1. Deep Ocean Topography Mid-Ocean Ridges and Hydrothermal Vents Sarah Fawcett

2. Mid-Ocean Ridges Linear mountain chains. Linear mountain chains. Some of the largest features on Earth. Some of the largest features on Earth. 5km-2.6km deep. 5km-2.6km deep. Roughly symmetrical in cross section. Roughly symmetrical in cross section. Thousands of kilometers wide. Thousands of kilometers wide. Volcanoes, earthquakes, hills and mountains. Volcanoes, earthquakes, hills and mountains.

3. Location of Ridges Mid-Atlantic Ridge Mid-Atlantic Ridge 1855 - Fontaine Maury identified “shallow middle ground”. 1855 - Fontaine Maury identified “shallow middle ground”. 1950s - Heezen & Ewing proposed a continuous mountain range. 1950s - Heezen & Ewing proposed a continuous mountain range. East Pacific Rise East Pacific Rise Largest oceanic ridge. Largest oceanic ridge. 1870s - Challenger Expedition 1870s - Challenger Expedition 1950-60s - described by Heezen and Ewing. 1950-60s - described by Heezen and Ewing.

4. Formation of Ridges Divergent tectonic plate motions. Tensional forces = thinning of oceanic crust and upwelling of magma, forming ridges.

5. Seafloor Spreading Lava buried by sediment as seafloor spreads away from ridge. Lava buried by sediment as seafloor 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 rates and transgression of ocean waters onto the continents. Correlation between global spreading rates and transgression of ocean waters onto the continents. Early Cretaceous - Global spreading rates uniformly high Early Cretaceous - Global spreading rates uniformly high Marine sediments Marine sediments

6. Seafloor Dating Paleomagnetic dating Paleomagnetic dating Curie Point Curie Point Use spreading rate to calculate age of rock. Use spreading rate to calculate age of rock. Age of the Seafloor Age of the Seafloor Gets older further from the ridge. Gets older further from the ridge.

7. Hydrothermal Vents Localized discharges of heated seawater. Cold water percolates down into the crust through fissures. Heated water rises and seeks a path to the surface. Bursts into the ocean as hot as 400ºC but intense pressure from overlying ocean prevents it from boiling. Accounts for amount of the Earth’s heat loss.

8. Growth of Vents Chimneys Chimneys Minerals leached from the crust - Zn, Fe, Cu. Minerals leached from the crust - Zn, 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 and Si. Compounds of Ba, Ca and Si.

9. Discovery of Vents 1977 on East Pacific Rise Near Galapagos Islands ALVIN Research submersible. Wood’s Hole Oceanographic Institute. Viewports, searchlights, mechanical arm, cameras. First temperature measurement.

10. Location of Hydrothermal Vents

11. Life at Hydrothermal Vents Harsh environment, yet abundant life: Harsh environment, yet abundant life: Tubeworms Tubeworms Crabs Crabs Shrimp Shrimp Clams Clams Anemones Anemones CHEMOSYNTHETIC BACTERIA CHEMOSYNTHETIC BACTERIA No photosynthesis No photosynthesis Bacteria convert sulfur to energy by chemosynthesis, forming base of foodchain. Bacteria convert sulfur to energy by chemosynthesis, forming base of foodchain. Animals eat bacteria or bacteria live inside their bodies. Animals eat bacteria or bacteria live inside their bodies. Origin of Life? Origin of Life?

12. Flow at Vents

13. Baker, Cormier, Langmuir and Zavala Hydrothermal plumes along segments of contrasting magmatic influence, 15º20’ - 18º30N, East Pacific Rise: Influence of axial faulting. Geochemistry Geophysics Geosystems. Volume 2. September 2004. AGU and the Geochemical Society. Hydrothermal plumes along segments of contrasting magmatic influence, 15º20’ - 18º30N, East Pacific Rise: Influence of axial faulting. Geochemistry Geophysics Geosystems. Volume 2. September 2004. AGU and the Geochemical Society. Theory: Greater incidence of hydrothermal vents on faster spreading ridge segments, not always the case - Tectonic forces can dominate. Theory: Greater incidence of hydrothermal vents on faster spreading ridge segments, not always the case - Tectonic forces can dominate. Segment of ridge between Orozco and Rivera transform faults (15º18’N - 18º30’N). Segment of ridge between Orozco and Rivera transform faults (15º18’N - 18º30’N). 133 rock cores. 133 rock cores. Comparison of hydrothermal environment of three adjacent but distinctly different segments. Comparison of hydrothermal environment of three adjacent but distinctly different segments. Prediction:17ºN segment should have less extensive hydrothermal plumes than16º segments - slower spreading rate. Prediction:17ºN segment should have less extensive hydrothermal plumes than16º segments - slower spreading rate. Opposite is true. Opposite is true.

14. 17ºN segment: plume incidence = mean of super fast spreading segments on the southern EPR. 17ºN segment: plume incidence = mean of super fast spreading segments on the southern EPR. Local permeability environment in the region controls amount of hydrothermal activity: Local permeability environment in the region controls amount of hydrothermal activity: 16ºN segment: little indication of faulting, model for fast spreading rates, may have hydrothermal activity suppressed by volcanic flows that act as an impermeable cap over much of the segment. 16ºN segment: little indication of faulting, model for fast spreading rates, may have hydrothermal activity suppressed by volcanic flows that act as an impermeable cap over much of the segment. Conclusion: Conclusion: Tectonic forces can control the extent and nature of hydrothermal activity. Tectonic forces can control the extent and nature of 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 ridge follows the existing global correlation between plume incidence and spreading rate. On a global scale, however this portion of the ridge follows the existing global correlation between plume incidence and spreading rate.