Atlantic Off Research Articles

Composition, age, and provenance of organic matter in NW African dust over the Atlantic Ocean

Eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992/1993 in the Northeast Atlantic off Northwest Africa (18°N, 22°W) afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance. The sample was subjected to microscopic examination and bulk, elemental, isotopic, black carbon, and molecular (lignin, lipid) analyses. The bulk elemental composition and organic carbon (OC) content (1.02% dry weight) establishes the dust's origin as continental upper crust and is typical of dusts that emanate from West Africa. These data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the Sahara and Sahel regions (e.g., NASA TOMS aerosol index). Microscopic examination reveals that charcoal‐like particles from vegetation fires (“black carbon” (BC)) are the most abundant morphologically distinct organic components. Accelerator mass spectrometry (AMS) 14C analysis yields conventional 14C ages for bulk OC of 1260 ± 40 years and BC of 2070 ± 35 years. Taken together with corresponding stable carbon isotopic compositions (δ13C, −18.9 and −15.1‰, respectively), these results suggest the presence of biomass and burning residues derived from predominantly C4 vegetation that accumulated in soils over the late Holocene. Molecular‐level measurements are also consistent with this scenario. For example, lignin‐derived phenols in the dustfall sample indicate a significant contribution of angiosperm grass‐type tissue. The altered nature of the lignin suggests storage as residues in soils. Solvent extractable (lipid) constituents include a marked leaf wax type component with a molecular and stable carbon isotopic composition similar to those observed in surface marine sediments in this region. The hydrocarbon fraction contained some diesel‐type contamination but the n‐alkanes (C23–C33) retained a prominent odd/even distribution, with δ13C ranging from −26.7 to −28.5‰. The suite of even carbon numbered n‐alkanols (C22–C32) is 14C dated at 647 ± 150 years, with δ13C values ranging from −23.9 to −30.4‰. The long‐chain n‐alkanoic acids (C22–C32) exhibited δ13C values ranging from −22.6 to −27.4‰. These waxes are evidently a mixed signal derived from contemporary C3 and C4 vegetation and from ablated soils and desiccated lake sediments of middle to late Holocene age. This molecular approach shows promise as a tool for continental paleoenvironmental assessment, particularly with respect to past vegetation cover, regional aridity, and wind systems.

A new anascan cheilostome bryozoan from Icelandic deep waters and its uniserial colony growth pattern

A calloporid cheilostome - Daisyella bathyalis sp. nov. - is described from the deep sea of the NE Atlantic off Iceland. This is the first northern hemisphere record of Daisyella Gordon, 1989, a calloporid anascan previously recorded from the deep sea around New Zealand. The generic attribution of fossil and Recent uniserial calloporids is discussed and a provisional key presented. Analysis of the colony growth pattern in D. bathyalis reveals: (1) the presence, unusually for a non-malacostegan cheilostome, of a proximal bud originating from the ancestrula; (2) a typically cruciform budding pattern with most zooids producing distal and paired distolateral buds but with some developing additional buds proximolaterally; and (3) a variety of interactions between growing branches, including overgrowth, abutment, cessation of growth before contacting a neighbour, and growth into the pore windows of zooids from older branches.

A method for aerosol profiling in the lower troposphere with coupled scatter and meteorological rawindsondes and first data from the tropical Atlantic off Sahara

We developed a simple prototype balloonborne aerosol scattering profiler by coupling a small nephelometer with a meteorological sonde and we performed one sounding over Sal Island, Cape Verde, in February 1996 during a turbid episode of dust transport with an aerosol optical thickness (AOT) larger than 0.6 at 870 nm . We also monitored space and time variations in AOT with both Meteosat and a Sun photometer. This allows us to document for the first time the vertical distribution of aerosols during the typical winter situation of low-altitude transport of African dust in the trade winds of the tropical North Atlantic. We derive the vertical profile of aerosol extinction from side-scattering nephelometer measurements by applying corrections for aerosol optical properties. We find that most of the aerosol extinction occurs between about 600 and 1400 m in altitude in a layer of dry air above the atmospheric marine boundary layer (MBL). Our results suggest that about 90% of the dust is transported above the MBL. They confirm previous findings of well-structured African dust layers observed at north mid-latitudes with lidar systems.

Variability in coastal zone color scanner (CZCS) Chlorophyll imagery of ocean margin waters off the US East Coast

The purpose of our study was to use the 7.5-year coastal zone color scanner (CZCS) image time series (Oct. 1978 to July, 1986) to study general patterns in near-surface phytoplankton chlorophyll concentrations in ocean margin waters off the US East Coast. We defined 21 relatively large study areas (>100 km 2) within the MAB and SAB to set boundaries for averaging and subsequent analyses. Our objective was to partition the observed CZCS-derived chlorophyll concentration (CSAT, mg m −3) variability of these 21 study areas within three general categories based on time scale: daily (i.e. day–week), seasonal and interannual. An additional objective was to determine relations between the temporal patterns in the 21 study areas. All available CZCS imagery (more than 3500 scenes of Level 1 imagery, i.e. top-of-the-atmosphere radiance in satellite swath coordinates) covering some or all of our area of interest (northwest Atlantic off the US East Coast) were obtained at full resolution, processed to Level 2 (water-leaving radiance, chlorophyll concentration and other derived products in satellite swath coordinates) and mapped to two different study regions located off the southeast and northeast coasts of the US. Satellite-derived estimates of near-surface chlorophyll concentrations (CSAT) were extracted on a pixel-by-pixel basis from each of the 21 study areas (chosen based on oceanographic criteria) from each of the daily composite CSAT images. For each image and when satellite coverage permitted, CSAT values were averaged to yield a time series of daily mean values for each of the 21 study areas. We used three basic approaches to quantify temporal and spatial patterns in the 21 time series: (1) multiple linear correlation, (2) structure functions (semi-variance calculations) and (3) empirical orthogonal functions (EOF). Our results show: (1) a simple annual CSAT cycle common to all ocean margin waters along the entire US East Coast, consisting of a broad peak in CSAT concentration during winter and minimum concentrations during the summer; (2) relatively subtle across- and along-shelf changes to the timing and relative magnitude of the winter CSAT maxima and summer minima, as well as the presence of secondary seasonal peaks in some regions; (3) high variability at time scales of days to weeks superimposed on the seasonal pattern; (4) high spatial coherence of the seasonal component between all 21 study areas; (5) high coherence of the days-to-weeks component between adjacent study areas, but generally low or no coherence for study areas not adjacent or near each other; and (6) detectable, but low interannual variability.

Rock magnetism of sediments in the Angola-Namibia upwelling system with special reference to loss of magnetization after core recovery

A rock magnetic study was performed on sediment cores from four sites in the South Atlantic off the western coast of Africa, which were taken during the Ocean Drilling Program Leg 175 (Sites 1078, 1082, 1084, and 1085). The sites are within the Angola-Namibia upwelling system, and the sediments have a high total-organic-carbon content. Concentration of ferrimagnetic minerals at these sites is very low, and the magnetic susceptibility is dominated by paramagnetic and diamagnetic minerals. Severe and rapid loss of remanent magnetization occurred during storage of the cores, with less than 10% of the initial intensity remaining a few months after core recovery. The loss of magnetization may prevail in organic-rich sediments. Changes of magnetic properties with time were examined using samples that were kept frozen before the experiment. Hysteresis parameters and the ratio of ARM (anhysteretic remanent magnetization) to SIRM (saturation isothermal remanent magnetization) indicate increases in the average magnetic grain size with the decay of magnetization, which suggests preferential dissolution of finer magnetic minerals. Loss of low-coercivity magnetic minerals with time was estimated from the decrease of S ratios. Low-temperature magnetometry revealed the presence of magnetite in the sediments even after the completion of sulfate reduction. Magnetization attributable to magnetite decreased with the loss of magnetization. This suggests the transformation of magnetite into non-magnetic phases, which is consistent with the decrease of S ratios.

Sulfate reduction and methane oxidation in continental margin sediments influenced by irrigation (South-East Atlantic off Namibia)

Sulfate reduction rates (SRR) and concentrations of SO 4 2−, H 2S, pyrite sulfur, total sulfur, CH 4, and organic carbon were measured with high depth resolution through the entire length of the SO 4 2−-zone and well into the CH 4-zone at two continental slope stations in the eastern South Atlantic (Benguela upwelling area). The sediments were characterized by a high organic carbon content of approx. 7.5% at GeoB 3703 and 3.7% at GeoB 3714. At GeoB 3703 SO 4 2− concentrations decreased linearly with depth to about 40 μM at the sulfate-methane transition zone (SMT) at 3.5 m, while at GeoB 3714, SO 4 2− remained at sea water concentration in the top 2 m of the sediment and then decreased linearly to about 70 μM at the SMT at 6 m. Direct rate measurements of SRR ( 35SO 4 2−) showed that the highest SRR occurred within the surface 3–5 cm with peak rates of up to 20 and 7 nmol SO 4 2− cm −3 day −1 at GeoB 3703 and GeoB 3714, respectively. SRR decreased quasi-exponentially with depth at GeoB 3703 and the cumulative SRR over the length of the SO 4 2− zone resulted in an areal SRR (SRR area) of 1114–3493 μmol m −2 day −1 (median value: 2221 μmol m −2 day −1) at GeoB 3703 with more than 80% of the total sulfate reduction proceeding in the top 30 cm sediment. At GeoB 3714 SRR exhibited more scatter with a cumulative SRR area of 398–1983 μmol m −2 day −1 (median value: 1251 μmol m −2 day −1) and with >60% of the total sulfate reduction occurring below a depth of 30 cm due partially to a deeply buried zone of sulfate reduction located between 3 and 5 m depths. SRR peaks were also observed in SMT of both cores, ostensibly associated with methane oxidation, but with rates about 10 times lower than at the surface. Modeled SRR balanced both methane oxidation rates and measured SRR within the SMT, but severely underestimated by up to 89% the total SRR area that were obtained from direct measurements. Modeled and measured SRR were reconciled by including solute transport by irrigation described by a non-local pore water exchange function (α) which had values of up to 0.3 year −1 in the top sediment, and decreased exponentially to zero (i.e., no irrigation) at 2–3 meters (i.e., above SMT). These results suggested that co-existing sulfate reduction processes and linear SO 4 2−-gradients can be maintained by a non-local transport mechanism such as irrigation, by which pore water in tubes or burrows is exchanged with bottom waters by activities of tube-dwelling animals, or some similar physical transport phenomenon (i.e., bubble ebullition). Further support for an irrigation mechanism was found in the observations of open tubes of up to 8 mm (ID) at depths down to 6 m, which also contained fecal pellets, indicating that these tubes were or had been inhabited.

Comparison of independent proxies in the reconstruction of deep-water circulation in the South-East Atlantic off Namibia

Independent proxies were assessed in two Late Quaternary sediment cores from the eastern South Atlantic to compare deep-water changes during the last 400 kyr. Two cores were recovered from beneath North Atlantic Deep Water (NADW) at approximately 3 000 m depth. Late Quaternary presence of NADW is indicated by the Cibicidoides wuellerstorfi assemblage on the Walvis Ridge (Core GeoB 1214) and the Bulimina alazanensis assemblage on the Namibian continental slope (Core GeoB 1710). The propagation of NADW is exclusively observed during interglacials, with maximum factor loadings in Stages 1, 5, 7, 9 and 11. These maxima are consistent with peaks in kaolinite/chlorite ratios and maxima of poorly crystalline smectite in the clay-mineral record. Kaolinite and poorly crystalline smectite are products of intense chemical weathering. They are injected into the NADW at low latitudes, north of the study area, and advected south. Chlorite, which is stable under cold weathering regimes, is a characteristic mineral of water masses of southern origin. During glacial stages, it is advected north with Southern Component Water (SCW). Above the NADW/SCW depths, kaolinite/chlorite ratios vary only slightly without a significant glacial-interglacial pattern, as measured in a core (GeoB 1712) from 1 000 m deep on the same profile of the Namibian continental slope off Walvis Bay.

A long-finned specimen of Beryx decadactylus caught in the North-eastern Atlantic off Rockall

A long-finned specimen of Beryx decadactylus caught in the North-eastern Atlantic off Rockall

Temporal evolution of the tracer signal in the Deep Western Boundary Current, tropical Atlantic

Four World Ocean Circulation Experiment (WOCE) repeat cruises (October 1990 to March 1994) in the tropical Atlantic off Brazil are used to study the spatial and temporal evolution of the chlorofluorocarbon (CFC) (components CFC‐11 and CFC‐12) and tritium signal in the upper North Atlantic Deep Water (NADW). Its shallowest part, located in the tropical Atlantic around 1600‐m depth, is the shallow upper North Atlantic Deep Water (SUNADW). It is characterized by a distinct tracer maximum, which is presumably received through winter time convection in the subpolar North Atlantic. Here we discuss the tracer fields and the temporal evolution of the tracer signal of the SUNADW in the tropical Atlantic along two meridional sections at 44° and 35°W and two zonal sections at 5° and 10°S off Brazil. The spatial and temporal development of the tracer field in the tropical Atlantic as well as the correlation with hydrographic parameters show that the temporal tracer change being due to the arrival of “younger” water is disturbed by other processes. In particular, the impact of variable mixing and spreading pathways on the observed tracer variability in the SUNADW is evident in the observations.

Hydrodynamical dispersion of dredged materials sequestered on the abyssal seafloor

This paper addresses the potential dispersion by hydrodynamical processes of dredged material disposed on the abyssal seafloor off the east coast of the United States. The importance of the large-scale mean currents and of the eddy kinetic energy of the large-scale flow are discussed both for the selection of potential isolation sites and for determining the potential dispersion pattern from selected sites. These processes play a particularly significant role in the Atlantic off the east coast of the United States. There the potential isolation sites are close to a highly energetic region of the abyssal circulation, the North Atlantic Deep Western Boundary Current. The Naval Research Laboratory Layered Ocean Model was used to simulate large-scale ocean circulation in the North Atlantic Subtropical Gyre. Numerical experiments were conducted using monthly climatological forcing. High horizontal resolution, 1/16°, was required to achieve a realistic level of kinetic energy in the deep ocean and a realistic deep mean flow. The prognostic variables came to statistical equilibrium after 50 years of simulation. Then the mean currents and eddy kinetic energy were calculated based on 4 years of simulated data. The patterns and magnitudes of the currents and kinetic energy from the simulation agreed with the observations. The simulated pathways of the Deep Western Boundary Current including bifurcations and reconnections conformed to current concepts of its circulation. The recirculation gyres under the Gulf Stream were simulated, as were the eddies, meanders and high levels of eddy kinetic energy northeast of the New England Seamount chain. The decrease in eddy kinetic energy to the south over the Hatteras Abyssal Plain and the weak currents in the region of 25°N to 30°N along 70°W were also in agreement with observations and verified the results of the site selection model. Tracers were released into the 1° squares that were chosen by the NRL site selection model as the best candidates for isolation of dredged material. Modest quantities of the tracers were dispersed beyond the initial release areas and only trace amounts were mixed out of the bottom layer of the model. The results of this study indicate that if contaminated material was released into the water column from isolation sites in the region chosen by the site selection model it would probably be dispersed over a limited area. However, the dispersion of the tracers was anisotropic and varied spatially among the sites. This underscores the need to conduct both boundary layer-scale and gyre-scale numerical simulations and careful measurement programs at the sites chosen for initial evaluation of deep-ocean isolation of dredged material. The next step is to run mesoscale models that use the results from this study as boundary conditions and the results from plume models of contaminant release to determine the amount of contaminated material that might leak out of the boundary layer into the deep-ocean circulation system.

The spreading of Antarctic bottom water in the tropical Atlantic

Hydrographic and tracer [chlorofluorocarbon (CFC), component F11] data in the tropical Atlantic off Brazil taken in spring 1994 are used to describe the development of the water mass characteristics of Antarctic Bottom Water (AABW) between 10°S and 11°N. To compute the AABW transports, geostrophic computations and directly measured velocity fields are combined. Velocity profiles were measured with the Pegasus profiling system and an ADCP attached to the CTD. The F11 increase from 10°S to 11°N, mainly in the upper part of the tracer-poor AABW, reveals the mixing of AABW along its path with the overlying North Atlantic Deep Water, which carries a significant F11 signal in the equatorial Atlantic. While propagating north of 5°S, the AABW shifts to higher salinities at a given temperature. About one-third of the northward flowing AABW at 10°S (4.8 Sv) and at 5°S (4.7 Sv) west of about 31°30′W enters the Guiana Basin, mainly through the southern half of the Equatorial Channel at 35°W (1.5–1.8 Sv). The other part recirculates and some of it flows through the Romanche Fracture Zone into the eastern Atlantic. In the Guiana Basin, west of 40°W, the sloping topography and the strong, eastward flowing deep western boundary current might prevent the AABW from flowing west: thus it has to turn north at the eastern slope of the Ceara Rise (2.2 Sv). At 44°W, north of the Ceara Rise, AABW flows west in the interior of the basin in a main core near 7°15′N (1.9 Sv). A net return flow of about 0.5 Sv was found north of 8°43′N. A large fraction of the AABW (1.1 Sv) enters the eastern Atlantic through the Vema Fracture Zone, leaving only 0.3 Sv of AABW for the western Atlantic basins.

Oxygen isotopes versus CLIMAP (18 ka) temperatures: A comparison from the tropical Atlantic

Glacial-interglacial differences in δ 18 O values of Globigerinoides sacculifer have been mapped in the western and central tropical Atlantic using data from surface and core sediments. Glacial-interglacial differences in the western tropical Atlantic, if attributed to temperature changes only, are at odds with temperature reconstructions performed by CLIMAP. In the Ceara Rise region delta δ 18 O values exceeding 2‰ are recorded. They can only be partly attributed to changes in the precipitation-evaporation regime, i.e., higher salinities and 18 O-enriched precipitation. An additional cooling of 1–2 °C as compared to CLIMAP9s results is required to balance the δ 18 O record. Thus, temperature changes from glacial to modern times amount to 2– 3 °C in the tropical Atlantic off the northern coast of Brazil.

Interannual variabilty of the earth’s radiation budget: some regional studies

A detailed study is presented of the interannual variability of the Earth's radiation budget (ERB) at the top of the atmosphere in three equatorial regions: the western Pacific over Indonesia, the eastern Pacific off the west coast of South America and the eastern Atlantic off the west coast of Africa. The objective is to try and understand the cloud, surface and ERB interactions that occur in these areas, each of which shows a large interannual signal in the net radiation balance. The period studied extends from March 1979 through to April 1985, for which coincident ERB and cloud data are available from the Nimbus-7 ERB and Cloud Climatology data sets. This period encompasses the exceptional 1982–1983 ENSO as well as the 1984 Atlantic warming event. Additionally, sea-surface temperature data from the Global Ocean Surface Temperature Atlas (GOSTA) data set are used in combination with the ERB data to partition the outgoing longwave radiation into surface emission and greenhouse-effect components. The methodology involves examination of the time series of anomalies in all of these quantities together with the formulation of statistical relationships amongst them. These methods firstly allow the shortwave (SW) and longwave (LW) components of the ERB anomalies to be identified. The SW and LW anomalies are themselves seen to be made up of different components and, much like the net balance, are often the residuals of two competing effects. This is exemplified in the eastern Pacific and Atlantic regions, which both experienced periods of anomalously high SSTs. In such areas the SW anomaly can arise due to an imbalance between the cooling effect of increased high cloudiness and warming due to reduction of low level cloud, whilst the LW anomaly is composed of warming due to the increase in high cloud amount and cooling due to increased surface emission. The result is that anomalies in the net balance term, which is ultimately the most important with regard to climate variability, are seen to arise as a result of complex interactions between the atmosphere, cloudiness and surface. © 1997 the Royal Meteorologcal Society.

Interannual variabilty of the earth's radiation budget: some regional studies

A detailed study is presented of the interannual variability of the Earth's radiation budget (ERB) at the top of the atmosphere in three equatorial regions: the western Pacific over Indonesia, the eastern Pacific off the west coast of South America and the eastern Atlantic off the west coast of Africa. The objective is to try and understand the cloud, surface and ERB interactions that occur in these areas, each of which shows a large interannual signal in the net radiation balance. The period studied extends from March 1979 through to April 1985, for which coincident ERB and cloud data are available from the Nimbus-7 ERB and Cloud Climatology data sets. This period encompasses the exceptional 1982–1983 ENSO as well as the 1984 Atlantic warming event. Additionally, sea-surface temperature data from the Global Ocean Surface Temperature Atlas (GOSTA) data set are used in combination with the ERB data to partition the outgoing longwave radiation into surface emission and greenhouse-effect components. The methodology involves examination of the time series of anomalies in all of these quantities together with the formulation of statistical relationships amongst them. These methods firstly allow the shortwave (SW) and longwave (LW) components of the ERB anomalies to be identified. The SW and LW anomalies are themselves seen to be made up of different components and, much like the net balance, are often the residuals of two competing effects. This is exemplified in the eastern Pacific and Atlantic regions, which both experienced periods of anomalously high SSTs. In such areas the SW anomaly can arise due to an imbalance between the cooling effect of increased high cloudiness and warming due to reduction of low level cloud, whilst the LW anomaly is composed of warming due to the increase in high cloud amount and cooling due to increased surface emission. The result is that anomalies in the net balance term, which is ultimately the most important with regard to climate variability, are seen to arise as a result of complex interactions between the atmosphere, cloudiness and surface. © 1997 the Royal Meteorologcal Society.

New and regenerated production in the South Atlantic off Brazil

Rates of assimilation of NH 4 +, NO 3 − and urea were determined at eight oceanic stations in March 1994 and one inshore station in December 1994 in the South Atlantic off Brazil by performing 15N tracer experiments on microbial populations from two depths (50% and 1% of surface light penetration). Carbon uptake rates were determined by 14C tracer experiments at the same depths. At each sampling site temperature and salinity profiles were obtained and ambient nutrient and phytoplankton biomass were measured. Concentrations of chlorophyll a were < 0.3 μg 1 −1 in the oceanic region and varied from 0.12 to 1.41 μg 1 −1 in the inshore region. On average NO 3 − was the main form of nitrogen available for phytoplankton (64–86% of total nitrogen) in oceanic waters, while at the inshore station, NO 3 − represented less than 32% of total nitrogen supply. Nonetheless, primary production was dominated by regenerated production. Uptake of reduced forms of nitrogen represented on average 74% of total nitrogen utilized by phytoplankton in the oceanic region and 96% at the inshore station. In oceanic waters, the mean f-ratio ratio (contribution of new to total production) was 0.16 and 0.30 at subsurface (50% I o and bottom (1% I o) of the euphotic zone, respectively. At the inshore station the mean f-ratio was 0.05 at the subsurface and 0.10 at the bottom of the euphotic zone. Temperature and salinity measurements showed occasional injections of NO 3 − into the euphotic zone, resulting from the intrusion of the South Atlantic Central Water on the continental shelf. Episodic enrichment of the base of the euphotic zone with NO 3 − enhanced the contribution of new to total production and led to a maximum f-ratio of 0.86 in oceanic waters and 0.26 in coastal waters.

Summer circulation patterns related to the upper tropospheric vortices over the Tropical South Atlantic

Daily 200-hPa relative vorticity data have been used to study the dominant patterns related to the cyclonic vortices over the South Atlantic Ocean in the vicinities of northeast Brazil, during the 1980–1989 period. Reference modes were obtained through empirical orthogonal function (EOF) analysis of the 200-hPa filtered vorticity anomalies over northeast Brazil, considering all the southern hemisphere (SH) summers within the study period. The amplitude time series of the first reference mode, separately for each SH summer, was correlated with the corresponding filtered vorticity anomalies in a larger area extending from 20°N to 40°S and between 120°W and 20°W. The correlation patterns feature a wave-like structure along eastern South America, with three main centers: the first one, over the South Atlantic off the northeast Brazil coast, is associated with the cyclonic vortices; the second one, over eastern Brazil, represents the corresponding anomalously amplified ridges; and the third one, over southern Brazil/Uruguay, is related to the equatorward incursions of midlatitude upper level troughs. This wave-like pattern is consistent with the vortex formation mechanism suggested in previous works. Another wave-like pattern southwest-northeast oriented is evident over the tropical southeastern Pacific, for some years. The internannual variability of these patterns is discussed in this paper.

Role of the midnight sun: comparative growth of pelagic juvenile cod (Gadus morhua) from the Arcto-Norwegian and a Nova Scotian stock

Size-at-age of pelagic juvenile cod from the north-east Atlantic off northern Norway was approximately twice that of cod from the north-west Atlantic, off south-western Nova Scotia, Canada. Arcto-Norwegian cod (AN, 17-48 mm standard length, SL, 34-90 d post-hatch), were sampled in July 1988 with a capelin pelagic trawl, while south-west Nova cod (NAFO region 4X, 7-32 mm SL and 32-105 d post-hatch) were sampled in May-June 1985-1986 with a Tucker trawl. Growth over the previous 14 d, back-calculated from otolith daily growth increments was 0.71 mm d −1 and 0.33 mm d −1 for AN and 4X cod respectively. Within and between stocks, water temperature and zooplankton biomass were significantly correlated with the 14 d index (linear model, r 2 =0.42), but an ANCOVA model comparing the AN and 4X regions was highly significant (r 2 =0.71), indicating additional factors. Gear selection was not found to be responsible. While genetic factors could produce this result, there is 48% more time during May-July for visual feeding north of the 71°N latitude off Norway compared with 43°N off eastern Canada, using the light intensity threshold for larval cod feeding. Our hypothesis of light-limited feeding opportunity is consistent with a size- and temperature-dependent consumption model, and with aquaculture methods, as well as the necessity for fast growth in the short northern summer for over-winter survival.

Marine Pollution: Science Intrudes on Brent Spar Saga

London—This time last year, the environmental group Greenpeace made headlines when its activists boarded an oil storage buoy called the Brent Spar and temporarily halted the Shell Oil company9s plan to scuttle it in the deep Atlantic off the west coast of Scotland. Greenpeace claimed that the sunken rig would pose a toxic threat. Last week, a panel of scientists passed judgment on Greenpeace9s claims—and both Greenpeace and Shell are claiming vindication. The panel concluded that Brent Spar, by itself, would have a very small impact on the marine environment, but it pointed out that repeated dumping of similar structures might have a large cumulative impact.

Science Intrudes on Brent Spar Saga

London—This time last year, the environmental group Greenpeace made headlines when its activists boarded an oil storage buoy called the Brent Spar and temporarily halted the Shell Oil company's plan to scuttle it in the deep Atlantic off the west coast of Scotland. Greenpeace claimed that the sunken rig would pose a toxic threat. Last week, a panel of scientists passed judgment on Greenpeace's claims—and both Greenpeace and Shell are claiming vindication. The panel concluded that Brent Spar, by itself, would have a very small impact on the marine environment, but it pointed out that repeated dumping of similar structures might have a large cumulative impact.

Revision of the family Pterobothriidae Pintner, 1931 (Cestoda : Trypanorhyncha)

The trypanorhynch cestode family Pterobothriidae Pintner, 1931 is revised. Valid species of the genus Pterobothrium Diesing, 1850 are defined. Ten species of pterobothriid cestodes, including five new species, are described from elasmobranchs taken in waters off Australia, the Indian Ocean, the Atlantic coast of North America, and in the S Atlantic off Senegal, West Africa. Six of the species, P. acanthotruncatum, P. lintoni, P. lesteri, sp. nov., P. pearsoni, P. southwelli, sp. nov., and P. australiense, sp. nov., are described from fishes in Australian waters and the Indian Ocean. The armature of Pterobothrium heteracanthum Diesing, 1850 is redescribed using light and scanning electron microscopy. New intermediate hosts, locality records, and synonyms are provided for P. crassicolle Diesing, 1850 from Atlantic coastal waters of North and South America. Details of the entire armature of Pterobothriurn crassicolle Diesing, 1850 from Micropogonias furnieri (Desmarest) from Rio de Janiero are included. Two new species of Pterobothrium, P. kingstoni, sp. nov., and P. senegalense, sp. nov., are described from dasyatid rays in waters of the Atlantic Ocean. P. kingstoni, sp. nov., from dasyatid rays taken in coastal waters off New England and Chesapeake Bay, Virginia, is distinguished by the presence of a wide band of hooks on the external face of the tentacle, a single row of 4 intercalary hooks, absence of a basal swelling and special armature and by a transverse base on hooks 4(4′) of each principal metabasal row. Pterobothrium senegalense, sp. nov., is described from Dasyatis centroura from Gorbe, Senegal, West Africa, and is distinguished by 3 intercalary rows of hooks that run over onto the external tentacular face but never occupy the midline, by the size and position of hooks in the first intercalary row, and position of the first intercalary row relative to the second and third rows. Pterobothrium southwelli, sp. nov., P. lesteri, sp. nov., and P. pearsoni are described from teleosts in the Indian Ocean. P. southwelli, sp. nov., is distinguished from congeners by a distinctive basal armature and prominent band of hooks on the external surface, a single intercalary row, uncinate hooks l(1′) in all metabasal principal rows, and absence of dentate hooks from the metabasal rows. P. lesteri, sp. nov., is unique in the combination of a basal row of 3 small hooks, a band of hooks, a single intercalary row of 3–4 hooks and in the possession of hooks 4(4′) with dentate tips and hooks 5(5′) with filamentous tips. P. pearsoni differs in possessing a band of hooks and 2 rows of intercalary hooks per principal row, basal armature restricted to the external surface, and uncinate hooks l(1′) combined with dentate hooks 4(4′)–5(5′) in all metabasal rows. Three species from Australian waters, P. lintoni (MacCallum, 1916), P. australiense, sp. nov., and P. acanthotruncatum, lack a well-developed band of hooks on the external face of the metabasal armature. P. lintoni (MacCallum, 1916), the senior synonymn of P. malleum MacCallum, 1916) and P. dasybati Yamaguti, 1934, is described from types and compared with new specimens from the Woods Hole region (USA) and Australia. New host records for adults and plerocerci of P. lintoni are reported from Australian waters off Queensland and South Australia. Pterobothrium chaeturichthydis (Yamaguti, 1952) is considered a synonym of P. lintoni. P. australiense, sp. nov., from Pristis zijsron near Townville, Queensland, differs from congeners in the possession of slender falcate hooks 1(1′), notched tips of hooks 5(5′), a single intercalary row of 3 hooks, and total absence of a band of hooks on the external tentacular face. P. australiense, sp. nov., is similar to P. acanthotruncatum but has falcate hooks at the start of each principal row, lacks the pairs of satellite microhooks on the external face adjacent to the principal rows and possesses a band of microhooks in the basal region of the external face of the tentacle. P. acanthotruncatum is reported from new hosts in Australia and from Sri Lanka and India. A key to the 12 currently recognised species of pterobothriids is provided.