ABSTRACTS

Oral Session 12 | Friday, October 7, 11:20–11:40 | Abstract 506

Shifts in the timing of the phytoplankton growing season along the west Antarctic Peninsula

A merged multi-sensor cloud-filled remote sensing dataset was analyzed to determine shifts in the phenology of the phytoplankton growing season from 1997-2021 for the West Antarctic Peninsula, which is rapidly warming. Sensitivity tests were performed to best define the start of the phytoplankton growing season based on satellite-derived Chl-a including threshold, rate of change, and cumulative sum approaches. Over the continental slope and shelf, the phytoplankton growing season is beginning later in the season over time. In southern continental shelf waters (60°S, 70°W), the phytoplankton growing season initiated 1-2 months later in recent years compared to the late 1990s. In northern coastal waters, the seasonality of the air-sea CO₂ flux has also shifted, showing evidence of a longer-lasting CO₂ sink extending later into the fall. Possible mechanisms were tested using coupled physical-biogeochemical modeling experiments, including changes in winds and decreased ice-associated early season water column stability. Phenology results will be discussed in the context of potential changes in absorption and backscattering caused by different phytoplankton groups, since coastal waters show a seasonal succession of large spring diatoms, summer cryptophytes, and late-season smaller diatoms. Future work will explore satellite-derived Chl-a algorithms and assess the potential to distinguish phytoplankton group using an in situ optical dataset collected in 2021, with concurrent IFCB imaging, HPLC pigments, QFT-ICAM hyperspectral absorption spectra, and above-water hyperspectral reflectance spectra. These data will improve understanding of the optical characteristics that make Antarctic phytoplankton unique in the global ocean.

Jessica Turner, University of Connecticut, 0000-0003-3392-0316

Heidi Dierssen, University of Connecticut, 0000-0003-4276-5530

Oscar Schofield, Rutgers University, 0000-0003-2359-4131

Hyewon Heather Kim, Woods Hole Oceanographic Institution

Sharon Stammerjohn, Institute of Arctic and Alpine Research, University of Colorado, Boulder

David Munro, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder