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

Abstract

Mineral dust aerosols play a major role in present and past climates. To date, we rely on climate models for estimates of dust fluxes to calculate the impact of airborne micronutrients on biogeochemical cycles. Here we provide a new global dust flux data set for Holocene and Last Glacial Maximum (LGM) conditions based on observational data. A comparison with dust flux simulations highlights regional differences between observations and models. By forcing a biogeochemical model with our new data set and using this model's results to guide a millennial‐scale Earth System Model simulation, we calculate the impact of enhanced glacial oceanic iron deposition on the LGM‐Holocene carbon cycle. On centennial timescales, the higher LGM dust deposition results in a weak reduction of <10 ppm in atmospheric CO2 due to enhanced efficiency of the biological pump. This is followed by a further ~10 ppm reduction over millennial timescales due to greater carbon burial and carbonate compensation.

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

“…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.…”

Reduced cooling following future volcanic eruptions

“…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).…”

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

“…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.…”

“…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.…”

“…3b,c and Fig. 3e,f) (Lambert et al, 2015;Mahowald et al, 1999Mahowald et al, , 2006. Even at present the estimated global value of dust deposition and atmospheric load varies largely between different studies (e.g.…”