- Magnificent Marine Algae Blooms Seen From Space
- The Precarious Future of Ocean Color Satellite Imagery
- Our Solar System: Now With 2 Million Years More Maturity
Posted: 23 Aug 2010 04:00 AM PDT
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When microscopic marine organisms known as phytoplankton multiply into a dense population at the ocean's surface, massive blooms can spread so far that they can only be seen from space. These algal blooms create beautiful patterns that can stretch for hundreds of miles and trace the ocean's swirling currents.
Phytoplankton are the foundation of the ocean food web and are critical to the health of nearly everything that lives there. They contain chlorophyll to perform photosynthesis and turn sunlight into energy which feeds their predators, and their predators' predators, all the way up through the food chain to large fish, mammals and birds such as sharks, sea lions and penguins.
Recent research suggests the fear that warming oceans could hamper phytoplankton growth may be real. The organisms depend on mixing of ocean water to bring nutrients such as phosphates and nitrates to the surface. As the ocean warms, it becomes more stratified, with the warmer water remaining at the top where the organisms need to be in order to do photosynthesis.
A big reduction in phytoplankton could threaten marine animals and the fisheries humans depend on. And it could create a climate feedback loop that would increase temperatures further. These organisms absorb carbon dioxide from the atmosphere and take it to the bottom of the ocean when they die, where it stays for thousands of years. So as their numbers decline, they will do less to keep global temperatures down.
In addition to capturing amazing images of the phytoplankton blooms, satellite data is one of the only ways to study them. Different species of phytoplankton change the way the ocean reflects light in different ways. The chlorophyll in the tiny organisms causes the ocean's surface to reflect green. Other pigments can make the water look red or brown. Some phytoplankton called coccolithophores are coated with white calcite that makes the water look bright turquoise when billions of them get together.
Click on any image in this gallery for a high-res version.
The large, beautiful bloom pictured above off the coast of Ireland on May 22, 2010 was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite. The phytoplankton may have benefited from iron and nutrients in the ash dumped onto the ocean surface for weeks by Iceland's Eyjafjallajökull Volcano.
Below, the Terra satellite imaged another brilliant bloom in the area on June 4, 2007. The bloom emanates from the mouth of the River Shannon and tapers off to the north.
Posted: 23 Aug 2010 02:00 AM PDT
The United States owns three orbiting satellites capable of measuring plant life in the world's oceans, and they're all on their last legs. That has ocean scientists pushing NASA to have its next satellite take an occasional look at the moon, a critical step for transmitting accurate images of the sea.
The three satellites, SeaWiFS, Aqua and Terra, have been flying far longer than they were designed to. SeaWiFs, for example, was built to last three to five years but has lasted 13. Critically, all of these satellites look at the moon on a monthly basis to calibrate the ocean color sensors, which degrade over time.
"If you're looking at long-term changes, you need to know how your instrument is changing," said Charles McClain, chief scientist of the SeaWiFS mission. "The best way to do that is to roll the space craft a little bit to look at the moon. It's easy to do, but it interferes with operations. We've put a request in for NPP to it, but it hasn't been approved."
NPP is the National Polar Orbiting Environmental Satellite System Preparatory Project, a joint NASA, Department of Defense and National Oceanic and Atmospheric Administration mission scheduled to launch in 2011.
If NPP doesn't get accurate measurements of ocean color, which are used to measure the amount of chlorophyll from plants in the surface ocean, the next scheduled satellite mission that will be capable of doing so is PACE. But that mission isn't scheduled until 2018, McClain said.
Keeping track of the amount of plant life in the ocean has become increasingly important for scientists researching global climate change and how ocean plants act as a carbon sink. Politically, getting NPP to do the necessary moon checkup is challenging because it's an operational satellite, meaning its primary objective is accurate weather forecasting and climate science.
"Operational and science satellites are different," said atmospheric scientist Leo Andreoli, chief scientist at Northrop Grumman Aerospace Systems. Northrop is a subcontractor building and testing the main sensor, called the Visible Infrared Radiometer Suite, on the NPP. "Operational satellites have to be replaced and have follow-ons, whereas scientific missions go up to see what they can see, and don't necessarily have to have a follow on."
"This is really gravy for them, having their science collected on an operational satellite," Andreoli added.
Despite being "gravy," Andreoli said, getting ocean color always has been part of the NPP mission, and getting ocean color from any satellite is tough. In 2008, they didn't think the sensor on NPP would be capable of it, but Andreoli said they've worked out algorithms and mathematical procedures to correct the problems with the sensor.
When it comes to looking at the moon for calibration, though, Andreoli says he's not sure the request will go through.
"I will say that being in the operation of satellites for many years that one does not like to take the satellite and turn it away from the earth because there is a risk you won't be able to get it to turn back," he said. "It needs to be weighed against the value of the mission."
So the future remains precarious for ocean scientists. In a best-case scenario, NPP will be able to get accurate measurements of chlorophyll and will serve as a backup when SEAWiFS, Aqua and Terra inevitably die.
In a worst case scenario, there will be a gap in the data until PACE goes up in 2018, which will calculate chlorphyll but also have the spectral coverage to explore new science objectives, McClain said.
Posted: 23 Aug 2010 02:00 AM PDT
New measurements of an old rock show that the solar system may be up to two million years older than scientists previously thought. The new birth date could resolve a major controversy among geochemists, and provides extra evidence that the solar system got its heavy elements from the explosion of a nearby supernova.
The currently accepted age of the solar system — about 4.56 billion years — was calculated by measuring parts of meteorites called calcium-aluminum-rich inclusions, which are thought to be the first solids to have condensed from the cloud of gas that formed the sun and planets.
The inclusions' ages come from measuring how much of certain radioactive isotopes, versions of the same element that have different atomic masses, and their decay products are in the rock. Because a parent isotope decays into a daughter isotope at a set rate, scientists can work backwards to get an age for the rock by comparing the amounts of these isotopes.
Each set of parent and daughter isotopes ought to give the same age for the solar system — but they don't. Tests comparing the relative amounts of aluminum and magnesium give ages about one million years older than tests comparing two different isotopes of lead. Resolving the difference is "one of the major problems in cosmochemistry today," according to geophysicist Andrew Davis of the University of Chicago.
One possible explanation is that earlier experiments used an impure rock. Much of the earlier work used inclusions from one meteorite called Allende, whose inclusions are relatively large and easy to analyze.
"That particular meteorite is fairly messed up," said cosmochemist Meenakshi Wadhwa of Arizona State University, a coauthor of a study in the August 22 Nature Geoscience reporting the new solar system age. The Allende meteorite melted and re-cooled at least once after it was formed on its parent asteroid, so the ages it gives "may not be as reliable."
So Wadhwa and Arizona State geochemist Audrey Bouvier found a more pristine rock to study. They used an inclusion from a three-pound meteorite called NWA 2364, which was found in Morocco in 2004 and appears to have remained unchanged since it formed.
"This meteorite is thus extremely rare and precious for the inclusions that it contains," Bouvier said.
Bouvier and Wadhwa subjected the inclusion to all kinds of violence, like repeatedly washing it with acid and dissolving the pieces in a solution of hydrogen fluoride and nitric acid, to remove any earthly contaminants and isolate the radiogenic elements. They measured the relative amounts of two isotopes of lead, lead-206 and lead-207. These lead isotopes come from the decay of two different versions of uranium, uranium-238 and uranium-235. Because uranium decays relatively quickly, and because the method compares two different isotopes at once, lead-lead dating is considered one of the best ways to age rocks.
"The dates with this chronometer are more precise than anything you can get from any other chronometer," Wadhwa said.
The researchers also considered new evidence that a classic equation used for lead-lead dating needs an update. In an earlier paper, Wadhwa and colleagues at Arizona State showed that a common assumption geochronologists make when finding rocks' ages — that certain types of uranium always appear in the same relative quantities in meteorites — is wrong.
Although they couldn't actually measure the different amounts of uranium in the meteorite, "we tried to take into account the possibility that you might have a different uranium composition than was assumed," Wadhwa said.
Bouvier and Wadhwa found that the meteorite inclusion formed 4,568.2 million years ago, between 0.3 and 1.9 million years earlier than the next best lead-lead measurements suggest. They also tested the relative amounts of aluminum and magnesium in the rock, and found the same exact age, resolving the difference found in earlier studies.
"This is an excellent and important study," commented Davis, who was not involved in the study. But it does raise some questions: What was wrong with Allende? Can the age be refined even further by actually measuring the uranium ratios? "It is important to measure ages on more calcium-aluminum-rich inclusions" in the future, Davis said.
To a 4.5 billion year old solar system, two million years might not sound like much. But it makes a big difference for understanding how the infant solar system formed, Wadhwa said.
"Most of what shaped the formation history of the solar system, and the planets and asteroids and all that, a lot of that happened within the first 5 to 10 million years," she said. "Being able to actually pinpoint to within something like 2 million years what the age of the solar system is does make a difference in terms of trying to resolve the sequence of events that happened subsequently."
The new age also means that some radioactive elements were much more abundant in the early solar system than previously thought. In particular, the new age suggests that there would be twice as much iron-60 in the early solar system.
"That kind of abundance can't be produced by anything but a supernova," Wadhwa said.
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