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