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Investigating tree-ring evidence for an Indian Ocean–Gulf of Alaska teleconnection

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Dexter Pakula

Authors:

Pakula, Dexter C.¹, Wiles, Greg C.², Wiesenberg, Nick³

(1) Geology Department, Carleton College, Northfield, Minnesota, USA, (2) Department of Earth Sciences, College of Wooster, Wooster, OH, USA, (3) Department of Earth Sciences, College of Wooster, Wooster, OH, USA,

Abstract:

In 1875, the winter monsoon season failed in India, initiating the 1876–1878 Great Drought and Global Famine. These years coincide with sharply reduced growth in select tree-ring chronologies from the Gulf of Alaska (GOA). Initiated by the recognition of these marker years, this study uses ring-width chronologies to explore an atmospheric teleconnection between the Indian Ocean and the GOA.

The Indian Ocean Dipole (IOD) and the Indian Ocean Basin Mode (IOBM) are major modes of climatic variability in the Indian Ocean. The IOD is represented by the Dipole Mode Index (DMI), which is the sea surface temperature (SST) anomaly difference between the tropical western Indian Ocean (50°E–70°E, 10°S–10°N) and the tropical south-eastern Indian Ocean (90°E–110°E, 10°S–0N°). The IOBM is defined by the SST anomalies spanning 40°E–110°E and 20°S–20°N.

We have identified significant positive and negative winter (January–March) correlations between the DMI/IOBM indices and tree-ring series from mountain hemlock, Sitka spruce, and red and yellow cedars. Ongoing assessments include modeling the DMI and IOBM using combinations of North Pacific tree-ring series. Preliminary results show that these chronologies can explain a significant portion of the variance in the winter DMI using a 110-year common calibration interval.

Dramatically reduced growth from 1875 to 1878 in the most strongly correlated chronologies underscores a connection between these catastrophic years in India and the GOA, though the underlying dynamics remain unclear. These initial findings support a linkage between Indian Ocean climate variability and the GOA, encouraging further investigation into DMI and IOBM reconstructions.