Globorotalia hirsuta (d'Orbigny, 1839)

The very clear relationships of this species with the physical environment (Fig. 20) reflect its adaptation to subtropical conditions. It is a good indicator of the vertical temperature and density gradient which is rare where the temperature gradient exceeds 5 °C and where the density contrast between the surface and 200 m (stratification) is larger than 1 kg/m3 in winter.

Globorotalia hirsuta is a deep-water dweller which reproduces in the surface waters during winter near Bermuda (Deuser et al., 1981; Deuser and Ross, 1989; Hemleben et al., 1985). The annual reproduction cycle gives an explanation for the well expressed relationships with winter conditions. Probably the species ascends from depth when the vertical contrasts in the water column are at a minimum and when the rise to shallow depth requires the least energy consumption for the species.

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Figure 20: Globorotalia hirsuta (d'Orbigny, 1839). Plots of relative abundance vs. selected physical parameters and latitude. For preferences in numeric form see appendix.

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