Dissolved rare earth element and neodymium isotope distributions in the South China Sea: Water mass source versus particle dissolution

Dissolved rare earth elements (REEs) and neodymium isotopes (ϵNd) have been jointly used to evaluate water mass mixing and lithogenic inputs in the ocean. As the largest marginal sea of the West Pacific, the South China Sea (SCS) is an ideal region for reconstructing past hydrological changes. However, its REE and ϵNd distributions and underlying controlling mechanisms remain poorly understood. On the basis of four seawater profiles spread across the SCS, this study presents dissolved REE concentrations and ϵNd data under summer condition to better understand the processes that potentially influence changes in these parameters and their marine cycling. The results show high concentrations of REEs and large variations in ϵNd (−6.7 to −2.8) in surface water, likely caused by the dissolution of riverine and marine particles. Comparison with published data from samples taken during the winter of different years in this and previous studies suggests a possible seasonal variability of middle REE enrichment. The SCS deep water shows a narrow ϵNd range from −4.3 to −3.4, confirming the dominant presence of the North Pacific Deep Water in the deep SCS. The intermediate water in the central SCS is characterized by a more negative ϵNd signal (–4.2 to –3.4) than that found in its counterpart in the West Pacific (–3.5 to –2.8), indicating alterations by deep water through three-dimensional overturning circulation from the northern to southern SCS below ~500 m. The contributions of external sources could be quantitatively estimated for the SCS in terms of Nd. The dissolution of particles from the SCS surrounding rivers (0.26–1.3 tons/yr in summer; 5.6–29 tons/yr in winter) and continental margins (2–12 tons/yr in summer; 23–44 tons/yr in winter) may play an important role in providing additional Nd to the SCS surface water

Strontium isotope evidence for Pre-Islamic cotton cultivation in Arabia

With a view to understanding the dynamics of ancient trade and agrobiodiversity, archaeobotanical remains provide a means of tracing the trajectories of certain agricultural commodities. A prime example is cotton in Arabia, a plant that is non-native but has been found in raw seed and processed textile form at Hegra and Dadan, in the region of al-ʿUlā, north-western Saudi Arabia—sites of critical importance given their role in the trans-Arabian trading routes during Antiquity. Here, we demonstrate that the measurement of strontium isotopes from pre-cleaned archaeological cotton is methodologically sound and is an informative addition to the study of ancient plant/textile provenance, in this case, putting forward evidence for local production of cotton in oasis agrosystems and possible external supply. The presence of locally-grown cotton at these sites from the late 1st c. BCE–mid 6th c. CE is significant as it demonstrates that cotton cultivation in Arabia was a Pre-Islamic socio-technical feat, while imported cotton highlights the dynamism of trade at that time

Holocene shifts in sub-surface water circulation of the North-East Atlantic inferred from Nd isotopic composition in cold-water corals

International audienceVariations of the Sub-Polar Gyre (SPG) and the Sub-Tropical Gyre (STG) circulation during the Holocene are believed to be related to regional and global climate over this time period. To improve our understanding of these phenomena we provide new constraints on variations in surface circulation patterns using neodymium isotopes (εNd) on precisely U-Th dated coral fragments of L. pertusa. The fragments were retrieved from two sediment cores taken from cold-water coral (CWC) mounds at ~ 127–134 m water depth in the Mingulay Reef Complex located on the Western British continental shelf. The results have been combined with εNd analyzed on seawater samples from two stations located on the continental shelf and margin in order to establish whether εNd is a reliable proxy of the ocean circulation variations and notably of the relative contribution of water originating from the SPG and STG. εNd values in CWCs from the Mingulay Reef Complex range from −14.5 ± 0.4 to −11.8 ± 0.3, highlighting two major variations. Unradiogenic εNd values (−14.5 ± 0.4) indicate a higher contribution of water from the SPG around 2.8 ka. Conversely, more radiogenic values at 3.4 ka (−11.8 ± 0.3) point to a declining SPG strength, accompanied by stronger northward penetration of STG water along the western European margin transported by the Shelf Edge Current (SEC) and/or cooler and fresher waters from the interior Seas. The eastward extension of the SPG at 2.8 ka is associated with lower 14C reservoir age (200 yrs) compared to periods associated with a higher contribution of STG waters. This indicates that 14C reservoir ages are mainly a function of vertical mixing of the sub-surface of the ocean. As stronger vertical ventilation is not associated with a higher proportion of local radiogenic surface water, we hypothesize it could represent vertical ventilation in the North-Eastern Atlantic. Active SPG is associated with a better ventilation of the water masses within the SPG and warmer climatic conditions in Northern Europe and in the Eastern Norwegian Sea linked to an intensification of the surface limb of the AMOC

Terrigenous provenance of late Oligocene–Miocene sediments in the central basin of the South China Sea and its implications for chemical weathering and climate change

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Assessing the provenance of ancient cotton at Hegra, Saudi Arabia (end of the 1st c. BC-5th c. AD) using new, modern strontium isotope results

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GG (Gas Graphitisation) : un banc de graphitisation polyvalent et évolutif, complémentaire d’AGE3 pour ECHoMICADAS

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A new method for quantitative analysis of helium isotopes in sediment pore-waters

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U-series dating of carbonate accretions reveals late Neolithic age for the rock paintings in Cangyuan, southwestern China

International audienceThe ancient rock paintings drawn with ochre on the limestone cliffs at 15 sites in Cangyuan County, in southwestern China, contain more than 1200 identifiable figures. The paintings portray scenes of daily life in a remote mountainous area. The inhabitants probably led a sedentary life of animal herding and cultivation and in the scenes they are engaged in activities such as dancing, hunting and fighting. These rock paintings have been known more than 50 years, and have been registered by the State Council of China as major cultural relics under national protection since 2001, but their ages have remained uncertain. In this study, we carried out MC-ICPMS U-series (n = 57) and AMS 14C (n = 4) dating of the carbonate accretions associated with the rock paintings at eight sites. Among them, 25 samples overlying pigment and 14 samples underlying pigment with insignificant initial 230Th contamination yielded highly precise U-series ages. The samples overlying pigment provided reliable minimum ages of 3760, 2920, 2680 and 1110 yr BP for the dated motifs at Sites 2, 7, 14, and 11, respectively. The age ranges for the underlying carbonate accretions overlap those of the overlying ones, from ~3800 to ~3200 yr BP at Site 2 and from ~3000 to ~2700 yr BP at Site 7, suggesting that rock painting was a long-lasting tradition in this region. The combination of all of the reliable U-series dates enables us to constrain the time interval of the main rock painting phase to ~3800–2700 yr BP, which is coeval with the regional late Neolithic culture

GG (Gas Graphitisation) : un banc de graphitisation polyvalent et évolutif, complémentaire d’AGE3 pour ECHoMICADAS

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