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661.
Earth surface processes and landforms may have coadjusted? with plant morphology, biomechanics and life‐history. We suggest that the colonization of land by plants at the early Silurian, and their propagation inside continents, represent critical phases of the coupling between geomorphic and biological processes on the Earth at a global scale. The consideration of this coupling involving geomorphic‐biological feedback mechanisms at the scales of ecological succession and organisms' evolution may promote the emergence of an evolutionary? geomorphology. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
662.
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
663.
The oiling rate (oiled birds/total birds) has become the international standard to analyze beached bird survey data. However, this index may not reliably track long-term changes in marine oil pollution in regions where other activities that kill seabirds vulnerable to oil, such as hunting and gill-netting, are also changing. We compare the oiling rate from beached bird surveys conducted in southeastern Newfoundland between 1984 and 2006 to an alternative approach, namely trends derived from a model examining the linear density of oiled birds (birds/km). In winter, there was no change in the oiling rate since 1984, while in summer oiling rates significantly increased. In contrast, the number of oiled birds/km showed a significant decline in both winter and summer. The discrepancy in these trends was attributed to steep declines in the number of unoiled birds found in both seasons. In winter, the decline in unoiled birds/km was related to a reduction in the legal murre hunt and less onshore winds, while in summer a reduced cod fishery resulting in fewer murres drowning in nets and warming summers may have lead to the decline. The significant declines in oiled birds/km over the past three decades are hopefully an indication of less oil being present in the marine environment. Although oiled bird densities since 2000 have remained relatively low for the region (winter: 0.58 birds/km, summer: 0.27 birds/km), they still exceed densities reported elsewhere in the world. 相似文献
664.
Alexandra Serna Johannes Pätsch Kirstin Dähnke Martin G. Wiesner H. Christian Hass Manfred Zeiler Dierk Hebbeln Kay-Christian Emeis 《Continental Shelf Research》2010
The German Bight/SE North Sea is considered a hot-spot of river-induced eutrophication, but the scarce observational data of river nitrate loads prior to the 1970s complicate the assessment of target conditions for environmental management and legislation. Stable nitrogen isotope ratios (δ15N) in sediment records can be used to decipher historical river nitrate contributions. To better constrain pre-1970s conditions, we determined δ15N in archive sediment samples (1950–1969) and dated cores from the Helgoland depositional area. We also modeled the δ15N in past situations (1960 and 1860) using an N-isotope-tracking ecosystem model. The modeled spatial distribution of δ15N in sediments for 1960 conditions and the observed spatial pattern of δ15N in archive sediment samples (1950–1969) represent a period of moderate eutrophication. The modeled spatial distribution of δ15N in sediments for 1860 conditions (pre-industrial) showed a moderate δ15N gradient from the Elbe river mouth (δ15N<4‰) to the open sea (δ15N∼5‰). This pattern contrasts with the δ15N pattern in modern surface sediments, which exhibits a steep and inverted δ15N gradient from the Elbe river mouth (δ15N>9‰) to the open sea (δ15N<7‰). Modeled δ15N for 1860 conditions are consistent with δ15N values observed in dated sediment cores that span the last 900 years. Value of δ15N in sediment cores increased from approximately 1860 to 2000 by 2.5‰. The increasing trend reflects changes in the abundance and isotopic composition of riverine nitrate loads caused by anthropogenic activities. Sensitivity tests suggest that loads and isotopic ratios of nitrogen forms other than nitrate (ammonium and organic nitrogen) have minor impact on the modeled surface sediments, despite their higher abundance in the riverborne loads in the past. Our results suggest that eutrophication of the German Bight predates the 1960 period of documented rapidly increasing river loads. Pre-industrial levels of δ15N modeled with 28% of the modern annual (1990–1999) atmospheric loads and 10% of the modern annual river loads agree best with levels of δ15N (∼6‰) observed in sediments of the cores dated to 1860. 相似文献
665.
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
666.
The concentrations of free dissolved carbon dioxide in lake water were measured with a newly developed CO2 sensor, which was installed in a through-flow measurement system. The results of measurements demonstrate the CO2 dynamics in lake Willersinnweiher. The CO2 concentrations showed a correlation with the oxidation of CH4 in the metalimnion and caused shifts in the carbonate system, thus affecting the autochthonous precipitation and dissolution of calcite.
From the results of measurement appears that the CO2 sensor is capable of very exact measurements of dissolved free CO2 in lake water. At the same time, the parameter is easily determined in the field without large expenditures. 相似文献
667.
Li Ping Weng Luuk K. Koopal Johannes C.L. Meeussen 《Geochimica et cosmochimica acta》2005,69(2):325-339
668.
José?F.?MolinaEmail author Stefano?Poli H?kon?Austrheim Johannes?Glodny Anatolij?Rusin 《Contributions to Mineralogy and Petrology》2004,147(4):484-504
Metasomatic amphibole-eclogite sequences grew in selvages of quartz veins from the Marun-Keu complex (Polar Urals, Russia) during high-pressure metamorphism. Relicts of a pre-metasomatic eclogite-facies assemblage are present in the wallrock layers as irregular patches. Wallrock interstitial quartz trails lying at a high angle to reaction fronts provide evidence for grain-scale pore channelisation which may be produced by intergranular-fluid compositional gradients parallel to the quartz trails. Disequilibrium at vein-wallrock scale is inferred from wallrock mineral heterogeneity and from variable initial Sr isotope ratios in mineral separates. Mass-balance calculations between relicts and wallrock assemblages reveal chemical imbalances caused by open system-behaviour with two way mass-transfer. The vein-wallrock system registers a prograde history from 408–434 °C (relicts) to 526–668 °C (vein precipitates). Vein and metasomatic assemblages formed during a single fluid-rock interaction process, implying high heating rates (100 °C/Ma), which could result from heat advection by large-scale fluid circulation.Editorial responsibility: W. Schreyer 相似文献
669.
Lemaire P. Wilhelm K. Curdt W. SchÜle U. Marsch E. Poland A. I. Jordan S. D. Thomas R. J. Hassler D. M. Vial J. C. KÜhne M. Huber M. C. E. Siegmund O. H. W. Gabriel A. Timothy J. G. Grewing M. 《Solar physics》1997,170(1):105-122
SUMER – Solar Ultraviolet Measurements of Emitted Radiation – is not only an extreme ultraviolet (EUV) spectrometer capable of obtaining detailed spectra in the range from 500 to 1610 Å, but, using the telescope mechanisms, it also provides monochromatic images over the full solar disk and beyond, into the corona, with high spatial resolution. We report on some aspects of the observation programmes that have already led us to a new view of many aspects of the Sun, including quiet Sun, chromospheric and transition region network, coronal hole, polar plume, prominence and active region studies. After an introduction, where we compare the SUMER imaging capabilities to previous experiments in our wavelength range, we describe the results of tests performed in order to characterize and optimize the telescope under operational conditions. We find the spatial resolution to be 1.2 arc sec across the slit and 2 arc sec (2 detector pixels) along the slit. Resolution and sensitivity are adequate to provide details on the structure, physical properties, and evolution of several solar features which we then present. Finally some information is given on the data availability and the data management system. 相似文献
670.
Observations of sunspot transition region oscillations 总被引:1,自引:0,他引:1
Oscillations with a period of 3 minutes are observed in the transition region of six sunspots with the Solar and Heliospheric Observatory - SOHO joint observing programme for velocity fields in sunspot regions. Observations of the transition region lines Ov 629 and Nv 1238, 1242 with the SUMER instrument show significant differences in the amplitude of the 3-minute oscillations from one sunspot to another, both in intensity and line-of-sight velocity. In four sunspots the central part of the umbra is observed. Two of these sunspots show coincidence between the maxima in peak line intensity and velocity directed towards the observer, as is expected for an upward-propagating acoustic wave. The two other sunspots show large oscillation amplitudes and a difference of 25° between maxima in intensity and blue shift. The possible effect of partial wave reflection on the observed phase relation is discussed. For one sunspot only a part of the umbra, close to the penumbra, was observed and the observations show a difference of 50° between maxima in intensity and blueshift. For the smallest sunspot the observations are found to be contaminated by contributions from an area without oscillations. Observed oscillations in line width are small, but probably significant in two sunspots. The observations of NOAA 8378 allow us to compare simultaneous recordings of the oscillations in the chromospheric Siii 1260 line with the oscillations in the transition region lines. We question the suggestion by Fludra (1999) that the sunspot transition region oscillations are a typical feature of the sunspot plumes. 相似文献