40
Weferetal.
temperature distributions in several regions (depending on the method for temperature reconstruction), for example 2-3 °C colder temperatures in
the western equatorial Atlantic rw olff et al. 1998).
The influence of orbital parameters on the waxing
and waning of global ice mass during the
Pleistocene has been firmly established.
Climate reconstruction is not limited to the Quaternary; it includes the warm climate of the Cretaceous, the Cretaceous/Tertiary boundary, and climate change throughout the Tertiary, especially in
connection with the opening and closing of gateways, mountain building and formation of ice caps
in Antarctica and in the Northern Hemisphere.
Progress in the understanding of past oceanic
climates and oflong-term climate change requires
the continuous improvement of existing proxies and
the development of new proxies. Many proxies are
already well established: e.g. microfossil assemblages for temperature reconstructions, and oxygen isotopes as a recorder of ice volume changes.
Basically, physicochemical quantities such as temperature or nutrient concentration are easier to determine than biological quantities that, even
regionally, can only be indirectly inferred using simplifying assumptions. There is, therefore, a great
demand for research in the field of organic
geochemistry, where the study of biomarkers is
becoming increasingly important for characterizing
the paleoenvironment (e.g. for paleo-PC0 2 reconstructions).
Several proxies have been newly developed in
recent years that still require further calibration and
testing with time series and time slices. Among
these are:
-li13C of individual organic components for the
reconstruction of [C0 2 (aq) and PC0 2 in surface
waters,
-Ba/Ca ratios in foraminifera for alkalinity reconstructions,
-boron isotopes in foraminiferal carbonate for
paleo-pH determinations,and
-organic components and isotopes for differentiating between marine and terrestrial organic material.
Water samples, plankton nets, and sediment trap
investigations, in conjunction with laboratory experiments, are of great importance in making these
calibrations. It should be noted that, quite generally, a single proxy is not sufficient to document a
specific parameter. The transformation from any
proxy to a desired parameter contains a certain
amount of error, so a number of proxies should always be used to describe a single parameter (multiproxy approach). One example is surface water
temperature determination using planktic
foraminifera, stable oxygen isotopes, MglCa ratios,
and alkenones.
A critical prerequisite for the optimal reconstruction of past environmental conditions is a good
temporal framework. For older time periods,
biostratigraphy using microfossil markers is the
backbone for dating sediments. Stratigraphic range
charts have to be continuously updated. Astronomical tuning is a relatively new tool that looks promising for high-resolution reconstructions of
biostratigraphically dated intervals in Tertiary deposits. Non-destructive measurements of sediment
characteristics such as magnetic susceptibility,
density, radioactivity, sediment color, and elemental composition have a great future for high-resolution time series (e.g. see Rack 1998). Data available under www.pangaea.delProjects/SFB261.
References
Abelmann A, Gersonde R (1992) Biosiliceous particle
flux in the Southern Ocean. Mar Chern 35: 503-536
Abrantes FF (1991) Variability of upwelling offNW
Africa during the latest Quaternary: Diatom evidence. Paleoceanography 6: 431-460
Altabet M (1996) Nitrogen and Carbon isotopic tracers
of the source and transformation of particles in the
deep sea. In: Ittekkot V, Schaefer P, Honjo S, Depetris
PJ (eds) Particle Flux in the Ocean. SCOPE Report, J
Wiley & Sons,pp 155-184
Altabet M, Curry WB (1989) Testing models of past
ocean chemistry using foraminifera 15N/14N.
Paleoceanography 3: 107-119
Altabet MA, Francois R (1994) Sedimentary nitrogen
isotopic ratio as a recorder for surface ocean nitrate
utilization. Global Biogeochem Cycles 8: 103-116
Altabet M, Deuser WG, Honjo S, Stienen C (1991) Seasonal and depth-related changes in the source of
sinking particles in the north Atlantic. Nature 354:
136-139
Weferetal.
temperature distributions in several regions (depending on the method for temperature reconstruction), for example 2-3 °C colder temperatures in
the western equatorial Atlantic rw olff et al. 1998).
The influence of orbital parameters on the waxing
and waning of global ice mass during the
Pleistocene has been firmly established.
Climate reconstruction is not limited to the Quaternary; it includes the warm climate of the Cretaceous, the Cretaceous/Tertiary boundary, and climate change throughout the Tertiary, especially in
connection with the opening and closing of gateways, mountain building and formation of ice caps
in Antarctica and in the Northern Hemisphere.
Progress in the understanding of past oceanic
climates and oflong-term climate change requires
the continuous improvement of existing proxies and
the development of new proxies. Many proxies are
already well established: e.g. microfossil assemblages for temperature reconstructions, and oxygen isotopes as a recorder of ice volume changes.
Basically, physicochemical quantities such as temperature or nutrient concentration are easier to determine than biological quantities that, even
regionally, can only be indirectly inferred using simplifying assumptions. There is, therefore, a great
demand for research in the field of organic
geochemistry, where the study of biomarkers is
becoming increasingly important for characterizing
the paleoenvironment (e.g. for paleo-PC0 2 reconstructions).
Several proxies have been newly developed in
recent years that still require further calibration and
testing with time series and time slices. Among
these are:
-li13C of individual organic components for the
reconstruction of [C0 2 (aq) and PC0 2 in surface
waters,
-Ba/Ca ratios in foraminifera for alkalinity reconstructions,
-boron isotopes in foraminiferal carbonate for
paleo-pH determinations,and
-organic components and isotopes for differentiating between marine and terrestrial organic material.
Water samples, plankton nets, and sediment trap
investigations, in conjunction with laboratory experiments, are of great importance in making these
calibrations. It should be noted that, quite generally, a single proxy is not sufficient to document a
specific parameter. The transformation from any
proxy to a desired parameter contains a certain
amount of error, so a number of proxies should always be used to describe a single parameter (multiproxy approach). One example is surface water
temperature determination using planktic
foraminifera, stable oxygen isotopes, MglCa ratios,
and alkenones.
A critical prerequisite for the optimal reconstruction of past environmental conditions is a good
temporal framework. For older time periods,
biostratigraphy using microfossil markers is the
backbone for dating sediments. Stratigraphic range
charts have to be continuously updated. Astronomical tuning is a relatively new tool that looks promising for high-resolution reconstructions of
biostratigraphically dated intervals in Tertiary deposits. Non-destructive measurements of sediment
characteristics such as magnetic susceptibility,
density, radioactivity, sediment color, and elemental composition have a great future for high-resolution time series (e.g. see Rack 1998). Data available under www.pangaea.delProjects/SFB261.
References
Abelmann A, Gersonde R (1992) Biosiliceous particle
flux in the Southern Ocean. Mar Chern 35: 503-536
Abrantes FF (1991) Variability of upwelling offNW
Africa during the latest Quaternary: Diatom evidence. Paleoceanography 6: 431-460
Altabet M (1996) Nitrogen and Carbon isotopic tracers
of the source and transformation of particles in the
deep sea. In: Ittekkot V, Schaefer P, Honjo S, Depetris
PJ (eds) Particle Flux in the Ocean. SCOPE Report, J
Wiley & Sons,pp 155-184
Altabet M, Curry WB (1989) Testing models of past
ocean chemistry using foraminifera 15N/14N.
Paleoceanography 3: 107-119
Altabet MA, Francois R (1994) Sedimentary nitrogen
isotopic ratio as a recorder for surface ocean nitrate
utilization. Global Biogeochem Cycles 8: 103-116
Altabet M, Deuser WG, Honjo S, Stienen C (1991) Seasonal and depth-related changes in the source of
sinking particles in the north Atlantic. Nature 354:
136-139