Sedimentary records of ODP Site 198-1209 on Shatsky Rise

The accumulation of wind blown (eolian) dust in deep-sea sediments reflects the aridity/humidity conditions of the continental region supplying the dust, as well as the "gustiness" of the climate system. Detailed studies of Pleistocene glacial-interglacial dust fluxes suggest changes in accumulation rates corresponding to orbital variations in solar insolation (Milankovitch cycles). While the orbital cycles found in sedimentary archives of the Pleistocene are intricately related to glacial growth and decay, similar global orbital signals recognized in deep-sea sediments of early Paleogene age, the last major greenhouse interval ~65-45 million years ago, could not have been linked to the waxing and waning of large ice sheets. Thus orbital signals recorded in early Paleogene sediments must reflect some other climate response to changes in solar insolation. To explore the potential connection between orbital forcing and the climate processes that control dust accumulation, we generated a high-resolution dust record for ~58 Myr old sediments from Shatsky Rise (ODP Site 1209, paleolatitude ~15°N-20°N). The dust accumulation data provide the first evidence of a correlation between dust flux to the deep sea and orbital cyclicity during the early Paleogene, indicating dust supply responded to insolation forcing during the last major interval of greenhouse climate. Furthermore, the relative amplitude of the dust flux response during the early Paleogene greenhouse was comparable to that during icehouse climates. Thus, subtle variations in solar insolation driven by changes in Earth's orbit about the Sun may have had a similar impact on climate during intervals of overall warmth as they did during glacial-interglacial states.

深海沉积物中风成（eolian）尘埃的堆积量，既反映了供给该尘埃的大陆区域的干湿状况，也体现了气候系统的阵风活跃度。针对更新世冰期-间冰期尘埃通量的详细研究显示，尘埃堆积速率的变化与太阳辐射的轨道变化（米兰科维奇循环（Milankovitch cycles））相对应。虽然更新世沉积记录中发现的轨道周期与冰盖的消长密切相关，但在早古近纪（early Paleogene）——即约6500万至4500万年前的最后一个主要温室气候期——的深海沉积物中识别出的类似全球轨道信号，却无法与大型冰盖的进退相联系。因此，早古近纪沉积物中记录的轨道信号，必然反映了气候系统对太阳辐射变化的其他响应机制。为探究轨道强迫（orbital forcing）与控制尘埃堆积的气候过程之间的潜在关联，我们针对来自Shatsky海山（Shatsky Rise）、大洋钻探计划（ODP）1209站位（古纬度约15°N~20°N）的约5800万年前沉积物，构建了高分辨率尘埃记录。本次尘埃堆积数据首次证实了早古近纪深海尘埃通量与轨道周期之间的相关性，表明在最后一个主要温室气候期内，尘埃供给量响应了太阳辐射强迫。此外，早古近纪温室气候期下尘埃通量响应的相对振幅，与冰室气候期下的振幅相当。因此，由地球绕日轨道变化所驱动的太阳辐射细微变化，在整体温暖的气候期内，对气候的影响或许与冰期-间冰期状态下的影响一致。