Dec 16, 2015 08:08 PM
'Freak' ocean waves hit without warning, new research shows
http://www.sciencedaily.com/releases/201...082200.htm
RELEASE: Mariners have long spoken of 'walls of water' appearing from nowhere in the open seas. But oceanographers have generally disregarded such stories and suggested that rogue waves -- enormous surface waves that have attained a near-mythical status over the centuries -- build up gradually and have relatively narrow crests.
New research from the University of Oxford in collaboration with the University of Western Australia, however, shows that the anecdotal evidence may not be so far from the truth. Rather than coming at the end of a series of increasingly large waves, rogue (or freak) waves emerge suddenly, being preceded by much smaller waves.
The mathematical modelling also demonstrates that the crests of these rogue waves are longer than the smaller waves that surround them.
The research is published in the journal Proceedings of the Royal Society A.
Professor Thomas Adcock, of Oxford's Department of Engineering Science, said: 'The waves we're dealing with here occur in deep water in the open ocean -- very different from the waves you'll see if you go to the beach, which is what most people are familiar with.
'In deep water, where waves are much less regular, you expect a larger wave from time to time. Our paper shows that, in contrast to what was previously thought, if you're the observer on a ship, rather than seeing a gradual build-up of waves, the rogue wave will come seemingly out of nowhere.
'This happens because large waves tend to move to the front of the wave group.'
The research made use of mathematical modelling based on non-linear physics. The investigators used hundreds of simulations of random waves to analyze the differences between linear and non-linear wave dynamics.
Professor Adcock said: 'These findings fit the anecdotal evidence you hear from mariners. They often describe "walls of water" coming at them in the open ocean that are impossible to steer around -- an observation supported by our modelling, which shows that rogue waves tend to have a much broader crest than traditionally predicted by linear theory.
'All of this means that in a very rough storm, you can't simply assume you'll get a warning before a freak wave hits. Seafarers need to be aware that a large wave may appear out of nowhere.'
Baby fish will be lost at sea in acidified oceans
http://www.sciencedaily.com/releases/201...082158.htm
RELEASE: The ability of baby fish to find a home, or other safe haven, to grow into adulthood will be severely impacted under predicted ocean acidification, University of Adelaide research has found.
Published in the journal Proceedings of the Royal Society B, the researchers report the interpretation of normal ocean sound cues which help baby fish find an appropriate home is completely confused under the levels of CO2 predicted to be found in oceans by the end of the century.
"Locating appropriate homes is a crucial step in the life cycle of fish," says Tullio Rossi, PhD candidate with the University's Environment Institute. "After hatching in the open ocean, baby fish travel to reefs or mangroves as safe havens to feed and grow into adults.
"Baby fish can find those places through ocean noise: snapping shrimps and other creatures produce sounds that the baby fish follow.
"But when ocean acidity increases due to increased CO2, the neurological pathways in their brain are affected and, instead of heading towards those sounds, they turn tail and swim away."
Mr Rossi conducted experiments with barramundi hatchlings, an important fisheries species. The study was in collaboration with other researchers including Professor Sean Connell (University of Adelaide), Dr Stephen Simpson (University of Exeter) and Professor Philip Munday (James Cook University).
He and his collaborators also found that high CO2 makes baby fish move slower and show more hiding behaviour compared to normal fish. This could make it more difficult for them to find food or habitat and to avoid predators.
Research leader Associate Professor Ivan Nagelkerken says marine researchers know that ocean acidification can change fish behaviours. But it hasn't been known how high CO2 would affect such crucial hearing behaviour as finding somewhere to settle.
"Such misinterpretation of sound cues and changes in other behaviours could severely impact fish populations, with the number of young fish finding safe habitats dramatically reduced through their increased vulnerability to predators and reduced ability to find food," Associate Professor Nagelkerken says.
http://www.sciencedaily.com/releases/201...082200.htm
RELEASE: Mariners have long spoken of 'walls of water' appearing from nowhere in the open seas. But oceanographers have generally disregarded such stories and suggested that rogue waves -- enormous surface waves that have attained a near-mythical status over the centuries -- build up gradually and have relatively narrow crests.
New research from the University of Oxford in collaboration with the University of Western Australia, however, shows that the anecdotal evidence may not be so far from the truth. Rather than coming at the end of a series of increasingly large waves, rogue (or freak) waves emerge suddenly, being preceded by much smaller waves.
The mathematical modelling also demonstrates that the crests of these rogue waves are longer than the smaller waves that surround them.
The research is published in the journal Proceedings of the Royal Society A.
Professor Thomas Adcock, of Oxford's Department of Engineering Science, said: 'The waves we're dealing with here occur in deep water in the open ocean -- very different from the waves you'll see if you go to the beach, which is what most people are familiar with.
'In deep water, where waves are much less regular, you expect a larger wave from time to time. Our paper shows that, in contrast to what was previously thought, if you're the observer on a ship, rather than seeing a gradual build-up of waves, the rogue wave will come seemingly out of nowhere.
'This happens because large waves tend to move to the front of the wave group.'
The research made use of mathematical modelling based on non-linear physics. The investigators used hundreds of simulations of random waves to analyze the differences between linear and non-linear wave dynamics.
Professor Adcock said: 'These findings fit the anecdotal evidence you hear from mariners. They often describe "walls of water" coming at them in the open ocean that are impossible to steer around -- an observation supported by our modelling, which shows that rogue waves tend to have a much broader crest than traditionally predicted by linear theory.
'All of this means that in a very rough storm, you can't simply assume you'll get a warning before a freak wave hits. Seafarers need to be aware that a large wave may appear out of nowhere.'
Baby fish will be lost at sea in acidified oceans
http://www.sciencedaily.com/releases/201...082158.htm
RELEASE: The ability of baby fish to find a home, or other safe haven, to grow into adulthood will be severely impacted under predicted ocean acidification, University of Adelaide research has found.
Published in the journal Proceedings of the Royal Society B, the researchers report the interpretation of normal ocean sound cues which help baby fish find an appropriate home is completely confused under the levels of CO2 predicted to be found in oceans by the end of the century.
"Locating appropriate homes is a crucial step in the life cycle of fish," says Tullio Rossi, PhD candidate with the University's Environment Institute. "After hatching in the open ocean, baby fish travel to reefs or mangroves as safe havens to feed and grow into adults.
"Baby fish can find those places through ocean noise: snapping shrimps and other creatures produce sounds that the baby fish follow.
"But when ocean acidity increases due to increased CO2, the neurological pathways in their brain are affected and, instead of heading towards those sounds, they turn tail and swim away."
Mr Rossi conducted experiments with barramundi hatchlings, an important fisheries species. The study was in collaboration with other researchers including Professor Sean Connell (University of Adelaide), Dr Stephen Simpson (University of Exeter) and Professor Philip Munday (James Cook University).
He and his collaborators also found that high CO2 makes baby fish move slower and show more hiding behaviour compared to normal fish. This could make it more difficult for them to find food or habitat and to avoid predators.
Research leader Associate Professor Ivan Nagelkerken says marine researchers know that ocean acidification can change fish behaviours. But it hasn't been known how high CO2 would affect such crucial hearing behaviour as finding somewhere to settle.
"Such misinterpretation of sound cues and changes in other behaviours could severely impact fish populations, with the number of young fish finding safe habitats dramatically reduced through their increased vulnerability to predators and reduced ability to find food," Associate Professor Nagelkerken says.
