A likely trigger of tropical glacier melt 20,000 years ago

An analysis of sediment carried by glaciers in both South America and East Africa indicates that tropical glaciers not just in South America but across the tropics began to melt earlier than expected at the end of the Last Glacial Maximum (26,000-19,000 years ago), before atmospheric carbon dioxide levels began to rise. The study's authors suggest that the early melting may have been triggered by rising temperatures at the North and South Poles, which reduced a heat-driven atmospheric circulation cycle that in turn slowed the movement of heat out of the tropics. The findings provide insights into mechanisms that create harmony between the Northern and Southern Hemispheres during glacial cycles--one of the greatest mysteries in paleoclimate research. While atmospheric greenhouse gases, especially carbon dioxide, are often used to explain why glacial cycles occur simultaneously in both hemispheres, other climate processes are also believed to play a role. Previous research suggests some tropical glaciers began melting earlier than glaciers in other parts of the world during the Last Glacial Maximum, before the rise in carbon dioxide, but these data are limited to South America and could have been the result of regional conditions. To determine if this phenomenon occurred across the tropics as a whole, Margaret Jackson et al. compared previously gathered Beryllium-10 isotope data from nine sites in South America (for which they recalculated harmonized ages) with 17 new and eight previously published glacial sediment datasets from East Africa. Together, the data from both continents confirmed that temperatures began to warm between 20,000 and 19,000 years ago, about 1,000 to 2,000 years before the spike in carbon dioxide levels.

Credit: 
American Association for the Advancement of Science