Tag Archives: oceans

El Hierro Submarine Eruption

El Hierro Submarine Eruption : Natural Hazards.

El Hierro Submarine Eruption

acquired October 23, 2011 download large image (779 KB, JPEG)
acquired October 23, 2011 download GeoTIFF file (3 MB, TIFF)

Off the coast of El Hierro, in the southwest reaches of the Canary Islands, Earth has been spewing gas and rock into the ocean. The island off the Atlantic coast of North Africa—built mostly from a shield volcano—has been rocked by thousands of tremors and earthquakes since July 2011, and an underwater volcanic eruption started in mid-October. The eruption is the first in the island chain in nearly 40 years.

On October 23, 2011, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color view of El Hierro and the North Atlantic Ocean surrounding it. A milky green plume in the water stretches 25-30 kilometers at its widest and perhaps 100 kilometers long, from a large mass near the coast to thin tendrils as it spreads to the southwest. The plume is likely a mix of volcanic gases and a blend of crushed pumice and seafloor rock.

Tremors were reported for the past several months from seismic stations on El Hierro, particularly in the northwest of the island. Then on October 12, 2011, the strength of the tremors significantly decreased while foaming, rock-strewn plumes appeared in the sea to the south of the island. The underwater plume of volcanic debris has persisted for nearly two weeks and has been mixed and dispersed by ocean surface currents. The eruption is occurring in water that is tens to a few hundred meters deep.

Geologist and blogger Erik Klemetti offered this analysis: “It looks like the main fissure might be 2-3 kilometers in length and is close to on strike with the rift axis for the main El Hierro edifice. Ramon Ortiz, coordinator of a government scientific team, said that if/when the eruption reaches shallower water, we should expect to see the surface water start to steam, followed by explosions of steam and magma and finally the emergence of an island.”

For local seismic information from El Hierro (in Spanish), visit the Instituto Geografico Nacional.

  1. References

  2. The Daily Mail (2011, September 29) Earthquake swarm on Canary Island of El Hierro sparks fears of volcanic eruption. Accessed October 25, 2011.
  3. Global Volcanism Program (2011, October 18) Smithsonian/USGS Weekly Volcanic Activity Report: Hierro. Accessed October 25, 2011.
  4. Klemetti, Erik (2011, October 21) Eruptions Blog: Vulcan’s View: Eruption News and Volcanoes From Space. Accessed October 25, 2011.

NASA Earth Observatory image created by Jesse Allen, using data from the MODIS Rapid Response team. Caption by Mike Carlowicz.

Instrument: 
Terra – MODIS

Sea level rise more from Antarctica than from Greenland during last interglacial

Sea level rise less from Greenland, more from Antarctica, than expected during last interglacial.

Where did all that extra water come from? Mainly from melting ice sheets on Greenland and Antarctica, and many scientists, including University of Wisconsin-Madison geoscience assistant professor Anders Carlson, have expected that Greenland was the main culprit.

But Carlson’s new results, published July 29 in Science, are challenging that assertion, revealing surprising patterns of melting during the last interglacial period that suggest that Greenland’s ice may be more stable — and Antarctica’s less stable — than many thought.

“The Greenland Ice Sheet is melting faster and faster,” says Carlson, who is also a member of the Center for Climatic Research in the Nelson Institute for Environmental Studies. But despite clear observations of that fact, estimates of just how much the ice will melt and contribute to sea level rise by the end of this century are highly varied, ranging from a few centimeters to meters. “There’s a clear need to understand how it has behaved in the past, and how it has responded to warmer-than-present summers in the past.”

The ice-estimation business is rife with unknown variables and has few known physical constraints, Carlson explains, making ice sheet behavior — where they melt, how much, how quickly — the largest source of uncertainty in predicting sea level rises due to climate change.

His research team sought a way to constrain where ice remained on Greenland during the last interglacial period, around 125,000 years ago, to better define past ice sheet behavior and improve future projections.

The researchers analyzed silt from an ocean-floor core taken from a region off the southern tip of Greenland that receives sediments carried by meltwater streams off the ice sheet. They used different patterns of radiogenic isotopes to identify sources of the sediment, tracing the silt back to one of three “terranes” or regions, each with a distinct geochemical signature. The patterns of sedimentation show which terranes were still glaciated at that time.

“If the land deglaciates, you lose that sediment,” Carlson explains. But to their surprise, they found that all the terranes were still supplying sediment throughout the last interglacial period and thus still had some ice cover.

“The ice definitely retreated to smaller than present extent and definitely raised sea level to higher than present” and continued to melt throughout the warm period, he adds, but the sediment analysis indicates that “the ice sheet seems to be more stable than some of the greater retreat values that people have presented.”

The team used their results to evaluate several existing models of Greenland ice sheet melting during the last interglacial period. The models consistent with the new findings indicate that melting Greenland ice was responsible for a sea level rise of 1.6 to 2.2 meters — at most, roughly half of the minimum four-meter total increase.

Even after accounting for other Arctic ice and the thermal expansion of warmer water, most of the difference must have come from a melting Antarctic ice sheet, Carlson says.

“The implication of our results is that West Antarctica likely was much smaller than it is today,” and responsible for much more of the sea level rise than many scientists have thought, he says. “If West Antarctica collapsed, that means it’s more unstable than we expected, which is quite scary.”

Ultimately, Carlson says he hopes this line of research will improve the representation of ice sheet responses to a warming planet in future Intergovernmental Panel on Climate Change (IPCC) reports. Temperatures during the last interglacial period were similar to those expected by the end of this century, and present-day temps have already reached a point that Greenland’s glaciers are melting.

The Science paper was co-authored by UW-Madison colleagues Elizabeth Colville, Brian Beard, Alberto Reyes, and David Ullman and Oregon State University researchers Robert Hatfield and Joseph Stoner, and supported by UW-Madison and the National Science Foundation.

Too late to turn back Rising oceans?

Rising oceans: Too late to turn the tide?.

If sea levels rose to where they were during the Last Interglacial Period, large parts of the Gulf of Mexico region would be under water (red areas), including half of Florida and several Caribbean islands. (Credit: Illustration by Jeremy Weiss)

ScienceDaily (July 18, 2011) — Thermal expansion of seawater contributed only slightly to rising sea levels compared to melting ice sheets during the Last Interglacial Period, a University of Arizona-led team of researchers has found.

The study combined paleoclimate records with computer simulations of atmosphere-ocean interactions and the team’s co-authored paper is accepted for publication in Geophysical Research Letters.

As the world’s climate becomes warmer due to increased greenhouse gases in the atmosphere, sea levels are expected to rise by up to three feet by the end of this century.

But the question remains: How much of that will be due to ice sheets melting as opposed to the oceans’ 332 billion cubic miles of water increasing in volume as they warm up?

For the study, UA team members analyzed paleoceanic records of global distribution of sea surface temperatures of the warmest 5,000-year period during the Last Interglacial, a warm period that lasted from 130,000 to 120,000 years ago.

The researchers then compared the data to results of computer-based climate models simulating ocean temperatures during a 200-year snapshot as if taken 125,000 years ago and calculating the contributions from thermal expansion of sea water.

The team found that thermal expansion could have contributed no more than 40 centimeters — less than 1.5 feet — to the rising sea levels during that time, which exceeded today’s level up to eight meters or 26 feet.

At the same time, the paleoclimate data revealed average ocean temperatures that were only about 0.7 degrees Celsius, or 1.3 degrees Fahrenheit, above those of today.

“This means that even small amounts of warming may have committed us to more ice sheet melting than we previously thought. The temperature during that time of high sea levels wasn’t that much warmer than it is today,” said Nicholas McKay, a doctoral student at the UA’s department of geosciences and the paper’s lead author.

McKay pointed out that even if ocean levels rose to similar heights as during the Last Interglacial, they would do so at a rate of up to three feet per century.

“Even though the oceans are absorbing a good deal of the total global warming, the atmosphere is warming faster than the oceans,” McKay added. “Moreover, ocean warming is lagging behind the warming of the atmosphere. The melting of large polar ice sheets lags even farther behind.”

“As a result, even if we stopped greenhouse gas emissions right now, the Earth would keep warming, the oceans would keep warming, the ice sheets would keep shrinking, and sea levels would keep rising for a long time,” he explained.

They are absorbing most of that heat, but they lag behind. Especially the large ice sheets are not in equilibrium with global climate,” McKay added. ”

Jonathan Overpeck, co-director of the UA’s Institute of the Environment and a professor with joint appointments in the department of geosciences and atmospheric sciences, said: “This study marks the strongest case yet made that humans — by warming the atmosphere and oceans — are pushing the Earth’s climate toward the threshold where we will likely be committed to four to six or even more meters of sea level rise in coming centuries.”

Overpeck, who is McKay’s doctoral advisor and a co-author of the study, added: “Unless we dramatically curb global warming, we are in for centuries of sea level rise at a rate of up to three feet per century, with the bulk of the water coming from the melting of the great polar ice sheets — both the Greenland and Antarctic Ice Sheets.”

According to the authors, the new results imply that 4.1 to 5.8 meters, or 13.5 to 19 feet, of sea level rise during the Last Interglacial period was derived from the Antarctic Ice Sheet, “reemphasizing the concern that both the Antarctic and Greenland Ice Sheets may be more sensitive to warming temperatures than widely thought.”

“The central question we asked was, ‘What are the warmest 5,000 years we can find for all these records, and what was the corresponding sea level rise during that time?'” McKay said.

Evidence for elevated sea levels is scattered all around the globe, he added. On Barbados and the Bahamas, for example, notches cut by waves into the rock six or more meters above the present shoreline have been dated to being 125,000 years old.

“Based on previous studies, we know that the sea level during the Last Interglacial was up to 8.5 meters higher than today,” McKay explained.

“We already knew that the vast majority came from the melting of the large ice sheets in Greenland and Antarctica, but how much could the expansion of seawater have added to that?”

Given that sea surface temperatures were about 0.7 degrees warmer than today, the team calculated that even if the warmer temperatures reached all the way down to 2,000 meters depth — more than 6,500 feet, which is highly unlikely — expansion would have accounted for no more than 40 centimeters, less than a foot and a half.

“That means almost all of the substantial sea level rise in the Last Interglacial must have come from the large ice sheets, with only a small contribution from melted mountain glaciers and small ice caps,” McKay said.

According to co-author Bette Otto-Bliesner, senior scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., getting the same estimate of the role ocean expansion played on sea level rise increases confidence in the data and the climate models.

“The models allow us to attribute changes we observe in the paleoclimate record to the physical mechanisms that caused those changes,” Otto-Bliesner said. “This helps tremendously in being able to distinguish mere correlations from cause-and-effect relationships.”

The authors cautioned that past evidence is not a prediction of the future, mostly because global temperatures during the Last Interglacial were driven by changes in Earth’s orbit around the sun. However, current global warming is driven by increasing greenhouse gas concentrations.

The seasonal differences between the northern and the southern hemispheres were more pronounced during the Last Interglacial than they will be in the future.

“We expect something quite different for the future because we’re not changing things seasonally, we’re warming the globe in all seasons,” McKay said.

“The question is, when we think about warming on a global scale and contemplate letting the climate system change to a new warmer state, what would we expect for the ice sheets and sea levels based on the paleoclimate record? The Last Interglacial is the most recent time when sea levels were much higher and it’s a time for which we have lots of data,” McKay added.

“The message is that the last time glaciers and ice sheets melted, sea levels rose by more than eight meters. Much of the world’s population lives relatively close to sea level. This is going to have huge impacts, especially on poor countries,” he added.

“If you live a meter above sea level, it’s irrelevant what causes the rise. Whether sea levels are rising for natural reasons or for anthropogenic reasons, you’re still going to be under water sooner or later.”

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Overfishing eats away at genetic diversity of fish

Overfishing eats away at genetic diversity of fish – environment – 15 July 2011 – New Scientist.

Plenty more fish in the sea? Maybe not for much longer. Overfishing is damaging the genetic diversity of fish to a greater degree than expected, leaving at-risk species vulnerable.

It was thought that even badly overfished species would remain genetically diverse, since millions of individual fish remain even in the most depleted species.

To test this assumption, Malin Pinsky and Stephen Palumbi of Stanford University in California gathered published data on genetic diversity in 37 overfished species and compared it with diversity in 51 of their lightly fished relatives.

To their surprise, they found that the overfished species carried, on average, about 18 per cent fewer genetic variants than their lightly fished relatives. “Contrary to what we expected, it looks like the [genetic] effects of overfishing are quite widespread,” Pinsky says.

At first glance, a drop in genetic diversity of just 18 per cent may seem small, given that some overfished species are thought to have suffered severe population crashes. However, widespread overfishing is just a few decades old, and if it continues it may lead to a further erosion of genetic diversity, says Pinsky.

Meanwhile, Michael Alfaro of the University of California, Los Angeles, and his colleagues have found another ominous sign for fish stocks.

Speedy evolution

They analysed the family tree of fish to see how quickly body size changes in each lineage, then noted which lineages are most heavily fished. The team found that species with unusually fast rates of evolution in body size are preferentially targeted by fishing.

Since changes in body size often lead to changes in other ecologically relevant traits, this means that fishing targets the most evolutionarily active groups of fish, Alfaro says.

“Humans are eating away the richest branches of the fish tree of life,” says Alfaro. “If you were going to come up with a plan to assault the fish tree of life, you would want to do it like this.”

The results add urgency to biologists’ call for more aggressive management of commercial fisheries. “These are not trends we would wish to see continue,” says Paul Bentzen, a fisheries geneticist at Dalhousie University in Halifax, Canada. “We need to be managing fisheries more effectively.”

That could involve measures such as shorter fishing seasons and an increase in the number of no-fishing zones. But the bottom line is that people need to catch fewer fish, Bentzen says.

Pinsky and Alfaro presented their findings at a meeting of the Society for the Study of Evolution in Norman, Oklahoma, last month

Google Earth 'Flood'

Google Earth ‘Flood’.

Google Earth layer for showing effects of rising sea levels

Try Globe Glider!

The Globe Glider extension for Google Earth is now available for beta testing…

 

Try it here!

 

Google Earth ‘Flood’

This network link for Google Earth will ‘flood’ an area of the globe to a certain height above sea level.

Click here to open the network link in Google Earth.

Go to the area that you want to see flooded and refresh the network link (right-click on the network link in Google Earth and choose ‘refresh’).

 

The elevation is set with the ‘elev’ parameter in the link. You can edit the network link and change the number after ‘?elev=’ to set a new elevation (in meters, 1000 feet = 305 m).

 

The ‘water’ level is inaccurate for larger areas because it doesn’t follow exactly the curvature of the earth.