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 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 Discharge of debris from ice at the margin of the Greenland ice sheet

2002 ◽  
Vol 48 (161) ◽  
pp. 192-198 ◽  
Author(s):  
Peter G. Knight ◽  
Richard I. Waller ◽  
Carrie J. Patterson ◽  
Alison P. Jones ◽  
Zoe P. Robinson
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Rate ◽  
Outlet Glacier ◽  
Tidewater Glaciers ◽  
Sediment Production ◽  
Basal Ice ◽  
Order Of Magnitude ◽  
Sediment Transfer ◽  
A Minor

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

Four decades of radar-echo sounding: The past, present, and future of radar applications for understanding subglacial environments 

2021 ◽  
Author(s):  
Winnie Chu
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Thermal Conditions ◽  
Machine Learning Algorithms ◽  
Polar Ice Sheets ◽  
Radar Echo ◽  
Radar Applications ◽  
Bed Roughness ◽  
Subglacial Environments ◽  
Echo Sounding

<p>Airborne radar sounding observations have been instrumental in understanding subglacial environments and basal processes of ice sheets. Since the advent of analog radar-echo sounding (RES) system in the early 1970s, there have been tremendous innovations in both RES hardware and signal processing techniques. These technological advancements have provided high-resolution ice thickness measurements, improved detection and characterization of subglacial hydrology, as well as improved understanding of basal thermal conditions, bed roughness and geomorphology, and other processes that govern the basal boundary of the polar ice sheets. In this talk, I will provide an overview of the recent developments in radar processing approaches and system designs and highlight some of the new understanding of ice sheet subglacial processes that emerge from these breakthroughs. I will end by discussing areas where future radar applications and discoveries may be possible, including the utilization of machine learning algorithms, space-borne radar missions, and ground-based passive radar platforms to provide long-term monitoring of ice sheet subglacial environments.</p>

scholarly journals Last Interglacial climate and sea-level evolution from a coupled ice sheet–climate model

2016 ◽  
Vol 12 (12) ◽  
pp. 2195-2213 ◽  
Author(s):  
Heiko Goelzer ◽  
Philippe Huybrechts ◽  
Marie-France Loutre ◽  
Thierry Fichefet
Keyword(s):  
Surface Temperature ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Last Interglacial ◽  
A Minor ◽  
The Antarctic ◽  
The Impact ◽  
And Sea Level

Abstract. As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG,  ∼  130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate–ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet–climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

scholarly journals The Mathematical Model of Ice Sheets and the Calculation of the Evolution of the Greenland Ice Sheet

1985 ◽  
Vol 31 (109) ◽  
pp. 281-292 ◽  
Author(s):  
S.S Grigoryan ◽  
S.A Buyanov ◽  
M.S Krass ◽  
P.A Shumskiy
Keyword(s):  
Mathematical Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Numerical Data ◽  
Climatic Conditions ◽  
The Mathematical Model

AbstractAn evolutionary mathematical model of ice sheets is presented. The model takes into account the basic climatic and geophysical parameters, with temperature parameterization. Some numerical data derived from experiments on the Greenland ice sheet are received. At present the Greenland ice sheet is found to be in a state essentially different from a stationary one corresponding to modern climatic conditions.

scholarly journals The Theory of Thermal Convection in Polar Ice Sheets

1976 ◽  
Vol 16 (74) ◽  
pp. 41-71 ◽  
Author(s):  
T.J. Hughes
Keyword(s):  
Thermal Convection ◽  
Critical Rayleigh Number ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Transient Creep ◽  
Steady State Creep ◽  
Polar Ice ◽  
Ice Streams ◽  
Basal Ice ◽  
Polar Ice Sheets

Abstract Application of thermal convection theory to polar ice sheets (Hughes, 1970, 1971. 1972[a],[c]) is reviewed and expanded. If it occurs, thermal convection is mainly concentrated near the bed of the ice sheet; resulting in active and passive convective flow, respectively below and above the ice density inversion. Convection begins as transient creep when a stress-independent critical Rayleigh number is exceeded, and stabilizes as steady-state creep when a stress-dependent critical Rayleigh number is exceeded. Transient- creep convection begins as unstable ripples in isotherms near the bed, with some ripples becoming upward bulges of basal ice which rapidly shrink laterally and grow vertically to become ascending dikes of recrystallized basal ice during steady-state creep. Sills of basal ice are injected horizontally between weakly coupled layers in the strata of cold ice slowly sinking en masse between dikes. Convection begins under domes of thick ice toward the ice-sheet center and a stable polygonal array of dikes may form if frictional heat creates hot ice at the bed as rapidly as convection flow redistributes hot basal ice in dikes and sills, Advective flow transports the converting ice toward the margin of the ice sheet where dikes converge at the heads of ice streams. Dike—sill convection then becomes ice-stream convection in which the entire ice stream behaves like a dike, uncoupling from the bed, and rising en masse. This would help explain why ice streams flow at surge velocities.

scholarly journals Using results from the PlioMIP ensemble to investigate the Greenland Ice Sheet during the mid-Pliocene Warm Period

2015 ◽  
Vol 11 (3) ◽  
pp. 403-424 ◽  
Author(s):  
A. M. Dolan ◽  
S. J. Hunter ◽  
D. J. Hill ◽  
A. M. Haywood ◽  
S. J. Koenig ◽  
...  
Keyword(s):  
Sea Level ◽  
Atmospheric Carbon Dioxide ◽  
Climate Models ◽  
Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Warm Period ◽  
Global Mean Temperature ◽  
Model Dependency

Abstract. During an interval of the Late Pliocene, referred to here as the mid-Pliocene Warm Period (mPWP; 3.264 to 3.025 million years ago), global mean temperature was similar to that predicted for the end of this century, and atmospheric carbon dioxide concentrations were higher than pre-industrial levels. Sea level was also higher than today, implying a significant reduction in the extent of the ice sheets. Thus, the mPWP provides a natural laboratory in which to investigate the long-term response of the Earth's ice sheets and sea level in a warmer-than-present-day world. At present, our understanding of the Greenland ice sheet during the mPWP is generally based upon predictions using single climate and ice sheet models. Therefore, it is essential that the model dependency of these results is assessed. The Pliocene Model Intercomparison Project (PlioMIP) has brought together nine international modelling groups to simulate the warm climate of the Pliocene. Here we use the climatological fields derived from the results of the 15 PlioMIP climate models to force an offline ice sheet model. We show that mPWP ice sheet reconstructions are highly dependent upon the forcing climatology used, with Greenland reconstructions ranging from an ice-free state to a near-modern ice sheet. An analysis of the surface albedo variability between the climate models over Greenland offers insights into the drivers of inter-model differences. As we demonstrate that the climate model dependency of our results is high, we highlight the necessity of data-based constraints of ice extent in developing our understanding of the mPWP Greenland ice sheet.

Trends and projections in ice sheet mass balance

2020 ◽  
Author(s):  
Andrew Shepherd ◽  
Keyword(s):  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Sea Levels ◽  
Global Sea Level

<p>In recent decades, the Antarctic and Greenland Ice Sheets have been major contributors to global sea-level rise and are expected to be so in the future. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite records of changes in polar ice sheet volume, flow and gravitational potential to produce a reconciled estimate of their mass balance. <strong>Since the early 1990’s, ice losses from Antarctica and Greenland have caused global sea-levels to rise by 18.4 millimetres, on average, and there has been a sixfold increase in the volume of ice loss over time. Of this total, 41 % (7.6 millimetres) originates from Antarctica and 59 % (10.8 millimetres) is from Greenland. In this presentation, we compare our reconciled estimates of Antarctic and Greenland ice sheet mass change to IPCC projection of sea level rise to assess the model skill in predicting changes in ice dynamics and surface mass balance.  </strong>Cumulative ice losses from both ice sheets have been close to the IPCC’s predicted rates for their high-end climate warming scenario, which forecast an additional 170 millimetres of global sea-level rise by 2100 when compared to their central estimate.</p>

scholarly journals Laboratory studies of the flow rates of debris-laden ice

2003 ◽  
Vol 37 ◽  
pp. 108-112 ◽  
Author(s):  
Tim H. Jacka ◽  
Shavawn Donoghue ◽  
Jun Li ◽  
William F. Budd ◽  
Ross M. Anderson
Keyword(s):  
Laboratory Tests ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Laboratory Studies ◽  
Polar Ice ◽  
Flow Rates ◽  
Basal Ice ◽  
Ice Flows ◽  
Polar Ice Sheets ◽  
Deformation Tests

AbstractIce-sheet basal ice is warmer than that above because of the heat from the Earth’s interior. The stresses acting on the basal ice are greatest. In addition, the basal ice often contains debris consisting of silt and small stones picked up from the rock over which the ice flows. Because the base is the warmest part of an ice sheet and the stress there is greatest, flow rates in the basal ice are large and often contribute most of the ice movement. It is therefore important, for accurate modelling of the ice sheets, to know whether the debris within the basal ice enhances or retards the flow of the ice. In this paper, we describe laboratory deformation tests in uniaxial compression and in simple shear, on sand-laden ice. We find no significant dependence of flow rate on sand content (up to 15% volume) in the stress range 0.13–0.5 MPa and temperature range –0.02 to –18.0°C. Further work needs to include laboratory tests on debris-laden ice extracted from the polar ice sheets. This work is underway.

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