CAN TROPICAL CYCLONE EVENTS FROM THE MISSISSIPPI RIVER DELTA, USA BE DETECTED BY FORAMINIFERAL SIGNATURES?

Tropical cyclones can cause unstable sediment to flow off-shelf causing deposition of event layers off the Mississippi River delta. Short cores (~40cm) taken after the hurricanes Rita, Katrina, and Ivan contained event deposits with foraminiferal assemblages distinct from the non-event sediment that overlies and underlies them. These event layers have low densities of foraminifera and high relative abundances of Textularia earlandi and Ammonia tepida. This research uses longer cores (~2m) to determine if the foraminiferal signature of hurricanes is preserved over a multi-decadal time-scale (based on Pb-210 age determinations). Four kasten cores (approximately 2m in length) were collected in 2007 at depths of 59m, 75m, 87m, and 473m on a transect between Southwest Pass and the Mississippi Canyon. Each core was sampled in 10-cm increments to find if hurricane units could be revealed by their foraminiferal signatures. The three cores along the Southwest Pass yield assemblages dominated by Epistominella vitrea, which becomes less abundant offshore. The near shore samples show signs of decreasing dissolved oxygen indicated by increasing percentages of E. vitrea and Buliminella morgani. Research thus far has not yielded foraminiferal assemblages comparable to the known assemblages in the event layers caused by Rita or Katrina. Varying densities of foraminifera, however suggest that the sedimentological and foraminiferal signature of tropical cyclones may be present but partially lost, obscured by bioturbation.