Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia

B.J Davies,V.R Thorndycraft,D Fabel,J.R.V Martin

doi:10.1016/j.quascirev.2018.09.025

Abstract

We present 14 new 10Be cosmogenic nuclide exposure ages quantifying asynchronous readvances during the Antarctic Cold Reversal from glaciers in the Baker Valley region of central Patagonia. We constrain glacier and ice-dammed palaeolake dynamics using a landsystems approach, concentrating on outlet glaciers from the eastern Northern Patagonian Icefield (NPI) and Monte San Lorenzo (MSL). Soler Glacier (NPI) produced lateral moraines above Lago Bertrand from 15.1 ± 0.7 to 14.0 ± 0.6 ka, when it dammed the drainage of Lago General Carrera/Buenos Aires through Río Baker at a bedrock pinning point. At this time, Soler Glacier terminated into the 400 m “Deseado” level of the ice-dammed palaeolake. Later, Calluqueo Glacier (MSL) deposited subaerial and subaqueous moraines in the Salto Valley near Cochrane at 13.0 ± 0.6 ka. These moraines were deposited in an ice-dammed palaeolake unified through the Baker Valley (Lago Chalenko; 350 m asl). The Salto Valley glaciolacustrine landsystem includes subaqueous morainal banks, ice-scoured bedrock, glacial diamicton plastered onto valley sides, perched delta terraces, kame terraces, ice-contact fans, palaeoshorelines and subaerial push and lateral moraines. Boulders from the subaqueous Salto Moraine became exposed at 12.1 ± 0.6 years, indicating palaeolake drainage. These data show an asynchronous advance of outlet glaciers from the Northern Patagonian Icefield and Monte San Lorenzo during the Antarctic Cold Reversal. These advances occurred during a period of regional climatic cooling, but differential moraine extent and timing of advance was controlled by topography and calving processes.

Highlights

IntroductionThe Antarctic Cold Reversal (ACR) dominates Southern Hemisphere palaeoclimate records up to at least 40S (Pedro et al, 2016), potentially affecting glaciers of the Northern Patagonian Icefield and Monte San Lorenzo ice cap (NPI and MSL, respectively; Fig. 1) in the Patagonian Andes of South America
We aim to test the synchronicity of glacier behaviour in the Baker Valley region of the central Patagonian Andes (Fig. 1) during the Last Glacial Termination and elucidate palaeoclimatic and topographic controls on moraine formation through new geomorphic mapping and cosmogenic exposure-age dating from previously undated ice margins of both Northern Patagonian Icefield (NPI) and Monte San Lorenzo (MSL) outlet glaciers
We used geomorphological mapping and cosmogenic nuclide dating from outlet glaciers of the eastern Northern

Summary

Introduction

The ACR dominates Southern Hemisphere palaeoclimate records up to at least 40S (Pedro et al, 2016), potentially affecting glaciers of the Northern Patagonian Icefield and Monte San Lorenzo ice cap (NPI and MSL, respectively; Fig. 1) in the Patagonian Andes of South America. Glacier readvances during the ACR have been documented in the tropical Andes (10e20S) (Jomelli et al, 2014, 2017), for Colonia Glacier of the NPI (Nimick et al, 2016), for Tranquilo Glacier of MSL (Sagredo et al, 2018), in Cordillera Darwin (54S) (Menounos et al, 2013), and in Torres del Paine (51S) (Fogwill and Kubik, 2005; García et al, 2012). Palaeoclimatic controls on glaciers and the role of the bi-hemisphere seesaw (Pedro et al, 2018) in modulating climate in central Patagonia remain poorly resolved

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