Sink rate

Extrapolated to 1978 from Noshkin and Bowen (1973) estimate of fallout deposited at 4000 m on their sinking rate model. 

In natural waters, sinking rates (mathematically equivalent to the flow velocity for a stationary cell) are predicted to increase in proportion to the square of the cell radius according to a Stokes law dependency. For a spherical organism ... 

Many particles reach the seafloor by sinking through the water column. This particle-byparticle accumulation is termed pelagic sedimentation. Sinking rates depend on particle size, shape, and density. The sinking rate of a particle in a fluid experiencing laminar flow can be estimated from Ostwald s modification of Stokes law. 

Thus, for particles with a similar density and shape, sinking rates increase with increasing diameter because of the decrease in surface area to volume ratio. As shown in Table 13-5, sand-sized grains reach the sediments in a few days, whereas clays can take centuries. If entrained in a current, sinking particles can also experience significant horizontal transport. 

Particle sinking rates are of considerable interest because the fester a particle can make the trip to the seafloor, the shorter the time it is subject to decomposition or dissolution and, hence, the greater its chances for burial in the sediments. The length of the trip is dictated by the depth to the seafloor, the horizontal current velocity, and the particle sinking rates. As shown in Figure 13.5, sedimentation rates decrease with increasing water depth. This relationship reflects the preservation issue and the feet that coastal waters tend to have larger sources of particles to the surfece zone. 

Particle Type Particle Diameter (micron) or Source Sinking Rate Time to Settle through 4 km Water Depth Horizontal Distance (km) Traveled in Sinking 1000 m through a Current of Icm/s Reference... 

Some particles, particularly the biogenous ones, are prone to alteration as they settle onto the sediments and then imdergo burial. The likelihood of particle preservation is generally enhanced in settings where the trip to the seafloor is short and burial rates are fast. The time a particle takes to settle onto the seafloor is determined by water depth and particle sinking rates. The latter is a function of particle shape and density. Seawater... 

In addition to undigested organic matter, fecal pellets also contain fragments of calcareous and siliceous hard parts and clay-sized grains of clay minerals. Fecal pellets can harbor viable bacterial and phytoplankton cells. Because of their fast sinking rates, fecal pellets reach the seafloor relatively intact. Their organic matter represents the major source of food for the benthos. 

Particle ballasting Packaging of particles which enhances their sinking rates and also appears to confer some protection against microbial attack. 

A linear PDF, such as the diffusion equation, can only have first-order and zero-order source or sink rates. But what if the source or sink term is of higher order An example would be the generalized reaction... 

In Chapter 2, we used the control volume technique represented by equation (2.1) to transport mass into and out of our control volume. Inside of the control volume, there were source and sink rates that acted to increase or reduce the mass of the compound. Anything left after these flux and source/sink terms had to stay in the control volume, and was counted as accumulation of the compound. 

Therefore, let us consider the following thought process if the end result of turbulence, when visualized from sufficient distance, looks like diffusion with seemingly random fluctuations, then we should be able to identify the terms causing these fluctuations in equation (5.18). Once we have identified them, we will relate them to a turbulent diffusion coefficient that describes the diffusion caused by turbulent eddies. Looking over the terms in equation (5.18) from left to right, we see an unsteady term, three mean convective terms, the three unknown terms, the diffusive terms, and the source/sink rate terms. It is not hard to figure out which terms should be used to describe our turbulent diffusion. The unknown terms are the only possibility. 

Carbon dioxide has a source/sink rate of - A C, where C is the water concentration of carbon dioxide. The concentration profile in the concentration boundary layer would be steeper near the interface, as illustrated in Figure E8.7.1. 

Bienfang, P.K. and Harrison, P.3., 1984. Co-variation of sinking rate and cell quota among nutrient replete marine phytoplankton. Mar. Ecol. Prog. Ser., 14 297-300. 

Bienfang, P. K. and Harrison, P. J., Sinking-rate response of natural assemblages of temperate and subtropical phytoplankton to nutrient depletion, Mar. Biol., 83, 293, 1984. 

Figure 6.3 The sinking rates for particles (<100 pm) that follow Stokes law and for particles typically greater than 0.1 to 0.2 mm in diameter settling velocity varies according to the square root of the diameter—as described by the impact law. (Modified from Krumbein and Sloss, 1963.)...

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