Sulfur oceanic sinks

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. 

Under low-dose conditions, forest ecosystems act as sinks for atmospheric pollutants and in some instances as sources. As indicated in Chapter 7, the atmosphere, lithosphere, and oceans are involved in cycling carbon, nitrogen, oxygen, sulfur, and other elements through each subsystem with different time scales. Under low-dose conditions, forest and other biomass systems have been utilizing chemical compounds present in the atmosphere and releasing others to the atmosphere for thousands of years. Industrialization has increased the concentrations of NO2, SO2, and CO2 in the "clean background" atmosphere, and certain types of interactions with forest systems can be defined. 

It is also possible that bacterial decomposition of sulfur containing organic compounds may account for some DMS in natural waters (31-36). Conversely, bacteria may also utilize DMS and therefore act as a sink (37-39). The contribution of bacterial processes to the DMS/DMSP cycle in open ocean environments has not been addressed and is as yet not understood. However, studies to better understand the biogeochemistry of DMS can not exclude bacterial processes (e.g. 4041). 

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. 

What are the sources (natural and man-made), sinks and residence times of sulfur compounds in the atmosphere-ocean-soil system ... 

The rapid absorption of the gas into water means that it is readily transferred into the oceans or other water bodied. Vegetation also acts as an important sink for sulfur dioxide. This can be particularly efficient when the vegetation is wet, such as when it is covered by dew or rainwater. However, even when the vegetation is not wet, sulfur dioxide can enter the leaves through the stomata and enhance deposition. This process is called dry deposition because although it involves water, the water is not in the atmosphere. 

Marine sediments are the main sink for seawater snlfate which demonstrates that the sedimentary sulfur cycle is a major component of the global snlfur cycle. The most important mechanisms for removing sulfate from the oceans to the... 

Large amounts of smoke from oil slick burning can result in oil rain. The formation and possible sinking of extremely viscous and dense residues can damage the sea bed and its inhabitants. The viscous residue may also be transported to shorelines and beaches by ocean tides or currents. Airborne irritants and possibility of secondary fire are sources of concern when combustion has to be carried out close to residential areas. Carbon monoxide, sulfur dioxide, and polycyclic aromatic hydrocarbons (PAH) are common toxic compounds emitted while burning oil on water. 

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... 

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