The biological carbon pump exports carbon fixed by photosynthesis out of the surface ocean and transfers it to the deep, mostly in the form of sinking particles. Despite the importance of the pump in regulating the air‐sea CO2 balance, the magnitude of global carbon export remains unclear, as do its controlling mechanisms. A possible sinking flux of carbon to the mesopelagic zone may be via the mixed‐layer pump: a seasonal net detrainment of particulate organic carbon (POC)‐rich surface waters, caused by sequential deepening and shoaling of the mixed layer. In this study, we present a full year of daily small‐particle POC concentrations derived from glider optical backscatter data, to study export variability at the Porcupine Abyssal Plain (PAP) sustained observatory in the Northeast Atlantic. We observe a strong seasonality in small‐particle transfer efficiency, with a maximum in winter and early spring. By calculating daily POC export driven by mixed‐layer variations, we find that the mixed‐layer pump supplies an annual flux of at least 3.0 ± 0.9 g POC·m−2·year−1 to the mesopelagic zone, contributing between 5% and 25% of the total annual export flux and likely contributing to closing a gap in the mesopelagic carbon budget found by other studies. These are, to our best knowledge, the first high‐frequency observations of export variability over the course of a full year. Our results support the deployment of bio‐optical sensors on gliders to improve our understanding of the ocean carbon cycle on temporal scales from daily to annual.

中文翻译：

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东北大西洋小颗粒碳输出通量的高频变化

生物碳泵将通过光合作用固定的碳从表层海洋输出，并将其转移到深层，主要以下沉颗粒的形式。尽管泵在调节海气二氧化碳平衡方面发挥着重要作用，但全球碳输出的规模及其控制机制仍不清楚。碳可能通过混合层泵沉入中层区域：由于混合层的连续加深和浅化而导致富含颗粒有机碳（POC）的地表水的季节性净去除。在这项研究中，我们提供了来自滑翔机光学反向散射数据的全年每日小颗粒 POC 浓度，以研究东北大西洋豪猪深海平原 (PAP) 持续观测站的输出变化。我们观察到小颗粒传输效率具有很强的季节性，在冬季和早春达到最大值。通过计算混合层变化驱动的每日 POC 输出，我们发现混合层泵每年向中层带提供至少 3.0 ± 0.9 g POC·m−2·year−1 的通量，贡献在 5% 到 5% 之间。占年度总出口流量的 25%，可能有助于缩小其他研究发现的中层碳预算缺口。据我们所知，这是对全年出口变化的首次高频观察。我们的研究结果支持在滑翔机上部署生物光学传感器，以提高我们对从每日到每年的时间尺度上的海洋碳循环的理解。