15
Air-Interface: d
18 O Records of Past
Meteoric Water Using Benthic Ostracods
from Deep Lakes
Ulrich von Grafenstein and Inga Labuhn
Introduction
Oxygen-isotope records offer an alternative way to quantitatively reconstruct paleoclimate, which, at first view, is
independent of an ecosystem’s reaction to climate change.
The ice core records from high latitude inland ice, where the
former precipitation and its isotopic composition (d
18 O P ) are
preserved in an almost original state, are widely accepted as
valuable sources of paleoclimate information. Worldwide
systematic observation of d
18 O P (Rozanski et al. 1992),
starting in the late sixties, together with the incorporation of
the water isotopes in several generations of general circulation models (Hoffmann et al. 1998; Jouzel et al. 1987) and
models of intermediate complexity have, not only increased
the confidence in d
18 O P as a powerful paleotemperature
indicator in a number of key regions, but have also
demonstrated its importance as a primary hydrometeorological parameter in regions where temperature dependence
is less evident or absent.
In non-polar regions, investigations have been conducted
on lake sediment (carbonate, bulk organic matter, cellulose,
diatoms), speleothems, tree rings and soil carbonate. While
all these terrestrial records respond to changes in the isotopic
composition of past precipitation (d
18 O P ), a number of secondary effects can alter the original atmospheric signal and
thus limit or exclude a quantitative interpretation. Detecting
past changes of d
18 O P therefore not only provides a valuable
paleoclimate proxy, but also largely facilitates the quantification of secondary effects in complex isotopic records. The
problem is to find material, like polar ice, which contains
quantitative information about the isotopic composition of
past precipitation and from which secondary effects can
either be excluded or quantified. Those include the alteration
of the primary signal (d
18 O P ) on its way to through the water
cycle (hydrological effects) and during the formation of
material in which it will be preserved (isotope fractionation
effects).
Lake sediments very often cover reasonably long periods
with relatively high accumulation rates, allowing sampling
resolutions from individual years to decades. Ostracod
valves preserved in those sediments can, with respect to their
dominance and habitat, be considered as the lacustrine
equivalent to benthic foraminifera in marine sediments (De
Deckker 2002). As such, they are ideally suited for the
geochemical characterization of former lake water, including
stable isotope studies (Holmes and Chivas 2002). A major
advantage they have compared to other materials, such as
bulk carbonate or organic matter, is that ostracod valves can
be relatively easily separated, cleaned (Danielopol et al.
2002), and assigned to different species for which biological
and behavioural information is available from the study of
modern materials (Horne et al. 2002). Moreover, the specific
fractionation can be calibrated using the valves of individuals that grew and calcified under known conditions (Chivas
et al. 2002; von Grafenstein et al. 1999a, b; Xia et al. 1997).
The same applies to benthic molluscs belonging to the
family of sphaeriides, which frequently can be found together with ostracods.
The focus of this chapter is on the special situation of
ostracods and molluscs in the profundal sediments of deep
lakes, where seasonal and long-term temperature changes are
almost absent and where the d
18 O of the local water regularly approaches the average of the entire water column due
to the cold season overturn. The fossil valves of these animals can be used to reconstruct precisely the isotopic composition of the lake water (d
18 O L ) and, depending on the
lake’s hydrologic setting, the isotopic composition of former
precipitation (d
18 O P ). The first part of this chapter provides
an overview of published deep-lake oxygen-isotope records.
The following two parts more specifically address the processes implicated in the signal transfer from the atmospheric
U. von Grafenstein (&) Á I. Labuhn
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91190
Gif-sur-Yvette, France
e-mail: Ulrich.von-Grafensstein.fr@lsce.ipsl.fr
© 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_15
179
Air-Interface: d
18 O Records of Past
Meteoric Water Using Benthic Ostracods
from Deep Lakes
Ulrich von Grafenstein and Inga Labuhn
Introduction
Oxygen-isotope records offer an alternative way to quantitatively reconstruct paleoclimate, which, at first view, is
independent of an ecosystem’s reaction to climate change.
The ice core records from high latitude inland ice, where the
former precipitation and its isotopic composition (d
18 O P ) are
preserved in an almost original state, are widely accepted as
valuable sources of paleoclimate information. Worldwide
systematic observation of d
18 O P (Rozanski et al. 1992),
starting in the late sixties, together with the incorporation of
the water isotopes in several generations of general circulation models (Hoffmann et al. 1998; Jouzel et al. 1987) and
models of intermediate complexity have, not only increased
the confidence in d
18 O P as a powerful paleotemperature
indicator in a number of key regions, but have also
demonstrated its importance as a primary hydrometeorological parameter in regions where temperature dependence
is less evident or absent.
In non-polar regions, investigations have been conducted
on lake sediment (carbonate, bulk organic matter, cellulose,
diatoms), speleothems, tree rings and soil carbonate. While
all these terrestrial records respond to changes in the isotopic
composition of past precipitation (d
18 O P ), a number of secondary effects can alter the original atmospheric signal and
thus limit or exclude a quantitative interpretation. Detecting
past changes of d
18 O P therefore not only provides a valuable
paleoclimate proxy, but also largely facilitates the quantification of secondary effects in complex isotopic records. The
problem is to find material, like polar ice, which contains
quantitative information about the isotopic composition of
past precipitation and from which secondary effects can
either be excluded or quantified. Those include the alteration
of the primary signal (d
18 O P ) on its way to through the water
cycle (hydrological effects) and during the formation of
material in which it will be preserved (isotope fractionation
effects).
Lake sediments very often cover reasonably long periods
with relatively high accumulation rates, allowing sampling
resolutions from individual years to decades. Ostracod
valves preserved in those sediments can, with respect to their
dominance and habitat, be considered as the lacustrine
equivalent to benthic foraminifera in marine sediments (De
Deckker 2002). As such, they are ideally suited for the
geochemical characterization of former lake water, including
stable isotope studies (Holmes and Chivas 2002). A major
advantage they have compared to other materials, such as
bulk carbonate or organic matter, is that ostracod valves can
be relatively easily separated, cleaned (Danielopol et al.
2002), and assigned to different species for which biological
and behavioural information is available from the study of
modern materials (Horne et al. 2002). Moreover, the specific
fractionation can be calibrated using the valves of individuals that grew and calcified under known conditions (Chivas
et al. 2002; von Grafenstein et al. 1999a, b; Xia et al. 1997).
The same applies to benthic molluscs belonging to the
family of sphaeriides, which frequently can be found together with ostracods.
The focus of this chapter is on the special situation of
ostracods and molluscs in the profundal sediments of deep
lakes, where seasonal and long-term temperature changes are
almost absent and where the d
18 O of the local water regularly approaches the average of the entire water column due
to the cold season overturn. The fossil valves of these animals can be used to reconstruct precisely the isotopic composition of the lake water (d
18 O L ) and, depending on the
lake’s hydrologic setting, the isotopic composition of former
precipitation (d
18 O P ). The first part of this chapter provides
an overview of published deep-lake oxygen-isotope records.
The following two parts more specifically address the processes implicated in the signal transfer from the atmospheric
U. von Grafenstein (&) Á I. Labuhn
Laboratoire des Sciences du Climat et de l’Environnement,
LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91190
Gif-sur-Yvette, France
e-mail: Ulrich.von-Grafensstein.fr@lsce.ipsl.fr
© 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_15
179