Simulation of the influence of solar radiation variations on the global climate with an ocean-atmosphere general circulation model

 Two simulations with a global coupled ocean-atmosphere circulation model have been carried out to study the potential impact of solar variability on climate. The Hoyt and Schatten estimate of solar variability from 1700 to 1992 has been used to force the model. Results indicate that the near-surface temperature simulated by the model is dominated by the long periodic solar fluctuations (Gleissberg cycle), with global mean temperatures varying by about 0.5 K. Further results indicate that solar variability and an increase in greenhouse gases both induce to a first approximation a comparable pattern of surface temperature change, i.e., an increase of the land-sea contrast. However, the solar-induced warming pattern in annual means and summer is more centered over the subtropics, compared to a more uniform warming associated with the increase in greenhouse gases. The observed temperature rise over the most recent 30 and 100 years is larger than the trend in the solar forcing simulation during the same period, indicating a strong likelihood that, if the model forcing and response is realistic, other factors have contributed to the observed warming. Since the pattern of the recent observed warming agrees better with the greenhouse warming pattern than with the solar variability response, it is likely that one of these factors is the increase of the atmospheric greenhouse gas concentration. Received: 14 October 1996 / Accepted: 9 May 1997     

Exploring the climate problems of Brazil’s Nordeste: a review

This article reviews the exploration of the climate dynamics of Brazil’s Nordeste in the course of a century. The drought-prone and semi-arid northern Nordeste of Brazil experiences a short rainy season around March–April, when the interhemispheric gradient of sea surface temperature (SST) in the tropical Atlantic is weakest and the Intertropical Convergence Zone (ITCZ) reaches its southernmost position in the course of the annual cycle. The recurrent Secas (droughts) have a severe socio-economic impact. During drought years, the interhemispheric SST gradient in the tropical Atlantic is steep and the ITCZ stays far North, while the waters of the eastern equatorial Pacific tend to be anomalously warm. Based on the extensive diagnostic exploration of the circulation mechanisms of interannual climate variability, empirical methods have been developed for the forecasting of the Nordeste rainy season. These have been applied in the real-time prediction of seasonal rainfall anomalies throughout the last decade of the 20th century.     

The multiresolution character of collocation

 An interesting theoretical connection between the statistical (non-stochastic) collocation principle and the multiresolution/wavelet framework of signal approximation is presented. The rapid developments in multiresolution analysis theory over the past few years have provided very useful (theoretical and practical) tools for approximation and spectral studies of irregularly varying signals, thus opening new possibilities for `non-stationary' gravity field modeling. It is demonstrated that the classic multiresolution formalism according to Mallat's pioneering work lies at the very core of some of the general approximation principles traditionally used in physical geodesy problems. In particular, it is shown that the use of a spatio-statistical (non-probabilistic) minimum mean-square-error criterion for optimal linear estimation of deterministic signals, in conjunction with regularly gridded data, always gives rise to a generalized multiresolution analysis in the Hilbert space L <sup>2</sup>(R), under some mild constraints on the spatial covariance function and the power spectrum of the unknown field under consideration. Using the theory and the actual approximation algorithms associated with statistical collocation, a new constructive framework for building generalized multiresolution analyses in L <sup>2</sup>(R) is presented, without the need for the usual dyadic restriction that exists in classic wavelet theory. The multiresolution and `non-stationary' aspects of the statistical collocation approximation procedure are also discussed, and finally some conclusions and recommendations for future work are given. Received: 26 January 1999 / Accepted: 16 August 1999     

Fluvial channel and overbank deposits from the Westphalian of the Durham coalfield, NE England

The Westphalian (Upper Carboniferous) Coal Measures of the Durham coalfield in NE England were deposited in lower and upper delta plain environments. Distributary channels crossed the plain and were separated by shallow, interdistributary lakes and bays. Detailed observation of three-dimensional (3-D) opencast (surface) mine exposures, in collaboration with subsurface borehole analysis, has revealed the existence of five varieties of channel deposits and two associated overbank facies within the Durham Coal Measures. Major distributary channels were the major avenues of sediment transport across the Coal Measures plain, were variably sinuous, mostly 1–2 km wide and deposited elongate belts of sand mostly up to 5 km wide. Proximal, major crevasse splay channels formed by the breaching of major channel banks during flood events, were straight, sand-filled and up to 400 m wide. Minor distributary channels formed by the sustained operation of such crevasses, varied from straight to highly sinuous, and deposited ‘shoestring’ sand/mud belts up to a few hundred metres wide. Minor crevasse channels, generally straight and up to 50 m wide, were formed through bank breaching of minor, and in a few cases major, distributaries. Distal feeder channels formed down-palaeocurrent extensions of minor distributaries which supplied interdistributary minor delta subsystems, were generally straight and up to 200 m wide. Of the two types of channel overbank (levee) deposits recognized, one, comprising thinly interbedded fine-grained sandstone and siltstone/claystone, is mostly, though not exclusively, associated with major distributary channels. The other, consisting of ‘massive’ siltstones with regularly spaced, thin claystone bands, is uniquely developed at the margins of minor distributary channels. The lower part of the Westphalian A succession in the northern Pennines records a change in the depositional environment upwards from a lower to upper delta plain. Through this transition, major channel deposits show evidence of having evolved from being of dominantly low sinuosity to being more variable in morphology. Channel sedimentation was profoundly influenced by regular, possibly seasonal, variations in flow stage and sediment load.     

Adsorption characteristics of perchloroethylene in natural sandy materials with low organic carbon content

Laboratory batch tests were conducted to investigate the sorption isotherms and sorption kinetics of the chlorinated hydrocarbon perchloroethylene (PCE) in five natural sandy materials with an organic carbon content (f _oc) in the range 0.080–0.540%. The amended non-linear dual-mode model can describe the sorption isotherms in materials with f _oc in the range 0.080–0.090%. For a sample with a much higher f _oc of 0.54%, the absorption isotherm was found to fit a linear model. These results may indicate that organic carbon is not the main factor influencing the sorption isotherm. The sorption kinetics of PCE in samples with f _oc in the range 0.080–0.090% are not first-order and are different from those observed in the samples with higher f _oc. The sorption process in the materials with lower f _oc involves fast sorption, fast desorption and an equilibrium stage. The results may imply that the factors affecting sorption kinetics of PCE in low f _oc media are pore filling and capillary condensation rather than organic carbon content.     

Plant Cover,Herbivory, and Resiliency in a Cape Cod Salt Marsh: Multi-year Responses and Recovery Following Manipulation of Nutrients and Competition

To assess responses and recovery of salt marsh grass species, we manipulated external nutrient supply and removed shoots of Spartina alterniflora or Spartina patens from fertilized and control plots in a Massachusetts marsh. The pulse-and-recovery experiment included treatments for 5 years, and recovery for an additional 7 years. Responses of these potential competitors sensitively depended on local contingencies of elevation and nutrient dose, and, moreover, the differences in outcomes were emphasized at longer time scales. Local contingencies became manifest as differences in responsiveness and resiliency of the different grass species, with differing time courses and longer-term outcomes as to what species were present. These features might explain the diverse results obtained in shorter-term salt marsh experiments, and provide a view of the complex suite of species-specific and external environmental variables that may control competitive interactions in general.     

Recognition of geochemical footprints of mineral systems in the regolith at regional to continental scales

Understanding the character of Australia's extensive regolith cover is crucial to the continuing success of mineral exploration. We hypothesise that the regolith contains geochemical fingerprints of processes related to the development and preservation of mineral systems at a range of scales. We test this hypothesis by analysing the composition of surface sediments within greenfield regional-scale (southern Thomson Orogen) and continental-scale (Australia) study areas. In the southern Thomson Orogen area, the first principal component (PC1) derived in our study [Ca, Sr, Cu, Mg, Au and Mo at one end; rare earth elements (REEs) and Th at the other] is very similar to the empirical vector used by a local company (enrichment in Sr, Ca and Au concomitant with depletion in REEs) to successfully site exploration drill holes for Cu–Au mineralisation. Mapping of the spatial distribution of PC1 in the region reveals several areas of elevated values and possible mineralisation potential. One of the strongest targets in the PC1 map is located between Brewarrina and Bourke in northern New South Wales. Here, exploration drilling has intersected porphyry Cu–Au mineralisation with up to 1 wt% Cu, 0.1 g/t Au, and 717 ppm Zn. The analysis of a comparable geochemical dataset at the continental scale yields a compositionally similar PC1 (Ca, Sr, Mg, Cu, Au and Mo at one end; REEs and Th at the other) to that of the regional study. Mapping PC1 at the continental scale shows patterns that (1) are spatially compatible with the regional study and (2) reveal several geological regions of elevated values, possibly suggesting an enhanced potential for porphyry Cu–Au mineralisation. These include well-endowed mineral provinces such as the Curnamona and Capricorn regions, but also some greenfield regions such as the Albany-Fraser/western Eucla, western Murray and Eromanga geological regions. We conclude that the geochemical composition of Australia's regolith may hold critical information pertaining to mineralisation within/beneath it.     

Paleo-environment and reservoir evolution of the Middle Ordovician Kelimoli Formation in the northern Tianhuan area,Ordos Basin,China: implications for high-quality reservoir development

The Middle Ordovician Kelimoli Formation carbonate reservoirs in the northern Tianhuan area, Ordos Basin, China are main exploration targets. Subsurface core samples, logging, drilling and production data from the area were used to characterise the carbonate reservoir and to construct a genetic model for exploration. The sedimentary facies identified include trough–continental rise, upper–lower slope, platform margin reef-shoal, open platform and evaporation-restricted platform. The slope and platform margin facies are potential zones for high-quality reservoirs. Porosity in the study area comprises intergrain, intercrystal, intragrain and intracrystal pores, fractures and vughs. The Sr/Ba (0.40–4.87) and V/(V + Ni) (0.64–0.97) ratios indicate deposition in a brackish water-dominated environment under reducing conditions, associated with sea-level fluctuations during the deposition of the Kelimoli Formation. The Sr/Ba, V/(V + Ni), ⁸⁷Sr/⁸⁶Sr ratios, δ¹⁸O values and crystal texture of dolomite samples suggest that meteoric water was involved in the diagenetic fluid in the near-surface depositional environment. Isotopes (δ¹³C and δ¹⁸O) and trace elements (Fe and Mn) allowed the identification of seepage-reflux and mixed-water dolomitisation. The crystal textures of the samples consist of micritic, bioclastic and reefal limestones, and dolomite with gypsum, which were easily dissolved during the early diagenetic stage. The epidiagenetic stage was the key period for the development of high-quality reservoirs because of large-scale bedding-parallel karstification from meteoric water. The reservoir zones, dominated by partially filled and unfilled vughs, and fractures, are favourable exploration targets in the northern Tianhuan area.     

Interactive effect of cadmium and zinc on chromium uptake in spinach grown in Vertisol of Central India

A pot culture experiment was conducted to study impact and interaction of multi-metals on growth, yield and metals uptake by spinach (variety All Green). Three levels of each chromium (0, 50 and 100 mg/kg), cadmium (0, 1 and 2 mg/kg) and zinc (0, 10 and 20 mg/kg) in combinations (total treatments 3 × 3 × 3 = 27) were applied in a Vertisol (5 kg). The results showed that increasing the concentration of chromium, cadmium and zinc in soil enhanced the respective metal concentrations in spinach root and shoot. When cadmium at 2 mg/kg along with chromium at 100 mg/kg soil was applied, chromium concentration and uptake were decreased in root and shoot. Meanwhile, zinc application had no significant effect on chromium uptake and concentration in spinach biomass. From the results, it was concluded that cadmium at higher dose had an antagonistic effect over chromium. On the other hand, in chromium, cadmium and zinc combinations particularly at their higher levels, a competition among each other was found. Therefore, the findings could be used as guidelines for controlling and management of heavy metals pollution in farmland.     

Importance of kelp-derived organic carbon to the scallop <Emphasis Type="Italic">Chlamys farreri</Emphasis> in an integrated multi-trophic aquaculture system

Bivalves and seaweeds are important cleaners that are widely used in integrated multi-trophic aquaculture (IMTA) systems. A beneficial relationship between seaweed and bivalve in the seaweed-based IMTA system has been confirmed, but the trophic importance of seaweed-derived particulate organic materials to the co-cultured bivalve is still unclear. We evaluated the trophic importance of the kelp Saccharina japonica to the co-cultured scallop Chlamys farreri in a typical IMTA farm in Sungo Bay (Weihai, North China). The dynamics of detritus carbon in the water were monitored during the culturing period. The proportion of kelp-derived organic matter in the diet of the co-cultured scallop was assessed via the stable carbon isotope method. Results showed that the detritus carbon in the water ranged from 75.52 to 265.19 μg/L, which was 25.6% to 73.8% of total particulate organic carbon (TPOC) during the study period. The amount of detritus carbon and its proportion in the TPOC changed throughout the culture cycle of the kelp. Stable carbon isotope analysis showed that the cultured scallop obtained 14.1% to 42.8% of its tissue carbon from the kelp, and that the percentages were closely correlated with the proportion of detritus carbon in the water (F =0.993, P= 0.003). Evaluation showed that for 17 000 tons (wet weight) of annual scallop production, the kelp contributed about 139.3 tons of carbon (535.8 tons of dry mass). This confirms that cultured kelp plays a similar trophic role in IMTA systems as it does in a natural kelp bed. It is a major contributor to the detritus pool and supplies a vital food source to filter-feeding scallops in the IMTA system, especially during winter and early spring when phytoplankton are scarce.