Shelf basin exchange along the Siberian continental margin: modification of Atlantic Water and Lower Halocline Water

Highlights • Atlantic Water modified by sea-ice melt and meteoric water at Barents Sea slope • LHW may be divided into different types by Principal Component Analysis (PCA) • high salinity LHW-type forms in the Barents and Kara seas • low salinity LHW-types form in the western Laptev Sea or enter via Vilkitsky Strait • PCA does not support a distinction between onshore and offshore LHW branches Abstract Salinity and stable oxygen isotope (δ18O) evidence shows a modification of Atlantic Water in the Arctic Ocean by a mixture of sea-ice meltwater and meteoric waters along the Barents Sea continental margin. On average no further influence of meteoric waters is detectable within the core of the Atlantic Water east of the Kara Sea as indicated by constant δ18O, while salinity further decreases along the Siberian continental slope. Lower halocline waters (LHW) may be divided into different types by Principal Component Analysis. All LHW types show the addition of river water and an influence of sea-ice formation to a varying extent. The geographical distribution of LHW types suggest that the high salinity type of LHW forms in the Barents and Kara seas, while other LHW types are formed either in the northwestern Laptev Sea or from southeastern Kara Sea waters that enter the northwestern Laptev Sea through Vilkitsky Strait. No further modification of LHW is seen in the eastern Laptev Sea but the distribution of LHW-types suggest a bifurcation of LHW at this location, possibly with one branch continuing along the continental margin and a second branch along the Lomonosov Ridge. We see no pronounced distinction between onshore and offshore LHW types, as the LHW components that are found within the halocline over the basin also show a narrow bottom-bound distribution at the continental slope that is consistent with a shelf boundary current as well as a jet of water entering the western Laptev Sea from the Kara Sea through Vilkitsky Strait

Surface salinity fields in the Arctic Ocean and statistical approaches to predicting anomalies and patterns

Significant salinity anomalies have been observed in the Arctic Ocean surface layer during the last decade. Using gridded data of winter salinity in the upper 50 m layer of the Arctic Ocean for the period 1950-1993 and 2007-2012, we investigated the inter-annual variability of the salinity fields, attempted to identify patterns and anomalies, and developed a statistical model for the prediction of surface layer salinity. The statistical model is based on linear regression equations linking the principal components with environmental factors, such as atmospheric circulation, river runoff, ice processes, and water exchange with neighboring oceans. Using this model, we obtained prognostic fields of the surface layer salinity for the winter period 2013-2014. The prognostic fields demonstrated the same tendencies of surface layer freshening that were observed previously. A phase portrait analysis involving the first two principal components exhibits a dramatic shift in behavior of the 2007-2012 data in comparison to earlier observations

The TRANSDRIFT III expedition: freeze-up studies in the Laptev Sea

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

Thermohaline structure and variability in the eastern Nansen Basin as seen from historical data

Newly available historical Russian data are used to quantify year-to-year variations in the structure and properties of the halocline and Atlantic Water layers in the eastern Nansen Basin. The data come from a series of aerial surveys of the central Arctic Ocean done during winter between 1973 and 1979, and repeated Polygon surveys of the shelf, slope, and basin north of Severnaya Zemlya in the 1980s, and thus allow a perspective on shelf-basin exchange. A water-mass census shows substantial survey-to-survey variability in several water-mass categories, with volumetric fluctuations of ∼17% in the Upper Polar Deep Water category, ∼14% in Atlantic Water, and ∼39% for cold surface waters with T \u3c −1.5°C. Mean water-mass production rates in the polygon area are found to be 0.6–1.2 Sv for Upper Polar Deep Water, and an effective loss rate of 0.75–1.5 Sv is found for Atlantic Waters. On average Atlantic Water loses 16% of its initial heat content within the 350 km-long survey area, possibly enhanced by double-diffusive processes. Mean upward heat fluxes above the Atlantic Water are estimated to be between 4 and 6 W/m2, based on heat budget considerations. Upward heat fluxes of this magnitude would have a major effect on sea ice, which is regularly observed to be thinner in this area of the Nansen Basin. Shallow-water profiles taken close to Severnaya Zemlya show cold and salty waters denser than offshore waters at similar depths, and evidence of convection is seen in many profiles taken over the continental shelf and slope, reflecting deep convective events extending in some cases below the deepest observed depth of 1000 m

The structure of Atlantic Water at Eurasian continental slope in summer 2007

Intensive field campaigns during the IPY (2007-2009) allowed unprecedented coverage of Eurasian continental slope by CTD measurements. These data allowed detailed mapping of the warm Atlantic water on its way from Fram Strait to the East Siberian Sea. Fourteen cross-slope sections, carried out by Russian, US and German scientists in August-September 2007 were used to determine position and properties of the warm Atlantic water core. Temperature and salinity data were examined against traditional concept of warm intermediate layer in the Arctic Ocean and in the view of recently introduced new ideas (e.g. seasonal oscillations in AW layer far from Fram Strait). Joined analysis of CTD data with long-term mooring observations demonstrated complex nature of warming-cooling pulses, which enter Arctic Ocean through Fram Strait and effect thermal conditions in Eurasian sector of the Arctic Ocean

Russian-German Cooperation: Laptev Sea System : [2. Workshop Russian-German Cooperation: Laptev Sea System ; St. Petersburg, November 1994]

PREFACE : The Laptev Sea System The Arctic Ocean, in particular the wide Eurasian shelf seas comprise some of the most sensitive elements of the global environment which are believed to respond at a very early time to Global Change. The renewed interest in the Arctic, the large scale international research efforts devoted to the Arctic, as well as the presently available new technology to carry out research in ice-infested areas, have opened many new avenues to conduct investigations On the variability of the depositional environments of the Eurasian shelf seas. The Laptev Sea is of particular importance in the string of the Eurasian shelf seas because feeding the Transpolar Drift of the Arctic sea-ice Cover it exports relatively the largest amounts of sea ice into the Open Arctic Ocean, because it is farthest away from the influence of the Atlantic and Pacific waters, and because it is under the influence of rapidly changing fresh water fluxes from the Siberian hinterland (Fig. 1, Sea ice drift paths in the Arctic Ocean). The morphology of the seafloor, the rapidly changing coast lines of the fragil Lena Delta Island frame work as well as the presence of submarine permafrost are examples for the dynamics of the entire Laptev Sea System. - Fig. 1 - In order to address the natural properties of the Laptev Sea System a joint research project is carried out between a number of Russian and German research institutions under the framework of the "Laptev Sea System Project" (Fig. 2, Research institutions under the framework of the "Laptev Sea System Project"). Every year expeditions are carried out in the area on Russian or German research vessels where multi-disciplinary and binational working groups are addressing some of the identified scientific themes. Results from these joint investigations are then discussed in a series of RussianIGerman workshops which are held alternatively in Russia or Germany. The second workshop 'Russian-German Cooperation: Laptev Sea System' was held in November 1994 in St. Petersburg in order to assess (1) the state of knowledge of the Laptev Sea and the adjacent continental margin of the deep Arctic, and (2) to develop a research strategy for the marine geosciences in the Laptev Sea and terrestrial werk in East Siberia. The workshop brought together more than 100 scientists, among them meteorologists, sea ice physicists, oceanographers, biologists, chemists, geologists and geophysicists from various Russian and German research institutions. The main goal of the workshop was to promote and coordinate scientific collaboration among scientists from Russia and Germany. Main emphasis have laid on first scientific results of the expeditions within the scope of the interdisciplinary Russian-German research project 'Laptev Sea System', that is present and past oceanography, ecology, and climatology of the Laptev Sea. The workshop was organized into serveral sessions which followed various themes of the environment of the Laptev Sea from their present situation to their geological record: (I) Ciimate and Ice (11) Modern Environment of the Laptev Sea (111) Environmental History of the Laptev Sea (IV) From Siberia to the Arctic Ocean: Land-Sea Connection (V) Strategy and Plans for Future Work (VI) Mid-long Term Perspectives The scientific content of this workshop is documented in this report containing most of the results and discussions. The publication of this volume serves various purposes. It is primarily a forum for scientists working in the Siberian shelf seas, in which the results of many years of research and preliminary shipboard results can be presented. In order to provide all the participants in the workshop with the opportunity for reporting their results, a speedy way of publication was chosen. Thus, each individual author has presented his opinions and views as he or she sees them, reflecting the diversity and complexity of the Laptev Sea system. On the other hand, this volume offers many researchers the possibility of acquainting themselves with methods and results of research into the East Siberian seas as carried out in other parts of the world. Finally, it is hoped that this collection of papers will function as another step toward joint research projects and are base for the expeditions to be carried out in 1995 and the following years. Many of the papers published identify major scientific problems, thus offering new perspectives for future scientific research in polar regions. The nature of the papers, the discussions and the disciplines of the attendees clearly demonstrate that the study of the Laptev Sea System is a multidisciplinary one in an interesting key area involving all branches of the natural sciences, such as ice physics, oceanography, biology and geology, in particular. It thus remains an important example for GLOBAL CHANGE and CLIMATE IMPACT research within international research efforts, e.g. International Arctic Science Committee (IASC), Arctic Ocean Sciences Board (AOSB) or the Nansen Arctic Drilling Programme (NAD). - Fig. 2 - The editors also made an effort, probably not wholly successful, to edit manuscripts by non-English-speaking authors to make them easier to understand. In this process, we hope we have not changed the meanings of the original papers. Above all we thank Bettina Rohr and Daniel Krüger who kindly assisted in editing the papers. The workshop has been sponsored by the German and Russian Ministries for Research and Technology and the meeting was held from the 21st to the 14th of November in 1994 in the Arctic and Antarctic Research Institute in St. Petersburg. We wish to thank these organizations for their financial and logistic support

On the Variability of Stratification in the Freshwater-Influenced Laptev Sea Region

In this paper, we investigate the seasonal and spatial variability of stratification on the Siberian shelves with a case study from the Laptev Sea based on shipboard hydrographic measurements, year-round oceanographic mooring records from 2013 to 2014 and chemical tracer-based water mass analyses. In summer 2013, weak onshore-directed winds caused spreading of riverine waters throughout much of the eastern and central shelf. In contrast, strong southerly winds in summer 2014 diverted much of the freshwater to the northeast, which resulted in 50% less river water and significantly weaker stratification on the central shelf compared with the previous year. Our year-long records additionally emphasize the regional differences in water column structure and stratification, where the northwest location was well-mixed for 6 months and the central and northeast locations remained stratified into spring due to the lower initial surface salinities of the river-influenced water. A 26 year record of ocean reanalysis highlights the region’s interannual variability of stratification and its dependence on winds and sea ice. Prior the mid-2000s, river runoff to the perennially ice-covered central Laptev Sea shelf experienced little surface forcing and river water was maintained on the shelf. The transition toward less summer sea ice after the mid-2000s increased the ROFI’s (region of freshwater influence) exposure to summer winds. This greatly enhanced the variability in mixed layer depth, resulting in several years with well-mixed water columns as opposed to the often year-round shallow mixed layers before. The extent of the Lena River plume is critical for the region since it modulates nutrient fluxes and primary production, and further controls intermediate heat storage induced by lateral density gradients, which has implications for autumnal freeze-up and the eastern Arctic sea ice volume. MAIN POINTS 1. CTD surveys and moorings highlight the regional and temporal variations in water column stratification on the Laptev Sea shelf. 2. Summer winds increasingly control the extent of the region of freshwater influence under decreasing sea ice. 3. Further reductions in sea ice increases surface warming, heat storage, and the interannual variability in mixed layer depth

The First Training Workshop on Permafrost Research Methods: IMPETUS 2007 : OSL-APECS-PYRN Training Workshop; St. Petersburg, Russia, 29 November to 2 December 2007

Fifty young researchers from 14 countries met in St. Petersburg, Russia, to learn about the latest methods used in permafrost research and engineering and to discuss future plans to address climate change issues in permafrost areas. This workshop was an official International Polar Year (IPY) event organized jointly by the Otto Schmidt Laboratory for Polar and Marine Sciences (OSL) in St. Petersburg, the Permafrost Young Researchers Network (PYRN), and the Association of Polar Early Career Scientists (APECS). The workshop 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 thermokarst lakes, and submarine permafrost detection. 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 borders. Presentations and speaker biographies are now available on the conference Web site (http://pyrn.ways.org/activities/pyrn-meetings/2007-saint-petersburg)