ALBERT

Description: In this study a scenario is developed of two adjacent Mediterranean Water eddies (meddies) as they were observed merging and drifting through the Iberian Basin. Observations are based on four RAFOS floats (at 850–1050 dbar), two hydrographic surveys (centered roughly at 38°N, 24°W), and trajectories of surface drifters (drogued at 100 m). In April 1991, the meddy A was identified and labeled by surface drifters. During the revisit one month later two meddies were encountered, B1 and B2, in the vicinity of the former meddy A. The coalescence of B1 (subsequently identified as A, one month older) and B2 is inferred from a simple kinematic model describing the observed movement of the RAFOS floats for up to three months after the second CTD survey. The deduced vorticity front, radius ∼15 km, within B1 was of insufficient strength to keep the core waters of B1 isolated and prevent the absorption of B1 by B2. The resulting meddy (B1 + B2) showed a clear near-surface dynamical signal. Its deep root (1800 m) could explain the expulsion from the meddy of the remaining RAFOS float and surface drifter at the time of the meddy's collision with the Josephine Seamount. For the first time, a set of Lagrangian and hydrographic observations give direct evidence that neighboring meddies can merge as predicted by theoretical considerations.

Description: Global mean and eddy fields from a four-year experiment with a 1/6° × 1/5° horizontal resolution implementation of the CME North Atlantic model are presented. The time-averaged wind-driven and thermohaline circulation in the model is compared to the results of a 1/3° × 2/5° model run in very similar configuration. In general, the higher resolution results are found to confirm that the resolution of previous CME experiments is sufficient to describe many features of the large-scale circulation and water mass distribution quite well. While the increased resolution does not lead to large changes in the mean flow patterns, the variability in the model is enhanced significantly. On the other hand, however, not all aspects of the circulation have improved with resolution. The Azores Current Frontal Zone with its variability in the eastern basin is still represented very poorly. Particular attention is also directed toward the unrealistic stationary anticyclones north of Cape Hatteras and in the Gulf of Mexico.

Description: To avoid an explicit simulation of the overflows across the Greenland-Scotland ridge, many models of the large-scale ocean circulation seek to include the net effect of the inflowing dense water masses by restoring temperature and salinity near the ridge to observed conditions. In this paper the authors examine the effect of different datasets for the northern restoring condition in two versions, eddy resolving and non-eddy resolving, of the model of the North and equatorial Atlantic that has been developed in recent years as a Community Modeling Effort for WOCE. It is shown that the use of smoothed climatological fields of temperature and salinity south of the Denmark Strait leads to strong deficiencies in the simulation of the deep flow field in the basin. A switch to actual hydrographic data from the Denmark Strait ignites a rapid dynamic response throughout the North Atlantic, affecting the transport and vertical structure of the deep western boundary current and, by virtue of the JEBAR efffect, the transport of the horizontal gyres. Meridional overturning and northward heat transport too weak in the cases with climatological boundary conditions, increase to more realistic levels in the subtropical North Atlantic. The initial response to switches in the high-latitude thermohaline forcing is mediated by fast waves along the westurn boundary, leading to changes in the deep western boundary current in low latitudes after about two years in the non-eddy-resolving cast. The initial timescale depends on the horizontal grid spacing of the model; in the high-resolution case, the first signal reaches the equator in a few months. The adjustment to a new, dynamic quasi equilibrium involves Kelvin waves along the equator and Rossby wave in the interior and is attained in less than two decades throughout the North Atlantic. It is suggested that these fast dynamic adjustment processes could play an important role in possible fluctuations of the thermohaline circulation, or transitions between different equilibrium states of the coupled ocean–atmosphere system, and may have determined the timescale of the observed climatic transitions before and during the last deglaciation.

Description: We have investigated the seasonal cycle and the interannual variability of the tropical Indian Ocean circulation and the Indian summer monsoon simulated by a coupled ocean-atmosphere general circulation model in a 26- year integration. Although the model exhibits significant climate drift, overall, the coupled GCM simulates realistically the seasonal changes in the tropical Indian Ocean and the onset and evolution of the Indian summer monsoon. The amplitudes of the seasonal changes, however, are underestimated. The coupled GCM also simulates considerable interannual variability in the tropical Indian Ocean circulation, which is partly related to the El Niño/Southern Oscillation phenomenon and the associated changes in the Walker circulation. Changes in the surface wind stress appear to be crucial in forcing interannual variations in the Indian Ocean SST. As in the Pacific Ocean, the net surface beat flux acts as a negative feedback on the SST anomalies. The interannual variability in monsoon rainfall, simulated by the coupled GCM, is only about half as strong as observed. The reason for this is that the simulated interannual variability in the Indian monsoon appears to be related to internal processes within the atmosphere only. In contrast, an investigation based on observations shows a clear lead-lag relationship between interannual variations in the monsoon rainfall and tropical Pacific SST anomalies. Furthermore, the atmospheric GCM also fails to reproduce this lead-lag relationship between monsoon rainfall and tropical Pacific SST when run in a stand-alone integration with observed SSTs prescribed during the period 1970–1988. These results indicate that important physical processes relating tropical Pacific SST to Indian monsoon rainfall are not adequately modeled in our atmospheric GCM. Monsoon rainfall predictions appear therefore premature.

Description: The annual cycle of meridional heat transport in the North and equatorial Atlantic Ocean is studied by means of the high-resolution numerical model that had been developed in recent years as a Community Modeling Effort for the World Ocean Circulation Experiment. Similar to previous model studies, there is a winter maximum in northward heat transport in the equatorial Atlantic and a summer maximum in midlatitudes. The seasonal variation in heat transport in the equatorial Atlantic, with a maximum near 8°N, is associated with the out-of-phase changes in heat content to the north and south of that latitude in connection with the seasonal reversal of the North Equatorial Countercurrent. The amplitude of the heat transport variation at 8°N depends on model resolution: forcing with the monthly mean wind stresses of Hellerman–Rosenstein (HR) gives an annual range of 2.1 PW in the case of a 1/3° meridional grid, and 1.7 PW in the case of a 1° grid, compared to 1.4 PW in a previous 2° model. Forcing with the wind stresses of Isemer–Hasse (IH) gives 2.5 PW in the 1/3° and 2.2 PW in the 1° model case. The annual range of heat transport in the subtropical North Atlantic is much less dependent on resolution but sensitive to the wind stress: it increases from 0.5 PW in the case of HR forcing to almost 0.8 PW with IH forcing. The annual cycle of heat transport can be understood in terms of wind-driven variations in the meridional overturning; variations in horizontal gyre transport have only little effect both in the equatorial and in the subtropical Atlantic. In all model solutions the seasonal variations in the near-surface meridional Ekman transport are associated with deep seasonal overturning cells. The weak shear of the deep response suggests that the large variations in heat transport on seasonal and shorter time scales should be of little consequence for observational estimates of mean oceanic heat transports relying on one-time hydrographic surveys.

Description: Cicosal sea surface height (SSH) data in the tropical and midlatitude North Atlantic are analyzed with and without water vapor (WV) correction to study the WV influence on along-track SSH anomaly profits, mesoscale SSH variability, wavenumber spectra, and objectively mapped fields of SSH anomaly. Three different WV datasets were used, one from the Fleet Numerical Oceanographic Center (FNOC) model and two from the Special Sensor Microwave/Imager (SSM/I) based on different WV retrieval algorithms. These WV dataset show significant differences, in particular in the tropics. However, the method for deriving SSH anomalies from altimeter height data Alters out much of the WV corrections. The residual WV effect on SSH anomaly is shown to be most significant in the seasonally migrating intertropical convergence zone of the tropical Atlantic: there the SSM/I corrections reduce the along-track mesoscale SSH variability by typically 1–1.5 cm. On seasonal timescales the maximum WV effect in this region is characterized by a 2–3-cm rms difference between SSH anomaly with and without SSM/I WV corrections, whereas FNOC corrections have almost no effect. Inferred seasonal velocity variations in the North Equatorial Countercurrent core (4° – 6°N) in the region of maximum WY influence (30° – 40°W) are reduced by about 20% and 30%, depending on whether SSM/I corrections by Emery or Wentz are used

Description: Observations of upper-ocean western boundary current (WBC) transports reveal asymmetries between the Northern and the Southern Hemispheres of the Atlantic Ocean. To find out what mechanism might cause these asymmetries the linearized steady-state vorticity equation is applied to the interior of a layer of constant thickness representing the upper Atlantic Ocean. WBC transports are then required to balance the interior volume flux deficit. The ocean is forced by climatological wind stress at the surface; thermohaline forcing is introduced by vertical motion at the lower boundary. A series of model runs using selected combinations of different basin geometries, wind stress fields, and thermohaline forcing patterns yields the following results: asymmetries of WBC transports cannot be explained by the topography shape of coastlines. The wind stress causes 12 Sv (Sv ≡ 1 × 106 m3 s −1) cross-equatorial transport to the north but it cannot account for the other WBC asymmetries. These can be explained by superimposing a thermohaline flow component to the wind-driven circulation. The best agreement with observations could be obtained from a model run driven by a sinking rate of 20 Sv in the northern North Atlantic and 4 Sv in the Weddell Sea compensated by 15 Sv return flow from other oceans via the Agulhas Current or Drake Passage and uniform upwelling of 9 Sv in the Atlantic. In tropical and subtropical latitudes this run reproduces all observed asymmetries, but in subpolar latitudes the model fails. Further conclusions can be drawn from the model results. (i) Up to 20 Sv northward transport of Antarctic Intermediate Water is needed at about 10°S to explain the difference of modeled transports and observations. For the same reasons an Antilles Current of up to 16 Sv is required. (ii) The major part of the northward heat transport in the North Atlantic has to occur via the tropical countercurrents and the North Equatorial Current. Only less than 7 Sv take the shortest way to the Caribbean via the Guyana Current. (iii) Fifty-six percent of the Florida Straits transport is wind driven.

Description: Accurate measurement of fluctuations in temperature and humidity are needed for determination of the surface evaporation rate and the air-sea sensible heat flux using either the eddy correlation or inertial dissipation method for flux calculations. These measurements are difficult to make over the ocean, and are subject to large errors when sensors are exposed to marine air containing spray droplets. All currently available commercial measurement devices for atmospheric humidity require frequent maintenance. Included in the objectives of the Humidity Exchange over the Sea program were testing and comparison of sensors used for measuring both the fluctuating and mean humidity in the marine atmosphere at high wind speeds and development of techniques for the protection of these sensors against contamination by oceanic aerosols. These sensors and droplet removal techniques are described and comparisons between measurements from several different systems are discussed in this paper. To accomplish these goals, participating groups devised and tested three methods of removing sea spray from the sample airstream. The best performance was given by a rotating semen device, the “spray Ringer.” Several high-frequency temperature and humidity instruments, based on different physical principles, were used in the collaborative field experiment. Temperature and humidity fluctuations were measured with sufficient accuracy inside the spray removal devices using Lyman-α hygrometers and a fast thermocouple psychrometer. Comparison of several types of psychrometers (using electric thermometers) and a Rotronic MP-100 humidity sensor for measuring the mean humidity illustrated the hysteresis of the Rotronic MP-100 device after periods of high relative humidity. Confidence in the readings of the electronic psychrometer was established by in situ calibration with repeated and careful readings of ordinary hand-held Assman psychrometers (based on mercury thermometers). Electronic psychrometer employing platinum resistance thermometers perform very well.

Description: The Deep Basin Experiment (DBE) is an international effort and apart of the World Ocean Circulation Experiment with the principal objective of improving our knowledge of the subthermocline circulation. The DBE fieldwork is focussed on the Brazil Basin and this report is concemed with a moored array situated along its southem boundary which was installed in early 1991 to measure the inflow and outflow to the Basin and to investigate the Brazil Current near 30S. This moored array was a joint undertaking by the Institut für Meereskunde of the University of Kiel and the Woods Hole Oceanographic Institution. Moorings were deployed on Meteor Cruise 15, leg I and retrieved on Meteor cruise 22, legs 3 and 4. A total of 57 conventional current meters and two Acoustic Doppler Current Profilers were set on 13 moarings with some concentration within the Brazil Current and the Vema Channel. CTDs were taken at each mooring site as well as in between. Some of the recovered instruments were reset in the Hunter Channel, a suspected additional connection between the Argentine Basin and the Brazil Basin. A later report will summarize this data after it is recovered in May 1994.

Description: New light is shed on Worthington's concept of the North Atlantic circulation, postulating the existence of two anticyclonic gyres. This concept, which seems to have been laid to rest in the last decade, has now been reinforced by the results of a simple linear Sverdrup circulation model yielding a band of westward transport all across the North Atlantic at about the Azores latitude. This narrow band is called the Azores Countercurrent (AzCC) and matches the position of westward flow required by Worthington's “northern gyre.” An anomaly in the meridional change of the wind-stress curl in the eastern North Atlantic has been identified as the driving mechanism. A comparison with observations shows that the AzCC is verified in many analyses of historical datasets and synoptic surveys. A lack of the AzCC in other analyses is probably due to missing meridional sections, strong smoothing, and the superimposed Ekman flow close to the sea surface directed to the southeast. The AzCC has not been verified in low-resolution general circulation models applying simplified wind-stress fields and large friction coefficients, but there is evidence for its existence in recent high-resolution models driven by realistic wind stresses. Based on these findings, a new pattern for the wind-driven upper ocean circulation of the midlatitude North Atlantic is presented.

Description: A sigma-coordinate, primitive equation ocean circulation model is used to explore the problem of the remnant generation of trapped waves about a tall, circular, isolated seamount by an incident oscillatory barotropic current. The numerical solutions are used to extend prior studies into the fully nonlinear regime, and in particular to quantify and interpret the occurrence of residual circulation. Specific attention is also devoted to the dependence of the resonance and rectification mechanisms on stratification, forcing frequency, and choice of subgrid-scale viscous closure. Resonantly generated trapped waves of significant amplitude are found to occur broadly in parameter space; a precise match between the frequency of the imposed incident current and the frequency of the trapped free wave is not necessary to produce substantial excitation of the trapped wave. The maximum amplification factors produced in these numerical solutions, O(100) times the strength of the incident current, are consistent with previous studies. In the presence of nonlinear advection, strong residual currents are produced. The time-mean circulation about the seamount is dominated by a strong bottom-intensified, anticyclonic circulation closely trapped to the seamount. Maximum local time-mean current amplitudes are found to be as large as 37% of the magnitude of the propagating waves. In addition to the strong anticyclonic residual flow, there is a weaker secondary circulation in the vertical-radial plane characterized by downwelling over the top of the seamount at all depths. Maximum vertical downwelling rates of several tens of meters per day occur at the summit of the seamount. The vertical mass flux implied by this systematic downwelling is balanced by a slow radial flux of mass directed outward along the flanks of the seamount. Time-mean budgets for the radial and azimuthal components of momentum show that horizontal eddy fluxes of momentum are responsible for transporting net radial and azimuthal momentum from the far field to the upper flanks of the seamount. There, Coriolis and pressure gradient forces provide the dominant balances in the radial direction. However, the Coriolis force and viscous effects provide the primary balance for the azimuthal component.

Description: The total transport of Antarctic Bottom Water across the Rio Grande Rise, including the western boundary, the Vema Channel, and the Hunter Channel is estimated from hydrographic measurements across these pathways. The contribution of the Vema Channel is greatest at 3.9 × 106 m3 s−1, which is very close to earlier estimates. The western boundary current contribution is 2.0 × 106 m3 s−1 and that of the Hunter Channel 0.7 × 106 m3 s−1. The lower values outside the Vema Channel are offset by the important source of mass they form to the lower density classes of bottom water. About 40% of the flow is concentrated in the highest density class representing the source of Weddell Sea Deep Water to the Brazil Basin. The flow structure is characterized by horizontal and vertical recirculation.

Description: The space-time structure and predictability of the El Niño/Southern Oscillation (ENSO) phenomenon was investigated. Two comprehensive datasets were analyzed by means of an advanced statistical method, one based on observational data and the other on data derived from an extended-range integration performed with a coupled ocean-atmosphere general circulation model. It is shown that a considerable portion of the ENSO-related low-frequency climate variability in both datasets is associated with a cycle involving slow propagation in the equatorial oceanic beat content and the surface wind field. The existence of this cycle implies the ability of climate predictions in the tropics up to lead times of about one year. This is shown by conducting an ensemble of predictions with our coupled general circulation model. For the first time a coupled model of this type was successfully applied to ENSO predictions.

Description: A hybrid coupled model (HCM) of the tropical ocean–atmosphere system is described. The ocean component is a fully nonlinear ocean general circulation model (OGCM). The atmospheric element is a statistical model that specifies wind stress from ocean-model sea surface temperatures (SST). The coupled model demonstrates a chaotic behavior during extended integration that is related to slow changes in the background mean state of the ocean. The HCM also reproduces many of the observed variations in the tropical Pacific ocean-atmosphere system. The physical processes operative in the model together describe a natural mode of climate variability in the tropical Pacific ocean–atmosphere system. The mode is composed of (i) westward-propagating Rossby waves and (ii) an equatorially confined air–sea element that propagates eastward. Additional results showed that the seasonal dependence of the anomalous ocean–atmosphere coupling was vital to the model's ability to both replicate and forecast key features of the tropical Pacific climate system. A series of hindcast and forecast experiments was conducted with the model. It showed real skill in forecasting fall/winter tropical Pacific SST at a lead time of up to 18 months. This skill was largely confined to the central equatorial Pacific, just the region that is most prominent in teleconnections with the Northern Hemisphere during winter. This result suggests the model forecasts of winter SST at leads times of at least 6 months are good enough to be used with atmospheric models (statistical or OGCM) to attempt long-range winter forecasts for the North American continent. This suggestion is confirmed in Part II of this paper.

Description: A 26-year integration has been performed with a coupled ocean-atmosphere general circulation model (CGCM). The oceanic part resolves all three oceans in the latitude band 70°N–70°S but is dynamically active only between 30°N and 30°S. The atmosphere is represented by a global low-order spectral model. The coupled model was forced by seasonally varying insolation. Although the simulated time-averaged mean conditions in both atmosphere and ocean show significant deviations from the observed climatology, the CGCM realistically simulates the interannual variability in the tropical Pacific. In particular, the CGCM simulates an irregular ENSO with a preferred time scale of about 3 years. The mechanism for the simulated interannual variability in the tropical Pacific is related to both the “delayed action oscillator” and the “slow SST mode.” It therefore appears likely that either both modes can coexist or they degenerate to one mode within certain locations of the parameter space. This hypothesis is also supported by calculations performed with simplified coupled models, in which the atmospheric GCM was replaced by linear steady-state atmosphere models. Further, evidence is found for an eastward migration of zonal wind anomalies over the western Pacific prior to the extremes of the simulated ENSO, indicating a link to circulation systems over Asia. Because an earlier version of the CGCM did not simulate interannual variability in the tropical Pacific, additional experiments with a simplified coupled model have been conducted to study the sensitivity of coupled systems to varying mean oceanic background conditions. It is shown that even modest changes in the background conditions can push the coupled system from one flow regime into another.

Description: Ocean deep velocity profiles were obtained by lowering a self-contained 153.6-kHz acoustic Doppler current profiler (ADCP) attached to a CTD-rosette sampler. The data were sampled during two Meteor cruises in the western tropical Atlantic. The ADCP depth was determined by integration of the vertical velocity measurements, and the maximum depth of the cast was in good agreement with the CTD depth. Vertical shears were calculated for individual ADCP velocity profiles of 140-300-m range to eliminate the unknown horizontal motion of the instrument package. Subsequent raw shear profiles were then averaged with respect to depth to obtain a mean shear profile and its statistics. Typically, the shear standard deviations were about 10(-3) s-1 when using up and down traces simultaneously. The shear profiles were then vertically integrated to get relative velocity profiles. Different methods were tested to transform the relative velocities into absolute velocity profiles, and the results were compared with Pegasus dropsonde measurements. The best results were obtained by integrating the raw velocities and relative velocities over the duration of the cast and correcting for the ship drift determined from the Global Positioning System. Below 1000-m depth a reduction of the measurement range was observed, which results either from a lack of scatterers or instrumental problems at higher pressures.

Description: Inertial separation of a western boundary current from an idealized continent is studied in a homogeneous ocean circulation model. A number of processes are identified that either encourage or prevent separation at a coastal promontory in this model. For a single-gyre wind forcing a free-slip boundary condition forces the stream to follow the coastline, whereas the no-slip condition allows separation at a sharp corner. A prescribed countergyre to the north of the stream is not necessary to achieve separation if the no-slip condition is used. "Premature" separation occurs for wind fields that do not extend beyond the latitude of the cape. For a more realistic wind field and coastline two distinct states of the stream are found. At small Reynolds numbers the current fails to separate and develops a stationary anticyclonic meander north of the cape. Stronger currents separate and drive a recirculation in the lee of the continent.

Description: North Atlantic air-sea heat and freshwater flux data from several sources are used to estimate the conversion rate of water from one density to another throughout the range of sea surface density. This cross-isopycnal mass flux varies greatly over the ocean, with a maximum of 32.2 × 106 m3 s−1 at σ = 26.1 kg m−3 (toward greater densities) and a minimum of −7.6 × 106 m3 s−1 (toward lesser densities) at σ = 23.0 kg m−3. The air-sea fluxes force water to accumulate in three density bands: one at the lowest sea surface densities generated by heating; one centered near the density of subtropical mode water; and one spanning subpolar mode water densities. The transfer of water to the highest and lowest densities is balanced by mixing, which returns water to the middle density range, and also by boundary sources or sinks. Integrating the cross-isopycnal flux over all densities gives an annual average sinking of about 9 × 1O6 m3 s−1, which presumably escapes across the equator and must be balanced by a similar inflow. Comparison with estimates from tracer studies suggests that the renewal of tracer characteristics at a given density may occur without the existence of an annual average mass source at that density, because along- and cross-isopycnal mixing can renew a tracer without supplying mass.

Description: Antarctic Bottom Water flows into the western North Atlantic across the equator, shifting from the western side to the eastern side of the trough between the American continents and the Mid-Atlantic Ridge as it continues north. This is puzzling because such large-scale motion is thought to be controlled by dynamics that disallows an eastern boundary current. Previous explanations for the transposition involve a (necessarily small-scale) density current that changes sides because of the change in sign of rotation across the equator, or a topographic effect that changes the sign of the effective mean vorticity gradient and thus requires an eastern boundary current. Here an alternative explanation for the overall structure of bottom flow is given. A source of mass to a thin bottom layer is assumed to upwell uniformly across its interface into a less dense layer at rest. A simple formula for the magnitude of the upwelling and thickness of the layer is derived that depends on the source strength to the bottom layer. For a strong enough source, the bottom layer thickness is zero along a grounding curve that separates the bottom water from the western boundary and confines it to the east. A band of recirculating interior flow occurs, supplied by an isolated northern and western boundary current. Similar structures appear to exist in the Antarctic Bottom Water of the western North Atlantic.

Description: Results of a three-dimensional primitive equation model are presented simulating turbulent mesoscale motions in the seasonal thermocline on an f plane. The model is based on a hybrid vertical coordinate scheme and conserves isopycnic potential vorticity. Mesoscale turbulence is modeled in terms of an unstable potential vorticity front. The model integration starts from a purely zonal, 60-km-wide geostrophically balanced jet, on which is superimposed a small initial perturbation. The most unstable mode exhibits a wavelength of 85 km and is driven by a mixed type of instability. Characteristic dynamical ingredients of the wave are enhanced cyclonic and anticyclonic relative vorticity in the troughs and the ridges, respectively, due to the curvature of the flow. Vertical motion of up to 10 m d−1 occurring downstream of the ridges (downwelling) and downstream of the troughs (upwelling) is driven by geostrophic advection of relative vorticity. The contrast of static stability across the front is changing during amplification of the instability: in troughs the stability is decreasing whereas in ridges it is increasing. The density field exhibits local anomalies of the isopycnals' depths (bumps) due to the ageostrophic cross-jet advection of potential vorticity streamers wound up in cyclones and anticyclones. Locally, the potential vorticity gradients are enhanced, creating a multiple front structure. The model results support observations and findings of earlier atmospheric and oceanic models. It is emphasized that mesoscale turbulent structures may have a profound influence on primary productivity, mixed-layer, and internal wave dynamics.

Description: In this paper, the historical hydrographic database for the south Indian Ocean is used to investigate (i) the hydrographic boundary between the subtropical gyre and the Antarctic Circumpolar Current (ACC), the subtropical front (STF), and especially (ii) the southern current band of the gyre. A current band of increased zonal speeds in the upper 1000 m is found just north of the STF in the west near South Africa and at the surface STF in the open Indian Ocean until the waters off the coast of Australia are reached. As neither any other investigation of this current nor a name for it are known, the flow has been called the South Indian Ocean Current (SIOC). This name is anologous to the same current band in the South Atlantic Ocean, the South Atlantic Current. The STF is located in the entire south Indian Ocean near 40-degrees-S. The associated current band of increased zonal speeds is the SIOC, which is found at or north of the STF. East of 100-degrees-E the SIOC separates from the STF and continues to the northeast. The zonal flow south of the STF is normally weak and serves to separate the South Indian Ocean and Circumpolar currents. Near Africa the SIOC has a typical volume transport of 60 Sv (1 Sv = 10(6) m3 s-1) in the upper 1000 m relative to deep potential density surfaces of sigma(4) = 45.87 kg m-3 (2800-3500 m) or sigma(2) = 36.94 kg m-3 (1500-2500 m). Near western Australia the SIOC is reduced to about 10 Sv as it turns to the northeast.

Description: Characteristic of the mesoscale variability in the Atlantic Ocean are investigated by analyzing the Geosat altimeter signal between 60°S and 60°N. The rms sea-surface variability for various frequency bands is studied, including the high-frequency eddy-containing band with periods 〈150 days. Wavenumber spectra and spatial eddy characteristics are analyzed over 10° by 10° boxes covering both hemispheres of the Atlantic Ocean. A comparison, with solutions of a high-resolution numerical experiment, developed as the Community Modeling Effort of the World Ocean Circulation Experiment, aids interpretation of the Geosat results in the tropical and subtropical Atlantic and provides a test of the model fluctuating eddy field. Results from Geosat altimetry show a wavenumber dependence close to k1−5 (k1 being the alongtrack wave-number) over almost the entire Atlantic Ocean except for areas in the tropical and subtropical Atlantic where the rms variability in the eddy-containing band is less than 5 cm, that is, not significantly different from the altimeter noise level. Characteristic eddy length scales inferred from Geosat data are linearly related with the deformation radius of the first baroclinic mode over the whole Atlantic Ocean, except for the equatorial regime (10°S to 10°N). The data-model comparison indicates that the high-resolution model with horizontal grid size of ⅓° and ° in latitude and longitude is quite capable of simulating observed eddy characteristics in the tropics and subtropics. In mid- and high latitudes, however, the model fails to simulate the pronounced poleward decrease in eddy scales. This leads to systematic discrepancies between the model and Geosat observation, with model scales being up to 50% larger than deduced from altimetry.

Description: The time history of upper-ocean temperatures in the tropical Pacific has been used as a predictor in a statistical prediction scheme to forecast SST anomalies in this region. The temperature variations were taken from the output of an oceanic general circulation model that was forced by observed winds for the period 1961 to 1985. Since such model data are presently used as initial conditions in prediction experiments with coupled ocean–atmosphere models, it is of particular interest to investigate up to what lead time tropical Pacific SST is predictable without the coupling of an atmosphere model to the ocean model. We compared our results with those obtained by the persistence forecast and with those obtained by using the wind stresses themselves as predictors in a statistical forecast model. It is shown that using the upper ocean temperatures from the ocean model forced by observed winds gives significantly better skills at lead times of 6 to 12 months compared to persistence and to the pure wind-stress model. Off-equatorial heat content anomalies at 5°N are shown to contribute significantly to the predictability at these lead times, while those at 12°N do not.

Description: The seasonal cycles found in moored current measurements in the equatorial Somali Current region and along the equator between 50° and 60°E are compared with the multilayer Geophysical Fluid Dynamics Laboratory model for the tropical Indian Ocean. The remote forcing of Somali Current transport variations by incident long equatorial waves from the equatorial interior subthermocline region is investigated by analyzing the model velocities of annual and semiannual period. Amplitudes and phases of linear equatorial Rossby and Kelvin waves were least-squares fitted to the model velocities between 5°S and 5°N, 55° and 86°E from 100-m to 1000-m depth. Two cases of wave fits are distinguished: the “free” Kelvin wave case, where the Kelvin waves were fitted independently, and the “reflected” Kelvin wave case, where they were coupled to the Rossby waves by the western boundary condition for a straight slanted (45° to the north) coastline. The wave field velocities explained 70% of the spatial variance in the equatorial model subregion and also compared reasonably well with observed current variations along the equator. At the western boundary, the short-wave alongshore transport due to reflected incident long waves was determined and found to be antisymmetric about the equator. The maximum transport variation for the semiannual period due to the short waves was about 5 × 106 m3 s−1 between 150- and 800-m depth at 3° north and south of the equator. Observational evidence for the western boundary transport variations and the sensitivity to changes in the incident wave field are discussed.

Description: A primitive equation model of an idealized ocean basin, driven by simple, study wind and buoyancy forcing at the surface, is used to study the dynamics of mesoscale eddies. Model statistics of a six-year integration using a fine grid (1/6° × 0.2°), with reduced coefficients of horizontal friction, are compared to those using a coarser grid (1/3° × 0.4°), but otherwise identical configuration. Eddy generation in both model cases is primarily due to the release of mean potential energy by baroclinic instability. Horizontal Reynolds stresses become significant near the midlatitude jet of the fine-grid case, with a tendency for preferred energy transfers from the eddies to the mean flow. Using the finer resolution, eddy kinetic energy nearly doubles at the surface of the subtropical gyre, and increases by factors of 3–4 over the jet region and in higher latitudes. The spatial characteristics of the mesoscale fluctuations are examined by calculating zonal wavenumber spectra and velocity autocorrelation functions. With the higher resolution, the dominant eddy scale remains approximately the same in the subtropical gyre but decreases by a factor of 2 in the subpolar areas. The wavenumber spectra indicate a strong influence of the model friction in the coarse-grid case, especially in higher latitudes. Using the coarse grid, there is almost no separation between the energetic eddy scale and the scale where friction begins to dominate, leading to steep spectra beyond the cutoff wavenumber. Using the finer resolution an inertial subrange with a k−3 power law begins to emerge in all model regions outside the equatorial belt. Despite the large increase of eddy intensity in the fine-grid model, effects on the mean northward transport of heat are negligible. Strong eddy fluxes of heat across the midlatitude jet are almost exactly compensated by changes of the heat transport due to the mean flow.

Description: A high-resolution model of the wind-driven and thermohaline circulation in the North and equatorial Atlantic Ocean is used to study the structure and variability of the boundary current system at 26°N, including the Florida Current, the Antilles Current, and the Deep Western Boundary Current (DWBC). The model was developed by Bryan and Holland as a Community Modeling Effort of the World Ocean Circulation Experiment. Subsequent experiments have been performed at IfM Kiel, with different friction coefficients, and different climatologies of monthly mean wind stress: Hellerman–Rosenstein (HR) and Isemer–Hasse (IH). The southward volume transports in the upper 1000 m of the interior Atlantic, at 26°N, are 25.0 Sv (Sv ≡ 106m3s−1) for HR, and 34.9 Sv for IH forcing, in good agreement with the transport from the integrated Sverdrup balance at this latitude (23.9 Sv for HR, 35.6 Sv for IH). The return flow of this wind-driven transport, plus the southward transport of the DWBC (6–8 Sv), is partitioned between the Florida Current and Antilles Current. With HR forcing, the transport through the Straits of Florida is 23.2 Sv; this increases to 29.1 Sv when the wind stresses of IH are used. The annual variation of the simulated Florida Current is very similar to previous, coarse-resolution models when using the same wind-stress climatology (HR); the annual range (3.4 Sv) obtained with HR forcing is strongly enhanced (6.3 Sv) with IH forcing. The meridional heat transport at 26°N, zonally integrated across the basin, is in phase with the Florida Current; its annual range increases from 0.44 PW (HR) to 0.80 PW (IH). The annual signal east of the Bahamas is masked by strong transport fluctuations on a time scale of O(100 days), caused by an instability of the Antilles Current. By averaging over several model years, an annual cycle is extracted, which is in phase with the wind stress curl over the western part of the basin.

Description: Two extended integrations of general circulation models (GCMs) are examined to determine the physical processes operating during an ENSO cycle. The first integration is from the Hamburg version of the ECMWF T21 atmospheric model forced with observed global sea surface temperatures (SST) over the period 1970–85. The second integration is from a Max Planck Institut model of the tropical Pacific forced by observed wind stress for the same period. Both integrations produce key observed features of the tropical ocean-atmosphere system during the 1970–85 period. The atmospheric model results show an eastward propagation of information from the western to eastern Pacific along the equator, although this signal is somewhat weaker than observed. The Laplacian of SST largely drives the surface wind field convergence and hence determines the position of large scale precipitation-condensation heating. This statement is valid only in the near-equatorial zone. Air-sea heat exchange is important in the planetary boundary layer in forcing the wind field convergence but not so important to the main troposphere, which is heated largely by condensation heating. The monopole response seen in the atmosphere above about 500 mb is due to a combination of factors, the most important being adiabatic heating associated with subsidence and tropic-wide variations in precipitation. The models show the role of air-sea heat exchange in the ocean heat balance in the wave guide is one of dissipation/damping. Total air-sea heat exchange is well represented by a simple Newtonian cooling parameterization in the near-equatorial region. In the wave guide, advection dominates the oceanic heat balance with meridional advection being numerically the most important in all regions except right on the equator. The meridional term is largely explained by local Ekman dynamics that generally overwhelm other processes in the regions of significant wind stress. The principal element in this advection term is the anomalous meridional current acting on the climatological mean meridional SST gradient. The eastward motion of the anomalies seen in both models is driven primarily by the ocean. The wind stress associated with the SST anomalies forces an equatorial convergence of heat and mass in the ocean. Outside the region of significant wind forcing, the mass source leads to a convergent geostrophic flow, which drives the meridional heat flux and causes warming to the east of the main wind anomaly. West of the main anomaly the wind and geostrophic divergence cause advective cooling. The result is that the main SST anomaly appears to move eastward. Since the direct SST forcing drives the anomalous wind, surface wind convergence, and associated precipitation, these fields are seen also to move eastward.

Description: The monthly mean wind stress climatology of Hellerman and Rosenstein (HR) is compared with the climatology of Isemer and Hasse (IH), which represents a version of the Bunker atlas (BU) for the North Atlantic based on revised parameterizations. The drag coefficients adopted by IH are 21% smaller than the values of BU and HR, and the calculation of wind speed from marine estimates of Beaufort force (Bft) is based on a revised Beaufort equivalent scale similar to the scientific scale recommended by WMO. The latter choice significantly increases wind speed below Bft 8, and effectively counteracts the reduction of the drag coefficients. Comparing the IH stresses with HR reveals substantially enhanced magnitudes in the trade wind region throughout the year. At 15°N the mean easterly stress increases from about 0.9 (HR) to about 1.2 dyn cm−1 (IH). Annual mean differences are smaller in the region of the westerlies. In winter, the effect due to the reduced drag coefficient dominates and leads to smaller stress values in IH; during summer season the revision of the Beaufort equivalents is more effective and leads to increased stresses. Implications of the different wind stress climatologies for forcing the large-scale ocean circulation are discussed by means of the Sverdrup transport streamfunction (ψs): Throughout the subtropical gyre a significant intensification of ψs takes place with IH. At 27°N, differences of more than 10 Sv (1 Sv ≡ 106 m3 s−1) are found near the western boundary. Differences in the seasonality of ψs are more pronounced in near-equatorial regions where IH increase the amplitude of the annual cycle by about 50%. An eddy-resolving model of the North Atlantic circulation is used to examine the effect of the different wind stresses on the seasonal cycle of the Florida Current. The transport predicted by the numerical model is in much better agreement with observations when the circulation is forced by IH than by HR, regarding both the annual mean (29.1 Sv vs 23.2 Sv) and the seasonal range (6.3 Sv vs 3.4 Sv).

Description: A low-cost underwater sound recorder has been developed and tested. It is designed to receive signals from sound sources that serve as navigation aids for RAFOS floats. This moored version of the RAFOS float (MAFOS) can monitor sound sources over many months and several hundred kilometers. It thus improves RAFOS navigation accuracy by enabling corrections for potential long-term clock drifts of the sound sources. MAFOS can also provide information on the local variation in the speed of sound due to natural hydrographic variability. In a first test, this usefulness has been proven and a warm, salty inhomogenity that traveled through a sound-source mooring array in the Iberian Basin has been observed.

Description: Responses in protease activity, caused by adding nutrients to batch cultures of a Vibrio sp., grown to equilibria in a chemostat system at 5 °C with C, N or P-limited media, was measured after O, 6 - 8 and 24 C±) hrs. Addition of the limiting nutrient gave the largest response in activity, due to an increase in bacterial numbers. Reduction in activity per cell was, however, observed in some cases. In field samples from the Skagerak, clear responses within 24 hrs were either absent or found when both C, N and P-sources were added. In the field samples, less changes were found in activity per cell. At three coastal stations, detectable responses were found to additions of P04 3- alone, or in some combinations. When measured, leucine incorporation gave a response pattern to P04 3- additions similar to that of protease activity.

Description: A direct microscopic method based on the response of bacterial cells to inhibition of DNA synthesis by nalidixic acid in the presence of growth-supporting yeast extract and designed to determine the number of viable bacteria, was tested in marine sediments bioturbated by the deposit-feeding polychaete Arenicola marina. The number of responsive cells in sediment samples ingested and egested by the polychaete, reflected similar differences and trends as total direct counts or plate counts. Nevertheless, application of that viable direct count technique in marine sediments suffered also from considerable systematic errors.

Description: For brackish water bodies at the North Sea coast which harbor red tide algal blooms during the summer months, phytoplankton densities and chlorophyll a data were compared with bacterial counts including plate counts of TCBS-agar-selected vibrios. Concentrations of chlorophyll a, the ratios of total viable counts on ZoBell agar to acridine orange direct counts (CFU/ AODC), and vibrio counts on TCBS-agar followed largely the same trends suggesting a strong linkage between phytoplankton biomass and heterotrophic cacteria. Enrichment experiments based on macroalgal extracts confirmed the extremely copiotrophic nature of TCBS-selected vibrios. Vibrio counts peaked during the bloom of a Cryptomonas sp. that was presumably grazed upon by a ciliate, Strombidium sp.. On the other hand, there were no indications of an analogous coincidence during mass developments of the potentially toxic dinoflagellate Glenodinium foliaceum.

Description: The near-bottom water layer is influenced by events in the sediment and by sedimentation from the productive surface layer. Microbial activity in this layer shows occasionally strong gradients from the pycnocline down to the sediment and it reacts to seasonal variations in oxygen content in the adjacent to the sediment. Comparison of mean values of bacterial stock and activity parameters in the productive surface layer and in the near-bottom layer shows, that despite of similar patterns of bacterial biomass and bacterial production in both layers, uptake velocity of leucine, peptidase activity, as well as turnover rates of leucine and hydrolysis rates of peptides are considerably lower in the near-bottom water layer. This is explained by effects of temperature, nutrient quality and oxygen depletion.

Description: Five strains of vibrio-shaped, mesophilic sulfate-reducing bacteria were isolated from the deep-sea hydrothermal vent site at 13° N on the East Pacific Rise. Phospholipid analyses demonstrated a high percentage of branched-chain fatty acids, including the known biomarker for Desulfovibrio, in all five strains. The cell-wall lipids showed a fatty acid composition markedly different from the phospholipids. While straight-chain fatty acids were predominant the biomarker fatty acid was absent. Based on the morphological characteristics and the fatty acid composition, we tentatively have assigned the isolates to the genus Desulfovibrio.

Description: The test compound p-nitrophenol during summer normally is rapidly degraded in the freshwater area of the Elbe river. In contrast, degradation of PNP is decreased significantly during periods of low temperature or low oxygen content. Thus the xenobiotic compound is carried to the North Sea. In estuarine and marine environments the degradation of PNP is diminished step by step towards the open sea and is finally ceased completely, mostly as a result of increasing salinity.

Description: Water samples were taken at bimonthly intervals (April - October 88) from three stations located in the Ria Formosa, a coastal lagoon in SE Portugal. Bacterial abundance and biovolume ranged between 1.2 - 18 x 106 cells/ml and 0.107 - 0.216 µm3 /cell, respectively. Lowest values were detected at the station close to the ocean and highest values at the station near a domestic effluent. Total bacterial counts showed slight temporal fluctuations while saprophyte numbers presented a much stronger variation, with maxima in summer. The biovolume exhibited minimal values in summer. Reasons for the different patterns of spatial and temporal variability of the bacterial population are discussed.

Description: During a one-year period the development of the Antarctic coastal seawater bacterioplankton was followed. Two field stations (surface and deep water = 20 m, respectively) were sampled daily in 1989 in " Terre Adelie area". The survey included physicochemical (temperature and particulate organic matter) and bacteriological (total and heterotrophic bacteria, bacterial production) measurements. Whereas bacterial parameters at the deep water station remained fairly constant, bacterial parameters in surface waters generally increased during the year obviously related to the formation of sea ice.

Description: Experiments on fecal coliform accumulation and depuration in the oyster Crassostrea gigas were performed under two seasons (winter, summer), under various conditions of bacterial concentration (from 101 to 103 CFU ml-1) and suspended matter (10 to 50 mg l-1). Contamination process in the bivalve is mainly influenced by the bacterial density in the seawater. Influence of suspended matter concentration was less effective. Maximal bacterial accumulation was reached within 30 min. in summer (18 °C) and 5 hours in winter (11 °C). Concerning depuration process a 10 fold decrease of initial contamination required 3 hours and a 100 fold decrease was achieved within 10 hours. Time required for depuration was mainly dependent on the initial bacterial concentration in the oyster.

Description: In 1988 and 1989 data about the distribution and activity of petroleum hydrocarbon degrading bacteria in the North Sea and Baltic Sea were collected. Crude oil degrading bacteria and the number of bacteria which especially degrade naphthalene were quantified using a modified dilution (MPN) method. Crude oil degrading bacteria were present in all of about 100 water samples, with as many as 103 ml-1 in sum. Naphthalene degrading bacteria were present in at least tenfold fewer numbers which corresponded with petroleum hydrocarbon (PHC) concentrations (ultraviolet fluorescence spectroscopy method, UVF) in more highly polluted areas. There is obviously a greater connection between this bacteria group and PHC pollutiori determined by UVF than between the more nonspecific group of crude oil degrading bacteria and UVF-determined PHC pollution. Data from the North Sea show an extremely high abundance of hydrocarbon degrading bacteria, even in winter, while in the southern Baltic Sea low numbers of bacteria were found and a slower crude oil degradation was observed.

Description: Between 28 August and 5 September 1982 thirty water samples (5 m depth) were taken on a transect between the Bothnian Bay and the Kiel Bight. Despite substantially differing hydrographical situations within the different subregions of the Baltic Sea, the total bacterial numbers showed a remarkable regional uniformity. Bacterial numbers fluctuated between 3 and 4 x 106 cells ml-1. A distinct pattern was observed: mean bacterial cell volumes were high in the Bothnian Bay (0.145 µm3) and low in the Gotland- and Bornholm Sea (0.094 and 0.091 µm3, respectively). The bacterial biomass fell in the range of 184 - 117 µg C 1-1. The activity parameters were somewhat more variable than bacterial numbers and biomass.

Description: Starvation affects marine bacteria also under anaerobic conditions. Some basic data obtained for anaerobic starvation survival of a fermentative and a sulfaterespiring strain indicate substantial differences. The fermentative strain, Listonella (= Vibrio) anguillarum, responded to, nutrient depletion with rapid reduction of their cell size (dwarfing) and decline of viable cell counts by three orders of magnitude. The sulfate-respiring Desulfovibrio vulgaris showed only minor reductions of the cell sizes and no loss of viability. Whereas a drastic decline of cellular protein concentrations in this strain indicated strong endogeneous respiration, starved cells of the fermenting Vibrio sp. showed increasing levels of protein after an initial decrease.

Description: The structure of biofilms on various surfaces exposed in Spain, England and Denmark was examined. The majority of the surfaces examined were antifouling paints. At all times a wide variety of protozoan species were present. Typical forms included ciliates and choanoflagellates, attached to the surface of the paint or an adherent biofilm of bacteria and diatoms. Closer examination of many films indicated an abundance of amoeboid protozoa, that were able to move about within the biofilm. The staining and examination of sections of biofilms under the light microscope indicated that the amoeboid protozoa were distributed throughout the biofilm. These protozoa moved through the film grazing on the other organisms present and showed several different patterns of activity. Ultimately this caused the disruption and subsequent sloughing of the biofilm.

Description: A new profiling bottom lander (Profiluren) mounted with microelectrodes can measure oxygen profiles through the undisturbed sediment-water interface with 25-50 µm spatial resolution. The high spatial resolution of the in situ profiles reveal the thickness of the diffusive boundary layer (DBL) and allow calculations of: 1) the diffusive oxygen flux through the DBL, 2) the limitation of mass transfer between sediment and water due to the DBL and, 3) the oxygen consumption in discrete layers of the mm thick aerobic zone of marine sediments. The lander is thus an excellent tool for in situ analysis of oxygen dynamics at the sediment-water interface. Here we demonstrate two in situ oxygen profiles from a Danish coastal sediment at 15 m water depth, and discuss the impact of high resolution oxygen measurements.

Description: Eight Pseudomonas-like bacteria isolated from the tube of the deep-sea hydrothermal vent Polychaete Alvinella pompejana were found to carry a 51.7 kb plasmid. All isolates but one were resistant to zinc (3 mM or more) and arsenate ions (200 mM or more). The strains were resistant to penicillin and chloramphenicol.

Description: In contrast to the current view on the trophic role of bacteria in pelagic environments, the impression of a rather unproductive bacterioplankton arose from an example of the deep mesotrophic Lake Constance. Based on measurements of bacterial DNA, thymidine incorporation rates and grazing rates, turnover times of bacterial biomass exceeding 10 days were estimated during the growth period. Similarly, low productivity of bacterioplankton was indicated by low RNA/DNA ratios (〈 1). Additional indications for a rather inactive bacterioplankton were provided by the observation of long lag phases in lake water cultures. Low bacterial productivity has also to be expected from energetic considerations. There is increasing evidence for low bacterial growth efficiencies under natural conditions. The presented material points to the possible need for reconsideration of current estimates of bacterial in situ growth.

Description: The priapulid worm Halicryptus spinulosus which occurs in sulfide-rich mud of Kiel Bight is covered with a dense epizoic biofilm. Several types of filamentous microorganisms can be distinguished by SEM confirming previous conclusions based on TEM investigations. The most conspicuous forms are firmly attached filaments resembling Thiothrix that accumulate at the cuticular setae. Enrichment experiments indicate the presence of sulfide-oxidizing bacteria. A vector hypothesis is postulated which implies that the redox requirements of the (S)­-oxidizing constituents of the biofilm are matched by the worm's frequent moves between oxic and anoxic layers of the sediment.

Description: The frequency distributions not only of the most bacteriological parameters measured are proved as bimodal. According to this the values should be subdivided into summer and winter values. The changes of bacterial number, biomass and some functional parameters like Vmax of glucose and production during the years 1980/81 could be described by a simple time series analysis. These results were compared with values from the same location measured during 1989/90. The application of different statist.ical methods for analyzing such data and the usefulness of nonparametric tests are discussed.

Description: Fatty acid composition of the Flexibacter strains Inp2 and Inp3 were found to be influenced by the presence of cAMP. Whilst cAMP inhibited the synthesis of linoleic and linolenic acid in Inp2, cerulenin inhibited the synthesis of Cl6:l. This suggests that lnp strains possess both the aerobic and anaerobic pathway for synthesis of unsaturated fatty acids (UFAs).

Description: Fecal coliforms, Salmonella and antigens linked to hepatitis A virus were searched for in shellfish collected in farms or natural beds along the French coast. Statistical analysis was performed on 176 test samples harvested at 8 different stations. For fecal coliforms, there were significant statistical differences between stations (F = 44.39; p 〈 0.001). Salmonella was found more frequently in 2 of the stations and was isolated more often in stations where mean fecal coliform contamination was high. The presence of antigens linked to hepatitis A virus was low (detection in only 2 stations where mean fecal coliform contamination was also low). No relation between viral and bacterial markers was observed at any of the stations.

Description: During the RV "Meteor" expedition in the Central Arabian Sea (MINDIK 87) the vertical distribution of particulate organic carbon and nitrogen, bacterial abundance, heterotrophic activity for glucose and the bacterial production determined by [3H-methyl]-thymidine incorporation were surveyed. At the time of observation (April-May) the study area was characterized by a stable pycnocline at 35 m and a nutricline at 50 to 55 m depth. Maxima for all biomass measurements were observed in the nutricline, whereas highest rates were detected in the nutrient-depleted surface layer above the nutricline. Based on these hydrographic conditions, a double vertical zonation was established also for microbiological and planktological events in the water column. The integrated bacterial production in the mixed surface layer (0-30 m) was half that in the layer underneath (30-100 m). This upper zone can be considered as a more or less closed sub-system and a significant amount of primary production (approximately 30 %) was channelled through the bacteria. Corresponding to the higher biomass in the lower zone the turnover of organic material was somewhat slower. This observation together with the presence of nutrients in the chemocline indicated a subsystem of more open character for exchange processes with underlying waters.

Description: In connection with the international monitoring programme of the Baltic Sea, supervised by the Helsinki Commission (HELCOM) microbiological investigations were carried out at 5 stations situated in the Western Baltic Sea. Data from the 3 most frequently monitored stations are presented with a special regard to station Kiel Bight. Total bacterial number shows a maximum value of 3 x 106 cells x ml-1 in July 1988 and 3.8 x 106 cells x ml-1 at 2 m depth in June 1989 and exhibits nearly the same pattern in annual variation as bacterial production, measured by thymidine incorporation. Number of saprophytic bacteria turned out to be a fraction of ≈ 0.1 % of total bacterial number. While maximum of total bacterial number was found to coincide with shortest turnover times of glucose and maximum of bacterial production, this was not observed with the number of saprophytes.

Description: During a monitoring cruise in May 1989 the vertical distribution of the total bacterial numbers and the numbers of saprophytic bacteria in the Gulf of Finland and in the Baltic Proper were surveyed. Water for microbiological analyses was taken at 12 stations from 8 - 15 different depths. In addition, the diurnal variation of the vertical distribution of saprophytic bacteria was examined at the entrance to the Gulf of Finland. The spatial and temporal variability of the saprophytic bacteria (CFU) was larger than the variability of the total- bacterial numbers. Vertically, the highest bacterial numbers were always found in the photic zone, with maximum values often above the thermocline. The saprophytic bacteria constituted less than 0,5 % of the total bacterial number.

Description: Survey of the density of red-tide organisms and bacterioplankton as well as simultaneous determinations of temperature, salinity, pH, secchi disc and dissolved oxygen were carried out at four stations in the Kaštela Bay (middle Adriatic Sea) on a weekly basis between June 15 and September 20, 1989. A close connection between bacterioplankton and Gonyaulax polyedra was observed during the bloom manifested by high coefficients of correlation between them in the surface layers. No correlation was established in the bottom layers since vertical gradients of bacterioplankton density were considerably weaker than in phytoplankton. These differences were also shown in strong vertical gradient of pH and 02-saturation.

Description: To study the structure and function of bacterial populations in the Bransfield Strait, Antarctica, which is located between S 62°-64° and W 56°-62°, twenty nine sampling stations were chosen. Samples were collected from seawater and sediment during austral summer (1989 Dec. - 1990 Jan.) and analyzed for total bacterial number, total saprophytic bacterial number, heterotrophic activity and extracellular enzyme activities. The number of total bacteria in seawater was between 1.0 x 104 cells/ml and 1.6 x 105 cells/ml, and total saprophytic bacteria were between 0.5 x 102 CFU/l and 8.0 x 104 CFU/l. The population density of saprophytic bacteria was significantly low, giving less than 10-4 of the total bacterial number, in this region. Turnover times of glucose and leucine in seawater were in the ranges of 41 to 2094 hrs, and 56 to 980 hrs, respectively. Turnover times of these organic matters were extremely variable depending on the sampling station and water depth. In the sediments, the enzyme activities of α-glucosidase, N-acetyl- β -glucosaminidase and aminopeptidase of the fast growing bacterial population were higher than those of the slow growing bacterial population, β-glucosidase activities, however, were higher in the slow growing bacterial population.

Description: Intact sediment cores from the Vøring-Plateau (Norwegian Sea) were incubated under in situ temperature on board ship with and without the addition of natural detritus to follow the reaction of deep-sea benthic microbial communities to nutrient enrichment. Concentration and enzymatic decomposition of organic material, total microbial number, biomass and production were followed in timecourse experiments. The addition of decomposable organic material caused an immediate stimulation of microbial metabolic processes: following the induction of enzymatic activity, microbial biomass production increased. During the initial period of incubation metabolic processes were also stimulated in the untreated "control" sediments. This "incubation effect" competed with the "feeding effect" caused by the enrichment with organic material.

Description: It is demonstrated that Microcoleus chthonoplastes forms typical bundles and a glycocalyx encasing several trichomes not only in nature but also under certain laboratory conditions if the appropriate sediments, light conditions and humidities are used. Mat formation, population dynamics, composition and vertical mobility of the two major mat forming cyanobacteria of the Mellum "Farbstreifen-Sandwatt" were studied using pure cultures and wild type material from Mellum. Nitrogen fixation by natural field populations, lab systems and isolated cultures were studied and the possibility of interspecies nitrogen transfer was tested. The colonization of sediments completely free of combined nitrogen by 0. limosa or M. chthonoplastes was not possible. Bi-partitioning of individual strata of 0. limosa in freshly inoculated sediments and individual developments of photoprotective pigments, curl and pinnacle structures in the course of laboratory experiments were observed. Although it is possible that two different strains of 0. limosa were inoculated repeatedly we can conclude from the experiments that adaptational pleomorphy (KRUMBEIN et al. 1989) within one clone is a possible explanation of the formation of two layers and differently reacting Oscillatoria-trichomes in laboratory experiments. These results are in agreement with "comet" structures described by CASTENHOLZ (1982).

Description: The method proposed for the measurement of the picoplankton density, uses epifluorescence microscopy, which allows the detection of all the cells with their own or/and induced fluorescence. Direct counts may lead to an overestimation of the viable counts since we cannot discriminate between living and dead cells. We appropriately modified the method of KOGURE et al. (1979) for the fraction of cells capable of division. This method is applied both to autofluorescent organisms and to all the cells stained by fluorochrome (DAPI). Direct counts are compared with those obtained from Marine Agar, a selective medium for marine heterotrophic bacteria. The results obtained in different Mediterranean areas allow us to realize how effective this method is in comparatively evaluating different planktonic dimensional fractions occurring in the marine ecosystem.

Description: Annual distribution of heterotrophic marine bacteria and seasonal characteristics were investigated in the intertidal water and sediments of the Yellow Sea near Kunsan, Korea. The heterotrophic marine bacteria ranged from 7.5 x 102 to 1.1 x 105 CFU ml-1 in water and 1.62 x 104 to 4.78 x 106 CFU g-1 dry sediment. As for the morphological distribution measured by epifluorescence microscopy, rod-shaped bacteria were more than 74 % of all cells during the investigation period. Average biovolume of sampled bacteria ranged from 3.19 ± 0.59 x 10-2 to 6.19 ± O.76 x 10-2 µm3 for coccoid bacteria, and from 4.57 ± 0.17 x 10-2 to 12.94 ± 0.21 x 10-2 µm3 for rod-shaped ones. Isolated bacteria showed utilization of various carbon sources such as glucose, maltose, lactose, xylose and arabinose, and tolerance to a range of salinities. In total 82 strains were isolated from seawater and 114 strains from sediments. Dominant genera were Pseudomonas, Vibrio, Flavobacterium and Acinetobacter in seawater, and Pseudomonas, Acinetobacter, Vibrio and Mycobacterium in sediments.

Description: Ecophysiological investigations on inner walls from two churches near the North Sea coast (Eilsum, Ostfriesland) and the inland lake Steinhuder Meer (Idensen, near Hannover) have shown that even in these environments hypersaline and highly alcaline conditions can occur. Thus the microorganisms occurring in such environments will have many relations with marine microorganisms. Halophilic and extremely halotolerant chemoorganotrophic bacteria have been isolated from these areas under conditions near the crystallization point of halite and at pH-values as high as pH 9.0. Some of these isolates are growing only under elevated sodium chloride or sulfate levels. Many of the isolates need salt concentrations highly above those of normal marine bacteria. They also adapt their internal and external (exudates) fatty acid patterns and metabolism to the changing salinities caused by brine seeping and evaporative forces. Many of the investigated bacteria are coccoid or coryneform. In many cases they considerably interfere with the mineral compounds of their immediate environment. In this way, they drastically change their own microenvironment as well as the character of the mineralogy. The typical pattern of fatty acids and compatible solute production under changing salinities are presently under investigation.

Description: The simultaneous incorporation of radiolabelled thymidine and leucine was followed in intact muddy sand sediments from the North Sea. As it could be shown, incorporation activities covaried over sediment depth. Parallel analysis of the enzymatic decomposition of organic material (by means of the hydrolysis of fluoresceindiacetate) revealed that stimulations of microbial biomass production coincided with stimulations of enzymatic activities although maxima of both processes occurred at different sediment depths.

Description: Microbial mats and microbial biofilms covering sedimentary environments of the deep sea, sea-marginal hypersaline systems and of intertidal sediments of the Wadden Sea are some of the most interesting objects of study for global and local fluxes of solutes and gases, as for the stabilization and transformation and diagenesis of recent and ancient sedimentary deposits. In their fossilized state as "stromatolites" they are the most reliable traces of life history on earth between 3. 7 and 0.45 billion years (GA) ago. The light transmittance into such systems is often a limiting factor for the development of microbial mats and films. The salt environment of hypersaline estuaries as well as the siliciclastic environment of the so-called Farbstreifen-Sandwatt, however, belong to those systems that have the deepest penetration of light in comparison to other mat systems. Both systems have been studied extensively by us. The processes within such mats are multiple and represent practically the total spectrum of biochemical and physical or fractal physical reactions of microorganisms. In this contribution the intimate interaction between oxygenic and anoxygenic photosynthesis, aerobic and anaerobic respirations, anaerobic and aerobic fermentation and the phenomenon of physical reactions within such mats is summarized on the basis of our work in hypersaline and in moderately saline conditions. Special emphasis is given to micro-environments and to the change from vertical to concentric orientation of physical and chemical processes within such mats. Several examples are given of fossil occurrences of similar mat systems.

Description: With different box and bottle experiments in situ and in the laboratory as well the potential capacity of the system for nitrification and denitrification was evaluated. With these measurements the efficiency of bacteria involved in these processes can be estimated. The reactivity of the systems was investigated in relation to different influencing factors, e.g. availability of nutrients, various sediment types and temperature. Dependent on the available nitrate denitrification rates between O-73 mg N m-2d-1 were observed.

Description: Pronounced fine-scale gradients of enzymatic degradation of organic material were observed in the uppermost horizons of deep-sea sediments of the Norwegian-Greenland Sea. Since these gradients coincided with the occurrence of dense populations of epibenthic agglutinated foraminiferans, it was hypothesized that the foraminiferans were the main contributors to the large pool of hydrolytic enzymes observed. Parallel analyses of the enzymatic activity associated with individual foraminiferans selected from the sediments confirmed this hypothesis. Measurements of bacterial biomass (by epifluorescence microscopy) and production (incorporation of tritiated leucine) suggest that in the specific ecological situation analysed, bacteria benefit from the metabolism of foraminiferans rather than being the main decomposers. The immediate degradation at the sediment surface without incorporation of the sedimented particles into the sediment may have an impact on the early diagenesis of organic material and its sedimentary record in these deep-sea sediments.

Description: Two common antigens were found among all the SRB tested. These antigens were also found in other bacteria and were therefore not specific for the SRB group. Cluster analysis of the antigen profiles showed that the injection water system from an oil rig contained one homogeneous serological group of Desulfovibrio desulfuricans.

Description: The activity of the community of heterotrophic bacteria in the Dead Sea water column was measured during a bloom of halobacteria in 1980-1981. With the development of the bloom, rates of incorporation of amino acids, glycerol and acetate increased. Concomitant with the decline in bacterial numbers, the incorporation rate of amino acids and acetate decreased, while glycerol uptake rates remained high. The thymidine incorporation rate was low even at the peak of the bloom, and became negligible afterwards. The results presented suggest that the bacterial community in the Dead Sea is not subjected to rapid turnover, and may remain static in a state of low activity for prolonged periods.

Description: During the last decade several surface active substances produced by microorganisms (biogenic surfactants, biosurfactants) have been described. Most of them are glycolipids composed of a hydrophilic sugar and one ore more lipophilic corynomycolic acids. A better biodegradability and lower toxicity of biosurfactants should be expected, because of their biogenic origin. However, data in this regard are missing. This paper presents results of toxicity testing series, in which four synthetic surfactants, two commercial oil dispersants, and six biosurfactants have been examinated. The test systems were 1. bacterial growth inhibition. 2. microalgae growth inhibition. 3. microflagellate growth inhibition. 4. biodegradation rate, and 5. bioluminescence inhibition (Microtox test). The multiplication of bacteria was stimulated by surfactants, whilst that of microflagellates and microalgae was inhibited. This may be due to the metabolic usage of surfactants, especially biosurfactants, by the bacteria. The bioluminescence was very sensitive to surfactants. No toxicity could be detected with the glucoselipid GL, produced by the marine bacterium Alcaligenes sp. MMl. Most biosurfactants were degraded faster and possess higher EC50-values than synthetic dispersants.

Description: During a screening for biosurfactants among marine microorganisms it was possible to isolate two marine bacteria producing glycolipids. One strain was identified as Arthrobacter sp. EK l which produced trehalose lipids, mainly a 2,3,4,2'­-trehalose tetraester. From the other pure culture identified as Alcaligenes sp. MM l a new glucose lipid was isolated.

Description: Deposit-feeding benthic macrofauna withdraw substantial amounts of bacterial biomass from marine sediments. On the other hand, burrowing macro-invertebrates can mediate epizoic and perizoic enrichment of bacteria by tapping or "conditioning" energy carriers (for heterotrophic and chemolithotrophic bacteria) that are stored in the sediment. Selected examples show how this applies particularly to reduced sediments.

Description: In anoxic sediment from Kiel Bight short-term incorporation of tritiated thymidine (tdr) into DNA was partly reduced by molybdate, a fairly specific inhibitor of sulfate-reducing bacteria (SRB). Preliminary incorporation experiments with cultures of SRB, however, failed to provide substantial clues if and how SRB account for incorporation of tdr in anoxic sediments. One single positive response in four strains tested was by two orders of magnitude too low to compare with aerobic heterotrophic bacteria.

Description: A previous investigation has shown that many terrestrial fungi do not produce nitrate reductase (Na-R). Recently, an examination of marine fungi revealed that all strains tested produce Na-R. Other authors, however, showed absence of this enzyme in a few marine strains. Our reinvestigation of an even broader spectrum of over 80 strains of marine fungi showed the presence of Na-R with only a few exceptions. Since the test was based on determination of nitrite, the first metabolite of Na-R activity, it cannot be excluded that the apparent absence of Na-R in these few cases was due only to a rapid turnover of nitrite by a very active nitrite reductase (Ni-R). Therefore, in all cases in which the presence of Na-R in this test was uncertain, the experiments were repeated by a method inhibiting Ni-R by fluoride and therefore accumulating nitrite which could then be detected. Using this method, it could be shown that in fact all marine fungi tested produce Na-R. Nitrogen often constitutes a limiting factor for growth of fungi. Natural seawater contains considerable amounts of nitrogen in the form of nitrate (up to 600 µg/l). If, however, marine fungi possess Na-R, they could use nitrate as a nitrogen source. Possession of Na-R therefore would constitute an important selective advantage explaining our results that all marine fungi investigated so far contain this enzyme.

Description: Interactions between bacteria and other organisms have been reported for almost all the taxonomic groups of plants and animals (from unicellular eukaryotes to marine mammals) living in the marine environment. However, in most cases, only few different types of interactions have been investigated or described for a particular organism. As an exception, bivalve mollusks, probably because they are appreciated as seafood in many countries, have been extensively studied by microbiologists. Taking this group of invertebrates as a significant model, the following types of interactions will be reviewed: trophic relationships, gut microflora, pathology, tegument and external skeleton epibiosis, endobiotic bacteria, human pathogen vectors, chemical mediated interactions. According to the techniques used to demonstrate the interactions, the level of information available for a particular case is highly variable, ranging from morphological descriptions to functional analysis of an interaction process. The significance of bacteria/organisms interactions for the surrounding environment will also be considered.

Description: In the Wadden Sea certain microbial mats occur in the sandy versicolored tidal flat sediments (e.g., SW' Mellum Island). Gradients of Fe, Cd, Cu and Pb in interstitial water indicate a succession of different bioinduced physicochemical environments from the surface to the buried mats, which causes a transfer of heavy metal species amongst different host minerals and carriers downcore.

Description: Cellbound and extracellular biosurfactants were detected by thin-layer chromatography, tensiometric measurements, blood agar lysis and their capability of stabilizing oil in water emulsions. Known trehalose lipids (RAPP et al. 1979, RISTAU et al. 1983) and one glucose lipid, formerly unknown, with excellent properties were isolated. Also emulsifying agents were found. They seemed to be high molecular weight substances. Mixtures of hydrocarbons containing aliphatics and aromatics were efficiently emulsified. Reduced activity after digestion by several proteases gives a first indication of the nature of the emulsifiers. Preliminary results with several marine microorganisms showed that most biogenic surfactants possess a good environmental compatibility (v. BERNEM 1984, LANG et al. 1986).

Description: Bacteria isolated from hypersaline microbial mats were tested for their ability to precipitate CaC03 under various growth conditions in artificial seawater. The amount of acetate transferred into CaC03 by bacterial metabolism was measured by acid base titration and Ca2+-determinations in liquid cultures. Addition of HC03- to sterile controls was used to estimate the contribution of abiogenic factors to CaCO:,-precipitation. In both cases, with bacteria or with HC03-, spindle, dumpbell, and spherical CaC03-aggregates were formed. The model derived from these experiments with and without bacteria can be used in more complicated systems to estimate the influence of other factors. The formation of CaC03 -particles in microbial mats in a saltern on Lanzarote ( Spain) not fitting into a general evaporation/precipitation pattern can be explained by this mechanism.

Description: An ultrastructural investigation was made of the symbiotic bacteria in the gills of the bivalve Thyasira sarsi from the Central Skagerrak. The bacteria were characterized by sulphur globules in the periplasmic space and by peripheral intracellular membrane stacks. Apart from the membrane system they were very similar to previously described sulphur-oxidizing symbionts of the same species from Bergen, Norway. Stable carbon isotope data and lack of C1 -metabolism enzymes gave additional evidence for sulphur-oxidizing symbionts in T. sarsi in the Skagerrak, too.

Description: Isolates of the marine wood-inhabiting Basidiomycete Nia vibrissa from various marine zones were investigated for nuclear status, colony growth and fructification. Eight of the eleven strains tested by microfluorimetry proved to be dikaryotic, three were monokaryotic. Investigation of colony growth showed better growth at 22°C than at 18°C; the addition of wood and incubation under light had no significant effect on growth. The combined influence of temperature (18, 22, 27°C) and salinity (O, 25, 50, 75, 100, 150, 200, 300 % of natural seawater) was tested and an increase of salinity optimum with increasing incubation temperature (PHOMA-PA TTERN) was shown for almost all strains. All dikaryotic strains showed clamp connections. Fructification occurred in both dikaryotic and monokaryotic strains and more frequently on seawater media than on deionized water media. Addition of wood increased fructification only slightly. Generally, the best fructification occurred around 18°C and in the salinity range with a concentration of between 25% - 150% seawater. Light and electron microscopy showed the typical structure of a gasteroid fructification with spores and both with and without peridia.

Description: Mono- and dikaryotic isolates of the marine wood-inhabiting Basidiomycete Nia vibrissa from various marine zones were investigated in semiquantitative tests for 15 enzymes in redox metabolism (laccase, peroxidase, tyrosinase), carbohydrate metabolism (amylase, cellulase, chitinase, β-glucosidase, laminarinase, pectate transeliminase, xylanase), fat metabolism (lipase), nitrogen metabolism (caseinase, gelatinase, nitrate reductase, urease). All experiments were conducted at 22°C on agar plates or test tubes wiU qedia containing synthetic seawater or deionized water. Most of the strains showed an identical enzyme pattern. Amylase, caseinase, cellulase, gelatinase, laminarinase, lipase, nitrate reductase, peroxidase and xylanase were found in all strains, tyrosinase in none. The production of enzymes did not show any significant differences as regards the nuclear status (mono- or dikaryon) or the biogeographical origin of the strains.

Description: Bacteria convert dissolved organic matter (DOM) into detrituslike particles and clump small particles into larger ones, which may then become available to higher consumers. Microbial aggregates produced in the laboratory from DOM and particles 〈100 µm (both sources derived from freshly collected North Sea macroalgae), were ingested by the epibenthic harpacticoid copepods Paramphiascella vararensis and Tisbe holothuriae in short-term laboratory experiments. The production of fecal pellets was used as an indicator of aggregate consumption. Results showed that between 1-3 pellets copepod-1 h-1 were produced by P. vararensis, independently of algal aggregate source and age. In contrast, T. holothuriae produced between 5-13 pellets copepod-1 h-1 depending on the type of algal aggregate source. Microscopical examination of ageing aggregates and pellets confirmed the presence of a rich bacterial flora as well as some protozoans that may provide nutrients for copepods. Enriched fecal material may also be disaggregated and transformed by microbial action into smaller particles and DOM ("fecal pellet loop"), demonstrating the various pathways for carbon flow within detritus-based nearshore food webs.

Description: Usually, the rate of disappearance of fecal bacteria in natural aquatic ecosystems is followed by the plate count method. When released in seawater, fecal bacteria enter a viable but non culturable state so that plate count method does not seem to be a suitable method for studying mortality of fecal bacteria. A method which consists in following the disappearance of radioactive tracer from bacterial DNA of 3H-thymidine labelled natural assemblages of bacteria has been proposed in the literature (SERVAIS et al. 1985) for measuring the mortality rate of autochthonous bacteria in aquatic ecosystems. A slight modification of this method allows its application to the study of the mortality of fecal bacteria in natural aquatic ecosystems. Mortality rates of autochthonous bacteria and Escherichia coli in the Belgian coastal zone of the North Sea have been compared. They are in the range 0.0001-0.0129 h-1 for the former and in the range 0.0065-0.027 h-1 for the latter. Grazing by microzooplankton has been identified as the major process responsible for bacterial (fecal and autochthonous) mortality.

Description: Microbiological investigations of a marine, brackish sandy sediment area in a water depth of 10 to 12 m showed relatively high numbers of bacteria (4 x 108 - 2,4 x 109 bacteria g-1 dry weight of sediment). Benthic ciliates were estimated too. Their numbers varied between 1 and 87, with a mean of 21 individuals per gram dry weight of sediment. In general, the overwhelming part (80%), were small forms of about 30 µm length. 54% of the ciliates were predominantly bacterivorous. In feeding experiments using a fluorescent dye (DT AF), stained bacteria could be seen directly within the food vacuoles of the small ciliates, but this was the case only when free suspended bacteria were present. No uptake was visible if sand grains were added, which were colonized with stained bacteria. From these results, indications can be seen that small benthic ciliates cannot remove attached sediment bacteria. Taking into account that ciliates choose distinct size classes and certain strains of bacteria, less than a fraction of the total mass of bacteria is probably available as a potential food. This fact, together with a permanent reduction of ciliates by metazoa, ciliates themselves and hydrodynamic perturbations can explain the relatively low, but more or less constant number of the ciliate fauna at such locations.