Ice Surface Changes Research Articles

Evaluation of Sea Ice Radiative Forcing according to Surface Albedo and Skin Temperature over the Arctic from 1982–2015

Rapid warming of the Arctic has resulted in widespread sea ice loss. Sea ice radiative forcing (SIRF) is the instantaneous perturbation of Earth’s radiation at the top of the atmosphere (TOA) caused by sea ice. Previous studies focused only on the role of albedo on SIRF. Skin temperature is also closely related to sea ice changes and is one of the main factors in Arctic amplification. In this study, we estimated SIRF considering both surface albedo and skin temperature using radiative kernels. The annual average net-SIRF, which consists of the sum of albedo-SIRF and temperature-SIRF, was calculated as −54.57 ± 3.84 W/m2 for the period 1982–2015. In the net-SIRF calculation, albedo-SIRF and temperature-SIRF made similar contributions. However, the albedo-SIRF changed over the study period by 0.12 ± 0.07 W/m2 per year, while the temperature-SIRF changed by 0.22 ± 0.07 W/m2 per year. The SIRFs for each factor had different patterns depending on the season and region. In summer, rapid changes in the albedo-SIRF occurred in the Kara and Barents regions. In winter, only a temperature-SIRF was observed, and there was little difference between regions compared to the variations in albedo-SIRF. Based on the results of the study, it was concluded that the overall temperature-SIRF is changing more rapidly than the albedo-SIRF. This study indicates that skin temperatures may have a greater impact on the Arctic than albedo in terms of sea ice surface changes.

Ice surface changes during recent glacial cycles along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica

Reconstructing past ice-sheet surface changes is key to testing and improving ice-sheet models. Data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past, present and future climate change. Here, we report the first cosmogenic multi-nuclide (10Be, 26Al, 36Cl) data from bedrock and erratics on nunataks along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica. Spanning elevations between 741 and 2394 m above sea level, the samples have apparent exposure ages between 2 ka and 5 Ma. The highest-elevation bedrock sample indicates (near-) continuous minimum exposure since the Pliocene, with a low apparent erosion rate of 0.15 ± 0.03 m Ma−1, which is similar to results from eastern Dronning Maud Land. In contrast to studies in eastern Dronning Maud Land, however, our data show clear indications of a thicker-than-present ice sheet within the last glacial cycle, with a thinning of ∼35–120 m during the Holocene (∼2–11 ka). Difficulties in separating suitable amounts of quartz from the often quartz-poor rock-types in the area, and cosmogenic nuclides inherited from exposure prior to the last deglaciation, prevented robust thinning estimates from elevational profiles. Nevertheless, the results clearly demonstrate ice-surface fluctuations of several hundred meters between the current grounding line and the edge of the polar plateau for the last glacial cycle, a constraint that should be considered in future ice-sheet model simulations.

Glacier decline in the Central Andes (33°S): Context and magnitude from satellite and historical data

Central Andes (33°S) represent a water-scarce region. During arid years, glacier runoff may constitute the main hydrological input at warm season and hence a steadfast deglacierization may represent a decrease in the regional water-budget. Ice-retreat enables landscape transitions from proglacial towards a paraglacial environment, allowing the formation of newly formed cryogenic deposits. Ice-surface changes in the Central Andes (33°S), including the high-mountain areas from Aconcagua, Mendoza and Maipo basins (Argentina and Chile), were studied using digitalized maps, aerial photographs, Landsat (1–8) and Sentinel-2A data for the period between 1956 and 2015. Band ratio and Normalized Difference Snow Index (NDSI) methods were tested using Landsat 8 and Sentinel-2A data for comparison. Geomorphological changes were assessed at Monos de Agua catchment (2750–4000 m a.s.l.) in the Aconcagua basin (Chile) as a regionally representative landscape transition case. Regional glacier shrinkage of 46 ± 5% between 1956 and 2016 was observed for the Central Andean sub-basins in both Argentina and Chile at 33°S. Overall, 107.1 ± 5 km2 of newly exposed surfaces are subject to permafrost conditions. Such insights raise concern in terms of current and future environmental assessments for newly formed cryospheric elements in water scarce regions.

Recent advances in understanding Antarctic subglacial lakes and hydrology.

It is now well documented that over 400 subglacial lakes exist across the bed of the Antarctic Ice Sheet. They comprise a variety of sizes and volumes (from the approx. 250 km long Lake Vostok to bodies of water less than 1 km in length), relate to a number of discrete topographic settings (from those contained within valleys to lakes that reside in broad flat terrain) and exhibit a range of dynamic behaviours (from ‘active’ lakes that periodically outburst some or all of their water to those isolated hydrologically for millions of years). Here we critique recent advances in our understanding of subglacial lakes, in particular since the last inventory in 2012. We show that within 3 years our knowledge of the hydrological processes at the ice-sheet base has advanced considerably. We describe evidence for further ‘active’ subglacial lakes, based on satellite observation of ice-surface changes, and discuss why detection of many ‘active’ lakes is not resolved in traditional radio-echo sounding methods. We go on to review evidence for large-scale subglacial water flow in Antarctica, including the discovery of ancient channels developed by former hydrological processes. We end by predicting areas where future discoveries may be possible, including the detection, measurement and significance of groundwater (i.e. water held beneath the ice-bed interface).

Change detection based on a support vector data description that treats dependency

Change detection is of great interest in many applications where image processing is involved; it is an essential step of image analysis in various applications, including remote sensing (e.g., assessing changes in a forest ecosystems), surveillance (e.g., monitoring ice surface changes to detect glacier flows and detecting changes caused by forest defoliation), and medical diagnosis (e.g., monitoring tumor growth). This paper aims to classify changes in multi-acquisition data using kernel-based support vector data description (SVDD). SVDD is a well-known method that enables one to map the data into a high-dimensional feature space in which a hypersphere encloses most patterns belonging to the unchanged class. In this work, we propose a new kernel function that combines the characteristics of basic kernel functions with new information about the feature distribution and the dependencies among samples. The dependencies among samples are characterized using copula theory; to our knowledge, this is the first time copula theory has been used in the SVDD framework. We demonstrate that the proposed kernel function is robust and has higher performance compared with classical support vector machine (SVM) and support vector data description (SVDD) methods.

Topography Mapping With a Portable Real-Aperture Radar Interferometer

In this letter, the requirements to derive topography from a portable terrestrial radar interferometer are introduced, the instrument design and the relationship between interferometric phase shift and surface topography are explained, and two examples of topographic maps from measurements at the Rhone glacier and Grabengufer rock glacier in Switzerland are presented. In the first case, an external digital elevation model was used to assess the error of topography mapping with the portable radar interferometer and to analyze ice surface changes of the glacier in the last 14 years. We found that the height error standard deviation is about 3 m within a distance of 2 km from the sensor and observed massive thinning of the Rhone glacier. In the second case, we used the terrestrial radar interferometer in order to measure the height difference between August 2009 and March 2010 over the rock glacier as a consequence of its destabilization.

Linkage of cave-ice changes to weather patterns inside and outside the cave Eisriesenwelt (Tennengebirge, Austria)

Abstract. The behaviour of perennial ice masses in karst caves in relation to the outside climate is still not well understood, though a significant potential of the cave-ice for paleo-climate reconstructions could be expected. This study investigates the relationship between weather patterns inside and outside the cave Eisriesenwelt (Austrian Alps) and ice-surface changes of the ice-covered part of the cave from meteorological observations at three sites (outside the cave, entrance-near inside and in the middle section of the cave) including atmospheric and ice surface measurements as well as an ablation stake network. Whereas ice loss in summer was a general feature from stake measurements for almost all measurement sites in the cave in 2007, 2008 and 2009 (values up to −15 cm yr−1), a clear seasonal signal of ice accumulation (e.g. in spring as expected from theory) was not observed. It is shown that under recent climate the cave ice mass balance is more sensitive to winter climate for the inner measurement site and sensitive to winter and summer climate for the entrance-near site. Observed ice surface changes can be well explained by cave atmosphere measurements, indicating a clear annual cycle with weak mass loss in winter due to sublimation, stable ice conditions in spring until summer (autumn for the inner measurement site) and significant melt in late summer to autumn (for the entrance-near site). Interestingly, surface ice melt did not contribute to ablation at the inner site. It is obvious from the spatial sample of ice surface height observations that the ice body is currently in rather balanced state, though the influence of show-cave management on ice mass-balance could not be clearly quantified (but a significant input on accumulation for some parts of the cave is rather plausible).

Elevated East Antarctic outlet glaciers during warmer-than-present climates in southern Victoria Land

We document Plio-Pleistocene changes in the level of Taylor Glacier, an outlet glacier in southern Victoria Land that drains Taylor Dome on the periphery of the East Antarctic Ice Sheet (EAIS). Chronologic control comes from 3He cosmogenic-nuclide analyses of 27 boulders sampled from drifts and moraines in Kennar Valley, a small hanging valley that opens onto a peripheral lobe of Taylor Glacier in the Quartermain Mountains. Assuming a constant boulder-erosion rate of 10 cm Myr −1, our preferred age model spans the last 3.1 Myr and calls for stepped ice recession from a local highstand ~ 200 m above the present base of Taylor Glacier at the mouth of Kennar Valley. The texture and sedimentology of all mapped moraines and drifts indicate deposition from cold-based ice, analogous with the modern Taylor Glacier at the mouth of Kennar Valley. The Kennar Valley glacial record shows an uncharacteristic relationship with average global temperatures, exhibiting higher-than-present ice levels during globally warm periods, including the Pliocene climatic optimum (~ 3.1 Ma) and Marine Oxygen Isotope Stage (MIS) 31 (~ 1.07 Ma). The Kennar Valley record also suggests that the rate of ice-surface lowering accelerated after the mid-Pleistocene transition at ~ 0.9 Ma. Correlation of our moraine record with published reports for fluctuations of Taylor Glacier elsewhere in the Quartermain Mountains, and with a dated moraine record from Ferrar Glacier (a second outlet for Taylor Dome), reveals similar ice-surface changes, highlighting minor, but widespread ice recession in southern Victoria Land since the mid- to late-Pliocene. Our record for minimal variability in the East Antarctic Ice Sheet contrasts with recent data from nearby marine cores that call for dynamic fluctuations in the volume of grounded ice in the Ross Embayment, and significant reduction of the West Antarctic Ice Sheet (WAIS) during warmer-than-present intervals. Taken together, these records from the Ross Embayment call for considerable variation in the response of marine-based West Antarctic ice and terrestrial East Antarctic outlet glaciers during Plio-Pleistocene time.

Electric resistance of water films on the surface of ice near the phase transition temperature

The electric resistance of the surface layer of a polycrystalline sample of freshwater ice has been measured on heating the sample up to the melting temperature. At the onset of ice melting, a monotonic decrease in the resistance of the ice surface changes to growth, and this again is followed by decrease in the course of melting. In the growth stage, the resistance exhibited a more than twofold increase. The observed behavior is related to breakage of a quasi-liquid surface layer possessing a higher conductivity, which is replaced by a layer of liquid water with a low conductivity.

A drop in mid‐summer shortwave radiation induced by changes in the ice‐surface condition in the central Arctic

Ice‐surface changes during summer and effects on solar heat input in the Arctic were analyzed using incoming shortwave radiation data from drifting buoys deployed in 2002, 2003, and 2004 as part of the North Pole Environmental Observatory project. Observed shortwave radiation was about half of the incoming shortwave radiation at the top of the atmosphere during early summer, suggesting cloudy skies. In each year, events occurred after mid‐summer during which time the shortwave radiation decreased 33% to one third of shortwave radiation at the top of the atmosphere. Snow‐depth data, aerial photos, and date of melt onset at the buoy site suggest that a decrease in snow/ice albedo induced by snow melting and melt‐pond formation modified the amount of shortwave radiation through multiple reflections. A simplified calculation of the ice‐albedo feedback revealed that the drop in shortwave radiation after mid‐summer was self damping.

Surface potentials of ice and thunderstorm charge separation

There is no general agreement on the nature of the mechanism which causes thunderstorms to become electrified1,2. Many scientists believe that charge is transferred when ice crystals collide with hailstones, and that subsequent gravitational separation results in field growth to breakdown magnitudes. Buser and Auf dermaur3 have proposed that the charging results from differences in the surface potential of ice. The measurements described here suggest that the surface potential of polycrystalline ice, such as would occur in a thunderstorm, is related simply to its past growth history. The sudden step in potential postulated by Buser and Aufdermaur as the ice surface changes from an evaporating to a growing state could not be detected. However, a natural hailstone grows by riming as it collects supercooled droplets, and these new measurements suggest that this effect results in much larger changes in surface potential.