A 4500 Year Assessment Of Hurricane Risk Along the Florida Gulf Coast – Lane Et Al 2011 – A Decadally-Resolved Paleohurricane Record Archived In The Late Holocene Sediments Of A Florida Sinkhole

I was alerted by Phil Lane of  Woods Hole Oceanographic Institution and MIT to an important new paper on multi-century risk of hurricane landfall along the Florida Gulf coast. The paper is

Lane, P., Donnelly, J.P., Woodruff, J.D., Hawkes, A.D., 2011. A decadally-resolved paleohurricane record archived in the late Holocene sediments of a Florida sinkhole. Marine Geology. v. 287. p. 14-30. doi:10.1016/j.margeo.2011.07.001

The abstract of the paper reads [highlight added]

A 4500-year record of hurricane-induced storm surges is developed from sediment cores collected from a coastal sinkhole near Apalachee Bay, Florida. Recent deposition of sand layers in the upper sediments of the pond was found to be contemporaneous with significant, historic storm surges at the site modeled using SLOSH and the Best Track, post-1851 A.D. dataset. Using the historic portion of the record for calibration, paleohurricane deposits were identified by sand content and dated using radiocarbon-based age models. Marine-indicative foraminifera, some originating at least 5 km offshore, were present in several modern and ancient storm deposits. The presence and long-term preservation of offshore foraminifera suggest that this site and others like it may yield promising microfossil-based paleohurricane reconstructions in the future. Due to the sub-decadal (~7 years) resolution of the record and the site’s high susceptibility to hurricane-generated storm surges, the average, local frequency of recorded events, approximately 3.9 storms per century, is greater than that of previously published paleohurricane records from the region. The high incidence of recorded events permitted a time series of local hurricane frequency during the last five millennia to be constructed. Variability in the frequency of the largest storm layers was found to be greater than what would likely occur by chance alone, with intervals of both anomalously high and low storm frequency identified. However, the rate at which smaller layers were deposited was relatively constant over the last five millennia. This may suggest that significant variability in hurricane frequency has occurred only in the highest magnitude events. The frequency of high magnitude events peaked near 6 storms per century between 2800 and 2300 years ago. High magnitude events were relatively rare with about 0–3 storms per century occurring between 1900 and 1600 years ago and between 400 and 150 years ago. A marked decline in the number of large storm deposits, which began around 600 years ago, has persisted through present with below average frequency over the last 150 years when compared to the preceding five millennia.”

The conclusion includes the text

The Mullet Pond record indicates that the most active interval for tropical cyclones in the Northeastern Gulf of Mexico during the late Holocene was 2800 to 2300 cal. yrs. B.P. Large storm deposits were rarely detected between 1900 and 1600 cal. yrs. B.P. and after 400 cal. yrs. B.P. A decline in the number of large storm deposits, which began around 600 years ago, has persisted through present with below average frequency over the last 150 years when compared to the preceding five millennia. However, given the stochastic nature of hurricane landfalls, any trend in basin-wide hurricane frequency during the late 20th century would not be detectable in a single sedimentary record. With an approximately 7-year temporal resolution and a record mean storm frequency of 3.9 events per century, Mullet Pond provides a richer and more detailed archive of storm activity than other existing paleohurricane records.

This is quite an important study. While a long-term trend in basin-wide hurricane frequency cannot be detected from a single location, this data does tell us that significant long-term variations in large-scale circulation features must occur in this region of the world, as such circulations control the path of hurricanes.  This is yet another study which documents the complex temporal variability of the climate system.

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