The late Cambrian Steptoean positive carbon isotope excursion (SPICE) is a distinct chemostratigraphic feature of the Paleozoic, marked by a 4–5‰ shift in carbonate δ¹³C that has been recognized across the globe during the Paibian Stage. The SPICE may be related to enhanced burial of organic matter and pyrite during the expansion of marine euxinia, which as a source of O₂ also results in a pulse of atmospheric oxygen. However, geochemical proxies have not clearly illustrated how the ocean redox evolved with atmospheric oxygen changes during the SPICE. This study presents new carbonate I/Ca data, a redox proxy for the upper ocean, from three basins. I/Ca values are low at Great Basin and South China from early into the peak of SPICE, indicating generally anoxic conditions in shallow waters. The overall increasing trend in I/Ca through the peak and recovery phase of the SPICE roughly correlates with the previously modeled rise in atmospheric oxygen. Spatially, the Georgina Basin (Mt. Whelan) might have recorded a relatively more oxic upper ocean compared to the Great Basin and South China. Earth system model simulations also demonstrate the importance of paleogeographic and oceanographic settings on local redox conditions, highlighting the redox heterogeneity during the SPICE.

晚寒武世阶梯正碳同位素漂移（SPICE）是古生代的一个独特的化学地层特征，其特征是碳酸盐δ ¹³ C发生了4-5‰的变化，这一变化在排边阶段已在全球范围内得到认可。SPICE可能与海洋真核扩张过程中有机物和黄铁矿的埋藏增强有关，海洋真核作为O _2的来源也导致了大气氧的脉冲。然而，地球化学指标尚未清楚地说明 SPICE 期间海洋氧化还原如何随大气氧变化而演变。这项研究提出了来自三个盆地的新碳酸盐 I/Ca 数据，这是上层海洋的氧化还原代理。从早期到 SPICE 高峰期，大盆地和华南地区的 I/Ca 值较低，表明浅水区普遍缺氧。通过 SPICE 的峰值和恢复阶段，I/Ca 的整体增加趋势与之前模拟的大气氧含量的增加大致相关。在空间上，与大盆地和华南相比，乔治娜盆地（惠兰山）可能记录了相对较高含氧量的上层海洋。地球系统模型模拟还证明了古地理和海洋环境对局部氧化还原条件的重要性，突出了 SPICE 期间的氧化还原异质性。