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T9
Assessing seasonality changes during the last termination by combined cuticle,
pollen, and oxygen isotope analysis
F. Wagner-Cremer 1 , A.J.C. Hincke 1 *, J.A.A. Bos 2 and A.F. Lotter 1
1 Palaeoecology, Laboratory of Palaeobotany and Palynology, Physical Geography, Utrecht University,
Budapestlaan 4, 3584CD Utrecht, The Netherlands
2 ADC ArcheoProjecten, Nijverheidsweg-Noord 114, 3812PN Amersfoort, The Netherlands
Earlier spring onset and the associated extension of the growing season in high latitudes
belong to the most conspicuous consequences of global warming. The natural dynamics
of growing season properties during past climate shifts, however, are extremely difficult to
assess since temperature reconstructions are rarely seasonally resolved and the
commonly-applied biotic proxies such as chironomids, macrofossils, or pollen are mainly
sensitive to summer temperatures. Here we use a newly developed leaf cuticle-based
proxy to reconstruct growing degree-days (GDD) in a quantitative way and to estimate
changes in the timing of spring onset over the last deglaciation.
By parallel, high-resolution cuticle, pollen, and stable oxygen stable-isotope analysis
performed on the same sediment core from Schleinsee (Southern Germany) we are
directly comparing spring and summer temperatures as well as approximate annual
temperature regimes. Based on this multi-proxy approach the issue of seasonality
changes during the last termination, covering the period from the Late Pleniglacial to the
Bølling/Allerød interstadial, will be discussed.
By deriving independent cuticle-based and pollen-based temperature records from a
single archive we will moreover assess the potential influence of seasonality on the pollen
record. Correlation of the local oxygen isotope record with Greenland ice-core stable
isotope records will enable a sound analysis of phase relationships between spring
conditions at high latitudes and in the Alpine region, which are today closely linked by the
activity of the North Atlantic Oscillation (NAO).
NAO-like sea level pressure dynamics exert complex spatial variability over the continental
North Atlantic realm, which impedes uncertainties in the proxy-based reconstructions of
past temperature where the seasonality of surface climate variability is not taken into
account. Pinning down seasonality through time may allow a mapping of seasonal
variability that places apparent discrepancies between continental temperature records
into a logical context. The determination of spatial patterns in seasonality changes during
natural climate shifts may contribute to a better assessment of the consequences resulting
from on-going human-induced warming.
Keywords: last termination; growing season; cuticle analysis; NAO