Showing papers by "Woods Hole Oceanographic Institution published in 1977"

Determination of total nitrogen in aqueous samples using persulfate digestion1

Abstract: Determination of total nitrogen in aqueous samples after potassium persulfate digestion compared favorably in both precision and nitrogen recovery with determinations obtained using Kjeldahl digestion.

Compositional variations of young basalts in the Mid-Atlantic Ridge rift valley near lat 36°49′N

Abstract: Fifty acoustically positioned samples of fresh basalt were collected by the submersible Alvin from the median valley of the Mid-Atlantic Ridge during the French American Mid-Ocean Undersea Study (FAMOUS) in the summer of 1974. The samples show regular compositional variations from the center of the rift valley (central lava flows) out to the rift valley walls (flank lava flows). The central lava samples show higher ratios of olivine relative to clinopyroxene and plagioclase phenocrysts and contain chrome spinel. Glasses of the flank lava samples are enriched in SiO 2 , TiO 2 , K 2 O, H 2 O, and FeO/MgO relative to central lava samples. Studies of the thickness of palagonite and manganese crusts indicate that the flank lava flows are considerably younger than the inferred spreading age of the crust on which they occur. Flank lavas are generally older than central lavas, but notable exceptions occur. The composition of the flank lava glass can be derived by the removal of approximately 29 wt percent of analyzed phenocrysts (in the ratio 5.7 plagioclase, 2.5 olivine, 1.8 clinopyroxene) from the central lava glass. In addition, other processes (possibly involving volatile transfer) must enrich the flank lavas in K 2 O, TiO 2 , and H 2 O. A model is proposed whereby this crystal fractionation occurs in a shallow, narrow (6-km-wide) magma chamber underlying the median valley. The chamber is compositionally zoned, and central lavas are fed from dikes tapping its hotter axial zone, whereas flank lavas are fed from the cooler, differentiated melt on the margins. The nature of the chemical variations in the lavas permits an estimate of the composition and thickness of the cumulates forming at the base of the chamber.

Sedimentary Polycyclic Aromatic Hydrocarbons: The Historical Record

Abstract: Polycyclic aromatic hydrocarbons in three sections of a dated sediment core from Buzzards Bay, Massachusetts, have been analyzed by gas chromatographic spectrometry. This historical information suggests that sedimentary polycyclic aromatic hydrocarbons, at least at this location, result primarily from the anthropogenic combustion of fossil fuels.

Morphology and tectonics of the inner rift valley at lat 36°50′N on the Mid-Atlantic Ridge

Abstract: A segment of the inner rift valley of the Mid-Atlantic Ridge was investigated in detail from the American submersible Alvin . Fifteen traverses were made across the floor and up the first major fault scarps in the valley walls. The asymmetric morphology of the inner floor is found to be the primary result of volcanic activity modified by tectonic activity. Analysis of the tectonic features revealed that the rift is evolving within a single stress field that has its least principal strain axis (the compressional axis) aligned with the valley axis of N20°E. This is in contrast to the direction normal to plate divergence (N0°E). The tectonic elements in the inner floor are primarily vertically dipping tension fractures, whereas the fault scarps of the flanking walls are closer to a 60° dip and reflect a component of downdip shear. The information base obtained from Alvin was broadened with information collected in the area with more conventional techniques. Through an analysis of this information, primarily the topography, it was possible to extrapolate the detailed observations obtained from the submersible to intervening areas to produce a comprehensive geological interpretation of the study area. An evolutionary model was developed which suggests that the inner rift is a product of axial volcanic activity. Shortly after formation, the original volcanic edifice is modified by vertical collapse, which leads to a reduction of the bottom relief. This process is reversed in the outer portions of the valley as uplift begins. Tensional extension changes into vertical shear as the volcanic blocks are incorporated into the walls and elevated. During the various stages of uplift, readjustment takes place on the terraces, which results in the preservation of the original volcanoes as recognizable units. This model, which spans 180,000 yr of inferred time, is examined in detail in an attempt to identify its weaknesses as well as to delineate the specific factual constraints upon which it is built. Alternate interpretations are proposed and tested in a similar fashion; the result is the identification of key problems that need to be solved.

Large benthic microbial communities in sulphide biota under Peru-Chile Subsurface Countercurrent

Abstract: BENTHIC observations off the coast of Chile have consistently disclosed the presence of large coherent microbial communities living at depths of about 50–280 m in the H2S-containing sediments of the shelf in contact with the deoxygenated waters of the Peru–Chile Subsurface Countercurrent (SCC). Similar observations were also made off Peru in 1969 by Gilbert T. Rowe, and in 1976 by G. T. Rowe and John Waterbury of Woods Hole Oceanographic Institution. The microflora, which has only been reported once before in the literature1, has been known for years by the local fishermen who call them estopa (Spanish for uncleansed wool or fiax) due to the filamentous appearance of its main components. In this report I describe this massive microbial community which includes organisms typical for sulphide biota, and may have unsuspected importance in the ecology and economy of the sea off western South America.

Distribution and Movement of Gulf Stream Rings

Abstract: The distribution, number and movement of cyclonic Gulf Stream rings were estimated from an analysis of 50 000 temperature records obtained from the National Oceanographic Data Center and Fleet Numerical Weather Central. The data were taken from 1970 through September 1976 in the region bounded by 20–40°N and 50–80°W. Additional ring observations from other sources were also used. Twenty-five ring time series, together with 26 single ring observations were obtained; approximately 11 rings were found to exist at one time. Rings typically moved westward, turned southwest when close to the Gulf Stream and appeared to coalesce with the Stream near Florida. On the average, two rings per year moved down this path with a mean speed of 3 km day−1 and an estimated life span of 2–3 years. Although ring observations were concentrated in the northwestern Sargasso Sea, several were documented east of 60°W. In addition to cold core rings several warm eddies were found south of the Stream; they consisted of at l...

Structure and Sedimentary History of Southeastern Mediterranean Sea-Nile Cone Area

Abstract: A detailed seismic, magnetic, and sonobuoy study of the southeastern Mediterranean and Nile cone area shows the details of recent sedimentation and tectonic activity, and especially the effects of salt deformation due to movement of a late Miocene evaporite sequence. The continental rise in this area can be divided into two major subprovinces: the Nile cone and the Levant platform. The name Levant platform is applied to the rough topography extending northward from the Sinai that separates the essentially smooth Nile cone on the west from the Cyprus basin on the east. The previously reported suggestion of two offshore fans (the Rosetta and Damietta) off the present mouths of the Nile is not confirmed; rather, one major feature is present--the Nile cone. Both the Levant pl tform and Nile cone have considerable thicknesses of Nile-derived sediment, but the topographic irregularities of the Levant platform result from greater vertical and horizontal flow of evaporites than on the Nile cone. The movements of evaporites have resulted in large numbers of collapse structures and a 100 km-long salt ridge at the northern edge of the Levant platform. The offshore Miocene evaporites are acoustically detectable (reflector M) and have been mapped. They are perhaps correlative with a nearshore reflector (P) that underlies much of the Nile cone area. Reflector P is either a middle to late Miocene carbonate sequence that prograded eastward during the Messinian regression or an erosional surface cut into pre-Messinian strata. This reflector marks the top of a broad anticlinal structure off the Nile delta and Sinai Peninsula. The volume of post-Messinian sediment (essentially all is Nile derived) is about 387,000 cu km (assuming an average sediment velocity of 2 km/sec), or an average sediment thickness of 1.89 km for the area and an average sedimentation rate of 37 cm/1,000 years.

Growth, production and energy transformations in the salt-marsh killifish Fundulus heteroclitus

Abstract: Populations of Fundulus heteroclitus (L.) at the beginning of a growth season in a New England salt marsh consist of 3 yearly age classes, with the 1-year-old class contributing most of the biomass. Calculation of production rates revealed that the young fish were the most active part of the population and that females were more productive than males. The entire population spent equal amounts of energy in growth and in metabolism. Including the young of the year, we obtained total production of 160 kg dry weight/ha, a value among the highest obtained for natural fish populations. About 5 to 15% of the production is available to predators. Rates of food consumption by F. heteroclitus are high enough to turn over the population of prey relatively often. Popululations of F. heteroclitus are thus capable of exerting an important influence on the abundance and distribution of their prey.

Megafaunal biomass in the deep sea

Abstract: THE conventional notion of the deep-sea ecosystem has been one where a rain of fine organic particles from above provides food for a great diversity of small creatures living in and on the sediments1–3. These, the meiofauna and macrofauna, live as deposit feeders, suspension feeders, and, in lesser proportion, as carnivores preying on other members of the fauna. The macrofauna in turn are thought to provide food for the generally more carnivorous megafauna, the echinoderms, decapods, and fishes. Although no data have been published concerning the abundance of the deep-sea megafauna in terms of biomass, the assumed trophic relationship and the Eltonian concept has led to the common feeling that the biomass of this component must be small in comparison to the meiofaunal and macrofaunal biomass4. Our data show that, on the contrary, the mega-faunal biomass approaches that measured in the macro-fauna. This observation re-focuses attention on the question of food supply to the deep sea, and implies that previously suggested falls of large dead animals from the pelagial5,6 may be important.

Slow recolonisation of deep-sea sediment

Abstract: USING the submarine ALVIN, experiments on deep-sea benthic communities have been designed to follow the recolonisation of defaunated deep-sea sediments and to provide estimates of growth rates and time to maturity in individual species. Small brood size and the high proportion of adults in a number of deep-sea benthic taxa suggest relatively low rates of recruitment, growth and mortality in the deep sea1. Large individuals (8.4 mm) of the deep-sea bivalve, Tindaria callistiformis, have been estimated to be at least 100 yr old2. Measurements of microbial activity and community respiration indicate rates one to three orders of magnitude lower than in shallow water3,4. In contrast with the view that there is a general slowing of life processes, the first in situ deep-sea measurements on molluscan borers in wood panels have indicated rapid rates of recruitment, growth and maturation. Wood is, however, an ephemeral resource and its occurrence in the deep sea is unpredictable, while the majority of deep-sea habitats are thought to be highly predictable, therefore favouring less opportunistic life histories.

Corrected age of the Pliocene/Pleistocene boundary

Abstract: Calcareous plankton datum-events are referred to the Pliocene/Pleistocene boundary at Le Castella, the stratotype Calabrian at Santa Maria di Catanzaro, and to deep-sea sediments in six piston cores The boundary is correlated by multiple overlapping criteria to a level equivalent to, or slightly younger than, the top of the Olduvai Event, giving a revised estimate of about 16 Myr for the age of the boundary The Pliocene I Pleistocene boundary is thus coeval with the earliest of four major climatic deteriorations in the Pleistocene, reconciling palaeoclimatic concepts with the chrono-stratigtaphical definition of the epoch

The Black Sea and the Sea of Azov

Abstract: The Black Sea is one of the world’s largest marginal seas, with an area of 432,000 km2 and a volume of 534,000 km3. Most of the basin is deeper than 2000 m (Fig. 1) and the maximum depth reached is 2206 m. It is connected by a narrow passage, the Kerch Strait, to the shallow Sea of Azov which has an area of about 37,500 km2 (excluding the Sivash or Putrid Sea) and a volume of about 470 km3. The average depth of the Sea of Azov is close to 12 m (Fig. 2). Sill depth between the two seas at the Kerch Strait is about 5 m. The Black Sea is connected to the Mediterranean Sea via the shallow Bosporus (sill depth about 50 m). The Sivash or Putrid Sea is a shallow area separated from the Sea of Azov by a 110-km-long sand bar called the Arabatskaya Strelka.

Sr-isotope, K, Rb, Cs, Sr, Ba, and rare-earth geochemistry of basalts from the FAMOUS area

Abstract: Ten basalt samples recovered from the FAMOUS area were selected so as to obtain representatives of a wide geographical and compositional range. The samples were analyzed for 87Sr/86Sr, K, Rb, Cs, Sr, Ba, and rare-earths. Sr-isotope ratios fall in the narrow range of 0.70288 to 0.70307, which implies that these samples were derived from an isotopically homogeneous source. The FAMOUS area lies in a geochemical transition zone between the Azores Plateau and “normal” ridge areas south of lat 33°N. The LIL (large-ion-lithophile) and Sr-isotope geochemistry of FAMOUS basalts is thus influenced by the Azores mantle plume; this results in higher Sr-isotope and LIL concentrations in these basalts than is typical of Mid-Atlantic Ridge basalts. Trace-element distributions in FAMOUS area basalts cannot be entirely accounted for by fractional crystallization models that are based on major-element chemistry. The LIL distribution in FAMOUS basalts could be due to variable extents of partial melting. Zonation within the magma chamber may result from incomplete mixing of successive batches of magma entering the chamber and could be further enhanced by fractional crystallization. The variation in partial melting would require significant increases in mantle temperature over a relatively short period of time. According to this model, the Mount Pluto magma represents the highest degree of partial melting and may mark the initiation of a new cycle of eruptive activity in the median valley.