| dc.description.abstract | As most of central Europe suffered a successive loss of tree species during glacial-interglacial cycles, some locations in the Mediterranean acted as refugia for tree diversity for much of the Quaternary. In this thesis, I present a high resolution pollen record for Marine Isotope Stages (MIS) 9-10 (297-370 ka) from Lake Ohrid, located on the border of North Macedonia and Albania. Lake Ohrid is characterized by a high floral biodiversity throughout the Quaternary and likely acted as glacial refugium. This makes the dynamics of vegetation changes in this area interesting for research, since it presents the opportunity to study these changes in a long continuous record.
The high resolution record makes it possible to interpret short-term climate oscillations, which were mainly present between 310-297 ka. The pollen record is in good correlation with marine and terrestrial proxies, which shows that Lake Ohrid responded to both long- (glacial-interglacial) and short-scale (millennial scale) climatic fluctuations.
Furthermore, the relation between pollen production and CO2 is investigated, by linking the pollen influx to atmospheric CO2 concentrations, to investigate this as a potential CO2 proxy. This showed a good overall correlation with a higher pollen influx for rising CO2, but on shorter timescales of ~10 kyr, the trend could be different. Besides pollen production, atmospheric CO2 levels may also have influence on carbon fractionation by plants. A new setup combining laser ablation, nano-combustion, gas chromatography and isotope ratio mass spectrometry (LA/nC/GC/IRMS) allows the measurements of carbon isotopes to single grains of Pinus pollen, which has been done for seven samples. The resulting δ13Cpollen values show no trend with CO2 levels, but interpretation of these values, using the ratio between intercellular and atmospheric CO2 (the ci/ca ratio), suggest that the physiological response of vegetation to e.g. rising CO2, is an increase in photosynthesis and a decrease in stomatal conductance. Although the ci/ca ratio stayed roughly constant over time, it is difficult to confidently interpret changes in ci with changing CO2, as it is not known if this is from ca changes or hydrology. | |
