Física Aplicada

Validation of the Surface Water and Ocean Topography (SWOT) KaRIn Sea Level Data

Thu, 01 Jan 2026 00:00:00 GMT

Validation of the Surface Water and Ocean Topography (SWOT) KaRIn Sea Level Data Gómez Enri, Jesús; Arribas-Rodriguez, B.; Tejedor Álvarez, María Begoña; Álvarez Esteban, Óscar; González Mejías, Carlos José; Vignudelli, S. The Ka-band interferometer (KaRIn) altimeter onboard U.S.-French Surface Water and Ocean Topography (SWOT) satellite is the first swath altimeter in operation. Its main innovation is its 2-D view of the Earth's surface, widening the ocean and land applications of satellite altimetry. The main objective of our work was to validate the sea level derived from KaRIn with the water levels from three tide gauges located around Spanish coasts at stations in Huelva, Barcelona, and Bilbao. To do this, we estimated the standard deviation of the differences (SDDs) between the altimeter and the ground-truth data. The accuracy of the Sentinel-3A (S3A) satellite was also computed for comparison. We analyzed two/one track at each location for SWOT/S3A. From the options available to compute the sea level anomaly (SLA) from SWOT, we tested the wet tropospheric correction (WTC), the mean sea surface (MSS), and the tidal model. The comparisons with the tide gauges revealed that the ECMWF model for the WTC gave a higher number of valid data and the same level of accuracy as the correction derived from the advanced microwave radiometer (AMR) instrument. The same accuracy was observed regardless of the MSS used (CNES and DTU). Finally, the FES tidal model improved the accuracy with respect to the DTU model. The average SDD of SWOT oscillates between 7:4 ± 0:8 cm (Bilbao) and 12:2 ± 2:3 cm (Barcelona). A more in-depth analysis of the SWOT data at the Barcelona station revealed a cycle with anomalous sea level anomalies not detected in the data screening. Removing that cycle, the average SDD dropped to 8:7 ± 1:7 cm. S3A showed 4%-24% better accuracy than SWOT.

From Coastal Flooding to Residual Beach Functionality: Implications of Sea-Level Rise for Coastal Management in Southern Spain

Fri, 16 Oct 2026 00:00:00 GMT

From Coastal Flooding to Residual Beach Functionality: Implications of Sea-Level Rise for Coastal Management in Southern Spain Contreras de Villar, Antonio; Contreras de Villar, Francisco; Vidal Pérez, Juan Manuel; Pérez Moreno, Cristina; Alonso del Rosario, José Juan; López García, Patricia; Jigena Antelo, Bismarck; Muñoz Pérez, Juan José Sea-level rise may substantially reduce the dry space available on sandy beaches, although its effects depend strongly on local beach characteristics. This study evaluates the residual spatial functionality of five beaches in southern Spain using two normalized indicators: residual available surface area (FA) and residual available beach width (FW). Both express the proportion of dry beach space remaining relative to a common present-day reference condition without wave run-up. The analysis builds on previously calculated inundation results for present conditions and representative Concentration Pathway (RCP) 4.5 and RCP 8.5 scenarios for 2026–2045 and 2081–2100, including astronomical tide, meteorological residual, sea-level rise, and wave run-up. Marked differences are observed among the studied beaches across both time periods. Under RCP 4.5 in 2026–2045, Torreguadiaro retains 85.1% of its reference area and 79.8% of its reference mean width. Rinconcillo retains 31.9% and 38.7%, respectively. Under RCP 8.5 in 2081–2100, these values decrease to 75.6% and 65.3% at Torreguadiaro. At Rinconcillo, they decrease to 7.1% and 17.6%. FA and FW also evolve differently among sites: their values remain relatively close at Malagueta but diverge markedly at Rinconcillo under the most severe scenario. Joint consideration of FA and FW therefore provides complementary information on the amount and configuration of residual dry beach space and may support comparison among beaches from a coastal management perspective.

Morpho-stratigraphic features of the northern shelf of the Strait of Gibraltar: Tectonic and sedimentary processes acting at different temporal scales

Mon, 01 Jan 2018 00:00:00 GMT

Morpho-stratigraphic features of the northern shelf of the Strait of Gibraltar: Tectonic and sedimentary processes acting at different temporal scales Luján Martínez, María; Lobo, Francisco José; Bruno Mejías, Miguel; De Castro, Sandra The northern shelf of the Strait of Gibraltar adjacent to Camarinal Sill, defined here as the Cape Paloma continental shelf, has been investigated by analyzing a set of geophysical data including multibeam bathymetric images, a side-scan sonar mosaic and high-resolution seismic profiles, and the simulation of water-mass circulation patterns along the northern coastal margin. The aim of the study was to establish the significance of factors determining the evolution of this shallow margin at different temporal scales and to assess the implications for bedform generation in strait settings, taking into account the complex tectonic evolution and the energetic hydrodynamic regime of the strait. Deformed basement rocks are part of the Betic-Rif thrust wedge, western Gibraltar Arc, mainly formed by the materials of the Flysch Complex units and covered by Pliocene to Quaternary post-orogenic deposits. A central high (Bajo de los Cabezos High) is delimited by lateral depressions, that nucleated two major depocentres with distinctive filling histories. The eastern depocentre is controlled by WNW-ESE faults cutting the Cretaceous-Miocene basement rocks; these faults generate horsts and grabens that could have contributed to the opening of the Strait of Gibraltar during the Pliocene. The largest and westernmost depocentre is related to the complete infilling of a shelf palaeovalley. The sediment cover is molded by different fields of submarine dunes and comet marks that indicate the influence of hydrodynamic processes on sediment transport at the coastal margin. The observations in the study area regarding bedform development must be placed into a wider context of strait sediment dynamics. The Cape Paloma continental shelf exhibits both erosional and depositional forms, due to its intermediate location between the strait, mostly dominated by erosional processes, and the Barbate Platform (northwest of the study area), mostly characterized by depositional forms. The long-term evolution of the sediment depocentres in the study area appears to be mainly influenced by the morpho-tectonic configuration of the margin, which in turn was established to a large extent by differential uplifting along the coast. In the shelf east of the central high, the basement horst and graben structure trapped sediments in the physiographic lows and fostered the formation of large-scale sediment banks. In the shelf west of the central high, the occurrence of a major infilled palaeovalley is in agreement with a gentle subsidence trend. The physiographic configuration is also thought to play a major role in defining short-term processes, particularly in confining a cyclonic eddy to the east of the Bajo de los Cabezos High during specific conditions of the tidal cycle. This eddy favors the recirculation of sediments in the coastal margin, as evidenced by small bedform fields that apparently show a wider distribution that the larger-scale, confined sediment banks, due to the instauration of the modern sediment dynamics after the complete shelf flooding. The sediment transport pattern established in the study area seems to be eventually captured by a submarine channel that provide an efficient mechanism for sediment export toward deep-water settings, where an extensive contourite depositional system has been documented

Characterization of marine heatwaves and their impacts on phytoplankton dynamics across contrasting marine ecoregions

Thu, 01 Jan 2026 00:00:00 GMT

Characterization of marine heatwaves and their impacts on phytoplankton dynamics across contrasting marine ecoregions Fernández Barba, Manuel Ángel El océano regula el clima de la Tierra absorbiendo y redistribuyendo dióxido de carbono (CO2) y calor atmosférico. Las emisiones antropogénicas han acelerado el calentamiento a largo plazo, dando lugar a temperaturas oceánicas récord. Superpuestas a estas tendencias, las olas de calor marinas (MHWs, por sus siglas en inglés) –períodos prolongados de temperaturas oceánicas excepcionalmente cálidas– están aumentando en magnitud y frecuencia, con profundas consecuencias para la estructura y el funcionamiento de los ecosistemas marinos. Dado que existen incertidumbres clave en torno a su correcta caracterización y a sus diversos impactos ecológicos regionales, esta tesis doctoral profundiza en la comprensión de las MHWs y sus efectos sobre la dinámica del fitoplancton en las ecorregiones marinas españolas (SMEs, por sus siglas en inglés) y en el Océano Austral (SO, por sus siglas en inglés). La tesis presenta la primera caracterización completa de MHWs superficiales (SMHWs) y de fondo (BMHWs) en las SMEs, a partir de observaciones satelitales y datos de reanálisis oceánico de alta resolución. Tanto las SMHWs como las BMHWs han adquirido mayor intensidad, duración y extensión geográfica en los últimos años. Las ecorregiones mediterráneas han registrado los mayores incrementos en el número de días anuales con SMHWs y BMHWs, mientras que la intensificación más acusada de las BMHWs (+0,5 °C en la última década) se ha producido en las plataformas someras del golfo de Cádiz y las islas Canarias. La evaluación conjunta revela que el 69 % de las zonas costeras españolas (profundidad inferior a 400 m) ha permanecido altamente expuesto a la coocurrencia de SMHWs y BMHWs intensas durante el período 1993–2022. Asimismo, 26 años de observaciones satelitales de color del océano de muy alta resolución documentan cambios regionalmente diferenciados en la fenología del fitoplancton, con floraciones que inician y terminan antes y exhiben una producción acumulada estacional reducida. El Modelado Empírico Dinámico (EDM, por sus siglas en inglés), mediante el Mapeo Cruzado Convergente (CCM, por sus siglas en inglés) y su extensión geográfica (GCCM), identifica relaciones causales unidireccionales y no estacionarias donde las MHWs modulan la dinámica del fitoplancton a escalas temporales estacionales e interanuales, mientras que la intensidad del viento actúa sobre escalas más cortas, con una capacidad predictiva que se acentúa durante los años de mayor intensidad y extensión de los eventos extremos. Asimismo, esta tesis ofrece la primera caracterización sistemática de las MHWs en el SO, incluyendo un marco metodológico adaptado a las regiones polares, a partir de observaciones satelitales y modelado numérico (1982–2021). Se han registrado incrementos decadales significativos en las propiedades de las MHWs, aunque con una marcada regionalidad: el sector Índico ha emergido como punto caliente de MHWs, el sector Atlántico ha exhibido las mayores magnitudes (anomalías locales de hasta 11 °C) y el sector Pacífico las duraciones más prolongadas (> 30 días). La superficie oceánica al sur de los 40°S que experimenta al menos una MHW anualmente se ha expandido un 20 % en los últimos años. Además, los análisis de balances de calor revelan que los flujos de calor aire-mar y la difusión vertical han dominado el inicio y la disipación de las MHWs, especialmente en las regiones polares y subantárticas meridionales, donde el retroceso sin precedentes del hielo marino ha desempeñado un papel clave. En estas regiones, la estratificación inducida por MHWs y los aportes de micronutrientes procedentes del deshielo marino han favorecido incrementos en la producción primaria neta (NPP, por sus siglas en inglés) de ~100 mg C m-2 day-1 respecto a los períodos sin MHWs. Si bien el CCM revela el papel central de las MHWs en la promoción de eventos de NPP elevada en las proximidades del borde estacional del hielo marino, la heterogeneidad zonal refleja las respuestas diferenciadas de los productores primarios a lo largo del vasto océano Austral. En conjunto, la investigación aquí desarrollada resalta el incremento global de las MHWs conforme el océano se calienta, a la vez que evidencia la marcada especificidad regional de las respuestas fitoplanctónicas. Estos hallazgos sitúan a las MHWs, más allá de meras anomalías térmicas, como elementos estructurales del funcionamiento de los ecosistemas marinos bajo el cambio climático acelerado.; The ocean regulates Earth’s climate by absorbing and redistributing atmospheric carbon dioxide (CO2) and heat. Anthropogenic emissions have accelerated long-term warming, resulting in unprecedented greenhouse gas concentrations and record-high ocean temperatures. Superimposed on these trends, extreme events such as marine heatwaves (MHWs) –prolonged periods of anomalously warm ocean temperatures– are increasing in magnitude and frequency, with profound consequences for global marine ecosystem structure and functioning. Despite growing attention, key uncertainties remain regarding their proper characterization and diverse regional ecological impacts. Accordingly, this doctoral thesis advances the understanding of MHWs and their effects on phytoplankton dynamics, as central regulators of marine biogeochemical cycles and climate. The investigation focuses on Spanish Marine Ecoregions (SMEs) and the Southern Ocean (SO), both areas of distinctive ecological relevance at different scales yet largely unexplored in terms of MHWs. The thesis begins by presenting the first complete characterization and assessment of surface (SMHWs) and bottom MHWs (BMHWs) across the SMEs, using highresolution satellite observations and ocean reanalysis data. A methodology separating long-term trends from extremes reveals that both SMHWs and BMHWs have become more intense, longer-lasting, and widespread in recent years. Mediterranean ecoregions have experienced the largest increases in annual SMHW and BMHW days, while the southern peninsular coasts have exhibited the highest SMHW intensities. The strongest BMHW intensification (+0.5 °C over the last decade) has occurred on shallow shelves of the Gulf of Cádiz (SA) and the Canary Islands (CAN). BMHWs have generally persisted longer than their surface counterparts, likely due to reduced atmospheric dissipation. However, their magnitude and persistence have scaled strongly with ocean bottom depth through deep-current advection. Further, BMHWs have matched or exceeded SMHW intensities in shallow coastal regions where the mixed layer reaches the seafloor. Joint assessment indicates that 69% of the Spanish coastal areas (< 400 m depth) have remained highly exposed to co-occurring intense SMHWs and BMHWs during 1993–2022, underscoring the need to integrate both in ecological and socioeconomic impact assessments. Additionally, analysis of 26 years of very-high-resolution satellite oceancolor observations documents regionally distinct shifts in phytoplankton phenology (i.e., the timing and intensity of blooms) across SMEs. Blooms have initiated and terminated earlier and have exhibited reduced cumulative seasonal production over the past decade, consistent with progressive upper-ocean warming. In addition, greater variability in seasonal cycles has been identified during climatically unstable years. To quantify the role of extreme events (MHWs and high-speed wind events, Windiness) in modulating phytoplankton blooms, Empirical Dynamic Modeling (EDM), including Convergent Cross Mapping (CCM) and its geographical extension (GCCM), is applied. The analysis identifies unidirectional, nonstationary causal relationships whereby extreme events can predict phytoplankton dynamics, but not conversely, with predictive skills strengthening during years of intensified and widespread extremes. MHWs influence phytoplankton at seasonal to interannual scales, whereas Windiness operates on shorter timescales. Together, these findings provide quantitative foundations for forecasting ecosystem responses under future climate change scenarios. This thesis also provides the first comprehensive characterization of MHWs in the SO, based on satellite observations and numerical modeling (1982–2021). A characterization framework adapted for polar regions, incorporating elevated reference thresholds (95th percentile combined with the long-term mean summer temperature), isolates ecologically relevant extreme events under long-term warming. Significant decadal increases in MHW properties have occurred, although strong regionality prevails. The Indian sector has emerged as a MHW hotspot, with events becoming more frequent (~2 events per decade), while the Atlantic sector has exhibited the largest magnitudes (anomalies up to 11 ºC locally) and the Pacific sector the longest durations (> 30 days), closely linked to strong El Niño events. Circumpolarly, the ocean surface south of 40ºS experiencing at least one MHW annually has expanded by 20% in recent years. Further, using a fully coupled global carbon-climate Earth system model, this work examines the local physical drivers of the intensification of SO MHWs. Heat-budget analyses show that ocean advection, air-sea heat fluxes, and vertical diffusion have contributed to both MHW onset and decay, whereas convective vertical mixing has acted oppositely. Air-sea fluxes and vertical diffusion have dominated overall, particularly in polar and southern subantarctic regions where unprecedented sea-ice decline has played a key role. In these regions, MHW-induced stratification and micronutrients (e.g., iron) inputs from sea-ice melt have promoted increases in net primary production (NPP). Under MHW conditions, mean NPP has increased by ~100 mg C m-2 day-1 , while minimum rates have increased by an order of magnitude relative to non-MHW periods. CCM quantifies spatiotemporal causal relationships between maximum sea surface temperature anomalies, sea-ice concentrations, mixed-layer depth, and NPP; highlighting the role of MHWs in promoting high-NPP events, particularly near the seasonal sea-ice edge. Zonal heterogeneity in predictive skill reveals the distinctive responses of primary producers inhabiting the vast SO to differing and changing physical conditions. Collectively, these findings represent a novel twofold contribution by providing the first characterization of MHWs in the SO and new perspectives on primary producer responses to these extreme events in highlatitude regions, with potential implications for improving forecasts of the ocean carbon cycle in a changing climate. Overall, the research conducted in this doctoral thesis highlights the global increase in MHW activity as the ocean warms, while also emphasizing the strong regional specificity of phytoplankton responses, which depend on the physical and biogeographic context in which these events develop. These findings position MHWs, beyond being simple thermal anomalies, as key structural elements in the functioning of marine ecosystems under accelerated climate change.