Download Deep Sea Hot Springs and their Ecosystems

EAS/BIOEE 154
Lecture 10
Introduction to Oceanography
Deep Sea Hydrothermal Vents & Seeps
Hydrothermal Vents
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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
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Result from the expulsion of cool fluid from compressed sediment.
Most often occur near subduction zones.
Significance of Mid-Ocean Ridge Hydrothermal Activity
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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
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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
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Precipitation of Anhydrite:
Ca2+ + SO42– = CaSO4
Removal of Mg , acidification
Mg2+ + 3H2O + Mg2Si2O6 = Mg3Si2O5(OH)4 + 2 H+
Reduction of sulfate to sulfide by oxidation of Fe
SO42- + 8 FeO = S2- + 4Fe2O3
Dissolution of metals
Fe2+rock + 2H+solution = Fe2+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:
Fe3+ + 3OH– = Fe(OH)3
2+
Life at Hydrothermal Vents
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1 new phylum
22 new families
Over 90 new genera
Over 500 species
250 strains of free-living bacteria
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EAS/BIOEE 154
Lecture 10
Biomass
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 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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EAS/BIOEE 154
Lecture 10
pancreas that oxidizes sulfide
Special Adaptations: “Night Vision”
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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
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Hydrothermal Vents and Us
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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
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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 midocean 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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Lecture 10
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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