Search

During the 2018–2019 Antarctic field season, the Subglacial Antarctic Lakes Scientific Access project team cleanly accessed Mercer Subglacial Lake, West Antarctica, to sample water and sediments beneath 1087 m of overlying ice. A multicorer was successful in sampling the sediment–water interface, with 4 deployments retrieving 10 cores between 0.3 and 0.4 m in length. Gravity coring was also successful, retrieving cores of 0.97 and 1.78 m in glacial diamict. However, sediment cores retrieved by the gravity cores were shorter than the core barrel penetration (as measured by mud streaks on the outside of the coring system), indicating that the system can likely be improved. This manuscript describes the design, implementation, successes, and lessons learned while coring sediments in a subglacial lake. [ABSTRACT FROM AUTHOR]

A clean hot-water drill was used to gain access to Subglacial Lake Whillans (SLW) in late January 2013 as part of the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project. Over 3 days, we deployed an array of scientific tools through the SLW borehole: a downhole camera, a conductivity-temperature-depth (CTD) probe, a Niskin water sampler, an in situ filtration unit, three different sediment corers, a geothermal probe and a geophysical sensor string. Our observations confirm the existence of a subglacial water reservoir whose presence was previously inferred from satellite altimetry and surface geophysics. Subglacial water is about two orders of magnitude less saline than sea water (0.37-0.41 psu vs 35 psu) and two orders of magnitude more saline than pure drill meltwater (<0.002 psu). It reaches a minimum temperature of -0.55°C, consistent with depression of the freezing point by 7.019 MPa of water pressure. Subglacial water was turbid and remained turbid following filtration through 0.45 mm filters. The recovered sediment cores, which sampled down to 0.8 m below the lake bottom, contained a macroscopically structureless diamicton with shear strength between 2 and 6kPa. Our main operational recommendation for future subglacial access through water-filled boreholes is to supply enough heat to the top of the borehole to keep it from freezing. [ABSTRACT FROM AUTHOR]

The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project will test the overarching hypothesis that an active hydrological system exists beneath a West Antarctic ice stream that exerts a major control on ice dynamics, and the metabolic and phylogenetic diversity of the microbial community in subglacial water and sediment. WISSARD will explore Subglacial Lake Whillans (SLW, unofficial name) and its outflow toward the grounding line where it is thought to enter the Ross Ice Shelf seawater cavity. Introducing microbial contamination to the subglacial environment during drilling operations could compromise environmental stewardship and the science objectives of the project, consequently we developed a set of tools and procedures to directly address these issues. WISSARD hot water drilling efforts will include a custom water treatment system designed to remove micron and sub-micron sized particles (biotic and abiotic), irradiate the drilling water with germicidal ultraviolet (UV) radiation, and pasteurize the water to reduce the viability of persisting microbial contamination. Our clean access protocols also include methods to reduce microbial contamination on the surfaces of cables/hoses and down-borehole equipment using germicidal UV exposure and chemical disinfection. This paper presents experimental data showing that our protocols will meet expectations established by international agreement between participating Antarctic nations. [ABSTRACT FROM PUBLISHER]

Inhabitants of a cryoconite hole formed in the Canada Glacier in the McMurdo Dry Valley region of Antarctica have been isolated and identified by small subunit (16S/18S) rDNA amplification, cloning, and sequencing. The sequences obtained revealed the presence of members of eight bacterial lineages (Acidobacterium, Actinobacteria, Cyanobacteria, Cytophagales, Gemmimonas, Planctomycetes, Proteobacteria, and Verrucomicrobia) and metazoan (nematode, tardigrade, and rotifer), truffle (Choiromyces), ciliate (Spathidium), and green algal (Pleurastrium) Eukarya. Bacterial recovery was ~20-fold higher at 4 °C and 15 °C than at 22 °C, and obligately psychrophilic bacteria were identified and isolated. Several of the rDNA molecules amplified from isolates and directly from cryoconite DNA preparations had sequences similar to rDNA molecules of species present in adjacent lake ice and microbial mat environments. This cryoconite hole community was therefore most likely seeded by particulates from these local environments. Cryoconite holes may serve as biological refuges that, on glacial melting, can repopulate the local environments. [ABSTRACT FROM AUTHOR]

Lake Vostok, the largest subglacial lake in Antarctica, is separated from the surface by ≈ 4 km of glacial ice. It has been isolated from direct surface input for at least 420 000 years, and the possibility of a novel environment and ecosystem therefore exists. Lake Vostok water has not been sampled, but an ice core has been recovered that extends into the ice accreted below glacial ice by freezing of Lake Vostok water. Here, we report the recovery of bacterial isolates belonging to the Brachybacteria, Methylobacterium, Paenibacillus and Sphingomonas lineages from a sample of melt water from this accretion ice that originated 3593 m below the surface. We have also amplified small-subunit ribosomal RNA-encoding DNA molecules (16S rDNAs) directly from this melt water that originated from α- and β-proteobacteria, low- and high-G+C Gram-positive bacteria and a member of the Cytophaga/Flavobacterium/Bacteroides lineage. [ABSTRACT FROM AUTHOR]

Although subglacial aquatic environments are widespread beneath the Antarctic ice sheet, subglacial biogeochemistry is not well understood, and the contribution of subglacial water to coastal ocean carbon and nutrient cycling remains poorly constrained. The Whillans Subglacial Lake (SLW) ecosystem is upstream from West Antarctica's Gould‐Siple Coast ~800 m beneath the surface of the Whillans Ice Stream. SLW hosts an active microbial ecosystem and is part of an active hydrological system that drains into the marine cavity beneath the adjacent Ross Ice Shelf. Here we examine sources and sinks for organic matter in the lake and estimate the freshwater carbon and nutrient delivery from discharges into the coastal embayment. Fluorescence‐based characterization of dissolved organic matter revealed microbially driven differences between sediment pore waters and lake water, with an increasing contribution from relict humic‐like dissolved organic matter with sediment depth. Mass balance calculations indicated that the pool of dissolved organic carbon in the SLW water column could be produced in 4.8 to 11.9 yr, which is a time frame similar to that of the lakes' fill‐drain cycle. Based on these estimates, subglacial lake water discharged at the Siple Coast could supply an average of 5,400% more than the heterotrophic carbon demand within Siple Coast embayments (6.5% for the entire Ross Ice Shelf cavity). Our results suggest that subglacial discharge represents a heretofore unappreciated source of microbially processed dissolved organic carbon and other nutrients to the Southern Ocean. Plain Language Summary: Antarctica's thick ice sheets cover a continent rich with liquid water. These subglacial aquatic environments are home to microbial ecosystems that process organic matter and nutrients important for all life. At the same time, subglacial water in Antarctica actively flows between basins and from subglacial basins to the edge of the continent where it mixes with seawater in coastal areas covered by ice shelves. The waters under these ice shelves are cold, dark, and contain low concentrations of organic carbon and nutrients. We used data from Whillans Subglacial Lake, which lies 800 m beneath the ice of West Antarctica, to understand the sources, sinks, and accumulation of organic matter in Antarctic subglacial aquatic environments. We then combined data from the same lake with data on subglacial hydrology in the region to determine whether inputs of subglacial organic matter and nutrients could be important in supporting life in the dark waters beneath the adjacent ice shelf. We found that the input of fresh water from the Antarctic continent to the surrounding ocean can meet the microbial demand for organic carbon and nutrients under the ice shelf. This work has implications for our understanding of Antarctica's influence on biology in the Southern Ocean. Key Points: A mass balance shows that dissolved organic carbon accumulation in Whillans Subglacial Lake is under hydrological and biological controlDifferences between the character of the water column and sediment porewater dissolved organic matter imply biological processingSubglacial outflows have the potential to subsidize biological activity under the world's largest ice shelf [ABSTRACT FROM AUTHOR]

The east lobe of Lake Bonney, a permanently ice-covered lake in the McMurdo Dry Valleys, Antarctica, has a mid-depth maximum N2O concentration of 43.3 µmol N L-1 (>700,000% saturation with respect to air), representing one of the highest concentrations reported for a natural aquatic system. δ15N and δ18O measurements indicate that this is the most isotopically depleted N2O yet observed in a natural environment (minimum δ15N-N2O of -79.6% vs. air-N2; minimum δ18O-N2O of -4.7% vs. Vienna standard mean ocean water), providing new end points for these parameters in natural systems. The extremely depleted nitrogen and oxygen isotopes, together with nitrogen isotopic isomer data for N2O, imply that most of the N2O was produced via incomplete nitrification and has undergone virtually no subsequent consumption. However, molecular evidence provides little support for metabolically active nitrifying populations at depths where the maximal N2O concentrations occur and contemporary biogeochemical reactions cannot explain the extreme excesses of N2O in Lake Bonney. The gas appears to be a legacy of past biogeochemical conditions within the lake, an d in the absence of a significant sink and the presence of a highly stable water column, gradients in N2O produced by past microbial activity could persist in the cold saline waters of Lake Bonney for >104 years. [ABSTRACT FROM AUTHOR]

The psychrophilic bacterium Paenisporosarcina sp. TG-14 was isolated from sediment-laden stratified basal ice from Taylor Glacier, McMurdo Dry Valleys, Antarctica. Here we report the draft genome sequence of this strain, which may provide useful information on the cold adaptation mechanism in extremely variable environments. [ABSTRACT FROM AUTHOR]

We report the draft genome sequence of Paenisporosarcina sp. strain TG-20, which is 4.12 Mb in size and consists of 4,071 protein-coding genes and 76 RNA genes. The genome sequence of Paenisporosarcina sp. TG-20 may provide useful information about molecular adaptations that enhance survival in icy subsurface environments. [ABSTRACT FROM AUTHOR]