Did the migration of the South Westerly Winds influence South Georgia's glaciers during the Holocene?

Abstract

The sub-Antarctic island of South Georgia is heavily glaciated with numerous tidewater glaciers. Considerable uncertainty remains regarding the island's glacial history and the response of its glaciers to Holocene climate variability. This uncertainty largely stems from a scarcity of well-dated climate records from the region. We address this uncertainty by reconstructing the palaeoceanography and proximal glacial history of Cumberland Bay through detailed analyses of a marine sediment core (core GC673, ca. 9.5 cal. kyr BP to Present; 6 km offshore in the Cumberland Trough; water depth 238 m) involving benthic foraminiferal and diatom assemblages, geochemical analysis (biogenic silica content, carbon:nitrogen ratios, total organic carbon), and portable X-ray fluorescence (pXRF) analysis. A key finding of our research is that the relative abundance of the benthic foraminifera Fursenkoina fusiformis serves as a valuable proxy for intense diatom blooms in this locality. These blooms likely occur as a result of increased terrestrial runoff linked to the spring and summer melt. A notable correlation between the abundance of F. fusiformis and the diatom accumulation rates exists, with peaks in both aligning with increased (though still scarce) relative abundance of ice-associated diatoms. We further suggest that Zr/Rb – commonly used as a grain size indicator – can be used as a proxy for glacial flour in this setting. Glacial flour is a dominant source of Fe on the South Georgia shelf and the strong negative correlation between Zr/Rb and Fe (R2=0.59), and positive correlation between Fe and diatom accumulation (R2=0.37), supports this. Our analyses reveal a sequence of distinct Holocene glacial advances. High primary productivity observed in the Early Holocene is closely associated with inferred meltwater released from glaciers as they retreated to the inner fjords in response to a prevailing warm climate at this time. Our proposed glacial advances appear to coincide with increases in long- distance pollen preserved within lake deposits in Cumberland Bay, implying a strengthening of the Southern Hemisphere Westerly Winds (SHWW over South Georgia, leading to enhanced winter snowfall and growth of the island’s glaciers. Our findings align with, and expand upon, previously published glacial trends inferred from plant macrofossil and pollen evidence from South Georgia’s peat bogs and dated glacial moraines. Ultimately, we conclude that the primary driver behind the productivity trends at site GC673 has been the diatom blooms prompted by greater glacier melt. Furthermore, we connect this increased melt to glacier growth during intervals of stronger SHWW over South Georgia.