Chasing the melting ice: evidence for the earliest Holocene glacier minimum in the Alps and precise dating of the subsequent advance at the end of the Preboreal

Abstract

The ongoing rapid glacier melting in the European Alps due to anthropogenic climate warming has led to the discovery of previously buried tree remnants at the retreating ice margins proving long-lasting Holocene glacier minima as analogous to the recent state of glaciation. Since 2018, remnants of multi-centennial-aged trees have become accessible at the retreating terminus of the Morteratsch Glacier, Swiss Alps. Some tree remnants prove multi-centennial glacier minima before c. 6.50 and 3.88 ka. However, the majority of the findings represent the oldest Holocene woods found to date on a glacier forefield in the European Alps. They demonstrate a distinct and previously unknown glacier minimum lasting at least 430 years, between c. 10.78 and 10.35 ka, during which the glacier was consistently smaller than c. 2020 CE. This earliest Holocene glacier minimum during the late-Preboreal was terminated by an advance of the Morteratsch Glacier c. 10.35 ka (i.e. 8349 ± 14 cal BCE) proven by several tree remnants with killing dates. The culmination of this glacier advance towards the end of the Preboreal is documented at few Alpine glaciers through moraines located slightly outside the later Little Ice Age limits and cosmogenic dated to around 10.2 ka. In a hemispheric comparison, the onset of the glacier minimum at Morteratsch Glacier corresponds with the oldest dates available for glacier extents as today, namely in western North America, and the dating of the late-Preboreal glacier culmination also corresponds with culmination ages in Scandinavia as well as in north-eastern North America and Greenland.