The Submesoscale Cascade in the South China Sea


The S. China Sea is understood to be one of the most energetic regional seas in the global ocean. The combination of the Kuroshio Current, the monsoon, strong tides, and the dramatic topography of the Luzon Straits lead to a rich physical forcing environment. In addition to the enhanced internal wave environment that has been the focus of much work (ASIAEX, NLIWI, and IWISE), the region southwest of Taiwan has been documented as a maximum in eddy kinetic energy. However, outside of the realm of internal wave processes, the physics of the submesoscale cascade of energy has been poorly studied.

Here, we describe the case for a new examination of sub-mesoscale processes in the S. China Sea. The focus will be the class of oceanographic variability that is poorly constrained in models including eddies, rings, vortices and filaments, and their interactions with smaller-scale phenomena. The work will focus on in-situ sampling with a heavy emphasis on autonomous instrument platforms, which have the ability to follow features of interest over weeks to months. The region of interest is just southwest of Taiwan, and is accessible to both Taiwan and UNOLS vessels. This topic has outstanding potential to produce new understanding of small-scale and rapidly evolving variability in the S. China Sea. With the momentum from recent Taiwan/U.S. partnerships (QPE, ITOP, OKMC, and IWISE) still strong, and the new Taiwan global-class vessel ready for work, the time is right for this program. It will continue an outstanding legacy of international partnership between Taiwan and the U.S.

Sampling activities for the May 2013 pilot program. The R/V Revelle conducted rapidly-repeated sections an Underway CTD, targeted microstructure sections using a Rockland Vertical Microstructure Profiler (VMP), persistent sections with two Slocum gliders (one equipped with microstructure sensors) and time series collected by two moorings deployed over the shelf.

Science Objectives

Investigate evolution of submesoscale eddies and filaments in the Kuroshio-influenced region off the SW coast of Taiwan. Questions include:

  • What role does the Kuroshio play in generating mesoscale and submesoscale variability modeled/observed off the SW coast of Taiwan?
  • How does this vary with atmospheric forcing? (This could be phrased as a contrast between opposing monsoons, but we will not be out there to sample the summer monsoon. We should witness significant variations in winter monsoon wind and heat flux, though, especial if we extend into the late winter/early spring.)
  • How do these features evolve in response to wintertime (strong) atmospheric forcing?
  • What role do these dynamics play in driving water mass evolution and interior stratification in the South China Sea?
  • What role do these dynamics/features have on the transition of water masses from northern SCS water into the Kuroshio branch water/current and local flow patterns?

Sampling activities for the January–February 2014 wintertime study. Light gray lines mark R/V Revelle's track, with red indicating where Triaxus survey operations were conducted. Blue lines mark the tracks of the four autonomous gliders, while green lines indicate Wirewalker drift paths. Yellow start mark WHOI mooring sites, while magenta start indicate the positions of the three NTU moorings.