Firn-air δ15N in modern polar sites and glacial–interglacial ice: a model-data mismatch during glacial periods in Antarctica?

Amaelle Landais; Jean-Marc Barnola; Kenji Kawamura; Nicolas Caillon; M. Delmotte; T. van Ommen; G. Dreyfus; Jean Jouzel; Valérie Masson-Delmotte; B. Minster; J. Freitag; M. Leuenberger; Jakob Schwander; C. Huber; D. M. Etheridge; Vin Morgan

doi:10.1016/j.quascirev.2005.06.007

Journal articles

Firn-air δ15N in modern polar sites and glacial–interglacial ice: a model-data mismatch during glacial periods in Antarctica?

Amaelle Landais ^{1, 2} Jean-Marc Barnola ³ Kenji Kawamura ⁴ Nicolas Caillon ¹ M. Delmotte ¹ T. van Ommen ^{5, 6} G. Dreyfus ^{1, 7} Jean Jouzel ¹ Valérie Masson-Delmotte ¹ B. Minster ¹ J. Freitag ⁸ M. Leuenberger ⁹ Jakob Schwander ⁹ C. Huber ⁹ D. M. Etheridge ¹⁰ Vin Morgan ^{5, 6}

1 IPSL - Institut Pierre-Simon-Laplace

2 Institute of Earth Sciences

3 LGGE - Laboratoire de glaciologie et géophysique de l'environnement

4 Center for Atmospheric and Oceanic Studies [Sendai]

5 ACE-CRC - Antarctic Climate and Ecosystems Cooperative Research Centre

6 AAD - Australian Antarctic Division

7 Department of Geosciences [Princeton]

8 Abteilung Klinische Sozialmedizin, Berufs- und Umweltdermatologie

9 Physics Institute

10 CSIRO Marine and Atmospheric Research

Abstract : The phase lag between atmospheric composition (air bubbles) and temperature (water isotopes) can be quantified from ice cores provided that the age difference between entrapped air and the surrounding air can be correctly estimated. This difference depends on the lock-in depth (LID), when air no longer mixes with the atmosphere. The LID can be estimated from firnification models or from the air isotopic composition (δ15N and δ40Ar). Both methods give consistent results for Greenland and one coastal site in Antarctica (Byrd). New firn measurements in Greenland (NorthGRIP) and Antarctica (Berkner Island, BAS depot, Dome C) confirm that firnification models correctly reproduce the present LID over a large range of surface conditions. However, a systematic mismatch is observed for the Last Glacial Maximum (LGM) in East Antarctic sites (Vostok, Dome C, Dome F) questioning the model's validity. Here we use new δ15N measurements from two coastal Antarctic sites (Kohnen Station and Law Dome) providing depth estimates again distinct from firnification model calculations. We show that this discrepancy can be resolved by revising the estimate of past accumulation rates. δ15N measurements can therefore help to constrain past accumulation rate and improve ice core dating.

Document type :

Journal articles

Domain :

Sciences of the Universe [physics] / Earth Sciences / Glaciology

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Firn-air δ15N in modern polar sites and glacial–interglacial ice: a model-data mismatch during glacial periods in Antarctica?

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Firn-air δ15N in modern polar sites and glacial–interglacial ice: a model-data mismatch during glacial periods in Antarctica?

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