N1 – Ocean Circulation

This research project investigates the Atlantic meridional overturning circulation (AMOC), a critical component of Earth's climate system that transports heat northward and influences climate patterns on decadal timescales. As climate change progresses, the AMOC is expected to weaken, potentially exacerbating global warming by reducing the ocean's capacity to remove heat and CO₂ from the atmosphere. However, current climate models show dramatic disagreement about future AMOC behaviour, including whether it may collapse by 2100. Recent observations have revealed surprising disconnects between observed and simulated AMOC processes that contradict long-held scientific assumptions, highlighting critical gaps in our understanding of this vital climate component.

Introducing an innovative approach that combines cutting-edge observations with unprecedented high-resolution global climate modelling, the project addresses the fundamental question: What processes dominate the transmission of information along the sequence from atmospheric forcing to convection to sinking and overturning, and how does resolving small-scale processes in the atmosphere and ocean change simulated AMOC variability and its impacts? The project employs the next-generation km-scale ICON climate model alongside autonomous ocean observations to identify missing processes responsible for AMOC variability.

By addressing critical uncertainties in AMOC projections, the project pursues three main objectives:

• determining the key processes that link deep ocean convection to large-scale overturning circulation, using seawater density diagnostics and autonomous underwater glider finescale observations in the subpolar North Atlantic;
•  characterising how regional processes in the subpolar Atlantic influence basin-scale AMOC behaviour, employing sophisticated tracer and particle-tracking methods in high-resolution simulations combined with modern observational techniques;
• re-evaluating the likelihood and consequences of AMOC slowdown, testing whether resolving small-scale processes leads to more extreme climate variability or, conversely, to a more resilient and stable climate system.

The research is structured into three interconnected work packages that combine observational and modelling approaches to revolutionise understanding of ocean circulation and climate:

Work package 1: Processes linking convection and overturning 

Lead: E. Frajka-Williams

We deploy long-endurance marine gliders in the subpolar North Atlantic spanning winter-to-spring to characterise how small-scale processes control the relationship between deep convection, boundary currents, and regional overturning. High-resolution simulations investigate turbulent mixing processes to identify key mechanisms controlling convection and water mass export.

Work package 2: Imprint of subpolar processes on basin-scale AMOC

Lead: J. Marotzke


We develop process-level understanding of how regional subpolar processes influence the wider AMOC system through sophisticated passive tracer and Lagrangian diagnostics in mesoscale-resolving simulations, combined with existing observational networks to quantify connections between local dense water formation and basin-scale circulation.

Work package 3: Consequences and collaboration

Lead: J. Marotzke / E. Frajka-Williams 


We test whether resolving small-scale processes leads to more extreme AMOC variability or greater climate resilience, evaluating how AMOC changes affect other climate system components including sea ice, carbon storage, European weather patterns, and Arctic conditions.