Differences in the Crustal and Uppermost Mantle Structure of the Bohemian Massif from Teleseismic Receiver Functions

A target of our study was the Bohemian Massif in Central Europe that was emplaced during the Variscan orogeny. We used teleseismic records from ten broadband stations lying within and around the massif. Different techniques of receiver function interpretation were applied, including 1-D inversion of R- and Q-components, forward modelling of V _s velocity, and simultaneous determination of Moho depth and Poissons ratio in the crust. These results provide new, independent information about the distribution of S wave velocity down to about 60 km depth. In the area of Bohemian Massif, the crustal thickness varies from 29 km in the NW to 40 km in the SE. A relatively simple velocity structure with gradually increasing velocities in the crust and uppermost mantle is observed in the eastern part of the Bohemian Massif. The western part of the massif is characterized by more complicated structure with low S wave velocities in the upper crust, as well as in the uppermost mantle. This could be related to tectono-magmatic activity in the Eger rift that started in the uppermost Cretaceous and was active in the West Bohemia-Vogland area till the late Cenozoic.     

Spatial and temporal variations of meiofaunal communities from the Western Sector of the Gulf of Batabanó, Cuba. I. Mangrove systems

The spatial and temporal variations of meiofaunal communities in mangrove systems were examined. Replicated cores were taken in mudflats between prop roots ofRhizophora mangle at five locations within the Gulf of Batabanó, Cuba, during 3 mo. There was a clear seasonality in the water column, but measured abiotic variables did not show obvious relations with meiofaunal patterns. The magnitude of change in salinity for each location appears to influence the meiofauna more than absolute values per se. The meiofauna from southern Pinar del Rio showed a higher variation in community structure, suggesting higher levels of stress in comparison with locations in eastern Isla, possibly due to the presence of human settlements, runoff from land, and apparent deterioration of mangroves. The considerable variation in the density and community structure estimates on global (geographical regions) and local (locations in the Gulf of Batabanó) scales could be caused by the high spatial variability in the mangrove microenvironment, coupled with associated methodological differences in the sampling. There was a low density of meiofauna (mean: 101 animals 10 cm⁻²) compared to other shallow tropical habitats. Mangroves from subtropical and temperate regions showed consistently higher meiofaunal densities than tropical mangroves, but causes of this putatively latitudinal pattern require further study. Future strategies for meiofaunal studies in mangrove systems should increase the temporal and spatial replication, include designed field experiments to test ecological hypotheses, and apply a species level approach with regards to nematode assemblages.     

Sector structure of the interplanetary magnetic field and anisotropy of 50–1000 GV cosmic rays

It is demonstrated that, at high rigidities (50 GV and beyond), all the main features of cosmic-ray anisotropy of solar origin can be explained in terms of regular particle motion —without diffusion being involved — in the large-scale interplanetary magnetic field (IMF). A simple model of the IMF is adopted with a corotating warped neutral sheet separating the regions of alternative polarities; the warped shape is indispensable for obtaining any form of anisotropy. Energy losses occurring along various computed trajectories are calculated to give the sidereal, solar and antisidereal intensity waves. The reliability of the variations obtained are checked by changing the parameters of the IMF model. Both the sense and amplitude of the polarity-dependent sidereal vector are compatible with those established experimentally. Also reproduced are the predictions of corotation in addition to the 3-hour phase of the semi-diurnal wave. The corotation is found to be near perfect at 50 GV, while it reduces at 100 GV. The model presented accounts for the change of solar daily vector that was observed in 1969.     

Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal calc-alkaline magmatism

Cenozoic magmatic activity in northern Chile led to the formation of two contrasting porphyry copper belts: (1) a Paleocene-Early Eocene belt comprising small porphyry copper deposits (e.g., Lomas Bayas) of normal calc-alkaline affinity; and (2) a Late Eocene-Early Oligocene belt hosting huge porphyry copper deposits (e.g., Chuquicamata) of adakitic affinity. Although the first belt comprises both volcanic and plutonic rocks (andesitic-basaltic and rhyolitic lavas and tuffs, and associated sub-volcanic porphyries and felsic stocks), the latter only includes intrusions (mostly granodioritic types, including porphyry copper deposits). We suggest that the Late Eocene-Early Oligocene belt formed when fast and oblique convergence between the South America and Farallon plates led to flat subduction and direct melting of the subducting plate, hence giving rise to plutonic rocks of adakitic affinity. The absence of volcanism, under prevailing compressional conditions, prevented the escape of SO₂ from the adakitic, sulfur-rich, highly oxidized magmas ("closed porphyry system"), which allowed formation of huge mineral deposits. On the contrary, coeval volcanic activity during formation of the Paleocene-Early Eocene calc-alkaline porphyries allowed development of "open systems", hence to outgassing, and therefore, to small mineral deposits.     

Estuarine phytoplankton group-specific responses to sublethal concentrations of the agricultural herbicide,atrazine

Atrazine is a common agricultural herbicide that is readily transported into estuaries through surface water runoff. In this study, we determined the short-term (24-48 h) sublethal effects of atrazine on estuarine phytoplankton biomass and community composition. Phytoplankton group-specific responses to atrazine exposure (25 microgh(-1)) were measured using natural water samples collected from two locations in Galveston Bay, Texas. Addition bioassays, coupled with HPLC pigment analysis, were used to quantify changes in the relative abundances of algal groups. For all algal groups except prasinophytes, the addition of atrazine in combination with nitrate was not significantly different from nitrate additions alone. These results suggest no significant negative effect of atrazine on phytoplankton under the specified environmental conditions for the bioassays. Although low concentrations of atrazine may have minimal impacts on phytoplankton, herbicide loadings need to be further characterized before generalizations can be applied to estuarine and coastal ecosystems.     

Transformation of the Geodetic Horizontal Control to Another Reference Ellipsoid

Studia Geophysica et Geodaetica -     

Net primary production and decomposition of salt marshes of the Ebre delta (Catalonia,Spain)

Net primary production was measured in three characteristic salt marshes of the Ebre delta: anArthrocnemum macrostachyum salt marsh,A. macrostachyum-Sarcocornia fruticosa mixed salt marsh andS. fruticosa salt marsh. Above-ground and belowground biomass were harvested every 3 mo for 1 yr. Surface litter was also collected from each plot. Aboveground biomass was estimated from an indirect non-destructive method, based on the relationship between standing biomass and height of the vegetation. Decomposition of aboveground and belowground components was studied by the disappearance of plant material from litter bags in theS. fruticosa plot. Net primary production (aboveground and belowground) was calculated using the Smalley method. Standing biomass, litter, and primary production increased as soil salinity decreased. The annual average total aboveground plus belowground biomass was 872 g m⁻² in theA. macrostachyum marsh, 1,198 g m⁻² in theA. macrostachyum-S. fruticosa mixed marsh, and 3,766 g m⁻² in theS. fruticosa biomass (aboveground plus belowground) was 226, 445, and 1,094 g m⁻², respectively. Total aboveground plus below-ground net primary production was 240, 1,172, and 1,531 g m⁻² yr⁻¹. There was an exponential loss of weight during decomposition. Woody stems and roots, the most recalcitrant material, had 70% and 83% of the original material remaining after one year. Only 20–22% of leafy stem weight remained after one year. When results from the Mediterranean are compared to other salt marshes dominated by shrubbyChenopodiaceae in Mediterranean-type climates, a number of similarities emerge. There are similar zonation patterns, with elevation and maximum aboveground biomass and primary production occurring in the middle marsh. This is probably because of stress produced by waterlogging in the low marsh and by hypersalinity in the upper marsh.     

"Little Ice Age" Research: A Perspective from Iceland

The development during the nineteenth and twentieth centuries of the sciences of meteorology and climatology and their subdisciplines has made possible an ever-increasing understanding of the climate of the past. In particular, the refinement of palaeoclimatic proxy data has meant that the climate of the past thousand years has begun to be extensively studied. In the context of this research, it has often been suggested that a warm epoch occurred in much of northern Europe, the north Atlantic, and other parts of the world, from around the ninth through the fourteenth centuries, and that this was followed by a decline in temperatures culminating in a "Little Ice Age" from about 1550 to 1850 (see e.g. Lamb, 1965, 1977; Flohn, 1978). The appelations "Medieval Warm Period" and "Little Ice Age" have entered the literature and are frequently used without clear definition. More recently, however, these terms have come under closer scrutiny (see, e.g. Ogilvie, 1991, 1992; Bradley and Jones, 1992; Mikami, 1992; Briffa and Jones, 1993; Bradley and Jones, 1993; Hughes and Diaz, 1994; Jones et al., 1998; Mann et al., 1999; Crowley and Lowery, 2000). As research continues into climatic fluctuations over the last 1000 to 2000 years, a pattern is emerging which suggests a far more complex picture than early research into the history of climate suggested. In this paper, the origins of the term "Little Ice Age" are considered. Because of the emphasis on the North Atlantic in this volume, the prime focus is on research that has been undertaken in this region, with a perspective on the historiography of historical climatology in Iceland as well as on the twentieth-century climate of Iceland. The phrase "Little Ice Age" has become part of the scientific and popular thinking on the climate of the past thousand years. However, as knowledge of the climate of the Holocene continues to grow, the term now seems to cloud rather than clarify thinking on the climate of the past thousand years. It is hoped that the discussion here will encourage future researchers to focus their thinking on exactly and precisely what is meant when the term "Little Ice Age" is used.