Marine records of Holocene glacier variability in the Kerguelen Islands (South Indian Ocean): sedimentology, chronology, and paleoclimatic drivers

The strength and the location of Southern Hemisphere winds (SHW) define an annular mode (SAM), a major component of interannual climatic variability in the Southern Hemisphere. SAM has a significant impact on mid-latitude westerly winds, but also acts on the meridional moisture transport over the Southern Ocean (for example, in the case of atmospheric rivers), with dramatic consequences on the cryosphere at high latitudes. Assessment of past, present and future changes in the SAM is essential for understanding climate variations and impacts at high latitudes. To date, Holocene proxy-based reconstructions of SAM are limited to South America, Australia/New Zealand, and Antarctica. In opposite, the paucity of SAM-related records for the Southern Indian Ocean presently limits our understanding of the spatial and temporal extent of SHW behavior in this region.

To this aim, we present a series of 30-m long marine records retrieved from a fjord fed by glacial melt of the Ampere glacier belonging to the Cook Ice Cap in the Kerguelen Archipelago (49˚20’S, 69˚20’E). A new chronological framework, based on Bayesian modelling of 50 radiocarbon ages along with ¹³⁷Cs and ²¹⁰Pb measures, allows reconstructing 4 kyrs of sediment discharge related to glacier variability. Sedimentological and geochemical analyses from XRF and GEOTEK core scanners highlight (i) a regional tephra at 950 cal BP; (ii) regular occurrences of floods during the LIA; and (iii) a background sedimentation related to glacial flour inputs through hypo- and hyperpycnal flows favoring very high sedimentation rates (1-2 cm.a^-1) in the fjord. Phases of glacier advances and retreats linked to moisture transport by SHW are reflected by fluctuations in sedimentological and geochemical signals, and correlated with moraines dating on land. Over the past 4 kyrs, four cycles of glacier advances/retreats can be evidenced, reflecting wet/dry periods in response to shifts in the position and changes in magnitude of the SHW, associated with moisture transport and precipitation in the Southern Indian Ocean. On centennial timescales, wet/dry periods inferred from Kerguelen are in-phase with Holocene SAM-related records from South America and Tasmania over the last 2 kyrs, suggesting the long-term glacier dynamic at Kerguelen is also related to a centennial expression of SAM.

Acknowledgments : Marion Dufresne Crew, ARTEMIS program, UGA-ARCA.