The iceberg watch

Navigators in stressful icy areas

From VovoOceanRace by Agathe Armand

Icebergs.

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.

Links :

• GeoGarage blog : Vendee Globe : Cape Horn and ice danger / Vendee Globe : stressful areas
• BYU : Current Antarctic large iceberg positions derived from ASCAT
• CLS : Vigisat
  

Where is Point Nemo?

Point Nemo is the location in the ocean that is farthest from land.

You can't get farther away from land than 'Point Nemo.' 

From NOAA

Want to get away from it all?
You can't do better than a point in the Pacific Ocean popularly known as 'Point Nemo,' named after the famous submarine sailor from Jules Verne's Captain Nemo (Twenty Thousand Leagues Under the Sea).

 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).

Mollweide projection.

 Nemo point with the Marine GeoGarage

(-48.958812, -123.434678)

The oceanic pole of inaccessibility (48°52.6′S 123°23.6′W) is the place in the ocean that is farthest from land.

It lies in the South Pacific Ocean, 2,688 km (1,670 mi) from the nearest lands: Ducie Island (part of the Pitcairn Islands) in the north, Motu Nui (part of the Easter Islands) in the northeast, and Maher Island (near the larger Siple Island, off the coast of Marie Byrd Land, Antarctica) in the south. Chatham Island lies farther west, and Southern Chile in the east.
- see Wikipedia Pole of inaccessibility -

 zoom on Nemo Point watermarked on Google Earth

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′S 150°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).

Links :

• GeoGarage blog : The longest straight line you can sail on Earth ? 
  

Image of the week : Swirls of color in the Yellow Sea

NASA, acquired February 24, 2015

From NASA

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.

 Yellow Sea with the Marine GeoGarage (NGA chart)

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.

US NOAA update with the Marine GeoGarage

As our public viewer is not yet available
(currently under construction, upgrading to a new viewer
as Google Maps API v2 is officially no more supported),
this info is primarily intended to our universal mobile application users
(Marine US iPhone-iPad on the Apple Store &
Weather 4D Android -App-in- on the PlayStore)
and also to our B2B customers which use our nautical charts layers
in their own webmapping applications through our GeoGarage API. 

 NOAA raster chart coverage

16 charts have been updated in the Marine GeoGarage

(NOAA update March 2015, released March 18, 2015)

• 12243 ed15 York River Yorktown to West Point
• 12244 ed15 Pamunkey And Mattaponi Rivers
• 16206 ed9 Nome Hbr. and approaches. Norton Sound;Nome Harbor
• 16430 ed7 Attu Island Theodore Pt. to Cape Wrangell
• 16474 ed9 Bay of Islands;Aranne Channel;Hell Gate
• 16476 ed11 Sweeper Cove. Finger and Scabbard Bays
• 16484 ed8 Atka Island to Chugul Island Atka Island
• 16487 ed7 Korovin Bay to Wall Bay-Atka Island;Martin Harbor
• 16516 ed8 Chernofski Harbor
• 16521 ed7 Unalaska Island Protection Bay to Eagle Bay
• 16603 ed9 Kukak Bay. Alaska Peninsula
• 16706 ed11 Passage Canal incl. Port of Whittier;Port of Whittier
• 16711 ed3 Port Wells. including College Fiord and Harriman Fiord
• 17323 ed13 Salisbury Sound. Peril Strait and Hoonah Sound
• 17330 ed10 West Coast of Baranof Island Cape Ommaney to Byron Bay
• 17381 ed11 Reb Bay. Prince of Wales Island
• 17384 ed10 Wrangell Harbor and approaches;Wrangell Harbor
• 17422 ed10 Behm Canal-western part;Yes Bay
• 11489 ed40 Intracoastal Waterway St. Simons Sound to Tolmato River
• 11490 ed21 Approaches to St. Johns River;St. Johns River Entrance
• 11491 ed39 St. Johns River-Atlantic Ocean to Jacksonville

Today 1026 NOAA raster charts (2236 including sub-charts) are included in the Marine GeoGarage viewer (see PDFs files)


How do you know if you need a new nautical chart?
See the changes in new chart editions.
NOAA chart dates of recent Print on Demand editions

Note : NOAA updates their nautical charts with corrections published in:

• U.S. Coast Guard Local Notices to Mariners (LNMs),
• National Geospatial-Intelligence Agency Notices to Mariners (NMs), and
• Canadian Coast Guard Notices to Mariners (CNMs)

While information provided by this Web site is intended to provide updated nautical charts, it must not be used as a substitute for the United States Coast Guard, National Geospatial-Intelligence Agency, or Canadian Coast Guard Notice to Mariner publications

Please visit the NOAA's chart update service for more info or the online chart catalog

Global warming is now slowing down the circulation of the oceans — with potentially dire consequences

The Atlantic circulation (AMOC) as part of the global overturning circulation of the oceans

in an animation from NASA, showing what happens globally to create the large, slow current called the thermohaline circulation.

From Washington Post by Chris Mooney 

Welcome to this week’s installment of “Don’t Mess with Geophysics.”
Last week, we learned about the possible destabilization of the Totten Glacier of East Antarctica, which could unleash over 11 feet of sea level rise in coming centuries.

And now this week brings news of another potential mega-scale perturbation.
According to a new study just out in Nature Climate Change by Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research and a group of co-authors, we’re now seeing a slowdown of the great ocean circulation that, among other planetary roles, helps to partly drive the Gulf Stream off the U.S. east coast.
The consequences could be dire – including significant extra sea level rise for coastal cities like New York and Boston.

 The Gulf Stream system is one of Earth's most important heat transport systems.

Now, though, scientists have found evidence for a slowdown of this system, which could have major implications for climate.

(Photo : Gulf of Mexico, NASA/GSFC/Aqua MODIS)

A vast, powerful, and warm current, the Gulf Stream transports more water than “all the world’s rivers combined,” according to the National Oceanic and Atmospheric Administration.
But it’s just one part of a larger regional ocean conveyor system – scientists technically call it the “Atlantic meridional overturning circulation” — which, in turn, is just one part of the larger global “thermohaline” circulation (“thermohaline” conjoins terms meaning “temperature” and “salty”).
For the whole system, a key driver occurs in the North Atlantic ocean.
Here, the warm Gulf Stream flows northward into cooler waters and splits into what is called the North Atlantic Current.
This stream flows still further toward northern latitudes — until it reaches points where colder, salty water sinks due to its greater density, and then travels back southward at depth.

This “overturning circulation” plays a major role in the climate because it brings warm water northward, thereby helping to warm Europe’s climate, and also sends cold water back towards the tropics.
Here’s a helpful visualization, from Rahmstorf and the Potsdam Institute, of how it works:

 Graph of the Atlantic Meridional Overturning Circulation by Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research.

Red colors are surface currents, blue colors are below the surface. “NADW” stands for North Atlantic Deep Water.

And here’s a wonderful video from NASA that visualizes the thermohaline circulation for the entire globe. Rahmstorf also has a blog post up at RealClimate.org explaining his research.

The day after fiction

The system above has a key vulnerability.
What keeps everything churning in the North Atlantic is the fact that cold salt water is more dense than warm water — so it sinks.
However, if too much ice melts in the region — from, say Greenland — a freshening of the cold salt water could occur.
If the water is less salty it will also be less dense, reducing its tendency to sink below the surface.

This could slow or even eventually shut down the circulation.
In the scientifically panned 2004 blockbuster film “The Day After Tomorrow,” it is precisely such a shutdown that triggers a New Ice Age, and utter global disaster and chaos.
That’s not going to happen, say scientists.
Not remotely.
Nonetheless, the new research finds that global warming does indeed seem to be slowing down the circulation. And while hardly catastrophic, that can’t be good news.
Among the very real effects, notes the Potsdam Institute’s Rahmstorf, could be a possible increase in U.S. sea level if the whole circulation were to break down — which would be seriously bad news for cities like New York and Boston.

 As more and more fresh water is released into the ocean by melting glaciers, the Atlantic's most powerful current, the Gulf Stream, is likely to slow down even more

The study uses a reconstruction of sea surface temperatures in the North Atlantic to find that starting in around 1970 or 1975, the overturning circulation started to weaken — an event likely triggered by an unusual amount of sea ice traveling out of the Arctic ocean, melting, and causing freshening.
The circulation then started to recover in the 1990s, but  “it seems this was only a temporary recovery, and now it’s actually further weakened,” says Rahmstorf.

 Despite all the warming that’s taken place since 1970, one little blip of the North Atlantic (shown here in green) has begun to actually cool.

The hypothesized reason for further declines presented by the paper is that the massive Greenland ice sheet may now be losing enough freshwater due to melting to weaken the circulation.
And indeed, it appears that a particular ocean region of the North Atlantic south of Greenland and between Canada and Britain is becoming colder — an indicator of less northward heat transport.

Rahmstorf points to a recent release by the National Climatic Data Center of the National Oceanic and Atmospheric Administration, finding that the winter of December 2014 through February 2015 was the warmest on record for the globe as a whole.
However, there were several anomalies — not just a cold winter for the eastern U.S., but also record cold temperatures in the middle of the North Atlantic:

 According to the National Climatic Data Center, the world just saw its warmest winter ever…except for in one spot in the north Atlantic ocean (the deepest blue color above), which set a record for cold. Which is not good. (NCDC)

“These new NOAA data got me quite worried because they indicate that this partial recovery that we describe in the paper was only temporary, and the circulation is on the way down again,” says Rahmstorf.

So far, the study finds, we’re looking at a circulation that’s about 15 to 20 percent weaker.
That may not sound like much, but the paper suggests a weakening this strong has not happened at any time since the year 900. Moreover, this is already more weakening than scientifically expected — and could be the beginning of a further slowdown that could have great consequences.
The U.N.’s Intergovernmental Panel on Climate Change, in 2013, said it was “very likely” that the Atlantic overturning circulation would weaken over the course of this century, but gave a gigantic range of from 1 to 54 percent, with best estimates at 11 and 34 percent.
We’re already in that window, suggests the new study, and it’s only 2015.
So what would happen if the circulation weakens even more substantially or even shuts down?

Why the U.S. suffers from a Gulf Stream system slowdown

One thing that will not happen from a shutdown of the circulation is a sudden, dramatic freezing of Europe.
It will certainly cool, relative to a world in which the circulation remains robust — but that will be offset by rising average temperatures due to global warming, says Rahmstorf.
The “Day After Tomorrow” scenario will not come to pass.

However, there are many other effects, ranging from dramatic impacts on fisheries to, perhaps most troubling of all, the potential for extra sea level rise in the North Atlantic region.
That may sound surprising, but here’s how it works.
We’re starting out from a situation in which sea level is “anomalously low” off the U.S. east coast due to the motion of the Gulf Stream.
This is for at least two reasons.
First, explains Rahmstorf’s co-author Michael Mann of Penn State University, there’s the matter of temperature contrast: Waters to the right or east of the Gulf Stream, in the direction of Europe, are warmer than those on its left or west.
Warm water expands and takes up more area than denser cold water, so sea level is also higher to the right side of the current, and lower off our coast.
“So if you weaken the ‘Gulf Stream’ and weaken that temperature contrast…sea level off the U.S. east coast will actually rise!” explains Mann by e-mail.

But there’s another factor, too, involving what is called the “geostrophic balance of forces” in the ocean.
This gets wonky, but the bottom line result is that “sea surface slope perpendicular to any current flow, like the Gulf Stream, has a higher sea level on its right hand side, and the lower sea level on the left hand slide,” says Rahmstorf.
(This would only be true in the northern hemisphere; in the southern it would be the opposite.)

 Sea surface temperature anomaly on 20 March 2015.

Note that this is relative to a baseline 1979-2000, which is already a cold period in the subpolar Atlantic.

Source: Climate Reanalyzer.

We’re on the left hand side of the Gulf Stream.
So weaken the flow, and you also raise the sea level.
(For further explanation, see here and here.)
Indeed, researchers recently found a sudden, 4-inch sea level rise of the U.S. East Coast in 2009 and 2010, which they attributed to a slowdown of the Atlantic overturning circulation.
Rahmstorf says that “for a big breakdown of the circulation, [sea level rise] could amount to one meter, in addition to the global sea level rise that we’re expecting from global warming.”
Shutting down the circulation would also almost certainly have effects on global weather — changing around major planetary heat transport processes tends to do that — though scientists don’t know yet what those would look like.

So in sum: It appears that we’ve just seen yet another surprise from the climate system — and yet another process, like the melting of Antarctica, that seems to be happening faster than previously expected.
And indeed, much like with that  melting, the upshot if the trend continues is an especially bad sea level rise for the United States — the country more responsible than any other on Earth for the global warming that we’re currently experiencing.

Links :

• Climate Central : Atlantic Circulation Weaker Than In Last Thousand Years