00:00These dark spots on the ice cap of Greenland are not simple imperfections.
00:05Every summer, the ice, usually of a bright white color,
00:09turns gray in some areas.
00:11This dark area, which remained a mystery for a long time,
00:14revealed its secret when it was discovered that this strange transformation
00:18was due to the appearance of algae with red, green and brown shades.
00:22What is particularly worrying is that this algae proliferation does not stop growing.
00:28The dark area darkens more,
00:30and the appearance of disturbing microbes could soon follow.
00:34It is now imperative that the rest of the world is worried about it.
00:38The ice cap of Greenland, a real ice giant,
00:41covers about 80% of the island
00:44and houses nearly 8% of the world's freshwater reserves in the form of ice.
00:48For most of the year, it has been an immaculate vast area.
00:53However, at the arrival of summer, when temperatures rise,
00:57changes begin to appear.
00:59The melting of the ice reveals rocky outcrops on the coast,
01:03while as it progresses deeper into the interior of the land,
01:07the white ice, once uniform, becomes darker.
01:10This area, about 400 km long and 100 km wide at its widest point,
01:16presents this intriguing phenomenon for two main reasons.
01:19The first reason is related to black carbon.
01:22Like the dust that accumulates on your furniture,
01:25the ice cap of Greenland undergoes a similar process.
01:28The wind transports dust particles and sweat to these icy regions.
01:33But unlike your furniture,
01:35it is impossible to eliminate this accumulation with a simple blow of a rag.
01:38On Greenland's ice, this mixture of fine particles has been around for millennia.
01:43Thus, this dark area is covered by a thin layer of dust accumulated over time.
01:48In 2014, researchers studied this deposit
01:52and found that the darkest regions of the ice contained a high concentration of black carbon.
01:57This black carbon did not form by chance.
02:00In reality, it is mainly a result of the smoke
02:03generated by former forest fires in northern Canada and Alaska.
02:07As we can imagine, black carbon being dark in color,
02:11it causes a darkening of the surface of the ice.
02:15The second major cause of the summer transformation of the ice cap
02:19concerns the algae mentioned earlier.
02:21These are mainly two species,
02:23Ancylonema alaskana and Ancylonema nordenskjöldi.
02:28These algae are particularly fond of cold water environments.
02:32During the winter, they enter a state of dormancy
02:35and remain deeply buried in the ice,
02:37waiting for favorable conditions to reappear.
02:40When spring arrives,
02:42these algae begin to gradually rise to the surface.
02:45As summer approaches,
02:47they are ready to bloom
02:49and take advantage of almost 24 hours of sunlight every day
02:52to photosynthesize and grow.
02:55In normal times, these algae display a green tint.
02:58But once exposed to the sun,
03:00they turn brown,
03:02which is a natural protection against harmful ultraviolet rays.
03:06This change in color also contributes to the darkening of the ice of Greenland.
03:11Until now, this behavior was normal.
03:14What is really worrying
03:16is that the flow of algae increases in size every year.
03:20This phenomenon is explained by the fact that it prospers thanks to phosphorus,
03:24an abundant nutrient in this region,
03:27coming from a mineral called hydroxyapatite.
03:30The latter is found in a rock
03:32that decomposes into tiny particles of dust,
03:34transported by the wind through the ice.
03:37With global warming,
03:39the rocks become drier
03:41and stronger winds raise more dust.
03:44This increase leads to more phosphorus,
03:47thus favoring an increased growth of algae.
03:50Do you get it?
03:51It is a cycle that increases year after year.
03:54The study of this phenomenon is therefore essential
03:56to understand why the dark zone continues to expand.
03:59Between 2000 and 2012,
04:01its surface increased by 12%.
04:04You may be wondering about the gravity of this situation.
04:07After all, isn't it just the ice that becomes darker?
04:11Well, not quite.
04:13Think of your aversion to wearing black clothes
04:16on a hot and sunny day.
04:19They absorb heat and suffocate you.
04:22This is explained by the fact that dark surfaces
04:25capture more sunlight.
04:28The same goes for ice.
04:30Together, dust, black carbon and algae flora
04:34are responsible for about 70% of the variability of albedo
04:38on the ice cap of Greenland.
04:40Albedo is a technical term
04:42that refers to the ability of a surface to reflect light.
04:45If we compare two surfaces,
04:47one white and bright,
04:49the other dark and rough,
04:51the white surface will reflect a large amount of light and heat,
04:54which will give it a high albedo.
04:57Conversely, the dark surface will absorb more light and heat,
05:01resulting in a low albedo.
05:03During the summer, the ice cap of Greenland
05:06suffers a decrease in its albedo.
05:08This means that the ice captures more sunlight,
05:11and when it absorbs more,
05:13it melts faster than expected.
05:15This is why it is crucial to understand the dynamics
05:18within the dark zone.
05:20This allows us to predict the speed
05:22of the melting of the ice cap of Greenland
05:24and its repercussions on the rest of the world.
05:27The ice cap of Greenland
05:29is the second largest in the world,
05:31covering an area equivalent
05:33to that of all the American lands
05:35located east of the Mississippi River.
05:37This massive mass of ice
05:39has an average thickness of 2.3 km.
05:42But unfortunately,
05:44the rate at which this ice melts has exploded.
05:47In the 1990s,
05:49Greenland lost about 25 billion tons of ice per year.
05:53Today, this figure has risen to about 234 billion,
05:57which is nearly ten times more than the melted ice every year.
06:00According to NASA,
06:02if the entire ice cap of Greenland
06:04were to melt,
06:06it would lead to an elevation of the sea level
06:08of about 7.40 meters.
06:10This could have catastrophic consequences
06:12for countries and coastal cities
06:14around the world.
06:16The Netherlands could be completely submerged,
06:18the Bahamas could be almost completely destroyed,
06:21and many islands in the Philippines
06:23could disappear.
06:25All this may seem like a distant reality,
06:27and it is true that most scientists
06:29estimate that it would take several hundred,
06:32even thousands of years
06:34for the ice cap to melt completely.
06:37However, it is important to understand
06:39that Greenland has not always been covered
06:41by this thick layer of ice.
06:43Recently, researchers have carefully examined
06:45the sediments collected at the bottom
06:47of an ice core more than 3 km deep,
06:50extracted from the center of Greenland.
06:52They discovered that the soil contained
06:54traces of soil wood,
06:56parts of insects,
06:57mushrooms,
06:58and even poppy seeds.
07:00Thus, these fossils constitute
07:02our first direct evidence
07:04that the Greenland ice cap
07:06melted in a recent geological past,
07:08about 400,000 years ago.
07:10At that time, Greenland was covered
07:12by a greenish tundra landscape,
07:14populated by insects and plants.
07:16This discovery is both fascinating
07:18and disturbing,
07:20because it indicates that the ice cap
07:22has collapsed in the past
07:24and could be more fragile
07:26than what scientists initially thought.
07:28There is also another concern.
07:30A recent study has taken
07:32meltwater from different places
07:34in the Greenland ice cap
07:36and found that these samples
07:38contained hundreds of thousands of microbes.
07:40The concern lies in the fact
07:42that these microbes could be released
07:44into the ocean in the future.
07:46In addition, some studies already suggest
07:48that the areas close to the important
07:50flow of meltwater
07:52present an increased risk
07:54of transmission of viruses to new hosts,
07:56including animals to humans.
07:58Although experts estimate
08:00that the probability that a virus
08:02threatening humanity
08:04comes from glaciers is very low,
08:06it is not zero.
08:08In fact, we have little knowledge
08:10of the thousands of microbial species
08:12living on the surface of the ice.
08:14And there is simply not enough data
08:16to fully assess the dangers
08:18that these organisms could represent.
08:20All this may seem worrying,
08:22but there is no need to panic for the moment.
08:24There is still a lot to understand
08:26about the meltwater that darkens
08:28the Greenland ice cap.
08:30We need more precise measurements
08:32of the relative abundance of dust,
08:34algae and black carbon,
08:36as well as a better understanding
08:38of the potential impact
08:40of these microbes on our lives.
08:42The more we acquire knowledge,
08:44the better we will be able to anticipate
08:46the events to come
08:48and prepare ourselves accordingly.
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