Climate history of the Southern Hemisphere Westerlies belt during the last glacial–interglacial transition revealed from lake water oxygen isotope reconstruction of Laguna Potrok Aike (52° S, Argentina)

Abstract

Abstract. The Southern Hemisphere Westerlies (SHW) play a crucial role in large-scale ocean circulation and global carbon cycling. Accordingly, the reconstruction of how the latitudinal position and intensity of the SHW belt changed during the last glacial termination is essential for understanding global climatic fluctuations. The southernmost part of the South American continent is the only continental mass intersecting a large part of the SHW belt. However, due to the scarcity of suitable palaeoclimate archives continuous proxy records back to the last glacial are rare in southern Patagonia. Here, we show an oxygen isotope record from cellulose and purified bulk organic matter of submerged aquatic moss shoots from Laguna Potrok Aike (52 • S, 70 • W), a deep maar lake located in semi-arid, extra-Andean Patagonia, covering the last glacial-interglacial transition (26 000 to 8500 cal BP). Based on the highly significant correlation between oxygen isotope values of modern aquatic mosses and their host waters and abundant well-preserved moss remains in the sediment record a high-resolution reconstruction of the lake water oxygen isotope (δ 18 O lw−corr ) composition is presented. The reconstructed δ 18 O lw−corr values for the last glacial are ca. 3 ‰ lower than modern values, which can best be explained by generally cooler air temperatures and changes in the moisture source area, together with the occurrence of permafrost leading to a prolonged lake water residence time. Thus, the overall glacial δ 18 O lw−corr level until 21 000 cal BP is consistent with a scenario of weakened or absent SHW at 52 • S compared to the present. During the last deglaciation, reconstructed δ 18 O lw−corr values reveal a significant two-step rise describing the detailed response of the lake's hydrological balance to this fundamental climatic shift. Rapid warming is seen as the cause of the first rise of ca. 2 ‰ in δ 18 O lw−corr during the first two millennia of deglaciation (17 600 to 15 600 cal BP) owing to more 18 O enriched precipitation and increasing temperature-induced evaporation. Following this interpretation, an early strengthening of the SHW would not be necessary. The subsequent decrease in δ 18 O lw−corr by up to 0.7 ‰ marks a millennial-scale transition period between 15 600 and 14 600 cal BP interpreted as the transition from a system driven by temperature-induced evaporation to a system more dominated by wind-induced evaporation. The δ 18 O lw−corr record resumes its pronounced increase around 14 600 cal BP. This further cumulative enrichment in 18 O of lake water could be interpreted as response to strengthened wind-driven evaporation as induced by the intensification and establishment of the SHW at the latitude of Laguna Potrok Aike (52 • S) since 14 600 cal BP.

Oxygen isotope ratios of chironomids, aquatic macrophytes and ostracods for lake-water isotopic reconstructions – Results of a calibration study in Patagonia

“…The data presented in Fig. 4 corroborate previous studies that d 18 O values of aquatic cellulose are highly suitable for lake water isotope reconstructions in Patagonia (Mayr et al, 2013;Zhu et al, 2014aZhu et al, , 2014b. The regression equation for the cellulosewater isotopic relation is indistinguishable in slope (0.97 ± 0.02) and intercept (29.6 ± 0.2) with the one obtained previously from Patagonian aquatic mosses (Mayr et al, 2013).…”

Revisiting an arid LGM using fluvial archives: a luminescence chronology for palaeochannels of the Murrumbidgee River, south‐eastern Australia

“…While understanding that past water balance is crucial for the reconstruction of palaeoenvironments of a given region, it is also important to identify the presence or absence of regional arid and humid phases at a broader hemispheric scale. For example, changes in Southern Hemisphere atmospheric circulation have commonly been linked to local palaeohydrological conditions (Shulmeister et al ., ; Zhu et al ., ). The intensification or displacement of major circulation belts such as the Southern Westerly Winds have been directly linked to precipitation records derived from glacial and lacustrine records (Moreno et al ., ; Kaplan et al ., ; McCulloch et al ., ).…”