Bacterioplankton responses to iron enrichment during the SAGE experiment

We studied the microbial food web in the upper 100 m of the water column in iron-limited sub-Antarctic HNLC waters south-east of New Zealand in the SAGE experiment in 2004, with focus on bacterioplankton. Samples were collected daily from inside and outside the iron enriched patch. Short term enrichment experiments were conducted on board in 4 L polycarbonate bottles with water outside the iron enriched patch to study single and combined effects of micronutrient additions on microbial food web. Low bacterial growth was recorded in the study area with community turnover times of 50 h or more during the study period. Measurements of bacterial standing stocks and production rates in the study show minor responses to the large scale iron enrichment, with increase in rates and stocks after the first enrichment and at the end of the study period after the third iron enrichment when solar radiation increased and wind mixing decreased. The average daily bacterial production rates were 31.5 and 33.7 mgCm⁻² d⁻¹ for the OUT and IN stations, respectively; thus overall there was not a significant difference between the control and the iron-enriched patch. In the bottle experiments bacterial thymidine incorporation showed responses to single iron and silicic acid enrichments and a major growth response to the combined iron and sucrose enrichments. Phytoplankton chlorophyll-a showed clear stimulation by single additions of iron and silicic acid and silicic acid enhanced the iron impact. Cobalt additions had no effect on bacteria growth and a negative effect on phytoplankton growth. Low bacterial in situ growth rates and the enrichment experiments suggest that bacteria are co-limited by iron and carbon, and that bacterial iron uptake is dependent on carbon supply by the food web. With the high iron quota (??mol Fe mol C⁻¹) bacteria may scavenge considerable amounts of the excess iron, and thus influence the relative importance of the microbial food web as a carbon sink.     

The response of phytoplankton to iron enrichment in Sub-Antarctic HNLCLSi waters: Results from the SAGE experiment

Areas of high nutrients and low chlorophyll a comprise nearly a third of the world’s oceans, including the equatorial Pacific, the Southern Ocean and the Sub-Arctic Pacific. The SOLAS Sea-Air Gas Exchange (SAGE) experiment was conducted in late summer, 2004, off the east coast of the South Island of New Zealand. The objective was to assess the response of phytoplankton in waters with low iron and silicic acid concentrations to iron enrichment. We monitored the quantum yield of photochemistry (F_v/F_m) with pulse amplitude modulated fluorometry, chlorophyll a, primary productivity, and taxonomic composition. Measurements of F_v/F_m indicated that the phytoplankton within the amended patch were relieved from iron stress (F_v/F_m approached 0.65). Although there was no significant difference between IN and OUT stations at points during the experiment, the eventual enhancement in chlorophyll a and primary productivity was twofold by the end of the 15-day patch occupation. However, no change in particulate carbon or nitrogen pools was detected. Enhancement in primary productivity and chlorophyll a were approximately equal for all phytoplankton size classes, resulting in a stable phytoplankton size distribution. Initial seed stocks of diatoms were extremely low, <1% of the assemblage based on HPLC pigment analysis, and did not respond to iron enrichment. The most dominant groups before and after iron enrichment were type 8 haptophytes and prasinophytes that were associated with ∼75% of chlorophyll a. Twofold enhancement of biomass estimated by flow cytometry was detected only in eukaryotic picoplankton, likely prasinophytes, type 8 haptophytes and/or pelagophytes. These results suggest that factors other than iron, such as silicic acid, light or physical disturbance limited the phytoplankton assemblage during the SAGE experiment. Furthermore, these results suggest that additional iron supply to the Sub-Antarctic under similar seasonal conditions and seed stock will most likely favor phytoplankton <2 ??m. This implies that any iron-mediated gain of fixed carbon will most likely be remineralized in shallow water rather than sink and be sequestered in the deep ocean.     

背景误差水平相关结构对四维变分资料同化的影响研究

为考察GRAPES全球四维变分同化（4DVar）的分析增量在谱空间的时间演变特征,分析当同化时间窗起始时刻与终止时刻背景误差水平相关特征明显不一致时对分析与预报造成的影响,对GRAPES全球4DVar的背景误差水平相关采用二阶自回归模型（SOAR）、集合资料同化生成扰动样本估计的水平相关模型以及基于这两者的背景误差谱空间融合模型进行比较。结果表明,SOAR的分析增量在20波以上的天气尺度波动的分析信息明显不足,而将集合资料同化样本所计算的水平相关的功率谱方差与SOAR功率谱方差进行融合,水平相关特征呈现出多尺度水平相关的特点,可以更好地吸纳观测信息,显著改善北半球形势场、温度与风场预报效果,南半球也有改善,对赤道地区的影响中性。表明研究发展的融合水平相关方案合理、实用。      

集合预报误差在GRAPES全球四维变分同化中的应用研究Ⅰ：局地化方案设计与动力平衡特征分析

通过引入流依赖的集合预报误差,使得同化分析与天气形势紧密相关,是改善初值分析质量的重要途径。文中在GRAPES（Global Regional Assimilation and PrEdiction System）全球四维变分资料同化（4DVar）中研究了如何有效应用集合预报误差,包括增加扩展控制变量时如何降低其计算消耗以及如何在局地化过程中保持不同变量之间的动力平衡。利用高斯分布的谱滤波实现水平局地化,利用垂直正交经验函数分解实现垂直局地化,并采用前8个主导特征模态来限制控制变量空间维数增加。引入20至180个集合样本,在水平二维局地化情形下,控制变量总数的增长可以限制在1.1—1.8倍,而在三维局地化情形下,控制变量总数的增长限制在1.7—7.1倍。对60个集合样本和1°水平分辨率内循环,4DVar引入扩展控制变量后墙钟时间增加了约30%。进一步,通过采用在非平衡分析变量上进行水平局地化,然后再将风压地转平衡关系重新叠加到非平衡分析变量上,使得分析更好地保持了风压平衡关系,初始场地面气压倾向变化减小。此外,虽然垂直局地化对分析平衡影响较大,但依靠目标函数中的数字滤波弱约束,分析变量之间仍能较好满足动力平衡关系。结果表明,GRAPES全球4DVar中发展的增加扩展控制变量、谱滤波实现水平局地化、非平衡分析变量进行水平局地化等有效应用集合预报误差的方法,适合集合样本数超过100个的情况,在分析质量改善的同时,4DVar系统的计算和存储消耗没有显著增加。      

Cipher, A Polarimeter Telescope Concept for Hard X-Ray Astronomy

The polarisation of astrophysical source emission in the energy range from a few tens of keV up to the MeV region is an almost unexplored field of high-energy astrophysics. Till date, polarimetry in astrophysics–in the energy domain from hard X-rays up to soft γ-rays–has not been pursued due to the difficulties involved in obtaining sufficient sensitivity. Indeed for those few instruments that are capable of performing this type of measurement (e.g. the COMPTEL instrument on the Compton Gamma-ray Observatory and the IBIS instrument on INTEGRAL), polarimetry itself plays a secondary role in the mission objectives, as the efficiencies (0.5% and 10% maximum, respectively) and polarimetric Q factors (0.1 and 0.3, respectively) are relatively limited. In order to perform efficient polarimetric measurements for hard X-ray and soft gamma-ray sources, with an instrument of relatively robust and simple design, a CdTe based telescope (CIPHER: Coded Imager and Polarimeter for High Energy Radiation) is under study. This instrument is based on a thick (10 mm) CdTe position-sensitive spectrometer comprising four modules of 32 × 32 individual pixels, each with a surface area of 2 × 2 mm² (about 160 cm² total detection area). The polarimetric performance and design optimisation of the CIPHER detection surface have been studied by use of a Monte Carlo code. This detector, due to its intrinsic geometry, can allow efficient polarimetric measurements to be made between 100 keV and 1 MeV. In order to predict the polarimetric performance and to optimise the design and concept of the CIPHER detection plane, a Monte Carlo code based on GEANT4 library modules was developed to simulate the detector behaviour under a polarised photon flux. The Compton double event efficiency, as well bi-dimensional double event distribution maps and the corresponding polarimetric modulation factor will be presented and discussed. Modulation Q factors better than 0.50 and double event total efficiencies greater than 10% were calculated in the energy range between 100 keV and 1 MeV. Herein we will present and discuss the general problems that affect polarimetric measurements in space, such as the inclination of the source with respect to the telescope optical axis and background radiation. Q factor calculations for several beam inclinations as well as for background together with simulated astronomical sources will be presented and discussed.     

Experimental investigation of bedload transport processes under unsteady flow conditions

Hydraulic engineering is usually based on theoretical analysis and/or numerical modelling simulation. As the dynamic behaviour of sediment movement under unsteady flow is still unclear, and field measurement is comparatively difficult during a large flood, prior investigations through flume experiments are required. A series of flume experiments, conducted using different inflow hydrographs without sediment supply from upstream, was carried out to investigate the sediment transport process under unsteady flow conditions. A series of triangular hydrographs were performed in the experiments. The results indicate that a temporal lag was found between the flow hydrograph peak and the sediment hydrograph peak because large size sand dunes lasted for a short period in the falling limb of the flow hydrograph. The temporal lag was found to be about equal to 6–15% of the flow hydrograph duration. Owing to the temporal lag, the total bedload yield in the rising period was less than that in the falling period. Furthermore, the measured total bedload yield in the unsteady flow experiments was larger than the predicted value, which was estimated by using the results obtained from the equivalent steady flow experiment. The peak bedload transport rate for unsteady flow conditions was also larger than the predicted value. The ratios of the measured to the predicted quantities mentioned above were found to be constant values for different shapes of hydrographs. It is, therefore, expected that the analytical results of sediment transport from equivalent steady flow can be a good reference for sediment transport under unsteady flow conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

GM(1,1)预测效果数值试验

采用不同类型原始数据对传统GM(1，1)进行了预测效果数值试验，然后通过对预测结果及传统GM(1，1)基本思想进行深入分析提出传统GM(1，1)存在的问题，并提出了相应的改进思路。     

冻土斜坡模型试验相似分析

南水北调工程、青藏铁路建设工程等一系列工程的实施,将进一步影响和加剧青藏高原多年冻土区斜坡稳定性问题,冻土区边坡开挖及斜坡稳定性是工程活动中必须解决的问题之一,冻土斜坡稳定性研究在国内尚属空白。通过相似模型试验对高原多年冻土区斜坡在自然和人类活动影响下的失稳机制和活动规律进行分析,是开展研究的重要手段。根据相似理论第一定律,对冻土斜坡模型试验进行了相似分析,应用积分类比法推导并建立了冻土斜坡模型试验的相似指标和相似判据,得出在用原状土作模型介质时,6个相似常数减少为2个相似常数,即cτ和cl。模型与原型的时间比例尺是由几何比例尺决定的,即cτ=c2l,仅有一个相似参数为自变量,另一个为因变量。据此对青藏高原多年冻土区青藏公路沿线K3035处冻土斜坡进行了相似模型设计和冻融模型试验。模型再现了K3035处7°斜坡在4个冻融循环条件下,坡体中部(水平、垂向)4#位移伸张计质点位移曲线随时间的变化特征。实验表明,斜坡土体中部在第一次冻融循环中已有滑动迹象,随着滑坎进一步后退和靠近观测基准点,必然出现一次较大的位移,直至周边土体出现滑塌为止。模型试验结果与现场观测资料相比较是令人满意的。     

Hydrocarbon Generation Characteristics of Source Rocks from Different Saline Environments in the Dongpu Depression,Bohai Bay Basin,China

The Dongpu Depression is a secondary salt-bearing tectonic unit in the Bohai Bay Basin, eastern China. The depositional environment of this depression regarding its Paleogene strata is clearly different in plane, including the saltwater environment(SE) in the north, the freshwater environment(FE) in the south and the brackish water environment(BE) in the middle. The result of oil and gas exploration in the Dongpu Depression shows that more than 90% of the proven oil reserves are distributed in the northern saltwater environment. Previous studies indicate that the organic geochemistry characteristics and the hydrocarbon generation capacity of the source rocks are very clearly diverse under different environments, which results in the significant differences in the proved reserves between the north and the south. In order to further explore the differences in the hydrocarbon generation capacity of the source rocks under distinct depositional environments and the mechanism of their occurrence, three samples from different depositional environments(W18-5 for SE, H7-18 for BE, CH9 for FE) were used for confined gold tube pyrolysis experiments. The results show that the CH4 yields of W18-5, H7-18 and CH9 increase with increasing temperature, the maximum yields being 405.62 mg/g TOC, 388.56 mg/g TOC and 367.89 mg/g TOC, respectively. The liquid hydrocarbon yields of W18-5, H7-18 and CH9 firstly increase with increasing temperature and then decrease after the critical temperatures. The maximum yields of C6-14 are 149.54 mg/g TOC, 140.18 mg/g TOC and 116.94 mg/g TOC, the maximum yields of C14+ being 852.4 mg/g TOC, 652.6 mg/g TOC and 596.41 mg/g TOC, respectively for W18-5, H7-18 and CH9. To summarize, the order of hydrocarbon potential from high to low is W18-5, H7-18 and CH9. On this basis, through analyzing the influencing factors of hydrocarbon differences, this paper reveals that the saltwater environment is characterized by 4 factors: higher salinity, halophilic algae, high paleo-productivity and a strongly reducing environment, which are beneficial to the enrichment of organic matter and lead to the formation of high levels of sapropelite and exinite. According to the variation of oil and gas components in the pyrolysis experiments, the hydrocarbon generation process is divided into three stages: kerogen cracking, oil cracking and C2-5 cracking. Combined with hydrocarbon generation characteristics and stages, the evolutionary model of hydrocarbon generation for source rocks under different environments is established.     

Architectures and evolution of arid alluvial fans: Insights from a flume experiment

Using time-lapse cameras and a 3D laser scanner,74 groups of geomorphic data of alluvial fans were obtained through flume experiments. Then a detailed sedimentary analysis based on these data was performed by using a quantitative software to reveal the sedimentary evolution process of the arid alluvial fan and its depositional architecture. Results suggest that there are obvious differences in hydrodynamics,water flow patterns and growth pattern during the evolution of arid alluvial fans. Based on these differences,the experiment is divided into three stages,including an early,middle,and late stage. In the early stage,the fan surface hydrodynamics was relatively strong,and the sheet flow dominated the deposition. According to the distribution of sheet flow deposits,it can be divided into wide-spread sheet flow deposition and local sheet flow deposition. In the middle period of the experiment,the hydrodynamic strength and expansion rate at the middle-distal part of the fan body reduced. The non-confined channel which is close to the source dominated the deposition,and terminal lobe was mainly deposited on the edge of the river channel. In the late stage of the experiment,the hydrodynamic further reduced causing by the large fan surface and confined channels were the main deposits. Through the flume experiment,an arid alluvial fan depositional architecture model with a three-layer structure has been established. The bottom layer is of a sheet flow lobe complex,the middle layer is characterized by unconfined channels and terminal lobes,and the top layer is constituted by stacked confined channels and small terminal lobes.