Isotopic Ratios Of Precipitation Research Articles

Annual variation in event-scale precipitation <i>δ</i><sup>2</sup>H at Barrow, AK, reflects vapor source region

Abstract. In this study, precipitation isotopic variations at Barrow, AK, USA, are linked to conditions at the moisture source region, along the transport path, and at the precipitation site. Seventy precipitation events between January 2009 and March 2013 were analyzed for δ2H and deuterium excess. For each precipitation event, vapor source regions were identified with the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) air parcel tracking program in back-cast mode. The results show that the vapor source region migrated annually, with the most distal (proximal) and southerly (northerly) vapor source regions occurring during the winter (summer). This may be related to equatorial expansion and poleward contraction of the polar circulation cell and the extent of Arctic sea ice cover. Annual cycles of vapor source region latitude and δ2H in precipitation were in phase; depleted (enriched) δ2H values were associated with winter (summer) and distal (proximal) vapor source regions. Precipitation δ2H responded to variation in vapor source region as reflected by significant correlations between δ2H with the following three parameters: (1) total cooling between lifted condensation level (LCL) and precipitating cloud at Barrow, ΔTcool, (2) meteorological conditions at the evaporation site quantified by 2 m dew point, Td, and (3) whether the vapor transport path crossed the Brooks and/or Alaskan ranges, expressed as a Boolean variable, mtn. These three variables explained 54 % of the variance (p<0. 001) in precipitation δ2H with a sensitivity of −3.51 ± 0.55 ‰ °C−1 (p<0. 001) to ΔTcool, 3.23 ± 0.83 ‰ °C−1 (p<0. 001) to Td, and −32.11 ± 11.04 ‰ (p = 0. 0049) depletion when mtn is true. The magnitude of each effect on isotopic composition also varied with vapor source region proximity. For storms with proximal vapor source regions (where ΔTcool <7 °C), ΔTcool explained 3 % of the variance in δ2H, Td alone accounted for 43 %, while mtn explained 2 %. For storms with distal vapor sources (ΔTcool > 7°C), ΔTcool explained 22 %, Td explained only 1 %, and mtn explained 18 %. The deuterium excess annual cycle lagged by 2–3 months during the δ2H cycle, so the direct correlation between the two variables is weak. Vapor source region relative humidity with respect to the sea surface temperature, hss, explained 34 % of variance in deuterium excess, (−0.395 ± 0.067 ‰ %−1, p<0. 001). The patterns in our data suggest that on an annual scale, isotopic ratios of precipitation at Barrow may respond to changes in the southerly extent of the polar circulation cell, a relationship that may be applicable to interpretation of long-term climate change records like ice cores.

Can we determine what controls the spatio-temporal distribution of d-excess and <sup>17</sup>O-excess in precipitation using the LMDZ general circulation model?

Abstract. Combined measurements of the H218O and HDO isotopic ratios in precipitation, leading to second-order parameter D-excess, have provided additional constraints on past climates compared to the H218O isotopic ratio alone. More recently, measurements of H217O have led to another second-order parameter: 17O-excess. Recent studies suggest that 17O-excess in polar ice may provide information on evaporative conditions at the moisture source. However, the processes controlling the spatio-temporal distribution of 17O-excess are still far from being fully understood. We use the isotopic general circulation model (GCM) LMDZ to better understand what controls d-excess and 17O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM). The simulation of D-excess and 17O-excess is evaluated against measurements in meteoric water, water vapor and polar ice cores. A set of sensitivity tests and diagnostics are used to quantify the relative effects of evaporative conditions (sea surface temperature and relative humidity), Rayleigh distillation, mixing between vapors from different origins, precipitation re-evaporation and supersaturation during condensation at low temperature. In LMDZ, simulations suggest that in the tropics convective processes and rain re-evaporation are important controls on precipitation D-excess and 17O-excess. In higher latitudes, the effect of distillation, mixing between vapors from different origins and supersaturation are the most important controls. For example, the lower d-excess and 17O-excess at LGM simulated at LGM are mainly due to the supersaturation effect. The effect of supersaturation is however very sensitive to a parameter whose tuning would require more measurements and laboratory experiments. Evaporative conditions had previously been suggested to be key controlling factors of d-excess and 17O-excess, but LMDZ underestimates their role. More generally, some shortcomings in the simulation of 17O-excess by LMDZ suggest that general circulation models are not yet the perfect tool to quantify with confidence all processes controlling 17O-excess.

Lead and sulfur isotopic ratios in precipitation and their relations to trans-boundary atmospheric pollution

We measured the lead (Pb) and sulfur (S) isotopic ratios in precipitation collected in Toyama Prefecture, Japan, to investigate their characteristics as tracers for trans-boundary air pollution. The Pb concentrations and isotopic ratios were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). A relatively higher 207Pb/206Pb isotopic ratio (area 3: Northern China, 0.869±0.003; area 4: Central China and Korea, 0.870±0.006) was assumed to be related to Northern Asian sources, whereas the samples influenced by Japanese air mass showed a lower 207Pb/206Pb ratio (area 5: Japan, 0.863±0.004). Sulfur ion was measured by Ion Chromatography (IC), and S isotopic ratios were measured by Mass Spectrometry. The S isotopic ratios' weighted average values (area 3: 4.9±1.4‰; area 4: 6.3±1.5‰) of the Asian continent showed a higher isotopic ratio than that of Japan (area 5: 3.6±1.8‰). It was difficult to use the NO3−/non-sea-salt SO42− (nss SO42−) (N/S) ratio's weighted average values to distinguish the Japanese origin (area 5: 0.71) from the continental origin (area 3: 0.68, area 4: 0.66). We attempted to use the S isotopic ratio in addition to the lead isotopic ratio to characterize the transported East Asian air pollution, and as a result we found that the combination of these isotopic ratios was useful for identifying the origin of air pollution in the East Asian region.

Stable isotope ratios in precipitation and their relationship with meteorological conditions in the Kumaon Himalayas, India

Summary For the first time, environmental isotopic (δ2H, δ18O, 3H) data, predominantly based on precipitation samples in the Kumaon Himalayas, India, have been used to understand the influence of various meteorological factors governing rainout processes in the region. Further, the data are also used to understand the orographic effects in precipitation and to estimate the altitude effect in stable isotopic ratios in precipitation, etc. The interpretation of the isotopic data revealed that the source of moisture for winter (October–February) and summer (May) precipitation in the Kumaon Himalayas is mainly from the Western Disturbances whereas for the remaining period the source is monsoonal (southwest). The δ2Η−δ18O relationship in the local precipitation during the monsoon season shows a distinct seasonal effect, with a slope of 7.6. The winter and summer precipitation samples measured higher environmental 3H compared to southwest monsoon samples, thus indicating continental evaporated moisture. There is wide range of altitude effects (δ18O variation per 100 m elevation: −0.30‰ [July–August]; −0.57‰ [September]) with the mean altitude effect being −2.61‰ and −0.36‰ per 100 m elevation for δ2H and δ18O respectively. These values are different from that reported earlier for the region based on the isotopic compositions of springs/rivers samples. The ‘altitude effect’ in successive precipitation is basically a temperature dependent phenomenon and is explained on the basis of adiabatic cooling related rainout process (dry adiabatic lapse rate, moist adiabatic lapse rate and saturated adiabatic lapse rate for moist air mass). The altitude effect is found to be more reliable in case of δ2Η, as deuterium is least affected by secondary evaporation. The effect of secondary evaporation has been observed on the true “altitude effect”. Secondary evaporation of rainfall increases the oxygen isotopic ratios and the increase is directly proportional to the vertical distance travelled by the raindrops through air.

Relations between oxygen stable isotopic ratios in precipitation and relevant meteorological factors in southwest China

The correlations of isotopic ratios in precipitation with temperature, air pressure and humidity at different altitudes, in southwest China, are analyzed. There appear marked negative correlations for the δ 18O in precipitation with precipitation amount, vapor pressure and atmospheric precipitable water (PW) at Mengzi, Simao and Tengchong stations on synoptic timescale; the marked negative correlations between the δ 18O in precipitation and the diurnal mean temperature at 400 hPa, 500 hPa, 700 hPa and 850 hPa are different from the temperature effect in middle-high-latitude inland. Moreover, the notable positive correlation between the δ 18O in precipitation and the dew-point deficit ΔT d at different altitudes is found at the three stations. On annual timescale, the annual precipitation amount weighted mean δ 18O display the negative correlations not only with annual precipitation but also with annual mean temperature at 500 hPa. It can be deduced that, in the years with abnormally strong summer monsoon, more warm and wet air from low-latitude oceans is transported northward along the vapor channel located in southwest China and generates abnormally strong rainfall on the way. Meanwhile, the abnormally strong condensation process will release more condensed latent heat into atmosphere, and lead to the rise of atmospheric temperature during rainfall, but decline of the δ 18O in precipitation. On the contrary, in the years with abnormally weak summer monsoon, the abnormally weak condensation process will release less condensed latent heat into atmosphere, and lead to the decline of atmospheric temperature during rainfall, but increase of the δ 18O in precipitation.

Iodine-129: Sample preparation, quality control and analyses of pre-nuclear materials and of natural waters from Lower Saxony, Germany

Sample preparation procedures for AMS measurements of 129I and 127I in environmental materials and some methodological aspects of quality assurance are discussed. Measurements from analyses of some pre-nuclear soil and thyroid gland samples and of a systematic investigation of natural waters in Lower Saxony, Germany, are described. Although the up-to-now lowest 129I/ 127I ratios in soils and thyroid glands were observed, they are still suspect to contamination since they are significantly higher than the pre-nuclear equilibrium ratio in the marine hydrosphere. A survey on all available 129I/ 127I isotopic ratios in precipitation shows a dramatic increase until the middle of the 1980s and a stabilization since 1987 at high isotopic ratios of about (3.6–8.3)×10 −7. In surface waters, ratios of (57–380)×10 −10 are measured while shallow ground waters show with ratios of (1.3–200)×10 −10 significantly lower values with a much larger spread. The data for 129I in soils and in precipitation are used to estimate pre-nuclear and modern 129I deposition densities.

Hydrogen and Oxygen Isotopic Ratios in Precipitation, River and Groundwaters in the Eastern area of the Hiei mountains

Hydrogen and Oxygen Isotopic Ratios in Precipitation, River and Groundwaters in the Eastern area of the Hiei mountains

Isotopic measurements of precipitation on central Asian glaciers (southeastern Tibet, northern Himalayas, central Tien Shan)

The glacial regions of central Asia considered in our study are influenced by tropical monsoons and western extratropical cyclones. Isotopic δ18O and δD data were obtained over 3 years in three climatic regions: Gongga massif of southeastern Tibet (windward slope of summer monsoon), Xixibangma massif on the northern slope of the Himalayas (leeward of summer monsoon), and the massifs of Pobeda‐Khan Tengry in the central Tien Shan (exposed to western airstreams). The survey reported here provides information from atmospheric precipitation, snow pits and a 23 m ice core. The significant differences of oxygen isotopic ratios (from −25.1 per mil to −9.5 per mil) indicate that the Indian and Pacific Oceans as well as the Atlantic Ocean are sources of moisture on the northern slope of the Himalayas and southeastern Tibet. Sharply changing isotopic ratios in precipitation corresponded to changing wind direction and were associated with different sources of air masses on the northern slope of the Himalayas and southeastern Tibet. Steady isotopic ratios in atmospheric precipitation and the absence of changing δ18O composition in a 23 m ice core suggest only one source of moisture in central Tien Shan. The relatively heavier oxygen isotopic ratios in atmospheric precipitation and ice core indicate the moisture from which the precipitation was derived originated over the Caspian or Mediterranean seas. Within the Eurasian continent, air masses developed over the Atlantic Ocean advance farther than those from the Pacific and Indian Oceans.