Pacific Northwest Plants Record Multiannual Atmosphere-Ocean Circulation Patterns

Carbon isotope ecology can be used as a measure of plant water stress. Plant water stress is complicated: multiple factors (e.g., evapotranspiration rates, temperature, precipitation, soil texture, and available water) control the magnitude of the isotopic expression. Often, large ocean-atmosphere pressure systems result in the convergence of constructive climate parameters that result in increased plant water stress; for example, El Nino and Pacific Decadal Oscillation (PDO) anomaly phases. We examined the biogeochemistry of three species (Thuja plicata: with a Pacific coastal habitat, Thuja occidentalis: native to the Great Lakes region, and Populus tremuloides: a cosmopolitan species found throughout North America). Coincident analyses of these species allowed for intercomparison between plants in habitats directly impacted by atmospheric-oceanic controls on water availability and those out of Pacific impact range. There are oscillatory patterns in the carbon isotope discrimination values (Delta C-13(leaf)) of Thuja plicata, but no clear patterns in Delta C-13(leaf) values of the other species. We compare the pattern in isotope discrimination of T. plicata with Pacific-driven multiannual environmental phenomena to determine whether these patterns could be related to the oscillation in Delta C-13(leaf) values. The data demonstrate a regular and significant 14- to 19-year periodicity, aligning most closely with PDO climate patterns. Thuja plicata likely records prolonged stress, like plant available water shortages, which coincide with PDO-associated shifts in precipitation, humidity, and evapotranspiration. These findings demonstrate that coastal Pacific ecosystems are vulnerable to changes in water availability connected to Pacific teleconnections, providing a new recording tool to examine multiannual climate anomalies.