Modeling δD-δ18O Steady-State of Well-Sealed Perennially Ice-Covered Lakes and Their Recharge Source: Examples From Lake Untersee and Lake Vostok, Antarctica

Dale T Andersen,David A Fisher,Klemens Weisleitner,Benoit Faucher,Denis Lacelle

doi:10.3389/feart.2020.00220

Dale T Andersen, David A Fisher + Show 3 more

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https://doi.org/10.3389/feart.2020.00220

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Abstract

Perennially ice-covered that are tightly sealed from the atmosphere represent a unique group of polar lakes. In these lakes, the δD-δ18O evolution of the water column and its steady-state is controlled by rates of recharge and freezing at the bottom of the ice cover. We developed a recursive model (FREEZCH9) that takes into account the changing salinity in the water column as a result of freezing and mixes the recharge water to the residual water in well-sealed perennially ice-covered lakes. Our model is tested against datasets from Lake Vostok and is used to assess the dD-d18O mass balance of Lake Untersee and evaluate if the lake is in isotopic steady-state. Our FREEZCH9 simulations fit well the predicted dD-d18O values of Lake Vostok and the overlying accreted ice. Simulations with FREEZCH9 also suggests that Lake Untersee is in isotopic steady-state and that its two input sources (i.e. subaqueous terminus melting of the Anuchin glacier and subglacial contributions) have similar dD-d18O composition. Our modeling demonstrates that Lake Untersee most likely did into receive additional input from surface streams during the last 300-500 years. FREEZCH9 may be also used to determine if the hypothetical groundwater systems of the McMurdo Dry Valleys are fully or partially recharged by subglacial lakes.

Highlights

In Antarctica, several hundred lakes have been identified and classified according to their ice cover regime (Figure 1A; Morgan et al, 2007; Vincent et al, 2008)
The freezing of nearly pure water with an initial δ18O composition of −35 over the temperature range of 0 to −4◦C will cause the δ18O of the residual water to rapidly decrease to value of −45
The FREEZCH9 modeling using 1% annual recharge and mixing with lake water suggests that the δ18O composition of Lake Untersee (−37.9 to −37.6 ) is in equilibrium with source waters having an average δ18O composition of −35.0

Summary

Introduction

In Antarctica, several hundred lakes have been identified and classified according to their ice cover regime (Figure 1A; Morgan et al, 2007; Vincent et al, 2008). Icecovered lakes are found along the warmer Antarctic Peninsula and other coastal regions These lakes lose their ice cover in austral summer and are typically recharged by a combination of local precipitation and glacial meltwater (e.g., Gibson, 1999; Lyons et al, 2013). The ice-cover regime of the lake (i.e., seasonally or perennially ice-covered) determines whether evaporation or freezing drives the evolution of the lake isotope chemistry (Miller and Aiken, 1996) Both seasonally ice-covered lakes and perennially icecovered lakes that develop summer moats have lake waters with δD-δ18O composition that are typically distributed below the Antarctic Meteoric Water Line (AMWL) (Figure 1B). The δ18O composition of evaporative lakes is determined by atmospheric parameters such as humidity and isotopic composition of the water vapor, and numerical models of the evolving salinity in the water column have been developed to estimate a lake’s δD-δ18O steady-state (i.e., Gibson, 1999; Horita, 2009)

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