INDICES: Impact of soil erosion on Dust emission, Climate and terrestrial ecosystems
Bertrand Guenet (CNRS/LSCE, Saclay, France)
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Through discussions and collaboration between scientists working on soil organic carbon and mineral dust, we realised that the same physical processes underline the estimation of eroded soil fluxes and the uplift of mineral dust from source regions (Chappell & Webb, 2016). These two communities have not yet worked jointly to develop the formalism that can be used by all groups. We propose in the following description, a six weeks joint meeting between these two groups to formulate a common approach and project future collaborations.
Background and Goals
Soil erosion leads to the redistribution of Soil Organic Carbon (SOC) stock within a landscape or a region, and causes both a release of CO2 during the decomposition of eroded material and a C storage from input tending to increase the SOC in redeposition areas. The role of erosion on the carbon balance is thus complex and still not well understood. An intense debate continues on whether soil erosion is a net source or sink with respect to the atmospheric CO2 reservoir (Lal, 2005; Van Oost et al., 2007). One of the central questions of this debate is whether eroded soils are mineralized faster or slower when they are transported compared to the mineralization rates of non-eroded material. Moreover, when erosion is driven by wind, erosion produce a substantial amount of dust transported within the atmosphere and impacting the atmospheric chemistry (Chappell et al., 2013). Mineral dust is an important player in the climate system both on short timescales since it influences weather prediction, but also on longer timescales such as glacial-interglacial transitions. It can scatter or absorb shortwave radiation, therefore influencing the temperature and the precipitation patterns. The mineralogy of dust confers to this aerosol its absorption properties as well as its content in key-nutrients (soluble-Fe and P) that are delivered to both the terrestrial and marine biosphere. These nutrients from mineral dust influence the carbon cycle through their deposition, and hence constitute a feedback on climate (Mahowald, 2011). Erosion impacts on soil carbon balance and on dust emissions are being studied by different scientific communities with very few interactions. The main goal of the INDICES project is to open bridges between the two communities to share tools, concepts and data and improve the representation of eolian erosion in Earth System Models (ESMs).
Up to today, no consensus emerged to represent erosion process in ESMs explaining why this phenomenon is almost totally neglected in ESMs (Naipal et al., 2015). Soil can be eroded by the rain or by the wind. For the rain, some approaches exist and some efforts are on-going to represent this phenomenon (Panagos et al., 2015; Naipal et al., submitted) but for wind erosion, there is no clear approach, easily adaptable to ESMs that to out knowledge, has been defined. No consensus has emerged either on how to represent the mineralogy of dust in ESMs as they treat dust as an aerosol with a constant mineralogy. All measurements of mineralogy from the field show that the reality is much more complex. We are in need to agree on a simple approach that integrates the knowledge acquired on how the mineralogy influences the most relevant dust properties (optical through its refractive index, and nutriments through variations in Fe and P).
Finally, both modellers and field researchers compose the consortium involved in the INDICES project. The assembled team will benefit from each participant’s experience, and hence create a synergy between modellers and their collaborators from the field. Consequently, original and mechanistic mathematical schemes will emerge from the INDICES project thanks to the inputs of the field researchers into the modelling aspect as well as new efforts to produce data useful to evaluate ESMs thanks to the inputs from the modellers into the field work.
The agenda of the program will be:
MAY 27 - MAY 31 : Training School on soil carbon, dust cycle and climate change
JUNE 3 - JUNE 7 : What is the extent in space and time of the available data?
JUNE 10 - JUNE 14: What are the already existing mathematical approaches?
JUNE 17 - JUNE 21: Is a unified approach feasible?
JUNE 24 - JUNE 28: Is a unified approach feasible? / Is a unified approach feasible?
JULY 1 - JULY 5 : Is a unified approach feasible? / Project papers based upon new approaches