The Ediacaran ocean recorded the largest negative carbonate carbon isotope (δC) excursion in Earth's history, the Shuram Excursion (SE). The relatively invariant character of organic carbon isotope (δC) profiles during the SE has been attributed to buffering by a large dissolved organic carbon (DOC) reservoir in the ocean. However, recent studies suggest that the DOC buffering may have been highly heterogeneous, a hypothesis that can be tested by assessing variability in the spatial and temporal ranges of δC buffering during the SE. In this study, we evaluated δC and δC records from multiple regions globally to test the heterogeneous buffering hypothesis. Making use of a high-precision astrochronological framework, we found that the buffering effect of DOC persisted for ∼2.7 Myr in Oman, ∼4.9 Myr in South China, and ∼5.9 Myr in Australia, demonstrating its temporal heterogeneity. Heterogeneous buffering is also demonstrated at a small spatial scale for South China sections based on a correlation framework subdividing the SE into three intervals: EN3a (δC decline from baseline to nadir), EN3b (δC stabilized at nadir), and EN3c (δC recovery from nadir value). The duration of δC buffering increased with water depth from shallow neritic to deep pelagic areas. The buffering effect terminated within EN3a in inner-shelf areas, within EN3b in an intra-shelf basin, and within EN3c in slope areas. Spatial variation in the offset between δC and δC values (ΔC) is consistent with multiple sources of sedimentary organic matter. An average of ∼26 ‰ in inner-shelf areas implies mainly fresh phytoplankton debris, whereas an average of ∼18 ‰ in slope areas is consistent with dominance of DOC, which is thought to have been present in abundance in deeper anoxic watermasses. Thus, our study supports a large DOC reservoir in the late Ediacaran ocean that led to heterogeneous buffering during the SE at both basinal and global scales. Large shallow-to-deep oceanic δC and δC gradients of similar magnitude existed both before and during the SE, indicating that the circulation and productivity dynamics of the Ediacaran ocean were not significantly changed by the SE. The downward expansion of oxidant-rich surface watermasses during the SE improved the ventilation of shelf oceans while leaving the deep ocean anoxic, setting the stage for rapid biological evolution on continental shelves during the Cambrian Explosion.

中文翻译：

---

Shuram 偏移期间 δ13Corg 和 δ13Ccarb 的异质耦合：对埃迪卡拉海洋中大型溶解有机碳库的影响


埃迪卡拉纪海洋记录了地球历史上最大的负碳酸盐碳同位素 (δ13C) 偏移，即舒拉姆偏移 (SE)。 SE期间有机碳同位素（δ13C）剖面相对不变的特征归因于海洋中大型溶解有机碳（DOC）库的缓冲。然而，最近的研究表明，DOC 缓冲可能具有高度异质性，这一假设可以通过评估 SE 期间 δ13C 缓冲的空间和时间范围的变化来检验。在本研究中，我们评估了全球多个地区的 δ13C 和 δ13C 记录，以检验异质缓冲假设。利用高精度天文年代学框架，我们发现DOC的缓冲效应在阿曼~2.7 Myr、华南~4.9 Myr和澳大利亚~5.9 Myr持续存在，证明了其时间异质性。华南地区的异质缓冲也在小空间尺度上得到了证明，该框架基于将 SE 细分为三个区间的相关框架：EN3a（δ13C 从基线下降到最低点）、EN3b（δ13C 稳定在最低点）和 EN3c（δ13C 从基线到最低点的恢复）最低值）。从浅海区到深海区，δ13C缓冲的持续时间随着水深的增加而增加。缓冲效应在陆架内区域的 EN3a 内、陆架内盆地的 EN3b 内以及斜坡区域的 EN3c 内终止。 δ13​​C 和 δ13C 值 (ΔC) 之间偏移的空间变化与沉积有机质的多种来源一致。内陆架区域的平均值~26‰意味着主要是新鲜的浮游植物碎片，而斜坡区域的平均值~18‰与DOC的主导地位一致，DOC被认为在更深的缺氧水体中大量存在。 因此，我们的研究支持了埃迪卡拉晚期海洋中存在一个大型 DOC 储层，这导致了东南部在盆地和全球尺度上的异质缓冲。 SE之前和期间都存在类似大小的大的浅海到深海δ13C和δ13C梯度，表明SE没有显着改变埃迪卡拉纪海洋的环流和生产力动态。东南时期富含氧化剂的表层水团向下扩张，改善了陆架海洋的通风，同时使深海缺氧，为寒武纪大爆发期间大陆架上的快速生物进化奠定了基础。