is as fine as 0.1 Ma level and can be further refined by
tuning in to the Earth’s orbital change (Milankovitch
cycles (20–100 kyr)) detectable in sediment cores. Drilling in corals and high-sedimentation-rate sites allows
for even higher temporal resolution. Since the ocean floors
are destroyed by subduction, the oldest core sample is
~170 myrs old (ice cores <~800 kyr) covering ages since
Jurassic. Drilling data contributed in defining the average
temperature change over this time period, mostly warmer
than the present Earth but covering the period without
continental ice (“greenhouse Earth”) and the period with
ice sheets present (“icehouse Earth”).
While the basic geological inferences come from
lithostratigraphy, core specimen also provides information
on past environments from oxygen isotope ratios and
planktonic or benthic microfossils to infer the surface
and bottom temperatures, which in turn infer continental
ice volumes. The balancing depth of the carbonate supply
and its dissolution rates called CCD (calcite compensation
depth) was found to have abruptly deepened at about the
time of the Antarctic glaciation (Pälike et al., 2012).
Recent finding dates the Antarctic glaciation onset to
33 Ma and to be influenced by the atmospheric carbon
dioxide; it also coincides with the separation of Australia
and South America from Antarctica. Such findings form
and advance the field of paleoceanography. It is now possible to infer atmospheric carbon dioxide concentrations
to link to past warm climates. These past time series in a
short time scale (decadal to millennial) indicate abrupt climate changes likely to be associated with the “flip-flop” of
deep-ocean circulation in the North Atlantic. In the longer
time scale is the shift from warm climates to the current era
with cryosphere. Organic carbon-rich layers from the
mid-Cretaceous suggested prevailing anoxic conditions
during warm ocean time (“greenhouse”). Drilling in high
latitudes elucidated continental glaciation timings as well
as developments of ocean current pathways (e.g., Antarctic bottom water or North Atlantic bottom water or isolation of Pacific and Atlantic Oceans at Isthmus of
Panama). A significant recent IODP discovery was
obtained by drilling in the Arctic Ocean for the first time
to go back 55 myrs and to find freshwater fern in 49 Ma
when there was no ice (IODP Exp. 302; Moran et al.,
2006). The cooling in the Arctic started about 46 Ma much
earlier than previously conceived.
There are numerous other key findings that are relevant
to shaping the Earth’s environment. Drilling across the
Cretaceous-Tertiary border time (65 Ma) clearly substantiated the bolide impact causing mass extinction and recovery. The Mediterranean Sea was dried near the end of the
Miocene creating salt deposition influenced by the restriction of the water flow into the sea (DSDP Leg 13).
Microbiology
The investigation of the deep biosphere has brought surprising results of finding microbes in excess of 500 m
depths into the sediments (Parkes et al., 1994).
The sub-seafloor microbes do not depend on photosynthesis. So far, the deepest record is finding active microbes
1,626 mbsf in 111-Ma-old sediments (Leg 210; Roussel
et al., 2008). Microbes are found to prevail in organic-rich
or hydrate-bearing sediments. Traces of microbes in volcanic rocks are also found (Mason et al., 2010; Exps.
304, 305); thus, the limit is not the sediments, but more
likely to be the thermal condition and energy supply
(e.g., Bach and Edwards, 2003). Studies of life
sub-seafloor have expanded recently with growing interests in defining the habitat, ecosystem, link to fluids, limiting environmental conditions, and the role of these life
forms in the Earth-life coevolution and geochemical
cycles. Drilling contaminates the core samples, and therefore, technological scrutiny to study only the
uncontaminated portion is required.
Solid earth processes
Oceanic bathymetric highs range from scattered seamounts to seamount chains to oceanic plateaus, not
directly linked to volcanisms at mid-ocean ridges. One
of the major discoveries about the genesis of these features
is that it is proven by ocean drilling that the bend between
the Emperor seamount chain and the Hawaiian chain is
produced not by the plate motion change but by the
change in the mantle upwelling motion (e.g., Tarduno
et al., 2009). This is an example that working hypotheses
will be modified by new findings.
Large igneous provinces (LIPs) are continental flood
basalts and oceanic plateaus created by a large supply of
mantle-derived magma in a relatively short period
(1–10 myrs) (Legs 130, 192, Ontong Java Plateau; Legs
119,120, 183, Kerguelen Plateau; Leg 198, Exp.
324, Shatsky Rise). Mantle plumes are considered the
likely source, and their impact on climate (greenhouse
Earth) and ocean anoxia (oxygen-depleted ocean) is not
well understood, partly because of the difficult core sampling strategy.
Plate subduction occurs both in accretionary tectonics
and subduction erosion tectonics around the Pacific Rim.
Recent deep drilling in the Nankai subduction zone has
revealed the tsunami genesis history in geological perspective (IODP NanTroSEIZE Exps.).
The database can be utilized for objectives that can be
achieved through global sampling not possible for a single
cruise such as compiling for rare-earth element distribution (Kato et al., 2011).
Ocean igneous crust
Ocean crustal rocks beneath the sediments have not been
recovered with significant continuous coring except for
recovering the topmost section for obtaining the date of
the seafloor formation. The basic structure of an oceanic
crust is estimated from geophysical (remote sensing) or
geological evidence offshore (exposures of rocks formed
at high pressure and temperature) and onshore (ophiolite
considered to be obducted oceanic crusts) to be about
OCEAN DRILLING
549
tuning in to the Earth’s orbital change (Milankovitch
cycles (20–100 kyr)) detectable in sediment cores. Drilling in corals and high-sedimentation-rate sites allows
for even higher temporal resolution. Since the ocean floors
are destroyed by subduction, the oldest core sample is
~170 myrs old (ice cores <~800 kyr) covering ages since
Jurassic. Drilling data contributed in defining the average
temperature change over this time period, mostly warmer
than the present Earth but covering the period without
continental ice (“greenhouse Earth”) and the period with
ice sheets present (“icehouse Earth”).
While the basic geological inferences come from
lithostratigraphy, core specimen also provides information
on past environments from oxygen isotope ratios and
planktonic or benthic microfossils to infer the surface
and bottom temperatures, which in turn infer continental
ice volumes. The balancing depth of the carbonate supply
and its dissolution rates called CCD (calcite compensation
depth) was found to have abruptly deepened at about the
time of the Antarctic glaciation (Pälike et al., 2012).
Recent finding dates the Antarctic glaciation onset to
33 Ma and to be influenced by the atmospheric carbon
dioxide; it also coincides with the separation of Australia
and South America from Antarctica. Such findings form
and advance the field of paleoceanography. It is now possible to infer atmospheric carbon dioxide concentrations
to link to past warm climates. These past time series in a
short time scale (decadal to millennial) indicate abrupt climate changes likely to be associated with the “flip-flop” of
deep-ocean circulation in the North Atlantic. In the longer
time scale is the shift from warm climates to the current era
with cryosphere. Organic carbon-rich layers from the
mid-Cretaceous suggested prevailing anoxic conditions
during warm ocean time (“greenhouse”). Drilling in high
latitudes elucidated continental glaciation timings as well
as developments of ocean current pathways (e.g., Antarctic bottom water or North Atlantic bottom water or isolation of Pacific and Atlantic Oceans at Isthmus of
Panama). A significant recent IODP discovery was
obtained by drilling in the Arctic Ocean for the first time
to go back 55 myrs and to find freshwater fern in 49 Ma
when there was no ice (IODP Exp. 302; Moran et al.,
2006). The cooling in the Arctic started about 46 Ma much
earlier than previously conceived.
There are numerous other key findings that are relevant
to shaping the Earth’s environment. Drilling across the
Cretaceous-Tertiary border time (65 Ma) clearly substantiated the bolide impact causing mass extinction and recovery. The Mediterranean Sea was dried near the end of the
Miocene creating salt deposition influenced by the restriction of the water flow into the sea (DSDP Leg 13).
Microbiology
The investigation of the deep biosphere has brought surprising results of finding microbes in excess of 500 m
depths into the sediments (Parkes et al., 1994).
The sub-seafloor microbes do not depend on photosynthesis. So far, the deepest record is finding active microbes
1,626 mbsf in 111-Ma-old sediments (Leg 210; Roussel
et al., 2008). Microbes are found to prevail in organic-rich
or hydrate-bearing sediments. Traces of microbes in volcanic rocks are also found (Mason et al., 2010; Exps.
304, 305); thus, the limit is not the sediments, but more
likely to be the thermal condition and energy supply
(e.g., Bach and Edwards, 2003). Studies of life
sub-seafloor have expanded recently with growing interests in defining the habitat, ecosystem, link to fluids, limiting environmental conditions, and the role of these life
forms in the Earth-life coevolution and geochemical
cycles. Drilling contaminates the core samples, and therefore, technological scrutiny to study only the
uncontaminated portion is required.
Solid earth processes
Oceanic bathymetric highs range from scattered seamounts to seamount chains to oceanic plateaus, not
directly linked to volcanisms at mid-ocean ridges. One
of the major discoveries about the genesis of these features
is that it is proven by ocean drilling that the bend between
the Emperor seamount chain and the Hawaiian chain is
produced not by the plate motion change but by the
change in the mantle upwelling motion (e.g., Tarduno
et al., 2009). This is an example that working hypotheses
will be modified by new findings.
Large igneous provinces (LIPs) are continental flood
basalts and oceanic plateaus created by a large supply of
mantle-derived magma in a relatively short period
(1–10 myrs) (Legs 130, 192, Ontong Java Plateau; Legs
119,120, 183, Kerguelen Plateau; Leg 198, Exp.
324, Shatsky Rise). Mantle plumes are considered the
likely source, and their impact on climate (greenhouse
Earth) and ocean anoxia (oxygen-depleted ocean) is not
well understood, partly because of the difficult core sampling strategy.
Plate subduction occurs both in accretionary tectonics
and subduction erosion tectonics around the Pacific Rim.
Recent deep drilling in the Nankai subduction zone has
revealed the tsunami genesis history in geological perspective (IODP NanTroSEIZE Exps.).
The database can be utilized for objectives that can be
achieved through global sampling not possible for a single
cruise such as compiling for rare-earth element distribution (Kato et al., 2011).
Ocean igneous crust
Ocean crustal rocks beneath the sediments have not been
recovered with significant continuous coring except for
recovering the topmost section for obtaining the date of
the seafloor formation. The basic structure of an oceanic
crust is estimated from geophysical (remote sensing) or
geological evidence offshore (exposures of rocks formed
at high pressure and temperature) and onshore (ophiolite
considered to be obducted oceanic crusts) to be about
OCEAN DRILLING
549