Alaska Ocean Observing System Data Management

Prince William Sound

Ocean Circulation

Although the daily currents in PWS can vary greatly, the seasonal currents are generally more predictable. The moored buoys around the Sound will provide continuous data that can be used to correct a computer simulation, or model, with data on real conditions. The model will then be able to provide better forecasts of ocean circulation in PWS over 24 and 48 hour periods.

Researcher Steve Okkonen is leading a team of oceanographers that will supplement the current data being collected with buoys in Hinchinbrook Entrance and Montague Straits to measure the amount of water that comes into and leaves the sound on a seasonal basis. Instruments on three buoys set up across each passage will measure the salinity, temperature and pressure of the water as it moves in and out of the Sound.

In addition, a salinity and temperature recorder has been placed on a boat to be taken along the perimeter of the Sound the summer of 2005 in order to develop a complete picture of the seasonal trends in temperature. This will give researchers a good idea of how much fresh water is coming into the Sound from the perimeter, and how much warm water is coming in from the south.

Researchers thus far have discovered that the circulation of PWS adheres to a cyclical model both in the summer and in the winter. During the radical temperature changes of the fall and spring the water mixes, often causing the currents to change, but in the summer and winter they always return to their old familiar gyre.

In the winter, this gyre is caused by warm winds that come up from the southeast, paralleling the coast along the Gulf of Alaska and into PWS. These winds push water up against the coast, causing the sea level to be slightly higher - about 10cm - along the coast than at that center of the Sound.

"Think of Prince William Sound as a bowl, with a couple of openings," Okkonen said. This subtle shape causes the water to want to flow in a counter-clockwise motion, coming in Hinchinbrook Entrance and leaving at Montague Straits. In the summer, the ocean is a lot calmer, with fewer winds to create the bowl affect. However, there is significantly more fresh water coming in from the Copper River Delta and from the many glaciers that flow into the Sound. The light freshwater creates its own layer on top of the salt water. "It will mound up around the perimeter," Okkonen said, creating a "summer analog to the winter situation."