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TitleNew occurrences of the White River Ash (east lobe) in Subarctic Canada and utility for estimating freshwater reservoir effect in lake sediment archives
AuthorPatterson, R T; Crann, C; Cutts, J A; Courtney Mustaphi, C J; Nasser, N A; Macumber, A L; Galloway, J M; Swindles, G T; Falck, H
SourcePalaeogeography, Palaeoclimatology, Palaeoecology vol. 477, 2017 p. 1-9, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20160123
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories; Yukon
AreaAlaska; United States
Lat/Long WENS-142.0000 -112.0000 63.0000 60.0000
Subjectsradiocarbon dating; volcanic ash; ash analyses; lakes; lake sediments; chronostratigraphy; deposition; Pocket Lake; White River Ash; Mount Churchill eruption; Bridge Lake; cryptotephra
Illustrationslocation maps; tables; photographs; graphs
ProgramTools for environmental impacts and adaptation for metal mining, Environmental Geoscience
Released2017 04 12
AbstractThe freshwater reservoir effect (FRE) in the Canadian Subarctic complicates development of high-resolution age-depth models based on
radiocarbon dates from lake sediments. Volcanic ashfall layers (tephras) provide an absolute chronostratigraphic marker that can be used to estimate age offsets. We describe the first recorded occurrence of a visible lacustrine tephra in the central Northwest Territories (CNT). The tephra, observed in Pocket Lake, near Yellowknife, is geochemically and stratigraphically attributed to the White River Ash Eastern Lobe (WRAe; A.D 833-850; 1117-1100 cal BP), which originated from an eruption of Mount Churchill, Alaska. We also observed the WRAe as a cryptotephra in Bridge Lake, 130 km to the NE, suggesting that records of this tephra are widespread in CNT lakes. The identification of this tephra presents opportunities for use of the WRAe as a dating tool in the region and to quantify the magnitude of the FRE in order to correct radiocarbon age depth models. Two well-dated sediment cores from Pocket Lake, containing a visible WRAe record, indicate a FRE of 200 years, which matches closely with the estimated FRE of 245 years at the lake sediment-water interface. Although additional results from other lakes in the region are required, this preliminary finding implies that FRE estimates for the late Holocene in the region, may be based either on down-core WRAe / radiocarbon age model offsets, or on radiocarbon dates obtained from the sediment-water interface.
Summary(Plain Language Summary, not published)
We document the occurrence of the White River Ash in lake sediments in the central Northwest Territories. We calibrate the age offset of a freshwater reservoir effect for radiocarbon based on tephrochronology.