Energetic overturning flows, dynamic interocean exchanges, and ocean warming observed in the South Atlantic

Abstract

Since the inception of the international South Atlantic Meridional Overturning Circulation initiative in the 21st century, substantial advances have been made in observing and understanding the Southern Hemisphere component of the Atlantic Meridional Overturning Circulation (AMOC). Here we synthesize insights gained into overturning flows, interocean exchanges, and water mass distributions and pathways in the South Atlantic. The overturning circulation in the South Atlantic uniquely carries heat equatorward and exports freshwater poleward and consists of two strong overturning cells. Density and pressure gradients, winds, eddies, boundary currents, and interocean exchanges create an energetic circulation in the subtropical and tropical South Atlantic Ocean. The relative importance of these drivers varies with the observed latitude and time scale. AMOC, interocean exchanges, and climate changes drive ocean warming at all depths, upper ocean salinification, and freshening in the deep and abyssal ocean in the South Atlantic. Long-term sustained observations are critical to detect and understand these changes and their impacts.

Should AMOC observations continue: how and why?

“…Initially, individual observing arrays set out to quantify the AMOC transports (either volume transport only, or volume transport anomaly only, or also including heat and freshwater transport estimates). More recently, the capability to address other property transports (nutrients and carbon) using the same infrastructure have come to light and been implemented [95][96][97]. Defining requirements for an Atlantic-wide MOC observing system will need consultation with stakeholders to identify: priorities for which observational parameters (measured or derived) should be provided, and what level of accuracy or precision is required; time resolution (whether monthly, seasonal or annual snapshots or averages are needed) and the latency or frequency in Table 2.…”

A blueprint for integrating scientific approaches and international communities to assess basin-wide ocean ecosystem status

“…Understanding and predicting AMOC change requires a comprehensive observing system that needs to cover both North and South Atlantic 8 . In addition to the 20-year-long RAPID-MOCHA oceanographic sensor array in the subtropical North Atlantic, the arrays in the subpolar North Atlantic (OSNAP array 9 ) and the subtropical South Atlantic (SAMOC/SAMBA arrays 10 ) need upgrading to include ecosystem-relevant physical and biogeochemical measurements. Using high-resolution climate-based predictions of past and future ocean circulation, with a focus on eddy-rich resolutions to support observational records and species dispersal studies, we can simulate the past 60 years under realistic forcing 11 , thus allowing very detailed comparisons with instrumental observations 5,12 .…”

Inclusive science in the South Atlantic

“…The overall demographics of those who have advanced in this fashion have skewed female, and this has led to a present-day SAMOC science team with a large fraction of women oceanographers in leadership or co-leadership positions that write influential papers. For example, the SAMOC observational review article that appears in this Collection is led by eleven women scientists, most of whom are leading or co-leading SAMOC programs 23 . SAMOC is not a large community, and thus the sample size is relatively small, which makes it hard to be conclusive as to the reasons behind SAMOC's inclusive culture.…”

“…The authors would like to acknowledge the SAMOC Executive Committee and the SAMOC scientists for their support in this endeavor and for participation in the voluntary survey. We also thank Shenfu Dong and Chris Meinen for their insightful comments on an early draft of the article, as well as Regina Rodrigues and the authors of a recent SAMOC review article 23…”