Seawater contains hydrogen and oxygen in the form of water, and sodium, chlorine, magnesium, sulfur, calcium, potassium, carbon and bromine as the 3.5% dissolved solids that occur in seawater. These are primarily the salts sodium chloride (77.8%) and magnesium chloride (10.9%). Other compounds include magnesium sulfide (4.7%), calcium sulfate (3.6%), potassium sulfate (2.5%), calcium carbonate (0.3%), magnesium bromide (0.2%) and other trace compounds. Carbon exists in seawater as dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate organic carbon (POC) and particulate inorganic carbon (PIC). Chlorine, sodium, and magnesium are, respectively, the first, second, and third most abundant element dissolved in seawater (on a molar basis). Sulfur, the fourth most abundant element dissolved in seawater, is present in oxygenated seawater as sulfate anion SO42-. Calcium, potassium, and bromine are, respectively, the fifth, sixth, and eighth most abundant elements dissolved in seawater; boron is the tenth, present as the borate ion (B(OH)4-) and undisassociated boric acid (B(OH)30). Fluorine is also a major component of seawater. Concentrations of manganese, high at the surface, decrease with depth as dissolved Mn2+ is sorbed onto sinking particles and removed to the sediment; the same is true of aluminum, which is present as the hydrolyzed Al (III) species Al(OH)3 and Al(OH)4-. A major source of such elements as manganese and aluminum to surface waters is dust deposition and this produces great variability in surface manganese. Additionally, gold occurs in seawater in surprising quantities, but no technology exists to extract in economically.