The nested structure of Arctic thermohaline intrusions

Arctic thermohaline intrusions have a “nested” temperature/salinity structure characterized by the lining up of widely separated profiles along a series of well-defined lines in the T–S plane. The nesting pattern is coherent across much of the Arctic Basin (>2000 km), and roughly 90% of the water column between 150 and 350 m depth is found to lie along these nesting lines. We propose the nested structure results from a type of slanted convection occurring within the thick, salt-finger stratified layers in the intrusions. The convection cells are reminiscent of those investigated in laboratory experiments done by Thorpe, Hutt, and Soulsby, and it is estimated that the cells have horizontal dimensions ranging from 50 to 100 km at depths close to the Atlantic Water temperature maximum. Simple theoretical ideas suggest the convective cells may appear when the intrusions reach a critical amplitude, driving them toward a nested configuration. Our analysis provides a new estimate of the effective lateral diffusivity due to the intrusions (≃50 m2 s−1), as well as an estimate of the vertical diffusivity near the core of the Atlantic Water layer (≃0.8×10−5 m2 s−1).