Rapid, concurrent formation of organic sulfur and iron sulfides during experimental sulfurization of sinking marine particles

The redox speciation and bonding environment of sulfur and iron in filter-bound, sinking marine particles from the eastern tropical North Pacific O₂-Deficient Zone were analyzed at the Stanford Synchrotron Radiation Lightsourse (SSRL). Glass fiber filter pieces were adhered onto Saint Gobain M60 S-free polyester tape and covered in 5-μm-thick SPEX 3520 polypropylene XRF film. ‘Bulk’ sulfur K-edge spectra (500 mm² spot size) were collected on beam line 14–3 on whole particles, solvent-extracted particles, HCl-extracted particles, and lipid extracts, before and after copper exposure. Additionally, a micro-focused X-ray beam was used to map S and Fe species by rastering over selected mapping areas at specific energies (for sulfur: 2472.0, 2472.9, 2473.9, 2474.25, 2476.15, 2477.8, 2481.4, 2482.6, and 2486.0 eV; for iron: 7116.0, 7128.0, 7133.0, 7139.0, and 7147.0 eV) to create elemental and chemical distribution maps. Full XAS spectra were collected from 2460 to 2540 eV (sulfur) or 6900 to 7500 eV (iron) at selected spots.Sulfur data were collected at SSRL beam line 14–3, which is equipped with a Si(111) (Φ = 90) double crystal monochromator and calibrated to the thiol pre-edge peak of thiosulfate at 2472.02 eV. The S Ka fluorescence line was measured with a Si Vortex Si drift detector (Hitachi) using Xspress3 pulse processing electronics (Quantum Detectors). The X-ray beam was focused using an axially symmetric focusing mirror (SIGRAY) to a size of 5 x 5 µm at a flux of ~8 x 10¹⁰ photons per second; maps were collected at a resolution of 5 mm². Sulfur XAS spectra were processed in the SIXPACK (Webb, 2005; Webb, 2020) software package using a K-edge E0 of 2473 and pre-edge and post-edge linear normalization ranges of –20 to –7 and 35 to 70 eV, respectively. Uncertainties reported in Table S3 refer to the confidence in the linear combination fit calculated in SIXPACK. Iron data were collected at SSRL beam line 2–3, a bending magnet workstation equipped with a Si(111) (Φ = 0) double crystal monochromator calibrated such that the first derivative of an Fe metal foil was set to 7112 eV. The beam line uses an axially symmetric focusing mirror (SIGRAY) to achieve a spot size of 5 x 5 µm at a flux of ~5 x 10⁸ photons per second at 7100 eV, and uses a similar fluorescence data collection system as above with 14-3 to collect k-edge Fe spectra from 6900 to 7500 eV and elemental maps of Ca, P, Mn, Ti, S, and other metals at 5-mm resolution.

本数据集针对东热带北太平洋缺氧区（O₂-Deficient Zone）中滤膜捕获的沉降海洋颗粒内硫与铁的氧化还原形态及键合环境，于斯坦福同步辐射光源（Stanford Synchrotron Radiation Lightsourse, SSRL）开展分析。
将玻璃纤维滤膜片段粘贴至圣戈班M60无硫聚酯胶带（Saint Gobain M60 S-free polyester tape）之上，并以厚度为5 μm的SPEX 3520聚丙烯XRF膜覆盖。
针对完整颗粒、溶剂萃取颗粒、盐酸萃取颗粒及脂质提取物，在铜暴露前后分别采集了“整体”硫K边光谱（光斑尺寸为500 mm²），测试所用光束线为14–3号线。
此外，研究采用微聚焦X射线束，通过在选定成像区域以特定能量逐行扫描，完成硫与铁物种的成像测绘：硫的扫描能量为2472.0、2472.9、2473.9、2474.25、2476.15、2477.8、2481.4、2482.6及2486.0 eV；铁的扫描能量为7116.0、7128.0、7133.0、7139.0及7147.0 eV，以此生成元素与化学分布图谱。
在选定点位采集完整的X射线吸收光谱（X-ray Absorption Spectroscopy, XAS）：硫的扫描范围为2460~2540 eV，铁的扫描范围为6900~7500 eV。

硫的XAS数据采集于SSRL 14–3光束线，该光束线配备Si(111)（Φ=90）双晶单色器，并以2472.02 eV处的硫代硫酸盐巯基预边缘峰进行能量校准。
采用Si Vortex硅漂移探测器（Hitachi）搭配Xspress3脉冲处理电子学系统（Quantum Detectors）测量S Ka荧光谱线。
X射线束通过轴对称聚焦镜（SIGRAY）聚焦至5×5 μm的光斑尺寸，通量约为8×10¹⁰ 光子/秒；成像测绘以5 mm²的分辨率完成。
硫的XAS光谱采用SIXPACK软件包（Webb, 2005; Webb, 2020）进行处理，K边能量零点（E₀）设为2473 eV，预边缘与后边缘的线性归一化范围分别为–20~–7 eV与35~70 eV。
表S3中报告的不确定度，对应于SIXPACK软件中线性组合拟合的置信度。

铁的XAS数据采集于SSRL 2–3光束线，该弯铁工作站配备Si(111)（Φ=0）双晶单色器，校准方式为将金属铁箔的一阶导数峰设为7112 eV。
该光束线采用轴对称聚焦镜（SIGRAY），在7100 eV处可实现5×5 μm的光斑尺寸，通量约为5×10⁸ 光子/秒；其荧光数据采集系统与14–3号线类似，可采集6900~7500 eV范围内的铁K边光谱，以及分辨率为5 mm的钙、磷、锰、钛、硫及其他金属的元素成像图谱。