In memory of Charles David Keeling     

Pieter  Tans Bert  Bolin 《Tellus. Series B, Chemical and physical meteorology》2006,58(5):329-330

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Flow of Canadian basin deep water in the Western Eurasian Basin of the Arctic Ocean     

Göran Björk  Leif G. Anderson  Martin Jakobsson  Dennis Antony  Björn Eriksson  Patrick B. Eriksson  Benjamin Hell  Sofia Hjalmarsson  Timothy Janzen  Sara Jutterström  Johanna Linders  Ludvig Löwemark  Christian Marcussen  K. Anders Olsson  Bert Rudels  Emma Sellén  Morten Sølvsten 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):577-586

The LOMROG 2007 expedition targeted the previously unexplored southern part of the Lomonosov Ridge north of Greenland together with a section from the Morris Jesup Rise to Gakkel Ridge. The oceanographic data show that Canadian Basin Deep Water (CBDW) passes the Lomonosov Ridge in the area of the Intra Basin close to the North Pole and then continues along the ridge towards Greenland and further along its northernmost continental slope. The CBDW is clearly evident as a salinity maximum and oxygen minimum at a depth of about 2000 m. The cross-slope sections at the Amundsen Basin side of the Lomonosov Ridge and further south at the Morris Jesup Rise show a sharp frontal structure higher up in the water column between Makarov Basin water and Amundsen Basin water. The frontal structure continues upward into the Atlantic Water up to a depth of about 300 m. The observed water mass division at levels well above the ridge crest indicates a strong topographic steering of the flow and that different water masses tend to pass the ridge guided by ridge-crossing isobaths at local topographic heights and depressions. A rough scaling analysis shows that the extremely steep and sharply turning bathymetry of the Morris Jesup Rise may force the boundary current to separate and generate deep eddies.  相似文献   

The subsurface of tidal-flat sediments as a model for the deep biosphere     

Bert Engelen  Heribert Cypionka 《Ocean Dynamics》2009,59(2):385-391

Subsurface sediments of tidal flats and the marine deep biosphere share several features. Although on different scales in time and space, geochemical profiles and microbial successions follow the same trends. Microbial activities are governed by the availability of electron acceptors and the quality of electron donors. Two deep-biosphere sites and a shallow site from a German North Sea tidal flat were exemplarily chosen to compare geochemical settings and microbiological features. At all sites, microbial abundance was elevated at sulfate–methane transition zones. The known discrepancy between cultivation-based and molecular diversity assessments is observed, but similar microbial community compositions are found with each of the approaches at deep and shallow sites. These findings lead to the conclusion that we are presently unable to draw a cutting line between the shallow and the deep subsurface. Rather, there appears to exist only one “subsurface biosphere” with gradual differences. Therefore, tidal flats serve as an excellent model to perform microbiological experiments and to test novel techniques before applying them to much deeper and older samples. Responsible editor: Meinhard Simon  相似文献   

Tectonic setting of the Balaram-Kui-Surpagla-Kengora granulites of the South Delhi Terrane of the Aravalli Mobile Belt,NW India and its implication on correlation with the East African Orogen in the Gondwana assembly     

Yengkhom Kesorjit Singh  Bert De Waele  Subrata Karmakar  Sunayana Sarkar  Tapas Kumar Biswal 《Precambrian Research》2010

Granulites are developed in various tectonic settings and during different geological periods, and have been used for continental correlation within supercontinent models. In this context the Balaram-Kui-Surpagla-Kengora granulites of the South Delhi Terrane of the Aravalli Mobile Belt of northwestern India are significant. The granulites occur as shear zone bounded lensoidal bodies within low-grade rocks of the South Delhi Terrane and comprise pelitic and calcareous granulites, a gabbro-norite-basic granulite suite and multiple phases of granites of the Ambaji suite. The granulites have undergone three major phases of folding and shearing. The F₁ and F₂ folds are coaxial along NE-SW axis, and F₃ folds are developed across the former along NW-SE axis. Thus, various types of interference patterns are produced. The granulite facies metamorphism is marked by a spinel–cordierite–garnet–sillimanite–quartz assemblage with melt phase and is synkinematic to the F₁ phase of folding. The peak thermobarometric condition is set at ≥850 °C and 5.5–6.8 kb. The granulites have been exhumed through thrusting along multiple ductile shear zones during syn- to post-F₂ folding. Late-stage shearing has produced cataclasites and pseudotachylites. Sensitive High Resolution Ion MicroProbe (SHRIMP) U–Pb dating of zircon from pelitic granulites and synkinematically emplaced granites indicate that: (1) the sedimentary succession of the South Delhi Terrane was deposited between 1240 and 860 Ma with detritus derived from magmatic sources with ages between 1620 and 1240 Ma; (2) folding and granulite metamorphism have taken place between ca. 860 and 800 Ma, and exhumation at around ca. 800–760 Ma; and (3) the last phase of granitic activity occurred at ca. 759 Ma. This shows, for the first time, that the granulites of the South Delhi Terrane are much younger than those of the Sandmata Granulite Complex of the northern part of the Aravalli Mobile Belt, the Saussar granulites of the Central India Mobile Belt and the Eastern Ghats Mobile Belt. Instead, they show similarities to the Neoproterozoic granulites of the Circum Indian Orogens that include the East African Orogen (East Africa and Madagascar), the Southern Granulite Terrane of India and much of Sri Lanka. We suggest that the South Delhi Basin probably marks a trace of the proto-Mozambique Ocean in NW India within Gondwana, that closed when the Marwar Craton, arc fragments (Bemarivo Belt in Madagascar and the Seychelles) and components of the Arabian-Nubian Shield collided with the Aravalli-Bundelkhand Protocontinent at ca. 850–750 Ma.  相似文献   

Analysis of Model Results for the Turning of the Wind and Related Momentum Fluxes in the Stable Boundary Layer     

Gunilla Svensson  Albert A. M. Holtslag 《Boundary-Layer Meteorology》2009,132(2):261-277

The turning of wind with height and the related cross-isobaric (ageostrophic) flow in the thermally stable stratified boundary layer is analysed from a variety of model results acquired in the first Global Energy and Water Cycle Experiment (GEWEX) Atmospheric Boundary Layer Study (GABLS1). From the governing equations in this particular simple case it becomes clear that the cross-isobaric flow is solely determined by the surface turbulent stress in the direction of the geostrophic wind for the quasi-steady state conditions under consideration. Most models indeed seem to approach this relationship but for very different absolute values. Because turbulence closures used in operational models typically tend to give too deep a boundary layer, the integrated total cross-isobaric mass flux is up to three times that given by research numerical models and large-eddy simulation. In addition, the angle between the surface and the geostrophic wind is typically too low, which has important implications for the representation of the larger-scale flow. It appears that some models provide inconsistent results for the surface angle and the momentum flux profile, and when the results from these models are removed from the analysis, the remaining ten models do show a unique relationship between the boundary-layer depth and the surface angle, consistent with the theory given. The present results also imply that it is beneficial to locate the first model level rather close to the surface for a proper representation of the turning of wind with height in the stable boundary layer.  相似文献   

Modelling the Arctic Stable Boundary Layer and its Coupling to the Surface     

G. J. Steeneveld  B. J. H. Van De Wiel  A. A. M. Holtslag 《Boundary-Layer Meteorology》2006,118(2):357-378

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Evaluation of a land-surface scheme at Cabauw     

M. B. Ek  A. A. M. Holtslag 《Theoretical and Applied Climatology》2005,80(2-4):213-227

Summary We study the response of the land-surface to prescribed atmospheric forcing for 31 May 1978 at Cabauw, Netherlands, using the land-surface scheme from the Coupled Atmospheric boundary layer-Plant-Soil (CAPS) model. Results from model runs show realistic daytime surface fluxes are produced using a canopy conductance formulation derived from Cabauw data (for 1987, a different year), and un-tuned parameterizations of root density (near-uniform with depth) and soil heat flux (reduced thermal conductivity through vegetation). Sensitivity of model-calculated surface heat fluxes to initial values of soil moisture is also examined. Results of this study provide the land-surface base state for a coupled land–atmosphere modeling study.  相似文献   

Petrography, geochemistry, and geochronology of granitoid rocks in the Neoproterozoic-Paleozoic Lufilian–Zambezi belt, Zambia: Implications for tectonic setting and regional correlation     

Crispin Katongo  Friedrich Koller  Urs Kloetzli  Christian Koeberl  Francis Tembo  Bert De Waele 《Journal of African Earth Sciences》2004,40(5):219

There are several pre-orogenic Neoproterozoic granitoid and metavolcanic rocks in the Lufilian–Zambezi belt in Zambia and Zimbabwe that are interpreted to have been emplaced in a continental-rift setting that is linked to the break-up of the Rodinia supercontinent. However, no geochemical data were previously available for these rocks in the Zambian part of the belt to support this model. We conducted petrographic and whole-rock chemical analyses of the Neoproterozoic Nchanga Granite, Lusaka Granite, Ngoma Gneiss and felsic metavolcanic rocks from the Lufilian–Zambezi belt in Zambian, in order to evaluate their chemical characteristics and tectonic settings. Other magmatic rocks of importance for understanding the evolution of the belt in Zambia, included in this study, are the Mesoproterozoic Munali Hills Granite and associated amphibolites and the Mpande Gneiss. The Neoproterozoic rocks have monzogranitic compositions, aluminum-saturation indices (ASI) < 1.1, and high contents of high field strength elements (HFSE) and rare earth elements (REE). The chondrite-normalised spider diagrams are similar to those of A-type granites from the Lachlan fold belt and show negative Sr, P, and Ti anomalies. On various tectonic discrimination diagrams the Neoproterozoic rocks plot mainly in A-type granite fields. These petrographic and trace element compositions indicate that these rocks are A-type felsic rocks, but they do not have features of granites and rhyolites emplaced in true continental-rift settings, as previously suggested. On the basis of the A-type features and independent regional geological and geochronological data, we suggest that the Neoproterozoic granitoid and felsic metavolcanic rocks were emplaced during the earliest extensional stages of continental rifting in the Lufilian–Zambezi belt. The apparent continental-arc like chemistry of the granitoid and felsic metavolcanic rocks is thus inferred to be inherited from calcalkaline sources. The Mesoproterozoic Munali Hills Granite and Mpande Gneiss have trace element features e.g., Nb–Ta depletions, which indicate that that these gneisses were emplaced in a convergent-margin setting. The MORB-normalised spider diagram of co-magmatic amphibolites exhibit a fractionated LILE/HFSE pattern recognized in subduction zones. This inference is consistent with remnants of ocean crust, juvenile Island arcs and ophiolites elsewhere in the Mesoproterozoic Irumide belt in Zambia and Zimbabwe. In addition, we report the first U–Pb zircon age of 1090.1 ± 1.3 Ma for the Munali Hills Granite. The age for the Munali Hills Granite provides new constraints on correlation and tectono-thermal activity in the Lufilian–Zambezi belt. The age of the Munali Hills Granite indicates that some supracrustal rocks in the Zambezi belt of Zambia, which were previously thought to be Neoproterozoic and correlated with the Katanga Supergroup in the Lufilian belt, are Mesoproterozoic or older. Consequently, previous regional lithostratigraphic correlations in the Lufilian–Zambezi belt would require revision.  相似文献   

Book reviews     

Bert Bolin  G. Shaw  Michel M. Verstraete  M. J. Salinger 《Climatic change》1986,9(3):363-366

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An evaluation of neutral and convective planetary boundary-layer parameterizations relative to large eddy simulations   总被引：2，自引：1，他引：2  

Keith W. Ayotte  Peter P. Sullivan  Anders Andrén  Scott C. Doney  Albert A. M. Holtslag  William G. Large  James C. McWilliams  Chin-Hoh Moeng  Martin J. Otte  Joseph J. Tribbia  John C. Wyngaard 《Boundary-Layer Meteorology》1996,79(1-2):131-175

This paper compares a number of one-dimensional closure models for the planetary boundary layer (PBL) that are currently in use in large-scale atmospheric models. Using the results of a large-eddy simulation (LES) model as the standard of comparison, the PBL models are evaluated over a range of stratifications from free convective to neutral and a range of surface shear stresses. Capping inversion strengths for the convective cases range from weakly to strongly capped. Six prototypical PBL models are evaluated in this study, which focuses on the accuracy of the boundary-layer fluxes of momentum, heat, and two passive scalars. One scalar mimics humidity and the other is a top-down scalar entrained into the boundary layer from above. A set of measures based on the layer-averaged differences of these fluxes from the LES solutions is developed. In addition to the methodological framework and suite of LES solutions, the main result of the evaluation is the recognition that all of the examined PBL parameterizations have difficulty reproducing the entrainment at the top of the PBL, as given by the LES, in most parameter regimes. Some of the PBL models are relatively accurate in their entrainment flux in a subset of parameter regimes. The sensitivity of the PBL models to vertical resolution is explored, and substantive differences are observed in the performance of the PBL models, relative to LES, at low resolution typical of large scale atmospheric models.  相似文献