Revisiting the dependence of thermocline-dwelling foraminiferal B/Ca on temperature and [CO32-], and its application in reconstruction of the subsurface carbonate system in the tropical western Pacific since 24 ka

• Published in: Acta Oceanologica Sinica
• Main Authors: Guo, Jingteng, Li, Tiegang, Xiong, Zhifang, Qiu, Xiaohua, Chang, Fengming
• Format: Report
• Language: English
• Published: SPRINGER 2019
• Subjects: planktonic foraminifera; B; Ca; carbonate chemistry; tropical western Pacific; South China Sea; Oceanography; Pacific; Planktonic foraminifera
• Online Access: http://ir.qdio.ac.cn/handle/337002/162977; http://ir.qdio.ac.cn/handle/337002/162978; https://doi.org/10.1007/s13131-019-1476-y

The B/Ca ratio of planktonic foraminifer shells has been used as a proxy for reconstructing past ocean carbonate chemistry. However, recent studies have revealed significant uncertainties associated with this proxy, such as whether seawater temperature or [CO32-] is the dominant control on the partition coefficient (K-D) of planktonic foraminiferal B/Ca. To address these uncertainties and thus improve our understanding of the planktonic foraminiferal B/Ca proxy, we analysed B/Ca ratios in the tests of Neogloboquadrina dutertrei (300-355 urn) and Pulleniatina obliquiloculata (355-400 mu m) in surface sediment samples from the tropical western Pacific and South China Sea. The relationship between these B/Ca ratios and bottom water calcite saturation states (Delta[CO32-]) is weak, thus suggesting only a small dissolution effect on the B/Ca of the two species. The correlation coefficients (R-2) between the B/Ca ratios of N. dutertrei and P. obliquiloculata and environmental parameters (e.g., temperature, salinity, phosphate, DIC and ALK) in the tropical western Pacific and South China Sea are not high enough to justify using B/Ca ratios as a palaeoenvironmental proxy in the study areas. The significant correlation between K-D values of N. dutertrei and P. obliquiloculata and carbonate system parameters (e.g., [CO32-], DIC, ALK, pH and [HCO3-]) in the study area reflect chemical links between the K-D denominator and these variables. Based on our surface sediment calibration, an empirical relationship between the K-D of N. dutertrei and temperature is proposed in the tropical western Pacific. We also generated a record of B/Ca ratios in N. dutertrei (300-355 mu m) from Core MD06-3052 in the tropical western Pacific over the past 24 ka to evaluate the application of the revised B/Ca proxy method. Based on the reconstructed empirical relationship for B/Ca and subsurface seawater ALK, we estimated subsurface seawater carbonate system parameters in the tropical western Pacific since 24 ka. In general, the estimated ...