Doklady Earth Sciences - This paper presents the results of a study on peat deposits and radiocarbon dating of basal peat horizons in 43 peatlands located on three key sites within Meshchera... 相似文献
Northern peatlands represent one of the largest biospheric carbon reservoirs in the world. Their southern margins act as new carbon reservoirs, which can greatly influence the global carbon dynamics. However, the Holocene initiation, expansion and climate sensitivity of these peatlands remain intensely debated. Here we used a compilation of basal peat ages across six isolated peatlands at the southern margins of northern peatlands to address these issues. We found that the earliest initiation event of these peatlands occurred after the Younger Dryas (YD, 12,800–11,700 years ago) period. The second initiation event and rapid expansion occurred since 5 ka cal. BP. The recession of East Asian summer monsoon (EASM) during the YD period and at around 5 ka cal. BP likely played a major role in controlling the initiation and expansion of these peatlands. The rapid expansion of these peatlands possibly contributed to the significant increases in atmospheric methane concentrations during the late Holocene because of the minerotrophic fens status and rapid expansion of them. These ecological processes are different from northern peatlands, indicating the special carbon sink and source implications of these peatlands in the global carbon cycle. 相似文献
Holocene histories of two polygonal peatlands in the low arctic of south-central Nunavut, Canada, are reconstructed using plant macrofossil and pollen stratigraphies of four cores. Peat accumulation began in both basins between 7600 and 8000 cal. yr BP, within less than 1000 years after deglaciation. Mid- to late-Holocene vegetation changes recorded in the peat cores may be related to permafrost aggradation, associated with a regional cooling trend inferred from a nearby lake sediment record. However, differences in the timing of changes among the peatland coring sites indicate that local autogenic processes have also played an important role. Peat accumulation rates have decreased considerably in the past 3000 to 5000 years compared to the early Holocene. Our results illustrate the complexity of peatland development and peat accumulation dynamics in areas of permafrost, resulting from the important influences of both internal autogenic factors and external environmental forces such as climatic change. 相似文献
Geologists investigate the evolution of the atmosphere, crust, and mantle through time by direct study of the rock record. However, the Hadean eon (>3.85 Ga) has been traditionally viewed as inaccessible due to the absence of preserved rocks. The discovery of >4.0 Ga detrital zircons from Western Australia in the 1980s — coupled with the development of new micro-analytical capabilities — made possible new avenues of early Earth research. The prevailing view that emerged is that the early Earth may have contained a stable hydrosphere, water-saturated or (near watersaturated) granitic magmas, and volcanic emanations dominated by neutral gas species (e.g., CO2, H2O, and SO2). The Hadean Earth may have been capable of supporting life ～200 Ma after accretion and perhaps earlier. Many of these models are formulated — or have been subsequently supported — by laboratory experiments of zircon. Important petrological variables such as temperature, pressure, oxygen fugacity, and component activities (e.g., SiO2/TiO2-activities) can be controlled. These experiments are fundamental for extrapolation to ‘deep time’ because they provide a means to understand primary chemistry preserved in ancient zircons. This review paper specifically focuses on zircon experimental studies (oxygen isotope fractionations, Ti-thermometry, and redox sensitive element incorporation into zircon), which have influenced our view of the very early Earth. 相似文献
Doklady Earth Sciences - New results are presented on the features of the deep velocity structure of two of the three main tectonic blocks that make up the Kola region—Murmansk and... 相似文献
Doklady Earth Sciences - The vertical isotopic profile of the ice core of a Messoyakha-1 bulgunniakh (pingo)—was obtained. The pingo is situated at 68°30′32″ N,... 相似文献
Peatlands are globally important ecosystems in terms of biodiversity, hydrology, and for the role they play in the carbon cycle. They store approximately one‐third of the carbon contained in the terrestrial biosphere, whilst covering only approximately 3% of the land and freshwater surface. Tropical peatlands represent an important component of this carbon store and can be found in Asia, Africa, South and Central America. However, tropical peatlands are also under severe threat of destruction from human activities including deforestation, agricultural expansion and resource exploitation. In South America, the Pastaza–Marañon foreland basin (PMFB) in NW Peru represents the most carbon dense landscape in Amazonia due to an abundance of peatlands, including nutrient‐poor ombrotrophic peat domes and river‐influenced minerotrophic swamps. The Aucayacu peatland in the PMFB is a nutrient‐poor peat dome and represents the oldest peatland yet reported in Amazonia. It is a relatively large peatland—it is estimated that Aucayacu has maximum dimensions of 33 km (NW‐SE) by 15 km (NE‐SW) (Fig. 1 ). The flora of the site is characterized by stunted vegetation due to low nutrient status, known as ‘pole’ and ‘dwarf’ forest, which at Aucayacu grows above a patchy understory of grasses and ferns (Fig. 2 ). Recent research has shown that Aucayacu has laid down peat up to 7.5 m deep in ～ 8900 years. 相似文献
Forested peatlands are widespread in boreal regions of Canada, and these ecosystems, which are major terrestrial carbon sinks, are undergoing significant transformations linked to climate change, fires and human activities. This study targets millennial‐scale vegetation dynamics and related hydrological variability in forested peatlands of the Clay Belt south of James Bay, eastern Canada, using palaeoecological data. Changes in peatland vegetation communities were reconstructed using plant macrofossil analyses, and variations in water‐table depths were inferred using testate amoeba analyses. High‐resolution analyses of macroscopic charcoal >0.5 mm were used to reconstruct local fire history. Our data showed two successional pathways towards the development of present‐day forested peatlands influenced by autogenic processes such as vertical peat growth and related drying, and allogenic factors such as the occurrence of local fires. The oldest documented peatland initiated in a wet rich fen around 8000 cal. a BP shortly after land emergence and transformed into a drier forested bog rapidly after peat inception that persisted over millennia. In the second site, peat started to accumulate from ~5200 cal. a BP over a mesic coniferous forest that shifted into a wet forested peatland following a fire that partially consumed the organic layer ~4600 cal. a BP. The charcoal records show that fires rarely occurred in these peatlands, but they have favoured the process of forest paludification and influenced successional trajectories over millennia. The macrofossil data suggest that Picea mariana (black spruce) persisted on the peatlands throughout their development, although there were periods of more open canopy due to local fires in some cases. This study brings new understanding on the natural variability of boreal forested peatlands which may help predict their response to future changes in climate, fire regimes and anthropogenic disturbances. 相似文献
Doklady Earth Sciences - Fluorcalciobritholite and fluorbritholite-(Ce)—rare-earth minerals from the apatite supergroup—have been found in the course of the study in monzogabbro from... 相似文献
Doklady Earth Sciences - This paper reports on the nature and history of the mineral-rich frost heave mounds—lithalsas—developed on the first terrace of the Sentsa River in Okinsky... 相似文献
The Swedish Deep Drilling Program (SDDP) has been initiated to study fundamental problems of the dynamic Earth system, its natural history and evolution. Many key scientific questions can be addressed through in situ investigations only, requiring deep continental drilling. Some are unique to Scandinavia, most are of international interest and significance. At present, five core projects ( Fig. 1 ) with international teams are integrating scientific problems with societal and industrial applications. If SDDP succeeds to attract the funding required, Sweden will have a number of world‐class boreholes at key locations by 2020. Figure 1 Open in figure viewer PowerPoint Locations of SDDP drilling project proposals. PFDP—Postglacial Fault Drilling Project; PaMVAS—Palaeoproterozoic mineralized volcanic arc systems: the Skellefte District; COSC—Collisional Orogeny in the Scandinavian Caledonides; DRL—The Dellen Impact Crater, a geoscientific deep rock laboratory; SELHO—Svecofennian accretion, an example of the early structural evolution in a large hot orogen; CISP—Concentric Impact Structures in the Palaeozoic: the Lockne and Siljan craters. Background and inset image from Blue Marble Next Generation data set (NASA Earth Observatory, http://earthobservatory.nasa.gov/Features/BlueMarble/ ). 相似文献
Polygonal patterned ground in polar regions of both Earth and Mars has received considerable attention. In comparison with the size, shape, and arrangement of the polygons, the diverse micro-relief and topography (termed here simply “relief”) of polygonal patterned ground have been understudied. And yet, the relief reflects important conditions and processes occurring directly below the ground surface, and it can be observed readily in the field and through remote sensing. Herein, we describe the relief characteristic of the simplest and relatively young form of patterned ground in the Dry Valleys of Antarctic. We also develop a numerical model to examine the generation of relief due to subsurface material being shouldered aside contraction cracks by incremental sand wedges growth, and to down-slope creep of loose granular material on the surface. We model the longterm subsurface deformation of ice-cemented permafrost as a non-linear viscous material. Our modeling is guided and validated using decades of field measurements of surface displacements of the permafrost and relief. This work has implications for assessing the activity of surfaces on Earth and Mars, and much larger scale potential manifestations of incremental wedging in icy material, namely the distinct paired ridges on Europa. 相似文献
The distribution of integrated resources of large and superlarge deposits (LSLDs) of rare earth elements (REEs) is compared to the current model of supercontinent cyclicity during Earth’s evolution. It is found that REE LSLDs are related predominantly to igneous complexes (carbonatite, nepheline syenites, syenite-alkaline granites, subalkaline granites), which are often additionally enriched in the hypergenic zone. A certain part of the resources is concentrated in independent hypergenic formations represented by placers and ion-adsorbed clays. Each supercontinent cycle—Kenoran, Columbian, Rodinian, Pangean, and Amasian—is expressed in the REE metallogeny in particular way: we revealed significant intercycle variations in the amount of REE LSLDs, the variety of their types, total accumulated resources, and some other characteristics. 相似文献
Permafrost dynamics play an important role in the surface hydrology and carbon balance of northern peatlands. Plant macrofossil analysis with radiocarbon dating has been widely used in detecting past permafrost dynamics in peatlands; however, there is a lack of permafrost‐specific plant indicator species, which makes it challenging to determine the exact timing of historical permafrost aggradation. We investigated the indicator value of oribatid mites in determining past permafrost dynamics in sub‐Arctic peatlands. Analyses of subfossil oribatid mite assemblages of Holocene peat profiles from two mires, one in northern Finland and one in northeastern European Russia, were carried out and interpreted using modern calibration data from the same study areas. The results were compared with previously published reconstructions of permafrost history based on plant macrofossil analyses from the same locations. The results suggest that the oribatid mites Carabodes labyrinthicus, Chamobates borealis and Neoribates aurantiacus are promising indicator species to detect past permafrost occurrence in peatlands. In addition, N. aurantiacus is clearly associated with the presence of lichens, which is particularly useful because lichen remains are rarely preserved in peat deposits. Results are in accordance with earlier studies showing that oribatid mites are useful indicators of past environmental change. 相似文献
