Preferential dust sources: a geomorphological classification designed for use in global dust-cycle models

We present a simple theoretical land-surface classification that can be used to determine the location and temporal behaviour of preferential sources of terrestrial dust emissions. The classification also provides information about the likely nature of the sediments, their erodibility and the likelihood that they will generate emissions under given conditions. The scheme is based on the dual notions of geomorphic type and connectivity between geomorphic units. We demonstrate that the scheme can be used to map potential modern-day dust sources in the Chihuahuan Desert, the Lake Eyre Basin and the Taklamakan. Through comparison with observed dust emissions, we show that the scheme provides a reasonable prediction of areas of emission in the Chihuahuan Desert and in the Lake Eyre Basin. The classification is also applied to point source data from the Sahara to enable comparison of the relative importance of different land surfaces for dust emissions. We indicate how the scheme could be used to provide an improved characterisation of preferential dust sources in global dust-cycle models

Airflow dynamics in transverse dune interdunes

Aeolian dune interdunes have been relatively ignored when compared with the research attention on the morphodynamics of the dune bodies themselves. This neglect is in spite of the possible significance of interdune dynamics for the geomorphology of the sand dune system as a whole, especially with regard to dune spacing.;This project involved the collection of geomorphologically relevant airflow data for four relatively simple transverse dune interdunes. The study locations were chosen in order to sample interdunes with different size and surface type characteristics, the dynamics of which were investigated for when incident flow was normal to the upwind crest. The findings confirm existing models of aeolian dune lee-side flow in terms of flow re-attachment length and recovery attributes. A consistent pattern of increasing near-surface velocity downwind of re-attachment provides a mechanism for interdunes as sand-free features. Where studies for comparison from other aeolian examples are limited, the field-measured turbulence shows the importance of the shear layer as a source of turbulence, and agrees with studies from subaqueous bedforms. The importance of shear stress variability and the possible contribution of turbulence structures to the maintenance of sediment transport at re-attachment where velocity and mean stress is low or negative is also emphasised. At the downwind edge of interdunes, the mean and turbulent velocity properties, and therefore morphodynamics, vary according to the interdune size. In this case, interdune length leads to greater recovery, and a balance exists in this region between the recovering flow at the surface, dissipating wake from above and the obstacle effect of the dune.;The flow dynamics are characterised for the different types of interdune observed. Dynamics accordant with the flow response model are seen to characterise the interdune setting with the closest spacing. The occurrence of other "extended" aeolian interdunes with a length well over that for flow separation demanded the development of a new descriptive model to characterise the dynamics therein. In this model, the variation in near-surface flow allowed process zones to be identified through the interdune. The geomorphological significance of the processes dominating each zone are discussed and comparisons are made between the flow response case and the new interdune model from this study