With the support of the Ministry of Science and Technology, China joined the International Ocean Drilling Program (IODP) in 1998. IODP-China has so far led the organization of 4+1 expeditions. Through the complimentary proposal project (CPP), Chinese scientists led the drilling expeditions of 349/367/368/368x to investigate the full history of rifting- breakup-spreading of the South China Sea (SCS) basin. In this paper, we summarize the latest achievements of IODP Expeditions 367/368/368x, which revealed surprising evidence for abundant magma intrusion and underplating at the distal northern margin of the SCS as well as rapid continent-ocean transition. Extensive in-depth exchanges and cooperation with the international scientific community have greatly enhanced the operation of ocean drilling platforms, management of the IODP organization, scientific and technical staff training, and public outreach. These experiences will further enhance international cooperation of China's oceanographic research.

More frequent and persistent marine heatwaves (MHWs) under global warming have exerted severe ecological and socioeconomic impacts. However, there are still limited studies on the air-sea interaction related to MHWs and how MHWs modulate regional climate. Spatiotemporal distribution of summer MHWs in the Northwest Pacific (NWP) and associated air-sea interaction were systematically studied based on daily Optimum Interpolation Sea Surface Temperature (OI SST) dataset from the National Oceanic and Atmospheric Administration (NOAA) and reanalysis dataset from the National Centers for Environmental Prediction (NCEP) during the period of 1982-2017. Empirical orthogonal function (EOF) analysis of MHWs' frequency shows a linear increasing trend in the first mode except for the Kuroshio extension region, while a north-south “dipole” pattern appears in the second mode, with characteristic of inter-decadal oscillation. Maximum intensity, duration, and cumulative intensity of MHWs all show a linear increasing trend. Maximum intensity and cumulative intensity rise most in the high latitudes, and the duration of MHWs varies significantly in the Kuroshio extension region. Analysis of air-sea interaction illustrates that, when MHWs occur in the mid or low latitudes, latent heat and sensible heat fluxes from the ocean to the overlying atmosphere play a dominant role, which impacts atmospheric circulation in the surrounding area. The atmospheric forcing is more significant when MHWs occur in the high latitudes, including longwave radiation and sensible heat fluxes.

In this paper, we discuss the principle of ecosystem complexity, and propose a method for evaluating the health of typical coral reef ecosystems in the South China Sea-"Organization and System Function Evaluation." The evaluation framework of this method includes four modules: the structure and function of coral reef ecosystems, the relationship between coral reef ecosystems and other marine ecosystems, the relationship with human social ecosystems, and the development constraints of coral reef ecosystems. The evaluation index system is divided into six levels, including target level, criterion level, factor level, and element level, totaling 67 indicators. We systematically put forward the process of coral reef ecosystem health evaluation, which improves the standardization and timeliness of coral reef health evaluation. The organizing power and system function evaluation method was used to evaluate the health of the coral reef ecosystem of the Paracel Islands from 2011 to 2018. The results show that the health index has fallen by 2.3%-2.4% annually since 2011. Except for a slight rebound in 2012 and 2015, the health index has shown a downward trend in the rest of the years. The overall evaluation is that the coral reef ecosystem of the Paracel Islands is sub-healthy. This result is consistent with the results of field investigations and questionnaire surveys on residents' lives around the Qilianyu Islands. We find that the development of fisheries in 2006-2008, the flooding of starfish in 2012, and the construction of islands and reefs in 2014-2015 had great impacts on the coral reef ecosystem. The fishery output dropped by 50%-80% in 10 years, which is also consistent with the evaluation results. It verifies the science and feasibility of the evaluation method from another angle.

Because of their unique habitat and metabolic pathways, marine microorganisms can produce a variety of bioactive substances with novel structures and functions, which make natural products from these marine microorganisms become a research hotspot of new marine drugs. Combining the methods and perspectives of bibliometrics, we review in this paper the research status of natural products from marine fungi and marine bacteria, the artificial synthesis of natural products of marine microorganisms, the biological activity and druggability evaluation of natural products from marine microorganisms, to clarify the current status and development trend of natural products from marine microorganisms.

In recent years, Phaeocystis has become the main causative species for algal blooms in the Beibu Gulf of China. It has deleterious effects on marine ecosystem and aquaculture, and causes nuclear power plant safety problems in Fangcheng. It is thus urgent to further analyze the causative species of Phaeocystis in the region. In February and March 2017, nine strains of Phaeocystis sp. identified by optical microscope were isolated during algal blooms in Qinzhou Bay and Weizhou Island; their SSU rDNA sequences were then analyzed using Maximum Likelihood (ML) phylogenetic tree. The results showed that all nine strains of Phaeocystis sp. were morphologically consistent with those of Phaeocystis globosa. Their genetic distance varied between 0.0000-0.0073; and in the phylogenetic tree, all clustered in the same branch with those P. globosa from other seawaters. Among them, WZS3-1 strain in the Beibu Gulf had the closest genetic relationship with P. globosa from Gulf of Mexico CCMP627, Surinam CCMP628, Ecuador CCMP1528, South Africa P162, China Sea RCC:K1398 and Santou97, exhibiting a genetic distance of 0.0000. Strains of WZS1, WZS2, WZS4, and WZS5 in the Beibu Gulf had a genetic distance of 0.0000 with Hong Kong SKLMP_T005 and Bohai BOHAI1. The intraspecific genetic distance of P. globosa (0.0000-0.0071) is significantly smaller than the interspecific genetic distance of P. globosa (0.0084-0.0440). As a result, these nine strains from Beibu Gulf all belong to P. globosa. The phylogenetic distance for strains of P. globosa do not reflect their geographical distance. The findings of this study are essential for Phaeocystis culture collection, their further ecophysiological study and understanding of occurrence mechanisms for Phaeocystis blooms in the Beibu Gulf.

The South China Sea (SCS) is the largest marginal sea in the western Pacific Ocean, connected with the western Pacific Ocean and the Indian Ocean through a series of straits. Multi-scale dynamic processes of ocean circulation and their environmental effects on marine biology and ecology have been a focus of SCS regional oceanography research. Since the first national marine census at the end of the 1950s, China has kept on increasing its support on marine research, especially on the construction of marine scientific observation platforms on research vessels. Entering the New Millennium, the main marine research institutes and universities in China, which operate research vessels, organized and supported Open Cruise for domestic scientists without charging for the shiptime. As a milestone, the Natural Science Foundation of China (NSFC) set up a Shiptime Sharing Project to support the Open Cruise since 2009, which has further promoted communications and cooperations among the domestic ocean research communities. Many important achievements have been made in the SCS regional oceanography. From the perspective of multi-scale ocean dynamics, we briefly review the history of ocean observations in the SCS and summarize the research progresses of key scientific issues in the SCS in recent years, including the water exchange between the SCS and western Pacific Ocean, the mesoscale and sub-mesoscale processes, the multi-scale interaction and its ecological environmental effects, among others. We also share some thoughts and prospects on observations and scientific investigations in the SCS in the future.

As one of the three high nutrient and low chlorophyll (HNLC) regions in the global oceans, the growth of phytoplankton in the subarctic North Pacific Ocean is restricted by the trace element iron, which plays an important role in nitrogen fixation, photosynthesis and metabolism of phytoplankton. For an open ocean, atmospheric deposition (atmospheric pollutants produced by human activities as well as dust) is an important source of iron, which can impact biological activities in the upper layer of the ocean. In this study, we use the daily-averaged atmospheric deposition model outputs from the Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS) for the period between December 1997 and November 2017, to quantify the flux of atmospheric deposition in the North Pacific Ocean and the corresponding spatial and temporal variability. The results show that the annual flux of atmospheric deposition into the North Pacific Ocean is 26.81 Tg·a^-1, with clear seasonal variation: high flux of atmospheric deposition flux happens during spring and peaks in May, and low values occur in winter. The spatial distribution of atmospheric deposition shows a prominent increasing from the Northwest Pacific Ocean to Northeast Pacific Ocean. In this study, we analysis the response of Particulate Organic Carbon (POC; Aug. 2010) and chlorophyll (Apr. 2001, Apr. 2008 and Aug. 2010) at station K2 (47°N, 160°E) in the Northwest Pacific Ocean to strong dust events, which are defined as the times when high flux of atmospheric decomposition happens. The results show that the POC flux and chlorophyll increase obviously after each dust event because the iron from atmospheric deposition can regulate the growth of phytoplankton and biological pump Thus, the dust events can stimulate the responses of marine ecosystem by promoting ocean primary production.

The Modaomen Estuary is the main outlet of the Xijiang River, where large-scale human intervention occurred since the 1980s, including sand excavation in the river network and estuarine regulation project, which inevitably caused the variation of tidal dynamics in the Modaomen Estuary. In this paper, we investigate the variation of tidal dynamics and its response to human intervention in recent 50 years by using statistical analysis and harmonic analysis on hydrological data, and hydrodynamic numerical simulation. The results reveal that the variation of tidal dynamics indicates a natural evolution trend of a river-dominated estuary, characterized by increase in tidal level and decrease in tidal range prior to the 1980s. However, after the 1980s sand excavation in the river network induced a decrease in tidal level and increase in tidal dynamics, while estuarine regulation project resulted in an increase in tidal level and decrease in tidal dynamics. In the inner estuary, tidal dynamics was more affected by sand excavation, with decrease in tidal level and increase in tidal dynamics. In the central estuary, tidal dynamics was affected by both sand excavation and estuarine regulation project, with increase in tidal level and decrease in tidal dynamics during the regulation project (1983-1993) but increase in tidal dynamics after the regulation project (1993-2003). In the outer estuary, tidal dynamics was co-affected by global sea-level rise and estuarine regulation project, with increase in tidal level and decrease in tidal dynamics.

Cyclic steps caused by supercritical turbidity currents are distributed widely along the West Penghu Canyon in the Taixinan Basin of the northeastern South China Sea. Turbidity currents occur frequently in this area due to high tectonic activities, marine factors such as typhoon and delivery of large sediments from rivers. Using high-resolution bathymetric data, we conduct quantitative analysis on the morphology of 23 net-erosional cyclic steps and 10 net-depositional cyclic steps along the West Penghu Canyon, and compute flow velocity of turbidity currents flowing through these cyclic steps. We find that the flow velocity of turbidity currents has an abrupt change in the transition of net-erosional cyclic steps, while the velocity decreases significantly in the transition from net-erosional to net-depositional cyclic steps. The former is mainly caused by the slope break in the canyon, while the latter is caused by the change from confined to unconfined environment. In addition, the net-depositional cyclic steps are located closer to the southwestern flank of the West Penghu Canyon; and we propose that this phenomenon should be mainly caused by turbidity currents affected by the Coriolis force. Investigating the evolution and controlling factors of cyclic steps in this area can help us better understand the interaction of submarine bedforms and turbidity currents, which plays a significant role in the geomorphological evolution along submarine canyons.

As the largest marginal sea in the western Pacific, the South China Sea (SCS) plays an important role in the global ocean and the global oceanographic research. In the past 40 years, chemical oceanographic research in the SCS achieved systematic new discoveries and new understandings; researchers put forward many new theoretical viewpoints, making important contributions to the development of oceanography. A subsurface layer was revealed in the SCS, maximum values of ecological environmental parameters represented by nitrite are present; and the depth ranges of water layers for different parameters are different, forming a thermocline ecosystem that has significantly different characteristics from the other ecosystems. The carbon cycle process in the SCS is very complex, and changes of the biological pump controlled by biological activities, and the regional and seasonal changes of carbon sources and sinks, are all great. The characteristics and intensity of carbon sources and sinks in the SCS are unique in different regions at different times. Annually, the SCS is a weak source of atmospheric carbon dioxide. The characteristics of ecological environment and the cycling process of chemical material in the Pearl River Estuary and deep-sea basins were found not only closely related to but also significantly different from that in shelf marginal seas and coral reefs, as the dissolved oxygen concentration is low in the bottom, and the Pearl River Estuary is basically an ecologically fragile area characterized by hypoxia. Based on the systematic understanding of the rapid material circulation and vertical transfer of chemical substances controlled by biological processes in the Nansha coral reef ecosystem, a new mechanism - “resembling drift-net theory” - was proposed to explain how the coral reef ecosystem could maintain high productivity. Systematic studies on the sedimentary chemistry of the SCS show that there is a close coupling between the sediments and chemical cycling of water bodies. The distribution of chemical substances in coral reefs or in sediment cores of the SCS can be used to retrieve historical environment changes. The paleo productivity of surface seawater in the SCS during the glacial period was 1.6 times higher than that of the interglacial period. A "biological explosion event" occurred in the southern SCS in the late Miocene. The productivity in that period was mainly affected by the monsoon and terrigenous nutrients input, while the influences of northeast monsoon and southwest monsoon differed in different regions. These new discoveries and new understandings in chemical oceanography of the SCS in the past 40 years have laid a strong foundation for further systematic and in-depth understanding of the oceanographic processes in the region. In the future, chemical oceanographic research will definitely provide scientific support for the sustainable utilization of resources and environment in the SCS.

Epsilon-proteobacteria is widely distributed, from deep-sea hydrothermal vent to surface sea water, from free-living environment to host-associated one. Chemotaxis plays an important role in bacteria survival through sensing and responding to environmental changes. Thus, some bacteria have evolved into many complex and diverse chemotaxis systems. Epsilon-proteobacteria can adapt to different environments; especially, some species can survive in the deep-sea extreme environments including hydrothermal vent and cold seep, whose chemotaxis system may have special characteristics. Bioinformatics analyses by BlastP and MIST database revealed that most Epsilon-proteobacteria species in the deep-sea hydrothermal vent have F3 type chemotaxis system. They all contain a single copy of CheV, which is a double domain fusion protein. Besides, a unique domain, CZB (C-terminal Zinc-Binding) domain, exists in chemoreceptors of deep-sea Epsilon- proteobacteria. A CZB-like domain is also identified in Epsilon-proteobacteria. Using the model strain Campylobacter jejuni 81-176, we confirmed that CheV can interact with all chemoreceptors with MA domain by bacterial two-hybrid experiments. Additionally, we demonstrated that CZB-like domain cannot bind Zn by ICP-Mass, but it can promote the interaction between chemoreceptor Tlp9 and CheV.

Microbe-mediated nitrification is an essential part of global nitrogen cycle; and nitrite-oxidizing bacteria (NOB), which catalyze the second step of nitrification, have received more and more attention recently. Up to date, those isolated NOB have been identified as four phyla, belonging to seven genera. Among them, Nitrospira bacteria become a hotspot for research due to the high diversity and wide ecological distribution. In this paper, we reviewed the composition, phylogenetic relationship, nitrite oxidizing and carbon fixation pathways of NOB. We also emphasized the functional importance on global nitrogen and carbon of NOB, and highlighted research prospect for NOB.

A new error-correction forecast model for sea surface temperature (SST) is proposed in this paper, where the SST errors are derived from the Group for High Resolution Sea Surface Temperature (GHRSST) data and operational numerical prediction SST product. First of all, the reliability of the GHRSST data was validated with the upper temperature data of Argo floats in the South China Sea. The results showed that the Root Mean Square Error (RMSE) between the two sets of data was about 0.3℃ while the correlation coefficient was 0.98; the GHRSST data could be used for the correction of operational numerical forecast model on SST in the South China Sea. After being corrected, the RMSEs of 24-hr, 48-hr and 72-hr SST forecast results were dropped from 0.8 ℃ to 0.5 ℃ compared with the upper temperature data of Argo floats. Meanwhile, the 24-hr, 48-hr and 72-hr SST forecast errors between the GHRSST data and model results were significantly reduced after the correction in the northern South China Sea (110°E -121°E, 13°N -23°N). During the influence of the cold air or the mesoscale eddy in the South China Sea, the effect of SST forecast correction was also quite significant. Therefore, this method should be considered to apply in the operational numerical forecast system on SST in the South China Sea.