Sea Surface Temperatures in the Indian Sub‐Antarctic Southern Ocean for the Last Four Interglacial Periods

• Published in: Geophysical research letters Vol. 48; no. 8
• Main Authors: Shukla, Sunil Kumar, Crosta, Xavier, Ikehara, Minoru
• Format: Journal Article
• Language: English
• Published: American Geophysical Union 28.04.2021
• Subjects: Climatology; Earth Sciences; Ocean, Atmosphere; Oceanography; Sciences of the Universe
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL090994

Interglacial periods (IG) offer an opportunity to understand natural climate variability and its drivers under potential warmer‐than‐present conditions. However, sea‐surface temperature (SST) records from the Southern Ocean (SO) are limited. The first SST record from the Sub‐Antarctic western Indian SO covering the last four IGs suggest warmer conditions during Marine Isotope Stage 5e than 9e, 7e, and Holocene. Each IG presents two (early and late) warm phases interrupted by a cooling, except Holocene that experienced a continuous warming. The early warm phase might be attributable to changes in northern summer insolation with feedbacks from Northern and Southern Hemisphere ice‐sheets, global oceanic circulation, and the carbon cycle. Conversely, the late warm phase might be due to changes in Southern Hemisphere summer insolation. Larger millennial‐scale SST variability for IGs older than Holocene could be attributed to a less stable thermohaline circulation, which resulted in more variable heat redistribution between the two hemispheres. Plain Language Summary Documenting the causes and consequences of climate variability during past warmer‐than‐present periods is essential to provide benchmarks to scenarios of future, projected climate variability. It is especially true for the Southern Ocean (SO) region, where the atmosphere, ocean, sea ice, cryosphere, and carbon cycle interact non‐linearly at different timescales. We here provide the first high‐resolution surface ocean temperature record covering the last four interglacial periods (IG) from the sub‐Antarctic region of the western Indian sector of the SO. Our new results confirm that the atmospheric CO2 concentrations and oceanic heat transport redistribution are important drivers for past IGs as suggested previously. These drivers are supplemented, during an interglacial early and late warmer phases, by Northern and Southern Hemisphere summer insolation, respectively. Our new results also show that millennial‐scale variations in surface ocean temperature were much larger during IGs older than the Holocene, which we attribute to more variable thermohaline circulation, and subsequent heat transport to the SO, in older IGs. Our results suggest that variable thermohaline circulation is an intrinsic feature of warm climate states and question its stability over the coming centuries. Key Points First high‐resolution sea‐surface temperature (SST) record in the western Indian Southern Ocean over the past four interglacial periods (IG) Warmer Marine Isotope Stage 5e than 9e, 7e, and Holocene due to a combination of insolation, CO2, and ocean‐cryosphere interactions Stronger millennial variability in IG beyond the Holocene is mainly attributed to ocean circulation