Yokoyama, Y., Esat, T. M., and Lambeck, K., 2001a. Coupled climate and sea-level changes deduced from Huon Peninsula coral
terraces of the last ice age. Earth and Planetary Science Letters,
193, 579–587.
Yokoyama, Y., Esat, T. M., and Lambeck, K., 2001b. Last glacial
sea-level change deduced from uplifted coral terraces of Huon
Peninsula, Papua New Guinea. Quaternary International,
83–85, 275–283.
Yokoyama, Y., Matsuzaki, H., and Esat, T. M., 2008. Prospects for
the new frontiers of earth and environmental sciences. Quaternary Geochronology, 3, 206–207.
Cross-references
Climate Change and Coral Reefs
Emerged Reefs
Glacial Control Hypothesis
Huon Peninsula, P.N.G.
Last Glacial Interstadials
Meltwater Pulses
Paleoclimate from Corals
Postglacial Trangression
Reef Classification, Response to Sea Level Rise
Sea Level Change and Its Effect on Reef Growth
Submerged Reefs
LAST GLACIAL LOWSTAND AND SHELF EXPOSURE
Yusuke Yokoyama
The University of Tokyo, Chiba, Japan
Definition
Occurred at the Last Glacial Maximum (19,000–
30,000 years ago) when sea level was lowered globally
to as much as 120–130 m.
Last Glacial Maximum (LGM) is the time when global
temperature was significantly lower than that of the present and ice sheets covered large areas of northern hemisphere continents. The conventional definition of the
LGM was made by an international research project group
in the 1980s (e.g., CLIMAP Project Members, 1981) as
was the time when low-latitude ocean temperature was at
its minimum. However, recent advances of paleoclimate
study show that the timing of the LGM is varied
depending on the locations on the Earth’s surface. Therefore, the most recent date of the “global” LGM is defined
as the time when the global ice volume was at its maximum and sea level was at its lowest (Mix et al., 2001).
There had been various estimates of the exact levels of
sea-level lowstand. Nakada and Lambeck (1988) and
Fleming et al. (1998) reviewed published sea-level
observations obtained from the sites far from former icecovered regions. They conducted corrections of glaciohydro-isostatic adjustments of solid earth (GIA) and
concluded that the LGM sea level was 125–130 m lower
than the present. Corals obtained from Barbados provided
the last 18,000 years of sea-level record and it led to the
conclusion that this level may have been 120 m lower than
the present (Fairbanks, 1989; Bard et al., 1990). On the
other hand, others claimed that the LGM level may have
been only $105 m (Peltier, 1994). Thus there were large
discrepancies for estimates of the sea level at the lowstand
during the last glacial.
The Australian continental shelf was targeted to tackle
this problem since it is located far from formerly glaciated
regions, hence expected GIA is minimal and those corrections are not sensitive to the ice-loading geometry. The
continental margins are tectonically stable as was
supported by the elevation of the last interglacial shorelines close to the present day sea level (Marshall and
Thom, 1976; Stirling et al., 1998). Ferland et al. (1995)
worked off Sydney using vibro-cores and concluded that
the shelf was exposed during the last glacial lowstand
shallower than À130 m. The high-energy sedimentary
environments prohibited further refinements. The northwestern shelf of Australia, on the other hand, is suited
for studying sea-level lowstand since the area is characterized by shallow and wide depressions and hence the conditions may have been favorable for the preservation of
former sea-level indicators (van Andel and Veevers,
1967; Yokoyama et al., 2000, 2001a). A series of gravity
and vibro-cores were recovered and micropaleontological
study with detailed radiocarbon dating shows that the
LGM sea level locally reached at 125þ/À4 m at least
between 22,000 and 19,000 years B.P. and the LGM was
terminated rapidly 19,000 years ago when approximately
10% of ice volume decreased. This probably created
a ca. 10–15 m rise in sea level (Yokoyama et al., 2000,
2001a). Local sea-level lowstands can be translated into
the so-called ice volume equivalent sea level, as much as
135 m (Yokoyama et al., 2000; Lambeck et al., 2002),
which can be obtained after GIA corrections. This was
the first observation, which extended back into the middle
of the LGM, and the GIA-corrected Barbados record was
consistent with the northwestern shelf result (Yokoyama
et al., 2000). This quantity was further supported by independent studies such as detailed microfossil examinations
(De Deckker and Yokoyama, 2009), GIA model (Milne
et al., 2002; Mitrovica, 2003), and the Sunda Shelf record
(Hanebuth et al., 2000, 2009). Predicted relative sea-level
values are available around the Australian continent
(Yokoyama et al., 2001b) and the model predictions are
confirmed from occurrence of ooids from the Great Barrier Reef, where this part of the shelf was also exposed
during the lowstand (Yokoyama et al., 2006). Various
impacts from such a lowstand on coral reef formations
are still under debate, since there are only a few LGM
coral observations so-far reported. Coral samples obtained
from deep-sea drilling currently being undertaken will
allow us to understand the mechanisms on this topic.
Bibliography
Bard, E., Hamelin, B., and Fairbanks, R. G., 1990. U–Th ages
obtained by mass spectrometry in corals from Barbados: sea
level during the past 130,000 years. Nature, 346, 456–458.
620
LAST GLACIAL LOWSTAND AND SHELF EXPOSURE
terraces of the last ice age. Earth and Planetary Science Letters,
193, 579–587.
Yokoyama, Y., Esat, T. M., and Lambeck, K., 2001b. Last glacial
sea-level change deduced from uplifted coral terraces of Huon
Peninsula, Papua New Guinea. Quaternary International,
83–85, 275–283.
Yokoyama, Y., Matsuzaki, H., and Esat, T. M., 2008. Prospects for
the new frontiers of earth and environmental sciences. Quaternary Geochronology, 3, 206–207.
Cross-references
Climate Change and Coral Reefs
Emerged Reefs
Glacial Control Hypothesis
Huon Peninsula, P.N.G.
Last Glacial Interstadials
Meltwater Pulses
Paleoclimate from Corals
Postglacial Trangression
Reef Classification, Response to Sea Level Rise
Sea Level Change and Its Effect on Reef Growth
Submerged Reefs
LAST GLACIAL LOWSTAND AND SHELF EXPOSURE
Yusuke Yokoyama
The University of Tokyo, Chiba, Japan
Definition
Occurred at the Last Glacial Maximum (19,000–
30,000 years ago) when sea level was lowered globally
to as much as 120–130 m.
Last Glacial Maximum (LGM) is the time when global
temperature was significantly lower than that of the present and ice sheets covered large areas of northern hemisphere continents. The conventional definition of the
LGM was made by an international research project group
in the 1980s (e.g., CLIMAP Project Members, 1981) as
was the time when low-latitude ocean temperature was at
its minimum. However, recent advances of paleoclimate
study show that the timing of the LGM is varied
depending on the locations on the Earth’s surface. Therefore, the most recent date of the “global” LGM is defined
as the time when the global ice volume was at its maximum and sea level was at its lowest (Mix et al., 2001).
There had been various estimates of the exact levels of
sea-level lowstand. Nakada and Lambeck (1988) and
Fleming et al. (1998) reviewed published sea-level
observations obtained from the sites far from former icecovered regions. They conducted corrections of glaciohydro-isostatic adjustments of solid earth (GIA) and
concluded that the LGM sea level was 125–130 m lower
than the present. Corals obtained from Barbados provided
the last 18,000 years of sea-level record and it led to the
conclusion that this level may have been 120 m lower than
the present (Fairbanks, 1989; Bard et al., 1990). On the
other hand, others claimed that the LGM level may have
been only $105 m (Peltier, 1994). Thus there were large
discrepancies for estimates of the sea level at the lowstand
during the last glacial.
The Australian continental shelf was targeted to tackle
this problem since it is located far from formerly glaciated
regions, hence expected GIA is minimal and those corrections are not sensitive to the ice-loading geometry. The
continental margins are tectonically stable as was
supported by the elevation of the last interglacial shorelines close to the present day sea level (Marshall and
Thom, 1976; Stirling et al., 1998). Ferland et al. (1995)
worked off Sydney using vibro-cores and concluded that
the shelf was exposed during the last glacial lowstand
shallower than À130 m. The high-energy sedimentary
environments prohibited further refinements. The northwestern shelf of Australia, on the other hand, is suited
for studying sea-level lowstand since the area is characterized by shallow and wide depressions and hence the conditions may have been favorable for the preservation of
former sea-level indicators (van Andel and Veevers,
1967; Yokoyama et al., 2000, 2001a). A series of gravity
and vibro-cores were recovered and micropaleontological
study with detailed radiocarbon dating shows that the
LGM sea level locally reached at 125þ/À4 m at least
between 22,000 and 19,000 years B.P. and the LGM was
terminated rapidly 19,000 years ago when approximately
10% of ice volume decreased. This probably created
a ca. 10–15 m rise in sea level (Yokoyama et al., 2000,
2001a). Local sea-level lowstands can be translated into
the so-called ice volume equivalent sea level, as much as
135 m (Yokoyama et al., 2000; Lambeck et al., 2002),
which can be obtained after GIA corrections. This was
the first observation, which extended back into the middle
of the LGM, and the GIA-corrected Barbados record was
consistent with the northwestern shelf result (Yokoyama
et al., 2000). This quantity was further supported by independent studies such as detailed microfossil examinations
(De Deckker and Yokoyama, 2009), GIA model (Milne
et al., 2002; Mitrovica, 2003), and the Sunda Shelf record
(Hanebuth et al., 2000, 2009). Predicted relative sea-level
values are available around the Australian continent
(Yokoyama et al., 2001b) and the model predictions are
confirmed from occurrence of ooids from the Great Barrier Reef, where this part of the shelf was also exposed
during the lowstand (Yokoyama et al., 2006). Various
impacts from such a lowstand on coral reef formations
are still under debate, since there are only a few LGM
coral observations so-far reported. Coral samples obtained
from deep-sea drilling currently being undertaken will
allow us to understand the mechanisms on this topic.
Bibliography
Bard, E., Hamelin, B., and Fairbanks, R. G., 1990. U–Th ages
obtained by mass spectrometry in corals from Barbados: sea
level during the past 130,000 years. Nature, 346, 456–458.
620
LAST GLACIAL LOWSTAND AND SHELF EXPOSURE