Toward a Holocene sediment budget of the central Kara Sea shelf

High-resolution acoustic data and several sediment gravity cores taken in the Ob and Yenisei estuaries and the central Kara Sea shelf allow us to balance the Holocene sediment budget of the central Kara Sea shelf and to reconstruct the sedimentary history. Cores were radiocarbon dated and linked to acoustic profiles using whole-core physical properties. The Ob and Yenisei estuaries, with their sea water fresh water mixing zone, act as major sediment sinks for fluvial derived terrigeneous material in Holocene times. Most of the suspended and large amounts of dissolved matter precipitate in this zone termed “marginal filter”. High thickness of Holocene sediments occurs between 72°N and 73°30`N where a distinct decrease in thickness is observed to the north. Two major acoustic Units could be differentiated, separated by a prominent reflector interpreted as the base of the Holocene. High-resolution echosound data suggest a fluvial dominated depositional environment for the early Holocene displaying lateral accretion as point bars and vertical accreted overbank deposits in a fluvial channel-levee-complex. During the early Holocene sea-level rise the marginal filter migrated progressively southward (upstream) to its present position forming a typical high-stand system tract in acoustic images. Estuarine sedimentation in a sedimentary environment similar to today started at approximately 5 Cal. kyrs. BP. An estimated total of 14.3 * 1010 t and 9.2 * 1010 t of fine-grained brackish-marine sediments, in the Ob and Yenisei estuaries, respectively, were accumulated during Holocene times. This is only about 75 % and about 50 % of Ob and Yenisei estuarine sediment budgets, respectively, estimated by extrapolation of recent river run-off data over the last 7500 years. Filled paleoriver channels indicate active river incision in the southern part of the Kara Sea shelf prior to the Holocene. New Parasound data obtained during the recent (2003) cruise of RV “Boris Petrov” and the interpretation of the existing data allow a first estimate of Holocene sediment volume deposited on the Kara Sea shelf

Intrinsically disordered regions of tristetraprolin and DCP2 directly interact to mediate decay of ARE-mRNA

The RNA-binding protein tristetraprolin (TTP) is a potent activator of mRNA decay, specifically for transcripts bearing AU-rich elements (AREs) in their 3′-untranslated regions. TTP functions as a mediator for mRNA decay by interacting with the decay machinery and recruiting it to the target ARE-mRNA. In this study, we report a weak, but direct interaction between TTP and the human decapping enzyme DCP2, which impacts the stability of ARE transcripts. The TTP–DCP2 interaction is unusual as it involves intrinsically disordered regions (IDRs) of both binding partners. We show that the IDR of DCP2 has a propensity for oligomerization and liquid–liquid phase separation in vitro. Binding of TTP to DCP2 leads to its partitioning into phase-separated droplets formed by DCP2, suggesting that molecular crowding might facilitate the weak interaction between the two proteins and enable assembly of a decapping-competent mRNA–protein complex on TTP-bound transcripts in cells. Our studies underline the role of weak interactions in the cellular interaction network and their contribution towards cellular functionality

Recent particulate organic carbon and total suspended matter fluxes from the Ob and Yenisei Rivers into the Kara Sea (Siberia)

The Ob and Yenisei Rivers account for more than one-third of the total fresh water supply to the Arctic Ocean. In the past, their sediment load and particulate organic carbon (POC) discharge into the Kara Sea has been measured at stations in the hinterland far south of the estuaries. Suspended matter has been sampled in the estuaries and southern Kara Sea within the framework of the joint RussianGerman "SIRRO" program (Siberian River Run-Off), allowing a reliable new estimate of fluxes from the rivers into the Kara Sea. Our estimates of annual supplies of sediment (3.76x10^6 t), particulate organic carbon(0.27x10^6 t) and particulate nitrogen (PN) (0.027x10^6 t) from the Ob River to the Kara Sea are lower than earlier estimates from the northernmost gauging station in the hinterland due to deposition of particulate matter in the Ob Bay. On the other hand, our estimates of the Yeniseis annual sediment (5.03x10^6 t), particulate organic carbon (0.57x10^6 t) and particulate nitrogen (0.084x10^6 t) supplies to the Kara Sea are probably too high, as they suggest a pure bypass system in the investigated area. We differentiate between an area of recent deposition in the south of the Kara Sea and an area of recent organic matter degradation further north

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

Late Quaternary fluvial dynamics of an ice sheet proximal shelf environment in the southern Kara Sea, West Siberia

Within the scope of SIRRO (Siberian River Run off) expeditions of RV Akademik Boris Petrov were carried out in the Kara Sea during August and September 1999, 2000 and 2001. One major aim of the project is characterisation and quantification of terrigenous sediment primarily supplied by Ob and Yenisei rivers. We used a high resolution CHIRP echosounding system for selected profiles and additionally the ships sonar was used to obtain data of Holocene sediment thickness. The main objective of this study is the identification and characterisation of sediment echo types in conjunction with geophysical and sedimentological investigations of the collected gravity cores.During the expedition the geological work concentrated on a detailed sediment profiling survey by means of an ELAC sediment echograph (operating frequency of 12 kHz, impulse length of 1 ms, and 200 W transmitting power) as well as a GeoChirp sytem (2-8 kHz), and the sampling of bottom sediments using Multicorer, Giant Box Corer, and Gravity Corer for ground truthing.The history and extent of the Quaternary glaciations in Eurasia is controverse. Within this context, the largest remaining uncertainty is how far the Kara Sea ice sheet extended towards the east during the LGM (Svendsen et al., 1999; Polyak et al., 2000, 2002; Stein et al. 2002). The key question related to this problem is: how did the discharge of the siberian rivers respond/interact to an proximal ice sheet?Based on echosounding results we are able to reconstruct the palaeo drainage network of Ob and Yenisei rivers. Both rivers incised into the recent shelf, leaving filled and unfilled river channels and river canyons/valleys behind. The rivers were in the braided/meandering stage depending on the variable shelf gradient. Asymmetrical channel levee complexes with incision depths of 60 meters and more developed. The rivers formed channel levee complexes which in some places border to glacial dominated morphology, which implies fluvial deflection by an ice shield. This finding denots the non existence of an ice sheet on large areas of the Kara Sea shelf. Furthermore mapping of sediment thickness and character reveals no evidence for an ice dammed lake, as postulated by some workers.Sidorchuk et al. (2001) found macromeanders formed during the LGM until 14000 years BP, fluvial features an order of magnitude bigger than recent fluvial dimensions. Although the mean precipitation was lower than today, they related these features to an increased discharge which main cause is in their opinion the existence of permafrost, whose degradation (as recent) leads to the development of increased groundwater flow. Therefore it seems reasonable to relate fluvial features on the Kara Sea shelf, developed during sea level lowstand, to a pronounced riverine discharge as proposed by Sidorchuk et al. (2001)