The biological transformation of dissolved inorganic carbon to organic carbon during photosynthesis in the ocean, marine primary production, is a fundamental driver of biogeochemical cycling, ocean health and Earth’s climate system. The organic matter created supports oceanic food webs, including fisheries, and is an essential control on atmospheric carbon dioxide levels. Marine primary productivity is sensitive to changes due to climate forcing, but observing the response at the global scale remains a major challenge. Sparsely distributed productivity measurements are made using samples collected and analysed on research vessels. However, there are never enough ships and scientists to enable direct observations at the global scale with seasonal to annual resolution. Today, global ocean productivity is estimated using remote-sensing ocean-colour observations or general circulation models with coupled biological models that are calibrated with the sparse shipboard measurements. Here we demonstrate the measurement of gross oxygen production by photosynthesis using the diel cycle of oxygen concentration detected with the array of Biogeochemical-Argo profiling floats. The global ocean net primary productivity computed from this data is 53 Pg C y⁻¹, which will be an important constraint on satellite and general circulation model-based estimates of the ocean productivity.

海洋光合作用过程中溶解的无机碳向有机碳的生物转化，即海洋初级生产，是生物地球化学循环、海洋健康和地球气候系统的基本驱动力。产生的有机物质支持包括渔业在内的海洋食物网，并且是对大气二氧化碳水平的重要控制。海洋初级生产力对气候强迫引起的变化很敏感，但在全球范围内观察响应仍然是一项重大挑战。使用在研究船上收集和分析的样本进行稀疏分布的生产力测量。然而，从来没有足够的船只和科学家能够在全球范围内以季节到年度分辨率进行直接观测。今天，全球海洋生产力是使用遥感海洋颜色观测或具有耦合生物模型的大气环流模型来估计的，这些模型用稀疏的船上测量值进行校准。在这里，我们展示了使用生物地球化学-Argo 剖面浮标阵列检测到的氧气浓度的昼夜循环通过光合作用测量总氧气产量。根据该数据计算的全球海洋净初级生产力为 53 Pg C y^-1，这将是对基于卫星和大气环流模型的海洋生产力估计的重要约束。