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Mode waters act as the ocean's memory

A team of NSF-supported oceanographers has found that the timing of winter storms, the position of eddies, and the path of the Kuroshio Extension, a current nicknamed the "conveyor belt of the North Pacific," are all critical factors in establishing the formation of mode waters. These thick layers of subsurface water have nearly homogeneous salinity, temperature and oxygen content.

Oceanographers from the University of Washington, Woods Hole Oceanographic Institute and the University of Rhode Island have studied the distribution and evolution of mode waters in the North Pacific Ocean for the past several years. Utilizing data from moorings, Global Ocean Observing System profiling floats, and satellite altimetry, they estimated the mode water volume, annual formation volume, and seasonal and inter-annual cycles for the past decade.

Mode waters act as an ocean's memory, capturing a cumulative record of previous winters. In the mid-latitudes, winter storms interact with the surface ocean to produce thick layers of cold, well-mixed water.  In the springtime, increased temperatures cause a cap of warmer water to cover the layer of cold water. This produces a thick layer of cool water trapped below the surface with nearly homogeneous properties. 

Mode waters can feed back into the atmosphere in subsequent seasons and influence the complex interactions between the ocean and atmosphere. It also affects how this coupled climate system transports and exchanges heat around the globe.

Image

  • map of mode water thickness
Mode water thickness map.
Luc Rainville, University of Washington

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