EARTH 222 Lecture 25: Hydrothermal Systems
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Department
Earth and Environmental Sciences
Course Code
EARTH 222
Professor
Brian Arbic

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April 3, 2017 Hydrothermal Systems • Background biology • Prior to 1977… • Biologists thought that photosynthesis supported all life on Earth • Organisms in the deep sea ate only what little debris from the surface waters • Scarce food meant that diversity of limited • Most animals were scavengers on the ocean bottom or filter feeders • Basis for life • Photosynthesis • Dominant form of primary production in the ocean and on land Requires water, CO2, nutrients, and energy • • CO2 + H2O —> CH2O + O2 • Respiration • Energy released fuels life processes for autotrophs and heterotrophs • Requires organic matter and O2 • CH2O + O2 —> CO2 + H2O • The hydrothermal discovery • In 1977, researchers aboard Alvin found an entire ecosystem at the Galapagos Ridge, far removed from the direct influence of the Sun • After temperature-sensitive equipment returned small temperature changes at one site along the Rift, cameras sent to the same site returned with pictures of heaps of clam shells Further submarine dives to vents have revealed temperatures as high as 464ºC and a • variety of unusual organisms • First reactions • This was potentially the greatest biological discover of the 20th century • Some unanswered questions • What did all of these organisms eat considering food is so scarce in the deep sea? • Were these organisms related to anything we already knew about? • Basics of hydrothermal vents • Hydrothermal circulation = heat driven circulation of water • Process • Sea water sinks through cracks in the sea surface This seawater is heated by the warm lithosphere, causing convection • • Hot water at >350ºC dissolved reduces chemicals • Vent fluids are ejected into the deep oceans • Types of hydrothermal vents • Diffused flow vents • Discharge warm 2-23ºC water that contains abundant hydrogen sulfide, nitrate,and oxygen • Black smokers • Discharge very hot water (~350ºC) at high flow rates • The temperature of water in black smokers—350ºC—is greater than the boiling point of water on Earth’s surface (100ºC) The high pressures at the bottom of the ocean prevents the 350ºC water in black • smokers from boiling • No oxygen nitrate, but high metal concentrations (Fe and Mn) • Metal leaches from crust • Superheated water meets cold deep water Metals become oxidized, forming Mn and Fe oxides • • Oxides form cloud of black particles • Key source of Fe and Mn to the ocean • Many metal ores formed in hydrothermal settings • Importance of black smokers • Iron is a limiting nutrient for photosynthesis in the oceans • Hydrothermal vents fertilize the oceans with Fe and Mn • Contribution of Fe and Mn from hydrothermal vents is roughly the same as the total input of Fe and Mn from all rivers put together • Chemicals in vent fluids sustain entire ecosystem black smokers • How does life thrive at mid-ocean ridges? Chemosynthesis (or chemolithoautotrophy) • • Involves carbon fixation using energy derived from reactions involving inorganic chemicals • Chemo = energy source (chemical reactions) • Litho =
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