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| Titel |
Holocene paleoceanography of Disko Bugt area, west Greenland |
| VerfasserIn |
Marie-Michèle Ouellet-Bernier, Anne de Vernal, Matthias Moros, Claude Hillaire-Marcel |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097351
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| Publikation (Nr.) |
 EGU/EGU2014-12922.pdf |
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| Zusammenfassung |
| Micropaleontological, palynological and isotopic analyses of sediment core MSM343300
(68°28,311’N, 54°00,118’W; 519 m water depth) raised off Disko Bugt area (West
Greenland) were undertaken in order to document Holocene paleoceanographical changes in
the Eastern Baffin bay, at a site now influenced by the Western Greenland Current.
Palynological analyses were performed with special attention paid to dinocysts in
order to characterize sea-surface conditions whereas isotopic analyses on benthic
foraminifers aimed at documenting the "deep" water mass bathing the shelf edge.
Palynological assemblages are largely dominated by dinocysts, which suggest high
pelagic productivity during the Middle and Late Holocene. The assemblages are
dominated by Islandinium minutum accompanied of the cyst of Pentapharsodinium
dalei, Brigantedinium spp., Operculodinium centrocarpum, Spiniferites elongatus,
Selenopemphix quanta and Islandinium? cezare. The application of the Modern analogue
technique (MAT) highlighted a major change in sea-surface conditions at ~7300 cal. yr
BP.
Harsh conditions with dense sea-ice cover, low temperature and low productivity
prevailed at surface from at least ~ 10 000 (age of core bottom) until ~7300 cal. yr BP with a
large dominance of Islandinium minutum in the dinocyst assemblages. The overall
low productivity resulted in low benthic foraminiferal abundances. However a few
benchmark isotopic values could be obtained. At ~10 000 cal. yr BP, delta 18O
values near +4opointed to the presence of cold and relatively saline waters at
the sea floor. A short interval corresponding to a large amplitude 13C excursion
is recorded at ~8200 cal. yr BP, with deltagalues as low as -4.5 and -6.03oin
Islandiella norcrossi and Nonionella labradorica, respectively, whereas 13C content in
total sedimentary organic carbon did not vary much from the background value
of ~ -22o. We tentatively concluded at some linkage with a sea floor methane
burst.
Postglacial conditions in surface waters were recorded from ~7300 cal. yr BP, with a
dinocyst diversity rise and increasing reconstructed summer temperatures, linked to incoming
West Greenland Current waters. This late settlement of interglacial conditions was
probably due to important discharge of ice and meltwaters from the Greenland
ice sheet (GIS) mostly through the Jakobshavn Isbrae. After a gradual transition,
optimal conditions were finally achieved at ~6000 cal. yr BP. Accordingly, 18O
values in Islandiella norcrossi showed a slight decrease from ~6000 to ~4900
cal. yr BP that might correspond to a temperature rise (-¤1°C) and/or a salinity
decrease in the sub-surface water mass occupying the sea-floor of the study site.
Cooling pulses were then recorded at ~4200-4000 and ~1500-1000 cal. yr BP. I.
norcrossi depicted slightly increasing 18O-contents between ~2100 and ~1100 cal. yr
BP, thus matching broadly the later cooler interval. Surface temperature finally
increased from ~1000 to ~800 cal. yr BP, initiating the Medieval Warm Period with a
reconstructed mean summer temperature of 10°C, while it is presently of ~4.4°C at the
site.
Throughout the postglacial, there is an opposition between SSTs and surface salinity, with
warmer intervals being characterized by more diluted surface waters, resulting from
higher freshwater discharge along the ice margin and notably the Jakobshavn Isbrae. |
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