Steric sea level changes estimated from historical ocean subsurface temperature and salinity analyses |
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| Authors: | Masayoshi Ishii Masahide Kimoto Kenji Sakamoto Sin-Iti Iwasaki |
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| Institution: | (1) Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, Japan;(2) Center for Climate System Research, University of Tokyo, Kashiwa 277-8586, Japan;(3) Climate Prediction Division, Japan Meteorological Agency, Tokyo 100-8122, Japan;(4) National Research Institute for Earth Science and Disaster Prevention, Tsukuba 305-0006, Japan;(5) Present address: Meteorological Research Institute of the Japan Meteorological Agency, Japan |
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| 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. |
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| Keywords: | Temperature analysis salinity analysis steric sea level TOPEX/Poseidon tide gauge crustal movement |
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