Biogeochemical Impacts of Dust on the Global Carbon Cycle - Mineral Dust: A Key Player in the Earth System - page 355

penetrates about 100 m into the oceans, so photosynthesis is confined to a surface
mixed layer of the oceans of about 100 m depth, within which the residence times
of nutrients and carbon are estimated to be of the order of weeks to a few years. The
internal mixing times of the oceans mean that they can be divided into very large
biogeochemical provinces with length scales of many hundreds of kilometres, over
which there is some coherence in the ecosystem structure (Longhurst 2007 ).
Terrestrial productivity is dominated by relatively long-lived (months to cen-
turies) plants, which therefore invest biogeochemical effort in creating carbon-rich
structural material (e.g. tree trunks). Plants grow from soil upwards and compete for
light and nutrients. Terrestrial plants grow associated with soils that are generally
centimetres to metres deep and developed over tens of thousands to millions of
years. Within soils and the associated plant community, nutrient elements are
recycled very efficiently, influenced by small-scale relatively large variations in pH
and redox (or oxygen status) regions. The nutrient status of soils depends in large
part on the supply of nutrients from the underlying rock and hence varies on length
scales of the surface expressions of rock types, kilometres to perhaps hundreds of
kilometres.
As discussed below, there are well-documented examples of dust transport
having biogeochemical impacts in both terrestrial and marine systems, although the
impacts are different in many ways in the two systems and considered separately
here. There have also been suggestions that dust can also act as a vehicle for the
transfer of bacteria and fungi through the atmosphere, although the biogeochemical
significance of such transfer is uncertain and not discussed further here (Griffin et al.
2003 , 2007 ).

14.2 Biogeochemical Impacts of Dust on Terrestrial Systems

14.2.1 Soil Formation

The existence of soil itself is fundamental to the functioning of most terrestrial
ecosystems, and dust supply can contribute to soil formation, with an attendant
impact on global biogeochemistry. In the areas of the world where the underlying
sedimentary material is itself loess (fine-grained sediment deposited by wind), the
soil is ultimately derived from this atmospherically transported dust. Such loess
sediments are particularly abundant in Asia, Europe and North America, but are
also known from South America (Muhs 2012 ). In other areas of the world, wind
transport of dust has provided at least a part of the soil in a particular region, as
reviewed by Muhs et al. ( 2012 ). The wind-blown material in a soil is identifiable by
its morphology or chemical composition, and the proportion of wind-blown material
in the overall soil varies from minor through to being a relatively large proportion
in some regions. Examples of the latter situation are areas such as the Canary Island
and Cape Verde downwind of large desert dust source regions, or areas where the