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| Titel |
The Eocene Arctic Azolla phenomenon: species composition, temporal range and geographic extent. |
| VerfasserIn |
Margaret Collinson, Judith Barke, Johan van der Burgh, Johanna van Konijnenburg-van Cittert, Martin Pearce, Jonathan Bujak, Henk Brinkhuis |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037648
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| Zusammenfassung |
| Azolla is a free-floating freshwater fern that is renowned for its rapid vegetative spread and
invasive biology, being one of the world’s fastest growing aquatic macrophytes. Two species
of this plant have been shown to have bloomed and reproduced in enormous numbers in the
latest Early to earliest Middle Eocene of the Arctic Ocean and North Sea based on samples
from IODP cores from the Lomonosov Ridge (Arctic) and from outcrops in Denmark
(Collinson et al 2009 a,b Review of Palaeobotany and Palynology 155,1-14; and
doi:10.1016/j.revpalbo.2009.12.001). To determine the geographic and temporal extent of
this Azolla phenomenon, and the spatial distribution of the different species, we have
examined samples from 15 additional sites using material from ODP cores and commercial
exploration wells. The sites range from the Sub-Arctic (Northern Alaska and Canadian
Beaufort Mackenzie Basin) to the Nordic Seas (Norwegian-Greenland Sea and North Sea
Basin).
Our data show that the Azolla phenomenon involved at least three species. These are
distinguished by characters of the megaspore apparatus (e.g. megaspore wall, floats, filosum)
and the microspore massulae (e.g. glochidia fluke tips). The Lomonosov Ridge (Arctic) and
Danish occurrences are monotypic but in other sites more than one species co-existed. The
attachment to one another and the co-occurrence of megaspore apparatus and microspore
massulae, combined with evidence that these spores were shed at the fully mature stage of
their life cycle, shows that the Azolla remains were not transported over long distances, a fact
which could not be assumed from isolated massula fragments alone. Our evidence, therefore,
shows that Azolla plants grew on the ocean surfaces for approximately 1.2 million years
(from 49.3 to 48.1 Ma) and that the Azolla phenomenon covered the area from Denmark
northwards across the North Sea Basin and the whole of the Arctic and Nordic seas.
Apparently, early Middle Eocene Northern Hemisphere middle and high latitude
environmental conditions were suitable for simultaneous widespread proliferation of
several Azolla species. This episode coincides with the termination of a period
known as the ‘Early Eocene Climatic Optimum’ (EECO). Both field data and general
circulation/climate model experiments invoke high precipitation conditions for the EECO and
these might have aided in the onset of massive Azolla proliferation in the Northern
Hemisphere. |
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