Ecologic and Paleoclimatic Implications of Morphologic Variation of Orbulina universa in the Indian Ocean.

Multivariate cluster analysis of various morphologic indices of Orbulina universa populations from the Indian Ocean indicate the existence of two major groups whose geographic distribution corresponds to the equatorial and central water masses. An abrupt change in shell porosity between populations of this planktonic foraminiferal species in plankton as well as sediment samples occurs within or near the 10 degrees S Hydrochemical Front. Orbulina universa is an excellent indicator of oceanographic conditions in the Indian Ocean today, and may be used as an independent check on shifts in water masses during the last glaciation.