Conventional glacier‐wide mass balances are commonly used to study the effect of climate forcing on glacier melt. Unfortunately, the glacier‐wide mass balances are also influenced by the glacier's dynamic response. Investigations on the effects of climate forcing on glaciers can be largely improved by analyzing point mass balances. Using a statistical model, we have found that 52% of the year‐to‐year deviations in the point mass balances of six glaciers distributed across the entire European Alps can be attributed to a common variability. Point mass balance changes reveal remarkable regional consistencies reaching 80% for glaciers less than 10 km apart. Compared to the steady state conditions of the 1962–1982 period, the surface mass balance changes are −0.85 m water equivalent (w.e.) a−1 for 1983–2002 and −1.63 m w.e. a−1 for 2003–2013. This indicates a clear and regionally consistent acceleration of mass loss over recent decades over the entire European Alps.
24 April 2017 in Journal of Geophysical Research: Oceans
Nioghalvfjerdsfjorden Glacier (79NG) is the largest of three marine‐terminating outlet glaciers draining the Northeast Greenland Ice Stream. To understand how Atlantic waters supply waters in the cavity beneath the floating 79NG, we analyze historic and recent bathymetric, hydrographic, and velocity observations obtained on the Northeast Greenland continental shelf. The bathymetry is characterized by a trough system, consisting of the Westwind Trough and the Norske Trough in the northern and southern part of the continental shelf, respectively. Atlantic waters recirculating in Fram Strait cross the shelf break and enter the trough system at its southeastern inlet toward the inner shelf. Warm Atlantic Intermediate Water (AIW) present below 200 m in the Norske Trough shows large contributions of the recirculating Atlantic water. We found that the bathymetry is sufficiently deep to provide a direct subsurface pathway for warm AIW between the shelf break and the 79NG cavity via the Norske Trough. Likewise, based on the hydrographic data, we show that the Norske Trough supplies AIW warmer than 1°C to the 79NG, which is not present in the Westwind Trough. Our moored and lowered velocity measurements indicate that a boundary current carries warm AIW along the northeastern slope of Norske Trough toward the 79NG. We suggest that anomalies in Atlantic water temperatures in Fram Strait could reach 79NG within less than 1.5 years, thereby modifying the glacier's basal melt rates.
Nioghalvfjerdsfjorden is a major outlet glacier in Northeast-Greenland. Although earlier studies showed that the floating part near the grounding line thinned by 30% between 1999 and 2014, the temporal ice loss evolution, its relation to external forcing and the implications for the grounded ice sheet remain largely unclear. By combining observations of surface features, ice thickness and bedrock data, we find that the ice shelf mass balance has been out of equilibrium since 2001, with large variations of the thinning rates on annual/multiannual time scales. Changes in ice flux and surface ablation are too small to produce this variability. An increased ocean heat flux is the most plausible cause of the observed thinning. For sustained environmental conditions, the ice shelf will lose large parts of its area within a few decades and ice modeling shows a significant, but locally restricted thinning upstream of the grounding line in response.
Between 2003 and 2007, North Gasherbrum Glacier on the northeastern slope of the Karakoram mountains in Asia underwent a dramatic acceleration, during which a velocity wave propagated down the glacier. There was a significant transfer of ice from up-glacier downstream, which resulted in a strong surface elevation increase over the lower tongue, but only a moderate advance of the glacier snout. We interpret this behaviour as that of a glacier surge, and we explain the observations by means of a simple version of the Kamb drainage-switching theory.
Fedchenko Glacier experienced a large thickness loss since the first scientific investigations in 1928. As the largest glacier in the Pamir Mountains, this glacier plays an important role for the regional glacier mass budget. We use a series of Global Navigation Satellite Systems observations from 2009 to 2016 and TanDEM-X elevation models from 2011 to 2016 to investigate recent elevation changes. Accounting for radar wave penetration minimizes biases in elevation that can otherwise reach up to 6 m in dry snow on Fedchenko Glacier, with mean values of 3–4 m in the high accumulation regions. The seasonal elevation changes reach up to ±5 m. The glacier surface elevation decreased along its entire length over multi-year periods. Thinning rates increased between 2000 and 2016 by a factor of 1.8 compared with 1928–2000, resulting in peak values of 1.5 m a−1. Even the highest accumulation basins above 5000 m elevation have been affected by glacier thinning with change rates between −0.2 and −0.4 m a−1 from 2009 to 2016. The estimated glacier-wide mass-balance rates are −0.27 ± 0.05 m w.e. a−1 for 2000 to 2011 and −0.51 ± 0.04 m w.e. a−1 between 2011 and 2016.
Surge-type glaciers are characterised by relatively short phases of enhanced ice transport and mass redistribution after a comparatively long quiescent phase when the glacier is virtually inactive. This unstable behaviour makes it difficult to assess the influence of climate change on those glaciers. We describe the evolution of the most recent surge of Bivachny Glacier in the Pamir Mountains, Tajikistan between 2011 and 2015 with respect to changes in its topography and dynamics. For the relevant time span, nine digital elevation models were derived from TanDEM-X data; optical satellite data (Landsat 5, 7 and 8, EO-1) as well as synthetic aperture radar data (TerraSAR-X and TanDEM-X) were used to analyse ice flow velocities. The comparison of the topography at the beginning of the surge with the one observed by the Shuttle Radar Topography Mission in 2000 revealed a thickening in the upper part of the ablation area of the glacier and a thinning further down the glacier as is typically observed during the quiescent phase. During the active phase, a surge bulge measuring up to around 80 m developed and travelled downstream for a distance of 13 km with a mean velocity of 4400 m year−1. Ice flow velocities increased from below 90 m year−1 duringthe quiescent phase in 2000 to up to 3400 m year−1 in spring 2014. After reaching the confluence with Fedchenko Glacier, the surge slowed down until it completely terminated in 2015. The observed seasonality of the glacier velocities with a regular speed-up during the onset of the melt period suggests a hydrological control of the surge related to the effectiveness of the subglacial drainage system.