Magnesium (Mg/Ca, δ26Mg), boron (B/Ca, δ11B), and calcium ([Ca2+]) geochemistry of Arctica islandica and Crassostrea virginica extrapallial fluid and shell under ocean acidification

• Main Authors: Alvarez Caraveo, Blanca, Guillermic, Maxence, Downey-Wall, Alan, Cameron, Louise P., Sutton, Jill N., Higgins, John A., Ries, Justin B., Lotterhos, Katie, Eagle, Robert A.
• Format: Text
• Language: English
• Published: 2024
• Subjects: Arctica islandica; Ocean acidification
• Online Access: https://doi.org/10.5194/egusphere-2024-1957; https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1957/

The geochemistry of biogenic carbonates has long been used as proxies to record changing seawater parameters. However, the effect of ocean acidification on seawater chemistry and organism physiology could impact isotopic signatures and how elements are incorporated into the shell. In this study, we investigated the geochemistry of three reservoirs important for biomineralization – seawater, the extrapallial fluid (EPF), and the shell – in two bivalve species, Crassostrea virginica and Arctica islandica . Additionally, we examined the effects of three ocean acidification conditions (ambient: 500 ppm CO 2 , moderate: 900 ppm CO 2 , and high: 2800 ppm CO 2 ) on the geochemistry of the same three reservoirs for C. virginica . We present data on calcification rates, EPF pH, measured elemental ratios (Mg/Ca, B/Ca), and isotopic signatures (δ 26 Mg, δ 11 B). In both species, comparisons of seawater and EPF Mg/Ca and B/Ca, [Ca 2+ ], and δ 26 Mg indicate that the EPF has a distinct composition that differs from seawater. Shell δ 11 B did not faithfully record seawater pH and δ 11 B-calculated pH values were consistently higher than pH measurements of the EPF with microelectrodes, indicating that the shell δ 11 B may reflect a localized environment within the entire EPF reservoir. In C. virginica , EPF Mg/Ca and B/Ca, as well as absolute concentrations of Mg, B, and [Ca 2+ ], were all significantly affected by ocean acidification, indicating that OA affects the physiological pathways regulating or storing these ions, an observation that complicates their use as proxies. Reduction in EPF [Ca 2+ ] may represent an additional mechanism underlying reduction in calcification in C. virginica in response to seawater acidification. The complexity of dynamics of EPF chemistry suggest boron proxies in these two mollusc species are not straightforwardly related to seawater pH, but ocean acidification does lead to both a decrease in microelectrode pH and ...