Decoupling of projected oceanic uptake of carbon and heat in the 21stcentury in a high carbon emission pathway

Eric Mortenson1, Andrew Lenton1, Thomas W. Trull2, Xuebin Zhang3, Elizabeth Shadwick4 and Matthew Chamberlain5, (1)CSIRO Hobart, Hobart, TAS, Australia, (2)Commonwealth Scientific and Industrial Research Organisation, Marine and Atmospheric Research, Antarctic Climate Ecosystems Cooperative Research Centre, Hobart, TAS, Australia, (3)CSIRO, Oceans & Atmosphere, Centre for Southern Hemisphere Oceans Research (CSHOR), Hobart, TAS, Australia, (4)CSIRO Marine and Atmospheric Research, Hobart, TAS, Australia, (5)CSIRO Australian Resources Research Center, Hobart, WA, Australia
The global oceans have been a major sink of anthropogenic CO2 and heat since the preindustrial era, thereby slowing the increase in atmospheric carbon and heat content. While air-sea exchange of both carbon and heat are dependent on similar mechanisms (i.e., air-sea differences and wind), with the general pattern of net storage showing agreement, there is the potential for a divergence due to mechanisms that do not affect both properties (e.g. chemical buffering capacity and temperature-mediated solubility of carbon). This study addresses the question, when, where, and by how much will the pathways for oceanic uptake of heat and carbon diverge in the “Business-as-Usual” (RCP8.5) scenario of atmospheric CO2 changes over the 21st century via the Ocean Forecasting Australia Model with an eddy-resolving horizontal resolution (0.1°). The experiment projects that 21st century cumulative uptake of carbon and heat will be three and five times higher, respectively, than estimates for the period 1870-1995, with a net storage of carbon of 250 Pg C and heat of 1.5*1024 J in the upper 700m of the global ocean. The simulation projects that the carbon uptake rate of the ocean will level off by the last quarter of the century, whereas the rate of increase of ocean heat content will continue to rise. Zonally-averaged analysis indicates that the Southern Ocean will remain the major hotspot for both heat and carbon uptake throughout the century, centered around 40° S. There is large interannual variability in the uptake of heat in the equatorial ocean (between 30° S and 30° N) but no substantial trend, and the oceans north of 40° N exhibit a decrease in carbon uptake after 2070. Further analysis utilizing a suite of simulations to break down the responses due to anthropogenic CO2 and heat forcing, respectively, will also be presented. Understanding the distinct trajectories of heat and carbon uptake is essential to projecting their impacts on the marine environment.