Digging in the Deep For Clues to Climate
Scientists take rock and sediment samples from far beneath the ocean floor to determine future atmospheric patterns
SCIENTISTS are delving deep under the ocean floor and uncovering clues to changes in the earth's climate.
In the waters of the eastern Pacific, they have just drilled their deepest-ever hole and are studying samples of rock and sediment millions of years old, hauled up from more than three miles beneath the surface of the ocean.
Members of the worldwide Ocean Drilling Program (ODP) hope that the samples will provide pointers to what the world's atmospheric patterns may be like decades and centuries from now.
Already the world's largest and most successful multinational earth-science research effort, ODP is gearing up to extend its researches to the North Atlantic next year.
Paleoceanographers and other scientists aboard ODP's research ship, JOIDES Resolution (the name stands for Joint Oceanographic Institutions for Deep Earth Sampling), have already produced evidence suggesting that theories on global warming will have to take account of climatic rhythms extending back into our planet's prehistoric past likely to be replicated in the future.
Lin Kay, an earth scientist with Britain's National Environmental Research Council (NERC), which is a major ODP participant, describes the work as "extremely important and exciting."
"The past not only tells us about the present - it offers us a guide to the future. By digging into rock deep beneath the ocean and looking at the story it tells, we are learning a great deal about global climate patterns," Dr. Kay says.
Following limited ocean drilling that began in 1968, the current $36-million program was launched nine years ago with an emphasis on reconstructing the fundamental mechanisms that created ocean basins, island chains, and mountain ranges.
Ocean drilling in the 1970s produced important information about the makeup of the 70 percent of our planet covered by water. An early achievement was recovery of a fragment of the oldest remaining sea floor - a relic of the middle Jurassic period 170 million years ago. At that time, one vast ocean covered the planet, the continents formed a single huge cluster, and global temperatures were much warmer than today.
ODP's early members included the United States, France, West Germany, Britain, and the former Soviet Union. The latter's membership is now in doubt, but other countries, including Japan and Australia, are becoming involved.
The US National Science Foundation funds ODP along with significant contributions from 19 countries. Texas A&M University in Galveston, Texas, is the program's science operator.
Once you get under it, the seabed is a happy hunting ground for earth scientists. On dry land, rocks can be more than 3 billion years old. Under-ocean rock is only 200 million years old. This is because it is constantly being replenished by volcanic activity, especially where the seabed meets the edges of continents.
In the last four or five years, Kay says, ODP's emphasis has swung toward probing links between seabed geology and the world environment. Concern about depletion of the ozone layer has been a driving force behind the switch of focus.
ODP research depends on the fact that all the time, anywhere on the earth, the effects of climate are being felt. In the sea, plankton take carbon dioxide (CO2) out of the air and are later fed on by larger creatures that fall to the seabed and die. The CO2, an important gas in global warming, remains locked in their tissue.
The "signatures" provided by dead creatures in layers of detritus vary according to the amount of CO2 in the atmosphere when they were alive. They also vary in relation to temperatures then prevailing and the salinity of the sea.
Jeremy Baldwin, a scientist at NERC, likens the process to the growth of rings in a tree trunk that tells us how old a tree is.
"If you correlate differences in the layers of undersea sediment to periods of high or low solar activity and to changes in Earth's orbit," he says, "you begin to establish patterns.
"In arithmetic we know that two plus two plus five will equal nine. ODP is trying to establish comparable rules using rock cores brought up from beneath the ocean. Once the information is organized and cross-referenced to other data, the links between past and likely future climatic activity can be established."
ODP scientists are elated by the record-breaking Hole 504B drilled in the Pacific between Ecuador and the Galapagos Islands.
Floating in water two miles deep, the 470-foot JOIDES Resolution with its 202-foot derrick drilled a hole 1 1/4 miles beneath the earth's crust. From the hole, it brought up cylinder-shaped core samples, each 31 feet long. While the drilling was going on, the ship was held stable by 12 powerful computer-controlled thrusters, the ship's propellers.
When a rock sample is hauled to the surface to the cry of "Core on deck," the 30 or so scientists on the ship immediately begin subjecting it to tests in a dozen on-board laboratories.
WHILE the cores are being analyzed in the floating laboratories, other scientists lower instruments back into the drill hole from which the sample has been removed and record the properties of the surrounding rock - a process known as down-hole logging.
Using a highly sophisticated technique, suspended television cameras are used to locate and reenter the bore hole - an action described by Mr. Baldwin as "roughly the equivalent of threading a needle miles away."
In drilling Hole 504B, the researchers had to use this method many times. In the last 40 days of drilling, a steel and tungsten-carbide bit bored vertically through 1,200 feet of hard rock.
According to Nick Shackleton of Cambridge University, a world authority on the Late Quaternary (the geology of the last million and a half years), rocks and sediments from the deep oceans can be used to explain the basic causes of climate variability.
"We are building up not just a description of past climate, but a detailed understanding of the mechanism of climate change," Dr. Shackleton says. "As we get better and better at it, we learn more about how the earth's climate system works. That is helping to improve the models we are using to predict future change."
In January, Allan Kemp of Southampton University told a London conference of earth scientists concerned with ODP that, by using an electron microscope to examine under-ocean rock samples, researchers may soon be able to create a year-by-year record of world weather patterns going back a million years.
Tony Rosell of Bristol University says the study of fossilized algae in undersea sediment promises to yield a detailed record of the earth's temperatures as ice caps advanced and retreated and sunspots waxed and waned.
Mr. Rosell uses the term "biomarker" to describe chemicals contained in marine algae trapped beneath the earth's crust.
Study of the biomarkers, he says, should indicate the amount of CO2 in the atmosphere and even the temperature of the sea when the algae died.