Subaquatic Dust Deposits - Mineral Dust: A Key Player in the Earth System - page 448

Fig. 17.7 Evolution of global ice volume and Southern Ocean dust and iron variability through
the Pliocene and Pleistocene epochs. a , benthic • 18 O stack. Orange shading indicates the intervals
where glaciations intensified. b , regression between benthic • 18 O and Fe mass accumulation rate
(MAR). C, Fe MAR ( red line ) and dust MAR. From Martinez-Garcia et al. ( 2011 )
plankton growth stimulation of dust and the resulting CO 2 effects throughout the last
4 million years. It was further hypothesised that mineral dust not only stimulates
plankton growth through nutrient supply but also by increasing export of organic
matter from the surface ocean to the deep sea through ballasting effects (Iversen
and Ploug 2010 ), which comes down to relatively large and heavy mineral particles
that sink to the sea floor at relatively high speed and on their way scavenge organic
matter from the surface ocean downward. If this ballasting process is fast enough,
there is less time for the organic tissue to be recycled and actual export of organic
matter can be realised. Obviously, the speed of the downward transport from surface
to deep ocean is directly related to the size of the dust particles that act as the
anchors. In contrast, the bio-availability of the nutrients that are potentially supplied
with the dust is most likely inversely related to the size of the dust particles; the
faster they sink, the smaller the chance that the phytoplankton can actually benefit
from the nutrients they carry. More research is needed to confirm this idea and
picture in detail what the role of the particle size of the deposited dust on the
ocean is, both in terms of nutrient supplier and in terms of carbon-pump accelerator
(Fig. 17.7 ).