Deep Ocean TopographyDeep Ocean Topography

Mid-Ocean Mid-Ocean Ridges Ridges

and and HydrothermHydrotherm

al Ventsal VentsSarah FawcettSarah Fawcett

Mid-Ocean RidgesMid-Ocean Ridges Linear mountain chains.Linear mountain chains. Some of the largest Some of the largest

features on Earth.features on Earth. 5km-2.6km deep.5km-2.6km deep. Roughly symmetrical in Roughly symmetrical in

cross section.cross section. Thousands of Thousands of

kilometers wide.kilometers wide. Volcanoes, Volcanoes,

earthquakes, hills and earthquakes, hills and mountainsmountains..

Location of RidgesLocation of Ridges Mid-Atlantic RidgeMid-Atlantic Ridge

1855 - Fontaine Maury 1855 - Fontaine Maury identified “shallow identified “shallow middle ground”.middle ground”.

1950s - Heezen & Ewing 1950s - Heezen & Ewing proposed a continuous proposed a continuous mountain range.mountain range.

East Pacific RiseEast Pacific Rise Largest oceanic ridge.Largest oceanic ridge. 1870s - 1870s - ChallengerChallenger

ExpeditionExpedition 1950-60s - described by 1950-60s - described by

Heezen and Ewing.Heezen and Ewing.

Formation of RidgesFormation of Ridges Divergent tectonic Divergent tectonic

plate motions.plate motions. Tensional forces = Tensional forces =

thinning of oceanic thinning of oceanic crust and crust and upwelling of upwelling of magma, forming magma, forming ridges.ridges.

Seafloor SpreadingSeafloor Spreading Lava buried by sediment as seafloor Lava buried by sediment as seafloor

spreads away from ridge.spreads away from ridge. Spreading Rates: Spreading Rates:

Slow - 10mm/yr (Southwest Indian Ridge)Slow - 10mm/yr (Southwest Indian Ridge) Fast - up to 160mm/yr (East Pacific Rise)Fast - up to 160mm/yr (East Pacific Rise)

Correlation between global spreading Correlation between global spreading rates and transgression of ocean waters rates and transgression of ocean waters onto the continents.onto the continents. Early Cretaceous - Global spreading rates uniformly Early Cretaceous - Global spreading rates uniformly

highhigh Marine sedimentsMarine sediments

Seafloor DatingSeafloor Dating Paleomagnetic Paleomagnetic

datingdating Curie PointCurie Point Use spreading rate to Use spreading rate to

calculate age of rock.calculate age of rock.

Age of the SeafloorAge of the Seafloor Gets older further Gets older further

from the ridge.from the ridge.

Hydrothermal VentsHydrothermal Vents Localized discharges of Localized discharges of

heated seawater.heated seawater. Cold water percolates down Cold water percolates down

into the crust through into the crust through fissures.fissures.

Heated water rises and Heated water rises and seeks a path to the surface.seeks a path to the surface.

Bursts into the ocean as hot Bursts into the ocean as hot as 400ºC but intense as 400ºC but intense pressure from overlying pressure from overlying ocean prevents it from ocean prevents it from boiling.boiling.

Accounts for amount of the Accounts for amount of the Earth’s heat loss.Earth’s heat loss.

Growth of VentsGrowth of Vents ChimneysChimneys

Minerals leached Minerals leached from the crust - Zn, from the crust - Zn, Fe, Cu.Fe, Cu.

Rapid growth rate.Rapid growth rate. ““Black Smokers”Black Smokers”

Hottest vents.Hottest vents. Iron monosulfide.Iron monosulfide.

““White Smokers”White Smokers” Cooler vents.Cooler vents. Compounds of Ba, Ca Compounds of Ba, Ca

and Si.and Si.

Discovery of VentsDiscovery of Vents 1977 on East Pacific 1977 on East Pacific

RiseRise Near Galapagos IslandsNear Galapagos Islands ALVINALVIN

Research submersible.Research submersible. Wood’s Hole Wood’s Hole

Oceanographic Institute.Oceanographic Institute. Viewports, searchlights, Viewports, searchlights,

mechanical arm, cameras.mechanical arm, cameras. First temperature First temperature

measurement.measurement.

Location of Location of Hydrothermal VentsHydrothermal Vents

Life at Hydrothermal Life at Hydrothermal VentsVents

Harsh environment, yet Harsh environment, yet abundant life:abundant life:

TubewormsTubeworms CrabsCrabs ShrimpShrimp Clams Clams AnemonesAnemones CHEMOSYNTHETIC BACTERIACHEMOSYNTHETIC BACTERIA

No photosynthesisNo photosynthesis Bacteria convert sulfur to Bacteria convert sulfur to

energy by chemosynthesis, energy by chemosynthesis, forming base of foodchain.forming base of foodchain.

Animals eat bacteria or Animals eat bacteria or bacteria live inside their bacteria live inside their bodies.bodies.

Origin of Life?Origin of Life?

Flow at VentsFlow at Vents

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Baker, Cormier, Langmuir and Baker, Cormier, Langmuir and ZavalaZavala

Hydrothermal plumes along segments of contrasting magmatic Hydrothermal plumes along segments of contrasting magmatic influence, 15º20’ - 18º30N, East Pacific Rise: Influence of axial influence, 15º20’ - 18º30N, East Pacific Rise: Influence of axial faultingfaulting. . Geochemistry Geophysics Geosystems. Volume 2. Geochemistry Geophysics Geosystems. Volume 2. September 2004. AGU and September 2004. AGU and the Geochemical Society.the Geochemical Society.

Theory: Greater incidence of hydrothermal vents on faster spreading Theory: Greater incidence of hydrothermal vents on faster spreading ridge segments, not always the case - Tectonic forces can dominate.ridge segments, not always the case - Tectonic forces can dominate.

Segment of ridge between Orozco and Rivera transform faults (15º18’N - Segment of ridge between Orozco and Rivera transform faults (15º18’N - 18º30’N).18º30’N).

133 rock cores.133 rock cores. Comparison of hydrothermal environment of three adjacent but distinctly Comparison of hydrothermal environment of three adjacent but distinctly

different segments.different segments. Prediction:17ºN segment should have less extensive hydrothermal Prediction:17ºN segment should have less extensive hydrothermal

plumes than16º segments - slower spreading rate.plumes than16º segments - slower spreading rate. Opposite is true.Opposite is true.

17ºN segment: plume incidence = mean of super 17ºN segment: plume incidence = mean of super fast spreading segments on the southern EPR.fast spreading segments on the southern EPR.

Local permeability environment in the region Local permeability environment in the region controls amount of hydrothermal activity: controls amount of hydrothermal activity: 16ºN segment: little indication of faulting, model for fast spreading 16ºN segment: little indication of faulting, model for fast spreading

rates, may have hydrothermal activity suppressed by volcanic flows rates, may have hydrothermal activity suppressed by volcanic flows that act as an impermeable cap over much of the segment.that act as an impermeable cap over much of the segment.

Conclusion: Conclusion: Tectonic forces can control the extent and nature of Tectonic forces can control the extent and nature of

hydrothermal activity. hydrothermal activity. Documented for several sites on the Mid-Atlantic Ridge.Documented for several sites on the Mid-Atlantic Ridge.

On a global scale, however this portion of the On a global scale, however this portion of the ridge follows the existing global correlation ridge follows the existing global correlation between plume incidence and spreading rate.between plume incidence and spreading rate.