The CaCO3 content of the sediment column is a function of production, dissolution, and dilution. In ocean cores carbonate content closely parallels oxygen isotope stratigraphy and has been widely used for stratigraphic correlation and to interpret paleoceanographic changes (e.g., Hayes et al., 1969; Prell, 1978; Dunn et al., 1981; Gardner, 1982; Pisias et al., 1985; O'Connell, 1990).
A total of 776 CaCO3 analyses is available for Site 1090, including 80 shipboard analyses on Hole 1090B (Table T5). The remaining analyses were done on samples from Holes 1090D and 1090E.
Samples were dried in a freeze-dryer, powdered, weighed to the nearest milligram, and analyzed for CaCO3 using a Coulometrics CO2 coulometer. The coulometer has an accuracy of 0.15% (±0.2 mg). The coulometrics titration technique measures all of the CO2 that is liberated by acidifying and heating sediment samples in a closed system. To do this, the powdered samples are placed in a test tube that is attached to the coulometer, placed in a heat shield, and 2-N HCl is pumped into the test tube. The liberated CO2 is transferred through scrubbers (solutions to remove interfering substances) by a CO2-free gas into an absorption cell, where it is titrated through coulometric means. The absorption cell contains an aqueous medium of ethanolamine and a coulometric indicator. The interaction of the CO2 and the cell solution creates a titratable acid. The coulometer forms a base electrically and titrates to an end point determined by the optical transmission of the indicator (Huffman, 1977). The pulse output was scaled and fed to a counter in terms of CO2. A stable coulometer reading indicates that all of the CO2 has been evolved and titrated. The reading was recorded and the results were calculated in micrograms carbon and CaCO3 (weight percent CaCO3 = percent Cinorg × 8.334). This method of calculation assumes that all of the CO2 is liberated from CaCO3.