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

• Published in: Paleoceanography and paleoclimatology 2021-02, Vol.36 (2), p.n/a
• Main Authors: El bani Altuna, N., Ezat, M. M., Greaves, M., Rasmussen, T. L.
• Format: Article
• Language: English
• Subjects: benthic foraminifera; Heinrich Stadials; Mg/Ca; northern Nordic Seas; stable isotopes
• ISSN: 2572-4517; 2572-4525
• DOI: 10.1029/2020PA004061

The 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. Plain Language Summary The Fram Strait is an area where warm and salty Atlantic water (AW) enters the Arctic Ocean from the North Atlantic Ocean. As it flows northwards in the Nordic Seas, the AW mass releases heat to the atmosphere and sinks to form deep cold water, both moderating regional climate and driving deep ocean circulation. To better understand future changes in ocean circulation and interactions under ongoing climate change, it is necessary to study past oceanic changes in relation to climate change. We investigated benthic foraminifera (single‐celled organisms with shells living at the sea floor) with the aim of reconstructing bottom water temperature variations during the last ice age during abrupt atmospheric warmings and coolings on millennial time scales. Our results show that during events of extremely low atmospheric temperature, the deep ocean from the northern North Atlantic to the Arctic Ocea