Late Pleistocene stable isotope record of planktonic foraminifera from ODP Site 124-769

A reconstruction of late Pleistocene surface water carbon isotopic (delta13C) variability is presented from Ocean Drilling Program (ODP) site 769 in the Sulu Sea in the western tropical Pacific. The Sulu Sea is a shallowly silled back arc basin with a maximum sill depth of 420 m. Site 769 was drilled on a bathymetric high in 3643 m of water and has average late Pleistocene sedimentation rates of 8.5 cm/kyr. The oxygen isotope record (delta18O) of Globigerinoides ruber at site 769 shows a strong correlation with the SPECMAP stacked delta18O record, attesting to the continuity of sediment archive at the site. Surface delta13C displays consistent glacial-interglacial variability which averages ~0.9 per mil and has varied from 0.75 to 1.1 per mil over the last 800 kyr. Comparison to surface water delta13C records in the South China Sea and western tropical Pacific suggests that the glacial-interglacial surface delta13C variability is regional in scale. Planktonic delta13C data from ODP site 677 in the eastern Pacific is also coherent with the site 769. Additionally, we have found that the site 769 surface delta13C record is coherent at periods of 100 and 41 kyr with deepwater delta13C records from the Pacific. The highest correlation occurs with the deep eastern Pacific, where benthic delta13C data from cores RC13-110 and ODP site 677 closely match the Sulu Sea surface water record. We evaluate several possible controls of surface water delta13C in the Sulu Sea that may explain the coherent timing with Pacific deepwater delta13C records. These include variations in terrestrial organic matter flux to the basin, the upwelling of subsurface water and productivity changes, and the influx of western Pacific intermediate water to the Sulu Sea. Our preferred explanation involves a region of upper intermediate water upwelling in the far western Pacific which has been shown to outgas CO2 from subsurface waters into surface waters. Upwelling also occurs in the area of Panama Basin site 677. These equatorial upwelling zones could potentially provide a route by which Pacific intermediate water can modulate the delta13C composition of certain Pacific surface water locations. Future reconstructions of late Pleistocene surface water delta13C variability in the western Pacific and Indonesian seas will be required to further evaluate the source of the glacial-interglacial surface water delta13C change.

本研究基于西热带太平洋苏禄海大洋钻探计划（Ocean Drilling Program, ODP）769站位，重建了晚更新世地表水碳同位素（δ¹³C）的变化特征。苏禄海为浅海槛弧后盆地，最大海槛深度达420米。769站位钻取于水深3643米的地形高地，晚更新世平均沉积速率为8.5 cm/kyr。该站位红拟抱球虫（Globigerinoides ruber）的氧同位素（δ¹⁸O）记录与SPECMAP堆叠氧同位素记录具有极强相关性，证实了本站位沉积记录的连续性。地表水δ¹³C呈现出清晰的冰期-间冰期旋回变化，平均值约为0.9‰，在过去80万年中变化范围为0.75‰至1.1‰。将其与南海及西热带太平洋的地表水δ¹³C记录对比后发现，冰期-间冰期尺度的地表水δ¹³C变化具有区域尺度特征。东太平洋ODP 677站位的浮游有孔虫δ¹³C数据同样与769站位记录具有一致性。此外，本研究发现769站位的地表水δ¹³C记录在100 kyr和41 kyr周期上与太平洋深水δ¹³C记录具有相干性。其中与东太平洋深水记录的相关性最高，来自岩芯RC13-110和ODP 677站位的底栖δ¹³C数据与苏禄海地表水记录匹配度极佳。本研究评估了苏禄海水表水δ¹³C变化的多种潜在控制机制，以解释其与太平洋深水δ¹³C记录的同步性。这些机制包括：陆源有机质向盆地的输入通量变化、次表层水上升流与生产力变化，以及西太平洋中层水涌入苏禄海。本研究支持的解释机制为：西太平洋远域存在上层中层水上升流区，该区域已被证实会将地下水中的CO₂释放至表层水中；巴拿马盆地677站位所在区域同样存在上升流。这些赤道上升流区可能为太平洋中层水调节特定太平洋区域地表水δ¹³C组成提供了通道。未来需开展西太平洋及印尼海的晚更新世地表水δ¹³C变化重建工作，以进一步评估冰期-间冰期尺度地表水δ¹³C变化的驱动源。