Investigation of a Ring Width Yellow Cedar (Cupressus nootkatensis) Series as a Record of Coolings Associated with Volcanic Eruptions

Figure 1. Title page of Amanda’s thesis including one of the key figures.

Amanda Flory (class of 2025) completed a thesis that investigated the interplay between the pace of the ocean-atmosphere climate in the Northeast Pacific that is dominated by Pacific Decadal Variability along with the volcanically-forced coolings inferred from tree-ring records. Her title page (above) summarizes the results with several known volcanic intervals linked with decade-long coolings. These coolings are inferred from a tree ring-width series located in coastal Southeast Alaska (Dude Mountain, Ketchikan, Alaska). In addition to her thesis work Amanda presented her results at the meeting of the Geological Society of America in the Spring of 2025. The take-home here is that the variability as recorded in the tree-ring record appears to be a combination internal variability of the Northeast Pacific [1] and volcanic forcing [2] contributing to the decadal variability in the climate.

Figure 2. The author (left) cores a yellow cedar (Cupressus nootkatensis) – Nick (middle) and Proto provide support.

Figure 3. Comparisons of Sitka, AK temperature records for the months of December through October of the growth year correlated with the Dude Mountain ring-width record.

This climate/tree-ring comparison (Figure 2) examines the moving correlation over time (since 1857) is based on a running 35-year correlation. Correlations change from positive (blue) to negative (red) and back to positive. This non-stationary response temperature is puzzling and is likely complex reflecting the ecological and climate-related thresholds at the site. Amanda explored the correlation between ocean heat content ([3]; see Figure 1: title page) and tree growth. The strong and steady relationship between the ocean heat content and growth suggests that the near-coastal tree-ring site is dominated by the ocean-atmosphere system immediately offshore.

Figure 4. Key volcanic events that correspond with decades of cooling.

As is the case with most theses, more crucial questions are raised and will continue to be investigated. These include continuing the examination of the yellow cedar climate response as well as applying new analyses that seek to tease out the volcanic response from the internal response of the Pacific Decadal variability in the record.

Acknowledgements: This work was supported by the National Science Foundation Grant AGS-2002454. We would like to thank Klawock’s Alaskan Youth Stewards (AYS) group for their expertise and guidance while conducting field work.

References:

[1] Schneider, N., and Cornuelle, B.D., 2005, The Forcing of the Pacific Decadal Oscillation:, doi:10.1175/JCLI3527.1.

[2] Wang, T., Otterå, O.H., Gao, Y., and Wang, H., 2012, The response of the North Pacific Decadal Variability to strong tropical volcanic eruptions: Climate Dynamics, doi:10.1007/s00382-012-1373-5

[3] Levitus, S. et al., 2012, World Ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010: Geophysical Research.

Source: https://woostergeologists.scotblogs.wooster.edu/2025/06/07/investigation-of-a-ring-width-yellow-cedar-cupressus-nootkatensis-series-as-a-record-of-coolings-associated-with-volcanic-eruptions/