Seasonal characteristics of the Indian Ocean Dipole during the Holocene epoch

The Indian Ocean Dipole (IOD)--an oscillatory mode of coupled ocean-atmosphere variability--causes climatic extremes and socio-economic hardship throughout the tropical Indian Ocean region. There is much debate about how the IOD interacts with the El Ni?o/Southern Oscillation (ENSO) and the Asian monsoon, and recent changes in the historic ENSO-monsoon relationship raise the possibility that the properties of the IOD may also be evolving. Improving our understanding of IOD events and their climatic impacts thus requires the development of records defining IOD activity in different climatic settings, including prehistoric times when ENSO and the Asian monsoon behaved differently from the present day. Here we use coral geochemical records from the equatorial eastern Indian Ocean to reconstruct surface-ocean cooling and drought during individual IOD events over the past approximately 6,500 years. We find that IOD events during the middle Holocene were characterized by a longer duration of strong surface ocean cooling, together with droughts that peaked later than those expected by El Ni?o forcing alone. Climate model simulations suggest that this enhanced cooling and drying was the result of strong cross-equatorial winds driven by the strengthened Asian monsoon of the middle Holocene. These IOD-monsoon connections imply that the socioeconomic impacts of projected future changes in Asian monsoon strength may extend throughout Australasia.     

Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch

The stability of the Antarctic ice shelves in a warming climate has long been discussed, and the recent collapse of a significant part, over 12,500 km2 in area, of the Larsen ice shelf off the Antarctic Peninsula has led to a refocus toward the implications of ice shelf decay for the stability of Antarctica's grounded ice. Some smaller Antarctic ice shelves have undergone periodic growth and decay over the past 11,000 yr (refs 7-11), but these ice shelves are at the climatic limit of ice shelf viability and are therefore expected to respond rapidly to natural climate variability at century to millennial scales. Here we use records of diatoms, detrital material and geochemical parameters from six marine sediment cores in the vicinity of the Larsen ice shelf to demonstrate that the recent collapse of the Larsen B ice shelf is unprecedented during the Holocene. We infer from our oxygen isotope measurements in planktonic foraminifera that the Larsen B ice shelf has been thinning throughout the Holocene, and we suggest that the recent prolonged period of warming in the Antarctic Peninsula region, in combination with the long-term thinning, has led to collapse of the ice shelf.     

Irregular tropical glacier retreat over the Holocene epoch driven by progressive warming

The causes and timing of tropical glacier fluctuations during the Holocene epoch (10,000 years ago to present) are poorly understood. Yet constraining their sensitivity to changes in climate is important, as these glaciers are both sensitive indicators of climate change and serve as water reservoirs for highland regions. Studies have so far documented extra-tropical glacier fluctuations, but in the tropics, glacier-climate relationships are insufficiently understood. Here we present a (10)Be chronology for the past 11,000?years (11?kyr), using 57 moraines from the Bolivian Telata glacier (in the Cordillera Real mountain range). This chronology indicates that Telata glacier retreated irregularly. A rapid and strong melting from the maximum extent occurred from 10.8?±?0.9 to 8.5?±?0.4?kyr ago, followed by a slower retreat until the Little Ice Age, about 200 years ago. A dramatic increase in the rate of retreat occurred over the twentieth century. A glacier-climate model indicates that, relative to modern climate, annual mean temperature for the Telata glacier region was -3.3?±?0.8 °C cooler at 11?kyr ago and remained -2.1?±?0.8 °C cooler until the end of the Little Ice Age. We suggest that long-term warming of the eastern tropical Pacific and increased atmospheric temperature in response to enhanced austral summer insolation were the main drivers for the long-term Holocene retreat of glaciers in the southern tropics.     

The climatic variations and development of yellow soil in Beibei since the Holocene epoch

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Extended megadroughts in the southwestern United States during Pleistocene interglacials

The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States (US) is a serious concern. Multi-year droughts during the instrumental period and decadal-length droughts of the past two millennia were shorter and climatically different from the future permanent, 'dust-bowl-like' megadrought conditions, lasting decades to a century, that are predicted as a consequence of warming. So far, it has been unclear whether or not such megadroughts occurred in the southwestern US, and, if so, with what regularity and intensity. Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials. Using molecular palaeotemperature proxies to reconstruct the mean annual temperature (MAT) in mid-Pleistocene lacustrine sediment from the Valles Caldera, New Mexico, we found that the driest conditions occurred during the warmest phases of interglacials, when the MAT was comparable to or higher than the modern MAT. A collapse of drought-tolerant C(4) plant communities during these warm, dry intervals indicates a significant reduction in summer precipitation, possibly in response to a poleward migration of the subtropical dry zone. Three MAT cycles ～2?°C in amplitude occurred within Marine Isotope Stage (MIS) 11 and seem to correspond to the muted precessional cycles within this interglacial. In comparison with MIS 11, MIS 13 experienced higher precessional-cycle amplitudes, larger variations in MAT (4-6?°C) and a longer period of extended warmth, suggesting that local insolation variations were important to interglacial climatic variability in the southwestern US. Comparison of the early MIS 11 climate record with the Holocene record shows many similarities and implies that, in the absence of anthropogenic forcing, the region should be entering a cooler and wetter phase.     

Decline of surface temperature and salinity in the western tropical Pacific Ocean in the Holocene epoch

In the present-day climate, surface water salinities are low in the western tropical Pacific Ocean and increase towards the eastern part of the basin. The salinity of surface waters in the tropical Pacific Ocean is thought to be controlled by a combination of atmospheric convection, precipitation, evaporation and ocean dynamics, and on interannual timescales significant variability is associated with the El Ni?o/Southern Oscillation cycles. However, little is known about the variability of the coupled ocean-atmosphere system on timescales of centuries to millennia. Here we combine oxygen isotope and Mg/Ca data from foraminifers retrieved from three sediment cores in the western tropical Pacific Ocean to reconstruct Holocene sea surface temperatures and salinities in the region. We find a decrease in sea surface temperatures of approximately 0.5 degrees C over the past 10,000 yr, whereas sea surface salinities decreased by approximately 1.5 practical salinity units. Our data imply either that the Pacific basin as a whole has become progressively less salty or that the present salinity gradient along the Equator has developed relatively recently.     

Meteoric smoke fallout over the Holocene epoch revealed by iridium and platinum in Greenland ice

An iridium anomaly at the Cretaceous/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65 million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly enter the atmosphere via ablating meteoroids remains largely unknown. Here we report a record of iridium and platinum fluxes on a climatic-cycle timescale, back to 128,000 years ago, from a Greenland ice core. We find that unexpectedly constant fallout of extraterrestrial matter to Greenland occurred during the Holocene, whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust-laden atmosphere of the last glacial age. We suggest that nanometre-sized meteoric smoke particles, formed from the recondensation of ablated meteoroids in the atmosphere at altitudes >70 kilometres, are transported into the winter polar vortices by the mesospheric meridional circulation and are preferentially deposited in the polar ice caps. This implies an average global fallout of 14 +/- 5 kilotons per year of meteoric smoke during the Holocene.     

Muted climate variations in continental Siberia during the mid-Pleistocene epoch

The large difference in carbon and oxygen isotope data from the marine record between marine oxygen isotope stage 12 (MIS 12) and MIS 11, spanning the interval between about 480 and 380 kyr ago, has been interpreted as a transition between an extremely cold glacial period and an unusually warm interglacial period, with consequences for global ice volume, sea level and the global carbon cycle. The extent of the change is intriguing, because orbital forcing is predicted to have been relatively weak at that time. Here we analyse a continuous sediment record from Lake Baikal, Siberia, which reveals a virtually continuous interglacial diatom assemblage, a stable littoral benthic diatom assemblage and lithogenic sediments with 'interglacial' characteristics for the period from MIS 15a to MIS 11 (from about 580 to 380 kyr ago). From these data, we infer significantly weaker climate contrasts between MIS 12 and 11 than during more recent glacial-interglacial transitions in the late Pleistocene epoch (about 130 to 10 kyr ago). For the period from MIS 15a to MIS 11, we also infer an apparent lack of extensive mountain glaciation.     

美国怎样实施教育产业化

教育始终是美国人所关心的国内社会政策的首要问题，其程度超过了对其他诸如经济、医疗保健及社会保障等问题的关心。人们关心教育，关心他们的孩子，在有关教育问题的全国性大讨论中，尽管充斥各种言辞且常常意见不一，但却创造了一种环境，使富有创见的思想在这个环境中滋生并迅速成长。从事教育产业的企业家们了解这些，并抓住这种机会，促进了以产业方式进行的教育改革。     

Names of Legal Profession in the United Kingdom and the United States

In the paper, I try to analyze the different divisions and titles in the United Kingdom and the United States. In the United Kingdom, the legal profession is traditionally divided into two branches, barristers and solicitors (the advocate in Scotland is equivalent to barrister); in the United States, there was never a formal separation of barrister and solicitor as in England, lawyers usually deal with a certain field of legal matters. In addition, I also try to speak something about the development and changes of "proctor", as well as the two kinds of "attorney" and their different development in the Great Britain and the United States.     

Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula

The disintegration of ice shelves, reduced sea-ice and glacier extent, and shifting ecological zones observed around Antarctica highlight the impact of recent atmospheric and oceanic warming on the cryosphere. Observations and models suggest that oceanic and atmospheric temperature variations at Antarctica's margins affect global cryosphere stability, ocean circulation, sea levels and carbon cycling. In particular, recent climate changes on the Antarctic Peninsula have been dramatic, yet the Holocene climate variability of this region is largely unknown, limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms. Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 °C over the past 12,000 years, tracking the Holocene decline of local (65° S) spring insolation. Our results, based on TEX(86) sea surface temperature (SST) proxy evidence from a marine sediment core, indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations. On millennial timescales, abrupt SST fluctuations of 2-4 °C coincide with globally recognized climate variability. Similarities between our SSTs, Southern Hemisphere westerly wind reconstructions and El Ni?o/Southern Oscillation variability indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula strengthened late in the Holocene epoch. We conclude that during the Holocene, Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies, which have a critical role in global carbon cycling.     

Lowland-upland migration of sauropod dinosaurs during the Late Jurassic epoch

Sauropod dinosaurs were the largest vertebrates ever to walk the Earth, and as mega-herbivores they were important parts of terrestrial ecosystems. In the Late Jurassic-aged Morrison depositional basin of western North America, these animals occupied lowland river-floodplain settings characterized by a seasonally dry climate. Massive herbivores with high nutritional and water needs could periodically experience nutritional and water stress under these conditions, and thus the common occurrence of sauropods in this basin has remained a paradox. Energetic arguments and mammalian analogues have been used to suggest that migration allowed sauropods access to food and water resources over a wide region or during times of drought or both, but there has been no direct support for these hypotheses. Here we compare oxygen isotope ratios (δ(18)O) of tooth-enamel carbonate from the sauropod Camarasaurus with those of ancient soil, lake and wetland (that is, 'authigenic') carbonates that formed in lowland settings. We demonstrate that certain populations of these animals did in fact undertake seasonal migrations of several hundred kilometres from lowland to upland environments. This ability to describe patterns of sauropod movement will help to elucidate the role that migration played in the ecology and evolution of gigantism of these and associated dinosaurs.     

美国金融危机评析

2008年9月,美国金融危机井喷式爆发,并迅速波及其他国家。受其影响,全球股市剧烈波动,实体经济也不断遭受冲击。本文将就本次金融危机产生的原因、谁该为这次危机负责、政府是否应该救市以及应该从中吸取哪些教训等一系列问题进行研究、探讨。     

Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch

The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago), when the Equator-to-pole temperature gradients were much smaller than today and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume. Recently the early Eocene has received considerable interest because it may provide insight into the response of Earth's climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future as a consequence of unabated anthropogenic carbon emissions. Climatic conditions of the early Eocene 'greenhouse world', however, are poorly constrained in critical regions, particularly Antarctica. Here we present a well-dated record of early Eocene climate on Antarctica from an ocean sediment core recovered off the Wilkes Land coast of East Antarctica. The information from biotic climate proxies (pollen and spores) and independent organic geochemical climate proxies (indices based on branched tetraether lipids) yields quantitative, seasonal temperature reconstructions for the early Eocene greenhouse world on Antarctica. We show that the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70° south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae. Notably, winters were extremely mild (warmer than 10?°C) and essentially frost-free despite polar darkness, which provides a critical new constraint for the validation of climate models and for understanding the response of high-latitude terrestrial ecosystems to increased carbon dioxide forcing.     

美国早期的图像广告与月份牌

在美国,印刷月份牌广告开始于19世纪.70年代新发展的彩色平版印刷技术促进了彩色月份牌迅速发展.月份牌上的图像常常与售卖的产品或服务关系不大,甚至毫不相干.印刷从业者们还在专业杂志上登广告声称可以提供包括月份牌在内的宣传新产品的图像.美国海报广告与月份牌给人印象最深的是那些丰富到惊人的人物衣着、华丽的装饰性文字搭配以及具象的形象,尽管两者有广泛的创造性,它们共享着某些共同的图像元素.