Coastal	  dispersal	  of	  Eulerian	  passive	  tracer:	  Comparative	  experiments	  in	  an	  estuary	   	  and	  a	  continental	  shelf	  margin	  	  Yota	  Suzue	  and	  Yusuke	  Uchiyama	  (Kobe	  University,	  Japan)	  	  	  ABSTRACT	  Coastal	  marginal	  seas	  and	  estuaries	  are	  generally	  dumpsites	  for	  waster	  water	  from	  sewage	  and	  power	  plants	  (e.g.,	  Uchiyama	  et	  al.,	  2014).	   	   Accidental	  leakage	  of	  toxic	  materials	   may	   result	   in	   serious	   hazardous	   incidents	   that	   should	   be	   predicted	   and	  assessed	   urgently	   upon	   the	   occurrence.	   	   We	   therefore	   develop	   an	   offline	   passive	   tracer	  model	   that	   computes	   3D	   dispersal	   of	   arbitrary	   Eulerian	   tracers	   with	   a	   point	   source	  capability	   by	   exploiting	   3D	   oceanic	   model	   reanalysis	   and	   prediction	   such	   as	   JCOPE2	  (Miyazawa	   et	   al.,	   2009).	   	   The	   purposes	   of	   the	   present	   study	   are	   to	   investigate	   (1)	  reproducibility	  of	  the	  offline	  tracer	  dispersal	  against	  the	  online	  result,	  and	  (2)	  difference	  in	  spatiotemporal	  variability	  of	  the	  leaked	  tracers	  in	  a	  semi-­‐enclosed	  estuary	  (viz.,	  Seto	  Inland	  Sea,	  Japan;	  SIS)	  and	  in	  an	  open	  coast	  environment	  on	  the	  continental	  margin	  off	  Shizuoka	  Prefecture	  on	  the	  Pacific	  side	  of	  Japan.	  
For	   the	   first	   objective,	   we	   analyze	   with	   the	   double-­‐nested	   JCOPE2-­‐ROMS	  downscaling	   system	   for	   the	   entire	   SIS	   at	   the	   horizontal	   resolution	   of	   600	   m.	   	   The	  release	   site	   is	   chosen	   on	   the	   southern	   coast	   of	   the	   Iyo	   Sea.	   	   The	   tracer	   has	   been	  discharged	   for	   11	   days	   in	   4	   different	   seasons	   since	   the	   1st	   day	   in	   Feb.,	   May,	   Aug.,	   and	  Nov.,	   2013,	   and	   tracked	   for	   31	   days	   after	   each	   release.	   	   Overall	   similarity	   in	   the	  dispersal	   pattern	   is	   obtained	   for	   both	   the	   online	   and	   offline	   cases,	   whereas	   some	  undesirable	   negative	   concentration	   arisen	   from	   a	   discrete	   advection	   scheme	   induces	   a	  slight	   deviation	   in	   the	   inventory	   of	   the	   released	   tracer	   between	   the	   two	   cases.	   	   Tidal	  oscillations	  enhance	  local	  dilution,	  while	  the	  month-­‐long	  transport	  is	  dominated	  rather	  by	   inter-­‐seasonal	   variability	   of	   the	   clockwise	   circulation	   of	   the	   SIS.	   	   The	   comparative	  offline	   tracer	   computation	   for	   the	   open	   coast	   off	   Shizuoka	   is	   conducted	   with	   another	  double-­‐nested	   JCOPE2-­‐ROMS	   downscaling	   model	   result	   for	   the	   Kuroshio	   region	   at	   the	  horizontal	  resolution	  of	  1	  km.	   	   The	  tracer	  release	  occurs	  near	  the	  Cape	  Omaezaki	  and	  is	  done	  in	  the	  same	  way	  as	  the	  SIS	  runs.	   	   The	  Kuroshio	  readily	  traps	  the	  released	  tracer	  in	  the	   offline	   open	   coast	   run,	   leading	   to	   immediate	   transport	   in	   the	   northeast	   direction.	   	  The	  seasonal	  difference	  of	  the	  tracer	  dispersal	  is	  apparent,	  depending	  on	  the	  locations	  of	  the	  Kuroshio	  axis.