Antarctic seabed gives up key climate data
Dropped into a hole melted through 267 feet of floating ice, a diamond-toothed drill had to travel another 2,776 feet through seawater before reaching the bottom of an offshore moat in Antarctica.
There, it pierced the ocean floor and began to drill back in time. It extracted a core sample about 3 inches in diameter and brought it up to a derrick built atop the Ross Ice Shelf.
Nearly a quarter-mile down, the drill bored into sediment that would astonish one of the largest groups of scientists ever assembled in Antarctica. It was a layer more than 300 feet thick of fossilized diatoms, microscopic algae that once bloomed near the ocean surface.
The diatom layer, laid down 2 million to 5 million years ago, was evidence that Antarctica has undergone past cycles of warming and cooling. It meant the Ross Ice Shelf -- a seemingly permanent slab of ice the size of Spain -- was once open water.
In other times, this information might be of interest only to specialists. But scientists with the Antarctic Geological Drilling project, or ANDRILL, believe the Antarctica of the past can show us what to expect from the warmer world of tomorrow.
In November and December, the ANDRILL team pulled 10 million years of critical climate information out of the Antarctic seabed. The diatom layer was a key prize, representing “a time when ... glaciers were in retreat, a different regime when there was a lot more water in the system,” said Reed P. Scherer, a diatom expert at Northern Illinois University.
In today’s terms, “more water in the system” could mean sea levels high enough to put low-lying places like Florida and Bangladesh underwater. If the Ross Ice Shelf again were to shrink or disappear because of higher global temperatures, it could signal dangerous changes for the rest of the planet.
For this reason, ANDRILL is one of the biggest scientific undertakings in the history of Antarctica and a showcase project for the International Polar Year, a major international cooperative research effort that began March 1 and continues until March 1, 2009. It is focusing hundreds of millions of dollars and vast expertise on the Arctic and Antarctic regions.
The project, much of which is related to global warming, brings together 150 scientists from the United States, New Zealand, Italy and Germany. The U.S. National Science Foundation provides two-thirds of ANDRILL’s $30-million cost. Last year’s drilling put 58 geologists, geochemists, volcanologists, sedimentologists, paleomagneticists, paleontologists, petrologists and others “on the ice.”
The samples they extracted provide “the best record of time ever established” in Antarctica, said Ross D. Powell, a Northern Illinois University geologist. Now, in a process that will take years, ANDRILL will try to match the new data with more complete geological histories from the rest of the world.
“We want to relate these warming events with other known world events,” said Powell, an expert in glacial sediments.
He reels off some of the questions they hope to answer:
“How did the Antarctic ice sheet react to temperature rises in the past, and how will it react in the future? What’s the critical point that triggers changes? Are there tipping points, like water temperature or air temperature, that we should be aware of? What was the global picture when this happened before?”
Antarctica was not always frigid. Forty million years ago, the Antarctic land mass was connected to the tip of South America and was home to thick vegetation and populations of animals similar to those in Australia.
But when Antarctica detached, a frigid circumpolar current began to spin around it like a giant freezer coil, trapping the continent in a super-cold climate. Glaciers and ice sheets grew up to 3 miles thick, covering 98% of Antarctica, which is larger than the U.S. and Mexico combined.
Though the chill has lasted ever since, the amount of ice in Antarctica has grown and shrunk many times during previous global climate changes. The ANDRILL core samples confirm at least 60 warming/cooling cycles in Antarctica in the last 10 million years.
But today’s warming trend appears different from those of the past. Most climate experts agree that the pace of change is unusually fast and that the cause seems to be human activities, primarily the burning of fossil fuels, which releases heat-trapping gases into the atmosphere.
The planet’s average annual temperature has risen 1.4 degrees Fahrenheit in the last 100 years, and parts of the Arctic and Antarctic regions have seen much bigger temperature increases, as much as 4.5 degrees since the 1950s.
The rising temperatures threaten to affect the three major types of ice associated with the Antarctic continent: the seasonal pack ice that grows outward from the shore each winter; the thick, semi-permanent ice shelves attached to the Antarctic coast; and the ice sheets that cover its rocky land.
Most catastrophic would be melting of the ice sheets. If the warmth causes even a small portion to thaw, the added water in the world’s oceans could create staggering human problems.
Experts watching the deterioration of ice sheets in Antarctica and Greenland predict that by the end of the century global sea levels may rise as much as 4.5 feet. Half a billion people live in coastal areas just 3 to 4 feet above sea level.
“My generation won’t have to deal with these large changes, but my grandchildren will,” said Robert Bindschadler, a NASA expert in ice-sheet dynamics.
The concerns about the ice shelves and pack ice are different. Because these formations already are afloat in the sea, melting them does not add more water to the world’s oceans, just as the water level in a glass doesn’t change as ice cubes melt.
But the pack ice and ice shelves help stabilize average global temperatures because their white surfaces reflect most of the sun’s heat back into space. If they melt away, the heat instead will be absorbed by the darker ocean surface, speeding the process of global warming.
The ice shelves also act as “plugs” that block the movement of Antarctic glaciers and ice sheets as gravity tries to pull them into the ocean. That helps regulate global sea levels by slowing the pace at which water is added to the ocean system.
In March 2002, scientists had a glimpse of how that equilibrium can be upset with the loss of West Antarctica’s Larsen B Ice Shelf, which had been stable for the last 12,000 years. At 650 feet thick and covering an area the size of Rhode Island, it had deteriorated with the increasingly warmer weather for several years when, within a matter of days, it shattered and fell into the ocean.
In the first 18 months after its disintegration, two NASA studies reported that the flow of glaciers behind the vanished ice shelf sped up, moving three to eight times faster than normal.
To know what changes may occur because of today’s global warming, scientists try to understand the planet’s past cycles of warming and cooling.
But ancient climate is researched from the geological record, and finding intact geology is extremely difficult in Antarctica, where the movement of glaciers and ice sheets has erased much of the continent’s sedimentary surface.
To find undisturbed layers, ANDRILL targeted a deep moat offshore from Ross Island. Drilling started in early November and stopped Dec. 26, when the drill reached its maximum depth, 4,176 feet below the bottom of the moat.
“The critical thing here is time, understanding how these events we see in the sediment fit into time,” said Powell, ANDRILL’s co-chief scientist for 2006 with New Zealand paleoclimatologist Tim Naish.
Powell said finding the diatom layers was crucial:
“They are the dominant fossil life forms in the cores, telling us the age of the rock and telling us about temperatures and water temperatures of their times.”
ANDRILL wants to issue its first major paper by the end of this year, Powell said. By then, the team hopes to be able to shed light on if and when the world might expect to have serious fallout from the current warming trends, such as rising seas and shifting growing seasons.
“Here we have a record from the horse’s mouth,” he said. “It’s what we hoped for, but we got more than we hoped for. It’s just an exceptional record.”
