Prince William Sound with its 3,000 miles of shoreline is surrounded by the Chugach Mountains to the east, west and north. Fifty-mile long Montague Island and several smaller islands form natural breakwaters between the Sound and the Gulf of Alaska. Between the barrier islands stretch underwater sills separating the Sound’s deep waters from the much shallower waters of the Gulf. Deep water renewal occurs during the winter when cold winds from interior Alaska cool the surface waters causing them to sink, while the warmer bottom water rises to the surface bringing rich nutrients which support huge plankton blooms in the spring.
This is actually a summer image and the same area is complete iced over in winter.