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SUMMARY:From iron cores to estuaries: the interaction of environmental flo
 ws with their transported particles - Dr Quentin Kriaa\, University of Twe
 nte
DTSTART:20241111T130000Z
DTEND:20241111T140000Z
UID:TALK222586@talks.cam.ac.uk
CONTACT:Kasia Warburton
DESCRIPTION:The difficulty to resolve large-scale environmental flows down
  to the size of the small particles they transport imposes to use simplifi
 ed models to predict them. In two contexts\, this seminar offers observati
 ons of subtle yet impactful effects of the dynamics of particles that shou
 ld be incorporated to refine such models.\n\nWe will start with ‘iron sn
 ow’ on Ganymede\, a natural satellite of Jupiter. The solidification of 
 its core leads to the formation of pure iron crystals at the core peripher
 y\, that sink deep in the core due to gravity. The settling dynamics of a 
 cloud of crystals is modelled experimentally with particle clouds of sub-m
 illimetric glass spheres settling in water. These clouds grow with depth d
 ue to the entrainment of ambient water into the clouds. The canonical mode
 l of entrainment by Morton et al. 1956 would predict their growth rate to 
 be unaffected by the particles’ size. Yet\, their growth rate is maximum
  for a specific particle size. This optimum originates from the partial de
 coupling between the settling particles and the flow\, as explained with c
 omplementary numerical simulations.\n\nWhen iron crystals reach very large
  temperatures in Ganymede’s core\, they remelt. Their dense molten snow 
 drives\na compositional convection that is assumed vigorous enough to powe
 r a magnetic field through dynamo. To test this assumption\, experiments a
 re conducted where sugar grains (aka the iron snow flakes) are continuousl
 y sieved above a water tank (aka the deep convective core). The size of gr
 ains controls particle-scale interactions with the flow\, with a\ncritical
  influence on the length scales and velocity scale of convection\, on the 
 laminar/turbulent nature of the flow\, and on the depth where sugar grains
  fully dissolve – with paramount implications for the emergence of dynam
 o in Ganymede.\n\nWe will finally focus on the dispersal of microplastics 
 (MP) in the ocean. Although most plastics have a density lower\nthan sea w
 ater and are thus expected to float\, recent observations show that the se
 a floor is an important sink of MP. To understand why\, I analyse the tran
 sport of light-density MP by turbidity currents driven by avalanching glas
 s spheres (aka sediments) in the lab. Unexpectedly\, MP deposit during exp
 eriments. In-situ observations reveal that glass\nspheres attach to the pl
 astics. This aggregation massively affects the transport of MP by enabling
  their deposition\, by\ndelaying the detrainment of rising MP\, and by enh
 ancing the transport of aggregates farther than the runout distance of\nse
 diments. These experiments suggest that buoyant MP entering the ocean from
  estuaries may be deposited along the\ncontinental margins when carried to
  the abyss by turbidity currents.
LOCATION:MR3\, CMS
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