Variability of Currents and Water Properties from Year-Long Observations in a Fjord Estuary

Abstract

Abstract Observations were made of velocity, temperature, and conductivity from a vertical array of sensors at a location in Puget Sound for 1 year commencing in September 1975. Winds were measured nearby on land, and water properties were measured along the Sound at 2- to 3-month intervals. Most dense bottom water entered the Sound below sill depth at about fortnightly intervals during early fall near the end of the coastal upwelling season. The fortnightly events were associated with large tides over the entrance sill. Density decreased about linearly until early winter when cold water entered the Sound first at the bottom in a series of step decreases, also at about fortnightly intervals. The largest was 1.6°C in 3-4 days. Density increased during each inflow interval lasting about 5 days, but the overall density continued to decrease until early February when the water column became isothermal but was still stratified. During late winter and early spring, density again increased through a series of fortnightly salinity intrusions, and the initial one was more than 0.5∘ in 5 days. Mean daily near-bottom speeds were up to about 20 cm/sec, implying a possible excursion exceeding the length of the Sound. Winds were observed to alter mean daily current profiles to more than half the water depth. These and other winter observations indicated deep-water renewal was much quicker than earlier estimates.