Isotope geochemistry of Ninetyeast Ridge basalts

The Ninetyeast Ridge lavas have Sr and Nd isotopic ratios intermediate between those of Indian Ocean MORBs and those of the very enriched Kerguelen hot spot. In an Nd-Sr isotope diagram, they also plot close to the fields of St. Paul Island lavas and of the early magmatism on Kerguelen Archipelago. The Ninetyeast Ridge lavas were generated by mixing among at least three components: a depleted, MORB-type component, such as the one erupted today on the Southeast Indian Ridge; a very enriched, high- Sr/ Sr, low-epsilon-Nd, OIB-type component (the Kerguelen hot spot); and an OIB-type component comparable to that sampled from the St. Paul (and Amsterdam) lavas. The Ninetyeast Ridge lavas show a typical Dupal anomaly signature and Pb, Sr, and Nd isotopic systematics indicate that the Kerguelen hot spot was involved in the ridge's formation as the Indian plate moved northward. The different sites cored during ODP Leg 121 show a trend in their isotopic compositions, from less radiogenic Pb/ Pb ratios and intermediate 87Sr/86Sr and 143Nd/**Nd ratios in the oldest lavas (Site 758) toward more radiogenic 206Pb/204Pb, higher epsilon-Nd, and lower 87Sr/86Sr values in the youngest lavas (Site 756). The lavas from Site 757 have 206Pb/204Pb ratios intermediate between those of the lavas from Sites 756 and 758 and higher 87Sr/86Sr and lower epsilon-Nd values. The relative proportions of the hot spot(s) and MORB component have evolved with time, reflecting differences of tectonic setting: the relative proportion of the Kerguelen hot spot component appears lower in the younger Site 756 lavas than in the older lavas from Sites 757 and 758. Site 756 coincides with the beginning of rifting at the Southeast Indian Ridge, about 43 Ma ago. The formation of the early Kerguelen Archipelago lavas may have drained most of the plume-derived material toward the Antarctic plate. Alternatively, the proximity of the spreading-ridge axis may account for the isotopic similarity of the Site 756 lavas to young lavas erupted on the Southeast Indian Ridge, from 33? to 37?S. The older lavas of Ninetyeast Ridge may have formed when the hot spot and ridge axis did not exactly coincide. The involvement of the third component, a St. Paul hot spot, in the genesis of the Ninetyeast Ridge lavas, especially for the Site 756 lavas, is clearly indicated by Sr, Pb, and Nd isotope systematics and also by trace element ratios. These data, together with those from the Kerguelen Plateau, indicate that the Kerguelen hot spot has been active more or less continuously in the South Indian Ocean for at least 115 Ma. This could indicate that the plume, and by inference the Dupal anomaly, is deep seated in origin.

Ice loss in the Canadian Arctic Archipelago

Though much attention has been focused in recent years on the melting of ice from Greenland and Antarctica, nearly half of the ice volume currently being lost to the ocean is actually coming from other mountain glaciers and ice caps. Ice loss from a group of islands in northern Canada accounts for much of that volume. In a study published in April 2011 in the journal Nature, a team of researchers led by Alex Gardner of the University of Michigan found that land ice in both the northern and southern Canadian Arctic Archipelago has declined sharply. The maps above show ice loss from surface melting for the northern portion of the archipelago from 2004-2006 (left) and 2007-2009 (right). Blue indicates ice gain, and red indicates ice loss. In the six years studied, the Canadian Arctic Archipelago lost an average of approximately 61 gigatons of ice per year. (A gigaton is a billion tons of ice.) The research team also found the rate of ice loss was accelerating. From 2004 to 2006, the average mass loss was roughly 31 gigatons per year; from 2007 to 2009, the loss increased to 92 gigatons per year. Gardner and colleagues used three independent methods to assess ice mass, all of which showed the same trends. The team used a model to estimate the surface mass balance of ice and the amount of ice discharged. They also compiled and analyzed measurements from NASA's Ice, Cloud and Land Elevation Satellite (ICESat) to assess changes in the surface height of ice. Finally, they gathered observations from NASA's Gravity Recovery and Climate Experiment (GRACE) to determine changes in the gravity field in the region, an indicator of the amount of ice gained or lost. The Canadian Arctic Archipelago generally receives little precipitation, and the amount of snowfall changes little from year to year. But the rate of snow and ice melting varies considerably, so changes in ice mass come largely from changes in summertime melt. During the 2004 to 2009 study period, the Canadian Arctic Archipelago experienced four of its five warmest years since 1960, likely fueling the melting. Gardner notes that from 2001 to 2004, the sum of melting from all mountain glaciers and ice caps around the world (but not the Greenland and Antarctic ice sheets) contributed an estimated 1 millimeter per year to global sea level rise. Recent estimates suggest the Greenland and Antarctic ice sheets add another 1.3 millimeters per year to sea level. "This means 1 percent of the land ice volume-mountain glaciers and ice caps-account for about half of all ice loss to the world's oceans," Gardner said. "Most of the ice loss is coming from the Canadian Arctic Archipelago, Alaska, Patagonia, the Himalayas, and the smaller ice masses surrounding the main Greenland and Antarctic ice sheets."

Perspectivas clásicas y contemporáneas sobre la estratificación social : Aportes de análisis de clase y de la perspectiva de las elites para el estudio de los estratos superiores

El presente artículo procura poner en consideración algunos elementos analíticos, presentes tanto en los estudios sociales de las elites como en las perspectivas sobre las clases sociales, que representan un aporte para la investigación de los procesos de estratificación social en general, y de los estratos superiores en particular. En esta dirección, se analizan los supuestos de los cuales derivan las dos principales perspectivas de clase, la relacional y la gradacional, así como las diferentes revisiones y reelaboraciones desarrolladas a lo largo del siglo XX. Por otro lado, se aborda críticamente el aporte de la perspectiva clásica de las elites y de algunos intentos de articulación entre dicho enfoque y la perspectiva de clase. El artículo concluye considerando algunas problematizaciones desarrolladas dentro de la bibliografía reciente sobre elites, con el fin de recuperar ciertos elementos analíticos valiosos para el estudio de los estratos superiores. En este sentido, intenta resaltar el aporte de los enfoques que procuran articular la dinámica de la reproducción con las de la recomposición e incluso disolución, operantes entre los grupos de elite y los estratos superiores

Dioses, Dios

"We are not jealous of gods, we do not serve them, we do not fear them, but at the risk of our lives, we attest for their multiple existence, and are stirred to be of their chancy keeping when they are no more remembered of". What could mean such a sentence written by René Char? Is it still possible to think and to experiment, here and now, after centuries of monotheism, something like a plurality of gods? What is it to be a pagan? Rereading Homer, and then Plato, Nietzsche and Lyotard, we could risk the following de´Çü nition: pagan is someone able to suppose, between performance and cosmos, that the one coming up to him is, may be, some god.

Perspectivas clásicas y contemporáneas sobre la estratificación social : Aportes de análisis de clase y de la perspectiva de las elites para el estudio de los estratos superiores

El presente artículo procura poner en consideración algunos elementos analíticos, presentes tanto en los estudios sociales de las elites como en las perspectivas sobre las clases sociales, que representan un aporte para la investigación de los procesos de estratificación social en general, y de los estratos superiores en particular. En esta dirección, se analizan los supuestos de los cuales derivan las dos principales perspectivas de clase, la relacional y la gradacional, así como las diferentes revisiones y reelaboraciones desarrolladas a lo largo del siglo XX. Por otro lado, se aborda críticamente el aporte de la perspectiva clásica de las elites y de algunos intentos de articulación entre dicho enfoque y la perspectiva de clase. El artículo concluye considerando algunas problematizaciones desarrolladas dentro de la bibliografía reciente sobre elites, con el fin de recuperar ciertos elementos analíticos valiosos para el estudio de los estratos superiores. En este sentido, intenta resaltar el aporte de los enfoques que procuran articular la dinámica de la reproducción con las de la recomposición e incluso disolución, operantes entre los grupos de elite y los estratos superiores

Dioses, Dios

"We are not jealous of gods, we do not serve them, we do not fear them, but at the risk of our lives, we attest for their multiple existence, and are stirred to be of their chancy keeping when they are no more remembered of". What could mean such a sentence written by René Char? Is it still possible to think and to experiment, here and now, after centuries of monotheism, something like a plurality of gods? What is it to be a pagan? Rereading Homer, and then Plato, Nietzsche and Lyotard, we could risk the following de´Çü nition: pagan is someone able to suppose, between performance and cosmos, that the one coming up to him is, may be, some god.