Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain
the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in
Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles
and JavaScript.
The ocean overturning circulation has been compared to a conveyor belt that transports heat and salt, as well as carbon and other elements around the globe. The initial schematic of this global ocean circulation has been enriched with added loops and more sophisticated pathways. But the vertical exchange of water between surface and abyss in the northern North Atlantic and the high southern latitudes continues to be an important determinant of the vigour of the circulation. In this focus, we present a collection of research articles and opinion pieces that explore the interplay between ocean overturning in the north and south and climate change.
The ocean overturning circulation is potentially sensitive to climate change. In the north and south alike, human influence is less pronounced than we thought, but that is no reason to relax our watchfulness.
A weakening of the Atlantic meridional overturning circulation has emerged from noise after years of painstaking measurements. Three independent lines of evidence suggest that an anthropogenic influence on this overturning is not yet detectable.
Conversion of Antarctic circumpolar upwelling waters to less dense water has mainly been attributed to surface heat fluxes. An analysis of water-mass transformation shows that the dominant process is the formation of sea ice near Antarctica and its melt offshore.
The North Atlantic Oscillation has varied markedly on multidecadal timescales. Analyses of climate simulations show that these variations have contributed to Arctic sea ice loss, Northern Hemisphere warming and tropical storm activity.
The mid-1990s’ warming of the North Atlantic subpolar gyre was probably related to strengthened overturning. Observations and numerical models suggest that a climate reversal to a cooling trend occurred around 2005.
The Atlantic meridional overturning circulation has weakened over the past decade. Examination of a global reanalysis that matches independent observations shows that the decline is consistent with recovery from an earlier invigoration.
Freshwater release from melting polar ice could weaken the Atlantic overturning circulation. Eddy-resolving ocean simulations reveal that the freshening has not yet significantly affected meridional overturning, but an effect may emerge soon.
Meltwater runoff from the Greenland ice sheet alters ocean surface salinity. Numerical simulations show that meltwater from southeastern Greenland is transported to the Labrador Sea more efficiently than that from southwestern Greenland.
Sea-ice formation is a key factor in the lower branch of the Southern Ocean overturning circulation. Observation-based data in conjunction with a water-mass transformation framework reveal that sea ice plays a central role in the upper branch too.
Unlike the Arctic, the Southern Ocean has shown little warming. An analysis of observations and numerical simulations suggests that Southern Ocean warming patterns are shaped by meridional overturning more than surface heating.