The discovery of two distant, massive clusters of galaxies in the ROSAT All-Sky Survey     

A. C. Edge  H. Ebeling  †  M. Bremer  H. Röttgering  M. P. van Haarlem  R. Rengelink  N. J. D. Courtney 《Monthly notices of the Royal Astronomical Society》2003,339(4):913-924

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Spring and summer phytoplankton communities in the Chukchi and Eastern Beaufort Seas   总被引：2，自引：0，他引：2  

Victoria Hill  Glenn Cota  Dean Stockwell 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3369

Phytoplankton pigments and size-fractionated biomass in the Chukchi and Beaufort Seas showed spatial and temporal variation during the spring and summer of 2002. Cluster analysis of pigment ratios revealed different assemblages over the shelf, slope and basin regions. In spring, phytoplankton with particle sizes greater than 5 μm, identified as diatoms and/or haptophytes, dominated over the shelf. Smaller (<5 μm) phytoplankton containing chlorophyll b, most likely prasinophytes, were more abundant over the slope and basin. Due to extensive ice cover at this time, phytoplankton experienced low irradiance, but nutrients were near maximal for the year. By summer, small prasinophytes and larger haptophytes and diatoms co-dominated in near-surface assemblages in largely ice-free waters when nitrate was mostly depleted. Deeper in the water column at 1–15% of the surface irradiance larger sized diatoms were still abundant in the upper nutricline. Phytoplankton from the shelf appeared to be advected through Barrow Canyon to the adjacent basin, explaining similar composition between the two areas in spring and summer. Off-shelf advection was much less pronounced for other slope and basin areas, which are influenced by the low-nutrient Beaufort gyre circulation, leading to a dominance of smaller prasinophytes and chlorophytes. The correlation of large-sized fucoxanthin containing phytoplankton with the higher primary production measurements shows promise for trophic status to be estimated using accessory pigment ratios.  相似文献   

Is the ‘superhot’ hard x-ray component in solar flares consistent with a thermal source?     

A. Gordon Emslie  Victoria Newman Coffey  Richard A. Schwartz 《Solar physics》1989,122(2):313-317

It has been shown by Brown and Emslie (1988) that any optically thin thermal bremsstrahlung source must emit an energy spectrumL () (keV s^–1 keV^–1) which has the property that higher derivatives alternate in sign, i.e., (–) ^j L(^j)() > 0 for allj. In this short note, we apply this test to the superhot component discussed by Linet al. (1981) in order to determine whether a strictly thermal interpretation of this component is valid. We find that all statistically significant higher derivatives do indeed have the correct sign; this strengthens the identification of this component as due to a thermal source.Presidential Young Investigator.  相似文献   

Sediment Organic Carbon in Todos Santos Bay, Baja California, Mexico     

Stephen V. Smith  Silvia E. Ibarra-Obando  Victoria Díaz-Castañeda  Francisco Javier Aranda-Manteca  José D. Carriquiry  Brian N. Popp  Oscar Gonzalez-Yajimovich 《Estuaries and Coasts》2008,31(4):719-727

Sediment grain size and organic carbon (OC) data collected over the past 50 years, together with δ¹³C values of OC in recently collected samples, were analyzed to improve understanding of sediment OC distribution and abundance in Todos Santos Bay. Sediments in the submarine canyon at the mouth of the bay and in quiet-water locations along the shore are fine grained, high in OC, and have generally low δ¹³C values; sediments in high-energy environments are low in OC and have high δ¹³C values. A bivariate isotopic mixing model indicates that none of the sediments contain >50% terrigenous OC (average ~30%), and that the terrigenous OC content of the sediments is a small proportion of the OC content of local soils. Sediment OC composition is apparently controlled by energy-related sorting and deposition, oxidation of much of the original terrigenous OC, and replacement of some terrigenous OC by marine OC.  相似文献   

Drought in Bulgaria and atmospheric synoptic conditions over Europe   总被引：1，自引：0，他引：1  

Liem Tran  C. Gregory Knight  Victoria Wesner 《GeoJournal》2002,57(3):149-157

Drought in Bulgaria is analyzed from the multiple viewpoints of statistical occurrence, spatial patterns, and synoptic conditions. A new index of drought, the SD (spatial-dryness) index, characterizes drought by both intensity and spatial extent. The occurrence of the SD index is analyzed using global gridded data sets. Examination of transitional probabilities of multiple months and years with drought occurrence suggests persistence is sufficiently frequent to be important for climate-related environmental planning. Finally, it is shown that specific seasonal synoptic patterns are associated with wet and dry conditions in Bulgaria. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The multiple chronological techniques applied to the Lake Suigetsu SG06 sediment core,central Japan     

Richard A. Staff  Takeshi Nakagawa  Gordon Schlolaut  Michael H. Marshall  Achim Brauer  Henry F. Lamb  Christopher Bronk Ramsey  Charlotte L. Bryant  Fiona Brock  Hiroyuki Kitagawa  Johannes van der Plicht  Rebecca L. Payne  Victoria C. Smith  Darren F. Mark  Alison Macleod  Simon P. E. Blockley  Jean‐Luc Schwenninger  Pavel E. Tarasov  Tsuyoshi Haraguchi  Katsuya Gotanda  Hitoshi Yonenobu  Yusuke Yokoyama  Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range).  相似文献   

Biogeochemistry of the Madeira river basin     

Dr. J. Mortatti  Dr. J. R. Ferreira  Dr. L. A. Martinelli  Dr. R. L. Victoria  A. C. F. Tancredi 《GeoJournal》1989,19(4):391-397

A biogeochemical characterization of the Madeira river basin has been made to evaluate the local and global effects of possible alterations in the ecosystem caused by recent intensive occupation in Rondonia state. During the period April 1983—January 1986, sampling was made both by land and river along the tributaries and main channel of the Madeira river. The parameters analysed lead to a detailed study of the physicochemical quality of the waters of the basin and their relationship with the local geology, associated with the transport of solid material and the hydrological behavior of the ecosystem.Penman's method adapted to tropical rainforest conditions was used to evaluate the potential evapotranspiration for the basin. Estimated potential evapotranspiration was 1420 mm/y, 77% due to the energy balance. Real evapotranspiration was 94% of the estimated potential and the main residence time of the rain water in the basin was 2 months. The isotopic behavior of Hydrogen and Oxygen in the river waters of the region was typical of great rivers, the values being more positive during the dry season and more negative during the rainy season. An isotopic gradient of ¹⁸O 0.038 ()/100 km, was established from Porto Velho station to the estuary, which was considered low when compared with the value of 0.063 ()/100 km, obtained for the Amazon river.In general, the waters of the tributaries were poor in dissolved ion species when compared with the main channel of the Madeira river. Seasonal variation in the transport of suspended sediment kept the same pattern, greater transport being observed on rising water than during high water. A transport of 2.85 million tons per day was observed in the Madeira river near the mouth.  相似文献   

Evolution of the early Earth: Constraints from Nd---Nd isotopic systematics     

Malcolm T. McCulloch  Victoria C. Bennett 《Lithos》1993,30(3-4):237-255

Combined ¹⁴⁷Sm---¹⁴³Nd and the now extinct [τ(1/2)₁₄₆=103×10⁶ yr] ¹⁴⁶Sm---¹⁴²Nd isotopic systematics are reported for early Archean gneisses from Greenland (Amîtsoq and Akilia associations), and Canada (Acasta gneiss). Using both field relationships and high resolution U---Pb SHRIMP ion-probe ages, it has been possible to identify the most ancient rocks in these terrains for isotopic analyses. Preliminary ¹⁴²Nd analyses of a still limited number of samples have failed to identify terrestrial ¹⁴²Nd anomalies. Effects, if present, are limited to < 10 ppm and we have thus been unable to confirm the +33±4 ppm ε₁₄₂ value claimed by Harper and Jacobsen (1992a, b) for a single sample. From the lack of ¹⁴⁶Sm---¹⁴²Nd effects we infer that large-scale fractionation events that may have occurred in the first 200 Ma of Earth history did not leave a significant nor widespread imprint on the early Archean mantle or crust. If a terrestrial magma ocean, with associated LREE fractionation, formed as a result of planetary accretion, then it had a lifetime of at most 250 m.y. before being remixed into the Earth's mantle.

The samples analysed in this study have a range of ε₁₄₃ values including highly positive values of up to +4.2. This requires that the earliest known Archean crust was differentiated from a reservoir that was strongly depleted in the LREE as compared with chondritic compositions. In the early Archean it is proposed that the depletions in LREE are a consequence of extraction of a limited fraction of the Earth's continental crust ( < 10%) from the upper 200 km of the mantle. A three reservoir model, consisting of the continental crust, depleted mantle and a more primitive mantle reservoir can be extended to account for both the present-day, as well as the evolving Nd isotopic composition of the Earth's crust and mantle. In contrast to previous models, the rate of growth of the continental crust is used as an input parameter to constrain the concomitant growth and evolution of the depleted mantle reservoir. Recycling of large volumes of bulk continental crust into the mantle is not considered to be an important process, nor is the existence of an additional major enriched component in the early Archean mantle.  相似文献   

A Decametric Scale Investigation of the Gravitational Constant     

M. Oldham  F. J. Lowes  R. J. Edge 《Geophysical Journal International》1993,113(1):83-94

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Martin Hotine     

R. C. A. Edge 《Journal of Geodesy》1969,43(1):8-12

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