* Astronomy

Members Login
Post Info TOPIC: Meddies


L

Posts: 131433
Date:
Ekman transport
Permalink  
 


Title: Localised subduction of anthropogenic carbon dioxide in the Southern Hemisphere oceans
Authors: Jean-Baptiste Sallée, Richard J. Matear, Stephen R. Rintoul & Andrew Lenton

The oceans slow the rate of climate change by absorbing about 25% of anthropogenic carbon dioxide emissions annually. The Southern Ocean makes a substantial contribution to this oceanic carbon sink: more than 40% of the anthropogenic carbon dioxide in the ocean has entered south of 40°S. The rate-limiting step in the oceanic sequestration of anthropogenic carbon dioxide is the transfer of carbon across the base of the surface mixed layer into the ocean interior, a process known as subduction. However, the physical mechanisms responsible for the subduction of anthropogenic carbon dioxide are poorly understood. Here we use observationally based estimates of subduction and anthropogenic carbon concentrations in the Southern Ocean to determine the mechanisms responsible for carbon sequestration. We estimate that net subduction amounts to 0.42±0.2PgC yr^-1 between 35°S and the marginal sea-ice zone. We show that subduction occurs in specific locations as a result of the interplay of wind-driven Ekman transport, eddy fluxes and variations in mixed-layer depth. The zonal distribution of the estimated subduction is consistent with the distribution of anthropogenic carbon dioxide in the ocean interior. We conclude that oceanic carbon sequestration depends on physical properties, such as mixed-layer depth, ocean currents, wind and eddies, which are potentially sensitive to climate variability and change.

Read more



__________________


L

Posts: 131433
Date:
Abyssal undular vortices
Permalink  
 


 Research on neutrinos allows the discovery of vortices in the abysses of the eastern Mediterranean

An INFN research project on neutrinos has made it possible to observe for the first time the presence of chains of marine vortices in the Mediterranean at depths of more than 3000 meters, large water structures of diameters of approximately 10 km, moving slowly at speeds of approximately 3 centimetres per second.
The article that describes this discovery (Abyssal undular vortices in the Eastern Mediterranean basin, Rubino et al.) is going to be published today in the online Nature Communications scientific journal and signed, among others, by researchers of INFN Roma1 and Catania Divisions and INFN National Laboratories of the South (LNS).

Read more



__________________


L

Posts: 131433
Date:
Ocean eddies
Permalink  
 


Eddies Found to be Deep, Powerful Modes of Ocean Transport

Researchers from Woods Hole Oceanographic Institution (WHOI) and their colleagues have discovered that massive, swirling ocean eddies - known to be up to 500 kilometres across at the surface - can reach all the way to the ocean bottom at mid-ocean ridges, some 2,500 metres deep, transporting tiny sea creatures, chemicals, and heat from hydrothermal vents over large distances.
The previously unknown deep-sea phenomenon, reported in the April 28 issue of the journal Science, helps explain how some larvae travel huge distances from one vent area to another, said Diane K. Adams, lead author at WHOI and now at the National Institutes of Health.

Read more 



__________________


L

Posts: 131433
Date:
RE: Meddies
Permalink  
 


Ocean surface currents have long been the focus of research due to the role they play in weather, climate and transportation of pollutants, yet essential aspects of these currents remain unknown.
By employing a new technique based on the same principle as police speed-measuring radar guns to satellite radar data, scientists can now obtain information necessary to understand better the strength and variability of surface current regimes and their relevance for climate change.
Scientists at the SeaSAR 2008 workshop held this week in ESRIN, ESA's European Centre for Earth Observation in Frascati, Italy, demonstrated how this new method on data from the Advanced Synthetic Aperture Radar (ASAR) instrument aboard ESAs Envisat, enabled measurements of the speed of the moving ocean surface.
Synthetic Aperture Radar (SAR) instruments, such as ASAR, record microwave radar backscatter in order to identify roughness patterns, which are linked to varying surface winds, waves and currents of the ocean surface. However, interpreting radar images to identify and quantify surface currents had proven very difficult.

Read more

__________________


L

Posts: 131433
Date:
Permalink  
 

Marine scientists have now figured out a way to "see through" the ocean's surface and detect what's below, with the help of satellites in space.

Using sensor data from several U.S. and European satellites, researchers from the University of Delaware, NASA's Jet Propulsion Laboratory and the Ocean University of China have developed a method to detect super-salty, submerged eddies called "Meddies" that occur in the Atlantic Ocean off Spain and Portugal at depths of more than a half mile. These warm, deep-water whirlpools, part of the ocean's complex circulatory system, help drive the ocean currents that moderate Earth's climate.

The research marks the first time scientists have been able to detect phenomena so deep in the ocean from space--and using a new multi-sensor technique that can track changes in ocean salinity.
The lead author of the study was Xiao-Hai Yan, Mary A. S. Lighthipe Professor of Marine Studies at the University of Delaware and co-director of UD's Centre for Remote Sensing. His collaborators included Young-Heon Jo, a postdoctoral researcher in the UD College of Marine Studies, W. Timothy Liu from NASA's Jet Propulsion Laboratory in Pasadena, California, and Ming-Xia He, from the Ocean Remote Sensing Institute at the Ocean University of China in Qingdao, China. Their results are reported in the April issue of the American Meteorological Society's Journal of Physical Oceanography.

"Since Meddies play a significant role in carrying salty water from the Mediterranean Sea into the Atlantic, new knowledge about their trajectories, transport, and life histories is important to the understanding of their mixing and interaction with North Atlantic water. Ultimately, we hope this information will lead to a better understanding of their impact on global ocean circulation and global climate change" - Xiao-Hai Yan.

First identified in 1978, Meddies are so named because they are eddies--rotating pools of water--that flow out of the Mediterranean Sea. A typical Meddy averages about 600 meters deep and 100 kilometres in diameter, and contains more than a billion tons (1,000 billion kilograms) of salt.

Coupling data collected by several different satellite-borne sensors, researchers from the University of Delaware, NASA's Jet Propulsion Laboratory, and the Ocean University of China have been able to "break through" the ocean's surface to detect "Meddies" -- super-salty warm-water eddies that originate in the Mediterranean Sea and then sink more than a half-mile underwater in the Atlantic Ocean. The Meddies are shown in red in this scientific figure.

While warm water ordinarily resides at the ocean's surface, the warm water flowing out of the Mediterranean Sea has such a high salt concentration that when it enters the Atlantic Ocean at the Strait of Gibraltar, it sinks to depths of more than 1,000 meters along the continental shelf. This underwater river then separates into clockwise-flowing Meddies that may continue to spin westward for more than two years, often coalescing with other Meddies to form giant, salty whirlpools that may stretch for hundreds of miles.

"Since the Mediterranean Sea is much saltier than the Atlantic Ocean, the Meddies constantly add salt to the Atlantic" - Xiao-Hai Yan.

Without this steady salt-shaker effect, he notes, the conveyor belt of ocean currents that help distribute heat from the tropics toward the North Pole might be diminished, resulting in colder temperatures in regions such as New England and northwestern Europe that currently experience more temperate climates.

"There is concern about global climate change shutting down the ocean currents that warm the Atlantic Ocean. The melting of sea ice at the North Pole could add enormous amounts of fresh water to the Atlantic, reducing its salinity enough to slow the sinking of cooler water, which would shut down the conveyor belt of ocean currents that help warm major regions of the planet" - Xiao-Hai Yan.

Yan and his team drew on data from several satellite sensors that can read an important signal of a Meddy's presence.

Altimeters flying aboard NASA's Topex/Poseidon and Jason satellites and the European Space Agency's European Remote Sensing and Environment (Envisat) satellites measured the height of the sea surface compared to average sea level, revealing the difference in altitude where a Meddy entered the Atlantic.
Specialised microwave radars called scatterometers, including the former NASA Scatterometer (NSCAT) on Japan's Midori-1 spacecraft and the current SeaWinds instrument on NASA's QuikSCAT spacecraft, measured the surface wind over the ocean, providing data needed to remove the surface variability "noise" caused by the wind blowing over the ocean's surface.
The scientists also analysed data provided by an infrared spectrometer known as the Advanced Very High Resolution Radiometer, which flies aboard National Oceanic and Atmospheric Administration satellites. This instrument maps the heat emitted by the ocean's top layer and showed the increase in temperature from a warm Meddy before it began sinking beneath the waves.

"By carefully removing the stronger surface signatures of upper ocean processes, we were able to unveil the surface signatures of deeper ocean processes, such as the Meddies, to these space-based sensors" - W. Timothy Liu .

While the technique is not yet 100 percent accurate, Yan and his colleagues are continuing to refine it and are exploring its application to other coastal regions of the world.
They are currently examining salinity variations in the East China Sea before and after the Three Gorges Dam--the largest dam in the world--was built. The data will help researchers assess the dam's impacts on the ecosystem and on water circulation patterns.

The research was supported by grants from the National Aeronautics and Space Administration, the Office of Naval Research and the National Oceanic and Atmospheric Administration.

Source

__________________
Page 1 of 1  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard