SEASONAL VARIABILITY OF THE LONG-CHAIN ALKENONE FLUX AND THE EFFECT ON THE U-37(K')-INDEX IN THE NORWEGIAN SEA

A seasonally-varying sedimentation pattern was observed for the alkeno ne flux measured with sediment traps in the northern North Atlantic. I n the Norwegian Sea (traps were set at 500, 1000 and 3000 m) the alken one flux varied between 0.1 and 7.1 mu g m(-2) d(-1) and followed the seasonal pattern of the bulk parameters. Maximum fluxes occurred from mid-October until mid-November and were also high in May. A surprising result was that considerably higher particle fluxes were observed at 3000 m. For the alkenone flux, the highest additional input of 250% wa s observed during the period when sediment resuspension was greatest i n summer. At the Barents Sea continental margin (traps Bt 1840 and 195 0 m) the alkenone fluxes follow the sedimentation pattern of the bulk parameters, with a less visible signal of distinct seasonality observe d in the 1950 m trap. The sedimentation of total alkenones varied betw een 0.8 and 144 mu g m(-2) d(-1) at 1840 m and between 0.5 and 31.0 mu g m(-2) d(-1) at 1950 m. Resuspension and lateral advection contribut ed significantly to measured fluxes in the two near-bottom traps. Alke none concentrations were determined in faecal pellets of Appendiculari a, ostracods and euphausids from selected samples at the Barents Sea s ite. The alkenone flux in pellets (4% to 24% of total) was 5 to 6 time s higher at 1950 m depth than at 1840 m and the major part (77-78%) of the total flux of C-37:3 reaching the near-bottom trap at 1950 m was associated with faecal pellets of the meso-zooplankton. Spatial and te mporal variations of the U-37(k') signals were observed, indicating th at the imprint in the alkenone signal depends on the origin and transp ort pathway of the organic material. Strong deviations occur in areas where nepheloid layers contribute particles of long residence times to the primary flux. (C) 1998 Elsevier Science Ltd. All rights reserved.