Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to late Pliocene/early Pleistocene climate cooling
Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to late Pliocene/early Pleistocene climate cooling
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DOI：
10.5194/cp-8-1435-2012
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发表时间：
2012-09
影响因子：
4.3
通讯作者：
J. Etourneau;C. Ehlert;M. Frank;P. Martinez;R. Schneider
中科院分区：
文献类型：
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作者：
J. Etourneau;C. Ehlert;M. Frank;P. Martinez;R. Schneider
全球晚上新世/早更新世冷却（~ 300 - 200万年前- Ma）与大多数主要沿海涌升区极高的硅藻和生物蛋白石产量同时发生。这一现象在纳米比亚近海的本格拉上升流系统（BUS）特别明显，在那里它被称为松山硅藻最大值（MDM）。我们的研究集中在一个新的硅藻硅同位素（δ 30 Si）记录覆盖在主DM在BUS。出乎意料的是，δ 30 Si信号的变化遵循生物蛋白石含量，其中最高的δ 30 Si值对应于最高的生物蛋白石含量。我们解释了MDM期间较高的δ 30 Si值，这是由于垫形成硅藻物种的高生产力导致表面沃茨中硅酸盐利用程度更强的结果。这是最有可能促进弱上升流强度占主导地位的BUS在上新世晚期/早更新世冷却结合一个大的硅酸盐供应来自强大的南大洋营养泄漏响应南极冰盖的扩张和由此产生的分层的极地海洋3.0-2.7 Ma前。类似的情况下，假设其他主要的沿海上升流系统（例如关闭加州）在这段时间内，这表明生物碳泵的效率可能是充分提高在这些地区的MDM期间有显着增加大气中的CO2输送到深海。此外，在南大洋和北太平洋，这减少了CO2释放到大气中的地表水分层的面积的同时代的扩展，导致进一步增强大气CO2 draw-down，从而显着贡献晚上新世/早更新世冷却。
The global Late Pliocene/Early Pleistocene cooling (~3.0–2.0 million years ago – Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela upwelling system (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilisation in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Late Pliocene/Early Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to Late Pliocene/Early Pleistocene cooling.