High-resolution Regional Ocean Model Research Articles

Influence of tidal mixing on bottom circulation in the Caroline Sea

Bottom circulation in the abyssal Caroline Sea is an important component of the global meridional overturning circulation. By use of a high-resolution regional ocean model, the influence of tidal mixing processes on bottom water and circulation in the Caroline Sea is investigated. Based on different configurations for diapycnal diffusivities of tidal mixing, three numerical experiments are performed: one completely without tidal mixing, one only with local tidal mixing due to the locally dissipated tidal energy, and one considering tidal mixing processes induced by the total dissipated tidal energy. The results show that tidal mixing processes in the abyssal Caroline Sea could sustain a relatively high horizontal density gradient and hence baroclinic pressure gradient not only across the two deep-water passages connecting to the open ocean, but also within the abyssal West Caroline Basin (WCB) and East Caroline Basin (ECB). Therefore, tidal mixing processes could maintain the large amounts of bottom water inflow, intensify the bottom basin/subbasin-scale horizontal circulation, and drive a more vigorous meridional overturning circulation in the abyssal WCB and ECB. Moreover, simulations of bottom water transport in the experiment with tidal mixing processes are more consistent with previous observations and estimates. These results suggest that tidal mixing processes play a crucial dynamic role in the bottom circulation, and is essential for ocean modelling.

Spatiotemporal heterogeneity in the increase in ocean acidity extremes in the northeastern Pacific

Abstract. The acidification of the ocean (OA) increases the frequency and intensity of ocean acidity extreme events (OAXs), but this increase is not occurring homogeneously in time and space. Here we use daily output from a hindcast simulation with a high-resolution regional ocean model coupled to a biogeochemical ecosystem model (ROMS-BEC) to investigate this heterogeneity in the progression of OAX in the upper 250 m of the northeastern Pacific from 1984 to 2019. OAXs are defined using a relative threshold approach and using a fixed baseline. Concretely, conditions are considered extreme when the hydrogen ion concentration ([H+]) exceeds the 99th percentile of its distribution in the baseline simulation where atmospheric CO2 was held at its 1979 level. Within the 36 years of our hindcast simulation, the increase in atmospheric CO2 causes a strong increase in OAX volume, duration, and intensity throughout the upper 250 m. The increases are most accentuated near the surface, with 88 % of the surface area experiencing near-permanent extreme conditions in 2019. At the same time, a larger fraction of the OAXs become undersaturated with respect to aragonite (ΩA < 1), with some regions experiencing increases up to nearly 50 % in their subsurface. There is substantial regional heterogeneity in the progression of OAX, with the fraction of OAX volume across the top 250 m increasing in the central northeastern Pacific up to 160 times, while the deeper layers of the nearshore regions experience “only” a 4-fold increase. Throughout the upper 50 m of the northeastern Pacific, OAXs increase relatively linearly with time, but sudden rapid increases in yearly extreme days are simulated to occur in the thermocline of the far offshore regions of the central northeastern Pacific. These differences largely emerge from the spatial heterogeneity in the local [H+] variability. The limited offshore reach of offshore-propagating mesoscale eddies, which are an important driver of subsurface OAX in the northeastern Pacific, causes a sharp transition in the increase in OAX between the rather variable thermocline waters of nearshore regions and the very invariant waters of the central northeastern Pacific. The spatially and temporal heterogeneous increases in OAX, including the abrupt appearance of near-permanent extremes, likely have negative effects on the ability of marine organisms to adapt to the progression of OA and its associated extremes.

Drift bottle data hint at large-scale ocean circulation changes

Over the last two decades, in an effort to engage youth in polar science, the Students On Ice (SOI; https://studentsonice.com/) project has become a platform for youth to partake in scientific expeditions around the globe. Among the various activities offered, youth are able to join cruises in the North Atlantic or Arctic, and drop sealed glass bottles into the ocean. Of the thousands that have been deployed, 5% of bottles have been recovered and reported back to SOI with details on when and where they were found. Here, we compare the observational bottle data with virtual particle trajectories from a high resolution regional ocean model. Although modelling results indicate a higher likelihood of bottles reaching the shores of the western Atlantic, the majority of recovered bottles were found on the eastern side of the Atlantic. We attribute this disparity to differences in population density in Canada and Europe, biasing the recovery rates. Despite this bias, we find that changes in recovery locations over time are consistent with changes in the main ocean currents associated with the contraction and expansion of the North Atlantic Subpolar Gyre, as simulated in our ocean model. In 2007, a large number of bottles were found in Norway, coinciding with a contracted North Atlantic Subpolar Gyre during 2004-2008. While between 2012-2016, the majority of bottles were recovered on the British Isles, during a time of gyre expansion. These results underline the importance of large scale oceanic cycles for tracking marine debris and pollution, and show how even simple data collection methods, such as drift bottles, can provide clues to the changes in the large scale ocean circulation.

Numerical investigation of the three-dimensional paths of plastic polymers in the Gulf of Naples

The high-resolution Campania Regional Ocean Model (CROM), coupled with an online Lagrangian particle tracking algorithm, is used to investigate the horizontal and vertical behavior of different (in terms of size and density) plastic polymer types during February and August 2016 in the Gulf of Naples. The transport of passive particles is evaluated based on the three-dimensional Eulerian velocity fields provided by the ocean model. The virtual particles are released in several hot spot areas in the Gulf of Naples where most of the marine debris is supposed to come from. A sensitivity analysis on the vertical sinking for negatively buoyant particles is carried out. The sinking behavior is determined by the settling velocity, which depends on the physical properties of the individual litter item as well as on the hydrodynamical features of the marine environment. Different numerical experiments are carried out to evaluate the effect of marine dynamics on three-dimensional transport.

Decadal variability of sea surface salinity in the Southeastern Indian Ocean: Roles of local rainfall and the Indonesian throughflow

The southeastern Indian Ocean (SEIO) exhibits prominent decadal variability in sea surface salinity (SSS), showing salinity decreases during 1995-2000 and 2005-2011 and increases during 2000-2005 and after 2011. These salinity changes are linked to the Indo-Pacific climate and have impacts on the regional marine environment. Yet, the underlying mechanism has not been firmly established. In this study, decadal SSS variability of the SEIO is successfully simulated by a high-resolution regional ocean model, and the mechanism is explored through a series of sensitivity experiments. The results suggest that freshwater transport of the Indonesian throughflow (ITF) and local precipitation are two major drivers for the SSS decadal variability. They mutually cause most of the variability, with a generally larger contribution of precipitation. Other processes, such as evaporation and advection driven by local winds, play a minor role. Further analysis shows that the decadal precipitation in the SEIO is mainly associated with the decadal variability of Ningaloo Niño. Ocean dynamic processes significantly modify the relationship between SSS and precipitation, greatly shortening their lag time. The changes in both volume transport and salinity of the ITF water can cause large salinity changes in the SEIO region. Although local wind forcing gives rise to considerable changes in evaporation rate and ocean current advection, its overall contribution to decadal SSS variability is small compared to local precipitation and the ITF.

Hydrology and Dynamics in the Gulf of Naples during Spring of 2016: In Situ and Model Data

The hydrology and circulation in the northwestern part of the Gulf of Naples are analyzed during the transition period from spring to summer (April–June) 2016 through numerical simulations and in situ observations. The simulations were performed with the high-resolution sigma-coordinate Campania Regional Ocean Model (CROM) encompassing the wider Campania coastal system. Temperature, salinity and density were measured at the Long Term Ecological Research Program Mare-Chiara sampling site located two miles from the coast, while current intensity and direction were measured in situ by an acoustic Doppler current profiler connected to an elastic beacon anchored at a short distance from the city of Naples. The modeled circulation scenarios and the marine hydrology provided by the model on a regular grid allow interpreting the observational data during the selected period. In turn, the model-data comparison clarifies the model performance in reproducing the nearshore marine dynamics, which goes beyond the actual model resolution.

Diagnosing the upper ocean variability in the Northern Bay of Bengal during the super cyclone Phailin using a high-resolution regional ocean model

Diagnosing the upper ocean variability in the Northern Bay of Bengal during the super cyclone Phailin using a high-resolution regional ocean model

Variability of Heat Content and Eddy Kinetic Energy in the Southeast Indian Ocean: Roles of the Indonesian Throughflow and Local Wind Forcing

Abstract Prominent interannual-to-decadal variations were observed in both heat content and mesoscale eddy activity in the southeast Indian Ocean (SEIO) during 1993–2020. The 2000–01 and 2008–14 periods stand out with increased 0–700-m ocean heat content (OHC) by ∼4.0 × 1021 J and enhanced surface eddy kinetic energy (EKE) by 12.5% over 85°–115°E, 35°–12°S. This study provides insights into the key dynamical processes conducive to these variations by analyzing observational datasets and high-resolution regional ocean model simulations. The strengthening of the Indonesian Throughflow (ITF) and anomalous cyclonic winds over the SEIO region during the two periods are demonstrated to be the most influential. While the ITF caused prevailing warming of the upper SEIO, the cyclonic winds cooled the South Equatorial Current and attenuated the warming in the subtropical SEIO by evoking upwelling Rossby waves. The EKE increase exerts significant influence on OHC only in the Leeuwin Current system. Dynamical instabilities of the Leeuwin Current give rise to high EKEs and westward eddy heat transport in climatology. As the Leeuwin Current was enhanced by both the ITF and local winds, the elevated EKEs drove anomalous heat convergence on its offshore flank. This process considerably contributes to the OHC increase in the subtropical SEIO and erases the wind-driven cooling during the two warm periods. This work highlights the vital role of eddies in regional heat redistribution, with implications for understanding time-varying ocean heat storage in a changing climate.

Quantifying Cross-Shelf Transport in the East Australian Current System: A Budget-Based Approach

Abstract Cross-shelf transport plays an important role in the heat, salt, and nutrient budgets of the continental shelf. In this study, we quantify cross-shelf volume transport and explore its dynamics within a high-resolution (2.5–6 km) regional ocean model of the East Australian Current (EAC) System, a western boundary current with a high level of mesoscale eddy activity. We find that the largest time-mean cross-shelf flows (>4 Sv per 100 km; 1 Sv ≡ 106 m3 s−1) occur inshore of the coherent western boundary current, between 26° and 30°S, while the strongest time-varying flows occur in the EAC southern extension, poleward of 32°S, associated with mesoscale eddies. Using a novel diagnostic equation derived from the momentum budget we show that the cross-shelf transport is dominated by the baroclinic and geostrophic component of the velocities, as the EAC jet is relatively free to flow over the variable shelfbreak topography. However, topographic interactions are also important and act through the bottom pressure torque term as a secondary driver of cross-shelf transport. The importance of topographic interaction also increases in shallower water inshore of the coherent jet. Downstream of separation, cross-shelf transport is more time-varying and associated with the interaction of mesoscale eddies with the shelf. The identification of the change in nature and drivers of cross-shelf transport in eddy versus jet dominated regimes may be applicable to understanding cross-shelf transport dynamics in other boundary current systems. Significance Statement Cross-shelf transport, i.e., the movement of water from the open ocean on or off the continental shelf, is not reported often as it is difficult to measure and model. We demonstrate a simple but effective method to do this and, using an ocean model, apply it to the East Australian Current System and show what drives it. The results show two distinct regimes, which differ depending on which part of the current system you are in. Our results help to place observations of cross-shelf transport in better context and provide a framework within which to consider the transport of other things such as heat and carbon from the open ocean to the continental shelf.

Conditions for Reliable Divergence Estimates from Drifter Triplets

Abstract Horizontal velocity gradients of a flow field and the related kinematic properties (KPs) of divergence, vorticity, and strain rate can be estimated from dense drifter deployments, e.g., the spatiotemporal average divergence (and other KPs) over a triangular area defined by three drifters and over a given time interval can be computed from the initial and final areas of said triangle. Unfortunately, this computation can be subject to large errors, especially when the triangle shape is far from equilateral. Therefore, samples with small aspect ratios are generally discarded. Here we derive the thresholds on two shape metrics that optimize the balance between retention of good and removal of bad divergence estimates. The primary tool is a high-resolution regional ocean model simulation, where a baseline for the average divergence can be established, so that actual errors are available. A value of 0.2 for the scaled aspect ratio Λ and a value of 0.86π for the largest interior angle θ are found to be equally effective thresholds, especially at scales of 5 km and below. While discarding samples with low Λ or high θ values necessarily biases the distribution of divergence estimates slightly toward positive values, this bias is small compared to (and in the opposite direction of) the Lagrangian sampling bias due to drifters preferably sampling convergence regions. Errors due to position uncertainty are suppressed by the shape-based subsampling. The subsampling also improves the identification of the areas of extreme divergence or convergence. An application to an observational dataset demonstrates that these model-derived thresholds can be effectively used on actual drifter data. Significance Statement Divergence in the ocean indicates how fast floating objects in the ocean spread apart, while convergence (negative divergence) captures how fast they accumulate. Measuring divergence in the ocean, however, remains challenging. One method is to estimate divergence from the trajectories of drifting buoys. This study provides guidance under what circumstances these estimates should be discarded because they are too likely to have large errors. The criteria proposed here are less stringent than some of the ad hoc criteria previously used. This will allow users to retain more of their estimates. We consider how position uncertainty affects the reliability of the divergence estimates. An observational dataset collected in the Mediterranean is used to illustrate an application of these reliability criteria.

An eddy pathway to marine heatwave predictability off eastern Tasmania

A systematic analysis of historical and modeled marine heatwaves (MHWs) off eastern Tasmania has been performed based on satellite observations and a high–resolution regional ocean model simulation, over the period from 1994–2016. Our analysis suggests that the distribution of large and intense mesoscale warm core eddies off northeast Tasmania contribute to the development of MHWs further south associated with changes in the circulation and transports. Importantly, we find that eddy distributions in the Tasman Sea can act as predictors of MHWs off eastern Tasmania. We used self-organizing maps to distinguish sea surface height anomalies (SSHA) and MHWs into different, but connected, patterns. We found the statistical model performs best (precision ~ 0.75) in the southern domain off eastern Tasmania. Oceanic mean states and heat budget analysis for true positive and false negative marine heatwave events revealed that the model generally captures ocean advection dominated MHWs. Using SSHA as predictor variable, we find that our statistical model can forecast MHWs off southeast Tasmania up to 7 days in advance above random chance. This study provides improved understanding of the role of circulation anomalies associated with oceanic mesoscale eddies on MHWs off eastern Tasmania and highlights that individual MHWs in this region are potentially predictable up to 7 days in advance using mesoscale eddy-tracking methods.

Coastal upwelling along the Uruguayan coast: Structure, variability and drivers

Summertime upwelling along the Uruguayan coast is studied for the first time using observational data and a high resolution regional ocean model. Simulations are performed with the CROCO model, with a horizontal resolution of 1/36° forced with NCEP-DOE daily mean winds and daily Río de la Plata discharges, together with climatological surface heat fluxes. A comparison between model results and actual observations indicates that the model reproduces seasonal, interannual and daily variability of the region. This allowed evaluating the role of the wind and freshwater discharge in the development of intense upwellings by running the model under different experimental setups. A Maximum Covariance Analysis between daily mean NCEP-DOE winds and satellite sea surface temperature data (MUR-GHRSST) was performed to identify intense observed summer coastal upwelling. The simulations were used to characterize the horizontal and vertical structure of observed intense upwellings along the Uruguayan coast in terms of temperature, salinity, vertical velocity and currents as well as their evolution for the first time. Finally, interannual simulations performed under different boundary conditions demonstrated the primary role of wind and secondary role of freshwater discharge anomalies in the generation of coastal upwelling. We also found that La Niña induces regional wind anomalies and river discharges that strongly favor upwelling in the Uruguayan estuarine coast, while El Niño does the opposite. • The 3-D structure of summertime upwelling along the Uruguayan coast was for the first time described using the CROCO model. • Climatological upwelling, centered at the oceanic coast was identified. • Subseasonal intense upwellings, centered at the estuarine coast, were identified and fully described. • Winds are the primary upwelling driver with secondary contribution of river discharge. • Wind and freshwater discharge conditions favor the development of upwelling during La Niña years.

Correction to: Projected climate change in the western North Pacific at the end of the 21st century from ensemble simulations with a high-resolution regional ocean model

Correction to: Projected climate change in the western North Pacific at the end of the 21st century from ensemble simulations with a high-resolution regional ocean model

Kilometer-Scale Larval Dispersal Processes Predict Metapopulation Connectivity Pathways for Paramuricea biscaya in the Northern Gulf of Mexico

Fine-scale larval dispersal and connectivity processes are key to species survival, growth, recovery and adaptation under rapidly changing disturbances. Quantifying both are required to develop any effective management strategy. In the present work, we examine the dispersal pattern and potential connectivity of a common deep-water coral, Paramuricea biscaya, found in the northern Gulf of Mexico by evaluating predictions of physical models with estimates of genetic connectivity. While genetic approaches provide estimates of realized connectivity, they do not provide information on the dispersal process. Physical circulation models can now achieve kilometer-scale resolution sufficient to provide detailed insight into the pathways and scales of larval dispersal. A high-resolution regional ocean circulation model is integrated for 2015 and its advective pathways are compared with the outcome of the genetic connectivity estimates of corals collected at six locations over the continental slope at depths comprised between 1,000 and 3,000 m. Furthermore, the likely interannual variability is extrapolated using ocean hindcasts available for this basin. The general connectivity pattern exhibits a dispersal trend from east to west following 1,000 to 2,000-m isobaths, corresponding to the overall westward near-bottom circulation. The connectivity networks predicted by our model were mostly congruent with the estimated genetic connectivity patterns. Our results show that although dispersal distances of 100 km or less are common, depth differences between tens to a few hundred meters can effectively limit larval dispersal. A probabilistic graphic model suggests that stepping-stone dispersal mediated by intermediate sites provides a likely mechanism for long-distance connectivity between the populations separated by distances of 300 km or greater, such as those found in the DeSoto and Keathley canyons.

Support for the Slope Sea as a major spawning ground for Atlantic bluefin tuna: evidence from larval abundance, growth rates, and particle-tracking simulations

Atlantic bluefin tuna (Thunnus thynnus) are commercially and ecologically valuable, but management is complicated by their highly migratory lifestyle. Recent collections of bluefin tuna larvae in the Slope Sea off northeastern United States have opened questions about how this region contributes to population dynamics. We analyzed larvae collected in the Slope Sea and the Gulf of Mexico in 2016 to estimate larval abundance and growth rates and used a high-resolution regional ocean circulation model to estimate spawning locations and larval transport. We did not detect a regional difference in growth rates, but found that Slope Sea larvae were larger than Gulf of Mexico larvae prior to exogenous feeding. Slope Sea larvae generally backtracked to locations north of Cape Hatteras and would have been retained within the Slope Sea until the early juvenile stage. Overall, our results provide supporting evidence that the Slope Sea is a major spawning ground that is likely to be important for population dynamics. Further study of larvae and spawning adults in the region should be prioritized to support management decisions.

Numerical Simulation of Deep-Sea Sediment Transport Induced by a Dredge Experiment in the Northeastern Pacific Ocean

Predictability of the dispersion of sediment plumes induced by potential deep-sea mining activities is still very limited due to operational limitations on in-situ observations required for a thorough validation and calibration of numerical models. Here we report on a plume dispersion experiment carried out in the German license area for the exploration of polymetallic nodules in the northeastern tropical Pacific Ocean in 4,200 m water depth. The dispersion of a sediment plume induced by a small-scale dredge experiment in April 2019 was investigated numerically by employing a sediment transport module coupled to a high-resolution hydrodynamic regional ocean model. Various aspects including sediment characteristics and ocean hydrodynamics were examined to obtain the best statistical agreement between sensor-based observations and model results. Results show that the model is capable of reproducing suspended sediment concentration and redeposition patterns observed during the dredge experiment. Due to a strong southward current during the dredging, the model predicts no sediment deposition and plume dispersion north of the dredging tracks. The sediment redeposition thickness reaches up to 9 mm directly next to the dredging tracks and 0.07 mm in about 320 m away from the dredging center. The model results suggest that seabed topography and variable sediment release heights above the seafloor cause significant changes especially for the low sedimentation pattern in the far-field area. Near-bottom mixing is expected to strongly influence vertical transport of suspended sediment.

Cyclone Hudhud-eddy induced phytoplankton bloom in the northern Bay of Bengal using a coupled model

The present study explored the role of the pre-existing cyclonic eddy on the chlorophyll-a (Chla) bloom after a cyclone pass over the northern Bay of Bengal (BoB). We used a high-resolution (~9 km) Regional Ocean Modeling System (ROMS) coupled with an established Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) model. In the study, we have considered cyclone Hudhud (category-4), which passed over a cyclonic eddy in the BoB during 7–12 October 2014. Before the passage of cyclone Hudhud, strong stratification in the upper ocean inhibited eddy-driven upwelling of nutrients to the mixed layer and limited the phytoplankton production. However, when cyclone Hudhud interacted with the cyclonic eddy, which further reduced the water column stability (one order less) of the upper ocean and initiated the wind-driven upwelling. This mechanism resulted in the easy upwelling of cold nutrient-rich water to the mixed layer. A case study presented here demonstrates ocean–atmosphere (eddy-cyclone) interaction and its influence on the mixed layer Chla production in the northern BoB. Our study showed that column integrated Chla value in the upper 100 m increased by 70% when cyclone Hudhud passed over a cyclonic eddy region in the BoB. The present study suggested that cyclonic eddy accompanied by cyclone Hudhud induced the Chla bloom in the Northern Bay during the post-monsoon season of 2014.

Projected sea-level changes in the marginal seas near China based on dynamical downscaling

AbstractProjections of future sea-level changes are usually based on global climate models (GCMs). However, the changes in shallow coastal regions, like the marginal seas near China, cannot be fully resolved in GCMs. To improve regional sea-level simulations, a high-resolution (~8 km) regional ocean model is set up for the marginal seas near China for both the historical (1994-2015) and future (2079-2100) periods under representative concentration pathways (RCPs) 4.5 and 8.5. The historical ocean simulations are evaluated at different spatiotemporal scales, and the model is then integrated for the future period, driven by projected monthly climatological climate change signals from 8 GCMs individually via both surface and open boundary conditions. The downscaled ocean changes derived by comparing historical and future experiments reveal greater spatial details than those from GCMs, e.g., a low dynamic sea level (DSL) centre of -0.15 m in the middle of the South China Sea (SCS). As a novel test, the downscaled results driven by the ensemble mean forcings are almost identical with the ensemble average results from individually downscaled cases. Forcing of the DSL change and increased cyclonic circulation in the SCS are dominated by the climate change signals from the Pacific, while the DSL change in the East China marginal seas is caused by both local atmosphere forcing and signals from the Pacific. The method of downscaling developed in this study is a useful modelling protocol for adaptation and mitigation planning for future oceanic climate changes.

The Role of the Mindoro-Sibutu Pathway on the South China Sea Multi–layer Circulation

AbstractThe role of the Mindoro Strait-Sibutu passage pathway in influencing the Luzon Strait inflow to the South China Sea (SCS) and the SCS multi-layer circulation is investigated with a high-resolution (0.1° × 0.1°) regional ocean model. Significant changes are evident in the SCS upper layer circulation (250-900 m) by closing the Mindoro-Sibutu pathway in sensitivity experiments, as Luzon Strait transport is reduced by 75%, from −4.4 Sv to −1.2 Sv. Because of the vertical coupling between the upper and middle layers, closing the Mindoro-Sibutu pathway also weakens clockwise circulation in the middle layer (900–2150 m), but there is no significant change in the deep layer (below 2150 m). The Mindoro-Sibutu pathway is an important branch of the SCS throughflow into the Indonesian Seas. It is also the gateway for oceanic waves propagating clockwise around the Philippines Archipelago from the western Pacific Ocean into the eastern SCS, projecting El Niño-Southern Oscillation sea level signals to the SCS, impacting its interannual variations and multi-layer circulation. The results provide insights into the dynamics of how upstream and downstream passage throughflows are coupled to affect the general circulation in marginal seas.

Dynamic Characteristics of a Submesoscale Front and Associated Heat Fluxes Over the Northeastern South China Sea Shelf

ABSTRACT Submesoscale fronts, which are ubiquitous phenomena in the ocean, contribute considerably to oceanic material transports and energy cascades because of their ageostrophy. The dynamic characteristics of a thermal front over the northeastern continental shelf of the South China Sea (SCS) in winter are investigated using a two-layer nested high-resolution regional ocean model system. Results show that a strong thermal front is generated over the slope of the SCS area in winter with a cross-front temperature difference of 5°C and a spatial scale of 6 km. The calculated Rossby number reaches O(1) at the front and is accompanied by strong secondary circulation; the vertical velocity can reach 40 m d−1. The calculated barotropic and baroclinic energy conversion reveals that background kinetic and potential energies provide the energy generation of a submesoscale front. Meanwhile, the submesoscale front induces strong horizontal and vertical heat fluxes of up to 8×105 and 1.7×103 W m−2, respectively. The heat flux promotes not only the cross-shelf exchange of heat in the horizontal direction but also the re-stratification of seawater in the vertical direction.