Abstract Title: Assessing species-specific oxygen isotopic temperature calibrations for Gulf of Maine bivalves

Abstract Submitted to: PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY

Abstract Text:

Oxygen isotope records from mollusk shells have been used extensively to reconstruct past ocean temperatures and hydrographic conditions. Due to its centuries-long lifespan, Arctica islandica is commonly used in paleoclimate reconstructions, while mollusk species with shorter lifespans, such as Mya arenaria, are often preserved in indigenous shell heaps from thousands of years ago. Current reconstructions implement an oxygen isotope-water temperature calibration derived from multiple species of aragonite mollusks (Grossman and Ku, 1986). To test for species-specific differences in the oxygen isotope-water temperature relationship, three Gulf of Maine mollusk species (Mercenaria mercenaria, M. arenaria, and A. islandica) were grown in controlled temperature treatments (6.21 ± 0.06, 8.91 ± 0.28, 11.83 ± 0.14°C) in a flow-through laboratory experiment for twenty weeks. We measured the 18O of the seawater (18Ow) in each tank throughout the experiment and the 18O of the growing edge of each shell (18Oc) at the conclusion of study (nmya = 56, nmer = 46, narc = 22). The 18Oc values for replicate individuals from the same species and tank agreed within ~± 0.2-0.6 ‰ (±1 SD, n = 4-10 replicates per species), which is above the analytical uncertainty of ~±0.09‰. Both 18Ow and 18Oc were used to calculate temperature using the calibration equation determined by Grossman and Ku (1986). Preliminary temperatures calculated from M. arenaria and M. mercenaria 18Oc values using the Grossman and Ku equation differed significantly from the measured tank temperatures (P < 0.05 for M. arenaria and M. mercenaria at all three temperatures), predicting temperatures that were ~1-4°C cooler and ~2-6°C warmer, respectively. Temperatures calculated from A. islandica 18Oc using the Grossman and Ku equation generally agreed with measured temperatures for each treatment. Based on these findings, the use of species-specific calibration equations may be necessary to account for differences in the ways that mollusk species such as M. mercenaria and M. arenaria record temperature. Conversely, our findings broadly reinforce the use of Grossman and Ku’s multi-species calibration for oxygen isotope records from A. islandica, though the relationship at lower temperatures may need to be studied further.