Transport of floating litter within Manila Bay, Philippines.

The increasing amount of marine litter is a global issue that is also being experienced within the Manila Bay Philippines. To better understand the behavior of litter within the bay, particle tracking simulations of floating litter released from several sources were conducted. Forward-in-time (PTM-FIT) simulation of particle movements showed that during the southwest monsoon season, litter particles released by river sources tend to accumulate toward five hotspots located along the northeastern coastline of the bay. Backward-in-time (PTM-BIT) simulation of particles released from the identified hotspots showed coastal and foreign sources contributing to the litter collected within these areas. PTM-FIT simulations during the southwest monsoon season showed that particles tend to circulate locally within the bay before being transported toward the hotspots. By contrast, PTM-FIT simulations during the northwest monsoon season showed that litter particles tend to travel toward the mouth of the bay, an implication for global marine litter pollution.

Wave-breaking modulation by infragravity waves during an extreme typhoon.

Herein, we present coastal-wave records under historically extreme conditions caused by a strong typhoon in Japan in 2017. The extreme typhoon generated large infragravity waves, reaching a height of 2 m in shallow water. We took advantage of the extraordinary conditions to analyze the effect of the energetic infragravity waves on the nearshore evolution of relatively short waves. Individual wave analyses clearly demonstrate that the instantaneous water-level rise and drawdown caused by the infragravity waves alternately decelerated and accelerated the breaking of short waves under extreme conditions. This mechanism transmitted the large short-wave energy on the infragravity wave crests to the shore, eventually increasing the height of the nearshore waves. This study provides in situ evidence that the infragravity waves significantly affect nearshore wave characteristics under extreme conditions.