Slope-enhanced fission of salty hetons under sea ice

Ocean responses to a single brine source under ice and over a sloping botto m are investigated in numerical experiments. Brine sources considered herei n are often much stronger than that anticipated from a single seawater free zing event in a time span of about 10 days. The authors have no evidence th at such strong sources exist in the ocean, but the consequent heton-like ed dies manifest interesting features over a bottom slope. The numerical model contains a stratified ocean capped by an ice layer. The convection initial ly generates a top cyclone and a submerged anticyclone vertically stacked t ogether. Under sea ice, the top cyclone dissipates in time and often breaks up into several distinct cyclonic vortices. Through heton-type couplings, the breakaway shallow cyclones are often able to tear the underlying anticy clone apart to form distinct anticyclones. Top cyclones are eventually anni hilated by ice-exerted friction, leaving submerged anticyclones in stable e xistence. Fission from a pair of vertically stacked baroclinic vortices is a fundamental process associated with a strong brine source under sea ice, A bottom slope generally enhances fission, often increasing the number of s ubsurface anticyclones or causing the resulting anticyclones to break farth er away from the source. The slope enhancement is consistent with the poten tial vorticity conservation requirement and a changing Rossby radius with w ater depths. The foregoing conclusions remain the same in cases with a stat ionary brine source moving rigidly with a uniform current. Under the less l ikely scenario of a stationary source embedded in a mean flow, brine waters spread downstream and become less effective in producing distinct vortices . Granting the occurrence of strong baroclinic vortices under sea ice, the preferable increase of anticyclones at depths may help explain the overwhel ming predominance of submerged anticyclones in the ice-covered Arctic Ocean .