Marine isotope stage 11 in the Eastern Mediterranean Sea: nearest analogue to the present day? [Elektronische Ressource] / vorgelegt von Lea Dagmar Numberger-Thuy

Tstegem

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2010
• Nombre de lectures: 34
• Langue: Deutsch
• Poids de l'ouvrage: 32 Mo

Extrait

Marine Isotope Stage 11 in the Eastern
Mediterranean Sea: nearest analogue to the present
day?







Dissertation
der Mathematisch-Naturwissenschaftlichen Fakultät
der Eberhard Karls Universität Tübingen
zur Erlangung des Grades eines
Doktors der Naturwissenschaften
(Dr. rer. nat.)






vorgelegt von
Lea Dagmar Numberger-Thuy
aus Flensburg



Tübingen
2010




























Tag der mündlichen Qualifikation: 21.02.2011
Dekan: Prof. Dr. Wolfgang Rosenstiel
1. Berichterstatter: Prof. Dr. Michal Ku čera
2. Berichterstatter: Prof. Dr. Gerhard Schmiedl














































"Chaos is found in greatest abundance wherever order is being sought. It always defeats order,
because it is better organized."

— Sir Terry Pratchett
Abstract.....................................................................................................................................2
Zusammenfassung ....................................................................................................................4
1. Introduction......6
1.1. Marine Isotope Stage 11........................................................................................... 6
1.2. The Mediterranean Sea – a natural climate laboratory...........................................11
1.2.1. Oceanography and bathymetry.......................................................................12
1.2.2. History of the Eastern Mediterranean Sea...................................................... 15
1.2.3. Climatology....................................................................................................16
1.2.4. Sapropel development....................................................................................18
1.3. Paleoceanographic methods in the Mediterranean Sea ..........................................20
1.3.1. Oxygen and carbon isotopes...........................................................................20
1.3.2. Magnesium/calcium ratio...............................................................................22
1.3.3. Sediment composition23
1.4. Biomarker proxies..................................................................................................24
1.4.1. Alkenone measurements.................................................................................
1.4.2. TEX index25 86
1.5. Microfossil assemblages.........................................................................................25
1.5.1. Benthic foraminifera.......................................................................................
1.5.2. Planktonic foraminifera..................................................................................26
2. Material and Methods.....................................................................................................29
2.1. Investigated sites and cores .................................................................................... 29
2.2. Sample processing31
2.3. Analysis of planktonic foraminifera assemblages..................................................
2.4. Morphotype evaluation of G. ruber........................................................................35
2.5. Analysis of benthic foraminifera assemblages .......................................................38
2.6. Stable isotope measurements40
2.7. XRF elemental scans ..............................................................................................41
2.8. Alkenone measurements.........................................................................................42
3. Results and Discussions.................................................................................................44
3.1. Chronostratigraphic framework..............................................................................44
3.2. Comparability of palaeoclimate trends and foraminifera assemblage dynamics in
the Eastern Mediterranean between MIS 11 and MIS 1..................................................... 49
3.3. Glacial-like winter conditions during early MIS 11 in the Eastern Mediterranean 66
3.4. Habitats, abundance patterns and isotope signals of morphotypes of the planktonic
foraminifer Globigerinoides ruber (d’Orbigny) in the Eastern Mediterranean Sea since the
Marine Isotope Stage 12..................................................................................................... 72
4. Conclusions....................................................................................................................89
Acknowledgements ................................................................................................................92
A. References......................................................................................................................93
B. Appendix......................................................................................................................115







1Abstract

Marine Isotope Stage 11 (MIS 11) is known to be the closest analogue to the Holocene (MIS
1) in terms of Earth’s orbital configuration during the last 400,000 years. This has often been used as
an argument to investigate climate trends of MIS 11, reconstructed from natural geological archives
in order to evaluate current and future climate developments. However, the orbital configuration
during MIS 11 was not exactly identical to that of MIS 1 and the comparability of climate trends
during both interglacials is currently hotly debated.
In this study, the first high resolution palaeoclimatic investigation of MIS 11 is presented
here for the Eastern Mediterranean Sea, known to yield an especially sensitive climate archive. High-
resolution, continuous multi-proxy palaeoclimatic data have been generated from two sediment cores
of this region (ODP Site 964: 36°16’N, 17°45’E, 3658 m; GeoTü-SL96 32°46’N, 19°12’E, 1399 m).
The records have been tied to an absolute time scale using an age model based on stable oxygen
isotopes, planktonic faunal abundance events and sapropel formations. As a proxy of surface water
conditions, assemblage compositions of planktonic foraminifera were determined in 404 samples and
supplemented with alkenone unsaturation ratios in one of the cores.
The new MIS 11 data indicate that MIS 11 sapropel formation and onset of interglacial
conditions in both cores correlated with the second insolation peak after Termination V. In contrast,
the MIS 1 sapropel S1 coincides with the first insolation peak after Termination I. An alignment of
these two sapropel formations is here considered to be the best option to evaluate future climate
trends of the recent interglacial. The position of the oxygen isotopic peak in GeoTü-SL96 is not
associated with a fully developed sapropel and is not clearly identifiable in the sediment record. In
contrast, both cores show a significant sapropel layer in MIS 1, indicating a different depth for the
oxycline during MIS 11. In addition, the size of the oxygen isotopic peak at ODP Site 964 is larger
than in the Holocene at the same site, indicating enhanced monsoonal activity and/or Black Sea
discharge during MIS 11, despite a weaker insolation forcing.
The alignment of MIS 11 sapropel to the second insolation maximum of MIS 11 reveals an
apparently delayed response of the pelagic system to deglaciation. The pre-sapropel interval of MIS
11 is characterised by glacial planktonic foraminiferal assemblages and apparently glacial alkenone
temperatures. Benthic foraminifera concentrations and Ba/Ca ratios in the sediment furthermore
suggest high productivity for the pre-sapropel interval. The most likely scenario to explain the
apparent delayed response, in stark contrast with global trends and pollen evidence from the
Mediterranean region, is high winter productivity during relatively cool and wet interglacial
conditions in early MIS 11, fuelled by enhanced influx of terrigenous material, leading to the
persistence of glacial planktonic foraminifera assemblages and alkenones representing the cold
season signal until the development of the MIS 11 sapropel.
Within the later part of MIS 11, planktonic foraminifera assemblage compositions show three
conspicuous phases. The assemblages occurring during these phases resemble faunas known from
2later sapropels. As they coincide with insolation maxima and low Ba/Ca and Fe/Al values in the
sediment, they appear to be controlled by orbitally driven maxima in seasonality and stratification
with low productivity and thus no sapropel formation. In addition, the planktonic foraminifera
assemblages throughout late MIS 11 remain dominated by the warm-water indicator G. ruber,
reaching an absolute maximum in late MIS 11 and the first hal