Geoscience Reference
In-Depth Information
hydrologic change to a change in the size of raindrops. Abundant atmospheric dust
would provide the nuclei for many small raindrops to form, resulting in gentle, non-
erosive rains. Conversely, a reduction in atmospheric dust load would result in large,
highly erosive drops. The momentum of a falling raindrop is the product of its mass
and velocity, so this interpretation is physically plausible.
Other workers have noted that the very high inputs of eolian dust to central Antarc-
tica and Greenland during the Last Glacial Maximum, which are clearly evident in the
Antarctic (Petit et al.,
1981
; Petit et al.,
1990
; EPICA Community Members,
2004
;
Jouzel et al., 2007) and Greenland ice cores (Svensson et al.,
2000
; Ruth,
2005
), are
consistent with shorter dust wash out times and a weaker global hydrological cycle.
It is also possible that a high concentration of atmospheric dust may in itself have
contributed to the lowering of sea surface temperatures evident in the tropical western
Pacific, especially in the warm shallow seas, or
West Pacific Warm Pool
, immediately
to the north of Australia. Given the growing recognition of the interactions between
present-day desertification processes, dust generation and the impact of dust particles
on scattering incoming solar radiation, it seems highly plausible that wind-blown dust
would be both a cause and an effect of Quaternary climatic fluctuations (McTainsh,
1989
; Harrison et al.,
2001
; Kohfeld and Harrison,
2001b
; McTainsh and Lynch,
1996
; Maher et al.,
2010
). An interesting illustration of this is the 200-year record
of wind-blown dust immediately following the 74 ka Toba volcanic super-eruption in
Sumatra identified by Zielinski et al. (
1996
) in the Greenland GISP2 ice core. Because
none of the preceding or following stadials showed a comparable dust signal, it is
probable that volcanic cooling and drought triggered by this eruption may have had a
global impact (Williams et al.,
2009a
). At the very least, there was sufficient climatic
impact from this eruption for dust to be mobilised from hitherto stable soil surfaces
in central Asia.
Interpreting the dust record from marine sediment cores is not always straight-
forward (Stuut and Lamy,
2004
). Certain desert rivers flowing into the ocean may
be carrying sediments eroded from fine-grained valley-fill deposits that were them-
selves originally derived from reworked loess, as in the Namib Desert of south-west
Africa. It is therefore important to avoid reliance on the putative dust record alone
where contamination from other sediment sources might have occurred (Gasse et al.,
2008
). However, where the only plausible sediment source is likely to have come
from continental eolian dust, as off the coast of Mauritania, variations in the dust
flux may provide useful first-order climatic information (deMenocal et al.,
2000
). In
this study, a sharp decline in the dust flux after 14.8 ka coincided with the abrupt
return of the summer monsoon in tropical Africa and the onset of the so-called
'African Humid Period' (deMenocal et al.,
2000
). The increase in dust flux from
5.5 ka onwards coincided with desiccation over the southern Sahara, southward dis-
placement of the Intertropical Convergence Zone and weakening of the summer
monsoon.
