The Experts below are selected from a list of 2913 Experts worldwide ranked by ideXlab platform
Glen Gawarkiewicz - One of the best experts on this subject based on the ideXlab platform.
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water mass distribution and polar front Structure in the western barents sea
Journal of Geophysical Research, 1998Co-Authors: C L Harris, Albert J Plueddemann, Glen GawarkiewiczAbstract:The water mass distribution in the western Barents Sea, the Thermohaline Structure of the western Barents Sea Polar Front, and the local formation of a dense water mass are described on the basis of an analysis of historical hydrographic data. This study concentrated on the frontal region between Bjornoya and Hopen Island where Arctic water is found on the Spitsbergen Bank and Atlantic water in the Bear Island Trough and Hopen Trench. The distributions of Atlantic and Arctic waters in relation to topography were consistent with the hypothesis that the location of the polar front is fixed at about the 250 m isobath by the barotropic circulation of Atlantic water within the Bear Island Trough and Hopen Trench. In winter, vertical gradients of temperature and salinity were weak throughout the frontal region, consistent with a barotropic, topographically controlled front. In summer, vertical gradients remained weak below 100 m depth but increased in the upper layer as a result of the presence of fresh, warm surface water produced by melting ice. The topographic control of Thermohaline properties at the surface was disrupted by the meltwater pool, and the meltwater contributed to water mass modification in the frontal region. The following seasonal cycle of water mass formation was hypothesized: Summer heating melts the sea ice on the Spitsbergen Bank and produces the surface meltwater pool. This meltwater not only increases vertical Thermohaline gradients on the bank but also crosses the front and freshens the surface layer throughout the western Barents Sea. Subsequent winter cooling, which creates ice over the bank, also forms dense water in the Bear Island Trough and Hopen Trench by convective mixing of Atlantic water and the overlying meltwater.
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topographic control of Thermohaline frontal Structure in the barents sea polar front on the south flank of spitsbergen bank
Journal of Geophysical Research, 1995Co-Authors: Glen Gawarkiewicz, Albert J PlueddemannAbstract:A combination of observations and process-oriented numerical modeling is used to investigate the Thermohaline Structure of the Barents Sea Polar Front on the south flank of Spitsbergen Bank. The Polar Front is the boundary between warm, saline North Atlantic Water and cool, fresh Arctic Water located over the outer edge of the bank. Observations from the Barents Sea Polar Front Experiment in August 1992 show that North Atlantic Water was present in waters of 250 m or deeper, with little vertical Structure beneath the upper 50 m of the water column. The mean velocity field over the south flank of the bank shows a westward flow of roughly 0.1 m s−1 in the North Atlantic Water and weak mean velocities over the outer edge of the bank. A primitive equation model is used with idealized bathymetry to show that the inflow of North Atlantic Water into the Barents Sea via the Bear Island Trough bifurcates at the sill between Nordkapp Bank and Sentral Bank, at the eastern edge of the Bear Island Trough. One branch of the North Atlantic Water recirculates westward, out of the Barents Sea and back into the Norwegian Sea. The flow of North Atlantic Water is barotropic and linear, following the bathymetry. The recirculating branch is sheared off at the sill, such that the core of recirculating flow is concentrated between the isobath coincident with the sill depth (∼260 m) and the center of the trough (∼500 m). Both the cross-bank Structure of the model Thermohaline fields, as well as the along-bank velocity, are very similar to the observations at a depth of 80 m. Thus the frontal Structure is controlled by the interaction of the barotropic inflow with the sill at the eastern edge of the Bear Island Trough and is not controlled by processes occurring over the bank.
Albert J Plueddemann - One of the best experts on this subject based on the ideXlab platform.
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water mass distribution and polar front Structure in the western barents sea
Journal of Geophysical Research, 1998Co-Authors: C L Harris, Albert J Plueddemann, Glen GawarkiewiczAbstract:The water mass distribution in the western Barents Sea, the Thermohaline Structure of the western Barents Sea Polar Front, and the local formation of a dense water mass are described on the basis of an analysis of historical hydrographic data. This study concentrated on the frontal region between Bjornoya and Hopen Island where Arctic water is found on the Spitsbergen Bank and Atlantic water in the Bear Island Trough and Hopen Trench. The distributions of Atlantic and Arctic waters in relation to topography were consistent with the hypothesis that the location of the polar front is fixed at about the 250 m isobath by the barotropic circulation of Atlantic water within the Bear Island Trough and Hopen Trench. In winter, vertical gradients of temperature and salinity were weak throughout the frontal region, consistent with a barotropic, topographically controlled front. In summer, vertical gradients remained weak below 100 m depth but increased in the upper layer as a result of the presence of fresh, warm surface water produced by melting ice. The topographic control of Thermohaline properties at the surface was disrupted by the meltwater pool, and the meltwater contributed to water mass modification in the frontal region. The following seasonal cycle of water mass formation was hypothesized: Summer heating melts the sea ice on the Spitsbergen Bank and produces the surface meltwater pool. This meltwater not only increases vertical Thermohaline gradients on the bank but also crosses the front and freshens the surface layer throughout the western Barents Sea. Subsequent winter cooling, which creates ice over the bank, also forms dense water in the Bear Island Trough and Hopen Trench by convective mixing of Atlantic water and the overlying meltwater.
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topographic control of Thermohaline frontal Structure in the barents sea polar front on the south flank of spitsbergen bank
Journal of Geophysical Research, 1995Co-Authors: Glen Gawarkiewicz, Albert J PlueddemannAbstract:A combination of observations and process-oriented numerical modeling is used to investigate the Thermohaline Structure of the Barents Sea Polar Front on the south flank of Spitsbergen Bank. The Polar Front is the boundary between warm, saline North Atlantic Water and cool, fresh Arctic Water located over the outer edge of the bank. Observations from the Barents Sea Polar Front Experiment in August 1992 show that North Atlantic Water was present in waters of 250 m or deeper, with little vertical Structure beneath the upper 50 m of the water column. The mean velocity field over the south flank of the bank shows a westward flow of roughly 0.1 m s−1 in the North Atlantic Water and weak mean velocities over the outer edge of the bank. A primitive equation model is used with idealized bathymetry to show that the inflow of North Atlantic Water into the Barents Sea via the Bear Island Trough bifurcates at the sill between Nordkapp Bank and Sentral Bank, at the eastern edge of the Bear Island Trough. One branch of the North Atlantic Water recirculates westward, out of the Barents Sea and back into the Norwegian Sea. The flow of North Atlantic Water is barotropic and linear, following the bathymetry. The recirculating branch is sheared off at the sill, such that the core of recirculating flow is concentrated between the isobath coincident with the sill depth (∼260 m) and the center of the trough (∼500 m). Both the cross-bank Structure of the model Thermohaline fields, as well as the along-bank velocity, are very similar to the observations at a depth of 80 m. Thus the frontal Structure is controlled by the interaction of the barotropic inflow with the sill at the eastern edge of the Bear Island Trough and is not controlled by processes occurring over the bank.
R A Ibrayev - One of the best experts on this subject based on the ideXlab platform.
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long term evolution of caspian sea Thermohaline properties reconstructed in an eddy resolving ocean general circulation model
Ocean Science, 2019Co-Authors: G S Dyakonov, R A IbrayevAbstract:Abstract. Decadal variability in Caspian Sea Thermohaline properties is investigated using a high-resolution ocean general circulation model including sea ice thermodynamics and air–sea interaction forced by prescribed realistic atmospheric conditions and riverine runoff. The model describes synoptic, seasonal and climatic variations of sea Thermohaline Structure, water balance, and sea level. A reconstruction experiment was conducted for the period of 1961–2001, covering a major regime shift in the global climate during 1976–1978, which allowed for an investigation of the Caspian Sea response to such significant episodes of climate variability. The model reproduced sea level evolution reasonably well despite the fact that many factors (such as possible seabed changes and insufficiently explored underground water infiltration) were not taken into account in the numerical reconstruction. This supports the hypothesis relating rapid Caspian Sea level rise in 1978–1995 with global climate change, which caused variation in local atmospheric conditions and riverine discharge reflected in the external forcing data used, as is shown in the paper. Other effects of the climatic shift are investigated, including a decrease in salinity in the active layer, strengthening of its stratification and corresponding diminishing of convection. It is also demonstrated that water exchange between the three Caspian basins (northern, middle and southern) plays a crucial role in the formation of their Thermohaline regime. The reconstructed long-term trends in seawater salinity (general downtrend after 1978), temperature (overall increase) and density (general downtrend) are studied, including an assessment of the influence of main surface circulation patterns and model error accumulation.
Bertrand Arnaud - One of the best experts on this subject based on the ideXlab platform.
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On the use of acoustic data to characterise the Thermohaline stratification in a tropical ocean
'Copernicus GmbH', 2021Co-Authors: Assunção, Ramilla Vieira, Bourlès Bernard, Lebourges-dhaussy Anne, Da Silva, Alex Costa, Vargas Gary, Roudaut Gildas, Bertrand ArnaudAbstract:The use of active acoustic to monitor abiotic Structures and processes in the ocean have been gaining ground in oceanography. In some systems, acoustics allow the robust estimation of the depth of the pycnocline or thermocline either directly or indirectly when the physical Structures drive the one of organisms. Here, we examined the feasibility of extracting the Thermohaline Structure (mixed-layer depth, upper and lower thermocline) from echosounder data collected in the oligotrophic Southwestern tropical Atlantic region at two seasons (spring and fall), more precisely in two areas with different Thermohaline conditions, at both day and night. For that, we tested three approaches: (i) the vertical extension of the epipelagic community; (ii) the use of acoustic gradients; and (iii) a cross-wavelet approach. Results show that, even if the Thermohaline Structure impacts the vertical distribution of acoustic scatters, the resultant structuring did not allow for a robust estimation of the Thermohaline limits indicating that other oceanographic or biological processes are acting. This result prevents for a fine-scale representation of the upper-layer turbulence from acoustic data. However, studying the proportion of acoustic biomass within each layer provides interesting insights on ecosystem Structure in different Thermohaline, seasonal and diel scenarios
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Surface Circulation and Vertical Structure of Upper Ocean Variability Around Fernando de Noronha Archipelago and Rocas Atoll During Spring 2015 and Fall 2017
'Frontiers Media SA', 2021Co-Authors: Costa Da Silva, Alex, Araujo Moacyr, Chaigneau Alexis, Dossa, Alina N., Eldin Gerard, Bertrand ArnaudAbstract:Using current, hydrographic and satellite observations collected off Northeast Brazil around the Fernando de Noronha Archipelago and Rocas Atoll during two oceanographic cruises (spring 2015 and fall 2017), we investigated the general oceanic circulation and its modifications induced by the islands. In spring 2015, the area was characterized by lower SST (26.6°C) and deep mixed-layer (∼90 m). At this depth, a strong current shear was observed between the central branch of the eastward flowing near-surface South Equatorial Current and the westward flowing South Equatorial Undercurrent. In contrast, in fall 2017, SST was higher (∼28.8°C) and the mixed-layer shallower (∼50 m). The shear between the central South Equatorial Current and the South Equatorial Undercurrent was weaker during this period. Interestingly, no oxygen-rich water from the south (retroflection of the North Brazil undercurrent) was observed in the region in fall 2017. In contrast, we revealed the presence of an oxygen-rich water entrained by the South Equatorial Undercurrent reaching Rocas Atoll in spring 2015. Beside these global patterns, island wake effects were noted. The presence of islands, in particular Fernando de Noronha, strongly perturbs central South Equatorial Current and South Equatorial Undercurrent features, with an upstream core splitting and a reorganization of single current core Structures downstream of the islands. Near islands, flow disturbances impact the Thermohaline Structure and biogeochemistry, with a negative anomaly in temperature (−1.3°C) and salinity (−0.15) between 200 and 400 m depth in the southeast side of Fernando Noronha (station 5), where the fluorescence peak (>1.0 mg m–3) was shallower than at other stations located around Fernando de Noronha, reinforcing the influence of flow-topography. Satellite maps of sea-surface temperature and chlorophyll-a confirmed the presence of several submesoscale features in the study region. Altimetry data suggested the presence of a cyclonic mesoscale eddy around Rocas Atoll in spring 2015. A cyclonic vortex (radius of 28 km) was actually observed in subsurface (150–350 m depth) southeast of Rocas Atoll. This vortex was associated with topographically induced South Equatorial Undercurrent flow separation. These features are likely key processes providing an enrichment from the subsurface to the euphotic layer near islands, supplying local productivity
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Surface Circulation and Vertical Structure of Upper Ocean Variability Around Fernando de Noronha Archipelago and Rocas Atoll During Spring 2015 and Fall 2017
'Frontiers Media SA', 2021Co-Authors: Silva Alex, Araujo Moacyr, Chaigneau Alexis, Dossa, Alina N., Eldin Gerard, Bertrand ArnaudAbstract:Place: Lausanne Publisher: Frontiers Media Sa WOS:000648090000001International audienceUsing current, hydrographic and satellite observations collected off Northeast Brazil around the Fernando de Noronha Archipelago and Rocas Atoll during two oceanographic cruises (spring 2015 and fall 2017), we investigated the general oceanic circulation and its modifications induced by the islands. In spring 2015, the area was characterized by lower SST (26.6 degrees C) and deep mixed-layer (similar to 90 m). At this depth, a strong current shear was observed between the central branch of the eastward flowing near-surface South Equatorial Current and the westward flowing South Equatorial Undercurrent. In contrast, in fall 2017, SST was higher (similar to 28.8 degrees C) and the mixed-layer shallower (similar to 50 m). The shear between the central South Equatorial Current and the South Equatorial Undercurrent was weaker during this period. Interestingly, no oxygen-rich water from the south (retroflection of the North Brazil undercurrent) was observed in the region in fall 2017. In contrast, we revealed the presence of an oxygen-rich water entrained by the South Equatorial Undercurrent reaching Rocas Atoll in spring 2015. Beside these global patterns, island wake effects were noted. The presence of islands, in particular Fernando de Noronha, strongly perturbs central South Equatorial Current and South Equatorial Undercurrent features, with an upstream core splitting and a reorganization of single current core Structures downstream of the islands. Near islands, flow disturbances impact the Thermohaline Structure and biogeochemistry, with a negative anomaly in temperature (-1.3 degrees C) and salinity (-0.15) between 200 and 400 m depth in the southeast side of Fernando Noronha (station 5), where the fluorescence peak (\textgreater1.0 mg m(-3)) was shallower than at other stations located around Fernando de Noronha, reinforcing the influence of flow-topography. Satellite maps of sea-surface temperature and chlorophyll-a confirmed the presence of several submesoscale features in the study region. Altimetry data suggested the presence of a cyclonic mesoscale eddy around Rocas Atoll in spring 2015. A cyclonic vortex (radius of 28 km) was actually observed in subsurface (150-350 m depth) southeast of Rocas Atoll. This vortex was associated with topographically induced South Equatorial Undercurrent flow separation. These features are likely key processes providing an enrichment from the subsurface to the euphotic layer near islands, supplying local productivity
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3D characterisation of the Thermohaline Structure in the southwestern tropical Atlantic derived from functional data analysis of in situ profiles
'Elsevier BV', 2020Co-Authors: Assunçao Ramilla, Silva, Alex C., Roy Amédée, Bourlès Bernard, Silva, Carlos Henrique S., Ternon Jean-francois, Araujo Moacyr, Bertrand ArnaudAbstract:International audienceThe dynamic of the Thermohaline Structure of the upper ocean, which depends on ocean-atmosphere interactions, drives most near surface oceanic processes, including the control of gases and heat fluxes, and nutrient availability in the photic layer. The Thermohaline Structure of the southwestern tropical Atlantic (SWTA), a key region for diagnosing variation of the Atlantic Meridional Overturning Circulation, has prime impact on global climate. Characterising the Thermohaline Structure is typically based on the application of classical statistical methods on vertical profiles. Such approach has important limitations since classical methods do not explicitly contemplate the vertical nature of the profiles. Functional Data Analysis (FDA) is a new alternative to solve such drawbacks. Here, we apply an FDA approach to characterise the 3D canonical Thermohaline Structure of the SWTA in austral spring and fall. Our results reveal a clear spatial pattern with the presence of three areas with significantly different Thermohaline Structure. Area 1, mostly located along the continental slope, reflects the western boundary current system, with low static stability and high frequency of occurrence of barrier layer (BL). Conversely, Area 2, located along the Fernando de Noronha chain, presents strong static stability with a well-marked thermocline. This area, under the influence of the eastern Atlantic, is characterised by a low BL frequency, which is seasonally modulated by the latitudinal oscillation of the Intertropical Convergence Zone, controlling the regime of precipitation. In turn, Area 3 behaves as a transition zone between A1 and A2 with the presence of the water core of maximum salinity in subsurface, and therefore presence of strong-moderate BL. Beyond this study, FDA approach emerges as a powerful way to describe, characterise, classify and compare ocean patterns and processes. It can be applied to in situ data but could also be used to deeply and comprehensively explore ocean model output
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3D characterisation of the Thermohaline Structure in the southwestern tropical Atlantic derived from functional data analysis of in situ profiles
2020Co-Authors: Assuncao R., Silva, Alex C., Bourlès Bernard, Silva, Carlos Henrique S., Ternon Jean-francois, Roy A., Araujo M., Bertrand ArnaudAbstract:The dynamic of the Thermohaline Structure of the upper ocean, which depends on ocean-atmosphere interactions, drives most near surface oceanic processes, including the control of gases and heat fluxes, and nutrient availability in the photic layer. The Thermohaline Structure of the southwestern tropical Atlantic (SWTA), a key region for diagnosing variation of the Atlantic Meridional Overturning Circulation, has prime impact on global climate. Characterising the Thermohaline Structure is typically based on the application of classical statistical methods on vertical profiles. Such approach has important limitations since classical methods do not explicitly contemplate the vertical nature of the profiles. Functional Data Analysis (FDA) is a new alternative to solve such drawbacks. Here, we apply an FDA approach to characterise the 3D canonical Thermohaline Structure of the SWTA in austral spring and fall. Our results reveal a clear spatial pattern with the presence of three areas with significantly different Thermohaline Structure. Area 1, mostly located along the continental slope, reflects the western boundary current system, with low static stability and high frequency of occurrence of barrier layer (BL). Conversely, Area 2, located along the Fernando de Noronha chain, presents strong static stability with a well-marked thermocline. This area, under the influence of the eastern Atlantic, is characterised by a low BL frequency, which is seasonally modulated by the latitudinal oscillation of the Intertropical Convergence Zone, controlling the regime of precipitation. In turn, Area 3 behaves as a transition zone between A1 and A2 with the presence of the water core of maximum salinity in subsurface, and therefore presence of strong-moderate BL. Beyond this study, FDA approach emerges as a powerful way to describe, characterise, classify and compare ocean patterns and processes. It can be applied to in situ data but could also be used to deeply and comprehensively explore ocean model output
Viktor Gouretski - One of the best experts on this subject based on the ideXlab platform.
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WOCE-Argo Global Hydrographic Climatology
2018Co-Authors: Viktor GouretskiAbstract:Abstract. The paper describes the new gridded WOCE-Argo Global Hydrographic Climatology (WAGHC) (Gouretski, 2018). The climatology has a one-fourth degree spatial resolution resolving the annual cycle of temperature and salinity on a monthly basis. Two versions of the climatology were produced differing by the spatial interpolation performed on isobaric or isopycnal surfaces respectively. The WAGHC climatology is based on the quality controlled temperature and salinity profiles obtained before January 2016 with the average climatological year being in the range 2008 to 2012. To avoid biases due to the significant step-like decrease of the data below 2 km the profile extrapolation procedure is implemented. We compare the WAGHC climatology to the one-fourth degree resolution isobarically averaged climatology WOA13, produced by the NOAA Ocean Climate Laboratory (Boyer et al., 2013) and diagnose a generally good agreement between these two gridded products. The differences between the two climatologies are attributed basically to the interpolation method and to the considerably extended data basis. Specifically, the WAGHC climatology improved the representation of the Thermohaline Structure both in the data poor polar regions and in several data abundant regions like the Baltic sea, Caspian sea, Gulf of California, Caribbean Sea, and the Weddell Sea. Further, the dependence of the ocean heat content anomaly (OHCA) time series on the baseline climatology was tested. Since the 1950s, the both baseline climatologies produce almost identical OHCA time series.
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World Ocean Circulation Experiment – Argo Global Hydrographic Climatology
'Copernicus GmbH', 2018Co-Authors: Viktor GouretskiAbstract:The paper describes the new gridded World Ocean Circulation Experiment-Argo Global Hydrographic Climatology (WAGHC). The climatology has a 1∕4° spatial resolution resolving the annual cycle of temperature and salinity on a monthly basis. Two versions of the climatology were produced and differ with respect to whether the spatial interpolation was performed on isobaric or isopycnal surfaces, respectively. The WAGHC climatology is based on the quality controlled temperature and salinity profiles obtained before January 2016, and the average climatological year is in the range from 2008 to 2012.To avoid biases due to the significant step-like decrease of the data below 2 km, the profile extrapolation procedure is implemented. We compare the WAGHC climatology to the 1∕4° resolution isobarically averaged WOA13 climatology, produced by the NOAA Ocean Climate Laboratory (Locarnini et al., 2013) and diagnose a generally good agreement between these two gridded products. The differences between the two climatologies are basically attributed to the interpolation method and the considerably extended data basis. Specifically, the WAGHC climatology improved the representation of the Thermohaline Structure, in both the data poor polar regions and several data abundant regions like the Baltic Sea, the Caspian sea, the Gulf of California, the Caribbean Sea, and the Weddell Sea. Further, the dependence of the ocean heat content anomaly (OHCA) time series on the baseline climatology was tested. Since the 1950s, both of the baseline climatologies produce almost identical OHCA time series. The gridded dataset can be found at https://doi.org/10.1594/WDCC/WAGHC_V1.0 (Gouretski, 2018).
