Mixing and Geometry in the North Atlantic Meridional Overturning Circulation

TL;DR

This paper investigates the 3D mixing structures and vertical transport pathways of the Atlantic Meridional Overturning Circulation using Lagrangian Coherent Structures, revealing new insights into deep water upwelling and downwelling zones.

Contribution

It introduces the application of Lagrangian Coherent Structures to analyze the geometry of mixing and vertical transport in the AMOC, identifying new upwelling connections.

Findings

Rapid ascent of deep waters at Flemish Cap

Confirmation of downwelling zone in Irminger Sea

Discovery of a previously unreported upwelling connection

Abstract

Vertical motions across the ocean are central to processes, like CO$_2$ fixation, heat removal or pollutant transport, which are essential to the Earth's climate. This work explores 3D conveyor routes {associated with} the Atlantic Meridional Overturning Circulation (AMOC). Our findings show the geometry of mixing structures in the upper and deep ocean layers by means of Lagrangian Coherent Structures. This tool identifies among others, zones linked to vertical transport and characterizes vertical transport time scales. We focus the study in two regions. The first one is the Flemish Cap region, a zone of interaction between the major AMOC components, where our analysis identifies a domain of deep waters that ascend very rapidly to the ocean surface. The second one is the Irminger Sea, where our analysis confirms the existence of a downwelling zone, and reveals a previously unreported upwelling connection between very deep waters and the ocean surface.