Marine dissolved organic carbon (DOC) is the ocean's largest exchangeable reservoir of organic carbon. The biogeochemical cycling of DOC plays an important role in ocean carbon storage on various timescales. Solid-phase extraction (SPE) is a process used to isolate DOC from seawater for biogeochemical analysis. This study examines how DOC isotopic (Δ¹⁴C, δ¹³C) and optical (absorbance) properties of SPE-DOM change as a function of eluent volume (and hydrophobicity). These properties were measured in 28 SPE-DOC fractions incrementally eluted from Bond Elut PPL (styrene-divinylbenzene polymer) cartridges, totaling 32 mL of methanol. We show that the early eluted SPE-DOC has distinctly different ∆¹⁴C and δ¹³C values than those eluted later. This study reveals isotopic heterogeneity as a function of SPE-DOC elution volume. These results show a partitioning of two distinct sources of SPE-DOC during elution, indicating a gradual transition from “marine-like” DOC to “terrestrial-like” DOC along a hydrophobicity continuum.

海洋溶解有机碳（DOC）是海洋上最大的可交换有机碳储集层。DOC的生物地球化学循环在各种时间尺度上都对海洋碳存储起着重要作用。固相萃取（SPE）是一种用于从海水中分离DOC进行生物地球化学分析的过程。本研究探讨如何DOC同位素（Δ ¹⁴ C，δ ¹³ C）和光（吸光度）SPE-DOM变化作为洗脱液体积（和疏水性）的函数的特性。在从Bond Elut PPL（苯乙烯-二乙烯基苯聚合物）小柱逐步洗脱的28个SPE-DOC馏分中测量了这些性质，总共有32 mL甲醇。我们表明，早期洗脱的SPE-DOC具有明显不同的Δ ¹⁴ C和δ ¹³C值比后来洗脱的值大。这项研究揭示了同位素异质性与SPE-DOC洗脱体积的关系。这些结果显示了洗脱过程中SPE-DOC两种不同来源的分配，表明从“海洋类” DOC到“陆地类” DOC沿疏水性连续体逐渐过渡。