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An ephemeral estuarine turbidity maximum (ETM) occurs at high water in the macrotidal Taf estuary (SW Wales, United Kingdom).
A new mechanism of ETM formation, due to resuspension and advection of material by flood tidal currents, is observed that
differs from classical mechanisms of gravitational circulation and tidal pumping. The flood tide advances across intertidal
sand flats in the main body of the estuary, progressively entraining material from the rippled sands. Resuspension creates,
a turbid front that has suspended sediment concentrations (SSC) of about 4,000 mg I−1 by the time it reaches its landward limit which is also the landward limit of salt penetration. This turbid body constitutes
the ETM. Deposition occurs at high slack water but the ETM retains SSC values up to 800 mg I−1, 1–2 orders of magnitude greater than ambient SSC values in the river and estuarine waters on either side. The ETM retreats
down the estuary during the ebb; some material is deposited thinly across emergent intertidal flats and some is flushed out
of the estuary. A new ETM is generated by the next flood tide. Both location and SSC of the ETM scale on Q/R3 where Q is tidal range and R is river discharge. The greatest expression of the ETM occurs when a spring tide coincides with
low river discharge. It does not form during high river discharge conditions and is poorly developed on neap tides. Particles
in the ETM have effective densities (120–160 kg m−3) that are 3–4 times less than those in the main part of the estuary at high water. High chlorophyll concentrations in the
ETM suggest that flocs probably originate from biological production in the estuary, including production on the intertidal
sand flats. 相似文献
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Darren F. Mark John Parnell Simon P. Kelley Sarah C. Sherlock 《Journal of Geochemical Exploration》2006,89(1-3):259
Integration of fluid inclusion analysis with high spatial resolution Ar–Ar dating of K-feldspar cements has been used to resolve and reconstruct palaeo-fluid flow. Fluid inclusion analysis allows discrimination of distinct cement phases, thereby identifying discrete episodes of fluid flow. Ar–Ar dating of the same cements via high spatial resolution laserprobe establishes absolute age constraints on the framework previously constructed. Integration of these two datasets yields temperature–composition–time data. 相似文献
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Stable isotope evidence for the atmospheric origin of CO2 involved in carbonation of MSWI bottom ash
Stable isotopes were used to constrain the origin of CO2 involved in the ageing process of municipal solid waste incineration (MSWI) bottom ash under open-air conditions. The δ13C and δ18O values of CaCO3 occurring in MSWI bottom ash samples of variable age and the δ13C of the residual organic matter content were measured, and laboratory assessments made of the isotopic fractionation accompanying CaCO3 neo-formation during accelerated carbonation experiments of bottom ash or pure lime with atmospheric or industrial CO2. The results indicate that stable isotopic compositions exhibited by fresh and aged bottom ash samples reflect non-equilibrium processes resembling those described in the carbonation of concrete and mortar. They also lead to conclusions on the prevalent involvement of atmospheric CO2 in the open-air carbonation of MSWI bottom ash. 相似文献