Downward flux

Downward flux of NO to the stratosphere a small difference between 26 and 27 may be important for this. 

Chapters 11 and 12 focus on the oceans. The first of these describes the use of U-series nuclides in the modern ocean, where they have been particularly useful during the last decade to study the downward flux of carbon. The second ocean chapter looks at the paleoceanographic uses of U-series nuclides, which include assessment of sedimentation rates, ocean circulation rates, and paleoproductivity. Both of these ocean chapters demonstrate that knowledge of the behavior of the U-series is now sufficiently well developed that their measurement provides useful quantitative information about much more than just the geochemistry of these elements. 

It is worth mentioning at this stage that the actual downward flux of °Th in the... 

The use of °Thxs to assess sedimentation rate relies on the assumption that the downward flux of °Thxs, Vm, equals the production of °Thxs, Pm The simple fact that °Th exists in the water column at all (Fig. 1) suggests that some advection must occur and that Vm niay not always exactly equal Pm Similarly, the spatial variability in °Th concentration in the water column (Henderson et al. 1999a) indicates that its rate of... 

Sedimentation Traps. Sediment traps (25) were installed in the hy-polimnion of Little Rock Lake to estimate the downward flux of Hg to the sediment surface. Traps were constructed of acrylic and Teflon following the design of Shafer (26). No metal components were used to avoid possible contamination artifacts. Traps were placed at 9 m at the 10-m-deep holesampling site. Traps were suspended from surface floats to prevent disturbing bottom sediments during deployment and retrieval. 

Stimulated by Levy s paper my attention turned towards tropospheric chemistry. First presented at the 1972 International Ozone Symposium in Davos, Switzerland, I proposed that in situ chemical processes could produce or destroy ozone in quantities larger than the estimated downward flux of ozone from the stratosphere to the troposphere (15, 16). Destruction of ozone occurs via reactions R5, R6 and R7 + R8. Ozone production takes place in environments containing sufficient NOx, via... 

Also shown are the separate contributions by ozone originating from the stratosphere (03s) and from photochemical production in the troposphere (03t). The data are summarized in Table 2. We note that both the downward flux of 03s and the tropospheric content of 03t in the NH are about 10% larger compared to the previous model version [18] due to model changes mentioned in Section 3. 

In the literature a wide range of estimates regarding the influx of ozone from the stratosphere into the troposphere is presented, derived by many different methods. Some studies report an annual flux between 200-870 Tg 03 yr 1 globally, whereas other studies report a flux between 500 and 1000 Tg 03 yr 1 for the NH only. With our model we estimate for the NH a net downward flux from the stratosphere of 580 Tg 03 yr1, which is partly balanced by an upward flux of ozone from photochemical production in the troposphere of 210 Tg 03 yr1, yielding a net downward cross-tropopause ozone transport of 370 Tg 03 yr 1. Globally, these values are 950, 370 and 580 Tg 03 yr 1, respectively. (Note that the troposphere-to-stratosphere ozone flux in the... 

Figure 4.2 shows the concentration of HTO in rainfall, in TU units, at Valentia on the southwest coast of Ireland from 1952 to 1972 (Weiss et al., 1979). Measurements at sea showed no difference in TU of rain and water vapour, when allowance was made for the isotopic difference in vapour pressure of HTO and H20. TU levels in water vapour and rain are higher well inland than at the coast by factors up to four (Eriksson, 1965). There are two reasons for this difference. The rainfall and humidity are usually less in continental areas, so that the downwards flux of HTO is less diluted with H20. Also, re-evaporation of HTO from land increases the atmospheric concentration at low levels. 

The shearing stress, r, exerted by the wind on the ground entails a downwards flux of momentum. In the aerodynamic boundary layer above the surface, the momentum is transferred by the action of eddy diffusion on the velocity gradient. The friction velocity is defined by w = t/pa and is a measure of the intensity of the turbulent transfer. Near to a rough surface, the production of turbulance by mechanical forces... 

An important parameter used to quantify dry deposition processes is the velocity of deposition (Kg) (Chamberlain, 1953). Vg is defined as the downward flux of aerosol or gas to a vegetation or soil surface, normalised to the ambient atmospheric gas or aerosol concentration above that surface. In the case of radionuclide deposition processes flux and concentration are, respectively, measured in units of radioactivity per unit area and volume, hence... 

Pakhomov EA, Froneman PW, Wassmann P, Ratkova T, Arashkevich E (2002) Contribution of algal sinking and zooplankton grazing to downward flux in the Lazarev Sea (Southern Ocean) during the onset of phytoplankton bloom a lagrangian study. Mar Ecol Prog Ser 233 73-88... 

A few substances are capable of showing both upward and downward fluxes. An example is ammonia. Ammonium in the soil, NH4 , is in equilibrium with ammonia gas, NH3(g)... 

Smith (231) found a higher value, 6 x 10 molecules cm sec 1, using tritium as a tracer, but he also found an exact balance between upward and downward fluxes. It should be noted that transport through the tropopause is both latitude dependent [Martell (165) Gudiksen, Fairhall, and Reed (88) and Fabian, Libby, and Palmer (60)] with the greatest contribution coming at midlatitudes [Reiter, et al. (207) Danielsen (45) and Smith (231)] and seasonal dependent, as determined from the ozone model of Junge and Czeplak (130). 

Ecological Controls on Alkenone Production and Downward Flux... 

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