Abstract The East Asian monsoon system influences the local oceanographic and climatic conditions of South China Sea (SCS), making the habitat depths of planktonic foraminifera (PF) specific for this region.The previous paleo-ocean reconstructions of SCS have been based on calcification habitat depths derived from other oceans, which may have affected the accuracy of interpretations. In this study, the calcification depths of Globigerinoides ruber, Globigerinoides sacculifer, and Neogloboquadrina dutertrei from sediment traps deployed at 1000 m depth off southwest Hainan Island from July 2012 to April 2013 were analyzed with regard to the stable isotopes of oxygen (δ18O) and carbon (δ13C) to calculate their regional apparent calcification depths (ACDs) with the overall aim to improve the reconstruction of the upper ocean thermal structure. ACDs and temperature estimated from foraminifera δ18O ranged from 0 to 42 m and 25°C for G. ruber, 30-65 m and 23.3°C for G. sacculifer, and 75-100 m and 20.3°C for N. dutertrei, respectively. The difference between the thermocline-species (N. dutertrei) and mixed-layer species (G. ruber and G. sacculifer) δ18O (∆δ18OTh–ML) and the temperature (∆T) shows water column stratification. The periods of lower and higher ∆T and ∆δ18O were in phase with the changes in regional overlying wind speed. Additionally, this study reveals that N. dutertrei lives and calcifies its shells within the base of the mixed-layer depth (MLD) and upper thermocline depth in SCS. Overall, the results from this study provide a new insight to understand the mixed-layer and thermocline depth in the northern SCS.

中文翻译：

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海南岛西南部浮游有孔虫钙化深度和温度及其古海洋意义

摘要 东亚季风系统影响了南海 (SCS) 当地的海洋和气候条件，使浮游有孔虫 (PF) 的栖息地深度成为该地区特有的。以前南海的古海洋重建都是基于钙化栖息地来自其他海洋的深度，这可能影响了解释的准确性。本研究对 2012 年 7 月至 2013 年 4 月海南岛西南外 1 000 m 深沉积物圈闭中 Globigerinoides ruber、Globigerinoides sacculifer 和 Neogloboquadrina dutertrei 的钙化深度进行了氧（δ18O）和碳的稳定同位素分析。 (δ13C) 计算其区域表观钙化深度 (ACDs)，总体目标是改善上层海洋热结构的重建。从有孔虫 δ18O 估计的 ACD 和温度范围分别为 0 到 42 m 和 G. ruber 的 25°C，G. sacculifer 的 30-65 m 和 23.3°C，以及 N. dutertrei 的 75-100 m 和 20.3°C . 温跃层物种 (N. dutertrei) 和混合层物种 (G. ruber 和 G. sacculifer) δ18O (Δδ18OTh–ML) 和温度 (ΔT) 之间的差异表明水柱分层。ΔT 和Δδ18O 的较低和较高的时期与区域上覆风速的变化同相。此外，这项研究表明，N. dutertrei 生活在 SCS 中混合层深度 (MLD) 和上温跃层深度的底部并使其壳钙化。总的来说，这项研究的结果为了解南海北部的混合层和温跃层深度提供了新的见解。