Seasonal and Interannual Variability of Exchange Between Delaware Bay and the Continental Shelf

Abstract This study of Delaware Bay, USA, uses a numerical particle tracking model to examine the exchange of material between the bay and adjacent continental shelf on seasonal timescales. Vertically averaged, near-bottom, and near-surface transport were targeted by simulating particles with three different types of behavior: neutrally buoyant, bottom-seeking (similar to silt settling), and surface-seeking (similar to the slow rise of buoyant material), respectively. Particle release locations are drawn from a space-filling distribution throughout the model domain, and the origin regions of particles that enter the bay vary seasonally, interannually, and with particle behavior. The mean along-shelf circulation is from the northeast to the southwest, and particles entering the bay tend to come from the northeast, within tens of kilometers from shore. Source regions of bottom-seeking particles that enter the bay are farther offshore than source regions of neutral or surface-seeking particles. Bottom-seeking particles also remain in the bay for longer times than particles with other behaviors. Particles of all behaviors are flushed out of Delaware Bay more quickly in winter than in summer. Although this study focuses on a specific region of eastern North America, the findings about sources of particles to the bay are likely applicable to other embayments with similar shelf circulation patterns and may guide efforts to better understand transport of pollutants, larvae, and other material.