Stratigraphic signature of the Perito Moreno ice-dammings during the Little Ice Age (southern Patagonia, Argentina)

Abstract

The spectacular water outburst occurring semi-periodically when the ice-dam formed by the external front of the Perito Moreno glacier collapses, is one of the most attracting events in the UNESCO ‘Parque Nacional Los Glaciares’ of southern Patagonia. These occurrences have been documented since 1936. Instead, evidence of previous events has been only indirectly provided by dendrochronology analysis. Here we show for the first time radiocarbon-dated sediment cores collected within a small inlet of Brazo Sur, that is, the southern arm of Lago Argentino that record ice-dammings in the Little Ice Age, at 324–266 cal yrs BP, as measured on a vegetal fragment sampled at ca. 14 cm from the top of a core. A common characteristic of the three sediment cores is the abrupt change in the stratigraphic record found at variable depths of 14–18 cm from the top of the cores. This change is marked by a hiatus spanning ca. 3200 years, separating planar-laminated sediments below from an alternation of erosional and depositional events above it, indicating recurring high-energy conditions generated by the emptying of the lake basin. In addition, we observed significant changes in the abundance of environmental indicators as testate amoebae below and above the hiatus. These well-preserved stratigraphic records highlight the key role of glaciolacustine deposits in reconstructing the glacial dynamics and palaeoclimate evolution of a glaciated region.

Climate and environmental history of Laguna Polo, Santa Cruz, Southern Patagonia (49 °S) since 1300 AD

“…The authors identi ed a relationship of testate amoebae and organic matter in Lago Fagnano, showing an increase on species as D. oblonga "oblonga", whereas that others like C. constricta "constricta" tend to decrease. Caffau et al (2022) in Lago Argentino, identify the response of testate amoebae assemblages to the collapse of the Perito Moreno glaciar front during the LIA also observed signi cant difference in the abundance of testate amoebae below and above the stratigraphic hiatus (i.e. the erosional surface).…”

“…Most of them are still considered pristine environments without any major anthropogenic impact, which is key to record and to understand natural climate variability, especially during the last millennia. On the eastern side of the Andes, in the Argentinean Patagonia, an increasing number of multiproxy paleoenvironmental studies have been conducted to identify the impact of the Medieval Climatic Anomaly (MCA) and/or the Little Ice Age (LIA), (Haberzettl et al 2005;Mayr et al 2005;Fey et al 2009; Kastner et al 2010;Caffau et al 2015Caffau et al , 2022. However, up to date, no studies focusing on the response of bioproxies such as testate amoebae and chironomids to the MCA or LIA exist in this region.…”

Physical Limnology and Sediment Dynamics of Lago Argentino, the World's Largest Ice‐Contact Lake

“…We dated two cores from the main lake basin and one from the brazos (“arms”: lacustrine glacial fjords) using the 1963–1965 137 Cs peak (Caffau et al., 2021; Piret et al., 2022). We measured 137 Cs counts at Macalester College using a Canberra high‐resolution, hyperpure germanium coaxial gamma detector (GC1518).…”