Global Change Abstracts The Swiss Contribution - SCNAT
Global Change Abstracts The Swiss Contribution - SCNAT
Global Change Abstracts The Swiss Contribution - SCNAT
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
168 <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 />
08.1-341<br />
Excess air as a potential tracer for paleohydrological<br />
conditions<br />
Klump S, Grundl T, Purtschert R, Kipfer R<br />
Switzerland, USA<br />
Paleontology , Hydrology , Geochemistry & Geophysics<br />
Geochimica et Cosmochimica Acta, 2007, V71, N15,<br />
AUG, SS, p A497.<br />
08.1-342<br />
Bedrock landsliding, river incision, and<br />
transience of geomorphic hillslope-channel<br />
coupling: Evidence from inner gorges in the<br />
<strong>Swiss</strong> Alps<br />
Korup O, Schlunegger F<br />
Switzerland<br />
Paleontology , Geomorphology , Geology<br />
<strong>The</strong> formation of inner gorges cut into bedrock<br />
has been explained as relief rejuvenation by fluvial<br />
incision in response to rapid base level drop,<br />
repeated glaciations, frequent pore pressuredriven<br />
landsliding focused at hillslope toes, or<br />
catastrophic outburst flows from natural dam<br />
failures. Prominent inner gorges occur in soft<br />
Mesozoic Bundner schist and lower Tertiary<br />
flysch units of the formerly glaciated Alpenrhein<br />
catchment, eastern <strong>Swiss</strong> Alps. <strong>The</strong>ir channel and<br />
hillslope morphologies differ from basins characterized<br />
by strong glacial or landslide imprints,<br />
while formally resembling the theoretically predicted<br />
transient response of detachment-limited<br />
bedrock rivers to rapid base level fall by headward<br />
knickpoint migration. Assuming a postglacial onset<br />
of fluvial bedrock incision into a Last Glacial<br />
Maximum surface in response to base level drop<br />
induced by downwasting of trunk valley glaciers<br />
requires downcutting rates E > 20 mm yr(-1) and<br />
requires hillslopes to adjust by frequent landsliding<br />
toward development of a threshold state. We<br />
test this scenario using data on surface uplift,<br />
geomorphometry, geomorphic hillslope coupling,<br />
and probabilistic slope stability models. We find<br />
that adjustment of inner gorge walls through<br />
landsliding is mainly strength limited and structurally<br />
controlled, and threshold conditions are<br />
restricted to the lower 25% of local hillslope relief.<br />
Mass movement processes on upper hillslopes remain<br />
largely decoupled from channel incision despite<br />
inferred postglacial specific sediment yields<br />
of 10(4) m(3) km(-2) yr(-1) from the studied basins.<br />
Conversely, several constraints imposed by fluvial<br />
bedrock detachment, postglacial sediment yields,<br />
and bedrock landsliding argue for a pre-Holocene<br />
origin for at least some of the inner gorges in the<br />
area. This implies partial protection of fluvial<br />
gorge topography by subglacial sediment fill during<br />
the last (Wurm) extensive glaciation and implies<br />
that glaciers were insufficient to fully eradicate<br />
fluvially sculpted bedrock topography. This<br />
leads us to conclude that lithology and major climate<br />
oscillations should be considered as further<br />
alternative controls on inner gorge formation.<br />
Journal of Geophysical Research Earth Surface,<br />
2007, V112, NF3, SEP 27 ARTN: F03027.<br />
08.1-343<br />
Millenial scale variations of the isotopic composition<br />
of atmospheric oxygen over Marine<br />
Isotopic Stage 4<br />
Landais A, Masson Delmotte V, Combourieu<br />
Nebout N, Jouzel J, Blunier T, Leuenberger M, Dahl<br />
Jensen D, Johnsen S<br />
Israel, France, Switzerland, Denmark<br />
Meteorology & Atmospheric Sciences , Paleontology<br />
, Cryology / Glaciology , Geochemistry &<br />
Geophysics<br />
During rapid events of the last glacial period (DO<br />
events), dramatic changes are recorded at high<br />
and low latitudes. Without a precise common<br />
timescale, links between changes in Greenland<br />
temperature and changes in biosphere productivity,<br />
hydrology regimes and sea level are difficult<br />
to establish. <strong>The</strong> composition of atmospheric<br />
oxygen (delta O-18(atm)) is influenced by global<br />
sea level changes, the global hydrologic cycle and<br />
the biosphere productivity. Since delta O-18(atm)<br />
is measured in ice cores it gives the opportunity<br />
to investigate the underlying processes with no<br />
timescale uncertainty. Here, we present the first<br />
high resolution (50 yrs) record of the isotopic composition<br />
of atmospheric oxygen (delta O-19(atm))<br />
measured in the air trapped in a Greenland ice<br />
core (NorthGRIP). Our record covers a sequence of<br />
DO events (18-19-20) corresponding to the Marine<br />
Isotopic Stage 4, similar to 75 to 60 ka ago. Our<br />
measurements reveal rapid changes of delta O-<br />
18(atm) associated with the DO events. With a few<br />
additional measurements of the third isotope of<br />
oxygen (O-17) during the DO event 19, we exclude<br />
the hypothesis that sea level changes are responsible<br />
for the isotopic variations. <strong>The</strong>y originate<br />
more likely from large changes in relative humidity<br />
and latitudinal repartition of the continental<br />
vegetation over the DO events.<br />
Earth and Planetary Science Letters, 2007, V258,<br />
N1-2, JUN 15, pp 101-113.