3000 YEARS OF INTENSE HURRICANE SURGE IN THE NORTHERN BAHAMAS

One of the largest diameter hurricanes ever recorded was Hurricane Floyd, which hit the eastern shores of Abaco Island in the Northern Bahamas on 14 September 1999 as a category 4 event (Saffir-Simpson scale). Hurricane Floyd was a powerful Cape Verde-style hurricane that caused +6.8 m of surge and 225 km/hr winds according to local eyewitnesses reports. In order to explore the frequency of similar events in prehistory, we extracted push cores to obtain hurricane overwash deposits from Blackwood Sinkhole on this same coastline. Topographically, the sinkhole is separated from the beach by 200 m of limestone that rises less than 4 m above sea level. However, the sinkhole is an anoxic basin that is 37 m deep, preserving laminated successions with abundant coarse-grained overwash deposits. Based on a near linear Bayesian age model developed from 11 radiocarbon dates, the uppermost overwash deposit is coeval with the Hurricane Floyd event at 1999.6 AD (95% confidence interval: 2008.8 to 1981.7 AD). The only other intense hurricane strike during this confidence interval was Hurricane Jeanne (2004, cat 3), which caused less than 3 m surge on this coastline. Thus, we interpret the late Holocene archive of overwash deposition in Blackwood Sinkhole as sampling a population of powerful hurricanes that caused extensive surge on the eastern shores of Abaco Island. Late Holocene intense hurricane surge at Blackwood Sinkhole replicates the record of intense hurricane strikes documented at Laguna Playa Grande in Puerto Rico (Donnelly and Woodruff, 2007, Nature), but at a higher resolution. This suggests a common origin for the population of intense storms striking both locales. The active intervals of intense hurricane strikes at Blackwood Sinkhole and Laguna Playa Grande are coincident with evidence for warmer sea surface temperatures in the tropical Atlantic Ocean, a slightly more northward position of the Intertropical Convergence Zone, and evidence for reduced El Niño forcing on central Caribbean precipitation. Recent cluster analysis of hurricanes (Kossin et al. 2010, Am. Met. Soc.) indicates that cyclogenesis and North American landfall of Cape Verde-style hurricanes are commonly associated with these ocean-atmospheric conditions, which often manifest during a positive phase of the Atlantic Meridional Mode (AMM).