The transfer of particulate organic carbon (POC) to dissolved organic carbon (DOC; OC transfer) is crucial for the marine carbon cycle. Sediment resuspension driven by hydrodynamic forcing can affect the burial of sedimentary POC and benthic biological processes in marginal sea. However, the role of sediment grain size fraction on OC transfer and the subsequent impact on OC cycling remain unknown. Here, we conduct sediment resuspension simulations by resuspending grain-size fractionated sediments (< 20, 20–63, and > 63 μm) into filtered seawater, combined with analyses of OC content, optical characteristics, C and C isotope compositions, and molecular dynamics simulations to investigate OC transfer and its regulations on OC bioavailability under sediment resuspension. Our results show that the relative intensities of terrestrial humic-like OC (refractory DOC) increase in resuspension experiments of < 20, 20–63, and > 63 μm sediments by 0.14, 0.01, and 0.03, respectively, likely suggesting that sediment resuspension drives refractory DOC transfer into seawater. The variations in the relative intensities of microbial protein-like DOC are linked to the change of terrestrial humic-like OC, accompanied by higher DOC content and reactivity in seawater, particularly in finer sediments resuspension experiments. This implies that transferred DOC likely fuels microbial growth, contributing to the subsequent enhancement of DOC bioavailability in seawater. Our results also show that the POC contents increase by 0.35 %, 0.66 %, and 0.93 % in < 20, 20–63, and > 63 μm resuspension experiments at the end of incubation, respectively. This suggests that the re-absorption of OC on particles may be a significant process, but previously unrecognized during sediment resuspension. Overall, our findings suggest that sediment resuspension promotes the OC transfer, and the magnitudes of OC transfer further influence the DOC and POC properties by inducing microbial production and respiration. These processes significantly affect the dynamics and recycling of biological carbon pump in shallow marginal seas.

中文翻译：

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沉积物再悬浮作为边缘海有机碳转移和再平衡的驱动力


颗粒有机碳（POC）向溶解有机碳（DOC；OC 转移）的转移对于海洋碳循环至关重要。水动力驱动的沉积物再悬浮会影响边缘海沉积物 POC 的埋藏和底栖生物过程。然而，沉积物粒度分数对有机碳转移的作用以及随后对有机碳循环的影响仍然未知。在这里，我们通过将粒度分馏沉积物（< 20、20–63 和 > 63 μm）重新悬浮到过滤海水中来进行沉积物再悬浮模拟，并结合 OC 含量、光学特性、C 和 C 同位素组成以及分子动力学分析模拟研究沉积物再悬浮下 OC 转移及其对 OC 生物利用度的调节。我们的结果表明，在 < 20、20-63 和 > 63 μm 沉积物的再悬浮实验中，陆地腐殖质类 OC（难熔 DOC）的相对强度分别增加了 0.14、0.01 和 0.03，这可能表明沉积物再悬浮驱动难降解的 DOC 转移到海水中。微生物类蛋白质 DOC 相对强度的变化与陆地类腐殖质 OC 的变化有关，伴随着海水中较高的 DOC 含量和反应性，特别是在较细的沉积物再悬浮实验中。这意味着转移的 DOC 可能会促进微生物生长，从而有助于随后提高海水中 DOC 的生物利用度。我们的结果还表明，在孵育结束时 < 20、20-63 和 > 63 μm 重悬实验中，POC 含量分别增加了 0.35 %、0.66 % 和 0.93 %。这表明颗粒上 OC 的重吸收可能是一个重要的过程，但之前在沉积物再悬浮过程中未被认识到。 总的来说，我们的研究结果表明，沉积物再悬浮促进了 OC 转移，并且 OC 转移的程度通过诱导微生物产生和呼吸进一步影响 DOC 和 POC 特性。这些过程显着影响浅海边缘海生物碳泵的动态和回收。