24
The Cryosphere and Sea Level
Catherine Ritz, Vincent Peyaud, Claire Waelbroeck,
and Florence Colleoni
Introduction
Several times during the history of the Earth extensive ice
sheets covered part of the continents. As a result, a significant proportion of freshwater was stored in solid form, which
caused a drop in sea level.
Because of their impact on other components of the Earth
system (atmosphere, ocean, land), the dynamics of these ice
masses must be taken into account in order to understand the
evolution of the climate over the time scale of the last
glacial-interglacial cycles. This topic can be addressed in
different ways, depending to the various scientific disciplines
and tools. One approach is to characterize these ice sheets
according to the traces they have left behind, whether on
land or in marine records. Marine sediments contain a record
of changes in the overall volume of ice over time through
changes in the oxygen isotopic composition of calcareous
fossils. Due to isotopic fractionation that takes place during
the evaporation of water, the drop in sea level during cold
periods has been accompanied by an enrichment of seawater,
not only in salt, but also in heavy isotopes of water (water
molecules containing the
18 O isotope of oxygen rather than
the most widespread isotope,
16 O. See Chap. 20, Volume 1).
This enrichment leads to variations in the isotopic composition of the calcareous shells of the foraminifera preserved
in the sediments. However, the isotopic composition of
foraminifera also depends on the temperature at which the
calcite was formed, so the benthic signal must be corrected
in order to deduce the variations in sea level.
Another approach is to try to understand the physical
mechanisms governing the formation and evolution of these
ice masses. In both cases, observations of the two large
remaining ice sheets, Antarctica and Greenland are pertinent.
Finally, numeric simulation uses all of the information gathered (mechanisms, data) to develop models to calculate the
evolution of the polar ice caps as they interact with the climate.
These tools (referred to later as ‘ice sheet models’) allow us to
study, for example, the role of the ice sheets in the climate
system, in particular the non-linear effects that can amplify the
forcings caused by variations in the Earth’s orbital parameters.
These models are also indispensable tools to assess the rise of
sea levels in the context of global warming.
What Is an Ice Sheet?
Some definitions of glaciological terms
An ice cap is a mass of freshwater ice which rests on the
ground. A notable difference between an ice cap and a
mountain glacier is that the highest point of an ice cap, usually
centered on a massif, is made of ice and called a dome, while a
glacier flows down from a mountain (or from an ice cap). Ice
caps can be of different sizes such as mountain peaks completely covered in ice in almost all the great mountain ranges of
the world as well as significantly larger ice caps on the Arctic
archipelagos (Fig. 24.1), in Iceland, on the Antarctic Peninsula and on some islands in the Southern Ocean. Finally, when
an ice mass covers the land on a continental scale it is called an
ice sheet. Two large ice sheets, in Greenland and Antarctica,
cover virtually the whole continent on which they lie. North
America and Northern Eurasia were partially covered by such
ice sheets during glacial periods (Fig. 24.1). Although ice caps
and ice sheets are driven by the same processes, the discussion
below focuses on ice sheets that are large enough to significantly modify sea level.
C. Ritz (&) Á V. Peyaud
Institute of Engineering, Univ. Grenoble Alpes, CNRS, IRD,
Grenoble INP, IGE, 38000 Grenoble, France
e-mail: catherine.ritz@univ-grenoble-alpes.fr
C. Waelbroeck
Laboratoire d’Océanographie et du Climat : Expérimentation et
Approches Numériques, LOCEAN/IPSL, Sorbonne UniversitéCNRS-IRD-MNHN, UMR7159, Paris, France
F. Colleoni
OGS (National Institute of Oceanography and Applied
Geophysics), Borgo Grotta Gigante 42/c, Viale Aldo Moro 44,
34010 Sgonico (TS), Italy
© 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_24
301
The Cryosphere and Sea Level
Catherine Ritz, Vincent Peyaud, Claire Waelbroeck,
and Florence Colleoni
Introduction
Several times during the history of the Earth extensive ice
sheets covered part of the continents. As a result, a significant proportion of freshwater was stored in solid form, which
caused a drop in sea level.
Because of their impact on other components of the Earth
system (atmosphere, ocean, land), the dynamics of these ice
masses must be taken into account in order to understand the
evolution of the climate over the time scale of the last
glacial-interglacial cycles. This topic can be addressed in
different ways, depending to the various scientific disciplines
and tools. One approach is to characterize these ice sheets
according to the traces they have left behind, whether on
land or in marine records. Marine sediments contain a record
of changes in the overall volume of ice over time through
changes in the oxygen isotopic composition of calcareous
fossils. Due to isotopic fractionation that takes place during
the evaporation of water, the drop in sea level during cold
periods has been accompanied by an enrichment of seawater,
not only in salt, but also in heavy isotopes of water (water
molecules containing the
18 O isotope of oxygen rather than
the most widespread isotope,
16 O. See Chap. 20, Volume 1).
This enrichment leads to variations in the isotopic composition of the calcareous shells of the foraminifera preserved
in the sediments. However, the isotopic composition of
foraminifera also depends on the temperature at which the
calcite was formed, so the benthic signal must be corrected
in order to deduce the variations in sea level.
Another approach is to try to understand the physical
mechanisms governing the formation and evolution of these
ice masses. In both cases, observations of the two large
remaining ice sheets, Antarctica and Greenland are pertinent.
Finally, numeric simulation uses all of the information gathered (mechanisms, data) to develop models to calculate the
evolution of the polar ice caps as they interact with the climate.
These tools (referred to later as ‘ice sheet models’) allow us to
study, for example, the role of the ice sheets in the climate
system, in particular the non-linear effects that can amplify the
forcings caused by variations in the Earth’s orbital parameters.
These models are also indispensable tools to assess the rise of
sea levels in the context of global warming.
What Is an Ice Sheet?
Some definitions of glaciological terms
An ice cap is a mass of freshwater ice which rests on the
ground. A notable difference between an ice cap and a
mountain glacier is that the highest point of an ice cap, usually
centered on a massif, is made of ice and called a dome, while a
glacier flows down from a mountain (or from an ice cap). Ice
caps can be of different sizes such as mountain peaks completely covered in ice in almost all the great mountain ranges of
the world as well as significantly larger ice caps on the Arctic
archipelagos (Fig. 24.1), in Iceland, on the Antarctic Peninsula and on some islands in the Southern Ocean. Finally, when
an ice mass covers the land on a continental scale it is called an
ice sheet. Two large ice sheets, in Greenland and Antarctica,
cover virtually the whole continent on which they lie. North
America and Northern Eurasia were partially covered by such
ice sheets during glacial periods (Fig. 24.1). Although ice caps
and ice sheets are driven by the same processes, the discussion
below focuses on ice sheets that are large enough to significantly modify sea level.
C. Ritz (&) Á V. Peyaud
Institute of Engineering, Univ. Grenoble Alpes, CNRS, IRD,
Grenoble INP, IGE, 38000 Grenoble, France
e-mail: catherine.ritz@univ-grenoble-alpes.fr
C. Waelbroeck
Laboratoire d’Océanographie et du Climat : Expérimentation et
Approches Numériques, LOCEAN/IPSL, Sorbonne UniversitéCNRS-IRD-MNHN, UMR7159, Paris, France
F. Colleoni
OGS (National Institute of Oceanography and Applied
Geophysics), Borgo Grotta Gigante 42/c, Viale Aldo Moro 44,
34010 Sgonico (TS), Italy
© 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_24
301