|Average concentration in ocean:||10.2 mmol/kg|
|Residence time:||12,000,000 years|
Potassium is present in seawater as the K+ ion.
The sodium residence time is from Tracers in the Sea (Broecker, W. S. and Peng, T.-H., 1982. Eldigo Press, Palisades, NY). It was calculated from the global average river input.
Potassium can be determined gravimetrically as potassium tetraphenylborate or by atomic absorption spectrometry.