ALBERT

Description: According to small subunit ribosomal RNA (ss rRNA) sequence comparisons all known Archaea belong to the phyla Crenarchaeota, Euryarchaeota, and—indicated only by environmental DNA sequences—to the 'Korarchaeota'1, 2. Here we report the cultivation of a new nanosized hyperthermophilic archaeon from a submarine hot vent. This archaeon cannot be attached to one of these groups and therefore must represent an unknown phylum which we name 'Nanoarchaeota' and species, which we name 'Nanoarchaeum equitans'. Cells of 'N. equitans' are spherical, and only about 400 nm in diameter. They grow attached to the surface of a specific archaeal host, a new member of the genus Ignicoccus3. The distribution of the 'Nanoarchaeota' is so far unknown. Owing to their unusual ss rRNA sequence, members remained undetectable by commonly used ecological studies based on the polymerase chain reaction4. 'N. equitans' harbours the smallest archaeal genome; it is only 0.5 megabases in size. This organism will provide insight into the evolution of thermophily, of tiny genomes and of interspecies communication.

Description: This study investigates and accounts for the influence of various ice cloud parameters on the retrieval of the surface solar radiation budget (SSRB) from reflected flux at the top of the atmosphere (TOA). The optical properties of ice clouds depend on ice crystal shape, size distribution, water content, and the vertical profiles of geometric and microphysical structure. As a result, the relationship between the SSRB and TOA-reflected flux for an ice cloud atmosphere is more complex and differs from that for water cloud and cloudless atmospheres. The sensitivities of the relationship between the SSRB and TOA-reflected flux are examined with respect to various ice cloud parameters. Uncertainties in the retrieval of the SSRB due to inadequate knowledge of various ice cloud parameters are evaluated thoroughly. The uncertainty study is concerned with both pure ice clouds and multiphase clouds (ice cloud above water cloud). According to the magnitudes of errors in the SSRB retrieval caused by different input variables, parameterized correction terms were introduced. If the input variables are known accurately, errors in the retrieval of the SSRB under a wide range of ice cloud conditions are expected to diminish substantially, to less than 10 W m−2 for 91% of the simulated ice cloud cases. In comparison, the same accuracy may be attained for only 19% of the retrievals for the same ice cloud cases using the retrieval algorithm designed for non-ice-cloud conditions.

Description: North Atlantic synoptic-scale processes are analyzed by bandpassing 6-hourly NCEP–NCAR reanalysis data (1958–98) for several synoptic ranges corresponding to ultrahigh-frequency variability (0.5–2 days), synoptic-scale variability (2–6 days), slow synoptic processes (6–12 days), and low-frequency variability (12–30 days). Climatological patterns of the intensity of synoptic processes are not collocated for different ranges of variability, especially in the lower troposphere. Intensities of synoptic processes demonstrate opposite trends between the North American coast and in the northeast Atlantic. Although north of 40°N the intensity of ultrahigh-frequency variability and synoptic-scale processes show similar interannual variability, further analysis indicates that secular changes, and decadal-scale and interannual variability in the intensities of synoptic processes may not be necessarily consistent for different synoptic timescales. Magnitudes of winter ultrahigh-frequency variability are highly correlated with the intensity of synoptic-scale processes in the 1960s and early 1970s. However, they show little agreement with each other during the last two decades, pointing to the remarkable change in atmospheric variability over the North Atlantic in late 1970s. North Atlantic ultrahigh-frequency variability in winter is highly correlated with surface temperature gradient anomalies in the Atlantic–American sector. These gradients are computed from the merged fields of SST and surface temperature over the continent. They demonstrate a dipolelike pattern associated with the North American coast on one hand, with the subpolar SST front and continental Canada on the other. High-frequency variability and its synoptic counterpart demonstrate different relationships with the North Atlantic Oscillation. Reliability of these results and their sensitivity to the filtering procedures are addressed by comparison to radiosonde data and application of alternative filters.

Description: Turbulent fluxes of momentum and sensible heat were estimated from sonic anemometer measurements gathered over the Labrador Sea during a winter cruise of the R/V Knorr. The inertial dissipation method was used to calculate turbulent fluxes of momentum. The resulting drag coefficients agree well with earlier findings. Sensible heat fluxes were computed using both cross-correlation and inertial dissipation techniques. There is good agreement between results from both methods, although there is more scatter in the correlation fluxes than the dissipation fluxes. The inertial dissipation method gives reasonable results even under conditions of high wind speeds and low air temperatures, which combined with the relatively warm sea surface temperatures lead to sensible heat fluxes of several hundred watts per square meter. Sensible heat fluxes obtained from the sonic anemometer measurements agree well with bulk turbulent fluxes according to the formulation of Isemer and Hasse.

Description: A key question in ecology is which factors control species diversity in a community1, 2, 3. Two largely separate groups of ecologists have emphasized the importance of productivity or resource supply, and consumers or physical disturbance, respectively. These variables show unimodal relationships with diversity when manipulated in isolation4, 5, 6, 7, 8. Recent multivariate models9, 10, however, predict that these factors interact, such that the disturbance–diversity relationship depends on productivity, and vice versa. We tested these models in marine food webs, using field manipulations of nutrient resources and consumer pressure on rocky shores of contrasting productivity. Here we show that the effects of consumers and nutrients on diversity consistently depend on each other, and that the direction of their effects and peak diversity shift between sites of low and high productivity. Factorial meta-analysis of published experiments confirms these results across widely varying aquatic communities. Furthermore, our experiments demonstrate that these patterns extend to important ecosystem functions such as carbon storage and nitrogen retention. This suggests that human impacts on nutrient supply11 and food-web structure12, 13 have strong and interdependent effects on species diversity and ecosystem functioning, and must therefore be managed together.

Description: BOOK REVIEWED: Plate Tectonics: An Insider's History of the Modern Theory of the Earth / edited by Naomi Oreskes Westview Press: 2001. 448 pp.

Description: Lowered acoustic Doppler current profilers (LADCPs) have matured from an experimental instrument to an operational hydrographic tool to study ocean dynamics. The data processing, however, is still in a rather primitive state. First, a method to estimate bottom-track velocities using the standard water profile data was developed. Then inverse solutions are presented that enhance the standard data processing by adding external constraints such as bottom-referenced velocity profiles. Depending on the depth of the profile and the ADCP range the inclusion of bottom-track data can reduce the local velocity errors by a significant factor. The least squares framework also allows for simplified error analysis of the LADCP system and some of the trade-offs are discussed.

Description: Zonal transports of North Atlantic Deep Water (NADW) in the South Atlantic are determined. For this purpose the circulation of intermediate and deep water masses is established on the basis of hydrographic sections from the World Ocean Circulation Experiment (WOCE) and some pre-WOCE sections, using temperature, salinity, nutrients, and anthropogenic tracers. Multiple linear regression is applied to infer missing parameters in the bottle dataset. A linear box-inverse model is used for a set of closed boxes given by sections and continental boundaries. After performing a detailed analysis of water mass distribution, 11 layers are prescribed. Neutral density surfaces are selected as layer interfaces, thus improving the description of water mass distribution in the transition between the subtropical and subpolar latitudes. Constraints for the inverse model include integral meridional salt and phosphorus transports, overall salt and silica conservation, and transports from moored current meter observations. Inferred transport numbers for the mean meridional thermohaline overturning are given. Persistent zonal NADW transport bands are found in the western South Atlantic, in particular eastward flow of relatively new NADW between 20° and 25°S and westward flow of older NADW to the north of this latitude range. The axis of the eastward transport band corresponds to the core of property distributions in this region, suggesting Wüstian flow. Part of the eastward flow appears to cross the Mid-Atlantic Ridge at the Rio de Janeiro Fracture Zone. Results are compared qualitatively with deep float observations and results from general circulation models

Description: Fifteen profiling floats were injected into the deep boundary current off Labrador. They were ballasted to drift in the core depth of Labrador Sea Water (LSW) at 1500-m depth and were deployed in two groups during March and July/August 1997. Initially, for about three months, the floats were drifting within the boundary current, and the flow vectors were used to determine the mean horizontal structure of the Deep Labrador Current, which was found to be about 100 km wide with an average core speed of 18 cm s−1. North of Flemish Cap the boundary current encounters complicated topography around “Orphan Knoll,” and there the LSW outflow splits up into different routes. One obvious LSW path is eastward through the Charlie Gibbs Fracture Zone and another route is a narrow recirculation toward the central Labrador Sea. A surprising result was that none of the floats were able to follow the boundary current southward to the Grand Banks area and exit into the subtropics. Trajectories and temperature profiles of the eastward drifting floats indicate the importance of the North Atlantic Current for dispersing the floats, even at the level of LSW.

Description: The analysis of high-resolution oceanographic data referring to velocity measurements carried out by means of a vessel-mounted acoustic Doppler current profiler on 12 November 2000 in the equatorial Atlantic, at 44°W between 4.5° and 6°N, reveals the presence of three large-amplitude internal solitary waves superimposed on the velocity field associated with the North Equatorial Countercurrent (NECC). These waves were found in the deep ocean, more than 500 km off the continental shelf and far from regions of topographic variations. They propagated toward the north-northeast, strongly inclined with respect to the main axis of the NECC and perpendicular to the Brazilian shelf, as well as to the North Brazil Current, and were characterized by maximum horizontal velocities of about 2 m s−1 and maximum vertical velocities of about 20 cm s−1. The large magnitudes of the measured velocities indicate that the observed waves represent disturbances evolving in a strongly stratified ocean. The distance separating the waves (about 70 km) indicates that the observed features cannot be considered as elements of a single train of internal solitary waves. The waves consist, instead, of truly disconnected, pulselike intense solitary disturbances. This behavior, which strongly differs from that typically observed for trains of tidally generated internal solitary waves, indicates that different mechanisms were possibly involved in their generation and/or evolution.

Description: Phytoplankton (〉100 µm) abundance was studied in the open waters of the Gulf of Aqaba during the summer stratification period of 1996. A succession took place among the major phytoplankton groups, with diatom numbers decreasing throughout the summer. The diazotrophic cyanobacteria Trichodesmium spp. became more prominent as the stratification period progressed; 5 Trichodesmium species were identified: T. thiebautii, T. erythraeum with tuft-shaped colonies and Trichodesmium sp. with puff-shaped colonies were common at ~102 colonies m-3 throughout the stratification period, whereas T. tenue and T. hildebrandtii were more rare. A bloom of T. thiebautii and T. erythraeum with 〉106 tuft colonies m-3 was observed in coastal waters of the Gulf during fall 1997. Tuft-shaped colonies were dominant near the surface, while puff-shaped colonies of Trichodesmium sp. were mainly found in the bottom half of the photic zone. These depth distributions were maintained for more than 2 mo, suggesting that the 2 colony types occupied distinct niches. Puff-shaped colonies were found to have higher chlorophyll a contents than tufts, but their photosynthetic activities were not significantly different. Fatty acid analysis of dominant plankton species yielded new trophic relationships for Trichodesmium spp. The Trichodesmium spp.-specific fatty acid C22:2 ω6 was found in Macrosetella gracilis (the sole copepod to graze on Trichodesmium spp.) and in chaetognaths, suggesting that these carnivorous zooplankton fed on M. gracilis. Furthermore, this fatty acid was observed in the filter-feeding Salpa maxima, which was abundantly present in the Gulf of Aqaba during June 1997.

Description: The ventilation of the permanent thermocline of the Southern Hemisphere gyres is quantified using climatological and synoptic observational data. Ventilation is estimated with three independent methods: the kinematic method provides subduction rates from the vertical and horizontal fluxes through the base of the mixed layer, the water age uses in situ age distribution of thermocline waters, and the annual-mean water mass formation through air–sea interaction is calculated. All three independent estimates agree within their error bars, which are admittedly large. The subduction rates are mainly controlled through their vertical and lateral components with only minor transient eddy contributions. The vertical transfer, derived from Ekman pumping, ventilates over most of the areas of the subtropical gyres, while lateral transfer occurs mainly along the Subtropical and Subantarctic Fronts, where it injects mode and intermediate waters. For the permanent thermocline the overall ventilation of the South Atlantic is about 21 Sv (Sv ≡ 106 m3 s−1). Of this, lateral transfer contributes 10 Sv, mainly in the Brazil–Malvinas confluence zone and to the northeast of Drake Passage. The effective vertical transfer at the bottom of the mixed layer is only two-thirds of the Ekman pumping due to strong northward forcing of the mixed layer itself. The Indian Ocean is ventilated at a rate of 35 Sv with equal lateral and vertical contributions. The South Pacific's overall ventilation is 44 Sv of which the lateral input contributes little more than half. West of 130°W, the South Pacific is ventilated through Ekman pumping and with only minor lateral transfer. In the east lateral transfer dominates between 10° and 20°S and along the Subantarctic Front in a narrow density range. Combining overall transports with earlier estimates for the Northern Hemisphere gives a ventilation of the World Ocean's permanent thermocline of about 160 Sv. Analysis of atmospheric reanalysis air–sea flux data reveals an overall increase in the formation of thermocline waters for all three Southern Hemisphere oceans.

Description: The combined and interactive effects of climatic and ecological factors are rarely considered in marine communities. We designed a factorial field experiment to analyze (1) the interactive effects of ambient UV radiation and consumers; and (2) the effects of photosynthetically active radiation (PAR 400 to 700 nm), UVA (320 to 400 nm) and UVB (280 to 320 nm) radiation on a marine hard-bottom community in Nova Scotia, NW Atlantic. Species recruitment and succession on ceramic tiles were followed for 5 mo. We found strong negative UV effects on biomass and cover of the early colonizing macroalga Pilayella littoralis, whereas UVB was more harmful than UVA radiation. Consumers, mainly gammarid amphipods, increased P. littoralis biomass when UV was excluded, probably through fertilization. These initially strong and interacting UV and consumer effects on total biomass and cover diminished as species succession progressed. Species diversity was not affected by experimental treatments, but significant shifts in species composition occurred, especially at the recruitment stage. Red algae were most inhibited by UV, whereas sedentary invertebrates and some brown algae tended to increase under UV exposure. Consumers suppressed green and filamentous brown algae, but favored the other groups. Again, these effects diminished during the later stages of succession. We conclude that UV radiation can be a significant structuring force in early successional benthic communities, and that consumers can mediate its effects.

Description: The effect of methane released from decomposing surficial gas hydrates (SGH) on standing stocks and activities of the small-sized benthic biota (SSBB; i.e. bacteria, fungi, protozoa, and meiobenthic organisms) was studied at about 790 m water depth, at the Hydrate Ridge, Cascadia subduction zone. Presence of SGH and elevated sulfide concentrations in the sediment were indicated by extensive bacterial mats of Beggiatoa sp. and clam fields of the bivalve mollusc Calyptogena sp. Vertical and horizontal distribution patterns of the SSBB biomass were derived from DNA and total adenylate (TA) sediment assays. Potential bacterial exoenzymatic hydrolytic activity was measured using fluorescein-di-acetate (FDA) as substrate. Estimates of chemoautotrophic production of particulate organic carbon (POC.) were determined by 14CO2 uptake incubations. Inventories of chl a and pheopigments were determined as parameters of surface water primary produced POC input. Average SSBB biomass in clam field sediments integrated over the upper 10 cm (765.2 gC m-2, SD 190.1) was 3.6 times higher than in the adjacent control sites (213 gC m-2, SD 125). Average SSBB biomass in bacterial mat sediments, which were almost devoid of eukaryotic organisms 〉 31 µm, was 209 gC m-2 (SD 65). Significant correlations between FDA, DNA and plant pigments imply that productivity of the SSBB at SGH sites is only partially uncoupled from the primary production of the surface water. Areal estimates of autotrophic Corg production at control sites, bacterial mat sites and in clam field sites were 5.7, 59.7 and 190.0 mgC m-2 d-1, respectively. Based on different models predicting vertical POC fluxes from surface water primary production and water depth, these autotrophic POC productions account for 5 to 17% (controls), 35 to 68% (bacterial mats), and 63 to 87% (clam fields) of the bulk POC (sum of allochthonous POC input through the water column and sedimentary autochthonous autotrophic POC production) provided at the various sites. At SGH sites inventories of chl a and pheopigments, integrated over the upper 10 cm of the sediment, were half of that found at the control sites. This might be due to enhanced degradation of phytodetritally associated organic matter. The resulting low molecular weight organic carbon compounds might stimulate and fuel sulfate reduction, which is conducted in a microbial consortium with anaerobic methane consuming archaea. This syntrophic consortium might represent a prominent interface between gas hydrate derived carbon and allochthonous Corg flow. We infer that degradation kinetics of SGH is affected by, e.g., seasonally varying input of allochthonous organic matter.

Description: The quasi-decadal salinity fluctuations in the upper 300 m of the Labrador Sea are investigated by partitioning all available salinity station data since 1948 by region and bottom depth. There are major freshwater anomalies in the early 1970s (the Great Salinity Anomaly), mid-1980s, and early 1990s. These vary in amplitude throughout the region, being least on the shelf and greatest over the slope region near the Labrador Current. The Labrador Sea cannot be considered a simple conduit for freshwater anomalies originating in the East Greenland Current. There is evidence that local processes modulate the anomaly. The freshwater anomalies in the Labrador Current are approximately twice as large as those in the East Greenland Current. The Baffin Island Current flowing southward through the western Davis Strait is the only local source of freshwater with sufficient volume to account for this increase. The propagation speed, 2–3 cm s−1, of the anomaly along the Labrador Sea margin is much less than the advection speed indicating a highly damped system. The connection of the North Atlantic Oscillation (NAO) with these quasi-decadal salinity fluctuations is most obvious in the Labrador Sea interior, where increased surface buoyancy flux during positive NAO drives deep convective mixing and thus terminates the fresh surface anomalies. Less clear are the processes by which NAO-forced changes of lateral freshwater flux modulate the salinity along the margin. The authors propose a feedback mechanism where, during years of low wind speed, freshwater accumulates offshore of the slope front in the surface layer. The increased upper-layer buoyancy prohibits further mixing, and low salinities persist.

Description: In 1997, a unique hydrographic and chlorofluorocarbon (CFC: component CFC-11) dataset was obtained in the subpolar North Atlantic. To estimate the synopticity of the 1997 data, the recent temporal evolution of the CFC and Labrador Sea Water (LSW) thickness fields are examined. In the western Atlantic north of 50°N, the LSW thickness decreased considerably from 1994–97, while the mean CFC concentrations did not change much. South of 50°N and in the eastern Atlantic, the CFC concentration increased with little or no change in the LSW thickness. On shorter timescales, local anomalies due to the presence of eddies are observed, but for space scales larger than the eddies the dataset can be treated as being synoptic over the 1997 observation period. The spreading of LSW in the subpolar North Atlantic is described in detail using gridded CFC and LSW thickness fields combined with Profiling Autonomous Lagrangian Circulation Explorer (PALACE) float trajectories. The gridded fields are also used to calculate the CFC-11 inventory in the LSW from 40° to 65°N, and from 10° to 60°W. In total, 2300 ± 250 tons of CFC-11 (equivalent to 16.6 million moles) were brought into the LSW by deep convection. In 1997, 28% of the inventory was still found in the Labrador Sea west of 45°W and 31% of the inventory was located in the eastern Atlantic. The CFC inventory in the LSW was used to estimate the lower limits of LSW formation rates. At a constant formation rate, a value of 4.4–5.6 Sv (Sv ≡ 106 m3 s−1) is obtained. If the denser modes of LSW are ventilated only in periods with intense convection, the minimum formation rate of LSW in 1988–94 is 8.1–10.8 Sv, and 1.8–2.4 Sv in 1995–97

Description: Time series of hydrographic and transient tracer (3H and 3He) observations from the central Labrador Sea collected between 1991 and 1996 are presented to document the complex changes in the tracer fields as a result of variations in convective activity during the 1990s. Between 1991 and 1993, as atmospheric forcing intensified, convection penetrated to progressively increasing depths, reaching 2300 m in the winter of 1993. Over that period the potential temperature (θ)/salinity (S) properties of Labrador Sea Water stayed nearly constant as surface cooling and downward mixing of freshwater was balanced by excavating and upward mixing of the warmer and saltier Northeast Atlantic Deep Water. It is shown that the net change in heat content of the water column (150–2500 m) between 1991 and 1993 was negligible compared to the estimated mean heat loss over that period (110 W m−2), implying that the lateral convergence of heat into the central Labrador Sea nearly balances the atmospheric cooling on a surprisingly short timescale. Interestingly, the 3H–3He age of Labrador Sea Water increased during this period of intensifying convection. Starting in 1995, winters were milder and convection was restricted to the upper 800 m. Between 1994 and 1996, the evolution of 3H–3He age is similar to that of a stagnant water body. In contrast, the increase in θ and S over that period implies exchange of tracers with the boundaries via both an eddy-induced overturning circulation and along-isopycnal stirring by eddies [with an exchange coefficient of O(500 m2 s−1)]. The authors construct a freshwater budget for the Labrador Sea and quantitatively demonstrate that sea ice meltwater is the dominant cause of the large annual cycle of salinity in the Labrador Sea, both on the shelf and the interior. It is shown that the transport of freshwater by eddies into the central Labrador Sea (140 cm between March and September) can readily account for the observed seasonal freshening. Finally, the authors discuss the role of the eddy-induced overturning circulation with regard to transport and dispersal of the newly ventilated Labrador Sea Water to the boundary current system and compare its strength (2–3 Sv) to the diagnosed buoyancy-forced formation rate of Labrador Sea Water.

Description: Comparisons are made between a time series of meteorological surface layer observational data taken on board the R/V Knorr, and model analysis data from the European Centre for Medium-Range Weather Forecasting (ECMWF) and the National Centers for Environmental Prediction (NCEP). The observational data were gathered during a winter cruise of the R/V Knorr, from 6 February to 13 March 1997, as part of the Labrador Sea Deep Convection Experiment. The surface layer observations generally compare well with both model representations of the wintertime atmosphere. The biases that exist are mainly related to discrepancies in the sea surface temperature or the relative humidity of the analyses. The surface layer observations are used to generate bulk estimates of the surface momentum flux, and the surface sensible and latent heat fluxes. These are then compared with the model-generated turbulent surface fluxes. The ECMWF surface sensible and latent heat flux time series compare reasonably well, with overestimates of only 13% and 10%, respectively. In contrast, the NCEP model overestimates the bulk fluxes by 51% and 27%, respectively. The differences between the bulk estimates and those of the two models are due to different surface heat flux algorithms. It is shown that the roughness length formula used in the NCEP reanalysis project is inappropriate for moderate to high wind speeds. Its failings are acute for situations of large air–sea temperature difference and high wind speed, that is, for areas of high sensible heat fluxes such as the Labrador Sea, the Norwegian Sea, the Gulf Stream, and the Kuroshio. The new operational NCEP bulk algorithm is found to be more appropriate for such areas. It is concluded that surface turbulent flux fields from the ECMWF are within the bounds of observational uncertainty and therefore suitable for driving ocean models. This is in contrast to the surface flux fields from the NCEP reanalysis project, where the application of a more suitable algorithm to the model surface-layer meteorological data is recommended

Description: The so-called equatorial stacked jets are analyzed with ship-board observations and moored time series from the Atlantic Ocean. The features are identified and isolated by comparing vertical wavenumber spectra at the equator with those a few degrees from the equator. Mode-filtering gives clear views of the jets in meridional sections, the typical extent being ±1° in latitude. The vertical structure can be well described (explaining 82% of the variance) by N−1-stretched cosines, with a Gaussian amplitude tapering in the vertical. The stretched wavelengths are somewhat variable. Fitting jets of a fixed (stretched) wavelength to four moored sensors in the depth range 1300–1900 m, allows one to track the vertical phase of the jets with an rms error of 30°–45°. The resulting fit from a 20-month moored time series shows long periods of unchanging jet conditions and intermittent times of high variability. There is no significant vertical propagation on these timescales nor a seasonal reversal. Using a composite from many different experiments, interannual variability is visible, however. A possible mechanism for the stacked jets is inertial instability, resulting from background meridional shears at the equator. A condition is that the Ertel potential vorticity becomes zero somewhere, due to meridional asymmetries in the zonal flows. The ship-board observations show that this may be approximately fulfilled by the instantaneous zonal low-mode flows at various depths, resulting from an excess of zonal momentum south of the equator most of the time. Inertial instability should act to redistribute this zonal momentum, and our mooring data show indeed persistent northward momentum flux, but not at the depth levels expected. The momentum transport might suggest that the jets can also flux or mix other properties across the equator.

Description: The circulation of water masses in the northeastern North Atlantic Ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes1. But the ocean circulation at depths below the reach of satellite observations is difficult to measure, and only recently have comprehensive, direct observations of whole ocean basins been possible2, 3, 4. Here we present quantitative maps of the absolute velocities at two levels in the northeastern North Atlantic as obtained from acoustically tracked floats. We find that most of the mean flow transported northward by the Gulf Stream system at the thermocline level (about 600 m depth) remains within the subpolar region, and only relatively little enters the Rockall trough or the Nordic seas. Contrary to previous work5, 6, our data indicate that warm, saline water from the Mediterranean Sea reaches the high latitudes through a combination of narrow slope currents and mixing processes. At both depths under investigation, currents cross the Mid-Atlantic Ridge preferentially over deep gaps in the ridge, demonstrating that sea-floor topography can constrain even upper-ocean circulation patterns.

Description: The sediment beneath and at various distances from the fish farm cages in Cephalonia bay (Eastern Mediterranean) was investigated seasonally through sediment profiling imagery (SPI) as well as through monitoring of geochemical variables and macrofaunal assemblages. The SPI images (SPI) repeatedly showed the same qualitative pattern along the benthic enrichment gradient with readily identifiable attributes such as depth of dark sediment, signs of outgassing and bioturbation marks. Quantitative comparisons showed that a large number of SPI attributes showed significant positive or negative correlation with geochemical and biological attributes describing the effect of fish farming on the seabed. All multivariate patterns obtained through the analysis of SPI attributes were highly correlated to those obtained from standard multivariate analysis of macrofauna during the respective seasons. It is argued that SPI provides an integrated assessment of the sedimentary conditions and therefore may be used as a complement of or even a substitute for standard sampling methods when mapping the effects of aquaculture on silty substrates

Description: Sediment incubation microcosms, multitrap apparatus and water column variables have been employed to describe the dynamic changes in benthic-pelagic coupling between nutrient pools in the Pontevedra ria, NW Spain, during spring and summer 1998. A comparison of the chemical characteristics of suspended and bed sediment together with sediment nutrient effluxes revealed that particulate organic nitrogen and carbon were progressively depleted upon transit through the nutrient pools. The main fate of particulate organic nitrogen reaching the bed sediment is denitrification, although resuspension is also important. An estimate of net denitrification (Dnet) was made at 2 muddy sites in the ria with a mass balance at the benthic boundary layer. First-order approximations calculate Dnet to be 178 and 182 µmolN m-2 h-1 at the 2 stations, and agree well with previous modelling estimates. Denitrification is highest when upwelling relaxes and the flux of organic matter to the sediment increases. Regular inputs of offshore water ensure water renewal and re-oxygenation of bottom waters, thus preventing anoxia, particularly in the summer. With upwelling, large quantities of ammonium are effluxed to the water column (250 µmolNH4+ m-2 h-1), probably as a result of the bed sediment resuspension engendered by upwelling and stirring of phytodetrital fluff held in suspension as neutrally buoyant material above the sediment surface. We hypothesise that hydrodynamical processes play an important role in determining the quantity of nutrients remineralised in the Pontevedra ria and, in the case of nitrogen, the rate of denitrification at the benthic boundary layer.

Description: The interannual variability of the tropical Indian Ocean sea surface temperature (SST) is studied with observational data and a hierarchy of coupled general circulation models (CGCMs). Special attention is given to the question whether an oscillatory dipole mode exists in the tropical Indian Ocean region with centers east and west of 80°E. Our observational analyses indicate that dipole-like variability can be explained as an oscillatory mode only in the context of ENSO (El Nino/Southern Oscillation). A dipole-like structure in the SST anomalies independent of ENSO was found also. Our series of coupled model experiments shows that ocean dynamics is not important to this type of dipole-like SST variability. It is forced by surface heat flux anomalies that are integrated by the thermal inertia ofthe oceanic mixed layer, which reddens the SST spectrum.

Description: Empirical orthogonal function (EOF) analyses (rotated or not) are widely used in climate research. In recent years there have been several studies in which EOF analyses were used to highlight potential physical mechanisms associated with climate variability. For example, several SST modes were identified such as the “Tropical Atlantic Dipole,” the “Tropical Indian Ocean Dipole,” and different SLP modes in the Northern Hemisphere winter. In this note it is emphasized that caution should be used when trying to interpret these statistically derived modes and their significance. Indeed, from a synthetic example it is shown that patterns derived from EOF analyses can be misleading at times and associated with very little climate physics.

Description: Gas hydrates occur at the sediment surface on the southern summit of Hydrate Ridge, Cascadia convergent margin. The hydrates are found in mounds several meters in diameter and up to 2 m high, and are covered by sediment and mats of the filamentous sulfur-oxidizing bacteria Beggiatoa. The mounds are surrounded by vesicomyid clams (Calyptogena pacifica, C. kilmeri), which in turn are encircled by solemyid bivalves (Acharax sp.). The zonation pattern of 3 species (Calyptogena spp. and Acharax sp., which harbor chemoautotrophic bacteria in their gills, and the chemoautotrophic Beggiatoa), is also reflected in a change in the entire community structure. Beggiatoa, Calyptogena spp. and Acharax sp. are shown to be characteristic species for the different communities. The Beggiatoa community directly overlaying the gas hydrates consists of seep endemic species in high densities: gastropods (Provanna laevis, P. lomana, Pyropelta corymba, Hyalogyrina sp. nov.), bivalves (Nuculana sp. nov.) and polychaetes (Ampharetidae, Polynoidae, Dorvilleidae). Based on pooled samples, the rarefaction curves show a decrease in species diversity in the Beggiatoa and Calyptogena communities. The hydrogen sulfide gradients in the porewater of sediments below the different communities dominated by either Beggiatoa, Calyptogena spp. or Acharax sp. vary by 3 orders of magnitude. The diffusive sulfide flux based on the measured sulfide concentration gradients is highest in Beggiatoa sp. communities (23 ± 13 mol m-2 yr-1), slightly less in Calyptogena communities (6.6 ± 2.4 mol m-2 yr-1), and low in Acharax communities (0.05 ± 0.05 mol m-2 yr-1). The difference in the sulfide environment is a factor influencing the distribution patterns of the chemoautotrophy-dependant and heterotrophic species at the deep-sea sediments containing gas hydrate.

Description: A colony of Humboldt penguins Spheniscus humboldti in central Chile was monitored from August 1995 to July 2000 to determine patterns of breeding and colony attendance and how these were affected by climatic (rainfall) and oceanographic (El Niño) factors. Nests were periodically checked for contents and roosting birds were counted from vantage points. Two main breeding events were observed: between August and January (spring event) and between April and June (autumn event). Whereas the spring event regularly produced offspring, the autumn event was systematically affected by rains, causing considerable nest desertion. Adults were present in the colony from August to May, abandoning the colony during winter after the nests were flooded. Juveniles occurred only between November and March. Adults moulted mainly in February, while juveniles moulted in January. During the 1997/98 El Niño episode, the number of breeding pairs was 55 to 85% lower than the mean, the onset of nesting was delayed, and abnormally heavy rainfall flooded nests. While the number of breeding pairs was significantly related to sea surface temperature anomalies (SSTA), breeding success was not. The attendance of adults and juveniles at the colony during El Niño was 25 and 73% lower, respectively, than the mean attendance. This 2-peak breeding strategy of Humboldt penguins appears to have evolved in response to the more favourable oceanographic and climatic conditions of Perú, where breeding is continuous and not interrupted by rains. Although less productive, the species probably maintains its autumnal breeding in central Chile because this provides additional offspring to supplement those regularly produced during the spring event.

Description: Experiments with a suite of North Atlantic general circulation models are used to examine the sources of eddy kinetic energy (EKE) in the Labrador Sea. A high-resolution model version (112°) quantitatively reproduces the observed signature. A particular feature of the EKE in the Labrador Sea is its pronounced seasonal cycle, with a maximum intensity in early winter, as already found in earlier studies based on altimeter data. In contrast to a previously advanced hypothesis, the seasonally varying eddy field is not related to a forcing by high-frequency wind variations but can be explained by a seasonally modulated instability of the West Greenland Current (WGC). The main source of EKE in the Labrador Sea is an energy transfer due to Reynolds interaction work (barotropic instability) in a confined region near Cape Desolation where the WGC adjusts to a change in the topographic slope: Geostrophic contours tend to converge upstream of Cape Desolation, such that the topographically guided WGC narrows as well and becomes barotropically unstable. The eddies spawned from the WGC instability area, dominating the EKE in the interior Labrador Sea, are predominantly anticyclonic with warm and saline cores in the upper kilometer of the water column, while the few cyclones originating as well from the instability area show a more depth-independent structure. Companion experiments with a ⅓° model exhibit the strength of the WGC, influenced by either changes in the wind stress or heat flux forcing, as a leading factor determining seasonal to interannual changes of EKE in the Labrador Sea

Description: Zooplankton grazing on bacterio- and phytoplankton was studied in the Gulf of Aqaba and the Northern Red Sea during Meteor Cruise Me 44-2 in February-March 1999. Protozoan grazing on bacterioplankton and autotrophic ultraplankton was studied by the Landry dilution method. Microzooplankton grazing on phytoplankton 〉6 µm was studied by incubation experiments in the presence and absence of microzooplankton. Mesozooplankton grazing was studied by measuring per capita clearance rates of individual zooplankton with radioactively labelled food organisms and estimating in situ rates from abundance values. Protozoan grazing rates on heterotrophic bacteria and on algae 〈6 µm were high (bacteria: 0.7 to 1.1 d-1, ultraphytoplankton: 0.7 to 1.3 d-1), while grazing rates on Synechococcus spp. were surprisingly low and undetectable in some experiments. Mesozooplankton grazing was weak, cumulative grazing rates being ca. 2 orders of magnitude smaller than the grazing rates by protozoans. Among mesozooplankton, appendicularians specialised on smaller food items and calanoid copepods on larger ones.

Description: Two new isomalabaricane triterpenes, stellettin H (1) and stellettin I (2), have been isolated from the marine sponge Rhabdastrella globostellata, collected from the Philippines. Stellettins A−D (3−6), (−)-stellettin E (7), and rhabdastrellic acid-A (8) were also isolated and characterized. Stellettin B (4) and (−)-stellettin E (7) showed selective cytotoxicity toward p21WAF1/Cip1-deficient human colon tumor (HCT-116) cells with IC50 values of 0.043 and 0.039 μM, respectively.

Description: Raf/MEK-1/MAPK cascade inhibitor activity-directed fractionation of the sponge Stylissa massa afforded eight known alkaloids:  aldisine (1), 2-bromoaldisine (2), 10Z-debromohymenialdisine (3), 10E-hymenialdisine (4), 10Z-hymenialdisine (5), hymenin (6), oroidin (7), and 4,5-dibromopyrrole-2-carbonamide (8). Both 4 and 5 showed significant enzyme inhibitory activity (IC50 3 and 6 nM, respectively). Secondary assays identified these compounds as potent MEK-1 inhibitors. Compounds 4 and 5 also inhibited the growth of human tumor LoVo cells.

Description: The increasing environmental pressures on estuarine and coastal waters call for improved monitoring techniques of chemical constituents to aid management decisions. Automated stripping voltammetry is a suitable technique for continuous, near real-time monitoring of trace metals in marine systems. This contribution describes the application of voltammetric monitoring techniques in estuarine and coastal waters of the UK and Spain. The high spatial and temporal resolution of the data obtained, allows a thorough interpretation of the trace metal sources and behaviour. Future trends in this field research include submersible sensors which can be remotely deployed for a period of several weeks.

Description: normous amounts of potential energy lie buried in marine sediments in the form of reduced carbon compounds. The most familiar form of this vast energy reserve is petroleum, which drives the lion's share of today's energy economy. The next most obvious submarine energy reserve, even more abundant than petroleum, is methane. At deep-sea conditions of low temperature and high pressure, large amounts of this natural gas are found in sub-seafloor reservoirs of frozen methane hydrates [1]. Yet there is another abundant, but less obvious, marine energy reserve: sediment-associated organic carbon, which represents about 2% of the dry weight of marine sediments along continental margins. Is it possible to tap into this vast, dispersed form of submarine energy? If so, how? The answer, in part, is that microbes already have tapped into this large energy reserve. Now, in two papers, one in this issue [2] and the other in a previous issue of Science [3], researchers harness microbially generated power by constructing a fuel cell that can exploit the naturally occurring voltage gradient created by microbial activity in marine sediments.

Description: In many marine environments, a voltage gradient exists across the water sediment interface resulting from sedimentary microbial activity. Here we show that a fuel cell consisting of an anode embedded in marine sediment and a cathode in overlying seawater can use this voltage gradient to generate electrical power in situ. Fuel cells of this design generated sustained power in a boat basin carved into a salt marsh near Tuckerton, New Jersey, and in the Yaquina Bay Estuary near Newport, Oregon. Retrieval and analysis of the Tuckerton fuel cell indicates that power generation results from at least two anode reactions: oxidation of sediment sulfide (a by-product of microbial oxidation of sedimentary organic carbon) and oxidation of sedimentary organic carbon catalyzed by microorganisms colonizing the anode. These results demonstrate in real marine environments a new form of power generation that uses an immense, renewable energy reservoir (sedimentary organic carbon) and has near-immediate application.

Description: Factors responsible for aggregations of jumbo flying squid Dosidicus gigas, an important component of the marine food web and target of commercial fisheries off the Costa Rica Dome in the Eastern Tropical Pacific Ocean (ETP), were examined during 2 years of different extreme oceanographic conditions: fall 1997 El Niño and fall 1999 La Niña. A high abundance of squid occurred in association with the well-developed countercurrent ridge (upwelling) off the Costa Rica Dome during fall 1997, but not during fall 1999, when the countercurrent ridge was less developed. Two features of the well-developed countercurrent ridge were considered important for the occurrence of high jumbo flying squid concentrations. Firstly, subsurface chlorophyll a (chl a) maxima were formed along the countercurrent ridge, resulting in integrated chl a concentrations in the upper 100 m being relatively high considering the generally low productivity of the ETP during an El Niño event. Secondly, a strong salinity front formed along the North Equatorial Countercurrent, which is possibly responsible for retention of jumbo flying squid in the ridge. Large yellowfin tuna Thunnus albacares, which mainly feed on micronekton (small fishes, cephalopods and swimming crabs), as do jumbo flying squid, were also more highly concentrated along the countercurrent ridge during 1997 than during 1999. It was noted that skipjack tuna Katsuwonus pelamis and small yellowfin tuna, which mainly feed on zooplankton, were associated with the equatorial ridge in the ETP, indicating that prey faunal components may also play an important part in the close association of jumbo flying squid with the countercurrent ridge.

Description: The oceanic carbon cycle is mainly determined by the combined activities of bacteria and phytoplankton, but the interdependence of climate, the carbon cycle and the microbes is not well understood. To elucidate this interdependence, we performed high-frequency sampling of sea water along a north-south transect of the Atlantic Ocean. Here we report that the interaction of bacteria and phytoplankton is closely related to the meridional profile of water temperature, a variable directly dependent on climate. Water temperature was positively correlated with the ratio of bacterial production to primary production, and, more strongly, with the ratio of bacterial carbon demand to primary production. In warm latitudes (25 degrees N to 30 degrees S), we observed alternating patches of predominantly heterotrophic and autotrophic community metabolism. The calculated regression lines (for data north and south of the Equator) between temperature and the ratio of bacterial production to primary production give a maximum value for this ratio of 40% in the oligotrophic equatorial regions. Taking into account a bacterial growth efficiency of 30%, the resulting area of net heterotrophy (where the bacterial carbon demand for growth plus respiration exceeds phytoplankton carbon fixation) expands from 8 degrees N (27 degrees C) to 20 degrees S (23 degrees C). This suggests an output of CO2 from parts of the ocean to the atmosphere.

Description: We examined how seabirds might be used to study marine environmental variables, which necessitates knowing location and the value of the variable to be studied. Five systems can potentially be used for determination of location: VHF (Very High Frequency) telemetry, PTT (Platform Terminal Transmitters) telemetry, GLS (Global Location Service) geolocation methods, dead reckoning and GPS (Global Positioning System), each with its own advantages with respect to accuracy, potential number of fixes and size. Temperature and light were used to illustrate potential difficulties in recording environmental variables. Systems currently used on seabirds for measurement of temperature respond slowly to environmental changes; thus, they may not measure sea surface temperature adequately when contact periods with water bodies are too short. Light can be easily measured for light extinction studies, but sensor orientation plays a large role in determining recorded values. Both problems can be corrected. The foraging behaviour of seabirds was also examined in order to identify those features which would be useful for determination of marine environmental variables at a variety of spatial and temporal scales. Area coverage by birds is highly dependent on breeding phase and tends to be concentrated in areas where prey acquisition is particularly enhanced. The identification of these sites may be of particular interest to marine biologists. 'Plungers' and 'divers' are potentially most useful for assessment of variables deeper within the water column, with some divers spending up to 90% of their time sub-surface. Few seabirds exploit the water column deeper than 20 m, although some divers regularly exceed 50 m (primarily penguins and auks), while 2 species dive in excess of 300 m. The wide-ranging behaviour of seabirds coupled, in many instances, with their substantial body size makes them potentially excellent carriers of sophisticated environmental measuring technology; however, the ethical question of how much the well-being of birds can, and should, be compromised by such an approach needs to be carefully considered.

Description: Aspects of the decay of stable frontal warm-core eddies in the deep ocean are investigated using a new numerical layered “frontal” model that solves the nonlinear, reduced-gravity, shallow-water equations for a horizontally inhomogeneous, viscous fluid on an f plane. After a discussion on aspects of the numerical techniques implemented to allow for the eddy expansions and contractions at the sea surface, for the first time the capability of a numerical model of reproducing the evolution of analytical nonstationary frontal vortices is explored. This step is necessary, as far as different phenomena related to the dynamics of these oceanic features are to be studied numerically. In fact the comparison between numerical and analytical inviscid solutions allows for a quantification of the numerical dissipation affecting the simulated solutions. This dissipation is found to be very small in this numerical model: The simulated lifetimes are larger than those of most of the frontal eddies observed in the World Ocean. On this basis, the eddy decay due to interfacial (linear and quadratic) friction, harmonic horizontal momentum diffusion, as well as linear ambient-water entrainment is investigated. It is found that interfacial friction represents a much more efficient mechanism than horizontal diffusion and water entrainment in inducing the eddy decay as well as in damping the eddy pulsations. It is thus suggested that internal wave radiation due to vortex pulsation can represent a relevant mechanism for the dissipation of the vortex energy in a stratified ambient ocean only episodically. Finally, a critical discussion about the appropriateness of the different approximations assumed in the investigation is presented. In particular, the appropriateness of the reduced-gravity assumption is discussed. Results are consistent with those obtained analytically in the frame of the frontal-geostrophic theory: Although the effect of an active ambient layer on the vortex dynamics is found to be virtually absent only for unrealistically large water depths, it appears that the reduced-gravity model describes warm-core eddies acceptably for values of the ratio between maximum vortex thickness and total water depth typical for Gulf Stream rings.

Description: Zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the Southern Hemisphere during all seasons. This is true not only in observations but also in an unforced 15 000-yr integration of a coarse-resolution (R15) coupled ocean–atmosphere model. Here it is documented how this mode of atmospheric variability, known as the Southern Annular Mode (SAM), generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the SAM. The positive phase of the SAM is associated with an intensification of the surface westerlies over the circumpolar ocean (around 60°S), and a weakening of the surface westerlies farther north. This induces Ekman drift to the north at all longitudes of the circumpolar ocean, and Ekman drift to the south at around 30°S. Through mass continuity, the Ekman drift generates anomalous upwelling along the margins of the Antarctic continent, and downwelling around 45°S. The anomalous flow diverging from the Antarctic continent also increases the vertical tilt of the isopycnals in the Southern Ocean, so that a more intense circumpolar current is also closely associated with positive SAM. In addition, the anomalous divergent flow advects sea ice farther north, resulting in an increase in sea ice coverage. Finally, positive SAM drives increases in poleward heat transport at about 30°S, while decreases occur in the circumpolar region. Ocean and sea ice anomalies of the opposite sign occur when the SAM is negative. The ocean and sea ice fluctuations associated with the SAM constitute a significant fraction of simulated ocean variability poleward of 30°S year-round. The robustness of the mechanisms relating the SAM to oceanic variability suggests that the SAM is likely an important source of large-scale variability in the real Southern Hemisphere ocean.

Description: Two configurations of a primitive-equation model of the North Atlantic are analyzed with respect to the simulated cycling of energy, mass, and heat in the upper ocean. One model is eddy-permitting (1/3° horizontal resolution), the other one is eddy-resolving (1/9° resolution), with both models using identical topographies and identical forcing fields at the surface and lateral boundaries. Besides showing some improvement in the simulated mean circulation and heat budgets, the eddy-resolving model reaches good agreement with satellite altimeter measurements of sea surface height variability. An unexpected finding of the model intercomparison is that simulated winter mixed layer depths in mid and high latitudes turn out to be systematically shallower by some 50 to 500 m in the higher resolution run, thereby agreeing better with observations than the 1/3° model results. This model improvement is related to enhanced levels of baroclinic instability leading to a decrease in potential energy and an associated increase in stratification. In the high-resolution model, shear-induced tilting of lateral density gradients generates stratification within the mixed layer itself, at a rate sufficient to set off an average surface heat loss of 5 W m–2 in mid and high latitudes. Although this is small compared to present uncertainties in surface heat fluxes, the resulting reduction in mixed layer depths may be important for an accurate simulation of water mass formation, air–sea gas exchange, and marine biological production. With traditional formulations of mixed layer physics assuming that properties are set by purely vertical mixing, and parameterizations of lateral subgrid-scale mixing often being tapered to zero in the mixed layer, present mixing schemes would have to be modified in order to account for eddy-induced generation of stratification in the surface mixed layer in noneddy-resolving ocean models.

Description: Time series of hydrographic and transient tracer (3H and 3He) observations from the central Labrador Sea collected between 1991 and 1996 are presented to document the complex changes in the tracer fields as a result of variations in convective activity during the 1990s. Between 1991 and 1993, as atmospheric forcing intensified, convection penetrated to progressively increasing depths, reaching 2300 m in the winter of 1993. Over that period the potential temperature (θ)/salinity (S) properties of Labrador Sea Water stayed nearly constant as surface cooling and downward mixing of freshwater was balanced by excavating and upward mixing of the warmer and saltier Northeast Atlantic Deep Water. It is shown that the net change in heat content of the water column (150–2500 m) between 1991 and 1993 was negligible compared to the estimated mean heat loss over that period (110 W m−2), implying that the lateral convergence of heat into the central Labrador Sea nearly balances the atmospheric cooling on a surprisingly short timescale. Interestingly, the 3H–3He age of Labrador Sea Water increased during this period of intensifying convection. Starting in 1995, winters were milder and convection was restricted to the upper 800 m. Between 1994 and 1996, the evolution of 3H–3He age is similar to that of a stagnant water body. In contrast, the increase in θ and S over that period implies exchange of tracers with the boundaries via both an eddy-induced overturning circulation and along-isopycnal stirring by eddies [with an exchange coefficient of O(500 m2 s−1)]. The authors construct a freshwater budget for the Labrador Sea and quantitatively demonstrate that sea ice meltwater is the dominant cause of the large annual cycle of salinity in the Labrador Sea, both on the shelf and the interior. It is shown that the transport of freshwater by eddies into the central Labrador Sea (140 cm between March and September) can readily account for the observed seasonal freshening. Finally, the authors discuss the role of the eddy-induced overturning circulation with regard to transport and dispersal of the newly ventilated Labrador Sea Water to the boundary current system and compare its strength (2–3 Sv) to the diagnosed buoyancy-forced formation rate of Labrador Sea Water.

Description: Vertical profiles of horizontal currents and hydrographic measurements from three cruises along 80.5°E from the coast of Sri Lanka to 6°S between December 1990 and September 1994 are used to investigate the scales of the Indian Ocean deep jets as well as internal wave parameters and dissipation at the equator. The deep jets at 80.5°E have a vertical wavelength of 660 sm (stretched meters) and amplitudes exceeding 10 cm s−1 in zonal velocity. They are observed throughout the water column and their flow direction reverses at 2° off the equator. The vertical positions of the jets differ among the cruises and are consistent with a flow reversal between the data collected in winter and summer. During September 1994, the jets were less pronounced. Due to the meridional distribution of their zonal velocity and the phase relationship between zonal velocity and vertical displacement, the jets are best described as nondispersive first-mode equatorial Rossby waves. The hydrographic data revealed thick layers of low stratification with vertical scales of 15–55 m in the upper 2000 m of the water column. They are found primarily within 1° of the equator and there is some evidence of correlation between the vertical position as well as the extent and the high strain zones of the deep jets. At vertical wavenumbers larger than those of the deep jets, shear and strain levels are five times larger than at off-equatorial locations and the compliant internal wave range (“roll-off range”) begins at a smaller wavenumber (kc ≈ 0.02 cpsm). An estimate of the average dissipation rate within the deep jets yielded = 7.5 × 10−10 W kg−1 between 500- and 2000-m depth. The elevated finescale internal wave field appears to be the main cause for the existence of the low stratification layers.

Description: We report how different zooplankton groups (doliolids, cladocerans and copepods) are able to influence the coastal pelagic food web, including the microbial food web, in waters of the NW Mediterranean. We studied the effect of grazing and of grazing-induced nutrient recycling mediated by different types of zooplankton grazing on a natural phytoplankton community. Experiments were conducted in semicontinuous 2-stage chemostats. The 1st stage vessels contained seawater from Blanes Bay, Spain (NW Mediterranean) including its natural phytoplankton community; the 2nd stage vessels contained the same seawater and copepods, cladocerans or doliolids. At daily intervals we transferred part of the medium from the 2nd to the 1st stage flasks, which contained ungrazed algae and excreted nutrients. In this way, the zooplankton could influence phytoplankton dynamics both by selective grazing and by differential excretion of limiting nutrients. In the 2nd stage flasks grazing changed the algal community composition. Doliolids and cladocerans promoted the growth of large algae and copepods shifted the size spectrum towards small sizes. This effect was transferred to the 1st stage flasks. Doliolids, cladocerans and copepods also affected the microbial food web in different ways. Size-selective grazing led to differences in the nanoplankton concentrations. These in turn affected bacterial concentrations in a trophic cascade. The potential to modify a given algal population increased with increasing selectivity of the grazer.

Description: Both surface texture and littorinid grazing are known to influence the establishment of many shallow-water benthic hard-bottom communities. However, the effects of these factors and their interactions have not yet been investigated in a quantifiable manner. This investigation aims to assess the interactive effect of both factors in a strictly standardized manner. Natural recruitment by diatoms, the barnacle Balanus improvisus and the tube-building polychaete Polydora sp. was monitored under a 2-factorial treatment: grazing by the periwinkle Littorina littorea (Factor 1; 2 levels: I or no snails per plate) on artificial recruitment plates of different initial surface rugosities (Factor 2; 5 levels: smooth, 0.1, 0.5, 1 and 5 mm rugosity elements), In the absence of grazers, barnacle recruitment decreased with increasing initial rugosity, polychaete recruitment peaked at intermediate rugosities, and diatoms exhibited contrasting recruitment patterns in an in vitro and an in situ experiment. When preferred recruitment sites coincided for Polydora and B. improvisus, a competition for space could be inferred from a negative correlation between the 2 species. However, when the overlap of requirements weakened on the 5 rugosities, the relationship was positive, but was not statistically significant. Grazing efficiency by L. littorea depended on initial rugosity, generally showing minimum values on intermediate rugosities which is attributable to a mismatch between radula dimensions and surface structures in these rugosity classes. Additionally, grazing effects tended to increase with higher prey densities. As all factors-initial rugosity, grazing, colonizer species-interact with each other, the outcome of recruitment under combined factors is difficult to predict from single factor effects.

Description: A unique open-ocean upwelling exists in the tropical South Indian Ocean (SIO), a result of the negative wind curl between the southeasterly trades and equatorial westerlies, raising the thermocline in the west. Analysis of in situ measurements and a model-assimilated dataset reveals a strong influence of subsurface thermocline variability on sea surface temperature (SST) in this upwelling zone. El Niño–Southern Oscillation (ENSO) is found to be the dominant forcing for the SIO thermocline variability, with SST variability off Sumatra, Indonesia, also making a significant contribution. When either an El Niño or Sumatra cooling event takes place, anomalous easterlies appear in the equatorial Indian Ocean, forcing a westward-propagating downwelling Rossby wave in the SIO. In phase with this dynamic Rossby wave, there is a pronounced copropagation of SST. Moreover, a positive precipitation anomaly is found over, or just to the south of, the Rossby wave–induced positive SST anomaly, resulting in a cyclonic circulation in the surface wind field that appears to feedback onto the SST anomaly. Finally, this downwelling Rossby wave also increases tropical cyclone activity in the SIO through its SST effect. This coupled Rossby wave thus offers potential predictability for SST and tropical cyclones in the western SIO. These results suggest that models that allow for the existence of upwelling and Rossby wave dynamics will have better seasonal forecasts than ones that use a slab ocean mixed layer. The lagged-correlation analysis shows that SST anomalies off Java, Indonesia, tend to precede those off Sumatra by a season, a time lead that may further increase the Indian Ocean predictability.

Description: The Eurofloat experiment was a joint initiative to examine the large-scale spreading of Mediterranean Water (MW) and Labrador Sea Water in the northeast North Atlantic. RAFOS float data from the southern (MW) portion of the Eurofloat experiment have been examined in conjunction with historical float data in order to calculate quasi-Eulerian means in an effort to separate and quantify the constituents of the spreading of the MW tongue east of the Mid-Atlantic Ridge. While recent studies focussed chiefly on the role of meddies in the shaping of the MW tongue, this analysis also examines the tongue's second constituent, that is, the “background” (non-meddy advective and diffusive) flow. The results suggest the existence of two regimes approximately to the north and south of the 36°N parallel (i.e., the latitude of the Gulf of Cadiz), which are distinguished by different types of dominant spreading mechanisms for MW. To the south of the Gulf of Cadiz, the background flow shows an incoherent and weak mean, whereas the mean velocity of the salt enhanced meddies is strong and to the southwest. In contrast, to the north of 36°N the mean velocity of the meddies seems to be less pronounced and the background flow is shown to be a major component in the northwestward spreading of the MW tongue. The two regimes are separated by the Azores Current, which previously has been hypothesized to act as a dynamic barrier to the southward advective spreading of the background regime, which the meddies are able to penetrate because of their high kinetic energy. Overall, the meddies are calculated to contribute to approximately half of the total salinity anomaly flux.