Acidification and CO₂-driven conditions in the Estuary and Gulf of St. Lawrence during 2024

This report presents an overview of marine acidification and CO₂-driven conditions in the Estuary and Gulf of St. Lawrence for 2024, based on data collected through the Atlantic Zone Monitoring Program and the Aquatic Climate Change Adaptation Services Program, led by Fisheries and Oceans Canada. Regional observations are compared against climatological means to assess anomalies and trends of the carbonate system. In 2024, key indicators, including pHT the carbonate system vulnerability index (CSVI), partial pressure of CO₂ (pCO₂), saturation states of aragonite (ΩA and calcite (ΩC), and the substrate-inhibitor ratio (SIR), reveal widespread and depth-dependent stressor patterns across the region. From 2020 and continuing into 2024, the 200 m depth horizon stands out as a zone of sustained vulnerability, with multiple indicators exceeding established stress thresholds and record-setting anomalies in several regions. Hypercapnia is observed at this depth in all deep regions except the Centre Gulf, indicating elevated CO₂ levels that may impair physiological function in marine organisms. The upward shoaling of proxies for calcium carbonate formation (SIR) and dissolution (ΩA and ΩC) may compress optimal habitat for calcifiers, with the Northwest Gulf and the Estuary emerging as hotspots of reduced buffering capacity and heightened sensitivity to CO₂-driven conditions.