Kazimierz Rozanski

Stable isotope composition of precipitation over southeast Asia

Spatial and temporal variability of the stable isotope composition of precipitation in the southeast Asia and western Pacific region is discussed, with emphasis on the China territory, based on the database of the International Atomic Energy Agency/World Meteorological Organization Global Network Isotopes in Precipitation and the available information on the regional climatology and atmospheric circulation patterns. The meteorological and pluviometric regime of southeast Asia is controlled by five different air masses: (1) polar air mass originating in the Arctic, (2) continental air mass originating over central Asia, (3) tropical-maritime air mass originating in the northern Pacific, (4) equatorial-maritime air mass originating in the western equatorial Pacific, and (5) equatorial-maritime air mass originating in the Indian Ocean. The relative importance of different air masses in the course of a given year is modulated by the monsoon activity and the seasonal displacement of the Intertropical Convergence Zone (ITCZ). Gradual rain-out of moist, oceanic air masses moving inland, associated with monsoon circulation, constitutes a powerful mechanism capable of producing large isotopic depletions in rainfall, often completely overshadowing the dependence of δ 18 O and δ 2 H on temperature. For instance, precipitation at Lhasa station (Tibetan Plateau) during rainy period (June-September) is depleted in 18 O by more than 6 ‰ with respect to winter rainfall, despite of 10°C higher surface air temperature in summer. This characteristic isotopic imprint of monsoon activity is seen over large areas of the region. The oceanic air masses forming the two monsoon systems, Pacific and Indian monsoon, differ in their isotope signatures, as demonstrated by the average δ 18 O of rainfall, which in the south of China (Haikou, Hong Kong) is about 2.5‰ more negative than in the Bay of Bengal (Yangoon). Strong seasonal variations of the deuterium excess values in precipitation observed in some areas of the studied region result from a complete reversal of atmospheric circulation over these areas and changing source of atmospheric moisture. High d-excess values observed at Tokyo and Pohang during winter (15-25‰) result from interaction of dry air masses from the northern Asian continent passing the Sea of Japan and the China Sea and picking up moisture under reduced relative humidity. The isotopic composition of precipitation also provides information about the maximum extent of the ITCZ on the continent during summer.

Isotope effects accompanying vacuum extraction of soil water for stable isotope analyses

Abstract The vacuum distillation method of extracting soil water for stable isotope analysis was tested for three different types of soil characterized by high water content: (1) pure sand, (2) cambisol with high organic matter content, developed on calcareous sandstone under temperate climatic conditions (Austria), and (3) tropical latosol poor in organic matter, developed on sandy clay sediment (Brazil). The method yields accurate and reproducible results for sand, provided that more than 98% of the original soil water is extracted. The time required for complete extraction is a function of sample size and the applied extraction temperature. Column experiments with the clayey soils revealed existence of a weakly bound, easily exchangeable pool of water which is isotopically different from the mobile water. The experiments showed that the extracted soil water is depleted in both deuterium and oxygen-18 by 5–10% and 0.3–0.5%, respectively, when compared with the percolate (mobile water). This depletion depends strongly on the soil type. The reproducibility for replicate extractions of soil water from clayey soils is around ±3% and 0.3% for δD and δ 18 O, respectively.

High-resolution lacustrine record of the late glacial/holocene transition in central Europe

Abstract In this paper we present the high-resolution record of proxy climatic data in central Europe during the final stages of the last deglaciation, derived from the annually laminated sediments of Lake Gościaz (central Poland). The isotopic, palynological and other microfossil data confirm sudden changes of climate at the onset and termination of the Younger Dryas (completed within 150 and 70 years, respectively), in close agreement with the previous estimates derived from the polar ice cores and marine sediments. In the upper YD some amelioration of climate took place already about 600 years before the main YD/Preboreal transition. Counting of annual varves in the lake sediments allows a direct estimate of the duration of the Younger sDryas in central Europe; it lasted approximately 1640 years, substantially longer than suggested by previous estimates derived from laminated lake sediments and glacial varves, but agreeing with the radiocarbon calibration data obtained for Barbados corals. The calendar ages of the boundaries of the YD, 12,920 and 11,280 cal BP, are tentatively set.

Chapter 7 – Isotopes in Groundwater Hydrology

Publisher Summary The concentration of stable isotopes in groundwater depends mainly on the origin of the water. The concentration of radioactive isotopes and dissolved compounds in groundwater depends on the initial concentration and residence time of groundwater in the aquifer. These two factors determine the amount of radioactive isotope(s) decayed, removed, or added during water-rock processes. As geochemical tools, stable and radioactive environmental isotopes provide information on the geochemical processes operating on groundwater and on the hydrogeological characteristics of aquifers. Information provided by environmental isotopes is also useful in modeling groundwater systems. This chapter discusses the scientific background of applications of environmental isotope techniques to groundwater hydrology. The stable isotope composition of groundwater reflects that of the precipitation in the recharge area that seeps through the soil and the unsaturated zone to reach the water table. Stable isotopes are often used to identify groundwater recharge by rivers and lakes. These water bodies frequently have isotopic compositions different from that of precipitation over the study area.

Natural radiocarbon measurements in Brazilian soils developed on basic rocks.

This paper presents 14 C, 13 C and chemical data of soil organic matter (SOM) in three soil profiles under native forests from Brazil: Londrina (southern), Piracicaba (southeastern) and Altamira (northern). The main objective is to use carbon isotopes in tropical and subtropical soils of Brazil to provide information about vegetation changes that occurred in relation to climate changes during the Holocene. 14 C data from SOM indicate that the organic matter in the soils studied is of at least Holocene age. 13 C data indicate that C 4 plants probably provided the dominant vegetation in Londrina and Piracicaba during the early and mid-Holocene and that C 3 plants provided the dominant vegetation in the Altamira region during the Holocene.

Interaction of dredging lakes with the adjacentgroundwater field: an isotope study

Abstract The paper presents the results of a study aimed at determining the water balance of small dredging lakes located in the temperate climatic zone (southern Austria) and their impact on the adjacent groundwater field using heavy stable isotopes of water, deuterium and oxygen-18. The isotope method of determining water balance of groundwater-controlled lakes was examined in some detail using the field data collected during this study. The calculations performed for different sets of input data revealed that the approach recommended in the literature, i.e. the use of oxygen-18 data, the air-based temperatures and the mean isotopic composition of evaporation flux calculated from the annual mean isotopic composition of precipitation assuming isotope equilibrium at the ground-level temperature, may lead to groundwater inflow rates which are underestimated by as much as 40%. The isotope-mass balance calculations performed independently for deuterium and oxygen-18 data can be reconciled within the overall uncertainty of the method, when the surface water temperature of a lake (with relative humidity adjusted accordingly) is used instead of ground-level air temperature, and the isotopic composition of the evaporation flux is adequately averaged, taking into account the seasonal variability of this flux for the given lake system. The sensitivity analysis of the isotope-mass balance calculations performed for the studied lake system suggests that the critical parameter for the overall accuracy of the method is the isotopic composition of the lake water and, to a lesser extent, of the subsurface inflow, in cases where the isotope enrichment of lake water is relatively small. In the studied case this enrichment reached only about 20% of the isotopic composition of the input. In general, the use of isotope-mass balance for determining subsurface inflow and outflow rates to dredging lakes would require a rather extensive monitoring of isotope and hydrological parameters of the studied system, performed on a monthly basis for at least one full hydrological year. The isotope and geochemical data gathered in the present study were used to derive mixing proportions of lake water with the downgradient groundwater field. The plume of the lake water could be traced up to about 4 km from the lakes, along the general direction of groundwater flow.

Six-year record of atmospheric carbon dioxide and methane at a high-altitude mountain site in Poland

Carbon dioxide and methane observations from the continental mountain station Kasprowy Wierch in the Tatra Mountains, southern Poland, are presented. They cover a six-year period from 1994 to 2000. Significant year-to-year variability of CO2 concentration was observed. The seasonal cycles 1996–1997 were similar, with a peak-to-peak amplitude of the selected and smoothed CO2 record of approximately 20 ppm and no significant increase of the annual mean values. For 1998 and 1999 large increases of the annual mean values by 3.3 and 4.0 ppm per year, respectively, were observed. This increase was accompanied by a reduction of the seasonal amplitude of the smoothed record to approximately 15 ppm in 1998 and 16 ppm in 1999. In 2000 the seasonal amplitude increased again to a value similar as in 1996/1997, whereas the mean annual value remained close to that recorded for 1999. Similar features can also be traced in the selected and smoothed CO2 record for Schauinsland station, Germany, located ca. 1000 km west of Kasprowy Wierch. These similarities strongly suggest that both stations are capturing the same large-scale European phenomena, most probably related to a disturbance of the CO2 cycle by the recent El Niño event. The mean CH4 mixing ratio at Kasprowy Wierch for the period 1996–1999 was about 30 ppb higher than over the Atlantic Ocean, confirming previous observations that the European continent is a net source of methane throughout the year. No significant seasonal cycle of methane has been observed at Kasprowy Wierch. The short-term changes of CO2 and CH4 are strongly correlated during winter months: the average monthly mean slope of the linear relationship between CH4 and CO2 was 10.7 ± 0.3 ppbCH4 per ppmCO2. During summer months this strong correlation breaks down. Diurnal changes of CO2 and CH4 mixing ratios observed at Kasprowy Wierch are typical for continental mountain sites, with a distinct minimum of CO2 during afternoon hours in summer and maximum during winter. For CH4, diurnal cycles have similar shape throughout the year, with a broad maximum during daytime. The mean peak-to-peak amplitudes for summer (July) were 4.5 ppm for CO2 and 30 ppb for CH4, whereas during winter (February) they diminished to 1.5 ppm and 10 ppb, respectively.

Atmospheric 14CO2 variations in the equatorial region

We present here first results of 14C02 monitoring at two sampling sites in the equatorial region of the South American continent (station Aychapicho, Ecuador and station Llano del Hato, Venezuela). We also include the data for two other stations representing undisturbed marine atmosphere at mid-latitudes of both hemispheres, far from large continental sources and sinks of CO2 (station Izana, Tenerife, Spain and station Cape Grim, Tasmania). Between 1991 and 1993,14C02 levels in the tropical troposphere were generally higher by 2-5%o when compared to mid-latitudes of both hemispheres. This apparent maximum of 14C in the tropics can be explained by two major factors: 1) emissions of 14C-free fossil fuel C02, restricted mainly to mid-latitudes of the northern hemisphere; and 2)14C depletion due to gas exchange with circumpolar Antarctic upwelling water, influencing mainly mid- and high southern latitudes. The e14C record so far available for the Aychapicho station provides direct evidence for a regional reduction of atmospheric 14C02 levels due to gas exchange with 14Cdepleted equatorial surface ocean in the upwelling regions and dilution with the 14C-depleted CO2 released in these areas. Recurrent ENSO events, turning on and off the 14C-depleted CO2 source in the tropical Pacific, lead to relatively large temporal variations of the atmospheric 14C level in this region.

Intercalibration of environmental isotope measurements; the program of the International Atomic Energy Agency.

ABSTRACT. We briefly present here the environmental isotope intercalibration programs of the International Atomic Energy Agency (IAEA). In fact, the IAEA has implemented two parallel programs during the last 20 years: for stable isotopes of light elements and for a radioactive isotope of hydrogen, tritium. This IAEA activity resulted in the preparation of a number of reference and intercomparison materials of various types, now stored in the Agency and available upon request.