Radionuclides measured on water bottle samples during SONNE cruise SO202 (INOPEX)

Boundary scavenging, or the enhanced removal of adsorption-prone elements from the ocean in areas of high particle flux, is an often cited, though not well-quantified, concept used to understand the oceanic distribution of many trace metals. Because 230Th and 231Pa are produced uniformly from uranium decay and removed differentially by scavenging, the process of boundary scavenging can be elucidated by a more detailed knowledge of their water column distributions. To this end, filtered seawater was collected across the gradients in particle flux which span the subarctic Pacific: in the west during the Innovative North Pacific Experiment (INOPEX) and in the east along Line P. Lateral concentration gradients of dissolved 230Th are small throughout the subarctic Pacific at 12 sites of variable particle flux. This contradicts the prediction of the traditional boundary scavenging model. A compilation of water column data from throughout the North Pacific reveals much larger lateral concentration gradients for 230Th between the subarctic North Pacific and subtropical gyre, over lateral gradients in scavenging intensity similar to those found within the subarctic. This reflects a biogeochemical-province aspect to scavenging. Upper water column distributions of 231Pa and 231Pa/230Th ratio are consistent with the influence of scavenging by biogenic opal, while deep waters (>2.5 km) reveal an additional 231Pa sink possibly related to manganese oxides produced at continental margins or ridge crests.

(Table 1) Concentrations and isotopic ratio of Argon in Cretaceous deep-sea basaltic glass of DSDP Hole 51-417D

The abundance and isotopic composition of rare gas in the mantle provides an important constraint on the origin and evolution of the Earth's atmosphere. One of sources of such information is basalts which erupted from ocean ridges. Ozima (1975, doi:10.1016/0016-7037(75)90054-X) stated that a high 40Ar/36Ar ratio in the mantle suggests sudden degassing at an early stage of the Earth's evolution. Several authors (Funkhouser et al., 1968, doi:10.1016/S0012-821X(68)80021-4; Darlymple and Moor, 1968, doi:10.1126/science.161.3846.1132) have reported excess 40Ar and high 40Ar/36Ar ratios in rapidly quenched rims of young deep-sea basalts. However, the Ar composition in old ridge basalts was not known. We report here a measurement of the isotopic composition of Ar in old deep-sea basalts. The Glomar Challenger drilled a Cretaceous ocean floor near the southern end of the Bermuda Rise in Deep Sea Drilling Project. The drilled site (Site 417) is on the magnetic anomaly MO which has been estimated to be 108 Myr old.

Contribuciones de Alberto Magno y Tomás de Aquino a la noción de ratio rei

El presente trabajo indaga la noción de razón real (ratio rei) a partir de algunos textos de Alberto Magno y de Tomás de Aquino; o más bien, la posible proyección que de dicha noción pudiera observarse desde la obra de Alberto hacia la de su discípulo Tomás. La profundidad semántica que esta noción conlleva obliga a examinarla desde diversos ángulos epistémicos, tales como la ontología, la gnoseología, la lingüística o la filosofía de la praxis, abarcando a su vez tanto el campo de la filosofía como de la teología. La intención definitiva de este trabajo consiste en mostrar que la famosa triple articulación lingüística dionisiana de causalidad, negación y eminencia únicamente puede entenderse adecuadamente conforme al vínculo que existe entre las rationes rerum y el deseo racional.

(Table 1) Characteristics of silicified sediments at DSDP Site 61-462 according to host-rock lithology, opal-CT-to-quartz ratio, and the origin of the quartz phase

This study deals with the mineralogical variability of siliceous and zeolitic sediments, porcellanites, and cherts at small intervals in the continuously cored sequence of Deep Sea Drilling Project Site 462. Skeletal opal is preserved down to a maximum burial depth of 390 meters (middle Eocene). Below this level, the tests are totally dissolved or replaced and filled by opal-CT, quartz, clinoptilolite, and calcite. Etching of opaline tests does not increase continously with deeper burial. Opal solution accompanied by a conspicuous formation of authigenic clinoptilolite has a local maximum in Core 16 (150 m). A causal relationship with the lower Miocene hiatus at this level is highly probable. Oligocene to Cenomanian sediments represent an intermediate stage of silica diagenesis: the opal-CT/quartz ratios of the silicified rocks are frequently greater than 1, and quartz filling pores or replacing foraminifer tests is more widespread than quartz which converted from an opal-CT precursor. As at other sites, there is a marked discontinuity of the transitions from biogenic opal via opal-CT to quartz with increasing depth of burial. Layers with unaltered opal-A alternate with porcellanite beds; the intensity of the opal-CT-to-quartz transformation changes very rapidly from horizon to horizon and obviously is not correlated with lithologic parameters. The silica for authigenic clinoptilolite was derived from biogenic opal and decaying volcanic components.