Fig. 2.

Difference in the means and 95% confidence intervals between Clacton and West Runton for racemization and decomposition in the FAA (A) and THAA (B) fractions of Valvata piscinalis (Vp) and Bithynia (B) shell and opercula. The y-axes for the [Ser]/[Ala] data are plotted in reverse, so that the direction of increased protein degradation for each of the indicators remains the same. The dashed line (0.00) indicates that there is no difference between the mean of the two sites. If the 95% confidence intervals fall below this zero line, then it is not possible to discriminate between Clacton and West Runton. The opercula are clearly better at discriminating between the sites than the shells, because they show a greater difference in means and have much smaller error bars. The use of opercula therefore increases the statistical confidence and temporal resolution.