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Between June 15 and August 10,1999, an Acoustic Doppler Current Profiler (ADCP) and a water level recorder (WLR) were deployed in the close vicinity of the unmanned light-vessel “Deutsche Bucht” in the German Bight. Together with locally recorded meteorological and hydrographical data (salinity and temperature), this in-situ data set is compared to the forecasts of the BSH circulation model “BSHcmod”. The meteorological measurements are used to assess the meteorological model input generated by an atmospheric model of the German Weather Service. Generally, we observed a good agreement between in-situ and model data. Differences between measured and predicted currents were observed at the surface and at mid-depth. They were caused mainly by missing ADCP data within the first 3 metres under the surface and by the coarse vertical grid spacing of the model which prevents the representation of sharp vertical gradients.

In order to investigate near-bottom suspended participate matter (SPM) dynamics and near-bottom currents, between January 18 and 25,1998, a small array of optical backscatter meters and current meters was deployed in the central North Sea close to the pipelines NORFRA and ZEEPIPE I. The data were supplemented by local wave measurements (WAVEC buoy) and shipborne measurements as CTD profiles, water samples for the determination of the SPM concentration, and meteorological data. At the position of the PIPE site previous Side Scan surveys indicated scouring processes at the ZEEPIPE I. Therefore, possible interactions between the pipe and SPM dynamics and currents should be investigated. A special challenge was the positioning of the instruments at a water depth of 60 metres. In the North Sea, January is known for rough weather and as intended two heavy storms hit the area. Due to rough sea during the first days of the experiment, we did not succeed to place the instruments directly beside the pipes. Unfortunately, two near-bottom current meters failed. However, the interaction between wind, waves, currents, and SPM concentration during periods with wind speeds up to 43 kn and peak waves of 11 m was observed and will be discussed. For the interpretation of the field data we used also the results of the European Shelf Wave Model which proved to be very reliable. High swell, generated by remote wind fields, proved to be the key mechanism for sediment mobilization. The vertical range which is influenced by wind, wind waves, and swell and its temporal variation was estimated.

A bottom mounted BroadBand ADCP was deployed for about two months in the German Bight (54° 15.3′, N, 7° 35.5′ E) at 40 m depth. The ADCP recorded current data and echo intensity between 3 and 38m depth with a vertical resolution of 1 m. The data, which provide continuous vertical current profiles, are investigated with regard to the vertical variations of residual and tidal currents and kinetic energies. To investigate the temporal variability of the current profiles, the time series are subdivided into 8-day intervals. Furthermore, the data are compared with historical data. According to the ADCP profiles, the water column can be subdivided into three layers: A primarily wind-driven near-surface layer (∼10m), a middepth layer with great directional variability, and a near-bottom layer of about 10 m thickness with a strictly logarithmic current profile.

One-month current and water-level time series from the northern North Sea are analyzed with regard to residual flows, volume transports, and tidal constituents. The data originate from theNORA andMOVENS field programs (along 59°N, July/August 1990 and roughly 62°N, September/October 1986 respectively). With regard to the residual flows, the results generally confirm the known circulation pattern of the northern North Sea. Differences between these and other investigations are due to the great short and long-term variability of the current systems. The main objective of this paper, however, is to describe tides and tidal streams. Firstly, we relate the tidal streams along 59°N to the spring and neap high waters at Aberdeen; secondly, up to 17 tidal constituents are determined by means of harmonic analysis.

Long-term near-bottom current meter data (September 1989 to January 1992) from the deep Peru Basin (7° 04′ S, 88° 28′ W), are analysed and discussed with respect to the dispersion of sediments mobilized due to potential deep-sea mining. The data were gathered during the DISCOL experiment and reveal a current regime that is characterized by an alternating sequence of relatively strong (>5 cm/s) quasi-unidirectional currents and weak currents (

Current data at a shoreface-connected ridge in the German Bight have been sampled in January 1990 and January 1991. During the 1991 experiment a violent southwest storm hit the area so that the storm-induced currents can be compared to those under moderate periods. The storm significantly changed the tide dominated spatial and temporal current regime. Estimates suggest, that all sediment grain sizes which occur in the ridge area (0.1 to 0.5 mm) can be resuspended due to the storm-induced intensification of the bottom currents.

The formation of a cyclonic cold-core eddy, separating from a branch of the North Atlantic current system at about 49° N and 21° W, could be observed during a hydrographic survey in April 1985. One month later the eddy was revisited, now 40 nautical miles northeastwards of its previous position and detached from its parent current. During a second hydrographic survey a neutrally buoyant SOFAR float was launched into the core of the eddy. The 9-months trajectory shows the signature of the cyclonic eddy for about 2 months. Later—after passing regions of strong horizontal shear—the float follows the movements of a counterrotating, i. e. anticyclonic mesoscale eddy. A discussion of the Lagrangian data will be given in this paper.

During the NOAMP Experiment (September '83 to May '86), 20 benthic storms with velocities of up to 27 cm/s and a duration of between 3 and 25 days, have been observed in a region centered at 47° 20′ N and 20° W. The calculation of streamfunction maps shows clearly, that all storms between September '83 and September '84 occur in connection with deep reaching synoptic vortices. These events are important mechanisms for the dispersion of tracers, which are released at the seabed. They enable the particles to pass the interface between the well-mixed bottom boundary layer and the stratified interior of the deep sea. The eddies, with lifetimes of up to several months, trap the particles and facilitate horizontal and vertical transports within the eddy. Each vortex, by means of its shear, deforms a parcel of contaminated water to thin sheets, respectively to thin filaments with regard to two dimensions. This makes small-scale mixing processes work effectively.

About 20 benthic storms, originated by deep reaching eddies, have been observed between September '83 and May '86 in the deep West European Basin. First results show, that these eddies influence the dispersion of tracers in the near-bottom layers significantly, e.g. due to deformation by shear. This paper is an attempt to estimate the eddy viscosity tensor in the bottom mixed layer. It will be examined as in to how far benthic storms and vortices result in changes of momentum transfer within this layer. The results indicate that the influence of these phenomena is mainly restricted on meso-scale processes.

The fluorescent tracer Rhodamine B was released at the light side of a river plume front with a strong salinity gradient. To survey greater parts of the proper front, the whole rhodamine patch could not always be completely covered with ship sections due to the fast front-parallel spreading of the rhodamine. Therefore, conventional analyzing methods are not applicable. The extraordinarily high correlation between salinity and rhodamine concentration suggested the idea to determine rhodamine concentration as a function of salinity, regarding the latter as a conservative property due to its smaller gradients and fluxes. Thereby the large scale deformation of the water mass and the advective term of the transport equation are eliminated in first approximation.

In spite of poor weather conditions, for which vertical mixing down to the bottom is expected in general, the rhodamine is still trapped between vertical and horizontal gradients 3 days after release. The turbulent flux through the front is so small that a significant transport through the front can probably only be effected by vortices occasionally occurring — as observed in the experiment of October '82.