Efficacy of ²³⁰Th normalization in sediments from the Juan de Fuca Ridge, northeast Pacific Ocean

详细信息    查看全文

• 作者：Kassandra Costa ; ^{kcosta@ldeo.columbia.edu} ; Jerry McManus ^{jmcmanus@ldeo.columbia.edu}
• 关键词：230Th normalization ; Sediment focusing ; Juan de Fuca Ridge
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2017
• 出版时间：15 January 2017
• 年：2017
• 卷：197
• 期：Complete
• 页码：215-225
• 全文大小：921 K
• 卷排序：197

文摘

230Th normalization is an indispensable method for reconstructing sedimentation rates and mass fluxes over time, but the validity of this approach has generated considerable debate in the paleoceanographic community. 230Th systematics have been challenged with regards to grain size bias, sediment composition (CaCO3), water column advection, and other processes. In this study, we investigate the consequences of these effects on 230Th normalization from a suite of six cores on the Juan de Fuca Ridge. The proximity of these cores (<30 km) suggests that they should receive the same particle rain rate of sediment, but the steep bathymetry of the ridge leads to substantial sediment redistribution and variable carbonate preservation, both of which may limit the usage of 230Th in this region. Despite anticipated complications, 230Th normalization effectively reconstructs nearly identical particle rain rates from all six cores, which are summarily unrelated to the total sedimentation rates as calculated from the age models. Instead the total sedimentation rates are controlled almost entirely by sediment focusing and winnowing, which are highly variable even over the short spatial scales investigated in this study. Furthermore, no feedbacks on 230Th systematics were detected as a consequence of sediment focusing, coarse fraction variability, or calcium carbonate content, supporting the robustness of the 230Th normalization technique.