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1.
A quantitative study of metazoan meiofauna was carried out on bathyal sediments (305, 562, 830 and 1210 m) along a transect within and beneath the oxygen minimum zone (OMZ) in the southeastern Pacific off Callao, Peru (12°S). Meiobenthos densities ranged from 1517 (upper slope, middle of OMZ) to 440–548 ind. 10 cm−2 (lower slope stations, beneath the OMZ). Nematodes were the numerically dominant meiofaunal taxon at every station, followed by copepods and nauplii. Increasing bottom-water oxygen concentration and decreasing organic matter availability downslope were correlated with observed changes in meiofaunal abundance. The 300-m site, located in the middle of the OMZ, differed significantly in meiofaunal abundance, dominance, and in vertical distribution pattern from the deeper sites. At 305 m, nematodes amounted to over 99% of total meiofauna; about 70% of nematodes were found in the 2–5 cm interval. At the deeper sites, about 50% were restricted to the top 1 cm. The importance of copepods and nauplii increased consistently with depth, reaching ∼12% of the total meiofauna at the deepest site. The observation of high nematode abundances at oxygen concentrations <0.02 ml l−1 supports the hypothesis that densities are enhanced by an indirect positive effect of low oxygen involving (a) reduction of predators and competitors and (b) preservation of organic matter leading to high food availability and quality. Food input and quality, represented here by chloroplastic pigment equivalents (CPE) and sedimentary labile organic compounds (protein, carbohydrates and lipids), were strongly, positively correlated with nematode abundance. By way of contrast, oxygen exhibited a strong negative correlation, overriding food availability, with abundance of other meiofauna such as copepods and nauplii. These taxa were absent at the 300-m site. The high correlation of labile organic matter (C-LOM, sum of carbon contents in lipids, proteins and carbohydrates) with CPE (Pearson's r=0.99, p<0.01) suggests that most of the sedimentary organic material sampled was of phytodetrital origin. The fraction of sediment organic carbon potentially available to benthic heterotrophs, measured as C-LOM/Total organic carbon, was on average 17% at all stations. Thus, a residual, refractory fraction, constitutes the major portion of organic matter at the studied bathyal sites.  相似文献   

2.
Trends among major metazoan meiofaunal taxa were investigated based on 56 deployments of a multicorer at 10 time points over a period of 11 years (1989–1999) at the Porcupine Abyssal Plain Sustained Observatory site (PAP-SO: 48°50′N 16°30′W, 4850 m depth). This area is characterised by a strong seasonality in the deposition of organic matter to the seafloor and by the massive increase in the density of holothurian species since 1996, the so-called ‘Amperima event’. Total meiofaunal densities ranged from 346 to 1074 ind.×10 cm−2 and showed a significant increase with time when time was represented by cruises, years and the ‘Amperima period’ (1996–1999) vs. the pre-Amperima period (1989–1994). This pattern was driven mainly by the nematodes, which were the dominant taxon (∼90% of total abundance). The third most abundant group, the polychaetes, also increased significantly in abundance over the time series, while the ostracods showed a significant decrease. Most other taxa, including the second-ranked group, the copepods (harpacticoids and nauplii), did not exhibit significant temporal changes in abundance. Ordination of taxon composition showed a shift from the pre-Amperima to the Amperima periods, a trend supported by the significant correlation between the x-ordinate and time. The majority (52–75%) of meiofaunal animals inhabited the top 2 cm of the 5 cm sediment cores analysed. There were significant increases in the proportion of total meiofauna, nematodes and copepods (but not polychaetes) inhabiting the 0–1 cm layer over time (represented by cruises) and between the pre-Amperima and Amperima periods in the case of copepods and polychaetes. During the intensively sampled period (1996–1997), there were indications of seasonal changes in the vertical distribution patterns of total meiofauna and nematodes within the sediment. We discuss the potential link between temporal variations in organic matter flux to the seafloor and meiofaunal populations, considering both qualitative and quantitative changes in fluxes and how they may be linked to climate variations.  相似文献   

3.
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   

4.
The natural isotope 234Th is used in a small-scale survey of particle transport and exchange processes at the sediment–water interface in the Benguela upwelling area. Results from water and suspended particulate matter (SPM) samples from the uppermost and lowermost water column as well as the underlying sediment of three stations are compared. The stations are situated in different sedimentological environments at 1200–1350 m water depth at the continental slope off Namibia. Highly differing extent and particle content of the bottom nepheloid layer (BNL) are determined from transmissometer data. Three models are presented, all explaining the 234Th depletion of the BNL and 234Th excess of the surface sediment that were observed. While the first model is based solely on local resuspension of surface sediment particles, the second evaluates the influence of vertical particle settling from the surface waters on the 234Th budget in the BNL. The third model explains 234Th depletion in the BNL by sedimentation of particles that were suspended in the BNL during long-range transport. Particle inventory of the BNL is highest at a depocenter of organic matter at 25.5°S, where strong deposition is presently taking place and lateral particle transport is suggested to predominate sediment accumulation. This is supported by the high settling flux of particles out of the BNL into the sediments of the depocenter, exceeding the vertical particle flux into sediment traps at intermediate depth in the same area by up to an order of magnitude. High particle residence/removal times in the BNL above the depocenter in the range of 5–9 weeks support this interpretation. Comparison with carbon mineralization rates that are known from the area reveals that, notwithstanding the large fraction of advected particles, organic carbon flux into the surface sediment is remineralized to a large extent. The deployment of a bottom water sampler served as an in situ resuspension experiment and provided the first data of 234Th activity on in situ resuspended particles. We found a mean specific activity of 86 disintegrations per minute (dpm) g−1 (39–339 dpm g−1), intermediate between the high values for suspended particles (in situ pump: 580–760 dpm g−1; CTD rosette: 870–1560 dpm g−1) and the low values measured at the sediment surface (26–37 dpm g−1). This represents essential information for the modeling of 234Th exchange processes at the sediment–water interface.  相似文献   

5.
We investigated the impact of sediment reworking fauna and hydrodynamics on mobilization and transport of organic matter and fine particles in marine sediments. Experiments were conducted in an annular flume using lugworms (Arenicola marina) as model organisms. The impact of lugworms on sediment characteristics and particle transport was followed through time in sediments experimentally enriched with fine particles (< 63 μm) and organic matter. Parallel experiments were run at low and high water current velocity (11 and 25 cm s− 1) to evaluate the importance of sediment erosion at the sediment–water interface. There was no impact of fauna on sediment composition and particle transport at current velocity below the sediment erosion threshold. At current velocity above the erosion threshold, sediment reworking by lugworms resulted in dramatic particle transport (12 kg dry matter m− 2) to an adjacent particle trap within 56 days. The transported matter was enriched 6–8 times in fine particles and organic matter when compared to the initial sediment. This study suggests that sediment reworking fauna is an important controlling factor for the particle composition of marine sediments. A. marina mediated sediment reworking greatly increases the sediment volume exposed to hydrodynamic forcing at the sediment–water interface, and through sediment resuspension control the content of fine particles and organic matter in the entire reworked sediment layer (> 20 cm depth).  相似文献   

6.
Boundary currents and internal waves determine cross-slope zonation of erosion and deposition in the Faeroe-Shetland Channel. Currents were measured at 8 and 34–50 m above the bottom at three mooring sites (502, 595 and 708 m depth) for 14 days. The structure of the water column was evaluated from CTD sections, and included nepheloid layers and particulate matter concentrations. Indicators for recent deposition in the sediment (organic carbon, phytopigments, 210Pb) were measured at eight stations across the slope. Strong near-bottom currents at the upper slope sustain down-slope particle transport in a benthic nepheloid layer, which is eroded under the influence of critically reflecting M2 internal tidal waves at 350–550 m, where the major pycnocline meets the sloping bottom. Beam attenuation profiles confirmed the presence of intermediate nepheloid layers intruding into the Channel along the major pycnocline, and elevated concentrations of particulate matter and chlorophyll-a were measured at this depth. Near-bottom currents decreased with depth, thus allowing particle deposition down the slope. Inventories of excess 210Pb activity in the sediment deeper than 600 m were higher than what was expected on the basis of atmospheric input of 210Pb and production in the water column, thus indicating additional lateral inputs. Simple calculations showed that off-slope input of particles from areas shallower than 600 m may be responsible for the enhanced deposition at greater depths.  相似文献   

7.
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   

8.
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   

9.
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   

10.
Vertical distributions of dissolved species across the sediment–water interface (SWI), including major cations (sodium, potassium, magnesium, calcium), minor cations (lithium, strontium, barium), redox sensitive species (dissolved manganese, iron, sulfate, sulfide, ammonium) and other chemical parameters (pH, alkalinity, soluble reactive phosphorous, dissolved silica) were studied in a Mediterranean lagoon used for intensive shellfish farming. In order to quantify the impact of this activity on diagenetic processes and the influence of seasonal changes, two stations contrasted with respect to organic carbon fluxes were sampled in Thau lagoon from March 2001 to August 2002 during four field campaigns in winter, spring, summer and fall. Well-defined layers enriched with redox sensitive species were observed following the conventional sequence of early diagenetic reactions. However, differences were observed between both stations in depths and thickness layers. Concentration gradients extended down to more than 92 cm depth at the central position of the lagoon (station C4 – 8 m depth) and down to 40 cm depth inside shellfish farming zones (station C5 – 9 m depth). Station C4 showed an unusual diagenetic signature: sharp dissolved oxygen, iron, nitrate and manganese gradients existed at the SWI but gradients of dissolved sulfide and alkalinity as well as other parameters (dissolved silica, Ba, etc.) were recorded only from 25 to 30 cm depth downward. Seasonal changes were observed in pore water composition as deep as 30–50 cm in station C4 (only 15 cm in station C5). The center of the lagoon is not directly subjected to biodeposits deriving from shellfish activity. Isotopic and bioturbation data allowed to rule out a reworking of the sediment deeper than a few centimeters. In addition to organic content of the sediment, physical parameters were likely to induce the 10–20 cm gap between dissolved iron and sulfide profile as well as the higher vertical extent of diagenetic sequence observed at station C4. Conversely to station C5, station C4 underwent stronger currents and wave effect probably generating advective transport of water through the sediment, but no permeability data were available to confirm this hypothesis. During summer, climatic conditions generated vertical stratification of the water column and transient suboxic conditions at the bottom. Such conditions drove the upward shift of redox fronts, compacting the diagenetic sequence. These effects were reinforced at station C5 by shellfish and its farm structures (mainly attenuation of current and increased heat absorption).  相似文献   

11.
Five photographic transects, covering some 830 m2 of seafloor in total, were analyzed to characterize the megabenthic community along a bathymetric gradient covering water depths from 1200 to 5500 m in the eastern Fram Strait. Megafaunal densities ranged between 11 and 38 ind. m−2. The highest densities were found at 1650 m and the lowest densities occurred at 3000 m depth. The number of taxa and morphotypes ranged between 4 at 5500 m and 27 at 1650 m water depth. Ophiocten gracilis, a small white unidentified amphipod, Kolga hyalina, and Bathycrinus carpenteri were the dominant and characteristic species on the slope and continental rise. Elpidia heckeri dominated in the Molloy Hole, the deepest depression known in the Arctic Ocean. Megafaunal zonation patterns appeared to be mainly controlled by food availability, as indicated by phytodetrital matter measured at the seafloor, and by benthic biomass in the sediments, as indicated by sediment-bound particulate proteins and phospholipids. By contrast, physical factors, including water depth and seabed properties such as sediment porosity and hard substrata (e.g., dropstones), appear to play a secondary role in determining megabenthic zonation patterns along the bathymetric HAUSGARTEN gradient.  相似文献   

12.
Between 1988 and 1994, twenty time-series sediment traps were deployed at different water depths in the Canary Island region, off Cape Blanc (Mauritania), and off Cape Verde (Senegal). Lithogenic particle fluxes and grain size distributions of the carbonate-free fraction of the trapped material show a high impact of dust transported either in the northeast trade winds or the Saharan Air Layer (SAL). Highest annual mean lithogenic fluxes (31.2–56.1 mg m-2 d-1) were observed at the Cape Blanc site, and largest annual mean diameters (>6 μm) were found off Cape Verde (14.5–16.9 μm) and off Cape Blanc (15.2–16.7 μm). Lowest annual lithogenic fluxes (11.4–21.2 mg m-2 d-1 ) and smallest mean diameters (13.5–13.7 μm) occurred in the Canary Island region. A significant correlation of organic carbon and lithogenic fluxes was observed at all sites. Off Cape Blanc, fluxes and mean diameters correlated well between upper (around 1000 m depth) and lower traps (around 3500 m depth), indicating a fast and mostly undisturbed downward transport of particulate matter. In contrast, a major correlation of fluxes without correlating mean diameters occurred in the Canary Island region, which translates into a fast vertical transport plus scavenging of laterally advected material with depth at this site. The seasonality of lithogenic fluxes was highest in the Canary Island region and off Cape Verde, reflecting strong seasonal patterns of atmospheric circulation, with highest occurrence of continental winds in the trade wind layer during winter. In addition, grain size statistics reflect a dominant change of dust transport in the trade winds during winter/spring and transport in the SAL during summer 1993 at the Cape Verde site. Highest lithogenic fluxes during winter were correlated with mean diameters around 10–13 μm, whereas lower fluxes during summer consisted of coarse grains around 20 μm. Annual mean dust input wascalculated from lithogenic fluxes in the range 0.7×106–1.4×106 t yr-1, roughly confirming both sediment accumulation rates and atmospheric model calculations reported previously from this area.  相似文献   

13.
Nematodes are the most abundant metazoans of deep-sea benthic communities, but knowledge of their distribution is limited relative to larger organisms. Whilst some aspects of nematode processing techniques, such as extraction, have been extensively studied, other key elements have attracted little attention. We compared the effect of (1) mesh size (63, 45, and 32 μm) on estimates of nematode abundance, biomass, and body size, and (2) microscope magnification (50× and 100×) on estimates of nematode abundance at bathyal sites (250–3100 m water depth) on the Challenger Plateau and Chatham Rise, south-west Pacific Ocean. Variation in the effectiveness of these techniques was assessed in relation to nematode body size and environmental parameters (water depth, sediment organic matter content, %silt/clay, and chloroplastic pigments). The 63-μm mesh retained a relatively low proportion of total nematode abundance (mean±SD=55±9%), but most of nematode biomass (90±4%). The proportion of nematode abundance retained on the 45-μm mesh in surface (0–1 cm) and subsurface (1–5 cm) sediment was significantly correlated (P<0.01) with %silt/clay (R2=0.39) and chloroplastic pigments (R2=0.29), respectively. Variation in median nematode body weight showed similar trends, but relationships between mean nematode body weight and environmental parameters were either relatively weak (subsurface sediment) or not significant (surface sediment). Using a low magnification led to significantly lower (on average by 43%) nematode abundance estimates relative to high magnification (P<0.001), and the magnitude of this difference was significantly correlated (P<0.05) with total nematode abundance (R2p=0.53) and the number of small (≤250 μm length) individuals (R2p=0.05). Our results suggest that organic matter input and sediment characteristics influence the abundance of small nematodes in bathyal communities. The abundance of small individuals can, in turn, influence abundance estimates obtained using different mesh sizes and microscope magnifications.  相似文献   

14.
The abundance, carbon isotopic composition (Δ14C and δ13C), and lipid biomarker (alkenones and saturated fatty acids) distributions of suspended particulate organic matter were investigated at three stations centered on the 2000, 3000, and 3500 m isobaths over the New England slope in order to assess particulate carbon sources and dynamics in this highly productive and energetic region. Transmissometry profiles reveal that particle abundances exhibit considerable fine structure, with several distinct layers of elevated suspended particulate matter concentration at intermediate water depths in addition to the presence of a thick bottom nepheloid layer at each station. Excluding surface water samples, the Δ14C values of particulate organic carbon (POC) indicated the presence of a pre-aged component in the suspended POC pool (Δ14C<+38‰). The Δ14C values at the 3000 m station exhibited greater variability and generally were lower than those at the other two stations where the values decreased in a more systematic matter with increasing sampling depth. These lower Δ14C values were consistent with higher relative abundances of terrigenous long-chain fatty acids at this station than at the other two stations. Two scenarios were considered regarding the potential provenances of laterally transported POC: cross-shelf transport of shelf sediment (Δ14C=?140‰) and along-slope transport of the slope sediment proximal to the sampling locations (Δ14C=?260‰). Depending on the scenario, isotopic mass balance calculations indicate allochthonous POC contributions ranging between 15% and 54% in the meso- and bathy-pelagic zone, with the highest proportions at the 3000 m station. Alkenone-derived temperatures recorded on suspended particles from surface waters closely matched in-situ temperatures at each station. However, alkenone-derived temperatures recorded on particles from the subsurface layer down to 250 m were lower than those of overlying surface waters, especially at the 3000 m station, implying supply of phytoplankton organic matter originally produced in cooler surface waters. AVHRR images and temperature profiles indicate that the stations were under the influence of a warm-core ring during the sampling period. The low alkenone-derived temperatures in the subsurface layer coupled with the lower Δ14C values for the corresponding POC suggests supply of OC on resuspended sediments underlying cooler surface waters distal to the study area, possibly further north or west. Taken together, variations in Δ14C values, terrigenous fatty acid abundances, and alkenone-derived temperatures among the stations suggest that input of laterally advected OC is a prominent feature of POC dynamics on the NW Atlantic margin, and is spatially heterogeneous on a scale smaller than the distance between the stations (<150 km).  相似文献   

15.
As part of the multidisciplinary programme BIOZAIRE devoted to studying deep-sea benthic ecosystems in the Gulf of Guinea, particulate input and its relationship with near-bottom hydrodynamics were monitored using long-term moorings from 2000 to early 2005. Particular attention was given to material input through the Congo (ex-Zaïre) submarine channel that extends 760 km from the Congo River mouth to the abyssal plain (>5100 m) near 6°S. Due to its direct connection to the Congo River, the Congo canyon and channel system are characterised by particularly active recent sediment transport. During this first in situ long-term monitoring along the channel, an energetic turbidity event was observed in January 2004 at three locations along the channel from 3420 to 4790 m in depth. This event tilted and displaced the moorings installed at 3420 m (site ZR′) and 4070 m (site ZD′), and resulted in high sediment deposition at all three mooring sites. The event moved at an average velocity of 3.5 m s−1 along the numerous channel meanders between 3420 and 4070 m, then at 0.7 m s−1 between 4070 m and the end of the channel at 4790 m. The particle cloud rose above the top of the valley at 4070 m (site ZD′), but not at 3420 m (site ZR′) where the channel was too deep. Lastly, the mooring line broke at site ZD′ in October 2004 probably due to a strong event like that of 2001 previously described by Khripounoff et al. [Khripounoff, A., Vangriesheim, A., Babonneau, N., Crassous, P., Denniellou, B., Savoye, B., 2003. Direct observation of intense turbidity activity in the Zaire submarine valley at 4000 m water depth. Marine Geology (194), 151–158]. Between these strong events, several peaks of high turbidity and particle flux occurred, but without noticeable current increases. These events were probably due to local sliding of sediment accumulated on the walls or terraces on the side of the channel. The area near 4000 m depth and the lobe appear to be the main depocentres of particulate input rich in organic matter derived from the Congo River.  相似文献   

16.
Three mooring arrays were deployed in the Palamós Canyon axis with sediment traps, current meters and turbidimeters installed near the bottom and in intermediate waters. Frequent sharp and fast turbidity peaks along with current speed increases were recorded, particularly at 1200 m depth in spring and summer. During these events, near-bottom water turbidity increased by up to more than one order of magnitude, current velocity by two to four times and horizontal sediment fluxes by one to three orders of magnitude. When these events occurred, 9–11 days integrated downward particle fluxes collected by the near-bottom sediment trap increased by two to three times. These events were identified as sediment gravity flows triggered by trawling activities along the northern canyon wall. Sediment eroded by the trawling nets at 400–750 m depth on this wall seems to be channeled through a gully and transported downslope towards the canyon axis, where the 1200 m mooring was located. The sediment gravity flows recorded at the 1200 m site were not detected at deeper instrumented sites along the canyon axis, suggesting that they affect local areas of the canyon without traveling long distances downcanyon. These observations indicate that trawling can generate frequent sediment gravity flows and increase sediment fluxes locally in submarine canyons. Furthermore, in addition to the various natural processes currently causing sediment gravity flows and other sediment transport events, human activities such as trawling must be taken into account in modern submarine canyon sediment dynamics studies.  相似文献   

17.
The Benthic Boundary Layer (BBL) assemblages from the Cap-Ferret Canyon (Bay of Biscay) were quantitatively sampled at two sites located within its main channel near mooring deployments (Mooring Sites MS 1: ca. 2400 m; MS 2: ca. 3000 m) with a suprabenthic sled equipped with four nets fishing at different heights above the bottom. The macrofaunal abundance above the sea-floor was mainly represented by Isopoda (42.2%), Amphipoda (19.0%), Euphausiacea (17.3%), Cumacea (13.5%), Mysidacea (2.8%) and Tanaidacea (2.6%). At both sampling sites, the highest total densities were generally recorded in the immediate vicinity of the sea floor (10–40 cm water layer), and a drastic decrease occurred higher in the BBL community. The BBL assemblages from the two sampling sites were similar in their faunal composition (major taxa), and their mean density estimates were not statistically different (MS 1 : 525.3 ind. 100 m−2; MS 2 : 283.3 ind. m−2) although the recorded values during each cruise were always lower at the deeper site. The BBL macrofauna abundance showed obvious temporal fluctuations at both sites, probably linked with a seasonal organic input from the euphotic zone (vertical flux) via phytodetritus deposition on the sea bottom.  相似文献   

18.
A study was carried out to assess primary production and associated export flux in the coastal waters of the western Antarctic Peninsula at an oceanographic time-series site. New, i.e., exportable, primary production in the upper water-column was estimated in two ways; by nutrient deficit measurements, and by primary production rate measurements using separate 14C-labelled radioisotope and 15N-labelled stable isotope uptake incubations. The resulting average annual exportable primary production estimates at the time-series site from nutrient deficit and primary production rates were 13 and 16 mol C m−2, respectively. Regenerated primary production was measured using 15N-labelled ammonium and urea uptake, and was low throughout the sampling period.The exportable primary production measurements were compared with sediment trap flux measurements from 2 locations; the time-series site and at a site 40 km away in deeper water. Results showed ∼1% of the upper mixed layer exportable primary production was exported to traps at 200 m depth at the time-series site (total water column depth 520 m). The maximum particle flux rate to sediment traps at the deeper offshore site (total water column depth 820 m) was lower than the flux at the coastal time-series site. Flux of particulate organic carbon was similar throughout the spring–summer high flux period for both sites. Remineralisation of particulate organic matter predominantly occurred in the upper water-column (<200 m depth), with minimal remineralisation below 200 m, at both sites. This highly productive region on the Western Antarctic Peninsula is therefore best characterised as ‘high recycling, low export’.  相似文献   

19.
Quantifying relative affinities of Po and Pb in different populations of marine particulate matter is of great importance in utilizing 210Po as a tracer for carbon cycling. We collected and analyzed water samples for the concentrations of dissolved and total 210Po and 210Pb from the upper 600 m of the water column at Bermuda Time-series Study site (September 1999–September 2000) to investigate their seasonality of concentrations and their activity ratio (210Po/210Pb activity ratio, AR). Sinking particles collected in sediment traps at depths of 500 m, 1500 m, and 3200 m from the Oceanic Flux Program (OFP) time-series sediment traps were analyzed over a period of 12 months (May 1999–May 2000). The objective was to compare the deficiencies of 210Po with respect to 210Pb in the water column to that measured in the sediment traps and to assess the relative affinities of Po and Pb with different particle pools.Inventories of 210Po in the upper 500 m water column varied by a factor of 2, indicating seasonal variations of particulate flux dominated the removal of 210Po. The 210Po/210Pb ARs in the dissolved phase were generally less than the secular equilibrium value (1.0) in the upper 600 m, while were generally greater than 1.0 in the particulate phase, indicating higher removal rates of 210Po relative to 210Pb by particulate matter. The measured fluxes of 210Po and 210Pb in the 500 m, 1500 m, and 3200 m traps increased with depth, while the 210Po/210Pb ARs decreased with depth except from May–August 1999. From the measured fluxes of 210Po and 210Pb at these three traps and the concentrations of 210Po and 210Pb in the water column, this region appears to be a sink for 210Pb which is likely brought-in by lateral advection.  相似文献   

20.
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   

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