Abstract:
The abyssal ocean is often viewed as quiescent, shaped by slow processes such as the overturning circulation. Yet growing observational evidence shows that the deep ocean is dynamic and frequently disturbed. An intriguing feature of the deep ocean is the benthic nepheloid layer (BNL): a thick layer of suspended particles that can extend thousands of metres above the seafloor. BNLs tend to occur in regions of high surface eddy kinetic energy and are associated with episodic bursts of strong bottom currents, known as benthic storms. Within these layers, particle-reactive palaeoceanographic tracers, such as thorium-230 and protactinium-231, behave in ways that challenge existing theoretical frameworks. These observations raise fundamental questions about how surface eddy activity communicates with the abyss, how particles and tracers are redistributed by benthic storms, and what the ecological consequences of such transient variability may be in an era of increasing deep-sea exploitation. 
 
In this talk, I'll present a set of observational and numerical modelling studies that link the physical and biogeochemical processes underlying the abyssal variability. Model simulations with both idealised and realistic regional domains show that deep-reaching mesoscale eddies associated with strong surface currents, such as the Gulf Stream, can perturb the abyssal ocean, resuspend fine sediments, and contribute to the development of BNLs. Additional particle supplies through advection enhance scavenging, altering the partitioning of particle-reactive trace elements between their dissolved and particulate phases. Far-reaching transport of particles associated with strong deep flows raises profound implications for the connectivity of deep marine ecosystems and for monitoring deep-sea environmental impacts.  

Biography:
Sean Chen is a research associate with the Nature's Carbon group at Imperial College London. Trained initially as a geologist and later as a physical oceanographer, he combines a wide range of techniques to address interdisciplinary problems in ocean and climate sciences. His research interests cover global marine carbon cycle, ocean circulation, palaeoclimate, and the evolving marine ecosystem under warming climate.