Responses of deep-sea benthos to sedimentation patterns in the North-East Atlantic in 1992

In an extended deep-sea study the response of the benthic community to seas onally varying sedimentation rates of organic matter were investigated at a fixed abyssal site in the NE Atlantic (BIOTRANS station or JGOFS station L 2 at 47 degrees N-20 degrees W, water depth > 4500 m) on four legs of METEO R expedition 21 between March and August 1992. The vertical Aux at 3500 m d epth and temporal variations in the chloroplastic pigment concentration, a measure of phytodetritus deposition, and of total adenylates and total phos pholipids, measures of benthic biomass, and of activity of hydrolytic enzym es were observed. The flux patterns in moored sediment traps of total chlor ophyll, POC and total flux showed an early sedimentation peak in March/Apri l 1992, followed by low fluxes in May and intermediate ones from June to Au gust. Thus 1992 differed from other years, in which one large flux peak aft er the spring phytoplankton bloom was observed. Unusually high concentratio ns of chloroplastic pigments were consistently observed in March 1992, refl ecting the early sedimentation input, At the same time biomass of small ben thic organisms (bacteria to meiobenthos) and activity of hydrolytic enzymes were higher compared to values from March 1985 and from the following mont hs in 1992, In May and August 1992 pigment concentrations and biomass and a ctivity parameters in the sediment were lower than during previously observ ed depositions of phyrodetrital matter in summer. The data imply that the d eep ocean benthic community reacts to small sedimentation events with trans ient increases in metabolic activity and only small biomass production. The coupling between pelagic and benthic processes is so close that interannua l variability in surface water production is "mirrored" by deep-sea benthic processes. (C) 1999 Elsevier Science Ltd, All rights reserved.