TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 62 (No. 2), pp. 155-170, 2006

Steric Sea Level Changes Estimated from Historical Ocean Subsurface Temperature and Salinity Analyses

Masayoshi Ishii1*, Masahide Kimoto2, Kenji Sakamoto3 and Sin-Iti Iwasaki4

1Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, Japan
2Center for Climate System Research, University of Tokyo, Kashiwa 277-8586, Japan
3Climate Prediction Division, Japan Meteorological Agency, Tokyo 100-8122, Japan
4National Research Institute for Earth Science and Disaster Prevention, Tsukuba 305-0006, Japan

(Received 29 August 2005; in revised form 12 November 2005; accepted 28 November 2005)

Abstract: An historical objective analysis of subsurface temperature and salinity was carried out on a monthly basis from 1945 to 2003 using the latest observational databases and a sea surface temperature analysis. In addition, steric sea level changes were mainly examined using outputs of the objective analyses. The objective analysis is a revised version of Ishii et al. and is available at 16 levels in the upper 700 m depth. Artificial errors in the previous analysis during the 1990s have been worked out in the present analysis. The steric sea level computed from the temperature analysis has been verified with tide gauge observations and TOPEX/Poseidon sea surface height data. A correction for crustal movement is applied for tide gauge data along the Japanese coast. The new analysis is suitable for the discussion of global warming. Validation against the tide gauge reveals that the amplitude of thermosteric sea level becomes larger and the agreement improves in comparison with the previous analysis. A substantial part of local sea level rise along the Japanese coast appears to be explained by the thermosteric effect. The thermal expansion averaged in all longitudes from 60°S to 60°N explains at most half of recent sea level rise detected by satellite observation during the last decade. Considerable uncertainties remain in steric sea level, particularly over the southern oceans. Temperature changes within MLD make no effective contribution to steric sea level changes along the Antarctic Circumpolar Current. According to statistics using only reliable profiles of the temperature and salinity analyses, salinity variations are intrinsically important to steric sea level changes in high latitudes and in the Atlantic Ocean. Although data sparseness is severe even in the latest decade, linear trends of global mean thermosteric and halosteric sea level for 1955 to 2003 are estimated to be 0.31 ± 0.07 mm/yr and 0.04 ± 0.01 mm/yr, respectively. These estimates are comparable to those of the former studies.

*Corresponding author E-mail: ism@jamstec.go.jp

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