--> --> Coupled Barrier Island-Bay Collapse During the 8.2 ka Sea-Level Event and Future Implications

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Coupled Barrier Island-Bay Collapse During the 8.2 ka Sea-Level Event and Future Implications

Abstract

Barrier islands and coastal lands across the globe are threatened by accelerating sea-level rise including the possibility of punctuated rapid rise due to ice stream collapse. The most recent global and near-instantaneous sea-level rise event occurred between 8.15 and 8.31 ka, when ice-equivalent sea-level rose between 0.8 and 2.2 m (1.6 and 4.4 mm/yr) with local sea-levels varying depending on their glacial-isostatic signature. These rates are within the current range of sea-level rise in some regions and below predicted rates for the end of this century. A significant portion of this rise occurred as a punctuated event believed to have lasted only about a century and is attributed to the final drainage of glacial Lake Agassiz-Ojibway. Although local glacial-isostatic factors resulted in a sea-level rise of only 0.2-0.56 m, this period of rapid sea-level rise led to the virtual destruction of Mustang Island, the most stable barrier island of the northwestern US Gulf Coast. Collapse of the barrier island resulted in dramatic changes in contiguous Corpus Christi Bay. Dinoflagellate cyst distributions within a drill core from the bay indicate a period of open marine salinities that occurred at the same time as a 15 kilometer landward shift of the bay-head delta. These results provide an analogue for predicting coastal morphodynamic response to accelerated sea-level rise and highlight the potential threat to restoration efforts.