Enabling clean access into Subglacial Lake Whillans: development and use of the WISSARD hot water drill system

Rack, Frank R

doi:10.1098/rsta.2014.0305

Cited by 20 publications

(18 citation statements)

References 57 publications

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“…We accessed the sub–ice shelf cavity of Ross Ice Shelf 3 km downstream of the grounding line of Whillans Ice Stream (Site GZ19, Figure ) using hot water drilling (Rack, ; Tulaczyk et al, ). This site is within the grounding zone as determined by the limits of ice flexure from differential synthetic aperture radar interferometry (Marsh et al, ).…”

Section: Methodsmentioning

confidence: 99%

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

et al. 2020

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Mass loss from the Antarctic ice sheet is sensitive to conditions in ice shelf grounding zones, the transition between grounded and floating ice. To observe tidal dynamics in the grounding zone, we moored an ocean pressure sensor to Ross Ice Shelf, recording data for 54 days. In this region the ice shelf is brought out of hydrostatic equilibrium by the flexural rigidity of ice, yet we found that tidal pressure variations at a constant geopotential surface were similar within and outside of the grounding zone. This implies that the grounding zone ocean cavity was overpressurized at high tide and underpressurized at low tide by up to 10 kPa with respect to glaciostatic pressure at the ice shelf base. Phase lags between ocean pressure and vertical ice shelf motion were tens of minutes for diurnal and semidiurnal tides, an effect that has not been incorporated into ocean models of tidal currents below ice shelves. These tidal pressure variations may affect the production and export of meltwater in the subglacial environment and may increase basal crevasse heights in the grounding zone by several meters, according to linear elastic fracture mechanics. We find anomalously high tidal energy loss at the K 1 constituent in the grounding zone and hypothesize that this could be explained by seawater injection into the subglacial environment at high tide or internal tide generation through interactions with topography. These observations lay the foundation for improved representation of the grounding zone and its tidal dynamics in ocean circulation models of sub-ice shelf cavities.Plain Language Summary One of the challenges for sea level rise prediction is understanding how the Antarctic ice sheets and the Southern Ocean interact. Ocean tides are an important component of this interaction, influencing ice shelf melting and the flow rate of grounded ice toward the coast. We report new observations relevant to this interaction: tidally varying ocean pressures where the ice first goes afloat to become an ice shelf. These tidal ocean pressure variations influence tidal currents below the ice shelf, and we propose that they also push seawater beneath the ice inland of the ice shelf and extend fractures at the ice shelf base. This study identifies tidal processes that may affect melt and fracture near the inland edge of ice shelves, a highly sensitive zone for ice dynamics.

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Section: Methodsmentioning

confidence: 99%

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

et al. 2020

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“…To minimize the potential for water exchange, the borehole water level was lowered prior to penetration into the lake cavity, which allowed lake water to enter the borehole and prevented drilling water from entering the lake proper [32]. A hot water drill and water treatment unit were designed specifically for the WISSARD project [47,48]. The drilling water was circulated through the treatment system, which consisted of two filtration modules (2.0 and 0.2 µm pore size) to remove particulates and two germicidal UV lamps that delivered dosages of 40 000 µW s −1 cm −1 at 185 nm and 175 000 µW s −1 cm −1 at 245 nm to destroy organics [46,47].…”

Section: Sampling Subglacial Lake Whillans (A) Clean Access Approachmentioning

confidence: 99%

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

Mikucki

Lee

Ghosh

et al. 2016

Phil. Trans. R. Soc. A.

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Liquid water occurs below glaciers and ice sheets globally, enabling the existence of an array of aquatic microbial ecosystems. In Antarctica, large subglacial lakes are present beneath hundreds to thousands of metres of ice, and scientific interest in exploring these environments has escalated over the past decade. After years of planning, the first team of scientists and engineers cleanly accessed and retrieved pristine samples from a West Antarctic subglacial lake ecosystem in January 2013. This paper reviews the findings to date on Subglacial Lake Whillans and presents new supporting data on the carbon and energy metabolism of resident microbes. The analysis of water and sediments from the lake revealed a diverse microbial community composed of bacteria and archaea that are close relatives of species known to use reduced N, S or Fe and CH4 as energy sources. The water chemistry of Subglacial Lake Whillans was dominated by weathering products from silicate minerals with a minor influence from seawater. Contributions to water chemistry from microbial sulfide oxidation and carbonation reactions were supported by genomic data. Collectively, these results provide unequivocal evidence that subglacial environments in this region of West Antarctica host active microbial ecosystems that participate in subglacial biogeochemical cyclingauthorsversionPeer reviewe

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“…These documents guided our approach to constructing, testing and monitoring the clean access system used during hot-water drilling. Construction of the drill and filtration systems (Rack 2016) and laboratory testing of the filtration system (Priscu et al 2013) have been published. Here, we present new data from samples collected during the actual hot-water drilling of three boreholes during two field seasons.…”

Section: Discussionmentioning

confidence: 99%

“…Figure 1 provides an overview of the various components of the drill (i.e. reservoir, filtration, UV modules, hot-water heaters and hose) and how they were integrated in the field (see also Priscu et al 2013, Rack et al 2014, Rack 2016. Sampling ports were plumbed between components in the drill system.…”

Section: Drill Systemmentioning

confidence: 99%

Environmentally clean access to Antarctic subglacial aquatic environments

et al. 2020

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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.

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Enabling clean access into Subglacial Lake Whillans: development and use of the WISSARD hot water drill system

Cited by 20 publications

References 57 publications

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

Environmentally clean access to Antarctic subglacial aquatic environments

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