Growth rate rather than temperature affects the B∕Ca ratio in the calcareous red alga Lithothamnion corallioides

[摘要] The B / Ca ratio in calcareous marine species isinformative of past seawater CO 3 2 - concentrations, but scarce dataexist on B / Ca in coralline algae. Recent studies suggest influences oftemperature and growth rates on B / Ca , the effect of which could be criticalfor the reconstructions of surface ocean pH and atmospheric p CO 2 . Inthis paper, we present the first laser ablation inductively coupled plasma massspectrometry (LA-ICP-MS) analyses of Mg, Sr, Li, and B inthe coralline alga Lithothamnion corallioides collected from different geographic settings and depthsacross the Mediterranean Sea and in the Atlantic Ocean. We produced thefirst data on putative temperature proxies ( Mg / Ca , Li / Ca , Sr / Ca , Mg / Li ) and B / Ca in a coralline algal species grown in different basins from across thephotic zone (12, 40, 45, and 66 m depth). We tested the B / Ca correlation with temperature proxies and growth rates in order to evaluatetheir possible effect on B incorporation. Our results suggested a growthrate influence on B / Ca , which was evident in the sample with the lowest growth rate of0.10 mm yr −1 (Pontian Isl., Italy; 66 m depth) and in Elba (Italy; 45 m depth), where the algal growth rate was the highest (0.14 mm yr −1 ). At thesetwo sites, the measured B / Ca was the lowest at 462.8  ±  49.2  µ mol mol −1 and the highest at 757.7  ±  75.5  µ mol mol −1 , respectively. A positivecorrelation between B / Ca and temperature proxies was found only in theshallowest sample from Morlaix (Atlantic coast of France; 12 m depth), wherethe amplitude of temperature variation ( Δ T ) was the highest (8.9  ∘ C). Still, fluctuations in B / Ca did not mirror yearly seasonaltemperature oscillations as for Mg / Ca , Li / Ca , and Sr / Ca . We concluded thatgrowth rates, triggered by the different Δ T and light availabilityacross depth, affect the B incorporation in L. corallioides .

[学科分类] 大气科学