Hydrology and biogeochemistry of subglacial environment of Greenland ice sheet

2021 ◽  
Author(s):  
Ankit Pramanik ◽  
Nick Hayes ◽  
Frank Pattyn ◽  
Sandra Arndt
Keyword(s):  
Water Flow ◽  
Chemical Weathering ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Biogeochemical Model ◽  
Model Framework ◽  
Outlet Glacier ◽  
Detailed Understanding ◽  
Subglacial Environment ◽  
Subglacial Environments

<p>The Greenland ice sheet surface melt has increased substantially in intensity and spatial extent over the recent decades. The rapid migration of melt towards upstream areas of Greenland ice sheet is expected to incur major changes in hydrological behaviour of the ice sheet and outlet glaciers along with changes in export fluxes of carbon, methane, and other nutrient fluxes, which, in turn, will further affect the downstream ecosystem of rivers, fjords and oceans. Subglacial environments are emerging as ecological hotspots, urging detailed understanding of interaction between subglacial hydrology and biogeochemistry. However, due to their inaccessibility, the hydrology and geochemistry of subglacial environment thus far lacks a detailed understanding. As such this area is now the focus of many major projects in Greenland and Antarctica. </p><p> </p><p>Under the NuttI (<strong>Nut</strong>rient fac<strong>t</strong>ories under the <strong>I</strong>ce) project, we aim to develop a hydrological-biogeochemical model framework to investigate seasonal and inter-annual evolution of subglacial hydrology system and quantify carbon and nutrient export from subglacial environments to proglacial rivers. We use the subglacial hydrology model GlaDS (Glacier Drainage System model) to simulate seasonal and interannual evolution of distributed and channelized subglacial water flow while calculating subglacial water storage, residence time, water flux and effective pressure. A subglacial erosion scheme is coupled to the model to calculate physical weathering occurring especially in early melt and peak melt season due to glacier sliding and higher water flow, respectively. All these parameters are used in a geochemical model to quantify subglacial chemical weathering fluxes. The meltwater becomes chemically enriched subglacially and reaches the glacier outlet through subglacial channels. We also intend to further develop the model to investigate processes such as subglacial cycling of silica and production of methane.</p><p> </p><p>We primarily use the coupled model to simulate Leverett glacier, a land-terminating outlet glacier in southwest Greenland which has been well studied with different geophysical measurements and long-term monitoring. The model output is validated with the in-situ measurement of discharge and export fluxes in the proglacial river of the land-terminating glacier. </p>

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.

Early Holocene ocean conditions off the Zachariæ Isstrøm, Northeast Greenland

2021 ◽  
Author(s):  
Joanna Davies ◽  
Anders Møller Mathiasen ◽  
Kristiane Kristensen ◽  
Christof Pearce ◽  
Marit-Solveig Seidenkrantz
Keyword(s):  
Climate Change ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Atlantic Water ◽  
The Arctic ◽  
Future Climate Change ◽  
Polar Regions ◽  
Ice Shelf ◽  
Outlet Glacier ◽  
The Impact

<p>The polar regions exhibit some of the most visible signs of climate change globally; annual mass loss from the Greenland Ice Sheet (GrIS) has quadrupled in recent decades, from 51 ± 65 Gt yr<sup>−1</sup> (1992-2001) to 211 ± 37 Gt yr<sup>−1</sup> (2002-2011). This can partly be attributed to the widespread retreat and speed-up of marine-terminating glaciers. The Zachariae Isstrøm (ZI) is an outlet glacier of the Northeast Greenland Ice Steam (NEGIS), one of the largest ice streams of the GrIS (700km), draining approximately 12% of the ice sheet interior. Observations show that the ZI began accelerating in 2000, resulting in the collapse of the floating ice shelf between 2002 and 2003. By 2014, the ice shelf extended over an area of 52km<sup>2</sup>, a 95% decrease in area since 2002, where it extended over 1040km<sup>2</sup>. Paleo-reconstructions provide an opportunity to extend observational records in order to understand the oceanic and climatic processes governing the position of the grounding zone of marine terminating glaciers and the extent of floating ice shelves. Such datasets are thus necessary if we are to constrain the impact of future climate change projections on the Arctic cryosphere.</p><p>A multi-proxy approach, involving grain size, geochemical, foraminiferal and sedimentary analysis was applied to marine sediment core DA17-NG-ST8-92G, collected offshore of the ZI, on  the Northeast Greenland Shelf. The aim was to reconstruct changes in the extent of the ZI and the palaeoceanographic conditions throughout the Early to Mid Holocene (c.a. 12,500-5,000 cal. yrs. BP). Evidence from the analysis of these datasets indicates that whilst there has been no grounded ice at the site over the last 12,500 years, the ice shelf of the ZI extended as a floating ice shelf over the site between 12,500 and 9,200 cal. yrs. BP, with the grounding line further inland from our study site. This was followed by a retreat in the ice shelf extent during the Holocene Thermal Maximum; this was likely to have been governed, in part, by basal melting driven by Atlantic Water (AW) recirculated from Svalbard or from the Arctic Ocean. Evidence from benthic foraminifera suggest that there was a shift from the dominance of AW to Polar Water at around 7,500 cal. yrs. BP, although the ice shelf did not expand again despite of this cooling of subsurface waters.</p>

scholarly journals Seasonal mass variations show timing and magnitude of meltwater storage in the Greenland Ice Sheet

2018 ◽  
Vol 12 (9) ◽  
pp. 2981-2999 ◽  
Author(s):  
Jiangjun Ran ◽  
Miren Vizcaino ◽  
Pavel Ditmar ◽  
Michiel R. van den Broeke ◽  
Twila Moon ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
High Accumulation ◽  
Outlet Glacier ◽  
Surface Mass ◽  
Meltwater Runoff

Abstract. The Greenland Ice Sheet (GrIS) is currently losing ice mass. In order to accurately predict future sea level rise, the mechanisms driving the observed mass loss must be better understood. Here, we combine data from the satellite gravimetry mission Gravity Recovery and Climate Experiment (GRACE), surface mass balance (SMB) output of the Regional Atmospheric Climate Model v. 2 (RACMO2), and ice discharge estimates to analyze the mass budget of Greenland at various temporal and spatial scales. We find that the mean rate of mass variations in Greenland observed by GRACE was between −277 and −269 Gt yr−1 in 2003–2012. This estimate is consistent with the sum (i.e., -304±126 Gt yr−1) of individual contributions – surface mass balance (SMB, 216±122 Gt yr−1) and ice discharge (520±31 Gt yr−1) – and with previous studies. We further identify a seasonal mass anomaly throughout the GRACE record that peaks in July at 80–120 Gt and which we interpret to be due to a combination of englacial and subglacial water storage generated by summer surface melting. The robustness of this estimate is demonstrated by using both different GRACE-based solutions and different meltwater runoff estimates (namely, RACMO2.3, SNOWPACK, and MAR3.9). Meltwater storage in the ice sheet occurs primarily due to storage in the high-accumulation regions of the southeast and northwest parts of Greenland. Analysis of seasonal variations in outlet glacier discharge shows that the contribution of ice discharge to the observed signal is minor (at the level of only a few gigatonnes) and does not explain the seasonal differences between the total mass and SMB signals. With the improved quantification of meltwater storage at the seasonal scale, we highlight its importance for understanding glacio-hydrological processes and their contributions to the ice sheet mass variability.

scholarly journals Sensitivity of Greenland Ice Sheet Projections to Model Formulations

2013 ◽  
Vol 59 (216) ◽  
pp. 733-749 ◽  
Author(s):  
H. Goelzer ◽  
P. Huybrechts ◽  
J.J. Fürst ◽  
F.M. Nick ◽  
M.L. Andersen ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Sea Level ◽  
Flow Model ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Glacier Dynamics

AbstractPhysically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6–18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14–31 % higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

scholarly journals Ice sheet mass loss caused by dust and black carbon accumulation

2015 ◽  
Vol 9 (2) ◽  
pp. 2563-2596
Author(s):  
T. Goelles ◽  
C. E. Bøggild ◽  
R. Greve
Keyword(s):  
Mass Loss ◽  
Black Carbon ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Carbon Accumulation ◽  
Model Framework ◽  
Ice Dynamics ◽  
Ablation Area ◽  
Ice Surface ◽  
Surface Melt

Abstract. Albedo is the dominating factor governing surface melt variability in the ablation area of ice sheets and glaciers. Aerosols such as mineral dust and black carbon (soot) accumulate on the ice surface and cause a darker surface and therefore a lower albedo. The dominant source of these aerosols in the ablation area is melt-out of englacial material which has been transported via ice flow. The darkening effect on the ice surface is currently not included in sea level projections, and the effect is unknown. We present a model framework which includes ice dynamics, aerosol transport, aerosol accumulation and the darkening effect on ice albedo and its consequences for surface melt. The model is applied to a simplified geometry resembling the conditions of the Greenland ice sheet, and it is forced by several temperature scenarios to quantify the darkening effect of aerosols on future mass loss. The effect of aerosols depends non-linearly on the temperature rise due to the feedback between aerosol accumulation and surface melt. The effect of aerosols in the year 3000 is up to 12% of additional ice sheet volume loss in the warmest scenario.

scholarly journals Quantifying supraglacial meltwater pathways in the Paakitsoq region, West Greenland

2017 ◽  
Vol 63 (239) ◽  
pp. 464-476 ◽  
Author(s):  
CONRAD KOZIOL ◽  
NEIL ARNOLD ◽  
ALLEN POPE ◽  
WILLIAM COLGAN
Keyword(s):  
Spatial Patterns ◽  
Surface Runoff ◽  
Significant Proportion ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Average Intensity ◽  
West Greenland ◽  
Surface Drainage ◽  
Subglacial Environment ◽  
Hydrology Model

ABSTRACTIncreased summer ice velocities on the Greenland ice sheet are driven by meltwater input to the subglacial environment. However, spatial patterns of surface input and partitioning of meltwater between different pathways to the base remain poorly understood. To further our understanding of surface drainage, we apply a supraglacial hydrology model to the Paakitsoq region, West Greenland for three contrasting melt seasons. During an average melt season, crevasses drain ~47% of surface runoff, lake hydrofracture drains ~3% during the hydrofracturing events themselves, while the subsequent surface-to-bed connections drain ~21% and moulins outside of lake basins drain ~15%. Lake hydrofracture forms the primary drainage pathway at higher elevations (above ~850 m) while crevasses drain a significant proportion of meltwater at lower elevations. During the two higher intensity melt seasons, model results show an increase (~5 and ~6% of total surface runoff) in the proportion of runoff drained above ~1300 m relative to the melt season of average intensity. The potential for interannual changes in meltwater partitioning could have implications for how the dynamics of the ice sheet respond to ongoing changes in meltwater production.

scholarly journals Recent changes on Greenland outlet glaciers

2009 ◽  
Vol 55 (189) ◽  
pp. 147-162 ◽  
Author(s):  
R. Thomas ◽  
E. Frederick ◽  
W. Krabill ◽  
S. Manizade ◽  
C. Martin
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Dynamic Changes ◽  
Laser Altimeter ◽  
Outlet Glacier ◽  
Thickness Change ◽  
Grounding Line ◽  
Break Up ◽  
Glacier Velocity

AbstractAircraft laser-altimeter surveys during the 1990s showed near-coastal parts of the Greenland ice sheet to be thinning; despite slow thickening at higher elevations, the ice sheet lost mass to the ocean. Many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers, indicating dynamic imbalance between glacier velocity and upstream snow accumulation. Results from more recent surveys, presented here, show that thinning rates have increased in most coastal regions. For almost half of the surveys, these increases might have resulted from increases in summer melting, but rapid thinning on others is indicative of dynamic changes that increased with time. In particular, thinning rates on the three fastest glaciers increased to tens of m a−1 after 2000, and other observations show an approximate doubling in their velocities. The deep beds of these glaciers appear to have a strong influence on rates of grounding-line retreat and thickness change, with periods of glacier acceleration and rapid thinning initiated by flotation and break-up of lightly grounded glacier snouts or break-up of floating ice tongues. Near-simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause. Nearby glaciers without deep beds are thinning far more slowly, suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on Greenland outlet-glacier acceleration

scholarly journals Remote sounding of Greenland supraglacial melt lakes: implications for subglacial hydraulics

2007 ◽  
Vol 53 (181) ◽  
pp. 257-265 ◽  
Author(s):  
Jason E. Box ◽  
Kathleen Ski
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lake Depth ◽  
Cross Sectional ◽  
Overburden Pressure ◽  
Ice Dynamics ◽  
Subglacial Environment ◽  
Lake Volume ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Lake Drainage

AbstractA supraglacial lake-depth retrieval function is developed, based on the correspondence between moderate-resolution imaging spectroradiometer (MODIS) reflectance and water depth measured during raft surveys. Individual lake depth, area and volume statistics, including short-term temporal changes for Greenland’s southwestern ablation region, were compiled for 2000–05. The maximum area of an individual lake was found to be 8.9 km2, the maximum volume 53.0 × 106 m3 and the maximum depth 12.2 m, sampling over 0.0625 km2 pixel areas. The total lake volume reaches >1 km3 in this region by July each year. The importance of melt lake reservoirs to Greenland ice-sheet flow may be a feedback between abrupt lake drainage events and ice dynamics. Lake-outburst volumes up to 31.5 × 106 m3 d−1 are capable of providing sufficient water via moulins to hydraulically pressurize the subglacial environment. Since the overburden pressure at the base of a flooded moulin is greater than that provided by ice, lake-outburst events seem capable of exerting sufficient upward force to lift the ice sheet locally, if water flow in the subglacial environment is constrained laterally. Considering a moulin with a 10 m2 cross-sectional area, basal pressurization can be maintained over lake-outburst episodes lasting hours to days.

scholarly journals Quantitative estimates of velocity sensitivity to surface melt variations at a large Greenland outlet glacier

2011 ◽  
Vol 57 (204) ◽  
pp. 609-620 ◽  
Author(s):  
M.L. Andersen ◽  
M. Nettles ◽  
P. Elosegui ◽  
T.B. Larsen ◽  
G.S. Hamilton ◽  
...  
Keyword(s):  
Fluid Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Absolute Magnitude ◽  
Flow Speed ◽  
Relative Importance ◽  
Outlet Glacier ◽  
Quantitative Estimates ◽  
Surface Melt ◽  
Glacier Flow

AbstractThe flow speed of Greenland outlet glaciers is governed by several factors, the relative importance of which is poorly understood. The delivery of surface-generated meltwater to the bed of alpine glaciers has been shown to influence glacier flow speed when the volume of water is sufficient to increase basal fluid pressure and hence basal lubrication. While this effect has also been demonstrated on the Greenland ice-sheet margin, little is known about the influence of surface melting on the large, marine-terminating outlet glaciers that drain the ice sheet. We use a validated model of meltwater input and GPS-derived surface velocities to quantify the sensitivity of glacier flow speed to changes in surface melt at Helheim Glacier during two summer seasons (2007–08). Our observations span ∼55 days near the middle of each melt season. We find that relative changes in glacier speed due to meltwater input are small, with variations of ∼45% in melt producing changes in velocity of ∼2–4%. These velocity variations are, however, of similar absolute magnitude to those observed at smaller glaciers and on the ice-sheet margin. We find that the glacier’s sensitivity to variations in meltwater input decreases approximately exponentially with distance from the calving front. Sensitivity to melt varies with time, but generally increases as the melt season progresses. We interpret the time-varying sensitivity of glacier flow to meltwater input as resulting from changes in subglacial hydraulic routing caused by the changing volume of meltwater input.

scholarly journals Ice flow around large obstacles as indicated by basal ice exposed at the margin of the Greenland ice sheet

1994 ◽  
Vol 40 (135) ◽  
pp. 359-367 ◽  
Author(s):  
Peter G. Knight ◽  
David E. Sugden ◽  
Christopher D. Minty
Keyword(s):  
Empirical Model ◽  
Basal Layer ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Flow ◽  
Subglacial Environment ◽  
Basal Ice ◽  
Convergence And Divergence ◽  
Basal Melting ◽  
Marginal Environment

AbstractSpatial variations in the debris-bearing basal ice layer exposed at the ice-sheet margin in West Greenland reflect the geography of basal melting and ice flow around large obstacles close to the margin. This paper demonstrates the character of the basal ice layer, which comprises fine material incorporated in an interior, subglacial environment and coarser material entrained in an ice-marginal environment. We develop an empirical model of ice flow close to a lobate margin of the ice sheet in which ice convergence and divergence, and limited subglacial melting affect the character and distribution of the basal ice at the margin. There is a tendency for the convergence and divergence to thicken the basal layer in lobate areas and to thin it in inter-lobate areas. Under certain circumstances, basal melting may remove much of the layer from beneath the snouts of larger lobes, thus causing the basal layer to be thickest in an intermediate location.

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