COI Funded Project: A History of Paleo-Hurricane Activity Recorded in the Stable Isotope Composition of Coral Skeleton
Project Duration: 6/1/99-12/31/00
Key Words: natural hurricane cycles, geochemical indicators, oxygen isotopes, coral reefs, Dominican Republic
Hurricanes often inflict catastrophic property damage and loss of
human life. In the light of recent predictions of increased hurricane
activity in the Atlantic basin, as well as explosive coastal population
growth, it is important to determine how these powerful storms could
change in response to changes in global climate (Knutson et al.
1998, Bove et al. 1999). One approach is to examine natural cycles
in hurricane frequency over several centuries and during times when
the world climate was different from that of today. Reliable and
comprehensive hurricane records are sparse prior to the 1940's,
which is too short a time-period to allow analysis of decadal and
centennial-scale trends. However, some of the numerous environmental
and geochemical changes effected by hurricanes remain preserved
in the geologic record. Using proxy techniques, we can extract this
evidence and extend the current record of hurricane activity back
This proposal describes a novel idea and a new technique to identify intense, landfalling hurricanes in the geologic record. It is based on the fact that hurricanes produce a large amount of rainfall with a very different oxygen isotope composition from that of normal summer rainfall. Hurricane rainfall is also isotopically distinct from water in lakes, rivers and streams, groundwater and the sea surface. It therefore comprises a natural isotope spike which is likely to be incorporated into the calcium carbonate skeletons of aquatic organisms. Although the isotope spike in seawater will quickly dissipate through mixing and dilution, if incorporated into skeletal carbonate it will remain preserved for centuries or even millennia as a record of each hurricanes' passage.
We predict that the CaCO3 skeletons of massive, long-lived corals inhabiting shallow reefs in the Caribbean and Gulf of Mexico contain this isotope spike and therefore preserve a record of many of the hurricanes which have made U.S. landfall over the past several centuries. We will test this prediction by measuring the isotope composition of corals from the Dominican Republic, an island hit by several intense hurricanes over the past few decades. Oxygen isotope measurements will be made on the new large format, high-resolution, high-transmission Carneca IMS 1270 ion microprobe at WHOI, an unconventional instrument for this type of analysis but ideally suited to the purpose of tracking hurricane signals which are large but of extremely short duration. Once we have demonstrated that our technique works, the project will be expanded to include other Atlantic sites and ocean basins, and extended back through the past several centuries or more. In future projects we will look for other geochemical and structural changes which together with the isotope signal will comprise a multi-variate, unambiguous "hurricane stamp" in different biological and inorganic carbonate accretions.
Originally published: January 25, 1999