Dear ISOGEOCHEM

Talbot & Johannessen (1992) show that nitrogen- and carbon-isotope ratios in lacustrine
organic matter are in general synchronous, so that as 15N increases 13C increases.
However, both isotopic systems are being controlled by two different parameters, namely,
nitrate/denitrification and plant material respectively.

A recent paper by Holmes et al. (1997) indicate in Fig 4. that this is predominantly not
the case. In general a positive delta 15N shift corresponds to a negative delta 13C shift.
However, there are a few exceptions to this trend.

My question is whether this trend is reflected by the variation in the environmental
regimes, since the ocean is predominantly controlled by zoo-/phyto-plankton and nitrate
availability?

Therefore, am I correct in stating that an increase in 15N corresponds with a decrease in
NO3- and an increase in N2O, which represents an oxic ocean setting and hence, more negative
delta 13C values; and vice versa decreasing 15N, increasing NO3-, decreasing N2O and
anoxia.  I'M ready to be hammered.......................

Tschuess

        Darren

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Darren R. Grocke

Department of Earth Sciences
University of Oxford
Parks Road
Oxford OX1 3PR
UNITED KINGDOM

Phone: +44 1865 272 019
Fax: +44 1865 272 072
E-mail: [log in to unmask]
http://www.earth.ox.ac.uk/~darreng/
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