Particulate matter fluxes in the southern and central Kara Sea compared to sediments: Bulk fluxes, amino acids, stable carbon and nitrogen isotopes, sterols and fatty acids.

The Kara Sea is one of the arctic marginal seas strongly influenced by fresh water and river suspension. The highlyseasonal discharge by the two major rivers Yenisei and Ob induces seasonal changes in hydrography, sea surfacetemperature, ice cover, primary production and sedimentation. In order to obtain a seasonal pattern of sedimentation inthe Kara Sea, sediment traps were deployed near the river mouth of the Yenisei (Yen) as well as in the central Kara Sea(Kara) within the framework of the GermanRussian project Siberian River run-off; SIRRO. Two and a half years oftime-series flux data were obtained between September 2000 and April 2003 and were analyzed for bulk components,amino acids, stable carbon and nitrogen isotopes as well as sterols and fatty acids.Sediment trap data show that much of the annual deposition occurred under ice cover, possibly enhanced byzooplanktonic activity and sediment resuspension. An early bloom of ice-associated algae in April/May occurred in thepolynya area and may have been very important to sustain the life cycles of higher organisms after the light limitation ofthe winter months due to no/low insolation and ice cover. The strong river input dominated the months JuneAugust inthe southern part of the Kara Sea. The central Kara Sea had a much shorter productive period starting in August and wasless affected by the river plumes. Despite different time-scales of sampling and trapping biases, total annual fluxes fromtraps were in the same order of magnitude as accumulation rates in surface sediments. Terrestrial organic carbonaccumulation decreased from 10.7 to 0.3 gCm 2 a 1 from the riverine source to the central Kara Sea. Parallel to this,preservation of marine organic matter decreased from 10% to 2% of primary productivity which was probably related todecreasing rates of sedimentation.