GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 281-8
Presentation Time: 9:00 AM-6:30 PM


VAN DUSEN, Ian L.1, BERBERIAN, Lori1, LARSEN, Darren J.1, GEIRSDÓTTIR, Áslaug2 and THORDARSON, Thorvaldur3, (1)Geology Department, Occidental College, Occidental Geology, Los Angeles, CA 90041, (2)Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavík, 101, Iceland, (3)Faculty of Earth Sciences, University of Iceland, Sæmundargötu 2, Reykjavik, 101, Iceland

Landscapes in the Icelandic Highlands are susceptible to soil erosional processes that can result in long-lasting, negative impacts on natural ecosystems. Geological archives, combined with observational datasets, demonstrate severe soil erosion has occurred in this region over various timescales (e.g. human to millennial) during the Holocene epoch (past ~10,000 years), and particularly during the past few millennia. However, it remains in question to what extent these landscape changes were triggered by natural forcing mechanisms (e.g. climate changes, volcanism) or the arrival of humans and their introduction of grazing livestock. This study analyzes the sediment sequence contained in Galtaból, a small (~1km2), shallow (~8-m-deep) lake in the north-central Icelandic Highlands, to determine the pattern and timing of past soil erosion events. From multiple overlapping sediment cores, we measured a suite of physical and environmental parameters related to landscape and environmental conditions, including magnetic susceptibility, greyscale reflectance, bulk density, loss on ignition, carbon and nitrogen elemental abundance and stable isotopes, and grain size distribution at multi-decadal to centennial resolution. Tephrochronology and radiocarbon dating confirm the continuous nature of the sedimentary record over the Holocene. Emerging results demonstrate that beginning ~1,500 years ago, erosional processes acting on the landscape transferred soil and terrigenous material into the lake in a manner not seen in the previous >8,000 years. This event appears to have predated the arrival of humans by over 300 years. This unprecedented landscape change is recorded by changes in sediment density, organic content, magnetic Susceptibility, greyscale, and grain size distribution. We suggest that harsh environmental conditions during the late Holocene were exacerbated by additional perturbations, including the effects of livestock grazing and tephra fall, which may have destabilized vegetation in the Highlands and led to persistent landscape instabilities. Ongiong work aims to synthesize lake sediment datasets with relict soil accumulations from the surrounding region to develop a comprehensive understanding of the timing, pattern, and underlying drivers of landscape changes in the Icelandic Highlands.