Geochemical, mineralogical, stable isotope, geochronological and grain size data of sediment core GRV13-2 from coastal lake Groenvlei, southern Cape coast, South Africa

South African coastal lake sediments provide an excellent opportunity to investigate environmental changes such as sea level and climate variability during the Holocene period. In this study we present a sediment record from the coastal lake Groenvlei located in the southern Cape region which is part of South Africa's year-round rainfall zone. In order to improve the understanding of palaeoenvironmental changes in this region, we provide a high-resolution multi-proxy data set derived from geochemical, mineralogical, isotopic and granulometric analyses. The age-depth model is based on 14C and 210Pb dating and reveals a basal age of 4210 + 200/- 120 cal BP. Differences in the mineralogical composition of deposited carbonates reflect changes in the past lake water chemistry, probably caused by variations in both sea level and climate. Compared to the present, mostly drier conditions and a greater marine influence due to a higher sea level are inferred for the period between 4210 and 2710 cal BP. However, the record also indicates the occurrence of short humid phases during this time, which were probably associated with heavy rainfall events. A transition layer was deposited between 2710 and 1210 cal BP, probably as a result of reworking of sediment. During this time, the lake passed through a major change finally turning into a freshwater system from at least 1210 cal BP until the present. Our data indicate that the marine influence on the lake decreased due to a lower sea level and climate became generally more humid after 1210 cal BP probably resulting in a greater lake-internal and -external bioproductivity. Based on a comparison with other palaeoenvironmental studies from South Africa, our record suggests a prevailing winter rainfall seasonality at the southern Cape coast between 4210 and 2710 cal BP and a stronger influence of summer rainfall from 1210 cal BP onwards.

南非沿海湖泊沉积物为研究全新世时期的海平面变化与气候波动等环境演化事件提供了绝佳契机。本研究获取了位于南非全年降雨区内的南开普地区沿海湖泊格伦弗莱（Groenvlei）的沉积物记录。为深化对该区域古环境演化的认知，本研究提供了一套基于地球化学、矿物学、同位素及粒度分析得到的高分辨率多代用指标数据集。本研究的年龄-深度模型基于14C与210Pb测年建立，其基底年代为4210+200/-120 cal BP（校准距今年）。沉积碳酸盐的矿物组成差异，可反映历史时期湖泊水体化学的变化，该变化大概率由海平面波动与气候变迁共同驱动。相较于现代，4210~2710 cal BP时段的气候整体更为干旱，且受海平面上升影响，该时期湖泊受到更强的海洋输入影响。但该沉积记录同时显示，此时期内存在若干短暂的湿润阶段，这可能与强降雨事件相关。在2710~1210 cal BP时段，湖泊沉积了一套过渡层，其成因可能与沉积物再搬运作用有关。在此期间，湖泊经历了重大环境转变，至少自1210 cal BP起直至现代，湖泊逐步演变为淡水体系。本研究数据表明，1210 cal BP之后，受海平面下降影响，湖泊受到的海洋输入影响减弱，且气候整体转向湿润，这或提升了湖泊内外的生物生产力水平。通过与南非其他古环境研究成果对比，本沉积记录显示，4210~2710 cal BP时段南开普海岸地区的降水季节格局以冬季降雨为主，而自1210 cal BP起，夏季降雨的影响显著增强。