Surprising Twist: Marine Heatwaves Boost Coastal CO2 Uptake by 11%

In a surprising turn for climate science, a recent analysis has found that marine heatwaves actually increase carbon dioxide (CO2) uptake by coastal waters by an average of 11%, challenging previous assumptions about the ocean's role in global warming. This unexpected boost is particularly strong in the polar and subpolar shelf seas, offering a complex new layer to our understanding of the ocean's fight against rising atmospheric CO2 levels. The study, which looked at data from 1985 to 2020, highlights how these extreme warming events, often seen as purely destructive, can have unforeseen effects on the global carbon budget. While warmer waters generally mean less CO2 can dissolve, this coastal phenomenon is driven by specific non-thermal factors: in polar areas, marine heatwaves lead to significant sea-ice loss, opening up more surface water for gas exchange and boosting the growth of tiny ocean plants through photosynthesis. This allows coastal shelf seas to absorb more CO2, contrasting sharply with the open ocean where heatwaves typically reduce CO2 uptake by around 8%. However, it's not all good news, as other research from 2025 indicates that marine heatwaves can disrupt the ocean's 'biological carbon pump', slowing the transport of carbon to the deep sea and potentially weakening a crucial long-term carbon storage process. This discovery forces scientists to refine climate models and better understand the intricate dance between ocean warming and carbon cycling. While this enhanced coastal CO2 uptake offers a small, localized buffer against climate change, experts caution against seeing it as a solution, calling it a 'fragile resilience.' The ongoing increase in marine heatwaves and their varied impacts across different ocean regions underline the urgent need for continuous, detailed monitoring to predict how our planet's natural systems will truly respond to a rapidly warming world.