We review what is known about the convective process in the open ocean, in which the properties of large volumes of water are changed by intermittent, deep-reaching convection, triggered by winter storms. Observational, laboratory, and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales, the large-scale circulation of the ocean, and the prevailing meteorology. Two aspects make ocean convection interesting from a theoretical point of view. First, the timescales of the convective process in the ocean are sufficiently long that it may be modified by the Earth's rotation; second, the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability. Moreover, the convective and geostrophic scales are not very disparate from one another. Detailed observations of the process in the Labrador, Greenland, and Mediterranean Seas are described, which were made possible by new observing technology. When interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection, great progress in our description and understanding of the processes at work is being made.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98RG02739

Open-ocean convection: Observations, theory, and models

The South Atlantic Ocean receives waters from the North Atlantic, the Weddell Sea, and from the Circumpolar Current through the Drake Passage. The circumpolar and North Atlantic waters are of widely different characteristics (temperature, salinity, oxygen and nutrients) but of overlapping density ranges, and as they enter the South Atlantic are caught up in the circulation imposed by the winds and thermohaline processes. Interleaving of these different characteristics takes place in various ranges of depth and density, and more than a dozen vertical extrema are created in the tracer fields. These are spread by lateral flow in recognizable layers. These patterns as seen on vertical sections and on isopycnals can be taken to indicate the sense of flow in various areas and depths, and I have used them, with the density field, to add the barotropic component to the baroclinic flow defined by the density field. This gives the total geostrophic flow at all depths in a manner that appears to be consonant with the tracer patterns, and that satisfies continuity of mass. The resulting flow field has the traditional western boundary current from the Weddell Sea to the equator, beneath a poleward flow north of 50°S. In the upper waters the flow pattern shows a cyclonic gyre in the Weddell Sea, a northward flow from the Antarctic along the western boundary from 55°S to 40°S, an anticyclonic gyre between 15°S and 40°S, and an eastward flow near 10°S. Below the upper layer the axis of the anticyclonic gyre shifts southward, to 35°S at 1500 m, and at greater depths the gyre is confined to the Brazil Basin, west of the Mid-Atlantic Ridge and north of the Rio Grande Rise. Below the crest of the Mid-Atlantic Ridge in the Brazil Basin waters from the south flow northward along the Ridge, and part of them crosses the Ridge at or near the equator and returns southward in the eastern basin, joined by waters from the North Atlantic. The northward abyssal flow in the Brazil Basin is not confined to the western boundary but extends some distance across the basin, diverted only slightly at 3500 m by the small deep remnant of the overlying anticyclonic gyre. From 3000 to 4000 decibars the flow within the Weddell Sea and the Argentine Basin form a single cyclonic gyre and the flow within the Cape Basin is cyclonic below 3000 m.

On the Total Geostrophic Circulation of the South Pacific Ocean: Flow Patterns, Tracers and Transports

Central Themes of South Atlantic Circulation.- On the Circulation of the South Atlantic Ocean.- Transient-Tracer Information on Ventilation and Transport of South Atlantic Waters.- The Circulation and its Variability of the South Atlantic Ocean: First Results from the TOPEX/POSEIDON Mission.- The Zonal WOCE Sections in the South Atlantic.- South Atlantic Heat Transport at 11 S.- Comment on the South Atlantic's Role in the Global Circulation 121 -.- The Exchange of Water between the South Indian and South Atlantic Oceans.- The Benguela: Large Scale Features and Processes and System Variability.- The Southern Boundary of the South Atlantic.- Antarctic Intermediate Water in the South Atlantic.- Lagrangian Measurements in the Malvinas Current.- Circulation in the Deep Brazil Basin.- The Deep Water Regime in the Equatorial.- Chlorofluoromethanes in the Deep Equatorial Atlantic Revisited.- Modelling the Ocean Circulation in the South Atlantic: A Strategy for Dealing with Open Boundaries.- Mass and Heat Transports in the South Atlantic Derived from Historical Hydrographic Data.- Long-term Observation of Particle Fluxes in the Eastern Atlantic: Seasonality, Changes of Flux with Depth and Comparison with the Sediment Record.- Silica Signals in the South Atlantic.- On the Bathymetry of the Hunter Channel.- Expeditions into the Past: Paleoceanographic Studies in the South Atlantic.- Inverse Modelling of the Glacial Atlantic CirculationSystem: Investigation of Data Requirements.- Chemical Hydrography of the South Atlantic During the Last Glacial Maximum: Cd vs. ?13C.- High Latitude Deep Water Sources During the Last Glacial Maximum and the Intensity of the Global Oceanic Circulation.- Late Quaternary Surface Circulation in the South Atlantic: The Stable Isotope Record and implications for Heat Transport and Productivity.- Climate Feedback and Pleistocene Variations in the Atlantic South Equatorial Current.- Late Quaternary Surface Temperatures and Productivity in the East-Equatorial South Atlantic: Response to Changes in Trade/Monsoon Wind Forcing and Surface Water Advection.- Late Quaternary Movements of the Angola- Benguela Front, SE Atlantic, and Implications for Advection in the Equatorial Ocean.- Late Quaternary Deep Circulation in the Western Equatorial Atlantic.- Late Quaternary Deep Water Circulation in the South Atlantic: Reconstruction from Carbonate Dissolution and Benthic Stable Isotopes.- Clay Mineral Fluctuations in Late Quaternary Sediments of the Southeastern South Atlantic: Implications for Past Changes of Deep Water Advection.

The South Atlantic: Present and Past Circulation

Circulation and bottom water production in the Weddell Sea

The exchange of mass and heat between the South Atlantic and the neighboring ocean basins was estimated using hydrographic data and inverse methods, in order to gain information on the links between the deep-water formation processes occurring within the Atlantic and the global thermohaline circulation. Results demonstrate that the global thermohaline cell associated with the formation and export of North Atlantic deep water (NADW) is closed primarily by a 'cold water path' in which deep water leaving the Atlantic ultimately returns as intermediate water entering the basin through Drake Passage. This conclusion conflicts with the suggestion by Gordon (1986) that the global thermohaline circulation associated with the formation of NADW is closed primarily by a 'warm water path', in which the export of NADW is compensated by an inflow of warm Indian Ocean thermocline water south of Africa.

W.R. Wright

Papers

Northward transport of antarctic bottom water in the western Atlantic Ocean

Abyssal circulation over the Greater Antilles Outer Ridge

Northern sources of energy for the deep Atlantic