Mass balance between input from land and authigenic mineral formation

1 I Mass balance between input from land and authigenic mineral formation 

The main mechanisms for delivery of dissolved constituents to the ocean are river inflow and atmospheric input. Formation of authigenic minerals (those minerals that form in situ) is the ultimate sink (Fig. 2.1) for these constituents. Authigenesis primarily involves precipitation of plant and animal shells, chemical reactions in sediments, and high-temperature reactions at hydrothermal regions. We begin with a brief review of the chemical reactions influencing the dissolved ion concentrations of rivers, and end with an attempt to balance the river sources with plausible sinks for the major seawater ions. 

Based on chemical measurements for river water and atmospheric particles, it is clear that river inflow is by far the most important mechanism for the delivery of dissolved major ions and elements to the ocean. This is not the case for all elements some of the trace metals such as iron and lead have important sources from atmospheric dust, but our discussion will focus on the flux of major elements to the ocean. The concentration and origin of the major ions to river water is presented in Table 2.1. Weathering of rocks on land is the origin of the cations, Na+, Mg , Ca and K , whereas the source of the anions Cl, SO4 and HCOj is partly from rock weathering and partly from the gases CO2, SO2 and HCl that are delivered to the atmosphere via volcanic emissions over geologic time. 

These values and their sources are from Holland (1978). Some of the total river water concentrations differ from those in Table 2.3, where the numbers are from Li (2000). 

The simplest conceptual model of seawater composition would be to assume that seawater contains ions in the same ratios as delivered by rivers, but at higher concentrations due to evaporation. Comparison of the relative ion concentrations (Fig. 2.3) indicates, however, that 

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