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 Surface velocity and mass balance of Livingston Island ice cap, Antarctica

2014 ◽  
Vol 8 (5) ◽  
pp. 1807-1823 ◽  
Author(s):  
B. Osmanoglu ◽  
F. J. Navarro ◽  
R. Hock ◽  
M. Braun ◽  
M. I. Corcuera
Keyword(s):  
Mass Balance ◽  
Surface Velocity ◽  
South Shetland Islands ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Ice Caps ◽  
Ice Cap ◽  
Livingston Island ◽  
Flux Gate ◽  
Frontal Ablation

Abstract. The mass budget of the ice caps surrounding the Antarctica Peninsula and, in particular, the partitioning of its main components are poorly known. Here we approximate frontal ablation (i.e. the sum of mass losses by calving and submarine melt) and surface mass balance of the ice cap of Livingston Island, the second largest island in the South Shetland Islands archipelago, and analyse variations in surface velocity for the period 2007–2011. Velocities are obtained from feature tracking using 25 PALSAR-1 images, and used in conjunction with estimates of glacier ice thicknesses inferred from principles of glacier dynamics and ground-penetrating radar observations to estimate frontal ablation rates by a flux-gate approach. Glacier-wide surface mass-balance rates are approximated from in situ observations on two glaciers of the ice cap. Within the limitations of the large uncertainties mostly due to unknown ice thicknesses at the flux gates, we find that frontal ablation (−509 ± 263 Mt yr−1, equivalent to −0.73 ± 0.38 m w.e. yr−1 over the ice cap area of 697 km2) and surface ablation (−0.73 ± 0.10 m w.e. yr−1) contribute similar shares to total ablation (−1.46 ± 0.39 m w.e. yr−1). Total mass change (δM = −0.67 &plusmn 0.40 m w.e. yr−1) is negative despite a slightly positive surface mass balance (0.06 ± 0.14 m w.e. yr−1). We find large interannual and, for some basins, pronounced seasonal variations in surface velocities at the flux gates, with higher velocities in summer than in winter. Associated variations in frontal ablation (of ~237 Mt yr−1; −0.34 m w.e. yr−1) highlight the importance of taking into account the seasonality in ice velocities when computing frontal ablation with a flux-gate approach.

scholarly journals Non-surface mass balance of glaciers in Iceland

2020 ◽  
Vol 66 (258) ◽  
pp. 685-697 ◽  
Author(s):  
Tómas Jóhannesson ◽  
Bolli Pálmason ◽  
Árni Hjartarson ◽  
Alexander H. Jarosch ◽  
Eyjólfur Magnússon ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Mass Balance ◽  
Volcanic Eruptions ◽  
Surface Mass Balance ◽  
Geothermal Heat ◽  
Surface Mass ◽  
Average Mass ◽  
Ice Cap ◽  
Geothermal Activity ◽  
Basal Melting

AbstractNon-surface mass balance is non-negligible for glaciers in Iceland. Several Icelandic glaciers are in the neo-volcanic zone where a combination of geothermal activity, volcanic eruptions and geothermal heat flux much higher than the global average lead to basal melting close to 150 mm w.e. a−1 for the Mýrdalsjökull ice cap and 75 mm w.e. a−1 for the largest ice cap, Vatnajökull. Energy dissipation in the flow of water and ice is also rather large for the high-precipitation, temperate glaciers of Iceland resulting in internal and basal melting of 20–150 mm w.e. a−1. The total non-surface melting of glaciers in Iceland in 1995–2019 was 45–375 mm w.e. a−1 on average for the main ice caps, and was largest for Mýrdalsjökull, the south side of Vatnajökull and Eyjafjallajökull. Geothermal melting, volcanic eruptions and the energy dissipation in the flow of water and ice, as well as calving, all contribute, and thus these components should be considered in mass-balance studies. For comparison, the average mass balance of glaciers in Iceland since 1995 is −500 to −1500 mm w.e. a−1. The non-surface mass balance corresponds to a total runoff contribution of 2.1 km3 a−1 of water from Iceland.

scholarly journals The importance of accurate glacier albedo for estimates of surface mass balance on Vatnajökull: Evaluating the surface energy budget in a Regional Climate Model with automatic weather station observations

2017 ◽  
Author(s):  
Louise Steffensen Schmidt ◽  
Guðfinna Aðalgeirsdóttir ◽  
Sverrir Guðmundsson ◽  
Peter L. Langen ◽  
Finnur Pálsson ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Mass Balance ◽  
Climate Model ◽  
Regional Climate ◽  
Volcanic Eruptions ◽  
Dust Storms ◽  
Surface Energy Budget ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Ice Cap

Abstract. A simulation of the surface climate of Vatnajökull ice cap, Iceland, made with the Regional Climate Model HIRHAM5 for the period 1980–2014, is used to estimate the evolution of the glacier mass balance. A new snow albedo parametrization is used for the simulation that describes the albedo with an exponential decay with time and is surface temperature dependant. The albedo scheme utilizes a new background map of the ice albedo created from observed MODIS data. The simulation is evaluated against observed daily values of weather parameters from five Automatic Weather Stations (AWSs) from 2001–2014, as well as in situ mass balance measurements from 1994–2014. The model simulates the observed parameters well at the station sites, albeit with a general underestimation of the net radiation. This is due to an underestimation of the incoming radiation and a general overestimation of the albedo. The average modelled albedo is overestimated in the ablation zone, which we attribute to an overestimation of the thickness of the snow layer and not taking dirt and volcanic ash deposition during dust storms and volcanic eruptions into account. A comparison with the specific summer, winter, and net mass balance for all of Vatnajökull from 1994–2014 shows a good overall fit during the summer, with the model underestimating the balance by only 0.04 m w.eq. on average, but a too large winter balance due to an overestimation of the precipitation at the highest areas of the ice cap. The average overestimation of the winter balance is 0.5 m w.eq., but a simple correction of the accumulation at the highest points of the glacier reduces this to 0.15 m w.eq. The model captures the evolution of the specific mass balance well, for example capturing a shift in the balance in the mid-1990s, which gives us confidence in the results for the entire model run. The model is therefore used to provide an estimate of the evolution of the specific surface mass balance of Vatnajökull from 1981, and we show the importance of bare glacier ice albedo to modelled mass balance and that processes not currently accounted for in RCMs, such as dust storms, are an important source of uncertainty in estimates of snow melt rate.

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 The importance of accurate glacier albedo for estimates of surface mass balance on Vatnajökull: evaluating the surface energy budget in a regional climate model with automatic weather station observations

2017 ◽  
Vol 11 (4) ◽  
pp. 1665-1684 ◽  
Author(s):  
Louise Steffensen Schmidt ◽  
Guðfinna Aðalgeirsdóttir ◽  
Sverrir Guðmundsson ◽  
Peter L. Langen ◽  
Finnur Pálsson ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Mass Balance ◽  
Climate Model ◽  
Regional Climate ◽  
Volcanic Eruptions ◽  
Dust Storms ◽  
Surface Energy Budget ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Ice Cap

Abstract. A simulation of the surface climate of Vatnajökull ice cap, Iceland, carried out with the regional climate model HIRHAM5 for the period 1980–2014, is used to estimate the evolution of the glacier surface mass balance (SMB). This simulation uses a new snow albedo parameterization that allows albedo to exponentially decay with time and is surface temperature dependent. The albedo scheme utilizes a new background map of the ice albedo created from observed MODIS data. The simulation is evaluated against observed daily values of weather parameters from five automatic weather stations (AWSs) from the period 2001–2014, as well as in situ SMB measurements from the period 1995–2014. The model agrees well with observations at the AWS sites, albeit with a general underestimation of the net radiation. This is due to an underestimation of the incoming radiation and a general overestimation of the albedo. The average modelled albedo is overestimated in the ablation zone, which we attribute to an overestimation of the thickness of the snow layer and not taking the surface darkening from dirt and volcanic ash deposition during dust storms and volcanic eruptions into account. A comparison with the specific summer, winter, and net mass balance for the whole of Vatnajökull (1995–2014) shows a good overall fit during the summer, with a small mass balance underestimation of 0.04 m w.e. on average, whereas the winter mass balance is overestimated by on average 0.5 m w.e. due to too large precipitation at the highest areas of the ice cap. A simple correction of the accumulation at the highest points of the glacier reduces this to 0.15 m w.e. Here, we use HIRHAM5 to simulate the evolution of the SMB of Vatnajökull for the period 1981–2014 and show that the model provides a reasonable representation of the SMB for this period. However, a major source of uncertainty in the representation of the SMB is the representation of the albedo, and processes currently not accounted for in RCMs, such as dust storms, are an important source of uncertainty in estimates of snow melt rate.

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.

scholarly journals A daily, 1 km resolution data set of downscaled Greenland ice sheet surface mass balance (1958–2015)

2016 ◽  
Vol 10 (5) ◽  
pp. 2361-2377 ◽  
Author(s):  
Brice Noël ◽  
Willem Jan van de Berg ◽  
Horst Machguth ◽  
Stef Lhermitte ◽  
Ian Howat ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Data Set ◽  
Surface Mass ◽  
Ice Caps ◽  
Elevation Model

Abstract. This study presents a data set of daily, 1 km resolution Greenland ice sheet (GrIS) surface mass balance (SMB) covering the period 1958–2015. Applying corrections for elevation, bare ice albedo and accumulation bias, the high-resolution product is statistically downscaled from the native daily output of the polar regional climate model RACMO2.3 at 11 km. The data set includes all individual SMB components projected to a down-sampled version of the Greenland Ice Mapping Project (GIMP) digital elevation model and ice mask. The 1 km mask better resolves narrow ablation zones, valley glaciers, fjords and disconnected ice caps. Relative to the 11 km product, the more detailed representation of isolated glaciated areas leads to increased precipitation over the southeastern GrIS. In addition, the downscaled product shows a significant increase in runoff owing to better resolved low-lying marginal glaciated regions. The combined corrections for elevation and bare ice albedo markedly improve model agreement with a newly compiled data set of ablation measurements.

scholarly journals The modelled surface mass balance of the Antarctic Peninsula at 5.5 km horizontal resolution

2016 ◽  
Vol 10 (1) ◽  
pp. 271-285 ◽  
Author(s):  
J. M. van Wessem ◽  
S. R. M. Ligtenberg ◽  
C. H. Reijmer ◽  
W. J. van de Berg ◽  
M. R. van den Broeke ◽  
...  
Keyword(s):  
Mass Balance ◽  
Antarctic Peninsula ◽  
Climate Model ◽  
Horizontal Resolution ◽  
Surface Mass Balance ◽  
Data Sets ◽  
High Accumulation ◽  
Surface Mass ◽  
Meltwater Runoff ◽  
The Antarctic

Abstract. This study presents a high-resolution (∼  5.5 km) estimate of surface mass balance (SMB) over the period 1979–2014 for the Antarctic Peninsula (AP), generated by the regional atmospheric climate model RACMO2.3 and a firn densification model (FDM). RACMO2.3 is used to force the FDM, which calculates processes in the snowpack, such as meltwater percolation, refreezing and runoff. We evaluate model output with 132 in situ SMB observations and discharge rates from six glacier drainage basins, and find that the model realistically simulates the strong spatial variability in precipitation, but that significant biases remain as a result of the highly complex topography of the AP. It is also clear that the observations significantly underrepresent the high-accumulation regimes, complicating a full model evaluation. The SMB map reveals large accumulation gradients, with precipitation values above 3000 mm we yr−1 in the western AP (WAP) and below 500 mm we yr−1 in the eastern AP (EAP), not resolved by coarser data sets such as ERA-Interim. The average AP ice-sheet-integrated SMB, including ice shelves (an area of 4.1  ×  105 km2), is estimated at 351 Gt yr−1 with an interannual variability of 58 Gt yr−1, which is dominated by precipitation (PR) (365 ± 57 Gt yr−1). The WAP (2.4  ×  105 km2) SMB (276 ± 47 Gt yr−1), where PR is large (276 ± 47 Gt yr−1), dominates over the EAP (1.7  ×  105 km2) SMB (75 ± 11 Gt yr−1) and PR (84 ± 11 Gt yr−1). Total sublimation is 11 ± 2 Gt yr−1 and meltwater runoff into the ocean is 4 ± 4 Gt yr−1. There are no significant trends in any of the modelled AP SMB components, except for snowmelt that shows a significant decrease over the last 36 years (−0.36 Gt yr−2).

scholarly journals Simulating the evolution of Hardangerjøkulen ice cap in southern Norway since the mid-Holocene and its sensitivity to climate change

2017 ◽  
Vol 11 (1) ◽  
pp. 281-302 ◽  
Author(s):  
Henning Åkesson ◽  
Kerim H. Nisancioglu ◽  
Rianne H. Giesen ◽  
Mathieu Morlighem
Keyword(s):  
Climate Change ◽  
Mass Balance ◽  
Ice Age ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Surface Mass ◽  
Ice Caps ◽  
Ice Cap ◽  
Length Changes

Abstract. Understanding of long-term dynamics of glaciers and ice caps is vital to assess their recent and future changes, yet few long-term reconstructions using ice flow models exist. Here we present simulations of the maritime Hardangerjøkulen ice cap in Norway from the mid-Holocene through the Little Ice Age (LIA) to the present day, using a numerical ice flow model combined with glacier and climate reconstructions. In our simulation, under a linear climate forcing, we find that Hardangerjøkulen grows from ice-free conditions in the mid-Holocene to its maximum extent during the LIA in a nonlinear, spatially asynchronous fashion. During its fastest stage of growth (2300–1300 BP), the ice cap triples its volume in less than 1000 years. The modeled ice cap extent and outlet glacier length changes from the LIA until today agree well with available observations. Volume and area for Hardangerjøkulen and several of its outlet glaciers vary out-of-phase for several centuries during the Holocene. This volume–area disequilibrium varies in time and from one outlet glacier to the next, illustrating that linear relations between ice extent, volume and glacier proxy records, as generally used in paleoclimatic reconstructions, have only limited validity. We also show that the present-day ice cap is highly sensitive to surface mass balance changes and that the effect of the ice cap hypsometry on the mass balance–altitude feedback is essential to this sensitivity. A mass balance shift by +0.5 m w.e. relative to the mass balance from the last decades almost doubles ice volume, while a decrease of 0.2 m w.e. or more induces a strong mass balance–altitude feedback and makes Hardangerjøkulen disappear entirely. Furthermore, once disappeared, an additional +0.1 m w.e. relative to the present mass balance is needed to regrow the ice cap to its present-day extent. We expect that other ice caps with comparable geometry in, for example, Norway, Iceland, Patagonia and peripheral Greenland may behave similarly, making them particularly vulnerable to climate change.

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