Enhanced sensitivity of oceanic CO<sub>2</sub> uptake to dust deposition by iron‐light colimitation

Nickelsen, Levin; Oschlies, Andreas

doi:10.1002/2014gl062969

Cited by 10 publications

(9 citation statements)

References 43 publications

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“…Isolating the surface iron fertilization effect by comparing LGM_dust to LGM_default, we obtain a decrease in

p {CO}_{2}^{atm}

of 4 ppm (Table ), about half of what Lambert et al () obtain from the same dust fields (with constant solubility parametrization, which results in higher SO fertilization than with our variable solubility method). The higher iron fertilization used in LGM_highFe raises this number to 28 ppm, which is close to 25 ppm, from a PI experiment that included a dust flux increase of comparable magnitude to LGM_highFe (Nickelsen & Oschlies, ). By comparing LGM_sed with LGM_default we can isolate the effect of changes in LGM sedimentary DFe release on

p {CO}_{2}^{atm}

: A decrease in global C remi produces a raise of 15 ppm.…”

Section: Resultsmentioning

confidence: 90%

Combined Effects of Atmospheric and Seafloor Iron Fluxes to the Glacial Ocean

et al. 2017

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Changes in the ocean iron cycle could help explain the low atmospheric CO2 during the Last Glacial Maximum (LGM). Previous modeling studies have mostly considered changes in aeolian iron fluxes, although it is known that sedimentary and hydrothermal fluxes are important iron sources for today's ocean. Here we explore effects of preindustrial‐to‐LGM changes in atmospheric dust, sedimentary, and hydrothermal fluxes on the ocean's iron and carbon cycles in a global coupled biogeochemical‐circulation model. Considering variable atmospheric iron solubility decreases LGM surface soluble iron fluxes compared with assuming constant solubility. This limits potential increases in productivity and export production due to surface iron fertilization, lowering atmospheric CO2 by only 4 ppm. The effect is countered by a decrease in sedimentary flux due to lower sea level, which increases CO2 by 15 ppm. Assuming a 10 times higher iron dust solubility in the Southern Ocean, combined with changes in sedimentary flux, we obtain an atmospheric CO2 reduction of 13 ppm. The high uncertainty in the iron fluxes does not allow us to determine the net direction and magnitude of variations in atmospheric CO2 due to changes in the iron cycle. Our model does not account for changes to iron‐binding ligand concentrations that could modify the results. We conclude that when evaluating glacial‐interglacial changes in the ocean iron cycle, not only surface but also seafloor fluxes must be taken into account.

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“…Isolating the surface iron fertilization effect by comparing LGM_dust to LGM_default, we obtain a decrease in

p {CO}_{2}^{atm}

p {CO}_{2}^{atm}

: A decrease in global C remi produces a raise of 15 ppm.…”

Section: Resultsmentioning

confidence: 90%

Combined Effects of Atmospheric and Seafloor Iron Fluxes to the Glacial Ocean

et al. 2017

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“…Iron fertilization simulations calculate the input flux of dissolved iron to the ocean surface assuming a constant solubility and using the glacial atmospheric dust field of Mahowald et al (2006) as modified by Nickelsen and Oschlies (2015) instead of the standard pre-industrial dust field; note that this is not entirely in agreement with more modern reconstructions, which could potentially have an influence on the induced biological blooms, both in magnitude and geographically (e.g., Albani et al, 2012Albani et al, , 2016. Four iron fertilization experiments were run with the lowest radiative forcing with LGM ice sheets, as well as one model run similar to the control run.…”

Section: Experimental Designmentioning

confidence: 99%

The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings in a general circulation model

Eggleston

Galbraith

2018

Biogeosciences

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Abstract. The complexity of dissolved gas cycling in the ocean presents a challenge for mechanistic understanding and can hinder model intercomparison. One helpful approach is the conceptualization of dissolved gases as the sum of multiple, strictly defined components. Here we decompose dissolved inorganic carbon (DIC) into four components: saturation (DIC sat ), disequilibrium (DIC dis ), carbonate (DIC carb ), and soft tissue (DIC soft ). The cycling of dissolved oxygen is simpler, but can still be aided by considering O 2 , O 2 sat , and O 2 dis . We explore changes in these components within a large suite of simulations with a complex coupled climatebiogeochemical model, driven by changes in astronomical parameters, ice sheets, and radiative forcing, in order to explore the potential importance of the different components to ocean carbon storage on long timescales. We find that both DIC soft and DIC dis vary over a range of 40 µmol kg −1 in response to the climate forcing, equivalent to changes in atmospheric pCO 2 on the order of 50 ppm for each. The most extreme values occur at the coldest and intermediate climate states. We also find significant changes in O 2 disequilibrium, with large increases under cold climate states. We find that, despite the broad range of climate states represented, changes in global DIC soft can be quantitatively approximated by the product of deep ocean ideal age and the global export production flux. In contrast, global DIC dis 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 among the simulations, DIC dis and DIC soft are also inversely correlated, dampening the overall changes in DIC. 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 DIC soft . As an example of the latter, we show that iron fertilization causes both DIC soft and DIC dis to increase and that the relationship between these two components depends on the climate state. We propose a simple framework to consider the global contribution of DIC soft + DIC dis to ocean carbon storage as a function of the surface preformed nitrate and DIC dis of dense water formation regions, the global volume fractions ventilated by these regions, and the global nitrate inventory.

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“…See also pre-existing global compilations of changes in ocean productivity in references (165,174). b Model-based estimates of CO 2 drawdown induced by increased LGM dust deposition [175][176][177][178][179][180][181][182]. The semi-circle on the x-axis in b marks the average of the model ensemble.…”

Section: Indirect Impacts On Biogeochemical Cyclesmentioning

confidence: 99%

Aerosol-Climate Interactions During the Last Glacial Maximum

Albani

Balkanski

Mahowald

et al. 2018

Curr Clim Change Rep

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Purpose of Review Natural archives are imprinted with signs of the past variability of some aerosol species in connection to major climate changes. In certain cases, it is possible to use these paleo-observations as a quantitative tool for benchmarking climate model simulations. Where are we on the path to use observations and models in connection to define an envelope on aerosol feedback onto climate? Recent Findings On glacial-interglacial time scales, the major advances in our understanding refer to mineral dust, in terms of quantifying its global mass budget, as well as in estimating its direct impacts on the atmospheric radiation budget and indirect impacts on the oceanic carbon cycle. Summary Even in the case of dust, major uncertainties persist. More detailed observational studies and model intercomparison experiments such as in the Paleoclimate Modelling Intercomparison Project phase 4 will be critical in advancing the field. The inclusion of new processes such as cloud feedbacks and studies focusing on other aerosol species are also envisaged.

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Enhanced sensitivity of oceanic CO₂ uptake to dust deposition by iron‐light colimitation

Cited by 10 publications

References 43 publications

Combined Effects of Atmospheric and Seafloor Iron Fluxes to the Glacial Ocean

Combined Effects of Atmospheric and Seafloor Iron Fluxes to the Glacial Ocean

The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings in a general circulation model

Aerosol-Climate Interactions During the Last Glacial Maximum

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Enhanced sensitivity of oceanic CO2 uptake to dust deposition by iron‐light colimitation

Cited by 10 publications

References 43 publications

Combined Effects of Atmospheric and Seafloor Iron Fluxes to the Glacial Ocean

Combined Effects of Atmospheric and Seafloor Iron Fluxes to the Glacial Ocean

The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings in a general circulation model

Aerosol-Climate Interactions During the Last Glacial Maximum

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Enhanced sensitivity of oceanic CO₂ uptake to dust deposition by iron‐light colimitation