Holocene climatic changes in the Kerguelen archipelago (South Indian Ocean) based on marine and lacustrine palaeoclimatic archives

Climatic variability in the Southern Hemisphere is largely controlled by the latitudinal position of the Southern Hemisphere Westerly Winds (SHW), whose migration influences precipitation, temperature, and Antarctic upwelling. This study presents the results of analyses of two lacustrine sediment cores from Lake Armor, located on the subantarctic Kerguelen Islands (49°15′S, 69°10′E), within the SHW belt. Lipid biomarkers (Glycerol Dialkyl Glycerol Tetraethers, n- alkanes, and their hydrogen isotopes) were used to reconstruct mean annual air temperature above freezing (MAF) and humidity conditions. These records are compared with a high-resolution diatom-based summer sea surface temperature (SST) reconstruction from marine core MD11-3353, situated 150 km southwest of Lake Armor. In the late glacial and Early Holocene, our results reveal a period of warm air temperature, comparable to current values and very warm sea surface temperature, 5 °C above the current values. Around 9000 cal a BP, an abrupt transition occurred, marked by a cooling of 5 °C in SST and 1.5 °C in MAF, interpreted as a northward migration of the SHW and associated oceanic fronts. The Mid-to-Late Holocene period is characterized by pronounced MAF variability, including a notably warm interval between 3000 and 2000 cal a BP, when n- alkane dD suggests the prevalence of wetter conditions. Since ∼250 cal a BP, a southward migration of the SHW has produced a 2.5 °C rise in MAF. Our findings are overall consistent with previous studies from the Indian Ocean, but permit us to go a step further as by comparing SSTs and air temperatures. This suggests that SST is not a reliable predictor of air temperature on the Kerguelen Islands, particularly during the Early Holocene. We hence argue that Kerguelen air temperature is predominantly controlled by the position of westerly winds, as an indicator of reorganisations in air mass trajectories. • First quantitative air temperature reconstruction in South Indian Ocean. • Strong consistency between biomarker results of two lacustrine sediments sequences. • Comparison between air and sea temperatures. • Atmospheric and oceanic systems not coupled on the Early Holocene. • Important cooling in SST and in air temperature at 9000 cal a BP.