A 550-YEAR MULTI-PROXY RECORD FROM LAKE SEDIMENT CORES REVEALS RECENT SOUTHERN HEMISPHERE WESTERLY WIND VARIABILITY IN THE AUCKLAND ISLANDS (51°S), NEW ZEALAND SUB-ANTARCTIC

The strength and latitudinal position of the Southern Hemisphere Westerly Winds (SHWW) are one of the primary controllers of air-ocean CO₂ flux in the Southern Ocean and directly influence precipitation patterns in the Southern Hemisphere mid-latitudes. There are few terrestrial records that capture changes in the SHWW, particularly at Sub-Antarctic latitudes where the modern westerly maximum is located. A high-resolution record of environmental change at the Auckland Islands (51°S) over the last 550 years has been compiled from short lake sediment cores collected from Lake Hinemoa. Down-core variations in the bulk sediment C/N ratio, magnetic susceptibility, and n-alkane distributions show an increase in the influx of terrestrial components beginning at 300 cal yr BP, while an overall decrease in wt.% biogenic silica suggests a decline in lake productivity. These changes are consistent with an increase in effective precipitation causing additional influx of lithogenic and terrestrial organic matter from the watershed and increased wind-driven mixing of the water column during a period of higher westerly flow. Observed changes are broadly correlated with shifts in the SAM index as reconstructed by Abram (2014). The δD of long chain n-alkanes (C₂₉ and C₃₁) from core tops appears to reflect local mean annual precipitation δD. A negative shift in δD down-core is coincident with the proposed period of increased wind strength, and suggests a change in precipitation source region during this time. The record from Lake Hinemoa appears to have an anti-phase relationship to some NZ records, but the interpreted increase in wind speed is similar to a lake record obtained from the same latitude in Southern South America, suggesting that observed changes at the Auckland Islands may be due to latitudinal shifts in the westerly maximum on centennial timescales.