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TitleLimited freshwater cap in the Eocene Arctic Ocean
AuthorNeville, L A; Grasby, S EORCID logo; McNeil, D HORCID logo
SourceScientific Reports vol. 9, no. 1, 4226, 2019 p. 1-6, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20180191
PublisherSpringer Nature
Mediapaper; on-line; digital
RelatedThis publication is related to Rock-Eval pyrolysis results for cuttings samples from the Natsek E-56 Well, Beaufort-Mackenzie Basin, Canada
File formatpdf; html
ProvinceNorthern offshore region
AreaArctic Ocean; Beaufort Sea
Lat/Long WENS 130.0000 -160.0000 88.0000 70.0000
Subjectsmarine geology; paleontology; stratigraphy; Paleogene; Eocene; paleogeography; paleoenvironment; paleoclimates; marine sediments; marine sediment cores; micropaleontology; microfaunas; microfossils; sediment transport; sediment distribution; source areas; stratigraphic correlations; organic geochemistry; bedrock geology; lithology; sedimentary rocks; shales; siltstones; sandstones; conglomerates; coal; Lomonosov Ridge; Eurasia; Eurasian Basin; Amerasian Basin; Azolla; Natsek E-56 Well; Dinoflagellates; Fresh water; Phanerozoic; Cenozoic; Tertiary
Illustrationslocation maps; geoscientific sketch maps; stratigraphic charts; tables; profiles
ProgramGEM2: Geo-mapping for Energy and Minerals Western Arctic Sverdrup Basin
Released2019 03 12
AbstractRemains of the freshwater fern Azolla, found in Eocene (~50 Ma ago) sediments in the modern central Arctic Ocean, have been used to suggest that seasonal freshwater caps covered the entire Arctic Ocean during that time, with significant impact on global ocean circulation and climate. However, these records are located on the Lomonosov Ridge, which during the Eocene was a continental fragment barely rifted from Eurasia, separating the smaller Eurasian Basin from the much larger Amerasian Basin to the west. As such, the Lomonosov Ridge does not necessarily record environmental conditions of the broader Arctic Ocean. We tested the hypothesis of freshwater caps by examining sediment records from the western Amerasian Basin. Here we show that in the larger Amerasian Basin the Azolla event is associated with marine microfauna along with allochthonous (terrestrially sourced) organic matter. We propose that Azolla events are related to an increased hydrologic cycle washing terrestrially sourced Azolla, and other organics, into the Arctic Ocean. If freshwater caps did occur, then they were at best restricted to the small Eurasian Basin and would have had a limited impact on Eocene global climate, contrary to current models.
Summary(Plain Language Summary, not published)
The Arctic region records evidence of extreme greenhouse conditions 50 million years ago, including thick forest cover and alligators living at 80 degrees north, that can serve as a proxy for understanding potential impacts of modern day global warming. Previous workers have suggested that the entire Arctic Ocean was covered by a freshwater lens during that time that significantly affected global climate. New work on sediment records in the Beaufort Sea, as part of the GEM Program, questions that interpretation and argues instead for more normal marine conditions. This has significant implications for climate models at that time and for understanding of how greenhouse conditions were ameliorated.

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