 |
| Titel |
Atmospheric drivers that compromise the assumed long-term stationarity between δ18O-based proxy records and NAO, winter air temperature and winter precipitation amount. |
| VerfasserIn |
Laia Comas Bru, Frank McDermott, Martin Werner |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135049
|
| Publikation (Nr.) |
 EGU/EGU2016-15846.pdf |
|
|
|
|
|
| Zusammenfassung |
| The control exerted by large scale atmospheric circulation modes on the oxygen isotopic
composition of precipitation (δ18Op) has been utilised to infer past atmospheric circulation
states using proxies that capture δ18Op at a wide range of locations. Such reconstructions
typically rely on the oxygen isotopic composition of terrestrial archives such as ice-cores, tree
rings, speleothems and lacustrine carbonates and are underpinned by assumptions about a
long term stationarity of the influence of the atmospheric teleconnection pattern of interest on
δ18Op. However, such reconstructions should also consider the uncertainties that arise from
non-stationarities in the δ18Op-NAO relationship during the instrumental period. Here,
new insights into the causes of these temporal non-stationarities are presented for
the European region using both observations (GNIP database) and the output of
an isotope-enabled general circulation model (ECHAM5-wiso). The results show
that, although the East Atlantic (EA) pattern is generally uncorrelated to δ18Op
during the instrumental period, its polarity affects the strength of the δ18Op-NAO
relationship in some European locations. Non-stationarities in this relationship can be
rationalised through changes in the sea-level pressure structure in the N. Atlantic region
as a result of the concomitant states of the NAO and EA patterns, which affect
the trajectories of the air-masses carrying moisture onto Europe and ultimately
the δ18Op signal. These shifts are consistent with those reported previously for
NAO-winter climate variables and the resulting non-stationarities mean that δ18O-based
NAO reconstructions could be compromised if the balance of positive and negative
NAO/EA states differs substantially in a calibration period compared with the period of
interest in the past. The same approach has been followed to assess the relationships
between δ18Op and both winter total precipitation and winter mean surface air
temperature, with similar results. This study also identifies regions within Europe
where temporal changes in the NAO, air temperature and precipitation can be more
robustly reconstructed using δ18O time series from natural archives, irrespective of
concomitant changes in the EA. Identification of such regions is crucial so that
resources can be focused into the areas least affected by such non-stationarities. |
|
|
|
|
|
|