末次冰消期以来东海内陆架沉积物活性铁命运及其环境响应^*

Fate of reactive iron in inner shelf sediments of the East China Sea in response to environmental evolution since the last deglaciation

摘要

陆架沉积物活性铁在海洋铁生物地球化学循环中扮演着重要角色,但是其对陆架沉积环境演化的响应机制还不明确。本研究以东海内陆架EC2005岩心沉积物为例,探讨末次冰消期以来沉积环境演化对东海内陆架活性铁命运的影响。EC2005岩心沉积物总铁/铝(Fe_T/Al)比值平均为0.54,活性铁/总铁(Fe_HR/Fe_T)比值平均为0.29,表明长江输入的陆源细粒沉积物是研究区主要的颗粒铁来源。活性铁组分的平均含量由高到低依次为易还原的(氢)氧化物铁(Fe_ox1,0.64%)、黄铁矿铁(Fe_py,0.32%)、可还原的(氢)氧化物铁(Fe_ox2,0.23%)、碳酸盐铁(Fe_carb,0.09%)。其中,Fe_py和Fe_carb含量随深度变化呈现出此消彼长的趋势,这是碳酸(氢)根离子和硫化物竞争亚铁离子的结果,受末次冰消期以来沉积环境和氧化还原状态的控制。Fe_ox1与有机碳含量的变化密切相关,并对Fe_py和Fe_carb含量的变化起着重要的控制作用。在陆相沉积环境中(17.3~13.1 ka),Fe_ox1主要转化为Fe_carb,Fe_py含量几乎为0;在海陆过渡环境中(13.1~7.3 ka),Fe_carb含量减少,Fe_py含量增加; 在海相沉积环境中(7.3 ka至今),Fe_py含量达到最大值,Fe_carb含量在表层显著增加。本研究强调了沉积环境演化对陆架活性铁命运的控制,为研究现代和深时海洋的C-S-Fe生物地球化学循环提供了新的视角。

Abstract

The reactive iron in shelf sediments plays an important role in the marine iron biogeochemical cycle,however,its response mechanism to the evolution of shelf sedimentary environments is still unclear. This study focuses on shelf sediments of core EC2005 from the East China Sea inner shelf to explore the influence of sedimentary environmental evolution on the fate of reactive iron since the last deglaciation. The average ratio of total iron to aluminum(Fe_T/Al)in core EC2005 sediments is 0.54,and the average ratio of reactive iron to total iron(Fe_HR/Fe_T)is 0.29,indicating that terrigenous fine-grained sediments input from the Changjiang River are the main source of particulate iron in the study area. The average content of reactive iron speciation from high to low is easily reducible(oxyhydr)oxide iron(Fe_ox1,0.64%),pyrite iron(Fe_py,0.32%),reducible(oxyhydr)oxide iron(Fe_ox2,0.23%)and carbonate iron(Fe_carb,0.09%). The relative contents of Fe_py and Fe_carb exhibit opposite trends along the core depth,indicating competition between carbonate(bicarbonate)ions and sulfide ions for ferrous iron during the early diagenetic process. This competition is primarily controlled by the sedimentary environment and redox state of the East China Sea inner shelf since the last deglaciation. Fe_ox1 is closely related to the change of organic carbon content and plays an important role in controlling the variations of Fe_py and Fe_carb contents. In continental environments(17.3-13.1 ka),Fe_ox1 is mainly converted into Fe_carb,and Fe_py content is almost zero. In transitional environments(13.1-7.3 ka),Fe_carb content decreases accompanied by an increase in Fe_py content. In marine environments(7.3 ka to present),Fe_py content reaches a maximum,and Fe_carb content increases significantly in the surface layers. Our findings highlight the control of the sedimentary environment on the fate of reactive iron in shelf sediments,providing a new perspective for studying modern and deep-time marine C-S-Fe biogeochemical cycles.

关键词

活性铁 / 东海内陆架 / 沉积环境 / 海平面变化 / 有机碳矿化

Key words

reactive iron / East China Sea inner shelf / sedimentary environment / sea level change / organic carbon mineralization

基金资助

*国家自然科学基金项目(编号: 42276060)和山东省优秀青年基金项目(编号: ZR2021YQ26)资助