve phytoplankton and zooplankton over time and space following surface currents. The model simulates the transition from coastal (large phytoplankton, e.g., diatoms) to offshore (picophytoplankton and microzooplankton) communities, and in between generates a large zooplankton maximum. The method was applied to four major upwelling systems (California, Peru, Northwest Africa, and Benguela) using latitudinal estimates of wind-driven nitrate supply and satellite-based surface currents. The resulting zooplankton simulations are patchy in nature; areas of high concentrations coincide with previously documented copepod and krill hotspots. The exercise highlights the importance of the upwelling process and surface currents in shaping plankton communities.

A long history of equatorial deep-water upwelling in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Zhang, Yi Ge; Pagani, Mark; Henderiks, Jorijntje; Ren, Haojia

2017-06-01

Cold, nutrient- and CO2-rich waters upwelling in the eastern equatorial Pacific (EEP) give rise to the Pacific cold tongue. Quasi-periodic subsidence of the thermocline and attenuation in wind strength expressed by El Niño conditions decrease upwelling rates, increase surface-water temperatures in the EEP, and lead to changes in regional climates both near and far from the equatorial Pacific. EEP surface waters have elevated CO2 concentrations during neutral (upwelling) or La Niña (strong upwelling) conditions. In contrast, approximate air-sea CO2 equilibrium characterizes El Niño events. One hypothesis proposes that changes in physical oceanography led to the establishment of a deep tropical thermocline and expanded mixed-layer prior to 3 million years ago. These effects are argued to have substantially reduced deep-water upwelling rates in the EEP and promoted a "permanent El Niño-like" climate state. For this study, we test this supposition by reconstructing EEP "excess CO2" and upwelling history for the past 6.5 million years using the alkenone-pCO2 methodology. Contrary to previous assertions, our results indicate that average temporal conditions in the EEP over the past ∼6.5 million years were characterized by substantial CO2 disequilibrium and high nutrient delivery to surface waters - characteristics that imply strong upwelling of deep waters. Upwelling appears most vigorous between ∼6.5 to 4.5 million years ago coinciding with high accumulation rates of biogenic material during the late Miocene - early Pliocene "biogenic bloom".

Far-reaching transport of Pearl River plume water by upwelling jet in the northeastern South China Sea

NASA Astrophysics Data System (ADS)

Chen, Zhaoyun; Pan, Jiayi; Jiang, Yuwu; Lin, Hui

2017-09-01

Satellite images from the Moderate Resolution Imaging Spectroradiometer (MODIS) show that there was a belt of turbid water appearing along an upwelling front near the Chinese coast of Guangdong, and indicate that the turbid water of the Pearl River plume water could be transported to a far-reaching area east of the Taiwan Bank. Numerical modeling results are consistent with the satellite observations, and reveal that a strong jet exists at the upwelling front with a speed as high as 0.8 m s- 1, which acts as a pathway for transporting the high-turbidity plume water. The dynamical analysis suggests that geostrophic equilibrium dominates in the upwelling front and plume areas, and the baroclinicity of the upwelling front resulting from the horizontal density gradient is responsible for the generation of the strong jet, which enhances the far-reaching transport of the terrigenous nutrient-rich water of the Pearl River plume. Model sensitivity analyses also confirm that this jet persists as long as the upwelling front exists, even when the wind subsides and becomes insignificant. Further idealized numerical model experiments indicate that the formation and persistence of the upwelling front jet depend on the forcing strength of the upwelling-favorable wind. The formation time of the jet varies from 15 to 158 h as the stress of the upwelling-favorable wind changes from 0.2 to 0.01 N m- 2. With the persistent transport of the nutrient-rich plume water, biophysical activities can be promoted significantly in the far-reaching destination area of the oligotrophic water.

Pliocene Warm Period Upwelling in the Southern Benguela Region

NASA Astrophysics Data System (ADS)

Petrick, B. F.; McClymont, E.; Felder, S.; Leng, M. J.; Rosell Mele, A.; Rueda, G.

2014-12-01

The mid-Pliocene has been proposed as a possible analogue for understanding future climate change and testing climate models. Previous work has shown that during the Pliocene the major upwelling systems were relatively warm, and thus either inactive, contracted, or upwelling warmer waters than present. Here we examine evidence from a core site located on the margins of the modern Benguela upwelling system, to test whether the upwelling cells had migrated or contracted relative to present during the Pliocene. We applied several organic geochemistry proxies and foraminiferal analyses to reconstruct the Pliocene history of ODP site 1087 (31º28'S, 15º19'E, 1374m water depth), including the UK37' index and TEX86 index (for reconstructing sea surface temperatures), chlorins (for estimating primary productivity) and planktonic foraminifera assemblages (for inferring water mass changes). These proxies show that between 3.5 and 3.0 Ma the southern Benguela region was significantly cooler than the northern Benguela region, the latter where the main upwelling cells are found today. Coupled with higher primary production, a shift in planktonic foraminifera assemblage, and an offset between the UK37' index and TEX86 index, we infer that more extensive upwelling was present in the southern Benguela region during the Pliocene. We infer that the main Benguela upwelling cells had shifted southward relative to today, as a result of changes in the local wind field. We find evidence for pronounced cooling and a shift in the planktonic foraminifera assemblage during the M2 and KM2 glacial stages, showing a sensitivity of Benguela upwelling to these short-lived climate events.

Biogeochemical cycling in the ocean. Part 1: Introduction to the effects of upwelling along the west coast of North America

NASA Technical Reports Server (NTRS)

Howe, John T.

1986-01-01

Coastal upwelling is examined as it relates to the cycling of chemical species in coastal waters along the west coast of North America. The temporal and spatial features of upwelling phenomena in the Eastern boundary regions of the North Pacific Ocean are presented and discussed in terms of upwelling episodes. Climate conditions affecting upwelling include: thermal effects, wind-induced shear stress which moves surface layers, and the curl of the wind stress vector which is thought to affect the extent and nature of upwelling and the formation of offshore convergent downwelling fronts. These effects and the interaction of sunlight and upwelled nutrients which result in a biological bloom in surface waters is modeled analytically. The roles of biological and chemical species, including the effects of predation, are discussed in that context, and relevant remote sensing and in situ observations are presented. Climatological, oceanographic, biological, physical, chemical events, and processes that pertain to biogeochemical cycling are presented and described by a set of partial differential equations. Simple preliminary results are obtained and are compared with data. Thus a fairly general framework has been laid where the many facets of biogeochemical cycling in coastal upwelled waters can be examined in their relationship to one another, and to the whole, to whatever level of detail or approximation is warranted or desired.

Spatial variability of Spanish sardine (Sardinella aurita) abundance as related to the upwelling cycle off the southeastern Caribbean Sea

PubMed Central

Cárdenas, Juan José; Achury, Alina; Astor, Yrene

2017-01-01

The Sardinella aurita fishery off northeastern Venezuela, region of seasonal wind-driven coastal-upwelling, accounts for 90% of the Caribbean Sea small pelagic catch. This law-protected artisanal fishery takes place up to ~10 km offshore. The spatial distribution, number of schools, and biomass of S. aurita were studied using eight hydro-acoustic surveys (1995–1998). The study included the analysis of satellite-derived sea surface temperature and chlorophyll-a. Surveys were grouped by strong, weak, and transitional upwelling seasons. Relationships between these observations were analyzed using Generalized Additive Models. Results show that during the primary upwelling season (January-May) sardines were widely distributed in upwelling plumes that extended up to 70 km offshore. In the other hand, during the weak upwelling season (September-October) higher sardine densities were found within 10 Km off the coastal upwelling foci. The number of small pelagic schools was directly correlated with small pelagic densities; however, regardless of the season, higher numbers of small pelagic schools were always closer to the shoreline, especially during warm conditions. These two behaviors increase the availability and catchability of sardines for the artisanal fishery during the warm season, regardless of the total stock size. Using this evidence, we pose the hypothesis that the collapse of the regional S. aurita fishery in 2005 was due to a combination of stressful habitat conditions sustained since 2004. These included bottom-up factors due to food scarcity caused by weak upwelling, combined with top-down stress due to overfishing, as sardines accumulated in narrow diminished upwelling plumes located close to the coast. The increased catchability within easily accessible upwelling foci led to the demise of this biological resource, which as of 2014 had not yet recovered. Environmental conditions affecting the sardine habitat needs to be taken into account for the management of this stock. For example, during years with weak upwelling, special measures should be taken during the warm season on the second half of the year to avoid further pressure on the stock. PMID:28654685

Dehumidification of Iberia by enhanced summer upwelling

NASA Astrophysics Data System (ADS)

Miranda, P. M.; Costa, V.; Nogueira, M.; Semedo, A.

2015-12-01

Dehumidification of Iberia by enhanced summer upwelling Miranda PMA, Costa V, Semedo AIDL, Faculdade de Ciências, University of LisbonA 24-year simulation of the recent Iberian climate, using the WRF model at 9km resolution forced by ERA-Interim reanalysis (1989-2012), is analysed for the decadal evolution of the upwelling forcing coastal wind and for column integrated Precipitable water vapour (PWV). Results indicate that, unlike what was found by Bakun et al. (2009) for the Peruvian region, a statistically significant trend in the upwelling favourable (northerly) wind has been accompanied by a corresponding decrease in PWV, not only inland but also over the coastal waters. Such increase is consistent with a reinforced northerly coastal jet in the maritime boundary layer contributing to atmospheric Ekman pumping of dry continental air into the coastal region. Diagnostics of the prevalence of the Iberian thermal low following Hoinka and Castro (2003) also show a positive trend in its frequency during an extended summer period (April to September). These results are consistent with recent studies indicating an upward trend in the frequency of upwelling in SW Iberia (Alves and Miranda 2013), and may be relevant for climate change applications as an increase in coastal upwelling (Miranda et al 2013) may lead to substantial regional impacts in the subtropics. Aknowledgements: Study supported by FCT Grant RECI/GEO-MET/0380/2012Alves JMR, Miranda PMA (2013) Variability of Iberian upwelling implied by ERA-40 and ERA-Interim reanalyses, Tellus A 2013, http://dx.doi.org/10.3402/tellusa.v65i0.19245.Bakun et al (2010) Greenhouse gas, upwelling-favorable winds, and the future of coastal ocean upwelling ecosystems, Global Change Biology, doi: 10.1111/j.1365-2486.2009.02094.xHoinka KP, Castro M (2003) The Iberian Peninsula thermal low. QJRMS, 129, 1491- 1511, doi: 10.1256/qj.01.189.Miranda et al (2013) Climate change and upwelling: response of Iberian upwelling to atmospheric forcing in a regional climate scenario. Climate Dynamics, doi: 10.1007/s00382-012-1442-9.

Microplankton biomass and diversity in the Vietnamese upwelling area during SW monsoon under normal conditions and after an ENSO event

NASA Astrophysics Data System (ADS)

Loick-Wilde, Natalie; Bombar, Deniz; Doan, Hai Nhu; Nguyen, Lam Ngoc; Nguyen-Thi, Anh Mai; Voss, Maren; Dippner, Joachim W.

2017-04-01

Investigating microplankton biomass and diversity under different climatological conditions is key to the understanding of cascading effects of climate change on nutrient cycles and biological productivity. Here we have used data collected during two contrasting summers along the coast of Viet Nam to show how climatological-driven changes can have a significant influence on the distribution of microplankton communities and their biomass via its impact on nutrient concentrations in the water column. The first summer in July 2003 followed a weak El-Nino Southern Oscillation (ENSO) event and was characterized by weak coastal upwelling, in the second summer during July 2004, upwelling was normal. Very low silicate (SiO4) concentrations and SiO4:DIN ratios characterized the source water mass for upwelling in July 2004, and dynamic SiO4 to dissolved inorganic nitrogen ratios (SiO4:DIN) mainly below the Redfield-Brzezinski ratio and DIN to phosphate ratios (DIN:PO43-) below the Redfield ratio were a common feature off Viet Nam. Much higher particle concentrations and PSi/PC ratios during normal upwelling revealed major changes in the microplankton community structure among summers. Small dinoflagellates (10-20 μm) prevailed ubiquitously during reduced upwelling. During normal upwelling, the diatom Rhizosolenia sp. dominated the cell-carbon biomass in the silicate poor upwelling waters. Trichodesmium erythraeum dominated in the Mekong-influenced and nutrient depleted offshore waters, where it co-occurred with Rhizosolenia sp. Both species were directly associated with the much higher primary production (PP) and N2 fixation rates that were quantified in earlier studies, as well as with much higher diversities at these offshore sites. Along the coast, the correlation between Rhizosolenia sp. and PP rates was less clear and the factors regulating the biomass of Rhizosolenia sp. in the upwelling waters are discussed. The very low silicate concentrations in the source water mass for upwelling and the offshore deflection of the Mekong river plume likely triggered the observed ecological differences in the microplankton communities off Viet Nam in the normal upwelling season compared to the post ENSO conditions.

Remote sensing and ichthyoplankton ecology of coastal upwelling fronts off central California

NASA Astrophysics Data System (ADS)

Bjorkstedt, Eric Peter

1998-11-01

Recruitment to many marine populations is determined by processes affecting survival and transport of planktonic larvae. Coastal upwelling poses a trade-off between larval access to high productivity supported by upwelled nutrients and increased risk of offshore transport and failure to return to coastal habitats. I used plankton surveys, remote sensing, and a simple model to investigate the role of coastal upwelling fronts and behavior in pelagic ecology and recruitment success, focussing on rockfish (Sebastes spp.) off central California. Distributions of early stage larvae suggest that coastal upwelling fronts reduce offshore transport of rockfish larvae, in contrast to distributions of taxa with life histories that minimize larval exposure to strong upwelling. Coincident distributions of larval fish, prey (i.e., small copepods and invertebrate eggs) and phytoplankton patches indicate that coastal upwelling fronts provide enhanced foraging conditions for larvae. Thus, coastal upwelling fronts may allow coastal taxa to successfully exploit high productivity during the upwelling season while reducing the risk of offshore transport. I developed a novel method for utilizing a single HF radar to resolve currents and detect fronts that matched sea surface temperature fronts generated by coastal upwelling. Fronts and currents detected with NF radar affect distributions and transport of planktonic larval fish and intertidal barnacle larvae, demonstrating that remote sensing with HF radar can support field and modelling research on ecological dynamics in coastal marine systems. I used an empirically-based model that incorporated the advection-foraging trade-off and long-distance swimming as an active settlement behavior to investigate optimal settlement strategies as a function of pelagic transport and growth. For parameters loosely describing pelagic stages of rockfish, the model predicts optimal settling strategies (ages and sizes) for pelagic juveniles that roughly match observed values for settling rockfish and suggests optimal spawning locations for adults. The model suggests that offshore transport is more important than growth in determining recruitment success. Thus, coastal upwelling fronts may favor recruitment more by reducing offshore transport than by providing rich food resources. Results of this model represent an initial step towards determining the role of active settlement behaviors in population dynamics and life history evolution.

Interactions between trophic levels in upwelling and non-upwelling regions during summer monsoon

NASA Astrophysics Data System (ADS)

Malik, A.; Fernandes, C. E. G.; Gonsalves, M.-J. B. D.; Subina, N. S.; Mamatha, S. S.; Krishna, K.; Varik, S.; Kumari, R.; Gauns, M.; Cejoice, R. P.; Pandey, S. S.; Jineesh, V. K.; Kamaleson, A. S.; Vijayan, V.; Mukherjee, I.; Subramanyan, S.; Nair, S.; Ingole, B.; LokaBharathi, P. A.

2015-01-01

Coastal upwelling is a regular phenomenon occurring along the southwest coast of India during summer monsoon (May-September). We hypothesize that there could be a shift in environmental parameters along with changes in the network of interactions between bacteria, phytoplankton, and zooplankton in upwelling and non-upwelling regions. During cruise # 267 on FORV Sagar Sampada, water samples were analysed for environmental and biological parameters from two transects, one upwelling region off Trivandrum (TVM) (8°26‧N, 76°20‧E-8°30‧N, 76°50‧E), and the other non-upwelling region off Calicut (CLT) (11°11‧N, 75°30‧E-11°14‧N,74°54‧E), about 230 nmi to the north. Meteorological, hydrological, and nutrient profiles confirmed upwelling off TVM. Bacteria, phytoplankton and zooplankton significantly responded. Primary and bacterial productivity enhanced together with increase in the percentage of viable bacteria (TVC). Pearson's correlation analysis pointed out the differences in bacterial interactions with other trophic levels at both transects. TVC played a prominent role in trophic interactions off TVM by depending on phytoplankton for substrate (r = 0.754). This contrasted with CLT where total counts (TC) played an important role. However, most interrelationships were less pronounced. Principal component analysis (PCA) confirmed the correlation analysis and further showed that the factor loadings of the biotic and abiotic parameters differed in strength and direction in the two regions. More importantly, the processes of mineralization by bacteria and uptake by phytoplankton are obviously more coupled off TVM as evidenced by the clustering of the related parameters in the PCA biplot. Canonical correspondence analysis also complements these findings and demonstrated that the abiotic factors influenced phytoplankton and bacteria similarly at TVM but differently at CLT. The impact on the trophic interrelationships is evident by the close association between all the variables in upwelling waters. Besides, bacteria may represent a more stable element in the food web, TVC for upwelling region and TC for non-upwelling region.

A Holocene record of ocean productivity and upwelling from the northern California continental slope

USGS Publications Warehouse

Addison, Jason A.; Barron, John A.; Finney, Bruce P.; Kusler, Jennifer E.; Bukry, David; Heusser, Linda E.; Alexander, Clark R.

2018-01-01

The Holocene upwelling history of the northern California continental slope is examined using the high-resolution record of TN062-O550 (40.9°N, 124.6°W, 550 m water depth). This 7-m-long marine sediment core spans the last ∼7500 years, and we use it to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with Holocene millennial-scale warm intervals. A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ13C and bulk sedimentary δ15N), and key microfossil indicators of upwelling were used to test this hypothesis. The record of biogenic accumulation in TN062-O550 shows considerable Holocene variability despite being located within 50 km of the mouth of the Eel River, which is one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at ∼2900 calibrated years before present (cal yr BP) indicates the onset of modern upwelling in the CCS, and this period also corresponds to the most intense period of upwelling in the last 7500 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification at TN062-O550 corresponds closely to that seen at nearby ODP Site 1019, as well as in the Santa Barbara Basin of southern California. Other CCS records with less refined age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we suggest that CCS warming may be conducive to upwelling intensification, though future changes are unclear as the mechanisms forcing SST variability may differ.

A Holocene record of ocean productivity and upwelling from the northern California continental slope

NASA Astrophysics Data System (ADS)

Addison, J. A.; Barron, J. A.; Finney, B.; Kusler, J. E.; Bukry, D.; Heusser, L. E.; Alexander, C. R., Jr.

2016-12-01

The Holocene upwelling history of the northern California continental slope is examined using a 7-m-long marine sediment core (TN062-O550; 40.9°N, 124.6°W, 550 m water depth) collected offshore from Eureka, CA, that spans the last 7,400 calibrated years before present (cal yrs BP). A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ13C and bulk sedimentary δ15N), and key microfossil indicators of upwelling were used to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with global Holocene millennial-scale warm intervals. Results show biogenic sediment accumulation in TN062-O550 varied considerably during the Holocene, despite being located within 50 km of the mouth of the Eel River, one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at 2900 cal yr BP indicates the onset of modern upwelling in the CCS, and that this period also corresponds to the most intense period of upwelling in the last 7,400 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification as recorded in TN062-O550 corresponds closely to that seen at nearby ODP Site 1019 as well as in the Santa Barbara Basin of southern California. Other CCS records with less high-quality age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone-derived sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we tentatively suggest that regional CCS warming may be conducive to upwelling intensification in the future.

Summertime sea surface temperature fronts associated with upwelling around the Taiwan Bank

NASA Astrophysics Data System (ADS)

Lan, Kuo-Wei; Kawamura, Hiroshi; Lee, Ming-An; Chang, Yi; Chan, Jui-Wen; Liao, Cheng-Hsin

2009-04-01

It is well known that upwelling of subsurface water is dominant around the Taiwan Bank (TB) and the Penghu (PH) Islands in the southern Taiwan Strait in summertime. Sea surface temperature (SST) frontal features and related phenomena around the TB upwelling and the PH upwelling were investigated using long-term AVHRR (1996-2005) and SeaWiFS (1998-2005) data received at the station of National Taiwan Ocean University. SST and chlorophyll-a (Chl-a) images with a spatial resolution of 0.01° were generated and used for the monthly SST and Chl-a maps. SST fronts were extracted from each SST images and gradient magnitudes (GMs); the orientations were derived for the SST fronts. Monthly maps of cold fronts where the cooler SSTs were over a shallower bottom were produced from the orientation. Areas with high GMs (0.1-0.2 °C/km) with characteristic shapes appeared at geographically fixed positions around the TB/PH upwelling region where SSTs were lower than the surrounding waters. The well-shaped high GMs corresponded to cold fronts. Two areas with high Chl-a were found around the TB and PH Islands. The southern border of the high-Chl-a area in the TB upwelling area was outlined by the high-GM area. Shipboard measurements of snapshot vertical sections of temperature (T) and salinity (S) along the PH Channel showed a dome structure east of PH Islands, over which low SST and high GM in the maps of the corresponding month were present. Clear evidence of upwelling (vertically uniform distributions of T and S) was indicated at the TB edge in the T and S sections close to TB upwelling. This case of upwelling may be caused by bottom currents ascending the TB slope as pointed out by previous studies. The position of low SSTs in the monthly maps matched the upwelling area, and the high GMs corresponded to the area of eastern surface fronts in the T/S sections.

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

NASA Astrophysics Data System (ADS)

Liao, Xiaomei; Zhan, Haigang; Du, Yan

2016-07-01

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

Intensification of Chile-Peru upwelling under climate change: diagnosing the impact of natural and anthropogenic forcing from the IPSL-CM5 model.

NASA Astrophysics Data System (ADS)

Jebri, B.; Khodri, M.; Gastineau, G.; Echevin, V.; Thiria, S.

2017-12-01

Upwelling is critical to the biological production, acidification, and deoxygenation of the ocean's major eastern boundary current ecosystems. A conceptual hypothesis suggests that the winds that favour coastal upwelling intensify with anthropogenic global warming due to increased land-sea temperature contrast. We examine this hypothesis for the dynamics of the Peru-Chile upwelling using a set of four large ensembles of coupled, ocean-atmosphere model simulations with the IPSL model covering the 1940-2014 period. In one large ensemble we prescribe the standard CMIP5 greenhouse gas (GHG) concentrations, anthropogenic aerosol, ozone and volcanic forcings, following the historical experiments through 2005 and RCP8.5 from 2006-2014, while the other ensembles consider separately the GHG, ozone and volcanic forcings. We find evidence for intensification of upwelling-favourable winds with however little evidence of atmospheric pressure gradients in response to increasing land-sea temperature differences. Our analyses reveal poleward migration and intensification of the South Pacific Anticyclone near poleward boundaries of climatological Peruvian and Chilean upwelling zones. This contribution further investigates the physical mechanisms for the Peru-Chile upwelling intensification and the relative role of natural and anthropogenic forcings.

Upwelling Dynamic Based on Satellite and INDESO Data in the Flores Sea

NASA Astrophysics Data System (ADS)

Kurniawan, Reski; Suriamihardja, D. A.; Hamzah Assegaf, Alimuddin

2018-03-01

Upwelling phenomenon is crucial to be forecasted, mainly concerning the information of potential fishery areas. Utilization of calibrated model for recorded upwelling such as INDESO gives benefit for historical result up to the present time. The aim of this study is to estimate areas and seasons of upwelling occurrences in the Flores Sea using data assimilation of satellite and modeling result. This study uses sea surface temperature, chlorophyll-a data from level 3 of MODIS image and sea surface height from satellite Jason-2 monthly for three years (2014-2016) and INDESO model data for sea surface temperature, sea surface height, and chlorophyll-a daily for three years (2014-2016). The upwelling is indicated by declining of sea surface temperature, sea surface height and increasing of chlorophyll-a. Verification is conducted by comparing the model result with recorded MODIS satellite image. The result shows that the area of southern Makassar Strait having occurrences of upwelling phenomenon every year starting in June, extended to July and August. The strongest upwelling occurred in 2015 covering more or less the area of 23,000 km2. The relation of monthly data of satellite has significantly correlated with daily data of INDESO model

Analysis of coastal upwelling and the production of a biomass

NASA Technical Reports Server (NTRS)

Howe, J. T.

1979-01-01

The coastal upwelling index derived from weather data is input to a set of coupled differential equations that describe the production of a biomass. The curl of the wind stress vector is discussed in the context of the physical extent of the upwelling structure. An analogy between temperature and biomass concentration in the upwelled coastal water is derived and the relationship is quantified. The use of remote satellite or airborne sensing to obtain biomass rate production coefficients is considered.

Contradictory Evidence on Wave Forcing of Tropical Upwelling in the Brewer-Dobson Circulation - A Suggested Resolution

NASA Technical Reports Server (NTRS)

Zhou, Tiehan; Geller, Marvin A.; Lin, Wuyin

2011-01-01

ERA-40 data are analyzed to demonstrate that wave forcing at lower latitudes plays a crucial role in driving the tropical upwelling portion of the Brewer-Dobson circulation. It is shown that subtropical wave forcing is correlated with tropical upwelling on both intraseasonal and interannual time scales when transient waves are taken into account, and that tropical wave forcing exerts its influence on tropical upwelling via its body force on the zonal mean flow.

Modeling of the mesoscale structure of coupled upwelling/downwelling events and the related input of nutrients to the upper mixed layer in the Gulf of Finland, Baltic Sea

NASA Astrophysics Data System (ADS)

Zhurbas, Victor; Laanemets, Jaan; Vahtera, Emil

2008-05-01

A high resolution numerical study is undertaken to simulate an upwelling event along the northern coast of the Gulf of Finland, 21-29 July 1999, which was documented well by in situ and remote measurements. The simulated sequence of SST maps shows a reasonably good resemblance to that of satellite infrared imagery, including both mesoscale coherent structures (filaments or squirts) and the whole process of post-upwelling relaxation of the temperature field. Upwelling along the northern coast of the Gulf is accompanied by downwelling along the southern coast so that two longshore baroclinic jets and related fronts are developed simultaneously. When the strong westerly winds producing the upwelling/downwelling weaken, the longshore jets become unstable and produce transverse jets, cold/warm water squirts. Using pseudo-random simulated fields of temperature and velocity of currents, the apparent lateral diffusivity due to squirts is directly estimated at 500 m2 s-1. The model is also applied to estimate nutrient transport. Simulated phosphate concentration in the surface layer at the cold side of upwelling front is found to be about 0.3 mmol m-3 which is consistent with observations. The total content of phosphorus and nitrogen in the upper 10 m layer of the Gulf introduced by the upwelling event is estimated to be 387 and 36 tons, respectively. It follows, that the upwelling event transports nutrients into the upper layer with clear excess of phosphorus (N:P = 36:387 = 0.093) compared to the Redfield ratio of 7.2. Therefore phosphorus input caused by upwelling during summer most likely promotes nitrogen-fixing cyanobacteria blooms.

Electrical image of passive mantle upwelling beneath the northern East Pacific Rise.

PubMed

Key, Kerry; Constable, Steven; Liu, Lijun; Pommier, Anne

2013-03-28

Melt generated by mantle upwelling is fundamental to the production of new oceanic crust at mid-ocean ridges, yet the forces controlling this process are debated. Passive-flow models predict symmetric upwelling due to viscous drag from the diverging tectonic plates, but have been challenged by geophysical observations of asymmetric upwelling that suggest anomalous mantle pressure and temperature gradients, and by observations of concentrated upwelling centres consistent with active models where buoyancy forces give rise to focused convective flow. Here we use sea-floor magnetotelluric soundings at the fast-spreading northern East Pacific Rise to image mantle electrical structure to a depth of about 160 kilometres. Our data reveal a symmetric, high-conductivity region at depths of 20-90 kilometres that is consistent with partial melting of passively upwelling mantle. The triangular region of conductive partial melt matches passive-flow predictions, suggesting that melt focusing to the ridge occurs in the porous melting region rather than along the shallower base of the thermal lithosphere. A deeper conductor observed east of the ridge at a depth of more than 100 kilometres is explained by asymmetric upwelling due to viscous coupling across two nearby transform faults. Significant electrical anisotropy occurs only in the shallowest mantle east of the ridge axis, where high vertical conductivity at depths of 10-20 kilometres indicates localized porous conduits. This suggests that a coincident seismic-velocity anomaly is evidence of shallow magma transport channels rather than deeper off-axis upwelling. We interpret the mantle electrical structure as evidence that plate-driven passive upwelling dominates this ridge segment, with dynamic forces being negligible.

Dynamics of upwelling annual cycle in the equatorial Atlantic Ocean

NASA Astrophysics Data System (ADS)

Wang, Li-Chiao; Jin, Fei-Fei; Wu, Chau-Ron; Hsu, Huang-Hsiung

2017-04-01

The annual upwelling is an important component of the equatorial Atlantic annual cycle. A simple theory is proposed using the framework of Zebiak-Cane (ZC) ocean model for insights into the dynamics of the upwelling annual cycle. It is demonstrated that in the Atlantic equatorial region this upwelling is dominated by Ekman processing in the west, whereas in the east it is primarily owing to shoaling and deepening of the thermocline resulting from equatorial mass meridional recharge/discharge and zonal redistribution processes associated with wind-driven equatorial ocean waves. This wind-driven wave upwelling plays an important role in the development of the annual cycle in the sea surface temperature of the cold tongue in the eastern equatorial Atlantic.

Initial observation of upwelling along east coast of Peninsular Malaysia musica gratis

NASA Astrophysics Data System (ADS)

Akhir, M.; Tanggang, F.

2013-12-01

There is no published evidence of upwelling in coastal area along the east coast of Peninsular Malaysia. However numbers of recent cruise data collected during the southwest monsoon found features of thermocline lifting and isolated cooler temperature water along the coast, These sign was observed along the 104°E from numbers of parallel transects. To confirm the presence of upwelling, satellite remote sensing data was used, and numerical model experiments were conducted. Cooler sea-surface temperature along the coast was observed from both in-situ and satellite data, while upward movement in the vertical profiles agreed with the location of upwelling from both in-situ and satellite data. Moreover, these data also show that the upwelled water band along the 104°E longitude stretch approximately 650 km long. Initially, southwesterly wind during this season is believed to be the important mechanism that contributed to this wind-induced Ekman upwelling. musica gratis

Poleward displacement of coastal upwelling-favorable winds through the 21st century

NASA Astrophysics Data System (ADS)

Rykaczewski, R. R.; Dunne, J. P.; Sydeman, W. J.; Garcia-Reyes, M.; Black, B.; Bograd, S. J.

2016-02-01

Coastal upwelling is a critical factor influencing the biological production, acidification, and deoxygenation of the ocean's major eastern boundary current ecosystems. A leading conceptual hypothesis projects that the winds that induce coastal upwelling will intensify in response to increased land-sea temperature differences associated with anthropogenic global warming. We examine this hypothesis using an ensemble of coupled, ocean-atmosphere models and find limited evidence for intensification of upwelling-favorable winds or atmospheric pressure gradients in response to increasing land-sea temperature differences. However, our analyses reveal consistent latitudinal and seasonal dependencies of projected changes in wind intensity associated with poleward migration of major atmospheric high-pressure cells. Summertime winds near poleward boundaries of climatological upwelling zones are projected to intensify, while winds near equatorward boundaries are projected to weaken. Developing a better understanding of future changes in upwelling winds is essential to identifying portions of the oceans susceptible to increased hypoxia, ocean acidification, and eutrophication under climate change.

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

NASA Astrophysics Data System (ADS)

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

1997-01-01

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

On the presence of coastal upwelling along the northeastern Tyrrhenian coast

NASA Astrophysics Data System (ADS)

Martellucci, Riccardo; Melchiorri, Cristiano; Costanzo, Lorenzo; Marcelli, Marco

2017-04-01

The Mediterranean region shows a high climate variability due to the interactions between mid-latitude and tropical processes. This variability makes the Mediterranean a potentially vulnerable region to climatic changes. The present research aims to investigate the hydrographical response to Northerly wind in the northeastern Tyrrhenian coast, to identify the relations between upwelling events and teleconnection patterns. In the Tyrrhenian basin northerly winds flow between North-East and North-West and could be considered upwelling favorable winds. This atmospheric circulation can causes a divergent flow near the coast that generates a subsurface water flows inshore toward the coast up to the surface layer that is upwelling. This phenomenon strongly influence the marine ecosystems, contributing to the supply of nutrients and affecting the primary producers. In this context multi-platform observing system is an important tool to follow the evolution of these phenomena. Sea temperature and wind field acquired by the C-CEMS Observing system were used to identify upwelling phenomena between 2012 and 2016, in the coastal area of Civitavecchia, Northern Tyrrhenian sea, Italy. Moreover a thirty years' wind-driven upwelling conditions have been studied in the area. ERA-Interim (ECMWF) wind data for the period 1982-2012 have been used to compute the distribution of upwelling favorable wind events. These have been compared to "Copernicus Marine Environment Monitoring Service" Sea Surface Temperature (SST) to compute upwelling events. Upwelling favorable wind has been defined in the sector between Northwest and Northeast (Wd >330°N & Wd < 30°N). Wind speed has been divided into three classes: between 4 m/s and 6 m/s, between 6 m/s and 8 m/s and greater than 8 m/s. Sea Surface Temperature have been analyzed to define SST field for wind-driven coastal upwelling assessment. SST minima along the coast was used to identify upwelling from satellite imagery. The two datasets were compared and only the days that presented those characteristics were chosen. ERA-Interim (ECMWF) sea level pressure data over the Europe for the period 1982 -2012 have been used to compute the most relevant teleconnection patterns through Empirical Orthogonal Function's analysis. An increase of upwelling events in the Tyrrhenian coast is observed in the last thirty years; the occurrence of upwelling events has a seasonal oscillation, with a maximum frequency during winter and spring seasons. In the last decade an increase of these events in winter and a decrease in spring is observed; also a recurrence of these events in summer season has been identified, without the specific contribution of one of atmospheric regimes. Data analyzed shows a decrement in Atlantic Ridge (AR) regime and an increment in West Blocking (WBL) regime, especially for the event characterized by wind speeds greater than 8m/s.

Sedimentary silicon isotope indicates the Kuroshio subsurface upwelling in the East China Sea

NASA Astrophysics Data System (ADS)

Zhao, Y.; Yang, S.; Su, N.

2017-12-01

The Kuroshio as the western boundary current of the North Pacific subtropical circulation, originates from east of the Philippine Islands, and flows northeastward along the eastern coast of Taiwan. It's subsurface water intrudes the East China Sea (ECS) and forms a typical upwelling on the inner shelf, which may play an important role in the material and heat transport, biogeochemical process and marine ecosystem of the ECS.To date, most previous studies on the Kuroshio subsurface upwelling focuse on the seasonal and interannual variations, and few researches touch on the upwelling evolution in the geologic past. In this study, eight short sediment cores were taken along the ECS inner shelf (upwelling area), which allow us to reconstruct the upwelling history over the last several hundred years. Although conventional indexes of oceanographic changes, such as salinity, temperature and hydrogen and oxygen isotope, provide valuable constraints on the modern oceanic circulation and water mass movements, how to reconstruct them from geologic records is always a challenging work. In this contribution, we present the data of stable silicon isotope, biogenic opal, diatom assemblages, element geochemistry and stable carbon and nitrogen isotopes of these core sediments, and aim to decipher the Kuroshio subsurface upwelling history on the ECS shelf. We will also illustrate the difference in δ30Si signals between small (<30 um) and large (>150 um) diatom fractions, and test whether it is an effective indicator for paleo-upwelling intensity.

Physical structure and algae community of summer upwelling off eastern Hainan

NASA Astrophysics Data System (ADS)

Xu, H.; Liu, S.; Xie, Q.; Hong, B.; Long, T.

2017-12-01

The upwelling system is the most productive ecosystem along the continental shelf of the northern South China Sea Shelf. It brings nutrient from bottom to surface and blooms biotic community driven by summer monsoon. In this study, we present observed results of physical and biotic community structures during August, 2015 in the upwelling system along Hainan eastern coast, which is one the strongest upwelling systems in the northern South China Sea. By using hydrological data collected by CTD, we found a significant cold water tongue with high salinity which extended from offshore to 100 m isobaths. However, dissolved oxygen (DO) showed a sandwich structure in which high core of DO concentration appeared at the layer from 5 m to 30 m. It possibly was caused by the advection transport of high DO from adjacent area. Basically, this upwelling system was constrained at northern area of 18.8ºN in horizontal due to the weakening summer monsoon in August. In addition, we collected water sample at the upwelling area and measured algae categories and concentration by high performance liquid chromatography (HPLC). Results show the biotic community was dominated by five types of algae mainly, they were diatoms, dinoflagellates, green algae, prokaryotes and prochlorococcus. And different patterns of different algae were demonstrated. In the upwelling area, diatoms and prokaryotes show opposite structures, and more complex pattern for the rest three algae indicating an active biotic community in the upwelling system.

Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by Ferrybox measurements in 2007-2013

NASA Astrophysics Data System (ADS)

Kikas, Villu; Lips, Urmas

2016-07-01

Ferrybox measurements have been carried out between Tallinn and Helsinki in the Gulf of Finland (Baltic Sea) on a regular basis since 1997. The system measures autonomously water temperature, salinity, chlorophyll a fluorescence and turbidity and takes water samples for further analyses at a predefined time interval. We aimed to show how the Ferrybox technology could be used to study the coastal upwelling events in the Gulf of Finland. Based on the introduced upwelling index and related criteria, 33 coastal upwelling events were identified in May-September 2007-2013. The number of events, as well as the frequency of their occurrence and intensity expressed as a sum of daily average temperature deviations in the 20 km wide coastal area, were almost equal near the northern and southern coasts. Nevertheless, the wind impulse, which was needed to generate upwelling events of similar intensity, differed between the northern and southern coastal areas. It is suggested that the general thermohaline structure adapted to the prevailing forcing and the estuarine character of the basin weaken the upwelling created by the westerly to southwesterly (up-estuary) winds and strengthen the upwelling created by the easterly to northeasterly (down-estuary) winds. Two types of upwelling events were identified - one characterized by a strong temperature front and the other revealing gradual decrease in temperature from the open sea to the coastal area, with maximum temperature deviation close to the shore.

A model study of the response of hypoxia to upwelling-favorable wind on the northern Gulf of Mexico shelf

NASA Astrophysics Data System (ADS)

Feng, Yang; Fennel, Katja; Jackson, George A.; DiMarco, Steven F.; Hetland, Robert D.

2014-03-01

The hypoxic region in the northern Gulf of Mexico, one of the largest man-made hypoxic zones in the world, has received extensive scientific study and management interest. A previous statistical study has concluded that in addition to anthropogenic nitrogen loading, the observed hypoxic extent is correlated to the duration of upwelling favorable (westerly) wind without elucidating the underlying mechanism. In this study, we use a three-dimensional, coupled hydrological-biogeochemical model to mechanistically examine how variations of the hypoxic area are related to the duration of upwelling-favorable wind. We performed scenario experiments with different durations of upwelling-favorable wind using realistic winds from summer 2002 (when upwelling-favorable winds were present only for about 1 month) and summer 2009 (when upwelling-favorable conditions started early and persisted for about 2 months). While the maximum simulated hypoxic area is approximately 15,000 km2 in both cases, the evolutions of the hypoxic area and the dates when its maximum extent are reached are different. With an early start of persistently upwelling-favorable wind in 2009, the hypoxic area reached its maximum in early summer and decreased afterwards. By contrast, the hypoxic area was small in early summer of 2002 and peaked during the short period of upwelling-favorable wind in late summer. The model revealed that the wind influences the evolution of the hypoxic area by changing the vertical and horizontal distributions of the low salinity, high chlorophyll water on the shelf.

Variability and Dynamics of the Yucatan Upwelling: High-Resolution Simulations

NASA Astrophysics Data System (ADS)

Jouanno, J.; Pallàs-Sanz, E.; Sheinbaum, J.

2018-02-01

The Yucatan shelf in the southern Gulf of Mexico is under the influence of an upwelling that uplifts cool and nutrient rich waters over the continental shelf. The analysis of a set of high-resolution (Δx = Δy ≈ 2.8 km) simulations of the Gulf of Mexico shows two dominant modes of variability of the Yucatan upwelling system: (1) a low-frequency mode related to variations in position and intensity of the Loop Current along the shelf, with upwelling intensified when the Loop Current is strong and approaches to the Yucatan shelf break and (2) a high-frequency mode with peak frequency in the 6-10 days band related to wind-forced coastal waves that force vertical velocities along the eastern Yucatan shelf break. To first order, the strength and position of the Loop Current are found to control the intensity of the upwelling, but we show that high-frequency winds also contribute (˜17%) to a net input of cool waters (<22.5°C) on the Yucatan shelf. Finally, although more observational studies are needed to corroborate the topographic character of the Yucatan upwelling system, this study reveals the key role played by a notch along the Yucatan shelf break: a sensitivity simulation without the notch shows a 55% reduction of the upwelling.

Spiraling pathways of global deep waters to the surface of the Southern Ocean.

PubMed

Tamsitt, Veronica; Drake, Henri F; Morrison, Adele K; Talley, Lynne D; Dufour, Carolina O; Gray, Alison R; Griffies, Stephen M; Mazloff, Matthew R; Sarmiento, Jorge L; Wang, Jinbo; Weijer, Wilbert

2017-08-02

Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60-90 years.Deep waters of the Atlantic, Pacific and Indian Oceans upwell in the Southern Oceanbut the exact pathways are not fully characterized. Here the authors present a three dimensional view showing a spiralling southward path, with enhanced upwelling by eddy-transport at topographic hotspots.

Changes in the partial pressure of carbon dioxide in the Mauritanian-Cap Vert upwelling region between 2005 and 2012

NASA Astrophysics Data System (ADS)

González-Dávila, Melchor; Magdalena Santana Casiano, J.; Machín, Francisco

2017-08-01

Coastal upwellings along the eastern margins of major ocean basins represent regions of large ecological and economic importance due to the high biological productivity. The role of these regions for the global carbon cycle makes them essential in addressing climate change. The physical forcing of upwelling processes that favor production in these areas are already being affected by global warming, which will modify the intensity of upwelling and, consequently, the carbon dioxide cycle. Here, we present monthly high-resolution surface experimental data for temperature and partial pressure of carbon dioxide in one of the four most important upwelling regions of the planet, the Mauritanian-Cap Vert upwelling region, from 2005 to 2012. This data set provides direct evidence of seasonal and interannual changes in the physical and biochemical processes. Specifically, we show an upwelling intensification and an increase of 0.6 Tg yr-1 in CO2 outgassing due to increased wind speed, despite increased primary productivity. This increase in CO2 outgassing together with the observed decrease in sea surface temperature at the location of the Mauritanian Cap Blanc, 21° N, produced a pH rate decrease of -0.003 ± 0.001 yr-1.

Upwelling Scales off the Coast of Peru: Comparison of Observation and Model

NASA Astrophysics Data System (ADS)

Vazquez, J.; Chin, T. M.; Armstrong, E. M.

2014-12-01

Upwelling regions of the world's oceans are home to some of the most productive fisheries. Yet these coastal areas provide unique challenges for remote sensing from satellite platforms because of both their proximity to land (radar interference) and typically small horizontal scales (< 50km) of upwelling processes. Comparisons are performed on the gradient of sea surface temperature (SST) fields derived from multiple sources: 1) the 0.25 degree resolution National Climatic Data Center (NCDC) Optimally Interpolated AVHRR+in-situ or AVHRR_OI, data set. 2) the 1km resolution Multi-scale Ultra-high Resolution (MUR) gridded SST data set, 3) the 0.25 degree resolution SST derived from the WindSat microwave sensor, 4) a 2km version of the Estimating the Circulation and Climate of the Ocean Model (HECCO2). Temporal and spatial correlations between HECCO2 and MUR, as well as between HECCO2 and NCDC, are examined through the dominant singular vectors (eigenmodes) of the covariance matrix for each pair of data sets. In both cases the first mode of covariability accounts for over 90% of the total variance. A simple technique based on SST gradients is then applied to the first mode to determine the upwelling scales based on HECCO2, MUR, and NCDC. Longitudinal sections at 8S, 20S, and 30S indicate that the upwelling scale decreases between 8S and 20S. At 20S the first mode of covariability between MUR and HECCO2 indicate an upwelling scale between 25 and 50km. Results are consistent when compared with chlorophyll-a data from MODIS-Aqua. Such upwelling scales are not seen in the WindSat data and reduced in the NCDC data. A reduction of the upwelling scale by a factor 0.2 between 8S and 20S is consistent with a dependence on the Coriolis parameter. A major conclusion of the work is that magnitudes of SST gradient and upwelling scales derived from MUR are consistent with those of the HECCO2 for the test period of October-November 2011. Additionally, it is shown that to resolve upwelling scales near the coast high resolution infrared data must be used in the analysis. Microwave derived SSTs, such as those from WindSat are of limited value when upwelling scales are less then 50km.

Natural ocean acidification at Papagayo upwelling system (north Pacific Costa Rica): implications for reef development

NASA Astrophysics Data System (ADS)

Sánchez-Noguera, Celeste; Stuhldreier, Ines; Cortés, Jorge; Jiménez, Carlos; Morales, Álvaro; Wild, Christian; Rixen, Tim

2018-04-01

Numerous experiments have shown that ocean acidification impedes coral calcification, but knowledge about in situ reef ecosystem response to ocean acidification is still scarce. Bahía Culebra, situated at the northern Pacific coast of Costa Rica, is a location naturally exposed to acidic conditions due to the Papagayo seasonal upwelling. We measured pH and pCO2 in situ during two non-upwelling seasons (June 2012, May-June 2013), with a high temporal resolution of every 15 and 30 min, respectively, using two Submersible Autonomous Moored Instruments (SAMI-pH, SAMI-CO2). These results were compared with published data from the 2009 upwelling season. Findings revealed that the carbonate system in Bahía Culebra shows a high temporal variability. Incoming offshore waters drive intra- and interseasonal changes. Lowest pH (7.8) and highest pCO2 (658.3 µatm) values measured during a cold-water intrusion event in the non-upwelling season were similar to those minimum values reported from upwelling season (pH = 7.8, pCO2 = 643.5 µatm), unveiling that natural acidification also occurs sporadically in the non-upwelling season. This affects the interaction of photosynthesis, respiration, calcification and carbonate dissolution and the resulting diel cycle of pH and pCO2 in the reefs of Bahía Culebra. During the non-upwelling season, the aragonite saturation state (Ωa) rises to values of > 3.3 and during the upwelling season falls below 2.5. The Ωa threshold values for coral growth were derived from the correlation between measured Ωa and coral linear extension rates which were obtained from the literature and suggest that future ocean acidification will threaten the continued growth of reefs in Bahía Culebra. These data contribute to building a better understanding of the carbonate system dynamics and coral reefs' key response (e.g., coral growth) to natural low-pH conditions, in upwelling areas in the eastern tropical Pacific and beyond.

Transient response of the Northwestern Iberian upwelling regime.

PubMed

Ferreira Cordeiro, Nuno Gonçalo; Dubert, Jesus; Nolasco, Rita; Desmond Barton, Eric

2018-01-01

The hydrography and dynamics of NW Iberian margin were explored for July 2009, based on a set of in situ and remote sensing observations. Zonal sections of standard CTD casts, towed CTD (SeaSoar), Acoustic Doppler Current Profilers (ADCP) and Lagrangian surveys were made to characterize cycles of upwelling and relaxation in this region. Two periods of northerly winds, bounded by relaxation periods, were responsible for the formation of an upwelling front extending to the shelf edge. An equatorward flow was quickly set up on the shelf responding to the northerly wind pulses. South of Cape Silleiro, the development and subsequent relaxation of an upwelling event was intensively surveyed in the shelf, following a Lagrangian drifter transported by the upwelling jet. This region is part of an upwelling center extending from Cape Silleiro to Porto, where the surface temperature was colder than the neighboring regions, under upwelling favorable winds. As these winds relaxed, persistent poleward flow developed, originating south of the upwelling center and consisting in an inner-shelf tongue of warm waters. During an event of strong southerly wind, the poleward flow was observed to extend to the whole continental shelf. Although the cruise was executed during summertime, the presence of river-plumes was observed over the shelf. The interaction of the plumes with the circulation on the shelf was also described in terms of coastal convergence and offshore advection. The sampling of the offshore and slope regions showed the presence of the Iberian poleward current offshore and a persistent equatorward flow over the upper slope.

Does upwelling intensity influence feeding habits and trophic position of planktivorous fish?

NASA Astrophysics Data System (ADS)

Lopez-Lopez, Lucia; Preciado, Izaskun; Muñoz, Isabel; Decima, Moira; Molinero, Juan Carlos; Tel, Elena

2017-04-01

Food web configuration is shaped by many factors, including primary production patterns and oceanographic features, such as upwelling events. In this study, we investigate variability in the trophic position, food web interlinks and energy pathways of four planktivorous demersal fish in the Southern Bay of Biscay- NE Atlantic. The study area is exposed to upwelling events of varying intensity and shows a significant spatial gradient along the coast. The two sampling years were characterized by markedly different conditions, with weak summer upwelling in 2012 and an intense upwelling season in 2013. We used a complementary approach based on stomach content analysis (SCA) and stable isotope analysis (SIA) to test the effects of upwelling intensity and persistence on the food-web. In particular we investigated whether different intensities shift the main flow of energy between the pelagic and benthic energy pathways. We found conspicuous interannual changes in the isotopic POM, whose δ15N was 2.5‰ lower during the productive 2013 season. Interannual changes in the isotopic signature of the fish species were also detected, although their values did not mirror variability at the basal level. The SCA results did not match the isotopic changes, which likely reflected dietary adjustments of the species during summer. The upwelling intensity gradient along the coast did not affect the nitrogen isotopic ratio of any group, however there was a significant effect of such gradient on the carbon isotopic ratio of the fish and euphausiid species. This effect was likely related to the higher primary production associated with intense upwelling conditions.

Potential and timescales for oxygen depletion in coastal upwelling systems: A box-model analysis

NASA Astrophysics Data System (ADS)

Harrison, C. S.; Hales, B.; Siedlecki, S.; Samelson, R. M.

2016-05-01

A simple box model is used to examine oxygen depletion in an idealized ocean-margin upwelling system. Near-bottom oxygen depletion is controlled by a competition between flushing with oxygenated offshore source waters and respiration of particulate organic matter produced near the surface and retained near the bottom. Upwelling-supplied nutrients are consumed in the surface box, and some surface particles sink to the bottom where they respire, consuming oxygen. Steady states characterize the potential for hypoxic near-bottom oxygen depletion; this potential is greatest for faster sinking rates, and largely independent of production timescales except in that faster production allows faster sinking. Timescales for oxygen depletion depend on upwelling and productivity differently, however, as oxygen depletion can only be reached in meaningfully short times when productivity is rapid. Hypoxia thus requires fast production, to capture upwelled nutrients, and fast sinking, to deliver the respiration potential to model bottom waters. Combining timescales allows generalizations about tendencies toward hypoxia. If timescales of sinking are comparable to or smaller than the sum of those for respiration and flushing, the steady state will generally be hypoxic, and results indicate optimal timescales and conditions exist to generate hypoxia. For example, the timescale for approach to hypoxia lengthens with stronger upwelling, since surface particle and nutrient are shunted off-shelf, in turn reducing subsurface respiration and oxygen depletion. This suggests that if upwelling winds intensify with climate change the increased forcing could offer mitigation of coastal hypoxia, even as the oxygen levels in upwelled source waters decline.

Influence of Coastal Upwelling on SST Trends along the South Coast of Java

PubMed Central

Varela, R.; Santos, F.; Gómez-Gesteira, M.; Álvarez, I.; Costoya, X.; Días, J. M.

2016-01-01

The south coast of Java has warmed at a much lower rate than adjacent ocean locations over the last three decades (1982–2015). This behavior can be observed during the upwelling season (July-October) and it is especially patent in August and September when upwelling attains the highest values. Although different warming rates (ocean-coast) had been previously observed in other areas around the world, this behavior was always linked to situations where upwelling increased or remained unchanged. South Java warming is observed at ocean locations and cooling near shore but under a scenario of decreasing upwelling (~30% in some cases). The origin of coastal cooling is due to changes in the vertical structure of the water column. A vein of subsurface water, which has cooled at a rate higher than 0.3°C per decade, is observed to enter from the northwestern part of the study area following the South Java Current. This water only manifests at surface near coast, where it is pumped up by coastal upwelling. PMID:27606676

Implications of Upwells as Hydrodynamic Jets in a Pulse Jet Mixed System

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

Pease, Leonard F.; Bamberger, Judith A.; Minette, Michael J.

2015-08-01

This report evaluates the physics of the upwell flow in pulse jet mixed systems in the Hanford Tank Waste Treatment and Immobilization Plant (WTP). Although the initial downward flow and radial flow from pulse jet mixers (PJMs) has been analyzed in some detail, the upwells have received considerably less attention despite having significant implications for vessel mixing. Do the upwells behave like jets? How do the upwells scale? When will the central upwell breakthrough? What proportion of the vessel is blended by the upwells themselves? Indeed, how the physics of the central upwell is affected by multiple PJMs (e.g., sixmore » in the proposed mixing vessels), non-Newtonian rheology, and significant multicomponent solids loadings remain unexplored. The central upwell must satisfy several criteria to be considered a free jet. First, it must travel for several diameters in a nearly constant direction. Second, its velocity must decay with the inverse of elevation. Third, it should have an approximately Gaussian profile. Fourth, the influence of surface or body forces must be negligible. A combination of historical data in a 12.75 ft test vessel, newly analyzed data from the 8 ft test vessel, and conservation of momentum arguments derived specifically for PJM operating conditions demonstrate that the central upwell satisfies these criteria where vigorous breakthrough is achieved. An essential feature of scaling from one vessel to the next is the requirement that the underlying physics does not change adversely. One may have confidence in scaling if (1) correlations and formulas capture the relevant physics; (2) the underlying physics does not change from the conditions under which it was developed to the conditions of interest; (3) all factors relevant to scaling have been incorporated, including flow, material, and geometric considerations; and (4) the uncertainty in the relationships is sufficiently narrow to meet required specifications. Although the central upwell satisfies these criteria when vigorous breakthrough is achieved, not all available data follow the free jet profile for the central upwell, particularly at lower nozzle velocities. Alternative flow regimes are considered and new models for cloud height, “cavern height,” and the rate of jet penetration (jet celerity) are benchmarked against data to anchor scaling analyses. This analytical modeling effort to provide a technical basis for scaling PJM mixed vessels has significant implications for vessel mixing, because jet physics underlies “cavern” height, cloud height, and the volume of mixing considerations. A new four-parameter cloud height model compares favorably to experimental results. This model is predictive of breakthrough in 8 ft vessel tests with the two-part simulant. Analysis of the upwell in the presence of yield stresses finds evidence of expanding turbulent jets, confined turbulent jets, and confined laminar flows. For each, the critical elevation at which jet momentum depletes is predicted, which compare favorably to experimental cavern height data. Partially coupled momentum and energy balances suggest that these are limiting cases of a gradual transition from a turbulent expanding flow to a confined laminar flow. This analysis of the central upwell alone lays essential groundwork for complete analysis of mode three mixing (i.e., breakthrough with slow peripheral mixing). Consideration of jet celerity shows that the rate of jet penetration is a governing consideration in breakthrough to the surface. Estimates of the volume of mixing are presented. This analysis shows that flow along the vessel wall is sluggish such that the central upwell governs the volume of mixing. This analysis of the central upwell alone lays essential groundwork for complete analysis of mode three mixing and estimates of hydrogen release rates from first principles.« less

Practical limitations on the use of diurnal temperature signals to quantify groundwater upwelling

USGS Publications Warehouse

Briggs, Martin A.; Lautz, Laura K.; Buckley, Sean F.; Lane, John W.

2014-01-01

Groundwater upwelling to streams creates unique habitat by influencing stream water quality and temperature; upwelling zones also serve as vectors for contamination when groundwater is degraded. Temperature time series data acquired along vertical profiles in the streambed have been applied to simple analytical models to determine rates of vertical fluid flux. These models are based on the downward propagation characteristics (amplitude attenuation and phase-lag) of the surface diurnal signal. Despite the popularity of these models, there are few published characterizations of moderate-to-strong upwelling. We attribute this limitation to the thermodynamics of upwelling, under which the downward conductive signal transport from the streambed interface occurs opposite the upward advective fluid flux. Governing equations describing the advection–diffusion of heat within the streambed predict that under upwelling conditions, signal amplitude attenuation will increase, but, counterintuitively, phase-lag will decrease. Therefore the extinction (measurable) depth of the diurnal signal is very shallow, but phase lag is also short, yielding low signal to noise ratio and poor model sensitivity. Conversely, amplitude attenuation over similar sensor spacing is strong, yielding greater potential model sensitivity. Here we present streambed thermal time series over a range of moderate to strong upwelling sites in the Quashnet River, Cape Cod, Massachusetts. The predicted inverse relationship between phase-lag and rate of upwelling was observed in the field data over a range of conditions, but the observed phase-lags were consistently shorter than predicted. Analytical solutions for fluid flux based on signal amplitude attenuation return results consistent with numerical models and physical seepage meters, but the phase-lag analytical model results are generally unreasonable. Through numerical modeling we explore reasons why phase-lag may have been over-predicted by the analytical models, and develop guiding relations of diurnal temperature signal extinction depth based on stream diurnal signal amplitude, upwelling magnitude, and streambed thermal properties that will be useful in designing future experiments.

Evaluation of the sinks and sources of atmospheric CO2 by artificial upwelling.

PubMed

Pan, Yiwen; Fan, Wei; Huang, Ting-Hsuan; Wang, Shu-Lun; Chen, Chen-Tung Arthur

2015-04-01

Artificial upwelling is considered a promising way to reduce the accumulation of anthropogenic carbon dioxide in the atmosphere. This practice could transport nutrient-rich deep water to the euphotic zone, enhance phytoplankton growth and consequently increase organic carbon exportation to the deep ocean via the biological pump. However, only a few studies quantitatively assess changes in oceanic CO2 uptake resulting from artificial upwelling. This article uses a simulation to examine the effect of hypothetical artificial upwelling-induced variations of CO2 fugacity in seawater (fCO2) using observed carbon and nutrient data from 14 stations, ranging from 21 to 43°N, in the West Philippine Sea (WPS), the East China Sea (ECS) and the Sea of Japan. Calculations are based on two basic assumptions: First, a near-field mixing of a nutrient-rich deep-ocean water plume in a stratified ocean environment is assumed to form given the presence of an artificial upwelling devise with appropriate technical parameters. Second, it is assumed that photosynthesis of marine phytoplankton could deplete all available nutrients following the stoichiometry of the modified Redfield ratio C/H/O/N/S/P=103.1/181.7/93.4/11.7/2.1/1. Results suggest artificial upwelling has significant effects on regional changes in sea-air differences (ΔfCO2sea-air) and the carbon sequestration potential (ΔfCO2mixed-amb). Large variations of ΔfCO2sea-air and ΔfCO2mixed-amb are shown to be associated with different regions, seasons and technical parameters of the artificial upwelling device. With proper design, it is possible to reverse the contribution of artificial upwelling from a strong CO2 source to sink. Thus, artificial upwelling has the potential to succeed as a geoengineering technique to sequester anthropogenic CO2, with appropriate technical parameters in the right region and season. Copyright © 2014 Elsevier B.V. All rights reserved.

Reconstructing Holocene Upwelling Conditions in Monterey Bay, California

NASA Astrophysics Data System (ADS)

Owen, P. W.; Wagner, A. J.; Addison, J. A.; Schwartz, V.; Barron, J. A.; Carlin, J. A.

2017-12-01

Upwelling along the eastern margin of the North Pacific is vital to the California Current System (CCS) and is a major contributing factor to the diverse marine ecosystems along the US West Coast. Prior studies hypothesize climate change will accelerate the alongshore equatorward winds that drive coastal upwelling, with the greatest increase in upwelling occurring within the poleward portion (N of 40°N) of the CCS. However, other studies have suggested that future upwelling changes in the southern portion (S of 35°N) of the CCS are less certain. Here we present a geological perspective into past Holocene upwelling along the central California coast from the Monterey Bay National Marine Sanctuary to provide a potential analogue for future upwelling conditions and a deeper understanding of CCS dynamics. A smear slide analysis of marine sediment cores taken from [1] the Pioneer Seamount off the Central California coast, [2] offshore of Pt. Año Nuevo, and [3] near the mouth of the Salinas River shows varying percentages of biogenic and terrigenous sediments during the past 11,000 years, with a shift toward greater biogenic silica sediments occurring approximately 3,000 cal yrs BP in the offshore site. In addition, an analysis of the diatom assemblages is used as a proxy for upwelling conditions. Preliminary results suggest a greater abundance of F. doliolus, a diatom species commonly used as a proxy for increased productivity and upwelling, occurs around 3,500 cal years BP. These results are then compared to existing calibrated X-ray computed tomography (CT) bulk density, total organic carbon (TOC), and biogenic silica (opal) measurements during periods of known climatic variability such as the Holocene Climate Optimum, Medieval Warm Period and Little Ice Age. Our results can provide a new high-resolution study of the central CCS throughout the Holocene, and give us a better understanding as to how future oceanic conditions may change the marine ecosystems along California's coast.

Upwelling Response to Hurricane Isaac in Geostrophic Oceanic Vortices

NASA Astrophysics Data System (ADS)

Jaimes, B.; Shay, L. K.; Brewster, J. K.; Schuster, R.

2013-05-01

As a tropical cyclone (TC) moves over the ocean, the cyclonic curl of the wind stress produces a region of upwelling waters under the TC center that is compensated by downwelling waters at regions outside the center. Direct measurements conducted during hurricane Rita and recent numerical studies indicate that this is not necessarily the case when TCs move over geostrophic oceanic features, where its background relative vorticity impacts wind-driven horizontal current divergence and the upwelling velocity. Modulation of the upwelling response in these energetic oceanic regimes impacts vertical mixing across the oceanic mixed layer base, air-sea fluxes into the atmosphere, and ultimately storm intensity. As part of NOAA Intensity Forecasting Experiment, an experiment was conducted during the passage of TC Isaac over the energetic geostrophic eddy field in the Gulf of Mexico in August 2012. Expendable bathythermographs, current profilers, and conductivity-temperature-depth probes were deployed in Isaac from NOAA WP-3D aircraft during four in-storm flights to measure oceanic variability and its impact on TC-driven upwelling and surface fluxes of heat and momentum. During intensification to hurricane, the cyclonic curl of the wind stress of Isaac extended over a region of more than 300 km in diameter (4 to 5 times the radius of maximum winds). Isaac's center moved over a cold cyclonic feature, while its right and left sides moved over warm anticyclones. Contrasting upwelling and downwelling regimes developed inside the region of cyclonic curl of the wind stress. Both positive (upwelling) and negative (downwelling) vertical displacements of 40 and 60 m, respectively, were measured inside the region of cyclonic curl of the wind stress, which are between 3 to 4 times larger than predicted vertical displacements for a quiescent ocean based on scaling arguments. Oceanic mixed layer (OML) currents of 0.2 to 0.7 m s-1 were measured, which are about 50% smaller than the expected velocity response under quiescent oceanic conditions. Although OML currents were measured inside the core of cyclonic curl of the wind stress, their orientation is not consistent with horizontally divergent flows typically found in upwelling regimes under TC centers. Theoretical predictions that consider background relative vorticity effects on the upwelling response mimic the contrasting upwelling/downwelling regimes inside the region of cyclonic curl of the wind stress. These results point to an important modulation of the OML current and upwelling response by background oceanic flows, where the upwelling velocity is a function of the curl of wind-intensified pre-storm geostrophic currents, rather than just a function of the curl of the wind stress. Thus, properly initializing temperature and salinity fields in numerical models is needed to accurately represent these oceanic processes in coupled forecast models.

Pathways of upwelling deep waters to the surface of the Southern Ocean

NASA Astrophysics Data System (ADS)

Tamsitt, Veronica; Drake, Henri; Morrison, Adele; Talley, Lynne; Dufour, Carolina; Gray, Alison; Griffies, Stephen; Mazloff, Matthew; Sarmiento, Jorge; Wang, Jinbo; Weijer, Wilbert

2017-04-01

Upwelling of Atlantic, Indian and Pacific deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of anthropogenic carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. Here we go beyond the two-dimensional view of Southern Ocean upwelling, to show detailed Southern Ocean upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution ocean and climate models. The northern deep waters enter the Antarctic Circumpolar Current (ACC) via narrow southward currents along the boundaries of the three ocean basins, before spiraling southeastward and upward through the ACC. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the southern ACC boundary, with a spatially nonuniform distribution, regionalizing warm water supply to Antarctic ice shelves and the delivery of nutrient and carbon-rich water to the sea surface. The timescale for half of the deep water to upwell from 30°S to the mixed layer is on the order of 60-90 years, which has important implications for the timescale for signals to propagate through the deep ocean. In addition, we quantify the diabatic transformation along particle trajectories, to identify where diabatic processes are important along the upwelling pathways.

A Numerical Study of the Effect of Periodic Nutrient Supply on Pathways of Carbon in a Coastal Upwelling Regime

NASA Technical Reports Server (NTRS)

Carr, Mary-Elena

1998-01-01

A size-based ecosystem model was modified to include periodic upwelling events and used to evaluate the effect of episodic nutrient supply on the standing stock, carbon uptake, and carbon flow into mesozooplankton grazing and sinking flux in a coastal upwelling regime. Two ecosystem configurations were compared: a single food chain made up of net phytoplankton and mesozooplankton (one autotroph and one heterotroph, A1H1), and three interconnected food chains plus bacteria (three autotrophs and four heterotrophs, A3H4). The carbon pathways in the A1H1 simulations were under stronger physical control than those of the A3H4 runs, where the small size classes are not affected by frequent upwelling events. In the more complex food web simulations, the microbial pathway determines the total carbon uptake and grazing rates, and regenerated nitrogen accounts for more than half of the total primary production for periods of 20 days or longer between events. By contrast, new production, export of carbon through sinking and mesozooplankton grazing are more important in the A1H1 simulations. In the A3H4 simulations, the turnover time scale of the autotroph biomass increases as the period between upwelling events increases, because of the larger contribution of slow-growing net phytoplankton. The upwelling period was characterized for three upwelling sites from the alongshore wind speed measured by the NASA Scatterometer (NSCAT) and the corresponding model output compared with literature data. This validation exercise for three upwelling sites and a downstream embayment suggests that standing stock, carbon uptake and size fractionation were best supported by the A3H4 simulations, while the simulated sinking fluxes are not distinguishable in the two configurations.

Steps in the intensification of Benguela upwelling over the Walvis Ridge during Miocene and Pliocene

NASA Astrophysics Data System (ADS)

Hoetzel, Sebastian; Dupont, Lydie M.; Marret, Fabienne; Jung, Gerlinde; Wefer, Gerold

2017-01-01

Upwelling is a significant part of the ocean circulation controlling largely the transport of nutrient-rich cold waters to the surface and therefore influencing ocean productivity and global climate. The Benguela upwelling system (BUS) is one of the major upwelling areas in the world. Previous reconstructions of the BUS mainly focused on the onset and intensification in southern and central parts, but changes of the northern part have been rarely investigated in detail. Using the Late Miocene to Pliocene organic-walled dinoflagellate cyst record of ODP Site 1081, we reconstruct and discuss the early upwelling history over the Walvis Ridge with a special focus on the movement of the Angola-Benguela Front (ABF). We suggest that during the Late Miocene the Angola Current flowed southwards over the Walvis Ridge more frequently than today because the ABF was probably located further south as a result of a weaker meridional temperature gradient. A possible strengthening of the meridional gradient during the latest Miocene to early Pliocene in combination with uplift of south-western Africa intensified the upwelling along the coast and increased the upwelling's filaments over the Walvis Ridge. An intermediate period from 6.2 to 5.5 Ma is shown by the dominance of Habibacysta tectata, cysts of a cool-tolerant dinoflagellate known from the northern Atlantic, indicating changing oceanic conditions contemporaneous with the Messinian Salinity Crisis. From 4.3 Ma on, the upwelling signal got stronger again and waters were well-mixed and nutrient-rich. Our results indicate a northward migration of the ABF as early as 7 Ma and the initial stepwise intensification of the BUS.

A theoretical study of topographic effects on coastal upwelling and cross-shore exchange

NASA Astrophysics Data System (ADS)

Song, Y. Tony; Chao, Yi

The effects of topographic variations on coastal upwelling and cross-shore exchange are examined with a theoretical, continuously stratified, three-dimensional coastal ocean model. The model takes into account topographic variations in both alongshore and cross-shore directions and allows analytical solutions with an Ekman surface layer that faithfully represents the physical nature of the coastal upwelling system. Theoretical solutions with any analytical form of alongshore-varying topography can be solved based on the perturbation method of Killworth [J. Phys. Oceanogr. 8 (1978) 188]. Analyses of the model solutions lead to the following conclusions: The variation of upwelling fronts and currents is shown to be caused by the combined effect of topography and stratification. Topographic variation causes uneven upwelling distribution and leads to density variation, which results in a varying horizontal pressure gradient field that causes the meandering currents. The variation index is dependent upon a bilinear function of their physical parameters--the ratio of the topographic variation depth to the total depth and Burger's number of stratification. Cross-shore slope is found to play a role in maintaining the meandering structure of the alongshore currents. The anticyclonic circulations can further induce downwelling on the offshore side of the current, while the cyclonic circulations enhance upwelling and form upwelling centers on the inshore side of the current. Alongshore topography does not change the total upwelled water, i.e., the total Ekman pumping is conserved. However, it increases cross-exchange of water masses by transporting inshore (offshore) water near topographic features far offshore (inshore) from the mean position of the front. The applicability and limitations of the theory are also discussed.

Growth and production of the copepod community in the southern area of the Humboldt Current System

NASA Astrophysics Data System (ADS)

Escribano, R.; Bustos-Ríos, E.; Hidalgo, P.; Morales, C. E.

2015-02-01

Zooplankton production is a critical issue for understanding marine ecosystem structure and dynamics, however, its time-space variations are mostly unknown in most systems. In this study, estimates of copepod growth and production (CP) in the coastal upwelling and coastal transition zones off central-southern Chile (∼35-37° S) were obtained from annual cycles during a 3 year time series (2004, 2005, and 2006) at a fixed shelf station and from spring-summer surveys during the same years. C-specific growth rates (g) varied extensively among species and under variable environmental conditions; however, g values were not correlated to either near surface temperature or copepod size. Copepod biomass (CB) and CP were higher within the coastal upwelling zone (<50 km) and both decreased substantially from 2004 to 2006. Annual CP ranged between 24 and 52 g C m-2 year-1 with a~mean annual P/B ratio of 2.7. We estimated that CP could consume up to 60% of the annual primary production (PP) in the upwelling zone but most of the time is around 8%. Interannual changes in CB and CP values were associated with changes in the copepod community structure, the dominance of large-sized forms replaced by small-sized species from 2004 to 2006. This change was accompanied by more persistent and time extended upwelling during the same seasonal period. Extended upwelling may have caused large losses of CB from the upwelling zone due to an increase in offshore advection of coastal plankton. On a larger scale, these results suggest that climate-related impacts of increasing wind-driven upwelling in coastal upwelling systems may generate a negative trend in zooplankton biomass.

High frequency responses of nanoplankton and microplankton to wind-driven upwelling off northern Chile

NASA Astrophysics Data System (ADS)

Aguilera, Victor; Escribano, Ruben; Herrera, Liliana

2009-08-01

Autotrophic and heterotrophic nanoplankton and microplankton vary widely in quantity and composition in coastal upwelling zones, causing a highly heterogeneous distribution of food resources for higher trophic levels. Here, we assessed daily changes in size-fractioned biomass and community structure of nanoplankton and microplankton at two upwelling sites off northern Chile, Mejillones (23°S) and Chipana (21°S), during summer 2006, winter 2006 and summer 2007 as related to changes in oceanographic conditions upon upwelling variation. We found highly-significant changes in quantity and community structure (species diversity and richness) of both nanoplankton and microplankton fractions after 3-5 days of observations. These changes were coupled to an intermittent upwelling regime reflected in the alongshore component of the wind. After a few days the whole community was modified in terms of species and size structure. Over-imposing this variability, during winter 2006 there was a strong perturbation of remote origin that substantially impacted temperature, oxygenation and stratification of the water column. This "abnormal" warming event altered the upwelling regime, but its impact on abundance and composition of the nanoplankton and microplankton fractions was uncertain. Over the short-time scale however, we found a strong coupling between daily changes in the alongshore component of wind and nanoplankton and microplankton abundances and their structure. All these findings indicate that despite the high biological productivity of this upwelling region, high frequency variation induced by wind forcing may be a major regulator of food resources (quantity and quality) for primary consumers, such as zooplankton, fish larvae and benthic organisms in the near-shore area. This high frequency variation may also impose a key constrain for prey-predator encounter rates and survival of short-lived zooplankton and invertebrate and fish larvae in the upwelling zone.

Abyssal Upwelling and Downwelling and the role of boundary layers

NASA Astrophysics Data System (ADS)

McDougall, T. J.; Ferrari, R. M.

2016-02-01

The bottom-intensified mixing activity arising from the interaction of internal tides with bottom topography implies that the dianeutral advection in the ocean interior is downwards, rather than upwards as is required by continuity. The upwelling of Bottom Water through density surfaces in the deep ocean is however possible because of the sloping nature of the sea floor. A budget study of the abyss (deeper than 2000m) will be described that shows that while the upwelling of Bottom Water might be 25 Sv, this is achieved by very strong upwelling in the bottom turbulent boundary layer (of thickness 50m) of 100 Sv and strong downwelling in the ocean interior of 75 Sv. This downwelling occurs within 10 degrees of longitude of the continental boundaries. This near-boundary confined strong upwelling and downwelling clearly has implications for the Stommel-Arons circulation.

N2O production by nitrifier denitrification in the Benguela Upwelling System

NASA Astrophysics Data System (ADS)

Frame, C. H.; Hou, L.; Lehmann, M. F.

2014-12-01

The Benguela upwelling system off the coast of southwestern Africa is an important zone of marine N2O production whose upwelling rates vary seasonally. Here we present N2O stable isotopic and isotopomeric data collected during a period of high upwelling (September 2013) and low upwelling (January 2014). During both periods, 15N-nitrite and 15N-ammonium tracer inucbation experiments were used to investigate N2O production by ammonia oxidizing microorganisms in the top 150m of the water column. N2O production from 15N-ammonium was not measurable during these incubations. However, we detected N2O production from 15N-nitrite, suggesting that nitrifier denitrification is a source of shallow N2O in this region. Furthermore, decreasing the pH of the incubation water enhanced the amount of N2O produced, suggesting that upwelling of CO2-rich/low-pH deep water may enhance N2O production in this region. Finally, we present our incubation data in the larger context of the N2O and nitrite isotopic and concentration profiles, with an eye toward comparing incubation-based N2O production rates with profile-based estimates.

Ocean response to typhoons in the western North Pacific: Composite results from Argo data

NASA Astrophysics Data System (ADS)

Lin, Sheng; Zhang, Wen-Zhou; Shang, Shao-Ping; Hong, Hua-Sheng

2017-05-01

Composite structures of ocean temperature and salinity anomalies caused by tropical cyclones (TCs) or typhoons in the western North Pacific Ocean were obtained from Argo data. These structures were used to analyze ocean responses to typhoons and the dynamic mechanisms inherent in those responses with a particular focus on upwelling. TC-induced cooling is often strongly rightward-biased in the surface layer, and shifts toward the typhoon track at depths exceeding roughly 100 m. In the central water column within approximately 75 km of the typhoon track, subsurface warming predicted by vertical mixing is restrained and replaced by cooling due to upwelling. Upwelling contributes 15% on average to temperature cooling in the near surface layer (10-30 m), 84% in the subsurface layer (30-250 m) and 94% in the deep layer (250-600 m) during the period of 0.5-2.5 days after the typhoon's passage. It is suggested that the sea surface cooling effect of vertical mixing can be enhanced by the upwelling. The effect of upwelling is also prominent in the salinity response to typhoons. The composite results from the Argo data clearly reveal basic ocean responses to typhoons and indicate the important role of upwelling therein.

Does mesoscale matters in decadal changes observed in the northern Canary upwelling system?

NASA Astrophysics Data System (ADS)

Relvas, P.; Luís, J.; Santos, A. M. P.

2009-04-01

The Western Iberia constitutes the northern limb of the Canary Current Upwelling System, one of the four Eastern Boundary Upwelling Systems of the world ocean. The strong dynamic link between the atmosphere and the ocean makes these systems highly sensitive to global change, ideal to monitor and investigate its effects. In order to investigate decadal changes of the mesoscale patterns in the Northern Canary upwelling system (off Western Iberia), the field of the satellite-derived sea surface temperature (SST) trends was built at the pixel scale (4x4 km) for the period 1985-2007, based on the monthly mean data from the Advanced Very High Resolution Radiometer (AVHRR) on board NOAA series satellites, provided by the NASA Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory. The time series were limited to the nighttime passes to avoid the solar heating effect and a suite of procedures were followed to guarantee that the temperature trends were not biased towards the seasonally more abundant summer data, when the sky is considerably clear. A robust linear fit was applied to each individual pixel, crossing along the time the same pixel in all the processed monthly mean AVHRR SST images from 1985 until 2007. The field of the SST trends was created upon the slopes of the linear fits applied to each pixel. Monthly mean SST time series from the one degree enhanced International Comprehensive Ocean-Atmosphere Data Set (ICOADS) and from near-shore measurements collected on a daily basis by the Portuguese Meteorological Office (IM) are also used to compare the results and extend the analysis back until 1960. A generalized warming trend is detected in the coastal waters off Western Iberia during the last decades, no matter which data set we analyse. However, significant spatial differences in the warming rates are observed in the satellite-derived SST trends. Remarkably, off the southern part of the Western Iberia the known upwelling pattern is clearly reflected in the warming field. There, the coastal upwelled waters show a weak warming trend when compared with the offshore waters. If we assume that the SST contrast between coastal and offshore waters is a proxy for the upwelling intensity, then this fact suggests the enhancement of the upwelling regime off SW Iberia since 1985. Although the seasonal nature of the upwelling in the region, the strengthening must be significant since it leaves a coherent imprint in the annual warming field. An analysis done on a monthly basis reveals that the central months of the classical upwelling season (July to September) are the responsible for this coherent mesoscale structure observed in the warming field off SW Iberia. The same conclusions are not clear for the mesoscale structure further north, where no significant differences are observed between the coastal and offshore warming rates. To investigate if our results, obtained for the period with satellite coverage (1985-2007), could be extended or not until 1960, we computed an upwelling index as the SST difference between coastal and offshore ICOADS SST. The analysis revealed that the trends are different whether we consider the whole time series or only the period investigated with the satellite imagery. We can suppose a relatively unchanged upwelling regime if we consider the period 1960-2005, but a rapid increase of intensity if we consider the period from 1985 onwards, particularly in the most southern regions, in agreement with the satellite imagery analysis. Our present results point out that mesoscale activity can account for larger changes in local SST than global average trends. In Eastern Boundary Upwelling Systems, where mesoscale structures play a major role in the description of the upwelling regime, to rely on sparse spatial observations to hypothesize about the decadal behaviour of the upwelling intensity at the basin scale may be questionable.

Transformation of Deep Water Masses Along Lagrangian Upwelling Pathways in the Southern Ocean

NASA Astrophysics Data System (ADS)

Tamsitt, V.; Abernathey, R. P.; Mazloff, M. R.; Wang, J.; Talley, L. D.

2018-03-01

Upwelling of northern deep waters in the Southern Ocean is fundamentally important for the closure of the global meridional overturning circulation and delivers carbon and nutrient-rich deep waters to the sea surface. We quantify water mass transformation along upwelling pathways originating in the Atlantic, Indian, and Pacific and ending at the surface of the Southern Ocean using Lagrangian trajectories in an eddy-permitting ocean state estimate. Recent related work shows that upwelling in the interior below about 400 m depth is localized at hot spots associated with major topographic features in the path of the Antarctic Circumpolar Current, while upwelling through the surface layer is more broadly distributed. In the ocean interior upwelling is largely isopycnal; Atlantic and to a lesser extent Indian Deep Waters cool and freshen while Pacific deep waters are more stable, leading to a homogenization of water mass properties. As upwelling water approaches the mixed layer, there is net strong transformation toward lighter densities due to mixing of freshwater, but there is a divergence in the density distribution as Upper Circumpolar Deep Water tends become lighter and dense Lower Circumpolar Deep Water tends to become denser. The spatial distribution of transformation shows more rapid transformation at eddy hot spots associated with major topography where density gradients are enhanced; however, the majority of cumulative density change along trajectories is achieved by background mixing. We compare the Lagrangian analysis to diagnosed Eulerian water mass transformation to attribute the mechanisms leading to the observed transformation.

Larval fish assemblages across an upwelling front: Indication for active and passive retention

NASA Astrophysics Data System (ADS)

Tiedemann, Maik; Brehmer, Patrice

2017-03-01

In upwelling areas, enrichment, concentration and retention are physical processes that have major consequences for larval fish survival. While these processes generally increase larval survival, strong upwelling can also increase mortality due to an offshore transport of larvae towards unfavorable habitats. In 2013 a survey was conducted along the Senegalese coast to investigate the upwelling effect with regard to larval fish assemblages and possible larval fish retention. According to water column characteristics two distinct habitats during an upwelling event were discriminated, i.e. the inshore upwelled water and the transition area over the deepest part of the Senegalese shelf. Along the two areas 42,162 fish larvae were collected representing 133 species within 40 families. Highest larval fish abundances were observed in the inshore area and decreasing abundances towards the transition, indicating that certain fish species make use of the retentive function of the inner shelf area as spawning grounds. Two larval fish assemblages overlap both habitats, which are sharply delimited by a strong upwelling front. One assemblage inhabited the inshore/upwelling area characterized by majorly neritic and pelagic species (Sparidae spp., Sardinella aurita), that seem to take the advantage of a passive retention on the shelf. The second assemblage consisted of a mix of pelagic and mesopelagic species (Engraulis encrasicolus, Carangidae spp. and Myctophidae spp.). Some species of the second assemblage, e.g. horse mackerels (Trachurus trachurus and Trachurus trecae), large finned-lantern fish (Hygophum macrochir) and foureyed sole (Microchirus ocellatus), revealed larval peak occurrences at intermediate and deep water layers, where the near-ground upwelling layer is able to transport larvae back to the shelf. This indicates active larval retention for species that are dominant in the transition area. Diel vertical migration patterns of S. aurita, E. encrasicolus and M. ocellatus revealed that a larval fish species may adapt its behavior to the local environment and do not necessarily follow a diurnal cycle. Field observations are essential to be integrated in larval drift models, since the vertical and horizontal larval distribution will have major consequences for survival. Comprehending larval survival mechanisms is necessary for the ultimate goal to understand and predict recruitment.

Decadal changes in the Canary Current Upwelling Ecosystem

NASA Astrophysics Data System (ADS)

Santos, A. M.; Luis, J. M.; Relvas-Almeida, P.

2013-12-01

The Canary Current Upwelling System (CCUS) covers the latitudinal range 12-43 degrees N and has some singularities in relation to the other three major Eastern Boundary Upwelling Systems (EBUS), namely a major interruption in the continuity of the system at the Strait of Gibraltar and it is the only one with a sardine species from a different genus (Sardina vs Sardinops). Long-term trends in ocean temperature and coastal upwelling were investigated using the AVHRR Pathfinder SST (sea surface temperature) Version 5.1 dataset, in situ SST from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS), and upwelling indices from the Pacific Fisheries Environmental Laboratory (PFEL). The analysis is applied to the eastern boundary of the North Atlantic, from 10 to 45 degrees N extending until 30 degrees W, focusing mainly in the CCUS because the strong dynamic link between the atmosphere and the ocean makes upwelling regions highly sensitive to global change and ideal to monitor and investigate its effects. The detail in SST variability results in a large extent from the fine analysis and the numerical processing carefully designed to avoid trend bias in the climatological studies. The obtained fields of SST trends show a generalized warming of the entire region. However, alternate patches of significantly different warming rates are observed, ranging from large scale down to mesoscale. Known coastal upwelling features are seen to warm at a lower rate than corresponding offshore waters, pointing to an intensification of the upwelling in the last decades. Wind data are used to attempt to explain the variability of some upwelling structures. Our results evidence the main role that mesoscale processes play in the modulation of the spatial and temporal variability of SST, namely at the decadal scale. This result prevents any global conclusion about the intensification of the upwelling at the scale of the entire CCUS. The bulk of the sardine population is located in the southern part of CCUS off NW Africa. Important fluctuations in landings have been observed in the last 70 years but they seem to be out of phase between the two sub-regions - the northern CCUS (Iberia) and southern CCUS (NW Africa). The explanation for these fluctuations has been related, at least partially, to environmental drivers but also to changes in exploitation. Landing time series of sardine, anchovy and sardinella were used to perform an exploratory analysis to investigate the relationships between small pelagic fish species in the CCUS and decadal changes in SST and coastal upwelling. This is a contribution to FCT (Portuguese Science and Technology Foundation) funded projects LONGUP (PTDC/AAC-CLI/105296/2008) and MODELA (PTDC/MAR/098643/2008).

Geographical gradients in selection can reveal genetic constraints for evolutionary responses to ocean acidification

PubMed Central

Gaitán-Espitia, Juan Diego; Marshall, Dustin; Dupont, Sam; Bacigalupe, Leonardo D.; Bodrossy, Levente; Hobday, Alistair J.

2017-01-01

Geographical gradients in selection can shape different genetic architectures in natural populations, reflecting potential genetic constraints for adaptive evolution under climate change. Investigation of natural pH/pCO2 variation in upwelling regions reveals different spatio-temporal patterns of natural selection, generating genetic and phenotypic clines in populations, and potentially leading to local adaptation, relevant to understanding effects of ocean acidification (OA). Strong directional selection, associated with intense and continuous upwellings, may have depleted genetic variation in populations within these upwelling regions, favouring increased tolerances to low pH but with an associated cost in other traits. In contrast, diversifying or weak directional selection in populations with seasonal upwellings or outside major upwelling regions may have resulted in higher genetic variances and the lack of genetic correlations among traits. Testing this hypothesis in geographical regions with similar environmental conditions to those predicted under climate change will build insights into how selection may act in the future and how populations may respond to stressors such as OA. PMID:28148831

Tracking the Surface Circulation in Coastal Upwelling off Central and Northern California over Long Times and Large Areas.

NASA Astrophysics Data System (ADS)

Largier, J. L.; Garcia-Reyes, M.; Bjorkstedt, E.; Paduan, J. D.

2016-12-01

More than a decade of HF Radar data off central and northern California provides an unprecedented view of the flow structures and interannual variability in surface circulation in a coastal upwelling area. The interaction of the alongshore shelf jet with shoreline features and mesoscale eddies is well represented in direct analyses of HFR data and also important in improving the performance of data-assimilating models. While invaluable for operational response in the short-term, this long-term record of surface circulation is equally invaluable in ecosystem oceanography. With direct measurement of currents, the different expressions of upwelling can be disaggregated. Wind forcing, transport patterns and water properties can be evaluated independently and indexed independently. In doing this, it becomes clear that wind-current-temperature correlations change from place to place and year to year in any given region and that a single "upwelling index" is a blunt tool to track changes in pelagic and benthic communities in coastal upwelling areas.

Estimates of upwelling rates in the Arabian Sea and the equatorial Indian Ocean based on bomb radiocarbon.

PubMed

Bhushan, R; Dutta, K; Somayajulu, B L K

2008-10-01

Radiocarbon measurements were made in the water column of the Arabian Sea and the equatorial Indian Ocean during 1994, 1995 and 1997 to assess the temporal variations in bomb 14C distribution and its inventory in the region with respect to GEOSECS measurements made during 1977-1978. Four GEOSECS stations were reoccupied (three in the Arabian Sea and one in the equatorial Indian Ocean) during this study, with all of them showing increased penetration of bomb 14C along with decrease in its surface water activity. The upwelling rates derived by model simulation of bomb 14C depth profile using the calculated exchange rates ranged from 3 to 9 m a(-1). The western region of the Arabian Sea experiencing high wind-induced upwelling has higher estimated upwelling rates. However, lower upwelling rates obtained for the stations occupied during this study could be due to reduced 14C gradient compared to that during GEOSECS.

Climate change and ocean deoxygenation within intensified surface-driven upwelling circulations.

PubMed

Bakun, Andrew

2017-09-13

Ocean deoxygenation often takes place in proximity to zones of intense upwelling. Associated concerns about amplified ocean deoxygenation arise from an arguable likelihood that coastal upwelling systems in the world's oceans may further intensify as anthropogenic climate change proceeds. Comparative examples discussed include the uniquely intense seasonal Somali Current upwelling, the massive upwelling that occurs quasi-continuously off Namibia and the recently appearing and now annually recurring 'dead zone' off the US State of Oregon. The evident 'transience' in causal dynamics off Oregon is somewhat mirrored in an interannual-scale intermittence in eruptions of anaerobically formed noxious gases off Namibia. A mechanistic scheme draws the three examples towards a common context in which, in addition to the obvious but politically problematic remedy of actually reducing 'greenhouse' gas emissions, the potentially manageable abundance of strongly swimming, finely gill raker-meshed small pelagic fish emerges as a plausible regulating factor.This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'. © 2017 The Author(s).

Diatoms Si uptake capacity drives carbon export in coastal upwelling systems

NASA Astrophysics Data System (ADS)

Abrantes, Fatima; Cermeno, Pedro; Lopes, Cristina; Romero, Oscar; Matos, Lélia; Van Iperen, Jolanda; Rufino, Marta; Magalhães, Vitor

2016-07-01

Coastal upwelling systems account for approximately half of global ocean primary production and contribute disproportionately to biologically driven carbon sequestration. Diatoms, silica-precipitating microalgae, constitute the dominant phytoplankton in these productive regions, and their abundance and assemblage composition in the sedimentary record is considered one of the best proxies for primary production. The study of the sedimentary diatom abundance (SDA) and total organic carbon content (TOC) in the five most important coastal upwelling systems of the modern ocean (Iberia-Canary, Benguela, Peru-Humboldt, California, and Somalia-Oman) reveals a global-scale positive relationship between diatom production and organic carbon burial. The analysis of SDA in conjunction with environmental variables of coastal upwelling systems such as upwelling strength, satellite-derived net primary production, and surface water nutrient concentrations shows different relations between SDA and primary production on the regional scale. On the global scale, SDA appears modulated by the capacity of diatoms to take up silicic acid, which ultimately sets an upper limit to global export production in these ocean regions.

Intensification of upwelling along Oman coast in a warming scenario

NASA Astrophysics Data System (ADS)

Praveen, V.; Ajayamohan, R. S.; Valsala, V.; Sandeep, S.

2016-07-01

The oceanic impact of poleward shift in monsoon low-level jet (MLLJ) is examined using a Regional Ocean Modeling System (ROMS). Two sets of downscaling experiments were conducted using ROMS with boundary and initial conditions from six CMIP5 models. While outputs from the historical run (1981-2000) acts as forcing for the first, the second uses RCP8.5 (2080-2099). By comparing the outputs, it is found that Oman coast will experience an increase in upwelling in tune with MLLJ shift. Consistent with the changes in upwelling and zonal Ekman transport, temperature, salinity, and productivity show significant changes near the Oman coast. The changes in MLLJ causes the coastal wind to angle against the Oman coast in such a fashion that the net upwelling increases in the next century and so does the marine productivity. This study contrasts the general view of weakening of upwelling along the Arabian coasts due to the weakening of monsoon winds.

Upwelling changes along the Arabian coast in a warming scenario

NASA Astrophysics Data System (ADS)

Praveen, V.; Ravindran, A. M.; Valsala, V.; Sandeep, S.

2016-12-01

The oceanic impact of poleward shift in Monsoon Low-Level Jet (MLLJ) is examined using a regional ocean model (ROMS). Two sets of downscaling experiments were conducted using ROMS with boundary and initial conditions from six CMIP5 models. While outputs from the historical run (1981-2000) acts as forcing for the first, the second uses RCP8.5 (2080-2099). By comparing the outputs, it is found that Oman coast will experience an increase in upwelling in tune with MLLJ shift. Consistent with the changes in upwelling and zonal Ekman transport, temperature, salinity and productivity show significant changes near the Oman coast. The changes in MLLJ causes the coastal wind to angle against the Oman coast in such a fashion that the net upwelling increases in the next century and so does the marine productivity. This study contrasts the general view of weakening of upwelling along the Arabian coasts due to the weakening of monsoon winds. Above findings has major implications on the livelihood and economy of the region

Precession-paced thermocline water temperature changes in response to upwelling conditions off southern Sumatra over the past 300,000 years

NASA Astrophysics Data System (ADS)

Wang, Xingxing; Jian, Zhimin; Lückge, Andreas; Wang, Yue; Dang, Haowen; Mohtadi, Mahyar

2018-07-01

Modern variations of sea surface temperature (SST) and thermocline water temperature (TWT) off southern Sumatra are responding to local upwelling conditions which are controlled by the Australian-Indonesian winter monsoon. The relationships between SST, TWT and upwelling during the past glacial-interglacial cycles are less clearly understood. In this study, SST and TWT variabilities over the past 300 kyr are reconstructed by using foraminiferal Mg/Ca-paleothermometry in sediment core SO139-74 KL off southern Sumatra (6°32.6‧S, 103°50‧E; 1690 m water depth). Whereas SST shows a clear glacial-interglacial cycle, TWT displays a predominant cycle at the precession band. Generally, the TWT record varies with total organic carbon content, revealing that similar to today, TWT and upwelling intensity off southern Sumatra vary in concert during the past 300 kyr. The lack of glacial-interglacial variability in the TWT suggests a limited role of glacial boundary conditions, such as changing sea level and ice volume, on the upwelling intensity in this region. The vertical gradients of upper water δ18O and temperature at this site also reveal precessional cyclicity. Our model simulation of air-sea interaction further supports the low TWTs during periods of enhanced upwelling and precession minimum.

A coupled ice-ocean model of upwelling in the marginal ice zone

NASA Technical Reports Server (NTRS)

Roed, L. P.; Obrien, J. J.

1983-01-01

A dynamical coupled ice-ocean numerical model for the marginal ice zone (MIZ) is suggested and used to study upwelling dynamics in the MIZ. The nonlinear sea ice model has a variable ice concentration and includes internal ice stress. The model is forced by stresses on the air/ocean and air/ice surfaces. The main coupling between the ice and the ocean is in the form of an interfacial stress on the ice/ocean interface. The ocean model is a linear reduced gravity model. The wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water, while the interfacial stress ice/ocean is proportional to the concentration of ice. A new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium. The upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion. Most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport. On the basis of numerical model, an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model.

Variability in bacterial community structure during upwelling in the coastal ocean

USGS Publications Warehouse

Kerkhof, L.J.; Voytek, M.A.; Sherrell, Robert M.; Millie, D.; Schofield, O.

1999-01-01

Over the last 30 years, investigations at the community level of marine bacteria and phytoplankton populations suggest they are tightly coupled. However, traditional oceanographic approaches cannot assess whether associations between specific bacteria and phytoplankton exist. Recently, molecular based approaches have been implemented to characterize specific members of different marine bacterial communities. Yet, few molecular-based studies have examined coastal upwelling situations. This is important since upwelling systems provide a unique opportunity for analyzing the association between specific bacteria and specific phytoplankton in the ocean. It is widely believed that upwelling can lead to changes in phytoplankton populations (blooms). Thus, if specific associations exist, we would expect to observe changes in the bacterial population triggered by the bloom. In this paper, we present preliminary data from coastal waters off New Jersey that confirm a shift in bacterial communities during a 1995 upwelling event recorded at a long-term earth observatory (LEO-15) in the Mid-Atlantic Bight. Using PCR amplification and cloning, specific bacterial 16S ribosomal RNA sequences were found which were present in upwelling samples during a phytoplankton bloom, but were not detected in non-bloom samples (surface seawater, offshore sites or sediment samples) collected at the same time or in the same area. These findings are consistent with the notion of specific associations between bacteria and phytoplankton in the ocean. However, further examination of episodic events, such as coastal upwelling, are needed to confirm the existence of specific associations. Additionally, experiments need to be performed to elucidate the mechanisms leading to the specific linkages between a group of bacteria and a group of phytoplankton.

Spatiotemporal variation of vertical particle fluxes and modelled chlorophyll a standing stocks in the Benguela Upwelling System

NASA Astrophysics Data System (ADS)

Vorrath, Maria-Elena; Lahajnar, Niko; Fischer, Gerhard; Libuku, Viktor Miti; Schmidt, Martin; Emeis, Kay-Christian

2018-04-01

Marine particle fluxes from high productive coastal upwelling systems return upwelled CO2 and nutrients to the deep ocean and sediments and have a substantial impact on the global carbon cycle. This study examines relations between production regimes on the shelf and over the continental margin of the Benguela Upwelling System (BUS) in the SE Atlantic Ocean. Data of composition and timing of vertical particle flux come from sediment trap time series (deployed intermittently between 1988 and 2014) in the regions Walvis Ridge, Walvis Bay, Luederitz and Orange River. We compare their seasonal variability to modelled patterns of chlorophyll concentrations in a 3-D ecosystem model. Both modelled seasonal chlorophyll a standing stocks and sampled particle flux patterns are highly correspondent with a bimodal seasonal cycle offshore the BUS. The material in the particle flux in offshore traps is dominantly carbonate (40-70%), and flux peaks in offshore particle flux originate from two independent events: in austral autumn thermocline shoaling and vertical mixing are decoupled from coastal upwelling, while fluxes in spring coincide with the upwelling season, indicated by slightly elevated biogenic opal values at some locations. Coastal particle fluxes are characterized by a trimodal pattern and are dominated by biogenic opal (22-35%) and organic matter (30-60%). The distinct seasonality in observed fluxes on the shelf is caused by high variability in production, sinking behaviour, wind stress, and hydrodynamic processes. We speculate that global warming will increase ocean stratification and alter coastal upwelling, so that consequences for primary production and particle flux in the BUS are inevitable.

Nutrient controls on new production in the Bodega Bay, California, coastal upwelling plume

NASA Astrophysics Data System (ADS)

Dugdale, R. C.; Wilkerson, F. P.; Hogue, V. E.; Marchi, A.

2006-12-01

A theoretical framework for the time-dependent processes leading to the high rates of new production in eastern boundary upwelling systems has been assembled from a series of past upwelling studies. As part of the CoOP WEST (Wind Events and Shelf Transport) study, new production in the Bodega Bay upwelling area and it's control by ambient nitrate and ammonium concentrations and the advective wind regime are described. Data and analyses are focused primarily on the WEST 2001 cruise (May-June 2001) when the two legs differed greatly in wind regimes but not nutrient concentrations. Elevated concentrations of ammonium in upwelled water with high nitrate were observed in both legs. Nitrate uptake by phytoplankton as a function of nitrate concentration was linear rather than Michaelis-Menten-like, modulated by inhibitory levels of ammonium, yielding coefficients that enable the specific nitrate uptake element of new production to be estimated from nutrient concentrations. The range of specific nitrate uptake rates for the two legs of WEST 2001 were similar, essentially a physiological response to nutrient conditions. However, the low "realization" of new production i.e. incorporation of biomass as particulate nitrogen that occurred in this system compared to the theoretical maximum possible was determined by the strong advective and turbulent conditions that dominated the second leg of the WEST 2001 study. These data are compared with other upwelling areas using a physiological shift-up model [Dugdale, R.C., Wilkerson, F.P., Morel, A. 1990. Realization of new production in coastal upwelling areas: a means to compare relative performance. Limnology and Oceanography 35, 822-829].

Variability of Phytoplankton Size Structure in Response to Changes in Coastal Upwelling Intensity in the Southwestern East Sea

NASA Astrophysics Data System (ADS)

Shin, Jung-Wook; Park, Jinku; Choi, Jang-Geun; Jo, Young-Heon; Kang, Jae Joong; Joo, HuiTae; Lee, Sang Heon

2017-12-01

The aim of this study was to examine the size structure of phytoplankton under varying coastal upwelling intensities and to determine the resulting primary productivity in the southwestern East Sea. Samples of phytoplankton assemblages were collected on five occasions from the Hupo Bank, off the east coast of Korea, during 2012-2013. Because two major surface currents have a large effect on water mass transport in this region, we first performed a Backward Particle Tracking Experiment (BPTE) to determine the coastal sea from which the collected samples originated according to advection time of BPTE particles, following which we used upwelling age (UA) to determine the intensity of coastal upwelling in the region of origin for each sample. Only samples that were affected by coastal upwelling in the region of origin were included in subsequent analyses. We found that as UA increased, there was a decreasing trend in the concentration of picophytoplankton, and increasing trends in the concentration of nanophytoplankton and microphytoplankton. We also examined the relationship between the size structure of phytoplankton and primary productivity in the Ulleung Basin (UB), which has experienced significant variation over the past decade. We found that primary productivity in UB was closely related to the strength of the southerly wind, which is the most important mechanism for coastal upwelling in the southwestern East Sea. Thus, the size structure of phytoplankton is determined by the intensity of coastal upwelling, which is regulated by the southerly wind, and makes an important contribution to primary productivity.

The NAO Influence on the Early to Mid-Holocene North Atlantic Coastal Upwelling

NASA Astrophysics Data System (ADS)

Hernandez, A.; Cachão, M.; Sousa, P.; Trigo, R. M.; Freitas, M. C.

2017-12-01

Coastal upwelling regions yield some of the oceanic most productive ecosystems, being crucial for the worldwide social and economic development. Most upwelling systems, emerging cold nutrient-rich deep waters, are located in the eastern boundaries of the Atlantic and Pacific basins, and are driven by meridional wind fields parallel to the coastal shore. These winds are associated with the subsiding branch of the large-scale Anticyclonic high pressure systems that dominate the subtropical ocean basins, and therefore can be displaced or intensified within the context of past and future climate changes. However, the role of the current global warming influencing the coastal upwelling is, as yet, unclear. Therefore it is essential to derive a long-term perspective, beyond the era of instrumental measurements, to detect similar warm periods in the past that have triggered changes in the upwelling patterns. In this work, the upwelling dynamics in the Iberian North Atlantic margin during the early and mid-Holocene is reconstructed, using calcareous nannofossils from a decadally resolved estuarine sediment core located in southwestern Portugal. Results suggest that the coastal dynamics reflects changes in winds direction likely related to shifts in the NAO-like conditions. Furthermore, the reconstructed centennial-scale variations in the upwelling are synchronous with changes in solar irradiance, a major external forcing factor of the climate system that is known to exert influence in atmospheric circulation patterns. In addition, these proxy-based data interpretations are in agreement with wind field and solar irradiance simulation modelling for the mid-Holocene. Therefore, the conclusion that the solar activity via the NAO modulation controlled the North Atlantic upwelling of western Iberia during the early and mid-Holocene at decadal to centennial timescales can be derived. The financial support for attending this meeting was possible through FCT project UID/GEO/50019/2013 - Instituto Dom Luiz

Modeling coastal upwelling around a small-scale coastline promontory

NASA Astrophysics Data System (ADS)

Haas, K. A.; Cai, D.; Freismuth, T. M.; MacMahan, J.; Di Lorenzo, E.; Suanda, S. H.; Kumar, N.; Miller, A. J.; Edwards, C. A.

2016-12-01

On the US west coast, northerly winds drive coastal ocean upwelling, an important process which brings cold nutrient rich water to the nearshore. The coastline geometry has been shown to be a significant factor in the strength of the upwelling process. In particular, the upwelling in the lee of major headlands have been shown to be enhanced. Recent observations from the Pt. Sal region on the coast of southern California have shown the presence of cooler water south of a small (350 m) rocky promontory (Mussel Pt.) during upwelling events. The hypothesis is that the small scale promontory is creating a lee side enhancement to the upwelling. To shed some light on this process, numerical simulations of the inner shelf region centered about Pt. Sal are conducted with the ROMS module of the COAWST model system. The model system is configured with four nested grids with resolutions ranging from approximately 600 m to the outer shelf ( 200 m) to the inner shelf ( 66 m) and finally to the surf zone ( 22 m). A solution from a 1 km grid encompassing our domain provides the boundary conditions for the 600 m grid. Barotropic tidal forcing is incorporated at the 600 m grid to provide tidal variability. This model system with realistic topography and bathymetry, winds and tides, is able to isolate the forcing mechanisms that explain the emergence of the cold water mass. The simulations focus on the time period of June - July, 2015 corresponding to the pilot study in which observational experiment data was collected. The experiment data in part consists of in situ measurement, which includes mooring with conductivity, temperature, depth, and flow velocity. The model simulations are able to reproduce the important flow features including the cooler water mass south of Mussel Pt. As hypothesized, the strength of the upwelling is enhanced on the side of Mussel Pt. In addition, periods of wind relaxation where the upwelling ceases and even begins to transform towards downwelling is analyzed.

High Resolution Upwelling Cycles in Guaymas and Cariaco Basins over the late Holocene: Coupling Between the Western Atlantic and Eastern Pacific?

NASA Astrophysics Data System (ADS)

Goni, M. A.

2005-12-01

The recent past history of sea surface temperature (SST) conditions in two wind-dominated upwelling systems, Guaymas Basin (Gulf of California) and Cariaco Basin (Venezuela) was investigated using the alkenone-based UK'37 index. Both of these systems undergo marked seasonal SST changes of 4-10 degrees C, which are associated with wind-driven upwelling and thermal stratification cycles. Both Guaymas and Cariaco Basins are also characterized by suboxic to anoxic bottom waters that result in undisturbed, varved sediments. Confirmation that the seasonal SST trends are accurately incorporated into the UK'37 ratios of sinking particles was achieved using sediment trap samples. Analyses of sediment cores from Guaymas and Cariaco Basins yielded high-resolution (decadal) records of SST conditions in the overlying water column from 1700 to 2000 AD. The trends in the UK'37 index revealed general increases in the SST at both sites over that last 300 years associated with the end of the little ice age. However, in addition to this long-term trend, higher-frequency (~ 50 years) changes in SST that ranged from 1-3 degrees C were observed. We speculate that these decadal trends in SST reflect variations in the intensity of wind-driven upwelling at these sites. Most interestingly, there is a marked contrast in the timing of the SST values between Guaymas and Cariaco so that periods of enhanced upwelling in Guyamas Basin are characterized by decreased upwelling in Cariaco Basin (and vice versa). We propose that these contrasting records reflect differences in the response of wind-driven upwelling to changes in the position of the Intertropical Convergence Zone over the western Atlantic and the subtropical High over the eastern Pacific. The connection between these two upwelling systems and its significance for paleoreconstruction studies will be explored further.

Micro-phytoplankton community structure in the coastal upwelling zone off Concepción (central Chile): Annual and inter-annual fluctuations in a highly dynamic environment

NASA Astrophysics Data System (ADS)

Anabalón, V.; Morales, C. E.; González, H. E.; Menschel, E.; Schneider, W.; Hormazabal, S.; Valencia, L.; Escribano, R.

2016-12-01

An intensification of upwelling-favorable winds in recent decades has been detected in some of the main eastern boundary current systems, especially at higher latitudes, but the response of coastal phytoplankton communities in the Humboldt Current System (HCS) remains unknown. At higher latitudes in the HCS (35-40°S), strong seasonality in wind-driven upwelling during spring-summer coincides with an annual increase in coastal chlorophyll-a and primary production, and a dominance of micro-phytoplankton. In order to understand the effects of potential upwelling intensification on the micro-phytoplankton community in this region, annual and inter-annual variability in its structure (total and taxa-specific abundance and biomass) and its association with oceanographic fluctuations were analyzed using in situ time series data (2002-2009) from a shelf station off Concepcion (36.5°S). At the annual scale, total mean abundance and biomass, attributed to a few dominant diatom taxa, were at least one order of magnitude greater during spring-summer than autumn-winter, in association with changes in upwelling and surface salinity and temperature, whereas macro-nutrient concentrations remained relatively high all the year. At the inter-annual scale, total abundance and biomass decreased during the upwelling season of the 2006-2009 period compared with the 2002-2006 period, notably due to lower abundances of Skeletonema and Leptocylindrus, but the relative dominance of a few taxa was maintained. The 2006-2009 period was characterized by higher upwelling intensity, colder and higher salinity waters, and changes in nutrient concentrations and ratios compared with the first period. The inter-annual changes in the micro-phytoplankton community were mostly associated with changes in surface salinity and temperature (changes in upwelling intensity) but also with changes in Si/N and N/P, which relate to other land-derived processes.

Association of whale sharks (Rhincodon typus) with thermo-biological frontal systems of the eastern tropical Pacific.

PubMed

Ryan, John P; Green, Jonathan R; Espinoza, Eduardo; Hearn, Alex R

2017-01-01

Satellite tracking of 27 whale sharks in the eastern tropical Pacific, examined in relation to environmental data, indicates preferential occupancy of thermo-biological frontal systems. In these systems, thermal gradients are caused by wind-forced circulation and mixing, and biological gradients are caused by associated nutrient enrichment and enhanced primary productivity. Two of the frontal systems result from upwelling, driven by divergence in the current systems along the equator and the west coast of South America; the third results from wind jet dynamics off Central America. All whale sharks were tagged near Darwin Island, Galápagos, within the equatorial Pacific upwelling system. Occupancy of frontal habitat is pronounced in synoptic patterns of shark locations in relation to serpentine, temporally varying thermal fronts across a zonal expanse > 4000 km. 80% of shark positions in northern equatorial upwelling habitat and 100% of positions in eastern boundary upwelling habitat were located within the upwelling front. Analysis of equatorial shark locations relative to thermal gradients reveals occupancy of a transition point in environmental stability. Equatorial subsurface tag data show residence in shallow, warm (>22°C) water 94% of the time. Surface zonal current speeds for all equatorial tracking explain only 16% of the variance in shark zonal movement speeds, indicating that passive drifting is not a primary determinant of movement patterns. Movement from equatorial to eastern boundary frontal zones occurred during boreal winter, when equatorial upwelling weakens seasonally. Off Peru sharks tracked upwelling frontal positions within ~100-350 km from the coast. Off Central America, the largest tagged shark (12.8 m TL) occupied an oceanic front along the periphery of the Panama wind jet. Seasonal movement from waning equatorial upwelling to productive eastern boundary habitat is consistent with underlying trophic dynamics. Persistent shallow residence in thermo-biological frontal zones suggests the role of physical-biological interactions that concentrate food resources.

Association of whale sharks (Rhincodon typus) with thermo-biological frontal systems of the eastern tropical Pacific

PubMed Central

Green, Jonathan R.; Espinoza, Eduardo; Hearn, Alex R.

2017-01-01

Satellite tracking of 27 whale sharks in the eastern tropical Pacific, examined in relation to environmental data, indicates preferential occupancy of thermo-biological frontal systems. In these systems, thermal gradients are caused by wind-forced circulation and mixing, and biological gradients are caused by associated nutrient enrichment and enhanced primary productivity. Two of the frontal systems result from upwelling, driven by divergence in the current systems along the equator and the west coast of South America; the third results from wind jet dynamics off Central America. All whale sharks were tagged near Darwin Island, Galápagos, within the equatorial Pacific upwelling system. Occupancy of frontal habitat is pronounced in synoptic patterns of shark locations in relation to serpentine, temporally varying thermal fronts across a zonal expanse > 4000 km. 80% of shark positions in northern equatorial upwelling habitat and 100% of positions in eastern boundary upwelling habitat were located within the upwelling front. Analysis of equatorial shark locations relative to thermal gradients reveals occupancy of a transition point in environmental stability. Equatorial subsurface tag data show residence in shallow, warm (>22°C) water 94% of the time. Surface zonal current speeds for all equatorial tracking explain only 16% of the variance in shark zonal movement speeds, indicating that passive drifting is not a primary determinant of movement patterns. Movement from equatorial to eastern boundary frontal zones occurred during boreal winter, when equatorial upwelling weakens seasonally. Off Peru sharks tracked upwelling frontal positions within ~100–350 km from the coast. Off Central America, the largest tagged shark (12.8 m TL) occupied an oceanic front along the periphery of the Panama wind jet. Seasonal movement from waning equatorial upwelling to productive eastern boundary habitat is consistent with underlying trophic dynamics. Persistent shallow residence in thermo-biological frontal zones suggests the role of physical-biological interactions that concentrate food resources. PMID:28854201

Dynamics of plankton populations in upwelling areas. [by remote sensors

NASA Technical Reports Server (NTRS)

Szekielda, K.

1974-01-01

Recent investigations of the upwelling area along the NW Coast of Africa which include studies with satellites are discussed. The detection of patchiness in temperature and plankton distribution in the upwelling area is of special interest because they can be investigated from space synoptically with repeated coverage. The recent satellite missions provide recordings in the infrared region of the electromagnetic spectrum (EMR) as well as in the visible part. The information from those two parts of the EMR is useful for establishing the sea surface temperature and plankton distribution in upwelling areas. The temperature distribution as observed with infrared sensors and the patchiness in plankton patterns are discussed as observed with the most recent satellites, namely the Earth Resources Technology Satellite (ERTS) and NOAA-2.

Differences between mono-generic and mixed diatom silicon isotope compositions trace present and past nutrient utilisation off Peru

NASA Astrophysics Data System (ADS)

Doering, Kristin; Ehlert, Claudia; Grasse, Patricia; Crosta, Xavier; Fleury, Sophie; Frank, Martin; Schneider, Ralph

2016-03-01

In this study we combine for the first time silicon (Si) isotope compositions of small mixed diatom species (δ30SibSiO2) and of large handpicked mono-generic (i.e. genus = Coscinodiscus) diatom samples (δ30SiCoscino) with diatom assemblages extracted from marine sediments in the Peruvian upwelling region in order to constrain present and past silicate utilisation. The extension of a previous core-top data set from the Peruvian shelf demonstrates that δ30SiCoscino values record near-complete Si utilisation, as these are similar to the isotopic composition of the subsurface source waters feeding the upwelling. In contrast, the δ30SibSiO2 of small mixed diatom species increase southward along the shelf as well as towards the shore. We attribute highest δ30SibSiO2 values partly to transient iron limitation but primarily to the gradual increase of Si isotope fractionation within the seasonal diatom succession, which are mainly recorded by small diatom species during intense bloom events. In contrast, lower δ30SibSiO2 values are related to initial Si isotope utilisation during periods of weak upwelling, when low Si(OH)4 concentrations do not permit intense blooms and small diatom species record substantially lower δ30Si signatures. As such, we propose that the intensity of the upwelling can be deduced from the offset between δ30SibSiO2 and δ30SiCoscino (Δ30Sicoscino-bSiO2), which is low for strong upwelling conditions and high for prevailing weak upwelling. We apply the information extracted from surface sediments to generate a record of the present-day main upwelling region covering the past 17,700 years and find that this location has also been characterized by a persistent offset (Δ30Sicoscino-bSiO2). By comparison with the diatom assemblages we show that the coastal upwelling system changed markedly between weak and strong upwelling conditions. In addition, our model calculations to quantify species-specific Si isotope fractionation effects based on the diatom assemblages indicate an overall minor influence that cannot explain the high amplitude in the measured δ30SibSiO2 record.

Coastal upwelling and downwelling forcing of circulation in a semi-enclosed bay: Ria de Vigo

NASA Astrophysics Data System (ADS)

Barton, E. D.; Largier, J. L.; Torres, R.; Sheridan, M.; Trasviña, A.; Souza, A.; Pazos, Y.; Valle-Levinson, A.

2015-05-01

Semi-enclosed bays in upwelling regions are exposed to forcing related to winds, currents and buoyancy over the shelf. The influence of this external forcing is moderated by factors such as connectivity to the open ocean, shelter by surrounding topography, dimensions of the bay, and freshwater outflows. Such bays, preferred locations for ports, mariculture, marine industry, recreational activities and coastal settlement, present a range of characteristics, understanding of which is necessary to their rational management. Observations in such a semi-enclosed bay, the Ria de Vigo in Spain, are used to characterize the influence of upwelling and downwelling pulses on its circulation. In this location, near the northern limit of the Iberian upwelling system, upwelling events dominate during a short summer season and downwelling events the rest of the year. The ria response to the external forcing is central to nutrient supply and resultant plankton productivity that supports its high level of cultured mussel production. Intensive field studies in September 2006 and June 2007 captured a downwelling event and an upwelling event, respectively. Data from eight current profiler moorings and boat-based MiniBat/ADCP surveys provided an unprecedented quasi-synoptic view of the distribution of water masses and circulation patterns in any ria. In the outer ria, circulation was dominated by the introduction of wind-driven alongshore flow from the external continental shelf through the ria entrances and its interaction with the topography. In the middle ria, circulation was primarily related to the upwelling/downwelling cycle, with a cool, salty and dense lower layer penetrating to the inner ria during upwelling over the shelf. A warmer, lower salinity and less dense surface layer of coastal waters flowed inward during downwelling. Without external forcing, the inner ria responded primarily to tides and buoyancy changes related to land runoff. Under both upwelling and downwelling conditions, the flushing of the ria involved shelf responses to wind pulses. Their persistence for a few days was sufficient to allow waters from the continental shelf to penetrate the innermost ria. Longer term observations supported by numerical modeling are required to confirm the generality of such flushing events in the ria and determine their typical frequency, while comparative studies should explore how these scenarios fit into the range of conditions experienced in other semi-enclosed bays.

Temporal variability and phylogenetic characterization of planktonic anammox bacteria in the coastal upwelling ecosystem off central Chile

NASA Astrophysics Data System (ADS)

Galán, Alexander; Molina, Verónica; Belmar, Lucy; Ulloa, Osvaldo

2012-01-01

The phylogenetic affiliation and temporal variability in the abundance of planktonic anammox bacteria were studied at a time-series station above the continental shelf off central Chile (∼36°S; bottom depth 93 m), a wind-driven, seasonal upwelling area, between August 2006 and April 2008. The study was carried out by cloning and sequencing the 16S rRNA gene and by using catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). Our results showed the presence of a single anammox bacteria-like ribotype during both upwelling and non-upwelling seasons, which was phylogenetically associated with a recently described oxygen-minimum-zone subcluster within the Candidatus Scalindua clade. Moreover, clear differences were observed in the temporal and vertical distribution of anammox cells. During the upwelling season (austral spring-summer), relatively high abundances (∼5500 cells mL -1) and large cells (0.8 μm 3-75.7 fg C cell -1) were found below 20 m depth. In contrast, during the non-upwelling season (austral fall-winter), lower abundances (∼600 cells mL -1) and smaller cells (0.1 μm 3-22.8 fg C cell -1) were found, predominantly associated with the bottom layer. Overall, our results indicate that the abundance and vertical distribution of anammox planktonic assemblages are related to the occurrence of seasonal, wind-driven, coastal upwelling, which in turn appears to offer favorable conditions for the development of these microorganisms. The dominance of a unique anammox bacteria-like ribotype could be related to the high environmental variability observed in the system, which prevents the establishment of other anammox lineages.

What drives the spatial variability of primary productivity and matter fluxes in the north-west African upwelling system? A modelling approach

NASA Astrophysics Data System (ADS)

Auger, Pierre-Amaël; Gorgues, Thomas; Machu, Eric; Aumont, Olivier; Brehmer, Patrice

2016-11-01

A comparative box analysis based on a multi-decadal physical-biogeochemical hindcast simulation (1980-2009) was conducted to characterize the drivers of the spatial distribution of phytoplankton biomass and production in the north-west (NW) African upwelling system. Alongshore geostrophic flow related to large-scale circulation patterns associated with the influence of coastal topography is suggested to modulate the coastal divergence, and then the response of nutrient upwelling to wind forcing. In our simulation, this translates into a coastal upwelling of nitrate being significant in all regions but the Cape Blanc (CB) area. However, upwelling is found to be the dominant supplier of nitrate only in the northern Saharan Bank (NSB) and the Senegalo-Mauritanian (SM) regions. Elsewhere, nitrate supply is dominated by meridional advection, especially off Cape Blanc. Phytoplankton displays a similar behaviour with a supply by lateral advection which equals the net coastal phytoplankton growth in all coastal regions except the Senegalo-Mauritanian area. Noticeably, in the Cape Blanc area, the net coastal phytoplankton growth is mostly sustained by high levels of regenerated production exceeding new production by more than twofold, which is in agreement with the locally weak input of nitrate by coastal upwelling. Further offshore, the distribution of nutrients and phytoplankton is explained by the coastal circulation. Indeed, in the northern part of our domain (i.e. Saharan Bank), the coastal circulation is mainly alongshore, resulting in low offshore lateral advection of nutrients and phytoplankton. Conversely, lateral advection transports coastal nutrients and phytoplankton towards offshore areas in the latitudinal band off the Senegalo-Mauritanian region. Moreover, this latter offshore region benefits from transient southern intrusions of nutrient-rich waters from the Guinean upwelling.

Do submesoscale frontal processes ventilate the oxygen minimum zone off Peru?

NASA Astrophysics Data System (ADS)

Thomsen, S.; Kanzow, T.; Colas, F.; Echevin, V.; Krahmann, G.; Engel, A.

2016-02-01

The Peruvian upwelling region shows pronounced near-surface submesoscale variability including filaments and sharp density fronts. Submesoscale frontal processes can drive large vertical velocities and enhance vertical tracer fluxes in the upper ocean. The associated high temporal and spatial variability poses a large challenge to observational approaches targeting these processes. In this study the role of submesoscale processes for the ventilation of the near-coastal oxygen minimum zone off Peru is investigated. We use satellite based sea surface temperature measurements and multiple high-resolution glider observations of temperature, salinity, oxygen and chlorophyll fluorescence carried out in January and February 2013 off Peru near 14°S during active upwelling. Additionally, high-resolution regional ocean circulation model outputs (ROMS) outputs are analysed. At the beginning of our observational survey a previously upwelled, productive and highly oxygenated water body is found in the mixed layer. Subsequently, a cold filament forms and the waters are moved offshore. After the decay of the filament and the relaxation of the upwelling front, the oxygen enriched surface water is found in the previously less oxygenated thermocline suggesting the occurrence of frontal subduction. A numerical model simulation is used to analyse the evolution of Lagrangian numerical floats in several upwelling filaments, whose vertical structure and hydrographic properties agree well with the observations. The floats trajectories support our interpretation that the subduction of previously upwelled water occurs in filaments off Peru. We find that 40 - 60 % of the floats seeded in the newly upwelled water is subducted within a time period of 5 days. This hightlights the importance of this process in ventilating the oxycline off Peru.

Evaluation of Water Residence Time, Submarine Groundwater Discharge, and Maximum New Production Supported by Groundwater Borne Nutrients in a Coastal Upwelling Shelf System

NASA Astrophysics Data System (ADS)

Luo, Xin; Jiao, Jiu Jimmy; Liu, Yi; Zhang, Xiaolang; Liang, Wenzhao; Tang, Danling

2018-01-01

The biogeochemical processes in the continental shelf systems are usually extensively influenced by coastal upwelling and submarine groundwater discharge (SGD). Using eastern Hainan upwelling shelf system as an example, this study fully investigates SGD and coastal upwelling and their effects on the coastal nutrient loadings to the mixing layer of eastern Hainan shelf. Based on the spatial distributions of 223Ra and 228Ra, water residence time is estimated to be 16.9 ± 8.9 days. Based on the mass balance models of 226Ra and 228Ra, the total SGD of the eastern Hainan shelf is estimated to be 0.8 × 108 and 1.4 × 108 m3 d-1, respectively. The groundwater borne dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) are estimated to be up to 1121.8 and 20.4 μM m2 d-1. The coastal upwelling delivers 2741.8 μM m2 d-1 DIN and 217.7 μM m2 d-1 DIP into the mixing layer, which are predominant in all the exogenous nutrient inputs. The groundwater borne DIN will support a maximum new production of 7.5 mM C m2 d-1, about up to 24.0% of the total new production in the study area. SGD-derived nutrient could be significant as a missing DIN to support the new production in the mixing layer of eastern Hainan shelf. The findings contribute to a better understanding of biogeochemical processes under the influences of SGD and coastal upwelling in the study area and other similar coastal upwelling systems.

Upwelling-derived oceanographic conditions impact growth performance and growth-related gene expression in intertidal fish.

PubMed

Fuentes, Eduardo N; Zuloaga, Rodrigo; Almarza, Oscar; Mendez, Katterinne; Valdés, Juan Antonio; Molina, Alfredo; Pulgar, Jose

2017-12-01

Growth is one of the main biological processes in aquatic organisms that is affected by environmental fluctuations such as upwelling (characterized by food-rich waters). In fish, growth is directly related with skeletal muscle increase; which represents the largest tissue of body mass. However, the effects of upwelling on growth, at the physiological and molecular level, are unknown. This study used Girella laevifrons (one of the most abundant intertidal fish in Eastern South Pacific) as a biological model, considering animals from upwelling (U) and non-upwelling (NU) areas. Here, we evaluated the effect of nutritional composition and food availability on growth performance and expression of key growth-related genes (insulin-kike growth factor 1 (igf1) and myosin heavy-chain (myhc)) and atrophy-related genes (muscle ring-finger 1 (murf1), F-box only protein 32 (atrogin-1) and BCL2/adenovirus E1B 19kDa-interacting protein 3 (bnip3)). We reported that, among zones, U fish displayed higher growth performance in response to nutritional composition, specifically between protein- and fiber-rich diets (~1g). We also found in NU fish that atrophy-related genes were upregulated with fiber-rich diet and during fasting (~2-fold at minimum respect U). In conclusion, our results suggest that the growth potential of upwelling fish may be a consequence of differential muscle gene expression. Our data provide a preliminary approach contributing on how upwelling influence fish growth at the physiological and molecular levels. Future studies are required to gain further knowledge about molecular differences between U and NU animals, as well as the possible applications of this knowledge in the aquaculture industry. Copyright © 2017 Elsevier Inc. All rights reserved.

Gradients in microbial methanol uptake: productive coastal upwelling waters to oligotrophic gyres in the Atlantic Ocean

PubMed Central

Dixon, Joanna L; Sargeant, Stephanie; Nightingale, Philip D; Colin Murrell, J

2013-01-01

Methanol biogeochemistry and its importance as a carbon source in seawater is relatively unexplored. We report the first microbial methanol carbon assimilation rates (k) in productive coastal upwelling waters of up to 0.117±0.002 d−1 (∼10 nmol l−1 d−1). On average, coastal upwelling waters were 11 times greater than open ocean northern temperate (NT) waters, eight times greater than gyre waters and four times greater than equatorial upwelling (EU) waters; suggesting that all upwelling waters upon reaching the surface (⩽20 m), contain a microbial population that uses a relatively high amount of carbon (0.3–10 nmol l−1 d−1), derived from methanol, to support their growth. In open ocean Atlantic regions, microbial uptake of methanol into biomass was significantly lower, ranging between 0.04–0.68 nmol l−1 d−1. Microbes in the Mauritanian coastal upwelling used up to 57% of the total methanol for assimilation of the carbon into cells, compared with an average of 12% in the EU, and 1% in NT and gyre waters. Several methylotrophic bacterial species were identified from open ocean Atlantic waters using PCR amplification of mxaF encoding methanol dehydrogenase, the key enzyme in bacterial methanol oxidation. These included Methylophaga sp., Burkholderiales sp., Methylococcaceae sp., Ancylobacter aquaticus, Paracoccus denitrificans, Methylophilus methylotrophus, Methylobacterium oryzae, Hyphomicrobium sp. and Methylosulfonomonas methylovora. Statistically significant correlations for upwelling waters between methanol uptake into cells and both chlorophyll a concentrations and methanol oxidation rates suggest that remotely sensed chlorophyll a images, in these productive areas, could be used to derive total methanol biological loss rates, a useful tool for atmospheric and marine climatically active gas modellers, and air–sea exchange scientists. PMID:23178665

A high-resolution Late Quaternary upwelling record from the anoxic Cariaco Basin, Venezuela

NASA Astrophysics Data System (ADS)

Peterson, L. C.; Overpeck, J. T.; Kipp, N. G.; Imbrie, J.

1991-02-01

Results are presented of a high-resolution study of the planktonic foraminiferal faunas from two piston cores recovered from the Cariaco Basin in the southern Caribbean Sea. The Cariaco Basin is a small anoxic marine basin on the northern continental margin of Venezuela in an area today characterized by both seasonal trade wind-induced upwelling and pronounced dry and wet seasons. Our data indicate that large changes in the intensity of upwelling, and hence trade wind strength, occurred in this region during the last glacial-interglacial transition and throughout the Holocene. During the last glacial lowstand of sea level, the Cariaco Basin was effectively isolated from the open Caribbean along its northern margin by the then largely emergent Tortuga Bank. Oxic conditions existed in the deep Cariaco Basin at this time, and surface productivity was low. About 12,600 years ago, the abrupt initiation of strong upwelling over the basin and the onset of permanent anoxia in the deep waters are coincident with the rapid rise of sea level that accompanied the peak interval of meltwater discharge from the Laurentide Ice Sheet into the Gulf of Mexico. Strong upwelling between 12,600 and about 10,000 years ago may be related to intensified trade winds resulting, in part, from cooler sea surface temperatures in the Caribbean and Gulf of Mexico. After about 10,000 years ago, upwelling intensity was reduced, though highly variable. A preliminary frequency domain analysis of the Holocene portion of the Cariaco Basin time series suggests that solar forcing may explain a significant component of the century-scale variability observed in the record of upwelling and trade wind strength.

Coastal upwelling by wind-driven forcing in Jervis Bay, New South Wales: A numerical study for 2011

NASA Astrophysics Data System (ADS)

Sun, Youn-Jong; Jalón-Rojas, Isabel; Wang, Xiao Hua; Jiang, Donghui

2018-06-01

The Princeton Ocean Model (POM) was used to investigate an upwelling event in Jervis Bay, New South Wales (SE Australia), with varying wind directions and strengths. The POM was adopted with a downscaling approach for the regional ocean model one-way nested to a global ocean model. The upwelling event was detected from the observed wind data and satellite sea surface temperature images. The validated model reproduced the upwelling event showing the input of bottom cold water driven by wind to the bay, its subsequent deflection to the south, and its outcropping to the surface along the west and south coasts. Nevertheless, the behavior of the bottom water that intruded into the bay varied with different wind directions and strengths. Upwelling-favorable wind directions for flushing efficiency within the bay were ranked in the following order: N (0°; northerly) > NNE (30°; northeasterly) > NW (315°; northwesterly) > NE (45°; northeasterly) > ENE (60°; northeasterly). Increasing wind strengths also enhance cold water penetration and water exchange. It was determined that wind-driven downwelling within the bay, which occurred with NNE, NE and ENE winds, played a key role in blocking the intrusion of the cold water upwelled through the bay entrance. A northerly wind stress higher than 0.3 N m-2 was required for the cold water to reach the northern innermost bay.

On the Hiatus in the Acceleration of Tropical Upwelling Since the Beginning of the 21st Century

NASA Technical Reports Server (NTRS)

Aschmann, J.; Burrows, J. P.; Gebhardt, C.; Rozanov, A.; Hommel, R.; Weber, M.; Thompson, A. M.

2014-01-01

Chemistry-climate models predict an acceleration of the upwelling branch of the Brewer-Dobson circulation as a consequence of increasing global surface temperatures, resulting from elevated levels of atmospheric greenhouse gases. The observed decrease of ozone in the tropical lower stratosphere during the last decades of the 20th century is consistent with the anticipated acceleration of upwelling. However, more recent satellite observations of ozone reveal that this decrease has unexpectedly stopped in the first decade of the 21st century, challenging the implicit assumption of a continuous acceleration of tropical upwelling. In this study we use three decades of chemistry transport-model simulations (1980-2013) to investigate this phenomenon and resolve this apparent contradiction. Our model reproduces the observed tropical lower stratosphere ozone record, showing a significant decrease in the early period followed by a statistically robust trend-change after 2002. We demonstrate that this trend-change is correlated with corresponding changes in the vertical transport and conclude that a hiatus in the acceleration of tropical upwelling occurred during the last decade.

Geographical gradients in selection can reveal genetic constraints for evolutionary responses to ocean acidification.

PubMed

Gaitán-Espitia, Juan Diego; Marshall, Dustin; Dupont, Sam; Bacigalupe, Leonardo D; Bodrossy, Levente; Hobday, Alistair J

2017-02-01

Geographical gradients in selection can shape different genetic architectures in natural populations, reflecting potential genetic constraints for adaptive evolution under climate change. Investigation of natural pH/pCO 2 variation in upwelling regions reveals different spatio-temporal patterns of natural selection, generating genetic and phenotypic clines in populations, and potentially leading to local adaptation, relevant to understanding effects of ocean acidification (OA). Strong directional selection, associated with intense and continuous upwellings, may have depleted genetic variation in populations within these upwelling regions, favouring increased tolerances to low pH but with an associated cost in other traits. In contrast, diversifying or weak directional selection in populations with seasonal upwellings or outside major upwelling regions may have resulted in higher genetic variances and the lack of genetic correlations among traits. Testing this hypothesis in geographical regions with similar environmental conditions to those predicted under climate change will build insights into how selection may act in the future and how populations may respond to stressors such as OA. © 2017 The Author(s).

Western boundary upwelling dynamics off Oman

NASA Astrophysics Data System (ADS)

Vic, Clément; Capet, Xavier; Roullet, Guillaume; Carton, Xavier

2017-05-01

Despite its climatic and ecosystemic significance, the coastal upwelling that takes place off Oman is not well understood. A primitive-equation, regional model forced by climatological wind stress is used to investigate its dynamics and to compare it with the better-known Eastern Boundary Upwellings (EBUs). The solution compares favorably with existing observations, simulating well the seasonal cycles of thermal structure, surface circulation (mean and turbulent), and sea-surface temperature (SST). There is a 1.5-month lag between the maximum of the upwelling-favorable wind-stress-curl forcing and the oceanic response (minima in sea-surface height and SST), which we attribute to onshore-propagating Rossby waves. A southwestward-flowing undercurrent (opposite to the direction of the near-surface flow) is also simulated with a core depth of 1000 m, much deeper than found in EBUs (150-200 m). An EKE budget reveals that, in contrast to EBUs, the upwelling jet is more prone to barotropic than baroclinic instability and the contribution of locally-generated instabilities to EKE is higher by an order of magnitude. Advection and redistribution of EKE by standing mesoscale features also play a significant role in EKE budget.

Upwelling regime off the Cabo Frio region in Brazil and impact on acoustic propagation.

PubMed

Calado, Leandro; Camargo Rodríguez, Orlando; Codato, Gabriel; Contrera Xavier, Fabio

2018-03-01

This work introduces a description of the complex upwelling regime off the Cabo Frio region in Brazil and shows that ocean modeling, based on the feature-oriented regional modeling system (FORMS) technique, can produce reliable predictions of sound speed fields for the corresponding shallow water environment. This work also shows, through the development of simulations, that the upwelling regime can be responsible for the creation of shadow coastal zones, in which the detection probability is too low for an acoustic source to be detected. The development of the FORMS technique and its validation with real data, for the particular region of coastal upwelling off Cabo Frio, reveals the possibility of a sustainable and reliable forecast system for the corresponding (variable in space and time) underwater acoustic environment.

Observations of a cycle of intense coastal upwelling and downwelling at the research site of the Shirshov Institute of Oceanology in the Black Sea

NASA Astrophysics Data System (ADS)

Zatsepin, A. G.; Silvestrova, K. P.; Kuklev, S. B.; Piotoukh, V. B.; Podymov, O. I.

2016-03-01

The paper presents the results of joint analysis of the response of vertical temperature and current velocity profile distributions in the coastal zone of the Gelendzhik region of the Black Sea to strong wind forcing in the third ten-day period of September 2013. This forcing was caused by the propagation of an atmospheric cyclone, which first initiated coastal upwelling that was later replaced by downwelling. We formulate a criterion for the development of full coastal upwelling and demonstrate its efficiency. We assume that frequent events of incomplete coastal upwelling and downwelling are associated with changes in the water dynamics (variations in the intensity and direction of the alongshore current) generally not related to local wind forcing.

Spectral measurements of ocean-dumped wastes tested in the marine upwelled spectral signature laboratory

NASA Technical Reports Server (NTRS)

Witte, W. G.; Usry, J. W.; Whitlock, C. H.; Gurganus, E. A.

1979-01-01

Transmission and inherent upwelled radiance measurements were made of various mixtures of three ocean-dumped industrial plant wastes in artificial seawater. Laboratory analyses were made of the physical and chemical properties of the various mixtures. These results and the laboratory measurements of beam attenuation and inherent upwelled radiance indicate a variety of chemical and spectral responses when industrial wastes are added to artificial seawater. In particular, increased levels of turbidity did not always cause increased levels of inherent reflectance.

Dynamics of plankton populations in upwelling areas

NASA Technical Reports Server (NTRS)

Szekielda, K. H. (Principal Investigator)

1975-01-01

The author has identified the following significant results. Spectral properties of the upwelled waters off the NW coast of Africa were studied with observations derived from aircraft and Skylab. Results indicate that the two-channel, ratio approach is ineffective in determining surface chlorophyll concentrations. Ocean color boundaries and temperature gradients were found to be directly correlated with each other and also with fishing effort in the upwelling region. Photographic and scanner data derived from Skylab were effective in locating ocean boundaries and mapping temperature distributions.

Late quaternary time series of Arabian Sea productivity: Global and regional signals

NASA Technical Reports Server (NTRS)

Clemens, Steven C.; Prell, W. L.; Murray, D. W.

1992-01-01

Modern annual floral and faunal production in the northwest Arabian Sea derives primarily from upwelling induced by strong southwest winds during June, July, and August. Indian Ocean summer monsoon winds are, in turn, driven by differential heating between the Asian continent and the Indian ocean to the south. This differential heating produces a strong pressure gradient resulting in southwest monsoon winds and both coastal and divergent upwelling off the Arabian Peninsula. Over geologic time scales (10(exp 4) to 10(exp 6) years), monsoon wind strength is sensitive to changes in boundary conditions which influence this pressure gradient. Important boundary conditions include the seasonal distribution of solar radiation, global ice volume, Indian Ocean sea surface temperature, and the elevation and albedo of the Asian continent. To the extent that these factors influence monsoon wind strength, they also influence upwelling and productivity. In addition, however, productivity associated with upwelling can be decoupled from the strength of the summer monsoon winds via ocean mechanisms which serve to inhibit or enhance the nutrient supply in the intermediate waters of the Indian Ocean, the source for upwelled waters in the Arabian Sea. To differentiate productivity associated with wind-induced upwelling from that associated with other components of the system such as nutrient sequestering in glacial-age deep waters, we employ a strategy which monitors independent components of the oceanic and atmospheric subsystems. Using sediment records from the Owen Ridge, northwest Arabian Sea, we monitor the strength of upwelling and productivity using two independent indicators, percent G. bulloides and opal accumulation. We monitor the strength of southwest monsoon winds by measuring the grain-size of lithogenic dust particles blown into the Arabian Sea from the surrounding deserts of the Somali and Arabian Peninsulas. Our current hypothesis is that the variability associated with the 41 kyr power in the G. bulloides and opal accumulation records derive from nutrient availability in the intermediate waters which are upwelled via monsoon winds. This hypothesis is testable by comparison with Cd records of intermediate and deep waters of the Atlantic and Indian Ocean.

Geodynamic constraints on deep-mantle buoyancy: Implications for thermochemical structure of LLSVP and large-scale upwellings under the Pacific Ocean.

NASA Astrophysics Data System (ADS)

Forte, A. M.; Glisovic, P.; Grand, S. P.; Lu, C.; Simmons, N. A.; Rowley, D. B.

2015-12-01

Convection-related data constrain lower-mantle density anomalies that contribute to mantle convective flow. These include global gravity and topography anomalies, plate motions and excess ellipticity of the core-mantle boundary (CMB). Each datum possesses differing wavelength and depth dependent resolution of heterogeneity and thus the strongest constraints on density anomalies are obtained by jointly inverting all data in combination. The joint-inversions employ viscous response functions (i.e. geodynamic kernels) for a flowing mantle. Non-uniqueness is greatly reduced by including seismic and mineral physics data into the joint inversions. We present the results of inversions where seismic and geodynamic data are singly and jointly inverted to map density anomalies. Employing mineral physical data we estimate thermal and compositional contributions to density anomalies. We evaluate the extent to which "Large Low Shear Velocity Provinces" (LLSVP) are anomalous and we determine their impact on the global pattern of convective flow. The inversions yield consistent maps of lower-mantle flow (see figure) that are dominated by two large upwellings, under the Western Pacific (next to the Caroline microplate) and Eastern Pacific (under the East Pacific Rise). These hot upwellings effectively delimit the margins of the Pacific LLSVP, suggesting intrinsic negative buoyancy within this structure impedes large-scale upwellings in the mantle above. These two upwellings do not resemble classical mantle "plumes" found in simple isoviscous and isochemical convection models but their contribution to mass and heat transport across the lower mantle is significant and thus behave similarly to plumes. The large scale of these upwellings may be understood in terms of the high viscosity in the lower mantle, inferred from geodynamic constraints on mantle rheology. Very-long time convection simulations initiated with present-day structure inferred from these inversions show the two Pacific upwellings possess remarkable geographic fixity and longevity extending over several hundred million years, again a consequence of the high viscosity in the lower mantle. These upwellings are fed by large heat flux across the CMB (from 12 to 20 TW) and should play a major role in the thermal evolution of the mantle.

Nearshore currents on the southern Namaqua shelf of the Benguela upwelling system

NASA Astrophysics Data System (ADS)

Fawcett, A. L.; Pitcher, G. C.; Shillington, F. A.

2008-05-01

Nearshore currents of the southern Namaqua shelf were investigated using data from a mooring situated three and a half kilometres offshore of Lambert's Bay, downstream of the Cape Columbine upwelling cell, on the west coast of South Africa. This area is susceptible to harmful algal blooms (HABs) and wind-forced variations in currents and water column structure are critical in determining the development, transport and dissipation of blooms. Time series of local wind data, and current and temperature profile data are described for three periods, considered to be representative of the latter part of the upwelling season (27 January-22 February), winter conditions (5-29 May) and the early part of the upwelling season (10 November-12 December) in 2005. Differences observed in mean wind strength and direction between data sets are indicative of seasonal changes in synoptic meteorological conditions. These quasi-seasonal variations in wind forcing affect nearshore current flow, leading to mean northward flow in surface waters early in the upwelling season when equatorward, upwelling-favourable winds are persistent. Mean near-surface currents are southward during the latter part of the upwelling season, consistent with more prolonged periods of relaxation from equatorward winds, and under winter conditions when winds were predominantly poleward. Within these seasonal variations in mean near-surface current direction, two scales of current variability were evident within all data sets: strong inertial oscillations were driven by diurnal winds and introduced vertical shear into the water column enhancing mixing across the thermocline, while sub-inertial current variability was driven by north-south wind reversals at periods of 2-5 days. Sub-inertial currents were found to lag wind reversals by approximately 12 h, with a tendency for near-surface currents to flow poleward in the absence of wind forcing. Consistent with similar sites along the Californian and Iberian coasts, the headland at Cape Columbine is considered to influence currents and circulation patterns during periods of relaxation from upwelling-favourable winds, favouring the development of a nearshore poleward current, leading to poleward advection of warm water, the development of stratification, and the creation of potentially favourable conditions for HAB development.

Across-shelf variability of phytoplankton composition, photosynthetic parameters and primary production in the NW Iberian upwelling system

NASA Astrophysics Data System (ADS)

Lorenzo, Luisa M.; Arbones, Belén; Tilstone, Gavin H.; Figueiras, Francisco G.

2005-02-01

Hydrographic conditions, phytoplankton composition and biomass, photosynthetic parameters and primary production were determined in the Ría de Vigo and adjacent shelf waters during April-May 1997 and September 1998. The sampling was designed to find the seasonal downwelling-upwelling and upwelling-downwelling transition periods characteristic of spring and autumn phytoplankton blooms. There was upwelling relaxation event followed by downwelling during both spring and autumn cruises. Temperature and salinity distributions showed that ría and shelf waters formed two distinct domains, which were separated by a thermohaline front at the mouth of the ría. The phytoplankton composition was completely different in the two environments. Cyanobacteria dominated on the shelf and constituted 46-66% of total phytoplankton biomass, while large phytoplankton (diatoms and dinoflagellates) were more abundant in the ría, especially during upwelling relaxation. However, the high shelf-ría exchange induced by a strong downwelling event on 7 September 1998 removed large phytoplankton (mainly diatoms) from the water column in the ría. Chlorophyll-specific maximum photosynthetic rates ( PmB) were significantly higher in the ría domain during upwelling relaxation, when autotrophic microplankton dominated in the interior. Primary production varied from 0.63 to 2.6 g C m -2 day -1 during the spring cruise and between 0.32 and 2.09 g C m -2 day -1 during the autumn cruise, with the highest values in the ría during both cruises. Primary production was relatively constant on the shelf with no significant differences between cruises, whereas differences were significant in the ría, with higher values during upwelling relaxation periods and lower values during downwelling. Analysis of light saturation parameters and light absorbed by phytoplanton in the water column suggests that photosynthesis was not light-limited either on the shelf or in the ría. It is concluded that upwelling-downwelling cycles were the main driving force, through changes in autotrophic microplankton biomass in the ría, that caused the variability observed in the ría-shelf system.

Simultaneous Quantification of Temperature, Pyroxenite Abundance, and Upwelling Rates in the Iceland Mantle Source

NASA Astrophysics Data System (ADS)

Brown, E.; Lesher, C. E.

2014-12-01

The compositions and volumes of basalts erupted at the earth's surface are a function of mantle temperature, mantle composition, and the rate at which the mantle upwells through the melting zone. Thus, basaltic magmatism has long been used to probe the thermal and physiochemical state of the earth's mantle. Great insight has been gained into the mantle beneath the global spreading ridge system, where the mantle source is assumed to be homogeneous peridotite that upwells passively [1]. However, it is now recognized that many basalt source regions are lithologically heterogeneous (i.e. containing recycled lithospheric material ranging from harzburgite to pyroxenite) and upwell at rates in excess of those governed by plate separation. To account for these complexities, we have developed a forward melting model for lithologically heterogeneous mantle that incorporates thermodynamically and experimentally constrained melting functions for a range of peridotite and pyroxenite lithologies. The model is unique because it quantifies mantle upwelling rates based on the net buoyancy of the source, thus providing a means for linking basalt compositions/volumes to mantle flow while accounting for source heterogeneity. We apply the model to investigate the mantle properties governing magmatism along different rift segments in Iceland, where lithologic heterogeneity and variable upwelling rates have been inferred through geochemical means [2,3]. Using constraints from seismically determined crustal thicknesses and recent estimates of the proportion of pyroxenite-derived melt contributing to Icelandic basalt compositions [4,5], we show that mantle sources beneath Iceland have excess potential temperatures >85 °C, contain <7% pyroxenite, and maximum upwelling rates ~14 times the passive rate. Our modeling highlights the dominant role of elevated mantle temperature and enhanced upwelling for high productivity magmatism in Iceland, and a subordinate role for mantle heterogeneity, which is required to account for much of the observed chemical and isotopic diversity. [1] Langmuir et al, 1992, AGU Geophys. Mono. Ser. 71 [2] Chauvel & Hemond, 2000, G-cubed, v 1 [3] Kokfelt et al, 2003, EPSL, v 214 [4] Sobolev et al, 2007, Science, v 316 [5] Shorttle et al, 2014, EPSL, v 395

The Effects of Ridge Axis Width on Mantle Melting at Mid-Ocean Ridges

NASA Astrophysics Data System (ADS)

Montesi, L.; Magni, V.; Gaina, C.

2017-12-01

Mantle upwelling in response to plate divergence produces melt at mid-ocean ridges. Melt starts when the solidus is crossed and stops when conductive cooling overcomes heat advection associated with the upwelling. Most mid-ocean ridge models assume that divergence takes place only in a narrow zone that defines the ridge axis, resulting in a single upwelling. However, more complex patterns of divergence are occasionally observed. The rift axis can be 20 km wide at ultraslow spreading center. Overlapping spreading center contain two parallel axes. Rifting in backarc basins is sometimes organized as a series of parallel spreading centers. Distributing plate divergence over several rifts reduces the intensity of upwelling and limits melting. Can this have a significant effect on the expected crustal thickness and on the mode of melt delivery at the seafloor? We address this question by modeling mantle flow and melting underneath two spreading centers separated by a rigid block. We adopt a non-linear rheology that includes dislocation creep, diffusion creep and yielding and include hydrothermal cooling by enhancing thermal conductivity where yielding takes place. The crustal thickness decreases if the rifts are separated by 30 km or more but only if the half spreading rate is between 1 and 2 cm/yr. At melting depth, a single upwelling remains the norm until the separation of the rifts exceeds a critical value ranging from 15 km in the fastest ridges to more than 50 km at ultraslow spreading centers. The stability of the central upwelling is due to hydrothermal cooling, which prevents hot mantle from reaching the surface at each spreading center. When hydrothermal cooling is suppressed, or the spreading centers are sufficiently separated, the rigid block becomes extremely cold and separates two distinct, highly asymmetric upwellings that may focus melt beyond the spreading center. In that case, melt delivery might drive further and further the divergence centers, whereas, when a single upwelling is retained, melt delivery would drive the spreading centers closer together. Thus, the system composed of two rifts is unstable and, if observed in nature, indicates either a transient geodynamic regime, like a recent change in spreading rates, or control structural or stress heterogeneities.

Modeling new production in upwelling centers - A case study of modeling new production from remotely sensed temperature and color

NASA Technical Reports Server (NTRS)

Dugdale, Richard C.; Wilkerson, Frances P.; Morel, Andre; Bricaud, Annick

1989-01-01

A method has been developed for estimating new production in upwelling systems from remotely sensed surface temperatures. A shift-up model predicts the rate of adaptation of nitrate uptake. The time base for the production cycle is obtained from a knowledge of surface heating rates and differences in temperature between the point of upwelling and each pixel. Nitrate concentrations are obtained from temperature-nitrate regression equations. The model was developed for the northwest Africa upwelling region, where shipboard measurements of new production were available. It can be employed in two modes, the first using only surface temperatures, and the second in which CZCS color data are incorporated. The major advance offered by this method is the capability to estimate new production on spatial and time scales inaccessible with shipboard approaches.

Numerical Study on the influence of Kuroshio Intrusion on Coastal upwelling off Coasts of China

NASA Astrophysics Data System (ADS)

Dezhou, Y.; Yin, B.

2016-02-01

Anomalous distribution of sea surface temperature (SST) has been observed off coasts of Zhejiang province, China in summer 2009 and 2012, respectively, where algal blooms are increasingly reported. Then, the rotated empirical orthogonal functions analysis has been employed to examine the 31 summertime SST fields. A distinct SST mode is identified in this upwelling area, and its principal components show a colder phase in 2009 and a warmer phase in 2012. At the same time, cruise data show colder and more saline bottom water in this upwelling area in summer 2009 relative to that in summer 2012, which implies a more nearshore Kuroshio branch current (NKBC) in summer 2009 and a more offshore NKBC in summer 2012. On the basis of regional ocean model system (ROMS), 20-year hindcast run has been successfully carried out. Model results faithfully reproduce the anomalous SST in summer 2009 and 2012. On the basis of the observational and modeled evidences, we propose that the anomalously cold or warm coastal upwelling is mainly attributed to the extremely shoreward or seaward shift of the NKBC. In other words, the more shoreward the NKBC shift, the colder the surface upwelling water is. In contrast, the more seaward the NKBC shift, the warmer the surface upwelling water is. Moreover, this paper shows a good example that the coastal environment may be profoundly influenced by the remote variation of Kuroshio east of Taiwan, which is highly correlated to the sea surface height east of Taiwan.

Weakened stratospheric quasibiennial oscillation driven by increased tropical mean upwelling.

PubMed

Kawatani, Yoshio; Hamilton, Kevin

2013-05-23

The zonal wind in the tropical stratosphere switches between prevailing easterlies and westerlies with a period of about 28 months. In the lowermost stratosphere, the vertical structure of this quasibiennial oscillation (QBO) is linked to the mean upwelling, which itself is a key factor in determining stratospheric composition. Evidence for changes in the QBO have until now been equivocal, raising questions as to the extent of stratospheric circulation changes in a global warming context. Here we report an analysis of near-equatorial radiosonde observations for 1953-2012, and reveal a long-term trend of weakening amplitude in the zonal wind QBO in the tropical lower stratosphere. The trend is particularly notable at the 70-hectopascal pressure level (an altitude of about 19 kilometres), where the QBO amplitudes dropped by roughly one-third over the period. This trend is also apparent in the global warming simulations of the four models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) that realistically simulate the QBO. The weakening is most reasonably explained as resulting from a trend of increased mean tropical upwelling in the lower stratosphere. Almost all comprehensive climate models have projected an intensifying tropical upwelling in global warming scenarios, but attempts to estimate changes in the upwelling by using observational data have yielded ambiguous, inconclusive or contradictory results. Our discovery of a weakening trend in the lower-stratosphere QBO amplitude provides strong support for the existence of a long-term trend of enhanced upwelling near the tropical tropopause.

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

NASA Astrophysics Data System (ADS)

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

2010-12-01

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

Recent decadal trends in Iberian water vapour: GPS analysis and WRF process study

NASA Astrophysics Data System (ADS)

Miranda, Pedro M. A.; Nogueira, Miguel; Semedo, Alvaro; Benevides, Pedro; Catalao, Joao; Costa, Vera

2016-04-01

A 24-year simulation of the recent Iberian climate, using the WRF model at 9km resolution forced by ERA-Interim reanalysis (1989-2012), is analysed for the decadal evolution of the upwelling forcing coastal wind and for column integrated Precipitable water vapour (PWV). Results indicate that, unlike what was found by Bakun et al. (2009) for the Peruvian region, a statistically significant trend in the upwelling favourable (northerly) wind has been accompanied by a corresponding decrease in PWV, not only inland but also over the coastal waters. Such increase is consistent with a reinforced northerly coastal jet in the maritime boundary layer contributing to atmospheric Ekman pumping of dry continental air into the coastal region. Diagnostics of the prevalence of the Iberian thermal low following Hoinka and Castro (2003) also show a positive trend in its frequency during an extended summer period (April to September). These results are consistent with recent studies indicating an upward trend in the frequency of upwelling in SW Iberia (Alves and Miranda 2013), and may be relevant for climate change applications as an increase in coastal upwelling (Miranda et al 2013) may lead to substantial regional impacts in the subtropics. The same analysis with ERA-Interim reanalysis data, which was used to force the WRF simulations, does not reveal the same signal in PWV, and indeed correlates poorly with the GPS observations, indicating that the data assimilation process makes the water vapour data in reanalysis unusable for climate change purposes. The good correlation between the WRF simulated data and GPS observations allow for a detailed analysis of the processes involved in the evolution of the PWV field. Akcnowledgements: Study done within FCT Grant RECI/GEO-MET/0380/2012, financially supported by FCT Grant UID/ GEO/50019/2013-IDL Alves JMR, Miranda PMA (2013) Variability of Iberian upwelling implied by ERA-40 and ERA-Interim reanalyses, Tellus A 2013, http://dx.doi.org/10.3402/tellusa.v65i0.19245. Bakun et al (2010) Greenhouse gas, upwelling-favorable winds, and the future of coastal ocean upwelling ecosystems, Global Change Biology, doi: 10.1111/j.1365-2486.2009.02094.x Hoinka KP, Castro M (2003) The Iberian Peninsula thermal low. QJRMS, 129, 1491- 1511, doi: 10.1256/qj.01.189. Miranda et al (2013) Climate change and upwelling: response of Iberian upwelling to atmospheric forcing in a regional climate scenario. Climate Dynamics, doi: 10.1007/s00382-012-1442-9.

Wind stress and heat fluxes over a Brazilian Coastal Upwelling

NASA Astrophysics Data System (ADS)

Dourado, Marcelo; Candella, Rogério

2017-04-01

Coastal upwelling zones have been intensively studied in the last decades especially due to their importance to the biological cycle. The coastal upwelling system of the Cabo Frio region (east coast of the Rio de Janeiro state, Brazil) keeps the surface water cold during most part of the year, what induces a stable atmospheric boundary layer associated to northeast winds. The main goal of this study is to investigate the wind stress and heat fluxes exchanges between the ocean and the atmosphere in that area. For this purpose, a set of hourly data meteorological and oceanographic data collected by a Wavescan metocean buoy anchored at 23o59S; 42oW, were used, as well as solar radiation and relative humidity from a terrestrial meteorological station from the Instituto Nacional de Meteorologia (InMet). COARE 3.0 algorithm was used to calculate the latent and sensible heat fluxes. In this discussion, positive values represent fluxes towards the ocean. The average net heat flux over our study period is 88 W m-2. The reduction of the net heat flux is due to the increase of the ocean latent heat loss, although a reduction in incoming shortwave radiation and an increase in ocean long wave cooling also contributes. The latent heat is 20 times larger than the sensible heat flux, but the mean value of the latent heat flux, 62 W m-2, is half the typical value found in open ocean. The temporal variability of both sensible and latent heat fluxes reflects their dependence on wind speed and air-sea temperature differences. When upwelling events, here periods when diurnal SST is lower than 18oC, are compared with undisturbed (without upwelling) events, it can be noted the sensible heat fluxes are positives and 10 times greater in magnitude. This is related to an increment, during these upwelling events, of the air-sea temperature difference and an increasing of the wind speed. The cold waters of the upwelling increase the air-sea temperature gradient and, also, the horizontal land-sea gradient. This could intensifies the sea breeze. At the same time, the latent heat flux to the atmosphere is reduced. As expected, cold waters from the upwelling imply in the reduction of the evaporation, and so the latent heat fluxes also reduce significantly. As upwelling events in this region are associated to the presence of the South Atlantic high pressure, NE winds, during these periods of cold water the net heat flux toward the ocean surface is intensified.

Spatial and temporal variability in coccolithophore abundance and distribution in the NW Iberian coastal upwelling system

NASA Astrophysics Data System (ADS)

Ausín, Blanca; Zúñiga, Diana; Flores, Jose A.; Cavaleiro, Catarina; Froján, María; Villacieros-Robineau, Nicolás; Alonso-Pérez, Fernando; Arbones, Belén; Santos, Celia; de la Granda, Francisco; Castro, Carmen G.; Abrantes, Fátima; Eglinton, Timothy I.; Salgueiro, Emilia

2018-01-01

A systematic investigation of the spatial and temporal variability in coccolithophore abundance and distribution through the water column of the NW Iberian coastal upwelling system was performed. From July 2011 to June 2012, monthly sampling at various water depths was conducted at two parallel stations located at 42° N. Total coccosphere abundance was higher at the outer-shelf station, where warmer, nutrient-depleted waters favoured coccolithophore rather than phytoplanktonic diatom blooms, which are known to dominate the inner-shelf location. In seasonal terms, higher coccosphere and coccolith abundances were registered at both stations during upwelling seasons, coinciding with high irradiance levels. This was typically in conjunction with stratified, nutrient-poor conditions (i.e. relaxing upwelling conditions). However, it also occurred during some upwelling events of colder, nutrient-rich subsurface waters onto the continental shelf. Minimum abundances were generally found during downwelling periods, with unexpectedly high coccolith abundance registered in subsurface waters at the inner-shelf station. This finding can only be explained if strong storms during these downwelling periods favoured resuspension processes, thus remobilizing deposited coccoliths from surface sediments, and hence hampering the identification of autochthonous coccolithophore community structure. At both locations, the major coccolithophore assemblages were dominated by Emiliania huxleyi, small Gephyrocapsa group, Gephyrocapsa oceanica, Florisphaera profunda, Syracosphaera spp., Coronosphaera mediterranea, and Calcidiscus leptoporus. Ecological preferences of the different taxa were assessed by exploring the relationships between environmental conditions and temporal and vertical variability in coccosphere abundance. These findings provide relevant information for the use of fossil coccolith assemblages in marine sediment records, in order to infer past environmental conditions, of particular importance for Paleoceanography. Both E. huxleyi and the small Gephyrocapsa group are proposed as proxies for the upwelling regime with a distinct affinity for different stages of the upwelling event: E. huxleyi was associated with warmer, nutrient-poor and more stable water column (i.e. upwelling relaxation stage) while the small Gephyrocapsa group was linked to colder waters and higher nutrient availability (i.e. early stages of the upwelling event), similarly to G. oceanica. Conversely, F. profunda is suggested as a proxy for the downwelling regime and low-productivity conditions. The assemblage composed by Syracosphaera pulchra, Coronosphaera mediterranea, and Rhabdosphaera clavigera may be a useful indicator of the presence of subtropical waters conveyed northward by the Iberian Poleward Current. Finally, C. leptoporus is proposed as an indicator of warmer, saltier, and oligotrophic waters during the downwelling/winter regime.

Bacterial and Archaeal Communities Variability Associated with Upwelling and Anthropogenic Pressures in the Protection Area of Arraial do Cabo (Cabo Frio region - RJ).

PubMed

Coelho-Souza, Sergio A; Araújo, Fábio V; Cury, Juliano C; Jesus, Hugo E; Pereira, Gilberto C; Guimarães, Jean R D; Peixoto, Raquel S; Dávila, Alberto M R; Rosado, Alexandre S

2015-09-01

Upwelling systems contain a high diversity of pelagic microorganisms and their composition and activity are defined by factors like temperature and nutrient concentration. Denaturing gradient gel electrophoresis (DGGE) technique was used to verify the spatial and temporal genetic variability of Bacteria and Archaea in two stations of the Arraial do Cabo coastal region, one under upwelling pressure and another under anthropogenic pressure. In addition, biotic and abiotic variables were measured in surface and deep waters from three other stations between these stations. Six samplings were done during a year and adequately represented the degrees of upwelling and anthropogenic pressures to the system. Principal Component Analysis (PCA) showed negative correlations between the concentrations of ammonia and phosphorous with prokaryotic secondary production and the total heterotrophic bacteria. PCA also showed negative correlation between temperature and the abundance of prokaryotic cells. Bacterial and archaeal compositions were changeable as were the oceanographic conditions, and upwelling had a regional pressure while anthropogenic pressure was punctual. We suggest that the measurement of prokaryotic secondary production was associated with both Bacteria and Archaea activities, and that substrate availability and temperature determine nutrients cycling.

Life in the sea of plenty: Seasonal and regional comparison of physiological performance of Euphausia hanseni in the northern Benguela upwelling system

NASA Astrophysics Data System (ADS)

Werner, Thorsten; Buchholz, Cornelia; Buchholz, Friedrich

2015-09-01

Variability in upwelling events may lead to periods of constrained food availability in the northern Benguela upwelling system (NBUS), thereby affecting the physiological state and metabolic activity of euphausiids. Most attention has so far been paid to seasonal effects but little is known about regional variability. Metabolic activity (expressed by respiration and excretion rates) and physiological state (expressed by reproductive effort and moult activity) in Euphausia hanseni were examined at different stations during austral summer (minimum upwelling) and austral winter (maximum upwelling). Overall, regional differences in physiological state, influencing metabolic activity, were greater than seasonal ones, indicating favourable conditions for growth and reproduction year-round. Higher respiration rates were found for females in more advanced stages of sexual development. Moult stage did not affect oxygen consumption rates, however. The physiological state of E. hanseni at the time of capture may serve as a meaningful indicator of the associated hydrographic conditions in the NBUS, to be further used in eco-system analysis on seasonal or long-term time scales. A latitudinal comparison of species highlights the extraordinary physiological plasticity of euphausiids.

Internal structure of the upwelling events at Punta Gallinas (Colombian Caribbean) from modis-sst imagery

NASA Astrophysics Data System (ADS)

Alonso, J.; Blázquez, E.; Isaza-Toro, E.; Vidal, J.

2015-10-01

The upwelling at Punta Gallinas in the Guajira Peninsula (Colombian Caribbean) was studied from the point of view of the Mathematical Morphology using 10 years of monthly composite MODIS-SST imagery. Among all the morphological operators, the skeleton is widely used to compute the axis of the of the SST fields for the observed upwelling events. The skeleton is characterized by means of the Geometrical Theory of Measurement using the fractal dimension. The upwelling in the area is driven by the dynamic of the ITCZ (InterTropical Convergence Zone) and the relationship between the area and the East-West component of the trade winds has a lag of about 4 months. It has been found that the fractal dimension of the skeleton and the area of the upwelling are related. Some relationship was found between the fractal dimension of the skeleton (its complexity) and the Southern Oscillation Index by means of linear regression and cross-spectral analysis finding coherent energy at 1 year, 6 months and in the low frequency band. Finally, a sensitivity analysis between fractal dimension and threshold SST points out to take an extreme care at the time of fixing the last one.

Phytoplankton succession in an isolated upwelled Benguela water body in relation to different initial nutrient conditions

NASA Astrophysics Data System (ADS)

Wasmund, Norbert; Nausch, Günther; Hansen, Anja

2014-11-01

Freshly upwelled water is poor in phytoplankton biomass but rich in nutrients. With its ageing, phytoplankton biomass increases whereas the nutrients are consumed. The overall aim of our investigation was to check the succession in the phytoplankton composition as a consequence of changing nutrient conditions. The experiments were carried out in mesocosms filled with surface water in the northern Benguela region and installed on board of R/V "Maria S. Merian". In the freshly upwelled water, phytoplankton took up nitrogen at a higher rate than phosphorus if compared with the Redfield ratio. Therefore, nitrogen was exhausted already by day 6. Nitrogen limitation after day 6 was indicated by decreasing chlorophyll a (chla) concentrations, primary production rates and productivity indices and increasing C/N ratios in particulate matter. Despite nitrogen limitation, phosphorus addition stimulated further growth, mainly of diatoms, pointing to luxury uptake. Cyanobacteria did not develop and nitrogen fixation was zero even with phosphorus and iron addition. Diatoms stay the most important group in the freshly upwelled water, but autotrophic and heterotrophic dinoflagellates increase strongly in the matured upwelled water. Mesocosms excluded disturbances by advective water transports, which influence the study of succssions under field conditions.

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

NASA Astrophysics Data System (ADS)

Hua-Sheng, Hong; Shao-Ling, Shang

1994-06-01

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

Upwelling Radiance at 976 nm Measured from Space Using a CCD Camera

NASA Technical Reports Server (NTRS)

Biswas, Abhijit; Kovalik, Joseph M.; Oaida, Bogdan V.; Abrahamson, Matthew J.; Wright, Malcolm W.

2015-01-01

The Optical Payload for Lasercomm Science (OPALS) Flight System on-board the International Space Station uses a charge coupled device (CCD) camera for receiving a beacon laser from Earth. Relative measurements of the background contributed by upwelling radiance under diverse illumination conditions and varying terrain is presented. In some cases clouds in the field-of-view allowed a comparison of terrestrial and cloud-top upwelling radiance. In this paper we will report these measurements and examine the extent of agreement with atmospheric model predictions.

A Simple Criterion to Estimate Performance of Pulse Jet Mixed Vessels

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

Pease, Leonard F.; Bamberger, Judith A.; Mahoney, Lenna A.

Pulse jet mixed process vessels comprise a key element of the U.S. Department of Energy’s strategy to process millions of gallons of legacy nuclear waste slurries. Slurry suctioned into a pulse jet mixer (PJM) tube at the end of one pulse is pneumatically driven from the PJM toward the bottom of the vessel at the beginning of the next pulse, forming a jet. The jet front traverses the distance from nozzle outlet to the bottom of the vessel and spreads out radially. Varying numbers of PJMs are typically arranged in a ring configuration within the vessel at a selected radiusmore » and operated concurrently. Centrally directed radial flows from neighboring jets collide to create a central upwell that elevates the solids in the center of the vessel when the PJM tubes expel their contents. An essential goal of PJM operation is to elevate solids to the liquid surface to minimize stratification. Solids stratification may adversely affect throughput of the waste processing plant. Unacceptably high slurry densities at the base of the vessel may plug the pipeline through which the slurry exits the vessel. Additionally, chemical reactions required for processing may not achieve complete conversion. To avoid these conditions, a means of predicting the elevation to which the solids rise in the central upwell that can be used during vessel design remains essential. In this paper we present a simple criterion to evaluate the extent of solids elevation achieved by a turbulent upwell jet. The criterion asserts that at any location in the central upwell the local velocity must be in excess of a cutoff velocity to remain turbulent. We find that local velocities in excess of 0.6 m/s are necessary for turbulent jet flow through both Newtonian and yield stress slurries. By coupling this criterion with the free jet velocity equation relating the local velocity to elevation in the central upwell, we estimate the elevation at which turbulence fails, and consequently the elevation at which the upwell fails to further lift the slurry. Comparing this elevation to the vessel fill level predicts whether the jet flow will achieve the full vertical extent of the vessel at the center. This simple local-velocity criterion determines a minimum PJM nozzle velocity at which the full vertical extent of the central upwell in PJM vessels will be turbulent. The criterion determines a minimum because flow in regions peripheral to the central upwelling jet may not be turbulent, even when the center of the vessel in the upwell is turbulent, if the jet pulse duration is too short. The local-velocity criterion ensures only that there is sufficient wherewithal for the turbulent jet flow to drive solids to the surface in the center of the vessel in the central upwell.« less

Phytoplankton community and environmental correlates in a coastal upwelling zone along western Taiwan Strait

NASA Astrophysics Data System (ADS)

Wang, Yu; Kang, Jian-hua; Ye, You-yin; Lin, Geng-ming; Yang, Qing-liang; Lin, Mao

2016-02-01

Upwelling system in western Taiwan Strait is important for facilitating the fishery production. This study investigated hydro-chemical properties, phytoplankton biomass, phytoplankton species composition, three-dimensional (horizontal, vertical and transect) distribution of phytoplankton abundance, as well as phytoplankton annual variation and the correlation of phytoplankton community with the upwelling of underlying current and nutrients according to samples of Fujian-Guangdong coastal upwelling zone in western Taiwan Strait from August 27 to September 8, 2009. The results manifest that the nutrient-rich cold and high salinity current on the continental shelf of South China Sea upwells to the Fujian-Guangdong coastal waters through Taiwan Bank and the surging strength to surface is weak while strong at 30-m layer. The thermohaline center of coastal upwelling shifts to the east of Dongshan Island and expanded to offshore waters in comparison with previous records. A total of 137 phytoplankton species belonging to 59 genera in 4 phyla are identified excluding the unidentified species. Diatom is the first major group and followed by dinoflagellate. Cyanobacteria mainly composed by three Trichodesmium species account for a certain proportions, while Chrysophyta are only found in offshore waters. The dominant species include Thalassionema nitzschioides, Pseudo-nitzschia pungens, Thalassionema frauenfeldii, Pseudo-nitzschia delicatissima, Rhizosolenia styliformis, Chaetoceros curvisetus, Diplopsalis lenticula and Trichodesmium thiebautii. Phytoplankton community mainly consists of eurythermal and eurytopic species, followed by warm-water species, tropic high-salinity species and oceanic eurythermic species in order. Phytoplankton abundance ranges from 1.00 × 102 ind./L ~ 437.22 × 102 ind./L with an average of 47.36 × 102 ind./L. For vertical distribution, maximum abundance is found at 30 m-depth and the surface comes second. Besides, the abundance below 30 m decreases with increasing water depth. The horizontal and transect distribution of phytoplankton abundance are both displayed in patchy size, and the peak area is the offshore waters from the east of Dongshan Island to the south of Zhangpu which is basically coincident with the thermohaline center of the upwelling, but the distribution range of phytoplankton high abundance is expanded out of the upwelling center. Phytoplankton abundances on 3 transects in offshore waters from the east of Dongshan Island to the south of Zhangpu are higher than that of nearshore waters and the other 5 transects. Moreover, the underlying current is accompanied by shade flora so as to offer a certain evidence for the presence of upwelling. Phytoplankton abundance at 30 m-depth and bottom both present low significant positive correlation with phosphate, while there are not significant correlations between the content of inorganic nitrogen and phytoplankton abundance in all water layers. The intensity and range of Fujian-guangdong coastal upwelling has a regulating effect on the species succession, abundance distribution and the location of phytoplankton peak area.

a Numerical Study of Basic Coastal Upwelling Processes.

NASA Astrophysics Data System (ADS)

Li, Zhihong

Available from UMI in association with The British Library. Two-dimensional (2-D) and three-dimensional (3 -D) numerical models with a second order turbulence closure are developed for the study of coastal upwelling processes. A logarithmic coordinate system is introduced to obtain increased resolution in the regions near the surface and bottom where high velocity shear occurs and in the upwelling zone where its width is confined to the coast. In the experiments performed in the 2-D model an ocean initially at rest is driven by a spatially uniform alongshore wind-stress. There is a development of an offshore flow in the surface layer and an onshore flow below the surface layer. In the wind-stress direction there is a development of a coastal surface jet. The neglect of the alongshore pressure gradient leads to the intensification of the jet, and the concentration of the onshore flow in an over-developed Ekman layer yielding an unrealistic deepening of a bottom mixed layer. When bathymetric variations are introduced, some modifications in the dynamics of upwelling are observed. On the shelf region there is another upwelling zone and isotherms are interested with the bottom topography. When an alongshore pressure gradient is added externally into the model, the strength of the coastal jet decreases and a coastal undercurrent exists at greater depth. In addition the return onshore flow is largely independent of depth and the deepening of the bottom mixed layer disappears. In the experiments performed in the 3-D model a wind-stress with limited domain is used. Coastally trapped waves are generated and propagate along the coastline leading to a development of an alongshore pressure gradient, which has a significant effect on upwelling. The evolution of the alongshore flow, vertical velocity and the temperature is determined by both remote and local wind due to the propagation of waves. As the integration proceeds, the flow pattern becomes remarkably 3-dimensional. Finally the influence of bathymetric variations on upwelling processes is examined.

Quantifying the impact of an upwelling filament on the physical-chemical-biological interactions off SW Iberia

NASA Astrophysics Data System (ADS)

Cravo, A.; Sanchez, R.; Monteiro, C.; Cardeira, S.; Madureira, M.; Rita, F.; Relvas, P.

2017-12-01

Upwelling filaments are mesoscale structures of cold water that stretch seaward in a tongue-like shape with origin in the coastal upwelling zone. Filaments off the Iberian Peninsula are recurrent, showing similarities with those in the Californian coast. The Cape São Vicente, the SW tip of the Iberian Peninsula, is the root of recurrent filaments observed in the satellite imagery during the upwelling season. However, the understanding of its physical and chemical impact on the biological productivity is rather limited. There, a relatively small filament ( 80 km long) was investigated through remote sensing and in situ multidisciplinary observations during an upwelling favourable wind relaxation event, but just after an intense upwelling period. A total of 42 CTD+Rosette casts up to 400 m depth were distributed on an almost regular grid of 15 km mean spacing guided by guided by satellite SST imagery transmitted to the ship in near-real time. The parameters sampled during the sea campaign included: velocity field sampled along the ship track through a hull-mounted 38 kHz RDI ADCP, meteorological variables, temperature, salinity, chlorophyll a, dissolved oxygen, nitrate, phosphate, silicate, cadmium, lead and zinc. The extent of the impact of the filament was evaluated by quantifying the cross-shelf transports of several properties. The amounts conveyed by the filament were much stronger than those expected by the wind-driven Ekman mechanism, showing that it represents an efficient feature for the exchange of water, dissolved and particulate matter from the productive shelf towards the oligotrophic offshore region. Considering the periods of strong upwelling events and the extent of their duration along the year, the amounts of exported matter will certainly enhance the biological productivity of these waters, including its fisheries. These filament data contribute to better understand the physical-chemical-biological interactions of this regional ecosystem.

The role of Southern Ocean mixing and upwelling in glacial-interglacial atmospheric CO2 change

NASA Astrophysics Data System (ADS)

Watson, Andrew J.; Naveira Garabato, Alberto C.

2006-02-01

Decreased ventilation of the Southern Ocean in glacial time is implicated in most explanations of lower glacial atmospheric CO2. Today, the deep (>2000 m) ocean south of the Polar Front is rapidly ventilated from below, with the interaction of deep currents with topography driving high mixing rates well up into the water column. We show from a buoyancy budget that mixing rates are high in all the deep waters of the Southern Ocean. Between the surface and ~2000 m depth, water is upwelled by a residual meridional overturning that is directly linked to buoyancy fluxes through the ocean surface. Combined with the rapid deep mixing, this upwelling serves to return deep water to the surface on a short time scale. We propose two new mechanisms by which, in glacial time, the deep Southern Ocean may have been more isolated from the surface. Firstly, the deep ocean appears to have been more stratified because of denser bottom water resulting from intense sea ice formation near Antarctica. The greater stratification would have slowed the deep mixing. Secondly, subzero atmospheric temperatures may have meant that the present-day buoyancy flux from the atmosphere to the ocean surface was reduced or reversed. This in turn would have reduced or eliminated the upwelling (contrary to a common assumption, upwelling is not solely a function of the wind stress but is coupled to the air-sea buoyancy flux too). The observed very close link between Antarctic temperatures and atmospheric CO2 could then be explained as a natural consequence of the connection between the air-sea buoyancy flux and upwelling in the Southern Ocean, if slower ventilation of the Southern Ocean led to lower atmospheric CO2. Here we use a box model, similar to those of previous authors, to show that weaker mixing and reduced upwelling in the Southern Ocean can explain the low glacial atmospheric CO2 in such a formulation.

The use of circulation weather types to predict upwelling activity along the Western Iberian Peninsula coast

NASA Astrophysics Data System (ADS)

Ramos, Alexandre M.; Cordeiro Pires, Ana; Sousa, Pedro M.; Trigo, Ricardo M.

2013-04-01

Coastal upwelling is a phenomenon that occurs in most western oceanic coasts due to the presence of mid-latitude high-pressure systems that generate equatorward winds along the coast and consequent offshore displacement of surface waters that in turn cause deeper, colder, nutrient-rich waters to arise. In western Iberian Peninsula (IP) the high-pressure system associated to northerly winds occurs mainly during spring and summer. Upwelling systems are economically relevant, being the most productive regions of the world ocean and crucial for fisheries. In this work, we evaluate the intra- and inter-annual variability of the Upwelling Index (UI) off the western coast of the IP considering four locations at various latitudes: Rias Baixas, Aveiro, Figueira da Foz and Cabo da Roca. In addition, the relationship between the variability of the occurrence of several circulation weather types (Ramos et al., 2011) and the UI variability along this coast was assessed in detail, allowing to discriminate which types are frequently associated with strong and weak upwelling activity. It is shown that upwelling activity is mostly driven by wind flow from the northern quadrant, for which the obtained correlation coefficients (for the N and NE types) are higher than 0.5 for the four considered test locations. Taking into account these significant relationships, we then developed statistical multi-linear regression models to hindcast upwelling series (April to September) at the four referred locations, using monthly frequencies of circulation weather types as predictors. Modelled monthly series reproduce quite accurately observational data, with correlation coefficients above 0.7 for all locations, and relatively small absolute errors. Ramos AM, Ramos R, Sousa P, Trigo RM, Janeira M, Prior V (2011) Cloud to ground lightning activity over Portugal and its association with Circulation Weather Types. Atmospheric Research 101:84-101. doi: 10.1016/j.atmosres.2011.01

Evaluation of upwelling infrared radiance from earth's atmosphere

NASA Technical Reports Server (NTRS)

Gupta, S. K.; Tiwari, S. N.

1975-01-01

Basic equations for calculating the upwelling atmospheric radiation are presented which account for various sources of radiation coming out at the top of the atmosphere. The theoretical formulation of the transmittance models (line-by-line and quasi-random band model) and the computational procedures used for the evaluation of the transmittance and radiance are discussed in detail. By employing the Lorentz line-by-line and quasi-random computer programs, model calculations were made to determine the upwelling radiance and signal change in the wave number interval of CO fundamental band. These results are useful in determining the effects of different interfering molecules, water vapor profiles, ground temperatures, and ground emittances on the upwelling radiance and signal change. This information is of vital importance in establishing the feasibility of measuring the concentrations of pollutants in the atmosphere from a gas filter correlation instrument flown on an aircraft or mounted on a satellite.

Temporal and spatial variability of dissolved organic and inorganic phosphorus, and metrics of phosphorus bioavailability in an upwelling-dominated coastal system

NASA Astrophysics Data System (ADS)

Ruttenberg, Kathleen C.; Dyhrman, Sonya T.

2005-10-01

High-frequency temporal and spatial shifts in the various dissolved P pools (total, inorganic, and organic) are linked to upwelling/relaxation events and to phytoplankton bloom dynamics in the upwelling-dominated Oregon coastal system. The presence and regulation of alkaline phosphatase activity (APA) is apparent in the bulk phytoplankton population and in studies of cell-specific APA using Enzyme Labeled Fluorescence (ELF®). Spatial and temporal variability are also evident in phytoplankton community composition and in APA. The spatial pattern of dissolved phosphorus and APA variability can be explained by bottom-controlled patterns of upwelling, and flushing times of different regions within the study area. The presence of APA in eukaryotic taxa indicates that dissolved organic phosphorus (DOP) may contribute to phytoplankton P nutrition in this system, highlighting the need for a more complete understanding of P cycling and bioavailability in the coastal ocean.

Bathymetric analysis of in-water upwelling-radiance data

NASA Astrophysics Data System (ADS)

Fay, Temple H.; Miller, H. V.; Clark, R. K.

1990-09-01

In June 1988, the Naval Ocean Research and Development Activity (NORDA) collected some "in-water" data using its Towed Underwater Pumping System (TUPS) in the near-shore waters off St. Andrews State Park, Shell Island, Florida. These in situ data include latitude; longitude; depth in meters; narrow-band upwelling at 465 nm, 507 nm, and 532 nm; broad-band downwelling collected at the surface; temperature; salinity; atid transmissivity. In this paper, we investigate the relationship between depth and the normalized upwelling irradiance (upwelling divided by downwelling) in the three bands. Algorithms used to calculate water depth from remotely sensed airborne and satellite multispectral data are applied to the TUPS data and results compared. The TEJPS data have the advantage over most aircraft- and satellite-collected data because they were collected over an essentially uniform bottom type (smooth sandy bottom with steady slope) and have no atmospheric contamination. A new algorithm for depth calculation is proposed.

Lagrangian Timescales of Southern Ocean Upwelling in a Hierarchy of Model Resolutions

NASA Astrophysics Data System (ADS)

Drake, Henri F.; Morrison, Adele K.; Griffies, Stephen M.; Sarmiento, Jorge L.; Weijer, Wilbert; Gray, Alison R.

2018-01-01

In this paper we study upwelling pathways and timescales of Circumpolar Deep Water (CDW) in a hierarchy of models using a Lagrangian particle tracking method. Lagrangian timescales of CDW upwelling decrease from 87 years to 31 years to 17 years as the ocean resolution is refined from 1° to 0.25° to 0.1°. We attribute some of the differences in timescale to the strength of the eddy fields, as demonstrated by temporally degrading high-resolution model velocity fields. Consistent with the timescale dependence, we find that an average Lagrangian particle completes 3.2 circumpolar loops in the 1° model in comparison to 0.9 loops in the 0.1° model. These differences suggest that advective timescales and thus interbasin merging of upwelling CDW may be overestimated by coarse-resolution models, potentially affecting the skill of centennial scale climate change projections.

Yearly variation of bacterial production in the Arraial do Cabo protection area (Cabo Frio upwelling region): An evidence of anthropogenic pressure

PubMed Central

Coelho-Souza, Sérgio A.; Pereira, Gilberto C.; Coutinho, Ricardo; Guimarães, Jean R.D.

2013-01-01

Arraial do Cabo is where upwelling occurs more intensively on the Brazilian coast. Although it is a protection area it suffers anthropogenic pressure such as harbor activities and sporadic sewage emissions. Short-time studies showed a high variability of bacterial production (BP) in this region but none of them evaluated BP during long periods in a large spatial scale including stations under different natural (upwelling and cold fronts) and anthropogenic pressures. During 2006, we sampled surface waters 10 times (5 in upwelling and 5 in subsidence periods) in 8 stations and we measured BP, temperature as well as the concentrations of inorganic nutrients, pigments and particulate organic matter (POM). BP was up to 400 times higher when sewage emissions were observed visually and it had a positive correlation with ammonia concentrations. Therefore, in 2007, we did two samples (each during upwelling and subsidence periods) during sewage emissions in five stations under different anthropogenic pressure and we also measured particles abundance by flow cytometry. The 12 samples in the most impacted area confirmed that BP was highest when ammonia was higher than 2 μM, also reporting the highest concentrations of chlorophyll a and suspended particles. However, considering all measured variables, upwelling was the main disturbing factor but the pressure of fronts should not be neglected since it had consequences in the auto-heterotrophic coupling, increasing the concentrations of non fluorescent particles and POM. Stations clustered in function of natural and anthropogenic pressures degrees and both determined the temporal-spatial variability. PMID:24688533

Yearly variation of bacterial production in the Arraial do Cabo protection area (Cabo Frio upwelling region): an evidence of anthropogenic pressure.

PubMed

Coelho-Souza, Sérgio A; Pereira, Gilberto C; Coutinho, Ricardo; Guimarães, Jean R D

2013-12-01

Arraial do Cabo is where upwelling occurs more intensively on the Brazilian coast. Although it is a protection area it suffers anthropogenic pressure such as harbor activities and sporadic sewage emissions. Short-time studies showed a high variability of bacterial production (BP) in this region but none of them evaluated BP during long periods in a large spatial scale including stations under different natural (upwelling and cold fronts) and anthropogenic pressures. During 2006, we sampled surface waters 10 times (5 in upwelling and 5 in subsidence periods) in 8 stations and we measured BP, temperature as well as the concentrations of inorganic nutrients, pigments and particulate organic matter (POM). BP was up to 400 times higher when sewage emissions were observed visually and it had a positive correlation with ammonia concentrations. Therefore, in 2007, we did two samples (each during upwelling and subsidence periods) during sewage emissions in five stations under different anthropogenic pressure and we also measured particles abundance by flow cytometry. The 12 samples in the most impacted area confirmed that BP was highest when ammonia was higher than 2 μM, also reporting the highest concentrations of chlorophyll a and suspended particles. However, considering all measured variables, upwelling was the main disturbing factor but the pressure of fronts should not be neglected since it had consequences in the auto-heterotrophic coupling, increasing the concentrations of non fluorescent particles and POM. Stations clustered in function of natural and anthropogenic pressures degrees and both determined the temporal-spatial variability.

Bleaching susceptibility and recovery of Colombian Caribbean corals in response to water current exposure and seasonal upwelling.

PubMed

Bayraktarov, Elisa; Pizarro, Valeria; Eidens, Corvin; Wilke, Thomas; Wild, Christian

2013-01-01

Coral bleaching events are globally occurring more frequently and with higher intensity, mainly caused by increases in seawater temperature. In Tayrona National Natural Park (TNNP) in the Colombian Caribbean, local coral communities are subjected to seasonal wind-triggered upwelling events coinciding with stronger water currents depending on location. This natural phenomenon offers the unique opportunity to study potential water current-induced mitigation mechanisms of coral bleaching in an upwelling influenced region. Therefore, coral bleaching susceptibility and recovery patterns were compared during a moderate and a mild bleaching event in December 2010 and 2011, and at the end of the subsequent upwelling periods at a water current-exposed and -sheltered site of an exemplary bay using permanent transect and labeling tools. This was accompanied by parallel monitoring of key environmental variables. Findings revealed that in 2010 overall coral bleaching before upwelling was significantly higher at the sheltered (34%) compared to the exposed site (8%). Whereas 97% of all previously bleached corals at the water current-exposed site had recovered from bleaching by April 2011, only 77% recovered at the sheltered site, but 12% had died there. In December 2011, only mild bleaching (<10% at both sites) was observed, but corals recovered significantly at both sites in the course of upwelling. No differences in water temperatures between sites occurred, but water current exposure and turbidity were significantly higher at the exposed site, suggesting that these variables may be responsible for the observed site-specific mitigation of coral bleaching. This indicates the existence of local resilience patterns against coral bleaching in Caribbean reefs.

Transport of terrigenous polycyclic aromatic hydrocarbons affected by the coastal upwelling in the northwestern coast of South China Sea.

PubMed

Ya, Miaolei; Wu, Yuling; Li, Yongyu; Wang, Xinhong

2017-10-01

Coastal upwelling prevails in the coast of Hainan Island, the northern South China Sea (SCS) during summer. We studied the influences of the upwelling on the horizontal and vertical transport of terrigenous polycyclic aromatic hydrocarbons (PAHs). PAHs in dissolved and suspended particulate phase of water samples were determined in the upper (depth < 1 m) and water column (depth > 10 m). PAH levels decreased sharply from inshore to offshore to open sea. The results showed that terrestrial input was the main source of coastal PAHs. Perylene, an important indicator of land plant-derived PAH, showed the significant correlation with PAHs (p < 0.005). This implied that fluvial transport was the primary pathway of terrigenous PAHs into the coast of northern SCS. Variations of the concentrations, compositions and diagnostic ratios of PAHs, accompanied the partition equilibrium in the water column, could indicate the selective degradation of PAHs by the plankton affected by upwelling. Different from the "traditional" transport pathway of PAHs in the water column (surface enrichment-depth depletion distribution), the upwelling could provide the original driver to elevate the upward diffusion of sediment entrained contaminants towards the intermediate even the upper waters. It could also enhance the outward diffusion of terrigenous PAHs accompanied by the offshore transport of the upper waters. Therefore, the transport pathway of PAHs can be summarized by the coastal upwelling rising PAHs with their subsequent transport offshore and settling in the adjacent open sea. Copyright © 2017 Elsevier Ltd. All rights reserved.

Bleaching Susceptibility and Recovery of Colombian Caribbean Corals in Response to Water Current Exposure and Seasonal Upwelling

PubMed Central

Bayraktarov, Elisa; Pizarro, Valeria; Eidens, Corvin; Wilke, Thomas; Wild, Christian

2013-01-01

Coral bleaching events are globally occurring more frequently and with higher intensity, mainly caused by increases in seawater temperature. In Tayrona National Natural Park (TNNP) in the Colombian Caribbean, local coral communities are subjected to seasonal wind-triggered upwelling events coinciding with stronger water currents depending on location. This natural phenomenon offers the unique opportunity to study potential water current-induced mitigation mechanisms of coral bleaching in an upwelling influenced region. Therefore, coral bleaching susceptibility and recovery patterns were compared during a moderate and a mild bleaching event in December 2010 and 2011, and at the end of the subsequent upwelling periods at a water current-exposed and -sheltered site of an exemplary bay using permanent transect and labeling tools. This was accompanied by parallel monitoring of key environmental variables. Findings revealed that in 2010 overall coral bleaching before upwelling was significantly higher at the sheltered (34%) compared to the exposed site (8%). Whereas 97% of all previously bleached corals at the water current-exposed site had recovered from bleaching by April 2011, only 77% recovered at the sheltered site, but 12% had died there. In December 2011, only mild bleaching (<10% at both sites) was observed, but corals recovered significantly at both sites in the course of upwelling. No differences in water temperatures between sites occurred, but water current exposure and turbidity were significantly higher at the exposed site, suggesting that these variables may be responsible for the observed site-specific mitigation of coral bleaching. This indicates the existence of local resilience patterns against coral bleaching in Caribbean reefs. PMID:24282551

Environmental Controls of Shellfish-Toxigenic Vibrio Bacteria in Oregon's Coasts and Estuaries

NASA Astrophysics Data System (ADS)

Gradoville, M. R.; Häse, C.; White, A. E.

2016-02-01

Vibrio species are a known and persistent concern for economically important aquaculture efforts. In Pacific Northwest shellfish hatcheries, vibriosis, caused by toxigenic Vibrio, has been responsible for major mortality events in recent decades — events that are often irregular and unpredictable. The success of shellfish hatcheries is critically linked to the chemical and biological composition of their seawater resources; thus, it is pertinent to understand the biogeochemical drivers of toxigenic Vibrio in their planktonic state. Recent evidence suggests that vibriosis outbreaks in Netarts Bay, Oregon may be related to wind-driven coastal upwelling, either through the advection of toxigenic Vibrio residing in upwelling source water, or through the creation of favorable growth conditions within the estuary. Here, we present data tracking shellfish-toxigenic Vibrio bacteria in Oregon estuaries and coastal waters through the 2015 upwelling season. Estuarine samples were collected from Netarts Bay and Yaquina Bay in May-October 2015 over a range of upwelling intensities, tidal heights, and biogeochemical conditions. Additionally, samples were collected at multiple depths from offshore coastal Oregon stations in order to test the hypothesis that toxigenic Vibrio reside in upwelling source waters. PCR-based methods were used to quantify the known shellfish pathogen V. coralliilyticus in estuary and seawater samples. These toxigenic Vibrio abundances were correlated to local environmental conditions, including temperature, salinity, carbonate chemistry, nutrients, and chlorophyll a concentrations, as well as coastal wind stress and upwelling intensity. Our analysis aims to define the environmental controls of toxigenic Vibrio in their free-living oceanic state, information that can be used to prevent future disease outbreaks in local shellfish hatcheries.

Oceanographic upwelling conditions influence signaling pathways involved in muscle growth of intertidal fish.

PubMed

Zuloaga, Rodrigo; Almarza, Oscar; Valdés, Juan A; Molina, Alfredo; Pulgar, José

2018-04-01

Few studies have addressed the impact of the upwelling oceanographical conditions on biological processes, such as growth, using a molecular and physiological approach. Upwelling conditions are characterized by low temperature seawater and high nutrient availability, which represents an ideal opportunity to understand how habitat modulates animal performance at different levels of biological complexity. We aimed to assess intraspecific variations in weight, oxygen consumption, protein content, and key signaling pathways involved in muscle-growth (protein kinase B (AKT) and extracellular signal-regulated kinase (ERK)) under experimental trials considering high/low seawater temperatures with full/restricted food rations. For this purpose, we studied Girella laevifrons, one of the most abundant fish species inhabiting rocky intertidal zones along the Eastern South Pacific coasts. Using fish obtained from upwelling (U) and non-upwelling (NU) zones, we reported that U animals displayed higher growth performance during both contrasting trials, with a weight gain (~3 g), lower oxygen consumption (~12%), and higher protein contents (~20%). Only ERK showed significant differences during the trials (~2-fold downregulation between NU and U fish). We also found that U fish increased protein ubiquitination in high water temperature and restricted food ration in contrast to NU fish. Our results help to elucidate how upwelling conditions may influence fish growth at physiological and molecular levels. Still, future analyses are necessary to improve the information regarding the impact of U and NU condition on animals, as well as the possible applications of this data in the aquaculture industry. Copyright © 2018 Elsevier Inc. All rights reserved.

The Origin and Mantle Dynamics of Quaternary Intraplate Volcanism in Northeast China From Joint Inversion of Surface Wave and Body Wave

NASA Astrophysics Data System (ADS)

Guo, Zhen; Wang, Kai; Yang, Yingjie; Tang, Youcai; John Chen, Y.; Hung, Shu-Huei

2018-03-01

We present a 3-D model of NE China by joint inversion of body and surface waves. The joint inversion significantly improves the resolution at shallow depths compared with body wave tomography alone and provides seismic evidence for the origin of Quaternary volcanism in NE China. Our model reveals that the mantle upwelling beneath the Changbaishan volcano originates from the transition zone and extends up to 60 km, and spreads at the base of the lithosphere with the upwelling head 5 times wider than the raising tail in the lower upper mantle. However, low velocities beneath the Halaha and Abaga volcanoes in the Xingmeng belt are confined to depths shallower than 150 km, suggesting that magmatism in the Xingmeng belt is more likely caused by localized asthenospheric upwelling at shallow depths rather than from the common deep source. A small-scale sublithospheric mantle convection may control the spatial and temporal distribution of Quaternary magmatism in NE China; that is, the upwelling beneath the Changbaishan volcano triggers the downwelling beneath the southern Songliao basin, where the high velocity imaged extends to 300 km. The downwelling may further induce localized upwelling in the surrounding areas, such as the Halaha and Abaga volcanoes. Thanks to the joint constraints from both surface and body waves, we can estimate the dimension of the convection cell. The convection cell is located between 42°N and 45°N, spreads around 500 km in the W-E direction measured from the distance between centers of downwelling and upwelling, and extends to 300 km vertically.

Mindanao Dome variability over the last 160 kyr: Episodic glacial cooling of the West Pacific Warm Pool

NASA Astrophysics Data System (ADS)

Bolliet, Timothé; Holbourn, Ann; Kuhnt, Wolfgang; Laj, Carlo; Kissel, Catherine; Beaufort, Luc; Kienast, Markus; Andersen, Nils; Garbe-Schönberg, Dieter

2011-02-01

We present sea surface, upper thermocline, and benthic δ18O data, as well as temperature and paleoproductivity proxy data, from the International Marine Global Change Study Program (IMAGES) Core MD06-3067 (6°31‧N, 126°30‧E, 1575 m water depth), located in the western equatorial Pacific Ocean within the flow path of the Mindanao Current. Our records reveal considerable glacial-interglacial and suborbital variability in the Mindanao Dome upwelling over the last 160 kyr. Dome activity generally intensified during glacial intervals resulting in cooler thermocline waters, whereas it substantially declined during interglacials, in particular in the early Holocene and early marine oxygen isotope stage (MIS) 5e, when upwelling waters did not reach the thermocline. During MIS 3 and MIS 2, enhanced surface productivity together with remarkably low SST and low upper ocean thermal contrast provide evidence for episodic glacial upwelling to the surface, whereas transient surface warming marks periodic collapses of the Mindanao Dome upwelling during Heinrich events. We attribute the high variability during MIS 3 and MIS 2 to changes in the El Niño Southern Oscillation state that affected boreal winter monsoonal winds and upper ocean circulation. Glacial upwelling intensified when a strong cyclonic gyre became established, whereas El Niño-like conditions during Heinrich events tended to suppress the cyclonic circulation, reducing Ekman transport. Thus, our findings demonstrate that variations in the Mindanao Dome upwelling are closely linked to the position and intensity of the tropical convection and also reflect far-field influences from the high latitudes.

Temporal variability of near-bottom dissolved oxygen during upwelling off central Oregon

NASA Astrophysics Data System (ADS)

Adams, Katherine A.; Barth, John A.; Chan, Francis

2013-10-01

In the productive central-Oregon coastal upwelling environment, wind-driven upwelling, tides, and topographic effects vary across the shelf, setting the stage for varied biogeochemical responses to physical drivers. Current, temperature, salinity, and dissolved oxygen (DO) measurements from three moorings deployed during the upwelling seasons of 2009-2011 off the central-Oregon coast are analyzed over three time bands (interannual, subtidal, tidal) to explore the relationship between mid (70 m) and inner-shelf (15 m) upwelling dynamics and the associated effect on DO. Topographic effects are observed in each time band due to the Heceta and Stonewall Bank complex. Seasonal cumulative hypoxia (DO < 1.4 mL L-1) calculations identify two regions, a well-ventilated inner shelf and a midshelf vulnerable to hypoxia (98 ± 15 days annually). On tidal timescales, along-shelf diurnal (K1) velocities are intensified over the Bank, 0.08 m s-1 compared with 0.03 m s-1 to the north. Interannual variability in the timing of spring and fall transitions, defined using glider-measured continental slope source water temperature, is observed on the midshelf. Interannual source water DO concentrations vary on the order of 0.1 mL L-1. Each spring and summer, DO decline rates are modulated by physical and biological processes. The net observed decrease is about 30% of the expected draw down due to water-column respiration. Physical processes initiate low-oxygen conditions on the shelf through coastal upwelling and subsequently prevent the system via advection and mixing from reaching the potential anoxic levels anticipated from respiration rates alone.

Influence of El Niño and Indian Ocean Dipole on sea level variability in the Bay of Bengal

NASA Astrophysics Data System (ADS)

Sreenivas, P.; Gnanaseelan, C.; Prasad, K. V. S. R.

2012-01-01

Zonally oscillating seasonal equatorial winds generate pairs of upwelling and downwelling Kelvin waves in the Equatorial Indian Ocean, which then advance in to the coastal Bay of Bengal. The first (second) equatorial upwelling Kelvin wave has its origin in the western (eastern) basin, whereas the downwelling Kelvin waves originate in the central basin. The observed interannual variability of these Kelvin waves is highly governed by the associated zonal wind changes in the central and eastern equatorial Indian Ocean during the anomalous years. The second downwelling (upwelling) Kelvin wave is absent (weak) during El Niño (La Niña) years, whereas the second upwelling Kelvin wave strengthened during El Niño years both in the equatorial Indian Ocean and Bay of Bengal. The large scale off equatorial Rossby waves occasionally feedback the equatorial Kelvin waves, which then strengthen the Bay of Bengal coastal Kelvin waves. The coastal Kelvin waves and the associated radiated Rossby waves from east play a dominant role in the mesoscale eddy generation in Bay of Bengal. The analysis of cyclogenesis characteristics in the bay over the past 65 years revealed that the active (suppressed) phases of cyclogenesis are coinciding with the downwelling (upwelling) planetary waves which influence the cyclone heat potential by altering the thermocline depth.

Late Pliocene Sea Surface Temperature contrast in the Benguela upwelling as recorded by foraminiferal Mg/Ca and alkenones

NASA Astrophysics Data System (ADS)

Leduc, G.; Garbe-Schoenberg, C.; Regenberg, M.; Schneider, R. R.

2011-12-01

Alkenone-based sea surface temperature (SST) in the Benguela region reveal quite warm and stable conditions between ~3.0 and 2.0 Ma, coinciding with a period of very high diatom production as revealed by mass accumulation rates (MAR) of biogenic opal (Marlow et al., 2000, Science; Etourneau et al., 2009, Geology). Such a pattern is difficult to believe with the general perception that high diatom productivity results from strong coastal upwelling associated with pronounced Surface Ocean cooling. Therefore we assessed whether different paleothermometers from the same sedimentary archive (i.e. ODP site 1082) provide different results for the Namibian upwelling system by performing a comparison between alkenone-derived temperatures and those from the planktonic foraminifera Globigerinoides bulloides, a species known to proliferate in upwelling regions. We used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for multiple in situ determination of Mg/Ca in single tests of G. bulloides. These measurements allow monitoring of contaminant phases linked to Mg-rich clays (monitored by Al/Ca) and Mn-rich foraminiferal tests, which contain substantial high Mg (monitored by Mn/Ca) (Pena et al., 2005, G-cubed). Moreover, using LA-ICP-MS measurements for Mg/Ca ratios on single specimens allows estimating the range of seasonal or vertical temperature variability by considering the intra-sample variance in the SST estimated from different specimens and/or different chambers within the same specimen. When compared to the Pliocene alkenone SST record, the Mg/Ca-ratios imply SSTs colder by ~10°C. A similar contrast in SST estimates between these two proxies was reported for the last 20 ka in the same region (Farmer et al., 2005, Paleoceanography). Such discrepancy can be reconciled by assuming that the two SST proxies are either strongly skewed towards warm (non-upwelling) and cold (upwelling) conditions for alkenones and Mg/Ca SST, respectively, or by the possibility that G. bulloides captures a temperature signal integrated over a larger water depth range. If representative for a specific season, downcore SST estimates from the two proxies may provide reliable evidences for changes in the seasonal temperature contrasts and thus upwelling intensity during the Pliocene. Even if the absolute temperature contrasts recorded between these two proxies have not dramatically changed between the Pliocene and Late Quaternary, the range of SST estimates between single specimen Mg/Ca values may hint to changes in past upwelling intensity. Accordingly, the scattering of intra-sample Mg/Ca values tends to increase together with the opal MAR, probably reflecting enhanced temperature contrasts at times of intense upwelling and diatom production which occurred during the cold season, one feature that is not captured by alkenone SST records.

Impact of Indian ocean dipole on the coastal upwelling features off the southwest coast of India

NASA Astrophysics Data System (ADS)

Nigam, Tanuja; Pant, Vimlesh; Prakash, Kumar Ravi

2018-05-01

A three-dimensional regional ocean model is used to examine the impact of positive Indian ocean dipole (pIOD) events on the coastal upwelling features at the southwest coast of India (SWCI). Two model experiments are carried out with different surface boundary conditions that prevailed in the normal and pIOD years from 1982 to 2010. Model experiments demonstrate the weakening of coastal upwelling at the SWCI in the pIOD years. The reduced southward meridional wind stress off the SWCI leads to comparatively lower offshore Ekman transport during August-October in the pIOD years to that in normal years. The suppressed coastal upwelling results in warmer sea surface temperature and deeper thermocline in the pIOD years during June-September. The offshore spatial extent of upwelled colder (< 22 °C) water was up to 75.5° E in August-September in normal years that was limited up to 76.2° E in pIOD years. The heat budget analysis reveals the decreased contribution of vertical entrainment process to the mixed layer cooling in pIOD years which is almost half of that of normal years in October. The net heat flux term shows warming tendency during May-November with a higher magnitude (+ 0.4 °C day-1) in normal years than pIOD years (+ 0.28 °C day-1). The biological productivity is found to reduce during the pIOD years as the concentration of phytoplankton and zooplankton decreases over the region of coastal upwelling at SWCI. Nitrate concentration in the pIOD years dropped by half during August-September and dropped by an order of magnitude in October as compared to its ambient concentration of 13 μmol L-1 in normal years.

Impact of Indian ocean dipole on the coastal upwelling features off the southwest coast of India

NASA Astrophysics Data System (ADS)

Nigam, Tanuja; Pant, Vimlesh; Prakash, Kumar Ravi

2018-06-01

A three-dimensional regional ocean model is used to examine the impact of positive Indian ocean dipole (pIOD) events on the coastal upwelling features at the southwest coast of India (SWCI). Two model experiments are carried out with different surface boundary conditions that prevailed in the normal and pIOD years from 1982 to 2010. Model experiments demonstrate the weakening of coastal upwelling at the SWCI in the pIOD years. The reduced southward meridional wind stress off the SWCI leads to comparatively lower offshore Ekman transport during August-October in the pIOD years to that in normal years. The suppressed coastal upwelling results in warmer sea surface temperature and deeper thermocline in the pIOD years during June-September. The offshore spatial extent of upwelled colder (< 22 °C) water was up to 75.5° E in August-September in normal years that was limited up to 76.2° E in pIOD years. The heat budget analysis reveals the decreased contribution of vertical entrainment process to the mixed layer cooling in pIOD years which is almost half of that of normal years in October. The net heat flux term shows warming tendency during May-November with a higher magnitude (+ 0.4 °C day-1) in normal years than pIOD years (+ 0.28 °C day-1). The biological productivity is found to reduce during the pIOD years as the concentration of phytoplankton and zooplankton decreases over the region of coastal upwelling at SWCI. Nitrate concentration in the pIOD years dropped by half during August-September and dropped by an order of magnitude in October as compared to its ambient concentration of 13 μmol L-1 in normal years.

Upwelling-Induced Primary Productivity in Coastal Waters of the Black Sea: Impact on Algorithms for Remote Sensing

NASA Technical Reports Server (NTRS)

Goldman, Joel C.; Brink, Kenneth K.; Gawarkiewicz, Glen; Sosik, Heidi M.

1997-01-01

This research program was a collaborative effort to investigate the impact of rapid changes in the water column during coastal upwelling, on biological and optical properties. These properties are important for constructing region or event-specific algorithms for remote sensing of pigment concentration and primary productivity and for comparing these algorithms with those used for the development of large scale maps from ocean color. We successfully achieved the primary objective of this research project which was to study in situ the dynamics of rapid spatial and temporal changes in properties of the water column during, coastal upwelling off the Crimean Coast in the Black Sea. The work was a collaborative effort between a group of biological and physical oceanographers from the Woods Hole Oceanographic Institution and from two oceanographic research institutions in the Crimea, Ukraine, located near the study site, the Marine Hydrophysical Institute (MHI) and the Institute of Biology of the Southern Seas (IBSS). The site was an ideal experimental model, both from a technical and economic standpoint, because of the predictable summer upwelling that occurs in the region and because of the availability of both a ship on call and laboratory and remote sensing facilities at the nearby marine institutes. We used a combination of shipboard measurements and remote sensing to investigate the physical evolution of rapid upwelling events and their impact on photoplankton and water column optical properties. The field work involved a two day cruise for mooring, deployment and a three day baseline survey cruise, followed by an eleven day primary cruise during, a summer upwelling event (anticipated by monitoring local winds and tracked by remote sensing imaging). An MHI ship was outfitted and used for these purposes.

Scaling Coastal Ecosystems to Oceanographic and Climatic Drivers: Making Sense of Community Variation on Rocky Shores Using the Comparative-Experimental Approach in Upwelling and Downwelling Systems

NASA Astrophysics Data System (ADS)

Menge, B. A.; Gouhier, T.; Chan, F.; Hacker, S.; Menge, D.; Nielsen, K. J.

2016-02-01

Ecology focuses increasingly on the issue of matching spatial and temporal scales responsible for ecosystem pattern and dynamics. Benthic coastal communities traditionally were studied at local scales using mostly short-term research, while environmental (oceanographic, climatic) drivers were investigated at large scales (e.g., regional to oceanic, mostly offshore) using combined snapshot and monitoring (time series) research. The comparative-experimental approach combines local-scale studies at multiple sites spanning large-scale environmental gradients in combination with monitoring of inner shelf oceanographic conditions including upwelling/downwelling wind forcing and their consequences (e.g., temperature), and inputs of subsidies (larvae, phytoplankton, detritus). Temporal scale varies depending on the questions, but can extend from years to decades. We discuss two examples of rocky intertidal ecosystem dynamics, one at a regional scale (California Current System, CCS) and one at an interhemispheric scale. In the upwelling-dominated CCS, 52% and 32% of the variance in local community structure (functional group abundances at 13 sites across 725 km) was explained by external factors (ecological subsidies, oceanographic conditions, geographic location), and species interactions, respectively. The interhemispheric study tested the intermittent upwelling hypothesis (IUH), which predicts that key ecological processes will vary unimodally along a persistent downwelling to persistent upwelling gradient. Using 14-22 sites, unimodal relationships between ecological subsidies (phytoplankton, prey recruitment), prey responses (barnacle colonization, mussel growth) and species interactions (competition rate, predation rate and effect) and the Bakun upwelling index calculated at each site accounted for 50% of the variance. Hence, external factors can account for about half of locally-expressed community structure and dynamics.

Diatoms as a paleoproductivity proxy in the NW Iberian coastal upwelling system (NE Atlantic)

NASA Astrophysics Data System (ADS)

Zúñiga, Diana; Santos, Celia; Froján, María; Salgueiro, Emilia; Rufino, Marta M.; De la Granda, Francisco; Figueiras, Francisco G.; Castro, Carmen G.; Abrantes, Fátima

2017-03-01

The objective of the current work is to improve our understanding of how water column diatom's abundance and assemblage composition is seasonally transferred from the photic zone to seafloor sediments. To address this, we used a dataset derived from water column, sediment trap and surface sediment samples recovered in the NW Iberian coastal upwelling system. Diatom fluxes (2.2 (±5.6) 106 valves m-2 d-1) represented the majority of the siliceous microorganisms sinking out from the photic zone during all studied years and showed seasonal variability. Contrasting results between water column and sediment trap diatom abundances were found during downwelling periods, as shown by the unexpectedly high diatom export signals when diatom-derived primary production achieved their minimum levels. They were principally related to surface sediment remobilization and intense Minho and Douro river discharge that constitute an additional source of particulate matter to the inner continental shelf. In fact, contributions of allochthonous particles to the sinking material were confirmed by the significant increase of both benthic and freshwater diatoms in the sediment trap assemblage. In contrast, we found that most of the living diatom species blooming during highly productive upwelling periods were dissolved during sinking, and only those resistant to dissolution and the Chaetoceros and Leptocylindrus spp. resting spores were susceptible to being exported and buried. Furthermore, Chaetoceros spp. dominate during spring-early summer, when persistent northerly winds lead to the upwelling of nutrient-rich waters on the shelf, while Leptocylindrus spp. appear associated with late-summer upwelling relaxation, characterized by water column stratification and nutrient depletion. These findings evidence that the contributions of these diatom genera to the sediment's total marine diatom assemblage should allow for the reconstruction of different past upwelling regimes.

Linking benthic community structure to terrestrial runoff and upwelling in the coral reefs of northeastern Hainan Island

NASA Astrophysics Data System (ADS)

Li, Xiubao; Wang, Daoru; Huang, Hui; Zhang, Jing; Lian, Jiansheng; Yuan, Xiangcheng; Yang, Jianhui; Zhang, Guoseng

2015-04-01

Near-shore coral reefs in northeastern Hainan Island are close to river mouths and aquaculture ponds, and also located at the center of the Qiongdong Upwelling (QDU). However, it is still unclear how terrestrial runoff and upwelling influence the community composition and spatial distribution of the benthos. During three cruises in 2010 and 2011 in Wenchang, northeastern Hainan Island, we determined a subset of environmental parameters in seawater (e.g. temperature, salinity, DO, dissolved inorganic nutrient (DIN), turbidity and transparency) and macroalgal δ15N and investigated the benthic communities (e.g. live coral cover, coral species richness, juvenile coral density, macroalgal cover and coverage of calcified algae) by video transect and visual census techniques at 10 stations (i.e. 1S-6D). The results showed that the QDU has influenced the reef waters in Wenchang. In 2011, the upwelling started in early May, peaked in July and disappeared in September and most upwelling events lasted for 1-2 weeks between May and July. The results also demonstrated that the reef water was nutrient enriched. Stations close to the river mouth and aquaculture ponds had higher levels of DIN and a higher percentage of ammonia in DIN, and there was consistently lower live coral cover, juvenile coral density and higher macroalgal cover. At some stations in this study, live coral cover was negatively correlated with macroalgal cover (i.e. 2S-6D). Live coral cover, species richness, and juvenile coral density all increased with the distance away from the river outlet and decreased with the rise of DIN. These results suggest that terrestrial runoff and upwelling stimulate nutrient enrichment, and that overgrowing macroalgae has an important influence on the coral communities in northeastern Hainan Island.

Wind modulation of upwelling at the shelf-break front off Patagonia: Observational evidence

NASA Astrophysics Data System (ADS)

Carranza, M. M.; Gille, S. T.; Piola, A. R.; Charo, M.; Romero, S. I.

2017-03-01

The South-Atlantic Patagonian shelf is the largest chlorophyll-a (Chl-a) hot spot in Southern Ocean color images. While a persistent 1500 km long band of high Chl-a along the shelf-break front (SBF) is indicative of upwelling, the mechanisms that drive it are not entirely known. Along-front wind oscillations can enhance upwelling and provide a nutrient pumping mechanism at shelf-break fronts of western boundary currents. Here we assess wind-induced upwelling at the SBF off Patagonia from daily satellite Chl-a and winds, historical hydrographic observations, cross-shelf Chl-a fluorescence transects from two cruises, and in situ winds and water column structure from a mooring site. Satellite Chl-a composites segregated by along-front wind direction indicate that surface Chl-a is enhanced at the SBF with southerly winds and suppressed with northerly winds. Northerly winds also result in enhanced Chl-a further offshore (˜25-50 km). Synoptic transects as well as mean hydrographic sections segregated by along-front winds show isopycnals tilted upward for southerly winds. Spring observations from the mooring also suggest that southerly winds destratify the water column and northerly winds restratify, in agreement with Ekman transport interacting with the front. Moreover, changes in water column temperature lag along-front wind forcing by 2-4 days. Our results suggest that oscillations in along-front winds, on timescales typical of atmospheric storms (2-10 days), can significantly modulate the upwelling and Chl-a concentrations at the SBF off Patagonia, revealing the importance of wind-induced upwelling for shelf-slope exchange at shelf-break fronts of western boundary currents.

The circulation dynamics associated with a northern Benguela upwelling filament during October 2010

NASA Astrophysics Data System (ADS)

Muller, Annethea A.; Mohrholz, Volker; Schmidt, Martin

2013-07-01

Upwelling filaments, a common feature in all the major upwelling systems, are also regularly observed in the Benguela upwelling system and are thought to provide an effective mechanism for the exchange of matter between the shelf and the open ocean. The mesoscale dynamics of a northern Benguela upwelling filament located at approximately 18.5°S were examined and the associated transport was quantified. The development of the filament was tracked using optimal interpolated SST satellite data and two transects were consequently sampled across the feature using a towed undulating CTD (ScanFish). Additional hydrographic, nutrient and biological parameters were investigated at several stations along each transect. Following 7 days of strong upwelling favorable winds, sampling coincided with a period of relative wind relaxation and the filament was presumably in a decaying state. The basic mesoscale structure of the investigated filament corresponded well to what had previously been described for filaments from other eastern boundary current systems. The cross-shore transport associated with the filament was found to be significantly greater than the integrated Ekman transport in the region. With the combination of the high resolution dataset and a MOM-4 ecosystem model the complex mesoscale flow field associated with the feature could be observed and the counterbalancing onshore transport, associated with subsurface dipole eddies, was revealed within the filament. The results further suggest that an interaction between the offshore bending of flow at the Angola-Benguela Front (ABF), the detachment of the strong poleward flow from the coast as the thermal front meanders and the observed dipole eddies may be driving filament occurrence in the region off Cape Frio.

Rapid response to coastal upwelling in a semienclosed bay

NASA Astrophysics Data System (ADS)

Gilcoto, Miguel; Largier, John L.; Barton, Eric D.; Piedracoba, Silvia; Torres, Ricardo; Graña, Rocío.; Alonso-Pérez, Fernando; Villacieros-Robineau, Nicolás.; de la Granda, Francisco

2017-03-01

Bays/estuaries forced by local wind show bidirectional exchange flow. When forced by remote wind, they exhibit unidirectional flow adjustment to coastal sea level. Acoustic Doppler Current Profiler observations over 1 year show that the Ria de Vigo (Iberian Upwelling) responds to coastal wind events with bidirectional exchange flow. The duration of the upwelling and downwelling events, estimated from the current variability, was 3.3 days and 2.6 days, respectively. Vectorial correlations reveal a rapid response to upwelling/downwelling, in which currents lag local wind by <6 h and remote wind by <14 h, less than the Ekman spinup (17.8 h). This rapidity arises from the ria's narrowness (nonrotational local response), equatorward orientation (additive remote and local wind responses), depth greater than the Ekman depth (penetration of shelf circulation into the interior), and vertical stratification (shear reinforcing shelf circulation). Similar rapid responses are expected in other narrow bays where local and remote winds act together and stratification enhances bidirectional flow.

Sensitivity studies with a coupled ice-ocean model of the marginal ice zone

NASA Technical Reports Server (NTRS)

Roed, L. P.

1983-01-01

An analytical coupled ice-ocean model is considered which is forced by a specified wind stress acting on the open ocean as well as the ice. The analysis supports the conjecture that the upwelling dynamics at ice edges can be understood by means of a simple analytical model. In similarity with coastal problems it is shown that the ice edge upwelling is determined by the net mass flux at the boundaries of the considered region. The model is used to study the sensitivity of the upwelling dynamics in the marginal ice zone to variation in the controlling parameters. These parameters consist of combinations of the drag coefficients used in the parameterization of the stresses on the three interfaces atmosphere-ice, atmosphere-ocean, and ice-ocean. The response is shown to be sensitive to variations in these parameters in that one set of parameters may give upwelling while a slightly different set of parameters may give downwelling.

On the subduction of oxygenated surface water in submesoscale cold filaments off Peru.

NASA Astrophysics Data System (ADS)

Thomsen, Soeren; Kanzow, Torsten; Colas, Francois; Echevin, Vincent; Krahmann, Gerd

2015-04-01

The Peruvian upwelling regime is characterized by pronounced submesoscale variability including filaments and sharp density fronts. Submesoscale frontal processes can drive large vertical velocities and enhance vertical tracer fluxes in the upper ocean. The associated high temporal and spatial variability poses a large challenge to observational approaches targeting submesoscale processes. In this study the role of submesoscale processes for both the ventilation of the near-coastal oxygen minimum zone off Peru and the physical-biogeochemical coupling at these scales is investigated. For our study we use satellite based sea surface temperature measurements in combination with multiple high-resolution glider observations of temperature, salinity, oxygen and chlorophyll fluorescence carried out in January and February 2013 off Peru near 14°S during active upwelling. Additionally, high-resolution regional ocean circulation model outputs (ROMS) are analysed. At the beginning of our observations a previously upwelled, productive and highly oxygenated body of water is found within the mixed layer. Subsequently, a cold filament forms and the waters are moved offshore. After the decay of the filament and the relaxation of the upwelling front, the oxygen enriched surface water is found within the previously less oxygenated thermocline suggesting the occurrence of frontal subduction. A numerical model simulation is used to analyse the evolution of passive tracers and Lagrangian floats within several upwelling filaments, whose vertical structure and hydrographic properties agree well with the observations. The simulated temporal evolution of the tracers and floats support our interpretation that the subduction of previously upwelled water indeed occurs within cold filaments off Peru. Filaments are common features within eastern boundary upwelling systems, which all encompass large oxygen minimum zones. However, most state of-the-art large and regional scale physical-biogeochemical ocean models do not resolve submesoscale filaments and the associated downward transport of oxygen and other solutes. Even if the observed subduction event only reaches into the still oxygenated thermocline the associated ventilation mechanism likely influences the shape and depth of the upper boundary of oxygen minimum zones, which would probably be even shallower without this process.

Oxygen cycling in the northern Benguela Upwelling System: Modelling oxygen sources and sinks

NASA Astrophysics Data System (ADS)

Schmidt, Martin; Eggert, Anja

2016-12-01

This paper elucidates the oxygen dynamics in the northern Benguela Upwelling System by means of process oriented, numerical modelling. Owing to the complex physical-biological interaction in this system, a coupled hydrodynamic-biogeochemical model is required to grasp the various aspects of the oxygen dynamics. We used high-resolution atmospheric fields derived from observations to force our model, available since 1999. The model results represent a 15 years, consistent data set of realistic hydrographic and ecosystem variables, including oxygen distribution patterns. After a concise description of the main aspects of the model, we use the model data to analyse the components contributing to the oxygen dynamics, namely, the ocean circulation, the exchange between ocean and atmosphere as well as the local biogeochemical oxygen cycling in the system. We thoroughly validate the model with available field observations and remote sensing data. The strengths of coastal upwelling, which controls the nutrient supply to the euphotic zone, as well as the poleward undercurrent that carries oxygen and nutrients to the shelf in the northern Benguela Upwelling System are well reproduced in the model. Among the biological oxygen sinks, mineralisation in the sediment, respiration of zooplankton and nitrification in the water column are important. We also found that vertical migration of zooplankton in response to the oxygen conditions provides a regulating feedback, which may prevent a complete deoxygenation of suboxic waters. As long as oxygen or nitrate are available in the bottom waters, the activities of chemolithoautotrophic sulphur bacteria on the sediment surface keep the redoxcline within the sediment and prevent the release of hydrogen sulphide into the water column. By horizontal integration of the simulated ocean-atmosphere oxygen flux, it can be shown that the Kunene upwelling cell between 16 ° S and 18 ° S is a boundary between the equatorial ocean, characterise by weak oxygen release to the atmosphere, and the subtropical Benguela Upwelling System governed by an enhanced and seasonal varying flux. Furthermore, a comparison of oxygen fluxes controlled by physical transport versus biogeochemical processes shows that the physical processes dominate in the northern Benguela Upwelling System.

Dynamical consequences of compositional and thermal density stratification beneath spreading centers

NASA Technical Reports Server (NTRS)

Sotin, C.; Parmentier, E. M.

1989-01-01

Dynamical consequences of compositional buoyancy and the combined effects of compositional and thermal buoyancy on mantle flow and crustal production are explored. The results show that for a low enough mantle viscosity, buoyant upwelling can significantly enhance the crustal thickness relative to that which would be produced by plate spreading alone, while for a mantle viscosity of 10 to the 22nd Pa s, upwelling due to plate spreading is dominant and crustal thickness is predicted to be a function of spreading rate. The results indicate that thermal and compositional density variations result in opposing buoyancy forces that can cause time-dependent upwelling.

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

Whitledge, T E

The regeneration of nitrogen is an important process that increases the efficiency of the upwelling ecosystem by enlarging their spatial scales. Ammonium regeneration was considered to contribute 42 to 72 percent of phytoplankton nitrogen requirements in the northwest Africa, Peru, and Baja California upwelling systems. Zooplankton are responsible for the largest portion of regenerated nitrogen; however, fish and benthic sediments may be nearly as large. Comparisons of the importance of ammonium regeneration in upwelling areas with coastal and open ocean regions indicate that the percentage contributions are similar. Future nutrient regeneration studies are needed to assess the recycling of benthicmore » sediments, microzooplankton, gelatinous zooplankton, demersal fish, bacterioplankton, and mollusks.« less

A Comparison of the Role of Episode Nutrient Supply on Pathways of Carbon in Upwelling Regimes

NASA Technical Reports Server (NTRS)

Carr, M. E.

1997-01-01

Nutrient supply is episode in the ocean even in regions of fairly high and continuous nutrient supply, such as coastal upwelling regimes. The structure of the ecosystem depends on nutrient availability and the different requirements of phytoplankton cells.

Short-term meso-scale variability of mesozooplankton communities in a coastal upwelling system (NW Spain)

NASA Astrophysics Data System (ADS)

Roura, Álvaro; Álvarez-Salgado, Xosé A.; González, Ángel F.; Gregori, María; Rosón, Gabriel; Guerra, Ángel

2013-02-01

The short-term, meso-scale variability of the mesozooplankton community present in the coastal upwelling system of the Ría de Vigo (NW Spain) has been analysed. Three well-defined communities were identified: coastal, frontal and oceanic, according to their holoplankton-meroplankton ratio, richness, and total abundance. These communities changed from summer to autumn due to a shift from downwelling to upwelling-favourable conditions coupled with taxa dependent changes in life strategies. Relationships between the resemblance matrix of mesozooplankton and the resemblance matrices of meteorologic, hydrographic and community-derived biotic variables were determined with distance-based linear models (DistLM, 18 variables), showing an increasing amount of explained variability of 6%, 16.1% and 54.5%, respectively. A simplified model revealed that the variability found in the resemblance matrix of mesozooplankton was mainly described by the holoplankton-meroplankton ratio, the total abundance, the influence of lunar cycles, the upwelling index and the richness; altogether accounting for 64% of the total variability. The largest variability of the mesozooplankton resemblance matrix (39.6%) is accounted by the holoplankton-meroplankton ratio, a simple index that describes appropriately the coastal-ocean gradient. The communities described herein kept their integrity in the studied upwelling and downwelling episodes in spite of the highly advective environment off the Ría de Vigo, presumably due to behavioural changes in the vertical position of the zooplankton.

Why coastal upwelling is expected to increase along the western Iberian Peninsula over the next century?

PubMed

Sousa, Magda Catarina; deCastro, Maite; Alvarez, Ines; Gomez-Gesteira, Moncho; Dias, João Miguel

2017-08-15

Former studies about coastal upwelling along the Western Iberian Peninsula (WIP) using historical data indicated contradictory results, showing either its strengthening or reduction, while previous studies using Global Climate Models (GCMs) indicated that global warming is likely to intensify this phenomenon although predicting different rates and not justifying the patterns found. Taking advantage of the recent high spatial resolution Regional Climate Models (RCMs) projections from EURO-CORDEX project (Representative Concentration Pathway, RCP 8.5), detailed higher accuracy estimations of the spatio-temporal trends of Upwelling Index (UI) along the WIP coast were performed in this study, integrating the coastal mesoscale effects within the framework of climate change. Additionally, this research brings new insights about the origin of the WIP coastal upwelling intensification over the next century. These new projections clarified the upwelling strengthening rates predicted along the coast of the WIP from 2006 to 2099 revealing more prominent changes in the northern limit of the region (25-30m 3 s -1 km -1 per decade between 41.5 and 42.5°N). Trends observed at high latitudes of the region were found to be induced by the displacement of the Azores High, which will intensify (0.03hPa per decade) and drift northeastward (10km per decade) during the 21st century. Copyright © 2017 Elsevier B.V. All rights reserved.

UPWELLING EFFECTS ON THE DISTRIBUTION OF NITRATE IN YAQUINA BAY, A COASTAL OREGON ESTUARY

EPA Science Inventory

Coastal Oregon in the summer is dominated by northwesterly winds. Upwelling of nutrient-rich water into the nearshore is controlled by the velocity and duration of these summer winds. Yaquina Bay estuary is a mesotidal drowned river valley that is typically vertically well-mixed ...

Differences in coastal and oceanic SST trends north of Yucatan Peninsula

NASA Astrophysics Data System (ADS)

Varela, R.; Costoya, X.; Enriquez, C.; Santos, F.; Gómez-Gesteira, M.

2018-06-01

The coastal area north of Yucatan has experienced a cooling SST trend from 1982 to 2015 during the upwelling season (May-September) that contrasts with the warming observed at the adjacent ocean area. Different drivers were analyzed to identify the possible causes of that unusual coastal cooling. Changes in coastal upwelling and in sea-atmosphere heat fluxes are not consistent with the observed coastal cooling. The eastward shift of the Yucatan Current observed over the last decades is hypothesized as the most probable cause of coastal cooling. This shift enhances the vertical transport of cold deeper water to the continental shelf from where it is pumped to the surface by upwelling favorable westerly winds.

Evaluation of ERTS data for certain oceanographic uses. [upwelling, water circulation, and pollution in Great Lakes

NASA Technical Reports Server (NTRS)

Strong, A. E. (Principal Investigator)

1973-01-01

The author has identified the following significant results. Upwelling along the eastern shore of Lake Michigan was occurring during the 3 and 21 August 1973 visits by ERTS-1. The NOAA-2 VHRR thermal-IR data are being digitized for comparison. Early indications are that these upwellings induced a calcium carbonate precipitate to form in the surface waters. It is most pronounced in the MSS-4 channel. On the lake bottom this jell-like sediment is known as marl and adds to the eutrophication of the lake. This phenomenon may help to explain the varve-like nature of bottom cores that have been observed in the Great Lakes.

A simple predictive model for the structure of the oceanic pycnocline

PubMed

Gnanadesikan

1999-03-26

A simple theory for the large-scale oceanic circulation is developed, relating pycnocline depth, Northern Hemisphere sinking, and low-latitude upwelling to pycnocline diffusivity and Southern Ocean winds and eddies. The results show that Southern Ocean processes help maintain the global ocean structure and that pycnocline diffusion controls low-latitude upwelling.

Mantle upwellings and convective instabilities revealed by seismic tomography and helium isotope geochemistry beneath eastern Africa

NASA Astrophysics Data System (ADS)

Montagner, Jean-Paul; Marty, Bernard; Stutzmann, Eléonore; Sicilia, Déborah; Cara, Michel; Pik, Raphael; Lévêque, Jean-Jacques; Roult, Geneviève; Beucler, Eric; Debayle, Eric

2007-11-01

The relationship between intraplate volcanism and continental tectonics has been investigated for North and East Africa using a high resolution three-dimensional anisotropic tomographic model derived from seismic data of a French experiment ``Horn of Africa'' and existing broadband data. The joint inversion for seismic velocity and anisotropy of the upper 400 km of the mantle, and geochemical data reveals a complex interaction between mantle upwellings, and lithosphere. Two kinds of mantle upwellings can be distinguished: The first one, the Afar ``plume'' originates from deeper than 400 km and is characterized by enrichment in primordial 3He and 3He/4He ratios higher than those along mid-ocean ridges (MOR). The second one, associated with other Cenozoic volcanic provinces (Darfur, Tibesti, Hoggar, Cameroon), with 3He/4He ratios similar to, or lower than MOR, is a consequence of shallower upwelling. The presumed asthenospheric convective instabilities are oriented in an east-west direction, resulting from interaction between south-north asthenospheric mantle flow, main plume head and topography on the base of lithosphere.

Impact of Equatorial Waves on the Variability of Upwelling Process Along West Coast of India

NASA Astrophysics Data System (ADS)

Prakash, K. R.; Nigam, T.; Pant, V.

2017-12-01

Coastal upwelling is a seasonal phenomenon along the south eastern Arabian Sea (SEAS) due to favourable wind setup during Indian Summer Monsoon Season (June-September). This upwelling brings subsurface cold and nutrient rich water to the surface layers. The cold water transported northward by the altered along shore current of west coast of India in the post-monsoon season. The different climatological forcing of positive Indian Ocean Dipole (IOD) and normal years were utilised to simulate the upwelling off the west coast of India using a three dimensional Regional Ocean Modelling System (ROMS). Strength of upwelling and the northward transport were found to be weaken for positive IOD simulations as compared to normal years. Analysis suggests that the meridional wind stress weakening resulted into a decrease in strength of West India Coastal Current (WICC) and, therefore, reduced magnitude of offshore Ekman transport. The mixed layer heat budget calculation also supports the findings by showing dominated vertical process in comparison to net heat flux effect. The post-monsoon northward transport of cold water was found to be correlated with the coastally trapped downwelling Kelvin waves. These waves are the only remote forcing from the Bay of Bengal that reaches to the south-eastern Arabian Sea during the months of October-December. The composite of sea surface height anomalies for the positive IOD and normal years shows that the downwelling Kelwin wave was absent during October-December.

Jurassic-Cretaceous paleogeography, paleoclimate and upwelling of the northern margin of Tethys

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

Golonka, J.; Krobicki, M.

The Jurassic and Cretaceous global paleogeographic reconstructions illustrate the changing configuration of mountains, land, shallow seas and deep ocean basins. Active plate boundaries, such as spreading centers and subduction zones, are also shown. The Pliensbachian, Toarcian, Bathonian, Oxfordian-Kimmeridgian, Tithonian-Berriasian, Valanginian, Albian, Turonian and Maastrichtian maps were generated The outlines of paleogeography are used as input for paleoclimatic modeling. The PALEOCLIMATE program models global atmospheric pressure, derive paleo-wind directions and estimate the likelihood of coastal upwelling. The program is based on the paleoclimatic methods first developed by Judith Parrish, adopted by C. R. Scotese and modified by M. I. Ross. Themore » maps depict air pressure, wind directions, humid zones and areas favorable for upwelling conditions plotted on the paleogeographic background. Paleoclimate modeling suggests that prevailing Jurassic-Cretaceous wind directions in the northern Tethys area were from north-northeast. These winds were parallel to the axis of Czorsztyn ridge. The ridge was uplifted between Magura and Pieniny basins as the result of extension during Jurassic supercontinent breakup. The upwelling may have been induced at the southeastern margin of the ridge. The model is consistent with rock records, especially from the upper part of ammonitico rosso type Czorsztyn formation. Mass occurrence of Tithonian and Berriasian brachiopods was probably controlled by upwelling-induced trophic relationships which is resulted in the intense growth of benthic organisms on the ridge. This is additionally supported by the presence of phosphorites at localities which corresponded to the continental shelf/slope transition.« less

Phytoplankton dynamics in relation to seasonal variability and upwelling and relaxation patterns at the mouth of Ria de Aveiro (West Iberian Margin) over a four-year period

PubMed Central

Calado, António José; Moita, Maria Teresa; Cunha, Marina R.

2017-01-01

From June 2004 to December 2007, samples were weekly collected at a fixed station located at the mouth of Ria de Aveiro (West Iberian Margin). We examined the seasonal and inter-annual fluctuations in composition and community structure of the phytoplankton in relation to the main environmental drivers and assessed the influence of the oceanographic regime, namely changes in frequency and intensity of upwelling events, over the dynamics of the phytoplankton assemblage. The samples were consistently handled and a final subset of 136 OTUs (taxa with relative abundance > 0.01%) was subsequently submitted to various multivariate analyses. The phytoplankton assemblage showed significant changes at all temporal scales but with an overriding importance of seasonality over longer- (inter-annual) or shorter-term fluctuations (upwelling-related). Sea-surface temperature, salinity and maximum upwelling index were retrieved as the main driver of seasonal change. Seasonal signal was most evident in the fluctuations of chlorophyll a concentration and in the high turnover from the winter to spring phytoplankton assemblage. The seasonal cycle of production and succession was disturbed by upwelling events known to disrupt thermal stratification and induce changes in the phytoplankton assemblage. Our results indicate that both the frequency and intensity of physical forcing were important drivers of such variability, but the outcome in terms of species composition was highly dependent on the available local pool of species and the timing of those events in relation to the seasonal cycle. We conclude that duration, frequency and intensity of upwelling events, which vary seasonally and inter-annually, are paramount for maintaining long-term phytoplankton diversity likely by allowing unstable coexistence and incorporating species turnover at different scales. Our results contribute to the understanding of the complex mechanisms of coastal phytoplankton dynamics in relation to changing physical forcing which is fundamental to improve predictability of future prospects under climate change. PMID:28472179

Phytoplankton dynamics in relation to seasonal variability and upwelling and relaxation patterns at the mouth of Ria de Aveiro (West Iberian Margin) over a four-year period.

PubMed

Vidal, Tânia; Calado, António José; Moita, Maria Teresa; Cunha, Marina R

2017-01-01

From June 2004 to December 2007, samples were weekly collected at a fixed station located at the mouth of Ria de Aveiro (West Iberian Margin). We examined the seasonal and inter-annual fluctuations in composition and community structure of the phytoplankton in relation to the main environmental drivers and assessed the influence of the oceanographic regime, namely changes in frequency and intensity of upwelling events, over the dynamics of the phytoplankton assemblage. The samples were consistently handled and a final subset of 136 OTUs (taxa with relative abundance > 0.01%) was subsequently submitted to various multivariate analyses. The phytoplankton assemblage showed significant changes at all temporal scales but with an overriding importance of seasonality over longer- (inter-annual) or shorter-term fluctuations (upwelling-related). Sea-surface temperature, salinity and maximum upwelling index were retrieved as the main driver of seasonal change. Seasonal signal was most evident in the fluctuations of chlorophyll a concentration and in the high turnover from the winter to spring phytoplankton assemblage. The seasonal cycle of production and succession was disturbed by upwelling events known to disrupt thermal stratification and induce changes in the phytoplankton assemblage. Our results indicate that both the frequency and intensity of physical forcing were important drivers of such variability, but the outcome in terms of species composition was highly dependent on the available local pool of species and the timing of those events in relation to the seasonal cycle. We conclude that duration, frequency and intensity of upwelling events, which vary seasonally and inter-annually, are paramount for maintaining long-term phytoplankton diversity likely by allowing unstable coexistence and incorporating species turnover at different scales. Our results contribute to the understanding of the complex mechanisms of coastal phytoplankton dynamics in relation to changing physical forcing which is fundamental to improve predictability of future prospects under climate change.

Linking the Modern and Recent Record of Cabo Frio Upwelling with Local Climate and Biogeochemical Processes in Hypersaline Coastal Lagoons, Região dos Lagos, Rio de Janeiro, Brazil

NASA Astrophysics Data System (ADS)

McKenzie, J. A.; Nascimento, G. S.; Albuquerque, A. L.; Belem, A. L.; Carreira, R.; Eglinton, T. I.; Vasconcelos, C.

2015-12-01

A unique marine and lagoonal system along the coast east of Rio de Janeiro is being investigated to understand the impact of climatic variability on the South Atlantic carbon cycle and biomineralisation processes involved in carbonate precipitation in the hypersaline coastal lagoons. The region is dominated by a semi-arid microclimate attributed to the local coastal upwelling phenomenon near Cabo Frio. The intensity of the upwelling affects the hydrology of the annual water and biogeochemical cycles in the lagoons, as well as biogeochemical signals of environmental change recorded in both onshore and offshore sediments. Preliminary results of δ18O and δD values of water samples collected monthly in Lagoa Vermelha and Brejo do Espinho from 2011 to 2014 show lower values for waters corresponding to the wet season, reflecting increased input of meteoric water. The higher values for waters collected during the dry season reflect the greater amount of evaporation with increased seasonal aridity. Radiocarbon dating of Holocene marine and lagoonal cores indicates that Mg-carbonate precipitation in the lagoons is associated with high evaporation. Modern field observations for the last 3 years suggest that the amount of carbonate precipitation is correlated with evaporitic conditions associated with the upwelling phenomenon. A calibration study of hydrogen isotopic fractionation in the modern lagoons is underway to define a relationship between δDlipid of suspended particles and δDwater of associated water. This isotopic relationship will be applied to material obtained in cores from the lagoons. Offshore cores will be studied using well-tested paleotemperature proxies to evaluate the intensity of the upwelling during the Holocene. In summary, linking the coastal upwelling with the lagoonal hydrology has the potential to furnish important insights about the relationship between the local climate and paleoceanographic circulation associated with the regional carbon cycle.

Export of pre-aged, labile DOM from a central California coastal upwelling system: Insights from D/L amino acids and Δ14C signatures

NASA Astrophysics Data System (ADS)

Walker, B. D.; Shen, Y.; Benner, R. H.; Druffel, E. R. M.

2014-12-01

Coastal upwelling zones are among the most productive regions in the world and play a major role in global carbon and nitrogen cycles. Recent research suggests that a substantial fraction of newly fixed organic matter is exported offshore in the form of dissolved organic matter (DOM). However, to date only a few studies have examined DOM composition in the context of production and export from upwelling systems. The ultimate fate and geochemical impact of coastal DOM exported to offshore and mesopelagic ecosystems also remains largely unknown. Between 2007-2009 we conducted a high-resolution biogeochemical time series at the Granite Canyon Marine Pollution Studies Lab in part to evaluate the seasonal production and export of DOM from the Central CA coast. Our previous work demonstrated substantial, albeit disparate, seasonal production of dissolved organic carbon and nitrogen (DOC, DON) - with high DON (and low C:N ratios) produced during upwelling and high DOC produced during summer/fall water column stratification (Walker and McCarthy, 2012). Here we present new total dissolved D/L amino acid (TDAA) and UV-oxidizable DOC radiocarbon (Δ14C) data with the goal of determining the relative sources (heterotrophic vs. autotrophic), bioavailability, microbial processing and 14C-ages of C-rich vs. N-rich DOM exported from this upwelling system. Our results suggest that C-rich DOM produced during water column stratification carries a large microbial signature (i.e. high D/L AA ratios and non-protein AA abundance), whereas N-rich DOM produced during upwelling appears to be fresh, autotrophic DOM (i.e. lowest D/L AA ratios and highest TDAA abundance). DOM Δ14C signatures also did not approximate in situ dissolved inorganic carbon (DIC), and instead were far more negative and highly correlated to water mass density. Together our results indicate a previously unrecognized source of highly labile yet pre-aged DOM potentially impacting offshore and mesopelagic ecosystems.

Wind-induced upwelling in the Kerguelen Plateau region

NASA Astrophysics Data System (ADS)

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

2014-11-01

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

Phosphorus cycling in the red tide incubator region of monterey bay in response to upwelling.

PubMed

Mackey, Katherine R M; Mioni, Cécile E; Ryan, John P; Paytan, Adina

2012-01-01

This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in northeastern Monterey Bay (the Red Tide Incubator region) of coastal California, with particular emphasis on how bacteria and phytoplankton that form harmful algal blooms mediate and respond to changes in P availability. In situ measurements of nutrient concentrations, phytoplankton community composition, and cell-specific alkaline phosphatase (AP) activity (determined via enzyme-labeled fluorescence assay) were measured during three cruises. Upwelling led to a 10-fold increase in dissolved inorganic (DIP) in surface waters, reaching ∼0.5 μmol L(-1). This DIP was drawn down rapidly as upwelling relaxed over a period of 1 week. Ratios of nitrate to DIP drawdown (∼5:1, calculated as the change in nitrate divided by the change in DIP) were lower than the Redfield ratio of 16:1, suggesting that luxury P uptake was occurring as phytoplankton bloomed. Dissolved organic (DOP) remained relatively constant (∼0.3 μmol L(-1)) before and immediately following upwelling, but doubled as upwelling relaxed, likely due to phytoplankton excretion and release during grazing. This transition from a relatively high DIP:DOP ratio to lower DIP:DOP ratio was accompanied by a decline in the abundance of diatoms, which had low AP activity, toward localized, spatially heterogeneous blooms of dinoflagellates in the genera Prorocentrum, Ceratium, Dinophysis, Alexandrium, and Scrippsiella that showed high AP activity regardless of ambient DIP levels. A nutrient addition incubation experiment showed that phytoplankton growth was primarily limited by nitrate, followed by DIP and DOP, suggesting that P regulates phytoplankton physiology and competition, but is not a limiting nutrient in this region. AP activity was observed in bacteria associated with lysed cell debris and aggregates of particulate organic material, where it may serve to facilitate P regeneration, as well as affixed to the surfaces of intact phytoplankton cells, possibly indicative of close, beneficial phytoplankton-bacteria interactions.

Phosphorus Cycling in the Red Tide Incubator Region of Monterey Bay in Response to Upwelling

PubMed Central

Mackey, Katherine R. M.; Mioni, Cécile E.; Ryan, John P.; Paytan, Adina

2012-01-01

This study explores the cycling of phosphorus (P) in the euphotic zone following upwelling in northeastern Monterey Bay (the Red Tide Incubator region) of coastal California, with particular emphasis on how bacteria and phytoplankton that form harmful algal blooms mediate and respond to changes in P availability. In situ measurements of nutrient concentrations, phytoplankton community composition, and cell-specific alkaline phosphatase (AP) activity (determined via enzyme-labeled fluorescence assay) were measured during three cruises. Upwelling led to a 10-fold increase in dissolved inorganic (DIP) in surface waters, reaching ∼0.5 μmol L−1. This DIP was drawn down rapidly as upwelling relaxed over a period of 1 week. Ratios of nitrate to DIP drawdown (∼5:1, calculated as the change in nitrate divided by the change in DIP) were lower than the Redfield ratio of 16:1, suggesting that luxury P uptake was occurring as phytoplankton bloomed. Dissolved organic (DOP) remained relatively constant (∼0.3 μmol L−1) before and immediately following upwelling, but doubled as upwelling relaxed, likely due to phytoplankton excretion and release during grazing. This transition from a relatively high DIP:DOP ratio to lower DIP:DOP ratio was accompanied by a decline in the abundance of diatoms, which had low AP activity, toward localized, spatially heterogeneous blooms of dinoflagellates in the genera Prorocentrum, Ceratium, Dinophysis, Alexandrium, and Scrippsiella that showed high AP activity regardless of ambient DIP levels. A nutrient addition incubation experiment showed that phytoplankton growth was primarily limited by nitrate, followed by DIP and DOP, suggesting that P regulates phytoplankton physiology and competition, but is not a limiting nutrient in this region. AP activity was observed in bacteria associated with lysed cell debris and aggregates of particulate organic material, where it may serve to facilitate P regeneration, as well as affixed to the surfaces of intact phytoplankton cells, possibly indicative of close, beneficial phytoplankton–bacteria interactions. PMID:22347222

Microbial Diversity of a Brazilian Coastal Region Influenced by an Upwelling System and Anthropogenic Activity

PubMed Central

Cury, Juliano C.; Araujo, Fabio V.; Coelho-Souza, Sergio A.; Peixoto, Raquel S.; Oliveira, Joana A. L.; Santos, Henrique F.; Dávila, Alberto M. R.; Rosado, Alexandre S.

2011-01-01

Background Upwelling systems are characterised by an intense primary biomass production in the surface (warmest) water after the outcrop of the bottom (coldest) water, which is rich in nutrients. Although it is known that the microbial assemblage plays an important role in the food chain of marine systems and that the upwelling systems that occur in southwest Brazil drive the complex dynamics of the food chain, little is known about the microbial composition present in this region. Methodology/Principal Findings We carried out a molecular survey based on SSU rRNA gene from the three domains of the phylogenetic tree of life present in a tropical upwelling region (Arraial do Cabo, Rio de Janeiro, Brazil). The aim was to analyse the horizontal and vertical variations of the microbial composition in two geographically close areas influenced by anthropogenic activity (sewage disposal/port activity) and upwelling phenomena, respectively. A lower estimated diversity of microorganisms of the three domains of the phylogenetic tree of life was found in the water of the area influenced by anthropogenic activity compared to the area influenced by upwelling phenomena. We observed a heterogenic distribution of the relative abundance of taxonomic groups, especially in the Archaea and Eukarya domains. The bacterial community was dominated by Proteobacteria, Cyanobacteria and Bacteroidetes phyla, whereas the microeukaryotic community was dominated by Metazoa, Fungi, Alveolata and Stramenopile. The estimated archaeal diversity was the lowest of the three domains and was dominated by uncharacterised marine Crenarchaeota that were most closely related to Marine Group I. Conclusions/Significance The variety of conditions and the presence of different microbial assemblages indicated that the area of Arraial do Cabo can be used as a model for detailed studies that contemplate the correlation between pollution-indicating parameters and the depletion of microbial diversity in areas close to anthropogenic activity; functional roles and geochemical processes; phylogeny of the uncharacterised diversity; and seasonal variations of the microbial assemblages. PMID:21304582

Upwelling Measurement Issues at the CERES Ocean Validation Experiment (COVE)

NASA Astrophysics Data System (ADS)

Fabbri, B. E.; Schuster, G. L.; Denn, F. M.; Arduini, R. F.; Madigan, J. J.; Rutan, D. A.

2016-12-01

The Clouds and the Earth's Radiant Energy System (CERES) satellite measures both solar-reflected and Earth-emitted radiation from the Earth's surface to the top of the atmosphere. One surface validation site is located at Chesapeake Light Station, approximately 25 kilometers east of Virginia Beach, Virginia (coordinates: 36.90N, 75.71W). In 1999, the CERES Ocean Validation Experiment (COVE) was established at Chesapeake Light Station. COVE is in its 17th year collecting radiometric and meteorological data. Other measurements over this time period include aerosol optical depth, water leaving radiance, precipitable water vapor and more. The issues we are trying to resolve for the upwelling flux are two-fold. First, there is the "shadow effect". In the morning, the shadow of the tower appears on the water in the field of view underneath the shortwave (SW) and longwave (LW) upwelling instruments. An attempt to understand the shading effect is made by separating the data into "shaded" and "unshaded" time periods using the Solar Azimuth (SA) angle. SA < 180 degrees are considered shaded, and SA > 180 degrees are considered unshaded. Upwelling SW shaded and unshaded datasets differ by a maximum of 9.5 W/m2 and a minimum of -0.7 W/m2 with the delta mean resulting in 3.6 W/m2. Upwelling LW shaded and unshaded datasets differ by a maximum of 8.0 W/m2 and a minimum of 1.0 W/m2 with the delta mean resulting in 3.7 W/m2. The second issue is the "tower radiating effect" which is especially noticeable on clear, sunny days. During these days, the tower tends to heat up and radiate extra heat energy that is measured by the LW instrument. We compare Infrared Radiation Thermometer (IRT) measurements to Precision Infrared Radiometer (PIR) measurements and make a case for using IRT measurements as upwelling LW.

Evaluation of the saturation state of Aragonite, at Baja California Coast, Mexico

NASA Astrophysics Data System (ADS)

Oliva, N. L.; Hernandez, J. M.; Camacho, V.; Deldagillo, F.; Torres, V.; Siqueiros-Valencia, A.; Castro, R.

2012-12-01

The carbonate ion is in excess in the surface waters of the world's ocean, and is necessary for the formation of carbonate structures such as oyster shells and echinoderm skeletons. Seasonal upwelling in the California Current system brings dense water with high partial pressure of carbon dioxide to the sea surface and into contact with the atmosphere in the near shore. In order to evaluate the saturation state of Aragonite (ΩA), from November 2009 to November 2011, biweekly monitoring of dissolved inorganic carbon (CID), total alkalinity (TA), temperature (T) and salinity (S), in the intertidal zone at "Arbolitos" was conducted. During the same period, a mooring buoy located 3 km from Arbolitos recorded data every 3 hours for T and carbon dioxide partial pressure (pCO2), at the sea and in the air 1 meter above the sea surface.The ΩA was calculated for both study sites where upwelling events occurred during the spring-summer months. The data at both Arbolitos and mooring buoy shows that during the upwelling season maximum DIC concentration (2150μmol kg -1) and maximum pCO2 (863 μatm) correspond to the lowest temperature (11°C) and ΩA values (1; equilibrium). During the ten upwelling events identified (T < 15 °C, pCO2 > 387 μatm), the ΩA values (3 to 1) were not lower than the saturation limit (value of 1).The results show that the calcifying organisms in this region are persisting in an environment with variable ΩA conditions. It was determined that the longer the duration of the upwelling event, the lower the ΩA value, and the higher the change in pCO2. The ΩA interval (approximately 3 to 1) is not the same from year to year. This suggests interannual variations in upwelling, possibly due to El Niño (present during the first six months of 2010), and La Niña conditions (from July 2010 to November 2011).; t; Characteristics of the ten events of upwelling, at arbolitos and at the moorign buoy. For both study sites it shows the duration, pCO2, ΩA y pH values.

Seasonal cycle of the mixed-layer heat and freshwater budget in the eastern tropical Atlantic

NASA Astrophysics Data System (ADS)

Rath, Willi; Dengler, Marcus; Lüdke, Jan; Schmidtko, Sunke; Schlundt, Michael; Brandt, Peter; Partners, Preface

2016-04-01

A new seasonal mixed-layer heat flux climatology is used to explore the mechanisms driving seasonal variability of sea surface temperature and salinity in the eastern tropical Atlantic (ETA) with a focus on the eastern boundary upwelling regions. Until recently, large areas at the continental margins of the ETA were not well covered by publically available hydrographic data hampering a detailed understanding of the involved processes. In a collaborative effort between African and European partners within the EU-funded PREFACE program, a new seasonal climatology for different components of the heat and freshwater budget was compiled for the ETA using all publically available hydrographic data sets and a large trove of previously not-publically available hydrographic measurements from the territorial waters of western African countries, either from national programs or from the FAO supported EAF-Nansen program. The publically available data includes hydrographic data from global data repositories including most recent ARGO floats and glider measurements. This data set was complemented by velocity data from surface drifter and ARGO floats to allow determining horizontal heat and freshwater advection. Monthly means of air-sea heat fluxes were derived from the TropFlux climatology while precipitation rates were derived from monthly mean fields of the Global Precipitation Climatology Project. Finally, microstructure data from individual measurement campaigns allow estimating diapycnal heat and salt fluxes for certain regions during specific months. A detailed analysis of the seasonal cycle of mixed-layer heat and freshwater balance in previously poorly covered regions in the eastern tropical Atlantic upwelling is presented. In both eastern boundary upwelling region, off Senegal/Mauritania and off Angola/Namibia, average net surface heat fluxes warm the mixed layer at a rate between 50 and 80 W/m2 with maxima in the respective summer seasons. Horizontal advection contributed to cooling of the mixed layer but a residual cooling term remains in both upwelling regions. A surprising result is that this residual is largest in the Angolan upwelling region, where upwelling-favourable winds are generally weaker than off Namibia and in the north-eastern upwelling region. The contributions of windstress-derived vertical advection and diapycnal heat and freshwater fluxes are discussed. In addition, the TropFlux climatology is evaluated against radiative and turbulent ocean-atmosphere heat and freshwater fluxes derived from ship-board observations.

Narrowing of the Upwelling Branch of the Brewer-Dobson Circulation and Hadley Cell in Chemistry-Climate Model Simulations of the 21st Century

NASA Technical Reports Server (NTRS)

Li, Feng; Stolarski, Richard S.; Pawson, Steven; Newman, Paul A.; Waugh, Darryn

2010-01-01

Changes in the width of the upwelling branch of the Brewer-Dobson circulation and Hadley cell in the 21st Century are investigated using simulations from a coupled chemistry-climate model. In these model simulations the tropical upwelling region narrows in the troposphere and lower stratosphere. The narrowing of the Brewer-Dobson circulation is caused by an equatorward shift of Rossby wave critical latitudes and Eliassen-Palm flux convergence in the subtropical lower stratosphere. In the troposphere, the model projects an expansion of the Hadley cell's poleward boundary, but a narrowing of the Hadley rising branch. Model results suggest that the narrowing of the Hadley cell ascent is also eddy-driven.

Do submesoscale frontal processes ventilate the oxygen minimum zone off Peru?

NASA Astrophysics Data System (ADS)

Thomsen, S.; Kanzow, T.; Colas, F.; Echevin, V.; Krahmann, G.; Engel, A.

2016-08-01

The Peruvian upwelling system encompasses the most intense and shallowest oxygen minimum zone (OMZ) in the ocean. This system shows pronounced submesoscale activity like filaments and fronts. We carried out glider-based observations off Peru during austral summer 2013 to investigate whether submesoscale frontal processes ventilate the Peruvian OMZ. We present observational evidence for the subduction of highly oxygenated surface water in a submesoscale cold filament. The subduction event ventilates the oxycline but does not reach OMZ core waters. In a regional submesoscale-permitting model we study the pathways of newly upwelled water. About 50% of upwelled virtual floats are subducted below the mixed layer within 5 days emphasizing a hitherto unrecognized importance of subduction for the ventilation of the Peruvian oxycline.

Analysis of longwave radiation for the Earth-atmosphere system

NASA Technical Reports Server (NTRS)

Tiwari, S. N.; Venuru, C. S.; Subramanian, S. V.

1983-01-01

Accurate radiative transfer models are used to determine the upwelling atmospheric radiance and net radiative flux in the entire longwave spectral range. The validity of the quasi-random band model is established by comparing the results of this model with those of line-by-line formulations and with available theoretical and experimental results. Existing radiative transfer models and computer codes are modified to include various surface and atmospheric effects (surface reflection, nonequilibrium radiation, and cloud effects). The program is used to evaluate the radiative flux in clear atmosphere, provide sensitivity analysis of upwelling radiance in the presence of clouds, and determine the effects of various climatological parameters on the upwelling radiation and anisotropic function. Homogeneous and nonhomogeneous gas emissivities can also be evaluated under different conditions.

Skylab investigation of the upwelling off the Northwest coast of Africa

NASA Technical Reports Server (NTRS)

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

1975-01-01

The upwelling off the NW coast of Africa in the vicinity of Cape Blanc was studied in February - March 1974 from aircraft and in September 1973 from Skylab. The aircraft study was designed to determine the effectiveness of a differential radiometer in quantifying surface chlorophyll concentrations. Photographic images of the S190A Multispectral Camera and the S190B Earth Terrain Camera from Skylab were used to study distributional patterns of suspended material and to locate ocean color boundaries. The thermal channel of the S192 Multispectral Scanner was used to map sea-surface temperature distributions offshore of Cape Blanc. Correlating ocean color changes with temperature gradients is an effective method of qualitatively estimating biological productivity in the upwelling region off Africa.

Vibrio diversity and dynamics in the Monterey Bay upwelling region

PubMed Central

Mansergh, Sarah; Zehr, Jonathan P.

2013-01-01

The Vibrionaceae (Vibrio) are a ubiquitous group of metabolically flexible marine bacteria that play important roles in biogeochemical cycling in the ocean. Despite this versatility, little is known about Vibrio diversity and abundances in upwelling regions. The seasonal dynamics of Vibrio populations was examined by analysis of 16S rRNA genes in Monterey Bay (MB), California from April 2006–April 2008 at two long term monitoring stations, C1 and M2. Vibrio phylotypes within MB were diverse, with subpopulations clustering with several different cultured representatives including Allivibrio spp., Vibrio penaecida, and Vibrio splendidus as well as with many unidentified marine environmental bacterial 16S rRNA gene sequences. Total Vibrio population abundances, as well as abundances of a Vibrio sp. subpopulation (MBAY Vib7) and an Allivibrio sp. subpopulation (MBAY Vib4) were examined in the context of environmental parameters from mooring station and CTD cast data. Total Vibrio populations showed some seasonal variability but greater variability was observed within the two subpopulations. MBAY Vib4 was negatively associated with MB upwelling indices and positively correlated with oceanic season conditions, when upwelling winds relax and warmer surface waters are present in MB. MBAY Vib7 was also negatively associated with upwelling indices and represented a deeper Vibrio sp. population. Correlation patterns suggest that larger oceanographic conditions affect the dynamics of the populations in MB, rather than specific environmental factors. This study is the first to target and describe the diversity and dynamics of these natural populations in MB and demonstrates that these populations shift seasonally within the region. PMID:24575086

Characterization of the structure and cross-shore transport properties of a coastal upwelling filament using three-dimensional finite-size Lyapunov exponents

NASA Astrophysics Data System (ADS)

Bettencourt, João. H.; Rossi, Vincent; Hernández-García, Emilio; Marta-Almeida, Martinho; López, Cristóbal

2017-09-01

The three-dimensional structure, dynamics, and dispersion characteristics of a simulated upwelling filament in the Iberian upwelling system are analyzed using Lagrangian tools. We used a realistic regional simulation of the western Iberian shelf which is concomitant with an in situ oceanographic campaign that surveyed the area. We compute 3-D fields of finite-size Lyapunov exponents (FSLE) from 3-D velocity fields and extract the field's ridges to study the spatial distribution and temporal evolution of the Lagrangian Coherent Structures (LCSs) evolving around the filament. We find that the most intense curtain-like LCSs delimit the boundaries of the whole filamentary structure whose general properties match well the observations. The filament interior is characterized by small dispersion of fluid elements. Furthermore, we identify a weak LCS separating the filament into a warmer vein and a colder filament associated with the interaction of a mesoscale eddy with the upwelling front. The cold upwelled water parcels move along the filament conserving their density. The filament itself is characterized by small dispersion of fluid elements in its interior. The comparison of LCSs with potential temperature and salinity gradient fields shows that the outer limits of the filament coincide with regions of large hydrographic gradients, similar to those observed, explaining the isolation of the interior of the filament with the surrounding waters. We conclude that the Lagrangian analysis used in this work is useful in explaining the dynamics of cross-shore exchanges of materials between coastal regions and the open ocean due to mesoscale processes.

Acidification mediated by a river plume and coastal upwelling on a fringing reef at the east coast of Hainan Island, Northern South China Sea

NASA Astrophysics Data System (ADS)

Dong, Xu; Huang, Haining; Zheng, Nan; Pan, Aijun; Wang, Sumin; Huo, Cheng; Zhou, Kaiwen; Lin, Hui; Ji, Weidong

2017-09-01

We investigated the dynamics of carbonate system which was greatly modulated by a river plume and coastal upwelling in July 2014 and July 2015 at the east coast of Hainan Island where a fringing reef distributes inshore. By using a three end-member mixing model, we semiquantitatively estimated the removal of dissolved inorganic carbon (DIC) mediated by biological production in the river plume and upwelled water to be 13 ± 17 and 15 ± 16 μmol kg-1, respectively. The enhanced organic production was mainly responsible for these DIC consumptions in both two regimes, however, nearly a half of DIC removal was attributed to biocalcification in the plume system while it was negligible in the upwelling system. Furthermore, the modeled results over reefs revealed that river plume and coastal upwelling were two major threats of acidification to coral communities at the east coast of Hainan Island during cruises. In comparison, the biological contribution to acidification was limited for balancing between organic production and biocalcification during July 2014 cruise, whereas the acidification was greatly intensified by organic degradation during July 2015 cruise. It was verified that naturally local acidification (physical and biological processes) played a major role in great pH decreases on a short-term scale, leading to coastal waters more vulnerable to anthropogenic "ocean acidification" (uptake of atmospheric CO2) by reducing buffering capacity of waters. Finally, effects of acidification associated with other local threats on a fringing reef were further depicted with a conceptual model.

Monsoonal upwelling in the western Arabian Sea since the middle Miocene

NASA Astrophysics Data System (ADS)

Zhuang, G.; Zhang, Y.

2017-12-01

The Asian monsoon has long been argued to be a product of the Himalaya-Tibetan Plateau, and simulation experiments have confirmed the key role of the Himalaya-Tibetan Plateau in transforming regional atmospheric and oceanic circulations. However, temporal constraints on the strengthening of the Asian monsoon inferred from foraminifer isotopic and faunal data and terrestrial climatic and ecological records are inconsistent with each other, which has obscured the tectonic-climatic linkage. In particular, discriminating the post-middle Miocene global cooling from the monsoon upwelling cooling is critical, but poorly understood due to the lack of adequate constraints for monsoonal upwelling. Here we present new middle to late Miocene biomarker-based reconstructions of sea-surface temperature (SST) for the western Arabian Sea. Our new SSTs capture a long-term ocean cooling since ca. 14.8 Ma and a major drop in SST in the period 11-10 Ma after which the SSTs reached similar values as the Holocene. The new SST record is consistent with planktonic foraminifer, siliceous biota, and geochemical tracer studies, suggestive of ocean cooling and high productivity associated with monsoonal upwelling. The 11-10 Ma ocean cooling is not clearly expressed in other tropical oceans, indicating that the ocean cooling in the western Arabian Sea is not a simple reflection of global cooling. We interpret the 11-10 Ma ocean cooling as representing the establishment of monsoonal upwelling in the western Arabian Sea, triggered by strong cyclonic activities as a result of the Neogene outward expansion of the Himalaya-Tibetan Plateau.

Climate change and decadal shifts in the phenology of larval fishes in the California Current ecosystem

PubMed Central

Asch, Rebecca G.

2015-01-01

Climate change has prompted an earlier arrival of spring in numerous ecosystems. It is uncertain whether such changes are occurring in Eastern Boundary Current Upwelling ecosystems, because these regions are subject to natural decadal climate variability, and regional climate models predict seasonal delays in upwelling. To answer this question, the phenology of 43 species of larval fishes was investigated between 1951 and 2008 off southern California. Ordination of the fish community showed earlier phenological progression in more recent years. Thirty-nine percent of seasonal peaks in larval abundance occurred earlier in the year, whereas 18% were delayed. The species whose phenology became earlier were characterized by an offshore, pelagic distribution, whereas species with delayed phenology were more likely to reside in coastal, demersal habitats. Phenological changes were more closely associated with a trend toward earlier warming of surface waters rather than decadal climate cycles, such as the Pacific Decadal Oscillation and North Pacific Gyre Oscillation. Species with long-term advances and delays in phenology reacted similarly to warming at the interannual time scale as demonstrated by responses to the El Niño Southern Oscillation. The trend toward earlier spawning was correlated with changes in sea surface temperature (SST) and mesozooplankton displacement volume, but not coastal upwelling. SST and upwelling were correlated with delays in fish phenology. For species with 20th century advances in phenology, future projections indicate that current trends will continue unabated. The fate of species with delayed phenology is less clear due to differences between Intergovernmental Panel on Climate Change models in projected upwelling trends. PMID:26159416

Sub-regional ecosystem variability in the Canary Current upwelling

NASA Astrophysics Data System (ADS)

Arístegui, Javier; Barton, Eric D.; Álvarez-Salgado, Xosé A.; Santos, A. Miguel P.; Figueiras, Francisco G.; Kifani, Souad; Hernández-León, Santiago; Mason, Evan; Machú, Eric; Demarcq, Hervé

2009-12-01

The Canary Current upwelling ecosystem (CanC) constitutes one of the four main eastern boundary upwelling ecosystems (EBUEs) of the world, thus hosting high productivity and fisheries. Recent observations indicate that the CanC region as a whole has been experiencing a progressive warming and a decrease in productivity over the last decades. This overall trend is however not directly reflected in the fisheries of the region. Here we update recent results and previous reviews on the CanC, covering aspects from the physical environment to fish populations and fisheries on a range of time scales. We approach these topics, when possible, through a comparative exploration of the biogeographical characteristics of different sub-regions comprising this ecosystem. This review shows that variability in coastline configuration, shelf width, coastal upwelling, nutrient fertilization, productivity, or retentive vs. dispersive physical mechanisms, among other factors, may help explain sub-regional differences in fish distributions and abundances in the CanC. Nevertheless, the lack of systematic information on the regional variability of physical and biological processes hampers an integrated understanding of the relative contribution of natural vs. human-induced variability in the populations of at least small-pelagic fishes and their associated fisheries.

The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon

NASA Astrophysics Data System (ADS)

Naqvi, S. W. A.; Moffett, J. W.; Gauns, M. U.; Narvekar, P. V.; Pratihary, A. K.; Naik, H.; Shenoy, D. M.; Jayakumar, D. A.; Goepfert, T. J.; Patra, P. K.; Al-Azri, A.; Ahmed, S. I.

2010-01-01

Extensive observations during the late Southwest Monsoon of 2004 over the Indian and Omani shelves, and along an east-west transect reveal a mosaic of biogeochemical provinces including an unexpected high-nutrient, low-chlorophyll condition off the southern Omani coast. This feature, coupled with other characteristics of the system, suggest a close similarity between the Omani upwelling system and the Peruvian and California upwelling systems, where primary production (PP) is limited by iron. An intensification of upwelling, reported to have been caused by the decline in the winter/spring Eurasian snow cover since 1997, is not supported by in situ hydrographic and chlorophyll measurements as well as a reanalysis of ocean colour data extending to 2009. Iron limitation of PP may complicate simple relationship between upwelling and PP assumed by previous workers, and contribute to the anomalous offshore occurrence of the most severe oxygen (O2) depletion in the region. Over the Indian shelf, affected by very shallow O2-deficient zone, high PP is restricted to a thin, oxygenated surface layer probably due to unsuitability of the O2-depleted environment for the growth of oxygenic photosynthesizers.

Ichthyoplankton transport from the African coast to the Canary Islands

NASA Astrophysics Data System (ADS)

Brochier, Timothée; Mason, Evan; Moyano, Marta; Berraho, Amina; Colas, Francois; Sangrà, Pablo; Hernández-León, Santiago; Ettahiri, Omar; Lett, Christophe

2011-08-01

The Canary Upwelling System (CUS), a major eastern boundary upwelling system, sustains large cross-border fisheries of small pelagic fish, which poses the question of stock connectivity. Studies suggest that ichthyoplankton transport from the northwest African coast to the Canary Islands (CI) is facilitated by coastal-upwelling associated filaments. Here we analyze connections between larval supply to the CI and sardine and anchovy populations that spawn over the continental shelf. For both species, ichthyoplankton observations (1) at the shelf and (2) near the island of Gran Canaria (GC) are used. Predictions of ichthyoplankton transport to GC are obtained from the Ichthyop Lagrangian transport model, which is forced by a high-resolution hydrodynamic model (ROMS) that reproduces the regional circulation. Results show that upwelling filaments play an important role in the transport of larvae to GC. However, (1) filaments are not the only mechanism, and (2) filament presence does not necessarily imply larval transport. Anchovy and sardine larval presence at GC appears to be independent of the respective adult spawning seasonality. Combining of observed and modeled data does not succeed in reproducing the observed larval patterns at GC. Various hypotheses are proposed to explain this discrepancy in larval transport to GC.

Mantle Upwellings Below the Ibero-Maghrebian Region with a Common Deep Source from P Travel-time Tomography

NASA Astrophysics Data System (ADS)

Civiero, C.; Custodio, S.; Silveira, G. M.; Rawlinson, N.; Arroucau, P.

2017-12-01

The processes responsible for the geodynamical evolution of the Ibero-Maghrebian domain are still enigmatic. Several geophysical studies have improved our understanding of the region, but no single model has been accepted yet. This study takes advantage of the dense station networks deployed from France in the north to Canary Islands and Morocco in the south to provide a new high-resolution P-wave velocity model of the structure of the upper-mantle and top of the lower mantle. These images show subvertical small-scale upwellings below Atlas Range, Canary Islands and Central Iberia that seem to cross the transition zone. The results, together with geochemical evidence and a comparison with previous global tomographic models, reveal the ponding or flow of deep-plume material beneath the transition zone, which seems to feed upper-mantle "secondary" pulses. In the upper mantle the plumes, in conjunction with the subduction-related upwellings, allow the hot mantle to rise in the surrounding zones. During its rising, the mantle interacts with horizontal SW slab-driven flow which skirts the Alboran slab and connects with the mantle upwelling below Massif Central through the Valencia Trough rift.

On vertical advection truncation errors in terrain-following numerical models: Comparison to a laboratory model for upwelling over submarine canyons

NASA Astrophysics Data System (ADS)

Allen, S. E.; Dinniman, M. S.; Klinck, J. M.; Gorby, D. D.; Hewett, A. J.; Hickey, B. M.

2003-01-01

Submarine canyons which indent the continental shelf are frequently regions of steep (up to 45°), three-dimensional topography. Recent observations have delineated the flow over several submarine canyons during 2-4 day long upwelling episodes. Thus upwelling episodes over submarine canyons provide an excellent flow regime for evaluating numerical and physical models. Here we compare a physical and numerical model simulation of an upwelling event over a simplified submarine canyon. The numerical model being evaluated is a version of the S-Coordinate Rutgers University Model (SCRUM). Careful matching between the models is necessary for a stringent comparison. Results show a poor comparison for the homogeneous case due to nonhydrostatic effects in the laboratory model. Results for the stratified case are better but show a systematic difference between the numerical results and laboratory results. This difference is shown not to be due to nonhydrostatic effects. Rather, the difference is due to truncation errors in the calculation of the vertical advection of density in the numerical model. The calculation is inaccurate due to the terrain-following coordinates combined with a strong vertical gradient in density, vertical shear in the horizontal velocity and topography with strong curvature.

Coastal Jets, Oceanic Upwelling, Mesoscale Eddies, and Clouds in the Southeast Pacific

NASA Astrophysics Data System (ADS)

Hong, X.; Wang, S.; Jiang, Q.; O'Neill, L. W.; Hodur, R.; Chen, S.; Martin, P.; Cummings, J. A.

2009-12-01

Coastal jets, oceanic upwelling, mesoscale eddies, and clouds in the Southeast Pacific (SEP) are studied using the two-way-coupled COAMPS/NCOM system with the NCODA for the ocean data assimilation. The coupled system was run for the period of the VAMOS Ocean-Cloud-Atmosphere-Land Study (VOCALS) field campaign from 20 October to 30 November, 2008. The investigation of the feedback between the atmosphere and the ocean is focused on the periods of the strong and the weak coastal jets. During the strong coastal jet period, colder and drier air along the coast results in larger surface heat fluxes and increased boundary layer height. More extensive and organized clouds are generated in the strongly unstable conditions in the atmospheric boundary layer. The oceanic upwelling is stronger and the upwelled cold water extends further offshore. During the weak coastal jet period, the cyclonic and anti-cyclonic oceanic eddies propagate westward more significantly. The inertial oscillations induced by the variations of the wind stress also increase in strength with stronger phase shifts between the oscillations in the upper and the lower layers of the ocean. In addition, the model results from the coupled system were evaluated with available observations from the VOCALS field campaign.

Record of massive upwellings from the Pacific large low shear velocity province

NASA Astrophysics Data System (ADS)

Madrigal, Pilar; Gazel, Esteban; Flores, Kennet E.; Bizimis, Michael; Jicha, Brian

2016-11-01

Large igneous provinces, as the surface expression of deep mantle processes, play a key role in the evolution of the planet. Here we analyse the geochemical record and timing of the Pacific Ocean Large Igneous Provinces and preserved accreted terranes to reconstruct the history of pulses of mantle plume upwellings and their relation with a deep-rooted source like the Pacific large low-shear velocity Province during the Mid-Jurassic to Upper Cretaceous. Petrological modelling and geochemical data suggest the need of interaction between these deep-rooted upwellings and mid-ocean ridges in pulses separated by ~10-20 Ma, to generate the massive volumes of melt preserved today as oceanic plateaus. These pulses impacted the marine biota resulting in episodes of anoxia and mass extinctions shortly after their eruption.

Coastal warming and wind-driven upwelling: A global analysis.

PubMed

Varela, Rubén; Lima, Fernando P; Seabra, Rui; Meneghesso, Claudia; Gómez-Gesteira, Moncho

2018-10-15

Long-term sea surface temperature (SST) warming trends are far from being homogeneous, especially when coastal and ocean locations are compared. Using data from NOAA's AVHRR OISST, we have analyzed sea surface temperature trends over the period 1982-2015 at around 3500 worldwide coastal points and their oceanic counterparts with a spatial resolution of 0.25 arc-degrees. Significant warming was observed at most locations although with important differences between oceanic and coastal points. This is especially patent for upwelling regions, where 92% of the coastal locations showed lower warming trends than at neighboring ocean locations. This result strongly suggests that upwelling has the potential to buffer the effects of global warming nearshore, with wide oceanographic, climatic, and biogeographic implications. Copyright © 2018 Elsevier B.V. All rights reserved.

Bio-Optical Measurements in Upwelling Ecosystems in Support of SIMBIOS. Chapter 4

NASA Technical Reports Server (NTRS)

Chavez, Francisco P.; Strutton, Peter G.; Kuwahara, Victor S.; Mahoney, Kevin L.; Drake, Eric

2003-01-01

The upwelling region of the equatorial Pacific Ocean, which spans one quarter of the earth s circumference, strongly impacts global biogeochemistry. This upwelling system has significant implications for global CO2 fluxes (Tans et al., 1990; Takahashi et al., 1997; Feely et al., 1999), as well as primary and secondary production (Chavez and Barber, 1987; Chavez and Toggweiler, 1995; Chavez et al., 1996; Dugdale and Wilkerson, 1998; Chavez et al., 1999; Strutton and Chavez, 2000). In addition, the region represents a vast oceanic (case 1) region over which validation data for SeaWiFS are needed. This project consists of an optical mooring program and cruise-based measurements focused on measuring biological and chemical variability in the equatorial Pacific and obtaining validation data for SeaWiFS.

A coupled ice-ocean model of ice breakup and banding in the marginal ice zone

NASA Technical Reports Server (NTRS)

Smedstad, O. M.; Roed, L. P.

1985-01-01

A coupled ice-ocean numerical model for the marginal ice zone is considered. The model consists of a nonlinear sea ice model and a two-layer (reduced gravity) ocean model. The dependence of the upwelling response on wind stress direction is discussed. The results confirm earlier analytical work. It is shown that there exist directions for which there is no upwelling, while other directions give maximum upwelling in terms of the volume of uplifted water. The ice and ocean is coupled directly through the stress at the ice-ocean interface. An interesting consequence of the coupling is found in cases when the ice edge is almost stationary. In these cases the ice tends to break up a few tenths of kilometers inside of the ice edge.

Oceanographic implications of the Cabo Catoche (Northeast Yucatan) upwelling and its effects on the coastal ecosystem

NASA Astrophysics Data System (ADS)

Reyes-Mendoza, O.; Marino-Tapia, I.; Herrera Silveira, J.; Cárdenas-Palómo, N.; Ruiz, G.

2013-05-01

The coasts of the world where upwelling events occur are intrinsically related to the human population, mainly because of their large fisheries, socioeconomic repercussion and implications concerning the health of the ecosystem. In the northeast of the Yucatan Peninsula occurs an upwelling event known as the Yucatan upwelling (YU) associated with the current of the same name. The mechanisms that generate the YU are still under discussion. In terms of seasonality it is agreed that this is annual, occurring between April and September. During spring and summer, the northeast coast of the Peninsula between CaboCatoche and Isla Contoy becomes a productive and diverse pelagic ecosystem, unique to the region. It is classified as a priority marine zone host to close to 59 species protected by the national laws. It is also recognized as an important priority marine site because of its fishery. Also, the largest global aggregation of whale sharks, the world's biggest fish, is found at this site. There is a strong connection between the physical and the biological components of the system, however the coastal extent, seasonality, and magnitude of these processes need to be determined. Therefore an in-situ study was designed in the coastal region of CaboCatoche, where a 50 km transect was positioned along shelf and another across shelf 20 km, where water was collected to determine nutrient concentrations and CTD profiles were casted during the summer of 2007, 2008 and 2011. Two acoustic profilers were installed 12 km from the coast, which recorded currents and temperature by 2 years. Another profiler located 17 km from the coast to recorded data by 8 years. Atmospheric pressure and temperature were measured, as a wind fields from NOAA. Maps were created for the vertical distribution of temperature (18-31°C), salinity (35-38 psu), density (22-27 kg/m3) and chlorophyll (0.05-12.7 mg/m3). Frequency periods were estimated for temperature, currents, wind and atmospheric pressure using spectral analysis and wavelets. In order to establish associations between the physical, chemical and biological variables multivariate analyses were performed. Based in temperature the results indicate that the upwelling occurs in pulses of two different time periods; 2-4 days and the other 8 to16 days, from March to September, associated with a decrease in sea level (-0.008±0.03 m) and variation in the V component of the current (0.007±0.006 m/s to the north). On the year the dominant tides are diurnal K1, O1 and semidiurnal M2, S2, and the U and V current component had the same periodicity during upwelling, but with not upwelling V hasn't it. The atmospheric temperature decreases the water column temperature near 10 degree during not upwelling, as also in upwelling but by other mechanisms. It is yet not possible to determine the mechanism responsible for this periodicity, however it is believed to be due to a combination of wind and Yucatan current variability. The Primary production has a response time of 2 to 3 days following the onset of the pulse and the Cla-a have an increase ten times more than the mean value.

Biogeochemical and ecological impacts of boundary currents in the Indian Ocean

NASA Astrophysics Data System (ADS)

Hood, Raleigh R.; Beckley, Lynnath E.; Wiggert, Jerry D.

2017-08-01

Monsoon forcing and the unique geomorphology of the Indian Ocean basin result in complex boundary currents, which are unique in many respects. In the northern Indian Ocean, several boundary current systems reverse seasonally. For example, upwelling coincident with northward-flowing currents along the coast of Oman during the Southwest Monsoon gives rise to high productivity which also alters nutrient stoichiometry and therefore, the species composition of the resulting phytoplankton blooms. During the Northeast Monsoon most of the northern Indian Ocean boundary currents reverse and favor downwelling. Higher trophic level species have evolved behavioral responses to these seasonally changing conditions. Examples from the western Arabian Sea include vertical feeding migrations of a copepod (Calanoides carinatus) and the reproductive cycle of a large pelagic fish (Scomberomorus commerson). The impacts of these seasonal current reversals and changes in upwelling and downwelling circulations are also manifested in West Indian coastal waters, where they influence dissolved oxygen concentrations and have been implicated in massive fish kills. The winds and boundary currents reverse seasonally in the Bay of Bengal, though the associated changes in upwelling and productivity are less pronounced. Nonetheless, their effects are observed on the East Indian shelf as, for example, seasonal changes in copepod abundance and zooplankton community structure. In contrast, south of Sri Lanka seasonal reversals in the boundary currents are associated with dramatic changes in the intensity of coastal upwelling, chlorophyll concentration, and catch per unit effort of fishes. Off the coast of Java, monsoon-driven changes in the currents and upwelling strongly impact chlorophyll concentrations, seasonal vertical migrations of zooplankton, and sardine catch in Bali Strait. In the southern hemisphere the Leeuwin is a downwelling-favorable current that flows southward along western Australia, though local wind forcing can lead to transient near shore current reversals and localized coastal upwelling. The poleward direction of this eastern boundary current is unique. Due to its high kinetic energy the Leeuwin Current sheds anomalous, relatively high chlorophyll, warm-core, downwelling eddies that transport coastal diatom communities westward into open ocean waters. Variations in the Leeuwin transport and eddy generation impact many higher trophic level species including the recruitment and fate of rock lobster (Panulirus cygnus) larvae. In contrast, the transport of the Agulhas Current is very large, with sources derived from the Mozambique Channel, the East Madagascar Current and the southwest Indian Ocean sub-gyre. Dynamically, the Agulhas Current is upwelling favorable; however, the spatial distribution of prominent surface manifestations of upwelling is controlled by local wind and topographic forcing. Meanders and eddies in the Agulhas Current propagate alongshore and interact with seasonal changes in the winds and topographic features. These give rise to seasonally variable localized upwelling and downwelling circulations with commensurate changes in primary production and higher trophic level responses. Due to the strong influence of the Agulhas Current, many neritic fish species in southeast Africa coastal waters have evolved highly selective behaviors and reproductive patterns for successful retention of planktonic eggs and larvae. For example, part of the Southern African sardine (Sardinops sagax) stock undergoes a remarkable northward migration enhanced by transient cyclonic eddies in the shoreward boundary of the Agulhas Current. There is evidence from the paleoceanographic record that these currents and their biogeochemical and ecological impacts have changed significantly over glacial to interglacial timescales. These changes are explored as a means of providing insight into the potential impacts of climate change in the Indian Ocean.

Controls on Mixing-Dependent Denitrification in Hyporheic Zones

NASA Astrophysics Data System (ADS)

Hester, E. T.; Young, K. I.; Widdowson, M. A.

2013-12-01

Interaction of surface water and groundwater in hyporheic sediments of river systems is known to create unique biogeochemical conditions that can attenuate contaminants flowing downstream. Oxygen, carbon, and the contaminants themselves (e.g., excess nitrate) often advect together through the hyporheic zone from sources in surface water. However, the ability of the hyporheic zone to attenuate contaminants in upwelling groundwater plumes as they exit to rivers is less known. Such reactions may be more dependent on mixing of carbon and oxygen sources from surface water with contaminants from deeper groundwater. We simulated hyporheic flow cells and upwelling groundwater together with mixing-dependent denitrification of an upwelling nitrate plume in shallow riverbed sediments using MODFLOW and SEAM3D. For our first set of model scenarios, we set biogeochemical boundary conditions to be consistent with situations where only mixing-dependent denitrification occurred within the model domain. This occurred where dissolved organic carbon (DOC) advecting from surface water through hyporheic flow cells meets nitrate upwelling from deeper groundwater. This would be common where groundwater is affected by septic systems which contribute nitrate that upwells into streams that do not have significant nitrate sources from upstream. We conducted a sensitivity analysis that showed that mixing-dependent denitrification increased with parameters that increase mixing itself, such as the degree of heterogeneity of sediment hydraulic conductivity (K). Mixing-dependent denitrification also increased with certain biogeochemical boundary concentrations such as increasing DOC or decreasing dissolved oxygen (DO) advecting from surface water. For our second set of model scenarios, we set biogeochemical boundary conditions to be consistent with common situations where non-mixing-dependent denitrification also occurred within the model domain. For example, when nitrate concentrations are substantial in water advecting from surface water, non-mixing-dependent denitrification can occur within the hyporheic flow cells. This would be common where surface water and groundwater have high nitrate concentrations in agricultural areas. We conducted a sensitivity analysis for this set of model scenarios as well, to evaluate controls on the relative balance of mixing-dependent and non-mixing-dependent denitrification. We found that non-mixing-dependent denitrification often has higher potential to consume nitrate than mixing-dependent denitrification. This is because non-mixing-dependent denitrification is not confined to the relatively small mixing zone between upwelling groundwater and hyporheic flow cells, and hence often has longer residence times available for consumption of existing oxygen followed by consumption of nitrate. Nevertheless, the potential for hyporheic zones to attenuate upwelling nitrate plumes appears to be substantial, yet is variable depending on geomorphic, hydraulic, and biogeochemical conditions.

The Indonesian Throughflow: Oceanographic responses to Holocene changes in the mean Pacific state

NASA Astrophysics Data System (ADS)

Jacobel, A. W.; Oppo, D.; Eglinton, T. I.; Gibbons, F. T.; Montlucon, D.; Rosenthal, Y.; Linsley, B. K.

2009-12-01

The Indonesian Throughflow (ITF), which transfers upper ocean waters from the Pacific to the Indian Ocean, plays an essential role in global ocean circulation and tropical climate regulation. The flow and mixing regimes of the ITF are affected by changes in temperature, winds and upwelling caused by the Asian Monsoon/Intertropical Convergence Zone (AM/ITCZ) and interannual variations in El Niño (EN). Because the ITF is located in the Western Pacific Warm Pool, an area from which the atmosphere derives a large portion of its heat and water budget, changes in the ITF have the potential to perturb atmospheric circulation globally. Despite the importance of this region to global climate, changes in the ocean-atmosphere climate phenomenon affecting the ITF are still poorly understood. Our study used organic geochemical proxies for upwelling in the Makassar Strait to investigate Holocene oceanographic changes in the ITF in response to EN and the AM/ITCZ. A core-top biomarker survey was performed on multi-core samples from the Makassar Strait and surrounding areas. Concentrations of cholesterol (an indicator of integrated primary productivity) were determined by Gas Chromatography-Mass Spectrometry and were then compared with maps of regional July-August SST and determined to accurately reflect regional upwelling. Based on the findings of the core-top survey, a down-core biomarker record was generated from core BJ8-03-70 GGC taken from the West Sulawesi Margin in the Eastern Makassar Strait, an area that experiences seasonal upwelling associated with the boreal summer Asian monsoon. Cholesterol data show a trend towards increasing concentrations (upwelling or thermocline shoaling) in the late Holocene with a considerable increase approximately 6,000 years before present. Additionally, upwelling intensity appears to show more centennial-millennial variability during the late Holocene. Evidence that the summer monsoon has decreased in strength over the course of the Holocene (e.g. Wang et al., 2005) suggests that the increase in cholesterol is not a response to an increase in monsoon-driven upwelling. Because a shallower thermocline is associated with weak trade winds (El Niño-like conditions in the modern ocean), we interpret these results to represent a mid Holocene transition to a more El Niño-like mean Pacific state. This interpretation is consistent with previous evidence (Moy et al., 2002 and Conroy et al., 2008, yet the timing and reason for this transition is not well constrained. Further work should seek to develop a higher-resolution, multi-proxy dataset to explore and explain this change.

Nitrogen uptake of phytoplankton assemblages under contrasting upwelling and downwelling conditions: The Ría de Vigo, NW Iberia

NASA Astrophysics Data System (ADS)

Seeyave, Sophie; Probyn, Trevor; Álvarez-Salgado, Xosé Antón; Figueiras, Francisco G.; Purdie, Duncan A.; Barton, Eric D.; Lucas, Michael

2013-06-01

Regenerated production (including organic nitrogen) is shown here to be important in the Ría de Vigo (Galicia, NW Iberia) in supporting both harmful algal bloom communities during the downwelling season, but also (to a lesser extent) diatom communities during stratified periods of weak to moderate upwelling. The Galician Rías, situated in the Iberian upwelling system, are regularly affected by blooms of toxic dinoflagellates, which pose serious threats to the local mussel farming industry. These tend to occur towards the end of summer, during the transition from upwelling to downwelling favourable seasons, when cold bottom shelf waters in the rías are replaced by warm surface shelf waters. Nitrate, ammonium and urea uptake rates were measured in the Ría de Vigo during a downwelling event in September 2006 and during an upwelling event in June 2007. In September the ría was well mixed, with a downwelling front observed towards the middle of the ría and relatively high nutrient concentrations (1.0-2.6 μmol L-1 nitrate; 1.0-5.6 μmol L-1 ammonium; 0.1-0.8 μmol L-1 phosphate; 2.0-9.0 μmol L-1 silicic acid) were present throughout the water column. Ammonium represented more than 80% of the nitrogenous nutrients, and the phytoplankton assemblage was dominated by dinoflagellates and small flagellates. In June the water column was stratified, with nutrient-rich, upwelled water below the thermocline and warm, nutrient-depleted water in the surface. At this time, nitrate represented more than 80% of the nitrogenous nutrients, and a mixed diatom assemblage was present. Primary phytoplankton production during both events was mainly sustained by regenerated nitrogen, with ammonium uptake rates of 0.035-0.063 μmol N L-1 h-1 in September and 0.078-0.188 μmol N L-1 h-1 in June. Although f-ratios were generally low (<0.2) in both June and September, a maximum of 0.61 was reached in June due to higher nitrate uptake (0.225 μmol N L-1 h-1). Total nitrogen uptake was also higher during the upwelling event (0.153-0.366 in June and 0.053-0.096 μmol N L-1 h-1 in September). Nitrogen uptake kinetics demonstrated a strong preference for ammonium and urea over nitrate in June.

Trace Element Geochemistry as a Tool for the Reconstruction of Upwelling Patterns at 12oS off Peru since the Last Glacial Maximum (LGM)

NASA Astrophysics Data System (ADS)

Boening, P.; Brumsack, H.; Wolf, A.

2002-05-01

Laminated sediments (core 106KL), recovered during R/V Sonne cruise 147 from the Peruvian upper slope mud lens at 12oS, were analyzed for bulk parameters (TOC, TIC, TS) and opal as well as major and trace element composition by XRF and ICP-MS in 5 cm intervals. The composition of the terrigenous-detrital sediment fraction is comparable to average shale. The sediments exhibit slight increases in biogenic silica (diatoms) and carbonate contents (foraminifera) in varying layers. The experimentally determined opal contents correlate well with Si/Al ratios. High TOC and P contents are due to enhanced primary productivity, high sedimentation rates and corresponding organic matter preservation under a strong OMZ. We distinguish between three different groups of elements: 1.) trace elements involved in bio-cycling (e.g. Cd, Ag, Ni, Cu) are highly enriched in the sediments due to their association with plankton, high sedimentation rates (preventing remobilization from the sediments) and fixation as sulfides. 2.) redox-sensitive elements (e.g. Re, Mo) are significantly enriched probably due to reduction and precipitation under suboxic/anoxic conditions. Diffusion of these elements from the water column into sub/anoxic sediments seems to be the controlling factor, besides sulfide precipitation. An average Re/Mo ratio of 1.3 indicates anoxic sedimentary conditions. Most trace elements correlate well with the TOC content presumably documenting productivity events. 3.) Al, Zr and Y are well correlated, presumably representing sporadic high-energy fluvial input from the continent or enhanced current velocities. The three element groups were used to reconstruct the upwelling patterns off Lima since the LGM: TOC content and Al-normalized trace element patterns from the bio/redox-sensitive fractions represent the signal from the water column, whereas Al, Y and Zr reflect the terrigenous input. During the LGM (about 17 ky BP) the site was hardly affected by upwelling as the upwelling cell was located more basinward. As the sea level rose during the Late Glacial (17-10 ky BP) the upwelling cell shifted towards the coast. The Early Holocene (10-5 ky BP) is not documented likely because strong currents (presumably the Peru counter current) eroded the slope. In the Late Holocene the upwelling cell was established at the site. However, a higher terrrigenous proportion and lower input from the water column suggest a basinward shifting of the upwelling cell during the Second Neoglacial (2000-2700 BP). Stronger Element/Al and TOC variabilities indicate the influence of El Nino during the Late Holocene.

Seasonal and annual variability of coastal sulphur plumes in the northern Benguela upwelling system.

PubMed

Ohde, Thomas; Dadou, Isabelle

2018-01-01

We investigated the seasonal and annual variability of surface sulphur plumes in the northern Benguela upwelling system off Namibia because of their significant impacts on the marine ecosystem, fishing industry, aquaculture farming and tourism due to their toxic properties. We identified the sulphur plumes in ocean colour satellite data of the medium resolution imaging spectrometer (MERIS) for the 2002-2012 time period using the differences in the spectral properties of Namibian Benguela optical water types. The sulphur events have a strong seasonal cycle with pronounced main and off-seasons forced by local and remote-driven processes. The main peak season is in late austral summer and early austral autumn at the beginning of the annual upwelling cycle caused by increasing equatorwards alongshore winds. The sulphur plume activity is high between February and April during the seasonal oxygen minimum associated with the seasonal reduction of cross-shore ventilation of the bottom waters, the seasonal southernmost position of the Angola Benguela Frontal Zone, the seasonal maximum of water mass fractions of South Atlantic and Angola Gyre Central Waters as well as the seasonal arrival of the downwelling coastal trapped waves. The off-season is in austral spring and early austral summer during increased upwelling intensity and enhanced oxygen supply. The annual variability of sulphur events is characterized by very high activities in years 2004, 2005 and 2010 interrupted by periods of lower activity in years 2002 to 2003, 2006 to 2009 and 2011 to 2012. This result can be explained by the relative contributions or adding effects of local and remote-driven forces (from the equatorial area). The probability for the occurrence of sulphur plumes is enhanced in years with a lower annual mean of upwelling intensity, decreased oxygen supply associated with decreased lateral ventilation of bottom waters, more southern position of the Angola Benguela Frontal Zone, increased mass fraction of South Atlantic Central Water and stronger downwelling coastal trapped waves. Understanding of the variability and forcing processes of the toxic sulphur events will help in the future to monitor and forecast them as well as to manage their social and economic consequences in the northern Benguela upwelling system off Namibia.

Variability of temperature and chlorophyll of the Iberian Peninsula near costal ecosystem during an upwelling event for the present climate and a future climate scenario

NASA Astrophysics Data System (ADS)

Lopes, José Fortes; Ferreira, Juan A.; Cardoso, Ana Cristina; Rocha, Alfredo C.

2014-01-01

Understanding the importance and the implication of the climate changes on coastal areas may be one of the major issues for this and next centuries. Climate changes may, indeed, impact the nearshore marine ecosystem, as coastal areas are very sensitive to the strength and the variability of the meteorological forcings. The main purpose of this work is to study temperature and phytoplankton distributions along the Portuguese near coastal zone during upwelling events in the present climate conditions and in a future climate scenario. The SRES-A2 IPCC scenario has been considered. We have used a three-dimensional model for coastal and shelf seas, including the following sub-models: hydrodynamical/physical, biological, sediment and contaminant. The forcings are provided by the interactions at the air-sea, considering the wind intensity and direction with the help of the WRF model (Weather Research and Forecast Model) and the coupled atmosphere-ocean model ECHAM5/MPI-OM. Results show that, for the future climate scenario, there is a reinforcement of the southward wind. The responses of the coastal ecosystem corresponds to the reinforcement of both, the southward (up to 10 cm/s) and the westward (up to 6 cm/s) induced upwelling currents. This, in turn generates an enlargement of the near coast upwelled cold layer, extending up to 60 km, as well as the rise of the warm layer temperature (up to 2.0 °C) and the spreading of the phytoplankton offshore. Significant changes in both the Chl-a vertical and the horizontal distribution patterns have been observed, as the nutrient supply to the upper layers depends on the strength of the upwelling, the bottom topography and orography of the coastal. These results confirm that changes in the strength and eventually the frequency of the upwelling favourable wind impact the phytoplankton distribution, which can have significant effect in the distribution and population of the upper level of the trophic chain of the coastal ecosystem.

Surface ocean carbon isotope anomalies on glacial terminations: An alternative view

NASA Astrophysics Data System (ADS)

Lund, D. C.; Cote, M.; Schmittner, A.

2016-12-01

Late Pleistocene glacial terminations are characterized by surface ocean carbon isotope minima on a global scale. During the last deglaciation (i.e. Termination 1), planktonic foraminiferal δ13C anomalies occurred in the Atlantic, Indian, Pacific, and Southern Oceans. Despite the apparently ubiquitous nature of δ13C anomalies on glacial terminations, their cause remains a matter of ongoing debate. The prevailing view is that isotopically light carbon from the abyss was upwelled in the Southern Ocean, resulting in outgassing of 13C-depleted carbon to the atmosphere and its advection to lower latitudes via mode and intermediate waters (Spero and Lea, 2002). Alternatively, carbon isotope minima may be driven by weakening of the biological pump related to circulation-driven changes in the oceanic preformed nutrient budget (Schmittner and Lund, 2015). Here we assess the deep upwelling and biological pump hypotheses using a new compilation of 70 globally-distributed planktonic δ13C records from the published literature. We find that 1) the mean deglacial δ13C anomaly is similar in all ocean basins, 2) the eastern tropical Pacific yields smaller mean δ13C anomalies than the western tropical Pacific, and 3) δ13C anomalies in the Southern Ocean decrease with increasing latitude. Our results are generally inconsistent with the deep upwelling hypothesis, which predicts that the δ13C signal should be largest in the Southern Ocean and upwelling regions. Instead, the spatial pattern in δ13C anomalies supports the biological pump hypothesis, which predicts that reduced export of light carbon from the euphotic zone triggers negative carbon isotope anomalies in the surface ocean and positive anomalies at intermediate depths. Upwelling of relatively 13C-enriched intermediate waters tends to moderate carbon isotope minima in upwelling regions. Our results suggest that the initial rise in atmospheric CO2 during Termination 1 was likely due to weakening of the biological pump associated with a reduction in the Atlantic Meridional Overturning Circulation, consistent with model results (Schmittner and Lund, 2015). Spero, H., and D. Lea (2002) Science 296, 522-525. Schmittner, A., and D. Lund (2015) Climate of the Past 11, 135-152.

Surface circulation and upwelling patterns around Sri Lanka

NASA Astrophysics Data System (ADS)

de Vos, A.; Pattiaratchi, C. B.; Wijeratne, E. M. S.

2013-09-01

Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean with the Arabian Sea on its western side and the Bay of Bengal on its eastern side. The region is characterised by bi-annually reversing monsoon winds resulting from seasonal differential heating and cooling of the continental land mass and the ocean. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and the Regional Ocean Modelling System (ROMS) configured to the study region and forced with ECMWF interim data. The model was run for 2 yr to examine the seasonal and shorter term (∼10 days) variability. The results confirmed the presence of the reversing current system in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the Southwest (SW) monsoon transporting 11.5 Sv and the westward flowing Northeast Monsoon Current (NMC) transporting 9.5 Sv during the Northeast (NE) monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the Island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the south coast. During the SW monsoon the Island deflects the eastward flowing SMC southward whilst along the east coast the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the south coast and is shown to be due to flow convergence and divergence associated with offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind driven flow along the east and west coasts: during the SW (NE) monsoon the flow along the western (eastern) coast was stronger and hence the upwelling centre was shifted to the east (west). The presence of upwelling along the south coast during both monsoon periods may explain the blue whale (Balaenoptera musculus) aggregations in this region.

Climate variability and Dinophysis acuta blooms in an upwelling system.

PubMed

Díaz, Patricio A; Ruiz-Villarreal, Manuel; Pazos, Yolanda; Moita, Teresa; Reguera, Beatriz

2016-03-01

Dinophysis acuta is a frequent seasonal lipophilic toxin producer in European Atlantic coastal waters associated with thermal stratification. In the Galician Rías, populations of D. acuta with their epicentre located off Aveiro (northern Portugal), typically co-occur with and follow those of Dinophysis acuminata during the upwelling transition (early autumn) as a result of longshore transport. During hotter than average summers, D. acuta blooms also occur in August in the Rías, when they replace D. acuminata. Here we examined a 30-year (1985-2014) time series of D. acuta from samples collected by the same method in the Galician Rías. Our main objective was to identify patterns of distribution and their relation with climate variability, and to explain the exceptional summer blooms of D. acuta in 1989-1990. A dome-shaped relationship was found between summer upwelling intensity and D. acuta blooms; cell maxima were associated with conditions where the balance between upwelling intensity and heating, leading to deepened thermoclines, combined with tidal phase (3 days after neap tides) created windows of opportunity for this species. The application of a generalized additive model based on biological (D. acuta inoculum) and environmental predictors (Cumulative June-August upwelling CUI JJA , average June-August SST JJA and tidal range) explained more than 70% of the deviance for the exceptional summer blooms of D. acuta, through a combination of moderate (35,000-50,000m 3 s -1 km -1 ) summer upwelling (CUI JJA ), thermal stratification (SST JJA >17°C) and moderate tidal range (∼2.5m), provided D. acuta cells (inoculum) were present in July. There was no evidence of increasing trends in D. acuta bloom frequency/intensity nor a clear relationship with NAO or other long-term climatic cycles. Instead, the exceptional summer blooms of 1989-1990 appeared linked to extreme hydroclimatic anomalies (high positive anomalies in SST and NAO index), which affected most of the European Atlantic coast. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Physico-chemical and biological factors influencing dinoflagellate cyst production in the Cariaco Basin

NASA Astrophysics Data System (ADS)

Bringué, Manuel; Thunell, Robert C.; Pospelova, Vera; Pinckney, James L.; Romero, Oscar E.; Tappa, Eric J.

2018-04-01

We present a 2.5-year-long sediment trap record of dinoflagellate cyst production in the Cariaco Basin, off Venezuela (southern Caribbean Sea). The site lies under the influence of wind-driven, seasonal upwelling which promotes high levels of primary productivity during boreal winter and spring. Changes in dinoflagellate cyst production is documented between November 1996 and May 1999 at ˜ 14-day intervals and interpreted in the context of in situ observations of physico-chemical and biological parameters measured at the mooring site. Dinoflagellate cyst assemblages are diverse (57 taxa) and dominated by cyst taxa of heterotrophic affinity, primarily Brigantedinium spp. (51 % of the total trap assemblage). Average cyst fluxes to the trap are high (17.1 × 103 cysts m-2 day-1) and show great seasonal and interannual variability. On seasonal timescales, dinoflagellate cyst production responds closely to variations in upwelling strength, with increases in cyst fluxes of several protoperidinioid taxa observed during active upwelling intervals, predominantly Brigantedinium spp. Cyst taxa produced by autotrophic dinoflagellates, in particular Bitectatodinium spongium, also respond positively to upwelling. Several spiny brown cysts contribute substantially to the assemblages, including Echinidinium delicatum (9.7 %) and Echinidinium granulatum (7.3 %), and show a closer affinity to weaker upwelling conditions. The strong El Niño event of 1997/98 appears to have negatively impacted cyst production in the basin with a 1-year lag, and may have contributed to the unusually high fluxes of cysts type Cp (possibly the cysts of the toxic dinoflagellate Cochlodinium polykrikoides sensu Li et al., 2015), with cyst type Cp fluxes up to 11.8 × 103 cysts m-2 day-1 observed during the weak upwelling event of February-May 1999. Possible trophic interactions between dinoflagellates and other major planktonic groups are also investigated by comparing the timing and magnitude of cyst production with proxies for phytoplanktonic communities (from photopigment data) and micro- to macrozooplankton abundance indicators (from palynological data) at the site. This work provides new, detailed insights into the ecology of cyst-producing dinoflagellates and will allow for more detailed interpretations of fossil assemblages extracted from sedimentary records in the basin and elsewhere.

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

NASA Technical Reports Server (NTRS)

Brock, John C.; Mcclain, Charles R.

1992-01-01

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

Changes in upwelling and surface productivity in the Eastern Pacific during Terminations I and II

NASA Astrophysics Data System (ADS)

Erdem, Z.; De Bar, M.; Stolwijk, D.; Schneider, R. R.; S Sinninghe Damsté, J.; Schouten, S.

2017-12-01

The Eastern Pacific coastal system is characterized by intense upwelling and consequently by an enhanced surface primary productivity. Combination of this high organic matter flux with sluggish bottom water ventilation results in one of the most pronounced oxygen minimum zones reaching from offshore California in the North to offshore Chile in the South. As a result of this process, the region is particularly interesting in view of nutrient and carbon cycling as well as ecosystem dynamics. The dynamics of the upwelling and oxygen concentrations are closely related to climatic conditions. Therefore, paleo-reconstructions of different settings are crucial in order to improve our understanding of the response of these nutrient-rich, oxygen-deficient, environments in relation to the recent global ocean warming, acidification and deoxygenation. In this study, we present downcore results from three different sites in the Eastern Pacific: offshore California (IODP site 1012), Peru (M77/2-52-2) and Chile (IODP site 1234). We applied different biomarkers as proxies to decipher changes in phytoplankton community composition, including the upwelling index based on long chain diols, and other common productivity indicators such as bulk organic carbon, carbonate and biogenic opal. In addition, application of carbon and nitrogen isotope ratios of total organic carbon and benthic foraminifera complement our multiproxy approach. Herewith we aim to compare at least two glacial-interglacial transitions with different magnitudes of deglacial warming along the Eastern Pacific upwelling systems at different latitudes. The data presented will cover the last 160 ka BP offshore California and Chile, and 30 ka BP offshore Peru enabling comparison between glacial Terminations I and II.

The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon

NASA Astrophysics Data System (ADS)

Naqvi, S. W. A.; Moffett, J. W.; Gauns, M. U.; Narvekar, P. V.; Pratihary, A. K.; Naik, H.; Shenoy, D. M.; Jayakumar, D. A.; Goepfert, T. J.; Patra, P. K.; Al-Azri, A.; Ahmed, S. I.

2010-07-01

Extensive observations were made during the late Southwest Monsoon of 2004 over the Indian and Omani shelves, and along a transect that extended from the southern coast of Oman to the central west coast of India, tracking the southern leg of the US JGOFS expedition (1994-1995) in the west. The data are used, in conjunction with satellite-derived data, to investigate long-term trends in chlorophyll and sea surface temperature, indicators of upwelling intensity, and to understand factors that control primary production (PP) in the Arabian Sea, focussing on the role of iron. Our results do not support an intensification of upwelling in the western Arabian Sea, reported to have been caused by the decline in the winter/spring Eurasian snow cover since 1997. We also noticed, for the first time, an unexpected development of high-nutrient, low-chlorophyll condition off the southern Omani coast. This feature, coupled with other characteristics of the system, such as a narrow shelf and relatively low iron concentrations in surface waters, suggest a close similarity between the Omani upwelling system and the Peruvian and California upwelling systems, where PP is limited by iron. Iron limitation of PP may complicate simple relationship between upwelling and PP assumed by previous workers, and contribute to the anomalous offshore occurrence of the most severe oxygen (O2) depletion in the region. Over the much wider Indian shelf, which experiences large-scale bottom water O2-depletion in summer, adequate iron supply from reducing bottom-waters and sediments seems to support moderately high PP; however, such production is restricted to the thin, oxygenated surface layer, probably because of the unsuitability of the O2-depleted environment for the growth of oxygenic photosynthesizers.

Record of the Pacific Large Low Shear Velocity Province Upwellings Preserved in the Cretaceous Large Igneous Provinces

NASA Astrophysics Data System (ADS)

Madrigal, P.; Gazel, E.; Flores, K. E.; Bizimis, M.; Jicha, B. R.

2015-12-01

As the surface expression of deep mantle dynamics, Large Igneous Provinces (LIPs) are associated with the edges of large low shear velocity provinces (LLSVP) rooted at the core-mantle boundary. Instabilities in the LLSVP can cause periodic upwellings of material in the form of mantle plumes, which impact the lithosphere forming LIPs. However, the time frames of these massive lava outpourings are still uncertain. While continental LIPs are more readily accessible, oceanic LIPs have only been studied through drilling and sampling of fragments accreted to continental margins or island arcs, hence, they are relatively less understood. The impact of oceanic LIPs on oceanic biota is conspicuously recorded in global occurrences of black shale deposits that evidence episodes of anoxia and mass extinctions shortly after the formation of LIPs that ultimately can affect life on the entire planet. Our new geochemical and geochronological data of accreted Pacific LIPs found in the coasts of Nicoya Peninsula in Costa Rica record three LIP pulses possibly reflecting upwelling periods of the LLSVP at 140, 120 and 90 Ma. In order to test different models of origin of these LIPS, we created a complete reconstruction of the Pacific Plate configuration from the Mid-Jurassic to Upper-Cretaceous to show the existing correlation between upwelling pulses at edges of the Pacific LLSVP, oceanic anoxic events and the age from Pacific LIPs. We propose that since the formation of the Pacific plate at circa 175-180 Ma, a series of upwellings that interacted with mid-ocean ridge systems separated by 10-20 Ma have affected the planet periodically forming oceanic LIPs that still can be found today on the Pacific seafloor and accreted along the plate margins.

Coastal Upwelling Supplies Oxygen-Depleted Water to the Columbia River Estuary

PubMed Central

Roegner, G. Curtis; Needoba, Joseph A.; Baptista, António M.

2011-01-01

Low dissolved oxygen (DO) is a common feature of many estuarine and shallow-water environments, and is often attributed to anthropogenic nutrient enrichment from terrestrial-fluvial pathways. However, recent events in the U.S. Pacific Northwest have highlighted that wind-forced upwelling can cause naturally occurring low DO water to move onto the continental shelf, leading to mortalities of benthic fish and invertebrates. Coastal estuaries in the Pacific Northwest are strongly linked to ocean forcings, and here we report observations on the spatial and temporal patterns of oxygen concentration in the Columbia River estuary. Hydrographic measurements were made from transect (spatial survey) or anchor station (temporal survey) deployments over a variety of wind stresses and tidal states during the upwelling seasons of 2006 through 2008. During this period, biologically stressful levels of dissolved oxygen were observed to enter the Columbia River estuary from oceanic sources, with minimum values close to the hypoxic threshold of 2.0 mg L−1. Riverine water was consistently normoxic. Upwelling wind stress controlled the timing and magnitude of low DO events, while tidal-modulated estuarine circulation patterns influenced the spatial extent and duration of exposure to low DO water. Strong upwelling during neap tides produced the largest impact on the estuary. The observed oxygen concentrations likely had deleterious behavioral and physiological consequences for migrating juvenile salmon and benthic crabs. Based on a wind-forced supply mechanism, low DO events are probably common to the Columbia River and other regional estuaries and if conditions on the shelf deteriorate further, as observations and models predict, Pacific Northwest estuarine habitats could experience a decrease in environmental quality. PMID:21533083

Assessing the Feasibility and Risks of Using Wave-Driven Upwelling Pumps to Enhance the Biological Sequestration of Carbon in Open Oceans

NASA Astrophysics Data System (ADS)

White, A.; Bjorkman, K.; Grabowski, E.; Letelier, R. M.; Poulos, S.; Watkins, B.; Karl, D. M.

2008-12-01

In 1976, John D. Isaacs proposed to use wave energy to pump cold and nutrient-rich deep water into the sunlit surface layers. The motivation for this endeavor has taken many forms over the years, from energy production to fueling aquaculture to the more recent suggestion that artificial upwelling could be used to stimulate primary productivity and anthropogenic carbon sequestration in oligotrophic regions of the ocean. However, the potential for biological carbon sequestration in response to upwelling will depend on the concentration of nutrients relative to that of dissolved inorganic carbon in the water being upwelled and on the response of the marine microbial assemblage to this nutrient enrichment. In June 2008, we tested a commercially available wave pump in the vicinity of Station ALOHA, north of Oahu, Hawaii in order to assess the logistics of at-sea deployment and the survivability of the equipment in the open ocean. Our engineering test was also designed to evaluate a recently published hypothesis (Karl and Letelier, 2008, Marine Ecology Progress Series) that upwelling of water containing excess phosphate relative to nitrogen compared to the canonical "Redfield" molar ratio of 16N:1P, would generate a two-phased phytoplankton bloom and enhance carbon sequestration. In this presentation, we analyze the results of this field test within the context of pelagic biogeochemical cycles. Furthermore, we discuss the deployment of a 300m wave pump, efforts to sample a biochemical response, the engineering challenges faced and the practical and ethical implications of these results for future experiments aimed at stimulating the growth of phytoplankton in oligotrophic regions.

Annual trend patterns of phytoplankton species abundance belie homogeneous taxonomical group responses to climate in the NE Atlantic upwelling.

PubMed

Bode, Antonio; Estévez, M Graciela; Varela, Manuel; Vilar, José A

2015-09-01

Phytoplankton is a sentinel of marine ecosystem change. Composed by many species with different life-history strategies, it rapidly responds to environment changes. An analysis of the abundance of 54 phytoplankton species in Galicia (NW Spain) between 1989 and 2008 to determine the main components of temporal variability in relation to climate and upwelling showed that most of this variability was stochastic, as seasonality and long term trends contributed to relatively small fractions of the series. In general, trends appeared as non linear, and species clustered in 4 groups according to the trend pattern but there was no defined pattern for diatoms, dinoflagellates or other groups. While, in general, total abundance increased, no clear trend was found for 23 species, 14 species decreased, 4 species increased during the early 1990s, and only 13 species showed a general increase through the series. In contrast, series of local environmental conditions (temperature, stratification, nutrients) and climate-related variables (atmospheric pressure indices, upwelling winds) showed a high fraction of their variability in deterministic seasonality and trends. As a result, each species responded independently to environmental and climate variability, measured by generalized additive models. Most species showed a positive relationship with nutrient concentrations but only a few showed a direct relationship with stratification and upwelling. Climate variables had only measurable effects on some species but no common response emerged. Because its adaptation to frequent disturbances, phytoplankton communities in upwelling ecosystems appear less sensitive to changes in regional climate than other communities characterized by short and well defined productive periods. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

Eruption histories and hypotheses of magma genesis of Mt. Baegdu volcano

NASA Astrophysics Data System (ADS)

Lim, C.; Lee, I.

2017-12-01

The tephra or cryptotephra are principally composed of alkaline glass shards, and INAA of individual grains offers a way of distinguishing chemical characteristics. That may be used to discriminate different events age and to correlate separate deposits of the same source volcanoes. The identification of tephra or cryptotephra layers presents an opportunity to define time-parallel marker horizons. With using INAA scanning method three newly identified tephras (named B-J, B-Sado and B-Ym) were detected and eruption ages identified between AT (29.24 cal. ka) and Aso-4 (88 ka) in five cores based on microscopic observation and the stratigraphic correlations between cores of the Holocene sediments in the southeastern East Sea/Japan Sea. By the correlation with TL (dark layer) data, the approximate age of B-J, B-Sado and B-Ym tephras were calculated as to be 50.6 ka, 67.6 ka, 86.8 ka, respectively. The intraplate Baegdusan (Changbai) volcanoes located on the border of China and North Korea have been explained by either hotspots by mantle plumes or asthenospheric mantle upwelling (wet plume) caused by stagnation slab of the subducted Pacific plate. To understand the origin of the Baegdusan volcanism, we performed geochemical analyses on the volcanic rocks and tephra deposits erupted from the Baegdusan volcanoes. We propose that the intraplate alkaline volcanism associated with Baekdusan volcanic region is fed by a mantle upwelling originating below the discontinuity subducting slab. The upwelling is a result of a slab neck into the subducting slabs. The Baekdusan volcano relies on a slab neck within subducting slab at depth to allow for a focused upwelling. Therefore, the magmatic progression of back-arc magmatism in Baekdusan volcanoes can be explained by the interaction of this Philippine Sea Plate Slab and upwelling mantle.

A hybrid origin of the Martian crustal dichotomy: Degree-1 convection antipodal to a giant impact

NASA Astrophysics Data System (ADS)

Citron, Robert I.; Manga, Michael; Tan, Eh

2018-06-01

The Martian crustal dichotomy is the stark ∼5 km difference in surface elevation and ∼26 km difference in crustal thickness between the northern lowlands and southern highlands that originated within 100s of Myr of Mars' formation. The origin of the dichotomy has broad implications for the geodynamic history of Mars, but purely exogenic or endogenic theories so far cannot explain all of the large scale geophysical observations associated with dichotomy formation. A giant impact can produce the shape and slope of the dichotomy boundary, but struggles to explain Mars' remanent crustal magnetic signatures and the ultimate formation of Tharsis. Degree-1 mantle convection can relate the crustal dichotomy to the formation of Tharsis, but does not explain the elliptical dichotomy shape and must be initiated by a large pre-existing viscosity jump in the mantle. We propose a hybrid model of dichotomy formation in which a giant impact induces degree-1 convection with an upwelling antipodal to the impact site. In this scenario, a giant impact in the northern hemisphere excavates crust, creating an initial difference in crustal thickness and possibly composition between the two hemispheres. Over 10s to 100s of Myr, the dominant upwelling(s) would migrate to be under the thicker, insulating crust in the southern hemisphere, generating melt that further thickens the southern crust. We examine this process using 3-D mantle convection simulations, and find that a hemispherical difference in crustal thickness and composition caused by a giant impact can induce degree-1 convection with the upwelling(s) antipodal to the impact site in <100 Myr.

Alkaline phosphatase activity at the southwest coast of India: A comparison of locations differently affected by upwelling

NASA Astrophysics Data System (ADS)

Mamatha, S. S.; Malik, Ashish; Varik, Sandesh; Parvathi, V.; Jineesh, V. K.; Gauns, Mangesh U.; LokaBharathi, P. A.

2015-01-01

The realization of the potential importance of phosphorus (P) as a limiting nutrient in marine ecosystem is increasing globally. Hence, the contribution of biotic variables in mobilizing this nutrient would be relevant especially in productive coastal waters. As alkaline phosphatase activity (APA) indicates the status of P for primary production in aquatic environments, we asked the following question: is the level of APA indicative of P sufficiency or deficiency in coastal waters, especially, where upwelling is a regular phenomenon? Therefore, we have examined the total APA, chlorophyll a along with phosphatase producing bacteria (PPB) and related environmental parameters from nearshore to offshore in coastal waters off Trivandrum and Kochi regions differently affected by upwelling during the onset of monsoon. Off Trivandrum, APA in the offshore waters of 5-m layer at 2.23 μM P h- 1 was > 4 times higher than nearshore. Thus, low APA could be indicative of P sufficiency in coastal waters and higher activity suggestive of deficiency in offshore waters off Trivandrum. In contrast, there was less difference in APA between near and offshore surface waters off Kochi. Our results show that the regions differently affected by upwelling respond differently according to ambient P concentration, distance from shore or depth of water. These observations could apparently be applicable to other coastal systems as well, where gradients in upwelling and phosphate runoff have been noticed. Further studies on other transects would throw more light on the extent and direction of the relationship between APA and ambient P concentration. Such studies would help in understanding the level of control of this nutrient on the productivity of coastal waters.

Defining seascapes for marine unconsolidated shelf sediments in an eastern boundary upwelling region: The southern Benguela as a case study

NASA Astrophysics Data System (ADS)

Karenyi, Natasha; Sink, Kerry; Nel, Ronel

2016-02-01

Marine unconsolidated sediment habitats, the largest benthic ecosystem, are considered physically controlled ecosystems driven by a number of local physical processes. Depth and sediment type are recognised key drivers of these ecosystems. Seascape (i.e., marine landscape) habitat classifications are based solely on consistent geophysical features and provide an opportunity to define unconsolidated sediment habitats based on processes which may vary in distribution through space and time. This paper aimed to classify unconsolidated sediment seascapes and explore their diversity in an eastern boundary upwelling region at the macro-scale, using the South African west coast as a case study. Physical variables such as sediment grain size, depth and upwelling-related variables (i.e., maximum chlorophyll concentration, austral summer bottom oxygen concentration and sediment organic carbon content) were included in the analyses. These variables were directly measured through sampling, or collated from existing databases and the literature. These data were analysed using multivariate Cluster, Principal Components Ordination and SIMPER analyses (in PRIMER 6 + with PERMANOVA add-in package). There were four main findings; (i) eight seascapes were identified for the South African west coast based on depth, slope, sediment grain size and upwelling-related variables, (ii) three depth zones were distinguished (inner, middle and outer shelf), (iii) seascape diversity in the inner and middle shelves was greater than the outer shelf, and (iv) upwelling-related variables were responsible for the habitat diversity in both inner and middle shelves. This research demonstrates that the inclusion of productivity and its related variables, such as hypoxia and sedimentary organic carbon, in seascape classifications will enhance the ability to distinguish seascapes on continental shelves, where productivity is most variable.

Cold cratonic roots and thermal blankets: How continents affect mantle convection

USGS Publications Warehouse

Trubitsyn, V.P.; Mooney, W.D.; Abbott, D.H.

2003-01-01

Two-dimensional convection models with moving continents show that continents profoundly affect the pattern of mantle convection. If the continents are wider than the wavelength of the convection cells (???3000 km, the thickness of the mantle), they cause neighboring deep mantle thermal upwellings to coalesce into a single focused upwelling. This focused upwelling zone will have a potential temperature anomaly of about 200??C, much higher than the 100??C temperature anomaly of upwelling zones generated beneath typical oceanic lithosphere. Extensive high-temperature melts (including flood basalts and late potassic granites) will be produced, and the excess temperature anomaly will induce continental uplift (as revealed in sea level changes) and the eventual breakup of the supercontinent. The mantle thermal anomaly will persist for several hundred million years after such a breakup. In contrast, small continental blocks (<1000 km diameter) do not induce focused mantle upwelling zones. Instead, small continental blocks are dragged to mantle downwelling zones, where they spend most of their time, and will migrate laterally with the downwelling. As a result of sitting over relatively cold mantle (downwellings), small continental blocks are favored to keep their cratonic roots. This may explain the long-term survival of small cratonic blocks (e.g., the Yilgarn and Pilbara cratons of western Australia, and the West African craton). The optimum size for long-term stability of a continental block is <3000 km. These results show that continents profoundly affect the pattern of mantle convection. These effects are illustrated in terms of the timing and history of supercontinent breakup, the production of high-temperature melts, and sea level changes. Such two-dimensional calculations can be further refined and tested by three-dimensional numerical simulations of mantle convection with moving continental and oceanic plates.

Physical processes affecting availability of dissolved silicate for diatom production in the Arabian Sea

NASA Technical Reports Server (NTRS)

Young, David K.; Kindle, John C.

1994-01-01

A passive tracer to represent dissolved silicate concentrations, with biologically realistic uptake kinetics, is successfully incorporated into a three-dimensional, eddy-resolving, ocean circulation model of the Indian Ocean. Hypotheses are tested to evaluate physical processes which potentially affect the availability of silicate for diatom production in the Arabian Sea. An alternative mechanism is offered to the idea that open ocean upwelling is primarily responsible for the high, vertical nutrient flux and consequent large-scale phytoplankton bloom in the northwestern Arabian Sea during the southwest monsoon. Model results show that dissolved silicate in surface waters available for uptake by diatoms is primarily influenced by the intensity of nearshore upwelling from soutwest monsoonal wind forcing and by the offshore advective transport of surface waters. The upwelling, which in the model occurs within 200 +/- 50 km of the coast, appears to be a result of a combination of coastal upwelling, Elkman pumping, and divergence of the coastal flow as it turns offshore. Localized intensifications of silicate concentrations appear to be hydrodynamically driven and geographically correlated to coastal topographic features. The absence of diatoms in sediments of the eastern Arabian Basin is consistent with modeled distributional patterns of dissolved silicate resulting from limited westward advection of upwelled coastal waters from the western continental margin of India and rapid uptake of available silicate by diatoms. Concentrations of modeled silicate become sufficiently low to become unavailable for diatom production in the eastern Arabian Sea, a region between 61 deg E and 70 deg E at 8 deg N on the south, with the east and west boundaries converging on the north at approximately 67 deg E, 20 deg N.

Phytoplankton biomass and microbial abundances during the spring upwelling season in the coastal area off Concepción, central-southern Chile: Variability around a time series station

NASA Astrophysics Data System (ADS)

Morales, Carmen E.; Anabalón, Valeria

2012-01-01

In the coastal system off Concepción, time series observations at a fixed station (St. 18) have shown strong seasonal changes in the oceanographic environment of the upper layer (<35 m depth), accompanied by large increases in phytoplankton biomass during the spring-summer upwelling season. These blooms, dominated by microplanktonic diatoms, have usually overshadowed the relevance of the smaller microbial components during upwelling. This study focuses on the variability of oceanographic conditions and their association with the structure of the planktonic community (size fractionated chlorophyll-a and microbial abundances) in the upper layer during the upwelling season, examining the extent to which St. 18 is representative of the coastal system off Concepción during springtime. For this purpose, data from three consecutive springs (2004, 2005, 2006) were compared, which included cruises for all years (8 stations around St. 18) as well as monthly sampling at St. 18. Most of the spatial (submesoscale) variability in chlorophyll-a and the microbial components was not significant, but data dispersion around mean values was high. Water column structure (temperature and salinity) in the upper layer explained a significant fraction (25-65%) of the spatial variability in most of the planktonic components; their responses to oceanographic variability were linear in some cases and non-linear in others. For the most part, St. 18 appears to adequately represent mean oceanographic conditions and the structure of planktonic communities in the coastal waters off Concepción during springtime, however spatial variability needs to be taken into account in the interpretations of temporal changes at this fixed station as well as in assessments of carbon flow within, and exportation processes from, this upwelling system.

Paleoproductivity and Nutrient Cycling on the Sumatra Margin during the Past Half Million Years

NASA Astrophysics Data System (ADS)

Gibson, K.; Mitt Schwamborn, T.; Thunell, R.; Tuten, E. C.; Swink, C.; Tappa, E.

2017-12-01

In the IndoPacific, changes in paleoproductivity on orbital timescales are often linked to changes in precession, particularly in areas of coastal upwelling. These changes are in turn related to variations in zonal wind patterns and thermocline tilt associated with the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), and commensurate changes in Asian, Indian, and Australian monsoon precipitation and wind-driven upwelling. Previous studies have revealed varying phase relationships amongst monsoon precipitation, upwelling variability and precession minima in the Indo-Pacific region. Regional records have additionally displayed power in the 41-kyr band, attributed to changes in deepwater ventilation and preservation, and the 100-kyr band, related to the influence of sea level on the Indonesian Throughflow (ITF). To provide further insight into the regional and distal forcing on paleoproductivity and nutrient cycling in this clearly complex region, we present %TOC, %CaCO3, and sedimentary δ15N data from core MD98-2152, off the Sumatra margin in a region influenced by both ITF variability and wind-driven upwelling. By comparing our paleoproductivity and paleonutrient data with planktonic δ18O (tuned to composite Chinese cave speleothem records) and benthic δ18O (tuned to the Lisiecki-Raymo Stack), we compare timing of local productivity changes to high latitude ice-volume changes and local hydrographic changes. A strong 23-kyr signal in the %TOC record supports the strong influence of precession on paleoproductivity in this region. In contrast, strong power in the 100 and 41-kyr bands is observed in %CaCO3 and δ15N with a relatively minor contribution from precession, indicating a complex relationship between nutrient cycling, upwelling, production, and preservation on the Sumatra coast.

Multiple mantle upwellings in the transition zone beneath the northern East-African Rift system from relative P-wave travel-time tomography

NASA Astrophysics Data System (ADS)

Civiero, Chiara; Hammond, James O. S.; Goes, Saskia; Fishwick, Stewart; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, J.-Michael; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rümpker, Georg; Stuart, Graham W.

2015-09-01

Mantle plumes and consequent plate extension have been invoked as the likely cause of East African Rift volcanism. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume connected to the large low-shear-velocity province beneath Southern Africa, the so-called African Superplume, to multiple lower-mantle sources along the rift. We present a new P-wave travel-time tomography model below the northern East-African, Red Sea, and Gulf of Aden rifts and surrounding areas. Data are from stations that span an area from Madagascar to Saudi Arabia. The aperture of the integrated data set allows us to image structures of ˜100 km length-scale down to depths of 700-800 km beneath the study region. Our images provide evidence of two clusters of low-velocity structures consisting of features with diameter of 100-200 km that extend through the transition zone, the first beneath Afar and a second just west of the Main Ethiopian Rift, a region with off-rift volcanism. Considering seismic sensitivity to temperature, we interpret these features as upwellings with excess temperatures of 100 ± 50 K. The scale of the upwellings is smaller than expected for lower mantle plume sources. This, together with the change in pattern of the low-velocity anomalies across the base of the transition zone, suggests that ponding or flow of deep-plume material below the transition zone may be spawning these upper mantle upwellings. This article was corrected on 28 SEP 2015. See the end of the full text for details.

Record of massive upwellings from the Pacific large low shear velocity province

PubMed Central

Madrigal, Pilar; Gazel, Esteban; Flores, Kennet E.; Bizimis, Michael; Jicha, Brian

2016-01-01

Large igneous provinces, as the surface expression of deep mantle processes, play a key role in the evolution of the planet. Here we analyse the geochemical record and timing of the Pacific Ocean Large Igneous Provinces and preserved accreted terranes to reconstruct the history of pulses of mantle plume upwellings and their relation with a deep-rooted source like the Pacific large low-shear velocity Province during the Mid-Jurassic to Upper Cretaceous. Petrological modelling and geochemical data suggest the need of interaction between these deep-rooted upwellings and mid-ocean ridges in pulses separated by ∼10–20 Ma, to generate the massive volumes of melt preserved today as oceanic plateaus. These pulses impacted the marine biota resulting in episodes of anoxia and mass extinctions shortly after their eruption. PMID:27824054

Retrieval of surface temperature by remote sensing. [of earth surface using brightness temperature of air pollutants

NASA Technical Reports Server (NTRS)

Gupta, S. K.; Tiwari, S. N.

1976-01-01

A simple procedure and computer program were developed for retrieving the surface temperature from the measurement of upwelling infrared radiance in a single spectral region in the atmosphere. The program evaluates the total upwelling radiance at any altitude in the region of the CO fundamental band (2070-2220 1/cm) for several values of surface temperature. Actual surface temperature is inferred by interpolation of the measured upwelling radiance between the computed values of radiance for the same altitude. Sensitivity calculations were made to determine the effect of uncertainty in various surface, atmospheric and experimental parameters on the inferred value of surface temperature. It is found that the uncertainties in water vapor concentration and surface emittance are the most important factors affecting the accuracy of the inferred value of surface temperature.

Enhanced incubation success for kokanee spawning in groundwater upwelling sites in a small Idaho stream

Treesearch

James W. Garrett; David H. Bennett; Frank O. Frost; Russell F. Thurow

1998-01-01

Kokanee (Oncorhynchus nerka lacustrine sockeye salmon) spawned in groundwater upwelling in the North Fork of the Payette River, Idaho. Intragravel water temperatures in groundwater-influenced redds exceeded surface flow water temperature by 2.4–2.6°C. In redds without groundwater influence, intragravel and water column temperatures did not differ by more than 0.2°C....

The physical oceanography of upwelling systems and the development of harmful algal blooms

PubMed Central

Pitcher, G.C.; Figueiras, F.G.; Hickey, B.M.; Moita, M.T.

2011-01-01

The upwelling systems of the eastern boundaries of the world’s oceans are susceptible to harmful algal blooms (HABs) because they are highly productive, nutrient-rich environments, prone to high-biomass blooms. This review identifies those aspects of the physical environment important in the development of HABs in upwelling systems through description and comparison of bloom events in the Benguela, California and Iberia systems. HAB development is dictated by the influence of wind stress on the surface boundary layer through a combination of its influence on surface mixed-layer characteristics and shelf circulation patterns. The timing of HABs is controlled by windstress fluctuations and buoyancy inputs at the seasonal, event and interannual scales. Within this temporal framework, various mesoscale features that interrupt typical upwelling circulation patterns, determine the spatial distribution of HABs. The inner shelf in particular provides a mosaic of shifting habitats, some of which favour HABs. Changes in coastline configuration and orientation, and bottom topography are important in determining the distribution of HABs through their influence on water stratification and retention. A spectrum of coastline configurations, including headlands, capes, peninsulas, Rías, bays and estuaries, representing systems of increasing isolation from the open coast and consequent increasing retention times, are assessed in terms of their vulnerability to HABs. PMID:22053120

Wind-driven changes of surface current, temperature, and chlorophyll observed by satellites north of New Guinea

NASA Astrophysics Data System (ADS)

Radenac, Marie-Hélène; Léger, Fabien; Messié, Monique; Dutrieux, Pierre; Menkes, Christophe; Eldin, Gérard

2016-04-01

Satellite observations of wind, sea level and derived currents, sea surface temperature (SST), and chlorophyll are used to expand our understanding of the physical and biological variability of the ocean surface north of New Guinea. Based on scarce cruise and mooring data, previous studies differentiated a trade wind situation (austral winter) when the New Guinea Coastal Current (NGCC) flows northwestward and a northwest monsoon situation (austral summer) when a coastal upwelling develops and the NGCC reverses. This circulation pattern is confirmed by satellite observations, except in Vitiaz Strait where the surface northwestward flow persists. We find that intraseasonal and seasonal time scale variations explain most of the variance north of New Guinea. SST and chlorophyll variabilities are mainly driven by two processes: penetration of Solomon Sea waters and coastal upwelling. In the trade wind situation, the NGCC transports cold Solomon Sea waters through Vitiaz Strait in a narrow vein hugging the coast. Coastal upwelling is generated in westerly wind situations (westerly wind event, northwest monsoon). Highly productive coastal waters are advected toward the equator and, during some westerly wind events, toward the eastern part of the warm pool. During El Niño, coastal upwelling events and northward penetration of Solomon Sea waters combine to influence SST and chlorophyll anomalies.

Fungal parasites infect marine diatoms in the upwelling ecosystem of the Humboldt current system off central Chile.

PubMed

Gutiérrez, Marcelo H; Jara, Ana M; Pantoja, Silvio

2016-05-01

This is the first report of fungal parasitism of diatoms in a highly productive coastal upwelling ecosystem, based on a year-round time series of diatom and parasitic Chytridiomycota abundance in the Humboldt Current System off Chile (36°30.80'S-73°07.70'W). Our results show co-variation in the presence of Skeletonema, Thalassiosira and Chaetoceros diatoms with attached and detached chytrid sporangia. High abundance of attached sporangia was observed during the austral spring, coinciding with a predominance of Thalassiosira and Skeletonema under active upwelling conditions. Towards the end of austral spring, a decreasing proportion of attached sporangia was accompanied by a decline in abundance of Skeletonema and Thalassiosira and the predominance of Chaetoceros, suggesting specificity and host density dependence of chytrid infection. The new findings on fungal parasitism of diatoms provide further support for the inclusion of Fungi in the current model of the role played by the marine microbial community in the coastal ocean. We propose a conceptual model where Fungi contribute to controlling the dynamics of phytoplankton populations, as well as the release of organic matter and the transfer of organic carbon through the pelagic trophic web in coastal upwelling ecosystems. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Effects of contrasting upwelling downwelling on benthic foraminiferal distribution in the Ría de Vigo (NW Spain)

NASA Astrophysics Data System (ADS)

Diz, Paula; Francés, Guillermo; Rosón, Gabriel

2006-04-01

Live benthic foraminifera in the superficial sediments from the muddy central axis of the Ría de Vigo were examined under two contrasting hydrographic conditions: downwelling and upwelling. During downwelling conditions the abundance of benthic foraminifera does not show large differences between sites with different organic carbon contents. The arrival of labile organic carbon to the seafloor delivered during upwelling events causes an increase in the abundance of the most significant species and the appearance of new species in the life assemblage. This suggests that benthic foraminiferal faunas strongly depend on high quality organic carbon supply and the sedimentary organic carbon is not a good indicator of food availability to benthic foraminifera. The response of benthic foraminifera to phytoplankton blooms differs between outer and inner sites. In outer and middle areas benthic foraminiferal assemblages show quick population growth in reaction to phytoplankton blooms (r-strategists), whereas in inner sites the most abundant species displays both growth and reproduction (k-strategists). It is suggested that r-strategy results of adaptation to perturbations on short time-scales (downwelling/upwelling cycles) under favourable microenvironmental conditions, while the k-strategy represents the adaptation to long term perturbations, such as relatively low oxygen concentrations and/or reducing microenvironmental conditions in the sediment.

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

PubMed

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

2018-02-12

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

The formation processes of phytoplankton growth and decline in mesoscale eddies in the western North Pacific Ocean

NASA Astrophysics Data System (ADS)

Chang, Yu-Lin; Miyazawa, Yasumasa; Oey, Lie-Yauw; Kodaira, Tsubasa; Huang, Shihming

2017-05-01

In this study, we investigate the processes of phytoplankton growth and decline in mesoscale eddies in the western North Pacific Ocean based on the in situ chlorophyll data obtained from 52 cruises conducted by the Japan Meteorological Agency together with idealized numerical simulations. Both the observation and model results suggest that chlorophyll/phytoplankton concentrations are higher in cold than in warm eddies in near-surface water (z > -70 m). In the idealized simulation, the isopycnal movements associated with upwelling/downwelling transport phytoplankton and nutrients to different vertical depths during eddy formation (stage A). Phytoplankton and nutrients in cold eddies is transported toward shallower waters while those in warm eddies move toward deeper waters. In the period after the eddy has formed (stage B), sunlight and initially upwelled nutrients together promote the growth of phytoplankton in cold eddies. Phytoplankton in warm eddies decays due to insufficient sunlight in deeper waters. In stage B, upwelling and downwelling coexist in both warm and cold eddies, contributing nearly equally to vertical displacement. The upwelling/downwelling-induced nitrate flux accounts for a small percentage (˜3%) of the total nitrate flux in stage B. The vertical velocity caused by propagating eddies, therefore, is not the primary factor causing differences in phytoplankton concentrations between stage-B warm and cold eddies.

Evidence for the interior evolution of Ceres from geologic analysis of fractures

USGS Publications Warehouse

Scully, Jennifer E. C.; Buczkowski, Debra; Schmedemann, Nico; Raymond, Carol A.; Castillo-Rogez, Julie C.; Scott King,; Bland, Michael T.; Ermakov, Anton; O'Brien, D.P.; Marchi, S.; Longobardo, A.; Russell, C.T.; Fu, R.R.; Neveu, M.

2017-01-01

Ceres is the largest asteroid belt object, and the Dawn spacecraft observed Ceres since 2015. Dawn observed two morphologically distinct linear features on Ceres's surface: secondary crater chains and pit chains. Pit chains provide unique insights into Ceres's interior evolution. We interpret pit chains called the Samhain Catenae as the surface expression of subsurface fractures. Using the pit chains' spacings, we estimate that the localized thickness of Ceres's fractured, outer layer is approximately ≥58 km, at least ~14 km greater than the global average. We hypothesize that extensional stresses, induced by a region of upwelling material arising from convection/diapirism, formed the Samhain Catenae. We derive characteristics for this upwelling material, which can be used as constraints in future interior modeling studies. For example, its predicted location coincides with Hanami Planum, a high-elevation region with a negative residual gravity anomaly, which may be surficial evidence for this proposed region of upwelling material.

Wind, Circulation, and Topographic Effects on Alongshore Phytoplankton Variability in the California Current

NASA Astrophysics Data System (ADS)

Fiechter, Jerome; Edwards, Christopher A.; Moore, Andrew M.

2018-04-01

A physical-biogeochemical model is used to produce a retrospective analysis at 3-km resolution of alongshore phytoplankton variability in the California Current during 1988-2010. The simulation benefits from downscaling a regional circulation reanalysis, which provides improved physical ocean state estimates in the high-resolution domain. The emerging pattern is one of local upwelling intensification in response to increased alongshore wind stress in the lee of capes, modulated by alongshore meanders in the geostrophic circulation. While stronger upwelling occurs near most major topographic features, substantial increases in phytoplankton biomass only ensue where local circulation patterns are conducive to on-shelf retention of upwelled nutrients. Locations of peak nutrient delivery and chlorophyll accumulation also exhibit interannual variability and trends noticeably larger than the surrounding shelf regions, thereby suggesting that long-term planktonic ecosystem response in the California Current exhibits a significant local scale (O(100 km)) alongshore component.

Atmosphere-ocean feedbacks in a coastal upwelling system

NASA Astrophysics Data System (ADS)

Alves, J. M. R.; Peliz, A.; Caldeira, R. M. A.; Miranda, P. M. A.

2018-03-01

The COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) modelling system is used in different configurations to simulate the Iberian upwelling during the 2012 summer, aiming to assess the atmosphere-ocean feedbacks in the upwelling dynamics. When model results are compared with satellite measurements and in-situ data, two-way coupling is found to have a moderate impact in data-model statistics. A significant reinforcement of atmosphere-ocean coupling coefficients is, however, observed in the two-way coupled run, and in the WRF and ROMS runs forced by previously simulated SST and wind fields, respectively. The increasing in the coupling coefficient is associated with slight, but potentially important changes in the low-level coastal jet in the atmospheric marine boundary layer. While these results do not imply the need for fully coupled simulations in many applications, they show that in seasonal numerical studies such simulations do not degrade the overall model performance, and contribute to produce better dynamical fields.

Palaeoceanography. Antarctic stratification and glacial CO2.

PubMed

Keeling, R F; Visbeck, M

2001-08-09

One way of accounting for lowered atmospheric carbon dioxide concentrations during Pleistocene glacial periods is by invoking the Antarctic stratification hypothesis, which links the reduction in CO2 to greater stratification of ocean surface waters around Antarctica. As discussed by Sigman and Boyle, this hypothesis assumes that increased stratification in the Antarctic zone (Fig. 1) was associated with reduced upwelling of deep waters around Antarctica, thereby allowing CO2 outgassing to be suppressed by biological production while also allowing biological production to decline, which is consistent with Antarctic sediment records. We point out here, however, that the response of ocean eddies to increased Antarctic stratification can be expected to increase, rather than reduce, the upwelling rate of deep waters around Antarctica. The stratification hypothesis may have difficulty in accommodating eddy feedbacks on upwelling within the constraints imposed by reconstructions of winds and Antarctic-zone productivity in glacial periods.

Sensitivity analysis of upwelling thermal radiance in presence of clouds

NASA Technical Reports Server (NTRS)

Subramanian, S. V.; Tiwari, S. N.; Suttles, J. T.

1981-01-01

Total upwelling radiance at the top of the atmosphere is evaluated theoretically in the presence of clouds. The influence of cloud heights, thicknesses and different cloud covers on the upwelling radiance is also investigated. The characteristics of the two cloud types considered in this study closely correspond to altocumulus and cirrus with the cloud emissivity as a function of its liquid water (or ice) content. For calculation of the integrated transmittance of atmospheric gases such as, H2O, CO2, O3, and N2O, the Quasi Random Band (QRB) model approach is adopted. Results are obtained in three different spectral ranges and are compared with the clearsky radiance results. It is found that the difference between the clearsky and cloudy radiance increases with increasing cloud height and liquid water content. This difference also decreases as the surface temperature approaches the value of the cloud top temperature.

Theoretical properties of Omega-loops in the convective zone of the Sun. 1: Emerging bipolar magnetic regions

NASA Technical Reports Server (NTRS)

Parker, E. N.

1994-01-01

It is proposed that the observed 500 G intensity of the magnetic fields emerging through the surface of the Sun can be understood from the Bernoulli effect in the upwelling Omega-loops of magnetic field. It is also proposed that the inferred 10(exp 5) G azimuthal flux bundles below the base of the convective zone can be understood as a consequence of the large-scale buoyancy associated with the upwelling fluid in and around the rising Omega-loop. The process fits in naturally with the Babcock-Leighton form of the solar alpha-omega-dynamo. The emerging Omega-loop implies the coherence of the upwelling all the way from the bottom of the convective zone, enhancing the convective heat transport to account for the observed variation of the solar irradiance by about two parts in 10(exp 3).

Three-Dimensional Spherical Models of Convection in the Earth's Mantle.

PubMed

Bercovici, D; Schubert, G; Glatzmaier, G A

1989-05-26

Three-dimensional, spherical models of mantle convection in the earth reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of mantle circulation. Thus, subduction zones and descending sheetlike slabs in the mantle are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs, which are cooler than the surrounding mantle. Cylindrical mantle plumes that cause hotspots such as Hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large-scale mantle circulation. Active sheetlike upwellings that could be associated with mid-ocean ridges did not develop in the model simulations, a result that is in agreement with evidence suggesting that ridges are passive phenomena resulting from the tearing of surface plates by the pull of descending slabs.

Does deep ocean mixing drive upwelling or downwelling of abyssal waters?

NASA Astrophysics Data System (ADS)

Ferrari, R. M.; McDougall, T. J.; Mashayek, A.; Nikurashin, M.; Campin, J. M.

2016-02-01

It is generally understood that small-scale mixing, such as is caused by breaking internal waves, drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes. However the observational evidence that the turbulent fluxes generated by small-scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom than above implies that small-scale mixing converts light waters into denser ones, thus driving a net sinking of abyssal water. Using a combination of numerical models and observations, it will be shown that abyssal waters return to the surface along weakly stratified boundary layers, where the small-scale mixing of density decays to zero. The net ocean meridional overturning circulation is thus the small residual of a large sinking of waters, driven by small-scale mixing in the stratified interior, and a comparably large upwelling, driven by the reduced small-scale mixing along the ocean boundaries.

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

NASA Technical Reports Server (NTRS)

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

1991-01-01

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

Shift in the species composition of the diatom community in the eutrophic Mauritanian coastal upwelling: Results from a multi-year sediment trap experiment (2003-2010)

NASA Astrophysics Data System (ADS)

Romero, Oscar E.; Fischer, Gerhard

2017-12-01

A multiannual, continuous sediment trap experiment was conducted at the mooring site CBeu (Cape Blanc eutrophic, ca. 20 °N, ca. 18 °W; trap depth = 1256-1296 m) in the high-productive Mauritanian coastal upwelling. Here we present fluxes and the species-specific composition of the diatom assemblage, and fluxes of biogenic silica (BSi, opal) and total organic carbon (TOC) for the time interval June 2003-Feb 2010. Flux ranges of studied parameters are (i) total diatoms = 1.2 ∗ 108-4.7 ∗ 104 valves m-2 d-1 (average = 5.9 × 106 valves ± 1.4 × 107); (ii) BSi = 296-0.5 mg m-2 d-1 (average = 41.1 ± 53.5 mg m-2 d-1), and (iii) TOC = 97-1 mg m-2 d-1 (average = 20.5 ± 17.8 mg m-2 d-1). Throughout the experiment, the overall good match of total diatom, BSi and TOC fluxes is reasonably consistent and reflects well the temporal occurrence of the main Mauritanian upwelling season. Spring and summer are the most favorable seasons for diatom production and sedimentation: out of the recorded 14 diatom maxima of different magnitude, six occurred in spring and four in summer. The diverse diatom community at site CBeu is composed of four main assemblages: benthic, coastal upwelling, coastal planktonic and open-ocean diatoms, reflecting different productivity conditions and water masses. A striking feature of the temporal variability of the diatom populations is the persistent pattern of seasonal groups' contribution: benthic and coastal upwelling taxa dominated during the main upwelling season in spring, while open-ocean diatoms were more abundant in fall and winter, when the upper water column becomes stratified, upwelling relaxes and productivity decreases. The relative abundance of benthic diatoms strongly increased after 2006, yet their spring-summer contribution remained high until the end of the trap experiment. The occurrence of large populations of benthic diatoms at the hemipelagic CBeu site is interpreted to indicate transport from shallow waters via nepheloid layers. We argue that a significant amount of valves, BSi and TOC produced in waters overlying the Banc d'Arguin and the Mauritanian shelf is effectively transported to the CBeu trap in intermediate waters at the outer Mauritanian slope. The impact of the intermediate and bottom-near nepheloid layers-driven transport in the transfer of valves and bulk particulates and its potential contribution to the export of biogenic materials from the shelf and uppermost slope might play a significant role in hemipelagial fluxes off Mauritania.

The Design and Analysis of Salmonid Tagging Studies in the Columbia Basin : Volume XVII : Effects of Ocean Covariates and Release Timing on First Ocean-Year Survival of Fall Chinook Salmon from Oregon and Washington Coastal Hatcheries.

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

Burgess, Caitlin; Skalski, John R.

2001-05-01

Effects of oceanographic conditions, as well as effects of release-timing and release-size, on first ocean-year survival of subyearling fall chinook salmon were investigated by analyzing CWT release and recovery data from Oregon and Washington coastal hatcheries. Age-class strength was estimated using a multinomial probability likelihood which estimated first-year survival as a proportional hazards regression against ocean and release covariates. Weight-at-release and release-month were found to significantly effect first year survival (p < 0.05) and ocean effects were therefore estimated after adjusting for weight-at-release. Negative survival trend was modeled for sea surface temperature (SST) during 11 months of the year overmore » the study period (1970-1992). Statistically significant negative survival trends (p < 0.05) were found for SST during April, June, November and December. Strong pairwise correlations (r > 0.6) between SST in April/June, April/November and April/December suggest the significant relationships were due to one underlying process. At higher latitudes (45{sup o} and 48{sup o}N), summer upwelling (June-August) showed positive survival trend with survival and fall (September-November) downwelling showed positive trend with survival, indicating early fall transition improved survival. At 45{sup o} and 48{sup o}, during spring, alternating survival trends with upwelling were observed between March and May, with negative trend occurring in March and May, and positive trend with survival occurring in April. In January, two distinct scenarios of improved survival were linked to upwelling conditions, indicated by (1) a significant linear model effect (p < 0.05) showing improved survival with increasing upwelling, and (2) significant bowl-shaped curvature (p < 0.05) of survival with upwelling. The interpretation of the effects is that there was (1) significantly improved survival when downwelling conditions shifted to upwelling conditions in January (i.e., early spring transition occurred, p < 0.05), (2) improved survival during strong downwelling conditions (Bakun units < -250). Survival decreased during weak downwelling conditions (Bakun units between -180 and -100). Strong to moderately strong correlations between January upwelling and April SST (r = 0.5), June SST (r = 0.6), and the North Pacific Index (NPI) of Aleutian Low strength (r > 0.7) suggest January is a period when important effects originate and play out over ensuing months. Significant inverse trend with survival (p < 0.05) was found for Bakun indices in December, indicating strong downwelling improved survival. Higher-than-average adult return rates were observed for cohorts from brood-years 1982-1983, strong El Nino years. Individual hatcheries were found to have unique age-class strength and age-at-return characteristics.« less

Kinetics of N-Utilization By Natural Phytoplankton Assemblages During Upwelling Events At The NW Iberian Shelf

NASA Astrophysics Data System (ADS)

Brion, N.; Elskens, M.; Dehairs, F.; Baeyens, W.

2003-04-01

The concentration-dependent uptakes of nitrate, ammonium and the effect of ammo-nium on the f-ratio were surveyed in surface waters of the NW Iberian shelf during June 1997, July 1998 and September 1999. Because relationships between rates and substrate concentrations were quite variable, ranging from linear to convex shaped curves, they were fitted to rational functions. Stepwize regression analysis yielded subsequent model equations with reasonable statistical properties which allowed describing all but all a few cases. Differentiating these equations with respect to the concentration gave the slope of the tangent to the curve, i.e., the variation in rate expected for a given perturbation of the ambient substrate concentration. The initial slope value was then used as an index to gauge the "affinity" of the plankton community for the nitrogen substrate utilization. In June 1997, the situation at the Iberian shelf showed no upwelling except near Cape Finistère. Overall, the phytoplankton community displayed a high "affinity" for both nitrate and ammonium and low f-ratio values, which is indicative of a re-generated production regime. High ammonium regeneration rates supported furthermore these observations. It was also demonstrated that the new production rates is only marginally sensitive to changes of the ambient nitrate and/or ammonium concentrations. This indicates that the production regime is rather stable throughout. Only at Cape Finistère, nitrate concentrations were high reflecting the onset of an upwelling event. In this zone, the phytoplankton community, taking advantage of its high affinity for nitrate enhanced both total N-uptake rate and f-ratio. In July 1998, the situation evolved towards an extension to the south of the upwelling event starting at Cape Finistère. In this southern zone of the upwelling the phytoplankton community displayed generally a lower affinity for nitrate (but not for ammonium) than in 1997. In spite of this lower affinity, nitrate uptake rate was dominant resulting in f-ratio values greater than 0.5, a characteristic of a new production regime. The new production rate is only marginally sensitive to increases of the ambient nitrate, but is drastically inhibited by small increases of the ambient ammonium. The situation of September 1999 was very close to that observed in July 1998, with higher nitrate concentrations in the coastal northern part of the sampling area dominated by upwelling.

Assessing the applicability of organic SST proxies in an upwelling region (Arabian Sea)

NASA Astrophysics Data System (ADS)

Lattaud, J.; van Erk, M. R.; Reichart, G. J.; Schulz, H.; S Sinninghe Damsté, J.; Schouten, S.

2017-12-01

Multiple organic proxies have the potential to reconstruct sea surface temperature (SST), but their behaviour is not completely understood within upwelling areas. This holds in particular for the recently developed Long chain Diol Index1 (LDI), based on the ratio of 1,15-diols over 1,13-diols, both likely produced by Eustigmatophytes. We tested the applicability of the LDI by comparing it to the more established temperature proxies TEX86 and Uk¢37 in a sediment core (spanning the last 76 ky) from the northern Arabian Sea and in surface sediments (Pakistan margin). In the surface sediments, Uk¢37- and LDI-SSTs agree well with annual mean SST, but the TEX86-SST substantially overestimates SST. A better agreement is observed, when the 0-200 m TEX86 calibration is used, suggesting TEX86 reflects subsurface temperatures. The results from the sediment core reveal that the SST records differ in absolute reconstructed temperature and show different patterns. TEX86 subsurface temperatures show a continuous increase toward the Holocene and no stadial/interstadial differences, while the LDI-SST is constant around 26°C with the exception of some short-term cooling events during periods of intensified upwelling. The Uk¢37-SST varies between 22 and 26°C and follows the global δ18Obenthic foram curve and thus is representing mean annual SST in this region3. During stadials, the reduced monsoon and low upwelling intensity resulted in warming of the subsurface waters2, as indicated by higher TEX86 temperatures, while global cooling led to colder surface waters as reflected in lower Uk¢37-SSTs, thus reducing the thermal gradient in the water column2. During the interstadials, which are periods of strong upwelling3, there is a high proportion of 1,14-diols (>40%). This probably disturbs the LDI-SST signal because the diatoms that produce the 1,14-diols are also generating small amounts of the 1,13-diols4. This suggests that care has to be taken in applying the LDI in upwelling regions. References 1Rampen et al., 2012 2Tierney et al., 2015 3Emeis et al., 1995 4Rampen et al., 2007

Ridge jumps associated with plume-ridge interaction: Mantle plume-lithosphere interaction and hotspot magmatism

NASA Astrophysics Data System (ADS)

Mittelstaedt, E.; Ito, G.

2007-12-01

Interaction of mantle plumes and young lithosphere near mid-ocean ridges can lead to changes in spreading geometry by shifts of the ridge-axis toward the plume as seen at various hotspots, notably Iceland and the Galapagos. Previous work has shown that, with a sufficient magma flux, heating of the lithosphere by magmatism can significantly weaken the plate and, in some cases, could cause ridge jumps. Upwelling hot asthenosphere can also weaken the plate through thermal and mechanical thinning of the lithosphere. Using the finite element code CITCOM, we solve the equations of continuity, momentum and energy to examine deformation in near-ridge lithosphere associated with relatively hot upwelling asthenosphere and seafloor spreading. The mantle and lithosphere obey a non-Newtonian viscous rheology with plastic failure in the cold part of the lithosphere simulated by imposing an effective yield stress. Temperatures of the lithospheric thermal boundary region are initially given a square-root of age thermal profile while a hot patch is placed at the bottom to initiate a mantle-plume like upwelling. The effect of upwelling asthenosphere on ridge jumps is evaluated by varying three parameters: the plume excess temperature, the spreading rate and the distance of the plume from the ridge axis. Preliminary results show plume related thinning and weakening of the lithosphere over a wide area (100's of km's) with the rate of thinning increasing with the excess temperature of the plume. Initially, thinning occurs as the plume approaches the lithosphere and asthenospheric material is forced out of the way. As the plume material comes into contact with the lithosphere, thinning occurs through heating and mechanical removal of the thermal boundary layer. Thinning of the lithosphere is one of the primary factors in achieving a ridge jump. Another is large tensile stresses which can facilitate the initiation of rifting at this weakened location. Model stresses induced by the buoyant asthenosphere are significant fractions of the lithospheric yield strength near the plume and reach a maximum at the center of plume upwelling. Models predict that ridge jumps are not likely to occur by lithosphere interaction with the hot upwelling plume alone but require the added effects of magmatic weakening at the hotspot.

Assessment of chlorophyll variability along the northwestern coast of Iberian Peninsula

NASA Astrophysics Data System (ADS)

Picado, A.; Alvarez, I.; Vaz, N.; Varela, R.; Gomez-Gesteira, M.; Dias, J. M.

2014-10-01

The northwestern coast of the Iberian Peninsula is characterized by a high primary production mainly supported by coastal upwelling, creating an extraordinary commercial interest for fisheries and aquaculture. Considering chlorophyll-a (Chl-a) as an indicator of primary production, its spatio-temporal variability was researched in this study in the surface water of this upwelling region from 1998 to 2007. Satellite derived Chl-a, Sea Surface Temperature (SST) and Ekman transport data as well as the inflow of the main rivers discharging into the study area were used to investigate the origin of the Chl-a concentration. Empirical Orthogonal Function (EOF) analysis of weekly Chl-a images was performed, as well as correlation analysis between Chl-a concentration, Ekman transport and river discharge. EOF results suggest that the highest Chl-a concentration occurs near the coast up to 60 km offshore. The interannual variability of Chl-a, SST and Ekman transport was also studied considering summer and winter months. Generally, 2005, 2006 and 2007 were the most productive years during the summer months with high Chl-a concentrations along the coast associated to the strong upwelling conditions observed. Otherwise, 1998 seemed to be the most productive year during winter. The absence of upwelling favorable conditions together with localized low SST and considerable discharges, suggests that the high Chl-a concentrations observed during this period are mainly due to the entrance of nutrients through river runoff. However, in winter, high concentrations of colored dissolved organic matter (CDOM), associated with river runoff, are present in the ocean surface, leading to an erroneous strong signal of the satellite. During winter correlations of 0.58 and 0.49 were found between Chl-a concentration and Douro and Minho discharges, respectively, evidencing that high Chl-a concentration was related with river runoff. Otherwise, during summer, Chl-a and Ekman transport exhibited a correlation of - 0.38 indicating that high Chl-a is associated to upwelling events. In summary, it was found that the spatio-temporal variability of Chl-a along the northwestern coast of Iberian Peninsula exhibited the clear influence of upwelling events during summer. Conversely, the variability during winter was mainly due to entrance of nutrients through the rivers discharge which flow into the area.

Seasonal and annual variability of coastal sulphur plumes in the northern Benguela upwelling system

PubMed Central

Dadou, Isabelle

2018-01-01

We investigated the seasonal and annual variability of surface sulphur plumes in the northern Benguela upwelling system off Namibia because of their significant impacts on the marine ecosystem, fishing industry, aquaculture farming and tourism due to their toxic properties. We identified the sulphur plumes in ocean colour satellite data of the medium resolution imaging spectrometer (MERIS) for the 2002–2012 time period using the differences in the spectral properties of Namibian Benguela optical water types. The sulphur events have a strong seasonal cycle with pronounced main and off-seasons forced by local and remote-driven processes. The main peak season is in late austral summer and early austral autumn at the beginning of the annual upwelling cycle caused by increasing equatorwards alongshore winds. The sulphur plume activity is high between February and April during the seasonal oxygen minimum associated with the seasonal reduction of cross-shore ventilation of the bottom waters, the seasonal southernmost position of the Angola Benguela Frontal Zone, the seasonal maximum of water mass fractions of South Atlantic and Angola Gyre Central Waters as well as the seasonal arrival of the downwelling coastal trapped waves. The off-season is in austral spring and early austral summer during increased upwelling intensity and enhanced oxygen supply. The annual variability of sulphur events is characterized by very high activities in years 2004, 2005 and 2010 interrupted by periods of lower activity in years 2002 to 2003, 2006 to 2009 and 2011 to 2012. This result can be explained by the relative contributions or adding effects of local and remote-driven forces (from the equatorial area). The probability for the occurrence of sulphur plumes is enhanced in years with a lower annual mean of upwelling intensity, decreased oxygen supply associated with decreased lateral ventilation of bottom waters, more southern position of the Angola Benguela Frontal Zone, increased mass fraction of South Atlantic Central Water and stronger downwelling coastal trapped waves. Understanding of the variability and forcing processes of the toxic sulphur events will help in the future to monitor and forecast them as well as to manage their social and economic consequences in the northern Benguela upwelling system off Namibia. PMID:29420587

Oceanographic, Air-sea Interaction, and Environmental Aspects of Artificial Upwelling Produced by Wave-Inertia Pumps for Potential Hurricane Intensity Mitigation

NASA Astrophysics Data System (ADS)

Soloviev, A.; Dean, C.

2017-12-01

The artificial upwelling system consisting of the wave-inertia pumps driven by surface waves can produce flow of cold deep water to the surface. One of the recently proposed potential applications of the artificial upwelling system is the hurricane intensity mitigation. Even relatively small reduction of intensity may provide significant benefits. The ocean heat content (OHC) is the "fuel" for hurricanes. The OHC can be reduced by mixing of the surface layer with the cold water produced by wave-inertia pumps. Implementation of this system for hurricane mitigation has several oceanographic and air-sea interaction aspects. The cold water brought to the surface from a deeper layer has higher density than the surface water and, therefore, tends to sink back down. The mixing of the cold water produced by artificial upwelling depends on environmental conditions such as stratification, regional ocean circulation, and vertical shear. Another aspect is that as the sea surface temperature drops below the air temperature, the stable stratification develops in the atmospheric boundary layer. The stable atmospheric stratification suppresses sensible and latent heat air-sea fluxes and reduces the net longwave irradiance from the sea surface. As a result, the artificial upwelling may start increasing the OHC (though still reducing the sea surface temperature). In this work, the fate of the cold water in the stratified environment with vertical shear has been studied using computational fluid dynamics (CFD) tools. A 3D large eddy simulation model is initialized with observational temperature, salinity, and current velocity data from a sample location in the Straits of Florida. A periodic boundary condition is set along the direction of the current, which allows us to simulate infinite fetch. The model results indicate that the cold water brought to the sea surface by a wave-inertia pump forms a convective jet. This jet plunges into the upper ocean mixed layer and penetrates the thermocline. On the way down, the jet partially mixes with the surrounding water reducing the temperature of the upper ocean. The OHC thus can either reduce or increase, depending on the wave-inertia pump parameters. Based on the model results, we discuss feasibility of the implementation of the artificial upwelling system for hurricane intensity mitigation.

Phytoplankton and nutrient distributions in a front-eddy area adjacent to the coastal upwelling zone off Concepcion (Chile): implications for ecosystem productivity.

NASA Astrophysics Data System (ADS)

Morales, Carmen; Anabalón, Valeria; Hormazábal, Samuel; Cornejo, Marcela; Bento, Joaquim; Silva, Nelson

2016-04-01

The impact that sub-mesoscale (1-10 km) to mesocale (50-100 km) oceanographic variability has on plankton and nutrient distributions (horizontal and vertical) in the coastal upwelling and transition zones off Concepcion was the focus of this study. Satellite time-series data (wind, sea-surface temperature (SST), and altimetry) were used to understand the dynamic context of in situ data derived from a short-term front survey (3 d) during the upwelling period (3-6 February, 2014). The survey included two transects perpendicular to the coast, covering the shelf and shelf-break areas just north of Punta Lavapie, a main upwelling center (˜37° S). Wind and SST time-series data indicated that the survey was undertaken just after a moderate upwelling event (end of January) which lead to a relaxation phase during early February. A submesoscale thermal front was detected previous to and during the survey and results from an eddy tracking algorithm based on altimetry data indicated that this front (F1) was flanked on its oceanic side by an anticyclonic, mesoscale eddy (M1), which was ˜25 d old at the sampling time. M1 strengthened the thermal gradient of F1 by bringing warmer oceanic water nearer to the colder coastal upwelling zone. The distributions of hydrographic variables and nutrients in the water column (<300 m depth) also denoted these two features. Phytoplankton biomass (Chl-a) and diatom abundance were highest in the surface layer (<20 m depth) between the coast and F1, with primary maxima in the latter, whereas they were highest at the subsurface (20-40 m depth) towards M1 and associated with secondary maxima. The distribution of dominant diatoms in the top layer (<100 m depth) indicated that both coastal and oceanic species were aggregated at F1 and in M1. These results suggest that the front-eddy interaction creates a complex field of submesoscale processes in the top layer, including vertical nutrient injections and lateral stirring, which contributes to the exportation of coastal communities to the open ocean in this region. We discuss how this interaction might affect ecosystem productivity in the coastal band.

A Model of the Spatial Structure and Productivity of Phytoplankton Populations during Variable Upwelling Off the Coast of Oregon

DTIC Science & Technology

1976-09-01

Univ., Corvallis, 71 p. barber, R. T. and J. H. Ryther, 1969. Organic chelators: factors affecting primary production in the Cromwell1 current upwelling...Mesoscale Air-Sea Interaction Group Technical Report I A MODEL OF THE SPATIAL STRUCTURE AND PRODUCTIVITY OF PHYTOPLANKTON POPULATIONS DURING...Variability in the wind stress affects the rate of ufpwelling and ultimtely the local biological productivity . To investigate the relationship between wind

Analysis of the Inshore California Current System Off Central California Using Naval Oceanographic Office Survey Data from 1997 to 2002

DTIC Science & Technology

2012-09-01

toward the coast due to upwelling . Acceleration potential on the 26.0 kg/m3 isopycnal showed persistent poleward inshore flow for all cruises and...100 km from shore that divided low offshore and high inshore spiciness. The 26.0 kg/m3 isopycnal sloped upward toward the coast due to upwelling ...8  Figure 3.  The boundary conditions (and the direction convention of the

Satellite observations of the 1982-1983 El Nino along the U.S. Pacific coast

NASA Technical Reports Server (NTRS)

Fiedler, P. C.

1984-01-01

Satellite infrared temperature images illustrate several effects of the 1982-1983 El Nino: warm sea-surface temperatures with the greatest anomalies near the coast, weakened coastal upwelling, and changes in surface circulation patterns. Phytoplankton pigment images from the Coastal Zone Color Scanner indicate reduced productivity during El Nino, apparently related to the weakened coastal upwelling. The satellite images provide direct evidence of mesosale changes associated with the oceanwide El Nino event.

Physical retrieval of precipitation water contents from Special Sensor Microwave/Imager (SSM/I) data. Part 1: A cloud ensemble/radiative parameterization for sensor response (report version)

NASA Technical Reports Server (NTRS)

Olson, William S.; Raymond, William H.

1990-01-01

The physical retrieval of geophysical parameters based upon remotely sensed data requires a sensor response model which relates the upwelling radiances that the sensor observes to the parameters to be retrieved. In the retrieval of precipitation water contents from satellite passive microwave observations, the sensor response model has two basic components. First, a description of the radiative transfer of microwaves through a precipitating atmosphere must be considered, because it is necessary to establish the physical relationship between precipitation water content and upwelling microwave brightness temperature. Also the spatial response of the satellite microwave sensor (or antenna pattern) must be included in the description of sensor response, since precipitation and the associated brightness temperature field can vary over a typical microwave sensor resolution footprint. A 'population' of convective cells, as well as stratiform clouds, are simulated using a computationally-efficient multi-cylinder cloud model. Ensembles of clouds selected at random from the population, distributed over a 25 km x 25 km model domain, serve as the basis for radiative transfer calculations of upwelling brightness temperatures at the SSM/I frequencies. Sensor spatial response is treated explicitly by convolving the upwelling brightness temperature by the domain-integrated SSM/I antenna patterns. The sensor response model is utilized in precipitation water content retrievals.

Mantle P wave travel time tomography of Eastern and Southern Africa: New images of mantle upwellings

NASA Astrophysics Data System (ADS)

Benoit, M. H.; Li, C.; van der Hilst, R.

2006-12-01

Much of Eastern Africa, including Ethiopia, Kenya, and Tanzania, has undergone extensive tectonism, including rifting, uplift, and volcanism during the Cenozoic. The cause of this tectonism is often attributed to the presence of one or more mantle upwellings, including starting thermal plumes and superplumes. Previous regional seismic studies and global tomographic models show conflicting results regarding the spatial and thermal characteristics of these upwellings. Additionally, there are questions concerning the extent to which the Archean and Proterozoic lithosphere has been altered by possible thermal upwellings in the mantle. To further constrain the mantle structure beneath Southern and Eastern Africa and to investigate the origin of the tectonism in Eastern Africa, we present preliminary results of a large-scale P wave travel time tomographic study of the region. We invert travel time measurements from the EHB database with travel time measurements taken from regional PASSCAL datasets including the Ethiopia Broadband Seismic Experiment (2000-2002); Kenya Broadband Seismic Experiment (2000-2002); Southern Africa Seismic Experiment (1997- 1999); Tanzania Broadband Seismic Experiment (1995-1997), and the Saudi Arabia PASSCAL Experiment (1995-1997). The tomographic inversion uses 3-D sensitivity kernels to combine different datasets and is parameterized with an irregular grid so that high spatial resolution can be obtained in areas of dense data coverage. It uses an adaptive least-squares context using the LSQR method with norm and gradient damping.

Zooplankton research off Peru: A review

NASA Astrophysics Data System (ADS)

Ayón, Patricia; Criales-Hernandez, Maria I.; Schwamborn, Ralf; Hirche, Hans-Jürgen

2008-10-01

A review of zooplankton studies conducted in Peruvian marine waters is given. After a short history of the development of zooplankton research off Peru, we review zooplankton methodology, taxonomy, biodiversity, spatial distribution, seasonal and interannual variability, trophodynamics, secondary production, and modelling. We review studies on several micro-, meso-, macro-, and meroplankton groups, and give a species list from both published and unpublished reports. Three regional zooplankton groups have been identified: (1) a continental shelf group dominated by Acartia tonsa and Centropages brachiatus; (2) a continental slope group characterized by siphonophores, bivalves, foraminifera and radiolaria; (3) and a species-rich oceanic group. The highest zooplankton abundances and biomasses were often found between 4-6°S and 14-16°S, where continental shelves are narrow. Species composition changes with distance from the shore. Species composition and biomass also vary strongly on short time scales due to advection, peaks of larval production, trophic interactions, and community succession. The relation of zooplankton to climatic variability (ENSO and multi-decadal) and fish stocks is discussed in the context of ecological regime shifts. An intermediate upwelling hypothesis is proposed, based on the negative effects of low upwelling intensity in summer or extremely strong and enduring winter upwelling on zooplankton abundance off Peru. According to this hypothesis, intermediate upwelling creates an optimal environmental window for zooplankton communities. Finally, we highlight important knowledge gaps that warrant attention in future.

Water masses in the Monterey Bay during the summer of 2000

NASA Astrophysics Data System (ADS)

Warn-Varnas, Alex; Gangopadhyay, Avijit; Hawkins, J. A.

2007-06-01

Water masses in Monterey Bay are determined from the CTD casts of the Monterey Ocean Observing System (MOOS) Upper-water-column Science Experiment (MUSE) August 2000 dataset. It is shown through cluster analysis that the MUSE 2000 CTD dataset contains 5 water masses. These five water masses are: bay surface water (BSW), bay warm water (BWW), bay intermediate water (BIW), sub arctic upper water (SUW) and North Pacific deep water (NPDW). The BWW is a new water mass that exists in one area and is attributed to the effects of solar heating. The volumes occupied by each of the water masses are obtained. The BIW water is the most dominant water mass and occupies 68.8% of the volume. The statistical means and standard deviations for each water parameter, including spiciness and oxygen concentration, are calculated during separate upwelling and relaxed periods. The water mass content and structure are analyzed and studied during upwelling and a relaxed period. During upwelling, along a CTD track off Pt. Ano Nuevo, the water mass T, S distribution tended to be organized along three branches. Off Pt. Ano Nuevo the innovative coastal observation network (ICON) model showed the formation of a cyclonic eddy during the analyzed upwelling period. In time the eddy moved southwest and became absorbed into the southerly flow during the initial phases of the following wind-relaxed period.

Mussel farming impact on pelagic production and respiration rates in a coastal upwelling embayment (Ría de Vigo, NW Spain)

NASA Astrophysics Data System (ADS)

Froján, María; Castro, Carmen G.; Zúñiga, Diana; Arbones, Belén; Alonso-Pérez, Fernando; Figueiras, Francisco G.

2018-05-01

This paper provides the first diagnosis of the impact of mussel farming on the primary production (PP) and the metabolic balance in a coastal upwelling region (Ría de Vigo). Measurements of size-fractionated PP and microbial plankton metabolism were performed outside (reference station; ReS) and inside the farming area (raft station; RaS). At ReS, integrated PP was higher during upwelling (1.05 ± 0.45 g C m-2 d-1) with microphytoplankton dominating carbon fixation (74 ± 14%). The significance of nanophytoplankton and picophytoplankton increased during winter linked to lower PP (0.24 ± 0.03 g C m-2 d-1). Water column at ReS was always autotrophic with net community production (NCP) ranging from 186 ± 67 mmol O2 m-2 d-1 during upwelling to 43 ± 22 mmol O2 m-2 d-1 in winter. At RaS, there was a decrease in PP attributable not only to mussel consumption but also to the lower irradiance under mussel rafts. Concomitant decrease in NCP was also observed (by 56%), yet remained autotrophic, supporting the view that under current conditions food does not limit mussel growth in the Ría, thus securing the carrying capacity of the system in terms of production.

Large Topographic Rises on Venus: Implications for Mantle Upwelling

NASA Technical Reports Server (NTRS)

Stofan, Ellen R.; Smrekar, Suzanne E.; Bindschandler, Duane L.; Senske, David A.

1995-01-01

Topographic rises on Venus have been identified that are interpreted to be the surface manifestation of mantle upwellings. These features are classified into groups based on their dominant morphology. Atla and Beta Regiones are classified as rift-dominated, Dione, western Eistla, Bell, and Imdr Regiones as volcano-dominated, and Themis, eastern Eistla, and central Eistla Regiones as corona-dominated. At several topographic rises, geologic indicators were identified that may provide evidence of uplifted topography (e.g., volcanic flow features trending upslope). We assessed the minimum contribution of volcanic construction to the topography of each rise, which in general represents less than 5% of the volume of the rise, similar to the volumes of edifices at terrestrial hotspot swells. The total melt volume at each rise is approximated to be 10(exp 4) - 10(exp 6) cu km. The variations in morphology, topography, and gravity signatures at topographic rises are not interpreted to indicate variations in stage of evolution of a mantle upwelling. Instead, the morphologic variations between the three classes of topographic rises are interpreted to indicate the varying influences of lithospheric structure, plume characteristics, and regional tectonic environment. Within each class, variations in topography, gravity, and amount of volcanism may be indicative of differing stages of evolution. The similarity between swell and volcanic volumes for terrestrial and Venusian hotspots implies comparable time-integrated plume strengths for individual upwellings on the two planets.

Kinematic and diabatic vertical velocity climatologies from a chemistry climate model

NASA Astrophysics Data System (ADS)

Marinke Hoppe, Charlotte; Ploeger, Felix; Konopka, Paul; Müller, Rolf

2016-05-01

The representation of vertical velocity in chemistry climate models is a key element for the representation of the large-scale Brewer-Dobson circulation in the stratosphere. Here, we diagnose and compare the kinematic and diabatic vertical velocities in the ECHAM/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model. The calculation of kinematic vertical velocity is based on the continuity equation, whereas diabatic vertical velocity is computed using diabatic heating rates. Annual and monthly zonal mean climatologies of vertical velocity from a 10-year simulation are provided for both kinematic and diabatic vertical velocity representations. In general, both vertical velocity patterns show the main features of the stratospheric circulation, namely, upwelling at low latitudes and downwelling at high latitudes. The main difference in the vertical velocity pattern is a more uniform structure for diabatic and a noisier structure for kinematic vertical velocity. Diabatic vertical velocities show higher absolute values both in the upwelling branch in the inner tropics and in the downwelling regions in the polar vortices. Further, there is a latitudinal shift of the tropical upwelling branch in boreal summer between the two vertical velocity representations with the tropical upwelling region in the diabatic representation shifted southward compared to the kinematic case. Furthermore, we present mean age of air climatologies from two transport schemes in EMAC using these different vertical velocities and analyze the impact of residual circulation and mixing processes on the age of air. The age of air distributions show a hemispheric difference pattern in the stratosphere with younger air in the Southern Hemisphere and older air in the Northern Hemisphere using the transport scheme with diabatic vertical velocities. Further, the age of air climatology from the transport scheme using diabatic vertical velocities shows a younger mean age of air in the inner tropical upwelling branch and an older mean age in the extratropical tropopause region.

Re-Emergence of Excess Bomb Radiocarbon in Upwelling Waters with High-Latitude Origins

NASA Astrophysics Data System (ADS)

Lindsay, C. M.; Lehman, S.

2016-02-01

The quantity of radiocarbon (14C) in the atmosphere was nearly doubled by nuclear weapons testing in the 1960s. Since then, the terrestrial biosphere and the ocean have absorbed most of the excess 14C from the atmosphere, although atmospheric radiocarbon activity (∆14C) continues to decline due to ongoing emissions of 14C-free CO2 from combustion of fossil fuels. The large transient decline in atmospheric ∆14C combined with gas exchange at the surface and spatially variable time scales of ocean mixing have led to large ∆14C gradients in the surface ocean between upwelling- and downwelling-dominated regions. These gradients continue to evolve over time. We examine the rate of change of surface ocean ∆14C between CLIVAR (2000-2011) and WOCE era (1990s) or other slightly earlier (1980s) datasets and find spatial patterns that reveal mixing between 14C-enriched mode waters, 14C-depleted deep waters and surface waters that are well-equilibrated with the atmosphere. The ∆14C of mode water reaching equatorial upwelling regions has increased between the WOCE and CLIVAR time periods, and the greater contribution of 14C to the low-latitude surface ocean appears to have significantly offset the ∆14C decline otherwise imparted by air-sea gas exchange with the atmosphere. Consequently, ∆14C gradients between low-latitude upwelling regions and gyre centers have weakened proportionally more than between gyre centers and regions where pre-industrial water still upwells, such as the Southern Ocean. Properly accounting for the re-emergence of water with post-industrial characteristics is important to constrain earth system models that seek to explain DIC, pH and other anthropogenically perturbed tracers in the surface ocean. Because of the history of ∆14C in the atmosphere, ocean ∆14C is a useful tracer for this purpose.

Variations of the Organic Matter Composition in the Sea Surface Microlayer: A Comparison between Open Ocean, Coastal, and Upwelling Sites Off the Peruvian Coast

PubMed Central

Zäncker, Birthe; Bracher, Astrid; Röttgers, Rüdiger; Engel, Anja

2017-01-01

The sea surface microlayer (SML) is the thin boundary layer between the ocean and the atmosphere, making it important for air-sea exchange processes. However, little is known about what controls organic matter composition in the SML. In particular, there are only few studies available on the differences of the SML of various oceanic systems. Here, we compared the organic matter and neuston species composition in the SML and the underlying water (ULW) at 11 stations with varying distance from the coast in the Peruvian upwelling regime, a system with high emissions of climate relevant trace gases, such as N2O and CO2. In the open ocean, organic carbon, and amino acids were highly enriched in the SML compared to the ULW. The enrichment decreased at the coastal stations and vanished in the upwelling regime. At the same time, the degradation of organic matter increased from the open ocean to the upwelling stations. This suggests that in the open ocean, upward transport processes or new production of organic matter within the SML are faster than degradation processes. Phytoplankton was generally not enriched in the SML, one group though, the Trichodesmium-like TrL (possibly containing Trichodesmium), were enriched in the open ocean but not in the upwelling region indicating that they find a favorable habitat in the open ocean SML. Our data show that the SML is a distinct habitat; its composition is more similar among different systems than between SML and ULW of a single station. Generally the enrichment of organic matter is assumed to be reduced when encountering low primary production and high wind speeds. However, our study shows the highest enrichments of organic matter in the open ocean which had the lowest primary production and the highest wind speeds. PMID:29375483

Variations of the Organic Matter Composition in the Sea Surface Microlayer: A Comparison between Open Ocean, Coastal, and Upwelling Sites Off the Peruvian Coast.

PubMed

Zäncker, Birthe; Bracher, Astrid; Röttgers, Rüdiger; Engel, Anja

2017-01-01

The sea surface microlayer (SML) is the thin boundary layer between the ocean and the atmosphere, making it important for air-sea exchange processes. However, little is known about what controls organic matter composition in the SML. In particular, there are only few studies available on the differences of the SML of various oceanic systems. Here, we compared the organic matter and neuston species composition in the SML and the underlying water (ULW) at 11 stations with varying distance from the coast in the Peruvian upwelling regime, a system with high emissions of climate relevant trace gases, such as N 2 O and CO 2 . In the open ocean, organic carbon, and amino acids were highly enriched in the SML compared to the ULW. The enrichment decreased at the coastal stations and vanished in the upwelling regime. At the same time, the degradation of organic matter increased from the open ocean to the upwelling stations. This suggests that in the open ocean, upward transport processes or new production of organic matter within the SML are faster than degradation processes. Phytoplankton was generally not enriched in the SML, one group though, the Trichodesmium -like TrL (possibly containing Trichodesmium ), were enriched in the open ocean but not in the upwelling region indicating that they find a favorable habitat in the open ocean SML. Our data show that the SML is a distinct habitat; its composition is more similar among different systems than between SML and ULW of a single station. Generally the enrichment of organic matter is assumed to be reduced when encountering low primary production and high wind speeds. However, our study shows the highest enrichments of organic matter in the open ocean which had the lowest primary production and the highest wind speeds.

The ichthyoplankton assemblage of the Canaries-African Coastal Transition Zone: A review

NASA Astrophysics Data System (ADS)

Rodriguez, J. M.; Moyano, M.; Hernandez-Leon, S.

2009-12-01

In this paper we review information on the ichthyoplankton assemblage of the Canaries-African Coastal Transition Zone (C-ACTZ). This CTZ shows the singularity that the Canary Archipelago interrupts the main flow of the Canary Current and Trade Winds, introducing large mesoscale variability, in the form of island warm wakes and cyclonic and anticyclonic eddies downstream of the islands. Besides, upwelling filaments stretch towards the archipelago from the African coastal upwelling, transporting phytoplankton, zooplankton and fish larvae. They also interact with eddies shed from the islands to exchange water properties and biogenic material. All these mesoscale features influence the composition, structure, abundance and distribution of the larval fish community (LFC) of the region. The Canary Current (CC) and eddies shed from the islands drag larvae of island neritic fish species into the oceanic region and contribute, along warm wakes, to the horizontal distribution of fish larvae. Upwelling and upwelling filaments transport larvae of African neritic species into the oceanic region. These larvae dominate the LFC and account for the relatively high average larval fish abundance found in the C-ACTZ during the summer upwelling season. Filaments originated in the region of Cape Juby-Cape Bojador are entrained around a quasi-permanent cyclonic eddy, trapped between Gran Canaria Island and the African coast, forming a system through which most of the African neritic larvae may return to the African shelf. However, some larvae reach the eastern islands of the Canary archipelago and they may be spread all over the neritic region of the archipelago by eddies shed from the islands. Also in summer, the distribution of the LFC of the C-ACTZ is vertically stratified and fish larvae seem to carry out little or not diel vertical migration. Overall, this study highlights the strong relationship between mesoscale oceanographic processes and the LFC in the C-ACTZ.

Oceanographic and climatic evolution of the southeastern subtropical Atlantic over the last 3.5 Ma

NASA Astrophysics Data System (ADS)

Petrick, Benjamin; McClymont, Erin L.; Littler, Kate; Rosell-Melé, Antoni; Clarkson, Matthew O.; Maslin, Mark; Röhl, Ursula; Shevenell, Amelia E.; Pancost, Richard D.

2018-06-01

The southeast Atlantic Ocean is dominated by two major oceanic systems: the Benguela Upwelling System, one of the world's most productive coastal upwelling cells and the Agulhas Leakage, which is important for transferring warm salty water from the Indian Ocean to the Atlantic Ocean. Here, we present a multi-proxy record of marine sediments from ODP Site 1087. We reconstruct sea surface temperatures (U37K‧ and TEX86 indices), marine primary productivity (total chlorin and alkenone mass accumulation rates), and terrestrial inputs derived from southern Africa (Ti/Al and Ca/Ti via XRF scanning) to understand the evolution of the Southeast Atlantic Ocean since the late Pliocene. In the late Pliocene and early Pleistocene, ODP Site 1087 was situated within the Benguela Upwelling System, which was displaced southwards relative to present. We recognize a series of events in the proxy records at 3.3, 3.0, 2.2, 1.5, 0.9 and 0.6 Ma, which are interpreted to reflect a combination of changes in the location of major global wind and oceanic systems and local variations in the strength and/or position of the winds, which influence nutrient availability. Although there is a temporary SST cooling observed around the initiation of Northern Hemisphere glaciation (iNHG), proxy records from ODP Site 1087 show no clear climatic transition around 2.7 Ma but instead most of the changes occur before this time. This observation is significant because it has been previously suggested that there should be a change in the location and/or strength of upwelling associated with this climate transition. Rather, the main shifts at ODP Site 1087 occur at ca. 0.9 Ma and 0.6 Ma, associated with the early mid-Pleistocene transition (EMPT), with a clear loss of the previous upwelling-dominated regime. This observation raises the possibility that reorganisation of southeast Atlantic Ocean circulation towards modern conditions was tightly linked to the EMPT, but not to earlier climate transitions.

Wind-driven coastal upwelling and westward circulation in the Yucatan shelf

NASA Astrophysics Data System (ADS)

Ruiz-Castillo, Eugenio; Gomez-Valdes, Jose; Sheinbaum, Julio; Rioja-Nieto, Rodolfo

2016-04-01

The wind-driven circulation and wind-induced coastal upwelling in a large shelf sea with a zonally oriented coast are examined. The Yucatan shelf is located to the north of the Yucatan peninsula in the eastern Gulf of Mexico. This area is a tropical shallow body of water with a smooth sloping bottom and is one of the largest shelves in the world. This study describes the wind-driven circulation and wind-induced coastal upwelling in the Yucatan shelf, which is forced by easterly winds throughout the year. Data obtained from hydrographic surveys, acoustic current profilers and environmental satellites are used in the analysis. Hydrographic data was analyzed and geostrophic currents were calculated in each survey. In addition an analytical model was applied to reproduce the currents. The results of a general circulation model were used with an empirical orthogonal function analysis to study the variability of the currents. The study area is divided in two regions: from the 40 m to the 200 m isobaths (outer shelf) and from the coast to the 40 m isobath (inner shelf). At the outer shelf, observations revealed upwelling events throughout the year, and a westward current with velocities of approximately 0.2 m s-1 was calculated from the numerical model output and hydrographic data. In addition, the theory developed by Pedlosky (2007) for a stratified fluid along a sloping bottom adequately explains the current's primary characteristics. The momentum of the current comes from the wind, and the stratification is an important factor in its dynamics. At the inner shelf, observations and numerical model output show a wind-driven westward current with maximum velocities of 0.20 m s-1. The momentum balance in this region is between local acceleration and friction. A cold-water band is developed during the period of maximum upwelling.

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Radiation and speciation of pelagic organisms during periods of global warming: the case of the common minke whale, Balaenoptera acutorostrata.

PubMed

Pastene, Luis A; Goto, Mutsuo; Kanda, Naohisa; Zerbini, Alexandre N; Kerem, Dan; Watanabe, Kazuo; Bessho, Yoshitaka; Hasegawa, Masami; Nielsen, Rasmus; Larsen, Finn; Palsbøll, Per J

2007-04-01

How do populations of highly mobile species inhabiting open environments become reproductively isolated and evolve into new species? We test the hypothesis that elevated ocean-surface temperatures can facilitate allopatry among pelagic populations and thus promote speciation. Oceanographic modelling has shown that increasing surface temperatures cause localization and reduction of upwelling, leading to fragmentation of feeding areas critical to pelagic species. We test our hypothesis by genetic analyses of populations of two closely related baleen whales, the Antarctic minke whale (Balaenoptera bonaerensis) and common minke whale (Balaenoptera acutorostrata) whose current distributions and migration patterns extent are largely determined by areas of consistent upwelling with high primary production. Phylogeographic and population genetic analyses of mitochondrial DNA control-region nucleotide sequences collected from 467 whales sampled in four different ocean basins were employed to infer the evolutionary relationship among populations of B. acutorostrata by rooting an intraspecific phylogeny with a population of B. bonaerensis. Our findings suggest that the two species diverged in the Southern Hemisphere less than 5 million years ago (Ma). This estimate places the speciation event during a period of extended global warming in the Pliocene. We propose that elevated ocean temperatures in the period facilitated allopatric speciation by disrupting the continuous belt of upwelling maintained by the Antarctic Circumpolar Current. Our analyses revealed that the current populations of B. acutorostrata likely diverged after the Pliocene some 1.5 Ma when global temperatures had decreased and presumably coinciding with the re-establishment of the polar-equatorial temperature gradient that ultimately drives upwelling. In most population samples, we detected genetic signatures of exponential population expansions, consistent with the notion of increasing carrying capacity after the Pliocene. Our hypothesis that prolonged periods of global warming facilitate speciation in pelagic marine species that depend on upwelling should be tested by comparative analyses in other pelagic species.

Nutrient pumping by submesoscale circulations in the mauritanian upwelling system

NASA Astrophysics Data System (ADS)

Hosegood, P. J.; Nightingale, P. D.; Rees, A. P.; Widdicombe, C. E.; Woodward, E. M. S.; Clark, D. R.; Torres, R. J.

2017-12-01

Observations made within a cold filament in the Mauritanian upwelling system demonstrate that intense submesoscale circulations at the peripheral edges of the filament are likely responsible for anomalously high levels of observed primary productivity by resupplying nutrients to the euphotic zone. Measurements made on the shelf within the recently upwelled water reveal that primary production (PP) of 8.2 gC/m-2 day-1 was supported by nitrate concentrations (NC) of 8 mmol m-3. Towards the front that defined the edge of the filament containing the upwelled water as it was transported offshore, PP dropped to 1.6 gC m-2 day-1 whilst NC dropped to 5.5 mmol m-3. Thus, whilst the observed nutrients on the shelf accounted for 90% of new production, this value dropped to ∼60% near the filament's front after accounting for vertical turbulent fluxes and Ekman pumping. We demonstrate that the N15 was likely to have been supplied at the front by submesoscale circulations that were directly measured as intense vertical velocities ⩾100 m day-1 by a drifting acoustic Doppler current profiler that crossed a submesoscale surface temperature front. At the same time, a recently released tracer was subducted out of the mixed layer within 24 h of release, providing direct evidence that the frontal circulations were capable of accessing the reservoir of nutrients beneath the pycnocline. The susceptibility of the filament edge to submesoscale instabilities was demonstrated by O(1) Rossby numbers at horizontal scales of 1-10 km. The frontal circulations are consistent with instabilities arising from a wind-driven nonlinear Ekman buoyancy flux generated by the persistent northerly wind stress that has a down-front component at the northern edge of the inshore section of the filament. The prevalence of submesoscale instabilities and their associated vertical circulations are proposed to be a key mechanism operating at sub-grid scales and sustaining new production throughout the upwelling system.

Isotopic constraints on the genesis and evolution of basanitic lavas at Haleakala, Island of Maui, Hawaii

NASA Astrophysics Data System (ADS)

Phillips, Erin H.; Sims, Kenneth W. W.; Sherrod, David R.; Salters, Vincent J. M.; Blusztajn, Jurek; Dulai, Henrietta

2016-12-01

To understand the dynamics of solid mantle upwelling and melting in the Hawaiian plume, we present new major and trace element data, Nd, Sr, Hf, and Pb isotopic compositions, and 238U-230Th-226Ra and 235U-231Pa-227Ac activities for 13 Haleakala Crater nepheline normative basanites with ages ranging from ∼900 to 4100 yr B.P. These basanites of the Hana Volcanics exhibit an enrichment in incompatible trace elements and a more depleted isotopic signature than similarly aged Hawaiian shield lavas from Kilauea and Mauna Loa. Here we posit that as the Pacific lithosphere beneath the active shield volcanoes moves away from the center of the Hawaiian plume, increased incorporation of an intrinsic depleted component with relatively low 206Pb/204Pb produces the source of the basanites of the Hana Volcanics. Haleakala Crater basanites have average (230Th/238U) of 1.23 (n = 13), average age-corrected (226Ra/230Th) of 1.25 (n = 13), and average (231Pa/235U) of 1.67 (n = 4), significantly higher than Kilauea and Mauna Loa tholeiites. U-series modeling shows that solid mantle upwelling velocity for Haleakala Crater basanites ranges from ∼0.7 to 1.0 cm/yr, compared to ∼10 to 20 cm/yr for tholeiites and ∼1 to 2 cm/yr for alkali basalts. These modeling results indicate that solid mantle upwelling rates and porosity of the melting zone are lower for Hana Volcanics basanites than for shield-stage tholeiites from Kilauea and Mauna Loa and alkali basalts from Hualalai. The melting rate, which is directly proportional to both the solid mantle upwelling rate and the degree of melting, is therefore greatest in the center of the Hawaiian plume and lower on its periphery. Our results indicate that solid mantle upwelling velocity is at least 10 times higher at the center of the plume than at its periphery under Haleakala.

Non-limiting food conditions for growth and production of the copepod community in a highly productive upwelling zone

NASA Astrophysics Data System (ADS)

Escribano, Rubén; Bustos-Ríos, Evelyn; Hidalgo, Pamela; Morales, Carmen E.

2016-09-01

Zooplankton production is critical for understanding marine ecosystem dynamics. This work estimates copepod growth and production in the coastal upwelling and coastal transition zones off central-southern Chile (~35 to 37°S) during a 3-year time series (2004, 2005, and 2006) at a fixed shelf station, and from spring-summer spatial surveys during the same period. To estimate copepod production (CP), we used species-biomasses and associated C-specific growth rates from temperature dependent equations (food-saturated) for the dominant species, which we assumed were maximal growth rates (gmax). Using chlorophyll-a concentrations as a proxy for food conditions, we determined a size-dependent half-saturation constant with the Michaelis-Menten equation to derive growth rates (g) under the effect of food limitation. These food-dependent C-specific growth rates were much lower (<0.1 d-1) than those observed in the field for the dominant species, while gmax for same species, in the range of 0.19-0.23 d-1 better represented the necessary growth to attain observed adult sizes of at least two copepods, Paracalanus cf. indicus and Calanus chilensis. Copepod biomass (CB) and rates of maximal copepod production (CPmax) obtained with gmax were higher in the coastal upwelling zone (<50 km from shore), and correlated significantly to oceanographic variables associated with upwelling conditions. Both CPmax and gmax exhibited negative trends at the fixed station from 2004 to 2006 in association with increased duration of upwelling in the latter year. Annual CPmax ranged between 24 and 52 g C m-2 y-1 with a mean annual P/B ratio of 7.3. We concluded that interannual variation in copepod production resulted from factors and processes regulating copepod abundance and biomass in the absence of bottom-up control, allowing copepods to grow without limitation due to food resources.

Impact of river discharge, upwelling and vertical mixing on the nutrient loading and productivity of the Canadian Beaufort Shelf

NASA Astrophysics Data System (ADS)

Tremblay, J.-É.; Raimbault, P.; Garcia, N.; Lansard, B.; Babin, M.; Gagnon, J.

2014-09-01

The concentrations and elemental stoichiometry of particulate and dissolved pools of carbon (C), nitrogen (N), phosphorus (P) and silicon (Si) on the Canadian Beaufort Shelf during summer 2009 (MALINA program) were assessed and compared with those of surface waters provided by the Mackenzie river as well as by winter mixing and upwelling of upper halocline waters at the shelf break. Neritic surface waters showed a clear enrichment in dissolved and particulate organic carbon (DOC and POC, respectively), nitrate, total particulate nitrogen (TPN) and dissolved organic nitrogen (DON) originating from the river. Silicate as well as bulk DON and DOC declined in a near-conservative manner away from the delta's outlet, whereas nitrate dropped non-conservatively to very low background concentrations inside the brackish zone. By contrast, the excess of soluble reactive P (SRP) present in oceanic waters declined in a non-conservative manner toward the river outlet, where concentrations were very low and consistent with P shortage in the Mackenzie River. These opposite gradients imply that the admixture of Pacific-derived, SRP-rich water is necessary to allow phytoplankton to use river-derived nitrate and to a lesser extent DON. A coarse budget based on concurrent estimates of primary production shows that river N deliveries support a modest fraction of primary production when considering the entire shelf, due to the ability of phytoplankton to thrive in the subsurface chlorophyll maximum beneath the thin, nitrate-depleted river plume. Away from shallow coastal bays, local elevations in the concentration of primary production and dissolved organic constituents were consistent with upwelling at the shelf break. By contrast with shallow winter mixing, nutrient deliveries by North American rivers and upwelling relax surface communities from N limitation and permit a more extant utilization of the excess SRP entering through the Bering Strait. In this context, increased nitrogen supply by rivers and upwelling potentially alters the vertical distribution of the excess P exported into the North Atlantic.

Simulations of the Quasi-Biennial Oscillation and its Effect on Stratospheric H2O, CH4, and Age of Air with an Interactive Two-Dimensional Model

DTIC Science & Technology

2002-11-22

November 2002. [1] A zonally averaged photochemical–dynamical model of the middle atmosphere is used to simulate the quasi-biennial oscillation ( QBO ) and... QBO period. Comparable changes in prescribed tropical heating have a smaller effect on the QBO period. The response of tropical upwelling, and QBO ...wave forcing is smaller than in the Northern Hemisphere, increased forcing produces stronger equatorial upwelling and a longer QBO period. In the

A redefinition of water masses in the Vietnamese upwelling area

NASA Astrophysics Data System (ADS)

Dippner, Joachim W.; Loick-Wilde, Natalie

2011-01-01

A redefinition of characteristic water masses in the Vietnamese upwelling area is presented based on five interdisciplinary cruises during different seasons and 331 CTD casts. In contrast to the previous definition of Rojana-anawat et al. (2001), we clearly can define water masses which serve as end members of mixing. This new definition is useful for an improved understanding of geographical positions of different water masses with respect to climate variability, the phytoplankton distribution and complex nutrient cycle in this area.

Late Quaternary Upwelling Variations in the Eastern Equatorial Atlantic Ocean as Inferred from Dinoflagellate Cysts, Planktonic Foraminifera, and Organic Carbon Content

NASA Astrophysics Data System (ADS)

Höll, Christine; Kemle-von Mücke, Sylvia

2000-07-01

Analysis of multiple proxies shows that eastern equatorial Atlantic upwelling was subdued during isotope stage 5.5, more intense during stages 4, 5.2, 5.4, and 6, and most intense early in stage 2. These findings are based on proxy measures from a core site about 600 km southwest of Liberia. The proxies include total organic carbon content, the ratio of peridinoid and oceanic organic-walled dinoflagellate cyst species, accumulation rates of calcareous dinoflagellates, estimates of sea surface paleotemperatures, the difference in stable oxygen isotope composition between two species of planktonic foraminifera that live at different water depths, and the abundance of the planktonic foraminifera Neogloboquadrina dutertrei. Most of these parameters consistently vary directly or inversely with one another. Slight discrepancies between the individual parameters show the usefulness of a multiple proxy approach to reconstruct paleoenvironments. Our data confirm that northern summer insolation strongly influences upwelling in the eastern equatorial Atlantic Ocean.

Observations of a diapycnal shortcut to adiabatic upwelling of Antarctic Circumpolar Deep Water

NASA Astrophysics Data System (ADS)

Silvester, J. Mead; Lenn, Yueng-Djern; Polton, Jeff A.; Rippeth, Tom P.; Maqueda, M. Morales

2014-11-01

In the Southern Ocean, small-scale turbulence causes diapycnal mixing which influences important water mass transformations, in turn impacting large-scale ocean transports such as the Meridional Overturning Circulation (MOC), a key controller of Earth's climate. We present direct observations of mixing over the Antarctic continental slope between water masses that are part of the Southern Ocean MOC. A 12 h time series of microstructure turbulence measurements, hydrography, and velocity observations off Elephant Island, north of the Antarctic Peninsula, reveals two concurrent bursts of elevated dissipation of O(10-6) W kg-1, resulting in heat fluxes ˜10 times higher than basin-integrated Drake Passage estimates. This occurs across the boundary between adjacent adiabatic upwelling and downwelling overturning cells. Ray tracing to nearby topography shows mixing between 300 and 400 m is consistent with the breaking of locally generated internal tidal waves. Since similar conditions extend to much of the Antarctic continental slope where these water masses outcrop, diapycnal mixing may contribute significantly to upwelling.

Upwelling rebound, ephemeral secondary pycnoclines, and the creation of a near-bottom wave guide over the Monterey Bay continental shelf

USGS Publications Warehouse

Cheriton, Olivia M.; McPhee-Shaw, Erika E.; Storlazzi, Curt D.; Rosenberger, Kurt J.; Shaw, William J.; Raanan, Ben Y.

2014-01-01

Several sequential upwelling events were observed in fall 2012, using measurements from the outer half of the continental shelf in Monterey Bay, during which the infiltration of dense water onto the shelf created a secondary, near-bottom pycnocline. This deep pycnocline existed in concert with the near-surface pycnocline and enabled the propagation of near-bottom, cold, semidiurnal internal tidal bores, as well as energetic, high-frequency, nonlinear internal waves of elevation (IWOE). The IWOE occurred within 20 m of the bottom, had amplitudes of 8–24 m, periods of 6–45 min, and depth-integrated energy fluxes up to 200 W m−1. Iribarren numbers (<0.03) indicate that these IWOE were nonbreaking in this region of the shelf. These observations further demonstrate how regional upwelling dynamics and the resulting bulk, cross-margin hydrography is a first-order control on the ability of internal waves, at tidal and higher frequencies, to propagate through continental shelf waters.

An equilibrium model for the coupled ocean-atmosphere boundary layer in the tropics

NASA Technical Reports Server (NTRS)

Sui, C.-H.; Lau, K.-M.; Betts, Alan K.

1991-01-01

An atmospheric convective boundary layer (CBL) model is coupled to an ocean mixed-layer (OML) model in order to study the equilibrium state of the coupled system in the tropics, particularly in the Pacific region. The equilibrium state of the coupled system is solved as a function of sea-surface temperature (SST) for a given surface wind and as a function of surface wind for a given SST. It is noted that in both cases, the depth of the CBL and OML increases and the upwelling below the OML decreases, corresponding to either increasing SST or increasing surface wind. The coupled ocean-atmosphere model is solved iteratively as a function of surface wind for a fixed upwelling and a fixed OML depth, and it is observed that SST falls with increasing wind in both cases. Realistic gradients of mixed-layer depth and upwelling are observed in experiments with surface wind and SST prescribed as a function of longitude.

Thermally-Driven Mantle Plumes Reconcile Hot-spot Observations

NASA Astrophysics Data System (ADS)

Davies, D.; Davies, J.

2008-12-01

Hot-spots are anomalous regions of magmatism that cannot be directly associated with plate tectonic processes (e.g. Morgan, 1972). They are widely regarded as the surface expression of upwelling mantle plumes. Hot-spots exhibit variable life-spans, magmatic productivity and fixity (e.g. Ito and van Keken, 2007). This suggests that a wide-range of upwelling structures coexist within Earth's mantle, a view supported by geochemical and seismic evidence, but, thus far, not reproduced by numerical models. Here, results from a new, global, 3-D spherical, mantle convection model are presented, which better reconcile hot-spot observations, the key modification from previous models being increased convective vigor. Model upwellings show broad-ranging dynamics; some drift slowly, while others are more mobile, displaying variable life-spans, intensities and migration velocities. Such behavior is consistent with hot-spot observations, indicating that the mantle must be simulated at the correct vigor and in the appropriate geometry to reproduce Earth-like dynamics. Thermally-driven mantle plumes can explain the principal features of hot-spot volcanism on Earth.

Arctic ocean-shelf exchange: Measurements in Barrow Canyon

NASA Astrophysics Data System (ADS)

Aagaard, K.; Roach, A. T.

1990-10-01

Two closely instrumented arrays were deployed within Barrow Canyon during 1986-1987 in an attempt to measure the outflow of dense, hypersaline plumes created during sea ice formation along the Alaskan coast. However, no hypersaline plumes were observed. Rather, we found cold, relatively fresh waters advected downcanyon by the mean flow alternating with upcanyon flow of warm and saline water upwelled onto the shelf. Upwelling was most frequent in the fall, and upcanyon speeds reached 60 cm s-1. At times the resulting onshore heat and salt fluxes were large enough to be of possible local significance, for example, to the surface heat budget. Contrary to earlier findings, the flow was only weakly correlated with the wind and the atmospheric pressure gradient. Instead, we found both upwelling and flow reversals to be coherent along the coast at sites 400 km apart, with phase differences corresponding to a typical speed of 2.3 m s-1. We suggest that the majority of these events are manifestations of shelf waves propagating eastward along the Arctic Ocean margin.

Causality of an extreme harmful algal bloom in Monterey Bay, California, during the 2014-2016 northeast Pacific warm anomaly

NASA Astrophysics Data System (ADS)

Ryan, J. P.; Kudela, R. M.; Birch, J. M.; Blum, M.; Bowers, H. A.; Chavez, F. P.; Doucette, G. J.; Hayashi, K.; Marin, R.; Mikulski, C. M.; Pennington, J. T.; Scholin, C. A.; Smith, G. J.; Woods, A.; Zhang, Y.

2017-06-01

An ecologically and economically disruptive harmful algal bloom (HAB) affected much of the northeast Pacific margin in 2015, during a prolonged oceanic warm anomaly. Caused by diatoms of the genus Pseudo-nitzschia, this HAB produced the highest particulate concentrations of the biotoxin domoic acid (DA) ever recorded in Monterey Bay, California. Bloom inception followed strong upwelling during the spring transition, which introduced nutrients and eliminated the warm anomaly locally. Subsequently, moderate and intermittent upwelling created favorable conditions for growth and accumulation of HAB biomass, which was dominated by a highly toxigenic species, P. australis. High cellular DA concentrations were associated with available nitrogen for DA synthesis coincident with silicate exhaustion. This nutrient influence resulted from two factors: (1) disproportionate depletion of silicate in upwelling source waters during the warm anomaly, the most severe depletion observed in 24 years, and (2) silicate uptake by the dense diatom bloom.

Mechanistic Drivers of Reemergence of Anthropogenic Carbon in the Equatorial Pacific

NASA Astrophysics Data System (ADS)

Zhai, Ping; Rodgers, Keith B.; Griffies, Stephen M.; Slater, Richard D.; Iudicone, Daniele; Sarmiento, Jorge L.; Resplandy, Laure

2017-09-01

Relatively rapid reemergence of anthropogenic carbon (Cant) in the Equatorial Pacific is of potential importance for its impact on the carbonate buffering capacity of surface seawater and thereby impeding the ocean's ability to further absorb Cant from the atmosphere. We explore the mechanisms sustaining Cant reemergence (upwelling) from the thermocline to surface layers by applying water mass transformation diagnostics to a global ocean/sea ice/biogeochemistry model. We find that the upwelling rate of Cant (0.4 PgC yr-1) from the thermocline to the surface layer is almost twice as large as air-sea Cant fluxes (0.203 PgC yr-1). The upwelling of Cant from the thermocline to the surface layer can be understood as a two-step process: The first being due to diapycnal diffusive transformation fluxes and the second due to surface buoyancy fluxes. We also find that this reemergence of Cant decreases dramatically during the 1982/1983 and 1997/1998 El Niño events.

Brook trout use of thermal refugia and foraging habitat influenced by brown trout

USGS Publications Warehouse

Hitt, Nathaniel P.; Snook, Erin; Massie, Danielle L.

2017-01-01

The distribution of native brook trout (Salvelinus fontinalis) in eastern North America is often limited by temperature and introduced brown trout (Salmo trutta), the relative importance of which is poorly understood but critical for conservation and restoration planning. We evaluated effects of brown trout on brook trout behavior and habitat use in experimental streams across increasing temperatures (14–23 °C) with simulated groundwater upwelling zones providing thermal refugia (6–9 °C below ambient temperatures). Allopatric and sympatric trout populations increased their use of upwelling zones as ambient temperatures increased, demonstrating the importance of groundwater as thermal refugia in warming streams. Allopatric brook trout showed greater movement rates and more even spatial distributions within streams than sympatric brook trout, suggesting interference competition by brown trout for access to forage habitats located outside thermal refugia. Our results indicate that removal of introduced brown trout may facilitate native brook trout expansion and population viability in downstream reaches depending in part on the spatial configuration of groundwater upwelling zones.

Microplastic abundance, distribution and composition along a latitudinal gradient in the Atlantic Ocean.

PubMed

Kanhai, La Daana K; Officer, Rick; Lyashevska, Olga; Thompson, Richard C; O'Connor, Ian

2017-02-15

Microplastics in the world's oceans are a global concern due to the potential threat they pose to marine organisms. This study investigated microplastic abundance, distribution and composition in the Atlantic Ocean on a transect from the Bay of Biscay to Cape Town, South Africa. Microplastics were sampled from sub-surface waters using the underway system of the RV Polarstern. Potential microplastics were isolated from samples and FT-IR spectroscopy was used to identify polymer types. Of the particles analysed, 63% were rayon and 37% were synthetic polymers. The majority of microplastics were identified as polyesters (49%) and blends of polyamide or acrylic/polyester (43%). Overall, fibres (94%) were predominant. Average microplastic abundance in the Atlantic Ocean was 1.15±1.45particlesm -3 . Of the 76 samples, 14 were from the Benguela upwelling and there was no statistically significant difference in microplastic abundance between upwelled and non-upwelled sites. Copyright © 2016 Elsevier Ltd. All rights reserved.

Cadmium in the Coastal Upwelling Area Adjacent to the California Mexico Border

NASA Astrophysics Data System (ADS)

Segovia-Zavala, J. A.; Delgadillo-Hinojosa, F.; Alvarez-Borrego, S.

1998-04-01

Cadmium concentrations ([Cd]) were measured in samples from the water column of the coastal upwelling zone adjacent to the California - Mexico border. Temperature and nutrient distributions showed an intense upwelling event during our sampling. Lowest [Cd] were found at locations offshore (50 km) (0·03-0·058 nM), whereas the maximum concentrations were found inshore (0·14-0·166 nM). Both nutrients and [Cd] were enriched in coastal waters. Our inshore [Cd] values are about 25% of those reported for waters off central California. This is possibly due to the intrusion of oligotrophic waters from the eastern edge of the North Pacific Central Gyre to the Southern California Bight. Multivariate analysis indicates that high [Cd]s were associated with high phytoplankton biomass, nutrients and low temperature. Our data present no evidence of a [Cd] gradient due to the San Diego and Tijuana sewage discharges, which indicates that they maintain a very local effect.

Recycled iron fuels new production in the eastern equatorial Pacific Ocean.

PubMed

Rafter, Patrick A; Sigman, Daniel M; Mackey, Katherine R M

2017-10-24

Nitrate persists in eastern equatorial Pacific surface waters because phytoplankton growth fueled by nitrate (new production) is limited by iron. Nitrate isotope measurements provide a new constraint on the controls of surface nitrate concentration in this region and allow us to quantify the degree and temporal variability of nitrate consumption. Here we show that nitrate consumption in these waters cannot be fueled solely by the external supply of iron to these waters, which occurs by upwelling and dust deposition. Rather, a substantial fraction of nitrate consumption must be supported by the recycling of iron within surface waters. Given plausible iron recycling rates, seasonal variability in nitrate concentration on and off the equator can be explained by upwelling rate, with slower upwelling allowing for more cycles of iron regeneration and uptake. The efficiency of iron recycling in the equatorial Pacific implies the evolution of ecosystem-level mechanisms for retaining iron in surface ocean settings where it limits productivity.

Physiological acclimation to elevated temperature in a reef-building coral from an upwelling environment

NASA Astrophysics Data System (ADS)

Mayfield, A. B.; Fan, T.-Y.; Chen, C.-S.

2013-12-01

Recent work has found that pocilloporid corals from regions characterized by unstable temperatures, such as those exposed to periodic upwelling, display a remarkable degree of phenotypic plasticity. In order to understand whether important reef builders from these upwelling reefs remain physiologically uncompromised at temperatures they will experience in the coming decades as a result of global climate change, a long-term elevated temperature experiment was conducted with Pocillopora damicornis specimens collected from Houbihu, a small embayment within Nanwan Bay, southern Taiwan that is characterized by 8-9 °C temperature changes during upwelling events. Upon nine months of exposure to nearly 30 °C, all colony (mortality and surface area), polyp ( Symbiodinium density and chlorophyll a content), tissue (total thickness), and molecular (gene expression and molecular composition)-level parameters were documented at similar levels between experimental corals and controls incubated at 26.5 °C, suggesting that this species can readily acclimate to elevated temperatures that cause significant degrees of stress, or even bleaching and mortality, in conspecifics of other regions of the Indo-Pacific. However, the gastrodermal tissue layer was relatively thicker in corals of the high temperature treatment sampled after nine months, possibly as an adaptive response to shade Symbiodinium from the higher photosynthetically active radiation levels that they were experiencing at that sampling time. Such shading may have prevented high light and high temperature-induced photoinhibition, and consequent bleaching, in these samples.

Macro-Scale Patterns in Upwelling/Downwelling Activity at North American West Coast

PubMed Central

Saldívar-Lucio, Romeo; Di Lorenzo, Emanuele; Nakamura, Miguel; Villalobos, Héctor; Lluch-Cota, Daniel; Del Monte-Luna, Pablo

2016-01-01

The seasonal and interannual variability of vertical transport (upwelling/downwelling) has been relatively well studied, mainly for the California Current System, including low-frequency changes and latitudinal heterogeneity. The aim of this work was to identify potentially predictable patterns in upwelling/downwelling activity along the North American west coast and discuss their plausible mechanisms. To this purpose we applied the min/max Autocorrelation Factor technique and time series analysis. We found that spatial co-variation of seawater vertical movements present three dominant low-frequency signals in the range of 33, 19 and 11 years, resembling periodicities of: atmospheric circulation, nodal moon tides and solar activity. Those periodicities might be related to the variability of vertical transport through their influence on dominant wind patterns, the position/intensity of pressure centers and the strength of atmospheric circulation cells (wind stress). The low-frequency signals identified in upwelling/downwelling are coherent with temporal patterns previously reported at the study region: sea surface temperature along the Pacific coast of North America, catch fluctuations of anchovy Engraulis mordax and sardine Sardinops sagax, the Pacific Decadal Oscillation, changes in abundance and distribution of salmon populations, and variations in the position and intensity of the Aleutian low. Since the vertical transport is an oceanographic process with strong biological relevance, the recognition of their spatio-temporal patterns might allow for some reasonable forecasting capacity, potentially useful for marine resources management of the region. PMID:27893826

Biological production in the Indian Ocean upwelling zones - Part 1: refined estimation via the use of a variable compensation depth in ocean carbon models

NASA Astrophysics Data System (ADS)

Geethalekshmi Sreeush, Mohanan; Valsala, Vinu; Pentakota, Sreenivas; Venkata Siva Rama Prasad, Koneru; Murtugudde, Raghu

2018-04-01

Biological modelling approach adopted by the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP-II) provided amazingly simple but surprisingly accurate rendition of the annual mean carbon cycle for the global ocean. Nonetheless, OCMIP models are known to have seasonal biases which are typically attributed to their bulk parameterisation of compensation depth. Utilising the criteria of surface Chl a-based attenuation of solar radiation and the minimum solar radiation required for production, we have proposed a new parameterisation for a spatially and temporally varying compensation depth which captures the seasonality in the production zone reasonably well. This new parameterisation is shown to improve the seasonality of CO2 fluxes, surface ocean pCO2, biological export and new production in the major upwelling zones of the Indian Ocean. The seasonally varying compensation depth enriches the nutrient concentration in the upper ocean yielding more faithful biological exports which in turn leads to accurate seasonality in the carbon cycle. The export production strengthens by ˜ 70 % over the western Arabian Sea during the monsoon period and achieves a good balance between export and new production in the model. This underscores the importance of having a seasonal balance in the model export and new productions for a better representation of the seasonality of the carbon cycle over upwelling regions. The study also implies that both the biological and solubility pumps play an important role in the Indian Ocean upwelling zones.

Persistent warmth across the Benguela upwelling system during the Pliocene epoch

NASA Astrophysics Data System (ADS)

Rosell-Melé, Antoni; Martínez-Garcia, Alfredo; McClymont, Erin L.

2014-01-01

A feature of Pliocene climate is the occurrence of "permanent El Niño-like" or "El Padre" conditions in the Pacific Ocean. From the analysis of sediment cores in the modern northern Benguela upwelling, we show that the mean oceanographic state off Southwest Africa during the warm Pliocene epoch was also analogous to that of a persistent Benguela "El Niño". At present these events occur when massive southward flows of warm and nutrient-poor waters extend along the coasts of Angola and Namibia, with dramatic effects on regional marine ecosystems and rainfall. We propose that the persistent warmth across the Pliocene in the Benguela upwelling ended synchronously with the narrowing of the Indonesian seaway, and the early intensification of the Northern Hemisphere Glaciations around 3.0-3.5 Ma. The emergence of obliquity-related cycles in the Benguela sea surface temperatures (SST) after 3 Ma highlights the development of strengthened links to high latitude orbital forcing. The subsequent evolution of the Benguela upwelling system was characterized by the progressive intensification of the meridional SST gradients, and the emergence of the 100 ky cycle, until the modern mean conditions were set at the end of the Mid Pleistocene transition, around 0.6 Ma. These findings support the notion that the interplay of changes in the depth of the global thermocline, atmospheric circulation and tectonics preconditioned the climate system for the end of the warm Pliocene epoch and the subsequent intensification of the ice ages.

Resource partitioning within major bottom fish species in a highly productive upwelling ecosystem

NASA Astrophysics Data System (ADS)

Abdellaoui, Souad; El Halouani, Hassan; Tai, Imane; Masski, Hicham

2017-09-01

The Saharan Bank (21-26°N) is a wide subtropical continental shelf and a highly productive upwelling ecosystem. The bottom communities are dominated by octopus and sparid fish, which are the main targets of bottom-trawl fishing fleets. To investigate resource partitioning within the bottom fish community, adult fish from 14 of the most abundant species were investigated for stomach content analysis. Samples were collected during two periods: October 2003 and May 2007. The diet of the analysed species showed more variation between periods than between size classes, suggesting that temporal or spatial variability in prey availability appears to play a significant role in their diet. Multivariate analysis and subsequent clustering led to a grouping of the species within five trophic guilds. Two species were fish feeders, and the others mainly fed on benthic invertebrates, where epibenthic crustaceans, lamellibranchs and fish were the most important groups in defining trophic guilds. We found that the studied species had a high rate of overlapping spatial distributions and overlapping trophic niches. In this highly productive upwelling ecosystem, where food resources may not be a limiting factor, inter-specific competition did not appear to be an important factor in structuring bottom fish communities. For the species that showed differences in the proportions of prey categories in comparison with other ecosystems, the rise of the proportion of epibenthic crustaceans in their diet was a common feature; a possible consequence of the benthic productivity of this highly productive upwelling ecosystem.

Response of the Benguela upwelling systems to spatial variations in the wind stress

NASA Astrophysics Data System (ADS)

Fennel, Wolfgang; Junker, Tim; Schmidt, Martin; Mohrholz, Volker

2012-08-01

In this paper we combine field observations, numerical modeling and an idealized analytical theory to study some features of the Benguela upwelling system. The current system can be established through a combination of observations and realistic simulations with an advanced numerical model. The poleward undercurrent below the equator-ward coastal jet is often found as a countercurrent that reaches the sea surface seaward of the coastal jet. The coastal band of cold upwelled water appears to broaden from south to north and at the northern edge of the wind band an offshore flow is often detected, which deflects the coastal Angola current to the west. These features can be explained and understood with an idealized analytical model forced by a spatially variable wind. A crucial role is played by the wind stress curl, which shapes the oceanic response through Ekman-pumping. The interplay of the curl driven effects and the coastal Ekman upwelling together with the coastal jet, Kelvin waves, and the undercurrent is the key to understand the formation of the three-dimensional circulation patterns in the Benguela system. While the numerical model is based on the full set of primitive equations, realistic topography and forcing, the analytic model uses a linear, flat-bottomed f-plane ocean, where the coast is a straight wall and the forcing is represented by an alongshore band of dome-shaped wind stress. Although the analytical model is highly idealized it is very useful to grasp the basic mechanisms leading to the response patterns.

Mass-specific respiration of mesozooplankton and its role in the maintenance of an oxygen-deficient ecological barrier (BEDOX) in the upwelling zone off Chile upon presence of a shallow oxygen minimum zone

NASA Astrophysics Data System (ADS)

Donoso, Katty; Escribano, Ruben

2014-01-01

A shallow oxygen minimum zone (OMZ) in the coastal upwelling zone off Chile may vertically confine most zooplankton to a narrow (< 50 m) upper layer. From laboratory experiments, we estimated oxygen consumption of the mesozooplankton community obtained in Bay of Mejillones, northern Chile (23°S) in May 2010, December 2010 and August 2011. Mass-specific respiration rates were in the range of 8.2-24.5 μmol O2 mg dry mass- 1 day- 1, at an average temperature of 12 °C. Estimates of the mesozooplankton biomass in the water column indicated that its aerobic respiration may remove daily a maximum of about 20% of oxygen available at the base of the oxycline. Since previous work indicates that zooplankton aggregate near the base of the oxycline, the impact of aerobic respiration on oxygen content might be even stronger at this depth. Mesozooplankton respiration, along with community respiration by microorganisms near the base of the oxycline and a strongly stratified condition (limiting vertical flux of O2), are suggested as being critical factors causing and maintaining a persistent subsurface oxygen-deficient ecological barrier (BEDOX) in the upwelling zone. This BEDOX layer can have a major role in affecting and regulating zooplankton distribution and their dynamics in the highly productive coastal upwelling zone of the Humboldt Current System.

Piecewise Delamination Drives Uplift in the Atlas Mountains Region of Morocco

NASA Astrophysics Data System (ADS)

Bezada, M. J.; Humphreys, E.; Martin Davila, J.; mimoun, H.; Josep, G.; Palomeras, I.

2013-12-01

The elevation of the intra-continental Atlas Mountains of Morocco and surrounding regions requires a mantle component of buoyancy, and there is consensus that this buoyancy results from an abnormally thin lithosphere. Lithospheric delamination under the Atlas Mountains and thermal erosion caused by upwelling mantle have each been suggested as thinning mechanisms. We use seismic tomography to image the upper mantle of Morocco by inverting teleseimic p-wave delay times, complemented with local delays, recorded on a dense array of stations in the Iberian peninsula and Morocco. A surface wave model provides constraint on the shallower layers. We determine the geometry of lithospheric cavities and mantle upwelling beneath the Middle Atlas and central High Atlas, and image delaminated lithosphere at ~400 km beneath the Middle Atlas. We propose discontinuous delamination of an intrinsically unstable Atlas lithosphere, enabled by the presence of anomalously hot mantle, as a mechanism for producing the imaged structures. The Atlas lithosphere was made unstable by a combination of tectonic shortening and eclogite loading during Mesozoic rifting and Cenozoic magmatism. The presence of hot mantle, sourced from regional upwellings in northern Africa or the Canary Islands, enabled the mobilization of this lithosphere. Flow around the retreating Alboran slab focused upwelling mantle under the Middle Atlas, where we image the most recent delamination. The Atlas Mountains of Morocco stand as an example of mantle-generated uplift and large-scale lithospheric loss in a mildly contractional orogen.

High-Latitude Neutral Density Structures Investigated by Utilizing Multi-Instrument Satellite Data and NRLMSISE-00 Simulations

NASA Astrophysics Data System (ADS)

Horvath, Ildiko; Lovell, Brian C.

2018-02-01

This study investigates various types of neutral density features developed in the cusp region during magnetically active and quiet times. Multi-instrument Challenging Minisatellite Payload data provide neutral density, electron temperature, neutral wind speed, and small-scale field-aligned current (SS-FAC) values. Gravity Recovery and Climate Experiment neutral density data are also employed. During active times, cusp densities or density spikes appeared with their underlying flow channels (FCs) and enhanced SS-FACs implying upwelling, fueled by Joule heating, within/above FCs. Both the moderate nightside cusp enhancements under disturbed conditions and the minor dayside cusp enhancements under quiet conditions developed without any underlying FC and enhanced SS-FACs implying the role of particle precipitation in their development. Observations demonstrate the relations of FCs, density spikes, and upwelling-related divergent flows and their connections to the underlying (1) dayside magnetopause reconnection depositing magnetospheric energy into the high-latitude region and (2) Joule heating-driven disturbance dynamo effects. Results provide observational evidence that the moderate nightside cusp enhancements and the minor dayside cusp enhancements detected developed due to direct heating by weak particle precipitation. Chemical compositions related to the dayside density spike and low cusp densities are modeled by Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar Extended 2000. Modeled composition outputs for the dayside density spike's plasma environment depict some characteristic upwelling signatures. Oppositely, in the case of low dayside cusp densities, composition outputs show opposite characteristics due to the absence of upwelling.

Counterintuitive effects of global warming-induced wind patterns on primary production in the Northern Humboldt Current System.

PubMed

Mogollón, Rodrigo; R Calil, Paulo H

2018-07-01

It has been hypothesized that global warming will strengthen upwelling-favorable winds in the Northern Humboldt Current System (NHCS) as a consequence of the increase of the land-sea thermal gradient along the Peruvian coast. The effect of strengthened winds in this region is assessed with the use of a coupled physical-biogeochemical model forced with projected and climatological winds. Strengthened winds induce an increase in primary production of 2% per latitudinal degree from 9.5°S to 5°S. In some important coastal upwelling sites primary production is reduced. This is due to a complex balance between nutrient availability, nutrient use efficiency, as well as eddy- and wind-driven factors. Mesoscale activity induces a net offshore transport of inorganic nutrients, thus reducing primary production in the coastal upwelling region. Wind mixing, in general disadvantageous for primary producers, leads to shorter residence times in the southern and central coastal zones. Overall, instead of a proportional enhancement in primary production due to increased winds, the NHCS becomes only 5% more productive (+5 mol C m -2 year -1 ), 10% less limited by nutrients and 15% less efficient due to eddy-driven effects. It is found that regions with a initial strong nutrient limitation are more efficient in terms of nutrient assimilation which makes them more resilient in face of the acceleration of the upwelling circulation. © 2018 John Wiley & Sons Ltd.

Sr/Ca and Mg/Ca in Glycymeris glycymeris (Bivalvia) shells from the Iberian upwelling system: Ontogeny and environmental control

NASA Astrophysics Data System (ADS)

Freitas, Pedro; Richardson, Christopher; Chenery, Simon; Monteiro, Carlos; Butler, Paul; Reynolds, David; Scourse, James; Gaspar, Miguel

2017-04-01

Bivalve shells have a great potential as high-resolution geochemical proxy archives of marine environmental conditions. In addition, sclerochronology of long-lived bivalve species (e.g. Arctica islandica) provides a timeline of absolutely dated shell material for geochemical analysis that can extend into the past beyond the lifetime of single individuals through the use of replicated crossmatched centennial to millennial chronologies. However, the interpretation of such records remains extremely challenging and complex, with multiple environmental and biological processes affecting element incorporation in the shell (e.g. crystal fabrics, organic matrix, biomineralization mechanisms and physiological processes). As a result, the effective use of bivalve shell elemental/Ca ratios as palaeoenvironmental proxies has been limited, often to species-specific applications or applications restricted to particular environmental settings. The dog-cockle, Glycymeris glycymeris, is a relatively long-lived bivalve (up to 200 years) that occurs in coarse-grained subtidal sediments of coastal shelf seas of Europe and North West Africa. Glycymeris glycymeris shells provide a valuable, albeit not fully explored, archive to reconstruct past environmental variability in an area lacking sclerochronological studies due to the rarity of long-lived bivalves and lack of coral reefs. In this study, we evaluate the potential of Sr/Ca and Mg/Ca ratios in G. glycymeris shells as geochemical proxies of upwelling conditions in the Iberian Upwelling System, the northern section of the Canary Current Eastern Boundary Upwelling System. Sr/Ca and Mg/Ca generally co-varied significantly and a clear ontogenetic, non-environmental related change in Sr/Ca and Ba/Ca variability was observed. High Sr/Ca and Mg/Ca ratios in older shells (> 10 years old) were found to be associated with the occurrence of growth lines deposited during the winter reduction in shell growth. Nevertheless, Sr/Ca and Mg/Ca variation in older shells was synchronous with contemporary environmental conditions, i.e. upwelling intensity and salinity. The use of Sr or Mg in G. glycymeris shells as valid geochemical environmental proxies in the Iberian Upwelling System remains complex and requires further research to unravel environmental and physiological/biomineralization controls. This study was financed by the Portuguese Fundação para a Ciência e Tecnologia (FCT) GLYCY Project (contract PTDC/AAC-CLI/118003/2010) and a sabbatical grant to PSF (Ref: SFRH/BSAB/127786/2016), co-supported by POCH and the European Social Fund. Funding for consumable costs was provided by Bangor University.

Verification of reflectance models in turbid waters

NASA Technical Reports Server (NTRS)

Tanis, F. J.; Lyzenga, D. R.

1981-01-01

Inherent optical parameters of very turbid waters were used to evaluate existing water reflectance models. Measured upwelling radiance spectra and Monte Carlo simulations of the radiative transfer equations were compared with results from models based upon two flow, quasi-single scattering, augmented isotropic scattering, and power series approximation. Each model was evaluated for three separate components of upwelling radiance: (1) direct sunlight; (2) diffuse skylight; and (3) internally reflected light. Limitations of existing water reflectance models as applied to turbid waters and possible applications to the extraction of water constituent information are discussed.

Visible to Near-infrared Spectral Reflectance, NGEE-Arctic Tram, Barrow, Alaska, 2015-2017

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

Meng, Ran; McMahon, Andrew; Rogers, Alistair

Canopy spectral reflectance collected from the NGEE-Arctic automated tram platform using a PP-Systems UniSpec-DC spectrometer. Downwelling radiance was measured using a 2 meter fiber optic cable connected to a cosine diffuser. Upwelling (i.e. reflected) radiance was measured using a 2 meter cable connected to a 12 degree field-of-view (FOV) lens. Canopy reflectance was calculated using the ratio of upwelling to downwelling radiance measured over a 99.99% reflectance Spectralon standard measured at the start of each measurement set.

Three-Dimensional Numerical Simulation on Passively Excited Flows by Distributed Local Hot Sources Settled at the D" Layer Below Hotspots and/or Large-Scale Cool Masses at Subduction Zones Within the Static Layered Mantle

NASA Astrophysics Data System (ADS)

Eguchi, T.; Matsubara, K.; Ishida, M.

2001-12-01

To unveil dynamic process associated with three-dimensional unsteady mantle convection, we carried out numerical simulation on passively exerted flows by simplified local hot sources just above the CMB and large-scale cool masses beneath smoothed subduction zones. During the study, we used our individual code developed with the finite difference method. The basic three equations are for the continuity, the motion with the Boussinesq (incompressible) approximation, and the (thermal) energy conservation. The viscosity of our model is sensitive to temperature. To get time integration with high precision, we used the Newton method. In detail, the size and thermal energy of the hot or cool sources are not uniform along the latitude, because we could not select uniform local volumes assigned for the sources within the finite difference grids throughout the mantle. Our results, thus, accompany some latitude dependence. First, we treated the case of the hotspots, neglecting the contribution of the subduction zones. The local hot sources below the currently active hotspots were settled as dynamic driving forces included in the initial condition. Before starting the calculation, we assumed that the mantle was statically layered with zero velocity component. The thermal anomalies inserted instantaneously in the initial condition do excite dynamically passive flows. The type of the initial hot sources was not 'plume' but 'thermal.' The simulation results represent that local upwelling flows which were directly excited over the initial heat sources reached the upper mantle by approximately 30 My during the calculation. Each of the direct upwellings above the hotspots has its own dynamic potential to exert concentric down- and up-welling flows, alternately, at large distances. Simultaneously, the direct upwellings interact mutually within the spherical mantle. As an interesting feature, we numerically observed secondary upwellings somewhere in a wide region covering east Eurasia to the Bering Sea where no hot sources were initially input. It seems that the detailed location of the secondary upwellings depends partly on the numerical parameters such as the radial profile of mantle viscosity especially at the D" layer, etc., because the secondary flows are provoked by dynamic interaction among the distributed direct upwellings just above the CMB. Our results suggest that if we assume not only non-zero time delays during the input of the local hot sources but also parameters related with the difference of their historical surface flux rates, the pattern of the passively excited flows will be different from that obtained with the simultaneously settled hot sources stated above. Second, we simultaneously incorporated simplified thermal anomaly models associated with both the distributed local hotspots and the global subduction zones, as dynamic origins in the initial condition for the static layered mantle. In this case, the simulation result represents that the pattern of secondary radial flows, being different from those in the earlier case, is sensitive to the relative strength between the positive dynamic buoyancy integrated over all of the local hot sources below the hotspots and the total negative buoyancy beneath the subduction zones.

Monsoon Variability In The Western Arabian Sea During Last 10,000 Years BP: A Planktic Foraminiferal Abundances And It's Stable Isotope Records

NASA Astrophysics Data System (ADS)

Singh, A. K.; Tiwari, M.; Sinha, D. K.; Ramesh, R.

2007-12-01

: The western Arabian Sea responds to the southwest monsoon winds by upwelling colder and nutrient rich waters from the deeper layers, causing a reduction in the sea surface temperature and enhanced biological productivity. A number of paleoclimatic studies have been carried out in this region to elucidate past monsoon variability (Sirocco et al., 1993; Gupta et al, 2003; Tiwari, 2005; Saher et.al.; 2007). Globigerina bulloides, a planktic foraminiferal species normally inhabiting surface ocean waters in temperate latitudes ( Be and Tolderlund , 1977) also becomes abundant at tropical latitudes upwelling occurs, and in these cases its abundance can exceed considerably. The conspicuous fluctuation in the abundance of Gg.bulloides during upwelling and non upwelling intervals is established through several studies ( Thiede and Junger, 1980, Gupta et al, 2003) This robust relation has been used as a proxy for wind velocity at several different times in the past in the Arabian Sea (Anderson et.al., 2002). A significant result from some of these centennially resolved Holocene records is declining abundance of Globigerina bulloides which is paralleled by reduced insolation record and this has been inferred as declining strength of Asian Monsoon. We are presenting here the data from the core SS4018 from near the Gulf of Aden, Western Arabian Sea taken at a water depth of 2830 m, precisely dated by the radiocarbon method using Accelerator Mass Spectrometry on planktonic foraminiferal separates. We have carried out the planktic foraminiferal census counts for each sample to know the relative abundance of key species. In addition to this, we have also employed multi- proxy approach such as oxygen and carbon isotopes of planktic foraminiferal tests, TOC, CaCO3 (%) to strengthen our interpretation and also to understand the relationships amongst the proxies themselves. Abundance of the key planktic foraminiferal species and other proxy records reveal at least 3 major climatic events (M-1, M-2 and M-3) during the last 10,000yrs. The earliest one (M-1) is a major decline in the upwelling intensity during 7.9.-5.6 kyBP. We have observed the lowest abundance of upwelling indicator species (UIS), it goes down from 70(%) to 30(%), mixed dweller (MD) and thermocline dweller (TD) species were showing their maximum abundance and at that time Organic carbon (OC) value revealed the lowest amount. Oxygen stable isotope records were also suggesting the same results. The second event at 5.5-2.2 kyBP (M-2) corresponds to average upwelling. We have observed the 2-3 high peaks of (UIS), on average UIS were showing around 50-55(%) of their abundance during this period, thus we have concluded the moderate intensity of SWM winds during M-2. The third event at last 2ky (M-3), decreasing trend in the strength of the SWM has been observed on the basis of sharp decline in the abundance of UIS and OC amount. For this interval, we have observed the increasing trend in the MD and TD planktic foraminiferal species.

Modelling of Continental Lithosphere Breakup and Rifted Margin Formation in Response to an Upwelling Divergent Flow Field Incorporating a Temperature Dependent Rheology

NASA Astrophysics Data System (ADS)

Tymms, V. J.; Kusznir, N. J.

2005-05-01

We numerically model continental lithosphere deformation leading to breakup and sea floor spreading initiation in response to an imposed upwelling and divergent flow field applied to continental lithosphere and asthenosphere. The model is used to predict rifted continental margin lithosphere thinning and temperature structure. Model predictions are compared with observed rifted margin structure for four diverse case studies. Prior to application of the upwelling divergent flow field the continental lithosphere is undeformed with a uniform temperature gradient. The upwelling divergent flow field is defined kinematically using boundary conditions consisting of the upwelling velocity Vz at the divergence axis and the half divergence rate Vx . The resultant velocity field throughout the continuum is computed using finite element (FE) code incorporating a Newtonian temperature dependent rheology. The flow field is used to advect the continental lithosphere material and lithospheric and asthenospheric temperatures. Viscosity structure is hence modified and the velocities change correspondingly in a feedback loop. We find the kinematic boundary conditions Vz and Vx to be of first order importance. A high Vz/Vx (greater than10), corresponding to buoyancy assisted flow, leads to minimal mantle exhumation and a well defined continent ocean transition consistent with observations at volcanic margins. For Vz/Vx near unity, corresponding to plate boundary driven divergence, mantle exhumation over widths of up to 100 km is predicted which is consistent with observations at non-volcanic margins. The FE method allows the upwelling velocity Vz to be propagated upwards from the top of the asthenosphere to the Earth's surface without the requirement of imposing Vx. When continental breakup is achieved the half divergence velocity Vx can be applied at the lithosphere surface and the upwelling velocity Vz left free. We find this time and space dependent set of boundary conditions is more plausible than a constant corner flow type solution and predicts levels of depth dependent stretching and continent ocean transitions consistent with observation. Depth dependent lithosphere stretching, which is observed at rifted continental margins, is predicted to occur before continental breakup and sea-floor spreading initiation. The model may be used to predict surface heat flow and bathymetry, and to provide estimates of melt production rates and cumulative thickness. We compare model predictions with observed margin structure for four diverse rifted margins: the Lofoten Margin (a mature volcanic margin), Goban Spur (a mature non-volcanic margin), the Woodlark Basin (a neotectonic young ocean basin) and the Faroe-Shetland Basin (a failed attempt at continental breakup). This work forms part of the NERC Margins iSIMM project. iSIMM investigators are from Liverpool and Cambridge Universities, Badley Geoscience & Schlumberger Cambridge Research supported by the NERC, the DTI, Agip UK, BP, Amerada Hess Ltd, Anadarko, Conoco¬Phillips, Shell, Statoil and WesternGeco. The iSIMM team comprises NJ Kusznir, RS White, AM Roberts, PAF Christie, A Chappell, J Eccles, R Fletcher, D Healy, N Hurst, ZC Lunnon, CJ Parkin, AW Roberts, LK Smith, V Tymms & R Spitzer.

Isotopic constraints on the genesis and evolution of basanitic lavas at Haleakala, Island of Maui, Hawaii

USGS Publications Warehouse

Phillips, Erin H.; Sims, K.W.W.; Sherrod, David R.; Salters, Vincent; Blusztajn, Jurek; Dulaiova, Henrieta

2016-01-01

To understand the dynamics of solid mantle upwelling and melting in the Hawaiian plume, we present new major and trace element data, Nd, Sr, Hf, and Pb isotopic compositions, and 238U–230Th–226Ra and 235U–231Pa–227Ac activities for 13 Haleakala Crater nepheline normative basanites with ages ranging from ∼900 to 4100 yr B.P. These basanites of the Hana Volcanics exhibit an enrichment in incompatible trace elements and a more depleted isotopic signature than similarly aged Hawaiian shield lavas from Kilauea and Mauna Loa. Here we posit that as the Pacific lithosphere beneath the active shield volcanoes moves away from the center of the Hawaiian plume, increased incorporation of an intrinsic depleted component with relatively low 206Pb/204Pb produces the source of the basanites of the Hana Volcanics. Haleakala Crater basanites have average (230Th/238U) of 1.23 (n = 13), average age-corrected (226Ra/230Th) of 1.25 (n = 13), and average (231Pa/235U) of 1.67 (n = 4), significantly higher than Kilauea and Mauna Loa tholeiites. U-series modeling shows that solid mantle upwelling velocity for Haleakala Crater basanites ranges from ∼0.7 to 1.0 cm/yr, compared to ∼10 to 20 cm/yr for tholeiites and ∼1 to 2 cm/yr for alkali basalts. These modeling results indicate that solid mantle upwelling rates and porosity of the melting zone are lower for Hana Volcanics basanites than for shield-stage tholeiites from Kilauea and Mauna Loa and alkali basalts from Hualalai. The melting rate, which is directly proportional to both the solid mantle upwelling rate and the degree of melting, is therefore greatest in the center of the Hawaiian plume and lower on its periphery. Our results indicate that solid mantle upwelling velocity is at least 10 times higher at the center of the plume than at its periphery under Haleakala.

Biological response to coastal upwelling and dust deposition in the area off Northwest Africa

NASA Astrophysics Data System (ADS)

Ohde, T.; Siegel, H.

2010-05-01

Nutrient supply in the area off Northwest Africa is mainly regulated by two processes, coastal upwelling and deposition of Saharan dust. In the present study, both processes were analyzed and evaluated by different methods, including cross-correlation, multiple correlation, and event statistics, using remotely sensed proxies of the period from 2000 to 2008 to investigate their influence on the marine environment. The remotely sensed chlorophyll- a concentration was used as a proxy for the phytoplankton biomass stimulated by nutrient supply into the euphotic zone from deeper water layers and from the atmosphere. Satellite-derived alongshore wind stress and sea-surface temperature were applied as proxies for the strength and reflection of coastal upwelling processes. The westward wind and the dust component of the aerosol optical depth describe the transport direction of atmospheric dust and the atmospheric dust column load. Alongshore wind stress and induced upwelling processes were most significantly responsible for the surface chlorophyll- a variability, accounting for about 24% of the total variance, mainly in the winter and spring due to the strong north-easterly trade winds. The remotely sensed proxies allowed determination of time lags between biological response and its forcing processes. A delay of up to 16 days in the surface chlorophyll- a concentration due to the alongshore wind stress was determined in the northern winter and spring. Although input of atmospheric iron by dust storms can stimulate new phytoplankton production in the study area, only 5% of the surface chlorophyll- a variability could be ascribed to the dust component in the aerosol optical depth. All strong desert storms were identified by an event statistics in the time period from 2000 to 2008. The 57 strong storms were studied in relation to their biological response. Six events were clearly detected in which an increase of chlorophyll- a was caused by Saharan dust input and not by coastal upwelling processes. Time lags of <8 days, 8 days, and 16 days were determined. An increase in surface chlorophyll- a concentration of up to 2.4 mg m -3 after dust storms in which the dust component of the aerosol optical depth was up to 0.9 was observed.

Surface circulation and upwelling patterns around Sri Lanka

NASA Astrophysics Data System (ADS)

de Vos, A.; Pattiaratchi, C. B.; Wijeratne, E. M. S.

2014-10-01

Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, with the Arabian Sea on its western side and the Bay of Bengal on its eastern side, and experiences bi-annually reversing monsoon winds. Aggregations of blue whale (Balaenoptera musculus) have been observed along the southern coast of Sri Lanka during the northeast (NE) monsoon, when satellite imagery indicates lower productivity in the surface waters. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The model was run for 3 years to examine the seasonal and shorter-term (~10 days) variability. The results reproduced correctly the reversing current system, between the Equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the southwest (SW) monsoon transporting 11.5 Sv (mean over 2010-2012) and the westward flowing Northeast Monsoon Current (NMC) transporting 9.6 Sv during the NE monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the southern coast. During the SW monsoon, the island deflects the eastward flowing SMC southward, whilst along the eastern coast, the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the southern coast, resulting from southward flow converging along the southern coast and subsequent divergence associated with the offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind-driven flow along the eastern and western coasts: during the SW (NE) monsoon, the flow along the western (eastern) coast was stronger, migrating the upwelling centre to the east (west).

Temporal Variations in Hotspot Volcanic Production Caused by Interactions Between Upwelling Mantle Plumes and Phase Transitions

NASA Astrophysics Data System (ADS)

Neuharth, D. J.; Mittelstaedt, E. L.

2017-12-01

Observations at numerous hotspots around the globe, such as Hawaii and Louisville, find periodic variations in volcanic production with time. For example, the volcanic production rate along the Hawaiian seamount chain varies from 0.05 to 0.25 km3/yr at periods of 15 Myr, while volcanic production rate along the Louisville seamount chain has consistently declined over the past 40 Myr. One possible explanation for these variations is long-term interaction of upwelling mantle plumes with mantle phase transitions. While previous studies carefully quantify the initial interaction and subsequent penetration or inhibition of a plume as it encounters the 660 km phase boundary and traverses the transition zone, the long-term interaction of plume upwelling and phase boundaries in the mantle is not well constrained. To assess the impact of plume-phase transition interaction on observed variability in hotspot volcanic output, we use the Advanced Solver for Problems in Earth's ConvecTion (ASPECT) code to numerically simulate upwelling of an isolated plume under the Anelastic Liquid Approximation (ALA). We use an axisymmetric 2D shell geometry with a 60° opening width and mantle thickness of 2855 km. Plume upwelling is initiated by imposing anomalously warm (ΔT 250 K) temperatures across a zone 200 km wide centered at the base of the model. At the 660 km and 410 km depth mantle phase transitions we simulate changes in density, viscosity, and the release of latent heat. Models are allowed to evolve for up to 1 Gyr. To test the effect of differing mantle compositions, we vary the Clapeyron slopes from 1 to 5 MPa and -0.5 to -6 MPa at the 410 km and 660 km phase transitions, respectively. Similar to other studies, results of preliminary simulations show an initial flattening of the plume head at the 660 km transition before penetration and subsequent acceleration across the 410 km transition, coinciding with mild shoaling of the 660 km, and deepening of the 410 km. Here, we will present analyses of mass flux periodicity and near-surface melt production rates and the implications on hotspot volcanic production rates.

Influences of riverine and upwelling waters on the coastal carbonate system off Central Chile and their ocean acidification implications

NASA Astrophysics Data System (ADS)

Vargas, Cristian A.; Contreras, Paulina Y.; Pérez, Claudia A.; Sobarzo, Marcus; Saldías, Gonzalo S.; Salisbury, Joe

2016-06-01

A combined data set, combining data from field campaigns and oceanographic cruises, was used to ascertain the influence of both river discharges and upwelling processes, covering spatial and temporal variation in dissolved inorganic carbon (DIC) and aragonite saturation state. This work was conducted in one of the most productive river-influenced upwelling areas in the South Pacific coasts (36°S). Additionally, further work was also conducted to ascertain the contribution of different DIC sources, influencing the dynamics of DIC along the land-ocean range. Six sampling campaigns were conducted across seven stations at the Biobío River basin, covering approximately 200 km. Three research cruises were undertaken simultaneously, covering the adjacent continental shelf, including 12 sampling stations for hydrographic measurements. Additionally, six stations were also sampled for chemical analyses, covering summer, winter, and spring conditions over 2010 and 2011. Our results evidenced that seaward extent of the river plume was more evident during the winter field campaign, when highest riverine DIC fluxes were observed. The carbonate system along the river-ocean continuum was very heterogeneous varying over spatial and temporal scales. High DIC and pCO2 were observed in river areas with larger anthropogenic effects. CO2 supersaturation at the river plume was observed during all campaigns due to the influence of low pH river waters in winter/spring and high-pCO2 upwelling waters in summer. δ13CDIC evidenced that main DIC sources along the river and river plume corresponded to the respiration of terrestrial organic matter. We have linked this natural process to the carbonate saturation on the adjacent river-influenced coastal area, suggesting that Ωaragonite undersaturation in surface/subsurface waters is largely modulated by the influence of both river discharge and coastal upwelling events in this productive coastal area. Conditions of low Ωaragonite might impact negatively physiological traits for marine organisms, such as bivalves, gastropods, and crustaceans. Therefore, local populations from river-influenced sites could be inherently more tolerant to ocean acidification than organisms living in regions with lower Ωaragonite variability.

Multiple mantle upwellings through the transition zone beneath the Afar Depression?

NASA Astrophysics Data System (ADS)

Hammond, J. O.; Kendall, J. M.; Stuart, G. W.; Thompson, D. A.; Ebinger, C. J.; Keir, D.; Ayele, A.; Goitom, B.; Ogubazghi, G.

2012-12-01

Previous seismic studies using regional deployments of sensors in East-Africa show that low seismic velocities underlie Africa, but their resolution is limited to the top 200-300km of the Earth. Thus, the connection between the low velocities in the uppermost mantle and those imaged in global studies in the lower mantle is unclear. We have combined new data from Afar, Ethiopia with 7 other regional experiments and global network stations across Kenya, Ethiopia, Eritrea, Djibouti and Yemen, to produce high-resolution models of upper mantle P- and S-wave velocities to the base of the transition zone. Relative travel time tomographic inversions show that within the transition zone two focussed sharp-sided low velocity regions exist: one beneath the Western Ethiopian plateau outside the rift valley, and the other beneath the Afar depression. Estimates of transition zone thickness suggest that this is unlikely to be an artefact of mantle discontinuity topography as a transition zone of normal thickness underlies the majority of Afar and surrounding regions. However, a low velocity layer is evident directly above the 410 discontinuity, co-incident with some of the lowest seismic velocities suggesting that smearing of a strong low velocity layer of limited depth extent may contribute to the tomographic models in north-east Afar. The combination of seismic constraints suggests that small low temperature (<50K) upwellings may rise from a broader low velocity plume-like feature in the lower mantle. This interpretation is supported by numerical and analogue experiments that suggest the 660km phase change and viscosity jump may impede flow from the lower to upper mantle creating a thermal boundary layer at the base of the transition zone. This allows smaller, secondary upwellings to initiate and rise to the surface. These, combined with possible evidence of melt above the 410 discontinuity can explain the seismic velocity models. Our images of secondary upwellings suggest that there is no evidence for a plume in the classical sense (i.e. a narrow conduit). Instead, we propose that secondary upwellings rise from the base of the transition zone and connect with the northeast flowing African superswell in the upper mantle.

The OMZ and nutrient features as a signature of interannual and low-frequency variability in the Peruvian upwelling system

NASA Astrophysics Data System (ADS)

Graco, Michelle I.; Purca, Sara; Dewitte, Boris; Castro, Carmen G.; Morón, Octavio; Ledesma, Jesús; Flores, Georgina; Gutiérrez, Dimitri

2017-10-01

Over the last decades, the Humboldt Current upwelling ecosystem, particularly the northern component off the coast of Peru, has drawn the interest of the scientific community because of its unique characteristics: it is the upwelling system with the biggest catch productivity despite the fact it is embedded in a shallow and intense oxygen minimum zone (OMZ). It is also an area of intense nitrogen loss and anammox activity and experiences large interannual variability associated with the equatorial remote forcing. In this context, we examined the oceanographic and biogeochemical variability associated with the OMZ off central Peru from a monthly time series (1996-2011) recorded off the coast of Callao (12° 02' S, 77° 29' W). The data reveal a rich spectrum of variability in the OMZ that includes frequencies ranging from seasonal to interannual scales. Due to the efficient oceanic teleconnection off Peru, the observed variability is interpreted in the light of an estimate of the equatorial Kelvin wave contribution to sea level anomalies considering the peculiarities of its vertical structure (i.e., the first two baroclinic modes). The span of the data set allows us to contrast two OMZ regimes. The strong regime is associated with the strong 1997-1998 equatorial Pacific El Niño, during which the OMZ adjusted to Kelvin-wave-induced downwelling conditions that switched off the upwelling and drastically reduced nutrient availability. The weak regime corresponds to the post-2000 period associated with the occurrence of moderate central Pacific El Niño events and enhanced equatorial Kelvin wave activity, in which mean upwelling conditions are maintained. It is shown that the characteristics of the coupling between physics and biogeochemistry is distinct between the two regimes with the weak regime being associated with a larger explained variance in biogeochemical properties not linearly related to the ENSO oceanic teleconnection. The data also reveal a long-term trend from 1999 corresponding to a deepening of the oxygen-deficient waters and warming. The implications of our results for understanding the OMZ dynamics off Peru are discussed.

Small pelagic fish reproductive strategies in upwelling systems: A natal homing evolutionary model to study environmental constraints

NASA Astrophysics Data System (ADS)

Brochier, T.; Colas, F.; Lett, C.; Echevin, V.; Cubillos, L. A.; Tam, J.; Chlaida, M.; Mullon, C.; Fréon, P.

2009-12-01

Although little is known about the individual-level mechanisms that influence small pelagic fish species’ reproductive strategy, Mullon et al. [Mullon, C., Cury, P., Penven, P., 2002. Evolutionary individual-based model for the recruitment of anchovy ( Engraulis capensis) in the southern Benguela. Canadian Journal of Fisheries and Aquatic Sciences 59, 910-922] showed that the observed anchovy spawning patterns in the southern Benguela Current system off South Africa could be accurately reproduced by simulating a natal homing reproductive strategy, i.e. individuals spawning at their natal date and place. Here we used a similar method, i.e., an individual-based model of the natal homing reproductive strategy, and applied it to other upwelling systems: the northern Humboldt Current system off Peru, the southern Humboldt Current system off Chile and the central Canary Current system off Morocco. We investigated the spatial (horizontal and vertical) and seasonal spawning patterns that emerged after applying different environmental constraints in the model, and compared these to observed spawning patterns of sardine and anchovy in their respective systems. The selective environmental constraints tested were: (1) lethal temperature; (2) retention over the continental shelf; and (3) avoidance of dispersive structures. Simulated horizontal spatial patterns and seasonal patterns compared reasonably well with field data, but vertical patterns in most cases did not. Similarly to what was found for the southern Benguela, temperature was a determinant constraint in the southern Humboldt. The shelf retention constraint led to selection of a particular spawning season during the period of minimum upwelling in all three of the upwelling regions considered, and to spatial patterns that matched observed anchovy spawning off Chile and sardine spawning off Morocco. The third constraint, avoidance of dispersive structures, led to the emergence of a spawning season during the period of maximum upwelling off Chile and Morocco, but not in Peru. The most accurate representation of observed spatio-temporal spawning patterns off Peru was achieved through a combination of shelf retention and non-dispersion constraints.

Synoptic-to-planetary scale wind variability enhances phytoplankton biomass at ocean fronts

NASA Astrophysics Data System (ADS)

Whitt, D. B.; Taylor, J. R.; Lévy, M.

2017-06-01

In nutrient-limited conditions, phytoplankton growth at fronts is enhanced by winds, which drive upward nutrient fluxes via enhanced turbulent mixing and upwelling. Hence, depth-integrated phytoplankton biomass can be 10 times greater at isolated fronts. Using theory and two-dimensional simulations with a coupled physical-biogeochemical ocean model, this paper builds conceptual understanding of the physical processes driving upward nutrient fluxes at fronts forced by unsteady winds with timescales of 4-16 days. The largest vertical nutrient fluxes occur when the surface mixing layer penetrates the nutricline, which fuels phytoplankton in the mixed layer. At a front, mixed layer deepening depends on the magnitude and direction of the wind stress, cross-front variations in buoyancy and velocity at the surface, and potential vorticity at the base of the mixed layer, which itself depends on past wind events. Consequently, mixing layers are deeper and more intermittent in time at fronts than outside fronts. Moreover, mixing can decouple in time from the wind stress, even without other sources of physical variability. Wind-driven upwelling also enhances depth-integrated phytoplankton biomass at fronts; when the mixed layer remains shallower than the nutricline, this results in enhanced subsurface phytoplankton. Oscillatory along-front winds induce both oscillatory and mean upwelling. The mean effect of oscillatory vertical motion is to transiently increase subsurface phytoplankton over days to weeks, whereas slower mean upwelling sustains this increase over weeks to months. Taken together, these results emphasize that wind-driven phytoplankton growth is both spatially and temporally intermittent and depends on a diverse combination of physical processes.

Short commentary on marine productivity at Arctic shelf breaks: upwelling, advection and vertical mixing

NASA Astrophysics Data System (ADS)

Randelhoff, Achim; Sundfjord, Arild

2018-04-01

The future of Arctic marine ecosystems has received increasing attention in recent years as the extent of the sea ice cover is dwindling. Although the Pacific and Atlantic inflows both import huge quantities of nutrients and plankton, they feed into the Arctic Ocean in quite diverse regions. The strongly stratified Pacific sector has a historically heavy ice cover, a shallow shelf and dominant upwelling-favourable winds, while the Atlantic sector is weakly stratified, with a dynamic ice edge and a complex bathymetry. We argue that shelf break upwelling is likely not a universal but rather a regional, albeit recurring, feature of the new Arctic. It is the regional oceanography that decides its importance through a range of diverse factors such as stratification, bathymetry and wind forcing. Teasing apart their individual contributions in different regions can only be achieved by spatially resolved time series and dedicated modelling efforts. The Northern Barents Sea shelf is an example of a region where shelf break upwelling likely does not play a dominant role, in contrast to the shallower shelves north of Alaska where ample evidence for its importance has already accumulated. Still, other factors can contribute to marked future increases in biological productivity along the Arctic shelf break. A warming inflow of nutrient-rich Atlantic Water feeds plankton at the same time as it melts the sea ice, permitting increased photosynthesis. Concurrent changes in sea ice cover and zooplankton communities advected with the boundary currents make for a complex mosaic of regulating factors that do not allow for Arctic-wide generalizations.

Upwelling and downwelling induced by mesoscale circulation in the DeSoto Canyon region

NASA Astrophysics Data System (ADS)

Nguyen, T. T.; Chassignet, E.; Morey, S. L.; Dukhovskoy, D. S.

2014-12-01

Ocean dynamics are complex over irregular topography areas, and the northeastern Gulf of Mexico, specifically the DeSoto Canyon region, is a challenge for modelers and oceanographers. Vertical movement of waters, especially upwelling, is observed to take place over the canyon's head and along the coast; however, it is not well understood. We focus on upwelling/downwelling processes induced by the Loop Current and its associated eddy field using multi-decadal Hybrid Coordinate Ocean Model simulations. The Loop Current, part of the Gulf Stream, can develop northward into the Gulf through the Yucatan Channel and exit through the Florida Straits. It can reach the continental slope of the study domain and directly depress the isopycnals. Cyclonic eddies in front of the Loop Current also induce upwelling underneath. On the other hand, the Loop Current sometimes impinges on the West Florida Shelf and generates a high pressure disturbance, which travels northward along the shelf into the study region. Consequently, large-scale downwelling occurs across the continental slopes. Our analysis of sea surface height shows that the Loop Current pressure disturbance tends to propagate along the shallow isobaths of 100 to 300 m in the topographic wave direction from south of the West Florida Shelf to the Mississippi Delta. In addition, after shedding a large anticyclonic eddy, the Loop Current retracts southward and can touch the southeastern corner of the West Florida Shelf. This can result in a higher pressure disturbance, and therefore stronger large-scale downwelling in the DeSoto Canyon region.

A wind-driven, hybrid latent and sensible heat coastal polynya off Barrow, Alaska

NASA Astrophysics Data System (ADS)

Hirano, Daisuke; Fukamachi, Yasushi; Watanabe, Eiji; Ohshima, Kay I.; Iwamoto, Katsushi; Mahoney, Andrew R.; Eicken, Hajo; Simizu, Daisuke; Tamura, Takeshi

2016-01-01

The nature of the Barrow Coastal Polynya (BCP), which forms episodically off the Alaska coast in winter, is examined using mooring data, atmospheric reanalysis data, and satellite-derived sea-ice concentration and production data. We focus on oceanographic conditions such as water mass distribution and ocean current structure beneath the BCP. Two moorings were deployed off Barrow, Alaska in the northeastern Chukchi Sea from August 2009 to July 2010. For sea-ice season from December to May, a characteristic sequence of five events associated with the BCP has been identified; (1) dominant northeasterly wind parallel to the Barrow Canyon, with an offshore component off Barrow, (2) high sea-ice production, (3) upwelling of warm and saline Atlantic Water beneath the BCP, (4) strong up-canyon shear flow associated with displaced density surfaces due to the upwelling, and (5) sudden suppression of ice growth. A baroclinic current structure, established after the upwelling, caused enhanced vertical shear and corresponding vertical mixing. The mixing event and open water formation occurred simultaneously, once sea-ice production had stopped. Thus, mixing events accompanied by ocean heat flux from the upwelled warm water into the surface layer played an important role in formation/maintenance of the open water area (i.e., sensible heat polynya). The transition from a latent to a sensible heat polynya is well reproduced by a high-resolution pan-Arctic ice-ocean model. We propose that the BCP, previously considered to be a latent heat polynya, is a wind-driven hybrid latent and sensible heat polynya, with both features caused by the same northeasterly wind.

Off-great-circle paths in transequatorial propagation: 1. Discrete and diffuse types

NASA Astrophysics Data System (ADS)

Tsunoda, Roland T.; Maruyama, Takashi; Tsugawa, Takuya; Yokoyama, Tatsuhiro; Ishii, Mamoru; Nguyen, Trang T.; Ogawa, Tadahiko; Nishioka, Michi

2016-11-01

There is mounting evidence that plasma structure in nighttime equatorial F layer evolves from large-scale wave structure (LSWS) in the bottomside F layer. This process cannot be ignored because equatorial plasma bubbles (EPBs) arise from large-amplitude LSWS; and, because intense radiowave scintillations are associated with EPBs, understanding the LSWS-to-EPB process is a crucial step toward reliable Space Weather Forecasting. In this regard, the transequatorial propagation (TEP) experiment appears to be the most useful among available research instruments. After a lapse of 30 years, the TEP experiment has been resurrected; a goal of this research is to understand TEP measurements well enough so that they can be used to diagnose the LSWS-to-EPB process. Toward this end, new results are presented in two companion papers. Herein (P1), off-great-circle (OGC) propagation paths are shown to consist of two types, discrete and diffuse. The new findings include the following: (1) a generalized multireflection model that can explain most of the observed properties; (2) the discrete type is supported by multireflections from an unstructured upwelling, (3) the diffuse type is supported by reflections from plasma structure in EPBs; and (4) the observed east-west (EW) asymmetry can be explained in terms of a distorted upwelling or plasma structure along the west wall of an upwelling. In Paper 2 (P2), a second form of observed EW asymmetry is explained in terms of plasma structure, which is not aligned with the geomagnetic field. The findings strongly confirm a close relationship between upwellings, ESF patches, and OGC paths.

On the impact of the resolution on the surface and subsurface Eastern Tropical Atlantic warm bias

NASA Astrophysics Data System (ADS)

Martín-Rey, Marta; Lazar, Alban

2016-04-01

The tropical variability has a great importance for the climate of adjacent areas. Its sea surface temperature anomalies (SSTA) affect in particular the Brazilian Nordeste and the Sahelian region, as well as the tropical Pacific or the Euro-Atlantic sector. Nevertheless, the state-of the art climate models exhibits very large systematic errors in reproducing the seasonal cycle and inter-annual variability in the equatorial and coastal Africa upwelling zones (up to several °C for SST). Theses biases exist already, in smaller proportions though, in forced ocean models (several 1/10th of °C), and affect not only the mixed layer but also the whole thermocline. Here, we present an analysis of the impact of horizontal and vertical resolution changes on these biases. Three different DRAKKAR NEMO OGCM simulations have been analysed, associated to the same forcing set (DFS4.4) with different grid resolutions: "REF" for reference (1/4°, 46 vertical levels), "HH" with a finer horizontal grid (1/12°, 46 v.l.) and "HV" with a finer vertical grid (1/4°, 75 v.l.). At the surface, a more realistic seasonal SST cycle is produced in HH in the three upwellings, where the warm bias decreases (by 10% - 20%) during boreal spring and summer. A notable result is that increasing vertical resolution in HV causes a shift (in advance) of the upwelling SST seasonal cycles. In order to better understand these results, we estimate the three upwelling subsurface temperature errors, using various in-situ datasets, and provide thus a three-dimensional view of the biases.

Atoll-phosphate genesis: Role of lagoonal biomass and possible role of endo-upwelling processes in phosphate concentration

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

Trichet, J.; Rougerie, F.

1990-06-01

Sedimentological and hydrogeological data in Niau, a closed atoll in French Polynesia where P-concentration has been measured, suggest the role played by lagoonal organic matter in P-accumulation and the possible role of endo-upwelling processes in P-input in the system. A 15 m deep core through the lagoonal deposits shows the succession of organic-rich strata in which the P-content can reach up to 1.3% P{sub 2}O{sub 5}. Such a pattern suggests that, whatever the source of P within the lagoon (lagoonal water, bird guano, or endo-upwelled solutions, see below), this element is likely to be incorporated in quantitatively important lagoonal biomassmore » whose decay releases phosphorus back to the sediment. An example of such biomass and organic matter is given by the large amounts of cyano-bacterial organic matter that are present in the lagoon of Niau. A source for island phosphate has recently been proposed to be relatively deep seawater, which would be endo-upwelled from depths of hundreds of meters ({approximately}500 m, where P content is approximately 1.5 mmol.m{sup {minus}3} PO{sub 4}-P) through the permeable reef-body up to its surface (i.e., to its lagoonal waters, where P content reaches 5 mmol.m{sup {minus}3} in Niau atoll). The energy necessary for the transport of such solutions would be geothermal (at the bottom of the water column, i.e., close to the volcanic substrate of the reef body) and solar at its top through evaporation.« less

Controls on the interannual variability of hypoxia in a subtropical embayment and its adjacent waters in the Guangdong coastal upwelling system, northern South China Sea

NASA Astrophysics Data System (ADS)

Zhang, Heng; Cheng, Weicong; Chen, Yuren; Yu, Liuqian; Gong, Wenping

2018-06-01

Coastal embayments located downwind of large rivers under an upwelling-favorable wind are prone to develop low-oxygen or hypoxic conditions in their bottom water. One such embayment is Mirs Bay, off the Guangdong coast, which is affected by upwelling and the Pearl River Estuary (PRE) plume during summer. The relative importance of physical and biochemical processes on the interannual variability of hypoxia in Mirs Bay and its adjacent waters was investigated using statistical analyses of monthly hydrographic and water quality monitoring data from 2001 to 2015. The results reveal that the southwesterly wind duration and the PRE river discharge together explain 49% of the interannual variability in the size of the hypoxic area, whereas inclusion of the nutrient concentrations inside Mirs Bay and phytoplankton on the shelf explains 75% of the interannual variability in the size of the hypoxic area. This finding suggests that the interannual variability of hypoxia in Mirs Bay is regulated by coupled physical and biochemical processes. Increase of the hypoxic area under a longer-lasting southwesterly wind is caused by increased stratification, extended bottom water residence time, and onshore transport of a low-oxygen water mass induced by stable upwelling. In contrast, a reduction in the size of the hypoxic area may be attributed to a decrease in the surface water residence time of the particulate organic matter outside Mirs Bay due to increased discharge from the PRE. The results also show that the effects of allochthonous particulate organic matter outside Mirs Bay on bottom hypoxia cannot be neglected.

A Novel Method of Measuring Upwelling Radiance in the Hydrographic Sub-Hull

NASA Astrophysics Data System (ADS)

Rüssmeier, N.; Zielinski, O.

2016-01-01

In this study we present a new method useful in collecting upwelling radiance (Lu) from a platform submerged in a hydrographic sub-hull or moon pool of a research vessel. The information analyzed here was obtained during a field campaign in the Northwestern European shelf seas aboard the new research vessel SONNE. As the platform was located at the center of the ship, there is minimal effect from pitch and roll which is known to influence upwelling radiance observations. A comparison of the measurements from this platform with a free falling hyperspectral profiler was performed to determine the degree of uncertainty that results from ship shadow. For given Lu(λ) in situ data we observed ±33% intensity deviations compared to profiling measurements that can be attributed to instrument shading during moon pool installation and environmental perturbations. Furthermore Lu(λ) in situ spectra variations were observed at lower wavelengths, therefore a form fitting algorithm was adapted to receive corresponding depths with identical spectral form from Lu(z, λ) profiler casts. During an east to west transect in North Sea with a schedule speed up to 12 knots in situ radiance reflectance rrs(7, λ) measurements at 7 meter depth were performed with this novel radiometer setup. In spite of any restrictions originating from the sub-hull installation, water masses mixing zone from CDOM dominated coastal waters in the Skagerrak Strait towards the open North Sea were successfully derived thus offering an underway applicable upwelling radiance sensing not suffering from sun glint or other typical restrictions of above water radiometer installations.

The Effect of Alongcoast Advection on Pacific Northwest Shelf and Slope Water Properties in Relation to Upwelling Variability

NASA Astrophysics Data System (ADS)

Stone, Hally B.; Banas, Neil S.; MacCready, Parker

2018-01-01

The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin-scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N-50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well-explained (R2 = 0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large-scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large-scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale.

Evidence of bottom-up limitations in nearshore marine systems based on otolith proxies of fish growth

USGS Publications Warehouse

von Biela, Vanessa R.; Kruse, Gordon H.; Mueter, Franz J.; Black, Bryan A.; Douglas, David C.; Helser, Thomas E.; Zimmerman, Christian E.

2015-01-01

Fish otolith growth increments were used as indices of annual production at nine nearshore sites within the Alaska Coastal Current (downwelling region) and California Current (upwelling region) systems (~36–60°N). Black rockfish (Sebastes melanops) and kelp greenling (Hexagrammos decagrammus) were identified as useful indicators in pelagic and benthic nearshore food webs, respectively. To examine the support for bottom-up limitations, common oceanographic indices of production [sea surface temperature (SST), upwelling, and chlorophyll-a concentration] during summer (April–September) were compared to spatial and temporal differences in fish growth using linear mixed models. The relationship between pelagic black rockfish growth and SST was positive in the cooler Alaska Coastal Current and negative in the warmer California Current. These contrasting growth responses to SST among current systems are consistent with the optimal stability window hypothesis in which pelagic production is maximized at intermediate levels of water column stability. Increased growth rates of black rockfish were associated with higher chlorophyll concentrations in the California Current only, but black rockfish growth was unrelated to the upwelling index in either current system. Benthic kelp greenling growth rates were positively associated with warmer temperatures and relaxation of downwelling (upwelling index near zero) in the Alaska Coastal Current, while none of the oceanographic indices were related to their growth in the California Current. Overall, our results are consistent with bottom-up forcing of nearshore marine ecosystems—light and nutrients constrain primary production in pelagic food webs, and temperature constrains benthic food webs.

Characterizing the Phytoplankton Community of the South China Sea

NASA Astrophysics Data System (ADS)

Aleman, M.; Subramaniam, A.; Hay, I.

2016-12-01

The South China Sea (SCS) is a semi-enclosed tropical basin that receives nutrients from two main sources: coastal upwelling and river runoff from the surrounding countries. The southwest (SW) summer monsoon that occurs between March and September drives upwelling off the coast of Vietnam, a rarity compared to most upwelling systems that are driven by eastern boundary current systems. The upwelling in the SCS and the intensity of the SW monsoon are sensitive to climate variability and are affected by phenomenon such as El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). The size and location of the Mekong River plume also varies from year to year due to the variation in rainfall and wind strength of the monsoon. The riverine input is also influenced by anthropogenic activity such as agriculture, damming, and land-use changes. Different nutrients are supplied from these two main sources and in different quantities, and affect the structure of the phytoplankton community. Phytoplankton comprise the base of the food web, supporting the growth of higher organisms and ultimately support fisheries. We need to understand how the supply of different nutrients alters the phytoplankton community of the SCS. We sampled 22 stations along the coast of Vietnam aboard the R/V Falkor of the Schmidt Ocean Institute during the pre-monsoon season. High performance liquid chromatography (HPLC) and flow cytometric techniques will be used to characterize the phytoplankton community. The relationship between the different water masses, nutrient sources, and phytoplankton community found in the SCS will be presented.

The Effect of Alongcoast Advection on Pacific Northwest Shelf and Slope Water Properties in Relation to Upwelling Variability

PubMed Central

Banas, Neil S.; MacCready, Parker

2018-01-01

Abstract The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin‐scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N–50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well‐explained (R 2 = 0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large‐scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large‐scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale. PMID:29938149

The Northern Appalachian Anomaly is a Modern Asthenospheric Upwelling

NASA Astrophysics Data System (ADS)

Menke, W. H.; Skryzalin, P. A.; Levin, V. L.; Harper, T. B.; Darbyshire, F. A.; Dong, T.

2016-12-01

The eastern North American coast is the site of significant seismic velocity heterogeneities. They are a record - albeit an ambiguous one - of lithospheric and asthenospheric processes operating at the continental margin. We focus on the Northern Appalachian Anomaly (NAA), a particularly strong slow velocity feature in the shallow mantle located in a westward indentation (or divot) of the continental lithosphere in southern New England. The NAA has been explained as a relic feature associated with the Great Meteor hotspot (GMHS), which traversed southern New England at 130-100 Ma. Here we consider the alternative hypothesis that it is a modern feature associated with small-scale asthenospheric upwelling unrelated to any hotspot. We show that the NAA is a narrow (400 km wide) columnar feature and that its travel time delays are consistent with an extremely strong ( 700K ) asthenospheric temperature anomaly. After analyzing several previously-published tomographic images and a new one described here, we conclude that it is most consistent with a strong local upwelling associated with the eastern edge of the Laurentian (pre-Cambrian) continental lithosphere.

The Impact of Ozone Depleting Substances on Tropical Upwelling, as Revealed by the Absence of Lower Stratospheric Cooling since the Late 1990s

NASA Astrophysics Data System (ADS)

Polvani, L. M.; Wang, L.; Aquila, V.; Waugh, D.

2016-12-01

The impact of ozone depleting substances on global lower stratospheric temperature trends is widely recognized. In the tropics, however, understanding lower stratospheric temperature trends has proven more challenging. While the tropical lower stratospheric cooling observed from 1979 to 1997 has also been shown to result almost entirely from ozone decreases, those ozone trends cannot be of chemical origin, as active chlorine is not abundant in the tropical lower stratosphere. The 1979-1997 tropical ozone trends are believed to originate from enhanced upwelling which, it is often stated, would be driven by increasing concentrations of well mixed greenhouse gases. In this study, using simple arguments based on observational evidence after 1997, combined with model integrations with incrementally added single forcings, we argue that ozone depleting substances, not well mixed greenhouse gases, have been the primary driver of temperature and ozone trends in the tropical lower stratosphere until 1997, and this has occurred because ozone depleting substances affect tropical upwelling and the entire Brewer-Dobson circulation.

A cool upwelling filament off Namibia, southwest Africa: preliminary measurements of physical and biological features

NASA Astrophysics Data System (ADS)

Shillington, F. A.; Peterson, W. T.; Hutchings, L.; Probyn, T. A.; Waldron, H. N.; Agenbag, J. J.

1990-11-01

Mesoscale physical and biological measurements were made in a cool upwelling filament in the Benguela Current system, off Namibia in February 1988. The filament had been visible on a satellite infra-red image 2 weeks prior to the survey, and was found to be in a decaying state. Temperature, salinity, 0-50 m integratred nitrate, ammonium, oxygen and plankton data have enabled a consistent picture of the structure to be formed, involving four different water bodies. These are (1) typical continental shelf upwelled water inside the shelf break, (2) filament water characterized by salinity of 35.2, high surface integrated nitrate, small phytoplankton cells, and large numbers of salps, (3) warm, blue oligotrophic water to the north, and (4) a warm, high salinity anticyclonic eddy to the south. It is suggested that this southern eddy may have originated from the Agulhas Current near Cape Town. Anomalously low nitrate concentrations, that could not be explained, were found in a 100 m thick layer between 100 and 200 m depth on the southern edge of the structure.

The making of a productivity hotspot in the coastal ocean.

PubMed

Wingfield, Dana K; Peckham, S Hoyt; Foley, David G; Palacios, Daniel M; Lavaniegos, Bertha E; Durazo, Reginaldo; Nichols, Wallace J; Croll, Donald A; Bograd, Steven J

2011-01-01

Highly productive hotspots in the ocean often occur where complex physical forcing mechanisms lead to aggregation of primary and secondary producers. Understanding how hotspots persist, however, requires combining knowledge of the spatio-temporal linkages between geomorphology, physical forcing, and biological responses with the physiological requirements and movement of top predators. Here we integrate remotely sensed oceanography, ship surveys, and satellite telemetry to show how local geomorphology interacts with physical forcing to create a region with locally enhanced upwelling and an adjacent upwelling shadow that promotes retentive circulation, enhanced year-round primary production, and prey aggregation. These conditions provide an area within the upwelling shadow where physiologically optimal water temperatures can be found adjacent to a region of enhanced prey availability, resulting in a foraging hotspot for loggerhead sea turtles (Caretta caretta) off the Baja California peninsula, Mexico. We have identified the set of conditions that lead to a persistent top predator hotspot, which increases our understanding of how highly migratory species exploit productive regions of the ocean. These results will aid in the development of spatially and environmentally explicit management strategies for marine species of conservation concern.

Opening of the South China Sea and Upwelling of the Hainan Plume

NASA Astrophysics Data System (ADS)

Yu, Mengming; Yan, Yi; Huang, Chi-Yue; Zhang, Xinchang; Tian, Zhixian; Chen, Wen-Huang; Santosh, M.

2018-03-01

Opening of the South China Sea and upwelling of the Hainan Plume are among the most challenging issues related to the tectonic evolution of East Asia. However, when and how the Hainan Plume affected the opening of the South China Sea remains unclear. Here we investigate the geochemical and isotopic features of the 25 Ma mid-ocean ridge basalt (MORB) in the Kenting Mélange, southern Taiwan, 16 Ma MORB drilled by the IODP Expedition 349, and 9 Ma ocean island basalt-type dredged seamount basalt. The 25 Ma MORBs reveal a less metasomatic depleted MORB mantle-like source. In contrast, the Miocene samples record progressive mantle enrichment and possibly signal the contribution of the Hainan Plume. We speculate that MORBs of the South China Sea which could have recorded plume-ridge source mixing perhaps appear since 23.8 Ma. On the contrary, the Paleocene-Eocene ocean island basalt-type intraplate volcanism of the South China continental margin is correlated to decompression melting of a passively upwelling fertile asthenosphere due to continental rifting.

BOREAS AFM-1 NOAA/ATDD Long-EZ Aircraft Flux data Over the SSA

NASA Technical Reports Server (NTRS)

Crawford, Timothy L.; Baldocchi, Dennis; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Gunter, Laureen; Dumas, Ed; Smith, David E. (Technical Monitor)

2000-01-01

This data set contains measurements from the Airborne Flux and Meteorology (AFM)-1 National Oceanographic and Atmospheric Administration/Atmospheric Turbulence and Diffusion Division (NOAA/ATDD) Long-EZ Aircraft collected during the 1994 Intensive Field Campaigns (IFCs) at the southern study area (SSA). These measurements were made from various instruments mounted on the aircraft. The data that were collected include aircraft altitude, wind direction, wind speed, air temperature, potential temperature, water mixing ratio, U and V components of wind velocity, static pressure, surface radiative temperature, downwelling and upwelling total radiation, downwelling and upwelling longwave radiation, net radiation, downwelling and upwelling photosynthectically active radiation (PAR), greenness index, CO2 concentration, O3 concentration, and CH4 concentration. There are also various columns that indicate the standard deviation, skewness, kurtosis, and trend of some of these data. The data are stored in tabular ASCII files. The NOAA/ATDD Long-EZ aircraft flux data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Mesoscale Variation of Mechanisms Contributing to Stability in Rocky Shore Communities

PubMed Central

Valdivia, Nelson; González, Andrés E.; Manzur, Tatiana; Broitman, Bernardo R.

2013-01-01

Environmental fluctuations can generate asynchronous species’ fluctuations and community stability, due to compensatory dynamics of species with different environmental tolerances. We tested this hypothesis in intertidal hard-bottom communities of north-central Chile, where a persistent upwelling centre maintains a mosaic in sea surface temperatures (SST) over 10s of kilometres along the shore. Coastal upwelling implies colder and temporally more stable SST relative to downstream sites. Uni- and multivariate analyses of multiyear timeseries of SST and species abundances showed more asynchronous fluctuations and higher stability in sites characterised by warmer and more variable SST. Nevertheless, these effects were weakened after including data obtained in sites affected by less persistent upwelling centres. Further, dominant species were more stable in sites exposed to high SST variability. The strength of other processes that can influence community stability, chiefly statistical averaging and overyielding, did not vary significantly between SST regimes. Our results provide observational evidence supporting the idea that exogenously driven compensatory dynamics and the stabilising effects of dominant species can determine the stability of ecosystems facing environmental fluctuations. PMID:23326592

Are Superplumes a Myth?

NASA Astrophysics Data System (ADS)

Steinberger, Bernhard; Conrad, Clinton

2017-04-01

Two large seismically slow lower mantle regions beneath the Pacific and Africa are sometimes referred to as "superplumes". This names evokes associations of large-scale active upwellings, however it is not clear whether these are real, or rather just regular mantle plumes occur more frequently in these regions. Here we study the implications of new results on dynamic topography, which would be associated with active upwellings, on this question. Recently, Hoggard et al. (2016) developed a detailed model of marine residual topography, after subtracting isostatic crustal topography. Combining this with results from continents, a global model can be expanded in spherical harmonics. Comparison with dynamic topography derived from mantle flow models inferred from seismic tomography (Steinberger, 2016) yields overall good agreement and similar power spectra, except at spherical harmonic degree two where mantle flow models predict about six times as much power as is inferred from observations: Mantle flow models feature two large-scale antipodal upwellings at the seismically slow regions, whereas the actual topography gives only little indication of these. We will discuss here what this discrepancy could possibly mean and how it could be resolved.

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

Tatsumi, Yoshiyuki; Kimura, Nobukazu; Itaya, Tetsumaru

K-Ar dates and chemical compositions of basalts in the Gregory Rift, Kenya, demonstrate marked secular variation of lava chemistry. Two magmatic cycles characterized by incompatible element relative depletion are recognized; both occurring immediately after the peak of basaltic volcanism and coeval with both trachyte/phonolite volcanism and domal uplift of the region. These cycles may be attributed to increasing degree of partial melting of mantle source material in association with thinning of the lithosphere by thermal erosion through contact with hot upwelling asthenospheric mantle. Cyclic variation in asthenosphere upwelling may be considered an important controlling process in the evolution of themore » Gregory Rift.« less

L' upwelling de la côte atlantique du Maroc entre 1994 et 1998

NASA Astrophysics Data System (ADS)

Makaoui, Ahmed; Orbi, Abdelattif; Hilmi, Karim; Zizah, Soukaina; Larissi, Jamila; Talbi, Mohammed

2005-12-01

The pelagic ecosystem of the Moroccan Atlantic coast is influenced by the spatiotemporal variability of upwelling. The changes in the physicochemical and biological parameters as well as their interrelationship and regrouping by the principal components analysis allowed us to subdivide the Atlantic coast in four active areas: two areas located at the north of Cape Juby (28°N), characterised by a summery activity and two areas located at the south, active permanently, with a variable intensity. To cite this article: A. Makaoui et al., C. R. Geoscience 337 (2005).

Three-dimensional spherical models of convection in the earth's mantle

NASA Technical Reports Server (NTRS)

Bercovici, Dave; Schubert, Gerald; Glatzmaier, Gary A.

1989-01-01

Three-dimensional spherical models of mantle convection in the earth reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of mantle circulation. Thus subduction zones and descending sheetlike slabs in the mantle are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs, which are cooler than the surrounding mantle. Cylindrical mantle plumes that cause hot spots such as Hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large-scale mantle circulation.

Non-hotspot volcano chains produced by migration of shear-driven upwelling toward the East Pacific Rise (Invited)

NASA Astrophysics Data System (ADS)

Ballmer, M. D.; Conrad, C. P.; Smith, E. I.; Harmon, N.

2013-12-01

While most oceanic volcanism is associated with the passive rise of hot mantle beneath the spreading axes of mid-ocean ridges (MOR), volcanism occurring off-axis reflects intraplate upper-mantle dynamics and composition, yet is poorly understood. Close to the East Pacific Rise (EPR), active magmatism propagated towards the spreading center to create a series of parallel volcanic ridges on the Pacific Plate ( ~3500 km in length for the Pukapuka, and ~500 km for the Sojourn, and Hotu-Matua ridges). Propagation of this volcanism by ~20 cm/a, as well as asymmetry in a variety of geophysical observables across the EPR, indicates strong lateral eastward pressure-driven flow in the asthenosphere; likely driven by upwelling beneath the South Pacific Superswell [1]. Although this pattern of large-scale mantle flow can account for the propagation of intraplate magmatism towards the EPR, it does not explain decompression melting itself. We hypothesize that shear-driven upwelling sustains off-axis volcanism. Unlike e.g. mantle plumes, shear-driven upwelling is a mechanism for mantle decompression that does not require lateral density heterogeneity to drive upwelling. For example, in the presence of shear across the asthenosphere, vertical flow emerges at the edges of viscosity heterogeneity [2]. These ingredients are present in the SE Pacific, where (1) shear across the asthenosphere is inferred to be greatest worldwide [2], and (2) lateral heterogeneity in mantle viscosity is indicated by geoid lineations that are associated with anomalies in seismic tomography [3]. Eastward pressure-driven flow from the South Pacific Superswell may separate into low-viscosity fingers thus providing viscosity heterogeneity [3]. Our three-dimensional numerical models [4] show that asthenospheric shear can excite upwelling and decompression melting at the tip of low-viscosity fingers that are propelled eastward by vigorous asthenospheric flow. This shear-driven upwelling is able to sustain intraplate volcanism that progresses towards the MOR, spreads laterally close to the axis, and weakly continues on the opposite plate. These predictions can explain the anomalously-fast eastward progression of volcanism, and its spatial distribution near the EPR. Moreover, for a heterogeneous mantle source involving a fertile mantle component embedded in a matrix of peridotite, the systematics of volcanism predicted by the models can account for the geochemical trend observed along the Pukapuka ridge (from C/FOZO [5] in the west toward MOR-basalt in the east), as well as the anomaly of MOR volcanism at the EPR-Pukapuka intersection (documenting C/FOZO influence). Our study highlights the role of horizontal asthenospheric flow and mantle heterogeneity in producing linear chains of intraplate volcanism independent of a (deep-rooted) buoyancy source. [1] Conder, J. A., D. W. Forsyth, E. M. Parmentier (2002): J. Geophys. Res., 107(B12), 2344. [2] Conrad, C. P., T. A. Bianco, E. I. Smith, P. Wessel (2011): Nature Geosci., 4, 317-321. [3] Harmon, N., D. W. Forsyth, D. S. Weeraratne, Y. Yang, S. C. Webb (2011): Earth Planet. Sci. Lett., 311, 306-315. [4] Ballmer, M. D., C. P. Conrad, E. I. Smith, N. Harmon (2013): Geology, 41, 479-482. [5] Zindler, A., Hart, S., 1986. Earth Planet. Sci. Lett., 14, 493-571.

Discriminating the biophysical impacts of coastal upwelling and mud banks along the southwest coast of India

NASA Astrophysics Data System (ADS)

Karnan, C.; Jyothibabu, R.; Arunpandi, N.; Jagadeesan, L.; Muraleedharan, K. R.; Pratihari, A. K.; Balachandran, K. K.; Naqvi, S. W. A.

2017-08-01

Coastal upwelling and mud banks are two oceanographic processes concurrently operating along certain stretches of the southwest (Kerala) coast of India during the Southwest Monsoon period (June-September), facilitating significant enhancement in plankton biomass. Mud banks have scientific and societal attention from time immemorial, predominantly due to the large fisheries associated with them. In this paper, for the first time, the specific biophysical roles of these oceanographic processes have been discriminated, based on a focused 18 weekly/fortnightly time-series study (April to September 2014) in a mud bank-upwelling area (off Alappuzha, southwest coast of India). In conjunction with standard hydrographical and satellite remote sensing data, we utilised a FlowCAM to track the biophysical linkage in terms of plankton composition abundance and size structure at three locations (M1, M2 and M3) in the study area. During the Pre-Southwest Monsoon (April-May), the entire study area was warmer with low nitrate concentration in the surface waters, which caused lower biomass of autotrophs compared to the Southwest Monsoon (June-September). By the onset of the Southwest Monsoon (June), drastic hydrographical transformations took place in the study domain due to the Coastal upwelling, reflected as the surfacing of significantly cool, high nutrient and hypoxic waters. Concurrently, mud bank formed at location M2 due to the presence of relatively high-suspended sediments in the region, creating a localised calm environment conducive for fishing activities. In response to the hydrographical transformations in the entire study area during the Southwest Monsoon, the autotrophic plankton biomass and size structure experienced significant change. The micro-autotrophs biomass that was low during the Pre-Southwest Monsoon (av. 0.33 ± 0.2 mgC L- 1 at surface and av. 0.07 ± 0.04 mgC L- 1 at subsurface) noticeably increased during the Southwest Monsoon (av. 1.6 ± 0.4 mgC L- 1 at surface and av. 1.3 ± 0.2 mgC L- 1 at subsurface). The seasonal mean bio-volume of micro-autotrophs followed the same pattern in all three locations with the dominance of smaller individuals during the Pre-Southwest Monsoon (av. 55 ± 4.4 × 103 μm3 individual- 1 at surface and av. 67.1 ± 38.4 × 103 μm3 individual- 1 at subsurface). Relatively large phytoplankton dominated during the Southwest Monsoon (av. 77.3 ± 5.5 × 103 μm3 individual- 1 at surface and av. 90.3 ± 4.9 × 103 μm3 individual- 1 at subsurface). Similar spatial change in the plankton composition, biomass and size structure in all three locations suggested the dominant role of coastal upwelling, and not the mud bank, in shaping the dominant autotrophic plankton in the study domain. The nutrient enrichment in the region associated with the coastal upwelling facilitated the predominance of a classical short food chain capable of supporting large fish stocks. In addition to relatively calm mud bank, the hypoxic, cool upwelled waters that existed in the subsurface induce the fish stock to concentrate in the surface waters, making the relatively calm mud bank and adjoining areas a rich fishing ground for the native fishers.

Record of Cyclical Massive Upwellings from the Pacific Large Low Shear Velocity Province in the Mesozoic

NASA Astrophysics Data System (ADS)

Gazel, E.; Madrigal, P.; Flores, K. E.; Bizimis, M.; Jicha, B. R.

2016-12-01

Global tomography and numerical models suggest that mantle plume occurrences are closely linked to the margins of the large low shear velocity provinces (LLSVPs). In these locations the ascent of material from the core-mantle boundary connects the deep Earth with surface processes through mantle plume activity, forming large igneous provinces (LIPs) and some of the modern hotspot volcanoes. Petrological and geodynamic evidence suggest a link between the formation of oceanic plateaus and the interactions of mantle plumes and mid-ocean ridges (MOR). Therefore, it is possible to trace the potential interactions between MORs and deep mantle plume upwellings by referencing the tectonic and magmatic evolution of the Pacific Plate in time to the current location of the LLSVP, considering the long-lived ( 500 Ma) existence of these thermochemical anomalies. We identified episodic upwellings of the Pacific LLSVP during the Mesozoic separated by 10 to 20 Ma, by reconstructing the kinematic evolution of the Pacific Plate in the last 170 Ma. The fact that the bulk emplacement of LIPs ( 120-80 Ma) in the Pacific coincides with the timing of the Cretaceous Normal Superchron, that can be related to fluctuations of mantle-core heat fluxes further supports the hypothesis of deep mantle origin for LIPs. The potential cyclicity of LIP emplacement could be tied to core heat fluctuations interacting with the lower mantle, the rheology contrast of material crossing the transition zone (either upwelling hot material or downgoing dense slabs as mantle avalanches), the rate of entrainment of recycled materials, or a combination of the processes mentioned. Recognizing patterns and possible cycles is crucial to the link between deep processes and life as these pulses impacted the marine biota resulting in episodes of anoxia and mass extinctions shortly after their eruption.

Hydrographic characterization of southeast Arabian Sea during the wane of southwest monsoon and spring intermonsoon.

PubMed

Vimal Kumar, K G; Dinesh Kumar, P K; Smitha, B R; Habeeb Rahman, H; Josia, Jacob; Muraleedharan, K R; Sanjeevan, V N; Achuthankutty, C T

2008-05-01

Seasonal variation of the hydrography along the southeast Arabian Sea is described using data collected onboard FORV Sagar Sampada in September--October 2003 (later phase of Southwest monsoon, SWM) and March--April 2004 (Spring inter monsoon, SIM). During the later phase of the SWM, upwelling was in the withdrawal phase and the frontal structure was clearer in the northern sections (13 and 15 degrees N lat) indicating strong upwelling in the area. The driving force of upwelling is identified as the combination of alongshore wind stress and remote forcing with a latitudinal variability. Although a more prominent upwelling was found in the north, a maximum surface Chlorophyll-a was found in the south (10 degrees N). During the SIM, the area was characterized by oligotrophic water with relatively high Sea Surface Temperature (>29 degrees C) and low salinity (33.8 to 35.4). During March, the surface hydrography was found to be controlled mainly by the intrusion of low-saline waters from the south, while during September by the high saline water from the north. The presence of various water masses [Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water (PGW), Red Sea Water (RSW)] and their seasonal variations in the region is discussed and their decreasing influence towards the south is noted during both periods of observation. During the SWM, the dynamic topography showed the equator-ward flow of the West India Coastal Current (WICC) at the surface and a pole-ward coastal under current at sub-thermocline depth. During the SIM, surface circulation revealed the WICC flowing pole-ward north of 13 degrees N, but equator-ward flow in the south, with a clockwise circulation around the Lakshadweep High.

Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing

NASA Astrophysics Data System (ADS)

Morrison, A.; Hogg, A.; Ward, M.

2011-12-01

The southern limb of the ocean's meridional overturning circulation plays a key role in the Earth's response to climate change. The rise in atmospheric CO2 during glacial-interglacial transitions has been attributed to outgassing of enhanced upwelling water masses in the Southern Ocean. However a dynamical understanding of the physical mechanisms driving the change in overturning is lacking. Previous modelling studies of the Southern Ocean have focused on the effect of wind stress forcing on the overturning, while largely neglecting the response of the upper overturning cell to changes in surface buoyancy forcing. Using a series of eddy-permitting, idealised simulations of the Southern Ocean, we show that surface buoyancy forcing in the mid-latitudes is likely to play a significant role in setting the strength of the overturning circulation. Air-sea fluxes of heat and precipitation over the Antarctic Circumpolar Current region act to convert dense upwelled water masses into lighter waters at the surface. Additional fluxes of heat or freshwater thereby facilitate the meridional overturning up to a theoretical limit derived from Ekman transport. The sensitivity of the overturning to surface buoyancy forcing is strongly dependent on the relative locations of the wind stress profile, buoyancy forcing and upwelling region. The idealised model results provide support for the hypothesis that changes in upwelling during deglaciations may have been driven by changes in heat and freshwater fluxes, instead of, or in addition to, changes in wind stress. Morrison, A. K., A. M. Hogg, and M. L. Ward (2011), Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing, Geophys. Res. Lett., 38, L14602, doi:10.1029/2011GL048031.

Wind-driven upwelling effects on cephalopod paralarvae: Octopus vulgaris and Loliginidae off the Galician coast (NE Atlantic)

NASA Astrophysics Data System (ADS)

Otero, Jaime; Álvarez-Salgado, X. Antón; González, Ángel F.; Souto, Carlos; Gilcoto, Miguel; Guerra, Ángel

2016-02-01

Circulation patterns of coastal upwelling areas may have central consequences for the abundance and cross-shelf transport of the larval stages of many species. Previous studies have provided evidences that larvae distribution results from a combination of subtidal circulation, species-specific behaviour and larval sources. However, most of these works were conducted on organisms characterised by small-sized and abundant early life phases. Here, we studied the influence of the hydrography and circulation of the Ría de Vigo and adjacent shelf (NW Iberian upwelling system) on the paralarval abundance of two contrasting cephalopods, the benthic common octopus (Octopus vulgaris) and the pelagic squids (Loliginidae). We sampled repeatedly a cross-shore transect during the years 2003-2005 and used zero inflated models to accommodate the scarcity and patchy distribution of cephalopod paralarvae. The probability of catching early stages of both cephalopods was higher at night. Octopus paralarvae were more abundant in the surface layer at night whereas loliginids preferred the bottom layer regardless of the sampling time. Abundance of both cephalopods increased when shelf currents flowed polewards, water temperature was high and water column stability was low. The probability of observing an excess of zero catches decreased during the year for octopus and at high current speed for loliginids. In addition, the circulation pattern conditioned the body size distribution of both paralarvae; while the average size of the captured octopuses increased (decreased) with poleward currents at daylight (nighttime), squids were smaller with poleward currents regardless of the sampling time. These results contribute to the understanding of the effects that the hydrography and subtidal circulation of a coastal upwelling have on the fate of cephalopod early life stages.

Buffering and Amplifying Interactions among OAW (Ocean Acidification & Warming) and Nutrient Enrichment on Early Life-Stage Fucus vesiculosus L. (Phaeophyceae) and Their Carry Over Effects to Hypoxia Impact.

PubMed

Al-Janabi, Balsam; Kruse, Inken; Graiff, Angelika; Winde, Vera; Lenz, Mark; Wahl, Martin

2016-01-01

Ocean acidification and warming (OAW) are occurring globally. Additionally, at a more local scale the spreading of hypoxic conditions is promoted by eutrophication and warming. In the semi-enclosed brackish Baltic Sea, occasional upwelling in late summer and autumn may expose even shallow-water communities including the macroalga Fucus vesiculosus to particularly acidified, nutrient-rich and oxygen-poor water bodies. During summer 2014 (July-September) sibling groups of early life-stage F. vesiculosus were exposed to OAW in the presence and absence of enhanced nutrient levels and, subsequently to a single upwelling event in a near-natural scenario which included all environmental fluctuations in the Kiel Fjord, southwestern Baltic Sea, Germany (54°27 ´N, 10°11 ´W). We strove to elucidate the single and combined impacts of these potential stressors, and how stress sensitivity varies among genetically different sibling groups. Enhanced by a circumstantial natural heat wave, warming and acidification increased mortalities and reduced growth in F. vesiculosus germlings. This impact, however, was mitigated by enhanced nutrient conditions. Survival under OAW conditions strongly varied among sibling groups hinting at a substantial adaptive potential of the natural Fucus populations in the Western Baltic. A three-day experimental upwelling caused severe mortality of Fucus germlings, which was substantially more severe in those sibling groups which previously had been exposed to OAW. Our results show that global (OAW), regional (nutrient enrichment) and local pressures (upwelling), both alone and co-occurring may have synergistic and antagonistic effects on survival and/or growth of Fucus germlings. This result emphasizes the need to consider combined stress effects.

Resource use of an aquacultured shellfish in the reverse estuary Bahía San Quintín, Baja California, México

NASA Astrophysics Data System (ADS)

Wilkinson, G. M.; Emery, K.; Camacho-Ibar, V.; Pace, M.; McGlathery, K.; Sandoval Gil, J.; Hernandez-Lopez, J.

2016-02-01

Shellfish aquaculture is prominent in many coastal and estuarine environments. Filter feeding by cultured shellfish connects the benthic and pelagic environments in coastal ecosystems. Bahía San Quintín is a reverse estuary in Baja California, Mexico, where Pacific oysters (Crassostrea gigas) are cultivated. While oysters likely feed heavily on phytoplankton especially during upwelling periods, we hypothesized that other forms of organic matter available in high quantities such as seagrass (Zostera marina) and macroalgae (Ulva spp.) must also be used by the oysters, especially in the most inshore portions of the bay. We measured the carbon and hydrogen stable isotope composition of oysters and their potential food resources at upper, mid, and lower bay sites during upwelling and non-upwelling seasons and applied a Bayesian mixing model to evaluate resource use. Hydrogen isotopes provided a large separation between potential food resources. Although we did not find any strong seasonal effects due to upwelling, there was a strong spatial gradient in resource use. Phytoplankton were most important at the lower (oceanic) site (median resource use for two sampling times, 68 and 79 %) and decreased up the estuary as macroalgae became more important (43 and 56 % at the upper site). At all sites for both sampling times, seagrass was an unimportant resource for oysters. The contrast between high phytoplankton use at the lower site and increased macroalgal use at the upper site is likely due to available resource biomass. Our results illustrate the adaptability of oysters to varying resource availability and the possibility of a higher system carrying capacity than that based on phytoplankton alone given multiple potential food sources.

Radiolarian Indices of Paleoproductivity Variation in the late Pleistocene Benguela Upwelling System, ODP Site 1084

NASA Astrophysics Data System (ADS)

Bittniok, B. B.; Lazarus, D. B.; Diester-Haass, L.; Billups, K.; Meyers, P.

2006-12-01

Changes in export productivity play a significant role in ocean carbon budgets and global climate change. Proxies for export productivity can be difficult to interpret: benthic foraminifera accumulation rates (BFAR) can be affected by carbonate dissolution in organic-carbon rich sediments; bulk opal can be affected by silica limitation of source waters. Recent work (Lazarus et al. 2006; Mar. Micropal.) has shown that a new index based on radiolarian faunal changes (WADE ratio) correlates well to total organic carbon (TOC) values from the same samples over the long term (latest Miocene-Recent) history of productivity in the Benguela Upwelling System (BUS). We present new data on variation in export productivity proxies (WADE, TOC, carbonate, radiolarian opal, BFAR) for the last glacial-interglacial cycle from ODP Site 1084, located just offshore from the main coastal upwelling cells of the BUS. Our age model, from mean Quaternary sedimentation rates (Leg 175 Scientific Results), is in accordance with cyclic variation in other climate sensitive parameters (carbonate and color reflectance). Although opal content and radiolarian preservation is only moderate in our samples, WADE values vary significantly and suggest higher productivity during the last glacial, in accordance with current interpretations of BUS history. Radiolarian opal accumulation is also higher during the last glacial, suggesting that silica limitation (opal paradox) conditions did not dominate over this time period. Similar results for bulk opal have been reported from late Quaternary piston cores from the more northerly Congo upwelling region (Schneider et al, 1997; Paleoc.). We conclude that WADE ratios are a useful proxy for late Pleistocene productivity in the BUS at glacial- interglacial time scales.

Controlling factors of the OMZ in the Arabian Sea

NASA Astrophysics Data System (ADS)

Resplandy, L.; Lévy, M.; Bopp, L.; Echevin, V.; Pous, S.; Sarma, V. V. S. S.; Kumar, D.

2012-05-01

In-situ observations indicate that the Arabian Sea oxygen minimum zone (OMZ) is only weakly influenced by the strong seasonal cycle of ocean dynamic and biogeochemistry forced by the asian monsoon system and it is spatially decorrelated from the coastal upwelling systems where the biological production is the strongest. In this study we examine the factors controlling the seasonality and the spatial distribution of the OMZ in the Arabian Sea using a coupled bio-physical model. We find that the oxygen concentration in the OMZ displays a seasonal cycle with an amplitude of 5-15 % of the annual mean oxygen concentration. The OMZ is ventilated by lateral ventilation along the western boundary current and in the coastal undercurrent along India during the summer monsoon and by coastal downwelling and negative Ekman pumping during the fall intermonsoon and winter monsoon. This ventilation is counterbalanced by strong coastal upwelling and positive Ekman pumping of low oxygen waters at the base of the OMZ during the spring intermonsoon. Although the factors controlling the OMZ seasonality are associated with the men circulation, we find that mesoscale dynamics modulates them by limiting the vertical ventilation during winter and enhancing it through lateral advection during the rest of the year. Processes explaining the establishment and spatial distribution of the OMZ were quantified using a perturbation experiment initialised with no OMZ. As expected, the oxygen depletion is triggered by strong biological activity in central Arabian Sea during winter and in western and eastern boundary coastal upwelling systems during summer. We find that the 3-D ocean dynamic largely controls the spatial distribution of the OMZ. The eastward shift ensues from the northward lateral transport of ventilated waters along the western and eastern coasts and the advection offshore of low oxygen waters formed in the upwelling system.

Thermal and chemical convection in planetary mantles

NASA Technical Reports Server (NTRS)

Dupeyrat, L.; Sotin, C.; Parmentier, E. M.

1995-01-01

Melting of the upper mantle and extraction of melt result in the formation of a less dense depleted mantle. This paper describes series of two-dimensional models that investigate the effects of chemical buoyancy induced by these density variations. A tracer particles method has been set up to follow as closely as possible the chemical state of the mantle and to model the chemical buoyant force at each grid point. Each series of models provides the evolution with time of magma production, crustal thickness, surface heat flux, and thermal and chemical state of the mantle. First, models that do not take into account the displacement of plates at the surface of Earth demonstrate that chemical buoyancy has an important effect on the geometry of convection. Then models include horizontal motion of plates 5000 km wide. Recycling of crust is taken into account. For a sufficiently high plate velocity which depends on the thermal Rayleigh number, the cell's size is strongly coupled with the plate's size. Plate motion forces chemically buoyant material to sink into the mantle. Then the positive chemical buoyancy yields upwelling as depleted mantle reaches the interface between the upper and the lower mantle. This process is very efficient in mixing the depleted and undepleted mantle at the scale of the grid spacing since these zones of upwelling disrupt the large convective flow. At low spreading rates, zones of upwelling develop quickly, melting occurs, and the model predicts intraplate volcanism by melting of subducted crust. At fast spreading rates, depleted mantle also favors the formation of these zones of upwelling, but they are not strong enough to yield partial melting. Their rapid displacement toward the ridge contributes to faster large-scale homogenization.

Impacts of ENSO on air-sea oxygen exchange: Observations and mechanisms

NASA Astrophysics Data System (ADS)

Eddebbar, Yassir A.; Long, Matthew C.; Resplandy, Laure; Rödenbeck, Christian; Rodgers, Keith B.; Manizza, Manfredi; Keeling, Ralph F.

2017-05-01

Models and observations of atmospheric potential oxygen (APO ≃ O2 + 1.1 * CO2) are used to investigate the influence of El Niño-Southern Oscillation (ENSO) on air-sea O2 exchange. An atmospheric transport inversion of APO data from the Scripps flask network shows significant interannual variability in tropical APO fluxes that is positively correlated with the Niño3.4 index, indicating anomalous ocean outgassing of APO during El Niño. Hindcast simulations of the Community Earth System Model (CESM) and the Institut Pierre-Simon Laplace model show similar APO sensitivity to ENSO, differing from the Geophysical Fluid Dynamics Laboratory model, which shows an opposite APO response. In all models, O2 accounts for most APO flux variations. Detailed analysis in CESM shows that the O2 response is driven primarily by ENSO modulation of the source and rate of equatorial upwelling, which moderates the intensity of O2 uptake due to vertical transport of low-O2 waters. These upwelling changes dominate over counteracting effects of biological productivity and thermally driven O2 exchange. During El Niño, shallower and weaker upwelling leads to anomalous O2 outgassing, whereas deeper and intensified upwelling during La Niña drives enhanced O2 uptake. This response is strongly localized along the central and eastern equatorial Pacific, leading to an equatorial zonal dipole in atmospheric anomalies of APO. This dipole is further intensified by ENSO-related changes in winds, reconciling apparently conflicting APO observations in the tropical Pacific. These findings suggest a substantial and complex response of the oceanic O2 cycle to climate variability that is significantly (>50%) underestimated in magnitude by ocean models.

Coastal Upwelling and Deep Fog: 50-year Worldwide Climatology

NASA Astrophysics Data System (ADS)

Koracin, D. R.

2015-12-01

An analysis is presented of the marine fog distribution based upon the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) ship observations taken during 1950-2007. Deep fog occurrence is reported in routine weather reports that are encoded in an ICOADS ship observation. Occurrence is estimated by the number of deep fog observations divided by the total present weather observations in a one-degree area centered on latitude and longitude grid point intersections. The mean fog occurrence for the summer (June-July-August) 1950-2007 was computed for each one degree point for the world. There are five major world locations with coastal SST minimums due to wind driven upwelling. Four of these are during the local summer on the eastern side of a semi-permanent anticyclone on eastern sides of northern and southern mid-latitudes of the Pacifica and the Atlantic. The fifth is during the SW monsoon in the Indian Ocean. For all five of these locations, the deep fog occurrence is at maximum during the upwelling season, with the greatest occurrences concentrated along the coast and isolated over the SST minimum. For the five coastal fog maxima, the greatest and longest duration occurrence along coast occurrence is associated with the coldest sea surface temperature and longest along coast occurrence, which is along N. California- S. Oregon. In contrast, the lowest occurrence of fog and the least along coast occurrence is associated with the warmest sea surface temperatures and least along coast occurrence along the SE Arabian Peninsula. The remaining three zones, Peru-Chile, NW Africa, and SW Africa are between the two extremes in fog occurrence, along coast coverage and sea surface temperature. Peru-Chile is more complex than the others as the Peru upwelling and fog appears the more dominant although ship observations are sparse along Chile.

Geodynamics of the East African Rift System ∼30 Ma ago: A stress field model

NASA Astrophysics Data System (ADS)

Min, Ge; Hou, Guiting

2018-06-01

The East African Rift System (EARS) is thought to be an intra-continental ridge that meets the Red Sea and the Gulf of Aden at the Ethiopian Afar as the failed arm of the Afar triple junction. The geodynamics of EARS is still unclear even though several models have been proposed. One model proposes that the EARS developed in a local tensile stress field derived from far-field loads because of the pushing of oceanic ridges. Alternatively, some scientists suggest that the formation of the EARS can be explained by upwelling mantle plumes beneath the lithospheric weak zone (e.g., the Pan-African suture zone). In our study, a shell model is established to consider the Earth's spherical curvature, the lithospheric heterogeneity of the African continent, and the coupling between the mantle plumes and the mid-ocean ridge. The results are calculated via the finite element method using ANSYS software and fit the geological evidence well. To discuss the effects of the different rock mechanical parameters and the boundary conditions, four comparative models are established with different parameters or boundary conditions. Model I ignores the heterogeneity of the African continent, Model II ignores mid-ocean spreading, Model III ignores the upwelling mantle plumes, and Model IV ignores both the heterogeneity of the African continent and the upwelling mantle plumes. Compared to these models is the original model that shows the best-fit results; this model indicates that the coupling of the upwelling mantle plumes and the mid-ocean ridge spreading causes the initial lithospheric breakup in Afar and East Africa. The extension direction and the separation of the EARS around the Tanzanian craton are attributed to the heterogeneity of the East African basement.

Longitudinal Biases in the Seychelles Dome Simulated by 34 Ocean-Atmosphere Coupled General Circulation Models

NASA Astrophysics Data System (ADS)

Nagura, M.; Sasaki, W.; Tozuka, T.; Luo, J.; Behera, S. K.; Yamagata, T.

2012-12-01

The upwelling dome of the southern tropical Indian Ocean is examined by using simulated results from 34 ocean-atmosphere coupled general circulation models (CGCMs) including those from the phase five of the Coupled Model Intercomparison Project (CMIP5). Among the current set of the 34 CGCMs, 12 models erroneously produce the upwelling dome in the eastern half of the basin while the observed Seychelles Dome is located in the southwestern tropical Indian Ocean (Figure 1). The annual mean Ekman pumping velocity is almost zero in the southern off-equatorial region in these models. This is in contrast with the observations that show Ekman upwelling as the cause of the Seychelles Dome. In the models that produce the dome in the eastern basin, the easterly biases are prominent along the equator in boreal summer and fall that cause shallow thermocline biases along the Java and Sumatra coasts via Kelvin wave dynamics and result in a spurious upwelling dome there. In addition, these models tend to overestimate (underestimate) the magnitude of annual (semiannual) cycle of thermocline depth variability in the dome region, which is another consequence of the easterly wind biases in boreal summer-fall. Compared to the CMIP3 models (Yokoi et al. 2009), the CMIP5 models are even worse in simulating the dome longitudes and magnitudes of annual and semiannual cycles of thermocline depth variability in the dome region. Considering the increasing need to understand regional impacts of climate modes, these results may give serious caveats to interpretation of model results and help in further model developments.; Figure 1: The longitudes of the shallowest annual-mean D20 in 5°S-12°S. The open and filled circles are for the observations and the CGCMs, respectively.

Seasonal variation of the South Indian tropical gyre

NASA Astrophysics Data System (ADS)

Aguiar-González, Borja; Ponsoni, Leandro; Ridderinkhof, Herman; van Aken, Hendrik M.; de Ruijter, Will P. M.; Maas, Leo R. M.

2016-04-01

Based on satellite altimeter data and global atlases of temperature, salinity, wind stress and wind-driven circulation we investigate the seasonal variation of the South Indian tropical gyre and its associated open-ocean upwelling system, known as the Seychelles-Chagos Thermocline Ridge (SCTR). Results show a year-round, altimeter-derived cyclonic gyre where the upwelling regime appears closely related to seasonality of the ocean gyre, a relationship that has not been previously explored in this region. An analysis of major forcing mechanisms suggests that the thermocline ridge results from the constructive interaction of basin-scale wind stress curl, local-scale wind stress forcing and remote forcing driven by Rossby waves of different periodicity: semiannual in the west, under the strong influence of monsoonal winds; and, annual in the east, where the southeasterlies prevail. One exception occurs during winter, when the well-known westward intensification of the upwelling core, the Seychelles Dome, is shown to be largely a response of the wind-driven circulation. At basin-scale, the most outstanding feature is the seasonal shrinkage of the ocean gyre and the SCTR. From late autumn to spring, the eastward South Equatorial Countercurrent (SECC) recirculates early in the east on feeding the westward South Equatorial Current, therefore closing the gyre before arrival to Sumatra. We find this recirculation longitude migrates over 20° and collocates with the westward advance of a zonal thermohaline front emerging from the encounter between (upwelled) Indian Equatorial Water and relatively warmer and fresher Indonesian Throughflow Water. We suggest this front, which we call the Indonesian Throughflow Front, plays an important role as remote forcing to the tropical gyre, generating southward geostrophic flows that contribute to the early recirculation of the SECC.

Meeting reproductive demands in a dynamic upwelling system: Foraging strategies of a pursuit-diving seabird, the marbled murrelet

USGS Publications Warehouse

Peery, M.Z.; Newman, S.H.; Storlazzi, C.D.; Beissinger, S.R.

2009-01-01

Seabirds maintain plasticity in their foraging behavior to cope with energy demands and foraging constraints that vary over the reproductive cycle, but behavioral studies comparing breeding and nonbreeding individuals are rare. Here we characterize how Marbled Murrelets (Brachyramphus marmoratus) adjust their foraging effort in response to changes in reproductive demands in an upwelling system in central California. We radio-marked 32 murrelets of known reproductive status (9 breeders, 12 potential breeders, and 11 nonbreeders) and estimated both foraging ranges and diving rates during the breeding season. Murrelets spent more time diving during upwelling than oceanographic relaxation, increased their foraging ranges as the duration of relaxation grew longer, and reduced their foraging ranges after transitions to upwelling. When not incubating, murrelets moved in a circadian pattern, spending nighttime hours resting near flyways used to reach nesting habitat and foraging during the daytime an average of 5.7 km (SD 6.7 km) from nighttime locations. Breeders foraged close to nesting habitat once they initiated nesting and nest attendance was at a maximum, and then resumed traveling longer distances following the completion of nesting. Nonbreeders had similar nighttime and daytime distributions and tended to be located farther from inland flyways. Breeders increased the amount of time they spent diving by 71-73% when they had an active nest by increasing the number of dives rather than by increasing the frequency of anaerobiosis. Thus, to meet reproductive demands during nesting, murrelets adopted a combined strategy of reducing energy expended commuting to foraging sites and increasing aerobic dive rates. ?? 2009 by The Cooper Ornithological Society. All rights reserved.

Changing surface water conditions for the last 500 ka in the Southeast Atlantic: Implications for variable influences of Agulhas leakage and Benguela upwelling

NASA Astrophysics Data System (ADS)

Petrick, Benjamin F.; McClymont, Erin L.; Marret, Fabienne; van der Meer, Marcel T. J.

2015-09-01

The Southeast Atlantic Ocean is an important component of global ocean circulation, as it includes heat and salt transfer into the Atlantic through the Agulhas leakage as well as the highly productive Benguela upwelling system. Here we reconstruct sea surface temperatures (SSTs) from Ocean Drilling Program (ODP) Site 1087 in the Southeast Atlantic to investigate surface ocean circulation patterns during the late Pleistocene (0-500 ka). The UK'37 index and dinoflagellate cyst assemblages are used to reconstruct SSTs, δDalkenone is used to reconstruct changes in sea surface salinity, and mass accumulation rates of alkenones and chlorine pigments are quantified to detect changing marine export productivity. The greatest amplitude of SST warming precedes decreases in benthic δ18O and therefore occurs early in the transition from glacials to interglacials. The δDalkenone, as a salinity indicator, increases before SSTs, suggesting that the pattern of Agulhas leakage is more complex than suggested by SST proxies. Marine isotope stage (MIS) 10 shows an anomalous pattern: it is marked by a pronounced increase in chlorine concentration, which may be related to enhanced/expanded Benguela upwelling reaching the core site. We find no evidence of an absence of Agulhas leakage throughout the record, suggesting that there is no Agulhas cutoff even during MIS 10. Finally, the ODP Site 1087 record shows an increasing strength of Agulhas leakage towards the present day, which may have impacted the intensity of the Atlantic meridional overturning circulation. As a result, the new analyses from ODP Site 1087 demonstrate a complex interaction between influences of the Benguela upwelling and the Agulhas leakage through the late Pleistocene, which are inferred here to reflect changing circulation patterns in the Southern Ocean and in the atmosphere.

Effects of seasonal anoxia on the distribution of phosphorus fractions in the surface sediments of southeastern Arabian Sea shelf

NASA Astrophysics Data System (ADS)

Sudheesh, V.; Movitha, M.; Hatha, A. A. Mohamed; Renjith, K. R.; Resmi, P.; Rahiman, Mujeeb; Nair, S. M.

2017-11-01

The seasonal upwelling along the southeastern Arabian Sea (SEAS) brings cold, nutrient-rich low oxygen subsurface water to the continental shelf. The subsurface oxygen deficiency due to upwelling is severe in some years, the intensity of which could profoundly influence the nutrient cycling along the SEAS. Herein, we studied the effect of seasonal anoxia on fractionation of phosphorus during the peak upwelling period of August 2013. Abundance of five fractions of phosphorus (P), namely exchangeable or loosely sorbed P (Pads), iron-bound P (PFe), authigenic P (Paut), detrital apatite plus other inorganic P (Pdet) and organic P (Porg), in surface sediments of SEAS shelf has been studied using a sequential extraction procedure (SEDEX) to examine their distributions and sources. Total P (TP) concentrations ranged from 209 to 1081 μg g-1 with an average of 508 ± 256 μg g-1. Among the five P fractions, the authigenic P was the dominant species, representing about 60% of TP. The relative abundance of P fractions was in the order: Paut>Pdet>Porg>PFe> Pads. Multivariate analyses revealed that the P fractions were primarily associated with the organic constituents and fine sediments. The hypoxic bottom condition associated with summer monsoon upwelling significantly reduced the concentrations of PFe, Pads and Porg in the surface sediments. The enhanced release of organic bound and iron oxides bound P under low oxygen condition was evident from the enhanced C/P and N/P ratios and lower C/N ratio in the sediments. The intense biomineralization of organic matter and reduction of Fe-Mn oxides due to the periodic anoxia resulted in the transformations of their associated P fractions and enhanced accumulation as authigenic calcium phosphate mineral.

SST cooling along coastal Java and Sumatra during positive Indian Ocean Dipole events

NASA Astrophysics Data System (ADS)

Delman, A. S.; McClean, J.; Sprintall, J.; Talley, L. D.; Bryan, F.; Johnson, B. K.; Carton, J.

2016-02-01

The evolution of positive Indian Ocean Dipole (pIOD) events is driven in part by anomalous SST cooling near the coasts of Java and Sumatra. However, the mechanisms and timeline of surface temperature changes near these two islands are distinct. Satellite data and mixed layer budgets in a forced ocean model simulation with 0.1° spatial resolution were used to characterize the dominant influences on SST in each region during pIOD events. Along the south coast of Java, where upwelling from southeasterly trade winds happens seasonally in June-September, strengthening/weakening of the trade winds has little effect on the interannual variability of SST. Instead, remotely-forced upwelling Kelvin waves are the primary mechanism for producing anomalous Java SST cooling in the early stages of a pIOD event. Other mechanisms that affect Java SST anomalies include inflows from the interior Indonesian Seas, mesoscale eddies, and air-sea heat fluxes; these influences can hasten the decay of cool Java SST anomalies and therefore may impact the strength and duration of pIOD events. Along the west coast of Sumatra, surface cooling is initially delayed by a deeper thermocline and a salinity-stratified barrier layer. Hence upwelling Kelvin waves do not substantially affect SST near Sumatra during the first 2-3 months of Java SST cooling; however, they do help drive surface cooling near Sumatra once the barrier layer has been sufficiently eroded by waters of decreasing temperature and increasing salinity. Upwelling Kelvin wave activity in the equatorial Indian Ocean starting in April is also shown to be a robust predictor of pIOD events later in the calendar year.

Estimating chlorophyll content and bathymetry of Lake Tahoe using AVIRIS data

NASA Technical Reports Server (NTRS)

Hamilton, Michael K.; Davis, Curtiss O.; Rhea, W. J.; Pilorz, Stuart H.; Carder, Kendall L.

1993-01-01

Data on chlorophyll content and bathymetry of Lake Tahoe obtained on August 9, 1990 by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) are compared to concurrent in situ surface and in-water measurements. Measured parameters included profiles of percent transmission of monochromatic light, stimulated chlorophyll fluorescence, photosynthetically available radiation, spectral upwelling and downwelling irradiance, and upwelling radiance. Several analyses were performed illustrating the utility of the AVIRIS over a dark water scene. Image-derived chlorophyll concentration compared extremely well with that measured with bottle samples. A bathymetry map of the shallow parts of the lake was constructed which compares favorably with published lake soundings.

The spatial variability of coastal surface water temperature during upwelling. [in Lake Superior

NASA Technical Reports Server (NTRS)

Scarpace, F. L.; Green, T., III

1979-01-01

Thermal scanner imagery acquired during a field experiment designed to study an upwelling event in Lake Superior is investigated. Temperature data were measured by the thermal scanner, with a spatial resolution of 7 m. These data were correlated with temperatures measured from boats. One- and two-dimensional Fourier transforms of the data were calculated and temperature variances as a function of wavenumber were plotted. A k-to-the-minus-three dependence of the temperature variance on wavenumber was found in the wavenumber range of 1-25/km. At wavenumbers greater than 25/km, a k-to-the-minus-five-thirds dependence was found.

Application of LANDSAT satellite imagery and oceanographic data for verification of an upwelling mathematical model. [Atlantic Coast of Brazil

NASA Technical Reports Server (NTRS)

Dejesusparada, N. (Principal Investigator); Tanaka, K.; Almeida, E. G.

1978-01-01

The author has identified the following significant results. Data obtained during the cruise of the Cabo Frio and from LANDSAT imagery are used to discuss the characteristics of a linear model which simulates wind induced currents calculated from meteorological conditions at the time of the mission. There is a significant correspondance between the model of simulated horizontal water circulation, sea surface temperature, and surface currents observed on LANDSAT imagery. Close approximations were also observed between the simulation of vertical water movement (upwelling) and the oceanographic measurements taken along a series of points of the prevailing currents.

Structure of sunspot penumbrae - Fallen magnetic flux tubes

NASA Technical Reports Server (NTRS)

Wentzel, Donat G.

1992-01-01

A model is presented of a sunspot penumbra involving magnetic flux tubes that have fallen into the photosphere and float there. An upwelling at the inner end of a fallen tube continuously provides additional gas. This gas flows along and lengthens the tube and is observable as the Evershed flow. Fallen flux tubes may appear as bright streaks near the upwelling, but they become dark filaments further out. The model is corroborated by recent optical high-resolution magnetic data regarding the penumbral filaments, by the 12-micron magnetic measurements relevant to the height of the temperature minimum, and by photographs of the umbra/penumbra boundary.

Relationships between chlorophyll density and ocean radiance as measured by U2/OCS: Algorithms, examples and comparison

NASA Technical Reports Server (NTRS)

Kim, H. H.; Hart, W. D.

1983-01-01

An ocean atmosphere radiative transfer process computation method which is suitable for determining lower boundary ocean albedo and other radiation components from spectral measurements of upwelling radiance taken from a high altitude platform is described. The method was applied to a set of color scanner data taken from slope water of the South Atlantic Bight to determine the influence of cholorophyll-a pigments in the sea on the ratio of upwelling radiance to down welling irradiance as a function of wavelength. The resulting chlorophyll concentrations are compared with measurements made by ships stationed along the flight path.

Polychaete response to fresh food supply at organically enriched coastal sites: Repercussion on bioturbation potential and trophic structure

NASA Astrophysics Data System (ADS)

Venturini, N.; Pires-Vanin, A. M. S.; Salhi, M.; Bessonart, M.; Muniz, P.

2011-12-01

We investigated the vertical distribution, abundance, specific and functional structure of polychaete assemblages at four organically enriched sites. The effects of fresh organic matter input from the water column driving by upwelling were evaluated. Temperature and salinity values indicate the intrusion of South Atlantic Central Water (SACW) in spring, a nutrient-rich water mass. The dominance of the conveyor belt transport (CONV) in the station influenced by SACW, in the spring survey, is associated with fresh organic matter input as indicated by higher amounts of polyunsaturated fatty acids. Conversely, the predominance of the diffusive mixing (DIFF) bioturbation category, in the sites without SACW influence is related to the preferential accumulation of more refractive food resources as indicated by higher concentrations of short chain saturated fatty acids. At the site influenced by SACW, the changes in polychaete assemblages were not all evident during proceeding upwelling conditions, but may persist at the end of the upwelling. Polychaetes in the study area seemed to be limited by the quality but not the quantity of food. The delay in polychaete response to fresh food supply may be related to the organic enrichment and the prevalence of refractory material in the sediments.

The potential for convection and implications for geothermal energy in the Perth Basin, Western Australia

NASA Astrophysics Data System (ADS)

Sheldon, Heather A.; Florio, Brendan; Trefry, Michael G.; Reid, Lynn B.; Ricard, Ludovic P.; Ghori, K. Ameed R.

2012-11-01

Convection of groundwater in aquifers can create areas of anomalously high temperature at shallow depths which could be exploited for geothermal energy. Temperature measurements in the Perth Basin (Western Australia) reveal thermal patterns that are consistent with convection in the Yarragadee Aquifer. This observation is supported by Rayleigh number calculations, which show that convection is possible within the range of aquifer thickness, geothermal gradient, salinity gradient and permeability encountered in the Yarragadee Aquifer, assuming that the aquifer can be treated as a homogeneous anisotropic layer. Numerical simulations of convection in a simplified model of the Yarragadee Aquifer show that: (1) the spacing of convective upwellings can be predicted from aquifer thickness and permeability anisotropy; (2) convective upwellings may be circular or elongate in plan view; (3) convective upwellings create significant temperature enhancements relative to the conductive profile; (4) convective flow rates are similar to regional groundwater flow rates; and (5) convection homogenises salinity within the aquifer. Further work is required to constrain the average horizontal and vertical permeability of the Yarragadee Aquifer, to assess the validity of treating the aquifer as a homogeneous anisotropic layer, and to determine the impact of realistic aquifer geometry and advection on convection.

The impact of ENSO on regional chlorophyll-a anomaly in the Arafura Sea

NASA Astrophysics Data System (ADS)

Dewi, D. M. P. R.; Fatmasari, D.; Kurniawan, A.; Munandar, M. A.

2018-03-01

The El Niño-Southern Oscillation (ENSO) is a naturally occurring phenomenon that involves fluctuating ocean temperature in the equatorial Pacific. ENSO influences ocean climate variability in Indonesia including the Arafura Sea. The relationship between oceanic chlorophyll-a and ENSO has been the focus of study over the past decade. Here we examine the impact of ENSO on regional chlorophyll-a anomaly in the Papua waters using 14 years of chlorophyll-a and sea surface temperature (SST) data from AQUA MODIS and sea level anomaly data from AVISO. It is found that when El Niño events occur the negative SST anomaly in the Papua waters as well as the enhanced upwelling cause the increase of chlorophyll-a concentration. The highest chlorophyll-a concentration (> 1 mg–cm-3) occured during El Niño and observed around the Aru archipelago. In contrast during La Niña event, the positive SST anomaly in Papua waters and the suppressed upwelling cause the decrease of chlorophyll-a concentration. Our results suggest that during El Niño (La Niña), the enhanced (suppressed) upwelling related to the significant decreasing (increasing) of sea level anomaly.

Venus - Mosaic of Bahet and Onatah Coronae

NASA Image and Video Library

1996-09-26

This mosaic of Magellan data in the Fortuna region of Venus, centered at 49 degrees north latitude, 2 degrees longitude, shows two coronae. Coronae are large circular or oval structures first identified in Soviet radar images of Venus. The structure on the left, Bahet Corona, is about 230 kilometers (138 miles) long and 150 kilometers (90 miles) across. A portion of Onatah Corona, over 350 kilometers (210 miles) in diameter, can be seen on the right of the mosaic. Both features are surrounded by a ring of ridges and troughs, which in places cut more radially-oriented fractures. The centers of the features also contain radial fractures as well as volcanic domes and flows. Coronae are thought to form due to the upwelling of hot material from deep in the interior of Venus. The two coronae may have formed at the same time over a single upwelling, or may indicate movement of the upwelling or the upper layers of the planet to the west over time. A 'pancake' dome, similar to low-relief domes see in the southern hemisphere, is located just to the southwest of Bahet. Resolution of the Magellan data is about 120 meters (400 feet). http://photojournal.jpl.nasa.gov/catalog/PIA00461

Exact Solutions for Wind-Driven Coastal Upwelling and Downwelling over Sloping Topography

NASA Astrophysics Data System (ADS)

Choboter, P.; Duke, D.; Horton, J.; Sinz, P.

2009-12-01

The dynamics of wind-driven coastal upwelling and downwelling are studied using a simplified dynamical model. Exact solutions are examined as a function of time and over a family of sloping topographies. Assumptions in the two-dimensional model include a frictionless ocean interior below the surface Ekman layer, and no alongshore dependence of the variables; however, dependence in the cross-shore and vertical directions is retained. Additionally, density and alongshore momentum are advected by the cross-shore velocity in order to maintain thermal wind. The time-dependent initial-value problem is solved with constant initial stratification and no initial alongshore flow. An alongshore pressure gradient is added to allow the cross-shore flow to be geostrophically balanced far from shore. Previously, this model has been used to study upwelling over flat-bottom and sloping topographies, but the novel feature in this work is the discovery of exact solutions for downwelling. These exact solutions are compared to numerical solutions from a primitive-equation ocean model, based on the Princeton Ocean Model, configured in a similar two-dimensional geometry. Many typical features of the evolution of density and velocity during downwelling are displayed by the analytical model.

Zooplankton Responses to Low-Oxygen Condition upon a Shallow Oxygen Minimum Zone in the Upwelling Region off Chile

NASA Astrophysics Data System (ADS)

Hidalgo, P.; Escribano, R.

2015-12-01

A shallow oxygen minimum zone (OMZ) is a critical component in the coastal upwelling ecosystem off Chile. This OMZ causes oxygen-deficient water entering the photic layer and affecting plankton communities having low tolerance to hypoxia. Variable, and usually species-dependent, responses of zooplankton to hypoxia condition can be found. Most dominant species avoid hypoxia by restricting their vertical distribution, while others can temporarily enter and even spent part of their life cycle within the OMZ. Whatever the case, low-oxygen conditions appear to affect virtually all vital rates of zooplankton, such as mortality, fecundity, development and growth and metabolism, and early developmental stages seem more sensitive, with significant consequences for population and community dynamics. For most study cases, these effects are negative at individual and population levels. Observations and predictions upon increasing upwelling intensity over the last 20-30 years indicate a gradual shoaling of the OMZ, and so that an expected enhancement of these negative effects of hypoxia on the zooplankton community. Unknown processes of adaptation and community-structure adjustments are expected to take place with uncertain consequences for the food web of this highly productive eastern boundary current ecosystem.

Turning Ocean Mixing Upside Down

NASA Astrophysics Data System (ADS)

Ferrari, Raffaele; Mashayek, Ali; Campin, Jean-Michael; McDougall, Trevor; Nikurashin, Maxim

2015-11-01

It is generally understood that small-scale mixing, such as is caused by breaking internal waves, drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes. However the observational evidence that small-scale mixing is more vigorous close to the ocean bottom than above implies that small-scale mixing converts light waters into denser ones, thus driving a net sinking of abyssal water. It is shown that abyssal waters return to the surface along weakly stratified boundary layers, where the small-scale mixing of density decays to zero. The net ocean meridional overturning circulation is thus the small residual of a large sinking of waters, driven by small-scale mixing in the stratified interior, and an equally large upwelling, driven by the reduced small-scale mixing along the ocean boundaries. Thus whether abyssal waters upwell or sink in the net cannot be inferred simply from the vertical profile of mixing intensity, but depends also on the ocean hypsometry, i.e. the shape of the bottom topography. The implications of this result for our understanding of the abyssal ocean circulation will be presented with a combination of numerical models and observations.

Piecewise delamination of Moroccan lithosphere from beneath the Atlas Mountains

NASA Astrophysics Data System (ADS)

Bezada, M. J.; Humphreys, E. D.; Davila, J. M.; Carbonell, R.; Harnafi, M.; Palomeras, I.; Levander, A.

2014-04-01

The elevation of the intracontinental Atlas Mountains of Morocco and surrounding regions requires a mantle component of buoyancy, and there is consensus that this buoyancy results from an abnormally thin lithosphere. Lithospheric delamination under the Atlas Mountains and thermal erosion caused by upwelling mantle have each been suggested as thinning mechanisms. We use seismic tomography to image the upper mantle of Morocco. Our imaging resolves the location and shape of lithospheric cavities and of delaminated lithosphere ˜400 km beneath the Middle Atlas. We propose discontinuous delamination of an intrinsically unstable Atlas lithosphere, enabled by the presence of anomalously hot mantle, as a mechanism for producing the imaged structures. The Atlas lithosphere was made unstable by a combination of tectonic shortening and eclogite loading during Mesozoic rifting and Cenozoic magmatism. The presence of hot mantle sourced from regional upwellings in northern Africa or the Canary Islands enhanced the instability of this lithosphere. Flow around the retreating Alboran slab focused upwelling mantle under the Middle Atlas, which we infer to be the site of the most recent delamination. The Atlas Mountains of Morocco stand as an example of large-scale lithospheric loss in a mildly contractional orogen.

Simulation of active tectonic processes for a convecting mantle with moving continents

USGS Publications Warehouse

Trubitsyn, V.; Kaban, M.; Mooney, W.; Reigber, C.; Schwintzer, P.

2006-01-01

Numerical models are presented that simulate several active tectonic processes. These models include a continent that is thermally and mechanically coupled with viscous mantle flow. The assumption of rigid continents allows use of solid body equations to describe the continents' motion and to calculate their velocities. The starting point is a quasi-steady state model of mantle convection with temperature/ pressure-dependent viscosity. After placing a continent on top of the mantle, the convection pattern changes. The mantle flow subsequently passes through several stages, eventually resembling the mantle structure under present-day continents: (a) Extension tectonics and marginal basins form on boundary of a continent approaching to subduction zone, roll back of subduction takes place in front of moving continent; (b) The continent reaches the subduction zone, the extension regime at the continental edge is replaced by strong compression. The roll back of the subduction zone still continues after closure of the marginal basin and the continent moves towards the upwelling. As a result the ocean becomes non-symmetric and (c) The continent overrides the upwelling and subduction in its classical form stops. The third stage appears only in the upper mantle model with localized upwellings. ?? 2006 The Authors Journal compilation ?? 2006 RAS.

Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling

NASA Astrophysics Data System (ADS)

Etourneau, J.; Robinson, R. S.; Martinez, P.; Schneider, R.

2013-03-01

The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pliocene-Pleistocene in the eastern equatorial Pacific (EEP) for the last 3.2 Myr. Our results indicate that the export production peak corresponds to a cold interval marked by high nutrient supply relative to consumption, as revealed by the low bulk sedimentary 15N/14N (δ15N) and alkenone-derived sea surface temperature (SST) values. This ~ 0.6 million years long episode of enhanced delivery of nutrients to the surface of the EEP was predominantly initiated through the upwelling of nutrient-enriched water sourced in high latitudes. In addition, this phenomenon was likely promoted by the regional intensification of upwelling in response to the development of intense Walker and Hadley atmospheric circulations. Increased nutrient consumption in the polar oceans and enhanced denitrification in the equatorial regions restrained nutrient supply and availability and terminated the high export production event.

COCMP Surface Current Mapping Reveals Eddy and Upwelling Jet off Cape Mendocino

NASA Astrophysics Data System (ADS)

Crawford, G. B.; Halle, C.; Largier, J.; Stone, S.

2008-12-01

Ocean surface currents are now being measured continuously over a roughly 2000 km stretch of the western US continental shelf from south of Tijuana, Mexico to the Columbia River. A long-standing gap in this coverage was finally filled on August 12, 2008, with the installation of a long-range Seasonde radar system at Shelter Cove, California (as a part of California's COCMP project). During its first three weeks of operation, this radar has revealed a large (~170 km diameter), stable, anticyclonic eddy southwest of Cape Mendocino in this poorly studied region. Upwelling-favorable winds appear to create an upwelling jet along the eastern edge of the eddy, leading to maximum daily-averaged current speeds up to 80 cm/s, and MODIS-derived chlorophyll concentrations up to 30 mg/m3 in the jet (compared to ~1 mg/m3 in the eddy center). AVHRR data reveal SST differences between the jet and the eddy center of 1.5 to 2.5 °C during these 3 weeks. These complex circulation structures modify water pathways and may interrupt nutrient delivery to locations farther south. We discuss the spatial and temporal evolution of these features.

A mid-twentieth century reduction in tropical upwelling inferred from coralline trace element proxies

NASA Astrophysics Data System (ADS)

Reuer, Matthew K.; Boyle, Edward A.; Cole, Julia E.

2003-05-01

The Cariaco Basin is an important archive of past climate variability given its response to inter- and extratropical climate forcing and the accumulation of annually laminated sediments within an anoxic water column. This study presents high-resolution surface coral trace element records ( Montastrea annularis and Siderastrea siderea) from Isla Tortuga, Venezuela, located within the upwelling center of this region. A two-fold reduction in Cd/Ca ratios (3.5-1.7 nmol/mol) is observed from 1946 to 1952 with no concurrent shift in Ba/Ca ratios. This reduction agrees with the hydrographic distribution of dissolved cadmium and barium and their expected response to upwelling. Significant anthropogenic variability is also observed from Pb/Ca analysis, observing three lead maxima since 1920. Kinetic control of trace element ratios is inferred from an interspecies comparison of Cd/Ca and Ba/Ca ratios (consistent with the Sr/Ca kinetic artifact), but these artifacts are smaller than the environmental signal and do not explain the Cd/Ca transition. The trace element records agree with historical climate data and differ from sedimentary faunal abundance records, suggesting a linear response to North Atlantic extratropical forcing cannot account for the observed historical variability in this region.

Biogenic sedimentation beneath the California Current system for the past 30 kyr and its paleoceanographic significance

USGS Publications Warehouse

Gardner, J.V.; Dean, W.E.; Dartnell, P.

1997-01-01

A north-south transect of 17 cores was constructed along the eastern boundary of the California Current system from 33?? to 42?? N to investigate the changes in biogenic sedimentation over the past 30 kyr. Percentages and mass accumulation rates of CaCO3, Corg, and biogenic opal were assembled at 500 to 1000 years/sample to provide relatively high resolution. Time-space maps reveal a complex pattern of changes that do not follow a simple glacial-interglacial two-mode model. Biogenic sedimentation shows responses that are sometimes time-transgressive and sometimes coeval, and most of the responses show more consistency within a limited geographic area than any temporal consistency. Reconstructed conditions during late oxygen isotope stage 3 were more like early Holocene conditions than any other time during the last 30 kyr. Coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central California margin but were weak along the northern California margin. Precipitation increased during the last glacial interval in the central California region, and the waters of the southern California margin had relatively low productivity. Productivity on the southern Oregon margin was relatively low at the beginning of the last glacial interval, but by about 20 ka, productivity in this area significantly increased. This change suggests that the center of the divergence of the West Wind Drift shifted south at this time. The end of the last glacial interval was characterized by increased productivity in the southern California margin and increased upwelling along the central California margin but upwelling remained weak along the northern California margin. A sudden (<300 years) decrease in CaCO3, Corg, and biogenic opal occurred at 13 ka. The changes suggest a major reorientation of the atmospheric circulation in the North Pacific and western North America and the establishment of a strong seasonality in the central California region. A carbonate preservation event occurred at 10 ka that appears to reflect the uptake of CO2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers. The Holocene has been a period of relatively high productivity in the southern California margin, relatively strong coastal upwelling along the central California margin, relatively weak upwelling along the northern California margin, and the northward migration of the divergence zone of the West Wind Drift.

Jupiter's belts and zones: Contradictory evidence for upwelling and downwelling

NASA Astrophysics Data System (ADS)

Ingersoll, Andrew P.; Juno Science Team

2017-10-01

Early authors (Hess and Panofsky 1951, Ingersoll and Cuzzi 1969, Barcilon and Gierasch 1970) noted that the zonal winds are cyclonic in the belts and anticyclonic in the zones. From the thermal wind equation they concluded that the air below the clouds is colder at the belts and warmer at the zones. Hot air rising and cold air sinking led to the notion of downwelling in the belts and upwelling in the zones, which agreed with observations of clear air and low ammonia vapor in the belts and cloudy air and high ammonia vapor in the zones (Gierasch et al. 1986). However, lightning in the belts seemed to contradict that idea, based on the assumption that lightning and convection require upwelling of moist air from below (Little et al. 1999, Ingersoll et al. 2000). Convergence of the eddy momentum flux on the poleward sides of the zones (Salyk et al. 2006) supports the inference based on lightning by implying convergence of the meridional flow in the zones. Here we argue that lightning in the belts does not require upwelling. Instead, there is a threshold for moist convection that is triggered when the thickness of the weather layer drops below a critical value (Li and Ingersoll 2006, Thomson and McIntyre 2016). We also argue that the convergence of the eddy momentum flux does not require equatorward flow. Instead, the meridional flow is controlled by the sign of the potential vorticity (PV) gradient, which is southward on the equatorward sides of the zones (Ingersoll et al. 2017), implying divergence of the meridional flow in the zones. This is a new idea and is based on the observation that the predicted flat parts of the PV staircase (Dritschel and McIntyre 2008), might actually be sloping inward, since the curvature of the zonal velocity profile U_yy exceeds beta at the centers of the westward jets (Ingersoll and Cuzzi 1969, Ingersoll et al. 1981, Limaye et al. 1986, Li et al. 2004, Read et al. 2006). These arguments agree with observations of upwelling in the zones, but they do not explain the near absence of a belt-zone signature below 2-3 bars, as implied by the recent Juno data (Bolton et al. 2017, Ingersoll et al. 2017).

Seismically imaging the Afar plume

NASA Astrophysics Data System (ADS)

Hammond, J. O.; Kendall, J. M.; Bastow, I. D.; Stuart, G. W.; Keir, D.; Ayele, A.; Ogubazghi, G.; Ebinger, C. J.; Belachew, M.

2011-12-01

Plume related flood basalt volcanism in Ethiopia has long been cited to have instigated continental breakup in northeast Africa. However, to date seismic images of the mantle beneath the region have not produced conclusive evidence of a plume-like structure. As a result the nature and even existence of a plume in the region and its role in rift initiation and continental rupture are debated. Previous seismic studies using regional deployments of sensors in East-Africa show that low seismic velocities underlie northeast Africa, but their resolution is limited to the top 200-300km of the Earth. Thus, the connection between the low velocities in the uppermost mantle and those imaged in global studies in the lower mantle is unclear. We have combined new data from Afar, Ethiopia with 6 other regional experiments and global network stations across Ethiopia, Eritrea, Djibouti and Yemen, to produce high-resolution models of upper mantle P- and S- wave velocities to the base of the transition zone. Relative travel time tomographic inversions show that the top 100km is dominated by focussed low velocity zones, likely associated with melt in the lithosphere/uppermost asthenosphere. Below these depths a broad SW-NE oriented sheet like upwelling extends down to the top of the transition zone. Within the transition zone two focussed sharp-sided low velocity regions exist: one beneath the Western Ethiopian plateau outside the rift valley, and the other beneath the Afar depression. The nature of the transition zone anomalies suggests that small upwellings may rise from a broader low velocity plume-like feature in the lower mantle. This interpretation is supported by numerical and analogue experiments that suggest the 660km phase change and viscosity jump may impede flow from the lower to upper mantle creating a thermal boundary layer at the base of the transition zone. This allows smaller, secondary upwellings to initiate and rise to the surface. Our images of secondary upwellings suggest that there is no evidence for a plume in the classical sense (i.e. a narrow conduit). Instead, we propose that secondary upwellings rise from the base of the transition zone and connect in the upper mantle. This coupled with measurements of seismic anisotropy suggest that mantle material flows northeast towards Arabia, and may be responsible for the dramatic dynamic topography observed in northeast Africa and western Arabia.

Contrasting Responses of the Humboldt Current Ecosystem between the Holocene and MIS5e Interglacials Revealed from Multiple Sediment Records

NASA Astrophysics Data System (ADS)

Salvatteci, R.; Schneider, R. R.; Blanz, T.; Martinez, P.; Crosta, X.

2016-12-01

The Humboldt Current Ecosystem (HCE) off Peru yields about 10% of the global fish catch, producing more fish per unit area than any other region in the world. The high productivity is maintained by the upwelling of cold, nutrient-rich water from the oxygen minimum zone (OMZ), driven by strong trade winds. However, the potential impacts of climate change on upwelling dynamics and oceanographic conditions in the near future are uncertain, threatening local and global economies. Here, we unravel the response of the HCE to contrasting climatic conditions during the last two interglacials (i.e. Holocene and MIS5e) providing an independent insight about the relation between climatic factors and upwelling and productivity dynamics. For this purpose, we used multiple cores to reconstruct past changes in OMZ and upwelling intensity, productivity and fish biomass variability. Chronologies for the Holocene were obtained by multiple 14C ages and laminae correlations among cores, while for the MIS5e they were mainly done by correlation of prominent features in several proxies with other published records. We used a multiproxy approach including alkenones to reconstruct sea surface temperatures, δ15N as a proxy for water column denitrification, redox sensitive metals as proxies for sediment redox conditions, and diatom and fish debris assemblages to reconstruct ecological changes. The results show a very different response of the HCE to climate conditions during the last 2 interglacials, likely driven by changes in Tropical Pacific dynamics. During the Holocene we find that 1) the Late Holocene exhibits higher multi-centennial scale variability compared to the Early Holocene, 2) increased upwelling and a weak OMZ during the mid-Holocene, and 3) long term increase in productivity (diatoms and fishes) from the Early to the Late Holocene. During the MIS5e we find an 1) intense OMZ, 2) strong water column stratification, 3) high siliceous biomass, and 4) low fish biomass compared to the Holocene and a regime shift towards more hemipelagic fishes. Our paleoreconstructions during the globally warm MIS5e are consistent with models indicating that the expected increase in stratification and atmospheric CO2 concentrations may significantly reduce fish capacity in the HCE with heavy ecological and economic consequences.

Time Evolution of the Mantle Thermal Structure in the African Hemisphere Before and After the Formation of Pangea

NASA Astrophysics Data System (ADS)

Zhang, N.; Zhong, S.

2008-12-01

The present-day mantle structure is characterized by the African and Pacific superplumes surrounded by subduction slabs. This structure has been demonstrated to result from dynamic interaction between mantle convection and surface plate motion history in the last 120 Ma. With similar techniques, mantle structure has been constructed back to about 100 Ma ago. However, due to the lack in global plate motion reconstructions further back in time, mantle structure for earlier times is poorly understood, despite of their importance in understanding the continental tectonics and volcanisms. Zhong et al. (2007) suggested that the mantle structures alternate between spherical harmonic degrees-1 and -2 structures, modulated by supercontinent processes. In their model, a supercontinent forms in the hemisphere with cold downwellings, and after supercontinent formation, the cold downwellings are replaced with hot upwellings due to return flows associated with circum-supercontinent subduction. This model implies that the African superplume is younger than 330 Ma when Pangea was formed, which is supported by volcanic activities recorded on continents around Pangea time. By using paleomagnetic-geologically reconstructed continental motions between 500 and 200 Ma in a three-dimensional spherical models of mantle convection, this study, for the first time, investigates the time evolution of mantle structures in the African hemisphere associated with Pangea formation. We show that cold downwellings first develop in the mantle between the colliding Laurentia and Gondwana, and that the downwellings are then replaced by upwellings after the formation of Pangea and as circum-Pangea subduction is initiated, consistent with Zhong et al. (2007) and Li et al. (2008). We find that the return flows in response to the circum-Pangea subduction are responsible for the upwellings below Pangea. We also find that even if the mantle in the African hemisphere is initially occupied by hot upwellings, the cold downwellings associated with convergence between Laurentia and Gondwana would destroy the hot upwellings and cause the hemisphere to be cold. These results are insensitive to model parameters such as convective vigor, internal heating rate, and the plate motions in the oceanic hemisphere. We therefore suggest that the African superplume is younger than 330 Ma when Pangea was formed.

Cetacean distributions relative to ocean processes in the northern California Current System

NASA Astrophysics Data System (ADS)

Tynan, Cynthia T.; Ainley, David G.; Barth, John A.; Cowles, Timothy J.; Pierce, Stephen D.; Spear, Larry B.

2005-01-01

Associations between cetacean distributions, oceanographic features, and bioacoustic backscatter were examined during two process cruises in the northern California Current System (CCS) during late spring and summer 2000. Line-transect surveys of cetaceans were conducted across the shelf and slope, out to 150 km offshore from Newport, Oregon (44.6°N) to Crescent City, California (41.9°N), in conjunction with multidisciplinary mesoscale and fine-scale surveys of ocean and ecosystem structure. Occurrence patterns (presence/absence) of cetaceans were compared with hydrographic and ecological variables (e.g., sea surface salinity, sea surface temperature, thermocline depth, halocline depth, chlorophyll maximum, distance to the center of the equatorward jet, distance to the shoreward edge of the upwelling front, and acoustic backscatter at 38, 120, 200 and 420 kHz) derived from a towed, undulating array and a bioacoustic system. Using a multiple logistic regression model, 60.2% and 94.4% of the variation in occurrence patterns of humpback whales Megaptera novaeangliae during late spring and summer, respectively, were explained. Sea surface temperature, depth, and distance to the alongshore upwelling front were the most important environmental variables during June, when humpbacks occurred over the slope (200-2000 m). During August, when humpbacks concentrated over a submarine bank (Heceta Bank) and off Cape Blanco, sea surface salinity was the most important variable, followed by latitude and depth. Humpbacks did not occur in the lowest salinity water of the Columbia River plume. For harbor porpoise Phocoena phocoena, the model explained 79.2% and 70.1% of the variation in their occurrence patterns during June and August, respectively. During spring, latitude, sea surface salinity, and thermocline gradient were the most important predictors. During summer, latitude and distance to the inshore edge of the upwelling front were the most important variables. Typically a coastal species, harbor porpoises extended their distribution farther offshore at Heceta Bank and at Cape Blanco, where they were associated with the higher chlorophyll concentrations in these regions. Pacific white-sided dolphin Lagenorhynchus obliquidens was the most numerous small cetacean in early June, but was rare during August. The model explained 44.5% of the variation in their occurrence pattern, which was best described by distance to the upwelling front and acoustic backscatter at 38 kHz. The model of the occurrence pattern of Dall's porpoise Phocoenoides dalli was more successful when mesoscale variability in the CCS was higher during summer. Thus, the responses of cetaceans to biophysical features and upwelling processes in the northern CCS were both seasonally and spatially specific. Heceta Bank and associated flow-topography interactions were very important to a cascade of trophic dynamics that ultimately influenced the distribution of foraging cetaceans. The higher productivity associated with upwelling near Cape Blanco also had a strong influence on the distribution of cetaceans.

Geographical coincidence of high heat flow, high seismicity, and upwelling, with hydrocarbon deposits, phosphorites, evaporites, and uranium ores.

PubMed

Libby, L M; Libby, W F

1974-10-01

Oil deposits occur in deep sediments, and appear to be organic matter that has been transformed through the action of geothermal heat and pressure. Deep sediments, rich in biological remains, are created by ocean upwelling, caused in part by high geothermal heat flow through the sea bottom. Such regions correlate with enhanced seismic activity. We look for correlations of seismicity, high heat flux, petroleum, uranium, phosphates, and salts, deposited from abundant plant life. These may be useful in discovering more petroleum and coal. We estimate that the known world reserves of petroleum and coal are about 10(-4) of the total of buried biogenic carbon.

Biomass in the upwelling areas along the northwest coast of Africa as viewed with ERTS-1

NASA Technical Reports Server (NTRS)

Szekielda, K.; Curran, R. J.

1973-01-01

Light penetration in water is affected by plankton, algae, and dissolved and suspended matter. As a consequence, the composition of backscattered light from below the air-sea interface is determined by the nature of the constituents in the water column. In contrast to the absorption spectrum of chemically pure chlorophyll in solution, algae suspensions absorb and scatter light more uniformly throughout the visible part of the electromagnetic spectrum. Because of their spectral absorption and scattering properties plankton concentration can be estimated by measuring the spectral backscattered radiance over water. Experiments using this approach were performed in upwelling regions along the northwest coast of Africa.

The Vertical Profile of Ocean Mixing

NASA Astrophysics Data System (ADS)

Ferrari, R. M.; Nikurashin, M.; McDougall, T. J.; Mashayek, A.

2014-12-01

The upwelling of bottom waters through density surfaces in the deep ocean is not possible unless the sloping nature of the sea floor is taken into account. The bottom--intensified mixing arising from interaction of internal tides and geostrophic motions with bottom topography implies that mixing is a decreasing function of height in the deep ocean. This would further imply that the diapycnal motion in the deep ocean is downward, not upwards as is required by continuity. This conundrum regarding ocean mixing and upwelling in the deep ocean will be resolved by appealing to the fact that the ocean does not have vertical side walls. Implications of the conundrum for the representation of ocean mixing in climate models will be discussed.

Transmission of the haplosporidian parasite MSX Haplosporidium nelsoni to the eastern oyster Crassostrea virginica in an upweller system.

PubMed

Sunila, I; Karolus, J; Lang, E P; Mroczka, M E; Volk, J

2000-08-31

The haplosporidian oyster parasite MSX (Multinucleated Sphere X) Haplosporidium nelsoni was transmitted to eastern oysters Crassostrea virginica. Hatchery-raised, MSX-free juvenile oysters were placed in upweller tanks. Water to the tanks was filtered through a screen with 1 mm2 openings and originated from the water column overlaying naturally infected oysters beds (MSX prevalence 17 to 57%). MSX was diagnosed by histopathological analysis. MSX-disease (57% prevalence) with increased mortality (19%) was observed 11 wk after the beginning of the exposure and mortality of 80% after 16 wk. The study demonstrates transmission of MSX via water-borne infectious agents capable of passing through a 1 mm filter.

Geographical Coincidence of High Heat Flow, High Seismicity, and Upwelling, with Hydrocarbon Deposits, Phosphorites, Evaporites, and Uranium Ores

PubMed Central

Libby, L. M.; Libby, W. F.

1974-01-01

Oil deposits occur in deep sediments, and appear to be organic matter that has been transformed through the action of geothermal heat and pressure. Deep sediments, rich in biological remains, are created by ocean upwelling, caused in part by high geothermal heat flow through the sea bottom. Such regions correlate with enhanced seismic activity. We look for correlations of seismicity, high heat flux, petroleum, uranium, phosphates, and salts, deposited from abundant plant life. These may be useful in discovering more petroleum and coal. We estimate that the known world reserves of petroleum and coal are about 10-4 of the total of buried biogenic carbon. Images PMID:16592185

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

NASA Technical Reports Server (NTRS)

Halpern, David; Feldman, Gene C.

1994-01-01

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

The Thermocline Layer and Chlorophyll-a Concentration Variability during Southeast Monsoon in the Banda Sea

NASA Astrophysics Data System (ADS)

Pusparini, Nikita; Prasetyo, Budi; Ambariyanto; Widowati, Ita

2017-02-01

Thermocline layer and chlorophyll-a concentration can be used to investigate the upwelling region. This investigation is focused in the Banda Sea because the upwelling event in this area is quite large and has a longer upwelling duration than other waters in Indonesia. In addition, Banda Sea is also influenced by climatic factors such as monsoon. The aim of this research is to determine the validation of secondary data (from satellite imagery data and model) and in situ observation data (from research cruise) and to determine the variability of thermocline layer and chlorophyll-a concentration during Southeast Monsoon in the Banda Sea. The data used in this study were chlorophyll-a concentration, seawater vertical temperature at depths 0-400 meters, and sea surface temperature from remote sensing and in situ data. Spatial and temporal analysis of all parameters was conducted by quantitative descriptive method. The results showed that the variability of thermocline layer and the chlorophyll-a distribution were strongly related to seasonal pattern. In most cases, the estimates of thermocline layer and chlorophyll-a concentration using remote sensing algorithm were higher than in situ measured values. The greatest variability occurred in the eastern Banda Sea during the Southeast Monsoon with shallower thermocline layer, more abundance of chlorophyll-a concentration, and lower sea surface temperature.

How well-connected is the surface of the global ocean?

PubMed

Froyland, Gary; Stuart, Robyn M; van Sebille, Erik

2014-09-01

The Ekman dynamics of the ocean surface circulation is known to contain attracting regions such as the great oceanic gyres and the associated garbage patches. Less well-known are the extents of the basins of attractions of these regions and how strongly attracting they are. Understanding the shape and extent of the basins of attraction sheds light on the question of the strength of connectivity of different regions of the ocean, which helps in understanding the flow of buoyant material like plastic litter. Using short flow time trajectory data from a global ocean model, we create a Markov chain model of the surface ocean dynamics. The surface ocean is not a conservative dynamical system as water in the ocean follows three-dimensional pathways, with upwelling and downwelling in certain regions. Using our Markov chain model, we easily compute net surface upwelling and downwelling, and verify that it matches observed patterns of upwelling and downwelling in the real ocean. We analyze the Markov chain to determine multiple attracting regions. Finally, using an eigenvector approach, we (i) identify the five major ocean garbage patches, (ii) partition the ocean into basins of attraction for each of the garbage patches, and (iii) partition the ocean into regions that demonstrate transient dynamics modulo the attracting garbage patches.

Parga Chasma: Coronae and Rifting on Venus

NASA Technical Reports Server (NTRS)

Smrekar, S. E.; Stofan, E. R.; Buck, W. R.; Martin, P.

2005-01-01

The majority of coronae (quasicircular volcano-tectonic features) are found along rifts or fracture belts, and the majority of rifts have coronae [e.g. 1,2]. However, the relationship between coronae and rifts remains unclear [3-6]. There is evidence that coronae can form before, after, or synchronously with rifts [3,4]. The extensional fractures in the rift zones have been proposed to be a result of broad scale upwelling and traction on the lower lithosphere [7]. However, not all rift systems have a significant positive geoid anomaly, as would be expected for an upwelling site [8]. This could be explained if the rifts lacking anomalies are no longer active. Coronae are generally accepted to be sites of local upwelling [e.g. 1], but the observed rifting is frequently not radial to the coronae and extends well beyond the coronae into the surrounding plains. Thus the question remains as to whether the rifts represent regional extension, perhaps driven by mantle tractions, or if the coronae themselves create local thinning and extension of the lithosphere. In the first case, a regional extension model should be consistent with the observed characteristics of the rifts. In the latter case, a model of lithospheric loading and fracturing would be more appropriate. A good analogy may be the propagation of oceanic intraplate volcanoes [9].

Mantle transition zone discontinuities beneath the Tien Shan

NASA Astrophysics Data System (ADS)

Yu, Youqiang; Zhao, Dapeng; Lei, Jianshe

2017-10-01

To better understand geodynamic processes of intracontinental mountain building, we conduct a systematic investigation of the mantle transition zone (MTZ) beneath the Tien Shan and its surrounding areas using a receiver function method under non-plane wave front assumption. The resulting apparent depths of the 410 km (d410) and 660 km (d660) discontinuities and the MTZ thickness display significant lateral variations. Both the central Tien Shan and the Pamir Plateau are characterized by a thick MTZ, which can be well explained by the existence of lithospheric segments resulted from possible break-off of the subducted slab or lithosphere delamination. A thin MTZ and an obviously depressed d410, which may be induced by asthenosphere upwelling associated with the dropping lithospheric segment, are revealed beneath the Kazakh Shield. Seismic evidence is obtained for the potential existence of lower mantle upwelling beneath the Tarim Basin based on the observed thin MTZ and relatively significant uplift of d660. The subduction of the Kazakh Shield and Tarim lithosphere driven by the India-Eurasia collision possibly plays an essential role in the formation and evolution of the Tien Shan orogenic belt, and the lower mantle upwelling revealed beneath the Tarim Basin may promote the uplift of the Tien Shan by softening the upper mantle.

Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling

NASA Astrophysics Data System (ADS)

Etourneau, J.; Robinson, R. S.; Martinez, P.; Schneider, R.

2013-08-01

The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pliocene-Pleistocene in the eastern equatorial Pacific (EEP) for the last 3.2 Myr. Our results indicate that the export production peak corresponds to a cold interval marked by high nutrient supply relative to consumption, as revealed by the low bulk sedimentary 15N/14N (δ15N) and alkenone-derived sea surface temperature (SST) values. This ∼0.6 million year long episode of enhanced delivery of nutrients to the surface of the EEP was predominantly initiated through the upwelling of nutrient-enriched water sourced in high latitudes. In addition, this phenomenon was likely promoted by the regional intensification of upwelling in response to the development of intense Walker and Hadley atmospheric circulations. Increased nutrient consumption in the polar oceans and enhanced denitrification in the equatorial regions restrained nutrient supply and availability and terminated the high export production event.

Development of Phaeocystis globosa blooms in the upwelling waters of the South Central coast of Viet Nam

NASA Astrophysics Data System (ADS)

Hai, Doan-Nhu; Lam, Nguyen-Ngoc; Dippner, Joachim W.

2010-11-01

Blooms of haptophyte algae in the south central coastal waters of Viet Nam often occur in association with upwelling phenomenon during the southwest (SW) monsoon. Depending on the magnitude of the blooms, damage to aquaculture farms may occur. Based on two years of data on biology, oceanography, and marine chemistry, the present study suggests a conceptual model of the growth of the haptophyte Phaeocystis globosa. At the beginning of the bloom, low temperature and abundant nutrient supply, especially nitrate from rain and upwelling, favour bloom development. Diatoms utilize available nitrate and phosphate; subsequently, higher ammonium concentration allows P. globosa to grow faster than the diatoms. At the end of the Phaeocystis bloom, free cells may become available as food for a heterotrophic dinoflagellate species, Noctiluca scintillans. During and after the phytoplankton bloom, remineralization by bacteria reduces dissolved oxygen to a very low concentration at depth, and favors growth of nitrate-reducing bacteria.A Lagrangian Harmful Algal Bloom (HAB) model, driven by a circulation model of the area, realistically simulates the transport of microalgae in surface waters during strong and weak SW monsoon periods, suggesting that it may be a good tool for early warning of HABs in Vietnamese coastal waters.

Different responses of chlorophyll-a concentration and Sea Surface Temperature (SST) on southeasterly wind blowing in the Sunda Strait

NASA Astrophysics Data System (ADS)

Wirasatriya, A.; Kunarso; Maslukah, L.; Satriadi, A.; Armanto, R. D.

2018-03-01

During southeast monsoon, along the western coast of Sumatra Island and southern coast of Java Island are known as the coastal upwelling areas denoted by the occurrence of Sea Surface Temperature (SST) cooling and chlorophyll-a blooming. Located between Sumatra and Java Islands, Sunda Strait waters may give different response to the southeasterly wind blowing above. Using SST and chlorophyll-a data obtained from daily MODIS level 3 during 2006–2016, this study demonstrated the evidence on how bathymetry and topography modified the effect of southeasterly wind on the spatial variability of SST and chlorophyll-a. All datasets were composed into monthly and monthly climatology. The area in the center of Sunda Strait had the lowest chlorophyll-a concentration and the warmest SST during the peak of upwelling season. The deep bottom topography and the absence of barrier land prevented the generation of wind driven coastal upwelling. However, the chlorophyll-a concentration in this area had the highest correlation with the wind speed which means that the variation of chlorophyll-a concentration in this area was highly depended on the variability of wind. On the other hand, the areas with shallow bathymetry and in front of Panaitan and Java Islands had higher chlorophyll-a concentration and cooler SSTs.

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.

Spatial distribution of common Minke whale (Balaenoptera acutorostrata) as an indication of a biological hotspot in the East Sea

NASA Astrophysics Data System (ADS)

Lee, Dasom; An, Yong Rock; Park, Kyum Joon; Kim, Hyun Woo; Lee, Dabin; Joo, Hui Tae; Oh, Young Geun; Kim, Su Min; Kang, Chang Keun; Lee, Sang Heon

2017-09-01

The minke whale (Balaenoptera acutorostrata) is the most common baleen whale among several marine mammal species observed in Korea. Since a high concentrated condition of prey to whales can be obtained by physical structures, the foraging whale distribution can be an indicator of biological hotspot. Our main objective is verifying the coastal upwelling-southwestern East Sea as a productive biological hotspot based on the geographical distribution of minke whales. Among the cetacean research surveys of the National Institute of Fisheries Science since 1999, 9 years data for the minke whales available in the East Sea were used for this study. The regional primary productivity derived from Moderate-Resolution Imaging Spectroradiometer (MODIS) was used for a proxy of biological productivity. Minke whales observed during the sighting surveys were mostly concentrated in May and found mostly (approximately 70%) in the southwestern coastal areas (< 300 m) where high chlorophyll concentrations and primary productivity were generally detected. Based on MODIS-derived primary productivity algorithm, the annual primary production (320 g C m-2 y-1) estimated in the southwestern coastal region of the East Sea belongs to the highly productive coastal upwelling regions in the world. A change in the main spatial distribution of minke whales was found in recent years, which indicate that the major habitats of mink whales have been shifted into the north of the common coastal upwelling regions. This is consistent with the recently reported unprecedented coastal upwelling in the mid-eastern coast of Korea. Based on high phytoplankton productivity and high distribution of minke whales, the southwestern coastal regions can be considered as one of biological hotspots in the East Sea. These regions are important for ecosystem dynamics and the population biology of top marine predators, especially migratory whales and needed to be carefully managed from a resource management perspective.

Dynamics and stoichiometry of nutrients and phytoplankton in waters influenced by the oxygen minimum zone in the eastern tropical Pacific

NASA Astrophysics Data System (ADS)

Franz, Jasmin; Krahmann, Gerd; Lavik, Gaute; Grasse, Patricia; Dittmar, Thorsten; Riebesell, Ulf

2012-04-01

The tropical South East Pacific is characterized by strong coastal upwelling on the narrow continental shelf and an intense oxygen minimum zone (OMZ) in the intermediate water layer. These hydrographic properties are responsible for a permanent supply of intermediate water masses to the surface rich in nutrients and with a remarkably low inorganic N:P stoichiometry. To investigate the impact of OMZ-influenced upwelling waters on phytoplankton growth, elemental and taxonomical composition we measured hydrographic and biogeochemical parameters along an east-west transect at 10°S in the tropical South East Pacific, stretching from the upwelling region above the narrow continental shelf to the well-stratified oceanic section of the eastern boundary regime. New production in the area of coastal upwelling was driven by large-sized phytoplankton (e.g. diatoms) with generally low N:P ratios (<16:1). While nitrate and phosphate concentrations were at levels not limiting phytoplankton growth along the entire transect, silicate depletion prohibited diatom growth further off-shore. A deep chlorophyll a maximum consisting of pico-/nano- (Synechococcus, flagellates) and microphytoplankton occurred within a pronounced thermocline in subsurface waters above the shelf break and showed intermediate N:P ratios close to Redfield proportions. High PON:POP (>20:1) ratios were observed in the stratified open ocean section of the transect, coinciding with the abundance of two strains of the pico-cyanobacterium Prochlorococcus; a high-light adapted strain in the surface layer and a low-light adapted strain occurring along the oxic-anoxic transition zone below the thermocline. Excess phosphate present along the entire transect did not appear to stimulate growth of nitrogen-fixing phytoplankton, as pigment fingerprinting did not indicate the presence of diazotrophic cyanobacteria at any of our sampling stations. Instead, a large fraction of the excess phosphate generated within the oxygen minimum zone was consumed by non-Redfield production of large phytoplankton in shelf surface waters.

Egg production and hatching success of Calanus chilensis and Acartia tonsa in the northern Chile upwelling zone (23°S), Humboldt Current System

NASA Astrophysics Data System (ADS)

Ruz, Paula M.; Hidalgo, Pamela; Yáñez, Sonia; Escribano, Rubén; Keister, Julie E.

2015-08-01

Oxygen Minimum Zones (OMZ's) are expanding and intensifying as result of climate change, affecting Eastern Boundary Upwelling Systems. Local effects of vertical movements of OMZ's that result from changes in upwelling intensity could reduce or expand the oxygenated surface layer that most zooplanktonic species inhabit in coastal areas. Using the copepods Calanus chilensis and Acartia tonsa as model organisms, an experimental test of the impact of different dissolved oxygen (DO) concentrations (between 0.5 and 5 ml L- 1) on egg production and hatching success was carried out and compared with field estimations of egg production, female and egg abundance in Mejillones Bay (23°S). Abundance of C. chilensis was highly variability and no consistent pattern in egg production and hatching success was found across DO levels, whereas A. tonsa egg production had maximum values between 2.6 and 4.7 ml O2 L- 1 and hatching success was positively correlated with DO (r = 0.75). In the field, temperature was the main factor controlling the dynamics of both species, while Chl-a and DO were also correlated with C. chilensis and A. tonsa, respectively. Principal Component Analysis showed that abundances of both copepods were controlled by temperature, stratification, OMZ depth, and Ekman transport, which together explained more than 70% of the total variance and were the main factors that modulated the populations of C. chilensis and A. tonsa in the upwelling zone of northern Chile (23°S). The differential responses of C. chilensis and A. tonsa to changes in DO concentrations associated with vertical movements of the OMZ suggest that C. chilensis may be better adapted to hypoxic conditions than A. tonsa, however both species are successful and persistent all year-round. We suggest that physiological responses of copepods could be used to evaluate population dynamics affected by the shoaling of OMZ's and the repercussions to trophic food webs of eastern boundary current systems.

Surface distribution of brachyuran megalopae and ichthyoplankton in the Columbia River plume during transition from downwelling to upwelling conditions

NASA Astrophysics Data System (ADS)

Roegner, G. Curtis; Daly, Elizabeth A.; Brodeur, Richard D.

2013-06-01

In the California Current coastal boundary zone, the spring transition between downwelling and upwelling conditions, along with the fluctuating structure of the Columbia River plume, creates highly dynamic interactions. In this study, we investigated whether the surface distribution of brachyuran larvae and ichthyoplankton would track the dynamics of the Columbia River plume. By happenstance, the cruise period coincided with the spring transition from downwelling to sustained upwelling conditions in 2010, a year when the transition was delayed and Columbia River flow was substantially higher than average. We used time series of wind and freshwater input to evaluate the influence of physical forcing on oceanographic patterns, and sampled hydrography and surface plankton concentrations within a 182 km2 grid off Willapa Bay, WA. Additionally, two longer transects, one cross-shelf and the other along-shore, were made to discern the extent of plume influence on larval crab and fish abundance. We found that plume waters that were trapped in a northward-flowing coastal-boundary current during downwelling conditions were advected offshore after several days of upwelling-favorable winds. Neustonic collections of brachyuran larvae and ichthyoplankton varied in response to this large seaward advective event. Megalopae of cancrid crabs exhibited patterns of both offshore transport (Cancer oregonensis/productus) and nearshore retention (C. magister). Additionally, abundant numbers of large juvenile widow (Sebastes entomelas) and yellowtail (S. flavidus) rockfish of a size appropriate for settlement were sampled during a period when ocean conditions favored high recruitment success. These results demonstrated that the response of planktonic crab larvae and ichthyoplankton to large-scale advection varied by species, with larger and more vagile fish exhibiting less evidence of passive transport than smaller crab larvae. Importantly, portions of the planktonic fish and crab community were able to maintain nearshore distributions in favorable settlement habitat, despite physical advection offshore.

Analysis on the Upwelling of the Anoxic Water Mass in Inner Tokyo Bay

NASA Astrophysics Data System (ADS)

Kitahara, Kouichi; Wada, Akira; Kawanaga, Mitsuhito; Fukuoka, Ippei; Takano, Tairyu

In the period of strong density stratification from early summer through early fall, the supply of oxygen from the sea surface to the deeper water is cut off. At the same time, organic matter decomposes near the ocean bottom, so that the anoxic water mass forms. In inner Tokyo Bay, when a northeasterly wind(directed from the inner bay toward the mouth of the bay)blows, the anoxic water mass upwells(an “Aoshio” occurs). In some cases fishes and shellfish die along the coast. Based on the report of results of continuous observations of water temperature, salinity and dissolved oxygen content presented by Fukuoka et al, 2005, here we have used an improved fluid flow model to carry out 3-dimensional calculations of the water level, water temperature, salinity and flow distributions. The computational results have reproduced the observational results well. The calculations showed that upwelling of the anoxic water mass that forms during the stratified period is not only affected by the continuously blowing northeasterly wind, but also by a continuous southwesterly wind that blew several days previously. Surface water blown against the coast by this continuous southwesterly wind is pushed downward; the calculations reproduced the process by which the rising force of this previously downwelled surface water also affects the phenomenon of anoxia. Furthermore, we presented the results of time dependent analysis of quantities relevant to water quality, including dissolved oxygen, which is closely related to the Aoshio, using the flow and diffusion model and a primary ecological model during the stratified ocean period, the sinking period and the upwelling period. We have compared the computed results to the results of continuous observations of dissolved oxygen during occurrence of an Aoshio in 1992 at observation point D-2, and confirmed that this model is an appropriate one to describe this phenomenon.

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

NASA Astrophysics Data System (ADS)

Schmidt, M.; Eggert, A.

2016-02-01

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

Preparing to predict: The Second Autonomous Ocean Sampling Network (AOSN-II) experiment in the Monterey Bay

NASA Astrophysics Data System (ADS)

Ramp, S. R.; Davis, R. E.; Leonard, N. E.; Shulman, I.; Chao, Y.; Robinson, A. R.; Marsden, J.; Lermusiaux, P. F. J.; Fratantoni, D. M.; Paduan, J. D.; Chavez, F. P.; Bahr, F. L.; Liang, S.; Leslie, W.; Li, Z.

2009-02-01

The Autonomous Ocean Sampling Network Phase Two (AOSN-II) experiment was conducted in and offshore from the Monterey Bay on the central California coast during July 23-September 6, 2003. The objective of the experiment was to learn how to apply new tools, technologies, and analysis techniques to adaptively sample the coastal ocean in a manner demonstrably superior to traditional methodologies, and to use the information gathered to improve predictive skill for quantities of interest to end-users. The scientific goal was to study the upwelling/relaxation cycle near an open coastal bay in an eastern boundary current region, particularly as it developed and spread from a coastal headland. The suite of observational tools used included a low-flying aircraft, a fleet of underwater gliders, including several under adaptive autonomous control, and propeller-driven AUVs in addition to moorings, ships, and other more traditional hardware. The data were delivered in real time and assimilated into the Harvard Ocean Prediction System (HOPS), the Navy Coastal Ocean Model (NCOM), and the Jet Propulsion Laboratory implementation of the Regional Ocean Modeling System (JPL/ROMS). Two upwelling events and one relaxation event were sampled during the experiment. The upwelling in both cases began when a pool of cold water less than 13 °C appeared near Cape Año Nuevo and subsequently spread offshore and southward across the bay as the equatorward wind stress continued. The primary difference between the events was that the first event spread offshore and southward, while the second event spread only southward and not offshore. The difference is attributed to the position and strength of meanders and eddies of the California Current System offshore, which blocked or steered the cold upwelled water. The space and time scales of the mesoscale variability were much shorter than have been previously observed in deep-water eddies offshore. Additional process studies are needed to elucidate the dynamics of the flow.

Crust and Mantle Deformation Revealed from High-Resolution Radially Anisotropic Velocity Models

NASA Astrophysics Data System (ADS)

Li, A.; Dave, R.; Yao, Y.

2017-12-01

Love wave tomography, which can achieve a similar model resolution as Rayleigh wave, so far has limited applications to the USArray data. Recently, we have developed high-resolution Love wave phase velocity maps in the Wyoming craton and Texas using data at the Transportable Array stations. 3-D, radially anisotropic velocity models are obtained by jointly inverting Love and Rayleigh wave phase velocities. A high-velocity anomaly extending to about 200 km depth beneath central Wyoming correlates with negative radial anisotropy (Vsv>Vsh), suggesting that mantle downwelling develops under the cratonic lithosphere. Surprisingly, the significantly low velocity beneath the Yellowstone hotspot, which has been interpreted as partial melting and asthenospheric upwelling, is associated with the largest radial anisotropy (Vsh>Vsv) in the area. This observation does not support mantle upwelling. Instead, it indicates that the upper mantle beneath the hotspot has experienced strong shear deformation probably by the plate motion and large-scale mantle flow. In Texas, positive radial anisotropy in the lower crust extends from the coast to the Ouachita belt, which is characterized by high velocity and negative radial anisotropy. In the upper mantle, large variations of velocity and anisotropy exit under the coastal plain. A common feature in these anisotropic models is that high-velocity anomalies in the upper mantle often correlate with negative anisotropy (Vsv>Vsh) while low-velocity anomalies are associated with positive anisotropy (Vsh>Vsv). The manifestation of mantle downweling as negative radial anisotropy is largely due to the relatively high viscosity of the high-velocity mantle block, which is less affected by the surrounding large-scale horizontal flow. However, mantle upwelling, which is often associated with low-velocity anomalies, presumably low-viscosity mantle blocks, is invisible in radial anisotropy models. Such upwelling may happen too quickly to make last effects or too slow to alter the dominant shear deformation in the asthenosphere.

Domoic acid production near California coastal upwelling zones, June 1998

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

Trainer, V L.; Adams, Nicolaus G.; Bill, Brian D.

2000-01-01

Sea lion mortalities in central California during May and June 1998 were traced to their ingestion of sardines and anchovies that had accumulated the neurotoxin domoic acid. The detection of toxin in urine, feces, and stomach contents of several sea lions represents the first proven occurrence of domoic acid transfer through the food chain to a marine mammal. The pennate diatoms, Pseudo-nitzschia multiseries and P. australis, were the dominant, toxin-producing phytoplankton constituting algal blooms near Monterey Bay, Half Moon Bay, and Oceano Dunes, areas where sea lions with neurological symptoms stranded. Toxic Pseudo-nitzschia were also found near Morrow Bay, Pointmore » Conception, Point Arguello, and Santa Barbara, demonstrating that these species were widespread along the central California coast in June 1998. Measurements of domoic acid during three cruises in early June showed the highest cellular toxin levels in P. multiseries near Point A?o Nuevo and in P. australis from Morro w Bay. Maximum cellular domoic acid levels were observed within 20 km of the coast between 0 and 5 m depth, although toxin was also measured to depths of 40 m. Hydrographic data indicated that the highest toxin levels and greatest numbers of toxic cells were positioned in water masses associated with upwelling zones near coastal headlands. Nutrient levels at these sites were less than those typically measured during periods of active upwelling, due to the 1998 El Ni?o event. The flow of cells and/or nutrients from coastal headlands into embayments where cells can multiply in a stratified environment is a possible mechanism of bloom development along the central California coast. This coupling of toxic Pseudo-nitzschia growth near upwelling zones with physical processes involved in cell transport will be understood only when long-term measurements are made at several key coastal locations, aiding in our capability to predict domoic-acid producing algal blooms.« less

A surplus production model including environmental effects: Application to the Senegalese white shrimp stocks

NASA Astrophysics Data System (ADS)

Thiaw, Modou; Gascuel, Didier; Jouffre, Didier; Thiaw, Omar Thiom

2009-12-01

In Senegal, two stocks of white shrimp ( Penaeusnotialis) are intensively exploited, one in the north and another in the south. We used surplus production models including environmental effects to analyse their changes in abundance over the past 10 years and to estimate their Maximum Sustainable Yield (MSY) and the related fishing effort ( EMSY). First, yearly abundance indices were estimated from commercial statistics using GLM techniques. Then, two environmental indices were alternatively tested in the model: the coastal upwelling intensity from wind speeds provided by the SeaWifs database and the primary production derived from satellite infrared images of chlorophyll a. Models were fitted, with or without the environmental effect, to the 1996-2005 time series. They express stock abundance and catches as functions of the fishing effort and the environmental index (when considered). For the northern stock, fishing effort and abundance fluctuate over the period without any clear trends. The model based on the upwelling index explains 64.9% of the year-to-year variability. It shows that the stock was slightly overexploited in 2002-2003 and is now close to full exploitation. Stock abundance strongly depends on environmental conditions; consequently, the MSY estimate varies from 300 to 900 tons according to the upwelling intensity. For the southern stock, fishing effort has strongly increased over the past 10 years, while abundance has been reduced 4-fold. The environment has a significant effect on abundance but only explains a small part of the year-to-year variability. The best fit is obtained using the primary production index ( R2 = 0.75), and the stock is now significantly overfished regardless of environmental conditions. MSY varies from 1200 to 1800 tons according to environmental conditions. Finally, in northern Senegal, the upwelling is highly variable from year to year and constitutes the major factor determining productivity. In the south, hydrodynamic processes seem to dominate and determine the primary production and the white shrimp stock productivity as well.

Evolution of the earliest mantle caused by the magmatism-mantle upwelling feedback: Implications for the Moon and the Earth

NASA Astrophysics Data System (ADS)

Ogawa, M.

2017-12-01

The two most important agents that cause mantle evolution are magmatism and mantle convection. My earlier 2D numerical models of a coupled magmatism-mantle convection system show that these two agents strongly couple each other, when the Rayleigh number Ra is sufficiently high: magmatism induced by a mantle upwelling flow boosts the upwelling flow itself. The mantle convection enhanced by this positive feedback (the magmatism-mantle upwelling, or MMU, feedback) causes vigorous magmatism and, at the same time, strongly stirs the mantle. I explored how the MMU feedback influences the evolution of the earliest mantle that contains the magma ocean, based on a numerical model where the mantle is hot and its topmost 1/3 is partially molten at the beginning of the calculation: The evolution drastically changes its style, as Ra exceeds the threshold for onset of the MMU feedback, around 107. At Ra < 107, basaltic materials generated by the initial widespread magmatism accumulate in the deep mantle to form a layer; the basaltic layer is colder than the overlying shallow mantle. At Ra > 107, however, the mantle remains compositionally more homogeneous in spite of the widespread magmatism, and the deep mantle remains hotter than the shallow mantle, because of the strong convective stirring caused by the feedback. The threshold value suggests that the mantle of a planet larger than Mars evolves in a way substantially different from that in the Moon does. Indeed, in my earlier models, magmatism makes the early mantle compositionally stratified in the Moon, but the effects of strong convective stirring overwhelms that of magmatism to keep the mantle compositionally rather homogeneous in Venus and the Earth. The MMU feedback is likely to be a key to understanding why vestiges of the magma ocean are so scarce in the Earth.

On the Influence of Anthropogenic Forcings on Changes in the Stratospheric Mean Age

NASA Technical Reports Server (NTRS)

Oman, Luke; Waugh, Darryn W.; Pawson, Steven; Stolarski, Richard S.; Newman, Paul A.

2009-01-01

A common feature of stratospheric simulations of the past or future is an increase in tropical upwelling and a decrease in mean age. Possible causes or these changes include (1) increases in tropical sea surface temperatures (SSTs) driven by increases in well-mixed greenhouse gases (WMGHGs), (2) the direct radiative effect of increases in WMGHGs, and (3) changes in ozone. Here we examine a suite of simulations from the Goddard Earth Observing System chemistry-climate model (GEOS CCM) to isolate the relative role of these three factors. Our analysis indicates that all three factors cause changes in the mean age, but the relative impact of each factor depends on the time period analyzed. Over the past 30-40 years ozone depletion is the major factor causing the decrease in mean age, with negligible changes due to direct radiative impact of WMGHG's. However, ozone is predicted to recover back to 1970 levels during the next 50-60 years, and this causes an increase in the mean age, whereas the continued increase in SSTs from increased levels of WMGHGs and the direct radiative impact of WMGHGs will still cause a decrease in the mean age. The net impact of these factors will still result in a decreasing mean age although the rate will be smaller than that of the past. The decreases in mean age are primarily caused by increases in upwelling in the tropical lower stratosphere. The increased upwelling from both increased tropical SSTs and polar ozone loss appears to be related to changes in zonal winds and increases in wave activity propagating into the stratosphere. The different contributions of changes in SSTs, WMGHGs, and ozone to the circulation of the stratosphere may help explain the large spread in the rate of change of tropical upwelling seen in previous studies.

Study of hydro-saline characteristics of soils a palm grove in basin of Ouargla (Northern Algerian Sahara)

NASA Astrophysics Data System (ADS)

Rezagui, D.; Bouhoun, M. Daddi; Boutoutaou, D.; Djaghoubi, A.

2016-07-01

Saharan soils are often faced with several problems of development, taking account the hydro-edaphic constraints, mainly of hydric types by water table, mechanical by gypso-calcareous crusts and saline by irrigation waters and upwelling of water table. Our work consists in doing a soil characterization of a palm grove in Ouargla in order to study the constraints hydro-halomorphes. The results show that irrigation water by two plies of Senonian and Mioplcène had a high salinity with a value of 2.83 and 5.10 dS.m-1 respectively. The conduct of irrigation is traditional random of submersion type. The palm grove has a poor drainage with a level of water table 156.67±15.71 cm and salinity of 31.37±34.04 dS.m-1. The drains are open type and their maintenance is not regular. This situation of management of irrigation-drainage promotes the upwelling of water table and the waterlogging in soils. The study of soil profiles shows the existence of mechanical obstruction of gypso-calcareous crusts which limit the entrenchment of the date palms and the leaching of salts. Soil salinity is excessive in profiles with a range of 8.98 ± 4.58 dS.m-1. This accumulation of salts is due to the dynamic ascending and descending of salts respectively under the effect of upwelling of water table and leaching by irrigation. The salinization, the upwelling of water table and the presence of gypso-calcareous crusts recorded in Ouargla testify to a degradation hydro-halomorphe and mechanic of soil which constitute the major constraints in the management of system irrigation-drainage and sustainable agricultural development of the palm groves of the basin of Ouargla. Some hydro-agricultural planning are necessary to apply in the oasis to improve the hydro-mechanical properties of soils in order to reduce their degradation.

Different Levels of Hypoxia Tolerance during Early Life History Stages of Key Fish Species from the Northern Benguela Upwelling Ecosystem Inferred from the Comparison of Eco-Physiological Traits

NASA Astrophysics Data System (ADS)

Geist, S. J.; Imam, R. M.; Kunzmann, A.; Ekau, W.

2016-02-01

Global change factors such as a pronounced Oxygen Minimum Zone and the shoaling of hypoxic waters are assumed to play a major role in controlling the recruitment of fish stocks in Upwelling Systems by affecting the planktonic early life history stages. Ecological and ecophysiological traits in the larval stages of five key fish species in the Northern Benguela Upwelling System (Sardine, Sardinops sagax; Anchovy, Engraulis encrasicolus; Cape horse mackerel, Trachurus capensis; Cape hake, Merluccius sp.; Pelagic goby, Sufflogobobius bibarbatus) were investigated during the GENUS (Geochemistry and Ecology of the Namibian Upwelling Ecosystem) research project . Analysis of vertical larval distributions in relation to the depth of hypoxic water layers showed gradual interspecific differences, suggesting lower hypoxia tolerance levels of the small pelagics Sardine and Anchovy. Cape horse mackerel juveniles and larvae exhibited very high tolerance levels to short-term hypoxia in respirometry stress experiments, close to the levels of the extremely hypoxia-tolerant Pelagic goby. In the latter two species, we also measured the highest activities of anaerobic enzymes (pyruvate kinase and lactate dehydrogenase) in early and late larval stages, compared to very low activities in Sardine larvae. A higher amount of anaerobic enzymatic activity is related to a higher capacity to break down metabolites that build up during phases of oxygen debt and thus help the larvae to quickly recover from hypoxia exposure. In consequence, a high hypoxia tolerance during their early life stages allows Cape horse mackerel and Pelagic goby to successfully reproduce in an environment characterized by frequent hypoxic events. The low hypoxia tolerance of Sardine larvae, eventually resulting in higher mortality rates, is likely to be an important factor to understand the poor reproductive success and continuing recruitment failures of this formerly dominant fish species of the NBUS during the last 40 years.

Bio-optical signatures and biogeochemistry from intense upwelling and relaxation in coastal California

NASA Astrophysics Data System (ADS)

Kudela, Raphael M.; Garfield, Newell; Bruland, Kenneth W.

2006-12-01

The NSF-sponsored Coastal Ocean Processes Wind Events and Shelf Transport (WEST) experiment investigates the interplay between wind-driven transport and shelf productivity; while eastern boundary shelves are characterized by high productivity due to upward fluxes of nutrients into the euphotic zone, wind forcing also represents negative physical and biological controls via offshore transport and deep (light-limiting) mixing of primary producers. Although this interaction has been well documented for eastern boundary systems generally and for California specifically, one of the primary goals of WEST was to characterize more fully the interplay between positive and negative effects of wind stress, which result in the consistently elevated biological productivity in these shelf regions. During 3 month-long summer cruises (2000-2002) we observed extremes in upwelling/relaxation, using both in situ instrumentation and remotely sensed data. Relationships between optical and physical properties were examined, with emphasis on biogeochemical implications. During 2000, the WEST region was optically dominated by phytoplankton and covarying constituents. During 2001 and 2002, periods of more intense upwelling favorable winds, we observed a transition to optical properties dominated by detrital and inorganic materials. In all years, the continental shelf break provided a natural boundary between optically distinct shelf and open ocean waters. During 2002, we obtained discrete trace-metal measurements of particulate iron and aluminum; we develop a bio-optical proxy for acetic-acid leachable iron from backscatter and fluorescence, and demonstrate that particulate iron is not well correlated to traditional upwelling proxies such as macronutrients, temperature, and salinity. We conclude that the shelf break between ca. 100 and 200 m water depth serves as a natural break point between coastal and oceanic water masses in this region, and that the elevated biomass and productivity associated with this eastern boundary current regime is dominated by these iron rich, shallow shelf waters.

Coastal counter-currents setup patterns in the Gulf of Cadiz

NASA Astrophysics Data System (ADS)

Relvas, P.; Juniór, L.; Garel, E.; Drago, T.

2017-12-01

Alongshore coastal counter-currents (CCC) are frequent features of Eastern Boundary Upwelling Systems, where they temporally alternate with upwelling driven jets of opposite direction. Along the northern margin of the Gulf of Cadiz inner shelf, these CCCs are oriented poleward (eastward) and responsible for sharp temperature increases during the upwelling season, along with potential decline in water quality at the coast. This research is based on a multi-year ADCP velocity time-series (2008-2017), recorded at a single location (23 m water depth) over 13 deployments up to 3 months-long. The analysis focuses on the water column alongshore velocities during current inversions (i.e., the transition from equatorward upwelling jets to poleward CCCs). A set of parameters were derived from the flow structure to identify distinct types of inversions and to hypothesize about their driving mechanisms. Results show that 77% of the inversions start near the bed, propagating then to the upper layers. The bottom layer also changes direction before the surface layer for most events (71%). The vertical shear in this case is one order of magnitude greater than in the (less frequent) opposite situation. No seasonal variability is observed in the CCC occurrences. However, the parameters analysed in this study suggest different types of inversion between winter and summer. In winter, inversions are well defined (low variability), with similar patterns near the surface and bed layers as a result of a strong barotropic component. In summer the inversion patterns are more variable. In particular, the upper and bed layers are often importantly decoupled during inversions, indicating the strengthening of baroclinicity. A categorization of inversions events is proposed based on cross-correlation and multi-variable analyses of the developed parameters. Various types of inversion are obtained, suggesting that CCCs are driven by different forcings that may act separately or jointly.

Boundary current instabilities, upwelling, shelf mixing and eutrophication processes in the Black Sea

NASA Astrophysics Data System (ADS)

Sur, Hali˙l. İ.; Özsoy, Emi˙n.; Ünlüata, Ümi˙t.

Satellite and in situ data are utilized to investigate the mesoscale dynamics of the Black Sea boundary current system with special emphasis on aspects of transport and productivity. The satellite data are especially helpful in capturing rapid sub-mesoscale motions insufficiently resolved by the in situ measurements. Various forms of isolated features, including dipole eddies and river plumes, are identified in the satellite images. Unstable flow structures at these sites appear to transport materials and momentum across the continental shelf. Species differentiation and competition are evident along the boundary current system and at the frontal regions during the development of early summer productivity. A time series of Coastal Zone Colour Scanner (CZCS) images indicate dynamical modulation of the springtime surface productivity in the southern Black Sea. Unstable meandering motions generated at Sakarya Canyon propagate east with speeds of ∼10-15 km d -1. Within weeks, a turbulent jet is created which separates from the coast, covering the entire southwestern sector. The nutrients driving the phytoplankton production (mainly Emiliana huxleyi) of the current system evidently originate from fluvial discharge entering from the northwestern region including the Danube river. The productivity pattern develops in early summer when the Danube inflow is at its peak, and through meandering motions spreads into an area several times wider than the continental shelf. In 1980, the CZCS data, and in 1991 and 1992, the Advanced Very High Resolution Radiometer (AVHRR) data indicate patches of upwelling along the west Anatolian coastline between Sakarya Canyon and Cape İnce ( Ince Burun) in summer. The upwelling phenomenon is outstanding because it occurs on a coast where normally the surface convergence near the coast implies downwelling, and under conditions of unfavorable winds. In 1992, the hydrographic data indicated the upwelling to be the result of a surface divergence of the boundary current, and sequences of satellite data indicate the role of transient dynamics. The in situ data showed the upwelling centres to be devoid of phytoplankton as well as fish eggs and larvae. The AVHRR and in situ hydrographic data in winter 1990 indicate cold water is formed over the entire western Black Sea continental shelf. The band of cold water decreases in width as it moves south and impinges on the headland at Baba Burnu, where it undergoes a sudden expansion. The maximum winter phytoplankton bloom sampled during the same period indicates explosive populations of diatoms following the band of cold water.

Investigating Eastern Equatorial Pacific Export Production and Carbonate Dissolution with XRF Core Scanning at ODP Site 846 Over the Last 5 Million Years

NASA Astrophysics Data System (ADS)

Jones, C.; Robinson, R. S.

2015-12-01

Coastal and equatorial upwelling in the Eastern Equatorial Pacific (EEP) are responsible for about 10% of the ocean's total production. The deep, cold, nutrient-rich waters supplied by upwelling originate in high latitudes, linking changes at high latitudes to the tropics. The Pliocene/Pleistocene transition which started around 2.7-3 million years ago (Ma) marked a period of higher variability in biological production and sea surface temperatures dominated by glacial/interglacial cycles. In addition, secular changes in the development of both Walker and Hadley cells appear to have impacted the strength of equatorial upwelling. However, the large positive production excursions, such as those found from 1.6 to 2.2 Ma, remain only moderately well characterized and both changes in high latitude nutrient supply and regional upwelling strength are implicated. ODP Site 846 is located in the heart of the EEP upwelling cold tongue and has ideal characteristics for examining these links and excursions. We present high-resolution (~0.5 ky) X-Ray Fluorescence (XRF) chemical profiles of Ca, Si, Ba, Mn, Fe, Al, and Ti, as well as a total nitrogen (TN%) record for the last 5 million years from ODP Site 846. We use these high resolution profiles in conjunction with other regional data to assess biogeochemical processes in the EEP over the last 5 million years. CaCO3 and SiO2 are the two dominant biogenic components and account for more than 95% of the sediment. BaSO4 and the discrete TN% measurements record total productivity. MnO and Fe2O3 are redox-sensitive species and are particularly suited to tracing dissolution related to excess bottom-water metabolic processes driven by high export production at the high-alkalinity Site 846. Al2O3 and TiO2 are tracers of terrigenous input. A transition between low amplitude and high amplitude carbonate cycles occurs at 2.8 Ma, coinciding with the Pliocene/Pleistocene transition to higher amplitude glacial cycles. Notable excursions from the baseline high carbonate system occur between 3.8 and 4.2 Ma, between 1.6 and 2.2 Ma, at 0.75 Ma, and within the last 0.1 Ma. These excursions are explored, and causes include heavy contributions from productivity-driven dissolution, some extended instances of CCD-driven dissolution and shifts in overlying productivity towards diatoms.

Upwellings mitigated Plio-Pleistocene heat stress for reef corals on the Florida platform (USA)

NASA Astrophysics Data System (ADS)

Brachert, T. C.; Reuter, M.; Krüger, S.; Kirkerowicz, J.; Klaus, J. S.

2015-10-01

The fast growing calcareous skeletons of zooxanthellate reef corals (z-corals) represent unique environmental proxy archives through their oxygen and carbon stable isotope composition (δ18O, δ13C). In addition, the accretion of the skeleton itself is ultimately linked to the environment and responds with variable growth rates (extension rate) and density to environmental changes. Here we present classical proxy data (δ18O, δ13C) in combination with calcification records from 15 massive z-corals. The z-corals were sampled from four interglacial units of the Florida carbonate platform (USA) dated approximately 3.2, 2.9, 1.8 and 1.2 Ma (middle Pliocene to early Pleistocene). The z-corals (Solenastrea, Orbicella, Porites) derive from unlithified shallow marine carbonates and were carefully screened for primary preservation suited for proxy analysis. We show that skeletal accretion was non-linear and responded with decreasing overall calcification rates (decreasing extension rate but increasing density) to warmer water temperatures. Under high annual water temperatures, inferred from subannually resolved δ18O data, skeletal bulk density was high, but extension rates and overall calcification rates were at a minimum (endmember scenario 1). Maximum skeletal density was reached during the summer season giving rise to a growth band of high density within the annually banded skeletons ("high density band", HDB). With low mean annual water temperatures (endmember scenario 2), bulk skeletal density was low but extension rates and calcification rates reached a maximum, and under these conditions the HDB formed during winter. Although surface water temperatures in the Western Atlantic warm pool during the interglacials of the late Neogene where ∼ 2 °C higher than they are in the present-day, intermittent upwelling of cool, nutrient rich water mitigated water temperatures off southwestern Florida in the middle of the Atlantic warm pool and created temporary refuges for z-coral growth. Based on the subannually resolved δ18O and δ13C records, the duration of the upwelling episodes causing the endmember 2 conditions was variable and lasted from a few years to a number of decades. The episodes of upwelling were interrupted by phases without upwelling (endmember 1) which lasted for at least a few years and led to high surface water temperatures. This variable environment is likely one of the reasons why the coral fauna is dominated by the eurytopic genus Solenastrea, also a species resistant to high turbidity. Over a period of ∼ 50 years, the oldest subannually resolved proxy record available (3.2 Ma) documents a persistent occurrence of the HDB during winter. In contrast, the HDB forms in summer in modern z-corals from the Florida reef tract. We suggest this difference to be the expression of a tendency towards decreasing upwelling since the middle Pliocene. The number of z-coral sclerochronological records for this time period is still, however, rather low and requires an improved resolution through data from additional time-slices. These data can contribute to predicting the effects of future ocean warming on z-coral health along the Florida reef tract.

Open oceanic productivity changes at mid-latitudes during interglacials and its relation to the Atlantic Meridional Overturning Circulation

NASA Astrophysics Data System (ADS)

Nave, Silvia; Lebreiro, S.; Kissel, C.; Guihou, A.; Figueiredo, M. O.; Silva, T. P.; Michel, E.; Cortijo, E.; Labeyrie, L.; Voelker, A.

2010-05-01

Variations in the interactions between marine ecosystems, thermohaline circulation, external forcing and atmospheric greenhouse gases concentrations are not yet fully represented in detailed models of the glacial-interglacial transitions. Most of the research on past productivity changes has been focused so far on high-productivity areas such as upwelling areas (i.e. equatorial or coastal upwelling areas) even though those regions appraise only a little part of the ocean. Accordingly, the importance of oceanic productivity changes over glacial/interglacial cycles should be better known, as it may also play an important role on the loss of photosynthetically generated carbon as a central mechanism in the global carbon cycle. Its understanding will help quantifying the parameters needed to run comprehensive climate models, and subsequently help to better predict climate change for the near future. A high-resolution study of oceanic productivity, bottom water flow speed, surface and deep-water mass, bottom water ventilation, and terrestrial input changes during two interglacials (Holocene and Marine Isotope Stage [MIS] 5), at an open ocean site approximately 300 km west off Portugal [IMAGES core MD01-2446: 39°03'N, 12°37'W, 3547 m water depth] was conducted within the AMOCINT project (ESF-EUROCORES programme, 06-EuroMARC-FP-008). Even though siliceous productivity is expectedly low for oceanic regions, it shows a robust and consistent pattern with increased values during cold phases of MIS 5, and during the glacial stages 4 and 6 suggesting higher nutrient availability, during these periods. The same pattern is observed for MIS2 and the last deglaciation. The opal record is fully supported by the organic carbon content and to the estimated productivity using foraminifera based FA20 and SIMMAX.28 transfer functions for a near location. The benthic δ13C record suggests less North Atlantic Deep Water (NADW) coincident with periods of higher productivity. The grain-size variations and magnetic properties, suggests stronger/faster bottom currents during cold phases, in agreement with a stronger component of Antarctic sourced Bottom Water (AABW) at the Eastern Atlantic Margin. The probable enhancement of AABW during these periods may also account for a higher preservation of siliceous biogenic particles at the ocean floor sediment/water interface. Given that MD01-2446 is placed far from the continent, productivity records should mainly reflect local conditions. Still, we should not fully discard the preservation of punctual influence of coastal processes derived from upwelling filament plumes at the Estremadura Plateau. Lebreiro et al., 1997 [Paleoceanography, 12, 718-727] reported for a near location, the dominance of pre-upwelling and post-upwelling related foraminifera species during MIS 6 implying less intense or persistent upwelling during MIS 6 than MIS 4. On the contrary, opal and organic carbon data reveals a clear increase in productivity also during MIS 6, reinforcing the idea that productivity variations are likely related to open ocean conditions and therefore, nutrients availability associated to the Atlantic Meridional Oceanic Circulation.

Plants as Indicators of Past and Present Zones of Upwelling Soil CO2 at the ZERT Facility

NASA Astrophysics Data System (ADS)

Apple, M. E.; Sharma, B.; Zhou, X.; Shaw, J. A.; Dobeck, L.; Cunnningham, A.; Spangler, L.; ZERT Team

2011-12-01

By their very nature, photosynthetic plants are sensitive and responsive to CO2, which they fix during the Calvin-Benson cycle. Responses of plants to CO2 are valuable tools in the surface detection of upwelling and leaking CO2 from carbon sequestration fields. Plants exposed to upwelling CO2 rapidly exhibit signs of stress such as changes in stomatal conductance, hyperspectral signatures, pigmentation, and viability (Lakkaraju et al. 2010; Male et al. 2010). The Zero Emission Research and Technology (ZERT) site in Bozeman, MT is an experimental facility for surface detection of CO2 where 0.15 ton/day of CO2 was released (7/19- 8/15/2010, and 7/18 - 8/15/2011) from a 100m horizontal injection well, (HIW), 1.5 m underground with deliberate leaks of CO2 at intervals, and from a vertical injector, (VIW), (6/3-6/24/2010). Soil CO2 concentrations reached 16%. Plants at ZERT include Taraxacum officinale (Dandelion), Dactylis glomerata (Orchard Grass), Poa pratensis, (Kentucky Bluegrass), Phleum pratense (Timothy), Bromus japonicus (Japanese Brome), Medicago sativa (Alfalfa) and Cirsium arvense (Canadian Thistle). Dandelion leaves above the zones of upwelling CO2 at the HIW and the VIW changed color from green to reddish-purple (indicative of an increase in anthocyanins) to brown as they senesced within two weeks of CO2 injection. Their increased stomatal conductance along with their extensive surface area combined to make water loss occur quickly following injection of CO2. Xeromorphic grass leaves were not as profoundly affected, although they did exhibit changes in stomatal conductance, accelerated loss of chlorophyll beyond what would normally occur with seasonal senescence, and altered hyperspectral signatures. Within two weeks of CO2 injection at the HIW and the VIW, hot spots formed, which are circular zones of visible leaf senescence that appear at zones of upwelling CO2. The hot spots became more pronounced as the CO2 injection continued, and were detectable until obscured by snow in the fall and winter. Residual hot spots were visible in the spring after a summer CO2 injection. At both the HIW and the VIW, dandelions were less abundant, if not scarce, in the hot spots when quantified the next year. We mounted a Star-Dot web camera on a scaffold, from which the camera photographs the area each day at noon. The camera remains in place year round and obtains images of the current and residual hot spots, and the growth, color changes, and senescence of the plants. We also quantified percent coverage of plant species along the HIW and the VIW. At the VIW, which received CO2 in 2010 but not in 2011, the site of the 2010 hot spot was detectable in 2011 as a scarcity of dandelion leaves. Therefore, previous, or antecedent, conditions influenced the distribution of species at the VIW and do not depend on continuous injection of CO2. Sudden and long-term shifts in species composition have important ecological implications and may serve as a means of surface detection of upwelling CO2.

Space measurements of tropospheric aerosols

NASA Technical Reports Server (NTRS)

Griggs, M.

1981-01-01

A global-scale ground-truth experiment was conducted in the summer of 1980 with the AVHRR sensor on NOAA-6 to investigate the relationship between the upwelling visible radiance and the aerosol optical thickness over oceans at different sites around the globe. The possibility of using inland bodies of water such as rivers, lakes and reservoirs has been recently investigated using the Landsat MSS7 (approximately 0.9 micron) channel. This upwelling near-infrared radiance is less influenced than the visible radiance by the suspended matter generally found in the inland bodies of water, and by the adjacency effect of the surrounding higher albedo land. It is found that the water turbidity has more influence than the adjacency effect and reduces the effectiveness of the technique for inland observations.

Ore deposits in Africa and their relation to the underlying mantle

NASA Technical Reports Server (NTRS)

Liu, H.-S.

1981-01-01

African magmatism is largely related to the tensional stress regimes of the crust which are induced by the hotter upwelling mantle rocks. These mantle rocks may provide emanating forces and thermal energy for the upward movements of primary ore bodies with fluid inclusions in the tensional stress regimes of the crust. In this paper, the Goddard Earth Gravity Model is used to calculate a detailed subcrustal stress system exerted by mantle convection under Africa. The resulting system is found to be correlated with the African metallogenic provinces. Recognition of the full spectrum of ore deposits in Africa that may be associated with the hotter upwelling mantle rocks has provided an independent evidence to support the hypothesis of mantle-derived heat source for ore deposits.

Eastern Boundary Upwelling Ecosystems: Review and Observing Needs

NASA Astrophysics Data System (ADS)

Chavez, F.; Garçon, V. C.; Dewitte, B.; Montes, I.

2015-12-01

Eastern Boundary Upwelling Systems (EBUS) cover less than 3% of the world ocean surface but play a significant role in the climate system, and contribute disproportionately to ocean biological productivity with up to 40% of the reported global fish catch. Coupled with the vast coastal human populations, these regions play key socio-economic roles. Human pressure on these productive ecosystems and their services is increasing, requiring new and evolving scientific approaches to collect information and use it in management. Here we review and compare the physical, chemical and biological characteristics of the four major EBUS: Benguela, California, Northwest Africa and Peru/Chile. Long-term trends and climate variability are emphasized. Technologies and systems for observing and understanding the changing marine ecosystems of EBUS are discussed.

Hydrogeology of a Danish Riparian Lowland: the Importance of Groundwater Upwelling on Nitrate Removal

NASA Astrophysics Data System (ADS)

Steiness, M.; van't Veen, S. G. W.; Jessen, S.; Engesgaard, P. K.

2016-12-01

Riparian zones are critical interfaces between streams and uplands with many of the characteristics for being key areas for nitrate removal. The hydrogeology is a controlling factor for the source, flow paths, magnitude of groundwater discharge to the stream, nitrate loading, and therefore the occurrence of "hot spots" with increased denitrification. A riparian lowland was investigated through field studies (geophysics, hydrogeology), water quality assessment, and flow and reactive transport modelling. One of the objectives was to understand the role of the landscape and hydrogeology on diffusive versus focused groundwater discharge and also nitrate removal. The investigated riparian zone is characterized by diffusive flow of groundwater to the stream from the northern bank (from a maize field) and groundwater upwelling in several places with overland flow to the stream from south (wetland area). Nitrate is effectively removed by pyrite oxidation (as shown by the reactive transport model high sulphate concentrations) on the northern side, whereas the groundwater-fed springs carry up to 74 mg/L nitrate. Groundwater flow modeling shows that upwelling may account for almost 25 % of the flow to the stream. Two other riparian zones were subsequently included and, on the catchment scale, the occurrence of diffusive and focused discharge is found to be common suggesting that riparian zones in this area are only partly effective in removing nitrate.

Water masses and mesoscale control on latitudinal and cross-shelf variations in larval fish assemblages off NW Africa

NASA Astrophysics Data System (ADS)

Olivar, M. Pilar; Sabatés, Ana; Pastor, Maria V.; Pelegrí, Josep L.

2016-11-01

We explore the associations between larval fish assemblages and oceanographic conditions in the upper ocean (top 200 m) along the African slope, from tropical (15°N) to subtropical (35°N) latitudes, during a period of intense upwelling. In this extensive region, the northward Mauritanian Current and Poleward Undercurrent carry South Atlantic Central Waters (SACW) while the southward Canary Upwelling Current transports North Atlantic Central Waters (NACW). South of Cape Blanc we only find SACW, and north of Cape Blanc there is NACW far offshore and a combination of NACW and SACW nearshore, separated by the Canary Upwelling Front (CUF). The larvae of different myctophid species serve as indicators of the water masses, e.g. S. veranyi and M. punctatum were found in some coastal stations that were dominated by NACW, while the tropical mesopelagic B. argyrogaster, H. macrochir, M. affine and S. kreffti were associated to the SACW. The along-slope offshore convergence of NACW and SACW takes place at the Cape Verde Frontal Zone (CVFZ), representing a region of extensive offshore export for larvae of coastal species, S. pilchardus and E. encrasicolus, far from their nearshore spawning area. The large-scale frontal systems (CVFZ and CUF) and mesoscale eddies contribute to retain larvae within productive waters, influencing both coastal and oceanic species.

Seasonal Synechococcus and Thaumarchaeal population dynamics examined with high resolution with remote in situ instrumentation

PubMed Central

Robidart, Julie C; Preston, Christina M; Paerl, Ryan W; Turk, Kendra A; Mosier, Annika C; Francis, Christopher A; Scholin, Christopher A; Zehr, Jonathan P

2012-01-01

Monterey Bay, CA is an Eastern boundary upwelling system that is nitrogen limited much of the year. In order to resolve population dynamics of microorganisms important for nutrient cycling in this region, we deployed the Environmental Sample Processor with quantitative PCR assays targeting both ribosomal RNA genes and functional genes for subclades of cyanobacteria (Synechococcus) and ammonia-oxidizing Archaea (Thaumarchaeota) populations. Results showed a strong correlation between Thaumarchaea abundances and nitrate during the spring upwelling but not the fall sampling period. In relatively stratified fall waters, the Thaumarchaeota community reached higher numbers than in the spring, and an unexpected positive correlation with chlorophyll concentration was observed. Further, we detected drops in Synechococcus abundance that occurred on short (that is, daily) time scales. Upwelling intensity and blooms of eukaryotic phytoplankton strongly influenced Synechococcus distributions in the spring and fall, revealing what appear to be the environmental limitations of Synechococcus populations in this region. Each of these findings has implications for Monterey Bay biogeochemistry. High-resolution sampling provides a better-resolved framework within which to observe changes in the plankton community. We conclude that controls on these ecosystems change on smaller scales than are routinely assessed, and that more predictable trends will be uncovered if they are evaluated within seasonal (monthly), rather than on annual or interannual scales. PMID:21975596

Seasonal variation of the Beaufort shelfbreak jet and its relationship to Arctic cetacean occurrence

NASA Astrophysics Data System (ADS)

Lin, Peigen; Pickart, Robert S.; Stafford, Kathleen M.; Moore, G. W. K.; Torres, Daniel J.; Bahr, Frank; Hu, Jianyu

2016-12-01

Using mooring time series from September 2008 to August 2012, together with ancillary atmospheric and satellite data sets, we quantify the seasonal variations of the shelfbreak jet in the Alaskan Beaufort Sea and explore connections to the occurrences of bowhead and beluga whales. Wind patterns during the 4 year study period are different from the long-term climatological conditions that the springtime peak in easterly winds shifted from May to June and the autumn peak was limited to October instead of extending farther into the fall. These changes were primarily due to the behavior of the two regional atmospheric centers of action, the Aleutian Low and Beaufort High. The volume transport of the shelfbreak jet, which peaks in the summer, was decomposed into a background (weak wind) component and a wind-driven component. The wind-driven component is correlated to the Pt. Barrow, AK alongcoast wind speed record although a more accurate prediction is obtained when considering the ice thickness at the mooring site. An upwelling index reveals that wind-driven upwelling is enhanced in June and October when storms are stronger and longer-lasting. The seasonal variation of Arctic cetacean occurrence is dominated by the eastward migration in spring, dictated by pack-ice patterns, and westward migration in fall, coincident with the autumn peak in shelfbreak upwelling intensity.

The latitudinal structure of recent changes in the boreal Brewer-Dobson circulation

NASA Astrophysics Data System (ADS)

Shi, C.; Guo, D.; Xu, J.; Powell, A. M., Jr.; Xu, T.

2015-09-01

Upwelling branch of the Brewer-Dobson circulation (BDC) controls the tropical lower stratospheric water vapor (WV) through dynamic cooling near the tropopause. Downwelling branch of BDC dominates the extratropical middle-lower stratospheric Hydrogen Chloride (HCl) by dynamic transport. Climatologically, a symmetric weakening BDC indicates increasing tropical lower stratospheric WV and decreasing extratropical middle-lower stratospheric HCl. However, the global ozone chemistry and related trace gas data records for the stratosphere data (GOZCARDS) show that the tropical lowermost stratospheric WV increased by 18 % decade-1 during 2001-2011 and the boreal mid-latitude lower stratospheric HCl rose 25 % decade-1 after 2006. We interpret this as resulting from a slowdown of the tropical upwelling and a speedup of the mid-latitude downwelling. This interpretation is supported by composite analysis of Eliasen-Palm Flux (EPF), zonal wind and regression of temperature on the EPF from the ERA-Interim data. Results present that the enhancing polar vortex and weakening planetary wave activity leads to a downwelling branch narrowing equatorward and a local speedup of 24 % at 20 hPa in the mid-latitudes. Moreover, there are regressive temperature increase of 1.5 K near the tropical tropopause and that of 0.5 K in the mid-latitude middle stratosphere, which also indicates the tropical upwelling slowdown and the mid-latitude downwelling speedup during 2001-2011.

An Altimetry-Derived Index of the Offshore Forcing on the "Pressure Point" of the West Florida Shelf: Anomalous Upwelling and Its Influence on Harmful Algal Blooms

NASA Astrophysics Data System (ADS)

Liu, Y.; Weisberg, R. H.; Lenes, J. M.; Zheng, L.; Hubbard, K.; Walsh, J. J.

2017-12-01

Gulf of Mexico Loop Current (LC) interactions with the West Florida Shelf (WFS) slope play an important role in shelf ecology through the upwelling of new inorganic nutrients across the shelf break. This is particularly the case when the LC impinges upon the shelf slope in the southwest portion of the WFS near the Dry Tortugas. By contacting shallow water isobaths at this "pressure point" the LC forcing sets the entire shelf into motion. Characteristic patterns of LC interactions with the WFS and their occurrences are identified from altimetry data using unsupervised neural network, self-organizing map. The duration of the occurrences of such LC patterns is used as an indicator of offshore forcing of anomalous upwelling. Consistency is found between the altimetry-derived offshore forcing and the occurrence and severity of WFS coastal blooms of the toxic dinoflagellate, Karenia brevis: years without major blooms tend to have prolonged LC contact at the "pressure point," whereas years with major blooms tend not to have prolonged offshore forcing. Resetting the nutrient state of the shelf by the coastal ocean circulation in response to deep-ocean forcing demonstrates the importance of physical oceanography in shelf ecology. A satellite altimetry-derived seasonal predictor for major K. brevis blooms is also proposed.

Offshore forcing on the "pressure point" of the West Florida Shelf: Anomalous upwelling and its influence on harmful algal blooms

NASA Astrophysics Data System (ADS)

Liu, Yonggang; Weisberg, Robert H.; Lenes, Jason M.; Zheng, Lianyuan; Hubbard, Katherine; Walsh, John J.

2016-08-01

Gulf of Mexico Loop Current (LC) interactions with the West Florida Shelf (WFS) slope play an important role in shelf ecology through the upwelling of new inorganic nutrients across the shelf break. This is particularly the case when the LC impinges upon the shelf slope in the southwest portion of the WFS near the Dry Tortugas. By contacting shallow water isobaths at this "pressure point" the LC forcing sets the entire shelf into motion. Characteristic patterns of LC interactions with the WFS and their occurrences are identified using unsupervised neural network, self-organizing map, from 23 years (1993-2015) of altimetry data. The duration of the occurrences of such LC patterns is used as an indicator of offshore forcing of anomalous upwelling. Consistency is found between the altimetry-derived offshore forcing and the occurrence and severity of WFS coastal blooms of the toxic dinoflagellate, Karenia brevis: years without major blooms tend to have prolonged LC contact at the "pressure point," whereas years with major blooms tend not to have prolonged offshore forcing. Resetting the nutrient state of the shelf by the coastal ocean circulation in response to deep-ocean forcing demonstrates the importance of physical oceanography in shelf ecology. A satellite altimetry-derived seasonal predictor for major K. brevis blooms is also proposed.

Joint effect of freshwater plume and coastal upwelling on phytoplankton growth off the Changjiang River

NASA Astrophysics Data System (ADS)

Tseng, Y.-F.; Lin, J.; Dai, M.; Kao, S.-J.

2013-06-01

Changjiang River discharges vast amount of unbalanced nutrients (dissolved inorganic nitrogen (N) and phosphorus (P) with N / P > 80 in general) into the East China Sea during summertime. To explore nutrient dynamics and P stress potential for phytoplankton, a cruise was conducted in the Changjiang plume during summer 2011. With 3-D observations of nutrients, chlorophyll a (Chl a), and bulk alkaline phosphatase activity (APA), we concluded that the Changjiang Diluted Water (CDW) and coastal upwelling significantly influenced the horizontal and vertical heterogeneities of phytoplankton P-deficiency in the plume. Allochthonous APA was detected at nutrient-enriched freshwater end. Excessive N (~10 to 112 µM) was obserevd throughout the entire plume surface. In the plume fringe where featured by stratification and excess N, diapycnal phosphate supply was blocked to stimulate APA for phytoplankton growth. We observed upwelling outcrops just attaching the turbidity front at seaward side, where Chl a peaked yet much less APA was detected. An external phosphate supply from subsurface, which stimulated phytoplankton growth but inhibited APA, was suggested and the supply was likely sourced from the Nearshore Kuroshio Branch Current. In such hydrographically complicated Changjiang plume, phosphate supply instead of its concentration was more important determining the expression of APA. Meanwhile, allochthounous APA may also alter the usefulness of APA as a P-stress indicator.

Joint effect of freshwater plume and coastal upwelling on phytoplankton growth off the Changjiang River

NASA Astrophysics Data System (ADS)

Tseng, Y.-F.; Lin, J.; Dai, M.; Kao, S.-J.

2014-01-01

The Changjiang (Yangtze) River discharges vast amount of unbalanced nutrients (dissolved inorganic nitrogen and phosphorus with N / P ratio > 80 in general) into the East China Sea in summer. To study nutrient dynamics and P-stress potential for phytoplankton, a cruise was conducted in the Changjiang plume during summer 2011. With 3-D observations of nutrients, chlorophyll a (Chl a), and bulk alkaline phosphatase activity (APA), we concluded that the Changjiang Diluted Water and coastal upwelling significantly influenced the horizontal and vertical heterogeneities of phytoplankton P deficiency in the Changjiang plume. Allochthonous APA was detected at nutrient-enriched freshwater end. Excessive N (~ 10 to 112 μM) was observed throughout the entire plume surface. In the plume fringe featuring stratification and excess N, diapycnal phosphate supply was blocked and phytoplankton APA was stimulated for growth. We observed an upwelling just attaching to the turbidity front at seaward side where Chl a peaked yet much less APA was detected. An external phosphate supply from subsurface, which promoted phytoplankton growth but inhibited APA, was suggested to be sourced from the Nearshore Kuroshio Branch Current. In the so hydrographically complicated Changjiang plume, phosphate supply instead of its concentration may be more important in determining the expression of APA. Meanwhile, allochthonous APA may also alter the usefulness of APA as a P-stress indicator.

Marine radiocarbon reservoir age variation in Donax obesulus shells from northern Peru: late Holocene evidence for extended El Niño

USGS Publications Warehouse

Etayo-Cadavid, Miguel F.; Andrus, C. Fred T.; Jones, Kevin B.; Hodgins, Gregory W. L.; Sandweiss, Daniel H.; Uceda-Castillo, Sandiago; Quilter, Jeffrey

2013-01-01

For at least 6 m.y., El Niño events have posed the greatest environmental risk on the Peruvian coast. A better understanding of El Niño is essential for predicting future risk and growth in this tropical desert. To achieve this we analyzed archaeological and modern pre-bomb shells from the surf clam Donax for the radiocarbon reservoir effect (ΔR) to characterize late Holocene coastal upwelling conditions in northern Peru (8°14′S). Mean ΔR values from these shells suggest that modern upwelling conditions in this region were likely established between A.D. 539 and A.D. 1578. Our radiocarbon data suggest that upwelling conditions ca. A.D. 539 were less intense than those in modern times. The observed coastal water enrichment in 14C may be consequence of frequent strong El Niño events or extended El Niño–like conditions. These ΔR-inferred marine conditions are in agreement with proposed extended El Niño activity in proxy and archaeological records of ca. A.D. 475–530. Extended El Niño conditions have been linked to political destabilization, societal transformation, and collapse of the Moche civilization in northern Peru. A return to such conditions would have significant impacts on the dense population of this region today and in the near future.

Ocean Drilling Program Leg 112, Peru continental margin: Part 2, Sedimentary history and diagenesis in a coastal upwelling environment

NASA Astrophysics Data System (ADS)

Suess, E.; von Huene, R.

1988-10-01

On the shelf and upper slope off Peru the signal of coastal upwelling productivity and bottom-water oxygen is well preserved in alternately laminated and bioturbated diatomaceous Quaternary sediments. Global sea-level fluctuations are the ultimate cause for these cyclic facies changes. During late Miocene time, coastal upwelling was about 100 km west of the present centers, along the edge of an emergent structure that subsequently subsided to form the modern slope. The sediments are rich in organic carbon, and intense microbially mediated decomposition of organic matter is evident in sulfate reduction and methanogenesis. These processes are accompanied by the formation of diagenetic carbonates, mostly Ca-rich dolomites and Mg-calcites. The downhole isotopic signatures of these carbonate cements display distinct successions that reflect the vertical evolution of the pore fluid environment. From the association of methane gas hydrates, burial depth, and low-chloride interstitial fluids, we suggest an additional process that could contribute to the characteristic chloride depletion in pore fluids of active margins: release of interlayer water from clays without a mineral phase change. The shelf sediments also contain a subsurface brine that stretches for more than 500 km from north to south over the area drilled. The source of the brine remains uncertain, although the composition of the oxygen isotopes suggests dissolution of evaporites by seawater.

Seasonal fluctuations of ichthyoplankton assemblage in the northeastern South China Sea influenced by the Kuroshio intrusion

NASA Astrophysics Data System (ADS)

Huang, Delian; Zhang, Xia; Jiang, Zhijian; Zhang, Jingping; Arbi, Iman; Jiang, Xin; Huang, Xiaoping; Zhang, Wenjing

2017-09-01

The distribution and assemblage of ichthyoplankton related to local hydrographic features, especially intrusion of the Kuroshio Current (KC) and Guangdong Coastal Current (GCC) in the northeastern South China Sea (NESCS) were investigated in this study. A total of 193 species of ichthyoplankton belonging to 141 genera and 66 families were recognized in summer 2015 and late-winter 2016. The ichthyoplankton assemblage was identified with distinct seasonal differences, and the differences were responded well with the oceanography conditions. In summer, the assemblages were identified into offshore and inshore groups, as controlled by the South China Sea Warm Current (SCSWC) in off-shelf, upwelling, and the diluted water from the Pearl River in inshore. In winter, three groups were divided, representing the southwestern inshore, intrusion of the KC in the eastern offshore, and the GCC in the northern inshore area, respectively. Furthermore, Sigmops gracilis and Vinciguerria sp.3 were probably brought into the NESCS by intrusion of the KC from the eastern Luzon Strait. In addition, high ichthyoplankton abundance was found in high chlorophyll a located in upwelling areas in the northern coastal area in summer and in the southwestern Taiwan Bank in winter, respectively. The nutrition outcropped by the upwelling together, and those brought from the Pearl River probably supported high food availability of the ichthyoplankton in the northern coast of the NESCS.

Connecting pigment composition and dissolved trace elements to phytoplankton population in the southern Benguela Upwelling zone (St. Helena Bay)

NASA Astrophysics Data System (ADS)

Das, Supriyo Kumar; Routh, Joyanto; Roychoudhury, Alakendra N.; Veldhuis, Marcel J. W.; Ismail, Hassan E.

2017-12-01

Rich in upwelled nutrients, the Southern Benguela is one of the most productive ecosystems in the world ocean. However, despite its ecological significance the role of trace elements influencing phytoplankton population in the Southern Benguela Upwelling System (SBUS) has not been thoroughly investigated. Here, we report pigment composition, macronutrients (nitrate, phosphate and silicate) and concentrations of dissolved Cd, Co, Fe and Zn during late austral summer and winter seasons in 2004 to understand the relationship between the selected trace elements and phytoplankton biomass in St. Helena Bay (SHB), which falls within the southern boundary of the SBUS. Chlorophyll a concentrations indicate higher phytoplankton biomass associated with high primary production during late summer in SHB where high diatom population is inferred from the presence of fucoxanthin. Diminished phytoplankton biomass and a shift from diatoms to dinoflagellates as the dominant phytoplankton taxa are indicated by diagnostic pigments during late winter. Dissolved trace elements (Cd, Co and Zn) and macronutrients play a significant role in phytoplankton biomass, and their distribution is affected by biological uptake and export of trace elements. Continuous uptake of Zn by diatoms may cause an onset of Zn depletion leading to a period of extended diatom proliferation during late summer. Furthermore, the transition from diatom to dinoflagellate dominated phytoplankton population is most likely facilitated by depletion of trace elements (Cd and Co) in the water column.

Stability of active mantle upwelling revealed by net characteristics of plate tectonics.

PubMed

Conrad, Clinton P; Steinberger, Bernhard; Torsvik, Trond H

2013-06-27

Viscous convection within the mantle is linked to tectonic plate motions and deforms Earth's surface across wide areas. Such close links between surface geology and deep mantle dynamics presumably operated throughout Earth's history, but are difficult to investigate for past times because the history of mantle flow is poorly known. Here we show that the time dependence of global-scale mantle flow can be deduced from the net behaviour of surface plate motions. In particular, we tracked the geographic locations of net convergence and divergence for harmonic degrees 1 and 2 by computing the dipole and quadrupole moments of plate motions from tectonic reconstructions extended back to the early Mesozoic era. For present-day plate motions, we find dipole convergence in eastern Asia and quadrupole divergence in both central Africa and the central Pacific. These orientations are nearly identical to the dipole and quadrupole orientations of underlying mantle flow, which indicates that these 'net characteristics' of plate motions reveal deeper flow patterns. The positions of quadrupole divergence have not moved significantly during the past 250 million years, which suggests long-term stability of mantle upwelling beneath Africa and the Pacific Ocean. These upwelling locations are positioned above two compositionally and seismologically distinct regions of the lowermost mantle, which may organize global mantle flow as they remain stationary over geologic time.

Submesoscale CO2 variability across an upwelling front off Peru

NASA Astrophysics Data System (ADS)

Köhn, Eike E.; Thomsen, Sören; Arévalo-Martínez, Damian L.; Kanzow, Torsten

2017-12-01

As a major source for atmospheric CO2, the Peruvian upwelling region exhibits strong variability in surface fCO2 on short spatial and temporal scales. Understanding the physical processes driving the strong variability is of fundamental importance for constraining the effect of marine emissions from upwelling regions on the global CO2 budget. In this study, a frontal decay on length scales of 𝒪(10 km) was observed off the Peruvian coast following a pronounced decrease in down-frontal (equatorward) wind speed with a time lag of 9 h. Simultaneously, the sea-to-air flux of CO2 on the inshore (cold) side of the front dropped from up to 80 to 10 mmol m-2 day-1, while the offshore (warm) side of the front was constantly outgassing at a rate of 10-20 mmol m-2 day-1. Based on repeated ship transects the decay of the front was observed to occur in two phases. The first phase was characterized by a development of coherent surface temperature anomalies which gained in amplitude over 6-9 h. The second phase was characterized by a disappearance of the surface temperature front within 6 h. Submesoscale mixed-layer instabilities were present but seem too slow to completely remove the temperature gradient in this short time period. Dynamics such as a pressure-driven gravity current appear to be a likely mechanism behind the evolution of the front.

Patterns and processes in the California Current System

NASA Astrophysics Data System (ADS)

Checkley, David M., Jr.; Barth, John A.

2009-12-01

The California Current System (CCS) is forced by the distribution of atmospheric pressure and associated winds in relation to the west coast of North America. In this paper, we begin with a simplified case of winds and a linear coast, then consider variability characteristic of the CCS, and conclude by considering future change. The CCS extends from the North Pacific Current (∼50°N) to off Baja California, Mexico (∼15-25°N) with a major discontinuity at Point Conception (34.5°N). Variation in atmospheric pressure affects winds and thus upwelling. Coastal, wind-driven upwelling results in nutrification and biological production and a southward coastal jet. Offshore, curl-driven upwelling results in a spatially large, productive habitat. The California Current flows equatorward and derives from the North Pacific Current and the coastal jet. Dominant modes of spatial and temporal variability in physical processes and biological responses are discussed. High surface production results in deep and bottom waters depleted in oxygen and enriched in carbon dioxide. Fishing has depleted demersal stocks more than pelagic stocks, and marine mammals, including whales, are recovering. Krill, squid, and micronekton are poorly known and merit study. Future climate change will differ from past change and thus prediction of the CCS requires an understanding of its dynamics. Of particular concern are changes in winds, stratification, and ocean chemistry.

Modelling the upwelling offthe east Hainan Island coast in summer 2010

NASA Astrophysics Data System (ADS)

Bai, Peng; Gu, Yanzhen; Li, Peiliang; Wu, Kejian

2016-11-01

A synoptic-scale upwelling event that developed offthe east coast of the Hainan Island (EHIU) in the summer of 2010 is defined well via processing the Moderate Resolution Imaging Spectroradiometer (MODIS) sea surface temperature (SST) data. The Regional Ocean Modeling System (ROMS) with high spatial resolution has been used to investigate this upwelling event. By comparing the ROMS results against tide station data, Argo float profiles and MODIS SST, it is confirmed that the ROMS reproduces the EHIU well. The cooler-water core (CWC) distinguished by waters < 27.5°C in the EHIU, which occurred in the east Qiongzhou Strait mouth area and was bounded by a high temperature gradient, was the focus of this paper. Vertical structure of the CWC suggests that interaction between the westward flow and the bathymetry slope played a significant role in the formation of CWC. Numerical experiments indicated that the westward flow in the Qiongzhou Strait was the result of tidal rectification over variable topography (Shi et al., 2002), thus tides played a critical role on the development of the CWC. The negative wind stress curl that dominated the east Qiongzhou Strait mouth area suppressed the intensity of the CWC by 0.2-0.4°C. Further, nonlinear interaction between tidal currents and wind stress enhanced vertical mixing greatly, which would benefit the development of the CWC.

Metagenomic Analysis of Upwelling-Affected Brazilian Coastal Seawater Reveals Sequence Domains of Type I PKS and Modular NRPS

PubMed Central

Cuadrat, Rafael R. C.; Cury, Juliano C.; Dávila, Alberto M. R.

2015-01-01

Marine environments harbor a wide range of microorganisms from the three domains of life. These microorganisms have great potential to enable discovery of new enzymes and bioactive compounds for industrial use. However, only ~1% of microorganisms from the environment can currently be identified through cultured isolates, limiting the discovery of new compounds. To overcome this limitation, a metagenomics approach has been widely adopted for biodiversity studies on samples from marine environments. In this study, we screened metagenomes in order to estimate the potential for new natural compound synthesis mediated by diversity in the Polyketide Synthase (PKS) and Nonribosomal Peptide Synthetase (NRPS) genes. The samples were collected from the Praia dos Anjos (Angel’s Beach) surface water—Arraial do Cabo (Rio de Janeiro state, Brazil), an environment affected by upwelling. In order to evaluate the potential for screening natural products in Arraial do Cabo samples, we used KS (keto-synthase) and C (condensation) domains (from PKS and NRPS, respectively) to build Hidden Markov Models (HMM) models. From both samples, a total of 84 KS and 46 C novel domain sequences were obtained, showing the potential of this environment for the discovery of new genes of biotechnological interest. These domains were classified by phylogenetic analysis and this was the first study conducted to screen PKS and NRPS genes in an upwelling affected sample PMID:26633360

Longitudinal biases in the Seychelles Dome simulated by 35 ocean-atmosphere coupled general circulation models

NASA Astrophysics Data System (ADS)

Nagura, Motoki; Sasaki, Wataru; Tozuka, Tomoki; Luo, Jing-Jia; Behera, Swadhin K.; Yamagata, Toshio

2013-02-01

Seychelles Dome refers to the shallow climatological thermocline in the southwestern Indian Ocean, where ocean wave dynamics efficiently affect sea surface temperature, allowing sea surface temperature anomalies to be predicted up to 1-2 years in advance. Accurate reproduction of the dome by ocean-atmosphere coupled general circulation models (CGCMs) is essential for successful seasonal predictions in the Indian Ocean. This study examines the Seychelles Dome as simulated by 35 CGCMs, including models used in phase five of the Coupled Model Intercomparison Project (CMIP5). Among the 35 CGCMs, 14 models erroneously produce an upwelling dome in the eastern half of the basin whereas the observed Seychelles Dome is located in the southwestern tropical Indian Ocean. The annual mean Ekman pumping velocity in these models is found to be almost zero in the southern off-equatorial region. This result is inconsistent with observations, in which Ekman upwelling acts as the main cause of the Seychelles Dome. In the models reproducing an eastward-displaced dome, easterly biases are prominent along the equator in boreal summer and fall, which result in shallow thermocline biases along the Java and Sumatra coasts via Kelvin wave dynamics and a spurious upwelling dome in the region. Compared to the CMIP3 models, the CMIP5 models are even worse in simulating the dome longitudes.

Community response of zooplankton to oceanographic changes (2002-2012) in the central/southern upwelling system of Chile

NASA Astrophysics Data System (ADS)

Medellín-Mora, Johanna; Escribano, Ruben; Schneider, Wolfgang

2016-03-01

A 10-year time series (2002-2012) at Station 18 off central/southern Chile allowed us to study variations in zooplankton along with interannual variability and trends in oceanographic conditions. We used an automated analysis program (ZooImage) to assess changes in the mesozooplankton size structure and the composition of the taxa throughout the entire community. Oceanographic conditions changed over the decade: the water column became less stratified, more saline, and colder; the mixed layer deepened; and the oxygen minimum zone became shallower during the second half of the time series (2008-2012) in comparison with the first period (2002-2007). Both the size structure and composition of the zooplankton were significantly associated with oceanographic changes. Taxonomic and size diversity of the zooplankton community increased to the more recent period. For the second period, small sized copepods (<1 mm) decreased in abundance, being replaced by larger sized (>1.5 mm) and medium size copepods (1-1.5 mm), whereas euphausiids, decapod larvae, appendicularian and ostracods increased their abundance during the second period. These findings indicated that the zooplankton community structure in this eastern boundary ecosystem was strongly influenced by variability of the upwelling process. Thus, climate-induced forcing of upwelling trends can alter the zooplankton community in this highly productive region with potential consequences for the ecosystem food web.

Phytoplankton production and taxon-specific growth rates in the Costa Rica Dome

PubMed Central

Selph, Karen E.; Landry, Michael R.; Taylor, Andrew G.; Gutiérrez-Rodríguez, Andrés; Stukel, Michael R.; Wokuluk, John; Pasulka, Alexis

2016-01-01

During summer 2010, we investigated phytoplankton production and growth rates at 19 stations in the eastern tropical Pacific, where winds and strong opposing currents generate the Costa Rica Dome (CRD), an open-ocean upwelling feature. Primary production (14C-incorporation) and group-specific growth and net growth rates (two-treatment seawater dilution method) were estimated from samples incubated in situ at eight depths. Our cruise coincided with a mild El Niño event, and only weak upwelling was observed in the CRD. Nevertheless, the highest phytoplankton abundances were found near the dome center. However, mixed-layer growth rates were lowest in the dome center (∼0.5–0.9 day−1), but higher on the edge of the dome (∼0.9–1.0 day−1) and in adjacent coastal waters (0.9–1.3 day−1). We found good agreement between independent methods to estimate growth rates. Mixed-layer growth rates of Prochlorococcus and Synechococcus were largely balanced by mortality, whereas eukaryotic phytoplankton showed positive net growth (∼0.5–0.6 day−1), that is, growth available to support larger (mesozooplankton) consumer biomass. These are the first group-specific phytoplankton rate estimates in this region, and they demonstrate that integrated primary production is high, exceeding 1 g C m−2 day−1 on average, even during a period of reduced upwelling. PMID:27275025

Phytoplankton production and taxon-specific growth rates in the Costa Rica Dome.

PubMed

Selph, Karen E; Landry, Michael R; Taylor, Andrew G; Gutiérrez-Rodríguez, Andrés; Stukel, Michael R; Wokuluk, John; Pasulka, Alexis

2016-03-01

During summer 2010, we investigated phytoplankton production and growth rates at 19 stations in the eastern tropical Pacific, where winds and strong opposing currents generate the Costa Rica Dome (CRD), an open-ocean upwelling feature. Primary production ( 14 C-incorporation) and group-specific growth and net growth rates (two-treatment seawater dilution method) were estimated from samples incubated in situ at eight depths. Our cruise coincided with a mild El Niño event, and only weak upwelling was observed in the CRD. Nevertheless, the highest phytoplankton abundances were found near the dome center. However, mixed-layer growth rates were lowest in the dome center (∼0.5-0.9 day -1 ), but higher on the edge of the dome (∼0.9-1.0 day -1 ) and in adjacent coastal waters (0.9-1.3 day -1 ). We found good agreement between independent methods to estimate growth rates. Mixed-layer growth rates of Prochlorococcus and Synechococcus were largely balanced by mortality, whereas eukaryotic phytoplankton showed positive net growth (∼0.5-0.6 day -1 ), that is, growth available to support larger (mesozooplankton) consumer biomass. These are the first group-specific phytoplankton rate estimates in this region, and they demonstrate that integrated primary production is high, exceeding 1 g C m -2 day -1 on average, even during a period of reduced upwelling.

FIRE_ACE_C130_RAMS

Atmospheric Science Data Center

2017-04-26

... NCAR C-130 Instrument:  Radiation Measurement System Spatial Coverage:  Fairbanks, Alaska and the ... Parameters:  Upwelling and Downwelling Total Solar Flux Infrared Flux and Narrowband Flux Order Data:  ...

Laboratory measurements of radiance and reflectance spectra of dilute primary-treated sewage sludge

NASA Technical Reports Server (NTRS)

Usry, J. W.; Witte, W. G.; Whitlock, C. H.; Gurganus, E. A.

1977-01-01

The feasibility of remotely monitoring ocean dumping of waste products such as acid and sewage sludge is evaluated. The laboratory arrangement, solar simulator, and test results from three experiments conducted in the laboratory are described. Radiance and reflectance spectra are presented for primary-treated sewage sludge mixed with two types of base water. Results indicate that upwelled reflectance varies in a near-linear manner with concentration and that the sludge has a practically flat signal response between 420 and 970 nm. Well-defined upwelled reflectance spectra were obtained for the sewage-sludge mixtures at all wavelengths and concentrations. The spectral-reflectance values appeared to be influenced by the type of base water, but this influence was small, especially for the mixtures with low concentrations of sewage sludge.

On the deep-mantle origin of the Deccan Traps

NASA Astrophysics Data System (ADS)

Glišović, Petar; Forte, Alessandro M.

2017-02-01

The Deccan Traps in west-central India constitute one of Earth’s largest continental flood basalt provinces, whose eruption played a role in the Cretaceous-Paleogene extinction event. The unknown mantle structure under the Indian Ocean at the start of the Cenozoic presents a challenge for connecting the event to a deep mantle origin. We used a back-and-forth iterative method for time-reversed convection modeling, which incorporates tomography-based, present-day mantle heterogeneity to reconstruct mantle structure at the start of the Cenozoic. We show a very low-density, deep-seated upwelling that ascends beneath the Réunion hot spot at the time of the Deccan eruptions. We found a second active upwelling below the Comores hot spot that likely contributed to the region of partial melt feeding the massive eruption.

The phenomenon of bloom development of the invasive potentially toxic dinoflagellate Gonyaulax polygramma in deep water areas of the Caspian Sea

NASA Astrophysics Data System (ADS)

Pautova, L. A.; Kravchishina, M. D.; Silkin, V. A.; Lisitzin, A. P.

2017-06-01

This work presents the first data on the occurrence of the invasive, potentially toxic dinoflagellate Gonyaulax polygramma in the composition of plankton phytocenoses in the Caspian Sea. It was revealed that G. polygramma plays the key role in the quantitative characteristics of summer plankton phytocenoses and its bloom during the summer seasons of 2010 and 2013 was comparable in biomass (15-16 g/m3) to a "red tide." In addition, the correlation between the G. polygramma bloom and the wind upwelling system in the eastern mid-Caspian region was established. For the first time, it is suggested that "bloom" of G. polygramma can also occur in deep-water halistatic areas (Derbent depression), remote from the upwelling system.

Method to analyze remotely sensed spectral data

DOEpatents

Stork, Christopher L [Albuquerque, NM; Van Benthem, Mark H [Middletown, DE

2009-02-17

A fast and rigorous multivariate curve resolution (MCR) algorithm is applied to remotely sensed spectral data. The algorithm is applicable in the solar-reflective spectral region, comprising the visible to the shortwave infrared (ranging from approximately 0.4 to 2.5 .mu.m), midwave infrared, and thermal emission spectral region, comprising the thermal infrared (ranging from approximately 8 to 15 .mu.m). For example, employing minimal a priori knowledge, notably non-negativity constraints on the extracted endmember profiles and a constant abundance constraint for the atmospheric upwelling component, MCR can be used to successfully compensate thermal infrared hyperspectral images for atmospheric upwelling and, thereby, transmittance effects. Further, MCR can accurately estimate the relative spectral absorption coefficients and thermal contrast distribution of a gas plume component near the minimum detectable quantity.

A note on specific variability of long surface gravity waves and drag coefficient in coastal upwelling zone

NASA Astrophysics Data System (ADS)

Krzyścin, Janusz

1990-01-01

In this paper we solve analytically wave kinematic equations and the wave energy transport equation, for basic long surface gravity wave in the coastal upwelling zone. Using Gent and Taylor's (1978) parameterization of drag coefficient (which includes interaction between long surface waves and the air flow) we find variability of this coefficient due to wave amplification and refraction caused by specific surface water current in the region. The drag coefficient grows towards the shore. The growth is faster for stronger current. When the angle between waves and the current is less than 90° the growth is mainly connected with the waves steepness, but when the angle is larger, it is caused by relative growth of the wave phase velocity.

Upwellings mitigated Plio-Pleistocene heat stress for reef corals on the Florida platform (USA)

NASA Astrophysics Data System (ADS)

Brachert, Thomas C.; Reuter, Markus; Krüger, Stefan; Kirkerowicz, Julia; Klaus, James S.

2016-03-01

The fast growing calcareous skeletons of zooxanthellate reef corals (z corals) represent unique environmental proxy archives through their oxygen and carbon stable isotope composition (δ18O, δ13C). In addition, the accretion of the skeleton itself is ultimately linked to the environment and responds with variable growth rates (extension rate) and density to environmental changes. Here we present classical proxy data (δ18O, δ13C) in combination with calcification records from 15 massive z corals. The z corals were sampled from four interglacial units of the Florida carbonate platform (USA) dated approximately 3.2, 2.9, 1.8 and 1.2 Ma (middle Pliocene to early Pleistocene). The z corals (Solenastrea, Orbicella, Porites) derive from unlithified shallow marine carbonates and were carefully screened for primary preservation suited for proxy analysis. We show that skeletal accretion responded with decreasing overall calcification rates (decreasing extension rate but increasing density) to warmer water temperatures. Under high annual water temperatures, inferred from sub-annually resolved δ18O data, skeletal bulk density was high, but extension rates and overall calcification rates were at a minimum (endmember scenario 1). Maximum skeletal density was reached during the summer season giving rise to a growth band of high density within the annually banded skeletons ("high density band", HDB). With low mean annual water temperatures (endmember scenario 2), bulk skeletal density was low but extension rates and calcification rates reached a maximum, and under these conditions the HDB formed during winter. Although surface water temperatures in the Western Atlantic warm pool during the interglacials of the late Neogene were ˜ 2 °C higher than they are in the present day, intermittent upwelling of cool, nutrient-rich water mitigated water temperatures off south-western Florida and created temporary refuges for z coral growth. Based on the sub-annually resolved δ18O and δ13C records, the duration of the upwelling episodes causing the endmember 2 conditions was variable and lasted from a few years to a number of decades. The episodes of upwelling were interrupted by phases without upwelling (endmember 1) which lasted for at least a few years and led to high surface water temperatures. This variable environment is likely one of the reasons why the coral fauna is dominated by the eurytopic genus Solenastrea, also a genus resistant to high turbidity. Over a period of ˜ 50 years, the oldest sub annually resolved proxy record available (3.2 Ma) documents a persistent occurrence of the HDB during winter. In contrast, the HDB forms in summer in modern z corals from the Florida reef tract. We suggest this difference should be tested as being the expression of a tendency towards decreasing interglacial upwelling since the middle Pliocene. The number of z coral sclerochronological records for the Plio-Pleistocene is still rather low, however, and requires more data and an improved resolution, through records from additional time slices. Nonetheless, our calcification data from the warm periods of past interglacials may contribute to predicting the effects of future ocean warming on z coral health along the Florida reef tract. The inconsistent timing of the HDB within single coral records or among specimens and time slices is unexpected and contrasts the common practice of establishing chronologies on the basis of the density banding.

Melt migration modeling in partially molten upper mantle

NASA Astrophysics Data System (ADS)

Ghods, Abdolreza

The objective of this thesis is to investigate the importance of melt migration in shaping major characteristics of geological features associated with the partial melting of the upper mantle, such as sea-floor spreading, continental flood basalts and rifting. The partial melting produces permeable partially molten rocks and a buoyant low viscosity melt. Melt migrates through the partially molten rocks, and transfers mass and heat. Due to its much faster velocity and appreciable buoyancy, melt migration has the potential to modify dynamics of the upwelling partially molten plumes. I develop a 2-D, two-phase flow model and apply it to investigate effects of melt migration on the dynamics and melt generation of upwelling mantle plumes and focusing of melt migration beneath mid-ocean ridges. Melt migration changes distribution of the melt-retention buoyancy force and therefore affects the dynamics of the upwelling plume. This is investigated by modeling a plume with a constant initial melt of 10% where no further melting is considered. Melt migration polarizes melt-retention buoyancy force into high and low melt fraction regions at the top and bottom portions of the plume and therefore results in formation of a more slender and faster upwelling plume. Allowing the plume to melt as it ascends through the upper mantle also produces a slender and faster plume. It is shown that melt produced by decompressional melting of the plume migrates to the upper horizons of the plume, increases the upwelling velocity and thus, the volume of melt generated by the plume. Melt migration produces a plume which lacks the mushroom shape observed for the plume models without melt migration. Melt migration forms a high melt fraction layer beneath the sloping base of the impermeable oceanic lithosphere. Using realistic conditions of melting, freezing and melt extraction, I examine whether the high melt fraction layer is able to focus melt from a wide partial melting zone to a narrow region beneath the observed neo-volcanic zone. My models consist of three parts; lithosphere, asthenosphere and a melt extraction region. It is shown that melt migrates vertically within the asthenosphere, and forms a high melt fraction layer beneath the sloping base of the impermeable lithosphere. Within the sloping high melt fraction layer, melt migrates laterally towards the ridge. In order to simulate melt migration via crustal fractures and cracks, melt is extracted from a melt extraction region extending to the base of the crust. Performance of the melt focusing mechanism is not significantly sensitive to the size of melt extraction region, melt extraction threshold and spreading rate. In all of the models, about half of the total melt production freezes beneath the cooling base of the lithosphere, and the rest is effectively focused towards the ridge and forms the crust. To meet the computational demand for a precise tracing of the deforming upwelling plume and including the chemical buoyancy of the partially molten zone in my models, a new numerical method is developed to solve the related pure advection equations. The numerical method is based on Second Moment numerical method of Egan and Mahoney [1972] which is improved to maintain a high numerical accuracy in shear and rotational flow fields. In comparison with previous numerical methods, my numerical method is a cost-effective, non-diffusive and shape preserving method, and it can also be used to trace a deforming body in compressible flow fields.

Double Mantle Plume Upwelling—A Possible Formation Mechanism of Beta Plateau and Devana Chasma,Venus

NASA Astrophysics Data System (ADS)

Ding, N.

2009-12-01

Ning Ding,Zuoxun Zeng,China University of Geosciences,Wuhan,430074,China NingDing.eagle@gmail.com Introduction:Venus represents a‘one plate planet’[1],and the uplift,fractures and volcanism in Beta Regio on Venus are considered to be formed by lithosphere uplift driven by a hot plume[2]. Based on the double peaking saddle landform,we suggest the tectonic pattern of double mantle plume upwelling to interpret the formation mechanism of Beta Plateau and Devana Chasma.We take a physical modeling to validate this possibility. Model:There is no ductile shear in Venus[3],so we use quartz sands to simulate the crust of Venus.We use two wood stickes 1.5cm in diameter rising from the rubber canvas slowly and straight till about half of the model,then falling down slowly and straight.The base is a hard rubber plate,in the center of which,there are two holes 3cm in diameter,and the distance between them is 5cm.The holes are covered by rubber canvas.We use the quartz sands in colours of white, red and black with particle size of 70 mess as the model materials. Result:Fig.1:At the beginning of the wood stickes upwelling,only fine radial cracks are formed above the upwelling from central to outside.With the upwelling continue,surface energy of the fine radial cracks increase and make the cracks unstable,finally,the fine radial cracks connect each other and form a fracture zone.And then the two mantle plume downwelling,the fracture zone is developed to form a chasma at the end. Fig.2:The four profiles all form reverse faults outside and normal faults inside.But the difference is the faults in the middle of the chasma goes deeper than others.It is the pattern of Beta Plateau where the tectonic rising is cut by Devana Chasma zone in the topographic features. Fig.3:From the tow fig., we can see two points similar:a.the elevation is high and distribution area is large around the area of two upwelling and it is high around the area of chasma,but the distribution area is small;b.both of them shows saddle shape and two highland connectting bya chasma. Discussion:Based on the‘Geology Map of V-17’,two highlands of Northern part of Devana Chasma,but the material Unit of North and South highland are different.The material Units of North highland are the oldest unit tt and t,the material Unit of South highland is pl and the material Unit of rift is r are both the youngest unit.From the Magellan SAR mosaic[5],we can clearly see Devana Chasma cut the material Unit of tt and pl.So the two highlands of Northern part of Devana Chasma are simultaneous formed.The younger material Unit of South highland of Northern part of Devana Chasma is because of the volcanic eruption of Theia Mons. Conclusion:The physical modeling validates the model of the double plume upwelling is a possible explanation. Acknowledgements:This research was supported by the National Teaching Bases For Geology(CUG)foundation funded. References:[1]I.López,Icarus2008[2]A.T.Basilevsky,Icarus2007[3]J.C.Aubele,2009,LPSC[4]A.V.Vezolainen,2003,Journalofgeophysicalres5earch[5]http://planetarynames.wr.usgs.gov/images/v17_comp&v29_comp.pdf Fig.1 Fig.2 Fig.3a,3b

Average Potential Temperature of the Upper Mantle and Excess Temperatures Beneath Regions of Active Upwelling

NASA Astrophysics Data System (ADS)

Putirka, K. D.

2006-05-01

The question as to whether any particular oceanic island is the result of a thermal mantle plume, is a question of whether volcanism is the result of passive upwelling, as at mid-ocean ridges, or active upwelling, driven by thermally buoyant material. When upwelling is passive, mantle temperatures reflect average or ambient upper mantle values. In contrast, sites of thermally driven active upwellings will have elevated (or excess) mantle temperatures, driven by some source of excess heat. Skeptics of the plume hypothesis suggest that the maximum temperatures at ocean islands are similar to maximum temperatures at mid-ocean ridges (Anderson, 2000; Green et al., 2001). Olivine-liquid thermometry, when applied to Hawaii, Iceland, and global MORB, belie this hypothesis. Olivine-liquid equilibria provide the most accurate means of estimating mantle temperatures, which are highly sensitive to the forsterite (Fo) contents of olivines, and the FeO content of coexisting liquids. Their application shows that mantle temperatures in the MORB source region are less than temperatures at both Hawaii and Iceland. The Siqueiros Transform may provide the most precise estimate of TpMORB because high MgO glass compositions there have been affected only by olivine fractionation, so primitive FeOliq is known; olivine thermometry yields TpSiqueiros = 1430 ±59°C. A global database of 22,000 MORB show that most MORB have slightly higher FeOliq than at Siqueiros, which translates to higher calculated mantle potential temperatures. If the values for Fomax (= 91.5) and KD (Fe-Mg)ol-liq (= 0.29) at Siqueiros apply globally, then upper mantle Tp is closer to 1485 ± 59°C. Averaging this global estimate with that recovered at Siqueiros yields TpMORB = 1458 ± 78°C, which is used to calculate plume excess temperatures, Te. The estimate for TpMORB defines the convective mantle geotherm, and is consistent with estimates from sea floor bathymetry and heat flow (Stein and Stein, 1992), and overlap within 1 sigma estimates from phase transitions at the 410 km (Jeanloz and Thompson, 1983) and 670 km (Hirose, 2002) seismic discontinuities. Variations in MORB FeOliq can be used to calculate the variance of TpMORB. FeOliq variations in global MORB show that 95% of the sub-MORB mantle has a T range of 165°C; 68% of MORB fall within temperature variations of ±30°C. In comparison, Te at Hawaii and Iceland are 1706°C and 1646°C respectively, and hence Te> is 248°C at Hawaii and 188°C at Iceland. Tp estimates at Hawaii and Iceland also exceed maximum Tp estimates at MORs (at 95% level) by 171 and 111°C respectively. These Te are in agreement with estimates derived from excess topography and dynamic models of mantle flow and melt generation (e.g., Sleep, 1990, Schilling, 1991, Ito et al., 1999). A clear result is that Hawaii and Iceland are hot relative to MORB. Rayleigh number calculations further show that for these Te, critical depths (i.e., the depths at which Ra > 1000) are < 130 km. Hawaii and Iceland are thus almost assuredly the result of thermally driven, active upwellings, or mantle plumes.

Influence of basin-scale and mesoscale physical processes on biological productivity in the Bay of Bengal during the summer monsoon

NASA Astrophysics Data System (ADS)

Muraleedharan, K. R.; Jasmine, P.; Achuthankutty, C. T.; Revichandran, C.; Dinesh Kumar, P. K.; Anand, P.; Rejomon, G.

2007-03-01

Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July-August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m -3), low surface primary production (2.55 mg C m -3 day -1) and low zooplankton biovolume (0.14 ml m -3). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO 3-N > 8.2 μM, PO 4-P > 0.8 μM, SiO 4-Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a - 0.25 mg m -3, PP - 9.23 mg C m -3 day -1), and mesozooplankton biovolume (1.12 ml m -3) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.

Testing compound-specific δ13C of amino acids in mussels as a new approach to determine the average 13C values of primary production in littoral ecosystems

NASA Astrophysics Data System (ADS)

Vokhshoori, N. L.; Larsen, T.; McCarthy, M.

2012-12-01

Compound-specific isotope analysis of amino acids (CSI-AA) is a technique used to decouple trophic enrichment patterns from source changes at the base of the food web. With this new emerging tool, it is possible to precisely determine both trophic position and δ15N or δ13C source values in higher feeding organisms. While most work to date has focused on nitrogen (N) isotopic values, early work has suggested that δ13C CSI-AA has great potential as a new tracer both to a record δ13C values of primary production (unaltered by trophic transfers), and also to "fingerprint" specific carbon source organisms. Since essential amino acids (EAA) cannot be made de novo in metazoans but must be obtained from diet, the δ13C value of the primary producer is preserved through the food web. Therefore, the δ13C values of EAAs act as a unique signature of different primary producers and can be used to fingerprint the dominant carbon (C) source driving primary production at the base of the food web. In littoral ecosystems, such as the California Upwelling System (CUS), the likely dominant C sources of suspended particulate organic matter (POM) pool are kelp, upwelling phytoplankton or estuarine phytoplankton. While bulk isotopes of C and N are used extensively to resolve relative consumer hierarchy or shifting diet in a food web, we found that the δ13C bulk values in mussels cannot distinguish exact source in littoral ecosystems. Here we show 15 sites within the CUS, between Cape Blanco, OR and La Jolla, CA where mussels were sampled and analyzed for both bulk δ13C and CSI-AA. We found no latitudinal trends, but rather average bulk δ13C values for the entire coastal record were highly consistent (-15.7 ± 0.9‰). The bulk record would suggest either nutrient provisioning from kelp or upwelled phytoplankton, but 13C-AA fingerprinting confines these two sources to upwelling. This suggests that mussels are recording integrated coastal phytoplankton values, with the enriched δ13C values likely linked to nearshore processes in the CA upwelling zone. Overall, these results clearly demonstrate, for the first time, the dual potential of δ13C CSI-AA to simultaneously indicate δ13C values of primary production, as well as to narrow major primary production sources. Our results suggest that, when applied to littoral filter feeders or other bio or paleo-archives, δ13C CSI-AA represents a new tool for reconstructing past perturbations to the marine carbon cycle.

Nitrate removal in deep sediments of a nitrogen-rich river network: A test of a conceptual model

USGS Publications Warehouse

Stelzer, Robert S.; Bartsch, Lynn

2012-01-01

Many estimates of nitrogen removal in streams and watersheds do not include or account for nitrate removal in deep sediments, particularly in gaining streams. We developed and tested a conceptual model for nitrate removal in deep sediments in a nitrogen-rich river network. The model predicts that oxic, nitrate-rich groundwater will become depleted in nitrate as groundwater upwelling through sediments encounters a zone that contains buried particulate organic carbon, which promotes redox conditions favorable for nitrate removal. We tested the model at eight sites in upwelling reaches of lotic ecosystems in the Waupaca River Watershed that varied by three orders of magnitude in groundwater nitrate concentration. We measured denitrification potential in sediment core sections to 30 cm and developed vertical nitrate profiles to a depth of about 1 m with peepers and piezometer nests. Denitrification potential was higher, on average, in shallower core sections. However, core sections deeper than 5 cm accounted for 70%, on average, of the depth-integrated denitrification potential. Denitrification potential increased linearly with groundwater nitrate concentration up to 2 mg NO3-N/L but the relationship broke down at higher concentrations (> 5 mg NO3-N/L), a pattern that suggests nitrate saturation. At most sites groundwater nitrate declined from high concentrations at depth to much lower concentrations prior to discharge into the surface water. The profiles suggested that nitrate removal occurred at sediment depths between 20 and 40 cm. Dissolved oxygen concentrations were much higher in deep sediments than in pore water at 5 cm sediment depth at most locations. The substantial denitrification potential in deep sediments coupled with the declines in nitrate and dissolved oxygen concentrations in upwelling groundwater suggest that our conceptual model for nitrate removal in deep sediments is applicable to this river network. Our results suggest that nitrate removal rates can be high in deep sediments of upwelling stream reaches, which may have implications for efforts to understand and quantify nitrogen transport and removal at larger scales.

Inorganic carbon fluxes on the Mackenzie Shelf of the Beaufort Sea

NASA Astrophysics Data System (ADS)

Mol, Jacoba; Thomas, Helmuth; Myers, Paul G.; Hu, Xianmin; Mucci, Alfonso

2018-02-01

The Mackenzie Shelf in the southeastern Beaufort Sea is a region that has experienced large changes in the past several decades as warming, sea-ice loss, and increased river discharge have altered carbon cycling. Upwelling and downwelling events are common on the shelf, caused by strong, fluctuating along-shore winds, resulting in cross-shelf Ekman transport, and an alternating estuarine and anti-estuarine circulation. Downwelling carries dissolved inorganic carbon (DIC) and other remineralization products off the shelf and into the deep basin for possible long-term storage in the world's oceans. Upwelling carries DIC and nutrient-rich waters from the Pacific-origin upper halocline layer (UHL) onto the shelf. Profiles of DIC and total alkalinity (TA) taken in August and September of 2014 are used to investigate the cycling of carbon on the Mackenzie Shelf. The along-shore transport of water and the cross-shelf transport of DIC are quantified using velocity field output from a simulation of the Arctic and Northern Hemisphere Atlantic (ANHA4) configuration of the Nucleus of European Modelling of the Ocean (NEMO) framework. A strong upwelling event prior to sampling on the Mackenzie Shelf took place, bringing CO2-rich (elevated pCO2) water from the UHL onto the shelf bottom. The maximum on-shelf DIC flux was estimated at 16.9×103 mol C d-1 m-2 during the event. The maximum on-shelf transport of DIC through the upwelling event was found to be 65±15×10-3 Tg C d-1. TA and the oxygen isotope ratio of water (δ18O-H2O) are used to examine water-mass distributions in the study area and to investigate the influence of Pacific Water, Mackenzie River freshwater, and sea-ice melt on carbon dynamics and air-sea fluxes of carbon dioxide (CO2) in the surface mixed layer. Understanding carbon transfer in this seasonally dynamic environment is key to quantify the importance of Arctic shelf regions to the global carbon cycle and provide a basis for understanding how it will respond to the aforementioned climate-induced changes.

Influence of Venus topography on the zonal wind and UV albedo at cloud top level: The role of stationary gravity waves

NASA Astrophysics Data System (ADS)

Bertaux, Jean-Loup; Khatuntsev, I. V.; Hauchecorne, A.; Markiewicz, W. J.; Marcq, E.; Lebonnois, S.; Patsaeva, M.; Turin, A.; Fedorova, A.

2016-06-01

Based on the analysis of UV images (at 365 nm) of Venus cloud top (altitude 67 ± 2 km) collected with Venus Monitoring Camera on board Venus Express (VEX), it is found that the zonal wind speed south of the equator (from 5°S to 15°S) shows a conspicuous variation (from -101 to -83 m/s) with geographic longitude of Venus, correlated with the underlying relief of Aphrodite Terra. We interpret this pattern as the result of stationary gravity waves produced at ground level by the uplift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to the cloud top level, break there, and transfer their momentum to the zonal flow. Such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the Earth by Lindzen (1981) but is not reproduced in the current GCM of Venus atmosphere from LMD. (Laboratoire de Météorologie Dynamique) In the equatorial regions, the UV albedo at 365 nm varies also with longitude. We argue that this variation may be simply explained by the divergence of the horizontal wind field. In the longitude region (from 60° to -10°) where the horizontal wind speed is increasing in magnitude (stretch), it triggers air upwelling which brings the UV absorber at cloud top level and decreases the albedo and vice versa when the wind is decreasing in magnitude (compression). This picture is fully consistent with the classical view of Venus meridional circulation, with upwelling at equator revealed by horizontal air motions away from equator: the longitude effect is only an additional but important modulation of this effect. This interpretation is comforted by a recent map of cloud top H2O, showing that near the equator the lower UV albedo longitude region is correlated with increased H2O. We argue that H2O enhancement is the sign of upwelling, suggesting that the UV absorber is also brought to cloud top by upwelling.

Observed longitude variations of zonal wind, UV albedo and H2O at Venus cloud top level: the role of stationary gravity waves generated by Venus topography

NASA Astrophysics Data System (ADS)

Bertaux, Jean-Loup; Hauchecorne, Alain; khatuntsev, Igor; Markiewicz, Wojciech; Marcq, emmanuel; Lebonnois, Sebastien; Patsaeva, Marina; Turin, Alexander; Fedorova, Anna

2016-10-01

Based on the analysis of UV images (at 365 nm) of Venus cloud top (altitude 67±2 km) collected with VMC (Venus Monitoring Camera) on board Venus Express (VEX), it is found that the zonal wind speed south of the equator (from 5°S to 15°S) shows a conspicuous variation (from -101 to -83 m/s) with geographic longitude of Venus, correlated with the underlying relief of Aphrodite Terra. We interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to the cloud top level, break there and transfer their momentum to the zonal flow. Such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the Earth but is not reproduced in the current GCM of Venus atmosphere from LMD.In the equatorial regions, the UV albedo of clouds at 365 nm and the H2O mixing ratio at cloud top varies also with longitude, with an anti-correlation: the more H2O, the darker are the clouds. We argue that these variations may be simply explained by the divergence of the horizontal wind field. In the longitude region (from 60° to -10°) where the horizontal wind speed is increasing in magnitude (stretch), it triggers air upwelling which brings both the UV absorber and H2O at cloud top level and decreases the albedo, and vice-versa when the wind is decreasing in magnitude (compression). This picture is fully consistent with the classical view of Venus meridional circulation, with upwelling at equator revealed by horizontal air motions away from equator: the longitude effect is only an additional but important modulation of this effect. We argue that H2O enhancement is the sign of upwelling because the H2O mixing ratio decreases with altitude, comforting the view that the UV absorber is also brought to cloud top by upwelling.

Oxygen Ion Upflow/Outflow Fluxes of Ionospheric Origin in the Stormtime Plasmasphere Boundary Layer

NASA Astrophysics Data System (ADS)

Erickson, P. J.; Zhang, S.; Foster, J. C.; Coster, A. J.

2017-12-01

During geomagnetic storm intervals, Earth's ionosphere is a source of heavy, cold O+ rich plasma to the inner magnetosphere, providing mass flux enhancement with strong dynamic geospace influence. Advancing understanding of the relative strength of ionospheric O+ sources is important for refining modeling of global ionosphere-thermosphere-plasmasphere response, and ultimately for quantitative understanding of the dynamics of energy inputs from solar wind to the magnetosphere. An important but often overlooked source of inner magnetospheric O+ can occur within the plasmasphere boundary layer, well equatorward of higher latitude processes. In particular, at the outer edge of the plasmasphere, O+ dynamics capable of accelerating heavy ions most probably occurs in two steps: (1) ion upflow with thermal velocities above the F2 electron density peak, and (2) ion outflow with suprathermal velocities at higher altitudes. Below approximately 500 km altitude in the near topside ionosphere, ion and electron precipitation in the 10s of eV to 10s of keV range can cause `backsplash' effects, providing sources of upwelling ions. Alternately, strong frictional ion heating from intense horizontal cross-field sub auroral polarization stream (SAPS) flows also provide significant ion temperature enhancements that lead to upwards velocities. Although these vertical flows are challenging to observe due to their short temporal nature and confined spatial extent, direct quantification of the upwelling O+ ion flux is available during several historical storm events using the Millstone Hill incoherent scatter radar, including the recent March 2015 storm interval. DMSP overflights and GPS based large scale TEC maps place these ionospheric radar measurements in correct geophysical context. Results show heavy ion upwelling fluxes lasting for at least 30 minutes to 1 hour (upper bound limited by observational restrictions), at rates exceeding 1E13 ions/m2/sec. We will present a summary of these observations and will quantitatively discuss estimates of the total O+ ion outflow involved, along with an exploration of the relative importance of the two leading mechanisms involved for these upwelling sources. Finally, we will discuss the implications in order to correctly model outflow effects within the inner magnetosphere.

Storm Driven Upwelling Responsible for pCO2-rich Water Intrusion in the South Atlantic Bight

NASA Astrophysics Data System (ADS)

Noakes, S.; Gledhill, D. K.

2016-02-01

Gray's Reef National Marine Sanctuary (GRNMS) is located approximately 20 miles offshore Georgia along the inner to middle shelf of the South Atlantic Bight (SAB). The University of Georgia (UGA) and the Pacific Marine Environmental Lab have maintained a high resolution pCO2 system for almost a decade on the National Data Buoy Center's buoy moored at GRNMS. To support the surface monitoring and set the stage for benthic monitoring at GRNMS, UGA and GRNMS have established a seafloor observatory that monitors pCO2, pH and water quality parameters. Traditional thought had held that given the relatively shallow water depth at GRNMS, the pCO2 measured on the surface could be extrapolated to the seafloor and utilized to monitor the benthic community. However, seafloor pCO2 data collected to date have revealed unusual episodes of subsurface pCO2-rich water moving through GRNMS that had not been previously identified by surface monitoring. Many of these events correspond with major storms that have either formed off the SAB or passed nearby GRNMS. Based on the surface data collected to date, temperature driven seasonal pCO2 changes occur naturally on an annual scale in the SAB which also affects the pH. However, the storms appear to have induced upwelling of pCO2-rich water from the deep Atlantic Ocean pushing it inward over the long continental shelf towards GRNMS. The result of the upwelling is a sharp increase of subsurface pCO2 lasting only days to weeks as compared to the seasonal cycle. It is part of the natural weather patterns for storms to form off the SAB or pass nearby, but depending on if the storm frequency increases due to global climate change, this process may become more of an impact on the benthic community. How this affects the benthic community has yet to be determined, but it is clear that they have adapted to seasonal fluctuations for survival. These upwellings are obviously adding to the SAB total carbon budget and affecting the benthic water quality, but to what extent have yet to be determined.

Phosphorus dynamics in biogeochemically distinct regions of the southeast subtropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Duhamel, Solange; Björkman, Karin M.; Repeta, Daniel J.; Karl, David M.

2017-02-01

The southeast subtropical Pacific Ocean was sampled along a zonal transect between the coasts of Chile and Easter Island. This remote area of the world's ocean presents strong gradients in physical (e.g., temperature, density and light), chemical (e.g., salinity and nutrient concentrations) and microbiological (e.g., cell abundances, biomass and specific growth rates) properties. The goal of this study was to describe the phosphorus (P) dynamics in three main ecosystems along this transect: the upwelling regime off the northern Chilean coast, the oligotrophic area associated with the southeast subtropical Pacific gyre and the transitional area in between these two biomes. We found that inorganic phosphate (Pi) concentrations were high and turnover times were long (>210 nmol l-1 and >31 d, respectively) in the upper water column, along the entire transect. Pi uptake rates in the gyre were low (euphotic layer integrated rates were 0.26 mmol m-2 d-1 in the gyre and 1.28 mmol m-2 d-1 in the upwelling region), yet not only driven by decreases in particle mass or cell abundance (particulate P- and cell- normalized Pi uptake rates in the euphotic layer were ∼1-4 times and ∼3-15 times lower in the gyre than in the upwelling, respectively). However these Pi uptake rates were at or near the maximum Pi uptake velocity (i.e., uptake rates in Pi amended samples were not significantly different from those at ambient concentration: 1.5 and 23.7 nmol l-1 d-1 at 50% PAR in the gyre and upwelling, respectively). Despite the apparent Pi replete conditions, selected dissolved organic P (DOP) compounds were readily hydrolyzed. Nucleotides were the most bioavailable of the DOP substrates tested. Microbes actively assimilated adenosine-5‧-triphosphate (ATP) leading to Pi and adenosine incorporation as well as Pi release to the environment. The southeast subtropical Pacific Ocean is a Pi-sufficient environment, yet DOP hydrolytic processes are maintained and contribute to P-cycling across the wide range of environmental conditions present in this ecosystem.

Upwelling to Outflowing Oxygen Ions at Auroral Latitudes during Quiet Times: Exploiting a New Satellite Database

NASA Astrophysics Data System (ADS)

Redmon, Robert J.

The mechanisms by which thermal O+ escapes from the top of the ionosphere and into the magnetosphere are not fully understood even with 30 years of active research. This thesis introduces a new database, builds a simulation framework around a thermospheric model and exploits these tools to gain new insights into the study of O+ ion outflows. A dynamic auroral boundary identification system is developed using Defense Meteorological Satellite Program (DMSP) spacecraft observations at 850 km to build a database characterizing the oxygen source region. This database resolves the ambiguity of the expansion and contraction of the auroral zone. Mining this new dataset, new understanding is revealed. We describe the statistical trajectory of the cleft ion fountain return flows over the polar cap as a function of activity and the orientation of the interplanetary magnetic field y-component. A substantial peak in upward moving O+ in the morning hours is discovered. Using published high altitude data we demonstrate that between 850 and 6000 km altitude, O+ is energized predominantly through transverse heating; and acceleration in this altitude region is relatively more important in the cusp than at midnight. We compare data with a thermospheric model to study the effects of solar irradiance, electron precipitation and neutral wind on the distribution of upward O+ at auroral latitudes. EUV irradiance is shown to play a dominant role in establishing a dawn-focused source population of upwelling O+ that is responsible for a pre-noon feature in escaping O+ fluxes. This feature has been corroborated by observations on platforms including the Dynamics Explorer 1 (DE-1), Polar, and Fast Auroral Snapshot SnapshoT (FAST) spacecraft. During quiet times our analysis shows that the neutral wind is more important than electron precipitation in establishing the dayside O+ upwelling distribution. Electron precipitation is found to play a relatively modest role in controlling dayside, and a critical role in controlling nightside, upwelling O+. This thesis provides a new database, and insights into the study of oxygen ion outflows during quiet times. These results and tools will be essential for researchers working on topics involving magnetosphere-ionosphere interactions.

Gulf of California biogeographic regions based on coastal zone color scanner imagery

NASA Astrophysics Data System (ADS)

SantamaríA-Del-Angel, Eduardo; Alvarez-Borrego, Saúl; Müller-Karger, Frank E.

1994-04-01

Topographically, the Gulf of California is divided into a series of basins and trenches that deepen to the south. Maximum depth at the mouth is greater than 3000 m. Most of the northern gulf is less than 200 m deep. The gulf has hydrographic features conducive to high primary productivity. Upwelling events have been described on the basis of temperature distributions at the eastern coast during winter and spring and at the western coast during summer. Tidal amplitude may be as high as 9 m in the upper gulf. On the basis of discrete phytoplankton sampling, the gulf was previously divided into four geographic regions. This division took into consideration only the space distribution, taxonomic composition, and abundance of microphytoplankton. With the availability of the coastal zone color scanner (CZCS) imagery, we were able to include the time variability of pigments to make a more detailed biogeographic division of the gulf. With weekly composites of the imagery, we generated time series of pigment concentrations for 33 locations throughout the gulf and for the whole life span of the CZCS. The time series show a clear seasonal variation, with maxima in winter and spring and minima in summer. The effect of upwelling at the eastern coast is clearly evident, with high pigment concentrations. The effect of the summer upwelling off the Baja California coast is not evident in these time series. Time series from locations on the western side of the gulf also show maxima in winter and spring that are due to the eddy circulation that brings upwelled water from the eastern side. Principal-component analysis was applied to define 14 regions. Ballenas Channel, between Angel de la Guarda and Baja California, and the upper gulf always appeared as very distinct regions. Some of these 14 regions relate to the geographic distributions of important faunal groups, including the benthos, or their life cycles. For example, the upper gulf is a place for reproduction and the nursery of many fish species, marine mammals and birds are specially abundant in Ballenas Channel, sardine spawning mostly occurs in the central gulf in spring, and shrimp are abundant off mainland Mexico.

Variability of the internal tide on the southern Monterey Bay continental shelf and associated bottom boundary layer sediment transport

USGS Publications Warehouse

Rosenberger, Kurt; Storlazzi, Curt; Cheriton, Olivia

2016-01-01

A 6-month deployment of instrumentation from April to October 2012 in 90 m water depth near the outer edge of the mid-shelf mud belt in southern Monterey Bay, California, reveals the importance regional upwelling on water column density structure, potentially accounting for the majority of the variability in internal tidal energy flux across the shelf. Observations consisted of time-series measurements of water-column currents, temperature and salinity, and near-bed currents and suspended matter. The internal tide accounted for 15–25% of the water-column current variance and the barotropic tide accounted for up to 35%. The subtidal flow showed remarkably little shear and was dominated by the 7–14 day band, which is associated with relaxations in the dominant equatorward winds typical of coastal California in the spring and summer. Upwelling and relaxation events resulted in strong near-bed flows and accounted for almost half of the current stress on the seafloor (not accounting for wave orbital velocities), and may have driven along-shelf geostrophic flow during steady state conditions. Several elevated suspended particulate matter (SPM) events occurred within 3 m of the bed and were generally associated with higher, long-period surface waves. However, these peaks in SPM did not coincide with the predicted resuspension events from the modeled combined wave–current shear stress, indicating that the observed SPM at our site was most likely resuspended elsewhere and advected along-isobath. Sediment flux was almost equal in magnitude in the alongshore and cross-shore directions. Instances of wave–current shear stress that exceeded the threshold of resuspension for the silty-clays common at these water depths only occurred when near-bed orbital velocities due to long-period surface waves coincided with vigorous near-bed currents associated with the internal tide or upwelling/relaxation events. Thus upwelling/relaxation dynamics are primarily responsible for variability in the internal tide, as well as transport of near-bottom sediment in the mid-self mud belt during the relatively quiescent summer months.

Geochemistry of Permian rocks from the margins of the Phosphoria Basin

USGS Publications Warehouse

Perkins, Robert B.; McIntyre, Brandie; Hein, James R.; Piper, David Z.

2003-01-01

The Permian Phosphoria Formation and interbedded units of the Park City Formation and Shedhorn Sandstone in western Wyoming represent deposition along a carbonate ramp at the eastern margin of the Phosphoria Basin, with portions of the Phosphoria units reflecting periods of upwelling and widespread phosphogenesis. Thickness-weighted slab-samples of these units were collected at a maximum interval of 3 m along an 80+ m-length of unweathered core and analyzed for major-, minor-, and trace-element contents. Interpretations of geochemistry were made within the confines of a previously recognized sequence stratigraphy framework. Major shifts in element ratios characteristic of terrigenous debris that occur at sequence boundaries at the base of the Meade Peak and Retort Members of the Phosphoria Formation are attributed to changing sediment sources. Inter-element relationships in the marine fraction indicate that bottom waters of the Phosphoria Basin were predominantly denitrifying during deposition of the Ervay, Grandeur, and Phosphoria sediments, although sulfate-reducing conditions may have existed during deposition of the lower Meade Peak sediments. Oxic conditions were prevalent during deposition of a large part of the Franson Member, which represents sedimentation in a shallow, inner- to back-ramp setting. Variations in sediment facies and organic matter and trace element contents largely reflect changes in Permian sea level. Changes in sea level in basin-margin areas, such as represented by the study section, may have affected the oxidation of settling organic matter, the foci of intersection of upwelling bottom waters with the photic zone, the rate of terrigenous sedimentation, and, ultimately, the overall environment of deposition. Our study suggests that phosphogenesis can occur under lowstand, transgressive, and highstand conditions in marginal areas, assuming water depths sufficient for upwelling to occur. Formation of phosphorite layers under upwelling conditions appears to have been most dependent on a lack of dilution by terrigenous sedimentation and carbonate shoaling. Differences in the geochemistry between two similar environments represented by the upper and lower Phosphoria units are largely attributed to higher rates of diluting terrigenous sediment during deposition of the upper unit. This is consistent with prior interpretations of a more shoreward setting for the upper Phosphoria.

Processes of 30-90 days sea surface temperature variability in the northern Indian Ocean during boreal summer

NASA Astrophysics Data System (ADS)

Vialard, J.; Jayakumar, A.; Gnanaseelan, C.; Lengaigne, M.; Sengupta, D.; Goswami, B. N.

2012-05-01

During summer, the northern Indian Ocean exhibits significant atmospheric intraseasonal variability associated with active and break phases of the monsoon in the 30-90 days band. In this paper, we investigate mechanisms of the Sea Surface Temperature (SST) signature of this atmospheric variability, using a combination of observational datasets and Ocean General Circulation Model sensitivity experiments. In addition to the previously-reported intraseasonal SST signature in the Bay of Bengal, observations show clear SST signals in the Arabian Sea related to the active/break cycle of the monsoon. As the atmospheric intraseasonal oscillation moves northward, SST variations appear first at the southern tip of India (day 0), then in the Somali upwelling region (day 10), northern Bay of Bengal (day 19) and finally in the Oman upwelling region (day 23). The Bay of Bengal and Oman signals are most clearly associated with the monsoon active/break index, whereas the relationship with signals near Somali upwelling and the southern tip of India is weaker. In agreement with previous studies, we find that heat flux variations drive most of the intraseasonal SST variability in the Bay of Bengal, both in our model (regression coefficient, 0.9, against ~0.25 for wind stress) and in observations (0.8 regression coefficient); ~60% of the heat flux variation is due do shortwave radiation and ~40% due to latent heat flux. On the other hand, both observations and model results indicate a prominent role of dynamical oceanic processes in the Arabian Sea. Wind-stress variations force about 70-100% of SST intraseasonal variations in the Arabian Sea, through modulation of oceanic processes (entrainment, mixing, Ekman pumping, lateral advection). Our ~100 km resolution model suggests that internal oceanic variability (i.e. eddies) contributes substantially to intraseasonal variability at small-scale in the Somali upwelling region, but does not contribute to large-scale intraseasonal SST variability due to its small spatial scale and random phase relation to the active-break monsoon cycle. The effect of oceanic eddies; however, remains to be explored at a higher spatial resolution.

Response of O2 and pH to ENSO in the California Current System in a high-resolution global climate model

NASA Astrophysics Data System (ADS)

Turi, Giuliana; Alexander, Michael; Lovenduski, Nicole S.; Capotondi, Antonietta; Scott, James; Stock, Charles; Dunne, John; John, Jasmin; Jacox, Michael

2018-02-01

Coastal upwelling systems, such as the California Current System (CalCS), naturally experience a wide range of O2 concentrations and pH values due to the seasonality of upwelling. Nonetheless, changes in the El Niño-Southern Oscillation (ENSO) have been shown to measurably affect the biogeochemical and physical properties of coastal upwelling regions. In this study, we use a novel, high-resolution global climate model (GFDL-ESM2.6) to investigate the influence of warm and cold ENSO events on variations in the O2 concentration and the pH of the CalCS coastal waters. An assessment of the CalCS response to six El Niño and seven La Niña events in ESM2.6 reveals significant variations in the response between events. However, these variations overlay a consistent physical and biogeochemical (O2 and pH) response in the composite mean. Focusing on the mean response, our results demonstrate that O2 and pH are affected rather differently in the euphotic zone above ˜ 100 m. The strongest O2 response reaches up to several hundreds of kilometers offshore, whereas the pH signal occurs only within a ˜ 100 km wide band along the coast. By splitting the changes in O2 and pH into individual physical and biogeochemical components that are affected by ENSO variability, we found that O2 variability in the surface ocean is primarily driven by changes in surface temperature that affect the O2 solubility. In contrast, surface pH changes are predominantly driven by changes in dissolved inorganic carbon (DIC), which in turn is affected by upwelling, explaining the confined nature of the pH signal close to the coast. Below ˜ 100 m, we find conditions with anomalously low O2 and pH, and by extension also anomalously low aragonite saturation, during La Niña. This result is consistent with findings from previous studies and highlights the stress that the CalCS ecosystem could periodically undergo in addition to impacts due to climate change.

Predicting Upwelling Radiance on the West Florida Shelf

DTIC Science & Technology

2006-09-30

Executive Director, Greater Tampa Chamber of Commerce . Finalist, 2004 Small Business of the Year, Florida Environmental Research Institute, W...Paul Bissett, Ph.D., Executive Director, Greater Tampa Chamber of Commerce . 6

Jovian Temperatures--Highest Resolution

NASA Image and Video Library

1997-09-24

This image, bottom panel, from NASA Galileo orbiter indicates the forces powering Jovian winds, and differentiates between areas of strongest upwelling and downwelling winds in the upper part of the atmosphere where winds are strong.

40 CFR 451.21 - Effluent limitations attainable by the application of the best practicable control technology...

Code of Federal Regulations, 2012 CFR

2012-07-01

... Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) EFFLUENT GUIDELINES AND STANDARDS... as video cameras, digital scanning sonar, and upweller systems; monitoring of sediment quality...

40 CFR 451.21 - Effluent limitations attainable by the application of the best practicable control technology...

Code of Federal Regulations, 2014 CFR

2014-07-01

... Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) EFFLUENT GUIDELINES AND STANDARDS... as video cameras, digital scanning sonar, and upweller systems; monitoring of sediment quality...

40 CFR 451.21 - Effluent limitations attainable by the application of the best practicable control technology...

Code of Federal Regulations, 2013 CFR

2013-07-01

... Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) EFFLUENT GUIDELINES AND STANDARDS... as video cameras, digital scanning sonar, and upweller systems; monitoring of sediment quality...

Radiolarian indicators of El Nino and anti-El Nino events in Holocene sediments of Santa Barbara basin

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

Weinheimer, A.L.

Radiolarian distributions and physical oceanographic data from the Santa Barbara basin indicate the following. Strong anti-El Nino periods can be characterized by (1) intermediate radiolarian density, (2) high percentage of transition-central radiolarian fauna, and (3) low percentage and number of warm-water radiolarian fauna. This distribution pattern is attributed to strong wind-driven upwelling and reduced northward transport by the California Countercurrent during anti-El Nino periods. Strong El Nino periods are typically (1) high in radiolarian density, and (2) low in percentage but high in number of warm-water fauna. This distribution is attributed to reduced wind-driven upwelling, enhanced northward countercurrent transport, andmore » geostrophic doming of the cold-water masses in the shear zone between the California Current and California Countercurrent.« less

Nonlocal impacts of the Loop Current on cross-slope near-bottom flow in the northeastern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Nguyen, Thanh-Tam; Morey, Steven L.; Dukhovskoy, Dmitry S.; Chassignet, Eric P.

2015-04-01

Cross-slope near-bottom motions near De Soto Canyon in the northeastern Gulf of Mexico are analyzed from a multidecadal ocean model simulation to characterize upwelling and downwelling, important mechanisms for exchange between the deep ocean and shelf in the vicinity of the 2010 BP Macondo well oil spill. Across the continental slope, large-scale depression and offshore movement of isopycnals (downwelling) occur more frequently when the Loop Current impinges upon the West Florida Shelf slope farther south. Upwelling and onshore movement of isopycnals occurs with roughly the same likelihood regardless of Loop Current impingement on the slope. The remote influence of Loop Current on the De Soto Canyon region downwelling is a consequence of a high-pressure anomaly that extends along the continental slope emanating from the location of Loop Current impact.