Paleoclimatic value of sediment pixel intensity time series from Lago Argentino, Patagonia

Abstract. The quantity and characteristics of sediment deposited in lakes are affected by climate to varying extents. As sediment is deposited, it provides a record of past climatic or environmental conditions. However, determining a direct relationship between specific climatic variables and measurable sediment properties, for instance between temperature and sediment optical reflectance, is complex. In this study, we investigate the suitability of sediment reflectance, recorded as digital pixel intensity (PxI), as a paleoclimate proxy at a large ice-contact lake in southern Patagonia, Lago Argentino. We also evaluate whether sediment PxI can be used to investigate the present-day climatic drivers of sedimentation across Lago Argentino. First, we show that sediment PxIs relate to underlying sediment composition, and are significantly correlated with XRF major element compositional data. Secondly, we find that PxIs correlate with both austral summer temperatures and austral summer wind speeds, but not with precipitation. PxI timeseries reach the correlation significance threshold for use as paleo-temperature or paleo-wind speed proxies. However, high spatial variability and the non-unique relationship between PxI and both temperature and wind speed challenges the necessary assumption of stationarity at Lago Argentino. While we do not find it suitable for use as a paleoclimatic proxy, significant correlations between PxI and instrumental climate data do chronicle current climatic controls on sediment deposition at Lago Argentino: high summer temperatures enhance settling of coarse, optically dark grains across the lake basin by promoting ice melt and lake stratification, while high wind speeds reduce the settling of fine, optically bright grains in the ice-proximal regions by transporting sediment-rich waters away from the glacier fronts. The assumptions required for quantitative paleoclimatic reconstruction must be carefully evaluated in complex lacustrine environments, but records unsuitable for use as proxies might nevertheless yield valuable information about the drivers of modern sedimentary transport and deposition.