Unprecedented Historical Erosion of US Gulf Coast: A Consequence of Accelerated Sea‐Level Rise?

Abstract

Most of the US Gulf Coast is composed of barrier islands, peninsulas, chenier plains, and mainland beaches that are the main line of defense for wetlands, estuaries, and urban and industrial centers from rising sea level and severe storms. These wave‐dominated shorelines are currently experiencing widespread erosion. Using newly acquired and existing results from 13 sites spanning south Florida to south Texas, we compare shoreline migration rates during the late Holocene (∼−4000 to 1850 CE) with historical changes since the mid‐19th century. The records show an overall trend of seaward growth during the late Holocene followed by landward migration or a decrease in the rate of growth during historical time. Diminishing offshore sand supply, human alteration of rivers and coastal sand transport, and severe storms have contributed to this change in shoreline trajectory, but their influence has been mostly limited in extent. The most likely cause of this reversal from coastal stability and growth to widespread shoreline retreat is the dramatic historical increase in the rate of sea‐level rise over the past century.

Spatially and Temporally Variable Impacts of Hurricanes on Shallow Sediment Structure

“…Flow diversion by seafloor bathymetric features such as sand ridges can enhance local sediment accumulation (Hayes, 1967), which may have occurred at the ebb tidal delta and concentrated sand transport to sites M12 and M20, resulting in these sites displaying sand layers that the eastern 12 and 20 m sites lacked despite being closer to the hurricane track (Figures 1b and 3). Furthermore, another likely reason for the lack of consistent sand bed deposition across these sites is the generally low sand availability for Dauphin Island and Fort Morgan (Anderson et al., 2023; Hollis et al., 2019; Otvos & Carter, 2013).…”

“…Most studies of modern subtidal storm beds in the Gulf of Mexico have occurred in the northwest region on the Texas and Louisiana shelves (Hayes, 1967; Keen et al., 2012; Morton, 1988), while fewer studies have been performed in the Mississippi Bight region (between the Chandeleur Islands and the Florida panhandle, including the Alabama coast; Figure 1; but see Bentley et al., 2002; Keen et al., 2006) despite proximity to major hurricane impacts within the last 20 years in addition to high small‐scale spatial and temporal variability in sediment type (Hummel & Smith, 1996). Therefore, direct sediment and hydrographic sampling of extreme storm events is important for constraining predictions of storm impacts to coastal sediments, especially in the understudied and highly erosive (Morton, 2008; Otvos & Carter, 2008) Alabama coastal sediments with generally low sand supply (Anderson et al., 2023; Hollis et al., 2019; Otvos & Carter, 2013).…”

The Future of Developed Barrier Systems - Part II: Alongshore Complexities and Emergent Climate Change Dynamics

“…Climate-driven shifts in storm intensity (e.g., Knutson et al, 2020) could also influence dune-storm stochasticity through an increase in dune overtopping and overwash flux. Likewise, because SLR contributes to shoreline retreat and overwash frequency, accelerations in the rate of SLR (e.g., Dangendorf et al, 2023;Hamlington et al, 2020;IPCC, 2014;Rohling et al, 2013) would likely accelerate shoreline retreat rates (e.g., Anderson et al, 2023;Mariotti & Hein, 2022) and therefore modify dune recovery processes. Cumulatively, changing climate factors are likely to significantly influence the timing of human decisions to modify management practices, and the long-term outcomes of climate adaptation measures in developed barrier systems.…”

The Future of Developed Barrier Systems: 2. Alongshore Complexities and Emergent Climate Change Dynamics

“…Climate-driven shifts in storm intensity (e.g., Knutson et al, 2020) could also influence dune-storm stochasticity through an increase in dune overtopping and overwash flux. Likewise, because SLR contributes to shoreline retreat and overwash frequency, accelerations in the rate of SLR (e.g., Dangendorf et al, 2023;Hamlington et al, 2020;IPCC, 2014;Rohling et al, 2013) would likely accelerate shoreline retreat rates (e.g., Anderson et al, 2023;Mariotti & Hein, 2022) and therefore modify dune recovery processes. Cumulatively, changing climate factors are likely to significantly influence the timing of human decisions to modify management practices, and the long-term outcomes of climate adaptation measures in developed barrier systems.…”