Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates

Lambert, Fabrice; Tagliabue, Alessandro; Shaffer, Gary; Lamy, Frank; Winckler, Gisela; Farı́as, Laura; Gallardo, Laura; Pol‐Holz, Ricardo De

doi:10.1002/2015gl064250

Cited by 113 publications

(164 citation statements)

References 81 publications

(111 reference statements)

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“…9c). This value is close to that reported by Lambert et al (2015). With all these processes considered in our previous study (Brovkin et al, 2012), we are still short of ca.…”

Section: The Standard Carbon Cycle Model Setupsupporting

confidence: 61%

Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity

2017

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Abstract. In spite of significant progress in paleoclimate reconstructions and modelling of different aspects of the past glacial cycles, the mechanisms which transform regional and seasonal variations in solar insolation into long-term and global-scale glacial-interglacial cycles are still not fully understood -in particular, in relation to CO 2 variability. Here using the Earth system model of intermediate complexity CLIMBER-2 we performed simulations of the coevolution of climate, ice sheets, and carbon cycle over the last 400 000 years using the orbital forcing as the only external forcing. The model simulates temporal dynamics of CO 2 , global ice volume, and other climate system characteristics in good agreement with paleoclimate reconstructions. These results provide strong support for the idea that long and strongly asymmetric glacial cycles of the late Quaternary represent a direct but strongly nonlinear response of the Northern Hemisphere ice sheets to orbital forcing. This response is strongly amplified and globalised by the carbon cycle feedbacks. Using simulations performed with the model in different configurations, we also analyse the role of individual processes and sensitivity to the choice of model parameters. While many features of simulated glacial cycles are rather robust, some details of CO 2 evolution, especially during glacial terminations, are sensitive to the choice of model parameters. Specifically, we found two major regimes of CO 2 changes during terminations: in the first one, when the recovery of the Atlantic meridional overturning circulation (AMOC) occurs only at the end of the termination, a pronounced overshoot in CO 2 concentration occurs at the beginning of the interglacial and CO 2 remains almost constant during the interglacial or even declines towards the end, resembling Eemian CO 2 dynamics. However, if the recovery of the AMOC occurs in the middle of the glacial termination, CO 2 concentration continues to rise during the interglacial, similar to the Holocene. We also discuss the potential contribution of the brine rejection mechanism for the CO 2 and carbon isotopes in the atmosphere and the ocean during the past glacial termination.

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“…9c). This value is close to that reported by Lambert et al (2015). With all these processes considered in our previous study (Brovkin et al, 2012), we are still short of ca.…”

Section: The Standard Carbon Cycle Model Setupsupporting

confidence: 61%

Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity

2017

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“…For example, during the last glacial maximum (LGM, 21,000 years BP) there was a global 2-4-fold increase in the dust cycle intensity (Lambert et al 2015), which would have increased the albedo of the troposphere in a similar manner as for the future increase in manmade aerosols. Conversely, the global cooling of 3-5 • C relative to the pre-industrial during the LGM (Shakun et al 2012) would have lowered the tropopause by up to 1.5 km, so that smaller more frequent eruptions would more easily penetrate the stratosphere, following the mechanism outlined by Aubry et al (2016).…”

Section: Discussionmentioning

confidence: 99%

Reduced cooling following future volcanic eruptions

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“…We limit the scope of our study to the effect of snow aging and mineral dust concentration in snow. Several lines of evidence suggest that dust deposition was substantially larger during glacial times (Kohfeld and Harrison, 2001;Lambert et al, 2015;Mahowald et al, 2006), particularly also at the southern margins of the NH ice sheets, the areas most affected by ablation. Dust is therefore likely to be an important player for the ice sheet ablation through its effect on snow albedo.…”

Section: Introductionmentioning

confidence: 99%

“…3d,f). Although the LGM dust deposition pattern is similar also in the reconstructions of Lambert et al (2015), the absolute values are substantially larger 15 in the latter compared to the model or Mahowald et al (1999). It should be mentioned that Ganopolski et al (2010) used the Mahowald et al (1999) data for present day and LGM, with their relative contributions scaled with sea level, as prescribed forcing in the surface energy and mass balance interface module.…”

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The importance of snow albedo for ice sheet evolution over the last glacial cycle

Ganopolski¹,

Willeit²

2017

Preprint

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Abstract. The surface energy and mass balance of ice sheets strongly depends on the amount of solar radiation absorbed at the surface, which is mainly controlled by the albedo of snow and ice. Here, using an Earth system model of intermediate complexity, we explore the role played by surface albedo for the simulation of glacial cycles. We show that the evolution of the Northern Hemisphere ice sheets over the last glacial cycle is very sensitive to the representation of snow albedo in the model. It is well known that the albedo of snow depends strongly on the snow grain size and the content of light absorbing 10 impurities. Excluding either the snow aging effect or the dust darkening effect on snow albedo leads to an excessive ice build-up during glacial times and consequently to a failure in simulating deglaciation. While the effect of snow grain growth on snow albedo is well constrained, the albedo reduction due to the presence of dust in snow is much more uncertain, because the light absorbing properties of dust vary widely as a function of dust mineral composition. We also show that assuming slightly different optical properties of dust leads to very different ice sheet and climate evolutions in the model. 15Conversely, ice sheet evolution is less sensitive to the choice of ice albedo in the model. We conclude that a proper representation of snow albedo is a fundamental prerequisite for a successful simulation of glacial cycles. IntroductionThe net surface mass balance of ice sheets is equal to the difference between accumulation, which is controlled by the hydrological cycle, and of ablation, which is determined by the surface energy balance. The surface energy balance strongly 20 depends on the amount of solar radiation absorbed at the surface. While the amount of radiation reaching the surface is mainly determined by the insolation at the top of the atmosphere and cloud cover, the fraction of radiation absorbed at the surface is controlled by its albedo. Since ice sheets are mostly covered by snow, the albedo of snow plays a crucial role for the surface energy and mass balance of ice sheets.The albedo of snow is a complex function of snow grain size and concentration of light-absorbing impurities (Warren, 1982; 25 Warren and Wiscombe, 1980). After snowfall, snow crystals undergo rapid transformations in size and shape, with a tendency for snow grains to grow larger with time (Colbeck, 1982). The rate of change is controlled by snow temperature and the temperature gradient inside the snow, with melt-freeze cycles beeing additionally very efficient in accelerating grain growth during snowmelt (Brun et al., 1992;. The change in snow grain size affects the interaction of the snow surface with the incoming solar radiation, with larger grains increasing the path that photons are traveling in the 30 snow and therefore decreasing its albedo. The decrease in albedo due to a growth of the optically equivalent snow grain size from 100 µm, typical for fresh snow, to 1000 µm, typical for melting snow, is ~10 % (Fig...

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Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates

Cited by 113 publications

References 81 publications

Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity

Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity

Reduced cooling following future volcanic eruptions

The importance of snow albedo for ice sheet evolution over the last glacial cycle

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Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates

Cited by 113 publications

References 81 publications

Simulation of climate, ice sheets and CO&lt;sub&gt;2&lt;/sub&gt; evolution during the last four glacial cycles with an Earth system model of intermediate complexity

Simulation of climate, ice sheets and CO&lt;sub&gt;2&lt;/sub&gt; evolution during the last four glacial cycles with an Earth system model of intermediate complexity

Reduced cooling following future volcanic eruptions

The importance of snow albedo for ice sheet evolution over the last glacial cycle

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Product

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Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity

Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity