Impact of Past AMOC Disruptions on Ocean Oxygenation

The global ocean plays a crucial role in redistributing and storing heat, carbon, nutrients and other essential elements in the Earth’s climate system. As a prominent part of the global ocean circulation, the Atlantic Meridional Overturning Circulation (AMOC) shapes the spatial distribution of these elements and links the atmosphere to the deep ocean.

The state of ocean oxygenation and the carbon storage capacity are tightly connected to biogeochemical activity. High oxygen levels facilitate the efficient remineralization of organic matter, helping to stabilize the CO₂ content in the upper ocean layers. In contrast, low oxygen levels enhance carbon storage in the deep ocean temporarily but increase the risk of pronounced outgassing during ocean circulation changes or upwelling events. Thus, ocean oxygenation acts both as an indicator and a control on biogeochemistry and thus long-term climate regulation.

Proxy data indicate substantial changes in AMOC strength in the past, particularly during Termination 1, when high freshwater fluxes disrupted deep water formation and significantly slowed down the ocean circulation. Despite these insights, the interplay between changes in ocean circulation, oxygenation and carbon storage and release during such abrupt events is still not fully understood.

To address these knowledge gaps, we used the Max Planck Institute for Meteorology Earth system model (MPI-ESM) coupled with the interactive Hamburg ocean carbon cycle model (HAMOCC) to simulate transient climate changes during the last deglaciation.

We focused on periods of major AMOC disruptions during the last deglaciation to investigate their impact on the ocean’s oxygen levels in the water column.

Preliminary results indicate a delayed increase of the global oxygen minimum zone (OMZ) volume following abrupt AMOC changes. The most significant changes in the oxygen levels can be observed in the Atlantic Sector of the Southern Ocean. Additionally, we explore the feedbacks between changes in oxygenation, carbon storage, and biological activity across these events.

This research provides new insights into the complex interplay between ocean circulation, oxygen dynamics, and carbon storage during deglacial periods, advancing our understanding of the mechanisms underlying abrupt climate events and their biogeochemical impacts.