Thermosteric sea level rise for the past 50 years; comparison with tide gauges and inference on water mass contribution

In this paper we compare sea level trends observed at a few selected tide gauges of good quality records with thermosteric (i.e., due to ocean temperature change) sea level trends over 1950-1998 using different gridded ocean temperature data sets from Levitus et al. (2000) [Levitus, S., Stephens, C., Antonov, J.I., Boyer, T.P., 2000. Yearly and Year-Season Upper Ocean Temperature Anomaly Fields, 1948-1998. U.S. Gov. Printing Office, Washington, D.C. pp. 23.], Ishii et al. (2003) [Ishii, M., Kimoto, M., Kachi, M., 2003. Historical ocean subsurface temperature analysis with error estimates, Mon. Weather Rev., 131, 51-73.] and Levitus et al. (2005) [Levitus S., Antonov, J.I., Boyer, T.P., 2005. Warming of the world ocean, 1955-2003. Geophys. Res. Lett. 32, L02604. doi:10.1029/2004GL021592.]. When using the Levitus data, we observe very high thermosteric rates at sites located along the northeast coast of the US, north of 37°N. Such high rates are not observed with the Ishii data. Elsewhere, thermosteric rates agree reasonably well whatever the data set. Excluding the northeast US coastline sites north of 37°N, we compare tide gauge-based sea level trends with thermosteric trends and note that, in spite of a significant correlation, the latter are too small to explain the observed trends. After correcting for thermosteric sea level trends, residual (observed minus thermosteric) trends have an average value of 1.4 ± 0.5 mm/year, which should have an eustatic (i.e., due to ocean mass change) origin. This result supports the recent investigation by Miller and Douglas (2004) [Miller, L., Douglas, B.C., 2004. Mass and volume contributions to 20th century global sea level rise. Nature 428, 406-408.] which suggests that a dominant eustatic contribution is needed to explain the rate of sea level rise of the last decades observed by tide gauges, and shows that Cabanes et al. (2001) [Cabanes, C., Cazenave, A., Le Provost, C., 2001. Sea level rise during past 40 years determined from satellite and in situ observations. Science 294, 840-842.] arrived at an incorrect conclusion due to peculiarities in the gridded Levitus et al. (2000) [Levitus, S., Stephens, C., Antonov, J.I., and Boyer, T.P., 2000. Yearly and Year-Season Upper Ocean Temperature Anomaly Fields, 1948-1998. U.S. Gov. Printing Office, Washington, D.C. pp. 23.] data set.