Al 'Apocalipse' Gore, por que a Terra experimenta uma era do gelo a cada 100.000 anos?

sexta-feira, outubro 28, 2016

Breathing more deeply: Deep ocean carbon storage during the mid-Pleistocene climate transition

Caroline H. Lear1, Katharina Billups2, Rosalind E.M. Rickaby3, Liselotte Diester-Haass4, Elaine M. Mawbey1 and Sindia M. Sosdian1

- Author Affiliations

1School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK
2School of Marine Science and Policy, University of Delaware, Lewes, Delaware 19716, USA
3Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
4Universität des Saarlandes, Zentrum für Umweltforschung, 66041 Saarbrücken, Germany

Source/Fonte: The Hollywood Reporter


The ∼100 k.y. cyclicity of the late Pleistocene ice ages started during the mid-Pleistocene transition (MPT), as ice sheets became larger and persisted for longer. The climate system feedbacks responsible for introducing this nonlinear ice sheet response to orbital variations in insolation remain uncertain. Here we present benthic foraminiferal stable isotope (δ18O, δ13C) and trace metal records (Cd/Ca, B/Ca, U/Ca) from Deep Sea Drilling Project Site 607 in the North Atlantic. During the onset of the MPT, glacial-interglacial changes in δ13C values are associated with changes in nutrient content and carbonate saturation state, consistent with a change in water mass at our site from a nutrient-poor northern source during interglacial intervals to a nutrient-rich, corrosive southern source during glacial intervals. The respired carbon content of glacial Atlantic deep water increased across the MPT. Increased dominance of corrosive bottom waters during glacial intervals would have raised mean ocean alkalinity and lowered atmospheric pCO2. The amplitude of glacial-interglacial changes in δ13C increased across the MPT, but this was not mirrored by changes in nutrient content. We interpret this in terms of air-sea CO2 exchange effects, which changed the δ13C signature of dissolved inorganic carbon in the deep water mass source regions. Increased sea ice cover or ocean stratification during glacial times may have reduced CO2outgassing in the Southern Ocean, providing an additional mechanism for reducing glacial atmospheric pCO2. Conversely, following the establishment of the ∼100 k.y. glacial cycles, δ13C of interglacial northern-sourced waters increased, perhaps reflecting reduced invasion of CO2 into the North Atlantic following the MPT.
  • Received 13 July 2016.
  • Revision received 26 September 2016.
  • Accepted 28 September 2016.
Gold Open Access: This paper is published under the terms of the CC-BY license.