Drivers of Ocean pH Variation in Front of Dotson Ice Shelf, West Antarctica

The highly productive Amundsen Sea Polynya in West Antarctica is bounded in the south by rapidly-melting ice shelves, including the Dotson Ice Shelf (DIS). We present a high-resolution, full-depth pH data set within 10 km of DIS using a Lab-On-Chip (LOC) spectrophotometric pH sensor on an ocean glider. The LOC performs well with a 0.01 difference in pH between sensor measurements and discrete samples. Over 19 days in January–February 2022, the pH sensor captured the variability resulting from summertime biological and physical processes. At depth, modified Circumpolar Deep Water entering the DIS cavity exhibited a relatively low pH (7.91). The outflow had a higher average pH (7.94) as a result of dilution by glacial meltwater, but its pH was 0.01 lower than that of surrounding water at the same density. The Antarctic Coastal Current transported unventilated surface water with a low pH emerging from below fast ice east of Bear Island, westward to the eastern side of DIS. Net primary production increased pH in the upper 50 m in front of DIS, whilst temperature change was responsible for 5%
of the change in pH. This study provides the first direct measurements of pH in the Amundsen Sea capable of deducing the impact of glacial meltwater on pH. It demonstrates the value, particularly in remote regions, of LOC pH sensors that have the longevity and stability to measure ocean pH without sensor drift.