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Fig. 14. Carbonate stable oxygen and carbon isotope depth profiles of the top 7 mm of a tufa stromatolite from the
lower section of the Westerh¨fer Bach (site WB4, 19.10.2007), and calculated palaeo-water temperatures. For
comparison, measured stream water temperatures of this site for May 2006, August 2006 and January 2007 are indicated
as dashed lines. Left hand side shows a cross polar view of the thin section analysed, with dense layers appearing darker
(D) and porous layer appearing lighter (P). From Shiraishi et al. (2008b), modified, with permission of Elsevier Ltd.
England, Belgium and France) appear to be
'reversed' to that of other locations and studies
(e.g. Germany, Japan) (Kano et al. 2003: 259).
This may partly reflect different methods applied
(palynomorphs: Geurts (1976: 18); insect larval
housings: Stirn (1964: 14); stable isotopes: Mat-
suoka et al. 2001; seasonal sampling: Kano et al.
2003). For example, the initial attempt to use of paly-
nomorphs for this purpose (Geurts 1976) has the
potential risk of a time shift between attachment of
pollen to the biofilm surface (e.g. in autumn) and
their incorporation into tufa laminae by calcification
(e.g. in the following spring time). Nonetheless,
porous-microsparitic and dense-microcrystalline
laminae may form at different seasons in different
places, possibly dependent on the kind of vegetation
(grassland, coniferous or deciduous woodland) and
corresponding shading at the sites in question.
For the Westerh ¨fer and Deinschwanger Bach,
seasonal sampling demonstrated that porous - micro-
sparitic form in winter - spring time and dense-
microcrystalline laminae in summer - autumn time
(Arp et al. 2001b), substantiated by the stable
oxygen isotope record (Shiraishi et al. 2008b). For
these both streams, spring discharge and chemical
composition reflect (seasonal and sporadic) changes
in rain fall in the catchment area. Strongest and
most regular seasonal fluctuations, however, have
been observed with respect to light irradiance and
stream water temperature. Although spot measure-
ments of irradiation show strong fluctuations for
single tufa-forming stream sites in the deciduous
woodlands, with values in October (after leaf fall)
commonly similar to values in June and July
(Fig. 15), the sum of irradiated light as dependent
on day length might be one steering variable in the
formation of seasonal laminae couplets. However,
temperature seems to be of greater significance.
Not only does it have an effect on physiological
activity of the microorganisms (e.g. the intensity
of photosynthesis; Bissett et al. 2008b), but also
on diffusion coefficients (specifically Ca
2þ
):
higher temperatures permit higher fluxes of Ca
2þ
because of increased diffusion rate, consequently
higher precipitation rate and formation of more
dense, microcrystalline laminae (Shiraishi et al.
2008b). Consequently, lamination in WB and DB
tufa stromatolites is considered to reflect seasonal
changes in irradiance (photosynthesis, biofilm
composition) and temperatures (diffusion coeffi-
cients). Similarly, Kano et al. (2003) interpret the
formation of dense summer - autumn laminae alter-
nating with porous winter - spring laminae in tufa
stromatolites of Shirokawa, Japan, as mainly
driven by differences in temperature. In any case,
a correct assignment of laminae to specific seasons
has to be achieved for each tufa - stromatolite-
forming stream by seasonal sampling (e.g. Kano
et al. 2003).
A second prerequisite for the interpretation of
palaeoclimate signals is that the proxies used, here
stable oxygen and carbon isotope ratios, reflect the
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