Program on the Environment

The National Oceanic and Atmospheric Administration’s (NOAA) Pacific Marine Environmental Lab (PMEL) Ocean Carbon Group specializes in ocean carbon cycling, as it is critical to understanding how climate change affects marine chemistry. Core to this work are precise measurements of dissolved inorganic carbon (DIC) and total alkalinity (TA). This research is reliant on oceanographic research vessels to collect these discrete samples. However, the diesel exhaust emitted by the research vessel, while transiting between stations, may unintentionally compromise the accuracy of these measurements. This study investigated whether emissions from the R/V Rachel Carson — a University of Washington research vessel used in the Washington Ocean Acidification Center (WOAC) research cruises — affected the integrity of DIC and TA samples collected during the September 2024 cruise. Seawater samples were collected when the engine was idling and when it was throttled at an increased RPM when transiting between stations. DIC samples were analyzed using Single-Operator Multiparameter Metabolic Analyzer (SOMMA) method, whereas, TA samples were analyzed using the open-cell titration method. Contrary to the initial hypothesis, samples collected while the engine of the ship was running predominantly did not show increased DIC concentrations. Variation was shown within the samples manifesting as a steady decline of DIC, likely due to CO₂ offgassing caused by procedural factors such as increased headspace in Niskin bottles as sample is dispensed from the bottle and delays in sample collection. These findings underscore the importance of following sampling procedures to maintain sample consistency. Although diesel emissions from the research vessel were not found to significantly alter the collected DIC or TA levels within this sample set, this research highlights a previously unexamined risk in ocean monitoring and supports the refinement of protocols to safeguard the accuracy of long-term climate data.