(Table 1, 2) Foraminifera biometric data, and boron isotopic composition of Globigerinoides sacculifer of sediments from the Ontong-Java Plateau

Sediment samples from the Ontong-Java Plateau in the Pacific and the 90° east ridge in the Indian Ocean were used to investigate whether shell size and early diagenesis affect d11B of the symbiont-bearing planktonic foraminifer Globigerinoides sacculifer. In pristine shells from both study locations we found a systematic increase of d11B and Mg/Ca with shell size. Shells in the sieve size class 515-865 µm revealed d11B values +2.1 to +2.3 per mil higher than shells in the 250-380 µm class. This pattern is most likely due to differences in symbiont photosynthetic activity and its integrated effect on the pH of the foraminiferal microenvironment. We therefore suggest smaller individuals must live at approximately 50-100 m water depth where ambient light levels are lower. Using the empirical calibration curve for d11B in G. sacculifer, only shells larger than 425 µm reflect surface seawater pH. Partial dissolution of shells derived from deeper sediment cores was determined by shell weight analyses and investigation of the shell surface microstructure by scanning electron microscopy. The d11B in partially dissolved shells is up to 2 per mil lower relative to pristine shells of the same size class. In agreement with a relatively higher weight loss in smaller shells, samples from the Ontong-Java Plateau show a more pronounced dissolution effect than larger shells. On the basis of the primary size effect and potential postdepositional dissolution effects, we recommend the use of shells that are visually pristine and, in the case of G. sacculifer, larger than 500 ?m for paleoreconstructions.

Alkenone stable carbon isotopes, carbonate stable carbon and oxygen isotopes, planktic foraminifera boron isotopes and atmospheric CO2 calculations and box model results from Ras il-Pellegrin section, Malta

The development of a permanent, stable ice sheet in East Antarctica happened during the middle Miocene, about 14 million years (Myr) ago. The middle Miocene therefore represents one of the distinct phases of rapid change in the transition from the "greenhouse" of the early Eocene to the "icehouse" of the present day. Carbonate carbon isotope records of the period immediately following the main stage of ice sheet development reveal a major perturbation in the carbon system, represented by the positive d13C excursion known as carbon maximum 6 ("M6"), which has traditionally been interpreted as reflecting increased burial of organic matter and atmospheric pCO2 drawdown. More recently, it has been suggested that the d13C excursion records a negative feedback resulting from the reduction of silicate weathering and an increase in atmospheric pCO2. Here we present high-resolution multi-proxy (alkenone carbon and foraminiferal boron isotope) records of atmospheric carbon dioxide and sea surface temperature across CM6. Similar to previously published records spanning this interval, our records document a world of generally low (~300 ppm) atmospheric pCO2 at a time generally accepted to be much warmer than today. Crucially, they also reveal a pCO2 decrease with associated cooling, which demonstrates that the carbon burial hypothesis for CM6 is feasible and could have acted as a positive feedback on global cooling.

利用MC-ICP-MS测定硼同位素及其在西藏地热和盐湖中的初步应用

Based on previous studies, boron can be separated from aqueous samples with Amberlite IRA-743 resin. Experiments on the elute temperature, elute volume and the dynamic resin exchange capacity have been performed in this study. Results show that the dynamic exchange capacity of the resin is 4.2mg B/g and at room temperature, boron fixed on the resin within this capacity level can be extracted quantitatively by using 5ml 2%HNO3. A new procedure has been developed for the measurement of boron isotope ratios in water samples using a Neptune MC-ICP-MS, after resolving the memory effect, which is a key problem, and investigating the impacts of mass bias and Si matrix effect. Using this method, it usually takes 20 min to perform one measurement on 0.1ppm boron solution with a precision of 0.23‰ (SD). If the relative deviation between a sample and the standard is large, the washout time needs to be doubled to achieve a higher precision. δ11B values of water samples from Yangbajing geothermal field vary from -10.53 to -9.13‰. Owing to the large difference B concentration and the small B isotope difference between deep geothermal water and surface water, B isotope ratios of the shallow geothermal fluids are dominated by the deep end member rather than the shallower one in the mixing process. As a consequence, δ11B-B relation is indicative basically of a dilution process. Vapor-liquid separation and calcite scaling also greatly influence B isotope fractionation. δ11B values of water samples from Dagejia geothermal field are from -15.98‰ to -11.67‰. Boron in Changma River near the field has two sources, freshwater lakes (Dajiamang Lake and Canke Lake) and geothermal waters. Finally, a preliminary discussion is included on boron geochemical characteristics of the salt lakes in Shuanghu area and other geothermal fields, to provide information for future studies on boron isotope geochemistry of geothermal systems and salt lakes in Tibet.

海洋生物碳酸盐硼同位素技术研究及其应用

近些年来，利用海洋生物碳酸盐硼同位素重建古海水pH，计算当时大气CO2含量，进而推测古气候的变化已成为国际同位素地球化学界研究的热点问题，被称为δ11B-pH技术。古海水的δ11Bsw是否恒定、B(OH)4−和B(OH)3间理论的硼同位素分馏系数4/3是多少以及碳酸盐的δ11Bcarb是否等于海水B(OH)4−的δ11B4值是该技术成功的三个关键。但到目前为止以上三项问题还没得到完全证实。 为确定方解石的硼同位素组成与海水pH的依赖关系，已进行过大量实验研究。他们的结果与预期的假设一致，支持了B(OH)4-是掺入方解石结构主要形式的假设。但近期 Pagani(2005)指出B(OH)4-也许不是掺入方解石结构的主要形式，B(OH)3也可能同时掺入进碳酸盐。肖应凯等(2006)的无机碳酸盐沉积实验发现碳酸盐沉积和母液间的硼同位素分馏系数大于1的异常现象，认为碳酸钙中镁或其它微量元素的存在是重要原因，推断这是在高pH生成Mg(OH)2沉积后11B优先掺入的缘故，推断有B(OH)3掺入碳酸盐的可能。 以前进行的沉积实验，只考虑到碳酸钙本身，确实证明了硼只以或主要以B(OH)4-参与进生物碳酸钙。但天然的海洋生物碳酸盐含有镁、锶、铁等微量元素，这些微量元素的存在可能会改变硼的参与行为，从而对硼同位素分馏产生影响。现代珊瑚礁中水镁石普遍存在，这是否会影响珊瑚的硼同位素组成而导致δ11B-pH技术的误差还值得研究。 针对以上问题，主要对硼掺入进Mg(OH)2的形式及分馏机理，现代珊瑚中镁、锶等微量元素与硼浓度及硼同位素的关系进行研究，并用生物碳酸盐的硼同位素对陆相产出有孔虫的沉积环境进行判别。 通过研究，得到以下几点认识： 1. 在Mg(OH)2从pH9.5～13的含硼合成海水中沉积时，Mg(OH)2沉积11B的变化范围为-1.20‰～28.26‰，高于合成海水的11B (-7.00±0.07‰)，沉积和海水间的硼同位素分馏系数固/液变化范围为1.0177～1.0569，平均值为1.0329，这是H3BO3优先掺入的结果，造成11B在Mg(OH)2沉积中富集。 2. Mg(OH)2沉积的硼浓度和硼在Mg(OH)2沉积与滤液间的分配系数Kd的变化范围分别为228.61 g/g～937.79 g/g和9.31～494.20。高pH值时硼掺入Mg(OH)2的过程中吸附作用占有重要位置。 3. Mg(OH)2吸附实验表明，硼掺入Mg(OH)2非常迅速，4 h能达到平衡。平衡后Mg(OH)2中硼浓度[B]固和固相与溶液相间的分配系数Kd随pH设定的升高和固液比的降低而降低。而且最高的[B]固和Kd均远高于硼被金属氧化物或粘土矿物吸附时的对应值，表硼具有很强的掺入Mg(OH)2的能力。 4. 吸附平衡时溶液相的11B液f (-19.2‰～-17.8‰)均低于原始溶液的11B液i (-7.00±0.07‰)，计算的Mg(OH)2与平衡溶液间的硼同位素分馏系数固-液变化范围为1.0186～1.0220，平均值为1.0203。这充分表明，硼掺入Mg(OH)2时11B优先进入固相，这是B(OH)3优先掺入的结果。 5. 硼以B(OH)3和B(OH)4-两种形式同时掺入Mg(OH)2，并以B(OH)3优先掺入为主，pH设定越低掺入的B(OH)3比例越高。 6. 硼将通过吸附和与Mg(OH)2的沉淀反应而掺入Mg(OH)2，两者共同决定了Mg(OH)2中硼同位素分馏特征。 7. Ca、Sr、B和Na在珊瑚中均得到富集，而Mg在珊瑚中却是贫化的。珊瑚的B浓度主要不是由这几种元素决定的。 8. 珊瑚δ11Bcarb的变化范围为22.8‰～27.9‰，平均为25.2‰。除与B浓度相关性明显外，珊瑚δ11Bcarb与其它四种元素的相关性不强。北海涠洲岛、灯楼角和三亚三地珊瑚与海水间的分馏系数carb-sw分别为0.9839、0.9847和0.9850。珊瑚与海水B(OH)3间的分馏系数carb-3的变化范围为0.9772～0.9800，平均值为0.9788，随pH升高carb-3减小。珊瑚的平均δ11Bcarb基本位于采用=0.9772时理论计算的δ11B4曲线之上，而且都低于原始合成海水的δ11Bcarb，表明硼是以B(OH)3和B(OH)4-两种形式同时掺入进珊瑚中的，并以B(OH)4-优先掺入为主。 9. 由于B(OH)4- 和B(OH)3同时进入到珊瑚中，d11Bcarb=d11B4的假设不能成立，由所测定生物碳酸盐的δ11Bcarb值计算的海水pH值会产生误差，使δ11B-pH技术变得更为复杂。 10. 实验模拟与自然的真实情况是有差距的，不能完全用实验模拟来代替自然的真实情况。 11.杨户庄剖面的第四纪早期有孔虫的生存环境是非海相环境，不是“海侵”或“海泛”的结果；同时也表明有孔虫并非是特有的海洋生物，它完全可以在陆相环境中存在。

Deep water formation in the North Pacific and deglacial CO2 rise

Deep water formation in the North Atlantic and Southern Ocean is widely thought to influence deglacial CO2 rise and climate change; here we suggest that deep water formation in the North Pacific may also play an important role. We present paired radiocarbon and boron isotope data from foraminifera from sediment core MD02-2489 at 3640 m in the North East Pacific. These show a pronounced excursion during Heinrich Stadial 1, with benthic-planktic radiocarbon offsets dropping to ~350 years, accompanied by a decrease in benthic d11B. We suggest this is driven by the onset of deep convection in the North Pacific, which mixes young shallow waters to depth, old deep waters to the surface, and low-pH water from intermediate depths into the deep ocean. This deep water formation event was likely driven by an increase in surface salinity, due to subdued atmospheric/monsoonal freshwater flux during Heinrich Stadial 1. The ability of North Pacific Deep Water (NPDW) formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity Earth system model. These experiments also show that breakdown of stratification in the North Pacific leads to a rapid ~30 ppm increase in atmospheric CO2, along with decreases in atmospheric d13C and D14C, consistent with observations of the early deglaciation. Our inference of deep water formation is based mainly on results from a single sediment core, and our boron isotope data are unavoidably sparse in the key HS1 interval, so this hypothesis merits further testing. However we note that there is independent support for breakdown of stratification in shallower waters during this period, including a minimum in d15N, younging in intermediate water 14C, and regional warming. We also re-evaluate deglacial changes in North Pacific productivity and carbonate preservation in light of our new data, and suggest that the regional pulse of export production observed during the Bølling-Allerød is promoted by relatively stratified conditions, with increased light availability and a shallow, potent nutricline. Overall, our work highlights the potential of NPDW formation to play a significant and hitherto unrealized role in deglacial climate change and CO2 rise.

Stable isotopes and element concentrations of samples from the Wadi Bih, United Arab Emirates

Ocean acidification triggered by Siberian Trap volcanism was a possible kill mechanism for the Permo-Triassic Boundary mass extinction, but direct evidence for an acidification event is lacking. We present a high-resolution seawater pH record across this interval, using boron isotope data combined with a quantitative modeling approach. In the latest Permian, increased ocean alkalinity primed the Earth system with a low level of atmospheric CO2 and a high ocean buffering capacity. The first phase of extinction was coincident with a slow injection of carbon into the atmosphere, and ocean pH remained stable. During the second extinction pulse, however, a rapid and large injection of carbon caused an abrupt acidification event that drove the preferential loss of heavily calcified marine biota.

B/Ca ratios in planktonic foraminifera

Boron isotope systematics indicate that boron incorporation into foraminiferal CaCO3 is determined by the partition coefficient, KD = [B/Ca](CaCO3)/[B(OH)4**-/HCO3**-](seawater), and [B(OH)4?/HCO3?](seawater), providing, in principle, a method to estimate seawater pH and PCO2. We have measured B/Ca ratios in Globigerina bulloides and Globorotaliainflata for a series of core tops from the North Atlantic and the Southern Ocean and in Globigerinoides ruber (white) from Ocean Drilling Program (ODP) site 668B on the Sierra Leone Rise in the eastern equatorial Atlantic. B/Ca ratios in these species of planktonic foraminifera seem unaffected by dissolution on the seafloor. KD shows a strong species-specific dependence on calcification temperature, which can be corrected for using the Mg/Ca temperature proxy. A preliminary study of G. inflata from Southern Ocean sediment core CHAT 16K suggests that temperature-corrected B/Ca was ~30% higher during the last glacial. Correspondingly, pH was 0.15 units higher and aqueous PCO2 was 95 ?atm lower at this site at the Last Glacial Maximum. The covariation between reconstructed PCO2 and the atmospheric pCO2 from the Vostok ice core demonstrates the feasibility of using B/Ca in planktonic foraminifera for reconstructing past variations in pH and PCO2.

Calculated sea surface temperatures of two sediment cores

The reconstruction of ocean history employs a large variety of methods with origins in the biological, chemical, and physical sciences, and uses modern statistical techniques for the interpretation of extensive and complex data sets. Various sediment properties deliver useful information for reconstructing environmental parameters. Those properties that have a close relationship to environmental parameters are called ''proxy variables'' (''proxies'' for short). Proxies are measurable descriptors for desired (but unobservable) variables. Surface water temperature is probably the most important parameter for describing the conditions of past oceans and is crucial for climate modelling. Proxies for temperature are: abundance of microfossils dwelling in surface waters, oxygen isotope composition of planktic foraminifers, the ratio of magnesium or strontium to calcium in calcareous shells or the ratio of certain organic molecules (e.g. alkenones produced by coccolithophorids). Surface water salinity, which is important in modelling of ocean circulation, is much more difficult to reconstruct. At present there is no established method for a direct determination of this parameter. Measurements associated with the paleochemistry of bottom waters to reconstruct bottom water age and flow are made on benthic foraminifers, ostracodes, and deep-sea corals. Important geochemical tracers are d13C and Cd/Ca ratios. When using benthic foraminifers, knowledge of the sediment depth habitat of species is crucial. Reconstructions of productivity patterns are of great interest because of important links to current patterns, mixing of water masses, wind, the global carbon cycle, and biogeography. Productivity is reflected in the flux of carbon into the sediment. There are a number of fluxes other than those of organic carbon that can be useful in assessing productivity fluctuations. Among others, carbonate and opal flux have been used, as well as particulate barite. Furthermore, microfossil assemblages contain clues to the intensity of production as some species occur preferentially in high-productivity regions while others avoid these. One marker for the fertility of sub-surface waters (that is, nutrient availability) is the carbon isotope ratio within that water (13C/12C, expressed as d13C). Carbon isotope ratios in today's ocean are negatively correlated with nitrate and phosphate contents. Another tracer of phosphate content in ocean waters is the Cd/Ca ratio. The correlation between this ratio and phosphate concentrations is quite well documented. A rather new development to obtain clues on ocean fertility (nitrate utilization) is the analysis of the 15N/14N ratio in organic matter. The fractionation dynamics are analogous to those of carbon isotopes. These various ratios are captured within the organisms growing within the tagged water. A number of reconstructions of the partial pressure of CO2 have been attempted using d13C differences between planktic and benthic foraminifers and d13C values of bulk organic material or individual organic components. To define the carbon system in sea water, two elements of the system have to be known in addition to temperature. These can be any combination of total CO2 , alkalinity, or pH. To reconstruct pH, the boron isotope composition of carbonates has been used. Ba patterns have been used to infer the distribution of alkalinity in past oceans. Information relating to atmospheric circulationand climate is transported to the ocean by wind or rivers, in the form of minerals or as plant andanimal remains. The most useful tracers in this respect are silt-sized particles and pollen.

Seawater carbonate chemistry, processes and elements during experiments with planktonic foraminifera Orbulina universa, 2004

We investigate the sensitivity of U/Ca, Mg/Ca, and Sr/Ca to changes in seawater [CO3[2-]] and temperature in calcite produced by the two planktonic foraminifera species, Orbulina universa and Globigerina bulloides, in laboratory culture experiments. Our results demonstrate that at constant temperature, U/Ca in O. universa decreases by 25 +/- 7% per 100 µmol [CO3[2-]] kg**-1, as seawater [CO3[2-]] increases from 110 to 470 µmol kg**-1. Results from G. bulloides suggest a similar relationship, but U/Ca is consistently offset by ~+40% at the same environmental [CO3[2-]]. In O. universa, U/Ca is insensitive to temperature between 15°C and 25°C. Applying the O. universa relationship to three U/Ca records from a related species, Globigerinoides sacculifer, we estimate that Caribbean and tropical Atlantic [CO3[2-]] was 110 +/- 70 µmol kg**-1 and 80 +/- 40 µmol kg**-1 higher, respectively, during the last glacial period relative to the Holocene. This result is consistent with estimates of the glacial-interglacial change in surface water [CO3[2-]] based on both modeling and on boron isotope pH estimates. In settings where the addition of U by diagenetic processes is not a factor, down-core records of foraminiferal U/Ca have potential to provide information about changes in the ocean's carbonate concentration.

Chemical and isotopic compositions of altered MORB from ODP Holes 187-1154A, 187-1155B, and 187-1160B

Boron and Pb isotopic compositions together with B-U-Th-Pb concentrations were determined for Pacific and Indian mantle-type mid-ocean ridge basalts (MORB) obtained from shallow drill holes near the Australian Antarctic Discordance (AAD). Boron contents in the altered samples range from 29.7 to 69.6 ppm and are extremely enriched relative to fresh MORB glass with 0.4-0.6 ppm B. Similarly the d11B values range from 5.5? to 15.9? in the altered basalts and require interaction with a d11B enriched fluid similar to seawater ~39.5? and/or boron isotope fractionation during the formation of secondary clays. Positive correlations between B concentrations and other chemical indices of alteration such as H2O CO2, K2O, P2O5, U and 87Sr/86Sr indicate that B is progressively enriched in the basalts as they become more altered. Interestingly, d11B shows the largest isotopic shift to +16? in the least altered basalts, followed by a continual decrease to +5-6? in the most altered basalts. These observations may indicate a change from an early seawater dominated fluid towards a sediment-dominated fluid as a result of an increase in sediment cover with increasing age of the seafloor. The progression from heavy d11B towards lighter values with increasing degrees of alteration may also reflect increased formation of clay minerals (e.g., saponite). A comparison of 238U/204Pb and 206Pb/204Pb in fresh glass and variably altered basalt from Site 1160B shows extreme variations that are caused by secondary U enrichment during low temperature alteration. Modeling of the U-Pb isotope system confirms that some alteration events occurred early in the 21.5 Ma history of these rocks, even though a significant second pulse of alteration happened at ~12 Ma after formation of the crust. The U-Pb systematics of co-genetic basaltic glass and variably low temperature altered basaltic whole rocks are thus a potential tool to place age constraints on the timing of alteration and fluid flow in the ocean crust.

(Table 1) B content, d11B, d18O, degree of alteration, and lithology of basalts from ODP Hole 504B

Boron contents and boron isotopic compositions were determined for the uppermost 1.3 km section of typical 6.2 Ma oceanic crust from DSDP/ODP Hole 504B, Costa Rica Rift, Galapagos Spreading Center. Both the boron content and the d11B value in the oceanic crust are controlled by two types of alteration: 1. (1) low-temperature alteration (0 to 60°C; Zones I and II) and 2. (2) high-temperature hydrothermal alteration (200 to 400°C; Zones III and IV). Basalts subjected to the low-temperature alteration are characterized by their relatively high boron contents (0.69 to 19.3 ppm) and high d11B values (+2.2 to +10.6?), indicating uptake of boron into secondary phases in equilibrium with seawater or evolved seawater. Hydrothermally altered basalts contain less abundant boron (0.17 to 0.52 ppm) and relatively constant d11B values (?0.1 to +1.0?). Although basalts from the upper part of these hydrothermal zones (<1300 mbsf) show equilibrated boron content and d11B value with aqueous fluid, effective leaching of boron from basalt is predominant in the lower part (>1300 mbsf). Original boron content and d11B value of the Hole 504B MORB were 0.35 ppm and +0.2?, respectively. The present data provide fundamental information in understanding of the distribution of boron and boron isotopes in the oceanic crust.