Coastally trapped waves around Palau

Abstract

Observations from around the main island group of Palau, located in the tropical Western Pacific, exhibit a persistent presence of baroclinic coastally trapped waves. The signals are found in records of temperature that were sustained on the fore-reef for seven months, May to December 2013, with the strongest signal from Typhoon Haiyan which passed over Kayangel Atoll, along with the northern most Palauan islands, in November of 2013. This strong forcing led to a large near- and sub-inertial response both in temperature and nearshore currents. We use semi-analytical models, such as the vertical structure equation and Brink and Chapman's (1985) model, to compute propagating modes for this oceanographic region providing a benchmark for comparison with the observations. These models provided a framework to account for the influence of local stratification, topography and the local Coriolis parameter on the wave guide around Palau. We found the maximum vertical displacements over the course of a 22-day period that included Typhoon Haiyan were 35.5 m and 45.7 m at the 57 m and 90 m isobaths, respectively, where temperatures ranged by 4.1 °C and 9.0 °C over that same period at those respective depths. The apparent omnipresence of coastally trapped waves throughout the observational window provide a regular cycling of temperature at depth, potentially conditioning benthic communities living on the outer reef slope to temperature swings.