MARE 425 Exam 4

• How do we know that water cycles through the HTV?

  1. The heat loss through the theoretical cooling of lava by conduction is larger than the heat loss measured at hydrothermal vents

  2. So water must help cool the lava

  3. There was also a missing sink for Mg2+, and the the input did not = the output, implying that there was a sink between the saltwater-basalt interaction inside the hydrothermal vents
• Locations at which HTV fluxes originate


  • Basement (surface rocks on ocean floor)
  • Deep Oceanic Basement Rocks
  • Flanks of Midocean Ridges
  • Axis (vents)
• Causes variations in vent fluid chemistry


  • Water temperature
  • Saltwater:rock ratio
  • Circulation rate
  • Depth + extent of reaction zone
• Types of vent systems

  • Hydrothermal vents
  • Cold/Continental Seeps
  • Lost City Vents
• Hydrothermal vents


  1. Location: Spreading zones, subduction zones, hotspots

  2. Water temperature: 300-500°C

  3. Mechanism: Lava emerges -> Lava cools -> Cracks -> Seawater enters cracks/ HTV -> seawater contacts magma and forms convection cells -> H2O will exit at axis
• Chemistry of hydrothermal vents

  • Saltwater enters reducing environment and becomes acidic, the sea water becomes depletes in Mg2+ and SO42-
  • As seawater leaves sulfide will precipitate along the walls of the HTV chimneys and react with FeS2 to create black precipitate
  • CaSO4 (anhydride) precipitates along the leading edges and fluids become enriched with Ca2+ and reacts with SO42- in seawater and forms anhydride
  • Enriched molecules: Ca2+, Mn2+, Fe2+, CO2, Li2+,Si
  • Depleted molecules: Mg2+, SO42-
  • DIC form: Carbonic acid
  • Precipitates: Iron and Zinc sulfide
• Chemistry of cold/continental seeps

  • Seep fluids are enriched in organic matter degradation products (H2S, CH4, NH4+, CO2)
  • The major precipitate = carbonates via methanogenesis and CH4
  • Enriched molecules: OM degradation products (NH4+, CO2)
  • Depleted molecules: Mg2+, SO42-
  • DIC form: Bicarbonate
  • Precipitates: carbonates
• Chemistry of Lost City Vents

  • Enriched molecules: CH4, H
  • Depleted molecules: Mg2+, CO2
  • DIC form: Carbonate ion
  • Precipitates: Carbonates
• Chemical characteristics of HTV end member

  • Sulfide reacts with FeS2, and creates black precipitates
  • CaSO4 precipitates along leading edge and fluids are enriched with Ca2+ and reacts with SO42- in seawater and forms anhydrides
• Primary producers at HTV

  • Chemoautolithotrophic bacteria
  • Riftia pachyptila( giant tube worms)
  • Calyptogena magnifica (giant clams)
• How primary producers at HTV make OM

  They obtain energy to fix CO2 from oxidation of H2S (Redox reaction with O2 as oxidizing agent)
• Metabolic classification of primary producers at HTV


  • Chemo: chemical energy to fix CO2 into organic matter
  • Auto: autotrophs
  • Litho: from rocks/ gets chemical energy from rocks
• Life at the HTV/vents is not independent of primary production at the surface of the ocean
• Importance of phosphorus


  • Phosphorus is needed by all animals to live (important nutrient)
  • Phosphorus is apart of many biomolecules that are needed to live: DNA, RNA, ATP, Phospholipids, Bone
  • Essential nutrient for plant growth
• Why phosphorus is speculated to limit primary productivity over geological times scales


  Because of its limited availability in the environment. Although N is limited, nitrogen fixation allows it to be available. So P, is usually more limited over time
• Major sources and sinks for phosphorus in the ocean

  • Sources: Rivers (largest input), Atmospheric deposition: Dust, marine bacteria, Volcanoes: volcanic gas (P4O10)
  • Sinks: Organic matter burial, Phosphorus sorption onto clays and iron oxyhydroxides, Phosphorite burial (Apatite burial; most important sink, but not well understood), Hydrothermal vents
• How have humans impacted the phosphorus flux from rivers

  • Doubled the Nitrogen input of POP
  • Anthropogenic sources: fertilizers and soil erosion
  • Anthropogenic sinks: dams
• Processes that impact the human phosphorus flux
• Form that most phosphorus in the ocean is speculated to be buried as


  Dissolved particle phosphorus: form that reaches ocean from rivers. BUT only 9% of P is in DOP from river
• Where are those phosphorus deposits found


  Coastal areas
• Why can you have P fluxes from oxic marine environments


  Because phosphorus will get buried in sediments. IN oxic sediments, it will sorp to iron hydroxide, but in the absence of iron hydroxide, Phosphorus will dissolve out of sediments
• How would the flux from phosphorus in freshwater sediments differ

  No flux out of the sediments in freshwater environments because SO42- is not a major ion, so sulfate reduction does not occur. Which results: No pyrite formed= not tying Fe2+/ Fe2+ is free to diffuse= might go back to aerobic sediments and will get oxidized = iron oxyhydroxide which will sorb to phosphorus
• Differences between the N and P cycles

  • Sinks: Phosphorus has NO biological sinks, Phosphorus and N have burial as sinks
  • Sources: P and N have rivers and atmospheric deposition as sources, P has NO biological equivalent to N2 fixation
  • Types of processes that control their cycles: P is dominated by geochemical processes, N cycle is dominated by biological processes
• Importance of nitrogen


  • Biolimiting element
  • Important nutrient: everything needs it to grow (proteins, amino acids, DNA, RNA)
  • Acts as an energy sources: nitrification is a chemoautotrophic process that generates energy
  • Acts as a electron acceptor for anaerobic respiration (denitrification)
  • Ability to cause environmental problems—Eutrophication
  • Some forms are toxic to humans
  • Play an important role in atmospheres chemistry: N2 is the most abundanct atmospheric gas, N2O is a greenhouse gas and ozone depletory
• Symbiotic and Cyanobacteria

  Need to be anaerobic; needs energy to break 3x bond (energy can come from light or organic matter)
• Nitrogenase enzyme


  • Responsible for reaction needs anaerobic conditions
• Ammonium Assimilation

  NH4+ -> Organic matter
• Ammonium Assimilation


  Uptake of nutrients (NH4+ is preferred form for organisms), need for organism growth
• Who performs Ammonium Assimilation


  • Bacteria, algae, large plants, fungi
• Ammonium Assimilation

  Aerobic or anaerobic
• Remineralization/Mineralization/Respiration and Excretion

  Organic Matter with nitrogen and NH4+
• Remineralization/Mineralization/Respiration and Excretion

  Releases important nutrient into the environment; major internal nutrient source
• Who performs Remineralization/Mineralization/Respiration and Excretion

  • Everybody
• Nitrification


  NH4+ -> NO3-; N-III -> N+V
• Nitrification

  Chemoautotrophic process that generates energy, side product is N2O (greenhouse gas and ozone depletor)
• Nitrification bacteria

  • Nitrosomonas: NH4+à NO2-
  • Nitrobacter: NO2- à NO3-
• Nitrification

  Aerobic conditions (need oxygen)
• Assimilatory NO3- (Nitrate) reduction

  NO3- à NH4+; N+v à N-III
• Assimilatory NO3- (Nitrate) reduction

  Nutrient uptake (How NO3- is taken up to make amino acids/other biomolecules)
• Who performs Assimilatory NO3- (Nitrate) reduction

  • Bacteria and phytoplankton