Climate variability in the Spanish Pyrenees during the last 30,000 yr revealed by the El Portalet sequence     

P. González-Sampériz  B.L. Valero-Garcés  G. Jalut  C. Martí-Bono  A. Navas  J.J. Dedoubat 《Quaternary Research》2006,66(1):38-52

Palynological, sedimentological and stable isotopic analyses of carbonates and organic matter performed on the El Portalet sequence (1802 m a.s.l., 42°48′00?N, 0°23′52?W) reflect the paleoclimatic evolution and vegetation history in the central-western Spanish Pyrenees over the last 30,000 yr, and provide a high-resolution record for the late glacial period. Our results confirm previous observations that deglaciation occurred earlier in the Pyrenees than in northern European and Alpine sites and point to a glacial readvance from 22,500 to 18,000 cal yr BP, coinciding with the global last glacial maximum. The patterns shown by the new, high-resolution pollen data from this continental sequence, chronologically constrained by 13 AMS ¹⁴C dates, seem to correlate with the rapid climate changes recorded in Greenland ice cores during the last glacial-interglacial transition. Abrupt events observed in northern latitudes (Heinrich events 3 to 1, Oldest and Older Dryas stades, Intra-Allerød Cold Period, and 8200 cal yr BP event) were also identified for the first time in a lacustrine sequence from the central-western Pyrenees as cold and arid periods. The coherent response of the vegetation and the lake system to abrupt climate changes implies an efficient translation of climate variability from the North Atlantic to mid latitudes.  相似文献   

Benthic foraminifers in upper Quaternary sediments of the southern Bering Sea: Distribution and paleoceanographic interpretations     

T. A. Khusid  I. A. Basov  S. A. Gorbarenko  M. P. Chekhovskaya 《Stratigraphy and Geological Correlation》2006,14(5):538-548

Composition and distribution of benthic foraminifers, being coupled with isotopic-geochemical data on Upper Pleistocene and Holocene sediments from the southern Bering Sea (Core GC-11; 53°31′ N, 178°51′E, water depth 3060 m), demonstrate variations in bottom water properties during the last 54 kyr. Their abundance increased to some extent during short periods corresponding to warm Dansgaard-Oeshger interstadials 14, 12, 8, and 2 of marine isotopic stages (MIS) 3 and 2. The first and second deglaciation phases separated by the Younger Dryas cooling episode are marked by significant abundance peaks of benthic foraminifers (an order magnitude higher than in the glacial period), although their share in community of benthic and planktonic foraminifers taken together decreases. Species typical of stable high-productivity areas gain the dominant position. A significant proportion of agglutinated species in the Holocene sediments is indicative of Ca ions deficiency that accelerates dissolution of carbonate tests up to their disappearance approximately 2.5–3 ka ago.  相似文献   

Spatiotemporal variations in vertical gravity gradients at the Campi Flegrei caldera (Italy): a case for source multiplicity during unrest?     

Joachim Gottsmann  Antonio G. Camacho  Kristy F. Tiampo  José Fernández 《Geophysical Journal International》2006,167(3):1089-1096

  相似文献   

The effective elastic thickness of the India Plate from receiver function imaging, gravity anomalies and thermomechanical modelling   总被引：2，自引：0，他引：2  

György Hetényi  Rodolphe Cattin  Jérôme Vergne  John L. Náb&#;lek 《Geophysical Journal International》2006,167(3):1106-1118

  相似文献   

Tide model errors and GRACE gravimetry: towards a more realistic assessment   总被引：10，自引：1，他引：10  

R. D. Ray  S. B. Luthcke 《Geophysical Journal International》2006,167(3):1055-1059

  相似文献   

Post-depositional 137Cs Mobility in the Sediments of Three Shallow Coastal Lagoons, SW England     

I. D. L. Foster  T. M. Mighall  H. Proffitt  D. E. Walling  P. N. Owens 《Journal of Paleolimnology》2006,35(4):881-895

We present ¹³⁷Cs profiles for three low lying coastal lagoons in Southwest England that show a decline in activity with sediment depth. ¹³⁷Cs inventories are lower than expected by comparison with local reference inventories despite the fact that sampling was undertaken in the deep-water zone of each lake where sediment and ¹³⁷Cs focusing would be expected. At all three locations, lake sediment ⁷Be and unsupported ²¹⁰Pb (²¹⁰Pb_un) inventories are not significantly lower than the local reference inventory. ¹³⁷Cs inventories in the study cores range from 38 to 95% of local reference inventories. The standing water level and mud: water interface at two sites are below maximum tide level and, at all three sites, salinity increases significantly in the water columns between low and high tide and in the pore waters of the underlying sediments. We suggest that the difference in hydrostatic pressure between sea level and standing water levels in the lagoons forces salt water up through the sediment column and that monovalent cations (especially Na⁺ and K⁺) replace ¹³⁷Cs on exchange sites leading to the upward migration and loss of ¹³⁷Cs. Rising sea levels may therefore contribute to remobilisation and release of ¹³⁷Cs to the aquatic environment from the sediments of coastal lagoons.  相似文献   

The relationship between depth, age and gravity in the oceans   总被引：2，自引：0，他引：2  

A. G. Crosby  D. McKenzie  J. G. Sclater 《Geophysical Journal International》2006,166(2):553-573

  相似文献   

Gravity signature of crustal subduction inferred from numerical modelling     

Anna Maria Marotta  Elisa Spelta  Catia Rizzetto 《Geophysical Journal International》2006,166(2):923-938

  相似文献   

Comparison of methods to model the gravitational gradients from topographic data bases   总被引：7，自引：0，他引：7  

Christopher Jekeli  Lizhi Zhu 《Geophysical Journal International》2006,166(3):999-1014

A number of methods have been developed over the last few decades to model the gravitational gradients using digital elevation data. All methods are based on second-order derivatives of the Newtonian mass integral for the gravitational potential. Foremost are algorithms that divide the topographic masses into prisms or more general polyhedra and sum the corresponding gradient contributions. Other methods are designed for computational speed and make use of the fast Fourier transform (FFT), require a regular rectangular grid of data, and yield gradients on the entire grid, but only at constant altitude. We add to these the ordinary numerical integration (in horizontal coordinates) of the gradient integrals. In total we compare two prism, two FFT and two ordinary numerical integration methods using 1" elevation data in two topographic regimes (rough and moderate terrain). Prism methods depend on the type of finite elements that are generated with the elevation data; in particular, alternative triangulations can yield significant differences in the gradients (up to tens of Eötvös). The FFT methods depend on a series development of the topographic heights, requiring terms up to 14th order in rough terrain; and, one popular method has significant bias errors (e.g. 13 Eötvös in the vertical–vertical gradient) embedded in its practical realization. The straightforward numerical integrations, whether on a rectangular or triangulated grid, yield sub-Eötvös differences in the gradients when compared to the other methods (except near the edges of the integration area) and they are as efficient computationally as the finite element methods.  相似文献   

Seismicity, structure and rheology of the lithosphere in the Lake Baikal region   总被引：2，自引：2，他引：2  

Brian Emmerson  James Jackson  Dan McKenzie  Keith Priestley 《Geophysical Journal International》2006,167(3):1233-1272

  相似文献