ABSTRACT

The ecological balance of nature is defined as an equilibrium between species richness (S) and species evenness (E) such that diversity (H) remains constant with time. Based on this definition, our approach identifies growth or decline in communities as perturbations from stasis and has successfully done so for benthic foraminiferal communities. Here, we examine whether this approach is appropriate for planktonic foraminifera. To do so, we utilized planktonic foraminiferal counts (39 samples, 66% recovery) from Maastrichtian sediments in the Weddell Sea from ODP Hole 690C. A total of 24 species were observed and both >63-µm and >150-µm fractions were counted. In the >63-µm fraction, nine communities were recognized while in the >150-µm fraction, there were 12. In both fractions at 70.45 Ma, a boundary was recognized and immediately after this boundary, a community in growth was identified. A trend of increasing diversity upcore was substantiated by regression on individual samples. For our purposes, the >150-µm fraction in this data set is sufficient to recognize community trends. The >150-µm fraction in Hole 690C has 82% of the sampling time in stasis and an average time per community is 0.85 Ma. The >63-µm fraction has 73% of the sampling time in stasis and an average time per community of 1.02 Ma.

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