title: Understanding cold bias: Variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals.
abstract: Coral skeletal Sr/Ca is a palaeothermometer commonly used to produce high resolution seasonal sea surface temperature (SST) records and to investigate the amplitude and frequency of ENSO and interdecadal climate events. The proxy relationship is typically calibrated by matching seasonal SST and skeletal Sr/Ca maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal Sr/Ca is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present Sr/Ca analyses of 3 genotypes of massive Porites spp. corals (the genus most commonly used for palaeoclimate reconstruction), cultured under seawater pCO2 reflecting modern, future (year 2100) and last glacial maximum (LGM) conditions. Skeletal Sr/Ca is indistinguishable between duplicate colonies of the same genotype cultured under the same conditions, but varies significantly in response to seawater pCO2 in two genotypes of Porites lutea, whilst Porites murrayensis is unaffected. Within P. lutea, the response is not systematic: skeletal Sr/Ca increases significantly (by 2-4%) at high seawater pCO2 relative to modern in both genotypes, and also increases significantly (by 4%) at low seawater pCO2 in one genotype. This magnitude of variation equates to errors in reconstructed SST of up to -5 °C.
authors.affiliation: Department of Earth and Environmental Sciences, University of St. Andrews, St. Andrews KY16 9AL, UK.
authors.forename: Catherine
authors.initials: C
authors.lastname: Cole
authors.affiliation: Department of Earth and Environmental Sciences, University of St. Andrews, St. Andrews KY16 9AL, UK.
authors.forename: Adrian
authors.initials: A
authors.lastname: Finch
authors.affiliation: Department of Marine and Environmental Sciences, Savannah State University, Savannah, GA USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Hintz
authors.affiliation: Department of Electrical and Computer Engineering, George Mason University, Fairfax, VA USA.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Hintz
authors.affiliation: Department of Earth and Environmental Sciences, University of St. Andrews, St. Andrews KY16 9AL, UK.
authors.forename: Nicola
authors.initials: N
authors.lastname: Allison
mesh_terms: D000064:Acclimatization / Q000235:genetics; D000818:Animals; D037421:Anthozoa / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002113:Calcification, Physiologic / Q000235:genetics*; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism; D002980:Climate; D003080:Cold Temperature; D005580:Fossils; D014644:Genetic Variation; D005838:Genotype; D012623:Seawater / Q000737:chemistry*; D013045:Species Specificity; D013324:Strontium / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide; D002118:Calcium; D013324:Strontium