Gross flux

The gross flux of carbon from atmosphere to ocean is thus ca. 80 Pg C/yr. There are several complications with the above calculation. The isotopic ratios must be steady-state values, which are unavailable due to the changes resulting from atmospheric atom bomb testing. The few available pre-bomb measurements from the late 1950s (Broecker et ah, 1960) together with determinations in corals (Druffel and Linick, 1978) are invaluable tools for determin-... 

The dynamics of canopy-scale net fluxes of water and CO2 exchanged between vegetation and the atmosphere are routinely measured today with micrometeorological methods (e.g., with eddy covariance www.daac.ornl.gov/FLUXNET/ fluxnet.html). Combining these methods with isotopic measurements allows to partition a net flux into its gross flux components. The approach here is similar to that used on the global scale to... 

By rearrangement we obtain estimates of the component gross fluxes ... 

The rest of the chapter is organized as follows. In Section 6.07.2 we discuss the chemical composition of hydrothermal fluids, why they are important, what factors control their compositions, and how these compositions vary, both in space, from one location to another, and in time. Next (Section 6.07.3) we identify that the fluxes established thus far represent gross fluxes into and out of the ocean crust associated with high-temperature venting. We then examine the other source and sink terms associated with hydrothermal circulation, including alteration of the oceanic crust, formation of hydrothermal mineral deposits, interactions/uptake within hydrothermal plumes and settling into deep-sea sediments. Each of these fates for hydrothermal material is then considered in more detail. Section 6.07.4 provides a detailed discussion of near-vent deposits, including the formation of polymetallic sulfides and... 

Hydrothermal plumes form wherever buoyant hydrothermal fluids enter the ocean. They represent an important dispersal mechanism for the thermal and chemical fluxes delivered to the oceans while the processes active within these plumes serve to modify the gross fluxes from venting, significantly. Plumes are of further interest to geochemists because they can be exploited in the detection and location of new hydrothermal fields and for the calculation of total integrated fluxes from any particular vent field. To biologists, hydrothermal plumes represent an... 

Only the net effect of shifting cultivation is included here. The gross fluxes from repeated clearing and abandonment are not included. 

As NEP is often small relative to the gross fluxes of photosynthesis and ecosystem respiration, the net flux is sometimes less than the error of measurement. More important than error is bias, and the approach is vulnerable to bias because both the fluxes of CO2 and the micro-meteorological conditions are systematically different day and night. Wind speeds below 17 cm s in a temperate zone forest, e.g., resulted in an underestimate of nighttime respiration (Barford et al., 2001). A similar relationship between nighttime wind speed and respiration in forests in the Brazilian Amazon suggests that the assumption that lateral transport is unimportant may have been invalid (Miller et al., in press). 

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