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A scientific Gold Mine

The poles are lands holding great promise for scientists. There are subglacial lakes still unsullied by man, 2.5 billion year-old Antarctic rocks that were witnesses to the “early Earth,” ecosystems teeming with animal species adapted to extreme conditions, territories still largely unexplored, and an abundance of unsolved mysteries.

 

Unsullied Lands

Antarctica has been locked under ice for 35 million years. In its central regions, the air temperature at the ice sheet surface mostly hovers around -50°C. However, water in liquid form does exist on the frozen continent. Not at the surface, where temperatures are far too low, but deep beneath the ice sheet, at the interface between the ice and the basement rocks. In fact, a host of lakes located at depths of thousands of meters have been discovered, the largest of which, Lake Vostok, has an area of nearly 14,000 km2.

How were such lakes able to form and, above all, last this long? The short answer is geothermal energy. Despite the prevailing cold in Antarctica, the Earth's heat can sometimes be powerful enough to melt the deep ice. The resulting water can then collect in hollows in the ground. “Subglacial lakes were first spotted by radar echo, but their influence can also be seen at the surface,” explains Catherine Ritz, at LGGE.1  “Above a lake, the surface of the ice forms a large, almost horizontal, flat expanse, whereas all around it the surface is sloping and undulating. Today, glaciologists have located over a hundred subglacial lakes, and they reckon that there are many more yet to be discovered. As a result, an exhaustive inventory of these lakes will soon be drawn up as part of the Subglacial Antarctic Lakes Environments (SALE) programs, a range of scientific missions involving American, British, French, Italian, and Russian researchers. “Improving our understanding of these lakes is of paramount importance for glaciologists,” Ritz points out. “Currently they are a major source of uncertainty when studying polar ice sheet motion, and especially ice flow towards the sea. We know that ice can flow by deforming, by sliding over the ground, or through deformation of the ground. For these last two types of flow, the pressure of the water located between the ice and the basement rocks plays a key role. So what impact might subglacial lakes have on such motion?”

But there is another question that also intrigues scientists: Could life have developed in such underground expanses of water, completely deprived of any light? Russian researcher Sabit Abysov was first to investigate whether there were any signs of life in the core samples drilled from the ice above Lake Vostok.2 He found an impressive number of bacteria there. “However, in the 1980s, not much importance was given to the possibility of contamination,” explains Philippe Normand, from the Laboratory for Microbial Ecology in Lyon.3 In fact, it turned out that these bacteria actually came from the kerosene used to prevent the borehole from getting blocked up too quickly. “Subsequent studies showed that the cores didn't actually contain any indigenous organisms.” But this didn't deter a team of Russian and French scientists, led by Professor Michel Blot.4 They began an inventory of bacteria present in the latest core samples from Vostok, samples drilled at depths of over 3500 meters in so-called refrozen ice, formed from the lake's water. Some of the most subtle techniques known to biology, and especially the polymerase chain reaction (PCR)5, were applied to the ice core. And it finally paid off. “Our research, performed in a clean room,6 revealed the presence of Hydrogenophilus thermoluteolus, a bacterium which feeds off hydrogen,” explains Normand, who has continued Blot's research. This was quite a surprise, especially when you realize that this type of organism only lives in certain hydrothermal vents in Japan, Yellowstone (US), and Australia. So could there be hot vents of this kind beneath Lake Vostok? “It is possible that cracks in the basement rocks could let water seep down into the crust and heat up, before finally gushing back up into the lake, as is the case with hydrothermal vents on the ocean floor,” Normand indicates. The presence of this bacterium in Lake Vostok raises a number of questions. How closely is it related to the Japanese, American, and Australian bacteria? What then might be their common ancestor? And if this bacterium has managed to survive in the lake, are there any other microorganisms there? Or predators? To answer these questions, it will be necessary to drill even deeper and, perhaps, reach the lake itself, something that many people object to, given the high risk of human contamination of this perfectly unsullied environment.

 

Life In Extreme Environments

Despite the ice and the freezing cold, the poles are home to many life forms. In fact, they're positively teeming with life. The remote French Southern and Antarctic Territories (which include Adélie Land and the islands of Crozet, Amsterdam, Saint-Paul, and Kerguelen) are a genuine haven for wildlife, where animals, frequently the only ones of their kind in the world, have developed novel physiological and behavioral responses to the extreme climate conditions.

 

pingoins

© Y. Handrich/CNRS - IPHC – CEPE

King penguins on parade on Possession Island (Crozet Archipelago). Potential partners can evaluate each other's health by the intensity of the UV light reflected by their beak's horn (in orange). This is due to closely apposed membranes which form photonic crystals reflecting in the UV range.


 

The undisputed champions when it comes to adapting to the cold are Emperor and King penguins, which are the object of intensive study. Researchers at IPHC7 in Strasbourg have discovered a particularly interesting small protein in the King penguin, called spheniscin (from the Latin word for penguin, Spheniscus) which is produced by the male's stomach at the end of the egg incubation period. “We have shown that the equivalent synthetic peptide has antibacterial and antifungal properties,” explains Yvon Le Maho, from IPHC. This could partly explain why food can remain intact in the male's stomach during the final two or three weeks of incubation of the egg. He can thus feed the newly-hatched bird by regurgitation in the absence of the female.

Another surprising–and recently discovered– fact about Emperor and King penguins is that their beaks can reflect ultraviolet light due to the distinctive spatial arrangement of the folded membranes of specialized keratinocytes aligned on their surface. This produces visual signals that enable penguins to choose their mates. “For a future mate, strong signals mean a healthy animal, and therefore one that's good at catching fish and providing the young with food,” explains Pierre Jouventin, from CEFE in Montpellier.8 The birds in the region can also recognize each other's calls (the Emperor penguin memorizes calls from its partner and offspring), or even one another's odor, a phenomenon still poorly understood in birds. For instance, researchers at CEFE have shown that petrels, sea birds one-third of whose brain is taken up by the olfactory bulb, use their highly developed sense of smell to find their nest, mate, and offspring.

 

poiscaille

© ICOTA

The Antarctic notothenioid fish Notothenia coriiceps, which is abundant in Terre Adélie.


Animal adaptation is also visible in the Southern Ocean. For example, the 122 species of the notothenioid family, fish that are particularly resistant to the cold, have invaded practically all ecological niches. They can be found on the ocean floor, in the intermediate (pelagic) layers, or immediately beneath the surface of the ice (the cryopelagic layer). Some species have even lost their red blood cells, letting them survive simply on the high oxygen content and viscosity of the cold Antarctic waters. “These fish have an especially well-developed vascular system, an end result of the nitric oxide present in their blood, itself due to the lack of hemoglobin,” explains researcher Guillaume Lecointre.9 These “ice fish,” will be carefully scrutinized during an international expedition studying the seas around Adélie Land in 2007 and 2008. No less than three ships will be used for this scientific mission. “Bottom-dwelling fish will be studied on an Australian ship, pelagic species on-board a Japanese ship, and hydrology and plankton on the French ship Astrolabe,” adds researcher Catherine Ozouf.10

Since all these species are adapted to their current environment, how will they react to global warming? “The ice-covered continent and the ice-cold surrounding ocean act as a real containment area for its inhabitants,” explains biologist Bruno David, director of the Biogeosciences Laboratory in Dijon.11 “The wildlife is adapted to the cold, and there won't be anywhere colder for them to go if they can't withstand warmer conditions. They will be forced to acclimatize, evolve, or disappear.” To get a better understanding of this phenomenon, David–an ex-paleontologist–and his colleagues have embarked on the study of a “model” animal, the sea urchin. Their research is part of Bianzo II, a program spearheaded and funded by Belgium. Their aim is to establish a predictive model of species migration or extinction. The area studied will extend as far as South America, with hope of “identifying those species which might migrate towards Antarctica as a result of climate change,” David explains. At the same time, a detailed analysis of the physiology and adaptability of these animals will be carried out. One group is of particular interest to the researchers: the cidarids. “Of the 80 species of sea urchin which inhabit the Antarctic, 20 or so belong to this group,” David points out. They are quite unusual in that they live in symbiosis with many other organisms that settle on their spines. How will these symbionts react to climate change? Will they adapt as well, or will they abandon their hosts? Just a few of the questions that the researchers will try to answer with the help of the animals they collect this winter on the German ship Polarstern.

 

Map

© Duclaux, Thèse Saint Etienne 2007

(CLICK TO ENLARGE)
Map of the ages of the bedrock of Terre Adélie showing the two major periods of structuring of the crust, 2.5 and 1.7 billion years ago.


 

A Geological Paradise

There is also much to learn about the underlying rocks of the Arctic and Antarctic regions. Since the early 1990s, French and Australian scientists have been carrying out a major scientific program in the Antarctic, in Adélie Land, and George V Land (between 135 and 145°E). “Earlier exploration dates back directly to the Australian expedition led by Sir Douglas Mawson (1911-1914) and to short missions by French polar expeditions around 1950 and 1960,” explains René-Pierre Ménot, from the Magma and Volcano Laboratory.12

Detailed geological mapping and dating has been carried out on a narrow coastal strip 250 kilometers long, together with several forays on a handful of nunataks (“isolated peaks” in the Inuktitut language) which emerge above the ice sheet up to 70 kilometers inland. Surprisingly, these rocks are between 1.5 and 2.5 billion years old and have not been subject to any major geological event since then. They are comparable to the rocks of the Southern Australian coastal margin, from which they were separated when the Southern Ocean was opened up 90 million years ago. They can thus provide valuable information about the supercontinent Rodinia, which unified most of the continental crust a billion years ago. “At that time, the planet was hotter and its outermost part, the lithosphere, wasn't as thick and rigid as it is today,” Ménot explains. “Lithospheric processes were completely different then.” Intensive analysis is being carried out on the rocks and minerals of the lithosphere to uncover the nature of these processes, and determine the physical conditions under which it formed. This should allow introduction of new thermodynamic constraints to the current numerical models. “Modeling the early Earth isn't an easy task, because we still have very little data available to make the models more accurate,” Ménot admits. New series of measurements, using indirect observation methods like gravity and magnetism, will be carried out jointly with Italian and German teams, and with the backing of the Institut Paul-Émile Victor. The aim is to “visualize” the rock formations through the overlying ice and thus better understand the processes at work when the Earth was younger.

But this type of research is not confined to Antarctica. Geophysicists are also scrutinizing the depths of the Earth near the North Pole, particularly in Iceland. The island is less than 20 million years old, and is the only place on Earth where scientists can study three geological phenomena on one single location: the remains of an ice cap, a hot spot (a zone where large quantities of magma from the mantle rise to the surface), and the mid-oceanic ridge which separates the Eurasian and North American tectonic plates. “This is an exceptional combination,” explains Françoise Bergerat from the Tectonics Laboratory in Paris.13 Iceland is subject to complex movements: vertical ones caused by the exceptional quantities of rising magma and by the melting of ice, and horizontal ones, due in particular to the continuous spreading on the Icelandic rift.”14

With twenty years' experience of working together, the Icelandic and French researchers are keen to get an even more accurate picture of the interactions between all these phenomena. For this, they will be relying on observations of structure, geomorphology, and sedimentology in the field, as well as analyses of deformations recorded by Iceland's permanent networks of GPS and seismic stations. “Iceland has set up the most advanced seismic network in the world,” says Bergerat. “Since there is very little 'background noise' in Iceland, their highly sensitive stations are able to record almost imperceptible micro-earthquakes.” The program, currently funded by the Institut Paul-Émile Victor,  involves researchers from several universities15 and is due to run for a further two years.

 

Fabrice Demarthon

 

  

Half a Century of Ice Core Drilling Programs

bonnet

© L. Médard/CNRS Photothèque

Ice core drawn from the Vostok site containing bedrock. Left: case for storing the ice cores.


The Americans were the first to carry out drilling operations in Antarctica, in the 1960s. In 1968, they drilled an ice core 2000 meters deep at the Byrd base. Shortly afterwards, the Russians initiated their own drilling program at the Vostok base. This drilling operation (which the French joined in 1982 and the Americans in 1989) had reached a depth of over 3600 meters by 1998, and was close to the huge Vostok subglacial lake. It has produced a core sample giving a record of the climate stretching back 400,000 years.

Since 1995, ten countries have joined forces in the EPICA project to begin a drilling program at Dome C. Although reaching a shallower depth of 3260 meters, it has provided ice core samples that stretch even further back into the past, to approximately 800,000 years ago. This is because the time period covered by the ice core record doesn't just depend on the depth of the borehole, but also on the snow precipitation and flow rate. The flow rate is itself linked to the temperature profile of the ice, Greenland, meanwhile, has seen the start of several major drilling programs: GRIP and GISP2, which were carried out at the beginning of the 1990s, followed by North GRIP, from 1996 to 2004. The time period covered by these ice core records is around 125,000 years.

S.E.

 

Notes :

1. Laboratoire de glaciologie et géophysique de l'environnement (CNRS / Université Grenoble-I joint lab).
2. The Vostok drilling station was set up by the Soviet Union in 1957. At the time, they were unaware of sitting above a genuine lake. The existence of the lake was only suspected at the beginning of the 1970s. Drilling began around the same time, culminating in 1999 by reaching a depth of 3623 meters.
3. CNRS / Université Lyon-I / Inra joint lab.
4. Laboratory for Plasticity and Expression of Microbial Genomes, Université de Grenoble.
5. A technique which makes a large number of copies of a piece of isolated DNA so that it can be sequenced.
6. Centre de génétique moléculaire et cellulaire (CNRS / Université Lyon-I joint lab).
7. Institut pluridisciplinaire Hubert Curien (CNRS / Université Strasbourg-I joint lab).
8. Centre d'écologie fonctionnelle et évolutive (CNRS / Universités Montpellier-I, II and III / Cirad / Ensa / EPHE Paris joint lab).
9. Laboratoire “Systématique, adaptation, evolution” (CNRS / Université Paris-VI / MNHN / IRD / ENS Paris joint lab).
10. Laboratoire “Écologie–biodiversité, évolution, environnement” (CNRS / Universités Paris-VI, VII and XII / ENS Cachan / MNHN / IRD joint lab).
11. CNRS / Université de Dijon joint lab.
12. Laboratoire “Magmas et Volcans” (CNRS / IRD / Universités Clermont-Ferrand and St-Étienne joint lab).
13. CNRS / Université Paris-VI / Université Cergy Pontoise joint lab.
14. Rift: continental or oceanic crust sunk between two major normal faults.
15. Universités Paris-VI, de Savoie, Rennes-I and Lille-I,

Contacts :

> Catherine Ritz,
catritz@lgge.obs.ujf-grenoble.fr
> Philippe Normand,
normand@biomserv.univ-lyon1.fr
> Catherine Ozouf,
ozouf@mnhn.fr
> Guillaume Lecointre,
lecointr@mnhn.fr
> Bruno David,
bruno.david@u-bourgogne.fr
> Yvon Le Maho,
yvon.lemaho@c-strasbourg.fr
> Pierre Jouventin,
pierre.jouventin@cefe.cnrs.fr
> Françoise Bergerat,
francoise.bergerat@lgs.jussieu.fr
> René-Pierre Ménot,
rene.pierre.menot@univ-st-etienne.fr


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