Search for: All records

Abstract Coastal saltmarshes keep pace with sea-level rise through in-situ production of organic material and incorporation of allochthonous inorganic sediment. Here we report rates of vertical accretion of 16 new sediment cores collected proximal to platform edges within saltmarshes located behind four barrier islands along the southeast United States coast. All but two of these exceed the contemporaneous rate of relative sea-level rise, often by a factor of 1.5 or more. Comparison with 80 additional measurements compiled across the Georgia Bight reveals that marshes situated closer to inlets and large bays generally accrete faster than those adjacent to small creeks or within platform interiors. These results demonstrate a spatial dichotomy in the resilience of backbarrier saltmarshes: marsh interiors are near a tipping point, but allochthonous mineral sediment fluxes allow enhanced local resilience along well-exposed and platform-edge marshes. Together, this suggests that backbarrier marshes are trending towards rapid, doughnut-like fragmentation. 

Abstract Landward migration of coastal ecosystems in response to sea-level rise is altering coastal carbon dynamics. Although such landscapes rapidly accumulate soil carbon, barrier-island migration jeopardizes long-term storage through burial and exposure of organic-rich backbarrier deposits along the lower beach and shoreface. Here, we quantify the carbon flux associated with the seaside erosion of backbarrier lagoon and peat deposits along the Virginia Atlantic Coast. Barrier transgression leads to the release of approximately 26.1 Gg of organic carbon annually. Recent (1994–2017 C.E.) erosion rates exceed annual soil carbon accumulation rates (1984–2020) in adjacent backbarrier ecosystems by approximately 30%. Additionally, shoreface erosion of thick lagoon sediments accounts for >80% of total carbon losses, despite containing lower carbon densities than overlying salt marsh peat. Together, these results emphasize the impermanence of carbon stored in coastal environments and suggest that existing landscape-scale carbon budgets may overstate the magnitude of the coastal carbon sink. 

Data set of measured sediment characteristics and vertical accretion rates of backbarrier marshes along the Georgia Bight. Data include bulk density (g/cm^3), water content (%), organic content (%), Pb-210 (Bq/kg), Cs-137 (Bq/kg), and calculated rates of vertical accretion (mm/yr) as measured from sediment cores collected during December 2017. Data are provided as CSV files. 

Marine transgression associated with rising sea levels causes coastal erosion, landscape transitions, and displacement of human populations globally. This process takes two general forms. Along open-ocean coasts, active transgression occurs when sediment-delivery rates are unable to keep pace with accommodation creation, leading to wave-driven erosion and/or landward translation of coastal landforms. It is highly visible, rapid, and limited to narrow portions of the coast. In contrast, passive transgression is subtler and slower, and impacts broader areas. It occurs along low-energy, inland marine margins; follows existing upland contours; and is characterized predominantly by the landward translation of coastal ecosystems. The nature and relative rates of transgression along these competing margins lead to expansion and/or contraction of the coastal zone and—particularly under the influence of anthropogenic interventions—will dictate future coastal-ecosystem response to sea-level rise, as well as attendant, often inequitable, impacts on human populations. Expected final online publication date for the Annual Review of Marine Science, Volume 16 is January 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.