Vertical zonation and distributions of calanoid copepods through the lower oxycline of the Arabian Sea oxygen minimum zone     

Karen F. Wishner  Celia Gelfman  Marcia M. Gowing  Dawn M. Outram  Mary Rapien  Rebecca L. Williams 《Progress in Oceanography》2008,78(2):163-191

This paper provides the first comprehensive analysis of calanoid copepod vertical zonation and community structure at midwater depths (300–1000 m) through the lower oxygen gradient (oxycline) (0.02 to 0.3 ml/L) of an oxygen minimum zone (OMZ). Feeding ecology was also analyzed. Zooplankton were collected with a double 1 m² MOCNESS plankton net in day and night vertically-stratified oblique tows from 1000 m to the surface at six stations during four seasons as part of the 1995 US Joint Global Ocean Flux Study (JGOFS) Arabian Sea project. The geographic comparison between a eutrophic more oxygenated onshore station and an offshore station with a strong OMZ served as a natural experiment to elucidate the influence of depth, oxygen concentration, season, food resources, and predators on the copepod distributions.Copepod species and species assemblages of the Arabian Sea OMZ differed in their spatial and vertical distributions relative to environmental and ecological characteristics of the water column and region. The extent and intensity of the oxycline at the lower boundary of the OMZ, and its spatial and temporal variability over the year of sampling, was an important factor affecting distributional patterns. Calanoid copepod species showed vertical zonation through the lower OMZ oxycline. Clustering analyses defined sample groups with similar copepod assemblages and species groups with similar distributions. No apparent diel vertical migration for either calanoid or non-calanoid copepods at these midwater depths was observed, but some species had age-related differences in vertical distributions. Subzones of the OMZ, termed the OMZ Core, the Lower Oxycline, and the Sub-Oxycline, had different copepod communities and ecological interactions. Major distributional and ecological changes were associated with surprisingly small oxygen gradients at low oxygen concentrations. The calanoid copepod community was most diverse in the most oxygenated environments (oxygen >0.14 ml/L), but the rank order of abundance of species was similar in the Lower Oxycline and Sub-Oxycline. Some species were absent or much scarcer in the OMZ Core. Two copepod species common in the Lower Oxycline were primarily detritivorous but showed dietary differences suggesting feeding specialization. The copepod Spinocalanus antarcticus fed primarily on components of the vertical particulate flux and suspended material, a less versatile diet than the co-occurring copepod Lucicutia grandis. Vertical zonation of copepod species through the lower OMZ oxycline is probably a complex interplay between physiological limitation by low oxygen, potential predator control, and potential food resources. Pelagic OMZ and oxycline communities, and their ecological interactions in the water column and with the benthos, may become even more widespread and significant in the future ocean, if global warming increases the extent and intensity of OMZs as predicted.  相似文献   

Comparative crystal chemistry by Robert M. Hazen and Larry W. Finger,Wiley, Chichester, 1982. No. of pages: xv+231 (incl. Indexes). Price: £19.50 (hardback)     

D. L. Hamilton 《Geological Journal》1984,19(1):81-81

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Geochemistry and petrology of howardite Miller Range 11100: A lithologically diverse piece of the Vestan regolith          下载免费PDF全文

Timothy Gregory  Katherine Helen Joy  Stanislav Strekopytov  Natalie Mary Curran 《Meteoritics & planetary science》2017,52(2):206-224

The howardite‐eucrite‐diogenite (HED) clan of meteorites, which most likely originate from the asteroid Vesta, provide an opportunity to combine in‐depth sample analysis with the comprehensive remote‐sensing data set from NASA's recent Dawn mission. Miller Range (MIL) 11100, an Antarctic howardite, contains diverse rock and mineral fragments from common HED lithologies (diogenites, cumulate eucrites, and basaltic eucrites). It also contains a rare pyroxferroite‐bearing lithology—not recognized in HED until recently—and rare Mg‐rich (Fo_86‐91) olivine crystals that possibly represent material excavated from the Vestan mantle. Clast components underwent different histories of thermal and impact metamorphism before being incorporated into this sample, reflecting the diversity in geological histories experienced by different parts of Vesta. The bulk chemical composition and petrography of MIL 11100 suggest that it is akin to the fragmental howardite meteorites. The strong lithological heterogeneity across this sample suggests that at least some parts of the Vestan regolith show heterogeneity on the mm‐scale. We combine the outcomes of this study with data from NASA's Dawn mission and hypothesize on possible source regions for this meteorite on the surface of Vesta.  相似文献   

Geomorphology and ancient settlements of the Southern Flank of MT. Cairo,lower Liri valley,Italy     

I. Peter Martini  Edith Mary Wightman 《Geoarchaeology》1987,2(2):131-147

The southern flank of Mt. Cairo in southern Lazio edges a valley which forms one of the major passageways from central to southern Italy. The mountainous landscape has affected the settlement pattern, as have historical events such as the Roman conquests and recent socio-economic evolution, which has led to industrialization of a traditional pastoral- agricultural setting. The slopes of calcareous Mt. Cairo are characterized by a cascade of normal faults which delimit landscape units such as the “uplands,” “steep slopes,” and the “mountain rise,” which contains well developed alluvial and colluvial fans. Along the lower mountain slopes, Bronze and Iron Age sites are consistently located higher than Roman ones. Archaeological remains and historical documents indicate that only after the Roman conquest was the agricultural potential of the flatter lower areas fully exploited. Roman villas were characteristically placed on the upper parts of the fans, where both access to different types of land and elevation above the mists of the valley were enjoyed. The Medieval period brought a trend back to higher sites and fortified villages. The uplands remained in use through the ages.  相似文献   

Demersal fish and habitat associations from visual surveys on the central California shelf     

Thomas E. Laidig  Diana L. Watters  Mary M. Yoklavich 《Estuarine, Coastal and Shelf Science》2009,83(4):629-637

In 2004, we surveyed demersal fishes and habitats on the continental shelf off central California (65–110 m depth) using the occupied submersible Delta. Our objectives were to estimate the relative abundance of habitats and to examine demersal fish species composition, diversity, density, and sizes relative to these habitats. A total of 112 transects were completed covering 32 km of seafloor. A higher density of fishes was estimated in boulder and cobble habitats than in mud and brachiopod beds. More than 80% of the fishes were small, measuring 20 cm or less in total length. Species with small maximum size (primarily pygmy rockfish, Sebastes wilsoni, and blackeye gobies, Rhinogobiops nicholsii) accounted for nearly half (49%) of the total number of 12,441 fishes. Most fishes were immature, with only 4 of 20 harvested species having more than 50% of the individuals larger than the size at first maturity. Our study area on the continental shelf may be an ontogenetic transition zone for immature fishes before they move to their adult habitat on the slope. Alternatively, historical fishing pressure may have contributed to the lack of large, mature fishes in the survey area. Understanding the importance of these habitats to fishes at various life stages will improve our ability to assess these deepwater fish stocks and effectively manage these living resources on an ecosystem basis.  相似文献   

Physical properties of calcareous ooze: Control by dissolution at depth     

Thomas C. Johnson  Edwin L. Hamilton  Wolfgang H. Berger 《Marine Geology》1977,24(4):259-277

Eighteen box cores of pelagic calcareous ooze from the Ontong Java Plateau in the western equatorial Pacific were subsampled and analyzed for the following physical properties: grain size, porosity, saturated density, mean grain density, compressional sound velocity and shear strength. In addition, weight percent CaCO₃ was determined, and micropaleontological analyses of the Foraminifera were performed to determine preservation and sedimentation rates. Mean grain size of the sediments decreases at deeper depositional sites, primarily because of dissolution and fragmentation of calcareous microfossils. This, in turn, results in the sediments in deeper water having lower sound velocities and less shear strength. The physical properties of calcareous ooze are not significantly affected by any reprecipitation or incipient cementation of calcite that may occur soon after deposition.  相似文献   

Compaction of Argillaceous sediments. (Developments in sedimentology, 18.): Herman H. Rieke III and George V. Chilingarian. Elsevier,Amsterdam, 1974, 424 pp., Dfl. 85.00     

Edwin L. Hamilton 《Marine Geology》1975,18(5):337-339

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Basalts and Phase Diagrams: An introduction to the Quantitative use of Phase Diagrams in Igneous Petrology by S. A. Morse. Springer-Verlag,New York, 1980. No. of pages: 493     

D. L. Hamilton 《Geological Journal》1982,17(3):247-248

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Fish assemblage structure on sandy beaches with different anthropogenic influences and proximity of spawning grounds          下载免费PDF全文

Hamilton H Pereira  Leonardo M Neves  Marcus R da Costa  Francisco G Araújo 《Marine Ecology》2015,36(1):16-27

Fish assemblages in an insular (preserved) and a continental (disturbed) sandy beach were compared to assess any changes that could be attributed to anthropogenic influences and/or the proximity of the fish spawning grounds. We expected that the closer geographical position to the spawning grounds and the small amount of anthropogenic disturbance on the insular beach would be likely to provide more suitable conditions for early fish development compared with the continental beach. A total of 192 samples (96 in each beach) were taken, yielding 68 fish species, mostly young‐of‐the‐year. Fish assemblage structure differed significantly between the two beaches. Moreover, the insular beach had higher number of species, number of individuals and biomass compared with the continental beach. The commercially important Clupeiformes Harengula clupeola, Anchoa tricolor and Anchoa januaria, Perciformes Micropogonias furnieri and Mugiliformes Mugil liza were typical species on the insular beach, partitioning the seasonal use of the beach. On the other hand, a few abundant non‐commercial species, mainly the Atheriniformes Atherinella brasiliensis and the Perciformes Eucinostomus argenteus and Diapterus rhombeus, occurred all year round at the continental beach. The high fish richness and abundance and the more conspicuous species turnover across seasons on the insular beach are probable indications of more complex and dynamic organization of the communities favored by better geographical position and less anthropogenic disturbance in the area.  相似文献   

Differentiation of clay resources on a limestone plain: The analysis of clay utilization during the Maya Formative at K'axob Belize     

Mary Lee Bartlett  Hector Neff  Patricia A. McAnany 《Geoarchaeology》2000,15(2):95-133

Differentiating clay resources in a uniform limestone plain, such as occurs in northern Belize, offers special challenges for the archaeologist. Combining data from soil mapping with petrographic and neutron activation analysis provides a mechanism for distinguishing possible resource areas. This study employed each of these differing avenues of analysis to determine possible clay resource areas used during the Maya Formative in northern Belize Central America. The results indicate that clay usage changed significantly from the Middle Formative period to the end of Late Formative period. These changes suggest a move to increased localized production and resource exploitation by the end of the period. © 2000 John Wiley & Sons, Inc.  相似文献