The hydrosphere

Detailed characterization of dissolved organic carbon is difficult to make a large number of compounds have been detected, but only a small portion of the total DOC has been identified. Identified species include amino acids, fatty acids, carbohydrates, phenols, and sterols. The amount of carbon in the oceans as DOC has been estimated as 1000 Pg and the amount present as particulate organic carbon as about 30 Pg (Mopper and Degens, 1979). 

DIC concentrations have been studied extensively since the appearance of a precise analytical technique (Dyrssen and Sill6n, 1967 Edmond, 1970). The aquatic chemistry of CO2 has been treated extensively reviews can be found in Skirrow (1975), Takcihashi et al. (1980), and Stumm and Morgan 

Two further reactions to be considered are the ionization of water and the borate equilibrium  

In order to be able to solve for hydrogen ion concentration, we define total borate (SB) and total carbon (SC = DIC) as  

Given any two of the four quantities SC, Aik, pH, Pcoj/ the other two can always be calculated provided appropriate equilibrium constants are available (the equilibrium constants depend on temperature, salinity, and pressure). The standard analytical technique for the carbonate species in seawater measures alkalinity and total carbon simultaneously in an acid titration. Hydrogen ion concentration can then be determined with the equation  

in its three phases, liquid water, ice and water vapour, is highly abundant at the Earth s surface, having a volume of 1.4 billion km3. Nearly all of this water ( 97%) is stored in the oceans, while most of the rest forms the polar ice-caps and glaciers (Table 1.1). Continental freshwaters represent less than 1% of the total volume, and most of this is groundwater. The atmosphere contains comparatively little water (as vapour) (Table 1.1). Collectively, these reservoirs of water are called the hydrosphere. 

The source of water for the formation of the hydrosphere is problematical. Some meteorites contain up to 20% water in bonded hydroxyl (OH) groups, while bombardment of the proto-Earth by comets rich in water vapour is another possible source. Whatever the origin, once the Earth s surface cooled to 100°C, water vapour, degassing from the mantle, was able to condense. Mineralogical evidence suggests water was present on the Earth s surface by 4.4 billion years 

Very little water vapour escapes from the atmosphere to space because, at about 15 km height, the low temperature causes the vapour to condense and fall to lower levels. It is also thought that very little water degasses from the mantle today. These observations suggest that, after the main phase of degassing, the total volume of water at the Earth s surface changed little over geological time. 

The rapid transport of water vapour in the atmosphere is driven by incoming solar radiation. Almost all the radiation that reaches the crust is used to evaporate liquid water to form atmospheric water vapour. The energy used in this transformation, which is then held in the vapour, is called latent heat. Most of the 

Cross-sectional area of Sun s rays striking the Earth s surface 

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The chemistry of the mineral—water iaterface and of aquatic environmental particles and coUoids is reviewed ia References 25 and 26. References 16 and 27 review the role of the hydrosphere ia the biogeochemistry of global change. 

As a possible method of concentrating trace amounts of bioactive organic compounds occurring in the hydrosphere, adsorption properties of various compounds have been explored by employing hydrous metal oxides as the adsorbents. To date, a family of organophosphoms compounds and carbonic acids were adsorbed onto hydrous iron oxide, along with the adsoi ption of monosaccharides onto hydrous zirconium oxide. 

Oxygen is the most abundant element on the earth s surface it occurs both as the free element and combined in innumerable compounds, and comprises 23% of the atmosphere by weight, 46% of the lithosphere and more than 85% of the hydrosphere ( 85.8% of the oceans and 88.81% of pure water). It is also, perhaps paradoxically, by far the most abundant element on the surface of the moon where, on average, 3 out of every 5 atoms are oxygen (44.6% by weight). 

About 80% of the earth s surface is covered with aqueous solution. This liquid layer, the oceans, is called the hydrosphere. The average depth of the hydrosphere is about three miles but at ocean deeps or trenches, it changes precipitously to depths over twice that. 

The composition of the earth s atmosphere differs from day to day, from altitude to altitude, and from place to place. The largest variation is in the concentration of water vapor. Water evaporates continually from the hydrosphere, from the soil, from leaves, from clothes drying, etc. At intervals, parts of the atmosphere become chilled until the dew point or frost point is reached and then any vapor in excess of the saturation amount is precipitated as rain or snow. 

Rubey, W. W. (1955). Development of the hydrosphere and atmosphere, with special reference to probable composition of the early atmosphere. In "Crust of the Earth" (A. Poldenvaart, ed.), pp. 631-650. Geological Society of America, New York. 

Just as in the case for the hydrosphere, the atmosphere participates in all of the major biogeochemical cycles (except for phosphorus). In turn, the chemical composition of the atmosphere dictates its physical and optical properties, the latter being of great importance for the heat balance of Earth and its climate. Both major constituents (O2, H2O) and minor ones (CO2, sulfur, nitrogen, and other carbon compounds) are involved in mediating the amounts and characteristics of both incoming solar and outgoing infrared radiation. 

While the hydrosphere has long been appreciated as essential to life on Earth, only in the past couple of decades have scientists expanded their exploration of the global hydrologic cycle and its roles across the spectrum of Earth science... 

Although it is one of the smallest reservoirs in terms of water storage, the atmosphere is probably the second most important reservoir in the hydrosphere (after the oceans). The atmosphere has direct connections with all other reservoirs and the largest overall volume of fluxes. Water is present in the atmosphere in solid, liquid, and vapor forms, all of which are important components of the Earth s natural greenhouse effect. Cycling of water within the atmosphere, both physically (e.g. cloud formation) and chemically, is also integral to other biogeochemical cycles and climate. Consult Chapter 17 for more details. 

In addition to biogeochemical cycles (discussed in Section 6.5), the hydrosphere is a major component of many physical cycles, with climate among the most prominent. Water affects the solar radiation budget through albedo (primarily clouds and ice/snow), the terrestrial radiation budget as a strong absorber of terrestrial emissions, and global temperature distribution as the primary transporter of heat in the ocean and atmosphere. 

Five components of the hydrosphere play major roles in climate feedbacks - atmospheric moisture, clouds, snow and ice, land surface, and oceans. Changes to the hydrologic cycle, among other things, as a result of altered climate conditions are then referred to as responses. Interactions with climate can best be explored by examirung potential response to a climate perturbation, in this case, predicted global warming. 

Though the hydrosphere continues to operate in response to the same forces it always has, humans have had an unmistakable role in altering some of its balances. In general, these impacts have had relatively little effect on the overall global water balance, and there is little chance that direct manipulation of the hydrosphere will alter water storage and cycling on a global basis. 

To this point, direct human impacts on the hydrosphere have remained restricted to the regional scale. Although they can still be important, particularly in terms of water supply, these direct manipulations of the hydrologic cycle are unlikely to affect the global water balance significantly. However, this is not to suggest that the global water cycle is immune to human influence its close ties to other physical and... 

This treatment of the carbon cycle is intended to give an account of the fundamental aspects of the carbon cycle from a global perspective. After a presentation of the main characteristics of carbon on Earth (Section 11.2), four sections follow 11.3, about the carbon reservoirs within the atmosphere, the hydrosphere, the biosphere... 

Comparison of Figs 13-6a and 13-6b clearly demonstrates the degree to which human activity has modified the cycle of sulfur, largely via an atmospheric pathway. The influence of this perturbation can be inferred, and in some cases measured, in reservoirs that are very distant from industrial activity. Ivanov (1983) estimates that the flux of sulfur down the Earth s rivers to the ocean has roughly doubled due to human activity. Included in Table 13-2 and Fig. 13-6 are fluxes to the hydrosphere and lithosphere, which leads us to these other important parts of the sulfur cycle. 

Foregoing any discussion of the very slow processes within the lithosphere, the immediate focal points are the atmosphere, the hydrosphere, and the interfaces between them, and the solid phases (sediment, the pedosphere, and lithosphere). For the aqueous phase the reservoirs are ... 

Ordinarily, the atmosphere is a self-cleansing system due to the abundance of O3, OH, NO2, and other reactive species. For example, hydrocarbon emissions from biota (such as terpenes) are oxidized in a matter of hours or days to CO and then on to CO2. Alternatively, carboxylic acids may be formed and then transferred to the hydrosphere or pedosphere by rain. The atmosphere acts much like a low-temperature flame, converting numerous reduced compounds to oxidized ones that are more readily removed from the air. The limit to the rate of oxidation can be defined by the concentration of OH... 

Heaton, T.H.E. (1987). Isotopic studies of nitrogen in the hydrosphere and atmosphere a review. Chemical Geology 0sotope Geoscience), Vol. 59, pp. 87-102. 

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