Temperature, growth season length and phytoplankton abundance in the Gulf of Maine

Abstract

I show that the relation between annual average phytoplankton concentration (as mg Chl-a.m-3) and in situ sea surface temperature, SST, is positive (Chl-a â 0.5 Ã SST, r = 0.8, p < 0.001) at an average temperature of 11oC (range 10oC â 12oC) in the Gulf of Maine. However, within seasonal observations 2005-2009 were predominant negatively associated. For the first, annual average relationship, the extension of the growth season with increasing temperature may be an important factor. I show that an increase by 1oC start the growth season 8 days earlier and lengthen the season with 13 days (temp > 10oC). Tentative calculations suggest that the increased length matches the increase in annual phytoplankton concentration. For the second, negative relationship, I suggest that warmer water during late summer increases stratification and limits nutrient supply to the upper productive layer.