Nanomolar concentrations, measurement ability

The ability to measure low nanomolar concentrations of dissolved nutrients opened up the possibility of conducting true tracer experiments in the vast bulk of the oceans. Experiments using tracer level additions (typically considered to be 10% of the ambient source concentration) had been Hmited to high nutrient environments in coastal and estuarine habitats. In oHgotrophic regimes, investigators commonly added a fixed tracer... 

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