Surface tracer flux

Surface tracer fluxes, such as freshwater fluxes, may be included by appropriate surface boundary conditions (Griffies et al., 2001). The tracer equations represent also the interface between the chemical-biological model components and the physical model. In this case, terms have to be added that describe sources and sinks due to chemical-biological reactions. 

The advantage of the k-profile scheme is its treatment of the convective limit. Since convection implies strong vertical mixing that destroys vertical gradients, the calculation of vertical fluxes from gradient formulas becomes inaccurate. This problem is circumvented in the k-profile approach by a special term in the expression for the turbulent vertical tracer fluxes, ww(J), which is active in the convective case and redistributes the surface flux, ivx(O), of a tracer X over the surface boundary layer in depth d. 

Tracer flux-gauge measurements of physical mechanisms of nutrient supply to the surface ocean, which place lower bounds on rates of new production. 

Development in recent years of fast-response instruments able to measure rapid fluctuations of the wind velocity (V ) and of fhe tracer concentration (c ), has made it possible to calculate the turbulent flux directly from the correlation expression in Equation (41), without having to resort to uncertain assumptions about eddy diffusivities. For example, Grelle and Lindroth (1996) used this eddy-correlation technique to calculate the vertical flux of CO2 above a foresf canopy in Sweden. Since the mean vertical velocity w) has to vanish above such a flat surface, the only contribution to the vertical flux of CO2 comes from the eddy-correlation term c w ). In order to capture the contributions from all important eddies, both the anemometer and the CO2 instrument must be able to resolve fluctuations on time scales down to about 0.1 s. 

One other measurement technique that has been used to measure Kl over a shorter time period, and is thus more responsive to changes in wind velocity, is the controlled flux technique (Haupecker et al., 1995). This technique uses radiated energy that is turned into heat within a few microns under the water surface as a proxy tracer. The rate at which this heat diffuses into the water column is related to the liquid film coefficient for heat, and, through the Prandtl-Schmidt number analogy, for mass as well. One problem is that a theory for heat/mass transfer is required, and Danckwert s surface renewal theory may not apply to the low Prandtl numbers of heat transfer (Atmane et al., 2004). The controlled flux technique is close to being viable for short-period field measurements of the liquid film coefficient. 

Th as a tracer is widely used and critical for two tasks to quantify fluxes and residences time of particles, and to calibrate trap efficiency by comparing estimated water-column 234Th fluxes with those measured by traps (Cochran et al. 2000). In surface waters, 234Th activities are the result of a balance between its continuous... 

Emissions are independent of the tracer concentration and can be considered as a surface flux. The injection of the emissions is integral part of the diffusion scheme in MOZART-3, i.e. as lower boundary for the fluxes, whereas TM5 and MOCAGE distribute the injected mass in a fixed ratio over selected layers in the boundary layer and apply their diffusion operator after the injection. The tendencies of the emissions P, therefore, have to be formulated either as 3D field including the diffusion or as 2D flux term. The diffusion in the IFS would have to be switched off if the 3D emissions-diffusion tendencies are applied. Air bom emissions such as the ones from aircraft would have to be included in the 3D chemistry tendencies, if the surface emissions are expressed as a flux. 

In the IPS, emission injection and diffusion are part of one subroutine. Surface emissions, and likewise (dry) deposition, can be treated as surface fluxes. If the applied CTM tendencies already included the effect of diffusion and convection, the respective routine in the IPS physics would have to be switched off for this GRG-tracer. 

A box model is comprised of some small number of ocean reservoirs, typically three to a few tens. The chemical characteristics of the seawater with each box is taken to be homogeneous (well mixed). Water flow in the ocean is described as fluxes between the boxes given in units of Sv (Sverdrups, lO ms ), these typically range to values less than 100 Sv. A flow between two boxes carries with it the chemical signature of the source box this numerical technique is called upstream differencing. Gas exchange acts to pull sea-surface gas concentrations, such as CO2 and " C02, toward equilibrium values with the atmosphere. The fluxes imposed between boxes are determined by tuning various tracers, usually toward observed values. 

Information about how the ocean circulated during the past is useful in understanding changes in ocean and atmospheric chemistry, changes in the fluxes of heat and freshwater between the ocean and atmosphere, and changes in global wind patterns. The circulation of surface waters in the ocean leaves an imprint on sea surface tempera-mre, and is also inextricably linked to the patterns of oceanic productivity. Much valuable information about past ocean circulation has been inferred from reconstructions of surface ocean temperarnre and productivity, which are covered in separate chapters. Here the focus is on the geochemical tracers that are used to infer the... 

Notice that in the compilation of Rn and C-determined gas exchange rates (Fig. 10.6) only one measurement has been made at wind speeds above Uio = 10m s. Since this regime is the most important for gas exchange and parameterizations in Fig. 10.6 differ by the most in this range, tracer release experiments have been devised to further refine the gas transfer-wind speed relations. In these experiments two tracers, one of which must be a gas, are released into the surface waters of the ocean (Watson et al, 1991). After injection of the tracers, the ship follows the center of the patch, while the progressive decreases in tracer concentrations are measured. The decreases are caused by dilution from mixing and the gas flux to the atmosphere. Since there are two tracers and two... 

The formulae for penetration and for the deposit density can be obtained by the following way [16]. At a particular coordinate, the fraction of the tracer mass deposited per unit tube length in unit time is the mass flux to the surface, divided by the mass carried by the gas flow per unit time. In a cylindrical tube the deposition rate is kmcg x itdc/y/J and the carried amount is Qcg. The two quantities have the same dimension and their ratio is... 

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