Spatial and temporal variability of chlorophyll-a concentrations in the coastal Gulf of Alaska, 1998-2011, using cloud-free reconstructions of SeaWiFS and MODIS-Aqua data

We examined the spatial and temporal variability of chlorophyll-a (chl-a) concentrations in the coastal Gulf of Alaska (GOA) using a 14-year time series of cloud-free reconstructions of SeaWiFS and MODIS-Aqua chl-a data. Coast-wide and regional relationships between chl-a and likely environmental drivers, including anomalies in sea surface temperature (SST), photosynthetically-available radiation (PAR), sea surface height (SSHa), freshwater discharge, and coastal upwelling were explored. Coast-wide chl-a showed strong seasonal variability with pronounced spring and fall blooms, but both the magnitude and the seasonal patterns showed considerable interannual variability. Coast-wide annual chl-a anomalies were positive in years with elevated PAR, low SST, and a reduction in downwelling-favorable winds - conditions that are indicative of reduced cyclonic circulation associated with a weak Aleutian Low. The apparent negative effect of strong cyclonic circulation in the GOA on chl-a levels was further supported by negative relationships between elevated sea levels and coast-wide chl-a in both the spring and fall. If chl-a concentrations in the coastal GOA reflect productivity, these results are contrary to the prevailing view that strong cyclonic circulation enhances productivity in the GOA. The variability in the chl-a in each of four distinct and spatially contiguous regions that differed in the timing and magnitude of the spring and fall blooms was associated with different combinations of environmental variables. (C) 2013 Elsevier Ltd. All rights reserved.