Browsing by Author "Sudre, Joël"
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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 Effect of Caribbean Water incursion into the Gulf of Mexico derived from absolute dynamic topography, satellite data, and remotely sensed chlorophyll a(European Geosciences Union, 2019-11) Delgado, Juan Antonio; Sudre, Joël; Tanahara, Sorayda; Montes Torres, Ivonne; Hernández-Ayón, José Martín; Zirino, AlbertoThe dynamics of the Loop Current (LC) and the detached Loop Current eddies (LCEs) dominate the surface circulation of the Gulf of Mexico (GoM) and transport Caribbean Water (CW) into the gulf. In this work, 25 years (1993–2017) of daily satellite data are used to investigate the variability of these physical processes and their effect on chlorophyll a (Chl a) concentrations from 1998 to 2017, including temporal changes, mean differences, and regional concentration tendencies. The physical variables analyzed are absolute dynamic topography (ADT) and oceanic currents. From the ADT and oceanic current monthly climatologies, it is shown that there is an annual intrusion of CW with an inward incursion that starts in spring, peaks in the summer, reaches to 28∘ N and 90.45∘ W, and then retreats in winter to approximately 26.5 ∘ N and 88.3 ∘ W. Minimum surface Chl a concentrations (< 0.08 mg m⁻³) are found during the summer–autumn period inside the region of maximum incursion of CW; the opposite is observed during the winter period when Chl a concentrations were at a maximum, e.g., > 0.14 mg m⁻³. The 3-year running averages of the ADT 40 cm isoline qualitatively reproduce the climatological pattern of 25 years showing that before 2002 CW was less intrusive. This suggests that from 2003 onward, larger volumes of oligotrophic waters from the Caribbean Sea have invaded the western GoM and reduced mean surface Chl a concentrations. A direct comparison between the 1998–2002 and 2009–2014 periods indicates that in the latter time interval, the Chl a concentration above waters deeper than 250 m has decreased significantly.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 Restricted Understanding upper water mass dynamics in the Gulf of Mexico by linking physical and biogeochemical features(Elsevier, 2022-01) Cervantes-Díaz, Gabriela Yareli; Hernández-Ayón, José Martín; Zirino, Alberto; Herzka, Sharon Zinah; Camacho-Ibar, Víctor; Norzagaray, Orión; Barbero, Leticia; Montes Torres, Ivonne; Sudre, Joël; Delgado, Juan AntonioIn the Gulf of Mexico (GoM), the upper 300 m of the water column contains a mixture of water types derived from water masses from the North Atlantic and the Caribbean Sea, namely Caribbean Surface Water (CSW), Subtropical Underwater (SUW), Gulf Common Water (GCW), and Tropical Atlantic Central Water (TACW). These are mainly altered by mesoscale processes and local evaporation, which modulate biogeochemical cycles. In this study, we improve our understanding of water mass dynamics by including biogeochemical data when evaluating the T-S relationship to define water-mass boundaries, particularly when the observed thermohaline characteristics overlap. The variables considered were apparent oxygen utilization (AOU), nitrate, and dissolved inorganic carbon (DIC). The data were obtained from eight cruises carried out in the central and southern regions of the GoM and an additional cruise that covered the entire coastal-ocean region. The new proposed boundaries were instrumental in clarifying the dynamics of surface waters. Of note, GCW on the western side of the GoM is not formed from the mixing of CSW and SUW but by the mixing of remnant CSW with TACW. In winter, a remnant of CSW mixed with GCW, and the biogeochemical composition of surface waters was affected, as observed from an increase in nitrate and DIC concentrations and positive AOU values. CSW was mainly detected at the surface during summer with negative AOU values, low DIC values, and almost undetectable nitrate concentrations. The presence or absence of CSW modulated the depth of the nitracline and likely influenced primary productivity.