Siple Dome Highlights: Stable isotopes
Jim White and Eric Steig
Stable isotopes of water (D/H and 18O/16O, and deuterium excess, the combination of these two) have been measured on the Siple Dome ice core. High temporal resolution sampling (roughly one year or less) has been done for the upper parts of the core as well as during parts of the glacial to interglacial transition. Low temporal resolution sampling has been completed for the whole core. Highlights are:
- Comparisons of the Siple Dome isotope record with Vostok and Byrd show that Siple Dome appears to have been a stable feature of West Antarctica for at least 100,000 years. Also, the height of the Dome has not changed significantly over this time. This information will be incorporated into a publication on the glaciology of the Dome.
- Climate in the Siple Dome region is highly impacted by ENSO. The dominant variability in the climate of Siple Dome (from D/H and 18O/16O) is clearly related to ENSO. Also, the deuterium excess, which tracks the climate of the Pacific moisture source region (ranging from 20 degrees South to the Antarctic coast) shows strong ENSO signals, as expected for that region of the Pacific Ocean. The ice core archive allows us to turn this relationship around and reconstruct ENSO in the past, potentially the past 10,000 years or longer. Initial results indicate that ENSO has been more active throughout the Holocene than suggested by other records. Also, the ability of the ice core to monitor both the climate teleconnection (climate of Siple Dome) as well as the Pacific sea surface temperatures directly (via deuterium excess), a capability unique to ice cores, has revealed that while the ocean signal of ENSO has remained steady during the Holocene, the teleconnection has varied in strength and in periodicity. Annalisa Schilla, a graduate student at CU, is taking the lead on a publication describing these results.
- Abrupt climate changes appear in the Siple Dome isotope record at 20,000 years before present as well as 15,000 years before present, and possibly at other times during the glacial period. The 20,000 year event, an abrupt warming of 5 to 6 degrees C in less than a human lifetime (50 years), comes at the time when the glacial period ends, and may be a clue to how this slow and gradual change began. Ken Taylor at DRI is taking the lead on a publication describing these results.
- The deuterium excess record of the glacial period is marked by a number of large changes that resemble the highly variable Greenland records more than the typical slowly varying Antarctic records. While the dating is not yet complete, there is an indication that these large and abrupt shifts in deuterium excess correlate with the Greenland records of Dansgaard- Oescheger events. This would point towards the Pacific region as the genesis region of these abrupt climate events. A publication on the full isotope record is currently being prepared in cooperation with a number of Siple Dome researchers.
- A series of shallow cores from Siple Dome have been analyzed for stable isotopes with sub-annual temporal detail. These records show first that the isotope changes are coherent, and thus we can interpret the changes as signals as opposed to noise. Also, the spatial pattern of snow accumulation over the past century inferred from the cross-dated cores shows periods of greater accumulation on both the Eastern and Western sides of the Dome, with gradual and coherent shifts in the pattern of accumulation that appear to be related to decadal scale changes in ENSO intensity. Trevor Popp, a graduate student at CU, is taking the lead on a publication describing these results.