The Foraminiferal Signature of Recent Gulf of Mexico Hurricanes

Abstract

We investigated foraminiferal assemblages contained within known deposits of Hurricanes Ivan (2004), Katrina (2005), and Rita (2005) on the continental shelf west of the Mississippi Delta to determine: 1) whether they differ significantly from assemblages of non-hurricane units and of a unit deposited by a river flood event, and 2) whether assemblage characteristics might provide insight into the provenance of the sediment. Cores and surface samples were collected along a transect southwest from Southwest Pass (~30-m water depth) to the head of the Mississippi Canyon (~170-m depth) in 2004, 2005, and 2007 following hurricane, non-hurricane, and Mississippi flood episodes. Discriminant analysis indicates that all unit types are generally distinguishable. Species that contribute most to the discrimination of units are mostly rare, while the species significant in the ANOVA are among the most abundant. Both abundant and rare species were useful for identifying the provenance of hurricane-deposited sediment. Seaward transport of sediment by hurricanes is indicated by the presence of rare marsh taxa (not recorded in non-hurricane units) and increased relative abundance of coastal taxa in the hurricane units. High relative abundances of taxa that are abundant in both the hurricane and non-hurricane units suggest a portion of the hurricane-deposited sediments were also locally derived. In summary, foraminifera can provide information on the provenance of hurricane-deposited sediment soon after deposition, but bioturbation can destroy this signal rapidly.