Fladen Ground Research Articles

Plankton of the fladen ground during FLEX 76 I. Spring development of the plankton community

Results from plankton sampling in the northern North Sea with the Continuous Plankton Recorder (CPR) and the Undulating Oceanographic Recorder (UOR) during the Fladen Ground Experiment in 1976 (FLEX 76) are summarised. The first evidence of the spring outbreak of phytoplankton was on 19 April, the day after the first signs of vertical stability of the water column were observed. This was followed by spawning of the euphausiid Thysanoessa inermis and rapid increase in the numbers of Calanus finmarchicus. C. finmarchicus was the most abundant species over the FLEX period (19 March to 3 June) and, together with T. inermis, accounted for over 80% of the dry weight of the zooplankton standing stock. By early June the standing crop of phytoplankton had been depleted and nutrients levels were reduced to very low concentrations in the upper 50 m.

Plankton of the fladen ground during FLEX 76 III. Vertical distribution, population dynamics and production of Calanus finmarchicus (Crustacea: Copepoda)

Samples taken in the northern North Sea with the Continuous Plankton Recorder (CPR), the Undulating Oceanographic Recorder (UOR), the Longhurst Hardy Plankton Recorder (LHPR) and by our colleagues from other participating Institutes during the Fladen Ground Experiment (FLEX 76) were used to describe the vertical distribution and population dynamics of Calanus finmarchicus (Gunnerus) and to provide estimates of the production and carbon budget of the population from 19 March to 3 June, 1976. Total production of the 19 March to 3 June, 1976. Total production of the nauplii and copepodite stages (including adults), during the exponential growth phase in May, was estimated to be in the range of 0.49 to 0.91 g C m-2 d-1 or 29.0 to 55 g dry wt m-2 (14.5 to 27.8 g C m-2) for the three successive 10 d periods in May. Two gross growth efficiencies (K 1) (20 and 34%), together with the lower value of C. finmarchicus production, were used to calculate the gross ingestion levels of algae as 2.45 and 1.44 g C m-2 d-1 (73.5 and 43.2 g C m-2 over the May period). These ingestion levels, together with the algae ingested by other zooplankton species, are greater than the estimated total phytoplankton production of 45.9 g C m-2 over the FLEX period. A number of factors are discussed which could explain the discrepancies between the production estimates. One suggestion is that the vertical distribution of the development stages of this herbivorous copepod and their diel and ontogenetic migration patterns enable it to efficiently exploit its food source. Data from the FLEX experiment indicated that the depletion of nutrients limited the size of the spring bloom, but that it was the grazing pressure exerted by C. finmarchicus which was responsible for the control and depletion of the phytoplankton in the spring of 1976 in the northern North Sea.

Plankton of the fladen ground during FLEX 76 II. Population dynamics and production of Thysanoessa inermis (Crustacea: Euphausiacea)

Samples taken in the northern North Sea with the Continuous Plankton Recorder (CPR), the Undulating Oceanographic Recorder (UOR) and the Longhurst-Hardy Plankton Recorder (LHPR) during the Fladen Ground Experiment in 1976 (FLEX 76) are used to describe the vertical distribution and population dynamics of Thysanoessa inermis (Kroyer) and to provide estimates of the production and carbon budget of the population from 19th March to 3 June 1976. Spawning occurred in late April and early May, in near synchronisation with the start of the spring bloom of phytoplankton. Eggs, nauplii and calyptopes reached maximum abundance in succession, and furciliae were numerous when sampling ceased in early June. Adults increased in length from a mean of 12.1 mm in mid-March to 17.5 mm in early June and the estimated production was 2.40 mg m-3 over the 74 d period. Total carbon ingested by the population of T. inermis was estimated to be 10 mg C m-2 d-1 in the upper 100m which was only 1.5% of the daily primary production of 0.68 gC m-2 measured over the FLEX period 26 March to 4 June 1976. The grazing by T. inermis on the phytoplankton population was assumed to have little effect on the control and depletion of the spring phytoplankton bloom during FLEX 77.

Brae Field Area, North Sea: ABSTRACT

Several hydrocarbon accumulations were discovered between 1975 and 1977 in Block 16/7 in United Kingdom waters along the western edge of the Viking graben. By 1978, 13 exploratory wells were completed, and development planning focused on the southern part of the area. The southern part of the Brae area is unique compared with other documented North Sea fields. An oil column of about 1,500 ft (457 m) is contained in Upper Jurassic conglomerate and sandstone shed off the Fladen Ground Spur as it was uplifted by faulting and as the Viking graben subsided. This major fault zone places Upper Jurassic against Devonian rocks and is the important seal along the west flank of the field. The cap rock and likely oil source are provided by the Upper Jurassic Kimmeridge Clay, which drapes a low anticline and dips eastward into the basin. Stratigraphic changes within the reservoir interval are abrupt. The depositional setting is interpreted as coalescing fan deltas spilled into the basin from adjacent uplands. Conglomerate and sandstone were deposited mainly subaerially on fan-delta surfaces, whereas laterally adjacent siltstone was laid down as fringing marine foresets. Complex diagenetic events have overprinted these facies. Other hydrocarbon accumulations similar in setting to the Brae field undoubtedly await discovery. End_of_Article - Last_Page 718------------

Diurnal Variation in Photosynthetic C02 Fixation of Marine Phytoplankton Populations

During Flex-program in April 1976 14 C0 2 , fixation experiments with natural phytoplankton populations were carried out on board of F.R.V. «ANTON DOHRN». Phytoplankton (mainly species of Chaetoceros, Nitzschia and Rhizosolenia ) was collected at 5.30, 12.00 and 18.00 GMT at several depths (10, 20 and 40 m) in Fladen Ground . The data suggest that daily fluctuations in photosynthetic activity exist as well as in the distribution of photoassimilated radioactive carbon into several photosynthetic products. Maximum 14 CO 2 , incorporation occurs in early morning and decreases in the afternoon irrespective of the light intensities used during the experiments. Maximum 14 C-labelling of the total amino acids occurred in early morning, maximum photosynthetic 14 C-incorporation into polysaccharides was observed at noon and maximum labelling of sugar phosphates occurred in the afternoon.

Windscale effluent in the waters and sediments of the Minch

A SYSTEMATIC intrusion of water of high 137Cs content into the north-eastern North Sea has been reported by the German Hydrographic Office1. Jefferies et al.2 later confirmed that a stream of water rich in radioactive caesium from Windscale passes northwards through the Hebridean Channel, around the north of Scotland and into the North Sea. Although the circulation pattern with respect to 137Cs has been significantly refined in recent reports3 and from German data for 1975 (ref. 4) and 1976 (Kautsky, personal communication) little attention has been paid to the status of other radionuclides in this stream. Such a study offers, however, an excellent opportunity of looking at the geochemical discrimination between, for example, 137Cs and the transuranic α-emitting nuclides; it seemed also that an examination of the changes of the ratio of 134Cs to 137Cs during this passage would give a good basis for estimation of the travel time. As a part of the Flex Programme (Fladen Ground Experiment—part of Jonsdap 76 international programme on the interplay of environment and a plankton bloom) in the North Sea in May–June 1976, we collected a series of sediment, water and biota samples for that purpose. We report here our analyses of samples from a large-volume water station and a 21-cm diameter sediment core taken in the Minch, 27 May 1976.

Meiobenthos of Sub-Littoral Muds

SUMMARYMeiobenthos, here defined as metazoans passing through a ½ mm screen, is described from core samples collected on muddy grounds at 100-140 m depth in the North Sea and off the west coast of Scotland between February 1962 and August 1963.Sixteen cores of 2·2 cm diameter were collected from Loch Nevis, and 14 from the Fladen ground. The top 7 cm of each core was passed through a 500μ then a 76μ screen. The residues were examined entire, and the nitrate of the finest mesh was subsampled.The fauna consisted mainly of nematodes, kinorhynchs, ostracods, copepods, polychaetes, and lamellibranchs. Between 61 and 97 % of the population consisted of nematodes, but copepods were second in importance and were more abundant than recorded on other subtidal grounds.The fine mesh (76μ) retained almost all specimens of every animal group except Nematoda. Numerically 38% of the nematode population passed through the fine sieve, but this represented only 18% by weight.The mean dry weight of meiobenthos on Fladen was calculated as 0·76 g/m2 and the average number of individuals was 196 × 104/m2.In Loch Nevis the corresponding weight was 1·28 g and the number 101 × 104. The loch had a larger and more varied population of all groups except nematodes, which were particularly abundant on Fladen.The data do not indicate significant population fluctuations throughout the year in the permanent meiobenthos.Compared with other subtidal grounds Nevis and Fladen seem to support much richer populations, and the high values for Fladen are of particular interest since this is a poor macrobenthos area.An attempt is made to indicate the possible level of meiobenthos productivity and it is suggested that there may be competition between meio- and macrobenthos for available organic matter which could result in a less efficient production of fish food.

Quantitative differences in the fauna of boreal mud associations

SUMMARYThe fauna of a muddy area in the northern North Sea (the Fladen ground) is compared with that of a similar area in a Scottish west-coast sea loch (Loch Nevis). These areas were selected because certain similarities in environmental features and in fauna, coupled with their marked difference in biomass, make them particularly suitable for studies of the factors affecting benthic production.For macrobenthos samples (from a grab) a coarse sieve with round holes of 1-3 mm diameter and a fine sieve with meshes of 0-5 mm side were used. Meiobenthos samples (from a corer) were sieved through a 0124 mm mesh and the total residue stained in rose bengal.The Fladen ground, depth 140 m, had annual bottom temperatures between 6-31 and 8-22 C and salinities between 35-20 and 35-2.50. The deposit was mainly of coarse silt with abundant tests of small Foraminifera. The fauna is redescribed. The characteristic species was the foraminifer Saccammina sphaerica. By separating empty tests from living specimens it is shown that this species was not so abundant as had been thought. The main lamellibranch was Thyasira equalis, not T. flexuosa as recorded in previous work. Other important species were the polychaetes Paraonis gracilis, Myriochele heeri, Spiophanes kroyeri, Tharyx sp., Lumbrineris impatiens, and Nephthys incisa. The standing crop of macrobenthos was 6-42 g/m2 wet weight.

RELATIONS BETWEEN PRIMARY PRODUCTION, CHLOROPHYLL AND PARTICULATE CARBON

In two very different areas in the North Sea, Aberdeen Bay (7 m) and the Fladen Ground (140 m) seasonal cycles of C14 uptake, chlorophyll and particulate organic carbon were observed. The ratios of C14 uptake to chlorophyll concentration showed marked variations seasonally. There were no signs of “dead” chlorophyll or of a decrease in the ratio due to nutrient deficiency. The ratios of chlorophyll to particulate carbon suggest that in coastal waters living plants generally form the most important part of the particulate carbon. At the deeper position the ratio was much smaller so that chlorophyll is not a good index of organic matter in the water.

Notes on oxygen sampling on the Fladen Ground

A comparison is made of oxygen and phosphate data from the Fladen Ground. It is found that the conversion factor for oxygen:phosphorus given by Sverdrup et al. (1942) does not agree with the changes below the euphotic zone and an alternative factor is calculated. Problems concerning surface exchange and production are also discussed.

A comparison of plant production estimates using14C and phosphate data

Organic production in the sea can be measured by studying the changes in phosphate throughout the water column. Results obtained by this method are compared with estimates of carbon uptake using 14C made on the Fladen Ground during 1955 and 1956. There is good general agreement between the two methods but some differences in the vertical distribution.The results are also used to calculate filtering rates of phytoplankton and sinking rates of zooplankton, and to compare observed and predicted vertical distributions of chlorophyll.

Plant production on the Fladen ground

The quantitative study of phytoplankton production may be pursued in many ways, but these ways can be divided into two general methods of approach. There is, first, the direct estimation of a production rate for a particular sample of the population; for example, the light-dark bottle technique for measuring oxygen production (Gaarder & Gran, 1927; Riley, 1939) and the new 14C technique (Steeman Nielsen, 1952). These estimates are made under conditions which must be, to some extent, artificial. Secondly, there is the direct estimation of relevant variables in the sea (phosphate, oxygen, chlorophyll concentration, etc.) from which production is calculated on the basis of hypotheses about the behaviour of phytoplankton. These hypotheses are, of necessity, simplifications of a mass of laboratory experiments and of previous field work. Riley, Stommel & Bumpus (1949) give a full account of this approach and of the difficulties involved in it.