Deglacial pattern of circulation and marine productivity in the upwelling region off central-south Chile     

Mahyar Mohtadi  Pamela Rossel  Carina B. Lange  Silvio Pantoja  Philipp Bning  Daniel J. Repeta  Maik Grunwald  Frank Lamy  Dierk Hebbeln  Hans-Jürgen Brumsack 《Earth and Planetary Science Letters》2008,272(1-2):221-230

A high-resolution sea surface temperature and paleoproductivity reconstruction on a sedimentary record collected at 36°S off central-south Chile (GeoB 7165-1, 36°33′S, 73°40′W, 797 m water depth, core length 750 cm) indicates that paleoceanographic conditions changed abruptly between 18 and 17 ka. Comparative analysis of several cores along the Chilean continental margin (30°–41°S) suggests that the onset and the pattern of deglacial warming was not uniform off central-south Chile due to the progressive southward migration of the Southern Westerlies and local variations in upwelling. Marine productivity augmented rather abruptly at 13–14 ka, well after the oceanographic changes. We suggest that the late deglacial increase in paleoproductivity off central-south Chile reflects the onset of an active upwelling system bringing nutrient-rich, oxygen-poor Equatorial Subsurface Water to the euphotic zone, and a relatively higher nutrient load of the Antarctic Circumpolar Current. During the Last Glacial Maximum, when the Southern Westerlies were located further north, productivity off central-south Chile, in contrast to off northern Chile, was reduced due to direct onshore-blowing winds that prevented coastal upwelling and export production.  相似文献   

Mechanisms controlling the air–sea flux in the North Sea     

A.E.F. Prowe  Helmuth Thomas  Johannes Ptsch  Wilfried Kühn  Yann Bozec  Laure-Sophie Schiettecatte  Alberto V. Borges  Hein J.W. de Baar 《Continental Shelf Research》2009,29(15):1801-1808

The mechanisms driving the air–sea exchange of carbon dioxide (CO₂) in the North Sea are investigated using the three-dimensional coupled physical–biogeochemical model ECOHAM (ECOlogical-model, HAMburg). We validate our simulations using field data for the years 2001–2002 and identify the controls of the air–sea CO₂ flux for two locations representative for the North Sea's biogeochemical provinces. In the seasonally stratified northern region, net CO₂ uptake is high () due to high net community production (NCP) in the surface water. Overflow production releasing semi-labile dissolved organic carbon needs to be considered for a realistic simulation of the low dissolved inorganic carbon (DIC) concentrations observed during summer. This biologically driven carbon drawdown outcompetes the temperature-driven rise in CO₂ partial pressure (pCO₂) during the productive season. In contrast, the permanently mixed southern region is a weak net CO₂ source (). NCP is generally low except for the spring bloom because remineralization parallels primary production. Here, the pCO₂ appears to be controlled by temperature.  相似文献   

Nitrogen and carbon cycling in the North Sea and exchange with the North Atlantic—A model study,Part II: Carbon budget and fluxes     

Wilfried Kühn  Johannes Pätsch  Helmuth Thomas  Alberto V. Borges  Laure-Sophie Schiettecatte  Yann Bozec  A.E. Friederike Prowe 《Continental Shelf Research》2010

The 3-d coupled physical–biogeochemical model ECOHAM (version 3) was applied to the Northwest-European Shelf (47°41′–63°53′N, 15°5′W–13°55′E) for the years 1993–1996. Carbon fluxes were calculated for the years 1995 and 1996 for the inner shelf region, the North Sea (511,725 km²). This period was chosen because it corresponds to a shift from a very high winter-time North Atlantic Oscillation Index (NAOI) in 1994/1995, to an extremely low one in 1995/1996, with consequences for the North Sea physics and biogeochemistry. During the first half of 1996, the observed mean SST was about 1 °C lower than in 1995; in the southern part of the North Sea the difference was even larger (up to 3 °C). Due to a different wind regime, the normally prevailing anti-clockwise circulation, as found in winter 1995, was replaced by more complicated circulation patterns in winter 1996. Decreased precipitation over the drainage area of the continental rivers led to a reduction in the total (inorganic and organic) riverine carbon load to the North Sea from 476 Gmol C yr⁻¹ in 1995 to 340 Gmol C yr⁻¹ in 1996. In addition, the North Sea took up 503 Gmol C yr⁻¹ of CO₂ from the atmosphere. According to our calculations, the North Sea was a sink for atmospheric CO₂, at a rate of 0.98 mol C m⁻² yr⁻¹, for both years. The North Sea is divided into two sub-systems: the shallow southern North Sea (SNS; 190,765 km²) and the deeper northern North Sea (NNS; 320,960 km²). According to our findings the SNS is a net-autotrophic system (net ecosystem production NEP>0) but released CO₂ to the atmosphere: 159 Gmol C yr⁻¹ in 1995 and 59 Gmol C yr⁻¹ in 1996. There, the temperature-driven release of CO₂ outcompetes the biological CO₂ drawdown. In the NNS, where respiratory processes prevail (NEP<0), 662 and 562 Gmol C yr⁻¹ were taken up from the atmosphere in 1995 and 1996, respectively. Stratification separates the productive, upper layer from the deeper layers of the water column where respiration/remineralization takes place. Duration and stability of the stratification are determined by the meteorological conditions, in relation to the NAO. Our results suggest that this mechanism controlling the nutrient supply to the upper layer in the northern and central North Sea has a larger impact on the carbon fluxes than changes in lateral transport due to NAOI variations. The North Sea as a whole imports organic carbon and exports inorganic carbon across the outer boundaries, and was found to be net-heterotrophic, more markedly in 1996 than in 1995.  相似文献   

Potential for remediation of acidic mining lakes evaluated by hydrogeochemical modelling: Case study Grünewalder Lauch (Plessa 117, Lusatia/Germany)     

Brigitte Nixdorf  Wilfried Uhlmann 《Limnologica》2010,40(2):167-174

About one third of several hundred mining lakes in Eastern Germany are highly acidified, and there is a need to restore them to neutral conditions because they constitute an environmental hazard for water resources and downstream environments. The aim of this study is to evaluate the efficiency of three different acid pit lake water remediation treatments: dilution with alkaline (river) water, limestone treatment and biological neutralization by organic carbon-driven alkalinity generation. The efficiency is evaluated for the acidic mining lake Grünewalder Lauch by adjusting input values into a geochemical model and making future projections. Current approaches, such as flooding with neutral surface water or extensive liming, are not suitable for many lakes because of a limited supply of alkaline water or high lime immobilizing potential of Fe- and Al-rich water in acidic lakes, respectively. Further treatment methods are, therefore, designed to combine water supply and biological measures with the management of water quality by the application of in-lake microbial processes. These processes are focused on the metabolic response of aquatic ecosystems to nutrient enrichment (enhancement of primary production and thereby organic carbon supply) and the microbial decomposition of organic matter and their effects on the gain or loss of alkalinity.The results and comparisons of different neutralization measures will be generalized by the application of hydrogeochemical models for alkalinity production showing

a)

the long term efficiency of the measures, depending on carbon turnover at the sediment/water interface,

b)

the development of bicarbonate buffering capacity as a consequence of biological measures,

c)

the importance of pyrite formation instead of FeS.

  相似文献   

STUDIES OF BRAZILIAN METEORITES XIII. MINERALOGY,PETROLOGY, AND CHEMISTRY OF THE PUTINGA,RIO GRANDE DO SUL,CHONDRITE     

K. Keil  D. Lange  M.N.C. Ulbrich  C.B. Gomes  E. Jarosewich  A. Roisenberg  M.J. Souza 《Meteoritics & planetary science》1978,13(2):165-175

The Putinga, Rio Grande do Sul, chondrite (fall, August 16, 1937), consists of major olivine (Fa_24.8), orthopyroxene (Fs_21.3), and metallic nickel-iron (kamacite, taenite, and plessite); minor maskelynite (Ab_81.0An_12.4Or_6.6) and troilite; and accessory chromite (Cm_79.0Uv_8.2Pc_1.8Sp_11.0) and whitlockite. Mineral compositions, particularly of olivine and orthorhombic pyroxene, as well as the bulk chemical composition, particularly the ratios of Fe°/Ni° (5.24), Fe_total/SiO₂ (0.58), and Fe°/Fe_total (0.27), and the contents of Fe_total (22.42%) and total metallic nickel-iron (7.25%) classify the meteorite as an L-group chondrite. The highly recrystallized texture of the stone, with well-indurated, poorly discernible chondrules; xenomorphic, well-crystallized groundmass olivine and pyroxene; and the occurrence of poikilitic intergrowth of olivine in orthopyroxene suggest that Putinga belongs to petrologic type 6. Maskelynite of oligoclase composition was formed by solid state shock transformation of previously existing well-crystallized plagioclase at estimated shock pressures of about 250–350 kbar. Thus, recrystallization (i.e., formation of well-crystallized oligoclase) must have preceded shock transformation into maskelynite.  相似文献   

Phosphorus burial as a function of paleoproductivity and redox conditions in Arabian Sea sediments   总被引：1，自引：0，他引：1  

S.J. Schenau  G.J. De Lange 《Geochimica et cosmochimica acta》2005,69(4):919-931

In this study the response of sedimentary phosphorus (P) burial to changes in primary productivity and bottom water oxygen concentrations during the Late Quaternary is investigated, using two sediment cores from the Arabian Sea, one recovered from the continental slope and the other from the deep basin. The average solid-phase P speciation in both cores is similar, authigenic and biogenic (fish debris) apatite make up the bulk of the P inventory (ca. 70%);whereas P adsorbed to iron oxides, organic P, and detrital apatite constitute minor fractions. Postdepositional redistribution has not significantly altered the downcore distribution of total solid-phase P. Phosphorus burial efficiencies are generally lower during periods of increased paleoproductivity. This is caused by (a) partial decoupling of the P export flux, consisting primarily of particulate organic P, and the P burial flux, consisting primarily of biogenic and authigenic apatite; and (b) the lack of increased rates of authigenic CFA formation during periods of higher P deposition. In addition, fluctuations in bottom water oxygen concentrations may have affected P burial in continental slope sediments. The results of this study indicate that higher primary productivity induces more efficient P cycling. On time scales exceeding the oceanic P residence time, this process may induce higher surface water productivity, thus creating a positive feedback loop. In the Arabian Sea, this feedback mechanism may have contributed to changes in sea surface productivity on sub-Milankovitch time scales because P, regenerated on the continental slopes of the Oman and Somalian coastal upwelling zones, is reintroduced into the photic zone relatively fast.  相似文献   

A Mössbauer spectroscopic study of the iron redox transition in eastern Mediterranean sediments     

Claar van der Zee  Caroline P. Slomp  Gert J. de Lange 《Geochimica et cosmochimica acta》2005,69(2):441-453

Fe cycling at two sites in the Mediterranean Sea (southwest of Rhodes and in the North Aegean) has been studied, combining the pore water determination of nutrients, manganese, and iron, citrate-bicarbonate-dithionite (CDB) and total sediment extractions, X-ray diffraction, and ⁵⁷Fe Mössbauer spectroscopy (MBS). At the Rhodes site, double peaks in the CDB-extractable Mn and Fe profiles indicate non-steady-state diagenesis. The crystalline iron oxide hematite, identified at both sites by room temperature (RT) MBS, appears to contribute little to the overall Fe reduction. MBS at liquid helium temperature (LHT) revealed that the reactive sedimentary Fe oxide phase was nanophase goethite, not ferrihydrite as is usually assumed. The pore water data at both sites indicates that upon reductive dissolution of nanophase goethite, the upward diffusing dissolved Fe²⁺ is oxidized by Mn oxides, rather than by nitrate or oxygen. The observed oxidation of Fe²⁺ by Mn oxides may be more common than previously thought but not obvious in sediments where the nitrate penetration depth coincides with the Mn oxide peak. At the Rhodes site, the solid-phase Fe(II) increase occurred at a shallower depth than the accumulation of dissolved Fe²⁺ in the pore water. The deeper relict Mn oxide peak acts as an oxidation barrier for the upward diffusing dissolved Fe²⁺, thereby keeping the pore water Fe²⁺ at depth. At the North Aegean site, the solid-phase Fe(II) increase occurs at approximately the same depth as the increase in dissolved Fe²⁺ in the pore water. Overall, the use of RT and cryogenic MBS provided insight into the solid-phase Fe(II) gradient and allowed identification of the sedimentary Fe oxides: hematite, maghemite, and nanophase goethite.  相似文献   

Preface     

W. P. De Lange  T. R. Healy 《Natural Hazards》2001,24(3):197-198

Preface

Preface  相似文献   

Study of the Evolutionary Characteristics of Precursor Information Fields in North China Region and Their Relation to Earthquakes     

Ping Jianjun  Luo Lange  Cao Suchao 《中国地震研究》2001,15(1):36-46

On the basis of previous study results about the seismic anomaly precursor information quantity, universal and synthetic mathematical expressions that describe the precursor information quantity of various seismic anomalies are further given. Starting from large amounts of data of earthquake cases, the problem of the sustained effective time of seismic anomaly was studied again and the mathematical relationship between the sustained effective time of seismic anomaly and continuing effective time of seismic anomaly was further established. About one million pieces of precursor observation data belonging to 371 items of hydrochemistry, deformation, geomagnetism, stress, water level, geoelectricity, etc. In North China region in the period of 1980～ 1997 were collected and sorted out, and the seismic anomaly precursor information quantity of these items was calculated item by item. The evolutionary characteristics of seismic anomaly precursor information field in North China region in about 20 years and their relation to earthquakes were studied; an index system for medium- and short-term predictions of earthquakes with Ms ≥ 5.0 in North China region was established. After having checked by the R-value scoring method, the index system for synthetic earthquake prediction was proved to be of certain efficacy in medium- and short-term earthquake prediction.  相似文献   

Tectonic observations in the northern Saih Hatat,Sultanate of Oman   总被引：1，自引：0，他引：1  

Wilfried Bauer  Ivan Callegari  Naila Al Balushi  Ghaliya Al Busaidi  Maryam Al Barumi  Yusra Al Shoukri 《Arabian Journal of Geosciences》2018,11(5):94

The Saih Hatat region, in northeastern Oman, is characterized by a large tectonic window, tectonically overlain during the upper Cretaceous by nappes composed of sedimentary rocks from the Mesozoic Hawasina ocean and the Samail ophiolite. In this window, the autochthonous sedimentary cover of the eastern Arabian Platform from the Late Neoproterozoic to the Cenomanian is well exposed. The oldest of these strata, the Hatat schists, were deformed into a NE-facing fold nappe during the upper Cretaceous. Within the overturned and thrusted lower limb of that fold nappe, we identified three small windows exposing stratigraphically younger Hiyam carbonates and Ordovician sandstone. The structural inventory of the windows and the surrounding area indicates three major tectonic phases. The first deformation led to NNE-SSW trending fold structures which probably formed simultaneously with the major fold nappe of the Hatat schists, followed by the extreme attenuation and thrusting of the lower limb of the fold nappe. The second phase was a gentle folding of the thrust with N-S oriented fold axes and third deformation phase that formed WNW-ESE oriented open folds. The windows are situated in the intersection of anticline axes of these two superposed fold generations and represent a mini basin-and-dome structure with an extension of just 1 km?×?1 km.  相似文献