Pliocene diatom and sponge spicule oxygen isotope ratios from the Bering Sea: isotopic offsets and future directions
Oxygen isotope analyses of different size fractions of Pliocene diatoms (δ 18O diatom) from the Bering Sea show no evidence of an isotope offset and support the use of bulk diatom species samples for palaeoceanographic reconstructions. Additional samples containing concentrations of sponge spicules produce δ 18O values several per mille (‰) lower than δ 18O diatom with a calculated mean offset of 3.9‰ ± 1.5. This difference is significantly greater than modern-day variations in water δ 18O through the regional water column. Despite the potential for oxygen isotope disequilibrium within δ 18O sponge, there appears to be some similarity between δ 18O sponge and a global stacked benthic δ 18O foram record. This highlights the potential for δ 18O sponge in palaeoenvironmental research at sites where carbonates are not readily preserved.