Bottom Trap Research Articles

Time-series records of particulate fluxes reveal temporal variations in hydrothermal activity in the Wocan hydrothermal field, Carlsberg Ridge

A mooring with two sediment traps and a current meter was deployed for 315 days near the Wocan hydrothermal field (∼650 m from the vent) on the Carlsberg Ridge to study the vertical and temporal variations in the composition and flux of the settling particles dispersed by the hydrothermal plume. The collected settling particles were characterized by a high content of hydrothermally derived minerals, including Cu-Fe-Zn sulfides, sulfates, native sulfur, Fe-oxyhydroxides, and Fe-oxides. Geochemically, the settling particles exhibited strong metal (e.g., Fe, Cu, Zn, Ga, Mo, Ag, Cd, and Pb) and S enrichment. The data indicate that the current direction, position of the trap (bearing and distance relative to the vent), and height above the bottom have strong impacts on the observations of the hydrothermal fluxes. The mean flux of particulate FeH, in the upper trap (225 m above the bottom (mab)) was 248 μg·cm−2·yr−1. However, in the dominant current direction (N90–135°), the FeH flux settling at the same distance was estimated to be 3.8–4.7 fold greater than this value. The settling flux of the FeH derived from the Wocan field decreased with increasing distance from the vents to a greater extent than the fields in the Atlantic Ocean and to a much greater extent than the fields in the Pacific Ocean. This difference can be explained by the much higher oxidation rates of the Fe (II) in the hydrothermal fields in the Indian and Atlantic Oceans. The settling fluxes in the upper and bottom traps (35 mab) were significantly different. The hydrothermal fluxes in the upper trap were influenced by the current direction, whereas the fluxes in the bottom trap were governed by sediment resuspension in addition to the current direction. Our data show temporal variations in the hydrothermal plume height and settling fluxes, which were largely attributed to the variations in the hydrothermal output. In addition, the temporal variability of the CaCO3 flux in the upper trap recorded the seasonal cycle of the primary productivity in the surface water.

Hydrodynamic effects on the ability of bottom traps to capture nutrient-rich sediments in shallow eutrophic lakes

Hydrodynamics are the key factor influencing sediment resuspension, transport and nutrient release in large shallow lakes. However, the hydrodynamic responses of bottom traps during pollutant capture remain unclear. In this study, a large eutrophic shallow lake was selected to carry out a field test of deep traps at the lake bottom. Based on observations of the lake current around the trap, the sedimentation rate of the particles in the trap and the nutrient content of the captured sediments, combined with the numerical simulation of the waves outside the trap, the effects of lake currents and waves on the sediment deposition in the traps were studied, and the response of the nutrient content of the sediments captured in the deep traps to the changes in lake currents and waves was analyzed. The results showed that the strong hydrodynamic force significantly promoted sediment deposition in the trap and enhanced the ability of the trap to capture sediments with high nutrient contents. The influences of waves and lake currents on the bottom trap capture of polluted sediments varied among different periods. Waves played the leading role in winter and spring, accelerating sediment capture in the bottom traps near the southern shore of eastern Lake Chaohu during this period. In summer, the lake current was the main dynamic factor contributing to the rapid deposition of particulate matter and the capture of sediments with high nutrient contents in the bottom traps of western Lake Chaohu. The multiple stepwise linear regression model based on lake current and wave data explained 37.6 % of the sediment deposition in the trap, and the model built for a single bottom trap explained more than 80 % of the deposition. After correcting the sediment deposition thickness in the trap by considering the water content of the sediment, the quantitative relation yield better inversion results for the sediment deposition process, and different thicknesses in the bottom trap were linked to different sediment deposition periods. According to the hydrodynamic strength in 2020, the thickness of the highly contaminated sediments captured by traps CC1-CC5 was calculated to be 1.09–1.93 m, and the corresponding TN and TP were 26.66–68.53 kg and 6.84–19.89 kg, respectively. This study provides a scientific analysis and guidance for the evaluation of endogenous nutrients captured by lake bottom trap methods.

Environmental mechanism of capturing nutrient-rich particles by the lake bottom trap in a large, shallow lake

Bottom traps capture and preserve nutrient-rich mobile bottom sediments by forming a weak hydrodynamic environment. In this study, Lake Chaohu, a large shallow lake in China, was considered the research object, and the influence of trap at the bottom of the lake on the physical, chemical, and biological characteristics of sediments and water were analysed by combining on-site monitoring and laboratory analysis. The results showed that the hydrodynamic intensity was attenuated by more than 65% at the bottom of the trap compared with that of the upper surface of the water body under different weather conditions, forming an obviously weak hydrodynamic environment. The weak dynamic environment and large sedimentation rate at the bottom of the trap were beneficial to the sedimentation and storage of fine particles that adsorb nutrients, such as nitrogen and phosphorus, in the water. Owing to the increase in local water depth, a low-temperature and low-dissolved oxygen environment was formed inside the trap. The abundance and diversity of microorganisms in the sediments inside the trap were reduced, and the abundance of nitrifying and denitrifying bacteria in the sediment was reduced by approximately 50%, indicating an environment favourable for nitrogen accumulation in the sediment in the trap. Therefore, the environment inside the bottom trap is favourable for capturing the high nutrient-rich particulate matter in the water, which provides theoretical support for use of the lake bottom traps for controlling the endogenous pollution of shallow lakes.

Percentage of the bycatch and discard composition in artisanal bottom trap fisheries

Data on bycatch in the fishing effort required to manage fisheries resources. Unfortunately, the data on small-scale and traditional fisheries is still lacking. It makes it challenging to make fishing policies and regulations. Survey activities and experimental fishing were conducted to determine and analyze the composition of the main catch, bycatch and discarded by the local fisher's bottom traps in Sibolga, North Sumatra, Indonesia. Five units of the trap with a size of 150 cm x 100 cm x 50 cm (length x width x height) were used to collect fish data. These five trap units operated in the fishing ground, where local fishers usually operate their fishing gear. The fishing operation carried out within 1 mile of the coastline with water depths ranging from 7-10 meters. The duration of trap setting around 5-7 days for each fishing operation. A motorboat operated with a weight of 5.8 GT. The results showed that the total bottom trap catch consisted of 329 individuals with a total weight of 151.4 kg and 12 demersal fish species. The main catch was 148 individuals (88.9 kg), or 44.7% of the total catch during the experiment i.e. Chepalapholis urodeta, Ephinephelus areolatus, Epinephelus chlorostigma, Plectropomus leopardus, Ephinepelus coioides, Lates calcarifer, Lutjanus malabaricus, and Lutjanus erytropterus. The bycatch was 151 individuals (57.1 kg) or 46.1% i.e. Lethrinus obsoletus, Lutjanus ehrenbergii, Acanthurus auranticavus, Platax teira, Nemipterus japonicus, Scarus rivulatus, Lutjanus johnii, Siganus canaliculatus, Caesio cuning, and Taeniura lymma.While the discarded catch amounted to 30 individuals (5.4 kg) or 9.2% i.e. Naso brevirostris, Diodon holocanthus, and Diadema setosum. The bycatch utilization obtained by fishers was 83.4%, and the unutilized was 16.6%. The percentage of fish sizes worthy for consumption was 135 individuals (74.6%), and the size unworthy for consumption was 46 individuals (25.4%).Keywords:Fishing groundFishing gear Fishing operation Main catchTrap

Population dynamics of blue crab (<i>Paralithodes platypus</i> Brandt, 1849) in the northwestern Bering Sea

State of the blue crab stock and production is considered for the Russian sector of the Bering Sea on the data of bottom trawl and trap surveys conducted by TINRO in 2005–2017 and fishery statistics. The commercial stock was assessed for 2018 by cohort analysis. The absolute majority of commercial males within the West Bering Sea fishing zone concentrated in two areas located at Koryak coast and at Cape Navarin, whereas the commercial aggregations were absent in the Olyutorsky Bay and Karaginsky Bay. The stock distribution between these two areas was unstable; recently the aggregation at Koryak coast increased to 72 % of the total number of commercial males in 2017. This dynamics is conditioned by both changes in reproduction and intensity of fishery. The total commercial stock of blue crab had increased since 2014 and reached the maximum of 18.133 × 106 ind. (males) in 2017 that exceeded significantly the level of 2005–2013. The blue crab fishery extends in the Bering Sea, since 2010 the portion of used TAC increased from approximately 93 % in 2011–2015 to 98 % in 2016–2017 and 99 % in 2018. State of the population is evaluated as satisfactory and stable.

Research on application of a new bottom trap technology to catch particles rich in nutrients in a large shallow lake

The resuspension and sedimentation of particulate matter and the release of nutrients from sediment are important factors affecting the eutrophication of shallow lakes. The capture and removal of particles rich in nitrogen, phosphorus, and other nutrients at the bottom of lakes is of great significance for improving the management and eutrophication status of lakes. This study investigated the feasibility of applying lake bottom trap technology in seven different locations in Lake Chaohu, which is the fifth largest freshwater lake in China. The results showed that the trap in the western part of Lake Chaohu had the highest sedimentation rate and could capture most of the nutrients. The sedimentation rates were higher in spring and summer than in autumn and winter. The bottom trap effectively collected and preserved chlorophyll a, organic matter, total nitrogen, and total phosphorus. The trap per meter length (15–20 m wide) could catch 20.7–27.6 m3 of particles rich in nutrients with a water content of 50–70%, organic matter content of 281.9–375.8 kg, total nitrogen content of 24.5–32.6 kg, and total phosphorus content of 10.5–14 kg. The proposed bottom trap had little impact on the benthic organism system of the lake. The bottom trap technology used in this study could solve the problem of nitrogen, phosphorus, and algae accumulation in lakes and reservoirs, broaden the utility of lake hydrodynamics in environmental pollution control, and provide new ideas and strategies for the control and management of cumulative pollution in shallow lakes and reservoirs.

Tingkat Pemanfaatan Ikan Umela (Lutjanus vitta) di Perairan Mapur yang didaratkan di Desa Kelong Kecamatan Bintan Pesisir Kabupaten Bintan

Brown strip red snapper or umela fish catched by fisherman in Kelong Village by bottom trap called ‘bubu’ in Mapur Waters. That fish high economic value and exported fish because high fish export market demand, as well as umela fish also made processed by society in Kelong Village such as fillet and increase the price in the market. This study was held in September 2018 until April 2020 in the landing fish Kelong Village. The study aimed at analyzed catch per unit effort (CPUE), maximum sustainable yield (MSY), level and utilization effort, as well as the total allowable catch (TAC) in umela fishing in the Mapur Waters that was landed in Kelong Village. The study used survey method, primary data retrieval is conducted with interviews fisherman directly and secondary data consists of supporting documents and literature. Data analysis was used Schaefer model in this study. The results obtained an average value of CPUE of 1.61 kg/unit, and maximum sustainable yield (MSY) value of 795.50 kg/unit with optimum capture effort (f opt) of 796 units, umela fish has not been said overfishing. The utilization rate of umela fish is 60% and categorized as medium, it is still possible to maximize utilization up to 80% followed by government controlled. As well as the total allowable catch (TAC) of 636.4 kg/unit, umela fishing could be upgraded but cannot exceed the conditions.

Ichthyofauna state of Lake Tempe, South Sulawesi

Abstract. Dina R, Lukman, Wahyudewantoro G. 2019. Ichthyofauna state of Lake Tempe, South Sulawesi. Pros Sem Nas Masy Biodiv Indon 5: 251-255. Lake Tempe is located in three regency areas in South Sulawesi, namely Wajo Regency, Sidrap Regency, and Soppeng Regency. Lake Tempe is known to have high productivity, including the productivity of its fish. This study aims to determine the status of the latest fish species at Lake Tempe. Sampling was carried out in 2016 and 2017. Fish were caught using diverse fishing gears, namely gillnet, bottom trap, surface trap, and net. Fish species were identified based on their morphology. Nineteen fish species were found, that were Barbonymus gonionotus, Trichopodus trichopterus, T. pectoralis, Glossogobius giuris, Glossogobius aureus, Osteochilus vittatus, Oreochromis niloticus, Oxyeleotris marmorata, Channa striata, Anabas testudineus, Clarias batrachus, Pangasianodon hypopthalmus, Monopterus albus, Stenogobius gymnopomus, Stenogobius sp., Megalops cyprinoides, Caranx sexfasciatus, Anguilla marmorata and Liposarcus pardalis. Most of the fish are introduced fish for consumption purposes. Besides that, it was also found a new non native fish found in Lake Tempe, namely Amazon sailfin catfish (Liposarcus pardalis). The fish species that have not been found were blue panchax (Aplocheilus panchax), wrestling halfbeak (Dermogenys pusilla), dussumier’s ponyfish (Karalla dussumieri), Lagusia micrachantus, kissing gourami (Helostoma teminckii) and carp (Cyprinus carpio). Some of fish found are known to be migratory fish species that also live in brackish or marine waters, namely Anguilla marmorata, Stenogobius sp., Megalops cyprinoides, and Caranx sexfasciatus.

Fishing methods for sustainable shrimp fisheries in the Canary Islands (North-West Africa)

During the past 20 years, experimental cruises have been conducted around the Canary Islands (North-West Africa) to investigate the biodiversity of the deep-sea ecosystem and to explore new fisheries resources. Although pandalid shrimps were shown to be very abundant in this region, information is lacking regarding the best fishing method for catching the different species of shrimp. Here, two types of traps were tested, a semi-floating shrimp trap and a traditional bottom trap, in an effort to improve the fishing gear effectiveness and to reduce the capture of non-target species. In total, nine species were captured, which were categorised into three main groups based on their depth of capture: Plesionika edwardsii, P. narval and P. holtuisi (100–400 m); P. ensis, P. martia, P. williamsi and Heterocarpus ensifer (400–800 m); and H. grimaldii and H. laevigatus (800–1 300 m). Significant differences were found in the capture of the different species: P. narval, P. ensis, P. edwardsii and H. ensifer were captured more readily using the semi-floating traps, whereas P. martia, P. williamsi, H. grimaldii and H. laevigatus were caught more efficiently with traditional bottom traps. This intra-specific difference in their capture was considered to be due to the differential motility of the species in the water column. There were indications that P. edwardsii and H. ensifer are an unexploited resource that has the potential to support a viable and sustainable fishery using semi-floating shrimp traps. Furthermore, the deeper-dwelling pandalid shrimps, H. laevigatus and H. grimaldi, could be a secondary target species using bottom traps.

Physical and biogeochemical processes controlling particle fluxes variability and carbon export in the Southern Adriatic

In the framework of the Vector Project downward particle fluxes have been measured in a station located in the centre of the South Adriatic Pit from November 2006 to August 2008.Sediment trap samples were collected at two different depths, below the photic layer (168m) and near the bottom (1174m), and analysed for total mass flux, for total and organic carbon, total nitrogen, carbonate, stable isotope of organic carbon (δ13Corg) and biogenic silica contents. The results have been integrated and compared with data obtained from previous research projects, carried out in the Southern Adriatic area in 1994–1995 and 1997–1998.Fluxes of particulate matter showed high seasonal and interannual variability, with maximum values in late winter–spring season. The organic carbon flux, followed the same seasonal trend, with higher values below the photic zone, and peaks in spring, related to blooms of silica and/or carbonates phytoplankton organisms (e.g., diatoms, coccolithophorids). The organic carbon export from the photic layer was of 5.2 and 2.1gCm−2y−1 reached the bottom.Climatological cycles and, in particular, the maximum depth of the convective vertical mixing determined the high fluxes measured in 1998 and in 2008 springs.Total mass fluxes measured at the bottom trap were twofold those measured below the photic layer, and showed a high lithogenic fraction, highlighting the presence of advective processes that appear particularly active in the area. These processes can be correlated with the spreading of dense waters coming from the north and central Adriatic, generally observed in spring. The elemental and isotopic composition of bottom trap samples, resulted similar to that of samples collected in the south-western Adriatic slope, corroborating the assumption that lateral advection other than vertical input were contributing to bottom particle fluxes.

Temperature-induced fractionation of oxygen isotopes of diatom frustules and growth water in Lake Sihailongwan in Northeast China

Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoenvironment, but have rarely been reported in China. In the present study, Lake Sihailongwan in Northeast China was selected for detailed investigation of oxygen isotopic fractionation between diatom frustules and lake water induced by growth temperature. This study involved a 2-year period of field monitoring of the lake water temperature at multiple depths and biweekly collections of traps for both sediment and water at shallow and bottom depths (7 and 49 m below the lake surface, respectively), diatom separation and purification of the trap sediments, and oxygen isotope measurement for diatom silica and lake water samples. The conditioned experiment conducted herein demonstrated that the laboratory device, methods and techniques used in this study were capable of generating reliable data for the typical oxygen isotope composition of diatom frustules. The data obtained revealed a prominent linear relationship between the oxygen isotope composition of the modern diatom and lake temperature during growth. The fractionation coefficient was about −0.185‰/°C−0.238‰/°C in the temperature range of 3.6–24°C, which is consistent with the observations from various aquatic environments and laboratory culture with different diatom taxa. These findings provide strong support for the dominant control of the growth temperature on the oxygen isotope fractionation between the diatom frustules and ambient water. A notable difference in the fractionation coefficient was observed between the surface and bottom diatom oxygen isotopes, suggesting that various depositional processes and taphonomic effects influenced the surface and bottom trap samples. Another factor leading to this difference may be that enrichment by evaporation and dilution by rainfall have a stronger influence on the surface. Overall, the results presented here demonstrate significant progress in evaluation of diatom oxygen isotopes in China and draw attention to the differences between surface and bottom diatom oxygen isotope compositions.

PENGARUH MINYAK CUMI PADA UMPAN BUBU DASAR TERHADAP HASIL TANGKAPAN IKAN-IKAN KARANG

Bottom trap have been used widely by coastal communities in North Sulawesi to catch coral fishes, since it simple in design, cheaper and easy to manage with a small boat. Unfortunately, the fishing practice of the traditional trap is usually conducted in destructive way, where fishermen cover the gear with live coral to attract fishing target. Although the gear’s design has evolved over centuries, there is still potential for improving its catching efficiency and selectivity. An attempt to understand the fishing process of bottom trap should therefore be focused on bait and how its chemical composition, visual and physical properties may stimulate target species to attack the bait and captured. Addition of squid liver oil to the bait could increase the fishing power of bottom trap gear. But scientific information’s about its applications are not available yet. Therefore, the objective of this research was to study the effect of squid liver oil on bait of bottom trap toward the capture of coral fishes. This research was done in Bangka Strait North of Minahasa, based on experimental method. Six units of bottom trap (bamboo) were operated ten nights in collecting data; where tree units of them used scad mackerel bait that injected by squid liver oil, and tree other units just used scad mackerel bait without squid liver oil; and the capture data were analyzed by ttest. The catch was 117 fish in total consist of 2 genera; 74 fish was caught by scad mackerel bait with squid liver oil, and 43 fish was caught by bait without squid liver oil. Analysis of ttest show that t0= 8.908>t0.05; 5= 3.250; which means that the addition of squid liver oil on bait could increase the catch of bottom trap.

Seasonal and water-depth variations in sediment luminescence and in sedimentation from sediment trap samples at Gerlache Strait, Antarctic Peninsula

AbstractSediment trap arrays were deployed in Brialmont Cove and Andvord Bay, eastern Gerlache Strait, from December 2001–March 2003. The recovered sediments (representing instantaneous deposition from the viewpoint of luminescence dating) encompass all the annual and local glaciomarine depositional processes. Magnetic susceptibility profiles were used to infer seasonality in the trap cores, and thus to select subsamples for luminescence measurements. Multi-aliquot infrared stimulated luminescence (IRSL) apparent ages were used to assess the effectiveness of ‘clock zeroing’ (by daylight) of light sensitive luminescence within fine silt polymineral samples from each trap depth. IRSL apparent ages for 24 samples indicate that the largest age-depth differences occur with the autumn season samples at both trap sites, suggesting a previously unrecognized and regional (within the Gerlache Strait) change in depositional controls in the autumn compared to other seasons. The apparent ages also indicate some differences between the fjords, and a more complex oceanographic regime at Andvord Bay than at Brialmont Cove. Dry-mass sediment fluxes varied from 0.4 to 0.7 g cm-2 yr-1, with the largest flux at Brialmont Cove (∼0.7 g cm-2 yr-1) occurring in the bottom trap, whereas at Andvord Bay, the largest flux (∼0.6 g cm-2 yr-1) occurred in the middle trap (∼45 m above seafloor).

Bathymetric and longitudinal distribution analyysis of the rockfish Helicolenus Dactylopterus (Delaroche, 1809) in the southern Tyrrhenian Sea (central Mediterranean)

This study provides information on bathymetric and longitudinal distribution heterogeneity of the rockfish Helicolenus dactylopterus in the southern Tyrrhenian Sea. Data were drawn from experimental bottom trawl (1996-2002) plus bottom trap (2001-02) surveys. The frequency of occurrence and mean relative density (N/km2) and biomass (kg/km2) indexes were calculated for two survey seasons (spring and autumn), four geographic sectors and three depth strata. MANOVA was used to test fish abundance among years, sectors and strata. Analysis of the length-frequency distributions was carried out by two-way (gears and depths) ANOVA, post hoc multiple comparisons for testing differences among depths and Student’s t test for testing differences between gears. Length-weight relationship was also estimated and the allometric coefficient was tested with the Student’s t test. The results showed a significant positive bathymetric gradient of sizes both for trawl and trap surveys; at same depths, fish caught by traps were significantly longer than those caught by trawl. In spring surveys, significant differences were found among strata for both abundance indexes; in autumn surveys, significant differences between depth strata were found only for density indices. The distribution and abundance patterns of H. dactylopterus along the southern Tyrrhenian Sea was homogeneous among sectors. Length-weight relationship showed a significant positive allometric growth.

Comparison of boundary conditions for predicting the collection efficiency of cyclones

Gas-particle flow in three cyclones was numerically modeled using the Eulerian–Lagrangian approach. A tangential lift-off boundary condition was developed and included in the CFD simulations of cyclone performance via a user-defined function. Particles were considered as detached from the surface if they met the criterion of tangential lift-off; otherwise they were captured by the surface. Prediction of the collection efficiency in cyclones was conducted using the three different boundary conditions: (1) bottom trap only; (2) cone and bottom trap; and (3) the tangential lift-off, which is a combination of trap and reflect. Comparison with experimental data in literature indicates that the tangential lift-off boundary condition yields more accurate predictions than other boundary conditions.

Efficiency of the silicate pump at a coastal oligotrophic site in the Mediterranean Sea

Abstract. A one-year survey of the sedimenting particulate material was conducted at the SOFi site located on the edge of the continental slope in the Gulf of Lions (Northwestern Mediterranean) between September 1999 and December 2000. The main focus of this paper was to establish an annual budget of biogenic silica export, to describe the seasonnal pattern of Si fluxes in relation to the organic and mineral C fluxes and to quantify the Si/C decoupling processes during sedimentation. The pattern of the downward flux of BSi was partly typical with increased daily sedimentation rates during spring followed by smaller peaks during summer. However, an unusual sedimentation event was recorded in the bottom trap in February before the spring thermal stratification occurred, and represented 37% of the annual BSi mass flux. The total annual BSi flux at the SOFi site was estimated from the bottom trap and amounted to 86.8 mmol Si m-2 y-1, while the organic carbon flux amounted to 154.9 mmol C m-2 y-1. The overall efficiency of C export to depth compared to surface primary production budgets was low (3%) and similar to values found for oligotrophic regions of the Eastern Mediterranean. On the other hand, we documented a very high efficiency of the Si export at the SOFi site, with 62% of the Si produced in the surface layer exported to the bottom trap. The excellent correlation between BSi and particulate organic C (POC) in the bottom trap further indicates that the bulk of the organic matter is transferred to depth in association with diatoms. However, the main fraction of the C produced by phytoplankton is lost in the water column through oxidation or metabolisation, while biogenic silica is more efficiently transferred to depth. This strong Si/C decoupling with depth is likely to be the cause of the spring depletion of silicic acid over the entire water column which was observed by mid-April in a companion study (Leblanc et al., 2003) and may cause a severe Si limitation of the diatom spring bloom in this oligotrophic region of the Gulf of Lions.

Shell-bearing plankton fluxes in the central Black sea, 1989–1991

Seasonal and vertical flux variations of coccolithophorids, discrete coccoliths, silicoflagellates, ebridians, and diatoms were investigated using time-series sediment traps deployed in the central Black Sea for 2 years from September 1989 through August 1990 (Year 1) and from October 1990 through September 1991 (Year 2). The following marine plankton groups were not observed during the enumeration: dinoflagellates, radiolarians, planktonic and benthic foraminifers, and pteropods. High fluxes of coccolithophorids, discrete coccoliths, and silicoflagellates occurred from September to December in Year 1 and October to December in Year 2. High ebridian fluxes occurred during short periods from October to November in Year 1 and from February to April in Year 2. High diatom fluxes occurred from September to January in Year 1 and from October to April in Year 2. The seasonal variations and magnitudes of most plankton assemblages were similar between the Shallow trap (at a depth of 400 m) and the Bottom trap (at a depth of 2090 m) suggesting that the plankton shells settled at a rate of 60 m d −1 or greater without significant loss or lateral input. The exception was the diatom flux in Year 2, which was offset by approximately 2 months between the Shallow and Bottom traps, suggesting a sinking speed of approximately 38±18 m d −1. The slower setting speed is attributed to Pseudo- nitzschia spp., which was the dominant diatom taxon in Year 2. Maximum flux magnitudes of each plankton assemblage were on average two times greater in Year 2 than in Year 1. Emiliania huxleyi, Distephanus pulchrus, and Pseudo- nitzschia spp. dominated the fluxes of coccolithophorids, silicoflagellates, and diatoms, respectively. Significant changes in taxonomic composition of the silicoflagellate and ebridian fluxes were observed between Year 1 and Year 2. The higher fluxes in Year 2 and the observed taxonomic changes imply that the upper water column in Year 2 was warmer and more eutrophic compared to Year 1, possibly linked to greater advection of nutrient-rich coastal waters to the center of the Black Sea through meso-scale eddies.

Phosphorus, carbon and nitrogen enrichment during sedimentation in a seasonally anoxic lake (Lake Lugano, Switzerland)

Sedimentation fluxes of major nutrients are investigated during 1996 and 1997 at three different depths and two locations in eutrophic southern basin of Lake Lugano (Switzerland). Horizontal differences between the two sites are on the order of 10-40% (but can exceed 50%), whereas differences related to interannual oscillations range between 5 and 24%. Particulate organic carbon (POC) and nitrogen (PN) fluxes show a constant increase of 5-20% from the upper to the bottom trap. This tendency remains more or less constant during the year. On the contrary, particulate phosphorus (PP) shows a seasonal variation, with higher accumulation rates from the I to the III trap in autumn and winter which can exceed +1200%. This phenomenon is due to the interaction between the dissolved phosphorus (DP) and the iron(oxi)hydroxides (Fe(OH)3) near the oxycline. Fe(OH)3 precipitates at the iron redox boundary, scavenging DP. This enrichment flux increases together with the development of the anoxic benthic layer. The efficiency of the iron redox layer in trapping upward diffusing P is related to the concentration of dissolved iron in the anoxic hypolimnion. In Lake Lugano the two considered sites present major difference of iron concentration, and this difference is reflected in the P sedimentation fluxes. The exposition of an additional sedimentation trap above the maximal oxycline height has allowed to gain insight into this phenomenon.

Ophiuroid growth within deep‐sea sediment traps: A problem for carbon flux measurements at continental margins

Large numbers of postlarvae of the bathyal ophiuroid Ophiocten gracilis were collected by two time‐series sediment traps moored on the continental slope of the NE Atlantic for 102 d at 1,000 and 1,400 m deep (469 and 69 mab), respectively. With time, the organisms collected were progressively larger, suggesting that a single cohort was growing within the collection funnel of the traps but above the preservative solution. We believe that specimens from this cohort occasionally lost their grip on the funnel surface and fell into the preservative. This conclusion is supported by (1) the presence of food within the stomachs of postlarvae (these do not feed in their planktonic phase) and (2) the size of specimens (much larger than those previously found in the plankton). The upper trap was well above the benthic nepheloid layer, and suspension of these organisms by ambient currents is highly unlikely. Ophiuroids contributed up to 7% of the total daily flux of particulate organic carbon (POC) in the top trap and almost 30% in the bottom trap, and although they are not normally considered components of downward particle flux, these specimens had been growing on the material entering the traps and so should be included in this portion. Not all of the epifaunal population will have fallen into the collecting cups, but those that fell had requirements for growth and respiration that were a considerable proportion of the daily flux of POC into the traps (up to 16%). If this epifaunal community (a minimum estimate) was distributed evenly within the cone, a high proportion of the settling material would have come into contact with ophiuroids as it slid down the inside walls of the cone. This problem with the sediment trap technique is probably restricted to the continental slope and shelf and will not occur over abyssal depths.

Particle fluxes and biogeochemical processes in an area influenced by seasonal retreat of the ice margin (northwestern Ross Sea, Antarctica)

Fluxes of biogenic components were determined using time-series sediment trap samples collected at site B (74°01.50′S, 175°05.55′E) in the northern Joides Basin of the Ross Sea from December 1994 to January 1996. In most cases, a great part of the material collected by traps (200 and 540 m depth) was biogenic, opal being the most abundant constituent followed by organic matter. The composition of particles shows a seasonal pattern in the upper trap, which is much less evident at depth. Fluxes showed a marked seasonality due to the presence, in winter, of ice cover. During the sampling period, mass fluxes varied from 0.03 to 120 mg m −2 day −1 and from 24 to 393 mg m −2 day −1 at the upper and bottom level, respectively. Values of 0–64 mg m −2 day −1 of biogenic silica and 0–7.8 mg m −2 day −1 of organic carbon were obtained at 200 m depth. Near-bottom fluxes were almost always much higher: 11–141 and 1.5–19 mg m −2 day −1, respectively. 210Pb fluxes are lower than expected, and this means that particles sink rapidly without reaching an equilibrium with the radiotracer. A mechanism of focusing affects the bottom trap and much more, the seafloor. At site B, we measured particle fluxes that are much lower than those obtained at other locations in the Ross Sea. This can be due to low production and export during the sampling period, and underlies the necessity to further investigate the interannual variability of these processes.