FRIESE FRONT 1999 - Cruise Objectives
The RIKZ-NIOZ cruise with Mitra in September 1999 involved two major topics: the present abundance and distribution of the benthic fauna, and the possible occurrence of an autumn phytoplankton bloom in relation to the hydrographic conditions. Compared to the programme of recent NIOZ-cruises with Pelagia during 1997 and 1998, some major extensions were envisaged:
1) a survey of the benthic fauna by both Triple-D and boxcorer. The Triple-D samples the ‘megafauna’, the larger (> 1 cm) macrobenthos and epibenthos living in and on the sediment. Density estimates of these medium-abundant (sub)adult older yearclasses are hardly achievable by boxcorer due to its limited sample size (0.07 m2). Most of the specimens found in the boxcorer sampling are small-sized species, with short life spans and high reproduction rates, or juveniles of longer-lived species. Simultaneous sampling should therefore reveal a more complete picture of the total biomass as well as the age-structure of many species. In the sampling programme, the central sections at 4.5o and 5o E (previously sampled by Triple-D in 1998) had priority, but it was planned to do also sections west and east of the Frisian Front area in addition. Analysis of variables like organic carbon and chlorophyll pigment content of upper sediment samples should reveal whether the Frisian Front is still a ‘special’ zone on the slope.
2) a hydrographic survey over a large area, including the waters at the English side of the Southern Bight. The key to understanding the productivity of the Frisian Front probably lays in the advection of English Coastal Water, and the new programme should map the hydrographic conditions over a large area, along a southwest-northeast axis, in the direction of the residual currents. The water sampling programme should include standard sampling for nutrients, suspended particulate matter and chlorophyll. In addition, the distribution of phytoplankton, bacteria and zooplankton (by vertical net hauls) should be determined. Surveys with Meetvis CTD and transmissometer were planned, to detect the possible presence or absence of the English silt plume during late summer. Also, the measurement of the composition of silt in water and sediment samples should reveal whether there are differences between subareas, and whether the muddy sediment at the Front can be related to a clear source.
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List of measurements |
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Bottom |
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Water column |
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(boxcorer & Triple-D) |
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(rosette sampler & vertical net) |
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median grain size |
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salinity, temperature |
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percentage silt (< 63 µm) |
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oxygen |
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particulate organic carbon |
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nutrients |
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chlorophyll pigments |
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suspended particulate matter |
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elemental composition |
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clay composition |
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clay composition |
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phytoplankton, chlorophyll and species |
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pollution (polybroom bifenyls) |
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transparant exopolymer particles |
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macrofauna, including larvae |
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bacterioplankton |
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megafauna |
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zooplankton, biomass and species |
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growth rate of bivalves |
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chitobiase activity (index sec. production) |
