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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]

This contribution provides an introduction to a sequence of five papers (CCE I- CCE V) that describe the impact of the Warm Anomaly of 2014–15 and El Niño 2015–16 on the pelagic food web of the southern California Current Ecosystem. These contributions analyze the influence of these two warm water perturbations on satellite-based measures of ocean fronts, export efficiency out of the euphotic zone, copepod egg production, mesozooplankton community structure, and a synthesis of primary production, mesozooplankton grazing, and gravitational fluxes of organic carbon.

This contribution provides an introduction to a sequence of five papers (CCE I- CCE V) that describe the impact of the Warm Anomaly of 2014–15 and El Niño 2015–16 on the pelagic food web of the southern California Current Ecosystem. These contributions analyze the influence of these two warm water perturbations on satellite-based measures of ocean fronts, export efficiency out of the euphotic zone, copepod egg production, mesozooplankton community structure, and a synthesis of primary production, mesozooplankton grazing, and gravitational fluxes of organic carbon.

Oceanic fronts are regions over the oceans where a significant change in the characteristics of the water masses is observed. Advanced Very High Resolution Radiometer (AVHRR) satellite imagery over the Bay of Bengal shows regions that are populated by frontal structures. Over the Bay of Bengal, some of the strongest gradients in temperature and salinity are observed. In recent years, there has been a tremendous growth in the availability of satellite imagery and the necessity of automated fast detection of the frontal features is needed for services like potential fishing zones over open oceans. In this article, an algorithm to infer oceanic fronts over the Bay of Bengal is described using changepoint analysis. The changepoint algorithm is combined in a novel way with a contextual median filter to detect frontal features in AVHRR imagery. The changepoint analysis is a non-parametric technique that does not put thresholds on the gradients of brightness temperatures of the satellite imagery. In the open oceans, the gradients of temperature and salinity are not sharp and changepoint analysis is found to be a useful complementary technique to the existing front detecting methods when combined with contextual median filters.

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.

Light penetration through the ocean creates underwater light color niches and photosynthetic organisms use specific strategies to capture light in these niches. The selection pressure for some cyanobacteria strains in the genus Synechococcus that change color to absorb either blue or green light (chromatic acclimaters, or generalists) is not well understood. Here, we tested the hypothesis that changes in ocean spectra brought about by mixing preferentially selects for generalists within a Synechococcus population. We investigated ocean conditions that led to high proportions of Synechococcus generalists versus specialists in a model ocean column, and compared simulations with in situ metagenomic and physical oceanographic data from major Bio‐GO‐SHIP cruises, supplemented with GEOTRACES and TARA Oceans, as well as the GOOS Argo Program and sea surface height from AVISO. We found that greater mixed layer depths selected for generalists in simulated Synechococcus populations, but did not account for much of the variance in the partitioning of light‐harvesting strategies in situ. Rather, oceanographic signatures for upwelling areas and ocean fronts explained more of the variation between Synechococcus generalists and specialists in the ocean. Our results motivate further study of the in situ light environments of upwelling zones and ocean fronts, which are currently understudied as potential light‐driven niche habitats. Plain Language Summary: The variety of pigments used by cyanobacteria to capture light for photosynthesis increases the colors of light available for use in the ocean. Some members of the cyanobacterial genus, Synechococcus, can change color to absorb either blue or green light (generalists), adding to the variety of light‐harvesting strategies. Though the reason for this color change is believed to be fluctuations in the underwater blue/green light field, this has not been tested directly. Using a mathematical model of the ocean column, we find the highest percentages of generalists in the Synechococcus population in deep ocean mixed layers. Comparison of model results to actual distributions of generalists indicate that deep mixing plays a smaller role than our model suggested, and that upwelling zones, where water is vertically moved to the surface, and ocean fronts, where major ocean currents meet, are also important habitats for Synechococcus generalists in the ocean. Key Points: Despite high correlation with modeled deep mixing, Synechococcus blue‐green acclimaters do not correlate with open ocean mixed layer depthsA high percentage of Synechococcus chromatic acclimaters correlate with low surface temperatures and low sea surface heightA high percentage of Synechococcus chromatic acclimaters are observed along paths of major ocean fronts, and upwelling zones [ABSTRACT FROM AUTHOR]

We tested the sensitivity of the vertical distributions and shell dissolution patterns of thecosome pteropods to spatial gradients associated with an eddy-associated front in the southern California Current System. The aragonite saturation horizon (Ωarag = 1.0) shoaled from >200 to 1.4, while peak dissolution occurred in depths where Ωarag = 1.0 to 1.4. Vertical habitat compression and increased shell dissolution may be expected to accompany future shoaling of waters that are undersaturated with respect to aragonite.

D'Asaro et al. measured the dissipation of eddy kinetic energy at the Kuroshio ocean front, found it to be 1–2 orders of magnitude larger than the value predicted by the law of the wall, and suggested that the enhancement is due to sub‐mesoscales, SM. To assess their suggestion, we employ two SM models. In the first model, the buoyancy flux is based on baroclinic instabilities only and there is no momentum flux (Reynolds stresses). The model is unable to reproduce the Kuroshio data. The second model includes baroclinic instabilities, wind stress, and Reynolds stresses. It reproduces the data satisfactorily. The analytic formula for the dissipation that we present can be used in ocean general circulation models to parameterize dissipation at ocean fronts other than Kuroshio, for example, Gulf Stream and ACC, an extension that could improve the predictions of climate studies. Key Points: Sub‐mesoscale based parameterization of the enhanced energy dissipation measured in the Kuroshio Current [ABSTRACT FROM AUTHOR]

The water temperature at 100–300 m depth layer impact on bigeye tuna distribution has been studied from data collected by 15 fishery survey vessels, surveying every day, in the Equatorial Pacific Ocean from February to March and June to September 2010. The in situ ocean temperature measurements at four depths (100, 150, 200, and 300 m), satellite data and TAO/TRITON moored buoy data were also augmented in this study. The results reveal stereoscopic temperature factors for the prediction of tuna fishing ground: horizontal temperature gradient (HTG), vertical temperature gradient (VTG) in the 100–300 m layer. Maximal catches were observed where (1) vertically there has a strong subsurface temperature front in the 150–200 m layer, with horizontal temperature gradient up to near 0.020 °C/km; (2) there have vertical temperature gradient between −0.088 and −0.066 °C/m. Meanwhile, the monthly tuna fishery catches decrease with the synchronized reduction of 20 °C isotherm depth in the ocean. [ABSTRACT FROM AUTHOR]

Albacore tuna (Thunnus alalunga) exhibit patchy concentrations associated with biological process at a wide range of spatial scales, resulting in variations in their catchability by fishing gears. Here, we investigated the association of catch variation for pelagic longlines in the South Pacific Ocean with oceanographic mesoscale structures (in horizontal dimension) and ambient conditions (in vertical dimension). The distribution of albacore tuna as indicated by catch per unit effort (CPUE) of longlines was significantly related to the presence of mesoscale structures, with higher CPUE found at locations closer to thermal fronts and with greater gradient magnitudes, as well as areas marked by peripheral contour line of the anticyclone indicated by Sea Surface Height Anomalies ~0.05 m. Surface mesoscale current velocity had the negative effect on the catch, probably as a result of decreased catchability by shoaling the hook depth. Vertical distribution of albacore in the survey region of South Pacific Ocean was hardly restricted by ambient temperature and oxygen concentration, though effect of ambient temperature was relevant and showed a negatively linear correlation with CPUE at the range of 20–24°C. On the contrary, albacore distribution was evidently dominated by the water depth and showed strong preference on water depth of 200 m, which was likely a representative feeding layer. The presence of prey resources and their accessibility by albacore revealed by mesoscale structures in the biological and physical processes, and catchability determined by the location of the baited hooks comprehensively contribute to the variability of catch. [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.

There is little readily available information on when and where oceanic fronts occur off the coast of California despite their important to fisheries management, environmental monitoring, search-and-rescue operations, and underwater sound. To help fill this gap, scientists at Moss Landing Marine Laboratories, together with NOAA's National Environmental Satellite Data and Information Service, with support from California Sea Grant, have produced a series of monthly maps showing the locations of fronts off the California coast. They were created using remote sensing data from the GOES-10 geostationary satellite. A total of 48 frontal maps were produced on a monthly basis over the four-year period from July 2000 to June 2004.

In cloudy areas, such as Central California, polar-orbiting satellites obtain relatively few clear glimpses of the ocean surface while geostationary ones have the chance to obtain many. In the case of the GOES-10 satellite, the ocean surface in the Eastern Pacific is scanned 24 times daily by instruments that gather measurements of infrared radiation emitted from the Earth’s surface on a 4-kilometer grid. Infrared radiation levels provide an estimate of ocean surface temperature when the ocean is not obscured by cloud cover.To construct maps of fronts, the core of the project, the scientists converted estimates of ocean temperature into estimates of temperature gradient—the change in ocean temperature over a certain distance.

This study investigates the sensitivity of the Sverdrup transport to the NCEP/NCAR, ERA-Interim, CCMP, and QSCAT wind products over the tropical North Pacific Ocean during the period of 2000–2008. Our analyses show that all of the S-E transports in the reanalysis/analysis winds are northward in the band of 7–9° N except the QSCAT wind, which produces more realistic southward transport as shown in the meridional geostrophic transports (MGTs) calculated from WOA13 and Argo data. At 24° N, high-resolution wind products can better estimate the meridional transport in this region. At 8° N, although the CCMP has the same high resolution as the QSCAT, it fails to produce more realistic ocean circulation just as the coarse resolution wind products do there. The unrealistically large wind stress curl and small zonal wind stress in winter in reanalysis/analysis wind products account for this discrepancy with the QSCAT. This discrepancy also suggests that the model physics used in these reanalysis wind products is deficient in depicting the ocean circulation in this region, where the ocean fronts and eddy activity are both active. [ABSTRACT FROM AUTHOR]

Validation of satellite-based retrieval of ocean parameters like Sea Surface Temperature (SST) and Sea Surface Salinity (SSS) is commonly done via statistical comparison with in situ measurements. Because in situ observations derived from coastal/tropical moored buoys and Argo floats are only representatives of one specific geographical point, they cannot be used to measure spatial gradients of ocean parameters (i.e., two-dimensional vectors). In this study, we exploit the high temporal sampling of the unmanned surface vehicle (USV) Saildrone (i.e., one measurement per minute) and describe a methodology to compare the magnitude of SST and SSS gradients derived from satellite-based products with those captured by Saildrone. Using two Saildrone campaigns conducted in the California/Baja region in 2018 and in the North Atlantic Gulf Stream in 2019, we compare the magnitude of gradients derived from six different GHRSST Level 4 SST (MUR, OSTIA, CMC, K10, REMSS, and DMI) and two SSS (JPLSMAP, RSS40km) datasets. While results indicate strong consistency between Saildrone- and satellite-based observations of SST and SSS, this is not the case for derived gradients with correlations lower than 0.4 for SST and 0.1 for SSS products.

Formed in the aftermath of the Deepwater Horizon event, the largest accidental marine oil spill, the Consortiumfor Advanced Research on Transport of Hydrocarbons in the Environment (CARTHE) focused on understanding the physical processes controlling the transport of material from a deep blowout all the way to the coast. Even though CARTHE was initially a modeling-oriented team, it progressively became more focused on observations in order to collect the data needed for model evaluation. A number of new technological advances needed to be made to collect the necessary data. This article reviews most of these, with special focus on surface sampling, where much of the oil is located during oil spills, as well as the measurement of near-field droplet size distribution. [ABSTRACT FROM AUTHOR]

Advances in satellite tracking and archival technologies now allow marine animal movements and behavior to be recorded at much finer temporal scales, providing a more detailed ecological understanding that can potentially be applicable to conservation and management strategies. Pelagic sharks are commercially exploited worldwide with current concerns that populations are declining, however, how pelagic sharks use exploited environments remains enigmatic for most species. Here we analyzed high-resolution dive depth profiles of two pelagic shark species with contrasting feeding strategies to investigate movement patterns in relation to environmental heterogeneity. Seven macropredatory blue (Prionace glauca) and six plankton-feeding basking (Cetorhinus maximus) sharks were tagged with pop-off satellite-linked archival tags in the North Atlantic Ocean to examine habitat use and investigate the function of dives. We grouped dives of both species into five major categories based on the two-dimensional dive profile shape. Each dive-shape class presented similar frequency and characteristics among the two species with U- and V-shaped dives predominating. We tested the spatial occurrence of different U- and V-shape dive parameters in response to environmental field gradients and found that mean depth and mean depth range decreased with increasing levels of primary productivity (chlorophyll “a”), whereas ascent velocities displayed a positive correlation. The results suggest that a planktivore and a macropredator responded behaviourally in similar ways to environmental heterogeneity. This indicates fine-scale dive profiles of shark species with different feeding strategies can be used to identify key marine habitats, such as foraging areas where sharks aggregate and which may represent target areas for conservation.

Advanced modelling studies and high-resolution observations have shown that flows related to instability of the mesoscale (~ 1-10 km scale) may provide both the fertilisation mechanism for nutrient-depleted (oligotrophic) surface waters and a subduction mechanism for the rapid export of phytoplankton biomass to the deep ocean. Here, a detailed multidisciplinary analysis of the data from an example high-resolution observational campaign is presented. The data provide direct observations of the transport of phytoplankton through baroclinic instability. Furthermore, the data confirm that this transport is constrained by the requirement to conserve angular momentum, expressed in a stratified water column as the conservation of potential vorticity. This constraint is clearly seen to produce long thin filaments of phytoplankton populations strained out along isopycnal vorticity annuli associated with mesoscale frontal instabilities. [ABSTRACT FROM AUTHOR]

Aim Understanding the spatial ecology of endangered species is crucial to predicting habitat use at scales relevant to conservation and management. Here, we aim to model the influence of biophysical conditions on habitat suitability for endangered fin whales Balaenoptera physalus, with a view to informing management in a heavily impacted ocean region. Location We satellite-tracked the movements of 67 fin whales through the California Current System ( CCS), a dynamic eastern boundary upwelling ecosystem in the Northeast Pacific. Methods We use a multi-scale modelling framework to elucidate biophysical influences on habitat suitability for fin whales in the CCS. Using generalized additive mixed models, we quantify the influence of a suite of remotely sensed variables on broadscale patterns of occupancy and present the first year-round, high-resolution predictions of seasonal habitat suitability. Further, we model the influence of contemporaneous biophysical conditions on individual-level residence times in high-use habitat. Results We present evidence of year-round habitat suitability in the southern California Current System, robust to interannual variability, establishing that North Pacific fin whales do not follow the canonical baleen whale migration model. Within the high-use habitat in the Southern California Bight ( SCB), individual-level residency in localized areas ( n = 16 for >30 days; n = 4 for >6 months) was associated with warm, shallow, nearshore waters (>18°C, <500 m), with cool waters (14-15°C) occurring over complex seafloor topographies and with convergent (sub)mesoscale structures at the surface. Main Conclusions Biophysical conditions in the southern CCS generate productive foraging habitats that can support the fin whale population year-round and allow for extended periods of residency in localized areas. High-use habitats for fin whales are colocated with areas of intense human use, including international shipping routes and a major naval training range. Seasonal habitat suitability maps presented here could inform the management of anthropogenic threats to endangered baleen whales in this globally significant biodiversity hotspot. [ABSTRACT FROM AUTHOR]

Shipping noise is a threat to marine wildlife. Grey seals are benthic foragers, and thus experience acoustic noise throughout the water column, which makes them a good model species for a case study of the potential impacts of shipping noise. We used ship track data from the Celtic Sea, seal track data and a coupled ocean-acoustic modelling system to assess the noise exposure of grey seals along their tracks. It was found that the animals experience step changes in sound levels up to ~ 20 dB at a frequency of 125 Hz, and ~ 10 dB on average over 10–1000 Hz when they dive through the thermocline, particularly during summer. Our results showed large seasonal differences in the noise level experienced by the seals. These results reveal the actual noise exposure by the animals and could help in marine spatial planning. [ABSTRACT FROM AUTHOR]

Aim The dispersal and distribution patterns of many marine organisms are driven by oceanographic conditions, which are influenced by global climate. Climate-driven oceanographic changes are thus likely to result in biogeographical changes. We assess how recent and predicted oceanographic changes affect the dispersal capacities and distributions of ecologically important (especially habitat-forming) marine organisms. Location We include studies from tropical, temperate and sub-polar regions to draw globally relevant conclusions. Methods We review biogeographical, biological and oceanographic studies to critically evaluate emerging trends in biogeographical responses to climate-driven oceanographic changes, and predict how future changes will affect marine ecosystems. Results Many oceanic dispersal pathways are being altered by climate change. These changes will affect marine ecosystems by differentially affecting the replenishment potential and connectivity of key habitat-forming species. In particular, the length of propagule pre-competency periods, propagule behaviour and the geographical distance between areas of suitable habitat will be critical in determining how oceanographic changes affect the pattern and success of dispersal events, including the likelihood of species experiencing poleward range shifts in response to a warming climate. Main conclusions Future climate-driven oceanographic changes are likely to strengthen or weaken different oceanic dispersal pathways, which will either increase or decrease the potential for dispersal and connectivity in various marine taxa according to the interaction between the local oceanographic, geographical and taxon-specific biological factors. A key focus for future work should be the development of fine-scale near-shore ocean circulation models that can be used to assess the dispersal response of key marine taxa under various marine climate change scenarios. [ABSTRACT FROM AUTHOR]

Abstract This contribution provides an introduction to a sequence of five papers (CCE I- CCE V) that describe the impact of the Warm Anomaly of 2014–15 and El Niño 2015–16 on the pelagic food web of the southern California Current Ecosystem. These contributions analyze the influence of these two warm water perturbations on satellite-based measures of ocean fronts, export efficiency out of the euphotic zone, copepod egg production, mesozooplankton community structure, and a synthesis of primary production, mesozooplankton grazing, and gravitational fluxes of organic carbon. [ABSTRACT FROM AUTHOR]

Primary productivity is limited by the availability of iron over large areas of the global ocean. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. However, source regions and supply mechanisms of iron to the global oceans remain poorly constrained. Shelf sediments are considered one of the largest sources of dissolved iron to the global ocean, and a large shelf sediment iron flux is prescribed in many biogeochemical models over all areas of bathymetry shallower than 1000 m. Here, we infer the likely location of shelf sediment iron sources in the Southern Ocean, by identifying where satellite chlorophyll concentrations are enhanced over shallow bathymetry (<1000 m). We further compare chlorophyll concentrations with the position of ocean fronts, to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry that are located more than 500 km from a coastline. Mean annual chlorophyll concentrations >2 mg m −3 are only found within 50 km of a continental or island coastline. These results suggest that sedimentary iron sources only exist on continental and island shelves. Large sedimentary iron fluxes do not seem present on seamounts and submerged plateaus. Large chlorophyll blooms develop where the western boundary currents detach from the continental shelves, and turn eastward into the Sub-Antarctic Zone. Chlorophyll concentrations are enhanced along contours of sea surface height extending off the continental shelves, as shown by the trajectories of virtual water parcels in satellite altimetry data. These analyses support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents, and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Our results indicate that upwelling at fronts in the open ocean is unlikely to deliver iron to the ocean surface from deep sources. Finally, we hypothesise how a reduction in sea level may have altered the distribution of shelf sediment iron sources in the Southern Ocean and increased export production over the Sub-Antarctic Zone during glacial intervals. [ABSTRACT FROM AUTHOR]

Synoptic atmospheric eddies are affected by lower tropospheric air-temperature gradients and by turbulent heat fluxes from the surface. In this study we examine how ocean fronts affect these quantities and hence the storm tracks. We focus on two midlatitude regions where ocean fronts lie close to the storm tracks: the north-west Atlantic and the Southern Ocean. An atmospheric climate model of reasonably high resolution (~50 km) is applied in a climate-length (60 year) simulation in order to obtain stable statistics. Simulations with frontal structure in the sea surface temperature (SST) in one of the regions are compared against simulations with globally smoothed SST. We show that in both regions the ocean fronts have a strong influence on the transient eddy heat and moisture fluxes, not just in the boundary layer, but also in the free troposphere. Local differences in these quantities between the simulations reach 20-40 % of the maximum values in the simulation with smoothed SST. Averaged over the entire region of the storm track over the ocean the corresponding differences are 10-20 %. The effect on the transient eddy meridional wind variance is strong in the boundary layer but relatively weak above that. The potential mechanisms by which the ocean fronts influence the storm tracks are discussed, and our results are compared against previous studies with regional models, Aquaplanet models, and coarse resolution coupled models. [ABSTRACT FROM AUTHOR]

Aim Knowledge and understanding of marine vertebrate spatial ecology are required to identify sources of threat and highlight areas for conservation. Olive ridley sea turtles Lepidochelys olivacea are in decline in some regions, and data for the Eastern Atlantic are sparse. Here, we seek to describe observed, and potential, post-nesting habitats for this species in the southeast Atlantic. We contextualize these with fisheries catch data to identify areas of potential threat from fisheries interaction for this species. Location West coast of Africa, southeast Atlantic. Methods We tracked 21 female olive ridley turtles, from two nesting sites, between 2007 and 2010. We used ensemble ecological niche modelling, integrated with knowledge on the physical and biological oceanographic environment, to identify regions where environmental variables exist that may be critical in defining post-nesting habitats for this species. We further integrate fisheries catch data to contextualize potential threat from fisheries. Results We describe key areas of observed, and potential, olive ridley turtle occurrence at sea, and reveal that there was considerable overlap of these conspecifics, from two distinct nesting regions, within the Angolan exclusive economic zone ( EEZ). With the inclusion of fisheries catch data for the region, we highlight areas that have the potential for conflict with fishing activities known to result in bycatch. Main conclusions This study demonstrates that it is imperative that marine conservation policy recognizes the spatial extent of highly migratory species with expansive ranges. It also highlights that deficiencies exist in current knowledge of bycatch, both in gear specificity and in catch per unit effort. With integration of vessel monitoring system (VMS) data and those on fisheries catch, knowledge and understanding of bycatch may be improved, and this will ultimately facilitate development of appropriate management strategies and long-term sustainability of fisheries and their supporting ecosystems. [ABSTRACT FROM AUTHOR]

Highlights: [•] We measured trace element concentrations in South Pacific albacore otoliths. [•] Classification accuracy to geographically distant capture locations was high. [•] Some evidence of different larval sources for the west and east South Pacific. [•] Cycling in otolith Sr:Ca and Ba:Ca was observed across life-history transects. [•] Patterns may reflect seasonal north-south movements across oceanic fronts. [Copyright &y& Elsevier]

Two sets of high-resolution subsurface hydrographic and underway surface chlorophyll a (Chl a) measurements are used, in conjunction with satellite remotely sensed data, to investigate the upper layer oceanography (mesoscale features and mixed layer depth variability) and phytoplankton biomass at the GoodHope line south of Africa, during the 2010–2011 austral summer. The link between physical parameters of the upper ocean, specifically frontal activity, to the spatially varying in situ and satellite measurements of Chl a concentrations is investigated. The observations provide evidence to show that the fronts act to both enhance phytoplankton biomass as well as to delimit regions of similar chlorophyll concentrations, although the front–chlorophyll relationships become obscure towards the end of the growing season due to bloom advection and ‘patchy’ Chl a behaviour. Satellite ocean colour measurements are compared to in situ chlorophyll measurements to assess the disparity between the two sampling techniques. The scientific value of the time-series of oceanographic observations collected at the GoodHope line between 2004 to present is being realised. Continued efforts in this programme are essential to better understand both the physical and biogeochemical dynamics of the upper ocean in the Atlantic sector of the Southern Ocean. [ABSTRACT FROM AUTHOR]

Two-dimensional (cross-shelf and depth) circulation by downwelling wind in the presence of a prograding front (with isopycnals that slope in the same direction as the topographic slope) over a continental shelf is studied using high-resolution numerical experiments. The physical process of interest is the cross-shelf circulation produced by northeasterly monsoon winds acting on the Kuroshio front over the East China Sea outer shelf and shelfbreak where upwelling is often observed. However, a general problem is posed and solved by idealized numerical and analytical models. It is shown that upwelling is produced shoreward of the front. The upwelling is maintained by (1) a surface bulge of negative vorticity at the head of the front; (2) bottom offshore convergence beneath the front; and (3) in the case of a surface front that is thin relative to water depth, also by upwelling due to the vorticity sheet under the front. The near-coast downwelling produces intense mixing due to both upright and slant-wise convection in regions of positive potential vorticity. The analytical model shows that the size and on-shore propagating speed of the bulge are determined by the wind and its shape is governed by a nonlinear advection-dispersion equation which yields unchanging wave-form solutions. Successive bulges can detach from the front under a steady wind. Vertical circulation cells develop under the propagating bulges despite a stable stratification. These cells can have important consequences to vertical exchanges of tracers and water masses. [ABSTRACT FROM AUTHOR]

Abstract: We investigate aspects of the secondary (cross-shelf) circulation at the Middle Atlantic Bight shelfbreak front using high-resolution data collected on the New England Shelf in August 2002. The alongshore shelfbreak jet coincides with the front at the seaward edge of the cold pool (remnant winter shelf water) and there is a suggestion of a cross-stream convergence centered at the jet core. Despite indications of convergence we found no evidence of a surface subduction on the seaward side of the front. At depth 70 m near the shelfbreak there was a patch of chlorophyll, located within a local temperature–salinity maximum which, though significantly below the euphotic zone, appeared to be photo-acclimated and viable. The chlorophyll feature could be the result of a local subduction by a larger scale eddy circulation seaward of the front. Dye tracer experiments directly observed the convergence at the foot of the shelfbreak front and subsequent upwelling of bottom boundary layer water along the shoreward side of the shelfbreak front. But, we found no evidence that this upwelling influenced productivity at the front. Further, since there was no cross-shelf maximum in subsurface chlorophyll at the front, we conclude that this productivity is in general, sustained by a broadly distributed local vertical nutrient flux from an underlying nutrient reservoir. [Copyright &y& Elsevier]

Catch statistics for the king mackerel ( Scomberomorus cavalla) recreational fishery off west-central Florida were derived from angler interviews conducted during 19 seasonal tournaments held in April–May and October–November of 2004 and 2005. Fishing location, number of fish per line per hour (catch per unit effort), and presence of baitfish from the tournament data were examined in the context of bathymetric gradients and other benthic features (e.g., wrecks or artificial reefs), and the location and persistence of oceanic fronts mapped using satellite imagery of sea surface temperature (AVHRR) and ocean color (MODIS and SeaWiFS). Generalized linear models were applied to identify the relationship between king mackerel catch rates and environmental data. The distance of fishing activity to the nearest front varied substantially, particularly when winds and front position were variable. However, baitfish presence with proximity to water clarity fronts (as defined by water-leaving radiance at 443 nm) significantly influenced successful king mackerel catch. Positive catch rates were significantly influenced by chlorophyll values and period (season and year). Additionally, intermediate water clarity (in the range 0.7–1.0 mW cm−2μm−1 sr−1) led to higher catch rates. Decreased water quality, primarily associated with a large Karenia brevis red tide, led to a lower number of catch and lower catch rates (122 king mackerel, 0.13 catch per unit effort) in fall 2005, compared to spring 2004 (179, 0.14), fall 2004 (360, 0.17) and spring 2005 (296, 0.21), despite a consistent seasonal effort. [ABSTRACT FROM AUTHOR]

• 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]

Analysis of ocean fronts’ uncertainties indicates that they result from indiscernibility of their spatial position and fuzziness of their intensity. In view of this, a flow hierarchy for uncertainty representation of ocean fronts is proposed on the basis of fuzzy-rough set theory. Firstly, raster scanning and blurring are carried out on an ocean front, and the upper and lower approximate sets, the indiscernible relation in fuzzy-rough theories and related operators in fuzzy set theories are adopted to represent its uncertainties, then they are classified into three sets: with members one hundred percent belonging to the ocean front, belonging to the ocean front’s edge and definitely not belonging to the ocean front. Finally, the approximate precision and roughness degree are utilized to evaluate the ocean front’s degree of uncertainties and the precision of the representation. It has been proven that the method is not only capable of representing ocean fronts’ uncertainties, but also provides a new theory and method for uncertainty representation of other oceanic phenomena. [ABSTRACT FROM AUTHOR]

Abstract: The moderate resolution imaging spectroradiometer (MODIS) on board the Aqua satellite measures visible and infrared radiation in 36 wavebands, providing simultaneous images of sea-surface temperature (SST) and chlorophyll-a (chl-a) concentration in the upper meters of the sea. For the first time, truly synoptic SST and chl-a- concentration images are available. These images are daily and of 1.1-km resolution. The strong contrasts in sea-surface temperature and surface chlorophyll-a concentration over the southwest Atlantic make satellite infrared and color images particularly appropriate tools for studying the Brazil–Malvinas (B/M) Current confluence. We examine two years (July, 2002–June, 2004) of Aqua/MODIS infrared and color images to document the precise structure of the B/M confluence simultaneously in SST and chl-a. We first compared MODIS weekly data with simultaneous independent satellite data. Spatial and temporal distributions are similar for both SST and color. Differences between MODIS and SeaWiFS (sea-viewing wide field-of-view sensor) are large in pigment-rich regions along the coast and shelf. Here, we focused on the offshore region where differences are small. For each season, exceptionally cloud-free 1.1-km resolution MODIS images showed two thermal fronts, one corresponding to the Brazil Current’s southernmost limit, the other, to the Malvinas Current’s northernmost limit. These two fronts remained quite close to each other (within 50km) and were separated by water with an SST and chl-a concentration typical of the continental shelf waters. In spring, the water rich in chl-a from the platform is squeezed between the two currents and entrained away from the coast in between the two thermal fronts. In the frontal region, SST gradient maxima trace the contour of the chl-a-rich water. Enlargements of the frontal region and of the turbulent region downstream of the frontal collision are presented and analyzed. MODIS documents in an unprecedented way the SST and chl-a filaments as they are distorted and mixed by meso- and sub-mesoscale structures in the strain-dominated region of the B/M confluence. It is suggested that a substantial part of the chl-a local maximum in the Malvinas return flow is of continental-shelf origin. [Copyright &y& Elsevier]

The study describes the annual cycle of southern elephant seals for the increasing colony of Peninsula Valdés, and compares it to the haul-out pattern reported for stable or decreasing sub-Antarctic colonies of the species. Data were collected during censuses of the entire colony (nine breeding seasons, two moulting seasons and one autumn--winter haul-out), monthly surveys of coastline and mark-recapture of pups. Pup production during the study period grew from 12 113 to 14 621 animals (1995-2003). Most relevant events of the cycle were similar for all colonies studied, independent of the geographical location, size or population trend. Compared with other locations where southern elephant seals breed and moult, distinct features for Peninsula Valdés were: i) breeding occurs earlier in the spring, and ii) most adult females reproduce and moult in the same colony. The increasing number of animals ashore was correlated with the expansion in pup production. Population trends and stability of demographic events could be related to a consistent physical environment (ocean fronts) during foraging phases of the annual cycle. [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]