UC Riverside

The ocean plays a dominant role in modulating Earth’s energy imbalance since the industrial age by absorbing and storing the excessive heat. In this dissertation, we utilize observation data sets and climate model simulations to investigate the global ocean circulation changes and ocean heat uptake (OHU) in a warming climate.We first explore the effects of historical ozone changes on Southern Ocean heat uptake and storage. We find that ozone-induced interior warming contributes to about 22% of the historical Southern Ocean warming over 1958-2005, with the heat is taken between 50-58°S but mainly stored at low latitudes due to ocean circulation anomaly induced equatorward heat redistribution. We then distinguish the different roles of troposphere ozone increases and stratosphere ozone depletion on OHU. We show that both ozone changes contribute to Southern Ocean interior warming but with distinct physical mechanisms: the former causes a subsurface warming in the Southern Ocean primarily via the deepening of isopycnals, while the latter via spiciness changes along isopycnals. Meanwhile, we also quantify the effects of anthropogenic aerosols and greenhouse gases in modulating oceanic heat since the industrial age. We show that, in response to anthropogenic aerosols, OHU diminishes in the subpolar Atlantic, and the Southern Ocean imports heat from the Indo-Pacific but exports heat into the Atlantic, which is comparable to OHU changes. Anthropogenic greenhouse gases, on the contrary, promote the OHU in the subpolar Atlantic and allow the Southern Ocean to import heat from the Atlantic but export heat to the Indo-Pacific. Nevertheless, interbasin heat exchange is far smaller than OHU changes. Finally, we explore the effects of Arctic sea ice loss on global ocean circulations and ocean heat redistribution. We find that Arctic sea ice loss enhances OHU in the subpolar North Atlantic while changes in ocean heat storage is timescale-dependent. Within a decade, the Atlantic meridional overturning circulation (AMOC) is little altered such that most of the taken heat is locally stored in the Atlantic. On a multidecadal to centennial timescale, the AMOC decelerates redistributing the heat to other basins through interbasin ocean heat exchanges, therefore leading to global ocean warming.