Using triple oxygen isotopes and oxygen-argon ratio to quantify ecosystem production in the mixed layer of northern South China Sea slope region

Quantifying the gross and net production is an essential component of carbon cycling and marine ecosystem studies.Triple oxygen isotope measurements and the O_2/Ar ratio are powerful indices in quantifying the gross primary production and net community production of the mixed layer zone,respectively.Although there is a substantial advantage in refining the gas exchange term and water column vertical mixing calibration,application of mixed layer depth history to the gas exchange term and its contribution to reducing indices error are unclear.Therefore,two cruises were conducted in the slope regions of the northern South China Sea in October 2014(autumn) and June 2015(spring).Discrete water samples at Station L07 in the upper 150 m depth were collected for the determination of δ~(17)0,δ~(18)O,and the O_2/Ar ratio of dissolved gases.Gross oxygen production(GOP) was estimated using the triple oxygen isotopes of the dissolved O_2,and net oxygen production(NOP) was calculated using O_2/Ar ratio and O_2 concentration.The vertical mixing effect in NOP was calibrated via a N_2O based approach.GOP for autumn and spring was(169±23) mmol/(m~2·d)(by O_2) and(189±26) mmol/(m~2·d)(by O_2),respectively.While NOP was 1.5 mmol/(m~2·d)(by O_2) in autumn and 8.2 mmol/(m~2·d)(by O_2) in spring.Application of mixed layer depth history in the gas flux parametrization reduced up to 9.5% error in the GOP and NOP estimations.A comparison with an independent O_2 budget calculation in the diel observation indicated a26% overestimation in the current GOP,likely due to the vertical mixing effect.Both GOP and NOP in June were higher than those in October.Potential explanations for this include the occurrence of an eddy process in June,which may have exerted a submesoscale upwelling at the sampling station,and also the markedly higher terrestrial impact in June.     

Implementation of Tidal Constituent Interpolation Method for the Israeli Coastline

Many ship-borne geodetic surveys at sea, such as Global Navigation Satellite System (GNSS)-based sea surface height (SSH) observation, acoustic profiling of the bottom, and others, deal with a dynamic topography which undergoes several changes during the survey campaign (e.g., changes in tide, salinity and currents). Those changes affect the measurements and may causes for some variations in the results. There are several methods for tidal variations correction, being the most dominant phenomena, such as tidal zoning, tidal constituent interpolation or ocean tidal models. In this study, we have implemented the tidal constituent interpolation method for the Israeli coastline in order to assess its quality and determine whether it is suitable for use in this particular region. This paper depicts the interpolation method, discusses some difficulties in the implementation for the Israeli coast and presents results from exemplary processing. In addition, we compare the results to those obtained using global and regional tidal models.     

Relationship between turbidity and fish diets in Lakes Waahi and Whangape,New Zealand

Abstract

Stomach contents of Gobiomorphus cotidianus,Retropinna retropinna, Gambusia affinis, and Anguilla australis were compared between two shallow lakes in the lower Waikato River basin, to examine the relationship between turbidity and diet. Lake Waahi and the south arm of Lake Whangape had been turbid (20–40 g suspended solids (SS) m^?3) and devoid of submerged macrophytes since the late 1970s and early 1980s, respectively. The main basin of Lake Whangape had been generally clearer (5 g SS m^?3) with dense beds of submerged macrophytes, but at the time of sampling (1987) water clarity had deteriorated (> c. 10 g SS m³) and submerged macrophytes had declined. The mysid Tenagomysis chiltoni was an important prey for all species of fish from turbid water bodies but was less important in stomachs of fish in the main basin of Lake Whangape. Apparently, mysids were not an important prey in Lake Waahi before it became turbid. Chironomid larvae and pupae dominated the diets of small fish in the main basin of Lake Whangape. Fish and mysids were the most important prey of shortfinned eels in both lakes, with mysids most important in Lake Waahi. High mysid densities in the turbid water bodies provide an alternative food resource apparently compensating for those lost by fish when water clarity declined and submerged macrophytes collapsed.     

苏北浅滩海底地下水排放及其对海域营养盐通量的贡献

海底地下水排放(SGD)是近海海域的一个重要的营养盐来源。本研究借助多种天然镭同位素对春季苏北浅滩海域的SGD及其携带入海的营养盐通量进行量化评估。研究发现:苏北浅滩海域的~(224)Ra、~(223)Ra和~(226)Ra等镭同位素的浓度水平较高,呈现近岸高、远岸低的分布趋势;根据~(224)Ra/~(226)Ra的"表观年龄模型"估算的水龄的分布情况推断,春季该海域表层水体主体流向为东北向,流速约为0.1m/s,这与前人物理海洋数值模拟结果一致;最终利用226Ra质量平衡模型发现海域的SGD通量为(46±29)cm/d,由其携带入海的溶解态无机氮、磷、硅营养盐(DIN、 DIP、 DSi)等的通量分别为(2.6±3.1)×1~09、(3.0±2.5)×10~6和(5.5±4.2)×10~8mol/d。     

硼同位素地球化学应用研究进展

硼的2个稳定同位素(10B和11B)间较大的同位素相对质量差导致自然界明显的硼同位素分馏,加上硼易溶于水和活泼的化学性质,使其在不同的地质环境下具有不同的同位素组成。现已查明自然界硼同位素组成(δ11B)的变化范围为-70‰~+75‰。较负的δ11B值见于非海相蒸发硼酸盐矿物和某些电气石,而较正的δ11B值见于盐湖卤水和蒸发海水。20世纪80年代以来,随着硼同位素测量方法的建立和改进,硼同位素地球化学研究领域不断拓宽。目前,硼同位素已成功地应用于判别沉积环境、示踪地下水污染、研究矿床成因、示踪海水入侵、重建古海洋与古气候条件和研究大陆化学风化等方面。综合概述了硼同位素的分馏机理、硼同位素在自然界的分布及其硼同位素在地球化学领域研究中取得的成果、最新进展以及研究中存在的问题,以促进硼同位素地球化学研究在我国的进一步发展。     

广东南澳岛大型海藻龙须菜与浮游植物对营养盐的竞争利用

广东南澳岛近海是我国龙须菜养殖的重要基地。为了探究龙须菜养殖对藻华防治的贡献,分别于2016年3月、5月和6月在广东南澳岛北部海域不同养殖功能海区进行采样,研究龙须菜养殖前后海水中营养盐含量和结构的变化,分析不同粒径的浮游生物对有机营养盐的水解利用,探讨龙须菜养殖对浮游植物竞争利用营养盐和生长产生的影响。结果表明,研究海区水质较清洁,无机氮磷含量较低,春季至夏季,随着龙须菜和浮游植物生物量增加,溶解无机磷(dissolved inorganic phosphorus,DIP)浓度不断下降,至6月南澳海区成为磷限制海域。在5月龙须菜生长高峰期,龙须菜养殖区和龙须菜鲍鱼混养区的DIP浓度显著低于鲍鱼区和非养殖区,龙须菜养殖区的叶绿素a浓度明显低于其他区域,亮氨酸氨肽酶(leucine amino peptide,LAP)和碱性磷酸酶(alkaline phosphatase,AP)活性显著升高,表明龙须菜养殖区浮游植物受到较为明显的营养胁迫。而龙须菜收割后,该养殖区的叶绿素a含量则显著上升,甚至高于其他区域。该结果表明在南澳岛海域,龙须菜养殖通过营养竞争关系(尤其是磷)抑制浮游植物的生长,大规模龙须菜养殖可能有助于抑制有害藻华的发生。     

Simulation of paleotectonic stress fields and quantitative prediction of multi-period fractures in shale reservoirs: A case study of the Niutitang Formation in the Lower Cambrian in the Cen'gong block,South China

Reservoirs where tectonic fractures significantly impact fluid flow are widespread. Industrial-level shale gas production has been established from the Lower Cambrian Niutitang Formation in the Cen'gong block, South China; the practice of exploration and development of shale gas in the Cen'gong block shows that the abundance of gas in different layers and wells is closely related to the degree of development of fractures. In this study, the data obtained from outcrop, cores, and logs were used to determine the developmental characteristics of such tectonic fractures. By doing an analysis of structural evolution, acoustic emission, burial history, logging evaluation, seismic inversion, and rock mechanics tests, 3-D heterogeneous geomechanical models were established by using a finite element method (FEM) stress analysis approach to simulate paleotectonic stress fields during the Late Hercynian—Early Indo-Chinese and Middle-Late Yanshanian periods. The effects of faulting, folding, and variations of mechanical parameters on the development of fractures could then be identified. A fracture density calculation model was established to determine the quantitative development of fractures in different stages and layers. Favorable areas for shale gas exploration were determined by examining the relationship between fracture density and gas content of three wells. The simulation results indicate the magnitude of minimum principal stress during the Late Hercynian — Early Indo-Chinese period within the Cen'gong block is −100 ∼ −110 MPa with a direction of SE-NW (140°–320°), and the magnitude of the maximum principal stress during the Middle-Late Yanshanian period within the Cen'gong block is 150–170 MPa with a direction of NNW-SSE (345°–165°). During the Late Hercynian — Early Indo-Chinese period, the mechanical parameters and faults play an important role in the development of fractures, and fractures at the downthrown side of the fault are more developed than those at the uplifted side; folding plays an important role in the development of fractures in the Middle-Late Yanshanian period, and faulting is a secondary control. This 3-D heterogeneous geomechanical modelling method and fracture density calculation modelling are not only significant for prediction of shale fractures in complex structural areas, but also have a practical significance for the prediction of other reservoir fractures.     

甲烷流体活动与沉积物中碳、氮同位素组成响应——南海东北部海洋IV号地区研究

南海东沙群岛东北部海洋IV号地区GC16站重力柱状沉积物中的有机碳、总氮,以及自生碳酸盐岩矿物的无机碳同位素组成分析结果表明,甲烷流体活动区硫酸盐甲烷转换带(SMTZ—sulfate methane transition zone)是重要的生物地球化学界面,该带内沉积物中有机碳、氮与无机碳同位素组成变化明显。GC16站SMTZ上界面以下的沉积物中有机碳、氮同位素组成分别比其上的沉积物负偏1.4‰PDB和0.93‰,反映该带内甲烷缺氧氧化作用(AOM—anaerobic oxidation of methane)与氨氧化作用发育。无机碳同位素组成表明SMTZ界面之下沉积物中的自生碳酸盐岩矿物为以微生物为媒介的甲烷驱动成因,地质历史时期(至柱状沉积物底部沉积时期)曾发生过2次较强烈的CH₄流体活动;目前该区甲烷流体活动较弱,甲烷流体影响深度与SMTZ上界面一致,未能到达海底。     

Zircon U–Pb and pyrite Re–Os age constraints on pyrite mineralization in the Yinjiagou deposit,China

We report new zircon U–Pb and pyrite Re–Os geochronological studies of the Yinjiagou poly-metallic deposit, sited along the southern margin of the North China Craton (SMNCC). In this deposit, pyrite, the most important economic mineral, is intergrown/associated with Mo, Cu, Au, Pb, Zn, and Ag. Prior to our new work, the age of chalcopyrite–pyrite mineralization was known only from its spatial relationship with molybdenite mineralization and with intrusions of known ages. The U–Pb and Re–Os isotope systems provide an excellent means of dating the mineralization itself and additionally place constraints on the ore genesis and metal source. Zircons separated from the quartz–chalcopyrite–pyrite veins include both detrital and magmatic groups. The magmatic zircons confine the maximum age of chalcopyrite–pyrite mineralization to 142.0 ± 1.5 Ma. The Re–Os results yield an age of 141.1 ± 1.1 Ma, which represents the age of the chalcopyrite–pyrite mineralization quite well. The common Os contents are notably low (0.5–20.1 ppt) in all samples. In contrast, the Re contents vary considerably (3.0–199.2 ppb), most likely depending on intensive boiling, which resulted in an increase of Re within the pyrite. This study demonstrates that the main chalcopyrite–pyrite mineralization occurred late in the magmatic history and was linked to a deeper intrusion involving dominant mantle-derived materials. This mineralization event might be related to the Early Cretaceous lithospheric destruction and thinning of the SMNCC.     

不同氮源对海洋微藻氮同位素分馏作用的影响

以海链藻(Thalassiosira pseudonana)为研究对象,分别考察了以硝酸盐、铵盐和尿素为氮源的氮同位素分馏作用。在建立相应理论模型基础上,分别计算出各个实验体系的ε值。结果表明,在藻类生长初期,δ^15N均较低,其δ^15N的积累主要发生在指数增长期,在稳定期达到最高,与氮源的初始δ^15N相同;不同氮源的氮同位素分馏作用也不相同,其中以铵盐最强,硝酸盐次之,尿素最弱。考虑到实际情况下氮化合物并非单一存在,作者还进一步考察了上述3种氮源混合后对其同位素分馏作用的影响,发现混合氮源体系的表观ε值介于单一氮源时的最大与最小ε值之间,该结果较好地解释了Montoya等(1991)在Chesapeak湾的现场实验结果。