When dissolved-carbon concentration and export diverge

Dissolved organic carbon concentration and annual river export can move in opposite directions because transport depends on water volume and the timing of chemistry. This methods note combines published Arctic river sampling evidence, load-estimation guidance, and uncertainty principles. It defines the dissolved fraction and river-section boundary, explains concentration–discharge covariance, and distinguishes sampled, time-weighted, and flow-weighted summaries. Fictional calculations demonstrate both the bias from multiplying separate means and a year with declining concentration but increasing export. The note examines seasonal coverage, station alignment, calibration limits, and correlated prediction errors. It does not estimate Arctic carbon emissions or identify the age and fate of exported carbon. Its practical implication is to publish water volume, carbon mass, sampling support, and reconstruction assumptions together before interpreting an annual change.