“Young Get Older, but Old Get Younger”: Counterintuitive Ocean Waters

Credit: Sarah Lee, Unsplash Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: AGU Advances Climate model projections for the Pacific basin suggest that warming waters will cause high-oxygen regions in the subtropical North Pacific to lose dissolved oxygen and low-oxygen regions in the Tropical Pacific to gain dissolved oxygen. The meridional change in dissolved oxygen loss modifies water age, with subtropical North Pacific waters becoming older (less oxygen) and Tropical Pacific waters becoming younger (more oxygen). In a model-based study, Taylor et al. [2026] show that this meridional contrast in oxygen and water mass age change arises from a slowdown of vertical velocities that is driven by a combination of Pacific basin and remote Southern Ocean heat forcing. Warming and stratification of the upper Pacific basin compresses the subtropical gyre, reducing ventilation along the base of the North Pacific ventilated thermocline. Warming in the mid-latitude Southern Ocean remotely reduces upwelling of old, low-oxygen water in the Tropical and North Pacific. This sets up the counterintuitive finding of “young gets older, but old gets younger.” Schematic of the response of present (black) and warmer (red) ocean circulation and dissolved oxygen (O2) to warming. The contours show the simulated 150-year age for the present (black) and warmer (red) ocean. Background shading shows the World Ocean Atlas (WOA23) dissolved oxygen concentrations, averaged 180-135°W. The arrows and hatched ellipses illustrate circulation change and associated dissolved oxygen change, respectively. Credit: Taylor et al. [2026], Figure 11 Citation: Taylor, B. A., Eddebbar, Y. A., Takano, Y., Talley, L. D., & Xie, S.-P. (2026). “Young get older, but old get younger”: Warming-induced circulation change explains contrasting pattern of projected Pacific deoxygenation. AGU Advances, 7, e2025AV002278. https://doi.org/10.1029/2025AV002278 —Eileen Hofmann, Editor, AGU Advances Text © 2026. The authors. CC BY-NC-ND 3.0Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.