Improvements in Cd stable isotope analysis achieved through use of liquid–liquid extraction to remove organic residues from Cd separates obtained by extraction chromatography

Organic compounds released from resins that are commonly employed for trace element separations are known to have a detrimental impact on the quality of isotopic analyses by MC-ICP-MS. A recent study highlighted that such effects can be particularly problematic for Cd stable isotope measurements (M. Gault-Ringold and C. H. Stirling, J. Anal. At. Spectrom., 2012, 27, 449–459). In this case, the final stage of sample purification commonly applies extraction chromatography with Eichrom TRU resin, which employs particles coated with octylphenyl-N,N-di-isobutyl carbamoylphosphine oxide (CMPO) dissolved in tri-n-butyl phosphate (TBP). During chromatography, it appears that some of these compounds are eluted alongside Cd and cannot be removed by evaporation due to their high boiling points. When aliquots of the zero-ε reference material were processed through the purification procedure, refluxed in concentrated HNO(3) and analyzed at minimum dilution (in 1 ml 0.1 M HNO(3)), they yielded Cd isotopic compositions (ε(114/110)Cd = 4.6 ± 3.4, 2SD, n = 4) that differed significantly from the expected value, despite the use of a double spike technique to correct for instrumental mass fractionation. This result was accompanied by a 35% reduction in instrumental sensitivity for Cd. With increasing dilution of the organic resin residue, both of these effects are reduced and they are insignificant when the eluted Cd is dissolved in ≥3 ml 0.1 M HNO(3). Our results, furthermore, indicate that the isotopic artefacts are most likely related to anomalous mass bias behavior. Previous studies have shown that perchloric acid can be effective at avoiding such effects (Gault-Ringold and Stirling, 2012; K. C. Crocket, M. Lambelet, T. van de Flierdt, M. Rehkämper and L. F. Robinson, Chem. Geol., 2014, 374–375, 128–140), presumably by oxidizing the resin-derived organics, but there are numerous disadvantages to its use. Here we show that liquid–liquid extraction with n-heptane removes the organic compounds, dramatically improving quality of the Cd isotope data for samples that are analyzed at or close to minimum dilution factors. This technique is quick, simple and may be of use prior to analysis of other isotope systems where similar resins are employed

Robustness of fossil fish teeth for seawater neodymium isotope reconstructions under variable redox conditions in an ancient shallow marine setting

Fossil fish teeth from pelagic open ocean settings are considered a robust archive for preserving the neodymium (Nd) isotopic composition of ancient seawater. However, using fossil fish teeth as an archive to reconstruct seawater Nd isotopic compositions in different sedimentary redox environments and in terrigenous‐dominated, shallow marine settings is less proven. To address these uncertainties, fish tooth and sediment samples from a middle Eocene section deposited proximal to the East Antarctic margin at Integrated Ocean Drilling Program Site U1356 were analyzed for major and trace element geochemistry, and Nd isotopes. Major and trace element analyses of the sediments reveal changing redox conditions throughout deposition in a shallow marine environment. However, variations in the Nd isotopic composition and rare earth element (REE) patterns of the associated fish teeth do not correspond to redox changes in the sediments. REE patterns in fish teeth at Site U1356 carry a typical mid‐REE‐enriched signature. However, a consistently positive Ce anomaly marks a deviation from a pure authigenic origin of REEs to the fish tooth. Neodymium isotopic compositions of cleaned and uncleaned fish teeth fall between modern seawater and local sediments and hence could be authigenic in nature, but could also be influenced by sedimentary fluxes. We conclude that the fossil fish tooth Nd isotope proxy is not sensitive to moderate changes in pore water oxygenation. However, combined studies on sediments, pore waters, fish teeth, and seawater are needed to fully understand processes driving the reconstructed signature from shallow marine sections in proximity to continental sources

Etablierung eines Luciferase-Reportergen-Assays unter Verwendung stabil transfizierter ROS 17/2.8-Zellen als molekularbiologisches Screeningsystem für neue osteoanabole Faktoren

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Timing and nature of AMOC recovery across Termination 2 and magnitude of deglacial CO2 change

Large amplitude variations in atmospheric CO 2 were associated with glacial terminations of the Late Pleistocene. Here we provide multiple lines of evidence suggesting that the B 20 p.p.m.v. overshoot in CO 2 at the end of Termination 2 (T2) B 129 ka was associated with an abrupt ( r 400 year) deepening of Atlantic Meridional Overturning Circulation (AMOC). In contrast to Termination 1 (T1), which was interrupted by the Bølling-Allerød (B-A), AMOC recovery did not occur until the very end of T2, and was characterized by pronounced formation of deep waters in the NW Atlantic. Considering the variable influences of ocean circulation change on atmospheric CO 2 , we suggest that the net change in CO 2 across the last 2 terminations was approximately equal if the transient effects of deglacial oscillations in ocean circulation are taken into account

Lead isotopes in deep-sea coral skeletons: ground-truthing and a first deglacial Southern Ocean record

Past changes in seawater lead (Pb) isotopes record the temporal evolution of anthropogenic pollution, continental weathering inp uts, and ocean current transport. To advance our ability to reconstruct this signature, we present methodological developments that allow us to make precise and accurate Pb isoto pe measurements on deep-sea coral aragonite, and apply our approach to generate the f irst Pb isotope record for the glacial to deglacial mid-depth Southern Ocean. Our refined methodology includes a two-step anion e xchange chemistry procedure and measurement using a 207 Pb- 204 Pb double spike on a ThermoFinnigan Triton TIMS instrument. By employing a 10 12 Ω resistor (in place of a 10 Ω resistor) to measure the low- abundance 204 Pb ion beam, we improve the internal precision on 206,207,208 Pb/ 204 Pb for a 2 ng load of NIST-SRM-981 Pb from typically ~420 ppm to ~260 ppm (2 s.e.), and the long term external reproducibility from ~960 ppm to ~580 ppm (2 s.d.). Furthermore, for a typical 500 mg coral sample with low Pb concentrations (~6-10 p pb yielding ~3-5 ng Pb for analysis), we obtain a comparable internal precision of ~150-250 ppm for 206,207,208 Pb/ 204 Pb, indicating a good sensitivity for tracing natural Pb sources to the oceans. Successful extraction of a seawater signal from deep-sea coral aragonite furth er relies on careful physical and chemical cleaning steps, which are necessary to remove anthr opogenic Pb contaminants and obtain results that are consistent with ferromanganese cru sts. Applying our approach to a collection of late glaci al and deglacial corals (~12-40 ka BP) from south of Tasmania at ~1.4-1.7 km water dep th, we generated the first intermediate water Pb isotope record from the Southern Ocean. Th at record reveals millennial timescale variability, controlled by binary mixing between tw o Pb sources, but no distinct glacial- interglacial Pb isotope shift. Mixing between natur al endmembers is fully consistent with our data and points to a persistence of the same Pb sou rces through time, although we cannot rule out a minor influence from recent anthropogenic Pb. Whereas neodymium (Nd) isotopes in the Southern Ocean respond to global ocean circulat ion changes between glacial and interglacial periods, Pb isotopes record more local ised mixing within the Antarctic Circumpolar Current, potentially further modulated by climate through changing terrestrial inputs from southern Africa or Australia. Such deco upling between Pb and Nd isotopes in the Southern Ocean highlights their potential to provid e complementary insights into past oceanographic variability

Extremely low long‐term erosion rates around the Gamburtsev Mountains in interior East Antarctica

The high elevation and rugged relief (>3 km) of the Gamburtsev Subglacial Mountains (GSM) have long been considered enigmatic. Orogenesis normally occurs near plate boundaries, not cratonic interiors, and large‐scale tectonic activity last occurred in East Antarctica during the Pan‐African (480–600 Ma). We sampled detrital apatite from Eocene sands in Prydz Bay at the terminus of the Lambert Graben, which drained a large pre‐glacial basin including the northern Gamburtsev Mountains. Apatite fission‐track and (U‐Th)/He cooling ages constrain bedrock erosion rates throughout the catchment. We double‐dated apatites to resolve individual cooling histories. Erosion was very slow, averaging 0.01–0.02 km/Myr for >250 Myr, supporting the preservation of high elevation in interior East Antarctica since at least the cessation of Permian rifting. Long‐term topographic preservation lends credence to postulated high‐elevation mountain ice caps in East Antarctica since at least the Cretaceous and to the idea that cold‐based glaciation can preserve tectonically inactive topography

Chapter 10 - Pleistocene Antarctic climate variability: ice sheet – ocean – climate interactions

During the Pleistocene, Earth experienced high-amplitude fluctuations in global temperature, atmospheric composition, ice sheet extent, and sea level that were forced by orbital variations in the seasonal distribution of solar energy across the planet. Subtle cyclical variations in forcing were greatly amplified by internal feedbacks in the Earth system, with processes in the polar regions influential for pole-to-equator temperature gradients and atmospheric carbon dioxide levels. Exploring the behaviour of the polar ice sheets and the Southern Ocean during this interval is crucial for understanding how the climate system operates and for constraining its sensitivity to future changes. Southern Ocean processes, including wind-driven upwelling, sea-ice formation, deep water production, and biological productivity, were instrumental in regulating Earth’s atmospheric carbon dioxide levels through Pleistocene glacial-interglacial cycles. On millennial timescales, rapid changes in ocean and atmospheric circulation were influenced by meltwater input from unstable ice sheet margins in both hemispheres, leading to highly variable regional and interhemispheric climate responses. This chapter provides an overview of the tools used in marine sediment and ice core archives to reconstruct Pleistocene changes in the Earth system. We discuss the mechanisms that controlled Earth’s climate over different timescales, and review the latest evidence that is revealing how the Antarctic Ice Sheet has both influenced and responded to Pleistocene climate change, including during intervals when Earth’s climate was similar to near-future projections. Despite experiencing ice volume changes that were modest in comparison to the advance and retreat of large Northern Hemisphere ice sheets, Antarctica has been a very active player in the ice sheet-ocean-climate system of the past 2.6 million years, and evidence increasingly suggests that it could respond dramatically to anthropogenic warming

Neodymium isotopic composition and concentration in the western North Atlantic Ocean: results from the GEOTRACES GA02 section

The neodymium (Nd) isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation. The modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete. Here we present new observational data for Nd isotopes and concentrations from twelve seawater depth profiles, which follow the flow path of North Atlantic Deep Water (NADW) from its formation region in the North Atlantic to the northern equatorial Atlantic. Samples were collected during two cruises constituting the northern part of the Dutch GEOTRACES transect GA02 in 2010. The results show that the different water masses in the subpolar North Atlantic Ocean, which ultimately constitute NADW, have the following Nd isotope characteristics: Upper Labrador Sea Water (ULSW), εNd = -14.2 ± 0.3; Labrador Sea Water (LSW), εNd = -13.7 ± 0.9; Northeast Atlantic Deep Water (NEADW), εNd = -12.5 ± 0.6; Northwest Atlantic Bottom Water (NWABW), εNd = -11.8 ± 1.4. In the subtropics, where these source water masses have mixed to form NADW, which is exported to the global ocean, upper-NADW is characterised by εNd values of -13.2 ± 1.0 (2sd) and lower-NADW exhibits values of εNd = -12.4 ± 0.4 (2sd). While both signatures overlap within error, the signature for lower-NADW is significantly more radiogenic than the traditionally used value for NADW (εNd = -13.5) due to the dominance of source waters from the Nordic Seas (NWABW and NEADW). Comparison between the concentration profiles and the corresponding Nd isotope profiles with other water mass properties such as salinity, silicate concentrations, neutral densities and chlorofluorocarbon (CFC) concentration provides novel insights into the geochemical cycle of Nd and reveals that different processes are necessary to account for the observed Nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column. While our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension, the results for open ocean seawater demonstrate, at an unprecedented level, the suitability of Nd isotopes to trace modern water masses in the strongly advecting western Atlantic Ocean