The devil's in the disequilibrium : sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model
Eggleston, Sarah (Universitat Autònoma de Barcelona. Institut de Ciència i Tecnologia Ambientals)
Galbraith, Eric (Universitat Autònoma de Barcelona. Institut de Ciència i Tecnologia Ambientals)

Fecha:	2018
Resumen:	Ocean dissolved inorganic carbon (DIC) storage can be conceptualized as the sum of four components: saturation (DICsat), disequilibrium (DICdis), carbonate (DICcarb) and soft tissue (DICsoft). Among these, DICdis and DICsoft have the potential for large changes that are relatively difficult to predict. Here we explore changes in DICsoft and DICdis in a large suite of simulations with a complex coupled climate-biogeochemical model, driven by changes in orbital forcing, ice sheets and the radiative effect of CO₂. Both DICdis and DICsoft vary over a range of 40 μmol kg⁻¹ in response to the climate forcing, equivalent to changes in atmospheric CO₂ on the order of 50 ppm for each. We find that, despite the broad range of climate states represented, changes in global DICsoft can be well-approximated by the product of deep ocean ideal age and the global export production flux, while global DICdis is dominantly controlled by the fraction of the ocean filled by Antarctic Bottom Water (AABW). Because the AABW fraction and ideal age are inversely correlated between the simulations, DICdis and DICsoft are also inversely correlated. This inverse correlation could be decoupled if changes in deep ocean mixing were to alter ideal age independently of AABW fraction, or if independent ecosystem changes were to alter export and remineralization, thereby modifying DICsoft. As an example of the latter, iron fertilization causes DICsoft to increase, and causes DICdis to also increase by a similar or greater amount, to a degree that depends on climate state. We propose a simple framework to consider the global contribution of DICsoft + DICdis to ocean carbon storage as a function of the surface preformed nitrate and DICdis of dense water formation regions, the global volume fractions ventilated by these regions, and the global nitrate inventory. More extensive sea ice increases DICdis, and when sea ice becomes very extensive it also causes significant O₂ disequilibrium, which may have contributed to reconstructions of low O₂ in the Southern Ocean during the glacial. Global DICdis reaches a minimum near modern CO₂ because the AABW fraction reaches a minimum, which may have contributed to preventing further CO₂ rise during interglacial periods.
Ayudas:	Ministerio de Economía y Competitividad MDM-2015-0552
Nota:	Unidad de excelencia María de Maeztu MdM-2015-0552
Derechos:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Lengua:	Anglès
Documento:	Article ; recerca ; Versió publicada
Publicado en:	Biogeosciences, Vol. 15 (2018) , p. 3761-3777, ISSN 1726-4189

DOI: 10.5194/bg-2017-328
DOI: 10.5194/bg-15-3761-2018

17 p, 7.3 MB

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Documentos de investigación > Documentos de los grupos de investigación de la UAB > Centros y grupos de investigación (producción científica) > Ciencias > Institut de Ciència i Tecnologia Ambientals (ICTA) > Integrated Earth System Dynamics Laboratory (IESD)
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