Agulhas ring injection into the South Atlantic during glacials and interglacials

[摘要] Recent proxies suggest that, at the end of the last glacial, there was asignificant increase in the injection of Agulhas rings into the SouthAtlantic (SA). This brought about a dramatic increase in the salt-influx(from the Indian Ocean) into the SA helping re-start the then-collapsedmeridional overturning cell (MOC), leading to the termination of the YoungerDryas (YD). Here, we propose a mechanism through which large variations inring production take place.

Using nonlinear analytical solutions for eddy shedding, we show that there arerestricted possibilities for ring detachment when the coast is oriented inthe north-south direction. We define a critical coastline angle below whichthere is rings shedding and above which there is almost no shedding. In thecase of the Agulhas region, the particular shape of the African continentimplies that rings can be produced only when the retroflection occurs beyonda specific latitude where the angle is critical. During glaciation, the windstress curl (WSC) vanished at a latitude lower than that of the criticalangle, which prohibited the retroflection from producing rings. When thelatitude at which the WSC vanishes migrated poleward towards its present dayposition, the corresponding coastline angle decreased below the criticalangle and allowed for a vigorous production of rings.

Simple process-oriented numerical simulations (using the Bleck and Boudramodel) are in satisfactory agreement with our results and enable us toaffirm that, during the glacials, the behavior of the Agulhas Current (AC)was similar to that of the modern East Australian Current (EAC), for whichthe coastline slant is supercritical.

[学科分类] 海洋学与技术