Isopycnic /(?)/

I·so·pyc·nic

Isopycnic

a.
  1. Having equal density, as different regions of a medium; passing through points at which the density is equal; as, an isopycnic line or surface. (Physics)

Isopycnic

n.
  1. A line or surface passing through those points in a medium, at which the density is the same. (Physics)