ALBERT

Description: Helium isotope measurements in six major basins in the Gulf of California show that the deep Guaymas Basin has 3He/4He 65–70% higher than atmospheric helium, clear evidence of mantle helium injection. Smaller 3He excesses observed in the Carmen and Farallon basins may be derived from this Guaymas Basin anomaly. The 3He concentrations in the Mazatlan Basin in the mouth of the Gulf of California are similar to average eastern Pacific values, indicating that the Gulf does not provide a significant flux of 3He into the general Pacific circulation. On the basis of temperature and salinity measurements an upper limit of 0.28°C can be placed on the amount of geothermal heating observed in any of the basins. The isotopic ratio of the injected Guaymas Basin helium is found to be 3He/4He = (1.10±0.06) × 10−5, almost identical to the helium signature observed at the Galapagos Rift but somewhat lower than the average ratio in oceanic basalt glasses.

Description: Processes from above and below influence the sea bottom and its sedimentary cover. The evolution of the lithosphere is being as passionately discussed today as was the evolution of the biosphere a century ago. The physical, chemical and biological interactions at the sea bottom, of "benthic boundary", call for interdisciplinary research.

Description: Fifty-four new heat flow measurements in the central troughs of the Guaymas basin support the hypothesis that they are sites of active intrusion. In the northern trough a distinct pattern of hydrothermal cooling is revealed, with venting along the western boundary fault of the trough. In the southern trough an analogous pattern is apparently superimposed upon a conductive cooling anomaly associated with a recent central intrusion. The discharge of thermal waters occurs along the boundary faults and through other faults associated with a possible horst block located in the north central floor of the southern trough. The heat flow patterns suggest that the intrusions are episodic and do not occur simultaneously along the length (15–40 km) of a spreading segment. A review of all available heat flow measurements for the Guaymas basin suggests that most of the recharge for a pervasive regional hydrothermal system is limited to the central depressions, with perhaps some contribution from pore water. The discharge of thermal waters occurs predominantly in the central depressions and possibly along the boundary transform faults and fracture zones. The regions of the basin more than a few kilometers in distance from the spreading axis, although presumably underlain by a hydrothermal system, are probably not the location of numerous vents or recharge zones.

Description: Studies of the last 125 million years of oceanographic and climatic history have benefited greatly from the impetus provided by the Deep Sea Drilling Project. Knowledge of the sedimentary and paleontologic record of the major ocean basins, in conjunction with study of pelagic marine sections exposed on land, has permitted both the testing of old and the development of new hypotheses to explain local and global ocean chemical, sedimentologic and biotic events. Some of the more striking and topical problems in paleoceanography are the oceanic “anoxic events” of early to middle Cretaceous age, the biotic crisis at the Cretaceous/Tertiary boundary, the Eocene/Oligocene extinctions and climatic and circulation events, the Messinian “salinity crisis” (late Miocene) and its effects on the world ocean, and Pleistocene glacial cycles and paleoceanography. Possible explanations of these events, which have been proposed over the last five years, are reviewed in this paper.

Description: Deep sea sediments contain more Cu, Ni, Ba, B etc., than transport of detrital terrigenous matter (TM) can explain. Longdistance transport in dissolved from is of no importance for many of these elements. Marine biological matter (BM) is enriched in Cu, Ni, Ba, B etc. Conservative mixing models, using BM and TM as inputs show that the compositional variations in pelagic sediments can be explained by these sources. Such mixing models have been used to estimate how the influx of BM and TM have varied with time, and to what extent different elements ares upplied by BM and TM. The results show that in Cenozoic Equatorial Pacific sediments CaCO₃, opaline silica, B, Ba, and Cu are predominantly biogenous. It is probable that also P and Ni belong to this group of elements, whereas almost all Al, Ti, Zr, V and Mn are delivered by TM or some volcanic processes. The accumulation rates (AR) for the biological constituents reached maxima during the L. Oligocene and the Miocene, and minima during the U. Oligocene and the Pleistocene; some AR from the Oligocene and the Miocene being 3-6 times higher than at present. The accumulation rate patterns for opaline silica, Ba and B co-vary, whereas the AR for CaCO₃ show another time dependance pattern. These AR-patterns are probably partly due to climatic variations. Plankton in Pacific Equatorial waters incorporate much more Cu, Ni, etc., than is required for the particulate transport of these elements to the ocean floor. This suggests that transport in particulate form of BM is an important source of Cu, Ba, B, etc. for the deep sea floor.

Description: Several tissues (e.g. kidney, blood, digestive gland) in oceanic cephalopods which do not exhibit in vivo bioluminescence, luminesce when homogenized in the presence of air or when simply exposed to air in a vial (blood). The source of the luminescence appears to be a luciferin: treatment of kidney homogenates and blood with a photophore extract presumably containing luciferase resulted in a 20-fold increase in light production. Luminescence was also found in the renal fluid, which may be the source of luminescent clouds produced by squids. The variability in luminescence found in some tissues of cephalopods appeared to be related to feeding. Luminescence was also detected in the digestive glands of midwater octopods.

Description: The means of detecting downwelling light for counterillumination in several midwater animals has been examined. Eyes and extraocular photoreceptors (drosal photosensitive vesicles in the enoploteuthid squid Abraliopsis sp. B and pineal organs in the myctophid fish Myctophum spinosum) were alternately exposed to overhead light or covered by a small opaque shield above the animal and the bioluminescent response of the animal was monitored. Covering either the eyes or the extraocular photoreceptors resulted in a reduction in the intensity of counterillumination. Preliminary experiments examining the bioluminescent feedback mechanism for monitoring intensity of bioluminescence during counterillumination in the midwater squid Abralia trigonura indicated that the ventral photosensitive vesicles are responsible for bioluminescent feedback.

Description: Infrared and Mössbauer spectroscopy show that the extent of the reduction of nontronite is dependent on the chemical composition of the nontronite and on the nature of the reducing agent. Hydrazine reversibly reduces about 10% of the iron in all of the nontronites studied irrespective of composition and it is suggested that the resulting ferrous iron occurs only in distorted octahedral sites. Similar conclusions are reached for the dithionite reduction of the nontronites containing little tetrahedral iron, but for those with more than one in eight silicons replaced by iron, changes brought about by dithionite treatment are irreversible due to dissolution of appreciable quantities of iron. Results from both spectroscopic techniques suggest that iron in tetrahedral sites is preferentially dissolved and that up to 80% of the structural iron can be reduced. Evidence is presented for the formation in these extensively reduced nontronites of a small amount of a mica-like phase resembling celadonite or glauconite, and, as dithionite is used for the pretreatment of soils, the implication of this observation is briefly discussed. The use of deuterated hydrazine as a reducing agent has enabled the nontronite absorption band near 850 cm-1 to be assigned to a Si-O (apical) stretching vibration, which is inactive in the infrared for perfect hexagonal symmetry, but which is activated by distortions in the tetrahedral layer