Stable carbon isotopic composition of Mytilus edulis shells: relation to metabolism, salinity, d13CDIC and phytoplankton.

Abstract Bivalve shells can potentially record the carbon isotopic signature of dissolved inorganic carbon (d 13 C DIC ) in estuarine waters, thereby providing information about past estuarine biogeochemical cycles. However, the fluid from which these animals calcify is a 'pool' of metabolic CO 2 and external dissolved inorganic carbon (DIC). The incorporation of respired 13 Cdepleted carbon into the skeletons of aquatic invertebrates is well documented, and may affect the d 13 C record of the skeleton. Typically, less than 10% of the carbon in the skeleton is metabolic in origin, although higher amounts have been reported. If this small offset is more or less constant, large biogeochemical gradients in estuaries may be recorded in the d 13 C value of bivalve shells. In this study, it is assessed if the d 13 C values of Mytilus edulis shells can be used as a proxy of d 13 C DIC as well as providing an indication of salinity. First, the d 13 C values of respired CO 2 (d 13 C R ) were considered using the d 13 C values of soft tissues as a proxy for d 13 C R . Along the strong biogeochemical gradient of the Scheldt estuary (The NetherlandsBelgium), d 13 C R was linearly related to d 13 C DIC (r 2 = 0.87), which in turn was linearly related to salinity (r 2 = 0.94). The mussels were highly selective, assimilating most of their carbon from phytoplankton out of the total particulate organic carbon (POC) pool. However, on a seasonal basis, tissue d 13 C varied differently than d 13 C DIC and d 13 C POC , most likely due to lipid content of the tissue. All shells contained less than 10% metabolic carbon, but ranged from near zero to 10%, thus excluding the use of d 13 C in these shells as a robust d 13 C DIC or salinity proxy. As an example, an error in salinity of about 5 would have been made at one site. Nevertheless, large changes in d 13 C DIC (>2&) can be determined using M. edulis shell d 13 C

An international intercomparison of stable carbon isotope composition measurements of dissolved inorganic carbon in seawater

We report results of an intercomparison of stable carbon isotope ratio measurements in seawater dissolved inorganic carbon (δ 13C‐DIC) which involved 16 participating laboratories from various parts of the world. The intercomparison involved distribution of samples of a Certified Reference Material for seawater DIC concentration and alkalinity and a preserved sample of deep seawater collected at 4000 m in the northeastern Atlantic Ocean. The between‐lab standard deviation of reported uncorrected values measured with diverse analytical, detection, and calibration methods was 0.11‰ (1σ ). The multi‐lab average δ 13C‐DIC value reported for the deep seawater sample was consistent within 0.1‰ with historical measured values for the same water mass. Application of a correction procedure based on a consensus value for the distributed reference material, improved the between‐lab standard deviation to 0.06‰. The magnitude of the corrections were similar to those used to correct independent data sets using crossover comparisons, where deep water analyses from different cruises are compared at nearby locations. Our results demonstrate that the accuracy/uncertainty target proposed by the Global Ocean Observing System (±0.05‰) is attainable, but only if an aqueous phase reference material for δ 13C‐DIC is made available and used by the measurement community. Our results imply that existing Certified Reference Materials used for seawater DIC and alkalinity quality control are suitable for this purpose, if a “Certified” or internally consistent “consensus” value for δ 13C‐DIC can be assigned to various batches.publishedVersio

Environmental Predictors of Diversity in Recent Planktonic Foraminifera as Recorded in Marine Sediments

© 2016 Fenton et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. [4.0 license]. The attached file is the published version of the article

A large metabolic carbon contribution to the δ13C record in marine aragonitic bivalve shells

International audienceIt is well known that the incorporation of isotopically light metabolic carbon (CM) significantly affects the stable carbon isotope (δ13C) signal recorded in biogenic carbonates. This can obscure the record of δ13C of seawater dissolved inorganic carbon (δ13CDIC) potentially archived in the shell carbonate. To assess the CM contribution to Mercenaria mercenaria shells collected in North Carolina, USA, we sampled seawater δ13CDIC, tissue, hemolymph and shell δ13C. All shells showed an ontogenic decrease in shell δ13C, with as much as a 4 ‰ decrease over the lifespan of the clam. There was no apparent ontogenic change in food source indicated by soft tissue δ13C values, therefore a change in the respired δ13C value cannot be the cause of this decrease. Hemolymph δ13C, on the other hand, did exhibit a negative relationship with height indicating that respired CO2 does influence the δ13C value of internal fluids and that the amount of respired CO2 is related to the size or age of the bivalve. The percent metabolic C incorporated into the shell (%CM) was significantly higher (up to 37 %, with a range from 5-37 %) than has been found in other bivalve shells, which usually contain less than 10 %CM. Interestingly, the hemolymph did contain less than 10 %CM, suggesting that complex fractionation might occur between hemolymph and calcifying fluids. Simple shell biometrics explained nearly 60 % of the observed variability in %CM, however, this is not robust enough to predict %CM for fossil shells. Thus, the metabolic effect on shell δ13C cannot easily be accounted for to allow reliable δ13CDIC reconstructions. However, there does seem to be a common effect of size, as all sites had indistinguishable slopes between the %CM and shell height (+0.19 % per mm of shell height)

δ13C in Mytilus edulis shells: relation to salinity, DIC, phytoplankton and metabolism

International audienceBivalve shells can potentially record the carbon isotopic signature of the dissolved inorganic carbon (δ13CDIC) in estuarine waters, thereby providing information about past estuarine biogeochemical cycles. However, the fluid from which these animals calcify is a ‘pool' of metabolic CO2 and external dissolved inorganic carbon (DIC). The incorporation of respired 13C depleted carbon into the skeletons of aquatic invertebrates is well documented, and may affect the 13CDIC record of the skeleton. Typically, less than 10 % of the carbon in the skeleton is metabolic in origin, although higher amounts have been reported. If this small offset is more or less constant, large biogeochemical gradients in estuaries may be recorded in the δ13C value of bivalve shells. In this study, it is assessed if the δ13C values of Mytilus edulis shells can be used as a proxy of δ13CDIC as well as provide an indication of salinity. First, the δ13C values of respired CO2 (δ13CR) was considered using the δ13C values of soft tissues as a proxy for δ13CR. Along the strong biogeochemical gradient of the Scheldt estuary (The Netherlands – Belgium), δ13CR was linearly related to δ13CDIC (r2 = 0.87), which in turn was linearly related to salinity (r2 = 0.94). The mussels were highly selective, assimilating most of their carbon from phytoplankton out of the total particulate organic carbon (POC) pool. However, on a seasonal basis, tissue δ13C varied differently than δ13CDIC and δ13CPOC, most likely due to lipid content of the tissue. All shells contained less than 10 % metabolic C, but ranged from near zero to 10 %, thus excluding the use of δ13C in these shells as a robust δ13CDIC or salinity proxy. As an example, an error in salinity of about five would have been made at one site. Nevertheless, large changes in δ13CDIC (>2 ‰) can be determined using M. edulis shell δ13C

Inter- and intra-annual variations of Pb/Ca ratios in clam shells (Mercenaria mercenaria): a record of anthropogenic lead pollution?

International audienceIn this study, we re-assess the use of bivalve shells as a proxy of lead pollution. Previous studies have stressed that shells display little variability compared to soft tissues and thus are better for pollution biomonitoring. However, in this manuscript we illustrate that there is large inter- and intra-annual Pb variability between shells of the clam Mercenaria mercenaria collected in North Carolina, USA. Therefore, year to year, as well as intra-annual variations in Pb/Ca ratios should be interpreted with caution. Despite this variability, we were able to obtain an annual Pb chronology from 1949 to 2002 using 11 shells collected at different times which clearly exhibited the late 1970's peak in Pb from leaded gasoline use. This indicates that when enough specimens are pooled together, bivalve shells can be used to reconstruct large, long term changes in environmental Pb concentrations. Our data compare well with other studies of aragonite clams from sites with low regional lead pollution. From this we conclude that the Cape Lookout region of North Carolina has not received extensive pollution over the 1949-2002 period. The Pb concentration in shells growing in the 1949-1976 period was not significantly different from those growing in the 1982-2002 period, although other proxies suggest that the 1949-1976 period should be considerably higher. Therefore, our data suggest that there is still a modern source of Pb in the coastal North Carolina environment

Barium uptake into the shells of the common mussel (Mytilus edulis) and the potential for estuarine paleo-chemistry reconstruction

International audienceIn this study we test if calcite shells of the common mussel, Mytilus edulis, contain barium in proportion to the water in which they grew. Similar to all bivalves analyzed to date, the [Ba/Ca]shell profiles are characterized by a relatively flat background [Ba/Ca]shell, interrupted by sharp [Ba/Ca]shell peaks. Previous studies have focused on these [Ba/Ca]shell peaks, but not on the background [Ba/Ca]shell. We show that in both laboratory and field experiments, there is a direct relationship between the background [Ba/Ca]shell and [Ba/Ca]water in M. edulis shells. The laboratory and field data provided background Ba/Ca partition coefficients (DBa) of 0.10 ± 0.02 and 0.071 ± 0.001, respectively. This range is slightly higher than the DBa previously determined for inorganic calcite, and slightly lower than foraminiferal calcite. These data suggest that M. edulis shells can be used as an indicator of [Ba/Ca]water, and therefore, fossil or archaeological M. edulis shells could be used to extend knowledge of estuarine dissolved Ba throughputs back in time. Moreover, considering the inverse relationship between [Ba/Ca]water and salinity, background [Ba/Ca]shell data could be used as an estuary specific indicator of salinity. The cause of the [Ba/Ca]shell peaks are more confusing, both the laboratory and field experiments indicate that they cannot be used as a direct proxy of [Ba/Ca]water or phytoplankton production, but may possibly be caused by barite ingestion

Experimental shift of diet and DIC stable carbon isotopes: influence on shell δ13C values in the Manila clam Ruditapes philippinarum

International audienceThe influences of diet and seawater dissolved inorganic carbon (DIC) on the carbon isotope composition of shell aragonite (δ13Cshell) in the Manila clam Ruditapes philippinarum reared under laboratory conditions were investigated. Clams were exposed to two successive negative carbon isotope shifts: a first shift in diet (δ13Cphytoplankton) and a second shift, 35 days later, in DIC (δ13CDIC). Both successive shifts induced a decrease in δ13Cshell. These results are the first to experimentally confirm an incorporation of respired carbon derived from food and carbon from DIC into shell carbonate of adult bivalves. Skeletal δ13C responded to changes in the δ13C of both diet and DIC in less than 7 days. Consequently, proxies based on δ13Cshell may be used with high temporal resolution. Using δ13Cphytoplankton as a proxy for the carbon isotope composition of respired carbon (δ13CR) resulted in a rather constant percentage of metabolic carbon (CM) into the shell carbonate over time (close to 12%). However, an accurate estimation of δ13CR is required in order to precisely estimate the percentage of metabolic carbon incorporated into the shell. Despite the significant incorporation of metabolic carbon into shell carbonate, our experimental results revealed that δ13Cshell was highly correlated with δ13CDIC (r² = 0.77, p < 0.0001). Thus it seems that δ13Cshell is a promising proxy of large scale variations in δ13CDIC and therefore of salinity in estuarine water