Multiple water isotope proxy reconstruction of extremely low last glacial temperatures in Eastern Beringia (Western Arctic)

• Main Authors: Porter, Trevor J., Froese, Duane G., Feakins, Sarah J., Bindeman, Ilya N., Mahony, Matthew E., Pautler, Brent G., Reichart, Gert-Jan, Sanborn, Paul T., Simpson, Myrna J., Weijers, Johan W H
• Other Authors: Stratigraphy and paleontology, Organic geochemistry, Stratigraphy & paleontology
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Eastern Beringia; Fossil plant waxes; Hydrated volcanic glass shards; Precipitation isotopes; Relict ice; Temperature reconstruction; Taverne; Geology; Global and Planetary Change; Ecology; Evolution; Behavior and Systematics; Archaeology; Tundra; Beringia; Yukon
• Online Access: https://dspace.library.uu.nl/handle/1874/330317

Precipitation isotopes are commonly used for paleothermometry in high latitude regions. Here we present multiple water isotope proxies from the same sedimentary context - perennially frozen loess deposits in the Klondike Goldfields in central Yukon, Canada, representing parts of Marine Isotope Stages (MIS) 4, 3 and 2 - allowing us to uniquely corroborate fractionations and temperature conversions during these Late Pleistocene cold stages. We include new and existing proxy data from: relict wedge ice, a direct archive for snowmelt; relict pore ice, an archive for bulk soil water integrating year-round precipitation; and hydrated volcanic glass shards and fossil plant waxes, which are also thought to integrate year-round precipitation but are subject to large fractionations. In some cases, our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean, new transfer functions calibrated specifically for northern North America (δDprecip = 3.1‰·°C-1 × T - 155‰; and δ18Oprecip = 0.41‰·°C-1 × T - 20.2‰), and novel insights on the apparent net fractionation correction for Eastern Beringian steppe-tundra plant waxes (εwax/precip = -59 ± 10‰). The snowmelt origin of wedge ice ensures a relatively constrained winter-spring seasonality of contributing precipitation, as supported by the consistency between water isotope measurements from Late Holocene wedge ice and modern winter-spring precipitation. Wedge ice dating to the transitional MIS 3/2 is isotopically depleted relative to modern spring-winter precipitation by an amount that indicates a temperature depression of ~14 ± 5 °C below modern. The soil water origin of pore ice, and other proxies integrating year-round precipitation from soil water, allows for a more variable precipitation seasonality. The isotopic composition of modern pore ice is consistent with mean annual precipitation. However, the isotopic composition of pore ice during MIS 3/2 converges on wedge ice ...