OCEA01 The Oceans Marine Chemistry

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OCEA-01 The OceansMarine Chemistry

• Types of salts or dissolved constituents
• Nutrient distribution
• Carbon Chemistry

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Salinity the total amount of solid material and
gases dissolved in water
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Seawater Properties
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Surface Salinity mostly reflects Precipitation
and Evaporation Processes
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Dissolved Constituents

• dissolved solids or gases (atom or molecule is
  surrounded by water molecules)

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Salts enter ocean from weathering (via rivers),
volcanoes, atmosphere, hydrothermal vents
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Sources into and Sinks out of Ocean
Ocean is in Steady State or Dynamic
Equilibrium Chemistry of ocean is not
changing Input fluxes Output fluxes OR Sources
Sinks
OCEAN
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Residence Time
Fluxes are in units of amount per time (e.g.
grams/year) Inventory is total amount (e.g.
grams) Residence time Inventory / Flux
In The average amount of time one atom of
constituent spends in ocean Approx. the amount
of time it takes for the concentration of a
constituent to significantly change
Inventory (total amount in ocean)
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Examples of Important Constituents

• The concentration of a constituent is mostly
  related to the ease with which it is removed from
  the ocean

• Element Concentration Residence Time
• chlorine (Cl) 1.95 x 104 mg/l 79 m.y.
• sodium (Na) 1.08 x 104 mg/l 260 m.y.
• calcium (Ca) 4.12 x 102 mg/l 8 m.y.
• carbon (C) 28 mg/l 200,000
• nitrogen (N) 11.5 mg/l 20,000
• phosphorus (P) 6 x 10-2 mg/l 70,000

BIOUNLIMITED (high concentrations)
BIOINTERMEDIATE (medium concentrations)
BIOLIMITING (low concentrations)
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Classifications based on role in biological cycles

• BIOUNLIMITED
• Not used by biology, not readily buried in
  sediments
• High concentrations
• BIOINTERMEDIATE
• Used by biology, but abundant supply so does not
  get used up.
• Medium concentrations
• BIOLIMITING
• Used by biology, readily buried in sediments
• Low concentrations

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Biolimiting NUTRIENTS Surface and Deep water
concentrations are different!

• PHOTOSYNTHESIS
• CO2 H2O gt CH2O O2
• carbon dioxide water becomes organic
  tissue oxygen

Actually, theres more happening CO2 PO4
NO3 H2O gt CH2O,P,N O2 carbon
dioxide phosphate nitrate water
becomes organic tissue oxygen
Overall effect of photosynthesis on ocean
chemistry Decreases dissolved carbon and
nutrients Increases dissolved oxygen
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Biolimiting NUTRIENTS Surface and Deep water
concentrations are different!

• RESPIRATION
• CH2O O2 gt CO2
  H2O
• Organic tissue oxygen becomes carbon
  dioxide water

Actually, theres more happening CH2O,P,N O2
gt CO2 PO4 NO3 H2O
organic tissue oxygen becomes carbon
dioxide phosphate nitrate water
Overall effect of respiration on ocean
chemistry Increases dissolved carbon and
nutrients Decreases dissolved oxygen
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Surface versus Deep Dissolved Nutrients

• Surface Ocean (light in upper 100 m)
• Photosynthesis dominates, so biolimiting nutrient
  concentrations are LOW
• Organic particles formed in surface ocean fall
  into deep ocean (exporting nutrients and carbon
  out of surface)
• Deep Ocean (dark below 100 m)
• Respiration of organic particles, releasing
  nutrients and CO2
• Biolimiting nutrient concentrations are HIGH

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At surface Photosynthesis
Uses PO4
Produces O2
1 mole 6.023 X 1023 molecules molecular mass
grams/mole µmol/kg 1 x 10-6 moles per kg
At depth Respiration
Uses O2
Produces PO4
O2
PO4
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Surface Water Phosphate (major nutrient)
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The Importance of Carbon

• Carbon Dioxide (CO2) is an atmospheric
  greenhouse gas
• Absorbs outgoing energy from Earths surface.
• Radiates that energy to heat up atmosphere and
  Earths surface.

CO2
CO2
Energy is emitted from gas
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Global Carbon Cycle
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Ocean Carbon Chemistry

• Dissolved Carbon occurs in several forms
• CO2 (dissolved gas)
• CO3 (carbonate ion)
• HCO3 - (bicarbonate ion)
• Dissolved Inorganic Carbon or DIC is the
  total DIC CO2 CO3 HCO3 - (eqn. 1)
• Carbon can change forms
• CO2 CO3 H2O ltgt 2HCO3 - (eqn. 2)

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Ocean Carbon Chemistry

• Ocean Carbon Chemistry determines atmospheric
  CO2 content (and therefore has a large influence
  on greenhouse warming)
• Examples
• Ocean temperature affects Solubility (how much
  CO2 gas from atmosphere can dissolve in ocean)
• Photosynthesis uses CO2 (will take CO2 out of
  atmosphere)

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Temperature has an effect on CO2 gas solubility

• DIC CO2 CO3 HCO3 - (eqn 1)

Cold more CO2 gas dissolves DIC increases (see
eqn 1) Warm less CO2 gas dissolves DIC decreases
(see eqn 1)
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Effects of Photosyn. Respir. on Carbon Chemistry

• DIC CO2 CO3 HCO3 - (eqn 1)
• CO2 CO3 H2O ltgt 2HCO3 - (eqn 2)

Surface Ocean Photosynthesis (uses up CO2),
so DIC in surface ocean decreases (see eqn
1) HCO3 - is converted to CO3 (eqn 2 is
driven to left) When DIC is low, CO2 from
atmosphere will dissolve into surface ocean and
greenhouse effect is lowered. Deep Ocean
Respiration (produces CO2), so DIC in deep
ocean increases (see eqn 1) CO3 is converted
to HCO3 - (eqn 2 is driven to right) Lots of
CO2 stored in deep ocean away from atmosphere.
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Surface versus Deep Ocean Carbon Chemistry

• DIC CO2 CO3 HCO3 - (eqn 1)
• CO2 CO3 H2O ltgt 2HCO3 - (eqn 2)

Surface Ocean Deep Ocean lower higher
lower higher higher lower
Carbon compound
CO2
DIC
CO3
Over long time scales, what is the main control
of whole ocean carbon (DIC) content?? ANSWER
SEDIMENTATION of CaCO3 (shells of
organisms) Organisms make CaCO3, but do not
control how much CaCO3 is buried. Burial of CaCO3
sediments is controlled by CO3 content of deep
ocean!
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CarbonateIon Profile
Calcite saturation line Value below which CaCO3
shells dissolve. No CaCO3 sediments in deepest
part of ocean
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Multiple Choice QUIZ

• Biolimiting nutrients
• A. have higher concentrations in the surface
  ocean compared to the deep ocean
• B. have highest concentrations when dissolved
  oxygen concentrations are highest
• C. are released during respiration
• D. have extremely long residence times compared
  to most other constituents because they are not
  readily removed from the ocean