scholarly journals Variations in snowpack melt on the Greenland ice sheet based on passive-microwave measurements

1995 ◽  
Vol 41 (137) ◽  
pp. 51-60 ◽  
Author(s):  
Thomas L. Mote ◽  
Mark R. Anderson
Keyword(s):  
Climate Change ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ablation Rate ◽  
Passive Microwave ◽  
Microwave Emission ◽  
The Arctic ◽  
Emission Model ◽  
The Impact ◽  
Microwave Data

AbstractA simple microwave-emission model is used to simulate 37 GHz brightness temperatures associated with snowpack-melt conditions for locations across the Greenland ice sheet. The simulated values are utilized as threshold values and compared to daily, gridded SMMR and SSM/I passive-microwave data, in order to reveal regions experiencing melt. The spatial extent of the area classified as melting is examined on a daily, monthly and seasonal (May-August) basis for 1979–91. The typical seasonal cycle of melt coverage shows melt beginning in late April, a rapid increase in the melting area from mid-May to mid-July, a rapid decrease in melt extent from late July through mid-August, and cessation of melt in late September. Seasonal averages of the daily melt extents demonstrate an apparent increase in melt coverage over the 13 year period of approximately 3.8% annually (significant at the 95% confidence interval). This increase is dominated by statistically significant positive trends in melt coverage during July and August in the west and southwest of the ice sheet. We find that a linear correlation between microwave-derived melt extent and a surface measure of ablation rate is significant in June and July but not August, so caution must be exercised in using the microwave-derived melt extents in August. Nevertheless, knowledge of the variability of snowpack melt on the Greenland ice sheet as derived from microwave data should prove useful in detecting climate change in the Arctic and examining the impact of climate change on the ice sheet.

scholarly journals Variations in snowpack melt on the Greenland ice sheet based on passive-microwave measurements

1995 ◽  
Vol 41 (137) ◽  
pp. 51-60 ◽  
Author(s):  
Thomas L. Mote ◽  
Mark R. Anderson
Keyword(s):  
Climate Change ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ablation Rate ◽  
Passive Microwave ◽  
Microwave Emission ◽  
The Arctic ◽  
Emission Model ◽  
The Impact ◽  
Microwave Data

AbstractA simple microwave-emission model is used to simulate 37 GHz brightness temperatures associated with snowpack-melt conditions for locations across the Greenland ice sheet. The simulated values are utilized as threshold values and compared to daily, gridded SMMR and SSM/I passive-microwave data, in order to reveal regions experiencing melt. The spatial extent of the area classified as melting is examined on a daily, monthly and seasonal (May-August) basis for 1979–91. The typical seasonal cycle of melt coverage shows melt beginning in late April, a rapid increase in the melting area from mid-May to mid-July, a rapid decrease in melt extent from late July through mid-August, and cessation of melt in late September. Seasonal averages of the daily melt extents demonstrate an apparent increase in melt coverage over the 13 year period of approximately 3.8% annually (significant at the 95% confidence interval). This increase is dominated by statistically significant positive trends in melt coverage during July and August in the west and southwest of the ice sheet. We find that a linear correlation between microwave-derived melt extent and a surface measure of ablation rate is significant in June and July but not August, so caution must be exercised in using the microwave-derived melt extents in August. Nevertheless, knowledge of the variability of snowpack melt on the Greenland ice sheet as derived from microwave data should prove useful in detecting climate change in the Arctic and examining the impact of climate change on the 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 Heterogeneous CO<sub>2</sub> and CH<sub>4</sub> content of glacial meltwater from the Greenland Ice Sheet and implications for subglacial carbon processes

2021 ◽  
Vol 15 (3) ◽  
pp. 1627-1644
Author(s):  
Andrea J. Pain ◽  
Jonathan B. Martin ◽  
Ellen E. Martin ◽  
Åsa K. Rennermalm ◽  
Shaily Rahman
Keyword(s):  
Greenhouse Gas ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mineral Weathering ◽  
Atmospheric Co2 ◽  
The Arctic ◽  
Co2 Concentrations ◽  
Geochemical Models ◽  
Atmospheric Co2 Concentrations ◽  
The Impact

Abstract. Accelerated melting of the Greenland Ice Sheet has increased freshwater delivery to the Arctic Ocean and amplified the need to understand the impact of Greenland Ice Sheet meltwater on Arctic greenhouse gas budgets. We evaluate subglacial discharge from the Greenland Ice Sheet for carbon dioxide (CO2) and methane (CH4) concentrations and δ13C values and use geochemical models to evaluate subglacial CH4 and CO2 sources and sinks. We compare discharge from southwest (a sub-catchment of the Isunnguata Glacier, sub-Isunnguata, and the Russell Glacier) and southern Greenland (Kiattut Sermiat). Meltwater CH4 concentrations vary by orders of magnitude between sites and are saturated with respect to atmospheric concentrations at Kiattut Sermiat. In contrast, meltwaters from southwest sites are supersaturated, even though oxidation reduces CH4 concentrations by up to 50 % during periods of low discharge. CO2 concentrations range from supersaturated at sub-Isunnguata to undersaturated at Kiattut Sermiat. CO2 is consumed by mineral weathering throughout the melt season at all sites; however, differences in the magnitude of subglacial CO2 sources result in meltwaters that are either sources or sinks of atmospheric CO2. At the sub-Isunnguata site, the predominant source of CO2 is organic matter (OM) remineralization. However, multiple or heterogeneous subglacial CO2 sources maintain atmospheric CO2 concentrations at Russell but not at Kiattut Sermiat, where CO2 is undersaturated. These results highlight a previously unrecognized degree of heterogeneity in greenhouse gas dynamics under the Greenland Ice Sheet. Future work should constrain the extent and controls of heterogeneity to improve our understanding of the impact of Greenland Ice Sheet melt on Arctic greenhouse gas budgets, as well as the role of continental ice sheets in greenhouse gas variations over glacial–interglacial timescales.

scholarly journals Economics of the disintegration of the Greenland ice sheet

2019 ◽  
Vol 116 (25) ◽  
pp. 12261-12269 ◽  
Author(s):  
William Nordhaus
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Social Cost ◽  
Climate Models ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Reduced Form ◽  
Small Contribution ◽  
Wide Range ◽  
The Impact

Concerns about the impact on large-scale earth systems have taken center stage in the scientific and economic analysis of climate change. The present study analyzes the economic impact of a potential disintegration of the Greenland ice sheet (GIS). The study introduces an approach that combines long-run economic growth models, climate models, and reduced-form GIS models. The study demonstrates that social cost–benefit analysis and damage-limiting strategies can be usefully extended to illuminate issues with major long-term consequences, as well as concerns such as potential tipping points, irreversibility, and hysteresis. A key finding is that, under a wide range of assumptions, the risk of GIS disintegration makes a small contribution to the optimal stringency of current policy or to the overall social cost of climate change. It finds that the cost of GIS disintegration adds less than 5% to the social cost of carbon (SCC) under alternative discount rates and estimates of the GIS dynamics.

Greenland fjord productivity under climate change - multiproxy late-Holocene records from two contrasting fjord systems

2020 ◽  
Author(s):  
Anna Bang Kvorning ◽  
Tania Beate Thomsen ◽  
Mimmi Oksman ◽  
Marit-Solveig Seidenkrantz ◽  
Christof Pearce ◽  
...  
Keyword(s):  
Climate Change ◽  
Primary Productivity ◽  
Negative Impact ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Age ◽  
Dinoflagellate Cyst ◽  
Coastal Marine ◽  
The Future ◽  
The Impact

&lt;p&gt;The Greenland Ice Sheet has been losing mass at an increasing rate over the past decades due to atmospheric and oceanic warming. As a result, freshwater discharge from the Greenland Ice sheet has doubled in the last two decades and is expected to strongly increase in the future, with a large impact on the functioning of coastal marine ecosystems. While glacier runoff delivers nutrients and labile carbon into the fjords, an increase in sediment inputs is expected to have a negative impact in primary productivity, due to increased turbidity and subsequent reduction in available light for photosynthesis. Bridging modern satellite, historical and paleo-records is a key approach, as our capacity to project future scenarios requires an understanding of long-term dynamics, and insight into past warm(er) climate periods that may serve as analogues for the future. We will present results from a master&amp;#8217;s project developed within the framework of project GreenShift: Greenland fjord productivity under climate change. Two high-resolution sediment core records from two contrasting fjord systems in NE and SW Greenland were analysed to assess the impact of Greenland Ice Sheet melt on sediment fluxes and primary productivity, focusing on the time period from the Little Ice Age until present. The overall goal of this work is to gain a better understanding of the possible linkages between GIS melt and productivity in Greenland fjord systems, with a view to improve future projections. We followed a multiproxy approach including grain-size distribution, organic carbon and biogenic silica fluxes; and dinoflagellate cyst analyses. Our preliminary results show an overall trend towards sea-surface freshening in recent decades for both fjords influenced by land-terminating (NE) and marine-terminating (SW) glaciers, alongside with important differences both in terms of sedimentary organic composition and dinoflagellate cyst assemblages. &amp;#160;&lt;/p&gt;

scholarly journals Influence of Arctic sea-ice loss on the Greenland ice sheet climate

2021 ◽  
Author(s):  
Raymond Sellevold ◽  
Jan T. M. Lenaerts ◽  
Miren Vizcaino
Keyword(s):  
Sea Ice ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Humid Atmosphere ◽  
Baffin Bay ◽  
Arctic Sea ◽  
Surface Melt ◽  
The Impact

AbstractThe Arctic is the region on Earth that is warming the fastest. At the same time, Arctic sea ice is reducing while the Greenland ice sheet (GrIS) is losing mass at an accelerated pace. Here, we study the seasonal impact of reduced Arctic sea ice on GrIS surface mass balance (SMB), using the Community Earth System Model version 2.1 (CESM2), which features an advanced, interactive calculation of SMB. Addressing the impact of sea-ice reductions on the GrIS SMB from observations is difficult due to the short observational records. Also, signals detected using transient climate simulations may be aliases of other forcings. Here, we analyze dedicated simulations from the Polar Amplification Model Intercomparison Project with reduced Arctic sea ice and compare them with preindustrial sea ice simulations while keeping all other forcings constant. In response to reduced sea ice, the GrIS SMB increases in winter due to increased precipitation, driven by the more humid atmosphere and increasing cyclones. In summer, surface melt increases due to a warmer, more humid atmosphere providing increased energy transfer to the surface through the sensible and latent heat fluxes, which triggers the melt-albedo feedback. Further, warming occurs throughout the entire troposphere over Baffin Bay. This deep warming results in regional enhancement of the 500 hPa geopotential heights over the Baffin Bay and Greenland, increasing blocking and heat advection over the GrIS’ surface. This anomalous circulation pattern has been linked to recent increases in the surface melt of the GrIS.

scholarly journals Geographic and seasonal variations in the surface properties of the ice sheets by satellite-radar altimetry

1993 ◽  
Vol 39 (133) ◽  
pp. 687-697 ◽  
Author(s):  
Curt H. Davis ◽  
H. Jay Zwally
Keyword(s):  
Brightness Temperature ◽  
Extinction Coefficient ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Passive Microwave ◽  
East Antarctica ◽  
Grain Sizes ◽  
Wave Forms ◽  
Microwave Data

AbstractGeosat-altimeter wave forms from the Greenland and Antarctic ice sheets are analyzed using an algorithm based upon a combined surface-and volume-scattering model. The results demonstrate that sub-surface volume-scattering occurs over major parts of the ice sheets. Quantitative estimates of geographic variations in the near-surface ice-sheet properties are derived by retracking individual altimeter wave forms. The derived surface properties correlate with elevation, latitude and microwave brightness-temperature data. Specifically, the extinction coefficient of snow obtained by this method varies from 0.48 to 0.13 m−1 over the latitudes from 65° to 72°N on the central part of the Greenland ice sheet and from 0.20 to 0.10 m−1 over a section of Wilkes Land in East Antarctica where the elevation increases from 2550 to 3150 m.Analysis of passive-microwave data over East Antarctica shows that the brightness temperature increases with elevation as the extinction coefficient decreases. Larger snow grain-sizes occur at lower elevations of the ice sheet because of higher mean annual temperatures. The larger grain-sizes increase the extinction coefficient of snow and decrease the emitted energy (brightness temperature) from greater snow depths. The passive-microwave data are also used to determine the average number of melt d year−1 (1979–87) for the central part of the Greenland ice sheet. For latitudes from 65° to 68.5° N, the average number of melt days decreases from 3.5 to 0.25 d year, whereas no melt events are observed for latitudes above 69°N over the 8 year period. Snow subjected to alternate melting and freezing has enhanced grain-sizes compared to that of dry snow. This accounts for the larger values and larger spatial variations of ke on the Greenland ice sheet compared to East Antarctica, where surface temperatures are never high enough to cause surface melting.

scholarly journals Indications of melt in near-surface ice-core stratigraphy: comparisons with passive-microwave melt signals over the Greenland ice sheet

1995 ◽  
Vol 21 ◽  
pp. 59-63 ◽  
Author(s):  
Clinton M. Rowe ◽  
Mark R. Anderson ◽  
Thomas L. Mote ◽  
Karl C. Kuivinen
Keyword(s):  
Ice Core ◽  
Isotope Analysis ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Passive Microwave ◽  
Data Sets ◽  
Near Surface ◽  
Stratigraphic Record ◽  
Surface Ice ◽  
Microwave Data

During the summer of 1993, a field program was conducted to collect several shallow firn cores from two locations in the southern region of the Greenland ice sheet. Stratigraphic evidence of melt from these cores was used for comparison with satellite-derived indications of melt. The shallow firn cores were examined for stratigraphic evidence of past melt events and were sampled for oxygen-isotope analysis to delineate the annual accumulation layers in the snowpack. The relative intensity of each year’s summer melt episode was compared to the corresponding melt frequency derived from microwave emissions. This comparison demonstrates that a linkage between the stratigraphic record and microwave data can be established. Both data sets indicate that there was less melt during the late 1970s and early 1980s than during the late 1980s, in general agreement with climate observations.

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