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Sea surface temperature (SST) fronts were analyzed in the Levantine Basin of the Mediterranean Sea over a 20-year period (2003–2022) using a high-resolution (~1 km) satellite dataset. Frontal gradients were strongest in regions of freshwater influence and around the Ierapetra eddies and Rhodes Gyre. Seasonally, maximum frontal activity was observed in fall and summer. Empirical orthogonal function (EOF) analysis revealed both monthly-to-seasonal variability and interannual variability in frontal gradients. Seasonal frontal variability is partially explained by atmospheric forcing; that is, wind stress curl (WSC) and net air–sea heat flux. The maximum frontal activity was observed in 2006, coinciding with the strongest WSC magnitude. The minimum frontal activity was observed in 2017, which saw the largest winter heat loss to the atmosphere. The highest frontal activity was typically observed in years with mild winters followed by strong Etesian winds. Over the study period (2003–2022), frontal gradients declined in the Levantine Basin. Our results suggest that years with a strong frontal boundary current (Asia Minor Current; AMC) coincide with reduced cross-shelf transport. Subsequent studies are recommended to concentrate on the variability in the frontal intensity of the AMC and associated cross-shelf transports, which are important for the oligotrophic Levantine Basin. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) fronts were analyzed in the Levantine Basin of the Mediterranean Sea over a 20-year period (2003–2022) using a high-resolution (~1 km) satellite dataset. Frontal gradients were strongest in regions of freshwater influence and around the Ierapetra eddies and Rhodes Gyre. Seasonally, maximum frontal activity was observed in fall and summer. Empirical orthogonal function (EOF) analysis revealed both monthly-to-seasonal variability and interannual variability in frontal gradients. Seasonal frontal variability is partially explained by atmospheric forcing; that is, wind stress curl (WSC) and net air–sea heat flux. The maximum frontal activity was observed in 2006, coinciding with the strongest WSC magnitude. The minimum frontal activity was observed in 2017, which saw the largest winter heat loss to the atmosphere. The highest frontal activity was typically observed in years with mild winters followed by strong Etesian winds. Over the study period (2003–2022), frontal gradients declined in the Levantine Basin. Our results suggest that years with a strong frontal boundary current (Asia Minor Current; AMC) coincide with reduced cross-shelf transport. Subsequent studies are recommended to concentrate on the variability in the frontal intensity of the AMC and associated cross-shelf transports, which are important for the oligotrophic Levantine Basin.

The Luzon Strait is a channel where warmer Kuroshio water from the Pacific Ocean intrudes into the South China Sea (SCS). Under climate change impact, the temperature in marginal seas, including the SCS, rises faster than in open oceans. We speculated that the variation of frontal intensity and its eco‐environmental impact in the Luzon Strait may be different from coastal waters, whose frontal intensity is increasing, thus stimulating phytoplankton growth. To confirm this speculation, 40‐year satellite, and multiple data sources were analyzed in the Luzon Strait. The results showed that strong frontal intensity (front coverage of over 60%) and higher Chlorophyll a content occurred simultaneously in the Luzon Strait during the winter monsoon period. Phytoplankton blooms were enhanced during El Niño years because the stronger Kuroshio intrusion generated stronger fronts and intensified local upwelling in the Luzon Strait. On an interannual scale, the frontal intensity and phytoplankton growth exhibited a significantly decreasing trend in the Luzon Strait over the past 40 years, since the faster warming in the SCS reduced the temperature difference between the Pacific Ocean and the SCS. Warming and weakening fronts reduced the mixed layer depth to the oligotrophic layer, thus limiting the phytoplankton growth. This study confirmed that faster temperature rises in marginal seas reduced the frontal intensity and phytoplankton growth in the strait between oceans and marginal seas. Plain Language Summary: Ocean fronts are the boundaries between two sides with distinct water mass properties and play an extremely important role in marine eco‐environment and global climate change. Studies have shown that thermal fronts are enhancing, thus stimulating chlorophyll growth in the coastal waters due to the intensification of global warming. However, the variation of frontal intensity in the open oceans may be different because warming in marginal seas rises faster than in oceans. To confirm this speculation, 40‐year satellite, and multiple data sources were analyzed in the Luzon Strait, a deep conduit between the Pacific Ocean and the South China Sea (SCS). This study found that the frontal intensity and phytoplankton growth exhibited a significantly decreasing trend in the Luzon Strait over the past 40 years, since the faster warming in the SCS reduced the temperature difference between the Pacific Ocean and the SCS. Warming and weakening fronts reduced the mixed layer depth to the oligotrophic layer, thus limiting the phytoplankton growth. Key Points: Strong ocean front and higher Chlorophyll a (Chl‐a) content occurred simultaneously in winterPhytoplankton blooms enhanced in El Niño years due to stronger Kuroshio intrusionGlobal warming decreased the frontal intensity and Chl‐a level over the past 40 years [ABSTRACT FROM AUTHOR]

This review will serve as an entry point for international researchers who would like to tap into the vast scientific potential of Chinese-language literature on oceanic fronts. We focused on observational physical oceanography studies of marine fronts. A thorough bibliographic search netted 95 papers published in 1982–2023, with a sharp increase in the total number of papers from 2006–2010 to 2011–2015, when this number almost tripled. This trend continued unabated through the early 2020s. The sharp increase in Chinese-language publications preceded by several years a rapid increase in English-language publications in the same field. Regionally, the overwhelming majority of papers is focused on the China Seas, particularly the East China Seas and northern South China Sea. Elsewhere, a number of papers were dedicated to the Southern Ocean and North Atlantic. Thematically, papers on remote sensing of ocean fronts dominate the literature, with special attention to the development of front-detection algorithms that can be applied to satellite data on sea surface temperature, salinity, chlorophyll, and sea level anomaly. Numerous papers on marine fronts in the China Seas present important results that have to be considered by international researchers. Overall, this review emphasizes the significant contributions made by Chinese oceanographers, particularly to studies of the frontal oceanography of the China Seas. [ABSTRACT FROM AUTHOR]

Since offshore waters are less affected by human activities and nutrient‐rich water masses, existing theories on periodic offshore blooms (POB) consider that the POB is proportional to the intensity of ocean fronts (nutrient supply from enhancing vertical mixing), ignoring external nutrient supply and external forcing (climatic oscillations). This study proposes an external dynamic mechanism of the POB on the basis of field observations and long‐term satellite remote sensing data (1981–2022) in Beibu Gulf, which is influenced by remarkable external forcing. A strong thermal front with an inverted‐V structure occurred in the central gulf every winter due to the strong wind stress. The intensity of the front on the east side is weaker due to the intrusion of the west‐Guangdong coastal current (WGCC). However, nutrient supply variation resulted in the POB's different intensity in different areas of the inverted‐V front. Chlorophyll a concentrations in the eastern (nutrients supplied by WGCC) and northern (nutrients supplied by vertical mixing) were obviously higher than that in the western front (limited nutrient supply) in winter. On an interannual scale, the intensity of POB in La Niña years is remarkably stronger than in El Niño years due to the stronger WGCC supplying more nutrients in La Niña. This study suggests that the intensity and range of POB are not proportional to the frontal intensity in the gulf, but are directly driven by the internal forcing (fronts and nutrient supply from WGCC), which is controlled by the external forcing. Plain Language Summary: It is accepted that the intensity of periodic offshore blooms (POB) is considered in proportion to the intensity of ocean fronts since the front enhances vertical mixing to upwell eutrophic water to the surface, thus stimulating primary productivity. However, this ignores external nutrient supply and external forcing (climatic oscillations). In this study, a combination of field observations and long‐term satellite remote sensing data (1981–2022) in Beibu Gulf showed that the POB in the gulf are driven by both the frontal activities and the nutrient supply from the water mass dynamics (vertical mixing and west‐Guangdong coastal current). The intrusion of west‐Guangdong coastal current (WGCC) weakens the frontal intensity but increases the Chlorophyll a concentration in the eastern gulf. Additionally, POB in La Niña years are remarkably stronger than that in El Niño years due to the stronger WGCC supplying more nutrients in La Niña years. Thus, the intensity and range of POB are mainly influenced by external forcing rather than the frontal intensity in the gulf. Key Points: West‐Guangdong coastal current (WGCC) intrusion weakens the intensity of eastern front but increases the Chlorophyll a (Chl‐a) level in the gulfChl‐a level in La Niña years is remarkably higher than that in El Niño years due to the stronger WGCC supplying more nutrients in La NiñaThe intensity of the bloom is not proportional to the frontal intensity, but controlled by external forcing and external nutrient supply [ABSTRACT FROM AUTHOR]

Typhoons greatly affect ocean hydrodynamics, thereby altering ocean productivity and biogeochemistry. This study used stable isotopes and geochemical indicators of particulate organic matter (POM) to investigate the impact of Typhoon Talim (2023) on marine productivity and POM dynamics in Zhanjiang Bay. During the typhoon, an ocean front formed in the upper bay, resulting in a nearly twofold increased POM and enhanced decomposition of resuspended POM, due to the strengthened vertical mixing. Despite of strong decomposition, the supplementation of terrestrial nutrient inputs maintained minimal changes in chlorophyll in the upper bay. By contrast, in the lower bay, chlorophyll and POM decreased significantly, primarily attributed to decomposition of fresh POM and nitrogen limitation resulting from high-salinity seawater intrusion induced by the typhoon. This study suggests that after typhoons, in the area where the ocean front forms, the decomposition degrades a large amount of resuspended POM, which is not conducive to the burial of organic carbon. • POM increased in the upper bay due to enhanced vertical mixing after the typhoon. • Typhoon induced formation of ocean front intensified decomposition of resuspended POM. • POM and Chl- a decreased in the lower bay due to decomposition induced by the typhoon. • Both regions experienced severe oxygen consumption due to POM decomposition. [ABSTRACT FROM AUTHOR]

The influence of floating marine debris (FMD) on coastal and marine communities and ecosystems is undeniable, and attention is increasingly focused on ecologically and biologically important coastal areas. To protect marine life and valuable resources from FMD pollution, identifying FMD accumulation zones is recognized as a priority. One of the coastal ocean processes found governing the distribution of FMD is water convergence (frontal zones). These fronts are driven by various oceanographical factors. To date, the transport and accumulation of FMD in relation to fronts in coastal areas is poorly understood. To address this knowledge gap, we reviewed various types of ocean fronts as well as FMD accumulation along frontal zones in coastal areas defined as the region between the coastline and the shelf break. Frontogenesis (physical processes related to frontal formation) were reviewed alongside studies on FMD accumulation in frontal zones to identify physical factors that drive the pathways and accumulation in these areas. This review will contribute to our understanding of accumulation hotspots of FMD within ocean fronts and identify gaps for further research on developing a proxy for FMD hotspot identification in ecologically important coastal areas. • Different frontal types are generated by various oceanographic processes, and coastal fronts are mainly driven by winds, tides, currents, upwelling and downwelling, bottom topography, plumes, and internal waves. • In coastal zones, floating marine debris accumulates along water convergences including gyres, eddies, slicks, salinity fronts, density fronts, thermohaline fronts and tidal fronts. • Frontal accumulated debris has an impact on marine species in coastal waters including important marine taxa such as seabirds, dolphins, and turtles. • Study on FMD accumulation in frontal zones has received more attention, with 72% of reviewed papers were published between 2017 and 2023, and the highest number of published papers (10 papers) in 2021. • This study suggests that future research exploring the impacts of frontogenesis on the transport and accumulation of FMD over the continental shelf zone would be valuable. [ABSTRACT FROM AUTHOR]

The contribution of ocean fronts to the properties and temporal evolution of Sea Surface Temperature (SST) structure functions have been investigated using a numerical model of the California Current system. First, the intensity of fronts have been quantified by using singularity exponents. Then, leaning on the multifractal theory of turbulence, we show that the departure of the scaling of the structure functions from a straight line, known as anomalous scaling, depends on the intensity of the strongest fronts. These fronts, at their turn, are closely related to the seasonal change of intensity of the coastal upwelling characteristics of this area. Our study points to the need to correctly reproduce the intensity of the strongest fronts and, consequently, properly model processes such as coastal upwelling in order to reproduce SST statistics in ocean models. Plain Language Summary: Forecasting the evolution of the Earth's climate requires to predict the evolution of the statistical characteristics of essential climate variables such as the Sea Surface Temperature. In this study, it has been found that some of such statistical properties depend on the intensity of the strongest fronts in the ocean. This implies that those ocean, or climate, models that fail to correctly predict their intensity will not be able to correctly reproduce the statistical characteristics of key variables such as temperature. The area analyzed in this study is the California Current system, where the strongest fronts are modulated by the seasonal evolution of the upwelling. Therefore, our results imply that such a system has to be correctly modeled, or parametrized, in order to properly reproduce the statistics of ocean temperatures. Key Points: The intensity of Sea Surface Temperature (SST) fronts is quantified using singularity exponents, which measure the continuity of the fieldAnomalous scaling of SST structure functions is correlated to the the intensity of the strongest frontsThe variability of the strongest fronts depends on the seasonal variability of the coastal upwelling in the area of study [ABSTRACT FROM AUTHOR]

Small yellow croaker (Larimichthys polyactis), a benthic fish species widely distributed in the Northwest Pacific Ocean, plays an important role in the fishery catch of coastal countries. A large amount of dead small yellow croaker floated on the sea surface near 30.2°N, 125.3°E in the East China Sea on 19 February 2017, and more than 9,000 kilograms were caught by fishermen, which had never been recorded before. This study aims to investigate the dynamic causes of this sudden death event based on available in-situ, satellite and modelling data. The event occurred near the overwintering ground of small yellow croaker, where a majority of these fish assembled in winter. There were persistent ocean fronts at target site with average intensity of 0.05°C/km at sea surface and bottom in February 2017, which was the strongest in the past 5 years from 2015 to 2019. The fronts provided nutrients and food to fish, and the intense gradients prevented fish from crossing, thus forming “water barriers” to restrict the horizontal movement of fish. Due to enhanced convection, the water was well-mixed, enabling the demersal croaker to float to sea surface. The sea temperature was particularly warm in winter 2017, but then experienced a significant drop by more than 4.5°C in 40 days according to satellite and modelling datasets due to the northerly wind and the southeastward movement of cold eddy. The drop of temperature led to ‘cold shock’ of fish, affecting their physiological regulation and survival. Under the combined influence of these factors, a large number of small yellow croaker died and aggregated near the target site. This paper has a great reference value for further study on the living habits of small yellow croaker and their responses to marine dynamic changes.

This study proposes a method to detect ocean fronts from in situ temperature and density glider measurements. This method is applied to data collected along the CalCOFI Line 90, south of the California Current System (CCS), over the 2006–2013 period. It is based on image-processing techniques commonly applied to sea surface temperature (SST) satellite data. Front detection results using glider data are consistent with those obtained in other studies carried out in the CCS. SST images of the Multi-scale Ultra-high Resolution (MUR) dataset were also used to compare the probability of occurrence or front frequency (FF) obtained with the two datasets. Glider and MUR temperatures are highly correlated. Along Line 90, frontal frequency exhibited the same maxima near the transition zone (~130 km offshore) as derived from MUR and glider datasets. However, marked differences were found in the bimonthly FF probability with high (low) front frequency in spring-summer for glider (MUR) data. Methodological differences explaining these contrasting results are investigated. Thermohaline-compensated fronts are more abundant towards the oceanic zone, although most fronts are detected using both temperature and density criteria, indicating a significant contribution of temperature to density in this region.

• Blooms of red Noctiluca scintillans (RNS) in the ECS bounded by major ocean fronts. • The 2000–2020 record shows an expansion in annual footprints of the RNS blooms. • Anomalous Yangtze river plume could advect RNS blooms further from shore. A recent study demonstrated the possibility of satellite-based detection of surface blooms of the heterotrophic dinoflagellate, red Noctiluca scintillans (RNS). The study further documented RNS bloom patterns in the East China Sea (ECS) between 2000 and 2017. Here, complemented by more recent satellite observations between 2018 and 2020, the 21-year bloom record shows that while bloom distributions vary in different years and annual cumulative bloom footprint shows an increasing trend, the 21-year cumulative bloom footprint is bounded by major ocean fronts such as the Kuroshio Front. Of all observations, 2020 is a critical year to "complete" the footprint as extra discharge from the 2020 Yangtze River flood event, combined with ocean currents, transports the bloom to the most northeast location of the footprint although the riverine influence reaches at least 128°E, well beyond the RNS footprint. [Display omitted] [ABSTRACT FROM AUTHOR]

This study proposes a method to detect ocean fronts from in situ temperature and density glider measurements. This method is applied to data collected along the CalCOFI Line 90, south of the California Current System (CCS), over the 2006–2013 period. It is based on image-processing techniques commonly applied to sea surface temperature (SST) satellite data. Front detection results using glider data are consistent with those obtained in other studies carried out in the CCS. SST images of the Multi-scale Ultra-high Resolution (MUR) dataset were also used to compare the probability of occurrence or front frequency (FF) obtained with the two datasets. Glider and MUR temperatures are highly correlated. Along Line 90, frontal frequency exhibited the same maxima near the transition zone (~130 km offshore) as derived from MUR and glider datasets. However, marked differences were found in the bimonthly FF probability with high (low) front frequency in spring-summer for glider (MUR) data. Methodological differences explaining these contrasting results are investigated. Thermohaline-compensated fronts are more abundant towards the oceanic zone, although most fronts are detected using both temperature and density criteria, indicating a significant contribution of temperature to density in this region. [ABSTRACT FROM AUTHOR]