Collagen glue has been used for nearly two centuries to consolidate bone material, although its prevalence in museum collections is only now becoming visible. Identifying and removing collagen glue ...is crucial before the execution of any geochemical or molecular analyses. Palaeolithic bone objects from old excavations intended for radiocarbon dating were first analysed using ZooMS (Zooarchaeology by Mass Spectrometry) to identify the animal species, however peaks characteristic of both cattle and whale were discovered. Two extraction methods for ZooMS were tested to identify the authentic animal species of these objects, which revealed that these were originally whale bone objects that had been consolidated with cattle collagen glue. This is the first time animal collagen glue has been identified in archaeological remains with ZooMS, illustrating again the incredible versatility of this technique. Another technique, Fourier Transform Infrared Spectroscopy in Attenuated Total Reflectance mode (FTIR-ATR), was also tested if it could rapidly identify the presence of collagen glue in archaeological bone material, which was not the case. Two other cleaning methods were tested to remove bone glue contamination prior to radiocarbon dating, along with two modified collagen extraction methods for ZooMS. These methods were applied to bone blank samples (FmC = 0.0031 ± 0.0002, (n = 219), 47 336 ± 277 yr BP) that were experimentally consolidated with collagen glue and to the Palaeolithic bone material (ca. 15 000 and 12 000 yr BP). The experimental bone blanks produced excellent
C ages, suggesting the cleaning methods were successful, however the
C ages for some of the Palaeolithic material remained too young considering their contextual age, suggesting that the collagen glue contamination had most likely cross-linked to the authentic collagen molecule. More research is needed in order to gain a deeper understanding of the occurrence and elimination of cross-linked collagen-based glues in material from museum collections.
This work presents iron isotope data in the western equatorial Pacific. Marine aerosols and top core margin sediments display a slightly heavy Fe isotopic composition (δ56Fe) of 0.33 ± 0.11‰ (2SD) ...and 0.14 ± 0.07‰, respectively. Samples reflecting the influence of Papua New Guinea runoff (Sepik River and Rabaul volcano water) are characterized by crustal values. In seawater, Fe is mainly supplied in the particulate form and is found with a δ56Fe between −0.49 and 0.34 ± 0.07‰. The particulate Fe seems to be brought mainly by runoff and transported across continental shelves and slopes. Aerosols are suspected to enrich the surface Vitiaz Strait waters, while hydrothermal activity likely enriched New Ireland waters. Dissolved Fe isotopic ratios are found between −0.03 and 0.53 ± 0.07‰. They are almost systematically heavier than the corresponding particulate Fe, and the difference between the signature of both phases is similar for most samples with Δ56FeDFe – PFe = +0.27 ± 0.25‰ (2SD). This is interpreted as an equilibrium isotopic fractionation revealing exchange fluxes between both phases. The dissolved phase being heavier than the particles suggests that the exchanges result in a net nonreductive release of dissolved Fe. This process seems to be locally significantly more intense than Fe reductive dissolution documented along reducing margins. It may therefore constitute a very significant iron source to the ocean, thereby influencing the actual estimation of the iron residence time and sinks. The underlying processes could also apply to other elements.
Key Points
Isotopic composition of dissolved and particulate Fe in seawaterIsotopic composition of Fe in marine aerosol, Sepik, and margin sedimentsNonreductive release would be an important source of dissolved Fe
Although Ni isotopes have been shown to be significantly fractionated in terrestrial samples, their use in continental environmental studies has not yet been evaluated. The present study focuses on ...an ultramafic (UM) massif (Barro Alto, Goiás, Brazil) because such areas are naturally rich in Ni. We present developed lateritic weathering profiles. The goal of the study is to evaluate the potential of using Ni isotopes in environmental continental studies by combining its isotopic signature with mineralogy, in order to better understand the geochemical cycling of Ni in UM settings during weathering. As such, Ni isotope values were measured in samples from the Barro Alto UM complex in the main stages of the lateritic weathering profile of UM rocks, including bedrock, ores (saprolitic and lateritic samples) and soil. The mineralogical composition of the samples, with a focus on the different Ni-bearing minerals, was also determined to decipher the potential links between isotopic fractionation and weathering dynamics. Isotopic signatures (δ60Ni) from the natural Ni geochemical cycle include: bedrock samples (δ60Ni=0.28±0.08‰), ore samples (saprolitic and lateritic, δ60Ni from −0.60 to 0.30‰) and soil samples (δ60Ni from −0.19 to −0.02‰). An overall trend of heavier isotope depletion was observed in the solid phase during weathering (Δ60NiSoil–Bedrock=−0.47‰). The mineralogical results were consistent with the literature and showed that the mineralogy of the lateritic part and soil was dominated by Fe-oxides, whereas clay minerals were the primary Ni phase scavengers in the saprolitic part of the profile. Thus, the formation of Ni-bearing clay minerals and Fe-oxides appeared to lead to depletion in heavier isotopes, which indicates preferential export of heavy isotopes in the dissolved phase. This result is consistent with isotopic signatures measured in the exchangeable pool of the solid phase (Δ60Niexch-total up to 0.47‰), and Ni isotopes appear to be a promising tracer to better understand the biogeochemical Ni cycling on the Earth's surface.
•Ultramafic rock weathering leads to depletion in Ni heavier isotopes.•Heavier Ni isotopes are exported into the dissolved or exchangeable phases.•Ni lateritic profiles appear to be a sink of isotopically light nickel.•Ni bearing phases ought to control Ni isotope composition.
Because hard tissues can be radiocarbon dated, they are key to establishing the archaeological chronologies, palaeoenvironmental reconstructions and historical-biogeographical processes of the last ...50,000 years. The advent of accelerator mass spectrometers (AMS) has revolutionized the field of archaeology but routine AMS dating still requires 60-200 mg of bone, which far exceeds that of small vertebrates or remains which hold a patrimonial value (e.g. hominid remains or worked bone artefacts). Here, we present the first radiocarbon dates obtained from minute amounts of bone (3-60 mg) using a MIni CArbon DAting System (MICADAS). An optimized protocol allowed us to extract enough material to produce between 0.2 and 1.0 mg of carbon for graphite targets. Our approach was tested on known-age samples dating back to 40,000 BP, and served as proof of concept. The method was then applied to two archaeological sites where reliable dates were obtained from the single bones of small mammals. These results open the way for the routine dating of small or key bone samples.
Museum collections are extremely valuable sources of material for ongoing research, although the conservation history of some objects is not always recorded, which can be problematic for chemical ...analyses. While most contamination is removed using the acid-base-acid treatment, this may not be the case for cross-linked contamination. The XAD resin protocol was implemented at the radiocarbon (14C) laboratory in the Muséum national d’Histoire naturelle, and the setup was tested using known age bone samples and a consolidated Palaeolithic bone. Known age samples were consolidated with shellac or Paraloid, aged for a month, treated with or without the XAD resin and 14C dated. Bone blank results showed that XAD resin was able to remove shellac, which was not the case for the ABA-only method. Results from VIRI I were more variable and VIRI F was possibly too young to show the effects of the consolidants. Two 14C dates on the Palaeolithic bone after XAD treatment are statistically the same, while a sample without XAD treatment was significantly older, suggesting that the contaminant was not fully removed by the ABA-only treatment. This study demonstrates the potential of the XAD treatment to clean heritage bone samples stored in museums prior to geochemical analyses.
Excess 231Pa and 230Th (231Paxs and 230Thxs) can be used to reconstruct past oceanic sedimentation (230Th‐normalized flux) and circulation changes ((231Pa/230Th)xs,0, hereafter Pa/Th). These ...quantities are determined by computing the detrital and authigenic contributions from bulk sediment measurement. The method relies on the use of a chosen constant value of the detrital (238U/232Th) activity ratio (hereafter (U/Th)det). In this study, we have extracted the detrital fraction of the sediments from North Atlantic deep‐sea core SU90‐08 (43°03′1N, 30°02′5W, 3,080m) and determined its (U/Th)det value over the last 40 ky. We find that (U/Th)det varied significantly through time with a minimum value of 0.4 during the Holocene and a maximum value of 0.7 during the Last Glacial Maximum (LGM). The sensitivity of sedimentary 230Th‐normalized flux and Pa/Th is tested for our study site and for other North Atlantic sites. We show that the sensitivity is highly dependent on the core location and its terrigenous material supply. The 230Th‐normalized flux and Pa/Th signals are very robust in cores with low detrital contributions, whereas they are very sensitive to (U/Th)det changes in cores with higher detrital contribution. In the latter case, changes in 230Th‐normalized flux and Pa/Th due to the choice of a constant (U/Th)det can largely exceed the uncertainty on the 230Th‐normalized flux and Pa/Th, inducing potential biases in the amplitude and temporal variability of reconstructed sedimentation and ocean circulation changes.
Key Points
The (238U/232Th) of the sediment detrital fraction of SU90‐08 varied between 0.4 and 0.7 over the last 40 ky
The influence of varying detrital (238U/232Th) value on widely used paleoceanographic proxies can exceed the uncertainty on the proxies
The sensitivity to the detrital (238U/232Th) value mainly depends on the detrital fraction proportion and terrigenous material supply
A massive diatom bloom forms annually in the surface waters of the naturally iron-fertilized Kerguelen Plateau (Southern Ocean). In this study, silicon isotopic signatures (δ30Si) of silicic acid ...(DSi) and suspended biogenic silica (BSi) were investigated through the whole water column with unprecedented spatial resolution, during the KEOPS-2 experiment (spring 2011). We used δ30Si measurements to track the sources of silicon that fuelled the bloom, and investigated the seasonal evolution of the Si biogeochemical cycle in the iron-fertilized area. We compared the results from stations with various degrees of iron enrichment and bloom conditions to an HNLC reference station. Dissolved and particulate δ30Si signatures were highly variable in the upper 500 m, reflecting the effect of intense silicon utilization in spring, while they were quite homogeneous in deeper waters. The Si isotopic and mass balance identified a unique Winter Water (WW) Si source for the iron-fertilized area that originated from southeast of the Kerguelen Plateau and spread northward. When the WW reached a retroflection of the Polar Front (PF), the δ30Si composition of the silicic acid pool became progressively heavier. This would result from sequential diapycnal and isopycnal mixings between the initial WW and ML water masses, highlighting the strong circulation of surface waters that defined this zone. When comparing the results from the two KEOPS expeditions, the relationship between DSi depletion, BSi production, and their isotopic composition appears decoupled in the iron-fertilized area. This seasonal decoupling could help to explain the low apparent fractionation factor observed in the ML at the end of summer. Taking into account these considerations, we refined the seasonal net BSi production in the ML of the iron-fertilized area to 3.0 ± 0.3 mol Si m−2 yr−1, which was exclusively sustained by surface water phytoplankton populations. These insights confirm that the isotopic composition of dissolved and particulate silicon is a promising tool to improve our understanding of the Si biogeochemical cycle since the isotopic and mass balance allows resolution of processes in the Si cycle (i.e. uptake, dissolution, mixing).
A high resolution δ18O record obtained on benthic foraminifera (Cibicides wuellerstorfi) combined with clay mineralogy, major element concentrations and Sr–Nd isotopes have been investigated for the ...ODP Site 659 located off North Africa in order to reconstruct African monsoon intensity between 6.2 and 4.9Myr. Mineralogical and geochemical results indicate that sedimentation on the Cape Verde plateau results from a mixture of sediments deriving from the neighbouring Saharan arid region and the wet African equatorial zone (Sahelian Band), characterised by a low and a high state of weathering, respectively. Past variations in terrigenous inputs from these areas allow us to track past extension and displacement of the West African Monsoon–ITCZ system. Maximal summer insolation induced a northward migration of the inter-tropical convergence zone (ITCZ), wetter conditions in the Sahel, and a diminishing of wind erosion over the South Sahara and Sahel. In addition, there was an increase in river input to the Cape Verde plateau of sediments derived from southern sedimentary sources, which are characterised by high kaolinite contents and CIA values and low K/Al and Ti/Al ratios. On the other hand, minimal summer insolation induced a southward movement of the ITCZ, drier climate in the Sahel and stronger easterly winds resulting in an increase in dust transport from the Sahara to the Cape Verde Plateau. Dust particles are characterised by high illite and smectite content and by a low chemical state of weathering (low CIA values and high K/Al and Ti/Al ratios). Finally, our results provide new clues regarding the re-flooding of the Mediterranean Sea at the end of the MSC (5.33Myr). This event was associated with enhanced aridity in the Sahara, implying a reorganisation of the atmospheric circulation and a southward migration of the ITCZ.
•New mineralogical and geochemical proxies to trace the displacement of the ITCZ•Evidence of the migration of the ITCZ over North Africa during the MSC•Evidence of enhanced aridity in the Sahara at the end of the Messinian Salinity Crisis