East pacific rise: hot springs and geophysical experiments

Benthic siphonophores: a review of the family Rhodaliidae (Siphonophora, Physonectae)

This paper reviews the present state of our knowledge concerning a little known family of physonect siphonophores, the Rhodaliidae. The members of this family are unusual in that they are short-stemmed, with the cormidia basically arranged into spirals around the spheroidal corm, and with the nectophores forming a corona around the base of a greatly enlarged pneumatophore. Unique to these animals is the possession of a dorsal aurophore, a structure that contains the considerably expanded pneumatochone, or gas-secreting area, of the pneumatophore. These and other unusual aspects of the morphology of the rhodaliids are described and compared with those in the more typical, long-stemmed physonect siphonophore. The history of the family Rhodaliidae is reviewed. The 37 specimens recorded in the literature, 15 of which belong to one species, originally were described under ten specific names. However, four of these names generally have been treated as synonyms of others, leaving six species within five genera. Whenever possible the extant material has been re-examined and, in addition, new specimens of five of the species have become available for study, as well as specimens of two new rhodaliid species. These studies, together with some additional information, have led to the suggestion that two of the original species, previously synonymized with another, should be resurrected as valid species, although a certain degree of intuitive reasoning is applied in one case, based mainly on differences in the geographical and bathymetric distributions of the relevant species. The systematics of the rhodaliid species is reviewed in detail and a key is provided for their identification. Recently, observations have been made on two rhodaliid species in situ , and these have conclusively proven that these animals are unique among the siphonophores in that their habitat is not planktonic, as previous authors asserted, but benthic. The observations indicate that the animals float above the substratum, tethered to it, like hot-air balloons, by their tentacles. The re-adoption of a benthic existence has led to many unique features being evolved in the rhodaliids, and some of these are discussed. The extraordinary size of the pneumatophore, especially in comparison with the planktonic physonects, appears to be a necessity since the gas that it contains is required to offset the excess density of the corm and enable near-neutral buoyancy to be attained. In order that the huge volumes of gas may be secreted, sometimes at pressures exceeding 300 atm (3 x 10 7 Pa) the gas gland or pneumadenia has become greatly enlarged and forms part of the peculiar structure, the aurophore. The role of both the pneumatophore and aurophore in buoyancy control is discussed in detail. One other outstanding feature of the rhodaliid siphonophores is the possession of two types of gastrozooid on its cormidial units. Only one of these gastrozooids carries a tentilla-bearing tentacle. The arrangement is thought to be a result of the necessity to adopt a method of feeding different from the more usual fishing net set by the planktonic siphonophores. There is little doubt, therefore, that the rhodaliids are a fascinating and very unusual family of siphonophores.

Aqueous high-temperature and high-pressure organic geochemistry of hydrothermal vent systems

Hydrothermal systems associated with oceanic spreading centers are now recognized as relatively common phenomena, and the organic chemical alterations occurring there are rapid and efficient. In the marine hydrothermal systems at water depths > 1.5 km, the conditions driving chemical reactions are high temperatures (up to >400 degrees C), confining pressures (>150 bar), and other parameters such as pH, Eh, and mineralogy in an aqueous open flow medium. Continental hydrothermal systems may also be of interest, as, for example, in failed or dormant rifts and regions around piercement volcanoes. Organic matter alteration by reductive reactions to petroleum hydrocarbons occurs in hydrothermal systems over a wide temperature window (approximately 60 to >400 degrees C), under elevated pressure, and in a brief geological time (years to hundreds of years). The products are rapidly moved as bulk phase or in fluids from the regions at higher temperatures to areas at lower temperatures, where the high molecular weight material separates from the bulk. These conditions are conducive to organic chemistry which yields concurrent products by primarily reduction (due to mineral buffering), oxidation (high thermal stress), and synthesis reactions. This chemistry is just beginning to be elucidated by the geochemical community, but there are various industrial applications which provide useful preliminary insight. Therefore, the behavior of organic matter (inclusive of methane to high molecular weight compounds > C40) in warm to supercritical water needs to be characterized to understand the implications of this novel phenomenon in geological and geochemical processes, and the chemistry occurring over the full temperature spectrum of hydrothermal systems is of relevance to origins of life research.

What determines the volume of the oceans?

The volume of Earth's oceans may be determined by a dynamic mechanism involving exchange of water between the crust and the mantle. Fast-spreading mid-ocean ridges are currently submerged to a depth at which the pressure is close to the critical pressure for seawater. This ensures optimal convective heat transport and, hence, maximal penetration of hydrothermal circulation along the ridge axes. The oceanic crust is hydrated to a depth of a kilometer or more and can therefore carry a substantial flux of water to the upper mantle when it is subducted. The current ingassing rate of water by this process is probably at least sufficient to balance the outgassing rate. If the oceans were shallower, as they may have been in the distant past, convective heat transport would be reduced and the depth of hydrothermal penetration and crustal hydration would decrease. Outgassing would exceed ingassing and ocean volume would increase. The system is self-stabilizing as long as the depth of the oceans does not exceed its present value. This mechanism could explain why continental freeboard has remained approximately constant since the Archean despite probable increases in continental area.

Percolation Theory, Thermoelasticity, and Discrete Hydrothermal Venting in the Earth's Crust

As hydrothermal fluid ascends through a network of cracks into cooler crust, heat is transferred from the fluid to the adjacent rock. The thermal stresses caused by this heating close cracks that are more or less vertical. This heating may affect network connections and destroy the permeable crack network. Thermoelastic stresses caused by a temperature difference of approximately 1000 degrees C can decrease the interconnectivity of a crack network to the percolation threshold. If the temperature is slightly less, thermoelastic stresses may focus the discharge in hydrothermal systems into discrete vents.

Preliminary description and nutritional characterization of a chemoorganotrophic archaeobacterium growing at temperatures of up to 110 ° isolated from a submarine hydrothermal vent environment

Summary: An extremely thermophilic coccoid bacterium, designated strain ES4, was isolated from a flange (a newly described geological structure associated with massive sulphide mounds) at the Juan de Fuca Ridge hydrothermal vent system. The organism is a salt-requiring obligately anaerobic chemoorganotroph which reduces elemental sulphur but can grow very poorly in the absence of sulphur. Organic substrates utilized include yeast extract, peptone and amino acid hydrolysate as well as individual amino acids, the peptide Leu-Ser and starch. When growing on a defined medium, ES4 requires a supplement of vitamins and 20 amino acids at trace concentrations. Growth is most rapid in the temperature range 90-99 °C, with a maximum growth temperature of about 110 °C. In the optimal temperature range for growth, ES4 has a doubling time of about 1 h and can reach densities of 109 cells ml-1. Insensitivity to the antibiotics vancomycin, streptomycin and chloramphenicol, and the presence of di- and tetra-ether phytanyl lipids, indicate that ES4 is an archaeobacterium.

Construction of protocellular structures under simulated primitive earth conditions

We have developed experimental approaches for the construction of protocellular structures under simulated primitive earth conditions and studied their formation and characteristics. Three types of envelopes; protein envelopes, lipid envelopes, and lipid-protein envelopes are considered as candidates for protocellular structures. Simple protein envelopes and lipid envelopes are presumed to have originated at an early stage of chemical evolution, interaction mutually and then evolved into more complex envelopes composed of both lipids and proteins. Three kinds of protein envelopes were constructed in situ from amino acids under simulated primitive earth conditions such as a fresh water tide pool, a warm sea, and a submarine hydrothermal vent. One protein envelope was formed from a mixture of amino acid amides at 80 degrees C using multiple hydration-dehydration cycles. Marigranules, protein envelope structures, were produced from mixtures of glycine and acidic, basic and aromatic amino acids at 105 degrees C in a modified sea medium enriched with essential transition elements. Thermostable microspheres were also formed from a mixture of glycine, alanine, valine, and aspartic acid at 250 degrees C and above. The microspheres did not form at lower temperatures and consist of silicates and peptide-like polymers containing imide bonds and amino acid residues enriched in valine. Amphiphilic proteins with molecular weights of 2000 were necessary for the formation of the protein envelopes. Stable lipid envelopes were formed from different dialkyl phospholipids and fatty acids. Large, stable, lipid-protein envelopes were formed from egg lecithin and the solubilized marigranules. Polycations such as polylysine and polyhistidine, or basic proteins such as lysozyme and cytochrome c also stabilized lipid-protein envelopes.

Hydrothermal Plume Measurements: A Regional Perspective

An extensive deep-tow survey around an active submarine vent field was conducted to map the three-dimensional distribution of hydrothermal emissions and calculate the hydrothermal discharge of heat and manganese. Emissions from the 10-kilometer-long vent field formed a nearly isopycnal plume about 250 meters thick and elongated in the direction of the local net current. Net export of hydrothermal discharge from both point and diffuse sources was estimated from the advective transport of the plume; the heat flux was 5.8 +/- 2.9 x 10(8) watts and the dissolved manganese flux was 0.2 +/- 0.1 moles per second. Flux measurements of this type could be expanded to encompass entire ridge segments, allowing comparison with theoretical thermal and chemical process models on a common spatial scale.

In Situ Measurements of Chemical Distributions in a Deep-Sea Hydrothermal Vent Field

Large changes in the concentration of sulfide around a hydrothermal vent in the Galápagos Rift provide direct evidence for the consumption of sulfide by the organisms of the vent community. These changes were detected with a new chemical analyzer capable of measuring silicate, sulfide, oxygen, and temperature on the sea floor at depths of 2500 meters. More than 10,000 measurements showed systematic variations in the sulfide and oxygen concentrations due to biogenic oxidation of sulfide in the hydrothermal solutions. Silicate concentration was highly correlated with temperature, but different trends were observed at different locations.