The Climate System

EESC 2100 Spring 2007

Lectures - Monday and Wednesday, 11:00 AM - 12:15 PM
Lab - Tuesday, 4:10 PM -7 PM

Elemental Abundances in Seawater

Why is the ocean salty?
- Weathering of continental rocks by chemical and physical processes.
- "Natural acid rain"; (CO₂ + H₂O --> HCO₃⁼; pH = 5.7 typically).
- Gradual dissolution of rocks to their elemental constituents.
- Dissolved products transported by rivers to oceans where they accumulate. Some accumulate very slowly, others more quickly.
- Global river dissolved load is ~0.1 ppt (100 ppm).
- Ocean dissolved load is typically ~35 ppt (35,000 ppm).
- Residence Time: t = ratio of input supply / amount present.
Average salinity is ~35 ppt, or 3.5% salt by weight.
These elements account for over 99.9% of the mass of salts in the ocean.

Element	Symbol	Abundance	Res. Time (t)
Elemental Abundances in Seawater


Chlorine	Cl	19.5 ppt	>100 Million years
Sodium	Na	10.8 ppt	83 Million years

Magnesium	Mg	1.3 ppt	16 Million years
Sulphur	S	0.9 ppt	13 Million years
Calcium	Ca	0.4 ppt	1 Million years
Potassium	K	0.4 ppt	12 Million years

Bromine	B	67 ppm
Carbon	C	28 ppm
Nitrogen	N	11 ppm	< 0.6 ppm [NO₃^-] in surface waters
Strontium	Sr	8 ppm
Oxygen	O	6 ppm
Boron	B	4 ppm
Silicon	Si	2 ppm