Environmental controls on branched tetraether lipid distributions in tropical East African lake sediments

Quantifying past continental temperature changes is an important aspect of paleoclimate research as it allows us to constrain the amplitude of natural variability, test predictive climate models, and provide a proper context for changes that may arise in response to anthropogenically-induced climate change. The recently developed biomarker-based methylation index of branched tetraethers/cyclization ratio of branched tetraethers (MBT/CBT) proxy shows potential as a new method for continental temperature reconstruction, but thus far it has only been applied successfully in ocean margin sediments. To assess whether this proxy is also applicable to the sedimentary record in tropical lacustrine systems, we investigated the distribution of branched glycerol dialkyl glycerol tetraethers (GDGTs) in recently deposited sediments from 46 lakes in tropical East Africa. These lakes span a substantial range in surface elevation (770-4500 m above sea level), and thus also a wide gradient of mean annual temperature. We find that, saline lakes excepted, branched GDGTs are universally abundant in the lakes investigated and can be used to predict mean annual air temperature (MAAT) with a high degree of accuracy. However, the existing global MBT/CBT calibration for MAAT based on soils predicts inaccurate temperatures when applied to our African lake dataset. This observation, together with the fact that surface water pH, and to lesser extent, lake depth appear to influence the distribution of branched GDGTs among sites, leads us to conclude that in situ production of branched GDGTs in lakes is likely. The robust relationship between branched GDGT distribution and the temperature and pH of African freshwater lakes makes these compounds suitable for paleoenvironmental reconstruction, however we urge caution in using branched GDGTs in lake sediments to infer past temperatures, unless their exact origin can be determined.     

热带气旋运动的动力学研究进展

热带气旋运动是由各种形式的外部强迫、内部过程及其相互作用所决定的。特别是环境气流与气旋环流以及β效应之间的相互作用可以产生次级的非对称气流,使热带气旋偏离大尺度环境气流的引导。这种偏差,被称为广义的β漂移。本文讨论了控制β漂移的物理因子和物理过程,尤其是涡旋结构与环境气流切变对它的影响,以及β漂移在热带气旋路径预报上的应用。另外,还总结了双台风相互作用、热带气旋摆动和与下垫面强迫有关的物理过程的影响。     

Identifying Optimum Locations for Tropical Testing of United States Army Materiel and Systems

This paper is an example of applied military geography focusing on a particular problem arising from the Panama Canal Treaty of 1977. One of the provisions of the treaty required the United States (US) military to completely withdraw from and relinquish its military and government facilities to the Republic of Panama prior to midnight on 31 December 1999. In so doing, the US army turned over to the Panama government all of its military bases, some of which had been used since World War I to test materiel, equipment and systems within a tropical environment. Given its global mission and responsibilities, the US army has a well‐established practice of testing its materiel, equipment and systems throughout the entire range of potential operating environments. The US experience in the Pacific in World War II and in Southeast Asia during the Vietnam War clearly demonstrated the need to test the performance of new equipment under the harsh conditions found in tropical jungles. Furthermore, since 1960, nearly 75 per cent of all international and internal armed conflicts have been in countries that are totally or partially in the tropics. This paper presents the findings of a scientific panel that was organised to propose a new location for testing US army materiel and systems within a tropical environment. Rather than simply choosing a location analogous to Panama, the panel sought to develop a methodology that could be employed for site selection based on any set of environmental criteria. This study is a classical locational analysis and reconfirms the integrative nature of geography and its utility for solving complex problems that cut across disciplinary boundaries.     

A multi‐dimensional analysis of pro‐glacial landscape change at Sólheimajökull,southern Iceland

Pro‐glacial landscapes are some of the most active on Earth. Previous studies of pro‐glacial landscape change have often been restricted to considering either sedimentological, geomorphological or topographic parameters in isolation and are often mono‐dimensional. This study utilized field surveys and digital elevation model (DEM) analyses to quantify planform, elevation and volumetric pro‐glacial landscape change at Sólheimajökull in southern Iceland for multiple time periods spanning from 1960 to 2010. As expected, the most intense geomorphological changes persistently occurred in the ice‐proximal area. During 1960 to 1996 the pro‐glacial river was relatively stable. However, after 2001 braiding intensity was higher, channel slope shallower and there was a shift from overall incision to aggradation. Attributing these pro‐glacial river channel changes to the 1999 jökulhlaup is ambiguous because it coincided with a switch from a period of glacier advance to that of glacier retreat. Furthermore, glacier retreat (of ~40 m yr^?1) coincided with ice‐marginal lake development and these two factors have both altered the pro‐glacial river channel head elevation. From 2001 to 2010 progressive increase in channel braiding and progressive downstream incision occurred; these together probably reflecting stream power due to increased glacier ablation and reduced sediment supply due to trapping of sediment by the developing ice‐marginal lake. Overall, this study highlights rapid spatiotemporal pro‐glacial landscape reactions to changes in glacial meltwater runoff regimes, glacier terminus position, sediment supply and episodic events such as jökuhlaups. Recognizing the interplay of these controlling factors on pro‐glacial landscapes will be important for understanding the geological record and for landscape stability assessments. Copyright © 2014 John Wiley & Sons, Ltd.     

Skill of western North Pacific tropical cyclone intensity forecast guidance relative to Weighted-Analog technique

The accuracy of the western North Pacific tropical cyclone intensity forecast guidance products available at the Joint Typhoon Warning Center (JTWC) is evaluated relative to a new skill metric called Weighted Analog Intensity Pacific (WAIP) that includes knowledge of the JTWC official track forecast and the current intensity, which is information that is available at the time the intensity forecast is generated. An intensity consensus technique called S5XX that includes statistical-dynamic intensity forecasts plus other dynamic and thermodynamic prediction techniques has statistically significant smaller errors than WAIP at 24 h and 48 h and has similar accuracy through 120 h. While the track consensus CONW is a critical input to the JTWC official track forecast, it has no skill relative to WAIP as an intensity forecast. Three regional numerical models also have no skill relative to WAIP, and especially at forecast intervals beyond 72 h because their mean absolute errors are statistically significantly larger than for WAIP. Furthermore, these regional models have statistically significant positive or negative intensity biases relative to the verifying intensities. However, an experimental consensus technique called CMES that includes these three regional models has small accuracy relative to WAIP in the 24 h to 72 h forecast intervals. Geographical-based comparisons of the intensity guidance products with the WAIP indicate almost all of the products are more accurate than WAIP over the South China Sea region. The statistical-dynamic consensus technique S5XX does have skill through 72 h for landfalling situations along the coasts of China and Southeast Asia. At 120 h, the WAIP has superior performance over the guidance products over most areas of the western North Pacific, but again the S5XX is more accurate than WAIP for landfalling tropical cyclones on the Philippine Islands, Southeast Asia, South China, and northeastern Japan. This information will be useful to the forecaster in deciding when and where (or how much) to rely on each guidance product in preparing the five-day intensity forecast once the official track forecast has been established.     

ParBreZo: A parallel,unstructured grid,Godunov-type,shallow-water code for high-resolution flood inundation modeling at the regional scale

Topographic data are increasingly available at high resolutions (<10 m) over large spatial extents to support detailed flood inundation modeling and loss estimation analyses required for flood risk management. This paper describes ParBreZo, the parallel implementation of a two-dimensional, Godunov-type, shallow-water code, to address the computational demand of high-resolution flood modeling at the regional scale (10²–10⁴ km²). A systematic approach to unstructured grid partitioning (domain decomposition) is presented, and the Single Process Multiple Data (SPMD) paradigm of distributed-memory parallelism is implemented so the code can be executed on computer clusters with distributed memory, shared memory, or some combination of the two (now common with multi-core architectures). In a fully-wetted, load-balanced test problem, the code scales very well with a parallel efficiency of close to 100% on up to 512 processes (maximum tested). A weighted grid partitioning is used to partially address the load balancing challenge posed by partially wetted domains germane to flooding applications, where the flood extent varies over time, while the partitioning remains static. An urban dam-break flood test problem shows that weighted partitions achieve a parallel efficiency exceeding 70% using up to 48 processes. This corresponds to a 97% reduction in execution time so results are obtained in a matter of minutes, which is attractive for routine engineering analyses. A hurricane storm surge test problem shows that a 10 m resolution, 12 h inundation forecast for a 40 km length of coastline can be completed in under 2 h using 512 processors. Hence, if coupled to a hurricane forecast system capable of resolving storm surge, inundation forecasts could be made at 10 m resolution with at least a 10 h lead time.     

The Quassaic Group,a Medial to Late Ordovician arenite sequence in the Marlboro Mountains Outlier,mid-Hudson Valley,New York,U.S.A

The Quassaic Group occurs as an outlier in the north-south trending Marlboro Syncline which extends 40 km between Kingston and Newburgh in southeastern New York. The group is comprised primarily of 3050 m of late Medial to medial Late Ordovician marine arenites. It is subdivided (oldest to youngest) into five formations: Creek Locks, Rifton, Shaupeneak. Slab Sides, and Chodikee. On the western limb of the syncline the group overlies a minimum of 610 m of the early late Medial Ordovician Bushkill Shale and the bottom three formations grade north and south to Bushkill Shale. Abundance of graded but occasionally conglomeratic beds, common tabular cross-lamination, much less common trough cross-lamination, comparative lack of channelling, general lack of shales, and scarcity of fossils indicate that the average depositional environment of the formations was near the base of the slope of a sedimentary apron or delta which lay to the southeast. The environment, however, probably extended from a basin plain, in the marginal Bushkill Shale, through the lower and middle slope and, rarely, to the upper slope. The occasional molasse-like deposits in the Shaupeneak Formation may indicate local transport of molasse to an upper slope position. The Quassaic Group thus records an initial, local extension of arenites of the lower slope of an apron or delta onto a downwarping basin plain in the Bushkill Trough. This was followed by progressive enlargement and extension of the delta slope with attendant shallowing, culminated by the appearance of molasse-like sediments. Subsequent deposition involved greater slope extension followed by recession with gradual deepening. These activities were prelude to the Hudson Valley Phase of the Taconian Orogeny which downfolded the Quassaic Group into the Marlboro Syncline during latest Ordovician times.     

Mapping the archaeological soil archive of sand and gravel mineral reserves in Britain

Primary sand and gravel deposits in Britain play an important role in preserving our cultural heritage and are also a valuable aggregate resource. While an understanding of the extrinsic properties of the soil archive (such as pH, redox, groundwater) can provide a firstorder assessment of the potential risk to any archaeologically sensitive deposits, we have very poor definition of spatial variations in the extrinsic properties of soil that influence archaeological preservation at a regional and national scale. Developments in digital geological mapping, remote sensing, and geochemical survey data undertaken by the British Geological Survey (BGS) have, however, significantly extended capabilities in this respect and can potentially be used to provide a primary assessment of the sensitivity of the present soil archive and the potential risk from changes to the soil process on cultural material in areas earmarked for aggregate extraction. Two of the major factors affecting archaeological preservation—soil acidification and groundwater—can be mapped or predicted at scales of better than 1:50,000 across increasingly large parts of the country using a combination of regional hydrogeological, geophysical, and geochemical data. Additional data from site investigations may further refine preservation potential as a function of changes in redox potential and acidity. These data, maps and models can be used to (1) better establish a baseline for archaeological preservation at a regional and national scale and (2) improve our understanding of how the physical and chemical properties of the near surface environment can be managed to sustainably preserve archaeological materials in areas impacted by sand and gravel extraction. © 2009 Wiley Periodicals, Inc.