Significant Sea Level Research Articles

Multidisciplinary study on the stratigraphy of the upper Cretaceous-Paleogene successions in the western Tajik Basin, Uzbekistan

The Tajik-Afghan Basin is a large basin in Central Asia, whose sediments document the area's long tectonic and climatic history from the Paleozoic to the present. However, the sedimentary characteristics and stratigraphy of these successions remain poorly understood. The study of this basin is critical for understanding the depositional conditions that prevailed during the transformation of this area from a part of the Western Oceanic Tethys to a more restricted Para-Tethys. In the southwestern corner of the Tajik Depression, a well-exposed sedimentary sequence associated with a large anticlinal limb was sampled. The authors proposed a new age model based on a combination of biostratigraphic data from planktic foraminifera, calcareous nannofossils, and strontium chemostratigraphy (87Sr/86Sr). The lower part of the studied section is of the upper Cenomanian age (95.5 Ma), while the upper part is assigned to the early Oligocene age (34.05 Ma). The carbon isotope profile shows several excursions linked to major paleoenvironmental events including the Oceanic Anoxic Event 2 (OAE2) and the Paleocene-Eocene Thermal Maximum (PETM). The latter is revealed in the study area for the first time. New sedimentological observations and interpretations of the depositional environments and sea-level cycles are provided. The deposition in the Aktash area occurred between upper coastal lagoonal and transitional environments before fully transitioning to continental environments in the Neogene. The stratigraphic record in Aktash is divided into large-scale progradation/ retrogradation cycles that can be tentatively linked to global sea-level signals.

Interannual Sea Level Variability along the U.S. East Coast during the Satellite Altimetry Era: Local versus Remote Forcing

Abstract The contributions of local and remote forcings to the interannual sea level anomalies (SLAs) along the U.S. East Coast (USEC) during the satellite altimetry era from 1993 to 2019 are quantified with analytical models assisted by statistical methods. The local forcings from alongshore wind stress, sea level pressure via inverted barometer (IB) effect, and river discharges together explain 47%, 60.4%, and 66.8% of coastal sea level variance in the South Atlantic Bight (SAB), Mid-Atlantic Bight (MAB), and Gulf of Maine (GOM), respectively, with river discharges having the minimum contribution. Over a longer period of 1960–2019, the contribution of local forcings reduces significantly, with the IB effect having the minimum contribution. The remote forcings associated with open-ocean signals from the east and from the northern boundary at the Scotian coast together with the Gulf Stream (GS) variability explain 45.7%, 28.5%, and 37.7% of coastal sea level variance in the SAB, MAB, and GOM, respectively, playing a role comparable to that of local forcings in the SAB. The open-ocean sea level signals from 35° to 38°N strongly influence coastal SLAs in the SAB. The coastal SLAs in the SAB are also affected by the upstream GS strength (28°–36°N) and basin-scale wind stress curl anomaly, which is linked to the meridional shift in the downstream GS (74°–68°W). Remote forcings from the subpolar North Atlantic and wind stress curl from the Grand Banks to the Scotian coast influence coastal SLAs in the GOM and MAB via the northern boundary of the USEC at the Scotian coast.

Analysis of high waves and coastal flooding event in Manado in mid-January 2021 (meteotsunami perspective)

Meteotsunami is atmospheric-induced ocean waves at the frequency of tsunami waves (2 minutes-2 hours). On January 17, 2021, the high waves tsunami-like due to lousy weather superimposed with the high tide were reported hitting the coastal area of Manado City, North of Sulawesi. This research examined the characteristic of that tsunami wave-like phenomenon. The sea level, atmospheric data (i.e., wind and air pressure), and weather satellite imagery were used in this study. The sea level, air pressure, and wind data were filtered to remove the low-frequency signal to obtain the amplitude of the high-frequency signal. The results showed that a high-frequency sea level signal’s maximum wave height (peak to trough) is up to 0.4 m. This condition responded to the increase in high-frequency maximum wind speed reaching 11 m/s associated with the convective system, such as the Cumulonimbus cloud system, detected 10 hours before the maximum high-frequency sea-level event. These circumstances meet the meteotsunami criteria, but the other parameter, such as air pressure, is not.

Anhydrite fabrics as an indicator for relative sea-level signatures in the sequence stratigraphic framework of a carbonate ramp

Evaporite deposits are increasingly recognized for their role in developing oil reservoirs. In the Shadegan Oilfield, anhydrite is an evaporite mineral identified in the Asmari Formation (Oligocene-Miocene) as clastic- and carbonate-evaporite assemblages. Our study found that diagenesis plays a critical role in controlling the distribution of different fabrics (texture and structure) in the area. The anhydrites resulted from two progressive processes: early diagenesis and formation of anhydrites related to supratidal to shallow settings, and late diagenesis and crystallization of anhydrites in deeper environments. The evaporite-bearing intervals provide an opportunity to investigate the interactions between sea-level fluctuations and the growth of anhydrites during the development of the carbonate ramp of the Asmari Formation. Despite previous studies on the Asmari Formation, little is known about the relationships between the occurrence of its anhydrite fabrics and sequence stratigraphic framework. In our study, the continuous shallowing-upward trends, exposure of sediments, and subsequent diagenesis were responsible for the deposition of anhydrite. Semi-arid to arid climates followed, resulting in stacking of anhydrite and dolomites, particularly in the upper parts of the Asmari, corresponding to the Burdigalian.

Inter-annual sea level change and transgression along a barrier Island coast

On the decadal time scale of coastal planning and management, relative sea-level rise is usually considered a trend or constant rate rather than a dynamic, time varying influence on coastal change. However, the coastal ocean sea level along the east coast of Florida and coastal regions further north is, to a first order, controlled at the interannual and decadal time scale by the dynamics of North Atlantic circulation and Gulf Stream (GS) flow, Every coastal region has its own distinctive annual sea-level cycle, and longer-term intra- and inter-decadal sea-level oscillations. This paper addresses the influence of the strong Florida coastal ocean sea-level signal on topographic evolution of the shoreface, coastal sediment budgets, and potential for coastal transgression at the decadal time scale.

Regime Shift of the Sea Level Trend in the South China Sea Modulated by the Tropical Pacific Decadal Variability

AbstractDuring the altimeter era, the sea level in the South China Sea (SCS) and western tropical Pacific (WTP) experienced significant decadal variability. The sea level rose during 1993–2009 and fell during 2010–2019. The decadal variability of Walker Circulation associated with the Pacific Decadal Oscillation can explain the sea level variability in the WTP to a great extent. The wind forced westward propagating Rossby waves increased (decreased) the sea level in the WTP during 1993–2009 (2010–2019). However, the interior wind forcing has a negligible contribution to the decadal variability of the sea level in the SCS. The remote forcing from WTP through the oceanic bridge was supposed to play a dominant role. The sensitive experiments of a 1½‐layer model and Regional Oceanic Modeling System suggested that the sea level signals via the Sibutu Passage and Mindoro Strait accounted for the decadal variability of sea level in the central basin of SCS.

Forcing Mechanisms of the Interannual Sea Level Variability in the Midlatitude South Pacific during 2004–2020

Over the past few decades, the global mean sea level rise and superimposed regional fluctuations of sea level have exerted considerable stress on coastal communities, especially in low-elevation regions such as the Pacific Islands in the western South Pacific Ocean. This made it necessary to have the most comprehensive understanding of the forcing mechanisms that are responsible for the increasing rates of extreme sea level events. In this study, we explore the causes of the observed sea level variability in the midlatitude South Pacific on interannual time scales using observations and atmospheric reanalyses combined with a 1.5 layer reduced-gravity model. We focus on the 2004–2020 period, during which the Argo’s global array allowed us to assess year-to-year changes in steric sea level caused by thermohaline changes in different depth ranges (from the surface down to 2000 m). We find that during the 2015–2016 El Niño and the following 2017–2018 La Niña, large variations in thermosteric sea level occurred due to temperature changes within the 100–500 dbar layer in the midlatitude southwest Pacific. In the western boundary region (from 30°S to 40°S), the variations in halosteric sea level between 100 and 500 dbar were significant and could have partially balanced the corresponding changes in thermosteric sea level. We show that around 35°S, baroclinic Rossby waves forced by the open-ocean wind-stress forcing account for 40 to 75% of the interannual sea level variance between 100°W and 180°, while the influence of remote sea level signals generated near the Chilean coast is limited to the region east of 100°W. The contribution of surface heat fluxes on interannual time scales is also considered and shown to be negligible.

Interannual to decadal sea level variability in the subpolar North Atlantic: the role of propagating signals

Abstract. The gyre-scale, dynamic sea surface height (SSH) variability signifies the spatial redistribution of heat and freshwater in the ocean, influencing the ocean circulation, weather, climate, sea level, and ecosystems. It is known that the first empirical orthogonal function (EOF) mode of the interannual SSH variability in the North Atlantic exhibits a tripole gyre pattern, with the subtropical gyre varying out of phase with both the subpolar gyre and the tropics, influenced by the low-frequency North Atlantic Oscillation. Here, we show that the first EOF mode explains the majority (60 %–90 %) of the interannual SSH variance in the Labrador and Irminger Sea, whereas the second EOF mode is more influential in the northeastern part of the subpolar North Atlantic (SPNA), explaining up to 60 %–80 % of the regional interannual SSH variability. We find that the two leading modes do not represent physically independent phenomena. On the contrary, they evolve as a quadrature pair associated with a propagation of SSH anomalies from the eastern to the western SPNA. This is confirmed by the complex EOF analysis, which can detect propagating (as opposed to stationary) signals. The analysis shows that it takes about 2 years for sea level signals to propagate from the Iceland Basin to the Labrador Sea, and it takes 7–10 years for the entire cycle of the North Atlantic SSH tripole to complete. The observed westward propagation of SSH anomalies is linked to shifting wind forcing patterns and to the cyclonic pattern of the mean ocean circulation in the SPNA. The analysis of regional surface buoyancy fluxes in combination with the upper-ocean temperature and salinity changes suggests a time-dependent dominance of either air–sea heat fluxes or advection in driving the observed SSH tendencies, while the contribution of surface freshwater fluxes (precipitation and evaporation) is negligible. We demonstrate that the most recent cooling and freshening observed in the SPNA since about 2010 were mostly driven by advection associated with the North Atlantic Current. The results of this study indicate that signal propagation is an important component of the North Atlantic SSH tripole, as it applies to the SPNA.

Coastal dune dynamics in embayed settings with sea-level rise – Examples from the exposed and macrotidal north coast of SW England

Coastal dune systems are natural forms of coastal defence, but are expected to exhibit increased erosion rates due to climate change impacts, notably sea-level rise and, potentially, increased storminess. This is especially the case in embayed coastal settings, i.e., where there are no significant sediment inputs into the beach/dune system from longshore sources. Dune development is closely linked to that of beaches that lie seaward, but their temporal dynamics tend to be asynchronous. So, whereas beaches are generally highly variable over a short- to medium-term (event–decadal) time scales, potentially obscuring a longer-term (decadal–centennial) sea-level signal, dunes display a low-pass filtered response which may contain a sea-level signal.In this study, we investigate the decadal-scale, inter-annual dynamics of 25 embayed coastal dune systems along the exposed and macrotidal north coast of SW England. We then compare the observed behaviour with that hindcasted from simple parametric models and forecast future dune retreat rates due to sea-level rise. We show that practically all exposed dune systems show retreat with a regionally-averaged retreat rate of the dune foot of 0.5 m yr−1. The majority of retreat occurred over a small number of especially energetic winters and it was found that dune retreat is not automatically linked to dune volumetric change. Many of the retreating dune systems display so called ‘dune roll-over’, characterised by removal of sediment from the dune face and deposition at the dune top. Observed dune retreat rates were 2–3 times larger than predicted using simple parametric retreat models forced by sea-level rise. This suggests that the retreat models are inappropriate and/or that sea-level rise in itself may be insufficient to explain the observed retreat and that increased winter storminess may be implicated.A key factor in driving dune retreat is considered to be the number of hours that waves reach the dune foot or the excess runup energy present at the dune foot elevation. Both sea-level rise and enhanced storminess will increase exposure of the dune foot to energetic wave action and this is expected to accelerate dune retreat rates in these settings. Application of parametric shoreline retreat models that account for the acceleration in rate of sea-level rise predicts c. 40 m of dune retreat by 2100 with a considerable range in retreat (20–75 m), resulting from uncertainty in model choice and parameterisation. Simply extrapolating the current dune retreat rate also results in c. 40 m of dune retreat by 2100, but this approach ignores the potential acceleration in dune retreat rate due to an increase in the rate of sea-level rise.The combination of analysis of multi-annual coastal dune morphological change along with application of dune retreat models can provide useful insights into future dune evolution for coastal planners and managers.

Evidence of regional sea-level rise acceleration for the North Sea

Global mean sea-level rise (SLR) has accelerated since 1900 from less than 2 mm yr−1 during most of the century to more than 3 mm yr−1 since 1993. Decision-makers in coastal countries, however, require information on SLR at the regional scale, where detection of an acceleration in SLR is difficult, because the long-term sea-level signal is obscured by large inter-annual variations with multi-year trends that are easily one order of magnitude larger than global mean values. Here, we developed a time series approach to determine whether regional SLR is accelerating based on tide gauge data. We applied the approach to eight 100-year records in the southern North Sea and detected, for the first time, a common breakpoint in the early 1990s. The mean SLR rate at the eight stations increases from 1.7 ± 0.3 mm yr−1 before the breakpoint to 2.7 ± 0.4 mm yr−1 after the breakpoint (95% confidence interval), which is unprecedented in the regional instrumental record. These findings are robust provided that the record starts before 1970 and ends after 2015. Our method may be applied to any coastal region with tidal records spanning at least 40 years, which means that vulnerable coastal communities still have time to accumulate the required time series as a basis for adaptation decisions in the second half of this century.

Characteristics of Ocean Waves in the Southern Ocean and Seasonal Prediction of Difficulty for the Vessels Crossing the Westerlies

In this study, the European Centre for Medium-Range Weather Forecasts reanalysis v5 (ERA5) wave height reanalysis data and sea-level pressure data from two seasonal prediction systems were used to study the wave characteristics of the Southern Ocean and the seasonal prediction of difficulty for the vessels crossing the westerlies. The results show that significant wave height, extreme wave height, and extreme wave processes were all much stronger in austral winter than in austral summer, making it more difficult for vessels to cross the westerlies in winter. Furthermore, the difficulty of crossing the westerlies has increased over the last 40 years, except in areas east of South America. We found that the monthly frequency of crossing the westerlies between 100° E and 75° W could be accurately estimated point by point using the monthly mean sea-level pressure difference between 30° S and 65° S. With a 1-month lead, the multi-model forecasts gave a fairly accurate forecast of such sea-level pressure difference signal between 150° E to 60° W for target months from May to December. Based on these assessments, we could estimate the difficulty of crossing the westerlies in some specific months in advance using a seasonal prediction system. We also found that the seasonal prediction system produced inaccurate predictions of sea-level pressure at high latitudes, which is the main barrier to further accurately estimating the difficulty of crossing the westerlies. These findings may provide support for predicting difficulty for the vessels crossing the westerlies with a 1-month lead and can provide planning for the route and the allocation of material reserves.

Towards improved analysis of short mesoscale sea level signals from satellite altimetry

Abstract. Satellite altimeters routinely supply sea surface height (SSH) measurements, which are key observations for monitoring ocean dynamics. However, below a wavelength of about 70 km, along-track altimeter measurements are often characterized by a dramatic drop in signal-to-noise ratio (SNR), making it very challenging to fully exploit the available altimeter observations to precisely analyze small mesoscale variations in SSH. Although various approaches have been proposed and applied to identify and filter noise from measurements, no distinct methodology has emerged for systematic application in operational products. To best address this unresolved issue, the Copernicus Marine Environment Monitoring Service (CMEMS) actually provides simple band-pass filtered data to mitigate noise contamination of along-track SSH signals. More innovative and suitable noise filtering methods are thus left to users seeking to unveil small-scale altimeter signals. As demonstrated here, a fully data-driven approach is developed and applied successfully to provide robust estimates of noise-free sea level anomaly (SLA) signals (Quilfen, 2021). The method combines empirical mode decomposition (EMD), used to help analyze non-stationary and non-linear processes, and an adaptive noise filtering technique inspired by discrete wavelet transform (DWT) decompositions. It is found to best resolve the distribution of SLA variability in the 30–120 km mesoscale wavelength band. A practical uncertainty variable is attached to the denoised SLA estimates that accounts for errors related to the local SNR but also for uncertainties in the denoising process, which assumes that the SLA variability results in part from a stochastic process. For the available period, measurements from the Jason-3, Sentinel-3, and SARAL/AltiKa missions are processed and analyzed, and their energy spectral and seasonal distributions are characterized in the small mesoscale domain. In anticipation of the upcoming SWOT (Surface Water and Ocean Topography) mission data, the SASSA (Satellite Altimeter Short-scale Signals Analysis, https://doi.org/10.12770/1126742b-a5da-4fe2-b687-e64d585e138c, Quilfen and Piolle, 2021) data set of denoised SLA measurements for three reference altimeter missions has already been shown to yield valuable opportunities to evaluate global small mesoscale kinetic energy distributions.

Last interglacial sea-level proxies in the glaciated Northern Hemisphere

Abstract. Because global sea level during the last interglacial (LIG; 130–115 ka) was higher than today, the LIG is a useful approximate analogue for improving predictions of future sea-level rise. Here, we synthesize sea-level proxies for the LIG in the glaciated Northern Hemisphere for inclusion in the World Atlas of Last Interglacial Shorelines (WALIS) database. We describe 82 sites from Russia, northern Europe, Greenland and North America from a variety of settings, including boreholes, riverbank exposures and along coastal cliffs. Marine sediments at these sites were constrained to the LIG using a variety of radiometric methods (radiocarbon, uranium–thorium, potassium–argon), non-radiometric methods (amino acid dating, luminescence methods, electron spin resonance, tephrochronology) as well as various stratigraphic and palaeo-environmental approaches. In general, the sites reported in this paper do not offer constraint on the global LIG highstand, but rather evidence of glacial isostatic adjustment (GIA)-influenced sea-level positions following the Marine Isotope Stage 6 glaciation (MIS 6; 191–130 ka). Most of the proxies suggest that sea level was much higher during the LIG than at the present time. Moreover, many of the sites show evidence of regression due to sea-level fall (owing to glacial isostatic uplift), and some also show fluctuations that may reflect regrowth of continental ice or increased influence of the global sea-level signal. In addition to documenting LIG sea-level sites in a large swath of the Northern Hemisphere, this compilation is highly relevant for reconstructing the size of MIS 6 ice sheets through GIA modelling. The database is available at https://doi.org/10.5281/zenodo.5602212 (Dalton et al., 2021).

Overview on GPlates: focus on plate reconstruction

Plate tectonic reconstructions have been employed in geosciences since 1970s, in the context of hydrocarbon exploration, regional geology and paleobiology. Such studies have given valuable inputs for climate and geodynamic computations, present-day mantle structure, models of plate motion, and the interpretation of the drift of hotspots, true polar wander (TPW), sea level and stratigraphic signals. However, geodynamic models generated in the past by incorporating global plate tectonic reconstructions have limitations. To overcome this, GPlates software brings forward a new era of interactive plate tectonic reconstruction software integrated with GIS databases that incorporates a wide variety of geological and geophysical data. Besides modelling tectonic and crustal evolution, GPlates has also been used in visualizing paleogeography and paleobathymetry, in understanding deep carbon cycle, subduction zone initiation, mantle evolution, investigating earthquakes and predicting future supercontinents. the software has been widely used in hydrocarbon exploration along the passive conjugate margins such as from the margins of South America and Africa and has provided promising results in acquiring new and more reliable prospecting criteria for petroleum systems. Additionally, it has become an integral tool for paleolatitude calculations, modelling of paleoclimate and paleoenvironment. This article reviews key plate reconstructions that have been carried out using GPlates, the typical constraints and the set of input parameters.

The impact of 3-D Earth structure on far-field sea level following interglacial West Antarctic Ice Sheet collapse

Prior to inferring ice sheet stability from past interglacial sea-level records, these records must first be corrected for the contaminating effects of glacial isostatic adjustment (GIA). Typical GIA corrections, however, neglect variability in the signal that may be introduced by Earth's 3-D rheological structure. We predict sea-level changes due to a collapse of the West Antarctic Ice Sheet (WAIS) over an idealized 6 kyr-duration interglacial using four viscoelastic Earth models. Two of these are 3-D viscosity models inferred from seismic tomography. The third is a 1-D (i.e., depth varying) viscosity model that is equivalent to the spherically averaged “background” viscosity profile adopted in both 3-D Earth models. The fourth is a 1-D model that has a higher upper mantle viscosity but still falls within the class of models inferred from independent global GIA studies. We find that the discrepancy between 3-D and 1-D Earth model calculations of sea level in the far field of the melt zone is of order 0.3 m or less, with the 1-D Earth models producing higher sea level than the 3-D simulations. This value is 10% of the global mean sea-level (GMSL) rise associated with modeled ice sheet collapse by the end of the model interglacial (∼3 m) and a similar fraction of far-field sea-level changes. However, the value is a significantly larger fraction (∼60%) of the geographically variable (i.e., non-GMSL) component of the far-field sea-level signal due to GIA associated with modeled WAIS collapse (±0.5 m). Neglecting lateral variations in Earth structure in modeling the response to excess melting of WAIS during the interglacial compounds any error introduced by neglecting such structure in predictions of interglacial sea-level change driven by the preceding glacial cycle.

Period‐Lengthening of the Mindanao Current Variability From the Long‐Term Tide Gauge Sea Level Measurements

AbstractLong‐term tide gauge sea level data from 1969 to 2014 at Davao (7.08°N, 125.63°E) and Malakal (7. 33°N, 134.46°E) are analyzed to examine the decadal frequency modulations embedded in the Mindanao Current (MC) variability. The MC variability inferred from the Davao–Malakal sea level was predominantly biennial in the 1970s. This prevailing period switched to interannual in the 1980s and lengthened to decadal during the last two decades. With the aid of the basin‐scale sea level information from satellite altimeter measurements, it is found that the sea level‐inferred MC variability represents the coherent changes of the wind‐driven tropical gyre in the western North Pacific. An investigation into the long‐term wind stress curl data reveals that its prevailing period underwent similar biennial→interannual→decadal transitions in the western tropical Pacific, implying the forced nature of the period‐lengthening of the MC variability during the past half‐a‐century. While the sign of the MC variability is largely determined by the Malakal sea level signals on the interannual and decadal time scales, the Davao sea level change becomes important when the time scale extends to multi‐decades.

Flow regime recognition in a long pipeline-riser system based on signals at the top of the riser

To identify conveniently multiphase flow regimes in subsea pipeline-risers, we study in this paper experimentally two-phase flows in a 1657 m long pipeline with an S-shaped riser to simulate field experiment, within a wide range of gas and liquid velocities. Three flow regimes, namely severe slugging, transitional flows, and stable flows, are analyzed based on three differential pressure and one pressure signals at the top of the riser; comparatively speaking, the positions of these signals in the experimental system are similar to those of the sea level signals in industrial fields, which are easy and less expensive to obtain. The obtained signals are decomposed into six scales via a multi-scale wavelet analysis, and further four statistical parameters on each scale are extracted, including mean values, standard deviations, ranges, and mean values of absolute. We compared the effects of six SVM classifiers with different kernel functions on the recognition rate of flow regimes, and it is found the recognition rates of SVM classifier with quadratic and cubic kernel functions are the highest. Further, the principal component analysis is employed to reduce the dimension of statistical parameters and it indicates that the recognition rate tends to increase with the rising number of principal components from 1 to 6, and it remains constant if the principal component number is further increased. Moreover, The results suggest that the recognition rate obtained from the pressure difference between the top of the riser and the separator peaks, and then it comes that from the pressure signal at the top of the riser, and that for the pressure difference signal at the top of the riser is the least satisfying one. As for the optimal differential pressure signals between the top of the riser and the separator, the results show that the recognition rate increases rapidly from 70.2% to 90.4% when the sample duration rising from 2.3 s to 18.6 s, and when the sample duration exceeds 74.4 s, the recognition rate exceeds 92.9% and remains unchanged.

The Role of the Mindoro-Sibutu Pathway on the South China Sea Multi–layer Circulation

AbstractThe role of the Mindoro Strait-Sibutu passage pathway in influencing the Luzon Strait inflow to the South China Sea (SCS) and the SCS multi-layer circulation is investigated with a high-resolution (0.1° × 0.1°) regional ocean model. Significant changes are evident in the SCS upper layer circulation (250-900 m) by closing the Mindoro-Sibutu pathway in sensitivity experiments, as Luzon Strait transport is reduced by 75%, from −4.4 Sv to −1.2 Sv. Because of the vertical coupling between the upper and middle layers, closing the Mindoro-Sibutu pathway also weakens clockwise circulation in the middle layer (900–2150 m), but there is no significant change in the deep layer (below 2150 m). The Mindoro-Sibutu pathway is an important branch of the SCS throughflow into the Indonesian Seas. It is also the gateway for oceanic waves propagating clockwise around the Philippines Archipelago from the western Pacific Ocean into the eastern SCS, projecting El Niño-Southern Oscillation sea level signals to the SCS, impacting its interannual variations and multi-layer circulation. The results provide insights into the dynamics of how upstream and downstream passage throughflows are coupled to affect the general circulation in marginal seas.

The study of low-frequency sea-level oscillations: case of Algiers harbor (Algeria)

Sea-level rise induced by global warming is increasingly threatening coastal populations, especially those living on low-lying coasts. However, coastal flooding can also be observed on a short scale but over larger areas. This sudden sea-level rise can be induced by meteorological or seismic phenomena and can cause disasters on the coast. Our work aims to study low-frequency sea-level oscillations induced by meteorological events. As a case study, sea-level disturbance events of June–July 2002 observed at Algiers harbor are examined by spectral analysis applied to the original sea-level signal measured from a tide gauge with a frequency sampling of 0.003 Hz. The original sea-level signal is filtered using cutoff frequencies of a band-pass filter to extract the meteorological oscillations. Results of the spectral analysis show periods of 16, 20, and 30 min that correspond to the frequency ranges of tsunamis, meteotsunamis, and seiches. The absence of a seismic event during this period suggests that these signals are related to the seiche phenomena that are very frequent in the Bay of Algiers. The main period of 20 min observed is similar to some main frequencies observed in Balearic Islands during the tsunami event of the 2003 Zemmouri earthquake. On the other hand, it is important to notice that the frequency sampling of 0.003 Hz is relatively low because it does not allow detection of infragravity waves and wind waves/swells. Indeed, these signals could help to better understand meteotsunamis, seiches, and harbor oscillations.

The 6–7 July 2010 meteotsunami along the coast of Portugal: insights from data analysis and numerical modelling

On 6 and 7 July 2010, uncommon sea waves were observed along the coast of Portugal. The Portuguese tide gauge network recorded the sea-level signals showing tsunami-like waves of heights varying from 0.14 to 0.6 m (crest-to-trough) and of periods in the range of 30 to 60 min. Analysis of both oceanic and atmospheric data revealed the occurrence of a meteotsunami in the night of July 6th that propagated from Lagos, south, up to Viana, north. Here, we present the first investigation of the 2010 meteotsunami that struck the coast of Portugal. We use the atmospheric pressure data to force the sea surface and numerically generate the 2010 meteotsunami. We then simulate the 2010 meteotsunami propagation over high-resolution bathymetric models using a validated nonlinear shallow water code. The comparison of the simulated waveforms with the records shows satisfactory agreement of wave heights and periods in most stations. Taking the 2010 event as a reference of meteotsunamis along the Portuguese coast, we further provide an insight into the meteotsunami hazard posed by events propagating from south to north of the country. This is done by considering a 2D Gaussian-shape pressure disturbance that propagates along the shelf under varying conditions of speed and incident angle. This allows identifying “hot spots” on the coast of Portugal where the focus of meteotsunami energy is favourable. Our results suggest that meteotsunamis present a real threat on the highly occupied Portuguese coast and therefore should be considered in tsunami hazard and forecasting strategies of the NE Atlantic countries.