Subaquatic Dust Deposits - Mineral Dust: A Key Player in the Earth System - page 437

The big advantages of subaquatic dust deposits are as follows:

￿ They are usually easy to date, thanks to carbonate-building organisms that deposit

contemporaneously with the settling dust particles. These carbonate tests can be
dated using, e.g. AMS 14 C dating • 18 O. In addition, paleaeo-magnetic properties
of the sediments can be used for dating.

￿ They reflect both wet and dry deposition of dust particles that were suspended in

the atmosphere, both at low and high altitudes. This is a big advantage compared
to, e.g. dust in ice cores, which are often at high altitudes and therefore only
register long-distance/high-altitude dust.

￿ The proxy-derived inferences can be verified using modern analogue techniques.

This is a big advantage compared to, e.g. loess deposits, which often do not have
a modern analogue.

￿ These deposits cover large parts of the Earth's surface.

17.2 From Desert Source to Subaquatic Sink: Dust

Transport Processes

The details of the processes of desert dust production, entrainment and deposition
are dealt with in Chaps. 3 , 5 and 8 . To be able to interpret the various subaqueous
deposits, these processes and their consequences for the resulting physical proper-
ties (e.g. particle-size distribution) of the deposited dust are very important. The
whole suite of processes that eventually lead to dust deposition was conceptualised
by Pye and Zhou ( 1989 ), see Fig. 17.2 .
Pye and Zhou ( 1989 ) argued that there are essentially two end-members to
atmospheric transport; low-level and high-level dust clouds travelling downwind.
Gravitational settling causes the coarser-grained particles to be deposited closer to
the source and finer-grained material further downwind. In addition to gravitational

rapid transport of dust clouds
over thousands of kilometers

Jet stream

high-level dust cloud

up to
10 km

strong
upward
air motion

descending
air motion

dust cloud forms loess deposit
which thins and becomes finer
in downwind direction

3 km

dust
source

dry deposition
of dust
in distal areas

wet deposition
of dust
in precipitation

Fig. 17.2 Schematic diagram showing different dust transport mechanisms in the high- and low-
level atmosphere (Redrawn from Pye and Zhou 1989 )