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

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.