Ice Raft Formation, Dispersion and Sedimentation on New England Salt Marshes

Ice-rafting of sediment is a major winter process in New England coastal marshes, increasing in intensity northwards. A survey of ice rafts conducted across three back-barrier salt marshes characterizes and quantifies sediment loads. The mean concentration of sediment in ice rafts increases to the north: 10.4g/L at Nauset, MA; 20.3g/L at Essex, MA, and 26.2g/L at Wells, ME. Inorganic sediment dominates 70% of ice rafts sampled. Ice raft dispersion across the marsh surface, while highly stochastic, is influenced by tidal amplitude, channel network density, meteorological. conditions, and marsh surface elevation. A numerical model of ice-rafted sediment deposition on New England salt marshes is derived. Mechanisms of ice raft sediment incorporation and dispersion, conceptual models of ice raft formation, and estimates of the relative magnitude of vectors are presented, with implications for the vertical accretion of northern marshes in a regime of rising sea level.