East pacific rise: hot springs and geophysical experiments

Physiological characteristics of Thiomicrospira sp. Strain L-12 isolated from deep-sea hydrothermal vents

Growth of the obligately chemolithotrophic Thiomicrospira sp. strain L-12, isolated from a hydrothermal vent at a depth of 2,550 m in the Galapagos Rift region, was optimal at pH 8 and required 200 mM Na+ and divalent ions (Ca2+ and Mg2+). The organism was microaerophilic and tolerated 300 microM sulfide without a decrease in the rate of CO2 incorporation. Growth and CO2 incorporation occurred within the temperature range of 10 to 35 degrees C, with both optimal at 25 degrees C. At the in situ pressure of 250 atm. the rate of CO2 incorporation was reduced by 25% relative to that measured at 1 atm: it was entirely suppressed at 500 atm. The results of this physiological characterization suggest that Thiomicrospira sp. strain L-12 can be an active autotroph in the hydrothermal environment.

Functional Characteristics of the Blood of the Deep-Sea Hydrothermal Vent Brachyuran Crab

Hemocyanin in the whole blood of the hydrothermal vent brachyuran crab, Bythograea thermydron, has a moderate oxygen affinity (P(50) = 6.6 millimeters of mercury at 2.6 degrees C; pH 7.5), which unlike that of other hemocyanins is independent of temperature over the range 2 degrees to 30 degrees C; carbon dioxide and pH have independent effects on the oxygen affinity of this pigment. The pH effect on affinity is moderate (Deltalog P(50)/DeltapH = -0.34), whereas increased carbon dioxide, which can act both directly and by changing pH, has a much larger effect (Deltalog P(50)/DeltapH = -0.81). This blood has a moderately high degree of cooperativity (Hill cooperativity coefficient, n, was 2.8) and a large oxygen-carrying capacity for a crustacean (4.5 milliliters of oxygen per 100 milliliters of blood). These properties characterize an oxygen transport system whose function appears to be largely independent of the wide range of environmental conditions encountered around the vents.

A Major Helium-3 Source at 15 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.

Blood Function in the Hydrothermal Vent Vestimentiferan Tube Worm

Extracellular hemoglobin in the whole blood of Riftia pachyptila has a high oxygen affinity (P50 = 1.8 millimeters of mercury at 3 degrees C), a moderate decrease in oxygen affinity at higher temperatures (P50 = 2.7 millimeters of mercury at 14 degrees C), a small effect of carbon dioxide on oxygen affinity (Delta log P50/Delta pH =-0.12), and a high oxygen carrying capacity (up to 11 milliliters of oxygen per 100 milliliters of blood). These characteristics are compatible with the high oxygen demand of chemoautotrophic metabolism in the variable vent environment.

Riftia pachyptila Jones: Observations on the Vestimentiferan Worm from the Galapagos Rift

The obturacular plume, composed of numerous tentacles, is suggested as a site for the uptake of molecular "food" by Riftia pachyptila (Pogonophora) from the Galápagos Rift; symbiotic bacteria are another possible source of nutrition. Differing organizations of the linings of the five major body cavities of Riftia demonstrate the inadequacy of "coelom" as a descriptive term.

Crustal Processes of the Mid-Ocean Ridge

Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 degrees N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0.5 percent of the world's rivers, but the effective transport rates of elements are comparable to those of rivers in that anomalies for individual elements are frequently between 100 and 1000 times the average river composition. The degree of subsurface dilution determines the final exit temperature and composition of the hydrothermal fluids, ranging from manganese domination at extreme dilution to iron at intermediate levels to sulfide deposition when low dilution occurs. The discovery of massive sulfide deposits on the East Pacific Rise is destined to have a profound impact on our understanding of ore-forming processes. Whether it will have any economic significance remains to be seen.

Seabed Minerals and the Law of the Sea

If, as seems likely, a comprehensive law-of-the-sea treaty is successfully concluded, minerals of the continental margins would be almost entirely controlled by coastal nations, and the right to produce minerals of the deep ocean floor would be licensed by an International Seabed Authority. Mineral production from the continental margins is likely to increase and diversify with time. The only minerals from the deep ocean floor for which there are reasonably good prospects of production within the next decade are the metalliferous muds from some of the deeps in the Red Sea (which lie within what is likely to be the jurisdiction of Saudi Arabia and Sudan) and nodules in the northeastern equatorial Pacific that contain recoverable metals, namely nickel, copper, cobalt, and possibly manganese, molybdenum, and vanadium.

Sulfide Deposits from the East Pacific Rise Near 21 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.

Geothermal System at 21 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.