312 research outputs found
Interannual variability of surface and bottom sediment transport on the Laptev Sea shelf during summer
No full textSediment transport dynamics were studied during ice-free conditions under different atmospheric circulation regimes on the Laptev Sea shelf (Siberian Arctic). To study the interannual variability of suspended particulate matter (SPM) dynamics and their coupling with the variability in surface river water distribution on the Laptev Sea shelf, detailed oceanographic, optical (turbidity and Ocean Color satellite data), and hydrochemical (nutrients, SPM, stable oxygen isotopes) process studies were carried out continuously during the summers of 2007 and 2008. Thus, for the first time SPM and nutrient variations on the Laptev Sea shelf under different atmospheric forcing and the implications for the turbidity and transparency of the water column can be presented.
The data indicate a clear link between different surface distributions of riverine waters and the SPM transport dynamics within the entire water column. The summer of 2007 was dominated by shoreward winds and an eastward transport of riverine surface waters. The surface SPM concentration on the southeastern inner shelf was elevated, which led to decreased transmissivity and increased light absorption. Surface SPM concentrations in the central and northern Laptev Sea were comparatively low. However, the SPM transport and concentration within the bottom nepheloid layer increased considerably on the entire eastern shelf. The summer of 2008 was dominated by offshore winds and northward transport of the river plume. The surface SPM transport was enhanced and extended onto the mid-shelf, whereas the bottom SPM transport and concentration was diminished. This study suggests that the SPM concentration and transport, in both the surface and bottom nepheloid layers, are associated with the distribution of riverine surface waters which are linked to the atmospheric circulation patterns over the Laptev Sea and the adjacent Arctic Ocean during the open water season. A continuing trend toward shoreward winds, weaker stratification and higher SPM concentration throughout the water column might have severe consequences for the ecosystem on the Laptev Sea shelf
Improved <i>L</i><i>p</i> Hardy Inequalities [Elektronisk resurs]
No full textPaper 1 : A geometrical version of Hardy's inequality for W_0^{1,p}(D).The aim of this article is to prove a Hardy-type inequality, concerning functions in W_0^{1,p}(D) for some domain D in R^n, involving the volume of D and the distance to the boundary of D. The inequality is a generalization of a previously proved inequality by M. and T. Hoffmann-Ostenhof and A. Laptev, which dealt with the special case p=2.Paper 2 : A Hardy inequality in the Half-space.Here we prove a Hardy-type inequality in the half-space which generalize an inequality originally proved by V. Maz'ya to the so-called L^p case. This inequality had previously been conjectured by the mentioned author. We will also improve the constant appearing in front of the reminder term in the original inequality (which is the first improved Hardy inequality appearing in the litterature).Paper 3 : Hardy type inequalities for Many-Particle systems.In this article we prove some results about the constants appearing in Hardy inequalities related to many particle systems. We show that the problem of estimating the best constants there is related to some interesting questions from Geometrical combinatorics. The asymptotical behaviour, when the number of particles approaches infinity, of a certain quantity directly related to this, is also investigated.Paper 4 : Various results in the theory of Hardy inequalities and personal thoughts.In this article we give some further results concerning improved Hardy inequalities in Half-spaces and other conic domains. Also, some examples of applications of improved Hardy inequalities in the theory of viscous incompressible flow will be given.</p
Variation in the seston C:N ratio of the Arctic Ocean and pan-Arctic shelves
No full textStudying more than 3600 observations of particulate organic carbon (POC) and particulate organic nitrogen (PON), we evaluate the applicability of the classic Redfield C:N ratio (6.6) and the recently proposed Sterner ratio (8.3) for the Arctic Ocean and pan-Arctic shelves. The confidence intervals for C:N ranged from 6.43 to 8.82, while the average C:N ratio for all observations was 7.4. In general, neither the Redfield or Sterner ratios were applicable, with the Redfield ratio being too low and the Sterner ratio too high. On a regional basis, all northern high latitude regions had a C:N ratio significantly higher than the Redfield ratio, except the Arctic Ocean (6.6), Chukchi (6.4) and East Siberian (6.5) Seas. The latter two regions were influenced by nutrient-rich Pacific waters, and had a high fraction of autotrophic (i.e. algal-derived) material. The C:N ratios of the Laptev (7.9) and Kara (7.5) Seas were high, and had larger contributions of terrigenous material. The highest C:N ratios were in the North Water (8.7) and Northeast Water (8.0) polynyas, and these regions were more similar to the Sterner ratio. The C:N ratio varied between regions, and was significantly different between the Atlantic (6.7) and Arctic (7.9) influenced regions of the Barents Sea, while the Atlantic dominated regions (Norwegian, Greenland and Atlantic Barents Seas) were similar (6.7–7). All observations combined, and most individual regions, showed a pattern of decreasing C:N ratios with increasing seston concentrations. This meta-analysis has important implications for ecosystem modelling, as it demonstrated the striking temporal and spatial variability in C:N ratios and challenges the common assumption of a constant C:N ratio. The non-constant stoichiometry was believed to be caused by variable contributions of autotrophs, heterotrophs and detritus to seston, and a significant decrease in C:N ratios with increasing Chlorophyll a concentrations supports this view. This study adds support to the use of a power function model, where the exponent is system-specific, but we suggest a general Arctic relationship, where POC = 7.4 PON0.89
tab1
No full textaerosol particles larger than 1 µm in the marine boundary layer over the Laptev, Kara and Barents Seas in summe
Ice-wedge stable isotopes at the Dmitry Laptev Strait (Northeast Siberian Arctic) – indications for Late Quaternary stratigraphy and paleoclimate
No full textIce wedges are the most abundant type of ground ice in the ice-rich permafrost deposits of the Northeast Siberian Arctic. They are formed by the periodic repetition of frost cracking and subsequent crack filling and refreezing in spring, mostly by melt water of winter snow. Ice wedges can be studied by means of stable-water isotopes. Their isotopic composition is directly linked to atmospheric precipitation (i.e. winter snow) and, therefore, indicative of past climate conditions during the cold season even though also genetic aspects, i.e. sublimation, melting and refreezing in the snowpack and the frost crack, have to be taken into account.
In this contribution we present stable-water isotope data of ice wedges from the Oyogos Yar coast of the Dmitry Laptev Strait (72.7°N, 143.5°E). Ice wedges and surrounding sediments were studied and sampled in 2002 and 2007. Ice-wedge stable-water isotopes were analyzed in the stable-isotope lab of the Alfred Wegener Institute in Potsdam, Germany. Sediments and ice wedges were dated using (a) OSL dating, (b) 36Cl/Cl dating (Blinov et al., 2009), (c) radiocarbon dating as well as (d) stratigraphic correlation based on ice-wedge stable isotopes.
Based on our chronology the studied ice wedges correspond to different stratigraphic units of the Late Quaternary. These are (1) an Ice Complex of MIS5 age (Wetterich et al., in press), (2) Early Weichselian (MIS4 to MIS3) flood plain deposits, (3) the Middle Weichselian Yedoma Ice Complex of MIS3 age and (d) Holocene themokarst deposits (Opel et al., 2011).
Ice wedge stable-water isotope data indicate substantial variations in Northeast Siberian Arctic winter climate conditions (δ18O) as well as shifts in the moisture generation and transport patterns (d excess) during the Late Quaternary, in particular between Glacial and Interglacial but also over the last centuries.
An ice wedge of the MIS5 Ice Complex exhibits mean δ18O and d excess values of -33‰ and 7‰, respectively, representing very cold winter temperatures. Small multi-stage ice wedges corresponding to the MIS4 to MIS3 flood plain deposits showed two clusters of isotope values: (1) in their lower parts, i.e. composite sand-ice wedges or “polosatics”, δ18O values of -31 to -28‰ (d excess of 0-5‰) and (2) in their upper parts (classical ice wedge) δ18O values of -34‰ (d excess of 5‰), reflecting rather different formation conditions than climate differences under very cold climate conditions. The huge syngenetic ice wedges of the Weichselian Yedoma Ice Complex (MIS3) are characterized by mean δ18O values of -33‰ to -29‰ and mean d-excess values between 4 and 8‰ corresponding to different altitude levels and reflecting cold to very cold winter temperatures. On top of the Ice Complex as well as in a thermokarst depression of Late Glacial origin, Holocene ice wedges could be found. They have been grown predominantly in the Middle to Late Holocene and exhibit mean δ18O values of about -25‰ and mean d-excess values of 8‰, mirroring distinctly warmer winter temperatures in the Holocene. Recently grown (modern) ice wedges of the last decades are characterized by mean δ18O values of about -21‰ and mean d excess values of 8‰, testifying the recent winter warming in the Arctic.
Blinov A, Alfimov V, Beer J, Gilichinsky D, Schirrmeister L, Kholodov A, Nikolskiy P, Opel T, Tikhomirov D, Wetterich S. 2009. Ratio of 36Cl/Cl in ground ice of east Siberia and its application for chronometry. Geochemistry Geophysics Geosystems 10, Q0AA03.
Opel T, Dereviagin AY, Meyer H, Schirrmeister L, Wetterich S, 2011. Palaeoclimatic Information from Stable Water Isotopes of Holocene Ice Wedges on the Dmitrii Laptev Strait, Northeast Siberia, Russia. Permafrost and Periglacial Processes 22, 84-100.
Wetterich S, Tumskoy V, Rudaya N, Kuznetsov V, Maksimov F, Opel T, Meyer H, Andreev AA, Schirrmeister L, in press. Ice Complex permafrost of MIS5 age in the Dmitry Laptev Strait coastal region (East Siberian Arctic). Quaternary Science Reviews
Spectral inequalities for discrete and continuous differential operators
No full textIn this thesis spectral inequalities and trace formulae for discrete and continuous differential operators are discussed.
We first investigate spectral inequalities for Jacobi operators with matrix-valued potentials and present a new, direct proof of a sharp inequality corresponding to a Lieb–Thirring inequality for the power 3/2 using the commutation method. For the special case of a discrete Schrödinger operator we also prove new inequalities for higher powers of the eigenvalues and the potential and compare our results to previously established bounds.
We then approximate a Schrödinger operator on L^2(\R) by Jacobi operators on \ell^2(\Z) and use the established inequalities to provide new proofs of sharp Lieb–Thirring inequalities for the powers \gamma=1/2 and \gamma=3/2. By means of interpolation we derive spectral inequalities for Jacobi operators that yield (non-sharp) Lieb–Thirring constants on the real line for powers 1/2<\gamma<3/2.
We then consider Schrödinger operators on a finite interval [0,b] with matrix-valued potentials and establish trace formulae of the Buslaev–Faddeev–Zakharov type. The results link sums of powers of the negative eigenvalues to terms dependent on the potential and scattering functions.
Finally, we discuss the Berezin inequality, which is well-known on sets of finite measure and find an analogous inequality for the magnetic operator with constant magnetic field on a set whose complement has finite measure. We obtain a similar bound for the Heisenberg sub-Laplacian.Open Acces
Organic carbon release from coastal erosion of the Bykovsky Peninsula, Laptev Sea, Russia
No full textArctic permafrost coasts make up about one third of the global coastline and are likely to witness some of the most
dramatic changes linked to changing environmental conditions in the 21st century. Increasing sea level, warming
sea temperatures, longer open water season and increasing open-water area all bear the potential to increase the
impact on sediment and nutrient pathways in the nearshore zone.
In this study, we focus on a well studied location, the Bykovsky Peninsula, southern Laptev Sea, Russia to provide
high resolution estimations of organic carbon release from its coastline. We build on recently published datasets
from studies related to coastal geomorphology, paleogeography and oceanography, all available at large scale, to
map and determine the fluxes of carbon coming from the coast throughout the second half of the twentieth century
and to provide prospective numbers on the release of organic carbon in the years to come
Recent freshening in the Kara sea (Siberia) recorded by stable isotopes in Arctic bivalve shells,
No full textOxygen and stable carbon isotope records along the growth direction on shells of the bivalve species Astarte borealis and Serripes groenlandicus reliably record all important aspects of the bottom water hydrography in the shallow southeastern Kara Sea, despite uncertainties about the isotopic range due to sparse sampling and the possibility of growth rate changes. Changing freshwater supply from the rivers Ob and Yenisei is the main cause for seasonal temperature and salinity variations near the three sampling locations in 20 to 70 m water depth as suggested by CTD measurements and modeling. Peak winter salinity of the simulated hydrographic data series and peak winter values in the isotope records follow negative trends, which indicate a freshening of the bottom water due to an increasing fraction of river water during the 1990s. This freshening affected the whole Kara Sea, and coincided with a lowering of regional air pressure gradients, as indicated by the declining Arctic oscillation index. The resulting weakening of the prevailing southwesterly winds diminished the inflow of saline Atlantic-derived water from the Barents Sea through the Kara Strait in the southwest, and, additionally, reduced the export of river water toward the north and northeast into the Arctic basin. Saline Atlantic-derived water thus was replaced by freshwater, which was successively accumulated in the Kara Sea and accordingly imprinted on the stable isotope composition of the bivalve shells. The 1990s freshening in the Kara Sea thus may be caused by natural variations rather than being a signal for global change
Intermediate and deep water paleoceanography of the northern North Atlantic over the past 21,000 years
No full textBenthic foraminiferal stable isotope records from four high-resolution sediment cores, forming a depth transect between 1237 m and 2303 m on the South Iceland Rise, have been used to reconstruct intermediate and deep water paleoceanographic changes in the northern North Atlantic during the last 21 ka (spanning Termination I and the Holocene). Typically, a sampling resolution of ~100 years is attained. Deglacial core chronologies are accurately tied to North Greenland Ice Core Project (NGRIP) ice core records through the correlation of tephra layers and changes in the percent abundance of Neogloboquadrina pachyderma (sinistral) with transitions in NGRIP. The evolution from the glacial mode of circulation to the present regime is punctuated by two periods with low benthic δ13C and δ18O values, which do not lie on glacial or Holocene water mass mixing lines. These periods correlate with the late Younger Dryas/Early Holocene (11.5–12.2 ka) and Heinrich Stadial 1 (14.7–16.8 ka) during which time freshwater input and sea-ice formation led to brine rejection both locally and as an overflow exported from the Nordic seas into the northern North Atlantic, as earlier reported by Meland et al. (2008). The export of brine with low δ13C values from the Nordic seas complicates traditional interpretations of low δ13C values during the deglaciation as incursions of southern sourced water, although the spatial extent of this brine is uncertain. The records also reveal that the onset of the Younger Dryas was accompanied by an abrupt and transient (~200–300 year duration) decrease in the ventilation of the northern North Atlantic. During the Holocene, Iceland-Scotland Overflow Water only reached its modern flow strength and/or depth over the South Iceland Rise by 7–8 ka, in parallel with surface ocean reorganizations and a cessation in deglacial meltwater input to the North Atlantic
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