228-2 Impact of Slope Aspect on the Preservation of the Isotopic Fingerprint of Glacial Meltwater in Mountain Groundwater Systems

Session: Advances in Mountain Hydrology: Connecting Cryosphere, Surface, and Subsurface Processes (Posters)

Presenting Author:

Authors:

Abstract:

Glacial meltwater is an important source of recharge to mountain aquifers, yet the preservation of its isotopic fingerprint in groundwater systems remains poorly quantified. Consequently, we do not fully understand how the eventual loss of glacier meltwater will affect mountain groundwater processes. This problem is compounded by the relative scarcity of data on the importance of glacial meltwater to hydrogeological and hydrogeochemical processes within and beyond the mountain block. In this study, we use chlorine-36 ratios (³⁶Cl/Cl),  tritium (³H), and results from stable isotopic mixing models to assess how slope aspect in glaciated watersheds affect the preservation of the isotope fingerprints of glacial meltwater in groundwater across two mountain systems: Glacier National Park, Montana, USA (GNP), and Mount Hood National Forest, Oregon, USA (MH). We hypothesize that the isotopic preservation of glacial meltwater will be strongly associated with ice preservation processes such that north-facing slopes will tend to retain glacial ice the longest and will preferentially preserve the isotopic fingerprint of glacial meltwater. At MH, springs emerging from north-facing slopes preserved the isotopic fingerprints of glacial meltwater signatures more than south-facing springs. However, there are fewer springs on north-facing slopes than south-facing slopes. In comparison, the isotopic fingerprint of glacial meltwater was better preserved in springs emerging from south-facing slopes in GNP. However, this is primarily due to the effects of hydrostratigraphy and not preferential ice preservation processes. As an additional test, we compare the ³⁶Cl/Cl and ³H data with elevation in both study sites. The ³H data show no correlation with elevation in MH or GNP. In fact, ³H does not appear to be robust when used solely to identify the preservation of glacial meltwater in either study site. The ³⁶Cl/Cl data shows a stronger correlation with elevation. Chlorine-36 also seems to capture the storage of bomb-pulse signals stored in glacial ice and transported in subglacial melt. Aspect is important in preserving the isotopic signal of glacial meltwater in MH, and it is likely important in GNP despite the hydrostratigraphic controls on groundwater flow. These data also show that the eventual loss of glacial ice will have detrimental effects on alpine springs and baseflow to alpine streams that are heavily dependent upon recharge from glacial meltwater.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9334

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.