Ocean iron fertilization could exacerbate climate change impacts in the tropics

New research published in Global Change Biology by a researcher from Bigelow Laboratory for Ocean Sciences and colleagues suggests that large-scale ocean iron fertilization, one of the strategies proposed for removing excess carbon dioxide from the atmosphere, could have negative consequences for marine ecosystems. The study utilized advanced models of ocean biogeochemistry and ecology to demonstrate that iron fertilization in the Southern Ocean could worsen nutrient shortages and productivity losses in the tropics, potentially impacting coastal fisheries. The findings emphasize the interconnected nature of the ocean and the need for comprehensive research on the pros and cons of marine carbon dioxide removal strategies.

As the ocean is the largest carbon sink on the planet, marine-based strategies like iron fertilization have gained attention for carbon dioxide removal. The basic concept involves adding micronutrients, such as iron, to certain ocean areas with limited nutrients, stimulating primary productivity, and increasing carbon dioxide absorption by phytoplankton. This carbon would then sink to the seafloor when the phytoplankton die.

Proponents of ocean iron fertilization highlight its advantages, such as not requiring land or freshwater and quicker implementation compared to other strategies. Previous studies have indicated that iron fertilization can effectively reduce atmospheric carbon.

However, early research also indicated that fertilization might exacerbate “nutrient robbing” by hindering the supply of critical nutrients from iron-limited areas to neighboring regions, resulting in reduced marine life and productivity in the tropics.

Moreover, a 2021 report by the U.S. National Academies of Science raised concerns about the insufficient knowledge base regarding marine carbon dioxide removal approaches like fertilization, especially regarding the interaction of fertilization with other climate change-induced ocean processes.

To address these knowledge gaps, the authors of the current study expanded on previous modeling work, incorporating recent research on iron utilization by phytoplankton and considering climate change and fisheries impacts.

Their results revealed a five percent decline in the biomass of fish and marine species in the tropics, including economically important coastal regions, due to large-scale iron fertilization. This decline would occur in addition to the 15 percent decline already expected due to climate change and ocean stratification.

While iron fertilization could remove up to 45 gigatonnes of carbon dioxide from the ocean surface between 2005 and 2100 according to the models, the authors stress that this amount is limited compared to current carbon emissions and the reductions needed to meet climate targets.

The study highlights the necessity of objective and rigorous research to evaluate the potential benefits and harms of ocean iron fertilization. It also underscores the importance of modeling efforts that consider the vast spatial and temporal scales involved.

The researchers emphasize the need to significantly scale up research in the coming years to make informed decisions about carbon dioxide removal strategies while addressing the urgent threats of climate change. Future studies should aim to improve existing models as our understanding of carbon, iron, and other nutrients in the ocean continues to evolve.

Source: Bigelow Laboratory for Ocean Sciences

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