Institute of Earth Sciences, China University of Geosciences (Beijing), Beijing 100083, China.
Institute of Earth Sciences, China University of Geosciences (Beijing), Beijing 100083, China.
Sci Total Environ. 2021 Nov 1;793:148562. doi: 10.1016/j.scitotenv.2021.148562. Epub 2021 Jun 22.
Understanding the environmental iron cycle influenced by natural and anthropogenic processes is significant to obtain the key information on earth-surface evolution. Iron isotope compositions and elemental compositions of the suspended particulate matter (SPM) in Zhujiang River were investigated to provide key insights for the earth-surface iron cycle. The δFe values of SPM display the range from -0.05‰ to 0.34‰ (averaged 0.19‰) while the iron contents range from 0.73 wt% to 7.63 wt% (averaged 4.15 wt%). The Chemical Index of Alteration (CIA) shows that the main weathering type of SPM is intermediate weathering (mean CIA value: 79.12). While the main chemical weathering types are similar, the δFe values vary dramatically, indicating that chemical weathering is not the governing factor of δFe values of SPM. Furthermore, evidence from the enrichment factors (EF, 0.78 to 1.29) of iron and Zinc isotopes reveals that the iron input from anthropogenic activities is quite limited. The significant correlation between (Fe/Ca)SPM and (Na/Ca)SPM, (Mg/Ca)SPM, (Al/Ca)SPM and (K/Ca)SPM (0.73 < r < 0.99, p < 0.01, n = 22) and the A-CN-K diagram could confirm that clay minerals (especially smectite and illite) are important components of SPM. Meanwhile, the higher enrichment rates of La, Pr and Nd with the increasing iron contents denote heavy minerals (mainly Fe oxides/oxy-hydroxides) are also important compositions of SPM. Based on the isotopic mass balance, it shows that the iron flux of SPM to the oceans during the wet season would reduce the δFe values of the bulk ocean by 0.3%. The present study reports the iron isotope and elemental compositions of Zhujiang SPM and identifies its influencing factors (weathering, anthropogenic inputs, and minerals effect), and also provides a quantitative reference for the intriguing question on the distinct δFe values of oceans, which is beneficial for understanding iron cycle in earth-surface system.
了解自然和人为过程影响下的环境铁循环对于获取地球表面演化的关键信息具有重要意义。本研究分析了珠江悬浮物中 Fe 同位素组成和元素组成，为地球表面铁循环提供了关键信息。珠江悬浮物的 δFe 值范围为-0.05‰至 0.34‰（平均值为 0.19‰），铁含量范围为 0.73wt%至 7.63wt%（平均值为 4.15wt%）。化学蚀变指数（CIA）表明，珠江悬浮物的主要风化类型为中度风化（平均 CIA 值：79.12）。尽管主要的化学风化类型相似，但 δFe 值变化显著，表明化学风化不是控制珠江悬浮物 δFe 值的主导因素。此外，铁和锌同位素富集因子（EF，0.78 至 1.29）的证据表明，人为活动输入的铁非常有限。（Fe/Ca）SPM 与（Na/Ca）SPM、（Mg/Ca）SPM、（Al/Ca）SPM 和（K/Ca）SPM 之间的显著相关性（0.73<r<0.99，p<0.01，n=22）和 A-CN-K 图可以证实粘土矿物（特别是蒙脱石和伊利石）是悬浮物的重要组成部分。同时，随着铁含量的增加，La、Pr 和 Nd 的富集率较高，表明重矿物（主要为 Fe 氧化物/氢氧化物）也是悬浮物的重要组成部分。根据同位素质量平衡，珠江悬浮物在雨季向海洋输送的铁通量会使大洋的 δFe 值降低 0.3%。本研究报告了珠江悬浮物的铁同位素和元素组成，并确定了其影响因素（风化、人为输入和矿物效应），为海洋中独特的 δFe 值这一有趣问题提供了定量参考，有助于理解地球表面系统中的铁循环。
