Drifting blocks of ice detached from the Antarctic glaciers, frozen cubes of a couple of metres – or even tens of kilometres.
They are a polar symbol, an environmental marker – and a huge hazard for the Volvo Ocean Race teams, sailing across the Southern Ocean from Auckland to Itajaí.
Abu Dhabi Race Team talk us through the iceberg updates they receive on the boat
and Phil Harmer's less technical approach to iceberg detection.
“So far, we’ve detected about 20 of them for the race,” says Franck Mercier of CLS.
The French company has been contracted by the organisers to deliver ice analysis and data that Alicante Race Control then uses to place the ice limits* for Leg 5.
So how exactly do you find an iceberg?
Well, it’s a tiny bit technical, and CLS has to use a lot of different data and up to four satellites for that.
First, the sea temperature.
The colder the water, the more likely they are to find drifting ice.
Currents have an effect, too, pushing it all around the Southern Ocean.
Secondly, the historical data CLS has gathered these past few years – they’ve been assisting several sailing races including the Vendée Globe and the Barcelona World Race.
And finally, the radar techniques.
Now we’re talking.
The brown and red squares are potential icy areas; the green and blue stars are detected icebergs.
CLS is working with space agencies, using their satellites to scan the sea surface in search of ice. They use altimetry techniques to draft a first exclusion zone, and SAR imagery to target the areas identified as potentially dangerous and scan them thoroughly.
Altimetry only spots the biggest icebergs, that is, ones bigger than
300m.
SAR imagery is much more precise, every standard image covering a
500km x 500km area.
SAR satellite sensors can detect smaller bits of ice
– up to 50m in the case of a high-resolution picture. That’s as
accurate as it gets, and it’s pretty expensive.
“Remember it’s not an exact science,” adds Franck, a French
researcher who knows the icebergs by name.
“We’re contributing to
decrease the risks, but we don’t suppress it.
“The idea is to detect the biggest icebergs to anticipate the
position of the smaller ones, which are still very dangerous for the
boats, all of this part of the ocean dynamic.”
Their biggest catch this time around?
A 1km long iceberg, first
spotted because of a cold water plume, then “photographed” three times.
Franck and his colleagues have done the calculations – it’s 150m
wide, 300m high, underwater part included, and it weighs 25 millions
tons, the equivalent of 50 super tankers.
And the current was pushing it north at 1.1 knot, straight towards the fleet’s predicted position.
So they’ve warned Race Management, who moved the ice limits north.
They can change one of the points of this virtual line no later than 30
degrees of longitude before the first boat reaches it.
“There’s definitely plenty of ice around,” comments Simon Fisher. Picture : Guo Chuan / Green Dragon Racing
Abu Dhabi Ocean Racing’s navigator is sat at the chart table and
looks at a satellite picture of the area, wearing a nervous grin.
His
boat is currently 2,000 nautical miles away from land – they simply
cannot afford to run into drifting ice.
In 2001-02, News Corp sailed through ice and it's not something the sailors recall fondly.
“All the blue dots are icebergs that have been picked up by the
various radars," adds Simon.
"So far they’re doing a good job at keeping
us out of it.”
It’s a matter of safety – but it goes way beyond that.
“There is very little scientific literature about Antarctic drifting
icebergs.
The existing data only goes back 10 years or so, when sailing
races took an interest.
“Because there is no record yet, we cannot really link the ice
activity in the area to the global warming theme.
We see more of these
icebergs, that’s true, but that’s also due to our improved techniques.
“The icebergs of the northern hemisphere come from the Artic polar
icecap and are studied more. They’re directly linked to the climate
change - and the quantity of sea ice decreases indeed.
“But in Antarctica, there is little change. In fact, the southern ice
field tends to increase in winter… it could be one of the consequences
of the global warming that causes an increase in the precipitations.
These are only hypotheses.”
(picture courtesy of volodiaja)
* Ice limits:A virtual
line the fleet must leave to starboard, it can be modified by Race
Management depending on the movement of the ice in the southern part of
the globe. An imaginary point has been placed every five degrees,
drawing a precise contour that can be adapted.
Ice limit changes on March 25:Leg 5
Sailing Instructions Amendment 8 has been posted and communicated to
the boats – waypoints 11 and 12 have been moved further north after the
detection of a new iceberg close to the ice limit line had been
confirmed, between 95 W and 100 W.
Map of distance to the nearest coastline (including oceanic islands, but not lakes) with red spots marking the poles of inaccessibility of main landmasses, Great Britain, and the Iberian Peninsula. Thin isolines are 250 km (160 mi) apart; thick lines 1,000 km (620 mi).
On Google Earth, a circle with the text "NEMO" printed next to it,
slightly darkened on the actual map itself, can be seen at this point.
By the way, in the The Mysterious Island (L'Île mystérieuse in French) another novel by Jules Verne, there is a reference to a "Lincoln Island", unknown (and fictitious) island also located in the Pacific no and so far (about 1500 Nm) NW from the Nemo Point at 34°57′S150°30′W
Map of the fictional Lincoln Island (The Mysterious Island).
This image originally drawn by Jules-Descartes Férat (1819–1889?) was originally featured
in the Hetzel edition of Mysterious Island, and has also been featured in more recent editions
(this particular instance was scanned from a recent edition).
Water covers 71 percent of Earth’s surface, giving rise to the
nickname “the Blue Marble” or “the Blue Planet.”
Satellites that observe
ocean color, however, show that it’s not that simple.
Materials in the
water—living or otherwise—are often stirred and mixed until the surface
swirls with hints of blue, green, tan, white, and brown.
One area where this is extremely apparent is the Yellow Sea, pictured here in an image acquired on February 24, 2015, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite.
“The region of Bohai Sea, Yellow Sea, and East China is one of the
most turbid and dynamic ocean areas in the world,” said ocean color
expert Menghua Wang of the National Oceanic and Atmospheric Administration.
In the image, the brown area along China’s Subei Shoal is turbid
water commonly seen in coastal regions.
According to Wang, shallow water
depths, tidal currents, and strong winter winds likely contributed to
the mixing of sediment through the water.
Some of the swirls in the image might be due to the Yellow Sea Warm
Current, which intrudes into the Yellow Sea in wintertime.
This branch
of the Kuroshio Current changes the temperature of the sea surface and
brings instability that could be the cause of the relatively dark swirls
in the lower-middle part of the image.
Interpreting satellite images of ocean color can be a challenge,
especially in complex regions like the Yellow Sea.
Upcoming missions
such as the Pre-Aerosol, Clouds, and ocean Ecosystem (PACE) should help scientists to better distinguish the particles and materials in the atmosphere and ocean.
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