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Suspended sediment fronts (SSFs) significantly affect water quality, ecology, and geomorphological evolution of estuarine and coastal waters. Based on 10‐year suspended sediment concentration data derived from satellite images, the multiscale spatio‐temporal variability of SSFs in the Bohai Sea was studied. Frontal probability (FP) was used to quantify the intensity of frontal activity. The 10‐year averaged FP was higher near the coast and decreased with increasing offshore distance. The arc‐shaped distributions of FP near the Yellow River Estuary revealed two tidal shear frontal zones. In the eastern Bohai Sea, 13 finger‐shaped high‐FP areas reflected the spatial pattern and fine structures of tidal sand ridges. The complex topography and strong tidal dynamics provided the essential conditions for frontogenesis. The seasonality of frontal activity was dominantly regulated by the change in wind waves associated with monsoons and stratification. The direct or indirect effects of sediment discharges from the Yellow River and Liaohe River on seasonal and annual variations of frontal activity only existed within close proximity to the estuaries. Frontal activity generally showed an interannual weakening trend, especially in the Laizhou Bay (−0.27%/yr), while an opposite trend was identified in the Liaodong Bay (0.10%/yr). This phenomenon was related to the interannual variations of wind speeds. Meanwhile, wind speed anomalies caused by El Niño‐Southern Oscillation events could explain the significant interannual fluctuations in frontal activity such that, frontal activity was significantly enhanced (suppressed) when El Niño (La Niña) events occurred, especially during 2015–2016 (2017–2018). Plain Language Summary: Suspended sediment fronts, one of the most common phenomena in estuarine and coastal waters, are defined as narrow zones with large spatial changes in suspended sediment concentration over relatively short distances. The Frontogenesis and frontal variability of the Bohai Sea, east coast of mainland China have unique patterns because of its complex hydro‐sedimentary environment, but no relevant studies have been systematically conducted yet. In this study, the intensity of frontal activity in the Bohai Sea was quantified by using satellite observation data spanning 10 years. Our analyses revealed that strong frontal activity mainly occurred in areas with dramatic changes in topography and shoreline and distinct tidal features. The seasonal and year‐to‐year variations of frontal activity were closely related to wind waves, stratification, riverine sediment input, and El Niño‐Southern Oscillation events. Nevertheless, their influence mechanisms varied in different regions. The new findings are of significance to further investigate the sedimentary patterns and the ecological effects of sub‐mesoscale processes in the Bohai Sea, and can also shed light on frontal variability of semi‐enclosed shallow seas worldwide. Key Points: Geostationary Ocean Color Imager remote sensing data were used to quantify suspended sediment front variations in the Bohai SeaSpatial patterns and seasonal‐to‐interannual variability of frontal activity were revealedEffects of dynamic factors on the spatio‐temporal variations of frontal activity were analyzed [ABSTRACT FROM AUTHOR]

Data assimilation (DA) provides better initial states of model runs by combining observational information and models. Ensemble-based DA methods that depend on the ensemble run of a model have been widely used. In response to the development of seamless prediction based on coupled models or even earth system models, coupled DA is now in the mainstream of DA development. In this paper, we focus on the technical challenges in developing a coupled ensemble DA system, which have not been satisfactorily addressed to date. We first propose a new DA framework DAFCC1 (Data Assimilation Framework based on C-Coupler2.0, version 1) for weakly coupled ensemble DA, which enables users to conveniently integrate a DA method into a model as a procedure that can be directly called by the model. DAFCC1 automatically and efficiently handles data exchanges between the model ensemble members and the DA method, and enables the DA method to utilize more processor cores in parallel execution. Based on DAFCC1, we then develop a sample weakly coupled ensemble DA system by combining the ensemble DA system GSI/EnKF and the coupled model FIO-AOW. This sample DA system and our evaluations demonstrate the effectiveness of DAFCC1 in both developing a weakly coupled ensemble DA system and accelerating the DA system. [ABSTRACT FROM AUTHOR]

The Fukushima nuclear accident in 2011 released large amounts of radionuclides, including Cs, into the Pacific Ocean. A quasi-global ocean radioactive transport model with horizontal grid spacing of 0.5°×0.5° and 21 vertical layers was thereafter established to study the long-term transport of the Fukushima-derived Cs in the ocean. The simulation shows that the plume of Cs would be rapidly transported eastward alongside the Kuroshio Current and its extensions. Contaminated waters with concentrations lower than 2 Bq/m would reach the west coast of North America 4 or 5 years after the accident. The Cs tends to be carried, despite its very low concentration, into the Indian and South Pacific Oceans by 2016 via various branches of ocean currents. Meanwhile, the Cs concentrations in the western part of the North Pacific Ocean decrease rapidly with time. Up to now the highly contaminated waters have remained in the upper 400 m, showing no evidence of significant penetration to deeper layers. [ABSTRACT FROM AUTHOR]