Environmental controls on the boron and strontium isotopic composition of aragonite shell material of cultured &amp;lt;i&amp;gt;Arctica islandica&amp;lt;/i&amp;gt;

Y.-W. Liu,A. D. Wanamaker,S. M. Aciego

doi:10.5194/bg-12-3351-2015

Environmental controls on the boron and strontium isotopic composition of aragonite shell material of cultured &lt;i&gt;Arctica islandica&lt;/i&gt;

Y.-W. Liu, A. D. Wanamaker + Show 1 more

Open Access

https://doi.org/10.5194/bg-12-3351-2015

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Abstract

Abstract. Ocean acidification, the decrease in ocean pH associated with increasing atmospheric CO2, 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 high-resolution strontium (87Sr / 86Sr and δ88 / 86Sr) and boron (δ11B) isotopic values in the aragonite shell of cultured Arctica islandica (A. islandica). The 87Sr / 86Sr 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 84Sr–87Sr double-spike-resolved shell δ88 / 86Sr 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 δ11B 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 δ11B 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 ΔpH (pHshell − pHsw) and seawater pH (pHsw) was observed (R2 = 0.35), where the pHshell 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 δ11B data. Instead, a rapid rise in δ11B 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.

Highlights

Since the onset of the Industrial Revolution
We examined the radiogenic and stable isotopic composition of strontium and the stable isotopic composition of boron recorded in the aragonitic shell material of cultured www.biogeosciences.net/12/3351/2015/
These results suggest that wellpreserved subfossil specimens may be used to determine the past isotopic composition (87Sr / 86Sr and δ88 / 86Sr) of seawater

Summary

Introduction

AD 1750) the global ocean has absorbed approximately 30 % of the emitted anthropogenic carbon dioxide (CO2) causing ocean acidification (IPCC, 2013). Anthropogenic CO2 is not evenly distributed among the ocean basins. The North Atlantic Ocean stores about 23 % of anthropogenic CO2 despite representing only 15 % of the global ocean area (Sabine et al, 2004). The North Atlantic Basin, compared to other regions, might be more susceptible to ocean acidification. In situ measurements of surface ocean pH are rare prior to about 1990 (Byrne et al, 2010; Dore et al, 2009), instrumental data show that the surface global ocean pH has decreased by approximately 0.05 pH units in the last 20–25 years (IPCC, 2013).

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