Millennial‐Scale Changes in Bottom Water Temperature and Water Mass Exchange Through the Fram Strait 79°N, 63‐13 ka

N El Bani Altuna,M Greaves,T L Rasmussen,M M Ezat

doi:10.1029/2020pa004061

Abstract

AbstractThe Svalbard margin, in the eastern Fram Strait with its high sediment accumulation, form a key area for the reconstruction of water mass and heat exchange between the North Atlantic and Arctic Ocean in relation to abrupt climate changes as seen in glacial Greenland Interstadial and Greenland Stadial (GI‐GS) events. Here, we present a bottom water temperature (BWT) record from the northern Nordic Seas (79°N) at 1,273 m water depth based on benthic foraminiferal Mg/Ca. The BWT reconstructions, combined with benthic foraminiferal stable isotopes, benthic foraminiferal fauna compositions and ice‐rafted debris (IRD), reveal at least two distinctive scenarios for the GI‐GS events during the last glacial period (13–63 ka). During GIs, conditions were similar to modern with high productivity, low BWT and deep convection. During GS6, GS8, and GS15 and during Heinrich Stadials (HSs), BWT increased up to 5°C ± 1°C generally concomitant with low planktic and benthic δ18O. Our results suggest, that during some GSs and HSs, deep water generation was reduced, allowing the subsurface Atlantic water (AW) to thicken and deepen down to at least the core site depth. A strong halocline during HSs and GSs prevented heat release from the subsurface AW, which we can now trace from 45°N in the North Atlantic to the Arctic Ocean >79°N. Surfacing of the salty Atlantic subsurface water preconditioned the Nordic seas for convection. Release of the subsurface heat from this vast reservoir must have contributed to the large and abrupt atmospheric warmings at the start of GIs.

Highlights

During the last glacial period, the climate of the northern hemisphere was affected by abrupt millennial-scale climate changes called Dansgaard-Oeschger (D-O) events (Dansgaard et al, 1982, 1993; Johnsen et al, 1992)
We present a bottom water temperature (BWT) record from the northern Nordic Seas (79°N) at 1,273 m water depth based on benthic foraminiferal Mg/Ca
Seven samples of Mg/Ca were measured in both species and show that the difference in BWT calculated from the two species is 0.72°C ± 0.17°C

Summary

Introduction

During the last glacial period, the climate of the northern hemisphere was affected by abrupt millennial-scale climate changes called Dansgaard-Oeschger (D-O) events (Dansgaard et al, 1982, 1993; Johnsen et al, 1992). During some GS events, layers with large amounts of ice-rafted debris (IRD) and dominance of the polar planktic foraminifera Neogloboquadrina pachyderma have been found at mid-latitudes in the Northern Hemisphere. These layers were deposited during Heinrich events occurring during Heinrich Stadials (HSs) or Heinrich-like Stadials, depending on the origin of the IRD (e.g., Bond & Lotti, 1995; Elliot et al, 2001; Hemming, 2004). These events are characterized by massive freshwater supply from the melting of icebergs traversing the North Atlantic Ocean (Bond et al, 1993; Heinrich, 1988)

Results

Discussion

Conclusion