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The salinity distribution from the surface layer to the middle layer of the ocean is being elucidated by a global salinity (and water temperature) observation
network called the Argo Project, which started in the 2000s. This is an international project to elucidate the global ocean structure by
putting many Argo floats into the ocean, which are drifting observation
instruments that go up and down by their own buoyancy adjustment function and
acquire data from the surface layer to the middle layer of the ocean.
