A Global Dynamic Model for the Neolithic Transition     

Kai W. Wirtz  Carsten Lemmen 《Climatic change》2003,59(3):333-367

During the Holocene strong gradients in the distribution of technologyincluding subsistence ways emerged on a global scale.These patterns were further amplified in historic times and are stillvisible through worldwide differences in national wealth.In order to evaluate major factors responsible for the shift fromforaging to food production we here employ quantitative methods bydeveloping a deterministic but simple model. After compiling existing maps of potential vegetation at 5000 BP theinhabited world is split into 197 regions with homogeneous environmentalconditions. Suitable variables for the macro-economic and culturaldevelopment in the Neolithic period are found to be farming to hunting-gatheringratio, number of agricultural economies and a technological development index.The model explicitly describes economic adaptation, growth and migrationof human populations together with the spread of their cultural characteristics; it accounts for over-exploitation of natural resources, crowdingmortality and the climate variability on a millennium scale.In a thorough model validation region specific trajectories are compared toarchaeological evidence revealing a high correspondence. Major parts of the knownsequence of Neolithic centers including the timing differences are robustlyreproduced. A series of known problems in prehistory is discussedcomprising the lag between domestication and full scale farming, the off-levelingof the technological boost following the transition, the emergence ofdistinct migration waves and sensitivity to climate fluctuations.Not mere population pressure but continuous innovation and competition betweensubsistence strategies is identified as a prime mover of agricultural development.The results suggest that few aspects of biogeography may have determined theobserved continental gradients in the number of domesticable species ultimatelyleading to an increasing differentiation in technology and demography.  相似文献   

Alkaline Degradation of Dissolved Organic Matter     

Thomas Brinkmann  Gudrun Abbt‐Braun  Fritz H. Frimmel 《洁净——土壤、空气、水》2003,31(3):213-224

The degradation of dissolved organic matter (DOM) was studied in alkaline solution. The products were characterised using UV/vis spectroscopy, size‐exclusion chromatography (SEC), and by the analysis of low‐molecular‐weight organic acids (LMWOA). The degradation experiments were performed with water from a brown water lake or its isolated fulvic acid fraction and sodium hydroxide at different reaction times and temperatures. Depending on the wavelength and the reaction time, the UV/vis absorbance between 230 nm and 600 nm increased or decreased. The behaviour of model compounds during reactions in alkaline media was compared to the UV/vis spectroscopic behaviour of DOM. The release of LMWOA was described by kinetic data and compared to the data of model reactions. Evidence was given for the carboxylic esters playing a significant role in the release of LMWOA only during the beginning of the alkaline degradation. The results gained by SEC with on‐line UV and DOC detection showed that the average size of DOM was decreasing, and that a major part of the degradation products consisted of low‐molecular‐weight mono‐ and dicarboxylic acids.  相似文献   

How depositional conditions control input, composition, and degradation of organic matter in sediments from the Chilean coastal upwelling region     

Jutta Niggemann  Timothy G. Ferdelman  Jens Kallmeyer  Carsten J. Schubert 《Geochimica et cosmochimica acta》2007,71(6):1513-1527

In a comprehensive study, we compared depositional conditions, organic matter (OM) composition, and organic carbon turnover in sediments from two different depositional systems along the Chilean continental margin: at ∼23° S off Antofagasta and at ∼36° S off Concepción. Both sites lie within the Chilean coastal upwelling system and have an extended oxygen minimum zone in the water column. However, the northern site (23° S) borders the Atacama Desert, while the southern site (36° S) has a humid hinterland. Eight surface sediment cores (up to 30 cm long) from water depths of 126-1350 m were investigated for excess ²¹⁰Pb (²¹⁰Pb_xs) activity, total organic and total inorganic carbon concentrations (TOC and TIC, respectively), C/N-ratios, organic carbon isotopic compositions (δ¹³C), chlorin concentrations, Chlorin Indices (CI), and sulfate reduction rates (SRR). Sediment accumulation rates obtained from ²¹⁰Pb-analysis were similar in both regions (0.04-0.15 cm yr⁻¹ at 23° S, 0.10-0.19 cm yr⁻¹ at 36° S), although total ²¹⁰Pb_xs fluxes indicated that the vertical particle flux was higher at 36° S than at 23° S. We propose that sediment focusing in isolated deposition centers led to high sediment accumulation rates at 23° S. Furthermore, there were no indications for sediment mixing at 23° S, while bioturbation was intense at 36° S. δ¹³C-values (−24.5‰ to −20.1‰ vs. VPDB) and C/N-ratios (molar, 8.6-12.8) were characteristic of a predominantly marine origin of the sedimentary OM in both investigated areas. The extent of OM alteration in the water column was partly reflected in the surface sediments as chlorin concentrations decreased and C/N-ratios and CI increased with increasing water depth of the sampling site. SRR were lower at 23° S (areal SRR 0.12-0.60 mmol m⁻² d⁻¹) than at 36° S (areal SRR 0.82-1.18 mmol m⁻² d⁻¹), which was partly due to the greater water depth of most of the sediments investigated in the northern region and consistent with a lower quality of the sedimentary OM at 23° S. Reaction rate constants for TOC degradation that were obtained from measured SRR (k_SRR; 0.0004-0.0022 yr⁻¹) showed a good correspondence to k_TOC that were derived from the depth profiles of TOC (0.0003-0.0014 yr⁻¹). Both, k_SRR and k_TOC, reflect differences in OM composition. At 36° S they were related to the degradation state of bulk OM (represented by C/N-ratios), whereas near 23° S they were related to the freshness of a small fraction of labile OM (represented by CI). Our study shows that although rates of organic carbon accumulation were similar in both investigated sites, the extent and kinetics of organic carbon degradation were closely linked to differing depositional conditions.  相似文献   

Sources and fate of amino sugars in coastal Peruvian sediments     

Jutta Niggemann  Carsten J. Schubert 《Geochimica et cosmochimica acta》2006,70(9):2229-2237

Amino sugars are involved in the marine carbon and nitrogen cycles and comprise a geochemically significant fraction of marine organic material (OM). However, information on abundance and distribution of these compounds in marine sediments is scarce. Three sediment cores (<50 cm) from the coastal region off Peru were investigated for concentrations of glucosamine (GlcN), galactosamine (GalN), mannosamine (ManN), and muramic acid (Mur). The sum of the four amino sugars accounted for 1.0-2.4% of organic carbon and 1.9-3.8% of nitrogen in the sediments. At the shallowest (102 m) and the deepest site (1278 m), carbon-normalized concentrations decreased down-core, suggesting preferential degradation of amino sugars compared to bulk sedimentary OM. At the site from the center of the oxygen minimum zone (238 m), amino sugar concentrations were high throughout the core, pointing to enhanced preservation of amino sugars under anoxic conditions. GlcN (44-56 mol%) and GalN (33-42 mol%) were the dominant amino sugars in all investigated samples, while ManN (6-14 mol%) and Mur (1-4 mol%) were significantly less abundant. Mur was predominantly associated with cell wall remains rather than with living bacteria, since bacterial abundances estimated based on Mur concentrations were up to 500 times higher than cell counts reported for sediments from this area. GlcN/GalN-ratios (1.1-1.7) indicated that chitin, a polymer of GlcN, was not a major contributor to the amino sugar pool of the investigated sediments. Furthermore, GlcN/Mur-ratios (13-68) are inconsistent with a predominant contribution of intact peptidoglycan, which exhibits a 1:1-ratio. The present study includes a compilation of previously published information on distribution and abundance of amino sugars in the marine environment. Both concentrations and ratios observed in the Peruvian sediments fall in the range of values reported for OM in water column and sediments from different oceanic regions and water depths. Although specific sources for the majority of sedimentary amino sugars remain unidentified, there are indications for a major prokaryotic origin. As suggested in previous studies, the uniform amino sugar compositions of altered marine OM and particularly the close association of GlcN and GalN, which is similar to the ratio observed in living bacteria, are consistent with a transformation of planktonic into bacterial OM.  相似文献   

Effects of suspended sediment on development and hatching of herring (Clupea harengus) eggs     

Thomas Kiørboe  Erik Frantsen  Carsten Jensen  Gorm Sørensen 《Estuarine, Coastal and Shelf Science》1981,13(1):107-111

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High-Spatial-Resolution Imaging Combining High-Order Adaptive Optics,Frame Selection,and Speckle Masking Reconstruction     

Carsten?DenkerEmail author  Dulce?Mascarinas  Yan?Xu  Wenda?Cao  Guo?Yang  Haimin?Wang  Philip?R.?Goode  Thomas?Rimmele 《Solar physics》2005,227(2):217-230

We present, for the first time, high-spatial-resolution observations combining high-order adaptive optics (AO), frame selection, and post-facto image correction via speckle masking. The data analysis is based on observations of solar active region NOAA 10486 taken with the Dunn Solar Telescope (DST) at the Sacramento Peak Observatory (SPO) of the National Solar Observatory (NSO) on 29 October 2003. The high Strehl ratio encountered in AO corrected short-exposure images provides highly improved signal-to-noise ratios leading to a superior recovery of the object’s Fourier phases. This allows reliable detection of small-scale solar features near the diffraction limit of the telescope. Speckle masking imaging provides access to high-order wavefront aberrations, which predominantly originate at high atmospheric layers and are only partially corrected by the AO system. In addition, the observations provided qualitative measures of the image correction away from the lock point of the AO system. We further present a brief inspection of the underlying imaging theory discussing the limitations and prospects of this multi-faceted image reconstruction approach in terms of the recovery of spatial information, photometric accuracy, and spectroscopic applications.The editors apologize to the authors: due to a misunderstanding during the editorial process, the publication of this paper has been delayed.  相似文献   

High-Resolution Hα Observations of Proper Motion in NOAA 8668: Evidence for Filament Mass Injection by Chromospheric Reconnection     

Chae  Jongchul  Denker  Carsten  Spirock  Tom J.  Wang  Haimin  Goode  Philip R. 《Solar physics》2000,195(2):333-346

There have been two different kinds of explanations for the source of cool material in prominences or filaments: coronal condensations from above and cool plasma injections from below. In this paper, we present observational results which support filament mass injection by chromospheric reconnection. The observations of an active filament in the active region NOAA 8668 were performed on 17 August 1999 at a wavelength of H–0.6 Å using the 65 cm vacuum reflector, a Zeiss H birefringent filter, and a 12-bit SMD digital camera of Big Bear Solar Observatory. The best image was selected every 12 s for an hour based on a frame selection algorithm. All the images were then co-aligned and corrected for local distortion due to the seeing. The time-lapse movie of the data shows that the filament was undergoing ceaseless motion. The H flow field has been determined as a function of time using local correlation tracking. Time-averaged flow patterns usually trace local magnetic field lines, as inferred from H fibrils and line-of-sight magnetograms. An interesting finding is a transient flow field in a system of small H loops, some of which merge into the filament. The flow is associated with a cancelling magnetic feature which is located at one end of the loop system. Initially a diverging flow with speeds below 10 km s^–1 is visible at the flux cancellation site. The flow is soon directed along the loops and accelerated up to 40 km s^–1 in a few minutes. Some part of the plasma flow then merges into and moves along the filament. This kind of transient flow takes place several times during the observations. Our results clearly demonstrate that reconnection in the photosphere and chromosphere is a likely way to supply cool material to a filament, as well as re-organizing the magnetic field configuration, and, hence, is important in the formation of filaments.  相似文献   

Large-scale climate variability and its effects on mean temperature and flowering time of Prunus and Betula in Denmark     

A. K. Gormsen  A. Hense  T. B. Toldam-Andersen  P. Braun 《Theoretical and Applied Climatology》2005,82(1-2):41-50

Summary Large-scale climate variability largely affects average climatic conditions and therefore is likely to influence the phenology of plants. In NW-Europe, the North Atlantic Oscillation (NAO) particularly influences winter climate and, through climate interactions on plants, flowering time of all tree species. In Denmark, like in many other NW-European countries, flowering of most tree species has become earlier since the end of the 1980’s. To quantify a possible relation between NAO and flowering time of tree species, two sources of phenological information from the Copenhagen area (Denmark) were analysed, i.e. pollen counts of the genus Betula and observed first bloom dates of Prunus avium. The Winter NAO explained 29 and 37% of the variation of monthly mean temperature for February and March, respectively. The influence of temperature on flowering time was up to 56% to 60% for the February–April mean. A direct correlation of Winter NAO-index and flowering time also revealed a clear relation but the time of influence was earlier (December to February). This was shown to be the likely result of a combination of direct and time-lagged effects of the NAO on air and sea surface temperature. The NAO signal is apparently stored in the North Sea and then influences temperature east up to the Baltic States. It is shown that Denmark is right in the centre of direct and time-lagged effects of the NAO. This offers the possibility of using the NAO-index for predicting flowering time of Prunus avium. The beginning of pollen flow appears to be influenced too much by short-term perturbations of the climate system decreasing the value of the NAO-index for prediction. However, it indicates a close relationship between natural climate variability, measured by the NAO index, and flowering time of tree species for Denmark.  相似文献   

Application of in situ-produced cosmogenic Be and Al to the study of lateritic soil development in tropical forest: theory and examples from Cameroon and Gabon     

R. Braucher  D. L. Bourls  E. T. Brown  F. Colin  J. -P. Muller  J. -J. Braun  M. Delaune  A. Edou Minko  C. Lescouet  G. M. Raisbeck  F. Yiou 《Chemical Geology》2000,170(1-4):95-111

Depth profiles of in situ-produced cosmogenic nuclides, including ¹⁰Be (T_1/2=1.5×10⁶ years) and ²⁶Al (T_1/20.73×10⁶ years), in the upper few meters of the Earth's crust may be used to study surficial processes, quantifying denudation and burial rates and elucidating mechanisms involved in landform evolution and soil formations. In this paper, we discuss the fundamentals of the method and apply it to two lateritic sequences located in African tropical forests.  相似文献   

The Multiscale TROPIcal CatchmentS critical zone observatory M-TROPICS dataset III: Hydro-geochemical monitoring of the Mule Hole catchment,south India     

Jean Riotte  Laurent Ruiz  Stéphane Audry  Benjamin Baud  Jean-Pierre Bedimo Bedimo  Laurie Boithias  Jean-Jacques Braun  Bernard Dupré  Jean-Louis Duprey  Mikael Faucheux  Christelle Lagane  Jean-Christophe Marechal  Hemanth Moger  Mandalagiri Subbarayappa Mohan Kumar  Harshad Parate  Olivier Ribolzi  Emma Rochelle-Newall  Buvaneshwari Sriramulu  Murari Varma  Muddu Sekhar 《水文研究》2021,35(5):e14196

Despite the importance of tropical ecosystems for climate regulation, biodiversity, water and nutrient cycles, only a few Critical Zone Observatories (CZOs) are located in the tropics. Among these, most are in humid climates, while very few data exist for semi-arid and sub-humid climates, due to the difficulty of estimating hydro-geochemical balances in catchments with ephemeral streams. We contribute to fill this gap by presenting a meteorological and hydro-geochemical dataset acquired at the Mule Hole catchment (4.1 km²), a pristine dry deciduous forest located in a biosphere reserve in south India. The dataset consists of time series of variables related to (i) meteorology, including rainfall, air temperature, relative humidity, wind speed and direction, and global radiation, (ii) hydrology, including water level and discharge at the catchment outlet, (iii) hydrogeology, including manual (monthly) and/or automated (from 15 min to hourly) groundwater levels in nine piezometers and (iv) geochemistry, including suspended sediment content in the stream and chemical composition of rainfall (event based), groundwater (monthly sampling) and stream water (storm events, 15 min to hourly frequency with an automatic sampler). The time series extend from 2003 to 2019. Measurement errors are minimized by frequent calibration of sensors and quality checks, both in the field and in the laboratory. Despite these precautions, several data gaps exist, due to occasional access restriction to the site and instrument destruction by wildlife. Results show that large seasonal and interannual variations of climatic conditions were reflected in the large variations of stream flow and groundwater recharge, as well as in water chemical composition. Notably, they reveal a long-term evolution of groundwater storage, suggesting hydrogeological cycles on a decadal scale. This dataset, alone or in combination with other data, has already allowed to better understand water and element cycling in tropical dry forests, and the role of forest diversity on biogeochemical cycles. As tropical ecosystems are underrepresented by Critical Zone Observatories, we expect this data note to be valuable for the global scientific community.  相似文献