Propagation of climatic events on ocean stratification, marine biology, and CO2: Case studies over the 1979–1999 period

We investigate the propagation of climatic events on ocean stratification, marine biology, and CO2 using a large-scale ocean general circulation model coupled to a simple biogeochemical model of plankton dynamics and the carbon cycle. The model was forced with satellite and reanalysis fields during 1979-1999. We focus on three climatic events: (1) the North Atlantic Oscillation, (2) El Niño events, and (3) the Antarctic Circumpolar Wave. Such climatic events caused variability in ocean stratification, approximated by the mixing depth (MD), from ±20 m in the subtropics to ±100 s of meters at high latitudes. In the subtropics, deepening of the MD resupplied nutrient-impoverished surface waters and increased marine biomass by 20-100%. In contrast, at high latitudes, shoaling of the MD lengthened the growing season (i.e., the length of time that light is available for plankton growth) and increased marine biomass by 10-20%. Variability in marine biology reached global peak-to-peak values of ±0.01 mg m-3 for surface chl a, ±3.4 Pg C yr-1 for primary production, and ±0.3 Pg C yr-1 for export production and its contribution to CO2 fluxes. Our model results suggest that changes in ocean stratification driven by short-term climatic events could be used to understand and quantify the feedbacks from marine biology to CO2 and climate.