Ancient Antarctic Air
A new core drilled through an ice field on the Antarctic Peninsula should contain ice dating back into the last ice age. If so, that will give new insight into past global climate changes. The expedition in early winter to the Bruce Plateau, an ice field straddling a narrow ridge on the northernmost tongue of the southernmost continent, yielded a core that was 1,462 feet long, the longest yet recovered from that region of Antarctica. Old ice can contain bubbles of trapped air from long ago. That air represents, unchanged, what the air composition was like thousands of years ago. There may be other frozen clues in the water itself.
Ice core analysis is a fairly new science; the first deep cores were drilled in the 1960s. However, it has already yielded a wealth of information. Scientists turned to ice cores in earnest in the early 1980s, primarily to determine the effect of anthropological activities on the Earth. Although not reaching back deep into geologic time, ice cores do represent times long before humans began to influence the environment, and are therefore very valuable. Scientists can gather from their constituents a record of temperature, precipitation, atmospheric composition, volcanic eruption, solar variability, sea-surface productivity. Ice core records are most applicable to the study of greenhouse gas concentrations. They are in fact the most detailed record available. Plotting the depth against age creates an ice core chronology.
Glaciers are the result of snow accumulation over long periods of time. When dry snow accumulates, it is preserved in layers. Water trapped in glaciers remains in a pristine condition, preserving for us today clues about the climatic conditions that prevailed when it was deposited. Trace elements and aerosols are deposited on the surface, and gases are trapped inside the snow. It is from the analysis of these impurities that data can be obtained. For example, carbon dioxide, methane, and oxygen remain in proportion to that in the atmosphere.
The Antarctic Peninsula core drilling was not easy to do. Bad weather delayed the transport to the remote drill site and snowstorms were a recurrent problem, preventing support flights in to the team. Twice, their drills became stuck deep in the ice.
Their ice core drilling effort was part of the much larger Larsen Ice Shelf System, Antarctica (LARISSA) project, designed to unravel past climate conditions in this part of the continent and monitor current ocean and atmospheric processes to better understand what likely caused portions of the massive Larsen Ice Shelf to disintegrate in 2002.
This large, interdisciplinary National Science Foundation project involved experts in the oceanography, biology and geology of the region, in addition to the ice core effort. The goal is to build a climate history of the region, hopefully determining if the ice shelf break up was part of a long term natural cycle or linked to the current warming trend.
The team began drilling on New Year’s Eve, December 31, 2009.
Two days later, the team had drilled 459 feet when the drill became stuck in the ice. Leaving that drill in the ice, they began drilling a second hole and by January 21, they had retrieved 1,256 feet of core before that drill also became stuck. A device was dropped into the hole to carry ethylene glycol (antifreeze) down to the top of the stuck drill. After several days, the drill broke free and drilling resumed.
The cores were carefully packed and kept frozen. Periodically, planes would come to pick up the ice filled tubes, packed in insulated boxes, and return them to freezers at Rothera station. Eventually the cores will be transferred to the U.S. research ship Nathaniel B. Palmer, shipped to the U.S. West Coast and brought to Columbus Ohio by refrigerated truck. The cores are expected to reach Ohio State by mid-summer.
When the ice arrives, researchers here will begin their analyses, measuring oxygen-isotopic ratios — a proxy for temperature, and concentrations of dust and various chemicals — including volcanic tracers, that collectively will reveal past climate conditions.
The upper parts of ice cores may be dated by counting annual rings, as with tree rings; by identification of annual layering scientists can ascertain the age of ice at a particular band. Specific events leave distinctive tracers that can be used to calibrate the ice core against another for which dates have already been established. Such markers are called "reference horizons." For example, the eruption of a volcano creates a reference horizon, and knowing the precise date of this eruption enables scientists to establish dates for bands above and below the eruption. Oxygen-18 ratios not only indicate ocean isotopic composition but can also correlate with marine isotope record of sea water oxygen isotopes. Radioactive decay can also be used as a dating mechanism. Lower down the ages are reconstructed by modeling accumulation rate variations and ice flow.
The scientists are hoping for answers to some specific Antarctic Peninsula questions:
* Have the climate trends around the Antarctic Peninsula been similar or dissimilar to those experienced by the rest of the continent?
* Was the climate on the peninsula warmer during the early Holocene period, some 8,000 to 6,000 years ago, as it was elsewhere around the globe.
* Can evidence trapped in the ice cores shed light on what caused the Larsen Ice Sheet to begin to disintegrate in recent years?
* Do the cores contain ice formed during the last glacial stage, or “ice age”Ě? If so, it might yield clues to what caused the change from those earlier, much colder climate conditions.
For further information: http://researchnews.osu.edu/archive/larissadrill.htm