Do dust emissions from sparsely vegetated regions dominate atmospheric iron supply to the Southern Ocean?

Abstract

Atmospheric deposition of dust aerosols is a significant source of exogenous iron (Fe) in marine ecosystems and is critical in setting primary marine productivity during summer. This dust‐borne input of Fe is particularly important to the Southern Ocean, which is arguably the most biogeochemically important ocean because of its large spatial extent and its considerable influence on the global carbon cycle. However, there is large uncertainty in estimates of dust emissions in the Southern Hemisphere and thus of the deposition of Fe‐containing aerosols onto oceans. Here we hypothesize that sparsely vegetated surfaces in arid and semiarid regions are important sources of Fe‐containing aerosols to the Southern Ocean. We test this hypothesis using an improved dust emission scheme in conjunction with satellite products of vegetation cover and soil moisture in an atmospheric chemistry transport model. Our improved model shows a twofold increase of Fe input into the Southern Ocean in austral summer with respect to spring and estimates that the Fe input is more than double that simulated using a conventional dust emission scheme in summer. Our model results suggest that dust emissions from open shrublands contribute over 90% of total Fe deposition into the Southern Ocean. These findings have important implications for the projection of the Southern Ocean's carbon uptake.

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

“…Remote sensing data are proving increasingly useful for representing spatial and temporal variability in vegetation within modelling schemes [157]. Plant characteristics (e.g., height, width and porosity) can now be quantified rapidly and over relatively large scales thanks to the recent progress in image-based techniques (e.g., [155]) and high-resolution remote sensing [152,154,180].…”

“…Remote sensing data have been used to represent the spatial and temporal variability in vegetation within drag partition schemes, increasing wind erosion and dust model sensitivities to land cover dynamics (e.g., [156,157]). Normalised Difference Vegetation Index (NDVI) and Leaf Area Index (LAI) data are most commonly used to estimate the vegetation cover fraction and λ as input to drag partition schemes, and to estimate z 0 for the land surface [150].…”

The GESAMP atmospheric iron deposition model intercomparison study

“…Indeed, since in direct measurements the fresh dust particles present low (<<1%) initial solubilities 15 (Chuang et al, 2005;Fung et al, 2000;Hand et al, 2004;Sedwick et al, 2007), the atmospheric processing of dust (Kumar et al, 2010;Meskhidze et al, 2003;Srinivas et al, 2014) is considered as the best candidate to explain the high aerosol solubilities commonly observed at lower loadings (Baker and Jickells, 2006;Sholkovitz et al, 2012;Oakes et al, 2012). These processes may alter also the global pattern of LFe deposition (Fan et al, 2004), especially within remote regions, such as the Atlantic, the Pacific (e.g., Sedwick et al, 2007) and the 20 Southern Ocean (Ito and Kok, 2017;Johnson et al, 2010Johnson et al, , 2011.…”

“…State-of-the-art global models clearly indicate a strong spatial and temporal variability of atmospheric LFe supply to the global ocean, that can be partly attributed to atmospheric processing. The global LFe deposition flux is currently estimated in the range of 0.4-1.1 Tg-Fe yr −1 (Ito and Kok, 2017;Ito and Shi, 2016;Ito and Xu, 2014;Johnson and Meskhidze, 2013;25 Luo et al, 2008;Myriokefalitakis et al, 2015;Wang et al, 2015).…”

“…The present-day emission estimates for natural sources as well as combustion aerosols from biomass burning are used together with anthropogenic emissions (Dentener et al, 2006;Ito et al, 2018). A total dust source of 5070 Tg yr -1 is dynamically calculated by a physically-based dust emission scheme (Kok et al, 2014a(Kok et al, , 2014b in the model for the present day 30 (Experiments 3 in Ito and Kok, 2017). The chemical composition of mineral dust and combustion Biogeosciences Discuss., https://doi.org /10.5194/bg-2018-285 Manuscript under review for journal Biogeosciences Discussion started: 10 July 2018 c Author(s) 2018.…”