Phytoplankton physiology can affect ocean surface temperatures

Abstract

A key biological link between ocean geochemical cycles, ocean color and sea surface temperature (SST) is the nitrogen-to-chlorophyll a (N:chl a) ratio of phytoplankton. This is because nitrogen is the limiting factor over approximately 2/3 of the ocean surface and light absorption depends on the concentration of chlorophyll a. Recent work has demonstrated systematic variability in this ratio. Using one-dimensional models at two locations we show that varying N:Chl a, rather than keeping a fixed mean value (0-150m), leads to lower chlorophyll a in the mixed layer, less light absorption within the mixed layer and cooler sea surface temperatures. At the equator the temperature reduction is 0.15°C throughout the year whereas at 35°N, a temperature difference of about l°C occurs during the summer. Although demonstrated at only two locations, this effect is likely to occur over large parts of the ocean.