this connection exists. New observations with the OSNAP array show little contribution from the Labrador Sea to overturning, and hydrographic observations from ships dating back to 1990 show similar results. Nevertheless, older estimates of LSW formation using different techniques suggest larger overturning. Atlantic upwelling For reasons of conservation of mass, the global ocean system must upwell an equal volume of water to that downwelled. Upwelling in the Atlantic itself occurs mostly due to coastal and equatorial upwelling mechanisms. Coastal upwelling occurs as a result of Ekman transport along the interface between land and a wind-driven current. In the Atlantic, this particularly occurs around the Canary Current and Benguela Current. Upwelling in these two regions has been modelled to be in antiphase, an effect known as "upwelling see-saw". Equatorial upwelling generally occurs due to atmospheric forcing and divergence due to the opposing direction of the Coriolis force either side of the equator. The Atlantic features more complex mechanisms such as migration of the thermocline, particularly in the Eastern Atlantic. Southern Ocean upwelling North Atlantic Deep Water is primarily upwelled at the southern end of the Atlantic transect, in the Southern Ocean. This upwelling comprises the majority of upwelling normally associated with AMOC, and links it with the global circulation. On a global scale, observations suggest 80% of deepwater upwells in the Southern Ocean. This upwelling supplies large quantities of nutrients to the surface, which supports biological activity. Surface supply of nutrients is critical to the ocean's functioning as a carbon sink on long timescales. Furthermore, upwelled water has low concentrations of dissolved carbon, as the water is typically 1000 years old and has not been sensitive to anthropogenic increases in the atmosphere. Because of its low carbon concentration, this upwelling functions as a carbon sink. Variability in the carbon sink over the observational period has been closely studied and debated. The size of the sink is understood to have decreased until 2002, and then increased until 2012. After upwelling, the water is understood to take one of two pathways: water surfacing near to sea-ice generally forms dense bottomwater and is committed to AMOC's lower cell; water surfacing at lower latitudes moves further northward due to Ekman transport and is committed to the upper cell. Slowdown or shutdown of the thermohaline circulation The slowdown or shutdown of the thermohaline circulation is a hypothesized effect of climate change on a major ocean circulation.