Reliable Late-Pleistocene Stratigraphic Ages and Shorter Groundwater Travel Times fromC in Fossil Snails from the Southern Great Basin     

Robert Brennan  Jay Quade 《Quaternary Research》1997,47(3):329-336

Both aquatic and land snails are common in the geologic record, but their utility in dating is greatly restricted by their well-documented tendency to yield¹⁴C dates inconsistent with true¹⁴C ages. In this study, we examine the use of¹⁴C ages from (1) small, previously unstudied, terrestrial snails to date hosting spring deposits and from (2) cooccuring aquatic snails to constrain groundwater travel times during the last glacial period. Our study area in the southern Great Basin encompasses Yucca Mountain, site of the proposed high-level nuclear waste repository, where information on the age and extent of past high water tables and on groundwater flow times is crucial to several licensing issues. Our results show that shells of small terrestrial snails belonging toValloniasp. yield¹⁴C dates consistent with¹⁴C ages of associated carbonized wood. These results imply that these taxa can provide reliable¹⁴C age control on the broadly distributed deposits in which they have been described. In contrast, cooccurring aquatic snails from fossil spring deposits yield¹⁴C ages generally greater than the control age. This is because the aquatic shells often formed in spring waters that had an initial¹⁴C deficiency. However, the magnitude of the deficiency is much less than that observed in nearby modern springs, arguing for much higher average¹⁴C contents in late Pleistocene groundwaters in these basins. If representative, this implies shorter groundwater travel times through aquifers in southern Nevada during late-glacial time.  相似文献   

Cosmic ray produced nitrogen in extra terrestrial matter     

K. J. Mathew  S. V. S. Murty 《Journal of Earth System Science》1993,102(3):415-437

Production rates of¹⁵N by both solar cosmic rays (SCR) and galactic cosmic rays (GCR) have been calculated for moon, as well as meteorites of various sizes. Our production rates of¹⁵N which considered both the reaction channels¹⁶O(p, pn)¹⁵O and¹⁶O(p, 2p)¹⁵N separately are about 30% higher than those by Reedy (1981) who considered only the channel¹⁶O(p, pn)¹⁵O and used an empirical scaling factor to estimate the contribution from¹⁶O(p, 2p)¹⁵N. Production ratio¹⁵N²¹ Ne is composition dependent and hence is different for various silicate minerals. Additionally the ratio¹⁵N/²¹Ne is very sensitive to the energy spectrum of the cosmic rays. This fact can be made use of in characterizing as well as in decoupling the SCR and GCR effects in extraterrestrial samples.  相似文献   

On the observed synoptic variability in the thermal structure of the upper northern Bay of Bengal during MONEX-79     

R R Rao  Basil Mathew 《Journal of Earth System Science》1988,97(1):21-34

The short-term variability observed in the near surface meteorological parameters and in the vertical thermal structure of the upper layers of the northern Bay of Bengal during a weak monsoonal regime is examined with the aid of time series measurements. The variability of the mixed layer depth is interpreted in terms of forced mixing caused by the surface wind stress and free mixing by buoyancy flux, Ekman pumping controlled by the curl of the surface wind stress, convergence associated with a clockwise gyral circulation and stratification caused by freshwater discharges from rivers. The daily-averaged current vectors in the upper layers indicate the presence of clockwise gyral circulation in the polygon area.  相似文献   

Winter-spring precipitation reconstructions from tree rings for northeast Mexico     

Jose Villanueva-Diaz  David W. Stahle  Brian H. Luckman  Julian Cerano-Paredes  Mathew D. Therrell  Malcom K. Cleaveland  Eladio Cornejo-Oviedo 《Climatic change》2007,83(1-2):117-131

The understanding of historic hydroclimatic variability is basic for planning proper management of limited water resources in northeastern Mexico. The objective of this study was to develop a network of tree-ring chronologies to reconstruct hydroclimate variability in northeastern Mexico and to analyze the influence of large-scale circulation patterns, such as ENSO. Precipitation sensitive tree-ring chronologies of Douglas-fir were developed in mountain ranges of the Sierra Madre Oriental and used to produce winter-spring precipitation reconstructions for central and southern Nuevo Leon, and southeastern Coahuila. The seasonal winter-spring precipitation reconstructions are 342 years long (1659–2001) for Saltillo, Coahuila and 602 years long (1400–2002) for central and southern Nuevo Leon. Both reconstructions show droughts in the 1810s, 1870s, 1890s, 1910s, and 1970s, and wet periods in the 1770s, 1930s, 1960s, and 1980s. Prior to 1800s the reconstructions are less similar. The impact of ENSO in northeastern Mexico (as measured by the Tropical Rainfall Index) indicated long-term instability of the Pacific equatorial teleconnection. Atmospheric circulation systems coming from higher latitudes (cold fronts or `nortes’) and others developed in the Gulf of Mexico (tropical storms, hurricanes) also influence the climatic conditions characterizing this region. The recent development of new and longer tree-ring chronologies for the region will contribute to a better understanding of the interannual and multidecadal climatic variability of northeastern Mexico.  相似文献   

Observational evidence of Mixed Rossby Gravity waves at the central equatorial Indian Ocean     

P. M. Muraleedharan  S. Prasanna Kumar  K. Mohana kumar  S. Sijikumar  K. U. Sivakumar  Teesha Mathew 《Meteorology and Atmospheric Physics》2015,127(4):407-417

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Studying Land Use Travel Demand Interaction Using 3S Technology for Tiruchirappalli City     

Nisha Radhakrishnan  R. Aswathy  Samson Mathew 《Journal of the Indian Society of Remote Sensing》2017,45(5):815-824

This paper gives an overview of a major application of modern geospatial tools such as remote sensing, GIS and GPS, i.e., 3S technology in estimating travel demand along Indian roads by considering the study area, Tiruchirappalli urban city in Tamil Nadu. In the study, an attempt was made to estimate travel demand based on the current land-use classification as the pattern of travel depends on the type of land use activity in a zone. IRS high resolution image Cartosat-1 of year 2009 was used to extract the land-use information required. The travel demand model developed was validated with the field obtained OD-matrix to understand the accuracy of the method considered.  相似文献   

Upper-Level Winds over Southern Ontario: O-QNet Wind Profiler and NARR Comparisons     

Peter A. Taylor  Wensong Weng  Zheng Qi Wang  Mathew Corkum  Khalid Malik  Shama Sharma 《大气与海洋》2017,55(1):1-11

Upper-level winds are primarily measured by tracking the position of radiosonde balloons as they rise through the atmosphere. Radiosondes are released from a global network at 0000 utc and 1200 utc each day, and data are quickly available to the world's weather services, as well as to the public. The network is relatively coarse spatially, and there are normally only two soundings per day. In an endeavour to provide better spatial and temporal upper-level regional wind measurements, the O-QNet (a demonstration very high frequency wind profiler network for Ontario and Quebec) was installed and has been operated by York, Western, and McGill Universities with support from Mardoc Inc., The Weather Network, and Environment and Climate Change Canada. Initial funding was provided by the Canada Foundation for Innovation, the Ontario Innovation Trust, and Mardoc Inc. The present paper reports primarily on comparisons between winds measured by the O-QNet profilers and the winds reported in the North American Regional Reanalysis (NARR). There is good agreement between the two, which provides support for the use of NARR data to investigate longer term variations in upper-level winds associated with climate change for this region.  相似文献   

Evaluation of radiative fluxes over the north Indian Ocean     

Ramesh Kumar  M. R.  Pinker  Rachel T.  Mathew  Simi  Venkatesan  R.  Chen  W. 《Theoretical and Applied Climatology》2018,132(3-4):983-988

Theoretical and Applied Climatology - Radiative fluxes are a key component of the surface heat budget of the oceans. Yet, observations over oceanic region are sparse due to the complexity of...  相似文献   

Understanding climate adaptation investments for communities living in desert Australia: experiences of indigenous communities     

Digby Race  Supriya Mathew  Matthew Campbell  Karl Hampton 《Climatic change》2016,139(3-4):461-475

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Holocene coastal change at Luce Bay,South West Scotland     

David E. Smith  Richard M. Tipping  Jason T. Jordan  Mathew Blackett 《第四纪科学杂志》2020,35(6):743-759

Coastal change during the Mid- to Late Holocene at Luce Bay, South West Scotland, is examined using morphological, stratigraphic and biostratigraphical techniques supported by radiocarbon dating. Deglaciation left extensive sediments, providing a source for depositional coastal landforms. Glacio-isostatic uplift resulted in the registration of evidence for former relative sea levels (RSLs), which support the pattern of Holocene RSL change for the northern Irish Sea as determined by shoreline-based Gaussian trend surface models. The rate of RSL rise was rapid from before ca. 8600 to ca. 7800 cal a bp , but then slowed, changing by <3 m over the next 3000 years, a pattern reflected in the convergence of shorelines predicted in the models. By ca. 4400 cal a bp RSL was falling towards present levels. As these changes were taking place, coastal barriers developed and dunes formed across them. In the West of the Bay, a lagoon forming to landward of the barriers and dunes acted as a sediment sink for dune sand. Changes in the coastal landscape influenced the occupation of the area by early human societies. This study illustrates the value of combining an understanding of process geomorphology, RSL and archaeology in studies of coastal change.  相似文献