Constraining Runoff Source Fraction Contributions from Alpine Glaciers through the Combined Application of Geochemical Proxies and Bayesian Monte Carlo Isotope Mixing Models

Abstract:

Processes that drive glacial ablation directly impact surrounding ecosystems and communities that are dependent on glacial meltwater as a freshwater reservoir: crucially, freshwater runoff from alpine and Arctic glaciers has large implications for watershed ecosystems and contingent economies. Furthermore, glacial hydrology processes are a complex and fundamental part of understanding high-latitude environments in the modern and predicting how they might change in the future. Specifically, developing better estimates of the origin of freshwater discharge, as well as the duration and amplitude of extreme melting and precipitation events, could provide crucial constraints on these processes and allow for glacial watershed systems to be modeled more effectively.

In order to investigate the universality of the temporal and spatial melt relationships that exist in glacial systems, I investigate the isotopic composition of glacial meltwater and proximal seawater including stable isotopes δ¹⁸O and δD, which have been measured in glacial water samples I collected from the alpine Athabasca Glacier in the Canadian Rockies.

This abstract is focused on extrapolating the relative contributions of meltwater sources – snowmelt, ice melt, and summer precipitation – using a coupled statistical-chemical model (Arendt et al., 2015). I apply δ¹⁸O and δD measurements of Athabasca Glacier subglacial water samples to a Bayesian Monte Carlo (BMC) estimation scheme. Importantly, this BMC model also assesses the uncertainties associated with these meltwater fractional contribution estimations, which provides an assessment of how well the system is constrained. By defining the proportion of overall melt that is coming from snow versus ice using stable isotopes, the volume of water generated by ablation can be calculated. This water volume has two important implications. First, communities that depend on glacial water for aquifer recharge can start assessing future water resources, as glacial decline will make snowmelt the dominant water reservoir. Second, the calculated source fraction water volumes are a starting point for additional geochemical models to investigate water storage within the subglacial hydrological network.