Changes in the hydrological cycle, ocean circulation, and carbon/nutrient cycling during the last interglacial and glacial transition

Abstract

A complex Earth system model has been forced by insolation changes for the last interglacial (LIG) for which geological records evidence a climate cooling that culminated in the last glacial inception. During an early warm period (127–125 ka B.P.) the Arctic/North Atlantic drainage basin north of 30°N receives ∼27,000 m3/s more fresh water mainly imported across the watershed of North America compared to a cooler period centered around 115 ka B.P. Together with a strong surface warming by up to 2 K, this results in a weaker North Atlantic overturning (reduced by ∼20%). Sea ice cover is reduced by 3 × 106 km2 in the Northern Hemisphere, stimulating a stronger productivity in the Barents and Kara seas. In the North Pacific a lowered salinity and a surface warming of more than 3 K increase the stratification. The eastern Pacific becomes nutrient poorer, which leads to a reduction in the export production in areas with vigorous upwelling. The climate cooling in the course of the LIG induces a carbon release by the terrestrial biosphere of 308 Gt, which is counteracted by an oceanic/sedimentary uptake of 290 Gt. The rest remains in the atmosphere increasing the pCO2 by 9 ppm. The large oceanic CO2 uptake corresponds to a rise of the calcite lysocline of about 300 m in the midlatitude Atlantic. The chemically interactive carbonate sediment pool in the Atlantic is reduced by 10%. For nearly the entire North Atlantic, our results are contradictory to the common interpretation of carbonate preservation proxies as a reliable tool for monitoring changes in deep water circulation.