70 resultados para Apparent Viscosity
Resumo:
The basement at Catoche Knoll consists of Paleozoic gneiss and amphibolite intruded by several generations of early Jurassic diabase dikes. Upon exposure to a 1-oersted field for 9 days, the diabase and amphibolite acquire a viscous remanent magnetization (VRM) which ranges from 42 to 2047% of their natural remanent magnetization (NRM). A magnetic field of similar intensity is observed in the paleomagnetic facility of the Glomar Challenger, and it is therefore doubtful if accurate measurements of magnetic moments in such rocks can be made on board unless the facility is magnetically shielded. The significant VRM also indicates the futility of attempting to discern magnetic lineations from an ocean floor composed of such rocks. No strong correlation exists between the Königsberger ratio, which is usually less than 1, and the tendency to acquire a VRM. The VRM decay is typical of a Richter aftereffect, but the relaxation times vary widely among the samples studied. A stable remanence is observed after alternating field demagnetization to 200 Oe. The range of magnetic inclinations in the diabase dikes is consistent with 40Ar/39Ar dates of 190 and 160 Ma. The inclinations suggest that the Catoche Knoll block tilted more than 20° to the north after the final dike intrusion.
Resumo:
Recent evidence that dissolved organic carbon (DOC) is a significant component of the organic carbon flux below the photic layer of the ocean (1), together with verification of high respiration rates in the dark ocean (2), suggests that the downward flux of DOC may play a major role in supporting respiration there. Here we show, on the basis of examination of the relation between DOC and apparent oxygen utilization (AOU), that the DOC flux supports ~10% of the respiration in the dark ocean. The contribution of DOC to pelagic respiration below the surface mixed layer can be inferred from the relation between DOC and apparent oxygen utilization (AOU, µM O2), a variable quantifying the cumulative oxygen consumption since a water parcel was last in contact with the atmosphere. However, assessments of DOC/AOU relations have been limited to specific regions of the ocean (3, 4) and have not considered the global ocean. We assembled a large data set (N = 9824) of concurrent DOC and AOU observations collected in cruises conducted throughout the world's oceans (fig. S1, table S1) to examine the relative contribution of DOC to AOU and, therefore, respiration in the dark ocean. AOU increased from an average (±SE) 96.3 ± 2.0 µM at the base of the surface mixed layer (100 m) to 165.5 ± 4.3 µM at the bottom of the main thermocline (1000 m), with a parallel decline in the average DOC from 53.5 ± 0.2 to 43.4 ± 0.3 µM C (Fig. 1). In contrast, there is no significant decline in DOC with increasing depth beyond 1000 m depth (Fig. 1), indicating that DOC exported with overturning circulation plays a minor role in supporting respiration in the ocean interior (5). Assuming a molar respiratory quotient of 0.69, the decline in DOC accounts for 19.6 ± 0.4% of the AOU within the top 1000 m (Fig. 1). This estimate represents, however, an upper limit, because the correlation between DOC and AOU is partly due to mixing of DOC-rich warm surface waters with DOC-poor cold thermocline waters (6). Removal of this effect by regressing DOC against AOU and water temperature indicates that DOC supports only 8.4 ± 0.3% of the respiration in the mesopelagic waters.
