A 15 000‐year record of climate change in northern New Mexico,USA, inferred from isotopic and elemental contents of bog sediments     

Luz M. Cisneros‐Dozal  Jeffrey M. Heikoop  Julianna Fessenden  R. Scott Anderson  Philip A. Meyers  Craig D. Allen  Marcey Hess  Toti Larson  George Perkins  Michael Rearick 《第四纪科学杂志》2010,25(6):1001-1007

Elemental (C, N, Pb) and isotopic (δ¹³C, δ¹⁵N) measurements of cored sediment from a small bog in northern New Mexico reveal changes in climate during the Late Pleistocene and Holocene. Abrupt increases in Pb concentration and δ¹³C values ca. 14 420 cal. YBP indicate significant runoff to the shallow lake that existed at that time. Weathering and transport of local volcanic rocks resulted in the delivery of Pb‐bearing minerals to the basin, while a ¹³C‐enriched terrestrial vegetation source increased the δ¹³C values of the sedimentary material. Wet conditions developed over a 300 a period and lasted for a few hundred years. The Younger Dryas period (ca. 12 700–11 500 cal. YBP) caused a reduction in terrestrial productivity reflected in decreasing C/N values, δ¹⁵N values consistently greater than 0‰ and low organic content. By contrast, aquatic productivity increased during the second half of this period, evidenced by increasing δ¹³C values at the time of highest abundance of algae. Dry conditions ca. 8 000–6 000 cal. YBP were characterised by low organic carbon content and high Pb concentrations, the latter suggesting enhanced erosion and aeolian transport of volcanic rock. The range in δ¹³C, δ¹⁵N and C/N values in the sedimentary record fall within the range of modern plants, except during the periods of runoff and drought. The sedimentary record provides evidence of natural climate variability in northern New Mexico, including short‐ (multi‐centennial) and long‐(millennial) term episodes during the Late Pleistocene and Holocene. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Estimating the impact of rural land management changes on catchment runoff generation in England and Wales     

T. M. Hess  I. P. Holman  S. C. Rose  Z. Rosolova  A. Parrott 《水文研究》2010,24(10):1357-1368

Although reviews of the scientific literature have failed to demonstrate conclusive evidence for the impact of rural land management on peak runoff rates, increasing emphasis is being placed by policy makers on its role in catchment‐scale flood risk management. Poor soil and field conditions can lead to higher rates of runoff from extreme rainfall events; however, the improvement of land condition will lead to differing runoff responses depending on land use, soil type and climatic regime. This study has evaluated the relative impact of improvement of field and soil conditions on peak daily runoff rates for a range of soils and vegetation cover types across England and Wales. It has shown that rural land management changes could be expected to make a positive contribution to sustainable flood risk management, especially for more frequent events. The greatest relative reduction in runoff can be achieved through the improvement of degraded permeable soils under managed grassland in drier regions. Taking a plausible scenario of land management improvement in arable and grassland systems, the relative reduction in peak runoff was estimated for 518 policy units as defined in the Environment Agency's Catchment Flood Management Plans. For the 1 in 100 year event, there were only a few policy units where the expected reduction in runoff exceeded 5%. Rural land management practices which are likely to be beneficial to flood risk management may afford some protection to areas where structural measures may not be implemented for cost–benefit reasons, and may help to offset some of the anticipated increases in flood risk associated with climate change. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Holocene sedimentation history of the major fan valleys of Monterey fan     

Gordon R. Hess  William R. Normark 《Marine Geology》1976,22(4):233-251

There are three major fan valleys on upper Monterey fan. Deep-tow geophysical profiles and 40 sediment cores provide the basis for evaluation of the sedimentation histories of these valleys. Monterey fan valley leads from Monterey canyon to a major suprafan and is bounded by levees that crest more than 400 m above the valley floor. The valley passes through a large z-bend or meander. Monterey East fan valley joins Monterey fan valley at the meander at about 150 m above the valley floor, and marks an earlier position of the lower Monterey fan valley. Ascension valley, a hanging contributary to the Monterey fan valley, appears to have once been the shoreward head of the lower part of the present Monterey fan valley. The relief of Monterey fan valley appears from deep-tow profiles to be erosional. The valley is floored with sand. Holocene turbidity currents do not overtop the levees 400 m above the valley floor, but do at times overflow and transport sand into Monterey East valley, producing a sandy floor. An 1100 m by 300 m dune field was observed on side scan sonar in Monterey East valley.Ascension fan valley was floored with sand during glacial intervals of lowered sea level, then was cut off from its sand source as sea level rose. A narrow (500 m), erosional, meandering channel was incised into the flat valley floor; the relief features otherwise appear depositional, with a hummocky topography perhaps produced in the manner of a braided riverbed. The sand is mantled by about 6 m of probable Holocene mud. Hummocky relief on the back side of the northwestern levees of both Ascension and Monterey valleys is characteristic of many turbidite valleys in the northeast Pacific. The hummocky topography is produced by dune-like features that migrate toward levee crests during growth.  相似文献   

A Study of the Earth-Affecting CMEs of Solar Cycle 24     

Phillip Hess  Jie Zhang 《Solar physics》2017,292(6):80

Using in situ observations from the Advanced Composition Explorer (ACE), we have identified 70 Earth-affecting interplanetary coronal mass ejections (ICMEs) in Solar Cycle 24. Because of the unprecedented extent of heliospheric observations in Cycle 24 that has been achieved thanks to the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instruments onboard the Solar Terrestrial Relations Observatory (STEREO), we observe these events throughout the heliosphere from the Sun to the Earth, and we can relate these in situ signatures to remote sensing data. This allows us to completely track the event back to the source of the eruption in the low corona. We present a summary of the Earth-affecting CMEs in Solar Cycle 24 and a statistical study of the properties of these events including the source region. We examine the characteristics of CMEs that are more likely to be strongly geoeffective and examine the effect of the flare strength on in situ properties. We find that Earth-affecting CMEs in the first half of Cycle 24 are more likely to come from the northern hemisphere, but after April 2012, this reverses, and these events are more likely to originate in the southern hemisphere, following the observed magnetic asymmetry in the two hemispheres. We also find that as in past solar cycles, CMEs from the western hemisphere are more likely to reach Earth. We find that Cycle 24 lacks in events driving extreme geomagnetic storms compared to past solar cycles.  相似文献   

Hydrogeologic and hydrochemical framework of the shallow groundwater system in the southern Voltaian Sedimentary Basin of Ghana. Reply to comments by Pradeep Raj     

Stephen Y. Acheampong  John W. Hess 《Hydrogeology Journal》1999,7(6):592-595

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Monte Carlo Simulations of Multiphase Flow Incorporating Spatial Variability of Hydraulic Properties   总被引：4，自引：0，他引：4  

Hedeff I. Essaid  Kathryn M. Hess 《Ground water》1993,31(1):123-134

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Ordinary and Z-mode emissions from the Jovian polar region     

M.L. Kaiser  M.D. Desch  W.M. Farrell  R.A. Hess  R.J. MacDowall 《Planetary and Space Science》1993,41(11-12)

The Ulysses Unified Radio and Plasma (URAP) experiment has detected a new component of Jupiter's radio spectrum in the frequency range from about 10 to 30 kHz. This component is emitted in the magnetoionic ordinary mode from a localized corotating source in the northern polar region. The source is centered at system III longitude 208°, near the meridian containing the North magnetic dipole axis, at a distance of nearly 4R_J from the planet and near the last closed field line. The emission frequency is somewhat above the electron plasma frequency in the source region, but well below the electron gyrofrequency. Accompanying this O-mode emission at lower frequencies is intense Z-mode emission, which is likely to play a significant role in the generation of the O-mode.  相似文献   

A method of characterizing the thermal relations in mountainous areas / the lower Beskid range in the Polish Carpathians as example     

M. Hess Dr.  T. Niedźwiedź Doc. Dr.  B. Obrębska-Starkelowa Doc. Dr. 《GeoJournal》1984,8(2):251-257

The method discussed in the present paper permits the determination in detail of the mesoclimatic conditions on the basis of standard data provided by a network of a measurement stations. The passage from the data available at certain points and obtained from meteorological stations to spatial conceptions leads along the determination of the relationships between the altitude, various forms of the relief, and the thermal indices of climate. Resulting from these data, the duration of the frostless period is a sensitive index in the scale of mesoclimate, besides all the other indices connected with the minimum air temperatures. The nomographs applied by the authors make it possible to construct detailed climatic maps, which — with the maps of other elements of the geographical environment — form a basis for the elaboration e.g. an agrocological map of habitats. Presented method of the evaluation of climate conditions can be applied to all mountain territories, in which a network of measurement stations enables the determination of the interdependencies between the chosen thermal parameters and the altitude, and the distinction of the impact of the convex and concave forms.  相似文献   

Polymer model of silicate melts     

Paul C Hess 《Geochimica et cosmochimica acta》1971

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Subduction-related Jurassic andesites in the northern Great Caucasus     

J. C. Hess  J. Aretz  A. G. Gurbanov  R. Emmermann  H. J. Lippolt 《International Journal of Earth Sciences》1995,84(2):319-333

During the Jurassic the major tectonic units of the Great Caucasus (Bechasyn, Front Range, Main Range and Southern Slope zone) were affected by intensive magmatic activity. Magmatism within the Bechasyn zone, the northernmost unit, which represents the southern part of the Variscan-consolidated Skythian platform is considered here. With the beginning of the Early Jurassic this zone was reactivated by subsidence, accompanied by the deposition of epicontinental shallow water sediments. The Lower Jurassic portion of this sedimentary pile was intruded by numerous sills which display a clear temporal and spatial evolution. The older basic rocks are lower in the profile than the younger, more acidic rocks. A set of 75 samples, representing all exposed sills and their feeder-dikes, was analyzed for major and 21 trace elements. All samples appear more or less affected by alteration under lower greenschist facies conditions. However, these alterations essentially took place on local scales and did not affect the overall chemistry. According to their main element composition the rocks constitute a calc-alkaline series ranging from basaltic—andesitic to rhyolitic. Most of the samples are andesites. Chemically, these andesites closely resemble modern orogenic andesites occurring at convergent plate margins. Altogether, the field evidence and the chemical and mineralogical data obtained show the investigated rocks to be comagmatic and derived from basalt—andesitic initial melts by magmatic fractionation processes. Tholeiitic melts have to be considered as parental magmas, which according to the trace element characteristics of the basalt-andesitic rocks, were generated from an enriched peridotitic mantle source. ⁸⁷Sr/⁸⁶Sr isotope ratios and ¹⁸O values confirm the mantle origin of this rock series. The observed compositional evolution can be explained as a result of olivine and clinopyroxene fractionation of the tholeitic melts followed by amphibole and plagioclase separation. ⁴⁰Ar/³⁹Ar measurements on biotite and plagioclase phenocrysts separated from these rocks vary between 190 and 180 Ma and thereby place the magmatic activity in the late Early Jurassic, in good agreement with the stratigraphic observations. Genetically, the calc-alkaline rocks are related to a subduction zone of the Andean type. Their chemical and isotopic compositions and their age setting corroborate the plate tectonic models for the evolution of the Caucasus orogenic belt during the Jurassic.Dedicated to the late A. M. Borsuk, initiator of the study  相似文献