μmol/kg
micromole per kilogram
Molalityexact by definition
The micromole per kilogram is 10⁻⁶ mol/kg. Chemical oceanography runs on it: dissolved oxygen, nitrate, phosphate and dissolved inorganic carbon in seawater are all reported in μmol/kg, because a per-kilogram basis does not change as a sample warms on its way up from depth.
| 1 μmol/kg | 0.000001 mol/kg |
Where the unit came from
The switch from per-litre to per-kilogram in oceanography was deliberate. Seawater density varies by several percent across the ocean's temperature and salinity range, so a per-volume concentration measured on deck is not the concentration that was at 2000 m. Per kilogram, it is.
Solvers that use molality