Temperature-Dependent Oxygen Utilization Rates of Mesopelagic Waters Along 149° E in the Western Pacific

Temperature regulates microbial respiration and organic matter remineralization, but its influence on oxygen consumption across broad open-ocean mesopelagic gradients remains poorly constrained. We combined transient-tracer-derived ventilation ages with apparent oxygen utilization to estimate in situ oxygen utilization rates (OUR) along the approximately 149° E section in the western Pacific. OUR was calculated from AOU-age gradients along isopycnal surfaces, and temperature dependence was evaluated with Arrhenius relationships across 16 latitude ranges and three depth intervals (200–1000, 200–600, and 600–1000 m). OUR generally decreased with depth but varied substantially with latitude, with relatively high upper-mesopelagic rates around 15–21° N. Significant Arrhenius relationships over 200–1000 m were obtained for 15 of 16 latitude ranges. Apparent activation energy (Ea) ranged from 50.1 to 318.2 kJ mol−1 and averaged 142.7 kJ mol−1. Ea values for 200–600 m generally followed the full-depth pattern, whereas 600–1000 m estimates were typically higher and more variable. A 1 °C increase corresponded to a 7.8–63.7% increase in OUR for the significant full-depth fits, averaging 24.8%. These results demonstrate pronounced spatial and vertical variability in apparent temperature sensitivity and highlight the need to account for regional and depth-dependent differences when evaluating warming effects on mesopelagic oxygen utilization and remineralization.