 |
| Titel |
Raman spectroscopy of bubbles and microbubbles in EDML antarctic ice core |
| VerfasserIn |
Christian Weikusat, Johannes Freitag, Sepp Kipfstuhl |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051994
|
|
|
|
|
|
| Zusammenfassung |
| Air bubbles entrapped in ice cores give the unique opportunity to measure and reconstruct the
composition of palaeo-atmospheres, which is mandatory for climate change interpretations
for our warming planet. However, the processes which occur during e.g. the entrapment of the
air during the firn-ice-transition, the hydrate formation due to pressure increase and processes
during deformation of the ice as well as relaxation after retrieval of an ice core, are still
poorly understood. One of the dangerous pitfalls in ice core interpretation, which is
sometimes underestimated by glaciologists, are the processes occurring after the retrieval of
the core due to pressure release and temperature changes during processing, transport and
storage. The identification and analysis of secondary relaxation features (such as
microbubbles or the so-called plate-like inclusions [1]) is thus an ongoing topic of high
importance. Detailed analyses of microstructure and associated micro-chemical composition
of inclusions in the ice can improve our understanding of these post-depositional
mechanisms.
Modern micro-Raman spectroscopy allows for the identification and quantification
of N2-O2 mixing ratios inside individual gas inclusions (bubbles, microbubbles,
clathrates) in ice cores. As N2 and O2 are the most important components in the Earth’s
atmosphere, changes of the N2-O2 mixing ratios can be used as a proxy for the
evolution of other gases (e.g. CO2). The benefits of this method to the understanding of
small-scale fluctuations in palaeo-atmospheric signals have been demonstrated (e.g.
[2]).
In the study presented here, N2-O2 mixing ratios of bubbles and microbubbles from several
depths of the EPICA DML ice core (Antarctica) were measured by Raman spectroscopy.
Comparative measurements were made for ice just below the firn-ice transition and also from
the bubble-clathrate transition zone. The results show that bubbles with diameters smaller
than ~200 μm are enriched in O2 compared to larger bubbles. The amount of O2-enrichment
is clearly correlated with the size of the microbubble, where the smallest bubbles show the
highest relative O2 contents. Given the distinctly larger diffusion constant for O2 compared
to N2 in ice [3], our results indicate that these microbubbles are secondary features produced
by relaxation of the ice core during storage. The same samples used for Raman
spectroscopy were additionally characterized by micro-CT measurements, giving
the opportunity to calculate mass balances and visualize the bubble/microbubble
distribution.
[1] A. Nedelcu et al., Raman spectra of plate-like inclusions in the EPICA-DML (Antarctica) ice core.
Journal of Glaciology, 2009, 55, 183-184
[2] T. Ikeda-Fukazawa et al., Variation in N2-O2 ratio of occluded air in Dome Fuji antarctic ice.
Journal of Geophysical Research, 2001, 106, 17799-17810
[3] T. Ikeda-Fukazawa et al., Effects of molecular diffusion on trapped gas composition in polar ice
cores. Earth and Planetary Science Letters, 2005, 229, 183-192 |
|
|
|
|
|
|