Horizontal profiles of longwave and shortwave radiation components over sea ice near Barrow, Alaska during the 2011 melt

An integrated instrument package for measuring and understanding the surface radiation budget of sea ice is presented, along with results from its first deployment. The setup simultaneously measures broadband fluxes of upwelling and downwelling terrestrial and solar radiation (four components separately), spectral fluxes of incident and reflected solar radiation, and supporting data such as air temperature and humidity, surface temperature, and location (GPS), in addition to photographing the sky and observed surface during each measurement. The instruments are mounted on a small sled, allowing measurements of the radiation budget to be made at many locations in the study area to see the effect of small-scale surface processes on the large-scale radiation budget. Such observations have many applications, from calibration and validation of remote sensing products to improving our understanding of surface processes that affect atmosphere-snow-ice interactions and drive feedbacks, ultimately leading to the potential to improve climate modelling of ice-covered regions of the ocean. The photographs, spectral data, and other observations allow for improved analysis of the broadband data. An example of this is shown by using the observations made during a partly cloudy day, which show erratic variations due to passing clouds, and creating a careful estimate of what the radiation budget along the observed line would have been under uniform sky conditions, clear or overcast. Other data from the setup's first deployment, in June 2011 on fast ice near Point Barrow, Alaska, are also shown; these illustrate the rapid changes of the radiation budget during a cold period that led to refreezing and new snow well into the melt season.

Isotope characterisation of Villars Cave stalagmites

We present a new mid-latitude speleothem record of millennial-scale climatic variability during OIS3 from the Villars Cave that, combined with former published contemporaneous samples from the same cave, gives a coherent image of the climate variability in SW-France between ~55 ka and ~30 ka. The 0.82 m long stalagmite Vil-stm27 was dated with 26 TIMS U-Th analyses and its growth curve displays variations that are linked with the stable isotopes, both controlled by the climatic conditions. It consists in a higher resolved replicate of the previously published Vil-stm9 and Vil-stm14 stalagmites where Dansgaard-Oeschger (DO) events have been observed. The good consistency between these three stalagmites and the comparison with other palaoeclimatic reconstructions, especially high resolution pollen records (ODP 976 from the Alboran Sea, Monticchio Lake record from southern Italy) and the nearby MD04-2845 Atlantic Ocean record, permits to draw a specific climatic pattern in SW-France during the OIS3 and to see regional differences between these sites. Main features of this period are: 1) warm events corresponding to Greenland Interstadials (GIS) that are characterized by low speleothem d13C, high temperate pollen percentages, warm temperatures and high humidity; among these events, GIS#12 is the most pronounced one at Villars characterized by an abrupt onset at ~46.6 ka and a duration of about 2.5 ka. The other well individualized warm event coincides with GIS#8 which is however much less pronounced and occurred during a cooler period as shown by a lower growth rate and a higher d13C; 2) cold events corresponding to Greenland Stadials (GS) that are clearly characterized by high speleothem d13C, low temperate pollen abundance, low temperature and enhanced dryness, particularly well expressed during GS coinciding with Heinrich events H5 and H4. The main feature of the Villars record is a general cooling trend between the DO#12 event ~45.5 ka and the synchronous stop of the three stalagmites at ~30 ka ±1, with a first well marked climatic threshold at ~41 ka after which the growth rate and the diameter of all stalagmites slows down significantly. This climatic evolution differs from that shown at southern Mediterranean sites where this trend is not observed. The ~30 ka age marks the second climatic threshold after which low temperatures and low rainfalls prevent speleothem growth in the Villars area until the Lateglacial warming that occurred at ~16.5 ± 0.5 ka. This 15 ka long hiatus, as the older Villars growth hiatus that occurred between 67.4 and 61 ka, are linked to low sea levels, reduced ocean circulation and a southward shift of the Polar Front that likely provoked local permafrost formation. These cold periods coincide with both low summer 65°N insolation, low atmospheric CO2 concentration and large ice sheets development (especially the Fennoscandian).

Lucha obrera, conflicto sindical y organización armada : El caso de la Juventud Trabajadora Peronista de Propulsora Siderúrgica [1973-1976]

El presente trabajo aborda el caso de la Juventud Trabajadora Peronista en la empresa Propulsora Siderúrgica de la localidad de Ensenada en el período 1973-1976, constituyendo éste un período clave en la historia política argentina en tanto significó el retorno del peronismo al poder luego de dieciocho años de proscripción legal. Enmarcada en la extensa constelación de experiencias de la ?nueva izquierda? que irrumpe con fuerza en Argentina a partir de fines de los años sesenta, y específicamente en la amplia experiencia de las fuerzas peronistas revolucionarias dentro de ella, la Juventud Trabajadora Peronista aparece como un espacio político-sindical especialmente rico para el estudio y análisis en el campo de la historia reciente argentina y dentro de ella de las prácticas sindicales radicalizadas. Fundada en 1973, la JTP nace como frente de masas sindical de la organización armada Montoneros. Fundada en el contexto histórico, político y social de retorno de Perón al país y de crisis del gobierno peronista, ésta seráparte de la emergencia de particulares formas de vínculo social en el que se entrecruzan elementos ligados a la práctica de los militantes obreros, sus agrupaciones sindicales, el proceso de radicalización general del período y la singular participación de las organizaciones armadas peronistas. Contemplado el entrecruzamiento entre organizaciones armadas revolucionarias, organizaciones sindicales combativas y la radicalización de sectores de la clase trabajadora, nuestro trabajo enfatiza la capacidad política obrera para imponer condiciones al capital, al gobierno y a sectores burocráticos del sindicalismo. Es en estos tres frentes de combate en los que se verán inmersos los sectores radicalizados de la clase obrera argentina que buscamos poner en un primer plano a lo largo de esta investigación