The circulation of the Atlantic Ocean may be idealized as a combination of separate vertical and horizontal cells that are gradually interconnected through relatively slow vertical motions. In the vertical cell, deep waters form at high latitudes of the North Atlantic and follow a long meridional trip to end in the lower layers of the Antarctic Circumpolar Current (ACC). These deep ACC waters leave the Atlantic Basin for up to hundreds of years, via the Southern Ocean, before returning to the Atlantic basin at shallower thermocline levels, as either intermediate subantarctic or Indian-Ocean central waters, that will progress northwards to ultimately reach the high-latitude surface North Atlantic. In the horizontal cells, the thermocline waters flow as partly isolated wind-driven transoceanic tropical, subtropical and subpolar gyres, connected precisely through the returning branch of the vertical cell.
This simple view of the vertical cell constitutes the basics of what is known as the Atlantic Meridional Overturning Circulation (AMOC), with North Atlantic Deep Waters (NADW) supplying the mean southward departure limb and with the returning limb being formed by the mean northward-flowing intermediate and surface waters. However, the vertical structure of the AMOC turns even more complex because of the formation of Antarctic Bottom Waters (AABW) around Antarctica, which combines with the NADW returning limb in what is known as the Southern Ocean vertical cell.
Together with mesoscale mixing, the returning limb of the AMOC is the major latitudinal connector of the intermediate and upper layers in the entire Atlantic Ocean. Thanks to these returning AMOC waters, the transoceanic gyres exchange mass, heat and all sorts of properties, causing that no single part of the Atlantic remains isolated: it connects the Southern Ocean and the subtropical and tropical gyres of both hemispheres. In particular, the AMOC has a major role on heat transport to high latitudes of the Atlantic Ocean, contributing to temperate the weather in northern Europe. This meridional heat transport can also drive substantial changes in the formation and characteristics of NADW, increasing the temperature of this southward deep flow. As these warmer waters reach the Southern Ocean, they can have a large impact in the melting of Antarctic continental ice and, hence, on sea level rise.
The South Atlantic Ocean stands as the most important and yet most unknown AMOC gateway, not only for the intermediate and surface northward returning AMOC limb but also for the deep and bottom layers: the southward flowing NADW and the Southern Ocean vertical cell. This is what we know as the South AMOC or SAMOC. In the returning limb, most of the complexity arises in the horizontal, as cold- fresh Southern Ocean waters through the Drake Passage and warm-salty Agulhas rings and filaments are incorporated to the South Atlantic, but have to escape from the subtropical and tropical gyres in order to reach the northern hemisphere. In the departing limb, the complexity stands out in the vertical, with NADW progressing through Mid-Atlantic Ridge constrictions before reaching the Southern Ocean and eventually upwelling near the continental slope of Antarctica, and AABW sinking along this continental slope and joining the deep vertical cell of the Southern and South Atlantic Oceans. The elucidation of these bidirectional pathways constitutes the core of the SACO proposal.
Role: co-PI
Website: in prep.
dates: 2023-2026