Abstract:

Land carbon sinks and marine carbon sinks are both important parts of the global carbon cycle， so they should be taken into account and coordinated to promote sink enhancement measures in order to achieve optimal results. Focusing on water pollution governance as the core linkage bridging these two ecosystems， the dynamics of the overall land-sea ecosystem’s biodiversity is modeled using a stochastic differential equation. This approach comprehensively captures the positive impacts of pollution governance efforts from both terrestrial and marine ecosystems， the natural degradation of biodiversity over time， and the continuous random disturbances caused by climate change or human interference. To study the decision-making of carbon sinks in collaborative land sea ecosystems， a stochastic differential game model is established to analyze the best strategies and benefits of three modes： decentralized decision-making for cost sharing， decentralized decision-making for pollution compensation， and centralized decision-making for collaborative governance. The impact of random factors in the model is identified by the changes of the biodiversity level of the entire land sea ecosystem， and virtual simulation analysis is conducted. By constructing and solving the Hamilton-Jacobi-Bellman equations for continuous time， the optimal effort levels， as well as the expected values and variances for biodiversity under each specific scenario are derived to find the Nash equilibrium.Research has shown that　1） Under the collaborative governance mode， the total carbon sink benefits of land sea ecosystems are the highest， followed by the cost sharing mode， and the pollution compensation mode is the lowest， which may be negative at high compensation prices. 2） The level of biodiversity under the pollution compensation mode is positively correlated with the compensation price. At high compensation prices， the pollution compensation mode has the highest level of biodiversity， but its stability is poor and the system's carbon aggregation benefits are low. 3） Improving the benefit allocation coefficient can significantly enhance the biodiversity level and the total carbon sink revenue of terrestrial and marine ecosystems under the cost-sharing model. However， for the pollution discharge compensation model， increasing the benefit allocation coefficient will lead to a decline in both.4） Although the total carbon sink benefits of land sea ecosystems are highest under the collaborative governance mode， the stability of biodiversity levels and total benefits is worse under this mode， requiring greater risk to be borne. And when the random interference factor increases， the volatility of the system carbon aggregate return under all modes increases significantly.The marginal contributions are in threefold　First， it expands carbon sink research by exploring coordinated land-sea ecosystem management. Second， it applies stochastic differential game models to identify synergy strategies， broadening methodological applications. Third， it reveals how stochastic disturbances affect biodiversity and carbon sequestration， offering insights for achieving the "dual carbon" goals.

Key words: natural ecosystem carbon sink, synergistic carbon sink mechanism, stochastic differential game, integrated land-sea coordination