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1.
This study aims to evaluate the effectiveness of currently available substrate data to designate marine reserves to meet conservation objectives. The case study site is Lyme Bay (approx. 2460 km2), in the western English Channel. An area of 240 km2 in Lyme Bay was designated ‘closed to bottom dredging’ in July 2008 with the aim of protecting reefs which are an important habitat for Eunicella verrucosa (pink sea fan). The effects of using different substrate data resolution on the selection of sites to protect a range of biotopes using the Marxan package are determined. The effect of including a closed area on the efficiency of a marine reserve network is also investigated. Findings suggest that substrate data did not capture the biodiversity of the area and that using no data at all was equally effective. If low resolution data are all that are available then other options, such as expert opinion, or other data, such as activity use information could be used instead. Including a predefined closed area into the analysis led to an increase in area required to meet conservation goals using high resolution biotope data. It also increased the area of the reserve using the three substrate layers with no increase in protection for biotopes. This suggests that when designing networks of marine protected area sites, including current protected areas may be inefficient, resulting in larger areas being protected with no increased conservation of marine biodiversity. Policy makers must be prepared to adapt management in light of these findings and be aware of the shortcomings of the data available for use in marine conservation planning.  相似文献   

2.
Krill (crustaceans of the family Euphausiacea) comprise an important prey field for vast array of fish, birds, and marine mammals in the California Current and other large marine ecosystems globally. In this study, we test the hypothesis that mesoscale spatial organization of krill is related to oceanographic conditions associated with coastal upwelling. To test this, we compiled a climatology of krill distributions based on hydroacoustic surveys off California in May–June each year between 2000 and 2009 (missing 2007). Approximately 53,000 km of ocean habitat was sampled, resulting in a comprehensive geo-spatial data set from the Southern California Bight to Cape Mendocino. We determined the location and characteristics of eight definite and two probable krill “hotspots” of abundance. Directional-dependence analysis revealed that krill hotspots were oriented in a northwest–southeast (135°) direction, corresponding to the anisotropy of the 200–2000 m isobath. Krill hotspots were disassociated (inversely correlated) with three upwelling centers, Point Arena, Point Sur, and Point Conception, suggesting that krill may avoid locations of strong offshore transport or aggregate downstream from these locations. While current fisheries management considers the entire coast out to the 2000 m isobath critical habitat for krill in this ecosystem, we establish here smaller scale structuring of this critical mid-trophic level prey resource. Identifying mesoscale krill hotspots and their oceanographic determinants is significant as these smaller ecosystem divisions may warrant protection to ensure key ecosystem functions (i.e., trophic transfer) and resilience. Furthermore, delineating and quantifying krill hotspots may be important for conservation of krill-predators in this system.  相似文献   

3.
Chlorofluoromethanes (CFMs) F-11 and F-12 were measured during August 1991 and November 1992 in the Romanche and Chain Fracture Zones in the equatorial Atlantic. The CFM distributions showed the two familiar signatures of the more recently ventilated North Atlantic Deep Water (NADW) seen in the Deep Western Boundary Current (DWBC). The upper maximum is centered around 1600 m at the level of the Upper North Atlantic Deep water (UNADW) and the deeper maximum around 3800 m at level of the Lower North Atlantic Deep Water (LNADW). These observations suggest a bifurcation at the western boundary, some of the NADW spreading eastward with the LNADW entering the Romanche and the Chain Fracture Zones. The upper core (σ1.5=34.70 kg m-3) was observed eastward as far as 5°W. The deep CFM maximum (σ4=45.87 kg m-3), associated with an oxygen maximum, decreased dramatically at the sills of the Romanche Fracture Zone: east of the sills, the shape of the CFM profiles reflects mixing and deepening of isopycnals. Mean apparent water “ages” computed from the F-11/F-12 ratio are estimated. Near the bottom, no enrichment in CFMs is detected at the entrance of the fracture zones in the cold water mass originating from the Antarctic Bottom Water flow.  相似文献   

4.
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5.
Continuous surface measurements of temperature, salinity, fluorescence and optical backscattering were made during R/V Thompson cruise no. TN053 in the northern Arabian Sea (“Bio-Optical cruise”; October–November, 1995). The cruise covered the early NE monsoon period. Optical measurements involved alternate estimates of total backscattering and acidified backscattering approximately every 1.5–2 min (measured after addition of a weak acid to dissolve calcium carbonate). The difference between total and acidified backscattering equals “acid-labile backscattering”. Total and acid-labile backscattering were converted to the concentration of particulate organic carbon (POC) and particulate inorganic carbon (PIC; calcium carbonate), respectively, and discrete samples taken along the cruise track were used for calibration. Backscattering data were frequently coherent with temperature, salinity, and density variability. Acid-labile backscattering values revealed that calcium carbonate accounted for 10–40% of the total optical backscattering in the region, and the semi-continuous records demonstrated distinct patches of coccolith-rich water. The northern Arabian Sea had the highest acid-labile backscattering. Results suggest that PIC : POC ratios can vary over about four orders of magnitude. Highest surface values of PIC : POC approached one in several places. We also report qualitative observations of phytoplankton community structure made aboard ship, on fresh samples.  相似文献   

6.
Mercury concentration and speciation were measured in surface and deep ocean waters of the South and equatorial Atlantic. In the surface waters, total Hg was 2.9±1.7 pM on average, with a significant fraction present as reactive Hg (1.7±1.2 pM). The reactive Hg fraction consisted of elemental Hg (Hg°) as the dominant species (1.2±0.8 pM). Measurements in surface waters also showed that Hg partitioned to the “colloidal” phase (0.33±0.28 pM) and was associated with particulate matter (0.1±0.05 pM). No dimethylmercury (DMHg;<0.01 pM) or monomethylmercury (MMHg; <0.05 pM) was detected in mixed layer samples. The highest DMHg concentrations were found in recently formed deep waters – Antarctic Intermediate Water and Antarctic Bottom Water and in the equatorial sub-thermocline region. Higher concentrations of DMHg coincided with higher values of apparent oxygen utilization, indicative of a link between microbial activity and methylated Hg production. The lowest-deep water DMHg concentrations were found in the core of the North Atlantic Deep Water. Incubation experiments on-board demonstrated that light enhanced the decomposition of DMHg, with MMHg as the major product. In deep waters, Hg° was still an important constituent and is likely formed as a decomposition product from MMHg. These results suggest that methylated Hg production occurs primarily in regions of high biological activity, and that ionic Hg is strongly complexed to organic matter (colloidal material) in open ocean surface waters.  相似文献   

7.
We discuss nitrous oxide (N2O) and methane (CH4) distributions in 49 vertical profiles covering the upper ∼300 m of the water column along two ∼13,500 km transects between ∼50°N and ∼52°S during the Atlantic Meridional Transect (AMT) programme (AMT cruises 12 and 13). Vertical N2O profiles were amenable to analysis on the basis of common features coincident with Longhurst provinces. In contrast, CH4 showed no such pattern. The most striking feature of the latitudinal depth distributions was a well-defined “plume” of exceptionally high N2O concentrations coincident with very low levels of CH4, located between ∼23.5°N and ∼23.5°S; this feature reflects the upwelling of deep waters containing N2O derived from nitrification, as identified by an analysis of N2O, apparent oxygen utilization (AOU) and NO3−, and presumably depleted in CH4 by bacterial oxidation. Sea-to-air emissions fluxes for a region equivalent to ∼42% of the Atlantic Ocean surface area were in the range 0.40–0.68 Tg N2O yr−1 and 0.81–1.43 Tg CH4 yr−1. Based on contemporary estimates of the global ocean source strengths of atmospheric N2O and CH4, the Atlantic Ocean could account for ∼6–15% and 4–13%, respectively, of these source totals. Given that the Atlantic Ocean accounts for around 20% of the global ocean surface, on unit area basis it appears that the Atlantic may be a slightly weaker source of atmospheric N2O than other ocean regions but it could make a somewhat larger contribution to marine-derived atmospheric CH4 than previously thought.  相似文献   

8.
Marine seismic surveying discerns subsurface seafloor geology, indicative of, for example, petroleum deposits, by emitting high-intensity, low-frequency impulsive sounds. Impacts on fish are uncertain. Opportunistic monitoring of acoustic signatures from a seismic survey on the inner continental shelf of North Carolina, USA, revealed noise exceeding 170 dB re 1 μ Pa peak on two temperate reefs federally designated as Essential Fish Habitat 0.7 and 6.5 km from the survey ship path. Videos recorded fish abundance and behavior on a nearby third reef 7.9 km from the seismic track. During seismic surveying, reef-fish abundance declined by 78% during evening hours when fish habitat use was highest on the previous three days without seismic noise. Despite absence of videos documenting fish returns after seismic surveying, the significant reduction in fish occupation of the reef represents disruption to daily pattern. This numerical response confirms that conservation concerns associated with seismic surveying are realistic.  相似文献   

9.
Chlorofluorocarbon (CFC) inventories provide an independent method for calculating the rate of North Atlantic Deep Water (NADW) formation. From data collected between 1986 and 1992, the CFC-11 inventories for the major components of NADW are: 4.2 million moles for Upper Labrador Sea Water (ULSW), 14.7 million moles for Classical Labrador Sea Water (CLSW), 5.0 million moles for Iceland–Scotland Overflow Water (ISOW), and 5.9 million moles for Denmark Strait Overflow Water (DSOW). The inventories directly reflect the input of newly formed water into the deep Atlantic Ocean from the Greenland, Iceland and Norwegian Seas and from the surface of the subpolar North Atlantic during the time of the CFC-11 transient. Since about 90% of CFC-11 in the ocean as of 1990 entered the ocean between 1970 and 1990, the formation rates estimated by this method represent an average over this time period. Formation rates based on best estimates of source water CFC-11 saturations are: 2.2 Sv for ULSW, 7.4 Sv for CLSW, 5.2 Sv for ISOW (2.4 Sv pure ISOW, 1.8 Sv entrained CLSW, and 1.0 Sv entrained northeast Atlantic water) and 2.4 Sv for DSOW. To our knowledge, this is the first calculation for the rate of ULSW formation. The formation rate of CLSW was calculated for an assumed variable formation rate scaled to the thickness of CLSW in the central Labrador Sea with a 10 : 1 ratio of high to low rates. The best estimate of these rates are 12.5 and 1.3 Sv, which average to 7.4 Sv for the 1970–1990 time period. The average formation rate for the sum of CLSW, ISOW and DSOW is 15.0 Sv, which is similar to (within our error) previous estimates (which do not include ULSW) using other techniques. Including ULSW, the total NADW formation rate is about 17.2 Sv. Although ULSW has not been considered as part of the North Atlantic thermohaline circulation in the past, it is clearly an important component that is exported out of the North Atlantic with other NADW components.  相似文献   

10.
Deep-water sharks are considered highly vulnerable species due to their life characteristics and very low recovery capacity against overfishing. However, there is still limited information on the ecology or population connectivity of these species. The aim of this study was to investigate if the species Centrophorus squamosus could make long displacements and thus confirm the existence of connectivity between different deep-water areas. In addition, the study was the first attempt to use tagging techniques on deep-water sharks, since it has never been undertaken before. Five C. squamosus were tagged with satellite tags (PAT) in the El Cachucho Marine Protected Area (Le Danois Bank) located in waters of the North of Spain, Cantabrian Sea (NE Atlantic). Data from four of these tags were recovered. One of the sharks travelled approximately 287 nm toward the north east (French continental shelf) hypothetically following the continental slope at a mean depth of 901±109 m for 45 days. Two other sharks spent almost 4 months traveling, in which time they moved 143 and 168 nm, respectively, to the west (Galician coast). Finally, another leafscale gulper shark travelled to the NW (Porcupine Bank) during a period of 3 months at a mean depth of 940±132 m. Depth and temperature preferences for all the sharks are discussed. Minimum and maximum depths recorded were 496 and 1848 m, respectively. The temperature range was between 6.2 and 11.4 °C, but the mean temperature was approximately 9.9±0.7 °C. The sharks made large vertical displacements throughout the water column with a mean daily depth range of 345±27 m. These preliminary results support the suggestion of a whole population in the NE Atlantic and confirm the capacity of this species to travel long distances.  相似文献   

11.
The suspended particulate organic matter (sPOM) around two isolated NE Atlantic seamounts, Seine (33°46′N 14°21′W; summit at ∼170 m) and Sedlo (40°19′N 26°40′W; summit at ∼780 m), was studied over a period of 2 years during four 2–4-week oceanographic surveys. Elemental (C and N), chlorophyll a and lipid biomarker concentrations and N stable isotopic values were variable close to the surface (40–90 m), although some chlorophyll a enrichment above the summits was discerned sporadically. Results from near-surface waters showed a generally “fresh”, mainly phytoplankton signature in sPOM with some seasonality, which was more pronounced around Sedlo. sPOM concentrations and composition changed with depth, apparently controlled by seasonality and proximity to the seamounts. A few metres above the Seine summit, the suspended particulate organic carbon (sPOC) concentrations and labile polyunsaturated fatty acids (% of lipids) were higher than elsewhere at similar depths (∼200 m) in summer 2004. In the same season at Sedlo, polyunsaturated fatty acids were also relatively more abundant (up to 43% of total lipids) around the topographic feature throughout the water column, indicating supply of more labile sPOM, perhaps by advection, downwelling or passive sinking of locally produced phytoplankton and/or in situ production. The high-quality sPOM that seems to be present around the seamounts could provide an important food source to the biological community.  相似文献   

12.
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13.
In the coastal waters of Johor Straits, Peninsular Malaysia, the dugongs occur and their habitat suitability model has yet not been attempted, while it could be critical information for developing their conservation strategies. This study derived spatially explicit dugong population information on the abundance and distribution of dugongs based on fisher surveys. The survey revealed the highest dugong abundance around eastern areas, followed by southern areas of Johor Straits. Degradation of seagrass habitat, which dugong uses as feeding ground, could be the main reason for reducing dugong sighting around western areas. A habitat suitability map was produced based on dugong presence and interacting environmental factors such as seagrass biomass, distance from shoreline, and water depth. Using ArcGIS mapping capability, the data layers on those environmental factors were fied into MaxEnt. The MaxEnt model output showed seagrass biomass as the highest contributing factor to the likelihood of dugong presence. The model also estimated 20 kg/m2 of seagrass biomass, 3 km distance from shoreline and a water depth of 25 m as the optimum habitat condition for dugong population. The combination of fisher interview, habitat suitability, and risk modeling has the ability to provide adequate information required for monitoring and developing policy strategies for sustainable management and conservation of marine mammals.  相似文献   

14.
In an extended deep-sea study the response of the benthic community to seasonally varying sedimentation rates of organic matter were investigated at a fixed abyssal site in the NE Atlantic (BIOTRANS station or JGOFS station L2 at 47°N–20°W, water depth >4500 m) on four legs of METEOR expedition 21 between March and August 1992. The vertical flux at 3500 m depth and temporal variations in the chloroplastic pigment concentration, a measure of phytodetritus deposition, and of total adenylates and total phospholipids, measures of benthic biomass, and of activity of hydrolytic enzymes were observed. The flux patterns in moored sediment traps of total chlorophyll, POC and total flux showed an early sedimentation peak in March/April 1992, followed by low fluxes in May and intermediate ones from June to August. Thus 1992 differed from other years, in which one large flux peak after the spring phytoplankton bloom was observed. Unusually high concentrations of chloroplastic pigments were consistently observed in March 1992, reflecting the early sedimentation input. At the same time biomass of small benthic organisms (bacteria to meiobenthos) and activity of hydrolytic enzymes were higher compared to values from March 1985 and from the following months in 1992. In May and August 1992 pigment concentrations and biomass and activity parameters in the sediment were lower than during previously observed depositions of phytodetrital matter in summer. The data imply that the deep ocean benthic community reacts to small sedimentation events with transient increases in metabolic activity and only small biomass production. The coupling between pelagic and benthic processes is so close that interannual variability in surface water production is “mirrored” by deep-sea benthic processes.  相似文献   

15.
Coral reef islands have a self-sustaining mechanism that expands and maintains the islands through the deposition of calcium carbonate (CaCO3) by marine organisms. However, the human societies established on such low-lying coral reef islands are vulnerable to rapid sea-level rises. Enhancing the self-sustaining mechanism of coral reefs will become one of the required sustainable countermeasures against sea-level rise. We examined the feasibility of mass culturing the large benthic foraminifera Baculogypsina sphaerulata, which is known as “living sand.” We developed a rearing system with the key components of an artificial lawn as a habitat and a stirring device to create vertical water currents. Batches of B. sphaerulata in two different size groups were reared to examine size growth and reproduction under the culture conditions. All culture batches reproduced asexually following generations over 6 months in culture. The small-sized group exhibited steady growth, whereas the large-sized group underwent a reduction in mean size because large individuals (> 1.5 mm2) died off. Similar traits of size structure between the culture batches and natural populations indicate that our culturing conditions can successfully reproduce environments similar to the habitat of this species. Reproduction, consistent size growth, and size structure similar to the natural population indicate that the examined rearing system is viable for culturing Foraminifera at a large scale.  相似文献   

16.
Total (unfiltered) silver concentrations in higher latitudes of the North Atlantic (52–68°N) are reported for the second Intergovernmental Oceanographic Commission (IOC) Global Investigation of Pollutants in the Marine Environment (GIPME) baseline survey of 1993. These silver concentrations (0.69–7.2 pM) are oceanographically consistent with those (0.24–9.6 pM) previously reported for lower latitudes in the eastern North and South Atlantic (Flegal et al., 1995). However, surface (⩽200 m) water concentrations of silver (0.69–4.6 pM) in the northern North Atlantic waters are, on average, ten-fold larger than those (0.25 pM) considered natural background concentrations in surface waters of the central Atlantic. In contrast, variations in deep far North Atlantic silver concentrations are associated with discrete water masses. Consequently, the cycling of silver in the far North Atlantic appears to be predominantly controlled by external inputs and the advection of distinct water masses, in contrast to the nutrient-like biogeochemical cycling of silver observed in the central Atlantic and Pacific oceans.  相似文献   

17.
The Lophelia pertusa community at Viosca Knoll (VK826) is the most extensive found to date in the Gulf of Mexico. As part of a multi-disciplinary study, the physical setting of this area was described using benthic landers, CTD transects and remotely operated vehicle observations. The site was broadly characterised into three main habitats: (1) dense coral cover that resembles biogenic reef complexes, (2) areas of sediment, and (3) authigenic carbonate blocks with sparse coral and chemosynthetic communities. The coral communities were dominated by L. pertusa but also contained numerous solitary coral species. Over areas that contained L. pertusa, the environmental conditions recorded were similar to those associated with communities in the north-eastern Atlantic, with temperature (8.5–10.6 °C) and salinity (～35) falling within the known species niche for L. pertusa. However, dissolved oxygen concentrations (2.7–2.8 ml l?1) and density (σΘ, 27.1–27.2 kg m?3) were lower and mass fluxes from sediment trap data appeared much higher (4002–4192 mg m?2 d?1). Yet, this species still appears to thrive in this region, suggesting that L. pertusa may not be as limited by lower dissolved oxygen concentrations as previously thought. The VK826 site experienced sustained eastward water flow of 10–30 cm s?1 over the 5-day measurement period but was also subjected to significant short-term variability in current velocity and direction. In addition, two processes were observed that caused variability in salinity and temperature; the first was consistent with internal waves that caused temperature variations of 0.8 °C over 5–11 h periods. The second was high-frequency variability (20–30 min periods) in temperature recorded only at the ALBEX site. A further pattern observed over the coral habitat was the presence of a 24 h diel vertical migration of zooplankton that may form part of a food chain that eventually reaches the corals. The majority of detailed studies concerning local environmental conditions in L. pertusa habitats have been conducted within the north-eastern Atlantic, limiting most knowledge of the niche of this species to a single part of an ocean basin. Data presented here show that the corals at VK826 are subjected to similar conditions in temperature, salinity, and flow velocity as their counterparts in the north-east Atlantic, although values for dissolved oxygen and density (sigma-theta: σΘ) are different. Our data also highlight novel observations of short-term environmental variability in cold-water coral habitat.  相似文献   

18.
A 1-D coupled physical-biogeochemical model is used to study the seasonal cycles of silicon and nitrogen in two High Nutrient Low Chlorophyll (HNLC) systems, the Antarctic Circumpolar Current (ACC) and the North Pacific Ocean, and a mesotrophic system, the North Atlantic Ocean. The biological model consists of nine compartments (diatoms, nano-flagellates, microzooplankton, mesozooplankton, two types of detritus, nitrate, ammonium and silicic acid) forced by irradiance, temperature, mixing and deep nitrate and silicic acid concentrations. At all sites, nanophytoplankton standing crop variations are low, in spite of variations in primary production, because of a “top–down” control by microzooplankton. Although nanophytoplankton sustain more than 60% of the annual primary production in these areas, their contribution to the export production does not exceed 1% of the total. The differences in the seasonal plankton cycle among these regions come mainly from differences in the dynamics of large phytoplankton (here diatoms). In the ACC, the chlorophyll maximum remains <1.5 mg m−3, as an unfavourable light/mixing regime and a likely trace-metal limitation keep diatoms from blooming. In the northeast Pacific, trace-metal limitation seems to keep diatoms from blooming throughout the year. In both these systems, light or iron limitations induce high Si/N uptake ratios. Incidentally these high Si/N uptake ratios lead to a net excess of silicic acid utilization over nitrate, and to a subsequent silicic acid limitation during the summertime. In the North Atlantic, under favourable light/mixing regime and nutrient-replete conditions at the onset of the growing period, diatoms outburst and sustain a bloom >3.5 mg Chl-a m−3. Thereafter, mesozooplankton grazing pressure and silicic acid limitation induce the collapse of the chlorophyll maximum and the persistence of lower chlorophyll concentrations in summer. Although the ACC and the North Pacific show HNLC features, they support a high biogenic silica production (1.9 and 1.07 mol Si m−2 yr−1) and export flux (0.79 and 0.61 mol Si m−2 yr−1), compared to the North Atlantic (production: 0.23 mol Si m−2 yr−1, export: 0.12 mol Si m−2 yr−1). The differences in Si production and export between the HNLC systems and the mesotrophic North Atlantic come from both higher Si concentrations and Si/N uptake ratios in the HNLC areas compared to the North Atlantic. Also, the low dissolution rate of biogenic silica compared to nitrogen degradation rate, and the inhibition of nitrate uptake by ammonium, reinforce the net excess of silicic acid utilization over nitrate. As a result, the model also illustrates the efficiency of the silica pump for the three sites: about 50% of the biogenic silica synthesized in the euphotic layer is exported out of the first 100 m, while only 4–11% of the particulate organic nitrogen escapes recycling in the surface layer.  相似文献   

19.
Cores raised during IODP Expedition 303 off southern Greenland (Eirik Ridge site 1305) and off the Labrador Coast (Orphan Knoll site 1302/1303) were analyzed to establish an isotope stratigraphy, respectively for the “inner” and “outer” basins of the Labrador Sea (LS). These isotopic data also provide information on the Atlantic Meridional Overturning Circulation (AMOC), notably with regard to the intensity of the Western Boundary Under Current (WBUC), which is tightly controlled by the production of Denmark Strait Overflow Water (DSOW), and the production of Labrador Sea Water (LSW) in the inner basin through winter cooling and convection. The upper 184 m of sediment at Eirik Ridge spans marine isotope stages (MIS) 32 to 1. At this site, two distinct regimes are observed: prior to MIS 20, the isotopic record resembles that of the open North Atlantic records of the interval, whereas a more site-specific pattern is observed afterwards. This later pattern was characterized by i) high DSOW production rates and strong WBUC during interglacial stages, as indicated by sedimentation rates, ii) large amplitude δ18O-shifts from glacial stages to interglacial stages (> 2.5‰) and iii) an overall range of δ18O-values significantly more positive than before. At Orphan Knoll, the 105 m record spans approximately 800 ka and provides direct information on linkages between the northeastern sector of the Laurentide Ice Sheet and the North Atlantic. At this site, a shift towards larger amplitude glacial/interglacial ranges of δ18O-values occurred after MIS 13, although isotopic records bear a typical North Atlantic signature, particularly during MIS 5, in contradiction to those of Eirik Ridge, where substages 5a to 5c are barely recognized. Closer examination of δ18O-records in planktic and benthic foraminifera demonstrates the presence of distinct deep-water masses in the inner vs. outer LS basins during MIS 11 and more particularly MIS 5e. Data confirm that the modern AMOC, with LSW formation, seems mostly exclusive to the present interglacial, and also suggest some specificity of each interglacial with respect to the production rate of DSOW and the AMOC, in general.  相似文献   

20.
We have assessed the impact of seasonal pulses of phyto-detritus towards the bottom of the Porcupine Abyssal Plain (PAP) in the NE Atlantic. Phytopigments were determined (HPLC) in sediment, near-bottom suspended matter and sediment trap samples to obtain an impression of the quantity and quality of the organic material reaching the bottom. Its supposed effect on the benthic community was estimated on the basis of in situ Sediment Community Oxygen Consumption (SCOC) rates, deck oxygen micro profiles as well as chlorophyll mixing and degradation rates. There was considerable interannual variation in the deposition of fresh organic material. In September 1996 the mass flux at 10 m above the bottom was 0.25 g DW m−2 d−1. The material caught in the trap was relatively fresh with a chlorophyll-a : phaeophorbide ratio of 1.33. During the other seasons (March 1997, July 1997 and October 1997) such fresh material was absent and even in July, the period in which fresh material is supposed to have arrived on the bottom, the ratio remained low, viz. 0.23. Based on these findings we conclude that in 1997 only small amounts of already degraded material arrived at the sea floor. On the basis of the large quantities of fresh material found in September 1996, the existence and subsequent deposition of autumn blooms should be considered.With in situ respirometry no effect of the differential quality and quantity of the settling detritus could be detected, whereas model parameters based on oxygen microprofiles demonstrated changes associated with the supposed seasonal cycle. Also the downcore pigment distribution of chlorophyll-a and derived mixing and degradation coefficients showed variations which were linked to the observed seasonal changes in input of organic matter.  相似文献   

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