Interannual variability in upper ocean heat content, temperature, and thermosteric expansion on global scales

Abstract

Satellite altimetric height was combined with approximately 1,000,000 in situ temperature profiles to produce global estimates of upper ocean heat content, temperature, and thermosteric sea level variability on interannual timescales. Maps of these quantities from mid‐1993 through mid‐2003 were calculated using the technique developed by Willis et al. [2003]. The time series of globally averaged heat content contains a small amount of interannual variability and implies an oceanic warming rate of 0.86 ± 0.12 watts per square meter of ocean (0.29 ± 0.04 pW) from 1993 to 2003 for the upper 750 m of the water column. As a result of the warming, thermosteric sea level rose at a rate of 1.6 ± 0.3 mm/yr over the same time period. Maps of yearly heat content anomaly show patterns of warming commensurate with ENSO variability in the tropics, but also show that a large part of the trend in global, oceanic heat content is caused by regional warming at midlatitudes in the Southern Hemisphere. In addition to quantifying interannual variability on a global scale, this work illustrates the importance of maintaining continuously updated monitoring systems that provide global coverage of the world's oceans. Ongoing projects, such as the Jason/TOPEX series of satellite altimeters and the Argo float program, provide a critical foundation for characterizing variability on regional, basin, and global scales and quantifying the oceans' role as part of the climate system.