Environmental controls on the boron and strontium isotopic composition of aragonite shell material of cultured <i>Arctica islandica</i>
Ocean acidification, the decrease in ocean pH associated with increasing atmospheric CO<sub>2</sub>, 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, t...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-06-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/12/3351/2015/bg-12-3351-2015.pdf |
| Summary: | Ocean acidification, the decrease in ocean pH associated with increasing
atmospheric CO<sub>2</sub>, 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
(<sup>87</sup>Sr / <sup>86</sup>Sr and δ<sup>88 / 86</sup>Sr) and boron (δ<sup>11</sup>B)
isotopic values in the aragonite shell of cultured <i>Arctica islandica</i> (<i>A. islandica</i>). The
<sup>87</sup>Sr / <sup>86</sup>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
<sup>84</sup>Sr–<sup>87</sup>Sr double-spike-resolved shell δ<sup>88 / 86</sup>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<sup>11</sup>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<sup>11</sup>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 ΔpH
(pH<sub>shell</sub> − pH<sub>sw</sub>) and seawater pH (pH<sub>sw</sub>) was observed
(<i>R</i><sup>2</sup> = 0.35), where the pH<sub>shell</sub> is the calcification pH of the shell
calculated from boron isotopic composition. This negative correlation
suggests that <i>A. islandica</i> partly regulates the pH of the extrapallial fluid. However,
this proposed mechanism only explains approximately 35% of the variance
in the δ<sup>11</sup>B data. Instead, a rapid rise in δ<sup>11</sup>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. |
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| ISSN: | 1726-4170 1726-4189 |