T379 North Pacific Environment and Paleoclimate from the Late Pleistocene to Present (Posters)

Wednesday, 25 October 2017
9:00 AM - 6:30 PM
Halls 4EF

STABLE ISOTOPE ECOLOGY AND PALEOCLIMATE IMPLICATIONS OF MODERN THUJA PLICATA IN THE PACIFIC NORTHWEST

Paper number: T379-5
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The global concentration of atmospheric carbon dioxide (pCO2 in ppm) and localized precipitation regimes have both changed since the start of the Industrial Revolution as a result of human influence. In the Pacific Northwest, precipitation has been substantially increasing over the past 100 years, and is projected to continue to do so, but precipitation in the form of snow specifically has been decreasing. How these changes have influenced ecosystems or individual organisms is not well understood. Here we use a combination of elemental analysis and stable isotope geochemistry to track those impacts on the Pacific red cedar (Thuja plicata), which also has a rich fossil record dating back into the Late Cretaceous. Seventy-eight Pacific red cedar specimens collected from 1876 through 2012 were sampled from several herbaria (n = 5). The elemental (C:N) and stable carbon isotope (δ13Cleaf) compositions were measured for leaf samples using an Elemental Analyzer and Cavity Ring-Down Spectrometer at the University of Michigan. A second parameter (Δleaf) was calculated by the subtracting δ13Cleaf from δ13Catmosphere values derived from direct and interpolated measurements. Δleaf reflects the deviation of a tree’s 13C fractionation from the moving atmospheric baseline — a result of the burning of fossil fuels (i.e., the Suess Effect). δ13Cleaf values ranged from -22.78 to –28.48‰ and showed more negative values with time. This demonstrates that δ13Cleaf values of T. plicata correlates with δ13Catmosphere, making Thuja a potentially useful recorder of the paleo-atmosphere at both historic and potentially longer time scales. Δleaf values were nearly constant with a mean of 18.31‰ and a standard deviation of 1.14‰, indicating that the water use efficiency of T. plicata is not affected by changes in pCO2 or precipitation over the period of Industrialization. Thuja plicata’s Eastern North American relative, Thuja occidentalis, exhibits a similar relationship (mean Δleaf value of 17.98‰, standard deviation of 1.11‰) in spite of growing in a significantly different climatic regime, with a. The consistency within this genus supports its potential use as a paleoclimate indicator across a broad range of (paleo-)environments.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-303102

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