The island-scale internal wave climate of Moorea, French Polynesia

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2012-01-01

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Analysis of five-year records of temperatures and currents collected at Moorea reveal strong internal wave activity at predominantly semi-diurnal frequencies impacting reef slopes at depths 30m around the entire island. Temperature changes of 1.5C to 3C are accompanied by surges of upward and onshore flow and vertical shear in onshore currents. Superimposed on annual temperature changes of approximately 3C, internal wave activity is high from Oct-May and markedly lower from Jun-Sep. The offshore pycnocline is broadly distributed with continuous stratification to at least 500m depth, and a subsurface fluorescence maximum above the strong nutricline at approximately 200m. Minimum buoyancy periods range from 4.8 to 6min, with the maximum density gradient occurring at 50 to 60m depth in summer and deepening to approximately 150 to 200m in winter. The bottom slope angle around all of Moorea is super-critical relative to the vertical stratification angle suggesting that energy propagating into shallow water is only a portion of total incident internal wave energy. Vertical gradient Richardson numbers indicate dominance by density stability relative to current shear with relatively limited diapycnal mixing. Coherence and lagged cross-correlation of semi-diurnal temperature variation indicate complex patterns of inter-site arrival of internal waves and no clear coherence or lagged correlation relationships among island sides. Semi-diurnal and high frequency internal wave packets likely arrive on Moorea from a combination of local and distant sources and may have important impacts for nutrient and particle fluxes in deep reef environments. © 2012 American Geophysical Union. All Rights Reserved.

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10.1029/2012JC007949

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Leichter, JJ, MD Stokes, JL Hench, J Witting and L Washburn (2012). The island-scale internal wave climate of Moorea, French Polynesia. Journal of Geophysical Research: Oceans, 117(6). 10.1029/2012JC007949 Retrieved from https://hdl.handle.net/10161/10769.

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Scholars@Duke

Hench

James Hench

Associate Professor of Oceanography

Research in my lab focuses on fluid dynamics in the coastal ocean and its effects on transport processes. We use field measurements, computational models, and theoretical analyses to understand fundamental physical processes in these systems. We also work extensively on interdisciplinary problems that have a significant physical component to better understand the effects of water motion on the geochemistry, biology, and ecology of shallow marine systems. 

Much of our research is on coral reef hydrodynamics and our lab leads the Physical Oceanographic component of the Moorea Coral Reef LTER project 

Current projects include: 1) wave-driven circulation and exchange in coral reef, lagoon, and pass systems; 2) extreme events and their effects on coral reef systems; 3) understanding the effects of rough bottoms such as corals on circulation and scalar mixing; 4) the impact of stratification on vertical mixing in a highly stratified wind-driven estuary; 5) larval transport around a coral reef island; 6) sponge excurrents; and 7) the effects of wave forcing on corallivory. 


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