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CHAPTER 12 • Last Glacial Maximum 225

12-10 Evidence for a Small Tropical Cooling
Reduced The evidence for a small tropical cooling in the CLIMAP
levels of reconstruction was based on the small changes in planktic
CO and CH 4 fauna and flora in low-latitude oceans. CLIMAP’s tech-
2
Similar solar
radiation nique for reconstructing sea-surface temperatures used
the assumption that the distribution of species and assem-
blages of plankton is mainly determined by the tempera-
Regional Regional ture of the water in which they live. At higher northern
cooling cooling latitudes during the glacial maximum, cold-adapted
species moved into areas where warm-adapted species
Ice Ice
prevail today, indicating a large cooling in these regions.
Across most low-latitude regions, however, the species
that existed at the glacial maximum were not much differ-
ent from the warm-adapted forms found there today
South Tropics North (Figure 12–19). This lack of change in tropical plankton
led CLIMAP to conclude that ocean temperatures in the
FIGURE 12-18 Lower CO and CH levels cooled the tropics cooled by an average of only 1.5°C at the glacial
2 4
glacial tropics The tropics were too distant from the glacial maximum.
ice sheets to feel their direct influence, and insolation values Evidence obtained from the biochemical composi-
in summer and winter were close to those today. Lower levels tion of plankton shells supports the CLIMAP estimates
of atmospheric CO and CH were the main cause of tropical in some regions. One technique is based on the relative
2 4
cooling. abundance of complex organic molecules called

Equator

B Indian Ocean
FIGURE 12-19 Planktic fauna of the
glacial maximum vs. that of today
The CLIMAP method of reconstructing
glacial maximum ocean temperatures
was based on temperature-sensitive
plankton assemblages. Planktic
A Atlantic Ocean assemblages in most low-latitude
regions of the (A) Atlantic, (B) Indian,
and (C) Pacific oceans differed only
Glacial plankton vs. plankton today slightly from those of today, indicating
(Percent difference) little glacial cooling. (Adapted from
> 50 25–50 10–25 < 10 T. C. Moore et al., “The Biological Record
of the Ice-Age Ocean,” Palaeogeography,
Palaeoclimatology, Palaeoecology 35 [1981]:
C Pacific Ocean 357–70.)