Solar irradiance over and under seasonal land-fast sea ice off Barrow, Alaska, in 2010

The amount of solar radiation transmitted through Arctic sea ice is determined by the thickness and physical properties of snow and sea ice. Light transmittance is highly variable in space and time since thickness and physical properties of snow and sea ice are highly heterogeneous on variable time and length scales. We present field measurements of under-ice irradiance along transects under undeformed land-fast sea ice at Barrow, Alaska (March, May, and June 2010). The measurements were performed with a spectral radiometer mounted on a floating under-ice sled. The objective was to quantify the spatial variability of light transmittance through snow and sea ice, and to compare this variability along its seasonal evolution. Along with optical measurements, snow depth, sea ice thickness, and freeboard were recorded, and ice cores were analyzed for chlorophyll a and particulate matter. Our results show that snow cover variability prior to onset of snow melt causes as much relative spatial variability of light transmittance as the contrast of ponded and white ice during summer. Both before and after melt onset, measured transmittances fell in a range from one third to three times the mean value. In addition, we found a twentyfold increase of light transmittance as a result of partial snowmelt, showing the seasonal evolution of transmittance through sea ice far exceeds the spatial variability. However, prior melt onset, light transmittance was time invariant and differences in under-ice irradiance were directly related to the spatial variability of the snow cover.

Particulate and phytoplankton absorption during POLARSTERN cruises ANT-XXVI/3 and ANT-XXVIII/3

The euphotic depth (Zeu) is a key parameter in modelling primary production (PP) using satellite ocean colour. However, evaluations of satellite Zeu products are scarce. The objective of this paper is to investigate existing approaches and sensors to estimate Zeu from satellite and to evaluate how different Zeu products might affect the estimation of PP in the Southern Ocean (SO). Euphotic depth was derived from MODIS and SeaWiFS products of (i) surface chlorophyll-a (Zeu-Chla) and (ii) inherent optical properties (Zeu-IOP). They were compared with in situ measurements of Zeu from different regions of the SO. Both approaches and sensors are robust to retrieve Zeu, although the best results were obtained using the IOP approach and SeaWiFS data, with an average percentage of error (E) of 25.43% and mean absolute error (MAE) of 0.10 m (log scale). Nevertheless, differences in the spatial distribution of Zeu-Chla and Zeu-IOP for both sensors were found as large as 30% over specific regions. These differences were also observed in PP. On average, PP based on Zeu-Chla was 8% higher than PP based on Zeu-IOP, but it was up to 30% higher south of 60°S. Satellite phytoplankton absorption coefficients (aph) derived by the Quasi-Analytical Algorithm at different wavelengths were also validated and the results showed that MODIS aph are generally more robust than SeaWiFS. Thus, MODIS aph should be preferred in PP models based on aph in the SO. Further, we reinforce the importance of investigating the spatial differences between satellite products, which might not be detected by the validation with in situ measurements due to the insufficient amount and uneven distribution of the data.

Acá es así. Hinchadas de fútbol, violencia y territorios. En: Avá, nº 9

de una hinchada de fútbol para hacer aceptables sus acciones violentas. La práctica violenta es parte de una forma de ser que define a los miembros de este grupo y que conforma un complejo sistema que otorga prestigio y honor a los practicantes de acciones violentas. La honra de los violentos se sustenta en una base de aceptación de las prácticas distintivas; base que es construida a través de distintas herramientas que confieren legitimidad a prácticas que son socialmente estigmatizadas. Analizaremos cómo ciertas particularidades del espacio, del barrio, son los asideros lógicos, que construyen los adherentes de la hinchada para reconocer la validez de sus acciones. Pretendemos desnudar la lógica subyacente de esta construcción: la retórica de instaurar la validez de las acciones en la morfología del espacio encubre que son los sentidos de las relaciones sociales las que validan prácticas y representaciones.

Marcelo D. Boeri. Apariencia y realidad en el pensamiento griego: Investigaciones sobre aspectos epistemológicos, éticos y de teoría de la acción en algunas teorías de la Antigüedad . 1ª ed. Buenos Aires, Colihue, 2007, 384 pp.

El eje temático que orienta la dirección y sentido de este libro es el clásico 'problema' que advierte todo el pensamiento antiguo y que, desde diversas concepciones, ha intentado resolver lo que podríamos denominar el tema de la apariencia-realidad, o tal vez parecer-ser. El Dr. Boeri dirige su mirada hacia los pensadores clásicos griegos y helenísticos y penetra hondo en sus textos no con un interés meramente histórico, sino, como él mismo lo advierte, filosófico y sistemático.

Sorman, Guy. Los verdaderos pensadores del siglo. Trad. de José E. Delos, Bs.As., Ed. Atlántida, S.A., 1989, 322 p.

Fil: Pró, Diego F..

En búsqueda de las huellas del posneoliberalismo venezolano y latinoamericano. Mario Ayala, Pablo Quintero (comps). Diez años de revolución en Venezuela. Historia, balance y perspectivas (1999-2009). Editorial MAIPUE, Buenos Aires, 2009. 384 páginas.

Fil: Astorga, Sergio. Universidad Nacional de Cuyo. Facultad de Ciencias Políticas y Sociales