Temperate shelf seas are productive areas with the potential to export high quantities of particulate organic carbon (POC), as sinking particles, to the sediments or off-shelf to the open ocean. The amount of carbon which can be exported depends partly on the amount of POC produced and on the remineralization processes occurring on the sinking material. Here, we assessed the relative seasonal importance of microbial respiration and bacterial production associated with suspended, slow- and fast-sinking particle fractions. The three fractions were collected in the Celtic Sea above and below the seasonal thermocline in November 2014, April and July 2015 using Marine Snow Catchers. The slow-sinking fraction had higher microbial respiration and bacterial production rates than the fast-sinking fractions, and these two fractions sustained rates of microbial respiration and bacterial production between 1 and 3 orders of magnitude lower than the suspended fraction. This low contribution of the slow- and fast-sinking fractions was consistent with their low contribution to the POC concentration at the two depths sampled. The POC-specific respiration rates associated with the slow- and fast-sinking fractions were low (median 0.17 and 0.08 d⁻¹, respectively), indicating low-sinking particle degradation. Our results indicate that ∼5% of the POC in surface waters can be exported below the thermocline.

中文翻译：

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温带大陆架海中快速下沉粒子部分对总浮游生物代谢的低贡献

温带陆架海是多产区域，有可能将大量颗粒有机碳 (POC) 作为下沉颗粒输出到沉积物或从架子输出到公海。可以输出的碳量部分取决于产生的 POC 量和下沉材料上发生的再矿化过程。在这里，我们评估了与悬浮、缓慢和快速下沉的颗粒部分相关的微生物呼吸和细菌生产的相对季节性重要性。2014 年 11 月、2015 年 4 月和 2015 年 7 月，使用海洋捕雪器在凯尔特海季节性温跃层上方和下方收集了这三个部分。缓慢下沉部分比快速下沉部分具有更高的微生物呼吸和细菌生产速率，并且这两个部分使微生物呼吸和细菌产生的速率比悬浮部分低 1 到 3 个数量级。缓慢和快速下沉部分的这种低贡献与其对两个采样深度的 POC 浓度的低贡献一致。与缓慢和快速下沉部分相关的 POC 特定呼吸率较低（中值 0.17 和 0.08 d^-1，分别），表明低下沉粒子降解。我们的结果表明，地表水中约 5% 的 POC 可以输出到温跃层以下。