DataSheet_1_Digging Deeper: Bioturbation increases the preserved sulfur isotope fractionation.docx

Bioturbation enhances mixing between the seafloor and overlying ocean due to changes the redox state of the sediment and influences the biogeochemical cycling of redox-sensitive elements such as sulfur. Before the widespread appearance of burrowing fauna over the Proterozoic-Phanerozoic transition, marine sediments were largely undisturbed and transport of material across the sediment-water interface was diffusion-dominated. Through both a microcosm experiment and numerical model, we show that the effect of bioturbation on marine sediments is to enhance the drawdown of sulfate from the water column into the sediment and thus “open-up” the sedimentary system. The key finding is that bioturbation increases the difference between the isotopic signature of seawater sulfate and pore water sulfide, the latter of which is preserved in sedimentary sulfide minerals. Our study empirically demonstrates a long-held assumption and helps identify the isotopic impact of bioturbation in the geological record and its environmental effects in modern marine systems.

生物扰动(bioturbation)通过改变沉积物的氧化还原状态，强化了海底与上覆海水之间的混合过程，并影响硫等氧化还原敏感元素的生物地球化学循环。在元古宙-显生宙转折期钻孔动物群广泛出现之前，海洋沉积物基本未受扰动，沉积物-水界面的物质传输以扩散作用为主导。本研究结合微宇宙实验与数值模型，证实生物扰动对海洋沉积物的作用是增强硫酸盐从水体向沉积物的垂向淋滤，进而"开放"沉积体系。本研究的核心发现为，生物扰动会扩大海水硫酸盐与孔隙水硫化物的同位素组成差异，而孔隙水硫化物会保存在沉积硫化物矿物中。本研究实证验证了一项长期存在的学术假设，同时有助于识别地质记录中生物扰动的同位素效应，及其在现代海洋系统中的环境影响。