The Last Termination in the Central South Atlantic

Abstract:

We present results from analysis of lake sediments and peat deposits from two basins on Nightingale Island (37°S), in the Tristan da Cunha archipelago, South Atlantic. The studies were focused on the time period 16.2-10.0 cal ka BP. A wide variety of proxies were used, including pollen and diatom analyzes, biogenic silica content, bulk C and N content, stable isotopes (¹³C and ¹⁵N), elemental concentrations and magnetic susceptibility measurements, to detect environmental changes that can be related to shifts of the circulation belts of the Southern Ocean. We find that the sediments are underlain by a >2 cal ka BP long hiatus, possibly representing a dried-out lake bed. Climate simulations corroborate that the area might have been exposed to arid conditions as a consequence of the Heinrich 1 event in the north and a southward displacement of the ITCZ. We interpret the results as being related to the position of the Subtropical Front (STF) and the Southern Hemisphere Westerlies (SHW). During 16.2-14.75 cal ka BP the SHW and STF were situated south of Tristan da Cunha. The data indicates moderate variability ending with a humidity peak and cooler conditions. The conditions during 14.7-14.1 cal ka BP were more stable with cool and arid conditions implying that the STF and SHW were both north of the islands during the first part of the Antarctic Cold Reversal. The period 14.1-12.7 cal ka BP indicates incessant latitudinal shifts of the zonal circulation, perhaps related the bipolar seesaw mechanisms. At 12.7 cal ka BP the Holocene warming began with a gradually drier and warmer climate as a result of a dampened AMOC during the Younger Dryas cooling in the north with ITCZ, STF and SHW being displaced southwards. Peak warming seems to have occurred in the earliest part of the Holocene, but this period was also characterized by humidity shifts, possibly an effect of retraction and expansion phases of SHW during AMOC variations in the north.