Deep-water Stations Research Articles

Phosphorus distribution, C:N:P ratios, and δ13Coc in arctic, temperate, and tropical coastal sediments: tools for characterizing bulk sedimentary organic matter

Onshore-offshore trends in phosphorus (P), organic carbon (OC), and total nitrogen (TN) concentration, P distribution, elemental organic C:N:P ratios, and stable carbon isotopic composition of OC ( δ 13 C oc ) of surficial sediments, are presented from three river-dominated coastal regimes: the Mackenzie River/Beaufort shelf in the Canadian Arctic; the Mississippi Delta and Louisiana shelf in the temperate Gulf of Mexico; and the tropical Amazon shelf. These parameters, measured in surficial sediments from the three sites, are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge. Trends in elemental ratio data from the Arctic transect, and a portion of the Gulf of Mexico transects, can be explained in terms of a two-end-member mixture of terrestrial and marine phytodetritus. In the arctic transect, covariation of organic C:P ratios with δ 13 C oc is consistent with a two-end-member mixture of terrestrial and marine organic matter. A similar relationship between C:P ratios and δ 13 C oc is not evident in Gulf of Mexico or Amazon shelf sediments. At these sites the two-end-member model fails to explain the data adequately. The most striking feature of the onshore-offshore trends in elemental OC:OP and OC:TN ratios is the occurrence of low ratios in sediments from deep-water stations in the Gulf of Mexico and all stations on the Amazon shelf, resulting from P and N enrichments exceeding the Redfield Ratio for marine plankton. Three explanations are discussed to account for these low ratios: (1) the dominance of refractory OP- and ON-compounds in the residuum of degraded organic matter; (2) differential sorption of OP- and N-compounds, regardless of lability, on the surfaces of the fine-grained sediments characteristic of these sites; and (3) a dominance of bacterial biomass, or components derived from bacterial biomass. Elemental ratios and δ 13 C oc signatures indicate that differential sorption may be most important in the deep-water Gulf of Mexico sites. In contrast, elemental ratios and δ 13 C oc on the Amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass, or derivative substances.

Deep-sea benthic foraminiferal recolonization of the 1991 Mt. Pinatubo ash layer in the South China Sea

A census count of Rose Bengal stained benthic foraminifera from the surface area on top of a 2 to 6 cm thick ashfall layer at three deep water stations along the western margin of the Philippines exhibits a unique assemblage composition of benthic foraminifera. The total number of benthic foraminifera is low and the ratio of living individuals to empty tests is high. Specific diversity is low, with a significant dominance of infaunal morphotypes including species of the genus Reophax ( R. scorpiurus, R. bilocularis and R. dentaliniformis), which are regarded as successful recolonizers. Assemblages below the ash layers are diverse and contain many epifaunal suspension-feeding agglutinated and calcareous foraminifera. The 1991 Mt. Pinatubo eruption caused mass mortality of benthic foraminifera in a vast area of the eastern South China Sea followed by step-wise recolonization of the ash substrate. Three years after the eruption, the benthic foraminiferal community structure is still far from recovery to background levels.

234Th:238U disequilibria in the Gulf of Mexico: the importance of organic matter and particle concentration

We have measured the concentrations of dissolved and particulate234Th, suspended particulate matter, dissolved organic carbon, nutrients and a suite of pigments along a transect in the shelf and slope waters of the Gulf of Mexico. The deep water station samples were collected in the presence (summer 1992) and absence (spring 1992) of a warm-core ring. In the summer, the station was at the periphery of a warm-core ring containing more oligotrophic, Caribbean water, while in the spring, only Gulf water was present. The234Th deficiency, which extends throughout a 1500 m water column in spring, indicates active lateral exchange of dissolved and particulate species. This study provides insight into the role of particles for234Th scavenging and differences in the scavenging intensities in the presence and absence of a warm-core ring. In addition, the possibility that the major carrier phase of thorium cycling could be dissolved organic carbon is suggested from the correlation between234Th (dissolved and total) and dissolved organic carbon concentrations. The average particle residence time for the whole water column in spring, seven days, was significantly shorter than that for summer, 21 days. This longer residence time in the summer is attributed to the presence of a warm-core ring which resulted in lower particle, DOC, and nutrient concentrations. Values of scavenging and particle residence times and234Th fluxes, and the significance of the correlations of these values with concentrations of particle mass and various pigments are discussed.

Observations on the Activity and Life History of the Scavenging Isopod Natatolana borealisLilljeborg (Isopoda: Cirolanidae) from Loch Fyne, Scotland

The activity and life history of the cirolanid isopod Natatolana borealisLilljeborg has been studied using (primarily) fish-baited traps deployed at a deep-water station (190 m) in Loch Fyne, Scotland. A voracious scavenger, it burrows into soft mud, emerging to feed when suitable food odours are detected in the water. Isopods were attracted significantly to baited vs. non-baited traps. Underwater video observations revealed that most animals were active in the vicinity of traps, that capture efficiency was low, but retention complete. Only traps on the sea-bed captured mancas or juveniles in any numbers. Any seasonal pattern in catch rate through the year was confounded by high variability. Only one (manca-)brooding female was ever caught in a trap (in April). It is assumed that brooding females desist from feeding. The sex ratio of isopods in most trap collections was thus significantly male dominated. Mancas were trapped during February to August. Growth rate was slowest in adults and was similar for males and females. The maximum growth rate occurred during autumn associated with the seasonal cycle in bottom water temperatures. Longevity was estimated (by following peaks in the size–frequency distributions with time) to be c. 2·5 years, with sexual maturity (based on oostegites/spurred appendix masculinae) achieved after c. 19 months. Semelparity is suggested. A low incidence of an unnamed epicaridean parasite is reported from the Clyde population. Natatolana borealisalso carried peritrich ciliate epizoites on their antennae. Possible predators are swimming crabs and gadid fish, e.g. whiting and cod.

Distribution and abundance of flatfish on the South American continental shelf from Suriname to Colombia

This study is based on data collected during four trawl surveys conducted in 1988 on the South American continental shelf from Suriname to Colombia. Members of four flatfish families were caught in depths ranging from 15 to 410 m at 264 of the 1200 stations trawled: Bothidae (13 genera, 30 species), Cynoglossidae (1 genus, 4 species), Soleidae (3 genera, 4 species) and Pleuronectidae (1 genus, 3 species). Flatfish comprised less than 5% of total catch by weight at most stations. Hierarchical cluster analysis revealed between 4 and 6 groups of stations in each survey characterized according to depth, temperature and species associations. Cynoglossids, soleids and some bothids characterized shallow-water stations while bothids and pleuronectids characterized intermediate and deep-water stations. Highest catches were taken off northern Venezuela and Colombia during times of increased upwelling and in areas influenced by river runoff. Mean density of flatfish was less than 0.0005 ind·m −2. The major species caught were Paralichthys tropicus, Paralichthys lethostigma, Cyclopsetta chittendeni, Syacium micrurum, Syacium papillosum,, Syacium sp. and Symphurus plagiusa and range extensions were found for six species.

Using an Army of Inverted Echo Sounders to Measure Dynamic Height and Geostrophic Current in the North Pacific Subtropical Gyre

Abstract In 1991, an array of five inverted echo sounders (IESs) was deployed about 100 km north of the island of Oahu, Hawaii, as part of the World Ocean Circulation Experiment deep-water station. IESs record the round-trip acoustic travel time from the seafloor to the sea surface, which is known to correlate well with dynamic height. CTD (conductivity-temperature-depth) casts made during monthly cruises to the deep-water station are used to calibrate the IES; the conversion factor from travel time to dynamic height is found to be −52.8 ± 0.9 dyn m s−1. The time series from the IESs show that there are fluctuations in dynamic height having timescales from weeks to months, which are not well resolved with the CTD sampling. The array of dynamic height can be used to compute geostrophic currents, which are shown to be only reasonably well correlated with acoustic Doppler current profiler (ADCP) measurements. Differences between the IES- and ADCP-derived currents probably exist because the velocity field has...

Vertical Structure of the Baroclinic Tides in the Central North Pacific Subtropical Gyre

Abstract Cruises are made monthly to the World Ocean Circulation Experiment deep-water station, about 100 km north of Oahu, Hawaii. During these cruises, the principal causes of variability in dynamic height are the internal tides having a range about 30% of the annual range in dynamic height. The internal tides have peak-to-peak vertical displacements of up to 30 dbar but show little vertical coherence. At the diurnal frequencies modal fits typically require 6–8 baroclinic modes to account for 90% of the variance, suggesting that the diurnal tide should not be described in terms of dynamic modes. The semidiurnal tide has about two to three times the amplitude of the diurnal tide and shows more vertical phase coherence, but still requires three or four modes to describe it. Generally, the dominant mode is the second or third mode.

Relation between sediment-water fluxes of oxygen and silicate and faunal abundance at continental shelf, slope and deep-water stations in the northwest Mediterranean

Measurements of sediment oxygen demand (SOD), silicate fluxes, benthic macroand meiofauna and phytopigments were made on continental shelf, slope and deep-water sediments in the northwest Meaiterranean in November-December 1991. The mean SOD (f SD), measured by onboard incubations of sediment cores with overlying water, was 301 + 83 pm01 m-' h-' for the shelf stations, 146 + 53 pm01 m-2 h-' for the slope stations, and 44 f 10 pm01 m-2 h-' for the deep-water stations. The SOD values for the slope and deep-water stations are comparable to earlier reported data from open oceanic sites. Considering the limited data set that we present, substantial downslope transport of organic matter at these stations cannot be concluded. Mean shcate effluxes from the sediment, measured in the same incubation experiments, amounted to 52 ? 14, 48 f 20 and 16 pm01 m-' h-' for shelf, slope and deep-water stations, respectively. Diffusive oxygen and silicate fluxes were calculated from pore-water profiles with Fick's first law of diffusion The irngatlon flux was defined as the difference between incubation and diffusive flux. The oxygen irngation flux contributed on average 39 ? 10%. 17 f 15% and 5 + 5% to the oxygen incubation flux for the shelf. slope and deep-water stahons. respectively, and showed a strong positive relation with macrofaunal density, illustrating the importance of macrofaunal activities on sediment-water solute exchanges. In contrast to the oxygen irrigation fluxes, the silicate irrigation fluxes showed less distinction between shelf and slope stations and contributed on average 60 + 6 %, 61 + 9 % and 19 % to the silicate incubation fluxes for the shelf, slope and deep-water stations, respectively. The relation between silicate irrigation flux and macrofaunal density was not significant. Another indication for the lack of organic matter transport across the slope was the monotonic decrease of faunal density, biomass and phytopigments w t h increasing depth. Only at the upper slope station were traces of a past deposition event found. Below this depth phytopigments were below detection level. The absence of phaeopigments in the near-bottom water and their high concentration in the shelf sediments indicated little resuspension of sediment.

Cadmium, copper, lead and zinc on transects through Arctic and Eastern Atlantic surface and deep waters

A total of 230 surface and 70 deep water samples was collected during several transects in the European Arctic and the East Atlantic. The distribution of Cd in surface waters of the Arctic is associated with the nutrient regime and the primary production. In the euphotic zone about 80% of dissolved Cd is eliminated by phytoplankton corresponding to a ΔCd: ΔPO 4 ratio of 1.7 × 10 −4. In addition, there is a reverse linear relationship with Chlorophyll a. Regional fluctuations could be demonstrated: the highest Cd concentrations (0.25 nmol·kg −1) were on the East Greenand shelf, by a factor of 3–4 lower values in the frontal systems, and medium levels (0.1 nmol·kg −1) were observed in the mixing waters of the Greenland Sea gyre. Eastern Atlantic Cd concentrations are sometimes near the detection limit (<0.02 nmol·kg −1) and 5–20 times lower in surface waters than in the Arctic study areas. In contrast Atlantic deep water values at the nutrient maxima were 2–3 times higher than in the Arctic study areas. Good correlations between Cd/Phosphate with a mean slope of 1.2 × 10 −4 were found for the deep water stations in the East Atlantic Basins. Lead showed the lowest dissolved concentrations in waters of the ice covered region of the East Greenland shelf (0.02 nmol·kg −1) and in the South Atlantic (0.05 nmol·kg −1), with increases by 10–20 times in the region of the Greenland Sea gyre and 3–5 times in the region of the westerlies. Concentrations in sea ice were 70 times higher than in the surrounding water masses. Regional averages of the Cu concentrations in Arctic areas fluctuate between 4 nmol·kg −1 on the East Greenland shelf and 1 nmol·kg −1 in the mixing waters of the Greenland Sea gyre. Interannual Cu distribution was rather constant in Arctic and Atlantic surface waters. Seven vertical profiles in Eastern Atlantic basins showed a strong correlation between Cu/SiO 2 with a slope of 0.028 nM/μM. Zn concentrations in surface waters of the Arctic region may have one source in the atmospheric input, as shown by high Zn concentrations of sea ice (1–13 nmol·kg −1) from the ice covered region. Lowest values (0.3–0.8 nmol·kg −1) were determined in 1989 between 35°S and 25°N in East Atlantic surface waters. The data for the trace metals are discussed in the context of the hydrography and the nutrient situation of the two areas under investigation.

Trace metal determinations by total-reflection X-ray fluorescence analysis in the open Atlantic Ocean

The Intergovernmental Oceanographic Commission (IOC), as a major component of its programme “Global Investigation of Pollution in the Marine Environment” (GIPME), maintains a long-standing project on “Open Ocean Baseline Studies of Trace Contaminants”. Initially, the Atlantic Ocean and trace metals were selected. A first cruise with the RV Meteor to the eastern parts of the south and north Atlantic Ocean was successfully organized, in March and April 1990, from Cape Town (South Africa) to Funchal (Madeira, Portugal). Thirteen scientists from laboratories in Europe and North America participated with the first author as coordinator. Four deep-water stations in the Cape Basin, Angola Basin, Cape Verde Abyssal Plain and Seine Abyssal Plain were regularly sampled for at least 36 depths. Additional samples were taken between stations. Samples were distributed to participants and a similar number of additional laboratories. As a central part of our own contribution to the project, we determined the trace heavy metals manganese, nickel, copper, zinc and lead and the lighter selenium by total-reflection X-ray fluorescence analysis. Additional methods applied, inter alia, were anodic stripping voltammetry for lead and cadmium and graphite furnace atomic absorption spectrometry (GFAAS) for cadmium, using two different extraction procedures. For the TXRF, the pre-enrichment of the trace metals and the separation from the salt matrix were performed by complexation with sodium dibenzyldithiocarbamate and reverse-phase chromatography. Generally, very low levels of trace elements were found in filtered and unaltered water samples from these remote areas of the open Atlantic Ocean. Typical examples of the distributions of trace metal concentrations on depth profiles from the four deep-water stations as well as intercomparisons between the stations are presented.

Life History and Productivity of Mysis Relicta in Lake Ontario

Mysis relicta is a common food of many fish species in Lake Ontario, yet little was known about its life history or production. We determined growth rates, cohort development patterns, reproductive patterns, and production of the population at a deep water station over a 4-year period. Four replicate vertical net hauls were collected monthly from April until October, each year. All animals were counted and 100 from each replicate were measured. The original mysid data of N.H.F. Watson, collected in 1971–72, were reanalyzed and the results compared with the present study. Most reproduction occurred in late autumn; the eggs hatched late the following winter; and the offspring reached maturity approximately 18 month later. In 1971 and 1972, abundances were similar to that in 1984 but cohort development was less synchronous. Average growth rate (1984–1987) in the first summer was 0.035 mm.d −1, through the winter it fell to 0.012 mm.d −1, and during the second summer it was 0.029 mm.d −1. Production was 1.90g.m −2 in 1984 and 2.62 g.m −2 in 1986. Examination of sources of error suggest these values might underestimate production by 11% to 27%. Immigration prevented the estimation of production in 1985 and 1987

Lead-210 and Polonium-210 Across the frontal Region Between the Kuroshio and the East China Sea, Northeast of Taiwan

Concentration profiles of Pb-210, Po-210 were measured on several KEEP (Kuroshio Edge Exchange Process) program stations. Results of both Pb-210 and Po-210 of surface water along B transect (from station 6115 to station 4531) showed an increasing trend toward deeper water. This reflected the more efficient removal of Pb-210, Po-210 from the shelf water. Vertical profiles of deep water station (i.e. 4531, 5131) did show Po-210 deficiencies, Po-210/Pb-210＜1, at upper layer (＜100m); and Po-210 excess in the middle layer (200m-500m). With Box Model calculation, the recycling efficiency of Pb-210 and Po-210 in the middle laycr is found to bc 2.9% and 85.4%. Vcrtical profilc of the near shelf-break station 512Am where upwelling of intrusion of Kuroshio water occurred, showed the feature of richness in Po-210. the profile of the station 5323, located at a very steep upper slope region, showed the feature of Pb-210 excess all over the water column. Some sediment particles shich contains excess Pb-210 might re-export from the outer shelf to slope water. The shelf water station was characterized with Po-210 excess in most of the water column except the very top layer (＜20m).

Mixing between oxic and anoxic waters of the Black Sea as traced by Chernobyl cesium isotopes

The Chernobyl nuclear power station accident in 1986 released readily measureable quantities of fallout 134Cs and 137Cs to Black Sea surface waters. This pulse-like input of tracers can be used to follow the physical mixing of the surface oxic waters, now labeled with the Chernobyl tracers, and the deeper anoxic waters, which were initially Chernobyl free. By 1988, there is clear evidence of Chernobyl Cs penetration below the oxic/anoxic interface at deep water stations in the western and eastern basins of the Black Sea. This rapid penetration of surface waters across the pycnocline cannot be explained by vertical mixing processes alone. Data from profiles at the mouth of the Bosporus suggest that significant ventilation of intermediate depths can occur as the outflowing Black Sea waters are entrained with the inflowing Mediterranean waters, forming a sub-surface water mass which is recognized by its surface water characteristics, i.e. initially a relatively high oxygen content and Chernobyl Cs signal. The lateral propagation of this signal along isopycnals into the basin interior would provide a rapid and effective mechanism for ventilating intermediate depths of the Black Sea. This process could also account for the lateral injection of resuspended margin sediments into the basin interior. The temperature and salinity data suggest that the entrainment process occurs at depths of 50–80 m, mixing waters from the Cold Intermediate Layer with the incoming, denser Mediterranean waters.

Seasonal variation in dissolved aluminium concentrations in coastal waters and biological limitation of the export of the riverine input of aluminium to the deep sea

Three surveys in the English Channel between 0° and 5°30′W in November 1985 and May and August 1986 show that Al concentrations vary with the seasonal cycle in dissolved nutrient concentrations. Lowest levels were measured in August (10.5 nM mean) and highest in November (28 nM). In winter, the distribution of Al is determined by the mixing of low Al surface northeast Atlantic water with high Al river water. In summer, where a thermocline is present, Al concentrations are lower above the thermocline. The ratio Al to Si removed during the spring bloom is similar to that observed in diatom culture experiments. A continued decrease in Al after diatom production has ceased suggests that Al removal may be generally linked to primary production. The mechanism of removal is unclear. Profiles of Al against depth from deep-water stations in the northeast Atlantic, north of the area consistently effected by Saharan dust inputs, are very similar to those for Si above the main thermocline. A biologically mediated removal process maintains low concentrations of Al in these and coastal waters, limiting the export of riverine Al into the deep sea.

Interactions of migrating zooplankton with shallow topography: predation by rockfishes and intensification of patchiness

Stratified net tows, multiple-frequency sonar and drifter drogues, combined with analysis of rockfish stomachs, were used to investigate the processes taking place when vertically migrating plankton are swept onto a shallow bank in the Southern California Bight. Euphausia pacifica, the dominant migrating plankter near the bank, was also a dominat item in the stomachs of Sebastes spp. when currents in predawn hours advected water from deep water toward the bank. In the morning, schools of 12 kHz scatterers, apparently rockfish, ascended tens of meters above the bottom toward the descending plankton. Net tow estimates of euphausiid biomass and the acoustic backscattering at 200 and 520 Hz were much lower above the bank than in a nearby deep-water area, particularly during early evening. At night and during predawn hours, a relatively high abundance of zooplankton, with densities similar to the deep-water area, was usually found near the edge of the bank. Causes of the observed recurrent lack of migrating plankton above a seamount in early evening could be diurnal predation by epibenthic fish or daytime advection of migrators around the seamount, thereby creating a “hole” above it. The formation of such “holes” can intensify the regional patchiness of plankton near shallow seamounts. Historical data of CalCOFI night-time tows show that the biomass of euphausiids, but not that of the weakly migrating chaetognaths, is significantly more variable (patchy) at stations near offshore shallow topography than at nearby deep-water stations. The similarity in the mean biomass of euphausiids at the two station sets suggests that the contribution of predation to the observed intensifications of patchiness may be insignificant.

Seasonal distribution of thermotolerant free-living amoebae. I. Willard's Pond.

A quantitative study of the seasonal distribution of thermotolerant (37 degrees C and 45 degrees C), small free-living amoebae (FLA) was conducted in Willard's Pond, a warm, monomictic lake in the Piedmont region of South Carolina. Correlation of physical and chemical parameters with the seasonal distribution was facilitated by partitioning the aquatic ecosystem into benthic, planktonic, and neustonic habitats. Population densities of FLA peaked in late summer in each habitat; however, species composition varied between habitats. Littoral sediment appeared to be the major habitat for FLA, with peaks in populations of Acanthamoeba and Naegleria in August, Hartmannella in July, and Vahlkampfia in May. Populations in profundal sediment underwent dramatic seasonal shifts, apparently in response to the seasonal chemical changes in the hypolimnion. Acanthamoeba was most prevalent in late summer, representing as much as 82% of the FLA in profundal sediment. Distribution patterns and species composition of FLA from surface water were similar to those from littoral sediment; however, a greater percentage of Naegleria was found in surface water. Numerous FLA were isolated from the neustonic community (surface film), and the number of FLA isolated in the surface film at the deep water station was found to be significantly (P less than 0.05) greater than the number from subsurface (5-10 cm) samples. In the water column, FLA populations consistently were highest in the detrital layer, which persisted at a depth of 3.0-3.4 m throughout the summer period. The large percentage of Naegleria contributing to FLA in the detrital layer suggests that Naegleria amoeboflagellates sink through the layer, flagellate, and swim back up, such migrations possibly being triggered by a reduction of nutrients below the layer or by the presence of anoxic, reducing conditions in the hypolimnion. In addition, weather events were found to play a major role in the redistribution of FLA between various habitats in the aquatic ecosystem, with such changes probably due to resuspension of FLA from littoral sediment by wind action and input from the watershed via runoff.

Predator-limited population growth of the copepod Pseudocalanus sp.

Author(s): Ohman, MD | Abstract: The impact of predators on population growth of Pseudocalanus sp. was investigated in Dabob Bay, Washington. Mortality of Pseudocalanus sp. was determined from stage-specific survivorship, from seasonal changes in mortality rates of adult males and females and from incidence of injuries to adult copepods. The principal predators of adult Pseudocalanus were identified as the predatory copepod Euchaeta elongata, the omnivorous euphausiid Euphausia pacifica and the chaetognath Sagirta elegans. Predator attack rates - and prey mortality rates - are highly density-dependent and thus sensitive to prey dispersion in the water column, particularly to layering in the vertical plane. Predation rates by the three principal predators exceeded 100% of the recruitment rate to adult Pseudocalanus sp. beginning in early summer, thus restricting population growth. Planktivorous fish predation (by adult three-spine stickleback, Gasterosteus aculeatus, and juvenile chum salmon, Oncorhynchus keta) on Pseudocalanus sp. adults was estimated to be two orders of magnitude lower than consumption rates by predatory zooplankton, at a deep water station in July. Analysis of seasonal changes in prey ingested by Sagitta elegans revealed that Pseudocalanus sp. was the major prey item of S. elegans in April (61.0% of prey) and in June (67.0% of prey), thereafter declining seasonally in importance. Predation by S. elegans varied seasonally with changes in chaetognath stage structure, vertical distribution and diapause, not size structure alone. Although chaetognath recruitment and population growth appear to be directly coupled to the abundance of Pseudocalanus sp., predation by S. elegans has little reciprocal impact on Pseudocalanus sp. population growth; hence asymmetries may occur in the in teraction of planktonic prey and predators. © 1986 IRL Press Limited.

The distribution of Mysidacea in the open ocean and near-bottom over slope regions in the northern North-east Atlantic Ocean during 1979

The vertical distribution of Mysidacea at one deep-water station in the Rockall Trough and at one deep-water station in the Porcupine Seabight is discussed together with near-bottom distributions of Mysidacea at two slope sites in the Seabight. Comparisons are made to investigate the effect of the shallowing of the sea-floor on mesopelagic and upper bathypelagic species. Of the 14 species in the survey area only six were relatively abundant. In one slope area which was intensively sampled the numerical abundance of some species tended to increase erratically with increased proximity to the bottom but other species seemed to be unaffected. It is thought that increased food availability near the bottom may be an important factor in causing increased abundance.

The distribution of Decapoda (Crustacea) in the open ocean and near-bottom over an adjacent slope in the northern North-east Atlantic Ocean during autumn 1979

The vertical distribution of Decapoda (Crustacea) at deep-water stations in the Rockall Trough and the Porcupine Seabight is discussed and compared to the near-bottom distribution of Decapoda on the continental slope of the Seabight. The vertical distribution of some species is unaffected by the shallowing of the sea floor in the slope area. Other species are found in much higher concentrations near-bottom over the slope than at similar depths at the adjacent deep-water stations and at least one species extends its lower vertical range. It is suggested that the increased food availability near-bottom may be the principal factor influencing aggregation.

Depositional fluxes of metals and phytoplankton in Windermere as measured by sediment traps1

Monthly sediment trap samples collected from a deep water station (42 m) in Windermere for a period of 1 year were analyzed for 0.5 M HCl extractable and total Fe, Mn, Al, Pb, Cu, Zn, total C, N, and total solids. Concomitant algal counts showed the year to be fairly typical in terms of the known sequence of phytoplankton.The annual depositional fluxes are compared with previously determined values based on sediment studies. The ratio of the annual trap to sediment flux for Al (≤ 1) indicates the absence of local sediment resuspension. The ratios for Fe, Pb, and Zn (1.1, 1.4, and 1.5, but not significantly &gt; 1) suggest some possible biogeochemical cycling at the sediment‐water interface. The deposition of Fe, Al, and Pb is predominantly associated with detrital material and occurs mainly during winter. The behavior of Zn is largely independent of other variables examined. The ratios for C (1.8), total solids (2.2), N (3.2), Mn (8.6), and Cu (9.5) are all significantly &gt; 1. The C and N values are thought to reflect the microbial breakdown of organic matter at the sediment surface and more particularly the preferential degradation of proteinaceous (i.e. N rich) material. The major influence on the deposition and recycling of Mn is its well known redox cycle involving oxidative precipitation and reductive remobilization. Cu undergoes an independent deposition‐remobilization cycle, probably related to uptake by diatoms and their rapid microbial decomposition after sedimentation.