turbidity current
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turbidity current short-lived, powerful, gravity-driven current consisting of a
dilute mixture of sediment and water of a density greater than the surrounding water; the sediment is supported by the turbulence of the water
within the flow. Two types are distinguished: low velocity (low-density turbidity currents), and high velocity (high-density currents). Turbidity currents may be triggered by various events, such as earthquakes, storm waves,
over-supply of sediment, and have a flow route starting on the continental
shelf, continuing downslope through a submarine canyon and ending (with deposition of the sediment as a deep-sea fan) on the continental rise (~sea-f1oor
topography and turbidite).
turbidity maximum phenomenon characteristic of many estuaries where freshwater
mixes with seawater. Due to the difference in density of freshwater and seawater, a countercurrent of seawater occurs underneath the outflowing freshwater from river through estuary to the sea. Settling sedimentary particles from
the freshwater layer are retransported up the estuary by the bottom countercurrent, causing an accumulation of suspended matter in the low brackish
zone of the estuary. This is called the turbidity-maximum zone.
turbulence irregular motion of a fluid superimposed upon other, more regular,
currents, and by which transport of momentum, heat and dissolved substances may occur, in addition to the transport by the regular current. The
transport of momentum gives an internal or boundary-layer friction that is
comparable to viscous friction, but that is much larger and therefore often
considered the sole friction force in the equations of motion. Oceanic
motions can nearly always be considered turbulent. Turbulent mixing of
heat and dissolved substances (eddy diffusion, ~eddy) is also much more
important in oceanographic practice than molecular diffusion.
turnover rate presents the fraction of the amount of a substance in a component
which is replaced over a certain time span. The biomass turnover rate or relative production (P/B ratio, where P = production and B = biomass) is a useful measure of the rate of functioning of a certain biomass in an ecosystem.
Turnover time is the reciprocal of the rate, i.e., the time needed to replace a
quantity of substance equal to the amount in the component.
turnover time ~turnover rate and ~time scales.
turtles, marine ~Reptilia, marine.
Tuscarora Expedition (1874) a US expedition under George Belknap, contemporaneous with the Challenger Deep-Sea Expedition, contributed to the knowledge of
temperature distribution and bottom deposits in the Pacific Ocean. Piano
wire was used for the deep-sea soundings using Sir William Thomson's (Lord
330
turbidity current short-lived, powerful, gravity-driven current consisting of a
dilute mixture of sediment and water of a density greater than the surrounding water; the sediment is supported by the turbulence of the water
within the flow. Two types are distinguished: low velocity (low-density turbidity currents), and high velocity (high-density currents). Turbidity currents may be triggered by various events, such as earthquakes, storm waves,
over-supply of sediment, and have a flow route starting on the continental
shelf, continuing downslope through a submarine canyon and ending (with deposition of the sediment as a deep-sea fan) on the continental rise (~sea-f1oor
topography and turbidite).
turbidity maximum phenomenon characteristic of many estuaries where freshwater
mixes with seawater. Due to the difference in density of freshwater and seawater, a countercurrent of seawater occurs underneath the outflowing freshwater from river through estuary to the sea. Settling sedimentary particles from
the freshwater layer are retransported up the estuary by the bottom countercurrent, causing an accumulation of suspended matter in the low brackish
zone of the estuary. This is called the turbidity-maximum zone.
turbulence irregular motion of a fluid superimposed upon other, more regular,
currents, and by which transport of momentum, heat and dissolved substances may occur, in addition to the transport by the regular current. The
transport of momentum gives an internal or boundary-layer friction that is
comparable to viscous friction, but that is much larger and therefore often
considered the sole friction force in the equations of motion. Oceanic
motions can nearly always be considered turbulent. Turbulent mixing of
heat and dissolved substances (eddy diffusion, ~eddy) is also much more
important in oceanographic practice than molecular diffusion.
turnover rate presents the fraction of the amount of a substance in a component
which is replaced over a certain time span. The biomass turnover rate or relative production (P/B ratio, where P = production and B = biomass) is a useful measure of the rate of functioning of a certain biomass in an ecosystem.
Turnover time is the reciprocal of the rate, i.e., the time needed to replace a
quantity of substance equal to the amount in the component.
turnover time ~turnover rate and ~time scales.
turtles, marine ~Reptilia, marine.
Tuscarora Expedition (1874) a US expedition under George Belknap, contemporaneous with the Challenger Deep-Sea Expedition, contributed to the knowledge of
temperature distribution and bottom deposits in the Pacific Ocean. Piano
wire was used for the deep-sea soundings using Sir William Thomson's (Lord