By analyzing samples of submarine volcanic glass near one of these areas, scientists found unexpected changes in isotopes of hydrogen and boron from the deep mantle. They expected to see the isotope "fingerprint" of seawater. But in volcanoes from the Manus Basin they also discovered evidence of seawater distilled long ago from a more ancient plate descent event, preserved for as long as 1 billion years.
The data indicate that these ancient oceanic "slabs" can return to the upper mantle in some areas, and that rates of hydrogen exchange in the deep Earth may not conform to experiments. The research is published in the February 26, 2012, advanced on line publication of Nature Geoscience.
As Carnegie coauthor Erik Hauri explained, "Hydrogen and boron have both light and heavy isotopes. Isotopes are atoms of the same element with different numbers of neutrons. The volcanoes in the Manus Basin are delivering a mixture of heavy and light isotopes that have been observed nowhere else. The mantle under the Manus Basin appears to contain a highly distilled ancient water that is mixing with modern seawater."
When seawater-soaked oceanic plates descend into the mantle, heavy isotopes of hydrogen and boron are preferentially distilled away from the slab, leaving behind the light isotopes, but also leaving it dry and depleted of these elements, making the "isotope fingerprint" of the distillation process difficult to identify. But this process appears to have been preserved in at least one area: submarine volcanoes in the Manus Basin of Papua New Guinea, which erupted under more than a mile of seawater (2,000 meters). Those pressures trap water from the deep mantle within the volcanic glass.
Lead author Alison Shaw and coauthor Mark Behn, both former Carnegie postdoctoral researchers, recognized another unique feature of the data. Lab experiments have shown very high diffusion rates for hydrogen isotopes, which move through the mantle as tiny protons. This diffusion should have long-ago erased the hydrogen isotope differences observed in the Manus Basin volcanoes.
"That is what we typically see at mid-ocean ridges," remarked Hauri. "But that is not what we found at Manus Basin. Instead we found a huge range in isotope abundances that indicates hydrogen diffusion in the deep Earth may not be analogous to what is observed in the lab."
The team's * finding means is that surface water can be carried into the deep Earth by oceanic plates and be preserved for as long as 1 billion years. They also indicate that the hydrogen diffusion rates in the deep Earth appear to be much slower than experiments show. It further suggests that these ancient slabs may not only return to the upper mantle in areas like the Manus Basin, they may also come back up in hotspot volcanoes like Hawaii that are produced by mantle plumes.
The results are important to understanding how water is transferred and preserved in the mantle and how it and other chemicals are recycled to the surface.
*Other researchers on the team include lead author A.M. Shaw and M.D. Behn from Woods Hole Oceanographic Institution, D.R. Hilton Scripps Institution of Oceanography and UC San Diego, C.G. Macpherson Durham University, and J.M. Sinton University of Hawaii.
The Carnegie Institution for Science (carnegieScience.edu) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.
Erik Hauri | EurekAlert!
In times of climate change: What a lake’s colour can tell about its condition
21.09.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
Did marine sponges trigger the ‘Cambrian explosion’ through ‘ecosystem engineering’?
21.09.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
22.09.2017 | Life Sciences
22.09.2017 | Medical Engineering
22.09.2017 | Physics and Astronomy