30 April 2015

Topographically-Trapped Ocean Variability Dominates Wind-Driven Circulation in the Bellingshausen Basin


Specific ocean bathymetry features like abyssal plains or mid-ocean ridges can have a strong impact on the ocean circulation. Several basins are known to trap significant amounts of energy. Understanding the pathways of this energy –mostly how and where it is dissipated- is important in the context of mixing of deep water masses, and ultimately for understanding the global overturning circulation. Altimeter observations indicated that the Bellingshausen Basin in the Southeast Pacific Ocean displayed an exceptional strong event of such topographically trapped variability in late 2009.Here we study the energetics of this episode using a 1-layer shallow-water model. A forward integration of this model indeed reproduces the observed event. We show that this event reflects the excitation of a topographically trapped barotropic mode. On average, 23% of the energy input by the wind stress is used to excite this mode, going up to 38% during the event of 2009. Interestingly, an even stronger excitation (50%) was identified for a similar episode in 2008. Key areas of energy dissipation are Eltanin Fracture Zone, the crest of the East Pacific Rise, and the Chile Rise/East Pacific Rise intersection.

Wilbert Weijer
Los Alamos National Laboratory (LANL)
Weijer, W.  2015.  "Modal Variability in the Southeast Pacific Basin: Energetics of the 2009 Event."  Deep-Sea Research II 114: 3-11, doi:10.1016/j.dsr2.2012.10.002.

This research was supported by the Regional & Global Climate Modeling Program of the US Department of Energy Office of Science, and by NSF-OCE award 0928473. Los Alamos National Laboratory is operated by the Los Alamos National Security, LLC for the National Nuclear Security Administration of the U.S. Department of Energy under contract DE-AC52-06NA25396.