Fluffy South Pole Snow Offers Insights Into Climate Cycles
April Flowers for redOrbit.com – Your Universe Online
A team of scientists, led by researchers at the University of California, San Diego, has found particles from the upper atmosphere trapped in a deep pile of Antarctic snow that hold clear chemical traces of global meteorological events.
The study was published in the early online edition of the Proceedings of the National Academy of Sciences and suggests anomalies in oxygen found in sulfate particles coincide with several episodes of the cyclical global disruption of weather known as El Niño. According to the researchers, these can be distinguished from similar signals left by the eruption of huge volcanoes.
“Our ability to link reliable chemical signatures to well-known events will make it possible to reconstruct similar short-term fluctuations in atmospheric conditions from the paleohistory preserved in polar ice,” said Mark Thiemens, dean of the Division of Physical Sciences and professor of chemistry and biochemistry at UC San Diego.
Thiemens’ team, which included several members of the Thiemen’s lab at UC San Diego as well as Joel Savarino of Laboratoire de Glaciologie et Géophysique de l’Environnment, excavated a pit six meters deep in the snow near the South Pole using shovels.
“At an elevation of 10,000 feet and 55 degrees below zero, this was quite a task,” Thiemens said. The team’s efforts exposed a 22-year record of snowfall. This pileup of individual flakes showed that some of the snow crystallized around particles of sulfate that formed in the tropics.
When sulfur dioxide – one sulfur and two oxygen molecules – mixes with air and gains two more oxygen molecules, atmospheric sulfates form. Prior studies by Thiemen’s group showed this process can happen in various ways, some of which favor the addition of variant forms of oxygen, or isotopes, with an extra neutron or two.
Relatively fluffy snow allowed the team to resolve this record of atmospheric chemistry on a much finer scale than could have been obtained with polar ice, which compresses months of precipitation so tightly that resolution has to be measured in years.
“That was key,” said Robina Shaheen, a project scientist in Thiemen’s research group who led the chemical analysis. “This record was every six months. That high resolution made it clear we can trace a seasonal event such as ENSO.”
The El Niño Southern Oscillation, or ENSO, is a complex global phenomenon that begins when trade winds falter for several months, allowing so-called Kelvin waves piled up in the tropical western Pacific to slosh toward South America in a warm stream that alters marine life. This can crash fisheries off the coast of Peru and Chile, and disrupt patterns of rainfall leaving parts of the planet drenched and others parched.
Sulfur dioxide is lifted high into the stratosphere by the warm air above the surface of the sea. The sulfur dioxide is then oxidized by ozone, which gives a distinct, anomalous pattern of oxygen variants to the resulting sulfate particles.
The scientists found traces of these oxygen anomalies in sulfates trapped in layers of snow within the Antarctic samples that fell during strong El Niño seasons.
Sulfur compounds can be shot high into the atmosphere by volcanic eruptions as well, where they react with ozone to produce sulfates with oxygen anomalies. In the period of time between 1980 and 2002 covered by this study, there were three large volcanic eruptions, including El Chichón, Pinatubo and Cerro Hudson as well as three ENSO events.