Subglacial discharge controls seasonal variations in the thermal structure of a glacial lake in Patagonia

Shin Sugiyama,Yasushi Fukamachi,Yoshihiro Yamamoto,Shuntaro Hata,Marius Schaefer,Masahiro Minowa,Christoph Schneider,Tobias Sauter

doi:10.1038/s41467-021-26578-0

Abstract

Water temperature in glacial lakes affects underwater melting and calving of glaciers terminating in lakes. Despite its importance, seasonal lake temperature variations are poorly understood because taking long-term measurements near the front of calving glaciers is challenging. To investigate the thermal structure and its seasonal variations, we performed year-around temperature and current measurement at depths of 58–392 m in Lago Grey, a 410-m-deep glacial lake in Patagonia. The measurement revealed critical impacts of subglacial discharge on the lake thermal condition. Water below a depth of ~100 m showed the coldest temperature in mid-summer, under the influence of glacial discharge, whereas temperature in the upper layer followed a seasonal variation of air temperature. The boundary of the lower and upper layers was controlled by the depth of a sill which blocks outflow of dense and cold glacial meltwater. Our data implies that subglacial discharge and bathymetry dictate mass loss and the retreat of lake-terminating glaciers. The cold lakewater hinders underwater melting and facilitates formation of a floating terminus.

Highlights

Water temperature in glacial lakes affects underwater melting and calving of glaciers terminating in lakes
A comprehensive study of three glacial lakes in Patagonia reported an absence of upwelling, but instead confirmed that subglacial discharge sinks deep into a lake because glacial meltwater is turbid and denser than lakewater[27]
Lake measurements were obtained in Lago Grey, a glacial lake on the southeastern edge of the Southern Patagonia Icefield (51.0°S, 73.2°W) (Fig. 1a)

Summary

Introduction

Water temperature in glacial lakes affects underwater melting and calving of glaciers terminating in lakes. Near the front of freshwater calving glaciers, no evidence has been reported for upwelling and active circulation This lack of circulation affects the lake thermal regime and underwater melting. Measurements of glacial lakes in Alaska[20,21], New Zealand[22,23], Himalaya[24,25], and Patagonia[26,27] showed relatively cold stratified water, implying insignificant underwater melting. The submerged ice destabilizes the glacier front by exerting a buoyant force, the observed ice front geometry provided an important implication for buoyancy-driven underwater calving These observations demonstrated that the stratification of a glacial lake dictates the calving mechanism and frontal dynamics of glaciers terminating in the lake. Observations over a period of 20 months revealed strong influences of subglacial discharge on the lake thermal structure

Methods

Results

Conclusion