Open cell and single-step method for total alkalinity titrations from samples collected on R/V Mirai cruises MR23-06C and MR23-07 in the North Pacific and Western Arctic from September to November 2023

Duplicate samples were collected for total alkalinity on two cruises in 2023 aboard the R/V Mirai (MR23-06C and MR23-07) in order to compare two different methods of total alkalinity titrations: the open cell with non-linear least squares fitting and single step with spectrophotometric endpoint detection. Measurements of dissolved inorganic carbon and pH on the total scale were also made as quality control checks. GLODAPv2 hinted at a potential offset between laboratories in the Pacific Ocean. We hypothesized that if non-negligible amounts of organic alkalinity were present, the different methods could be titrating different amounts leading to differences between the methods. The results show that any offset is within the uncertainty of the analytical precision and presence of organic alkalinity in open ocean waters remains inconclusive.