Supplemental Material for Borehole waters from Hole U1601C (Atlantis Massif) provide constraints for a deep-sourced formation water that (could) feed the Lost City Hydrothermal Field

This work is in support of a paper that will be submitted tomorrow (1/25/26) Geochemistry, Geophysics, Geosystems.

 This document contains text related to the calculations of the water isotope discussion in the manuscript and additional tables and figures. Tables, which are presented in the attached spreadsheet and available online (10.5281/zenodo.18364583), include data from the chemical analysis of collected water samples (Table S1), temperature data from conductivity, temperature, depth (CTD) deployments (Table S2), and more detail of the water isotope discussion (Table S3). Figures included additional plots of chemical data (Figures S1-S4) and scanning electron micrographs (SEM) images of material collected from filtered water that were collected using Kuster Flow-Through Samplers (KFTSs) in the borehole (Lang et al., 2025a) (Figures S5-S9). We also include a more thorough discussion of the water isotope data. This portion of the supplemental materials includes references and Figures S10 and S11.