Insights into the origin of a Mediterranean biodiversity hotspot based on palynological and biomarker analyses of Lake Ohrid sediments from Early Pleistocene (> 1.2 Ma)

地中海植物多样性热点地区，如目前的奥赫里德地区，通常与南部冰川树避难所有关。现有的古植物学证据表明，在过去的五个气候周期中，西南巴尔干地区已经庇护了温带树木种群。该项目旨在利用高分辨率的孢粉学、木炭和脂质生物标志物分析，研究南部避难所植物生物多样性的起源，并重建奥赫里德盆地内早更新世水生和陆地生态系统对气候变化的反应。我们目前对地中海地区早更新世气候和植物群的了解主要是基于由海洋岩心补充的零碎陆地档案。为了提高我们对这一时期气候和植物群演变的认识，2013年在奥赫里德湖的ICDP钻探中取回了一个新的550米长的岩心。初步的地球化学，花粉和硅藻分析表明，在过去的136万年连续沉积，并表明有机碳，花粉和硅藻组合的重大变化对应的特征海洋同位素阶段（MIS）地层。考虑到这一时期全球冰量减少，海洋岩芯中观测到的冰量减少导致气候周期缩短，本提案的研究目标是：（i）确定奥赫里德湖形成期间和中更新世过渡期开始之前南部避难所的植物多样性，重点是残留的亚热带物种，㈡奥赫里德盆地环境和水文变化的重建导致湖泊的形成，（iii）确定奥赫里德盆地自湖泊形成以来在受气候控制的气候制度下陆地和水生生态系统变化的主要驱动因素（41-kyr周期）之间的MIS 43和MIS 35，和（iv）定量重建和评估的性质和幅度之间的气候变率MIS 43和MIS 35在东地中海地区。这些目标将在三个工作包中得到解决，这三个工作包将提供第一个高分辨率的花粉和非花粉孢粉和木炭记录，河流，泥炭地和湖泊相的脂质生物标志物清单，以及研究区域早更新世的第一个花粉和生物标志物定量气候重建。在相同的时间间隔内，补充的火山灰年代学，沉积学，地球化学和硅藻分析将提供独立的年龄控制点，并将完善我们对湖泊水文变化的理解，推动水生生物群落的更替。

Mediterranean hotspots of plant diversity, such as the Ohrid region at present, are commonly associated with southern glacial tree refugia. Existing paleobotanical evidence suggests that SW Balkans have sheltered temperate tree populations over the last five climatic cycles. This project aims to use high-resolution palynological, charcoal and lipid biomarker analyses to study the origins of plant biodiversity at a southern refugium and to reconstruct the response of aquatic and terrestrial ecosystems to climate variability over the Early Pleistocene within the Ohrid Basin. Our current knowledge about EarIy Pleistocene climate and flora in the Mediterranean region is based mostly on fragmentary terrestrial archives complemented by marine cores. In an effort to improve our understanding of the climate and flora evolution over this interval, a new 550m-long core was retrieved in 2013 within the ICDP drilling at Lake Ohrid. Preliminary geochemical, pollen and diatom analyses show continuous sedimentation over the last 1.36 million years and indicate major shifts in organic carbon, pollen and diatom assemblages corresponding to the characteristic marine isotope stage (MIS) stratigraphy. Considering the reduced global ice volume and shorter climatic cycles paced by obliquity observed in marine cores during this period, the research objectives of this proposal are: (i) the determination of the floristic diversity in a southern refugium during the formation of Lake Ohrid and prior to the onset of the Mid- Pleistocene transition with a focus on relict subtropical species, (ii) the reconstruction of environmental and hydrological changes in the Ohrid Basin leading to the formation of the lake, (iii) the identification of the main drivers of terrestrial and aquatic ecosystem change in the Ohrid Basin since the formation of the lake under an obliquity-controlled climate regime (41-kyr cycles) between MIS 43 and MIS 35, and (iv) the quantitative reconstruction and assessment of the nature and amplitude of climate variability between MIS 43 and MIS 35 in the Eastern Mediterranean region. These objectives will be addressed in three work packages that will deliver the first highly-resolved pollen and non-pollen palynomorph and charcoal record, a lipid biomarker inventory of fluvial, peatland and lacustrine phases, as well as the first pollen- and biomarker-derived quantitative climate reconstructions for the Early-Pleistocene in the study region. Complementary tephrochronological, sedimentological, geochemical and diatom analyses over the same interval will provide independent age control points and will refine our understanding of changes in lake hydrology driving aquatic organism community turnovers.