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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14567

Changing phytoplankton phenology in the marginal ice zone west of the Antarctic Peninsula

Jessica S. Turner*, Heidi Dierssen, Oscar Schofield, Heather H. Kim, Sharon Stammerjohn, David R. Munro, Maria Kavanaugh

*Corresponding author:

ABSTRACT: Climate change is altering global ocean phenology, the timing of annually occurring biological events. We examined the changing phenology of the phytoplankton accumulation season west of the Antarctic Peninsula to show that blooms are shifting later in the season over time in ice-associated waters. The timing of the start date and peak date of the phytoplankton accumulation season are occurring later over time from 1997 to 2022 in the marginal ice zone and over the continental shelf. A divergence is seen between offshore waters and ice-associated waters, with offshore bloom timing becoming earlier, yet marginal ice zone and continental shelf bloom timing shifting later. Higher chlorophyll-a concentration (Chl-a) in the fall season is seen in recent years, especially over the northern continental shelf. Minimal long-term trends in annual Chl-a occurred, likely due to the combination of later start dates in spring and higher Chl-a in fall. The most likely mechanism for later spring start dates is increasing spring wind speed, leading to deeper wind mixing in a region experiencing sea ice loss. Later phytoplankton bloom timing over the marginal ice zone and continental shelf will have consequences for surface ocean carbon uptake, food web dynamics, and trophic cascade.