Global Change Abstracts The Swiss Contribution - SCNAT

162 Global Change Abstracts – The Swiss Contribution | Past Global Changes
Switzerland, Peoples R China
Paleontology , Marine & Freshwater Biology
Pennsylvanian phylloid algal reefs are widespread
and well exposed in south Guizhou, China. Here
we report on reefs ranging from 2 to 8 m thickness
and 30-50 m lateral extension. Algae, the
main components, display a wide spectrum of
growth forms, but are commonly cyathiform
(cup-shaped) and leaf-like (undulate plates). The
algal reef facies is dominated by boundstone. Algal
thalli form a dense carpet whose framework
pores are filled with marine cement and peloidal
micrite. The peloidal matrix is dense, partly laminated
or clotted with irregular surfaces and often
gravity defying. Algal reefs in Guizhou differ from
examples reported to date by the high biodiversity
of organisms other than phylloids: e.g., the
intergrowth of algae with corals (some of which
are twice the size of algal thalli) and numerous
large brachiopods. This contrasts to previous
views that phylloid algal “meadows” dominated
the actual seafloor, excluding other biota. Also,
the pervasive marine cements (up to 50%) including
botryoidal cement are noteworthy. Algal reefs
developed at platform margins, a depositional
environment similar to that of modern Halimeda
mounds in Java, Australia and off Bahamas, and to
that of time-equivalent examples reported from
the Canadian Arctic Archipelago. Whereas nutrients
appear decisive in the growth of Halimeda
reefs, algal reefs reported herein seemingly grew
under conditions of low nutrient levels. Overall,
algal reefs in Guizhou challenge previous views
on growth forms, diversity patterns, and depositional
environments and add to the spectrum of
these partly puzzling biogenic structures.
Facies, 2007, V53, N4, NOV, pp 615-623.
08.1-323
Long-term drought severity variations in
Morocco
Esper J, Frank D, Buentgen U, Verstege A, Luterbacher
J
Switzerland
Plant Sciences , Forestry , Meteorology & Atmospheric
Sciences , Paleontology
Cedrus atlantica ring width data are used to reconstruct
long-term changes in the Palmer Drought
Severity Index (PDSI) over the past 953 years in
Morocco, NW Africa. The reconstruction captures
the dry conditions since the 1980s well and places
this extreme period within a millennium-long
context. PDSI values were above average for most
of the 1450-1980 period, which let recent drought
appear exceptional. However, our results also indicate
that this pluvial episode of the past millen-
nium was preceded by generally drier conditions
back to 1049. Comparison of PDSI estimates with
large-scale pressure field reconstructions revealed
steady synoptic patterns for drought conditions
over the past 350 years. The long-term changes
from initially dry to pluvial to recent dry conditions
are similar to PDSI trends reported from N
America, and we suggest that they are related to
long-term temperature changes, potentially teleconnected
with ENSO variability and forced by
solar irradiance changes.
Geophysical Research Letters, 2007, V34, N17, SEP
5 ARTN: L17702.
08.1-324
Modern pollen assemblages as climate indicators
in southern Europe
Finsinger W, Heiri O, Valsecchi V, Tinner W,
Lotter A F
Netherlands, Switzerland
Meteorology & Atmospheric Sciences , Plant Sciences
, Paleontology
Aim and Location Our aim is to develop pollen-climate
inference models for southern Europe and
to test their performance and inference power by
cross-validation with modern climate data. Surface
sediments collected from lakes along a climate
gradient from the winter-cold/summer-wet
Alps to winter-wet/summer-dry Sicily were analysed
for modern pollen assemblages. Methods For
each lake, mean monthly temperatures, seasonal
precipitation and site-specific climate uncertainties
have been estimated. Pollen-climate relationships
were studied using numerical analyses, and
inference models were derived by partial least
squares (PLS) and weighted-averaging PLS (WA-PLS)
regressions for January and July temperatures (T),
and for winter, spring and summer precipitation
(P). In order to assess whether these variables are
also of ecological importance for vegetation in the
subregions, we split the data set into an Alpine
and a Mediterranean subset. Results Low bootstrap
cross-validated root mean square errors of
prediction (RMSEP) for January T (1.7 degrees C),
July T (2.1 degrees C) and summer P (38 mm), as
well as low RMSEPs expressed as a percentage of
the gradient length (8-9%), indicate a good inference
power. Models revealed excellent to good
performance statistics for January T, July T and
summer P (r(2)= 0.8), and for winter and spring P
(r(2) =c. 0.5). We show that the variables with the
highest explanatory power differ between the two
subregions. These are summer T and P for the Alpine
set, and January T, winter P and July T for the
Mediterranean set. Main conclusions The study
reveals the influence of climatic conditions dur-