Glacial lake outburst floods enhance benthic microbial productivity in perennially ice-covered Lake Untersee (East Antarctica)

Benoit Faucher,Liam Jasperse,Ian Douglas Clark,Dale Thomas Andersen,Denis Lacelle,Nicole Britney Marsh

doi:10.1038/s43247-021-00280-x

Abstract

Benthic ecosystems of perennially ice-covered lakes in Antarctica are highly sensitive to climate-driven changes. Lake Untersee has been in hydrological steady-state for several hundred years with a high pH water column and extremely low levels of dissolved inorganic carbon. Here, we show that glacial lake outburst floods can replenish carbon dioxide-depleted lakes with carbon, enhancing phototrophic activity of the benthic ecosystem. In 2019, a glacial lake outburst flood brought 17.5 million m3 of water to Lake Untersee, the most substantial reported increase for any surface lake in Antarctica. High-resolution grain-size and carbon isotope analyses of microbial mats suggest that glacial lake outburst floods have occurred periodically over the Holocene and help explain the complex patterns of carbon cycling and sequestration observed in the lake. Our findings suggest that periodic flooding events may provide biological stimuli to other carbon dioxide-depleted Antarctic ecosystems and perhaps even icy lakes on early Mars.

Highlights

Benthic ecosystems of perennially ice-covered lakes in Antarctica are highly sensitive to climate-driven changes
The only descriptions have been of a small glacial lake outburst floods (GLOFs) in the Larsemann Hills (76,320 m3) between 2017 and 2019, where ice-dammed lakes drained near the Russian Progress station[14], and the catastrophic drainage of a surface meltwater lake (600–750 million m3) on the Amery Ice Shelf to the ocean below in East Antarctica in 20198
The laser altimetry data indicates that the water level of Lake Untersee increased by 2.0 m between December 12th, 2018 and February 7th, 2019 (Fig. 3), and images from the time-lapse digital camera installed on our meteorological station revealed the sudden release of water through the ice cover on Jan 14–15th, 2019 (Fig. 4)

Summary

Introduction

Benthic ecosystems of perennially ice-covered lakes in Antarctica are highly sensitive to climate-driven changes. Ice-covered lakes are found in many regions of Antarctica, such as the McMurdo Dry Valleys (MDV), Bunger Hills, Vestfold Hills, Larsemann Hills, Schirmacher Oasis, and the Sôya Coast[1,2,3] The majority of these lakes develop moats during the austral summer and are typically recharged annually by glacial meltwater that transports dissolved inorganic and organic carbon (DIC, DOC), cations and anions, nutrients, and sometimes other allochthonous materials[4,5]. We provide evidence from Lake Untersee, a large ultra-oligotrophic perennially ice-covered lake in Dronning Maud Land (East Antarctica), that GLOFs can replenish the water column with dissolved carbon dioxide (CO2) to help sustain the long-term primary production of benthic phototrophic communities. Despite the ultra-oligotrophic, low-light conditions, and lack of a seasonal moat, the lake hosts a benthic microbial ecosystem composed of photosynthetic microbial mats, small cuspate pinnacles, and large conical stromatolitic structures to depths of at least 130 m27–30

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