The phrase "cold tongue" means to be silent, not sharing thoughts or opinions openly. It refers to someone who is unwilling to speak or express themselves. Full definition
Satellites had spotted cold tongues of surface water extending westward from the South American coast, an indicator of a strong La Niña, El Niño's opposite number. (sciencemag.org)
Seasonal sea surface cooling in the equatorial Pacific cold tongue controlled by ocean mixing (realclimate.org)
The eastern Pacific Ocean cold tongue appeared as Earth's climate cooled and subpolar waters expanded in the Pleistocene. (science.sciencemag.org)