Brian Mcghee, age ll, of Peterborough, Ont., Canada, for his question:

What causes the directions of the ocean currents?

Visitors from another world would see our earth as a very watery planet. For almost 7l% of it is covered by seas linked together in a world wide ocean. And all these mighty waters are mixed and merged in a constant turmoil of ocean currents and tossing tides..

Swift surface currents sweep around all the major oceans, circling clockwise in the northern hemisphere and counterclockwise south of the equator. And deeper currents inch in other directions along the ocean floors. These upstairs and downstairs currents form a global picture. Its basic pattern is caused and directed by the sun and our . Spinning globe. These forces act together on the 330 million cubic miles of fluid water in the world oceans.

The bulging equator gets the most solar heat from the direct rays of the overhead sun. Its warm ocean water expands, and sea level rises higher than elsewhere. Its sea surface tends to flow downhill toward the poles. The chilly polar waters tend to condense and sink and flow in deep sea currents toward the equator. This simple flow between the poles and equator is modified by other factors, especially at the surface of the oceans.

The earth spins eastward and its rotation speed dwindles from l,000 miles an. Hour at the equator to nothing at the poles. This speed variation affects both the waves and the winds that blow them. It causes the tricky coriolis effect that bends or deflects all moving objects to the right in the northern hemisphere and to the left in the southern hemisphere. The trade winds are deflected to blow toward the equator from the northeast and the southwest.

The fast rotation at the bulging waist of the world tends to run ahead of the sea, leaving waters behind to pile up along the western shores. This westerly course is abetted by the trade winds. In the temperate zones the angles change. The prevailing winds and ocean currents move westward. The winds sweep on in unbroken paths around the globe. But the ocean currents are barricaded by bordering continents. When they reach the shores, they must turn and veer in other directions.

North of the equator, the earth's rotation makes the ocean's currents veer right at every turn and hence form huge eddies swinging around in a clockwise direction. In the southern hemisphere, the same rotation trickery makes the ocean currents veer left at every turn and hence swing around in a counterclockwise direction.

Oceanographers are charting more of the deep ocean currents and still trying to fathom their courses. But the global pattern of surface currents is well understood. These great eddies swirl to the right through the north Atlantic and pacific and to the left through the south Atlantic and pacific. Their directions are governed by a complex interaction of solar heat and the spinning earth, the bulging equator and the fluid nature of liquid water.