THE EFFECTIVENESS OF TRADITIONAL PALEOTEMPESTOLOGY PROXIES IN BACKBARRIER MARSHES FROM THE SOUTHEASTERN ATLANTIC COAST

Sedimentological and micropaleontological paleotempestology proxies are only effective if they consistently record hurricane strikes in sedimentary archives and the resulting storm signatures are preserved. Two studies from North and South Carolina suggest that one such approach, storm overwash enriched with offshore-indicative foraminifers, fails both criteria.

In the first study, sediments and microfossils from four marshes along Onslow Bay, NC, were analyzed immediately after Hurricane Irene made landfall (August 27, 2011). Irene did not produce sandy overwash deposits similar to those found in many marshes; additionally, the storm signature did not contain significant numbers of displaced marine foraminifers. Only one subenvironment, the tidal creek at Alligator Bay, received shallow-marine foraminifers and this was the sole marsh with meteorological conditions that were ideal for such transport: a relatively high maximum onshore wind [18.5 m/s], a substantial storm surge [0.94 m] and winds blowing from offshore. This spatio-laterally limited storm signature will probably not be detectable in the marsh strata from this region in the future and is discouragingly similar to the downcore record of storms preserved in these marshes: only five archived storm deposits from the past 1,500 years.

In the second study, analysis of sediment and microfossils from fifteen 3-m cores revealed a lack of spatio-lateral continuity for paleohurricane deposits from the marshes of Folly Island, SC. The offshore-indicative microfossil content of some deposits was taphonomically altered or destroyed, and in many cases cores taken 10 m apart provided significantly different storm records. In several low-marsh cores, where bioturbation is more intense, storm deposits were unrecognizable using foraminiferal or sedimentological criteria.

The North Carolina (Irene) study demonstrates that micropaleontological proxies may only work under ideal meteorological conditions and both studies indicate that preservation of storm deposits is highly variable. The results of these studies suggest that only the most robust storms produce a durable sedimentological or micropaleontological record of hurricane landfall and such a record is often destroyed via bioturbation before it is preserved in the marginal-marine strata.