A Late Miocene to Late Pleistocene Reconstruction of Precipitation Isotopes and Climate from Hydrated Volcanic Glass Shards in Central Alaska and Yukon

Precipitation stable hydrogen isotope ratios (dDprecip), a proxy for mean air temperatures, are reconstructed for the last 6.7 Ma using the hydrogen isotope ratios of hydrated volcanic glass shards (dDglass), from a regional network of volcanic ash beds (tephras) at continental sites in central Yukon and eastern Alaska. Bulk tephras from the Eastern Alaska Range (EAR) and Lost Chicken Mine (LC) were collected from outcrops, and glass shards were isolated by heavy liquid separation, organic removal with H2O2, carbonate removal with 10% HCl, and optical verification under cross-polarized light at the University of Toronto Mississauga. Major and minor element geochemistry of the EAR and LC tephras was analysed at the University of Alberta using a JOEL 8900R Superprobe. Pure glass separates of the Grubstake, Klondike and Thistle Creek tephras were obtained from the University of Alberta tephrochronology collection. The dD of all tephras was analysed by pyrolysis TC/EA-IRMS at the University of Oregon using a Finnigan MAT 253 isotope ratio mass spectrometer. Finally, fossil (bacteria-derived) branched-chain GDGTs associated with the EAR and LC sedimentary units were recovered from by solvent extraction, isolated using column-chromatography techniques, and quantified at the University of Toronto Mississauga using an Agilent Technologies 1290 Series II UHPLC AB Sciex 4500 QTrap triple quadrupole mass spectrometer. The composite tephra dD record confirms the Pliocene climate of the study region was highly variable but generally warmer-than-today on average. By comparison, the latest Miocene and middle to late Pleistocene were characterised by more depleted precipitation on average, which is likely explained by cooler conditions. Although regional orographic barriers and pan-Arctic boundary conditions (e.g., Canadian Arctic Archipelago development, vegetation and surface albedo) may have been different from today, and probably also had some influence on precipitation isotopes in the study region, our record shares many of the hallmarks of climate variability reflected in other Yukon-Alaska terrestrial and marine (North Pacific) proxy records covering this period which implies that large-scale climate trends were most important to the Late Cenozoic climate history of this region. This study demonstrates the viability of using hydrated volcanic glass shards as a climate proxy for investigating climate changes over long timescales in this region.

Identifier
Source https://www.polardata.ca/pdcsearch/PDCSearchDOI.jsp?doi_id=13114
Metadata Access http://www.polardata.ca/oai/provider?verb=GetRecord&metadataPrefix=fgdc&identifier=13114_fgdc
Provenance
Creator Porter, Trevor; Otiniano, Gerard; Benowitz, Jeff; Bindeman, Ilya; Davies, Lauren; Froese, Duane; Jensen, Britta; Phillips, Michael
Publisher Canadian Cryospheric Information Network
Contributor Polar Data Catalogue
Publication Year 2019
Rights Research programs, CCIN, or ArcticNet take no liability for the use or transmission of this data
OpenAccess true
Contact trevor.porter(at)utoronto.ca; pdc(at)uwaterloo.ca
Representation
Language English
Format Computer file
Discipline Environmental Research
Spatial Coverage (-148.210W, 63.061S, -139.420E, 64.070N)
Temporal Coverage Begin 2016-09-01T00:00:00Z
Temporal Coverage End 2019-10-14T00:00:00Z