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Free Content Spatial and temporal variability of turbulent mixing in an estuary

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Observations with a microstructure/CTD profiler and an ADCP during five cruises in 1994/95 provide a glance at the turbulent mixing climate of a partially mixed estuary, the Hudson River. The cruises took place under widely varying conditions of river discharge and external forcing by water level fluctuations in New York Bight. Tidal and fortnightly variability patterns of stratification, shear and mixing characteristics were qualitatively repeatable, largely following the description of Peters (1997). (i) Longer-term variations of buoyancy frequency and Richardson number (Ri) during flood were weakly correlated with the river discharge. (ii) All flood tides had substantial mixing. Cruise-to-cruise variations of turbulent dissipation rate, salt flux, and stress were large and correlated with variations in Ri. (iii) During ebb tides, mixing was weak in response to stable stratification during neaps, and it increased dramatically toward spring tides parallel with the occurrence of low Ri. Cruise-to-cruise variations of mixing became small toward spring tide. (iv) The largest vertical salt flux occurred during spring ebbs, which provided about 30% of the total fortnightly salt flux; floods throughout the fortnightly cycle providing most of the remainder. (v) The observed "level" of small-scale mixing, i.e. stress and vertical salt flux, was consistent with the integral momentum and salt budgets in the uniform segment of the Hudson where the bulk of the measurements were taken. (vi) One topographically forced flow feature examined, lee waves behind a trench across the river, was associated with elevated mixing.

Document Type: Research Article


Publication date: 1999-11-01

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  • The Journal of Marine Research publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. In the area of biology, studies involving coupling between ecological and physical processes are preferred over those that report systematics. Authors benefit from thorough reviews of their manuscripts, where an attempt is made to maximize clarity. The time between submission and publication is kept to a minimum; there is no page charge.
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