Deep convection in the World Ocean

TLDR

Polar regions influence climate, and oceanic deep convection occurs in two distinct types: classic shelf‑slope sinking and more recently observed open‑ocean convection. The paper surveys the known deep‑convection areas of the world ocean, covering both classic shelf‑slope and recently observed open‑ocean convection. Deep convection is driven by sea‑ice freezing and brine ejection that generates dense water which sinks along continental slopes under Coriolis, gravity, and friction, entraining surrounding warm water. Open‑ocean convection occurs in narrow 20–50 km zones, produces ~10 m³ s⁻¹ of deep water, is confined to cyclonic circulation regions, involves multiple water masses, requires preconditioning and surface forcing, and often ends violently within ~2 weeks.

Abstract

A brief discussion of, and a little speculation about, the relevance of the polar regions on climate is given. The main body of the paper gives a survey of the known deep convection areas of the world ocean. There are two distinct types of convection. The first is the classic sinking occurring on continental shelf slope systems, as typified by various locations around the Antarctic coast. The freezing of sea ice, and resulting brine ejection, creates dense salty water on the shelf which descends the slope under a balance of Coriolis, gravity, and frictional forces, entraining the surrounding warm deep water as it goes. The second process is the more recently observed open‐ocean convection, occurring in locations such as the Mediterranean, the Labrador Sea, and two locations in the Weddell gyre, and is hypothesized to occur in the Greenland Sea. Open‐ocean convection has many overall similarities in all these areas: it occurs in narrow (20–50 km) areas; it forms about 10 m³ s −l of deep water; it occurs only in regions of cyclonic mean circulation; more than one water mass in the mean circulation is involved; a preconditioning seems to be required; some surface forcing (cooling or sea ice formation) is necessary; a violent breakup of the water mass frequently occurs on time scales of 2 weeks.