North Atlantic Deep Water Production during the Last Glacial Maximum.

Jacob N W Howe,Cristiano M Chiessi,Alexander M Piotrowski,Stefan Mulitza,Taryn L Noble,Germain Bayon

doi:10.1038/ncomms11765

Abstract

Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial–interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters.

Highlights

Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2
Modern North Atlantic Deep Water (NADW) has a characteristic eNd value of À 13.5 while seawater in the deep Southern Ocean shows eNd values around À 8.5, because it has a greater proportion of Pacific Deep Water (PDW) which has an eNd of À 3.5
The change observed in the deep South Atlantic between the Last Glacial Maximum (LGM) and Holocene (Fig. 3) is consistent with a lower flux of NADW into the Southern Ocean under cooler, glacial conditions[24,25]

Summary

Introduction

Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. We present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial–interglacial changes in water mass distributions These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We present Holocene and LGM seawater eNd reconstructions, based on foraminiferal eNd measurements from 24 cores (Supplementary Table 1, Supplementary Fig. 1) spanning from 46° S to 40° N in the Atlantic Ocean These reconstructions are used to decipher the nature of changes in Atlantic water mass distributions between glacial and interglacial conditions. When compared with benthic foraminiferal carbon isotope values, the neodymium isotope measurements reveal that more respired organic carbon was stored in the deep Atlantic Ocean during the LGM than in the Holocene

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Conclusion