Pathways, Form Drag, and Turbulence in Simulations of an Ocean Flowing Through an Ice Mélange

Abstract

AbstractA collection of calved icebergs frozen in place by surrounding sea ice (a “mélange”) is common in many Greenlandic fjords. Being an obstacle to ocean currents, a mélange alters ocean dynamics and thermodynamics over the many kilometers that it extends out in front of the glacier. Here we focus on a set of dynamics—flow pathways, form drag, and turbulence—using many simulations that each resolve the flow around hundreds of volume‐occupying, but otherwise passive, cuboid “icebergs.” Some streaks of fast flow do arise where currents are squeezed through gaps between icebergs but, on average, the near‐surface current is slowed. Maximum average currents speeds are instead found at or below the drafts of the deepest icebergs. Form drag scales with U2h when few icebergs exist and smoothly transitions to scaling with NUh2 when many icebergs exist, where U is the far‐field flow velocity, N is the buoyancy frequency, and h is a typical iceberg draft. Turbulence predominately occurs in wakes behind the icebergs (as opposed to below icebergs due to internal wave breaking). Consequently, turbulent dissipation is elevated at depths less than or near the drafts of larger icebergs (∼100 m).