Projected AMOC Weakening Controls Future Diatom Decline in the Subpolar North Atlantic Ocean
Abstract
Climate models consistently project a decline in diatom net primary production (NPP) under highemission scenarios in the highly productive subpolar North Atlantic. However, the magnitude of this decline remains highly uncertain and varies substantially across models, limiting our ability to anticipate its ecological and biogeochemical consequences. Several recent studies using individual Earth system models have identified a mechanistic relationship between the projected weakening of the Atlantic Meridional Overturning Circulation (AMOC) and the availability of NO 3 for phytoplankton growth in the subpolar North Atlantic. These findings suggest that uncertainty in the future evolution of the AMOC may be a major driver of the spread in diatom NPP projections. Here, we analyze an ensemble of Earth system models to test this hypothesis and to better constrain projections of diatom NPP. We first show that a robust inter-model relationship exists between projected changes in AMOC intensity and NO 3 availability in the subpolar North Atlantic. We then apply an emergentconstraint framework to estimate the future sensitivity of diatom NPP to nitrate changes, using satellite-based reconstructions of historical NPP and nitrate variability. Combining these two approaches yields a constrained relationship between projected AMOC weakening and the associated decline in diatom NPP. Our results confirm that uncertainty in the magnitude of future AMOC weakening constitutes the dominant source of uncertainty in diatom NPP projections. Nevertheless, they suggest a smaller decrease in diatom NPP than previously anticipated for a plausible range of AMOC decline.
Plain Language Summary Diatoms are microscopic algae that play a key role in ocean ecosystems and the global carbon cycle. In the subpolar North Atlantic, one of the most productive ocean regions, climate models predict that diatom productivity will decline during the 21st century under high greenhouse gas emissions. However, this projected decline varies widely between models, making it difficult to anticipate its ecological consequences. One explanation involves the Atlantic Meridional Overturning Circulation (AMOC), a large current system transporting nutrient-rich waters toward the North Atlantic. If the AMOC weakens, fewer nutrients such as nitrate would reach the surface ocean, reducing phytoplankton growth. Here, we analyze several climate models to understand this relationship. We show that models projecting stronger AMOC weakening also project larger decreases in surface nitrate. Using satellite observations of present-day productivity and nitrate variability, we estimate how diatom productivity responds to nitrate changes. Combining these observations with model projections, we obtain improved estimates of future diatom productivity. Our results indicate that uncertainty in AMOC weakening is the main driver of model disagreement, and suggest that the future decrease in diatom productivity may be smaller than previously anticipated.
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BibTeX
@article{doleac2026projected,
title = {{Projected AMOC Weakening Controls Future Diatom Decline in the Subpolar North Atlantic Ocean}},
author = {S Doléac and Marina Levy and L Bopp},
journal = {Earth's Future},
year = {2026},
month = sep,
doi = {10.1029/2025ef007992},
url = {https://cnrs.hal.science/hal-05736600v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Projected AMOC Weakening Controls Future Diatom Decline in the Subpolar North Atlantic Ocean
AU - S Doléac
AU - Marina Levy
AU - L Bopp
PY - 2026
DA - 2026/09/03
JO - Earth's Future
DO - 10.1029/2025ef007992
UR - https://cnrs.hal.science/hal-05736600v1
AB - Climate models consistently project a decline in diatom net primary production (NPP) under highemission scenarios in the highly productive subpolar North Atlantic. However, the magnitude of this decline remains highly uncertain and varies substantially across models, limiting our ability to anticipate its ecological and biogeochemical consequences. Several recent studies using individual Earth system models have identified a mechanistic relationship between the projected weakening of the Atlantic Meridional Overturning Circulation (AMOC) and the availability of NO 3 for phytoplankton growth in the subpolar North Atlantic. These findings suggest that uncertainty in the future evolution of the AMOC may be a major driver of the spread in diatom NPP projections. Here, we analyze an ensemble of Earth system models to test this hypothesis and to better constrain projections of diatom NPP. We first show that a robust inter-model relationship exists between projected changes in AMOC intensity and NO 3 availability in the subpolar North Atlantic. We then apply an emergentconstraint framework to estimate the future sensitivity of diatom NPP to nitrate changes, using satellite-based reconstructions of historical NPP and nitrate variability. Combining these two approaches yields a constrained relationship between projected AMOC weakening and the associated decline in diatom NPP. Our results confirm that uncertainty in the magnitude of future AMOC weakening constitutes the dominant source of uncertainty in diatom NPP projections. Nevertheless, they suggest a smaller decrease in diatom NPP than previously anticipated for a plausible range of AMOC decline. Plain Language Summary Diatoms are microscopic algae that play a key role in ocean ecosystems and the global carbon cycle. In the subpolar North Atlantic, one of the most productive ocean regions, climate models predict that diatom productivity will decline during the 21st century under high greenhouse gas emissions. However, this projected decline varies widely between models, making it difficult to anticipate its ecological consequences. One explanation involves the Atlantic Meridional Overturning Circulation (AMOC), a large current system transporting nutrient-rich waters toward the North Atlantic. If the AMOC weakens, fewer nutrients such as nitrate would reach the surface ocean, reducing phytoplankton growth. Here, we analyze several climate models to understand this relationship. We show that models projecting stronger AMOC weakening also project larger decreases in surface nitrate. Using satellite observations of present-day productivity and nitrate variability, we estimate how diatom productivity responds to nitrate changes. Combining these observations with model projections, we obtain improved estimates of future diatom productivity. Our results indicate that uncertainty in AMOC weakening is the main driver of model disagreement, and suggest that the future decrease in diatom productivity may be smaller than previously anticipated.
SN - 2328-4277
SN - 2328-4277
ER -