Paleoceanographic records in the Chukchi Basin, western Arctic Ocean during the late Quaternary

The late Quaternary paleoceanographic changes in the western Arctic Ocean are revealed by quantitative studies of foraminiferal abundance, ice-rafted detritus (IRD) and its mineralogical and petrological compositions, planktonic Neogloboquadrina pachyderma (sin.) (Nps)-δ¹⁸O and -δ¹³C, biogenic and non-biogenic components in Core M03 token from the Chukchi Basin during the Second Chinese National Arctic Expedition cruise. Seven IRD events appeared at MIS 7, 5, 3 and 1. These IRD were carried in massive icebergs, which were exported to the Beaufort Sea through the M'Clure Strait Ice Stream, Canadian Arctic Archipelago, and then transported into the Chukchi Basin by the Beaufort Gyre. Low IRD deposition occurred during the glacial times when more extended ice cover and weakened Beaufort Gyre, while the open water condition and the intensified Beaufort Gyre during interglacial periods favored the IRD deposition. Therefore, the IRD events not only indicate the provenance of coarser detritus and ice export events, but also reflect the evolutionary histories of the Beaufort Gyre and North American ice sheet. Seven light Nps-δ¹⁸O and -δ¹³C excursions could respond to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines, but was irrelevant to the warm Atlantic water and freshwater inputs. Whereas, the heavy Nps-δ¹⁸O and -δ¹³C values separately reflect the lessened Arctic freshwater and Pacific water, and well-ventilated surface water from the continental shelf and halocline water. Variations of CaCO₃ content and planktonic foraminiferal abundance during the interglacial and glacial periods can demonstrate the incremental or diminishing input of the Atlantic water, while the total organic carbon (TOC) and opal contents increased and decreased during the glacial and interglacial periods, respectively, which could be related to the TOC degradation, opal dissolution and redox conditions of interface between the bottom water and sediments.     

黑河流域中上游地区降水δ18O变化特征

水资源短缺和合理利用是黑河流域面临的一个严峻问题,解决问题的关键就是要深入了解水循环过程.降水作为水循环中一个重要环节,分析其环境同位素变化特征是应用同位素示踪技术研究水循环过程所必须的前提.根据黑河流域中上游地区取得的降水水样和降水气象资料,分析了该区域降水中δ¹⁸O的变化特征.结果表明:降水δ¹⁸O受降水量、季节、高度和温度等众多因素综合影响,其中温度占主导地位;由于位于干旱内陆地区,降水中δ¹⁸O的季节变化幅度较大,可达20‰以上;降水δ¹⁸O与降水前后平均气温的相关性显著,分别高于δ¹⁸O与降水前气温或降水后气温的相关性.从空间上来看,山区或上游地区降水δ¹⁸O与气温之间的相关性显著,分别高于δ¹⁸O与山前或山前盆地的相关性.     

山脉走向对降水中δ18O垂直递减率的影响——以黑河流域上游祁连山区为例

准确定量计算降水中稳定同位素的垂直递减率对水文、古气候及古海拔高度重建等研究有重要意义.使用方差分析方法,分析了黑河流域上游祁连山区3个站点2007年10月至2008年9月降水中δ¹⁸O与海拔的关系.结果表明：由于青藏高原北缘气候特征受西风环流控制,水汽的主要运移路径与祁连山脉走向基本平行,导致降水过程中缺乏水汽沿海拔爬升的过程,以及存在广泛的水汽混合等因素的影响,使得在显著性水平α=0.05下,祁连山区海拔1600～3300 m之间降水中δ¹⁸O在年尺度和季节尺度上均没有表现出明显的高程效应,其年均值为-7.1‰.结果说明除水汽来源外,山脉走向与主要水汽运移轨迹之间的空间关系也是影响降水中稳定同位素特征的重要因素.最后,讨论了青藏高原降水δ¹⁸O垂直递减率的区域变化特征.     

敦煌伊塘湖沉积物有机碳同位素揭示的末次盛冰期以来湖面变化

对甘肃敦煌伊塘湖沉积物进行了野外钻探采样,采用光释光测年技术确定了沉积物的年代,测定了总有机碳含量(TOC)、碳氮比(TOC/TN)和有机质稳定碳同位素组成(δ13℃org)等环境代用指标.结果表明,23ka至今,湖区沉积物δ13℃org在-27.84‰～-22.86‰之间变化,可与TOC对比.干旱气候条件下湖泊沉积物的δ13℃org变化主要受到沉水植物和挺水植物含量变化的控制,生长于较深水的沉水植物δ13Corg值偏正,而生长于较浅水的挺水植物δ13℃org值偏负;另外,部分时期有外源陆生植物产生的有机质输入,影响沉积物的碳同位素值.总体上,干旱区湖相沉积物δ13Crg值可指示湖水面的变化、间接指示气候干湿变化.δ13Corg变化的时间序列显示出明显的冰期-间冰期变化,从末次盛冰期到全新世暖期可将伊塘湖的环境演化分为4个阶段:23～ 13ka是一个气候不稳定时期,整体呈冷干并且湖面水位偏低,但后期有转暖的趋势;13～9ka为冰期向全新世暖期的过渡阶段;9～5ka整体湖面水位偏高、气候暖湿,含有短时间的干事件;5ka至今有变干的趋势.23ka以来,伊塘湖区的湖泊环境演化受全球大气环流与水汽输送路径控制.     

若尔盖铀矿田碳氧同位素特征及其成因

研究了若尔盖铀矿田中灰岩、硅灰岩及方解石脉的碳氧同位素组成,结果表明产于地层中的灰岩、硅灰岩及方解石脉的δ13C值为-1.48‰～3.18‰,平均为1.51‰,为海洋沉积碳酸盐岩的碳同位素组成特征;δ18O值为-12.81‰～-3.71‰,平均为-9.92‰,在铀矿田中δ18O值最高.与成矿作用关系最为密切的含矿方解石脉δ13C值为-2.78‰～-4.81‰,平均为-3.93‰,明显表现为地幔来源的特点;δ18O值为-13.14‰～-15.05‰,平均为-13.87‰,其值在铀矿田中介于地层中岩石(脉)与矿区方解石脉之间.矿区方解石脉的δ13C值为-3.53‰～-6.35‰,平均为-4.93‰,与含矿方解石脉的碳同位素组成相近,表明其亦是成矿作用的产物;δ18O值为-16.00‰～-24.75‰,平均为-19.36‰,在铀矿田中δ18O值最低,明显表现为深部来源特征.综合若尔盖铀矿田的碳氧同位素组成特征,暗示其成矿流体应当来源于地幔.     

Isotopic temporal and spatial variations of tropical rivers in Thailand reflect monsoon precipitation signals

Stable isotopic compositions (δ¹⁸O and d-excess) from 25 rivers in Thailand were analysed monthly during 2013–2015. Results indicated that monsoon precipitation fundamentally influences the river isotopes. The overland flow supplied from monsoon precipitation and human-altered flow regimes produces considerable isotopic variability. Spatial and temporal variations were observed among four principal geographical regions. The seasonality of monsoon precipitation in mountainous Thailand produced large variations in isotopic compositions because most rainfall occurred during the southwest monsoon, and dry conditions prevailed during the northeast monsoon. The northern and northeastern regions are mountainous, highland areas. Low δ¹⁸O values were found in these regions, likely because of altitude effects on precipitation. Conversely, monsoonal precipitation continually supplies rivers in southern Thailand all year round, producing higher and more consistent δ¹⁸O values than in the other regions. The Chao Phraya plain in the central region experienced enrichment of δ¹⁸O river runoff related to evaporation in irrigation systems. Larger catchment areas and longer residence times resulted in more pronounced evaporation effects, producing lower values of d-excess and local river water line slopes compared with precipitation. The isotopic differences between river waters and precipitation were utilized to determine river recharge elevations and water transit time. The methods presented here can be used to explore hydrological interactions in other tropical river basins.     

海相碳酸盐岩碳同位素地层学研究中存在的问题及建议——以二叠系研究为例

以二叠系碳同位素地层学研究为例,在有条件控制的实验模拟基础上发现：1）采集到的地质样品一般都是不同碳酸盐矿物的混合样品,这些不同碳酸盐矿物具有不同的碳氧同位素比值（δ13C和δ18O）;2）自然露头和采石场剖面样品的无机碳氧稳定同位素组成会在可预见的时间内发生足以影响研究结果的淋滤交代作用;3）利用地层中碳酸盐样品的δ...     

原油中硫代金刚烷的分析鉴定和地球化学应用

硫代金刚烷在原油中普遍存在,其独特的分子结构和形成过程使其在石油工业中具有广泛应用。对目前在硫代金刚烷分析鉴别、成因机制、热稳定性和在油气领域应用等方面的研究进展及存在问题进行了系统总结。结果表明:目前原油中硫代金刚烷主要包括烃源岩生烃演化和热化学硫酸盐还原(TSR)作用两种成因机制,其中烃源岩生烃演化可形成原油中初始含量的硫代金刚烷,TSR作用可进一步生成大量的硫代金刚烷;硫代金刚烷的笼数越高热稳定性越高,在高成熟时可以发生热裂解作用;硫代金刚烷随TSR作用增强而不断富集,是TSR作用可靠的分子标志物;硫代金刚烷的δ^34S值通过TSR作用来改变,能够反映TSR作用的成因类型;在未遭受TSR作用的前提下,原油中硫代金刚烷的初始含量和δ^34S值代表着原始烃源岩的特征,可以应用于原油族群的划分。从目前的研究现状来看,硫代金刚烷的具体成因机制和详细的热稳定性界限还不甚明确;应用硫代金刚烷的含量来判识TSR作用时,要结合硫同位素和其他指标参数等结果才最为可靠;硫代金刚烷目前主要应用于TSR作用判识研究,在油-油对比和油-源对比方面的研究尚待进一步加强。     

Sources and distribution of particulate organic carbon in Great Wall Cove and Ardley Cove,King George Island,West Antarctica

Concentrations of chlorophyll-a (Chl-a), particulate organic carbon (POC) and its stable carbon isotope composition (δ13C) were analyzed to investigate the biogeochemical characteristics and sources of...     

广西桂林杨堤晚泥盆世弗拉期-法门期之交上、下 Kellwasser事件的差异与海洋生产力变化

对广西桂林晚泥盆世弗拉期-法门期(Frasnian-Famennian,简称F-F)之交杨堤剖面的碳酸盐岩碳同位素、生物成因 Ba、Al、Si和氧化还原指标的综合分析,表明该地区F-F之交生产力较低,且两次Kellwasser事件具有不同特点:下Kellwasser (LKW)事件时期并未出现明显缺氧环境,生态系统中初级生产力和最终生产力均相对较高,δ13C小幅度正偏是由生产力上升 引起;上Kellwasser(UKW)事件时期海平面上升,陆源输入物极少,氧含量急剧下降,初级生产力有所增加,最终生产力锐减, 此时的δ13C大幅正偏是由于缺氧条件下有机碳缓慢积累埋藏保存所致.