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1.
Beyond the shelf break at ca. 150 m water depth, sulfate reduction is the only important process of organic matter oxidation in Black Sea sediments from the surface down to the sulfate–methane transition at 2–4 m depth. Sulfate reduction rates were measured experimentally with 35SO42−, and the rates were compared with results of two diffusion-reaction models. The results showed that, even in these non-bioirrigated sediments without sulfide reoxidation, modeling strongly underestimated the high reduction rates near the sediment surface. A hybrid modeling approach, in which experimentally measured rates in the upper sediment layers force a model that includes also the deeper layers, probably provides the most realistic estimate of sulfate reduction rates. Areal rates of sulfate reduction were 0.65–1.43 mmol SO42− m−2 d−1, highest in sediments just below the chemocline. Anaerobic methane oxidation accounted for 7–11% of the total sulfate reduction in slope and deep-sea sediments. Although this methane-driven sulfate reduction shaped the entire sulfate gradient, it was only equivalent to the sulfate reduction in the uppermost 1.5 cm of surface sediment. Methane oxidation was complete, yet the process was very sluggish with turnover times of methane within the sulfate–methane transition zone of 20 yr or more.  相似文献   

2.
Although a great amount of information is available on bacteria inhabiting deep-sea sediments, the occurrence of fungi in this environment has been poorly studied and documented. We report here the occurrence of fungi in deep-sea sediments from ∼5000 m depth in the Central Indian Basin (9–16°S and 73–76°E). A total of 181 cultures of fungi, most of which belong to terrestrial sporulating species, were isolated by a variety of isolation techniques. Species of Aspergillus and non-sporulating fungi were the most common. Several yeasts were also isolated. Maximum species diversity was observed in 0–2 cm sections of the sediment cores. Direct staining of the sediments with Calcofluor, a fluorescent optical brightener, revealed the presence of fungal hyphae in the sediments. Immunofluorescence using polyclonal antibodies raised against a deep-sea isolate of Aspergillus terreus (# A 4634) confirmed its presence in the form of hyphae in the sub-section from which it was isolated. A total of 25 representative species of fungi produced substantial biomass at 200 bar pressure at 30° as well as at 5 °C. Many fungi showed abnormal morphology at 200 bar/5 °C. A comparison of terrestrial isolates with several deep-sea isolates indicated that the former could grow at 200 bar pressure when growth was initiated with mycelial inocula. However, spores of a deep-sea isolate A. terreus (# A 4634), but not the terrestrial ones, showed germination at 200 bar pressure and 30 °C. Our results suggest that terrestrial species of fungi transported to the deep sea are initially stressed but may gradually adapt themselves for growth under these conditions.  相似文献   

3.
During ‘Meteor’ expedition ‘DIVA 2’ in 2005 the abyssal macro- and megafauna communities were studied in the northern Cape Basin, in the northern Angola Basin and in the eastern and western Guinea Basin. Water depths varied between 5040 and 5670 m.Surface deposit feeding or predatory ophiuroids dominated the megafaunal community in the northern Cape Basin, sponges, sipunculids and fish in the northern Angola Basin, and asteroids, crustaceans and fish in the eastern Guinea Basin, while in the western Guinea Basin sipunculids dominated.In the northern Cape Basin, peracarid crustaceans were the dominant macrofaunal group, followed by polychaetes and bivalves. In the Guinea Basin, polychaetes, peracarid crustaceans and bivalves dominated, although omnivorous or predatory free-living nematodes of macrofaunal size (>0.5 mm) made up 40–60% of the total abundance, with maxima in the western basin.The chlorophyll a content of sediments was lower in the northern Cape and Angola Basins than in the Guinea Basin, which was consistent with the differences in water masses, primary production and flux rate of organic matter in the three basins of the South-East Atlantic. The differences in structure and function of the macro- and megafauna communities in the three basins correlated with the differences in the amount of food reaching the seafloor in tropical and subtropical settings.  相似文献   

4.
In order to study temporal variations of the genetic material in the continental shelf and deep-sea sediments of the extremely oligotrophic Cretan Sea, samples were collected on seasonal basis from August 1994 to September 1995, with a multiple corer, at seven stations (from 40 to 1540 m depth). Surface sediments (0–1 cm) were sub-sampled and analyzed for nucleic acid content (DNA, RNA) and bacterial density. DNA concentrations in the sediments were high (on annual average, 25.0 μg g-1) and declined with increasing water depth, ranging from 3.5 to 55.2 μg g-1. DNA concentrations displayed wide temporal changes also at bathyal depths confirming the recent view of the large variability of the deep-sea environments. Also RNA concentrations decreased with increasing water depth (range: 0.4–29.9 μg g-1). The ratio of RNA to DNA did not show a clear spatial pattern but was characterized by significant changes between sampling periods. DNA concentrations were significantly correlated with protein and phytopigment concentrations in the sediment, indicating a possible relationship with the inputs of primary organic matter from the photic layer. Bacterial densities were generally high (range: 0.9–4.6×108 cells g-1) compared to other deep-sea environments and decreased with increasing water depth. Estimates of the bacterial contribution to the sedimentary genetic material indicated that bacterial-DNA accounted, on annual average, for a small fraction of the total DNA pool (4.3%) but that bacterial-RNA represented a significant fraction of the total sedimentary RNA (26%). Bacterial contribution to nucleic acids increased, even though irregularly, with increasing depth. In deep-sea sediments, changes in RNA concentrations appear to be largely dependent upon bacterial dynamics. Estimates of the overall living contribution to the DNA pools (i.e. microbial plus meiofaunal DNA) indicated that the large majority (about 90%) of the DNA in continental and deep-sea sediments of the eastern Mediterranean was detrital. The non-living DNA pools reach extremely high concentrations up to 0.41 g DNA m-2 cm-1. Thus, especially in deep benthic habitats, characterized by low inputs of labile organic compounds, detrital DNA could represent a suitable and high quality food source or a significant reservoir of nucleic acid precursors for benthic metabolism.  相似文献   

5.
Density, taxonomic composition at higher taxon level and vertical distribution of benthic macrofaunal communities and sediment characteristics (pore water, nitrogen, organic carbon, sulfur, C/N ratio, n-alcohol biomarkers) were examined at three deep sites on the Congo–Gabon continental margin. This study was part of the multidisciplinary BIOZAIRE project that aimed at studying the deep benthic ecosystems in the Gulf of Guinea. Sampling of macrofaunal communities and of sediment was conducted during three cruises (January 2001, December 2001 and December 2003) at two downslope sites (4000 m depth), one located near the Congo submarine channel (15 km in the south) and the other one far from the channel (150 km in the South). The third area located 8 km north of the Congo channel in the surroundings of a giant pockmark at 3160 m depth was sampled during one cruise in December 2003.At these three locations the macrofaunal communities presented relatively high densities (327–987 ind. 0.25 m−2) compared with macrofaunal communities at similar depths; that is due to high levels of food input related to the Congo river and submarine system activities that affect the whole study area. The communities were different from each other in terms of taxonomic composition at higher taxon level (phylum, class, order for all the groups except for the polychaetes classified into families). The polychaetes dominated the communities and were responsible for the increase in densities observed at both deep sites (4000 m) between January 2001 and December 2003 whereas the tanaidaceans, the isopods and the bivalves were the other most abundant taxa responsible for the spatial differences between these sites. The community at 3150 m differed from the two deep communities by higher abundances in bivalves, nemerteans and holothuroids. The composition of the polychaete community also differed among sites.In the vicinity of the Congo channel, the expected positive effect of the additional organic matter transported through the turbiditic currents on to the surrounding benthic communities was not observed, as the increase in densities during the study period was higher at the site located away from the Congo channel than near the channel (80% vs 30%). That may be due to the low food value of the organic matter of terrestrial origin carried through the turbidites, and/or to the disturbance caused by these turbidites. Conversely, far from the channel the macrofaunal communities benefit from organic matter of higher energetic value originating mainly from marine sources, but also from continental sources, carried by the Congo plume or by near-bed currents across or along the continental slope. Spatial and temporal variability in trophic and physical characteristics of the sediment habitat at both deep sites also affected the vertical distribution of the macrofaunal communities.The activities of the very active Congo system structure the deep macrofaunal communities on a large area in terms of densities, composition and vertical distribution. The food input is enhanced at regional scale as well as the heterogeneity of the sediment characteristics, mainly in terms of organic matter quality (marine vs terrigenous). In turn, the densities are enhanced as well as the regional diversity of the macrofaunal communities in terms of taxonomic composition and distribution.  相似文献   

6.
Large organic falls to the benthic environment, such as dead wood or whale bones, harbour organisms relying on sulfide-oxidizing symbionts. Nothing is known however, concerning sulfide enrichment at the wood surface and its relation to wood colonization by sulfide-oxidizing symbiotic organisms.In this study we combined in situ hydrogen sulfide and pH measurements on sunken wood, with associated fauna microscopy analyses in a tropical mangrove swamp. This shallow environment is known to harbour thiotrophic symbioses and is also abundantly supplied with sunken wood. A significant sulfide enrichment at the wood surface was revealed. A 72 h sequence of measurements emphasized the wide fluctuation of sulfide levels (0.1–>100 μM) over time with both a tidal influence and rapid fluctuations. Protozoans observed on the wood surface were similar to Zoothamnium niveum and to vorticellids. Our SEM observations revealed their association with ectosymbiotic bacteria, which are likely to be sulfide-oxidizers. These results support the idea that sunken wood surfaces constitute an environment suitable for sulfide-oxidizing symbioses.  相似文献   

7.
Although the organization patterns of fauna in the deep sea have been broadly documented, most studies have focused on the megafauna. Bivalves represent about 10% of the deep-sea macrobenthic fauna, being the third taxon in abundance after polychaetes and peracarid crustaceans. This study, based on a large data set, examined the bathymetric distribution, patterns of zonation and diversity–depth trends of bivalves from the Porcupine Seabight and adjacent Abyssal Plain (NE Atlantic). A total of 131,334 individuals belonging to 76 species were collected between 500 and 4866 m. Most of the species showed broad depth ranges with some ranges extending over more than 3000 m. Furthermore, many species overlapped in their depth distributions. Patterns of zonation were not very strong and faunal change was gradual. Nevertheless, four bathymetric discontinuities, more or less clearly delimited, occurred at about 750, 1900, 2900 and 4100 m. These boundaries indicated five faunistic zones: (1) a zone above ∼750 m marking the change from shelf species to bathyal species; (2) a zone from ∼750 to 1900 m that corresponds to the upper and mid-bathyal zones taken together; (3) a lower bathyal zone from ∼1900 to 2900 m; (4) a transition zone from ∼2900 to 4100 m where the bathyal fauna meets and overlaps with the abyssal fauna and (5) a truly abyssal zone from approximately 4100–4900 m (the lower depth limit of this study), characterized by the presence of abyssal species with restricted depth ranges and a few specimens of some bathyal species with very broad distributions. The ∼4100 m boundary marked the lower limit of distribution of many bathyal species. There was a pattern of increasing diversity downslope from ∼500 to 1600 m, followed by a decrease to minimum values at about 2700 m. This drop in diversity was followed by an increase up to maximum values at ∼4100 m and then again, a fall to ∼4900 m (the lower depth limit in this study).  相似文献   

8.
Macrofaunal polychaete communities (>500 µm) in the South Eastern Arabian Sea (SEAS) continental margin (200–1000 m) are described, based on three systematic surveys carried out in 9 transects (at ~200 m, 500 m and 1000 m) between 7°00′and 14°30′N latitudes. A total of 7938 polychaetes belonging to 195 species were obtained in 136 grab samples collected at 27 sites. Three distinct assemblages were identified in the northern part of the SEAS margin (10–14°30′N), occupying the three sampled depth strata (shelf edge, upper and mid-slope) and two assemblages (shelf edge and slope) in the south (7–10°N). Highest density of polychaetes and dominance of a few species were observed in the shelf edge, where the Arabian Sea oxygen minimum zone (OMZ) impinged on the seafloor, particularly in the northern transects. The resident fauna in this region (Cossura coasta, Paraonis gracilis, Prionospio spp. and Tharyx spp.) were characteristically of smaller size, and well suited to thrive in the sandy sediments in OMZ settings. Densities were lowest along the most northerly transect (T9), where dissolved oxygen (DO) concentrations were extremely low (<0.15 ml l−1, i.e.<6.7 μmol l−1). Beyond the realm of influence of the OMZ (i.e. mid-slope, ~1000 m), the faunal density decreased while species diversity increased. The relative proportion of silt increased with depth, and the dominance of the aforementioned species decreased, giving way to forms such as Paraprionospio pinnata, Notomastus sp., Eunoe sp. and lumbrinerids. Relatively high species richness and diversity were observed in the sandy sediments of the southern sector (7–9°N), where influence of the OMZ was less intense. The area was also characterized by certain species (e.g. Aionidella cirrobranchiata, Isolda pulchella) that were nearly absent in the northern region. The gradients in DO concentration across the core and lower boundary of the OMZ, along with bathymetric and latitudinal variation in sediment texture, were responsible for differences in polychaete size and community structure on the SEAS margin. Spatial and temporal variations were observed in organic matter (OM) content of the sediment, but these were not reflected in the density, diversity or distribution pattern of the polychaetes.  相似文献   

9.
Cold-seep environments and their associated symbiont-bearing megafaunal communities create islands of primary production for macro- and meiofauna in the otherwise monotonous and nutrient-poor deep-sea environment. To examine the spatial variation and distribution patterns of metazoan meiobenthos in different seepage-related habitats, samples were collected in two regions off Norway: several pockmarks associated with the Storegga Slide including the Nyegga pockmark area (730 m; 64°N), and the active, methane-venting Håkon Mosby Mud Volcano (HMMV) west of the Barents Sea (1280 m; 72°N). Based on sediment geochemistry and associated epifauna, three different habitat types were distinguished across the two regions: (1) reduced sediment with suboxic conditions, sometimes covered by bacterial mats, (2) sediment colonised by chemosynthetic, siboglinid tubeworms, and (3) sediment outside the influence of seepage and without a large chemosynthetic fauna. Meiofaunal communities varied strongly in terms of generic diversity and dominance among the different habitat types. Control sites and Siboglinidae polychaete fields both supported high nematode genus richness similar to normal deep-sea sediments, whereas the reduced sediments yielded a genus-poor nematode community dominated by one or two successful species. Meiofaunal densities in the different habitats were negatively correlated with macrobenthic densities. An extremely dense (>11,000 ind. 10 cm–2), mono-specific nematode population appeared to be restricted to the bacterial mats at HMMV. It consisted of a new cryptic species of the Halomonhystera disjuncta complex, which has been described from intertidal habitats in the North Sea. The reduced seep sediments at Nyegga did not yield H. disjuncta but were dominated by Terschellingia longicaudata, another cosmopolitan nematode species known to be abundant in organic-rich, oxygen-poor, shallow-water environments. These observations point to a past or recent connection between margins and shallow-water habitats.  相似文献   

10.
The diet of slope dwelling macrourid fishes in the eastern North Pacific is poorly known. We collected several hundred stomach samples to investigate the feeding habits of Coryphaenoides acrolepis and Albatrossia pectoralis, the two dominant slope dwelling macrourids off the continental United States. Coryphaenoides acrolepis exhibited a pronounced ontogenetic shift in diet. Specimens <15 cm pre-anal fin length (PAF) consumed primarily polychaetes, amphipods, cumaceans and mysids, while larger individuals consumed increasingly larger, more pelagic prey such as fish, squid, and large crustaceans. Scavenging was also very important to specimens >15 cm with scavenged food constituting approximately 20% of the weight of total prey and occurring in approximately 20% of fish 21–29 cm. Albatrossia pectoralis consumed primarily midwater fish and squid, and we believe that it feeds in the water column. There were significant differences between the diets of A. pectoralis and C. acrolepis suggesting some degree of niche separation between macrourid species on the continental slope of the eastern North Pacific. Both species are at the top of the food web on the upper continental slope and, because of their abundance, may exert significant pressures on their prey populations.  相似文献   

11.
The San Clemente cold seep lies within 100–200 km of other reducing habitats in the NE Pacific, offering an opportunity to compare diversity and species overlap among reducing habitats (i.e. whale‐, kelp‐, and wood‐falls) at similar depths within a single region. Video observations from the research submersible Alvin at the San Clemente seep (1800 m depth) indicated clumps (‘thickets’) of vestimentiferans distributed as meter‐scale patches interspersed with vesicomyid clam beds and black sediments. Sediment‐core samples were collected at distances of 0 to 80–200 m along randomly oriented transects radiating outward from vestimentiferan thickets to evaluate changes in macrofaunal community structure from thickets into the background community. Macrofaunal abundance was elevated at distances of 0–1 m compared to 80–200 m (i.e. the ‘background’ community). The tube‐building frenulate worms Siboglinum spp., along with peracarid crustaceans, dominated sediments within 1 m of vestimentiferan thickets. Species diversity was depressed within 1 m of thickets but with high rates of species accumulation, suggesting that seep sites greatly increase sediment heterogeneity and facilitate colonization by non‐background macrofaunal species. Stable isotope data indicate chemosynthetic nutrition for some dominant macrofaunal species within 1 m of tubeworm thickets. The macrofaunal community near vestimentiferan thickets in San Clemente seep contains intermediate levels of species richness and diversity compared to other deep‐sea seep areas in the northeast Pacific. There was low species overlap between the San Clemente seep macrofauna and communities in reducing habitats near wood‐, whale‐, and kelp‐falls at similar depths within the region, suggesting that seeps harbor a distinct infaunal community.  相似文献   

12.
Although the carbonate compensation depth (CCD) for calcite, generally located in the depth range 4000–5000 m, is often proposed as a physiological barrier to deep-ocean colonization, many organisms with calcareous exoskeletons are found in the deepest oceanic trenches. Serpulid polychaetes inhabiting unprotected calcareous tubes are unlikely deep-sea inhabitants, yet, they are found at all oceanic depths from intertidal to hadal. Here we review and revise the published and unpublished records of Serpulidae from below 5000 m depth. We also describe tube ultrastructure and mineralogical content of available deep-sea serpulid tubes to obtain insights into their biomineralisation. Species belonging to the genera Bathyditrupa, Bathyvermilia, Hyalopomatus, Pileolaria (spirorbin) and Protis were found at depths from 5020 to 9735 m. However, only specimens of Protis sp. were truly hadal (>6000 m) being found at 6200–9700 m. Hadal specimens of Protis have irregularly oriented prismatic tube microstructure similar to that found in more shallow-water representatives of the genus. Initial EDX analysis suggested a mostly calcitic composition (i.e., the most stable CaCO3 polymorph) on the basis of high Mg levels. Surprisingly, however, tubes of Bathyditrupa hovei and a species of Protis analysed using the more reliable method of laser Raman spectroscopy were found to be composed of aragonite. The compensation depth for this less stable CaCO3 polymorph in the oceans is usually 2000–3000 m. We found no obvious structural adaptations to life at extreme depths in the studied serpulid tubes and how serpulids are able to biomineralise and maintain their tubes below the CCD remains to be explained.  相似文献   

13.
The composition of suprabenthic crustacean assemblages, their diversity, production (P) and production/biomass (P/B) ratios, were analyzed at species level along two transects situated to the north (N) and south (S) of Mallorca (Balearic Islands, western Mediterranean) at depths between 134 m and 760 m, based on a ca. bi-monthly sampling performed between August 2003 and June 2004. Differences with depth and season in assemblage composition and diversity were analyzed as a function of the contrasting environmental features (e.g. water mass dynamics) of the two areas. We identified 187 species (18 decapods, 5 euphausiids, 16 mysids, 76 gammaridean amphipods, 13 hyperiids, 1 caprellid, 21 isopods and 37 cumaceans). Substantial mesoscale variability in the deep-sea suprabenthic assemblages coupled with diversity trends between the N and S transects were found. Seasonality was the most important gradient influencing the dynamics of suprabenthos over the upper (350 m) and middle (650–750 m) slope in the N area. Conversely, the S area appeared to be more stable temporally with depth as the main gradient inducing assemblage differences. Different depth-related patterns were observed both for diversity and P/B. To the north diversity was very low at the shelf-break, increasing on the upper-slope (H′ > 3.00) and then decreasing again on the middle-slope. To the south diversity increased smoothly downward, reaching the highest values on the middle-slope. Regarding productivity, P/B was highest at intermediate depths to the north (over ca. 450–500 m), while to the south highest P/Bs were found deeper (over ca. 600–650 m). The higher P/B at intermediate depths found along N are likely due to higher % of organic matter (OM) in sediments, a product of oceanographic frontal systems. In particular, P/B was higher along N among omnivores and detritus feeders (e.g. Andaniexis mimonectes, Lepechinella manco and combined cumaceans), coupled to enriched OM in sediments, while along S mesoplanktonic carnivores (Rhachotropis spp.) had higher P/Bs. We conclude that on the north slope the influence of frontal systems and more active flow dynamics of different water masses (WIW and LIW) increases natural disturbance in the area, increasing productivity and diversity of suprabenthic peracarids in the Benthic Boundary Layer. Also, species showed a displacement of their average distributions (their Centres of Gravity, CoG) to shallower depths along N, which is another indicator of more favorable habitat conditions for suprabenthos in the 400–500 m range at N.  相似文献   

14.
Scleractinian corals create three-dimensional reefs that provide sheltered refuges, facilitate sediment accumulation, and enhance colonization of encrusting fauna. While heterogeneous coral habitats can harbor high levels of biodiversity, their effect on the community composition within nearby sediments remains unclear, particularly in the deep sea. Sediment macrofauna from deep-sea coral habitats (Lophelia pertusa) and non-coral, background sediments were examined at three sites in the northern Gulf of Mexico (VK826, VK906, MC751, 350–500 m depth) to determine whether macrofaunal abundance, diversity, and community composition near corals differed from background soft-sediments. Macrofaunal densities ranged from 26 to 125 individuals 32 cm−2 and were significantly greater near coral versus background sediments only at VK826. Of the 86 benthic invertebrate taxa identified, 16 were exclusive to near-coral habitats, while 14 were found only in background sediments. Diversity (Fisher’s α) and evenness were significantly higher within near-coral sediments only at MC751 while taxon richness was similar among all habitats. Community composition was significantly different both between near-coral and background sediments and among the three primary sites. Polychaetes numerically dominated all samples, accounting for up to 70% of the total individuals near coral, whereas peracarid crustaceans were proportionally more abundant in background sediments (18%) than in those near coral (10%). The reef effect differed among sites, with community patterns potentially influenced by the size of reef habitat. Taxon turnover occurred with distance from the reef, suggesting that reef extent may represent an important factor in structuring sediment communities near L. pertusa. Polychaete communities in both habitats differed from other Gulf of Mexico (GOM) soft sediments based on data from previous studies, and we hypothesize that local environmental conditions found near L. pertusa may influence the macrofaunal community structure beyond the edges of the reef. This study represents the first assessment of L. pertusa-associated sediment communities in the GOM and provides baseline data that can help define the role of transition zones, from deep reefs to soft sediments, in shaping macrofaunal community structure and maintaining biodiversity; this information can help guide future conservation and management activities.  相似文献   

15.
The mid-domain effect was tested to evaluate the bathymetric patterns of the polychaete species richness in the Upper and Lower Gulf of California as a possible hypothesis to explain the species richness gradient, exploring the overlapping of species depth ranges towards the middle continental shelf. The bathymetric gradient of the number of species was estimated with the depth ranges of 554 polychaete species, and the mid-domain effect was tested using a Monte Carlo simulation program at bands of 10 m depth. The Upper (251 species) and Lower (491 species) Gulf regions showed clear differences in their faunal composition (Jaccard similarity index = 0.34); the species richness pattern was characterized by a highly significant presence of polychaetes with short depth ranges (< 10 m). The richness distribution could be described as a cubic polynomial curve, but the maximum values in both Gulf regions (141 and 317 species, respectively for Upper and Lower Gulf regions) are strongly biased to shallow waters (40 m). This is not consistent with the peak of diversity at 60–70 m predicted by the model. The observed patterns cannot be reproduced by the mid-domain effect, suggesting the existence of non-random factors affecting the species richness gradients in the Gulf.  相似文献   

16.
Sulfate reduction rate measurements by the 35SO42− core injection method were carried out in situ with a benthic lander, LUISE, and in parallel by shipboard incubations in sediments of the Black Sea. Eight stations were studied along a transect from the Romanian shelf to the deep western anoxic basin. The highest rates measured on an areal basis for the upper 0–15 cm were 1.97 mmol m−2 d−1 on the shelf and 1.54 mmol m−2 d−1 at 181 m water depth just below the chemocline. At all stations sulfate reduction rates decreased to values <3 nmol cm−3 d−1 below 15 cm depth in the sediment. The importance of sulfate reduction relative to the total mineralization of organic matter was very low, 6%, on the inner shelf, which was paved with mussels, and increased to 47% on the outer shelf at 100 m depth. Where the oxic–anoxic interface of the water column impinged on the sea floor at around 150 m depth, the contribution of sulfate reduction increased from >50% just above the chemocline to 100% just below. In the deep sea, mean sulfate reduction rates were 0.6 mmol m−2 d−1 corresponding to an organic carbon oxidation of 1.3 mmol m−2 d−1. This is close to the mean sedimentation rate of organic carbon over the year in the western basin. A comparison with published data on sulfate reduction in Black Sea sediments showed that the present results tend to be higher in shelf sediments and lower in the deep-sea than most other data. Based on the present water column H2S inventory and the H2S flux out of the sediment, the calculated turnover time of H2S below the chemocline is 2100 years.  相似文献   

17.
Concentrations of dissolved sulfate and sulfur isotopic ratios of dissolved sulfide in surface sediments of the Peru shelf and upper slope indicate that the sediments can be divided into two depth intervals based on the dominant biogeochemical reactions. Although rates of bacterial sulfate reduction are high throughout Peru surface sediments, chemistry of the upper interval (<10–20 cm) is dominated by chemoautotrophic oxidation of dissolved sulfide and elemental sulfur, while the lower interval (>10–20 cm) is dominated by dissimilatory sulfate reduction. In three of the four cores examined here, pore water concentrations of sulfate in the top 10 cm of the sediment are significantly higher than those of the overlying seawater. Peak sulfate concentrations in pore water (37–53 mmol/l) are ∼1.3–1.9 times that of seawater sulfate and are located 1–6 cm below the sediment/water interface (SWI). The excess sulfate is most likely produced by oxidation of elemental sulfur coupled to reduction of nitrate, a reaction mediated by a facultative chemoautotrophic sulfide-oxidizing bacterium, Thioploca spp. Numerical simulations demonstrate that the anomalously high concentrations of dissolved sulfate can be produced by steady-state or non-steady-state processes involving high rates of bacterial oxidation of elemental sulfur. If bacterial sulfur oxidation is a transient phenomenon, then it is probably triggered by seasonal or El Niño-induced changes in water-column chemistry of the Peru undercurrent.  相似文献   

18.
Over the last thirty years, many shallow estuarine bays, located in Scandinavian sheltered coastal environments, have been subject to the increased dominance of opportunistic species of filamentous green algae, oxygen deficiency in bottom waters and the alteration of flora and fauna. Human-induced eutrophication has been held responsible for these recent changes, but from this study the importance of climatic factors emerges. This research is based on the analysis of sediment cores from 8 shallow areas (d < 50 cm) along the Bohuslän archipelago, Swedish west coast, and focuses on their recent (< 100 years) sedimentary evolution. Evidence of hydrodynamic change was observed in the sediments, where modern fining-upward sequences contrast with the expected coarsening upward model due to ongoing land uplift. Heavy metal concentrations from modern pollution and 14C dating of mollusk shells and eelgrass roots provided the age control, and allowed to place these changes within the last three decades. Data were compared with historical meteorological records (seasonal warming, modification of dominant winds and upwelling and reduction of sea-ice), and a clear connection emerged between the environmental changes and variations in the North Atlantic Ocean weather pattern. The increase of winter temperature and reduction of reworking winter sea-ice in these sheltered bays increased the storing of nutrients in the sediments and the turnover of organic matter, favoring the early growth stage of opportunistic algae in the most sheltered areas of the archipelago. This, together with human-induced modifications (overfishing and eutrophication), increased the possibility of opportunistic explosions, which in turn determined a reduced water exchange, the increased deposition of fine sediments and organic matter and evolving hypoxic conditions.  相似文献   

19.
It is essential to maximize the information that can be gathered in deep-sea studies by thoroughly assessing sample processing methods. Nematodes are commonly used for the study and monitoring of deep-sea floor habitats, but the potential effects of different methods on the quantification of community attributes remain to be quantified. Here, we consider key methodological elements by comparing the effect of sediment depth and mesh size (63, 45, and 32 μm) on: (1) estimates of nematode community attributes, and (2) the sampling effort required to detect changes in these attributes at a bathyal site on the Chatham Rise, south-west Pacific Ocean. The 63 μm mesh retained most (95%) of the nematode biomass but a lower proportion (53–71%) of the nematode abundance. Retention efficiency of common species on this mesh ranged from 12 (Hapalomus sp.) to >88% (Comesomatidae spp.). The 63 μm mesh yielded significantly lower diversity estimates than the finer meshes, and failed to detect differences in community structure observed using the 45 and 32 μm mesh sizes. Sediment depth had a substantial effect on all measured community attributes, highlighting the importance of sufficient core penetration into the sediment (≥5 cm) for adequately characterizing nematode distribution. Power analysis showed that using a 32 μm mesh and deepest core penetration led to relatively few (3–8) samples being required to detect significant changes in nematode diversity indices relative to coarser mesh sizes. Characterization of nematode diversity and community structure using appropriate and robust methods of sampling is suggested as a sensitive and efficient tool for the assessment of anthropogenic impacts on deep-sea ecosystems.  相似文献   

20.
The numbers of benthic foraminiferans at four sites in the Clyde Sea area showed no consistent temporal variation throughout 1993. In the finest surface sediments, numbers ranged between 200 and 400 cells cm−3, compared to only 25–50 cells cm−3in the coarsest sediments. On two occasions, high populations of cells less than 63 μm were found in the surface layers. These were thought to represent recruitment peaks since these ‘ juvenile ’ cells grew rapidly when maintained in the laboratory. A total of 56 taxa were identified from the region, the greatest diversity being recorded in the finest sediments. Rose Bengal stained foraminiferans (i.e. presumed living) were found below the anoxic–oxic boundary. The fate of these cells was considered by examining their ability to migrate through fine sediments, and their capacity to survive (based on evidence of pseudopodial activity) periods of anoxia. This study has highlighted the numerical importance of foraminiferans, particularly in fine surface coastal sediments, but questions whether the high populations of ‘ stained ’ cells found in deeper sediments play a significant ecological role.  相似文献   

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