323,865 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
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
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
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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