1) Temperatures: Coastlands with warm currents offshore tend to have mild climates for their latitudes. Coastlands with cold currents off-shore are cooler than they would otherwise be.
The effect of a warm current off-shore is especially pronounced if the prevailing wind is on-shore. Thus, the British Isles is some 10° – 16°C warmer than the average for its latitudes because westerly winds bring the warmth of the North Atlantic Drift on-shore.
The Labrador coast, on the other hand, in the same latitude, is frozen for most of the winter months because of the cold Labrador Current and the icy winds which blow out from the interior of Canada in winter. The figures below illustrate the effects on temperature of some ocean currents:
Summer temperatures are reduced when onshore winds cross cold ocean currents; for example, on the coast of California and coast of Peru. In San Francisco, September is much warmer than either July or August because winds are then predominantly off-shore so that the ocean and cold current can have little effect on temperature. The figures illustrate the contrast between west and east coast in summer.
2) Precipitation: Winds blowing on-shore over warm ocean currents bring a lot of rain, particularly if a mountainous relief obstructs the passage of the wind inland, for example Western Britain and Norway. Winds blowing over cold currents are dry, for example, those off the South Californian coast. Here cooling of the winds offshore robs the air of valuable moisture. When the winds do cross the coast, they are heated and thus become drier.
3) Fogs: Fogs are produced when warm and cold currents come in close contact with one another. The warm moist air over the warm ocean current is cooled by contact with the cooler air over the cold ocean current. This cooling results in condensation of moisture to form mist and fogs. Such fogs are prevalent along the Labrador and Newfoundland coasts where air over the Labrador and Gulf Stream currents is mixed. Similar fogs occur in the Western Pacific around the shores of Japan (meeting place of the Kuro Siwo and Oya Siwo ocean currents) .
On-shore winds in summer along the Californian and Peruvian coasts (cold currents off-shore) also produce fogs. The cooling of the moisture-laden wind results in the formation of fog off-shore and in the coastal waters. This fog effectively shuts out much of the sun’s warmth.
The Uses of Oceans
Oceans are important to man in various other ways, in addition to their influence on the climate (temperature and rainfall) of adjoining coastlands.
Oceans are the natural routes by which goods from one continent reach another at the lowest possible cost. There are no construction costs involved in ocean routes, except maintenance costs which are confined only to the ships themselves and the harbours. Ocean vessels are designed to carry either cargoe or passengers or both.
Fish is a major source of food and protein to man. One of the major problems facing man in the world today is that of providing enough food for the teeming population. There are tremendons stocks of fish in seas and oceans, where they feed on minute plant and animal organisms called plankton. The Grand Banks of Newfoundland, Canada, is one of the world’s largest fishing grounds. The chief fish caught here is cod, which is consumed fresh or dried, salted, smoked, canned or packed in ice for export to mainland America, Central and South America and southern Europe. The surrounding islands of Japan is another major fishing area of the world. In West Africa open sea fishing is becoming increasingly important in Nigeria, Ghana, Senegal, and Mauritania.
When discussing the uses of the oceans one must not fail to mention the vast mineral deposits in ocean beds. There are coal deposits in some ocean beds, and off-shore marine mining takes place. Coal is used as a domestic fuel, industrial power, and as a vital raw material for the chemical industry. Petroleum (mineral oil) is also found in off-shore areas. In Nigeria, for example, there are many off-shore oil wells.
Finally, in many parts of the world the seas and oceans are important recreation centres where people go to sail or swim and play at the beaches. The Bar Beach in Lagos is a fine example of a recreation ground.