Contrasting biogeochemical characteristics of the Oubangui River and tributaries (Congo River basin)

The Oubangui is a major tributary of the Congo River. We describe the biogeochemistry of contrasting tributaries within its central catchment, with watershed vegetation ranging from wooded savannahs to humid rainforest. Compared to a 2-year monitoring record on the mainstem Oubangui, these tributaries show a wide range of biogeochemical signatures, from highly diluted blackwaters (low turbidity, pH, conductivity, and total alkalinity) in rainforests to those more typical for savannah systems. Spectral analyses of chromophoric dissolved organic matter showed wide temporal variations in the Oubangui compared to spatio-temporal variations in the tributaries, and confirm that different pools of dissolved organic carbon are mobilized during different hydrological stages. d13C of dissolved inorganic carbon ranged between -28.1 per mil and -25.8 per mil, and was strongly correlated to both partial pressure of CO2 and to the estimated contribution of carbonate weathering to total alkalinity, suggesting an important control of the weathering regime on CO2 fluxes. All tributaries were oversaturated in dissolved greenhouse gases (CH4, N2O, CO2), with highest levels in rivers draining rainforest. The high diversity observed underscores the importance of sampling that covers the variability in subcatchment characteristics, to improve our understanding of biogeochemical cycling in the Congo Basin.AFRIVAL: ‘‘African river basins: catchment-scale carbon fluxes and transformations’

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

Rapid Environmental Change over the Past Decade Revealed by Isotopic Analysis of the California Mussel in the Northeast Pacific

The anthropogenic input of fossil fuel carbon into the atmosphere results in increased carbon dioxide (CO2) into the oceans, a process that lowers seawater pH, decreases alkalinity and can inhibit the production of shell material. Corrosive water has recently been documented in the northeast Pacific, along with a rapid decline in seawater pH over the past decade. A lack of instrumentation prior to the 1990s means that we have no indication whether these carbon cycle changes have precedence or are a response to recent anthropogenic CO2 inputs. We analyzed stable carbon and oxygen isotopes (δ13C, δ18O) of decade-old California mussel shells (Mytilus californianus) in the context of an instrumental seawater record of the same length. We further compared modern shells to shells from 1000 to 1340 years BP and from the 1960s to the present and show declines in the δ13C of modern shells that have no historical precedent. Our finding of decline in another shelled mollusk (limpet) and our extensive environmental data show that these δ13C declines are unexplained by changes to the coastal food web, upwelling regime, or local circulation. Our observed decline in shell δ13C parallels other signs of rapid changes to the nearshore carbon cycle in the Pacific, including a decline in pH that is an order of magnitude greater than predicted by an equilibrium response to rising atmospheric CO2, the presence of low pH water throughout the region, and a record of a similarly steep decline in δ13C in algae in the Gulf of Alaska. These unprecedented changes and the lack of a clear causal variable underscores the need for better quantifying carbon dynamics in nearshore environments

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 d 13 C record in marine aragonitic bivalve shells

Abstract It is well known that the incorporation of isotopically light metabolic carbon (C M C, on the other hand, did exhibit a negative relationship with shell height indicating that respired CO 2 does influence the d 13 C value of internal fluids and that the amount of respired CO 2 is related to the size or age of the bivalve. The percent metabolic C incorporated into the shell (%C M ) was significantly higher (up to 37%, with a range from 5% to 37%) than has been found in other bivalve shells, which usually contain less than 10%C M . Interestingly, the hemolymph did contain less than 10%C M , suggesting that complex fractionation might occur between hemolymph and calcifying fluids. Simple shell biometrics explained nearly 60% of the observed variability in %C M , however, this is not robust enough to predict %C M for fossil shells. Thus, the metabolic effect on shell d 13 C cannot easily be accounted for to allow reliable d 13 C DIC reconstructions. However, there does seem to be a common effect of size, as all sites had indistinguishable slopes between the %C M and shell height (+0.19% per mm of shell height)

Use of historical and baseline specimens to track responses of molluscan primary consumers to the effects of the 2010 Deepwater Horizon hydrocarbon spill

Documenting direct and indirect effects of environmental stressors on benthic marine communities requires incorporation of baseline and historical data. For instance, hydrocarbons from the 2010 Gulf of Mexico Deepwater Horizon well explosion is impacting coastal areas long affected by natural hydrocarbon seeps, petroleum exploration and development, and other anthropogenic effects. In Louisiana, exploration in coastal areas that began in the 1920s, expanded greatly with the development of the first mobile drilling barge in 1933. In total nearly 50,000 wells are reported to have been drilled in the Gulf of Mexico region. Given this historical context, we are assessing pathways and rates at which hydrocarbons from the 2010 spill are incorporated into northern Gulf of Mexico coastal food webs using sclerochronological techniques to unlock the high-resolution records preserved within molluscan shells. We are using specimens collected from the early 20th century through August 2010. We are examining changes in live history traits (growth rate, recruitment, mortality, reproduction) of a variety of primary consumer species, including the commercially important oyster Crassostrea virginica. The species range from epifaunal, sessile, filter feeders; to infaunal, mobile, deposit feeders; to epifaunal, mobile, omnivorous grazers. In this way, multiple pathways into coastal food webs are monitored. Because environmental perturbations are recorded on multiple scales by the accretionary growth of mollusk shells, we are monitoring the incorporation of crude oil components into shells, e.g., the trace metals V and Ni, and simultaneously measuring changes in growth rate, survivorship, and post-spill larval recruitment. Life-history parameters are calculated from ontogenetic δ13C and δ18O profiles of the mollusks\u27 shells. In this way, we will track secondary impacts (not related to fouling by direct contact) of hydrocarbons through trophic levels of the coastal ecosystem