The Southern Ocean has shown little warming over recent decades, in stark contrast to the rapid warming observed in the Arctic. Along the northern flank of the Antarctic Circumpolar Current, however, the upper ocean has warmed substantially. Here we present analyses of oceanographic observations and general circulation model simulations showing that these patterns—of delayed warming south of the Antarctic Circumpolar Current and enhanced warming to the north—are fundamentally shaped by the Southern Ocean’s meridional overturning circulation: wind-driven upwelling of unmodified water from depth damps warming around Antarctica; greenhouse gas-induced surface heat uptake is largely balanced by anomalous northward heat transport associated with the equatorward flow of surface waters; and heat is preferentially stored where surface waters are subducted to the north. Further, these processes are primarily due to passive advection of the anomalous warming signal by climatological ocean currents; changes in ocean circulation are secondary. These findings suggest the Southern Ocean responds to greenhouse gas forcing on the centennial, or longer, timescale over which the deep ocean waters that are upwelled to the surface are warmed themselves. It is against this background of gradual warming that multidecadal Southern Ocean temperature trends must be understood.
At a glance
- Transient response of a global ocean–atmosphere model to a doubling of atmospheric carbon dioxide. J. Phys. Oceangr. 20, 722–749 (1990). , &
- Transient responses of a coupled ocean–atmosphere model to gradual changes of atmospheric CO2. Part 1: Annual mean response. J. Clim. 4, 785–818 (1991). , , &
- Timescales of climate response. J. Clim. 17, 209–217 (2004).
- Deep-ocean heat uptake and equilibrium climate response. Clim. Dynam. 40, 1071–1086 (2013). , &
- Time-varying climate sensitivity from regional feedbacks. J. Clim. 26, 4518–4534 (2013). , &
- 1029–1136 (IPCC, Cambridge Univ. Press, 2013). et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.)
- The ocean’s role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing. Phil. Trans. R. Soc. A 372, 20130040 (2014). et al.
- 383–464 (IPCC, Cambridge Univ. Press, 2013). et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.)
- Global warming pattern formation: sea surface temperature and rainfall. J. Clim. 23, 966–986 (2010). et al.
- Different magnitudes of projected subsurface ocean warming around Greenland and Antarctica. Nature Geosci. 4, 524–528 (2011). et al.
- The Gent-McWilliams parameterization: 20/20 hindsight. Ocean Modelling 39, 2–9 (2011).
- Assessment of Southern Ocean mixed-layer depths in CMIP5 models: historical bias and forcing response. J. Geophys. Res. 118, 1845–1862 (2013). et al.
- The effect of the sea ice freshwater flux on Southern Ocean temperatures in CCSM3: deep-ocean warming and delayed surface warming. J. Clim. 24, 2224–2237 (2011). &
- The passive and active nature of ocean heat uptake in idealized climate change experiments. Clim. Dynam. 38, 667–684 (2012). &
- Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion. Nature Geosci. 6, 376–379 (2013). , , , &
- Signatures of the Antarctic ozone hole in Southern Hemisphere surface climate change. Nature Geosci. 4, 741–749 (2011). et al.
- Oceanic response to changes in the latitude of the Southern Hemisphere subpolar westerly winds. J. Clim. 17, 1040–1054 (2004). &
- The role of poleward-intensifying winds on Southern Ocean warming. J. Clim. 20, 5391–5400 (2007). , , , &
- Interhemispheric asymmetry in transient global warming: the role of Drake Passage. Geophys. Res. Lett. 40, 1587–1593 (2013). , , &
- Aerosol climate feedback due to decadal increases in Southern Hemisphere wind speeds. Geophys. Res. Lett. 37, L02805 (2010). et al.
- Closure of the meridional overturning circulation through Southern Ocean upwelling. Nature Geosci. 5, 171–180 (2012). &
- Constructing the residual circulation of the ACC from observations. J. Phys. Oceanogr. 32, 3315–3327 (2002). &
- An improved in situ and satellite SST analysis for climate. J. Clim. 15, 1609–1625 (2002). , , , &
- Objectively analyzed air-sea heat fluxes for the global ice-free oceans (1981–2005). Bull. Am. Meteorol. Soc. 88, 527–539 (2007). &
- EN4: quality controlled ocean temperature and salinity profiles and monthly objective analyses with uncertainty estimates. J. Geophys. Res. 118, 6704–6716 (2013). , &
- Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections. J. Oceanogr. 65, 287–299 (2009). &
- Decadal-scale temperature trends in the Southern Hemisphere ocean. J. Clim. 21, 4749–4765 (2008).
- 255–316 (IPCC, Cambridge Univ. Press, 2013). et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.)
- 143–176 (Blackwell, 2010). et al. in Understanding Sea Level Rise and Variability (eds Church, J. A. et al.)
- Decadal steric and sea surface height changes in the Southern Hemisphere. Geophys. Res. Lett. 38, L08604 (2011). &
- Quantifying underestimates of long-term upper-ocean warming. Nature Clim. Change 4, 999–1005 (2014). , , &
- An overview of CMIP5 and the experimental design. Bull. Am. Meteorol. Soc. 93, 485–498 (2012). , &
- Simulations of processes associated with the fast warming rate of the southern midlatitude ocean. J. Clim. 23, 197–206 (2010). , , &
- Ocean heat uptake and its consequences for the magnitude of sea level rise and climate change. Geophys. Res. Lett. 39, L18608 (2012). &
- Dominance of the Southern Ocean in anthropogenic carbon and heat uptake in CMIP5 models. J. Clim. 28, 862–886 (2015). et al.
- What processes drive the ocean heat transport? Ocean Modelling 38, 171–186 (2011). &
- The role of eddies in the Southern Ocean temperature response to the southern annular mode. J. Clim. 22, 806–818 (2009). , , , &
- Antarctic climate response to stratospheric ozone depletion in a fine resolution ocean climate model. Geophys. Res. Lett. 39, L20705 (2012). &
- Antarctic Ocean and sea ice response to ozone depletion: a two timescale problem. J. Clim. 28, 1206–1226 (2015). , , , &
- The Antarctic sea ice response to the ozone hole in climate models. J. Clim. 27, 1336–1342 (2014). &
- Hydrostatic, quasi-hydrostatic, and nonhydrostatic ocean modeling. J. Geophys. Res. 102, 5733–5752 (1997). , , &
- A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers. J. Geophys. Res. 102, 5753–5766 (1997). , , , &
- The ocean’s role in the transient response of climate to abrupt greenhouse gas forcing. Clim. Dynam. 44, 2287–2299 (2015). et al.
- Shortwave and longwave radiative contributions to global warming under increasing CO2. Proc. Natl Acad. Sci. USA 111, 16700–16705 (2014). , , &
- Mechanisms of ocean heat uptake in a coupled climate model and the implications for tracer based predictions of ocean heat uptake. Geophys. Res. Lett. 33, L07608 (2006). &
- Impacts of climate change on the subduction of mode and intermediate water masses in the Southern Ocean. J. Clim. 22, 3289–3302 (2009). , &
- Meridional displacement of the Antarctic Circumpolar Current. Phil. Trans. R. Soc. A. 372, 20130273 (2014).
- The influence of recent Antarctic ice sheet retreat on simulated sea ice area trends. Geophys. Res. Lett. 40, 4328–4332 (2013). &
- The response of the Southern Ocean and Antarctic sea ice to fresh water from ice shelves in an Earth System Model. J. Clim. 29, 1655–1672 (2016). , , &
- Improvements to NOAA’s historical merged land–ocean temperature analysis (1880–2006). J. Clim. 21, 2283–2296 (2008). , , &
- PHC: a global ocean hydrography with a high quality Arctic Ocean. J. Clim. 14, 2079–2087 (2001). , &
- Coordinated Ocean-ice Reference Experiments (COREs). Ocean Modelling 26, 1–46 (2009). et al.
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