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

Abstract

Abstract. Ocean acidification, the decrease in ocean pH associated with increasing atmospheric CO 2 , is likely to impact marine organisms, particularly those that produce carbonate skeletons or shells. Therefore, it is important to investigate how environmental factors (seawater pH, temperature and salinity) influence the chemical compositions in biogenic carbonates. In this study we report the first highresolution strontium ( 87 Sr / 86 Sr and δ 88 / 86 Sr) and boron (δ 11 B) isotopic values in the aragonite shell of cultured Arctica islandica (A. islandica). The 87 Sr / 86 Sr ratios from both tank water and shell samples show ratios nearly identical to the open ocean, which suggests that the shell material reflects ambient ocean chemistry without terrestrial influence. The 84 Sr-87 Sr double-spike-resolved shell δ 88 / 86 Sr and Sr concentration data show no resolvable change throughout the culture period and reflect no theoretical kinetic mass fractionation throughout the experiment despite a temperature change of more than 15 • C. The δ 11 B records from the experiment show at least a 5 ‰ increase through the 29-week culture season (January 2010-August 2010), with low values from the beginning to week 19 and higher values thereafter. The larger range in δ 11 B in this experiment compared to predictions based on other carbonate organisms (2-3 ‰) suggests that a species-specific fractionation factor may be required. A significant correlation between the pH (pH shell − pH sw ) and seawater pH (pH sw ) was observed (R 2 = 0.35), where the pH shell is the calcification pH of the shell calculated from boron isotopic composition. This negative correlation suggests that A. islandica partly regulates the pH of the extrapallial fluid. However, this proposed mechanism only explains approximately 35 % of the variance in the δ 11 B data. Instead, a rapid rise in δ 11 B of the shell material after week 19, during the summer, suggests that the boron uptake changes when a thermal threshold of > 13 • C is reached.

Strontium, magnesium, and barium incorporation in aragonitic shells of juvenile Arctica islandica: Insights from temperature controlled experiments

“…Their calibration is difficult to assess because they do not show any data aside from a regression equation. Since then, however, both Sr/Ca and/or Mg/Ca in A. islandica shells have been difficult to match to seawater temperature (Foster et al, 2008(Foster et al, , 2009Schöne et al, 2010Schöne et al, , 2011bLiu et al, 2015;Marali et al, 2017a). The lack of a consistent relationship between environmental conditions and Mg/Ca or Sr/Ca ratios in A. islandica shells is likely due to physiological processes during biomineralization (e.g., Foster et al, 2009).…”

Isotope systematics of subfossil, historical, and modern Nautilus macromphalus from New Caledonia

“…Evidence from the geologic record, however, suggests that Δ 44/40 Ca SW-Shell is sensitive to seawater carbonate state. Culturing experiments show that the pH of extrapallial fluid from Arctica islandica bivalves is at least partially regulated during shell formation, but can vary with ambient pH [ 66 ]. If Nautilus similarly regulates the pH and potentially the saturation state of extrapallial fluid during shell precipitation, then variation in Δ 44/40 Ca SW-Shell would be driven by mass-dependent isotope effects during transport into the extrapallial fluid rather than with varying saturation state and precipitation rate at the site of precipitation, as has been observed in inorganic systems.…”

The revolution of crossdating in marine palaeoecology and palaeoclimatology

“…Such information can test and improve the skill of numerical climate models, which poorly capture variability in these spectral domains. Once crossdated sclerochronologies have been constructed [2], novel proxies, such as nitrogen [51] and boron isotopes [52], or emerging geochemical proxies, promise to provide essential constraints on marine ecosystems, ocean acidification and climate. The recent metagenomic discovery that bivalve shell carbonate contains environmental DNA [53] heralds the possibility of using crossdated shell series to reconstruct marine biodiversity across major anthropogenic transitions, enabling reconstructions of marine ecosystem baselines and rates of biodiversity loss.…”