Climate variability and patterns of deposition in subalpine lakes during the late Holocene and Anthropocene, Glacier National Park, Montana, USA
Abstract
Lake sediment cores reflect changing environmental conditions as well as the complexities of spatial sediment sourcing, transport and deposition. In alpine valleys, glacier advance and retreat is largely responsible for driving sediment flux. The source region of transportable sediment within the basin (valley floor, hillslopes, glacier headwall, channels) also evolves with the glacier footprint and therefore with climate. Basin hydrology and sediment transport is likely to be enhanced due to ice loss during glacial retreat. Organic deposition in alpine lakes is also sensitive to climate and glacier proximity. A sequence of lakes within two major valleys in the Many Glacier region of Glacier National Park, Montana, USA have multiple sediment sources which include glacial erosion, hillslope processes, and fluvial environments between lakes. We focus on a downlake transect of cores from Fishercap Lake in the Swiftcurrent Valley to better understand variability in organic and inorganic deposition in the lake, and compare this to lake core records in the adjacent Grinnell Valley.
Fishercap Lake is less than 0.25 square km , shallow (~0.8 m), with a dense gravel layer less than a meter below the sediment-water interface that is uniform across the lake. Radiocarbon ages at the gravel unit, which may reflect a period of non-deposition/erosion or partial lake desiccation, are between ~1300-1660 AD. The most upvalley reach of the lake is 1-m deep with a basal age of 4400 radiocarbon years. High resolution C/N analyses of this core suggests changing organic sources over the late Holocene in response to climate variability during this time. In contrast, lakes in Grinnell Valley are larger and significantly deeper (10-30 m). Organic compositions are typically 1-4%, far less than in Fishercap Lake. Differences in the depositional records likely reflect lake morphology, basin hydrology, glacier proximity and geomorphic sources of sediment, despite similar drainage basin sizes and identical climate forcing during this time. These observations have implications for our interpretations of lake core records of climate change in alpine valleys.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP34B..02M
- Keywords:
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- 1630 Impacts of global change;
- GLOBAL CHANGE;
- 1807 Climate impacts;
- HYDROLOGY;
- 1824 Geomorphology: general;
- HYDROLOGY;
- 1861 Sedimentation;
- HYDROLOGY