A Study on Pathways of Major River Waters in Long Island Sound

The Connecticut River, as the primary freshwater source of the Long Island Sound, enters near the estuary mouth. By applying a numerical simulation with dye pulses, continuous dye, and an age tracer, the river water pathways and the corresponding time scales are detected. The surface pathways are confirmed by drifter observations. Model results show that the river\u27s special geographical position, river discharge, and wind stress cause seasonal variation of the river water pathways. Down-estuary freshwater transport exists all year long; however, up-estuary transport has distinct seasonal patterns. During summer low discharge, 41% of the river water intrudes up-estuary with the bottom inflow along the deep channel. In winter, the intensified westerly winds force the river water to spread down-estuary; the up-estuary transport is nearly shut down. During spring high discharge, 28% of the river water moves up-estuary alongshore as a surface-intensified coastal buoyant current. Annually, 25% of the river water circulates up-estuary (with 1-yr retention rate of 20%); 21% stays in eastern Sound; and the remaining 54% directly leaves the Sound. The long-term average river water age in the Sound is 238 days, increasing up-estuary from 194 to 289 days. Three scenarios of summer wind forcing with different spatial variations are tested. Though the Sound is tidal-mixing dominated, mild winds still alter the position and strength of the estuarine exchange flow, either by enhancing the cross-estuary winds or lateral straining. On the shelf, wind enhances cross-shelf river water distribution. The sensitivities of circulation, salinity, and numerical drifter tracks to different atmospheric forcing also are studied. The highly spatial-varying wind forcing model has better performance in the simulation of surface drifter tracks. The Housatonic River, as the second largest freshwater source, enters from the northern shore of the central Sound. The seasonal river water pathways are described through water age distributions. In spring, river water moves up-estuary alongshore with coastal buoyant currents. In summer, the surface down-estuary flows in the western Sound block the up-estuary river water transport; the river water moves southward cross-estuary from the river mouth and then moves down estuary. In winter, the prevailing westerly winds drive the river water eastward down-estuary alongshore