Using stable isotopes to understand seasonal and interannual dynamics in moisture sources and atmospheric circulation in precipitation          下载免费PDF全文

Yu Tang  Xianfang Song  Yinghua Zhang  Dongmei Han  Likun Ai  Tianbao Zhao  Yajun Wang 《水文研究》2017,31(26):4682-4692

Stable isotopes in precipitation are useful tracers to strengthen understanding of climate change and hydrological processes. In this study, the moisture sources of 190 precipitation events in Beijing were analysed using the Hybrid Single‐particle Lagrangian Integrated Trajectory model, based on which we studied the relation between variations in precipitation δ¹⁸O and dynamics in moisture sources and atmospheric circulation in seasonal and interannual timescales. Categorization of 7 groups of moisture sources was performed, among which oceanic moisture sources presented lower δ¹⁸O in precipitation than continental moisture sources. The results show that seasonal variations of precipitation δ¹⁸O were caused by changes of moisture sources. In summer, moisture from proximal oceans dominated vapour transport to Beijing due to increasing monsoon strength and resulted in a relatively small variation of precipitation δ¹⁸O. At the interannual timescale, the variations of δ¹⁸O in summer precipitation were related to dynamics in oceanic moistures, showing depleted values when the contribution of oceanic moistures, especially the proportion of long‐distance oceanic moisture, was high. Further analysis indicated that changes of oceanic moisture sources were controlled by the strength of summer monsoons. These findings address the complexity of moisture sources in midlatitude monsoon areas and suggest that isotopic signals in precipitation have the potential to deduce changes in moisture sources and atmospheric circulation and can therefore serve for palaeoclimate reconstruction.  相似文献   

Groundwater recharge in an arid grassland as indicated by soil chloride profile and multiple tracers          下载免费PDF全文

Tianming Huang  Zhonghe Pang  Jilai Liu  Lihe Yin  W. Mike Edmunds 《水文研究》2017,31(5):1047-1057

Previous studies have shown that shallow groundwater in arid regions is often not in equilibrium with near‐surface boundary conditions due to human activities and climate change. This is especially the case where the unsaturated zone is thick and recharge rate is limited. Under this nonequilibrium condition, the unsaturated zone solute profile plays an important role in estimating recent diffuse recharge in arid environments. This paper combines evaluation of the thick unsaturated zone with the saturated zone to investigate the groundwater recharge of a grassland in the arid western Ordos Basin, NW China, using the soil chloride profiles and multiple tracers (²H, ¹⁸O, ¹³C, ¹⁴C, and water chemistry) of groundwater. Whereas conventional water balance and Darcy flux measurements usually involve large errors in recharge estimations for arid areas, chloride mass balance has been widely and generally successfully used. The results show that the present diffuse recharge beneath the grassland is 0.11–0.32 mm/year, based on the chloride mass balance of seven soil profiles. The chloride accumulation age is approximately 2,500 years at a depth of 13 m in the unsaturated zone. The average Cl content in soil moisture in the upper 13 m of the unsaturated zone ranges from 2,842 to 7,856 mg/L, whereas the shallow groundwater Cl content ranges from 95 to 351 mg/L. The corrected ¹⁴C age of shallow groundwater ranges from 4,327 to 29,708 years. Stable isotopes show that the shallow groundwater is unrelated to modern precipitation. The shallow groundwater was recharged during the cold and wet phases of the Late Pleistocene and Holocene humid phase based on palaeoclimate, and consequently, the groundwater resources are nonrenewable. Due to the limited recharge rate and thick unsaturated zone, the present shallow groundwater has not been in hydraulic equilibrium with near‐surface boundary conditions in the past 2,500 years.  相似文献   

Reaction softening by dissolution–precipitation creep in a retrograde greenschist facies ductile shear zone,New Hampshire,USA          下载免费PDF全文

R. J. McAleer  D. L. Bish  M. J. Kunk  K. R. Sicard  P. M. Valley  G. J. Walsh  B. A. Wathen  R. P. Wintsch 《Journal of Metamorphic Geology》2017,35(1):95-119

We describe strain localization by a mixed process of reaction and microstructural softening in a lower greenschist facies ductile fault zone that transposes and replaces middle to upper amphibolite facies fabrics and mineral assemblages in the host schist of the Littleton Formation near Claremont, New Hampshire. Here, Na‐poor muscovite and chlorite progressively replace first staurolite, then garnet, and finally biotite porphyroblasts as the core of the fault zone is approached. Across the transect, higher grade fabric‐forming Na‐rich muscovite is also progressively replaced by fabric‐forming Na‐poor muscovite. The mineralogy of the new phyllonitic fault‐rock produced is dominated by Na‐poor muscovite and chlorite together with late albite porphyroblasts. The replacement of the amphibolite facies porphyroblasts by muscovite and chlorite is pseudomorphic in some samples and shows that the chemical metastability of the porphyroblasts is sufficient to drive replacement. In contrast, element mapping shows that fabric‐forming Na‐rich muscovite is selectively replaced at high‐strain microstructural sites, indicating that strain energy played an important role in activating the dissolution of the compositionally metastable muscovite. The replacement of strong, high‐grade porphyroblasts by weaker Na‐poor muscovite and chlorite constitutes reaction softening. The crystallization of parallel and contiguous mica in the retrograde foliation at the expense of the earlier and locally crenulated Na‐rich muscovite‐defined foliation destroys not only the metastable high‐grade mineralogy, but also its stronger geometry. This process constitutes both reaction and microstructural softening. The deformation mechanism here was thus one of dissolution–precipitation creep, activated at considerably lower stresses than might be predicted in quartzofeldspathic rocks at the same lower greenschist facies conditions.  相似文献   

Impact of the North Atlantic Oscillation on streamflow in Western Iran          下载免费PDF全文

Hossein Tabari  Hirad Abghari  Parisa Hosseinzadeh Talaee 《水文研究》2014,28(15):4411-4418

The Middle East region, where arid and semi‐arid regions occupy most of the land, is extremely vulnerable to any natural or anthropogenic reductions in available water resources. Much of the observed interannual‐decadal variability in Middle Eastern streamflow is physically linked to a large‐scale atmospheric circulation patterns such as the North Atlantic Oscillation (NAO). In this work, the relationship between the NAO index and the seasonal and annual streamflows in the west of Iran was statistically examined during the last four decades. The correlations were constructed for two scenarios (with and without time lag). The associations between the annual and seasonal streamflows and the simultaneous NAO index were found to be poor and insignificant. The possibility of streamflow forecasting was also explored, and the results of lag correlations revealed that streamflow responses at the NAO signal with two and three seasons delays. The highest Spearman correlation coefficient of 0.379 was found between the spring NAO index and the autumn streamflow series at Taghsimab station, indicating that roughly 14% of the variance in the streamflow series is associated with NAO forcing. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

A study of internal solitary waves observed on the continental shelf in the northwestern South China Sea   总被引：3，自引：1，他引：2  

XU Zhenhu  YIN Baoshu  HOU Yijun  FAN Zhisong  Antony K LIU 《海洋学报(英文版)》2010,29(3):18-25

Based on in-situ time series data from the acoustic Doppler current profiler (ADCP) and thermistor chain in Wenchang area, a sequence of internal solitary wave (ISW) packets was observed in September 2005, propagating northwest on the continental shelf of the northwestern South China Sea (SCS). Corresponding to different stratification of the water column and tidal condition, both elevation and depression ISWs were observed at the same mooring location with amplitude of 35 m and 25 m respectively in different days. Regular arrival of the remarkable ISW packets at approximately the diurnal tidal period and the dominance of diurnal internal waves in the study area, strongly suggest that the main energy source of the waves is the diurnal tide. Notice that the wave packets were all riding on the troughs and shoulders of the internal tides, they were probably generated locally from the shelf break by the evolution of the internal tides due to nonlinear and dispersive effects.  相似文献   

Quaternary evolution of the northern North Sea margin through glacigenic debris‐flow and contourite deposition     

《第四纪科学杂志》2017,32(3):416-426

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Differing controls on river‐ and lake‐water hydrogen and oxygen isotopic values in the western United States     

Anna King Henderson  Bryan Nolan Shuman 《水文研究》2010,24(26):3894-3906

Surface water oxygen and hydrogen isotopic values are commonly used as proxies of precipitation isotopic values to track modern hydrologic processes while proxies of water isotopic values preserved in lake and river sediments are used for paleoclimate and paleoaltimetry studies. Previous work has been able to explain variability in USA river‐water and meteoric‐precipitation oxygen isotope variability with geographic variables. These studies show that in the western United States, river‐water isotopic values are depleted relative to precipitation values. In comparison, the controls on lake‐water isotopic values are not well constrained. It has been documented that western United States lake‐water input values, unlike river water, reflect the monthly weighted mean isotopic value of precipitation. To understand the differing controls on lake‐ and river‐water isotopic values in the western United States, we examine the seasonal distribution of precipitation, evaporation and snowmelt across a range of seasonality regimes. We generate new predictive equations based on easily measured factors for western United States lake‐water, which are able to explain 69–63% of the variability in lake‐water hydrogen and oxygen isotopic values. In addition to the geographic factors that can explain river and precipitation values, lake‐water isotopic values need factors related to local hydrologic and climatic characteristics to explain variability. Study results suggest that the spring snowmelt runs off the landscape via rivers and streams, depleting river and stream‐water isotopic values. By contrast, lakes receive seasonal contributions of precipitation in proportion to the seasonal fraction of total annual precipitation within their watershed. Climate change may alter the ratio of snow to rain fall, affecting water resource partitioning between rivers and lakes and by implication of groundwater. Paleolimnological studies must account for the multiple drivers of water isotopic values; likewise, studies based on the isotopic composition of fossil material need to distinguish between species that are associated with rivers versus lakes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Tropical precipitation anomalies and d‐excess evolution during El Niño 2014‐16          下载免费PDF全文

Ricardo Sánchez‐Murillo  Ana M. Durán‐Quesada  Christian Birkel  Germain Esquivel‐Hernández  Jan Boll 《水文研究》2017,31(4):956-967

The last 2014‐16 El Niño event was among the three strongest episodes on record. El Niño considerably changes annual and seasonal precipitation across the tropics. Here, we present a unique stable isotope data set of daily precipitation collected in Costa Rica prior to, during, and after El Niño 2014‐16, in combination with Lagrangian moisture source and precipitation anomaly diagnostics. δ²H composition ranged from ‐129.4 to +18.1 (‰) while δ¹⁸O ranged from ‐17.3 to +1.0 (‰). No significant difference was observed among δ¹⁸O (P=0.186) and δ²H (P=0.664) mean annual compositions. However, mean annual d‐excess showed a significant decreasing trend (from +13.3 to +8.7 ‰) (P<0.001) with values ranging from +26.6 to ‐13.9 ‰ prior to and during the El Niño evolution. The latter decrease in d‐excess can be partly explained by an enhanced moisture flux convergence across the southeastern Caribbean Sea coupled with moisture transport from northern South America by means of an increased Caribbean Low Level Jet regime. During 2014‐15, precipitation deficit across the Pacific domain averaged 46% resulting in a very severe drought; while a 94% precipitation surplus was observed in the Caribbean domain. Understanding these regional moisture transport mechanisms during a strong El Niño event may contribute to a) better understanding of precipitation anomalies in the tropics and b) re‐evaluate past stable isotope interpretations of ENSO events in paleoclimatic archives within the Central America region.  相似文献   

Freshwater influx,hydrographic reorganization and the dispersal of ice‐rafted detritus in the sub‐polar North Atlantic Ocean during the last deglaciation     

WILLIAM AUSTIN  VINCENT RINTERKNECHT 《第四纪科学杂志》2013,28(5):527-535

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Paleogene of the Huanghekou Sag in the Bohai Bay Basin,NE China: deposition–erosion response to a slope break system of rift lacustrine basins     

Hao Liu  Qinglong Xia  Ian D. Somerville  Yuan Wang  Xinhuai Zhou  Chengmin Niu  Xiaofeng Du  Xintao Zhang 《Geological Journal》2015,50(1):71-92

The sequence architecture and depositional systems of the Paleogene lacustrine rift succession in the Huanghekou Sag, Bohai Bay Basin, NE China were investigated based on seismic profiles, combined with well log and core data. Four second‐order or composite sequences and seven third‐order sequences were identified. The depositional systems identified in the basin include: fan delta, braid delta, meander fluvial delta, lacustrine and sublacustrine fan. Identification of the slope break was conducted combining the interpretation of faults of each sequence and the identification of syndepositional faults, based on the subdivision of sequence stratigraphy and analysis of depositional systems. Multiple geomorphologic units were recognized in the Paleogene of the Huanghekou Sag including faults, flexures, depositional slope break belts, ditch‐valleys and sub‐uplifts in the central sag. Using genetic division principles and taking into consideration tectonic features of the Paleogene of the Huanghekou Sag, the study area was divided into the Northern Steep Slope/Fault Slope Break System, the Southern Gentle Slope Break System and T10 Tectonic Slope Break System/T10 Tectonic Belt. Responses of slope break systems to deposition–erosion are shown as: (1) basin marginal slope break is the boundary of the eroded area and provenance area; (2) ditch‐valley formed by different kinds of slope break belts is a good transport bypass for source materials; (3) shape of the slope break belt of the slope break system controls sediments types; (4) the ditch‐valley and sub‐sag of a slope break system is an unloading area for sediments; and (5) due to their different origins, association characteristics and developing patterns, the Paleogene slope break belt systems in the Huanghekou Sag show different controls on depositional systems. The Northern Fault Slope Break system controls the deposition of a fan delta‐lacustrine‐subaqueous fan, the Southern Gentle Slope Break system controls the deposition of a fluvial–deltaic–shallow lacustrine and sublacustrine fan, and the T10 Tectonic Slope Break System controls the deposition of shallow lacustrine beach bar sandbodies. The existence of a slope break system is a necessary but not a sufficient condition for studying sandbody development. The formation of effective sandbodies along the slope break depends on the reasonable coupling of effective provenance, necessary association patterns of slope break belt, adequate unloading space and creation of definite accommodation space. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献