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Volume 6 Issue 10, October 2013

During glacial periods, ice sheets covered continental margins through much of Arctic North America, Greenland and western Eurasia. Marine structures suggest that an ice sheet up to a kilometre in depth periodically covered the East Siberian continental shelf as well. The image shows the Korean icebreaker Araon conducting a swath bathymetric survey on the Arctic Ocean.

Letter p842; News & Views p807

IMAGE: SEUNG PIL HAN

COVER DESIGN: DAVID SHAND

Editorial

  • The latest report on global warming brings yet another rise in confidence that human actions are altering the Earth's climate. But in contrast to its 2007 predecessor, it is unlikely to cause a stir.

    Editorial

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Correspondence

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In the press

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Research Highlights

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News & Views

  • Phosphorus is an important element for biogeochemical development. According to a set of experiments, martian phosphate minerals dissolve more quickly than terrestrial ones, possibly providing nutrients in aqueous environments for early martian life.

    • Matthew Pasek
    News & Views
  • During the Last Glacial Maximum, ice sheets in Eurasia terminated at the edge of the Laptev Sea. Seismic data now suggest that a separate ice sheet was repeatedly centred further east, in the East Siberian Sea, during previous glacial periods.

    • Julie Brigham-Grette
    News & Views
  • The neurotoxin methylmercury can accumulate in marine food webs, contaminating seafood. An analysis of the isotopic composition of fish in the North Pacific suggests that much of the mercury that enters the marine food web originates from low-oxygen subsurface waters.

    • Daniel Cossa
    News & Views
  • Intrusions of magma into the crust help accommodate the divergence between tectonic plates. A magnetotelluric survey of the crust and mantle beneath Afar, Ethiopia, has identified enough magma to accommodate plate separation there for about 50,000 years.

    • W. Roger Buck
    News & Views
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Review Article

  • Methane is an important greenhouse gas, responsible for about 20% of the warming induced by long-lived greenhouse gases since pre-industrial times. A compilation of observations and results from chemical transport, ecosystem and climate chemistry models suggests that a rise in wetland and fossil fuel emissions probably accounts for the renewed increase in global methane levels after 2006.

    • Stefanie Kirschke
    • Philippe Bousquet
    • Guang Zeng
    Review Article
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Letter

  • Phosphate is thought to be a chemical nutrient essential for life, but the low solubility of phosphate minerals means that abiogenesis on Earth had to overcome the hurdle of phosphate-limited environments. Dissolution experiments of phosphate minerals commonly found on Mars suggest that phosphate may have been more readily available in early martian environments.

    • C. T. Adcock
    • E. M. Hausrath
    • P. M. Forster
    Letter
  • Anthropogenic aerosols are highly spatially variable, whereas greenhouse gases are largely well-mixed at the global scale, but both affect climate. Nevertheless, climate simulations suggest that regional changes in sea surface temperature and precipitation to changes in greenhouse gas and aerosol forcings are similar.

    • Shang-Ping Xie
    • Bo Lu
    • Baoqiang Xiang
    Letter
  • Iceberg calving—implicated in the retreat of ice shelves—is a complex process constrained by few observations. Numerical simulations suggest that the pattern of iceberg calving is controlled by the geometry of the glacier, and that regions of Greenland and Antarctica may be particularly vulnerable to catastrophic calving-driven retreat.

    • J. N. Bassis
    • S. Jacobs
    Letter
  • During glacial periods, ice sheets covered continental margins through much of Arctic North America, Greenland and western Eurasia. Marine structures suggest that an ice sheet up to a kilometre in depth periodically covered the East Siberian continental shelf as well.

    • Frank Niessen
    • Jong Kuk Hong
    • Sung-Ho Kang
    Letter
  • The subduction zone beneath Costa Rica experiences infrequent large earthquakes in its northwestern part, whereas slow slip dominates in the southeast. Seismic data reveal a disparity in fluid accumulation in the overriding continental crust that correlates with this change in seismic behaviour, implying that spatial gradients in fluid content may control subduction-zone seismicity.

    • Pascal Audet
    • Susan Y. Schwartz
    Letter
  • Volcanic eruptions can be cyclical, alternating between intense activity and repose over periods of hours to days. Numerical simulations of a viscous, gas-rich magma show that ascent through the volcanic conduit naturally induces a periodic pulse of pressurized gas to travel through the magma, which, on reaching the surface, can trigger the cyclical eruptions.

    • Chloé Michaut
    • Yanick Ricard
    • R. Steve J. Sparks
    Letter
  • The buoyancy of magma should cause it to rise into the crust, preventing it from ponding in the uppermost mantle. Magnetotelluric data from the Dabbahu rift segment, Ethiopia, identify a magma reservoir that extends well into the mantle beneath the rift, and is so large that it should persist for thousands of years.

    • M. Desissa
    • N. E. Johnson
    • G. J. K. Dawes
    Letter
  • Mid-ocean ridges are composed of segmented faults and magma reservoirs. Seismic images from the East Pacific Rise show that the magma reservoirs are segmented on the same fine scale as the surface faults, and that distinct lava eruptions are sourced from largely isolated magma lenses.

    • Suzanne M. Carbotte
    • Milena Marjanović
    • Michael R. Perfit
    Letter
  • Earth’s crust formed from melted mantle, yet the earliest record of this process is recorded only in crustal rocks. Isotopic dating of mantle rocks in the Ujaragssuit Nunât intrusion, southwest Greenland, identify melting events that occurred up to 4.36 Gyr ago, providing a mantle record of ancient melting to complement the crustal record.

    • Judith A. Coggon
    • Ambre Luguet
    • Peter W. U. Appel
    Letter
  • The mode of carbon storage in Earth’s mantle is unclear. High-pressure laboratory experiments on mantle analogue materials reveal that significant quantities of carbon can be stored in tiny defects within the minerals, providing an efficient mechanism for carbon storage in the mantle.

    • Jun Wu
    • Peter R. Buseck
    Letter
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Article

  • Mercury enters marine food webs in the form of microbially generated monomethylmercury. An analysis of the mercury isotopic composition of nine species of North Pacific fish suggests that microbial production of monomethylmercury below the surface mixed layer contributes significantly to the mercury contamination of marine food webs.

    • Joel D. Blum
    • Brian N. Popp
    • Marcus W. Johnson
    Article
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