Environmentally clean access to Antarctic subglacial aquatic environments

Abstract

Subglacial Antarctic aquatic environments are important targets for scientific exploration due to the unique ecosystems they support and their sediments containing palaeoenvironmental records. Directly accessing these environments while preventing forward contamination and demonstrating that it has not been introduced is logistically challenging. The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project designed, tested and implemented a microbiologically and chemically clean method of hot-water drilling that was subsequently used to access subglacial aquatic environments. We report microbiological and biogeochemical data collected from the drilling system and underlying water columns during sub-ice explorations beneath the McMurdo and Ross ice shelves and Whillans Ice Stream. Our method reduced microbial concentrations in the drill water to values three orders of magnitude lower than those observed in Whillans Subglacial Lake. Furthermore, the water chemistry and composition of microorganisms in the drill water were distinct from those in the subglacial water cavities. The submicron filtration and ultraviolet irradiation of the water provided drilling conditions that satisfied environmental recommendations made for such activities by national and international committees. Our approach to minimizing forward chemical and microbiological contamination serves as a prototype for future efforts to access subglacial aquatic environments beneath glaciers and ice sheets.

Enhanced trace element mobilization by Earth’s ice sheets

“…Sample Collection, Processing, Storage, and Analysis. SLM water samples were retrieved using a standard 10-L Niskin bottle precleaned with 1.2 M HCl (followed by copious rinsing with ultrapure water [UPW]; Milli-Q; 18.2 MΩ cm −1 ) and 3% H 2 O 2 and lowered through an ∼0.6-m-diameter borehole drilled using a microbiologically clean, hot water drilling system (17,18). A 10-L Niskin bottle was retrieved in six casts into the lake from 29 December 2018 to 4 January 2019.…”

“…Second, much of the water in the borehole originates from melting of the ice sheet side wall, not hot water injected into the borehole from the drill. Procedural blanks taken from an access port on the hot water drilling system of the borehole return water [Port 9 (18)] were very low compared with measured values from the lake water (SI Appendix, Table S3), with the exception of Zn, where blanks were ∼40 nM (i.e., 55% of the dZn value at SLM). Finally, the Niskin bottle was slowly lowered to middepth in the lake water column (lake water column = 15-m deep); hence, the bottle passed through ∼7.5 m of lake water, flushing it with more than 8 vol of lake water before samples were collected.…”

“…Ice sheet subglacial meltwaters have recently been identified as important sources of reactive sediment, solute, and nutrients to downstream ecosystems (13)(14)(15)(16), highlighting a potentially important yet poorly understood contribution to global carbon cycling (1). The majority of samples have been collected from comparatively accessible glacial field sites, with extremely limited data available from Antarctic subglacial environments due to extreme technological and logistical challenges of access (17,18). Given the paucity of data, we do not understand the implications of changing ice sheet melt for biogeochemical cycling in the polar regions and their impact on local and regional processes (19).…”

Subglacial erosion has the potential to sustain microbial processes in Subglacial Lake Whillans, Antarctica

“…To ensure the clean access of the lake, microbial cells in the drilling water, and any exposed surfaces of the hose, cables and equipment deployed, were reduced and killed by the use of four complementary methods 1,69,70 . The efficiency of this technology was thoroughly tested before its use and in the field; the results of these tests together with a more detailed description can be found in Priscu et al 69 and Michaud et al 70 . Sediment core samples were taken using a UWITEC gravity multi-corer, with a diameter of 6 cm and a 50 cm length 61 , which provided a 38-cm-long sediment core 11 .…”

Development of a clean hot water drill to access Subglacial Lake CECs, West Antarctica

“…To minimise chemical contamination from the drill hose, it will be used extensively in drilling to 500 m during the test season. At the SLCECs site, it will be flushed again with clean hot water (>85°C) for at least 1 h to remove any residual chemicals leaching from the inner PA11 core (Michaud and others, 2020). Similarly, the drill hose outer will be cleaned by the hose cleaning unit.…”