Interdecadal Sea Level Variations in the Pacific: Distinctions Between the Tropics and Extratropics

Abstract Long tide gauge records from Fremantle and San Diego are used to examine interdecadal sea level fluctuations and their relationship to Pacific climate variability. The sea level difference between the tide gauges and the Southern Oscillation Index (SOI) provide a consistent depiction of trade wind variations along the equator over the past century. The sea level difference and SOI exhibit weak interdecadal variability prior to the late 1970s, followed by an extended 40‐year period of high levels at San Diego and low at Fremantle, and low SOI levels signifying weakened equatorial trade winds. By referencing the tide gauge records to global mean sea level, we infer that Pacific trade winds exhibited weak departures from mean conditions on interdecadal time scales prior to the late 1970s and that a prolonged El Niño‐like lull dominated the tropics at the end of the century. A recent shift suggests that the trades are reverting back to the El Niño‐like state. These tropical interdecadal variations have counterparts in the extratropical North Pacific after the 1970s, as captured by the Pacific Decadal Oscillation, but the early twentieth century quiescent phase in the tropical Pacific is not reflected in the extratropics, which exhibits more energetic oscillatory behavior over the same time span.