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7. Deep Sea Reducing Habitats

  History of Deep Sea Exploration   Discovery of hydrothermal vents

  Hydrothermal Vents

  Living in reducing environments   Chemosynthesis   Life history strategies

  Other Reducing Habitats   Cold Seeps

  Whale Falls

Dr Rhian G. Waller 21st April 2010 Reading: Van Dover et al., 2002, Science 295: 1253-7

Deep-Sea Reducing Habitats   “Habitat where energy from reduced inorganic

chemical species (e.g. H2S, H2, CH4) is converted, through microbial endosymbiosis, into biomass of higher organisms”

  Whole communities driven by chemosynthesis

  Whole ecosystem – micro – macro fauna living off chemosynthesis

  “Oasis” of diversity on deep-sea floor

  General deep-sea is sediments - ~1g/m2 biomass

  Reducing Habitats - >10kg/m2 biomass

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Deep Sea Exploration   Forbes’ Azoic Hypothesis

  1844

  “The deep ocean (below 550m) is lifeless

  Too cold, too much pressure, no light

  Caused controversy

  James Clark Ross

  Micheal Sars

  Wyville Thomson & William Carpenter

  1868 – 1870

  HMS Lightening & HMS Porcupine

  Life to 1000m

HMS Challenger Expedition   1872 – 1876

  70,000 nautical miles

  492 deep soundings; 133 bottom dredges; 151 pelagic trawls

  “How do species live in the deep-sea?”

  Discovered 4700 new species

  Discovered “food fall”

  Laid the foundation of oceanographic research

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1% of Deep Sea Explored   “We know more about the

surface of the moon than the bottom of our oceans”

  Majority of the world is deep-sea

  USS San Francisco

  2005

  Uncharted seamount

  200m depth

Hydrothermal Vent Discovery   1977 – Geology Cruise to Galapagos Rift

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Hydrothermal Vent Discovery   1977 – Geology Cruise to Galapagos Rift

Lonsdale, 1977

  1977 – Geology Cruise to Galapagos Rift

Hydrothermal Vent Discovery

Lonsdale, 1977

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  1979 – Biologists go to Galapagos Vents   DSV Alvin & Lulu

Hydrothermal Vent Discovery

  Found abundant life

Hydrothermal Vents   Fissures and conduits

  Allow water to get close to, heated by magma

  Tectonic plates

  Hotspots

  Water is “superheated” and escapes back to seafloor

  Picks up minerals from rock

  Up to ~400°C

  Pressure & salinity increase boiling point

  Can form chimneys

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Hydrothermal Vents   Superheated water hits cold water

  Precipitation of minerals   Anhydrite

  Sulphides   Copper, Iron, Zinc

  Black Smoker   Hot water   High sulphides

  White Smoker   Cooler water

  Barium, calcium, silicon

Hydrothermal Vents

  Black Smoker

  ~ >300°C

  White Smoker

  <300°C

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Global Hydrothermal Vents

Longevity of Vents

  Vents are volatile & ephemeral

  Clogged conduits   Sulphide build

up   Tectonic shifts

  Expanded conduits

Tunnicliffe, 1991

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Estimated by:

Heat loss in rocks decades (Macdonald et al., 1980)

Clam ages 4-40 years

(Lutz et al, 1988; Fisher et al., 1988)

Sulphide Radiochronology 15-60 years (Stakes & Moore, 1989; Lalou et al., 1984)

Living in Reducing Habitats

  “Extremophiles”

  Organisms that live and thrive in geochemically extreme conditions

  Conditions that would usually be detrimental

  Hyperthermophiles

  Live in temps greater than 80°C

  Enzymes that function at higher temps

  Chemosynthesis

  Primary production without using sunlight

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Living in Reducing Habitats

  Chemosynthesis   Only bacteria can do this

  Endosymbionts

+ 24 Hydrogen sulfide (H2S)

+ 18 Water (H2O)

6 Carbon dioxide (CO2)

Glucose (C6H12O6)

+ 6 Oxygen (O2)

+ 24 sulfur (S)

Endosymbiosis

  Evolved endosymbiosis with chemosynthetic bacteria   Riftia

  Trophosome

  Clams/mussels   Gills

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Living in Reducing Habitats

Van Dover, 2000

  Very high growth rates

  Grow to reproductive size fast

Other Reducing Habitats…   Cold Seeps

  Cold water carrying hydrocarbons, methane and hydrogen sulphate

  Whale Falls   Break down of lipids by bacteria creates sulphates

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Cold Seeps   First discovered in 1984

  Gulf of Mexico, 3000m depth

  Often form brine pools

  Salinity 3-5 times greater than normal

  Salt leached from rocks

  High quantities of hydrogen sulphide, methane & hydrocarbons

  Emit at a slower, more dependable rate than hydrothermal vents

  Longer lived organisms

  50 - 100’s on years

Brine Pools

Salt diapir

Gas reservoir

seabed

Methane bubbles

Sediment

Bathymodiolus childressi

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Cold Seeps   Mostly along continental margins

  Gases and oils seep from sediments

  Brine pools can form in other areas of high salt   Antarctica

  Salt excluded from sea ice formation

  Carbonate formation   Precipitation from seep waters as byproduct of microbial

metabolism

Whale Falls   Whale carcass that has fallen to the seafloor

  Shallow water   Scavengers quickly take over   Carcass devoured in months

  Deep water   Fewer scavengers

  Body lasts longer (10s of years)   Specialized ecosystem

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Whale Falls   Three stages of decomposition

  Mobile Scavengers

  Hagfish, sleeper sharks consume flesh

  Enrichment Opportunistic

  Smaller organisms move in and feed

  Sulfophilic

  Bacteria (anaerobic) break down lipids in bones

Whale Falls   Sulphate reducing bacteria

  Use dissolved sulphate in water for chemosynthesis

  Excrete hydrogen sulphide

  Support chemosynthetic bacteria communities

Smith and Baco, 2003

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44

30

Hydrothermal vent endemic

369 Deep Sea

10

~106 to 107

Whale endemic

>40 360 11

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Food Webs

  Are organisms at reducing environments that use both forms of primary production

Van Dover, 1990

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Conclusions   Chemosynthetically driven communities and ecosystems

  Hydrothermal Vents   Hot water, sulphides

  Cold Seeps   Cold water, hydrocarbons, sulphides

  Whale Falls   Cold water, lipids

  Faunal adaptations   Thermophiles   Chemosynthesis

  endosymbiosis   Faster growth rates