Size-related isotopic trends in Maastrichtian planktic foraminifera of DSDP Core 44-390A (Appendix B)

The species studied include Planoglobulina acervulinoides, Planoglobulina multicamerata, Pseudoguembelina palpebra, and Racemiguembelina fructicosa. Delta18O and delta13C data indicate a deeper surface water paleohabitat for P. multicamerata than the other three taxa, and ontogenetic increases in delta18O values suggest all these taxa underwent vertical migrations from shallow to deeper surface waters.

Changes in delta13C values through ontogeny include sharp increases in delta13C composition in the juvenile size intervals, a decrease in the rate of delta13C change through intermediate size intervals, and reversals to a negative trend in delta13C values in terminal size intervals. The intermediate and terminal growth changes in delta13C signals are similar to ontogenetic trends observed in some extant and Paleogene planktonic foraminifera and may result from decreasing metabolic rates through ontogeny or endosymbiont digestion prior to gametogenesis.