Morphology of a ‘superfast’ Mid-Ocean Ridge crest and flanks: The East Pacific Rise, 7°–9° S     

J. R. Cochran  J. A. Goff  A. Malinverno  D. J. Fornari  C. Keeley  X. Wang 《Marine Geophysical Researches》1993,15(1):65-75

Detailed bathymetric data from a Hydrosweep multibeam sonar survey of a 250 km-long portion of the superfast-spreading southern East Pacific Rise crest and flanks show that the along-axis variation in morphology and axial depth differs significantly from that observed at the fast-spreading northern East Pacific Rise. While the deep mantle upwelling pattern is similar under the northern and southern East Pacific Rise, our observations require that the connectivity of the shallow, subcrestal plumbing system be more efficient beneath the super-fast spreading southern East Pacific Rise than beneath the slower spreading northern East Pacific Rise.  相似文献   

Temporal Trends of Dissolved Trace Metals in Jamaica Bay,NY: Importance of Wastewater Input and Submarine Groundwater Discharge in an Urban Estuary   总被引：1，自引：0，他引：1  

Aaron J. Beck  J. Kirk Cochran  Sergio A. Sañudo-Wilhelmy 《Estuaries and Coasts》2009,32(3):535-550

Jamaica Bay, NY, is a highly urbanized estuary within the boroughs of New York City conspicuously lacking published information on dissolved trace metal concentrations. The current study examines the distribution and cycling of trace metals in that embayment with data gathered during cruises in November 2004, April 2005, and June 2006. Most of the metal distributions (Fe, Zn, Co, Ag, Cu, Pb, Ni) in the water column are explained by the input of substantial volumes of treated wastewater effluent. However, several lines of evidence suggest that submarine groundwater discharge (SGD) is also an important source of dissolved Fe, Zn, Co, Ni, and isotopically distinct stable Pb ratios (²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb) in the Bay. Conversely, the recirculated seawater component of SGD is an apparent sink for dissolved Mo. This study provides the first measurements of dissolved trace metals in the Jamaica Bay water column and subterranean estuary and provides evidence for trace metal input due to SGD.  相似文献   

Total body burden and tissue distribution of polyfluorinated compounds in harbor seals (Phoca vitulina) from the German Bight   总被引：1，自引：0，他引：1  

Lutz Ahrens  Ursula Siebert 《Marine pollution bulletin》2009,58(4):520-525

Total body burden and tissue distribution of polyfluorinated compounds (PFCs) were investigated in harbor seals (Phoca vitulina) from the German Bight in 2007. A total number of 18 individual PFCs from the following groups could be quantified in the different tissues: perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs) and their precursors perfluorinated sulfinates (PFSiAs), perfluorinated sulfonamides, and sulfonamido ethanols. Perfluorooctanesulfonate (PFOS) was the predominant compound in all measured seal tissues (up to 1665 ng g⁻¹ wet weight in liver tissue). The dominant PFCAs were perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA), but their concentrations were much lower compared to PFOS. The mean whole body burden in harbor seals of all detected PFCs was estimated to be 2665 ± 1207 μg absolute. The major amount of the total PFCs burden in the bodies was in blood (38%) and liver (36%), followed by muscle (13%), lung (8%), kidney (2%), blubber (2%), heart (1%), brain (1%), thymus (<0.01%) and thyroid (<0.01%). These data suggest large differences in body burden and accumulation pattern of PFCs in marine mammals.  相似文献   

Isotopic abundance in the CN coma of comets: Ten years of measurements     

R. Schulz  E. Jehin  D. Hutsemékers  A. Cochran  J.A. Stüwe 《Planetary and Space Science》2008,56(13):1713-1718

Over the past 10 years the isotopic ratios of carbon (¹²C/¹³C) and nitrogen (¹⁴N/¹⁵N) have been determined for a dozen comets, bright enough to allow obtaining the required measurements from the ground. The ratios were derived from high-resolution spectra of the CN coma measured in the B²∑⁺−X²∑⁺ (0, 0) emission band around 387 nm. The observed comets belong to different dynamical classes, including dynamically new as well as long- and short-period comets from the Halley- and Jupiter-family. In some cases the comets could be observed at various heliocentric distances. All values determined for the carbon and nitrogen isotopic ratios were consistent within the error margin irrespective of the type of comet or the heliocentric distance at which it was observed. Our investigations resulted in average ratios of ¹²C/¹³C=91±21 and nitrogen ¹⁴N/¹⁵N=141±29. Whilst the value for the carbon isotopic ratio is in good agreement with the solar and terrestrial value of 89, the nitrogen isotopic ratio is very different from the telluric value of 272.  相似文献   

Lake morphometry and wind exposure may shape the plankton community structure in acidic mining lakes     

Guntram Weithoff  Michael Moser  Ursula Gaedke 《Limnologica》2010,40(2):161-166

Acidic mining lakes (pH <3) are specific habitats exhibiting particular chemical and biological characteristics. The species richness is low and mixotrophy and omnivory are common features of the plankton food web in such lakes. The plankton community structure of mining lakes of different morphometry and mixing type but similar chemical characteristics (Lake 130, Germany and Lake Langau, Austria) was investigated. The focus was laid on the species composition, the trophic relationship between the phago-mixotrophic flagellate Ochromonas sp. and bacteria and the formation of a deep chlorophyll maximum along a vertical pH-gradient. The shallow wind-exposed Lake 130 exhibited a higher species richness than Lake Langau. This increase in species richness was made up mainly by mero-planktic species, suggesting a strong benthic/littoral - pelagic coupling. Based on the field data from both lakes, a nonlinear, negative relation between bacteria and Ochromonas biomass was found, suggesting that at an Ochromonas biomass below 50 μg C L⁻¹, the grazing pressure on bacteria is low and with increasing Ochromonas biomass bacteria decline. Furthermore, in Lake Langau, a prominent deep chlorophyll maximum was found with chlorophyll concentrations ca. 50 times higher than in the epilimnion which was build up by the euglenophyte Lepocinclis sp. We conclude that lake morphometry, and specific abiotic characteristics such as mixing behaviour influence the community structure in these mining lakes.  相似文献   

Human impact on Holocene sediment dynamics in the Eastern Mediterranean – the example of the Roman harbour of Ephesus          下载免费PDF全文

Friederike Stock  Maria Knipping  Anna Pint  Sabine Ladstätter  Hugo Delile  Andreas G. Heiss  Hannes Laermanns  Piers D. Mitchell  René Ployer  Martin Steskal  Ursula Thanheiser  Ralf Urz  Volker Wennrich  Helmut Brückner 《地球表面变化过程与地形》2016,41(7):980-996

During the past millennia, many erosion and accumulation processes have been modified by anthropogenic impact. This holds especially true for the environs of ancient settlements and their harbours along the Mediterranean coasts. Our multi‐proxy investigations in the Roman harbour and the harbour canal of Ephesus (western Turkey) reveals that humans have significantly triggered soil erosion during the last three millennia. Since the eighth century bc , and especially since the Hellenistic period, a high sedimentation rate indicates fast alluviation and delta progradation of the Küçük Menderes. Deforestation, agriculture (especially ploughing) and grazing (especially goats) were the main reasons for erosion of the river catchment area. One consequence was significant siltation of the Hellenistic/Roman harbour basin. This sediment trap archives the human impact, which was strongly enhanced from Hellenistic/Roman to Byzantine times (second/first centuries bc to the sixth/seventh centuries ad ), evidenced by high sedimentation rates, raised values of heavy metal contaminations [lead (Pb), copper (Cu)], the occurrence of fruit tree pollen and of intestinal parasites. From the middle to the end of the first millennium ad , the influence of Ephesus declined, which resulted in a decrease of human impact. Studies of several ancient settlements around the Mediterranean Sea tell a comparable story. They also confirm that during their most flourishing periods the human impact totally overprinted the climatic one. To detect the latter, geo‐bio‐archives of relatively pristine areas have to be investigated in detail. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

What is the Parent of CH in the Coma of Comet C/1995 O1 (Hale-Bopp)?     

Cochran  Anita L.  Boice  D. C.  Barker  Edwin S.  Laffont  Celine 《Earth, Moon, and Planets》1997,78(1-3):85-91

The ratio of CH₄/CO in comets is an important indicator of the region of their formation. However, it is difficult to measure the quantity of CH⁺. The Giotto Ion Mass Spectrometer experiment observed a quantity of CH⁺ which seemed inconsistent with the amount of CH⁺. Thus, it was proposed that a source of the CH⁺ was a distributed source in the dust. We tested this hypothesis by observing the CH emission strength in comet Hale-Bopp as a function of dustiness. We see no strong correlation between the dust and the gas. Thus, for Hale-Bopp,dust is unlikely to be a dominant source of CH. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Effects of gravity-gradient torque on the rotational motion of a triaxial satellite in a precessing elliptic orbit     

John E. Cochran 《Celestial Mechanics and Dynamical Astronomy》1974,8(4):534-534

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High-Dispersion Spectroscopy of the Sodium (NA) Emission within the Inner Coma of C/1995 O1 (Hale-Bopp)     

Barker  E. S.  Cochran  A. L.  Cochran  W. D. 《Earth, Moon, and Planets》1997,78(1-3):93-98

Very-high spectral resolution observations of the neutral Na emission have enabled measurements of the velocity dispersions of the Na atoms within ∼40,000 km of the opto center of Hale-Bopp. Asymmetric Na D line profiles imply both an in situ or core Na source and a secondary Na source at locations within the inner coma. The core velocity distribution had a FWHM of 2 km s^-1. The extended source FWHM increased with distance from the nucleus (up to ∼6 km s^-1, but appeared smaller in the more dusty regions (∼2.5–3.0 km s^-1) of the inner coma. The D₂/D₁ line strength ratio was consistent with an optically thin inner coma. Within 5,000 km of the opto center the continuum spatial intensity profiles decreased as ∼r^-1 while the Na D emission decreased at less than r^-1. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Longitudinal variability of methane and ammonia bands on jupiter: II. Temporal variations     

William D. Cochran  Anita L. Cochran 《Icarus》1983,56(1):116-121

A set of spectra was obtained of the Jovian Equatorial Zone central meridian 6190 Å CH₄ and 6450 Å NH₃ bands in February 1980, a year after the data reported by W.D. Cochran and A.L. Cochran ((1980) Icarus42, 102–110). These new data confirm the results of the previous study, and also permit a search for temporal, as well as longitudinal, variability of these molecular absorption bands. The new data set shows a correlation of NH₃ and CH₄ equivalent widths, as well as a lack of any strong correlation of red continuum reflectivity with equivalent width. These trends were also exhibited by the 1979 data. Longitude regions of larger or smaller than average equivalent width seem still to be evident a year later, with some slight drift in longitude. An increase in the average CH₄ and NH₃ equivalent width over the entire planet was detected during the one year interval. This is easily understood as the result of a global decrease in the mean altitude of the NH₃ cloud.  相似文献