Extreme short-term stable isotope variability revealed by continuous rainwater analysis (original) (raw)
Related papers
Journal of Geophysical Research, 2009
1] A unified approach of observation and modeling was applied to the investigation of three circulation types that typically bring rain to southeastern Australia. Observations from the Melbourne University Network of Isotopes in Precipitation of high-resolution variations in the ratios of 18 O and 2 H were collected for (1) mixed frontal, (2) convective, and (3) stratiform precipitation events. Isotopic content of precipitation varied over both high and low frequencies because of influences from local variations in rain intensity and rainout by large-scale precipitation. Deuterium excess showed a weak relationship with rainfall amount on intraevent time scales but was stronger under convective rainfall conditions. As a supplement to the observations, a version of the National Center for Atmospheric Research Community Atmosphere Model running an isotope hydrology scheme simulated the mixed frontal and stratiform events by nudging with reanalyses. The simulations represented well the evolution of vapor profiles of 18 O and deuterium excess. Trajectories for the mixed frontal case illustrated the structure of the vapor profiles, revealing a convergence of air masses from different source regions. Deuterium excess in precipitation was represented less accurately by the model, indicating a possible shortcoming in the parameterization of postcondensation processes in the general circulation model. By combining observations and modeling in this way, detail of the structure and history of the events was provided that would be unavailable from the sampling of precipitation alone.
Spatial and temporal variation in precipitation isotopes in the Sydney Basin, Australia
Journal of Hydrology, 2013
The δ 2 H and δ 18 O composition of 816 precipitation samples collected between February 2005 and October 2009 from four sites across the Sydney Basin, Australia, were analysed, representing the first published precipitation isotope dataset for the region. Monthly values, weighted averages and local meteoric water lines are presented for use in hydrological applications. The four year precipitation weighted average values ranged from δ 2 H=−20.16‰, δ 18 O=−4.50‰ and d=15.88‰ for Lucas Heights in the coastal region to δ 2 H=−29.48‰, δ 18 O=−5.97‰ and d=18.33‰ for Mt Werong in the highlands west of Sydney. For the Sydney Basin as a whole we recommend an overall local meteoric water line of δ 2 H=8.01±0.05·δ 18 O+16.8±0.3. Precipitation in the Sydney Basin is isotopically different from the nearest GNIP sites with a significantly higher D-excess. High D-excess values may be the result of low humidity at the sea surface during evaporation at mid latitude sources, however recycling of moisture either locally or along a moisture transport trajectory may also be an important factor. A clear coastal effect was observed but generally temperature and amount effects were found to be weak. Please download published original from http://dx.Please download published original from http://dx.
Journal of Tropical Forest Science, 2017
We present the temporal variability of the oxygen (δ 18 O) and hydrogen (δ 2 H) isotope signatures in precipitation at Pasoh Forest Reserve (FR), a tropical rainforest in Peninsular Malaysia. We investigated the daily and seasonal variability of stable isotope signatures in precipitation, particularly in relation to the effects of monsoon seasons, rainfall characteristics and larger scale trends compared with those at nearby Global Network of Isotopes in Precipitation (GNIP) monitoring stations. The isotope signatures did not differ between monsoon seasons but were correlated with amount of rainfall, its intensity and duration. The effect of amount of rainfall on isotope composition was clearly detected and comparable with long-term mean monthly statistics of nearby GNIP stations. Unfortunately the effect was obscured at the daily timescale and, for monthly rainfall, not averaged over the long-term. No large deuterium excess was detected at the daily timescale for small-scale rainfall events. The δ 18 O in precipitation water was more closely correlated with the 60-day antecedent rainfall index than with the amount of rainfall each day. These findings suggested that the isotopic composition in the study area was the result of a rainout on a larger scale in addition to the local scale and specific rain events.
Data Descriptor: Daily observations of stable isotope ratios of rainfall in the tropics
Nature Scientific Reports, 2019
We present precipitation isotope data (δ 2 H and δ 18 O values) from 19 stations across the tropics collected from 2012 to 2017 under the Coordinated Research Project F31004 sponsored by the International Atomic Energy Agency. Rainfall samples were collected daily and analysed for stable isotopic ratios of oxygen and hydrogen by participating laboratories following a common analytical framework. We also calculated daily mean stratiform rainfall area fractions around each station over an area of 5° x 5° longitude/latitude based on TRMM/GPM satellite data. Isotope time series, along with information on rainfall amount and stratiform/convective proportions provide a valuable tool for rainfall characterisation and to improve the ability of isotope-enabled Global Circulation Models to predict variability and availability of inputs to fresh water resources across the tropics. Background & Summary. This database is an outcome of the International Atomic Energy Agency's (IAEA)
Global and Planetary Change, 2006
An integral part of isotopes in the Program for Intercomparison of Land-surface Parameterisation Schemes (iPILPS) [Henderson-Sellers, A., in press. Improving land-surface parameterization schemes using stable water isotopes; introducing the iPILPS initiative. Global and Planetary Change, in press] is that the models' outputs be evaluated against measured values of δ 2 H and δ 18 O in the various simulated environmental compartments. This paper outlines the steps taken in Australia to initiate measurement of these stable water isotopes (SWIs) in the field, at a cool-temperate forest site in S.E. Australia near Tumbarumba, specifically to facilitate the model evaluation process. The selected sampling methodologies are detailed within the context of a conceptual model developed to describe the land-atmosphere exchange systems. This model has also been used to make a priori estimations of the isotopic values to be expected in each measured sub-system. As the data resulting from the Tumbarumba field campaign emerge, they will be compared with these working hypotheses to evaluate and, where necessary, amend the conceptual model. Initial comparisons based on preliminary data are presented here. The new observations derived in March 2005 should allow the land surface schemes used in weather forecast and climate change models to better reflect the environments for which they are attempting to make predictions.
Water isotopes in precipitation
Quaternary Science Reviews, 2000
O concentrations are observed in precipitation both on a geographical and on a temporal basis. These variations, resulting from successive isotopic fractionation processes at each phase change of water during its atmospheric cycle, are well documented through the IAEA/WMO network. Isotope concentrations are, in middle and high latitudes, linearly related to the annual mean temperature at the precipitation site. Paleoclimatologists have used this relationship to infer paleotemperatures from isotope paleodata extractable from ice cores, deep groundwater and other such sources. For this application to be valid, however, the spatial relationship must also hold in time at a given location as the location undergoes a series of climatic changes. Progress in water isotope modeling aimed at examining and evaluating this assumption has been recently reviewed with a focus on polar regions and, more speci"cally, on Greenland. We extend this review in comparing the results of two di!erent isotopic AGCMs (NASA/GISS and ECHAM) and in examining, with a more global perspective, the validity of the above assumption, i.e. the equivalence of the spatial and temporal isotope}temperature relationships. These results con"rm the dominating role of local temperature changes on the paleo isotope signal in most regions. However, the exact calibration of this valuable paleothermometer is biased by, for example, the seasonality of precipitation and other factors. We forced the two models by the climatic boundary conditions of the mild-holocene at 6 kyr BP which only slightly di!ers from today's climate. The isotope response on this weak forcing is quite heterogeneous. The only robust common response is the intensi"cation of the hydrological cycle in low latitudes and, therefore, isotopically more depleted precipitation in the tropics and subtropics. We also examine recent progress made in modeling: the relationship between the conditions prevailing in moisture source regions for precipitation and the deuterium excess of that precipitation.
Hydrology and Earth System Sciences, 2015
In the Asian monsoon region, variations in the stable isotopic composition of speleothems have often been attributed to the "amount effect". However, an increasing number of studies suggest that the "amount effect" in local precipitation is insignificant or even non-existent. To explore this issue further, we examined the variability of daily stable isotopic composition (δ 18 O) in precipitation from September 2011 to November 2014 in Nanjing, eastern China. We found that intra-seasonal variations of δ 18 O during summer were not significantly correlated with local rainfall amount but could be linked to changes in the moisture source location and rainout processes in the source regions. Our findings suggest that the stable isotopes in summer precipitation could signal the location shift of precipitation source regions in the inter-tropical convergence zone (ITCZ) over the course of the monsoon season. As a result, changes in moisture source location and upstream rainout effect should be taken into account when interpreting the stable isotopic composition of speleothems in the Asian monsoon region. In addition, the temperature effect on isotopic variations in non-monsoonal precipitation should also be considered because precipitation in the non-monsoon season accounts for about half of its annual precipitation.
Annual, monthly and daily analyses of stable isotopes in precipitation are commonly made worldwide, yet only a few studies have explored the variations occurring on short timescales within individual precipitation events, particularly at mid-latitude locations. This study examines hydrogen isotope data from sequential, intra-event samples from sixteen precipitation events during different seasons and a range of synoptic conditions over an 18-month period in Birmingham, UK. Precipitation events were observed simultaneously using a vertically-pointing micro rain radar (MRR), which, for the first time at a mid-latitude location, allowed high resolution examination of the microphysical characteristics (e.g. rain rate, fall velocity, drop size distributions) that may influence the local isotopic composition of rainwater. The range in δD from 242 samples from 16 events was -87.0‰ to +9.2‰, whilst the largest variation observed in a single event was 55.4‰. In contrast to previous work, the results indicate that some mid-latitude precipitation events do indeed show significant intra-event trends that are strongly influenced by precipitation processes and parameters such as rain rate, melting level height and droplet sizes. Inverse relationships between rain rate and isotopic composition are observed, representing an example of a local type of ‘amount effect’, a still poorly-understood process occurring at different scales. For these particular events the mean δ value may therefore not provide all the relevant information. This work has significance for the testing and development of isotope-enabled cloud resolving models and land surface models at higher resolutions, and provides improved insights into a range of environmental processes that are influenced by sub-sampled precipitation events.
Correction to “Stable isotopic compositions in Australian precipitation”
Journal of Geophysical Research, 2011
Stable deuterium (dD) and oxygen-18 (d 18 O) isotopes in 1962 to 2002 precipitation from the seven Australian stations of the Global Network of Isotopes in Precipitation (GNIP) were used to investigate isotope characteristics including temporal and spatial distributions across different regions of Australia. On the basis of 1534 samples, the local meteoric water line (LMWL) was established as dD = 7.10d 18 O + 8.21. d 18 O showed a depletion trend from north and south to central Australia (a continental effect) and from west to east. Precipitation amount effects were generally greater than temperature effects, with quadratic or logarithmic correlations describing d/T and d/P better than linear relationships. Nonlinear stepwise regression was used to determine the significant meteorological control factors for each station, explaining about 50% or more of the d 18 O variations. Geographical control factors for d 18 O were given by the relationship d 18 O (‰) = −0.005 longitude (°) − 0.034 latitude (°)-0.003 altitude (m) − 4.753. Four different types of d-excess patterns demonstrated particular precipitation formation conditions for four major seasonal rainfall zones. Finally, wavelet coherence (WTC) between d 18 O and SOI confirmed that the influence of ENSO decreased from east and north to west Australia.
Seasonality of isotopes in precipitation: A global perspective
Journal of Geophysical Research, 2009
1] We use data from Global Network of Isotopes in Precipitation (GNIP) database to explore how the atmosphere's meridional circulation cells control the latitudinal and seasonal distribution of d 18 O and d-excess in precipitation. We demonstrate that the atmospheric general circulation (AGC) cells determine variations of zonally averaged isotopic composition of meteoric water; the local isotopic minimum near the equator coincides with the intertropical convergence (ITC), and two maxima on either side of the ITC coincide with the subtropical highs (STHs). Both the ITC and STHs migrate cum sole, as part of the systematic annual migration of the meridional cells. This migratory circulation pattern controls the phase of the annual oscillation of the precipitation d 18 O. At latitudes equatorward of the STHs, d 18 O reaches its maximum in the winter of the respective hemisphere and at higher latitudes in the summer. From the monthly latitudinal distribution of the vertical velocity at the 500-hPa level, we obtain the seasonal variations of the latitudinal positions of the subtropical moisture source regions and their climates. The sea surface temperature and relative humidity at the moisture source regions are used to predict seasonal changes of the d-excess of water vapor evaporated from the source regions. The GNIP data is consistent with the predicted phase of the d-excess. However, the observed magnitude of the seasonal oscillation is greater than the predicted values. This work provides a baseline for understanding the influence of subtropical moisture source regions and other climatological factors on the d-excess.