scholarly journals Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet

2021 ◽  
Author(s):  
Jon R. Hawkings ◽  
Benjamin S. Linhoff ◽  
Jemma L. Wadham ◽  
Marek Stibal ◽  
Carl H. Lamborg ◽  
...  
Keyword(s):  
Natural Waters ◽  
Inorganic Mercury ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Annual Runoff ◽  
Arctic Ecosystems ◽  
High Mercury ◽  
Southwestern Margin ◽  
High Concentrations ◽  
Dissolved Mercury

AbstractThe Greenland Ice Sheet is currently not accounted for in Arctic mercury budgets, despite large and increasing annual runoff to the ocean and the socio-economic concerns of high mercury levels in Arctic organisms. Here we present concentrations of mercury in meltwaters from three glacial catchments on the southwestern margin of the Greenland Ice Sheet and evaluate the export of mercury to downstream fjords based on samples collected during summer ablation seasons. We show that concentrations of dissolved mercury are among the highest recorded in natural waters and mercury yields from these glacial catchments (521–3,300 mmol km−2 year−1) are two orders of magnitude higher than from Arctic rivers (4–20 mmol km−2 year−1). Fluxes of dissolved mercury from the southwestern region of Greenland are estimated to be globally significant (15.4–212 kmol year−1), accounting for about 10% of the estimated global riverine flux, and include export of bioaccumulating methylmercury (0.31–1.97 kmol year−1). High dissolved mercury concentrations (~20 pM inorganic mercury and ~2 pM methylmercury) were found to persist across salinity gradients of fjords. Mean particulate mercury concentrations were among the highest recorded in the literature (~51,000 pM), and dissolved mercury concentrations in runoff exceed reported surface snow and ice values. These results suggest a geological source of mercury at the ice sheet bed. The high concentrations of mercury and its large export to the downstream fjords have important implications for Arctic ecosystems, highlighting an urgent need to better understand mercury dynamics in ice sheet runoff under global warming.

scholarly journals No evidence for large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet.

2022 ◽  
Author(s):  
Christian Jørgensen ◽  
Jens Søndergaard ◽  
Martin Larsen ◽  
Kristian Kjeldsen ◽  
Diogo Rosa ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Field Work ◽  
The Arctic ◽  
Mercury Chloride ◽  
Climate Conditions ◽  
Direct Measurements ◽  
Southwestern Margin ◽  
Dissolved Mercury ◽  
Control Study

In the current Matters Arising we present results from verifying control measurements of dissolved mercury (Hg) in glacial meltwater from the Greenland Ice Sheet (GrIS), which significantly challenges the conclusions of the recent publication by Hawkings et al. (2021). By direct measurements of meltwater in the same glacial catchment area, we demonstrate that the input Hg concentration for the regional upscaling in Hawkings et al (2021) is likely vastly over-estimated with major implications for the validity of the asserted extreme yield of Hg from the GrIS. In addition, we present a plausible explanation for the high Hg concentration values in the study, namely hitherto unidentified cross-contamination of water samples by mercury chloride (HgCl2), which was present and used for other purposes during field work. Together, the result of our control study potentially invalidates the suggested implications of geologically sourced Hg under the southwestern margin of the GrIS on the Arctic ecosystem in both current and future climate conditions.

scholarly journals GPS based surface displacements – a proxy for discharge and sediment transport from the Greenland Ice Sheet

2014 ◽  
Vol 8 (4) ◽  
pp. 3829-3850 ◽  
Author(s):  
B. Hasholt ◽  
S. A. Khan ◽  
A. B. Mikkelsen
Keyword(s):  
Sediment Transport ◽  
Global Positioning System ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Winter Precipitation ◽  
Annual Runoff ◽  
Surface Displacements ◽  
Global Positioning ◽  
Loss Of Mass ◽  
Gps Observations

Abstract. The elastic respond of the Earth's surface to mass changes has been measured with Global Positioning System (GPS). Mass loss as accumulated runoff and sediment transport from a 10 000 km2 segment of the Greenland Ice Sheet (GrIS) correlated very well (R2 = 0.83) with GPS measured uplift. Accumulated winter precipitation correlated fairly well with surface depression (R2 = 0.69). The relationships are based on seven years of runoff and sediment transport observations from the Watson River (2007–2013), winter precipitation from Kangerlussuaq Airport and GPS observations at Kellyville. GPS recordings of surface subsidence and uplift from 1996–2013 are used to calculate 18 years time series of annual runoff, sediment and solute transport and winter precipitation. Runoff and related transport of sediment and solutes increase over the period, while winter precipitation (land depression) tends to decrease. Based on the entire GPS record (1996–2013), it is shown that until 2005–2006 the mass balance of this segment of the GrIS was rather stable – since then there has been an increasing loss of mass, culminating in 2012.

scholarly journals Seasonal to decadal variability in ice discharge from the Greenland Ice Sheet

2018 ◽  
Author(s):  
Michalea D. King ◽  
Ian M. Howat ◽  
Seongsu Jeong ◽  
Myoung J. Noh ◽  
Bert Wouters ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Decadal Variability ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Annual Runoff ◽  
Meltwater Runoff ◽  
Front Position ◽  
Glacier Front ◽  
The Impact ◽  
Annual Discharge

Abstract. Rapid changes in thickness and velocity have been observed at many marine-terminating glaciers in Greenland, impacting the volume of ice they export, or discharge, from the ice sheet. While annual estimates of ice-sheet wide discharge have been previously derived, higher-resolution records are required to fully constrain the temporal response of these glaciers to various climatic and mechanical drivers that vary in sub-annual scales. Here we derive the first continuous, ice-sheet wide record of total ice sheet discharge for the 21st century, resolving a seasonal variability of 6 %. The amplitude of seasonality varies spatially across the ice sheet from 5 % in the southeastern region to 9 % in the northwest region. We analyze seasonal to annual variability in the discharge time series with respect to both modelled meltwater runoff, obtained from RACMO2.3p2, and glacier front position changes over the same period. We find that year-to-year changes in total ice sheet discharge are related to annual front changes (r2 = 0.59, p = 10−4) and that the annual magnitude of discharge is closely related to cumulative front position changes (r2 = 0.79), which show a net retreat of > 400 km, or an average retreat of > 2 km at each surveyed glacier. Neither maximum seasonal runoff or annual runoff totals are correlated to annual discharge, which suggests that larger annual quantities of runoff do not relate to increased annual discharge. Discharge and runoff, however, follow similar patterns of seasonal variability, with near-coincident periods of acceleration and seasonal maxima. These results suggest that changes in glacier front position drive secular trends in discharge, whereas the impact of runoff is likely limited to the summer months when observed seasonal variations are substantially controlled by the timing of meltwater input.

scholarly journals Brief Communication: Sudden drainage of a subglacial lake beneath the Greenland Ice Sheet

2015 ◽  
Vol 9 (1) ◽  
pp. 103-108 ◽  
Author(s):  
I. M. Howat ◽  
C. Porter ◽  
M. J. Noh ◽  
B. E. Smith ◽  
S. Jeong
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Subglacial Lake ◽  
Long Term Storage ◽  
Meltwater Runoff ◽  
Hydrologic System ◽  
Sudden Release ◽  
Southwestern Margin ◽  
Term Storage

Abstract. We report on the appearance of a 2 km wide, 70 m deep circular depression located 50 km inland of the southwestern margin of the Greenland Ice Sheet that provides the first direct evidence for concentrated, long-term storage, and sudden release, of meltwater at the bed. Drainage of the lake may have been triggered by the recent increase in meltwater runoff. The abundance of such lakes and their potential importance to the ice sheet's hydrologic system and flow regime remain unknown.

scholarly journals Basal ice microbiology at the margin of the Greenland ice sheet

2010 ◽  
Vol 51 (56) ◽  
pp. 71-79 ◽  
Author(s):  
Jacob C. Yde ◽  
Kai W. Finster ◽  
Rob Raiswell ◽  
Jørgen P. Steffensen ◽  
Jan Heinemeier ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Chemical Processes ◽  
Anoxic Sediment ◽  
Basal Ice ◽  
Complex Microbial Community ◽  
Fe Nanoparticles ◽  
High Concentrations ◽  
Subglacial Environments

AbstractBasal ice at the margin of the Greenland ice sheet was studied with respect to its physical characteristics and microbiological community. The basal ice contained high concentrations of dissolved ferrous Fe and must therefore be anoxic. Oxygen consumption experiments indicate that 50% of the oxidation was due to biological activity while the rest could be attributed to chemical processes, most likely weathering reactions with ferrous Fe. At least six different Fe-containing mineral sources were detected in basal ice together with potential bioavailable Fe nanoparticles. An active denitrifier population was identified due to formation of30N-dinitrogen gas after amendment of anoxic sediment slurries with15N-NO3−. Sulfate reduction could not be detected. The solid ice facies contained an abundant (∼108cells cm−3) and complex microbial community that harbored representatives of at least eight major phyla within the domain Bacteria. The clone library was dominated by members of theβ-subdivision of proteobacteria of which the largest proportion was affiliated to the genus Rhodoferax that comprises facultative aerobic iron reducers. The second most abundant phylum was Bacteroidetes. The solid ice facies had many physical similarities with the overlying debris-rich banded ice facies, indicating that they formed by similar subglacial processes and harbor similar microbial communities. This study extends our knowledge of life in subglacial environments such as beneath ice sheets. GenBank accession numbers: HM439882-HM439950; HQ144215-HQ144221.

scholarly journals Brief Communication: Sudden drainage of a subglacial lake beneath the Greenland Ice Sheet

2014 ◽  
Vol 8 (5) ◽  
pp. 5361-5374
Author(s):  
I. M. Howat ◽  
C. Porter ◽  
M. J. Noh ◽  
B. E. Smith ◽  
S. Jeong
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Subglacial Lake ◽  
Long Term Storage ◽  
Meltwater Runoff ◽  
Hydrologic System ◽  
Sudden Release ◽  
Southwestern Margin ◽  
Term Storage

Abstract. We report on the appearance of a 2 km wide, 70 m deep circular depression located 50 km inland of the southwestern margin of the Greenland Ice Sheet that provides the first direct evidence for concentrated, long-term storage, and sudden release, of meltwater at the bed. Drainage of the lake may have been triggered by the recent increase in meltwater runoff. The abundance of such lakes and their potential importance to the ice sheet's hydrologic system and flow regime remain unknown.

scholarly journals The past, present, and future viscous heat dissipation available for Greenland subglacial conduit formation

2017 ◽  
Vol 11 (1) ◽  
pp. 303-317 ◽  
Author(s):  
Kenneth D. Mankoff ◽  
Slawek M. Tulaczyk
Keyword(s):  
Heat Dissipation ◽  
Heat Budget ◽  
Water Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Fold Increase ◽  
Annual Runoff ◽  
Geothermal Heat ◽  
Viscous Heat ◽  
Ice Velocity

Abstract. Basal hydrology of the Greenland Ice Sheet (GIS) influences its dynamics and mass balance through basal lubrication and ice–bed decoupling or efficient water removal and ice–bed coupling. Variations in subglacial water pressure through the seasonal evolution of the subglacial hydrological system help control ice velocity. Near the ice sheet margin, large basal conduits are melted by the viscous heat dissipation (VHD) from surface runoff routed to the bed. These conduits may lead to efficient drainage systems that lower subglacial water pressure, increase basal effective stress, and reduce ice velocity. In this study we quantify the energy available for VHD historically at present and under future climate scenarios. At present, 345 km3 of annual runoff delivers 66 GW to the base of the ice sheet per year. These values are already ∼ 50 % more than the historical 1960–1999 value of 46 GW. By 2100 under IPCC AR5 RCP8.5 (RCP4.5) scenarios, 1278 (524) km3 of runoff may deliver 310 (110) GW to the ice sheet base. Hence, the ice sheet may experience a 5-to-7-fold increase in VHD in the near future which will enhance opening of subglacial conduits near the margin and will warm basal ice in the interior. The other significant basal heat source is geothermal heat flux (GHF), which has an estimated value of 36 GW within the present-day VHD area. With increasing surface meltwater penetration to the bed the basal heat budget in the active basal hydrology zone of the GIS will be increasingly dominated by VHD and relatively less sensitive to GHF, which may result in spatial changes in the ice flow field and in its seasonal variability.

scholarly journals Seasonal to decadal variability in ice discharge from the Greenland Ice Sheet

2018 ◽  
Vol 12 (12) ◽  
pp. 3813-3825 ◽  
Author(s):  
Michalea D. King ◽  
Ian M. Howat ◽  
Seongsu Jeong ◽  
Myoung J. Noh ◽  
Bert Wouters ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Decadal Variability ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Annual Runoff ◽  
Meltwater Runoff ◽  
Front Position ◽  
Glacier Front ◽  
The Impact ◽  
Annual Discharge

Abstract. Rapid changes in thickness and velocity have been observed at many marine-terminating glaciers in Greenland, impacting the volume of ice they export, or discharge, from the ice sheet. While annual estimates of ice-sheet-wide discharge have been previously derived, higher-resolution records are required to fully constrain the temporal response of these glaciers to various climatic and mechanical drivers that vary in sub-annual scales. Here we sample outlet glaciers wider than 1 km (N=230) to derive the first continuous, ice-sheet-wide record of total ice sheet discharge for the 2000–2016 period, resolving a seasonal variability of 6 %. The amplitude of seasonality varies spatially across the ice sheet from 5 % in the southeastern region to 9 % in the northwest region. We analyze seasonal to annual variability in the discharge time series with respect to both modeled meltwater runoff, obtained from RACMO2.3p2, and glacier front position changes over the same period. We find that year-to-year changes in total ice sheet discharge are related to annual front changes (r2=0.59, p=10-4) and that the annual magnitude of discharge is closely related to cumulative front position changes (r2=0.79), which show a net retreat of >400 km, or an average retreat of >2 km, at each surveyed glacier. Neither maximum seasonal runoff or annual runoff totals are correlated to annual discharge, which suggests that larger annual quantities of runoff do not relate to increased annual discharge. Discharge and runoff, however, follow similar patterns of seasonal variability with near-coincident periods of acceleration and seasonal maxima. These results suggest that changes in glacier front position drive secular trends in discharge, whereas the impact of runoff is likely limited to the summer months when observed seasonal variations are substantially controlled by the timing of meltwater input.

scholarly journals Author Correction: Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet

2021 ◽  
Author(s):  
Jon R. Hawkings ◽  
Benjamin S. Linhoff ◽  
Jemma L. Wadham ◽  
Marek Stibal ◽  
Carl H. Lamborg ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Southwestern Margin
Sign in / Sign up

Export Citation Format

Share Document