ACCELERATING SEA-LEVEL RISE AND ISLAND EROSION IN CHESAPEAKE BAY, VIRGINIA

Ongoing erosion of Chesapeake Bay islands threatens coastal communities and critical habitat. However, the main driver of this island loss—either sea level rise or intense storm events or both—remains unresolved, due to the short length of instrumental storm observations. Here we reconstruct erosion and storm frequency from an 8.3 m long vibra-core that demonstrates that sea-level rise has been the primary facilitator of island loss during the past 700 years. Core PCT VC1 (37.748383°,-75.871917°) was collected in 15 meters of water from the main channel of Pocomoke Sound (Virginia) in east-central Chesapeake Bay. Core chronology was constrained using radiocarbon dating as well as land clearance and pollution horizons. As a proxy for island erosion, fossil pollen was extracted from the core in order to identify downcore variation in the presence of marsh taxa (e.g., Poaceae, Amaranthaceae and Cyperaceae)—relative to overall pollen assemblage—which are typically restricted to shallow water. Likewise, deposition of coarse sediment in the same core, entrained from shallow sand flats flanking our site, was used to reconstruct past storm activity at 1-cm (~annual resolution). Both proxy records appear consistent with instrumental observations from the past 100 years but do not support a strong causal relationship between storm activity and island erosion on long timescales. Marsh taxa occurrence is relatively stable over most of the last 700 years, despite considerable changes in storm activity, but increases dramatically as sea-level rise accelerates after 1930 CE.