The influence of internal tides on phytoplankton photosynthetic response to light was studied in the Lower St. Lawrence Estuary. Photosynthesis at saturating light intensity responded to variations in the vertical density gradient, which were linked to the internal tides. The photosynthetic response was lag-correlated to the vertical water stratification. This suggests that the link between photosynthesis and the internal tides may have resulted from phytoplankton light adaptation. 相似文献
The subject is reviewed, notwithstanding the existence of a number of disagreeing and/or controversial results found in the literature. First, a brief critical reexamination of the methodology is presented. Second, it is attempted to put the results, or partial conclusions by different authors, using different methods and referring to different geographical regions, into a working scheme. This is done by investigating, as far as possible, the relationships between the electrical conductivity information and other types of geophysical and geological information for each geographical area investigated. It appears almost impossible to draw general conclusions that hold for the entire Earth. Conclusions are given for those areas with some very well-defined geomorphological characters. Unfortunately, the available investigations still appear to give a poor coverage of several types of geographic areas with specific tectonic characteristics, and certainly the scientific coverage by electromagnetic methods of investigation cannot be compared with those available today from seismological methods. Investigating the electrical conductivity structure of the lower crust certainly opens relevant heuristic possibilities, but there appears to be a great need both for a refinement in the basic methodology, and for a better coverage of the investigated areas. 相似文献
An attempt is made, for an anticyclonic stable situation in the atmospheric boundary layer during November 1978, to estimate the dissipation length. The turbulent dissipation and the turbulent kinetic energy, as measured on a 100 m high mast, exhibit large variability, due to the sporadic turbulent structure of the stable layer, and associated variability of the Richardson number. A comparison with different parameterizations of the turbulent dissipation rate allows a validation of these parameterizations. 相似文献
This paper gives an account of the main historical episodes which influenced settlement patterns in the Maltese Islands. It covers the period from early colonization, when mankind first set foot on the islands, through the Middle Ages, the arrival of the Knights and the effect this had on the local economy, to the period under the British Crown and the years prior Independence. Special reference is made to the main island, and the factors which had a significant influence on population movements. 相似文献
Osmium isotope ratios for two types of platinum group mineral (PGM) nuggets of eluvial (residual) origin, associated with the Freetown Layered Gabbro Complex, were determined in-situ using an ion microprobe. The values for erlichmanite nuggets are 1.08. Those for PGM inclusions in Pt–Fe alloy nuggets are higher, ranging from 1.2 to 2.1. Ratios of187Os/186Os vary between the nuggets, but they are consistent within individual nuggest. The data suggest early formation of the erlichmanite nuggets, prior to a postulated substantial contribution of crustal Os. The Pt–Fe alloy nuggets, on the other hand, were formed later in a residual melt which was contaminated by crustal Os due to the assimilation (<10%) or the gaseous/fluid transport of Os from Archaean host rocks into the magma. The lack of systematic mineralogical and chemical changes of the Complex and extensive granulitization in the adjacent host rocks and xenoliths may favor the latter process.The lack of high187Os/186Os ratios, consistent187Os/186Os values within individual nuggets and their textures and mineralogy suggest that the studied PGM nuggets were not formed during lateritization or in low-temperature depositional environments. 相似文献
A newly developed marine electromagnetic (E-M) system was used to create apparent porosity maps of the uppermost 20 m of sediments on the seafloor. Measurements of electrical conductivity were interpreted to give the porosity of the bottom sediments and underlying units. The data were collected continuously in a surveying mode using two receivers at different spacings to improve the resolution of porosity as a function of depth. The variations in apparent porosity over the area correlate well with information obtained from cores and acoustic profiles.
Acoustic profiles indicated the presence of biogenic gas in the central region of the survey area. The absence of distinct changes in apparent porosity over regions of gas allows us to conclude that the concentration of gas trapped within the Queen Charlotte muds does not exceed about 4% of the sediment by volume if we assume that the gas displaces fluid in the sediment.
A buried, lower porosity layer was detected, its position reflecting changes in the depth to the glaciomarine layer. Mapped variations in apparent porosity are well correlated with features on the acoustic record. This illustrates the system's ability to obtain continuous profiles of apparent porosity over seafloor features. The marine E-M survey provided rapid areal coverage, and, combined with the acoustic profiles, information on the porosity of deeper units. 相似文献
We have studied the possible synthesis of organic molecules by the absorption of galactic cosmic rays in an N2CH4H2 Titan model atmosphere. The cosmic-ray-induced ionization results in peak electron densities of 2 × 103 cm?3, with NH4+, C3H9+, and C4H9+ being among the important positive ions. Details of the ion and neutral chemistry relevant to the production of organic molecules are discussed. The potential importance of reactions with CH4 and H2 is also demonstrated. Although the integrated production rate of organic matter due to the absorption of the cosmic ray cascade is much less than that by solar ultraviolet radiation, the production of nitrogen-bearing organic molecules by cosmic rays may be greater. 相似文献