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Holocene Sediment Budget and Evolution of the inner Kara Sea Shelf

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Citation:
Dittmers, K. , Niesen, F. and Stein, R. (2004): Holocene Sediment Budget and Evolution of the inner Kara Sea Shelf , European Geosciences Union First General Assembly, Nice (F)April 2004. .
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Abstract:

Within the scope of SIRRO (Siberian River Run off) expeditions ofRV "Akademik Boris Petrov" were carried out in the Kara Sea duringAugust and September 1999-2003. One major aim of the project is thecharacterisation and quantification of terrigenous sediment primarilysupplied by Ob and Yenisei rivers. The main objective of the presentstudy is the identification and characterisation of sediment echo typesin conjunction with geophysical and sedimentological investigations ofthe collected gravity cores.During the expeditions the geological work concentrated on a detailedsediment profiling survey by means of an ELAC sediment echograph (12kHz), as well as a CHIRP system (2-8 kHz) and in 2003 PARASOUND (3,5kHz). For ground truthing bottom sediments were sampled usingMulticorer, Giant Box Corer, and Gravity Corer.High-resolution acoustic data and sediment gravity cores taken in theinner Kara Sea shelf during several expeditions up to 78 N allow us tobalance the Holocene sediment budget and to reconstruct the sedimentaryhistory. Cores were radiocarbon dated and linked to acoustic profilesusing whole-core physical properties. Two major acoustic Units could bedifferentiated, separated by a prominent unconform reflectorinterpreted as the base of the Holocene.Total Holocene sediment volume (above the unconformity) was determinedby echosounding surveys. Porosity of logged gravity cores wassubtracted from the total volume. The inner Kara Sea shelf, measuring299746 km2 yields a total Holocene sediment mass of 183,5 *1010t. TheOb and Yenisei estuaries, with their sea water / fresh water mixingzone, act as major sediment sinks for fluvial derived terrigeneousmaterial in Holocene times. About 50% of the river supplied matter ,i.e. 23,3 *1010t precipitate in this zone termed "marginal filter".Coastal erosion accounts for about the same amount of sediment influxas river runoff accumulating to 100*1010t. The last 83*1010t arethought to originate in reworked/eroded sediments during the floodingof the shelfHigh-resolution echosounding data generally suggest a fluvial dominateddepositional environment for the shelf during early Holocene displayinglateral accretion as point bars and vertical accreted overbank depositsin a fluvial channel-levee-complex. During the early Holocene sea-levelrise estuarian facies in the incised channels migrated progressivelysouthward (upstream) to its present position forming a typical highstandsystem tract in acoustic images. The migration of the depocentercould be documented in accumulation rates of AMS dated sediment cores.

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