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# The North Atlantic Subpolar Gyre and Phytoplankton Bloom Under Potential Future Climate Scenarios

## Details

**Authors** Sophy Oliver, Andrew Yool, Lee de Mora, Stephen Kelly, Spencer K. Liddicoat, Alexandra Loveridge, Robin S. Smith, Ekaterina Popova

**Year** 2026

**Publisher** Journal of Geophysical Research: Oceans

**Kind of work** article

**Discipline** Oceanography

**Applied** false

[Read it at the publisher](https://doi.org/10.1029/2025JC023561) 
10.1029/2025JC023561

## In authors' words

### Abstract

The North Atlantic phytoplankton bloom (NAB) forms the base of the food web upon which marine ecosystem services throughout the northern North Atlantic rely. The NAB's nutrient supply is predominantly driven by deep winter mixing, which is most pronounced in the subpolar gyre where it has been projected to abruptly decline within the next few decades. Here we use idealized experiments with an Earth system model to investigate how mixed layer depth, surface nutrients and chlorophyll concentrations over the gyre may respond to positive carbon emissions followed by both zero and negative emissions mitigation efforts initiated at various Global Warming Levels (GWLs). Results show a decline in all three variables during positive emissions, with the warmer the GWL the less likely the prospect of recovery back to pre-industrial conditions. In the scenario where carbon emissions are held at zero once reaching a GWL of 1.5°C, the NAB started to recover toward preindustrial conditions. However, zero emissions after 2.5°C and warmer showed a continued decline in the NAB. These results suggest a tipping threshold may lie between 1.5 and 2.5°C GWL, beyond which only negative emissions can achieve recovery of the NAB.

### What they set out to do (purpose)

To test how the North Atlantic spring phytoplankton bloom and its physical drivers respond to different peak global-warming levels and to zero- or negative-emissions mitigation pathways.

### Who or what was studied (sample)

Idealized Earth-system-model experiments simulating the North Atlantic subpolar gyre across a range of global warming levels and post-peak emissions pathways.

### How they did it (methods)

An Earth system model was run under positive emissions followed by zero- or negative-emissions scenarios initiated at different global warming levels, tracking mixed layer depth, surface nutrients, and chlorophyll concentration over the subpolar gyre.

### What they found (results)

The modeled bloom began recovering toward pre-industrial conditions when warming was held at 1.5°C under zero emissions, but continued to decline under zero emissions when warming exceeded 2.5°C, indicating a tipping threshold for bloom recovery lies between 1.5°C and 2.5°C of global warming.

## Commentary

### In short

The finding shows that a single continuous driver, peak warming level, can push a coupled physical-biological system across a threshold separating two qualitatively distinct long-term outcomes for the whole ecosystem.

**Patterns it shows** D, S, R

**Added** 2026-09-28

**How to cite this** Sophy Oliver, Andrew Yool, Lee de Mora, Stephen Kelly, Spencer K. Liddicoat, Alexandra Loveridge, Robin S. Smith, Ekaterina Popova (2026). The North Atlantic Subpolar Gyre and Phytoplankton Bloom Under Potential Future Climate Scenarios. Journal of Geophysical Research: Oceans.