[en] Net ecosystem CO₂ exchange was measured over a mountain birch forest in northern Finland throughout the growing season. The maximal net CO₂ uptake rate of about - 0.5 mg(CO₂) m^-2s^-1 was observed at the end of July. The highest nocturnal respiration rates in early August were 0.2 mg(CO₂)m^-2s^-1. The daily CO₂ balances during the time of maximal photosynthesis were about -15 g(CO₂)m^-2d^-1. The mountain birch forest acted as a net sink of CO₂ from 30 June to 28 August. During that period the net CO₂ balance was -448 g(CO₂)m^-2. The inter annual representativeness of the observed balances was studied using a simplified daily balance model, with daily mean global radiation and air temperature as the input parameters. The year-to-year variation in the phenological development was parameterized as a function of the cumulative effective temperature sum. The daily balance model was used for estimating the variability in the seasonal CO₂ balances due to the timing of spring and meteorological factors. The sink term of CO₂ in 1996 was lower than the 15-year mean, mainly due to the relatively late emergence of the leaves. (author)

[en] The carbon dioxide exchange in arctic and subarctic terrestrial ecosystems has been measured using the eddy-covariance method at sites representing the latitudinal and longitudinal extremes of the European Arctic sea areas as part of the Land Arctic Physical Processes (LAPP) project. The sites include two fen (Kaamanen and Kevo) and one mountain birch ecosystems in subarctic northern Finland (69^o N); fen, heath land, and snow bed willow ecosystems in northeastern Greenland (74^o N); and a polar semi desert site in Svalbard (79^o N). The measurement results, which are given as weekly average diurnal cycles, show the striking seasonal development of the net CO₂ fluxes. The seasonal periods important for the net CO₂ fluxes, i.e. winter, thaw, pre-leaf, summer, and autumn can be identified from measurements of the physical environment, such as temperature, albedo, and greenness. During the late winter period continuous efflux is observed at the permafrost-free Kaamanen site. At the permafrost sites, efflux begins during the thaw period, which lasts about 3-5 weeks, in contrast to the Kaamanen site where efflux continues at the same rate as during the winter. Seasonal efflux maximum is during the pre-leaf period, which lasts about 2-5 weeks. The summer period lasts 6 weeks in NE Greenland but 10-14 weeks in northern Finland. During a high summer week, the mountain birch ecosystem had the highest gross photosynthetic capacity, GP_max, followed by the fen ecosystems. The polar semi desert ecosystem had the lowest GP_max. By the middle of August, noon uptake fluxes start to decrease as the solar elevation angle decreases and senescence begins within the vascular plants. At the end of the autumn period, which lasts 2-5 weeks, topsoil begins to freeze at the end of August in Svalbard; at the end of September at sites in eastern Greenland; and one month later at sites in northern Finland. (author)

[en] Turbulent fluxes of CO₂ were continuously measured by eddy correlation for three months in 1997 over a gramineous fen in a high-arctic environment at Zackenberg (74^o28'12''N, 20^o34'23''W) in NE-Greenland. The measurements started on 1 June, when there was still a 1-2 m cover of dry snow, and ended 26 August at a time that corresponds to late autumn at this high-arctic site. During the 20-day period with snow cover, fluxes of CO₂ to the atmosphere were small, typically 0.005 mg CO₂ m^-s-1 (0.41 g CO₂ m^-2d^-1), whereas during the thawed period, the fluxes displayed a clear diurnal variation. During the snow-free period, before the onset of vegetation growth, fluxes of CO₂ to the atmosphere were typically 0.1 mg CO₂ m^-2s^-1 in the afternoon, and daily sums reached values up to almost 9 g CO₂ m^-2d^-1. After 4 July, downward fluxes of CO₂ increased, and on sunny days in the middle of the growing season, the net ecosystem exchange rates attained typical values of about -0.23 mg m^-s-1 at midday and max values of daily sums of -12 g CO₂ m^-2d^-1. Throughout the measured period the fen ecosystem acted as a net-sink of 130 g CO₂ m^-2. Modeling the ecosystem respiration during the season corresponded well with eddy correlation and chamber measurements. On the basis of the eddy correlation data and the predicted respiration effluxes, an estimate of the annual CO₂ balance the calendar year 1997 was calculated to be a net-sink of 20 g CO₂ m^-2yr^-1. (author)

[en] Measurements of landscape-scale methane emission were made over an aapa mire near Kaamanen in Finnish Lapland (69^o 8' N, 27^o WE, 155 m ASL). Emissions were measured during the spring thaw, in summer and in autumn. No effect of water table position an CH₄ emission was found as the water table remained at or above the surface of the peat. Methane emission fluxes increased with surface temperature from which an activation energy of -99 kJ mol^-1 was obtained. Annual emission from the site, modeled from temperature regression and short-term flux measurements made in three separate years, was calculated to be 5.5 ± 0.4 g CH₄ m^-2y^-1 of which 0.6 ± 0.1 g CH₄ m^-2y^-1 (11 %) was released during the spring thaw which lasted 20 to 30 days. The effect of global warming an the CH₄ budget of the site was estimated using the central scenario of the SILMU (Finnish Research Program on Climate Change) model which predicts annual mean temperature increases of 1.2, 2.4 and 4.4 ^oC in 2020, 2050 and 2100, respectively. Maximum enhancements in CH₄ emission due to warming were calculated to be 18, 40 and 84 % for 2020, 2050 and 2100, respectively. Actual increases may be smaller because prediction of changes in water table are highly uncertain. (author)

[en] By analyzing normalized variables, it was found that the latitudinal secular variations of the rainwater deuterium fractionation ratio δ²H, oxygen fractionation ratio δ¹⁸O, vapor pressure, and surface temperature were almost non-linear, occurred in parallel, and decreased with latitude. The rate of depletion around the equator is asymmetric and smaller to the south of 45^o S than to the north of 45^o N. In the east Mediterranean, the rate of change of δ¹⁸O with height was found to be -.2 %o per 100 m and that of δ²H is comparable with the dry lapse rate in the atmosphere. Analysis of the annual time series of δ²H at Alexandria has indicated that variations show sinusoidal waveform with a major cycle of two years that accounts for 68 % of the total variance. Although the quasi-biannual cycle in the atmosphere has small amplitude in the lower layers of the atmosphere at East Mediterranean latitudes, the major cycle in annual series of δ²H or δ¹⁸O may be linked to the quasi-biannual oscillation in the atmosphere. It was also found that the first three empirical orthogonal functions (EOF) account for 72 % of the seasonal variation of δ²H and share 68 % of the seasonal variation of δ¹⁸O. Share of variances of monthly EOF in the months of the year indicate that the main underlying factors that cause fractionation processes for δ²H and δ¹⁸O are similar across the East Mediterranean especially in late winter and early spring. (author)

[en] The original version of this article unfortunately contained a mistake. Figures 4 and 5 captions were interchanged. The correct captions are given below.

[en] Equations 1–4 have been typed wrongly during the steps of corrections and some figures and tables are placed way too far from the citations.

[en] Current predictions of the effects of climate change indicate that the Arctic may experience a larger than average increase in temperature with consequent changes to the length of the snow-free active summer period, winter snow depth and amount and frequency of summer precipitation being highly probable. This paper reports on measurements of carbon dioxide flux at a high arctic site at Ny-Aalesund (78^o 56' N, 11^o 55' E), Svalbard and the physical climate variables that largely control this flux. lt is shown that during three important precipitation-free periods of the active summer period, namely post snow melt, high summer, and early autumn, the net balance between CO₂ flux from the soil (due to respiration of roots and soil organisms) and CO₂ assimilation by the vegetation is controlled largely by soil temperature and solar radiation. A simple combined photosynthetic assimilation-soil respiration model is shown to be capable of simulating the net CO₂ flux during mid-summer, but is less proficient in the post snow melt period and in early autumn when the simple models' inability to simulate the effects of emergent growth and ponding during the former and senescence, freezing temperatures and dew during the latter indicates the need for a more complex descriptive model. The net CO₂ flux during the measurement periods progresses from a net CO₂ source of 0.3 gC m^-2d^-1 during late snow melt to a mid summer net CO₂ sink of -0.39 gC m^-2d^-1, returning to a net CO₂ source of 0.1 gC m^-2d^-1 in the early autumn. Simple extrapolation of the data indicates that, during the active summer season in 1995, this site was a net sink of CO₂ of approximately -9 gC m^-2. (author)

[en] Changes were made in the 5th author name, section 4.3.2 Spatial variations of cloud fraction based on latitude, section 4.3.4 Spatial variations of cloud fraction based on vegetation cover, section 5 Summary and conclusions, and Table 3.

[en] Determining agro-climatic zones (ACZs) is traditionally made by cross-comparing meteorological elements such as air temperature, rainfall, and water deficit (DEF). This study proposes a new method based on correlations between monthly DEFs during the crop cycle and annual yield and performs a multivariate cluster analysis on these correlations. This ‘correlation method’ was applied to all municipalities in the state of São Paulo to determine ACZs for coffee plantations. A traditional ACZ method for coffee, which is based on temperature and DEF ranges (Evangelista et al.; RBEAA, 6:445–452, 2002), was applied to the study area to compare against the correlation method. The traditional ACZ classified the “Alta Mogina,” “Média Mogiana,” and “Garça and Marília” regions as traditional coffee regions that were either suitable or even restricted for coffee plantations. These traditional regions have produced coffee since 1800 and should not be classified as restricted. The correlation method classified those areas as high-producing regions and expanded them into other areas. The proposed method is innovative, because it is more detailed than common ACZ methods. Each developmental crop phase was analyzed based on correlations between the monthly DEF and yield, improving the importance of crop physiology in relation to climate.