Abstract
Ice core records show that atmospheric CO2 concentrations and Antarctic temperature were lower during the ‘lukewarm interglacials’ from 800 to 430 ka than the subsequent five interglacials. These different interglacial ‘strengths’ have been hypothesised to be controlled by Antarctic overturning circulation. How these variations in Antarctic overturning relate to Northern Atlantic overturning circulation, a major driver of Northern Hemisphere climate, is uncertain. Here we present a high-resolution record of authigenic neodymium isotopes—a water mass tracer that is independent of biological processes—and use it to reconstruct Atlantic overturning circulation during the last 800 kyr. This record reveals a similar proportion of North Atlantic Deep Water during the ‘lukewarm interglacials’ and the more recent interglacials. This observation suggests that the provenance of deep water in the Atlantic Ocean can be decoupled from ventilation state of the Southern Ocean and consequently the atmospheric concentration of carbon dioxide.
Highlights
Ice core records show that atmospheric CO2 concentrations and Antarctic temperature were lower during the ‘lukewarm interglacials’ from 800 to 430 ka than the subsequent five interglacials
The cause of the transition from ‘lukewarm interglacials’ to warmer interglacials around 430 ka, termed the mid-Bruhnes event (MBE)[3], is still unknown, it has been hypothesised to be due to changes in the concentration of atmospheric carbon dioxide caused by changes in Southern Ocean structure altering the deep-to-surface exchange of CO24
Atlantic meridional overturning circulation (AMOC), which includes the formation of North Atlantic Deep Water (NADW) in the seas surrounding the North Atlantic, has an important influence on the Northern Hemisphere climate because it contributes to the meridional transport of heat[8]
Summary
Ice core records show that atmospheric CO2 concentrations and Antarctic temperature were lower during the ‘lukewarm interglacials’ from 800 to 430 ka than the subsequent five interglacials. We present a high-resolution record of authigenic neodymium isotopes—a water mass tracer that is independent of biological processes—and use it to reconstruct Atlantic overturning circulation during the last 800 kyr This record reveals a similar proportion of North Atlantic Deep Water during the ‘lukewarm interglacials’ and the more recent interglacials. Similar εNd values at Site ODP 929 occurred during all the interglacials of the past 800 kyr suggesting a similar proportion of NADW relative to AABW at ODP 929 during all of the interglacials before and after the MBE By comparing these results with other paleoclimate reconstructions, we conclude that the provenance of water in the deep Atlantic was decoupled from the ventilation state of the Southern Ocean and the atmospheric concentration of carbon dioxide
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