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

Abstract

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.