Linkages between Holocene paleoclimate and paleohydrogeology preserved in a Yucatan underwater cave
Linkages between Holocene paleoclimate and paleohydrogeology preserved in a Yucatan underwater cave
复制标题
DOI：
10.1016/j.quascirev.2010.06.034
复制
发表时间：
2010-09
影响因子：
4
通讯作者：
P. J. Hengstum;E. Reinhardt;P. Beddows;Jeremy J. Gabriel
中科院分区：
文献类型：
--
作者：
P. J. Hengstum;E. Reinhardt;P. Beddows;Jeremy J. Gabriel
来自尤卡坦半岛(墨西哥)阿克顿哈洞的三个沉积物岩心跨越了过去4200年，表明水下洞穴可以记录区域水文地质和气候的变化。分析了底栖生物微体化石(遗体阿米巴、有孔虫)、有机质地球化学(δ13C、δ15N、C/N)和粒度分布。然而，微化石古生态被证明是最有用的指示阿克屯哈沉积岩芯中的三个盐度阶段。阶段1(>；4300yr BP)含有主要的有孔虫(单形有孔虫，78%)，这表明充斥洞穴的陨石透镜最初是微咸水的(盐度>；3.5g，L−1)。第二阶段(2800-4300Cal yr BP)既有淡水遗迹阿米巴(Centropyxis spp.)3期(<；2800yrBP)，表明L−1的陨石晶状体略有新鲜。第三阶段(<；2800yrBP)的分界是：隐阿米巴的丰度(90%)和多样性增加，包括白纹伊蚊和长白菜的定殖化，而单纯隐阿米巴的数量减少(10%)。这最后的动物群转移代表了洞穴现代淡水条件的开始(L−1)。这种最终的更新与C/N比的显著降低(例如，核心2：∼27到19)是同步的，这表明相邻中心的初级生产力得到了扩大。δ15N值在1.53.5‰之间变化，观测到的周期可能来自高降雨事件(如飓风)期间进入洞穴的陆地OM输入增加的间隔。洞穴中观察到的古环境变化与区域降水模式、含水层补给以及热带辐合带向南迁移所引起的风暴活动密切相关。因此，在全新世中晚期，区域气候变化对尤卡坦东部地下水产生了影响。然而，全新世海平面上升减速和含水层闭塞可能是促成因素。这些结果表明，水下洞穴沉积物和微体化石可以作为含水层演化和气候变化的有用指标。
Three sediment cores spanning the last 4200 years from Aktun Ha Cave on the Yucatan Peninsula (Mexico) demonstrate that underwater caves can document changes to regional hydrogeology and climate. Benthic microfossils (testate amoebae, foraminifera), organic matter geochemistry (δ13C, δ15N, C/N), and particle size distributions were analyzed. However, microfossil paleoecology proved the most useful for indicating three salinity phases in the Aktun Ha sediment cores. Phase 1 (>4300 yr BP) contains predominantly foraminifera (Physalidia simplex, 78%) that indicate the meteoric lens flooding the cave was initially brackish (salinity >3.5 g L−1). Phase 2 (2800–4300 Cal yr BP) has both freshwater testate amoebae (Centropyxis spp. 40%) and P. simplex (42%), which indicates a slight freshening of the meteoric lens to 1.5–2 g L−1. Phase 3 (<2800 yr BP) is demarcated by an increase in testate amoebae abundance (90%) and diversity, including the colonization of Lagenodifflugia vas and Difflugia oblonga, with a reduction in P. simplex (10%). This last faunal shift represents the initiation of modern freshwater conditions in the cave (1.5 g L−1). This final freshening is synchronous with a significant reduction in the C/N ratio (e.g., Core 2: ∼27 to 19), which suggests an expansion of primary productivity in the adjacent cenote. The δ15N values ranged from 1.5 to 3.5‰ with observed cycles likely from intervals of increased terrestrial OM input into the cave during high rainfall events (e.g., hurricanes). The observed paleoenvironmental shifts in the cave correlate well with regional precipitation patterns, aquifer recharge, and storm activity caused by southward migration of the Intertropical Convergence Zone. Therefore, regional climate change impacted eastern Yucatan groundwater during the mid to late Holocene. However, decelerating Holocene sea-level rise and aquifer occlusion are likely contributing factors. These results demonstrate that underwater cave sediments and microfossils can be useful proxies for aquifer evolution and climate change.