Lecture 2 - Major Ions in Sea WaterWhy do we care about the major ions?What is the composition of seawater?What defines Major Ions? What are their concentrations?What are their properties?

Density:

distributions and controls (salinity and temperature)

Density of Seawater

σ

What is salinity? What are and σ? What are their units?

σ = (ρ - 1) 1000

if ρ = 1.0250 gm/cm3

then σ = 25.0

σ as S σ as T

Q. Why?

Q. How is salinity measured? 1. gravimetric 2. analyze all the ions and sum 3. relative to halogens (Cl- + Br- + I-) using Knudsen equation from 1911 (n = 9 samples) S ‰ = 0.030 + 1.8059 Cl ‰ (or gms per kg)4. Conductivity UNESCO, 1981 Defined the Practical Salinity Scale (PSS)

See Millero 1993S = 35.000 (don’t use units like PSU)

Waters will move mostly along surfaces of constant density.

Surface density, isopycnal outcrops

Sea Surface Salinity

Q. Why does surface salinity vary? DS = 30 to 37What are broad patterns and what controls salinity?

Evaporation and Precipitation Effects on Surface Salinity

All original salinity signatures acquired at the sea surfaceModified in the ocean interior by mixing.Becomes tracers for water masses.

Salinity Cross Section in Altantic Ocean

Salinity Cross Section (Pacific Ocean)

Sea Surface Temperature – Annual Average

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 SO4

2- 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° written as main species

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 mol NaCl = 1 mol Na+ + 1 mol Cl-

Concentrations

molar (M) mol / ltr H2Omolal mol / kg H2OSW mol / kg SW (H2O + salt)

Q Why??

molmmol 10-3

mmol 10-6

nmol 10-9

pmol 10-12 (Q How many atoms?)

Example:

We want to make a solution with Na+ = 468.96 mmol/kgfrom NaCl (table salt)

DIC

Liverpool and NIO

Si and gases

Units

cationsNa+ > Mg2+ > Ca2+ > K+> Sr2+

anionsCl- >>SO4

2- >HCO3-> Br->F-

B(OH)3

From Pilson

Q. mol balanceQ. charge balance

What are the properties of the major ions?

Some major ions are conservative. These are Na+, K+, Cl-, SO4

2-, Br-, B(OH)3 and 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‰) More recently (S‰ = 1.8065 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)

Superposition of vertical biological flux on horizontal circulation

Results in low surface water and highdeep water concentrations.

Results in higher concentrations inthe older deep Pacific than the younger deep Atlantic

Nutrient Like Profiles

Example: Comparison of vertical profiles of nutrients from the Atlantic and Pacific

PO4 SiShallow remineralizationSoft parts

Deep remineralizationHard parts

Calcium (Ca)

DCa = 0.1 / 10.2 = +1.0 % with depth

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

2-

(from de Villiers, 1999)

Non-Conservative Major Elements

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

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.

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

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

Ca

River water ≠ seawater

HCO3- > Cl-

Ca2+ > Na+

Example of using seawater ratios:From Christner et al (2014) Nature, 512, 310 “A microbial ecosystem beneath the West Antarctic ice sheet”

Crustal and seawater components to Subglacial Lake Whillans (SLW) waters

The weathering products probably came from sulfide oxidation, carbonation reactions,and carbonate dissolution.