The role of sediment in the energy balance and biogeochemistry of glaciers in the McMurdo Dry Valleys, Antarctica
Sediment, also frequently referred to as cryoconite meaning "ice dust", is deposited on the glaciers via wind. Upon deposition, due to it's lower albedo, it melts in to the glacier and is also redistributed via melt water. This sediment can change the glacier surface morphology and optical properties. It also carries with it biota that is ready to grow and utilize nutrients as soon as conditions are favorable. It is unclear how much this darker sediment influences glacier melt, and when melt water is produced, how much the release of weathering products and microbial activity alters the chemistry of the water as it flows through sediment-laden areas. This drives questions such as:
How does seasonal and interannual glacier surface change affect ablation and meltwater generation?
Where is sediment in the ice profile and how does it influence melt?
How do sediment deposits influence nutrient cycling on the glacier?
The glaciers are the headwaters of the Dry Valleys ecosystem and developing an understanding of the amount and chemical signature of water delivered to the downstream system is critical for understanding the broader ecosystem function. Additionally, fine sediment influences melt across the Antarctic continent. This work can contribute to our knowledge of the energy balance of the larger ice-masses and better predict their dynamics in the face of a changing climate.
Seasonality of solute flux and water source chemistry in a coastal glaciated watershed undergoing rapid change: Wolverine Glacier Watershed, Alaska
This research, in collaboration with the U.S. Geological Survey Alaska Science center, is focused on the changing water sources and solute fluxes of a costal glacierized watershed that is seeing rapid deglaciation. Glacierized watersheds are valuable to the ecosystem from source to the near-shore marine environment through regulating stream temperature and flow, providing critical habitat, and economic benefits such as tourism and fisheries. Glaciers in costal Alaska are rapidly loosing mass, and it is unclear the what effects are on the downstream system. As glaciers retreat and bare ground is exposed, flow pathways both subglacial and in the surrounding watershed will be altered resulting in new water sources and locations in which to acquire or loose solutes. Even in steady state there is much research to be done on the timing and location of solute and water sources in glacierized watersheds.
Can we develop a framework to analyze seasonal water and solute sources?
What is the seasonal variability of solute flux and what are the relative contributions of the glacier and the surrounding watershed?
We are conducting this study in the Wolverine Glacier watershed. The Wolverine Glacier is one of the USGS benchmark glaciers, and the subject of much glaciological research. We are capitalizing an expanding on this extensive understanding through the addition of water quality sensors at the USGS Stream Gauge and two seasons of regular water chemistry samples coupled with water quality sondes and streamflow measurements in representative locations throughout the watershed. Additionally, we are working to test transferability of a hydrometeorologic framework we developed for the Wolverine watershed to other glacierized watersheds. Glacierized watersheds are locations of high weathering and solute export, yet our estimations of total annual solute flux and seasonal dynamics of weathering are limited. This is due in part to the fact that we have limited ability to sample these systems and to scale point measurements to entire seasons. Our hydrometeorologic framework allows us to classify the flow season by shifts in the relationship between electrical conductivity and streamflow. We can use the shifting dynamics of these easily collected datasets to better understand shifting solute sources but also contextualize point sampling and compare hydrologic function across glacierized watersheds.
The spatial distribution of hydrologic exchange between hillslopes, valley bottoms, and streams
Hydrologists have been studying how watershed structure influences the patterns of water transfer from hillslopes to streams for over 100 years. Yet we are still challenged to find definitive scaling laws between watershed area and streamflow. This work focused on the influence of watershed structural elements in the exchange of water between hillslopes, the valley bottom, and the stream and how this evolves from peak snowmelt to late summer baseflow. We used dilution gauging to develop rating curves at 52 stage recording stations nested as subwatersheds in the U.S. Forest Service Tenderfoot Creek Experimental Forest. We coupled this continuous discharge record with a series of mass recovery measurements throughout the season to quantify gross hydrologic gains and losses. We found that watershed area is only a significant predictor at large spatial scales and high flow states. As you move to smaller spatial scales, the movement of water into and out of the channel overwhelms the influence of contributing area on the discharge observed at a point. Gross hydrologic gains and losses in this setting were strongly controlled by the underlying lithology and the number of in-channel steps respectively.