Mystery of huge underwater 'crop circles' solved

This image shows mysterious ‘crop circles’ on the seabed off the Island of Møn, Denmark. 

Image credit: Jacob Topsøe Johansen.

From CS Monitor

Mysterious underwater rings of eelgrass, off the coast of Denmark, are the result of poison, biologists say.
The rings weren't created by fairies, bombs, or visiting aliens, say researchers.

They're not the work of World War II bombs or aliens or fairies.
Instead, mysterious underwater rings spotted off the coast of Denmark are the result of poison, biologists say.

Striking rings of green eelgrass — some of them up to 49 feet (15 meters) wide — can occasionally be spotted in the clear Baltic water off the coast of Denmark's island of Møn.
The formations were captured in tourist photos in 2008 and again in 2011, sparking the type of speculation that's usually reserved for crop circles.

 This is an eelgrass plant growing off the cliffs of Island Mon in Denmark.

The plants create a circle formation. Credit: Ole Pedersen

But biologists Marianne Holmer from University of Southern Denmark and Jens Borum from University of Copenhagen assure that the circles have "nothing to do with either bomb craters or landing marks for aliens."
"Nor with fairies, who in the old days got the blame for similar phenomena on land, the fairy rings in lawns being a well known example," Holmer and Borum said in a statement today (Jan. 30).

 On Sunday, June 19, 2011, this quincunx of five circles
was videotaped underwater where Nils Natorp, Manager of the Mons Klint
Research Center on the eastern coast of the Danish island of Mon in the Baltic
Sea, was taking visitors on a field trip.

Mr. Natorp contacted two divers to go in the water to see what the circles were made of and the divers confirmed the plants are eelgrass.

But how the circles were made to persist in the water was still a mystery.

Aerial video of the June 19, 2011,

The biologists concluded that the rings formed because of the radiating pattern in which the eelgrass grows — and dies when exposed to toxins.
In the mud around the eelgrass, the scientists detected high levels of sulfide, a substance that's poisonous to eelgrass and can build up naturally in a chalky seabed like the one off Møn (or unnaturally when agricultural pollutants enter an ecosystem).
"Most mud gets washed away from the barren, chalky seabed, but like trees trap soil on an exposed hillside, eelgrass plants trap the mud," Holmer and Borum explained.
"And therefore there will be a high concentration of sulfide-rich mud among the eelgrass plants."
Though it might resemble a type of seaweed, eelgrass is actually a flowering plant.
And when it grows, it expands outward in all directions, creating circle-shaped colonies.
While healthy adult eelgrass plants seem to be able to withstand the sulfide in their environment, the old plants at the heart of the colonies drop dead, the researchers said.

"The result is an exceptional circular shape, where only the rim of the circle survives — like fairy rings in a lawn," Holmer and Borum added.
Fairy rings in a lawn are typically blamed on the outward growth of fungi, but other fairy circles on land have long puzzled scientists.
A famous example can be found in the desert grasslands of Namibia in southern Africa, where researchers have offered up a wide range of explanations for the vast field of circular patches, from ants and termites to gas seeps and resource competition.

The explanation for the eelgrass fair rings is detailed in this month's edition of the journal Marine Biology.

Bahamas WLP update in the Marine GeoGarage

14 charts have been updated since the last release :

• B12   Abaco Chart
• B28   Ab- Sandy Pt.
• B35   Ab-Foxown
• B155   Ab- Gorda Cay
• B156   Ab- Mores Island
• B161   Abaco, Western Bight
• B165   Ab- Allens-Pen Area
• B171   Ab- West End Rocks
• B185   Abacoight - Redshanks Cay
• B186   Abacoight - Burrows & Water Cay
• B187   Ab- Normans Castle
• B188   Ab- Basin Harbour Cay
• B189   Ab- Point of Bank Anchorage
• B222   Ab- Schooner Bay

Today, 295 charts for Bahamas (from WLP) are published on the Marine GeoGarage

Unprecedented trade wind strength is shifting global warming to the oceans, but for how much longer?

Méditerranean sea-surface temperature

Sea-surface temperature in the Mediterranean Sea from January 2011 to May 2012
as measured by multiple Earth-observation missions.

From The Guardian

New research attributes the surface warming slowdown to accelerating trade winds mixing more heat into the oceans

  

  Research looking at the effects of Pacific Ocean cycles has been gradually piecing together the puzzle explaining why the rise of global surface temperatures has slowed over the past 10 to 15 years.
A new study just published in Nature Climate Change, led by Matthew England at the University of New South Wales, adds yet another piece to the puzzle by examining the influence of Pacific trade winds.

Pacific trade winds

While the rate of surface temperature warming has slowed in recent years, several studies have shown that the warming of the planet as a whole has not.
This suggests that the slowed surface warming is not due as much to external factors like decreased solar activity or more pollutants in the atmosphere blocking sunlight, but more due to internal factors shifting the heat into the oceans.
In particular, the rate at which the deep oceans have warmed over the past 10 to 15 years is unprecedented in the past half century.

Research led by Masahiro Watanabe of the Japanese Atmosphere and Ocean Research Institute suggests this is mainly due to more efficient transfer of heat to the deep oceans.
Consistent with model simulations led by Gerald Meehl, Watanabe finds that we sometimes expect "hiatus decades" to occur, when surface air temperatures don't warm because more heat is transferred to the deep ocean layers.
A paper published last year by Yu Kosaka and Shang-Ping Xie from the Scripps Institution of Oceanography found that accounting for the changes in Pacific Ocean surface temperatures allowed their model to reproduce the slowed global surface warming over the past 10 to 15 years.
However, the mechanism causing these Pacific Ocean changes has remained elusive.

The new study published by Matthew England's team helps explain how and why more heat is being funneled into the deeper ocean layers.
The study indicates that a dramatic acceleration in equatorial trade winds, associated with a negative phase of a cycle called the Interdecadal Pacific Oscillation (IPO) has invigorated the circulation of the Pacific Ocean.
This has caused more heat from the surface to be mixed down into deeper ocean layers, while bringing cooler waters to the surface.
The combination of these two processes cools global surface temperatures.
Like the rate at which heat is accumulating in the deep oceans, the recent strengthening of the trade winds is unprecedented, as the bottom frame in the figure below shows.

Top frame: Global surface temperature anomalies.

Bottom frame: Pacific wind stress anomalies. From England et al. (2014).

Not only is this acceleration of trade winds unprecedented, but it also far exceeds anything captured by climate models.
Hence they have difficulty reproducing the recent slowdown in surface warming.
The catch is that oscillations eventually change phases, so as England notes, the strengthened trade winds and faster rate of ocean heat accumulation are only temporary.

"the heat uptake is by no means permanent: when the trade wind strength returns to normal - as it inevitably will - our research suggests heat will quickly accumulate in the atmosphere. So global temperatures look set to rise rapidly out of the hiatus, returning to the levels projected within as little as a decade."

The study estimates that by shifting more heat into the oceans, the strengthening trade winds can account for 0.1–0.2°C cooling of surface temperatures over the past 10 to 15 years. This would account for most of the slowed rate of warming, especially when combined with a recent study showing that the global surface warming slowdown is not as large as previously thought. The lead author of that paper, Kevin Cowtan said of this study,

"I think Professor England has uncovered the biggest piece in the puzzle of recent temperature trends"

In the figure below, the England study compares observed surface temperature changes (black and grey) with IPCC model projections (red), and projections made by models that incorporate these changes in trade winds (green and blue). The models including trade winds can reproduce the surface warming slowdown. However, once the IPO cycle shifts and winds return to previous levels, the models see an accelerated warming at the surface, and temperatures start to catch back up to the IPCC model projections.

Annual (grey bars) and a five-year running mean (black solid line) global surface temperature measurements. Climate model projections are shown in red.

The blue and green show results from an ocean and a coupled climate model adjusted by the trade-wind-induced surface cooling.

From England et al. (2014).

A consistent picture is emerging in the climate research; increases in the strength of trade winds force more heat to be mixed down into the ocean, leading to a temporary slowing of rising surface temperatures.
The next piece of the puzzle will involve explaining the cause of the dramatic, unprecedented trade wind acceleration.
The IPO cycle can explain about half of the wind changes, but climate scientists are still investigating other possible contributing factors.
In any case, England concludes that surface temperatures may rapidly warm when the IPO phase shifts again in the next decade or so, and it will eventually be as though the surface warming slowdown never occurred.

"We should be very clear: the current hiatus offers no comfort - we are just seeing another pause in [surface] warming before the next inevitable rise in global temperatures."

Links :

• The Guardian : Global warming 'pause' due to unusual trade winds in Pacific ocean, study finds
• ESA : Is global warming hiding underwater ?

Earth's magnetic field : lesson from ESA

An introduction to Earth's magnetic field: what it is, where it comes from and what it's used for.

Why it matters

Earth's magnetic field is continuously changing.

Magnetic north wanders, and every few hundred thousand years the polarity gradually flips, so that a compass would point south instead of north.

To learn more about Earth's magnetic field, the three Swarm satellites were launched on 22 November.

Like 3D compasses, they are measuring the strength and direction of the magnetic field.

Spider crabs vs. stingray

BBC Life - Creatures of the Deep

Huge stingray crashes a spider crab party