Climate-Biogeochemical Coupling in an Antarctic Coastal Ecosystem: Chlorophyll, Nutrient, and Bacterial Production

The regional climate and oceanic variability along the West Antarctic Peninsula (WAP) are affected by teleconnections of the El Niño-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM), which in turn cause high seasonal and interannual variability of biogeochemical processes, with sea ice as a mediating physical forcing. Here we investigate a link between climate forcing and biogeochemistry using interdecadal (1992-2014) observations during austral spring-summer (October-March) at Palmer Station (64.8°S, 64.1°W). By employing empirical orthogonal function (EOF) and general linear models (GLMs) via stepwise regression, we examined 1) seasonal and interannual variability of phytoplankton bloom (chlorophyll or Chl), bacterial production (BP), and nutrient (N, P, and Si) drawdown and 2) a scenario of climate and physical forcing mechanisms shaping the variability. Results showed that season-long growth of phytoplankton causes ~30% of N, P variability. This variability was predicted by increased water column stability as result of both spring sea ice melt under winter El Niño/-SAM and increased wind forcing due to a +SAM phase in the spring. In contrast, early spring diatom blooms, which cause ~20% of Si variability, were predicted by early spring retreat of sea ice. High BP (³H-leucine incorporation) years also appeared under an increased water column stability setting and co-occured with positive Chl anomaly years, demonstrating a close phytoplankton-bacterial coupling, presumably due to consumption of phytoplankton-derived organic matter. Future works focus on quantifying impacts of pure physical processes (e.g. sea ice, meteoric melt fractions, UCDW intrusion) on these biogeochemical parameters using optimal multiparameter (OMP) analysis with salinity and δ¹⁸O endmembers. By demonstrating controls of large-scale climate forcing on key biological variables, our findings may provide a better understanding for predicting ecological and biogeochemical responses to long-term climate change along the WAP.