scholarly journals Surface mass balance, ice velocity and near-surface ice temperature on Qaanaaq Ice Cap, northwestern Greenland, from 2012 to 2016

2017 ◽  
Vol 58 (75pt2) ◽  
pp. 181-192 ◽  
Author(s):  
Shun Tsutaki ◽  
Shin Sugiyama ◽  
Daiki Sakakibara ◽  
Teruo Aoki ◽  
Masashi Niwano
Keyword(s):  
Mass Balance ◽  
Snow Accumulation ◽  
Surface Mass Balance ◽  
Outlet Glacier ◽  
Near Surface ◽  
Surface Mass ◽  
Ice Cap ◽  
In Situ Data ◽  
Ice Velocity ◽  
Surface Ice

ABSTRACT To better understand the processes controlling recent mass loss of peripheral glaciers and ice caps in northwestern Greenland, we measured surface mass balance (SMB), ice velocity and near-surface ice temperature on Qaanaaq Ice Cap in the summers of 2012–16. The measurements were performed along a survey route spanning the terminus of an outlet glacier to the upper reaches (243–968 m a.s.l.). The ice-cap-wide SMB ranged from −1.10 ± 0.29 to −0.13 ± 0.26 m w.e. a−1 for the years from 2012/13 to 2015/16. Mass balance showed substantially large fluctuations over the study period under the influence of summer temperature and snow accumulation. Ice velocity showed seasonal speedup only in the summer of 2012, suggesting an extraordinary amount of meltwater penetrated to the bed and enhanced basal ice motion. Ice temperature at a depth of 13 m was −8.0°C at 944 m a.s.l., which was 2.5°C warmer than that at 243 m a.s.l., suggesting that ice temperature in the upper reaches was elevated by refreezing and percolation of meltwater. Our study provided in situ data from a relatively unstudied region in Greenland, and demonstrated the importance of continued monitoring of these processes for longer timespans in the future.

scholarly journals Strong changes in englacial temperatures despite insignificantchanges in ice thickness at Dôme du Goûter glacier (Mont-Blanc area)

2019 ◽  
Author(s):  
Christian Vincent ◽  
Adrien Gilbert ◽  
Bruno Jourdain ◽  
Luc Piard ◽  
Patrick Ginot ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Mass Balance ◽  
Snow Accumulation ◽  
Surface Mass Balance ◽  
Near Surface ◽  
Surface Mass ◽  
Precipitation Decrease ◽  
High Elevations ◽  
The Impact ◽  
Very High

Abstract. The response of very high elevation glaciated areas on Mont Blanc to climate change has been analyzed using observations and numerical modeling. Unlike the changes at low elevations, we observe very low glacier thickness changes, of about −2.6 m on the average since 1993. The slight changes in horizontal ice flow velocities and submergence velocities suggest a decrease of about 10 % in ice flux and surface mass balance. This is due to snow accumulation changes and is consistent with the precipitation decrease observed in meteorological data. Conversely, measurements performed in deep boreholes since 1994 reveal strong changes in englacial temperature reaching 1.5 °C at a depth of 50 m. We conclude that at such very high elevations, current changes in climate do not lead to visible changes in glacier thickness but cause invisible changes within the glacier in terms of englacial temperatures. Our analysis from numerical modeling shows that glacier near-surface temperature warming is enhanced by increasing melt-frequency at high elevations although the impact on surface mass balance is low. This results in a non-linear response of englacial temperature to currently rising air temperatures. In addition, borehole temperature inversion including a new dataset confirms previous findings of similar air temperature changes at high and low elevations in the Alps.

scholarly journals Simulating asymmetric growth and retreat of Hardangerjøkulen ice cap in southern Norway since the mid-Holocene

2016 ◽  
Author(s):  
Henning Åkesson ◽  
Kerim H. Nisancioglu ◽  
Rianne H. Giesen ◽  
Mathieu Morlighem
Keyword(s):  
Mass Balance ◽  
Ice Age ◽  
Dynamical Response ◽  
Surface Mass Balance ◽  
Outlet Glacier ◽  
Surface Mass ◽  
Ice Caps ◽  
Ice Cap ◽  
Length Changes ◽  
Southern Norway

Abstract. Changes to the volume of glaciers and ice caps currently amount to half of the total cryospheric contribution to sea-level rise and are projected to remain substantial throughout the 21st century. To simulate glacier behavior on centennial and longer time scales, models rely on simplified dynamics and tunable parameters for processes not well understood. Model calibration is often done using present-day observations, even though the relationship between parameters and parametrized processes may be altered for significantly different glacier states. In this study, we simulate the evolution of the Hardangerjøkulen ice cap in southern Norway from the mid-Holocene through the Little Ice Age (LIA) to the present-day. For both the calibration and transient experiments, we run an ensemble using a two-dimensional ice flow model with local mesh refinement. For the Holocene, we apply a simple surface mass balance forcing based on climate reconstructions. For the LIA until 1962, we use geomorphological evidence and measured outlet glacier positions to find a mass balance history, while from 1963 until today we use direct mass balance measurements. Given a linear climate forcing, we find that Hardangerjøkulen grew from ice-free conditions in the mid-Holocene, to its maximum LIA extent in a highly non-linear fashion. During the fastest stage of growth (2200-1200 BP), the ice cap tripled its ice volume over only 1000 years. We also reveal an intriguing spatial asymmetry during advance and retreat; the western ice cap and the northern outlet glacier Midtdalsbreen grow first and disappear first. In contrast, the eastern part, including the northeastern outlet glacier Blåisen, grows last and disappears last. Furthermore, volume and area of several outlet glaciers, as well as of the entire ice cap, vary out-of-phase for multiple centuries during the late Holocene, before varying in-phase approaching the LIA. We relate this to bed topography and the mass balance-altitude feedback, and challenge canonical linear assumptions between ice cap extent and glacier proxy records. Thus, we provide new insight into long-term dynamical response of ice caps to climate change, relevant for paleoglaciological studies and future predictions. Our model simulates ice cap extent and outlet glacier length changes from the LIA until today that are close to observations. We show that present-day Hardangerjøkulen is extremely sensitive to surface mass balance changes, mainly due to a strong mass balance-altitude feedback for the gently sloping surface topography of the ice cap.

scholarly journals Calibrating a surface mass-balance model for Austfonna ice cap, Svalbard

2007 ◽  
Vol 46 ◽  
pp. 241-248 ◽  
Author(s):  
Thomas Vikhamar Schuler ◽  
Even Loe ◽  
Andrea Taurisano ◽  
Trond Eiken ◽  
Jon Ove Hagen ◽  
...  
Keyword(s):  
Mass Balance ◽  
Snow Accumulation ◽  
Balance Model ◽  
Data Series ◽  
Model Parameters ◽  
Surface Mass Balance ◽  
Svalbard Archipelago ◽  
Accumulation Pattern ◽  
Surface Mass ◽  
Ice Cap

AbstractAustfonna (8120km2) is by far the largest ice mass in the Svalbard archipelago. There is considerable uncertainty about its current state of balance and its possible response to climate change. Over the 2004/05 period, we collected continuous meteorological data series from the ice cap, performed mass-balance measurements using a network of stakes distributed across the ice cap and mapped the distribution of snow accumulation using ground-penetrating radar along several profile lines. These data are used to drive and test a model of the surface mass balance. The spatial accumulation pattern was derived from the snow depth profiles using regression techniques, and ablation was calculated using a temperature-index approach. Model parameters were calibrated using the available field data. Parameter calibration was complicated by the fact that different parameter combinations yield equally acceptable matches to the stake data while the resulting calculated net mass balance differs considerably. Testing model results against multiple criteria is an efficient method to cope with non-uniqueness. In doing so, a range of different data and observations was compared to several different aspects of the model results. We find a systematic underestimation of net balance for parameter combinations that predict observed ice ablation, which suggests that refreezing processes play an important role. To represent these effects in the model, a simple PMAX approach was included in its formulation. Used as a diagnostic tool, the model suggests that the surface mass balance for the period 29 April 2004 to 23 April 2005 was negative (–318mmw.e.).

scholarly journals Strong changes in englacial temperatures despite insignificant changes in ice thickness at Dôme du Goûter glacier (Mont Blanc area)

2020 ◽  
Vol 14 (3) ◽  
pp. 925-934 ◽  
Author(s):  
Christian Vincent ◽  
Adrien Gilbert ◽  
Bruno Jourdain ◽  
Luc Piard ◽  
Patrick Ginot ◽  
...  
Keyword(s):  
Numerical Modelling ◽  
Mass Balance ◽  
Snow Accumulation ◽  
Surface Mass Balance ◽  
Near Surface ◽  
Surface Mass ◽  
Precipitation Decrease ◽  
High Elevations ◽  
The Impact ◽  
Very High

Abstract. The response of very-high-elevation glaciated areas on Mont Blanc to climate change has been analysed using observations and numerical modelling over the last 2 decades. Unlike the changes at low elevations, we observe very low glacier thickness changes, of about −2.6 m on average since 1993. The slight changes in horizontal ice flow velocities and submergence velocities suggest a decrease of about 10 % in ice flux and surface mass balance. This is due to less snow accumulation and is consistent with the precipitation decrease observed in meteorological data. Conversely, measurements performed in deep boreholes since 1994 reveal strong changes in englacial temperature reaching a 1.5 ∘C increase at a depth of 50 m. We conclude that at such very high elevations, current changes in climate do not lead to visible changes in glacier thickness but cause invisible changes within the glacier in terms of englacial temperatures. Our analysis from numerical modelling shows that glacier near-surface temperature warming is enhanced by increasing melt frequency at high elevations although the impact on surface mass balance is low. This results in a non-linear response of englacial temperature to currently rising air temperatures. In addition, borehole temperature inversion including a new dataset confirms previous findings of similar air temperature changes at high and low elevations in the Alps.

scholarly journals Sensitivity of net mass-balance estimates to near-surface temperature lapse rates when employing the degree-day method to estimate glacier melt

2009 ◽  
Vol 50 (50) ◽  
pp. 80-86 ◽  
Author(s):  
Alex S. Gardner ◽  
Martin Sharp
Keyword(s):  
Mass Balance ◽  
Lapse Rate ◽  
Surface Mass Balance ◽  
Near Surface ◽  
Surface Mass ◽  
Degree Day ◽  
Ice Cap ◽  
Air Temperatures ◽  
Free Air ◽  
Lapse Rates

AbstractGlacier mass-balance models that employ the degree-day method of melt modeling are most commonly driven by surface air temperatures that have been downscaled over the area of interest, using digital elevation models and assuming a constant free air lapse rate that is often taken to be the moist adiabatic lapse rate (MALR: –6.5°Ckm–1). Air-temperature lapse rates measured over melting glacier surface are, however, consistently less steep than free air values and have been shown to vary systematically with lower-tropospheric temperatures. In this study, the implications of including a variable near-surface lapse rate in a 26 year (1980–2006) degree-day model simulation of the surface mass balance of Devon Ice Cap, Nunavut, Canada, are examined and compared with estimates derived from surface air temperatures downscaled using a constant near-surface lapse rate equal to the measured summer mean (–4.9°Ckm–1) and the MALR. Our results show that degree-day models are highly sensitive to the choice of lapse rate. When compared with 23 years of surface mass-balance measurements from the northwest sector of the ice cap, model estimates are significantly better when surface air temperatures are downscaled using a modeled daily lapse rate rather than a constant lapse equal to either the summer mean or the MALR.

scholarly journals Reconstruction of historical surface mass balance, 1984–2017 from GreenTrACS multi-offset ground-penetrating radar

2020 ◽  
pp. 1-10
Author(s):  
Tate G. Meehan ◽  
H. P. Marshall ◽  
John H. Bradford ◽  
Robert L. Hawley ◽  
Thomas B. Overly ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ground Penetrating Radar ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Surface Mass Balance ◽  
Snow Density ◽  
Surface Mass ◽  
Age Model ◽  
Ground Penetrating ◽  
Good Agreement

Abstract We present continuous estimates of snow and firn density, layer depth and accumulation from a multi-channel, multi-offset, ground-penetrating radar traverse. Our method uses the electromagnetic velocity, estimated from waveform travel-times measured at common-midpoints between sources and receivers. Previously, common-midpoint radar experiments on ice sheets have been limited to point observations. We completed radar velocity analysis in the upper ~2 m to estimate the surface and average snow density of the Greenland Ice Sheet. We parameterized the Herron and Langway (1980) firn density and age model using the radar-derived snow density, radar-derived surface mass balance (2015–2017) and reanalysis-derived temperature data. We applied structure-oriented filtering to the radar image along constant age horizons and increased the depth at which horizons could be reliably interpreted. We reconstructed the historical instantaneous surface mass balance, which we averaged into annual and multidecadal products along a 78 km traverse for the period 1984–2017. We found good agreement between our physically constrained parameterization and a firn core collected from the dry snow accumulation zone, and gained insights into the spatial correlation of surface snow density.

scholarly journals Observationally constrained surface mass balance of Larsen C ice shelf, Antarctica

2017 ◽  
Vol 11 (6) ◽  
pp. 2411-2426 ◽  
Author(s):  
Peter Kuipers Munneke ◽  
Daniel McGrath ◽  
Brooke Medley ◽  
Adrian Luckman ◽  
Suzanne Bevan ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Regional Climate ◽  
Snow Accumulation ◽  
Airborne Radar ◽  
Surface Mass Balance ◽  
Spatial And Temporal Patterns ◽  
Ice Shelf ◽  
The West ◽  
Surface Mass

Abstract. The surface mass balance (SMB) of the Larsen C ice shelf (LCIS), Antarctica, is poorly constrained due to a dearth of in situ observations. Combining several geophysical techniques, we reconstruct spatial and temporal patterns of SMB over the LCIS. Continuous time series of snow height (2.5–6 years) at five locations allow for multi-year estimates of seasonal and annual SMB over the LCIS. There is high interannual variability in SMB as well as spatial variability: in the north, SMB is 0.40 ± 0.06 to 0.41 ± 0.04 m w.e. year−1, while farther south, SMB is up to 0.50 ± 0.05 m w.e. year−1. This difference between north and south is corroborated by winter snow accumulation derived from an airborne radar survey from 2009, which showed an average snow thickness of 0.34 m w.e. north of 66° S, and 0.40 m w.e. south of 68° S. Analysis of ground-penetrating radar from several field campaigns allows for a longer-term perspective of spatial variations in SMB: a particularly strong and coherent reflection horizon below 25–44 m of water-equivalent ice and firn is observed in radargrams collected across the shelf. We propose that this horizon was formed synchronously across the ice shelf. Combining snow height observations, ground and airborne radar, and SMB output from a regional climate model yields a gridded estimate of SMB over the LCIS. It confirms that SMB increases from north to south, overprinted by a gradient of increasing SMB to the west, modulated in the west by föhn-induced sublimation. Previous observations show a strong decrease in firn air content toward the west, which we attribute to spatial patterns of melt, refreezing, and densification rather than SMB.

scholarly journals Local surface mass-balance reconstruction from a tephra layer – a case study on the northern slope of Mýrdalsjökull, Iceland

2016 ◽  
Vol 63 (237) ◽  
pp. 79-87 ◽  
Author(s):  
CHRISTOPH MAYER ◽  
JULIA JAENICKE ◽  
ASTRID LAMBRECHT ◽  
LUDWIG BRAUN ◽  
CHRISTOF VÖLKSEN ◽  
...  
Keyword(s):  
Mass Balance ◽  
Volcanic Eruptions ◽  
Surface Mass Balance ◽  
Ablation Zone ◽  
Tephra Layer ◽  
Surface Geometry ◽  
High Accumulation ◽  
Surface Mass ◽  
Ice Caps ◽  
Ice Cap

ABSTRACTMost Icelandic glaciers show high-accumulation rates during winter and strong surface melting during summer. Although it is difficult to establish and maintain mass-balance programs on these glaciers, mass-balance series do exist for several of the ice caps (Björnsson and others, 2013). We make use of the frequent volcanic eruptions in Iceland, which cause widespread internal tephra layers in the ice caps, to reconstruct the surface mass balance (SMB) in the ablation zone. This method requires information about surface geometry and ice velocity, derived from remote-sensing information. In addition, the emergence angle of the tephra layer needs to be known. As a proof-of-concept, we utilize a prominent tephra layer of the Mýrdalsjökull Ice Cap to infer local SMB estimates in the ablation area back to 1988. Using tephra-layer outcrop locations across the glacier at different points in time it is possible to determine local mass changes (loss and redistribution) for a large part of the ablation zone, without the use of historic elevation models, which often are not available.

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 A regression model for the mass-balance distribution of the Vatnajökull ice cap, Iceland

2003 ◽  
Vol 37 ◽  
pp. 189-193 ◽  
Author(s):  
Guðefinna Aðalgeirsdóttir ◽  
G. Hilmar Gudmundsson ◽  
Helgi Björnsson
Keyword(s):  
Linear Regression ◽  
Regression Model ◽  
Mass Balance ◽  
Surface Mass Balance ◽  
Negative Mass ◽  
Equilibrium Line Altitude ◽  
Surface Mass ◽  
Ice Cap ◽  
Maximum Value ◽  
Slope Direction

AbstractA non-linear regression model describing the mass-balance distribution of the whole Vatnajökull ice cap, Iceland, for the years 1992–2000 is presented. All available data from some 40 locations over this 9 year period were used to determine the parameters of the model. The regression model uses six adjustable parameters which all have a clear physical interpretation. They are the slope, direction and the height of the equilibrium-line altitude (ELA) plane, two altitude mass-balance gradients, and a maximum value of the surface mass balance. It is found that the temporal variation of the observed mass-balance distribution can be accurately described through annual shifts of the ELA. Annual shifts in ELA are on the order of 100 m, which is of the same magnitude as the change expected to be caused by the climate variation predicted during the next decades. A slight trend towards a more negative mass balance is detected during this 9 year period.

Sign in / Sign up

Export Citation Format

Share Document