Linking the karst record to atmospheric, precipitation, and vegetation dynamics in Portugal
Linking the karst record to atmospheric, precipitation, and vegetation dynamics in Portugal
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DOI：
10.1016/j.chemgeo.2020.119949
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发表时间：
2020-12
期刊：
影响因子：
3.9
通讯作者：
Diana L. Thatcher;A. Wanamaker;R. Denniston;C. Ummenhofer;F. Regala;Nuno Jorge;Jonathan A. Haws;Alaina G. Chormann;D. Gillikin
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文献类型：
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作者：
Diana L. Thatcher;A. Wanamaker;R. Denniston;C. Ummenhofer;F. Regala;Nuno Jorge;Jonathan A. Haws;Alaina G. Chormann;D. Gillikin
洞穴沉积可能是古气候数据的宝贵来源，特别是当大气环流模式、降水变异性、植被变化以及流经岩溶环境的水的化学演变可以从机械上与洞穴沉积物代理联系在一起的时候。特别是，需要对控制降水同位素组成和雨水从陆地表面向洞穴迁移过程中的演变的因素进行评估，以有力地发展洞穴作为对水文气候敏感的指标。降水和大气变化密切相关的一个地区是伊比利亚西部，那里的降雨量受到北大西洋涛动(NAO)偶极子亚速尔高压的强烈影响。因此，为了更好地表征影响葡萄牙降水同位素组成的因素，并评估利用该地区的石笋作为水文气候(和NAO敏感)指标的可能性，我们调查了葡萄牙大陆十个地点数十年来的全球降水同位素网络(GNIP)数据。此外，我们使用了不止一个水文年的降雨量和来自葡萄牙西部洞穴Buraca Gloriosa(BG)的同位素数据、正在进行的洞穴分析以及BG六年的环境监测。通过归一化植被指数(NDVI)对极端干旱和极端潮湿冬季的降雨量和植被进行综合分析。夏季植被密度与前一个冬季雨季的降雨量以及先前的方解石降水有关，将在很大程度上控制BG石笋中稳定的碳同位素特征(δ13C)。冷季补给可能是洞穴系统渗漏水氧同位素组成(δ18O)的主导因素，而水量效应对降水δ18O值起主要控制作用。根据HYSPLIT模型，绝大多数水汽来源来自大西洋，而不是地中海或其他地方；因此，降水中δ18O值的变化(由此推断，滴水和石笋的值也是如此)主要反映了降水量的变化，而不是温度或源区的变化。这些数据共同构成了对葡萄牙洞穴系统中同位素替代品控制的重要分析。
Cave deposits can be valuable sources of paleoclimate data, especially when atmospheric circulation patterns, precipitation variability, vegetation changes, and the chemical evolution of waters moving through the karst environment can be mechanistically linked to speleothem proxies. In particular, an evaluation of the factors that control the isotopic composition of precipitation and the evolution of rainwater during migration from the land surface to the cave are needed to robustly develop speleothems as hydroclimate-sensitive proxies. One area in which precipitation and atmospheric variability are closely linked is western Iberia, where rainfall is strongly influenced by the Azores High, part of the North Atlantic Oscillation (NAO) dipole. Therefore, in order to better characterize the factors that influence the isotopic composition of precipitation in Portugal and to evaluate the potential of using stalagmites from this region as hydroclimate (and NAO-sensitive) proxies, we investigated Global Network of Isotopes in Precipitation (GNIP) data from ten mainland Portugal sites spanning multiple decades. In addition, we use more than one hydrologic year of precipitation amount and isotope data from Buraca Gloriosa (BG), a cave in western Portugal, the site of on-going speleothem analyses, as well as six years of environmental monitoring from BG. We present an integrated analysis of rainfall and vegetation through the normalized difference vegetation index (NDVI) following extremely wet and dry winters. Summer vegetation density, related to the amount of precipitation in the preceding winter wet season, as well as prior calcite precipitation (PCP), would largely control the stable carbon isotopic signature (δ13C) in stalagmites at BG. Cool season recharge is likely the dominant factor for the oxygen isotopic composition (δ18O) of water percolating through the cave system, while amount effects exert the primary control on precipitation δ18O values. Based on HYSPLIT modeling, moisture sources overwhelmingly originate from the Atlantic Ocean as opposed to the Mediterranean or elsewhere; thus, variability in δ18O values in the precipitation (and, thus, by inference, those of the dripwater and stalagmites) are primarily reflecting changes in precipitation amount and not changing temperatures or source regions. Together these data constitute an important analysis of the controls of isotope proxies in Portuguese cave systems.