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31.
Christopher L. Dupont James. W. Moffett Robert R. Bidigare Beth A. Ahner 《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(12):1961-1974
Dissolved and particulate concentrations of the biogenic thiols cysteine (Cys), arginine–cysteine (Arg–Cys), glutamine–cysteine (Gln–Cys), γ-glutamate–cysteine (γ-Glu–Cys) and glutathione (GSH) were measured in the subartic Pacific Ocean in the summer of 2003 using high performance liquid chromatography (HPLC) with precolumn derivatization as reported in previous work. In this study, a preconcentration protocol for the derivatized thiols was utilized to extend detection limits of dissolved thiols to picomolar levels. The measured concentrations of particulate and dissolved thiols were uncoupled, with distinctive depth profiles and large differences in the particulate to dissolved ratios between individual compounds. Glutathione was the most abundant particulate thiol whereas the most abundant dissolved thiol was γ-Glu–Cys, with concentrations as high as 15 nM. Given the relatively small pool of intracellular γ-Glu–Cys and the very low dissolved concentrations of GSH, we hypothesize that glutathione released from cells is rapidly converted to the potentially degradation resistant γ-Glu–Cys outside the cell. The relatively high concentrations of other dissolved thiols compared to particulate concentrations implies both biological exudation and slow degradation rates. Some thiols appear to vary with changes in nutrient availability but this effect is difficult to decouple from changes in community structure inferred from pigment analyses. Dissolved thiol concentrations also exceed typical metal concentrations in the subartic Pacific, supporting previous arguments that they may be important in metal speciation. 相似文献
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Positive gravity anomalies indicate two dense conduits or eruptive centers beneath the northern summit of Sio Guyot, western Mid-Pacific Mountains. The low amplitude of the positive anomalies and the gravity lows flanking the guyot can be explained by crust 2.5 times the normal Pacific Ocean crustal thickness extending to a depth of 22 ± 2 km. The excess mass of the seamount is 100% locally isostatically compensated by the mass deficit below; this compensation may result from flexural loading and voluminous sill injection near a former ridge-crest transform fault system trending roughly ENE and NNW. 相似文献
35.
Thermodynamic characterization of the partitioning of iron between soluble and colloidal species in the Atlantic Ocean 总被引:2,自引:1,他引:2
Recent electrochemical measurements have shown that iron (Fe) speciation in seawater is dominated by complexation with strong organic ligands throughout the water column and have provided important thermodynamic information about these compounds. Independent work has shown that iron exists in both soluble and colloidal fractions in the Atlantic Ocean. Here we have combined these approaches in samples collected from a variety of regimes within the Atlantic Ocean. We measured the partitioning of Fe between soluble (< 0.02 μm) and colloidal (0.02 to 0.4 μm) size classes and characterized the concentrations and conditional stability constants of Fe ligands within these size classes. Results suggest that equilibrium partitioning of Fe between soluble and colloidal ligands is partially responsible for the distribution of Fe between soluble and colloidal size classes. However, a significant fraction of the colloidal Fe was inert to ligand exchange as soluble Fe concentrations were generally lower than values predicted by a simple equilibrium partitioning model.In surface waters, strong ligands with conditional stability constants of 1013 relative to total inorganic Fe appeared to dominate speciation in both the soluble and colloidal fractions. In deep waters these ligands were absent, and instead we found ligands with stability constants 12–15 fold smaller that were predominantly in the soluble pool. Nevertheless, significant levels of colloidal Fe were found in these samples, which we inferred must be inert to coordination exchange. 相似文献
36.
In this paper we review levels of net loss, what happens to the gear once it has been lost, and the resulting levels of ‘ghost catches’ made in passive net fisheries in the EU. We also consider ghost catches resulting from lost gear in other types of fisheries, and the extent to which the value of ghost catches has been quantified. We consider why fishing gear is lost, and profile common management responses. We present a cost benefit model to assess the relative cost effectiveness of different management measures, and suggest that gear retrieval programmes may provide less value for money than other management responses. 相似文献
37.
Mussel Periostracum from Deep-Sea Redox Communities as a Microbial Habitat: 3. Secondary Inhabitants
Abstract. Vacated microborings in periostracum of live mussels of the Florida Escarpment redox community (depth of 3266 m) become a habitat for a prolific secondary microbiota consisting of a variety of prokaryotic and a few eukaryotic organisms. Periostracum surface is also colonized by diverse microorganisms, dominated by presumed chemolithotrophic bacteria with stacks of intracellular lamellae. Unlike sheltered microflora within borings, the surface community is heavily grazed upon by numerous archaeogastropods and ciliates. 相似文献
38.
James R. Coull 《Ocean & Coastal Management》1992,18(2-4)
The fisheries systems which have developed in the European Economic Community (EEC) and Eastern Canada show striking similarities and contrasts. Both show efforts directed at conserving the resource base while setting limits for annual catches and allocating shares in these catches among fishermen. Canada has had less pressure on its resources and has been more successful in restraining over-fishing tendencies; it also has a more fully co-ordinated and effective management system. On the other hand the EEC has greater efficiency in catching, marketing and processing, and in recent times has had less government aid. Better systems would combine Canadian management efficiency with EEC economic efficiency. 相似文献
39.
To improve resolution of seismic-reflection profiles in continental slope water depths of 900 to 1500 m, a single hydrophone
was towed about 150 m off the bottom to receive reflected signals from a surface-towed sparker sound source. That deep-towed
hydrophone data show that valleys which appear V-shaped in records from a surface-towed hydrophone are flat-bottomed, and
that subbottom reflections from an erosional unconformity can be much better resolved. The data produced by this technique
are very hepful when used in conjunction with records from conventional surface-towed seismic-profiling equipment. 相似文献
40.