Evolution and morphology of a contourite depositional system based on new evidence from 3D-seismic data offshore Madagascar (Paleogene, Morondava Basin).

Numerous bottom current-controlled depositional and erosional features, which together form Contourite Depositional Systems (CDS), have been recognized in deep-water settings over the past decade. Most of these systems are described based on two-dimensional (2D) seismic data, whereas only a few CDS have been characterised from high-resolution 3D data. Here we document a newly identified CDS that formed during the Paleocene within the Morondava Basin, offshore west Madagascar, through analysis of a depth-migrated 3D seismic survey, enhanced by the implementation of seismic attributes. Three seismic units (SU) mark the main evolutionary stages of the CDS: (a) the onset (SU1), (b) drift growth (SU2), and (c) burial (SU3) stages. The growth stage documents lateral upslope migration of a mounded drift and its associated moat. The increasing, long-term influence of bottom currents along the foot of the slope occurred simultaneously with plate tectonic, climatic and oceanographic changes. Evidence amassed from the CDS highly erosive bounding discontinuities, internal discontinuities, and moat architecture all indicate the intermittent behaviour of the currents over shorter time frames during its formation. Drift deposits form under the influence of weaker currents, while discontinuities appear to record the most vigorous currents, producing the large-scale morphology of the system.

Isolation of the South China Sea from the North Pacific Subtropical Gyre since the latest Miocene due to formation of the Luzon Strait.

The North Pacific subtropical gyre (NPSG) plays a major role in present global ocean circulation. At times, the gyre has coursed through the South China Sea, but its role in the evolutionary development of that Sea remains uncertain. This work systematically describes a major shift in NPSG paleo-circulation evident from sedimentary features observed in seismic and bathymetric data. These data outline two contourite depositional systems-a buried one formed in the late Miocene, and a latest Miocene to present-day system. The two are divided by a prominent regional discontinuity that represents a major shift in paleo-circulation during the latest Miocene (~ 6.5 Ma). The shift coincides with the further restriction of the South China Sea with respect to the North Pacific due to the formation of the Luzon Strait as a consequence of further northwest movement of the Philippine Sea plate. Before that restriction, data indicate vigorous NPSG circulation in the South China Sea. Semi-closure, however, established a new oceanographic circulation regime in the latest Miocene. This work demonstrates the significant role of recent plate tectonics, gateway development, and marginal seas in the establishment of modern global ocean circulation.

Mediterranean isolation preconditioning the Earth System for late Miocene climate cooling.

A global Neogene cooling trend culminated ~7 million years ago with the onset of Greenland glaciation. Increased ocean-atmosphere interaction and low- to high-latitude circulation are thought to be key factors in reorganizing late Miocene global temperature and precipitation patterns, but the drivers of this reorganization have yet to be identified. Here, we present new information about the evolution of the Atlantic-Mediterranean gateway that generated Mediterranean overflow. We use sedimentary and palaeogeographic evidence to constrain the timing and dimensions of this gateway and document the initiation of a saline plume of water within the North Atlantic. Today, this saline jet entrains and transports Eastern North Atlantic water and its dissolved inorganic carbon into the interior of the ocean, contributing to the drawdown of CO2 and the sensitivity of the ocean to atmospheric changes. We show that during the Miocene this transport emerged simultaneously with gateway restriction and propose that the resulting interaction of ocean-surface and ocean-interior carbon inventories would have greatly enhanced ocean-atmosphere exchange, preconditioning the Earth System for late Miocene cooling.

Paleoceanography. Onset of Mediterranean outflow into the North Atlantic.

Sediments cored along the southwestern Iberian margin during Integrated Ocean Drilling Program Expedition 339 provide constraints on Mediterranean Outflow Water (MOW) circulation patterns from the Pliocene epoch to the present day. After the Strait of Gibraltar opened (5.33 million years ago), a limited volume of MOW entered the Atlantic. Depositional hiatuses indicate erosion by bottom currents related to higher volumes of MOW circulating into the North Atlantic, beginning in the late Pliocene. The hiatuses coincide with regional tectonic events and changes in global thermohaline circulation (THC). This suggests that MOW influenced Atlantic Meridional Overturning Circulation (AMOC), THC, and climatic shifts by contributing a component of warm, saline water to northern latitudes while in turn being influenced by plate tectonics.

Heart surgery with cardiopulmonary bypass in pregnant women

Objetivo: Se analiza la experiencia del Instituto Nacional de Cardiología Ignacio Chávez con cirugía a corazón abierto con circulación extra-corpórea en pacientes embarazadas. Hay poca información disponible a este respecto. Métodos: Quince pacientes se sometieron a cirugía a corazón abierto con circulación extracor-pórea durante el embarazo entre los años 1972 y 1998. En 13 pacientes el procedimiento consistió en reemplazo valvular con prótesis (12 mitrales, una aórtica), en una se practicó resección del trombo en una prótesis mitral de disco y en la paciente restante se cerró una comunicación interauricular. Resultados: Trece pacientes estaban en clase funcional III a IV y se operaron en situación de extrema urgencia. Ocho de estas mujeres presentaban disfunción aguda de una prótesis mitral mecánica o biológica. Hubo dos muertes operatorias para una incidencia de 13.3 por ciento. En estos dos casos hubo también muerte fetal. Cinco muertes fetales (38.5 por ciento) ocurrieron en las trece mujeres que sobrevivieron al procedimiento quirúrgico. Conclusiones: Debido al gran riesgo fetal, la cirugía con circulación extracorpórea durante el embarazo debe indicarse sólo en casos de extrema urgencia. El embarazo no aumenta el riesgo materno per se pero la mortalidad elevada es resultado de la grave situación que conduce a la intervención quirúrgica. La mortalidad fetal permanece alta.