Contrasting hydrography and phytoplankton distribution in the upper layers of cyclonic eddies in the Mozambique Basin and Mozambique Channel

Hydrographic data collected in cyclonic eddies in the Mozambique Channel and Basin revealed notable differences in temperature and salinity at a depth of 100 m, the upper mixed layer, the nitracline depths, and vertical distribution of chlorophyll-a (Chl-a). Differences in temperature and salinity did not show any consistent patterns. In contrast, the differences in the upper mixed layer, nitracline depths and the vertical Chl-a profile appeared to be driven by combined effects of eddy dynamics (i.e. shoaling of isopleths) and the seasonal variation in light availability and mixing conditions in the upper layers. Cyclonic eddies studied during austral spring and summer in the Mozambique Channel exhibited shallower upper mixed layers and nitracline depths, and deeper euphotic zones. Distinct subsurface Chl-a maxima (SCM) were associated with the stratified conditions in the upper layers of these eddies. In contrast, a cyclonic eddy studied during mid-austral winter in the Mozambique Basin had a shallower euphotic zone, deeper upper mixed layer and uniform Chl-a profiles. Another eddy sampled in the Mozambique Basin toward the end of winter showed a less pronounced SCM and roughly equal euphotic zone and upper mixed layer depths, suggestive of a transition from a well-mixed upper layer during winter to stratified conditions in summer.     

Geochemical evolution during the cracking of crude oil into gas under different pressure systems

Two comparative simulation experiments(a normal atmospheric-pressure opening system and a 20 MPa closed system)were conducted to study the geochemical evolution of n-alkane,sterane,and terpane biomarkers in the process of oil cracking into gas under different pressures.With an initial experimental temperature set at 300°C,the temperature was increased to 650°C at a heating rate of 30°C/h.The products were tested every 50°C starting at 300°C,and a pressure of 20 MPa was achieved using a water column.The low-maturity crude oil sample was from the Paleogene system in the Dongying sag in eastern China.The threshold temperature obtained for the primary oil cracking process in both pressure systems was 450°C.Before the oil was cracked into gas,some components,including macromolecular n-alkanes,were cracked into medium-or small-sized n-alkanes.The secondary oil cracking of heavy hydrocarbon gases of C2–5to methane mainly occurred between 550°C to 650°C,and the parameters Ln(C1/C2)and Ln(C1/C3),as well as the dry coefficients,increased.Overpressure inhibited the oil cracking process.In the 20 MPa system,the oil conversion rate decreased,the temperature threshold for gas generation rose,and oil cracking was inhibited.Compared with the normal pressure system,high-carbon n-alkanes and other compounds in the 20 MPa pressure system were reserved.Furthermore,the parameters∑C21-/∑22+,Ln(C1/C2),and Ln(C1/C3),as well as the dry coefficients,decreased within the main temperature range.During secondary oil cracking(550°C to 600°C),the Ph/nC18and Pr/nC17decreased.High pressure influenced the evolution of the biomarkers Ts and Tm,C31homohopane,C29sterane,and their related maturity parameters to different extents during oil cracking under different temperature ranges.     

羌塘盆地上三叠统土门格拉组烃源岩生物标志物地球化学特征

首次对羌塘盆地上三叠统土门格拉组烃源岩生物标志化合物特征进行了研究,揭示了生物标志化合物对该地区有机质生源构成、沉积环境和成熟度的指示意义。研究结果表明：土门格拉组烃源岩中的有机母质为混合来源,既有陆生植物来源,又有低等水生生物来源,烃源岩的沉积环境为具有一定盐度的还原环境。烃源岩成熟度参数显示,土门格拉组烃源岩有机质演化程度已达到高成熟阶段。生物标志化合物的这些特征进一步证实了土门格拉组烃源岩具有较好的生烃潜力。     

太湖浮游藻类的后向散射分离及其叶绿素a浓度反演

浮游藻类的后向散射是水体光谱构成的重要组成部分,作为水体辐射传输模型中的重要参数,高精度的藻类后向散射系数对水体叶绿素a浓度的遥感反演精度至关重要。本文以简化的辐射传输模型-生物光学模型为基础,尝试性分离了太湖浮游藻类的后向散射系数。通过藻类后向散射规律分析,建立了浮游藻类吸收、后向散射特征的叶绿素a反演模型,改善了叶绿素a浓度的遥感反演精度。分析表明：藻类颗粒物的后向散射系数与吸收系数之间存在反比关系,且在560 nm、700 nm附近存在明显的散射峰,与叶绿素a浓度之间相关性显著;低密度藻类水体总悬浮颗粒的后向散射以非色素颗粒为主导,适合采用经典的指数模型模拟后向散射系数,而藻类密度较高的富营养化水体,水体总悬浮颗粒的后向散射以藻类颗粒为主导,传统的指数模型已不适用;采用分离藻类后向散射系数的方法,使得叶绿素a浓度的反演值与真实值相关系数从0.66提高到0.98,相对误差从55%降低到38%,均方根误差(RMSE)也由60.95 μg/L降低至13.98 μg/L。其真实性检验表明,与经典指数模型方法相比,利用藻类颗粒后向散射分离方法反演叶绿素a浓度,能够显著改善反演精度。     

甘肃侏罗纪植物化石Ginkgo huttonii角质层地球化学特征

对甘肃民和盆地侏罗纪植物化石Ginkgo huttonii(Sternb．)Heer的角质层与现生银杏Ginkgo biloba的角质层进行了地球化学特征对比分析,结果表明植物化石角质层有机物特征符合石油形成中沥青的演化特点。通过有机物组分含量分析,它们相当于中国中、新生代油源岩有机质类型中的腐泥型一腐殖腐泥型。对烃组分三角图进行投点,落入Ⅱ型干酪根范围内。通过有机质中的一些指标分析,发现Ginkgo huttonii的角质层处于低成熟阶段,与煤中显微组分角质体的成烃模式基本一致。另外,角质层的可溶有机质分布特征表明,植物化石角质层对陆相高蜡原油的形成有一定的作用,证明高等植物对蜡质有贡献。当前研究及古植物学资料表明,银杏是一种有利于煤成油的植物。     

海洋中型浮游动物的选择性摄食对浮游植物群落的控制

海洋中型浮游动物的选择性摄食很大程度上影响着浮游植物种群的变化,控制着海洋初级生产力的节律、规模和归宿。从海洋中型浮游动物选择性摄食对有害藻华的控制、中型浮游动物的选择性摄食机制、中型浮游动物选择性摄食的研究方法和中型浮游动物的选择性摄食模型四个方面探讨了中型浮游动物选择性摄食对控制浮游植物种群演替的贡献,为进一步预测和控制有害藻华发生提供科学依据。     

三角褐指藻及其藻际细菌对不同无机氮源的响应

海洋生态系统中,浮游植物和细菌之间的相互作用是影响营养盐供应和再生、海洋初级生产力和生物地球化学循环的基本生态关系.为研究营养盐、浮游植物和细菌之间的关系,在实验室内培养条件下,通过改变氮源的形态(硝态氮和铵态氮)和浓度,研究海洋浮游植物三角褐指藻(Phaeodactylum tricornutum)的藻际细菌在不同营...     

Planktonic stages of Maurolicus muelleri (Teleostei Sternoptychidae) in New Zealand waters

The seasonality and distribution, abundance, and hydrological affinities of the planktonic stages of the sternoptychid Maurolicus muelleri (Grnelin, 1788) are described for the New Zealand region. Spawning occurred from August to March, and the planktonic stages were widespread around New Zealand. Spawning probably takes place around midday at depths greater than 250 m. Eggs and larval stages were present over temperature ranges of 9.0–15.5°c and 13–22°c respectively.     

Role of mean circulation,tides, and waves in the transport of bottom sediment on the New Zealand continental shelf

Evaluation of velocity data on water movements over the New Zealand continental shelf has revealed that the mean circulation by itself is too slow to induce transport of bottom sediments. Tides generally have higher velocities, but are still not the main transporting agent except in the tide‐dominated Cook and Foveaux. Straits. Waves have the potential to stir sediments on the inner and middle shelf (less than about 70 m deep) during annual storms, and probably down to 130 m depth during the maximum 25‐y storm.

For sediment transport to take place, energies of at least two of the major water movements would have to complement one another. Optimum conditions for transport probably occur during storm periods when wave‐suspended sediment is readily moved by tides and the mean circulation.

The direction of transport is mainly along the continental shelf and is largely in response to prevailing weather patterns coincident with the direction of the mean circulation and strongly reinforced by the appropriate phase of the tide.     

Variations in silicate concentration affecting photosynthetic carbon fixation by spring phytoplankton assemblages in surface water of the Strait of Malacca

The Strait of Malacca (SoM), the world’s busiest sea-route, is increasingly polluted as the rapid development of world trades, affecting phytoplankton primary productivity therein. The variations of surface phytoplankton biomass, size-structure and carbon fixation were investigated across the SoM during the spring period (May 4 to 9, 2011). Chlorophyll a concentration increased from 0.12 μg/L at the northwest entrance of the SoM to a maximal 0.63 μg/L at narrowest section, and decreased to 0.10 μg/L at the southeast entrance. Photosynthetic carbon fixation by phytoplankton coincided well with Chl a biomass, and increased from 10.8 to 22.3 μg C/(L d), then decreased to 9.21 μg C/(L d); while the carbon fixation rate showed an inverse pattern to the changes of Chl a, and decreased from 87.1 to 35.5 μg C/(μg Chl a d) and increased thereafter to 95.3 μg C/(μg Chla·d). Picophytoplankton cells (<3 μm) contributed to more than 60% and 50% of the total Chl a and carbon fixation at both the entry waters; while the contributions of pico-cells decreased sharply to the minimum of 18.3% and 27.5% at the narrowest part of the SoM. In particular, our results showed that the silicate concentration positively regulated Chl a biomass and carbon fixation, reflecting that the higher silicate favoured the growth of phytoplankton and thus led to higher primary production in this strait.