Carbon isotope (δ¹³C) records from marine sediments and sedimentary rocks have been extensively used in Cenozoic chemostratigraphy. The early Paleogene interval in particular has received exceptional attention because negative carbon isotope excursions (CIEs) documented in the sedimentary record, for example, at the Paleocene Eocene Thermal Maximum (PETM), ca ∼56 Ma, are believed to reflect significant global carbon cycle perturbations during the warmest interval of the Cenozoic era. However, while bulk carbonate δ¹³C values exhibit robust correlations across widely separated marine sedimentary basins, their absolute values and magnitude of CIEs vary spatially, especially over time intervals characterized by major deviations in global carbon cycling. Moreover, bulk carbonates in open‐marine environments are an ensemble of different components, each with a distinct isotope composition. Consequently, a comprehensive interpretation of the bulk‐δ¹³C record requires an understanding of co‐evolution of these components. In this study, we dissect sediments, from the late Paleocene‐early Eocene interval, at ODP Site 1209 (Shatsky Rise, Pacific Ocean) to investigate how a temporally varying bulk carbonate ensemble influences the overall carbon isotope record. A set of 45 samples were examined for δ¹³C and δ¹⁸O compositions, as bulk and individual size fractions. We find a significant increase in coarse‐fraction abundance across the PETM, driven by a changing community structure of calcifiers, modulating the size of the CIE at Site 1209 and thus making it distinct from those recorded at other open‐marine sites. These results highlight the importance of biogeography in the marine stable isotope record, especially when isotope excursions are driven by climate‐ and/or carbon cycle changes. In addition, community composition changes will alter the interpretation of weight percent coarse fraction as proxy for carbonate dissolution.

中文翻译：

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特定于规模分数的稳定同位素变异作为解释早期始新世大体积沉积物碳同位素记录的框架

碳同位素（δ ¹³ C）记录海洋沉积物和沉积岩已经在新生代化学地层被广泛使用。特别是早期古近纪间隔特别受到关注，因为沉积记录中记录的负碳同位素偏移（CIE）（例如，古新世始新世最大温度（PETM），约56 Ma）被认为反映了重要的全球碳循环。在新生代最温暖的时间间隔内发生扰动。然而，虽然散装碳酸盐δ ¹³C值在广泛分离的海洋沉积盆地中显示出稳固的相关性，它们的绝对值和CIE的大小在空间上变化，尤其是在以全球碳循环的主要偏差为特征的时间间隔内。此外，开放海洋环境中的散装碳酸盐是不同组分的集合，每个组分都有不同的同位素组成。因此，散装δ全面解读¹³ Ç记录不需要这些部件的协同进化的理解。在这项研究中，我们从新世晚期至始新世晚期的ODP站点1209（Shatsky Rise，太平洋）剖析了沉积物，以研究随时间变化的整体碳酸盐集合体如何影响总体碳同位素记录。一组45个样品进行了检查为δ ¹³C和δ ^18种ö组合物，体积和个体大小的级分。我们发现，通过改变钙化石的群落结构，调节站点1209上CIE的大小，从而使其不同于其他海洋开放站点上记录的CIE，可以使整个PETM的粗级分丰度显着增加。这些结果凸显了生物地理学在海洋稳定同位素记录中的重要性，尤其是当同位素偏移是由气候和/或碳循环变化驱动时。此外，群落组成的变化将改变对粗粒级分重量百分比的解释，以替代碳酸盐的溶解。