The Changing Role of Stratospheric Ozone and Greenhouse Gasses in Modifying the Southern Ocean Carbon Sink

As the largest oceanic sink of anthropogenic CO₂, the Southern Ocean (SO) plays a key role for climate and climate change, absorbing between 5 and 10 percent of the global CO₂ emissions from human activities each year. Factors influencing the efficiency of the Southern Ocean CO₂ sink include, for example, the rate and level of change of CO₂ in the atmosphere and the associated changes in climate, including warming and winds. In particular, winds in the Southern Ocean have been observed to increase in the past 50 years, with this increase linked both to the change of stratospheric ozone and to the observed increase in greenhouse gasses. Here, we use a set of model simulations with the UKESM1 model run from 1950 to the end of the 21st century, we explore the relative contribution of changing greenhouse gases and ozone recovery in driving the evolution of the Southern Ocean carbon sink. Our runs encompass three sets of forcing: one with no ozone, one with ozone but no ozone recovery, and one with best estimated ozone recovery. This set therefore bookends possible evolution of ozone this century and thus the response of the ocean carbon state. Our results demonstrate the critical role of changes in wind distribution in the likely evolution of the SO carbon sink over the course of the 21st century.