Polynyas represent regions of enhanced primary production due to the low, or absent, sea-ice cover coupled with the proximity of nutrient sources. However, studies throughout the Southern Ocean suggest elevated primary production does not necessarily result in increased carbon export. Three coastal polynyas in East Antarctica and an off-shelf region were visited during the austral summer of 2016/2017 to examine the vertical distribution of particulate organic carbon (POC). Carbon export was also examined using thorium-234 (234Th) as a proxy at two of the polynyas. Our results show that concentrations and integrated POC stocks were higher within the polynyas compared to the off-shelf sites. Within the polynyas, vertical POC concentrations were higher in the Mertz and Ninnis polynyas compared to the Dalton polynya. Similarly, higher carbon export was measured in the diatom-dominated Mertz polynya, where large particles (53 μm) represented a significant fraction of the particulate 234Th and POC, compared to the small flagellate-dominated Dalton polynya, where almost all the particulate 234Th and POC were found in the smaller size fraction (1 - 53 μm). The POC to Chlorophyll-a ratios suggests that organic matter below the mixed layer in the polynyas consisted largely of fresh phytoplankton at this time of the year. In combination with a parallel study on phytoplankton production at these sites, we find that increased primary production at these polynyas does lead to greater concentrations and export of POC and a higher POC export efficiency.

Southern Ocean eddies shape the foraging ecology of marine apex predators such as marine mammals and seabirds. A growing number of animal tracking studies show that predators alter their swimming, diving, and foraging behavior in mesoscale eddies. However, little is known about how Southern Ocean eddies influence the distribution of mesopelagic micronekton (fish, squid, and crustaceans), which are major prey items of megafauna. Studies in other parts of the world have found that eddies can impact the abundance and community composition of micronekton. Here, we analyze acoustic observations from a 14-day survey of a mesoscale eddy, its surrounding waters, and the Sub-Antarctic frontal waters where the eddy originated. We report and interpret spatial patterns of acoustic backscattering at 18 kHz, a proxy indicating combined changes in species, size, and abundance of micronekton. We find that the vertical distribution of Deep Scattering Layers matched the underwater light conditions characteristic of the eddy core, periphery, and surrounding waters, at scales smaller than 10 km. Furthermore, the average water-column integrated acoustic backscattering values in the eddy core were only half of the values measured in the Sub-Antarctic Zone waters surrounding the eddy. By contrast, the acoustic properties of the eddy core were similar to those measured in the Polar Front Zone, where the eddy originated 27 days before our sampling. These results show that, as for physical and chemical tracers, the eddy maintained its biological characteristics from its source waters creating a unique habitat compared to its surrounding waters.