Holocene evolution of a drowned melt-water valley in the Danish Wadden Sea     

Jørn B.T. Pedersen  Steffen Svinth 《Quaternary Research》2009,72(1):68-104

Cores from the salt marshes along the drowned melt-water valley of river Varde Å in the Danish Wadden Sea have been dated and analysed (litho- and biostratigraphically) to reconstruct the Holocene geomorphologic evolution and relative sea level history of the area. The analysed cores cover the total post-glacial transgression, and the reconstructed sea level curve represents the first unbroken curve of this kind from the Danish Wadden Sea, including all phases from the time where sea level first reached the Pleistocene substrate of the area. The sea level has been rising from − 12 m below the present level at c. 8400 cal yr BP, interrupted by two minor drops of < 0.5 m at c. 5500 cal yr BP and 1200 cal yr BP, and one major drop of ∼ 1.5 m at c. 3300 cal yr BP. Sediment deposition has been able to keep pace with sea level rise, and the Holocene sequence consists in most places of clay atop a basal peat unit overlying sand of Weichselian age and glacio-fluvial origin. In its deepest part, the basal peat started to form around 8400 cal yr BP, and reached a thickness of up to 3.5 m. This thickness is about half of the original, when corrected for auto-compaction. The superimposed clay contains small (63-355 μm) red iron stains in the top and bottom units, and foraminifers of the calcareous type in the middle. The fact that iron stains and foraminifers in no cases coexist, but always exclude each other is interpreted as a result of the difference between salt-marsh facies (iron stains) and tidal-flat facies (foraminifers). This represents a novel and easy way to distinguish between these two otherwise often undistinguishable sedimentary facies in the geological record.  相似文献   

The 1732 Surtseyan eruption of Eggøya,Jan Mayen,North Atlantic: deposits,distribution, chemistry and chronology     

Eirik Gjerløw  Armann Höskuldsson  Rolf-Birger Pedersen 《Bulletin of Volcanology》2015,77(2):1-21

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Characterization of soil organic carbon in drained thaw-lake basins of Arctic Alaska using NMR and FTIR photoacoustic spectroscopy   总被引：2，自引：0，他引：2  

Joel A. Pedersen  Myrna A. SimpsonJames G. Bockheim  Kartik Kumar 《Organic Geochemistry》2011,42(8):947-954

Arctic soils contain a large fraction of Earth’s stored carbon. Temperature increases in the Arctic may enhance decomposition of this stored carbon, shifting the role of Arctic soils from a net sink to a new source of atmospheric CO₂. Predicting the impact of Arctic warming on soil carbon reserves requires knowledge of the composition of the stored organic matter. Here, we employ solid state ¹³C nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared-photoacoustic spectroscopy (FTIR-PAS) to investigate the chemical composition of soil organic matter collected from drained thaw-lake basins ranging in age from 0 to 5500 years before present (y BP). The ¹³C NMR and FTIR-PAS data were largely congruent. Surface horizons contain relatively large amounts of O-alkyl carbon, suggesting that the soil organic matter is rich in labile constituents. Soil organic matter decreases with depth with the relative amounts of O-alkyl carbon decreasing and aromatic carbon increasing. These data indicate that lower horizons are in a more advanced stage of decomposition than upper horizons. Nonetheless, a substantial fraction of carbon in lower horizons, even for ancient thaw-lake basins (2000-5500 y BP), is present as O-alkyl carbon reflecting the preservation of intrinsically labile organic matter constituents. Climate change-induced increases in the depth of the soil active layer are expected to accelerate the depletion of this carbon.  相似文献   

Solar wind and magnetosphere plasma diagnostics by spacecraft electrostatic potential measurements   总被引：1，自引：0，他引：1  

A. Pedersen 《Annales Geophysicae》1995,13(2):118-129

Several satellites (GEOS-1, GEOS-2, ISEE-1, Viking and CRRES) carried electric field experiments on which probes were driven by a current from the satellite to be close to the plasma potential. The potential difference between an electric field probe and its spacecraft (with conductive surfaces) can be used to determine the ambient electron density and/or electron flux with limited accuracy but with high time resolution, of the order of 10–100 ms. It is necessary for the development of this diagnostic method to understand the photoemission characteristics of probes and satellites. According to the electric field experiments on the above-mentioned satellites, all materials develop very similar photoemission properties when they are beyond the influence of atmospheric oxygen. The photoelectron yield steadily increases over the first few months in space and reaches values well above those measured on clean surfaces in the laboratory. The method can be used for solar radiation levels corresponding to distances from 0.4 to 5 AU from the Sun.  相似文献   

A scaling parameter for turbulence in baroclinic convective boundary layers     

S. K. Pedersen  G. D. Stubley 《Boundary-Layer Meteorology》1994,68(3):319-325

The influence of baroclinicity on the structure and levels of turbulence in the convective boundary layer depends on both the magnitude and orientation of geostrophic wind shear and the level of convection. The geostrophic Richardson number, a Richardson number defined in the present work and based on the geostrophic wind shear, is shown to be a single non-dimensional parameter which determines the influence of baroclinicity on convective turbulence structure.  相似文献   

Occurrence of an exceptional carbonate dissolution episode during early glacial isotope stage 6 in the Southeastern Atlantic     

P. Bertrand  J. Giraudeau  B. Malaize  P. Martinez  M. Gallinari  T. F. Pedersen  C. Pierre  M. Th. Vnec-Peyr 《Marine Geology》2002,180(1-4):235-248

Concentration and mass accumulation rate profiles from Southeastern Atlantic sediment cores located off Namibia show that an exceptional episode in benthic carbonate dissolution occurred during early glacial isotope stage 6 (substages 6.6 and 6.5) between about 186 000 and 170 000 yr BP. Although this episode is restricted to or is more pronounced in this region than in other areas of the Atlantic Ocean, its exceptional character with respect to older and younger climatic episodes at the same site cannot be fully explained by local factors alone, but requires a combination of local and global influences. The onset of the carbonate dissolution episode is related to a more efficient transfer of organic matter from surface eutrophic areas to the lower and is due to low sea level, while its termination relates to a change in either global ocean alkalinity or bottom water circulation. An evaluation of the magnitude of this local carbonate dissolution episode suggests that its contribution to a global alkalinity change may have been significant. Carbonate dissolution was probably amplified by stronger upwelling activity of the Benguela System linked to an exceptional northern excursion of the boreal summer ITCZ during early glacial isotope stage 6. This low latitude global linkage may explain how this carbonate dissolution event as well as other ‘anomalies’ observed for early stage 6, like an important Dole effect minimum or a ‘cold’ Mediterranean sapropel, are related.  相似文献   

Impacts of non-plane waves on two-station measurements of phase velocities     

Helle A. Pedersen 《Geophysical Journal International》2006,165(1):279-287

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Application of transition metal isotope tracers in global change research   总被引：1，自引：0，他引：1  

宋金明  ThomasF.Pedersen 《中国海洋湖沼学报》2005,23(2):218-225

High-precision isotope composition determinations using multicollector, magnetic-sector inductively coupled plasma mass spectrometry (MC-ICPMS) have recently revealed that some transition metal isotopes such as those of Mo, Fe, Cu, Zn etc. can be used as biogeochemical tracers in global change research.The Mo isotope system may be useful in paleoredox investigations indicating that δ^97 ^95Mo in seawater may co-vary with changes in the relative proportions of anoxic and oxic sedimentation in the ocean, and that this variation may be recorded in δ^97 ^95Mo of anoxic sediments. The Mo continental flux into the oceans and the global Mo isotope budget can be estimated from δ^97 ^95M0 values. The Fe isotope composition in seawater is an important issue because Fe plays a controlling role in biological productivity in the oceans and its abundance in seawater may have substantial effect on climate changes. Iron isotope fractionations could result from bio- and abio-processes and have about 0.1% variation ( δ^56 ^54Fe), so Fe isotopes considered alone cannot be used to distinguish the products of abiotic and biotic Fe processing in geological records. Cu and Zn isotopes are also used as biogeochemical tracers, but the researches are relatively less. This review mainly focuses on the methods for preparation, purification and determination of new isotope tracer samples, and on isotope applications in marine environmental changes.  相似文献   

Trends in marine climate change research in the Nordic region since the first IPCC report     

M. W. Pedersen  A. Kokkalis  H. Bardarson  S. Bonanomi  W. J. Boonstra  W. E. Butler  F. K. Diekert  N. Fouzai  M. Holma  R. E. Holt  K. Ø. Kvile  E. Nieminen  K. M. Ottosen  A. Richter  L. A. Rogers  G. Romagnoni  M. Snickars  A. Törnroos  B. Weigel  J. D. Whittington  P. Woods  J. Yletyinen  A. S. A. Ferreira 《Climatic change》2016,134(1-2):147-161

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Holocene sea‐level reconstruction in the Young Sound region,Northeast Greenland     

Jørn Bjarke Torp Pedersen  Aart Kroon  Bjarne Holm Jakobsen 《第四纪科学杂志》2011,26(2):219-226

A relative sea‐level curve over the Holocene is constructed for the Young Sound region in northeastern Greenland. The reconstruction is derived by dating the heights of raised beach ridges in coastal plains using optically stimulated luminiscence (OSL), and by dating palaeoterrestrial surface levels now buried beneath the intertidal frame using the ¹⁴C technique. The relative sea‐level curve reveals a rapid fall of at least 10 mm a^?1 from ca. 9500 to 7500 a ago, which slowed to 2 mm a^?1 until it reached the present sea level ca. 3000 a ago. This part of the curve is based on the raised beach ridge data. Thereafter, relative sea level continued to fall, to reach a minimum level at about 0.5 m below the present sea level ca. 2300 a ago. Since then, relative sea level has experienced a slow rise of about 0.2 mm a^?1. This part of the curve uses the data from the palaeoterrestrial surfaces. The study supplements other estimates of Holocene relative sea‐level changes and supports the observations of a decreasing trend in the timing of the cross point and in minimum relative sea level from South to North Greenland. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献