Interannual variability of seasonal phytoplankton blooms in the north polar Atlantic in response to atmospheric forcing

The year-to-year variability of timing, intensity, and spatial distribution of surface phytoplankton during spring-summer seasons is examined in the north polar region of the Atlantic using satellite-derived chlorophyll a concentration (Chl) over 7 years (1998-2004). Each year phytoplankton bloom differed in onset, temporal evolution, and intensity. This interannual variability is to a large degree controlled by local weather, as indicated by the analysis of coincident meteorological data. The atmospheric forcing was parameterized in terms of the generation rate of turbulent kinetic energy (TKERT) supplied from the atmosphere to the ocean. Timing of the bloom is delayed in years with high TKERT supplied to the ocean in March. In April, Chl (local and regionally averaged) and TKERT are inversely related to one another. The late winter and early spring atmospheric conditions influence the seasonal Chl patterns. The seasonal (April-August) Chl correlates well with net heat flux, wind energy, and TKERT in March and April, but the correlation can be negative or positive in different areas of the north polar Atlantic. The correlation between TKERT and seasonal Chl is positive in the Greenland Gyre (higher seasonal Chl corresponds to higher TKERT in March-April) and negative in the regions of East Greenland and North Atlantic/West Spitsbergen Currents. The most likely explanation for the positive correlation between TKERT and Chl within the Greenland Gyre is that higher TKERT in spring increases the seasonal supply of nutrients into surface waters.