Seasonal Cycles. Port Valdez receives large amounts of precipitation, most of which falls as snow during the winter. At northern latitudes, seasonal cycles of light and temperature vary considerably between summer and winter. As air temperature rises in the spring, snow and glacial ice begin to melt. The water column within the Port begins to stratify in late April and May as surface waters warm and freshwater flows increase. Freshwater runoff into the Port reaches a maximum between July and September (Xxxxxx and Burbank, 1973). The water remains vertically stratified in layers defined by differing temperatures and salinities between April and September. While the water is stratified, the top layer of warm, less dense freshwater forms a layer 2 to 20 m thick with salinities approaching 0 o/oo (Xxxx et al., 1973; Xxxxxx and Burbank, 1973). Surface stratification continues into October. During fall and winter, as surface waters cool and freshwater runoff decreases, the top layer becomes more similar in temperature and salinity to the lower layer of water. By December, winds erode stratification layers and the water column mixes (Xxxxxx and Xxxxx, 1988; Xxxx et al., 1973). Mixing circulates nutrients from the depths to the surface and returns oxygen-xxxx xxxxxx to the bottom.
