Age model and Plio-Pleistocene benthic stable oxygen isotope ratios of ODP Site 184-1143 in the Sourh China Sea

Based on benthic foraminiferal delta18O from ODP Site 1143, a 5-Myr astronomical timescale for the West Pacific Plio-Pleistocene was established using an automatic orbital tuning method. The tuned Brunhes/Matuyama paleomagnetic polarity reversal age agrees well with the previously published age of 0.78 Ma. The tuned ages for several planktonic foraminifer bio-events also agree well with published dates, and new ages for some other bio-events in the South China Sea were also estimated. The benthic delta18O from Site 1143 is highly coherent with the Earth's orbit (ETP) both at the obliquity and precession bands for the last 5 Myr, and at the eccentricity band for the last 2 Myr. In general, the 41-kyr cycle was dominant through the Plio-Pleistocene although the 23-kyr cycle was also very strong. The 100-kyr cycle became dominant only during the last 1 Myr. A comparison of the benthic delta18O between the Atlantic (ODP 659) and the East and West Pacific (846 and 1143) reveals that the Atlantic-Pacific benthic oxygen isotope difference ratio (Delta delta18OAtl-Pac) displays an increasing trend in three time intervals: 3.6-2.7 Ma, 2.7-2.1 Ma and 1.5-0.25 Ma. Each of the intervals begins with a rapid negative shift in Delta delta18OAtl-Pac, followed by a long period with an increasing trend, corresponding to the growth of the Northern Hemisphere ice sheet. This means that all three intervals of ice sheet growth in the Northern Hemisphere were accompanied at the beginning by a rapid relative warming of deep water in the Atlantic as compared to that of the Pacific, followed by its gradual relative cooling. This general trend, superimposed on the frequent fluctuations with glacial cycles, should yield insights into the processes leading to the boreal glaciation. Cross-spectral analyses of the Delta delta18OAtl-Pac with the Earth's orbit suggests that after the initiation of Northern Hemisphere glaciation at about 2.5 Ma, obliquity rather than precession had become the dominant force controlling the vertical structure or thermohaline circulation in the paleo-ocean.

本数据集基于大洋钻探计划（Ocean Drilling Program, ODP）1143站位的底栖有孔虫氧同位素δ¹⁸O数据，采用自动轨道调谐方法建立了西太平洋上新世-更新世的5百万年天文年代标尺。经调谐得到的布容（Brunhes）-松山（Matuyama）古地磁极性反转年龄，与已发表的0.78 Ma年龄高度吻合。针对数个浮游有孔虫生物事件的调谐年龄，同样与已公布的测年结果一致；同时还估算了南海部分其他生物事件的新年龄。1143站位的底栖δ¹⁸O序列在过去5百万年间，于斜度和进动频段均与地球轨道（ETP）呈现高度相干性，在过去2百万年间则在偏心率频段同样具备高度相干性。总体而言，尽管23千年周期的信号也十分显著，但41千年周期在上新世-更新世期间始终占据主导地位；100千年周期仅在过去1百万年间成为主导周期。对比大西洋（ODP 659站位）与东、西太平洋（846和1143站位）的底栖δ¹⁸O序列后发现，大西洋-太平洋底栖氧同位素差值（Δδ¹⁸O_Atl-Pac）在三个时间段呈现持续增长趋势：3.6–2.7 Ma、2.7–2.1 Ma及1.5–0.25 Ma。每个时间段均以Δδ¹⁸O_Atl-Pac的快速负偏移为起始，随后进入一段长期增长阶段，这与北半球冰盖的发育过程相对应。这意味着，北半球冰盖发育的三个阶段均伴随如下过程：相较于太平洋深层水，大西洋深层水在阶段初期发生快速相对增温，随后逐渐发生相对降温。这一整体趋势叠加冰期旋回下的频繁波动，可为研究北方冰期形成过程提供新的认识。对Δδ¹⁸O_Atl-Pac与地球轨道进行交叉谱分析结果表明，在北半球冰川作用于约2.5 Ma启动后，斜度而非进动成为控制古海洋垂直结构或温盐环流的主导因素。