scholarly journals Dissolved organic nutrients dominate melting surface ice of the Dark Zone (Greenland Ice Sheet)

2019 ◽  
Vol 16 (16) ◽  
pp. 3283-3296 ◽  
Author(s):  
Alexandra T. Holland ◽  
Christopher J. Williamson ◽  
Fotis Sgouridis ◽  
Andrew J. Tedstone ◽  
Jenine McCutcheon ◽  
...  
Keyword(s):  
Organic Phase ◽  
Stream Water ◽  
Inorganic Nitrogen ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Western Coast ◽  
Ice Surface ◽  
Cryoconite Hole ◽  
Melting Surface ◽  
Surface Ice

Abstract. Glaciers and ice sheets host abundant and dynamic communities of microorganisms on the ice surface (supraglacial environments). Recently, it has been shown that Streptophyte glacier algae blooming on the surface ice of the south-western coast of the Greenland Ice Sheet are a significant contributor to the 15-year marked decrease in albedo. Currently, little is known about the constraints, such as nutrient availability, on this large-scale algal bloom. In this study, we investigate the relative abundances of dissolved inorganic and dissolved organic macronutrients (N and P) in these darkening surface ice environments. Three distinct ice surfaces, with low, medium and high visible impurity loadings, supraglacial stream water and cryoconite hole water, were sampled. Our results show a clear dominance of the organic phase in all ice surface samples containing low, medium and high visible impurity loadings, with 93 % of the total dissolved nitrogen and 67 % of the total dissolved phosphorus in the organic phase. Mean concentrations in low, medium and high visible impurity surface ice environments are 0.91, 0.62 and 1.0 µM for dissolved inorganic nitrogen (DIN), 5.1, 11 and 14 µM for dissolved organic nitrogen (DON), 0.03, 0.07 and 0.05 µM for dissolved inorganic phosphorus (DIP) and 0.10, 0.15 and 0.12 µM for dissolved organic phosphorus (DOP), respectively. DON concentrations in all three surface ice samples are significantly higher than DON concentrations in supraglacial streams and cryoconite hole water (0 and 0.7 µM, respectively). DOP concentrations are higher in all three surface ice samples compared to supraglacial streams and cryoconite hole water (0.07 µM for both). Dissolved organic carbon (DOC) concentrations increase with the amount of visible impurities present (low: 83 µM, medium: 173 µM and high: 242 µM) and are elevated compared to supraglacial streams and cryoconite hole water (30 and 50 µM, respectively). We speculate that the architecture of the weathering crust, which impacts on water flow paths and storage in the melting surface ice and/or the production of extracellular polymeric substances (EPS), containing both N and P in conjunction with C, is responsible for the temporary retention of DON and DOP in the melting surface ice. The unusual presence of measurable DIP and DIN, principally as NH4+, in the melting surface ice environments suggests that factors other than macronutrient limitation are controlling the extent and magnitude of the glacier algae.

scholarly journals Seasonal changes of ice surface characteristics and productivity in the ablation zone of the Greenland Ice Sheet

2015 ◽  
Vol 9 (2) ◽  
pp. 487-504 ◽  
Author(s):  
D. M. Chandler ◽  
J. D. Alcock ◽  
J. L. Wadham ◽  
S. L. Mackie ◽  
J. Telling
Keyword(s):  
Remote Sensing ◽  
Surface Albedo ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Characteristics ◽  
Biological Processes ◽  
Ablation Zone ◽  
Ice Surface ◽  
Surface Productivity ◽  
Cryoconite Hole

Abstract. Field and remote sensing observations in the ablation zone of the Greenland Ice Sheet have revealed a diverse range of ice surface characteristics, primarily reflecting the variable distribution of fine debris (cryoconite). This debris reduces the surface albedo and is therefore an important control on melt rates and ice sheet mass balance. Meanwhile, studies of ice sheet surface biological processes have found active microbial communities associated with the cryoconite debris, which may themselves modify the cryoconite distribution. Due to the considerable difficulties involved with collecting ground-based observations of the ice surface, our knowledge of the physical and biological surface processes, and their links, remains very limited. Here we present data collected at a field camp established in the ice sheet ablation zone at 67° N, occupied for almost the entire melt season (26 May–10 August 2012), with the aim of gaining a much more detailed understanding of the physical and biological processes occurring on the ice surface. These data sets include quadrat surveys of surface type, measurements of ice surface ablation, and in situ biological oxygen demand incubations to quantify microbial activity. In addition, albedo at the site was retrieved from AVHRR (Advanced Very High Resolution Radiometer) remote sensing data. Observations of the areal coverage of different surface types revealed a rapid change from complete snow cover to the "summer" (summer study period) ice surface of patchy debris ("dirty ice") and cryoconite holes. There was significant correlation between surface albedo, cryoconite hole coverage and surface productivity during the melt season, but microbial activity in "dirty ice" was not correlated with albedo and varied widely throughout the season. While this link suggests the potential for a remote-sensing approach to monitoring cryoconite hole biological processes, very wide seasonal and spatial variability in net surface productivity demonstrates the need for caution when extrapolating point measurements of biological processes to larger temporal or spatial scales.

scholarly journals Nutrient cycling in supraglacial environments of the Dark Zone of the Greenland Ice Sheet

2019 ◽  
Author(s):  
Alexandra T. Holland ◽  
Christopher J. Williamson ◽  
Fotis Sgouridis ◽  
Andrew J. Tedstone ◽  
Jenine McCutcheon ◽  
...  
Keyword(s):  
Nutrient Cycling ◽  
Organic Phase ◽  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Nutrient Ratios ◽  
Ice Algae ◽  
Data Set ◽  
Dissolved Phosphorus ◽  
Surface Ice

Abstract. Glaciers and ice sheets host abundant and dynamic communities of microorganisms on the ice surface (supraglacial environments). Recently, it has been shown that Streptophyte ice algae blooming on the surface ice of the south-west coast of the Greenland Ice Sheet are a significant contributor to the 15-year marked decrease in albedo. Currently little is known about the constraints, such as the nutrient cycling, on this large-scale algal bloom. In this study, we present a preliminary data set that investigates the conversion of dissolved inorganic nutrients to the dissolved organic phase occurring in these darkening surface ice environments. Our results show a clear dominance of the organic phase, with 93 % of the total dissolved nitrogen and 67 % of the total dissolved phosphorus in the organic phase. Correlations between algal abundance and dissolved organic carbon and nitrogen, indicate ice algae are driving the dissolved nutrient phase shift occurring in these supraglacial environments. Dissolved organic nutrient ratios in these supraglacial environments are notably higher than the Redfield Ratio (DON : DOP = 49, 78, 116) and DOC : DOP = 797, 1166, 2013), suggesting these environments may be phosphorus limited.

scholarly journals Seasonal changes of ice surface characteristics and productivity in the ablation zone of the Greenland Ice Sheet

2014 ◽  
Vol 8 (1) ◽  
pp. 1337-1382 ◽  
Author(s):  
D. M. Chandler ◽  
J. D. Alcock ◽  
J. L. Wadham ◽  
S. L. Mackie ◽  
J. Telling
Keyword(s):  
Remote Sensing ◽  
Microbial Activity ◽  
Surface Albedo ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Characteristics ◽  
Biological Processes ◽  
Ablation Zone ◽  
Ice Surface ◽  
Cryoconite Hole

Abstract. Field and remote sensing observations in the ablation zone of the Greenland Ice Sheet have revealed a diverse range of ice surface characteristics, primarily reflecting the variable distribution of fine debris (cryoconite). This debris reduces the surface albedo and is therefore an important control on melt rates and ice sheet mass balance. Meanwhile, studies of ice sheet surface biological processes have found active microbial communities associated with the cryoconite debris, which may themselves modify the cryoconite distribution. Due to the considerable difficulties involved with collecting ground-based observations of the ice surface, our knowledge of the physical and biological surface processes, and their links, remains very limited. Here we present data collected at a field camp established in the ice sheet ablation zone at 67° N, occupied for almost the entire melt season (26 May–10 August 2012), with the aim of gaining a much more detailed understanding of the physical and biological processes occurring on the ice surface. These data sets include quadrat surveys of surface type, measurements of ice surface ablation, and in-situ biological oxygen demand incubations to quantify microbial activity. In addition, albedo at the site was retrieved from AVHRR remote sensing data. Observations of the areal coverage of different surface types revealed a rapid change from complete snow cover to the "summer" ice surface of patchy debris ("dirty ice") and cryoconite holes. There was significant correlation between surface albedo, cryoconite hole coverage and cryoconite hole productivity during the main melt season, but microbial activity in "dirty ice" was not correlated with albedo and varied widely throughout the season. While this link suggests the potential for a remote-sensing approach to monitoring cryoconite hole biological processes, very wide seasonal and spatial variability in net surface productivity demonstrates the need for caution when extrapolating point measurements of biological processes to larger temporal or spatial scales.

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 Combined diurnal variations of discharge and hydrochemistry of the Isunnguata Sermia outlet of the Greenland Ice Sheet give in sight on sub glacial conditions

2016 ◽  
Author(s):  
Joseph Graly ◽  
Joel Harrington ◽  
Neil Humphrey
Keyword(s):  
Diurnal Cycle ◽  
Stream Water ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Solute Concentration ◽  
High Flow ◽  
Rock Material ◽  
Diurnal Changes ◽  
Stream Discharge ◽  
Pressure Threshold

Abstract. In order to examine daily cycles in meltwater routing and storage in the Isunnuguata Sermia outlet of the Greenland Ice Sheet, variation in outlet stream discharge and in major element hydrochemistry were assessed over a six day period in July, 2013. Discharge was assessed from hourly photography of the outlet from multiple vantages, including where mid-stream naled ice provided a natural gauge. pH, electrical conductivity, suspended sediment, and alkalinity were measured in samples of stream water collected every three hours. Element and ion concentrations were subsequently measured in a laboratory setting. Photography and stream observations reveal that although river width and stage have only slight diurnal variation, there are large changes in discharge shown in the portion of the width characterized by standing waves and fast flow. Width of this active channel approximately doubles over a diurnal cycle. Together with changes in flow over the naled, these features allow an observationally based relative record of stream discharge in this unconstrained alluvial setting. Peaks in discharge were offset by 3–7 hours from peak melt of the interior ice surface. Concentration of dissolved solutes follows a sinusoidal diurnal cycle, except for large and variable increases in dissolved solutes during the stream’s waning flow. Diurnal changes in solute concentration average 31 % of the base value. Diurnal solute concentration minima and maxima lag peak and minimum stream discharge by 3–6 hours. This phase shift between discharge and solute concentration suggests that during high flow, water is either encountering more rock material or is stored in longer contact with rock material. We suggest that expansion of a distributed subglacial hydrologic network into seldom accessed regions during high flow could account for these phenomena, and for a spike of partial silicate reaction products during waning flow, which itself suggests a pressure threshold-triggered release of stored water.

scholarly journals Glacier algae accelerate melt rates on the western Greenland Ice Sheet

2019 ◽  
Author(s):  
Joseph M. Cook ◽  
Andrew J. Tedstone ◽  
Christopher Williamson ◽  
Jenine McCutcheon ◽  
Andrew J. Hodson ◽  
...  
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Algal Growth ◽  
Greenland Ice Sheet ◽  
Remote Sensing Data ◽  
Radiation Absorption ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Active Growth ◽  
Ice Surface

Abstract. Melting of the Greenland Ice Sheet (GrIS) is the largest single contributor to eustatic sea level and is amplified by the growth of pigmented algae on the ice surface that increase solar radiation absorption. This biological albedo reducing effect and its impact upon sea level rise has not previously been quantified. Here, we combine field spectroscopy with a novel radiative transfer model, supervised classification of UAV and satellite remote sensing data and runoff modelling to calculate biologically-driven ice surface ablation and compare it to the albedo reducing effects of local mineral dust. We demonstrate that algal growth led to an additional 5.5–8.0 Gt of runoff from the western sector of the GrIS in summer 2016, representing 6–9 % of the total. Our analysis confirms the importance of the biological albedo feedback and that its omission from predictive models leads to the systematic underestimation of Greenland’s future sea level contribution, especially because both the bare ice zones available for algal colonization and the length of the active growth season are set to expand in the future.

scholarly journals Melt probabilities and surface temperature trends on the Greenland ice sheet using a Gaussian mixture model

2021 ◽  
Author(s):  
Daniel Clarkson ◽  
Emma Eastoe ◽  
Amber Leeson
Keyword(s):  
Surface Temperature ◽  
Gaussian Mixture Model ◽  
Mixture Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Gaussian Mixture ◽  
Ice Surface ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Ice Surface Temperature ◽  
Model Components

Abstract. The Greenland ice sheet has experienced significant melt over the past six decades, with extreme melt events covering large areas of the ice sheet. Melt events are typically analysed using summary statistics, but the nature and characteristics of the events themselves are less frequently analysed. Our work examines melt events from a statistical perspective by modelling 19 years of Moderate Resolution Imaging Spectroradiometer (MODIS) ice surface temperature data using a Gaussian mixture model. We use a mixture model with separate model components for ice and meltwater temperatures at 1139 locations spaced across the ice sheet. By considering the uncertainty of the ice surface temperature measurements, we use the two categories of model components to define a probability of melt for a given observation rather than using a fixed melt threshold. This probability can then be used to estimate the expected number of melt events at a given location. Furthermore, the model can be used to estimate temperature quantiles at a given location, and analyse temperature and melt trends over time by fitting the model to subsets of time. Fitting the model to data from 2001–2009 and 2010–2019 shows increases in melt probability for significant portions of the ice sheet, as well as the yearly expected maximum temperatures.

scholarly journals High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet

2014 ◽  
Vol 7 (1) ◽  
pp. 129-148 ◽  
Author(s):  
K. Lindbäck ◽  
R. Pettersson ◽  
S. H. Doyle ◽  
C. Helanow ◽  
P. Jansson ◽  
...  
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Airborne Radar ◽  
Ice Thickness ◽  
Equilibrium Line Altitude ◽  
Bed Topography ◽  
Ice Surface ◽  
Ice Sheet Dynamics

Abstract. We present ice thickness and bed topography maps with high spatial resolution (250 to 500 m) of a and-terminating section of the Greenland Ice Sheet derived from combined ground-based and airborne radar surveys. The data have a total area of ~12000 km2 and cover the whole ablation area of the outlet glaciers of Isunnguata Sermia, Russell, Leverett, Ørkendalen and Isorlersuup up to the long-term mass balance equilibrium line altitude at ~1600 m above sea level. The bed topography shows highly variable subglacial trough systems, and the trough of the Isunnguata Sermia Glacier is over-deepened and reaches an elevation of several hundreds of meters below sea level. The ice surface is smooth and only reflects the bedrock topography in a subtle way, resulting in a highly variable ice thickness. The southern part of our study area consists of higher bed elevations compared to the northern part. The covered area is one of the most studied regions of the Greenland Ice Sheet with studies of mass balance, dynamics, and supraglacial lakes, and our combined dataset can be valuable for detailed studies of ice sheet dynamics and hydrology. The compiled datasets of ground-based and airborne radar surveys are accessible for reviewers (password protected) at doi.pangaea.de/10.1594/pangaea.830314 and will be freely available in the final revised paper.

Increase of ice discharge from Greenland's peripheral tidewater glaciers over recent decades

2021 ◽  
Author(s):  
Marco Möller ◽  
Beatriz Recinos ◽  
Ben Marzeion
Keyword(s):  
Mass Loss ◽  
Cross Sections ◽  
Ice Sheet ◽  
Regression Tree ◽  
Greenland Ice Sheet ◽  
Tidewater Glaciers ◽  
Glacier Ice ◽  
Extrapolation Scheme ◽  
Flux Gate ◽  
Surface Ice

<p>The Greenland Ice Sheet is losing mass at increasing rates. Substantial amounts of this mass loss occur by ice discharge. The ice sheet is surrounded by thousands of peripheral glaciers, which are dynamically decoupled from the ice sheet, and which account for ~10 % of the global glacier ice volume outside the two main ice sheets. Rather low-lying along the coasts, these peripheral glaciers are also losing mass at increasing, but disputed, rates. The total absence of knowledge about the role and share of solid ice discharge in this mass loss adds to the controversy. Since the quantification of ice discharge is still pending, a full understanding of ice mass loss processes in this globally important glacier region is substantially hampered.</p><p>Here, we present the first estimation of ice discharge from Greenland's peripheral tidewater glaciers. For each of these 760 glaciers, we combine an idealized rectangular flux gate cross sections derived from modelling with the Open Global Glacier Model with surface ice flow velocities derived from the ITS_LIVE and MEaSUREs remote sensing datasets to calculate glacier specific ice discharge on both annual and multi-annual time scales over the period 1985 to 2018. For the few glaciers not covered by either of the employed original datasets or modelling methods we use a regression tree-based extrapolation scheme to estimate the necessary input data for our calculation.</p><p>Our findings indicate a significant overall increase of ice discharge over the study period although several individual glaciers show contrasting developments. This increase became especially apparent across the southern parts of Greenland. Our results also show that the total of the ice discharge from Greenland's peripheral tidewater glaciers is dominated by few major contributors and that this dominance is completely time-independent.</p>

scholarly journals A Detailed Oxygen-18 Profile From The Greenland Ice-Sheet Margin Through The Wisconsinan-Holocene Transition

1990 ◽  
Vol 14 ◽  
pp. 356 ◽  
Author(s):  
Niels Reeh ◽  
Anne Letréguilly ◽  
Hans Oerter
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Crucial Importance ◽  
Potential Yield ◽  
Mining Areas ◽  
Layer Sequence ◽  
North East ◽  
Core Profile ◽  
Field Season ◽  
Surface Ice

About 1500 surface-ice samples for δ18O analysis were collected in the 1988 field season along a 750 m profile perpendicular to the margin of the Greenland ice sheet at Pakitsoq, ca 40 km north-east of Jakobshavn, central West Greenland. The purpose of the study was to evaluate how well the continuity of the layer sequence is preserved in ice-margin records, a question of crucial importance for evaluating the potential yield of using ice margins as “mining areas” for easily accessible old ice for climate and environmental studies. More than half of the 1500 samples were taken continuously as 20 cm samples along a 170 m section through the Wisconsinan-Holocene transition which, previously, had been located at the surface of the ice margin. Along this transition section δ18O values decrease by about 6‰ from −31.5 to 37.5‰ on an average. Detailed studies were made of surface elevations and surface structures (e.g. blue bands) along the “horizontal core” profile which, moreover, was photographed section by section, thus enabling the δ-record to be correlated with surface features. Results of the δ18O analyses are promising. Even though ice from the blue bands has δ-values that are 7–8‰ higher than those of the surrounding white ice, there seems to be no discontinuity in the white-ice δ-record across the blue bands.

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