Search

Using N,N-bis(1-methylheptyl)acetamide (N503) synergized with TBP-NaFeCl 4 (T Fe), a ternary composite extraction membrane known as T Fe N-PIM was created. Under optimum membrane phase conditions, the mass transfer properties of T Fe N-PIM-Li(Ⅰ) and its Li/Mg selective separation performance by electric field augmentation were examined, and confirmed the mechanism of T Fe N-PIM-Li(Ⅰ) electric field enhanced mass transfer. The findings demonstrate a homogeneous distribution of [FeCl 4 -] in the T Fe N-PIM membrane phase and a decrease in the water contact angle as the T Fe content increases. In the T Fe N-PIM membrane, the cation binding order of the composite carrier was H+>Li+>Na+>Mg2+, and the mass transfer was carried out at the interface of the two phases of the membrane through the mechanism of "cation exchange-neutralization", in which Li(Ⅰ) was bonded with the carrier in the form of 2N503-LiFeCl 4 -2TBP, and showed a fixed-site "hopping" mass transfer characteristics under the reinforcement of electric field. The mass transfer process of the T Fe N-PIM- Li(Ⅰ) system under electric field enhancement conforms to the first-order kinetic rate equation, and the voltage (5–45 V) is positively correlated with the permeability coefficient P Li(Ⅰ) but decreases the Li/Mg selectivity of T Fe N-PIM. The S Li(Ⅰ)/Mg(Ⅱ) of T Fe N-PIM was 9.18 at 3 V. After three cycles of 72 h cycling at 40 V, the decrease rate of P Li(Ⅰ) was <7.42 %, which showed good stability. [Display omitted] • A ternary composite extraction membrane (T Fe N-PIM) of N503 synergy with TBP-NaFeCl 4 (T Fe) was prepared. • The increase in permeability coefficient stabilization after T Fe /N503 > 2/1 (w/w) in T Fe N-PIM. • Voltage accelerates the "ion hopping" rate of Li(Ⅰ) in T Fe N-PIM. • Voltage positively correlates with permeability coefficient but reduces Li/Mg selectivity of T Fe N-PIM. • The separation factor of T Fe N-PIM for Li/Mg at 3 V was 9.18. [ABSTRACT FROM AUTHOR]

The use of Li/Ca, Na/Ca and Li/Mg ratios in biogenic aragonite exhibits high potential for reconstructing environmental parameters such as temperature and/or salinity. To date however, only a little is known about the mechanisms controlling the incorporation of monovalent metals such as Li+ and Na+ in aragonite. In this study, the effects of temperature and growth rate on Li and Na incorporation into abiotically precipitated aragonite were experimentally investigated. The results for aragonite overgrowths at 5, 15 and 25 °C and for the surface normalized growth rate range 10–8.6 ≤ r p ≤ 10–7.1 (mol/m2/s) suggest that apparent distribution coefficients (i.e., D Me + = C Me + C Ca aragonite m Me + m Ca solution) of Li and Na are mainly controlled by mineral growth rate, whereas temperature has a minor effect. The combined effect of growth rate and temperature on D Li and D Na can be described as: Log D Li = 0.836 ± 0.028 Log r p − 0.026 ± 0.002 T + 2.958 ± 0.221 ; R 2 = 0.97 Log D Na = 0.456 ± 0.030 Log r p − 0.018 ± 0.002 T − 0.253 ± 0.234 ; R 2 = 0.90 where Log r p is the growth rate in mol/m2/s and T is the temperature in degrees Celsius. The D Li and D Na values increase at increasing mineral growth rate, but also decrease as a function of temperature in experiments with similar normalized growth rate. These observations suggest that the incorporation of Li and Na in abiotic aragonite is controlled by the density of mineral surface defect sites that are correlated with the degree of saturation of the reactive solution with respect to aragonite. Interestingly, no correlation between Li/Mg in the aragonite overgrowths and temperature of formation was observed in this study. This difference of Li/Mg and temperature correlations between abiotic aragonite and natural biogenic samples is intriguing and underlines the need for robust understanding of elemental incorporation during carbonate mineral formation, and proxy calibrations specific for growth conditions (e.g., abiotic versus biogenic). The results of this study do not support the use of Li/Mg as a temperature proxy in abiotic aragonite. • Mineral growth rate influences the D Li and D Na between aragonite and the fluids. • Temperature has a minor effect on D Li and D Na values compared to the growth rate. • Linear correlations between D Li and D Na and saturation exist at different temperatures. • Incorporation of Li and Na is likely controlled by the density of defect sites. • No correlation between Li/Mg in the aragonite overgrowths and temperature was found. [ABSTRACT FROM AUTHOR]

The coral Li/Mg temperature proxy is revisited through an in-depth trace element analysis of scleractinians collected live from tropical to polar environments. The dataset consists of Li/Ca, Mg/Ca, Sr/Ca and Li/Mg ratios from 64 coral specimens belonging to 8 different taxa, including both reef-building zooxanthellate and cold-water non-zooxanthellate species, from a wide range of water temperature (−1 to 29.5 °C), salinity (34.71 to 38.61), and depth (3 to 670 m). Our results showed that the reliability of the Li/Mg temperature proxy is strongly limited by the organic matter associated with the coral skeleton, which is most evident within the green bands observed in tropical corals. Organic-rich bands can double the Mg content otherwise present in the skeleton, which may ultimately lead to a temperature overestimation exceeding 15 °C. We found that this bias can be overcome by the treatment of coral skeletons with a specific oxidizing cleaning protocol. We also detected the presence of calcite deposits within the aragonite skeleton of some Antarctic living coral specimens, which strongly affects the robustness of the Li/Mg proxy given its temperature sensitivity of ~1.5 °C/1% calcite. Therefore, to obtain reliable reconstructions a correction needs to be applied when organic matter and/or calcite contamination is present, which requires the scrupulous assessment of the integrity of the aragonite prior to geochemical analyses. Given that some species entrap more organic matter than others, and that some are more prone to calcite contamination, a taxon-related effect is apparent. Here we show that the tropical species Porites spp., Pseudodiploria strigosa and Orbicella annularis , and the cold-water species Madrepora oculata , Caryophyllia antarctica and Flabellum impensum , are all suitable candidates for reconstructing seawater temperatures. The integrated results across a wide temperature range, from extreme cold to tropical shallow waters, yield an overall precision for the Li/Mg-temperature proxy of ±1.0 °C, as quantified by the standard error of estimates. If calculated from the 95% prediction intervals, the uncertainty of the temperature estimates is ±0.9 °C at 1 °C, ±1.5 °C at 12 °C and ± 2.6 °C at 25 °C. However, the uncertainty for the tropical corals (e.g. Porites) can be reduced to ±0.6 °C if a Li/Mg and Sr/Ca multi-regression approach is applied. [ABSTRACT FROM AUTHOR]

In contrast to Li/Ca and Mg/Ca, Li/Mg is strongly anticorrelated with temperature in aragonites precipitated by the benthic foraminifer Hoeglundina elegans and a wide range of scleractinian coral taxa. We propose a simple conceptual model of biomineralization that explains this pattern and is consistent with available abiotic aragonite partition coefficients. Under this model the organism actively modifies seawater within its calcification pool by raising its [Ca 2+ ], using a pump that strongly discriminates against both Li + and Mg 2+ . Rayleigh fractionation during calcification effectively reverses this process, removing Ca 2+ while leaving most Li + and Mg 2+ behind in the calcifying fluid. The net effect of these two processes is that Li/Mg in the calcifying fluid remains very close to the seawater value, and temperature-dependent abiotic partition coefficients are expressed in the biogenic aragonite Li/Mg ratio. We further show that coral Sr/Ca is consistent with this model if the Ca 2+ pump barely discriminates against Sr 2+ . In H. elegans the covariation of Sr/Ca and Mg/Ca requires either that the pump more strongly discriminates against Sr 2+ , or that cation incorporation is affected by aragonite precipitation rate via the mechanism of surface entrapment. In either case Li/Mg is minimally affected by such ‘vital effects’ which plague other elemental ratio paleotemperature proxies. [ABSTRACT FROM AUTHOR]

• Li/Mg shows strong relationship with temperature across all biogenic aragonites. • Aragonitic stylasterid Li/Mg is the most robust temperature proxy. • Li/Mg of high-Mg calcites also exhibit an exponential relationship to temperature. • Database of temperature proxy data compiled and corrected for interlaboratory bias. The Li/Mg, Sr/Ca and oxygen isotopic (δ 18 O) compositions of many marine biogenic carbonates are sensitive to seawater temperature. Corals, as cosmopolitan marine taxa with carbonate skeletons that can be precisely dated, represent ideal hosts for these geochemical proxies. However, efforts to calibrate and refine temperature proxies in cold-water corals (<20 °C) remain limited. Here we present skeletal Li/Mg, Sr/Ca, δ 18 O and carbon isotope (δ 13 C) data from live-collected specimens of aragonitic scleractinian corals (Balanophyllia, Caryophyllia, Desmophyllum, Enallopsammia, Flabellum, Lophelia , and Vaughanella), both aragonitic and high-Mg calcitic stylasterid genera (Stylaster and Errina), and shallow-water high-Mg calcite crustose coralline algae (Lithophyllum, Hydrolithon , and Neogoniolithon). We interpret these data in conjunction with results from previously explored taxa including aragonitic zooxanthellate scleractinia and foraminifera, and high-Mg calcite octocorals. We show that Li/Mg ratios covary most strongly with seawater temperature, both for aragonitic and high-Mg calcitic taxa, making for reliable and universal seawater temperature proxies. Combining all of our biogenic aragonitic Li/Mg data with previous calibration efforts we report a refined relationship to temperature: Li/Mg All Aragonite = 5.42 exp ⁡ (− 0.050 × T (° C)) (R 2 = 0.97). This calibration now permits paleo-temperature reconstruction to better than ±3.4 °C (95% prediction intervals) across biogenic aragonites, regardless of taxon, from 0 to 30 °C. For taxa in this study, aragonitic stylasterid Li/Mg offers the most robust temperature proxy (Li/Mg Stylasterid (Arag) = 5.64 exp ⁡ (− 0.046 × T (° C)) (R 2 = 0.95)) with a reproducibility of ±2.3 °C. For the first time, we show that high-Mg calcites have a similar exponential relationship with temperature, but with a lower intercept value (Li/Mg = 0.63 exp ⁡ (− 0.050 × T (° C) (R 2 = 0.92)). This calibration opens the possibility of temperature reconstruction using high-Mg calcite corals and coralline algae. The commonality in the relationship between Li/Mg and temperature transcends phylogeny and suggests a similar abiogenic trace metal incorporation mechanism. [ABSTRACT FROM AUTHOR]