ALBERT

Description: Brief communication "Snow profile associated measurements (SPAM) – a new instrument for quick snow profile measurements" The Cryosphere Discussions, 5, 1737-1748, 2011 Author(s): P. Lahtinen A new instrument concept (SPAM) for snow profile associated measurements is presented. The potential of the concept is demonstrated by presenting preliminary results obtained with the prototype instrument. With this concept it is possible to retrieve rapid snow profiles of e.g. light extinction, reflectance, temperature and snow layer structure with high vertical resolution. As a side-product, also snow depth is retrieved.

Description: Modeling the impact of wintertime rain events on the thermal regime of permafrost The Cryosphere Discussions, 5, 1697-1736, 2011 Author(s): S. Westermann, J. Boike, M. Langer, T. V. Schuler, and B. Etzelmüller In this study, we present field measurements and numerical process modeling from Western Svalbard showing that the ground surface temperature below the snow is impacted by strong wintertime rain events. During such events, rain water percolates to the bottom of the snow pack, where it freezes and releases latent heat. In the winter season 2005/2006, on the order of 20 to 50 % of the wintertime precipitation fell as rain, thus confining the surface temperature to close to 0 °C for several weeks. The measured average ground surface temperature during the snow-covered period is −0.6 °C, despite of a snow surface temperature of on average −8.5 °C. For the considered period, the temperature threshold below which permafrost is sustainable on long timescales is exceeded. We present a simplified model of rain water infiltration in the snow coupled to a transient permafrost model. While small amounts of rain have only minor impact on the ground surface temperature, strong rain events have a long-lasting impact. We show that consecutively applying the conditions encountered in the winter season 2005/2006 results in the formation of an unfrozen zone in the soil after three to five years, depending on the prescribed soil properties. If water infiltration in the snow is disabled in the model, more time is required for the permafrost to reach a similar state of degradation.

Description: Investigating changes in basal conditions of Variegated Glacier prior and during its 1982–1983 surge The Cryosphere Discussions, 5, 1461-1494, 2011 Author(s): M. Jay-Allemand, F. Gillet-Chaulet, O. Gagliardini, and M. Nodet The Variegated Glacier (Alaska) is known to surge periodically after a sufficient amount of cumulative mass balance is reached, but this observation is difficult to link with changes in the basal conditions. Here, using a 10-year dataset, consisting in surface topography and surface velocity observations along a flow line for 25 dates, we have reconstructed the evolution of the basal conditions prior and during the 1982–1983 surge. The model solves the full-Stokes problem along the central flow line using the finite element method. For the 25 dates of the dataset, the basal friction parameter distribution is inferred using the inverse method proposed by Arthern and Gudmundson (2010). This method is here slightly modified by incorporating a regularisation term in the cost function to avoid short wave length changes in the friction parameter. Our results indicate that dramatic changes in the basal conditions occurred between 1973 to 1983. Prior to the surge, periodical changes can be observed between winter and summer, with a regular increase of the sliding from 1973 to 1982. During the surge, the basal friction decreased dramatically and an area of very low friction moved from the upper part of the glacier to its terminus. Using a more complex friction law, these changes in basal sliding are then interpreted in terms of basal water pressure. It confirms that dramatic changes took place in the subglacial drainage system of Variegated Glacier, moving from a relatively efficient drainage system prior to the surge to an inefficient one during the surge. By reconstructing the water pressure evolution at the base of the glacier it is possible to infer realistic scenarios for the hydrological history leading to the occurrence of a surge.

Description: Warming of waters in an East Greenland fjord prior to glacier retreat: mechanisms and connection to large-scale atmospheric conditions The Cryosphere Discussions, 5, 1335-1364, 2011 Author(s): P. Christoffersen, R. I. Mugford, K. J. Heywood, I. Joughin, J. A. Dowdeswell, J. P. M. Syvitski, A. Luckman, and T. J. Benham Hydrographic data acquired in Kangerlugssuaq Fjord and adjacent seas in 1993 and 2004 are used together with ocean reanalysis to elucidate water mass change and ice-ocean-atmosphere interactions in East Greenland. The hydrographic data show substantial warming of fjord waters between 1993 and 2004 and warm subsurface conditions coincide with the rapid retreat of Kangerlugssuaq Glacier in 2004–2005. The ocean reanalysis shows that the warm properties of fjord waters in 2004 are related to a major peak in oceanic shoreward heat flux into a cross-shelf trough on the outer continental shelf. The heat flux into this trough varies according to seasonal exchanges with the atmosphere as well as from deep seasonal intrusions of subtropical waters. Both mechanisms contribute to high (low) shoreward heat flux when winds from the northeast are weak (strong). The combined effect of surface heating and inflow of subtropical waters is seen in the hydrographic data, which were collected after periods when along-shore coastal winds from the north were strong (1993) and weak (2004). We show that coastal winds vary according to the pressure gradient defined by a semi-permanent atmospheric pressure system over Greenland and a persistent atmospheric low situated near Iceland. The magnitude of this pressure gradient is controlled by longitudinal variability in the position of the Icelandic Low.

Description: Recent wind driven high sea ice export in the Fram Strait contributes to Arctic sea ice decline The Cryosphere Discussions, 5, 1311-1334, 2011 Author(s): L. H. Smedsrud, A. Sirevaag, K. Kloster, A. Sorteberg, and S. Sandven Arctic sea ice area decrease has been visible for two decades, and continues at a steady rate. Apart from melting, the southward drift through Fram Strait is the main loss. We present high resolution sea ice drift across 79° N from 2004 to 2010. The ice drift is based on radar satellite data and correspond well with variability in local geostrophic wind. The underlying current contributes with a constant southward speed close to 5 cm s −1 , and drives about 33 % of the ice export. We use geostrophic winds derived from reanalysis data to calculate the Fram Strait ice area export back to 1957, finding that the sea ice area export recently is about 25 % larger than during the 1960's. The increase in ice export occurred mostly during winter and is directly connected to higher southward ice drift velocities, due to stronger geostrophic winds. The increase in ice drift is large enough to counteract a decrease in ice concentration of the exported sea ice. Using storm tracking we link changes in geostrophic winds to more intense Nordic Sea low pressure systems. Annual sea ice export likely has a significant influence on the summer sea ice variability and we find low values in the 60's, the late 80's and 90's, and particularly high values during 2005–2008. The study highlight the possible role of variability in ice export as an explanatory factor for understanding the dramatic loss of Arctic sea ice the last decades.

Description: Spatio-temporal measurements and analysis of snow depth in a rock face The Cryosphere Discussions, 5, 1383-1418, 2011 Author(s): V. Wirz, M. Schirmer, S. Gruber, and M. Lehning Snow in rock faces plays a key role in the alpine environment for permafrost distribution, snow water storage or run off in spring. However, a detailed assessment of snow depths in steep rock walls has never been attempted. To understand snow distribution in rock walls a high-resolution terrestrial laser scanner (TLS), including a digital camera, was used to obtain snow depth (HS) data with a resolution of one metre. The mean HS, the snow covered area and their evolution in the rock face were compared to a neighbouring smoother catchment and a flat field station at similar elevation. Further we analyzed the patterns of HS distribution in the rock face after different periods and investigated the main factors contributing to them. In a first step we could show that with TLS reliable information on surface data of a steep rocky surface can be obtained. In comparison to the flatter sites in the vicinity, mean HS in the rock face was lower during the entire winter, but trends of snow depth changes were similar. We observed repeating accumulation and ablation patterns in the rock face, while maximum snow depth loss always occurred at those places with maximum snow depth gain. Further analysis of the main factors contributing to the snow depth distribution in the rock face revealed terrain-wind-interaction processes to be dominant. Processes related to slope angle seem to play a role, but no linear function of slope angle and snow depth was found. Further analyses should involve measurements in rock faces with other characteristics and higher temporal resolutions to be able to distinguish individual processes better. Additionally the relation of spatial and temporal distribution of snow depth to terrain-wind interactions should be tested.

Description: Utility of late summer transient snowline migration rate on Taku Glacier, Alaska The Cryosphere Discussions, 5, 1365-1382, 2011 Author(s): M. Pelto On Taku Glacier, Alaska a combination of field observations of snow water equivalent (SWE) from snowpits and probing in the vicinity of the transient snowline (TSL) are used to quantify the mass balance gradient. The balance gradient is determined from the difference in elevation and SWE from the TSL to snowpits at 1000 m from 1998–2010 and ranges from 2.6–3.8 mm m −1 . Probing transects from 950 m–1100 m directly measure SWE and yield a slightly higher balance gradient of 3.3–3.8 mm m −1 . TSL is identified in MODIS and Landsat 4 and 7 Thematic Mapper imagery for 31 dates during the 2004–2010 period on Taku Glacier to assess the consistency of its rate of rise and usefulness in assessing mass balance. In 2010, the TSL rose from 750 m on 28 July, 800 m on 5 August, 875 m on 14 August, 925 m on 30 August, and to 975 m on 20 September. The mean observed probing balance gradient was 3.3 mm m −1 and TSL rise was 3.7 m day −1 , yielding an ablation rate of 12.2 mm day −1 on Taku Glacier from mid-July to mid-September. A comparison of the TSL rise in the region from 750–1100 m on Taku Glacier during eleven different periods of more than 14 days during the ablation season with repeat imagery indicates a mean TSL rise of 3.7 m day −1 on Taku Glacier, the rate of rise is relatively consistent ranging from 3.0 to 4.8 m day −1 . This is useful for ascertaining the final ELA if imagery or observations are not available within a week or two of the end of the ablation season. From mid-July-mid-September the mean ablation from 750–1100 m determined from the TSL rise and the observed balance gradient varied from 11 to 18 mm day −1 on Taku Glacier during the 2004–2010 period.

Description: Spatial and temporal variability of snow accumulation in Dronning Maud Land, East Antarctica, including two deep ice coring sites at Dome Fuji and EPICA DML The Cryosphere Discussions, 5, 2061-2114, 2011 Author(s): S. Fujita, P. Holmlund, I. Andersson, I. Brown, H. Enomoto, Y. Fujii, K. Fujita, K. Fukui, T. Furukawa, M. Hansson, K. Hara, Y. Hoshina, M. Igarashi, Y. Iizuka, S. Imura, S. Ingvander, T. Karlin, H. Motoyama, F. Nakazawa, H. Oerter, L. E. Sjöberg, S. Sugiyama, S. Surdyk, J. Ström, R. Uemura, and F. Wilhelms To better understand the spatio-temporal variability of the glaciological environment in Dronning Maud Land (DML), East Antarctica, investigations were carried out along the 2800-km-long Japanese-Swedish IPY 2007/2008 traverse. The route covers ice sheet ridges and two deep ice coring sites at Dome Fuji and EPICA DML. The surface mass balance (SMB) distribution was derived based on analysis of isochrones within snow pits, firn cores and subsurface radar signals. The SMB averaged over various time scales in the Holocene was determined. This was then compared with various glaciological data. We find that the large-scale distribution of the SMB depends on the surface elevation, continentality and interactions between ice sheet ridges and the prevailing counterclockwise windfield in DML. A different SMB is found for the windward and leeward sides of the ridges. Local-scale variability in the SMB is essentially governed by bedrock topography which determines the local surface topography. In the eastern part of DML, the accumulation rate in the second half of the 20th century is found to be higher by 15 % compared to averages over longer periods of 722 a or 7.9 ka before AD 2008. A similar trend has been reported for many inland plateau sites in East Antarctica.

Description: Relative effect of slope and equilibrium line altitude on the retreat of Himalayan glaciers The Cryosphere Discussions, 5, 2571-2604, 2011 Author(s): T. N. Venkatesh, A. V. Kulkarni, and J. Srinivasan A majority of glaciers in the Himalayas have been retreating. In this paper, we show that there are two major factors which control the advance/retreat of the Himalayan glaciers. They are the slope of the glacier and changes in the equilibrium line altitude. While it is well known, that these factors are important, we propose a new way of combining them and use it to predict retreat. Our model has been applied to the movement of eight Himalayan glaciers during the past 25 years. The model explains why the Gangotri glacier is retreating while Zemu of nearly the same length is stationary, even though they are subject to similar environmental changes. The model has also been applied to a larger set of glaciers in the Parbati basin, for which retreat based on satellite data is available, though over a shorter time period.

Description: Brief Communication: Can recent ice discharges following the Larsen-B ice-shelf collapse be used to infer the driving mechanisms of millennial-scale variations of the Laurentide ice sheet? The Cryosphere Discussions, 5, 3113-3127, 2011 Author(s): J. Alvarez-Solas, A. Robinson, and C. Ritz The effects of an ice-shelf collapse on inland glacier dynamics have recently been widely studied, especially since the breakup of Antarctic Peninsula's Larsen-B ice shelf in 2002. Several studies have documented acceleration of the ice streams that were flowing into the former ice shelf. The mechanism responsible for such a speed-up lies with the removal of the ice-shelf backforce. Independently, it is also well documented that during the last glacial period, the Northern Hemisphere ice sheets experienced large discharges into the ocean, likely reflecting ice flow acceleration episodes on the millennial time scale. The classic interpretation of the latter is based on the existence of an internal thermo-mechanical feedback with the potential to generate oscillatory behavior in the ice sheets. Here we would like to widen the debate by considering that Larsen-B-like glacial analog episodes could have contributed significantly to the registered millennial-scale variablity.