Global Oceanic Production and Climate Change

Abstract

Even a cursory glance at the global Coastal Zone Color Scanner (CZCS) composites of oceanic phytoplankton biomass reveals that the regions of highest biomass are geographically separated and distinct. Three main regions can be distinguished - the northern hemisphere temperate oceans, the Equatorial divergences and the southern hemisphere temperate waters around 40–50°S. In the three regions the large scale mechanisms which control algal growth and primary production are quite different. Spring blooms dominate the northern hemisphere oceans, whereas divergence and interaction between the western boundary currents and the west wind drift dominate the processes in Equatorial and southern hemisphere regions respectively. Interactions between ocean biology and climate change occur at a variety of scales. The large scale circulation of the world ocean determines rates of subduction and upwelling and hence feeds back upon plankton growth, the global carbon cycle and climate change. CZCS composites show clear interannual variability in biomass in the Equatorial Pacific in response to El Nino Southern Oscillation (ENSO) events and there is some evidence of large interannual variability in the region of the Subtropical Convergence in the S Hemisphere. There are not yet sufficient data to make a clear statement about the large scale effects of climate change on oceanic production. In each of the three main reions it is the mesoscale interaction of physics and biology which controls the availability of nutrients and the increase in biomass at scales of a few kilometres. Given that it is the biology which is partly responsible for reducing the pCO2 in surface waters and that exchange with deep waters is also important, subtle small scale interactions between the mesoscale physics and the stability of surface waters will have a large effect on algal growth and the atmospheric carbon flux.