Rapid glacier recession at Monte San Lorenzo (Patagonia) in response to abrupt Southern Hemisphere warming 13.0–12.0 ka BP

Abstract

Mid-latitude Patagonian glaciers are sensitive to changes in the complex coupled ocean-atmospheric climate system of the Southern Hemisphere. Here, we investigate glacier response to a period of rapid climate warming immediately post-dating the Antarctic Cold Reversal (ACR). We analyse a sequence of 13 ice margins, four of them dated, from an outlet valley of the Monte San Lorenzo ice cap (47.3°S). We constrain glacier recession of 31.7 km over a period of ~1 kyr from 13.2 ± 0.4 to 12.1 ± 0.4 ka. The average rate of recession was 35.2 m a −1 over this 1-kyr period, increasing from 12.75 m a −1 at the start of the record (moraines M1 to M4) to 50 m a −1 from M9 to M12. This recession occurred during a period of rapid warming when the austral westerlies shifted polewards. It is likely that ice extent stabilized during the Holocene, with ice occupying the M13 moraine during repeated Holocene neoglacials, before anthropogenic warming caused recession at a rate of 55.5 m a −1 from 1985 to 2016. We conclude that 20th century rates of recession were higher than those during post-ACR warming, though of a similar order of magnitude.

Modelled sensitivity of Monte San Lorenzo ice cap, Patagonian Andes, to past and present climate

“…The 'Moraine Mounds' (M4) are located 5.2 km behind the Esmeralda Moraines (Martin et al, 2019 and Figure 1), dated to 12.8 ka (Glasser et al, 2012), and are 37 km from the present ice margin and above 350 m asl. By 12.5 ± 0.3 ka, Glaciar Calluqueo had receded to M9 (Martin et al, 2022). Lago Chelenko drained between 12.4 and 11.8 ka (Thorndycraft et al, 2019) (Figure 1), during the rapid post-ACR warming after 12.8 ka.…”

“…The M12 moraines, lateral moraines just above the Holocene-age M13 moraines, are dated to 12.1 ± 0.4 ka. Recession over 50 km therefore occurred at a mean rate of 50.3 m yr −1 between 12.8 (M4) and 12.1 ka (M12) (Martin et al, 2022).…”

“…Using empirical observations of the patterns of palaeoglacier recession and landsystem change north of MSL, based on geomorphological mapping, sedimentology and cosmogenic nuclide dating (at this site, mostly Glasser et al, 2012;Davies et al, 2018;Martin et al, 2019Martin et al, , 2022, it is possible to reconstruct the past ice surface and ELA for palaeoglaciers (Osmaston, 2005;Braithwaite, 2008;Rea, 2009;Sagredo et al, 2014). Due to the relationship between precipitation and temperature at the ELA of land-terminating glaciers (Ohmura et al, 1992;Bendle and Glasser, 2012;Chandler and Lukas, 2017), these data, when combined with existing temperature records, can be used to estimate palaeo-precipitation at glacier ELAs.…”

“…In this study, the GlaRe ice-surface reconstruction GIS tool for ArcGIS (Pellitero et al, 2016) was used to calculate palaeo three-dimensional ice-surface for the present-day glacier and when the glacier occupied the post-ACR M12 (mean age 12.1 ± 0.4 ka) and M13 moraines (both limits from Martin et al (2022); Figures 1, 2). GlaRe reconstructs a three-dimensional ice surface based upon a given bed topography and an element of the reconstructed ice margin (e.g.…”

“…Geomorphological and chronological data collected from valleys around MSL show that glaciers receded rapidly through the Last Glacial-Interglacial Transition (LGIT; 15 to 11.7 ka BP; Lowe and Hoek, 2001) and Holocene (11.7 ka onwards; Rasmussen et al, 2014) (Sagredo et al, 2016(Sagredo et al, , 2018Davies et al, 2018;Martin et al, 2019Martin et al, , 2022Thorndycraft et al, 2019;Mendelová et al, 2020). During this time, large-scale climatic events such as the Antarctic Cold Reversal (ACR) impacted Patagonia (Moreno et al, 2009;2018;Tonello et al, 2009;Waldmann et al, 2010;Kilian and Lamy, 2012;Oehlerich et al, 2015;Quade and Kaplan, 2017;Kaplan et al, 2020).…”