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Forest fires are a fundamental force in Earth's dynamics with a direct impact on human health, food security, and biodiversity. From air quality to landscape configuration and resource availability, the consequences of fire have influenced the development of society throughout history. Their effects on the oceans, though less known, are equally significant.

Fires release particles and nutrients into the atmosphere that travel long distances and are deposited in ocean waters, influencing the development of phytoplankton, aquatic photosynthetic microorganisms that absorb COâ‚‚ from the atmosphere. This phenomenon, similar to when agricultural land is fertilized to increase production, influences Earth's carbon cycle and, therefore, has consequences for global climate balance.

A new study led by researchers from the Barcelona Supercomputing Center—Centro Nacional de Supercomputación (BSC-CNS) and ICREA, in the journal Nature Climate Change, provides new information on the link between forest fires and marine ecosystems. The work shows that climate change could significantly increase fires, especially in boreal areas, and, therefore, associated iron emissions, as well as the supply of this micronutrient to the ocean, boosting phytoplankton productivity.

"Climate-driven fires arise from more favorable weather conditions for fire, such as low humidity and high temperatures, which in turn are influenced by anthropogenic climate change. Understanding these fires and their impact on the fertilization of key ocean regions like the North Atlantic is essential for more accurately predicting future atmospheric CO₂ levels," states ICREA and AXA Professor Carlos Pérez García-Pando, co-leader of the BSC's Atmospheric Composition group and senior co-author of the study.

Researchers have used advanced climate models to project the increase in iron emissions from fires, especially at high latitudes of the Northern Hemisphere. In areas of the North Atlantic characterized by iron scarcity, the deposition of these nutrients could increase the productivity of phytoplankton, which is not only the base of the marine food chain but also fundamental in the carbon cycle, as these microorganisms absorb large amounts of CO₂ from the atmosphere through photosynthesis.

Increase in marine productivity in the North Atlantic

The study concludes that this increase in iron emissions from climate-driven fires, projected to be between 1.7 and 1.8 times higher than current projections that only consider the direct effect of human activity on their future evolution, could increase marine productivity in the North Atlantic due to atmospheric deposition by up to 40% in the summer months by the end of the 21st century.

However, the research also considers the projected decrease in other essential nutrients in vast oceanic areas due to climate change, which could diminish the ocean's capacity to absorb CO₂ and attenuate the positive effects of increased iron deposition.

"Quantifying this nutrient source for phytoplankton is important for gaining a more precise idea of how much CO₂ will remain in the atmosphere in the coming decades. By determining how climate-driven fires will increase the supply of iron to the ocean, we are revealing a crucial feedback loop in the Earth system that we must understand to address climate change," indicates Elisa Bergas-Massó, BSC researcher and lead author of the study.

The work points to the need for a multidisciplinary approach to understanding the role of fire in the Earth system, encompassing atmospheric science, oceanography, and climate policy, as well as the importance of improving observations and models to better quantify these effects and their final impact on CO₂ absorption.

"The results of this study are crucial for improving projections of the carbon cycle and ocean health under a changing climate, paving the way for more accurate climate models and better-informed future climate change adaptation policies," concludes Maria Gonçalves Ageitos, BSC and UPC researcher and senior co-author of the study.