13
Ground-Air Interface: The Loess Sequences,
Markers of Atmospheric Circulation
Denis-Didier Rousseau and Christine Hatté
Abstract
Atmospheric circulation is responsible for the rapid
distribution of heat and moisture across the Earth and
hence determines our weather and regional climate, today
and in the past. During past climate cycles, the atmosphere has been much more dustier, except during the
interglacials, inducing uncertainties about the impact of
mineral aerosols on the past climate dynamics. There are
abundant traces of the combination of past atmospheric
dynamics and paleodust cycle such as eolian mineral
material transported and deposited in terrestrial archives
as loess. Records from loess deposits consistently suggest
that atmospheric dynamics was highly variable, during
the past climate cycles, much more than presently where
the only sources of dust are the major deserts. In this
chapter we explained the four main categories of
parameters allowing to identify loess deposits as reliable
markers for past air circulation.
Overview of Loess
Loess is an aeolian sediment which is relatively common in
continental areas (Fig. 13.1). In Europe and North America,
it is dispersed near former polar deserts or near the frontal
moraines of the gigantic ice sheets that developed on these
continents during the ice ages. In Asia, however, the situation is different, since the Loess Plateau is located south of
the deserts of northern China and southern Mongolia. The
loess sediments thus cover vast regions of the northern
hemisphere, at latitudes where very few other records of the
glacial paleoclimates are available, while in more southern
latitudes, lakes, peat bogs, speleothems and marine sediments collected close to the coast provide continental
records of a high quality. In Southern Hemisphere, loess is
mostly associated with fluvial and piedmont deposits in the
Pampean plains in South America, and fluvial abrasion and
glacial grinding in New Zealand.
Loess is a fine sediment transported mainly by wind to
various altitudes depending on the particle grain size, but
also on the state of the substratum and on the environmental
conditions in the region of origin of the material (Fig. 13.2).
Dust emission is favored by a low rate of vegetation
development and extension of river-emerged banks, source
of fine mineral dust. Loess deposits are thus specific to
glacial times with low sea-levels thus high river incision and
weak vegetation development.
To simplify, coarse material is carried over distances of
less than hundred kilometers and transport is mainly by
saltation, that is to say, by a series of jumps. However, fine
material (clay), which may be of local or remote origins,
may equally have been transported over hundreds of kilometers to altitudes of several kilometers in the form of
mineral dust and may have been redeposited through wet or
dry deposition (depending on whether or not they are
associated with precipitations). Loess is therefore usually a
marker for air circulation in the past.
To illustrate our words and the research potential of loess
sequences, most of our examples will be drawn from the
extensively studied Nussloch loess sequence (Rhine Valley,
Germany).
D.-D. Rousseau (&)
École Normale Supérieure de Paris, Laboratoire de Météorologie
Dynamique, UMR CNRS 8539, Université Paris Sciences et
Lettres, 24 Rue Lhomond, 75231 Paris, France
e-mail: denis-didier.rousseau@lmd.ens.fr
Lamont-Doherty Earth Observatory of Columbia University,
Palisades, NY 10964, USA
C. Hatté
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, Université Paris-Saclay, 91190 Gif-Sur-Yvette,
France
© Springer Nature Switzerland AG 2021
G. Ramstein et al. (eds.), Paleoclimatology, Frontiers in Earth Sciences,
https://doi.org/10.1007/978-3-030-24982-3_13
157
Ground-Air Interface: The Loess Sequences,
Markers of Atmospheric Circulation
Denis-Didier Rousseau and Christine Hatté
Abstract
Atmospheric circulation is responsible for the rapid
distribution of heat and moisture across the Earth and
hence determines our weather and regional climate, today
and in the past. During past climate cycles, the atmosphere has been much more dustier, except during the
interglacials, inducing uncertainties about the impact of
mineral aerosols on the past climate dynamics. There are
abundant traces of the combination of past atmospheric
dynamics and paleodust cycle such as eolian mineral
material transported and deposited in terrestrial archives
as loess. Records from loess deposits consistently suggest
that atmospheric dynamics was highly variable, during
the past climate cycles, much more than presently where
the only sources of dust are the major deserts. In this
chapter we explained the four main categories of
parameters allowing to identify loess deposits as reliable
markers for past air circulation.
Overview of Loess
Loess is an aeolian sediment which is relatively common in
continental areas (Fig. 13.1). In Europe and North America,
it is dispersed near former polar deserts or near the frontal
moraines of the gigantic ice sheets that developed on these
continents during the ice ages. In Asia, however, the situation is different, since the Loess Plateau is located south of
the deserts of northern China and southern Mongolia. The
loess sediments thus cover vast regions of the northern
hemisphere, at latitudes where very few other records of the
glacial paleoclimates are available, while in more southern
latitudes, lakes, peat bogs, speleothems and marine sediments collected close to the coast provide continental
records of a high quality. In Southern Hemisphere, loess is
mostly associated with fluvial and piedmont deposits in the
Pampean plains in South America, and fluvial abrasion and
glacial grinding in New Zealand.
Loess is a fine sediment transported mainly by wind to
various altitudes depending on the particle grain size, but
also on the state of the substratum and on the environmental
conditions in the region of origin of the material (Fig. 13.2).
Dust emission is favored by a low rate of vegetation
development and extension of river-emerged banks, source
of fine mineral dust. Loess deposits are thus specific to
glacial times with low sea-levels thus high river incision and
weak vegetation development.
To simplify, coarse material is carried over distances of
less than hundred kilometers and transport is mainly by
saltation, that is to say, by a series of jumps. However, fine
material (clay), which may be of local or remote origins,
may equally have been transported over hundreds of kilometers to altitudes of several kilometers in the form of
mineral dust and may have been redeposited through wet or
dry deposition (depending on whether or not they are
associated with precipitations). Loess is therefore usually a
marker for air circulation in the past.
To illustrate our words and the research potential of loess
sequences, most of our examples will be drawn from the
extensively studied Nussloch loess sequence (Rhine Valley,
Germany).
D.-D. Rousseau (&)
École Normale Supérieure de Paris, Laboratoire de Météorologie
Dynamique, UMR CNRS 8539, Université Paris Sciences et
Lettres, 24 Rue Lhomond, 75231 Paris, France
e-mail: denis-didier.rousseau@lmd.ens.fr
Lamont-Doherty Earth Observatory of Columbia University,
Palisades, NY 10964, USA
C. Hatté
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, Université Paris-Saclay, 91190 Gif-Sur-Yvette,
France
© Springer Nature Switzerland AG 2021
G. Ramstein et al. (eds.), Paleoclimatology, Frontiers in Earth Sciences,
https://doi.org/10.1007/978-3-030-24982-3_13
157