Zemskova Varvara E, He Tai-Long, Wan Zirui, Grisouard Nicolas
Department of Physics, University of Toronto, Toronto, ON, Canada.
Nat Commun. 2022 Jul 13;13(1):4056. doi: 10.1038/s41467-022-31560-5.
Uptake of atmospheric carbon by the ocean, especially at high latitudes, plays an important role in offsetting anthropogenic emissions. At the surface of the Southern Ocean south of 30S, the ocean carbon uptake, which had been weakening in 1990s, strengthened in the 2000s. However, sparseness of in-situ measurements in the ocean interior make it difficult to compute changes in carbon storage below the surface. Here we develop a machine-learning model, which can estimate concentrations of dissolved inorganic carbon (DIC) in the Southern Ocean up to 4 km depth only using data available at the ocean surface. Our model is fast and computationally inexpensive. We apply it to calculate trends in DIC concentrations over the past three decades and find that DIC decreased in the 1990s and 2000s, but has increased, in particular in the upper ocean since the 2010s. However, the particular circulation dynamics that drove these changes may have differed across zonal sectors of the Southern Ocean. While the near-surface decrease in DIC concentrations would enhance atmospheric CO uptake continuing the previously-found trends, weakened connectivity between surface and deep layers and build-up of DIC in deep waters could reduce the ocean's carbon storage potential.
海洋对大气中碳的吸收，尤其是在高纬度地区，在抵消人为排放方面发挥着重要作用。在南纬30度以南的南大洋表面，海洋碳吸收在20世纪90年代一直在减弱，但在21世纪有所增强。然而，海洋内部原位测量数据的稀少使得计算表层以下碳储存的变化变得困难。在这里，我们开发了一种机器学习模型，该模型仅使用海洋表面可用的数据就能估算南大洋深度达4千米处的溶解无机碳（DIC）浓度。我们的模型速度快且计算成本低。我们将其应用于计算过去三十年中DIC浓度的趋势，发现DIC在20世纪90年代和21世纪有所下降，但自2010年代以来有所增加，特别是在海洋上层。然而，推动这些变化的特定环流动力学在南大洋的纬向区域可能有所不同。虽然DIC浓度在近表层的下降将增强大气对CO的吸收，延续之前发现的趋势，但表层和深层之间连通性的减弱以及深水中DIC的积累可能会降低海洋的碳储存潜力。
