Investigating Climate-Related Changes in Meridional Overturning Circulation during the Holocene

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Under this award the PIs hope to improve documentation and understanding of climatic changes during the Holocene which would provide insight into possible future man-induced climatic perturbation. Specifically the PIs will try to reconstruct changes in the intensity of the Atlantic meridional overturning circulation (MOC), often viewed as one of the key factors that could affect the future evolution of global climate. Variations in the rate of the MOC have the potential to cause, amplify, and/or propagate climatic change regionally and even globally. The PIs are proposing to investigate the possible occurrence of Holocene climatic changes associated with changes in the MOC and to relate these changes to North Atlantic surface hydrography. Changes in MOC will be constrained by measuring ex.231Pa/ex.230Th (Pa/Th) at high resolution in three high accumulation rate cores from the North Atlantic. Pa/Th is a dynamical proxy providing quantitative estimates of the rate of MOC but which could be obscured by changes in particle scavenging. To take into account the latter, the PIs will also measure Pa/Th in three cores representing the major regions of boundary scavenging in the North Atlantic. The three primary cores span a depth from 1650m to 4500m and thus hold the potential to document changes in circulation that influence intermediate and deep waters. These changes will be compared directly to variations in planktonic foraminifera d18O, sea surface temperature, and drift ice indices in the same cores to establish the relationship between North Atlantic surface hydrography and MOC. The Pa/Th record will also be compared to benthic foraminifera d13C and sortable silt sediment grain size, two complementary measures of the intensity of Atlantic MOC. These profiles will then be related to existing marine, terrestrial and ice records to evaluate the importance of Atlantic MOC in overall Holocene climate trends as well as shorter-term variability (e. g.,8.2 ka event, Little Ice Age, "1.5 kyr cycle").