The ocean tides are a key driver of a range of Earth system processes. Tidal energy drives vertical mixing with consequences for ocean circulation, climate, and biological production, and the tidal stream transport sediments, pollutants, and other matter through the ocean. On long time-scales tidal drag acts to slow down Earth’s spin, which means the Moon must move away from Earth to conserve angular momentum. The problem here is that the age of the moon doesn’t fit today’s recessions rate and it has been suggested that the tides must have been much weaker for prolonged periods of Earth’s history. Numerical modelling efforts over the past decade have shown that the tides today are very large and a poor representation of past tides, and that for the past 1.5 Gyr, tidal dissipation rates have been around 45% of present-day values. Here, we present a new series of high-resolution simulations of Phanerozoic tides and discuss sensitivity to topography, forcing, and ocean stratification. The results confirm previous results about dissipation rates obtained at lower resolution. Furthermore, we apply proxies for tides collated from the geological literature for three selected periods (the Devonian, Jurassic, and Cretaceous) and show that our simulations mostly conform well with the proposed tidal characteristics from the proxies. The simulations also show that the most important controller of tides on long scales is tectonics: the locations of the continents set the size of ocean basins, and basins of the right size can host very large tides due to tidal resonance. Consequently, the supercontinent cycle generates a corresponding supertidal cycle with weak tides during supercontinent stages and a series of tidal maxima during the dispersion and assembly of the supercontinent.

How to cite: Green, M., Guo, B., Perez, I., Byrne, H., and Hadley-Pryce, D.: 1.5 Gyr of tides: how inaccurate are deep-time tidal model simulations?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4535, https://doi.org/10.5194/egusphere-egu23-4535, 2023.

Ever since the Moon formed close to the Earth, it has been forced by tidal interactions to drift away through orbital angular momentum pumping. Available geological data provide snapshots of the lunar orbital history, the earliest registered to date at ~3.2 Ga. However, a complete theoretical reconstruction of the lunar orbit, which traces its evolution from the present state to a post-impact nosy neighbor at ~4.5 Ga was missing. Namely, previous tidal models attempting this reconstruction are either empirical, or numerically costly, and are always incompatible with the well-constrained lunar age. We undertake a systematic exploration of the time-varying tidal dissipation in the Earth’s oceans and solid interior to provide, for the first time, a history of the lunar orbit that fits the present measurement of its recession and the estimated lunar age. Our work extends a lineage of earlier works on the semi-analytical treatment of fluid tides on varying bounded surfaces, allowing us to mimic the time-varying effect of continentality on Earth. We further couple the oceanic response with solid bodily tidal deformations using an Andrade rheology. The modeled oceanic tidal response is effectively barotropic and is parametrized by only two parameters describing the oceanic thickness and the timescale of dissipation. Our resulting tidal response reconstructs a history of the lunar orbit that is predominantly shepherded by robust resonant excitations in the Earth’s paleo-oceans. This lunar orbital reconstruction is in good agreement with the available geological proxies, which predicates the dominance of long-wavelength flows in controlling the tidal history, instead of the continentality-driven basin modes. The generated tidal resonances caused significant and, relatively, rapid variations in the lunar semi-major axis, the Earth’s length of the day, and the Earth’s obliquity. Consequently, these astronomical features should have driven significant paleo-climatic variations through tidal heating and the changing insolation.

How to cite: Farhat, M., Auclair-Desrotour, P., Boué, G., and Laskar, J.: The resonant tidal evolution of the Earth-Moon distance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14664, https://doi.org/10.5194/egusphere-egu23-14664, 2023.

Sessile intertidal organisms are exposed to extreme variations in conditions during exposure (e.g., solar heating and desiccation) that can affect their health and development – and cause mass mortality events. Exposure is strongly dependent on the tides, which locally and regionally vary in magnitude, character, and phasing. Using the blue mussel Mytilus edulis as an example species, we hypothesise that organisms at locations that experience the lowest low tides during the middle of the day experience stronger heating than organisms at locations where the lowest tides occur during the early morning and early evening. In order to test this hypothesis, biomimetic loggers were calibrated to estimate mussel thermal characteristics and placed at two macro-tidal shores (North and South Wales, UK) dominated by semi-diurnal tides, which have a tidal phase difference of ~4 hours. At both locations, the highest temperatures were recorded when low tides occurred in the middle of the day; however, significantly higher temperatures were found for South Wales where spring low tides occur in the middle of the day and exposure durations are longer, whereas midday low tides in North Wales coincide with neap tides and shorter exposure durations. Our results suggest that heat stress for intertidal organisms may be more severe in intertidal areas where spring low tides occur in the middle of the day when solar radiation and air temperature are greatest. A global outlook will also be presented depicting potential high-risk zones for mussels and other sessile organisms. These results may be of importance for shoreline management and shellfish cultivation, especially with regards to future changing climate.

How to cite: Robins, P., Wilmes, S., Perks, E., Gimenez, L., and Malham, S.: The impact of tidal phasing on intertidal heat stresses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5875, https://doi.org/10.5194/egusphere-egu23-5875, 2023.

Internal tides, internal waves of tidal frequency, are generated by the flow of barotropic tidal currents over topography. Arabian Sea is a region of the northwestern Indian Ocean bounded to the east by the Indian peninsula. Though Arabian Sea and Bay of Bengal reside almost at the same latitudinal belt yet there is difference in the tide’s properties at the two basins. Internal tides in the Arabian Sea are complex and recent modeling studies have suggested that the semidiurnal internal tides show the largest seasonal variability among other regions in the world. However, the generation and propagation mechanism of internal tides, as well as their temporal variability, are unknown in this region. Therefore, we used in-situ observations collected at AD09 (8°N, 73°E) from November 2018 to December 2019 in this study. Salinity has a major role in governing the near-surface stratification, whereas temperature fluctuations govern the subsurface stratification at this location. The rectilinear zonal flow dominates the ellipticity of both semidiurnal and diurnal motions, indicating the generation of internal tides at the slopes. The maximum isopycnal displacement is observed during April at 100 m depth. Furthermore, the semidiurnal barotropic tides rotates in the clockwise direction, while the diurnal rotates in a counter-clockwise direction. Moreover, baroclinic semidiurnal tidal currents rotate anticlockwise at all depths, whereas diurnal tidal currents rotate both clockwise and anticlockwise at various depths. The strongest baroclinic currents, based on the magnitude of the semi-major axis for K₁ are found near 100 m, dominated by rectilinear flow, whereas for M₂, they are found at depths below 125 m. The maximum kinetic energy of the internal wave is observed at 90 m depth, and the analysis shows both diurnal and semidiurnal frequency dominates in the Arabian Sea, as the constituents M₂, S₂, K₁, and O₁ forms the most energetic part of the spectrum. In contrast, on the eastern part of the Indian peninsula in the Andaman Sea and Bay of Bengal, semidiurnal frequency dominates. Arabian Sea exhibits remarkable seasonal variability driven by the Indian monsoon system and seasonal variations in stratification influence the properties of internal tides in this basin. Hence, the study provides a major insight into the characteristics of internal tides over eastern Arabian Sea region.

How to cite: Makar, P., Rao, A. D., Badarvada, Y., and Pant, V.: Study of Internal Tides characteristics in the Eastern Arabian Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13066, https://doi.org/10.5194/egusphere-egu23-13066, 2023.

Low-frequency non-astronomical changes of ocean tides of (1 cm) have been documented in water level measurements around the globe, but their causative mechanisms remain poorly understood in many cases. While anthropogenic developments (e.g., harbor dredging) are certainly a leading factor at individual sites, the spatially coherent tidal variability seen in areas with distributed tide gauge information is revealing of natural processes. Here we use a general circulation model, configured on a 1/12° horizontal grid, to spatially map the influence of ocean stratification changes on the global M₂ tide from 1993 to 2019. We partition the problem into separate yearly simulations of short duration (40 days) and relax each forward integration to the year’s “true” stratification, as provided by an eddying ocean reanalysis. The simulations reveal typical stratification-driven M₂ amplitude changes of 0.5 cm on interannual time scales, as calculated at positions of 40 coastal tide gauges in three particular regions (New Zealand & Australia, Florida & Gulf of Mexico, Northeast Pacific). Most of the identified fluctuations at the coast are present in the barotropic tidal component, suggesting an origin in changing tidal conversion at remote topography or turbulent energy dissipation in shallow water. In addition, we fit linear rates to the yearly M₂ solutions over the 1993–2019 time span and compare the resulting in-phase and quadrature trends to a novel (but still tentative) estimate of M₂ trends in the open ocean from TOPEX-Jason satellite altimetry. The two solutions bear gross resemblance to each other and indicate large spatial-scale trends of ~1 cm cy^-1 in the barotropic M₂ tide in the Indian Ocean, the western and northern Pacific (e.g., in the Gulf of Alaska), and Baffin Bay. Our results highlight that efforts seeking to explain interannual to secular changes of tides at the coast and in the open ocean must consider both sea level rise and contemporary changes in ocean stratification.

How to cite: Opel, L., Schindelegger, M., and Ray, R. D.: Impact of contemporary ocean stratification on the global tides: A preliminary modeling study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11720, https://doi.org/10.5194/egusphere-egu23-11720, 2023.

    Thanks to its current accuracy and maturity, altimetry is considered as a fully operational observing system dedicated to various applications such as climate studies. Altimeter measurements are corrected from several geophysical parameters in order to isolate the oceanic variability and tide correction is one of the most critical. The accuracy of tidal models has been much improved for the last 25 years leading to centimetric accuracy in the open ocean. The last release of the global tidal model, referenced as FES2014b was distributed in mid-2016.

The underlying unstructured mesh resolution of FES2014b was increased in areas of interest like shallow waters and on the slope of the continental shelves, and the error of the pure hydrodynamic ocean solution has been divided by a factor of 2 compared to the previous version (FES2004). Still, some significant errors remain in some regions, due to the omission of compound tides and bathymetric errors (in shelf/coastal seas), seasonal sea ice effects, and lack of available data for assimilation (in the high latitudes).

To address the reduction of these errors and face the new challenges of the tide correction for HR altimetry, in particular, the forthcoming SWOT mission, a new global tide model FES2022 has been developed, focusing particularly on shallow waters and high latitudes.
This new tidal solution uses higher spatial resolution in coastal areas, extending systematically the model mesh to the narrowest coastal systems (fjords, estuaries, …), and the model bathymetry has been upgraded in many places thanks to an international collaboration effort. The hydrodynamic modeling benefits also from further improvements which allow producing very accurate hydrodynamic simulations. The use of the most recent altimeter standards and high inclination altimeters like Cryosat-2, Saral/AltiKa, and even Sentinel-3, also allowed retrieving some tide observations in the highest latitudes to help improving the polar tides modeling.

    Results show a great improvement in the FES2022 hydrodynamic solution compared to FES2014’s one. The assimilation procedure was conducted, and a specific loading tide solution was produced. The final FES2022 tidal solution was validated in comparison to the FES2014b, EOT20, GOT, and TPXO9v5 models, for the missions Jason 3, Sentinel-3A, and Cryosat-2.  Some validations of the new FES2022 tidal current are also presented here.

How to cite: Michel Lionel, T., Florent, L., Loren, C., Mathilde, C., Damien, A., Ergane, F., Mei-ling, D., Ramiro, F., Yannice, F., Gerald, D., and Nicolas, P.: The new FES2022 tidal atlas., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9008, https://doi.org/10.5194/egusphere-egu23-9008, 2023.

With the continued rise in global mean sea level, accurate operational predictions of tidal height and total water levels have become crucial for early warning of potential extreme events in the coastal region. Ocean tides play an important role in extreme sea level events, with high oceanic tides increasing the likelihood of coastal flooding. The Dutch Continental Shelf Model in Flexible Mesh (DCSM-FM) is developed at Deltares to operationally estimate the total water levels to help trigger early warning systems to combat these extreme events along the Dutch coastline. At the boundaries of this model, a tidal forcing is applied from global ocean tide models to better incorporate the ocean tidal height estimations within the model.

In this study, a regional Empirical Ocean Tide model for the Northwest European Continental Sea (EOT-NECS) is developed with the aim to apply better tidal forcing along the boundary of the regional DCSM-FM. EOT-NECS is developed at DGFI-TUM by using thirty years of multi-mission along-track satellite altimetry to derive tidal constituents which are estimated both empirically and semi-empirically. Compared to the previous global iteration, EOT20, EOT-NECS showed a reduction in the root-square-sum error for the eight major tidal constituents of 0.525 cm compared to in-situ tide gauges.

Water levels of DCSM-FM are forced from a number of sources. At the open model boundaries, a combination of water levels from multiple global tide models, an estimation of the surge levels through an Inverse Barometer Correction based on the local atmospheric pressure, and the forcing of the density driven mean sea surface height from a global ocean recirculation model is used. A part of the water level signal is generated within the model domain. This is based on tidal potential within the model domain, meteorological forcing and baroclinic processes. In the 2D depth-averaged version of the model, the contribution of the latter is forced through a static water level field from the 3D version of the model, representing the Mean Dynamic Topography.

When applying constituents from EOT-NECS at the boundaries of DCSM-FM, an overall improvement of 0.42 cm was seen in the root-mean-square error of tidal height estimations made by DCSM-FM, with some regions exceeding a 1 cm improvement. The results demonstrate that there is a large importance in using the appropriate tide model(s) as boundary forcings and in this manuscript, the use of EOT-NECS has a clear positive impact on the total water level estimations made in the northwest European continental seas.

How to cite: Laan, S., Hart-Davis, M., Schwatke, C., Backeberg, B., Dettmering, D., Zijl, F., Verlaan, M., and Seitz, F.: European altimetry-derived tide model for improved tide and water level forecasting along the Dutch Continental Shelf, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1786, https://doi.org/10.5194/egusphere-egu23-1786, 2023.