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| Titel |
The Big Freeze: Diatoms record Arctic sea ice at 47 Ma |
| VerfasserIn |
C. E. Stickley, N. Koc |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250020317
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| Zusammenfassung |
| Early middle Eocene (50-45 Ma) oceanic sediments drilled by Integrated Ocean Drilling
Program (IODP) Expedition 302, “The Arctic Coring Expedition” (ACEX) contain abundant
marine and freshwater siliceous microfossils. Diatoms are the most diverse group and
comprise, on the whole, endemic and typically heavily silicified Paleogene assemblages
characterised by Hemiaulus spp. Surprisingly, species of the finely silicified diatom
Synedropsis are also preserved from 47 Ma, contributing up to 60% of the assemblages and
with colony integrity commonly still intact. We show from multiple lines of evidence that, as
for extant species of this genus, Synedropsis spp. were dwelling in sea ice rather than
components of the sea ice-associated plankton. This discovery is unusual since sea ice
dwelling diatoms are generally too delicate to be preserved in the fossil record.
Their presence in the ACEX sediments predates existing sea ice-related diatom
records by 16 Myr in Antarctica and by 37 Myr in the (sub)Arctic. The ACEX
Synedropsis spp. therefore represent the earliest known fossil record of sea ice
diatoms.
One of the earlier key results of ACEX had been the unexpected discovery of ice rafted
debris (IRD) in long core sediments dating back to the middle Eocene (46 Ma)
(Moran et al., 2006, Nature, 441; St. John, 2008, Paleoceanography, 23). Although
IRD transportation by both icebergs (glacial) and sea ice was acknowledged in
these earlier works no further attempt was made to define which type of ice was
dominant or the temporal significance of either. Synedropsis spp. not only prove that sea
ice was present in the middle Eocene Arctic since 47 Ma, but that it was stable
enough to have supported a significant biomass at this time. Our data record the
critical transition from an ice-free to a sea ice-dominated environment at the very
start of the long term Cenozoic climatic cooling trend. Importantly, Synedropsis
spp. may be a means by which to determine the extent of middle Eocene sea ice in
the central Arctic and its temporal fluctuations during this critical phase. Since
very little is still known about the early sea ice history of the region, this makes
an important contribution towards understanding the past cryospheric patterns of
the region, and will be invaluable for planning future drilling projects to the area. |
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