Mean sea level is closely monitored on a global scale, but one of the surprising discoveries made by Topex/Poseidon is the amplitude of seasonal signals.

The mean variation in sea level is in fact more than 10 centimetres between cold and warm ocean seasons. Comparing the figures shown here, we can see a difference in the mean sea level anomalies recorded in February and October  of around 10 cm in the Atlantic and 20 cm in the Mediterranean which, as it is a semi-enclosed sea, amplifies this type of phenomenon.

It is also noticeable that this cycle is roughly two months out of step with the calendar seasons, because of the inertia of the oceans in propagating heat or cold to deeper waters.