EXTRACTING THE RECORD OF STORMS FROM THE SEDIMENTS OF LONG ISLAND SOUND

Storms are common processes that remobilize and transport large volumes of sediments, modifying the seafloor and coastlines. Previous studies have documented hurricanes passing through the Long Island Sound region in 1693, 1893, throughout the 1900’s with some particularly devastating ones such as the 1938 Long Island Express and Super Storm Sandy in 2013. The changing climatic conditions and warming of the oceans as reported by Intergovernmental Panel on Climate Change (IPCC) 2018 demonstrates that storms can occur more frequently with stronger winds, waves and larger storm surges. The Long Island coasts are heavily populated. We therefore need to understand the record of past events to better understand the future.

As part of The Long Island Sound Cable Fund Habitat Mapping we acquired multibeam bathymetry, acoustic backscatter, subbottom profiles, 45 sediment cores up to ~2 m in length and 350 grabs from Central Long Island Sound. Based on the core photos, grain size variability, lithological descriptions, physical properties (bulk density and magnetic susceptibility) and heavy metals we have characterized the seafloor into: 1) low energy environments where the sediments are composed of clayey silts and silty clays, have been homogenized by bioturbation and not much change has occurred through time. 2) High-energy environments are characterized by sediment reworking and transport with sand beds containing sharp lower and upper contacts, laminae and lenses, and sediment reworking evidenced by floating lithic clasts, shell fragments and wood. 3) Depositional environments where potential unconformities are revealed by truncated strata, sharp contacts and dramatic changes in sedimentation. 4) As part of the objectives of the program we have also identified areas disturbed by pipelines, cables and dredging.

Storm deposits have been tentatively identified in high-energy environments and depositional environments with substantial evidence for sediment erosion. Heavy metals have provided relative ages at ~1960 and late 1850’s related to a pronounced peak in lead do to the use of leaded gasoline and the beginning of industrialization. We are awaiting results from radiocarbon dating to better fine tune these deposits to the historic and instrumental record of storms that have affected these parts of LIS.