248
the South Atlantic and fed the high diatom production around Antarctica (the "opaline silica ring").
Increased diatom production in high latitudes was
also observed in the northem Pacific. Ice-rafted material could trave1 with surface currents over long
distances and record the repeated growth and waning
of large ice sheets in deep-sea sediments.
5.6.8 Summary (Paleoceanography)
Chapter 5 Oceanic Sediments
This summary only deals with some important points of
this cooling history. The evidence or "proxies" for this evolution is more complicate and includes some methods not
mentioned here (see also Abreu and Anderson 1998; Wilson et al. 1998).
Other specific topics in paleoceanography, such as the
evolution and nature of the pre-Cretaceous ocean basins,
the evolution of sediment-forming micro-organisms, the
migration of faunal and floral communities in relation to
the changing configuration of the ocean basins, or the history of sea water chemistry cannot be discussed here.
Paleogeography, volcanism, circulation and greenhouse gases of the atmosphere and the ocean are closely
linked. Their interplay has largely determined the past global climate and, in particular, the biogenic marine sedimentation. The nature and areal distribution of marine sediments (e.g. carbonates, biosiliceous
sediments, black shales) serve, among other methods, as "proxies" for the reconstruction of the environmental conditions of former ocean basins. The following processes playamajor role:
- Decreasing reflection of solar radiation (albedo)
due to transgressions, enlarged areas of vegetation, and retreat of glaciers, furthers global
warming.
- Extraction of atmospheric CO 2 by silicate weathering, organic carbon burial (the biological
pump), and net dissolution of marine carbonate
lead to global cooling. The latter two processes,
including recycling of nutrients and oxygenation
of deep water, are largely controlled by
thermohaline ocean circulation. This in turn is
influenced by ocean basin topography and the
opening or closure of marine gateways. It is
strengthened by high meridional temperature
gradients and weakened by warm and higher
saline deep water (as in the Cretaceous ocean).
- All of these (and some more) processes form a
complex feedback system in which rninor
changes of single factors can be amplified or
subdued.
- It appears that the post-Cretaceous cooling history and the Neogene sedimentary processes of
the large ocean basins are now fairly understood.
the South Atlantic and fed the high diatom production around Antarctica (the "opaline silica ring").
Increased diatom production in high latitudes was
also observed in the northem Pacific. Ice-rafted material could trave1 with surface currents over long
distances and record the repeated growth and waning
of large ice sheets in deep-sea sediments.
5.6.8 Summary (Paleoceanography)
Chapter 5 Oceanic Sediments
This summary only deals with some important points of
this cooling history. The evidence or "proxies" for this evolution is more complicate and includes some methods not
mentioned here (see also Abreu and Anderson 1998; Wilson et al. 1998).
Other specific topics in paleoceanography, such as the
evolution and nature of the pre-Cretaceous ocean basins,
the evolution of sediment-forming micro-organisms, the
migration of faunal and floral communities in relation to
the changing configuration of the ocean basins, or the history of sea water chemistry cannot be discussed here.
Paleogeography, volcanism, circulation and greenhouse gases of the atmosphere and the ocean are closely
linked. Their interplay has largely determined the past global climate and, in particular, the biogenic marine sedimentation. The nature and areal distribution of marine sediments (e.g. carbonates, biosiliceous
sediments, black shales) serve, among other methods, as "proxies" for the reconstruction of the environmental conditions of former ocean basins. The following processes playamajor role:
- Decreasing reflection of solar radiation (albedo)
due to transgressions, enlarged areas of vegetation, and retreat of glaciers, furthers global
warming.
- Extraction of atmospheric CO 2 by silicate weathering, organic carbon burial (the biological
pump), and net dissolution of marine carbonate
lead to global cooling. The latter two processes,
including recycling of nutrients and oxygenation
of deep water, are largely controlled by
thermohaline ocean circulation. This in turn is
influenced by ocean basin topography and the
opening or closure of marine gateways. It is
strengthened by high meridional temperature
gradients and weakened by warm and higher
saline deep water (as in the Cretaceous ocean).
- All of these (and some more) processes form a
complex feedback system in which rninor
changes of single factors can be amplified or
subdued.
- It appears that the post-Cretaceous cooling history and the Neogene sedimentary processes of
the large ocean basins are now fairly understood.