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 westerly winds (SHW) play a crucial role in the large-scale ocean circulation and global carbon cycling. Accordingly, the reconstruction of its latitudinal position and intensity is essential for understanding global climatic fluctuations during the last glacial cycle. The southernmost part of the South American continent is of great importance for paleoclimate studies as the only continental mass intersecting a large part of the SHW belt. However, continuous proxy records back to the last Glacial are rare in southern Patagonia, owing to the Patagonian Ice Sheets expanding from the Andean area and the scarcity of continuous paleoclimate archives in extra-Andean Patagonia. Here, we present an oxygen isotope record from cellulose and purified bulk organic matter of aquatic moss shoots from the last glacial-interglacial transition preserved in the sediments of Laguna Potrok Aike (52° S, 70° W), a deep maar lake located in semi-arid, extra-Andean Patagonia. The highly significant correlation between oxygen isotope values of aquatic mosses and their host waters and the abundant well-preserved moss remains allow a high-resolution oxygen isotope reconstruction of lake water (δ18Olw) for this lake. Long-term δ18Olw variations are mainly determined by δ18O changes of the source water of lake, surface air temperature and evaporative 18O enrichment. Under permafrost conditions during the Glacial, the groundwater may not be recharged by regional precipitation. The isolated groundwater could have had much less negative δ18O values than glacial precipitation. The less 18O depleted source water and prolonged lake water residence time caused by reduced interchange between in- and outflows could have resulted in the reconstructed glacial δ18Olw that was only ca. 3‰ lower than modern values. The significant two-step rise in reconstructed δ18Olw during the last deglaciation demonstrated the response of isotope composition of lake water to fundamental climatic shifts. Rapid deglacial warming is supposed to cause the 18O enrichment of lake water by ca. 2‰ during the first rise between 17 600 and 15 600 cal BP by increasing temperature-induced evaporation and more 18O enriched precipitation. After a millennial transition period of receding values by up to 0.7‰, the reconstructed δ18Olw resumed pronounced increase since 14 600 cal BP. This cumulative enrichment in 18O of lake water could be interpreted as a response to the strengthened wind-driven evaporation, implying the intensification and establishment of the SHW at the latitude of Laguna Potrok Aike (52° S). During the early Holocene the SHW exerted its full influence on the lake water balance, reflected by reconstructed δ18Olw approaching modern values, indicating a strongly evaporative steppe climate in the Laguna Potrok Aike region.

Atmospheric controls on hydrogen and oxygen isotope composition of meteoric and surface waters in Patagonia

“…9 summarizes the main factors influencing the hydrogen and oxygen isotopic composition of precipitation and surface waters in the SHW core zone of Patagonia around 50°S. We conclude that the Pacific is the main moisture source in upwind and Andean Patagonia also dominating the primary isotope imprint of precipitation, while on downwind sites in the interior of Patagonia descending air masses (Foehn effects), rainout of moisture orographically enriched in light isotopologues and potentially moisture recycling overrides the isotopic signature of the initial moisture source In consequence, detailed isotope studies are a prerequisite for calibration and correct interpretation of isotope proxies from soils (Tuthorn et al, 2014), sediments (Zhu et al, 2014), and tree-rings (Lavergne et al, 2017) from Patagonia. In light of our results further primary data on the isotopic composition of precipitation is urgently needed given the scarce isotopic information available and the high variability imprinted onto precipitation in this area.…”

“…So far no comprehensive study has yet been carried out, which addresses the interplay between isotopic effects and moisture origin over the total area of Patagonia. Such information is of interest for understanding the regional hydrological cycle and the significance of isotopic proxies used in regional palaeoclimate studies (Moy et al, 2008;Mayr et al, 2013;Zhu et al, 2014). However, the database for the calibration of isotope proxies from this remote region is generally poor.…”

Lateglacial and Holocene climatic changes in south-eastern Patagonia inferred from carbonate isotope records of Laguna Potrok Aike (Argentina)

“…Hydrological reconstructions from Laguna Potrok Aike have been an important part of the discussion about the role of SHW for climate. As the water balance of this lake sensitively responds to wind intensity variations , hydrological proxies from its Lateglacial sediment record are largely in accord with changes of atmospheric CO 2 concentrations Zhu et al, 2014). However, hydrological reconstructions for the Holocene so far are based mainly on the total inorganic carbon record of Laguna Potrok Aike (Haberzettl et al, 2005;Hahn 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, 2004;Zhu et al, 2014). 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, 1999;Kaplan et al, 2004;McCulloch et al, 2005).…”