3.2 Water column dissolved Cr sampling
IN2018_V02, IN2018_V04, and GP13 samples were collected using an autonomous trace metal clean rosette system and gravity filtered through acid-cleaned 0.2 µm filters (Pall Acropak) into acid cleaned LDPE bottles in a class 100 clean van. IN2018 samples were acidified to pH < 2 (2 mL L-1 sub-boiling distilled concentrated HCl) on land and stored for 3-26 months before analysis. GP13 samples were stored frozen until 2019, at which point they were thawed, acidified as for IN2018 samples, and stored at least 7 months before analysis. DY110 samples were collected with a conventional CTD-rosette, gravity filtered through acid-cleaned 0.2 µm filters (Pall Acropak) acidified to pH ≈ 2 (1 mL L-1 concentrated HCl), and stored for at least 3 months before analysis. Sampling and sample handling are discussed in detail elsewhere for ACE (Rickli et al., 2019), M77/4 (Nasemann et al., 2020) and Line P (Janssen & Cullen, 2015).