Physical processes controlling mud depocenter development on continental shelves – Geological, oceanographic, and modeling concepts

Abstract

Mud depocenters (MDCs) represent major proximal-marine sinks for fine-grained terrigenous material, carbon, and contaminants on modern continental shelves. Throughout the past decades, several studies have shed light on the physical processes controlling MDC development at various timescales, ranging from controlled flume experiments and in-situ oceanographic monitoring, to stratigraphic analyses of recent and ancient deposits based on seismo-acoustic and sediment-core data. Thereby, key mechanisms related to the formation and maintenance dynamics of MDCs have been discovered: a) cross-shore bottom transport of suspended mud through gravity flows, b) interaction of mud with density gradients associated with oceanic fronts, c) resuspension and dispersal control of mud by internal waves, d) bedload deposition of mud forming laminated bedding under energetic flow conditions, and e) mud resuspension resulting from chronic bottom trawling.Among the physical processes identified or proposed, three conceptual paradigms for MDC development can be distinguished: 1. continuous supply, associated with a steady sediment supply and hemipelagic settling in relatively calm conditions; 2. continual resuspension-deposition cycles, wherein parts of an MDC area are subject to multiple cycles of resuspension, redeposition and reworking before ultimate burial; and 3. episodic sedimentation and erosion, in which extreme events such as riverine floods and atmospheric storms dominate the total, long-term sediment flux. Although the predominance of each of these paradigms within a single MDC depends to a large degree on the timescales considered, case studies tend to emphasize processes associated with only one of these three paradigms. As a result, the relative, long-term contribution of individual processes remains largely uncertain for many MDCs. The ability of numerical models to accurately predict medium to long-term mud accumulation is restricted not only by computational costs, but also by insufficient parametrizations of the muddy sedimentation process. These remain challenging to constrain due to the multiplicity and complexity of factors affecting the cohesive properties of mud, including its state of consolidation, and the amount and type of organic matter present. Bridging the gap between individual events and long-term accumulation is the key to a more complete understanding of sedimentation processes in MDCs.