Exploring the development laws of new quality productivity and leveraging its role in empowering marine economy high-quality development (MEHQ) is of great significance for promoting the construction of a maritime power in China, achieving the goals of Chinese-style modernization and solidifying the country’s advantages in marine economic development. This paper systematically reviews the mechanisms and effects of new quality productivity (NQP) in empowering MEHQ. Using panel data from 17 cities along the Bohai Sea from 2010 to 2022, we comprehensively measure the combined levels of NQP and MEHQ. Employing various statistical analysis methods, including benchmark regression models, multiple mediation effect models, and spatial Durbin models, we empirically test the mechanisms and spatial spillover effects of NQP in empowering MEHQ. The results indicate that NQP has a significant positive driving effect on MEHQ, and this conclusion remains valid after a series of robustness tests. The empowering effect of NQP on MEHQ mainly occurs through three pathways: marine technological innovation, optimization of marine industrial structure, and improvement of marine resource allocation efficiency. There is a positive correlation between NQP and MEHQ, with significant agglomeration phenomena, reflecting the non-uniform characteristics of spatial distribution. NQP not only empowers MEHQ but also exhibits significant spatial spillover effects, promoting MEHQ in adjacent regions and releasing growth dividends.

With the acceleration of urbanization, city clusters of different levels have emerged. They play a significant role in the process of carbon emissions. Based on the improved STIRPAT model and using the five most important city clusters in northern China as the research object, this study investigates carbon emissions (carbon emissions refer to CO₂ emissions) from 2005 to 2021 and the urbanization factors that affect carbon emissions. The study found that energy urbanization has the most significant positive impact on carbon emissions from the overall perspective, while population urbanization has the most substantial negative effect. The total emissions of the Beijing–Tianjin–Hebei urban cluster far exceeding those of the other four clusters. The factor with the least impact on carbon emissions in the Beijing–Tianjin–Hebei city cluster, the Central Plains city cluster, and the Guanzhong Plain city cluster is energy urbanization. The impact of technological urbanization factors can be positive or negative, the role of spatial urbanization factors is not significant. The northern city clusters should start with transforming energy structure, promote industrial upgrading through innovation, encourage green production and consumption, increase the use of efficient scientific and technological products and services, and promote the development of new urbanization.

The integration of sea and land ecological economies is crucial for the development of a high-quality sea–land economy. This study explores and proposes the concept of a sea–land-integrated ecological economy. By constructing the evaluation index system for developing a sea–land-integrated ecological economy, the development level, evolution process, and development trend prediction of a sea–land-integrated ecological economy were evaluated and analysed in cities around the Bohai Sea from 2009 to 2019 using methods such as a model for assessing the development level, a spatio-temporal autocorrelation model, and an exploratory spatio-temporal data analysis model. The results of the study show that (1) the development level of the ecological economy of the cities of Bohai Rim’s sea–land integration generally had an upward trend; however, the magnitude significantly varied between cities; (2) the spatio-temporal autocorrelation pattern formed three major agglomerations with Dalian in the north, Yantai and Qingdao in the south, and Tianjin and Tangshan in the centre as the core cities and contained low agglomerations and scattered L–H spatio-temporal heterogeneous units; and (3) the integration prediction curve for 2020–2029 indicates that the level value for integration of most cities will improve over time.

New quality productivity (NQP) has infused fresh impetus into the construction and development of the modern marine industrial system (MMI), becoming a pivotal force in driving the high-quality development of the marine economy. This paper elucidates the value implications of NQP in fostering the formation and expansion of the MMI. By clarifying the internal mechanisms of this system, we delineate the goal orientation of the MMI enabled by NQP. We conduct an in-depth exploration of the enabling process of the MMI across five dimensions: innovation-driven growth, factor matching, integrated development, supply-demand adaptation, and green and low-carbon practices. The paper highlights that leveraging NQP can unlock the potential of traditional industries, strategically position emerging and future industries, enhance the impetus for innovation in marine science and technology, optimize the environment for marine industry development, accelerate industrial and digital integration, and improve policies related to green industries, technologies, and sustainable development. These measures aim to further implement the maritime power strategy and promote the empowerment and enhancement of the high-quality development of the marine economy.

China’s steel industry has not yet implemented a carbon tax policy, and its benefits and impacts are still in the theoretical research stage. In addition, enterprises have an insufficient ability to respond to changes in production and sales, which seriously affects the market’s stability. The government should simultaneously start from multiple perspectives, such as energy conservation, emission reduction, dynamic adjustments, and business decisions. Therefore, this research constructs a repeated dynamic game model including carbon tax policy and other mixed reduction policies, and studies the stability and related indicators of the market. The results are as follows: (1) the output adjustment policies that enterprises can implement will show an increasing trend under the single carbon tax policy. (2) The output adjustment policies that enterprises with larger output will also show an increasing trend under the mixed emission reduction policy when emission reduction targets continue to increase. (3) Smaller-output enterprises need to be more cautious in formulating their production plans, and their output adjustment policies will be restricted and affected by more factors. In summary, enterprises should comprehensively consider emission reduction policies, output adjustment policies and other enterprises’ output changes, to ensure that the steel market will not fall into an imbalanced state.

With the increasingly competitive environment in the steel market and the proposed dual carbon goals, the government will need to consider many factors, such as the realization of energy conservation and emission reduction targets, the production game between enterprises, and the adjustment of production strategies of enterprises. Therefore, this research constructs a repeated dynamic game model including carbon trading policy and other mixed reduction policies, introduces a bounded rationality output adjustment strategy, and studies the response, stability, and complexity of different scenarios in the steel industry. The results are as follows: (1) With the gradual increase in emission reduction targets, the output adjustment policies that enterprises can implement will show an increasing trend under the single carbon trading policy. (2) Under the mixed emission reduction policy, the output adjustment policies that affect enterprises with larger outputs will show an increasing trend when targets continue to increase. (3) Smaller-output enterprises will be restricted and affected by more factors, such as emission reduction targets and larger output enterprises. (4) The influence of carbon trading benchmarks on market stability region is not obvious. In summary, enterprises should comprehensively consider emission reduction policies, output adjustment policies, carbon trading benchmarks, and other factors to ensure that the enterprises and the entire market will not fall into an imbalanced state.