Researchers solve riddle of the rock pools

The rock goby can change both its color and brightness to match its background in just one minute. -  Alice Lown
The rock goby can change both its color and brightness to match its background in just one minute. – Alice Lown

Research from the University of Exeter has revealed that the rock goby (Gobius paganellus), an unassuming little fish commonly found in rock pools around Britain, southern Europe, and North Africa, is a master of camouflage and can rapidly change colour to conceal itself against its background.

Whether hiding from predators or from families hunting in rock pools, the rock goby can change both its colour and brightness to match its background in just one minute.

Dr Martin Stevens from the Centre for Ecology and Conservation at the University of Exeter’s Penryn Campus in Cornwall said: “Anyone who’s been rock pooling will probably have encountered rock gobies, and may even have thought they could see them change colour in buckets. Our research shows that this is the case and that rock gobies can rapidly tune their appearance to match their background.”

The researchers found that when gobies were photographed on a bright white or dark background, they could change their brightness accordingly. When photographed on coloured backgrounds they altered their colour, becoming either more red or blue.

Undertaking this rapid visual change should be a major advantage for the fish when trying to avoid predators. Gobies find themselves under intense predation pressure at low tide from birds and at high tide from larger fish. To remain concealed they must rapidly respond as they are pushed over many different backgrounds by tides and waves.

The researchers collected the gobies from Gyllyngvase beach in Falmouth, Cornwall then photographed them against different backgrounds over time to quantify the speed and extent of the colour change. The results show that the fish were capable of rapid visual change for concealment.

The colour change is driven by special cells in the fishes’ bodies called ‘chromatophores’. These are found in many animals and work to condense or spread pigments of different colour over the body, changing the appearance of the fish. This process is guided by the visual system of the goby when it moves onto a new background.

Studies of colour change for camouflage have previously been undertaken in animals including chameleons, cuttlefish, flatfish, and crabs, but rarely have studies directly quantified the changes in colour and brightness that occur, how fast this happens, and how they affect camouflage matching.

Yellowstone geyser eruptions influenced more by internal processes

<IMG SRC="/Images/994664490.jpg" WIDTH="350" HEIGHT="396" BORDER="0" ALT="This is a map showing the location of Daisy and Old Faithful geysers in Yellowstone's Upper Geyser Basin. Inset map of Yellowstone National Park shows the weather station at Yellowstone Lake, seismic stations LKWY and H17A, and strainmeter B944. – Images taken from: Shaul Hurwitz, Robert A. Sohn, Karen Luttrell, Michael Manga, "Triggering and modulation of geyser eruptions in Yellowstone National Park by earthquakes, earth tides, and weather", Journal of Geophysical Research: Solid Earth, DOI:10.1002/2013JB010803″>
This is a map showing the location of Daisy and Old Faithful geysers in Yellowstone’s Upper Geyser Basin. Inset map of Yellowstone National Park shows the weather station at Yellowstone Lake, seismic stations LKWY and H17A, and strainmeter B944. – Images taken from: Shaul Hurwitz, Robert A. Sohn, Karen Luttrell, Michael Manga, “Triggering and modulation of geyser eruptions in Yellowstone National Park by earthquakes, earth tides, and weather”, Journal of Geophysical Research: Solid Earth, DOI:10.1002/2013JB010803

The intervals between geyser eruptions depend on a delicate balance of underground factors, such as heat and water supply, and interactions with surrounding geysers. Some geysers are highly predictable, with intervals between eruptions (IBEs) varying only slightly. The predictability of these geysers offer earth scientists a unique opportunity to investigate what may influence their eruptive activity, and to apply that information to rare and unpredictable types of eruptions, such as those from volcanoes.

Dr. Shaul Hurwitz took advantage of a decade of eruption data-spanning from 2001 to 2011-for two of Yellowstone’s most predictable geysers, the cone geyser Old Faithful and the pool geyser, Daisy.

Dr. Hurwitz’s team focused their statistical analysis on possible correlations between the geysers’ IBEs and external forces such as weather, earth tides and earthquakes. The authors found no link between weather and Old Faithful’s IBEs, but they did find that Daisy’s IBEs correlated with cold temperatures and high winds. In addition, Daisy’s IBEs were significantly shortened following the 7.9 magnitude earthquake that hit Alaska in 2002.

The authors note that atmospheric processes exert a relatively small but statistically significant influence on pool geysers’ IBEs by modulating heat transfer rates from the pool to the atmosphere. Overall, internal processes and interactions with surrounding geysers dominate IBEs’ variability, especially in cone geysers.

Ancient tides quite different from today — some dramatically higher

The ebb and flow of the ocean tides, generally thought to be one of the most predictable forces on Earth, are actually quite variable over long time periods, in ways that have not been adequately accounted for in most evaluations of prehistoric sea level changes.

Due to phenomena such as ice ages, plate tectonics, land uplift, erosion and sedimentation, tides have changed dramatically over thousands of years and may change again in the future, a new study concludes.

Some tides on the East Coast of the United States, for instance, may at times in the past have been enormously higher than they are today – a difference between low and high tide of 10-20 feet, instead of the current 3-6 foot range.

And tides in the Bay of Fundy, which today are among the most extreme in the world and have a range up to 55 feet, didn’t amount to much at all about 5,000 years ago. But around that same time, tides on the southern U.S. Atlantic coast, from North Carolina to Florida, were about 75 percent higher.

The findings were just published in the Journal of Geophysical Research. The work was done with computer simulations at a high resolution, and supported by the National Science Foundation and other agencies.

“Scientists study past sea levels for a range of things, to learn about climate changes, geology, marine biology,” said David Hill, an associate professor in the School of Civil and Construction Engineering at Oregon State University. “In most of this research it was assumed that prehistoric tidal patterns were about the same as they are today. But they weren’t, and we need to do a better job of accounting for this.”

One of the most interesting findings of the study, Hill said, was that around 9,000 years ago, as the Earth was emerging from its most recent ice age, there was a huge amplification in tides of the western Atlantic Ocean. The tidal ranges were up to three times more extreme than those that exist today, and water would have surged up and down on the East Coast.

One of the major variables in ancient tides, of course, was sea level changes that were caused by previous ice ages. When massive amounts of ice piled miles thick in the Northern Hemisphere 15,000 to 20,000 years ago, for instance, sea levels were more than 300 feet lower.

But it’s not that simple, Hill said.

“Part of what we found was that there are certain places on Earth where tidal energy gets dissipated at a disproportionately high rate, real hot spots of tidal action,” Hill said. “One of these today is Hudson Bay, and it’s helping to reduce tidal energies all over the rest of the Atlantic Ocean. But during the last ice age Hudson Bay was closed down and buried in ice, and that caused more extreme tides elsewhere.”

Many other factors can also affect tides, the researchers said, and understanding these factors and their tidal impacts is essential to gaining a better understanding of past sea levels and ocean dynamics.

Some of this variability was suspected from previous analyses, Hill said, but the current work is far more resolved than previous studies. The research was done by scientists from OSU, the University of Leeds, University of Pennsylvania, University of Toronto, and Tulane University.

“Understanding the past will help us better predict tidal changes in the future,” he said. “And there will be changes, even with modest sea level changes like one meter. In shallow waters like the Chesapeake Bay, that could cause significant shifts in tides, currents, salinity and even temperature.”

Ebb and flow of the sea drives world’s big extinction events

If you are curious about Earth’s periodic mass extinction events such as the sudden demise of the dinosaurs 65 million years ago, you might consider crashing asteroids and sky-darkening super volcanoes as culprits.

But a new study, published online today (June 15, 2008) in the journal Nature, suggests that it is the ocean, and in particular the epic ebbs and flows of sea level and sediment over the course of geologic time, that is the primary cause of the world’s periodic mass extinctions during the past 500[sc1] million years.

“The expansions and contractions of those environments have pretty profound effects on life on Earth,” says Shanan Peters, a University of Wisconsin-Madison assistant professor of geology and geophysics and the author of the new Nature report.

In short, according to Peters, changes in ocean environments related to sea level exert a driving influence on rates of extinction, which animals and plants survive or vanish, and generally determine the composition of life in the oceans.

Since the advent of life on Earth 3.5 billion years ago, scientists think there may have been as many as 23 mass extinction events, many involving simple forms of life such as single-celled microorganisms. During the past 540 million years, there have been five well-documented mass extinctions, primarily of marine plants and animals, with as many as 75-95 percent of species lost.

For the most part, scientists have been unable to pin down the causes of such dramatic events. In the case of the demise of the dinosaurs, scientists have a smoking gun, an impact crater that suggests dinosaurs were wiped out as the result of a large asteroid crashing into the planet. But the causes of other mass extinction events have been murky, at best.

“Paleontologists have been chipping away at the causes of mass extinctions for almost 60 years [sc2], ” explains Peters, whose work was supported by the National Science Foundation. “Impacts, for the most part, aren’t associated with most extinctions. There have also been studies of volcanism, and some eruptions correspond to extinction, but many do not.”

Arnold I. Miller, a paleobiologist and professor of geology at the University of Cincinnati, says the new study is striking because it establishes a clear relationship between the tempo of mass extinction events and changes in sea level and sediment: “Over the years, researchers have become fairly dismissive of the idea that marine mass extinctions like the great extinction of the Late Permian might be linked to sea-level declines, even though these declines are known to have occurred many times throughout the history of life. The clear relationship this study documents will motivate many to rethink their previous views.”

Peters measured two principal types of marine shelf environments preserved in the rock record, one where sediments are derived from erosion of land and the other composed primarily of calcium carbonate, which is produced in-place by shelled organisms and by chemical processes. “The physical differences between (these two types) of marine environments have important biological consequences,” Peters explains, noting differences in sediment stability, temperature, and the availability of nutrients and sunlight.

In the course of hundreds of millions of years, the world’s oceans have expanded and contracted in response to the shifting of the Earth’s tectonic plates and to changes in climate. There were periods of the planet’s history when vast areas of the continents were flooded by shallow seas, such as the shark- and mosasaur-infested seaway that neatly split North America during the age of the dinosaurs.

As those epicontinental seas drained, animals such as mosasaurs and giant sharks went extinct, and conditions on the marine shelves where life exhibited its greatest diversity in the form of things like clams and snails changed as well.

The new Wisconsin study, Peters says, does not preclude other influences on extinction such as physical events like volcanic eruptions or killer asteroids, or biological influences such as disease and competition among species. But what it does do, he argues, is provide a common link to mass extinction events over a significant stretch of Earth history.

“The major mass extinctions tend to be treated in isolation (by scientists),” Peters says. “This work links them and smaller events in terms of a forcing mechanism, and it also tells us something about who survives and who doesn’t across these boundaries. These results argue for a substantial fraction of change in extinction rates being controlled by just one environmental parameter.”

  1. The study starts in the Ordovician
  2. 100 years would refer to larger-scale changes in faunal composition

Modelling the impact of the Severn Tidal Power Project

A team of Cardiff University School of Engineering researchers are making it possible to more accurately predict the impact of using the world’s second highest tidal range as a source of energy.

Led by Professor Roger Falconer, researchers from Hydro-environmental Research Centre have designed and built Wales’ first physical model of the Severn Estuary. This will now be used to more accurately study the impact of proposed Severn Tidal Power projects, including a Barrage and other forms of tidal renewable energy.

Located in the Hyder Hydraulics Laboratory, the model is the first of its kind capable of investigating the full environmental impact of different options for a barrage and lagoons in the Severn estuary and has been funded by the Welsh Assembly Government’s Welsh European Funding Office (WEFO).

Designed to resemble as closely as possible all the unique characteristics of the estuary which stretches from west of Carmarthen Bay (near Tenby) to Gloucester, the model is located in a 6m x 4m tidal basin. It will allow for improved computer simulations of flooding patterns, inter-tidal habitat area changes, sediment transport and bed changes, such as erosion and deposition. Modelling of changes in beach morphology and general water quality characteristics, such as light intensity in the water column, nutrients and faecal bacteria levels, with and without the proposed Barrage will also be possible.

One option for a Cardiff to Western Barrage would stretch from Lavernock Point to Brean Down and is estimated to cost around £15 billion. The massive structure could potentially harness the tidal energy of the Severn estuary and, within 14 years, could generate about 5% of the UK’s supply of electricity.

Built in collaboration with a project with Swansea University, the model features a computer controlled oscillating weir, which is used to generate tides of varying amplitude and period. It has a removable model barrage that allows conditions before and after the construction of the barrage to be simulated. It also allows for the impact of other tidal energy devices, including tidal lagoon and tidal stream turbines, to be examined.

Jane Davidson, the Welsh Assembly Government’s Minister for Environment, Sustainability and Housing, who officially unveiled the model, said: “The Estuary is famous for having the second highest tidal range in the world. An ability to model this will be of international importance and will further enhance the reputation for excellence of Cardiff University and its School of Engineering.

“The Welsh Assembly and UK Governments are currently undertaking a feasibility study on the effect that different options for a barrage and lagoons would have – for example on flooding risk and siltation. I look forward to hearing of progress made by Professor Falconer, and researchers from other universities, in using the physical and computer models to increase understanding of these hydro-environmental impacts.”

Professor Roger Falconer, Halcrow Professor of Water Management, and Director of the Hydro-environmental Research Centre said: “A number of studies relating to the potential impact of a barrage have been carried out since the proposal was first mooted. However, this physical model, which is close in design to the actual basin, will enable us for the first time to look in-depth and over the long term at the potential impact of a barrage or other tidal-range development on the surrounding aquatic environments and habitats.”

“Combine this facility with the computer models already in place at the Centre, and we should be able to identify problems and establish appropriate solutions over time.”

Earthquake Season in the Himalayan Front

Scientists have long searched for what triggers earthquakes, even suggesting that tides or weather play a role. Recent research spearheaded by Jean-Philippe Avouac, professor of geology and director of the Tectonics Observatory at the California Institute of Technology, shows that in the Himalayan mountains, at least, there is indeed an earthquake season. It’s winter.

For decades, geologists studying earthquakes in the Himalayan range of Nepal had noted that there were far more quakes in the winter than in the summer, but it was difficult to assign a cause. “The seasonal variation in seismicity had been noticed years ago,” says Avouac. Now, over a decade of data from GPS receivers and satellite measurements of land-water storage make it possible to connect the monsoon season with the frequency of earthquakes along the Himalaya front. The analysis also provides key insight into the timescale of earthquake nucleation in the region.

Avouac will present the results of the study on December 12 at the annual meeting of the American Geophysical Union (AGU) in San Francisco. They are also available online through the journal Earth and Planetary Science Letters, and will appear in print early next year.

The world’s tallest mountain range, the Himalaya continues to rise as plate tectonic activity drives India into Eurasia. The compression from this collision results in intense seismic activity along the front of the range. Stress builds continually along faults in the region, until it is released through earthquakes.

Avouac and two collaborators from France and Nepal–Laurent Bollinger and Sudhir Rajaure–began their earthquake seasonality investigation by analyzing a catalog of around 10,000 earthquakes in the Himalaya. They saw that, at all magnitudes above this detection limit, there were twice as many earthquakes during the winter months–December through February–as during the summer. That is, in winter there are up to 150 earthquakes of magnitude three per month, and in summer, around 75. For magnitude four, the winter average is 16 per month, while in summer the rate falls to eight per month. They ran the numbers through a statistical calculation and ruled out the possibility that the seasonal signal was due merely to chance.

“The signal in the seismicity is real; there is no discussion,” Avouac says. “We see this seasonal cycle,” he adds. “We didn’t know where it came from but it is really strong. We’re looking at something that is changing on a yearly basis-the timescale over which stress changes in this region is one year.”

Earlier studies suggested that seasonal variations in atmospheric pressure set off earthquakes, and this had been proposed for seasonal seismicity following the 1992 Landers, California, quake.

The scientists turned to satellite measurements of water levels in the region. Using altimetry data from TOPEX/Poseidon, a satellite launched in 1992 by NASA and the French space agency CNES (Centre National d’Etudes Spatiales), they evaluated the water level in major rivers of the Ganges basin to within a few tens of centimeters. They found that the water level over the whole basin begins its four-meter rise at the onset of the monsoon season in mid-May, reaching a maximum in September, followed by a slow decrease until the next monsoon season.

They combined river level measurements with data from NASA’s GRACE–Gravity Recovery and Climate Experiment–mission, which studies, among other things, groundwater storage on landmasses. The data revealed a strong signal of seasonal variation of water in the basin. Paired with the altimetry data, these measurements paint a complete picture of the hydrologic cycle in the region.

In the Himalaya, monsoon rains swell the rivers of the Ganges basin, increasing the pressure bearing down on the region. As the rains stop, the river water soaks through the ground and the built-up load eases outward, toward the front of the range. This outward redistribution of stress after the rains end leads to horizontal compression in the mountain range later in the year, triggering the wintertime earthquakes.

The final piece connecting winter earthquake frequency to season, and lending insight into the process by which earthquakes nucleate, lay in GPS data. Installation of GPS instruments across the Himalayan front began in 1994, and now they provide a decade’s worth of measurements showing land movement across the region. Instead of looking at vertical motions, which are widely believed to be sensitive to weather and the same forces that cause tides on Earth, the scientists concentrated on horizontal displacements. The lengthy records, analyzed by Pierre Bettinelli during his graduate work at Caltech, show that horizontal motion is continuous in the range front. Stress constantly builds in the region. But just as water levels near their lowest in the adjacent Ganges basin and earthquakes begin their doubletime, horizontal motion reaches its maximum speed.

“We had been staring at [the seasonal signal] for years, and then the satellite data came in and we deployed the GPS network and suddenly it became crystal clear,” says Avouac. “It’s like something you dream of.”

While many scientists have suggested that changing water levels can influence the earthquake cycle, a definitive mechanism had yet to be pinpointed. “There are two main avenues by which people have tried to understand the physics of earthquakes: Earth tides and aftershocks,” says Avouac. With the water level data, he could show that the rate at which stress builds along the rangefront, rather than the absolute level of stress, triggers earthquakes.

Although Earth tides induce stress levels similar to what builds up during seasonal water storage, they only vary over a 12-hour period. The Himalayan signal shows that it is more likely that earthquakes are triggered after stress builds for weeks to months, which matches the timescale of seasonal stress variation in that region.

About other earthquake-prone regions Avouac says, “seasonal variation has been reported in other places, but I don’t know any other place where it is so strong or where the cause of the signal is so obvious.”

Other authors on the paper are Pierre Bettinelli, Mireille Flouzat, and Laurent Bollinger of the Commissariat a l’Énergie Atomique, France; Guillaume Ramillien of the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, France; and Sudhir Rajaure and Som Sapkota of the National Seismological Centre in Nepal.

Avouac will present details of the group’s findings at AGU on Wednesday, December 12, at 2 p.m., Moscone West room 3018, in session T33F: Earthquake geology, active tectonics, and mountain building in south and east Asia.

Rising tides intensify non-volcanic tremor in Earth’s crust

For more than a decade geoscientists have detected what amount to ultra-slow-motion earthquakes under Western Washington and British Columbia on a regular basis, about every 14 months. Such episodic tremor-and-slip events typically last two to three weeks and can release as much energy as a large earthquake, though they are not felt and cause no damage.

Now University of Washington researchers have found evidence that these slow-slip events are actually affected by the rise and fall of ocean tides.

“There has been some previous evidence of the tidal effect, but the detail is not as great as what we have found,” said Justin Rubinstein, a UW postdoctoral researcher in Earth and space sciences.

And while previous research turned up suggestions of a tidal pulse at 12.4 hours, this is the first time that a second pulse, somewhat more difficult to identify, emerged in the evidence at intervals of 24 to 25 hours, he said.

Rubinstein is lead author of a paper that provides details of the findings, published Nov. 22 in Science Express, the online edition of the journal Science. Co-authors are Mario La Rocca of the Istituto Nazionale di Geofisica e Vulcanologia in Italy, and John Vidale, Kenneth Creager and Aaron Wech of the UW.

The most recent tremor-and-slip events in Washington and British Columbia took place in July 2004, September 2005 and January 2007. Before each, researchers deployed seismic arrays, each containing five to 11 separate seismic monitoring stations, to collect more accurate information about the location and nature of the tremors. Four of the arrays were placed on the Olympic Peninsula in Washington and the fifth was on Vancouver Island in British Columbia.

The arrays recorded clear twice-a-day pulsing in the 2004 and 2007 episodes, and similar pulsing occurred in 2005 but was not as clearly identified. The likely source from tidal stresses, the researchers said, would be roughly once- and twice-a-day pulses from the gravitational influence of the sun and moon. The clearest tidal pulse at 12.4 hours coincided with a peak in lunar forcing, while the pulse at 24 to 25 hours was linked to peaks in both lunar and solar influences.

The rising tide appeared to increase the tremor by a factor of 30 percent, though the Earth distortion still was so small that it was undetectable without instruments, said Vidale, a UW professor of Earth and space sciences and director of the Pacific Northwest Seismograph Network.

“We expected that the added water of a rising tide would clamp down on the tremor, but it seems to have had the opposite effect. It’s fair to say that we don’t understand it,” Vidale said.

“Earthquakes don’t behave this way,” he added. “Most don’t care whether the tide is high or low.”

The researchers were careful to rule out noise that might have come from human activity. For instance, one of the arrays was near a logging camp and another was near a mine.

“It’s pretty impressive how strong a signal those activities can create,” Rubinstein said, adding that the slow-slip pulses were recorded when those human activities were at a minimum.

The work was funded by the National Science Foundation, and instruments were provided by the Incorporated Research Institutions for Seismology, Istituto Nazionale di Geofisica e Vulcanologia and Earthscope.