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GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 196-8
Presentation Time: 10:15 AM

CARBONATE CLUMPED ISOTOPE RECORD OF LGM-HOLOCENE CLIMATE CHANGE ACROSS THE PACIFIC NORTHWEST US: INSIGHTS FROM LOESS-PALEOSOLS AND PLUVIAL LAKES


LECHLER, Alex R.1, HUNTINGTON, Katharine2, BREECKER, Dan O.3, SWEENEY, Mark R.4 and SCHAUER, Andrew J.2, (1)Department of Geosciences, Pacific Lutheran University, Tacoma, WA 98447, (2)Earth and Space Sciences, University of Washington, Seattle, WA 98195, (3)Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, (4)Earth Sciences Department, University of South Dakota, Vermillion, SD 57069, LechleAR@plu.edu

Across the Pacific Northwest (PNW) United States, diverse paleoenvironments of the last glacial and deglacial periods preserve rich stratigraphic and geochemical records of regional climate response to global pCO2 changes and the regional advance and retreat of large, continental ice sheets. Here we integrate findings from radiocarbon dating and clumped isotope thermometry of carbonates to provide new, quantitative measures of terrestrial, LGM-Holocene paleoenvironmental change across the PNW. Samples were collected from loess-paleosol sequences in the Palouse of eastern Washington state and from lacustrine deposits in the Summer Lake remnant of pluvial Lake Chewaucan in east-central Oregon. Average clumped isotope temperatures (T(Δ47)) for LGM-aged pedogenic carbonate in Palouse loess-paleosol sequences (9 ± 4°C) are significantly lower than those for Holocene-aged carbonate in these sequences (T(Δ47) = 18 ± 2°C). Calculated LGM soil water δ18OVSMOW values (-14.2 ± 1.8‰) are also offset relative to those for Holocene-aged samples (-10.3 ± 1.3‰), whereas calculated soil CO2 δ13CVPDB values are similar for the Holocene (-16.9 ± 0.2‰), and LGM (-16.7 ± 1.1‰). Together, these paleoclimate metrics indicate LGM conditions of pedogenic carbonate formation in the C3-grassland soils of the Palouse were measurably colder (9 ± 5°C) than during the Holocene, likely as a result of colder mean annual conditions and potentially reflective of a more arid LGM paleoclimate in the Palouse. Contemporaneous lacustrine carbonate T(Δ47) and 14C records obtained from Summer Lake Basin, OR suggest late last glacial (27-17 ka BP) water temperatures in pluvial Lake Chewaucan were 6 ± 4°C. These values agree with recently-published carbonate T(Δ47) records of similar age from the neighboring Lake Abert remnant that were interpreted to reflect LGM-to-Holocene mean annual temperature warming of 7 ± 3°C (Hudson et al., 2017). Assuming warm-season carbonate formation in Palouse loess-paleosols and pluvial Lake Chewaucan, these records suggest region-wide mean annual and warm season temperature increase on the order of 7-9°C across the PNW US since the LGM, magnitudes consistent with climate model simulations for the region.

Session No. 196

T46. North Pacific Environment and Paleoclimate from the Late Pleistocene to Present I
Tuesday, 24 October 2017: 8:00 AM-12:00 PM
Room 609 (Washington State Convention Center)
Geological Society of America Abstracts with Programs. Vol. 49, No. 6
doi: 10.1130/abs/2017AM-303031
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