Divergent trends in land and ocean temperature in the Southern Ocean over the past 18,000 years

Over the past 18,000 years, sea surface temperatures for the Southern Ocean do not align with those of the adjacent, high-latitude landmasses. During the late glacial period, the ocean surface warmed rapidly to present-day temperatures, whereas the land warmed only slowly, as evidenced by the lagged response of forest and glaciers^2,3. However, in the Holocene epoch, land-based records suggest strong warming whereas marine records indicate that ocean surface temperatures cooled. Here we present reconstructions of summer temperature for Campbell Island, in the Southern Ocean, over the past 16,500 years based on fossil pollen. We find a pronounced warming 12,500-11,000 years ago, a cooling until 9,200 years ago, and a rapid warming to a peak between 6,000 and 5,000 years ago, followed by minor cool intervals from 5,200-4,000, 3,000-1,700 and 700-100 years ago. As expected, our temperature reconstructions show a late glacial lag behind nearby records of sea surface temperature ^6,7, and opposing trends in the Holocene. We suggest that this discrepancy arises because land-based reconstructions record summer temperatures, whereas marine proxies generally reflect annual temperatures. We conclude that the divergence of the records therefore reflects changes in the seasonality of atmospheric heat transport. As atmospheric heat transport is tied to the Southern Hemisphere westerly winds, we attribute our observed changes to shifts in the position and intensity of the southern westerlies.