Vegetation in western Central Mexico during the last 50 000 years: modern analogs and climate in the Zacapu Basin     

A. Correa‐Metrio  S. Lozano‐García  S. Xelhuantzi‐López  S. Sosa‐Nájera  S. E. Metcalfe 《第四纪科学杂志》2012,27(5):509-518

The late glacial and the transition towards the Holocene marked a period of significant environmental change at a global scale. In western Central Mexico, few records span beyond the Holocene, and little is known about Pleistocene climatic and environmental variability. Here we report on the pollen record of a composite sequence made of three cores that cover the last 50 ka (thousands of calibrated radiocarbon years before present) in the Zacapu Basin, western Central Mexico (～1970 m asl). The conjunction of modern pollen rain from the area with the composite fossil pollen sequence from cores Cantabria, Cantabria 1 and CEMCA Point‐1 provided a detailed history of the vegetation of the area. Recognition of modern environmental patterns through individual modern pollen taxa proved difficult, but multivariate analysis separated different vegetation types. No‐modern‐analog communities relative to the modern vegetation cover of the area were evident, especially during periods of drought. Apparently, summer precipitation was significant before 40 ka and after the deglaciation. However, this moisture source declined from ～40 to 10 ka because tradewinds from the Gulf of Mexico were blocked by the eastern mountains of Central Mexico as a result of lower temperatures. By contrast, westerly and northerly winds were enhanced by maximum ice cover from ～19 to 17 ka, providing abundant winter precipitation and therefore preventing extreme drought in the area. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Sediment bioavailable organic matter,deposition rates and mixing intensity in the Setúbal–Lisbon canyon and adjacent slope (Western Iberian Margin)     

R. García  L. Thomsen  H.C. de Stigter  E. Epping  K. Soetaert  E. Koning  P.A. de Jesus Mendes 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(8):1012-1026

The role of the Setúbal–Lisbon canyon in accumulation and transport of labile organic matter from the coastal sea and ocean surface water towards the deep sea was assessed by investigating the distribution of organic matter of different quality in sedimentary aggregates and surface sediments of the canyon and adjacent slopes. Total hydrolysable amino acids (THAA) and organic carbon (Corg) were measured from aggregates, and contents of Corg, chlorophyll a (chl a), phaeopigments (phaeo), chloroplastic pigment equivalents (CPE) from sediments. As indices of organic matter (OM) quality THAA:Corg, degradation index (DI), chl a:phaeo, chl a:Corg and C:N ratio were determined. Sediment profiles of chl a and the isotope 210 of lead (²¹⁰Pb) were used as tracers in a transport model to estimate deposition rates and background levels of the tracers, and sediment mixing rates (Db). Whereas bulk Corg contents of canyon and slope sediments were practically similar at all depths, higher contents of THAA, chl a and CPE, as well as higher THAA:Corg, DI and chl a:Corg, in aggregates and sediments from the upper reaches of the canyon indicate that labile organic matter accumulates in the upper canyon. This is confirmed by higher chl a and ²¹⁰Pb deposition and Db calculated from the model. Hence, the Setúbal–Lisbon canyon, specially the upper region, acts as a natural trap of organic matter that is transported to the region via lateral transport and vertical settling from primary productivity. Organic matter might be further transported in downward canyon direction via rebound processes. The chl a and ²¹⁰Pb profiles reveal active sediment mixing by physical processes and/or animal reworking.  相似文献   

A proposed adiabatic formulation of 3‐dimensional global atmospheric models based on potential vorticity     

YONG LI  J. RUGE  J. R. BATES  A. BRANDT 《地球，A辑:动力气象学与海洋学》2000,52(2):129-139

A 2‐time‐level finite difference atmospheric general circulation model based on the semi‐Lagrangian advection of pseudo potential vorticity (which becomes potential vorticity in that part of the domain where the hybrid vertical coordinate becomes isentropic) has been formulated. At low levels, the hybrid vertical coordinate is terrain following. The problem of isentropic potential vorticity possibly becoming ill‐defined in the regions of planetary boundary layer is thus circumvented. The divergence equation is a companion to the (pseudo) potential vorticity equation and the model is thus called a PV‐D model. Many features of a previously developed shallow water PV‐D model are carried over: a modification of the PV equation needed to give computational stability of long Rossby waves; a semi‐Lagrangian semi‐implicit treatment of both the linear and the nonlinear terms; the use of an unstaggered grid in the horizontal; the use of a nonlinear multigrid technique to solve the nonlinear implicit equations. A linear numerical stability analysis of the model's gravity–inertia waves indicates that the potential temperature needs to be separated into horizontal mean and perturbation parts. This allows an implicit treatment of the vertical advection associated with the mean in the thermodynamic equation. Numerical experiments with developing baroclinic waves have been carried out and give realistic results.  相似文献   

CONTRIBUTIONS OF PROF.ZHU KEZHEN TO THE DEVELOPMENT OF METEOROLOGY IN CHINA-IN MEMORY OF HIS CENTENARY BIRTHDAY          下载免费PDF全文

Tao Shiyan 《Acta Meteorologica Sinica》1990,4(4):395-398

The year of 1990 is the 100th anniversary of birth of Prof.Zhu Kezhen(Chu Kochen),a great founder of China's modern meteorology who devoted all his life to its flourishing in the country.It has long been a generally-accepted fact that our meteorology of today,in both practical and theoretical aspects,is owed to his enormous contribution.We publish the special issue of the journal just to cherish the memory of his contribution and of his brilliant example of meticulous scholarship, assiduity in study and eagerness to pursue truth, which serve as a powerful source of continuous encouragement to advance the modernization of our meteorological undertakings.  相似文献   

Biomass size spectrum of net plankton in the southern Huanghai Sea in autumn          下载免费PDF全文

ZUO Tao  WANG Jun  TANG Qi-sheng  JIN Xian-shi 《海洋学报》2008,30(5)

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叠加变形有限应变分解及其应用探讨     

王涛  王晓霞 《地球科学与环境学报》1991,(4)

本文提出了二维不同类型叠加变形的有限应变分解方法。只要测定有限应变及能代表各期主应变面的面理或剪切指向,就可以计算出各期构造应变。  相似文献   

Jurassic‐to‐present thermal history of the central High Atlas (Morocco) assessed by low‐temperature thermochronology     

Luis Barbero  Antonio Teixell  María‐Luisa Arboleya  Pedro del Río  Peter W. Reiners  Blaid Bougadir 《地学学报》2007,19(1):58-64

Apatite fission track (AFT) and (U–Th)/He data from the High Atlas have been obtained for the first time to constrain the tectono‐thermal evolution of the central part of the chain. Results from Palaeozoic basement massifs indicate long residence at low temperatures, consistently with their original location out of the deepest Mesozoic rift troughs and indicating minor exhumation. The best rocks for extracting the Alpine history of the Atlas Mountains are Jurassic intrusives, which yield AFT ages centred on c. 80 Ma; thermal models based on AFT data and constrained by (U–Th)/He suggest that these ages are included in a slow cooling trend from intrusion age to c. 50 Ma ago that we attribute to post‐rift thermal relaxation. This is followed by a stability period of c. 30 Ma and then by a final exhumational cooling until present exposure. Eocene intrusives yield AFT ages similar to those of Rb–Sr and K–Ar suggesting rapid emplacement in the uppermost crust.  相似文献   

Trends,rhythms and events in Plio-Pleistocene African climate     

Martin H. Trauth  Juan C. Larrasoaña  Manfred Mudelsee 《Quaternary Science Reviews》2009,28(5-6):399-411

We analyzed published records of terrigenous dust flux from marine sediments off subtropical West Africa, the eastern Mediterranean Sea, and the Arabian Sea, and lake records from East Africa using statistical methods to detect trends, rhythms and events in Plio-Pleistocene African climate. The critical reassessment of the environmental significance of dust flux and lake records removes the apparent inconsistencies between marine vs. terrestrial records of African climate variability. Based on these results, major steps in mammalian and hominin evolution occurred during episodes of a wetter, but highly variable climate largely controlled by orbitally induced insolation changes in the low latitudes.  相似文献   

北喀斯喀特边缘IODP 311航次断面的地震结构、天然气水合物含量和滑塌构造   总被引：1，自引：0，他引：1  

George Spence  Caroll Lopez  Tao He  杨传胜 《海洋地质前沿》2008,24(11):44-47

北喀斯喀特活动边缘的增生楔沉积物中含有分布广泛的天然气水合物一直延伸到海底下几百米的深度。为了评估天然气水合物的长期能源潜力和它在全球气候变化及边坡稳定性中的作用，2005年9月IODP311航次建立了一个详细的地质模型来解释水合物的形成与分解以及它与穿过大陆边缘流体流的伴生关系。在考察前，先在大陆坡上进行地震试验以提供支持钻井的地球物理信息。  相似文献   

The role of basement inheritance faults in the recent fracture system of the inner shelf around Alboran Island,Western Mediterranean     

A.?Maestro-GonzálezEmail author  P.?Bárcenas  J.?T.?Vázquez  V.?Díaz-del-Río 《Geo-Marine Letters》2008,28(1):53-64

Fractures associated with volcanic rock outcrops on the inner shelf of Alboran Island, Western Mediterranean, were mapped on the basis of a side-scan sonar mosaic. Absolute maximum fracture orientation frequency is NW–SE to NNW–SSE, with several sub-maxima oriented NNE–SSW, NE–SW and ENE–WSW. The origin of the main fracture systems in Neogene and Quaternary rocks of the Alboran Basin (south Spain) appears to be controlled by older structures, namely NE–SW and WNW–ESE to NW–SE faults which cross-cut the basement. These faults, pre-Tortonian in origin, have been reactivated since the early Neogene in the form of strike-slip and extensional movements linked to the recent stress field in this area. Fracture analysis of volcanic outcrops on the inner continental shelf of Alboran Island suggests that the shelf has been deformed into a narrow shear zone limited by two NE–SW-trending, sub-parallel high-angle faults, the main orientation and density of which have been influenced by previous WNW–ESE to NW–SE basement fractures.  相似文献