Open AccessMg/Ca, Sr/Ca, and stable‐isotope (δ 18 O and δ 13 C) ratio profiles from the fan mussel Pinna nobilis : Seasonal records and temperature relationships
Author(s) -
Freitas Pedro,
Clarke Leon J.,
Kennedy Hilary,
Richardson Christopher,
Abrantes Fátima
Publication year - 2005
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2004gc000872
Subject(s) - calcite , geology , mussel , strontium , isotopes of calcium , isotopes of strontium , mineralogy , analytical chemistry (journal) , calcium , zoology , oceanography , chemistry , biology , ecology , environmental chemistry , organic chemistry
We present new annually resolved δ 18 O, δ 13 C, Mg/Ca, and Sr/Ca ratio records for two shells of the fast growing Mediterranean fan mussel Pinna nobilis , collected from proximal Spanish coast sea grass meadows. The relationship between the potential geochemical proxies and ontogenetic and environmental controlling factors is investigated. Specifically, the use of shell Mg/Ca and Sr/Ca ratios as potential calcification temperature proxies, the latter calculated from measured shell δ 18 O values, has been assessed. The δ 18 O cycles along the growth axis indicate that our P. nobilis specimens are ∼10.5 and ∼4.5 years old. Shell Sr/Ca ratios do not exhibit any consistent interannual cyclicity and are not correlated to temperature. A subtle ontogenetic effect on shell Mg/Ca ratios was observed during the first 4.5 years of recorded growth but was highly evident during the organism's later growth years. In P. nobilis shells, different mechanisms influence ontogenetic variation in shell Mg/Ca and δ 18 O records. Shell Mg/Ca ratios from the first 4.5 years of growth correlate significantly to temperature, in a best fit relationship described by the equation Mg/Ca = 17.16 ± 1.95 * exp(0.022 ± 0.004 * T). P. nobilis shell Mg/Ca records therefore are a valid temperature proxy only during an early growth phase. For the same range of temperatures, shell Mg/Ca ratios in P. nobilis are approximately 1/3 lower than those reported for inorganic calcite but 3 to 4 times higher than in another bivalve species, Mytilus trossulus , and 4 to 16 times higher than in foraminifera. We suggest these offsets are due to a higher degree of similarity between seawater and calcification‐fluid composition in P. nobilis than in other bivalves and foraminifera. The observed shell Mg/Ca ratio change per °C of 2.2% also is lower than that observed for inorganic and other biogenic calcites. Our findings strongly support taxon‐ and species‐specific Mg/Ca–temperature relationships for bivalves and other calcifying organisms. An appreciation of the physiology and calcification mechanisms of any biogenic carbonate archive therefore is paramount prior to the application of stable‐isotope and element/Ca ratio proxies for paleotemperature reconstructions.