Ericson and Wollin’s (1968) plots of the number of G. menardii per gram of
sediment vs. distance downward in cores from the eastern Caribbean Sea (Fig. 10.18)
show that it drops to very low relative abundance for long sections of the core. The
“events” represented by variations in species composition can be dated by
radiochemical age determinations. The increase in G. menardii at about 10,000 years
ago (YBP) coincided with the recession of the Wisconsin ice sheet as dated in
terrestrial deposits. It seems likely, then, that global cooling during the last ice age
caused the paucity of G. menardii from 75,000 to 10,000 YBP. So, we can use the rest
of the record to date prior glacial and interglacial epochs, provided that the core has
no gaps. Correlation of large numbers of cores has provided the general pattern, so
that gaps in particular cores can be detected.
Fig. 10.18 Several examples of core profiles of the relative abundance of G. menardii
in core samples from the Caribbean Sea. Radiocarbon dates are shown on the right-
hand edges of the profiles. Abundance scales are varied between cores to make the
plots look more similar.
(^) (After Ericson & Wollin 1968.)