EAS/BIOEE 154 Lecture 10 Introduction to Oceanography Deep Sea Hydrothermal Vents & Seeps

Hydrothermal Vents  Result from the reaction between seawater and hot rock of the ocean floor.  Most occur along mid-ocean ridges; have now been found on all ocean ridges  Can also be associated with subduction zone or hot spot volcanism. Seeps  Result from the expulsion of cool fluid from compressed sediment.  Most often occur near subduction zones. Significance of Mid-Ocean Ridge Hydrothermal Activity  Hydration/metamorphism of oceanic crust: this water is released in explosive volcanism in subduction zones  Control of the chemical composition of seawater  Source of base metal ores, e.g., copper, lead, zinc, throughout history  Unique biological communities  Locale of the origin of life? Hydrothermal processes  Because they cool rapidly from high temperature, lava flows are generally highly fractured, allowing seawater to penetrate the crust.  In the oceanic crust, seawater reacts with the rock, transforming the water from a cold, oxidized, alkaline solution to a hot, reduced, and acidic one that is rich in dissolved metals. Hydrothermal Reactions  Precipitation of Anhydrite: 2+ 2– Ca + SO4 = CaSO4 2+  Removal of Mg , acidification 2+ + Mg + 3H2O + Mg2Si2O6 = Mg3Si2O5(OH)4 + 2 H  Reduction of sulfate to sulfide by oxidation of Fe 2- 2- SO4 + 8 FeO = S + 4Fe2O3  Dissolution of metals 2+ + 2+ + Fe rock + 2H solution = Fe solution + 2H rock  Once water temperatures reach 350-400˚ C, water begins to transition to a supercritical fluid, its density decreases rapidly and it rises to the surface.  Finally, hydrothermal fluid mixes with cold, alkaline, oxidized seawater at the surface, the metals precipitate as hydroxides and sulfides: 3+ – Fe + 3OH = Fe(OH)3 Life at Hydrothermal Vents  1 new phylum  22 new families  Over 90 new genera  Over 500 species  250 strains of free-living bacteria

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Biomass 2  Up to 30 kg/m  10-100 greater than estuaries  1000 greater than deep sea floor Why the abundance of life around hydrothermal vents? What is their energy source? Chemosynthesis  Aerobic CO2 + H2S + O2 + H2O → [CH2O] + H2SO4  Anaerobic CO2 + 6H2 → [CH2O] + CH4 + 3H2O Trophic Relationships in Vent Ecosystems  Bacteria divided between free-living types and symbionts  Example hosts of the latter: . Tube Worm Riftia pachyptila . Giant Clam Calyptogena magnifica . Mussel Bathymodiolus thermophilus  Many vent “bacteria” are not bacteria, but entirely unrelated organisms called “archaea”. Many archaea are extremophiles - thriving at high temperature or high salt content. Tube Worm Riftia pachyptila  No mouth  No anus  No digestive tract  Dependent upon bacteria living in its gut or “troposome”  Gill extracts sulfide, carbon dioxide & oxygen and blood delivers these to troposome  In return, bacteria provide nourishment for Riftia Giant Clam Calyptogena magnifica  Symbiotic bacteria in its gill  Generally lives in cooler water than Riftia Mussel Bathymodiolus thermophilus  Has symbiotic bacteria  Also filters free-living bacteria from water Special Adaptations: Sulfide Toxicity Sulfide is toxic: binds to hemoglobin molecule in place of oxygen, causing suffocation; inhibits cell metabolism by interfering with cytochrome c oxidase, an enzyme that promote production of ATP Riftia’s Solution to the Sulfide Problem  Specialized hemoglobin molecule with separate site to bind sulfide  This also keeps it from interfering with cytochrome c oxidase Other Solutions to the Sulfide Problem  Clam Calyptogena: Separate molecule in blood to bind sulfide; specialized cells on gill surface to oxidize sulfide  Vent crab Bythogrea microps (grazer, no symbionts) has specialized

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pancreas that oxidizes sulfide Special Adaptations: “Night Vision”  Atlantic vent shrimp Rimicaris exoculata are eyeless  Symbiotic bacteria in gills - must stay near vents.  Shrimp have interesting patch on back with pigment rhodopsin, which is infrared-sensitive; Patch connected to nervous system; provides the ability to “see” infrared radiation emitted by vents. Life Cycles and Reproduction  Suitable environments for these organisms are highly restricted  Individual vents have restricted life-spans  Disruption by volcanic eruptions and earthquakes pose further hazards  These conditions favor rapid growth, continuous reproduction, high fecundity Tube worm life cycles  Tube worm Riftia grows at 1 m per year  Genetic similarity decreases with distance.  38 day larval stage; should allow dispersal up to 100 km  Do eruptions trigger reproduction? Very high concentrations of larvae are found in megaplumes Hydrothermal Vents and Us  Hydrothermal activity is a major source of ores of base metals such as copper, zinc, and lead.  Troodos Mtns in Cyprus are made of upthrust oceanic crust; they contain copper ore deposits formed during hydrothermal activity 90 Ma ago.  Copper in Troodos has been mined for at least 5000 years and export to Europe; helped initiate bronze age technology and civilization “Seeps” of the Continental Margin  Methane (from breakdown of organic matter) leaking from sediment supports chemosynthetic communities similar to vents  Oxidation of methane provides energy CH4 +3O2 → CO2 + 2H2O  Similar fauna to vent communities, some species the same

Some Study Questions

Explain the connection between hydrothermal activity at mid- ocean ridges and explosive volcanoes, such as Mt. St. Helens, at subduction zones. Why do some many hydrothermal vent waters have temperatures in the range of 350°-400°C? What is the “black smoke” emitted by some vents? Explain why it forms. Why is hydrogen sulfide toxic to so many animals? How does the tube worm Riftia survive sulfide toxicity?

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How can Riftia survive without a mouth? Why would the vent shrimp Rimicaris exoculata have evolved “infrared eyes” on its back and lost its normal eyes? What role have hydrothermal vents played in the development of civilization?

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