Abstract

Abstract. Changes in the depth of the freshwater–seawater interface in epishelf lakes have been used to infer long-term changes in the minimum thickness of ice shelves; however, little is known about the dynamics of epishelf lakes and what other factors may influence their depth. Continuous observations collected between 2011 and 2014 in the Milne Fiord epishelf lake, in the Canadian Arctic, showed that the depth of the halocline varied seasonally by up to 3.3 m, which was comparable to interannual variability. The seasonal depth variation was controlled by the magnitude of surface meltwater inflow and the hydraulics of the inferred outflow pathway, a narrow basal channel in the Milne Ice Shelf. When seasonal variation and an episodic mixing of the halocline were accounted for, long-term records of depth indicated there was no significant change in thickness of ice along the basal channel from 1983 to 2004, followed by a period of steady thinning at 0.50 m a−1 between 2004 and 2011. Rapid thinning at 1.15 m a−1 then occurred from 2011 to 2014, corresponding to a period of warming regional air temperatures. Continued warming is expected to lead to the breakup of the ice shelf and the imminent loss of the last known epishelf lake in the Arctic.

Highlights

  • Polar aquatic ecosystems that depend on ice for their physical containment, for their surface covering, or as a source of freshwater are highly sensitive to climate conditions (White et al, 2007; Prowse et al, 2011; Wrona et al, 2016)

  • In this study we aimed to identify factors controlling changes in the water column structure and the depth of the halocline of the last known epishelf lake in the Arctic, in Milne Fiord, Ellesmere Island, and to evaluate how these variations were related to changes in the spatial extent of the lake and to the state of the Milne Ice Shelf (MIS)

  • The epishelf lake was apparent in the first water samples obtained in the fjord in 1983 (Jeffries, 1985), but it clearly thinned through time, and we investigate these changes in more detail below

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Summary

Introduction

Polar aquatic ecosystems that depend on ice for their physical containment, for their surface covering, or as a source of freshwater are highly sensitive to climate conditions (White et al, 2007; Prowse et al, 2011; Wrona et al, 2016). Recent thinning and collapse of ice shelves in the Arctic due to climate warming (Vincent et al, 2001; Copland et al, 2007; Mueller et al, 2003, 2017a; England et al, 2008; White et al, 2015a) has resulted in physical changes of epishelf lakes in the region, including the complete loss of several lakes and a substantial reduction in the depth of the freshwater layer of the few that remained (Mueller et al, 2003, 2017b; Veillette et al, 2008; White et al, 2015b) Given their sensitivity to the state of the impounding ice shelf, observing changes to the water column structure of epishelf lakes can potentially provide a relatively simple way to monitor changes in the integrity of the impounding ice shelf (Mueller et al, 2003; Veillette et al, 2008). Epishelf lakes are numerous in Antarctica and are distributed around the margins of the continental ice sheet (Heywood, 1977; Gibson and Andersen, 2002; Laybourn-Parry et al, 2006; Smith et al, 2006) and were once relatively numerous along the northern coast

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