Late Quaternary climatic inferences from southern Patagonia (∼53°S): A holistic palaeoecological approach to tracking the behaviour of the southern westerly winds

Abstract

The glacial and vegetation patterns of Patagonia are strongly correlated to the behaviour of the Southern westerly winds (SWWs) with palaeoenvironmental evidence for the behaviour of the SWWs interpreted as past changes in southern hemisphere climate and ocean currents. To fully define shifts in the position and intensity of the SWWs palaeoenvironmental data sets must be generated from climate sensitive proxies with sites located in regions that are responsive to changes in effective moisture. Here we present a c. 15,700 yr-old record from a peat bog at Punta Arenas (53◦09′S) which was analysed for pollen, pollen preservation, charcoal and organic content to reconstruct changes in the surrounding vegetation, fire history and mire surface wetness. The peat bog lies in a closed basin and so environmental changes likely reflect changes in effective moisture primarily driven by fluctuations in precipitation. During the Late glacial the landscape was virtually treeless and dominated by cold-tolerant steppe/tundra vegetation. This was followed by substantial vegetation changes as Nothofagus woodland expanded and the local site transitioned from a small lake to a fen and later a raised mire. The Early and Mid-Holocene (11,600–6000 cal a BP) was marked by a period of sustained drier conditions evidenced by reduced pollen preservation and increased fire activity. After c. 4600 cal a BP there was a shift to increased effective moisture superimposed with higher magnitude and higher frequency changes in precipitation. The palaeoenvironmental record presented here is used to better define the nature and timing of latitudinal shifts in the position of the SWWs. Careful interpretation of the Nothofagus pollen signal is required as during drier periods small increases in humidity can drive large woodland responses in the pollen record while during periods of higher humidity the woodland may appear to be unresponsive to climatic changes.