ArMOC: Overturning circulation in the new Arctic

The ArMOC project will provide new, fundamental knowledge about key oceanic processes for the Arctic overturning circulation and their sensitivity to climate change. ArMOC will accordingly lead to reduced uncertainties in projections of Arctic climate change and an improved understanding of the role of the Arctic Ocean in global ocean circulation changes.


The primary objective of ArMOC is to understand how present and future Arctic climate change impacts the Arctic overturning circulation, which feeds the lower limb of the AMOC.

We will achieve this through the following secondary objectives:
1. Quantify changes in AW modification along the AWBC.
2. Identify changes in AW pathways in present and future climates using Lagrangian simulations.
3. Determine the effects of a changing climate on the Arctic overturning circulation.

Project Summary

The Arctic overturning circulation involves the production of water masses that are key to the global ocean circulation associated with the Atlantic Meridional Overturning Circulation (AMOC). Arctic climate is, however, rapidly changing, and it is currently not known how the Arctic overturning circulation is responding. Dense-water formation that is a requirement to sustain the AMOC has canonically been thought to take place through deep convection in the Labrador and Greenland Seas. However, recent observations and model results suggest that the main source of dense water to the lower limb of the AMOC is Atlantic Water (AW) that gradually transforms to denser waters on its path along the Atlantic Water Boundary Current (AWBC) in the Nordic Seas and Arctic Ocean. The recent sea-ice retreat along the margins of the Arctic Ocean has partially uncovered the AWBC, exposing it to the atmosphere in winter and, hence, allowing further modification of the AW. As the transition towards a seasonally ice-free Arctic continues, more years of enhanced convection can be expected, leading to a possible strengthening of the Arctic overturning circulation. The Arctic overturning circulation could therefore be a stabilizing factor in a weakening AMOC, highlighting the importance of understanding its drivers and its response to climate change.

ArMOC will accordingly provide:

1. A step-change in our understanding of the Arctic overturning circulation in present and future climates by providing a first quantification using the approach of thermohaline streamfunctions.

2. A comprehensive understanding of the entire AWBC system around the Nordic Seas and the Arctic Ocean from observations, including new, unique wintertime data from Argo floats, and high-resolution models.

3. Novel insights on AW pathways and transformation within the Arctic Ocean, and whether these are expected to change under future global warming, through Lagrangian analysis with high- and low-resolution models.

Project Details
Funding Agency: 
Research Council of Norway
NERSC Principal Investigator: 
Yanchun He
Project Deputy Leader at NERSC: 
Helene R. Langehaug
Coordinating Institute: 
Nansen Environmental and Remote Sensing Center
Project Status: