Water column

About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.

Observations of Stratified Turbulent Mixing in an Estuary: Neap-to-spring Variations During High River Flow

Abstract: Observations of turbulent mixing, stratification and currents were made with a free-falling microstructure profiler and a 600-kHz ADCP in the Hudson River off Manhattan in May 1994. The ship was anchored in a relatively straight and uniform channel about 15 m deep. Over 4 days of intense observations from 19 to 24 May 1994, the progression from neap tides to spring tides caused a severe reduction in stratification from an initial top-to-bottom salinity difference of 18 to 3–6. While low gradient Richardson numbers, Ri , occurred only in the weakly stratified bottom layer on flood during neap tides, low Ri spanned the water column on the second half of ebb during spring tides. Turbulent dissipation rates varied roughly inversely to Ri . During neap conditions, turbulent mixing was intense only in the bottom layer on flood, where eddy diffusivities, K ρ , reached more than 10 −2 m 2 s −1 , while mixing was weak in the centre of the halocline near 5 m. During spring tides, strong mixing occurred throughout the water column during the latter part of ebb with typical K ρ ≈5×10 −3 m 2 s −1 and typical vertical salt flux of 0·0015 kg m −2 s −1 . If it existed in isolation, this flux would eliminate the haline stratification on a time scale of 4 h. Ebb-time bands of low Ri and intense mixing showed increasing phase lag with increasing distance from the bottom. The spring-tide, ebb-time internal turbulent stress was relatively uniform with depth with a typical magnitude of 0·4 Pa (4 dyne cm −2 ). Turbulent overturning (Thorpe) scales ranged from below 1 cm in the neap-tide halocline to a few metres in the weakly stratified bottom layer on flood. The strong spring-tide, ebb-time mixing had Thorpe scales of typically 0·5 m throughout the water column. Ozmidov scales tracked Thorpe scales except in the weakly stratified layer above the bottom.

Biogenic Matter Diagenesis on the Sea Floor: A Comparison Between Two Continental Margin Transects

Abstract: Benthic chamber measurements of the reactants and products involved with biogenic matter diagenesis (oxygen, ammonium, nitrate, silicate, phosphate, TCOP, alkalinity) were used to define fluxes of these solutes into and out of the sediments off southern and central California. Onshore to offshore transects indicate many similarities in benthic fluxes between these regions. The pattern of benthic organic carbon oxidation as a function of water depth, combined with published sediment trap records, suggest that the supply of organic carbon from vertical rain can just meet the sedimentary carbon oxidation + burial demand for the central California region between the depths 100-3500 m. However, there is not enough organic carbon raining through the upper water column to support its oxidation and burial in the basins off southern California. Lateral transport and focusing of refractory carbon within these basins is proposed to account for the carbon buried. The organic carbon burial efficiency is greater off southern California (40-60%) compared to central California (2-20%), even though carbon rain rates are comparable. Oxygen uptake rates are not sensitive to bottom water oxygen concentrations nor to the bulk wt. % organic carbon in surficial sediments. Nitrate uptake rates are well defined by the depth of oxygen penetration into the sediments and the overlying water column nitrate concentration. Nitrate uptake accounts for about 50% of the total denitrification taking place in shelf sediments and denitrification (0. l-l .O mmolN/m*d) occurs throughout the entire study region. The ratio of carbon oxidized to opal dissolved on the sea floor is constant (0.8 t 0.2) through a wide range of depths, supporting the hypothesis that opal dissolution kinetics may be dominated by a highly reactive phase. Sea floor carbonate dissolution is negligible within the oxygen minimum zone and reaches maximal rates