Estimate of Ocean Carbon Sink: Current Status and Reflections

Ocean carbon sink has become an important measure to achieve “carbon neutrality” in order to tackle climate change. In this paper, we systematically reviewed the observation and simulation methods of ocean carbon sink, comprehensively summarized the technological trends of carbon sink research, and prospected the innovative directions of ocean carbon sink in the future research. Benefiting from the development of ¹³C and ¹⁴C measurement techniques and the “Box model”, carbon isotope tracer method was the first practice to realize the estimation of air-sea CO₂ exchange flux, which laid a foundation for the development of later air-sea gas transport study. Afterwards, tracking the composition change of atmospheric O₂ inventory became an important method to retrieve the magnitude of the ocean carbon sink. By comparing with the terrestrial carbon sink, this method expounded the important position of the ocean carbon sink from the perspective of the Earth system. At present, p(CO₂) field observation is the most widely used method for ocean carbon sink research, which effectively reveals the spatial and temporal pattern of global air-sea CO₂ exchange flux. On this basis, the numerical model gains the ability to analyse the variation process of the oceanic carbon cycle and becomes a crucial method to quantitatively study the exchange of the complex control process. An more important fact is that the numerical model greatly broadens the temporal and spatial category of ocean carbon sink research, and promotes the multi-disciplinary cooperation in many areas, which is the vital foundation for the future innovation and development of ocean carbon sink research. Under the context of climate change, exhaustive exploration of the impact of anthropogenic activities on ocean carbon sinks should be the most important direction of future research.