14
Air-Ground Interface: Reconstruction
of Paleoclimates Using Speleothems
Dominique Genty and Ana Moreno
Speleothems: Description, Distribution,
Formation and Preservation
The term speleothem refers to carbonate deposits in caves:
mainly stalactites, stalagmites and stalagmite floors. It is
taken from the English (speleothem) which has its roots in
Greek signifying ‘subject’ (thema) and ‘cave’ (spelaion).
Composed of calcium carbonate, speleothems are most
commonly made of calcite (ones in aragonite are rarer and
less studied). Carbonate massifs which contain caves, within
which speleothems are found, are widely scattered around
the globe, and are found at all latitudes and in all continents,
although less frequently in the southern hemisphere
(Fig. 14.1).
Speleothems acquire their geochemical and structural
characteristics as a result of the infiltration of rainwater
through a limestone or dolomitic environment. The formation process is basically comprised of three steps: (1) at
ground level, CO 2 (produced by the roots of plants and by
microorganisms in the soil) is dissolved in rainwater; (2) the
dissolution of the surrounding rock (limestone, dolomitic
limestone, calcareous dolomites) either at ground level
(known as dissolution in an open system – at the meeting of
the three elements: air, water and rock), or at the level of the
many tiny fissures in the surrounding carbonate (closed
system); (3) once it arrives in the underground gallery, there
is degassing of CO 2 and precipitation of CaCO 3 .
Drops of water, emerging from micro-fissures, form stalactites at the ceiling of the gallery, and stalagmites on the
ground. It is the latter which is most frequently studied
because of its simple structure (resembling inverted interlocking calcite cups). The physical and chemical parameters
that allow us to reconstruct paleoclimates from speleothems
(stable isotopes, trace elements, growth rate) depend partly
on the precipitation conditions of the calcite (the temperature
in the cave, flow rate, moisture level) and, partly on the
geochemical characteristics of the water supplying the speleothems (McDermott 2004; Fairchild and Baker 2012).
Speleothems, once formed, seldom undergo subsequent
changes (no erosion, no internal recirculation, some rare
examples of diagenesis, such as, for example, the transformation of aragonite into calcite). The calcite in speleothems
is a material that can be dated as far back as 500 ka using
radiometric methods (U-Th series dating) or even as far back
as several million years depending on their geochemical
characteristics (U-Pb dating).
Growth and Chronology of Speleothems
The growth of speleothems is determined by the presence of
infiltrating water. As a result, extremely dry or cold climates
(water freezing above ground), causes a halt in growth
(hiatus) except in certain exceptional circumstances found in
the mountains (Luetscher et al. 2015). The speed of growth
of a stalagmite depends not only on the amount of water
infiltrating into the karst, but also on a number of environmental factors such as the Ca
2+ concentration of the infiltrating water, the thickness of the film of water on the
surface of the speleothem, the temperature and the partial
pressure of CO 2 in the cave’s atmosphere. Geochemical
modeling of growth shows that the dominant factors are the
flow rate and the Ca
2+ content of the water (Dreybrodt
D. Genty (&)
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay,
91190 Gif-sur-Yvette, France
e-mail: dominique.genty@lsce.ipsl.fr;
dominique.genty@u-bordeaux.fr
EPOC (Environnements et Paléoenvironnements Océaniques et
Continentaux), Université de Bordeaux, bat. B18N, Allée Geoffroy
Saint-Hilaire, 33615 Pessac Cedex, France
A. Moreno
Instituto Pirenaico de Ecología—CSIC, Avda. Montañana 1005,
50059 Saragossa, Spain
© 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_14
169
Air-Ground Interface: Reconstruction
of Paleoclimates Using Speleothems
Dominique Genty and Ana Moreno
Speleothems: Description, Distribution,
Formation and Preservation
The term speleothem refers to carbonate deposits in caves:
mainly stalactites, stalagmites and stalagmite floors. It is
taken from the English (speleothem) which has its roots in
Greek signifying ‘subject’ (thema) and ‘cave’ (spelaion).
Composed of calcium carbonate, speleothems are most
commonly made of calcite (ones in aragonite are rarer and
less studied). Carbonate massifs which contain caves, within
which speleothems are found, are widely scattered around
the globe, and are found at all latitudes and in all continents,
although less frequently in the southern hemisphere
(Fig. 14.1).
Speleothems acquire their geochemical and structural
characteristics as a result of the infiltration of rainwater
through a limestone or dolomitic environment. The formation process is basically comprised of three steps: (1) at
ground level, CO 2 (produced by the roots of plants and by
microorganisms in the soil) is dissolved in rainwater; (2) the
dissolution of the surrounding rock (limestone, dolomitic
limestone, calcareous dolomites) either at ground level
(known as dissolution in an open system – at the meeting of
the three elements: air, water and rock), or at the level of the
many tiny fissures in the surrounding carbonate (closed
system); (3) once it arrives in the underground gallery, there
is degassing of CO 2 and precipitation of CaCO 3 .
Drops of water, emerging from micro-fissures, form stalactites at the ceiling of the gallery, and stalagmites on the
ground. It is the latter which is most frequently studied
because of its simple structure (resembling inverted interlocking calcite cups). The physical and chemical parameters
that allow us to reconstruct paleoclimates from speleothems
(stable isotopes, trace elements, growth rate) depend partly
on the precipitation conditions of the calcite (the temperature
in the cave, flow rate, moisture level) and, partly on the
geochemical characteristics of the water supplying the speleothems (McDermott 2004; Fairchild and Baker 2012).
Speleothems, once formed, seldom undergo subsequent
changes (no erosion, no internal recirculation, some rare
examples of diagenesis, such as, for example, the transformation of aragonite into calcite). The calcite in speleothems
is a material that can be dated as far back as 500 ka using
radiometric methods (U-Th series dating) or even as far back
as several million years depending on their geochemical
characteristics (U-Pb dating).
Growth and Chronology of Speleothems
The growth of speleothems is determined by the presence of
infiltrating water. As a result, extremely dry or cold climates
(water freezing above ground), causes a halt in growth
(hiatus) except in certain exceptional circumstances found in
the mountains (Luetscher et al. 2015). The speed of growth
of a stalagmite depends not only on the amount of water
infiltrating into the karst, but also on a number of environmental factors such as the Ca
2+ concentration of the infiltrating water, the thickness of the film of water on the
surface of the speleothem, the temperature and the partial
pressure of CO 2 in the cave’s atmosphere. Geochemical
modeling of growth shows that the dominant factors are the
flow rate and the Ca
2+ content of the water (Dreybrodt
D. Genty (&)
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay,
91190 Gif-sur-Yvette, France
e-mail: dominique.genty@lsce.ipsl.fr;
dominique.genty@u-bordeaux.fr
EPOC (Environnements et Paléoenvironnements Océaniques et
Continentaux), Université de Bordeaux, bat. B18N, Allée Geoffroy
Saint-Hilaire, 33615 Pessac Cedex, France
A. Moreno
Instituto Pirenaico de Ecología—CSIC, Avda. Montañana 1005,
50059 Saragossa, Spain
© 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_14
169