Several aspects of the vortex asymmetry leeward of islands were studied with laboratory experimen... more Several aspects of the vortex asymmetry leeward of islands were studied with laboratory experiments conducted at the LEGI-Coriolis in Grenoble (France). A total of sixty-seven experiments were conducted and the impact of rotation and stratification on small-scale inertial instabilities was considered. The experimental setup mimics the upper thermocline layer on the top of a deep barotropic ocean. Symmetric, asymmetric and multiple islands arrangements were considered during the experiments. Preliminary results suggest that small-scale inertial instability could affect the dynamics of anticyclonic vortices in the far-field wake but also in the near-field wake one or two diameter behind the island. The stabilizing impact of the stratification may lead to stable anticyclones even for finite relative vorticity (ξ/f<-1). Moreover, asymmetrical island or archipelago geometry may also induce significant asymmetries in the wake. 1.
A satellite image of an ocean front coincident with in situ measurements from a towed, profiling ... more A satellite image of an ocean front coincident with in situ measurements from a towed, profiling instrument (SeaSoar) is examined for evidence of submesoscale baroclinic instability (BCI). The image was taken on 19 September 2012 at 03:34 UTC and consists of brightness temperatures collected at high pixel resolution (390-m) over the Northeast Atlantic. The front (1) results from the convergence of water by the mesoscale eddy field, (2) is characterized by a 0.7°C change in temperature over a 15-km distance, and (3) is populated by submesoscale vortices along the front boundary. While horizontal shear instability (HSI) is one mechanism for generating such vortices (Munk et al., 2000), here we consider an alternative hypothesis: that observed eddies are the result of BCI within the ocean surface boundary layer (SBL; Eldevik and Dysthe, 2002). Only a single image is available due to cloud coverage. The present study is framed as a comparison between predicted and observed sizes of the most unstable mode. In most cases, we find good agreement between the two scales. We conclude that BCI provides a plausible explanation for the observed submesoscale eddies.
In the sub-mesoscale ocean vortices tend to be predominantly cyclonic [4]. Inertial instability (... more In the sub-mesoscale ocean vortices tend to be predominantly cyclonic [4]. Inertial instability (hereafter II), which is a centrifugal instability mechanism in the presence of the Coriolis force, is a destructive mechanism that acts only on anti-cyclones, and therefore is hypothesized to cause this asymmetry. Furthermore, since II is in fact the growth of the overturning vorticity, thus creating vertical mixing, it is expected to contribute to nutrient enrichment from the deep, affecting primary production and the oceanic carbon cycle. Linear stability analysis [6] shows that three-dimensional unstable modes of parallel shear flow (without curvature) may have stronger growth rates than the standard two-dimensional barotropic modes when the absolute vorticity is negative, thus II is more significant than shear instability in the destruction of strong anticyclonic shear. For circular vortices (with curvature), vortex columns are unstable to 3D perturbations where the generalized Rayle...
Understanding the global carbon budget and its changes is crucial to current and future life on E... more Understanding the global carbon budget and its changes is crucial to current and future life on Earth. The marine component represents the largest reservoir of the global carbon cycle. In addition to physical processes that govern carbon fluxes at the air-sea interface and regulate the atmospheric carbon budget, complex internal sources and sinks, including inorganic, geologic, microbiological and biological processes also impact carbon distributions and storage. Therefore, it is essential to observe and understand the whole system. This is a daunting task, as many of the processes are distributed throughout the ocean, laterally and vertically over scales ranging from centimeters to thousands of kilometers. Ship and satellite observations both offer a partial view but, for ships, are either too short term and localized and satellites, despite their large spatial coverage, lack the spatial resolution. Ocean robots, such as deep diving autonomous underwater vehicles (AUVs) and gliders...
Long-term trends in oxygen, salinity, and nutrients were followed in the Southeastern Mediterrane... more Long-term trends in oxygen, salinity, and nutrients were followed in the Southeastern Mediterranean (SEMS) deep waters from 2002 to 2020. Results show a net decrease in oxygen since 2008 of −0.5 ± 0.1 μmol kg−1 yr−1 in the bathypelagic depths (1,200–2,000 m). Multiannual variability in oxygen levels superimposed this trend, and is likely associated with variations in thermohaline fluxes. The 2020 mean oxygen concentration of 179.5 ± 2.3 μmol kg−1 is comparable to the pre-Eastern Mediterranean Transient (EMT) mean value. The post-EMT signature is clearly demonstrated in both oxygen and salinity over the period of 2002–2013, but since 2014 it diminished, mainly due to mixing of the Aegean deep water (AegDW) mass with the overlying old Adriatic water mass. This trend reflects a switch back to the pre-EMT regime, characterized by thermohaline homogeneity of the deep water column in the SEMS. The long-term decline of deep water oxygen levels is also accompanied by a corresponding increas...
This study reports exceptional penetrations of the Sharpchin Barracudina Paralepis coregonoides i... more This study reports exceptional penetrations of the Sharpchin Barracudina Paralepis coregonoides into pelagic, open-sea sediment traps in the Levant Basin of the SE Mediterranean Sea. This first substantiated record of the species at the Levant Basin has been observed in two sediment traps at 180 and 280 m depth, 50 km offshore the coast of Israel. Over one year of deployment (November 2016 till November 2017), 483 adult individuals have been repeatedly entrapped inside the automatic sediment traps that were covered with a 25 mm baffler mesh for the first half year and then replaced with a smaller 1 cm mesh for the second half. This undesirable catch of such an elusive and understudied species provided a unique opportunity to revise its distribution, abundance and genetic divergence. The continuous entrapment throughout the year of sexually mature individuals has confirmed that this species is common to the SE Mediterranean. In order to avoid unwanted entrapments that disrupt biogeoc...
Deep Sea Research Part II: Topical Studies in Oceanography, 2019
Abstract The eastern Levantine basin (ELB) is an ultra-oligotrophic, warm and saline marine syste... more Abstract The eastern Levantine basin (ELB) is an ultra-oligotrophic, warm and saline marine system, significantly affected by climate change during the past several decades. The deployment of the first moored station at the ELB (DeepLev), at 1500 m water depth, ~50 km offshore Haifa, Israel, aimed at enhancing synchronized measurements of physical and biogeochemical dynamics. The station carries an array of sediment traps and sensors that measure physical, chemical, and biological attributes along the water column. Here we describe the station and present sediment-flux data from the first 1.5 years of operation (since November 2016). We show that, despite DeepLev's offshore location and the open-sea characteristics of the water column, lateral transport from the continental margin contributes the greatest fraction of particulate flux to the seafloor at this site. This mostly occurs via intermediate nepheloid layer plumes entering the study area between depths of 180 and 800 m. Bottom currents are weak (average ± SD = 3.5 ± 2 cm s−1) and are unlikely to cause significant resuspension. Based on sedimentation rates obtained from nearby sediment cores and sediment particle fluxes sampled in the traps, calculated accumulation rates of total particulate matter and of particulate organic carbon at the seafloor were 95–108 g m−2 y−1 and 0.5–0.6 g m−2 y−1, respectively. Offshore changes in sedimentation rates and in surface sediment elemental ratios indicate that sediment originating from the continental margins is transported at least 100 km offshore.
Along-stream variations in the dynamics of the Antarctic Circumpolar Current (ACC) impact heat an... more Along-stream variations in the dynamics of the Antarctic Circumpolar Current (ACC) impact heat and tracer transport, regulate interbasin exchange, and influence closure of the overturning circulation. Topography is primarily responsible for generating deviations from zonal-mean properties, mainly through standing meanders associated with regions of high eddy kinetic energy. Here, an idealized channel model is used to explore the spatial distribution of energy exchange and its relationship to eddy geometry, as characterized by both eddy momentum and eddy buoyancy fluxes. Variations in energy exchange properties occur not only between standing meander and quasi-zonal jet regions, but throughout the meander itself. Both barotropic and baroclinic stability properties, as well as the magnitude of energy exchange terms, undergo abrupt changes along the path of the ACC. These transitions are captured by diagnosing eddy fluxes of energy and by adopting the eddy geometry framework. The latte...
Several aspects of the vortex asymmetry leeward of islands were studied with laboratory experimen... more Several aspects of the vortex asymmetry leeward of islands were studied with laboratory experiments conducted at the LEGI-Coriolis in Grenoble (France). A total of sixty-seven experiments were conducted and the impact of rotation and stratification on small-scale inertial instabilities was considered. The experimental setup mimics the upper thermocline layer on the top of a deep barotropic ocean. Symmetric, asymmetric and multiple islands arrangements were considered during the experiments. Preliminary results suggest that small-scale inertial instability could affect the dynamics of anticyclonic vortices in the far-field wake but also in the near-field wake one or two diameter behind the island. The stabilizing impact of the stratification may lead to stable anticyclones even for finite relative vorticity (ξ/f<-1). Moreover, asymmetrical island or archipelago geometry may also induce significant asymmetries in the wake. 1.
A satellite image of an ocean front coincident with in situ measurements from a towed, profiling ... more A satellite image of an ocean front coincident with in situ measurements from a towed, profiling instrument (SeaSoar) is examined for evidence of submesoscale baroclinic instability (BCI). The image was taken on 19 September 2012 at 03:34 UTC and consists of brightness temperatures collected at high pixel resolution (390-m) over the Northeast Atlantic. The front (1) results from the convergence of water by the mesoscale eddy field, (2) is characterized by a 0.7°C change in temperature over a 15-km distance, and (3) is populated by submesoscale vortices along the front boundary. While horizontal shear instability (HSI) is one mechanism for generating such vortices (Munk et al., 2000), here we consider an alternative hypothesis: that observed eddies are the result of BCI within the ocean surface boundary layer (SBL; Eldevik and Dysthe, 2002). Only a single image is available due to cloud coverage. The present study is framed as a comparison between predicted and observed sizes of the most unstable mode. In most cases, we find good agreement between the two scales. We conclude that BCI provides a plausible explanation for the observed submesoscale eddies.
In the sub-mesoscale ocean vortices tend to be predominantly cyclonic [4]. Inertial instability (... more In the sub-mesoscale ocean vortices tend to be predominantly cyclonic [4]. Inertial instability (hereafter II), which is a centrifugal instability mechanism in the presence of the Coriolis force, is a destructive mechanism that acts only on anti-cyclones, and therefore is hypothesized to cause this asymmetry. Furthermore, since II is in fact the growth of the overturning vorticity, thus creating vertical mixing, it is expected to contribute to nutrient enrichment from the deep, affecting primary production and the oceanic carbon cycle. Linear stability analysis [6] shows that three-dimensional unstable modes of parallel shear flow (without curvature) may have stronger growth rates than the standard two-dimensional barotropic modes when the absolute vorticity is negative, thus II is more significant than shear instability in the destruction of strong anticyclonic shear. For circular vortices (with curvature), vortex columns are unstable to 3D perturbations where the generalized Rayle...
Understanding the global carbon budget and its changes is crucial to current and future life on E... more Understanding the global carbon budget and its changes is crucial to current and future life on Earth. The marine component represents the largest reservoir of the global carbon cycle. In addition to physical processes that govern carbon fluxes at the air-sea interface and regulate the atmospheric carbon budget, complex internal sources and sinks, including inorganic, geologic, microbiological and biological processes also impact carbon distributions and storage. Therefore, it is essential to observe and understand the whole system. This is a daunting task, as many of the processes are distributed throughout the ocean, laterally and vertically over scales ranging from centimeters to thousands of kilometers. Ship and satellite observations both offer a partial view but, for ships, are either too short term and localized and satellites, despite their large spatial coverage, lack the spatial resolution. Ocean robots, such as deep diving autonomous underwater vehicles (AUVs) and gliders...
Long-term trends in oxygen, salinity, and nutrients were followed in the Southeastern Mediterrane... more Long-term trends in oxygen, salinity, and nutrients were followed in the Southeastern Mediterranean (SEMS) deep waters from 2002 to 2020. Results show a net decrease in oxygen since 2008 of −0.5 ± 0.1 μmol kg−1 yr−1 in the bathypelagic depths (1,200–2,000 m). Multiannual variability in oxygen levels superimposed this trend, and is likely associated with variations in thermohaline fluxes. The 2020 mean oxygen concentration of 179.5 ± 2.3 μmol kg−1 is comparable to the pre-Eastern Mediterranean Transient (EMT) mean value. The post-EMT signature is clearly demonstrated in both oxygen and salinity over the period of 2002–2013, but since 2014 it diminished, mainly due to mixing of the Aegean deep water (AegDW) mass with the overlying old Adriatic water mass. This trend reflects a switch back to the pre-EMT regime, characterized by thermohaline homogeneity of the deep water column in the SEMS. The long-term decline of deep water oxygen levels is also accompanied by a corresponding increas...
This study reports exceptional penetrations of the Sharpchin Barracudina Paralepis coregonoides i... more This study reports exceptional penetrations of the Sharpchin Barracudina Paralepis coregonoides into pelagic, open-sea sediment traps in the Levant Basin of the SE Mediterranean Sea. This first substantiated record of the species at the Levant Basin has been observed in two sediment traps at 180 and 280 m depth, 50 km offshore the coast of Israel. Over one year of deployment (November 2016 till November 2017), 483 adult individuals have been repeatedly entrapped inside the automatic sediment traps that were covered with a 25 mm baffler mesh for the first half year and then replaced with a smaller 1 cm mesh for the second half. This undesirable catch of such an elusive and understudied species provided a unique opportunity to revise its distribution, abundance and genetic divergence. The continuous entrapment throughout the year of sexually mature individuals has confirmed that this species is common to the SE Mediterranean. In order to avoid unwanted entrapments that disrupt biogeoc...
Deep Sea Research Part II: Topical Studies in Oceanography, 2019
Abstract The eastern Levantine basin (ELB) is an ultra-oligotrophic, warm and saline marine syste... more Abstract The eastern Levantine basin (ELB) is an ultra-oligotrophic, warm and saline marine system, significantly affected by climate change during the past several decades. The deployment of the first moored station at the ELB (DeepLev), at 1500 m water depth, ~50 km offshore Haifa, Israel, aimed at enhancing synchronized measurements of physical and biogeochemical dynamics. The station carries an array of sediment traps and sensors that measure physical, chemical, and biological attributes along the water column. Here we describe the station and present sediment-flux data from the first 1.5 years of operation (since November 2016). We show that, despite DeepLev's offshore location and the open-sea characteristics of the water column, lateral transport from the continental margin contributes the greatest fraction of particulate flux to the seafloor at this site. This mostly occurs via intermediate nepheloid layer plumes entering the study area between depths of 180 and 800 m. Bottom currents are weak (average ± SD = 3.5 ± 2 cm s−1) and are unlikely to cause significant resuspension. Based on sedimentation rates obtained from nearby sediment cores and sediment particle fluxes sampled in the traps, calculated accumulation rates of total particulate matter and of particulate organic carbon at the seafloor were 95–108 g m−2 y−1 and 0.5–0.6 g m−2 y−1, respectively. Offshore changes in sedimentation rates and in surface sediment elemental ratios indicate that sediment originating from the continental margins is transported at least 100 km offshore.
Along-stream variations in the dynamics of the Antarctic Circumpolar Current (ACC) impact heat an... more Along-stream variations in the dynamics of the Antarctic Circumpolar Current (ACC) impact heat and tracer transport, regulate interbasin exchange, and influence closure of the overturning circulation. Topography is primarily responsible for generating deviations from zonal-mean properties, mainly through standing meanders associated with regions of high eddy kinetic energy. Here, an idealized channel model is used to explore the spatial distribution of energy exchange and its relationship to eddy geometry, as characterized by both eddy momentum and eddy buoyancy fluxes. Variations in energy exchange properties occur not only between standing meander and quasi-zonal jet regions, but throughout the meander itself. Both barotropic and baroclinic stability properties, as well as the magnitude of energy exchange terms, undergo abrupt changes along the path of the ACC. These transitions are captured by diagnosing eddy fluxes of energy and by adopting the eddy geometry framework. The latte...
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