NOAA/WDS Paleoclimatology - Antarctic Intermediate Water properties since 400 ka recorded in benthic foraminifera

Reconstruction of intermediate water properties is important for understanding feedbacks within the ocean-climate system, particularly since these water masses are capable of driving high–low latitude teleconnections. Nevertheless, information about intermediate water mass evolution through the late Pleistocene remains limited. This paper examines changes in Antarctic Intermediate Water (AAIW), the most extensive intermediate water mass in the modern ocean through the last 400 kyr using the stable isotopic composition (δ18O and δ13C) and trace element concentration (Mg/Ca and B/Ca) of two benthic foraminiferal species from the same samples: epifaunal Planulina wuellerstorfi and infaunal Uvigerina peregrina. Our results confirm that the most reasonable estimates of AAIW temperature and Δ[CO2−3] are generated by Mg/CaU. peregrina and B/CaP. wuellerstorfi, respectively. We present a 400 kyr record of intermediate water temperature and Δ[CO2−3] from a sediment core from the Southwest Pacific (DSDP site 593; 40°30′S, 167°41′E, 1068 m water depth), which lies within the core of modern AAIW. Our results suggest that a combination of geochemical analyses on both infaunal and epifaunal benthic foraminiferal species yields important information about this critical water mass through the late Pleistocene. When combined with two nearby records of water properties from deeper depths, our data demonstrate that during interglacial stages of the late Pleistocene, AAIW and Circumpolar Deep Water (CPDW) have more similar water mass properties (temperature and δ13C), while glacial stages are typified by dissimilar properties between AAIW and CPDW in the Southwest Pacific. Our new Δ[CO2−3] record shows short time-scale variations, but a lack of coherent glacial–interglacial variability indicating that large quantities of carbon were not stored in intermediate waters during recent glacial periods.

中层水团属性的重建工作，对于厘清海洋-气候系统内部的反馈机制具有重要意义，尤其考虑到此类水团可驱动高纬度与低纬度间的遥相关过程。然而，目前关于更新世晚期中层水团演化的相关资料仍较为有限。本文以采自同一样品的两种底栖有孔虫——表生种*Planulina wuellerstorfi*与内生种*Uvigerina peregrina*的稳定同位素组成（δ¹⁸O、δ¹³C）及微量元素浓度（Mg/Ca、B/Ca）为代用指标，探究了过去40万年里现代海洋中分布最广的中层水团——南极中层水（Antarctic Intermediate Water, AAIW）的演化特征。本研究结果证实，分别利用*U. peregrina*的Mg/Ca比值与*P. wuellerstorfi*的B/Ca比值，可最合理地估算AAIW的温度与碳酸根离子浓度差（Δ[CO₃²⁻]）。我们基于西南太平洋海域一处位于现代AAIW核心区域的沉积岩芯（深海钻探计划（Deep Sea Drilling Program, DSDP）593站位：南纬40°30′，东经167°41′，水深1068米），构建了过去40万年的中层水温度与Δ[CO₃²⁻]演化记录。研究结果表明，同时对内生与表生底栖有孔虫开展地球化学分析，可为我们提供更新世晚期这一关键水团的重要信息。结合另外两份来自更深水深的邻近海域水团属性记录，我们的数据显示：更新世晚期的间冰期阶段，西南太平洋海域的AAIW与环极深层水（Circumpolar Deep Water, CPDW）的水团属性（温度与δ¹³C）更为相似；而冰期阶段则以两者属性存在显著差异为典型特征。我们新获得的Δ[CO₃²⁻]记录呈现出短时间尺度的波动，但未出现显著的冰期-间冰期旋回变化，这表明在近期冰期时段，并无大量碳储存在中层水体中。