editorial Emissions of CO from the continents and underlying mantle are emerging as potentially important drivers of past climate fluctuations. n the face of human-induced climate change, Earth’s carbon cycle has come I under intense scrutiny. The cycling of carbon between shallow reservoirs — stores of fossil fuels, the atmosphere, oceans, soils and the biosphere — is a familiar concept. But, as discussed in a range of papers in this issue, the carbon cycle extends beyond these surface stocks deep into the Earth. Unlike our neighbouring planet Venus, Earth has maintained for billions of years a temperature range that is hospitable to life, not least thanks to the slow cycling of carbon between the planet’s interior and surface: carbon locked into the crust is transported into the Earth at subduction zones and released back to the surface via metamorphism and volcanism. The size of the deep carbon stocks is vast. The crust Credit: Tim Paulsen and mantle may contain 100,000 times that of the shallow carbon reservoirs . But the natural emission of carbon from our rather than subduction zone plate Measurements of diffuse emissions — planet’s interior occurs slowly, for the most boundaries, could also be drivers of past through the crust and along faults — in part giving Earth’s systems a chance to climate fluctuations. Trace element analyses just a small section of the East African Rift adjust to and counter these emissions with show that many minerals created by a pulse are astonishingly high . Foley and Fischer natural sequestration. of volcanism about 580 million years ago, explore the possible causes for such high Significant fluctuations in climate before during the warm Ediacaran period, were carbon contents in a Perspective on humans had an influence may reflect sourced from carbonatite volcanoes. These page 891. They argue that carbon is added periods when Earth’s slow, deep carbon are a specific type of volcano that, as the to and concentrated within continents cycle was out of balance. Reconstructions name suggests, are carbon rich and release from below, via mantle convection and of waxing and waning magma production large volumes of mantle-derived CO during mantle plume activity. At times in the past over the past 720 million years had pointed eruptions (p930; N&V p884). These unusual when the abundance of rifts on Earth was to potential links between transitions to volcanoes are typically found in continental greater than today, continental breakup greenhouse states, continental breakup and rift zones, not subduction zones, implying could have released up to 170 Mt of dispersal, and periods of intense volcanic that the warm Ediacaran climate could carbon per year. Although orders of activity above subduction zones . ultimately have resulted from a pulse of CO magnitude lower than human emissions, When continents rift and split apart, from the mantle. this is still a sufficient amount of as is happening in the East African Rift Further support for a link between carbon to significantly alter climate system today, a new ocean basin forms in continental rifting and past climate change on geologic timescales. the gap. The surface area required for the comes from work by Brune and colleagues If we wish to understand the influence creation of oceanic lithosphere is usually (p941; Sketch-Up p886) in which plate the deep carbon cycle on past climate compensated by the consumption of older tectonic reconstructions and carbon cycle upheavals, we may need to pay more oceanic lithosphere elsewhere on the modelling show that periods with elevated attention to carbon storage and release from planet, via subduction at tectonic plate palaeo-atmospheric CO concentrations continental crust, rather than focussing boundaries. Sinking plates, in turn, release coincided with episodes of extensive mostly on subduction zones. ❐ fluid and volatiles, including carbon, that continental rifting; particularly between about trigger volcanism at the surface. In this 160 and 100 million years ago, as Pangaea and Published online: 1 December 2017 way, subduction zone volcanoes, similar Gondwana broke apart to form the Atlantic https://doi.org/10.1038/s41561-017-0030-3 to those found in the Cascades and Andes Ocean. During these times, the continental mountain ranges today, could be the rift systems were far longer than at present source of high CO emissions that led to and could have released more than three times References 2 1. DePaolo, D. MRS Energy Sustain. https://doi.org/10.1557/ past greenhouse conditions . as much CO as rift systems emit today. mre.2015.10 (2015). However, it now seems that carbon Such an important role for continental 2. McKenzie, N. R. et al. Science 352, 444–447 (2016). emissions from continental plate interiors, rifts in the deep carbon cycle makes sense. 3. Lee, H. et al. Nat. Geosci. 9, 145–149 (2016). Nature GeoscieNce | VOL 10 | DECEMBER 2017 | 877 | www.nature.com/naturegeoscience © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Nature Geoscience – Springer Journals
Published: Dec 1, 2017
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