High-Resolution Benthic Mg/Ca Temperature Record of the Intermediate Water in the Denmark Strait Across D-O Stadial-Interstadial Cycles

• Published in: Paleoceanography and Paleoclimatology
• Main Authors: Sessford, E. G., Tisserand, A. A., Risebrobakken, B., Andersson, C., Dokken, T., Jansen, E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Geophysical Union 2018
• Subjects: Arctic; Greenland; Dansgaard-Oeschger events; Denmark Strait; Foraminifera*; Iceland; North Atlantic; Sea ice
• Online Access: https://archimer.ifremer.fr/doc/00504/61589/65890.pdf; https://doi.org/10.1029/2018PA003370; https://archimer.ifremer.fr/doc/00504/61589/

Dansgaard-Oeschger (D-O) climate instabilities that took place during Marine Isotope Stage 3 are connected to changes in ocean circulation patterns and sea ice cover. Here we explore in detail the configuration of the water column of the Denmark Strait during D-O events 8-5. How the ocean currents and water masses within the Denmark Strait region responded and were connected to the North Atlantic are discussed. We investigate sediment core GS15-198-36CC, from the northern side of the Greenland-Iceland Ridge, at 30-year temporal resolution. Stable carbon and oxygen isotope reconstructions based on benthic foraminifera, together with a high-resolution benthic foraminiferal record of Mg/Ca paleothermometry, is presented. The site was bathed by warm intermediate waters during stadials and cool but gradually warming intermediate water during interstadials. We suggest that stadial conditions in the Denmark Strait are characterized by a well-stratified water column with a warm intermediate water mass that lies beneath a cold fresh body of water where sea ice and brine rejection work in consort to uphold the halocline conditions. Interstadial periods are not a pure replicate of modern times, but rather have two modes of operation, one similar to today, and the other incorporating a brief period of warm intermediate water and increased ventilation. Plain Language Summary During the last ice age (30-40 thousand years ago), rapid warmings- Dansgaard-Oeschger events-up to 15 degrees C occurred over Greenland resulting in Arctic air temperature warmings, droughts over Africa, stronger monsoons over Asia, and global sea level. These climatic changes are connected by the global telecommunicator: the Atlantic Meridional Overturning Circulation, which is largely driven by changes in ocean water properties that take place in the Denmark Strait. We use sediment cores from the Denmark Strait to extract archives of past abrupt change in ocean temperature to investigate the dynamic changes in ocean circulation across Dansgaard-Oeschger events. Geochemical analysis of microfossils that lived on the seafloor reveals that during the cold periods the presence of sea ice is linked to warming waters at intermediate depth in the Denmark Strait and likely a decrease in the strength of the overturning circulation. During the warm period, intermediate waters cooled suggesting a heat release to the atmosphere due to the absence of sea ice. Our research indicates that the absence or presence of Arctic sea ice is linked to these climate disturbances in the past and is likely linked to the global climate changes the Earth is experiencing today.