Pollen and spores of sites GeoB8331 and GeoB8323, Namaqualand Mudbelt, Holocene South Africa

To better understand Holocene vegetation and hydrological changes in South Africa, we analyzed pollen and microcharcoal records of two marine sites GeoB8331 and GeoB8323 from the Namaqualand mudbelt offshore the west coast of South Africa covering the last 9900 and 2200 years, respectively. Our data corroborate findings from literature that climate developments apparently contrast between the summer rainfall zone (SRZ) and winter rainfall zone (WRZ) over the last 9900 years, especially during the early and middle Holocene. During the early Holocene (9900-7800 cal.yr BP), a minimum of grass pollen suggests low summer rainfall in the SRZ, and the initial presence of Renosterveld vegetation indicates relatively wet conditions in the WRZ. Towards the middle Holocene (7800-2400 cal. yr BP), a rather moist savanna/grassland rich in grasses suggests higher summer rainfall in the SRZ resulting from increased austral summer insolation and a decline of fynbos vegetation accompanied by an increasing Succulent Karoo vegetation in the WRZ possibly suggests a southward shift of the Southern Hemisphere westerlies. During the last 2200 years, a trend towards higher aridity was observed for the SRZ, while the climate in the WRZ remained relatively stable. The Little Ice Age (ca. 700-200 cal. yr BP) was rather cool in both rainfall zones and drier in the SRZ while wetter in the WRZ.为深入探究南非全新世的植被与水文变化，我们对南非西海岸近海纳米夸兰泥带（Namaqualand mudbelt）的两个海洋位点GeoB8331与GeoB8323的花粉及微炭屑记录展开分析，二者的时间跨度分别为过去9900年与2200年。本研究数据印证了已有文献的研究结论：过去9900年间，夏季降雨区（Summer Rainfall Zone, SRZ）与冬季降雨区（Winter Rainfall Zone, WRZ）的气候演化特征存在显著分异，这一差异在全新世早中期尤为突出。全新世早期（9900~7800校正距今年，cal. yr BP），禾本科花粉含量的低值指示夏季降雨区夏季降水偏少，而雷诺斯特维尔德（Renosterveld）植被的首次出现则表明冬季降雨区气候相对湿润。进入全新世中期（7800~2400校正距今年），以禾本科为主的湿润稀树草原/草原广泛发育，指示夏季降雨区因南半球夏季太阳辐射增强而降水增多；与此同时，冬季降雨区的石楠灌丛（Fynbos）植被占比下降，肉质卡鲁（Succulent Karoo）植被占比逐步上升，这一现象或指示南半球西风带发生南移。在过去2200年间，夏季降雨区呈现出干旱化加剧的趋势，而冬季降雨区的气候则保持相对稳定。小冰期（约700~200校正距今年）期间，两个降雨区均整体偏冷，其中夏季降雨区更为干旱，冬季降雨区则更为湿润。