Stable isotope ratios of foraminifera from DSDP Hole 90-588A (Table 2)

High-resolution stable isotopic records are presented for the epi-benthic foraminifer Cibicidoides, the inferred shallow-dwelling planktonic Globigerinoides quadrilobatus, and the inferred deep-dwelling planktonic Globoquadrina dehiscens from the middle Miocene (~16-12 Ma) of Deep Sea Drilling Project site 588A, Lord Howe Rise, southwest Pacific. High-resolution, multiple species oxygen and carbon isotopic data define the timing and character of the well-known middle Miocene climatic-oceanographic transition with a resolution comparable to Quaternary records. The benthic foraminiferal delta18O record is marked by several large fluctuations from ~16 to 14.8 Ma, followed by a series of rapid (<50 kyr) delta18O increases that suggest a new state of the ocean-climate system after 14.8 Ma. The total middle Miocene benthic oxygen isotopic increase of 1.2 per mil is largely incorporated in two steps, an increase of 0.8 per mil from 14.5 to 14.0 Ma and a second increase of 0.7 per mil from 13.45 to 12.45 Ma. Each step is comprised of a series of marked delta18O increases, indicative of rapid East Antarctic ice sheet growth and contemporaneous deepwater cooling. A strong covariance of 0.7 per mil between the benthic and deep-dwelling planktonic species from 14.5 to 14.0 Ma (including a rapid increase from 14.1 to 14.05 Ma) suggests a 0.7 per mil increase in the delta18O composition of seawater (delta18Osw) because of East Antarctic ice sheet growth. Comparison of the delta18O record of Gs. quadrilobatus suggests that surface waters warmed at this site by ~3°C from 14.1 to 13.6 Ma. Carbon isotopic time series for each species generally covary throughout the early to middle Miocene interval (~16-12 Ma), confirming that delta13C variations in this interval largely represent reservoir changes. High-resolution delta13C data allow improved resolution of the latter five of six delta13C maxima within the well-known early to middle Miocene carbon isotopic excursion (the Monterey Carbon Isotopic Excursion from 17.0 to 13.5 Ma). This is useful for global correlation. The last of these maxima ends with a 1 per mil decrease centered from 13.9 to 13.7 Ma, ~300 kyr after the delta18O increase considered to reflect East Antarctic ice growth. Covariance between benthic delta18O and delta13C from ~16 to 13.8 Ma suggests a sensitive relation between global carbon cycling and the ocean-climate system prior to 13.8 Ma. Episodic increases in organic carbon burial may have contributed to deep-sea benthic delta13C maxima and synchronous global cooling. The positive relationship ended at ~13.8 Ma, indicative of changing relations between global carbon cycling and the ocean-climate system brought on by the increased stability of the East Antarctic ice sheet after a major growth phase from 14.5 to 14.0 Ma.

本数据集提供了西南太平洋豪勋爵海隆（Lord Howe Rise）深海钻探计划（Deep Sea Drilling Project）588A站位中中新世（约1600万至1200万年前，Ma）的高分辨率稳定同位素记录，样品涵盖底表栖有孔虫（epi-benthic foraminifer）圆辐虫属（Cibicidoides）、推断为浅栖的浮游有孔虫（planktonic foraminifer）四叶球室虫（Globigerinoides quadrilobatus），以及推断为深栖的浮游有孔虫（planktonic foraminifer）Globoquadrina dehiscens。高分辨率多物种氧、碳同位素数据明确了公认的中中新世气候-海洋转型事件的发生时序与特征，其分辨率可与第四纪记录相媲美。
底栖有孔虫δ¹⁸O记录显示，在约1600万至1480万年前存在多次大幅波动，随后在1480万年前之后出现一系列快速（<50千年，kyr）的δ¹⁸O升高事件，暗示海洋-气候系统进入了新的状态。中中新世底栖氧同位素总增幅达1.2‰，主要分为两个阶段：1450万至1400万年前增幅0.8‰，以及1345万至1245万年前的第二次增幅0.7‰。每个阶段均由一系列显著的δ¹⁸O升高事件构成，指示东南极冰盖（East Antarctic ice sheet）快速扩张与同期深水冷却。
1450万至1400万年前，底栖与深栖浮游物种的δ¹⁸O值呈现0.7‰的强协变关系（包括1410万至1405万年前的快速升高），表明由于东南极冰盖扩张，海水氧同位素组成（δ¹⁸Osw）升高了0.7‰。对四叶球室虫（Globigerinoides quadrilobatus）δ¹⁸O记录的对比显示，该站位表层海水在1410万至1360万年前升温约3℃。
各物种的碳同位素时间序列在早-中中新世时段（约1600万至1200万年前）整体呈现协变特征，证实该时段内δ¹³C变化主要反映了海洋储库变化。高分辨率δ¹³C数据进一步提升了早-中中新世著名碳同位素漂移事件（蒙特利碳同位素漂移（Monterey Carbon Isotopic Excursion），时限为1700万至1350万年前）所包含的6个碳同位素最大值中后5个的分辨率，这一结果对全球地层对比具有重要价值。其中最后一个最大值以1‰的降幅结束，降幅中心位于1390万至1370万年前，较被认为反映东南极冰盖扩张的δ¹⁸O升高事件晚约30万年。
约1600万至1380万年前，底栖δ¹⁸O与δ¹³C呈现协变关系，表明1380万年前之前全球碳循环与海洋-气候系统存在敏感关联。有机碳埋藏的阶段性增加可能促成了深海底栖δ¹³C最大值与同步的全球降温。这种正相关关系在约1380万年前终止，指示在1450万至1400万年前的大规模冰盖扩张阶段之后，东南极冰盖稳定性增强，由此引发了全球碳循环与海洋-气候系统之间关系的改变。