Physical problems of the benthic boundary layer

Abstract

Abstract.Since the boundary layer at the sea bed has a number of features in common with boundary layers found in laboratory scale flows and in meteorology, a brief review is given first of the properties which may be inferred from experience in these fields or from theoretical studies. Measurements of velocity profiles, turbulence, and shearing stress which have been made near the bottom, in deep water, and on the continental shelf, are described in relation to this background. In particular, the logarithmic form of the velocity profile near the bed and deductions from it appear to be valid in certain conditions, but the occurrence of ripples and other bed forms is a complicating feature. The relation of the dynamical aspects of the flow to the transport of sediment as bed load and in suspension is discussed. The diffusive properties of the layer are then considered, in relation to fluxes near the sea-sediment interface and to the formation of nepheloid layers or layers well mixed in temperature and salinity.

The Significance of Syncytial Tissues for the Position of the Hexactinellida in the Metazoa

“…The only stable orien− tation for this species was to have been lying flat on the sea floor, a posture that is incompatible with a suspension−feed− ing poriferan. Not only is the limited local current flow greatly reduced within the benthic boundary layer, the thick− ness of which is dependent on the flow regime (Bowden 1978;reviewed by Nowell and Jumars 1984), but the pore system is also liable to being clogged by fine particles, espe− cially given the tendency of obstructions in the boundary layer to induce sediment resuspension (Carey 1983). This is true even if the sponge produced large quantities of mucus as some modern taxa do to prevent clogging (Barthel and Gutt 1992).…”

“…The lack of upward growth exacerbates other problems in a muddy environment. In the deep ocean, almost the entire sponge would have been contained within the 1 cm thick vis− cous sub−layer (Bowden 1978), which would have restricted the effects of turbulence on the local chemistry, maintaining a constant low oxygenation state but limiting oxygen replen− ishment. There is also a risk of burial of the entire sponge, and even with the sponge lying on the surface, nearly half of the surface area would be unavailable for filter feeding.…”

Shallow water tidal currents in close proximity to the seafloor and boundary-induced turbulence

“…The estimates of ζ 0 are very sensitive to the accuracy of the fit. At several segments of the imperfect log-fit, ζ 0 became almost zero, which is not unusual in oceanographic research (e.g., Bowden 1978), but this may lead to higher uncertainty of u * estimates.…”

“…7b, where the mean velocity U (1) at ζ=1 mab (Ludwick 1975;Bowden 1978;Elliott 2002) was calculated based on that measured at ζ=0.48 mab using the log-layer model (Eq. 1).…”

Modeling of the near-field distribution of pollutants coming from a coastal outfall

“…In this layer, the flow is affected by the processes occurring at the boundary. Strong gradients of physical, chemical, and biological properties may occur in this layer as well Bowden (1978). The thickness of the BBL is generally of the order of meters above the seabed.…”