Lecture 2 - Major Ions in Sea Water

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Lecture 2 - Major Ions in Sea Water
What is the composition of seawater? What defines
Major Ions? What are their concentrations? What
are their properties?
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How are the major ions of seawater defined? What
are the major ions? Elements versus
species? moles versus grams conversions (See
EH Table 1.2)
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cations Na gt Mg2 gt Ca 2 gt KgtSr2
anions Cl- gtgt SO42- gt HCO3-gt F-
B(OH)3?
Units
DOM, Si and gases
Liverpool and NIO
DIC
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Some major ions are conservative. These are Na,
K, SO4, Br, B and F. What does this mean?
conservative. How do you demonstrate this? What
are the consequences? Do conservative major ions
have a constant concentration in the ocean? Law
of Constant Proportions (Me/S constant) The
Law breaks down in estuaries, evaporite basins,
hydrothermal vents.
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Some Major Ions are non-conservative Examples Ca
, Mg, Sr, Dissolved Inorganic Carbon
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Non-Conservative Major Elements
Calcium (Ca) ?Ca 0.5 to 1.0 with
depth Why?? CaCO3 (s) Ca2 CO32- Alkalinity
HCO3 2 CO3 Predict DAlkalinity DAlkalinity
2 D Ca From N. Atlantic to N. Pacific DCa
100 130 mM DAlk 120 130 mM Still an
Excess Ca Problem! What is the source?
(from de Villiers, 1999)
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Mid water Ca maximum. Compare with D
Alkalinity Could this be due to diffuse
source low-temperature hydrothermal input from
mod-ocean ridges?
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Ca correlates with He3 and Si These are also
Hydrothermal Vent Tracers
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Inverse Mg Ca Relationship from EPR at 17?S
113?W (from de Villiers, 1999)
Note significant variability in Mg (normalized to
S 35)! In this case 1 variability.
Hydrothermal Origin??
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East Pacific Rise , from Von Damm et al., (1985)
Mg
Ca
Alk
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Sr also increases with depth (2) and N. Atl
to N. Pac Distributions similar to PO4 (excellent
correlation)
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Excellent Correlation Sr vs PO4
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But why? The mineral phase Celestite (SrSO4)
produced by Acantharia protozoa is proposed as
the transport phase.
Acantharia shell and cyst
Acantharia are marine planktonic protozoans
Examples from sediment traps at Bermuda
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Review questions about salinity 1. How is the
salinity of seawater defined? Units? (see
editorial by Millero (1993)). 2. What techniques
have been used to measure the salinity of
seawater? Precision? 3. How does salinity vary
in the surface ocean? 4. What controls this
variability?
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Density of Seawater
s
What is salinity? What are ? and s? What are
their units?
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Annual average surface salinity
What processes influence surface salinity? Can
salinity be changed away from the surface?
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Salinity
Is salinity making the water column stable? Where
and where not?
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Annual average surface temperature
Identify influences of the wind-driven
circulation on surface temperature
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Potential Temperature
Identify the influence of the wind-driven
circulation.
Temperature must be responsible for
stratification. But everywhere?
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Surface density, isopycnal outcrops
Waters will move mostly along surfaces of
constant density.
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Evaporation and Precipitation Effects on Surface
Salinity
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Sea Surface Salinity
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Salinity Cross Section in Altantic Ocean
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Salinity Cross Section (Pacific Ocean)
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Paleo-temperature application Sr/Ca in corals
decreases with increasing temperature.
Application to western Pacific warm pool