Dataset: Dissolved and total organic carbon concentrations of seawater collected in the northwestern Atlantic in 2024 during three cruises aboard the Atlantic Explorer (AE2412, AE2426b, AE2427)

Seawater was collected from Niskin bottles or the ship’s underway system. Samples were processed to obtain the concentrations of dissolved organic carbon and total organic carbon. The seawater for total organic carbon (TOC) was aliquoted directly into a combusted glass vial. For dissolved organic carbon (DOC), seawater was filtered with a 0.2 µM Omnipore filter (Whatman) mounted in a Teflon filter holder into a combusted glass vial. Both types of samples were acidified to pH~3 with concentrated hydrochloric acid (HCl) and stored at 4°C until analysis with a Shimadzu TOC-L. Blanks (MilliQ water) and standard curves with potassium hydrogen phthalate were interspersed into the sample runs. The coefficient of variability between replicate injections was <1%. Comparisons to standards provided by Prof. D. Hansell (University of Miami) were made daily.