Seasonal transport variations in the straits connecting Prince William Sound to the Gulf of Alaska

摘要

Exchange of water between Prince William Sound and the Gulf of Alaska has a significant impact on its circulation and biological productivity. Current meter records from moored instruments in the two major straits connecting Prince William Sound to the Gulf of Alaska are analyzed to characterize the seasonal variations in water exchange. Eight individual deployments, each lasting for about 6 months, were made during the years 2005-2010. Two moorings were placed across each passage to account for horizontal flow variability. Monthly averaged, depth-integrated transport in winter is characterized by a strong barotropic inflow through Hinchinbrook Entrance and outflow through Montague Strait. The transport through each passage can reach 0.2Sv, which could replenish the volume of Prince William Sound in as little as 3 months. Depth-integrated transport is weaker and more variable in direction in summer than in winter, implying that Prince William sound is not always a simple flow-through system. Monthly transports range between -0.05 and 0.08Sv in each passage, and the corresponding flushing times exceed 1 year. The flow through both passages is highly baroclinic in the summer, so that the layer transport can be significant. For example, the deep inflow through Hinchinbrook Entrance can reach 0.05Sv, which would flush the deep regions of Prince William Sound (>400 m) in only 23 days. The transport imbalance between Montague Strait and Hinchinbrook Entrance cannot be accounted for by considering other terms in a volume budget such as local freshwater input, meaning the imbalance is mostly a result of under-resolving the cross-strait flow variability. The magnitude of the monthly mean depth-integrated transport through Montague Strait and Hinchinbrook Entrance depends non-linearly on the shelf winds. Strong downwelling conditions, characteristic of the winter, drive inflow through Hinchinbrook Entrance, which is balanced by outflow through Montague Strait. Weak downwelling or upwelling conditions, characteristic of the summer, allow deep water from below the shelf break to flow in through Hinchinbrook Entrance.