El Niño–Southern Oscillation (ENSO) has a strong influence on the climate of the Changjiang River basin, China, most notably upon extreme events such as flooding and drought. However, long-term historical records, which reveal the impacts of ENSO variability on climatic and environmental changes in this region, are scarce. A sediment core (G9) was collected from the estuarine delta of the Changjiang River. And its elemental ratios, mineral compositions, and grain size distribution were analyzed to investigate the links between sediment parameters in this region and the history of ENSO variability during the last century. Observed variations in K2O/Na2O, Al2O3/SiO2, and Rb/Sr ratios are synchronous with changes in mineral compositions and grain size throughout the sediment core. Lower K2O/Na2O, Al2O3/SiO2, and Rb/Sr ratios generally correspond to lower ratios of clay minerals to rock-forming minerals and larger grain sizes, which in turn correspond to periods of flooding in the Changjiang River basin. Such trends probably reflect increased physical erosion and the transport of greater amounts of coarse-grained suspended matter to the estuary. These geochemical proxies are also positively correlated with sea surface temperature anomalies in the Niño-3.4 region (120°W–170°W, 5°S–5°N) (using a low-pass filter with a cut-off of 13 years). We therefore conclude that (1) ENSO-related flood events in the Changjiang River basin have a strong influence on physical erosion processes in the upper catchment area and thereby influence the grain size distribution, elemental ratios, and mineral compositions of the estuarine sediments; and (2) the geochemical records presented here can serve as a proxy for ENSO-driven regional weathering variations on decadal to centennial time scales, because they could potentially be recorded in longer sediment cores recovered from the Changjiang River estuary.

•Photosynthesis and respiration dominate chemistry variations in Luhuitou reef water.•Trace element concentrations in reef water show divergent diurnal variations.•Concentrations of V, W, and Y correlate with DO, DIC, pH and TA in reef water.•Biological activity governs the variations of dissolved V, W, and Y in reef water.Bioactive trace elements play an important role in metabolic processes and, ultimately, marine productivity. An understanding of the complex interactions between biogeochemical processes and trace elements in reef ecosystems is important for establishing geochemical proxies for marine productivity or biological activity. In an attempt to illustrate this relationship, concentrations of dissolved trace elements (V, As, Se, W, and Y), dissolved oxygen (DO), and carbonate system parameters were measured over diurnal cycles on the Luhuitou fringing reef, located in the northern South China Sea. Prominent diurnal variations in DO and carbonate system parameters indicate that biological activities, especially photosynthesis and respiration, are the primary controls on reef water chemistry. The trace elements V, W, and Y co-varied significantly with seawater pH and DIC, implying that they participate in community photosynthesis and respiration. In contrast, As and Se demonstrated divergent diurnal to semi-diurnal behaviors, and their concentrations were not correlated with carbonate system parameters, suggesting that they were involved in other biogeochemical processes. The biologically controlled behaviors of V, W, and Y suggest that their records could potentially serve as geochemical proxies for marine productivity.

A method with simplified chemical treatment has developed to determine high-precision δ11B in silicate rocks by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using sample-standard-bracketing (SSB) mode. Boron in silicate rocks was extracted by digesting with HF, and purified by a single ion-exchange chromatographic step through a column filled with AG MP anion resin. Only one dryness process was involved in the entire chemical treatment procedure. This simplified procedure diminishes the risk of boron contamination and losses during chemical treatment. An introduction system with a PFA spray chamber and a sapphire injector was adopted to decrease boron memory during the measurement on MC-ICP-MS, which provides high-precision δ11B results. The internal precision for δ11B was better than ±0.05‰ (2σ standard error), and the external precision for δ11B was better than ±0.30‰ (2σ standard error) estimated by the long-term results of SRM 951. The δ11B of a series of international rock standard references were measured by this method. Some of the samples have δ11B reference values, and our results agree well with them within analytical errors. This indicates that our method is feasible for high-precision δ11B measurement in various silicate rocks, and our results may provide δ11B reference values for these rock standards.

A method has been developed to determine high-precision stable Nd isotopic compositions in geological samples by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using sample-standard-bracketing (SSB) mode. Nd was pre-concentrated and purified through a two-column ion-exchange chromatographic procedure. The recovery for Nd is generally better than 96%, and the interferences, such as Ce and Sm can be efficiently removed, allowing negligible influence on the stable Nd isotopic composition during mass spectrometry measurement. The internal precision for the stable Nd isotopic compositions, ε142Nd, ε145Nd, ε146Nd and ε148Nd were generally better than ±0.2 (2 SEM), and the external precision was generally better than ±0.2 (1 SD) for ε142Nd, ε145Nd and ε146Nd, and better than ±0.5 (1 SD) for ε148Nd based on the long-term results of the Nd standard solutions, such as La Jolla, Nd-GIG and NIST 3135a. Both the internal and external precisions are comparable to those by double-spike method. The averages of our measured ε142Nd, ε145Nd, ε146Nd and ε148Nd results of La Jolla are identical to those by the double-spike method within analytical error. Thus, our method can provide comparable results with the double-spike method, but does not bring any inconvenience of calibrating double spikes, and the efficiency is greatly improved. This provides a more convenient way for studying stable Nd isotopes in geological processes. By using this method, the stable Nd isotopic compositions for a series of international rock standard references were measured.

A new method for high-precision measurements of stable (δ88/86Sr) and radiogenic (87Sr/86Sr) Sr isotope ratios was developed on the MC-ICP-MS using a standard-sample-standard bracketing protocol. By carefully monitoring and controlling the accumulation of the on-peak backgrounds (i.e. the carryover memory) on the instrument, our method can provide an external precision of around ±0.010‰ to ±0.014‰ for δ88/86Sr measurements. Such precision is comparable to that achieved by double-spike TIMS method (DS-TIMS), and 2–3 times better than those of the previously reported results by MC-ICP-MS without spiking. The results of the standard seawater IAPSO are also identical to those by DS-TIMS. However, our method is more advantageous, efficient and convenient to use for routine Sr isotopic analysis than the DS-TIMS method as there is no need to prepare and calibrate the 84Sr-87Sr double spike. Using this method, we measured the δ88/86Sr values in a series of international geological rock standards, which show large variability, with the lowest value (±0.20‰) registered in JG-2, a terrestrial granite, and the highest value (0.539‰) in UB-N, a serpentinite. This may provide an additional means for isotopic characterization of geological processes, adding a new dimension over the traditional use of radiogenic Sr isotopic ratio 87Sr/86Sr.

A method has been developed to determine high-precision Sr/Ca and Mg/Ca ratios in corals by laser ablation inductively coupled plasma optical emission spectrometry (LA-ICP-OES) using aqueous solution standard calibration. Simultaneous determination of the signals of the entire analytical wavelengths by ICP-OES and the high performance of the new type of LA system (Resonetics 193 nm ArF excimer laser-ablation system, RESOlution M-50) improve the precision for elemental ratios. Repeated measurements on a coral base synthesized working standard, BH-7, provide precisions of about 0.4% and 0.8% for the Sr/Ca and Mg/Ca ratios, respectively, which are better than the formerly reported precision by the LA-ICP-MS method, about 1%. Such precision is comparable to those obtained by the solution nebulization-ICP-OES (SN-ICP-OES) method, and is adequate for paleoclimate reconstruction. In addition, the LA-ICP-OES can provide results with much higher spatial/time resolution. Comparisons between the LA and SN methods were handled by measuring along the same track of a coral. The Sr/Ca results by these two methods agree quite well with each other. The LA-ICP-OES method is very promising for the analysis of element/Ca ratios in coral and other carbonates used in paleoclimate studies such as stalagmite. Systematic discrepancy, however, was observed in the Mg/Ca ratios, likely due to the existing state of magnesium in the coral skeleton.

This study examines the accumulation of major and trace elements in peat deposits in central Yunnan Province, southwestern China. The ashes of an approximately 2 m long core spanning 32.7–11.4 ka are analyzed to assess the elemental contributions of organic materials and to identify elemental paleoclimatic proxies in peats. Peat ash, which is mainly composed of silicate materials, makes up 20–80% of each of the samples. The analysis shows that organic materials are a significant source of many of the elements in the ashes. Among these elements, P and V are the most typical, with their concentrations in the ashes closely correlating to the total organic carbon (TOC) content of the peats. Al, Na, Sc, Cr, Co, Ni, Cu, Ge, Pb, and Th are also associated with biogenic materials, particularly in the lower section (below 122 cm) of the core, where the organic material content is high. Ca, Sr, Mg, and Mn appear to have been part of carbonate deposits, such as authigenic FeCO3 and MnCO3 in the anoxic peats, whereas, K, Ti, Zn, Ga, Rb, Y, rare earth elements (REEs), Zr, Hf, Nb, Ta, Ba, and U are mainly associated with silicate materials. Local weathering products, rather than dust from northern China, are the main sources for the silicate materials in these peats. Some elemental ratios such as K/Rb and K2O/Na2O can reliably indicate changes in local chemical weathering intensity, and their variation patterns match the changes in the East Asian summer monsoon (EASM) very well. The less intensive chemical weathering indicated by lower K/Rb and K2O/Na2O ratios generally corresponds to weaker EASM strength during ∼30 to ∼10 ka, which is consistent with the fact that weaker summer monsoons may arouse drier climates, and do not favor intense chemical weathering. This suggests that select elemental ratios in peats/organic rich sediments may be informative proxies for monsoon climate changes.Highlights► Major and trace elements of the ashes of a peat core from Southwest China were analyzed. ► Quite some elements, in particular P, V and Pb were significantly contributed from organic materials (OM). ► Such OM contributions may bias the paleoclimatic interpretation of related elements. ► K and Rb are free from OM contributions, and K/Rb clearly indicated changes in local chemical weathering. ► The weathering changes appeared to associate with changes in East Asian Summer monsoon.

Geochemical records preserved in the long-lived carbonate skeleton of corals provide one of the few means to reconstruct changes in seawater pH since the commencement of the industrial era. This information is important in not only determining the response of the surface oceans to ocean acidification from enhanced uptake of CO2, but also to better understand the effects of ocean acidification on carbonate secreting organisms such as corals, whose ability to calcify is highly pH dependent. Here we report an ∼200 year δ11B isotopic record, extracted from a long-lived Porites coral from the central Great Barrier Reef of Australia. This record covering the period from 1800 to 2004 was sampled at yearly increments from 1940 to the present and 5-year increments prior to 1940. The δ11B isotopic compositions reflect variations in seawater pH, and the δ13C changes in the carbon composition of surface water due to fossil fuel burning over this period. In addition complementary Ba/Ca, δ18O and Mg/Ca data was obtained providing proxies for terrestrial runoff, salinity and temperature changes over the past 200 years in this region. Positive thermal ionization mass spectrometry (PTIMS) method was utilized in order to enable the highest precision and most accurate measurements of δ11B values. The internal precision and reproducibility for δ11B of our measurements are better than ±0.2‰ (2σ), which translates to a precision of better than ±0.02 pH units. Our results indicate that the long-term pre-industrial variation of seawater pH in this region is partially related to the decadal–interdecadal variability of atmospheric and oceanic anomalies in the Pacific. In the periods around 1940 and 1998 there are also rapid oscillations in δ11B compositions equivalent changes in pH of almost 0.5 U. The 1998 oscillation is co-incident with a major coral bleaching event indicating the sensitivity of skeletal δ11B compositions to loss of zooxanthellate symbionts. Importantly, from the 1940s to the present-day, there is a general overall trend of ocean acidification with pH decreasing by about 0.2–0.3 U, the range being dependent on the value assumed for the fractionation factor α(B3–B4) of the boric acid and borate species in seawater. Correlations of δ11B with δ13C during this interval indicate that the increasing trend towards ocean acidification over the past 60 years in this region is the result of enhanced dissolution of CO2 in surface waters from the rapidly increasing levels of atmospheric CO2, mainly from fossil fuel burning. This suggests that the increased levels of anthropogenic CO2 in atmosphere has already caused a significant trend towards acidification in the oceans during the past decades. Observations of surprisingly large decreases in pH across important carbonate producing regions, such as the Great Barrier Reef of Australia, raise serious concerns about the impact of Greenhouse gas emissions on coral calcification.

Oxygen and hydrogen stable isotopes (δ18O and δD) in precipitation collected in every event from 2007 to 2009 in Guangzhou, South China, are presented in this paper. The total correlation between δ18O and δD is obtained as δD = (8.46 ± 0.13) δ18O + (15.0 ± 0.9). More negative δ18O and δD generally occur during summer and autumn, while less negative or even positive δ18O and δD occur during winter and spring. Significant negative correlations between precipitation δ18O and temperature, and between precipitation δ18O and precipitation amount are observed. Regression line changes from year to year are likely due to changes in moisture sources for the precipitation. The moisture contributed by adjacent seas or local evaporation account for the main precipitation during winter and early spring, while summer monsoon brings huge amounts of moisture from remote seas associated with higher temperature and larger precipitation amounts. Seasonal variations of the precipitation D-excess provide more details for changes in moisture sources. Higher D-excess values during winter and early spring are estimated to correspond to a lesser proportion of remote moisture, while lower D-excess values during summer and autumn correspond to larger remote moisture transported by summer monsoons. This generally agrees with the results of model analysis on single isobaric backward trajectories for air parcels during specific time periods. Results of this study imply that precipitation δ18O and δD, as well as some related paleoclimate proxies such as δ18O in speleothem and tree ring, and δD in plant-derived organic compounds and tree ring, currently cannot indicate changes in temperature or precipitation amount separately, but should be comprehensive proxies for monsoon climate.Research highlights► Rainwater δ18O and δD of each precipitation event during 2007–2009 in Guangzhou were analyzed. ► These isotopes show monsoon-style patterns with lower values in summers and higher values in winters. ► Precipitation amount, air temperature, as well as moisture sources control the rainwater isotopes. ► The δ18O and d-excess, coupled with model analysis on air-mass trajectories and typhoon paths can generally trace changes in moisture sources.

Major, trace and organic elements of a laterite profile developed on Neogene basalts in northern Hainan Island, South China were reported in this paper, the aim of which was to investigate element mobilization and re-distribution during extreme weathering. The results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution. Organic matter (OM) can significantly improve the transport of insoluble elements. Among all the elements, Th is the least mobile. As for the general conservative elements during incipient chemical weathering, such as Fe, Ti, Zr, Hf, Nb and Ta, the removals are up to 20–40% in the upper profile. However, these elements behave as conservatively as Th in the lower profile. In the middle profile, oxic environment occurs, accompanied with significant OM decomposition. The Mn and Ce transferred downward are readily oxidized into insoluble Mn(IV) and Ce(IV) and precipitate in the oxic front. Important OM decomposition decreases the capacity of transfer of insoluble elements in aqueous solution. Consequently, Al significantly precipitates in the oxic front, and REEs, with the exception of Ce, precipitate largely in the OM-depleted layers. Co and U are also concentrated in the oxic front in association with Mn and Ce, respectively. However, Cr shows a negative correlation with Mn because its response to redox condition changes is reversed from that of Mn. Mn oxides/hydroxides, Fe oxides/hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for REEs except for Ce in the profile; REEs with high concentrations in the profile seem closely associated with Mn oxides/hydroxides. Remarkable, highly correlated, Ce and Gd anomalies are observed in the profile. Ce anomalies are caused by Ce precipitation in the oxic environment and successive decomposition of organic matter. Gd anomalies are likely to have resulted from lower stability constants of Gd–OM complexes compared to those of neighboring REEs. The overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re-distribution of the elements during extreme weathering.

•Multi-proxy mineralogical and geochemical records to investigate the climatic evolution of the ISM during the interval 32.7–11.4 ka BP.•δ13CTOC values in the Baoxiu peat core are thought to record surface air temperature.•Decipher the phase relationship between the ISM and EASM during the last glacial period.There have been few investigations of the phase relationship between the Indian summer monsoon (ISM) and the East Asian summer monsoon (EASM) during the last glacial period. We present multi-proxy mineralogical and geochemical records from a peat core taken from the Baoxiu Basin, central Yunnan, southwest China, to investigate changes in chemical weathering and climate associated with the ISM in southwest China spanning the interval ∼32.7–11.4 ka BP. The results suggest that the LGM period (23–18 ka BP) was characterized by cold and dry climatic conditions. A comparison of proxy data from Baoxiu peat with other related proxy climate records reveals that broadly synchronous variations in the ISM and EASM on orbital timescales can be attributed to solar radiation forcing in the Northern Hemisphere. In addition, four synchronous weak millennial-scale monsoonal events coincide well with cooling events recorded in the NGRIP ice core (corresponding to the Younger Dryas, and Heinrich events H1, H2, and H3). Significantly, the strengths of the two Asian monsoons show an inverse relationship during the interval 23–19 ka BP, probably resulting from El Niño-like conditions in the tropical Pacific.Download high-res image (394KB)Download full-size image

A method has been developed to determine high-precision stable Nd isotopic compositions in geological samples by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using sample-standard-bracketing (SSB) mode. Nd was pre-concentrated and purified through a two-column ion-exchange chromatographic procedure. The recovery for Nd is generally better than 96%, and the interferences, such as Ce and Sm can be efficiently removed, allowing negligible influence on the stable Nd isotopic composition during mass spectrometry measurement. The internal precision for the stable Nd isotopic compositions, ε142Nd, ε145Nd, ε146Nd and ε148Nd were generally better than ±0.2 (2 SEM), and the external precision was generally better than ±0.2 (1 SD) for ε142Nd, ε145Nd and ε146Nd, and better than ±0.5 (1 SD) for ε148Nd based on the long-term results of the Nd standard solutions, such as La Jolla, Nd-GIG and NIST 3135a. Both the internal and external precisions are comparable to those by double-spike method. The averages of our measured ε142Nd, ε145Nd, ε146Nd and ε148Nd results of La Jolla are identical to those by the double-spike method within analytical error. Thus, our method can provide comparable results with the double-spike method, but does not bring any inconvenience of calibrating double spikes, and the efficiency is greatly improved. This provides a more convenient way for studying stable Nd isotopes in geological processes. By using this method, the stable Nd isotopic compositions for a series of international rock standard references were measured.

A method has been developed to determine high-precision Sr/Ca and Mg/Ca ratios in corals by laser ablation inductively coupled plasma optical emission spectrometry (LA-ICP-OES) using aqueous solution standard calibration. Simultaneous determination of the signals of the entire analytical wavelengths by ICP-OES and the high performance of the new type of LA system (Resonetics 193 nm ArF excimer laser-ablation system, RESOlution M-50) improve the precision for elemental ratios. Repeated measurements on a coral base synthesized working standard, BH-7, provide precisions of about 0.4% and 0.8% for the Sr/Ca and Mg/Ca ratios, respectively, which are better than the formerly reported precision by the LA-ICP-MS method, about 1%. Such precision is comparable to those obtained by the solution nebulization-ICP-OES (SN-ICP-OES) method, and is adequate for paleoclimate reconstruction. In addition, the LA-ICP-OES can provide results with much higher spatial/time resolution. Comparisons between the LA and SN methods were handled by measuring along the same track of a coral. The Sr/Ca results by these two methods agree quite well with each other. The LA-ICP-OES method is very promising for the analysis of element/Ca ratios in coral and other carbonates used in paleoclimate studies such as stalagmite. Systematic discrepancy, however, was observed in the Mg/Ca ratios, likely due to the existing state of magnesium in the coral skeleton.

A method with simplified chemical treatment has developed to determine high-precision δ11B in silicate rocks by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using sample-standard-bracketing (SSB) mode. Boron in silicate rocks was extracted by digesting with HF, and purified by a single ion-exchange chromatographic step through a column filled with AG MP anion resin. Only one dryness process was involved in the entire chemical treatment procedure. This simplified procedure diminishes the risk of boron contamination and losses during chemical treatment. An introduction system with a PFA spray chamber and a sapphire injector was adopted to decrease boron memory during the measurement on MC-ICP-MS, which provides high-precision δ11B results. The internal precision for δ11B was better than ±0.05‰ (2σ standard error), and the external precision for δ11B was better than ±0.30‰ (2σ standard error) estimated by the long-term results of SRM 951. The δ11B of a series of international rock standard references were measured by this method. Some of the samples have δ11B reference values, and our results agree well with them within analytical errors. This indicates that our method is feasible for high-precision δ11B measurement in various silicate rocks, and our results may provide δ11B reference values for these rock standards.