Scientific access into Mercer Subglacial Lake: scientific objectives, drilling operations and initial observations

John C Priscu,Jonas Kalin,Molly O Patterson,Billy Collins,Chloe Gustafson,Al Gagnon,Martyn Tranter,Edward Krula,Matthew R Siegfried,Anatoly Mironov,W Berry Lyons,David M Harwood,Brent C Christner,John E Dore,Graham Roberts,Mark Bowling,Dar Gibson,Ok-Sun Kim,Robert Zook,Joel Barker,Christina Davis,Wei Li,Dennis Duling,Justin Burnett,Amy Leventer,Kathy Kasic,M L Skidmore ,Alexander B Michaud ,Timothy D Campbell ,B E Rosenheim ,Christopher B Gardner ,Trista J Vick‐Majors ,James S Mcmanis ,John R Winans ,H A Fricker ,Ryan A Venturelli ,C W Elsworth

doi:10.1017/aog.2021.10

Abstract

AbstractThe Subglacial Antarctic Lakes Scientific Access (SALSA) Project accessed Mercer Subglacial Lake using environmentally clean hot-water drilling to examine interactions among ice, water, sediment, rock, microbes and carbon reservoirs within the lake water column and underlying sediments. A ~0.4 m diameter borehole was melted through 1087 m of ice and maintained over ~10 days, allowing observation of ice properties and collection of water and sediment with various tools. Over this period, SALSA collected: 60 L of lake water and 10 L of deep borehole water; microbes >0.2 μm in diameter from in situ filtration of ~100 L of lake water; 10 multicores 0.32–0.49 m long; 1.0 and 1.76 m long gravity cores; three conductivity–temperature–depth profiles of borehole and lake water; five discrete depth current meter measurements in the lake and images of ice, the lake water–ice interface and lake sediments. Temperature and conductivity data showed the hydrodynamic character of water mixing between the borehole and lake after entry. Models simulating melting of the ~6 m thick basal accreted ice layer imply that debris fall-out through the ~15 m water column to the lake sediments from borehole melting had little effect on the stratigraphy of surficial sediment cores.

Highlights

The Antarctic subglacial environment is one of the least explored regions on Earth
The Subglacial Antarctic Lakes Scientific Access (SALSA) access borehole was drilled through the Mercer Ice Stream (1087 m thick) and entered the 15 m deep water column of SLM in late December 2018
The primary objective of the SALSA project was to examine the role of subglacial water, ice, sediment, rock and paleoclimate on microbial carbon cycling within the water column and sediments of SLM

Summary

Introduction

The Antarctic subglacial environment is one of the least explored regions on Earth. From the few successful attempts to access this environment, information about its nature has transformed the way we view the continent (Priscu and Christner, 2004; Fricker and others, 2007; Priscu and others, 2008; Siegfried and Fricker, 2018; Venturelli and others, 2020; Vick-Majors and others, 2020). The step was no longer present on December following borehole reaming but was replaced by a dispersed region of elevated SC from 960 to 1073 m This increase in SC is associated with warmer borehole water temperatures reflecting hot water input from the 29 December ream together with the introduction of upward displaced lake water resulting from differences between return pump and drilling flow rates. As shown by the height discrepancy of 7 m between the Vlb values calculated using conservation of volume and SC relationships, the amount of dissolved solids present in peaks 1 and 2 combined is in excess of the amount that can be attributed to the upwardly displaced initial plug of lake water These results indicate an additional source of salts to the borehole water, which likely originated from debris-rich basal ice melt

28 December

Findings

Conclusions