Dataset: Carbonate chemistry analyses (total alkalinity, DIC, and d13C of DIC) from discrete bottle samples and CTD data from 12 stations sampled during R/V Endeavor cruise EN669 in the Gulf of Maine during August 2021

These data were collected on R/V Endeavor cruise EN669 from 12 stations across the Gulf of Maine. Water samples were collected using Niskin bottles on the CTD rosette. Equipment included a Seabird Scientific SBE9plus CTD equipped with a transmissometer, oxygen, and fluorescence sensors.

Total Alkalinity, Dissolved Inorganic Carbon (DIC), and d13C-DIC:
Samples for total alkalinity (TA), dissolved inorganic carbon (DIC), and d13C-DIC were collected simultaneously. Water from the Niskins was passed through a 0.45-micron cartridge filter and all bubbles were removed from the line. Ground-glass stoppered 250-milliliter (mL) bottles were rinsed 3 times with flowing, filtered seawater and then filled. Each sample bottle was left to overflow for approximately double the amount of time it took to fill the bottle. Excess water was gently dumped out to leave a ~2-3 mL headspace below the ground glass fitting. Following collection, samples were poisoned with 100 microliters of saturated mercuric chloride solution. Bottles were sealed with a greased stopper (Apiezon-L). A rubber band was placed over the stopper to ensure sample closure. Samples were stored cool and in the dark prior to analysis at the Woods Hole Oceanographic Institution.

DIC and d13C analyses were performed first immediately after opening the bottle. DIC and d13C-DIC were determined simultaneously using an Apollo AS-D1 analyzer connected to a Picarro G-2121i cavity ringdown system on a 5 mL sample of seawater. Samples were run in at least triplicate and calibrated against seawater Certified Reference Materials. Isotopic values were calibrated against an in-house seawater standard that was intercalibrated against known solid materials (NBS-19, IAEA-C2, and NBS-20). Intercalibration was performed on the same Picarro instrument using an Automate-Liaison front-end unit. Total alkalinity was determined using an open-system Gran titration on 5-mL samples in triplicate, using a Metrohm 805 Dosimat and a robotic Titrosampler, calibrated against seawater Certified Reference Materials.