| 摘要: |
| 大气降水δ18O值的空间分布可以为理解现代大气中的水分输送提供空间信息，也可以为解释古气候代用指标的环境意义提供基础。本文整理了黄土高原44个站点的实测降水δ18O数据，基于纬度和海拔构建回归模型并得到了黄土高原降水δ18O的同位素景观图谱，结合实测资料和图谱结果分析了降水δ18O的年内变化和空间分布特征，并评价了两种全球降水同位素景观图谱产品的适用性，得出以下结论：（1）黄土高原降水δ18具有明显的年内变化特征，春夏季相对富集，秋冬季较为贫化。（2）黄土高原降水δ18O高值区多出现在南部的渭河谷地一带，低值区则主要出现在西部高原山地和北部边缘。（3）黄土高原北部与西部降水δ18温度效应更为明显，向南和向东延伸，温度效应逐渐弱化。（4）两种全球降水同位素景观图谱产品对δ18值的最佳模拟结果均出现在夏季，冬季模拟较差。 |
| 关键词: 黄土高原 降水 氧稳定同位素 空间分布 |
| DOI：10.7515/JEE222017 |
| CSTR： |
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| 基金项目:甘肃省杰出青年基金项目（20JR10RA112）；国家自然科学基金项目（41971034）；陇原青年创新创业人才项目（甘组通字[2022]77号） |
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| Spatial distribution of δ18O in precipitation across the Loess Plateau |
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YANG Gahong, WANG Shengjie, ZHANG Mingjun
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1. College of Geography and Environmental Science, Northwest Normal University, Lanzhou 730070, China
2. Key Laboratory of Resource Environment and Sustainable Development of Oasis of Gansu Province, Northwest Normal University, Lanzhou 730070, China
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| Abstract: |
| Background, aim, and scope The spatial distribution of stable oxygen isotope compositions in precipitation provides geographical information for understanding the transport, mixing, moisture source, hydrological processes and phase transformation of water in the modern atmosphere, and is a spatial basis for interpreting the isotope characteristics in paleoclimatic proxy records. Located at a transition region from humid to an arid climate, the Loess Plateau has aroused a lot of attentions in tracing hydrological circulation using the stable water isotope technique, compared to the isotope-enable general circulation model, the interpolation-based method is more effective and convenient to produce global and regional isoscapes with relatively high spatial resolution. In past decades, a number of observations of stable oxygen isotopes in precipitation has been conducted across the Loess Plateau, which is useful to verify the existing global isoscape products and create an improved isoscape on a regional scale. Materials and methods The measured δ18O values in precipitation at 44 sampling stations with altitudes ranging from 381 m to 3553 m across the Loess Plateau were compiled, and the long-term mean data on a monthly basis were acquired for these stations. The δ18O isoscape of precipitation in the study area was established based on a regression model using latitude and altitude for each month in the geographic information system. Combining the regression-derived prediction and spatially interpolated residuals at the sampling stations, a monthly δ18O isoscape of precipitation in the Loess Plateau was produced. The observed and modelled isoscapes were spatially examined for different latitudes (southern, middle, and northern sections), longitudes (western, middle, and eastern sections) and altitudes (high, middle and low altitudes). The temperature effect of precipitation isotopes was also analyzed for different regions. The applicability of two global precipitation isotope products was assessed in the Loess Plateau, including the online isotopes in precipitation calculator (OIPC) and the regionalized cluster-based water isotope prediction (RCWIP), and other several measurement like root mean square error, mean absolute error and mean bias error were applied. Results The results show that: (1) the δ18O values across the Loess Plateau exhibit an obvious intra-annual variation, that is, the heavy isotopes are relatively enriched in spring and summer season and depleted in autumn and winter season. (2) The δ18O values in the Weihe River Valley of the southern section are generally higher, while the δ18O values in the western mountains and northern margins are relatively lower. (3) Temperature effect of precipitation isotopes is more obvious at the northern and western sections, and the effect shows a weakening trend from north (and west) to south (and east). (4) The best seasonal predictions of δ18O values for the two global isoscape products across the Loess Plateau are in summer, and the predictions are relatively weak in winter. Discussion The finding provides a scientific basis for future observation network improvement, and the identified areas with spatial diversity of precipitation isotope compositions should be focused on. Considering the altitude-dependent stable isotope compositions across the Loess Plateau, the future work is still needed at the high altitudes at the western margin where the precipitation is usually much depleted in heavy isotopes than the same latitudes. More monitoring along the altitude gradient is helpful to understand the spatial pattern of the mountainous region. Influenced by the monsoon, the precipitation events in winter are usually less than those in other seasons, causing the limited isotope composition records in winter. So the stable isotope composition in winter precipitation (mostly snowfall) should also be paid more attention. As observed in some cities like Lanzhou, the local topography and underlying surface may impact the stable isotopes in precipitation, and some local-scale observations may also provide useful information about the local land-atmosphere interaction and the representativeness of precipitation sampling. In addition, the spatial pattern of correlation coefficients between air temperature and stable isotope compositions indicated that the temperature effect of precipitation isotopes is not spatial consistent for the entire region. Conclusions The isoscape model based on latitude and altitude is effective to predict the spatial distribution of precipitation isotopes across the Loess Plateau. The observed and modelled δ 18O values show similarities on the relationship between isotopes and environmental parameters such as latitude, altitude and temperature. Recommendations and perspectives Precipitation isoscape greatly depend on the observed isotope input, and future observations at the mountainous regions are still needed to improve the isotope prediction. The newly produced isoscapes of δ18O values in this study show better predictions compared to previous global products and may provide a useful basis for climate, hydrological and ecological applications. |
| Key words: Loess Plateau precipitation stable oxygen isotope spatial distribution |
