Global Change Abstracts The Swiss Contribution - SCNAT

164 Global Change Abstracts – The Swiss Contribution | Past Global Changes
08.1-327
Carbon dioxide release from the North Pacific
abyss during the last deglaciation
Galbraith E D, Jaccard S L, Pedersen T F, Sigman D
M, Haug G H, Cook M, Southon J R, Francois R
Canada, USA, Switzerland
Paleontology , Meteorology & Atmospheric
Sciences , Oceanography
Atmospheric carbon dioxide concentrations were
significantly lower during glacial periods than
during intervening interglacial periods, but the
mechanisms responsible for this difference remain
uncertain. Many recent explanations call
on greater carbon storage in a poorly ventilated
deep ocean during glacial periods(1-5), but direct
evidence regarding the ventilation and respired
carbon content of the glacial deep ocean is sparse
and often equivocal(6). Here we present sedimentary
geochemical records from sites spanning the
deep subarctic Pacific that-together with previously
published results(7)- show that a poorly ventilated
water mass containing a high concentration
of respired carbon dioxide occupied the North Pacific
abyss during the Last Glacial Maximum. Despite
an inferred increase in deep Southern Ocean
ventilation during the first step of the deglaciation
(18,000-15,000 years ago)(4,8), we find no
evidence for improved ventilation in the abyssal
subarctic Pacific until a rapid transition similar
to 14,600 years ago: this change was accompanied
by an acceleration of export production from the
surface waters above but only a small increase in
atmospheric carbon dioxide concentration (8). We
speculate that these changes were mechanistically
linked to a roughly coeval increase in deep water
formation in the North Atlantic (9-11), which
flushed respired carbon dioxide from northern
abyssal waters, but also increased the supply of
nutrients to the upper ocean, leading to greater
carbon dioxide sequestration at mid-depths and
stalling the rise of atmospheric carbon dioxide
concentrations. Our findings are qualitatively
consistent with hypotheses invoking a deglacial
flushing of respired carbon dioxide from an isolated,
deep ocean reservoir(1-5,12), but suggest that
the reservoir may have been released in stages,
as vigorous deep water ventilation switched between
North Atlantic and Southern Ocean source
regions.
Nature, 2007, V449, N7164, OCT 18, pp 890-U9.
08.1-328
Smithian-Spathian boundary event: Evidence
for global climatic change in the wake of the
end-Permian biotic crisis
Galfetti T, Hochuli P A, Brayard A, Bucher H, Weissert
H, Vigran J O
Switzerland, France
Meteorology & Atmospheric Sciences , Paleontology
, Geology
One of the most important carbon cycle perturbations
following the end-Permian mass extinction
event straddles the Smithian-Spathian boundary
(SSB) (Olenekian, Early Triassic). This anomaly
is characterized by a prominent positive carbon
isotope excursion known from Tethyan marine
rocks. Its global significance is established here
by a new high paleolatitude record (Spitsbergen).
Paleontological evidence, such as Boreal palynological
data (Barents Sea, Norway) and global patterns
of ammonoid distribution, indicates a synchronous
major change in terrestrial and marine
ecosystems near the SSB. The reestablishment of
highly diverse plant ecosystems, including the
rise of woody gymnosperms and decline of the
formerly dominating lycopods, is interpreted as
an effect of a major climate change. This hypothesis
is supported by modeling of ammonoid paleobiogeography,
the distribution patterns of which
are interpreted as a proxy for sea surface temperatures
(SST). The latest Smithian thus appears to
have been a time of a warm and equable climate
as expressed by an almost flat pole to equator SST
gradient. In contrast, the steep Spathian SST gradient
suggests latitudinally differentiated climatic
conditions. We propose that this drastic climate
change and the global carbon cycle perturbation
were triggered by a massive end-Smithian CO 2 injection.
The SSB event could therefore represent
one of the causes for stepwise and delayed recovery
of marine and terrestrial biotas in the wake of
the end- Permian biotic crisis.
Geology, 2007, V35, N4, APR, pp 291-294.
08.1-329
Dating of syngenetic ice wedges in permafrost
with Cl-36
Gilichinsky D A, Nolte E, Basilyan A E, Beer J, Blinov
A V, Lazarev V E, Kholodov A L, Meyer H, Nikolskiy
P A, Schirrmeister L, Tumskoy V E
Russia, Germany, Switzerland
Cryology / Glaciology , Paleontology
A new method of permafrost dating with the cosmogenic
radionuclide Cl-36 is presented. In the
first application, syngenetic ice wedges are dated
using the ratio of Cl-36 and Cl concentrations in
ice as the signal. Cl-36 is produced in the atmo-