Week 6 (09/29/2009) Summary – Joseph Kiker
Topic: Quaternary Sea Level
Papers Discussed:
Lambeck, K., T.M. Esat, E.-K. Potter, 2002. Links between climate and sea levels for the past three
million years, Nature, v. 419, p. 199-206.
Peltier and Fairbanks, 2006. Global glacial ice volume and Last Glacial Maximum duration from an
extended Barbados sea level record. Quaternary Science Reviews, v. 25, pp. 3322-3337.
Clark, P.U., Dyke, A.S., Shakun, J.D. and Carlson, A.E., 2009. The last glcial maximum. Science, v.
325, pp.710-714.
Readings for the week of 9/29/09 focused on sea level fluctuations predominantly during the Last Glacial
Maximum (LGM). These three papers: “Links between climate and sea levels for the past three million years”,
“Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record”,
and “The Last Glacial Maximum” employed a wide range of sea level proxies in an attempt to determine the
spatial impact of this event with respect to both time and climate change.
Lambeck et al. 2002 in “Links between climate and sea levels for the past three million years” examines
fluctuations in sea level and climate by examining foraminifera in two sediment cores (Caribbean Sea and
Equatorial Atlantic) and corals (Huon Peninsula and Bonaparte Gulf). A five million year record of 18O was
established using foraminifera. Low 18O characterize the interval from 3 ma to 5 ma. Therefore, this period is
indicative of relatively high temperatures and reduced ice in polar caps (Lambeck et al., 2002). At ~ 3 ma to
present the trend in 18O is increasing with cyclic oscillations on timescales of ~ 40 ka and ~100 ka suggesting
Milankovitch cycles as a possible climate forcing mechanism. Coral reefs form in close proximity to sea level
and therefore are good proxies for paleo-sea level. Uranium-series dating of corals allows for the determination
of age, sea level and height in the geologic record at certain localities (Lambeck et al., 2002). Data provided by
Lambeck et al., 2002 shows that glacial oscillations and sea level changes are initially driven by variations in
insolation. However, once ice-sheets become well-established other forcings such as Milankovitch cycles, icesheet dynamics, and shifts in ocean circulation may have strong influences on climatic changes.
Peltier and Fairbanks 2006 in “Global glacial ice volume and Last Glacial Maximum duration from an
extended Barbados sea level record” investigate changes in both global ice volume and sea level for the LGM
primarily by using U/Th dated corals and running a model (ICE-5G) which takes into account a variety of
factors influencing global glacial ice volume. The ICE-5G model predicts known sea level histories (SE
Hudson Bay, Canada, Boston, MA, Baie Des Anges, France, Wairu Valley, Zn, Angermanalven, Sweden,
Arisaig NW, Scotland, Kuwait Bay, Kuwait, and Scott Coast, Antarctic) fairly well for the past 32,000 years.
The ICE-G model coupled with the sea level record for Barbados verify that the post LGM rise of eustatic sea
level was close to the widely supported estimate of 120 m (Peltier and Fairbanks 2006). Data also shows that
the LGM may have occurred 26 ka rather than the generally accepted date of 21 ka (Peltier and Fairbanks
2006).
Clark et al. 2009 in “The Last Glacial Maximum” attempt to constrain the LGM with respect to ice-sheet and
mountain glacier extent. They used 14C ages and terrestrial cosmogenic nuclides to determine the time of
global ice sheet maxima for different ice sheets. Relative sea level data from previous research was used to
constrain the occurrence of the LGM to the interval 26.5 ka to 19 ka. Sea surface temperature, atmospheric
CO2, and 18O data from previous researchers was analyzed to determine the role of climatic forcing during the
LGM. The data presented by Clark et al. 2009 supports the assertion that the LGM spanned from ~33 ka to 19
ka with both the onset of glaciation and deglaciation varying spatially. For instance, small ice-sheets at midPage 1 of 3
and high northern latitudes and the West Antarctic Ice Sheet reached their maxima extent possibly as early as 33
ka. Clark et al. 2009 speculate the majority of ice-sheets reached their full extent by 26.5 ka. At 19 ka ice
sheets and even Northern Hemisphere mountain glaciers began to retreat. This indicates that increase in
Northern Hemisphere insolation was most likely the primary mechanisms for triggering deglaciation. However,
it is important to note that the onset of deglaciation in some ice sheets and mountain glaciers was delayed and
retreat did not occur until after 19 ka. Therefore, regional controls on deglaciation in these areas must have
delayed their response to changes in insolation (Clark et al., 2009).
These three papers attempt to determine the extent of the LGM and global and regional controls on
glaciation/deglaciation by examining sea level histories. Fluctuations in sea level at a given locality can be used
to examine changes in global ice volume. However, only areas where little subsidence or tectonic uplift occur
record accurate sea level histories. Data presented in these three papers demonstrates the difficulty involved in
defining a geologic time interval (i.e. LGM) on a global scale. Most importantly these researchers show that the
LGM was not occurring at the same time everywhere. Insolation may have been the primary mechanism for
glaciation and deglaciation, but other regional controls on ice volume were also important in delaying the onset
of glaciation associated with the LGM. Atmospheric CO2 and tropical SSTs data suggests that the carbon cycle
and other ocean feedbacks are also responsible for global warming and therefore deglaciation (Clark et al.
2009). Spatial variation in the occurrence of the LGM suggests that regional controls may influence an areas
response to changes in insolation. Therefore globally, the extent of the LGM can be loosely defined as
occurring from 33 ka to 19 ka. However, regionally the LGM may be defined more precisely.
Page 2 of 3