An effect of dissolved nutrient concentrations on alkenone-based temperature estimates

The ratio of 37-carbon diunsaturated to diunsaturated and triunsaturated alkenones (U-37(K')) produced by some haptophytes is widely used as a proxy for past sea surface temperatures. However, our isothermal culturing experiments with Emiliania huxleyi clone CCMP372 show U-37(K') values to also vary with nutrient availability and cell division rate. These results provide a reasonable explanation for large isothermal variation in U-37(K') values of single coccolithophorid strains grown in culture. They also suggest that alkenone-based estimates of past sea surface temperatures may have been influenced by dissolved nutrient concentrations as well as by temperature.