大含水层地下水中古气候变化信息的提取与重构-以雷州半岛为例

Groundwater abstraction in many aquifers worldwide has surpassed a sustainable yield. Increased need of water for human consumption and irrigation increases the water demand continuously. In some cases very limited modern recharge takes place with available groundwater recharged over long time and under very different climates in the past. Some of these groundwater systems may be used as palaeoclimate proxies, with information about major recharge episodes in the past. This is particularly true for low-recharge aquifers, where groundwater often has long transit times. The stored information in these groundwater systems may record climatic information such as groundwater recharge temperature, rainfall sources and rainfall intensities. Linked to a chronological record these provide a framework to assess aquifer recharge-history and its vulnerability or resilience to future climatic changes or increased groundwater extraction. These are two key scientific questions to be addressed and major tasks of the proposal to identify the recharge periods and relevant changes in temperature and precipitation intensity in the large groundwater aquifers in the Northern China and Leizhou Peninsula..A) Use isotopic and geochemical data available from large aquifers to estimate recharge times and palaeorecharge temperatures. The proposal will initially target emblematic aquifers (“flag basins”) in Northern China, and possibly the other large aquifers by creating a GIS based database. .B) Compare and potentially correlate major climatic events derived from groundwater basins with those obtained from higher resolution continental proxy records. This will be done at a continental scale (individual basins) and global scale (between different basins), focusing in the Northern China. Several conceptualizations of basin response from the palaeogroundwater record will be modeled and compared. The model's response will be calibrated against available data. Calculated response of modeled basins will also be used to identify additional data needs. .C) Discuss and improve the methods of age determination and palaeoclimate interpretation based on groundwater signals (e.g. stable and radioactive isotopes, noble gases, other geochemical parameters) with a case study in Leizhou Peninsula. Three campaigns are planned during four years, to collect groundwater for analyses of groundwater age by using ATTA method (85Kr, 81Kr) and 14C, and the recharge temperature by using the noble gases, and the palaeoclimatic signals by using the proxy of stable isotopes (18O and 2D)..The proponent put forward the idea and research network of G@GPS (Groundwater@Global Palaeoclimate Signals, www.gw-gps.com) in 2010, and has been active since then as leading INQUA palaeogroundwater IFG http://www.terpro.eu/ and the co-chair of groundwater and climate change commission of IAH.

作为潜在古气候记录的地下水在全球广泛分布，可弥补冰川、黄土等其他载体空间分布的局限，在低纬度地区尤其具有独特的意义。随着地下水测龄技术的进步，相应的古气候记录从14C的约5万年可延伸至81kr的近百万年；基于惰性气体的补给温度可用于水中氢氧同位素信号的解构。以已有国内外地下水中的古气候信息为基础，探索重构我国北方（华北、东北、西北）地区近5万年来的温度、降水变化及主要的补给事件。同时，以雷州半岛为实证研究区，现场采样并测试地下水至百万年尺度的表观年龄，通过实测同位素、惰性气体等，提取古气候变化信息，与北方地区比对，解译区域差异的原因。主要研究内容：大含水层已有古气候变化信息的收集与数据库建设；大含水层古气候变化信息的重构；雷州半岛深层地下水中古气候变化信息的提取与重构。该研究在第四纪古气候变化研究上具有理论新意，在地下水开发利用潜力与管理方面具有实际意义，可弥补华南地下水年龄测定上的空白。

国际上大含水层古气候变化信息的提取和对比研究，以及潜在气候变异与变化条件下地下水补给与演化对于揭示未来全球环境变化、地下水可持续利用及未来地球研究意义重大。作为潜在古气候记录的地下水在全球广泛分布，可弥补冰川、黄土等其他载体空间分布的局限，在低纬度地区尤其具有独特的意义。主要研究内容：以已有国内外地下水中的古气候信息为基础同时，以雷州半岛为实证研究区，现场采样并测试地下水至百万年尺度的表观年龄，通过实测同位素、惰性气体等，提取古气候变化信息，与北方地区比对，解译区域差异的原因。以雷州半岛南北地下水补给区为中心，按照地下水流方向采集约50口监测井的样品，研究了放射性及稳定同位素的变化特征，对当地地下水开展定年工作。同时采用模型和稀有气体温度计方法对古地下水接受补给时的环境温度进行反演。研究发现，雷州半岛中深层地下水的年龄大部分小于24000a，地下水年龄从补给区到排泄区逐渐增加，表现为放射性同位素含量逐渐减少。惰性气体温度反演结果表明研究区末次冰盛期LGM与现代大气温度间的温差达5.4℃以上，氘氧同位素随时间的变化指示当地LGM期间气候十分干冷，从而造成地下水补给可能在LGM时期发生中断（未“捕捉”到LGM时期的地下水样品）。这一点的环境变化信息明显与华北平原存在差异。另外，氘氧稳定同位素与NGT和过量Ne的关系表明降雨量而非温度很可能是控制当地大气降水中氘氧同位素的主要因素，现代大气降水中的氘氧同位素与温度和降水量的关系同样支持这一结论。通过四年的研究工作，完成了由项目资助标注的论文25篇，在该项目的支持下指导博士生10名（其中一名为中山大学与海德堡大学联合培养博士）、硕士生15名，已毕业博士7名，硕士13名。项目负责人作为执行主编在国际第四纪协会（INQUA）会刊QUATERNARY INTERNATIONAL (SCI 刊物）编辑一期专刊。