Oceanographic Linkages Indicate an Alternative Route for Eel Larval

European eel larvae are generally believed to initially follow a westerly drift route into the Gulf Stream, but new research results on bio-physical linkages in the Sargasso Sea point to a shorter route towards Europe.

As both European and American eel populations are in a drastic decline, there is an urgent need for a better understanding of the early oceanic phase of their life cycle.

New findings from the Danish Galathea 3 Expedition to the eel's spawning sites in the Sargasso Sea now point to an alternative route for larval drift towards Europe and shed light on the conditions for larval growth and feeding

Scientific results published in Proceedings of the Royal Society show the importance of including the climatic influence on oceanic processes when assessing the conditions for the early life of eel and the background of a declining recruitment to the eel populations.

"Our studies in the Sargasso Sea demonstrate a significant relationship between the physical and biological conditions in the area. A front established where warm tropical waters meet colder North Atlantic water has a key role in the larval life of eel" says Senior Scientist Peter Munk from DTU Aqua -- National Institute of Aquatic Resources, Technical University of Denmark.

The front retains eel larvae within a zone of enhanced feeding conditions and influences their drift towards the continent.

European eel larvae are generally believed to initially follow a westerly drift route from the spawning site and subsequently drift with the Gulf Stream. But the study's demonstration of a strong linkage between larval distributions and the fronts in the area suggests another possibility.

The front between the warm and cold waters leads to a current which, contrary to the predominant currents in the area, is directed eastward, and the distribution of larvae indicates that they could use this "subtropical counter current" as a shorter and faster route towards Europe.

These oceanic processes are affected by climate change, and the study shows the importance of including them in the understanding of the life cycle completion of eel and the fluctuations in stock sizes.

Other research finding from the Galathea 3 Expedition has just been published in Biology Letters and describes the diet of eel larvae. The scientists brought home very small eel larvae (5-25 mm) from the Sargasso Sea to find out what they actually eat.

It has been assumed that the eel's long journey to the Sargasso Sea was linked to the feeding opportunities in the area for the newly hatched eel larvae. So far, knowledge about what and if eel larvae eat has been sparse, as only very few larvae have been found with identifiable prey items in the gut.

The eel larvae from the Galathea 3 Expedition have now been analysed using DNA barcoding, which makes it possible to identify the various plankton organisms found in the otherwise unidentifiable gut contents.

The findings show that even the smallest eel larvae eat remarkably diverse marine organisms. Gelatinous zooplankton, in particular, e.g. small jellyfish, play an important role in their diet. The study suggests that the frontal zone in the Sargasso Sea provides ample feeding opportunities for the eel larvae.

The findings relating to larval diet may be very useful in connection with artificial reproduction and rearing of the European eel, where one of the major questions is what to feed to the eel larvae.

The studies of larval diet were conducted by Associate Professor Lasse Riemann from the University of Copenhagen in collaboration with, amongst others, scientists from DTU Aqua.
P. Munk, M. M. Hansen, G. E. Maes, T. G. Nielsen, M. Castonguay, L. Riemann, H. Sparholt, T. D. Als, K. Aarestrup, N. G. Andersen, M. Bachler. Oceanic fronts in the Sargasso Sea control the early life and drift of Atlantic eels. Proceedings of the Royal Society B: Biological Sciences, 2010; DOI: 10.1098/rspb.2010.0900

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Vast iceberg 'may disrupt ocean currents'

A vast iceberg snapped from the Mertz Glacier Tongue which broke off the Antarctic continent this month could disrupt the world's ocean currents and weather patterns, scientists warn.Australian researchers say the iceberg - the size of Luxembourg - could block an area that produces a quarter of the world's dense and very cold seawater. They say a slowdown in the production of this water could result in colder winters in the north Atlantic. The iceberg is currently floating south of Australia. Dr Neal Young, a glaciologist at the Antarctic Climate and Ecosystems Research Centre in Tasmania, told the BBC that any disruption to the production of the super cold water - known as bottom water - in the region would affect ocean currents, and consequently weather patterns, for years to come. "This area accounts for about 25% of the production of bottom water in Antarctica, and therefore it will reduce the overturning circulation rate," he said. "You won't see it immediately, but it has downstream effects. And it will also have implications for penguins and other wildlife in the region that normally use this area for feeding." The iceberg is sitting in an area of open water surrounded by sea-ice, known as a polynya. Bottom water produced by polynyas sinks to the bottom of the sea and drives the conveyor-belt like ocean circulation around the globe. Benoit Legresy, a French glaciologist, said the iceberg broke from the Mertz Glacier Tongue, a 160km spit of floating ice protruding from East Antarctica south of Melbourne. It was dislodged by another, older, iceberg known as B9B which split off in 1987. "The ice tongue was almost broken already. It was hanging like a loose tooth," Mr Legresy said. "If they [the icebergs] stay in this area - which is likely - they could block the production of this dense water, essentially putting a lid on the polynya," he added.

Rip Currents Pose Greater Risk To Swimmers Than To Shoreline, Study Suggests

Rip currents — powerful, channeled currents of water flowing away from the shore — represent a danger to human life and property. Rip currents are responsible for more than one hundred deaths on our nation's beaches each year, according to the United States Lifesaving Association, and if rip currents persist long enough they can cause beach erosion.

Henry Bokuniewicz, Professor in the School of Marine and Atmospheric Sciences at Stony Brook University, and Ph.D. candidate Michael Slattery found that rip currents at East Hampton Village Beach lasted on average a little over one minute, not long enough to substantially alter the shoreline. They will present their findings October 14th at the American Shore and Beach Preservation Association's 2009 National Coastal Conference, "Integrating Coastal Science & Policy."
With funding from the East Hampton Beach Preservation Society and the Halpern Foundation, Dr. Bokuniewicz and graduate student Michael Slattery set up a video camera to record an image of a half mile stretch of the East Hampton Village Beach every 20 seconds. In the images, rip currents can be detected as a gap in the line of incoming waves. They collected over 500 hours of video images and observed hundreds of rip currents in this short stretch of coast.
The monitoring showed that the rip currents were not associated with man-made structures and they were short lived, with the most persistent rip currents lasting no more than a few minutes. "Most rip currents we observed did not last long enough to change the character of the shoreline, although they could pose a risk to swimmers unfortunate enough to encounter them," said Dr. Bokuniewicz.
Besides gathering statistics on the occurrence of rip currents, Dr. Bokuniewicz and Michael Slattery are studying the wave patterns that lead to rip currents. Rip currents are generated by a combination of waves, including, long, low, barely perceptible waves that appear along the ocean shoreline, called "infragravity waves." Infragravity waves cannot be measured directly and computer models are inadequate for predicting them. Bokuniewicz and Slattery are using a novel approach to study these waves; they deploy seismometers to measure the noise created by breaking waves.
"It appears that very slow, long-period changes in the amount of wave noise are precursors to the generation of rip currents," said Dr. Bokuniewicz. "We are hopeful that seismometers can be used to measure wave patterns that we can't easily observe in any other way. In the future, we hope to utilize this method to monitor and ultimately forecast wave conditions that cause rip currents."
Adapted from materials provided by Stony Brook University, via EurekAlert!, a service of AAAS.

High Sea Level Along U.S. Atlantic Coast Due To Ocean Current And Wind Changes

Persistent winds and a weakened current in the Mid-Atlantic contributed to higher than normal sea levels along the Eastern Seaboard in June and July, according to a new NOAA technical report.

After observing water levels six inches to two feet higher than originally predicted, NOAA scientists began analyzing data from select tide stations and buoys from Maine to Florida and found that a weakening of the Florida Current Transport—an oceanic current that feeds into the Gulf Stream—in addition to steady and persistent Northeast winds, contributed to this anomaly.
“The ocean is dynamic and it’s not uncommon to have anomalies,” said Mike Szabados, director of NOAA’s Center for Operational Oceanographic Products and Services. “What made this event unique was its breadth, intensity and duration.”
The highest atypical sea levels occurred closer to where the anomaly formed in the Mid-Atlantic, where cities like Baltimore, Md., at times experienced extreme high tides as much as two feet higher than normal. Data from NOAA’s National Water Level Observation Network tide stations, Atlantic Oceanographic and Meteorological Laboratory, and National Data Buoy Center, are published in the report.
Impacts of the event were amplified by the occurrence of a perigean-spring tide, the natural timing of the season and month when the moon is closest to the Earth and its gravitational pull heightens the elevation of the water. The combined effects of this tide with the sea level anomaly produced minor flooding on the coast.
“The report is a good first assessment,” said NOAA Oceanographer William Sweet, Ph.D. “However, NOAA, with our academic partners, should continue to investigate the broader causes behind the event. Further analysis is needed to fully understand what is driving the patterns we observed.”
The full report, Elevated East Coast Sea Level Anomaly: June-July 2009, is available as a PDF.
Adapted from materials provided by National Oceanic and Atmospheric Administration.

Warming Of Arctic Current Over 30 Years Triggers Release Of Methane Gas

The warming of an Arctic current over the last 30 years has triggered the release of methane, a potent greenhouse gas, from methane hydrate stored in the sediment beneath the seabed.

Scientists at the National Oceanography Centre Southampton working in collaboration with researchers from the University of Birmingham, Royal Holloway London and IFM-Geomar in Germany have found that more than 250 plumes of bubbles of methane gas are rising from the seabed of the West Spitsbergen continental margin in the Arctic, in a depth range of 150 to 400 metres.
Methane released from gas hydrate in submarine sediments has been identified in the past as an agent of climate change. The likelihood of methane being released in this way has been widely predicted.
The data were collected from the royal research ship RRS James Clark Ross, as part of the Natural Environment Research Council's International Polar Year Initiative. The bubble plumes were detected using sonar and then sampled with a water-bottle sampling system over a range of depths.
The results indicate that the warming of the northward-flowing West Spitsbergen current by 1° over the last thirty years has caused the release of methane by breaking down methane hydrate in the sediment beneath the seabed.
Professor Tim Minshull, Head of the University of Southampton's School of Ocean and Earth Science based at that the National Oceanography Centre, says: "Our survey was designed to work out how much methane might be released by future ocean warming; we did not expect to discover such strong evidence that this process has already started."
Methane hydrate is an ice-like substance composed of water and methane which is stable in conditions of high pressure and low temperature. At present, methane hydrate is stable at water depths greater than 400 metres in the ocean off Spitsbergen. However, thirty years ago it was stable at water depths as shallow as 360 metres.
This is the first time that such behaviour in response to climate change has been observed in the modern period.
While most of the methane currently released from the seabed is dissolved in the seawater before it reaches the atmosphere, methane seeps are episodic and unpredictable and periods of more vigorous outflow of methane into the atmosphere are possible. Furthermore, methane dissolved in the seawater contributes to ocean acididfication.
Graham Westbrook Professor of Geophysics at the University of Birmingham, warns: "If this process becomes widespread along Arctic continental margins, tens of megatonnes of methane per year – equivalent to 5-10% of the total amount released globally by natural sources, could be released into the ocean."
The team is carrying out further investigations of the plumes; in particular they are keen to observe the behaviour of these gas seeps over time.
Journal reference:
Westbrook, G.K. et al. Escape of methane gas from the seabed along the West Spitsbergen continental margin. Geophysical Research Letters, 2009; DOI: 10.1029/2009GL039191
Adapted from materials provided by National Oceanography Centre, Southampton (UK).

Fauna play key role in circulating seas

Creatures large and small may play an unsuspectedly important role in the stirring of ocean waters, according to a study released Wednesday.So-called ocean mixing entails the transfer of cold and warm waters between the equator and poles, as well as between the icy, nutrient-rich depths and the sun-soaked top layer.It plays a crucial part in marine biodiversity and, scientists now suspect, in maintaining Earth's climate.The notion that fish and other sea swimmers might somehow contribute significantly to currents as they moved forward was first proposed in the mid-1950s by Charles Darwin, grandson of the the legendary evolutionary biologist of the same name.But this was dismissed by modern scientists as a fishy story.In 1960s, experiments compared the wake turbulence created by sea creatures with overall ocean turbulence. They showed that the whirls kicked up by microscopic plankton or even fish quickly dissipated in dense, viscous water.On this evidence, sea creatures seemed to contribute nothing to ocean mixing. The clear conclusion was that the only drivers of note were shifting winds and tides, tied to the gravitational tug-of-war within our Solar System.But the new study, published in the British science journal Nature, goes a long way toward rehabilitating the 20th century Darwin, and uses the quiet pulse of the jellyfish to prove the case.Authors Kakani Katija and Joan Dabiri of the California Institute of Technology devised a laser-based system for measuring the movement of liquid.They donned scuba gear and then released dye in the path of swarm of jellyfish in a saltwater lake on the Pacific island of Palau.The video images they captured showed a remarkable amount of cold water followed the jellyfish as they moved vertically, from deeper chillier waters toward the warmer layers of the surface.Katija and Dabiri say the 1960s investigators had simply been looking in the wrong place.They had been on the alert for waves or eddies -- signs that the sea was being stirred up in the creatures' wake -- rather than vertical displacement of water.What determines the amount of water that is mixed is the size and shape of the animal, its population and migratory patterns.Churning of the seas is a factor in the carbon cycle.At the surface, plankton gobble up carbon dioxide (CO2) through photosynthesis. When they die, their carbon-rich remains may fall gently to the ocean floor, effectively storing the CO2 for millennia -- or, alternatively, may be brought back to upper layers by sea currents.William Dewar of Florida State University in a commentary, also published in Nature, said the new paper challenged conventional thinking."Should the overall idea of significant biogenic mixing survive detailed scrutiny, climate science will have experienced a paradigm shift," he said.

Cold Water Ocean Circulation Doesn't Work As Expected

The familiar model of Atlantic ocean currents that shows a discrete "conveyor belt" of deep, cold water flowing southward from the Labrador Sea is probably all wet.

New research led by Duke University and the Woods Hole Oceanographic Institution relied on an armada of sophisticated floats to show that much of this water, originating in the sea between Newfoundland and Greenland, is diverted generally eastward by the time it flows as far south as Massachusetts. From there it disburses to the depths in complex ways that are difficult to follow.
A 50-year-old model of ocean currents had shown this southbound subsurface flow of cold water forming a continuous loop with the familiar northbound flow of warm water on the surface, called the Gulf Stream.
"Everybody always thought this deep flow operated like a conveyor belt, but what we are saying is that concept doesn't hold anymore," said Duke oceanographer Susan Lozier. "So it's going to be more difficult to measure these climate change signals in the deep ocean."
And since cold Labrador seawater is thought to influence and perhaps moderate human-caused climate change, this finding may affect the work of global warming forecasters.
"To learn more about how the cold deep waters spread, we will need to make more measurements in the deep ocean interior, not just close to the coast where we previously thought the cold water was confined," said Woods Hole's Amy Bower.
Lozier, a professor of physical oceanography at Duke's Nicholas School of the Environment and Bower, a senior scientist in the department of physical oceanography at the Woods Hole Institution, are co-principal authors of a report on the findings to be published in the May 14 issue of the research journal Nature.
Their research was supported by the National Science Foundation.
Climatologists pay attention to the Labrador Sea because it is one of the starting points of a global circulation pattern that transports cold northern water south to make the tropics a little cooler and then returns warm water at the surface, via the Gulf Stream, to moderate temperatures of northern Europe.
Since forecasters say effects of global warming are magnified at higher latitudes, that makes the Labrador Sea an added focus of attention. Surface waters there absorb heat-trapping carbon dioxide from the atmosphere. And a substantial amount of that CO2 then gets pulled underwater where it is no longer available to warm Earth's climate.
"We know that a good fraction of the human caused carbon dioxide released since the Industrial revolution is now in the deep North Atlantic" Lozier said. And going along for the ride are also climate-caused water temperature variations originating in the same Labrador Sea location.
The question is how do these climate change signals get spread further south? Oceanographers long thought all this Labrador seawater moved south along what is called the Deep Western Boundary Current (DWBC), which hugs the eastern North American continental shelf all the way to near Florida and then continues further south.
But studies in the 1990s using submersible floats that followed underwater currents "showed little evidence of southbound export of Labrador sea water within the Deep Western Boundary Current (DWBC)," said the new Nature report.
Scientists challenged those earlier studies, however, in part because the floats had to return to the surface to report their positions and observations to satellite receivers. That meant the floats' data could have been "biased by upper ocean currents when they periodically ascended," the report added.
To address those criticisms, Lozier and Bower launched 76 special Range and Fixing of Sound floats into the current south of the Labrador Sea between 2003 and 2006. Those "RAFOS" floats could stay submerged at 700 or 1,500 meters depth and still communicate their data for a range of about 1,000 kilometers using a network of special low frequency and amplitude seismic signals.
But only 8 percent of the RAFOS floats' followed the conveyor belt of the Deep Western Boundary Current, according to the Nature report. About 75 percent of them "escaped" that coast-hugging deep underwater pathway and instead drifted into the open ocean by the time they rounded the southern tail of the Grand Banks.
Eight percent "is a remarkably low number in light of the expectation that the DWBC is the dominant pathway for Labrador Sea Water," the researchers wrote.
Studies led by Lozier and other researchers had previously suggested cold northern waters might follow such "interior pathways" rather than the conveyor belt in route to subtropical regions of the North Atlantic. But "these float tracks offer the first evidence of the dominance of this pathway compared to the DWBC."
Since the RAFOS float paths could only be tracked for two years, Lozier, her graduate student Stefan Gary, and German oceanographer Claus Boning also used a modeling program to simulate the launch and dispersal of more than 7,000 virtual "efloats" from the same starting point.
"That way we could send out many more floats than we can in real life, for a longer period of time," Lozier said.
Subjecting those efloats to the same underwater dynamics as the real ones, the researchers then traced where they moved. "The spread of the model and the RAFOS float trajectories after two years is very similar," they reported.
"The new float observations and simulated float trajectories provide evidence that the southward interior pathway is more important for the transport of Labrador Sea Water through the subtropics than the DWBC, contrary to previous thinking," their report concluded.
"That means it is going to be more difficult to measure climate signals in the deep ocean," Lozier said. "We thought we could just measure them in the Deep Western Boundary Current, but we really can't.
Journal reference:
Amy S. Bower, M. Susan Lozier, Stefan F. Gary & Claus W. Böning. Interior pathways of the North Atlantic meridional overturning circulation. Nature, 2009; 459 (7244): 243 DOI: 10.1038/nature07979
Adapted from materials provided by Duke University.

The Agulhas Current, In The Southern Hemisphere, May Influence Climate In Europe

The PhD project presented by Gema Martínez-Méndez from the Institute of Environmental Science and Technology at the Universitat Autonoma de Barcelona focuses on the Agulhas Current and the ensuing warm water transports from the tropical Indian Ocean to the southern tip of Africa.

The data generated provide for the first time evidence in support of the hypothesis that the Agulhas water "leakage" into the Atlantic can affect the climate in Europe.
Her PhD thesis "Surface and Deep Circulation off South Africa: Agulhas Leakage Influence on the Meridional Overturning Circulation During the Last 345 kyr" presented data on a major ocean current in the southern hemisphere, the Agulhas Current, which transports warm waters from the tropical Indian Ocean to the southern tip of Africa. These new data profiles are not yet fully exploited and need to be implemented in global ocean models.
But they do provide for the first time robust evidence in support of the hypothesis that the Agulhas water "leakage" into the Atlantic contributes to the strength of the Atlantic Ocean circulation at large, and the Gulf Stream in particular and therefore can stabilise or destabilise climate in Europe. This knowledge will improve predictive capabilities which aim to project future climate developments in the North Atlantic region under global climate warming scenarios, such as those employed by the Intergovernmental Panel on Climate Change (IPCC).
The Agulhas Current influences rainfall patterns and weather systems in southern Africa. A part of the warm waters are transported around South Africa into the South Atlantic and influence the ocean circulation of the entire Atlantic Ocean. Climate models predict that the amount of this water "leakage" from the Indian Ocean into the Atlantic may in fact strengthen or weaken the Gulf Stream in the North Atlantic with consequences for climate in Europe, including the Iberian Peninsula. Measurements in the ocean so far have not permitted to test if a connection between the Agulhas Current around South Africa and the climate in Europe indeed exists.
For her project, Martínez-Méndez used stable isotope gas mass spectrometry and inductively coupled plasma mass spectrometry to analyse isotopic and chemical components in the sediments underneath the Agulhas Current which document variations of this current in the past. The data profiles document that systematic changes occurred in the Agulhas Current which were directly connected with global climate changes.
A combination of temperature sensitive isotopes and trace elements which are preserved in the shells of marine micro-plankton indicate that under cold climatic conditions such as the ice ages, when the rest of the world dramatically cooled, the influence of the Agulhas Current strengthened and the oceans around South Africa warmed. Ocean warming is documented also by the high abundance of tropical plankton which was preserved in the seafloor sediments. When global climate began to warm at the end of cold periods, the Agulhas Current initially became stronger and then abruptly weakened to assume a strength similar to that of today.
The implications from this research are that the flow of water coming from the tropical Indian Ocean can occasionally form a warm water pool at the southern tip of Africa. Under appropriate conditions, this water is abruptly released into the Atlantic Ocean. Because these waters also have high concentrations of salt they ultimately stimulate a density anomaly in the South Atlantic which triggers internal waves in the deep water and ultimately influence the Gulf Stream in the north.
This past December, Gema Martínez-Méndez presented the results of her PhD project at the General Assembly Fall Meeting of the AGU in San Francisco. The conference was attended by more than 12,000 researchers from the Earth Sciences worldwide representing a diverse range of expertise such as geophysics, meteorology, geochemistry, glaciology, oceanography and climatology. Out of over 16,000 research presentations, ICTA researcher Gema Martínez-Méndez's paper was chosen as one of the best student presentations and she was awarded with the 2008 AGU Fall Meeting Outstanding Student Presentation Award.
Gema Martínez-Méndez holds a degree in Marine Sciences from the University of Vigo, a European Masters from Kiel University in Germany and she received her PhD in Environmental Sciences in September 2008 from ICTA at the Universitat Autònoma de Barcelona. Her PhD project was embedded in the marine climatology projects "Transecto climático interhemisférico: comprensión de los cambios oceanográficos y climáticos rápidos en Iberia durante los dos últimos ciclos glaciales-interglaciales (TRANSCLIM)" and "Clima Ibérico y Circulación Meridional Atlántica (CIMERA)". Both are funded by the Spanish Ministry for Science and Innovation and directed by Dr Rainer Zahn, ICREA research professor at the UAB Department of Geology.
Adapted from materials provided by Universitat Autonoma de Barcelona, via EurekAlert!, a service of AAAS.

Plankton study helps forecast toxic tides

The coastal ocean can be likened to a parfait of enormous proportions. Rather than being homogeneous, it’s a layered affair of water, nutrients and organisms.
Among the layers are those that contain large concentrations of plankton. These layers are usually just a few yards below the surface, only a few feet thick but potentially miles long. They serve as ecological hot spots, providing food for other creatures. But they can also be the scene of huge algal blooms that cause toxic red tides.
Just how those plankton layers form has been unclear. Now in a paper in Science, William M. Durham and Roman Stocker of the Massachusetts Institute of Technology and John O. Kessler of the University of Arizona have shown that plankton’s swimming and shape play a role.
Stocker, who studies the large-scale consequences of the motility of plankton, said that the single-celled organisms tended to swim upward during the day and down at night. If the water is still, they just go straight up and down.
But ocean currents set up layers of faster- and slower-moving water. At the boundary between two layers, shear forces occur that act on the plankton, causing them to swim in an inclined direction and, if the forces are strong enough, making them tumble and spin. Because they are no longer swimming upward, the tumbling plankton become trapped at this boundary, joined by more and more plankton as they swim up into the zone. The findings should help in efforts to forecast red tides, Stocker said.
``It points oceanographers in the right direction in terms of what they should measure to predict these things,” Stocker said. ``They need to measure vertical shear, and measure something about cell morphology.”— New York Times News Service

Oil In Ocean Shows Up On NASA Images: Half Of The Oil In The Ocean Bubbles Up Naturally From Seafloor

About half of the oil in the ocean bubbles up naturally from the seafloor, with Earth giving it up freely like it was of no value. Likewise, NASA satellites collect thousands of images and 1.5 terrabytes of data every year, but some of it gets passed over because no one thinks there is a use for it.

Scientists recently found black gold bubbling up from an otherwise undistinguished mass of ocean imagery. Chuanmin Hu, an optical oceanographer at the University of South Florida, St. Petersburg, and colleagues from the National Oceanic and Atmospheric Administration (NOAA) and the University of Massachusetts–Dartmouth (UMass), found that they could detect oil seeping naturally from the seafloor of the Gulf of Mexico by examining streaks amid the reflected sunlight on the ocean's surface.
Most researchers usually discard such "sun glint" data as if they were over-exposed photos from a camera. "Significant sun glint is sometimes thought of as trash, particularly when you are looking for biomass and chlorophyll," said Hu. "But in this case, we found treasure."
The new technique could provide a more timely and cost-effective means to survey the ocean for oil seeps, to monitor oil slicks, and to differentiate human-induced spills from seeps.
Oil decreases the roughness of the ocean surface. Depending on the angles of the camera and of the light reflection, oil creates contrasting swaths that can show up in airborne images as either lighter or darker than the surrounding waters.
The detection and monitoring of oil spills and seeps by satellite is not new. Visible, infrared, microwave, and radar sensors have all been used, with synthetic aperture radar (SAR) being the most popular and reliable method in recent years according to the study authors. SAR imagery can be very expensive, the authors note, and timely, repeat coverage is not always possible, particularly in tropical regions.
Using imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA's Terra and Aqua satellites, Hu and colleagues assert, is far cheaper because the data is collected daily and provided freely by NASA, without the need for special observation requests. And the polar orbits of Terra and Aqua allow images of oil slicks to be collected several times per week in tropical regions and perhaps several times a day at higher latitudes. The description of the new technique was published in January in Geophysical Research Letters.
Hu actually happened upon the oil imagery while looking for signs of harmful algal blooms—commonly referred to as "red tide"—in the western Gulf of Mexico. Examining MODIS images, he kept noticing streaks across the sun glint reflections. After conferring with study co-authors Xiaofeng Li and William Pichel of NOAA and Frank Muller-Karger of UMass, Hu became aware that the streaks could be oil from natural seeps on the seafloor.
Hu and colleagues then defined a geographic area of the western Gulf and obtained MODIS images for the month of May for nine consecutive years (2000 to 2008) from NASA's Goddard Space Flight Center, Greenbelt, Md. The team reviewed more than 200 images containing sun glint, and found more than 50 with extensive oil slicks.
Exactly how much oil naturally seeps out of the seafloor is unknown, and most estimates are very crude because there has never been a proper global survey made for the public record. Researchers identified the natural seepage rate as a critical unanswered question when the National Academy of Sciences compiled its third Oil in the Sea report in 2003.
"This capacity for detecting oil in the ocean has great potential, not just for oil seeps but for responding to oil spills," said Chris Reddy, a marine chemist at the Woods Hole Oceanographic Institution in Massachusetts. "Scientists might be able to use this to forensically study old spills, to watch how new ones evolve in real time, and to rule out a spill when there is none. Ultimately, this could lead to a better use of our public resources."
The technique could be useful for detecting and monitoring oil spills from ships and other platforms, though Hu emphasized that the spills must be large enough (at least hundreds of meters or feet) to be visible in the MODIS imagery. If there is suspicion of a large human-caused spill, for instance, researchers would be able to review ocean imagery to see if the slick was present before the alleged spill, indicating a natural seepage. On the other hand, MODIS satellite imagery collected on a regular basis could help coastal managers track and mitigate the effects of large accidental spills.
The new method is not perfect, as cloud cover or a lack of sun glint can limit its use. Hu and colleagues suggest it may be best used as a complement to SAR, which penetrates cloud cover and can be tilted to get the necessary imaging angle.
"If you can get an image on a two- to three-day time frame and anywhere on the globe, that's pretty spectacular," said Reddy. "The first few days are critical to tracking oil in the ocean, so it helps to be able to use technology in real time to make informed decisions about cleanup."
Adapted from materials provided by NASA/Goddard Space Flight Center.

Tandem Mission Brings Ocean Currents Into Sharper Focus

What's true for television screens and digital images also applies to satellite data. The more resolution, the better.

When the two ocean-observing satellites OSTM/Jason-2 and Jason-1 begin their tandem mission in February, they'll be flying in a new configuration designed to get the most detailed measurements possible of the ocean surface. They'll enable scientists to distinguish much smaller ocean features than they could with only one satellite and see more quickly how these features change over time.

"The goal is to map global ocean currents--their locations and their speed," says JPL's Lee-Lueng Fu, project scientist for OSTM/Jason-2 and Jason-1. This information will enhance operational applications, such as ship routing or tracking pollution in the ocean, he says, as well as research efforts. "Currents and eddies contain most of the kinetic energy in the ocean. They transport heat, nutrients and carbon dioxide--critical elements of our climate system."

The maneuvers to put the two satellites in place for this new mission began on January 26 and will continue for about 10 days.

This will be Jason-1's second tandem mission. Launched in 2001, Jason-1 took the place of the aging Topex/Poseidon, continuing the sea surface height measurements begun by Topex/Poseidon in 1992. After the two satellites were calibrated and their data compared to make sure that their measurements were exactly the same, Topex/Poseidon was gently nudged just far enough ahead of Jason-1 to put its ground tracks midway between those of Jason-1. The two spacecrafts collected data simultaneously during this "interleaved" tandem mission for three years until Topex/Poseidon ceased operation in January 2006.

Jason-1 has now been replaced by the Ocean Surface Topography Mission/Jason-2 satellite, launched in June 2008. As before, the newer satellite moved into orbit close to its predecessor soon after launch and the spacecraft were calibrated. OSTM/Jason-2's data were validated to ensure that it adds seamlessly to the 16-year-long continuous record of sea surface height measurements.

Now it's time for Jason-1 to step aside. For this new interleaved tandem mission, scientists are taking advantage of Jason-1's still healthy propulsion system to put it into a much different position than Topex/Poseidon was in the previous mission. Topex/Poseidon remained so close to Jason-1 that the two spacecraft were flying almost simultaneously over the same region. When maneuvers are complete for this new tandem mission, Jason-1 will be in the same orbit as OSTM/Jason-2 but much further away, about five days behind on the other side of Earth. Its ground tracks will fall mid-way between those of OSTM/Jason-2.

It takes 10 days for the satellites to cover the globe and return to any one place over the ocean. So, in this new tandem configuration, Jason-1 will fly over the same region of the ocean that OSTM/Jason-2 flew over five days earlier. Working together, the two spacecraft will measure the surface topography of the ocean twice as often as would be possible with one satellite. "Over a 10-day period, the two satellites will provide the detailed measurements needed to map small, rapidly changing currents and eddies," says Fu.

Getting to this new operational orbit will take some precise maneuvering. "The first thing we'll do is a planned burn using the spacecraft's four thrusters to bring the spacecraft down 10 kilometers," says Glenn Shirtliffe, JPL Jason-1 project manager. "Then we'll evaluate the burn--check to see how close we've come to our target--and we'll bring it down 10 more kilometers for a total of 20 altogether."

At this lower altitude, the spacecraft's route around the Earth is shorter and it will make the trip faster. "Once it reaches its position on the opposite side of Earth from OSTM/Jason-2," Shirtliffe continues, "it will make the same trip back up to put at the same altitude as OSTM/Jason-2, 1336 kilometers (830 miles).

"We will be testing with precise orbit determination systems to be sure it is exactly where it should be," he says. "Our sea surface height measurement depends on precise location. Once we've boosted up to our operational orbit we'll turn on the altimeter, check the other instruments, and verify that we're flying the way we predicted." Mission partner CNES designed the maneuver, and JPL is performing the uplink to the spacecraft.

"We've tried to plan this mission to get optimal results," says Fu. "In the past we once had four altimeters making measurements of the sea surface, now we have only the two Jason's. That makes these measurements even more important than before."

Adapted from materials provided by NASA/Jet Propulsion Laboratory

Climate Clues In Southern Ocean: Ocean Currents Surprisingly Resistant To Intensifying Winds

The Antarctic Circumpolar Current is the current system with the largest volume transport in the world ocean. Between 40° and 60°S strong westerlies move about 140 million cubic meters of water per second around the Antarctic continent (this is about five times the transport of the Gulf Stream).

Vertical motions associated with this current have been responsible for transporting a substantial fraction of the anthropogenic carbon dioxide emissions from the atmosphere to the deep ocean, thereby effectively damping the rate of global warming.
Investigations in this key region of the world ocean have been hampered by a sparse database due to the logistical challenges for ship based expeditions in the high-latitude Southern Ocean.
“In our study we used data obtained by the international Argo Programme”, explains Prof. Claus Böning from the Leibniz Institute of Marine Sciences (IFM-GEOMAR) in Kiel, Germany. Argo is a system of currently 3000 autonomous free-floating robotic systems which are surveying the world ocean. Every 10 days these buoys measure temperature and salinity profiles over the upper 2000 meters. These measurements are transmitted to land stations via satellite. “For this study about 52,000 profiles of more than 600 Argo-drifters in the Southern Ocean were used and compared with historic ship measurements”, explains oceanographer Astrid Dispert from IFM-GEOMAR. For this analysis the extensive archives of the Australian marine research centre in Hobart, Tasmania were also used.
As expected, the observations in the subpolar ocean demonstrate an increase of water temperature and a decrease in salinity at the same time. Nevertheless, in contradiction to the simulations of various climate models the data show no significant changes in water transport. “Our results point to one important thing: Eddies which are currently not resolved in climate models might be the key process in controlling the transport of the ACC”, Prof. Böning explains. Hence, his conclusion is that investigations with high-resolution ocean models are required to test this hypothesis. “Of course, besides the simulations we also need further observations”, adds Prof. Martin Visbeck (IFM-GEOMAR). “Thanks to the international Argo observations programme we now have continuously access to data from a worldwide network of more than 3000 profiling-drifters. This is a quantum leap in the field of ocean observations, which, together with high resolution modelling gives us new insights about long-term changes in the ocean.“
Further investigations have to show whether the results are robust. If confirmed, this would in one way be good news: Until now the Southern Ocean is the biggest oceanic sink for anthropogenic carbon dioxide and therefore a crucial regulator for the atmospheric carbon dioxide concentration. Climate models predicted a severe reduction in the southern ocean carbon dioxide uptake due to wind-forced changes in the current fields. Now high-resolution models are needed to assess the role of the hitherto unresolved ocean eddies in the Southern Ocean’s response to the progressive changes in the atmospheric conditions.
Journal reference:
Böning et al. The response of the Antarctic Circumpolar Current to recent climate change. Nature Geoscience, December 2008; DOI: 10.1038/ngeo362
Adapted from materials provided by Leibniz Institute of Marine Sciences (IFM-GEOMAR), via AlphaGalileo.

Ocean Currents Off South Africa Influence Gulf Stream

Variations in the strength of the Gulf Stream can in part attributed to currents off South Africa. Oceanographers at the Leibniz Institute of Marine Sciences (IFM-GEOMAR), Kiel and the University of Cape Town developed a computer model to study the currents systems in unsurpassed detail. To their surprise, they found the impact of small-scale fluctuations of the Agulhas Current south of Africa is detectable all the way into the North Atlantic Ocean.

The Agulhas Current is, like the Gulf Stream, one of the strongest currents in the world ocean. It carries warm and salty water from the tropical Indian Ocean along South Africa’s east coast. South-west of Cape Town it makes an abrupt turn back into the Indian Ocean. In this process huge rings of water with diameters of hundreds of kilometre are cut off at intervals of 3 to 4 months. These so-called “Agulhas Rings” carry extra heat and salt into the South Atlantic, making this a key region for the whole Atlantic Ocean.
"Even when it might seem strange for oceanographers in far-away from Germany to investigate currents near South Africa“ says Dr Arne Biastoch of the IFM-GEOMAR in Kiel, first author of the research papers. "Surprisingly, one can follow the influence of the Agulhas Current right up to the North Atlantic Ocean. This has important consequences for observational programmes in the North Atlantic that attempt to determine the much feared long-term, climatic changes in the Gulf Stream system.“
The new studies show that normal changes from year to year in the formation of Agulhas Rings lead within a few years to an increase in the flux of warm water across the equator from the South to the North Atlantic Ocean. This far-reaching influence was not known before.
"Studies of this kind can only be carried out using very large computer models, which have to simulate fine details in the ocean currents“, adds Prof. Claus Böning from IFM-GEOMAR.
In close international collaboration with colleagues of France and South Africa a new, high-resolution ocean model was developed and intensively tested. It calculates the evolution of the currents on a fine mesh of approximately 40 million grid points. For the simulation supercomputers at the University of Kiel and in Stuttgart were used for a period of over 6 months. The analysis of the enormous amounts of data will keep the scientists of Kiel and their international colleagues busy for years.
This research was recently published both in Nature and Geophysical Research Letter.
Adapted from materials provided by Leibniz Institute of Marine Sciences, via AlphaGalileo.

Adopted from Science Daily

'Fish Technology' Draws Renewable Energy From Slow Water Currents

Slow-moving ocean and river currents could be a new, reliable and affordable alternative energy source. A University of Michigan engineer has made a machine that works like a fish to turn potentially destructive vibrations in fluid flows into clean, renewable power.

The machine is called VIVACE. VIVACE is the first known device that could harness energy from most of the water currents around the globe because it works in flows moving slower than 2 knots (about 2 miles per hour.) Most of the Earth's currents are slower than 3 knots. Turbines and water mills need an average of 5 or 6 knots to operate efficiently.
VIVACE stands for Vortex Induced Vibrations for Aquatic Clean Energy. It doesn't depend on waves, tides, turbines or dams. It's a unique hydrokinetic energy system that relies on "vortex induced vibrations."
Vortex induced vibrations are undulations that a rounded or cylinder-shaped object makes in a flow of fluid, which can be air or water. The presence of the object puts kinks in the current's speed as it skims by. This causes eddies, or vortices, to form in a pattern on opposite sides of the object. The vortices push and pull the object up and down or left and right, perpendicular to the current.
These vibrations in wind toppled the Tacoma Narrows bridge in Washington in 1940 and the Ferrybridge power station cooling towers in England in 1965. In water, the vibrations regularly damage docks, oil rigs and coastal buildings.
"For the past 25 years, engineers—myself included—have been trying to suppress vortex induced vibrations. But now at Michigan we're doing the opposite. We enhance the vibrations and harness this powerful and destructive force in nature," said VIVACE developer Michael Bernitsas, a professor in the U-M Department of Naval Architecture and Marine Engineering.
Fish have long known how to put the vortices that cause these vibrations to good use.
"VIVACE copies aspects of fish technology," Bernitsas said. "Fish curve their bodies to glide between the vortices shed by the bodies of the fish in front of them. Their muscle power alone could not propel them through the water at the speed they go, so they ride in each other's wake."
This generation of Bernitsas' machine looks nothing like a fish, though he says future versions will have the equivalent of a tail and surface roughness a kin to scales. The working prototype in his lab is just one sleek cylinder attached to springs. The cylinder hangs horizontally across the flow of water in a tractor-trailer-sized tank in his marine renewable energy laboratory. The water in the tank flows at 1.5 knots.
Here's how VIVACE works: The very presence of the cylinder in the current causes alternating vortices to form above and below the cylinder. The vortices push and pull the passive cylinder up and down on its springs, creating mechanical energy. Then, the machine converts the mechanical energy into electricity.
Just a few cylinders might be enough to power an anchored ship, or a lighthouse, Bernitsas says. These cylinders could be stacked in a short ladder. The professor estimates that array of VIVACE converters the size of a running track and about two stories high could power about 100,000 houses. Such an array could rest on a river bed or it could dangle, suspended in the water. But it would all be under the surface.
Because the oscillations of VIVACE would be slow, it is theorized that the system would not harm marine life like dams and water turbines can.
Bernitsas says VIVACE energy would cost about 5.5 cents per kilowatt hour. Wind energy costs 6.9 cents a kilowatt hour. Nuclear costs 4.6, and solar power costs between 16 and 48 cents per kilowatt hour depending on the location.
"There won't be one solution for the world's energy needs," Bernitsas said. "But if we could harness 0.1 percent of the energy in the ocean, we could support the energy needs of 15 billion people."
The researchers recently completed a feasibility study that found the device could draw power from the Detroit River. They are working to deploy one for a pilot project there within the 18 months.
This work has been supported by the U.S. Department of Energy, the Office of Naval Research, the National Science Foundation, the Detroit/Wayne County Port Autrhority, the DTE Energy Foundation, Michigan Universities Commercialization Initiative, and the Link Foundation. The technology is being commercialized through Bernitsas' company, Vortex Hydro Energy.
Journal reference:
. VIVACE (Vortex Induced Vibration for Aquatic Clean Energy): A New Concept in Generation of Clean and Renewable Energy from Fluid Flow. Journal of Offshore Mechanics and Arctic Engineering, December 2008
Adapted from materials provided by University of Michigan.

Oceanographers Uncover The Physics Of Rip Currents

Rip currents flow in very erratic patterns, not in steady courses as previously believed -- which may help explain why they can be so dangerous even for experienced swimmers. Oceanographers have discovered the behavior by tracking the motion of colored dye added to a wave pool generating rip currents.

NEWARK, Del. -- Each year, an estimated 100 people drown in ocean rip currents. A strong current can sweep even the strongest swimmer out to sea. Researchers are now making waves studying rip currents, revealing the life-saving information you need to know about these dangerous ocean currents.

There's something lurking in the ocean -- creating panic in even the best swimmers!

"It came really quick, like we went under a wave, and then the next thing we know it was just, like, pulling us out," says 18-year old Phoebe Brown. Not a shark, it's a rip current. And it can drag unsuspecting swimmers out to sea, up to eight feet per second.

Rip currents form at breaks in sandbars hidden underwater, creating a strong channel of water that pulls anything in its path far away from shore. Traditionally, oceanographers believed rip currents had a steady, uniform course. Now, new research shows the flow of water moves in an erratic pattern.

Oceanographer James Kirby, Jr, says, "Flow patterns get very, very complicated and very, very unpredictable, and we're trying to come to an understanding of what causes all that complication."

In a study at the University of Delaware in Newark, Kirby added colored dye to a wave pool generating rip currents. The dye's course is recorded as it moves through the current. The dye's movement shows an irregular rip current pattern -- making it more difficult to escape.

"It's very difficult for a swimmer once he's actually caught in the flow even to establish a sense of orientation and decide which way to swim," Kirby tells DBIS. He also says some rip currents can last for weeks and even months at a time, in the same location.

To avoid unpredictable rip currents, keep an eye out for signs of one, like broken wave patterns and discolored water. If you end up caught in a rip current...

"Number one is don't panic," says Jesse Steele, a lifeguard at Bethany Beach in Delaware. "Swim parallel to shore."

BACKGROUND: A professor at the University of Delaware has created a comprehensive computer model that predicts the physical processes in the area from the high tide mark on shore to a depth of 10 meters, called the nearshore ocean.Wave weight, current movement and naturally occurring sediment transport, are analyzed by computers to from a computer model. The model allows weather forecasters to quickly predict dangerous surf conditions and issue immediate warnings. It can even predict some dangerous events weeks before they occur. Swimmers and life guards have more tools to identify rip currents, for example. The model would also be useful for builders designing shore properties.

WHAT ARE RIP CURRENTS? A rip current is a strong flow of water returning seaward along the shore. When wind and waves push water to the shore, the previous backwash is often pushed sideways by the oncoming waves. The backwash streams along the shoreline until it finds an exit back to the sea. The resulting rip current is usually narrow and located in trenches between sandbars, under piers, or along jetties. The current is strongest at the surface and can dampen incoming waves, which might make the area seem deceptively calm. That's one thing to look for when searching for rip currents: unusually calm waters. The color of the water may be different from the surrounding area, and the waterline will be lower on the shore near a rip current.

IT'S NOT THE UNDERTOW: Many of the deaths resulting from rip currents are wrongly attributed to an undertow. The two are related, but distinct. Rip currents occur if there's a place along the beach where the incoming waves aren't as strong, so that the escaping water goes through that weak spot. If there is no spot with weaker surf, the accumulated water flows down and under the waves and back out to sea, forming an undertow.

TIDES AND THE MOON: Rip currents are sometimes erroneously called "rip tides." They are not tides, although particularly low tides can lead to stronger rip currents. What are tides? The strength of gravity depends on the distance from the source; the closer you are, the stronger the "pull" that you feel. The moon's gravity acts on the earth, but the diameter of the earth is large enough compared to the distance of the moon that one side of our planet -- the one nearer the moon -- feels the moon's gravity much more strongly than the side further away from the moon. In effect, the earth is "stretched" by the difference in the moon's gravity across the earth, and this gives rise to the tides. That's why there are two tidal bulges on the earth, one on the near side, and one on the far side.

SAFETY TIPS: The most common advice for escaping a rip current is not to panic and try to swim against the current directly back to shore. People become exhausted very quickly and can easily drown. Instead, you should swim parallel to the beach and then let the waves bring you into shore.

The American Geophysical Union contributed to the information contained in the TV portion of this report.

New Ocean Current Discovered

Scientists at the Georgia Institute of Technology have discovered a new climate pattern called the North Pacific Gyre Oscillation. This new pattern explains, for the first time, changes in the water that are important in helping commercial fishermen understand fluctuations in the fish stock. They're also finding that as the temperature of the Earth is warming, large fluctuations in these factors could help climatologists predict how the oceans will respond in a warmer world."We've been able to explain, for the first time, the changes in salinity, nutrients and chlorophyll that we see in the Northeast Pacific," said Emanuele Di Lorenzo, assistant professor in Georgia Tech's School of Earth and Atmospheric Sciences.Since 1945, fishermen in the California current of the Pacific Ocean have been tracking temperature, salinity and nutrients, among other things, in the ocean to help them predict changes in fish populations like sardines and anchovies that are important for the industry. Studying this data, along with satellite images, Di Lorenzo discovered a pattern of current that he named the North Pacific Gyre Oscillation.Recent satellite data suggest that this current is undergoing intensification as the temperature of the Earth has risen over the past few decades."Although the North Pacific Gyre Oscillation is part of a natural cycle of the climate system, we find evidence suggesting that its amplitude may increase as global warming progresses," said Di Lorenzo.If this is true, this newly found climate pattern mey help scientists predict how the ecosystem of the Pacific Ocean is likely to change if the world continues to warm, as predicted by the Intergovernmental Panel on Climate Change.The research appears in the April 30 edition of the journal Geophysical Research Letters.Source: Georgia Institute of Technology.

Supergyre missing deep ocean current identified assertained an important factor in climate regulation

Australian scientists have identified the missing deep ocean pathway – or ‘supergyre’ – linking the three Southern Hemisphere ocean basins in research that will help them explain more accurately how the ocean governs global climate।

The new research confirms the current sweeping out of the Tasman Sea past Tasmania and towards the South Atlantic is a previously undetected component of the world climate system’s engine-room – the thermohaline circulation or ‘global conveyor belt’.
Wealth from Oceans Flagship* scientist Ken Ridgway says the current, called the Tasman Outflow, occurs at an average depth of 800-1,000 metres and may play an important role in the response of the conveyor belt to climate change.
Published in August in Geophysical Research Letters the findings confirm that the waters south of Tasmania form a ‘choke-point’ linking the major circulation cells in the Southern Hemisphere oceans.
“In each ocean, water flows around anticlockwise pathways or ‘gyres’ the size of ocean basins,” Mr Ridgway says. “These gyres are the mechanism that distribute nutrients from the deep ocean to generate life on the continental shelves and slopes. They also drive the circulation of the world’s oceans, creating currents and eddies and help balance the climate system by transferring ocean heat away from the tropics toward the polar region.”
He says the conventional picture of the Southern Hemisphere mid-latitude circulation comprises basin-wide but quite distinct gyres contained within the Indian, Pacific and Atlantic Oceans। However model simulations had suggested that these gyres are connected.

The CSIRO team analysed thousands of temperature and salinity data samples collected between 1950 and 2002 by research ships, robotic ocean monitors and satellites in the region between 60°S and the Equator. They identified linkages between these gyres to form a global-scale ‘supergyre’ that transfers water to all three ocean basins.
Mr Ridgway and co-author Mr Jeff Dunn say identification of the supergyre improves the ability of researchers to more accurately explain how the ocean governs global climate.
Completed as part of the BLUElink ocean forecasting project, this research provides the missing deep-flow connection between the Pacific and Indian Oceans. It has long been known that north of Australia a system of currents in the ocean’s upper 300m, called the Indonesian Throughflow, drains water from the Pacific into the Indian Ocean through the Indonesian archipelago – a process which influences Australian rainfall.
Mr Ridgway says Tasmania figures as a critical converging point providing a northern boundary to the mid-water funnel that is bordered at latitudes near 50°S.
“The interconnected gyre system and the East Australian Current provide the mechanism by which SubAntarctic Mode Water and Antarctic Intermediate Water are distributed between the ocean basins,” he says। “The flows of these water masses have strong influences on the global climate and so monitoring changes in the transport of the Tasmanian connection may be an important measurement of the state of the global climate system.

“Recognising the scales and patterns of these subsurface water masses means they can be incorporated into the powerful models used by scientists to project how climate may change,” he says.
* The goal of the Wealth from Oceans Flagship is to position Australia by 2020 as an international benchmark in the delivery of economic, social and environmental wealth based on leadership in understanding ocean systems and processes.
Note: This story has been adapted from a news release issued by CSIRO Australia।

Could Ocean Currents Change?

Records from ice cores show that around 8,200 years ago the Northern Hemisphere's climate abruptly cooled। Many scientists link this event to the final drainage of Lake Agassiz, a large glacial lake covering much of central Canada that formed at the foot of North America's continental glaciers. This drainage is thought to have freshened waters in the northern Atlantic Ocean, slowing down the density-driven oceanic circulation that helps to distribute heat.

Noting that an actual chronology of events must be established before scientists can speculate on causes of this cooling, Hillaire-Marcel et al. study oceanic records downstream from Lake Agassiz's flood discharge route. They find that the lake's drainage occurred between 8,500 and 8,350 years ago but that sea-surface and deep-current conditions, derived from oceanic sediment cores, lack significant concurrent changes in the northern Atlantic.
Instead, the data shows that the 8,200-year-old cooling event was generated by several factors, including melting of North American continental glaciers and subsequent rapid sea level rise which induced a large-scale reorganization of broad oceanic circulation patterns.
Reference for first article: David J. W. Piper: Atlantic Division, Geological Survey of Canada, Dartmouth, Nova Scotia, Canada and C. Hillaire-Marcel and Anne de Vernal: Geochemistry and Geodynamics Research Centre, University of Quebec at Montréal and McGill University (GEOTOP-UQAM-McGill), Montreal, Quebec, Canada; "The ~8.4 ka Lake Agassiz drainage event in the northwest North Atlantic", Geophysical Research Letters (GRL) paper 10.1029/2007GL030396, २००७

Warmer surface temperatures in the North Atlantic may affect the mighty current that encircles Antarctica
In the northern Atlantic Ocean, cold salty water sinks, forming the North Atlantic Deep Water, a southward moving water mass centered around the depth of 2.5 kilometers (1.6 miles). This sunken water is replaced by water essentially originating in the Antarctic Circumpolar Current and flowing across the equator northward through surface currents such as the Gulf Stream and the North Atlantic Current.
In a sensitivity study using a coarse-resolution ocean general circulation model in an idealized single-basin configuration with a circumpolar channel, Fu kar and Vallis find that deep water production diminishes as surface temperature increases in the north, affecting the basin's overturning circulation and stratification.
This induces a change in water mass properties in the southern circumpolar region, causing a substantially higher volume transport around Antarctica. The authors note that significant variations in certain critical model parameters do not change this result. If their model holds true, a change of surface buoyancy in the Northern Hemisphere may significantly influence the stratification and transport of the Antarctic Circumpolar Current.
Reference for second article: Neven S. Fu kar: Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, U.S.A.; Geoffrey K. Vallis: Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Princeton, New Jersey, U.S.A.; also at Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, U.S.A.,"Interhemispheric influence of surface buoyancy conditions on a circumpolar current" Geophysical Research Letters (GRL) paper 10.1029/2007GL030379, 2007
Note: This story has been adapted from a news release issued by American Geophysical Union।

Deep Ocean's most turbulent areas has big impact on Climate

More than a mile beneath the Atlantic's surface, roughly halfway between New York and Portugal, seawater rushing through the narrow gullies of an underwater mountain range much as winds gust between a city's tall buildings is generating one of the most turbulent areas ever observed in the deep ocean।

In fact, the turbulence packs an energy wallop equal to about five million watts -- comparable to output from a small nuclear reactor, according to a landmark study led by Florida State University researcher Louis St. Laurent and described in the August 9 edition of the journal Nature.
The study -- an international collaboration of scientists from the United States and France -- documents for the first time the turbulent conditions in an undersea mountain range known as the Mid-Atlantic Ridge. It provides never-before-seen evidence that deep water turbulence swirling in the small passageways of such mountains is generating much of the mixing of warm and cold waters in the Atlantic Ocean.
Better understanding of the mechanisms of mixing is crucial, says St। Laurent, an assistant professor of physical oceanography at FSU and the study's co-principal investigator, because mixing produces the overall balance of water temperatures that helps control the strength of the Gulf Stream -- the strong, warm ocean current that starts in the Gulf of Mexico, flows along the U.S. east coast to Canada and on to Europe, and plays a crucial climate role.

"Oceanographers are working hard to understand how processes in the ocean help to keep the Earth's climate stable," St. Laurent said. "We are aware that the climate is warming, but we don't yet fully understand how the changes will affect society. Our work will result in better models for predicting how the ocean will affect the climate in the future and a better understanding of sea-level rise, weather patterns such as El Nino, and the impact of these events on fisheries."
St. Laurent compared the flow of seawater through underwater gullies in the Mid-Atlantic Ridge to the wind, so familiar to hikers, that blows through mountain passages on land.
"That wind creates a condition known as turbulence, which can blow the hat from your head," St। Laurent said. "In the ocean, turbulence is produced when water flows quickly though oceanic passages. The turbulence stirs the almost freezing-water near the bottom with warmer water that is closer to the surface much as you would mix cream into coffee by stirring it with a spoon.

"We know that the mixing of warm surface water with very cold deep water is one of several factors that influence the Earth's climate," he said. "The mixing we observed and measured for our study allows the warmth at the surface of the ocean to 'diffuse' deep into the sea. The overall balance between warm and cold water in the Atlantic helps control the strength of the Gulf Stream, which moves heat away from the Earth's equator toward regions that receive much less heating from the sun's rays."
St. Laurent's co-principal investigator and co-author was Andreas M. Thurnherr, a former postdoctoral researcher in the FSU oceanography department and now a scientist at Columbia University. The field study took place in August 2006 during a three-week expedition aboard a French research vessel to a location close to the Azores, volcanic islands 2,000 miles east of the U.S. and west of Europe that comprise an above-sea portion of the mostly submerged Mid-Atlantic Ridge.
To measure the energy generated by the extraordinarily intense turbulence more than a mile below the ocean's surface, St. Laurent and crew used a custom-made instrument called the "turbulence profiler," outfitted with special sensors.
"The turbulence profiler measured the output using 'watts,' the same unit of measurement as printed on light bulbs," St. Laurent said. "In the undersea mountain passage where we intentionally looked, we found turbulence levels as large as one-10th watt per cubic meter of seawater. This is a huge amount of energy when you add all the seawater in the passage, equal to around five million watts, which is comparable to output from a nuclear reactor."
Article: "Overflow Mixing of Lower Thermocline Water on the Crest of the Mid-Atlantic Ridge"

Note: This story has been adapted from a news release issued by Florida State University.

Oceanic storms create oases in the watery desert

THE SARGASSO Sea, like other mid-ocean regions of the world, is warmer, saltier, bluer, and clearer than most other parts of the North Atlantic.
The prevailing oceanographic wisdom has suggested that such open waters were mostly desert-like, unproductive regions populated by a few smaller plant species।

For two decades, scientists have puzzled over how vast blooms of microscopic plants can form in the middle of otherwise barren mid-ocean regions.
High activity
Now a research team led by the Woods Hole Oceanographic Institution (WHOI) has shown that episodic, swirling current systems known as eddies act to pump nutrients up from the deep ocean to fuel such phytoplankton blooms.
Dennis McGillicuddy, a WHOI oceanographer and leader of the Eddies Dynamics, Mixing, Export, and Species composition (EDDIES) project, found that biological activity was surprisingly high when the ocean was stirred by certain types of eddies.
Natural nutrient source
He and colleagues published their work in the May 18 issue of the journal Science. The team's observations showed oxygen and other biologically important elements being consumed at a higher rate than the theories and models could account for. There had to be some natural nutrient source.
Now, McGillicuddy and colleagues have found that eddy-driven nutrient transport actually primes the ocean's "biological pump," fertilizing the waters with nutrients from the deep, according to a WHOI press release.
Population explosion
Fed by this unusual upwelling, the phytoplankton population explodes and, in turn, attracts more zooplankton and other animals higher up the food chain.
The fate of all of that biomass is also important, as plankton blooms can remove substantial amounts of carbon dioxide from surface waters and sink it to the deep ocean.
The eddies (distinct parcels of water) are formed by differences in ocean temperature and salinity that give water different densities.
On a rotating planet, these different water masses tend to dance around one another rather than mix.
The density inside an eddy can be higher or lower than the surrounding water, like high and low-pressure systems in the atmosphere.
The balance between density and pressure differences, along with earth's rotation (the Coriolis force) gives eddy currents their distinctive clockwise or counterclockwise spin.
The direction of the spin depends on whether the eddy contains cooler "mode water" or a warmer core. In nearly six months of ship-based work in the summers of 2004 and 2005, the researchers employed a combination of remote sensing, video plankton recorders, electronic plankton nets, ocean drifters, tracers, and traditional measurements of water properties and current speeds.
Swirling currents
Working from a long-debated but mostly untested hypothesis, EDDIES investigators measured how these swirling currents can perturb the layers of the ocean and cause an upwelling of nutrient-rich water into the sunlit "euphotic" zone— the top 330 feet (100 metres) that light penetrates.
They started with NASA satellite measurements of sea surface height to locate eddies in the Sargasso Sea, south and east of the Gulf Stream in the North Atlantic.
The 18-member research team then sailed into those eddies with their research vessels.