Processus sédimentaires et activité de la Veine d'Eau Méditerranéenne au cours du Quaternaire terminal dans le Golfe de Cadix

Cette thèse représente une étude pluridisciplinaire des dépôts actuels et anciens dans lapartie orientale du Golfe de Cadix afin d'améliorer la compréhension de la dynamique de laMOW et de caractériser les forçages à l'origine des variations sédimentaires observées depuisle Pléistocène terminal. Le schéma de circulation actuel est parfaitement conforme à ladistribution des faciès sédimentaires et montre l'omniprésence des cicatrices de glissement.La morphologie du fond marin et la force de Coriolis exercent un contrôle important surl'orientation et l'intensité des différentes branches de la MOW. La diminution de la vitesse etde la compétence de cet écoulement vers l'Ouest s'accompagne d'une diminution de lagranularité des dépôts. L'étude chronostratigraphique et sismique permet de contraindre dansle temps et l'espace la mise en place des séquences contouritiques. Le climat est un facteur decontrôle majeur de la sédimentation des 50 000 dernières années. Associées aux fluctuationsclimatiques hautes fréquences, les variations glacio-eustatiques apparaissent responsables duchangement important des conditions de sédimentation mis en évidence dès l'entrée dansl'interglaciaire actuel. Enfin, la mise en place polyphasée des systèmes chenal-lobes situés audébouché des chenaux contouritiques montre l'interaction entre les processus contouritiqueset les processus gravitaires. L'activité de ces systèmes paraît contrôlée par la MOW, lamorphologie du fond et les changements climatiques ayant affecté le Quaternaire terminal

Indian monsoon variations during three contrasting climatic periods : the Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 125 (2015): 50-60, doi:10.1016/j.quascirev.2015.06.009.In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4,200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4,200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric teleconnections to remote phenomena in the North Atlantic, Eurasia or the Indian Ocean.The work of C.Z. was supported by the ANR MONOPOL

Studying Past Deep-ocean Circulation and the Paleoclimate Record in the Gulf of Cadiz

Deep marine currents are strongly influenced by climatic changes. They also deposit, rework, and sort sediment, and can generate kilometer-scale sedimentary bodies (drifts). These drifts are made of thoroughly bioturbated, stacked sedimentary sequences called contourites [Gonthier et al., 1984]. As a consequence, change in the direction or intensity of currents can be recorded in the sediment

Prognostic value of right ventricular dilatation on computed tomography pulmonary angiogram for predicting adverse clinical events in severe COVID-19 pneumonia

BackgroundRight ventricle dilatation (RVD) is a common complication of non-intubated COVID-19 pneumonia caused by pro-thrombotic pneumonitis, intra-pulmonary shunting, and pulmonary vascular dysfunction. In several pulmonary diseases, RVD is routinely measured on computed tomography pulmonary angiogram (CTPA) by the right ventricle-to-left ventricle (LV) diameter ratio > 1 for predicting adverse events.ObjectiveThe aim of the study was to evaluate the association between RVD and the occurrence of adverse events in a cohort of critically ill non-intubated COVID-19 patients.MethodsBetween February 2020 and February 2022, non-intubated patients admitted to the Amiens University Hospital intensive care unit for COVID-19 pneumonia with CTPA performed within 48 h of admission were included. RVD was defined by an RV/LV diameter ratio greater than one measured on CTPA. The primary outcome was the occurrence of an adverse event (renal replacement therapy, extracorporeal membrane oxygenation, 30-day mortality after ICU admission).ResultsAmong 181 patients, 62% (n = 112/181) presented RVD. The RV/LV ratio was 1.10 [1.05–1.18] in the RVD group and 0.88 [0.84–0.96] in the non-RVD group (p = 0.001). Adverse clinical events were 30% and identical in the two groups (p = 0.73). In Receiving operative curves (ROC) analysis, the RV/LV ratio measurement failed to identify patients with adverse events. On multivariable Cox analysis, RVD was not associated with adverse events to the contrary to chest tomography severity score > 10 (hazards ratio = 1.70, 95% CI [1.03–2.94]; p = 0.04) and cardiovascular component (> 2) of the SOFA score (HR = 2.93, 95% CI [1.44–5.95], p = 0.003).ConclusionRight ventricle (RV) dilatation assessed by RV/LV ratio was a common CTPA finding in non-intubated critical patients with COVID-19 pneumonia and was not associated with the occurrence of clinical adverse events

Processus sédimentaires et activité de la Veine d'Eau<br />Méditerranéenne au cours du Quaternaire terminal dans le<br />Golfe de Cadix

This thesis represents a multidisciplinary approach of present and past deposits in theeastern part of the Gulf of Cadiz in order to improve the understanding of the MOW dynamicsand to characterise the forcing parameters at the origin of the sedimentary variability that hasbeen observed since the Late Pleistocene. The present circulation pattern perfectly reflects thesedimentary facies distribution and shows widespread failure scars. The seafloor morphologyand the Coriolis force play an important role on the orientation and intensity of the distinctMOW branches. The westward decrease of both velocity and competence of the MOW comeswith a reduction of the deposit grain-size. Chronostratigraphic and seismic studies allowconstraining the contouritic sequence deposits at temporal and spatial scales. Climate is amajor forcing parameter on the sedimentation during the last 50 000 years. In addition tohigh-frequency climatic changes, glacio-eustatic variations appear to be responsible for theimportant change of the sedimentation environment at the early beginning of the presentinterglacial period. Finally, the multiphased formation of the channel-lobe systems located atthe mouth of the contouritic channels shows the interaction between contouritic and gravityprocesses. The activity of these systems appears mainly controlled by the MOW, the seafloormorphology and the climatic change during the Late Quaternary.Cette thèse représente une étude pluridisciplinaire des dépôts actuels et anciens dans lapartie orientale du Golfe de Cadix afin d'améliorer la compréhension de la dynamique de laMOW et de caractériser les forçages à l'origine des variations sédimentaires observées depuisle Pléistocène terminal. Le schéma de circulation actuel est parfaitement conforme à ladistribution des faciès sédimentaires et montre l'omniprésence des cicatrices de glissement.La morphologie du fond marin et la force de Coriolis exercent un contrôle important surl'orientation et l'intensité des différentes branches de la MOW. La diminution de la vitesse etde la compétence de cet écoulement vers l'Ouest s'accompagne d'une diminution de lagranularité des dépôts. L'étude chronostratigraphique et sismique permet de contraindre dansle temps et l'espace la mise en place des séquences contouritiques. Le climat est un facteur decontrôle majeur de la sédimentation des 50 000 dernières années. Associées aux fluctuationsclimatiques hautes fréquences, les variations glacio-eustatiques apparaissent responsables duchangement important des conditions de sédimentation mis en évidence dès l'entrée dansl'interglaciaire actuel. Enfin, la mise en place polyphasée des systèmes chenal-lobes situés audébouché des chenaux contouritiques montre l'interaction entre les processus contouritiqueset les processus gravitaires. L'activité de ces systèmes paraît contrôlée par la MOW, lamorphologie du fond et les changements climatiques ayant affecté le Quaternaire terminal

Processus sédimentaires et activité de la veine d'eau méditarranéenne au cours du Quaternaire terminal dans le Golfe de Cadix

Cette thèse représente une étude pluridisciplinaire des dépôts actuels et anciens dans la partie orientale du Golfe de Cadix afin d'améliorer la compréhension de la dynamique de la MOW et de caractériser les forçages à l'origine des variations sédimentaires observées depuis le Pléistocène terminal. Le shémas de circulation actuel est parfaitement conforme à la distribution des faciès sédimentaires et montre l'omniprésence des cicatrices de glissement. La morphologie du fond marin et la force de Coriolis exercent un contrôle important sur l'orientation et l'intensité des différentes branches de la MOW. La diminution de la vitesse et de la compétence de cet écoulement vers l'Ouest s'accompagne d'une diminution de la granularité des dépôts. L'étude chronostratigraphique et sismique permet de contraindre dans le temps et l'espace la mise en place des séquences contouritiques. Le climat est un facteur de contrôle majeur de la sédimentation des 50 000 dernières années. Associées aux fluctuations climatiques hautes fréquences, les variations glacio-eustatiques apparaissent responsables du changement important des conditions de sédimentation mis en évidence dès l'entrée dans l'interglaciaire actuel. Enfin, la mise en place polyphasée des systèmes chenal-lobes situés au débouché des chenaux contouritiques montre l'interaction entre les processus contouritiques et les processus gravitaires. L'acivité de ces systèmes paraît contrôlée par la MOW, la morphologie du fond et les changements climatiques ayant affecté le Quaternaire terminal.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Les courants marins autour du Groenland

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Sediment failure types, preconditions and triggering factors in the Gulf of Cadiz

International audienceA series of morphological structures, such as scars and escarpments related to seafloor instabilities, were observed in the Gulf of Cadiz using multibeam bathymetry and acoustic imagery. According to the geometry of the slide scars, the slope angle, the surrounding seafloor morphology and the mechanical parameters of the sediment, we suggest the likely mechanisms initiating the failures for the different types of observed structures. Most of the small-scale sediment failures (≤2 km2) seem directly related to dome-like structures (where slopes are steep) or are located in the vicinity of such structures (fluid flows). It appears that progressive deformation or fluid flow related to the growing of dome-like structures may have weakened the sediments sufficiently to bring 7°-steep slopes to metastable conditions (with a factor of safety close to 1.0). The other instability types are likely related to high-magnitude (Ms > 6) earthquakes, which are prone to occur in this area (located in the neighbourhood of the 1755 Lisbon earthquake area). Some particular large-scale structures were observed among these seafloor features, for example on the Guadalquivir Bank. On this bank, a series of successive large scars (at least 4 km long), composed of multiple and very regular arcuate segments (1 km in diameter), were observed at different bathymetric levels (every 40 m). These structures might be related to a deep-rooted detachment zone (e.g. successive listric faults) and triggered by high-magnitude earthquakes or by accumulated displacement along a tectonic discontinuity. This would explain such a large-scale deformation, providing a regular escarpment of 40 m high without any sediment flow downslope, thereby suggesting an ongoing (or unfinished) deformation

Origin and architecture of a Mass Transport Complex on the northwest slope of Little Bahama Bank (Bahamas): Relations between off-bank transport, bottom current sedimentation and submarine landslides

International audienceThe analysis of the sedimentary dynamics of the carbonate slope of the northwest part of Little Bahama Bank (LBB, Bahamas) reveals a complex interaction between slope destabilisations, off-bank sediment export and longitudinal transport, the latter being driven by the Antilles and the Florida currents, at the northern end of the Florida Strait. Their combined action since the middle Miocene resulted in an extensional growth slope, previously called ‘LBB Drift’ (Mullins et al., 1980). Deposition within this extensional growth slope is dominated by either platform-derived downslope sedimentation or bottom current sedimentation. The latter induces the formation of a plastered drift, showing both upslope and downslope migrations, which do not correspond to the ‘LBB Drift’ as described by Mullins et al. (1980). Interestingly, a large submarine landslide affects the upper part of this plastered drift, and displays a complex and striking geomorphology on the seafloor. A new high-quality multibeam echosounder and seismic dataset allowed a detailed characterisation of the architecture of this Mass Transport Complex (MTC). A 44 km-long circular incision at 275 m and 460 m water depths, with a steep external edge (from 40 to 70 m high), forms the only present day evidence of this ancient MTC. It comprises confined Mass Transport Deposits (MTDs), which are delimited by frontal and lateral edges that developed inside the plastered drift. The top of this plastered drift is marked by a major erosional surface, most likely induced by an increase in oceanic current circulation. Channelised geometries, laterally associated with overspill deposits, developed within the depression induced by the MTC, and are an additional evidence of bottom current activity in this area. In addition, recent pockmarks are visible on the seafloor in front of the circular scarp of the MTC and probably relate to fluid escape, originating from the underlying MTDs' compressional area

Synthèse cartographique de la pente des Bahamas

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