Dear Dr Forizs,

Isotopic stratification in lake waters is known to occur in summer, when
the thermocline prevents vertical mixing and therefore surface water
becomes slightly enriched in heavy isotopes. This has been observed in many
cases, but not much is reported in the literature.

However, in the case of a shallow lake as Lake Balaton, I believe that you
cannot expect such a stratification: winds are usually sufficient to keep
the water column well mixed. You may rather expect that horizontal mixing
is insufficient. For example, a difference in isotopic composition was
observed in a similar lake, the Neusiedlersee (which is also not too far
from Lake Balaton), between a zone of reeds and the open lake: in reeds,
during summer the water was more enriched in heavy isotopes of about 10-15
per mil in deuterium, which corresponds to about 2-3 per mil in O-18.
(Zimmermann & Ehhalt (1970): Stable isotopes in the study of water balance
of Lake Neusiedl, Austria. In: Isotope Hydrology 1970, IAEA, Vienna,
pp.129-138). This enrichment can be explained theoretically, but
essentially is due to the fact that reeds hinder horizontal mixing.

I do not know whether this helps to explain your data. If however you want
to compare with the situation in Lake Neusiedl, I suggest you to get in
touch with Dr. Dieter Rank in Vienna ([log in to unmask]). Dieter has
continued to study the Neusiedlersee and he should be able to tell you
more, and provide his publications on the lake (whose references I do not
have at hand, in this moment).

Roberto Gonfiantini



At 08.21 27/04/2005 +0200, you wrote:
>Dear Listmembers,
>
>could any of you tell me a publication about the vertical d18O profile
>of lake water (if there is any)?
>I think that during strong evaporation the uppermost warm water layer is
>enriched in 18O, but I do not know any published data.
>
>Best regards
>Istvan Forizs
>
>
>--
>-------------------------------------------------------------------------
>Dr. FÓRIZS István ......... Istvan FORIZS Ph.D.
>Magyar Tudományos Akadémia, Geokémiai Kutatóintézet
>Institute for Geochemical Research, Hungarian Academy of Sciences
>Cím/Address: H-1112 Budapest, Budaörsi út 45.   Hungary
>Tel./Phone: (36-1)-309-2600/ mellék/extension 1151
>Fax: (36-1)-319-3137
>Http://www.geokemia.hu/people/forizs_hu.html
>-------------------------------------------------------------------------

Prof. Roberto Gonfiantini
Istituto di Geoscienze e Georisorse
Institute of Geosciences and Georesources
Area della Ricerca del CNR
Via G. Moruzzi, 1
I-56124 Pisa
Italy
Phone +39-050-315-2358
e-mail [log in to unmask]