The Last Termination in the South Indian Ocean: A unique terrestrial record from Kerguelen Islands (49°S) situated within the Southern Hemisphere westerly belt

Abstract

International audienceThe awareness of the significance of the Southern Ocean in the Earth's climate system has become increasingly obvious. The deglacial atmospheric CO2 rise during warming periods in Antarctica has been attributed to CO2 ventilation from the deep ocean caused by enhanced upwelling around the Antarctic Divergence. It has been hypothesized that, more intense Southern Hemisphere westerly winds aligned with the Antarctic Circumpolar Current due to a southward shift of the wind belt from its Last Glacial Maximum equator-ward position, are the main drivers. Reconstructions of past changes in atmospheric circulation in the Southern Hemisphere are still scarce and the overall picture is patchy with sometimes contradictory results. For obvious reasons, most terrestrial records originate from southern South America and New Zealand. Here we present a terrestrial record from the Indian sector of the Southern Ocean, from Kerguelen Islands located at 49°S. A peat record is investigated using a multi-proxy approach (pollen and plant macrofossils, magnetic susceptibility, XRF analyses, biogenic silica content, Rock-Eval6 analysis and humification degree). Peat accumulation starts at about 16,000 cal yr BP with relatively warm and dry conditions. The most prominent change in our proxy data occurs at 13,600 cal yr BP, when peat ponds were established on the peat surface, resulting in lacustrine-type deposits, as a result of very high humidity, and with proxies implying very windy conditions. Within chronological uncertainties, this onset coincides with the onset of the so-called Oceanic Cold Reversal, based on the deuterium excess data in the EPICA Dome C ice core record. Kerguelen Islands are located in the moisture source area of Dome C and a change in atmospheric circulation at that time could explain both records. Around 12,900 cal yr BP, at the end of the Antarctic Cold Reversal, pond/lake sediments give way to more peaty deposits, with proxies suggesting slightly drier, less windy and probably warmer conditions. Kerguelen Islands became less influenced by the Southern Hemisphere westerly winds and these conditions were amplified during the early Holocene climate optimum as found in Antarctic ice core records

Holocene dynamics of the southern westerly winds over the Indian Ocean inferred from a peat dust deposition record

“…S8). The variations in SWW in the last 6.6 kyr that we infer from the AMS dust record should therefore be regarded as moderate changes, compared to the oscillations in SWW that have been associated with glacial/inter-glacial periods (e.g., De Deckker et al, 2012;Van der Putten et al, 2015). Essentially, the ensemble of paleo-climate records shown in Fig.…”

Radiocarbon Evidence for the Contribution of the Southern Indian Ocean to the Evolution of Atmospheric CO2 Over the Last 32,000 Years

“…The combined effects of the more pronounced glacial stratification and weakened upwelling ultimately resulted in the observed decoupling of shallow (PS69/912) to middepth waters (records below ~2,500 m) from surface waters. Along with the glacial expansion of Antarctic sea ice (Xiao et al, ) and a potential displacement of wind systems (Menviel et al, ; Van der Putten et al, ), these factors likely contributed to the accumulation of old, sequestered biogenic carbon, and perhaps to some extent MOR‐derived volcanic CO 2 in glacial deep waters of the lower cell (Figure ).…”

A refined paleotemperature calibration for New Zealand limnic environments using differentiation of branched glycerol dialkyl glycerol tetraether (brGDGT) sources

“…Lipid paleothermometers have become a valuable tool for the reconstructions of marine and terrestrial paleoclimate (Zink et al ., ; Castañeda and Schouten, ; Pearson et al ., ; Woltering et al ., ; Foster et al ., ). The development of such proxies is especially beneficial for providing additional robust paleotemperature data for the Southern Hemisphere and enhancing existing multi‐proxy paleoclimate records used to develop regional reconstructions (Andres et al ., ; Turney et al ., ; Gasse et al ., ; Lüer et al ., ; Björck et al ., ; van der Putten et al ., ). This is particularly the case for New Zealand, where deep‐time records of paleoenvironmental change are comparatively few (Wilmshurst et al ., ; Vandergoes et al ., ; Newnham et al ., , ; Heyng et al ., ) but essential to better understand the climate evolution of the south‐west Pacific region.…”