The spatial extent and dynamics of the Antarctic Cold Reversal
Résumé
Antarctic ice cores show that a millennial-scale cooling
event, the Antarctic Cold Reversal (14,700 to 13,000 years
ago), interrupted the last deglaciation1–3. The Antarctic Cold
Reversal coincides with the Bølling–Allerød warm stage in the
North Atlantic, providing an example of the inter-hemispheric
coupling of abrupt climate change generally referred to
as the bipolar seesaw4–9. However, the ocean–atmosphere
dynamics governing this coupling are debated10–15. Here we
examine the extent and expression of the Antarctic Cold
Reversal in the Southern Hemisphere using a synthesis of
84 palaeoclimate records.We find that the cooling is strongest
in the South Atlantic and all regions south of 40 S. At
the same time, the terrestrial tropics and subtropics show
abrupt hydrologic variations that are significantly correlated
with North Atlantic climate changes. Our transient global
climate model simulations indicate that the observed extent of
Antarctic Cold Reversal cooling can be explained by enhanced
northward ocean heat transport from the South to North
Atlantic10, amplified by the expansion and thickening of sea
ice in the Southern Ocean. The hydrologic variations at lower
latitudes result from an opposing enhancement of southward
heat transport in the atmosphere mediated by the Hadley
circulation. Our findings reconcile previous arguments about
the relative dominance of ocean5,10,11 and atmospheric14,15 heat
transports in inter-hemispheric coupling, demonstrating that
the spatial pattern of past millennial-scale climate change
reflects the superposition of both.