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Global connections between aeolian dust, climate and
ocean biogeochemistry at the present day and at the last
glacial maximum
B A Maher, J M Prospero, D Mackie, D. Gaiero, P P Hesse, Yves Balkanski
To cite this version:
B A Maher, J M Prospero, D Mackie, D. Gaiero, P P Hesse, et al.. Global connections between aeolian
dust, climate and ocean biogeochemistry at the present day and at the last glacial maximum. Earth-
Science Reviews, Elsevier, 2009, 99 (1-2), pp.61-97. �10.1016/j.earscirev.2009.12.001�. �hal-02870475�
Global connections between aeolian dust, climate and ocean biogeochemistry at the present
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day and at the last glacial maximum.
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B. A. Maher
a*
, J.M. Prospero
b
, D. Mackie
c
, D. Gaiero
d
, P.P. Hesse
e
, Y. Balkanski
f
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a
Centre for Environmental Magnetism & Palaeomagnetism, Lancaster Environment Centre,
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University of Lancaster, LA1 4YQ, UK
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b
Marine and Atmospheric Chemistry & The Cooperative Institute for Marine and Atmospheric
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Studies, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600
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Rickenbacker Causeway, Miami FL 33149, USA
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c Department of Chemistry, University of Otago, Dunedin, New Zealand
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d
Centro de Investigaciones Geoquímicas y Procesos de la Superficie, Facultad de Ciencias
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Exactas Físicas y Naturales, Universidad Nacional de Córdoba, Avda. Vélez Sársfield 1611,
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X5016CGA – Córdoba, Argentina
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e
Department of Environment and Geography, Macquarie University, NSW 2109, Sydney,
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Australia
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f
Laboratoire des Sciences du Climat et de l'Environnement, l'Orme des Merisiers, 91191 Gif
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sur Yvette Cedex, France.
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*Corresponding author b.maher@lancs.ac.uk, tel. +44 1524 510268, fax +44 1524 510269
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Abstract
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Palaeo-dust records in sediments and ice cores show that wind-borne mineral aerosol (‘dust’) is
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strongly linked with climate state. During glacial climate stages, for example, the world was
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much dustier, with dust fluxes two to five times greater than in interglacial stages. However, the
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influence of dust on climate remains a poorly quantified and actively changing element of the
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Earth’s climate system. Dust can influence climate directly, by the scattering and absorption of
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solar and terrestrial radiation, and indirectly, by modifying cloud properties. Dust transported to
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the oceans can also affect climate via ocean fertilization in those regions of the world’s oceans
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where macronutrients like nitrate are abundant but primary production and nitrogen fixation are
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limited by iron scarcity. Dust containing iron, as fine-grained iron oxides/oxyhydroxides and/or
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within clay minerals, and other essential micronutrients (e.g. silica) may modulate the uptake of
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carbon in marine ecosystems and, in turn, the atmospheric concentration of CO
2
. Here, in order
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to critically examine past fluxes and possible climate impacts of dust in general and iron-bearing
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dust in particular, we consider present day sources and properties of dust, synthesise available
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records of dust deposition at the last glacial maximum (LGM); evaluate the evidence for changes
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in ocean palaeo-productivity associated with, and possibly caused by, changes in aeolian flux to
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the oceans at the LGM; and consider the radiative forcing effects of increased LGM dust
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loadings.
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Keywords: aerosols, dust, climate change, palaeoclimatology, radiative forcing, iron
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fertilisation.
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1. Introduction
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Palaeo-dust records show that wind-borne mineral aerosol (here referred to as ‘dust’) is strongly
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linked with climate state. Studies of dust in sediments and ice cores show that dust
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concentrations and fluxes have changed greatly in association with changes in climate, for
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example, in the transitions from glacial to interglacial regimes. During glacial climate stages, the
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world was much dustier, with dust fluxes two to five times greater than in interglacial stages (e.g.
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Kohfeld and Harrison, 2001). However, the influence of dust on climate remains a poorly
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quantified and actively changing element of the Earth’s climate system. We know from present-
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day studies that dust can influence climate directly, by changing the radiative properties of the
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atmosphere through the scattering and absorption of solar and terrestrial radiation, and indirectly,
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by acting as ice nuclei (Sassen et al., 2003) and modifying cloud properties which, in turn, can
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impact both the radiative balance of the Earth and the hydrological cycle (Arimoto, 2001). Dust
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transported to the oceans can also affect climate indirectly, by supplying elements such as Fe, an
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essential micronutrient in enzymes essential to photosynthesis (Martin et al., 1991);
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phytoplankton in about 40% of the world ocean are Fe-limited (Moore et al., 2002). Thus, dust
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delivery to the ocean can modulate the uptake of carbon in marine ecosystems and, in turn, the
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atmospheric concentration of CO
2
.
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Dust not only can affect climate, but the generation and transport of dust is itself extremely
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sensitive to climate. At the present day, the most obvious link is with aridity – the globally
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dominant sources of dust are all located in arid or semi-arid regions. Global model estimates of
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present-day dust mobilization rates are poorly constrained, reflecting the scarcity of temporal and
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spatial data coverage, and range between ~ 1 and 3.5 Pg yr
-1
(e.g. Tanaka and Chiba, 2006;
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Zender et al., 2003; Engelstaedter et al., 2006); optimized multi-model estimates yield a range of
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1.5 to 2.6 Pg yr-1(Cakmur et al., 2006). Estimates of deposition to the oceans range from about
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0.3 to 2 Pg yr
-1
(Zender et al., 2004; Mahowald et al., 2005). Human activities can have an
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impact on dust mobilization but here too estimates are poorly constrained and range from 0 to 50
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% of global dust emissions (e.g. Tegen et al., 2004; Mahowald et al., 2004; Yoshioka et al.,
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2005).
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As recorded in sediments and ice cores, there have been large and systematic variations in dust
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loading in the past. The large changes in dust emissions and transport seen from the palaeo-dust
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record may reflect a variety of processes: changes in sources and source conditions; changes in
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vegetative cover; sub-aerial erosion of emergent continental shelves; deflation from periglacial
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deposits; variations in wind speed and gustiness; changed wind patterns linking sources to
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deposition areas; changes in deposition along the dust transport path. In order to interpret the
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palaeo-record and to anticipate future changes in climate, we need to have a better understanding
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of the factors that affect dust mobilization and its subsequent climatic impacts.
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The complex linkages between climate and the dust generation-transport process on glacial-
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interglacial time scales is illustrated in figure 1. There are many processes that can affect the dust
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cycle either directly or indirectly under any specific climate scenario. The relative importance of
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any specific process can change dramatically when shifting from one climate state to another –
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e.g., during glacial stages, low sea levels expose coastal sediments and glacial action can produce
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unvegetated, unconsolidated deposits all of which can become major sources of dust. A major
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driver in the Earth's climate system is atmospheric CO
2
. Figure 1 shows how dust transport to the
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oceans could conceivably modify ocean productivity and atmospheric CO
2
and the consequent
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impacts on other climate variables including the dust cycle. One major objective of
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palaeoclimatology is to use the dust record in ice cores and sediments, coupled with our
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knowledge of Earth surface processes today, to improve our understanding of these linkages in
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the current climate state and to use this information to better interpret the Earth's past climate
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history.
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For the future, dust cycle models predict large changes in aeolian transport from the continents to
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the oceans over coming centuries, in response to anthropogenic climate change (e.g. Mahowald
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et al., 2006). In order to anticipate the effects of future changes in dust emissions, it is important
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to identify the impacts of past and present-day dust flux changes in terms of feedbacks with
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regard to radiative forcing of dust aerosols and any ocean fertilization and resultant productivity-
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driven changes in atmospheric CO
2
.
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