(Table 1) Concentrations of Os, Ir, Pt and 187Os/188Os ratios for ODP Hole 138-849D samples

Osmium isotope composition (187Os/188Os) and concentrations of Os, Ir and Pt are reported for an early Pleistocene section from the ODP Site 849 in the eastern equatorial Pacific. Using the data obtained in this study, the contributions from detrital and extraterrestrial particulate matter to Os concentration and 187Os/188Os of sediment are estimated. Our calculations show that detrital contributions to sedimentary Os are too small (<2%) to significantly shift measured bulk sediment 187Os/188Os away from seawater values. A moderate but significant negative correlation between 187Os/188Os and 3He/188Os indicate that the average particulate extraterrestrial Os flux to this site is 1.21 ± 0.47 pg cm**-2/ kyr, which constitutes <=3% of total Os burial flux. The estimates of detrital and extraterrestrial Os are used to calculate the seawater 187Os/188Os in the early Pleistocene. The most notable features of this early Pleistocene 187Os/188Os record are: (1) glacial–interglacial 187Os/188Os differences are insignificant within errors of estimates, (2) glacial 187Os/188Os values are higher compared to those reported for the late Pleistocene glacials. Comparison of 187Os/188Os values at Site 849 to the late Pleistocene records suggests that average seawater 187Os/188Os change has been modest (~5%) since the early Pleistocene. Assuming that 187Os/188Os difference between the glacial periods of the late and the early Pleistocene results solely from temperature dependence of weathering rates, it has been calculated that average surface temperature during the late Pleistocene glacials was 0.8 ± 0.2 °C lower than glacials in the early Pleistocene. This inference is consistent with temperature estimates based on a recent study of pCO2 reconstruction in the Pleistocene. This observation based on limited studies of marine 187Os/188Os records seems to suggest that temperature played an important role in influencing chemical weathering during the Pleistocene glacials. However, more studies are needed to confirm if this temperature-weathering feedback was operational throughout the Pleistocene. A significant down core Ir–3He co-variation coupled with similar burial fluxes of Ir at Site 849 and at LL44 GPC-3 in the north Pacific point to the utility of Ir concentration as a point paleoflux tracer. However, a twofold difference in Ir burial fluxes between the eastern and the western equatorial Pacific suggests that calibration in space and time is required to use Ir concentration as a robust indicator of paleoflux through time. Significant co-variation of concentrations of Os and total alkenone during the glacials coupled with lighter d13C of benthic foraminifera indicates that productivity and carbon burial played a dominant control on scavenging of Os at Site 849. In a broader context, this data set encourages future investigation of response of PGE behavior to paleoceanographic processes.

本数据集收录了东赤道太平洋大洋钻探计划（Ocean Drilling Program, ODP）849站位早更新世剖面的锇同位素组成（¹⁸⁷Os/¹⁸⁸Os），以及锇（Os）、铱（Ir）与铂（Pt）的浓度数据。基于本研究获取的实验数据，我们估算了陆源与地外颗粒物对沉积物中锇浓度及¹⁸⁷Os/¹⁸⁸Os比值的贡献。计算结果显示，沉积物中陆源锇的占比极低（<2%），不足以使测得的沉积物整体¹⁸⁷Os/¹⁸⁸Os比值偏离海水同位素基准值。¹⁸⁷Os/¹⁸⁸Os与³He/¹⁸⁸Os之间存在显著的中度负相关关系，表明该站位的平均地外颗粒物锇通量为1.21 ± 0.47 pg·cm⁻²·kyr⁻¹，该通量占总锇埋藏通量的比例不超过3%。
基于陆源和地外锇的贡献估算结果，我们计算了早更新世海水的¹⁸⁷Os/¹⁸⁸Os比值。该早更新世¹⁸⁷Os/¹⁸⁸Os记录最显著的特征为：（1）冰期-间冰期的¹⁸⁷Os/¹⁸⁸Os差异在估算误差范围内可忽略不计；（2）早更新世冰期的¹⁸⁷Os/¹⁸⁸Os比值高于晚更新世冰期的已报道数值。将849站位的¹⁸⁷Os/¹⁸⁸Os比值与晚更新世记录对比后发现，自早更新世以来，海水平均¹⁸⁷Os/¹⁸⁸Os的变化幅度较小（约5%）。
假设晚更新世与早更新世冰期的¹⁸⁷Os/¹⁸⁸Os差异仅由风化速率的温度依赖性所致，计算得出晚更新世冰期的平均地表温度较早更新世冰期低0.8 ± 0.2 ℃。该推论与近期一项基于更新世pCO₂重建的温度估算结果一致。这项基于有限海洋¹⁸⁷Os/¹⁸⁸Os记录的观测结果表明，温度在更新世冰期的化学风化过程中发挥了重要作用，但仍需更多研究证实这种温度-风化反馈机制在整个更新世时期均有效。
849站位与北太平洋LL44 GPC-3站位的铱埋藏通量相近，且岩芯中铱与³He存在显著的共变关系，这表明铱浓度可作为一种有效的古通量示踪剂。然而，赤道东太平洋与赤道西太平洋的铱埋藏通量存在两倍差异，这意味着若要将铱浓度作为可靠的古通量随时间变化的指示指标，需进行空间与时间上的校准。冰期阶段锇浓度与总烯酮（alkenone）含量显著共变，加之底栖有孔虫（benthic foraminifera）的δ¹³C值较轻，表明生产力与碳埋藏对849站位锇的清除沉降过程占据主导控制作用。
从更广泛的研究视角来看，本数据集可为未来探究铂族元素（Platinum Group Elements, PGE）行为对古海洋过程的响应提供重要支撑。