Phasing of orbital forcing and Antarctic climate over the past 470,000 years from an extended Dome Fuji O2/N2 chronology

Details Phasing of orbital forcing and Antarctic climate over the past 470,000 years from an extended Dome Fuji O2/N2 chronology Phasing of orbital forcing and Antarctic climate over the past 470,000 years from an extended Dome Fuji O2/N2 chronology

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmpp33a1005k&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #PP33A-1005

Astronomy and Astrophysics

Astronomy

1620 Climate Dynamics (0429, 3309), 3344 Paleoclimatology (0473, 4900), 4910 Astronomical Forcing, 4932 Ice Cores (0724), 4934 Insolation Forcing

Scientific paper

In order to investigate the roles of orbital and greenhouse-gas forcings on climate, one needs a chronology of Antarctic ice cores with an accuracy better than ~2 kyr (~1/10 of precession cycle). Recently, Kawamura et al. (2007, Nature) established such an Antarctic chronology for the past 360 kyr using the O2/N2 ratio of trapped air in the Dome Fuji and Vostok ice cores (Dome Fuji data available from http://www.ncdc.noaa.gov/paleo/icecore/antarctica/domefuji/domefuji.html). The O2/N2 ratio in these cores is depleted relative to the atmospheric ratio through physical fractionation during bubble close-off, and the magnitude of fractionation is linked to the magnitude of original snow metamorphism by local summer insolation. Thus, an accurate chronology can be constructed by orbital tuning between O2/N2 and local summer (solstice) insolation without the need to assume a lag. The new chronology permits comparisons between Antarctic climate, insolation and atmospheric greenhouse gas variations, thus providing a possible way to separate the respective contributions. We are currently measuring the O2/N2 ratio in the period 320- 470 kyr to extend the previous chronology, using the second Dome Fuji core (which recently reached 3035 m depth or ~720 kyr; , the first core reached 2503 m or ~340 kyr). We improved the quality of the new data by storing the core at low temperature (-46 to -50°C) after transportation from Dome Fuji. The new values for 320-340 kyr agree well with the previous data corrected for O2/N2 depletion during storage. Although the measurement is still ongoing, we find a promising resemblance between the raw O2/N2 data and the local summer insolation. Complete results will be reported for the current measurements and resulting chronology for the past 470 kyr, covering Marine Isotope Stage 11 and Termination V, and climatic implications will be discussed with special focus on the timing of orbital forcing and climatic changes.

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