T250 On the Edge—New Insights into Ice-Marginal Conditions II

Friday, 30 October 2020
10:00 AM - 2:00 PM
Meeting Rooms

QGG MARIE MORISAWA AWARD: EROSIONAL AND ECOLOGICAL RESPONSE TO CLIMATE CHANGE IN A PERIGLACIAL LANDSCAPE 14-8 KA, CENTRAL APPALACHIA

Paper number: T250-8
Program: Technical Sessions
Time: 11:05 AM – 11:20 AM

Authors

Abstract

Thawing permafrost landscapes are important exporters of carbon and sediment. Warming impacts hydrology and surface processes but also ecology through changes in dominant vegetation. Ecology, in turn, affects a landscape’s sediment, water and carbon budget. This has implications for the rapidly changing modern Arctic, yet feedbacks between erosion, vegetation and carbon export under warming remain unclear. Analog sites from ancient permafrost landscapes south of the extent of the Laurentide ice sheet show large-scale vegetation change during deglaciation, but comparatively little work has been done on the sedimentary records of these sites, particularly their depositional process, rate, and timing. Here we target sediments preserved in a central Appalachian peat bog to understand sedimentation of a permafrost landscape across the last deglacial warming. We use ground-penetrating radar, radiocarbon and geochemistry to quantify sedimentation volume, style, and provenance, and correlate depositional changes to global climate and local vegetation change. We show how bulk geochemistry in sediments track the relative contribution of dust versus locally derived sediment. Solifluction, which deposited coarse debris on basin margins, was active as late as ~14 ka; however, in the bog center, both peat and clastic sedimentation rates, controlled mostly by dust, were low through the warming associated with the Bolling-Allerod (BA) ~15-13 ka. This sedimentation history, paired with the expansion of grasses in the basin during the BA, leads us to conclude the area remained dry despite warming through the Younger Dryas (YD). In contrast, between ~10-9 ka, water level rose rapidly, concurrent with deposition of fines on basin margins, which we interpret as effects of increased rainfall and slopewash. Post-YD sediment geochemically resembles dust more than BA sediments despite negligible dust flux in the early Holocene, implying a flushing of dust stored on hillslopes that had not occurred during the drier BA. Thus, we interpret that during late glacial warming, hillslope processes were driven predominantly by temperature changes rather than moisture. In contrast, during early Holocene warming, increased rainfall enhanced erosion via fluvial processes and instigated vegetation turnover in response to erosion.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357460

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