Is there a quasi 60-year oscillation in global tides?

Abstract

We analyze long-term tide gauge records to examine whether there is a quasi 60-year oscillation in global tides. We find that there is a significant 55-year cycle at more than half of the tide gauges analyzed. For M2 tide, the amplitudes of the 55-year cycle range from 1.82 ± 0.80 mm (Los Angles) to 26.34 ± 6.75 mm (Cuxhaven), while for S2 tide, the amplitudes of the 55-year cycle range from 1.02 ± 0.48 mm (San Francisco) to 8.61 ± 2.25 mm (Cuxhaven). At Cuxhaven, shallow water constituents M4, MS4 and M6 tides which obtain energy from M2 and S2 tides also show significant 55-year cycles. It is found that the 55-year cycle significantly influences the estimation of the long-term trend of tidal amplitudes at Newlyn, Cuxhaven, Eastport and Victoria. The influence of the 55-year cycle on long-term trends of tidal amplitudes at Cuxhaven is the strongest among these stations. At Cuxhaven, the long-term trend of M2 (S2) amplitudes sharply increases from 0.68 ± 0.10 (0.22 ± 0.03) mm/yr to 0.93 ± 0.06 (0.31 ± 0.03) mm/yr when the 55-year cycle is removed. It is also found that the 55-year cycle in tides can partly explain the rapid change in M2 and S2 tides since 1980s in the North Atlantic. Quasi-60 year variations in sea levels and sea water temperature may be responsible for the 55-year cycle in tides while the detailed mechanisms still need further research.