Seamount Scientists Offer New Comprehensive View of Deep-Sea Mountains
Lying beneath the ocean is spectacular terrain ranging from endless chains of mountains and isolated peaks to fiery volcanoes and black smokers exploding with magma and other minerals from below Earth’s surface. This mountainous landscape, some of which surpasses Mt. Everest heights and the marine life it supports, is the spotlight of a special edition of the research journal Oceanography.
These massive underwater mountains, or seamounts, are scattered across every ocean and collectively comprise an area the size of Europe. These deep and dark environments often host a world teeming with bizarre life forms found nowhere else on Earth. More than 99 percent of all seamounts remain unexplored by scientists, yet their inhabitants, such as the long-lived deepwater fish orange roughy, show signs of habitat destruction and over exploitation from intense international fishing efforts.
Scientists from Scripps Institution of Oceanography at UC San Diego and colleagues from the National Oceanic Atmospheric Administration, Oregon State University, University of British Columbia and Woods Hole Oceanographic Institution were among those who contributed their expertise in seamount chemistry, physics, geology, hydrology, oceanography, biology and fisheries conservation to this special interdisciplinary effort to delve into the extremely broad research supported by seamounts and to communicate the science and threats facing them to the public.
“One of the key goals of this special issue was to bring together the extremely diverse seamount research community that ranges from fisheries science and conservation all the way to mantle geochemistry,” said Hubert Staudigel – a research geologist at Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps and the lead guest editor of the special issue. “In my eyes, this volume of Oceanography goes beyond that by presenting amazing new research in a way that the public can understand and get excited about.”
“This issue of Oceanography offers a broad perspective on seamount research of all major disciplines to raise awareness of the diversity of seamount research and to promote collaboration among seamount scientists,” wrote the editors of the issue, which represents the most comprehensive volume of peer-reviewed research on the subject to date.
“I was pleased to see how many of the contributions in this special issue deal with very practical and societally important issues of seamounts,” said U.S. Geological Survey Director Marcia McNutt.
This Oceanography issue is the result of the work of a National Science Foundation-funded biogeoscience research coordination network organized by Staudigel and the co-editors of the volume.
This comprehensive synthesis will establish new collaborations between scientists while at the same time offer a unique educational opportunity for the public to learn about an important feature on Earth that remains vastly unexplored.
Science Team Finds Subtropical Waters Flushing Through Greenland Fjord
Recent changes in ocean circulation in the North Atlantic are delivering larger amounts of subtropical waters to the high latitudes. A research team led by Fiamma Straneo, a physical oceanographer at Woods Hole Oceanographic Institution, found that subtropical waters are reaching Greenland's glaciers, driving melting and likely triggering an acceleration of ice loss. Melting ice also means more fresh water in the ocean, which could flood into the North Atlantic and disrupt a global system of currents, known as the Ocean Conveyor. (Credit: Woods Hole Oceanographic Institution)
Waters from warmer latitudes — or subtropical waters — are reaching Greenland’s glaciers, driving melting and likely triggering an acceleration of ice loss, reports a team of researchers led by Fiamma Straneo, a physical oceanographer from the Woods Hole Oceanographic Institution (WHOI).
“This is the first time we’ve seen waters this warm in any of the fjords in Greenland,” says Straneo. “The subtropical waters are flowing through the fjord very quickly, so they can transport heat and drive melting at the end of the glacier.”
Greenland’s ice sheet, which is two-miles thick and covers an area about the size of Mexico, has lost mass at an accelerated rate over the last decade. The ice sheet’s contribution to sea level rise during that time frame doubled due to increased melting and, to a greater extent, the widespread acceleration of outlet glaciers around Greenland.
While melting due to warming air temperatures is a known event, scientists are just beginning to learn more about the ocean’s impact — in particular, the influence of currents — on the ice sheet.
“Among the mechanisms that we suspected might be triggering this acceleration are recent changes in ocean circulation in the North Atlantic, which are delivering larger amounts of subtropical waters to the high latitudes,” says Straneo. But a lack of observations and measurements from Greenland’s glaciers prior to the acceleration made it difficult to confirm.
The research team, which included colleagues from University of Maine, conducted two extensive surveys during July and September of 2008, collecting both ship-based and moored oceanographic data from Sermilik Fjord — a large glacial fjord in East Greenland.
Sermilik Fjord, which is 100 kilometers (approximately 62 miles) long, connects Helheim Glacier with the Irminger Sea. In 2003 alone, Helheim Glacier retreated several kilometers and almost doubled its flow speed.
Deep inside the Sermilik Fjord, researchers found subtropical water as warm as 39 degrees Fahrenheit (4 degrees Celsius). The team also reconstructed seasonal temperatures on the shelf using data collected by 19 hooded seals tagged with satellite-linked temperature depth-recorders. The data revealed that the shelf waters warm from July to December, and that subtropical waters are present on the shelf year round.
“This is the first extensive survey of one of these fjords that shows us how these warm waters circulate and how vigorous the circulation is,” says Straneo. “Changes in the large-scale ocean circulation of the North Atlantic are propagating to the glaciers very quickly — not in a matter of years, but a matter of months. It’s a very rapid communication.”
Straneo adds that the study highlights how little is known about ocean-glacier interactions, which is a connection not currently included in climate models. “We need more continuous observations to fully understand how they work, and to be able to better predict sea-level rise in the future,” says Straneo.
The paper was chosen for advanced online publication Feb. 14, 2010, by Nature Geosciences; it will also appear in the March 2010 printed edition of the journal
Climate ‘Tipping Points’ May Arrive Without Warning, Says Top Forecaster
Icebergs breaking off from the Dawes Glacier in the Endicott Arm
A new University of California, Davis, study by a top ecological forecaster says it is harder than experts thought to predict when sudden shifts in Earth’s natural systems will occur — a worrisome finding for scientists trying to identify the tipping points that could push climate change into an irreparable global disaster.
“Many scientists are looking for the warning signs that herald sudden changes in natural systems, in hopes of forestalling those changes, or improving our preparations for them,” said UC Davis theoretical ecologist Alan Hastings. “Our new study found, unfortunately, that regime shifts with potentially large consequences can happen without warning — systems can ‘tip’ precipitously.
“This means that some effects of global climate change on ecosystems can be seen only once the effects are dramatic. By that point returning the system to a desirable state will be difficult, if not impossible.”
The current study focuses on models from ecology, but its findings may be applicable to other complex systems, especially ones involving human dynamics such as harvesting of fish stocks or financial markets.
Scientists widely agree that global climate change is already causing major environmental effects, such as changes in the frequency and intensity of precipitation, droughts, heat waves and wildfires; rising sea level; water shortages in arid regions; new and larger pest outbreaks afflicting crops and forests; and expanding ranges for tropical pathogens that cause human illness.
And they fear that worse is in store. As U.S. presidential science adviser John Holdren recently told a congressional committee: “Climate scientists worry about ‘tipping points’ … thresholds beyond which a small additional increase in average temperature or some associated climate variable results in major changes to the affected system.”
Among the tipping points Holdren listed were: the complete disappearance of Arctic sea ice in summer, leading to drastic changes in ocean circulation and climate patterns across the whole Northern Hemisphere; acceleration of ice loss from the Greenland and Antarctic ice sheets, driving rates of sea-level increase to 6 feet or more per century; and ocean acidification from carbon dioxide absorption, causing massive disruption in ocean food webs.
Beyond the Abyss: Deep Sea Creatures Build Their Homes from Materials That Sink from Near the Ocean Surface
Evidence from the Challenger Deep -- the deepest surveyed point in the world's oceans -- suggests that tiny single-celled creatures called foraminifera living at extreme depths of more than ten kilometres build their homes using material that sinks down from near the ocean surface.
Evidence from the Challenger Deep — the deepest surveyed point in the world’s oceans — suggests that tiny single-celled creatures called foraminifera living at extreme depths of more than ten kilometres build their homes using material that sinks down from near the ocean surface.
The Challenger Deep is located in the Mariana Trench in the western Pacific Ocean. It lies in the hadal zone beyond the abyssal zone, and plunges down to a water depth of around 11 kilometres.
“The hadal zone extends from around six kilometres to the deepest seafloor. Although the deepest parts of the deepest trenches are pretty inhospitable environments, at least for some types of organism, certain kinds of foraminifera are common in the bottom sediments,” said Professor Andrew Gooday of the National Oceanography Centre, Southampton (NOCS) and member of a UK-Japanese team studying these organisms in samples collected during a Japan-USA-Korea expedition to study life in the western depression of the Challenger Deep.
The researchers, whose findings appear in the latest issue of the journal Deep Sea Research, used the remotely operated vehicle KAIKO, operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), to take core samples from the soft sediment of the trench floor. Among many foraminiferans with an organic shell (or ‘test’), they found four undescribed specimens with agglutinated tests.
“The Challenger Deep is an extreme environment for agglutinated foraminifera, which construct their tests from a wide range of particles cemented together by calcareous or organic matter,” said Gooday. “At these great depths, particles made from biologically formed calcite and silica, as well as minerals such as quartz, should dissolve, leaving only clay grains available for test building.”
“Our observations demonstrate that coccoliths, and probably also planktonic foraminiferan tests, reach the Challenger Deep intact,” said Gooday. “These particles were probably transported to these extreme depths in rapidly sinking marine snow, the aggregated remains of phytoplankton that lived in the sunlit surface ocean, or in faecal pellets from zooplankton.”
It seems likely, therefore, that at least some agglutinated foraminifera living at extreme hadal depths build their homes from material that sinks down from the ocean above, rather like manna from heaven.
This study was supported by the Japan Society for the Promotion of Science and the OCEANS 2025 Strategic Research Programme of the UK Natural Environment Research Council.
Ice Is ‘Rotten’ in the Beaufort Sea
Recent observations show that Beaufort Sea ice was not as it appeared in the summer of 2009. Sea ice cover serves as an indication of climate and has implications for marine and terrestrial ecosystems.
In early September 2009, satellite measurements implied that most of the ice in the Beaufort Sea either was thick ice that had been there for multiple years or was thick, first-year ice.
However, in situ observations made in September 2009 by Barber et al. show that much of the ice was in fact “rotten” ice — ice that is thinner, heavily decayed, and structurally weak due to a uniform temperature throughout.
The authors suggest that satellite measurements were confused because both types of ice exhibit similar temperature and salinity profiles near their surfaces and a similar amount of open water between flows. The authors note that while an increase in summer minimum ice extent in the past 2 years could give the impression that Arctic ice is recovering, these new results show that multiyear ice in fact is still declining.
The results have implications for climate science and marine vessel transport in the Arctic. The research appears in the journal Geophysical Research Letters.
Authors include David G. Barber, Ryan Galley, Matthew G. Asplin, Kerri-Ann Warner and Mukesh Gupta, Centre for Earth Observation Science, Faculty of Environment, Earth and Resources, University of Manitoba; Roger De Abreu, Canadian Ice Service, Environment Canada; Monika Pućko, Centre for Earth Observation Science, Faculty of Environment, Earth and Resources, University of Manitoba, and Freshwater Institute, Fisheries and Oceans; Simon Prinsenberg, Bedford Institute of Oceanography, Fisheries and Oceans; Stéphane Julien, Laurentian Region, Canadian Coast Guard.
50th Anniversary of World’s Deepest Dive
Fifty years ago, two men voyaged to the bottom of the deepest sea. Nobody has been back since.
On Jan. 23, 1960, Navy Lt. Don Walsh and Swiss explorer Jacques Piccard, in the submersible Trieste, descended seven miles into the Mariana Trench in the Pacific Ocean. The feat was celebrated Saturday at the Naval Undersea Museum, where the vessel’s successor, Trieste II, is displayed.
“The surprising thing is that more people have walked on the surface of the moon than have been to the deepest part of the world’s ocean,” said museum director Bill Galvani. “These two guys went in 1960. No one has been back since. No one has been even close. In the meantime, we’ve sent 12 people to the moon and many people into space. We know more about the surface of the moon, and even the opposite side of the moon, than we do about the deep ocean.”
Piccard died in 2008, leaving Walsh as the only living person to have made the 37,799-foot dive, 200 miles south of Guam. The 78-year-old Walsh, who lives in southwest Oregon, will be attending another Trieste anniversary event Saturday in San Diego.
The Trieste was designed by Piccard’s father, Auguste Piccard, and built in Italy in 1953. The U.S. Navy bought it in 1958. Walsh, then a 28-year-old Navy submariner, became its officer in charge.
The strange-looking vessel was called a bathyscaphe, or “deep ship.” There was just enough room in its 7-foot crew sphere for two people. Most of the vessel was huge tanks of lighter-than-water gasoline that functioned as a big balloon. To descend, air tanks were filled with seawater. To return to the surface, steel pellets were released.
Twenty-five-foot waves pounded the Trieste on the morning of the historic dive as it bobbed on the surface with its headquarters ship, the USS Lewis. At about 8 a.m., its heavy door clanked shut, and the vessel slipped under the waves. No other vessel had ever dived deeper than 12,300 feet, and the Trieste hadn’t gone below 23,000 feet.
Between 4,000 and 7,000 feet, drops began seeping in, but decreased as the dive continued. Walsh and Piccard were jolted by a big bang at 31,000 feet, as if something had broken. They couldn’t find a problem, so they kept going.
At 34,000 feet, the water beneath them began to lighten up as Trieste’s light reflected off the seafloor. At 36,000 feet, they still hadn’t reached it, however, nor at 37,000. Finally, they released just enough shot to make an easy landing. The depth gauge read 37,800 feet.
“Jacques and I shook hands and expressed our feelings of relief and joy,” Walsh said. “It was a great day for all of us who had worked so hard for nearly five months at Guam.”
They didn’t take any pictures because the Trieste had stirred up so much bottom sediment that there was no visibility.
“It was like being in a bowl of milk for our entire time on the bottom,” Walsh said.
At 1:30 p.m., after sitting at the bottom for only 20 minutes, the Trieste dumped ballast and headed home so it could reach the surface before sundown. The ascent took 3 1/2 hours.
Back in the states, Walsh and Piccard became heroes. They were ordered back to Washington, D.C., to be acclaimed by political and military heavyweights, including President Dwight D. Eisenhower, and wound up on the cover of Life magazine.
Fleet of Underwater Gliders to Explore Oceans
Glider under water. (Credit: IFM-GEOMAR)
The Leibniz Institute of Marine Sciences (IFM-GEOMAR) in Kiel, Germany, recently obtained the biggest fleet of so-called gliders in Europe. These instruments can explore the oceans like sailplanes up to a depth of 1000 metres. In doing so they only consume as much energy as a bike light. In the next years up to ten of these high-tech instruments will take measurements to better understand many processes in the oceans. Currently scientists and technicians prepare the devices for their first mission as a ’swarm’ in the tropical Atlantic.
They may look like mini-torpedoes, yet exclusively serve peaceful purposes. The payload of the two-metre-long yellow diving robots consists of modern electronics, sensors and high-performance batteries. With these devices the marine scientists can collect selective measurements from the ocean interior while staying ashore themselves. Moreover, the gliders not only transmit the data in real time, but they can be reached by the scientists via satellite telephone and programmed with new mission parameters.
As such the new robots represent an important supplement to previous marine sensor platforms.
“Ten year ago we started to explore the ocean systematically with profiling drifters. Today more than 3,000 of these devices constantly provide data from the ocean interior,” explains Professor Torsten Kanzow, oceanographer at IFM-GEOMAR. This highly successful programme has one major disadvantage: the pathways of the drifters cannot be controlled.
“The new gliders have no direct motor, either. But with their small wings they move forward like sailplanes under water,” says Dr. Gerd Krahmann, a colleague of Professor Kanzow. In a zigzag movement, the glider cycles between a maximum depth of 1000 metres and the sea surface.
“By telephone we can ‘talk’ to the glider and upload a new course everytime it comes up,” explains Krahmann. A glider can carry out autonomous missions for weeks or even months. Every glider is equipped with instruments to measure temperature, salinity, oxygen and chlorophyll content as well as the turbidity of the sea water.
The IFM-GEOMAR has been the first institute in Europe to be committed to the new technology. “We tested different devices and we had to learn the hard way, too,” oceanographer Dr. Johannes Karstensen says. “This way we have been able to contribute to the glider development, and now we have gathered knowledge required for successful glider operations,” he adds.
Within the context of a special investment IFM-GEOMAR was able to obtain six new gliders adding to a total of nine altogether, which is the biggest fleet of that kind in Europe.
A very successful mission using a single glider took place between August and October 2009 in the Atlantic Ocean, south of the Cape Verde Islands. The robot carried out measurements along a more than 1000 kilometres long track autonomously, before it was recovered by the German research vessel METEOR.
Now, for the first time the scientists in Kiel prepare a whole fleet of gliders for a concerted mission. After final tests the robots will be released mid-March 2010 at about 60 nautical miles north-east of the Cape Verde Island of Sao Vicente. For two months they will investigate physical and biogeochemical quantities of the Atlantic Ocean around the oceanographic long-term observatory TENATSO.
Goals of the experiment lead jointly by Prof. Torsten Kanzow, Prof. Julie LaRoche (marine biology) and Prof. Arne Körtzinger (marine chemistry) are to get new insights into water circulation and stratification as well as their impact on chemical and biological processes. With the glider swarm the scientists can sample a complete “sea-volume” and not just a single point or a single cross-section in the ocean. The gliders will be remotely controlled from a control centre at the IFM-GEOMAR in Kiel.
“This technology enables us to observe the upper layers of the ocean much more effectively and thus much less expensive than previously,” says Prof. Dr. Martin Visbeck, Deputy Director of the IFM-GEOMAR and Head of the research division Ocean Circulation and Climate Dynamics.
Melting Tundra Creating Vast River of Waste Into Arctic Ocean
The increase in temperature in the Arctic has already caused the sea-ice there to melt. According to research conducted by the University of Gothenburg, if the Arctic tundra also melts, vast amounts of organic material will be carried by the rivers straight into the Arctic Ocean, resulting in additional emissions of carbon dioxide.
Several Russian rivers enter the Arctic Ocean particularly in the Laptev Sea north of Siberia. One of the main rivers flowing into the Laptev Sea is the Lena, which in terms of its drainage basin and length is one of the ten largest rivers in the world. The river water carries organic carbon from the tundra, and research from the University of Gothenburg shows that this adds a considerable amount of carbon dioxide to the atmosphere when it is degraded in the coastal waters.
The increase in temperature in the Arctic, which has already made an impact in the form of reduced sea-ice cover during the summer, may also cause the permafrost to melt. “Large amounts of organic carbon are currently stored within the permafrost and if this is released and gets carried by the rivers out into the coastal waters, then it will result in an increased release of carbon dioxide to the atmosphere,” says Sofia Hjalmarsson, native of Falkenberg and postgraduate student at the Department of Chemistry.
In her thesis, Sofia Hjalmarsson has studied the carbon system in two different geographical areas: partly in the Baltic Sea, the Kattegat and the Skagerrak, and partly in the coastal waters north of Siberia (the Laptev Sea, the East Siberian Sea and the Chukchi Sea). The two areas have in common the fact that they receive large volumes of river water containing organic carbon and nutrients, mainly nitrogen.
Loss of Sea Ice Stirs Up Arctic Waters
The Arctic Ocean is generally considered a remarkably quiet ocean, with very little mixing, because a cover of sea ice prevents wind from driving the formation of internal waves. To study this effect and investigate how melting sea ice might affect ocean mixing in the Arctic, data was analyzed from the northern Chukchi Sea.
The analysts found that when the ocean was mostly covered with ice, even strong winds did not generate much response in it. On the other hand, during the summers when less sea ice was present, wind generated large internal oscillations and increased turbulence. The extent of Arctic sea ice in the summer has been declining significantly in recent years, likely resulting in increased internal wave generation, the authors note.
Because internal waves bring deeper waters closer to the surface, the results have important implications for Arctic Ocean ecosystems and ocean dynamics.
The research is published in Geophysical Research Letters. The authors include Luc Rainville and Rebecca A. Woodgate: Applied Physics Laboratory, University of Washington, Seattle, Washington, USA.
Rise in Human-Made Carbon Dioxide Affects Ocean Acoustics
Breaking waves generate low-frequency sound in the ocean in addition to other natural and man-made sources. In the layer of water at the depth of minimal speed of sound (deep sound channel), low-frequency sound can travel thousands of kilometers in the ocean. (Credit: Photo credit Steven Businger)
Carbon dioxide emissions from human activities aren’t just warming the planet. Another problem of rising atmospheric carbon dioxide is that CO2 is being absorbed by the oceans, which increases seawater acidity (lowers the seawater pH). This process, termed ‘ocean acidification’, has received growing scientific and public interest because it threatens certain groups of marine organisms, including corals. Only recently have researchers realized that human-made carbon dioxide not only warms and acidifies the ocean — it also affects acoustical properties of seawater, making it more transparent to low-frequency sound.
Oceanographers Tatiana Ilyina and Richard Zeebe of the School of Ocean and Earth Science and Technology at the University of Hawaii write in the journal Nature Geoscience that seawater sound absorption will drop by up to 70% during this century. The scientists have examined the effects of man-made carbon dioxide under business-as-usual emissions and provide projections of the magnitude, time scale, and regional extent of changes in underwater acoustics resulting from ocean acidification.
When carbon dioxide dissolves in seawater, it produces carbonic acid and increases the hydrogen ion concentration (acidity). The seawater pH has declined by about 0.1 units compared to preindustrial levels — corresponding to about 25% increase in acidity. These changes may appear small, but pH is measured on a logarithmic scale — analogous to the Richter scale, which measures the strength of Earthquakes. For example, a drop of pH by one unit implies a ten-fold increase in acidity. Low-frequency sound absorption depends on the concentration of dissolved chemicals such as boric acid, which in turn, depends on seawater pH. This is the reason why changes in seawater pH affect ocean acoustics.
“If we continue to emit carbon dioxide at business-as-usual rates, the pH of surface seawater will drop by 0.6 units by the year 2100. As a result, the absorption of 200 Hz sound would decrease by up to 70%,” says Tatiana Ilyina. For example, the middle C of the piano is tuned to 261.6 Hz; in the ocean, sound around this frequency is produced by natural phenomena such as rain, wind, and waves), by marine mammals, and by human activities such as construction, shipping, and use of sonar systems.
“Most people know that when they turn on the air conditioner or drive a vehicle, they emit carbon dioxide, which causes climate change and ocean acidification. The surprise now is that it also affects sound absorption in the ocean,” says Zeebe. “What is happening over time is that the low frequencies become louder at distance. It’s similar to the effect when you slowly turn up the bass on your stereo.”
However, underwater sound propagation is much more complex; it depends on spatial distribution of sound sources and environmental parameters. Some areas in the ocean will be affected more strongly than others. Areas with large sound absorption reduction and intense noise sources, for example from shipping, could become “acoustic hot spots” in the future. The largest changes are projected to occur in the surface ocean waters in high latitudes, for instance, in the North Pacific and in the Southern Ocean, and in the areas of deep water formation such as the North Atlantic, where man-made CO2 invasion is the greatest.
Sound can travel farther at depth of about 1000 m (the depth of the so called deep sound channel) than at the surface. Most of the anthropogenic and natural sounds are generated at the surface, but they can leak into the deep sound channel, bend there, and travel over thousands of kilometers in the ocean. “With time, as anthropogenic CO2 penetrates into the deep ocean, the changes in sound absorption will also propagate well below the deep sound channel axis,” says Ilyina. “Sound absorption will continue to decrease even after reductions in CO2 emissions because ocean pH will continue to decrease.”
Human activities such as naval, commercial, and scientific applications extensively use low-frequency sound due to its long-range propagation. Also marine mammals rely on low-frequency sound to find food and mates. As a result, ocean acidification may not only affect organisms at the bottom of the food chain by reducing calcification in plankton and corals, but also higher trophic level species, such as marine mammals by lowering sound absorption in the ocean.
“We don’t fully understand what the impacts of these changes in ocean acoustics will be,” says Ilyina. “Because of decreasing sound absorption, underwater sound could travel farther, and this could lead to growing noise levels in the oceans. Increasing transparency of the oceans to low-frequency sounds could also enable marine mammals to communicate over longer distances.” The scientists say that further research is needed to address these questions.
