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| Titel |
Planktic foraminiferal assemblages from laminated sediments of the northeastern Arabian Sea: a high-resolution study over the last two millennia |
| VerfasserIn |
Philipp Munz, Andreas Lückge, Michael Siccha, Michal Kucera, Hartmut Schulz |
| 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 |
250097958
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| Publikation (Nr.) |
 EGU/EGU2014-13588.pdf |
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| Zusammenfassung |
| Modern planktic foraminiferal assemblages in the Arabian Sea are largely controlled by
seasonal shifts of surface water properties. Boreal summer (June–September) heating of the
Asian landmass and Tibetan Plateau leads to northward migration of the ITCZ and develops
an intense atmospheric pressure gradient. Strong monsoonal winds from the southwest lead to
coastal- and open ocean upwelling, especially in the western Arabian Sea along the coast of
Somalia and Oman. Opposite directed dry and cold winds lead to deep convective mixing
during boreal winter (January–March) and breakup of the thermal stratification. Deepening of
the mixed-layer thus enables nutrient transport into the photic zone with enhanced primary
production.
Here we study planktic foraminiferal assemblages from the dominantly winter monsoon
controlled Pakistan Margin off Karachi. We sampled annually laminated sediments from box
core SO90-39KG and ca. 2-m-long piston core SO130-275KL from the same station. High
sedimentation rates and varve-like lamination provides a particular record with very precise
age control. Box core 39KG offers a record of the last 100 years with 2-year-resolution and
275KL provides a ca. 10-year-resolution during the last 2100 years. We calculated
foraminiferal flux rates after photometric identification and subtraction of light-colored event
layers, consisting solely of terrigeneous matter to enable comparison with flux rates from
sediment trap stations.
We identified a total of 28 planktic foraminiferal (PF) species/morphotypes in the fraction
>150μm. During the relatively short period of the past two millennia, several species showed
comparatively large fluctuations on decadal time scales, not seen in bioturbated records.
Globigerina bulloides, a species generally associated with high primary production rates,
fluctuates between ca. 10% and 45%. Highest relative share was observed during periods
1593–1413, 1023–923, 483–393, 63– -7 years AD. Average PF accumulation rates follow a
general decreasing trend from ca. 30,000 individuals cm-2 kyr-1 at 100 years BC to 9,000
ind. cm-2 kyr-1 at 1890 years AD, suggesting a decrease in absolute PF production. |
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