Organic matter assimilation and selective feeding by holothurians in the deep sea: some observations and comments     

Michael L. Ginger  David S. M. Billett  Karen L. Mackenzie  Konstandinos Kiriakoulakis  Renato R. Neto  Daniel K. Boardman  Vera L. C. S. Santos  Ian M. Horsfall  George A. Wolff   《Progress in Oceanography》2001,50(1-4)

The selective feeding behaviour and assimilation efficiencies of deep-sea holothurians were investigated in order to assess their impact on carbon and nitrogen remineralisation on the Porcupine Abyssal Plain (PAP; 49°N 16°W, 4850 m water depth). Unfortunately, reliable determination of organic matter in the gut contents of the organisms proved to be difficult, because of the lysis of cells associated with the death of the animals on recovery. This was expressed in high levels of free fatty acids in the gut contents of Oneirophanta mutabilis, which we ascribe to unregulated lipolysis of phospholipids and triacylglycerides. It was not possible to estimate accurately the contribution that such material made to the gut contents, but based on the distributions of sterols in the gut sediments, it is likely to have been substantial. Therefore, all assimilation efficiencies calculated for holothurians in the deep sea should be treated with caution.Fortuitously, a bloom of holothurians that feed on the sediment surface (namely Amperima rosea and Ellipinion molle) during the period of study provided an opportunity indirectly to assess the impact of megafauna on organic matter cycling at the PAP. Observations suggest that the depletion of phytosterols from the surficial sediments between July and October 1997 resulted from the selective uptake of fresh phytodetritus by the blooming species. Deep-sea holothurians do not biosynthesise sterols de novo and an estimate of the sterol required by the increased population of A. rosea and E. molle is equivalent to the sterol flux to the seafloor during the spring/summer of 1997. The implications are dramatic. Firstly, these and other megafauna apparently turned over and selectively removed phytosterols from the freshly arrived phytodetritus and the surficial sediment (0–5 mm) at the PAP in less than four months. Secondly, their action impacted the food resource available to other organisms. Finally, as phytosterols are expensive to biosynthesise and are apparently an important resource for holothurians, we speculate that the supply of these compounds to the sedimentary community may be one important control on their population in the abyssal ocean.  相似文献   

Final dissolved organic carbon broad community intercalibration and preliminary use of DOC reference materials   总被引：1，自引：0，他引：1  

Jonathan H. Sharp  Craig A. Carlson  Edward T. Peltzer  Dawn M. Castle-Ward  Karen B. Savidge  Katherine R. Rinker 《Marine Chemistry》2002,77(4):1819

A broad community intercalibration exercise for accurate measurement of dissolved organic carbon (DOC) in seawater has been carried out over a period of 5 years. A set of 10 natural samples with DOC content from 40 to 200 μM C were accompanied by two glucose standards and a “zero C” blank; all sealed in glass ampoules. Samples were sent to all interested analysts for “blind” analysis; 62 laboratories in 17 countries participated. A total of 59 separate analyses were determined to be acceptable by screening criteria based on standards and blank; another nine sets of analyses did not pass the screening. The majority of the analyses, both those passing and those that did not, were performed with high temperature combustion (HTC) methods, six sets of analyses were done using wet chemical oxidation methods.From the 53 sets of acceptable HTC analyses, the coefficient of variation (%CV) for analytical comparability of the samples was 10% (“community precision”). It is estimated that the individual replicate injection precision for most instruments was approximately 2% and that no additional variability was caused by differences within the ampoules of individual samples. The additional variability over 2% was likely a result of both random and systematic differences in analytical capabilities from instrument to instrument and from day to day for individual instruments. With an arbitrary selection after the fact, smaller subsets of analysts can show comparability better than 10% and duplicate or triplicate runs on different days of the full sets of samples in several laboratories showed comparability in the 2–6.5% range. Experienced oceanic analysts, with internal or shared reference materials, can now show reproducibility and comparability at a level closer to 2%.Preliminary use of DOC reference materials by 14 participants showed day-to-day reproducibilities for their laboratories in the 2–6% range in most cases; several with poorer reproducibility do not normally perform DOC analyses on samples with concentrations as low as the deep ocean reference used here. Use of these reference materials can also give a demonstration of comparability between laboratories. For credibility of DOC analyses, it is necessary for analysts to use community reference materials and report results of their analytical performance with these references.This paper does not identify individual data nor should it be considered an evaluation of individual laboratories or analysts. The purpose is to show the summary picture of the international community of DOC analysts as it existed in the mid- to late 1990s.  相似文献   

A comparison of black smoker hydrothermal plume behavior at Monolith Vent and at Clam Acres Vent Field: Dependence on source configuration     

Bemis  Karen G.  Rona  Peter A.  Jackson  Darrell  Jones  Christopher  Silver  Deborah  Mitsuzawa  Kyohiko 《Marine Geophysical Researches》2002,23(2):81-96

Quantitative visualization of acoustic images is used to compare the properties and behavior of high temperature hydrothermal plumes at two sites with different source configurations, increasing our understanding of how plume behavior reflects source configuration. Acoustic imaging experiments were conducted at the Clam Acres area of the Southwest Vent Field, 21°N East Pacific Rise and at Monolith Vent, North Cleft segment, Juan de Fuca Ridge. At Clam Acres, black smokers discharge from two adjacent chimneys which act as point sources, whereas multiple vents at Monolith Vent define a distributed elliptical source. Both plumes exhibit consistent dilution patterns, reasonable fits to the expected power law increase in centerline dilution with height, and simple bending of plume centerlines in response to ambient currents. Our data suggest that point source vents are associated with ordered plume structure, normal entrainment rates, and initial expansion of isosurfaces while distributed source vents are associated with disorganized plume structure, variable entrainment rates, and initial contraction of isosurfaces.  相似文献   

Experimental investigations into processes controlling stream and hyporheic temperatures,Fryxell Basin,Antarctica     

Karen Cozzetto  Diane McKnight  Thomas Nylen  Andrew Fountain 《Advances in water resources》2006

Glacial meltwater streams in the McMurdo Dry Valleys, Antarctica exhibit daily cycles in temperature with maxima frequently reaching 10–15 °C, often 10 °C above air temperatures. Hydrologic and biogeochemical processes occurring in these streams and their hyporheic zones strongly influence the flux of water, solutes, and sediment to the ice-covered lakes on the valley bottoms. The purpose of this study was to identify the dominant processes controlling water temperature in these polar desert streams and to investigate in particular the role of hyporheic exchange. In order to do this, we analyzed stream temperature patterns on basin-wide, longitudinal, and reach scales. In the basin-wide study, we examined stream temperature monitoring data for seven streams in the Lake Fryxell Basin. For the longitudinal study, we measured temperatures at seven sites along a 5-km length of Von Guerard Stream.  相似文献   

From public to private to … mutual? Restructuring water supply governance in England and Wales     

Karen J. Bakker 《Geoforum》2003,34(3):359-374

A little over a decade after privatization, the water supply industry in England and Wales is undergoing a period of restructuring; many water companies have withdrawn from equity markets, some have separated asset ownership from operation and maintenance, and others have made proposals to return water supply infrastructure to public control through ‘mutuals’ or ‘customer corporations’. This paper situates the restructuring of the water industry within broader debates over ‘associative self-governance’ taking place in Britain. Underpinned by a conceptual framework drawing on insights from regulation theory, in which governance models are enacted through regulatory practice, the interrelationship between restructuring and re-regulation of the water supply industry is analyzed. The paper argues that the failure of the post-privatization regulatory model to contain the contradictions between stable returns and the efficiency imperative, on the one hand, and politically acceptable rates of return and the equity imperative, on the other, led to a re-regulation of the water supply industry, which was a key factor in restructuring. Restructuring has entailed multiple strategies (diversification, internationalization, vertical de-integration, mutualization, securitization), which are briefly analyzed. In contrast to analyses which depict restructuring as a ‘retreat of the market’, the analysis presented in this paper emphasizes the continuity of the commercial governance model applied in the water supply industry in 1989. In interpreting restructuring as an industry response to re-regulation of services provision, the paper interrogates the incentive structure underpinning current proposals for a ‘mutual’ future for public services in Britain.  相似文献   

Social Attitudes Predict Biases in Geographic Knowledge*     

Dennis D. Kerkman  David Stea  Karen Norris  Jennifer L. Rice 《The Professional geographer》2004,56(2):258-269

Three principal components were found to underlie Texas university students' experiences with and attitudes toward Canada, the United States, and Mexico: diversity orientation, Mexican experiences, and Canadian experiences. Diversity orientation included positive attitudes toward Hispanics, Canadians, minorities, interethnic friendships, and dating and was negatively correlated with natio‐centrism (e.g., believing U.S. citizens receive the world's best education). Diversity orientation and natio‐centrism were not related to experiences with Mexico or Canada. Students estimated the locations of Canadian cities too far north and Mexican cities too far south. Biased estimates for Mexican cities were negatively correlated with diversity orientation, not experience with Mexico.  相似文献   

Chemical evolution of mid-ocean ridge hot springs     

Teresa Suter Bowers  Karen L. Von Damm  John M. Edmond 《Geochimica et cosmochimica acta》1985,49(11):2239-2252

Chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the East Pacific Rise at 21°N and 10 hot springs from the southern trough of the Guaymas Basin, Gulf of California provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers, mixing of the hydrothermal endmember with seawater, and reaction of an EPR-type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from DSDP hole 477 in the Guaymas Basin. Results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the East Pacific Rise and several vents in Guaymas Basin. Mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the East Pacific Rise and drill cores in Guaymas Basin. The hypothesis that Guaymas Basin hydrothermal fluids result from interaction of an EPR-type fluid with sediment cover in Guaymas Basin is supported by calculations which predict an increase in pH to a value similar to Guaymas Basin fluids, an order-of-magnitude decrease in metal concentrations, and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment, and observed mineral assemblage distribution with depth.  相似文献   

Siderophiles and volatiles in Apollo-16 rocks and soils     

John T Wasson  Karen L Robinson  Philip A Baedecker 《Geochimica et cosmochimica acta》1975,39(11):1475-1485

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Employer Recruitment and Hispanic Labor Migration: North Carolina Urban Areas at the End of the Millennium     

Karen D. Johnson&#x;Webb 《The Professional geographer》2002,54(3):406-421

The North Carolina Hispanic population has grown at a rapid pace in recent years. Before 1980, the majority of Hispanics in North Carolina were engaged primarily in migrant agricultural work. Hispanics who are part of the new influx are arriving in urban areas and are working at nonagricultural pursuits. Previous research and anecdotal evidence suggest that Hispanic newcomers come from other U.S. jurisdictions and from abroad. Labor migration occurs in response to demand for labor, and labor demand is meditated by employers’ preferences and hiring practices. However, focusing solely on employer demand for labor ignores the role of past U.S. immigration policy and the large growth in services employment in the Sunbelt that have fueled the Hispanic in–migration. This research project explored the attitudes and recruiting behavior of employers in the Triangle region of North Carolina. A newspaper content analysis was undertaken, and interviews were conducted with selected intermediaries and a group of employers. Qualitative analysis of the data collected revealed that these employers utilize the social networks of their immigrant Hispanic employees to recruit new workers. They also use a variety of other recruiting methods to recruit Hispanics both locally and from abroad. If this practice is widespread, it may be fueling the influx of Hispanic immigrants to North Carolina. Employers interviewed extolled the work ethic of Hispanic workers and often bypassed native–born workers, whom they felt were inferior employees. These findings have ramifications for future immigration policy and for the success of welfare–to–work programs. Employer demand for labor is one factor that must be considered when formulating new immigration policy.  相似文献   

Quantitative estimates of interplate coupling inferred from outer rise earthquakes     

Xinping Liu  Karen C. McNally 《Pure and Applied Geophysics》1993,140(2):211-255

Interplate coupling plays an important role in the seismogenesis of great interplate earthquakes at subduction zones. The spatial and temporal variations of such coupling control the patterns of subduction zone seismicity. We calculate stresses in the outer rise based on a model of oceanic plate bending and coupling at the interplate contact, to quantitatively estimate the degree of interplate coupling for the Tonga, New Hebrides, Kurile, Kamchatka, and Marianas subduction zones. Depths and focal mechanisms of outer rise earthquakes are used to constrain the stress models. We perform waveform modeling of body waves from the GDSN network to obtain reliable focal depth estimates for 24 outer rise earthquakes. A propagator matrix technique is used to calculate outer rise stresses in a bending 2-D elastic plate floating on a weak mantle. The modeling of normal and tangential loads simulates the total vertical and shear forces acting on the subducting plate. We estimate the interplate coupling by searching for an optimal tangential load at the plate interface that causes the corresponding stress regime within the plate to best fit the earthquake mechanisms in depth and location.We find the estimated mean tangential load over 125–200 km width ranging between 166 and 671 bars for Tonga, the New Hebrides, the Kuriles, and Kamchatka. This magnitude of the coupling stress is generally compatible with the predicted shear stress at the plate contact from thermal-mechanical plate models byMolnar andEngland (1990), andVan den Buekel andWortel (1988). The estimated tectonic coupling,F _tc , is on the order of 10¹²–10¹³ N/m for all the subduction zones.F _tc for Tonga and New Hebrides is about twice as high as in the Kurile and Kamchatka arcs. The corresponding earthquake coupling forceF _ec appears to be 1–10% of the tectonic coupling from our estimates. There seems to be no definitive correlation of the degree of seismic coupling with the estimated tectonic coupling. We find that outer rise earthquakes in the Marianas can be modeled using zero tangential load.  相似文献