Total dissolved organic carbon measurements at standard depths in the water column from nine CalCOFI cruises, 2008-2017.

Water column bottle samples at multiple depths are taken during CalCOFI cruises (since 2006, ongoing) at various CTD stations, and measurements of total organic carbon (TOC) are performed onshore in the lab. TOC includes both dissolved and particulate organic carbon (DOC and POC, respectively). In open ocean waters, POC is subtracted from TOC, and likely provides an accurate estimate of DOC because particles are typically small and homogeneously distributed in the sample. In coastal waters, and at stations where relatively high chlorophyll concentrations are present, the TOC measurement is not easily converted to DOC by subtracting POC values. Experience has shown that particles in these regions are large and inhomogeneously distributed. Therefore, samples collected in the CCE are reported as TOC, expressed as micromoles of carbon per liter of sea water.