Does dissolved rock affect CO2 sequestration in the ocean?

In the culinary world, adjusting the proportions of ingredients in a recipe can lead to the creation of entirely new flavors. Similarly, the binding of CO2 in the sea is sensitive to changes in the substances found in the water. 

This acid-binding capacity, also known as alkalinity, is primarily produced by the weathering of rocks and their subsequent introduction into the ocean. An increase in erosion on land results in a higher rate of weathering of silicates and carbonates, which in turn contributes to the ocean’s alkalinity.

A team of researchers led by Nele Lehmann from the Hereon Institute for Carbon Cycles, in collaboration with the Alfred Wegener Institute Helmholtz-Zentrum für Polar- und Meeresforschung (AWI), sought to identify the factors contributing to alkalinity using a statistical model, with funding provided by the Deutscher Akademischer Austauschdienst (DAAD). 

“The model we used is a statistical, not a mechanistic model. We applied it to identify the factors influencing alkalinity based on our compiled data set and to describe their interdependencies,”explained Lehmann.

The model identified several factors that influence alkalinity, including the degree of erosion, area fraction of carbonate, temperatures, catchment size, and soil thickness. The study found that the ocean’s ability to sequester CO2 would be significantly affected by climate change. 

If global warming progresses slowly, alkalinity could drop by as much as 68 percent by 2100, depending on the watersheds. However, rapidly advancing warming would lead to higher temperatures and increased precipitation in temperate climate zones, which could boost alkalinity by up to 33 percent.

Lehmann cautions that this increase in alkalinity does not imply that higher emissions are beneficial for the climate. “The impact of alkalinity is small compared to the amounts of man-made CO2 emitted around the world. The process of weathering unfolds its effects over much longer periods of time,” she said.

To conduct their study, the researchers first searched for existing data, specifically targeting alkalinity measurements near erosion measurement sites. They then investigated the factors influencing alkalinity using their new model. 

A significant limitation of their study is the scarcity of erosion rate measurements, particularly in higher latitudes, due to the complexity and expense of obtaining such data. Consequently, the research is primarily focused on mid-latitudes.

Lehmann’s next objective is to examine alkalinity and erosion rates in the Arctic, where data is sparse and climate change is making a noticeable impact. It is possible that the most significant changes in alkalinity flux may occur in this region. A critical question that remains to be answered is whether erosion itself is being altered as a direct result of climate change.

The study is published in the journal Nature Communications.

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