Of the dissolution indexes examined, FRAG and BENTH record greater-amplitude and higher-frequency variations than carbonate content or the proportion of coarse fraction (Figs. F4, F5, F6, F7). Presumably, FRAG and BENTH are more sensitive measures of carbonate dissolution because they can be high where carbonate content is high (e.g., LaMontagne et al., 1996), such as within the upper lysocline (Berger, 1967).
Plots between the various indexes, such as FRAG vs. each of carbonate content, size faction, and BENTH (Fig. F8), show some insights and complexities facing dissolution interpretations. Trends of FRAG and BENTH display a good correlation (r2 = 0.77) across the sample set, and both probably provide good indicators of carbonate dissolution, at least for most samples in this study. However, planktonic and benthic counts are far less time consuming than fragmentation counts, so BENTH is a much easier measurement. A bivariate plot of FRAG and carbonate content shows a broad relationship of high carbonate content with low FRAG, but with weak correlation (r2 = 0.03). At moderate to low carbonate content (<70 wt% for this study), FRAG may become problematic because significant numbers of fragments may have been dissolved and the residual assemblage can contain resistant tests. A plot of FRAG against coarse fraction shows that FRAG varies widely (0%–80%) when fine-grained material dominates bulk sediment (<10 wt% coarse) but is fairly constant when coarse-grained material comprises a significant fraction. As mentioned previously, the relative abundance of nannofossils complicates grain size interpretations in these sediments.