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

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. Plain Language Summary Future shoreline positions are difficult to predict because of the many natural and anthropogenic stressors that influence erosion and accretion over various spatial and temporal scales. This study provides documentation of a regime shift in coastal barrier evolution from stability or growth over the previous few thousand years to nearly ubiquitous erosion in historical time. Declining sediment supply, severe storms, and human alterations to the coast contributed to this change, but the Gulf‐wide extent of coastal change is mainly a result of historical acceleration of sea‐level rise. Management practices will need to adapt to this new state of continuous coastal retreat as the rate of sea‐level rise will continue to increase in the future. Key Points Data from 13 sites across the Gulf Coast quantify shoreline migration rates during the late Holocene relative to historical time Shoreline growth during the late Holocene transitioned to landward migration or a decrease in the rate of growth during historical time This reversal from coastal stability and growth to widespread shoreline retreat is likely due to historical accelerated sea‐level rise