The Effects of Hurricanes Katrina and Rita on the Seabed of the Louisiana Shelf

The legacy of hurricanes Katrina and Rita on land has been one of human devastation and long-term damage to the infrastructure of communities along the northern Gulf of Mexico. In addition, these hurricanes had major impacts on offshore regions of the shelf and slope. A multi-institution, rapid-response effort investigated the immediate effects of the storms on the seabed off the Louisiana coast. These studies revealed intense reworking of surface sediment layers during the storm passage and re-deposition of materials following the hurricanes over a broad area of the shelf and slope. The pattern of deposition varied significantly along the region between the Mississippi and Atchafalaya rivers, depending on both the characteristic of the shelf and the paths of the storms. Geochemical tracers indicate the origin of the materials in the post-hurricane layers was predominantly local sediments mobilized by the intense wave activity during the storms. The combined impact of the hurricanes was a massive disturbance of benthic communities throughout the region, including marked erosion of the seabed in the shallower regions of the shelf and elevated deposition of sediments in the deeper regions. The total amounts of sediment, carbon and nitrogen re-deposited following the storm far exceeded the combined annual inputs of these materials by the Mississippi/Atchafalaya Rivers. The characterization of these storm deposits provides an opportunity to investigate the history of hurricane activity in the recent past based on the sedimentary record preserved in this region.