Research into enhanced weathering

Lab experiments show that enhanced silicate weathering is a promising technique for capturing CO2 from the air and storing it in the oceans. But are these weathering rates determined under artificial lab conditions also representative for silicate weathering and CO2 drawdown in natural coastal sediments? 

Coastal Carbon conducts large-scale experiments investigating the rate of ESW and associated CO2 uptake under realistic natural settings as well as potentially important influences on the biogeochemical cycling in coastal ecosystems.

Multiple research trajectories

The seabed is characterized by various forms of biological activity, which could potentially induce higher dissolution rates compared to sterile laboratory conditions. Recent research shows that the interplay between microbial metabolism and macrofaunal bioturbation could substantially increase the rate of silicate weathering under natural conditions. Then again, bioturbation rates can be subject to strong fluctuations. Experiments in the natural seabed are therefore crucial to properly assess actual weathering rates and CO2 drawdown potential under natural conditions. 

It is also crucial to determine if enhanced silicate weathering rates have adverse impacts on local ecosystems. Therefore, we must determine to what extent end-products of enhanced weathering bio-accumulate in macrofauna and investigate if enhanced silicate weathering alters the microbial community composition.

To answer these questions, Coastal Carbon focuses on two research trajectories: first, a large-scale mesocosm setup was constructed allowing monitoring of silicate weathering in a (simulated) natural coastal seabed; second, long-term impacts of weathering on biota are investigated by conducting field studies in locations where silicate particles have been naturally weathering for a long time. 

Simulating natural conditions in a mesocosm research facility

A unique mesocosm infrastructure dedicated to silicate weathering research was constructed by University of Antwerp in Ostend (Belgium) at the Marine Station Ostend (MSO). The facility consists of 20 tanks each replicating one square meter of North Sea seafloor.

Each tank includes a 40 cm layer of North Sea sediments and 600 L of seawater. In addition, also lugworms (Arenicola marina), an important and widespread bioturbator, were added to the majority of the tanks. To investigate the interactions between enhanced silicate weathering and lugworms, olivine (a fast weathering silicate) was added to some tanks in different compositions. 

Sample analysis 

Weekly sampling of the overlying water and pore water allows accurate monitoring of multiple variables, including alkalinity, dissolved inorganic carbon and trace metal accumulation, over time. Sediment sampling enables detailed studies of  the olivine weathering at the grain scale over time. 

This facility is unique as it is hosting the longest running olivine weathering experiment in a natural coastal sediment environment worldwide.

Coastal oceans as a real-life knowledge base

Silicate weathering is a process with a characteristic time scale of decades to centuries. As a result, long-term ecosystem impacts cannot be simulated in short-term mesocosm experiments. To explore the feasibility of enhanced silicate weathering in marine conditions, we must take advantage of the coastal ocean itself as an unique knowledge reservoir. Coastal Carbon aims to undertake field studies to locations in the world where silicates naturally enter the ocean and evaluate silicate weathering and its interactions with the coastal environment on site. 

Boarding the R.V. Belgica

In addition to olivine, basalt is one of the target minerals for enhanced weathering. With the new Belgian research vessel Belgica, we will set sail for the Icelandic continental shelf, where the seafloor is subject to basaltic mineral input from the nearby Kjós catchment area and erosion on the so-called ‘black beaches’.

We will apply an innovative, fully integrated model-data approach combining RV Belgica field campaigns with state-of-the art numerical models.

Research at green Hawaiian beaches

In the summer of 2022, we went to Papakōlea beach in Hawaii, one of only five natural olivine beaches in the world. The beach is situated in an old cinder cone that was formed by a volcano eruption almost 50 000 years ago, and olivine has been weathering in the area ever since. The sand on the beach and in the water contain about 40% olivine, a fast weathering silicate, making the area ideal for studies of olivine weathering in a natural setting, as well as evaluation of long-term effects of the process.

We used flow-through incubations to study the dissolution rate of olivine in these natural sediments. Sediment was packed into containers, through which water was pumped to simulate waves and tidal flows. We sampled the water at regular times to measure the accumulation of olivine dissolution products, and in this way, we can calculate how rapidly the olivine is weathering. 

Coastal Carbon is a research project, focusing on coastal enhanced silicate weathering (ESW), a negative emissions technology (NET) that uses the natural process of silicate weathering for the removal of CO2 from the atmosphere.

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