Hawaiian lava--down to the core?

It's the one of the sad truths about science that someone develops a theory of why a thing occurs, and then someone else rejects the theory based on new information.

It's good for science, but can be tough on the person who put a lot of time and effort into the original theory.

Recently, there's been a controversy over the source of the Hawaiian Islands.

There is general consensus that the molten rock for the Hawaiian volcanoes comes from a hot spot that drives deep in the Earth.

But how deep?

At the Earth's surface is the crust, which is a few miles to a few dozen miles thick, depending on where you're checking. The mantle extends roughly another 2,000 miles down, and the core 2,000 miles more, until you reach the legendary “Center of the Earth.” (It would be hard to reach that center, since it's believed to be in the middle of an immense solid iron sphere.)

At the least, the plume of magma that forms the Hawaiian hot spot goes down into the planet's mantle.

The elements that make up different parts of the planet's interior come in different mixtures, and some folks have suggested that the detection of certain chemical signatures in Hawaiian lava indicate the plume may extend all the way down to the boundary between the mantle and the core.

One of the elements on which these calculations are made is Osmium, a hard, heavy metal often found in conjunction with iron—the main component of the planet's core.

The theory: If there is a fair amount of Osmium in certain proportions in Hawaiian lavas, it must be coming from somewhere near the planet's core, and this suggests that the plume reaches all the way down to the edge of the core.

Tossing a little cold water on that hot topic, an international team of researchers found that it's possible to get that proportion of Osmium isotopes from within the upper mantle—that you don't need to go all the way down to the core to get it.

The scientists, whose work was published in the journal Science, include Ambre Luguet, Graham Pearson, Geoff Nowell, Scott Dreher, Judith Coggon and Stephen Parman of the Northern Centre for Isotopic and Elemental Tracing at the University of Durham in the United Kingdom, and Zdislav Spetsius of the Russian Yakutian Research and Design Institute of Diamond Mining Industry, a part of the ALROSA Joint-Stock Company.

But they concede that the idea of using lavas to try to prove where the hot spot originates is cool.

“The possibility of observing the chemical signature of core-mantle interaction in magmas erupted at the Earth's surface is one of the most exciting prospects in mantle geochemistry,” they write, in their article, “Enriched Pt-Re-Os Isotope Systematics in Plume Lavas Explained by Metasomatic Sulfides.”

But their research shows it is possible for the melting of existing rocks within the Earth's upper mantle to produce the same Osmium chemical signatures found in Hawaiian lavas on Hualalai, the submarine volcano Loihi and Mauna Loa.

It doesn't mean that the Hawaiian plume isn't reaching down to the interface between mantle and core, but just that this particular bit of Osmium-based information isn't sufficient to prove it.

The Osmium signature “observed in plume-related lavas can have an upper-mantle origin,” the writers say. And as a result, it “cannot be taken to be a unique signature of core-mantle interaction.”

As often happens in science, a theory bites the dust, but provides ample ground for new scientific inquiry.

© 2007 Jan W. TenBruggencate

Mystery of the Hawaiian-Emperor Bend, solved?

The Hawaiian Island chain, as most people know it, runs from Hawai'i to Kaua'i and Ni'ihau, but the islands are only the tail of a string of volcanoes that runs all the way to the Aleutians.

What baffles science is why this long string makes a distinct turn midway.

(Image: The Hawaiian-Emperor Chain extends 3,700 miles northwest from the main Hawaiian Islands, and then makes a right turn beyond Midway and Kure, continuing as a line of seamounts that eventually disappears at the northern edge of the Pacific tectonic plate. The blue line follows the course of the chain and the red arrow marks the right turn. Credit: Modified from Google Earth.)

Current geological thinking is that the massive Pacific plate, which forms part of the Earth's crust, is constantly moving, its edges sliding along or under or over other plates, or being shoved away from others by volcanic activity. And a feature called the Hawaiian hot spot punches volcanoes up through the plate.

Like a pencil marking a line of dots on a page, the hot spot under the moving plate leaves a line of volcanoes.

But what could have caused the bend in the line? Some movement of the hot spot? A dramatic change in the direction in which the plate moves? The question was tackled in a recent paper in Science Magazine by geologists David Clague, former director of the Hawaiian Volcano Observatory now working with the Monterey Bay Aquarium Research Institute, and Warren Sharp, of the Berkeley Geochronology Center.

They conclude that the bend in the 129-volcano Hawaiian-Emperor Chain (the name for the combination of the Hawaiian Archipelago south of the bend and the Emperor Seamounts north of it), occurred about 50 million years ago.

They carefully determined the ages at which rocks in the chain were created, using the latest dating techniques available. In many cases, they were using rock samples collected in the 1960s, but whose ages had been established years ago with less effective equipment. With the new technology, many dates changed.

They found that the rocks from Kimmei seamount, in the bend and 2,270 miles from the active Kīlauea volcano on the Big Island, are 47.9 million years old, give or take a couple of hundred thousand years. That's several million years older than earlier estimates.

Samples from seamounts to the north and south show a continual progression in age as the chain goes north. When they compared ages of rocks to distance from Kīlauea, Sharp and Clague found that the Pacific Plate appears to move steadily, although with some speed-ups and slow-downs.

And they concluded that the change in direction, as represented by the Hawaiian-Emperor Bend (HEB), didn't happen suddenly.

“The new ages reveal that the HEB formed over a period of several million years...Initiation of the HEB occurred north of Daikakuji, near Kimmei seamount, where the chain's trend rotates from nearly due south to southeasterly,” they write.

Elsewhere in the paper, they say the bend took as much as 8 million years.

So, what was going on in and around the Pacific 50 million years ago that might have been associated with the change?

There was new volcanic activity along more than 1,300 miles of the plate's western edge, an area called the Izu-Bonin-Mariana arc. Rocks from that area also date to 50 million years ago.

That new activity may have been part of the change in the planet's geology that allowed the plate to slide more westward than southward.

The association of the Hawaiian-Emperor Bend with the Izu-Bonin-Mariana activity has previously been discounted, because earlier dates of the rocks suggested they happened several million years apart. The new dates from the bend suggest the bend was happening at the same time the activity at the western end of the plate took place, and that the one may have helped cause the other.

As followers of murder mysteries know, just a slight change in the timeline can turn someone with an airtight alibi into a prime suspect.

In geology, the same thing can take place.

© 2007 Jan W. TenBruggencate

Whales crowd seamounts off Hawaii at night

Bumps on the ocean floor, the biggest ones called seamounts, are known to attract many kinds of marine life—and new research indicates that this includes whales.

(Image: Cuvier's beaked whale. Credit: National Marine Fisheries Service Southwest Fisheries Science Center.)

Seamounts seem to create changes in current flows, concentrate some kinds of marine life, and attract predators of that marine life to those concentrations.

Fishermen have long known that they could improve their catch of certain species by seeking out places where the ocean floor changes elevation.

Researchers recently furthered our understanding of what goes on at seamounts by putting microphones on seamounts and listening for who showed up.

They used Cross Seamount, a feature about 100 miles south of O'ahu. The seamount rises from ocean two miles deep all around it to a depth of just 1,200 feet. It has a flattish summit about three by four miles across.

A sound recording system, referred to as a high-frequency acoustic recording package, was installed at the seamount for six months in 2005. It recorded for five minutes at a time, turning on every 25 minutes.

The results of the recording study was published this week in the journal Biology Letters, in a paper entitled “Temporal patterns in the acoustic signals of beaked whales at Cross Seamount.” The team conducting the research included Dave Johnston of the University of Hawai'i's Joint Institute for Marine and Atmospheric Research, Mark McDonald of Whale Acoustics, Jeff Polovina and Reka Domokos of NOAA's Pacific Island Fisheries Science Center., and Sean Wiggins and John Hildebrand of the Marine Physical Laboratory at Scripps Institution of Oceanography.

Scientists have long known that things happen around seamounts.

“Seamounts can have profound effects on the local physical and biological environment,” the authors write. “They can structure the velocity and vorticity of ocean currents and alter the vertical structure of water properties. These changes in the physical environment can alter local biological and ecological phenomena.”

But while a lot is known about what can happen, there's not a lot known about what actually does happen around the 4600 or so seamounts in the Pacific Basin alone. Previous studies shows that tuna fitted with electronic data recorders visit seamounts frequently, as do sharks. Above the surface, seabirds congregate there.

The fact that all those predators show up at seamounts suggests they provide a food source.

Not much was known about whales and seamounts, although there have been studies showing baleen whales are found in the seamounts of the Mediterranean and blue whales travel between deep ocean canyons and seamounts.

The Cross Seamount sensors recorded the echolocation signals and feeding signals of beaked whales, possibly Cuvier's beaked whales and Blainville's beaked whales, both of which have been spotted in Hawaiian waters.

Previous research by Robin Baird of Cascadia Research Collective, has found that both species appear to be semi-permanent residents of Hawaiian waters. The smaller Blainville's whale grows to 14 to 15 feet in length and can weight a ton. The Cuvier's whale reaches 18 to 19 feet and can weight three tons.

The Cross Seamount studies indicated the whales were primarily working the summit of the seamount at night, and that their sounds included both echolocation and what are called “feeding buzzes.”

The animals were present during the entire April to October period during which the microphones were in place.

The researchers' best guess is that the whales are attracted to the seamount for its tendency to have higher quantities of food resources than the surrounding ocean.

These are fish, crustaceans and other forms of life that scientists call nekton.

Nekton are ocean creatures capable of movement, like shrimps, fish and whales themselves. The term distinguishes them from plankton, which are smaller creatures that mostly move with the water and lack the ability to travel independent of currents.

“Concentrations of micronekton (those roughly 1 inch to four inches in length) were aggregated over the seamount in near-surface waters at night, and dense concentrations of nekton were detected across the surface of the summit,” the paper says.

The seamount may also be a convenient feeding spot in part because predators can “trap” prey against the surface of the seamount summit, making feeding easier, they say.

© 2007 Jan W. TenBruggencate

Wave power Hawai'i, new energy technology off Maui

An Australian company will build off the coast of Maui a wave power plant capable of producing 2.7 megawatts of electricity from the rising and falling of the ocean.

(Images: (top to bottom) What the Oceanlinx platform will look like on the surface, how it works, how the power gets to shore. Graphics courtesy Oceanlinx and Hawaiian Electric.)

Oceanlinx has a technology that allows the waves to force a column of air through a turbine. A rising wave shoves the air through the turbine one way. A falling wave sucks it through the turbine the other. It's designed so the turbine keeps turning in the same direction.

(For more information see www.oceanlinx.com.)

The Oceanlinx system is just one of a broad range of wave power systems. Some are fixed to the coastline, sucking energy from the crashing of waves on the land. Others use big submerged buoys that bob up and down in the water column. Others have floaters on the surface. And there are lots more.

An existing system off the Marine air station at Kāne'ohe, operated by Ocean Power Technologies, uses its PowerBuoy system, in which mostly submerged buoys create electricity as they are rocked up and down by the waves. (For more information see www.oceanpowertechnologies.com.)

“Ocean energy today is where wind was 15 to 20 years ago—with many competing technologies,” said Michael May, president of Hawaiian Electric.

The $20 million Oceanlinx system is to be built more than half a mile from shore at Pa'uwela point in Maui's Ha'ikū district. The company is performing its environmental studies, and hopes to have three wave platforms installed and working by the end of 2009.

Maui Electric has agreed to buy the power, although a formal purchase power agreement has not yet been completed. The cost of the system will be borne by Oceanlinx and investors, and a Hawaiian Electric unregulated subsidiary, Renewable Hawaii Inc., has signed a memorandum of understanding to possibly invest in it.

Oceanlinx says that among the benefits of its wave system is that it can be used in many different depths of water, has few moving parts and can be readily scaled up by adding units.

A seafloor power cable carries the energy from the moored units to the island.

Hawaiian Electric's May credited state Rep. Cynthia Thielen with being a persistent voice in support of ocean energy. Oceanlinx chairman David Weaver said he hopes the technology will be expanded to other parts of Hawai'i.

“The Oceanlinx technology is an ideal fit for Maui, with its excellent wave climate, and we hope to be able to continue working with Hawai'i on wave energy projects in the future,” Weaver said in a press release.

© 2007 Jan W. TenBruggencate

Keeping limu: strategies and common sense

In ancient Hawai'i, seaweeds were a primary spice—a way of providing different flavors to foods. (Image: The invasive but edible seaweed Gracilaria salicornia. Source: Hawaii Coral Reef Initiative Research Program.)

Most folks know about the role of various limu in fish dishes like poke. Seaweeds also could be used as a condiment, eaten alongside other foods rather than mixed with them.

The early Hawaiians would often have eaten their limu fresh or salted, said University of Hawai'i botany professor emeritus Isabella Abbot, but the realities of today's world are that folks seek something that seems fresh even though it may be several days old—so it will require some storage technology. And that's the problem challenged by Robert E. Paull and Nancy Jung Chen, of the University of Hawai'i's College of Tropical Agriculture and Human Resources.

They conducted extensive studies with one of the most popular seaweeds, Gracilaria.

Gracilaria comes in several forms in Hawai'i, several of them native, but one, Gracilaria salicornia, an imported, invasive one. The most commercially desireable form is known in Hawaiian as limu manauea and in Japanese as ogo. It is Gracilaria coronopifolia.

In the journal Postharvest Biology and Technology, Paull and Chen outlined their results.

They found that the seaweeds change in many different ways after collection. Among the changes are color, production of ethylene, leakage of fluids, and changes in protein content.

They studied using different temperatures, keeping the limu in light and dark, heat treatments and more.

They found that when kept just above freezing, the samples went limp and changed color after just one night. At 18 degrees Fahrenheit above freezing, the color changes occurred after a couple of days. A little warmer than that made little difference.

Their conclusion was that the best way to store it without special treatment was to keep it in darkness at about 61 degrees Fahrenheit, which is about 29 degrees above freezing. This didn't keep the limu usable beyond about four days, but the quality was better during the storage period.

The authors said they found that a five-minute hot dip in seawater at about 108 degrees Fahrenheit, followed by storage in 60-degree water would extend the useful life of some samples.

They said one of the best ways to keep limu for an extended period is one that seems like common sense: keep it submerged in seawater in darkness. This can extend its useful life from four days to four weeks.

“Seaweed submerged in seawater in the dark had an extended postharvest life” of about a month, the scientists said in their abstract.

That system works in part because it takes advantage of a natural characteristic of many seaweeds. One of the ways they reproduce is for pieces to break off, drift in the ocean for a while, and settle elsewhere. In order for that to work, they need to remain alive after breaking off.

They are hard-wired to survive for a long time while drifting in salt water.

If you're not in a position to haul around a bucket of water for your seaweeds, the best thing is to do preserve it in salt.

“That's what the Hawaiians did,” Abbott said.

© 2007 Jan W. TenBruggencate