January 1994, Page 48
Sea Level Changes Document 20,000-Year Mideast
By Ruth E. Steele
Observant visitors see the evidence all around them that the
Middle East was not always so arid as it is today. Mighty canyons
carved by raging rivers stand austere and bone-dry today. Bones of
jungle predators and great grazing beasts of the grasslands lie
buried in clay laid down by lakes and streams in lands where the
infrequent raindrops now vanish instantly into windblown sand.
Shifting winds uncover abundant stone-age tools in waterless
deserts. And in many parts of the Middle East great mounds of
man-made rubble attest to vanished cities where not even nomads pass
Middle Easterners ponder the forces that halved the population of
Iraq, birthplace of the world's first cities more than 5,000 years
ago, and of Syria, the breadbasket of the Roman Empire 2,000 years
ago. Today, these forces are widening the swath of Sahara sand that
separates the grasslands of Central Africa from the fertile coastal
strip of North Africa. Is the contemporary highly visible
desertification of the Middle East and Africa manmade, or an
irresistible force of nature?
Two American scientists, David K. Jacobs of the American Museum
of Natural History in New York and Dork L. Sahagian of Ohio State
University in Columbus, maintain the answer can be found etched into
coastal rocks all over the globe. Writing earlier this year in the
scientific journal Nature, they point out that worldwide sea
levels vary by as much as 25 feet roughly every 20,000 years.
These variations are not accounted for by ice ages, which do not
occur so frequently or so regularly, and which can store enough
water in glaciers to reduce ocean levels by up to 300 feet. The
smaller and more frequent variations in sea level, the U.S.
scientists believe, result from a known 20,000-year cycle of change
in the earth's axis of rotation that tips the Northern Hemisphere,
where most of the land is, toward the sun.
This slight tilt increases monsoonal rains. As the rains
increase, much of the runoff fills lake basins and aquifers instead
of draining to the sea. Enough water can be stored in the now dry
Tarim basin of western China, Sahagian and Jacobs say, to lower the
worldwide sea level by three and-a-half feet.
The Caspian Sea, between Iran and the former Soviet Union, can
hold enough water in addition to its present volume to lower
worldwide sea levels by one foot. Other known basins and aquifers
can catch and hold enough rain to lower the world's seas by many
It is during such periods of heavier rainfall that much of Syria
or the Sudan can produce rain-watered grain crops without
irrigation, the Sahara can become savannah grassland, and the great
river valleys of the Nile, the Indus and the Tigris and Euphrates
can support dozens of cities where only villages stand today.
Then, as the northern hemisphere tilts away from the sun again
and the rains slacken, lakes and aquifers begin to empty, the
process of desiccation resumes, sea levels rise, and plants, animals
and humans begin the migrations and adaptations to shifting rainfall
belts that humanity has seen throughout its recorded history.
Much of the physical evidence of ancient climate changes that has
vanished under the sands of the Arabian peninsula and other desert
areas can be traced from earth satellites, according to Dr. Farouk
El-Baz, Egyptian-born director of the Center for Remote Sensing at
Boston University. Last March he outlined the course of a vanished
river which once originated in the Hijaz mountains of western Saudi
Arabia and flowed eastward for more than 500 miles to the Arabian
There it formed a delta that is the site of much of present-day
Kuwait, according to Dr. El-Baz. He cites as visible proof of his
theory the granitic and basaltic gravel, unrelated to local rock
formations, found in Kuwait today. This gravel, he said, appears to
have been swept along by the river from the distant Hijaz mountains.
Because such hidden rivers frequently prove to be the source of
underground water, Dr. El-Baz points out that this one could prove
to be such a source for Saudi Arabia. He believes that what he calls
the ''Kuwait River" flowed for some 6,000 years, reaching a width of
three miles in places, during a relatively moist epoch in the
earth's history. That moist period ended some 5,000 years ago, he
said, so it is uncertain how much residue of the river may remain
under its former bed.
Since most of its course is hidden by sand dunes running on a
north-south orientation across central Saudi Arabia, the river's
existence was detected only by close examination of satellite
images. Because the nearby Nile and the Tigris and Euphrates rivers
supported major human civilizations at the time the "Kuwait River"
was flowing, Dr. El-Baz speculates, surveys of its course also may
reveal archeological remains of important human