THE FORAMINIFERAL SIGNATURE OF HURRICANES RITA, KATRINA, AND IVAN AND THE 2011 MISSISSIPPI RIVER FLOODING EVENT IN CORES FROM SOUTHWEST PASS TO THE MISSISSIPPI CANYON, GULF OF MEXICO, USA

Deposits from Hurricanes Rita (2005), Katrina (2005), and Ivan (2004) have been detected in cores from the offshore Mississippi Delta using down core activities of ⁷Be, ²³⁴Th, and ²¹⁰Pb as well as X-radiography. However, as these radionuclides are relatively short-lived, their utility for the identification of hurricane events decreases with progressively older deposits. Foraminifera, on the other hand, can be preserved for geologically significant amounts of time. Here we set out to investigate whether foraminiferal assemblages contained within recent, known hurricane deposits differ significantly from those of non-hurricane deposits, and whether these differences might give insight on the provenance of this hurricane-deposited sediment.

Cores were collected along the same transect during three different cruises: 2004, 2005, and 2007. The transect runs southwest from Southwest pass (~30m water depth) to the edge of the Mississippi Canyon (~70m depth). Cores were selected to enable analysis of spatial and temporal changes in foraminiferal assemblages.

The 2004 and 2005 core tops reflect the nature of the seafloor foraminiferal community immediately after a hurricane; relatively rich in textulariids. The 2007 core top samples reflect the community after a few years of relatively quiet hurricane seasons: high-density assemblages dominated by Epistominella vitrea. In addition, a cruise along the same transect was conducted in August, 2011, immediately following a major flooding event of the Mississippi River. Surface samples along the transect contain assemblages very different again from those of 2004/2005 and 2007: nearly all the foraminifera were live (stained) juveniles of Nonionella opima.

Each hurricane and non-hurricane unit within each core has been compared pairwise using ANOVA. While hurricane units can be statistically discrete from the pre- and post-hurricane units, the different hurricane units can also be statistically discrete from one another. Cluster analyses of all down core samples show a fair amount of separation between hurricane versus non-hurricane deposits, although units from within the same core tend to be more closely grouped than those from another core.