The Mid‐Pliocene Warm Period (MPWP, 2.9 to 3.3 Ma), along with older Pliocene (3.2 to 5.3 Ma) records, offers potential past analogues for our 400‐ppmv world. The coastal geology of western and southern coasts of the Republic of South Africa exposes an abundance of marine deposits of Pliocene and Pleistocene age. In this study, we report differential GPS elevations, detailed stratigraphic descriptions, standardized interpretations, and dating of relative sea‐level indicators measured across ~700 km from the western and southern coasts of the Cape Provinces. Wave abrasion surfaces on bedrock, intertidal sedimentary structures, and in situ marine invertebrates including oysters and barnacles provide precise indicators of past sea levels. Multiple sea‐level highstands imprinted at different elevations along South African coastlines were identified. Zone I sites average +32 ± 5 m (six sites). A lower topographic Zone II of sea stands were measured at several sites around +17 ± 5 m. Middle and late Pleistocene sites are included in Zone III. Shoreline chronologies using ⁸⁷Sr/⁸⁶Sr ages on shells from these zones yield ages from Zone I at 4.6 and 3.0 Ma and Zone II at 1.04 Ma. Our results show that polar ice sheets during the Plio‐Pleistocene were dynamic and subject to significant melting under modestly warmer global temperatures. These processes occurred during a period when CO₂ concentrations were comparable to our current and rapidly rising values above 400 ppmv.

中文翻译：

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南非共和国上新世-更新世地层学和海平面估计对400 ppmv CO2世界的影响

中上新世暖期（MPWP，2.9至3.3 Ma）以及较旧的上新世（3.2至5.3 Ma）记录，为我们的400 ppmv世界提供了可能的过去类似物。南非共和国西部和南部海岸的沿海地质环境揭示了丰富的上新世和更新世时代的海洋沉积物。在这项研究中，我们报告了从开普省西部和南部沿海约700 km处测得的不同的GPS高程，详细的地层描述，标准化的解释以及相对海平面指标的日期。基岩，潮间带沉积结构以及包括牡蛎和藤壶在内的原位海洋无脊椎动物的波浪磨蚀表面提供了过去海平面的精确指示。沿着南非海岸线，在不同海拔上印有多个海平面高位。I区站点平均+32±5 m（六个站点）。在+17±5 m左右的几个位置测量了海位的较低地形II区。第三区包括中更新世晚期。使用的海岸线年代这些区域的贝壳上的⁸⁷ Sr / ⁸⁶ Sr年龄产生的I区年龄为4.6和3.0 Ma，II区年龄为1.04 Ma。我们的结果表明，上新世间的极地冰盖是动态的，并且在全球温度略微升高的情况下会发生明显的融化。这些过程发生在一个时期，当时的CO ₂浓度与我们目前的水平相当，并且在400 ppmv以上迅速上升。