Abstract

Anthropogenic emissions of greenhouse gases have led to an increase in CO₂ and temperature in the atmosphere, as well as an increase in the sea surface temperature (SST). It has been suggested that a rise in SST leads to an increase in ocean stratification, surface nutrient limitation, and a po... Show moreAnthropogenic emissions of greenhouse gases have led to an increase in CO₂ and temperature in the atmosphere, as well as an increase in the sea surface temperature (SST). It has been suggested that a rise in SST leads to an increase in ocean stratification, surface nutrient limitation, and a possible decrease in the abundance of phytoplankton in the surface ocean. Here, we investigate long-term changes in surface phytoplankton, specifically diatoms, diazotrophs, and small plankton abundance using monthly output from a hindcast (1958-2007) simulation of the Community Earth System Model. We find that annual-mean modeled phytoplankton chlorophyll concentration is similar to that observed from satellites, and that small phytoplankton dominate the surface ocean chlorophyll field at most locations. Seasonal evolution of the phytoplankton shows small plankton and diatoms peak in the summer months, while diazotroph abundance peaks in the spring season. Linear trends in the abundance of the three groups reveals the response of each group to past climate change. Small plankton and diatoms exhibit similar trends: increasing concentration with time in the Arctic and Southern Ocean, but decreasing concentration with time in the subtropics. Diazotrophs show a decrease in concentration with time in the subtropical regions. Show less