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Arbeitsgebiet:
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A new proxy
archive of climate change is established. By now shell material
collected alive from Finnish, Swedish and Norwegian rivers
is used.
The preparation for increment analysis includes embedding
of the shells in epoxy resin, cutting along the axis of maximum
growth and grinding and polishing of
the cross-sections. Immersion in Mutvei’s solution will reveal internal
growth patterns in the shells based on differential etching and staining. Then,
the samples are digitized and increment widths measured with image analysis software.
Inherent age-related growth trends are extracted from the chronologies. Growth
rates tend to decrease with increasing age. This age trend is estimated with
growth functions (Weibull or Hugershoff functions) or cubic splines. Age trend
removal is completed by dividing measured by predicted growth. Standardization
removes the high mean / variance correlation by transforming the non-stationary
data into a series of stationary growth (SGI data). The SGI chronology contains
information of temperature and food availability. SGI chronologies can be used
to verify other temperature proxy records. Growth records of different individuals
are combined with each other and overall growth patterns and cycles analyzed.
In addition, shells are micromilled for oxygen and stable carbon isotopes. The
polished shell sections are ultrasonically rinsed with demineralized water. Following
the shape of the growth increments, CaCO3 (aragonite) powder is milled between
two winter lines from youth portions in the outer shell layer under a stereomicroscope
at 20X magnification. Samples are analyzed with a continuous-flow mass spectrometer
equipped with a Gas Bench. The oxygen isotope composition of mollusk shells contains
useful paleoenvironmental information and is controlled by both the ∂18O
(∂18Owater) and the temperature of the ambient water in which the animals
live. Oxygen isotope ratios of shell aragonite (∂18Oshell) can be used
to calculate water temperatures if the ∂18Owater values are known.
Preliminary results convincingly demonstrate that a combined geochemical and
sclerochronological approach can provide reliable information on past continental
climate and climate cycles. Latter will also provide a look into the closer
future.
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