D/L values of Asx, Glx, Ala and Val for the free amino acid (FAA, panels on the left) and total hydrolysable amino acid (THAA, panels on the right) fraction of bleached Bithynia tentaculata opercula from Amersfoort, Neumark-Nord 1 and 2. Ranges for samples from UK sites correlated with MIS 5e and MIS seven are indicative only, as effective diagenetic temperatures are likely to have differed significantly between Britain and continental Europe. The boundary of the box closest to zero indicates the 25th percentile, the dashed line within the box marks the mean and the boundary of the box farthest from zero indicates the 75th percentile. The 10th and 90th percentiles are represented by lines above and below the boxes. The results of each duplicate analysis are included in order to provide a statistically significant sample size.