scholarly journals An empirical algorithm to map perennial firn aquifers and ice slabs within the Greenland Ice Sheet using satellite L-band microwave radiometry

2022 ◽  
Vol 16 (1) ◽  
pp. 103-125
Author(s):  
Julie Z. Miller ◽  
Riley Culberg ◽  
David G. Long ◽  
Christopher A. Shuman ◽  
Dustin M. Schroeder ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Snow Accumulation ◽  
Rapid Expansion ◽  
Microwave Radiometry ◽  
Subsurface Water ◽  
L Band ◽  
Water Saturated

Abstract. Perennial firn aquifers are subsurface meltwater reservoirs consisting of a meters-thick water-saturated firn layer that can form on spatial scales as large as tens of kilometers. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting and high snow accumulation. Widespread perennial firn aquifers have been identified within the Greenland Ice Sheet (GrIS) via field expeditions, airborne ice-penetrating radar surveys, and satellite microwave sensors. In contrast, ice slabs are nearly continuous ice layers that can also form on spatial scales as large as tens of kilometers as a result of surface and subsurface water-saturated snow and firn layers sequentially refreezing following multiple melting seasons. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting but in areas where snow accumulation is at least 25 % lower as compared to perennial firn aquifer areas. Widespread ice slabs have recently been identified within the GrIS via field expeditions and airborne ice-penetrating radar surveys, specifically in areas where perennial firn aquifers typically do not form. However, ice slabs have yet to be identified from space. Together, these two ice sheet features represent distinct, but related, sub-facies within the broader percolation facies of the GrIS that can be defined primarily by differences in snow accumulation, which influences the englacial hydrology and thermal characteristics of firn layers at depth. Here, for the first time, we use enhanced-resolution vertically polarized L-band brightness temperature (TVB) imagery (2015–2019) generated using observations collected over the GrIS by NASA's Soil Moisture Active Passive (SMAP) satellite to map perennial firn aquifer and ice slab areas together as a continuous englacial hydrological system. We use an empirical algorithm previously developed to map the extent of Greenland's perennial firn aquifers via fitting exponentially decreasing temporal L-band signatures to a set of sigmoidal curves. This algorithm is recalibrated to also map the extent of ice slab areas using airborne ice-penetrating radar surveys collected by NASA's Operation IceBridge (OIB) campaigns (2010–2017). Our SMAP-derived maps show that between 2015 and 2019, perennial firn aquifer areas extended over 64 000 km2, and ice slab areas extended over 76 000 km2. Combined together, these sub-facies are the equivalent of 24 % of the percolation facies of the GrIS. As Greenland's climate continues to warm, seasonal surface melting will increase in extent, intensity, and duration. Quantifying the possible rapid expansion of these sub-facies using satellite L-band microwave radiometry has significant implications for understanding ice-sheet-wide variability in englacial hydrology that may drive meltwater-induced hydrofracturing and accelerated ice flow as well as high-elevation meltwater runoff that can impact the mass balance and stability of the GrIS.

scholarly journals An empirical algorithm to map perennial firn aquifers, ice slabs, and perched firn aquifers within the Greenland Ice Sheet using satellite L-band microwave radiometry

2021 ◽  
Author(s):  
Julie Z. Miller ◽  
Riley Culberg ◽  
David G. Long ◽  
Christopher A. Shuman ◽  
Dustin M. Schroeder ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Snow Accumulation ◽  
Rapid Expansion ◽  
Microwave Radiometry ◽  
Subsurface Water ◽  
L Band ◽  
Water Saturated

Abstract. Perennial firn aquifers are subsurface meltwater reservoirs formed from a water-saturated firn layer. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting and high snow accumulation. Widespread perennial firn aquifers have been identified within the Greenland Ice Sheet (GrIS) via field expeditions, airborne ice-penetrating radar surveys, and satellite microwave sensors. In contrast, ice slabs are nearly-continuous ice layers that form on spatial scales of kilometers as a result of surface and subsurface water-saturated snow and firn layers sequentially refreezing following multiple melting seasons. They have been observed within the percolation facies of glaciated regions experiencing intense seasonal surface melting, but in areas where snow accumulation is at least ~25 % lower as compared to perennial firn aquifer areas. Widespread ice slabs have recently been identified within the GrIS via field expeditions and airborne ice-penetrating radar surveys, specifically in areas where perennial firn aquifers typically do not form. However, ice slabs have yet to be inferred from space. Together, these two ice sheet features represent distinct, but related, sub-facies within the broader percolation facies of the GrIS that can be defined primarily by differences in snow accumulation, which influences the englacial hydrology and thermal characteristics of firn layers at depth. Here, for the first time, we use enhanced-resolution vertically-polarized L-band brightness temperature (TBV) imagery (2015–2019) generated using observations collected over the GrIS by NASA’s Soil Moisture Active Passive (SMAP) satellite to map both perennial firn aquifer and ice slab areas as a continuous system over the percolation facies. We also map “perched” firn aquifer areas, which we define as areas where shallow water-saturated firn layers transiently form on top of buried ice slabs, or other semi-impermeable layers within the snow and firn. An empirical algorithm previously developed to map the extent of Greenland’s perennial firn aquifers via fitting exponentially decreasing temporal L-band signatures to a set of sigmoidal curves is recalibrated to also map the extent of ice slab and perched firn aquifer areas using airborne ice-penetrating radar surveys collected by NASA’s Operation Ice Bridge (OIB) campaigns (2010–2017). Our SMAP-derived maps show that between 2015 and 2019, perennial firn aquifer areas extended over ~64,000 km2, ice slab areas extended over ~76,000 km2, and perched firn aquifer areas extended over ~37,000 km2. Combined together, these three sub-facies are the equivalent of ~24 % of the percolation facies of the GrIS. As Greenland’s climate continues to warm, and seasonal surface melting increases in extent, intensity, and duration, quantifying the possible rapid expansion of each of these sub-facies using satellite L-band microwave radiometry has significant implications for understanding ice sheet-wide variability in englacial firn hydrology resulting in meltwater-induced hydrofracturing and accelerated ice flow as well as high-elevation run-off that can impact the mass balance and stability of the GrIS.

scholarly journals Evaluation of Surface Melt on the Greenland Ice Sheet using SMAP L-Band Microwave Radiometry

2021 ◽  
pp. 1-1
Author(s):  
Mohammad Mousavi ◽  
Andreas Colliander ◽  
Julie Z. Miller ◽  
Dara Entekhabi ◽  
J. Johnson ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Microwave Radiometry ◽  
L Band ◽  
Surface Melt

Changes in Greenland ice sheet elevation attributed primarily to snow accumulation variability

Nature ◽  
2000 ◽  
Vol 406 (6798) ◽  
pp. 877-879 ◽  
Author(s):  
J. R. McConnell ◽  
R. J. Arthern ◽  
E. Mosley-Thompson ◽  
C. H. Davis ◽  
R. C. Bales ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation

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 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 Surface melting over the Greenland ice sheet from enhanced resolution passive microwave brightness temperatures (1979–2019)

2020 ◽  
Author(s):  
Paolo Colosio ◽  
Marco Tedesco ◽  
Xavier Fettweis ◽  
Roberto Ranzi
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Spatial Resolution ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Passive Microwave ◽  
High Temporal Resolution ◽  
Ice Dynamics ◽  
Enhanced Resolution

Abstract. Surface melting is a major component of the Greenland ice sheet (GrIS) surface mass balance, affecting sea level rise through direct runoff and the modulation on ice dynamics and hydrological processes, supraglacially, englacially and subglacially. Passive microwave (PMW) brightness temperature observations are of paramount importance in studying the spatial and temporal evolution of surface melting in view of their long temporal coverage (1979–to date) and high temporal resolution (daily). However, a major limitation of PMW datasets has been the relatively coarse spatial resolution, being historically of the order of tens of kilometres. Here, we use a newly released passive microwave dataset (37 GHz, horizontal polarization) made available through the NASA MeASUREs program to study the spatiotemporal evolution of surface melting over the GrIS at an enhanced spatial resolution of 3.125 Km. We assess the outputs of different detection algorithms through data collected by Automatic Weather Stations (AWS) and the outputs of the MAR regional climate model. We found that surface melting is well captured using a dynamic algorithm based on the outputs of MEMLS model, capable to detect sporadic and persistent melting. Our results indicate that, during the reference period 1979–2019 (1988–2019), surface melting over the GrIS increased in terms of both duration, up to ~4.5 (2.9) days per decade, and extension, up to 6.9 % (3.6 %) of the GrIS surface extent per decade, according to the MEMLS algorithm. Furthermore, the melting season has started up to ~4 (2.5) days earlier and ended ~7 (3.9) days later per decade. We also explored the information content of the enhanced resolution dataset with respect to the one at 25 km and MAR outputs through a semi-variogram approach. We found that the enhanced product is more sensitive to local scale processes, hence confirming the potential interest of this new enhanced product for studying surface melting over Greenland at a higher spatial resolution than the historical products and monitor its impact on sea level rise. This offers the opportunity to improve our understanding of the processes driving melting, to validate modelled melt extent at high resolution and potentially to assimilate this data in climate models.

scholarly journals Snow Accumulation Studies on the Thule Peninsula, Greenland

1968 ◽  
Vol 7 (49) ◽  
pp. 59-76 ◽  
Author(s):  
Steven J. Mock
Keyword(s):  
Regional Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
Surface Slope ◽  
Ice Flow ◽  
Accumulation Pattern ◽  
Flow Phenomena ◽  
Independent Parameters

AbstractData from stake measurements, marker boards and pits along a 136 km trail crossing the Thule peninsula sector of the Greenland ice sheet have been used to determine both the regional and local distribution of snow accumulation, On a regional scale trend surfaces of mean annual accumulation can be adequately predicted from a model using distance from moisture source and elevation as independent parameters. A series of step- or wave-like features break the smooth profile of the ice. sheet and cause profound changes in accumulation rates on a local scale. The accumulation pattern over these features can be predicted from surface slope and departure from regional elevation. Profiles of’ surface and subsurface topography indicate a direct relationship between subsurface hills and step-like features, but cannot be quantitatively accounted for by existing ice-flow theory. Detailed accumulation studies in conjunction with a program of spirit leveling in the vicinity of Camp Century has revealed the development a shallow valley-like feature. Within this feature accumulation rates have increased indicating that it is the result of flow phenomena.

scholarly journals Mass balance of the northeast sector of the Greenland ice sheet: a remote-sensing perspective

2000 ◽  
Vol 46 (153) ◽  
pp. 265-273 ◽  
Author(s):  
Eric Rignot ◽  
Guillaume Buscarlet ◽  
Beáta Csathó ◽  
Sivaprasad Gogineni ◽  
William Krabill ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Ice Shelf ◽  
Synthetic Aperture Radar Interferometry ◽  
Model Predictions ◽  
Grounding Line ◽  
Ice Production ◽  
Inland Ice

AbstractSynthetic-aperture radar interferometry data and airborne ice-sounding radar (ISR) data are employed to obtain modern estimates of the inland ice production from Nioghalvfjerdsbræ (NB) and Zachariae Isstrøm (ZI), the two largest glaciers draining the northeast sector of the Greenland ice sheet. Ice fluxes are measured at the grounding line (14.2 ±1 km3 ice a−1 for NB and 10.8 ±1 km3 ice a−1 for ZI) with an ice thickness deduced from ice-shelf hydrostatic equilibrium, and along an ISR profile collected upstream of the grounding line (14.3 ± 0.7 km3 ice a−1 for NB and 11.6 ± 0.6 km3 ice a−1 for ZI). Balance fluxes calculated from a map of snow accumulation and model predictions of surface melt are 11.9 ± 2 km3 ice a−1 for NB and 10.0 ± 2 km3 ice a−1 for ZI at the grounding line, and 12.2 and 10.3 km3 ice a−1, respectively, at the ISR line. The two glaciers therefore exhibit a negative mass balance equivalent to 14% of their balance flux, with a ±12% uncertainty. Independently, we detect a retreat of the grounding line of NB between 1992 and 1996 which is larger at the glacier center (920 ± 250 m) than on the sides (240 ± 50 m). The corresponding ice-thinning rates (2 ± 1 m a−1 at the glacier center and 0.6 ± 0.3 m a−1 on the sides) are too large to be accommodated by temporal changes in ablation or accumulation, and must be due to dynamic thinning.

scholarly journals Snow Accumulation in North Greenland

1958 ◽  
Vol 3 (24) ◽  
pp. 237-248 ◽  
Author(s):  
C. Bull
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
The Mean ◽  
Precipitation Records ◽  
Available Information ◽  
North Greenland

AbstractMeasurements of the annual snow accumulation have been made at many points on a traverse of north Greenland. In lat. 77–78° N. the annual accumulation above 1800 m. was about 13 gm. cm.−2in the years 1948–53 and, in contrast to results which have been obtained further south, did not vary with longitude. In 1953–54 the accumulation was greater. The annual accumulation in north and central Greenland has varied significantly over the last 50 years, but similar variations are not shown in the precipitation records at coastal stations. Using all the available information, the mean annual accumulation on the Greenland Ice Sheet has been calculated as 29±3 gm. cm.−2.

Sign in / Sign up

Export Citation Format

Share Document