Calcium carbonate and organic carbon content, and stable isotope composition of sediment core Y71-3-2

Planktic stable isotopes by Mix for this paper and Pisias and Mix (1997)

(Table 2) Stable carbon and oxygen isotope record of benthic foraminifera of eastern Mediterranean Sea sediment cores

The paleoproductivity, paleo-oxygenation, and paleohydrographic configuration of the southeastern Mediterranean during the late Holocene was reconstructed on the basis of the isotopic composition of the epibenthic Heterolepa floridana, shallow-endobenthic Uvigerina mediterranea, and the deeper endobenthic Bulimina inflata from two high-resolution cores GA-112 (470 m) and GA-110 (670 m). The Delta d13C between H. floridana and U. mediterranea reveals four intervals of enhanced productivity, from 3.3-2.6, 2.3-1.9, 1.5-1.1, and 0.8-0.4 kyr BP, coinciding with increased nutrient supply by the Nile River. The entire basin was well aerated, with oxygen consumption varying between 1.0 and 3.5 mL O2/L. Oxygen consumption increases toward present day, probably because of higher accumulation of total organic carbon at 1.7 kyr BP, coinciding with the appearance of the mesotropic benthic species. The hydrographic configuration of the basin has changed during the course of the last 3.75 kyr. The Levantine Intermediate Water (LIW) deepens below 470 m between 3.3 and 2.0 kyr, and especially between 2.5 and 2.0 kyr. During the last 1.5 kyr, the LIW becomes shallower than 470 m, similar to the present day. The change in the hydrographic configuration reflects changes in evaporation/precipitation ratio and in temperature.

(Table T1) Stable carbon and oxygen isotope ratios of benthic foraminifera in the Late Pliocene-Pleistocene section of ODP Site 181-1123 in the Southwest Pacific

Stable isotope records were generated for a late Pliocene-early Pleistocene interval from Ocean Drilling Program (ODP) Site 1123 in the southwest Pacific (41°47 S, 171°30 W; 3290 m water depth). Based on these data, new revisions were made to the shipboard splice and composite section. The isotope records will be used to evaluate the influence of North Atlantic and Southern Ocean deepwater masses on water entering the Pacific in the Deep Western Boundary Current. Three holes were cored at Site 1123, yielding a complete composite section over approximately the last 4.7 m.y. A representative spliced record ("the splice") was developed aboard ship based on magnetic susceptibility, gamma ray attenuation bulk density, and percent reflectance data from the three adjacent holes (Carter, McCave, Richter, Carter, et al., 1999, doi:10.2973/odp.proc.ir.181.2000). No gaps in the sedimentary record were detected for the multiple-cored section of Site 1123. In addition to the isotope data, postcruise revisions to the splice and composite section based on stable isotope data are described here.

Size-based variation in intertissue comparisons of stable carbon and nitrogen isotopic signatures of bull sharks (Carcharhinus leucas) and tiger sharks (Galeocerdo cuvier)

Stable isotopes are important tools for understanding the trophic roles of elasmobranchs. However, whether different tissues provide consistent stable isotope values within an individual are largely unknown. To address this, the relationships among carbon and nitrogen isotope values were quantified for blood, muscle, and fin from juvenile bull sharks (Carcharhinus leucas) and blood and fin from large tiger sharks (Galeocerdo cuvier) collected in two different ecosystems. We also investigated the relationship between shark size and the magnitude of differences in isotopic values between tissues. Isotope values were significantly positively correlated for all paired tissue comparisons, but R2 values were much higher for δ13C than for δ15N. Paired differences between isotopic values of tissues were relatively small but varied significantly with shark total length, suggesting that shark size can be an important factor influencing the magnitude of differences in isotope values of different tissues. For studies of juvenile sharks, care should be taken in using slow turnover tissues like muscle and fin, because they may retain a maternal signature for an extended time. Although correlations were relatively strong, results suggest that correction factors should be generated for the desired study species and may only allow coarse-scale comparisons between studies using different tissue types.

Seasonal variations in stable isotope ratios of two biomanipulation fishes and seston in a large pen culture in hypereutrophic Meiliang Bay, Lake Taihu

This paper reports on seasonal changes in stable carbon and nitrogen isotope ratios of seston and muscle tissue of silver carp and bighead carp during 2004 and 2005, focusing primarily on the carbon sources and trophic relationships among phytoplankton, zooplankton and silver carp and bighead carp in a large fish pen of Meiliang Bay (Lake Taihu, China). delta C-13 showed a minimal value in March 2005 and a maximal value in August 2005 in seston both inside and outside the pen, whereas delta N-15 of seston showed the minimum in winter and the maximum during algal blooms. A positive correlation between delta C-13 of silver carp and that of seston suggested that temporal variation Of delta C-13 in seston was preserved in fish via the food chain. The differences of delta C-13 among seston, zooplankton and muscle tissue of silver carp and bighead carp ranged only 0.2-1.7%, indicating that plankton production was the primary food source of filter-feeding fishes. According to a mass balance model, we estimated that the contributions of zooplankton to the diets of silver carp and bighead carp were 45.7% and 54.3%, respectively, based on the delta N-15 values of zooplankton and planktivorous fishes. (C) 2007 Elsevier B.V. All rights reserved

Stable isotope changes in freshwater shrimps (Exopalaemon modestus and Macrobrachium nipponensis): trophic pattern implications

Trophic patterns of omnivorous freshwater shrimps, Exopalaemon modestus and Macrobrachium nipponensis, were investigated in two shallow eutrophic lakes by using stable isotope analysis. delta N-15 and delta C-13 of M. nipponensis and E. modestus increased with increasing body weight, which might be attributed to larger individuals ingesting organisms that feed higher up the food chain and/or increased assimilation of benthic food items with enriched isotopic signatures. Of the freshwater shrimps occurring in the studied lakes, those from Lake Taihu had significantly elevated delta N-15 and delta C-13 values (4.3% and 1.8%, respectively) compared with those from the less eutrophic Lake Chaohu, indicating that the isotopic signature might partially reflect the trophic states of their habitats. Mixing model results suggested that the benthic food web provides the primary carbon source for both shrimp species, and that E. modestus assimilated relatively more pelagic food sources than M. nipponensis in these lakes.

Stable carbon isotope variations in surface bloom scum and subsurface seston among shallow eutrophic lakes

Carbon stable isotope analysis of surface bloom scum and subsurface seston samples was conducted in shallow eutrophic lakes in China during warm seasons from 2003 to 2004. delta C-13 values of bloom scum were always higher (averaged 5 parts per thousand) than those of seston in this study, and the possible reasons were attributed to (i) direct use of atmospheric CO2 at the air-water interface, (ii) decrease in C-13 fractionation due to higher carbon fixation, (iii) active CO2 transport, and/or (iv) HCO3 accumulation. Negative correlation between delta C-13(scum) - delta C-13(seston) and pH in the test lakes indicated that phytoplankton at the subsurface water column increased isotopic enrichment under the-carbon limitation along with the increase of pH, which might in turn decreased the differences in 313 C between the subsurface seston and the surface scums. Significant positive correlations of seston 8 13C with total concentrations of nitrogen and phosphorus in water column suggested that the increase in delta C-13 of seston with trophic state was depending on nutrient (N or P, or both) supply. Our study showed that delta C-13 of phytoplankton was indicative of carbon utilization, primary productivity, and nutrient supply among the eutrophic lakes. (C) 2007 Elsevier B.V All rights reserved.

14C as a tool to trace terrestrial carbon in a complex lake system: implications for foodweb structure and carbon cycling

Carbon and nitrogen stable isotope analysis (SIA) has identified the terrestrial subsidy of freshwater food-webs but relies on different 13C fractionation in aquatic and terrestrial primary producers. However dissolved inorganic carbon (DIC) is partly comprised of 13C depleted respiration of terrestrial C and ‘old’ C derived from weathering of catchment geology. SIA thus fails to differentiate between the contribution of old and recently fixed terrestrial C. DIC in alkaline lakes is partially derived from weathering of 14C-free carbonaceous bedrock This
yields an artificial age offset leading samples to appear significantly older than their actual age. As such, 14C can be used as a biomarker to identify the proportion of autochthonous C in the food-web. With terrestrial C inputs likely to increase, the origin and utilisation of ‘old’ or ‘recent’ allochthonous C in the food-web can also be determined. Stable isotopes and 14C were measured for biota, particulate organic matter (POM), DIC and dissolved organic carbon (DOC) from Lough Erne, Northern Ireland, a humic but alkaline lake. High winter δ15N values in calanoid zooplankton (δ15N =24‰) relative to phytoplankton and POM (δ15N =6‰ and 12‰ respectively) may reflect several microbial trophic levels between terrestrial C and calanoids. Furthermore winter calanoid 14C ages are consistent with DOC from inflowing rivers (87 and 75 years BP respectively) but not phytoplankton (355 years BP). Summer calanoid δ13N, δ15N and 14C (312 years BP) indicate greater reliance on phytoplankton. There is also temporal and spatial variation in DIC, DOC and POM C isotopes.

14C as a tool to trace terrestrial carbon in a complex lake system: implications for food-web structure and carbon cycling

Globally lakes bury and remineralise significant quantities of terrestrial C, and the associated flux of terrestrial C strongly influences their functioning. Changing deposition chemistry, land use and climate induced impacts on hydrology will affect soil biogeochemistry and terrestrial C export¹ and hence lake ecology with potential feedbacks for regional and global C cycling. C and nitrogen stable isotope analysis (SIA) has identified the terrestrial subsidy of freshwater food webs. The approach relies on different ¹³C fractionation in aquatic and terrestrial primary producers, but also that inorganic C demands of aquatic primary producers are partly met by ¹³C depleted C from respiration of terrestrial C, and ‘old’ C derived from weathering of catchment geology. SIA thus fails to differentiate between the contributions of old and recently fixed terrestrial C. Natural abundance ¹⁴C can be used as an additional biomarker to untangle riverine food webs² where aquatic and terrestrial δ ¹³C overlap, but may also be valuable for examining the age and origin of C in the lake. Primary production in lakes is based on dissolved inorganic C (DIC). DIC in alkaline lakes is partially derived from weathering of carbonaceous bedrock, a proportion of which is¹⁴C-free. The low ¹⁴C activity yields an artificial age offset leading samples to appear hundreds to thousands of years older than their actual age. As such, ¹⁴C can be used to identify the proportion of autochthonous C in the food-web. With terrestrial C inputs likely to increase, the origin and utilisation of ‘fossil’ or ‘recent’ allochthonous C in the food-web can also be determined. Stable isotopes and 14C were measured for biota, particulate organic matter (POM), DIC and dissolved organic carbon (DOC) from Lough Erne, Northern Ireland, a humic alkaline lake. Temporal and spatial variation was evident in DIC, DOC and POM C isotopes with implications for the fluctuation in terrestrial export processes. Ramped pyrolysis of lake surface sediment indicates the burial of two C components. ¹⁴C activity (507 ± 30 BP) of sediment combusted at 400˚C was consistent with algal values and younger than bulk sediment values (1097 ± 30 BP). The sample was subsequently combusted at 850˚C, yielding 14C values (1471 ± 30 BP) older than the bulk sediment age, suggesting that fossil terrestrial carbon is also buried in the sediment. Stable isotopes in the food web indicate that terrestrial organic C is also utilised by lake organisms. High winter δ ¹⁵N values in calanoid zooplankton (δ ¹⁵N = 24%¸) relative to phytoplankton and POM (δ ¹⁵N = 6h and 12h respectively) may reflect several microbial trophic levels between terrestrial C and calanoids. Furthermore winter calanoid 14C ages are consistent with DOC from an inflowing river (75 ± 24 BP), not phytoplankton (367 ± 70 BP). Summer calanoid δ ^13C, δ ¹⁵N and ¹⁴C (345 ± 80 BP) indicate greater reliance on phytoplankton.

¹ Monteith, D.T et al., (2007) Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry. Nature, 450:537-535

² Caraco, N., et al.,(2010) Millennial-aged organic carbon subsidies to a modern river food web. Ecology,91: 2385-2393.

Seasonally resolved growth of freshwater bivalves determined by oxygen and carbon isotope shell chemistry

By means of a monitoring experiment in two rivers in the Netherlands, we establish a relationship between seasonally resolved growth rates in unionid freshwater bivalves and their environment. We reconstructed these seasonally resolved growth rates by using relationships of stable isotopes in the shells and their ambient river water. The reconstructed growth rates reveal that shells grow fastest in spring-early summer, when highest food availability occurs in the rivers. In addition, the reconstructed growth rates show that onset and cessation of growth are mainly influenced by water temperature.

Global vegetation and terrestrial carbon cycle changes after the last ice age

•In current models, the ecophysiological effects of CO2 create both woody thickening and terrestrial carbon uptake, as observed now, and forest cover and terrestrial carbon storage increases that took place after the last glacial maximum (LGM). Here, we aimed to assess the realism of modelled vegetation and carbon storage changes between LGM and the pre-industrial Holocene (PIH). •We applied Land Processes and eXchanges (LPX), a dynamic global vegetation model (DGVM), with lowered CO2 and LGM climate anomalies from the Palaeoclimate Modelling Intercomparison Project (PMIP II), and compared the model results with palaeodata. •Modelled global gross primary production was reduced by 27–36% and carbon storage by 550–694 Pg C compared with PIH. Comparable reductions have been estimated from stable isotopes. The modelled areal reduction of forests is broadly consistent with pollen records. Despite reduced productivity and biomass, tropical forests accounted for a greater proportion of modelled land carbon storage at LGM (28–32%) than at PIH (25%). •The agreement between palaeodata and model results for LGM is consistent with the hypothesis that the ecophysiological effects of CO2 influence tree–grass competition and vegetation productivity, and suggests that these effects are also at work today.

Muscle delta C-13 change in Nile tilapia (Oreochromis niloticus): Effects of growth and carbon turnover

The contribution of growth and turnover to the muscle delta C-13 change process was investigated using mathematical models which associate delta C-13 change to time of intake of a new diet or increase in body mass. Two groups of Nile tilapia (Oreochromis niloticus) were fed on diets based on C3 (sigma C-13 = - 25.64 +/- 0.06 parts per thousand) or C4 (delta C-13= -16.01 +/- 0.06 parts per thousand) photosynthetic cycle plants to standardize the muscle delta C-13. After establishing the carbon isotopic equilibrium, fish (mean mass 24.12 +/- 6.79 g) then received the other treatment diet until a new carbon isotopic equilibrium could be established, characterizing T1 (C3-C4) and T2 (C4-C3) treatments. No significant differences were observed in fish productive performance. Good fits were obtained for the models that associated the delta C-13 change to time, resulting in carbon half-life values of 23.33 days for T1 and 25.96 days for T2. Based on values found for the muscle delta C-13 change rate from growth (0.0263 day(-1) and 0.0254 day(-1)) and turnover (0.0034 day(-1) and 0.0013 day(-1)), our results indicate that most of the delta C-13 change could be attributed to growth. The application of model that associated the delta C-13 change to body mass increase seems to produce results with no apparent biological explanation. The delta C-13 change rate could directly reflect the daily ration and growth rate, and consequently the isotopic change rates of carbon and other tissue elements can be properly used to assess different factors that may interfere in nutrient utilization and growth. (c) 2006 Published by Elsevier B.V.