Variations in the Southern Hemisphere Westerlies Over the Last 23,000 Years from Lake Records in the Falkland Islands

• Main Author: Spoth, Meghan M
• Format: Text
• Language: English
• Published: DigitalCommons@UMaine 2020
• Subjects: leaf wax; biomarkers; pollen; sediment core; tephra; Mt. Usborne; Atmospheric Sciences; Climate; Earth Sciences; Geochemistry; Geology; Glaciology; Sedimentology; Southern Ocean; Alpine Lake
• Online Access: https://digitalcommons.library.umaine.edu/etd/3264; https://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=4334&context=etd

The Southern Hemisphere Westerlies (SHW) are an important driver of climate in the mid-latitudes of the Southern Hemisphere. Abrupt latitudinal migration of this coupled atmospheric-oceanic system is thought to be linked to the onset of the Termination at the end of the last ice age and to subsequent climatic variation through the late-glacial period and Holocene. However, the timing and spatial extent of these shifts, as well as variations in wind intensity, are poorly constrained, hindering our understanding of abrupt climate change in the Southern Hemisphere. In addition, future changes in the position and intensity of the SHW are a critical part of model projections, because the SHW affect Southern Ocean upwelling and CO2 sequestration. Insight into the future behavior of the SHW can come from examination of past fluctuations. My focus is the South Atlantic region, thought to be a key area for interactions between the SHW and other components of the climate system. However, there are few terrestrial datasets constraining past variations in the SHW in this region and many of these appear contradictory. This study is comprised of two alpine lake sediment cores extracted from tarns occupied by alpine glaciers during the last ice age on Mount Usborne of East Falkland (51oS). This terrestrial record, which spans the last 23 ka, uses stratigraphy, organic content, biomarkers (with a focus on plant wax), isotopic composition of plant waxes, and a preliminary pollen record to identify relative wind intensity, wetness, precipitation source, and temperature of the site. Moisture source is particularly useful as it can be tied to the average position of the SHW over time, with enriched precipitation reflecting a southerly location and depleted precipitation indicating a northerly shifted wind belt. My data suggest climate at Mount Usborne was cold and windy until 16.4 ka, when the SHW moved south and the area may have warmed. This shift represents the local expression of the onset of the Termination. Following a brief ...