OXYGEN ISOTOPE CONTENT OF COCCOLITHS GROWN IN CULTURE

Coccoliths of three species of marine algae, Coccolithophoridae, cultured at constant temperatures over a range of 8 to 28°C were analyzed for oxygen isotopic composition. The physiological condition of the cell is shown to influence the isotopic composition of the coccoliths. Coccoliths grown in batch culture at high and variable growth rates showed no apparent relationship between isotopic composition and temperature, whereas batch cultures cultivated at slower growth rates showed a strong positive correlation between temperature and oxygen isotopic composition. The 18O composition of coccoliths grown under steady-state conditions in a chemostat under nitrate-limited conditions shows a definite temperature dependence that closely parallels that of equilibrium precipitation of calcium carbonate. The temperature dependence suggests the usefulness of nanno-fossils as a new paleotemperature tool, sensitive to changing oceanic temperatures. © 1979.