03399nas a2200193   4500008004100000245013900041210006900180260005400249490001000303520272200313653001303035653000903048653002403057653001403081653001303095100002403108700002503132856004803157       2020                        eng d00aThe effect of sediment on hydrological and biogeochemical connectivity of glaciers within the McMurdo Dry Valley ecosystem, Antarctica0 aeffect of sediment on hydrological and biogeochemical connectivi  aBoulder, CObUniversity of Colorado Boulderc20200 vPh.D.3 a<p>Glaciers are an integral part of polar and alpine landscapes, providing water, inorganic, and organic material subsidies to downstream ecosystems. These subsides regulate downstream temperature, streamflow, and sediment supplies. Warming in high altitude and high latitude environments due to climate change is resulting in rapid and substantial mass loss of glaciers. In order to better predict impacts and future change to glaciers and downstream environments, we endeavor to better understand glacier physical and biogeochemical processes. Glaciers in the McMurdo Dry Valleys (MDVs) of Antarctica are very sensitive to slight changes in the energy balance. Small temperature or solar radiation increases can result in outsize increases in glacier melt, which is the main source of water for the MDV ecosystem. Sediment on the glacier surface is thought to be a key factor driving both melt and biogeochemical cycling on glaciers. This dissertation examines the distribution of sediment on the MDVs glacier surfaces, how it may have driven recent glacier morphological change, and identifies sediment-driven biogeochemical processes on the MDV glaciers. To do so, we carried out field data collection, field- and lab-based nutrient uptake experiments, geospatial analysis, and coupled sediment and energy balance modeling. We find that the glacier surfaces have changed in response to recent warm events by increasing roughness and the density of meltwater channels on the glacier surface. The increase in roughness occurred in already rough areas that serve as collection points for wind- and water-transported sediment. The rough surfaces and sediment have low albedo and can absorb a higher amount of energy, spurring additional melt. The distribution of sediment on the surface and in the top meter of ice is a reflection of patterns of wind deposition and seasonal melt on the glacier. The total amount of sediment in the top meter of ice agrees with previously measured rates of sediment deposition and follows a valley-wide pattern. The depth of the peak sediment concentration in the top meter of ice is a function of the thermal history of the glacier&ndash; both summer energy balance and winter sublimation rates. We also find that the biota living in the sediment is capable of removing nutrients from glacier melt water, modulating the amount and form of nutrients delivered to downstream ecosystems. This research clarifies the role of glaciers within the larger MDV ecosystem. It also advances our understanding of surficial glacier melt and biogeochemistry, which can improve predictions of how the functional role of glaciers within their larger ecosystems will evolve due to climate change.</p>10aglaciers10aLTER10aMcMurdo Dry Valleys10ameltwater10asediment1 aBergstrom, Anna, J.1 aGooseff, Michael, N.  uhttps://www.proquest.com/docview/240827383901744nas a2200205   4500008004100000022001400041245006100055210005900116260001200175300001400187490000700201520112200208653001501330653001301345653001701358100002401375700002401399700002101423856009401444       2016                        eng d  a0022-143000aGlaciers in equilibrium, McMurdo Dry Valleys, Antarctica0 aGlaciers in equilibrium McMurdo Dry Valleys Antarctica  c07/2016  a976 - 9890 v623 a<p>The McMurdo Dry Valleys are a cold, dry polar desert and the alpine glaciers therein exhibit small annual and seasonal mass balances, often &lt;&plusmn;0.06 m w.e. Typically, winter is the accumulation season, but significant snow storms can occur any time of year occasionally making summer the accumulation season. The yearly equilibrium line altitude is poorly correlated with mass balance because the elevation gradient of mass balance on each glacier can change dramatically from year to year. Most likely, winds redistribute the light snowfall disrupting the normal gradient of increasing mass balance with elevation. Reconstructed cumulative mass balance shows that the glaciers have lost &lt;2 m w.e. over the past half century and area changes show minimal retreat. In most cases these changes are less than the uncertainty and the glaciers are considered in equilibrium. Since 2000, however, the glaciers have lost mass despite relatively stable summer air temperatures suggesting a different mechanism in play. Whether this trend is a harbinger of future changes or a temporary excursion is unclear.</p>10aAntarctica10aglaciers10amass balance1 aFountain, Andrew, G1 aBasagic, Hassan, J.1 aNiebuhr, Spencer  uhttps://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002214301600086103517nas a2200349   4500008004100000245015900041210006900200260003400269490000900303520243200312653001502744653002002759653002402779653001402803653002802817653001702845653001302862653001402875653001402889653001302903653002402916653002002940653001402960653001702974653002102991653002103012653001503033653002003048100002503068700002503093856004903118       2011                        eng d00aHydrologic controls of nutrient fluxes in glacial meltwater streams at inter-annual, seasonal, and daily timescales in the McMurdo Dry Valleys, Antarctica0 aHydrologic controls of nutrient fluxes in glacial meltwater stre  bPennsylvania State University0 vM.S.3 a<p>In the McMurdo Dry Valleys of Antarctica, glaciers are hydrologically linked to closed-basin lakes at the valley floor by glacial meltwater streams. Streams flow through porous, well-defined channels with extensive chemically active hyporheic zones. Temporally varying dynamics of meltwater generation and sub-stream thaw depth are thought to control the potential for the hyporheic zone and benthic communities to influence transport of nutrients and dissolved ions downstream. Using the McMurdo LTER database, patterns in stream discharge, electrical conductivity (both with 15-minute sampling intervals), and solute chemistry (weekly sampling intervals) were examined on eight MDV streams from 1990-2008. Discharge and electrical conductivity values were highly variable among streams. Discharge values were highly dependent upon glacial source area, but meteorological and topographical complexities create large variability at all time scales. The longer streams were found to have much higher electrical conductivity values than the shorter streams, suggesting that there are more opportunities for hyporheic weathering reactions along longer stream reaches. Weekly sampled water solutes from each stream&#39;s entire record were plotted against the discharge recorded at the time when the sample was taken. Silicate concentrations displayed a decreasing logarithmic relationship, while nutrient concentrations had no apparent relationship. This suggests that with the exception to bioreactive solutes, the majority of hyporheic interactions could possibly be characterized by electrical conductivity and discharge. To attain information on in-stream nutrient dynamics and nutrient fluxes, glacial source water at the upper reach of Green Creek and stream outlet water at the lower reach of Green Creek were sampled hourly for two separate diel periods during the 2008-09 austral summer. Both dates were in late January under two distinct flow conditions (~0.5 L/s and ~10 L/s). Under low flow conditions, nutrient cycling was found to be uptake dominated. High flow conditions showed both uptake and regeneration with much higher nutrient loads, but as in the low flow conditions, no apparent temporal trends were found. Nutrient concentrations could not be predicted using the two parameters of discharge and electrical conductivity with in-stream nutrient dynamics likely too complicated at the sub-daily scale.</p>10aAntarctica10abiogeochemistry10achemical weathering10adischarge10aelectrical conductivity10aglacial melt10aglaciers10ahydrology10ahyporheic10aMCM LTER10aMcMurdo Dry Valleys10anutrient fluxes10anutrients10apolar desert10asolute chemistry10astream chemistry10astreamflow10awater chemistry1 aWeaver, Mitchell, R.1 aGooseff, Michael, N.  uhttps://etda.libraries.psu.edu/catalog/11568