NOAA/WDS Paleoclimatology - Verlorenvlei, South Africa 1400 Year Diatom Abundance Data

The austral westerlies strongly influence precipitation and ocean circulation in the southern temperate zone, with important consequences for cultures and ecosystems. Global climate models anticipate poleward retreat of the austral westerlies with future warming, but the available paleoclimate records that might test these models have been limited to South America and New Zealand, are not fully consistent with each other and may be complicated by influences from other climatic factors. Here we present the first high-resolution diatom and sedimentological records from the winter rainfall region of South Africa, representing precipitation in the equatorward margin of the westerly wind belt during the last 1400 yr. Inferred rainfall was relatively high ~1400-1200 cal yr BP, decreased until ~950 cal yr BP, and rose notably through the Little Ice Age with pulses centred on ~600, 530, 470, 330, 200, 90, and 20 cal yr BP. Synchronous fluctuations in Antarctic ice core chemistry strongly suggest that these variations were linked to changes in the westerlies. Equatorward drift of the westerlies during the wet periods may have influenced Atlantic meridional overturning circulation by restricting marine flow around the tip of Africa. Apparent inconsistencies among some aspects of records from South America, New Zealand and South Africa warn against the simplistic application of single records to the Southern Hemisphere as a whole. Nonetheless, these findings in general do support model projections of increasing aridity in the austral winter rainfall zones with future warming.

南半球西风带（austral westerlies）对南温带的降水与海洋环流具有强烈调控作用，其变化对区域文明与生态系统均具有重要影响。全球气候模型预测，未来气候增温背景下，南半球西风带将向极地方向退缩；但现有用于验证这些模型的古气候记录（paleoclimate records）仅覆盖南美与新西兰两地，且各记录间并非完全一致，同时还可能受到其他气候因子的干扰而变得更为复杂。本研究首次报道了来自南非冬季降水区的高分辨率硅藻（high-resolution diatom）与沉积学记录（sedimentological records），该记录反映了过去1400年间西风带向赤道侧边缘区域的降水变化情况。研究推断，约1400~1200校准年前（cal yr BP）的降水相对偏高，至约950校准年前降水逐渐减少，并在小冰期（Little Ice Age）期间显著回升，其降水峰值分别出现在约600、530、470、330、200、90以及20校准年前。南极冰芯化学记录（Antarctic ice core chemistry）所呈现的同步波动强烈表明，这些降水变化与南半球西风带的变动存在密切关联。湿期阶段西风带向赤道侧的漂移，可能通过限制非洲南端周边的海洋洋流，进而对大西洋经向翻转环流（Atlantic meridional overturning circulation）产生影响。南美、新西兰与南非三地的古气候记录在部分维度上存在明显差异，这警示我们不可简单地将单区域记录直接推广至整个南半球。尽管如此，本研究的整体发现仍支持了全球气候模型的预测：未来气候增温背景下，南半球冬季降水区将愈发干旱。