Dataset: FLEX 1976 (Fladen Ground Experiment March-June 1976, northern North Sea)
FLEX'76, a project part of JONSDAP'76
1. The project JONSDAP'76
The Fladen Ground Experiment 1976 (FLEX'76) was part of the third phase of the cooperative data collection program JONSDAP, which begun in 1970 by the countries bordering on the North Sea. For the first time within JONSDAP it was planned to include biological and chemical measurements, as well as physical ones, in 1976. Intensive measurement programs were performed, one concentrating on the currents flowing into and out of the open borders of the North Sea (INOUT) for 40 days in March/April and one in which the dependence of the spring plankton bloom on the vertical temperature structure was studied in the Fladen Ground area for 100 days from March to June (FLEX), see Fig. 1. Around 90 % of the planned program with moored systems and 75 % of the measurements from moving ships were able to be carried out successfully.
->Fig.1 http://www.ifm.zmaw.de/uploads/RTEmagicC_d6fee23f6a.gif.gif
Graphical presentations of the data have been compiled in the two-volume FLEX/INOUT Atlas and distributed to all JONSDAP'76 participants and many libraries, the main purpose being the facilitation of interdisciplinary evaluations.
->FLEX/INOUT Vol. 63; ->FLEX/INOUT Vol. 64
2. The structure of JONSDAP'76
During the period 1970 – 1974 the considerable progress made in modelling mathematically the residual water movements of the North Sea was noted by some marine biologists who came to believe, though their views were not accepted by all their collegues, that the growth and decay of marine populations could be simulated within acceptable limits by applying model techniques that used equations with a finite number of constants. Quantifying these constants, however, called for data sets consisting of the simultaneous measurement in a selected area of as many different parameters as possible.
About the same time as the JONSIS Group devised its plan for a large-scale exercise in 1976 a group of marine scientists from several different fields, but all working at the "Sonderforschungsbereich Meeresforschung (SFB 94)" in Hamburg, proposed a multidisciplinary field exercise aimed at producing a data set for the running and testing of ecosystem models. The basic idea was to investigate the dependence of the "spring bloom" of phytoplankton in the northern North Sea on such factors as radiation, advection, vertical stratification, nutrient concentrations, remineralization and zooplankton grazing. Intensive current measurements in and around the study area were an important part of the plan and it quickly became apparent that it would be highly desirable to combine the JONSIS and SFB plans if at all possible. Consequently JONSDAP'76 had two complementary phases: INOUT for the work linked to the investigation of the circulation regimes and FLEX, the FLaden Ground Experiment, for the ecosystem work.
3. FLEX 1976
In order to follow the history of a plankton bloom it is necessary to sample both the population and the water mass in which it is developing in great detail in both time and space. Ideally the sampling ships should drift in the water body containing the plankton patch and take measurements at fixed intervals but some trial runs attemped by German scientists in 1975 showed that this was not practical in the FLEX area because of the vertical shear that is found here. The large complexity of the program can be seen from the large number of participating ships which is shown in Fig. 2 together with mean surface temperature and phytoplanton (0-100 m) at the Central Station.
->Fig.2 http://www.ifm.zmaw.de/uploads/RTEmagicC_860405927c.gif.gif
It was agreed instead that the area to be studied should be a square of side 100 km in the Fladen Ground in the northern North Sea (Fig. 3) which became known as the "FLEX box" and that the station at the centre of this region (Central Station) should be occupied throughout the exercise by the research vessels "Meteor" and "Anton Dohrn" alternatively.
->Fig. 3 http://www.ifm.zmaw.de/uploads/RTEmagicC_a7a8c16744.gif.gif
From Lenz et al. (1980)
Current meter stations laid not only close to this station but also at various other points in and around the edges of the FLEX box gave a measure of spatial and temporal variability of the current regimes that might be affecting the plankton population being sampled. Other ships investigated the horizontal distribution of the biological and physical fields within the entire FLEX box or over part of it by taking surface samples continuously and by towing instruments like the Continous Plankton Recorder, the Undulating Oceanographic Recorder, the Delphin and Thermistor chains. Mini-grid investigations were also undertaken for special patch studies on small scales. Fig. 3 shows examples of grids that were sampled. In addition to the multi-faceted sampling of the plankton bloom some special experiments were undertaken in order to give background information about the scales of diffusion, turbulence and Lagrangian motions that might be affecting the development of the bloom.
4. Key points of FLEX
It was agreed instead that the area to be studied should be a square of side 100 km in the Fladen Ground of the northern North Sea (see Fig. 1) which became known as the "FLEX box" and that the station at the centre of this region (Central Station) should be occupied throughout the exercise by the R.V.'s "Meteor" and "Anton Dohrn" alternately. Current meter stations lay not only close to this station but also at various other points in and around the edges of the FLEX box gave a measure of the spatial and temporal variability of the current regimes that might be affecting the plankton population being sampled. Other ships investigated the horizontal distribution of the biological and physical fields within the entire FLEX box or over part of it by taking surface samples continuously and by towing instruments like the Continuous Plankton Recorder, the Undulating Oceanographic Recorder, the Dolphin and Thermistor chains. Mini-grid investigations were also undertaken for special patch studies on small scales. Fig. 3 shows examples of grids that were sampled. The evaluation of the records from the undulating instruments has proved to be difficult because of the volume and general variability of the data obtained: processing routines for these data are still being developed.
In addition to the multi-faceted sampling of the plankton bloom some special experiments were undertaken in order to give background information about the scales of diffusion, turbulence and Lagrangian motions that might be affecting the development of the bloom. These experiments consisted of:
(a) Diffusion studies carried out by the R.V.'s "Anton Dohrn", "F. Heincke" and "Gauss" in which each ship monitored the dispersion of rhodamine dye injected at the surface or into the thermocline.
(b) Parachute drogue tracking for a few days by R.V.'s "Friedrich Heincke" and "Planet" respectively.
(c) An aeroplane from the Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (DFVLR) took a series of air photographs during the first diffusion experiment on 28 April and surveyed the backscattering of the surface by a multi channel-radiometer 16 times between 4 April and 5 May.
(d) The sea state was measured continuously and successfully at four positions within the FLEX box by moored Waverider buoys for almost the whole of the FLEX period. Internal oscillations were measured, furthermore, from 22 April to 5 May, along a 5.2 km profile by acoustic techniques. The results are satisfactory and show good agreement with the Waverider records.
(Text and figures were taken from: Lenz, Ramster and Weidemann, 1980)
Andreas Moll & Günther Radach, created August 2007