OS4.2 | Tides across the Earth system
EDI
Tides across the Earth system
Co-organized by G3
Convener: Michael Schindelegger | Co-conveners: Sophie-Berenice WilmesECSECS, Michael Hart-DavisECSECS, Stefan Talke, Clément VicECSECS
Orals
| Tue, 25 Apr, 14:00–15:45 (CEST)
 
Room 1.14
Posters on site
| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)
 
Hall X5
Posters virtual
| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)
 
vHall CR/OS
Orals |
Tue, 14:00
Tue, 16:15
Tue, 16:15
Tides play a pervasive role in the Earth system. They supply mechanical energy to fuel ocean turbulent dissipation and mixing, which in turn sustain the meridional overturning circulation, they modulate ice-shelf basal melt rates, cause coastal erosion, affect marine ecosystems and ocean biogeochemistry, and may raise or lower the sea-level baseline for storm surges. There are also tides in the atmosphere, which can impart terrestrial weather and climate variability well into the geospace. Looking down, precise measurements of solid Earth tides and the closely related ocean tidal loading are a unique means of probing Earth's interior and the frequency dependence of viscoelastic properties. Moreover, corrections for ocean tide signals underlie many Earth observation applications, including analyses of satellite altimetry and gravimetry data to determine sea level and ocean mass changes on local to global scales.

This session is open to research on any aspect of tides in the ocean, atmosphere, and solid Earth. We invite contributions on progress in numerical and empirical modelling of surface and internal tides in the ocean, the implications of internal tides for mixing and ocean circulation, modelling and observation of tidal variability, tidal analysis, atmosphere-ionosphere coupling through tides, and research into the role of tides in shaping Earth's ability to host life. Contributions may highlight tidal processes at any spatial and temporal scale on Earth and other planets.

Orals: Tue, 25 Apr | Room 1.14

Chairpersons: Michael Schindelegger, Sophie-Berenice Wilmes
14:00–14:05
14:05–14:25
|
EGU23-4535
|
solicited
|
Highlight
|
On-site presentation
Mattias Green, Bin Guo, Iael Perez, Hannah Byrne, and David Hadley-Pryce

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.

14:25–14:35
|
EGU23-14664
|
ECS
|
Highlight
|
On-site presentation
Mohammad Farhat, Pierre Auclair-Desrotour, Gwenaël Boué, and Jacques Laskar

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.

14:35–14:45
|
EGU23-5875
|
On-site presentation
Peter Robins, Sophie Wilmes, Emily Perks, Luis Gimenez, and Shelagh Malham

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.

14:45–14:55
|
EGU23-13066
|
ECS
|
On-site presentation
Pragnya Makar, Ambarukhana Devendra Rao, Yadidya Badarvada, and Vimlesh Pant

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.

14:55–15:05
|
EGU23-13302
|
ECS
|
Virtual presentation
|
|
Friederike Pollmann, Jonas Nycander, Carsten Eden, and Dirk Olbers

Energetically consistent parameterizations of small-scale turbulent mixing rely on internal gravity wave energetics. A crucial ingredient is the generation of internal waves by the interaction of the barotropic tide with rough seafloor topography. Owing to the orientation of topographic obstacles and the directionality of barotropic tidal currents, this process is inherently anisotropic, but so far, this dependence on horizontal direction was not taken into account in global estimates of internal tide generation. We present the global application of a new method based on linear theory that resolves the horizontal direction of the internal tide generation, showing the substantial anisotropy of this process. How this in turn affects vertical mixing and the ocean state is evaluated with the aid of the internal gravity wave model IDEMIX, a backbone of energetically consistent parameterizations of wave-induced mixing.

How to cite: Pollmann, F., Nycander, J., Eden, C., and Olbers, D.: The anisotropy of internal tide generation: Global estimates for the M2 tide and implications for tidally driven mixing parameterizations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13302, https://doi.org/10.5194/egusphere-egu23-13302, 2023.

15:05–15:15
|
EGU23-11720
|
ECS
|
On-site presentation
Lana Opel, Michael Schindelegger, and Richard D. Ray

Low-frequency non-astronomical changes of ocean tides of O(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.

15:15–15:25
|
EGU23-9008
|
Virtual presentation
Tchilibou Michel Lionel, Lyard Florent, Carrere Loren, Cancet Mathilde, Allain Damien, Fouchet Ergane, Dabat Mei-ling, Ferrari Ramiro, Faugere Yannice, Dibarboure Gerald, and Picot Nicolas

    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.

15:25–15:35
|
EGU23-1786
|
ECS
|
On-site presentation
Stendert Laan, Michael Hart-Davis, Christian Schwatke, Björn Backeberg, Denise Dettmering, Firmijn Zijl, Martin Verlaan, and Florian Seitz

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.

15:35–15:45
|
EGU23-825
|
ECS
|
On-site presentation
|
Adam Ciesielski, Thomas Forbriger, Walter Zürn, and Andreas Rietbrock

Since the times of Doodson it has been established that a record of length T is required to resolve tidal harmonics with a frequency separation 1/T. This rule, known as Rayleigh criterion, does not consider the actual resolution provided by the signal-to-noise ratio of the data. Available tidal analysis software, like Eterna, seek gravimetric parameters for a priori defined groups (sums) of harmonics that are assumed otherwise indistinguishable. The residual between the predicted tidal signal for groups and the recording is minimized with simple least squares (LS) fit.

We developed the new software, RATA, that abandons the concept of groups, so each tidal harmonic present in the catalogue receives its set of tidal parameters that are free to vary. The resulting ill-conditioned matrix is stabilized by Tikhonov regularization (ridge regression) in the LS objective function. To validate the results, we used the moving window analysis (MWA) technique for a priori groups, with the resulting local response model as the a priori model. Compared to the standard approach, which used the Wahr-Dehant-Zschau elastic analysis model, we clearly see that bias and beating patterns are significantly smaller or almost vanish. Hence, the local response model can capture the apparent temporal variations by appropriate tidal parameters within the MWA groups.

While the most information in each group is carried by the tidal wave with the largest amplitude, influence of other harmonics must be properly considered in estimated amplitudes and phases. Therefore, if amplification factor or phase from any other large amplitude harmonic in the group is significantly different from the expectation, the grouping parametrization might lead to an inaccurate (biased) estimate of tidal parameters. The trade-off parameter between data residuals and the model difference to the reference model is chosen at the corner of the misfit curve, indicating expected level of noise in the data. The resulting model parameters indicate “data-driven” groups to be inferred from significant harmonics in the inversion. To demonstrate the method and how it may be used to reveal system properties hidden by wave grouping, we analyzed 11.5 years gravity recordings from the superconducting gravimeter SG056 at the BFO (Black Forest Observatory, Schiltach). As a result, we distinguished 61 significant groups of harmonics for the local tidal response model, with no clear evidence that more groups are resolvable. Some of them highly violate Rayleigh criterion.

How to cite: Ciesielski, A., Forbriger, T., Zürn, W., and Rietbrock, A.: Regularization Approach to Tidal Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-825, https://doi.org/10.5194/egusphere-egu23-825, 2023.

Posters on site: Tue, 25 Apr, 16:15–18:00 | Hall X5

Chairpersons: Michael Hart-Davis, Michael Schindelegger
X5.361
|
EGU23-3227
|
ECS
Iael Perez, J. A. Mattias Green, Justyna Bulawa, Amy Ewing, Laura A. M. Fitzgerald, Jennifer M. Hewitt, and Olivia Pampaloni

Recent numerical tidal modelling efforts strongly suggest that present day tides are anomalously large in comparison to the tides over the past 1.5 Gyr. Whilst these results can be qualitatively explained from dynamical principles, there are only a few quantitative validations of deep-time tidal simulations done using tidal proxies. One reason for this is a lack of easily accessible proxies for tides and something we are proposing to rectify here. Through extensive literature searches, we have identified over 600 publications containing potential tidal proxies and processed around 300 of them to date.

From the literature, we have identified proxies for three tidal properties. Under favourable circumstances, the geological record can provide direct estimates of the tidal range. These situations are rare (~10 papers have this information to date), but it is the best proxy for validation purposes. Tidal currents can be constrained by indirect methods. The presence of black shales indicates a poorly ventilated water column, which in turn is a sign of weak tides. By plotting the location of tidal mixing fronts and ensuring that they are located so black shales end on the stratified side of the front, we have a potential proxy for large-scale tidal current speeds. Tidal currents can also be constrained locally by investigating the dimensions of current ripples in the sediments. Finally, day-length, which is directly linked to global tidal dissipation rates, can often be inferred from the variation and cyclicity in layer composition and thickness in tidalites. These are vertically accreted laminated facies of a succession of couplets composed of sand and clay or silt and clay, with thicknesses of millimeters to centimeters, and they are at the heart of our inventory. Further potential proxies involve using paleobiology to track ranges of intertidal species (to obtain tidal ranges) and use microfossil assemblages as another mean of tracking tidal mixing from (and hence constrain current speed). As a proof-of-concept application, we revisit tidal model simulations from five deep-time slices showing that the methods we propose are viable as tidal proxies. The model simulations and proxies usually agree within the uncertainties of both methods.

The database will be made available to the community once the information currently in it has been quality controlled and used in our initial publications. Furthermore, any information that may be of use is welcome and we would love to hear about any potential tidal proxies you may have.

How to cite: Perez, I., Green, J. A. M., Bulawa, J., Ewing, A., Fitzgerald, L. A. M., Hewitt, J. M., and Pampaloni, O.: The tidal proxy database: development, application, and a call for help, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3227, https://doi.org/10.5194/egusphere-egu23-3227, 2023.

X5.362
|
EGU23-9698
Sophie-Berenice Wilmes, Vivi Kathrine Pedersen, Michael Schindelegger, and Mattias Green

Simulations of the tides from the Last Glacial Maximum (26.5 – 19 kyr BP) to the present show large amplitude and dissipation changes, especially in the semi-diurnal band during the deglacial period. New reconstructions of global ice sheet history and sea levels covering the last glacial cycle allow us to extend the tidal simulations from the last interglacial (~125 kyr BP) to the present. Climate during this period was far from stable with periods of ice sheet advance and lower sea levels interspaced with ice sheet melting and sea level increases. Here, using the sea level and ice history from Gowan et al. (2021; 80 kyr BP to present) and sea level simulations based on the ICE6G_C ice history (Peltier et al., 2015; 122 kyr BP to present), we present simulations of tidal amplitudes and dissipation over the last glacial cycle using the tide model OTIS for the tidal constituents M2, S2, K1 and O1. Our results show large variations in amplitudes and dissipation over this period for the M2 tidal constituent with several tidal maxima, whereas for the other constituents, changes are mainly regional. Due to the lower sea levels and altered bathymetry, open ocean dissipation was enhanced with respect to present day levels for most of the glacial cycle for all constituents. This result is important in the context of historical ocean mixing rates. We further highlight the impacts of the differences in bathymetry and ice sheet reconstructions on global tidal dissipation.

Gowan, E.J., Zhang, X., Khosravi, S., Rovere, A., Stocchi, P., Hughes, A.L., Gyllencreutz, R., Mangerud, J., Svendsen, J.I. and Lohmann, G., (2021), A new global ice sheet reconstruction for the past 80 000 years, Nature Communications, 12(1), 1-9.

Peltier, W. R., Argus, D. F., and Drummond, R. (2015), Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model, J. Geophys. Res. Solid Earth, 120, 450– 487, doi:10.1002/2014JB011176.

How to cite: Wilmes, S.-B., Pedersen, V. K., Schindelegger, M., and Green, M.: Evolution of tides and tidal dissipation over the last glacial cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9698, https://doi.org/10.5194/egusphere-egu23-9698, 2023.

X5.363
|
EGU23-17440
Michael Schindelegger

The lunar semidiurnal (M2) tide of the Gulf of Maine and Bay of Fundy is remarkable not only for its large amplitude but also for its spatially coherent temporal changes of ∼1–3 cm on secular to seasonal time scales. Previous work suggests a role for ocean stratification in causing the tide's seasonal modulation, while the forcing factors for lower-frequency M2 variability are yet unknown. Here I show, using a regional baroclinic modeling framework, that changes in ocean stratification also matter on interannual time scales and account for ∼40% of the observed M2 changes at tide gauges from 1994 to 2019. Masking experiments and energy diagnoses reveal that the modeled variability is primarily driven by fluctuations in barotropic-to-baroclinic energy conversion on the continental slope south of the gulf's mouth, with a ∼7% (0.30 GW) drop in the area-integrated conversion rate inducing a 1-cm amplitude increase along the Massachusetts coast. Evidence is given for the same process to have caused the near-monotonic M2 amplitude decrease throughout the 1980s, as slope waters warmed due to a northerly shift of the Gulf Stream. I present results from model-based M2 projections for the end of the 21st century and highlight possibly competing roles of stratification changes and sea level rise in driving the tide's response to future climate change.

How to cite: Schindelegger, M.: On seasonal to secular M2 variability in the Gulf of Maine, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17440, https://doi.org/10.5194/egusphere-egu23-17440, 2023.

X5.364
|
EGU23-1886
Andreas Boesch

The German Federal Maritime and Hydrographic Agency (BSH) operates the Tidal Information Service that is responsible for producing and publishing tidal predictions for German waters. Traditionally, the predictions are produced for tide gauge locations, which are situated almost exclusively at or close to the coastline. Water level observations from the tide gauges are used as input data for the respective tidal analyses. BSH strives to extend these point-wise predictions to an area-wide data set for the German Bight based on simulated water levels. This shall serve the increasing demands in the context of research, shipping and offshore activities. High quality area-wide tidal data might also be usable for the reduction of measurements from satellite altimetry in this region.

We present tidal analyses based on simulated water levels using the hydrodynamic-numerical model HBM. This model runs operationally at BSH. Many grid points that cover the Wadden Sea run dry around low water and require special attention in the analyses. Tidal parameters, such has the mean lunitidal intervals and tidal ranges, are compared with data from tide gauges. One challenge is the harmonisation of tidal predictions based on model data with those based on tide gauge observations, in order to produce consistent products. The results from this work could also help to improve the implementation of tides in HBM in the future.

How to cite: Boesch, A.: Towards area-wide operational tide predictions for the German Bight, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1886, https://doi.org/10.5194/egusphere-egu23-1886, 2023.

X5.365
|
EGU23-1260
|
ECS
Michael Hart-Davis, Richard Ray, Loreto Bordas Diaz, Christian Schwatke, Denise Dettmering, and Florian Seitz

 

Ocean tide models are created for a variety of applications ranging from serving as an altimetry correction to being applied as numerical model boundary forcings. DGFI-TUM’s Empirical Ocean Tide (EOT) and NASA's Goddard Ocean Tide (GOT) models are derived based on sea-level anomalies (SLA) from multi-mission satellite altimetry. All SLA measurements are corrected for geophysical effects, which means that the estimations of tides are reliant on the accuracy of these respective correction models. Within these corrections, tidal signals or frequencies that align closely with those of tides may be present which have clear downstream implications on the derivation of ocean tides from along-track satellite altimetry. 

In this study, the two different ocean tide models have been used as they utilise different techniques for tidal estimations but both are dependent on the chosen altimetric corrections. In the global EOT20 model, altimetric corrections played an important role in improving the accuracy of the model in the coastal region. However, these coastal optimised corrections may be influencing the open ocean performance of the model. This has meant that further investigations should take place to describe the best set of altimetry corrections to optimise the accuracy of tide estimations made by the EOT model in all regions. Additionally, several versions of the GOT model have been developed to contrast the influences of the different corrections both for the open ocean and coastal regions. 

In this presentation, the impact of different geophysical corrections (e.g. ionospheric, internal tide and mesoscale) are presented with the aim to conclude on the optimal set-up of these corrections for empirical tide models. Results here are shown in different experiments that include assessing the impacts of ocean tide estimations on both along-track as well as modelled estimations.

How to cite: Hart-Davis, M., Ray, R., Bordas Diaz, L., Schwatke, C., Dettmering, D., and Seitz, F.: Towards the optimisation of altimetry corrections for improved ocean tide modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1260, https://doi.org/10.5194/egusphere-egu23-1260, 2023.

X5.366
|
EGU23-6410
|
ECS
Nataline Simon, Pierre Jamin, Alain Dassargues, Frédéric Nguyen, David Caterina, and Serge Brouyère

For a long time, characterization of aquifers has been mainly based on the monitoring of groundwater heads variations. This approach allowed to demonstrate that pressure changes induced by earth tides have a significant and measurable impact on groundwater heads monitored in confined aquifers. Nowadays efficient methods provide a direct estimation of groundwater fluxes. This is the case of the Finite Volume Point Dilution Method (FVPDM), a single-well tracer experiment that allows continuously monitoring and quantifying groundwater flux variations over time. Yet, the potential effect of earth tides on local groundwater flow has never been investigated. In this context, FVPDM tests have been performed in a confined aquifer in order to monitor groundwater fluxes over several tidal cycles. Results show significant groundwater flux variations over time (around 20% of the flux value), clearly correlated with pressure changes induced by earth tides. Subsurface heterogeneities could explain the fact that earth tides induce groundwater flow variations. Indeed, groundwater heads variations induced by earth tides depend on the local specific storage (in confined conditions) of aquifer. Any spatial variation of this parameter could induce variations of the hydraulic gradient and thus of groundwater fluxes. Therefore, these preliminary observations seem to open new perspectives for subsurface characterization by showing how groundwater flow variations measured in confined aquifer and induced by earth tides can be used as a marker of subsurface heterogeneities.

How to cite: Simon, N., Jamin, P., Dassargues, A., Nguyen, F., Caterina, D., and Brouyère, S.: Observations of the effect of earth tides on groundwater fluxes variations at the scale of a borehole, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6410, https://doi.org/10.5194/egusphere-egu23-6410, 2023.

Posters virtual: Tue, 25 Apr, 16:15–18:00 | vHall CR/OS

vCO.11
|
EGU23-5480
|
ECS
Marios Nikolaidis and Chris Danezis

Tide gauges remain the fundamental instrument for the determination of the absolute sea level and its variation over time. Following the establishment of the PYTHEAS national tide gauge network, which consists of five tide gauge stations located in strategic positions along the coastline of the government-controlled areas of the Republic of Cyprus, sea level observations were collected and analyzed. The main objective of this research is the determination, for the first time, of the most important tidal datums to support hydrographic surveying activities and promote critical environmental studies, such coastal erosion. Through the analysis of the data the following tidal datums were determined: Mean Sea Level (MSL), Mean Tide Level (MTL), Mean High Water (MHW), Mean Higher High Water (MHHW), Mean Low Water (MLW), Higher High Water (HHW) and Lower Low Water (LLW). These datums were estimated from sea level observations collected over the time span between January 2018 to April 2022. The dataset underwent through a complete quality control procedure, which was designed according to the latest international standards and included, among others, the influence of the tide gauge stability and the barometric pressure on the time series, and the detection and elimination of outliers. Furthermore, a thorough harmonic analysis was carried out, by means of the Harmonic Analysis Method of Least Squares (HAMELS), on the sea level observation dataset to highlight the effect periodic motions of the Earth, Sun and Moon have on local tide. In the context of this research, a total number of 68 tidal constituents were identified. Moreover, by using the Doodson X0 filter, the astronomical impact on the sea level was estimated by separating the astronomical influence component from the meteorological residuals. Data processing and analysis were carried out using custom in-house developed software. Finally, the estimated mathematical values of the tidal constituents, each of which describe a specific cosine curve, were utilized to calculate a tidal prediction up to December 2026.

How to cite: Nikolaidis, M. and Danezis, C.: Determination of Tidal Datums and Tide Characterization and Prediction in Cyprus via the PYTHEAS National Tide Gauge Network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5480, https://doi.org/10.5194/egusphere-egu23-5480, 2023.