Dataset: Oxygen to argon molar ratios measured in surface waters of Station ALOHA between June 16 and June 23, 2019 onboard R/V Kilo Moana cruise KM1910.

Samples for O2/Ar analyses were collected at three different depths within the mixed layer (5, 15, and 25 m) with 12-L Niskin® bottles attached to a CTD rosette. Seawater samples, collected in triplicate, were transferred to 12mL Labco Exetainer® screw cap vials with rubber septa. The vials were filled from the bottom using Tygon® tubing and allowed to overflow at least 3 times their volume. Samples were poisoned with 50 μL of saturated mercuric chloride solution and stored in the dark immersed in water at 4°C until analysis on board, within 2 days of collection.