@article {4032, title = {Impacts of permafrost degradation on a stream in Taylor Valley, Antarctica}, journal = {Geomorphology}, volume = {285}, year = {2017}, month = {05/2017}, pages = {205 - 213}, abstract = {

The McMurdo Dry Valleys (MDV) of Antarctica are an ice-free landscape that supports a complex, microbially dominated ecosystem despite a severely arid, cold environment (b 5 cm water equivalent/y, \− 18 \°C mean annual air temperature). Recent observations of permafrost degradation in the coastal zones of the MDV suggest that this region is nearing a threshold of rapid landscape change. In 2012, substantial thermokarst development was observed along several kilometers of the west branch of Crescent Stream in Taylor Valley mostly in the form of bank failures, whereas the adjacent east branch was unaffected. The objective of this study was to quantify the changes to the stream banks of the west branch of Crescent Stream and to determine the impacts on the composition of the stream bed material. Three annually repeated terrestrial LiDAR scans were compared to determine the rates of ground surface change caused by thermokarst formation on the stream bank. The areal extent of the thermokarst was shown to be decreasing; however, the average vertical rate of retreat remained constant. Field measurements of bed materials indicated that the west branch and the reach downstream of the confluence (of east and west branches) consistently contained more fines than the unaffected east branch. This suggests that the finer bed material is a result of the thermokarst development on the west branch. These finer bed material compositions are likely to increase the mobility of the bed material, which will have implications for stream morphology, stream algal mat communities, and downstream aquatic ecosystems.

}, keywords = {LTER-MCM}, doi = {10.1016/j.geomorph.2017.02.009}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0169555X16308467}, author = {Sudman, Zachary and Michael N. Gooseff and Andrew G Fountain and Joseph S. Levy and Maciek K. Obryk and David J. Van Horn} } @mastersthesis {4192, title = {The impacts of thermokarst activity on a stream in the McMurdo Dry Valleys}, volume = {M.S.}, year = {2015}, month = {2015}, pages = {70}, school = {University of Colorado}, type = {masters}, address = {Boulder, CO}, abstract = {

The McMurdo Dry Valleys (MDV) of Antarctica are a unique ice-free landscape that is host to vibrant ecosystems despite the harsh environment (\<10 cm water equivalent/yr, -20\°C mean air temperature). Aquatic ecosystems in the MDV are dependent on the ephemeral glacial runoff streams which feed the closed basin perennially ice covered lakes. The upland zones of the Dry Valleys have been shown to have some of the slowest ground surface change rates in the world. However, recent observations in the coastal valley transition zones suggest that this area may be nearing a threshold of rapid landscape change.

One of the recent observations that supports this idea is the discovery of extensive thermokarst degradation (permafrost thaw features) along the banks of Crescent Stream in Taylor Valley. In 2012, a large stretch of the West Branch of Crescent Stream was found to have significant thermokarst bank failures, while the adjacent East Branch was found to be unaffected. The thermokarst impacts within this setting are important to understand because of the disturbances that massive sediment loading can impose on downstream biological communities.

Annually repeated terrestrial LiDAR scans (3) were compared to determine the rates of ground surface change due to thermokarst degradation. It was found that the areal extent of the thermokarst was decreasing, however the average linear rates of retreat remained constant. Field measurements including, pebble counts, fine sediment counts, and sieve samples were analyzed to determine the effects of the thermokarst on the stream bed material. It was found that the West Branch and the reach downstream of the confluence were consistently finer than the unaffected East Branch. This suggests that the finer bed material is due to the thermokarst bank degradation. Stream power was calculated for multiple reaches to be used as a metric for the mobilization of the streambed material. It was found that both branches infrequently experience flows substantial enough to mobilize the bed material. Even the finer bed material of the impacted West Branch reach required flows that had a 5 \% chance of exceedance for mobilization of the bed. These findings suggest the West Branch of Crescent Stream and the biota supported by this branch of the stream, continue to adjust to the sediment introduced from the thermokarst bank degradation.

}, keywords = {LTER-MCM, Antarctica, Dry valleys, earth sciences, stream, thermokarst}, url = {https://search.proquest.com/docview/1717582573}, author = {Sudman, Zachary and Michael N. Gooseff} }