 |
| Titel |
Post-depositional migration and signal reconstruction of methanesulfonic
acid (MSA) in polar ice cores |
| VerfasserIn |
Matthew Osman, Sarah B. Das, Olivier Marchal, Matthew J. Evans |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250147347
|
| Publikation (Nr.) |
 EGU/EGU2017-11500.pdf |
|
|
|
|
|
| Zusammenfassung |
| Methanesulfonic acid (MSA; CH3SO3H) in polar ice cores is a unique proxy of marine
primary productivity, synoptic atmospheric transport, and regional sea ice behavior. However,
MSA can be unstable within the ice column, leading to uncertainties surrounding the integrity
of its paleoclimatic signal. Here, we use ice core records coupled with forward and inverse
numerical models to investigate the post-depositional processes affecting the migration of
MSA within the firn and ice column, and attempt to reconstruct the original signal in
the ice column. The forward model, detailing the vertical diffusive transport of
soluble impurities through supercooled liquid pathways, allows us to systematically
assess the contribution of varying influences on the post-depositional migration
of MSA. Our results show that two site-specific variables in particular, i) snow
accumulation rate, and ii) seasonal concentration gradients of Na+(typically the
highest concentration sea salt), may be sufficient to reasonably predict the timing
and magnitude of MSA migration within the ice column. However, at present the
temporal accuracy of the forward MSA migration model remains limited by inadequate
constraints on the diffusion coefficient of MSA, DMS−. Specifically, we find that
previous estimates of DMS−are unable to reproduce, within significant uncertainty, the
progressive phase alignment of the MSA and Na+signals observed in real Antarctic ice
cores.
To attempt to correct for the effects of post-depositional migration, we combine
recent high-resolution West Antarctic MSA data using sequential methods from
optimal control theory (a Kalman filter and a related fixed-interval smoother) to
reconstruct and provide uncertainty estimates on the original, pre-migrated MSA
profile. We find that although the reconstructed MSA profile provides a reasonable
estimate of the original MSA signal, the large uncertainties associated with this
reconstructed signal cannot be objectively discriminated against the migrated MSA data.
On the other hand, our results suggest that records undergoing severe migration
may still be useful for inferring ∼decadal and lower-frequency climate variability. |
|
|
|
|
|
|