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Im Rahmen des Projektes „IMPETUS – Deutsch-russisches Kompetenznetzwerk in der Meeresforschung“ sollte die Kooperation auf dem Gebiet der Polar- und Meeresforschung nachhaltig über das Otto-Schmidt-Labor für Polar- und Meeresforschung (OSL) in St. Petersburg ausgebaut werden. Ziel des Projektes war der Aufbau eines wissenschaftlichen Netzwerkes zur Anbahnung bilateraler und internationaler Kooperationen und die Intensivierung der Kommunikation und des Informationsaustausches mit Polar- und Meeresforschern aus der Russischen Föderation. Hierzu wurden sechs Arbeitstreffen mit insgesamt 259 Teilnehmern aus 28 Nationen am OSL durchgeführt.

Aufgabenstellung des Verbundvorhabens Die Arktis spielt eine wichtige Rolle im Klimageschehen unserer Erde, da diese Region das globale Klima aktiv beeinflusst. Mit zunehmender Besorgnis wird deshalb beobachtet, dass das Ausmaß und die Geschwindigkeit des Klimawandels in der Arktis während der letzten Jahre stark zugenommen haben. So hat die durchschnittliche Meereisbedeckung in den Sommermonaten der letzten 30 Jahre um bis zu 40% abgenommen (Abb. 1), und Prognosen zeigen, dass sich dieser Vorgang über Dominoeffekte beschleunigen wird. Dies wird besonders die sibirischen Schelfmeere betreffen. Abb. 1: Durchschnittliche Meereisbedeckung des Arktischen Ozeans im September in den Jahren 1979 bis 2009. Von zentraler Bedeutung für die Meereisproduktion und das Ökosystem der arktischen Schelfmeere sind offene Wasserflächen, die sogenannten Polynjasysteme, die sich in den Wintermonaten entlang der Küsten zwischen Festeis und Packeis bilden (Abb. 2). Sie reagieren sehr sensibel und schnell auf Veränderungen in der ozeanischen und atmosphärischen Zirkulation und können somit als Modell dafür herangezogen werden, wie sich die klimatischen Veränderungen auf die Arktis auswirken werden. Im Rahmen des Verbundvorhabens „System Laptev-See: Eurasische Schelfmeere im Umbruch – Ozeanische Fronten und Polynjasysteme in der Laptev-See“ haben das Arktische und Antarktische Forschungsinstitut (AARI, St. Petersburg), die Stiftung Alfred-Wegener-Institut für Polar- und Meeresforschung (AWI, Bremerhaven), das Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR, Kiel), das Lena-Delta-Reservat (LDR, Tiksi), die Akademie der Wissenschaften und der Literatur Mainz und die Universität Trier Polynja- und Frontensysteme am Beispiel der Laptev-See studiert. Erste Auswirkungen der aktuellen klimatischen Veränderungen auf die Fronten- und Polynjasysteme sollten erfasst und die Folgen für die globale Klimaentwicklung aufgezeigt werden. Hierzu wurden kontinuierliche Messungen von ozeanographis

Projekt Nr.: RUS 06/017, Projekttitel „POMOR – Deutsch-Russischer Masterstudiengang für angewandte Meeres- und Polarwissenschaften“. Laufzeit 01.01.2007 - 30.04.2010.

During the IPY, two international hands-on training workshops were held at the Otto-Schmidt Laboratory for Polar and Marine Research at the Arctic and Antarctic Research Institute in St. Petersburg, Russia. These workshops were under the conference heading of IMPETUS, meaning to be the catalyst for new collaborations between young Russian researchers and their international counterparts.IMPETUS 2007 provided insights into the latest techniques and methods used in permafrost research in fields as diverse as permafrost modeling, investigations of mountain ice segregation, bubbling from thermakarst lakes, and submarine permafrost. It brought together experts to provide young investigators with a multidisciplinary and cross-border perspective on permafrost research, a much needed approach in a discipline marked by strong research history yet strongly entangled within national boarders.IMPETUS 2008 focused on the latest techniques and methods used in polar ocean observation in research fields including nutrient and primary production monitoring, data transmission, remote sensing in oceanography and meteorology, sea-ice monitoring, seafloor mapping and Arctic drilling, coastal sediment dynamics, and climate modeling. It brought together experts to provide young researchers with a cross-border perspective in polar ocean research, a needed approach in a field characterized by the presence of many different, partially overlapping disciplines.Both IMPETUS workshops improved existing and built up new collaborations and networks including the whole range from early to senior career scientists. The success of these workshops highlights the need for a sense of belonging among scientists beyond the traditional nationally and disciplinarily established boarders.

This paper examines the role of atmospheric forcing in modifying the pathways of riverine water on the Laptev Sea shelf, using summer-to-winter hydrographic surveys from 2007-2009. Over the two consecutive winter seasons of 2007-2008 and 2008-2009 in the area of the winter coastal polynya, our data clearly link winter surface salinity fields to the previous summer conditions, with substantially different winter salinity patterns preconditioned by summer atmospheric forcing. In the summer of 2007 dominant along-shore westerly winds in the cyclonic regime force the Lena River runoff to flow eastward. In contrast, in the summer of 2008 dominant along-shore easterly winds over the East Siberian Sea and on-shore northerly winds over the Laptev Sea in the anticyclonic regime lock the riverine water in the vicinity of the Lena Delta. Over the coastal polynya area in the southeastern Laptev Sea these patterns precondition a surface salinity difference of 8-16 psu between the winters of 2008 and 2009. Overall, this indicates a residence time of at least half a year for riverine water on the Laptev Sea shelf. Future climate change associated with enhanced summer cyclonicity over the eastern Arctic may turn more riverine water eastward along the eastern Siberian coast, resulting in weaker vertical density stratification over the Laptev Sea shelf with possible impact on the efficiency of vertical mixing and polynya dense water production.

This paper examines the role of the Arctic Ocean Atlantic water (AW) in modifying the Laptev Sea shelf bottom hydrography on the basis of historical records from 1932 to 2008, field observations carried out in April–May 2008, and 2002–2009 cross‐slope measurements. A climatology of bottom hydrography demonstrates warming that extends offshore from the 30–50 m depth contour. Bottom layer temperature‐time series constructed from historical records links the Laptev Sea outer shelf to the AW boundary current transporting warm and saline water from the North Atlantic. The AW warming of the mid‐1990s and the mid‐2000s is consistent with outer shelf bottom temperature variability. For April–May 2008 we observed on‐shelf near‐bottom warm and saline water intrusions up to the 20 m isobath. These intrusions are typically about 0.2°C warmer and 1–1.5 practical salinity units saltier than ambient water. The 2002–2009 cross‐slope observations are suggestive for the continental slope upward heat flux from the AW to the overlying low‐halocline water (LHW). The lateral on‐shelf wind‐driven transport of the LHW then results in the bottom layer thermohaline anomalies recorded over the Laptev Sea shelf. We also found that polynya‐induced vertical mixing may act as a drainage of the bottom layer, permitting a relatively small portion of the AW heat to be directly released to the atmosphere. Finally, we see no significant warming (up until now) over the Laptev Sea shelf deeper than 10–15 m in the historical record. Future climate change, however, may bring more intrusions of Atlantic‐modified waters with potentially warmer temperature onto the shelf, which could have a critical impact on the stability of offshore submarine permafrost.

This paper examines a hydrographic response to the wind‐driven coastal polynya activity over the southeastern Laptev Sea shelf for April–May 2008, using a combination of Environmental Satellite (Envisat) advanced synthetic aperture radar (ASAR) and TerraSAR‐X satellite imagery, aerial photography, meteorological data, and SBE‐37 salinity‐temperature‐depth and acoustic Doppler current profiler land‐fast ice edgemoored instruments. When ASAR observed the strongest end‐of‐April polynya event with frazil ice formation, the moored instruments showed maximal acoustical scattering within the surface mixed layer, and the seawater temperatures were either at or 0.02°C below freezing. We also find evidence of the persistent orizontal temperature and salinity gradients across the fast ice edge to have the signature of geostrophic flow adjustment as predicted by polynya models.

C51A-0489: The terrigenous carbon export into the Arctic shelf systems is a major component of the Arctic Organic Carbon (OC) cycle. Mac Guire et al.(2009)in their review on the Arctic Carbon Cycle recommendate to strengthen observations and design the research sector of 'scaling' that is a key challenge to link the processes observed and understood on fine scales to larger scales, e.g., needed for modeling. Here, remote sensing observations can become important tools. Recent development of satellite ocean color sensors such as MODIS, SeaWiFS, MERIS has been accompanied by an increased effort to establish Ocean Colour (OC) algorithms (e.g., for chlorophyll, suspended matter, coloured dissolved organic matter). The ‘OCoc-from Ocean Colour to Organic Carbon’ project (IPY-project 1176), funded by the German Research Foundation (DFG), is an Ocean Colour study joined with the Arctic Coastal Dynamics ACD network and Arctic Circum-polar Coastal Observatory Network ACCO-Net (IPY-project 90). OCoc uses MERIS data for synoptical monitoring of terrigenous suspended and organic matter in the late-summer ice-free waters of the Laptev See region. MERIS Reduced Resolution (RR)-LIB data are processed towards optical aquatic parameters using Beam-Visat4.2 and the MERIS Case2 Regional processor for coastal application (C2R). Calculated aquatic parameters are optical coefficients and calculated concentrations of chlorophyll, total suspended matter and coloured dissolved organic matter absorption from the water leaving reflectances. The Laptev Sea is characterized by a very shallow topography and considerable Regions of Fresh water Influence ROFIs. The maximum river discharge of the Lena River, the second largest Arctic river in terms of annual fresh water discharge happens during the spring ice-breakup in June. Fluvial systems serve as point sources for high fluxes of dissolved and particulate terrigenous materials. The Laptev Sea coast is a highly dynamic mainly sedimentary ice-rich

The spatial and temporal changes in the Lena River runoff over the last 9 thousand years are reconstructed through studying the freshwater microfossils in sediment cores obtained from the Laptev Sea inner shelf immediately adjacent to the Lena delta and subject to the freshening effect of river water inflowing the sea through the main arms of the delta (the Trofimovskaya, Bykovskaya, and Tumatskaya arms), the sediments having been thoroughly AMS (14)C dated. The freshwater species of diatoms (predominantly the river ones) and green algae that enter the shelf with river water served as indicators of river runoff. The reconstruction of paleosalinity of the sea surface water in the regions under study is based on the relationships (established earlier) between the distribution of freshwater diatoms in the surface layers of sediments in the Arctic seas and the gradients of water salinity in summer. Data on variations in the composition of aquatic microfossil associations in sediments and the reconstructed paleosalinity in the regions of the eastern and western paleovalleys of the Lena River are used to determine the main paleohydrologic events that controlled the variations in the Lena runoff into the shelf zone of the Laptev Sea during the Holocene.

The spatial and temporal changes in the Lena River runoff over the last 9 thousand years are reconstructed through studying the freshwater microfossils in sediment cores obtained from the Laptev Sea inner shelf immediately adjacent to the Lena delta and subject to the freshening effect of river water inflowing the sea through the main arms of the delta (the Trofimovskaya, Bykovskaya, and Tumatskaya arms), the sediments having been thoroughly AMS (14)C dated. The freshwater species of diatoms (predominantly the river ones) and green algae that enter the shelf with river water served as indicators of river runoff. The reconstruction of paleosalinity of the sea surface water in the regions under study is based on the relationships (established earlier) between the distribution of freshwater diatoms in the surface layers of sediments in the Arctic seas and the gradients of water salinity in summer. Data on variations in the composition of aquatic microfossil associations in sediments and the reconstructed paleosalinity in the regions of the eastern and western paleovalleys of the Lena River are used to determine the main paleohydrologic events that controlled the variations in the Lena runoff into the shelf zone of the Laptev Sea during the Holocene.

Combined delta O18/salinity data reveal a distinctive water mass generated during winter sea ice formation which is found predominantly in the coastal polynya region of the southern Laptev Sea. Export of the brine-enriched bottom water shows interannual variability in correlation with atmospheric conditions. Summer anticyclonic circulation is favoring an offshore transport of river water at the surface as well as a pronounced signal of brine-enriched waters at about 50 m water depth at the shelf break. Summer cyclonic atmospheric circulation favors onshore or an eastward, alongshore water transport, and at the shelf break the river water fraction is reduced and the pronounced brine signal is missing, while on the middle Laptev Sea shelf, brine-enriched waters are found in high proportions. Residence times of bottom and subsurface waters on the shelf may thereby vary considerably: an export of shelf waters to the Arctic Ocean halocline might be shut down or strongly reduced during "onshore'' cyclonic atmospheric circulation, while with "offshore'' anticyclonic atmospheric circulation, brine waters are exported and residence times may be as short as 1 year only.

The hydrography of the Laptev Sea is significantly influenced by river water and sea-ice processes, which are highly variable over the annual cycle. Despite of an estuarine structure the inner and outer shelf regions are decoupled at times as documented by the stability of a warm intermediate layer formed during summer below the Lena River plume. We demonstrate that a remnant of this warm layer is preserved below the fast ice until the end of winter, while only slightly farther to the north, offshore of the land fast ice in the polynya region, the pycnocline is eroded and no signature of this layer is found. The warm intermediate layer (WIL) formed during summer can be used as tracer for Laptev Sea shelf waters throughout the winter. There by, residence times of southern Laptev Sea waters can be estimated to be at least from summer to the end of winter/spring of the following year. (C) 2009 Elsevier Ltd. All rights reserved.