Growth rate determinations from radiocarbon in bamboo corals (genus Keratoisis)

Radiocarbon (¹⁴C) measurements are an important tool for determining growth rates of bamboo corals, a cosmopolitan group of calcitic deep-sea corals. Published growth rate estimates for bamboo corals are highly variable, with potential environmental or ecological drivers of this variability poorly constrained. Here we systematically investigate the application of ¹⁴C for growth rate determinations in bamboo corals using 55 ¹⁴C dates on the calcite and organic fractions of six bamboo corals (identified as Keratoisis sp.) from the western North Atlantic Ocean. Calcite ¹⁴C measurements on the distal surface of these corals and five previously published bamboo corals exhibit a strong one-to-one relationship with the ¹⁴C of dissolved inorganic carbon (DI¹⁴C) in ambient seawater (r²=0.98), confirming the use of Keratoisis sp. calcite ¹⁴C as a proxy for seawater ¹⁴C activity. Radial growth rates determined from ¹⁴C age-depth regressions, ¹⁴C plateau tuning and bomb ¹⁴C reference chronologies range from 12 to 78μmy^-1, in general agreement with previously published radiometric growth rates. We document potential biases to ¹⁴C growth rate determinations resulting from water mass variability, bomb radiocarbon, secondary infilling (ontogeny), and growth rate nonlinearity. Radial growth rates for Keratoisis sp. specimens do not correlate with ambient temperature, suggesting that additional biological and/or environmental factors may influence bamboo coral growth rates.