Reconstruction of intermediate water circulation in the tropical North Atlantic during the past 22,000 years

Abstract

Decades of paleoceanographic studies have reconstructed a well-resolved water mass structure for the deep Atlantic Ocean during the Last Glacial Maximum (LGM). However, the variability of intermediate water circulation in the tropics over the LGM and deglacial abrupt climate events is still largely debated. This study aims to reconstruct intermediate northern- and southern-sourced water circulation in the tropical North Atlantic during the past 22kyr and attempts to confine the boundary between Antarctic Intermediate Water (AAIW) and northern-sourced intermediate water (i.e., upper North Atlantic Deep Water (NADW) or Glacial North Atlantic Intermediate Water) in the past. High-resolution Nd isotopic compositions of fish debris and acid-reductive leachate of bulk sediment in core VM12-107 (1079m depth) from the Southern Caribbean are not in agreement. We suggest that the leachate method does not reliably extract the Nd isotopic compositions of seawater at this location, and that it needs to be tested in more detail in various oceanic settings. The fish debris εNd values display a general decrease from the early deglaciation to the end of the Younger Dryas, followed by a greater drop toward less radiogenic values into the early Holocene. We propose a potentially more radiogenic glacial northern endmember water mass and interpret this pattern as recording a recovery of the upper NADW during the last deglaciation. Comparing our new fish debris Nd isotope data to authigenic Nd isotope studies in the Florida Straits (546 and 751m depth), we propose that both glacial and deglacial AAIW do not penetrate beyond the lower depth limit of modern AAIW in the tropical Atlantic.