Greenland ice sheet

The Greenland ice sheet is an excellent observatory for global climate change. Meltwater from the 1.8 million km2 large ice sheet influences oceanic temperature and salinity, nutrient fluxes and global sea level (IPCC 2013). Surface reflectivity is a key driver of surface melt rates (Box et al. 2012). Mapping of different ice-sheet surface types provides a clear indicator of where changes in ice-sheet surface reflectivity are most prominent. Here, we present an updated version of a surface classification algorithm that utilises NASA’s Moderate resolution Imaging Spectroradiometer (MODIS) sensor on the Terra satellite to systematically monitor ice-sheet surface melt (Fausto et al. 2007). Our aim is to determine the areal extent of three surface types over the 2000–2014 period: glacier ice, melting snow (including percolation areas) and dry snow (Cuffey & Paterson 2010). Monthly 1 km2 resolution surface-type grids can be downloaded via the CryoClim internet portal (www.cryoclim.net). ...

Greenland ice-core δ 18 O-temperature reconstructions suggest a dramatic cooling during the Younger Dryas (YD; 12.9–11.7 ka), with temperatures being as cold as the earlier Oldest Dryas (OD; 18.0–14.6 ka) despite an approximately 50 ppm rise in atmospheric CO 2 . Such YD cooling implies a muted Greenland climate response to atmospheric CO 2 , contrary to physical predictions of an enhanced high-latitude response to future increases in CO 2 . Here we show that North Atlantic sea surface temperature reconstructions as well as transient climate model simulations suggest that the YD over Greenland should be substantially warmer than the OD by approximately 5 °C in response to increased atmospheric CO 2 . Additional experiments with an isotope-enabled model suggest that the apparent YD temperature reconstruction derived from the ice-core δ 18 O record is likely an artifact of an altered temperature-δ 18 O relationship due to changing deglacial atmospheric circulation. Our results thus su...

We present a simplified atmospheric correction algorithm for the snow/ice albedo retrieval using single view satellite measurements. The validation of the technique is performed using Ocean and Land Colour Instrument (OLCI) on board Copernicus Sentinel - 3 satellite and ground spectral or broadband albedo measurements from locations on the Greenland ice sheet and in the French Alps. Through comparison with independent ground observations, the technique is shown to perform accurately in a range of conditions from a 2100 m elevation mid-latitude location in the French Alps to a network of 15 locations across a 2390 m elevation range in seven regions across the Greenland ice sheet. Retrieved broadband albedo is accurate within 5% over a wide (0.5) broadband albedo range of the (N = 4,155) Greenland observations and with no apparent bias.

The Greenland Ice Sheet (GIS) is the largest storage of freshwater in the Northern Hemisphere. Its development is closely coupled to the interaction between variations in global climate and ocean circulation. The feedback mechanism between ice sheet and interglacial warming climate is meltwater discharge and enhanced freshwater input into the ocean. The Baffin Bay is an important pathway for Arctic Ocean water and meltwater and therefore freshwater input into the Atlantic Ocean. Melville Bay, a sparsely investigated area within northeast Baffin Bay along the west coast of Greenland, is presently a focus of freshwater input and drains about 27% of the GIS runoff [1]. We investigate potentially changing provenances of silicate detrital material discharged by meltwater into Melville Bay throughout the Holocene. Signatures of radiogenic isotopes strontium (Sr), lead (Pb) and neodymium (Nd) serve as reliable provenance tracers based on their resistance to weathering and transport process...

Quantifying the biogeochemical cycling of carbon in glacial ecosystems is of great significance for regional, and potentially global, carbon flow estimations. The concentration and quality of organic carbon (OC) is an important indicator of biogeochemical and physical processes that prevail in an ice-sheet ecosystem. Here we determine the content and quality of OC in debris from the surface of the Greenland ice sheet (GrIS) using microscopic, chromatographic, spectrophotometric and high-temperature combustion techniques. The total OC content in the debris increased with distance from the edge of the ice sheet, from virtually zero to >6% dry weight at 50 km inland, and there was a peak in the carbohydrate proportion and the microbial abundance at ∼6km inland. The highest (galactose + mannose)/(arabinose + xylose) ratios, indicating maximum autochthonous microbial production, were found at >10km inland. We propose that three key processes influence the carbon cycling on the GrIS...

In the North Atlantic, cold, relatively salty water sinks in the icy Labrador and Greenland seas, forming North Atlantic Deep Water (NADW).This circulates through the global ocean, driving ocean overturning and global heat transport and, thus, impacting global climate. As one of the most climatically sensitive regions on Earth, the North Atlantic has experienced abrupt changes to its oceanatmosphere‐cryosphere system, triggered by fluctuations in meltwater delivery to source areas of NADW formation.For about the past 100 thousand years, these abrupt jumps in climate state have manifested as ‘Dansgaard/Oeschger’ (D/O) oscillations (millennial‐scale warm‐cold oscillations) and 'Heinrich' events in ice and marine sediment cores, respectively [e.g., Dansgaard et al., 1993; Bond and Lotti, 1995]. These Heinrich events are characterized as huge input of ice‐rafted debris (IRD) and meltwater pulses, documenting episodes of sudden instability and collapse of the current Greenland ic...

Nature Communications 7: Article number: 10525 (2016); Published: 22 January 2016; Updated: 17 November 2016 The authors wish to add ‘Mads H. Ribergaard’ and ‘John Mortensen’ to the author list of this Article for the provision of oceanographic data. This has now been updated in both the PDF and HTML versions of the Article.

We propose a new ice sheet model validation framework – the Cryospheric Model Comparison Tool (CMCT) – that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, the model initial condition as well as...

SignificanceA major uncertainty concerning the 21st century climate is the ice sheet response to global warming. Paleodata indicate rapid ice sheet destabilizations during the last deglaciation, which could lead to an underestimation of sea level rise, as suggested in recent publications. Therefore, we explore the impact of different scenarios of Greenland partial melting in the very sensitive Sahel region. We first demonstrate that such a melting induces a drastic decrease of West African monsoon precipitation. Moreover, we quantify the agricultural area losses due to monsoon changes. Consequently, we pinpoint a large potential for migration of millions of people in the coming decades. Thus, the ice sheet destabilization provokes not only coastal damages but also large population migration in monsoon area.

Melting of the Greenland Ice Sheet is a leading cause of land-ice mass loss and cryosphere-attributed sea level rise. Blooms of pigmented glacier ice algae lower ice albedo and accelerate surface melting in the ice sheet’s southwest sector. Although glacier ice algae cause up to 13% of the surface melting in this region, the controls on bloom development remain poorly understood. Here we show a direct link between mineral phosphorus in surface ice and glacier ice algae biomass through the quantification of solid and fluid phase phosphorus reservoirs in surface habitats across the southwest ablation zone of the ice sheet. We demonstrate that nutrients from mineral dust likely drive glacier ice algal growth, and thereby identify mineral dust as a secondary control on ice sheet melting.

Surface ablation of the Greenland ice sheet is amplified by surface darkening caused by light‐absorbing impurities such as mineral dust, black carbon, and pigmented microbial cells. We present the first quantitative assessment of the microbial contribution to the ice sheet surface darkening, based on field measurements of surface reflectance and concentrations of light‐absorbing impurities, including pigmented algae, during the 2014 melt season in the southwestern part of the ice sheet. The impact of algae on bare ice darkening in the study area was greater than that of nonalgal impurities and yielded a net albedo reduction of 0.038 ± 0.0035 for each algal population doubling. We argue that algal growth is a crucial control of bare ice darkening, and incorporating the algal darkening effect will improve mass balance and sea level projections of the Greenland ice sheet and ice masses elsewhere.

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 Arct...

Fjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these fjords are limited making it difficult to assess linkages between the fjord, coastal water masses, and freshwater discharge from GIS. Here we present a decade‐long monthly hydrographic time series from a southwest Greenland fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures. During summer, runoff from GIS leads to a pronounced freshening of the fjord. In general, the fjord's seasonal circulation system damps the seasonal variation in temperature in the fjord. This leads to a ...

We present a new record of eolian dust flux to the western Subarctic North Pacific (SNP) covering the past 27,000 years based on a core from the Detroit Seamount. Comparing the SNP dust record to the North Greenland Ice Core Project (NGRIP) ice core record shows significant differences in the amplitude of dust changes to the two regions during the last deglaciation, while the timing of abrupt changes is synchronous. If dust deposition in the SNP faithfully records its mobilization in East Asian source regions, then the difference in the relative amplitude must reflect climate‐related changes in atmospheric dust transport to Greenland. Based on the synchronicity in the timing of dust changes in the SNP and Greenland, we tie abrupt deglacial transitions in the 230Th‐normalized 4He flux record to corresponding transitions in the well‐dated NGRIP dust flux record to provide a new chronostratigraphic technique for marine sediments from the SNP. Results from this technique are complemente...