New glacier evidence for ice-free summits during the life of the Tyrolean Iceman

Pascal Bohleber,Martin Stocker-Waldhuber,Andrea Fischer,Ling Fang,Margit Schwikowski

doi:10.1038/s41598-020-77518-9

Abstract

Detailed knowledge of Holocene climate and glaciers dynamics is essential for sustainable development in warming mountain regions. Yet information about Holocene glacier coverage in the Alps before the Little Ice Age stems mostly from studying advances of glacier tongues at lower elevations. Here we present a new approach to reconstructing past glacier low stands and ice-free conditions by assessing and dating the oldest ice preserved at high elevations. A previously unexplored ice dome at Weißseespitze summit (3500 m), near where the “Tyrolean Iceman” was found, offers almost ideal conditions for preserving the original ice formed at the site. The glaciological settings and state-of-the-art micro-radiocarbon age constraints indicate that the summit has been glaciated for about 5900 years. In combination with known maximum ages of other high Alpine glaciers, we present evidence for an elevation gradient of neoglaciation onset. It reveals that in the Alps only the highest elevation sites remained ice-covered throughout the Holocene. Just before the life of the Iceman, high Alpine summits were emerging from nearly ice-free conditions, during the start of a Mid-Holocene neoglaciation. We demonstrate that, under specific circumstances, the old ice at the base of high Alpine glaciers is a sensitive archive of glacier change. However, under current melt rates the archive at Weißseespitze and at similar locations will be lost within the next two decades.

Highlights

Detailed knowledge of Holocene climate and glaciers dynamics is essential for sustainable development in warming mountain regions
The influence of ice dynamics at the ice divide is negligible for ice age interpretation
While only the highest elevation sites remained ice-covered throughout the Holocene, summits around 3000–4000 m were likely ice-free during the Mid-Holocene or covered by glaciers distinctly smaller than today

Summary

Introduction

Detailed knowledge of Holocene climate and glaciers dynamics is essential for sustainable development in warming mountain regions. In combination with known maximum ages of other high Alpine glaciers, we present evidence for an elevation gradient of neoglaciation onset. It reveals that in the Alps only the highest elevation sites remained ice-covered throughout the Holocene. Constraining the maximum age of the stagnant ice near bedrock can indicate past ice-free periods, followed by n eoglaciation[13]. This age information alone contains important information on paleoclimatic conditions. Only human artifact findings were discussed in connection with low stands of high-elevation glaciers in the Alps; at Schnidejoch pass (2750 m, Bernese A lps7) and the “Tyrolean Iceman” in the Eastern. Dating the ice with today’s radiometric techniques could have told us if the Iceman had died in a mostly ice-free environment, or if he fell into a crevasse on a glacier-covered Tisenjoch

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