Saturday, February 26, 2011

The Oceanic Winds and Currents of Antiquity

Man first began to acquire knowledge of the waves and currents of the seas and oceans in pre-historic times. Observations on tides are recorded by Aristotle and Strabo, and the earliest exploration of the oceans was primarily for cartography and mainly limited to its surfaces and of the creatures that fishermen brought up in nets, though depth soundings by lead line were taken. And when Louis Antoine de Bougainville, who voyaged between 1766 and 1769, and James Cook, who voyaged from 1768 to 1779, carried out their explorations in the South Pacific, information on the oceans themselves formed part of the reports.

James Rennell wrote the first scientific textbooks about currents in the Atlantic and Indian oceans during the late 18th and at the beginning of 19th century. Sir James Clark Ross took the first modern sounding in deep sea in 1840, and Charles Darwin published a paper on reefs and the formation of atolls as a result of the second voyage of HMS Beagle in 1831-6, with Fitzroy publishing a report in four volumes of the three voyages of the Beagle.

The steep slope beyond the continental shelves was not discovered until 1849. Matthew Fontaine Maury's “Physical Geography of the Sea,” 1855 was the first textbook of oceanography. The first successful laying of transatlantic telegraph cable in August 1858 confirmed the presence of an underwater "telegraphic plateau" mid-ocean ridge.

In all, the knowledge of the oceans and their currents, and how the winds affect these currents, is relatively new. However, the basic understanding that a weather sailing ship “driven forth before the wind” went where the winds and currents took it, was known anciently. This is because there are a number of ocean currents found around the Earth. A current is like a vast river within the ocean, flowing from one place to another. These currents are caused by differences in temperature, differences in salinity, and by wind. Currents are responsible for a vast amount of movement of the water found in the Earth’s oceans.

Generally, these currents do not change within the Atlantic, Pacific and Indian Oceans, and their direction, which is constant, is driven by the Earth’s rotation and affected by the Coriolis Effect, which causes currents to bend downhill toward the poles. For this reason, currents in the southern hemisphere rotate in counter-clockwise gyres, and currents in the northern hemisphere rotate in clockwise gyres. Understanding this is what allowed Columbus to drop down to the Canary Islands off the coast of Africa and then turn west into the gyre that took him to the Caribbean Islands in the Western Hemisphere. For this same reason, Europeans were unable to sail west into the Atlantic Ocean from northern latitudes because the clockwise gyre brought the currents against them. For this reason, it took the small Viking ships using oars to move westward along the coastal waters of Iceland and Greenland to reach Canada—but stopped any large scale sailing westward into those waters.

Within the Arabian Sea, currents change semi-annually, between blowing inland and blowing out to sea. The Trade Winds blowing north and west off the coast of Australia, and mostly westward through Indonesia, do not change, but are constant all year long. With currents moving along the northern reaches of the Arabian Sea in a westward direction, shipping did not move eastward from Arabia toward India and Indonesia without enormous effort and very lengthy voyages, which entailed stopping frequently along the shores. For this reason, the Portuguese found it almost impossible to sail around Africa and north into the Arabian Sea and then east toward China. Once they discovered the Southern Ocean currents (Prevailing Westerlies and West Wind Drift) moving swiftly eastward across the southern reaches of the Indian Ocean, they were able to make their journey looping wide around southern Africa and then toward Australia, catching the Trade Winds northward and to China and Indonesia.

While Mesoamerican and most other theorists like to draw lines across a map and claim the Lehi Colony sailed eastward from Arabia, through Indonesia, and then across the Pacific Ocean to Central America, the currents described above would not have allowed any sailing ship in 600 B.C., especially a weather ship “driven forth before the wind” to have made such a journey. The only currents that would have taken a ship from the southern coast of Arabia to the Western Hemisphere would have taken a ship south from Arabia, then southeast through the Indian Ocean, and then eastward in the currents of the Southern Ocean. No other way using currents and winds could a ship “driven forth before the winds” have left the southern Arabian Peninsula and sailed to the Western Hemisphere.

No comments:

Post a Comment