Abstract. The Solomon Sea is a place of intense Low Latitudes Western Boundary current transiting to the equator where mesoscale activity is superimposed on internal tides. In this marginal sea, the cumulated effects of these dynamical constraints result in water mass transformation as observed by in situ observations. The objective of this paper is to document the M2 internal tides in the Solomon Sea and their impacts based on two regional simulations with and without tides. Because the Solomon Sea is under the influence of ENSO, the characteristics of the internal tides are analyzed for two contrasted ENSO conditions: the 1997–1998 El Niño and the 1999 La Niña. The generation, propagation and dissipation of the internal tides are sensitive to changes in stratification and mesoscale activity between El Niño and La Niña. Mode 1 is the dominant mode to propagate baroclinic tidal energy within the Solomon Sea, but the El Niño conditions, with stratification closer to the surface, are favorable for the propagation of mode 2. The la Niña case with a high level of mesoscale activity favors the appearance of incoherent internal tides. These results illustrate the complexity in predicting internal tides in order to access meso and submesoscale signatures from altimetric missions, including the future SWOT mission. Diapycnal mixing induced by the internal tides is efficient in eroding the salinity maximum of the upper thermocline water, and in cooling the surface temperature interacting with the atmosphere. Such effects are particularly visible far from the strong currents, where particles may experience the tidal effects during a longer time. Nevertheless, the impacts are different when considering particular ENSO conditions. The interaction of internal tides with the surface mesoscale activity reduces surface cooling during El Niño 1998, but increases surface warming during La Niña 1999, with possible impacts on regional air sea interaction.
Time series of sea level heights have been collected at different stations along the Cameroon coast. The dataset covers a period ranging from 2007 to 2012. Tide data measured by float type recorders have been digitalized and quality-controlled with tools developed at Laboratoire d'Etudes Géophysique et Océanographie Spatiale (LEGOS). Short gaps in the data have been interpolated while large gaps were not. Tide constituents were retrieved through harmonic analysis using 123 waves having a period ranging from long ones to eighth-diurnal ones. The reconstructed signal is used to assess the quality of both the data and the analysis and the erroneous records were examined and corrected. The effect of the hourly averaging of the raw data on the quality of the analysis is also investigated. The tide constituents having the largest amplitudes are, as expected, the semi-diurnal, diurnal, fourth-diurnal and long term constituents. The major components of semi-diurnal waves are the M2 and S2 tides. The M2 tide height ranges between 0.5 and 0.85 m. The maximum height is found at Cameroon estuary and the minimum at the Kribi station located in the South coast. The S2 constituent varies similarly as the M2 constituent. Its amplitude ranges between 0.18 and 0.52 m. The lowest S2 amplitude occurs also at Kribi station. In the Dibamba estuary the spectrum shows a larger number of significant semi-diurnal and fourth-diurnal waves than other zones. Concerning diurnal waves, the dominant one is the K1 tide and its amplitude is homogeneous along the coast. The influence of the long-term components is the strongest in the Cameroon estuary due to important fluctuations of the rivers run-off.
Internal tides (ITs) in the Indonesian seas were largely investigated and hotspots of intensified mixing identified in the straits in regional models and observations. Both of them indicate strong mixing up to 10⁻⁴cm/s even close to the surface and show that tides at spring-neap cycle cool by 0.2°C the surface water at ITs’ generation sites.These findings supported the idea of strong and surfaced mixing capable of providing cold and nutrient-rich water favorable for the whole ecosystem. However, it has never been assessed through an ad-hoc study. Our aim is to provide a quantification of ITs impact on chlorophyll-a through a coupled model, whose physical part was validated against the INDOMIX data in precedent studies and the biogeochemical part is compared to in-situ samples and satellite products. In particular, explicit tides’ inclusion within the model improves the representation of chlorophyll and of the analyzed nutrients. Results from harmonic analysis of chlorophyll-a demonstrate that tidal forcing modify spring/neap tides’ variability on the regions of maximum concentration in correspondence to ITs’ génération areas and to plateau sites where barotropic tides produce large friction reaching the surface. The adoption of measured vertical diffusivities explains the biogéochemical tracers’ transformation within the Halmahera Sea and used to estimate the nutrients’ turbulent flux, with an associated increase in new production of ~25% of the total and a growth in mean chlorophyll of ~30%. Hence, we confirm the key role of ITs in shaping vertical distribution and variability of chlorophyll as well as nutrients in the maritime continent.
Tides and internal tides (IT) in the ocean can significantly affect local to regional ocean temperature and even sea surface temperature (SST), via processes such as vertical mixing, vertical advection and transport of water masses. Offshore of the Amazon River, IT have already been detected and studied; however, their impact on temperature, SST and associated processes are not known in this region. In this work, we use high resolution (1/36°) numerical simulations with and without the tides from an ocean circulation model (NEMO) which explicitly resolves the internal tides (IT), to assess how they can affect ocean temperature in the studied area. We distinguish the analysis for two contrasted seasons, from April to June (AMJ) and from August to October (ASO), since the seasonal stratification off the Amazon River modulates the IT’s response and their influence in temperature.  The IT are well reproduced by the model, and are in good agreement with observations, for both their generation and their propagation. The simulation with tides is in better agreement with satellite SST data compared to the simulation without tides. During ASO season, stronger meso-scale currents, deeper and weaker pycnocline are observed in contrast to the AMJ season. Results show that the observed coastal upwelling during ASO season is well reproduced by the model including tides, whereas the no-tide simulation is too warm by +0.3 °C at sea surface. In the subsurface above the thermocline, the tide simulation is cooler by -1.2 °C, and warmer below the thermocline by +1.2 °C compared to the simulation without the tides. The study further highlights that the IT induce vertical mixing on their generation site along the shelf break and on their propagation pathways towards the open ocean. This process explains the cooler temperature at the ocean surface and in the subsurface water above the thermocline and a warming in the deeper layers (below the thermocline). The surface cooling induced in turn an increase of the net heat flux from the atmosphere to the ocean surface, which could induce significant changes in the local and even for the regional tropical Atlantic atmospheric circulation and precipitation. We therefore demonstrate that IT, mainly via vertical diffusivity along their propagation pathways of approximately 700 km offshore, and tides over the continental shelf, play a key role on the temperature structure off the Amazon River mouth, particularly in the coastal cooling enhanced by IT.  
Abstract. The impact of internal and barotropic tides on the vertical and horizontal temperature structure off the Amazon River was investigated during two highly contrasted seasons (AMJ: April–May–June; ASO: August–September–October) over a 3-year period from 2013 to 2015. Twin regional simulations, with and without tides, were used to highlight the general effect of tides. The findings reveal that tides have a cooling effect on the ocean from the surface (∼ 0.3 ∘C) to above the thermocline (∼ 1.2 ∘C), while warming it up below the thermocline (∼ 1.2 ∘C). The heat budget analysis indicates that the vertical mixing is the dominant process driving temperature variations within the mixed layer, while it is associated with both horizontal and vertical advection to explain temperature variations below. The increased mixing in the simulations including tides is attributed to breaking of internal tides (ITs) on their generation sites over the shelf break and offshore along their propagation pathways. Over the shelf, mixing is driven by the dissipation of the barotropic tides. In addition, the vertical terms of the heat budget equation exhibit wavelength patterns typical of mode-1 IT. The study highlights the key role of tides and particularly how IT-related vertical mixing shapes the ocean temperature off the Amazon. Furthermore, we found that tides impact the interactions between the upper ocean interface and the overlying atmosphere. They contribute significantly to increasing the net heat flux between the atmosphere and the ocean, with a notable seasonal variation from 33.2 % in AMJ to 7.4 % in ASO seasons. This emphasizes the critical role of tidal dynamics in understanding regional-scale climate.
