Large scale forcing through the Antarctic food web: Physical drivers of the interannual variability at Palmer Station, Antarctica

Plankton dynamics in the Western Antarctic Peninsula (WAP) are characterized by high interannual variability. Here we examined phytoplankton bloom cycles and krill population dynamics associated with variability in the Southern Annular Mode (SAM) and Multivariate ENSO index (MEI). During the 20-year Palmer LTER (PAL LTER) time-series in Palmer Station, Antarctica (1991-present), peaks in chlorophyll-a concentration have occurred every 4-6 years. These high chlorophyll-a anomalies corresponded to large krill spawning events, which produced the start of a new krill cohort the following season, evidenced in penguin gut contents. Principle component and empirical orthogonal function analyses of the regional SeaWiFS surface chlorophyll-a anomalies revealed that the first three modes of surface chlorophyll-a variability described 33% of the total variability, and were correlated to the combined SAM (December, January, February; DJF) and annual MEI index. In the Palmer Station region, there was an inverse relationship between surface chlorophyll-a and the combined SAM (DJF)/Yearly MEI index such that chlorophyll-a peaks tended to occur during periods of weak La Niña and negative/neutral SAM events. Physical mechanisms will be discussed.