Physical associations with seasonal and interannual variability of bacterial production in the coastal waters of the western Antarctic Peninsula

We conducted a decadal (2002-2014) time series analysis of bacterial production (BP) at Palmer Station B, Antarctica (64.8°S, 64.1°W) to examine how large-scale climate and local physical forcing predict its seasonal and interannual variability.  The monthly averages of bacterial production rates ranged from 11±6 mgC m^-2 d^-1 in October to 44±29 mgC m^-2 d^-1 in January, which accounts for a low fraction (~2% on average) of ¹⁴C-derived primary production (PP) as expected in polar waters.  For most years, ³H-leucine incorporation was significantly correlated with both PP and chlorophyll a (Chl) across depths (discrete depth 0 to 50m; r² = 0.20-0.53, all P < 0.05), indicating a tight phytoplankton-bacterial coupling.  Empirical Orthogonal Function (EOF) decomposition reveals that the most common seasonal variability pattern (leading EOF mode, 44% of total seasonal variability) for bacterial production rates is elevated BP rates from December to February (DJF).  The strong phytoplankton-bacterial coupling was also implied by an overall good agreement between years with positive bacterial production anomalies and of the same for Chl.  Favorable conditions for the DJF bacterial production included an early spring sea ice retreat and increased water column stability via a shallow seasonal mixed layer depth, which was previously shown as a scenario favorable for phytoplankton blooms.  Our results indicate that bacteria in the coastal waters along the western Antarctic Peninsula rely on dissolved organic carbon (DOC) released by primary producers given an absence of extraterrestrial DOC inputs to fuel their production and that physical conditions favorable for high phytoplankton accumulations thus also predict high bacterial production rates.