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?
Review questions from OCN210
1. How is the salinity of seawater defined? Units?
(see editorial by Millero (1993) at the end of this Lecture).
2. What techniques have been used to measure the salinity of seawater?
Precision?
3. How does salinity vary in the surface ocean?
4. What control this variability?
Density of Seawater
σ
What is salinity? What are ρ and σ? What are their units?
Annual average surface salinity
What processes influence surface salinity?
Can salinity be changed away from the surface?
Salinity
Is salinity making the water column stable? Where and where not?
Annual average surface temperature
Identify influences of the wind-driven circulation on surface temperature
Potential Temperature
Temperature must be responsible
for stratification. But everywhere?
Identify the influence of the
wind-driven circulation.
Surface density, isopycnal outcrops
Waters will move mostly along surfaces of constant density.
Evaporation and Precipitation Effects on
Surface Salinity
How are the major ions of seawater defined?
What are the major ions?
Elements versus species
moles versus grams - conversions
cations
Na+ > Mg2+ > Ca 2+ > K+>Sr2+
anions
Cl- >> SO42- > HCO3-> FB(OH)3°
Units
Si and gases
Liverpool
DIC
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, evaporites,
hydrothermal vents.
Some Major Ions are non-conservative
Ca, Mg, Sr, Dissolved Inorganic Carbon
Non-Conservative Major Elements
Calcium (Ca)
∆Ca = +0.5% with depth
Why??
CaCO3 (s) = Ca2+ + CO32Alkalinity ≈ HCO3 + 2 CO3
Predict ∆Alkalinity
∆Alkalinity = 2 ∆ Ca
From N. Atlantic to N. Pacific
∆Ca = 100 – 130 µM
∆Alk = 120 – 130 µM
Still an Excess Ca Problem!
What is the source?
(from de Villiers, 1999)
Mid water Ca maximum.
Compare with ∆ Alkalinity
Could this be due to diffuse source
low-temperature hydrothermal
input from mod-ocean ridges?
Ca correlates with He3 and Si
These are also Hydrothermal Vent Tracers
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??
East Pacific Rise , from Von Damm et al., (1985)
Mg
Ca
Alk
Sr – also increases with depth (~2%) and N. Atl to N. Pac
Distributions similar to PO4 (excellent correlation)
Excellent Correlation
Sr vs PO4
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
From sediment traps at Bermuda
Sea Surface Salinity
Salinity Cross Section in Altantic Ocean
Salinity Cross Section (Pacific Ocean)
Paleo-temperature application
Sr/Ca in corals decreases with
increasing temperature.
Application to western Pacific
warm pool