El Niño-like pattern in ice age tropical Pacific sea surface temperature

Sea surface temperatures (SSTs) in the cold tongue of the eastern equatorial Pacific exert powerful controls on global atmospheric circulation patterns. We examined climate variability in this region from the Last Glacial Maximum (LGM) to the present, using a SST record reconstructed from magnesium/calcium ratios in foraminifera from sea-floor sediments near the Galápagos Islands. Cold-tongue SST varied coherently with precession-induced changes in seasonality during the past 30,000 years. Observed LGM cooling of just 1.2 degrees C implies a relaxation of tropical temperature gradients, weakened Hadley and Walker circulation, southward shift of the Intertropical Convergence Zone, and a persistent El Ni?o-like pattern in the tropical Pacific. This is contrasted with mid-Holocene cooling suggestive of a La Ni?a-like pattern with enhanced SST gradients and strengthened trade winds. Our results support a potent role for altered tropical Pacific SST gradients in global climate variations.     

Ice age paleotopography

A gravitationally self-consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the Last Glacial Maximum (LGM). The results show that LGM ice volume was approximately 35 percent lower than suggested by the CLIMAP reconstruction and the maximum heights of the main Laurentian and Fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level. Use of these Ice Age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the CLIMAP data set.     

The salinity,temperature, and delta18O of the glacial deep ocean

We use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from Ocean Drilling Program cores to reconstruct salinity and temperature of the deep ocean during the Last Glacial Maximum (LGM). Our data show that the temperatures of the deep Pacific, Southern, and Atlantic oceans during the LGM were relatively homogeneous and within error of the freezing point of seawater at the ocean's surface. Our chloride data show that the glacial stratification was dominated by salinity variations, in contrast with the modern ocean, for which temperature plays a primary role. During the LGM the Southern Ocean contained the saltiest water in the deep ocean. This reversal of the modern salinity contrast between the North and South Atlantic implies that the freshwater budget at the poles must have been quite different. A strict conversion of mean salinity at the LGM to equivalent sea-level change yields a value in excess of 140 meters. However, the storage of fresh water in ice shelves and/or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level.     

Tropical climate at the last glacial maximum inferred from glacier mass-balance modeling

Model-derived equilibrium line altitudes (ELAs) of former tropical glaciers support arguments, based on other paleoclimate data, for both the magnitude and spatial pattern of terrestrial cooling in the tropics at the last glacial maximum (LGM). Relative to the present, LGM ELAs were maintained by air temperatures that were 3.5 degrees to 6.6 degrees C lower and precipitation that ranged from 63% wetter in Hawaii to 25% drier on Mt. Kenya, Africa. Our results imply the need for a approximately 3 degrees C cooling of LGM sea surface temperatures in the western Pacific warm pool. Sensitivity tests suggest that LGM ELAs could have persisted until 16,000 years before the present in the Peruvian Andes and on Papua, New Guinea.     

Mediterranean moisture source for an early-Holocene humid period in the northern Red Sea

Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about 3 per thousand reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff, which thereafter decreased to modern values. The northern Red Sea humid interval is best explained by enhancement and southward extension of rainfall from Mediterranean sources, possibly involving strengthened early-Holocene Arctic Oscillation patterns and a regional monsoon-type circulation induced by increased land-sea temperature contrasts. We conclude that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene.     

Dust: a diagnostic of the hydrologic cycle during the last glacial maximum

Dust concentrations in ice of the last glacial maximum (LGM) are high in ice cores from Greenland and Antarctica. The magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the LGM was about half of that at present. This notion is consistent with a large decrease (5 degrees Celsius) in ocean temperature during the LGM, as recently deduced from measurements of strontium and calcium in corals.     

Penny ice cap cores, baffin island, canada, and the wisconsinan foxe dome connection: two states of hudson bay ice cover

Ice cores from Penny Ice Cap, Baffin Island, Canada, provide continuous Holocene records of oxygen isotopic composition (delta18O, proxy for temperature) and atmospheric impurities. A time scale was established with the use of altered seasonal variations, some volcanic horizons, and the age for the end of the Wisconsin ice age determined from the GRIP and GISP2 ice cores. There is pre-Holocene ice near the bed. The change in delta18O since the last glacial maximum (LGM) is at least 12.5 per mil, compared with an expected value of 7 per mil, suggesting that LGM ice originated at the much higher elevations of the then existing Foxe Dome and Foxe Ridge of the Laurentide Ice Sheet. The LGM delta18O values suggest thick ice frozen to the bed of Hudson Bay.     

The history of South American tropical precipitation for the past 25,000 years

Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.     

Oligotrophy and nitrogen fixation during eastern mediterranean sapropel events

Nitrogen isotopic measurements in fossil chlorophyll from late Pleistocene organic-rich sediments (sapropels) in the eastern Mediterranean Sea provide geochemical evidence for stratified, nutrient-depleted surface water and extensive nitrogen fixation. This evidence is reconciled with previous indications of high productivity by invoking a model of sapropel formation in which increased river discharge facilitates development of a specialized phytoplankton population whose annual mass sinking provides the organic flux to generate sapropels. This interpretation is consistent with the widespread occurrence of mat-forming diatoms that thrive in stratified water and can harbor diazotrophic bacterial symbionts, but does not support eutrophication of surface waters by enhanced river runoff or a circulation reversal.     

Recent plant diversity changes on Europe's mountain summits

In mountainous regions, climate warming is expected to shift species' ranges to higher altitudes. Evidence for such shifts is still mostly from revisitations of historical sites. We present recent (2001 to 2008) changes in vascular plant species richness observed in a standardized monitoring network across Europe's major mountain ranges. Species have moved upslope on average. However, these shifts had opposite effects on the summit floras' species richness in boreal-temperate mountain regions (+3.9 species on average) and Mediterranean mountain regions (-1.4 species), probably because recent climatic trends have decreased the availability of water in the European south. Because Mediterranean mountains are particularly rich in endemic species, a continuation of these trends might shrink the European mountain flora, despite an average increase in summit species richness across the region.     

第四纪末次盛冰期以来福建柏的潜在地理分布变迁

采用MaxEnt模型,对濒危孑遗植物福建柏末次盛冰期、全新世中期、现代和未来4个时期适生分布区情况及动态变迁过程进行模拟,探讨影响其分布的主要因素及对气候变化的响应。结果表明:1）平均气温日较差、最暖季平均温度、最干月降雨量对福建柏空间分布适宜性影响最大;2）福建柏分布对全球气候变化响应较为敏感,末次盛冰期其分布最广,为194.04万km²,随气候变暖,全新世中期和未来其分布范围分别缩小33.48万km²和31.26万km²;3）与现在相比,未来气候条件下福建柏整体呈“南北收缩”“东西扩张”分布趋势。研究结果不仅对我国热带和亚热带常绿阔叶林生物地理界限具有一定指示意义,也可为全球气候变暖背景下福建柏种质资源的保护和合理利用提供重要的理论基础。     

甘肃少数民族地区农村土地流转新路径探究

土地流转是中国实现农业现代化的前提条件。在甘肃少数民族地区,由于经济文化欠发达,土地流转面临着特殊的境遇和矛盾,需要深入研究甘肃少数民族地区农村土地流转瓶颈的深刻原因,探索适合民族地区土地流转的科学模式,从而有效推进民族地区农业现代化进程。     

Larval testes of the tobacco budworm: a new source of insect ecdysteroids

Testes of last-instar larvae of the tobacco budworm release five times more ecdysteroid into incubation medium (judged by radioimmunoassay) in 2.5 hours than is found in testis homogenates. Incubation of testicular components indicates that the testis sheath may be the site of ecdysteroid synthesis. Fractionation of hemalymph, testis homogenate, and incubation medium by high-performance liquid chromatography produces a distinct ecdysteroid pattern in each case. Thus, released testis ecdysteroids are probably converted to other forms for use, sequestration, or general circulation. Their functions are unknown.     

Atlantic meridional overturning circulation during the Last Glacial Maximum

The circulation of the deep Atlantic Ocean during the height of the last ice age appears to have been quite different from today. We review observations implying that Atlantic meridional overturning circulation during the Last Glacial Maximum was neither extremely sluggish nor an enhanced version of present-day circulation. The distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the Atlantic only slightly greater than today. However, evidence from multiple water-mass tracers supports a different distribution of deep-water properties, including density, which is dynamically linked to circulation.     

Global change and agricultural management options for groundwater sustainability

According to the general circulation models (CGMs) for future climate projections, a temperature increase, precipitation decrease, and an increase in the variability of extreme events may be expected in the future, likely reducing available water resources. For the western Mediterranean, future climate change projections indicate that temperature increase may range from 1.5 °C to 3.6 °C, and the precipitation decline will reach between 10% and 20%, which may result in a significant reduction of natural groundwater recharge. With the use of modelling tools, the amount of groundwater recharge under different climate change scenarios and varying agricultural management practices can be predicted, and water budget attributes can be estimated, which may allow for quantifying impacts, and assist in defining adaptation strategies. For the Inca–Sa Pobla basin (Balearic Islands, Spain), under future climate change projections, agricultural management alternatives of crop type distribution and irrigation demands are required for planned adaptation strategies. In the area, where irrigation water for agricultural practices originates from groundwater resources, adaptation measures based on a change from mixed crops to potatoes and a 20% decrease of agricultural land cultivation have proven to be efficient for the hydrologic system and associated wetland sustainability.     

Olive groves: ``The life and identity of the Mediterranean'

Olive tree cultivation in theMediterranean goes back to ancient times. Evensince the Roman Age, olive cultivation spreadto the entire Mediterranean basin. Thislongevous tree integrates and identifieseconomically, socially, and culturally theinhabitants of this basin and determines itsrural landscape. For the residents of theMediterranean, olive oil constituted the mainsource of nutritional fats, their most valuableexport product, and was identified with theirculture. Even now, olive cultivation has amultiple importance for the Mediterranean. Theolive groves, which grow mostly on inclined,shallow, and low fertility soils, and onhand-made stone terraces, have limited wateringrequirements and sustain the fragile naturalresources of the Mediterranean. Today,olive cultivation in the Mediterranean is anadditional income source and supports thepopulation in rural areas during the winterperiod, which profit from summer and seatourism activity. Although anagro-ecosystem, the olive grove resembles thenatural Mediterranean ecosystem and abandonmenttransforms them into natural Mediterranean typeforests. Their change of use from olivecultivation to pasture degrades the ecosystemand decreases the natural resources, because ofover-grazing. At this time, two major factorsthreaten the traditional olive cultivation (i)the competition of the intensive olive grovesin plain and irrigated areas and (ii) thecheaper seed-oils, which intensify theabandonment of traditional olive groves andchange them into pasture, resulting in thedeterioration of the ecosystem. Olivecultivation has left its mark on life in theMediterranean and has contributed to thesustainability of natural resources.Nevertheless, it succumbs under the pressure ofcurrent socioeconomic situations. Today, theconservation of olives in productionconstitutes a necessity for the fragileMediterranean ecosystems and a challenge foreverybody involved.     

Mediterranean action plan: an interim evaluation

The Mediterranean Action Plan is an extensive program of regional environmental cooperation on technical and institutional approaches to pollution monitoring, environmental assessment, and policy-making. The simultaneous development of a regional monitoring network and legal instruments to protect the Mediterranean from pollution is an important achievement, which provides a firm basis for continuing cooperative efforts.     

地中海农耕文化的革命

本文通过以叙述地中海气候及其相应的植物为开端,从当地农作物的品种、作物栽培和加工技术等方面论述地中海农耕文化的衍变历史,揭示出发生在地中海地区的若干次农业革命给人类社会带来的影响。同时通过将之与世界其它主要几个农耕文化相比较印证,希望对亚洲和非洲如何更快地发展自身农业的问题有所启发。     

Stratospheric memory and skill of extended-range weather forecasts

We use an empirical statistical model to demonstrate significant skill in making extended-range forecasts of the monthly-mean Arctic Oscillation (AO). Forecast skill derives from persistent circulation anomalies in the lowermost stratosphere and is greatest during boreal winter. A comparison to the Southern Hemisphere provides evidence that both the time scale and predictability of the AO depend on the presence of persistent circulation anomalies just above the tropopause. These circulation anomalies most likely affect the troposphere through changes to waves in the upper troposphere, which induce surface pressure changes that correspond to the AO.     

日本图书馆的流通服务特色的启示

馆舍和设备是流通服务的前提和基础,日本图书馆的馆舍和设备现代化水平较高。日本图书馆工作人员的人性化服务态度和服务方式具有鲜明的个性。日本图书馆的＂读者第一、服务至上＂服务意识更是对改善我国图书馆的服务质量具有借鉴和启示作用。