Water-Mass Coordinates Isolate the Historical Ocean Warming Signal

Abstract Persistent warming and water cycle change due to anthropogenic climate modifies the temperature salinity distribution of ocean over time. This “forced” signal is often masked by background internal variability system. Analyzing in water-mass-based coordinate systems has been proposed as an alternative traditional Eulerian (e.g., fixed-depth, zonally averaged) systems. The impact thought be reduced water-mass coordinates, enabling a cleaner separation forced from variability—or higher “signal-to-noise” ratio. Building on previous analyses comparing one-dimensional here we recast two-dimensional systems—temperature–salinity ( T – S ), latitude–longitude, latitude–depth—onto directly comparable equal-volume framework. We compare variability, or “noise” between these remapped 500-yr preindustrial control run CMIP6 model. find that median lowest (and roughly equivalent) latitude–depth space, compared with latitude–longitude coordinates. A large proportion space can attributed processes operate time scale greater than 10 years. Overall, signal-to-noise ratio coordinates but regions high historical change. Conversely, have Thus, conclude climatic more robustly identified Significance Statement Changes are driven both human-induced modes natural system, such El Niño–Southern Oscillation. It difficult isolate “signal” fluctuations Water-mass-based methods, which “follow” parcel around ocean, improve “Eulerian” (i.e., performed at fixed latitude, longitude, depth) frames reference they less impacted noise. However, it cleanly methods methods. Here, aim quantify extent frameworks isolating onto equivalent grid, clean comparison them, doing so increases warming. These results emphasize utility analyzing long-term ocean.