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| Titel |
Changes in the northern Adriatic molluscan community from the Holocene transgression up to the present |
| VerfasserIn |
Ivo Gallmetzer, Alexandra Haselmair, Adam Tomašových, Michael Stachowitsch, Martin Zuschin |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127497
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| Publikation (Nr.) |
 EGU/EGU2016-7380.pdf |
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| Zusammenfassung |
| The northern Adriatic Sea is one of the few modern, epicontinental seas comparable to typical
Palaeozoic shelf environments. It has a shallow average water depth (<50 m) and was formed
at the end of the last glaciation when the sea level rose. Since historical times this part of the
Adriatic has been strongly influenced by human activities through multiple direct or indirect
impacts (e.g. fishing, coastal building development, pollution, eutrophication, increased
sedimentation), making it one of the most degraded marine ecosystems worldwide. Our study
was designed to reconstruct major environmental changes here since the onset of the
Holocene transgression using down-core changes in death assemblages of molluscs as
indicators for ecological shifts. The sediment cores were taken at three different
stations (Brijuni Islands, Croatia, off Piran, Slovenia, and off Venice, Italy), each
representative of specific sediment and nutrient conditions and degrees of habitat
exploitation. The cores were 1.5 m long and had diameters of 90 or 160 mm. For the
molluscan shell analyses, sediment subsamples were examined for species composition,
abundance, taxonomic similarity and ecological interactions (e.g. frequencies of drilling
predation). In total, 98,700 valves and shells were investigated and 113 bivalve and 178
gastropod species recorded. Sedimentation rates derived from 210Pb dating are
very low, between 0.15 cm/yr at Brijuni and 0.25 cm/yr at Piran. The dating of
Lucinella divaricata, Timoclea ovata and Gouldia minima shells with 14C calibrated
amino-acid racemisation (AAR) revealed that the cores at all three stations cover
at least 6000 to 8000 years, i.e. the whole Holocene transgression period. Time
averaging is high, especially in the lower core layers of Piran station, probably due to
strong bioturbation. Surface mixed-layer assemblages tend to show right-skewed
postmortem age-frequency distributions, whereas subsurface assemblages show
unimodal or uniform shapes. Molluscan assemblages show significant interregional
differences that correlate with sedimentation rate, grain size, and the occurrence of
organic pollutants and heavy metals. Down-core changes in molluscan communities
are also conspicuous in all cores. They partly reflect long-term changes in water
depth, vegetation cover or grain size distribution caused by natural fluctuations of
environmental conditions over the past millennia. In the uppermost core layers,
however, these changes can be interpreted as indicators of anthropogenic impacts. |
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