Sulfide Deposits from the East Pacific Rise Near 21{degrees}N

Massive sulfide deposits were discovered from the diving saucer Cyana on the accreting plate boundary region of the East Pacific Rise near 21 degrees N. The deposits form conical and tubular structures lying on a basaltic basement. Mineralogical and geochemical analyses showed two main types of intimately associated products: a polymetallic sulfide-rich material composed of pyrite and marcasite in association, zinc-rich phases, and copper-rich compounds, and an iron-rich oxide and hydroxide material (also called gossan) composed largely of goethite and limonite. Silicate phases such as opaline, silica, iron-silicon clay, and trace amounts of mica and zeolite are encountered in both types of material. Possible mechanisms for the formation of the sulfide deposits on the East Pacific Rise are discussed.     

Seismic Images of Active Magma Systems Beneath the East Pacific Rise Between 17{degrees}05' and 17{degrees}35'S

Seismic reflection data from the East Pacific Rise between 17 degrees 05' and 17 degrees 35'S image a magma lens that varies regularly in depth and width as ridge morphology changes, confirming the notion that axial morphology can be used to infer ridge magmatic state. However, at 17 degrees 26'S, where the ridge is locally shallow and broad, the magma lens is markedly shallower and wider than predicted from regional trends. In this area, submersible dives reveal recent volcanic eruptions. These observations indicate that it is where the width and depth of the magma chamber differ from regional trends, indicating an enhanced magmatic budget, that is diagnostic of current magmatism.     

A Major Helium-3 Source at 15{degrees}S on the East Pacific Rise

An extensive plume of water enriched with helium-3 has been discovered in the deep Pacific Ocean at latitude 15 degrees S on the East Pacific Rise. In the core of the plume, at a depth of 2500 meters over the ridge crest, the helium-3/helium-4 ratio is 50 percent higher than the ratio in atmospheric helium, indicating a strong injection of mantle or primordial helium at the spreading center axis through local hydrothermal systems. The helium-3 plume is completely absent east of the rise, but it can be traced over 2000 kilometers to the west above a newly observed physical feature: a density discontinuity here caled the "ridge-crest front." The injected plume provides a unique deep-sea tracer with an asymmetric distribution which shows that the deep circulation across the rise is from east to west. The striking intensity and lateral extent of this helium-3 anomaly, compared to observations at known oceanic hydrohrmal sites, suggest that the largest hydrothermal fields in the ocean are yet to be discovered and that they will be found near 15 degrees S on the East Pacific Rise.     

Geothermal System at 21{degrees}N, East Pacific Rise: Physical Limits on Geothermal Fluid and Role of Adiabatic Expansion

Pressure-volume-temperature relations for water at the depth of the magma chamber at 21 degrees N on the East Pacific Rise suggest that the maximum subsurface temperature of the geothermal fluid is about 420 degrees C. Both the chemistry of the discharging fluid and thermal balance considerations indicate that the effective water/rock ratios in the geothermal system are between 7 and 16. Such low ratios preclude effective metal transport at temperatures below 350 degrees C, but metal solubilization at 400 degrees C and above is effective even at such low ratios. It is proposed that the 420 degrees C fluid ascends essentially adiabatically and in the process expands, cools, and precipitates metal sulfides within the upper few hundred meters of the sea floor and on the sea floor itself.     

Flight of Winter Moths Near 0{degrees}C

Some noctuid winter moths fly at near 0 degrees C by maintaining an elevated(30 degrees to 35 degrees C) thoracic muscle temperature. Geometrid winter moths sustain themselves in free flight at subzero muscle temperatures. However, the temperature characteristics of citrate synthase and pyruvate kinase from both of these different kinds of moths and from a sphinx moth that flies with a muscles temperature of 40 degrees C are nearly identical. Furthermore, mass-specific rates of energy expenditure of both kinds of winter moths are also similar at given thoracic temperature (near 0 degrees C). The geometrids that are able to fly with a thoracic temperature near 0 degrees C do so largely because of unusually low wing-loading, which permits a low energetic cost of flight.     

Diorites from the Mid-Atlantic Ridge at 45{degrees}N

Diorites, associated with basalts, basalt breccias, and serpentinized peridotites, occur in situ on the faulted scarps of two seamounts from the western High Fractured Plateau of the Mid-Atlantic Ridgeat 45 degrees N.     

Bacterial Sulfate Reduction Above 100{degrees}C in Deep-Sea Hydrothermal Vent Sediments

The currently known upper temperature limit for growth of organisms, shared by a number of archaebacteria, is 110 degrees C. However, among the sulfate-reducing bacteria, growth temperatures of greater than 100 degrees C have not been found. A search for high-temperature activity of sulfate-reducing bacteria was done in hot deep-sea sediments at the hydrothermal vents of the Guaymas Basin tectonic spreading center in the Gulf of California. Radiotracer studies revealed that sulfate reduction can occur at temperatures up to 110 degrees C, with an optimum rate at 103 degrees to 106 degrees C. This observation expands the upper temperature limit of this process in deep-ocean sediments by 20 degrees C and indicates the existence of an unknown group of hyperthermophilic bacteria with a potential importance for the biogeochemistry of sulfur above 100 degrees C.     

Thermal Properties of Meteoritic Iron from -150{degrees} to 300{degrees} Celsius

Thermal diffusivity and specific heat have been measured by the flash method on a small specimen of meteoritic iron from the Canyon Diablo fall. Measurements have been made over the temperature range -150 degrees to 300 degrees C from which thermal conductivity values have been calculated.     

Magnetic Anomalies over the Mid-Atlantic Ridge near 27{degrees}N

Ten magnetic profiles across the mid-Atlantic ridge near 27 degrees N show trends that are parallel to the ridge axis and symmetrical about the ridge axis. The configuration of magnetic bodies that could account for the pattern supports the Vine and Matthews hypothesis for the origin of magnetic anomalies over oceanic ridges. A polarity-reversal time scale inferred from models for sea-floor spreading in the Pacific-Antarctic ridge and radiometrically dated reversals of the geomagnetic field indicates a spreading rate of 1.25 centimeters per year during the last 6 million years and a rate of 1.65 centimeters per year between 6 and 10 million years ago. A similar analysis of more limited data over the mid-Atlantic ridge near 22 degrees N also indicates a change in the spreading rate. Here a rate of 1.4 centimeters per year appears to have been in effect during the last 5 million years; between 5 and 9 million years ago, an increased rate of 1.7 centimeters per year is indicated. The time of occurrence and relative magnitude of these changes in the spreading rate, about 5 to 6 million years ago and 18 to 27 percent, respectively, accords with the spreading rate change implied for the Juan de Fuca ridge in the northeast Pacific.     

Interplanetary Magnetic Field Polarity and the Size of Low-Pressure Troughs Near 180{degrees}W Longitude

When the interplanetary magnetic field is directed away from the sun, the area of wintertime low-pressure (300-millibar) troughs near 180 degrees W longitude is significantly larger than when the field is toward the sun. This relation persists during most of the winters of 1951 to 1973.     

Heat Transport by Currents Across 25{degrees}N Latitude in the Atlantic Ocean

The heat transported by currents across 25 degrees N in the Atlantic Ocean is estimated from oceanographic measurements to be 1.1 x 10(15) watts northward. This figure agrees, within estimated error, with the value obtained from charts of energy exchange between ocean and atmosphere but is smaller by a factor of 2 than the recent value derived from satellite radiation measurements.     

Activity Coefficients of Aqueous Sodium Chloride from 15{degrees} to 50{degrees}C Measured with a Glass Electrode

Values of the mean activity coefficient of sodium chloride at 15 degrees , 250, 380 and 50 degrees C were determined for aqueous NaCl solutions of 0.01 to 1.0 molal from electromotive force measurements on the cell: (sodium-sensitive glass electrode, aqueous sodium chloride, silver chloride-silver).     

Carbon Dioxide Transport by Ocean Currents at 25{degrees}N Latitude in the Atlantic Ocean

Measured concentrations of CO(2), O(2), and related chemical species in a section across the Florida Straits and in the open Atlantic Ocean at approximately 25 degrees N, have been combined with estimates of oceanic mass transport to estimate both the gross transport of CO(2) by the ocean at this latitude and the net CO(2) flux from exchange with the atmosphere. The northward flux was 63.9 x 10(6) moles per second(mol/s); the southward flux was 64.6 x 10(6) mol/s. These values yield a net CO(2) flux of 0.7 x 10(6) mol/s (0.26 +/- 0.03 gigaton of C per year) southward. The North Atlantic Ocean has been considered to be a strong sink for atmospheric CO(2), yet these results show that the net flux in 1988 across 25 degrees N was small. For O(2) the equivalent signal is 4.89 x 10(6) mol/s northward and 6.97 x 10(6) mol/s southward, and the net transport is 2.08 x 10(6) mol/s or three times the net CO(2) flux. These data suggest that the North Atlantic Ocean is today a relatively small sink for atmospheric CO(2), in spite of its large heat loss, but a larger sink for O(2) because of the additive effects of chemical and thermal pumping on the CO(2) cycle but their near equal and opposite effects on the CO(2) cycle.     

A Climatic Freshening of the Deep Atlantic North of 50{degrees}N over the Past 20 Years

Observations made in summer 1981 show a significant and widespread decrease in salinity, averaging 0.02 per mil, in deep waters of the subpolar North Atlantic over the past two decades. This implies a relatively rapid response of deep water formation to climatic perturbation.     

Crystal Structure of Krypton Difluoride at -80{degrees}C

Krypton difluoride is tetragonal, space group P4(2)/ mnm, with two linear molecules per unit cell aligned in planes perpendicular to the tetrad axes. The alignment alternates by 90 degrees between successive planes. The kryptonfluorine bond distance is 1.89 +/- 0.02 angstroms.     

Supercooling of Water to -92{degrees}C Under Pressure

The temperature at which "clean" supercooled water freezes has been determined as a function of pressure up to 3 kilobars, using a differential thermal analysis technique on subdivided water samples. The supercooling limit of such samples, -38 degrees C at normal pressure, is lowered by initial increase of pressure, reaching a minimum value of -92 degrees C at 2.00 kilobars.     

Xenon Hexafluoride: Structure of a Cubic Phase at -80{degrees}C

The crystal structure of a cubic phase of composition XeF(6) has been determined at -80 degrees C. There are no simple molecules in the complex structure which involves 1008 atoms distributed over 1600 positions per unit cell. Ions of XeF(5)+ and F- are associated in tetrameric and hexameric rings of point group symmetries 4 and 32, respectively. The structure contains right-and left-handed conformations of both tetramers and hexamers. The handedness of the tetramers is dis-ordered but the orientation is ordered. The handedness of the hexamers is ordered but the orientation is disordered.     

Biochemistry at 100{degrees}C: Explosive Secretory Discharge of Bombardier Beetles (Brachinus)

The defensive chemical spray of bombardier beetles is ejected at 100 degrees C, with a heat content of about 0.2 calorie per milligram.