Circulation of Prince William Sound, Alaska

Abstract

The circulation of Prince William Sound, Alaska, is described using hydrographic (1974–1989), current meter (1977–1979), and acoustic Doppler current profiler (1986–1990) observations from both the sound and the adjacent Gulf of Alaska. Ancillary data include data for winds, freshwater runoff, and satellite‐tracked drifters. Prince William Sound is a small inland sea in that it is wide enough to have appreciable horizontal cyclonic circulation. It is also a fjord in that it has basin depths to 700 m but is stilled at 180 m to the open ocean. The general circulation pattern is defined by a portion of the westward flowing Alaska Coastal Current on the Gulf of Alaska shelf that enters Prince William Sound through Hinchinbrook Entrance and transits the sound from east to west before exiting through Montague Strait and rejoining the coastal current. However, there is much variability in this circulation, especially in the transport through Hinchinbrook Entrance. In addition, some of the water entering the sound becomes involved in the cyclonic circulation in the northern sound and so has a longer residence time. The circulation is strongly mediated by seasonal and interannual variations in winds and freshwater runoff as well as by local topography both inside and outside the sound. In winter, the strong cyclonic winds over the Gulf of Alaska cause coastal downwelling and strong flow in the upper layers into Prince William Sound through Hinchinbrook Entrance and out through Montague Strait. In summer, the downwelling ceases, allowing subsurface denser water to rise above the sill and flow into the sound through the bottom layers of Hinchinbrook Entrance. We conclude that the best transport data came from Montague Strait, from which we estimate that ∼40% of the volume of Prince William Sound is flushed in summer (May–September). This estimated volume rises to about 200% in winter (October–April).

Calcium carbonate corrosivity in an Alaskan inland sea

“…The red circle delineates the single station (PWS2) that was sampled during every survey of PWS from 2009 through 2012. surface layer (Niebauer et al, 1994;Musgrave et al, 2013;Halverson et al, 2012b;Vaughan et al, 2001). Downwellingfavorable winds, which dominate from September through May, drive surface flow into PWS through Hinchinbrook Entrance, with compensatory outflow through Montague Strait (Niebauer et al, 1994;Halverson et al, 2012a). This "flowthrough" scenario is reduced and more complex between May and September, when winds are only weakly downwelling favorable or upwelling favorable and surface flows are typically weaker with reversals through either strait becoming more common (Halverson et al, 2012a;Niebauer et al, 1994).…”

“…This observation has only been made once, and we speculate that this is related to the synchronicity between when our measurements were collected and when downwelling conditions abated on the shelf. Being that deep water renewal events occur during nondownwelling periods (Niebauer et al, 1994) and can flush bottom waters in as rapidly as a month (Halverson et al, 2012a), calcite undersaturation could build up during stagnant winter months in the deepest portions of PWS but be extinguished by the time our survey takes place in May given this is the time seasonal downwelling conditions are on the decline (Mathis et al, 2014b;Weingartner, 2007). Yearto-year differences in downwelling forcing on the shelf can be large (Mathis et al, 2014b), and likely determine if calcite undersaturation is observed given our set cruise schedule.…”

“…The lowest TA / DIC ratios were in this water with values of 1.01 (Table 1). The high DIC relative to TA in deep water was presumed to result from the remineralization of organic matter that was produced in the euphotic zone and delivered to depth, and from the seasonal exchange of deep water with the adjacent GOA (Niebauer et al, 1994) that has a low TA / DIC ratio (Mathis and Evans, unpublished data, 2013). pH T , arag , and pCO 2 became decoupled in low salinity surface water that had concurrent low TA / DIC ratios (Fig.…”

“…Bathymetry data are from a digital elevation model (DEM) provided by the National Oceanic and Atmospheric Administration (NOAA) National Geophysical Data Center (NGDC; http://www.ngdc.noaa.gov/mgg/coastal/). The red circle delineates the single station (PWS2) that was sampled during every survey of PWS from 2009 through 2012. surface layer (Niebauer et al, 1994;Musgrave et al, 2013;Halverson et al, 2012b;Vaughan et al, 2001). Downwellingfavorable winds, which dominate from September through May, drive surface flow into PWS through Hinchinbrook Entrance, with compensatory outflow through Montague Strait (Niebauer et al, 1994;Halverson et al, 2012a).…”

“…Downwellingfavorable winds, which dominate from September through May, drive surface flow into PWS through Hinchinbrook Entrance, with compensatory outflow through Montague Strait (Niebauer et al, 1994;Halverson et al, 2012a). This "flowthrough" scenario is reduced and more complex between May and September, when winds are only weakly downwelling favorable or upwelling favorable and surface flows are typically weaker with reversals through either strait becoming more common (Halverson et al, 2012a;Niebauer et al, 1994). However, transport at this time can be highly baroclinic, with inflow at depth flushing the deepest portions of PWS (> 400 m) in as fast as a month (Halverson et al, 2012a).…”