On the implementation of a three-dimensional circulation model for Prince William Sound, Alaska

Abstract

The POM (Princeton Ocean Model), a three-dimensional, primitive equation ocean circulation model, is applied to Prince William Sound, Alaska. A 3-D concentration equation for passive tracers is added to POM to explore transport pathways and rates, plus retention zones and residence times. The 3-D structures of the current, density, and passive tracer concentration are examined for realistic bottom topography, idealized Alaskan coastal water inflow/outflow, and idealized wind-forcing. Based on observational evidence and ecological concerns, the ‘lake/river hypothesis’ (i.e. the effect of weak versus strong throughflow on the ecology of the Sound) is explored to determine its influence on the circulation and transport patterns of passive tracers. Strong inflow through Hinchinbrook Entrance (river-like case) is crucial to the vigorous cyclonic circulation in the Sound and strong coupling to offshore influences, while with a weak inflow (lake-like case), the circulation in the Sound is much weaker and weakly coupled to offshore influences. The strength of the inflow and the wind direction are particularly important for determining the nature of the secondary branches of the throughflow in the northwestern Sound and the position, strength, and number of cyclonic and anticyclonic gyres. Mesoscale eddies are induced in the deep basins that have not yet been studied observationally. The advection of buoyant (relatively fresh) coastal water into the Sound significantly influences the circulation pattern and upper-layer density stratification. Idealized winter and summer wind-forcing generate distinctive surface circulation patterns that are important to the transport pathways, residence times, and retention zones of passive tracers; for example, northward and westward winds increase the northernmost penetration of passive tracers entering the Sound from offshore and the residence time substantially.