Biogeochemistry

  • Review Article |

    A synthesis of recent research shows that the effects of human actions have already altered the regional hydrology and energy balance of parts of the Amazon basin, and that interactions between deforestation, fire and climate change are likely to further alter carbon storage, precipitation patterns and river discharge.

    • Eric A. Davidson
    • , Alessandro C. de Araújo
    •  & Steven C. Wofsy
  • Brief Communications Arising |

    • Bradley J. Cardinale
  • Letter |

    It has been suggested that the Cambrian ocean was oxygen deficient, but physical evidence for widespread anoxia has been lacking. Now, sulphur isotope data from Cambrian rocks at six different locations around the world is presented, with the finding of a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record, which is thought to be indicative of a global carbon cycle perturbation at the time. With the help of a box model, these isotope shifts support the idea of large-scale anoxic and sulphidic conditions in the later Cambrian ocean.

    • Benjamin C. Gill
    • , Timothy W. Lyons
    •  & Matthew R. Saltzman
  • Letter |

    It is thought that rises in atmospheric oxygen concentrations occurred about 2.3 and 0.8 billion years ago, with the latter implicated in the subsequent evolutionary expansion of complex biota. Sulphur isotope fractionation data from an ancient sedimentary succession in Scotland now suggest that the terrestrial environment was already sufficiently oxygenated to support a biota adapted to an oxygen-rich atmosphere about 1.2 billion years ago.

    • John Parnell
    • , Adrian J. Boyce
    •  & Sam Spinks
  • 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 |

    Concentrations of dissolved inorganic carbon (DIC) decrease in the surface mixed layers during spring and summer in most of the oligotrophic ocean. The missing DIC is thought to be converted to particulate carbon by photosynthesis, but known mechanisms do not seem to supply enough nutrients for the photosynthesis. Here it is shown that short-lived transport events connect deep-water nitrate stocks with nutrient-poor surface waters.

    • Kenneth S. Johnson
    • , Stephen C. Riser
    •  & David M. Karl
  • Letter |

    Anthropogenic global warming is likely to be amplified by positive feedback from the global carbon cycle; however, the magnitude of the climate sensitivity of the global carbon cycle, and thus of its positive feedback strength, is under debate. By combining a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO2 data from three ice cores, this climate sensitivity is now shown to be much smaller than previously thought.

    • David C. Frank
    • , Jan Esper
    •  & Fortunat Joos