Hurricanes (tropical cyclones) and nor’easters (mid-latitude cyclones) are high-energy storms often impacting the Outer Banks (OBX) barrier islands of North Carolina (NC), USA. Storm hazards include, but are not limited to, high speed winds, coastal flooding, storm surges, and increased precipitation. As a consequence of increased storm strength and frequency, loss of life, property damage, and erosion to beaches, barrier islands, and marshes have amplified over the past 40 years. In a recent report by the National Oceanic and Atmospheric Administration (NOAA), US taxpayers expended ~$1.05 trillion on hurricane and nor’easter impacts from 1980 to 2020. Identifying historical hurricanes and nor’easters in the geologic record as washover deposits can aid in the understanding of past events and prediction of future impacts to the OBX. Storm events yielding washover deposits can be identified, mapped, and quantified using various geologic, geophysical, and remote-sensing techniques. To identify both modern and historic coastal storms, nine sediment cores and 2300 meters of ground penetrating radar (GPR) data were collected, and five trenches were dug from the surface to the water table on three washover fans on Hatteras and Pea islands, NC. Grain size distributions were measured at centimeter intervals from trenches and sediment cores. GPR data were used to map spatial extents and measure sediment thicknesses in washover deposits down to ~1 m. Radiocarbon and short-lived isotopic dating techniques were employed to ascertain ages of washover deposits identified within cores. Additionally, historical surface analyses, hurricane tracks, and buoy data from NOAA were used to correlate washover deposits to known historic and modern hurricanes or nor’easters. To date, this project has identified several discrete washover events associated with Hurricane Sandy (2012) and several nor’easters across the northern (Pea Island) and middle/southern (Hatteras Island) study sites. Radiocarbon dating from plant material indicates these sites contain a ~500 cal yr BP record of washover deposition. The significance of this project is to evaluate differential impacts of nor’easters and hurricanes on the geomorphic evolution of Pea and Hatteras islands through the integration of data from multiple methodologies.

Systemic modification of coastal systems in the northern Gulf of Mexico is generated by rapid geomorphic change due to storms, relative sea level rise, significant reduction in sediment supply, and anthropogenic alteration. Policy makers, engineers, and scientists must understand the overall geologic evolution as well as small scale processes associated with past sea level cycles to make informed decisions when addressing current and future sea level rise. After the Last Glacial Maximum, sea level rose rapidly during marine isotope stage (MIS) 2 (approximately 29-14 ka) leading to a transgressive reworking of lithosomes. As sea level continued to rise, Holocene sediments underwent significant reworking and backstepping resulting in drowned paleovalley architecture. Coastal geomorphic evolution is partially preserved within the geologic record specifically within incised valleys and shelf deposits. This study synthesizes ~700 km of boomer geophysical data collected in 2021, 19 sediment cores, microfossil analyses, and radiocarbon dates to create a geomorphic evolutionary framework of the Pascagoula-Biloxi paleovalley and associated fill along the innershelf of the northern Gulf of Mexico. Sediment cores described within the footprint of the Pascagoula-Biloxi paleovalley consist of muddy bedding overlying muddy sand and sandy mud with Pleistocene clay around 450-500 cm downcore. One such core contained large wood chunks dated to ~11 ka cal yr BP resting on a Pleistocene clay basal facies. Preserved wood indicates either rapid burial or an anoxic system, in this case - likely a swamp. Along the edge of the Pascagoula-Biloxi paleovalley, a sediment core exhibits well preserved interbedded clay and peat layers also dated to ~11 ka cal yr BP. These similar ages indicate terrestrial/shoreline deposition, and these data provide constraints to reconstruct the immature paleo shoreline and associated features of the early Holocene.

Paleotempestology assists in extending the instrumental storm record through sedimentary-based, high-resolution records of storms over millennia. A fundamental understanding of the paleorecord provides essential context for modern climate models and, therefore, a broader understanding of our climate system. The Texas (TX) coastline receives the second largest number of hurricane landfalls per year in the United States; since 1900, 92 tropical storms and hurricanes have made landfall on the TX coast. During storm impacts, coastal downwelling storm channels deliver coarse sediment to the muddy shelf. This return flow or “backwash” process results in thin but expansive storm deposits in the region, making it ideal for paleotempestological reconstructions. In this work, three sediment cores from the central TX shelf, approximately six kilometers off the coast of Matagorda Island, were collected and analyzed. Several historic and Holocene storm events have been identified in cores by conducting detailed grain size analysis at one-centimeter intervals. Bayesian-based age models couple short-lived isotopic dating techniques (210-Pb and 137-Cs) with radiocarbon ages. X-ray fluorescence (XRF) analysis is used to determine geochemical signatures of the sediments and thus the material source for cross validating the depositional mechanism. Specifically, XRF is utilized to differentiate the effects of the 1929 Colorado River diversion relative to marine deposition. Our new record of tropical cyclone (TC) occurrence from the TX shelf is compared to paleoclimate models and proxy records of El Niño Southern Oscillation (ENSO) and Gulf of Mexico (GOM) sea surface temperature (SST). Preliminary results suggest that periods of decreased ENSO and increased GOM SST correspond with enhanced TX TC activity. Understanding these complex climatic interactions will help us to understand the changes in TC activity expected in the future against the background of accelerating climate change. Given that the frequency of extreme ENSO events is projected to increase, changes in the occurrence and severity of ENSO-TX TC events may prove detrimental to many coastal populations.