Interannual Variability in Upper-Ocean Heat Content, Temperature and Thermosteric Expansion on Global Scales

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 time scales. 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 some 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 mid-latitudes 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 worlds 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 ocean's role as part of the climate system.