Sea Level and the Southern Oscillation

Summary

An average curve for the world annual mean sea level for the century 186-1960 has been obtained from a carefully selected world series of tide gauge records. We have eliminated data from tectonically unstable areas and other obviously anomalous records. Five-year running means provide us with a residual curve that may approach a eustatic standard (probably glacio-eustatic). The lowest point of sea level was about 1890; the mean rise from 1900-1950 was 1-2 mm annually, but the fastest decade was 1946-1956 with 55mm. The pattern varies somewhat if plotted ocean by ocean.

The non-smoothed, annual curve shows a 2-3 year cyclicity of 10-30mm amplitude. For the world curve this periodicity resembles the 2-3 year atmospheric pressure cycle known as the “Southern Oscillation”, being in phase with the S. E. Pacific node. The reciprocal, Indian Ocean node is well reflected in the Indian Ocean, and periodically dominates over the Pacific pattern in the Atlantic Ocean.

When the effect of a pressure anomaly of I mb is taken as equivalent to 10mm departure of sea level, it is found that that is still a large residual generally in the same phase. It would seem that steric effects and associated wind systems are mainly responsible.