Figure 6. Temperature ranges calculated from oxygen isotopic compositions of late Holocene A. opercularis shells from the southern North Sea (shown as solid blue bars), compared with ranges calculated from modern shells (Hickson et al. 1999; red bars) and values from instrumental records of sea-surface temperature (Lane and Prandle 1996, figure 2b). The specimen name is shown on the bar, together with (for subfossil specimens) the corrected radiocarbon date for that shell. The data from instrumental records are for the ±3 ranges about the 10-year means of extreme summer and winter temperatures (vertical broken lines) and for the span between the medians of these ranges (horizontal black bar).