Geoscience Reference
In-Depth Information
(in general up to 20-30%), and later on a drastic decrease to 5% (e.g.
Diploneis
dombilitiensis
), is noteworthy.
The diatom record shows substantial differences within this subzone. In the lower
part marine-brackish and brackish-marine forms predominate similar to the preced-
ing unit. In the central part an increase in freshwater taxa from ca. 10% up to ca.
35% is observed, but then decrease to 2% at the B4/B5 limit. The most abundant of
them is the planktonic species
A. islandica
. More brackish preferring species reveal
a similar trend. Here the
P. calcar-avis
dominates; its content increases towards the
top where it reaches its maximum abundance. Likewise the percentage of
T. nitzs-
chioides
is high, but it shows a decrease towards the next subunit from ca. 40% to
only 5% at a depth of 94 cm.
Zone B5 (94-48 cm)
In this subzone, brackish-marine planktonic diatoms are the most abundant species,
but their content decreases towards the core top. A slight increase in benthic
diatoms is observed in this subzone. This small increase continues also in zone
B6. In addition, we can see an increase in brackish and brackish-fresh diatoms.
T. nitzschioides
,
A. octonarius
and
A. islandica
show a strong decline, whereas
P. calcar-avis
increases initially though its content finally decreases from c.a. 60
to 35%. An interesting feature is the appearing of sea-ice species, which reach
up to 7%, and indicate inflow of cold, marine water, e.g.
Fragilariopsis cylindrus
(Grunow) Krieger and
Pauliella taeniata
(Grunow) Round and Basson.
Zone B6 (48-20 cm)
The lower part of this subzone is still dominated by brackish-marine plank-
tonic species, although they show a strong upward decreasing trend. In general
taxa of higher salinity requirements decrease. Regarding salinity in zone B6,
brackish-fresh, brackish and brackish-marine species (
P. calcar-avis, A. octonar-
ius
,
Thalassiosira baltica
(Grunow) Ostenfeld) are dominants, respectively, in the
uppermost part. Notable is a steady increase of halophilus taxa, which according
ity between 0.18 and 0.9 psu, e.g.
Aulacoseira granulata
(Ehrenberg) Simonsen,
Pseudostaurosira brevistriata
(Grunow in Van Heurck) Williams and Round,
Staurosira construens
var
. binodis
Ehrenberg. Characteristic for this subzone is also
very low percentages of the marine
T. nitzschioides
.
We cannot exclude that the diatom flora composition (which abundance is very
low in this subzone) is affected by sediment disturbance caused by coring procedure
or a gravity slide in zone B6 indicated by the sediment texture in the uppermost part
of the core.
5.5.5 Periodicity (Frequency) Analysis
In order to investigate if the periodical facies changes have regional or even global
signatures, we have carried out periodicity analysis of two proxy variables: p-wave
