Approximately 2 mg of the homogenized coral powder (CaCO3)
was weighed out to yield a dissolved Ca concentration of 100 ppm
to minimize matrix-induced mass discrimination (Rosenthal et al.,
1999). Coral powders were dissolved and diluted with ultra-pure
concentrated HNO3 and 0.1 ppb of an indium (In) was added which
served as an internal standard to correct for instrument drift and
sample matrix effect. A detailed discussion of relevant methods can
be found in Prouty et al. (2008). In brief, major and minor element
analyses were carried out on a high-resolution double focusing magnetic
sector-field inductively coupled plasma mass spectrometer
(HR-SF-ICP-MS) (Finnigan Element2). The samples were analyzed
using a self-aspirating 20 μL min−1 nebulizer attached to a quartz
cyclonic spray chamber, using argon as a carrier gas. A washout
time of 1 min was applied to unknowns and standards and 90 s to
blanks. Both low and medium resolution analytical modes were
used with a 10% and 80% mass window, respectively, in order to
maximize instrument sensitivity. The signal intensity was obtained
by integration of the counting signal of the scanning mass over a
4 min acquisition period.