Fig. 6.

Conceptual model of the effect of bleach on different amino acid fractions in a shell (upper figure modified from Sykes et al., 1995). The highly racemized FAA in the matrix (1) are removed first, leading to a small drop in concentration but a decrease in the D/L value. A rise in D/L coincides with a rapid drop in concentration as the intact proteins of the matrix (2) are removed. Prolonged bleaching may selectively remove amino acids in the intra-crystalline fraction or begins to etch the carbonate, thereby exposing intra-crystalline amino acids (3). This coincides with only a small drop in concentration. At this point the bleaching could induce further racemization, or it could oxidize the less-racemized molecules. The increase in racemization is minimal, however.