Tidal Cycles in the Arabian Gulf


All aspects of my life in Saudi Arabia--my work schedule, daily departure time, selection of field sites, even my choice of leisure activities, like snorkeling--were influenced by the tides.

Low tide: team drags a boat across sand flat

Low tide: team drags a boat across sand flat.

The tidal cycle on the Saudi Gulf coast is one of the most erratic on the planet. Tides, the rise and fall of the surface level of the sea, are created by two tractive forces: the interacting gravitational pulls from the moon and sun, and the centrifugal force of the revolving Earth. The independent gravitational pulls of the moon and sun act upon all water on the Earth's surface, causing it to move along the surface of the Earth in the directions of the moon and sun, respectively. This bulging action results in high tides in the directions of attraction and low tides in the troughs between the bulges where water has been displaced.

In this simplified model--simplified because it doesn't take into account things like irregularities in the ocean floor--the tidal bulges stay aligned with the moon and sun, and the rotation of the Earth on its axis creates alternating high and low tides at any fixed point on the Earth's surface. Put another way, the Earth moves beneath the tidal bulges, causing the bulges to appear to move across the surface of the ocean.

In the Arabian Gulf, there are two places, called amphidromic points (amphi = around + dromas = running), at which tidal fluctuation is zero. The tides in the Gulf rotate around these points like water sloshing around a wash basin. The Saudi Gulf coast experiences both diurnal tides (one high and one low per day) and semidiurnal tides (two high and two low per day), depending on the time of year.

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