POSTER Session 4

RETHINKING ANTARCTIC POLYNYAS: MINIMIZING OCEAN COLOR REMOTE SENSING ADJACENCY EFFECTS ALONG ICY COASTS

Antarctic coastal polynyas, areas of open water enclosed by sea ice, are hotspots of primary production. In addition to supporting rich Antarctic coastal marine ecosystems, polynyas are also thought to support a disproportionate sink of atmospheric CO2, owing to their intense productivity. Past ocean color estimates of Antarctic coastal chlorophyll a (Chl) derived using l2gen/SeaDAS atmospheric correction have shown the highest Chl away from the ice edge. In-situ observations indicate elevated Chl concentrations extend near the coast and ice edge, however. This discrepancy is likely due to the adjacency effect along icy coastlines. Here, we investigate the bias caused by adjacency by evaluating field data in comparison to imagery from different atmospheric correction algorithms (POLYMER and l2gen), different phytoplankton parameters, and radiative transfer modeling, and we explore how these biases may affect our estimates of polynya productivity and particulate organic carbon concentrations. Our analysis shows that POLYMER and l2gen Chl products diverge within 40 km from the coast, with POLYMER Chl about a factor of four greater within 10 km of the coast. Fluorescence line height, a Chla proxy less susceptible to adjacency effects, supports higher Chl values near icy coastlines and mirrors spatial patterns in POLYMER Chl. Simulations also corroborate that adjacency impacts occur out to 40 km from the ice edge. Considering adjacency effects has the potential to revise our concept of Antarctic polynya productivity, with much higher productivity near the ice edge than previously thought.

Hilde Oliver, Woods Hole Oceanographic Institution, USA, [email protected], https://orcid.org/0000-0002-5507-3333

Jessica Turner, University of Connecticut, USA, [email protected]

Alexandre Castagna, Ghent University, Belgium, [email protected]

Henry Houskeeper, Woods Hole Oceanographic Institution, USA, [email protected]

Heidi Dierssen, University of Connecticut, USA, [email protected]

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