Publications

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2014
Orsi, AJ, Cornuelle BD, Severinghaus JP.  2014.  Magnitude and temporal evolution of Dansgaard-Oeschger event 8 abrupt temperature change inferred from nitrogen and argon isotopes in GISP2 ice using a new least-squares inversion. Earth and Planetary Science Letters. 395:81-90.   10.1016/j.epsl.2014.03.030   AbstractWebsite

Polar temperature is often inferred from water isotopes in ice cores. However, non-temperature effects on 3180 are important during the abrupt events of the last glacial period, such as changes in the seasonality of precipitation, the northward movement of the storm track, and the increase in accumulation. These effects complicate the interpretation of 8180 as a temperature proxy. Here, we present an independent surface temperature reconstruction, which allows us to test the relationship between delta O-18(ice) and temperature, during Dansgaard-Oeschger event 8, 38.2 thousand yrs ago using new delta N-15 and delta Ar-40 data from the GISP2 ice core in Greenland. This temperature reconstruction relies on a new inversion of inert gas isotope data using generalized least-squares, and includes a robust uncertainty estimation. We find that both temperature and delta O-18 increased in two steps of 20 and 140 yrs, with an overall amplitude of 11.80 +/- 1.8 degrees C between the stadial and interstadial centennial-mean temperature. The coefficient alpha = d delta O-18/dT changes with each time-segment, which shows that non-temperature sources of fractionation have a significant contribution to the delta O-18 signal. When measured on century-averaged values, we find that alpha = d delta O-18/dT = 0.32 +/- 0.06%(0)/degrees C, which is similar to the glacial/Holocene value of 0.328%(o)/degrees C. (C) 2014 Elsevier B.V. All rights reserved.

2008
Kobashi, T, Severinghaus JP, Barnola JM.  2008.  4 +/- 1.5 degrees C abrupt warming 11,270 yr ago identified from trapped air in Greenland ice. Earth and Planetary Science Letters. 268:397-407.   10.1016/j.epsl.2008.01.032   AbstractWebsite

Nitrogen and argon isotopes in air trapped in a Greenland ice core (GISP2) show two prominent peaks in the interval 11,800-10,800 B.P., which indicate two large abrupt warming events. The first abrupt wanning (10 +/- 4 degrees C) is the widely documented event at the end of the Younger Dryas. Here, we report on the second abrupt warming (4 +/- 1.5 degrees C), which occurred at the end of a short lived cooler interval known as the Preboreal Oscillation (11,270 +/- 30 B.P.). A rapid snow accumulation increase suggests that the climatic transition may have occurred within a few years. The character of the Preboreal Oscillation and the subsequent abrupt warming is similar to the Dansgaard-Oeschger (D/O) events in the last glacial period, suggestive of a common mechanism, but different from another large climate change at 8,200 B.P., in which cooling was abrupt but subsequent warming was gradual. The large abrupt warming at 11,270 B.P. may be considered to be the final D/O event prior to the arrival of the present stable and warm epoch. (c) 2008 Elsevier B.V. All rights reserved.