PIC/POC

Measurements and calculations of PIC and POC were made using standard procedures (e.g., refs.^75,76). Coccolithophore samples from each treatment were dehydrated and weighed to determine their TPM weight. The particulate inorganic matter (PIM), i.e., CaCO₃, in each sample was dissolved by addition of 2% HCl. Each sample was then re-weighed after removing the PIM, yielding the particulate organic matter (POM) weight. TC (%) of the non-acidified samples and POC (%) of the acidified samples were measured with a Costech Elemental Analyzer attached to an IRMS (the latter was used for carbon isotope measurements described in the carbon isotope methods section). Carbon-loss measurements were verified with acetanilide (C = 71.26 wt%) and atropine standards (C = 70.83 wt%). Each TC weight was calculated by multiplying TC (wt%) by the TPM weight, and POC weight was calculated by multiplying the (wt%) carbon in POM by the POM weight. PIC weight was then calculated as the difference between TC weight and POC weight. POC (wt%) and PIC (wt%) were then calculated by, respectively, dividing the POC and PIC weights by the TPM weight. The PIC/POC ratio was calculated by dividing PIC (wt%) by POC (wt%). Three of the calculated PICs (wt%) were eliminated due to weak signal-to-noise ratios of their TC (wt%) measurements.