crocodylomorph morphology (external mandibular fenestrae, extensive osteoderm cover and limbs adapted to terrestrial locomotion), it is hypothesized that they were ectothermic and poikilothermic ambush predators spending most of their time motionless, and mouth-gape basking like modern crocodylians. However, during the late Kimmeridgian-early Tithonian there is evidence for a subclade of teleosaurids that became more pelagic (Foffa et al., 2019). The oxygen isotopecomposition of teleosaurid apatite indicates that they kept a body temperature lower than that of ichthyosaurs and plesiosaurs, but close to those of metriorhynchids. However, more estuarine living environments can be characterized by more negative δ 18 O values as a result of the mixing between
571 riverine detrital particles and remineralization of estuary sediments (e.g., Lawrence and 572 Kamber, 2006).
573 On the other hand, the vertical distribution of dissolved εNd at all estuarine stations 574 shows unradiogenic Nd isotope values throughout the entire water column (average εNd ~ 575 −19.6 ± 1.2; Figures 6C and 7B), and the values are similar to the εNd (±2σ) values of the 576 detrital and bulk sediment leachate samples (Figure 9). Because terrigenous suspended 577 particles have a short residence time of a few days within the St. Lawrence Estuary (Syvitski 578 et al., 1983; Lucotte et al. 1991) and the water depth in the EGSL is quite low (<500 m), we 579 hypothesize that rapid scavenging by the salt-induced coagulation of colloidal matter and 580 subsequent dissolution of the labile mineral phases influenced the εNd values in the water 581 column of the EGSL. Moreover, the EGSL is considered to be a subarctic region, with air 582 temperatures below zero degrees Celsius during the winter, allowing the formation of sea ice 583 (Saucier, 2003; de Vernal et al., 2011). Diagrams of the winter temperature and salinity data 584 from a station south of Anticosti Island (Galbraith, 2006) reveal that during winter, the upper 585 120 m of the water column is characterized by a high salinity (approximately 31.8) and near- 586 freezing temperatures (approximately −2°C) due to cooling and brine rejection during ice 587 formation. Thus, brine rejection during sea ice formation may also play a significant role in 588 the distribution of the relatively homogeneous Nd isotope values in EGSL seawater (Haley 589 and Polyak 2013). The flow from the surface to the bottom of the high-density brines may 590 homogenize the Nd isotopecomposition of the water column. Similar observations have been 591 reported by Porcelli et al. (2009), Haley and Polyak (2013) and Laukert et al. (2017) in the 592 Arctic Ocean.
University, New Brunswick, New Jersey, USA
Abstract The carbon isotopecomposition ( δ 13 C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is re ﬂected by the δ 13 C of foraminifera tests. Here more than 1700 δ 13 C observations of the benthic foraminifera genus Cibicides from late Holocene sediments ( δ 13 C Cibnat ) are compiled and compared with newly updated estimates of the natural (preindustrial) water column δ 13 C of dissolved inorganic carbon ( δ 13 C DICnat ) as part of the international Ocean Circulation and Carbon Cycling (OC3) project. Using selection criteria based on the spatial distance between samples, we ﬁnd high correlation between δ 13 C Cibnat and δ 13 C DICnat , con ﬁrming earlier work. Regression analyses indicate signi ﬁcant carbonate ion (2.6 ± 0.4) × 10 3 ‰/(μmol kg 1 ) [CO 3 2 ] and pressure ( 4.9 ± 1.7) × 10 5 ‰ m 1 (depth) effects, which we use to propose a new global calibration for predicting δ 13 C DICnat from δ 13 C Cibnat . This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship ( δ 13 C DICnat = δ 13 C Cibnat ). However, these effects and the error reductions are relatively small, which suggests that most conclusions from previous studies using a one-to-one relationship remain robust. The remaining standard error of the regression is generally σ ≅ 0.25‰, with larger values found in the southeast Atlantic and Antarctic (σ ≅ 0.4‰) and for species other than Cibicides wuellerstor ﬁ. Discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic δ 13 C record.
2.4.1. Total evaporation method
The TIMS total evaporation method was developed in order to overcome the mass fractionation by collecting all the ionized isotopes of the whole sample .
The method employed in this study was previously described and was transposed to zirconium . “Peak center” (mass calibration and ion beam centering in the detector) and lenses optimization were realized using the major zirconium isotope: 90 Zr + for the SPEX solutions isotope determinations and the nuclear samples concentration determinations or 91 Zr + for the enriched 91 Zr spike solutions isotope and concentration determinations. The zirconium isotope 90 Zr + or 91 Zr + target intensity was adapted depending on the analysis. It was typically of 7.5 V on 91 Zr + for 91 Zr spike solution isotopecomposition and concentration determination, 4 V on 90 Zr + for the SPEX solution isotopecomposition determination, 3.5 V for samples 2 and 3 concentration determination and 1 V for sample 1 concentration determination. Data acquisition was ended when the evaporation filament current reached a maximum value of 6.5 A and the ion beam intensity decreased down to a 10 mV signal.
3 Laboratoire des Sciences du Climat et de l’Environnement, Orme des Merisiers, CE Saclay, 91191 Gif-sur-Yvette Cedex, France
4 The Niels Bohr Institute, Blegdamsvej, DK-2100 Copenhagen, Denmark
ABSTRACT. High-resolution records of isotopecomposition (dD) and accumulation of snow have been obtained from 10–12 m deep snow pits dug in the vicinity of Vostok station during the 1979/80 and 1999/2000 Antarctic field seasons. We employ meteorological, balloon-sounding and snow-stake data to interpret the isotope record in terms of past temperature changes. Our reconstruction suggests that snow accumulation rate and the near-surface air temperature at Vostok have varied during the past 200 years between 15 and 30 kg m –2 a –1 , and between –56 and –558C, respectively, with a slight general tendency to increase from the past to the present. Both parameters reveal a 50 year periodicity that correlates with the Pacific Decadal Oscillation index, implying a climatic teleconnection between central Antarctica and the tropical Pacific.
Prior to this study and the recent study of Baronas et al. (2017), our knowledge of Ge isotope systematics in seawater was limited by the analytical difficulties to precisely measure Ge isotopecomposition in sub-nanomolar amounts of Ge in seawater. Our newly developed method offers the following advantages 1) utilization of a double-spike which permits correction of potential Ge isotope mass fractionation in the case of incomplete recovery, 2) sufficient sensitivity using hydride-generation system to measure Ge in seawater at very low concentrations (e.g. surface waters), 3) a preconcentration technique using co-precipitation with Fe-oxyhydroxides which can be set up on a research cruise, allowing the rapid separation of Ge from large volumes of seawater. Additional developments are still required to consistently achieve quantitative recovery (i.e. 100 % yield) of Ge from large seawater volume. Potential blank contamination should also be kept at the minimum (i.e. below 1pM equivalent) in order to improve the measurement of the most analytically challenging surface seawater, especially from nutrient-depleted regions where significant Ge/Si fractionation is expected. In this case, Ge isotope systematics may provide an important new proxy to investigate nutrient limitation for biological productivity and their sources in surface seawater, both of which resulting in contrasting trends in δ 30 Si and Ge/Si ratios.
Fe, however, our estimate of the Baffin mantle δ 66 Zn (0.20 ± 0.03‰) is significantly lower than some previous estimates. Comparison of our new data with those for Archean and Proterozoic komatiites is consistent with the Fe and Zn isotopecomposition of the mantle remaining constant from at least 3 Ga to the present day. By focusing on large-degree partial melts (e.g. komatiites and picrites) we are potenitally biasing our record to samples that will inevitably have interacted with, entrained and melted the ambient shallow mantle during ascent. For a major element such as Fe, that will continuosly participate in melting as it rises through the mantle, the final isotopic compositon of the magama will be a weighted average of the complete melting column. Thus it is unsuprising that minimal Fe isotope variation are seen between localities. In contrast, the unique geochemical signatures (e.g. He and W) displayed by the Baffin Island picrites are inferred to solely originate from the lowermost mantle and will be continuously diluted upon magma ascent.
Previous studies of komatiites show that there is no detectable dif- ferences between the average Cr isotopecomposition of komatiites and that of mantle peridotites ( Sossi et al., 2018 ), suggesting that there is no Cr isotope fractionation during their formation. This is expected when the greater fraction of Cr komatiites contains and smaller fractionation factors at higher temperatures are considered. The conditions that ko- matiite form reduce the compatibility of Cr (Appendix 1). Brieﬂy, melting a source that contains garnet and the higher temperatures de- creases the compatibility of Cr in the mantle. The higher degree of melting also leads to a higher fraction of the initial Cr entering the liquid phase (Fig. A.2.). These e ﬀects are shown using non-modal melting models ( Sossi and O’Neill, 2017 ). In order to balance the Cr in the system, the δ 53 Cr diﬀerence between the melt and the mantle will decrease as a greater faction of Cr is removed from the mantle.
when referencing seasonality, temperature is considered as the variable of interest. However, the tropics have relatively small seasonal temperature variability compared with higher latitudes, the core is situated along the north-eastern coast of Brazil which may be influenced by the shift in the ITCZ (Jaeschke et al., 2007). Temperature and salinity have op- posing effects on the overall oxygen isotopecomposition. Surface-dwelling species of planktonic foraminifera, T. sac- culifer (Fig. 2i: vii); G. ruber (Fig. 2viii: xiii); and the ther- mocline dwelling N. dutertrei (Fig. 2xiv: xix) were picked from the core top. All species are symbiotic (Schiebel and Hemleben, 2017) which limits the depth of the maximum growth. A one-way ANOVA was used to test, whether the means of each species are equal or whether the alternative hypothesis that one or more of the species means differs from one another, with the following hypothesis:
lighter Mo isotopes during transport after sulphide weathering, thereby producing heavy residual waters. To examine for the Bacalar stromatolite data in light of these scenarios, a mixing model was developed between the most Mo-poor Bacalar stromatolite of this study and the continental crust, assuming a crustal Mo concentration of 1100 ppb (Rudnick and Gao, 2003). Even if Bacalar stromatolites fortuitiously plot along modern « the river array », the mixing model reveals a likely dilution of the Mo isotope signal by detrital contamination (Figure 5.1). Moreover, Siebert et al. (2015) shown that the second argument is poorly supported at present and appears dependent of many environmental effects (e.g., climate, organic matter, degree of weathering) that can cause to either light or heavy isotopes of Mo to be retained during weathering. The Bacalar stromatolites nonetheless record fractionated Mo from their environment, and the mixing calculation shows that one can define a “minimum” molybdenum isotopic composition of the formation waters based on the molybdenum isotopecomposition of the least-contaminated stromatolite grown in this water body.
In contrast to Li elemental ratios, Li isotope ratios have been investigated only in modern foraminifera and corals. Modern corals have Li isotopic composition ranging from +17 to +25‰ (Marriott et al., 2004a,b; Rollion-Bard et al., 2009), significantly fractionated relative to seawater but with an average δ 7 Li similar to inorganic aragonite (around +19‰). The intra-specimen variability for corals is relatively low, less than ±2‰, but small systematic differences exists between species (Rollion-Bard et al., 2009). Present-day planktic foraminifera δ 7 Li range between +27 and +31‰ (Hall et al., 2005; Hathorne and James, 2006; Misra and Froelich, 2012) with a median value of 30‰, very close to modern seawater (31‰), making them targets for past work reconstructing the Li isotopecomposition of the Cenozoic ocean (Hathorne and James, 2006; Misra and Froelich, 2012). However, Li isotopic fractionation in foraminifera may depend upon seawater dissolved inorganic carbon (DIC) concentration of seawater (Vigier et al., 2015). In addition, well-preserved planktic foraminifera are not very abundant in the geological record prior to the Cenozoic (Wilkinson, 1979). Finally, Ullmann et al. (2013b) for belemnite and Pogge von Strandmann et al., (2017) for brachiopods have shown that the shell of these organisms may preserve Li isotopecomposition of the ocean over geological timescales.
demonstrated in meteoric water and ice cores. Based on theory and experiments, it has been suggested that this excess originates from evaporation of ocean water into under ‐saturated air. However, there has never been direct demonstration of this excess in marine vapor. Here, we present results of the first measurements of d 17 O and d 18 O in vapor samples collected over the South Indian and the Southern Oceans. Our data show the existence of 17 O‐ excess in marine vapor and also clear negative correlation between 17 O‐excess and relative humidity. Thus, 17 O‐ excess is useful for constraining oceanic humidity in hydrological and climatic models. Using the obtained values of 17 O‐excess, we estimated the fractionation factor between H 2 18 O and H 2 16 O for diffusion in air above the ocean ( 18 a diff ). The new estimation of 18 a diff (1.008) is larger than the widely accepted value in hydrological studies. Citation: Uemura, R., E. Barkan, O. Abe, and B. Luz (2010), Triple isotopecomposition of oxygen in atmospheric water v a p o r , G e o p h y s . R e s . L e t t . , 3 7 , L 0 4 4 0 2 , d o i : 1 0 . 1 0 2 9 / 2009GL041960.
d 13 Cnormalized~d 13 Cuntreated 3:32z0:99 C : N
The Kolmogorov-Smirnov test was used to test for normality of the data (K-S d = 0.083 and d = 0.081, p.0.20). Analyses of variance (ANOVA), followed by an Unequal N HSD post-hoc test, were used to compare carbon and nitrogen isotope values among species; dolphin calves were excluded from these analyses. In addition, we performed a cluster analysis aiming to detect isotopic patterns among delphinids species. For this analysis, we used Ward’s method (minimum variance) and Euclidean distances . ANOVAs were also used to verify differences in d 13 C and d 15 N values among adult males, adult females and calves of Guiana dolphins from Guanabara and Sepetiba bays. The Student’s t-test was performed to compare male and female dolphins from Ilha Grande Bay.
Effects of fluid preservation on sea star stable isotope compositions: How useful can museum collections be for trophic ecology studies?
Baptiste LE BOURG a , Gilles LEPOINT a , Pierre BALTHASART b , Loïc N. MICHEL a,c .
a: Laboratory of Oceanology, University of Liège, 4000 Liège, Belgium, b: Collectif des Enseignements en Biologie, University of Liège, 4000 Liège, Belgium, c: Deep Environment Laboratory (LEP), Ifremer Brittany, 29280 Plouzané, France
26 ± 5 per meg, respectively. δ 018 O and 17 O-excess of the
soil water (respectively δ 018 O SW and 17 O-excess SW ) average
− 2.89 ± 0.19 ‰ and 16 ± 8 per meg, respectively (Table S2).
The isotope difference is thus significant for δ 018 O, less sig- nificant for 17 O-excess, according to the analytical error. Al- though evaporative kinetic fractionation of the top soil water suctioned by the porous cup under vacuum cannot be ruled out, isotopic exchanges between the soil water and oxygen- bearing phases of the rhizosphere may also have impacted the soil water isotopic composition (Bowling et al., 2017; Chen et al., 2016; Oerter et al., 2014; Orlowski et al., 2016). Hereinafter, we consider the isotope signatures of the water absorbed by the roots of F. arundinacea to be equivalent to the irrigation water that fed the saturation level at the base of the tank. This water was reached by the deepest roots, as observed on a cross section of the soil after the end of the experiment, and likely reached the upper roots by capillarity. The transpiration of F. arundinacea increases rapidly from