Abstract
The Southern Ocean plays a critical role in the uptake, transport and
storage of carbon by the global oceans. It is the ocean’s largest sink
of CO2, yet it is also among the regions with the lowest storage of
anthropogenic carbon. This behaviour results from the unique combination
of high winds driving the upwelling of deep waters and the subduction
and northwards transport of surface carbon. Here we identify the
indirect effect of climate-related changes in ocean conditions relative
to the direct effect of anthropogenic changes in atmospheric CO2 on the
reorganisation of carbon in the Southern Ocean using a combination of
modelling and observations. We show that the effect of climate
variability and climate change on the storage of carbon in the Southern
Ocean is nearly as large as the effect of anthropogenic CO2 during the
period 1998-2018 compared with a climatology around the year 1995. We
identify a distinct climate fingerprint in dissolved inorganic carbon
(DIC), with elevated DIC concentration in the surface ocean that
reinforces the anthropogenic CO2 signal, and reduced DIC concentration
in the subsurface ocean that offsets the anthropogenic CO2 signal. The
fingerprint is strongest at lower latitudes (30°S-55°S). This
fingerprint could serve to monitor the highly uncertain evolution of
carbon within this critical ocean basin, and better identify its
drivers.