Ocean Edge Research Articles

Comprehensive Investigation on Spatiotemporal Variations of Tropical Cyclone Activities in the Western North Pacific, 1950–2019

Tropical Cyclones (TCs) are the most severe natural disasters in the Western North Pacific Ocean (WNP). While previous studies reported evident changes over certain regions or seasons between typical periods, there is a lack of a complete picture of the long-term variations in TC activities in the WNP. This study carried out a comprehensive investigation on the spatiotemporal variations in TC genesis locations and transit pathways in the WNP, based on the TC best-track datasets from the China Meteorological Administration Shanghai Typhoon Institute. The results showed that the TC genesis and occurrence frequencies showed drastic decreases and westward shifts in the WNP from 1950 to 2019. The greatest decrease in TC genesis occurred for Tropical Depressions (TDs: 10.8−17.1 m/s) and Typhoons (TYs: > 32.7 m/s). The number of Tropical Storms (TSs: 17.2−32.6 m/s) and the mean intensity (2 min maximum sustained wind speed) of TCs overall showed no evident change. The decadal average of TC genesis frequency increased by 63% in the near-coast seas (WNPO), but decreased by 46% near the central Pacific Ocean (WNCP), demonstrating a westward shift for TC genesis locations. The TC genesis and occurrence frequencies also showed significant declines in the southern Philippine Sea (SPS) and South China Sea (SCS), while they showed a lower reduction in the Eastern East China Sea (EECS), the northern ocean edge of TC genesis areas, resulting in an increase in the average latitude of TC genesis locations, a spurious northward shift. The La Niña and El Niño years showed contrasting effects on TC genesis frequency and landfall ratios. There were greater instances of TC genesis and greater landfall ratios during the La Niña mature phase, while there were fewer TC formations and lower landfall ratios during the short duration (SD) El Niño developing phase. The TC genesis locations showed a distinct northwestward shift during La Niña years compared to those during El Niño years.

Numerical study of meteotsunamis driven by atmospheric gravity waves in coastal waters of Buenos Aires Province, Argentina

The generation and propagation of meteorological tsunamis (meteotsunamis) were numerically investigated in coastal waters of Buenos Aires Province. This study was carried out using a vertically integrated ocean model driven by a theoretical atmospheric forcing. This forcing simulates a train of nondispersive atmospheric gravity waves (AGW) propagating within a bounded area that moves at the speed of the synoptic systems. Firstly, a study case of simultaneous AGW and meteotsunami activity was simulated to validate the implemented methodology. Subsequently, after several numerical experiments, it was obtained that the amplitude, the dominant period, and the direction of propagation of the AGW train were the parameters that have the largest impact on the simulated meteotsunami amplitude. Maximum meteotsunami wave height (0.85 m) was obtained at Punta Rasa (the northern extreme of the coast of Buenos Aires Province) when the AGW reached this location. Numerical outcomes also showed that the meteotsunamis would propagate like ocean edge waves. In these cases, the continuous transference of energy from the atmosphere to the ocean could be possible (Greenspan resonance). Even though the implemented theoretical forcing is realistic, the numerical experiments revealed that some particular issues should be enhanced to better simulate the genesis and propagation of the meteotsunamis in coastal waters of the Buenos Aires Province. These issues are analyzed and discussed in this paper.

Consumed tectonic plates in Southeast Asia: Markers from the Mesozoic to early Cenozoic stratigraphic units in the northern and central Philippines

Tectonic reconstruction models of Southeast Asia all invoke in the early Cenozoic the collision of Mesozoic oceanic plates, which have been fragmented, consumed along subduction zones or emplaced onto the overriding plate. However, with marked variations in these models, we reinvestigate the tectonic evolutionary landscape of Southeast Asia through the lens of Philippine geology. In particular, we present revisions to the more recent models by adopting the unique approach of integrating data that we have gathered for the past 17 years from the Upper Mesozoic to Lower Cenozoic stratigraphic formations in northern and central Philippines. These formations, which resulted mainly from submarine mass transport processes, evolved in response to early arc-related processes of oblique subduction, frontal wedge deformation, terrane accretion and strike slip faulting. Additional key constraints for the revisions include: (1) the timing of early Cenozoic magmatism in eastern Luzon; (2) the spatial distribution of the Upper Mesozoic to Lower Cenozoic sedimentary formations with respect to other key features (e.g. distribution of Mesozoic ophiolite fragment and continent-derived rocks) in the Philippine arc; (3) the paleolatitudinal position of Luzon and surrounding regions and; (4) the movement of the surrounding plates since the Late Mesozoic.In revising previous models, a subduction zone (proto-East Luzon Trough) separating Benham Plateau and the Philippine arc was placed to explain the spatial distribution of Eocene arc-related formational units and Mesozoic ophiolite materials comprising the accretionary complex east of Luzon at ~40 Ma period. During this time, Luzon was modeled at the southern margin of the East Asia Sea or the proto-Philippine Sea Plate. Mesozoic ophiolitic complexes that line the eastern Philippine arc as well as the ophiolitic and pelagic limestone and chert fragments included in the arc-derived, Eocene formations in Luzon could very well be traces of the now consumed East Asia Sea-proto-Philippine Sea Plate. Within the same period, we modified the Palawan Microcontinental Block (PCB), positioned at the trailing edge of the proto-South China Sea to include the whole Mindoro island and the Romblon Island Group in Central Philippines. Pieces of the consumed Izanagi Plate, the proto-South China Sea and continental-derived sediments from Asia mainland are reflected in the Mesozoic metamorphic rocks and the Eocene sedimentary formation in western Mindoro. Finally, we model Cebu, Bohol and Negros islands in Central Philippines as being at the leading oceanic edge of the Indo-Australian Plate during the early Cenozoic. With the northward movement of the Indo-Australian plate and the trench roll back of the southern margins of the Philippine Sea Plate, the accretion of the Cretaceous arc-related rocks of Cebu, Bohol and Negros onto the Philippine arc by the end of Eocene or early Oligocene becomes a possibility.

An Improved Algorithm for Refinement of Overlapping Images of Marine Organisms

Li, K.; Jia, L., and Shi, X., 2020. An improved algorithm for refinement of overlapping images of marine organisms. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 67–71. Coconut Creek (Florida), ISSN 0749-0208.Aiming at the shortcomings of the current ocean Ocean image edge detection algorithm, such as poor real-time performance, slow Ocean image processing and limited storage space, an improved ocean Ocean image overlay Ocean image refinement algorithm is designed. Collect overlapping Ocean images of marine organisms and store large amounts of Ocean images in SDRAM memory; use traditional SOBEL operators to detect overlapping portions of ocean Ocean images, use non-maximum suppression to refine Ocean image edges, and clearly and accurately display ocean edges through VGA interface Ocean image. The experimental results show that the method can locate the edge of the overlapping Ocean images of marine organisms more accurately, and the refinement process has better real-time performance, which can be applied to more complex edge detection of overlapping Ocean images of marine organisms.

An event of simultaneous activity of atmospheric gravity waves and meteotsunami in the inner continental shelf of the Buenos Aires Province, Argentina

The aim of this paper is to investigate an event of simultaneous activity of atmospheric gravity waves (AGW) and meteotsunami recorded on December 1–2, 2013, in the inner continental shelf of Buenos Aires Province, Argentina. The Weather Research and Forecasting (WRF) model was implemented to simulate high-frequency atmospheric disturbances. WRF outputs were used to drive an oceanic model (Tide And Wind Induced Circulation, TAWIC) to reproduce the observed meteotsunami. WRF model was validated using twenty-five data series of atmospheric pressure, and a high-resolution atmospheric pressure data series observed at Mar del Plata. TAWIC model was validated using a high-resolution sea-level data series recorded at Mar del Plata. WRF model was able to capture the main synoptic and mesoscale features during the simulated period. Wavelet and cross-wavelet analysis showed that the spectral structures of the AGW and meteotsunami were satisfactorily simulated. AGW propagated following the storm track, and its activity area was mainly bounded between Mar del Plata and Punta Médanos. Numerical simulations showed that the meteotsunami was practically negligible westwards Quequén Port and at the Río de la Plata mouth, and that it was amplified when the AGW propagated along the coast. Numerical results suggest that the meteotsunami can be seen like an ocean edge wave propagating along the coast of the Buenos Aires Province.

El sentimiento de arraigo territorial en segundo-residentes en la costa del estado de Paraná, Brasil.

Este estudio aborda el sentimiento de arraigo territorial en segundo-residentes en los municípios balnearios de la Costa del Estado brasileño de Paraná: Matinhos, Guaratuba y Pontal do Paraná. Estos asentamientos inician en este territorio de una forma aún tímida en la década de 1920, ocupando franjas cercanas a la Costa, siguiendo el modelo de urbanización para el ocio y segundas residências de Europa.Aunque algunos autores señalan que en el turismo en segundas residências no hay arraigo local (O'Reilly, 1995; Müller, 2002; Aronsson, 2004; Duval, 2004), a partir de investigaciones en Europa, este estudio busca identificar elementos en los propietarios de segundas residências en la Costa del Paraná que puedan indicar enlaces de arraigo con los territorios donde hicieron sus inversiones. La investigación utilizó indicadores de arraigo territorial ya probados por Gubert y Pollini (1992). El objetivo es verificar si hay modelos referenciales en cuanto a valores y las posibles causas de un comportamiento isonomo o diferenciado en los tres municípios investigados.La metodología utilizada para el estudio de situaciones complejas como el sentimiento de arraigo territorial es una combinación de estudio de caso, con investigación cuantitativa, utilizando la técnica de cuestionarios (Survey). Se aplicaron 280 cuestionarios, buscando responder al problema planteado: ¿habría una relación de competencia entre los residentes en los balnearios, con una perspectiva localista y los segundo-residentes, que frecuentan el territorio ocasionalmente, desde una perspectiva cosmopolita?

Wind forcing controls on river plume spreading on a tropical continental shelf

AbstractThe Berau Continental Shelf is located close to the Equator in the Indonesian Archipelago, hosting a complex of coral reefs along its oceanic edge. The Berau coral reefs have a very high biodiversity, but the area is under serious risk due to river‐derived nutrients and sediments. The region is characterized by weak winds, moderate tides, and almost absent Coriolis forcing. Existing knowledge about river plume behavior in tropical environments is limited. The aim of this paper is to investigate the influence of the subtle physical forcing on the dynamics of the Berau river plume. A three‐dimensional model (ECOMSED) was calibrated with observational data. The model was forced by freshwater input from the Berau river distributaries, tides at the open boundaries, and measured hourly wind. The model reproduces the freshwater dynamics on the shelf adequately and highlights that the river plume spreads symmetrically for river forcing only. Tides cause vertical mixing and suppress the cross‐shelf spreading of the river plume. However, the spreading of the river plume over the shelf is mainly controlled by the weak monsoonal winds, resulting in a seasonal development. During the Southeast Monsoon, the southerly winds push the plume northeastward and cause a stratified water column in the northern part of the continental shelf. Northerly winds during the Northwest Monsoon disperse the plume to the south, promoting a vertically well‐mixed water column. The results can be used to predict the possible impact of land‐use changes in the steadily developing Berau region on coral reef health.

Fortnightly tides and subtidal motions in a choked inlet

Amplitudes of semi-diurnal tidal fluctuations measured at an ocean inlet system decay nearly linearly by 87% between the ocean edge of the offshore ebb-tidal delta and the backbay. A monochromatic, dynamical model for a tidally choked inlet separately reproduces the evolution of the amplitudes and phases of the semi-diurnal and diurnal tidal constituents observed between the ocean and inland locations. However, the monochromatic model over-predicts the amplitude and under-predicts the lag of the lower-frequency subtidal and fortnightly motions observed in the backbay. A dimensional model that considers all tidal constituents simultaneously, balances the along-channel pressure gradient with quadratic bottom friction, and that includes a time-varying channel water depth, is used to show that that these model-data differences are associated with nonlinear interactions between the tidal constituents that are not included in non-dimensional, monochromatic models. In particular, numerical simulations suggest that the nonlinear interactions induced by quadratic bottom friction modify the amplitude and phase of the subtidal and fortnightly backbay response. This nonlinear effect on the low-frequency (subtidal and fortnightly) motions increases with increasing high-frequency (semi-diurnal) amplitude. The subtidal and fortnightly motions influence water exchange processes, and thus backbay temperature and salinity.

Disasters, Natural and Unnatural: Reflections on March 11, 2011, and Its Aftermath

On March 11, 2011, at 2:46 p.m. local time, an earthquake with an epicenter 130 kilometers east of Sendai off the Pacific coast of northern Japan shook the Tohoku region more violently than any tremor in a thousand years. The quake was approximately 9.0 in magnitude, and it in turn triggered a set of tsunami hurtling across the Pacific Ocean, striking first the coast of Tohoku with waves of unprecedented height and strength, along a coastline stretching roughly 400 kilometers. In Fukushima, 180 kilometers west-southwest of the epicenter, 15-meter waves roared over seawalls supposedly protecting a nuclear reactor built just a few meters from the ocean's edge, starting a chain of events that resulted in an explosion the following day that began the release of radioactive materials (which continues still), sparking high anxiety if not palpable panic in Tokyo, the center of which is 240 kilometers to the south-southwest of the Fukushima nuclear complex.

Tidal and subtidal flow patterns on a tropical continental shelf semi‐insulated by coral reefs

The present study sets out to describe the tidal and subtidal water motion at the Berau coastal shelf, which represents a tropical continental shelf area of variable width hosting a complex of barrier reefs along its oceanic edge. Moored and shipboard measurements on currents and turbulence were made as part of the multidisciplinary East Kalimantan Research Program. These results and collected data on sea levels, meteorology and bathymetry, were used to setup and calibrate a three‐dimensional barotropic hydrodynamic model in the ECOMSED environment, which is derived from the Princeton Ocean Model. Concurrent profile measurements of flow velocity and Reynolds stress with an acoustic Doppler current profiler were used to infer values of the drag coefficient on locations on the shelf and within the barrier reef environment. The drag coefficients determined from shelf measurements differed less than 20% from optimal model settings. Diurnal and semidiurnal tides have the same character, propagating across the isobaths with amplitudes that increase toward the coast. The tidal amplification is captured in a one‐dimensional model, revealing an analogy with the Amazon Shelf. Regarding the subtidal depth‐mean flow, tidal Eulerian residual currents dominate over monsoon‐driven currents. Lagrangian mean flows reveal freshwater pathways from the coast to the coral reef environment. At a regional scale, the reef complex is established to be semitransparent to tides. The barrier reef influences the tidal phases rather than the amplitudes, especially in the shelf region that is fringed by the reefs. This may explain why tidal phases predicted from hydrodynamic models of tropical continental shelves often feature substantial discrepancies from observations.

Sapere Aude!

Sapere Aude!

Electromagnetic Induction in a Thin Strip

Summary Electromagnetic induction in a thin strip is investigated to provide further understanding of the geomagnetic effects at an ocean edge. A solution to the equations is found by an analytic technique. It is shown that even in the case where the integrated conductivity is finite, infinite field strengths occur at the edges accompanied by rapid changes in phase.

Geology and geochemistry of the clastic sequences from Northwestern Panay (Philippines): Implications for provenance and geotectonic setting

Whole-rock geochemical analysis of samples from the clastic sequences in Northwestern Panay revealed different compositional ranges for the Buruanga Peninsula and Antique Range. The results provide additional evidence that Northwestern Panay consists of two distinct terranes as a result of the arc-continent collision between the Palawan Microcontinental Block and the Philippine Mobile Belt. Major element compositions of clastic rocks from the Buruanga Peninsula (Saboncogon Formation) revealed that they belong to a continental margin tectonic setting whereas the Antique Range sedimentary rocks (Lagdo Formation) show an affinity to an oceanic island arc setting. The Fragante Formation of the Antique Range shows some similarities in tectonic setting and provenance with Buruanga Peninsula clastic rocks, which suggests a Buruanga Peninsula sediment contribution during its time of formation. Furthermore, provenance analyses from combined major and trace element data indicate a more silicic source for the Buruanga Peninsula clastics and a more mafic derivation for the sedimentary rocks of the Antique Range. These findings are consistent with previous studies suggesting that the Buruanga Peninsula forms part of the Palawan Microcontinental Block and the Antique Range belongs to the Philippine Mobile Belt. The Palawan Microcontinental Block is believed to be a drifted continental fragment from the Mesozoic East Asian accretionary complex in the southern part of the Eurasian mainland, which represents the continental margin setting and felsic source of the Buruanga Peninsula clastic rocks. Meanwhile, the oceanic island setting and mafic source of the Antique Range clastic rocks represent the volcanic rocks of the Philippine Mobile Belt that were formed as a result of the subduction of the leading oceanic edge of the Palawan Microcontinental Block.

Crustal structure of the continent-ocean transition off the Côte d'Ivoire-Ghana transform margin: implications for thermal exchanges across the palaeotransform boundary

Crustal structure of the continent–ocean transition off the Côte d'Ivoire–Ghana transform margin is determined by 2‐D modelling of wide‐angle seismic data and gravity data. The resulting models, together with geological data recently collected by drilling on the margin, are compared with available thermomechanical models of transform margins. In particular, we test the predicted effects on the transform margin crust of continental heating by the adjacent oceanic lithosphere. These effects include: (i) ductile flow of the lower continental crust either parallel to the transform direction or perpendicular to it, from the continent towards the ocean; and (ii) thermal uplift of the transform margin. In the region of the Côte d'Ivoire–Ghana transform margin, the seismic and gravity data indicate that the continental crust remains uniform in thickness as the continent–ocean boundary is approached. The interpreted models lack a transitional domain between continental and oceanic crusts, and abnormally thin oceanic crust is found along the margin. These results exclude large‐scale ductile flow of lower continental crust during the margin formation. The geological data are, moreover, not consistent with thermal uplift of the margin during the period of contact between the transform margin and the spreading centre. Our geophysical and geological data thus infer only moderate heating of the transform continental margin by the adjacent oceanic lithosphere. Moderate heating of the Côte d'Ivoire–Ghana transform margin during margin formation implies that the thermal exchange between the transform margin and the adjacent spreading centre were lower than predicted by available thermal models. Two main factors may have contributed to reduce thermal exchanges across the continent–ocean boundary. The first factor is that the oceanic edge may have been colder than assumed by thermal models. An abnormally cold spreading axis along the transform margin when the oceanic crust was emplaced is supported by the atypical structure of the oceanic crust along the Côte d'Ivoire–Ghana transform margin. The oceanic crustal structure is similar to that found along oceanic fracture zones, where oceanic crust is also emplaced near a ridge–transform intersection. In both cases, abnormally low thermal gradients at the spreading centre along the transform margin may be explained by the cumulative effect of: (i) a cold edge effect of the adjacent continental lithosphere; (ii) accretion at the end of a ridge segment, away from the main magma supply point along the spreading axis; and (iii) an efficient upward cooling of the oceanic lithosphere owing to deep hydrothermal circulation within the faulted lithosphere. The second factor causing moderate thermal exchanges is the possibility of large amounts of water in oceanic lithospheric faults, which reduces the lateral thermal conduction in the lithosphere, since water is much less conductive than rock. During the margin formation, the oceanic edge thus seems to have acted as a thermal buffer between the cold continental margin and the hot spreading centre. We propose that this thermal buffer hypothesis may be generalized to most transform margins, implying a lower amount of continental heating than assumed by the available thermomechanical models.

Climate Change and the Episodicity of Sediment Flux of Small California Rivers

We studied the streamflow and sediment flux characteristics of the 20 largest streams entering the Pacific Ocean along the central and southern California coast, extending for 750 km from Monterey Bay to just south of the U.S./Mexico border. Drainage basins ranged in area from 120 to 10,800 km2, with headwater elevations ranging from 460 to 3770 m. Annual streamflow ranged from 0 to a maximum of $$1\times 10^{9}$$ m3/yr for the Santa Clara River in 1969, with an associated suspended sediment flux of $$46\times 10^{6}$$ ton. Trend analyses confirm that El Niño/Southern Oscillation–induced climate changes recur on a multidecadal time scale in general agreement with the Pacific/North American climate pattern: a dry climate extending from 1944 to about 1968 and a wet climate extending from about 1969 to the present. The dry period is characterized by consistently low annual river sediment flux. The wet period has a mean annual suspended sediment flux about five times greater, caused by strong El Niño events that produce floods with an average recurrence of ca. 5 yr. The sediment flux of the rivers during the three major flood years averages 27 times greater than the annual flux during the previous dry climate. The effects of climate change are superimposed on erodibility associated with basin geology. The sediment yield of the faulted, overturned Cenozoic sediments of the Transverse Ranges is many times greater than that of the Coast Ranges and Peninsular Ranges. Thus, the abrupt transition from dry climate to wet climate in 1969 brought a suspended sediment flux of 100 million tons to the ocean edge of the Santa Barbara Channel from the rivers of the Transverse Range, an amount greater than their total flux during the preceding 25‐yr dry period. These alternating dry to wet decadal scale changes in climate are natural cycles that have profound effects on fluvial morphology, engineering structures, and the supply of sediment and associated agricultural chemicals to the ocean.

The Effect of a Simple Model of the Pacific Ocean on Sq Variations

The problem solved is that of electromagnetic induction in a thin non-uniformly conducting hemispherical shell underlain by, and insulated from, a perfectly conducting sphere. Since the shell is assumed thin, only the component of a varying magnetic field normal to the shell induces electric current in the shell. This mode of induction is termed vertical component induction. The conductance and configuration of the surface shell are simple approximations to those of the Pacific Ocean. Calculations are made of the effect of induction by the Sq variation field and results are presented for typical “land” and “ocean” regions, and for a profile of stations near the ocean edge. The results from this profile of stations are compared to observations made by SCHMUCKER (1970) near the coast of California. The calculated and observed daily variations of the vertical component of the magnetic field are in qualitative agreement.

Induction in Arbitrarily Shaped Oceans II

Analytic edge corrections are developed suitable for matching with approximate solutions (derived otherwise) for perfectly conducting oceans. By comparison with the solution of a particular problem, it is verified that the matched solutions are good all the way to the edge of the idealized oceans. They reproduce accurately the well known singularity on the coastline, and this property is essential if the solutions are in turn to match those for finite conductivity. Often an appreciable (oscillating) magnetic field passes beneath the “ocean”, and this should perhaps be included in future calculations involving ocean edge effects.

H-polarization induction over an ocean edge coupled to the mantle by a conducting crust

Summary. The Wiener—Hopf technique is used to obtain an exact analytical solution for the problem of H-polarization induction over the edge of a perfectly conducting thin sheet, representing an ocean, electrically connected to a perfectly conducting mantle through a slab of finite conductivity and thickness, which represents the Earths crust. It is shown that the induced currents resulting from this type of induction process are drawn up into the sea from the cust and mantle with the greatest concentration of current near the ocean edge. The surface impedance over the land surface, is calculated for various mantle depths and is shown to increase sharply as the coastline is approached. The magnetic field along the ocean floor is also plotted as a function of distance from the coastline, and the results are found to agree very well with those calculated previously by approximate and numerical methods.

Electromagnetic induction over the edge of a perfectly conducting ocean: the H-polarization case

Summary. Using the Wiener—Hopf technique, a solution is obtained for the problem of H-polarization electromagnetic induction at an ocean edge. The ocean is represented by a perfectly conducting thin sheet. The implications of the solution for magnetotelluric and geomagnetic sounding are discussed.

Shoreline development controls and public access to the ocean's edge

Abstract The San Diego Coast Regional Commission, faced with the responsibility of approving, approving with conditions, or denying permits for development proposed along the scenic coastal bluffs of San Diego county, has adopted guidelines for bluff‐top development which assures retention of scenic vistas and provision of public access while permitting private landowners “reasonable use”; of their property. These unique guidelines delineate certain environmental and aesthetic parameters within which bluff‐top development may take place. Portions of the guidelines are presented, and some of the factors leading to their formulation and adoption are discussed.