Response of East African climate to orbital forcing during the last two glacial-interglacial cycles: The Lake Naivasha Coring Project

高质量的晚更新世热带气候年表在讨论热带迫使冰川消退，即从冰期向间冰期过渡的问题上变得越来越重要。这一假说的关键论点是，热带气候比高纬度的冰量领先数千年。热带强迫的冰川消退也有助于解释为什么冰期同时出现在两个半球，尽管轨道变化导致的太阳辐射变化在两个半球产生了相反的影响。奈瓦沙湖提供了一个独特的机会，通过反映在沉积物中的沉积学和古生态变化，研究最近两个冰川-间冰期周期(约175 KYR)期间热带气候的连续变化。我们提出了一个分两步重建这一时期湖泊历史的策略：(A)进行高分辨率地震调查，以表征奈瓦沙盆地的沉积环境、湖平面波动和新构造。这项调查还将为(B)目前湖区两个50米和40米长的沉积物岩芯的最佳选址提供指导。这些沉积物记录有望填补现今湖泊以南暴露的一个经过充分研究的剖面(现在为175-60KYR)和上世纪60年代S研究的两个沉积岩芯(至今为25KYR)之间的空白。

High-quality chronologies of late Pleistocene tropical climate have become increasingly important in discussions concerning tropical forcing of deglaciation, i.e., the transition from a glacial to an interglacial. The key argument of this hypothesis is that tropical climate leads high-latitude ice volumes by several thousand years. A tropical forcing of deglaciation would also help to explain why ice ages occur in both hemispheres simultaneously, although the changes in solar irradiance from orbital variations have opposite effects in the two hemispheres. Lake Naivasha provides a unique opportunity to study a continuous record of tropical climate changes during the last two glacial-interglacial cycles (approximately 175 kyr) through sedimentologic and paleoecologic changes reflected in the sediments. We propose a two-step strategy to reconstruct the lake history during this period: (A) a high-resolution seismic survey to characterize the depositional setting, lake-level fluctuations and neotectonics in the Naivasha basin. This survey will also guide up to the best sites for (B) two 50- and 40-m-long sediment cores from the present lake area. These sediment records are expected to fill the gap between a well-studied section exposed south of the present lake (175 to 60 kyr before present) and two sediment cores studied in the 1960's (25 kyr to present).