Lei Yang

The Zhejiang region preserves a complete evolutionary trajectory from hunter-gatherer to early state-level societies, which offers critical material for examining social complexity. Nevertheless, the lack of continuous, high-quality Holocene paleoenvironmental archives in this area hampers a thorough assessment of the human–environment interaction over time. This study investigates pollen, ostracod, foraminiferal and particle-size proxies to reconstruct regional environmental dynamics from core TQ1 in Taizhou Bay spanning 14.8–0.4 cal ka BP based on AMS ¹⁴C dating. Core TQ1 records a transition from predominantly terrestrial influence during the late deglaciation to increasing marine influence during the early Holocene. Based on paleoenvironmental changes, the Holocene can be further divided into three stages. Stage 1 (11.5–8.5 cal ka BP) was characterized by a coastal environment with stronger hydrodynamics; arboreal pollen declined while herbs, ferns and algae increased. Stage 2 (8.5–4.2 cal ka BP) represented the peak transgression with open marine conditions and maximum microfossil abundance, and forest recovery as terrestrial herbs and algae decreased. Stage 3 (4.2–0.4 cal ka BP) shifted back to nearshore shallow-sea conditions, with persistently high arboreal percentages and sustained pollen input from forested terrestrial source areas. The intense paleoenvironmental changes, coupled with the evolutionary processes of ancient cultures in the adjacent areas, provide new evidence for a deeper understanding of regional cultural evolution.

The reduction in Yangtze River-derived suspended particulate matter significantly impacts adjacent marine sedimentation. Although traditionally considered the primary sediment source for the Zhejiang-Fujian Mud Belt, environmental magnetic evidence contradicts this, indicating local rivers predominantly supply the muddy tidal flats south of central Zhejiang. This study focuses on analyzing sediment provenance in the central Zhejiang offshore area. Magnetic analysis shows the sediments are characterized by low magnetic mineral concentration and fine grain size, highly similar to the adjacent Jiaojiang River’s riverbed sediment and suspended particulate matter, distinct from the Yangtze. Consistent magnetic characteristics in high-energy flood layers further confirm the Jiaojiang River as the stable main source. The robust chronology, established by ²¹⁰Pb and ¹³⁷Cs dating, revealed significantly accelerated sedimentation after 1980. End-Member Modeling Analysis shows nearshore sediments are dominated by fine-grained components, with their proportion rising in the long term; meanwhile, coarse-grained components plummeted after 1990, indicating a shift toward stable, low-energy deposition. The contradiction between accelerated sedimentation and weakened hydrodynamics likely stems from Jiaojiang River basin human activities, enhancing local fine-grained sediment supply and trapping efficiency.

Due to natural and anthropogenic disturbances, natural gas hydrates with morphologies of nodules and chunks dissociate and release massive free gas, creating large cavities within fine-grained marine sediments. However, it is still a challenge to quantify the impact of gas cavities on mechanical properties of cavitied fine-grained marine sediments as there is a lack of efforts focusing on the inner structure visualization. In this study, an oedometer test and X-ray computed tomography scans are jointly conducted on marine clayey silt with gas cavities, and the confined compressibility as well as the inner structure change under an undrained condition are explored, followed by development of a theoretical model depicting the void ratio change. The results show that vertical loading induces a void ratio reduction, and the reduced void ratio can fully recover after being unloaded. Although being fully recovered, unrecovered changes of the inner structure still remain after being unloaded. Examples include closed cracks in the lower matrix, new occurring cracks in the upper matrix, and the fragmented gas cavity. In addition, the void ratio linearly increases with the increasing inverse of normalized pore gas pressure, while the coefficient of the effective stress linearly decreases with the increasing inverse of normalized vertical loading stress. The proposed theoretical model captures the essential physics behind undrained confined deformation of fine-grained marine sediments with gas cavities when subjected to loading and unloading.

The concentration of heavy metals in sediment is an important factor for assessing the quality of the nearshore environment. Geochemical background values are the normal concentrations of heavy metals in the natural environment. The use of different background values results in different evaluation results. Heavy metal (Cu, Pb, Zn, Cr, Cd, As, and Hg) concentration profiles along a sediment core were investigated to obtain background values and assess the depositional processes and contamination levels in Laizhou Bay. Apart from As and Hg, all other metals had similar distribution patterns and could be divided into four stages since marine isotope stage (MIS) 2. The results of the enrichment factor, geoaccumulation index, Pearson’s correlation coefficient, Nemerow pollution index, principal component analysis, and potential ecological risk index showed that element enrichment or contamination in the core sediments was absent and that all heavy metals were mainly naturally sourced. The changes in heavy metals since MIS 2 in the core sediments were predominantly related to the sedimentary environment, sediment sources, and mean grain size. The average values of the heavy metals in the U2 unit formed during the Middle Holocene can be used as reference values for background values.

The recognition of submarine cable magnetic anomaly (SCMA) signals is a challenging task in magnetic signal data processing. In this study, a multi-task convolutional neural network (MTCNN) model is proposed to simultaneously recognize abnormal signals and locate abnormal regions. The residual block is added to the shared feature backbone to improve the ability of the network to extract high-level features and maintain the gradient stability of the model in the training process. The long short-term memory (LSTM) block is added to the classification branch task to learn the internal relationship of the magnetic anomaly time series, so as to improve the network’s ability to recognize magnetic anomalies. Our proposed model can accurately recognize the SCMA signals collected in the East China Sea and the South China Sea. The classification accuracy and the ability to locate the abnormal regions are close to the manual labeling of human analysts. The newly developed model can help analysts reduce the probability of missing and misjudging submarine cable magnetic anomalies, improve the efficiency and accuracy of interpretation, and could even be deployed to an unmanned platform to realize the automatic detection of SCMAs.

Land reclamation not only provides valuable space for urban development, but also creates an upper aquifer in fill materials. Analysis of groundwater level (GWL) fluctuations in coastal aquifer formed due to land reclamation can provide important insight into the groundwater system (GWS) evolution, including the connectivity between the GWL and influencing variables (ocean tide and rainfall). This study presents wavelet analysis, multichannel SSA-wavelet analysis (MSSA-WA), and lag correlations to analyze the response of GWL to ocean tide and rainfall in the reclamation area of Zhoushan Island, China. The MSSA-WA results and the lag correlations show that the MSSA-WA provides better analysis results, specifically, clay layer and rainfall filtered information. The influence of the influencing variables on the upper GWL is relatively greater than the clay layer, and rainfall has a relatively stronger impact on GWLs than tides. The GWLs of the upper layer, SW18 and SW21, which are heavily influenced by influencing variables, can be predicted through variations in influencing variables. Finally, the analysis of the results shows that the lithology of different aquifers, offshore distance, preferential flow path, and pressure load can be factors between tides and GWLs. For rainfall and GWLs, different lithology of aquifers, properties of vadose zone, and topography can be influential factors. The combination method provides an optimization method for GWL fluctuations in coastal reclamation area with combined MSSA and wavelet analysis for correlation analysis between GWL and influencing variables (ocean tide and rainfall) and analysis of corresponding causes and influencing factors.