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)
How are the major ions of seawater defined? ans: major ions contribute to salinity (e.g. 35.000‰) salinity can be determined to 0.001 ppt = 1 ppm = 1 mg kg-1 Elements versus species? e.g., Na is an element Na+ is a species (cation) S is an element SO42- is a species (anion) What are the major ions? n = 11 ans: cations = Na+ > Mg2+ > Ca2+ ~ K+ > Sr2+ anions = Cl- >> SO42- > HCO3- > Br- > F- neutral = B(OH)3° moles versus grams – conversions (See E&H Table 1.2) 1 mol = 6.02 x 1023 atoms mol kg-1 = g(solute)/kg (water) g(solute)/mol. wt. 1 molNaCl = 1 mol Na+ + 1 molCl-
From Pilson cations Na+ > Mg2+ > Ca2+ > K+> Sr2+ anions Cl- >>SO42- >HCO3-> Br->F- B(OH)3 Units Si and gases Liverpool and NIO DIC
Some major ions are conservative. These are Na+, K+, Cl-, SO42-, Br-, B(OH)3and F-. What does this mean? conservative. Q. How do you demonstrate this? What are the consequences? Do conservative major ions have a constant concentration in the ocean? Q Law of Constant Proportions(major ion/S‰ = constant) Knudsen equation ( S = 0.030 + 1.8050 Cl‰) The Law breaks down in estuaries, evaporite basins, hydrothermal vents. Q
Some Major Ions are non-conservative Examples: Ca2+, Mg2+, Sr2+, Dissolved Inorganic Carbon (HCO3-) Non-conservative behavior due to: biological production hydrothermal ridge crest solutions river water (as in estuaries)
Nutrient Like Profiles Superposition of vertical biological flux on horizontal circulation Results in low surface water and high deep water concentrations. Results in higher concentrations in the older deep Pacific than the younger deep Atlantic
Example: Comparison of vertical profiles of nutrients from the Atlantic and Pacific PO4 Si Shallow remineralization Soft parts Deep remineralization Hard parts
Non-Conservative Major Elements Calcium (Ca) Ca = 0.1 / 10.2 = +1.0 % with depth Why?? CaCO3 (s) = Ca2+ + CO32- (from de Villiers, 1999)
Sr – also increases with depth (~2%) and N. Atl to N. Pac Distributions similar to PO4 (excellent correlation)
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
Inverse Mg – Ca Relationship from EPR at 17S; 113W (from de Villiers, 1999) Note significant variability in Mg (normalized to S = 35)! In this case ~1% variability. Hydrothermal Origin??
Black Smoker Fluids, East Pacific Rise , from Von Damm et al., (1985) Mg Ca Alk
River water ≠ seawater HCO3- > Cl- Ca2+ > Na+
Density of Seawater σ See Millero 1993 S = 35.000 Q. How is salinity measured? Q. Why does salt make water more dense? What is salinity? What are and σ? What are their units?
Surface density, isopycnal outcrops Waters will move mostly along surfaces of constant density.
Sea Surface Salinity Q. Why does surface salinity vary? DS = 30 to 37
Excellent Correlation Sr vs PO4
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 controls this variability?
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.