Late quaternary sedimentation processes and sediment accumulation changes off Portugal [Elektronische Ressource] / vorgelegt von Ulrich Alt-Epping

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Informations

• Publié par: universitat_bremen
• Publié le: 01 janvier 2008
• Nombre de lectures: 11
• Langue: English
• Poids de l'ouvrage: 25 Mo

Extrait

Late Quaternary Sedimentation Processes and
Sediment Accumulation Changes off Portugal
Dissertation
zur Erlangung des Doktorgrades
der Naturwissenschaften
im Fachbereich 5 Geowissenschaften
der Universität Bremen
vorgelegt von
Ulrich Alt-Epping
Bremen im Januar 2008 Tag des Kolloquiums:
2. Oktober 2008
Gutachter:
Prof. Dr. Dierk Hebbeln
Prof. Dr. Ralph Schneider Table of Contents
Table of Contents

Summary 1
Zusammenfassung 3


1 Introduction
1.1 Scientific Rationale 5
1.2 Implementation 6


2 Portuguese Margin
2.1 Northern Shelf 9 2.2 Central 11
2.3 Southern Shelf 13
2.4 Hydrography and Marine Productivity 13
2.5 North Atlantic Oscillation 15
2.6 Previous Work 17


3 Material and Methods
3.1 Material 19
3.1.1 Surface Samples 19
3.1.2 Sediment Cores 21
3.2 Methods – Introduction and Application 22
3.2.1 Carbon, Nitrogen and CaCO Content 23 3
13
3.2.2 Stable Carbon Isotope Ratios ( C ) 24 org
15
3.2.3 Nitrogen Isotope Ratios (N) 25
18
3.2.4 Oxygen Isotope Ratios (O) 27
3.2.5 Element abundance – XRF Spectroscopy 28
3.2.6 Magnetic Susceptibility 28
3.2.7 Grain-size Analyses and Modelling 29


4 Provenance of Organic Matter and Nutrient Conditions on a River- and Upwelling
,
Influenced Shelf: A Case Study from the Portuguese Margin (Alt-Epping U., M. Mil-Homens,
D. Hebbeln, F. Abrantes, R. Schneider; Marine Geology 243, pp.169-179, 2007)
4.1 Abstract 31 4.2 Introduction 32

v Table of Contents
4.3 Regional Setting 33 4.3.1 Shelf Sediments 33
4.3.2 Marine Productivity 34 4.3.3 Fluvial Supply 35
4.4 Material and Methods 36
4.5 Results 37
4.5.1 Douro Region 37 4.5.2 Nazaré Region 38
4.5.3 Tagus 40 4.5.4 Sines Region 41
4.6 Discussion 44
4.6.1 Organic Matter Sources 44
4.6.2 Stable Nitrogen Isotopes 46
4.7 Summary 47 4.8 Acknowledgements 48
4.9 References 49
5 Variations in Sediment Provenance during the past 3000 years off the Tagus River,
Portugal (Alt-Epping, U., J.-B.W. Stuut, D. Hebbeln, R. Schneider; submitted to Marine Geology)

5.1 Abstract 53 5.2 Introduction 54
5.3 Regional Setting 55
5.4 Material and Methods 57
5.5 Results 58
5.5.1 Plutur Box Cores 58
5.5.2 GeoB 8903 59 5.6 Discussion 63
5.6.1 Plutur Box Cores 63
5.6.2 GeoB 8903 64
5.6.2.1 Age Model
5.6.2.2 Hydrography, Organic Matter Provenance and Nutrient Conditions 65
5.6.2.3 Grain-Size Analyses 66
5.6.2.4 Relation to NAO 67
5.6.2.5 Long Term Variations 70
5.7 Summary 71 5.8 Acknowledgements 72
5.9 References 73

vi Table of Contents
6 Holocene Environmental Conditions on the Portuguese Margin
(Alt-Epping, U., D. Hebbeln, R. Schneider, S. Lebreiro; in preparation)

6.1 Abstract 79 6.2 Introduction 80
6.3 Regional Setting 81
6.4 Material and Methods 83
6.5 Results 85 6.5.1 Core MD03-2698 85
6.5.2 Core D13882 86
6.5.3 Age Model and Mass Accumulation Rates 87
6.6 Discussion 89 6.6.1 Provenance 89
6.6.2 Nutrient Budget and Marine Productivity 91
6.7 Environmental Implications 92
6.8 Acknowledgements 93 6.9 References 94


7 Sedimentological record of tsunamis on shallow-shelf areas: The case of the 1969AD and
1755AD events on the Portuguese Shelf off Lisbon (Abrantes, F., U. Alt-Epping, S. Lebreiro, A.
Voelker, R. Schneider; Marine Geology 249, pp. 283-293, 2008)

7.1 Abstract 97 7.2 Introduction 98
7.3 Materials and Methods 100 7.4 Chronology 101
7.5 Results and Discussion 106
7.5.1 Last Century Record 106
7.5.2 Historical (last 2000 years) Record 107
7.6 Conclusions 112 7.7 Acknowledgements 112
7.8 References 113


8 General Conclusions
8.1 Present Day Setting 117
8.2 Centennial Variations 118 8.3 Long-Term Changes 119
8.4 Grain-Size Effects 119 8.5 Tsunami 120
vii Table of Contents
9 Perspectives 123


10 Appendix 1: Complementary Data

10.1 Visual and Seismic Observations 126 10.1.1 SES 127
10.1.2 ROV
10.1.3 Dive 1 128
10.1.4 Dive 2 130
10.1.5 Dive 3 131
10.1.6 Dive 4 133
10.2 Estuary Core PO287-1 135
10.3 Prodelta Box Cores 135
18 37
10.4 GeoB 8903 – O and U ’ Index 136 k
10.5 GeoB 8903 – Element Abundance 138
11 Appendix 2: Literature Values of Selected Proxies 141


12 References for Chapters 1-10 153
viii Summary
Summary
Changes in the marine and continental environment comprise variations in climatic,
hydrographic, biological or sedimentological parameters. Furthermore, such environmental
changes occur on different timescales, ranging from seasons to millennia. Hence, a synoptic
environmental reconstruction requires the combined interpretation of several parameters,
which stand for specific environmental “boundary conditions” – such as temperature, wind
strength, precipitation or biological productivity – plus an account for different temporal
resolutions by an appropriate sampling design.
One of the dominating environmental mechanisms, that exceed a strong influence on
European environmental conditions, is the North Atlantic Oscillation (NAO). Particularly over
the Iberian Peninsula, the NAO determines precipitation as well as wind strength and hence
the intensity of coastal upwelling along the western Portuguese margin. These environmental
variations are finally recorded in sediments of the western Portuguese shelf, which combine
marine and continental inputs from the Portuguese coastal realm and from the Iberian hinter-
land. Additionally to the high sensibility of shelf sediments to environmental fluctuations, the
combined deposition of marine and continental material leads to high sedimentation rates,
allowing paleoenvironmental reconstructions on a high temporal resolution.
To identify the present day situation of sediment supply from riverine and marine
sources, surface samples from four different regions along the western Portuguese shelf are
analysed in terms of the provenance of their organic matter.
In the northern sampling region off the Douro River mouth, river discharged,
continental input is combined with marine, autochthonously produced material. Sediments
close to the Nazaré Canyon contain small amounts of continental material, which is probably
transported southwards along the coast. Surface sediments inside the Tagus Estuary show a
clear imprint of continental organic material, but also evidence for anthropogenic and
agricultural pollution. The decrease of continental organic contributions on the Tagus Prodelta
is visible by an increasingly marine source signature in the organic matter off the Tagus
Estuary mouth, including a preferential transport of estuarine material southward towards the
canyons. The southern sampling region off Cape Sines is characterised by exclusively marine
input, due to the absence of major rivers in the vicinity.
Supplementary, visual and hydroacoustic investigations with a remotely operated
vehicle (ROV) and with a parametric echosound system along the coast reveal a highly
variable sediment texture with sharp boundaries between different sediment textures.
An evaluation of changing sediment properties during the past 3000 years on a high
temporal resolution is obtained by a multi-proxy analysis of a 5.4m long gravity core from the
Tagus Prodelta (GeoB 8903). Data from this core shows no changes in hydrographic
conditions nor in the quantity of terrigenous organic matter input through time. Instead,
physical sediment properties such as magnetic susceptibility and grain-size indicate changes
in sediment supply and transport mechanisms around 2000yrs BP and 600yrs BP (i.e.
1Summary
AD1400). A detailed analysis of the grain-size spectra yields three lithic end-members of the
sediment, which are clearly related to organic and inorganic sediment properties. The
magnetic susceptibility signal is carried by the finest end-member, organic carbon is related to
an intermediate end-member and the calcium carbonate correlates with the coarsest sediment
component. These results allow inferences about sources and transport mechanisms of each
end-member and of the associated proxy. The end-members also show a correlation with the
North Atlantic Oscillation, which has a strong impact on environmental conditions in the
research area. These findings further emphasise the importance of an integrated interpretation
of multi-proxy data by revealing a clear association of organic and inorganic sediment
properties to a specific grain-size spectrum.
A long-term view on regional environmental changes is obtained by the analysis of a
deep sea core MD03-2698 and its comparison to a piston core from the Tagus prodelta. These
cores cover the Holocene and the last Deglaciation. The comparison between the deep