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Abstract 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. 

Abstract 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 , core depths of , and vertical half‐widths of , 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. 

Abstract 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. 

Abstract Fjord circulation modulates the connection between marine‐terminating glaciers and the ocean currents offshore. These fjords exhibit both overturning and horizontal recirculations, which are driven by water mass transformation at the head of the fjord via subglacial discharge plumes and distributed meltwater plumes. However, little is known about how various fjord characteristics influence the interaction between 3D fjord circulation and glacial melt. In this study, high‐resolution numerical simulations of idealized glacial fjords demonstrate that recirculation strength controls melt, which feeds back on overturning and recirculation. The relationships between overturning, recirculation, and melt rate are well predicted by vorticity balance, reduced‐order melt parameterizations, and empirical scaling arguments. These theories allow us to take into account the near‐glacier horizontal velocities, which yield improved predictions of fjord overturning, recirculation, and glacial melt. 

Abstract Interaction between the atmosphere and ocean in sea ice–covered regions is largely concentrated in leads, which are long, narrow openings between sea ice floes. Refreezing and brine rejection in these leads inject salt that plays a key role in maintaining the polar halocline. The injected salt forms dense plumes that subsequently become baroclinically unstable, producing submesoscale eddies that facilitate horizontal spreading of the salt anomalies. However, it remains unclear which properties of the stratification and leads most strongly influence the vertical and horizontal spreading of lead-input salt anomalies. In this study, the spread of lead-injected buoyancy anomalies by mixed layer and eddy processes are investigated using a suite of idealized numerical simulations. The simulations are complemented by dynamical theories that predict the plume convection depth, horizontal eddy transfer coefficient, and eddy kinetic energy as functions of the ambient stratification and lead properties. It is shown that vertical penetration of buoyancy anomalies is accurately predicted by a mixed layer temperature and salinity budget until the onset of baroclinic instability (~3 days). Subsequently, these buoyancy anomalies are spread horizontally by eddies. The horizontal eddy diffusivity is accurately predicted by a mixing-length scaling, with a velocity scale set by the potential energy released by the sinking salt plume and a length scale set by the deformation radius of the ambient stratification. These findings indicate that the intermittent opening of leads can efficiently populate the polar halocline with submesoscale coherent vortices with diameters of ~10 km, and they provide a step toward parameterizing their effect on the horizontal redistribution of salinity anomalies. 

Abstract Previous studies have concluded that the wind-input vorticity in ocean gyres is balanced by bottom pressure torques (BPT), when integrated over latitude bands. However, the BPT must vanish when integrated over any area enclosed by an isobath. This constraint raises ambiguities regarding the regions over which BPT should close the vorticity budget, and implies that BPT generated to balance a local wind stress curl necessitates the generation of a compensating, nonlocal BPT and thus nonlocal circulation. This study aims to clarify the role of BPT in wind-driven gyres using an idealized isopycnal model. Experiments performed with a single-signed wind stress curl in an enclosed, sloped basin reveal that BPT balances the windsonlywhen integrated over latitude bands. Integrating over other, dynamically motivated definitions of the gyre, such as barotropic streamlines, yields a balance between wind stress curl and bottom frictional torques. This implies that bottom friction plays a nonnegligible role in structuring the gyre circulation. Nonlocal bottom pressure torques manifest in the form of along-slope pressure gradients associated with a weak basin-scale circulation, and are associated with a transition to a balance between wind stress and bottom friction around the coasts. Finally, a suite of perturbation experiments is used to investigate the dynamics of BPT. To predict the BPT, the authors extend a previous theory that describes propagation of surface pressure signals from the gyre interior toward the coast along planetary potential vorticity contours. This theory is shown to agree closely with the diagnosed contributions to the vorticity budget across the suite of model experiments.