δO and δC of Permian brachiopods: A record of seawater evolution and continental glaciation

Two hundred sixty-four δ¹⁸O and δ¹³C values of Permian articulate brachiopod shells were analyzed and 81 of these values were characterized as well preserved and biostratigraphically well defined. These were then utilized for construction of baseline oxygen and carbon isotope curves for the Permian interval. In addition, 21 δ¹³C whole rock values are reported for the Wordian and Capitanian.The early Permian, Asselian to Artinskian, times are characterized by ∼ 2.5‰ decrease in oxygen isotope values, from ∼ − 0.7‰ to − 3.3‰ (V-PDB). This is attributed to a ∼ 4-7 °C increase in temperature in the Southern Urals, concomitant with the retreat of the Permo-Carboniferous ice sheets and return of the ¹⁸O-depleted melt water into the oceans. The Late Permian samples from Iran (Jolfa at Kuh-e-Ali-Bashi) and China (Meishan) yield δ¹⁸O values, and presumably temperatures, similar to those that followed the termination of the large-scale glaciation in the Lower Permian. In between, the upper Kungurian to Capitanian samples from the Delaware Basin (Guadalupe Mountains) are enriched in ¹⁸O, at − 1.5‰ to − 3‰. We have no definitive explanation for these data, but tentatively suggest that the “anomaly” can potentially be a result of evaporative enrichment of seawater in ¹⁸O, due to intracratonic arid setting of the basin. The ¹⁸O-enriched nature of the Zechstein samples (− 1.2‰ to + 2.5‰), on the other hand, is in all probability a reflection of the high evaporation rates in the Zechstein sea.The Permian interval is characterized by a relatively constant δ¹³C, at about 4‰. The exceptions are again the brachiopods from the Delaware Basin (Guadalupe Mountains), which show ∼ 1.6‰ increase in the Guadalupian, to values of up to 5.9‰ in the Wordian. A tentative explanation, as in the case of oxygen, is based on the proposition that the semi-enclosed Delaware Basin was likely stratified, with sequestration of the ¹³C-depleted carbon to the deeper water layers and a complementary ¹³C enrichment in the upper oxygenated layer. The coeval open ocean water DIC may have been similar to that of the remainder of the Permian interval, at ∼ 4‰, as indicated by whole rock carbonate samples from Oman, Sicily, and Iran. In the latest Permian, the trend mimics the well-known δ¹³C drop at the Permian/Triassic boundary.     

Variation in bulk tissue, fatty acid and monosaccharide δ13C values between autotrophic and heterotrophic plant organs

The flowers of 23 species of grass and herb plants were collected from a mesotrophic grassland to assess natural variability in bulk, monosaccharide and fatty acid δ¹³C values from one plant community and were compared with previous analyses of leaves from the same species. The total mean bulk δ¹³C value of flower tissues was −28.1‰, and there was no significant difference between the mean δ¹³C_flower values for grass (−27.8‰) and herb (−28.2‰) species. On average bulk δ¹³C_flower values were 1.1‰ higher than bulk δ¹³C_leaf values, however, the δ¹³C_flower and δ¹³C_leaf values of grasses did not differ between organs suggesting that carbon isotope discrimination is different in grass and herb species. The abundance of different monosaccharides abundance varied between plant types, i.e. xylose concentrations in the grass flowers were as high as 40%, compared with up to 15% in the herb species, but the general relationship δ¹³C_arabinose > δ¹³C_xylose > δ¹³C_glucose > δ¹³C_galactose which had been observed in leaves was similar in flowers (total mean δ¹³C values = −25.9‰, −27.2‰, −28.8‰ and −28.1‰, respectively). However, the average 5.4‰ depletion in the δ¹³C values of the C_16:0, C_18:2 and C_18:3 fatty acids in flowers compared to bulk tissue was significantly greater than observed for leaves. The trend C_16:0 < C_18:2 < C_18:3 previously observed in leaves was also observed in grass flowers (δ¹³C_C16:0 = −33.8‰; δ¹³C_C18:2 = −33.1‰; δ¹³C_C18:3 = −34.2‰) but not herb flowers (δ¹³C_C16:0 = −34.1‰; δ¹³C_C18:2 = −32.4‰; δ¹³C_C18:3 = −34.5‰). We conclude: (i) that the biological processes influencing carbon isotope discrimination in grass flowers are different from herbs flowers; and, (ii) that a range of post-photosynthetic fractionation effects caused the observed differences between flower and leaf δ¹³C values, especially the significant ¹³C-depletion in flower fatty acid δ¹³C values.     

Isotopic evolution of Glacial Lake Agassiz: New insights from cellulose and porewater isotopic archives

Significantly differing estimates of the oxygen-isotope composition of Lake Agassiz have been obtained from two co-existing isotopic archives within a sediment core originating from Montcalm, Manitoba, in the southern basin of the ancient proglacial lake. Oxygen-isotope analysis of cellulose extracted from the sediments, which originated during the Lockhart phase ∼ 11,700-11,000 ¹⁴C yr BP, suggests that phytoplankton lived in surface waters having δ¹⁸O around − 18 ± 1‰ VSMOW, substantially enriched relative to connate porewaters in the same core, which indicate bottom waters had much lower values of around − 24.5 ± 0.5‰ VSMOW. This difference may be attributable to seasonal isotopic stratification of the upper part of the water column in the 250 m-deep lake. Modern observations from analogous environments in northern Canada suggest that inflow of evaporatively enriched runoff from the large area of deglaciated terrain contributing to Lake Agassiz, possibly enhanced by evaporation from the surface of the lake itself, could readily account for sufficient seasonal ¹⁸O enrichment in the epilimnion. Sediment porewaters, in contrast, have preserved the isotopic signature of hypolimnion waters supplied by a mixture of glacial meltwater and precipitation-derived runoff from the Laurentide Ice Sheet, and lack discernable isotopic alteration by evaporation. These new estimates are combined with inferred lake water compositions from other isotopic archives to develop a speculative framework for the isotopic evolution of the lake, providing improved constraints on the probable isotopic composition of Lake Agassiz outflow over time, which has important implications for efforts to trace and model its changing discharge.     

A simplified procedure for GC/C/IRMS analysis of underivatized 19-norandrosterone in urine following HPLC purification

Nandrolone and/or its precursors are included in the World Anti-doping Agency (WADA) list of forbidden substances and methods and as such their use is banned in sport. 19-Norandrosterone (19-NA) the main metabolite of these compounds can also be produced endogenously. The need to establish the origin of 19-NA in human urine samples obliges the antidoping laboratories to use isotope ratio mass spectrometry (IRMS) coupled to gas chromatography (GC/C/IRMS). In this work a simple liquid chromatographic method without any additional derivatization step is proposed, allowing to drastically simplify the urine pretreatment procedure, leading to extracts free of interferences permitting precise and accurate IRMS analysis. The purity of the extracts was verified by parallel analysis by gas chromatography coupled to mass spectrometry with GC conditions identical to those of the GC/C/IRMS assay. The method has been validated according to ISO17025 requirements (within assay precision of ±0.3‰ and between assay precision of ±0.4‰). The method has been tested with samples obtained after the administration of synthetic 19-norandrostenediol and samples collected during pregnancy where 19-NA is known to be produced endogenously. Twelve drugs and synthetic standards able to produce through metabolism 19-NA have shown to present δ¹³C values around −29‰ being quite homogeneous (−28.8 ± 1.5; mean ± standard deviation) while endogenously produced 19-NA has shown values comparable to other endogenous produced steroids in the range −21 to −24‰ as already reported. The efficacy of the method was tested on real samples from routine antidoping analyses.     

Carbonate horizons, paleosols, and lake flooding cycles: Beds I and II of Olduvai Gorge, Tanzania

This study documents the petrology and stable isotope geochemistry of carbonates from six horizons from Beds I and II of Olduvai Gorge, Tanzania. The studied succession, immediately below and above Tuff IF, consists of interbedded waxy and earthy claystones with discrete carbonate horizons and thin sandstones. The succession was deposited in response to repeated flooding and withdrawal of a saline-alkaline lake. The carbonates and their overlying disconformities are important because they help define the surfaces on which hominin activity took place and allow very high-resolution correlation of geographically separated levels of hominin exploitation.The range of different carbonates includes unambiguous land-surface and pedogenic features including calcified rootmat horizons, rhizocretions, and micritic nodules, together with less determinate sparry calcite nodules. Stellate nodules are interpreted as pseudomorphs after sulfate-roses. The carbonate nodules are synsedimentary features, truncated by fluvial and other erosional surfaces. The isotopic composition of the carbonates is variable with δ¹⁸O ranging from −7.0‰ to −4.3‰, and δ¹³C from −8.5‰ to −1.6‰. A covariant increase in δ¹³C and δ¹⁸O repeats in each carbonate horizon and in individual nodules (inner to outer layers): it reflects the evolution of synsedimentary groundwaters. At times of low lake level, the carbonates started to precipitate from meteoric waters with low isotopic values and continued to form as lake levels rose and the waters became increasingly saline. Some of the samples have a last-stage cement of strontium rich dolomite, which supports late-stage flooding by the saline-alkaline lake. Previous studies of carbonate horizons from Olduvai have interpreted carbon isotope values in terms of changes in C₃ and C₄ plants that colonized the land surface. This study demonstrates that in some instances the isotope values from carbonates deposited in these lake marginal settings reflect changes in hydrology rather than vegetation.     

Oxygen and carbon isotope compositions of middle Cretaceous vertebrates from North Africa and Brazil: Ecological and environmental significance

In order to investigate mid-Cretaceous terrestrial climates of low paleolatitudes, Moroccan, Tunisian and Brazilian vertebrate apatites have been analyzed for their oxygen and carbon isotope compositions of phosphates (δ¹⁸O_p) and carbonates (δ¹⁸O_c, δ¹³C_c). At each site, coexisting theropod dinosaurs, titanosaurid sauropods, pterosaurs, crocodilians, turtles and fish have distinct δ¹⁸O_p and δ¹³C_c values reflecting their ecologies, diets and foraging environments. Oxygen isotope compositions of surface waters (δ¹⁸O_w) estimated from turtle and crocodile δ¹⁸O_p values range from − 5.0 ± 1.0‰ to − 2.4 ± 1.0‰, which do not differ from mean annual rainwater values occurring today under inter-tropical sub-arid to arid climates. High water temperatures ranging from 21 ± 6 °C to 34 ± 2 °C deduced from fish δ¹⁸O_p values are in agreement with those published for mid-Cretaceous low latitudes. Temporary or seasonal droughts are inferred from high δ¹⁸O_p values of lungfish teeth, even though lower reptile δ¹⁸O_p values suggest the use of distinct and most likely larger or regularly renewed bodies of water. Environmental conditions of the studied low latitude regions during the Aptian-Cenomanian interval were somewhat similar to those experienced today under semi-arid to arid tropical or equatorial climates, but with higher mean surface temperatures than present-day ones.     

Estimation of growth and food consumption in juvenile Japanese flounder Paralichthys olivaceus using carbon stable isotope ratio δC under laboratory conditions

To estimate the accumulated food consumption and growth of juvenile Japanese flounder Paralichthys olivaceus, we investigated the relationships between individual food consumption and growth, and the change in the stable carbon isotope ratio (δ¹³C). Japanese flounder juveniles were individually reared and their diet was switched from one formulated feed EP1 (δ¹³C = − 19.47‰) to another EP3 (δ¹³C = − 17.21‰) and fed at different feeding regimes. After the switch, the δ¹³C content of the dorsal muscle was exponentially shifted to a different level in proportion to the feeding and growth rates. Therefore, measuring the carbon stable isotope ratio is a useful tool for estimating the food consumption and growth rate of juveniles. In addition, since the velocity of change and the asymptotic value of the carbon stable isotope ratio varied in muscle, caudal fin and liver tissue, different tissues can be used for different time scale estimations.     

Evaluation of the Salinic I tectonic, Cancañiri glacial and Ireviken biotic events: Biochemostratigraphy of the Lower Siluriansuccession in the Niagara Gorge area, Canada and U.S.A.

Well-preserved brachiopods from the Niagara Gorge area, Anticosti Island, Britain, Gotland and Estonia were utilised to delineate a complex isotopic evolution for Llandovery-Wenlock seawater. The Sr-isotope record reflects the Salinic I tectophase of the Late Llandovery in the continuous increase in ⁸⁷Sr/⁸⁶Sr values from 0.708070 to 0.708346. The Salinic II tectophase is marked by relative constancy of Sr isotope values until the Late Wenlock when it rises from 0.708345 to 0.708430. The second tectonic phase was therefore likely only of a regional nature. The carbon isotopes during the Llandovery fall within a band of about − 1‰ to + 3‰, a range comparable to modern low-latitude brachiopods. A large positive δ¹³C excursion of about 3‰, identifies the Ireviken event/excursion, characterizes the Early Wenlock. The biotic crisis and the isotope excursion itself may be ultimately related to the onset and duration of the Cancañiri glaciation, although a direct causative scenario is as yet unknown. The oxygen isotopic trends of well-preserved brachiopods clearly reflect a warm climate interval during the latest Llandovery associated with the Silurian sea level highstand. Subsequently, in the Early Wenlock, the sea level fell with the onset of the Cancañiri glaciation in the southern hemisphere. This is reflected in a significant positive δ¹⁸O excursion, particularly in brachiopods from the Niagara Gorge area. Brachiopods from lower latitudes were awash in warm tropical currents and therefore exhibit somewhat more negative δ¹⁸O values, indicating a lesser cooling gradient.     

Variation among diets in discrimination of δC and δN in the amphipod Allorchestes compressa

Discrimination of stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) was examined for the amphipod Allorchestes compressa Dana using controlled laboratory experiments. Amphipods were fed exclusively on single diets (fresh or decomposed macroalgae or seagrass) for three weeks. Macrophyte type (i.e. seagrass, brown algae or red algae) had a greater influence on the stable isotope ratios of A. compressa than the state of decomposition of the macrophyte material. The experiments revealed that δ¹³C in A. compressa stabilised at values lower than those of the diets, which contrasts to the general assumption that consumer-diet discrimination of δ¹³C ranges from 0 to + 1‰. Amphipods fed on seagrass yielded the lowest δ¹³C values, which were 9 to 10‰ lower than their diet, while amphipods fed on macroalgae had values 2 to 4‰ lower than their diet. In addition, contrary to the general assumption that consumer-diet discrimination of δ¹⁵N ranges from + 3 to + 5‰, discrimination of δ¹⁵N was as low as − 1 and + 1 when A. compressa was fed on brown and red algae, respectively, but as high as + 3‰ when fed on seagrass. The results show that discrimination of stable isotopes of carbon and nitrogen can vary considerably depending on the food source, demonstrating that validation of assumptions about discrimination are critical for interpreting stable isotope data from field studies.     

Effects of temperature and salinity on the standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi

The standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi to changes in temperature (15-30 °C), salinity (0-45‰) and a combination thereof was investigated. The rate of oxygen consumption of the shrimp was determined using a YSI oxygen meter. At a constant salinity of 35‰ the respiration rate of P. peringueyi increased with an increase in temperature and ranged between 0.260 and 0.982 μl O₂ mg wwt^− 1 h^− 1. The Q₁₀ value over the temperature range 15-25 °C was estimated at 3.13. At a constant temperature of 15 °C the respiration rate of P. peringueyi also increased with an increase in salinity and ranged between 0.231 and 0.860 μl O₂ mg wwt^− 1 h^− 1. For combination experiments the absence of any significant difference in the respiration rate of P. peringueyi at the four temperatures over the salinity range 15-35‰ suggests that the shrimp is well adapted to inhabiting environments characterised by variations in salinity and temperature such as those encountered within the middle and lower reaches of permanently open estuaries with substantial freshwater inflow. On the other hand, the total mortality of the shrimp recorded at salinities < 5‰ at all four temperatures suggests that the upper distribution of the shrimp may reflect physiological constraints. Similarly, the increase in the respiration rate of the shrimp at the four temperatures at salinities > 35‰ suggests that the shrimp may experience osmotic stress in freshwater deprived permanently open and intermittently open estuaries where hypersaline conditions may develop.     

Ancient forests and grasslands in the desert: Diet and habitat of Late Pleistocene mammals from Northcentral Sonora, Mexico

Despite high taxonomic diversity elsewhere in North America during the Pleistocene, vertebrate faunas are exceedingly rare in the region of northern Mexico. Térapa, a unique fossil site located in the present-day desert of Northcentral Sonora, Mexico (29°41′N, 109°39′W, 605 m elevation), contributes to our understanding of the paleoecology and paleoclimate of the region during the Late Pleistocene, ca. 43,000-40,000 cal. yr BP. At least 60 vertebrate taxa, including amphibians, turtles, a crocodilian, snakes, birds and many mammals, have been recovered from an 11-m thick sequence of fossiliferous sediments. The diversity and tropical affinity of these taxa suggest a more-forested environment than the thornscrub desert habitat present in this region today.Isotopic analyses of tooth enamel carbonate from ancient mammalian herbivores suggest that the Sonoran desert has undergone considerable climate change since the Late Pleistocene. Bulk carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes from nine mammalian fossils indicate a habitat mosaic with variations in diet that include browsers, mixed feeders and C4 hyper-grazers (δ¹³C range of − 10‰ to 2‰). Unique to this site are δ¹³C tooth enamel values of − 6.1 and − 5.6 ‰ for the deer Odocoileus, which suggest a more variable diet than strict browsing, including possibly feeding on CAM and/or C4 plants. Serial sampling of carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes for ancient mammal teeth with hypsodont dentitions (fossil Equus and Bison,) as well as δ¹⁸O meteroric water estimates from well-supported climatic models suggest a cooler and more equable environment at Térapa during the Late Pleistocene. These results also support previous habitat reconstructions inferred from the macrobotanical and packrat midden records of northern Sonora (Mexico). High-resolution stable isotope geochemistry indicates that: 1) ancient Térapa was covered with forest and grassland habitats that extended northward into Mexico by about 350 km relative to their present-day northern limits during the Late Pleistocene; and 2) an Amount Effect (AE) is demonstrated in the fossil record at Térapa even though the climate was less seasonal compared to the modern desert habitat.     

Survival,osmoregulation and ammonia-N excretion of blue swimmer crab, Portunus pelagicus, juveniles exposed to different ammonia-N and salinity combinations

Ammonia-N toxicity to early Portunus pelagicus juveniles at different salinities was investigated along with changes to haemolymph osmolality, Na⁺, K⁺, Ca²⁺ and ammonia-N levels, ammonia-N excretion and gill Na⁺/K⁺-ATPase activity. Experimental crabs were acclimated to salinities 15, 30 and 45‰ for one week and 25 replicate crabs were subsequently exposed to 0, 20, 40, 60, 80, 100 and 120 mg L^− 1 ammonia-N for 96-h, respectively. High ammonia-N concentrations were used to determine LC₅₀ values while physiological measurements were conducted at lower concentrations. When crabs were exposed to ammonia-N, anterior gill Na⁺/K⁺-ATPase activity significantly increased (p < 0.05) at all salinities, while this only occurred on the posterior gills at 30‰. For crabs exposed to 20 and 40 mg L^− 1 ammonia-N, both posterior gill Na⁺/K⁺-ATPase activity and ammonia-N excretion were significantly higher at 15‰ than those at 45‰. Despite this trend, the 96-h LC₅₀ value at 15‰ (43.4 mg L^− 1) was significantly lower (p < 0.05) than at both 30‰ and 45‰ (65.8 and 75.2 mg L^− 1, respectively). This may be due to significantly higher (p < 0.05) haemolymph ammonia-N levels of crabs at low salinities and may similarly explain the general ammonia-N toxicity pattern to other crustacean species.     

Effects of body size and environment on diet-tissue δC fractionation in fishes

δ¹³C data are often used in trophodynamic research where diet-tissue fractionation (Δδ¹³C) is assumed to be 0-1‰ per trophic level and unaffected by the size of animals or their environment. Variation in Δδ¹³C will influence conclusions about food sources, energy pathways and trophic level. To assess the effects of body size, age and environmental conditions on Δδ¹³C, European sea bass (Dicentrarchus labrax) were reared on constant diets of dab (Limanda limanda) or (Ammodytes marinus) for 2years under natural environmental regimes. Bass were sampled approximately monthly to determine Δδ¹³C for muscle, heart and liver tissue and were 1.66‰, − 0.18‰, − 1.77‰ (sandeel diet) and 1.34‰, − 1.18‰, − 1.75‰ (dab diet) respectively. Arithmetic lipid correction increased Δδ¹³C to > 2‰ for muscle and liver. Δδ¹³C was dependent on body mass and experimental duration (age) and generally declined with weight or time even after correction for lipid content. For liver, increasing temperature increased Δδ¹³C. The Δδ¹³C estimates from this study were compared with all available published Δδ¹³C estimates for fish. Bass muscle Δδ¹³C was similar to previous estimates for fish white muscle Δδ¹³C (1.56 ± 1.10‰) and whole body Δδ¹³C (1.52 ± 1.13‰). Fractionations derived in this study, combined with those from the literature, support the use of diet-tissue fractionation values of between 1‰-2‰ for δ¹³C, rather than the commonly used 0‰ − 1‰. For muscle Δδ¹³C, 1.5‰ is appropriate.     

Combined effects of temperature and salinity on critical thermal minima of pacific white shrimp Litopenaeus vannamei (Crustacea: Penaeidae)

Critical thermal minima (CTMin) were determined for the Pacific white shrimp Litopenaeus vannamei juveniles from four different acclimation temperatures (15, 20, 25, and 30 °C) and salinities (10‰, 20‰, 30‰, and 40‰). The lowest and highest CTMin of shrimp ranged between 7.2 °C at 15 °C/30‰ and 11.44 °C at 30 °C/20‰ at the cooling rate of 1 °C h⁻¹. Acclimation temperature and salinity, as well as the interaction of both parameters, had significant effects on the CTMin values of L. vannamei (P<0.01). Yet, the results showed a much more profound effect of temperature on low thermal tolerance of juveniles. Only 40‰ salinity had an influence on the CTMin values (P<0.01). As the acclimation temperature was lowered from 30 to 15 °C thermal tolerance of the shrimp significantly increased by 3.25–4.14 °C. The acclimation response ratio (ARR) of the Pacific white shrimp exposed to different combinations of salinity and temperature ranged between 0.25 and 0.27. When this species is farmed in sub-tropical regions, its pond water temperature in the over-wintering facilities (regardless of the water salinity level) must never fall below 12 °C throughout the cold season to prevent mortalities.     

Stable isotope fractionation in the digestive gland, muscle and gills tissues of the marine mussel Mytilus galloprovincialis

Mytilus galloprovincialis is a common species in the Mediterranean. It is a sedentary filter-feeding organism that assimilates carbon and nitrogen isotopic ratios in tissues from its food sources. The δ¹³C and δ¹⁵N values have been used to demonstrate differences in isotopic composition between digestive gland, muscle and gills of this mussel. For δ¹³C, mean values were - 21.99 ± 0.50‰, - 19.70 ± 0.44‰, and - 19.96 ± 0.44‰, respectively; and for δ¹⁵N, they were 5.16 ± 0.90‰, 7.67 ± 0.79‰ and 7.77 ± 0.85‰, respectively. The fractionation or enrichment factor for ¹³C values between digestive gland and muscle, between digestive gland and gills, and between muscle and gills were - 2.29 ± 0.16‰, - 2.04 ± 0.14‰ and 0.27 ± 0.07‰, respectively, within the expected range of ¹³C fractionation at filter feeders reported elsewhere. In contrast, low fractionation values were found for ¹⁵N with - 2.45 ± 0.24‰, - 2.51 ± 0.16‰ and - 0.11 ± 0.16‰, between digestive gland and muscle, between digestive gland and gills, and between muscle and gills, respectively. Through isotopic fractionation of M. galloprovincialis, the depleted values were found in the digestive gland, followed by gills and then by muscle tissue. Statistical analysis (PERMANOVA) was performed to check for significant differences in δ¹³C and δ¹⁵N isotopic signatures between tissues and localities. The current study demonstrates significant differences in the δ¹³C and δ¹⁵N isotopic composition between digestive gland, muscle and gills tissues in M. galloprovincialis living in the oligotrophic environment of the Balearic Islands.     

The rate of oxygen utilization by cells

The discovery of oxygen is considered by some to be the most important scientific discovery of all time—from both physical-chemical/astrophysics and biology/evolution viewpoints. One of the major developments during evolution is the ability to capture dioxygen in the environment and deliver it to each cell in the multicellular, complex mammalian body—on demand, i.e., just in time. Humans use oxygen to extract approximately 2550 calories (10.4 MJ) from food to meet daily energy requirements. This combustion requires about 22 mol of dioxygen per day, or 2.5 × 10^− 4 mol s^− 1. This is an average rate of oxygen utilization of 2.5 × 10^− 18 mol cell^− 1 s^− 1, i.e., 2.5 amol cell^− 1 s^− 1. Cells have a wide range of oxygen utilization, depending on cell type, function, and biological status. Measured rates of oxygen utilization by mammalian cells in culture range from < 1 to > 350 amol cell^− 1 s^− 1. There is a loose positive linear correlation of the rate of oxygen consumption by mammalian cells in culture with cell volume and cell protein. The use of oxygen by cells and tissues is an essential aspect of the basic redox biology of cells and tissues. This type of quantitative information is fundamental to investigations in quantitative redox biology, especially redox systems biology.     

Seasonal variations in bulk tissue, fatty acid and monosaccharide δC values of leaves from mesotrophic grassland plant communities under different grazing managements

Leaves of 26 grass, herb, shrub and tree species were collected from mesotrophic grasslands to assess natural variability in bulk, fatty acid and monosaccharide δ¹³C values under different grazing management (cattle- or deer-grazed) on three sample dates (May, July and October) such that interspecific and spatiotemporal variations in whole leaf tissues and compound-specific δ¹³C values could be determined. The total mean leaf bulk δ¹³C value for plants was −28.9‰ with a range of values spanning 7.5‰. Significant interspecific variation between bulk leaf δ¹³C values was only determined in October (P = <0.001) when δ¹³C values of the leaf tissues from both sites was on average 1.5‰ depleted compared to during July and May. Samples from May were significantly different between fields (P = 0.03) indicating an effect from deer- or cattle-grazing in young leaves. The average individual monosaccharide δ¹³C value was 0.8‰ higher compared with whole leaf tissues. Monosaccharides were the most abundant components of leaf biomass, i.e. arabinose, xylose, mannose, galactose and glucose, and therefore, fluctuations in their individual δ¹³C values had a major influence on bulk δ¹³C values. An average depletion of ca. 1‰ in the bulk δ¹³C values of leaves from the deer-grazed field compared to the cattle-grazed field could be explained by a general depletion of 1.1‰ in glucose δ¹³C values, as glucose constituted >50% total leaf monosaccharides. In October, δ¹³C values of all monosaccharides varied between species, with significant variation in δ¹³C values of mannose and glucose in July, and mannose in May. This provided an explanation for the noted variability in the tissue bulk δ¹³C values observed in October 1999. The fatty acids C_16:0, C_18:2 and C_18:3 were highly abundant in all plant species. Fatty acid δ¹³C values were lower than those of bulk leaf tissues; average values of −37.4‰ (C_16:0), −37.0‰ (C_18:2) and −36.5‰ (C_18:3) were determined. There was significant interspecific variation in the δ¹³C values of all individual fatty acids during October and July, but only for C_18:2 in May (P = <0.05). This indicated that seasonal trends observed in the δ¹³C values of individual fatty acids were inherited from the isotopic composition of primary photosynthate. However, although wide diversity in δ¹³C values of grassland plants ascribed to grazing management, interspecific and spatiotemporal influences was revealed, significant trends (P = <0.0001) for fatty acid and monosaccharide δ¹³C values: δ¹³C_16:0 < δ¹³C_18:2 < δ¹³C_18:3 and δ¹³C_arabinose > δ¹³C_xylose > δ¹³C_glucose > δ¹³C_galactose, respectively, previously described, appear consistent across a wide range of species at different times of the year in fields under different grazing regimes.     

Mineral nutrition and heterotrophy in the water conservative holoparasite Hydnora Thunb. (Hydnoraceae)

There are large gaps in our understanding of parasite–host nutrient relationships. Our goal was to evaluate transdermal water loss, parasite–host mineral relationships, and heterotrophy in the holoparasitic genus Hydnora. We estimated in situ transdermal water loss in Hydnora and measured nutrient profiles and δ¹³C and δ¹⁵N signatures for Hydnora and hosts in southern Africa and Madagascar. For comparison we also measured δ¹³C and δ¹⁵N for aerial hemiparasites at the same sites. Transdermal water loss in Hydnora ranged from 0.14 ± 0.02 to 0.38 ± 0.04 mg cm⁻² h⁻¹ and was comparable to transpiration rates for water conservative xerophytes. Concentrations of P and K were higher in Hydnora relative to CAM hosts; other mineral concentrations were significantly lower in the parasite or were not different. δ¹³C signatures of holoparasites and hemiparasites relative to their hosts reflected host metabolism and differences in commitment to heterotrophic C gain. Holoparasite δ¹³C values were significantly enriched (by 0.55‰ ± 0.23) compared to host shoot and depleted compared to host root tissues (by −0.97‰ ± 0.12). Holoparasite δ¹³C values were not significantly different compared to the estimated whole host δ¹³C value. δ¹⁵N values for holoparasites and hemiparasites were significantly correlated with hosts. The water conservative nature of Hydnora spp. combined with parasite–host mineral nutrition profiles are suggestive of active processes of solute uptake. Stable isotope fractionation in host tissues dictated significant differences between parasite and host (shoot and root) δ¹³C signatures. The confirmation of complete heterotrophy and the lack of a confounding transpiration stream may make Hydnora a promising model organism for the examination of parasite solute uptake.     

δN and δC analysis of a Posidonia sinuosa seagrass bed

Potential food sources and dominant invertebrates and fishes were collected for the examination of variability in ¹³C/¹²C and ¹⁵N/¹⁴N to determine the sources of carbon available to consumers within a Western Australian Posidonia sinuosa-dominated seagrass bed. Autotrophs showed a wide distribution of δ¹³C values, with P. sinuosa at −11.3 ± 0.8‰ and macroalgae ranging from −16.6 to −31.7‰. This variation allowed us to successfully identify macroalgae as the main contributor of carbon to the trophic structure, although no distinction could be made between epiphytic macroalgae on seagrass, or allochthonous macroalgal sources. The range in δ¹⁵N ratios among potential food items at the trophic base was too small to make it useful as tracer of nitrogen flow pathways, but it consistently increased from macrophytes and detritus (4.1–6.8‰), to invertebrates (5.7–7.4‰) located near the middle of the food web, to fishes (8.3–11.9‰), with piscivorous species such as Leviprora inops generally having a higher ¹⁵N. δ¹³C of seston (−12.8‰) and sedimentary organic matter (−8.7‰) indicate that seagrass material is the main contributor to these two carbon pools, and that very little of it contributes to animal biomass.     

The oxygen isotope composition of planktonic foraminifera from the Cariaco Basin,Venezuela: Seasonal and interannual variations

Material collected during a three-year sediment trapping experiment in the Cariaco Basin, Venezuela (January 1997 to December 1999) is used to examine both temporal and inter-species variability in the oxygen isotope composition of planktonic foraminifera. Specifically, this study compares the oxygen isotope composition of six species of planktonic foraminifera (Globigerinoides ruber (pink), Globigerina bulloides, Neogloboquadrina dutertrei, Orbulina universa, Globorotalia menardii and Globorotalia crassaformis) with the climatology and hydrography of the region, and evaluates the application of each species for use in paleoceanographic reconstructions. The isotope results are consistent with known depth habitats for all six species. The lowest δ¹⁸O values (− 1 to − 2‰) were measured on G. ruber (pink) and G. bulloides, two species that live in the surface mixed layer. Values for deeper-dwelling species such as N. dutertrei, G. menardii and G. crassaformis are higher, predominantly ranging from 0 to − 0.5‰. Temperature estimates derived using species-specific paleotemperature equations indicate that G. ruber (pink) accurately estimates sea surface temperatures (SSTs) throughout the year, while G. bulloides temperature estimates are similar to measured surface temperatures only during the upwelling season (January–April). For the remainder of the year, the δ¹⁸O-derived temperatures for G. bulloides typically are lower than the measured SST. Although the maximum flux of all species occurs during upwelling, the flux-weighted annual mean isotopic composition of the six species indicates that only G. bulloides is biased towards this season. Therefore, we conclude that the sediment δ¹⁸O record of G. ruber (pink) is most suitable for estimating past values of mean annual SST, while G. bulloides provides information on conditions during spring upwelling. The depth of calcification of N. dutertrei varies seasonally in response to changes in the depths of the thermocline and chlorophyll maximum. As a result, the δ¹⁸O difference between G. ruber (pink) and N. dutertrei provides an estimate of the annual surface to thermocline temperature gradient in the basin.