Globorotalia crassaformis (Galloway and Wissler, 1927)

The broad tolerances of this species (Fig. 19) with respect to physical parameters reflect its broad biogeographic occurrence in low to mid latitudes with a clear preference for the North Atlantic. A tendency exists towards narrower tolerances for summer conditions. The data suggests a broad preference for warmer water tropical-subtropical environments. The relation of relative abundance and temperatures at 200 m is well expressed and relates to the deeper water habitat of this species. Plankton observations show relations with the equatorial undercurrent in the Atlantic, as a distinct water mass below the seasonal thermocline (Jones, 1964). The preference for elevated salinities and relatively warm environments may be reflected in the broad range of surface water density tolerated by this species. The broad tolerances for vertical temperature gradients, surface water densities, and stratification are reminiscent of the bimodal distributions seen in G. bulloides and G. glutinata and may suggest some relation with productivity pattern in low latitudes. In plankton tows, however, the species occurs below the seasonal thermocline and the deep chlorophyll maximum (Ravelo and Fairbanks, 1992). See discussion section.

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Figure 19: Globorotalia crassaformis (Galloway and Wissler, 1927). Plots of relative abundance vs. selected physical parameters and latitude. For preferences in numeric form see appendix.

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