Environmental controls on the boron and strontium isotopic composition of aragonite shell material of cultured Arctica islandica

[摘要] Ocean acidification, the decrease in ocean pH associated with increasingatmospheric CO₂, is likely to impact marine organisms, particularlythose that produce carbonate skeletons or shells. Therefore, it is importantto investigate how environmental factors (seawater pH, temperature andsalinity) influence the chemical compositions in biogenic carbonates. Inthis study we report the first high-resolution strontium(⁸⁷Sr / ⁸⁶Sr and δ^{88 / 86}Sr) and boron (δ¹¹B)isotopic values in the aragonite shell of cultured Arctica islandica (A. islandica). The⁸⁷Sr /⁸⁶Sr ratios from both tank water and shell samples showratios nearly identical to the open ocean, which suggests that the shellmaterial reflects ambient ocean chemistry without terrestrial influence. The⁸⁴Sr–⁸⁷Sr double-spike-resolved shell δ^{88 / 86}Sr and Srconcentration data show no resolvable change throughout the culture periodand reflect no theoretical kinetic mass fractionation throughout theexperiment despite a temperature change of more than 15 °C. Theδ¹¹B records from the experiment show at least a5‰ increase through the 29-week culture season (January 2010–August 2010),with low values from the beginning to week 19 andhigher values thereafter. The larger range in δ¹¹B in thisexperiment compared to predictions based on other carbonate organisms (2–3‰) suggests that a species-specific fractionationfactor may be required. A significant correlation between the ΔpH(pH_shell − pH_sw) and seawater pH (pH_sw) was observed(R² = 0.35), where the pH_shell is the calcification pH of the shellcalculated from boron isotopic composition. This negative correlationsuggests that A. islandica partly regulates the pH of the extrapallial fluid. However,this proposed mechanism only explains approximately 35% of the variancein the δ¹¹B data. Instead, a rapid rise in δ¹¹B ofthe shell material after week 19, during the summer, suggests that the boronuptake changes when a thermal threshold of > 13 °C is reached.

[学科分类] 地球化学与岩石