M161 Surface Seawater Isotopic Composition

On the RV Meteor during EUREC4A, seawater samples for isotopic analysis were collected from a depth of 10 m using the ship's Conductivity, Temperature, and Depth (CTD) profiler. Samples were collected daily from the CTD cast closest to 1900 UTC. An intensive observation period sampling a full diurnal cycle every two hours was also collected from 10-11 February 2020 while the Meteor was on station for 24 hours at the northern intersection of its meridional transect and the HALO circle (14.18 N, 57.24 W). Seawater samples were treated with CuCl to prevent isotopic alteration by biotic activity. All samples were then sealed in 2-mL vials without headspace, sealed in parafilm, and stored in a refrigerator at ~4º C during the cruise, at ambient temperatures for shipment, and then again in a refrigerator at ~4º C prior to lab measurement. Meteor seawater samples were processed on a Picarro L-2140-i at the University of New Mexico Center for Stable Isotopes. Bulk uncertainties are ±0.23 and ±0.56 per mil for δ18O and δD respectively.