Expanded Understanding of the Western Antarctic Peninsula Sea‐Ice Environment Through Local and Regional Observations at Palmer Station.

The Western Antarctic Peninsula (WAP) has been experiencing rapid regional warming since at least the 1950s, however, the impacts of this warming at the local scale are variable and nuanced. Previous studies that have linked sea‐ice variability to biogeochemical cycles and food web dynamics often combine local‐scale biogeochemical data with coarse‐resolution regional satellite sea‐ice data, which may not adequately capture local sea‐ice conditions. In this study, we analyzed local‐scale in situ sea‐ice observations collected as part of a 28‐year record (1992–2020) from the Palmer Long‐Term Ecological Research site at Anvers Island, mid‐WAP, in conjunction with isotopically‐derived sea‐ice meltwater (SIM) fractions and satellite‐derived sea‐ice motion and concentration, to quantify the variability and long‐term trends in local sea‐ice behavior. In situ sea ice observations at Palmer Station displayed higher variability than satellite observations and showed no significant declines over this time, despite region‐wide declines identified in prior studies. Higher spring SIM fractions were attributed to strong northward sea‐ice motion throughout the winter. Applying these local‐scale sea‐ice insights to similarly scaled stratification and chlorophyll‐a measurements, we found that a longer‐lasting, more consistent sea‐ice pack led to greater water column stratification following the spring sea‐ice retreat. Greater sea‐ice persistence and stronger stratification led to larger peaks in chlorophyll‐a, though sea‐ice metrics did not explain the positive temporal trends in either stratification strength or chlorophyll‐a. Through this study, we identify how local sea‐ice observations and meltwater data can enhance satellite data to build an understanding of the intricate connections between ice, water column dynamics, and phytoplankton. Plain Language Summary: The western coast of the Antarctic Peninsula is one of the fastest‐warming places on the planet. The coastal ocean here is home to large amounts of marine algae (phytoplankton), which supports a rich ecosystem. Prior studies have noted that sea ice plays a role in determining how abundant phytoplankton are in the water, but these studies typically use sea‐ice measurements from regional‐scale satellites, which do not always provide details about how sea ice is behaving at the local scale. Here, we analyze a daily sea‐ice record that was acquired locally through visual observation, as well as local‐scale ocean water samples that detect how much sea‐ice meltwater is present. We found that, despite regional warming, high year‐to‐year variability masks long‐term trends in the local sea‐ice record, and that the movement of sea ice during winter influences how much sea ice melts in place when it retreats in the spring. We also found that years with greater winter sea‐ice coverage led to summers with more ideal conditions for phytoplankton growth (e.g., shallower and more stratified water), though sea ice does not appear to be the primary driver behind recent increases in phytoplankton. Key Points: Local‐scale sea‐ice measurements at Palmer Station show higher daily and interannual variability than satellite‐based measurementsNorthwestward winter ice movement typically preceded elevated spring sea‐ice meltwater near Palmer StationLocal sea‐ice retreat influences water column stratification and Chlorophyll‐a but does not explain increasing trends in these parameters [ABSTRACT FROM AUTHOR]