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Nancy H. Bigelow

Publications and source records attributed to Nancy H. Bigelow.

3 recordsLinked to original sources
USGS2025

Assessing coastal wetland carbon and mineral accumulation response to changing climate, Cape Espenberg, Alaska

The Arctic is experiencing warming and ecological shifts due to climate change and the compounding effects of polar amplification. Arctic Alaskan coastal marsh environments, such as the Cape Espenberg barrier beach system, offer an opportunity to determine the carbon cycle response to changing climate by examining sediment records that have been preserved through time as shoreline-parallel, linear geometry prograding geomorphic features. This study determines the carbon and mineral accumulation trends in marsh environments at Cape Espenberg for both paleo (~776 CE to 1850 CE) and modern (post-1850 CE) time frames. A comprehensive physical and chemical dataset, including radioisotope (137Cs, 210Pb, 14C), stable isotope (δ13C), element concentration (%C, %N, C:N), and dry bulk density, has been built for several sediment cores. Results indicate that carbon and mineral accumulation rates have increased from paleo to modern times, potentially because of better growing and preservation conditions for organic matter in a modern climate. Paleoclimate trends in the Medieval Climate Anomaly (MCA) and warm periods interspersed within the Little Ice Age (LIA) also correlate with greater contributions of wetland organic matter, as evidenced by lighter δ13C values. Cold climate periods within the LIA correlate with increased aquatic organic matter sourcing and heavier δ13C values, with some spikes of wetland sources interspersed throughout the LIA. Future temperatures are predicted to rise with global climate change, which may continue to expand carbon stores in Arctic coastal wetland sediments. This has been observed in the swale environments at Cape Espenberg, where increasingly favourable growing and soil-preservation conditions (i.e. wet/anoxic soils and lower salinity to limit organic material decay, higher temperatures to promote growth) are increasing the carbon storage within Arctic coastal carbon reservoirs.

Alaska↗
USGS2019

Late-Glacial paleoecology of the Middle Susitna Valley, Alaska: Environmental context for human dispersal

We present here the results of multi-proxy analyses (sediment geochemistry, diatoms, and pollen) from sediment cores collected at four lakes in the middle Susitna Valley, Alaska. These lakes form a transect from the tundra to the boreal forest. The retrieved cores span from ~12,000 cal yr BP to the present, with age control provided by radiometric dates and tephra deposits, some of which are newly identified. Results indicate that deglaciation occurred before 12,000 cal yr BP and that by that time, the lakes were deep, productive, and surrounded by shrub tundra. The lake with the highest sampling resolution indicates a brief climatic reversal ~11,500 cal yr BP with decreased diatom-inferred lake level and lowered lake productivity, and reduced shrub presence. During the early to middle Holocene, all of the sedimentary records provide evidence of climatic amelioration with tree expansion and productive lakes. A middle to late Holocene climatic deterioration with reduced trees and a shallower, less productive lake is also indicated. In addition, the prominent Watana tephra at ~4,000 cal yr BP likely reduced lake productivity and affected the vegetation. Even though the region was relatively productive soon after deglaciation, people did not occupy the region until ~11,000 cal yr BP, about 1000 years later, and then only sparsely. By the middle and late Holocene, the region was more densely populated and this shift in human occupancy presumably reflects changes in resource abundance, especially caribou. Whether the Watana ashfall influenced caribou abundance and thus people, is still under investigation, but given the tephra’s effect on vegetation and lake productivity, it seems likely.

Alaska↗