The role of biological rates in the simulated warming effect on oceanic CO2 uptake

Abstract

AbstractMarine biology plays an important role in the ocean carbon cycle. However, the effect of warming‐induced changes in biological rates on oceanic CO2 uptake has been largely overlooked. We use an Earth system model of intermediate complexity to investigate the effect of temperature‐induced changes in biological rates on oceanic uptake of atmospheric CO2 and compare it with the effects from warming‐induced changes in CO2 solubility and ocean mixing and circulation. Under the representative CO2 concentration pathway RCP 8.5 and its extension, by year 2500, relative to the simulation without warming effect on the ocean carbon cycle, CO2‐induced warming reduces cumulative oceanic CO2 uptake by 469 Pg C, of which about 20% is associated with the warming‐induced change in marine biological rates. In our simulations, the bulk effect of biological‐mediated changes on CO2 uptake is smaller than that mediated by changes in CO2 solubility and ocean mixing and circulation. However, warming‐induced changes in individual biological rates, including phytoplankton growth, phytoplankton mortality, and detritus remineralization, are found to affect oceanic CO2 uptake by an amount greater than or comparable to that caused by changes in CO2 solubility and ocean physics. Our simulations, which include only a few temperature‐dependent biological processes, demonstrate the important role of biological rates in the oceanic CO2 uptake. In reality, many more complicated biological processes are sensitive to temperature change, and their responses to warming could substantially affect oceanic uptake of atmospheric CO2.