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Abstract The Indonesian seas, with their complex passages and vigorous mixing, constitute the only route and are critical in regulating Pacific–Indian Ocean interchange, air–sea interaction, and global climate events. Previous research employing remote sensing and numerical simulations strongly suggested that this mixing is tidally driven and localized in narrow channels and straits, with only a few direct observations to validate it. The current study offers the first comprehensive temporal microstructure observations in the south of Lombok Strait with a radius of 0.05° and centered on 115.54oE and 9.02oS. Fifteen days of tidal mixing observations measured potential temperature and density, salinity, and turbulent energy dissipation rate. The results revealed significant mixing and verified the remotely sensed technique. The south Lombok temporal and depth averaged of the turbulent kinetic energy dissipation rate, and the diapycnal diffusivity from 20 to 250 m are $$\varepsilon$$ ε = 4.15 ± 15.9) × 10–6 W kg–1 and $$K\rho$$ K ρ = (1.44 ± 10.7) × 10–2 m2s–1, respectively. This $$K\rho$$ K ρ is up to 104 times larger than the Banda Sea [ $$K\rho$$ K ρ = (9.2 ± 0.55) × 10–6 m2s–1] (Alford et al. Geophys Res Lett 26:2741–2744, 1999) or the “open ocean” $$K\rho$$ K ρ = 0.03 × 10–4 m2s−1 within 2° of the equator to (0.4–0.5) × 10–4 m2s−1 at 50°–70° (Kunze et al. J Phys Oceanogr 36:1553–1576, 2006). Therefore, nonlinear interactions between internal tides, tidally induced mixing, and ITF plays a critical role regulating water mass transformation and have strong implications to longer-term variations and change of Pacific–Indian Ocean water circulation and climate.

The Indonesian seas, with their complex passages and vigorous mixing, constitute the only route and are critical in regulating Pacific–Indian Ocean interchange, air–sea interaction, and global climate events. Previous research employing remote sensing and numerical simulations strongly suggested that this mixing is tidally driven and localized in narrow channels and straits, with only a few direct observations to validate it. The current study offers the first comprehensive temporal microstructure observations in the south of Lombok Strait with a radius of 0.05° and centered on 115.54oE and 9.02oS. Fifteen days of tidal mixing observations measured potential temperature and density, salinity, and turbulent energy dissipation rate. The results revealed significant mixing and verified the remotely sensed technique. The south Lombok temporal and depth averaged of the turbulent kinetic energy dissipation rate, and the diapycnal diffusivity from 20 to 250 m are ε = 4.15 ± 15.9) × 10–6 W kg–1 and K ρ = (1.44 ± 10.7) × 10–2 m2s–1, respectively. This K ρ is up to 104 times larger than the Banda Sea [ K ρ = (9.2 ± 0.55) × 10–6 m2s–1] (Alford et al. Geophys Res Lett 26:2741–2744, 1999) or the "open ocean" K ρ = 0.03 × 10–4 m2s−1 within 2° of the equator to (0.4–0.5) × 10–4 m2s−1 at 50°–70° (Kunze et al. J Phys Oceanogr 36:1553–1576, 2006). Therefore, nonlinear interactions between internal tides, tidally induced mixing, and ITF plays a critical role regulating water mass transformation and have strong implications to longer-term variations and change of Pacific–Indian Ocean water circulation and climate. [ABSTRACT FROM AUTHOR]

Diapycnal mixing in the ocean interior is largely fueled by internal tides. Mixing schemes that represent the breaking of internal tides are now routinely included in ocean and earth system models applied to the modern and future. However, this is more rarely the case in climate simulations of deep‐time intervals of the Earth, for which estimates of the energy dissipated by the tides are not always available. Here, we present and analyze two IPSL‐CM5A2 earth system model simulations of the Early Eocene made under the framework of DeepMIP. One simulation includes mixing by locally dissipating internal tides, while the other does not. We show how the inclusion of tidal mixing alters the shape of the deep ocean circulation, and thereby of large‐scale biogeochemical patterns, in particular oxygen distributions. In our simulations, the absence of tidal mixing leads to a relatively stagnant and poorly ventilated deep ocean in the North Atlantic, which promotes the development of a basin‐scale pool of oxygen‐deficient waters, at the limit of complete anoxia. The absence of large‐scale anoxic records in the deep ocean after the Cretaceous anoxic events suggests that such an ocean state most likely did not occur at any time across the Paleogene. This highlights how crucial it is for climate models applied to the deep‐time to integrate the spatial variability of tidally driven mixing as well as the potential of using biogeochemical models to exclude aberrant dynamical model states. Key Points: Inclusion of realistic near‐field tidal mixing substantially modifies global deep ocean circulation in the Early EoceneThese tidally driven changes yield significantly different biogeochemical properties of water masses, in particular in the AtlanticThe simulation that includes tidal mixing compares more favorably to inferences from the O2 proxy record [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Spatial patterns of the Primorye Current, as a band of cold water along the coast of Primorye (northwestern East/Japan Sea), are considered on the data of satellite images and standard sections obtained in 2000–2020. The data of AVHRR and MODIS scanners mounted on the satellites NOAA, Terra and Aqua are used with spatial resolution of 1.0–1.1 km. Temperature and salinity profiles in the upper 500 m layer were measured at the standard sections directed southward and east-southeastward from Vladivostok. The new data contradict a false supposition about the current origin from the Okhotsk Sea that is preserved in the name of “Liman Current”, still used sometimes. The cold-water area prolongs from the southern Tatar Strait to Peter the Great Bay but is definitely separated from the Amur Liman. Its core with the lowest SST is usually located on the external shelf of Primorye, outside of the Tatar Strait. Shape of the cold-water area is complicated and highly variable; it looks seldom as an alongshore flow, but more frequently as chains of eddies or filaments. In winter, the Primorye Current is presented usually as a wide uninterrupted alongshore belt with many intrusions to the warmer waters. This belt is distorted in spring by mesoscale eddies. In summer, the cold-water zone is narrowed and sometimes interrupted between 43 and 45°N; the cold waters interact with large anticyclonic eddies which transport the warm subtropic water close to the shore. The cold-water zone begins to extend again in fall season: large eddies and cold intrusions spread offshore, and upwellings appear at the coast. In November–December, summer stratification is destroyed and the warm water advection is weakened, so the solid band of cold water mixed by convection occupies a vast area of the northwestern East/Japan Sea off the coast of Primorye. Observed structural patterns show that the cold water at the sea surface along the coast of Primorye is produced on the shelf by upwellings or tidal mixing. Possible mechanisms of the cold spot inducing are discussed. [ABSTRACT FROM AUTHOR]

Upwelling is a widespread phenomenon in the ocean and plays key roles in the marine environment, marine fishery and air–sea carbon exchange. In coastal regions, the upwelling is usually modulated by tides and complex topography, but the dynamical mechanism is still unclear and yet to be quantified. In this study, a three-dimensional (3D) regional ocean model is used to investigate tide-induced upwelling and its mechanisms quantitatively in the mouth of a semi-closed bay, the Bohai Strait, which is a tide-dominated coastal region. The results show that the upwelling mainly occurs near the tidal front in the north of the Laotieshan Channel and the southern region of the front, with the most active upwelling existing off promontories and small islands. Numerical sensitivity experiments indicate that the upwelling in the study area is mainly caused by tides, accounting for approximately 86% of the total. The 3D balance of the vertical component of the vorticity based on the model results quantifies the dynamic processes of the upwelling and reveals that tides induce the upwelling through tidal mixing and nonlinear effects. In the tidal front zone, the upwelling is mainly caused by baroclinic processes related to tidal mixing. Off promontories and small islands, we first reveal that the upwelling is driven by both the tidal mixing and nonlinear effect related to centrifugal force rather than just one of the two mechanisms, and the latter plays a dominant role in producing the upwelling. The strong nonlinear effect is attributed to the periodic movement of barotropic tidal currents rather than the mean flow. [ABSTRACT FROM AUTHOR]

Abstract Barotropic and baroclinic tides were simulated for the Coral and Tasman Seas off eastern Australia and compared to a simulation without tides. Both simulations included geostrophic currents and replicated a current analogous to the East Australian Current (EAC). Tides and tidal currents in most of this region are weak, generally 1–2 cm s−1, with the exception of the far northwest portion of the Coral Sea. Even these weak tides were found to impact the mean EAC-like current transport, enhancing it by 1–4 Sv in some areas. Southward flow increased over the continental shelf. Tides did not appear to impact eddy formation, size, or rotational speed; however, they affected eddy propagation. Cyclonic eddies propagated northward faster with tides than without tides. Tides impacted cross-shelf transport of colder water, with significantly more on-shore transport occurring with tides, particularly equatorward of the diurnal critical latitudes. Cross-shelf transport of nutrient rich water onto the shelf is important in this oligotrophic region. Although the prime source of vertical shear and mixing were mean currents and eddies, tides played a secondary role. Tides influenced mixing by increasing vertical temperature diffusivities to 10−4 to 10−3 m2 s−1 over portions of the continental slope and over rough topography, particularly in regions near the diurnal critical latitudes (27°–30°). In conclusion, even small tides can significantly impact the circulation through their effects on the mean currents, eddy rotation velocities, eddy propagation, and mixing.

Barotropic and baroclinic tides were simulated for the Coral and Tasman Seas off eastern Australia and compared to a simulation without tides. Both simulations included geostrophic currents and replicated a current analogous to the East Australian Current (EAC). Tides and tidal currents in most of this region are weak, generally 1–2 cm s−1, with the exception of the far northwest portion of the Coral Sea. Even these weak tides were found to impact the mean EAC-like current transport, enhancing it by 1–4 Sv in some areas. Southward flow increased over the continental shelf. Tides did not appear to impact eddy formation, size, or rotational speed; however, they affected eddy propagation. Cyclonic eddies propagated northward faster with tides than without tides. Tides impacted cross-shelf transport of colder water, with significantly more on-shore transport occurring with tides, particularly equatorward of the diurnal critical latitudes. Cross-shelf transport of nutrient rich water onto the shelf is important in this oligotrophic region. Although the prime source of vertical shear and mixing were mean currents and eddies, tides played a secondary role. Tides influenced mixing by increasing vertical temperature diffusivities to 10−4 to 10−3 m2 s−1 over portions of the continental slope and over rough topography, particularly in regions near the diurnal critical latitudes (27°–30°). In conclusion, even small tides can significantly impact the circulation through their effects on the mean currents, eddy rotation velocities, eddy propagation, and mixing. [ABSTRACT FROM AUTHOR]

Upwelling is a widespread phenomenon in the ocean and plays key roles in the marine environment, marine fishery and air–sea carbon exchange. In coastal regions, the upwelling is usually modulated by tides and complex topography, but the dynamical mechanism is still unclear and yet to be quantified. In this study, a three-dimensional (3D) regional ocean model is used to investigate tide-induced upwelling and its mechanisms quantitatively in the mouth of a semi-closed bay, the Bohai Strait, which is a tide-dominated coastal region. The results show that the upwelling mainly occurs near the tidal front in the north of the Laotieshan Channel and the southern region of the front, with the most active upwelling existing off promontories and small islands. Numerical sensitivity experiments indicate that the upwelling in the study area is mainly caused by tides, accounting for approximately 86% of the total. The 3D balance of the vertical component of the vorticity based on the model results quantifies the dynamic processes of the upwelling and reveals that tides induce the upwelling through tidal mixing and nonlinear effects. In the tidal front zone, the upwelling is mainly caused by baroclinic processes related to tidal mixing. Off promontories and small islands, we first reveal that the upwelling is driven by both the tidal mixing and nonlinear effect related to centrifugal force rather than just one of the two mechanisms, and the latter plays a dominant role in producing the upwelling. The strong nonlinear effect is attributed to the periodic movement of barotropic tidal currents rather than the mean flow.

The role of wave breaking (WB) in the ocean dynamics in the Bohai Sea, China under typhoon condition is systematically investigated utilizing a coupled wave-current model. The influences of WB on ocean dynamics and processes (mixing coefficient, temperature, mixed layer depth, and current) during the entire typhoon period (including the pre-typhoon, during-typhoon and after-typhoon stages) are comprehensively detected and discussed. Experimental results show that WB greatly enhances the turbulent mixing at about top 10 m depth under typhoon condition, the increase can be up to 10 times that of the normal weather. At the same time, WB generally strengthens the sea surface cooling by ∼1.2°C at the during-typhoon stage, about 3 times that in normal weather. The mixed layer depth, is rapidly increased by ∼1.6–3.6 m during typhoon due to WB, particularly, the deepening is stronger in the region from 120.5°E to 121.0°E on account of close to the typhoon eye. In addition, WB renders the current speed more uniformly within the entire depth in the Bohai Sea, the change in speed is ∼0.2 m/s, whereas the alternation in current vector is generally opposite to the wind direction except for the typhoon eye region, reflecting that WB has an inhibitory effect on the typhoon-forced current change. The effects of WB on vertical mixing coefficient response to the typhoon rapidly, while the impacts of WB on temperature, and mixed layer depth present hysteretic responses to typhoon. Finally, the mechanisms and distribution characteristics of WB-induced mixing and tidal mixing are compared under typhoon condition. [ABSTRACT FROM AUTHOR]

In summer, westward residual flow in the Qiongzhou Strait (QS) drives a water transport through the strait into the Beibu Gulf, playing a vital role in modifying the gulf-scale circulation. By utilizing multi-source observations, realistic simulations, as well as idealized modeling, the water exchange process at the western entrance of the QS was explored from the perspective of thermal structure. High-resolution satellite sea-surface temperature images captured an interesting thermal phenomenon in the studied region, i.e., a trident-shaped warm water tongue. Validations of numerical results suggested satisfactory model performance in reproducing the trident-shaped warm water tongue. Modeling results together with cruise observations indicates extremely weak stratification in the studied region, which is a result of local intense tidal mixing. The cold upwelling water developed at the eastern side of the strait arrived at the western entrance by the westward residual flow, and then encountered and communicated with the well-mixed warm gulf water there. The alternatively deep/shallow topography (sea trough/ridge) triggers spatial variability in tidal current intensity: stronger currents over the deep area with weaker flow above the shallow region leads to alternatively warm/cold thermal distribution in the cross-isobath direction. Further investigation demonstrates that, through modifying the circulation and regulating the intensity of upwelling on the eastern side of the QS, wind also makes a significant contribution to the thermal distribution at the western entrance of the QS. [ABSTRACT FROM AUTHOR]

As a ubiquitous movement in the ocean, tides are vital for marine life and numerous marine activities such as fishing and ocean engineering. Tidal dynamics are complicated in the East Asian marginal seas (EAMS) due to changing complex topography and coastlines related to human activities (e.g., land reclamation and channel deepening) and natural variability (e.g., seasonal variations of ocean stratification and river flow). As an important tool, numerical models are widely used because they can provide basin-scale patterns of tidal dynamics compared to point-based tide gauges. This paper aims to overview the development history of the numerical simulation of tides in the EAMS, including the Bohai Sea, the Yellow Sea, the East China Sea, the East/Japan Sea, and the South China Sea, provide comprehensive understanding of tidal dynamics, and address contemporary research challenges. The basic features of major tidal constituents obtained by tidal models are reviewed, and the progress in the inversion of spatially and temporally changing model parameters via the adjoint method are presented. We review numerical research on how a changing ocean environment induces tidal evolution and how tides and tidal mixing influence ocean environment in turn. The generation, propagation, and dissipation of internal tides in the EAMS are also reviewed. Although remarkable progresses in tidal dynamics have been made, nonstationary tidal variations are not fully explained yet, and further efforts are needed. In addition, tidal influences on ocean environment still receive limited attention, which deserves special attention. [ABSTRACT FROM AUTHOR]

Estuarine plume frontal zones typically form a vertical two-layer structure with low-salinity and a high-temperature plume during the summertime. However, two field surveys in the Changjiang River Estuary and its adjacent shelf waters identified a significant surface cold-water zone (CWZ) formation in the summers of 2014 and 2015. The sea surface temperature of the CWZ was 4°C lower than the multi-year summer average. Satellite images showed that the CWZ mainly appeared in the Yangtze Shoal during the periods of July 1–17, 2014, and July 3–19, 2015. A three-dimensional physical-biogeochemical coupled model was used to explore the formation mechanism of the CWZ. Our investigation revealed that an uncharacteristic northerly wind during the southerly monsoon resulted in a significant onshore retreat of the plume front. Vertical tidal mixing is stronger than the decreased stratification in the former plume-covered region, which resulted in the formation of the CWZ. This process was accompanied by relatively lower net heat flux, which also promoted CWZ formation. The formation of CWZ had a strong ecological impact; enhanced vertical mixing transported nutrients from the lower layer to the surface column, relaxing the CWZ’s phosphate limitation. CWZ formation also increased the depth of the mixed layer and turbidity level in the water column, forming a temporary light limitation in the center. At the margin of the CWZ, it formed a patch with a high concentration of chlorophyll a. The underwater light was sufficient once the plume was restored and the CWZ was stratified again, and the phytoplankton grew rapidly in the center of the CWZ.

With their complex narrow passages and vigorous mixing, the Indonesian seas provide the only low-latitude pathway between the Pacific and Indian Oceans and thus play an essential role in regulating Pacific-Indian Ocean exchange, regional air-sea interaction, and ultimately, global climate phenomena. While previous investigations using remote sensing and numerical simulations strongly suggest that this mixing is tidally driven, the impacts of monsoon and El Niño Southern Oscillation (ENSO) on tidal mixing in the Indonesian seas must play an important role. Here we use high-resolution sea surface temperature from June 2002 to June 2021 to reveal monsoon and ENSO modulations of mixing. The largest spring-neap (fortnightly) signals are found to be localized in the narrow passages/straits and sills, with more vigorous tidal mixing during the southeast (boreal summer) monsoon and El Niño than that during the northwest (boreal winter monsoon) and La Niña. Therefore, tidal mixing, which necessarily responds to seasonal and interannual changes in stratification, must also play a feedback role in regulating seasonal and interannual variability of water mass transformations and Indonesian throughflow. The findings have implications for longer-term variations and changes of Pacific–Indian ocean water mass transformation, circulation, and climate. [ABSTRACT FROM AUTHOR]

Dynamic processes in the coastal waters play an important role in regulating the marine pollution distribution caused by riverine inputs and are relevant for coastal management. Here, the coastal water properties were investigated from field measurements and modeling hydrodynamic processes in the northeastern coast of Sumatra. The present study found that the river discharges affect a low salinity of 28–29 psu in the surface waters along near the coastal line. The river discharge might influence by strong La Niña with high rainfall in December 2010. However, the authors suggested that the effect of tidal mixing is stronger than the freshwater discharges, resulting in vertically well-mixed coastal waters in the region. The observed tidal range of 200 cm indicates a strong tidal mixing in the waters. The tidal elevation contributes more than 70% of the total measured sea elevation. The tidal current signal in which the flow pattern simulations show no significant differences among tide and wind-tide driven currents, is also dominant (77%). [ABSTRACT FROM AUTHOR]

Abstract Strong tidal currents in and around the narrow straits of the Lesser Sunda Islands, Indonesia, affect ocean sea surface temperatures (SST) via non-linear tide-induced mixing. A fortnightly spring–neap cycle in tidal currents can induce a similar cycle in SST, which has been observed to occur in and south of Lombok Strait. Here we report on an atmospheric response to the fortnightly SST cycle which is detected in relative humidity and air temperature measurements at Bali. The fortnightly cycles in both the ocean SST and the Bali atmospheric data have a strong seasonal cycle, with peak signals occurring during boreal summer.

The importance of the Malacca Strait to trade is important but its importance in terms of ocean connectivity is often ignored. This paper is a study of the propagation of tide and sea level anomalies (SLA) (i.e., non-tidal component) in the Malacca Strait using a well calibrated numerical model. Four main tidal constituents are examined at different sections of the strait. Tidal amplitude in terms of water level and volumetric flux of these four constituents are derived using harmonic analysis. It is shown that the tidal flux propagation pattern behaves differently from the tidal water level propagation pattern in the strait. Detailed analysis of the tidal amplitudes of both water level and volumetric flux makes the location of the tidal mixing zone in the strait becomes apparent. Analyzing the SLA with regards to flux and net flux volume at each cross section in the strait shows that the tidal mixing zone plays a role in obstructing the propagation of SLA from Andaman Sea and Singapore Strait. [ABSTRACT FROM AUTHOR]

The vertical structure of internal tide dissipation rate ϵ is essential to the parameterization of the internal tide‐induced mixing, yet its diversity has always been oversimplified in ocean circulation models. Based on a high‐vertical‐resolution (10 m) simulation around the exits of the Indonesian throughflow, the diversity in ϵ profiles near both the bottom and the thermocline was investigated by a hierarchical clustering classification. Five typical near‐bottom vertical structures of ϵ were found, of which the bottom‐intensified structure is dominant. From the maximum dissipation depths to the shallower water, all five profiles obey the same decaying function. There are three typical near‐thermocline structures of ϵ: one menifests the thermocline‐intensified pattern and the other two feature a surface‐intensified pattern characterized by a monotonic increase from 500‐m depth to the surface. All three vertical structures near thermocline could be scaled by the reciprocal of the Richardson number. Plain Language Summary: Tidal currents flow over the uneven seafloor back and forth every day, causing mixing between adjacent vertical layers in the ocean. This process, known as tidal mixing, occurs in the whole ocean and is strong around the exits of the Indonesian throughflow (ITF). The vertical distribution of the tidal mixing is one of the primary elements that shapes the profiles of temperature and salinity and modulates the transports in the Indonesian seas. Previous studies suggested that tidal mixing is intensified at the bottom and the thermocline without considering its diversity in the real ocean. The diversity in the profiles of the tidal mixing around the exits of the ITF is explored. We found that, adjacent to the bottom topography, the mixing is intensified not only at the bottom but also at depths of hundreds of meters above the bottom and all of profiles obey the same decaying law from the maximum mixing depths to the shallower water. Near the thermocline, the tidal mixing is thermocline‐intensified away from the archipelago and surface‐intensified near the archipelago. These findings shed light on the vertical structures of tidal mixing in the ocean and are potentially valuable to improve the performance of ocean circulation models. Key Points: Diversity in the profiles of tide‐induced dissipation rate around the exits of the Indonesian throughflow is investigatedFive typical profiles are revealed near the bottom, obeying the same decaying law from the maximum dissipation depths to shallower waterThree typical profiles near the thermocline are also revealed, all of which can be scaled with the reciprocal of the Richardson number [ABSTRACT FROM AUTHOR]

Anadyr Strait, located at the northernmost reaches of the Bering Sea, influences pan‐Arctic climate through processes occurring in the strait as the Siberian Coastal Current carries water from the subpolar North Pacific Ocean into the western Arctic Ocean. A sharp sea surface temperature front near the Anadyr Strait segregates a tongue‐shaped mass of warm water from areas of cold‐water upwelling proximate to the Siberian coast. To clarify dynamical processes in this region, we conducted shipboard observations through and near the Anadyr and Bering straits during the summers of 2017 and 2018. Microstructure measurements show enhanced turbulence near the sea floor as strong throughflow occurs in the narrow straits. Direct observations of ocean currents indicate that the semidiurnal barotropic tide partly contributes to the near‐bottom currents driving mixing. Frictional effects accompanying the barotropic current are examined using a three‐dimensional regional model. Bottom friction produces a westward Ekman current in the bottom boundary layer, which then causes upwelling of underlying cold water on the western (Siberian) side of the Anadyr Strait. Secondary circulation across the strait is also maintained by the near‐surface eastward velocity, which is established by the steep slope of the main thermocline. Plain Language Summary: Water from the North Pacific passing through the narrow straits of the Bering Sea can affect climate change in the western Arctic Ocean. Anadyr Strait is an important pathway in the northern Bering Sea, but the oceanographic processes occurring there are poorly understood because of a paucity of in situ observations. We obtained new data from the region in the summers of 2017 and 2018, which allows us to study the mechanisms generating the near‐surface cold water in Anadyr Strait that has been identified from satellites. Our study reveals that the cold water is lifted up to the surface from the bottom layer when a strong current passes through the strait. According to our direct measurements and numerical simulations, friction between the current and the sea floor generates cold‐water upwelling and the horizontal temperature front. This improved understanding of ocean processes in the northern Bering Sea will help improve our understanding of how the North Pacific and Arctic oceans will interact as climate varies. Key Points: The sea surface temperature front near Anadyr Strait was investigated during two shipboard surveys in the summers of 2017 and 2018Coastal upwelling of cold water occurs as part of cross‐strait cell circulation, where bottom friction is the controlling factorStratified throughflow with semidiurnal tidal oscillation facilitates the development of the frictional bottom boundary layer [ABSTRACT FROM AUTHOR]

Multiyear current meter records from five sites are used to examine subsurface renewal processes in the southern Strait of Georgia. The lower layer inflow of dense oceanic‐derived water over the ~100‐m deep sill in Boundary Pass near the entrance to the strait reaches peak velocities during spring tides and rarely reverses direction. Corresponding changes in water density over the sill are inversely correlated with inflow velocity and, it is assumed, with temporal (t) variations in bottom layer thickness, h(t), arising from the fortnightly variations in tidal‐mixing. The dense bottom water crossing the sill transforms into a gravity current whose velocity is dependent on both h and sill depth, H. Gravity flow velocities, which peak at h(t)/H ~ 0.3 and weaken for h → 0 (neap tides) and h → H (spring tides), modulate the cross‐sill exchange with the strait. The density anomaly, Δρ, of the gravity flow determines its terminal depth and along‐strait extent. Lower‐density gravity flows generated during spring tides separate from the sloping bottom of the southern strait, but the higher‐density flows formed during neap tides can penetrate over 100 km northward to the deep central basin. The most extensive bottom intrusions occur monthly near neap tides in summer, when the underlying estuarine circulation delivers dense upwelled water from the coast to the sill. These deep inflows are accompanied by strong middepth outflow. There are typically three to five monthly replacement episodes each summer, but fewer during strong El Niño years due to reduced coastal upwelling. Key Points: Gravity currents formed over broad sills can strongly affect estuarine exchange and subsurface intrusions into coastal basinsGravity flows entering the southern Strait of Georgia vary fortnightly due to tidally induced changes in bottom layer thickness at the sillThe number of major bottom‐water intrusions entering the southern strait in summer is greatly reduced during major El Niño events [ABSTRACT FROM AUTHOR]

• Analyze momentum of a river plume with multiple outlets by salinity and depth space. • Investigate the impacts of tidal advection and tidal mixing on the river plume. • Downstream barotropic freshwater transport surpasses upstream baroclinic transport. Tides play a crucial role in regulating the dispersal and dynamics of a river plume. However, the impact of tides on the dynamics and transport of freshwater in a medium-scale river plume, particularly with multiple outlets, is still not well understood. Using the Hanjiang River Plume in the northern South China Sea as an example, we analyze the momentum and volume of the plume based on salinity space. We also investigate the effects of tidal advection and tidal mixing. Tidal advection propels plume water from the bulge downstream, resulting in a plume type with intermediate surface-advected and bottom-advected characteristics. Tidal mixing causes the plume to come into contact with the seafloor, leading to bottom-advected plumes. Tidal advection leads to the accumulation of plume water in high salinity space, while tidal mixing mitigates this effect, as the plume water near the estuary with relatively low salinity is effectively mixed. In the absence of tidal forcing, vertical shear is the main contributor to the total freshwater flux. However, when tidal effects are taken into account, the contribution of vertical shear to the total freshwater flux decreases and becomes comparable to the advection term. The downstream buoyant flow is primarily controlled by geostrophic balance. The barotropic current carries freshwater downstream, overpowering the upstream transport by the baroclinic current, resulting in a net downstream freshwater transport. Tidal advection enhances this downstream freshwater transport, while tidal mixing has the opposite effect. [ABSTRACT FROM AUTHOR]

The Shantar Islands National Park (northwestern shelf of the Sea of Okhotsk) was established to preserve the biological diversity of unique natural marine and terrestrial ecosystems. The water structure and dynamics in the basin of the Shantar Islands has been studied based on the analysis of multisensor satellite images (Terra/Aqua MODIS, Landsat-7 ETM+, Landsat-8 OLI/TIRS, Sentinel-2A MSI) and field oceanographic observations. The circulation over the shelf in the Shantar Islands region is strongly determined by strong tidal currents and freshwater discharge. The water structure is formed under the influence of intense local tidal mixing and the propagation of low-saline river plumes in the shallow parts of the main bays of the Shantar archipelago. The interaction of tidal currents with the complex topography and bathymetry (peninsulas, capes, islands, straits, and shallow-water regions of the shelf) leads to a high level of submesoscale activity and the generation of various types of submesoscale structures, including jet currents and eddies. [ABSTRACT FROM AUTHOR]

Abstract Fronts are ubiquitous phenomena in oceans, and they play a significant role in marine hydrodynamics and ecology. During the stratified season of a shelf sea, the coastal front is usually considered as a single front, i.e., the tidal mixing front. However, using high resolution (~1 km) Multi-scale Ultra-high Resolution (MUR) analysis sea surface temperature (SST) data, this study observes persistent double fronts along the Yellow Sea coast in summertime. The double fronts comprise the well-known offshore tidal mixing front and a nearshore front, and the nearshore front has not been previously reported. The climatological (2002–2017) monthly mean result shows that the double fronts with two SST gradient peaks exceeding ~2 °C/100 km and opposite SST gradient directions basically remain unchanged from June to August, whereas the frontal spacing decreases in September. Analyses based on a two-layer concept model suggest that a topographic slope along with tidal mixing could induce the pattern of double fronts. The frontogenesis of nearshore thermal front could be associated with the different responses of the water column of different water depths to insolation. The offshore movement of the nearshore front in September could be related to the fast cooling of nearshore water and intensified offshore wind, and the topographic slope is important for determining the pattern of double fronts (loose or tight). This study shows a new pattern of coastal fronts in the stratified season, and indicates the significance of high resolution satellite data. The discovery of the double front pattern implies the influence of coastal fronts during the stratified season on marine ecology and environment in a shelf sea might be underestimated. Highlights • SST double fronts in the Yellow Sea in the summertime were observed using high resolution (~1 km) satellite analysis data. • The double fronts consist of a nearshore front and an offshore tidal mixing front with opposite SST gradient directions. • A two-layer concept model suggests that a topographic slope along with tidal mixing could induce the double fronts. [ABSTRACT FROM AUTHOR]

The response of the thermohaline structure of water off the western Kamchatka shelf of the Sea of Okhotsk to the wind-driven upwelling and tidal mixing is analyzed, and the results are presented. The upwelling intensity was estimated based on the offshore Ekman mass transport (the upwelling index). The mean position of the tidal mixing front was determined using the spatial distribution of the Simpson-Hunter stratification parameter. The hydrographic observations and the results of the upwelling index calculation revealed the occurrence of the summer transient upwelling on the western Kamchatka shelf under certain synoptic conditions. The favorable meteorological conditions for the upwelling development were associated with the propagation of atmospheric cyclones to the Kamchatka Peninsula. The zone of intensive tidal mixing is located in the northwestern part of the Kamchatka shelf in the open part of the Shelikhov Bay. The western Kamchatka tidal mixing front which separates tidally mixed coastal water from stratified open shelf water emerges in May during the period of seasonal thermocline formation and disappears in July due to enhanced thermal stratification. The wind-driven coastal upwelling and the tidal mixing might support the high biological productivity of the western Kamchatka shelf. [ABSTRACT FROM AUTHOR]

The spatial and temporal variability of tidal mixing in Bohai Sea is studied using a numerical approach. In calculating tidal mixing, accurate barotropic tidal current is obtained via a harmonic analysis package utilizing the simulated current output from a high-resolution regional ocean model. And a "small-scale" roughness map is adopted to describe the detailed topographic features of Bohai Sea. It is shown that the tidal mixing estimated in Bohai Sea is much higher than the level of global background, and fluctuates considerably at some regions within a single day. In Liaodong Bay, Bohai Bay and Bohai Strait, the mixing varies greatly, with the peak value of O (10−2) m2 s−1. The order of magnitude of mixing in Laizhou Bay is about O (10−5∼10−3) m2 s−1. Mixing with background level of O (10−5) m2 s−1 only appears in central area. Result also shows that rough topography plays relatively a more important role than tidal current in enhancing diapycnal mixing in Bohai Sea. The distributions of tidal mixing in selected sections reveal that the vertical stratification in Bohai Sea is not obvious, generally renders a barotropic structure. [ABSTRACT FROM AUTHOR]

We use 25 years of Advanced Very High-Resolution Radiometer (AVHRR) data from NOAA Polar Orbiting Environmental Satellites received by six Australian and two Antarctic reception stations to construct a detailed climatology of sea surface temperature (SST) around Australasia. The data have been processed following international GHRSST protocols to help reduce instrument bias using in situ data, with only night-time nearly cloud-free data used to reduce diurnal bias and cloud contamination. A pixel-wise climatology (with four annual sinusoids) and linear trend are fit to the data using a robust technique and monthly non-seasonal percentiles derived. The resulting Atlas, known as the SST Atlas of Australian Regional Seas (SSTAARS), has a spatial resolution of ~2 km and thus reveals unprecedented detail of regional oceanographic phenomena, including tidally-driven entrainment cooling over shelves and reef flats, wind-driven upwelling, shelf winter water fronts, cold river plumes, the footprint of the seasonal boundary current flows and standing mesoscale features in the major offshore currents. The Atlas (and associated statistics) will provide a benchmark for high-resolution ocean modelers and be a resource for ecosystem studies where temperatures, and their extremes, impact on ocean chemistry, species ranges and distribution. [ABSTRACT FROM AUTHOR]

It has been frequently observed that there are surface cold patches (SCPs) in the Yellow Sea in summer. Although previous studies based on monthly mean temperature distribution found that these SCPs are a result of tidal mixing and tide-induced upwelling, tidal mixing and upwelling alone cannot explain all the occurrences. In our study we found that the three typical patches, namely, the Shandong SCP, the Subei SCP, and the Mokpo SCP, have different temporal patterns over a spring-neap tidal cycle; hence, they have different generating mechanisms. Based on a multiple-year simulation, the latter two show conspicuous spring-neap variations. The highest temperature occurs during the neap tide phase (about two days after a quarter moon). Because of weak upwelling and mixing, strong stratification is established and the SCPs are suppressed or even disappear. The opposite holds for the spring tide phase (about two days after a new or full moon). This is quite different from the Shandong SCP, which does not display a distinct difference between spring and neap tides. Buoy observations and composite analyses with data from the Moderate Resolution Imaging Spectroradiometer (MODIS) further support this conclusion. [ABSTRACT FROM AUTHOR]

Phytoplankton concentrations display strong temporal variability at different time scales. Recent advances in automated moorings enable detailed investigation of this variability. In this study, we analyzed phytoplankton fluctuations at four automated mooring stations in the North Sea, which measured phytoplankton abundance (chlorophyll) and several environmental variables at a temporal resolution of 12–30 min for two to nine years. The stations differed in tidal range, water depth and freshwater influence. This allowed comparison of the predictability and environmental drivers of phytoplankton variability across different time scales and geographical regions. We analyzed the time series using wavelet analysis, cross correlations and generalized additive models to quantify the response of chlorophyll fluorescence to various environmental variables (tidal and meteorological variables, salinity, suspended particulate matter, nitrate and sea surface temperature). Hour-to-hour and day-to-day fluctuations in chlorophyll fluorescence were substantial, and mainly driven by sinking and vertical mixing of phytoplankton cells, horizontal transport of different water masses, and non-photochemical quenching of the fluorescence signal. At the macro-tidal stations, these short-term phytoplankton fluctuations were strongly driven by the tides. Along the Dutch coast, variation in salinity associated with the freshwater influence of the river Rhine played an important role, while in the central North Sea variation in weather conditions was a major determinant of phytoplankton variability. At time scales of weeks to months, solar irradiance, nutrient conditions and thermal stratification were the dominant drivers of changes in chlorophyll concentrations. These results show that the dominant drivers of phytoplankton fluctuations differ across marine environments and time scales. Moreover, our findings show that phytoplankton variability on hourly to daily time scales should not be dismissed as environmental noise, but is related to vertical and horizontal particle transport driven by winds and tides. Quantification of these transport processes contributes to an improved predictability of marine phytoplankton concentrations. [ABSTRACT FROM AUTHOR]

The 18.6-year modulation of the short-period tides related to the precession of the moon’s ascending node probably modulates vertical mixing in the ocean through microscale dissipation processes of internal waves. It is hypothesized that the modulation of mixing contributes to the bidecadal variability in physical and biogeochemical variables in the North Pacific and its marginal seas. Previous studies support this hypothesis. However, the quantitative importance of this modulation remains far from clear. Even qualitatively, we do not understand well the mechanism linking the modulation of mixing and the bidecadal variability in the ocean. To verify the hypothesis, it is necessary to evaluate the quantitative importance of ocean variability as a result of the direct ocean response to the modulation of mixing, which requires us to quantitatively discuss the response to both atmospheric forcing variations and mixing modulation. One promising way to do this is via numerical experiments using a reliable ocean model that can reproduce both the mean states and temporal variations through realistic processes. It is also important to obtain more information about bidecadal variability based on observations. [ABSTRACT FROM AUTHOR]

Estuarine ecosystem diversity and function can be degraded by low oxygen concentrations. Understanding the spatial and temporal patterns of dissolved oxygen (DO) variation and the factors that predict decreases in DO is thus essential to inform estuarine management. We investigated DO variability and its drivers in Elkhorn Slough, a shallow, well-mixed estuary affected by high nutrient loading and with serious eutrophication problems. Long-term (2001-2012), high-resolution (15 min) time series of DO, water level, winds, and solar radiation from two fully tidal sites in the estuary showed that hypoxia events close to the bottom are common in the summer at the more upstream estuarine station. These events can occur in any lunar phase (spring to neap), at any time of the day, and both on sunny or cloudy days. They are, however, short-lived (lasting in average 40 min) and mainly driven by momentary low turbulent diffusion around slack tides (both at high and low water). Tidal advective transport explains up to 52.1% of the daily DO variability, and the water volume (or DO reservoir) contained in the estuary was not sufficient to avoid hypoxia in the estuary. Solar radiation was responsible for a positively correlated DO daily cycle but caused a decreased in the averaged DO in the summer at the inner station. Wind-driven upwelling reduced the average DO at the more oceanic station during spring. The approach we employed, using robust techniques to remove suspect data due to sensor drift combined with an array of statistical techniques, including spectral, harmonic, and coherence spectrum analysis, can serve as a model for analyses of long-term water quality datasets in other systems. Investigations such as ours can inform coastal management by identifying key drivers of hypoxia in estuaries. [ABSTRACT FROM AUTHOR]

Recent studies show that the glaciers draining both the West Antarctic and the Greenland Ice Sheets are experiencing an accelerated ice loss, highlighting the possibility of large-scale ice sheet retreat and sea level rise in the coming centuries and millennia. These sea level changes would vary spatially and could significantly alter global tides as the latter are highly dependent on bathymetry (or water column thickness under ice shelves) and basin shape. This paper investigates how the principal semidiurnal (M2) tidal amplitudes and energy dissipation respond to the nonuniform sea level changes induced by complete ice sheet collapses. The sea level changes are calculated using gravitationally self-consistent sea level theory, and the tides are simulated using an established tidal model. Results from the simulations show global and spatially heterogeneous changes in tidal amplitudes. In addition, pronounced changes in tidal energy dissipation occur in both the open ocean and in shelf-seas, also altering the location of tidal mixing fronts. These changes have the potential to impact ocean mixing, and hence large-scale currents and climate patterns, and the contribution of shelf-sea to the global carbon cycle. The new results highlight the importance of considering changes in the tides in predictions of future climate and reconstructions of past climate phases such as the Last Interglacial. [ABSTRACT FROM AUTHOR]

Chlorophyll-a is the predominant phytoplankton pigment responsible for determining primary productivity. In the present study, we used satellite-based data of chlorophyll-a, surface wind, and precipitation from 2003 to 2019 to investigate the variability of chlorophyll-a in the northern Maluku Sea and the Sulu Sill and examine its generating mechanism. We found that the chlorophyll-a bloom in the northern Maluku Sea occurs during the southeast monsoon season, while in the Sulu Sill, the chlorophyll-a concentration is higher than that in the northern Maluku Sea and occurs throughout the year. In the northern Maluku Sea, the chlorophyll-a bloom is generated by coastal upwelling. The maximum southerly wind during the southeast monsoon generates the strongest offshore Ekman Mass Transport (EMT) in the northern Maluku Sea triggering coastal upwelling. However, the power spectra analysis of satellite-derived chlorophyll-a shows strong peaks and amplitudes at both fortnightly (MSf) and monthly (Mm) frequencies, indicating that tidal mixing is an important generating mechanism for chlorophyll-a blooms in the Sulu Sill. Shallow bathymetry in the Sulu Sill may aid tidal mixing in effectively transporting nutrients from the near bottom to the sea surface, increasing chlorophyll-a concentration. • Chlorophyll-a bloom in the northern Maluku Sea (Sulu Sill) occurs during the southeast monsoon season (throughout year). • In the northern Maluku Sea, the chlorophyll-a bloom is generated by coastal upwelling due to strongoffshore Ekman Transport. • In the Sulu Sill, tidal mixing is an important mechanism for chlorophyll-a blooms which has strong MSf and Mm signals. [ABSTRACT FROM AUTHOR]

The intrusion of Circumpolar Deep Water (CDW) is the primary source of heat, salt and nutrients onto Antarctica's continental shelves and plays a major role in the shelf physical and biological processes. Different studies have analyzed the processes responsible for the transport of CDW across the Ross Sea shelf break, but until now, there are no continuous observations that investigate the timing of the intrusions. Also, few works have focused on the effect of the tides that control these intrusions. In the Ross Sea, the CDW intrudes onto the shelf in several locations, but mostly along the troughs. We use hydrographic observations and a mooring placed on the outer shelf in the middle of the Drygalski Trough in order to characterize the spatial and temporal variability of CDW inflow onto the shelf. Our data span from 2004 to the beginning of 2014. In the Drygalski Trough, the CDW enters as a 150 m thick layer between 250 and 400 m, and moves upward towards the south. At the mooring location, about 50 km from the shelf break, two main CDW cores can be observed: one on the east side of the trough spreading along the west slope of Mawson Bank from about 200 m to the bottom and the other one in the central-west side from 200 m to about 350 m depth. A signature of this lighter and relatively warm water is detected by the instruments on the mooring at bottom of the Drygalski Trough. High frequency periodic CDW intrusion at the bottom of the trough is related to the diurnal and spring/neap tidal cycles. At lower frequency, a seasonal variability of the CDW intrusion is noticed. A strong inflow of CDW is observed every year at the end of December, while the CDW inflow is at its seasonal minimum during the beginning of the austral fall. In addition an interannual variability is also evident. A change of the CDW intrusion before and after 2010 is observed. [ABSTRACT FROM AUTHOR]

Spatial and temporal measurement data describing spring-neap variations of velocity, salinity, and suspended sediment concentration (SSC) in the North Passage Deepwater Navigational Channel (DNC) of the Yangtze Estuary, China, were obtained in the wet season of 2012. These data were collected in the middle of the DNC and apparently document the formation of a rather stable density stratification interface and salt wedge, especially during neap tides and slack waters. The convergent zone of residual currents, salinity transport, and sediment transport during neap and spring tides oscillates in the middle and lower reach of the DNC. It encourages the formation of a near-bed high-SSC layer, which favours siltation in the dredged channel. Both the near-bed gradient Richardson number and the bulk/layer Richardson number vary dramatically from around zero to several hundred from spring to neap tides. Stratification and turbulence damping effects near the estuarine turbidity maximum (ETM) area induce the upper half (near water surface) of the water body to be ebb-dominant and the lower part (near-bed) to be flood-dominant, which is a previously undocumented phenomenon in this region. These data reveal that the residual pattern of currents, salt flux and sediment flux are of critical differences in a stratified estuary, and that the salinity-induced baroclinic pressure gradient is a major factor controlling the vertical velocity structure. In addition, field observations indicate that the salinity and sediment transport of residuals generated by internal tidal asymmetry plays a dominant role in maintaining a stable density stratification interface near the estuarine front. [ABSTRACT FROM AUTHOR]

Channel constrictions within an estuary can influence overall estuary-sea exchange of salt or suspended/dissolved material. The exchange is modulated by turbulent mixing through its effect on density stratification. Here we quantify turbulent mixing in Hikapu Reach, an estuarine channel in the Marlborough Sounds, New Zealand. The focus is on a period of relatively low freshwater input but where density stratification still persists throughout the tidal cycle, although the strength of stratification and its vertical structure vary substantially. The density stratification increases through the ebb tide, and decreases through the flood tide. During the spring tides observed here, ebb tidal flow speeds reached 0.7 m s-1 and the buoyancy frequency squared was in the range 10-5 to 10-3 s-2. Turbulence parameters were estimated using both shear microstructure and velocimeterderived inertial dissipation which compared favourably. The rate of dissipation of turbulent kinetic energy reached 1 ? 10-6 m² s-3 late in the ebb tide, and estimates of the gradient Richardson number (the ratio of stability to shear) fell as low as 0.1 (i.e. unstable) although the results show that bottom-boundary driven turbulence can dominate for periods. The implication, based on scaling, is that the mixing within the channel does not homogenise the water column within a tidal cycle. Scaling, developed to characterise the tidal advection relative to the channel length, shows how riverine-driven buoyancy fluxes can pass through the tidal channel section and the stratification can remain partially intact. [ABSTRACT FROM AUTHOR]

A 2-km-resolution model of the eastern Bering Sea is developed to capture dynamical processes on the scale of the Rossby radius of deformation on tidal to seasonal time scales. The model spans the region from 178°E to the Alaskan coast and from roughly 50° to 66°N, including the Aleutian Islands in the south and the Bering Strait in the north. The high resolution throughout ensures that the mesoscale dynamics of significant subregions of the domain, such as the Aleutian Island passes, Bering Sea slope, and the shelf canyons, are captured simultaneously without the concern for loss of interconnectivity between regions. Simulations are performed for the ice-free season (June–October) of 2009, with tidal and atmospheric forcing. The model compares favorably with observations from AVHRR and Envisat satellites, Argo drifters, and Bering Sea shelf moorings. The mesoscale dynamics of the mixing and exchange flow through the eastern Aleutian Island passes, which exhibit strong diurnal and two-week variability, are well represented. The two-week oscillation in volume flux through the largest of these passes, Amukta Pass, is found to be out of phase with the transport through the neighboring passes (e.g., Seguam and Samalga passes). Mesoscale structure is also found to be ubiquitous along the mixing front of the cold pool. Structures at the scale of O(20 km) persist and play a role in determining the pattern of erosion of the water mass as the shelf warms and mixes. On the Bering Sea shelf, tidal motions are dominant, and variability on the horizontal scale of the first-mode internal tide develops (O(30 km)) from the shelf break to the onshore edge of the Bering shelf cold pool. [ABSTRACT FROM AUTHOR]

The response of tidally driven processes on the Patagonian Shelf to sea-level rise (SLR) is revisited using large but realistic levels of change in a numerical tidal model. The results relate to previous studies through significant differences in the impact, depending on how SLR is implemented. This is true for how the boundary at the coastline is treated, i.e., if we allow for inundation of land or assume flood defences along the coast, but also for how the sea-level change itself is implemented. Simulations with uniform SLR provide a different, and slightly larger, response than do runs where SLR is based on observed trends. In all cases, the effect on the tidal amplitudes is patchy, with alternating increases and decreases in amplitude along the shelf. Furthermore, simulations with a realistic future change in vertical stratification, thus affecting tidal conversion rates, imply that there may be a small but significant decrease in the amplitudes along the coast. Associated processes, e.g., the location of mixing fronts and potential impacts on biogeochemical cycles on the shelf are also discussed. [ABSTRACT FROM AUTHOR]

Spring neap variations in stratification and chlorophyll fluorescence were studied during the summers of 2011–2014 in a tidal sea (Yatsushiro Sea, Japan) using monitoring data and hydrodynamic models. Vertical profiles of salinity, temperature and chlorophyll fluorescence were collected nearly weekly from nine stations in this sea during the same period. Composite analysis using vertical profiles of density clearly indicated enhancement of the stratification during the neap tide and a vertically mixed water column during the spring tide in the tidal area. Interregional differences were revealed in the variation of chlorophyll fluorescence with the spring neap tidal cycle. More notable increases in chlorophyll fluorescence were observed during the neap tide in the tidal area around the narrow strait than in the inner area. Temporal stratification led to an increase in the chlorophyll fluorescence in the tidal strait during the neap tide. [ABSTRACT FROM AUTHOR]

Observations reveal a near-surface circulation around the periphery of Rhode Island Sound (RIS) that occurs in summer stratified conditions and disappears in winter when weak solar insolation and wind stirring result in strong vertical mixing. According to a series of numerical simulations and theoretical analysis, we attribute the summer intensification of this “periphery current” to a circulation produced by seasonal bottom thermal fronts often observed from May to September. The strength of the thermal fronts is proportional to the surface solar radiation. Meanwhile, the simulations capture a continuous topographically rectified tidal residual current in RIS and a pair of opposite-sign headland eddies around Montauk Point in Block Island Sound (BIS). Our analysis suggests the importance of nonlinear vorticity advection and frictional torques in BIS. On the other hand, the vorticity balance shows the importance of velocity torque by contributing to the opposite headland gyres, while the effect by planetary vorticity stretching is negligible over BIS but important in RIS. [ABSTRACT FROM AUTHOR]

The eight main tidal constituents have been implemented in the global ocean general circulation model with approximate 1° horizontal resolution. Compared with the observation data, the patterns of the tidal amplitudes and phases had been simulated fairly well. The responses of mean circulation, temperature and salinity are further investigated in the global sense. When implementing the tidal forcing, wind-driven circulations are reduced, especially those in coastal regions. It is also found that the upper cell transport of the Atlantic meridional overturning circulation (AMOC) reduces significantly, while its deep cell transport is slightly enhanced from 9×10 m/s to 10×10 m/s. The changes of circulations are all related to the increase of a bottom friction and a vertical viscosity due to the tidal forcing. The temperature and salinity of the model are also significantly affected by the tidal forcing through the enhanced bottom friction, mixing and the changes in mean circulation. The largest changes occur in the coastal regions, where the water is cooled and freshened. In the open ocean, the changes are divided into three layers: cooled and freshened on the surface and below 3 000 m, and warmed and salted in the middle in the open ocean. In the upper two layers, the changes are mainly caused by the enhanced mixing, as warm and salty water sinks and cold and fresh water rises; whereas in the deep layer, the enhancement of the deep overturning circulation accounts for the cold and fresh changes in the deep ocean. [ABSTRACT FROM AUTHOR]

• The energy-based estimation includes internal tides generated locally and remotely. • Elevated tidal dissipation and mixing occurred near Madagascar Island. • Majority of energy radiated from the continental slope dissipates in the deep ocean. The semi-diurnal internal tidal energetics near Madagascar Island in the Southwest Indian Ocean were analyzed based on a numerical simulation. The baroclinic energy budget revealed that internal tides radiating from the north of Madagascar Island (NMI) and the south of Madagascar Island (SMI), especially those from the continental slope, were the dominant energy sources of the baroclinic energy dissipation in the deep ocean of surrounding areas. In NMI and SMI, the most intense baroclinic energy dissipation and internal tide-induced diapycnal mixing occurred near ridges and seamounts, with depth-integrated energy dissipation of O (10-1-100) W·m−2, dissipation rates of O (10-7-10-6) W·kg−1 and diapycnal diffusivity of O (10-3-10-2) m2·s−1, about one order of magnitude larger than those in most areas of the Mozambique Channel near the 200-m isobath. These estimates based on the numerical simulation were comparable with previous results based on microstructure measurements or fine-scale parameterizations, and suggested that the remotely generated internal tides played an important role in the baroclinic energy dissipation in the deep ocean. [ABSTRACT FROM AUTHOR]

Tidal fronts are associated with the transition between homogeneous and vertically stratified water and are characterized by the simultaneous availability of light and nutrients that enhance the growth of marine productivity. We study the variability in the position of two tidal fronts located in Patagonia Argentina: the San Matías and Valdés fronts. The rate of tidal dissipation in these regions is among the highest of the world oceans. The study is based on the analysis of over 1200 satellite derived sea surface temperature images. The results indicate that the mean monthly position of both fronts is strongly linked to the characteristics of the bottom topography. In response to increasing surface heat flux the fronts displace toward shallower areas. Similarly, a slight displacement towards deeper waters is observed when the heat flux decreases. High frequency variability is revealed by the standard deviation around monthly averages. At the mouth of the San Matías gulf, the front location variability in the spring–neap cycle is around 10 km, while east of the Valdés Peninsula the fortnightly cycle is masked by high frequency fluctuations (~30 km) governed by meanders and meso-scale filaments. A simple conceptual model is proposed which suggests that the mean frontal position is determined by the bottom topography while its seasonal variability is driven by the surface heat flux, and the front intensity is modulated by the spring–neap transition. [ABSTRACT FROM AUTHOR]

Amos, C.L.; Martino, S.; Sutherland, T.F., and Al Rashidi, T., 2015. Sea surface temperature trends in the coastal zone of British Columbia, Canada. Coastal sea surface temperature (SST), measured daily at the British Columbia (BC) Lighthouse network of stations, has been analyzed in this paper. A network of 14 of the 27 stations had (near) continuous data sets. These stations were clustered previously into exposed (northern/outer) and sheltered (southern/inner) sites. SST trends, evaluated between 1973 and 2010, show that the temperature contrast between these clusters is becoming greater: The northern/exposed stations are strongly influenced by interdecadal (Pacific Decadal oscillation [PDO]) and multidecadal oscillations in the north Pacific that are coherent with HadISST1.1 data for the region. There is no statistically significant warming trend for this region. The stations in the Strait of Georgia are much less influenced by the PDO and show a statistically significant mean increase in SST of up to 0.56°C/decade (Anomaly 1). This is higher than the global average and contrasts markedly with the trends from the northern stations. The warming trends of the southern stations are significant at all months of the year but are most evident during summer (July-September). The summertime anomalies in temperature at Active Pass are significantly correlated ( p < 0.001) with the temperature of the Fraser River water. Temperature differences between the Strait of Georgia and the outer shelf (Anomaly 2) are increasing in time; this is particularly evident since 2000. Monthly averaged MODIS satellite data (4×4-km resolution) show that trends in SST at two selected sites in the Strait of Georgia are very similar to the BC Lighthouse measurements and support the spatial extrapolation of the Lighthouse measurements. At present rates of SST rise, the southern coastal waters of BC will be about 3°C warmer by the end of the 21st century. [ABSTRACT FROM AUTHOR]

A physical-biological coupled model was used to estimate the effect of the physical processes at the Strait of Gibraltar over the biogeochemical features of the Atlantic Inflow (AI) towards the Mediterranean Sea. This work was focused on the seasonal variation of the biogeochemical patterns in the AI and the role of the Strait; including primary production and phytoplankton features. As the physical model is 1D (horizontal) and two-layer, different integration methods for the primary production in the Biogeochemical Fluxes Model (BFM) have been evaluated. An approach based on the integration of a production-irradiance function was the chosen method. Using this Plankton Functional Type model (BFM), a simplified phytoplankton seasonal cycle in the AI was simulated. Main results included a principal bloom in spring dominated by nanoflagellates, whereas minimum biomass (mostly picophytoplankton) was simulated during summer. Physical processes occurring in the Strait could trigger primary production and raise phytoplankton biomass (during spring and autumn), mainly due to two combined effects. First, in the Strait a strong interfacial mixing (causing nutrient supply to the upper layer) is produced, and, second, a shoaling of the surface Atlantic layer occurs eastward. Our results show that these phenomena caused an integrated production of 105 g C m − 2 year − 1 in the eastern side of the Strait, and would also modify the proportion of the different phytoplankton groups. Nanoflagellates were favored during spring/autumn while picophytoplankton is more abundant in summer. Finally, AI could represent a relevant source of nutrients and biomass to Alboran Sea, fertilizing the upper layer of this area with 4.95 megatons nitrate year − 1 (79.83 gigamol year − 1 ) and 0.44 megatons C year − 1 . A main advantage of this coupled model is the capability of solving relevant high-resolution processes as the tidal forcing without expensive computing requirements, allowing to assess the effect of these phenomena on the biogeochemical patterns at longer time scales. [ABSTRACT FROM AUTHOR]