AMS radiocarbon dates and pollen analysis of ODP Hole 175-1078C

ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.大洋钻探计划（Ocean Drilling Program, ODP）1078站位位于安哥拉近海海域，是首个记录安哥拉植被演化历史的研究位点。该岩芯上部11米覆盖了过去3万年的沉积记录，已通过孢粉分析以十年至百年的分辨率开展研究；同时以百年分辨率对烯酮海表温度估算结果进行了分析。本研究针对冰期盛期、冰消期与间冰期阶段的海表温度及植被演化过程展开探究。冰期阶段安哥拉地区植被覆盖极为稀疏开阔，以草原、灌丛、荒漠与半荒漠为主，指示当时气候寒冷干旱。约2.2万年前，随着南极地区最早的温度抬升同步启动的森林扩张，标志着区域气候向暖湿状态转变。我们推断，在海因里希事件1（Heinrich Event 1）发生期间，安哥拉-本格拉锋面与刚果气团边界向北偏移，导致海表温度降低，但安哥拉北部低地仍留存有热带雨林。约1.5万年前，热带雨林与旱林面积出现扩张。全新世时期，旱林与米翁博稀树草原扩张范围进一步扩大。同样在安哥拉地区，全球公认的8千年前与4千年前的气候事件亦对区域植被造成了影响。过去2000年以来，稀树草原植被成为区域优势植被类型。