PAMS	  2015@Naha,	  Japan	  	  Effects	  of	  fluctuating	  Kuroshio	  path	  on	  larval	
  dispersal	
  in	  the	  Seto	  Inland	  Sea	  	  Taichi	  Kosako1,	  Yusuke	  Uchiyama1	  and	  Satoshi	  Mitarai2	
  (1:	  Kobe	  Univ.,	  Japan,	  2:	  Okinawa	  Inst.	
  Sci.	
  Tech.,	  Japan)	  	  Abstract	  	  Spatiotemporal	  variations	
  of	  the	  Kuroshio	  drifting	  off	  the	  Shikoku	  Island,	  Japan,	  are	  recognized	
  to	  influence	  on	  the	  estuarine	
  circulation	  in	  the	  Seto	  Inland	
  Sea	
  (SIS,	  e.g.,	  Uchiyama	   et	   al.,	   2012).	   	   In	   general,	   the	   ambient	   currents	   passively	   transport	
   marine	  species	
   particularly	   in	   their	   pelagic	   larval	
   stage.	   Therefore	   the	   coastal	
   dispersal	   of	   the	  larvae	  in	  the	  SIS	  is	  largely	  influenced	  by	  the	  transient	  impact	  from	  the	  Kuroshio	
  through	  its	   seasonal	   and	   inter-­‐annual	
   variability.	   In	   the	   present	   study,	   we	   conduct	   a	  double-­‐nested	   high-­‐resolution	   SIS	
   modeling	   based	
   on	
   ROMS	   for	   consecutive	   six	   years	  from	  2008	  and	  2013.	  An	  offline	  Lagrangian	  particle	
  tracking	
  is	  then	  carried	  out	  with	  the	  ROMS	   reanalysis	   to	   emulate	   the	   pelagic	
   larval	   dispersal	
   in	   the	   SIS.	   Primary	
   objectives	  are	   to	   investigate	   (1)	   correlation	   between	   the	   structure	   of	   the	   Kuroshio	
   path	   and	
  associated	  volume	  transport	  in	  the	  SIS,	  and	  (2)	  effects	  of	  the	  Kuroshio	
  path	  on	  the	  larval	  dispersal	   analyzed	
   with	   the	   Lagrangian	   probability	   density	   functions	   for	   the	   particles	  released	  in	  the	  entire	  SIS	  (e.g.,	  Mitarai	  et	  al.,	  2009).	
  When	
   the	   Kuroshio	   detaches	   far	   from	   (attaches	   to)	   the	   Cape	   Shionomisaki,	   the	  outgoing	   southward	
   volume	   transport	   at	   the	   Kii	   Channel	
   increases	   (decreases)	   due	   to	  the	  meridional	  pressure	  gradient	  force	  (Uchiyama	  et	  al.,	
  2012).	
   	   The	  volume	  transport	  in	   the	   SIS	   mostly	   occurs	
   from	   the	   Bungo	   Channel	   to	   the	   Kii	   Channel	   to	   form	   the	   subtidal	  clockwise	  circulation	  with	  prominent	
  seasonal	  variability.	
   	   Apparent	  seasonality	  is	  also	
  found	  in	  the	  modeled	  larval	  dispersal	  in	  the	  SIS.	
   	   The	
  fraction	  of	  the	  released	  particles	
  arriving	   at	   the	   coastal	
   areas	   after	   the	   advection	   time	   of	   30	   days	   is	   about	   5%	   larger	   in	  summer	   than	
   in	   winter.	   	   Substantially	   more	   particles	
   remain	   in	   the	
   released	   area	   in	  summer	  than	  in	  winter.	   	   For	  example,	  the	  fraction	  of	  the	  particles	  staying	
  in	
  the	  Harima	  Sea	   in	   summer	   is	   as	   1.3	   times	
   much	   as	   that	   in	   winter.	   	   	   The	   persistent	   clockwise	  circulation	   is	   generally	
   more	   energetic	   in	   winter	   to	   promote	   the	   eastward	   mean	   particle	  transport,	
  inducing	  this	  seasonality.	   	   In	  addition,	
  sub-­‐regional	  cyclonic	  and	  anticyclonic	  circulations	  during	  summer	  result	
  in	
  formation	  of	  isolated	  water	  that	  enhances	  particles	  trapped	  in	  the	  circulations.