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Quantifying turbulent mixing and oxygen fluxes in a Mediterranean-type, microtidal estuary

journal contribution
posted on 2003-09-01, 00:00 authored by J Sharples, Michael Coates, John SherwoodJohn Sherwood
Experiments were carried out on an intermittent estuary during its closed (summer) and open (winter) states to identify the physical processes responsible for vertical mixing across the halocline, and to quantify vertical fluxes of oxygen and salt between water layers. During the blocked phase a two-layer structure was observed, with a brackish surface layer overlying old seawater. Within a deep basin the wind-driven turbulent mixing was consistent with the measured surface-layer turbulent dissipation, but the dissipation in the bottom layer appeared to be driven by internal seiching. In the shallow regions of the estuary vertical fluxes of dissolved oxygen were indicative of oxygen demand by respiration and remineralization of organic material in bottom water and sediments. During the estuary's open phase a three-layer structure was observed, having a fresh, river-derived surface layer, a middle layer of new seawater, and a bottom layer of old seawater. In the shallower regions surface-layer turbulent diffusion was consistent with the strong, gusty winds experienced at the time. The dissolved oxygen of the incoming seawater decreased to very low values by the time it reached the upstream deep basin as a result of the low cross-pycnocline oxygen flux being unable to compensate for the oxygen utilization. At least 50 % of the cross-pycnocline salt fluxes in the shallow reaches of the open estuary are suggested to be driven by Holmboe instabilities.

History

Journal

Ocean dynamics

Volume

53

Issue

3

Pagination

126 - 136

Publisher

Springer

Location

Berlin, Germany

ISSN

1616-7341

eISSN

1616-7228

Language

eng

Publication classification

C1 Refereed article in a scholarly journal

Copyright notice

2003, Springer-Verlag