Strong winds in Southern Ocean storms drive air-sea carbon and heat fluxes. These fluxes are integral to the global climate system and the wind speeds that drive them are increasing. The current scatterometer constellation measuring vector winds remotely undersamples these storms and the higher winds within them, leading to potentially large biases in Southern Ocean wind reanalyses and the fluxes that derive from them. This observing system design study addresses these issues in two ways. First, we describe an addition to the scatterometer constellation, called Southern Ocean Storms -- Zephyr, to increase the frequency of independent observations, better constraining high winds. Second, we show that potential reanalysis wind biases over the Southern Ocean lead to uncertainty over the sign of the net winter carbon flux. More frequent independent observations per day will capture these higher winds and reduce the uncertainty in estimates of the global carbon and heat budgets.

Palmer Deep Canyon is one of the biological hotspots associated with deep bathymetric features along the Western Antarctic Peninsula. The upwelling of nutrient-rich Upper Circumpolar Deep Water to the surface mixed layer in the submarine canyon has been hypothesized to drive increased phytoplankton biomass productivity, attracting krill, penguins and other top predators to the region. However, observations in Palmer Deep Canyon lack a clear in-situ upwelling signal, lack a physiological response by phytoplankton to Upper Circumpolar Deep Water in laboratory experiments, and surface residence times that are too short for phytoplankton populations to reasonably respond to any locally upwelled nutrients. This suggests that enhanced local upwelling may not be the mechanism that links canyons to increased biological activity. Previous observations of isopycnal doming within the canyon suggested that a subsurface recirculating feature may be present. Here, using in-situ measurements and a circulation model, we demonstrate that the presence of a recirculating eddy may contribute to maintaining the biological hotspot by increasing the residence time at depth and retaining a distinct layer of biological particles. Neutrally buoyant particle simulations showed that residence times increase to upwards of 175 days with depth within the canyon during the austral summer. In-situ particle scattering, flow cytometry, and water samples from within the subsurface eddy suggest that retained particles are detrital in nature. Our results suggest that these seasonal, retentive features of Palmer Deep Canyon are important to the establishment of the biological hotspot.

Diel vertical migration (DVM) is a common behavior in zooplankton populations world-wide. Every day, zooplankton leave the productive surface ocean and migrate to deep, dark waters to avoid visual predators and return to the surface at night to feed. This behavior may also help retain migrating zooplankton in biological hotspots. Compared to fast and variable surface currents, deep ocean currents are sluggish, and can be more consistent. The time spent in the subsurface layer are driven by day length and the depth of surface mixed layer. A subsurface, recirculating eddy has recently been described in Palmer Deep Canyon, a submarine canyon adjacent to a biological hotspot. Previous circulation model simulations have shown that residence times of particles increase with depth within this feature. We hypothesize that DVM into the subsurface eddy increases local retention of migrating zooplankton in this biological hotspot and that shallower mixed layers and longer day length would increase the time in the subsurface layer. We demonstrate that vertically migrating particles have residence times on the order of 30 days, which is significantly greater than residence times of near-surface, non-migrating particles. The interaction of DVM with this subsurface feature may be important to the establishment of the biological hotspot within Palmer Deep Canyon by retaining critical food resources in the region. Similar interactions between DVM behavior and subsurface circulation features, modulated by mixed layer depth and day length, may also increase residence times of local zooplankton populations elsewhere.

Multi-decadal expansion in the winter maximum sea ice extent (SIE) around Antarctica was interrupted by contraction, beginning in 2016 and continuing into 2019. This unexpected behavior motivates a closer look at factors controlling the position of the outer ice margin.We analyzed sea ice concentration (SIC) estimates derived from passive microwave sensors with differing resolutions (SSM/I, AMSR-E and AMSR2) to identify spatial and temporal statistics of the sea ice edge deVned by 15% SIC. The low-pass Vltered position of the ice edge is similar in different products, with the maximum northward position determined by proximity to the relatively warm waters of the Antarctic Circumpolar Current. Higher resolution SIC products reveal greater spatial detail along the convoluted margin, resulting in a relatively longer sea ice perimeter. Spectral analysis does not identify statistically signiVcant peaks in length scales along the margin; however, visual comparison with geostrophic velocities and sea surface temperature inferred from satellite altimetry suggests that advection of sea ice by mesoscale eddies is an important mechanism for deforming the ice edge in some regions, such as the Bellingshausen Sea. We analyze a high-resolution (dx=5 km), coupled ocean-sea ice model which realistically represents the annual expansion of sea ice to quantify the dynamic and thermodynamic roles of eddies in sea-ice mass balance and SIE. These eddy effects on the sea ice edge are not well represented in coarser-grid ocean reanalysis products such as ECCO-2, motivating an investigation of how to represent eddy/sea-ice interactions in global climate models.