marine geosciences providing important input data for
modeling the evolution of past climates.
The further development of absolute dating techniques
by Urey and others, the approaches of Emiliani (cf. 1992,
Shackleton and many others learned to use the variability
of the fractionation of heavy and light O-isotopes between
glacials and interglacials to determine sea surface and bottom temperatures. They also linked them to the transfer
processes of large amounts of freshwater from the oceans
through evaporation/precipitation to and from the large
glacial ice sheets, resulting in isochronous isostatic sealevel changes on the order of 120–140 m. It was soon recognized that ocean sediment cores represented one of the
best global archives of past climatic changes. CLIMAP,
a large US-led paleoclimate project soon, used this fact
to establish the global distribution of climatically important parameters, and they succeeded to publish a map of
quantitative ocean surface temperature reconstructions
for the time slice of the last glacial maximum (CLIMAP,
1976). At the same time they detected in the time series
deduced from some Southern Ocean sediment cores a systematic and regular variability of a number of paleoceanographic parameters (Hays et al., 1976) which could be
linked to the Milankovitch frequencies (for eccentricity,
obliquity, and precession) which had been postulated in
close collaboration with Milankovitch to regulate the regular Quaternary glacial-interglacial alterations already by
Köppen and Wegener (1924). Imbrie and Imbrie (1979)
thought – at that time – they had solved the mystery of
the ice ages.
However, during recent decades, new discoveries in
marine geology have provided a deeper insight into the
last Glacial period. In particular, the dated and regionalized ice-rafted debris (IRD) in sediments of North Atlantic
and the Arctic Sea as well as correlation with the oxygen
isotope signature effected in Greenland ice cores have
led to the event stratigraphy based on climate cycles (the
Dansgaard-Oeschger cycles). These cycles are determined
by alteration between warm (Greenland interstadials, GI)
and cold (Greenland stadials, GS) events and describe
the pacing of climate variation during the last
100,000 years (see Björck et al. 1998 and the
“Dansgaard-Oeschger Cycles,” “Encyclopedia of
Paleoclimate and Ancient Environments”). Some of the
cold events are called the “Heinrich Events” after the
marine geologist who mapped the extension of sea iceaffected sediments which can be seen distributed basinwide in North Atlantic (see Heinrich 1988, and “Ice
Rafted Debris (IRD),” this volume). For the late Pleistocene to Holocene, Bond et al. (1997) discovered cold
events (the “Bond Events”), based mainly on petrologic
proxies of drift ice sediments in North Atlantic. Dating
of the sediments led to identification of a climate cycle
for the time span between the Marine Isotopic Stage 3
(MIS 3) and the Little Ice Age (the “Bond Cycle”) with a
pacing of % 1,470 Æ 500 years (Bond et al. 1997).
Although the driving mechanisms of this cyclicity is still
intensely debated, identification of climatic cycles below
the orbitally forced Milankovitch pacing has opened a
new wide field for cooperation between geologists, oceanographers, climatologists, and modelers.
In the meantime, numerous paleoclimatic and oceanographic proxies have been developed (Fischer and Wefer,
1999), which allow to reconstruct quantitatively a vast
array of ocean and climate properties. Some of them can
be applied to the longtime series which are available
through the acquisition of the cores obtained through the
deep-sea drilling activities, in some areas actually
reaching into Jurassic sediments.
Paleoceanography has developed into an important
branch of the marine geosciences and by providing quantitative boundary conditions to climate modelers is
reaching an ever-increasing importance for establishing
possible scenarios for future climates.
Seafloor spreading and plate tectonics:
the new paradigm
It was the work of seagoing geophysicists which eventually led to the acceptance of plate tectonics. The
pioneering efforts of E. C. Bullard on earth magnetism,
heat flow, and seismic surveying and of M. Ewing and
his associates in all aspects of marine geophysics were of
central importance in this development (although
M. Ewing did not himself advocate seafloor spreading).
These scientists also were instrumental in elucidating the
structure of continental margins (Ewing et al., 1950;
Bullard and Gaskell, 1941).
The turning point in the scientific revolution which
shook the earth sciences and which culminated in plate
tectonics is generally taken to be the seminal paper of Hess
(1962). Hess started his distinguished career working with
the Dutch geophysicist, F. A. Vening-Meinesz, on the
gravity anomalies of deep-sea trenches. These investigations resulted in the hypothesis that trenches may be surface expressions of the downgoing limbs of mantle
convection cells. As a naval officer, Hess discovered and
mapped a great number of flat-topped seamounts, whose
morphology suggested widespread sinking of the seafloor.
Stimulated by subsequent discoveries on the mid-ocean
ridge (rift morphology, heat flow, and others), he proposed
his idea of the seafloor being generated at the center of the
mid-ocean ridge, moving away and downward as it ages,
finally to disappear into trenches. The term “seafloor
spreading” was introduced by Dietz (in 1961, cf. Vine
and Matthews, 1963; Le Pichon, 1968) for this postulated
phenomenon. Seafloor spreading and its offspring plate
tectonics have since become the basic framework within
which the data of marine geology are interpreted.
As previously mentioned Russian marine geoscientists
were slow to follow because their country was dominated
by “fixists,” and the new ideas about “seafloor spreading”
and “plate tectonics” were only slowly accepted. It took
MARINE GEOSCIENCES: A SHORT, ECCLECTIC AND WEIGHTED HISTORIC ACCOUNT
441
modeling the evolution of past climates.
The further development of absolute dating techniques
by Urey and others, the approaches of Emiliani (cf. 1992,
Shackleton and many others learned to use the variability
of the fractionation of heavy and light O-isotopes between
glacials and interglacials to determine sea surface and bottom temperatures. They also linked them to the transfer
processes of large amounts of freshwater from the oceans
through evaporation/precipitation to and from the large
glacial ice sheets, resulting in isochronous isostatic sealevel changes on the order of 120–140 m. It was soon recognized that ocean sediment cores represented one of the
best global archives of past climatic changes. CLIMAP,
a large US-led paleoclimate project soon, used this fact
to establish the global distribution of climatically important parameters, and they succeeded to publish a map of
quantitative ocean surface temperature reconstructions
for the time slice of the last glacial maximum (CLIMAP,
1976). At the same time they detected in the time series
deduced from some Southern Ocean sediment cores a systematic and regular variability of a number of paleoceanographic parameters (Hays et al., 1976) which could be
linked to the Milankovitch frequencies (for eccentricity,
obliquity, and precession) which had been postulated in
close collaboration with Milankovitch to regulate the regular Quaternary glacial-interglacial alterations already by
Köppen and Wegener (1924). Imbrie and Imbrie (1979)
thought – at that time – they had solved the mystery of
the ice ages.
However, during recent decades, new discoveries in
marine geology have provided a deeper insight into the
last Glacial period. In particular, the dated and regionalized ice-rafted debris (IRD) in sediments of North Atlantic
and the Arctic Sea as well as correlation with the oxygen
isotope signature effected in Greenland ice cores have
led to the event stratigraphy based on climate cycles (the
Dansgaard-Oeschger cycles). These cycles are determined
by alteration between warm (Greenland interstadials, GI)
and cold (Greenland stadials, GS) events and describe
the pacing of climate variation during the last
100,000 years (see Björck et al. 1998 and the
“Dansgaard-Oeschger Cycles,” “Encyclopedia of
Paleoclimate and Ancient Environments”). Some of the
cold events are called the “Heinrich Events” after the
marine geologist who mapped the extension of sea iceaffected sediments which can be seen distributed basinwide in North Atlantic (see Heinrich 1988, and “Ice
Rafted Debris (IRD),” this volume). For the late Pleistocene to Holocene, Bond et al. (1997) discovered cold
events (the “Bond Events”), based mainly on petrologic
proxies of drift ice sediments in North Atlantic. Dating
of the sediments led to identification of a climate cycle
for the time span between the Marine Isotopic Stage 3
(MIS 3) and the Little Ice Age (the “Bond Cycle”) with a
pacing of % 1,470 Æ 500 years (Bond et al. 1997).
Although the driving mechanisms of this cyclicity is still
intensely debated, identification of climatic cycles below
the orbitally forced Milankovitch pacing has opened a
new wide field for cooperation between geologists, oceanographers, climatologists, and modelers.
In the meantime, numerous paleoclimatic and oceanographic proxies have been developed (Fischer and Wefer,
1999), which allow to reconstruct quantitatively a vast
array of ocean and climate properties. Some of them can
be applied to the longtime series which are available
through the acquisition of the cores obtained through the
deep-sea drilling activities, in some areas actually
reaching into Jurassic sediments.
Paleoceanography has developed into an important
branch of the marine geosciences and by providing quantitative boundary conditions to climate modelers is
reaching an ever-increasing importance for establishing
possible scenarios for future climates.
Seafloor spreading and plate tectonics:
the new paradigm
It was the work of seagoing geophysicists which eventually led to the acceptance of plate tectonics. The
pioneering efforts of E. C. Bullard on earth magnetism,
heat flow, and seismic surveying and of M. Ewing and
his associates in all aspects of marine geophysics were of
central importance in this development (although
M. Ewing did not himself advocate seafloor spreading).
These scientists also were instrumental in elucidating the
structure of continental margins (Ewing et al., 1950;
Bullard and Gaskell, 1941).
The turning point in the scientific revolution which
shook the earth sciences and which culminated in plate
tectonics is generally taken to be the seminal paper of Hess
(1962). Hess started his distinguished career working with
the Dutch geophysicist, F. A. Vening-Meinesz, on the
gravity anomalies of deep-sea trenches. These investigations resulted in the hypothesis that trenches may be surface expressions of the downgoing limbs of mantle
convection cells. As a naval officer, Hess discovered and
mapped a great number of flat-topped seamounts, whose
morphology suggested widespread sinking of the seafloor.
Stimulated by subsequent discoveries on the mid-ocean
ridge (rift morphology, heat flow, and others), he proposed
his idea of the seafloor being generated at the center of the
mid-ocean ridge, moving away and downward as it ages,
finally to disappear into trenches. The term “seafloor
spreading” was introduced by Dietz (in 1961, cf. Vine
and Matthews, 1963; Le Pichon, 1968) for this postulated
phenomenon. Seafloor spreading and its offspring plate
tectonics have since become the basic framework within
which the data of marine geology are interpreted.
As previously mentioned Russian marine geoscientists
were slow to follow because their country was dominated
by “fixists,” and the new ideas about “seafloor spreading”
and “plate tectonics” were only slowly accepted. It took
MARINE GEOSCIENCES: A SHORT, ECCLECTIC AND WEIGHTED HISTORIC ACCOUNT
441