Accumulation rates of ODP Site 177-1090

Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean (Martin et al., 1990, doi:10.1038/345156a0; Martin, 1990, doi:10.1029/PA005i001p00001). Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40 parts per million by volume (p.p.m.v.) of the decrease (80-100 p.p.m.v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles (Watson et al., 2000, doi:10.1038/35037561; Kohfeld et al., 2005, doi:10.1126/science.1105375; Martínez-Garcia et al., 2009, doi:10.1029/2008PA001657; Sigman et al., 2010, doi:10.1038/nature09149; Hain et al., 2010, doi:10.1029/2010gb003790). So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (Lambert et al., 2008, doi:10.1038/nature06763; Wolf et al., 2006, doi:10.1038/nature04614) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles (Martínez-Garcia et al., 2009; Lambert et al., 2008; Wolff et al., 2006), providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.

粉尘可通过改变大气辐射平衡，并向海洋输送铁及其他必需的限制性微量营养素，具备调控全球气候的潜能（Martin et al., 1990, doi:10.1038/345156a0; Martin, 1990, doi:10.1029/PA005i001p00001）。
事实上，冰期期间南大洋（Southern Ocean）的粉尘供给量会上升，而亚南极带的铁肥化（iron fertilization）作用，可能对晚更新世冰期旋回中观测到的大气二氧化碳浓度下降（降幅为80~100体积百万分率（ppmv））贡献了最高达40体积百万分率的降幅（Watson et al., 2000, doi:10.1038/35037561; Kohfeld et al., 2005, doi:10.1126/science.1105375; Martínez-Garcia et al., 2009, doi:10.1029/2008PA001657; Sigman et al., 2010, doi:10.1038/nature09149; Hain et al., 2010, doi:10.1029/2010gb003790）。
然而迄今为止，更早地质时期南大洋的粉尘沉积规模，及其在更新世冰期旋回形成与演化中的作用仍不明确。本研究基于亚南极带大西洋区段的大洋钻探计划（Ocean Drilling Program, ODP）1090站位的海洋沉积物分析，构建了过去400万年南大洋粉尘与铁供给的高分辨率记录。
我们的粉尘与铁沉积记录，与覆盖过去80万年的南极冰芯粉尘通量重建结果（Lambert et al., 2008, doi:10.1038/nature06763; Wolf et al., 2006, doi:10.1038/nature04614）高度吻合，这表明这两类记录载体均记录了适用于南大洋大部分区域的大规模沉积变化，验证了此前对冰芯数据的解读。
将该记录延伸至南极冰芯覆盖时段之外后发现：与过去300万年冰期旋回相对渐进的增强过程不同，南大洋粉尘与铁通量在约125万年前的中更新世气候转型期出现了急剧升高。
该发现补充了此前针对晚更新世冰期旋回的观测结果（Martínez-Garcia et al., 2009; Lambert et al., 2008; Wolff et al., 2006），为南大洋高粉尘输入与地球过去100万年所特有的强冰期旋回之间的紧密关联提供了新证据。