Pleistocene brown bears in the mid-continent of North America

Current biogeographic models hypothesize that brown bears migrated from Asia to the New World ~100 to 50 thousand years ago but did not reach areas south of Beringia until ~13 to 12 thousand years ago, after the opening of a mid-continental ice-free corridor. We report a 26-thousand-year-old brown bear fossil from central Alberta, well south of Beringia. Mitochondrial DNA recovered from the specimen shows that it belongs to the same clade of bears inhabiting southern Canada and the northern United States today and that modern brown bears in this region are probably descended from populations that persisted south of the southern glacial margin during the Last Glacial Maximum.     

Radiocarbon Dates of Pre-Mankato Events in Eastern and Central North America

1) A group of samples from horizons previously correlated with the upper part of the Cary substage confirms the correlation as reasonable and is consistently related in time to the dates of the peat layer at Two Creeks and subsequent Mankato events. 2) A major glaciation affected the Great Lakes region beginning 25,000 or more yr ago and reaching its maximum extent about 18,000 yr ago. It is represented by drift correlated in Ohio with the Cary substage and, at least in part, with the Tazewell substage; in Illinois and adjacent states it is correlated with most of the Tazewell substage and with the Farmdale loess. 3) The ecology and other associations implied by the dated samples are more consistent with glacial than with nonglacial conditions. 4) The lower till at Sidney, Ohio (W-188), on which is developed a soil considered a correlative of the Fox series soil on gravels and also buried by till of the major glaciation of 25,000 to 18,000 yr ago, indicates an earlier glaciation extensively exposed in Ohio and believed to be an early Wisconsin event. Table 2. List of samples and dates arranged by age groups. See PDF for Table 5) An earlier glaciation, or glaciations, is implied at several localities by peat, gyttja, or wood more than 30,000 yr old, overlain by till. 6) The time interval between the middle group and the old group of samples, which has been determined within conservative radiocarbon limits to be greater than 3000 yr, is possibly of the order of 16,000 yr, as suggested by the depth of leaching at Sidney, Ohio. (The ages of all the samples discussed are listed in Table 2.) 7) An attempt should now be made to fix more closely the dates of the old samples and to reexamine in the field the stratigraphic sequence in the light of the radiocarbon dates discussed.     

Causes of Decadal Climate Variability over the North Pacific and North America

The cause of decadal climate variability over the North Pacific Ocean and North America is investigated by the analysis of data from a multidecadal integration with a state-of-the-art coupled ocean-atmosphere model and observations. About one-third of the low-frequency climate variability in the region of interest can be attributed to a cycle involving unstable air-sea interactions between the subtropical gyre circulation in the North Pacific and the Aleutian low-pressure system. The existence of this cycle provides a basis for long-range climate forecasting over the western United States at decadal time scales.     

Radiocarbon dating and archeology in North America

The history of the development of a radiocarbon chronology shows how the establishment of the times of events and the order of them has greatly improved the understanding of prehistory in North America. This is true also of other parts of the world. Too little has been said of existing discordance between archeologically determined sequences, and interregional associations, and the radiocarbon chronology. It does appear that these will be resolved as additional dates are added and as the results become more finely calibrated so that secular variations may be accounted for. The collaborative aspect of the venture was apparent at the outset. Nevertheless no one expects an archeologist to delve into nuclear physics and geochemistry, and vice versa. There is great need, nevertheless, for the man in the laboratory to comprehend the difficulties of sample collecting and of judgement of the significance of the source of organic matter to be dated. At the same time, the archeologist must become more familiar with the importance of the various steps in the processing of the sample and with, what is most vital, interpretation of the significance of the numbers that appear on the counters.     

The first glacial maximum in North America

Despite marine evidence for at least 50 Pliocene-Pleistocene ice sheet advances, only the most recent one has been accurately reconstructed from terrestrial evidence, because there are few techniques for dating older glacial deposits. Here we show that the cosmic ray-produced nuclides beryllium-10 and aluminum-26 can be used to date tills that overlie paleosols.     

On Pleistocene Surface Temperatures of the North Atlantic and Arctic Oceans

Two additional interpretations are given for the important data of D. B. Ericson on the correlation of coiling directions of Globigerina pachyderma in late Pleistocene North Atlantic sediments with ocean surface temperatures. One interpretation relates the distribution of this species to the distribution and circulation of ocean water masses. On the basis of our ice-age theory, our second interpretation uses the data and correlations of Ericson to establish temperature limits of a thermal node, a line on which glacial and interglacial temperatures were equal, for the North Atlantic Ocean. This line crosses the strait between Greenland and Scandinavia. Further, Ericson's interpretation of the 7.2 degrees C isotherm implies that the glacial-stage surface waters of the Arctic Ocean were between 0 degrees and 3.5 degrees C.     

北美农业收入支持政策的变革

尽管北美自由贸易协定(NAFTA)保留了成员国制定和执行国内农业政策的自主权,但是,近年来,美国、加拿大和墨西哥三国的农业政策在某些方面逐步走到了一起.尤其突出的是农业收入支持政策的一致性趋向,三个国家都削减了对农业生产者的收入支付,制定了反周期计划.     

北美大豆食品现状

一、大豆食品在北美的历史大豆在中国有四五千年历史，大约在公元前164年中国发明了豆奶和豆腐。900年后，这些大豆食品加工方法传入日本和太平洋周边国家，大约在1712年大豆进入欧洲、CalVonLinne′给大豆定学名为Glycinemax（意思是带有大根瘤的田野坚果），然而欧洲的土壤和气候条件限制了大豆的生产。1764年大豆传到北美，1年后在佐治亚州种植，随着栽培技术和机械收获技术的发展，大豆作为动物饲料和食用油在北美逐步发展起来。1998／99年度全世界大豆产品超过1.56亿t，85％用于榨油和豆粕，10％用于食品（在美国只有大约1％），5％…     

北美种子质量控制体系

一、北美种子质量控制的历史与现状在美国和加拿大，种子质量控制的历史可追溯到１９世纪初期，当由州立大学和政府实验站培育出第一个新品种时，相应的新品种种子质量控制也应运而生。在此之前，美、加大部分大田作物都是由其他国家的作物品种衍生而来，每当新品种诞生就被随机分发到农民手中，这些品种常常被丢失或混杂。１９００—１９２０年间，全美各州纷纷成立组织，向农民分发“学院培育”的品种，这些组织很快发展成州立实验站，进而又成为作物改良机构或种子质量控制组织机构———种子认证机构。从２０世纪２０—４０年代，在全美…     

晚近北美森林土壤研究动态

本文综合介绍了北美森林土壤晚近的主要研究方向、苗头、新趋势以及研究方法技术的发展等情况,并与中国森林土壤学研究作了相互比较。     

Dietary change and evolution of horses in North America

The evolution of high-crowned molars among horses (Family Equidae) is thought to be an adaptation for abrasive diets associated with the spread of grasslands. The sharpness and relief of the worn cusp apices of teeth (mesowear) are a measure of dietary abrasion. We collected mesowear data for North American Equidae for the past 55.5 million years to test the association of molar height and dietary abrasion. Mesowear trends in horses are reflective of global cooling and associated vegetation changes. There is a strong correlation between mesowear and crown height in horses; however, most horse paleopopulations had highly variable amounts of dietary abrasion, suggesting that selective pressures for crown height may have been weak much of the time. However, instances of higher abrasion were observed in some paleopopulations, suggesting intervals of stronger selection for the evolution of dentitions, including the early Miocene shortly before the first appearance of Equinae, the horse subfamily in which high-crowned dentitions evolved.     

北欧和中欧的原木价格

据《木材资源季刊》了解,由于制材部门对原木的需求量下降,2012年欧洲原木价格总体低于2011年。欧洲大陆的许多制材厂由于木材市场渐弱而被迫减产。北欧国家的原木价格下跌最严重,而东欧的价格却非常稳定,甚至在2012年底有小幅上涨的趋势。以美元计算,西欧大多主要原木市场的原木价格在过去2年里呈走低趋势,但是由于美元贬值而导致的价格略涨使这种趋势在2012年4季度（4Q／12）被打破了。但以当地的货币计算的话,原木价格保持在2012年4季度（4Q／12）水平几乎未变。     

中国中北部青檀的AFLP分析

为揭示中国中北部青檀的遗传多样性,本研究从贵州、北京、甘肃、江苏、安徽、山东、河南7省12个种群收集了31 份青檀样品,对其进行AFLP分析。利用从26 对AFLP引物组合中筛选出的6对引物对样本DNA进行扩增,共产生223条谱带,其中211 条为多态性条带,比率达94.26%。结果显示中国中北部的青檀材料之间存在较高的遗传多样性,且AFLP 技术可以有效地对其进行分析。31 个样品的遗传相似系数在0.6413-0.9193之间,平均为0.7489,聚类分析结果显示样品首先按照种群聚在一起,但也有交叉。     

北美区域农业政策及其效果分析

本文分析了北美区域农业政策产生的背景、主要内容、最新进展,并对其效果进行了简要评估.     

美国的烟草育种及应用现状

美国是世界上进行烟草育种研究最早和培育烟草品种最多的国家,它拥有世界上杰出的育种专家和一流的育种公司,在烟草育种研究方面处于绝对领先的地位。一、美国烟草品种资源的收集和育种美国是世界上烟草种质资源收集种类最多的国家之一,在保存和鉴定方面成绩显著。1957年美国在科罗拉多州科林斯堡建起世界上第一座国家种子贮藏室,温度为4℃,相对湿度为32%,种质容量达50万份,可安全保存10年以上。1897—1935年的30多年间先后19次派人到中国考察,搜集了大量的植物资源。20世纪30年代曾二次派出考察队到烟草起源中心南美洲安第斯山区搜集古老类…