Browsing by Author "Dewitte, Boris"
Now showing 1 - 20 of 45
Results Per Page
Sort Options
Item Open Access A global ocean oxygen database and atlas for assessing and predicting deoxygenation and ocean health in the open and coastal ocean(Frontiers Media, 2021-12-21) Grégoire, Marilaure; Garçon, Véronique; Garcia, Hernan; Breitburg, Denise; Isensee, Kirsten; Oschlies, Andreas; Telszewski, Maciej; Barth, Alexander; Bittig, Henry C.; Carstensen, Jacob; Carval, Thierry; Chai, Fei; Chavez, Francisco; Conley, Daniel; Coppola, Laurent; Crowe, Sean; Currie, Kim; Dai, Minhan; Deflandre, Bruno; Dewitte, Boris; Diaz, Robert; Garcia-Robledo, Emilio; Gilbert, Denis; Giorgetti, Alessandra; Glud, Ronnie; Gutierrez, Dimitri; Hosoda, Shigeki; Ishii, Masao; Jacinto, Gil; Langdon, Chris; Lauvset, Siv K.; Levin, Lisa A.; Limburg, Karin E.; Mehrtens, Hela; Montes Torres, Ivonne; Naqvi, Wajih; Paulmier, Aurélien; Pfeil, Benjamin; Pitcher, Grant; Pouliquen, Sylvie; Rabalais, Nancy; Rabouille, Christophe; Recape, Virginie; Roman, Michaël; Rose, Kenneth; Rudnick, Daniel; Rummer, Jodie; Schmechtig, Catherine; Schmidtko, Sunke; Seibel, Brad; Slomp, Caroline; Sumalia, U. Rashid; Tanhua, Toste; Thierry, Virginie; Uchida, Hiroshi; Wanninkhof, Rik; Yasuhara, MoriakiIn this paper, we outline the need for a coordinated international effort toward the building of an open-access Global Ocean Oxygen Database and ATlas (GO₂DAT) complying with the FAIR principles (Findable, Accessible, Interoperable, and Reusable). GO₂DAT will combine data from the coastal and open ocean, as measured by the chemical Winkler titration method or by sensors (e.g., optodes, electrodes) from Eulerian and Lagrangian platforms (e.g., ships, moorings, profiling floats, gliders, ships of opportunities, marine mammals, cabled observatories). GO₂DAT will further adopt a community-agreed, fully documented metadata format and a consistent quality control (QC) procedure and quality flagging (QF) system. GO₂DAT will serve to support the development of advanced data analysis and biogeochemical models for improving our mapping, understanding and forecasting capabilities for ocean O₂ changes and deoxygenation trends. It will offer the opportunity to develop quality-controlled data synthesis products with unprecedented spatial (vertical and horizontal) and temporal (sub-seasonal to multi-decadal) resolution. These products will support model assessment, improvement and evaluation as well as the development of climate and ocean health indicators. They will further support the decision-making processes associated with the emerging blue economy, the conservation of marine resources and their associated ecosystem services and the development of management tools required by a diverse community of users (e.g., environmental agencies, aquaculture, and fishing sectors). A better knowledge base of the spatial and temporal variations of marine O₂ will improve our understanding of the ocean O₂ budget, and allow better quantification of the Earth’s carbon and heat budgets. With the ever-increasing need to protect and sustainably manage ocean services, GO₂DAT will allow scientists to fully harness the increasing volumes of O₂ data already delivered by the expanding global ocean observing system and enable smooth incorporation of much higher quantities of data from autonomous platforms in the open ocean and coastal areas into comprehensive data products in the years to come. This paper aims at engaging the community (e.g., scientists, data managers, policy makers, service users) toward the development of GO₂DAT within the framework of the UN Global Ocean Oxygen Decade (GOOD) program recently endorsed by IOC-UNESCO. A roadmap toward GO₂DAT is proposed highlighting the efforts needed (e.g., in terms of human resources).Item Restricted A theoretical model of strong and moderate El Niño regimes(Springer, 2019-06-01) Takahashi, Ken; Karamperidou, Christina; Dewitte, BorisThe existence of two regimes for El Niño (EN) events, moderate and strong, has been previously shown in the GFDL CM2.1 climate model and also suggested in observations. The two regimes have been proposed to originate from the nonlinearity in the Bjerknes feedback, associated with a threshold in sea surface temperature (\(T_c\)) that needs to be exceeded for deep atmospheric convection to occur in the eastern Pacific. However, although the recent 2015–16 EN event provides a new data point consistent with the sparse strong EN regime, it is not enough to statistically reject the null hypothesis of a unimodal distribution based on observations alone. Nevertheless, we consider the possibility suggestive enough to explore it with a simple theoretical model based on the nonlinear Bjerknes feedback. In this study, we implemented this nonlinear mechanism in the recharge-discharge (RD) ENSO model and show that it is sufficient to produce the two EN regimes, i.e. a bimodal distribution in peak surface temperature (T) during EN events. The only modification introduced to the original RD model is that the net damping is suppressed when T exceeds \(T_c\), resulting in a weak nonlinearity in the system. Due to the damping, the model is globally stable and it requires stochastic forcing to maintain the variability. The sustained low-frequency component of the stochastic forcing plays a key role for the onset of strong EN events (i.e. for \(T>T_c\)), at least as important as the precursor positive heat content anomaly (h). High-frequency forcing helps some EN events to exceed \(T_c\), increasing the number of strong events, but the rectification effect is small and the overall number of EN events is little affected by this forcing. Using the Fokker–Planck equation, we show how the bimodal probability distribution of EN events arises from the nonlinear Bjerknes feedback and also propose that the increase in the net feedback with increasing T is a necessary condition for bimodality in the RD model. We also show that the damping strength determines both the adjustment time-scale and equilibrium value of the ensemble spread associated with the stochastic forcing.Item Open Access Actividad de las ondas ecuatoriales y su impacto en la Temperatura Superficial del Mar en el Fenómeno El Niño 2002/2003(Instituto Geofísico del Perú, 2014-10) Mosquera Vásquez, Kobi Alberto; Dewitte, Boris; Illig, Serena; Takahashi, Ken; Garric, G.Es conocida la importancia para el Perú de pronosticar el Fenómeno El Niño (FEN) con la mayor confiabilidad y tiempo de anticipación posible. Para mejorar estos pronósticos, es necesario conocer y entender de manera precisa cada uno de los procesos físicos que están involucrados en el cambio de la Temperatura Superficial del Mar (TSM), variable que caracteriza la presencia de El Niño. Desde hace muchos años la comunidad científica está envuelta en alcanzar este objetivo, para lo cual se ha desarrollado mucho trabajo técnico-científico realizando observaciones in situ o mediante satélites, estudios estadísticos y teóricos, así como simulaciones con modelos numéricos complejos y simples del océano y atmosfera. Lamentablemente, como ya se sabía, y se ha vuelto a ver en este año 2014, los eventos El Niño pueden diferir bastante entre ellos y, además, aún existen vacíos científicos que limitan las predicciones del FEN. El objetivo del presente documento es mostrar, basándose en el trabajo de Mosquera-Vásquez et al. (2013), la actividad de las ondas Kelvin y Rossby ecuatoriales, así como su contribución en el cambio de la anomalía de la TSM en el Fenómeno El Niño 2002/2003, que puede ser considerado del tipo de “Pacífico Central” o “Modoki” (ver Takahashi, 2014). Para esto se realizó un análisis del balance de energía utilizando los datos oceánicos de un Modelo Oceánico de Circulación General (OGCM, por sus siglas en inglés) perteneciente a MERCATOR (http://www.mercator-ocean.fr/html/produits/index_en.html). Este modelo fue forzado por datos de viento y flujos de calor y agua superficiales observados, pero sin asimilación de datos oceánicos subsuperficiales. Los resultados fueron validados exitosamente con información in situ y satelital.Item Restricted Assessing the impact of downscaled winds on a regional ocean model simulation of the Humboldt system(Elsevier, 2013-05) Cambon, Gildas; Goubanova, Katerina; Marchesiello, Patrick; Dewitte, Boris; Illig, Serena; Echevin, VincentSimulating the oceanic circulation in Eastern Boundary Upwelling Systems (EBUS) is a challenging issue due to the paucity of wind stress products of a sufficiently high spatial resolution to simulate the observed upwelling dynamics. In this study, we present the results of regional simulations of the Humboldt current system (Peru and Chile coasts) to assess the value of a statistical downscaling model of surface forcing. Twin experiments that differ only from the momentum flux forcing are carried out over the 1992–2000 period that encompasses the major 1997/98 El Niño/La Niña event. It is shown that the mean biases of the oceanic circulation can be drastically reduced simply substituting the mean wind field of NCEP reanalysis by a higher resolution mean product (QuikSCAT). The statistical downscaling model improves further the simulations allowing more realistic intraseasonal and interannual coastal undercurrent variability, which is notoriously strong off Central Peru and Central Chile. Despite some limitations, our results suggest that the statistical approach may be useful to regional oceanic studies of present and future climates.Item Restricted Boundaries of the Peruvian oxygen minimum zone shaped by coherent mesoscale dynamics(Nature Research, 2015) Bettencourt, Joao; López, Cristobal; Hernández-García, Emilio; Montes Torres, Ivonne; Sudre, Joël; Dewitte, Boris; Paulmier, Aurélien; Garçon, VéroniqueDissolved oxygen in sea water is a major factor affecting marine habitats and biogeochemical cycles. Oceanic zones with oxygen deficits represent significant portions of the area and volume of the oceans and are thought to be expanding. The Peruvian oxygen minimum zone is one of the most pronounced and lies in a region of strong mesoscale activity in the form of vortices and frontal regions, whose effect in the dynamics of the oxygen minimum zone is largely unknown. Here, we study this issue from a modeling approach and a Lagrangian point of view, using a coupled physical-biogeochemical simulation of the Peruvian oxygen minimum zone and finite-size Lyapunov exponent fields to understand the link between mesoscale dynamics and oxygen variations. Our results show that, at depths between 380 and 600 meters, mesoscale structures have a relevant dual role. First, their mean positions and paths delimit and maintain the oxygen minimum zone boundaries. Second, their high frequency fluctuations entrain oxygen across these boundaries as eddy fluxes that point towards the interior of the oxygen minimum zone and are one order of magnitude larger than mean fluxes. We conclude that these eddy fluxes contribute to the ventilation of the oxygen minimum zone.Item Open Access Cambios en el ciclo estacional de la profundidad de la termoclina en el Pacífico ecuatorial antes y después del año 2000(Instituto Geofísico del Perú, 2016-08) Mosquera Vásquez, Kobi Alberto; Dewitte, BorisPara contar con una mejor comprensión de los mecanismos que provocan los cambios de las propiedades del ENSO después del año 2000, se requiere, en un primer paso, una investigación exhaustiva de los cambios observados en el ciclo estacional de la circulación ecuatorial. En esta investigación, que espera contribuir con lo indicado arriba, se usa observaciones suficientemente largas para evaluar los cambios en la estacionalidad en escalas de tiempo decadal. Asimismo, se analizan productos de oceánico y atmosférico, así como las simulaciones con modelos simples para tratar de interpretar dinámicamente los cambios en la estacionalidad.Item Restricted Change in El Niño flavours over 1958-2008: implications for the long-term trend of the upwelling off Peru(Elsevier, 2012-11-15) Dewitte, Boris; Vazquez-Cuervo, J.; Goubanova, Katerina; Illig, Serena; Takahashi, Ken; Cambon, G.; Purca, S.; Correa, D.; Gutierrez, D.; Sifeddine, A.; Ortlieb, L.The tropical Pacific variability has experienced changes in its characteristics over the last decades. In particular, there is some evidence of an increased occurrence of El Niño events in the central Pacific (a.k.a. ‘Central Pacific El Niño’ (CP El Niño) or ‘El Niño Modoki’), in contrast with the cold tongue or Eastern Pacific (EP) El Niño which develops in the eastern Pacific. Here we show that the different flavours of El Niño imply a contrasted Equatorial Kelvin Wave (EKW) characteristic and that their rectification on the mean upwelling condition off Peru through oceanic teleconnection is changed when the CP El Niño frequency of occurrence increases. The Simple Ocean Data Assimilation (SODA) reanalysis product is first used to document the seasonal evolution of the EKW during CP and EP El Niño. It is shown that the strong positive asymmetry of ENSO (El Niño Southern Oscillation) is mostly reflected into the EKW activity of the EP El Niño whereas during CP El Niño, the EKW is negatively skewed in the eastern Pacific. Along with slightly cooler conditions off Peru (shallow thermocline) during CP El Niño, this is favourable for the accumulation of cooler SST anomalies along the coast by the remotely forced coastal Kelvin wave. Such a process is observed in a high-resolution regional model of the Humboldt Current system using the SODA outputs as boundary conditions. In particular the model simulates a cooling trend of the SST off Peru although the wind stress forcing has no trend. The model is further used to document the vertical structure along the coast during the two types of El Niño. It is suggested that the increased occurrence of the CP El Niño may also lead to a reduction of mesoscale activity off Peru.Item Open Access La distribución de las lluvias en la vertiente del Pacífico peruano y su relación con El Niño(Instituto Geofísico del Perú, 2017-01) Rau, Pedro; Bourrel, Luc; Dewitte, Boris; Labat, DavidEn 1892, se difundió la primera observación documentada de la corriente costera “El Niño”, denominada por aquel entonces: “Contracorriente marítima en Paita y Pacasmayo” (Carranza, 1892) y donde se intentaba explicar las lluvias torrenciales acaecidas en 1891. Un siglo y cuarto después, aun continúa el reto de poder comprender el efecto de este fenómeno sobre las lluvias a diferentes escalas de espacio y tiempo, especialmente en regiones del planeta como la Vertiente del Pacífico Peruano (VPP), donde sus efectos son experimentados frecuentemente. En el presente artículo se responde a preguntas comunes sobre la distribución de las lluvias en la VPP y el impacto del Fenómeno El Niño o ENSO (El Niño Oscilación del Sur en inglés), basándose en una revisión del estado del arte en la temática, las metodologías y los nuevos aportes.Item Restricted Diversity of moderate El Niño events evolution: role of air–sea interactions in the eastern tropical Pacific(Springer, 2019-06) Dewitte, Boris; Takahashi, KenIn this paper we investigate the evolution of moderate El Niño events during their developing phase with the objective to understand why some of them did not evolve as extreme events despite favourable conditions for the non-linear amplification of the Bjerknes feedback (i.e. warm SST in Austral winter in the eastern equatorial Pacific). Among the moderate events, two classes are considered consisting in the Eastern Pacific (EP) El Niño events and Central Pacific (CP) events. We first show that the observed SST variability across moderate El Niño events (i.e. inter-event variability) is largest in the far eastern Pacific (east of 130°W) in the Austral winter prior to their peak, which is associated to either significant warm anomaly (moderate EP El Niño) or an anomaly between weak warm and cold (moderate CP El Niño) as reveals by the EOF analysis of the SST anomaly evolution during the development phase of El Niño across the El Niño years. Singular value decomposition (SVD) analysis of SST and wind stress anomalies across the El Niño years further indicates that the inter-event SST variability is associated with an air-sea mode explaining 31% of the covariance between SST and wind stress. The associated SST pattern consists in SST anomalies developing along the coast of Ecuador in Austral fall and expanding westward as far as 130°W in Austral winter. The associated wind stress pattern features westerlies (easterlies) west of 130°W along the equator peaking around June-August for EP (CP) El Niño events. This air-sea mode is interpreted as resulting from a developing seasonal Bjerknes feedback for EP El Niño events since it is shown to be associated to a Kelvin wave response at its peak phase. However equatorial easterlies east of 130°W emerge in September that counters the growing SST anomalies associated to the air-sea mode. These have been particularly active during both the 1972 and the 2015 El Niño events. It is shown that the easterlies are connected to an off-equatorial southerly wind off the coast of Peru and Ecuador. The southerly wind is a response to the coastal SST anomalies off Peru developing from Austral fall. Implications of our results for the understanding of the seasonal ENSO dynamics and diversity are discussed in the light of the analysis of two global climate models simulating realistically ENSO diversity (GFDL_CM2.1 and CESM).Item Open Access Dynamics of the carbonate system across the Peruvian Oxygen Minimum Zone(Frontiers Media, 2019-10-16) Hernandez-Ayon, Jose M.; Paulmier, Aurélien; Garcon, Veronique; Sudre, Joel; Montes Torres, Ivonne; Chapa-Balcorta, Cecilia; Durante, Giovanni; Dewitte, Boris; Maes, Cristophe; Bretagnon, MarineThe oxygen minimum zone (OMZ) of Peru is recognized as a source of CO₂ to the atmosphere due to upwelling that brings water with high concentrations of dissolved inorganic carbon (DIC) to the surface. However, the influence of OMZ dynamics on the carbonate system remains poorly understood given a lack of direct observations. This study examines the influence of a coastal Eastern South Pacific OMZ on carbonate system dynamics based on a multidisciplinary cruise that took place in 2014. During the cruise, onboard DIC and pH measurements were used to estimate pCO₂ and to calculate the calcium carbonate saturation state ( Ω aragonite and calcite). South of Chimbote (9ºS), water stratification decreased and both the oxycline and carbocline moved from 150m depth to 20–50m below the surface. The aragonite saturation depth was observed to be close to 50m. However, values <1.2 were detected close to 20m along with low pH (minimum of 7.5), high pCO2 (maximum 1,250μatm), and high DIC concentrations (maximum 2,300 μmol kg⁻¹). These chemical characteristics are shown to be associated with Equatorial Subsurface Water (ESSW). Large spatial variability in surface values was also found. Part of this variability can be attributed to the influence of mesoscale eddies, which can modify the distribution of biogeochemical variables, such as the aragonite saturation horizon, in response to shallower (cyclonic eddies) or deeper (anticyclonic eddies) thermoclines. The analysis of a 21-year (1993–2014) data set of mean sea surface level anomalies (SSHa) derived from altimetry data indicated that a large variance associated with interannual timescales was present near the coast. However, 2014 was characterized by weak Kelvin activity, and physical forcing was more associated with eddy activity. Mesoscale activity modulates the position of the upper boundary of ESSW, which is associated with high DIC and influences the carbocline and aragonite saturation depths. Weighing the relative importance of each individual signal results in a better understanding of the biogeochemical processes present in the area.Item Open Access Emergent constraint on oxygenation of the upper South Eastern Pacific oxygen minimum zone in the twenty-first century(Nature Research, 2024-05-28) Almendra, Ivan; Dewitte, Boris; Garçon, Véronique; Muñoz, Praxedes; Parada, Carolina; Montes Torres, Ivonne; Duteil, Olaf; Paulmier, Aurélien; Pizarro, Oscar; Ramos, Marcel; Koeve, Wolfgang; Oschlies, AndreasThe erosion of marine sediments is a pressing issue for coastal areas worldwide. Established methods to mitigate coastal erosion fail to provide lasting and sustainable solutions to protect marine ecosystems. Here we demonstrate the application of mild electrical stimulations to precipitate calcareous mineral binders from seawater in the pores of marine soils via electrodeposition, an alternative approach to mitigating coastal erosion. Results of electrochemical laboratory experiments unveil that the polymorphs, precipitation sites, intrusion mechanisms, and effects of electrodeposited minerals in marine sands vary as a function of the magnitude and duration of applied voltage, soil relative density, and electrolyte ionic concentration. Surprisingly, in addition to the precipitation of calcium carbonate and magnesium hydroxide, the formation of hydromagnesite is also observed due to electrically driven fluctuations in the local pH. These electrodeposits lead to enhanced mechanical and hydraulic properties of the marine sands, indicating that electrodeposition routes could be developed to reinforce marine soils in coastal areas that more closely mimic natural systems.Item Open Access ENSO diversity driving low-frequency change in mesoscale activity off Peru and Chile(Nature Research, 2020-10-21) Conejero, Carlos; Dewitte, Boris; Garçon, Véronique; Sudre, Joël; Montes Torres, IvonneTransient mesoscale oceanic eddies in Eastern Boundary Upwelling Systems are thought to strongly affect key regional scale processes such as ocean heat transport, coastal upwelling and productivity. Understanding how these can be modulated at low-frequency is thus critical to infer their role in the climate system. Here we use 26 years of satellite altimeter data and regional oceanic modeling to investigate the modulation of eddy kinetic energy (EKE) off Peru and Chile by ENSO, the main mode of natural variability in the tropical Pacific. We show that EKE tends to increase during strong Eastern Pacific (EP) El Niño events along the Peruvian coast up to northern Chile and decreases off central Chile, while it is hardly changed during Central Pacific El Niño and La Niña events. However the magnitude of the EKE changes during strong EP El Niño events is not proportional to their strength, with in particular the 1972/1973 El Niño event standing out as an extreme event in terms of EKE increase off Peru reaching an amplitude three times as large as that during the 1997/1998 El Niño event, and the 2015/2016 El Niño having instead a weak impact on EKE. This produces decadal changes in EKE, with a similar pattern than that of strong EP El Niño events, resulting in a significant negative (positive) long-term trend off Peru (central Chile).Item Open Access ENSO regimes: reinterpreting the canonical and Modoki El Niño(American Geophysical Union (AGU), 2011-05) Takahashi, Ken; Montecinos, Aldo; Goubanova, Katerina; Dewitte, BorisWe propose that the first two empirical orthogonal function (EOF) modes of tropical Pacific sea surface temperature (SST) anomalies do not describe different phenomena (i.e., El Niño‐Southern Oscillation (ENSO) and “El Niño Modoki”) but rather the nonlinear evolution of ENSO. We introduce two new uncorrelated indices (E and C), based on the leading EOFs, that respectively account for extreme warm events in the eastern and cold/moderate warm events in the central equatorial Pacific, corresponding to regimes with different evolution. Recent trends in ENSO can be described as an increase in the central Pacific (C) variability that is associated with stronger cold events, as well as a reduction in the eastern Pacific (E) variability within the cold/moderate warm regime, consistent with model projections. However, little can be said observationally with respect to the extreme warm regime.Item Open Access Estudio numérico y observacional de la dinámica de viento Paracas, asociado al transporte eólico hacia el océano frente a la costa de Ica - Perú(Universidad Peruana Cayetano Heredia, 2013) Quijano Vargas, Julio Jesús; Takahashi, Ken; Dewitte, BorisEl Viento Paracas (VP), es una tormenta de arena y polvo que ocurre en el departamento de Ica. Según Escobar (1993), la máxima ocurrencia se da entre Julio y Setiembre entre las 12:00 y 17:00 horas, con velocidades superficiales 17 m/s aproximadamente, sin embargo, se desconoce sobre los mecanismos que gatillan el VP. Esta investigación utiliza simulación numérica y datos de una campaña observacional para estudiar eventos específicos, los días 7 y 8 de setiembre 2011. Los resultados sugieren que la zona comprendida en 15S-20S en 75W es una región clave en donde el gradiente de presión a nivel del mar se intensifica horas antes de iniciar el fenómeno, este factor regional sería el responsable de intensificar el viento por la madrugada del día del evento. La topografía local juega un rol muy importante al alterar la magnitud del viento localmente, el viento costero se debilita a barlovento y se acelera a sotavento de un obstáculo topográfico. Este mecanismo local puede canalizar el flujo de escala regional lo suficientemente cerca al suelo para generar turbulencia local. Esta turbulencia se pudo cuantificar mediante el cálculo de la velocidad de fricción el cual debió exceder de 0.72m/s para dar inicio al VP. La simulación numérica subestimó este valor umbral así que se optó por corregirlo, para luego estimar las potenciales fuentes de polvo y calcular sus trayectorias. Se realizaron experimentos numéricos que comprobaron la hipótesis planteada, la cantidad de radiación de onda corta que llega al suelo es importante para alcanzar el valor de fricción umbral requerido y generar un VP.Item Open Access Evaluating future climate change exposure of marine habitat in the South East Pacific based on metabolic constraints(Frontiers Media, 2023-01-05) Parouffe, Alexandra; Garçon, Véronique; Dewitte, Boris; Paulmier, Aurélien; Montes Torres, Ivonne; Parada, Carolina; Mecho, Ariadna; Veliz, DavidOn-going climate change is now recognized to yield physiological stresses on marine species, with potentially detrimental effects on ecosystems. Here, we evaluate the prospect of using climate velocities (CV) of the metabolic index (Φ) for assessing changes in habitat in the South East Pacific. Our approach is based on a species with mean ecophysiotype (i.e. model species) and the use of a global Earth System Model simulation (CESM-LE) under RCP 8.5 scenario. The SEP is chosen as a case study as it hosts an Oxygen Minimum Zone and seamounts systems sustaining local communities through artisanal fisheries. Our results indicate that CVΦ pattern is mainly constrained by the oxygen distribution and that its sign is affected by contrasting oxygen trends (including a re-oxygenation in the upper OMZ) and warming. We further show that CVΦ is weakly dependent on physiological traits composing Φ, which conveys to this metrics some value for inferring the projected mean displacement and potential changes in viability of metabolic habitat in a region where physiological data are scarce. Based on sensitivity experiments to physiological traits and natural variability, we propose a general method for inferring broad areas of climate change exposure regardless of species-specific Φ. We show in particular that for the model used here, the upper OMZ region can be considered a “safe” area for the species with ecophysiotype close to that of 71 species used to derive the model species. Limitations of the approach and perspectives of this work are also discussed.Item Open Access Experimentos numéricos en la implementación de una configuración tropical en el Pacífico usando el modelo oceánico ROMS(Instituto Geofísico del Perú, 2015-04) Mosquera Vásquez, Kobi Alberto; Dewitte, Boris; Illig, SerenaSe describen los esfuerzos realizados con el uso de un Modelo Oceánico de Circulación General (OGCM, por sus siglas en inglés) conocido como Regional Ocean Modeling System (ROMS) sobre el océano Pacífico Ecuatorial (15°S y 15°N). El ROMS utiliza las condiciones iniciales y de frontera del Simple Ocean Data Assimilation (SODA 2.1.6; Carton y Giese, 2008) y es forzado por flujos superficiales del reanalysis de ERA-I. En esta etapa se realizaron doce experimentos con el objetivo principal de representar correctamente la profundidad de la termoclina en su estado promedio y su variabilidad interanual.Item Open Access Física de El Niño extraordinario(Instituto Geofísico del Perú, 2015-04) Takahashi, Ken; Dewitte, BorisDesde el punto de vista de impactos, la capacidad de pronóstico de largo plazo de El Niño extraordinario es claramente de gran importancia para el Perú. Afortunadamente, en los últimos años se ha iniciado una línea de investigación a nivel internacional enfocada en estos eventos, empujada por la posibilidad que la frecuencia de ellos aumente con el calentamiento global (Cai et al., 2014). Sin embargo, hay que recordar que las manifestaciones de El Niño en el Perú pueden ser particulares. Un ejemplo de esto es que El Niño 1972-73, que tuvo bastante menos impactos por lluvias en el Perú que los dos extraordinarios, tuvo un calentamiento en el Pacífico Central máximo casi igual que los de 1982-93 y 1997-98 (anomalía de TSM en la región Niño 3.4 ≈ 2°C). Claramente, es necesario poder distinguir entre estas posibilidades. Lamentablemente los modelos climáticos usados para el pronóstico a nivel internacional son particularmente deficientes en el Pacífico Oriental (Reupo y Takahashi, 2014ab), ya que varios de los procesos físicos relevantes no son bien representados (Takahashi et al., 2014). Por lo tanto, se debe tener mucho cuidado en la interpretación de los modelos y es necesario que los científicos peruanos tomen el liderazgo en la investigación científica orientada a resolver estos problemas.Item Open Access High‐resolution modeling of the Eastern Tropical Pacific oxygen minimum zone: sensitivity to the tropical oceanic circulation(American Geophysical Union (AGU), 2014-08) Montes Torres, Ivonne; Dewitte, Boris; Gutknecht, Elodie; Paulmier, Aurélien; Dadou, Isabelle; Oschlies, Andreas; Garçon, VéroniqueThe connection between the equatorial mean circulation and the oxygen minimum zone (OMZ) in the Eastern Tropical Pacific is investigated through sensitivity experiments with a high‐resolution coupled physical‐biogeochemical model. A validation against in situ observations indicates a realistic simulation of the vertical and horizontal oxygen distribution by the model. Two sets of climatological open‐boundary conditions for the physical variables, which differ slightly with respect to the intensity and vertical structure of the Equatorial Current System, are shown to lead to contrasting characteristics of the simulated OMZ dynamics. From a Lagrangian perspective, the mean differences near the coast originate to a large extent from the different transport of deoxygenated waters by the secondary Tsuchiya Jet (secondary Southern Subsurface Countercurrent, sSSCC). The O₂ budget further indicates a large difference in the balance between tendency terms, with advection exhibiting the largest difference between both simulations, which is shown to result from both linear and nonlinear advection. At regional scale, we also find that the variability of the physical contribution to the rate of O₂ change is one order of magnitude larger than the variability associated with the biogeochemical contribution, which originates from internal high‐frequency variability. Overall our study illustrates the large sensitivity of the OMZ dynamics to the equatorial circulation.Item Restricted Inference of super-resolution ocean pCO₂ and air-sea CO₂ fluxes from non-linear and multiscale processing methods(EGU General Assembly, 2014) Hernández Carrasco, Ismael; Sudre, Joel; Garçon, Veronique; Yahia, Hussein; Dewitte, Boris; Garbe, Christoph; Illig, Serena; Montes Torres, Ivonne; Dadou, Isabelle; Paulmier, Aurélien; Butz, AndréIn recent years the role of submesoscale activity is emerging as being more and more important to understand global ocean properties, for instance, for accurately estimating the sources and sinks of Greenhouse Gases (GHGs) at the air-sea interface. The scarcity of oceanographic cruises and the lack of available satellite products for GHG concentrations at high resolution prevent from obtaining a global assessment of their spatial variability at small scales. In this work we develop a novel method to reconstruct maps of CO₂ fluxes at super resolution (4km) using SST and ocean colour data at this resolution, and CarbonTracker CO₂ fluxes data at low resolution (110 km). The responsible process for propagating the information between scales is related to cascading properties and multiscale organization, typical of fully developed turbulence. The methodology, based on the Microcanonical Multifractal Formalism, makes use, from the knowledge of singularity exponents, of the optimal wavelet for the determination of the energy injection mechanism between scales. We perform a validation analysis of the results of our algorithm using pCO₂ ocean data from in-situ measurements in the upwelling region off Namibia.Item Open Access Influencia de la variabilidad decadal en El Niño-Oscilación Sur(Instituto Geofísico del Perú, 2015-05) Takahashi, Ken; Dewitte, BorisEl Niño-Oscilación Sur (ENOS) es un fenómeno que depende en forma fundamental del acoplamiento entre el océano y la atmósfera. En particular, el crecimiento de su fase cálida se desarrolla mediante el proceso de retroalimentación positiva de Bjerknes (1969), el cual consiste en una amplificación mutua entre la lluvia, los vientos del oeste y el calentamiento superficial en el Pacífico Ecuatorial (ver Dewitte et al., 2014). Por otro lado, el proceso de amplificación no actúa indefinidamente, ya que al mismo tiempo que un evento cálido crece, el contenido de calor oceánico es descargado de la zona ecuatorial y esto lleva al fin del evento cálido (ej. modelo carga-descarga; Dewitte et al., 2014). Para la fase fría los procesos son similares, pero en la dirección opuesta.
- «
- 1 (current)
- 2
- 3
- »