PFTs and Export Production 1960–2006 Geoscientific Instrumentation Methods and Data Systems Long-term trends in ocean plankton production and particle export between 1960–2006 PFTs and Export Production 1960–2006

Abstract

We analyse long-term trends in marine primary and particle export production and their link to marine phytoplankton community composition over the period 1950–2006 using a hindcast simulation of the ocean component of the Community Climate System Model to which the Biogeochemical Elemental Cycling Model had been coupled. In our sim-5 ulation, global primary and export production decreased by 6 % and 7 %, respectively over the last 50 yr. These changes go along with a 8 % decrease in small phytoplank-ton biomass and 5 % decrease in zooplankton biomass. Diatom biomass decreases by 3 % with strong temporal and spatial variability. Strongest decreases in primary and export production occured in the Western Pacific, where increased stratification leads 10 to a decrease in total phytoplankton and a decrease in diatom fraction. This causes decreases in zooplankton biomass and a lower export efficiency. Strong phytoplankton composition changes occur in the Southern Ocean and North Atlantic, where increased wind stress leads to stronger mixing, which reduces the biomass of small phytoplank-ton, while diatoms profit from higher nutrient inputs and lower grazing pressure. The 15 relative fraction of diatoms correlates positively with the export efficiency (r = 0.8) in most areas except the Northern Pacific and Antarctic Circumpolar Current, where the correlation is negative (r = −0.5). However, long-term trends in global export efficiency are ultimately driven by decreases in small phytoplankton and consequent decreases in coccolithophore biomass.