@phdthesis {4098, title = {Quantifying sources, distribution, and processing of light absorbing aerosols in the cryosphere: A comparison of dissolved and refractory black carbon in polar and high mountain regions}, volume = {Ph.D.}, year = {2016}, school = {University of Colorado}, type = {doctoral}, address = {Boulder, CO}, abstract = {

Light absorbing aerosols (LAAs) in snow and ice are one of the least understood parameters in global climate models due to complicated physical processes within the cryosphere and too few\ in situ\ observations. Ground observations are limited due to the difficulty of collecting and preserving samples for analysis from remote environments.
In order to help build a larger repository of ground observations, this dissertation explores the concentration and composition of black carbon (BC) in snow and glacial melt-water across the polar regions in the Arctic and Antarctic, as well as major mountain regions such as the Himalayas, Rockies, and Andes Mountains.

Three state-of-the-art methods for BC detection are applied in this dissertation. The first chapter identifies chemical signatures of past and present sources of dissolved black carbon (DBC) in Antarctic lakes, utilizing a DBC molecular marker method. Here we find that DBC with a woody signature is preserved in the deep, ancient brines of Antarctic lake bottom waters. In contrast, the surface waters are enriched in BC from fossil fuels. The second chapter, which also utilizes the DBC molecular marker

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technique, explores DBC across the cryosphere. We show that DBC concentrations are surprisingly high in the bottom waters of Antarctic lakes compared to other remote regions of the cryosphere, even those located near point sources. Aged snow also contains higher DBC concentrations than fresh snow suggesting that dry deposition brings the majority of BC to the cryosphere. Additionally, the DBC composition across samples from the cryosphere are similar due to high amounts of solar exposure leading to photodegradation, except in fresh snow with a wildfire signature. The third and fourth chapters utilize the Single Particle Soot Photometer to measure refractory black carbon (rBC). The third chapter also applies spectral albedo measurements and the light absorption heating method to find that\ coal dust from an active mine in Svalbard, Norway significantly reduces the spectral reflectance of the surrounding Arctic surface snow.\ The fourth chapter reports aerosol rBC concentrations in the boundary layer of the McMurdo Dry Valleys, as well as in snow from the accumulation area of the Commonwealth Glacier. Here we determine that aerosol concentrations increase during high wind events, but there is no significant trend in deposition in the snow pit. This could be due to sporadic deposition during katabatic wind events.

These findings support the importance of real\ in-situ\ observations in order to fully understand the role of BC in the global carbon cycle. It is also evident that local environmental processes can control the concentrations and composition of BC in the cryosphere. These ground-based measurements will likely serve as ground validation for future remote sensing of snow/ice impurities and LAAs deposition models.

}, keywords = {LTER-MCM, applied sciences, black carbon, cryosphere, earth sciences, glacial melt, health and environmental sciences, light absorbing aerosols, polar regions, snow}, url = {https://search.proquest.com/docview/1834518541?accountid=14503}, author = {Khan, Alia L. and Diane M. McKnight} } @mastersthesis {4094, title = {Ecology and biogeography of freshwater diatoms in ponds of McMurdo Dry Valleys and parts of the Ross Island}, volume = {M.S.}, year = {2014}, school = {University of Colorado}, type = {masters}, address = {Boulder, CO}, abstract = {

The McMurdo Dry Valleys (MDVs) and the exposed coastal areas of the nearby Ross Island in Antarctica represent some of the coldest, driest places in the world. However, during the austral summer warmer temperatures and constant sunlight allow microbial life to flourish nearly anywhere there is water. Diatoms are single-celled algae encapsulated in a silica shell and diatom communities constitute an important component of the microbial mats that grow in the streams, lakes and ponds in these regions. As part of the Long Term Ecological Research station in the McMurdo Dry Valleys diatom communities have been studied extensively in the streams over the last 20 years. Although the diatoms present in pond microbial mats at Cape Royds have been previously studied, modern-day knowledge of the characteristics of diatom communities in ponds and small lakes throughout the region is limited. This work sought to find the relationships between water chemistry and diatom community structure in ponds. Because water flow is not a factor in ponds and small lakes, influences of salinity, nutrients, pH and other factors can be more easily distinguished. This study looked at 24 separate bodies of water in the Taylor Valley, Labyrinth region in Wright Valley, Cape Royds and McMurdo Station area on Ross Island. The results suggest that geography, dispersal and historical environmental conditions play a significant role in structuring diatom communities, in addition to water chemistry. The results also expand the knowledge of habitat preferences for some of the species present in this region.

}, keywords = {LTER-MCM, biological sciences, freshwater diatoms, health and environmental sciences, McMurdo Dry Valleys, ponds}, url = {https://search.proquest.com/docview/1655818365?accountid=14503}, author = {Sakaeva, A.}, editor = {Diane M. McKnight} }