Submesoscale coherent vortices (SCVs) are long-lived subsurface-intensified eddies that advect heat, salt, and biogeochemical tracers throughout the ocean. Previous observations indicate that SCVs are abundant in the Arctic because sea ice suppresses surface-intensified mesoscale structures. Regional observational and modeling studies have indicated that SCVs may be similarly prevalent beneath Antarctic sea ice, but there has been no previous systematic attempt to observe these eddies. This study presents the discovery of eddies in the Southern Ocean's seasonally sea ice-covered region using the Marine Mammals Exploring the Oceans Pole to Pole (MEOP) hydrographic measurements. Eddies are identified via a novel algorithm that utilizes anomalies in spice, isopycnal separation, and dynamic height along MEOP seal tracks. This algorithm is tested and calibrated by simulating the MEOP seal tracks using output from a 1/48° global ocean/sea ice model, in which subsurface eddies are independently identified via the Okubo–Weiss parameter. Approximately 60 detections of cyclonic and over 100 detections of anticyclonic SCVs are identified, with typical dynamic height anomalies of ~0.05 m²s⁻², core depths of ~200m, and vertical half-widths of ~100m, similar to their Arctic counterparts. The eddies exhibit a pronounced geographical asymmetry: cyclones are exclusively observed in the open ocean, while ~90% of the anticyclones are located on the continental shelf, consistent with injection of low-potential vorticity waters by surface buoyancy loss. These findings provide a first observational characterization of eddies in the seasonally ice-covered Southern Ocean, which will serve as a basis for future investigation of their role in near-Antarctic circulation and tracer transport.

The Antarctic continental shelf (ACS) hosts processes that impact the climate system globally,which has motivated ongoing efforts to characterize its state, circulation, and variability. However, the natureand consequences of eddies over the ACS, and their contributions to the budgets of heat and freshwater, remainsystematically understudied. This study uses hydrographic measurements collected from instrumented seals,supported by a high‐resolution model of the southern Weddell Sea, to characterize eddies and their role invertical heat transport around the entire ACS. A key finding is that eddies are ubiquitous, and exhibit frequent (2%–10% of hydrographic casts) occurrences of O(1) bulk Richardson numbers, indicative of submesoscalevariability. However, along‐track density power spectra exhibit wavenumber dependences of ~k^-3, consistentwith quasigeostrophic turbulence. Approximately 0.3% of the points in the surface mixed layer satisfyconditions favorable for symmetric instability, although its prevalence is likely higher than this due to therelatively coarse resolution of the seal tracks. Vertical heat transports, estimated from a regional model‐calibrated parameterization of submesoscale restratification, are largest in shelf regions hosting dense water,which have previously been identified as key sites of warm water intrusions onto the ACS. These regions alsoexhibit the largest seasonal cycles, with elevated winter eddy activity and heat fluxes accompanying theformation of high salinity shelf waters. These findings indicate that eddies may contribute substantially to ACSheat and tracer budgets, and motivate further study of their role in determining the pathways and fate of heat thatintrudes onto the ACS.

The Southern Ocean connects the ocean's major basins via the Antarctic Circumpolar Current (ACC), and closes the global meridional overturning circulation (MOC). Observing these transports is challenging because three-dimensional mesoscale-resolving measurements of currents, temperature, and salinity are required to calculate transport in density coordinates. Previous studies have proposed to circumvent these limitations by inferring subsurface transports from satellite measurements using data-driven methods. However, it is unclear whether these approaches can identify the signatures of subsurface transport in the Southern Ocean, which exhibits an energetic mesoscale eddy field superposed on a highly heterogeneous mean stratification and circulation. This study employs Deep Learning techniques to link the transports of the ACC and the upper and lower branches of the MOC to sea surface height (SSH) and ocean bottom pressure (OBP), using an idealized channel model of the Southern Ocean as a test bed. A key result is that a convolutional neural network produces skillful predictions of the ACC transport and MOC strength (skill score of ∼0.74 and ∼0.44, respectively). The skill of these predictions is similar across timescales ranging from daily to decadal but decreases substantially if SSH or OBP is omitted as a predictor. Using a fully connected or linear neural network yields similarly accurate predictions of the ACC transport but substantially less skillful predictions of the MOC strength. Our results suggest that Deep Learning offers a route to linking the Southern Ocean's zonal transport and overturning circulation to remote measurements, even in the presence of pronounced mesoscale variability.

Antarctic Bottom Water (AABW) formation and transport constitute a key component of the global ocean circulation. Direct observations suggest that AABW volumes and transport rates may be decreasing, but these observations are too temporally or spatially sparse to determine the cause. To address this problem, we develop a new method to reconstruct AABW transport variability using data from the GRACE (Gravity Recovery and Climate Experiment) satellite mission. We use an ocean general circulation model to investigate the relationship between ocean bottom pressure and AABW: we calculate both of these quantities in the model, and link them using a regularized linear regression. Our reconstruction from modeled ocean bottom pressure can capture 65%–90% of modeled AABW transport variability, depending on the ocean basin. When realistic observational uncertainty values are added to the modeled ocean bottom pressure, the reconstruction can still capture 30%–80% of AABW transport variability. Using the same regression values, the reconstruction skill is within the same range in a second, independent, general circulation model. We conclude that our reconstruction method is not unique to the model in which it was developed and can be applied to GRACE satellite observations of ocean bottom pressure. These advances allow us to create the first global reconstruction of AABW transport variability over the satellite era. Our reconstruction provides information on the interannual variability of AABW transport, but more accurate observations are needed to discern AABW transport trends.

Antarctic ice shelves are losing mass at drastically different rates, primarily due to differing rates of oceanic heat supply to their bases. However, a generalized theory for the inflow of relatively warm water into ice shelf cavities is lacking. This study proposes such a theory based on a geostrophically constrained inflow, combined with a threshold bathymetric elevation, the Highest Unconnected isoBath (HUB), that obstructs warm water access to ice shelf grounding lines. This theory captures ∼ 90% of the variance in melt rates across a suite of idealized process-oriented ocean/ice shelf simulations with quasi-randomized geometries. Applied to observations of ice shelf geometries and offshore hydrography, the theory captures ∼80% of the variance in measured ice shelf melt rates. These findings provide a generalized theoretical framework for melt resulting from buoyancy-driven warm water access to geometrically complex Antarctic ice shelf cavities.

The design of non-eddy-resolving numerical models requires a good understanding and an appropriate representation of the eddy-mean flow feedback. To understand this feedback, we propose a diagnostic framework that links eddy geometry with the eddy-mean energy exchange terms in the Lorenz energy diagram. This framework provides explicit mathematical formulas that link eddy-mean energy exchange rates with both the mean state structure and the properties of eddy momentum ellipses and eddy buoyancy ellipses. Considering that the mean flow contains both along- and cross-stream variations, we decompose the eddy-mean kinetic energy exchange term into 3 components: one associated with the cross-stream variation in mean flow (M_C), one associated with the along-stream variation in mean flow (M_A), and one associated with the variation in mean flow (M_R). We also state the corresponding geometric formulas. The geometric interpretation of M_C is consistent with barotropic instability theories and the literature on eddy geometry. As for M_A, the weakening (strengthening) of mean flow in the along-stream direction corresponds to eddy kinetic energy generation (decay) through M_A. M_A and a portion of M_R are related under the quasi-geostrophic assumption. From a global integral perspective, both the along-stream and cross-stream variations in the mean flow contribute considerably to eddy-mean kinetic energy exchange. At the Kuroshio Extension, both the mean state energy level and eddy energy level are key to shaping the spatial pattern of eddy-mean energy exchange. This framework offers a tool for geometrically interpreting eddy-mean energy exchange, which may offer guidance for eddy parameterizations.

Eastern boundary upwelling systems (EBUSs) host equatorward wind-driven near-surface currents overlying poleward subsurface undercurrents. Various previous theories for these undercurrents have emphasized the role of poleward alongshore pressure gradient forces (APFs). Energetic mesoscale variability may also serve to accelerate undercurrents via mesoscale stirring of the potential vorticity gradient imposed by the continental slope. However, it remains unclear whether this eddy rectification mechanism contributes substantially to driving poleward undercurrents in EBUS. This study isolates the influence of eddy rectification on undercurrents via a suite of idealized simulations forced either by alongshore winds, with or without an APF, or by randomly generated mesoscale eddies. It is found that the simulations develop undercurrents with strengths comparable to those found in nature in both wind-forced and randomly forced experiments. Analysis of the momentum budget reveals that the along-isobath undercurrent flow is accelerated by isopycnal advective eddy momentum fluxes and the APF and retarded by frictional drag. The undercurrent acceleration may manifest as eddy momentum fluxes or as topographic form stress depending on the coordinate system used to compute the momentum budget, which reconciles these findings with previous work that linked eddy acceleration of the undercurrent to topographic form stress. The leading-order momentum balance motivates a scaling for the strength of the undercurrent that explains most of the variance across the simulations. These findings indicate that eddy rectification is of comparable importance to the APF in driving poleward undercurrents in EBUSs and motivate further work to diagnose this effect in high-resolution models and observations and to parameterize it in coarse-resolution ocean/climate models.

Eastern boundary upwelling systems (EBUSs) are among the most productive regions in the ocean because deep, nutrient-rich waters are brought up to the surface. Previous studies have identified winds, mesoscale eddies and offshore nutrient distributions as key influences on the net primary production in EBUSs. However uncertainties remain regarding their roles in setting cross-shore primary productivity and ecosystem diversity. Here, we use a quasi-two-dimensional (2D) model that combines ocean circulation with a spectrum of planktonic sizes to investigate the impact of winds, eddies, and offshore nutrient distributions in shaping EBUS ecosystems. A key finding is that variations in the strength of the wind stress and the nutrient concentration in the upwelled waters control the distribution and characteristics of the planktonic ecosystem. Specifically, a strengthening of the wind stress maximum, driving upwelling, increases the average planktonic size in the coastal upwelling zone, whereas the planktonic ecosystem is relatively insensitive to variations in the wind stress curl. Likewise, a deepening nutricline shifts the location of phytoplankton blooms shore-ward, shoals the deep chlorophyll maximum offshore, and supports larger phytoplankton across the entire domain. Additionally, increased eddy stirring of nutrients suppresses coastal primary productivity via “eddy quenching,” whereas increased eddy restratification has relatively little impact on the coastal nutrient supply. These findings identify the wind stress maximum, isopycnal eddy diffusion, and nutricline depth as particularly influential on the coastal ecosystem, suggesting that variations in these quantities could help explain the observed differences between EBUSs, and influence the responses of EBUS ecosystems to climate shifts.