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?

How are the major ions of seawater defined?

What are the major ions?

Elements versus species?

moles versus grams – conversions (See E&H Table 1.2)

DIC

Liverpool and NIO

DOM, Si and gases

Units

cationsNa+ > Mg2+ > Ca 2+ > K+>Sr2+

anionsCl- >> SO4

2- > HCO3-> F-

B(OH)3

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.

Some Major Ions are non-conservative

Examples:Ca, Mg, Sr, Dissolved Inorganic Carbon

Calcium (Ca)

Ca = +0.5% to +1.0% with depth

Why??CaCO3 (s) = Ca2+ + CO3

2-

Alkalinity ≈ HCO3 + 2 CO3

Predict AlkalinityAlkalinity = 2 Ca

From N. Atlantic to N. Pacific Ca = 100 – 130 M Alk = 120 – 130 M

Still an Excess Ca Problem!What is the source?

(from de Villiers, 1999)

Non-Conservative Major Elements

Mid water Ca maximum.Compare with Alkalinity

Could this be due to diffuse sourcelow-temperature hydrothermalinput from mod-ocean ridges?

Ca correlates with He3 and SiThese are also Hydrothermal Vent Tracers

Inverse Mg – Ca Relationshipfrom EPR at 17S; 113W(from de Villiers, 1999)

Note significant variability in Mg(normalized to S = 35)!

In this case ~1% variability.

Hydrothermal Origin??

Mg

Alk

East Pacific Rise , from Von Damm et al., (1985)

Ca

Sr – also increases with depth (~2%) and N. Atl to N. PacDistributions similar to PO4 (excellent correlation)

Excellent CorrelationSr vs PO4

Acantharia shell and cyst

Examples from sediment traps at Bermuda

Acantharia are marine planktonicprotozoans

But why? The mineral phase Celestite (SrSO4) produced by Acanthariaprotozoa is proposed as the transport phase.

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?

Density of Seawater

σ

What is salinity? What are 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

Identify the influence of the wind-driven circulation.

Temperature must be responsible for stratification. But everywhere?

Waters will move mostly along surfaces of constant density.

Surface density, isopycnal outcrops

Evaporation and Precipitation Effects on Surface Salinity

Sea Surface Salinity

Salinity Cross Section in Altantic Ocean

Salinity Cross Section (Pacific Ocean)

Paleo-temperature application

Sr/Ca in corals decreases withincreasing temperature.

Application to western Pacificwarm pool