effects of the isotope fractionation were mainly caused by
the evaporation of large quantities of water from the ocean
to be bound in the glacial ice sheets during Glacials, both
on the northern and the southern hemisphere, respectively
released during Interglacials.
Paleoceanographic proxies (or proxy variables): There
are numerous proxies which have been developed over the
past decades which allow describing paleoceanographic
properties of past oceans (Fischer and Wefer, 1999).
Beside biotic proxies such as pelagic microfossils there
are numerous geochemical and oganochemical tools to
address variations of the surface water and bottom properties and circulation (including temperature and salinity)
and water mass stratification. Biogenic Barium can
be used to describe paleoproductivity and nutrient distributions. A variety of radiogenic isotopes can be used
as tracers for bioproductivity and particle fluxes in
the oceans. The carbon isotope ratios of alkenones
help to assess past carbon dioxide distributions
(Paleoceanographic Proxies).
Grain size and current strength: McCave et al. (1995)
used sophisticated grain size analyses of relatively finegrained terrigenous sediments, in their attempts to reconstruct the vigor of bottom water currents in the North
Atlantic during the transition from the Last Glacial Maximum (LGM) to the Holocene. They used well-dated sediment cores from the Rockall area and were able to prove
the stratification and strength of the bottom currents during a time of an intense reorganization of the North Atlantic current systems. This is but one example of numerous
in the world ocean. Similar attempts have been made to
describe the flow of the Antarctic Bottom Water in the
Southern Ocean.
Global Conveyor Belt: Ocean surface waters are warm
in the tropics but cold close to the poles. But it was known
since the Russian explorer Krusenstern’s circumglobal
expedition almost 200 years ago that the deep oceans were
cold all over. With the first systematic hydrographic investigations such as carried out during the German “Meteor”
expedition to the South Atlantic Ocean (Wüst, 1936) it
was recognized that cold waters which had gotten their
most important hydrologic properties in the polar regions
filled many deep-sea basins. They were dense enough to
sink as part of the thermohaline circulation into the oceanic deep-sea basins where their flow was controlled by
the morphology of the gateways. Minor differences in
their densities controlled the mode of their layering in
the Atlantic Ocean with water of Arctic in many areas
below those of Antarctic origin. Broecker (1991), after
having determined by means of radiocarbon dating and
thus the last time when these waters were able to exchange
carbon dioxide with the atmosphere, established the
young “ages” of bottom waters in the deep Atlantic Ocean,
contrasting the old ones in the deep North Pacific Ocean.
Based on this pattern and combining it with the large-scale
circulation system of ocean surface waters he coined the
term “great ocean conveyor belt.” How this ocean circulation system has been changing going back in time has
been subject of controversial debates ever since, because
there is no question that ocean deep-water masses were
much warmer during the earliest than during the late
Cenozoic (Zachos et al., 1993).
Atmospheric circulation: The atmospheric circulation
and its past variations leave many traces in deep-sea sediments. Dust plumes originating from desert systems like
the Sahara in North Africa are exported across the African
coast. They document through increased accumulation
rates (Thiede et al., 1982) and grain sizes (Sarnthein and
Koopmann, 1980) during glacial intervals an intensification of the glacial atmospheric circulation. Similar messages can be deduced from the dust records in ice cores
(Svensson et al., 2000) or South Pacific dust records
(Thiede, 1979). It can be concluded that the glacial atmospheric circulation not only changed its patterns but also
increased in intensity due to the steeper temperature gradients between low and high latitudes. Conclusions about
former atmospheric circulation patterns can also be
reached by looking at the distributions of pollen, spores,
and other biotic remains of terrestrial origin preserved in
deep-sea sediments as well as the distribution of organic
matter of terrestrial origin (Fischer and Wefer, 1999).
Time slices versus time series: The progress in dating
techniques of pelagic sediments was a prerequisite for
establishing reconstructions of the paleoceanographic
properties of certain regions both in terms of a welldefined time slice as well as time series. One of the best
examples for the former is the reconstruction of the surface properties of planet Earth during the Last Glacial
Maximum produced by CLIMAP (CLIMAP Project
Members, 1976). The first time series which allowed
proving Milankovitch frequency controlled time series
from the ocean was published by Hays et al. (1976), but
since then numerous time series of paleoceanographic
data sets have been documented in the results of the
deep-sea drilling projects.
Milankovitch Frequencies: When Köppen and Wegener (1924) published their monograph “The Climate of
the Geological Past,” the time scales of the late Cenozoic
alterations between Glacials and Interglacials were only
vaguely known. However, they had established a close
cooperation with Milutin Milankovitch. They were convinced that the geometry of the Earth´s orbit around the
sun with its regular changes of eccentricity, obliquity,
and precession are controlling the insolation (amount of
incoming solar radiation) and hence are important climate
boundary
conditions.
Milankovitch
published
(Milankovitch, 1941) the detailed data of the
Milankovitch frequencies only decades later. But it was
one of the major successes of the CLIMAP project
(Hays et al., 1976) that it found two sediment cores from
the southernmost Indian Ocean which could be dated precisely enough and which reflected the paleoceanographic
responses to the Late Quaternary glacial-interglacial
changes. Thus Köppen and Wegener`s (1924) claim could
be substantiated by well-dated time series derived from
the very best global climate archive. In the meantime the
630
PALEOCEANOGRAPHY
the evaporation of large quantities of water from the ocean
to be bound in the glacial ice sheets during Glacials, both
on the northern and the southern hemisphere, respectively
released during Interglacials.
Paleoceanographic proxies (or proxy variables): There
are numerous proxies which have been developed over the
past decades which allow describing paleoceanographic
properties of past oceans (Fischer and Wefer, 1999).
Beside biotic proxies such as pelagic microfossils there
are numerous geochemical and oganochemical tools to
address variations of the surface water and bottom properties and circulation (including temperature and salinity)
and water mass stratification. Biogenic Barium can
be used to describe paleoproductivity and nutrient distributions. A variety of radiogenic isotopes can be used
as tracers for bioproductivity and particle fluxes in
the oceans. The carbon isotope ratios of alkenones
help to assess past carbon dioxide distributions
(Paleoceanographic Proxies).
Grain size and current strength: McCave et al. (1995)
used sophisticated grain size analyses of relatively finegrained terrigenous sediments, in their attempts to reconstruct the vigor of bottom water currents in the North
Atlantic during the transition from the Last Glacial Maximum (LGM) to the Holocene. They used well-dated sediment cores from the Rockall area and were able to prove
the stratification and strength of the bottom currents during a time of an intense reorganization of the North Atlantic current systems. This is but one example of numerous
in the world ocean. Similar attempts have been made to
describe the flow of the Antarctic Bottom Water in the
Southern Ocean.
Global Conveyor Belt: Ocean surface waters are warm
in the tropics but cold close to the poles. But it was known
since the Russian explorer Krusenstern’s circumglobal
expedition almost 200 years ago that the deep oceans were
cold all over. With the first systematic hydrographic investigations such as carried out during the German “Meteor”
expedition to the South Atlantic Ocean (Wüst, 1936) it
was recognized that cold waters which had gotten their
most important hydrologic properties in the polar regions
filled many deep-sea basins. They were dense enough to
sink as part of the thermohaline circulation into the oceanic deep-sea basins where their flow was controlled by
the morphology of the gateways. Minor differences in
their densities controlled the mode of their layering in
the Atlantic Ocean with water of Arctic in many areas
below those of Antarctic origin. Broecker (1991), after
having determined by means of radiocarbon dating and
thus the last time when these waters were able to exchange
carbon dioxide with the atmosphere, established the
young “ages” of bottom waters in the deep Atlantic Ocean,
contrasting the old ones in the deep North Pacific Ocean.
Based on this pattern and combining it with the large-scale
circulation system of ocean surface waters he coined the
term “great ocean conveyor belt.” How this ocean circulation system has been changing going back in time has
been subject of controversial debates ever since, because
there is no question that ocean deep-water masses were
much warmer during the earliest than during the late
Cenozoic (Zachos et al., 1993).
Atmospheric circulation: The atmospheric circulation
and its past variations leave many traces in deep-sea sediments. Dust plumes originating from desert systems like
the Sahara in North Africa are exported across the African
coast. They document through increased accumulation
rates (Thiede et al., 1982) and grain sizes (Sarnthein and
Koopmann, 1980) during glacial intervals an intensification of the glacial atmospheric circulation. Similar messages can be deduced from the dust records in ice cores
(Svensson et al., 2000) or South Pacific dust records
(Thiede, 1979). It can be concluded that the glacial atmospheric circulation not only changed its patterns but also
increased in intensity due to the steeper temperature gradients between low and high latitudes. Conclusions about
former atmospheric circulation patterns can also be
reached by looking at the distributions of pollen, spores,
and other biotic remains of terrestrial origin preserved in
deep-sea sediments as well as the distribution of organic
matter of terrestrial origin (Fischer and Wefer, 1999).
Time slices versus time series: The progress in dating
techniques of pelagic sediments was a prerequisite for
establishing reconstructions of the paleoceanographic
properties of certain regions both in terms of a welldefined time slice as well as time series. One of the best
examples for the former is the reconstruction of the surface properties of planet Earth during the Last Glacial
Maximum produced by CLIMAP (CLIMAP Project
Members, 1976). The first time series which allowed
proving Milankovitch frequency controlled time series
from the ocean was published by Hays et al. (1976), but
since then numerous time series of paleoceanographic
data sets have been documented in the results of the
deep-sea drilling projects.
Milankovitch Frequencies: When Köppen and Wegener (1924) published their monograph “The Climate of
the Geological Past,” the time scales of the late Cenozoic
alterations between Glacials and Interglacials were only
vaguely known. However, they had established a close
cooperation with Milutin Milankovitch. They were convinced that the geometry of the Earth´s orbit around the
sun with its regular changes of eccentricity, obliquity,
and precession are controlling the insolation (amount of
incoming solar radiation) and hence are important climate
boundary
conditions.
Milankovitch
published
(Milankovitch, 1941) the detailed data of the
Milankovitch frequencies only decades later. But it was
one of the major successes of the CLIMAP project
(Hays et al., 1976) that it found two sediment cores from
the southernmost Indian Ocean which could be dated precisely enough and which reflected the paleoceanographic
responses to the Late Quaternary glacial-interglacial
changes. Thus Köppen and Wegener`s (1924) claim could
be substantiated by well-dated time series derived from
the very best global climate archive. In the meantime the
630
PALEOCEANOGRAPHY