GeoGarage blog

Thursday, November 16, 2017

Canada CHS layer update in the GeoGarage platform

55 nautical raster charts updated & 3 new charts added

The mystery 'shadow zone' in the Pacific Ocean that hasn't moved in more than 1,500 years due to the unique shape of the seabed and its impact on currents

The 'shadow zone' covers an area 3,700 by 1,250 (6,000 by 2,000 km) where the North Pacific meets the Indian Ocean, between 0.6 and 1.5 miles (one and 2.5 km) below the surface

From DailyMail by Tim Collins

The 'shadow zone' covers an area 3,700 by 1,250 miles (6,000 by 2,000 km)
It is found between 0.6 and 1.5 miles (1 and 2.5 km) beneath the ocean's surface
Experts used computer modelling of ocean currents to work out how it formed
It revealed the shape of the ocean floor prevents any upward currents forming

In the North Pacific, way below the surface, hangs water that hasn't seen the sun in a millennium.
Tibor Kranjec / Eyeem

A mysterious patch of water in the Pacific Ocean hasn't touched the surface since the fall of the Roman empire.
Experts used computer modelling of deep sea currents to reveal the reason why the vast 'shadow zone' has remained near stagnant for around 1,500 years.
They found that it sits in between layers of water with currents driven by heat from the Earth below and whipped up by wind above.

The unique shape of the ocean floor means that upwards currents don’t reach high enough to push the layer upwards, leaving it in a no man’s land between the two.

A mysterious patch of water in the Pacific Ocean hasn't touch the surface since the fall of the Roman empire.

Experts found that it sits in between geothermal driven currents below and wind driven currents above

An international team of researchers, including the University of New South Wales (UNSW) and Stockholm University, studied the strange region, between 0.6 and 1.5 miles (one and 2.5 km) down.
It covers an area 3,700 by 1,250 miles (6,000 by 2,000 km), where the North Pacific meets the Indian Ocean.

Carbon dating has previously been used to identify its age and location, but scientists didn't understand what caused it to form.
By including the shape of the ocean floor in their simulation, the team was able to measure its impact on the movement of currents.
They found that water at the bottom of the ocean, heated by geothermal energy deep within the planet, was unable to rise above 1.5 miles (2.5km) below the surface.

C. de Lavergne et al./ Nature, 2017

Instead of travelling upwards, currents loop back on themselves horizontally, leaving the layer directly above untouched.
Dr Casimir de Lavergne, lead author from UNSW, said: 'Carbon-14 dating had already told us the most ancient water lied in the deep North Pacific.
'But until now we had struggled to understand why the very oldest waters huddle around the depth of 1.2 miles (2km).
'What we have found is that at around 1.2 miles (2km) below the surface of the Indian and Pacific Oceans there is a 'shadow zone' with barely any vertical movement that suspends ocean water in an area for centuries.'

While the researchers have unlocked one part of the puzzle, their results also have the potential to tell us much more.
The lack of contact with the ocean's surface means oxygenation of the zone is very low.
That means marine life is restricted, but not completely absent.

It is hoped that the research could help scientists better understand the capacity of the oceans to absorb heat trapped by rising greenhouse gases.
'When this isolated shadow zone traps millennia old ocean water it also traps nutrients and carbon,' added fellow author from Stockholm University, Dr Fabien Roquet.
'[These factors] have a direct impact on the capacity of the ocean to modify climate over centennial time scales.'

The full findings of the study were published in the journal Nature.

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Wednesday, November 15, 2017

Antarctica's warm underbelly revealed

Hotspots are located under West Antarctica; in contrast, the East is broadly relatively cold

From BBC by Jonathan Amos

This is the best map yet produced of the warmth coming up from the rocks underneath the Antarctic ice sheet.

Measurements suggest a hot plume of mantle rock below West Antarctica.
(Helene Seroussi et al./JGR Solid Earth; Business Insider)

This "geothermal heat flux" is key data required by scientists in order to model how the White Continent is going to react to climate change.
If the rock bed's temperature is raised, it makes it easier for the ice above to move.
And if global warming is already forcing change on the ice sheet, a higher flux could accelerate matters.

The map was made by researchers at the British Antarctic survey and is published in the journal Geophysical Research Letters.
"The heat coming from the Earth’s interior is important to understand the overall conditions that control the dynamics at the base of the ice sheet and hence the ice flow,” explained Yasmina Martos, currently affiliated to the US space agency.
"If this heat flux is elevated, the ice base can melt and produce water that acts as a sliding film.
"One result of our study is that the heat flux is higher underneath West Antarctica, where more ice is currently melting, than underneath East Antarctica.
"Even a little melting at the base helps the ice sheet to slide faster.
We also identified areas of low heat flux, which will help stabilising the ice sheet," she told BBC News.

A map of Antarctica shows where Totten Glacier is.

Map: Chad A. Greene, University of Texas Institute for Geophysics, 2017

The West contributes most to sea level rise currently, but this is a consequence of warm ocean water eroding glacier fronts - not from the interior ice sheet being melted by underlying warm rock
No-one has actually drilled through the kilometres of ice in Antarctica to take the temperature of the bed.

Instead, the BAS team inferred the likely warmth of rocks from their magnetism.
This property can be sensed by instruments flown across the surface of the ice sheet by planes.

What happens next is a smart calculation.
Scientists know the temperature (580C) at which hot minerals lose their magnetism, so if they can gauge how close to the rock-ice interface this occurring then they have a means of estimating the heat flux.
The new map is said to represent a 30-50% improvement on previous efforts.

Surface wind causes warm water to upwell at the continental shelf break, the warm water melts Totten Ice Shelf from below, and the glacier responds by speeding up.

Chad A. Greene, University of Texas Institute for Geophysics, 2017

It supports - but with far more detail - the established idea that East and West Antarctica are very different provinces.
The East is a giant chunk of old, cold continental crust.
The West, however, underwent recent rifting in the Cretaceous (100 million years ago) that has pulled it apart.
"This rifting has thinned the crust and brought hot material from deep down in the Earth - from hundreds of km down - to within 100km or so, or even maybe less, of the rock surface," said co-author Tom Jordan.
"It confirms what you would expect from the sparse, exposed geology in West Antarctica where we have volcanoes."

One of the great advances in polar science in the past decade is the recognition that there is a really extensive hydrological network under the ice sheet.
Rivers of water feed huge subglacial lakes that fill and burst their banks periodically. Satellites see the top of the ice sheet heave and relax when this happens.

Illustration of flowing water under the Antarctic ice sheet.

Blue dots indicate lakes, lines show rivers.

Marie Byrd Land is part of the bulging "elbow" leading to the Antarctic Peninsula, left center.

Credit: NASA / NSF/Zina Deretsky

Any projections of future change in Antarctica and its contribution to sea level rise through the loss of ice have to take this basement hydrology into account, and the variations in geothermal heat flux are a critical part of the overall picture.
One research project that will see an immediate benefit from the map’s data is the quest to drill the oldest ice on the continent.
Europe, America, China and others are seeking a location where they can collect a core of frozen material that contains a record of past climate stretching back at least 1.5 million years.
This information - about historic atmospheric conditions including carbon dioxide levels - can be deciphered from tiny air bubbles trapped in the ice.

Map of antarctic ice flow speeds (2011).

(NASA's Goddard Space Flight Center Scientific Visualisation Studio)

But the whole endeavour depends on the base of the ice sheet being undisturbed.
Places with a warm rock underbelly are therefore to be avoided, obviously.
"It is very exciting to see the implications this new heat map has for many communities, including new generations of ice sheet and sea level models," said Dr Martos.
"I am very glad we are contributing an important aspect at unprecedented detail. The Earth’s interior has a lot to tell us in terms on how the ice behaves."

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