Effects of remote storms on cross-shelf exchange at Matanzas Inlet, FL

Transport of water and suspended particles across the inner-shelf provide an exchange mechanism between back-barrier systems, the nearshore, and the inner-shelf. These processes are important for larval transport, sediment transport, and mixing of coastal waters. To investigate the processes that control transport from an inlet to the inner-shelf, instrumentation were deployed at two sites across from Matanzas Inlet, FL, from January to April 2018, to measure water level, velocity, salinity, temperature, and suspended-sediment concentrations.

Over the three-month observation period, numerous weather events caused sediment resuspension and movement. The most commonly observed events were extratropical cyclones formed in the Mid-Atlantic Bight, Gulf of Maine, and New Brunswick and Nova Scotia. Cold fronts and the dry conveyors of these systems created northerly winds, large wave events, and strong southward currents that resuspended sediments and induced transport of sediment south along the Florida coast. Extratropical cyclones forming over the southern United States and South-Atlantic Bight were also observed to influence sediment transport. Westerly winds blew over the continent and had less influence on the water, creating smaller waves and having little effect on the currents, which tended to flow north. Although small, these waves were capable of resuspending sediment and led to a weak flow of sediment south or a large flow of sediment north along the coast. The location of the storms has a major influence on the direction of the wind and the resulting waves and currents. Storm periods like the one observed led to large quantities of sediment moving south. It is possible that years with less of these northern winter storms could lead to sediments flowing north. In either case, increasing frequency of extratropical storms will result in an increase in erosion along the entire east coast of the United States.