Ground-penetrating radar (GPR) point measurements of ice thickness in Austria

Glacier thickness is an important factor in the course of glacier retreat in a warming climate. Thiese study data presents the results (point data) of GPR surveys on 66 Austrian mountain glaciers carried out between 1995 and 2014. The glacier areas range from 0.001 to 18.4 km**2, and their ice thickness has been surveyed with an average density of 36 points/km**2 . The glacier areas and surface elevations refer to the second Austrian glacier inventory (mapped between 1996 and 2002). According to the glacier state recorded in the second glacier inventory, the 64 glaciers cover an area of 223.3±3.6 km**3. Maps of glacier thickness have been calculated by Fischer and Kuhn (2013) with a mean thickness of 50±3 m and contain an glacier volume of 11.9±1.1 km**3. The mean maximum ice thickness is 119±5 m. The ice thickness measurements have been carried out with the transmitter of Narod and Clarke (1994) combined with restively loaded dipole antennas (Wu and King, 1965; Rose and Vickers, 1974) at central wavelengths of 6.5 (30 m antenna length) and 4.0 MHz (50 m antenna length). The signal was recorded trace by trace with an oscilloscope. 168 m/µs as used by Haeberli et al. (1982), Bauder (2001), and Narod and Clarke (1994), the signal velocity in air is assumed to be 300 m/µs. Details on the method can be are found in Fischer and Kuhn (2013), as well as Span et al. (2005) and Fischer et al. (2007).

Dissolved organic carbon (DOC) in Arctic ground ice, from northwest Canada, east Siberia, and Alaska

Thermal permafrost degradation and coastal erosion in the Arctic remobilize substantial amounts of organic carbon (OC) and nutrients which have accumulated in late Pleistocene and Holocene unconsolidated deposits. Permafrost vulnerability to thaw subsidence, collapsing coastlines and irreversible landscape change are largely due to the presence of large amounts of massive ground ice such as ice wedges. However, ground ice has not, until now, been considered to be a source of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and other elements which are important for ecosystems and carbon cycling. Here we show, using biogeochemical data from a large number of different ice bodies throughout the Arctic, that ice wedges have the greatest potential for DOC storage, with a maximum of 28.6 mg/L (mean: 9.6 mg/L). Variation in DOC concentration is positively correlated with and explained by the concentrations and relative amounts of typically terrestrial cations such as Mg2+ and K+. DOC sequestration into ground ice was more effective during the late Pleistocene than during the Holocene, which can be explained by rapid sediment and OC accumulation, the prevalence of more easily degradable vegetation and immediate incorporation into permafrost. We assume that pristine snowmelt is able to leach considerable amounts of well-preserved and highly bioavailable DOC as well as other elements from surface sediments, which are rapidly frozen and stored in ground ice, especially in ice wedges, even before further degradation. We found that ice wedges in the Yedoma region represent a significant DOC (45.2 Tg) and DIC (33.6 Tg) pool in permafrost areas and a freshwater reservoir of 4200 km**3. This study underlines the need to discriminate between particulate OC and DOC to assess the availability and vulnerability of the permafrost carbon pool for ecosystems and climate feedback upon mobilization.

(Table 1) Normalized difference vegetation index in control and warming plots, Abisco Research Station

Extreme winter warming events in the sub-Arctic have caused considerable vegetation damage due to rapid changes in temperature and loss of snow cover. The frequency of extreme weather is expected to increase due to climate change thereby increasing the potential for recurring vegetation damage in Arctic regions. Here we present data on vegetation recovery from one such natural event and multiple experimental simulations in the sub-Arctic using remote sensing, handheld passive proximal sensors and ground surveys. Normalized difference vegetation index (NDVI) recovered fast (2 years), from the 26% decline following one natural extreme winter warming event. Recovery was associated with declines in dead Empetrum nigrum (dominant dwarf shrub) from ground surveys. However, E. nigrum healthy leaf NDVI was also reduced (16%) following this winter warming event in experimental plots (both control and treatments), suggesting that non-obvious plant damage (i.e., physiological stress) had occurred in addition to the dead E. nigrum shoots that was considered responsible for the regional 26% NDVI decline. Plot and leaf level NDVI provided useful additional information that could not be obtained from vegetation surveys and regional remote sensing (MODIS) alone. The major damage of an extreme winter warming event appears to be relatively transitory. However, potential knock-on effects on higher trophic levels (e.g., rodents, reindeer, and bear) could be unpredictable and large. Repeated warming events year after year, which can be expected under winter climate warming, could result in damage that may take much longer to recover.