scholarly journals Improved representation of the contemporary Greenland ice sheet firn layer by IMAU-FDM v1.2G

2021 ◽  
Author(s):  
Max Brils ◽  
Peter Kuipers Munneke ◽  
Willem Jan van de Berg ◽  
Michiel van den Broeke
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Liquid Water Content ◽  
Climate Forcing ◽  
Air Content ◽  
The Past ◽  
Meltwater Runoff ◽  
Surface Elevation Change ◽  
Increased Sensitivity ◽  
Surface Melt

Abstract. The firn layer that covers 90 % of the Greenland ice sheet (GrIS) plays an important role in determining the response of the ice sheet to climate change. Meltwater can percolate into the firn layer and refreeze at greater depths, thereby temporarily preventing mass loss. However, as global warming leads to increasing surface melt, more surface melt may refreeze in the firn layer, thereby reducing the capacity to buffer subsequent episodes of melt. This can lead to a tipping point in meltwater runoff. It is therefore important to study the evolution of the Greenland firn layer in the past, present and future. In this study, we present the latest version of our firn model, IMAU-FDM (Firn Densification Model), with an application to the GrIS. We improved the density of freshly fallen snow, the dry-snow densification rate and the firn's thermal conductivity using recently published parameterizations and by calibrating to an extended set of observations of firn density, temperature and liquid water content at the GrIS. Overall, the updated model settings lead to higher firn air content and higher 10 m firn temperatures, owing to a lower density near the surface. The effect of the new model settings on the surface elevation change is investigated through three case studies located at Summit, KAN-U and FA-13. Most notably, the updated model shows greater inter- and intra-annual variability in elevation and an increased sensitivity to climate forcing.

scholarly journals Atmospheric and oceanic climate forcing of the exceptional Greenland ice sheet surface melt in summer 2012

2013 ◽  
Vol 34 (4) ◽  
pp. 1022-1037 ◽  
Author(s):  
Edward Hanna ◽  
Xavier Fettweis ◽  
Sebastian H. Mernild ◽  
John Cappelen ◽  
Mads H. Ribergaard ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Climate Forcing ◽  
Sheet Surface ◽  
Oceanic Climate ◽  
Surface Melt

scholarly journals The effect of a Holocene climatic optimum on the evolution of the Greenland ice sheet during the last 10 kyr

2018 ◽  
Vol 64 (245) ◽  
pp. 477-488 ◽  
Author(s):  
LISBETH T. NIELSEN ◽  
GUðFINNA AÐALGEIRSDÓTTIR ◽  
VASILEIOS GKINIS ◽  
ROMAN NUTERMAN ◽  
CHRISTINE S. HVIDBERG
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Early Holocene ◽  
Climate Forcing ◽  
The Holocene ◽  
The Past ◽  
Holocene Climatic Optimum ◽  
Surface Temperatures ◽  
Climatic Optimum

ABSTRACTThe Holocene climatic optimum was a period 8–5 kyr ago when annual mean surface temperatures in Greenland were 2–3°C warmer than present-day values. However, this warming left little imprint on commonly used temperature proxies often used to derive the climate forcing for simulations of the past evolution of the Greenland ice sheet. In this study, we investigate the evolution of the Greenland ice sheet through the Holocene when forced by different proxy-derived temperature histories from ice core records, focusing on the effect of sustained higher surface temperatures during the early Holocene. We find that the ice sheet retreats to a minimum volume of ~0.15–1.2 m sea-level equivalent smaller than present in the early or mid-Holocene when forcing an ice-sheet model with temperature reconstructions that contain a climatic optimum, and that the ice sheet has continued to recover from this minimum up to present day. Reconstructions without a warm climatic optimum in the early Holocene result in smaller ice losses continuing throughout the last 10 kyr. For all the simulated ice-sheet histories, the ice sheet is approaching a steady state at the end of the 20th century.

scholarly journals Brief communication: Firn data compilation reveals the evolution of the firn air content on the Greenland ice sheet

2018 ◽  
Author(s):  
Baptiste Vandecrux ◽  
Michael MacFerrin ◽  
Horst Machguth ◽  
William T. Colgan ◽  
Dirk van As ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Retention Capacity ◽  
Near Surface ◽  
Air Content ◽  
Data Compilation ◽  
Surface Melt ◽  
Firn Core

Abstract. The firn covering the Greenland ice sheet interior can retain part of the surface melt, buffering the ice sheet’s contribution to sea level, but its characteristics are still little known. Using remote-sensing observations from 2000–2017, we estimate that firn covers 1,405,500 ± 17,250 km2 of the ice sheet. We present 344 firn-core-derived observations of the top 10 m firn air content (FAC10), indicative of the firn’s meltwater retention capacity. FAC10 remained stable in the coldest 74 % of the firn area during 1953–2017, while FAC10 decreased in the warmest and driest 12 % of the firn area between 1997–2008 and 2011–2017, resulting in a loss of 180 ± 78 km3 (−26 ± 11 %) of air from the near-surface firn.

scholarly journals The importance of insolation changes for paleo ice sheet modeling

2014 ◽  
Vol 8 (1) ◽  
pp. 337-362
Author(s):  
A. Robinson ◽  
H. Goelzer
Keyword(s):  
Temperature Anomaly ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Climatic Forcing ◽  
Near Surface ◽  
Ice Volume ◽  
The Past ◽  
Ice Sheet Modeling ◽  
Surface Melt ◽  
Continental Ice Sheets

Abstract. The growth and retreat of continental ice sheets in the past has largely been a response to changing climatic forcing. Thus, the calculation of surface melt is an important aspect of paleo ice sheet modeling. Changes in insolation are often not accounted for in calculations of surface melt, under the assumption that the near-surface temperature transmits the majority of the climatic forcing to the ice sheet. To assess how this could affect paleo simulations, here we investigate the importance of different orbital configurations for estimating melt on the Greenland ice sheet. We find that during peak Eemian conditions, increased insolation contributes 20–50% to the surface melt anomaly. However, this percentage depends strongly on the temperature anomaly at the time. Furthermore, the spatial pattern of surface conditions in terms of temperature and albedo exert a strong influence on the relative importance of insolation in the melt calculations. In coupled simulations, the additional insolation-induced melt translates into up to threefold more ice volume loss, compared to output using a model that does not account for insolation changes. We also introduce a simple correction factor that allows reduced complexity melt models to account for changes in insolation.

Greenland land-terminating glaciers velocity trends during the last two decades

2021 ◽  
Author(s):  
Paul Halas ◽  
Jeremie Mouginot ◽  
Basile de Fleurian ◽  
Petra Langebroek
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Limited Area ◽  
Ice Dynamics ◽  
Basal Sliding ◽  
Surface Melt ◽  
Ice Sheet Dynamics ◽  
The Impact

<div> <p>Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise. Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding. The sliding component of glaciers has been observed to be strongly related to surface melting, as water can eventually reach the bed and impact the subglacial water pressure, affecting the basal sliding.  </p> </div><div> <p>The link between ice velocities and surface melt on multi-annual time scale is still not totally understood even though it is of major importance with expected increasing surface melting. Several studies showed some correlation between an increase in surface melt and a slowdown in velocities, but there is no consensus on those trends. Moreover those investigations only presented results in a limited area over Southwest Greenland.  </p> </div><div> <p>Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.  </p> </div><div> <p>Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration. This trend however does not seem to be observed on the whole ice sheet and is probably specific to this region’s climate forcing. </p> </div><div> <p>Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.</p> </div>

scholarly journals Meteorological Drivers and Large-Scale Climate Forcing of West Antarctic Surface Melt

2019 ◽  
Vol 32 (3) ◽  
pp. 665-684 ◽  
Author(s):  
Ryan C. Scott ◽  
Julien P. Nicolas ◽  
David H. Bromwich ◽  
Joel R. Norris ◽  
Dan Lubin
Keyword(s):  
Sea Ice ◽  
Ice Sheet ◽  
Climate Forcing ◽  
West Antarctica ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
West Antarctic ◽  
Ice Concentration ◽  
Surface Melt ◽  
Marine Air

Understanding the drivers of surface melting in West Antarctica is crucial for understanding future ice loss and global sea level rise. This study identifies atmospheric drivers of surface melt on West Antarctic ice shelves and ice sheet margins and relationships with tropical Pacific and high-latitude climate forcing using multidecadal reanalysis and satellite datasets. Physical drivers of ice melt are diagnosed by comparing satellite-observed melt patterns to anomalies of reanalysis near-surface air temperature, winds, and satellite-derived cloud cover, radiative fluxes, and sea ice concentration based on an Antarctic summer synoptic climatology spanning 1979–2017. Summer warming in West Antarctica is favored by Amundsen Sea (AS) blocking activity and a negative phase of the southern annular mode (SAM), which both correlate with El Niño conditions in the tropical Pacific Ocean. Extensive melt events on the Ross–Amundsen sector of the West Antarctic Ice Sheet (WAIS) are linked to persistent, intense AS blocking anticyclones, which force intrusions of marine air over the ice sheet. Surface melting is primarily driven by enhanced downwelling longwave radiation from clouds and a warm, moist atmosphere and by turbulent mixing of sensible heat to the surface by föhn winds. Since the late 1990s, concurrent with ocean-driven WAIS mass loss, summer surface melt occurrence has increased from the Amundsen Sea Embayment to the eastern Ross Ice Shelf. We link this change to increasing anticyclonic advection of marine air into West Antarctica, amplified by increasing air–sea fluxes associated with declining sea ice concentration in the coastal Ross–Amundsen Seas.

scholarly journals Topographic and Glaciological Controls on Holocene Ice-Sheet Margin Dynamics. Central West Greenland

1990 ◽  
Vol 14 ◽  
pp. 307-310 ◽  
Author(s):  
C.R. Warren ◽  
N.R.J. Hulton
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Glacial Maximum ◽  
Warm Climate ◽  
Short Term ◽  
The West ◽  
West Greenland ◽  
The Past

The retreat of the West Greenland ice sheet from its Sisimiut (Wisconsinan) glacial maximum, was punctuated by a series of Stillstands or small readvances that formed numerous moraines. These landforms have been interpreted in the past as the result of short-term, regional falls in ablation-season temperatures. However, mapping of the geomorphological evidence south of Ilulissat (Jakobshavn) suggests that retreat behaviour was not primarily governed by climate, and therefore that the former ice margins are not palaeoclimatically significant. During warm climate ice-sheet wastage, the successive quasi-stable positions adopted by the ice margin were largely governed by topography. The retreat of the inherently unstable calving glaciers was arrested only at topographically-determined locations where stability could be achieved.

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 Greenland ice sheet melt area from MODIS (2000–2014)

2020 ◽  
pp. 57-60
Author(s):  
Robert S. Fausto ◽  
Dirk Van As ◽  
Jens A. Antoft ◽  
Jason E. Box ◽  
William Colgan
Keyword(s):  
Global Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Internet Portal ◽  
Sheet Surface ◽  
Glacier Ice ◽  
Key Driver ◽  
Surface Melt ◽  
Global Sea Level ◽  
Terra Satellite

The Greenland ice sheet is an excellent observatory for global climate change. Meltwater from the 1.8 million km2 large ice sheet infl uences oceanic temperature and salinity, nutrient fl uxes and global sea level (IPCC 2013). Surface refl ectivity is a key driver of surface melt rates (Box et al. 2012). Mapping of diff erent ice-sheet surface types provides a clear indicator of where changes in ice-sheet surface refl ectivity are most prominent. Here, we present an updated version of a surface classifi cation algorithm that utilises NASA’s Moderateresolution 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 (Cuff ey & Paterson 2010). Monthly 1 km2 resolution surface-type grids can be downloaded via the CryoClim internet portal (www.cryoclim.net). In this report, we briefl y describe the updated classifi cation algorithm, validation of surface types and inter-annual variability in surface types.

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