A Semi-Liquid Ocean Bottom Hypothesis: hydrodynamic controls on organic carbon distribution in oxygen-deficient settings
EMBARGOED UNTIL 2026-11-26
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Date
2023
Publication Type
Doctoral Thesis
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yes
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EMBARGOED UNTIL 2026-11-26
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Abstract
The thesis project lies at the interface of biogeochemistry, microbiology, and sedimentology, a combination which has not been applied in this context yet. It centres on the Semi-Liquid Ocean Bottom-hypothesis (SLOB), which states that the accumulation of organic matter in low-oxygen settings results in a “soupy” surface sediment texture where most organic carbon is present in large aggregates with minimal mineral content. Occurring in abundance in local depocenters, these lowdensity particles will influence sediment hydrodynamic properties and lower the critical threshold of motion. In addition, such settings often sustain a flocculent layer suspended over the more compacted sedimentary layer. Its preferential displacement initiates repeated resettlingresuspension cycles at already low-energy events, often forming bottom nepheloid layers. These are hotspots of microbial activity, which opens the question about whether the lower threshold of motion of OC-rich sediment and its repeated reintroduction into biologically active zones may significantly influence whether a sedimentary environment represents a sink or source of carbon to the environment. Moreover, lateral transport of organic matter has become a hot topic of discussion in paleoceanography after increasing numbers of studies report asynchronous records in coexisting organic proxies, which may compromise how we understand organic carbon storage in the global ocean. This project aims at identifying the conditions necessary to initiate the dislocation process and frame its extent on a regional scale.
This study focuses on fifteen globally distributed, primarily marine, oxygen-deficient settings, where the potential for resuspension, lateral transport, and the concurrent ageing of organic carbon is investigated using a novel combinatory approach. Experimental assays on surface sediments aim to test and reconstruct erosion resistance and response to current motion. The subsequent application of a traditional biogeochemical toolset and radiocarbon measurements on different sedimentary categories (e.g., grain size fractions or density fractions) allows for approximating the individual study sites’ potential for the transport of sedimentary organic carbon.
The implications of this study are intricate but universally applicable to any field of research that handles surface sediments of high organic carbon content. In brief, the results that emerged from this thesis project highlight the care that must be taken in interpreting any sedimentary record of such nature.
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published
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Examiner : Eglinton, Timothy Ian
Examiner : Lever, Mark Alexander
Examiner : Blattmann, Thomas M.
Examiner : Mollenhauer, Gesine
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ETH Zurich
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Subject
BIOGEOCHEMICAL CYCLE (BIOGEOCHEMISTRY); Sedimentology-marine cores; hydrodynamic processes; CARBON CYCLE (GEOCHEMISTRY); RADIOCARBON DATING (GEOLOGY)
Organisational unit
03868 - Eglinton, Timothy I. (emeritus) / Eglinton, Timothy I. (emeritus)