The jellyfish-like salp: most efficient filter-feeder in the deep, scientists discover

Salps drift, sometimes in long chains, in the open ocean.
There they are the sea's most efficient filter-feeders, grazing on food particles from large to small.

From NSF News

What if trains, planes and automobiles all were powered simply by the air through which they move? What if their exhaust and by-products helped the environment?

Such an energy-efficient, self-propelling mechanism already exists in nature.

The salp, a small, barrel-shaped organism that resembles a streamlined jellyfish, gets everything it needs from ocean waters to feed and propel itself.

Scientists believe its waste material may help remove carbon dioxide (CO2) from the upper ocean and the atmosphere.

Now researchers at the Woods Hole Oceanographic Institution (WHOI) and MIT have found that the half-inch to 5-inch-long creatures are even more efficient than had been believed.

"This innovative research is providing an understanding of how a key organism in marine food webs affects important biogeochemical processes," said David Garrison, director of the National Science Foundation (NSF)'s biological oceanography program, which funded the research.

Reporting this week in the journal Proceedings of the National Academy of Sciences (PNAS), the scientists have found that mid-ocean-dwelling salps are capable of capturing and eating extremely small organisms as well as larger ones, rendering them even hardier--and perhaps more plentiful--than had been believed.

"We had long thought that salps were about the most efficient filter-feeders in the ocean," said Larry Madin, WHOI Director of Research and one of the paper's authors.

"But these results extend their impact down to the smallest available size fraction, showing they consume particles spanning four orders of magnitude in size. This is like eating everything from a mouse to a horse."

Salps capture food particles, mostly phytoplankton, with an internal mucus filter net. Until now, it was thought that included only particles larger than the 1.5-micron-wide holes in the mesh; smaller particles would slip through.

But a mathematical model suggested salps somehow might be capturing food particles smaller than that, said Kelly Sutherland, who co-authored the PNAS paper after her PhD research at MIT and WHOI.

In the laboratory at WHOI, Sutherland and her colleagues offered salps food particles of three sizes: smaller, around the same size as, and larger than the mesh openings.

"We found that more small particles were captured than expected," said Sutherland, now a post-doctoral researcher at Caltech. "When exposed to ocean-like particle concentrations, 80 percent of the particles that were captured were the smallest particles offered in the experiment."

The finding helps explain how salps--which can exist either singly or in "chains" that may contain a hundred or more--are able to survive in the open ocean where the supply of larger food particles is low.

"Their ability to filter the smallest particles may allow them to survive where other grazers can't," said Madin.

Perhaps most significantly, the result enhances the importance of the salps' role in carbon cycling. As they eat small, as well as large, particles, "they consume the entire 'microbial loop' and pack it into large, dense fecal pellets," Madin says.

The larger and denser the carbon-containing pellets, the sooner they sink to the ocean bottom. "This removes carbon from the surface waters," said Sutherland, "and brings it to a depth where you won't see it again for years to centuries."

And the more carbon that sinks to the bottom, the more space there is for the upper ocean to accumulate carbon, hence limiting the amount that rises into the atmosphere as CO2, said paper co-author Roman Stocker of MIT.

"The most important aspect of this work is the very effective shortcut that salps introduce in the process of particle aggregation," Stocker said. "Typically, aggregation of particles proceeds slowly, by steps, from tiny particles coagulating into slightly larger ones."

"Now, the efficient foraging of salps on particles as small as a fraction of a micrometer introduces a substantial shortcut in this process, since digestion and excretion package these tiny particles into much larger particles, which thus sink a lot faster."

This process starts with the mesh made of fine mucus fibers inside the salp's hollow body.

Salps, which can live for weeks or months, swim and eat in rhythmic pulses, each of which draws seawater in through an opening at the front end of the animal. The mesh captures the food particles, then rolls into a strand and goes into the gut, where it is digested.

"It was assumed that very small cells or particles were eaten mainly by other microscopic consumers, like protozoans, or by a few specialized metazoan grazers like appendicularians," said Madin.

"This research indicates that salps can eat much smaller organisms, like bacteria and the smallest phytoplankton, organisms that are numerous and widely distributed in the ocean."

The work, also funded by the WHOI Ocean Life Institute, "implies that salps are more efficient vacuum cleaners than we thought," said Stocker.

"Their amazing performance relies on a feat of bioengineering--the production of a nanometer-scale mucus net--the biomechanics of which remain a mystery."

Recording the blues might explain whale speak

Whale song

From SFGate

After three months of work, a team of San Francisco State scientists has amassed more than 4,000 recordings of underwater moans and bubbling chatter made by blue whales off the California coast - a collection that could help explain how the largest of ocean animals communicates.

Yet the scientists still don't know whether the whales' calls represent a kind of cetacean groupthink, a beacon for possible mates, or perhaps a social signal that an entire group is migrating or moving toward some new source of food.

Roger Bland, an acoustical physicist at San Francisco State University, and his colleagues have analyzed 4,378 blue whale songs recorded as the animals swam past an undersea observing station on the Pioneer Seamount, 50 miles out from Mavericks, the famed surfing spot north of Half Moon Bay.

Four hydrophones captured the loud and eerie sounds. Each is a burst of warbles, a little like someone gargling underwater, followed exactly 130 seconds later by a loud, long, deep-toned and sad-sounding moan.

Like humpbacks and fin whales, only the male blues are believed to vocalize. Yet unlike most whales, which have widely varied song repertoires, the blue whales all communicate at the same pitch, Bland said.

"We can only speculate what they mean and wonder just what adaptive advantage the (songs) may give the whales in their evolution," he said.

The songs Bland and his colleagues recorded seemed most often to be associated with either fast travel that might have happened during their migration or while they milled about near abundant masses of krill.

So far, the scientists analyzed only the long, mournful moans the whales make - known as their "B calls" - while their bubblings remain to be scrutinized.

But each of the calls made by the whales sounded exactly the same - precisely four octaves below middle C on the human scale. And where the calls did vary occasionally, their pitch differed by barely half of 1 percent. By comparison, a tiny change in human musical pitch between the notes middle C and C sharp would mark a change of fully 6 percent, a change that might go unnoticed by tone-deaf humans but would be clear to musicians.

One possibility for such mass accuracy, Bland and his colleague suggest, is that female blues may be able to locate a group of males by their sounds, which may be slightly higher or lower in pitch when the males are swimming toward the females or away from them. That effect is called the Doppler Shift - the change in pitch heard as a siren or a train whistle is nearing or speeding away.

Blue whales live in all the oceans of the world, and in each region the species and subspecies vary. But all are endangered because their numbers were decimated by worldwide hunting before international protections imposed in 1966.

They are the largest animals ever known to have lived: more than 100 feet long and weighing up to 200 tons for the south Pacific species, and somewhat less in the north Pacific.

Bland's colleagues working on this latest report include Michael D. Hoffman, a former S.F. State student, and Newell Garfield, an S.F. State oceanographer and director of the university's Romberg Tiburon Center for Environmental Studies. They published the results of their study in the July issue of the Journal of the Acoustical Society of America.

Links :

• SFStatesNews : Blue whales align the pitch of their songs with extreme accuracy, study finds
• LiveScience : Using blue whales' perfect pitch to drive people insane
  

Greenland glacier calves island four times the size of Manhattan

From University of Delaware

A University of Delaware researcher reports that an "ice island" four times the size of Manhattan has calved from Greenland's Petermann Glacier. The last time the Arctic lost such a large chunk of ice was in 1962.

"In the early morning hours of August 5, 2010, an ice island four times the size of Manhattan was born in northern Greenland," said Andreas Muenchow, associate professor of physical ocean science and engineering at the University of Delaware's College of Earth, Ocean, and Environment. Muenchow's research in Nares Strait, between Greenland and Canada, is supported by the National Science Foundation (NSF).

Satellite imagery of this remote area at 81 degrees N latitude and 61 degrees W longitude (position in the Marine GeoGarage), about 620 miles [1,000 km] south of the North Pole, reveals that Petermann Glacier lost about one-quarter of its 43-mile long [70 km] floating ice-shelf.

Trudy Wohlleben of the Canadian Ice Service discovered the ice island within hours after NASA's MODIS-Aqua satellite took the data on Aug. 5, at 8:40 UTC (4:40 EDT), Muenchow said.
These raw data were downloaded, processed, and analyzed at the University of Delaware in near real-time as part of Muenchow's NSF research.

Petermann Glacier, the parent of the new ice island, is one of the two largest remaining glaciers in Greenland that terminate in floating shelves. The glacier connects the great Greenland ice sheet directly with the ocean.

The new ice island has an area of at least 100 square miles and a thickness up to half the height of the Empire State Building.

"The freshwater stored in this ice island could keep the Delaware or Hudson rivers flowing for more than two years. It could also keep all U.S. public tap water flowing for 120 days," Muenchow said.

The island will enter Nares Strait, a deep waterway between northern Greenland and Canada where, since 2003, a University of Delaware ocean and ice observing array has been maintained by Muenchow with collaborators in Oregon (Prof. Kelly Falkner), British Columbia (Prof. Humfrey Melling), and England (Prof. Helen Johnson).

"In Nares Strait, the ice island will encounter real islands that are all much smaller in size," Muenchow said. "The newly born ice-island may become land-fast, block the channel, or it may break into smaller pieces as it is propelled south by the prevailing ocean currents. From there, it will likely follow along the coasts of Baffin Island and Labrador, to reach the Atlantic within the next two years."

The last time such a massive ice island formed was in 1962 when Ward Hunt Ice Shelf calved a 230 square-mile island, smaller pieces of which became lodged between real islands inside Nares Strait.
Petermann Glacier spawned smaller ice islands in 2001 (34 square miles) and 2008 (10 square miles). In 2005, the Ayles Ice Shelf disintegrated and became an ice island (34 square miles) about 60 miles to the west of Petermann Fjord.

Links :

• Wired : Enormous ice block breaks off Greenland glacier
  

Sable island : the graveyard of the Atlantic

Map: known shipwrecks since 1583

From Maritime Museum of the Atlantic

Sable Island, a 44-km-long sand bar about 150 miles east south east of Halifax, Nova Scotia, is renowned for its wild horses (position in the Marine GeoGarage).

For sailors, it was the graveyard of the Atlantic, an island hidden by waves, storms and fog that meant only death and destruction.
Since 1583 there have been over 350 recorded shipwrecks on Sable Island.
Very little now remains of the ships that were wrecked on the island: a shoe buckle, a few coins, ship name boards, timbers buried in the sand.

courtesy of Geographicus

Why so many wrecks?

• Location: Sable lies near one of the world's richest fishing grounds. It is also near one of the major shipping routes between Europe and North America. Hundreds of vessels sailed past each year.

• It's a very stormy place: Sable lies right in the path of most storms that track up the Atlantic coast of North America. Storms were extremely treacherous for sailing ships. Vessels were simply blown onto Sable.

• Fog shrouds the island: in summer warm air from the Gulf Stream produces dense banks of fog when it hits air cooled by the Labrador Current around Sable. Sable has 125 days of fog a year. Toronto has 35.

• The currents around Sable are tricky: Sable lies near the junction of three major ocean currents, the Gulf Stream, the Labrador Current and the Belle Isle Current.

There have been few shipwrecks on Sable since 1947.
Prior to then the sextant was the principal instrument used to fix a ship's position.
Sextants were accurate, but they worked by taking a sighting from the sun or the stars.
They were useless in dense fog or cloudy skies.

In bad weather, the captain navigated by "dead reckoning", using the ship's speed and direction to estimate his position.
But even in good conditions this was educated guessing.
Currents and storms confused the calculations of the best skippers.
Many accounts of shipwrecks report that the captain simply lost his way: he misjudged his ship's position and bumped into Sable Island by mistake.

After World War II radar and other advanced navigational equipment became widely used on commercial vessels.
Sable ceased to be a major threat to shipping.
Only one vessel has been lost since 1947, the small yacht Merrimac which sank on July 27, 1999.

Links :

• Sable island : a story of survival
• Strange map : the graveyard of the Atlantic
• Virtual Museum
• Video
  

Generating energy from ocean waters off Hawaii

The $250 million successful USA renewable energy effort dismissed with one paragraph in 1997 and dropped even from the NREL website

From ScienceDaily

Researchers at the University of Hawaii at Manoa say that the Leeward side of Hawaiian Islands may be ideal for future ocean-based renewable energy plants that would use seawater from the oceans' depths to drive massive heat engines and produce steady amounts of renewable energy.

The technology, referred to as Ocean Thermal Energy Conversion (OTEC), is described in the Journal of Renewable and Sustainable Energy, which is published by the American Institute of Physics (AIP).

It involves placing a heat engine between warm water collected at the ocean's surface and cold water pumped from the deep ocean.
Like a ball rolling downhill, heat flows from the warm reservoir to the cool one.
The greater the temperature difference, the stronger the flow of heat that can be used to do useful work such as spinning a turbine and generating electricity.

The history of OTEC dates back more than a half century.
However, the technology has never taken off -- largely because of the relatively low cost of oil and other fossil fuels.
But if there are any places on Earth where large OTEC facilities would be most cost competitive, it is where the ocean temperature differentials are the greatest.

Analyzing data from the National Oceanic and Atmospheric Administration's National Oceanographic Data Center, the University of Hawaii's Gérard Nihous says that the warm-cold temperature differential is about one degree Celsius greater on the leeward (western) side of the Hawaiian Islands than that on the windward (eastern) side.

This small difference translates to 15 percent more power for an OTEC plant, says Nihous, whose theoretical work focuses on driving down cost and increasing efficiency of future facilities, the biggest hurdles to bringing the technology to the mainstream.

"Testing that was done in the 1980s clearly demonstrates the feasibility of this technology," he says. "Now it's just a matter of paying for it."

Links :

• OTEC News
  
• U.S. Department of Energy selects Lockheed Martin to advance OTEC utility power plans
• Sarasvati project