At an altitude of 3,810 meters with an annual average temperature of -54 °C, researchers at the Dome Fuji Station in Antarctica drill deep into the ice sheet to obtain rare ice cores. Life there is said to be nonexistent on the ice because no liquid water exists as all the water becomes frozen. Under these extreme conditions, which are harsh not only for humans but also for many other life forms, unexpected phenomena occur; biodiversity is extremely low, and one cannot catch a cold due to the absence of viruses. The ice buried under the ice sheet snow is starting to tell a vivid history of the environments and organisms that inhabited the area over the past 700,000 years. Professor Hideaki Motoyama (National Institute of Polar Research), Project Director, tells the story.

Ice cores and moss pillars: the two targets

Our projects mainly target ice cores and moss pillars. The National Institute of Polar Research obtains the samples. Then, researchers from the National Institute of Polar Research (NIPR) and the National Institute of Genetics (NIG) extract genetic information, and researchers from NIPR and NIG with the Institute of Statistical Mathematics and the National Institute of Informatics analyze the data. We have been promoting such integrated research for the past 10 years. Among those studies, I take part in the research on snow and ice. As snow keeps falling, the top layers of the ice sheet are new, and the bottom layers are old snow. The huge amount of ice covering Antarctica is called the “Antarctic ice sheet”. We drill into the ice sheet to a depth of more than 3,000 meters, and obtain an ice core sample that formed over 700,000 years ago. From this ice, we can determine historic temperatures and atmospheric compositions, such as concentrations of carbon dioxide and methane, on Earth. For example, it has been revealed that the earth has been experiencing major climate changes in a 100,000-year cycle (glacial-interglacial cycle), with 70,000 to 80,000 years of cold climate and 10,000 to 30,000 years of warm climate, since 700,000 to 800,000 years ago. It has also been established that the last glacial global temperature was 5 to 6 °C lower than the current temperature and was much colder in the polar regions. Even though major climate changes can be studied based on marine sediment, the deposition rate is very low. The temporal resolution is much higher in the Antarctic ice sheet due to the considerable amount of snowfall, which provides an advantage in specifying the ages with high precision. Additionally, the preservation of past atmospheric contents is unique to glaciers and ice sheets, making them valuable data sources.

Analyzing the ancient microbiota in ice cores

Not only can ice core analyses provide the history of the earth’s climate and environment, they can also help discover how organisms have reacted and evolved in response to the major climate changes captured in the ice cores, and the organisms’ genes can be studied. However, we have begun to understand that it is extremely difficult to conduct such analyses because there are far fewer microbiota than expected due to the absence of life activities on the ice. However, the bottom of  the Antarctic ice sheet has been melted by geothermal heat.  The melting point of water is lower in this deep section due to the pressure applied by the weight of ice, and there are water veins 3,000 meters below the surface where the temperature is - 2 °C. Currently, we are conducting our analyses by focusing on the sampled water.

The most difficult genome sample on earth?!

 In this analysis, Takahiro Segawa, a Project Research Associate (NIPR, Transdisciplinary Research Integration Center (TRIC), center in the photograph), first extracts the genomic information from the samples, followed by an analysis of the genetic information by Shinji Kondo, a Project  Associate Professor (NIPR, TRIC, right in the photograph). For example, if we find a fragment of cyanobacteria, which conducts photosynthesis, we compare it to the genetic sequences of similar known species. Then, we often find a low match between the two, indicating the existence of unknown genome contents. The difficult part of this work is that there are only a few samples and it is not easy to find long DNA sequences because many of them are old and broken. Another challenge is "contamination," which pertains to the technical accuracy of the research. This requires us to prove that a sample is really from the time period claimed.

Following the hints given by moss pillars

As we advance our research, the most interesting aspect lies in studies of global changes in ice cores and their microbe systems, including one which Professor Satoshi Imura (the National Institute of Polar Research) is carrying out to determine how moss pillars fit into the earth's biological system and what they can reveal. Moss pillars are symbiotic communities of microbiota, approximately 30 cm in diameter and 60 m in height, living at the bottom of lakes and swamps scattered around the Antarctic Syowa Station. In the polar regions, water is a relatively more stable environment compared to the land. After comparing moss pillar samples with all databases of microbiota on Earth, we found that the same types of species found in moss pillars also exist in the Arctic and mid-latitudes. This means that the same species live in both cold and warm environments, which provides the opportunity to elucidate how their genes differ among geographic regions. Using ice cores, we can trace the changes and genetics of the biosphere in chronological order and understand that the ice cores contain genes conferring cold tolerance in cold ages. Conversely, we can also reveal which genes are suited to warm environments by looking at microorganisms in interglacial periods. In this age of global environmental crises, we hope our research helps build a sustainable society and offer implications for whether or not humankind can avoid extinction.

(Text in Japanese: Hideaki Motoyama, Rue Ikeya. Photographs: Mitsuru Mizutani. Published: April 1, 2014)