On November 1, 1952, the United States detonated the first thermonuclear bomb on the Eniwetok atoll in the Marshall Islands. The 10.4 megaton bomb launched radioactive elements such as tritium, strontium, cesium and an isotope of chlorine (chlorine 36) high into the stratosphere where they were carried by winds around the world to gradually return to earth in rain and snow.
Nine years later, in October 1961, the Soviet Union detonated the largest thermonuclear weapon, a 58 megaton bomb (2,600 times larger than the bomb that destroyed Hiroshima) on Novaya Zemlya.
One of the unintended consequences of these explosions was that climate scientists drilling ice cores in ice sheets and glaciers have been able to use the layers of radioactive materials laid down as markers for dating the cores. But no more.
For example in 1990 Dr. Lonnie Thompson of Ohio State University’s Byrd Polar Research Center found just these sort of radioactive markers twelve meters down on the Grigoriev Glacier in the Tien Shan mountain range. From this Thompson could deduce that the ice at that level had formed within in a couple of years of the Novaya Zemlya blast. [For more details on the above and Lonnie Thompson’s work in general, see Mark Bowen’s fine book Thin Ice: Unlocking the Secrets of Climate in the World’s Highest Mountains]
Photo, above, right, by Thomas Nash from Byrd Polar Research Center
Since these radioactive markings exist on glaciers around the world from Asia to Africa to South America as well as in the polar regions, they have been very used repeatedly for establishing initial ice-core dating points.
Khan Tengri (6995m) in the Tien Shan mountain range. Photograph: Simon Garbutt
Thompson spent part of last year drilling cores on the Naimona’nyi glacier at 19,849 feet (6,050 meters) on the Tibetan Plateau. To Thompson’s surprise none of the three cores that his team drilled showed levels of the usual radioactive materials. “We’ve drilled 13 cores over the years from these high-mountain regions and found these signals in all but one – this one,” Thompson explained.
The researchers did manage to find a small amount of a lead isotope, lead-210, which permitted them to date the top of the core to approximately 1944 A.D. Natalie Kehrwald, doctoral student working on Thompson’s team explained the significance of the event:
“We were able to get a date of approximately 1944 A.D.,” Kehrwald said, “and that, coupled with the other missing signals, means that no new ice has accumulated on the surface of the glacier since 1944,” nearly a decade before the atomic tests.
Recently, I wrote about the demise of alpine glaciers around the world and the consequences that their disappearance would have for hundreds of millions or more people who depend on glacier meltwater for their drinking supplies and for irrigation. Thompson’s discovery makes that threat all the more serious.
“When you think about the millions of people over there who depend on the water locked in that ice, if they don’t have it available in the future, that will be a serious problem,” he said.
Seasonal runoff from glaciers like Naimona’nyi feeds the Indus, the Ganges and the Brahmaputra rivers in that part of the Asian subcontinent. In some places, for some months each year, those rivers are severely depleted now, the researchers said. The absence of new ice accumulating on the glaciers will only worsen that problem.
“The current models that predict river flow in the region have taken recent glacial ‘retreat’ into account,” said Kehrwald, “but they haven’t considered that some of these glaciers are actually thinning until now.”
“If the thinning isn’t included, then whatever strategies people adopt in their efforts to adapt to reductions in river flow simply won’t work.”
Thompson fears that what’s happening to the Naimona’nyi glacier may be happening to many other high-altitude glaciers around the world. “I think that this has tremendous implications for future water supplies in the Andes, as well as the Himalayas, and for people living in those regions.”
The absence of the radioactive signals in the 2006 Naimona’nyi core also suggests that Thompson and his colleagues have been lucky with their previous expeditions to other ice fields.
“We have to wonder — if we were to go back to previous drill sites, some drilled in the 1980s, and retrieved new cores — would these radioactive signals be present today?” he asked.
“My guess is that they would be missing.” The researchers’ recent work has shown similar thinning on glaciers in Africa, South America and in Asia in the past few years.
It has been widely recognized that alpine glaciers have been retreating, but it was assumed that snowfall and ice formation were counterbalancing at least part of the melting. The fact that no new ice has accumulated on the Naimona’nyi glacier since 1944 means that the glacier is not simply retreating, but is also thinning. In other words, the mass balance is not only being depleted at the front, it is not being restored at the top, which means the glaciers are disappearing faster than expected. Bad news. Very bad news indeed.
Crossposted at Daily Kos