Tracking the southern hemisphere westerlies during and since the last glacial maximum with multiproxy lake records from the Falkland Islands (52 °S)

Abstract

The Southern Hemisphere Westerlies (SHW) and their linkages with key ocean and atmospheric processes have the potential to drive abrupt climate change. The westerlies migrate seasonally and are thought to have shifted during past climate events, such as the last glacial termination. However, the timing, magnitude, direction, and mechanisms behind such shifts remain a topic of ongoing study. Here, we contribute to the understanding of past temporal and spatial changes in the SHW by mapping their fluctuations in the South Atlantic region from the last glacial maximum (LGM) to present. We use lake sediment proxies, including plant wax isotopes extracted from two tarns on Mt. Usborne, East Falkland (51.7 °S) to infer changes in paleoclimate and in the mean annual position of the SHW over the last ∼23,000 years. Together, the proxies indicate that the position of the SHW during the LGM lay north of the Falkland Islands. We interpret our plant wax isotopic record as showing a southward migration of the mean annual position of the wind belt beginning just before ∼21 ka, accompanied by warming at Mt. Usborne at ∼16.5 ka. The late-glacial climate was variable at the field site, and the mean annual position of the SHW may have fluctuated around the latitude of the Falkland Islands. The early Holocene was characterized by relatively warm, dry conditions with high evaporation rates, and the SHW may have lain south of the islands. A brief southern excursion at 7–6 ka was followed by gradual northward migration of the SHW for the remainder of the Holocene to the pre-industrial position. This northward migration was paired with increasingly wet, cool conditions in the Falkland Islands, and the islands appear to be experiencing some of the wettest conditions of the last 23,000 years during the late Holocene.