Environmental sciences

  • Letter |

    The positive relationship between biodiversity and ecosystem function is well established, but the specific shape of the relationship can vary. Here, experimental evolution is used to show that the strength and slope depends on evolutionary history, with specialists and generalists that have evolved from the same ancestor giving rise to different diversity–function relationships.

    • Dominique Gravel
    • , Thomas Bell
    •  & Nicolas Mouquet
  • Letter |

    Three distinct models for the recently discovered super-Earth (masses 2–10 times that of Earth) planet GJ 1214b that are consistent with its mass and radius have been suggested. Breaking the degeneracy between these models requires obtaining constraints on the planet's atmospheric composition. Here, a ground based measurement of the transmission spectrum of GJ 1214b between 780 and 1,000 nm is reported. The lack of features in this spectrum rules out cloud free atmospheres composed primarily of hydrogen. If the planet's atmosphere is hydrogen-dominated, then it must contain clouds or hazes that are optically thick at pressures <200 mbar. Alternatively, the data are also consistent with the presence of a dense water vapour atmosphere.

    • Jacob L. Bean
    • , Eliza Miller-Ricci Kempton
    •  & Derek Homeier
  • Letter |

    The deformation style at moderately active volcanoes — such as Eyjafjallajökull, Iceland, which underwent an explosive summit eruption earlier this year — is little understood. These authors show that deformation associated with the eruptions at Eyjafjallajökull was unusual as it did not relate to pressure changes within a single magma chamber, and infer that this behaviour might be attributed to its off-rift setting with a 'cold' subsurface structure and limited magma at shallow depth.

    • Freysteinn Sigmundsson
    • , Sigrún Hreinsdóttir
    •  & Kurt L. Feigl
  • Letter |

    Secondary organic aerosol (SOA) particles can scatter radiation and act as cloud condensation nuclei, and thereby influence the Earth's radiation balance. It is generally assumed that SOA particles are liquid, but these authors show that they can adopt an amorphous solid state under ambient conditions. The findings challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere.

    • Annele Virtanen
    • , Jorma Joutsensaari
    •  & Ari Laaksonen
  • Letter |

    Global-mean surface temperatures have risen, fallen and risen again during the twentieth century, with some differences between the Northern and Southern hemispheres. The cooling is usually thought to be due to a peak in sulphate aerosol production or to changes in the climate of the world's oceans that arise over decades. Here it is shown that an abrupt change in sea surface temperatures accounts for much of the Northern Hemisphere cooling. The event was too rapid to have been caused by aerosols or multidecadal variability.

    • David W. J. Thompson
    • , John M. Wallace
    •  & Phil D. Jones
  • Letter |

    Climate change is often associated with an increase in the frequency of extreme weather events, such as heat waves or intense precipitation. Here, however, downscaled climate model simulations have been used to show that the frequency of North Atlantic polar lows — intense storms that are considerably smaller than the weather-dominating synoptic depressions — is projected to decrease by the end of the twenty-first century.

    • Matthias Zahn
    •  & Hans von Storch
  • Letter |

    Populations that become extinct because of environmental degradation pass a tipping point, after which extinction is inevitable. But theory predicts that the population's dynamics indicate what is coming beforehand, through the phenomenon of critical slowing down. It has now been shown that critical slowing down can be used to anticipate extinction in experimental populations of Daphnia magna.

    • John M. Drake
    •  & Blaine D. Griffen
  • Letter |

    Cloud simulation is one of the most challenging tasks in regional to global-scale modelling. In many cases, the physical mechanisms responsible for observed cloud dynamics are unknown, making it difficult to realistically simulate their structure and behaviour. These authors show that open cellular clouds — characterized by low albedo — can be created by precipitation-driven downdrafts and that the resulting cloud structure forms an oscillating, self-organizing cloud field.

    • Graham Feingold
    • , Ilan Koren
    •  & Wm. Alan Brewer
  • Letter |

    Many ecological systems have chaotic or near-chaotic dynamics. In such cases, it has proved difficult to test whether data fit particular models that might explain the dynamics, because the noise in the data make statistical comparison with the model impossible. This author has devised a statistical method for making such inferences, based on extracting phase-insensitive summary statistics from the raw data and comparing with data simulated using the model.

    • Simon N. Wood
  • Letter |

    The annual burial of organic carbon in lakes and reservoirs exceeds that of ocean sediments, but inland waters are components of the global carbon cycle that receive only limited attention. Here the authors find that the mineralization of organic carbon in lake sediments exhibits a strong positive relationship with temperature, suggesting that warmer water temperatures lead to more mineralization and less organic carbon burial.

    • Cristian Gudasz
    • , David Bastviken
    •  & Lars J. Tranvik
  • Letter |

    Emissions of African dust increased sharply in the early 1970s, but the human contribution to land degradation and dust mobilization remains poorly understood. Now, a 3,200-year record of dust deposition off northwest Africa has been constructed. On the basis of this dust record and a proxy record for West African precipitation, it is suggested that human-induced dust emissions from the Sahel region have contributed to the atmospheric dust load for more than 200 years.

    • Stefan Mulitza
    • , David Heslop
    •  & Michael Schulz
  • Letter |

    Evidence for multicellular life before 1.6–1.0 billion years ago is scarce and controversial. Here the authors report organized, macroscopic structures from Gabon that date to 2.1 billion years ago, have a consistent structure and seem to show evidence of multicellular colonial organization. Coming not long after the rise in atmospheric oxygen concentration, these fossils might be considered harbingers of the multicellular life that drastically expanded about a billion years later.

    • Abderrazak El Albani
    • , Stefan Bengtson
    •  & Alain Meunier
  • Review Article |

    Global climate and the atmospheric partial pressure of carbon dioxide are correlated over recent glacial cycles, with lower partial pressure of carbon dioxide during ice ages, but the causes of the changes in the partial pressure of carbon dioxide are unknown. Here the authors review the evidence in support of the hypothesis that the Southern Ocean is an important driver of glacial/interglacial changes in the partial pressure of carbon dioxide.

    • Daniel M. Sigman
    • , Mathis P. Hain
    •  & Gerald H. Haug
  • Letter |

    Removing the protected status from poorly performing conservation areas, selling the land and using the money better elsewhere is controversial, but has a simplistic appeal. Here, it is shown that such degazetting can reap significant conservation benefits, even for the well-designed Australian network of protected areas, and even when there is a significant economic cost to transferring protected status to a new area.

    • Richard A. Fuller
    • , Eve McDonald-Madden
    •  & Hugh P. Possingham
  • Letter |

    One potential mechanism for maintaining biodiversity is negative feedback between a species and its specific enemies, meaning that other species can grow in its vicinity better than further individuals of the species in question. These authors show that in a tropical forest it is the soil biota that is the main cause of this feedback, and that this effect can explain the diversity.

    • Scott A. Mangan
    • , Stefan A. Schnitzer
    •  & James D. Bever
  • Letter |

    Volcanic eruptions release a large amount of sulphur dioxide. This is oxidized to sulphate and can then form sulphate aerosol, which can affect the Earth's radiation balance. Here, past volcanic eruptions and atmospheric conditions are investigated by using sulphur and triple oxygen isotope measurements of atmospheric sulphate preserved in the rock record. The results show that seven eruption-related sulphate aerosol deposition events occurred in the mid-Cenozoic era in the northern High Plains of North America.

    • Huiming Bao
    • , Shaocai Yu
    •  & Daniel Q. Tong
  • Letter |

    Large amounts of methane are oxidized to carbon dioxide in marine sediments by communities of specific archaea and bacteria. Indirect evidence indicates that the anaerobic oxidation of methane might proceed as the reverse of archaeal methane production from carbon dioxide, with methyl-coenzyme M reductase (MCR) as the methane-activating enzyme. Here it is found that purified MCR from Methanothermobacter marburgensis can convert methane into methyl-coenzyme M, supporting the 'reverse methanogenesis' theory.

    • Silvan Scheller
    • , Meike Goenrich
    •  & Bernhard Jaun
  • Letter |

    A major pursuit in the chemical community involves the search for efficient and inexpensive catalysts that can produce large quantities of hydrogen gas from water. Here, a molybdenum-oxo complex has been identified that can catalytically generate hydrogen gas either from pure water at neutral pH, or from sea water. The work has implications for the design of 'green' chemistry cycles.

    • Hemamala I. Karunadasa
    • , Christopher J. Chang
    •  & Jeffrey R. Long