The effects of varying CO2 concentration on lipid composition and carbon isotope fractionation in Emiliania huxleyi.

We have measured the stable carbon isotopic composition of bulk organic matter (POC), alkenones, sterols, fatty acids, and phytol in the coccolithophorid Emiliania huxleyi grown in dilute batch cultures over a wide range of CO2 concentrations (1.1–53.5 μmol L−1). The carbon isotope fractionation of POC (εPOC) varied by ca. 7‰ and was positively correlated with aqueous CO2 concentration [CO2aq]. While this result confirms general trends observed for the same alga grown in nitrogen-limited chemostat cultures, considerable differences were obtained in absolute values of εPOC and in the slope of the relationship of εPOC with growth rate and [CO2aq]. Also, a significantly greater offset was obtained between the δ13C of alkenones and bulk organic matter in this study compared with previous work (5.4, cf. 3.8‰). This suggests that the magnitude of the isotope offset may depend on growth conditions. Relative to POC, individual fatty acids were depleted in 13C by 2.3‰ to 4.1‰, phytol was depleted in 13C by 1.9‰, and the major sterol 24-methylcholesta-5,22E-dien-3β-ol was depleted in 13C by 8.5‰. This large spread of δ13C values for different lipid classes in the same alga indicates the need for caution in organic geochemical studies when assigning different sources to lipids that might have δ13C values differing by just a few ‰. Increases in [CO2aq] led to dramatic increases in the alkenone contents per cell and as a proportion of organic carbon, but there was no systematic effect on values of U37k′ used for reconstructions of paleo sea surface temperature

River regulation alters drivers of primary productivity along a tropical river-estuary system

Worldwide, rivers continue to be dammed to supply water for humans. The resulting regulation of downstream flow impacts on biogeochemical and physical processes, potentially affecting river and estuarine productivity. Our study tested the hypothesis that primary production in the downstream freshwater reaches of a dammed river was less limited by light and nutrients relative to downstream estuarine primary production. In a tropical dryland Australian river estuary, we found that water-column primary productivity was highest at freshwater sites that had lowest light attenuation. Nitrogen may also have limited primary productivity. Below the freshwater zone was a region of macrotidal mixing with high concentrations of suspended soil particles, nutrients and chlorophyll a, and lower but variable primary productivity rates. Light controlled productivity, but the algal cells may also have been osmotically stressed due to increasing salinity. Further downstream in the estuary, primary productivity was lower than the freshwater reaches and light and nutrient availability appear to be a factor. Therefore the reduced magnitude of peak-flow events due to flow regulation, and the resulting decrease in nutrient export, is likely to be negatively impacting estuarine primary production. This has implications for future development of dams where rivers have highly seasonal flow

Preservation effects on the isotopic and elemental composition of skeletal structures in the deep-sea bamboo coral Lepidisis spp. (Isididae)

Trace elements and stable isotopes (δ13C and δ15N) in deep-sea coral have been used as proxies to reconstruct past climate, and to investigate food web structure. However, there is a paucity of information regarding the effect of preservation on the ch

Preservation effects on the isotopic and elemental composition of skeletal structures in the deep-sea bamboo coral Lepidisis spp. (Isididae)

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