Grain Size seperation and sediment mixing in Artic Ocean sediments: evidence from the strontium isotope systematic

The (87)Rb/(86)Sr and (87)Sr/(86)Sr ratios of Laptev Sea sediments, of Arctic Ocean sediments and of suspended particulate matter (SPM) from Siberian rivers (Lena and Khatanga) form 'pseudo-isochrons' due to grain-size separation processes which are referred to as 'Lena Mixing Envelope' (LME) and as 'Flood Basalt Envelope' (FBE). At the land-ocean transition the reduction of the particle velocity causes a deposition of coarser grained material and the contact with saline water enhances a precipitation of finer-grained material. The coarse-grained material is enriched in Sr showing less radiogenic (87)Sr/(86)Sr ratios whereas fine grained material is depleted in Sr relative to Rb showing more radiogenic (87)Sr/(86)Sr ratios, The experimentally determined spread of the (87)Rb/(86)Sr and (87)Sr/(86)Sr ratios as a function of grain size in one sediment sample is on the same order as the natural spread of the (87)Sr/(86)Sr ratios observed in all samples from the Arctic Ocean. Chemical Index of Alteration (CIA) for the Lena river SPM tend to confirm previous observations that chemical alteration is negligible in the Arctic environment. Thus, these 'pseudo-isochrons' reflect an average age and the average isotope composition in the river drainage area. Calculated apparent ages from the FBE reflect the age of the Siberian flood basalt of about 220 Ma and the initial ratio of 0.707(1) reflects their mantle origin. The age calculated from the LME of about 125 Ma reflects accidentally the Jurassic and Cretaceous age of the sediments drained by the Lena river and the initial ratio of 0.714(1) reflects the crustal origin of their source rocks. Comparison of geographical locations reveals that all samples from the eastern Laptev Sea (east of 120 degrees E) fall along the LME whereas all samples from the western Laptev Sea (west of 120 degrees E) fall between LME and FBE. Mixing calculations based on (143)Nd/(144)Nd measurements, not influenced by grain size, show that about 75% of the western Laptev Sea sediments originate from the Lena drainage area whereas about 25% of the sediments are delivered from the Siberian flood basalt province. Sediments from the central Arctic Ocean are isotopically related to the Lena drainage area and the Siberian flood basalt province. However, sediments from the Arctic Ocean margins close to Novaya Semlya, Greenland, the Fram Strait and Svalbard originate from sources not yet identified. (C) 1999 Elsevier Science B.V. All rights reserved

Arctic coastal dynamics of Eurasia – results of two ACD-related INTAS projects : extended abstract

Under the framework of the Arctic Coastal Dynamics (ACD) program two projects of the International Association for the Promotion of Co-operation with Scientists from the New Independent States of the Former Soviet Union (INTAS) focused on ACD related topics. The objectives of the first project "Arctic coastal dynamics of Eurasia: classification, modern state and prediction of its development based on GIS technology" (2002-2004) had been to develop a coastal classification and to generate GIS based map products for the coastal Zone of the Eurasian Arctic. The Russian Part of the circum-Arctic ACD classification and segmentation has been completed within this project. The overall objective of the second project "Arctic coasts of Eurasia: dynamics, sediment budget and carbon flux in connection with permafrost degradation" (2002-2005) is to quantify the material flux through coastal erosion in order to improve our understanding of the Arctic sediment and organic carbon budget. This presentation summarizes the main results of the two projects and provides an overview of more specific results which are shown in a series of Posters

Expedition to the Lena and Yana Rivers

The Russian icebreaker KAPITAN DRANITSYN carried out the TRANSDRIFT III expedition to the Laptev Sea (October 1 to 30., 1995), the largest ice factory in the Arctic Ocean and source region of the Transpolar Drift. In this shelf region, ice free for only three months a year, a comprehensive interdisciplinary working program concerning the causes and effects of annual freeze-up was performed. Unlike our previous expeditions to the Laptev Sea, which focused On oceanographical, hydrochemical, ecological, and sedimentological processes during the brief ice-free period in summer, this expedition studied these processes during the extreme physical change through the onset of ice formation in autumn. This is the first study of its kind under these conditions, and gave important clues to the rapid (14 to 40 days) freeze-up, which has significant year-round effects for the Laptev Sea and global environment. Freeze-up began one month later than usual (a 40 year record) close to the Novosibirskie Islands in low salinity surface waters due to heat stored in an intermediate water layer between 10 and 25 m water depth. Later, huge tracts of turbid, dirty ice were found off the Lena Delta where an unusually high phytoplankton concentration for this time of year occurred. The origin of these anomalies, and whether they are anomalies at all, and their relationship to global environment in real time are the focus of continuing research