Global Change Abstracts The Swiss Contribution - SCNAT
Global Change Abstracts The Swiss Contribution - SCNAT
Global Change Abstracts The Swiss Contribution - SCNAT
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182 <strong>Global</strong> <strong>Change</strong> <strong>Abstracts</strong> – <strong>The</strong> <strong>Swiss</strong> <strong>Contribution</strong> | Past <strong>Global</strong> <strong>Change</strong>s<br />
leaf area index (LAI), using both global vegetation<br />
models and palaeoecological data. Prior simulations<br />
indicate lowered LAIs at the Last Glacial<br />
Maximum (LGM), but this is the first attempt to<br />
corroborate predictions against observations. Location<br />
Eastern North America and eastern Beringia.<br />
Methods Using a dense surface pollen data set<br />
and remotely sensed LAIs from the Moderate Resolution<br />
Imaging Spectroradiometer (MODIS) instrument,<br />
we evaluate the ability of analogue-based<br />
techniques to reconstruct modern LAIs from pollen<br />
data. We then apply analogue techniques to<br />
LGM pollen records, calculate the ratio of LGM to<br />
modern LAIs (RLAI) and compare reconstructed<br />
RLAIs to RLAIs simulated by BIOME4. Sensitivity<br />
experiments with BIOME4 distinguish the effects<br />
of CO 2 and climate on glacial LAIs. Results Modern<br />
LAIs are skilfully predicted (r(2) = 0.83). Data<br />
and BIOME4 indicate that LAIs at the LGM were up<br />
to 12% lower than modern values in eastern North<br />
America and 60-94% lower in Beringia. In eastern<br />
North America, LGM climates partially counteracted<br />
CO 2-driven decreases in LAI, while in Beringia<br />
both contributed to lowered LAIs. Main conclusions<br />
In both regions climate is the primary<br />
driver of LGM LAIs. <strong>The</strong> decline in eastern North<br />
America LAIs is smaller than previously reported,<br />
so regional vegetation feedbacks to LGM climate<br />
may have been less significant than previously<br />
supposed. CO 2 exerts both physiological and community<br />
effects upon LAI, by regulating resource<br />
availability for leaf production and by influencing<br />
the competitive balance among species and hence<br />
the composition and structure of plant communities.<br />
Pollen-based reconstructions using analogue<br />
methods do not incorporate the physiological effect<br />
and so are upper estimates of full-glacial LAIs.<br />
BIOME4 sensitivity experiments indicate that the<br />
community and physiological effects together<br />
caused 10% to 20% decrease in LAIs at the LGM, so<br />
simulated RLAIs that are 80-100% of reconstructed<br />
RLAIs are regarded as consistent with data.<br />
<strong>Global</strong> Ecology and Biogeography, 2008, V17, N1,<br />
JAN, pp 122-134.<br />
08.1-379<br />
A matter of divergence: Tracking recent warming<br />
at hemispheric scales using tree ring data<br />
Wilson R, D’arrigo R, Buckley B, Büntgen U, Esper J,<br />
Frank D, Luckman B, Payette S, Vose R, Youngblut D<br />
Scotland, USA, Switzerland, Canada<br />
Paleontology , Meteorology & Atmospheric Sciences<br />
, Plant Sciences , Forestry<br />
No current tree ring (TR) based reconstruction of<br />
extratropical Northern Hemisphere (ENH) temperatures<br />
that extends into the 1990s captures the<br />
full range of late 20th century warming observed<br />
in the instrumental record. Over recent decades,<br />
a divergence between cooler reconstructed and<br />
warmer instrumental large-scale temperatures<br />
is observed. We hypothesize that this problem is<br />
partly related to the fact that some of the constituent<br />
chronologies used for previous reconstructions<br />
show divergence against local temperatures<br />
in the recent period. In this study, we compiled TR<br />
data and published local /regional reconstructions<br />
that show no divergence against local temperatures.<br />
<strong>The</strong>se data have not been included in other<br />
large-scale temperature reconstructions. Utilizing<br />
this data set, we developed a new, completely<br />
independent reconstruction of ENH annual temperatures<br />
(1750-2000). This record is not meant to<br />
replace existing reconstructions but allows some<br />
degree of independent validation of these earlier<br />
studies as well as demonstrating that TR data can<br />
better model recent warming at large scales when<br />
careful selection of constituent chronologies is<br />
made at the local scale. Although the new series<br />
tracks the increase in ENH annual temperatures<br />
over the last few decades better than any existing<br />
reconstruction, it still slightly under predicts<br />
values in the post-1988 period. We finally discuss<br />
possible reasons why it is so difficult to model<br />
post- mid-1980s warming, provide some possible<br />
alternative approaches with regards to the instrumental<br />
target and detail several recommendations<br />
that should be followed in future large-scale<br />
reconstruction attempts that may result in more<br />
robust temperature estimates.<br />
Journal of Geophysical Research Atmospheres,<br />
2007, V112, ND17, SEP 11 ARTN: D17103.<br />
08.1-380<br />
Relation between rock uplift and denudation<br />
from cosmogenic nuclides in river sediment in<br />
the Central Alps of Switzerland<br />
Wittmann H, von Blanckenburg F, Kruesmann T,<br />
Norton K P, Kubik P W<br />
Switzerland, Germany<br />
Geology , Paleontology , Cryology / Glaciology<br />
A north-south traverse through the <strong>Swiss</strong> Central<br />
Alps reveals that denudation rates correlate with<br />
recent rock uplift rates in both magnitude and<br />
spatial distribution. This result emerges from a<br />
study of in situ-produced cosmogenic Be-10 in riverborne<br />
quartz in Central Alpine catchments. As a<br />
prerequisite, we took care to investigate the potential<br />
influence of shielding from cosmic rays due<br />
to snow, glaciers, and topographic obstructions;<br />
to calculate a possible memory from Last Glacial<br />
Maximum (LGM) glaciation; and to identify a<br />
watershed size that is appropriate for systematic