Prediction of pelagic calcification rates using satellite measurements

A technique for directly measuring coccolithophore calcification using 14C was first described four decades ago [Paasche, E., 1962. Coccolith formation. Nature 193, 1094–1095; Paasche, E., 1963. The adaptation of the Carbon-14 method for the measurement of coccolith production in, Coccolithus huxleyi. Physiologia Plantarum 16, 186–200]. Nonetheless, few direct measurements of calcification have been made in the field that could be used for development of a calcification algorithm for remote sensing. We analyzed 10 datasets of 14C- or 45Ca-based calcification and photosynthesis, containing results from almost 1000 euphotic water samples, in various oceans. We derived a calcification algorithm based on day length, sample depth, sea-surface temperature, chlorophyll a concentration, and suspended calcite concentration (otherwise known as particulate inorganic carbon or “PIC”). The advantage of this algorithm is that inputs can be derived by satellite. Results demonstrated that, like primary production algorithms, our calcification algorithm showed a significant relation between measured and predicted values (P<0.0005). However, the RMS errors were greater than for typical primary production algorithms. We generated preliminary images of global calcification using moderate resolution imaging spectrometer (MODIS) data from 2002 and estimated global monthly calcification rates. An annual global calcification estimate based on these images is 1.6±0.3 Pg y−1 and is somewhat higher than previous, entirely independent, estimates made by others.