Deep Sea Research Part I Oceanographic Research Papers

Published by Elsevier
Online ISSN: 0967-0637
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Article
The inner ear structure of Antimora rostrata and its coupling to the swim bladder were analyzed and compared with the inner ears of several shallow-water species that also have similar coupling. The inner ear of Antimora has a long saccular otolith and sensory epithelium as compared to many other fishes. Some parts of the membranous labyrinth are thick and rigid, while other parts are thinner but attached tightly to the bony capsule. The partially rigid membranous labyrinth, along with its intimate connection to the swim bladder, may help the inner ear follow the sound oscillations from the swim bladder with better precision than would occur in a less rigid inner ear. In addition, the saccular sensory epithelium has an elaborate structure and an anterior enlargement that may be correlated with increased hearing sensitivity. Some of the features in the inner ear of Antimora may reflect the functional specialization of deep-water living and support the hypothesis that there is enhanced inner ear sensitivity in some deep-sea fishes.
 
Article
E.m.f. measurements were made over the temperature range 273.15–318.15 K, and at five salinities from 20 to 40, using the cellwhere p°=101.325 kPa, and BH+ and B are the conjugate acid–base pair of 2-amino-2hydroxymethyl-1,3-propanediol (‘tris’) – each present at a concentration of 0.04 mol kg-1. The results were used to assign pH values based on the ‘total’ hydrogen ion scale to such buffer solutions based on this acid–base pair. Additional measurements were made over a range of buffer concentrations at a salinity of 35; these were used to calculate the stoichiometric (ionic medium) dissociation constant for ‘tris–H+’ in synthetic sea water.
 
Article
The analysis of 48 bottom trawl collections from the Catalan Sea below a depth of 1000 m has allowed the identification of two distinct demersal fish assemblages, occurring on the middle and lower slope. The Middle Slope Assemblage (MSA) and Lower Slope Assemblage (LSA), restricted to the middle (1000–1425 m) and lower (1425–2250 m) slope, respectively, each consist of two groups with distinct structures. While one group is relatively homogeneous, the other can be considered as comprising a faunal transition. Each assemblage is dominated by species possessing very different characteristics. The preponderance of middle and large size fish with high energy requirements in the MSA is replaced, in the LSA, by smaller and more passive species with lower energy requirements. These differences are reflected in a series of ecological parameters such as abundance, biomass, mean fish weight, species richness and mean species richness. A pronounced decrease in the value of these parameters is generally seen with increasing depth, reflecting the increasingly oligotrophic conditions. Furthermore, the highly stable environmental conditions of the western Mediterranean (where water temperature and salinity rarely change below a depth of 150 m), suggest that the observed zonations may be determined by biological factors. It is possible to relate the observed faunistic changes with the vertical distribution of mesopelagic organisms. These organisms play a fundamental role in the feeding ecology of demersal fish species of the slope, either directly as prey or indirectly by enriching the sediments, and thus determining the distribution of sedimentivorous invertebrate species.
 
Article
The precision of spectrophotometric measurements of indicator absorbance ratios is sufficient to allow evaluation of small isotopically induced differences in the dissociation constant of boric acid (KB). The quotient of 11KB and 10KB, obtained using isotopically ⩾99% pure borate/boric acid buffers, provides an equilibrium constant for the reaction 10B(OH)3+11B(OH)4−⇔11B(OH)3+10B(OH)4− which heretofore had not been experimentally determined. Previous theoretical and semi-empirical evaluations of this equilibrium, which is important for assessments of the paleo-pH of seawater and the paleo-pCO2 of the atmosphere, have yielded constants, 11–10KB=10KB/11KB, that have ranged between 1.0194 and approximately 1.033. The experimentally determined value 11–10KB=1.0285±0.0016 (mean±95% confidence interval) obtained at 25 °C and 0.63 molal (mol kg−1 H2O) ionic strength is in much better agreement with recent theoretical assessments of 11–10KB that have ranged between 1.026 and 1.033, than the much-cited original estimate (1.0194) of Kakihana et al. (1977) [Fundamental studies on the ion-exchange separation of boron isotopes. Bulletin of Chemical Society of Japan 50, 158–163]. Since the activity quotient for the fractionation reaction is almost equal to unity, it is expected that the 11–10KB value obtained in this study will be applicable over a wide range of solution compositions and ionic strengths.
 
Article
Vertical and surface-water distributions of 10Be and 9Be in the South Atlantic Ocean were studied. The major input of 9Be to the surface waters of the region is from the partial dissolution of eolian dusts, with the extent of the dissolution being about seven times that of aluminum from the dust particles. The gradients in surface-water 10Be concentrations appear to reflect the magnitude of the local precipitation. The imprinting of the surface water signals onto the deep water masses appears rapid, particularly in regions of enhanced productivity. Bottom waters of Antarctic origin have characteristic isotope signatures that can be traced along their advective route into the Guinea Basin of the eastern Atlantic. Elevated 9Be concentrations in the Angola Basin are indicative of diagenetic input in this region of restricted circulation. The corresponding anomalous 10Be in the bottom waters indicates historically lower surface-water 10Be/9Be ratios in the region, perhaps as a result of the further southward penetration of the Inter-Tropical Convergence Zone at those times.The budgets of 10Be and 9Be in the South Atlantic were estimated. The results show that crossequator transport of 10Be and 9Be from the North Atlantic is 0.3 ± 1023 atoms/year and 5.7 ±106 mol/year, respectively, accounting for less than 5% of 10Be and about 10% of 9Be entering the North Atlantic. There is a net export across 50°S to the Antarctic/Indian/Pacific Oceans of 0.9 ±1023 atoms/year for 10Be and 7.5 ± 106 mol/year for 9Be. Using 10Be as a tracer, we evaluate accumulation rates of lithogenic minerals to be 1.7 ± 1014 g/year in the North Atlantic and 4.8 ± 1013 g/year in the South Atlantic. While the North Atlantic rate agrees with the observed eolian dust input, the estimated lithogenic flux in the South Atlantic is about twice the eolian input, suggesting that the riverine input of 9Be to the open ocean may become non-negligible in areas of low eolian dust flux.
 
Article
The accumulation of man-made chlorofluorocarbons (CFCs) in subsurface water masses is directly related to their formation rate, and the water mass formation rate can be calculated from its CFC inventory. CFC-11 inventories between 65°N and 10°S in the Atlantic Ocean have been calculated for Eighteen Degree Water (EDW) and the components of North Atlantic Deep Water (NADW) from data collected primarily between 1996 and 1998 as part of the World Ocean Circulation Experiment (WOCE). CFC-11 inventories for individual water masses are 5.4 million moles for EDW, 10.5 million moles for Upper Labrador Sea Water (ULSW) (4.6 million moles south of 42°N), 23.4 million moles for Classical Labrador Sea Water (CLSW), 10.4 million moles for Iceland-Scotland Overflow Water (ISOW), and 8.3 million moles for Denmark Strait Overflow Water (DSOW). The estimated error for these inventories is about ±10%. The sum of the NADW components (ULSW, CLSW, ISOW, DSOW) is 53.2 million moles which is about half of the total CFC-11 inventory, 103.8 million moles, in the North Atlantic Ocean. Maps of water column inventories illustrate the formation mechanisms and spreading pathways within these water masses. The inventories directly reflect the input of newly formed water in the North Atlantic over the time scale of the CFC transient, about 3 decades. The interior regions of the North Atlantic contain most (75–80%) of the CFC-11 inventory in NADW indicating strong recirculation and mixing of newly formed NADW from the DWBC into the interior with a time scale of 2–3 decades. Average water mass formation rates between 1970 and 1997 are: 3.3 Sv for EDW, 3.5 Sv for ULSW (2.0 Sv from the central Labrador Sea and 1.5 Sv from the southern Labrador Sea), 8.2 Sv for CLSW, 5.7 Sv for ISOW, and 2.2 Sv for DSOW. Estimated errors are ±20% for CLSW and ±16% for the other water masses. The total for NADW, which forms the deep limb of the North Atlantic Meridional Overturning Circulation, is 19.6 Sv. An extensive test of the effects of temporal variability on the average formation rate calculated from the CFC inventory indicates that the error introduced by the assumption of a constant water mass formation rate is no greater than 15% for CLSW and 10% for the other water masses.
 
Article
The solubilities of dilute mixtures of the trichlorotrifluorethane CFC-113 in pure water and seawater over the temperature range −0.89 to 39.59°C were measured by gas chromatography. The data were fitted by an equation in temperature and salinity of the form used previously to describe the solubilities of other gases. The deviation from the fitted curve is ±1.5% and the average precision of replicate measurements at each temperature and salinity is ∼1.2%.
 
Article
Polysaccharide-specific staining techniques reveal the existence and high abundance of a class of large, discrete, transparent particles in seawater and diatom cultures formed from dissolved exopolymers exuded by phytoplankton and bacteria. Transparent exopolymer particles (TEP), ranged from 28 to 5000 particles ml−1 and 3 to 100s μm in longest dimension at five coastal stations off California. A high percentage of seemingly free-living bacteria (28–68%) were attached to these transparent sheets and films, suggesting that they may alter the distributions and microenvironments of marine microbes in nature. Preliminary coagulation experiments demonstrated that TEP are major agents in the aggregation of diatoms and in the formation of marine snow. The existence of microbial exudates acting as large, discrete particles, rather than as dissolved molecules or as coating on other particles, suggests that the transformation of dissolved organic matter into particulate form in the sea can occur via a rapid abiotic pathway as well as through conventional microbial uptake. The existence of these particles has far reaching implications for food web structure, microbial processes, carbon cycling and particulate flux in the ocean.
 
Article
Methane oxidation rates were measured in samples from a deep-sea lateral hydrothermal plume generated from a vent field on the Endeavour Segment of the Juan de Fuca Ridge. Specific CH4 oxidation rates of up to 0.15 day−1, corresponding to turnover times on the order of 1 week, are the highest such rates so far reported for the water column of any marine environment. Specific methane oxidation rates within the plume were found to be highest at distances of 2–5 k downplume from the vent field of origin. Ambient CH4 oxidation rates were highest in the lateral plume immediately above the vent field where CH4 concentrations were maximal. Methane oxidation rates appeared to be sufficient to account for the majority of CH4 loss in the plume which could not be attributed to dilution. Oxidation of vent-derived CH4 within the lateral plume can contribute an amount of organic carbon equivalent to up to 150% of that reaching the depth of the plume from surface primary production, suggesting that microbial CH4 oxidation can have a significant impact on local deep-sea productivity in the immediate vicinity of oceanic spreading centers.
 
Article
Anthropogenic 129I (t1/2=15.7 My) discharged by the nuclear fuel reprocessing facilities at Sellafield (UK) and La Hague (France) is a promising tracer of physical and biogeochemical processes in the North Atlantic and Arctic Oceans. To improve understanding of its releases and dispersal, 129I was measured in archived seawater samples that had been collected as part of previous tracer studies, thus allowing direct comparison of 129I with other anthropogenic radionuclides. A sample collected in the eastern subtropical North Atlantic in 1969 was selected in order to directly measure the impact of weapons-fallout 129I in the oceans. The measured 129I/127I ratio of the sample is 0.53±0.08×10-10 (0.53±0.08IU: 1IU≡129I/127I=10-10), compared to the pre-anthropogenic ratio of ∼10-12 (0.01 IU). The ratio of 129I to 137Cs is 2.0±0.6 (atom ratio), 1.6±0.6 when corrected for 7 yr of radioactive decay from the bomb-input peak. This observed ratio is ten times higher than predicted from fission yields, possibly reflecting the greater volatility of iodine relative to cesium. 129I/137Cs ratios in Scottish and Norwegian Coastal waters, sampled in 1976 and 1978, are in good agreement with predictions based on the available release data. Reprocessing 129I is clearly seen in the northern Greenland Sea (>6 IU) and in Denmark Straits Overflow Water (1.4 IU) in samples collected during the TTO/NAS program in 1981. The strength of the tracer signal in the overflow water – the ratio of the concentration in the overflow core to its minimum value in the station profile – is approximately four times higher for 129I than for the other tracers measured (137Cs, 90Sr, and 3H).
 
Article
Levels of 137Cs and 129I measured in 1993 in the Barents and Kara Seas and western Arctic Ocean were in excess of fallout levels, owing mainly to inputs of Atlantic-origin water contaminated by discharges from the Sellafield (U.K.) and La Hague (France) nuclear reprocessing plants. A pronounced concentration gradient in 129I extended across the Arctic Ocean, with levels in surface mixed layer water decreasing from 100–200×107 at/l in the Barents and Kara Seas to 80×107 at/l in the Makarov Basin and then to <3×107 at/l in the Canada Basin. Elevated levels of 129I and 137Cs were measured in halocline and Atlantic layer water in the Makarov and Canada Basins, reflecting the labelling of these water masses by discharges from the European reprocessing plants. In contrast, surface mixed layer and upper halocline water layers in the Canada Basin were characterized by relatively low 129I and 137Cs signals associated with Pacific-origin water contaminated mainly by nuclear weapons fallout. A “front” between Atlantic-origin and Pacific-origin water located over the Mendeleyev Ridge was delineated by changes of an order of magnitude in the 129I and 137Cs concentrations. The 129I and 137Cs input functions for Atlantic water entering the Arctic Ocean were estimated from fallout and Chernobyl inputs and reconstructed discharge records for Sellafield and La Hague using transfer factors for a reference location at 60°N in the Norwegian Coastal Current. 129I/137Cs tracer measurements were then used in a simple mixing/advection model to estimate “transit times” to sampling locations in the Arctic Ocean. By 1993, the dynamic range of the model was sufficient to establish transit times of 1–2 yr from the Norwegian Coastal Current to the southern Barents Sea, 2–4 yr to the western Kara Sea and 5–6 yr to the deep waters (>330 m water depth) of the Novaya Zemlya Trough. Although the dynamic range of the model in 1993 was sufficient only to establish a lower limit of 6 yr for transit to the Makarov and Canada Basins, the continuing increase in 129I releases from La Hague will have expanded the transit time range of the 129I/137Cs tracer model to 10 yr by 1997.
 
Article
A test of the hypothesis that photosynthetic fractionation, εp, is affected by variations in diffusive transport of CO2aq into phytoplankton cells was conducted in Monterey Bay over a 4 yr period. Counter to predictions based on diffusive CO2aq transport were observations of very weak to non-existent correlations between εp and: (i) CO2aq concentration, (ii) mean phytoplankton community growth rate, (iii) cell size, (iv) carbon demand, or (v) [CO2aq]-normalized functions of ii–iv. The preceding decoupling between εp and CO2 supply/demand and the low fractionation associated with carboxylation (εf) implied in this study are consistent with several recent reports of active bicarbonate uptake and utilization in similar coastal environments. If the frequent low εp seen here is indicative of such carbon acquisition, it suggests that active bicarbonate transport in situ (1) may not be restricted to diatoms, (2) can be present even in high-[CO2aq] low-growth-rate waters, (3) may be a common feature of low-latitude upwelling environments, and (4) may help explain the common dichotomy between marine planktonic and terrestrial C3 autotrophs.
 
Article
To improve our understanding of the environmental constraints exerted on vent fauna, we investigated sulphide chemistry in the habitats of Riftia pachyptila and Alvinella pompejana, at the Genesis and Elsa EPR 13°N sites. Temperature, pH and sulphide measurement series were acquired in situ, around the organisms, from the submersible Nautile. Hot fluid samples were also collected to evaluate end-member composition at these sites. Under the assumption of conservative mixing, pH, total sulphide concentration and sulphide speciation gradients in relation to temperature were modelled. From the comparison of measured and calculated concentrations, deviation from conservative behaviour was highlighted for total sulphide versus temperature. While the observed sulphide depletion around tubeworms suggests significant subsurface removal or biological consumption, the apparent sulphide enrichment in the alvinellid environment may reveal either conductive cooling of diffusing fluids or a secondary sulphide source. The calculated sulphide speciation appears to be contrasted at the two sites studied. Because of the low iron content in Genesis fluid, iron sulphide would not constitute a dominant sulphide species and the toxic H2S form would be predominant in the mixing zone. By contrast, iron is expected to play a dominant role in sulphide speciation at the Elsa site where the end-member is iron rich. With respect to sulphide, the conditions encountered in the different habitats considered in this study are strongly contrasted. A low fluid flux was observed in the R. pachyptila habitat, contrasting with previous ideas, and suggests that sulphide availability could be a major limiting factor. Particularly, the bioavailable HS− form is expected to vary weakly along the mixing gradient. In contrast, sulphide in the A. pompejana environment is shown to be particularly high, about one order of magnitude higher than observed for other Eastern Pacific alvinellids. At Genesis, because of the acidic pH and low iron conditions encountered, exposure to high levels of toxic sulphide is expected. A. pompejana thus appears to be particularly tolerant to such toxic conditions, but, as previously suggested, less severe conditions may also be found when iron is rich enough in the medium to dominate sulphide chemistry.
 
Article
We have investigated the geochemical flux to sediment traps deployed close to the Totem vent site, 13°N EPR. An important emphasis has been to investigate what proportion of this settling flux derives from direct co-precipitation of vent-fluid material as polymetallic sulphides and what proportion is in the form of Fe oxyhydroxide material which not only co-precipitates vent-fluid metals but can also scavenge dissolved material from seawater. Mass fluxes and major element compositions (Fe, S, Al, Mn, CaCO3 and Corg) for our near vent samples compare well with results from previously reported Pacific hydrothermal sediment trap studies, both at this site and on the Endeavour Ridge. Our samples record large fluxes of Cu, Zn and Pb, as well as V and P, all of which are in excess over typical open-ocean trap values. If P and V are transported to the traps as sinking Fe-oxyhydroxide material from the neutrally buoyant plume, we calculate that 10–20% of the Fe entering the near vent traps occurs as oxidised material with the remaining 80–90% being supplied by polymetallic sulphides. Shale-normalised REE distribution patterns for near-vent trap samples are similar to those for local vent fluids and sulphidic sediments. Detailed mass balance calculations, however, reveal evidence for additional input from hydrothermal Fe-oxyhydroxide material with a scavenged REE composition that is less “evolved” than that reported for local neutrally buoyant plume particles. U fluxes into the near vent traps are high and consistent with uptake by sulphides. 210Pb fluxes are also high and appear dominated by co-precipitation direct from vent-fluids as Pb-sulphides. In contrast, Fe-oxyhydroxide scavenging from seawater can account for the entire 230Th and 232Th fluxes reported. If the scavenging processes identified here were similarly active in neutrally buoyant plumes, we would predict hydrothermal scavenging to impact ocean biogeochemical cycles significantly, e.g. causing removal of ca. 10% of the dissolved 230Th production from the deep water column, out to a distance of ca. 10–100 km off-axis, along the entire 60,000 km global ridge-crest.
 
Article
The contributions of marine and terrigenous organic carbon in modern organic sediments from the equatorial East Atlantic was quantified, based on the stable carbon isotope composition standardized for sea surface temperature and water depth. In our binary σ¹³C mixing model, the marine end member −26 ∞ is redefined at 23°C and 0 m water depth and the terrigenous end member, independent of SST and water depth, at − 26 ∞. Terrigenous carbon fractions account for more than 60% of total organic carbon (TOC) on the shelf off East Liberia and the Ivory Coast and off Gabon. On the upper slope the land-derived fraction decreases in general to less than 20% of the high TOC concentrations, which can reach 3.5 wt%.
 
Article
Compositions of ultrafiltered dissolved organic matter (UDOM) and ultrafiltered particulate organic matter (UPOM) were characterized in samples collected from a depth profile (20–4000 m) in the North Pacific at Station Aloha. 13C Nuclear Magnetic Resonance (NMR) analyses together with δ13C values, carbon/nitrogen (C/N) ratios and molecular characterizations of UDOM and UPOM indicate different bulk chemical compositions and sources for these two size fractions. Carbohydrates and amino acids are the major biomolecules present in UDOM and UPOM. At all depths, UPOM had higher amino acid and lower carbohydrate contents compared to UDOM. UDOM and UPOM samples showed a decrease in the relative contribution of carbohydrates to the total organic carbon with increasing depth, whereas the contributions of lipids increased. Amino acids did not show any clear depth trends for UDOM, but decreased in UPOM. The compositional trends with depth indicate that selective degradation processes, which preferentially remineralize reactive biomolecules such as carbohydrates, affect UDOM and UPOM compositions in the water column.Molecular analyses of carbohydrates and amino acids characterized ∼9% of the C in UDOM and ∼28% of the C in UPOM. Although a relatively small proportion of the total C was characterizable with molecular analyses, the depth trends and the ratio of amino acids to carbohydrates in UPOM and UDOM were similar to those determined by 13C NMR. This suggests that the organic matter fraction characterized by molecular analyses is representative of the molecularly uncharacterized fraction of organic matter. It is postulated that the molecularly uncharacterized fraction is encapsulated or shielded by a hydrolysis-resistant matrix or the individual amino acid and sugar units have been altered to form a chemical entity unrecognizable by the molecular analyses.
 
Article
The relation of microbial biomass and extracellular enzymatic activities to substrate availability was investigated for the first time in deep-sea sediments of the Eastern Mediterranean basin, along a transect from the Gulf of Taranto (Italy) to the coasts of Egypt and Israel. Chloroplastic pigment equivalents (CPE), indicating the input of phytodetritus to the sediments, decreased from the shallow coastal stations around 200m water depth (4–6 μg cm−2) to the oligotrophic abyssal basins of the Ionian and Levantine Seas around 3000m water depth (0.1–1 μg cm−2). However, at two stations in the Hellenic Trench, at 4620 m and 3750 m, as well as in the Pliny Trench south of Crete at 4260 m, strikingly high accumulations of CPE above 10 μg cm−2 were recorded. The presence of relatively fresh detritus at these depths can only be explained by lateral flux of organic material down the steep slopes and its capture in the adjacent trenches. Consistently, microbial activity potentials in the trenches exceeded those at the abyssal plain by an order of magnitude. Microbial biomass was about 0.1 mg C cm −2 in the trenches and the coastal stations, compared to less than 0.05 mg C cm −2 at the abyssal plain stations. The increased availability of a potential food resource appears to have stimulated the deep-sea microbial assemblages to the same extent as those of shallower stations, suggesting that microbial activity in deep-sea sediments is mainly regulated by the level of food supply.
 
Article
Recent studies have revealed that lateral transport and focusing of particles strongly influences the depositional patterns of organic matter in marine sediments. Transport can occur in the water column prior to initial deposition or following sediment re-suspension. In both cases, fine-grained particles and organic-rich aggregates are more susceptible to lateral transport than coarse-grained particles (e.g., foraminiferal tests) because of the slower sinking velocities of the former. This may lead to spatial and, in the case of redistribution of re-suspended sediments, temporal decoupling of organic matter from coarser sediment constituents. Prior studies from the Argentine Basin have yielded evidence that suspended particles are displaced significant distances (100–1000 km) northward and downslope by strong surface and/or bottom currents. These transport processes result in anomalously cold alkenone-derived sea-surface temperature (SST) estimates (up to 6 °C colder than measured SST) and in the presence of frustules of Antarctic diatom species in surface sediments from this area. Here we examine advective transport processes through combined measurements of compound-specific radiocarbon ages of marine phytoplankton-derived biomarkers (alkenones) from core tops and excess 230Th (230Thxs)-derived focusing factors for late Holocene sediments from the Argentine Basin. On the continental slope, we observe 230Thxs-based focusing factors of 1.4–3.2 at sites where alkenone-based SST estimates were 4–6 °C colder than measured values. In contrast, alkenone radiocarbon data suggest coeval deposition of marine biomarkers and planktic foraminifera, as alkenones in core tops were younger than, or similar in age to, foraminifera. We therefore infer that the transport processes leading to the lateral displacement of these sediment components are rapid, and hence probably occur in the upper water column (<1500 m).
 
Article
A 153 kHz narrowband acoustic Doppler current profiler (ADCP) was used to measure volume backscattering strength (Sv) during a deepwater oceanographic survey of cetacean and seabird habitat in the northeastern Gulf of Mexico. Sv was positively related to zooplankton and micronekton biomass (wet displacement volume) in ‘sea-truth’ net hauls made with a 1 m2 Multiple Opening-Closing Net Environmental Sensing System (MOCNESS). A subset of these MOCNESS tows was used to explore the relationship between the numerical densities of various taxonomic categories of zooplankton and the ADCP backscatter signal. Crustaceans, small fish, and fragments of non-gas-bearing siphonophores in the net samples all showed significant, positive correlations with the acoustic signal, while other types of gelatinous zooplankton, pteropod and atlantid molluscs, and gas-filled siphonophore floats showed no significant correlation with Sv. Previously published acoustic scattering models for zooplankton were used to calculate expected scattering for several general zooplankton types and sizes for comparison with the field data. Even though gelatinous material often made up a large fraction of the total biomass, crustaceans, small fish, and pteropods were most likely the important scatterers. Since only crustacean and small fish densities were significantly correlated with Sv, it is suggested that Sv at 153 kHz can be used as a relative proxy for the abundance of these organisms in the Gulf of Mexico.
 
Article
Temporal changes in δ15N values of sinking particles collected with sediment traps in the Benguela upwelling regime off southwest Africa mirrored variations in the input of inorganic nitrogen to the surface water. Reductions in δ15N (to as low as 2.5‰) corresponded to low sea surface temperatures during austral spring and late austral autumn/early winter, indicating increased nitrate availability due to the presence of recently upwelled water. High particulate fluxes accompanied the low δ15N values and sea surface temperatures, reflecting increased productivity, fueled by the upwelled nutrients. High δ15N values (up to 13.1‰) coincided with high sea surface temperatures and low particle fluxes. In this area, the seaward extension of upwelling filaments, which usually occurs twice yearly, brings nutrient-rich water to the euphotic zone and leads to elevated productivity and relatively lower δ15N values of the particulate nitrogen. Satellite images of ocean chlorophyll show that productivity variations coincide with δ15N changes. The observed isotopic pattern does not appear to have been caused by variations in the species composition of the phytoplankton assemblage. Calculations based on δ15N of the sinking particulate nitrogen show that the surface nitrate pool was more depleted during late austral summer/early fall and mid-winter and that supply exceeded demand during the intense spring bloom and in late austral fall. The main uncertainty associated with these estimates is the effect of diagenesis on δ15N and possible variability in preservation of the isotope signal between periods of high and low particle flux.
 
Article
The traditionally used “Redfield” formula for the average composition of the organic tissue of marine phytoplankton, (CH2O)106(NH3)16(H3PO4), is found to be in disagreement with observations regarding its oxygen and hydrogen content. Based on considerations of metabolite composition and various observations, a new formula is proposed, C106H175O42N16P, which should be a better approximation to mean algal elemental composition. Estimates suggest that Redfield's algal Corg/N/P ratio of 106/16/1 is consistent with oxidation ratios between 140 and 160, rather than the traditional value of 138.
 
Article
We investigated amino acids and pigments in particles settling through the water column of the Southern Ocean and showed that spatial and temporal differences in phytoplankton source and consumer population influence sinking particle composition. Sediment traps were deployed along 170°W from November 1996 to March 1998 as part of the United States Joint Global Ocean Flux Study (US JGOFS) Antarctic Environment Southern Ocean Process Study (AESOPS) program. Peak fluxes of amino acids and pigments occurred during austral spring and summer (November–April) and were highest in the Antarctic Circumpolar Current (ACC). Compositional changes in pigments and total hydrolyzed amino acids demonstrate how the source of sinking particles varies with latitude and suggest that sinking material was most degraded in relatively diatom-depleted regions and toward the end of the high-flux period (February–March). At the Subantarctic Front, high proportions of pheophytin and β-alanine illustrate the important role of microbes in degradation. Further south at the Antarctic Polar Front, glycine, pyropheophorbide, and pheophorbide enrichments reflected a greater contribution of diatoms and greater processing by zooplankton grazers. Even further south in the ACC, enrichments of the diatom pigment fucoxanthin, diatom cell wall indicators glycine and serine, and diatom frustule-bound amino acids suggested the settling of empty frustules and aggregates. Despite being protected by the mineral, diatom-bound amino acids were not preferentially preserved between shallow and deep traps, possibly because of silica dissolution and a relatively small amount of organic carbon remineralization. Our results show that organic matter at diatom-rich stations is removed by mechanisms that do not result in the appearance of organic matter degradation indicators. Recent observations that calcium carbonate has a higher carrying capacity for sinking organic matter than silica may be related to diatom silicification, physiological status and decomposition pathway.
 
Article
A spectrofluorometric method is described that provides a relatively rapid analysis of chlorophylls and phaeopigments (chl a, chl b, chl c, phe a, phe b, phe c) including 8-desethyl-8-vinyl derivatives of chl a and chl b (pchl a, pchl b) and their phaeopigments (pphe a, pphe b). Fluorescence of pigments in 90% acetone is measured at 24 fixed excitation and emission wavelenghts by means of a programming system. Standardization is performed from pure solutions of the n different compounds (n = 10). Pigment concentrations in crude acetone extracts of marine phytoplankton or algal cultures are determined by resolving a system of 24 linear equations and n + 1 unknowns using the least squares approximation technique in a matrix form. The method appears very well adapted to routine analysis of chlorophylls in oligotrophic waters where free-living prochlorophytes are generally abundant; its use, however, is not limited to such areas. The discrimination between chl a and 8-desethyl-8-vinyl chl a is clearly achieved. The discrimination between chl b and 8-desethyl-8-vinyl chl b is not so efficient, although pchl b appears better assessed in oligotrophic waters than chl b. Some shortcomings could be related to the presence of identified or unidentified representative pigments and insufficient information on the fluorescence characteristics of the extracts. However, the pigment analysis could be improved potentially by including new representative but spectrally different pigment standards and/or fluorescence measurements at additional fixed wavelenghts.
 
Location of the trap mooring in the equatorial Paci"c. Shallow trap at 1357 m, deep trap at 4363 m and sea #oor depth 4880 m.
Oceanographic features (temperature, salinity, phosphate (PO ), nitrate (NO ), chlorophyll-a and silica (SiO )) at the trap deployment site on September 04, 1992.
Comparison of averages of grouped amino acids from shallow and deep traps (all data).
Comparison of amino acid and hexosamine contents in shallow and deep traps. THAA, total hydrolysable amino acid; THHA, total hydrolysable hexosamine.
Preliminary information on trap location, sampling duration and sinking particle #ux at the 1753. E longitude on the equator (sea #oor depth 4880 m)
Article
Sinking matter collected by sediment traps, which were deployed in the equatorial Pacific Ocean at 175°E for about 11 months during 1992–1993, were analyzed for their flux and labile components in terms of amino acids and hexosamines. The samples provided a temporal resolution of 15 days and were collected from 1357 (shallow trap) and 4363 m (deep trap) depths where sea floor depth was 4880 m. Particle flux along with major components (carbonate, organic matter, biogenic opal and lithogenic material) and amino acid parameters showed distinct temporal variations, which were more pronounced in the shallow trap relative to deep trap. A coupling between the fluxes in the shallow and deep traps was more evident during the period of maximum particle flux, which seems to be connected with the short reappearance of non-El Niño conditions in equatorial Pacific during the 1991–1993 El Niño event. The biogeochemical indicators C/N, Asp/Bala, Glu/Gaba, Bala+Gaba mol%, THAA-C% and THAA-N% implied that the increase in sinking flux was associated with upwelling and enhanced surface production. Degradation of sinking particulate organic matter between the shallow and deep traps was also evident. Occasionally higher mass and major component fluxes in the deep trap relative to the shallow trap are attributed to contribution of resuspended particulates from sea floor (nepheloid layer) or to laterally advected particulates from nearby areas. Carbonate and opal composition of the sinking flux showed a predominance of calcareous plankton; however, Asp/Gly mol ratio and Ser+Thr mol% indicated enhanced occurrence of diatoms during the periods of higher flux.
 
Article
The analysis of hydrographic time series from moored sensors from the eastern end of the Sargasso Sea has shown that in the late 1980s the Subtropical Mode Water was dominated by high temperatures. The 18 Degree Water observed during this period was warmer and saltier than the definition given by Worthington, with an increase in values over the observation period. Although severe winter conditions in 1988 led to the formation of colder types of 18 Degree Water at the eastern part of the Sargasso Sea, they were not incorporated in the subtropical gyre. Simultaneous current meter measurements indicated eastward flow within the “southern recirculation gyre” during spring that might have been responsible for the fact that these cold Mode Water types have not been entrained into the gyre. The meteorological forcing fields show considerable interannual variability that is, in part, mimicked by changes in the 18 Degree Water properties. Due to the strong influence of the advection field on the 18 Degree Water properties, the relationship between the surface forcing and 18 Degree Water properties remains qualitative. The continuing influence of further mild winters after 1989, however, is manifested in rising temperatures within the Mode Water range.
 
Article
Grazing and growth rates of nano- and microzooplankton were measured as part of the 1989 North Atlantic Bloom Experiment, an interdisciplinary research program of the Joint Global Ocean Flux Study (JGOFS). Samples for shipboard experimental incubations were collected from the mixed layer of a drogued water mass (46°20′N, 17°50′W) over a 2 week period in May. Grazing and growth rates, measured using the size fractionation and dilution techniques, were calculated from changes in chlorophylls, accessory pigments, and cell abundances. The phytoplankton community was dominated by phytoflagellates, primarily prymnesiophytes, which passed 10 μm mesh. Chlorophyll a (Chl a) increased at an average rate of 0.9 doublings day−1 when incubated at 60 % I0. Grazing by nano- and microzooplankton removed 37–100% of estimated primary production in samples from 10 m, and 100% of that at 30 m. An attempt was made to budget estimated rates of community grazing to major groups of nano- and microzooplankton, using measured biomass and specific ingestion or growth rates from laboratory studies. Aplastidic microflagellates were apparently the most important herbivores. In addition to ciliates and heterotrophic dinoflagellates, various developmental stages of copepods were abundant in the <200 μm fraction. Predation within the microzooplankton community appeared to be substantial. Given the evidence of tight coupling between production and consumption within the upper water column, little material appeared to be available for direct export from the mixed layer to depth during this phase of the spring bloom.
 
Article
Polychlorodibenzo-p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs) are among the more toxic anthropogenic contaminants. They are fat-soluble and accumulate in animal tissues. Exposure to PCDD/Fs can cause several endocrine, reproductive and developmental problems in animals, including human beings. Several studies have demonstrated that fish and invertebrates living in association with sediments are exposed to and accumulate contaminants, but to date there have been no studies of PCDD/Fs contamination in deep-sea regions. Specimens of Aristeus antennatus (Risso, 1816) were collected from depths of 600–2500 m at different points in the Mediterranean Sea, from the western basin off the coast of Barcelona to the central basin off the Peloponnesian Peninsula, with otter trawl gear. Amounts of PCDD/Fs were measured in different animal tissues by high resolution gas chromatography coupled to high resolution mass spectrometry (HRGC–HRMS). This is the first study to report the presence of PCDD/Fs in deep-sea organisms dwelling at depths below 600 m. A. antennatus presented levels of PCDD/Fs of the same order of magnitude, or slightly higher, as those found in shallow-water species (Melicertus kerathurus) with respect to land-generated contamination. This highlights the widespread distribution of these pollutants and the potential threat posed to the biodiversity of fragile and vulnerable ecosystems such as the deep-sea. PCDD/F levels detected in the edible parts (muscle) of the commercial shrimp A. antennatus were clearly below the toxic limit value established by European legislation. Levels followed the trend muscle<ovary<hepatopancreas, according to the lipid content of the organs in question. The specific profile of toxic PCDD/F congeners in the studied Penaeid shrimp specimens was characterized mainly by octachlorodibenzo-p-dioxin (OCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF) and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) congeners. Moreover, non 2,3,7,8-substituted congeners bioaccumulated in this species, as observed in shallow-water crustaceans. PCDD/Fs were found in the shrimp A. antennatus throughout the Mediterranean Sea. Total PCDD/Fs burdens were higher in shrimps caught in the western Mediterranean than in those caught at eastern Mediterranean sites. There was a tendency for higher levels of PCDD/F contamination in samples obtained from deeper (2500 m) than from shallower sites (600 m).
 
Article
One hundred and fifty specimens of the elasipod holothurian Penilpidia ludwigi (von Marenzeller, 1893) were collected in sediment traps moored near the seabed in the La Fonera Canyon (Catalan Sea, north-western Mediterranean) and on the adjacent continental slope. These provide the third record of this apparently endemic Mediterranean species and the first record from the western Mediterranean. This was the only holothurian species trapped and the most abundant macroscopic organism found in the traps between 1200 and 1700 m depth over the whole sampling period (March–November 2001). It was particularly abundant in spring during the main flux of organic particles in the canyon. This coupling suggests that Penilpidia may aggregate at the seafloor during these events, making food availability a plausible explanation of the seasonal occurrence. Lateral transport of material re-suspended locally or up-canyon by near bottom currents appear to be the mechanism behind this uncommon occurrence, although in situ observations have recently been made on the swimming capability of this holothurian. The occurrence of benthic organisms in sediment traps set close to the seabed can provide information on bathyal benthic and benthopelagic populations.
 
Okhotsk Sea core LV 27-2-4 geochemical and lithological records versus depth in core: (a) d 18 O of planktonic foraminifera Globigerina bulloides (%, PDB standard),  
Changes of organic carbon (Corg. wt%, a, b, c); calcium carbonate (wt%, d, e, f); biogenic opal (wt%, g, h, i); and IRD (# of terrigenic grains/g of dry sediment, j, k, l) in cores LV 28-40-5, LV 27-2 and 934 according to the age model of LV 27-2 and early results (Gorbarenko et al., 2007, 2003b) versus calendar time. Upper panel indicates the Polar Circulation Index record (PCI) (Mayewski et al., 1997). The vertical lines correlate the OS cores proxy changes with variability of PCI.
Changes in the BF records and geochemical proxy in core LV 27-2-4 versus time: (a) BF biodiversity (number species/sample), (b) abundance (LN number shells/g dry sediment), (c) Corg (wt%), (d) opal (wt%), (e) percentage of species A. weddellensis, (f) % of U. auberiana, (f 0 ) % of V. ochotica, (g) % of U. peregrina, (g 0 ) % of C. teretis, (h) % of N. labrodoricum, (h') % of B. tenuata, (i) % of B. spissa and (i 0 ) % of C. laevigata. Vertical lines show the boundaries of changes in the BF species complex and their abundance consistent with the environment change boundaries shown in Fig. 2. Broken vertical lines indicate a time span coeval with the cold Heinrich event 1, environmental change inside the BA, abrupt species and environmental changes at 10 and 1.4 kyr age. Vertical cross line bar shows a sediment interval poor in BF (less than 100 individuals per sample).  
Changes in the diatom and IRD records in core LV 27-2-4 versus time: (a) abundance (# valves /g sediment), (b) IRD, (c), (d), (e) percentages of oceanic, near-sea-ice and sea-ice diatom groups, respectively; the relative abundance of dominating and sub-dominating species-(f) P. sulcata, (g) N. seminae, (h) T. latimarginata, (i) B. bathyophata, (j) T. gravida plus T. antarctica, and (k) P. hebetata. The vertical lines indicate the boundaries of ecological changes in the diatom complex and are shown similar to those in Figs. 2 and 4.
Changes in the radiolarian and agrochemical records in core LV 27-2-4 versus time: (a) % of biogenic opal, (b) d 18 O of Globigerina bulloides, (c) radiolarian absolute abundance (LN # rad/g), and percentage of species—(d) C. davisiana, (e) Plagoniidae spp., (f) S. venustum, (g) C. borealis, and (h) D. hirundo. Vertical lines indicate the boundaries of ecological changes in the radiolarian complex, similar to those of Fig. 5.  
Article
Lithological, geochemical, and micropaleontological data indicate that the Late Glacial of the northwestern Okhotsk Sea (OS) is characterised by severe climatic and environmental conditions with mainly perennial sea ice coverage and low productivity accompanied by weak deep-water ventilation and a temperate formation of the upper Sea of Okhotsk Intermediate Water (SOIW). The age model of the studied core sediments was constructed by AMS 14C dating. The most severe environmental conditions occurred during the period 15.8–14.8 kyr, synchronous with cold Heinrich event 1. Insignificant regional environmental amelioration accompanied by an increase of productivity and ice weakening during summer occurred almost simultaneously with the Bølling–Allerøed (BA) warming. The obtained results distinguished both the Bølling and Allerøed warmings as having different environmental conditions. Oxygen content in the surface sediment was low, as seen from the production of the benthic foraminifera (BF) species. During 12.6–11.1 kyr, synchronous with the Younger Dryas (YD) cold event, the regional environment conditions were cold, but not as severe as the glacial ones. Some climatic warming since the Preboreal has stimulated sea ice melting and surface amelioration during the summer season, which in turn led to a productivity rise and changes in the water column and bottom environment. Some increase in the surface water stratification and the intensified oceanic diatom and surface radiolarian production is parallel with the development of a mesopelagic regime of productivity. The surface sediment condition favours BF abundance and domination by BF species tolerant to oxygen deficiencies. During the Boreal period more stable surface conditions were accompanied by continuously high productivity and an intensifying of its mesopelagic regime.Significant regional climate warming since the Atlantic (9 kyr ago) strongly intensified the summer sea ice melting in the OS, and this created considerable surface environment amelioration with the preferential transport of bacteria and phytodetritus into the SOIW. Further considerable warming of the regional climate from 6 kyr ago contributed to slight sea ice changes, surface water warming, and the enhancement of its stratification; all typical for most of the OS. Along with a high nutrient supply from the Amur River, the NW OS experienced a strong diatom production increase with the maximum amount occurring during the last 3.6 kyr. This changed the productivity type and organic matter export into the water column while increasing the feeding of the “productive” Plagoniidae spp. group and decreasing the microbial biomass supply into the upper SOIW. Some sea surface water cooling or saltier conditions at the beginning of the Subatlantic (2.4–1.8 kyr) was followed by its warming or freshening 1.5–1.0 kyr ago, which likely correlated with the Medieval Warm Period. In turn, that probably led to strong surface water stratification, productivity deterioration and considerable changes in the overall NW OS environment. The established sequence of the northwestern OS environmental changes during the Late Glacial–Holocene is related to the Northern Hemispheric climate changes and was likely forced by atmospheric teleconnection in line with the polar circulation index variability.
 
Article
Sediment trap data from four sites in the northeast Atlantic (48°N 20°W, 28°N 22°W, 24°N 23°W, 19°N 20°W) are presented for fluxes of total mass, organic matter, calcium carbonate, opal and lithogenous material. The results from these sites are compared with other published sediment trap data from this area to consider regional scale variations in the quantity and composition of settling ocean particulate matter along a transect at 20°W from 48°N to 19°N. There are clearly gradients of decreasing mass flux going south from 48°N which reverse around 25–30°N to increase again toward the North Africa upwelling regime. Flux seasonality is greater at the more northern sites. Opal fluxes are high at the more northern sites and the flux of lithogenic material is greater further south. Plankton species composition also changes along the transect. The changes in the mass and composition of sedimenting material along the transect are consistent with known changes in surface water plankton abundance and with fluxes inferred from sediment core results. Carbon fluxes measured by sediment traps and inferred from sediment core data in this area appear to be consistent with one another. These results provide increased confidence in the use of various ocean flux measurement techniques to derive estimates of ocean carbon cycling.
 
Article
The second leg (CD61) of a two cruise investigation of coccolithophore biogeochemistry in the NE subarctic Atlantic provided the opportunity to make a detailed study of a cyclonic eddy in the vicinity of 61°N 20°W. The eddy field in the NE Atlantic is thought to be particularly important with regard to the physics of this region, and may influence the resulting chemical and biological properties of subarctic Atlantic waters. This eddy was ca. 50 km in diameter, moved at ca. 1.5 km d−1 to the north of east, with a geostrophic circulation around the feature of ca. 25 cm s−1 and probably extended as far as the ocean floor, where it may have interacted with the bottom topography. The horizontal salinity, nitrate and biological gradients between adjacent waters and the eddy were less marked in the present study than in a previous investigation of a cyclonic eddy in the vicinity of 48N 22°W (Mittelstaedt, 1987), possibly due to the surface waters of the eddy mixing with surrounding waters. Satellite image sequences clearly link this feature with those studied in a mesoscale coccolithophore bloom studied in the same region on a previous cruise (CD60). Rates of primary production within the eddy were almost twice the mean values reported for Ocean Weather Station India (OWSI) at this time of year, but were similar to those noted during studies at the MLML site to the SE of the eddy location. Other biological rate measurements also indicated that the NE sub-polar Atlantic in mid-summer is more active than previously thought. Despite the extensive coccolithophore bloom studied immediately previously by CD60, there was no measurable coccolithophore calcification in the waters within the eddy in the present study. This is consistent with phytoplankton taxonomic data, which demonstrates that coccolithophore abundance was almost one hundred fold lower at this location on CD61 relative to CD60 and that lith and coccolithophore abundances were grestest in the water column beneath the mixed layer, suggesting sinking. These observations suggest that the decline of the bloom had occurred in the period between the two cruises.
 
Article
Turbidity currents resulting from underwater earthquakes that cause slumps and bring mud into suspension are common in the ocean. The 1929 Grand Banks earthquake, which generated a large turbidity current, is a particular interest because, as the current advanced, all the submarine telegraph cables situated downslope were broken in sequence. Since the location and breakage times are known, these successive breakages provided a unique set of observations of the current's downhill propagation speed. They show that the current's propagation rate was drastically reduced as it advanced toward the abyssal plain.
 
Article
Changes in winter and spring mixed layer depths in the North Pacific on decadal and basin scales affect biological production. Intransition zones these depths were 30–80% greater during 1977–1988 than during 1960–1976; in the subarctic zone they were 20–30 shallower. We attribute these changes to an intensification of the Aleutian Low Pressure System. A deeper mixed layer might increase phytoplankton production in nutrient-poor regions by supplying more deep nutrients; it might decrease production in light-poor regions by mixing cells into darker water. A plankton population dynamics model suggests that a deeper subtropical mixed layer and a shallower subarctic mixed layer both would increase primary and secondary production by about 50%, and these increases were found not to be very sensitive to model parameter values; in the transition zone, however, the predicted change in production was smaller and more sensitive to changes in model parameters. Increases in higher tropic levels have been observed in subtropical and subarctic zones during 1977–1988. This is consistent with model results and the idea that the subtropical zone is nutrient-poor, the subartic zone is light-poor, and the transition zone is not consistently limited by any one thing. Further, our results show changes in mixed layer depths occur on decadal and basin scales and may be an important mechanism linking variation in the atmosphere and oceanic ecosystem productivity.
 
Article
Functioning of the Black Sea ecosystem has profoundly changed since the early 1970s under cumulative effects of excessive nutrient enrichment, strong cooling/warming, over-exploitation of pelagic fish stocks, and population outbreak of gelatinous carnivores. Applying a set of criteria to the long-term (1960–2000) ecological time-series data, the present study demonstrates that the Black Sea ecosystem was reorganised during this transition phase in different forms of top-down controlled food web structure through successive regime-shifts of distinct ecological properties. The Secchi disc depth, oxic–anoxic interface zone, dissolved oxygen and hydrogen sulphide concentrations also exhibit abrupt transition between their alternate regimes, and indicate tight coupling between the lower trophic food web structure and the biogeochemical pump in terms of regime-shift events.
 
Article
The Weddell Deep Water (WDW) warmed substantially along the Greenwich meridian following the Weddell Polynya of the 1970s. Areas affected by the polynya contained ∼14 GJ/m2 more heat in 2001 than in 1977. This warming would require a flux of ∼390 W/m2 if it were to take place over a year. Large variations in heat content of the WDW are found between the Antarctic coast and Maud Rise (64°S). The small variation found north of Maud Rise is opposite in phase to that to the south, and the warming was close to monotonic south of 68°S. The mean warming of WDW along the section is ∼0.032 °C per decade, comparable to the warming of the Antarctic Circumpolar Current. The mean warming compares with a surface heat flux of 4 W/m2 over the 25 year period, an order of magnitude higher than the warming of the global ocean. As variation in mean salinity of the WDW follows the warming/cooling events, variation in inflow probably explains a cooling event between 1984 and 1989, and a warming event between 1989 and 1992. Cooling during the late 1990s is probably related to the reappearance of a polynya like feature in some winter months as an area 100 km in diameter close to Maud Rise with 10–20% lower sea ice concentrations than the surrounding ocean.
 
Article
The seasonal and interannual variations of the Sea surface Salinity (SSS) are analysed in the tropical Atlantic (15°S–30°N, 80°W-15°E) from observations collected by merchant ships between 1977 and 1989 and earlier by ORSTOM research vessels. The harmonic analysis of SSS shows a well defined seasonal cycle both within a 5°N–15°N zonal belt and west of 50°W at higher latitudes. In the eastern Atlantic between 10 and 20°N (along the shipping lanes West Africa-South Africa and West Africa-Brazil), SSS increased from 1977 to 1985, particularly near 10°N. SSS variability is mostly related to the river outflow (Amazon, Orinoco and Congo) west of 40°W and in southern Gulf of Guinea. In the eastern Atlantic, precipitation associated with the ITCZ largely control the SSS seasonal variations.
 
Article
Simulations of the interannual variability of the deep-water formation processes in the Adriatic basin for the years 1979–1999 are performed using the Princeton Ocean Model (POM) with a ∼10 km grid and 6-h atmospheric forcing provided by the European Center for Medium Weather Forecast (ECMWF). Focus is given to the pattern and amplitude of the interannual variability of the water mass formation processes in terms of deep-water formation sites, rates and characteristics. The connection of this variability with the interannual variability of (a) the atmospheric forcing and (b) the open boundary characteristics is investigated. The model performance is tested against the few available observations of deep-water formation processes inside the basin and generally shows a good agreement with the main characteristics of the mixed layer and the deep-water formation rates. A strong interannual variability is found in the calculated deep-water formation rate of the basin, which is highly dependent on the interannual variability of the atmospheric forcing. This rate becomes three times larger than climatology during the biennium 1992–1993, and during all years it is associated mostly with the events of enhanced buoyancy loss and not with the mean winter buoyancy fields. Advection through the open boundary plays an important role in determining the characteristics and volume of deep water formed inside the Adriatic basin, but it is the high frequency atmospheric forcing that determines the amplitude of the interannual variability of deep-water formation rates.
 
Article
Changes in the oceanographic climate of the Arctic Ocean during the 1990s have been linked to anomalous heat and volume transports of Atlantic Water (AW) from the Nordic Seas. This paper focuses on the variability in the AW temperature in the Norwegian Sea and in the Barents Sea Opening (BSO), using 16 years of data from five regular hydrographic sections across the flow of AW from the Faroe–Shetland inflowing area to the Barents Sea and Fram Strait. In a section across the BSO, data from 102 surveys were analysed. Here time series for mean temperatures and salinities are constructed for 10,50,100,200,300, and 400 m depths. While seasonal- and shorter-period variability has largest amplitudes in the water masses above 200 m depth, interannual variability in temperature has largest amplitudes near the bottom. At 400 m depth, the amplitudes of the interannual variations are of the order of 1°C and exceed the magnitude of the seasonal cycle. Two warm periods, 1983–1984 (W1) and 1990–1992 (W2), and one cold period, 1986–1988 (C1), are discussed. W1 and partly C1 can be traced back to the Iceland–Scotland Gap, from where they were advected with the mean flow of AW northwards along the eastern flank of the Nordic Seas. The temperature anomalies decreased in magnitude while they moved towards the north. W2 had a different characteristic, as it can be explained by reduced heat loss to the atmosphere, or by an increased advection speed, within the Nordic Seas. The anomaly was strengthened along the flow towards the north. The salinity anomalies were advected with the AW and strengthened by fresh-water fluxes along their pathway inside the Nordic Seas. In the BSO the temperature anomalies indicate that the AW inflow to the Barents Sea occurs in two branches along the southern slope of the BSO. The anomalies are recirculated in the Barents Sea and return to the BSO along the northern slope of the section.
 
Article
Determinations of the activity of the respiratory electron transport system (ETS), during the FRAM III expedition permit us to estimate oxygen utilization rates (RO2) from the surface to 2000 m under the polar pack ice in the Nansen Basin just north of Svalbard (83°N, 7°E) during April 1981. We found RO2 at in situ temperatures ranging from 20 pM O2 min−1 just below the ice to 0.2 pM O2 min−1 at 2000 m. These rates are low compared to most other ocean regions, but they could decrease particulate organic carbon and nitrogen by 76% and 74%, respectively, over a period of ∼6 months. The RO2 calculations based on measurements made at 0 °C yielded a power function of RO2 vs. depth (Z) of RO2=67Z−0.5534. When this RO2 profile was superimposed on a more recent oxygen utilization rate profile made using the 3He–3H–AOU method (OUR), in the same vicinity of the Nansen Basin during 1987 (OUR=52Z–0.4058, [Zheng, Y., Schlosser, P., Swift, J.W., Jones, E.P., 1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]), the agreement of the two profiles was close. On one hand, this was to be expected because RO2 is the biological basis of OUR, on the other hand, it was a surprise because the methodologies are so different. Nitrate mineralization obtained from ETS activities also compared favorably with calculations based on the data of Zheng et al. [1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]. Chlorophyll ranged from 6 ng L−1 at 5 m to 0.06 ng L−1 at 2000 m. Particulate organic carbon (POC) decreased from 0.93 μM C just below the ice to less than 0.4 μM C at 500 m. Particulate organic nitrogen (PON) was not detectable below 70 m, however in the upper 70 m it ranged from 0.16 to 0.04 μM N. The C/N mass ratio over these depths ranged from 5.8 to 11.3. Annual carbon productivity as calculated to balance the total water column respiration was 27 g C m−2 y−1. The integrated respiration rate between 50 and 4000 m suggests that exported production and carbon flux from the 50 m level was 24 g C m−2 y−1. These are minimal estimates for the southern Nansen Basin because they are based on measurements made at the end of the Arctic winter.
 
Article
The large-scale circulation and the distributions of temperature, salinity and density in the Bay of Bengal during early winter (October-–December 1983) are presented. The surface circulation relative to 1000 db level surface indicates a northward flowing eastern boundary current from north of 8°N west of the Andaman-Nicobar Islands and, to its west, a large cyclonic gyre between 19° and 13°N. The wind stress curl for November suggests that this gyre is primarily wind driven. The north-flowing eastern boundary current of the Bay of Bengal is fed by the monsoon drift current during late October. This eastern boundary current extends up to 19°N and merges with the cyclonic gyre. The southwestward flow of the cyclonic gyre along the central east coast of India is strengthened by the freshwater discharge from the northern part of the Bay. Warm and saline equatorial waters advect northward through the eastern boundary current, which coupled with the process of winter cooling at the head of the Bay leads to sharp temperature inversions (about 2°C) at 50 m depth in the north-northwestern Bay. The volume transport associated with the eastern boundary current across 12°N between 88° and 92°E 6 × 106m3s−1 in the upper 200 m.
 
Article
Continuous measurements of temperature, salinity, nutrients, oxygen, partial pressure of CO2, pH, flourescence of chlorophyll, and light scattering were undertaken during the Paciprod cruise in August 1986. Underway measurements were performed on two tracks perpendicular and parallel to the Peruvian coast near 15°S, and continuous vertical profiles were obtained on two transects perpendicular to the coast. The upwelling was intense, as indicated by the thickness of the Eckman layer and the large extent of cold water and nutrients. Offshore upwellings were marked by decreases of temperature and increases in the nutrient content of the mixed layer. The surface water was largely undersaturated with oxygen and supersaturated with respect to CO2. Partial pressures of CO2 as high as 1000 μatm was observed at the source of the upwelling. Oxygen-poor waters were found immediately below the thermocline. Water layers with near zero nitrate concentration show that the denitrification was intense in the equatorial subsurface water beyond the shelf. The occurrence of these low nitrate cores situated westward of upward tilts of the isotherms was linked to the circulation. An increase of fluorescence and ligth scattering accompanied the decrease in nitrate and nitrite concentrations in oxygen-depleted water. Denitrification was lower in the shelf water and in the less saline subantarctiv water. The mixed layer indicated a high nutrient-low chlorophyll situation on the whole area studied. Four main surface zones with different features were distinguished along a transect perpendicular to the coast. The fluorescence is relatively high and increases seaward in the first zone situated between the upwelling center and 22 km offshore. This corresponds to the biological conditioning described by MacIsaacet al. (Deep-Sea Research, 32, 503–529, 1985). In the second and third zones, the biomass is low, silicate or nitrate concentrations are probably limiting, and grazing may control production, especially in the third zone where ammonium appears. In the subtropical water, the fourth zone, the biomass is very low and the N/Si/P ratios in sea water are approximately 4/3/1.
 
Article
The 3-D circulation of the Ensenada Front, located off southern California and northern Baja California, is examined using hydrographic and mixed-layer drifter measurements. The measurements resolve sub-mesoscle motions (10 km scale) and trace the flow over a 400 km extent, from deep water into the continental margin. Along the Ensenada Front, the cool, relatively fresh, southeastward-flowing waters of the California Current were observed to turn abruptly onshore and flow eastward for approximately 200 km before resuming a southeastward trajectory. Embedded in the onshore flow was a 60 km wide, surface-intensified (> 30 cm s−1), high speed filament, which bifurcated after resuming a southeastward course, and appeared to feed into a complex set of flows that were strongly influenced by the mesoscale eddy field. Various water mass properties are used to trace the along-front evolution of the filament and its demise. Estimates of vorticity and divergence in the filament are made on the scale of drifter clusters, deployed in diamond patterns with a separation of 10 km. Potential vorticity appears to be conserved along drifter trajectories, and suggests a divergent, upwelling (5 m day−1) filament with convergent flow along the sides. Such a pattern is consistent with a model of constant wind stress blowing along the filament.
 
Article
The analysis of the first mesoscale experiment in the middle Adriatic Sea reveals the horizontal and vertical scale of the eddy field. The mesoscale variability is characterized by 10–20 km in diameter eddies. They are lower thermocline intensified, and the velocities in the upper and lower thermocline levels range from 10 to 1 cm s−1, respectively. The eddies are small because of the local Rossby radius deformation (5.4 and 2.8 km for the first and second internal baroclinic mode, respectively) and because they are second baroclinic mode intensified. The Levantine Intermediate Water is found in tongue-like features intruding between the intense eddy field.
 
Article
Zooplankton community structure and trophic ecology were investigated in the marginal ice zone of the Southern Scotia Sea during the austral winter of 1988 as part of the AMERIEZ program. In the study area, near the South Orkneys (34–49°W, 57–61.5°S), water emerging from the Weddell Sea mixed with Scotia Sea water to form a complex field of mesoscale eddies and meanders. Three primary zooplankton communities were identified: a shallow cold water assemblage typical of Weddell Sea water; a shallow/upper mesopelagic assemblage of subantarctic species introduced into the southern Scotia Sea with warm core eddies from the Polar Front; and a deep (>400 m) mesopelagic community with circumtantartic species. Zooplankton numerical dominants were cyclopoid copepods (mostly Oithona spp.); biomass dominants were four calanoid copepods, Calanoides acutus, Rhincalanus gigas, Calanus propinquus and Metridia gerlachei. Calanoides acutus and R. gigas were undergoing winter diapause in the mesopelagic zone (>400 m) whereas M. gerlachei and C. propinquus were distributed throughout the water column. In the subantarctic eddies M. gerlachei was replaced by M. lucens as a dominant and R. gigas was more abundant than in cold water to the south.
 
Article
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.
 
Article
We use the first seven years of the Bermuda Atlantic Time Series (BATS) core data set (1989–1995) to examine periodicity of and correlations between potential forcing and photosynthetic performance (Pbopt). This analysis, which focuses on seasonal to annual time scales, points to a strong annual periodicity for many of the parameters investigated, with weaker annual Pbopt variability. As has been previously demonstrated for primary production at the BATS location, shorter time scale variability induced by mesoscale events (e.g. fronts, eddies) is likely driving the majority of variability in Pbopt. Of the parameters examined, chlorophyll, temperature and mixing depth demonstrate the strongest correlations with Pbopt. Decomposition of the temperature signal into principal components further suggests that physical mixing is correlated with Pbopt, whereas the true thermal level is less important. Macronutrients and grazing indices are uncorrelated with Pbopt. Because only chlorophyll and mixing depth (of the parameters investigated) are strongly correlated with Pbopt, we suggest that light history was the dominant forcing variable at the time scales examined for Pbopt at the BATS location for 1989–1995. However, when vertical mixing is minimal, other factors, which are equally or more important in forcing Pbopt and ultimately integrated primary production, are likely acting at scales that may not be readily discernible with the BATS sampling scheme. These results are discussed in the context of a mixing-photoadaptation rate constant model that functionally describes Pbopt-mixing depth relationships and shows a great deal of consistency with observations.
 
Article
Phytoplankton productivity north of 42°N in the NE Atlantic is dominated by intense blooms in spring and early summer. Detailed analyses of deep-water sediment trap samples over a 17 month period, encompassing two such bloom events, reveal that the removal fluxes of the particle-reactive radionuclides 210Pb and 230Th are generally linearly related to mass flux, as observed elsewhere, up to 120 mg m−2 day−1. Above mass fluxes of 120 mg m−2 day−1 , the 230Th flux is limited close to its water column production rate in a trap at 3100 m, and somewhat in excess of its production rate in a trap at 4465 m (full water column depth 4555 m). The 210 Pb flux is also similarly limited in both traps. These limits are ascribed to the differing behaviour of the fastersettling bloom material, rather than to quantitative scavenging of water column radionuclides. Finite dissolved and particulate activities for both radionuclides are observed in the water column. Comparison of activity ratios in surface particulate and trap material indicates that the trap material does not represent surface material which has settled without modification through the water column. Rather the activity ratio of the trap material is similar to the activity ratio of particulate material in the integrated water column overlying the shallower trap, but the underlying mechanisms controlling the scavenging limitation remain unclear. Comparison of data from the 3 100 m trap in “clear water” 1455 m above the sea floor, with those from the second only 90 m above, illustrates that re-entrainment of current-resuspended near-bottom material must contribute to the deep trap. As a result, the intercepted 230Th in the deep trap regularly exceeds production in the overlying water column throughout the year. The mean CaCO3 230Th and 232Th fluxes to this deep trap agree to within 10% of their long-term fluxes measured in a core from the trap site, although 210Pb fluxes to the trap are only 70% of the flux recorded by the sediment.
 
Article
Time series measurements of size-fractionated chlorophyll a concentrations and primary production were made over the course of the spring bloom in and adjacent to a mesoscale eddy in the N.E. Atlantic as part of the U.K. Biogeochemical Ocean Flux Study 1990 Lagrangian Bloom Experiment. Substantial production, dominated by the >5μm and >1–5,μm fractions, was recorded before the main growth phase of the bloom, although total chlorophyll a concentrations varied little over this period. The main growth phase of the bloom, which occurred over approximately one week, was dominated by the > 1–5 μm fraction; a principal constituent was the small diatom Nanoneis hasleae, which almost entirely displaced larger diatoms more typical of a spring bloom population. The >5 um phytoplankton fraction became dominant for approximately two weeks following the main bloom growth phase but was replaced at the end of the observation period by the > 1–5 μm and 0.2-1 μm fractions. Phytoplankton taxonomic data for the 1990 bloom period were very different to the more typical bloom conditions of 1989. An intercomparison of14C production measurements made by U.K. and Dutch participants during the period of the Experiment using common samples gave total column productivities differing by <4%.
 
Article
A unique CFC time series was collected along the 35°W meridian in the tropical Atlantic during eight cruises from 1990 to 1999, in order to investigate the large-scale variability of the circulation of the North Atlantic Deep Water (NADW) through transient tracer distributions. Within the upper NADW (UNADW), it appears that CFC distributions, are highly variable; cores of maximal CFC concentrations are closely associated with salinity and are principally caused by the local dynamics of equatorial and extra-equatorial deep jets within the three particular regimes of the 3–1°S, 1°S–1°N and 1–3°N bands. CFC distribution within the lower NADW (LNADW) is less heterogeneous and linked to oxygen. A double core has been observed for 1999, possibly due to the recirculation of the deep flow constrained by the circulation of the underlying Antarctic Bottom Water (AABW). The variability of the maximal concentrations presumably results from the seasonal or semi-annual variability of the regional deep circulation. For both layers, the temporal evolution of the mean concentrations has been traced throughout the 1990s. At the UNADW level, the temporal increase of the CFC concentration within the 3°S–3°N band is mainly due to the transient signal from the atmosphere. This increase is clearly dominant compared with the local dynamics. Similar behavior has been observed for the LNADW in the 3°S–1°N band, corresponding to the equatorial channel. An attempt has been made to access the transit time for the NADW pathway from the Labrador and Nordic Seas to the tropics. The mean transit time around 25 yr for the UNADW has been compared to other evaluations from hydrographic measurements.
 
Article
Long-term monitoring of diatom fluxes during 1990–1998 was conducted at Station AB in the Bering Sea and Station SA in the central subarctic Pacific in order to decipher the relationships between sinking diatom and the upper water mass environments. The total diatom flux at Station AB was generally twice as high as that at Station SA. The dominant species in the sinking flora was primarily Neodenticula seminae at both stations, which was a significant contributor to organic carbon flux. The flora at Station AB was represented by relatively abundant coastal taxa including Chaetoceros resting spores. These results suggest more favorable conditions for diatom production at Station AB compared with those at Station SA. The possible influences of oligotrophic and temperate water masses were discerned from the positive SST anomaly and the occurrence of a few specimens of temperate species. The cumulative annual fluxes of total diatoms at Stations AB and SA are apparently related to the variation in the mean annual depth of mixed layer. At Station SA, annual mean of total diatom flux showed a negative correlation with the Pacific Decadal Oscillation (PDO) Index, which suggests a significant relationship between surface water turbidity and diatom production. At Station AB, the annual change of coastal diatom flux was correlated with the PDO and the winter value of the Arctic Oscillation, which may suggest a significant influence of Alaskan Stream waters via the Aleutian Islands and intensity of surface water mixing.
 
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