Temperature and vital effect controls on bamboo coral ( Isididae ) isotope geochemistry: A test of the “lines method”

Deep‐sea bamboo corals hold promise as long‐term climatic archives, yet little information exists linking bamboo coral geochemistry to measured environmental parameters. This study focuses on a suite of 10 bamboo corals collected from the Pacific and Atlantic basins (250–2136 m water depth) to investigate coral longevity, growth rates, and isotopic signatures. Calcite samples for stable isotopes and radiocarbon were collected from the base the corals, where the entire history of growth is recorded. In three of the coral specimens, samples were also taken from an upper branch for comparison. Radiocarbon and growth band width analyses indicate that the skeletal calcite precipitates from ambient dissolved inorganic carbon and that the corals live for 150–300 years, with extension rates of 9–128 μ m/yr. A linear relationship between coral calcite δ 18 O and δ 13 C indicates that the isotopic composition is influenced by vital effects ( δ 18 O: δ 13 C slope of 0.17–0.47). As with scleractinian deep‐sea corals, the intercept from a linear regression of δ 18 O versus δ 13 C is a function of temperature, such that a reliable paleotemperature proxy can be obtained, using the “lines method.” Although the coral calcite δ 18 O: δ 13 C slope is maintained throughout the coral base ontogeny, the branches and central cores of the bases exhibit δ 18 O: δ 13 C values that are shifted far from equilibrium. We find that a reliable intercept value can be derived from the δ 18 O: δ 13 C regression of multiple samples distributed throughout one specimen or from multiple samples within individual growth bands.