The nature and significance of the feedback of changes in terrestrial vegetation on global atmospheric and climatic change

The potential feedback on global atmospheric and climate change of climate-driven changes in terrestrial vegetation is examined by systematically relating the surface exchanges of energy, mass and momentum to two dimensions of vegetation, structure and taxonomy, such that the significance of climate driven changes in these characteristics can be assessed. A detailed quantitative understanding of this feedback is an important prerequisite to realistic and dynamic representations of the Earth's surface within general circulation and biological models (GCMs and GBMs). Without realistic representations of terrestrial vegetation within these models, any forecasts of future climates by these models must be suspect.Several general conclusions are drawn. The first is that the indirect feedbacks, those associated with the clouds and aerosols of the planetary boundary layer, appear to be very powerful but as yet their behaviour and connections with the underlying surface are both poorly understood and captured within GCMs.The physical structure of vegetation, the disposition of biomass in 3-D, is the characteristic that most strongly influences the exchange of momentum (via aerodynamic roughness) and solar radiation (via albedo). Vegetation structure and species composition determine the most important of the mass exchanges, evapotranspiration. Of all of the surface exchanges, the parameterization of evapotranspiration (E ) and the simulation of the water balance over time is the most critical.Lastly, the problems of scaling and spatial heterogeneity, the sub-grid variability of the modellers, looms as a difficult, but not insoluble, problem. It remains a critical problem however, and the detailed parameterization of the various big leaf models stands in absurd contrast to the simplistic generalization of the spatial heterogeneity of terrestrial landscapes.Plant ecologists can contribute to the task of improving the representation of vegetated landscapes within GCMs. There is need to simply and unify the way in which vegetation can be grouped at landscape scales. A classification that is based on function rather than phylogeny is required. The definition of Vegetation Functional Types (VFTs) would expedite research on both the impact of, and feedback on, climate change.     

Annual variation of atmospheric carbonyl sulfide in the marine atmosphere in the Southern Indian Ocean

Measurements of the concentrations of carbonyl sulfide (COS) in the marine atmosphere were made over a period of two years in the southern Indian Ocean (Amsterdam Island, 37°50 S–77°31 E; March 1987–February 1988 and April 1989–February 1990). The mean atmospheric COS concentration for the whole period was 475±48 pptv (n=544). Atmospheric COS concentrations show no significant seasonal variation with a summer to winter ratio of 1.05. Taking into account the observed variability of the atmospheric COS concentration (10%), a value of 1.4 yr is estimated as a lower limit for the atmospheric COS lifetime. A comparison of the COS data at Amsterdam Island with those obtained in the Southern Hemisphere in the past 12 yr does not reveal any significant trend in the tropospheric background COS mixing ratio.     

Flow directions in ash-flow tuffs: a comparison of geological and magnetic susceptibility measurements, Tshirege member (upper Bandelier Tuff), Valles caldera, New Mexico, USA

This study concludes that the elongation axis (K ₁) of the ellipsoid of anisotropic magnetic susceptibility (AMS) is a suitable proxy for flow axis in ashflow tuffs. 153 oriented samples (176 specimens) were studied from 18 sites in the 1.1 Ma Tshirege member of the Bandelier Tuff. These sites are distributed around the Valles caldera at distances of 5–25 km outside of the rim.K ₁ axes correlate well with postulated radial flow axes at 13 sites.K ₁ also agrees with measured geological flow indicators, mainly imbricated larger clasts, at 7 sites. At 2 of the 5 sites where significant disagreement is seen between theoretical radial flow directions and measuredK ₁ axes, theK ₁ axes correspond well with geological flow indicators, indicating that the divergence of flow from the predicted radial flow pattern is real. Two major topographic buttresses are suggested as the cause of flow divergence for the Tshirege ash flows: the San Pedro buttress northwest of the caldera, and the San Miguel buttress in the southeast. In situK ₁ axes plunge about 7° toward the source at two-thirds of the sites; therefore the plunge ofK ₁ is a plausible in situ indicator for thedirection of flow. Multiple flow zones in sections of several meters thickness indicate changes of flow direction that are both rapid and large during ash-flow emplacement. These observations raisre the question of how best to represent mean flow directions in ash-flow sheets: by eigenvector methods, by vector-sum methods, or by modes. A method for measuring imbrication of larger clasts using apparent dips in vertical joints is outlined. Imbrication, determined in this way at one-third of the sites, dips toward the source, i.e., up-flow. The minimum (K ₃) axis of the AMS ellipsoid correlates with the flow foliation rather than with the larger clast imbrication. The flow axes of ash flows correspond with theK ₁ axes, not with the declination ofK ₃ axes as suggested by some authors. Initial dip of the sampled ash flows is not large and does not affect the paleomagnetic remanence direction, which is reversed with a mean ofD=173.5°,I=-38.4°, ₉₅=3.4°N=18. This mean is not different at the 95% confidence level from that of earlier workers. The mean pole, at 098.0°E, 74.8°N,A ₉₅=3.3°,N=18, is about 15° far-sided relative to the expected time-averaged geomagnetic pole, suggesting a history of emplacement too short to adequately average secular variation.     

Distribution and fluxes of metals in the St. Lawrence River from the outflow of Lake Ontario to Québec City

Six anchor stations in the St. Lawrence River from the outflow of Lake Ontario to Quebec City, were occupied for ca. 24 hours in June 1987 during low flow conditions. Samples of water and suspended particulate matter were separated by continuous-flow centrifugation, and were collected every two hours.During this sampling period, fluxes of dissolved forms of zinc, copper and nickel increased in Lac St. François and downstream relative to the sum of the fluxes for the two upstream stations at the outflow of Lake Ontario. Increases in the flux of dissolved zinc and copper were pronounced below Montreal and above Lac St. Pierre. For particulate forms of metals, all five metals show that there are significant inputs in the section of the St. Lawrence River between Lac St. François and the station just above the entrance to Lac St. Pierre.The average concentrations of dissolved cadmium, lead, zinc, copper and nickel ranged from 7–23 ng/l; 9–35 ng/l; 0.434–0.939 g/l; 0.15–0.89 g/l and 0.58–1.12 g/l respectively.Regression analysis of the dissolved and particulate metal concentrations suggests that the concentration of dissolved cadmium, lead, zinc and nickel can be predicted from the regression equation and the determination of particulate metal concentration. This prediction appears to be independent of the suspended particulate matter concentration which varies from ca. 1 to 10 mg/l from the outflow of Lake Ontario to Québec City.     

Impact of Urban Surroundings on Some Limnological Characteristics of a Tropical Aquatic Ecosystem

The water quality of an urban pond in the thickly populated area of Varanasi city (5 km apart) was studied and compared with a rural pond in the Banaras Hindu University campus for transparency, conductivity and nutrient richness (Cl^?, SO, PO? P, NO? N, organic carbon, Ca²⁺, Mg²⁺, K⁺, Na⁺) at three depths (surface, 1.5 m, 3 m) at monthly intervals between February 1982 and February 1983. This was done to assess the effects of urban surroundings of a very ancient city sector on pond water quality in reference to that of a rural pond. The rural pond had a lush growth of 12 macrophytic species, whereas the urban one had only such a growth with many phytoplanktonic species. Transparency was maximum in the winter season and the rural pond water was more transparent, while the electrolytical conductance was maximum in the rainy season, being higher in the urban pond. Electrolytical conductivity was negatively correlated to transparency: urban: EC = 1081.612–6.575 T, r² = 0.897, F_1,11 = 96, P <0.005; rural: EC = 728.981–4.328 T, r₂ = 0.892, F_1,11 = 91, P <0.005. Chloride and sulphate concentrations were highest in summer months, but the former was much higher in the urban pond while the latter in the rural pond. NO₃–N was highest in the rainy season in the rural pond and in early winter in the urban one and showed a definite trend with change in depth. PO₄–P also varied with depth and time and it was higher in late summer and the early rainy season in the rural pond and in early winter in the urban pond. But both these nutrients were much higher in the urban pond. The maximum organic carbon concentration was found in the rainy season in the rural pond and in summer months in the urban pond. The variation of organic carbon with depth was distinct. Both summer and winter seasons showed almost similar values of calcium concentration in the rural pond, but in the urban pond it was maximum in summer. Organic carbon and calcium were higher in the urban pond. The magnesium concentration was highest in rainy months in both the ponds, but the periodicity of the minimum differed. The distribution of calcium with depth was not well defined. The highest concentration of potassium was found in the winter season in both the ponds. The sodium concentration in the rural pond was observed maximum in summer and minimum in the rainy season, but in the urban pond the trend was different. The variation of potassium and sodium with depth was not well defined. Magnesium and sodium were also higher in the urban pond but potassium was almost at the same concentration in both the ponds. The effect of urbanisation may be one of the factors which might be responsible to the shift of the species composition towards phytoplanktonic flora.     

Na-rich carbonate inclusions in perovskite and calzirtite from the Guli intrusive Ca-carbonatite,polar Siberia

Carbonate phases, some rich in Na₂O and comparatively rich in SrO and BaO, occur as inclusions in perovskite and calzirtite (Ca₂Zr₅Ti₂O₁₆) in the carbonatite of the Guli complex, Siberia. This is the first record of alkali carbonates, akin to nyerereite [Na₂Ca(CO₃)₂], in plutonic igneous rocks. The inclusion populations suggest that the parental magma of the complex was Ca-rich but developed Na-rich differentiates during the latest stages. This points to the dominant calcic carbonatites of the complex not being derivatives of alkali-rich parental carbonatites. These alkali-rich carbonate inclusions (and rare inclusions of djerfisherite) have been preserved due to the resistance of perovskite and calzirtite to processes of leaching, hydrothermal alteration and weathering.     

High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle

Synthetic spinel harzburgite and lherzolite assemblages were equilibrated between 1040 and 1300° C and 0.3 to 2.7 GPa, under controlled oxygen fugacity (f _{O 2}). f _{O 2} was buffered with conventional and open double-capsule techniques, using the Fe−FeO, WC-WO₂-C, Ni−NiO, and Fe₃O₄−Fe₂O₃ buffers, and graphite, olivine, and PdAg alloys as sample containers. Experiments were carried out in a piston-cylinder apparatus under fluid-excess conditions. Within the P-T-X range of the experiments, the redox ratio Fe³⁺/ΣFe in spinel is a linear function of f _{O 2} (0.02 at IW, 0.1 at WCO, 0.25 at NNO, and 0.75 at MH). It is independent of temperature at given Δlog(f _{O 2}), but decreases slightly with increasing Cr content in spinel. The Fe³⁺/ΣFe ratio falls with increasing pressure at given Δlog(f _{O 2}), consistent with a pressure correction based on partial molar volume data. At a specific temperature, degree of melting and bulk composition, the Cr/(Cr+Al) ratio of a spinel rises with increasing f _{O 2}. A linear least-squares fit to the experimental data gives the semi-empirical oxygen barometer in terms of divergence from the fayalite-magnetite-quartz (FMQ) buffer:

On the practice of estimating fractal dimension

Coastlines epitomize deterministic fractals and fractal (Hausdorff-Besicovitch) dimensions; a divider [compass] method can be used to calculate fractal dimensions for these features. Noise models are used to develop another notion of fractals, a stochastic one. Spectral and variogram methods are used to estimate fractal dimensions for stochastic fractals. When estimating fractal dimension, the objective of the analysis must be consistent with the method chosen for fractal dimension calculation. Spectal and variogram methods yield fractal dimensions which indicate the similarity of the feature under study to noise (e.g., Brownian noise). A divider measurement method yields a fractal dimension which is a measure of complexity of shape.