Publication Date:
2016-11-14
Description:
Ice cores provide several environmental archives that give us insights into the history of the climate of
the earth. Stable water isotopes can be used for long term temperature trends during Holocene and
young Pleistocene while trace elements indicate seasonal patterns on short term and glacials on long
term scales. Nevertheless, syn- and postdepositional processes influence the originally deposited
signal of those proxies. As there is lack of continuous data-based annual accumulation distribution in
Antarctica, it is still not clear, how single species are deposited in snow and how the signal can be
interpreted. Especially the temporal variability of deposition dependent on seasonal accumulation is a
fact that needs to be unterstood. Therefore, in this master thesis we try to explain, how the deposition
of proxies is coupled with accumulation and show implications for an interpretation of distinct proxy
signals. For this purpose, snow profiles with a length of 50 cm were taken at four different locations,
which are along a path of 40 m. The main site was sampled 41 times within a period of 53 days, while
the other three locations were used as reference for spatial variance. With that setup, especially the
temporal resolution was in the focus of interest. The liner were cut into distinct samples of 1 cm
(0-30 cm depth) and 2 cm (30-50 cm depth) and analyzed on several trace elements (Na+, Cl-, NO3
-, SO42-, Ca2+, Mg2+ and MSA) using a Dionex IC 2100 ion chromatograph. δ18O and δ2H measurements
were conducted using cavity ring-down spectroscopy (CRDS) and an Picarro analyzer. Study area is
the EPICA drill site Kohnen (75°0‘ S; 0°4‘ E) in Dronning Maud Land, Antarctica with an
accumulation rate of 64 mm w.e. per year and upward tendency towards higher values.
We performed a time-depth-correlation taking recent ablation stake measurements into account and
plotted the isotopic and aerosol record on the basis of an estimated accumulation distribution. We used
a value of 0.5 cm a-1 snow per winter month which is, based on density data from the snow liner, about
1.83 mm w.e. The validity of the temporal correlation was done by conservative aerosol records of sea
salt components Na+ and Cl-. In general, the case study reveals poor correlation between isotopic
record and surface temperature on the small temporal and special scale. We observed a lack of
summer signal and high dependence on short term climate fluctuations like high precipitation events
during extended winter season. Nevertheless, those small scale variations cannot be seen in the
isotopic record as smoothing exceeds the temporal resolution. 2H-excess in uppermost snow layers and
the trend of δ18O versus δ2H confirms high influence of evaporation and sublimation effects on the
snow surface that alter the real deposition signal. The allocation of summer and winter to ice core data
therefore seems to be based on a high noise influence. Furthermore we showed that local and short
time intervals can drastically influence the deposited tracer signals. Wind erosion by strong wind
events or squalls may highly disturb the continuous stratigraphy of snow and firn. Finally, we state the
urgent need of continuous accumulation distribution in Antarctica to verify patterns shown in this
thesis and carry out further observations in higher resolution.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Thesis
,
notRev
Format:
application/pdf
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