Composition and degradation of organic matter in sediments from the Peru-Chile upwelling region [Elektronische Ressource] / vorgelegt von Jutta Niggemann

Niggemju

Informations

• Publié par: universitat_bremen
• Publié le: 01 janvier 2005
• Nombre de lectures: 15
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Composition and degradation of organic matter in sediments
from the Peru-Chile upwelling region






Dissertation
zur Erlangung des Doktorgrades
der Naturwissenschaften
- Dr. rer. nat. -



im Fachbereich Geowissenschaften
der Universität Bremen

vorgelegt von


Jutta Niggemann






Bremen
April 2005























Tag des Promotionskolloquiums: 26. August 2005

Gutachter:
1. Prof. Dr. Bo Barker Jørgensen
2. Prof. Dr. Kai-Uwe Hinrichs

Prüfer:
Prof. Dr. Jörn Peckmann
PD. Dr. Sabine Kasten






Man sieht nur mit dem Herzen gut.
Das Wesentliche ist für die Augen unsichtbar.

„Der kleine Prinz“
Antoine de Saint-Exupéry TABLE OF CONTENTS

Abstract Thesis Abstract 1
Kurzfassung 5

Chapter 1: General Introduction 9
1. Introduction 10
2. Objectives and outline of this thesis 32
3. Contributions to publications 34

Accumulation and early diagenesis of sedimentary organic material Chapter 2: 39
in the Chilean coastal upwelling region

Spatial distribution of organic matter composition, sulfate reduction Chapter 3: 77
rates, and Thioploca biomass in surface sediments off Peru

Chapter 4: Fatty acid biogeochemistry of sediments from the Chilean coastal 107
upwelling region: sources and diagenetic changes

Chapter 5: Sources and fate of amino sugars in coastal Peruvian sediments 137

Chapter 6: A Chlorin Index: A new parameter for organic matter freshness in 153
sediments
B Amino acid biogeo- and stereochemistry in coastal Chilean 157
sediments
C Anaerobic oxidation of methane and sulfate reduction along the 161
Chilean continental margin

Chapter 7: Concluding Remarks and Perspectives 165

References Chapter 8: 173

Danksagung 199

V Thesis Abstract
THESIS ABSTRACT

The Peru-Chile upwelling region is the largest coastal upwelling system of the world.
As part of the projects “Peru-Upwelling” (RV Sonne cruise 147) and PUCK (RV Sonne
cruise 156) sediments from the Peruvian and Chilean upwelling region have been investigated
for organic geochemical composition and microbiological parameters. This thesis presents a
biogeochemical characterization of surface sediments from the shelf and continental slope off
Peru (9-14°S) and Chile (23°S and 36°S). Main objective was the characterization of
sedimentary organic matter (OM) composition, with respect to sources and quality, and with
special focus on early diagenetic degradation processes.
The general influence of depositional conditions on the accumulation and composition
of sedimentary OM, and on the associated sedimentary processes, became evident from the
comparison of sediments from two different depositional systems off Chile as well as from
the examination of the spatial distribution of sediment characteristics off Peru. It could be
shown that besides vicinity to actual upwelling centers and upwelling intensity, winnowing
and redistribution by bottom currents in combination with effects of seafloor topography
provide a major control on the sediment composition.
There were no indications for input of terrestrial OM to the investigated sediments.
Elemental (C/N-ratio) and carbon isotopic compositions of the sedimentary OM were
characteristic for a predominantly marine origin, and specific terrestrial biomarkers could not
be identified. In particular, analysis of the molecular carbon isotopic composition revealed a
non-terrestrial source for long-chain fatty acids, typically regarded as biomarkers for higher
plant input. Lacking evidence for terrestrial OM in the sediments is in accordance with
limited river discharge and small eolian input from the vegetation poor and extremely dry
Atacama Desert that borders most of the investigated coastal area. Terrestrial input was also
undetectable in sediments depositing near Concepción (36°S), where several rivers, draining
the more humid hinterland of central Chile, enter the coastal Pacific. Here, an expected
terrestrial signal was possibly concealed by the high marine input. Chlorin concentrations as a
measure for input of phytoplankton detritus were on average a factor 10 higher in sediments
off Peru than off Chile, partly reflecting higher annual primary production rates in the
perennial upwelling region off Peru, whereas upwelling and productivity off Chile display
strong seasonality. Characteristic biomarkers for diatoms (brassicasterol) and dinoflagellates
(dinosterol) were abundant in sediments off Peru and highly correlated to OM concentrations,
indicating that these phytoplankton organisms, typically dominating in highly productive
1Thesis Abstract
coastal upwelling areas, were major contributors to sedimentary OM.
Bacteria could be identified as an important source of sedimentary OM. In sediments
off Chile, bacterial specific fatty acids (iso- and anteiso C -C ) accounted for 12-34% of all 14 17
identified fatty acids. Highest percentages were observed at the sediment surface of sites from
the oxygen-minimum-zone, reflecting both, intense bacterial reworking at these shallow sites
and accumulation of bacterial biomass in the absence of oxygen. Sediments from the oxygen-
minimum-zone also displayed the highest concentrations of the fatty acid 10-methyl-16:0,
indicative for the presence of sulfate- and/or iron-reducing bacteria of Desulfobacter and
Geobacter species. In contrast, imprints of the large sulfur bacteria Thioploca on the OM
-2composition could not be revealed, even though biomasses up to 250 g m were observed off
Peru. It could be shown that dead bacterial biomass accounts for a significant fraction of
sedimentary OM. The amino sugar muramic acid uniquely found in bacterial cell walls was
used to estimate bacterial cell numbers in sediments off Peru. These numbers were up to
500 times higher than cell counts reported for sediments in this area. It was further estimated
that at most 5-36% of individual D-amino acids in Chilean sediments were associated with
peptidoglycan of living cells.
Different parameters have been applied to assess the quality or freshness of the
sedimentary OM. Water depth was the main factor controlling OM freshness at the sediment
surface, e.g. the fractions of labile compounds such as chlorins, fatty acids, and amino acids
decreased with increasing water depth. Since bottom water oxygen concentrations were
closely related to water depths it was impossible to identify effects of oxygen availability on
OM freshness. C/N-ratios, representing bulk OM quality, generally increased with increasing
water depth and were highest at sites where refractory material accumulated. The amino acid
based degradation index, derived from principal component analysis of the molecular amino
acid composition, has successfully been applied to characterize OM freshness in sediments
off central Chile, but did not reflect changes in the degradation state of sedimentary OM off
northern Chile. A new parameter for OM freshness in sediments, the Chlorin Index, has been
evolved and was routinely applied in this study. Low Chlorin Indices indicative for fresh OM
were found in sediments from shallow water depth, whereas higher values characterized the
more degraded state of sedimentary OM at greater water depths. Another quality parameter
was derived from principal component analysis of the molecular fatty acid composition. This
fatty acid index reflected OM alteration in water column and sediments off Chile and showed
a good correspondence to other quality indicators applied in this study. Reactivities of bulk
OM, chlorins, and individual fatty acids have been estimated from down-core decreasing
2 Thesis Abstract
concentrations in dated sediments. The reaction rate constants for bulk OM decreased with
increasing water depth, suggesting that water column degradation also affects long-term
reactivity of sedimentary OM. Among the fatty acids, in accordance with findings of earlier
studies, polyunsaturated were the most, long-chain saturated fatty acids the least reactive
compounds.
Bacterial sulfate reduction was the quantitatively most important terminal electron
acceptor process in the investigated sediments. Measured sulfate reduction rates (SRR) were
therefore regarded to reflect the availability of sedimentary OM for microbial degradation.
The SRR generally decreased with increasing water depth, following the water depth
dependence of sedimentary OM quality. Overall, the SRR showed a good correspondence
with the chemically defined parameters applied in this study to assess the quality of the
sedimentary OM. The predominance of sulfate reduction for OM remineralization in anoxic
marine sediments was stressed by the good correspondence of reaction rate constants, that
were obtained for bulk OM on the one hand from measured SRR, and on the other hand from
the down-core decrease in OM concentratio