Atmospheric CO2 measurements and error analysis on seasonal air–sea CO2 fluxes in the Bay of Biscay

Atmospheric molar fraction of CO₂ (xCO₂^atm) measurements obtained on board of ships of opportunity are used to parameterize the seasonal cycle of atmospheric xCO₂ (xCO₂^atm) in three regions of the eastern North Atlantic (Galician and French offshore and Bay of Biscay). Three selection criteria are established to eliminate spurious values and identify xCO₂^atm data representative of atmospheric background values. The filtered data set is fitted to seasonal curve, consisting of an annual trend plus a seasonal cycle. Although the fitted curves are consistent with the seasonal evolution of xCO₂^atm data series from land meteorological stations, only ship-board measurements can report the presence of winter xCO₂^atm minimum on Bay of Biscay. Weekly air–sea CO₂ flux differences (mmol C·m^− 2 day^− 1) produced by the several options of xCO₂^atm usually used (ship-board measurements, data from land meteorological stations and annually averaged values) were calculated in Bay of Biscay throughout 2003. Flux error using fitted seasonal curve relative to on board measurements was minimal, whereas land stations and annual means yielded random (− 0.2 ± 0.3 mmol C·m^− 2·day^− 1) and systematic (− 0.1 ± 0.4 mmol C·m^− 2 day^− 1), respectively. The effect of different available sources of sea level pressure, wind speed and transfer velocity were also evaluated. Wind speed and transfer velocity parameters are found as the most critical choice in the estimate of CO₂ fluxes reaching a flux uncertainty of 7 mmol C·m^− 2·day^− 1 during springtime. The atmospheric pressure shows a notable relative effect during summertime although its influence is quantitatively slight on annual scale (0.3 ± 0.2 mmol C·m^− 2·day^− 1). All results confirms the role of the Bay of Biscay as CO₂ sink for the 2003 with an annual mean CO₂ flux around − 5 ± 5 mmol C m^− 2 day^− 1.     

Suspended sediment and erosion dynamics in Kugmallit Bay and Beaufort Sea during ice-free conditions

The Mackenzie River is the largest river on the North American side of the Arctic and its huge freshwater and sediment load impacts the Canadian Beaufort Shelf. Huge quantities of sediment and associated organic carbon are transported in the Mackenzie plume into the interior of the Arctic Ocean mainly during the freshet (May to September). Changing climate scenarios portend increased coastal erosion and resuspension that lead to altered river-shelf-slope particle budgets. We measured sedimentation rates, suspended particulate matter (SPM), particle size and settling rates during ice-free conditions in Kugmallit Bay (3–5 m depth). Additionally, measurements of erosion rate, critical shear stress, particle size distribution and resuspension threshold of bottom sediments were examined at four regionally contrasting sites (33–523 m depth) on the Canadian Beaufort Shelf using a new method for assessing sediment erosion. Wind induced resuspension was evidenced by a strong relationship between SPM and wind speed in Kugmallit Bay. Deployment of sediment traps showed decreasing sedimentation rates at sites along an inshore–offshore transect ranging from 5400 to 3700 g m^− 2 day^− 1. Particle settling rates and size distributions measured using a Perspex settling chamber showed strong relationships between equivalent spherical diameter (ESD) and particle settling rates (r² = 0.91). Mean settling rates were 0.72 cm s^− 1 with corresponding ESD values of 0.9 mm. Undisturbed sediment cores were exposed to shear stress in an attempt to compare differences in sediment stability across the shelf during September to October 2003. Shear was generated by vertically oscillating a perforated disc at controlled frequencies corresponding to calibrated shear velocity using a piston grid erosion device. Critical (Type I) erosion thresholds (u) varied between 1.1 and 1.3 cm s^− 1 with no obvious differences in location. Sediments at the deepest site Amundsen Gulf displayed the highest erosion rates (22–54 g m^− 2 min^− 1) with resuspended particle sizes ranging from 100 to 930 µm for all sites. There was no indication of biotic influence on sediment stability, although our cores did not display a fluff layer of unconsolidated sediment. Concurrent studies in the delta and shelf region suggest the importance of a nepheloid layer which transports suspended particles to the slope. Continuous cycles of resuspension, deposition, and horizontal advection may intensify with reduction of sea ice in this region. Our measurements coupled with studies of circulation and cross-shelf exchange allow parameterization and modeling of particle dynamics and carbon fluxes under various climate change scenarios.     

东京都市圈轨道交通发展及其启示

研究东京都市圈发展历程、相应各阶段轨道交通发展特征及其相互关系,对揭示轨道交通在都市圈形成与发展具有重要作用。     

杭州湾跨海大桥钢管桩拔除施工技术

结合杭州湾跨海大桥北航道桥大型临时工程钢管桩拔除施工实践,对海上桥梁工程临时钢管桩拔除施工工艺、施工方案及设备选择等进行总结,为海上桥梁工程临时钢管桩的拔除提供了宝贵的施工经验。     

基于FVCOM的象山港海域潮汐潮流与温盐结构特征数值模拟

基于有限体积法的FVCOM模型,建立了象山港海域的三维潮汐潮流和温盐数值模型,计算中考虑了潮流、风、太阳辐射和径流因素的影响。模拟结果与2009年的监测资料进行了对比验证,结果表明建立的模型可以模拟该海域的水流运动和温盐分布特征。通过对数值结果分析得到了该海域的同潮图、潮流椭圆图、潮流性质和温盐分布等。结果表明,象山港的潮汐属于非正规半日浅海潮;M2分潮流椭圆长轴从口门到湾顶逐渐减小,其走向与岸线的方向基本一致;狭湾内呈现往复流特征而口门外开阔海域呈旋转流特征。湾口和湾顶部有着显著的温度差和盐度差,海水温度由湾口向湾顶部逐渐增大,盐度分布则正好相反。狭湾内距离湾口不同位置的横向温度、盐度垂向分布结构特征各不相同。     

苏州市公共交通优先通行技术及策略研究

苏州市正面临着出行向机动化方式转变的关键时期,公交优先作为缓解城市拥堵的重要策略,是苏州城市可持续发展的重要保障。文章首先分析了优先发展公共交通对苏州的重要意义,阐述了苏州公交发展所面一陆的挑战,接着探讨了如何从规划、政策、服务、管理和具体技术措施如公交专用道的车道位置选择、公交专用道的隔离方式与交通标志设置、公交专用道的停靠站设置形式等几方面保障公交优先发展。文章最后提出了苏州优先发展公共交通的几点建议。     

东京轨道交通发展的特点和启示

轨道交通作为城市交通系统中的重要组成部分,在城市的社会活动、经济活动中发挥着举足轻重的作用。以东京轨道交通系统为对象,分析其轨道交通系统的组成部分,阐述东京轨道交通网络的发展历程。并结合太原市实际情况,总结东京轨道交通发展特点和启示,希望对我国城市轨道交通系统的建设研究有所借鉴。     

Navigating Institutional Constraints in the Process of Computational Environmental Modeling

Abstract

The use of computational models has proliferated in the last few decades due to the practical benefits that they offer in terms of understanding complex systems. However, the process of developing a computational model is not only shaped by scientific and practical concerns. Modelers must also navigate the institutional structures in which the models are constructed and implemented. In the process, they must often draw upon existing or create new social relationships that can, themselves, alter the institutional structures they are attempting to navigate. In this article, I use an ethnographic approach to examine three examples in which the process of building and implementing a computational model was constrained by institutional factors and the strategies the modelers used to navigate them. The research was conducted with computational modelers at the Chesapeake Bay Program who are involved in constructing the Chesapeake Bay modeling system for nutrient management in the watershed. Modelers in this context had to: build relationships with the broader scientific community to reinforce the “believability” of the model, draw upon institutional relationships in order to work around limitations on data-sharing between organizations, and manage differing incentive structures to motivate and coordinate the research needed to complete the model     

加利福尼亚州车辆合乘系统运行效果

为了解加利福尼亚州HOV系统的运行效果,基于交通量检测器收集的数据,对HOV系统进行全面分析、评价。最终得到4个主要结论：1）与多条普通车道构成的高速公路相比,包含1条HOV车道的高速公路损失了20%的通行能力;2）HOV车道通常处于两种运行状态,一种是HOV车道未被充分利用,另一种是HOV车道处于超负荷、降级运行状态;3）HOV车道未显著提高小汽车合乘比例;4）在一个相当出色的交通管理系统中,HOV车道并未从整体上缓解道路交通拥堵状况。     

胶州湾海底隧道综合超前地质预报技术研究与实践

本文以胶州湾海底隧道为例,研究了超前地质预报中经常采用的预报手段,并概括了国内的综合超前预报研究现状,提出了综合超前地质预报的概念,指出了其优缺点和适用性。针对三线海底隧道,提出了具体的综合超前地质预报流程。运用本文所提出的三线海底隧道综合超前预报方法对胶州湾海底隧道的服务隧道和左线主隧道进行了多次综合超前地质预报,预报效果良好,工程进展顺利,取得了良好的经济效益。