The role of carbon dioxide during the onset of Antarctic glaciation

Earth's modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted in environmental changes that promoted Antarctic glaciation ~33.7 million years ago. Onset of Antarctic glaciation reflects a critical tipping point for Earth's climate and provides a framework for investigating the role of atmospheric carbon dioxide (CO(2)) during major climatic change. Previously published records of alkenone-based CO(2) from high- and low-latitude ocean localities suggested that CO(2) increased during glaciation, in contradiction to theory. Here, we further investigate alkenone records and demonstrate that Antarctic and subantarctic data overestimate atmospheric CO(2) levels, biasing long-term trends. Our results show that CO(2) declined before and during Antarctic glaciation and support a substantial CO(2) decrease as the primary agent forcing Antarctic glaciation, consistent with model-derived CO(2) thresholds.     

Coccoliths as paleoclimatic indicators of pleistocene glaciation

Selected species of Coccolithophoridae from recent sediments and mid-Wisconsin glacial sediments of the North Atlantic were examined in an attempt to determine cooling effects. All species showed a definite shift southward during the glacial period. The average shift in this planktonic population was 15 degrees of latitude, with the greatest change in the eastern Atlantic. A paleoisotherm map can be drawn on the basis of the temperature boundaries of coccolithophorids. The species boundaries indicate a possible shift in position of the subtropical gyral to a glacial position roughly parallel to the 33-degree line of latitude.     

Seven million years of glaciation in greenland

Glacial till, glaciomarine diamictites, and ice-rafted detritus found in marine cores collected off the shore of southeast Greenland record multiple Late Cenozoic glaciations beginning in the Late Miocene. Distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast Greenland margin. Glaciers advanced to the sea during several intervals in the Pliocene and Pleistocene. North Atlantic glaciation may have nucleated in southern Greenland rather than further north because of the high mountains and the high levels of precipitation in this region.     

Evolution of the eastern tropical Pacific through Plio-Pleistocene glaciation

A tropical Pacific climate state resembling that of a permanent El Ni?o is hypothesized to have ended as a result of a reorganization of the ocean heat budget approximately 3 million years ago, a time when large ice sheets appeared in the high latitudes of the Northern Hemisphere. We report a high-resolution alkenone reconstruction of conditions in the heart of the eastern equatorial Pacific (EEP) cold tongue that reflects the combined influences of changes in the equatorial thermocline, the properties of the thermocline's source waters, atmospheric greenhouse gas content, and orbital variations on sea surface temperature (SST) and biological productivity over the past 5 million years. Our data indicate that the intensification of Northern Hemisphere glaciation approximately 3 million years ago did not interrupt an almost monotonic cooling of the EEP during the Plio-Pleistocene. SST and productivity in the eastern tropical Pacific varied in phase with global ice volume changes at a dominant 41,000-year (obliquity) frequency throughout this time. Changes in the Southern Hemisphere most likely modulated most of the changes observed.     

Climate and groundwater recharge during the last glaciation in an ice-covered region

A multitracer study of a small aquifer in northern Switzerland indicates that the atmosphere in central Europe cooled by at least 5 degreesC during the last glacial period. The relation between oxygen isotope ratios (delta18O) and recharge temperatures reconstructed for this period is similar to the present-day one if a shift in the delta18O value of the oceans during the ice age is taken into account. This similarity suggests that the present-day delta18O-temperature relation can be used to reconstruct paleoclimate conditions in northern Switzerland. A gap in calculated groundwater age between about 17,000 and 25,000 years before the present indicates that during the last glacial maximum, local groundwater recharge was prevented by overlying glaciers.     

无花果晚秋未成熟果的加工利用

为了增加无花果设施栽培的经济效益，对晚秋未成熟果的加工利用进行了多方面的探索，取得了初步的成果，为市场又增添了一种营养保健、抗癌防衰、美容润肤的新型绿色保健食品。本介绍了晚秋无花果的系列产品加工工艺。     

North american pleistocene stages reconsidered in light of probable pliocene-pleistocene continental glaciation

Confusion due to the conceptual usage of classic North American Pleistocene stage terms indicates the need for a new or revised terminology. The Pliocene-Pleistocene boundary has tentatively been dated about 2.5 +/- 0.1 x 10(6) years. Glacial deposits in the central United States older than about 2.2 x 10(6) years may span that boundary.     

The size and duration of the Sumatra-Andaman earthquake from far-field static offsets

The 26 December 2004 Sumatra earthquake produced static offsets at continuously operating GPS stations at distances of up to 4500 kilometers from the epicenter. We used these displacements to model the earthquake and include consideration of the Earth's shape and depth-varying rigidity. The results imply that the average slip was >5 meters along the full length of the rupture, including the approximately 650-kilometer-long Andaman segment. Comparison of the source derived from the far-field static offsets with seismically derived estimates suggests that 25 to 35% of the total moment release occurred at periods greater than 1 hour. Taking into consideration the strong dip dependence of moment estimates, the magnitude of the earthquake did not exceed Mw = 9.2.     

Silurian of central Texas: a first record for the region

Silurian outcrops, not previously recorded from central Texas, have been identified from the Llano uplift, where they occur in collapse structures within the Lower Ordovician Honeycut Formation of the Ellenburger Group. The formation is a pinkish-gray granular limestone, contains fossils of probable Wenlock age, and is named the Starcke Limestone.     

Reconciling the magnitude of the microscopic and macroscopic hydrophobic effects

The magnitude of the hydrophobic effect, as measured from the surface area dependence of the solubilities of hydrocarbons in water, is generally thought to be about 25 calories per mole per square angstrom (cal mol-1 A-2). However, the surface tension at a hydrocarbon-water interface, which is a "macroscopic" measure of the hydrophobic effect, is approximately 72 cal mol-1 A-2. In an attempt to reconcile these values, alkane solubility data have been reevaluated to account for solute-solvent size differences, leading to a revised "microscopic" hydrophobic effect of 47 cal mol-1 A-2. This value, when used in a simple geometric model for the curvature dependence of the hydrophobic effect, predicts a macroscopic alkane-water surface tension that is close to the macroscopic value.     

广西番茄晚疫病流行原因及防治

番茄是广西种植的主要蔬菜种类之一,产品远销我国北方、广东、香港和澳门等地,在农业经济中占有重要的地位.     

我国马铃薯晚疫病的发生与防治

从病原、发生规律、预测预报、抗病育种和防治等5个方面对我国马铃薯晚疫病的研究进行了综述。目前,我国马铃薯晚疫病菌生理小种的组成仍以1、3、4的不同组合为主;我国已在6个省(区、市)发现了A2交配型。病种薯是马铃薯晚疫病主要的初侵染来源,中心病株的出现是发生的重要标志,6～8月份的降雨是流行的关键因素。培育具有水平抗性的品种是目前抗病育种的重点。为减少瑞毒霉抗性菌株的出现,可将瑞毒霉与瑞毒锰锌、大生和波尔多液等轮换施用。     

启蒙与体制化:晚清近代农学的兴起

本文从古代中国的“经验农学”与近代西方的“实验农学”的本质区别入手,重点阐述晚清知识阶层对近代西方农学知识的认知、提倡、引进、传播的过程,同时指出了晚清政府在农学启蒙中所确立的发展近代农业科技的兴农措施,促进了从经验农学向实验农学的历史性转变,推动了近代农业科技从启蒙到体制化的历史进程。     

The 2011 magnitude 9.0 Tohoku-Oki earthquake: mosaicking the megathrust from seconds to centuries

Geophysical observations from the 2011 moment magnitude (M(w)) 9.0 Tohoku-Oki, Japan earthquake allow exploration of a rare large event along a subduction megathrust. Models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places. Sources of high-frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip. Relative to the M(w) 8.8 2010 Maule, Chile earthquake, the Tohoku-Oki earthquake was deficient in high-frequency seismic radiation--a difference that we attribute to its relatively shallow depth. Estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event.     

清末农会的社会影响

清末农会从倡导至组建历经多年,对中国社会诸方面产生了深远影响。农会组织的引入开启了国人解决农业问题的现代思路。在现代民主思想的传播与制度安排、农民维权意识及国家观念的增强等方面具有重要启蒙作用。农会的组织活动带来了新的农业思想及耕作方式。农会为传统乡绅权力提供了新的载体,缓解了社会变革给清政府带来的压力,在一定程度上延续了清政府的统治。