Deglacial variability of Antarctic Intermediate Water penetration into the North Atlantic from authigenic neodymium isotope ratios

Abstract

Understanding intermediate water circulation across the last deglacial is critical in assessing the role of oceanic heat transport associated with Atlantic Meridional Overturning Circulation variability across abrupt climate events. However, the links between intermediate water circulation and abrupt climate events such as the Younger Dryas (YD) and Heinrich Event 1 (H1) are still poorly constrained. Here, we reconstruct changes in Antarctic Intermediate Water (AAIW) circulation in the subtropical North Atlantic over the past 25 kyr by measuring authigenic neodymium isotope ratios in sediments from two sites in the Florida Straits. Our authigenic Nd isotope records suggest that there was little to no penetration of AAIW into the subtropical North Atlantic during the YD and H1. Variations in the northward penetration of AAIW into the Florida Straits documented in our authigenic Nd isotope record are synchronous with multiple climatic archives, including the Greenland ice core δ18O record, the Cariaco Basin atmosphere Δ14C reconstruction, the Bermuda Rise sedimentary Pa/Th record, and nutrient and stable isotope data from the tropical North Atlantic. The synchroneity of our Nd records with multiple climatic archives suggests a tight connection between AAIW variability and high‐latitude North Atlantic climate change.

Coherent Response of Antarctic Intermediate Water and Atlantic Meridional Overturning Circulation During the Last Deglaciation: Reconciling Contrasting Neodymium Isotope Reconstructions From the Tropical Atlantic

“…The last deglaciation presents an ideal target to test our understanding of the relation between AAIW and AMOC. Some previous observational studies of the last deglaciation suggested that the northward penetration of AAIW in the tropical Atlantic should be positively correlated with the AMOC strength (Came et al, ; Huang et al, ; Xie et al, ). This positive correlation seems to be consistent with the notion that AAIW, as part of the North Brazil Current (NBC), contributes to the return branch of North Atlantic Deep Water (NADW) (Lumpkin & Speer, ; Rintoul, ; Schmitz & McCartney, ; Zhang et al, ).…”

Meltwater Impacts on the Ocean Circulation since the Last Glacial Maximum

“…DISCUSSION 61 tually weaker during those periods Xie et al, 2012). Our results, therefore, seem to agree with the second hypothesis.…”

“…It is believed that the climate swings that followed the LGM were frequently accompanied by changes in the ocean circulation (e.g., Broecker, 1994;McManus et al, 2004;Praetorius et al, 2008). Proxy records show that during cold periods there were reductions in the AMOC while the warm periods were marked by the AMOC's (Xie et al, 2012). Also, the δ The Atlantic Ocean's deglacial evolution:…”

Silicon isotopes indicate enhanced carbon export efficiency in the North Atlantic during deglaciation

“…Neodymium isotope evidence points both towards a volumetric increase in AAIW at intermediate depths of the equatorial regions 13,14 but also to a decline in AAIW in the Florida Straits during HS1 (ref. 15). While nutrient proxies cannot determine the origins of the water, they do indicate that the mid-depths of the South Atlantic were more enriched in Si(OH) 4 relative to other nutrients during HS1 than they are today 16,17 , suggestive of a northwards advance of AAIW into the North Atlantic during HS1 (ref.…”