The sedimentary record of the 2005 hurricane season from the Mississippi and Alabama coastlines

The instrumental record of hurricane activity is too short to fully capture the occurrence of the rare but most destructive hurricanes. Therefore, obtaining a record of present and past landfalling hurricanes, and their extent of geological and ecological impacts, is one means to assess future risk, reveal the spatial and temporal variability of hurricane activity and decipher its relationship with global climatic changes. We rapidly dispatched survey teams to collect the readily available, but perishable data of Hurricanes Katrina and Rita storm surge from two salt marshes in Mississippi and one salt marsh in Alabama. In Mississippi, we recorded Hurricane Katrina storm surge heights greater than 7.5m North American Vertical Datum 88 (NAVD88) with inland extents in excess of 700 m, whereas in Alabama the maximum recorded storm surge was 3.43m NAVD88. At one salt marsh in Mississippi, we recorded the maximum inland extent and elevation of maximum penetration of Hurricane Rita as 370m and 3.43m NAVD88, respectively. We observed a three-dimensional distribution of hurricane-induced storm surge deposits that tapered landward, overlying salt marsh sediment. There was a sharp or erosional boundary between the pre-storm surge and storm surge sedimentary units, which was accompanied by a change in color and lithology. The overlying storm surge sediment unit was coarser than the pre-storm surge unit with a lower organic content. The thickness of the Hurricanes Katrina and Rita storm surge sediments ranged from 9 to 13 cm and approximately 7 cm, respectively. Foraminiferal analyses revealed a virtual absence of tests within the storm surge sediments, whereas abundant agglutinated foraminifera were found in the underlying salt marsh deposits.