Adsorption of amino acid-containing organic matter by calcite and quartz

Adsorption experiments using fulvic acid with calcite and quartz demonstrate that carbonate surfaces are able to selectively adsorb aspartic acid-rich organic matter. Quartz does not have this ability, instead exhibiting a preference for the aspartic acid-poor fraction. The relative abundance of aspartic acid in the fraction adsorbed onto calcite is highly dependent on the ratio of fulvic acid to calcite. At high ratios, fulvic acid is adsorbed with a relative abundance of aspartic acid that is more than twice that in the original fulvic acid. With decreasing ratios, there is a concomitant decrease in the relative abundance of aspartic acid in the adsorbed fraction. Selective adsorption may be the most likely mechanism by which aspartic acid-rich organic matter is included in non-biogenic car- bonates such as ooids. This process may be a factor influencing the distribution of amino acids within ooids, their rate of growth, and may ultimately be a factor in limiting their size.