River-dominated ocean margins

River-dominated ocean margins (RiOMars) are dynamic regions that receive inputs of organic carbon (OC) derived from both terrestrial and marine sources. The importance of 

The high vertical flux of particulates in river/estuarine plume regions commonly results in the accumulation of particles in the formation of a benthic boundary layer (BBL) and/or mobile and fluid muds (see chapter 6 for more details). The BBL is defined by Boudreau and Iprgensen (2001, p. 1) as those portions of sediment and water columns that are affected directly in the distribution of their properties and processes by the presence of 

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Mobile mud high-porosity BBL-upper seabed layer where diagenetic transformation processes are enhanced and commonly occur in river-dominated ocean margins. 

Considerable geographic variability exists in the distribution of the source rocks contributing salts to river and groundwaters. As shown in Table 21.3, most of the evaporites, which are the dominant natural source of Na and Cl in river water, lie in marginal and endorheic (internal) seas. Some of these subsurfece evaporite deposits dissolve into groundwaters, which eventually carry Na and Cl into the ocean. Carbonates are the prevalent rock type between 15°N and 65°N. Precambrian-age crustal rocks and meta-morphic minerals predominate between 25°S and 15°N and north of 55°N. Shales and sandstones represent on average 16% of the terrestrial surfece lithology. 

Whereas the composition of dissolved main solid compounds in seawater is rather constant all over the oceans, the freshwater in the Baltic Sea outbalanced by river discharge is dominated by calcium bicarbonate. For this reason, significant anomalies are observed in Baltic waters from the standard composition of seawater (Nehring and Rohde, 1966), in particular in the brackish surface water, with amount increasing toward the eastern and northern margins of the Baltic Sea. Directly measured densities of Baltic water compared with density determined from the seawater equation of state with Baltic water salinity measured by chlorinity titration resulted in a deviation of up to 0.123 kg/m (Millero and Kremling, 1976). This may result in uncertainties in estimating the thermodynamic properties of Baltic water, for example, the vertical stability. 

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