Quizet

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

  Prior to HTV discovery, Mg2+ inputs were not equal to outputs, and radioactive dating can tell us the age of water leaving vents
• Where do HTV fluxes originate (4 locations)?

  Basement-surface rocks (on seafloor at top - in direct contact with seawater): low temperatures, high water to rock ratio

  
  

  Deep oceanic basement rock (moving down into sediment): low temperature, low water to rock ratio

  
  

  Flank (moving up volcano): medium temperature, medium water to rock ratio

  
  

  Axis (peak of volcano where eruption occurs): high temperature, low water to rock ratio
• Which HTV region has the largest fluxes?

  Flux is greatest at the axis, direction of flux varies with the element
• What causes variations in the vent fluid chemistry?

  Rock chemistry (influences chemistry of seawater), reaction temperature, depth and extent of reaction zone (small or large place, at surface of in HTV), water to rock ratio (affects water chemistry), water circulation rate (how long water will be in contact with rock)
• Describe the different types of vent systems.


  Hydrothermal vents: located at spreading zone, high temperature chemical reactions with low water to rock ratio, conductive and convective heat flow, fast water circulation

  
  

  Seeps: located at continental margins and subduction zones, temperature a few degrees warmer than sea water, flow rate half that of HTV

  
  

  Lost City: 15km from spreading zone, warm water, high pH
• How do you know if an element behaves conservatively through the HTV system, and what are the chemical characteristics of the HTV end member fluid?


  At the HTV end member, Mg and SO4 are both high, and maintain a linear decrease to net zero at the ocean end member. Since SO4 and Mg are both zero and linear, HTV are sinks for both. Opposite, Rb is high at HTV meaning HTVs are a source for Rb to the ocean.
• Who are the primary producers at HTV, how do they make OM and where do they get their energy?


  Chemolithoautotrophic bacteria: energy comes from chemical reactions (chemo), chemicals come from rocks (litho), fix CO2 into organic matter (auto)

  
  

  Giant tube worms: absorb O2, H2S, and CO2 though plume; trophosome is composed of endosymbiotic sulfur bacteria, which can make organic matter for tube worm to respire. Tube worm can tolerate H2S because it binds at a different location than oxygen on the hemoglobin

  
  

  Large clams: have symbiotic sulfur bacteria and N2 fixing bacteria
• Is life at vents independent of primary production at the surface of the ocean?


  No, the reaction used by chemolithoautotrophic bacteria (CO2 + H2S + O2 = CH2O + H2SO4) is not independent of photosynthesis because it involves O2, which photosynthesis produces
• Where are HTVs found?

  On divergent (80%) and convergent (10%) plate boundaries as well as hot spots (10%)
• Importance of HTVs?


  Balance geochemical cycles of certain elements like magnesium (Mg2+), and balance heat budget of the ocean
• How does HTV balance the heat budget of ocean?

  Lava cools by conduction and convection via direct contact with saltwater
• What do HTV fluxes tell us (positive/negative)?


  Positive flux: element is gained by rock, meaning it is a sink and the element is removed from seawater (Mg(2+), SO4(2-))

  
  

  Negative flux: element is gained by seawater, it is a source of element to the ocean (Rb, Si, Ca, K)
• Describe the chemical process of hydrothermal vents.


  Mg(2+) and SO4(2-) get stripped out of seawater, which forms Mg rich metamorphic minerals and sulfur minerals (pyrite/fool's gold)

  Lava hardens and cracks (like ice in water), which allows for cold seawater to seep into hydrothermal vents, heat up, and rise. The water warms and reacts with the crust, becomes acidic, loses O2, and picks up metals and H2S before coming out of chimney
• Describe the chemical process of continental seeps.


  Vent fluid similar to seawater chemistry but is enriched in organic matter degradation product (H2S, CH4, NH4+, all forms of CO2). If brines are involved, enriched in Cl (high chlorinity measurement). Seeps are depleted in Ca2+, Mg2+, SO4(2-), making it a sink for these elements. Major precipitates are carbonates (highly enriched in 12C, very negative 13C values). Methanogenesis occurs, and kinetic fractionation produces C12 from methane
• What are the two types of HTV seeps?


  At continental platform, brines mix with pore H2Os and move downward (because they are dense with brine) and exit out of fault planes (ex. Florida Escarpment)

  
  

  At subduction zones, pore water gets pushed out of sediments as they are subducted (ex. Oregon Margin)
• Explain Marcet's Principle at HTV.


  Sulfate being reduced out of water at HTV makes them one place Marcet's Principle does not apply, sulfate is one of the major ions in the ocean
• Why are "black smoker" chimneys dark and "white smoker" chimneys light?


  Black smoker: sulfide minerals precipitate, the color comes from vent fluid exiting and minerals within reacting with seawater

  
  

  White smoker: ZnS (zinc sulfide) precipitates
• List the pH and chemicals associated with HTV

  pH 3-5, depleted in Mg(2+) and SO4(2-), enriched in Fe(2+), Mn (2+) Ca(2+), precipitant pyrite, sulfide, minerals, CaSO4, source of energy H2S, form of CO2 is H2CO3
• List the pH and chemicals associated with seeps


  pH 8, depleted in Mg(2+), SO4(2-), Ca(2+), O2, enriched in CH4, CO2, NH4(+), H2S, precipitant carbonates, source of energy sulfate reduction and methanogenesis, form of CO2 is CO3(2-)
• List the pH and chemicals associated with lost city


  pH 9-11, depleted in Mg(2+) and CO2, enriched in H2, CH4, precipitant carbonates, source of energy H2 and CH4, form of CO2 is CO3(2-)
• Importance of phosphorus?


  Makes up nucleic acids (DNA, RNA), phospholipids (make up cell membrane), bones, and ATP
• Why is phosphorus speculated to limit primary production over geologic time scales?


  Nitrogen requirements of phytoplankton can be met by nitrogen fixation, where N2 gas (which nobody can use) is converted to NH4+ (which everybody can use). We have a huge supply of nitrogen from atmosphere, unlike phosphorus, so nitrogen will never run out
• What are the major sources for phosphorus in the ocean?

  Rivers (primary input to ocean)

  
  

  Atmospheric deposition (dust, marine bacteria, organic material)

  
  

  Volcanoes (localized, regional impact; magnitude/length of eruption determines amount transported to the ocean, P4O10 gas is produced from volatilization of basalt, condensed into water soluble polyphosphates)
• What are the major sinks of phosphorus in the ocean?


  Burial in sediment via organic matter burial (largest transport of phosphorus from water column, less than 10% reaches sea floor)

  
  

  Phosphorus sorption/scavenging (phosphorus clings to clays and iron oxyhydroxides, most sorption occurs within the sediment itself)

  
  

  Phosphorite/apatite burial (most important sink in sediment, potentially when phosphorus becomes available within sediment from organic matter or unsticking from iron oxyhydroxide coatings, released into porewater and forms a new mineral called CFA)

  
  

  Hydrothermal vents (vent fluid is enriched in reduced iron, when it hits the seawater and interacts with oxygen, it forms iron oxyhydroxides; phosphorus is electrostatically attracted to this mineral)
• How have humans affected the phosphorus flux from rivers (how much and by what processes)?


  Human activity has nearly doubled phosphorus input to the ocean; humans have increased inputs with fertilizers and sewage (fertilizer phosphorus comes from mining P deposits) and decreased inputs with dams (phosphorus is transported as particles to ocean, dams trap particles/prevent them from entering the ocean)
• In what form is most phosphorus in the ocean speculated to be buried as, and where do you find these deposits?


  Particulate (91%), near shore
• Describe the interaction between iron and phosphorus under oxic and anoxic conditions.


  When iron is in it's oxidized form, it gets mixed down/buried and finds itself in the anaerobic (anoxic) zone. The iron, originally in the oxidized form, gets reduced to iron II. The reduced form is soluble and now aqueous, so the phosphate stuck to it is now free (could go back up, but will likely find another iron oxyhydroxide). In anaerobic sediments, anaerobic respiration typically stops at sulfate reduction because it's a major ion in seawater and unlikely to run out. The sulfate gets reduced to form H2S, which forms pyrite (FeS2), binding the Fe and preventing phosphate from attaching
• Why can you have phosphorus fluxes from oxic marine sediments?


  In marine sediments, iron will unbind from phosphorus during reduction and bind instead to H2S, which is a product of sulfate reduction. The phosphorus is then free to move back up to oxic sediments and potentially out into the water column. In freshwater sediments, sulfate is limited so H2S is not formed and this process does not take place.
• How would the flux of phosphorus from freshwater sediments compare, why?


  Marine sediments: sulfate reduction occurring means iron gets tied up and phosphate could potentially diffuse out to the water

  
  

  Freshwater sediments: sulfate not as present, meaning sulfate reduction does not take place and no pyrite is formed to bind iron
• Describe the forms of phosphorus


  Inorganic: PO4(3-) (phosphate), PH3 (phosphene gas), and various mineral forms (apatite (phosphorite), Fe-P, Al-P)

  Organic: DOP (dissolved organic phosphorus) and POP (particulate organic phosphorus)
• Is the phosphorus budget balanced?

  No- there is a missing sink, burial is likely underestimated due to limited sampling. Sediment cores tell us burial rates of pre-industrial times because it hasn't settles yet.
• Limiting nutrient in different environments?


  Freshwater: phosphorus limits primary production (phosphorus from runoff water containing detergents caused algal bloom)

  
  

  Tropical waters: phosphorus limits primary production in places with reefs (and therefore carbonate sediments)

  
  

  Marine waters: nitrogen limits primary production
• Importance of nitrogen?


  Essential element for all organisms - proteins, nucleic acids

  
  

  Energy source (chemoautrophic process: nitrification)

  
  

  Electron acceptor (NO3-, denitrification)

  
  

  Nutrient for bacteria and phytoplankton

  
  

  Causes environmental problems: eutrophication

  
  

  Can be toxic to humans (NO3-, blue baby syndrome)

  
  

  Important gases in atmosphere (N2 and N2O)
• What are the major sources and sinks for nitrogen?


  Sources: N2 fixation, rivers, and atmospheric deposition (rain, snow, sleet; wet deposition)

  
  

  Sinks: denitrification, burial, and annamox (amount unknown)
• How have humans affected the input of new nitrogen into the environment, and where is it coming from?


  Almost doubled amount of nitrogen going into ocean, largely through application of fertilizer using Haber-Bosch process (artificial fertilizer; 3H2 + N2 = 2 NH3)
• What are some of the effects of too much nitrogen in coastal waters?

  Eutrophication: too much nitrogen > algal bloom > dead algae (organic matter) > gets respired > depletion of oxygen (hypoxic or anoxic/low O2 or no O2) > fish/shellfish die, loss of habitat, coral die
• What are the forms of nitrogen in the environment?


  Ammonium (NH4+), -III

  
  

  Dinitrogen gas (N2), 0

  
  

  Nitrous oxide (N2O), +I

  
  

  Nitrate (NO3-), +III

  
  

  Nitrite (NO2-), +V (most reduced form)
• Explain nitrogen cycle- nitrate fixation.


  N2- > NH4+ (reduction, 0 to -III)

  
  

  Importance: gets "new" nitrogen into environment, takes a form of nitrogen and converts it into a form all organisms can use

  
  

  Who: Symbiotic bacteria and cyanobacteria

  
  

  Conditions: high energy requirement, comes from light (photosynthetic) and carbon compounds (heterotrophic), nitrogenase (functions under anaerobic conditions), anaerobic conditions or abiotic conditions (lightening, fossil fuel combustion, and Haber-Bosch process)
• Explain nitrogen cycle- ammonium assimilation.


  NH4+ > Organic Nitrogen

  (no ox change, -III)

  
  

  Importance: nitrogen is required for growth

  
  

  Who: algae, bacteria, fungi, macroalgae

  
  

  Conditions: aerobic or anaerobic environment
• Explain nitrogen cycle- remineralization.


  Organic Nitrogen > NH4+

  (no ox change, -III)

  
  

  Importance: major internal source of nitrogen in ecosystems

  
  

  Who: all organisms via excretion

  
  

  Conditions: aerobic or anaerobic environment