Abstract

The causes underlying Holocene glacier fluctuations remain elusive, despite decades of research efforts. Cosmogenic nuclide dating has allowed systematic study and thus improved knowledge of glacier-climate dynamics during this time frame, in part by filling in geographical gaps in both hemispheres. Here we present a new comprehensive Holocene moraine chronology from Mt. San Lorenzo (47°S) in central Patagonia, Southern Hemisphere. Twenty-four new 10Be ages, together with three published ages, indicate that the Río Tranquilo glacier approached its Holocene maximum position sometime, or possibly on multiple occasions, between 9,860 ± 180 and 6,730 ± 130 years. This event(s) was followed by a sequence of slightly smaller advances at 5,750 ± 220, 4,290 ± 100 (?), 3,490 ± 140, 1,440 ± 60, between 670 ± 20 and 430 ± 20, and at 390 ± 10 years ago. The Tranquilo record documents centennial to millennial-scale glacier advances throughout the Holocene, and is consistent with recent glacier chronologies from central and southern Patagonia. This pattern correlates well with that of multiple moraine-building events with slightly decreasing net extent, as is observed at other sites in the Southern Hemisphere (i.e., Patagonia, New Zealand and Antarctic Peninsula) throughout the early, middle and late Holocene. This is in stark contrast to the typical Holocene mountain glacier pattern in the Northern Hemisphere, as documented in the European Alps, Scandinavia and Canada, where small glaciers in the early-to-mid Holocene gave way to more-extensive glacier advances during the late Holocene, culminating in the Little Ice Age expansion. We posit that this past asymmetry between the Southern and Northern hemisphere glacier patterns is due to natural forcing that has been recently overwhelmed by anthropogenic greenhouse gas driven warming, which is causing interhemispherically synchronized glacier retreat unprecedented during the Holocene.

Highlights

  • Following an early Holocene glacier minimum, most of the glacierised areas around the world experienced a phase of renewed glacier advances, a phenomenon commonly known as Neoglaciation (Porter and Denton 1967)

  • Quartz isolation and beryllium extraction were performed at the Cosmogenic Nuclide Laboratory at the Lamont-Doherty Earth Observatory (LDEO), Columbia University (NY, United States), following Schaefer et al (2009). 10Be/Be isotope ratios were measured at the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory (CAMS LLNL)

  • Given the frontal sections of all of the RT6 moraines are not preserved, we cannot precisely determine the maximum glacier extent during these events; based on the geometry and slope of the lateral ridges, we infer that the Río Tranquilo glacier reached an extent of between 6 and 7 km from the headwall

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Summary

Introduction

Following an early Holocene glacier minimum, most of the glacierised areas around the world experienced a phase of renewed glacier advances, a phenomenon commonly known as Neoglaciation (Porter and Denton 1967) Since their recognition by the middle of the last century, numerous studies have attempted to decipher the causes underlying these glacier fluctuations (e.g., Grove 2004) by comparing the sequence and temporal phasing of advances in disparate regions of the world with terrestrial or extraterrestrial climate-forcing mechanisms (e.g., Denton and Karlen 1973; Bond et al, 2001; Denton and Broecker 2008). Significant gaps remain in our knowledge of centennial- and millennial-scale glacier responses under natural climate variability

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