Assessing the Tree-ring Oxygen Isotope Hurricane Proxy along the Atlantic and Gulf Coastal Seaboards, USA

A recent increase in hurricane activity has put coastal populations at risk. To better understand hurricane activity, it is necessary to look beyond the modern instrumental record, using proxy records to establish modes of past variability. The utility of a newly developed tree-ring oxygen isotope proxy is further assessed. I present oxygen isotope time series from three sites: Francis Marion and Sandy Island, South Carolina and Eglin Air Force Base, Florida. Proxy results are verified against the instrumental record of hurricane occurrence. The sites record similar percentages (45% for Francis Marion and Sandy Island, 63% for Eglin Air Force Base) of hurricanes that tracked within 200 km of the sites. Potential reasons for missing storms include initial storm water composition, lack of precipitation, or drought.

In Florida, a longer record was developed (1710–1950). For the period 1850– 1950, the proxy captured 24% of hurricane events. This decrease is similar to the Valdosta, Georgia study and is attributed to changes in the Pacific Decadal Oscillation. At both sites, during cool phase PDO, the number of storms recorded by the proxy increases, but the percentage of activity recorded decreases. The identification of periods (1710– 1720, 1760–1780, 1810–1830, and 1840–1850) of multiple negative anomalies inferred to be hurricane events at both sites provide evidence for short increases in hurricane activity that match to periods of increased activity in the Caribbean and the Lesser Antilles. The data show that hurricane activity fluctuates over time and do not support an increasing trend in hurricane frequency.

Spectral and wavelet analysis of the oxygen isotope time series from these sites reveal frequencies similar to the Quasi-biennial Oscillation, the El-Niño Southern Oscillation, and the North Atlantic Oscillation. Major shifts in the oxygen isotope data in the 1960s in both Florida and South Carolina are concurrent with climate shifts observed globally that are linked to the Atlantic Multi-decadal Oscillation and/or the Pacific Decadal Oscillation. Spectral analysis of the Florida time series also reveals 11 and 22– year cycles that are coincident with sunspot and Hale solar cycles.