Observations on the characteristics of the exchange flow in the Dardanelles Strait

A mooring section at each end of the Dardanelles Strait was deployed by the Naval Research Laboratory on 28-29 August 2008 and maintained until 11 October 2009. Each section was equipped with two bottom-mounted Barny moorings and a vertical string that together delivered concurrent bottom pressure, temperature, salinity, and almost full-water column current velocity observations. These observations at the mooring sections indicated that on longer timescales (monthly or longer), the exchange through the Dardanelles Strait showed little variability and had a two-layer structure with brackish waters moving approximately southward in the upper layer and more saline Aegean waters flowing roughly northward underneath. On shorter time scales (synoptic), there were pronounced fluctuations in both layers. In the northern section, some manifested as almost simultaneous reversals of the flow direction in both layers with lighter upper-layer waters backing into the Sea of Marmara and dense lower-layer waters moving toward the Aegean Sea. In the southern section, some of the exchange variability consisted of a three-layer flow structure with upper brackish and bottom salty layers moving toward the Aegean Sea and a middle salty layer flowing toward the Sea of Marmara. This three-layer exchange persisted from a day to a week. Synoptic flow variability in the upper layer was partly related to both the along-strait wind stress and the bottom pressure anomaly gradient, while lower-layer current fluctuations were coherent with the bottom pressure anomaly gradient