patterns has provided the answer.
Mapping the Zoogeography of the Past
(^) During the 1970s, the CLIMAP program studied the pelagic zoogeography during a
glacial epoch by mapping the distributions of relative abundance of forms like G.
menardii. The questions of importance to those doing the study did not concern the
fate of a given species; they concerned global climate patterns. Therefore, while
distributional maps for species were presumably studied, they were not published,
except for the comparison study of surface sediments (Kipp 1976). Maps published by
McIntyre et al. (1976) show the distribution of faunal assemblages identified by a
factor analysis procedure. This classification of species into assemblages was
performed on faunal data from the tops of cores (Kipp 1976). For example, G.
menardii belongs to a set constituted principally of five species called the “gyre
margin” assemblage. All these foraminifera are most abundant, or are only found,
around the margin of the North Atlantic central gyre. Globoquadrina deutertrei is
another abundant member of this assemblage. Next, the degree of occurrence of an
assemblage in samples from the 18,000 YBP level, the peak of the last glaciation, was
determined and plotted. At this point, interpretation takes off like a great pterodactyl.
(^) Note the circularity in the argument before we proceed. CLIMAP used the
stratigraphy of (g CaCO 3 (g sediment)−1) to determine the location in each core of the
18,000 YBP level, a variable known to parallel the calcite oxygen-18/oxygen-16 ratio,
a measure mostly of glacial withdrawal of water from the seas. However, sediment
concentration of CaCO 3 is mostly due to foraminiferan shell production, the same
biological process used in the next steps to characterize conditions. Moreover, “...
floral and faunal curves and stratigraphic boundaries proved useful for corroborative
time control within the period 0 to 130,000 BP” (McIntyre et al. 1976). Nevertheless,
the results are extremely interesting. A sausage should be judged by its final flavor
and texture, not on what goes into it!
(^) The 18,000 YBP distribution of the gyre margin assemblage (Fig. 10.19) shows that
these forms retreated during the glacial into the equatorial zone of the eastern
Atlantic, off Africa. During the ice ages, tropical and subtropical pelagic species
probably are not reduced everywhere to low abundance, rather their ranges contract to
small refugia where conditions remain suitable for their survival.
Fig. 10.19 Distributional map of percentage contribution (numbers by station dots) of
the central gyre margin assemblage (mostly G. menardii) at the 18,000 YBP level in
selected cores. The very low percentages in the North Atlantic and Caribbean indicate
either recurring expatriation from the eastern tropical Pacific refugium of the glacial