Dissipative and reflective beaches in a large lake and the physical effects of lake level regulation

Nearshore environments in Flathead Lake, Montana, USA, were described as dissipative or reflective on the basis of: the surf similarity parameter , grain size, morphology, number of breaking waves and angle of wave incidence. The relative resistance to foreshore and backshore erosion caused by anthropogenic lake level regulation was compared between these two nearshore configurations. Reflective systems were characterized by dynamic gravel beach faces and steep inshore shelves armored by wave-washed cobble. In contrast, dissipative systems were characterized by sand-sized substratum, broad flat inshore shelves and the presence of multiple linear bars approximately 350 m offshore. Five decades of regulated lake levels have resulted in extensive shoreline erosion (970 ha on the north shore of the lake) and a general reshaping of both types of nearshore environments, although dissipative shorelines eroded faster (5.7 m/year maximum and 2.0 m/year average). The presence of docks and other man-made structures on reflective beaches accelerated erosion by intercepting longshore gravel transport. This analysis provided a physical basis for understanding the effects of lake level regulation on shoreline ecology and management.     

Remote sensing analysis of physical complexity of North Pacific Rim rivers to assist wild salmon conservation

Salmon populations are highly variable in both space and time. Accurate forecasting of the productivity of salmon stocks makes effective management and conservation of the resource extremely challenging. Furthermore, widespread and consistent data on the productivity of species‐specific and total salmon stocks in a river are almost nonexistent. Ranking rivers based on physical complexity derived from remote sensing allows rivers to be objectively compared. Our approach considered rivers with great geomorphic complexity (e.g. having expansive, multichanneled floodplains and/or on‐channel lakes) as likely to have greater productivity of salmon than rivers flowing in constrained or canyon‐bound channels. Our objective was to develop a database of landscape metrics that could be used to rank the rivers in relation to potential salmon productivity. We then examined the rankings in relation to existing empirical (monitoring) data describing productivity of salmon stocks. To extract the metrics for each river basin we used a digital elevation model and multispectral satellite imagery. We developed procedures to extract channel networks, floodplains, on‐channel lakes and other catchment features; variables such as catchment area, channel elevation, main channel length, floodplain area, and density of hydrojunctions (nodes) were measured. We processed 1509 catchments in the North Pacific Rim including the Kamchatka Peninsula in Russia and western North America. Overall, catchments were most physically complex in western Kamchatka and western Alaska, and particularly on the Arctic North Slope of Alaska. We could not directly examine coherence between potential and measured productivity except for a few rivers, but the expected relationship generally held. The resulting database and systematic ranking are objective tools that can be used to address questions about landscape structure and biological productivity at regional to continental extents, and provide a way to begin to efficiently prioritize the allocation of funding and resources towards salmon management and conservation. Copyright © 2010 John Wiley & Sons, Ltd.     

The XMM Cluster Survey: forecasting cosmological and cluster scaling-relation parameter constraints

We forecast the constraints on the values of  σ₈, Ω_m  and cluster scaling-relation parameters which we expect to obtain from the XMM Cluster Survey (XCS). We assume a flat Λ cold dark matter Universe and perform a Monte Carlo Markov Chain analysis of the evolution of the number density of galaxy clusters that takes into account a detailed simulated selection function. Comparing our current observed number of clusters shows good agreement with predictions. We determine the expected degradation of the constraints as a result of self-calibrating the luminosity–temperature relation (with scatter), including temperature measurement errors, and relying on photometric methods for the estimation of galaxy cluster redshifts. We examine the effects of systematic errors in scaling relation and measurement error assumptions. Using only  ( T , z )  self-calibration, we expect to measure Ω_m to ±0.03 (and  Ω_Λ  to the same accuracy assuming flatness), and σ₈ to ±0.05, also constraining the normalization and slope of the luminosity–temperature relation to ±6 and ±13 per cent (at 1σ), respectively, in the process. Self-calibration fails to jointly constrain the scatter and redshift evolution of the luminosity–temperature relation significantly. Additional archival and/or follow-up data will improve on this. We do not expect measurement errors or imperfect knowledge of their distribution to degrade constraints significantly. Scaling-relation systematics can easily lead to cosmological constraints 2σ or more away from the fiducial model. Our treatment is the first exact treatment to this level of detail, and introduces a new 'smoothed ML' (Maximum Likelihood) estimate of expected constraints.     

ELECTROLYTIC CORROSION OF IRON METEORITES

Six iron meteorites were electrolyzed and the resulting corrosion was studied by a potentiostatic technique. It was found that both iron and nickel in the kamacite phase dissolve, and that neither iron nor nickel dissolve from taenite. The rate of corrosion was shown to be inversely proportional to the nickel content. However, structure, as well as nickel content, plays an important part in the electrolytic process. The Coya Norte, Chile meteorite dissolved more rapidly and more easily (at a lower potential) than did pure iron even though the Coya Norte meteorite contains 5.5% nickel.     

北阿尔金巴什考供盆地南缘花岗杂岩体特征及锆石SHRIMP定年

北阿尔金巴什考供盆地南缘花岗杂岩体呈近东西向分布,长约49公里,出露面积约90平方公里,与围岩之间为明显的侵入接触关系,接触界线为不规则的渡状、锯齿状。围岩为前寒武纪砂岩、片岩、泥岩及凝灰质砂岩。该杂岩体主要由巨斑花岗岩、红色花岗岩、灰白色似斑状花岗岩和粉红色似斑状花岗岩组成。杂岩体的主元素含量变化不大,SiO2为65．14％- 75．66％,全碱含量为7．49-8．96％,K2O／Na2O比值为1．12-2．68,岩石的里特曼指数平均为2．34,CIPW标准矿物计算均出现刚玉(AC)(平均为1．78),说明岩石铝过饱和;杂岩体的稀土总量变化于89．44×10-6-335．28×10-6之间,不同岩石类型均有负铕异常,且从巨斑花岗岩→灰白色似斑状花岗岩→红色似斑状花岗岩→红色花岗岩,负铕异常越来越明显,表现在Eu／ Eu+值由0．65→0．51→0．48→0．30。在微量元素蛛网图上,所有样品的微量元素丰度均高于原始地幔值,并具有相似的配分模式,即在Ba、Nb、Sr、P、Ti处呈明显的低谷,显示出S型花岗岩的特征。锆石SHRIMP U-Pb定年得出,巨斑花岗岩、红色中细粒花岗岩、灰白色和粉红色似斑状花岗岩的年龄分别为474．3±6．8Ma、446．6±5．2Ma、434．5±3．8Ma和431．1±3．8Ma。结合区域地质特征,我们认为,该杂岩体形成于同碰撞-碰撞后的构造环境。     

A Clovis well at the type site 11,500 B.C.: The oldest prehistoric well in America

An enigmatic circular pit uncovered during archaeological excavations at the Clovis type site, Blackwater Draw, New Mexico, in 1964 has been reexposed and posited as a water well excavated by Clovis people around 11,500 B.C. The prehistoric well, the oldest in the New World, was probably a dry hole. Other Clovis wells may exist in the area. The excavation of wells near where there had been surface water shortly before adds to the evidence for drought during the Pleistocene-Holocene transition. © 1999 John Wiley & Sons, Inc.