ALBERT

Description: The boron isotopic ratio of 11B/10B (δ11BSRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ11BSRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ11BSRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca 〈 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes.

Description: The neodymium isotopic composition (εNd) of seawater is one of the most important geochemical tracers to investigate water mass provenance, which can also serve as a proxy to reconstruct past variations in ocean circulation. Nd isotopes have recently also been used to reconstruct past circulation changes in the Mediterranean Sea on different time scales. However, the modern seawater εNd dataset for the Mediterranean Sea, which these reconstructions are based on, is limited and up to now only 160 isotopic measurements are available for the entire basin. The lack of present-day data also limits our understanding of the processes controlling the Nd cycle and Nd isotopic distribution in this semi-enclosed basin. Here we present new εNd data from 24 depth profiles covering all Mediterranean sub-basins, which significantly increases the available dataset in the Mediterranean Sea. The main goal of our study is to better characterize the relationship between the dissolved Nd isotope distributions and major water masses in the Mediterranean Sea and to investigate the impact and relative importance of local non-conservative modifications, which include input of riverine particles and waters, aeolian-derived material and exchange with the sediments at continental margins. This comprehensive εNd dataset reveals a clear εNd – salinity correlation and a zonal and depth gradient with εNd systematically increasing from the western to the eastern Mediterranean basin (average εNd = −8.8 ± 0.8 and −6.7 ± 1 for the entire water column, respectively), reflecting the large-scale basin circulation. We have evaluated the conservative εNd behaviour in the Mediterranean Sea and quantified the non-conservative components of the εNd signatures by applying an Optimum Multiparameter (OMP) analysis and results from the Parametric Optimum Multiparameter (POMP) analysis of Jullion et al. (2017). The results of the present study combined with previously published Nd isotope values indicate that dissolved εNd behaves overall conservatively in the open Mediterranean Sea and show that its water masses are clearly distinguishable by their Nd isotope signature. However, misfits between measured and OMP- and POMP-derived εNd values exist in almost all sub-basins, especially in the eastern Levantine Basin and Alboran Sea at intermediate-deep depths, which can be explained by the influence of detrital lithogenic εNd signatures through interaction with highly radiogenic Nile sourced volcanic fractions and unradiogenic sediments, respectively. The radiogenic signature acquired in the eastern Levantine Basin is carried by the Levantine Intermediate Water and transferred conservatively to the entire Mediterranean at intermediate depths. Our measured εNd values and OMP- and POMP-derived results indicate that non-conservative contributions originating from sediment sources are then propagated by water mass circulation (with distinct preformed εNd) along the Mediterranean Sea through advection and conservative mixing. Mediterranean εNd effectively traces the mixing between the different water masses in this semi-enclosed basin and is a suitable water mass tracer.

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology, 36(4), (2021): e2020PA004153, https://doi.org/10.1029/2020PA004153.

Description: Variations in Mediterranean thermohaline circulation of the Quaternary are still not well constrained whereas they have been considered to have an influence on the Atlantic Meridional Overturning Circulation and on the oxygenation of waters in the deep basins of the Mediterranean Sea. εNd analyses have been carried out on planktonic foraminifera of cores collected in the central Mediterranean Sea to constrain water mass exchange between the Eastern and Western Mediterranean Sea (EMS and WMS) during the last climatic cycle. εNd records from the WMS and EMS display similar higher values during warm substages of interglacial Marine Isotopic Stage (MIS) 1 and 5. This suggests an efficient connection between the two Mediterranean sub-basins and the transfer of radiogenic waters to the Tyrrhenian Sea via the Levantine Intermediate Water (LIW). Conversely, during glacial MIS, εNd of the intermediate depth of the Tyrrhenian Sea are less radiogenic than the EMS, implying limited hydrological connection between sub-basins during low sea-level stands. Superimposed on these glacial-interglacial variations, increased εNd occurred during Heinrich Stadial events. This suggests a reduction in the formation of unradiogenic WIW in the Gulf of Lions due to the input of relatively fresh surface Atlantic water to the WMS and/or the inflow of radiogenic glacial LIW and upper EMDW to the Tyrrhenian Sea as a result of an active EMS convection related to saltier and colder conditions. Such potential millennial-scale pulses of LIW intrusion into the Tyrrhenian Sea may have led to an enhanced Mediterranean Outflow Water intensity in the Gibraltar Strait.

Description: The research leading to this paper was funded by the French National Research Agency under the “Investissements d'avenir” program (Grant ANR-11-IDEX-0004-17-EURE-0006), the MEDSENS Project (Grant ANR-19-CE01-0019) and the INSU LEFE-IMAGO PALMEDS Project. The authors gratefully acknowledge the support provided by Louise Bordier during Nd isotopic composition analyses.

Description: 2021-08-15

Description: Dissolved rare earth elements (REEs) distribution in marginal sea is of significant importance to understand geochemical cycling of REEs in the ocean. We determined REEs concentrations of four vertical profiles of seawater collected by KK1803 cruise (R/V Jiageng) from April to May 2018 in the northern South China Sea (SCS), the largest marginal sea of the western Pacific Ocean. These seawater stations are located from the northern to the central SCS that allow to evaluate the REEs sources of surrounding rivers and water masses from the western Pacific Ocean to the SCS. All seawater samples were filtered on board by using 0.45 mm membrane. (MilliPore Corp.). The results show that surface seawater REEs concentration are higher than the subsurface water indicating that surface seawater REEs distribution is likely impacted by terrigenous input through river discharges. Below the subsurface water, REEs concentrations generally increase with depths and are similar to what has been observed in open oceans.

Description: The Tara Pacifc expedition (2016–2018) provided an opportunity to investigate calcifcation patterns in extant corals throughout thePacifc Ocean. Cores from colonies of the massive Porites and Diploastrea genera were collected fromdiferent environments to assess calcifcation parameters of long-lived reef-building corals. In this study, we compared the calcifcation and carbonate chemistryup-regulation of Diploastrea heliopora and Porites corals from across a range of environments. To this, we analyzed the skeletal geochemistry and growth parameters of 39 colonies of Porites (n=33) and Diploastrea (n=6) collected across the tropical Pacifc Ocean during the Tara Pacifc expedition (2016–2018). Te collected corals represent a suite of cores exposed to various hydrological conditions of seawater temperature (SST: 22.4–29.8 °C), salinity (SSS: 31.5–36.1), and carbonate chemistry (total scale pHsw: 8.01–8.09). Te average chemical composition of the calcifying fuid (pHcf, [CO32−]cf, DICcf, Ωcf) was derived from paired boron isotope (δ11B) and B/Ca analyses of core-top samples corresponding to the last 6 years of growth (2010–2016). Based on these data, we assessed the impact of the ambient seawater properties (SST, salinity, carbonate chemistry) on the cf composition of these slow-growing reef-building genera at the Pacifc basin scale.