Orbital scale variation of primary productivity in the central equatorial Indian Ocean (Maldives) during the early Pliocene
Orbital scale variation of primary productivity in the central equatorial Indian Ocean (Maldives) during the early Pliocene
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DOI：
10.1016/j.palaeo.2017.05.012
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发表时间：
2017-08
期刊：
影响因子：
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通讯作者：
H. Deik;L. Reuning;M. Pfeiffer
中科院分区：
文献类型：
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作者：
H. Deik;L. Reuning;M. Pfeiffer
我们研究了中央赤道印度洋（ODP Site 716，马尔代夫）上升流系统对 3.64 至 4.19 Ma 之间轨道强迫的响应。上新世早期的这个时间间隔的特点是全球平均气温比现在高得多，并且主要海洋的纬向和经向海面温度梯度减小。二氢卟酚是叶绿素的降解产物，也是初级生产力的潜在指标，此前曾被证明可以记录该地点的轨道尺度变化。为了确认二氢卟酚记录了初级生产力并了解控制轨道变化的机制，我们将浮游有孔虫组合的变化与沉积物中的二氢卟酚含量进行了比较。交叉小波分析证明了温跃层物种丰度与二氢卟酚含量之间的同相关系，表明上升流和较浅的温跃层驱动了生产力的变化。众所周知，台地周围碳酸盐中的文石含量反映了海平面和/或气候的变化，高值通常表明海平面高位。研究区间的文石含量显示岁差和偏心率天文周期，而初级生产力指标仅显示岁差周期。文石含量与进动带上温跃层物种相对丰度之间的负相关意味着海平面低位期间初级生产力增加。这种相位耦合与印度洋中部的第四纪生产力记录一致，该记录被认为是由厄尔尼诺-南方涛动（ENSO）轨道引起的变化控制的。因此，我们认为，尽管全球边界条件发生了重大变化，但类似的机制在上新世早期仍然活跃。
We investigate the response of the central equatorial Indian Ocean (ODP Site 716, Maldives) upwelling system to orbital forcing between 3.64 and 4.19 Ma. This time interval in the early Pliocene was characterized by global average temperatures considerably warmer than present and reduced zonal and meridional sea surface temperature gradients across the major oceans. Chlorin, a degradation product of chlorophyll and a potential indicator of primary productivity, was previously shown to record orbital scale variations at this site. To confirm that chlorin records primary productivity and to understand the mechanism controlling the orbital variations, we compare changes in the planktic foraminiferal assemblages with the chlorin content of the sediment. Cross wavelet analysis demonstrates the in-phase relationship between the abundance of thermocline species and chlorin content, indicating that upwelling and a shallower thermocline drive the productivity changes. The aragonite content in periplatform carbonates is known to reflect variations in sea-level and/or climate, with high values generally indicating sea-level highstands. The aragonite content in the studied interval shows precession and eccentricity astronomical cycles, whereas the primary productivity proxies show only precessional cycles. The negative correlation between aragonite content and the relative abundance of thermocline species on the precessional band implies that the primary productivity increased during sea-level lowstands. This phase coupling is consistent with Quaternary productivity records from the central Indian Ocean that were proposed to be controlled by orbital induced variations of the El Niño-Southern Oscillation (ENSO). We therefore propose that a similar mechanism was active in the early Pliocene despite major changes in the global boundary conditions.