重庆地区石笋记录中Mg／Ca比值及古气候意义

Climatic significance of the Mg/Ca ratio from speleothems in Chongqing

在重庆梁天湾洞石笋LT1431．9～15.02ka．B．P．古气候重建成果已发表的此基础上，本文选取Mg／Ca比值这一新的替代指标，探讨其在重庆地区独特的水热组合模式下的古气候指示意义，从而进一步探讨了该时段的气候变化。研究结果发现，重庆地区Mg／Ca比值与碳同位素的正相关关系较好（R^2=0．60），可能与碳酸钙溶液在到达洞顶之前提前沉淀或滴率减小机制有关，它间接响应了降水的变化。运用Mg／Ca值变化对古气候的重建结果与以前的研究基本相符，说明Mg／Ca比值可以作为古降水的指标，但需同碳氧稳定同位素结合起来讨论，以便相互验证，提高古环境解译的准确性。

The TIMS-U series dating and the oxygen and carbon stable isotopes in the stalagmite LT14 col- lected from Liangtianwan cave in Chongqing have been precisely reported before, and the paleoclimatic change during 31.9-15.02 ka. B. P has also been reconstructed. On the basis, we choose the Mg/Ca ratio as a new proxy to discuss its plaeoclimatic significance under the unique climate mode in Chongqing area for un- derstanding the climatic change in detail. The results show that the Mg/Ca ratio is positively correlated with carbon stable isotopes（R2=0. 60）, and it may be controlled by rainfall variation linked to prior calcite precip- itation in the epikarst or on the cave ceiling or by a drip-rate mechanism. However, we should pay attention to the interruption of temperature change, such as H1 event. Most of the paleoclimatic reconstructions by using Mg/Ca ratio in this paper are the same as the previous research. Therefore, the change of Mg/Ca ratio appears to have respond to past rainfall, but still need to combine with oxygen and carbon stable isotopes, in order to validate with each other and improve precision degree for explaining paleoclimate.