We test
for trace element proxies in the high-magnesium calcite
fraction o
f bamboo coral internodes by comparing environmental conditions and growth rates to the specimen-mean compositions o
f 73 corals that were live-caught at depths ranging
from 3 to 3950 m and collected
from habitats ranging
from tropical coral ree
fs to the Antarctic slope. Comparisons were done at a large geographic scale (LGS) and
for a well sampled area south o
f Australia, across depths at a single site, in order to help separate the e
ffects o
f environmental variables that co-vary at one spatial scale, but not the other. Thirty-seven trace elements were measured using solution-based Sector Field ICP-MS, o
f which seventeen were signi
ficantly detected in more than a third o
f the specimens. Only eight element/calcium ratios correlated signi
ficantly with any environmental variable at the large geographic scale, and only
four did so at the local level. At the LGS, the highest correlation was between ambient temperature and Mg/Ca, which accounted
for 89% o
f the variance across specimens, spanned all
four Isidid sub-
families and was independently signi
ficant in the two best sampled sub-
families. The predictive (geometric mean) relationship is
spanning a temperature range o
f −1.9 to 26.8 °C, Mg/Ca ratios
from 58.6 to 155.1 mmol/mol, and an uncertainty (RMS) o
f 2.78 °C. The numbers in parentheses are 95% CIs. The slope o
f the regression does not di
ffer signi
ficantly
from that o
f abiotic high-Mg calcites, which suggests that the temperature-dependent incorporation o
f Mg into the carbonate results
from kinetic reactions at the crystal sur
face. Analysis at the SH scale
for the sub-set o
f specimens
for which we had data suggests is also a
ffected by growth rates. There were no obvious trace element correlates at either spatial scale o
f salinity or oxygen levels that could not be accounted
for by covariance between these environmental parameters and, in most cases, temperature. Single and multiple correlation analyses also con
firm previous suggestions that Ba/Ca in bamboo coral calcite is a proxy
for seawater barium and hence re
fractory nutrients, suggest that Sr/Ca is in
fluenced by specimen-mean Mg/Ca ratios and water temperature as well as possibly seawater Sr/Ca, and
falsi
fy
for bamboo corals P/Ca (as well as P/Cd and Cd/Ca) as a proxy
for seawater phosphate levels. The predictive relationship between Isidid skeletal-mean Ba/Ca and seawater silicate concentrations appears to be linear, and is given by
spanning a silicate range o
f 0.5 to 120 μmol kg
−1, a Ba/Ca range o
f 0.0042 to 0.0195 mmol/mol, and with an uncertainty (RMS) o
f 33.1 μmol kg
−1. Mn/Ca di
fferences among specimens and sites are highly signi
ficant and appear to re
flect seawater Mn, suggesting a proxy
for this micronutrient. The compilation o
f growth rate data across 34 specimens indicates a wide range o
f growth rates even among con-
familial specimens
from within a single habitat, and suggests both ambient temperature and
food availability underlie at least part o
f this variability.