Distribution and export of particulate organic carbon in East Antarctic coastal polynyas

<p dir="ltr">No description su<a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/polynyas" target="_blank">Polynyas</a> represent regions of enhanced <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/primary-production" target="_blank">primary production</a> because of the low, or absent, sea-ice cover coupled with the proximity of nutrient sources. However, studies throughout the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/southern-ocean" target="_blank">Southern Ocean</a> suggest elevated primary production does not necessarily result in increased carbon export. Three coastal polynyas in East <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/antarctic-region" target="_blank">Antarctica</a> and an off-shelf region were visited during the austral summer from December 2016 to January 2017 to examine the vertical distribution and concentration of <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/particulate-organic-matter" target="_blank">particulate organic carbon</a> (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 (average 50% and 39%, respectively), 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 suggest that organic matter below the mixed layer in the polynyas consisted largely of fresh <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/phytoplankton" target="_blank">phytoplankton</a> at this time of the year. In combination with a parallel study on <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/phytoplankton" target="_blank">phytoplankton</a> 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.pplied</p>