Beschreibung: Within the Russian-German research project on "Siberian River Run-off (SIRRO)" devoted to the freshwater discharge and its influence on biological, geochemical, and geological processes in the Kara Sea, sedimentological and organic-geochemical investigations were carried-out on two well-dated sediment cores from the Yenisei Estuary area. The main goal of this study was to quantify the terrigenous organic carbon accumulation based on biomarker and bulk accumulation rate data, and its relationship to Yenisei river discharge and climate change through Holocene times. The biomarker data at both cores clearly indicate the predominance of terrigenous organic matter, reaching 70 to 100% and 50 to 80% of the total organic carbon within and directly north of the estuary, respectively. During the last about 9 Cal. kyrs. BP represented in the studied sediment section, siliciclastic sediment and (terrigenous) organic carbon input was strongly influenced by postglacial sea-level rise and climate-related changes in river discharge. The mid-Holocene Climatic Optimum is documented by maximum river discharge between 8.2 and 7.3 Cal. kyrs. BP. During the last 2000 years river discharge probably became reduced, and accumulation of both terrigenous and marine organic carbon increased due to increased coagulation of fine-grained material.

Beschreibung: 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.

Beschreibung: Investigations of lithogenic and biogenic particle fluxes using long-term sediment traps are still very rare in the northern high latitudes and restricted to the arctic marginal seas and sub-arctic regions. Here, for the first time, data on the variability of fluxes of lithogenic matter, carbonate, opal, and organic carbon as well as biomarker composition from the central Arctic Ocean are presented for a one-year period. The study has been carried out on material obtained from a long-term mooring system equipped with two multi-sampling-traps (150 and 1550 m water depth) and deployed on the southern Lomonosov Ridge close to the Laptev Sea continental margin from September 1995 to August 1996. In addition, data from surface-sediments were included in the study to get more information about the flux and sedimentation of organic carbon in this area. Annual fluxes of lithogenic matter, carbonate, opal, and particulate organic carbon are 3.9 g/m**2/y, 0.8 g/m**2/y, 2.6 g/m**2/y, 1.5 g/m**2/y, respectively, at the shallow trap and 11.3 g/m**2/y, 0.5 g/m**2/y, 2.9 g/m**2/y, 1.05 g/m**2/y, respectively, at the deep trap. Both the shallow as well as the deep trap show significant differences in vertical flux values over the year. Higher values were found from mid-July to end of October (total flux of 75-130 mg/m**2/d in the shallow trap and 40-225 mg/m**2/d in the deep trap, respectively). During all other months, fluxes were fairly low in both traps (most total flux values 〈10 mg/m**2/d1). The interval of increased fluxes can be separated into (1) a mid-July/August maximum caused by increased primary production as documented in high abundances of marine biomarkers and diatoms, and (2) a September/October (absolute) maximum caused by increased influence of Lena river discharge indicated by maximum lithogenic flux and high portions of terrigenous/fluvial biomarkers in both traps. Here, total fluxes in the deep trap were significantly higher than in the shallow trap, suggesting a lateral sediment flux at greater depth. The lithogenic flux data also support the importance of sediment input from the Laptev Sea for the sediment accumulation on the Lomonosov Ridge on geological time scales, as indicated in sedimentary records from this region.