Quantifying Ocean Heat Content Changes Related to ENSO, Seasonal Variability, and Trends in Isopycnal Heave

Changes in the height of isopycnal surfaces, or heaving, are indicative of ocean circulation and heat content variability. Quantifying internal variations in heave is critical for constraining trends in heat content associated with anthropogenic influence. We calculate heave by applying a novel dynamic warping algorithm to temperature and salinity vertical profiles and computing the vertical adjustment required to align the profiles with a time-averaged profile. Synthetic tests demonstrate that the warping method and more conventional methods for calculating heave yield nearly identical heave estimates. However, the warping method can also identify profiles with foreign water mass intrusions, which are otherwise undetected in density coordinates. Profiles with significant lateral intrusions are excluded from the analysis, as they include along-isopycnal processes that are not indicative of vertical heave. We calculate heave for all the Argo profiles in the North Pacific Ocean, then use a linear model to partition heave into contributions related to seasonal variability, the El-Niño Southern Oscillation, and decadal heave trends. Significant warming trends dominate in the high-latitude North Pacific, with a total heat uptake of 0.81 W m-2 in the upper 1850 m of the ocean. Seasonal variability and ENSO dominate in the equatorial regions, with a strong zonal gradient in ENSO-related heave expression and complex vertical structures of seasonal variability. From early 2008 to the end of the 2009 El Niño event, the heat content in the North Pacific increased by 1.06 W m-2. We also find long-term shifts in the position of the Kuroshio current and coherent wave patterns in the deep Equatorial Pacific. Ongoing work extends this analysis to the global Argo array to further constrain long-term changes in global ocean heat content.