DOES GROWTH-RATE AFFECT KETONE UNSATURATION AND INTRACELLULAR CARBON ISOTOPIC VARIABILITY IN EMILIANIA-HUXLEYI

We present the first results of U-37(K') and epsilon(alkenone) from Em iliania huxleyi grown in chemostat cultures at constant temperature bu t at variable growth rates. A small change in U-37(K) with growth rate was found for a noncalcifying strain of E. huxleyi, whereas results f rom a calcifying strain showed no systematic variation between U-37(K' ) and growth rate. We conclude that nutrient-limited growth rate effec ts will not produce serious errors in paleotemperature determinations using U-37(K) or U-37(K'). However, U-37(K') values for the two strain s differed significantly and apparent temperatures calculated using un saturation ratios obtained from chemostat experiments are very differe nt from those derived from batch culture experiments. Results of isoto pic analyses of alkenones and bulk cells indicate no effect of growth rate on epsilon(alkenone) (epsilon(alkenone) = 4.2 +/- 0.2 parts per t housand). Constancy of epsilon(alkenone) values is a requirement for e nvironmental and paleoenvironmental interpretations. These results ind icate that isotopic analyses of alkenones are ideal markers for paleo- [CO2(aq)] determinations.