Areal extent of the benthic front and variation of the scale height in Pacific Deep and Bottom Waters

Abstract

The areal extent of the benthic front—a continuous surface separating the cold Bottom Water and the warmer Deep Water in the Pacific—is studied on the basis of observed potential temperature and salinity profiles. The extent of the benthic front indicates spreading of the Bottom Water from the Antarctic circumpolar region into the Pacific. It is found that the Bottom Water spreads as far north as 20°N as a recognizable entity in temperature profiles. Farther north the vertical mixing between these two water masses has effectively erased the characteristics of the benthic front. A vertical diffusion and advection model has been used to calculate the mixing parameter, or scale height, for both the Deep and the Bottom Water. This parameter is unique in characterizing the potential temperature profiles, and its variation in the Pacific has been mapped. It is found that both the scale height for the Bottom Water and the thickness of the Bottom Water layer itself decrease northward. On the other hand, the scale height for the Deep Water and the thickness of the Deep Water layer both increase toward the north. Thus the scale height is related to the thickness in each of these water masses, and its systematic variation has significant implications for the nature of large-scale mixing and circulation in the Pacific.