to digital products. BODC maintains the GDA-CE and
continuously updates the global bathymetric grid
(https://www.bodc.ac.uk/data/online_delivery/gebco/
gebco_08_grid/).
3. The IHO has embedded GEBCO in the Inter-Regional
Coordination Program. IHO operates and maintains the
GEBCO Gazetteer of Undersea Feature Names and
publishes on behalf of GEBCO bathymetric publications (Ward, 2010) (http://www.iho.int/srv1/).
4. The University of New Hampshire (UNH) conducts
since 2004 in cooperation with GEBCO the “Nippon
Foundation/GEBCO Postgraduate Certificate in Ocean
Bathymetry Training Program” in order to train academics and hydrographers in ocean mapping (http://
ccom.unh.edu/gebco-students-scholars).
Bibliography
Carpine-Lancre, J., et al., 2003. The History of GEBCO 1903–2003.
Lemmer: GITC bv. ISBN 90-806205-4-8.
Ward, R., 2010. General bathymetric chart of the oceans. Hydro
International, 14(5), 45.
Cross-references
General Bathymetric Chart of the Oceans (GEBCO)
Plate Tectonics
GENERAL OCEAN CIRCULATION - ITS SIGNALS IN
THE SEDIMENTS
Hermann Kudrass
MARUM-Center for Marine Environmental Sciences,
University of Bremen, Bremen, Germany
Definition
The worldwide pattern of ocean circulation is governed by
a balance of surface and deep and bottom currents.
Ocean circulation
Ocean circulation is driven by the higher solar radiation at
low latitudes compared to the radiation at high latitudes
and the resulting differences in evaporation. The transport
routes and the velocity of currents are determined by the
Earth’s rotation, the atmospheric circulation, and the configuration of the ocean basins. The meridional heat and
salt transfer by warm tropical and subtropical water is
mostly confined to the western side of the ocean
basins and cold-water flow towards the equator along the
eastern side. A considerable part of the poleward
warm-water flow at the surface is balanced by cold
bottom water flowing towards the equator. At a global
scale, this flow pattern is simplified by the salt conveyor
belt or the thermohaline circulation (Figure 1). On geological time scales, this circulation pattern considerably varied, mainly driven by changes of solar insolation and
plate tectonic movements. The reconstruction of these
changes, the main subject of paleoceanography, entirely
relies on the record of ocean currents preserved in marine
sediments.
Surface currents and bottom currents produce different
sedimentary records. Surface currents are mainly recorded
in the underlying sediments by contrasting regional distributions of specific proxy parameters. In contrast, the signals of the subsurface currents, which flow in direct
contact with the seafloor, can be more directly deduced
from the sediment properties and composition.
Surface currents
A great variety of proxy parameters in the sedimentary
archives is used to decode the extent and intensity of surface currents. First of all, the remains of surface-dwelling
organisms of coccolithophorids, diatoms, radiolaria,
planktonic foraminifera, pteropods, and dinoflagellates
are good indicators for characterizing temperature, salinity, and fertility of the surface water. Geochemical composition of calcareous and siliceous tests (e.g., Mg/Ca, P, Ba,
Cd) and their isotopic compositions (C, O, Si, Nd), as well
as organic carbon and biomarkers (e.g., alkenones) and
their isotopic compositions (C, N, H), are successfully
used to identify origin and transport paths of the surface
waters. In case that the surface currents are in contact with
the seafloor, benthic communities also contain a record of
changes, like corals for the ENSO signals (Cobb et al.,
2003) or benthic foraminifera for the Indonesian
Throughflow (Holbourn et al., 2011). In special cases,
the spread of debris from drifting icebergs can define
ocean-wide transport paths. A successful strategy to decipher changes in global oceanic circulation is the drilling of
sediment core transects, e.g., by the International Ocean
Drilling Program (IODP). The transects usually compromise drill holes along the postulated transport path. In special cases, the opening or closing of gateways by plate
tectonic movements was investigated (e.g., Tasmanian
Gateway for the Circum-Antarctic Current (Exon et al.,
2004), mid-American uplift for the initiation of the Gulf
Current (Pisias et al., 1995; Haug and Tiedemann, 1998),
or the latitudinal shifts and intensity changes of the Equatorial Current in the Pacific Ocean (Lyle and Wilson,
2006)).
Bottom currents
As for the surface currents, the properties of bottom waters
are documented by benthic biological communities of
mollusks, ostracods, deep-water corals, and epi- and
endobenthic foraminifera, as well as the isotopic and elemental composition of their shells, skeletons, and tests.
Thus, changes in bottom currents can be reconstructed
from fossilized remains of these organisms. In addition,
bottom currents generate a much more direct sedimentary
record than the surface currents, as they directly impact the
sediment. First of all, the fine-scale structure and the composition of the sediments are shaped by the flow, which
generates typically silty laminated sediments in extended
GENERAL OCEAN CIRCULATION - ITS SIGNALS IN THE SEDIMENTS
269
continuously updates the global bathymetric grid
(https://www.bodc.ac.uk/data/online_delivery/gebco/
gebco_08_grid/).
3. The IHO has embedded GEBCO in the Inter-Regional
Coordination Program. IHO operates and maintains the
GEBCO Gazetteer of Undersea Feature Names and
publishes on behalf of GEBCO bathymetric publications (Ward, 2010) (http://www.iho.int/srv1/).
4. The University of New Hampshire (UNH) conducts
since 2004 in cooperation with GEBCO the “Nippon
Foundation/GEBCO Postgraduate Certificate in Ocean
Bathymetry Training Program” in order to train academics and hydrographers in ocean mapping (http://
ccom.unh.edu/gebco-students-scholars).
Bibliography
Carpine-Lancre, J., et al., 2003. The History of GEBCO 1903–2003.
Lemmer: GITC bv. ISBN 90-806205-4-8.
Ward, R., 2010. General bathymetric chart of the oceans. Hydro
International, 14(5), 45.
Cross-references
General Bathymetric Chart of the Oceans (GEBCO)
Plate Tectonics
GENERAL OCEAN CIRCULATION - ITS SIGNALS IN
THE SEDIMENTS
Hermann Kudrass
MARUM-Center for Marine Environmental Sciences,
University of Bremen, Bremen, Germany
Definition
The worldwide pattern of ocean circulation is governed by
a balance of surface and deep and bottom currents.
Ocean circulation
Ocean circulation is driven by the higher solar radiation at
low latitudes compared to the radiation at high latitudes
and the resulting differences in evaporation. The transport
routes and the velocity of currents are determined by the
Earth’s rotation, the atmospheric circulation, and the configuration of the ocean basins. The meridional heat and
salt transfer by warm tropical and subtropical water is
mostly confined to the western side of the ocean
basins and cold-water flow towards the equator along the
eastern side. A considerable part of the poleward
warm-water flow at the surface is balanced by cold
bottom water flowing towards the equator. At a global
scale, this flow pattern is simplified by the salt conveyor
belt or the thermohaline circulation (Figure 1). On geological time scales, this circulation pattern considerably varied, mainly driven by changes of solar insolation and
plate tectonic movements. The reconstruction of these
changes, the main subject of paleoceanography, entirely
relies on the record of ocean currents preserved in marine
sediments.
Surface currents and bottom currents produce different
sedimentary records. Surface currents are mainly recorded
in the underlying sediments by contrasting regional distributions of specific proxy parameters. In contrast, the signals of the subsurface currents, which flow in direct
contact with the seafloor, can be more directly deduced
from the sediment properties and composition.
Surface currents
A great variety of proxy parameters in the sedimentary
archives is used to decode the extent and intensity of surface currents. First of all, the remains of surface-dwelling
organisms of coccolithophorids, diatoms, radiolaria,
planktonic foraminifera, pteropods, and dinoflagellates
are good indicators for characterizing temperature, salinity, and fertility of the surface water. Geochemical composition of calcareous and siliceous tests (e.g., Mg/Ca, P, Ba,
Cd) and their isotopic compositions (C, O, Si, Nd), as well
as organic carbon and biomarkers (e.g., alkenones) and
their isotopic compositions (C, N, H), are successfully
used to identify origin and transport paths of the surface
waters. In case that the surface currents are in contact with
the seafloor, benthic communities also contain a record of
changes, like corals for the ENSO signals (Cobb et al.,
2003) or benthic foraminifera for the Indonesian
Throughflow (Holbourn et al., 2011). In special cases,
the spread of debris from drifting icebergs can define
ocean-wide transport paths. A successful strategy to decipher changes in global oceanic circulation is the drilling of
sediment core transects, e.g., by the International Ocean
Drilling Program (IODP). The transects usually compromise drill holes along the postulated transport path. In special cases, the opening or closing of gateways by plate
tectonic movements was investigated (e.g., Tasmanian
Gateway for the Circum-Antarctic Current (Exon et al.,
2004), mid-American uplift for the initiation of the Gulf
Current (Pisias et al., 1995; Haug and Tiedemann, 1998),
or the latitudinal shifts and intensity changes of the Equatorial Current in the Pacific Ocean (Lyle and Wilson,
2006)).
Bottom currents
As for the surface currents, the properties of bottom waters
are documented by benthic biological communities of
mollusks, ostracods, deep-water corals, and epi- and
endobenthic foraminifera, as well as the isotopic and elemental composition of their shells, skeletons, and tests.
Thus, changes in bottom currents can be reconstructed
from fossilized remains of these organisms. In addition,
bottom currents generate a much more direct sedimentary
record than the surface currents, as they directly impact the
sediment. First of all, the fine-scale structure and the composition of the sediments are shaped by the flow, which
generates typically silty laminated sediments in extended
GENERAL OCEAN CIRCULATION - ITS SIGNALS IN THE SEDIMENTS
269