Sulfur weathering flux

Referring again to Fig. 13-6a, the materials that constitute the oceanic sinks for sulfur are recycled over time by exposure to weathering on the continents. The rates at which these processes occur help to regulate the flux of sulfur into rivers. 

To begin the discussion, we will present briefly a view of the modern carbon cycle, with emphasis on processes, fluxes, reservoirs, and the "CO2 problem". In Chapter 4 we introduced this "problem" here it is developed further. We will then investigate the rock cycle and the sedimentary cycles of those elements most intimately involved with carbon. Weathering processes and source minerals, basalt-seawater reactions, and present-day sinks and oceanic balances of Ca, Mg, and C will be emphasized. The modern cycles of organic carbon, phosphorus, nitrogen, sulfur, and strontium are presented, and in Chapter 10 linked to those of Ca, Mg, and inorganic C. In conclusion in Chapter 10, aspects of the historical geochemistry of the carbon cycle are discussed, and tied to the evolution of Earth s surface environment. 

Figure 14 The simplified geochemical cycles of carbon and sulfur, including burial and weathering of sedimentary carbonates, organic matter, evaporites, and sulfides. The relative fluxes of burial and weathering of organic matter and sulfide minerals plays a strong role in controlling the concentration of atmospheric O2.

Arsenic(As) in ocean is mainly removed by formation of pyrite in marine sediments. The production rate of sulfur in pyrite is 3.3 X 10 mol my (2.5 X 10 ° g my ) (Holland 1978). As/S ratio of pyrite in sediments previously reported is (8.7 3) x 10" (Huerta-Diaz and Morse 1992). Thus, As sink by pyrite is (1.7-3.9) x 10 mol my . This flux seems to be not different from As input to ocean ((1.6-8.1) x lO mol my (Table 5.3). As concentration of ocean is considered to be controlled by hydrothermal input, riverine input and pyrite output. Fluxes by volcanic gas from atmosphere and by weathering of ocean-floor basalt are small, compared with hydrothermal, riverine and pyrite As fluxes. Residence time of As in seawater is estimated as the amount of As in seawater (4.2 x 10 g) divided by As input to seawater (1.6-8.1) X 10 mol my which is equal to (1.7-3.8) x 10" year. This is shorter than previously estimated one (10 year by Holland 1978). Subducting sulfur flux is estimated to be 6.1 x 10 g my from S contents of altered basalt and sediments ( 0.1 wt%) (Kawahata and Shikazono 1988) and subducting rates of... 

---