Expressions of climate perturbations in western Ugandan crater lake sediment records during the last 1000 years
Expressions of climate perturbations in western Ugandan crater lake sediment records during the last 1000 years
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DOI：
10.5194/cp-10-1581-2014
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发表时间：
2014-01-01
影响因子：
4.3
通讯作者：
Tyler, J. J.
中科院分区：
文献类型：
--
作者：
Mills, K.;Ryves, D. B.;Tyler, J. J.
赤道东非地区的气候制度错综复杂，对全新世晚期各种时间和空间尺度上的气候波动十分敏感。了解湖泊沉积记录中的生物和地球化学指标如何记录和解释这些变化，仍然是回答东非古记录中气候变化的性质、空间范围和同步性等基本问题的关键挑战。使用成对湖泊的方法，即相邻的湖泊拥有相同的地质、气候和景观，可以预期这些系统将对外部气候强迫做出类似的反应。对乌干达西部两个火山口湖泊的沉积岩心进行了研究，时间跨度近1000年，以评估硅藻群落对晚全新世气候和环境变化的响应，并使用冗余分析(RDA)测试对多个驱动因素的响应。Nyamogusingiri湖和Kyasanduka湖似乎作为独立的系统运作，通过不同的硅藻记录记录类似的水文响应信号。然而，虽然他们的硅藻化石记录显示了对外部(例如气候)驱动因素的个人化、间接反应，但推断的湖泊水位显示出类似的总体趋势，并反映了在乌干达和整个东非观察到的更广泛的模式。这些湖泊似乎对大规模的气候扰动很敏感，有证据表明中世纪气候异常干燥(MCA；公元1000-1200年)。Nyamogusingiri湖的硅藻记录表明，小冰期(公元16001800年)的主要阶段是干燥的气候，而较浅的Kyasanduka湖的硅藻反应更为复杂(地下水可能起关键作用)，可能更多地是由二氧化硅和其他营养物质的变化驱动的，而不是湖泊水位。这两个乌干达湖泊对区域气候驱动因素的敏感性在公元1800年左右崩溃，当时生态系统的重大变化似乎是对湖泊集水区内日益增长的文化影响的反应，尽管这两个替代记录似乎都对20世纪中期东非记录的干旱做出了回应。数据突显了硅藻群落对外部驱动因素(气候或文化)的反应的复杂性，即使在邻近的浅水湖泊中也是如此。这项研究还说明了多湖、多代理景观方法对了解区域水文变化的重要性和必要性，这将允许对气候重建、气候强迫和生态系统响应模型进行严格测试。
Equatorial East Africa has a complex regional patchwork of climate regimes, sensitive to climate fluctuations over a variety of temporal and spatial scales during the late Holocene. Understanding how these changes are recorded in and interpreted from biological and geochemical proxies in lake sedimentary records remains a key challenge to answering fundamental questions regarding the nature, spatial extent and synchroneity of climatic changes seen in East African palaeo-records. Using a paired lake approach, where neighbouring lakes share the same geology, climate and landscape, it might be expected that the systems will respond similarly to external climate forcing. Sediment cores from two crater lakes in western Uganda spanning the last similar to 1000 years were examined to assess diatom community responses to late Holocene climate and environmental changes, and to test responses to multiple drivers using redundancy analysis (RDA). These archives provide annual to sub-decadal records of environmental change.Lakes Nyamogusingiri and Kyasanduka appear to operate as independent systems in their recording of a similar hydrological response signal via distinct diatom records. However, whilst their fossil diatom records demonstrate an individualistic, indirect response to external (e. g. climatic) drivers, the inferred lake levels show similar overall trends and reflect the broader patterns observed in Uganda and across East Africa. The lakes appear to be sensitive to large-scale climatic perturbations, with evidence of a dry Medieval Climate Anomaly (MCA; ca. AD 1000-1200). The diatom record from Lake Nyamogusingiri suggests a drying climate during the main phase of the Little Ice Age (LIA) (ca. AD 16001800), whereas the diatom response from the shallower Lake Kyasanduka is more complex (with groundwater likely playing a key role), and may be driven more by changes in silica and other nutrients, rather than by lake level. The sensitivity of these two Ugandan lakes to regional climate drivers breaks down in ca. AD 1800, when major changes in the ecosystems appear to be a response to increasing cultural impacts within the lake catchments, although both proxy records appear to respond to the drought recorded across East Africa in the mid-20th century.The data highlight the complexity of diatom community responses to external drivers (climate or cultural), even in neighbouring, shallow freshwater lakes. This research also illustrates the importance of, and the need to move towards, a multi-lake, multi-proxy landscape approach to understanding regional hydrological change which will allow for rigorous testing of climate reconstructions, climate forcing and ecosystem response models.