Ocean Tides Research Articles

Elastic deformation plays a non-negligible role in Greenland\u2019s outlet glacier flow

Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. Here we study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities.

Self-attraction and loading feedback on ocean dynamics in both shallow water equations and primitive equations

We introduce the effects of self-attraction and loading (SAL) to the momentum equations of a barotropic global ocean tide model as well as a baroclinic general circulation model. We show for the M2 tidal dynamics, that an explicit treatment of SAL is favourable compared to a scalar approximation or even disregarding the effects all together. For the general circulation the influence on the ocean bottom pressure is shown to be about 1 hPa for short time periods along the coasts and about 0.5 hPa for longer periods in resonant basins in the southern ocean. In contrast to previous studies, we additionally examine the effects of surface pressure anomalies over the continents in the computation of SAL which is shown to have an influence of about 0.5 hPa along the coasts. With those results, we demonstrate that the explicit treatment of SAL is important for satellite applications.

Comparison of GPS-derived ocean tide loading displacements with models in New Zealand

ABSTRACT We investigate the tidal displacement signals of two principle semidiurnal () and diurnal () tidal constituents in New Zealand. We calculate the predicted loading displacements using the latest ocean tide models and Earth models. The results show that, for the constituent, the tide models FES2014b and TPXO9-Atlas have subtle differences, and the vector differences between the Earth models shows that the regularity of the influence of the Earth model is weak. The vector difference of constituent have significant spatial coherence (about 0.2 mm). The residuals of constituent in the up component subtract about 0.2 mm across the entire areas after considering the anelastic dispersion. We find that the clear regional-scale spatial coherence of the residuals exists in both constituents in all models even if spatial water density and compressibility have been considered. However, the spatial coherence of residuals disappears when the network-mean value removed, and the reduction of RMS for constituent is close to the theoretical error of body tide (about 0.5 mm). We also find that for the different ocean tide models, part of the differences in residuals between the observations and predictions would be attributed to the choice of geocentric reference frame.

Analytical Calculations of Some Effects of Tidal Forces on Plants on the International Space Station

Among the phenomena attributable to the Moon’s actions on living organisms, one of them seems to be related to analytical fluid mechanics: along the route of the International Space Station around the Earth, experiments on plants have revealed leaf oscillations. A parametric resonance due to a short period of microgravitational forces could explain these oscillations. Indeed, Rayleigh-Taylor’s instabilities occurring at the interfaces between liquid-water and its vapor verify a second-order Mathieu differential equation. This is the case of interfaces existing in the xylem channels of plant stems filled with sap and air-vapor. The magnitude of the instabilities depends on the distances between the Moon, the Sun, and the Earth. They are analogous, but less spectacular, to those that occur during ocean tides.

The sensitivity of ocean tide loading displacements to the structure of the upper mantle and crust of Taiwan Island

Ocean tide loading (OTL) displacements are sensitive to the shallow structure of the solid Earth; hence, the high-resolution spatial pattern of OTL displacement can provide knowledge to constrain the shallow Earth structure, especially in coastal areas. In this study, we investigate the sensitivity of the modeled M2 OTL displacement over Taiwan Island to perturbations of three physical quantities, namely, the density, bulk modulus, and shear modulus in the upper mantle and crust. Then, we compare the sensitivity of the modeled M2 OTL displacement to Earth models with the sensitivity to ocean tide models using root mean square (RMS) differences. We compute the displacement Green’s function and OTL displacement relative to the center of mass of the solid Earth (CE) reference frame, analyze the sensitivity to the three physical quantities in the CRUST1.0 model and the Preliminary Reference Earth Model (PREM), and present their spatial patterns. We find that displacement Green’s functions and OTL displacements are more sensitive to the two elastic moduli than the density in the upper mantle and crust. Moreover, their distinctive sensitivity patterns suggest that the three physical quantities might be constrained independently. The specific relationships between the perturbed structural depths and the distance ranges of peak sensitivities from the observation points to the coastline revealed by the shear modulus can mitigate the nonuniqueness problem in inversion. In particular, the horizontal tidal components observed by the Global Positioning System (GPS) can yield better results in inversions than the vertical component owing to the smaller OTL model errors and the higher structural sensitivity (except for the shear modulus in the asthenosphere).

A Century of Tidal Variability in the North Pacific Extracted From Hourly Geomagnetic Observatory Measurements at Honolulu

AbstractPrevious analyses of hourly tide‐gauge data taken at Honolulu since 1905 have shown that both sea level and the amplitude of the tides have increased synchronously over time, and a process has been proposed whereby the common cause is an increase in ocean temperature. Validation with independent data of this change in tides, as well as the proposed cause, has been lacking. Ocean tides also generate magnetic fields that reach far outside the ocean, and tidal signals are clearly seen in the hourly data since 1905 from the Honolulu geomagnetic observatory. Here, it is found that the tidal amplitudes have increased synchronously in the tide‐gauge and magnetic records, providing independent support for the previous results. Further information about the changing ocean is likely contained in the historical data from geomagnetic observatories as well as the global coverage of modern satellite magnetic surveys.

Grounding‐Zone Flow Variability of Priestley Glacier, Antarctica, in a Diurnal Tidal Regime

AbstractTidal modulation of ice streams and their adjacent ice shelves is a real‐world experiment to understand ice‐dynamic processes. We observe the dynamics of Priestley Glacier, Antarctica, using Terrestrial Radar Interferometry (TRI) and GNSS. Ocean tides are predominantly diurnal but horizontal GNSS displacements also oscillate semi‐diurnally. The oscillations are strongest in the ice shelf and tidal signatures decay near‐linearly in the TRI data over 10 km upstream of the grounding line. Tidal flexing is observed 6 km upstream of the grounding line including cm‐scale uplift. Tidal grounding line migration is small and 40% of the ice thickness. The frequency doubling of horizontal displacements relative to the ocean tides is consistent with variable ice‐shelf buttressing demonstrated with a visco‐elastic Maxwell model. Taken together, this supports previously hypothesized flexural ice softening in the grounding‐zone through tides and offers new observational constraints for the role of ice rheology in ice‐shelf buttressing.

Corrosion behavior of reinforcing bars in cracked reinforced concrete pile before and after CFRP wrapping

Due to the drying-wetting cycle caused by the ocean tide, the pre-stressed reinforced concrete (RC) piles serving in the splash zone of the seaport wharf have more serious chloride-induced corrosion problem, resulting in urgent need of repair and maintenance of those RC piles by carbon fibre reinforced polymer (CFRP). In this paper, corrosion behavior of the reinforcing bars in cracked RC pile before and after CFRP wrapping is studied, where the RC piles were simulated by the cylinder specimens with embedded steel bar in the centre. The maximum corrosion crack widths were designed as 0.1mm, 0.15mm, 0.2mm, 0.25mm, and 0.3mm. Before CFRP wrapping, the concrete surfaces were treated by corrosion inhibitor and CFRP wrapping. Results show that, CFRP wrapping repair after corrosion inhibitor treatment and CFRP wrapping directly on the concrete surface, have a good effect on preventing the internal reinforcement from continually being corroded by chloride ions when the corrosion crack width in the concrete cover of the RC specimens is 0.25mm, especially for the former method.

Study on the process of chloride invasion and deposition in concrete under dry-wet cycles and continuous loading

Concrete for marine construction is not only eroded by seawater but also affected by ocean tides. The corrosion of the concrete structure is severe in the tidal range zone and the splash zone under the frequent dry-wet cycles environment. In order to investigate the process of chloride invasion and deposition in concrete under continuous loading, this paper applied pre-loading to concrete samples and evaluated pore distribution, chloride ions invade, and deposition of chlorine salts in concrete samples under dry-wet cycles with the use of salt weighing method, X-ray diffraction (XRD) and micro-CT. The results showed that the chloride salt quickly invaded into the samples under the influence of dry-wet cycles. With dry-wet cycles, chlorine salt is deposited in the pores of the samples, and the amount of chloride salt deposition increased with time. The pre-applied stress loading condition inhibited the salt deposition process. The results of the XRD analysis showed that chloride ions combined with calcium ions and deposited in the cracks and pores of the concrete after penetrating into concrete.

The cabled observatory vent imaging sonar deployed on the Ocean Observatories initiative’s cabled array

The Cabled Observatory Vent Imaging Sonar (COVIS) was installed on the Ocean Observatories Initiative’s Cabled Array observatory at ASHES hydrothermal vent field on Axial Seamount in July 2018. Diffuse hydrothermal flows are identified by maps made using the standard deviation of thephase change between pings separated in time by fractions of 1 s. The results demonstrate significant influences of ocean tides and bottom currents on diffuse hydrothermal discharge. The same data are used to estimate diffuse heat flux, providing two-dimensional maps of heat flux density at a rate of one per day. Sonar data are also used to generate three-dimensional backscatter images of the buoyant plumes above major sulfide structures. These backscatter images show substantial changes in plume bending in the presence of ambient currents and potentially the variations of outflow fluxes. The intensity of acoustic backscatter decreases significantly for highly bent plumes as compared to nearly vertical plumes, reflecting enhanced mixing of plume fluids with seawater driven by ambient currents. A forward model of acoustic backscatter from a buoyancy driven plume yields a reasonable match with the observation, paving the way for inversely estimating the source heat flux of a hydrothermal plume. [Work sponsored by NSF.]

Hydro-geomechanical characterisation of a coastal urban aquifer using multiscalar time and frequency domain groundwater-level responses

Hydraulic properties of coastal, urban aquifers vary spatially and temporally with the complex dynamics of their hydrogeology and the heterogeneity of ocean-influenced hydraulic processes. Traditional aquifer characterisation methods are expensive, time-consuming and represent a snapshot in time. Tidal subsurface analysis (TSA) can passively characterise subsurface processes and establish hydro-geomechanical properties from groundwater head time-series but is typically applied to individual wells inland. Presented here, TSA is applied to a network of 116 groundwater boreholes to spatially characterise confinement and specific storage across a coastal aquifer at city-scale in Cardiff (UK) using a 23-year high-frequency time-series dataset. The dataset comprises Earth, atmospheric and oceanic signals, with the analysis conducted in the time domain, by calculating barometric response functions (BRFs), and in the frequency domain (TSA). By examining the damping and attenuation of groundwater response to ocean tides (OT) with distance from the coast/rivers, a multi-borehole comparison of TSA with BRF shows this combination of analyses facilitates disentangling the influence of tidal signals and estimation of spatially distributed aquifer properties for non-OT-influenced boreholes. The time-series analysed covers a period pre- and post-impoundment of Cardiff’s rivers by a barrage, revealing the consequent reduction in subsurface OT signal propagation post-construction. The results indicate that a much higher degree of confined conditions exist across the aquifer than previously thought (specific storage = 2.3 × 10−6 to 7.9 × 10−5 m−1), with implications for understanding aquifer recharge, and informing the best strategies for utilising groundwater and shallow geothermal resources.

Volcano–air–sea interactions in a coastal tuff ring, Jeju Island, Korea

Abstract The Holocene tuff ring of Songaksan, Jeju Island, Korea, is intercalated with wave-worked deposits at the base and in the middle parts of the tuff sequence. They are interpreted to have resulted from fair-weather wave action at the beginning of the eruption and storm wave action during a storm surge event in the middle of the eruption, respectively. The tuff ring is overlain by another marine volcaniclastic formation, suggesting erosion and reworking by marine processes because of post-eruption changes in sea-level. Dramatic changes in the chemistry, accidental componentry and ash-accretion texture of the pyroclasts are also observed between the tuff beds deposited before and after the storm invasion. The ascent of a new magma batch, related to the chemical change, could not be linked with either the Earth and ocean tides or the meteorological event. However, the changes in the texture of the pyroclasts suggest a sudden change in the diatreme fill from water-undersaturated to supersaturated because of an increased supply of external water into the diatreme. Heavy rainfall associated with the storm is inferred to have changed the water saturation in the diatreme. Songaksan demonstrates that there was intimate interaction between the volcano and the environment.

Coastal flooding generated by ocean wave- and surge-driven groundwater fluctuations on a sandy barrier island

Three years of observations of groundwater elevations, ocean tides, surge, and waves, and rainfall are used to study coastal groundwater-driven flooding along the ocean side of a barrier island. Increases in surge and wave-driven water levels (setup) during 26 ocean storms with little rainfall, including the passage of 3 hurricanes, caused O(1 m) increases in groundwater heads under the dunes on the ocean side of the island, nearly double previously reported magnitudes. The inland propagation of the resulting pulses in groundwater levels is consistent with an analytical model (without recharge) based on shallow aquifer theory (Nash Sutcliffe model efficiencies of >0.7, maximum water-table level estimates within 0.1 m of observations). Infiltration of precipitation results in approximately a threefold increase in the groundwater level relative to the amount of rainfall. The analytical model (with recharge) driven with estimated ocean shoreline water levels (based on the 36-hr-averaged offshore tide, surge, and wave height) and measured precipitation predicts the maximum water-table height within 0.15 m of that observed across the barrier island during Hurricane Matthew, which was the only wave event during the 3-yr data set with more than 0.1 m rainfall.Citizen-science reports from a smartphone app (iFlood) are used to evaluate the regional application of the model. Twenty-five ocean-side reports associated with 7 ocean storms (6 of which had minimal rainfall) between Sept 2019 and Feb 2020 showed flooding on natural (permeable) land surfaces along 70 km of the northern Outer Banks barrier island, from Corolla to Rodanthe, NC. The analytical model (with recharge) predicts flooding that is consistent with the timing and location for 19 of the 25 reports. Applying the model regionally suggests that more than 10% of the land area on the ocean side of the northern Outer Banks would be inundated by coastal groundwater even in the absence of rainfall for an ocean storm that generates a 2.25 m increase in the shoreline water level.

Anelasticity and Lateral Heterogeneities in Earth's Upper Mantle: Impact on Surface Displacements, Self‐Attraction and Loading, and Ocean Tide Dynamics

AbstractSurface displacement and self‐attraction and loading (SAL) elevation induced by ocean tides are known to be affected by material properties of the solid Earth. Recent studies have shown that, in addition to elasticity, anelasticity considerably impacts surface displacements due to ocean tide loading (OTL). We employ consistent 3D seismic elastic and attenuation tomography models to construct 3D elastic and anelastic earth models, and derive corresponding averaged 1D elastic/anelastic models. We apply these models to systematically study the impact of anelasticity and lateral heterogeneity on M2 OTL displacements and SAL elevation. We find that neglecting lateral heterogeneities highly underestimates displacements and SAL elevation in mid‐ocean‐ridge regions and in some coastal areas of North and Central America. In comparison to PREM, 3D anelastic models can increase the predicted amplitudes of the vertical displacement and SAL elevation by up to 1.5 mm. The increased amplitudes reduce the discrepancy between GPS‐observed OTL displacements and their predictions based on PREM in places like Cornwall (England), Brittany (France), and the Ryukyu Islands (Japan). Applying our results to ocean tides, we discover that the impact on ocean tide dynamics exceeds the predicted SAL elevation correction with an RMS of about 1 mm, reaching an RMS of more than 5 mm in areas like North Atlantic or East Pacific. Due to the fact that such a value reaches the accuracy of modern data‐constrained tidal models, we regard the impact of anelastic shear relaxation as significant in tidal modeling.

Error Assessment of GRACE and GRACE Follow‐On Mass Change

AbstractWe carry out a comprehensive error assessment of Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow‐On (GFO) Release‐6 (RL06) solutions from the Center for Space Research (CSR) at the University of Texas at Austin, NASA Jet Propulsion Laboratory (JPL), and Geoforschungszentrum (GFZ). The study covers the period April 2002 to August 2020 and uses two different methods, one based upon open ocean residuals (OOR) and the other a Three‐Cornered Hat (TCH) calculation. General results from the two methods are similar. With 300 km Gaussian smoothing OOR RMS errors for CSR, JPL, and GFZ solutions are ∼2.01, 3.19, and 3.67 cm, respectively. With additional decorrelation filtering OOR RMS values are reduced to ∼1.24, 1.53, and 1.69 cm, respectively. TCH analysis also shows that CSR has the lowest noise levels with similar RMS values, and additional decorrelation filtering reduces error levels. TCH may underestimate errors if there are common errors among geophysical background models. Errors in GFO's first two years (25 solutions for 2018.06 to 2020.08) are comparable to those of GRACE when zonal degree 2 and 3 coefficients are replaced by Satellite Laser Ranging estimates. The OOR method reveals mismodeled intra‐seasonal dynamic ocean signals associated with the Argentine Gyre during de‐aliasing, while the TCH method shows differences between ocean tide models near Australia and Antarctica. Both OOR and TCH RMS analysis offer a means to assess the noise level of GRACE/GFO estimated mass change. The actual uncertainty of GRACE/GFO estimate averaged (or totaled) over a given region is also affected by other error sources.

Regional Evaluation of Minor Tidal Constituents for Improved Estimation of Ocean Tides

Satellite altimetry observations have provided a significant contribution to the understanding of global sea surface processes, particularly allowing for advances in the accuracy of ocean tide estimations. Currently, almost three decades of satellite altimetry are available which can be used to improve the understanding of ocean tides by allowing for the estimation of an increased number of minor tidal constituents. As ocean tide models continue to improve, especially in the coastal region, these minor tides become increasingly important. Generally, admittance theory is used by most global ocean tide models to infer several minor tides from the major tides when creating the tidal correction for satellite altimetry. In this paper, regional studies are conducted to compare the use of admittance theory to direct estimations of minor tides from the EOT20 model to identify which minor tides should be directly estimated and which should be inferred. The results of these two approaches are compared to two global tide models (TiME and FES2014) and in situ tide gauge observations. The analysis showed that of the eight tidal constituents studied, half should be inferred (2N2, ϵ2, MSF and T2), while the remaining four tides (J1, L2, μ2 and ν2) should be directly estimated to optimise the ocean tidal correction. Furthermore, for certain minor tides, the other two tide models produced better results than the EOT model, suggesting that improvements can be made to the tidal correction made by EOT when incorporating tides from the two other tide models. Following on from this, a new approach of merging tidal constituents from different tide models to produce the ocean tidal correction for satellite altimetry that benefits from the strengths of the respective models is presented. This analysis showed that the tidal correction created based on the recommendations of the tide gauge analysis provided the highest reduction of sea-level variance. Additionally, the combination of the EOT20 model with the minor tides of the TiME and FES2014 model did not significantly increase the sea-level variance. As several additional minor tidal constituents are available from the TiME model, this opens the door for further investigations into including these minor tides and optimising the tidal correction for improved studies of the sea surface from satellite altimetry and in other applications, such as gravity field modelling.

Observing tidal and storm generated wave height impact on groundwater levels in a tropical delta (the Sundarbans)

Groundwater level (GWL) of coastal aquifers are strongly influenced by the ocean tide at sub-daily to seasonal scale. Similarly, GWL are influenced by storm induced ocean wave surge lasting few hours to a day. There has not been a detailed study on the conjunctive impact of such tidal and storm waves on coastal groundwater and its vulnerability. Through our coastal and field-laboratory observations at one of the world’s most extreme climate affected regions, the Ganges river mega-delta, we delineate the influence of ocean wave surge impacts on the shallow (<24 m below ground level [m bgl]) and deep (115 m bgl) aquifers GWL. Our study on the multi-layered delta-front aquifers, adjoining the tropical BoB shows that the high-temporal resolution GWL fluctuation due to wave surges are instantaneous, rapid and synchronous at all depths of the aquifers. The potential rise of ocean waves caused by tropical cyclone Bulbul (November 2019) significantly increases the GWL, both in shallow and deeper aquifer. Using multivariate statistics and machine learning techniques, we have attempted to quantify the rise of GWL during each of the ocean wave surge event. The model shows good predictability for deeper groundwater, however it is unable to quantify the shallower GWL of each of the ocean wave surge during storm events. Such phenomenon indicates aquifer vulnerability, thereby posing an emerging threat to drinking water availability to millions of groundwater-dependent inhabitants in coastal areas, globally, which may rapidly intensify with increasing rates of tropical cyclones and sea level rise in recent times and impending future.

Streamflow and Tidal Dynamics in the Lower Pee Dee Basin: Hurricane Impacts

Over past years, extreme tropical storm events along the North and South Carolina coasts—and subsequent river flooding—have warranted the need for a better understanding of the hydrologic response to these events to protect life, property, businesses, and natural and cultural resources. Our focus in this study is the Pee Dee and Waccamaw River systems, which ultimately flow into Winyah Bay near Georgetown, South Carolina. River flows, coupled with the tidal nature of these freshwater systems, are complex and difficult to predict. The objective of the work is to analyze publicly available data from gauging stations along those river system as measured during Hurricanes Matthew and Florence and Tropical Storm Bertha—three uniquely different storm systems that produced varying rainfall depth, duration, and intensity across the Pee Dee Basin. The most important factor in tidal river analysis is the location of the stagnation point , where downstream river flow exactly balances upstream tidal flow. River flow only controls water level upstream of a tidal stagnation point, while ocean tide controls the water level downstream of a tidal stagnation point. An analysis of major flooding following Hurricanes Matthew, Florence, and Tropical Storm Bertha was used to determine the river flows associated with tidal stagnation at each stream gauge active during these storms. A major limitation of the analysis was a lack of flow data for the tidal channels in Georgetown County, which resulted in uncertainty in the flow associated with stagnation and uncertainty in the role played by each of the creeks that connect the Pee Dee and Waccamaw Rivers. Ignorance of the roles of these creeks most limited understanding of the relative importance of Pee Dee and Waccamaw flow to cause stagnation near Pawleys Island and Hagley gauges on the Waccamaw River and the Socastee gauge on the Atlantic Intracoastal Waterway.

Evaluation of global ocean tide models based on tidal gravity observations in China

Previous studies show that the calculated loading effects from global ocean tide models do not match actual measurements of gravity attraction and loading effects in Southeast Asia. In this paper, taking advantage of a unique network of gravity tidal stations all over the Chinese mainland, we compare the observed and modeled tidal loading effects on the basis of the most recent global ocean tide models. The results show that the average efficiencies of the ocean tidal loading correction for O1, K1, M2 are 77%, 73% and 59%, respectively. The loading correction efficiencies using recent ocean tidal models are better than the 40 years old Schwiderskis model at coastal stations, but relative worse at stations far from ocean.

EOT20: a global ocean tide model from multi-mission satellite altimetry

Abstract. EOT20 is the latest in a series of empirical ocean tide (EOT) models derived using residual tidal analysis of multi-mission satellite altimetry at DGFI-TUM. The amplitudes and phases of 17 tidal constituents are provided on a global 0.125∘ grid based on empirical analysis of seven satellite altimetry missions and four extended missions. The EOT20 model shows significant improvements compared to the previous iteration of the global model (EOT11a) throughout the ocean, particularly in the coastal and shelf regions, due to the inclusion of more recent satellite altimetry data as well as more missions, the use of the updated FES2014 tidal model as a reference to estimated residual signals, the inclusion of the ALES retracker and improved coastal representation. In the validation of EOT20 using tide gauges and ocean bottom pressure data, these improvements in the model compared to EOT11a are highlighted with the root sum square (RSS) of the eight major tidal constituents improving by ∼ 1.4 cm for the entire global ocean with the major improvement in RSS (∼ 2.2 cm) occurring in the coastal region. Concerning the other global ocean tidal models, EOT20 shows an improvement of ∼ 0.2 cm in RSS compared to the closest model (FES2014) in the global ocean. Variance reduction analysis was conducted comparing the results of EOT20 with FES2014 and EOT11a using the Jason-2, Jason-3 and SARAL satellite altimetry missions. From this analysis, EOT20 showed a variance reduction for all three satellite altimetry missions with the biggest improvement in variance occurring in the coastal region. These significant improvements, particularly in the coastal region, provide encouragement for the use of the EOT20 model as a tidal correction for satellite altimetry in sea-level research. All ocean and load tide data from the model can be freely accessed at https://doi.org/10.17882/79489 (Hart-Davis et al., 2021). The tide gauges from the TICON dataset used in the validation of the tide model, are available at https://doi.org/10.1594/PANGAEA.896587 (Piccioni et al., 2018a).