CAN VOLCANIC EVENTS FORCE DECADAL COOLING IN THE NORTH PACIFIC?

The Pacific Decadal Oscillation (PDO) that describes sea-surface temperatures (SSTs) in the North Pacific and is a primary driver of climate in the Gulf of Alaska (GOA) region. Characterized by decade-long regimes that feature either a negative, cool or a positive, warm SSTs pattern along the Gulf of Alaska. Fluctuations in the PDO have major impacts on marine and water resources in the North Pacific and downwind North America. The short observational record of the PDO (1900-present) only covers 4-5 regime shifts, so longer records are needed to characterize how sensitive this phenomena is to climate forcing. While the mechanisms behind PDO shifts are not well understood, modeling experiments suggest that large stratospheric volcanic eruptions have previously shifted the PDO into a negative mode. Stratospheric tropical eruptions eject sulfateaerosols into the atmosphere, modifying the Earth’s albedo and eventually cooling globalSSTs. Several large volcanic eruptions documented in ice cores are known to cool SSTs in the North Pacific as evidenced by SST-sensitive tree ring records across the GOA.

This study aims to quantify the magnitude and duration of post-volcanic cooling in the GOA using high-elevation Yellow Cedar (Cupressus nootkatensis) tree rings from Dude Mountain, Ketchikan, Alaska. This well replicated (1400-2023) ring-width record that is sensitive primarily to summer temperatures show significant cooling following a volcanic eruption in the 1450’s, in addition to the previously recognized 1600’s, 1690’s, and 1809 volcanic events. The question why this site is so sensitive to these shifts and is a strong recorder of volcanic forcing is being investigated and is likely because this site is near elevational tree-line and sensitive to the PDO. The further analysis of this record will contribute to a more complete understanding how the PDO responds to volcanic cooling events.