The Laizhou Bay area contains a large amount of Quaternary brine resources, which have been gradually depleted by long-term high-intensity mining. The local brine genesis is still controversial, and the dominant theory of the evaporation of brine formation limits the exploration of brine resources to the land area, while the confirmation of freezing brine formation would greatly expand the brine storage range. In this research paper, the genesis of underground brines was analyzed based on the major ion concentrations of 62 samples of underground brines at different depths at 24 stations along the south coast of Laizhou Bay. The results show that the underground brines originated from seawater; however, their chemical components were changed during the evolution process after formation. The hydrogeochemical modeling results show that the mixing of seawater and fresh groundwater also affects the chemical composition of brines. The large-scale exploitation of brine resources in recent decades has also led to significant changes in the chemical composition of the underground brine in Laizhou Bay compared with the earlier period. The special geographic environment and the development of the brine chemical industry have led to the evolution of underground brines in Laizhou Bay being affected by a variety of factors, which makes the traditional analysis of brine genesis in this region not applicable. Furthermore, although evaporation and concentration are the dominant factors in the formation of brine, there is still a lack of evidence to rule out the existence of the freezing pathway.

Deep-sea polymetallic nodules are associated with rich rare substances, such as rare-earth elements (REEs), Mo, Ti, Te, Li, which are currently in demand and are used in various applications. Deep-sea sediments near nodules are another important source of REEs, which will increase the resource potential of polymetallic nodules. Given the similarity of the mining technologies for deep-sea REEs and polymetallic nodules, this study proposed environmentally friendly mining options and developed a technoeconomic evaluation model by combining deep-sea polymetallic nodules and REEs. Using the Clarion-Clipperton Fracture Zone as an example, this study revealed that the development of polymetallic nodules together with REEs of nearby sediments in the form of by-products will improve the economic and environmental benefits. In addition, the effects of discount rate, cost, and price on the economic benefits of nodule mining were discussed, and a technical development direction was proposed based on scientific and technological needs.

Against the backdrop of global warming, the marine low-carbon economy has emerged as a crucial pathway to achieving carbon peaking and carbon neutrality goals. This paper develops an evaluation index system for the marine low-carbon economy and carbon emission reduction. Using data from China’s coastal provinces (2012–2021), the study employs methods such as the entropy weight method, the coupled coordination model, K-means++ clustering, and grey correlation analysis to analyze the interaction between the marine low-carbon economy and carbon emission reduction. The study revealed the following findings: (1) From 2012 to 2022, the development of the marine low-carbon economy exhibited an “N”-shaped pattern, while the trend of carbon emission reduction generally followed the opposite pattern due to a “lag” effect. (2) The coordination between the two systems improved gradually, reaching an intermediate level from 2018 to 2021. (3) Among the internal factors related to the interaction between the marine low-carbon economy and carbon emission reduction, fossil energy consumption and wetland areas are the primary sensitivity factors. (4) External factor analysis through the use of grey correlation analysis revealed that the structure of the marine industry and technological innovation are the main drivers of the interaction, while carbon market trading showed the lowest correlation out of all the external factors, indicating that the mechanism design needs further improvement. (5) Compared with other coastal countries, China still has much room for progress in regard to the construction of MPAs and the restoration of blue carbon ecosystems. This paper introduces a method to quantify the development level of the marine low-carbon economy and assess the effects of marine carbon emission reduction, analyzing the coupling coordination between China’s marine low-carbon economy and carbon emission reduction. This research provides a foundation for Chinese policymakers and offers insights into green and sustainable development of the global marine economy.

The Laizhou Bay area in China harbors a significant amount of Quaternary brine resources, which have been gradually depleted due to intensive long-term exploitation. It is widely accepted that underground Quaternary brine in Laizhou Bay originates from seawater. However, there are disputes regarding the specific form of seawater concentration and the geological processes leading to brine formation. Revealing the genesis of shallow brine in different geological environments is of great scientific significance for resource production and environmental protection. This study analyzed the hydrodynamic conditions of underground brine and adjacent strata based on grain size data, and the possible formation mechanisms of brine layers at different depths were discussed. The mineralization of underground brine is a complex process controlled by various factors, such as specific meteorological and paleogeographic environments, topography, and hydrogeological conditions. On the southern coast of Laizhou Bay, there are three ways in which underground brine layers are formed: residual evaporation from lagoons during the initial regression stage, the hypersaline zone in estuarine lagoons during high-sea-level periods, and brine formation from seawater evaporation on intertidal flats. Turbulent sea–land interactions and the development of river deltas are also necessary conditions for brine mineralization, as they are favorable for replenishing, transporting, and storing underground brine layers.

The excessive exploitation of groundwater is becoming a serious global issue. Different from other regions, groundwater extraction in coastal areas usually stops and moves inland after causing seawater intrusion. The abundant salt fields in the Laizhou Bay area of China provide a unique case of maintaining high-intensity underground brine mining even after seawater intrusion. The intensive exploitation of underground brine has led to significant changes in the groundwater flow field. However, there is still a lack of research on how different factors affect the groundwater level in this mining situation. In this paper, time series analysis methods were used to investigate the impact of brine water extraction, tidal fluctuations, and precipitation on the groundwater level in the Laizhou Bay area. The results indicate that brine extraction is the main factor controlling the changes in groundwater level, with the cessation and resumption of extraction resulting in a 93.4 cm increase and a 122.5 cm decrease, respectively. Different rainfall patterns can also lead to an increase in groundwater levels, especially when a heavy rainfall event can cause a 61.2 cm increase. Tidal fluctuations can cause periodic fluctuations in the groundwater level, with a variation amplitude of approximately 11% of the tide itself.

Improving natural resource total factor productivity (NTFP) is sential for easing resource and environmental constraints, advancing high-quality development, and supporting China’s dual-carbon goals. This study aims to evaluate the static efficiency, intertemporal productivity change, regional heterogeneity, and hierarchical frontier differences in environmentally adjusted natural resource total factor productivity in China’s aggregated agriculture, forestry, animal husbandry, and fishery sector from 2008 to 2020. To achieve this aim, we apply a non-radial, non-oriented undesirable-output SBM-DEA model under constant returns to scale, national, regional, and province-specific frontier comparisons. A Global Malmquist–Luenberger index is further used to decompose productivity change into efficiency change and technical change. The analysis shows an overall upward trajectory in national mean NTFP, a persistent eastern advantage, and co-movement among provincial, regional, and national frontier indices, while the dynamic productivity change indicates that productivity improvement was driven mainly by technical change rather than efficiency change. Sensitivity analyses using alternative undesirable-output specifications and cluster-based groupings support the robustness of the main conclusions and inform more targeted discussion and policy implications.