1,106 research outputs found
Sea ice production and water mass modification in the eastern Laptev Sea
No full textA simple polynya flux model driven by standard atmospheric forcing is used to investigate the ice formation that took place during an exceptionally strong and consistent western New Siberian (WNS) polynya event in 2004 in the Laptev Sea. Whether formation rates are high enough to erode the stratification of the water column beneath is examined by adding the brine released during the 2004 polynya event to the average winter density stratification of the water body, preconditioned by summers with a cyclonic atmospheric forcing (comparatively weakly stratified water column). Beforehand, the model performance is tested through a simulation of a well-documented event in April 2008. Neglecting the replenishment of water masses by advection into the polynya area, we find the probability for the occurrence of density-driven convection down to the bottom to be low. Our findings can be explained by the distinct vertical density gradient that characterizes the area of the WNS polynya and the apparent lack of extreme events in the eastern Laptev Sea. The simple approach is expected to be sufficiently rigorous, since the simulated event is exceptionally strong and consistent, the ice production and salt rejection rates are likely to be overestimated, and the amount of salt rejected is distrusted over a comparatively weakly stratified water column. We conclude that the observed erosion of the halocline and formation of vertically mixed water layers during a WNS polynya event is therefore predominantly related to wind- and tidally driven turbulent mixing processe
Halocline water modification and along slope advection at the Laptev Sea continental margin
No full textA general pattern in water mass distribution and potential shelf–basin exchange is revealed at the Laptev Sea continental slope based on hydrochemical and stable oxygen isotope data from the summers 2005–2009. Despite considerable interannual variations, a frontal system can be inferred between shelf, continental slope and central Eurasian Basin waters in the upper 100 m of the water column along the continental slope. Net sea-ice melt is consistently found at the continental slope. However, the sea-ice meltwater signal is independent from the local retreat of the ice cover and appears to be advected from upwind locations.
In addition to the along-slope frontal system at the continental shelf break, a strong gradient is identified on the Laptev Sea shelf between 122° E and 126° E with an eastward increase of riverine and sea-ice related brine water contents. These waters cross the shelf break at ~ 140° E and feed the low-salinity halocline water (LSHW, salinity S < 33) in the upper 50 m of the water column. High silicate concentrations in Laptev Sea bottom waters may lead to speculation about a link to the local silicate maximum found within the salinity range of ~ 33 to 34.5, typical for the Lower Halocline Water (LHW) at the continental slope. However brine signatures and nutrient ratios from the central Laptev Sea differ from those observed at the continental slope. Thus a significant contribution of Laptev Sea bottom waters to the LHW at the continental slope can be excluded. The silicate maximum within the LHW at the continental slope may be formed locally or at the outer Laptev Sea shelf. Similar to the advection of the sea-ice melt signal along the Laptev Sea continental slope, the nutrient signal at 50–70 m water depth within the LHW might also be fed by advection parallel to the slope. Thus, our analyses suggest that advective processes from upstream locations play a significant role in the halocline formation in the northern Laptev Sea
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Halocline water modification and along-slope advection at the Laptev Sea continental margin
No full textA general pattern in water mass distribution and
potential shelf–basin exchange is revealed at the Laptev Sea
continental slope based on hydrochemical and stable oxygen
isotope data from the summers 2005–2009. Despite considerable
interannual variations, a frontal system can be inferred
between shelf, continental slope and central Eurasian Basin
waters in the upper 100 m of the water column along the continental
slope. Net sea-ice melt is consistently found at the
continental slope. However, the sea-ice meltwater signal is
independent from the local retreat of the ice cover and appears
to be advected from upwind locations.
In addition to the along-slope frontal system at the continental
shelf break, a strong gradient is identified on the
Laptev Sea shelf between 122° E and 126° E with an eastward
increase of riverine and sea-ice related brine water contents.
These waters cross the shelf break at ~140° E and feed
the low-salinity halocline water (LSHW, salinity S < 33) in
the upper 50 m of the water column. High silicate concentrations
in Laptev Sea bottom waters may lead to speculation
about a link to the local silicate maximum found within the
salinity range of ~33 to 34.5, typical for the Lower Halocline
Water (LHW) at the continental slope. However brine
signatures and nutrient ratios from the central Laptev Sea
differ from those observed at the continental slope. Thus a
significant contribution of Laptev Sea bottom waters to the
LHW at the continental slope can be excluded. The silicate maximum within the LHW at the continental slope may be
formed locally or at the outer Laptev Sea shelf. Similar to
the advection of the sea-ice melt signal along the Laptev Sea
continental slope, the nutrient signal at 50–70 m water depth
within the LHW might also be fed by advection parallel to the
slope. Thus, our analyses suggest that advective processes
from upstream locations play a significant role in the halocline
formation in the northern Laptev Sea.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.ocean-science.net/
Stable dissolved silicon isotopes measured on CTD and underway samples during AMK73 in the Laptev Sea
No full textDissolved stable silicon isotopes were determined in seawater samples collected during the 73rd expedition onboard RV Akademik Mstislav Keldysh (AMK73) in the Laptev Sea in October 2018 under ice free conditions. Seawater samples were filtered inline from Niskin bottles or the ship's underway system, acidified to 0.1% v/v with HCl and kept at 4°C until analysis on land. Samples were measured for δ29Si(OH)4 with reference to international reference material NBS28 on a Nu Plasma II MC-ICP-MS (The University of Edinburgh, School of Geosciences) using the MAGIC co-precipitation method and purified through column chemistry. International standards BigBatch, ALOHA300 and ALOHA1000 were run alongside seawater samples for inter-comparability. Final values were converted to δ30Si(OH)4 using the conversion factor of 1.96 for comparability. Reproducibility is 0.05 and 0.1‰ for δ29Si(OH)4 and δ30Si(OH)4 respectively. This dataset includes salinity, silicic acid concentrations and stable silicon isotope signatures of seawater, which provides useful information on the silicon biogeochemical cycle of the Laptev Sea, as influenced by the Lena river
Clay mineral composition of surface sediment from the Siberian and Laptev Seas (fig 1)
No full textClay mineral composition of surface sediment from the Siberian and Laptev Seas (fig 1
Extension across the Laptev Sea continental rifts constrained by gravity modeling
No full textThe Laptev Shelf is the area where the Gakkel Ridge, an active oceanic spreading axis, approaches a continental edge, causing a specific structural style dominated by extensive rift structures. From the latest Cretaceous to the Pliocene, extension exerted on the Laptev Shelf created there several deep subsided rifts and high-standing basement blocks. To understand syn-rift basin geometries and sediment supply relationships across the Laptev Shelf, accurate extension estimates are essential. Therefore, we used 2-D gravity modeling and 3-D gravity inversion to constrain the amount of crustal stretching across the North America-Eurasia plate boundary in the Laptev Shelf. The latest Cretaceous-Cenozoic extension in that area is partitioned among two rift zones, the Laptev Rift System and the New Siberian Rift. These rifts were both overprinted on the Eurasian margin that had been stretched by 190-250 km before the Late Cretaceous. While the Laptev Rift System, connected to the Gakkel Ridge, reveals increasing extension toward the shelf edge (190-380 km), the New Siberian Rift is characterized by approximately uniform stretching along strike (110-125 km). The architecture of the Laptev Rift System shows that the finite extension of about 500 km is sufficient to entirely eliminate crystalline continental crust. In the most stretched rift segment, continental mantle is exhumed at the base of the Late Mesozoic basement. The example of the Laptev Rift System shows that extension driven by divergent plate movement is a sufficient cause to produce almost complete continental breakup without an increased heat input from the asthenospheric mantle
Russian-German Cooperation: Laptev Sea System : [2. Workshop Russian-German Cooperation: Laptev Sea System ; St. Petersburg, November 1994]
No full textPREFACE : 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
Local velocity-adapted motion events for spatio-temporal recognition
No full textIn this paper, we address the problem of motion recognition using event-based local motion representations. We assume that similar patterns of motion contain similar events with consistent motion across image sequences. Using this assumption, we formulate the problem of motion recognition as a matching of corresponding events in image sequences. To enable the matching, we present and evaluate a set of motion descriptors that exploit the spatial and the temporal coherence of motion measurements between corresponding events in image sequences. As the motion measurements may depend on the relative motion of the camera, we also present a mechanism for local velocity adaptation of events and evaluate its influence when recognizing image sequences subjected to different camera motions. When recognizing motion patterns, we compare the performance of a nearest neighbor (NN) classifier with the performance of a support vector machine (SVM). We also compare event-based motion representations to motion representations in terms of global histograms. A systematic experimental evaluation on a large video database with human actions demonstrates that (i) local spatio-temporal image descriptors can be defined to carry important information of space-time events for subsequent recognition, and that (ii) local velocity adaptation is an important mechanism in situations when the relative motion between the camera and the interesting events in the scene is unknown. The particular advantage of event-based representations and velocity adaptation is further emphasized when recognizing human actions in unconstrained scenes with complex and non-stationary backgrounds.QC 20100525 QC 20111115</p
Structure and geology of the continental shelf of the Laptev Sea, Eastern Russian Arctic
No full textThe Laptev Sea is of great significance for studying the processes of the initial breakup of continents. It is the southern termination of the Gakkel spreading ridge and thus the location of structural features resulting from a continental margin/spreading ridge intersection. The present-day understanding of the Laptev Shelf geology is based on the Russian multichannel seismic reflection data and extrapolation of the terrestrial geology. Geologic and plate-kinematic data are used to constrain the interpretation of the seismic reflection data. The Laptev Rift System consists of several deep subsided rifts and high standing blocks of the basement. From west to east these are: the West Laptev and South Laptev rift basins, Ust' Lena Rift, East Laptev and Stolbovoi horsts, Bel'kov-Svyatoi Nos and Anisin rifts. The central and eastern parts of the shelf have the greatest contrasts in the gravity field ranging from −60 mGal over the rifts to 50 mGal over the horsts. The rifts contain up to five seismic stratigraphic units bounded by clear regional reflectors and underlain by folded heterogeneous basement. They are suggested to be Late Cretaceous to Holocene in age and reflect different stages of spreading ridge/continental margin interaction. The estimated total thickness of the rift-related sediments varies between 4 and 8–10 km while the sedimentary cover on the uplifts is significantly reduced and generally does not exceed 1–2 km. An eastward decrease of the total thickness of the sedimentary sections from about 10 km in the South Laptev Basin to 4–5 km in the Bel'kov-Svyatoi Nos Rift and the simplicity of the entire rift structure may indicate a rejuvenation of the rifts in the same direction. The entire rift system is covered by the uppermost seismic unit, which probably reflects a deceleration of the rifting during the last reorganization of the North American/Eurasian plate interaction since about 2 Ma
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