Geoscience Reference
In-Depth Information
Krammer, and
Stephanodiscus alpinus
Hustedt are dominant. The above-
enumerated taxa are planktonic and the content of benthic ones is low. However, at
the depth of 436 cm a drastic decrease in the content of planktonic forms is observed.
They are replaced by benthic, typical freshwater forms showing in that part of the
profile their maximum abundance, e.g.
Cymatopleura elliptica
(Brebisson) Smith,
Diploneis dombilitensis
(Ehrenberg) Cleve,
Gyrosigma attenuatum
(Kützing) Cleve.
At the boundary between zones A and B a distinct change in diatom preferences
with respect to salinity can be observed.
Zone B1 (417-354 cm)
In this subzone a major decrease in benthic forms is recorded with planktonic
forms becoming the most abundant ones. They reach up to 90% of relative abun-
dance at the B1/B2 boundary. In the lower part of the subzone still freshwater and
brackish water forms dominate. At the depth of ca. 380 cm a drastic increase of
brackish-marine and marine-brackish forms and simultaneously a drastic decrease
of freshwater species is recorded. Dominant above this depth a rapid increase
in relative abundance in marine planktonic forms, e.g.
Pseudosolenia calcar-
avis
(Schultze) Sundstrom,
Thalassionema nitzschioides
(Grunow) Grunow, is
observed. There are also indicator species implying inflow of warm oceanic waters,
e.g.
Actinocyclus octonarius
Ehrenberg and
Thalassiosira oestrupii
(Ostenfeld)
Hasle.
Zone B2 (354-333 cm)
In this subzone a significant increase of freshwater, planktonic diatoms, e.g.
A. islandica
, is observed. It is accompanied with a decrease in brackish-marine and
marine-brackish diatoms. The hitherto dominant marine-brackish and brackish-
marine species, such as
P. calcar-avis
and
T. nitzschioides
, decrease. Freshwater
diatom species which often occur together with diatoms living in more salty waters
increase in this subzone.
Zone B3 (333-250 cm)
Marine, marine-brackish, planktonic forms reaching up to 65% strongly dominate
the diatom record. The most abundant of them is the marine species
T. nitzschioides
,
but a decrease in its abundance is observed at a depth of ca. 285 cm. At the same
time a clear but also temporary increase of brackish-marine and brackish species is
noted, e.g.
P. calcar-avis
and
A. octonarius.
In this unit a general increase in marine
diatoms is recorded, e.g.
T. oestrupii.
Zone B4 (250-94 cm)
Planktonic forms dominate in this zone, but their abundance decreases systemati-
cally up to 52% at the depth of ca. 130 cm, followed by an upward increase and
amounts to 80% at the B4/B5 limit. An increase in the content of benthic species
