The Southern Yellow Sea (SYS) is a crucial component of global marine ecosystems, characterized by high primary productivity and dynamic biogeochemical processes. However, systematic investigations of the spatiotemporal dynamics of phytoplankton biomass in this region remain limited despite increasing climate and anthropogenic pressures. In this study, long-term spatiotemporal variations in phytoplankton biomass in the SYS were analyzed using satellite-derived chlorophyll-a (Chl-a) data from 2000 to 2023. The results reveal contrasting long-term Chl-a trends between offshore and nearshore waters, primarily driven by differences in nutrient supply and regional responses to global warming. Based on the temporal variability in Chl-a concentration, the SYS was classified into three distinct biogeographical regions using the Piecewise Linear Representation method integrated with clustering analysis. Distinct spatial patterns emerged in phytoplankton phenology across the SYS: in the central SYS, spring blooms initiated earlier but with reduced intensity and shorter duration, primarily due to earlier stratification and diminished nutrient replenishment from subsurface waters. In contrast, nearshore regions exhibited delayed summer bloom onset and weakened intensity, reflecting prolonged nutrient accumulation periods amid declining nutrient availability. Along the southern coast of the Shandong Peninsula, winter blooms intensified over time, sustained by the strengthening of frontal systems that enhance nutrient supply and retention. This study provides critical insights into the complex interplay between climate-induced physical changes, nutrient dynamics, and phytoplankton bloom phenology, offering a robust methodological foundation applicable to similar marginal seas worldwide.

Particulate organic carbon (POC) is critical to the coastal carbon cycle of the Yellow Sea (YS), a typical marginal sea, but its interannual-to-multiyear variability and driving mechanisms remain unclear due to the limitations of traditional linear or single-factor analyses. To address this gap, we employed model-derived surface POC data from 2003 to 2023 and wavelet coherence analysis to investigate POC variability and regulating mechanisms at multi-scales in the YS. The dominant spatiotemporal mode of surface POC exhibits pronounced seasonality, a consistent coastal-offshore gradient (higher in coastal waters), and a spring maximum, which is regulated by the seasonal alternation controlled by coastal production or input and offshore stratification or ventilation. Wavelet analysis reveals distinct subregional differences in driving mechanisms of POC variability at interannual-to-multiyear scales. Colored dissolved organic matter (CDOM) is the optimal single driver in most subregions, while sea surface temperature (SST) dominates in the Southern Yellow Sea Cold Water Mass (SYSCWM). Specific optimal multi-factor combinations include CDOM+sea surface wind speed (SSW) in the Northern Yellow Sea Cold Water Mass (NYSCWM), chlorophyll a (Chl a)+Photosynthetically Available Radiation (PAR)+partial pressure of carbon dioxide (pCO2) in the SYSCWM, CDOM+Chl a+suspended matter (SPM) in the Jiangsu Shoal (JSS) and CDOM+sea surface salinity (SSS) in the Changjiang River estuary (CRE). These findings clarify the subregional heterogeneity of POC variability and its driving mechanisms in the YS at interannual-to-multiyear scales, and provide a robust scientific basis for accurate regional carbon budget assessments and the optimization of marine numerical models.

Phytoplankton blooms represent a typical ecological process in marine systems. Climate change drives shifts in its phenology, both directly via impacts on physiology and indirectly by modifying stratification intensity, nutrients, light availability, and grazing pressure. Using satellite remote sensing and reanalysis data from 2000 to 2022, this study partitions the Yellow Sea based on interannual variability in the Yellow Sea Cold Water Mass (YSCWM). Clear spatial differences in autumn bloom phenology are observed within the YSCWM. Earlier initiation dominates the Southern YSCWM (SYSCWM), while delayed later initiation concentrates in the Northern YSCWM (NYSCWM) and along the SYSCWM’s eastern margins. This pattern can be explained by the differences in regional hydrodynamics, i.e., the Yellow Sea Warm Current (YSWC) enhances upwelling and convergence in some YSCWM areas, boosting nutrient supply and earlier blooms, whereas weaker circulation-driven nutrient supply causes the bloom delay. Interannual variation analysis further reveals that the bloom timing is regulated by seasonal YSCWM dissipation since intensified autumn northerly winds accelerate dissipation and nutrient supply, thereby advancing blooms, while weaker northerly winds and stable circulation delay bloom progress by maintaining strong thermocline stability. These findings provide further insights into the underlying mechanisms driving autumn bloom dynamics and support ecosystem monitoring efforts in shelf seas.

Ocean alkalinity enhancement (OAE) implemented through wastewater treatment plants increases the alkalinity of the effluents and discharges them into the ocean, referred to as wastewater-based OAE. However, the alkalization capability and its carbon storage stability when adding alkaline minerals to wastewater treatment are uncertain. In this study, total alkalinity was enhanced to more than 10 millimoles per kilogram and phosphate removal was improved when we added olivine to wastewater in a laboratory setting. The alkalization rate by olivine dissolution in aerobically treated wastewater was 20 times higher than in seawater. We estimated the potential of carbon sequestration through wastewater-based OAE to be 18.8 ± 6.0 teragrams of CO 2 per year globally, with notable potential in the 20°N to 60°N region.

Access to high-quality marine geophysical and biogeochemical in-situ data poses a challenge for model evaluation and parameter calibration of the Coastal China Sea (CCS). We describe a new regional ocean database for CCS (RODCCS) with original data from six repositories. The database covers the region of 116-135°E in longitude and 20-42°N in latitude, which embraces the Bohai Sea, the Yellow Sea, the East China Sea and a part of the Sea of Japan. About 3.9 million data points are collected and sorted according to variable types, including temperature, salinity, dissolved oxygen, silicate, nitrate, nitrite, ammonium, phosphate, Chlorophyll a, dissolved inorganic carbon, dissolved organic carbon, and particulate organic carbon. These data are quality-controlled (QCed) with six QC checks and stored in a Network Common Data Format (NetCDF) file. RODCCS includes twelve NetCDF files, each with a unified structure. The database is easily accessed and of high quality after QC checks, making it suitable for a wide range of marine modelling as well as field research for the CCS.

Utilisation of dissolved organic phosphorus (DOP) by marine microbes as an alternative phosphorus (P) source when phosphate is scarce can help sustain non-Redfieldian carbon:nitrogen:phosphorus ratios and efficient ocean carbon export. Alkaline phosphatase (AP) is an important enzyme group that facilitates the remineralisation of DOP to phosphate and thus its activity is a promising proxy for DOP-utilisation, particularly in P-stressed regions. In order tounderstand the global spatial patterns and rates of microbial DOP utilization and their environmental controls, we compiled a Global Alkaline Phosphatase Activity Dataset (GAPAD) with 4083 measurements collected from 79 published manuscripts and one database， and further investigated the possible mechanisms controlling global ocean APA. We find that DOP concentration, salinity, excess phosphate (P*), and chlorophyll a concentrations are critical factors in predicting global patterns of APA, which together explain as much as 39% of the variance in the observed APA dataset. Among all environmental factors, DOP concentration explains the most variance in the observed APA data and is negatively correlated with APA. P* is negatively correlated with APA，while chlorophyll a concentration is positively correlated. Moreover, wind speed, dust iron deposition rate, and zinc concentration are also possible important environmental factors controlling APA. Using structural equation modeling, DOP and P* concentrations have a total negative effect on APA of -0.36. and -0.2 respectively, while chlorophyll a concentration and salinity have a total positive effect of 0.16 and 0.24. Via a set of numerical competition experiments between an AP-producing phytoplankton and a non AP-producing competitor, AP-producing phytoplankton are found to have an advantage in regions with low P*, but only alongside sufficiently high DOP and DIN concentrations. This trend arises due to the trade-off between P acquisition and N allocation to AP synthesis and is not affected by varying the model assumptions regarding nutrient supplies, N-demand, and key physiological traits. Extending our results to the global ocean using DIN, DIP, and DOP datasets enables us to pinpoint key regions where optimal conditions for DOP-utilisation are prevalent. These findings align closely with the patterns illuminated by our APA dataset. Our results show that on a global scale, when phosphate limitation is severe, plankton utilize DOP through producing AP, and this will help understand the biogeographical shift of different microbial groups in response to future climate change. Further work is needed to include the parallel role of the trace metal co-factors iron and zinc in driving AP synthesis and its spatial distribution in our modelling experiments.

Dissolved oxygen (DO) is a crucial element for both biotic and abiotic processes in marine ecosystems, but has declined globally in recent decades. Therefore, there is an urgent need for solid large-scale and continuous estimation of DO concentration in vital ecosystems, such as coastal areas. A random forest (RF) model for DO in South Yellow Sea (SYS) was developed by integrating satellite data and simulation data during 2011-2019. The root mean squared error (RMSE) for the training and test sets were 0.514 mg/L and 0.732 mg/L, respectively. Spatiotemporal distributions of DO of multiple layers in the study area during 2011-2019 were very well reproduced by the RF model and showed a slight decline trend in most SYS areas, while more intense decline occurred in the deep central SYS. The analysis of the mechanisms of DO decline in the South Yellow Sea cold water mass (SYSCWM), located in the deep central SYS, indicates that the deoxygenation here is largely due to biological activities. This finding may have implications for studies on drivers of deoxygenation in coastal areas. Furthermore, integrating satellite data with machine learning models can offer a powerful approach to capturing the continuous spatiotemporal characteristics of ocean parameters over large spatial scales.

InstructionMicrobial community respiration (MCR) strongly controls the fate of organic carbon in the ocean. The balance between MCR and primary production strongly determines whether the ocean is a net sink or source of CO2 to the atmosphere. Thus, it is necessary to estimate MCR to better understand the role of oceans in the global carbon cycle. Methods based on apparent oxygen utilization (AOU) are predominant while electron transport system (ETS) assay gets increasing attention. Although methods get developed, few studies on MCR have been performed on a seasonal cycle. Because MCR is strongly associated with the temperature which changes along with the succession of seasons, it is urgent to study the MCR on a seasonal cycle.MethodsThus, we measured MCR using in vivo tetrazolium salt 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride (INT) reduction rates (ETS) and oxygen-optode methods (AOU) simultaneously we measured the MCR based on AOU and ETS methods simultaneously from November 2020 to November 2021 in Aoshan Bay, China.ResultsThe highest AOU appeared in autumn, followed by summer, spring, and winter, whereas the highest ETS activity appeared in summer, followed by spring, autumn and winter. The seasonal trend of MCR estimated from AOU and ETS were not consistent, and further analysis indicated that oxygen consumption induced by nitrification caused the overestimation of MCR in autumn evaluated from AOU.DiscussionMicrobial groups that were strongly correlated with MCR estimated by ETS had the ability to degrade various substrates and could get energy directly from light. It should be careful to notice the deviation of assumed organic carbon demand based on ETS caused by the alternation of day and night. Furthermore, the pattern of bacterial groups associated with year-round MCR was distinct from season-specific MCR. This study raised a warning for caution when estimating MCR based on AOU and it was better to fully take the photoheterotrophy into account when assuming organic carbon remineralization based on ETS.

Since the industrial revolution, nearly one-third of anthropogenic carbon dioxide emissions have been absorbed by the ocean which has a huge potential for negative emissions. Ocean alkalinity enhancement is considered to be one of the most potential marine negative emission technologies. Olivine which is widely distributed over the world is one of the silicate alkaline minerals and has a high weathering rate. The efficiency of ocean alkalinity enhancement is affected by the dissolution rate and diffusion rate of olivine. On the offshore olivine reaction platform, the method of grinding olivine to accelerate its dissolution based on clean energy and diffusing high-alkalinity seawater through ocean currents to accelerate the absorption of atmospheric carbon dioxide has broad application prospects. With the exploration of offshore oil and gas resources in China, the combination of olivine offshore reaction platform and offshore oil and gas platform can not only save the construction cost of olivine offshore platform, but also capture the carbon dioxide during the producing process of oil and gas, which will further increase the efficiency of carbon sequestration.

Utilisation of dissolved organic phosphorus (DOP) by marine microbes as an alternative phosphorus (P) source when phosphate is scarce can help sustain non-Redfieldian carbon:nitrogen:phosphorus ratios and efficient ocean carbon export. However, global spatial patterns and rates of microbial DOP utilisation are poorly investigated. Alkaline phosphatase (AP) is an important enzyme group that facilitates the remineralisation of DOP to phosphate and thus its activity is a good proxy for DOP-utilisation, particularly in P-stressed regions. We present a Global Alkaline Phosphatase Activity Dataset (GAPAD) with 4083 measurements collected from 79 published manuscripts and one database. Measurements are organised into four groups based on substrate and further subdivided into seven size fractions based on filtration pore size. The dataset is globally distributed and covers major oceanic regions, with most measurements collected in the upper 20 m of low-latitude oceanic regions during summer since 1997. This dataset can help support future studies assessing global ocean P supply from DOP utilisation and provide a useful data reference for both field investigations and modelling activities.

Understanding how marine microbial food webs and their ecosystem functions are changing is crucial for projections of the future ocean. Often, simplified food web models are employed and their solutions are only evaluated against available observations of plankton biomass. With such an approach, it remains unclear how different underlying trophic interactions affect interpretations of plankton dynamics and functioning. Here, we quantitatively compare four hypothetical food webs to data from an existing mesocosm experiment using a refined version of the Minimum Microbial Food Web model. Food web representations range from separated food chains to complex food webs featuring additional trophic links including intraguild predation (IGP). Optimization against observations and taking into account model complexity ensures a fair comparison of the different food webs. Although the different optimized model food webs capture the observations similarly well, projected ecosystem functions differ depending on the underlying food web structure and the presence or absence of IGP. Mesh‐like food webs dominated by the microbial loop yield higher recycling and net primary production (NPP) than models dominated by the classical diatom‐copepod food chain. A high degree of microzooplankton IGP increases NPP and organic matter recycling, but decreases trophic transfer efficiency (TTE) to copepods. Copepod production, the trophic role of copepods, and TTE are more sensitive to initial biomass changes in chain‐like than in complex food webs. Measurements resolving trophic interactions, in particular those quantifying IGP, remain essential to reduce model uncertainty and allow sound conclusions for ecosystem functioning in plankton ecosystems.

Bacterioplankton community is the major engine that drives the biogeochemical cycling of various nutrient and essential elements in the coastal ecosystem. Unraveling the mechanisms governing the succession of such complex bacterioplankton communities in dynamic environment is a challenging issue in environmental science. In this study, we investigated the diversity patterns and succession mechanisms of both free-living and particle-attached bacterioplankton communities that have been exposed to low oxygen and typhoon Lekima. The community evenness was the lowest in August when the temperature was high and dissolved oxygen was low. Similar patterns in community succession were observed for free-living and particle-attached bacterioplankton community after the passing through of typhoon Lekima. Both the free-living and particle-attached bacterioplankton communities in the surface and bottom water columns were strongly affected by geo-environmental factors, among which temperature was the common factor, suggesting that the metabolic theory of ecology also underlie the dynamic patterns of bacterioplankton communities. Although the surface and bottom bacterioplankton compositions were initially different taxonomically and shaped by different environmental conditions, they followed a similar succession pattern over the sampling months. Temperature, dissolved inorganic carbon and dissolved inorganic phosphorus were the major factors associated with the variations of surface bacterioplankton ASVs. Time-decay relationship, in which community similarity decreases with increasing time interval, was clearly observed. Such pattern shall be attributed to the combined effects of time and the changing environmental factors over the sampling months, rather than time alone. Integrating multiple lines of evidences, we demonstrated that determinism governed the succession of both free-living and particle-attached bacterioplankton communities in the coastal maricultural ecosystem, with higher stochastic ratio in habitable months (i.e. fall). This study is expected to provide valuable mechanistic insights into the succession of disturbed complex bacterioplankton communities.

This paper reviewed the research progress and prospects of alkaline phosphatase and its activity in the ocean, aiming to better understand marine biogeochemical cycles and ecosystem functions and provide a scientific basis for related research topics. Alkaline phosphatase, mainly produced by phytoplankton, zooplankton and bacteria and identified according to the pore size of filters, was of great significance for regulating marine carbon, nitrogen and phosphorus cycles and biological community compositions. Furthermore, alkaline phosphatase activity, generally quantified by hydrolyzing fluorogenic model substrates, had specific horizontal, vertical and seasonal distribution characteristics in the global ocean. Some typical environmental factors were found to be capable of affecting alkaline phosphatase activity, including solar radiation, sea temperature, river input, upwelling, dissolved organic phosphorus, dissolved inorganic phosphorus, dissolved inorganic nitrogen, metal ions and virus lysis, zooplankton predation and excretion.

The zooplankton components in biogeochemical models drive top-down control of primary production and remineralisation, and thereby exert a strong impact on model performance. Who eats whom in oceanic plankton ecosystem models is often largely determined by body size. However, zooplankton of similar size can have different prey-size spectra. Thus, models with solely size-structured trophic interactions may not capture the full diversity of feeding interactions and miss important parts of zooplankton behavior. We apply an optimality-based plankton ecosystem model to analyse trophic interactions in a suite of mesocosm experiments in the Peruvian upwelling region. Sensitivity analyses reveal a dominant role of trophic structure for model performance, which cannot be compensated by parameter optimisation. The single most important aspect governing model performance is the trophic linking between dinoflagellates and ciliates. Only with a bidirectional link, i.e., both groups can prey on each other, is the model able to reproduce the differential development of the microzooplankton communities in the mesocosms. Thus, we conclude that a solely size-based trophic structure may not be appropriate to represent the most important trophic interactions in plankton ecosystems. The diversity of feeding interactions needs to be adequately represented to capture community dynamics. (C) 2017 The Authors. Published by Elsevier B.V.

Both atmospheric deposition and benthic remineralisation influence the marine nitrogen cycle, and hence ultimately also marine primary production. The biological and biogeochemical relations in the eastern tropical South Pacific (ETSP) among nitrogen deposition, benthic denitrification and phosphorus regeneration are analysed in a prognostic box model of the oxygen, nitrogen and phosphorus cycles in the ETSP. Atmospheric nitrogen deposition ( ≈ 1.5 Tg N yr−1 for the years 2000–2009) is offset by half in the model by reduced N2 fixation, with the other half transported out of the model domain. Model- and data-based benthic denitrification in our model domain are responsible for losses of 0.19 and 1.0 Tg Tg N yr−1, respectively, and both trigger nitrogen fixation, partly compensating for the NO3− loss. Model- and data-based estimates of enhanced phosphate release via sedimentary phosphorus regeneration under suboxic conditions are 0.062 and 0.11 Tg N yr−1, respectively. Since phosphate is the ultimate limiting nutrient in the model, even very small additional phosphate inputs stimulate primary production and subsequent export production and NO3− loss in the oxygen minimum zone (OMZ). A sensitivity analysis of the local response to both atmospheric deposition and benthic remineralisation indicates dominant stabilising feedbacks in the ETSP, which tend to keep a balanced nitrogen inventory; i.e. nitrogen input by atmospheric deposition is counteracted by decreasing nitrogen fixation; NO3− loss via benthic denitrification is partly compensated for by increased nitrogen fixation; enhanced nitrogen fixation stimulated by phosphate regeneration is partly counteracted by stronger water-column denitrification. Even though the water column in our model domain acts as a NO3− source, the ETSP including benthic denitrification might be a NO3− sink.

A marine bacterium Pseudoalteromonas sp.QY202 with high κ-carrageenase activity was isolated from the surface of Chondrus crispus.The κ-carrageenase was purified to electrophoretic homogeneity from the culture supernatant by a procedure of ammonium sulfate precipitation,desalting and DEAE-sepharose ion exchange chromatography,and the characterization of the enzyme was studied.The results show that the enzyme is purified 23.1 folds with a total recovery yield of 43.9% and gives a single band on SDS-PAGE with a molecular mass of 33.2 kDa.The optimum temperature and pH for enzyme activity are 40 ℃ and pH8.0,respectively.The enzyme is stable at temperatures below 40 ℃ and over a range of pH7.0-8.0.For κ-carrageenan,the enzyme gave a Km value of 1.6 mg/mL.The enzyme activity could be enhanced by the presence of Na＋ and K＋,whereas enormously inhibited by Hg^2＋and Cu^2＋.The main hydrolysis products of κ-carrageenan by the enzyme are κ-neocarradiaose and κ-neocarratetraose.

The fermentation conditions of marine bacterium Cellulophaga sp. QY201 for endoglucanase production were investigated in this paper. The results showed that the optimal liquid fermentation medium was (w/v):CMCNa 0.5 %, CaSein 0.3 %, NaCl 3 %, MgSO4·7H2O 0.3 %, Na2HPO4 0.15 %, NaH2PO4 0.1 %, and pH=7.0. After fermentation for 36 h at 100 r/min and 28 ℃, the yield of endoglucanase was up to 7.85 U/mL, which was 2.5 times higher than that under the original conditions. All of this lays a solid foundation for large-scale preparation and application of endoglucanase.