Coastal oceans as real-life knowledge base

Alkalinity release from mineral dissolution or precipitation is often slow, typically occurring over decades to centuries.

However, some natural sites exhibit high alkalinity release rates due to the composition of their coastal sediments. The Coastal Ocean Alkalinization team focuses on field studies in such locations, where seafloor alkalinity production is naturally elevated. These studies help us understand the interactions between coastal sediments, water, and air, and allow us to assess potential long-term impacts on local ecosystems.

Up to 2025, the Geobiology lab has participated in three large-scale field campaigns: a measurement campaign at the green olivine beaches of Hawaii, measurements along the basalt-rich coastline of Iceland, and the salt march ponds in Blakeney (UK).

In the salt-marsh ponds of Blakeney (Norfolk, UK), bioturbated and unbioturbated basins occur naturally only a few meters apart, offering a unique setting to study the interactions between natural alkalinity-generating processes. Coastal sediments play a key role in the marine carbon cycle, yet the influence of sediment-dwelling animals on alkalinity production remains insufficiently understood.

Bioturbators alter oxygen penetration and redox conditions, shifting the balance between calcium-carbonate dissolution in the upper sediment and pyrite formation in the deeper, anoxic layers. To unravel how these opposing processes respond to animal activity, we conducted in-situ sediment–water flux measurements, detailed geochemical profiling, fauna identification and assessments of bioturbation intensity across contrasting ponds.

This fieldwork was supported by VLIZ BMRI granted to A. Hylén

Iceland is known as the land of ice and fire for a reason. It is a volcanic island comprised largely of basalt. The seafloor on the continental shelf continuously receives basalt from Iceland’s famous black basalt beaches. In the summer of 2023, we set sail for the southern coast of Iceland with the new Belgian research vessel Belgica to study basalt weathering on the seafloor.

We used benthic chamber landers to measure weathering directly on the seafloor and collected samples for experiments on the ship and analysis at home. The results from the field measurements will be used together with state-of-the art numerical models to investigate silicate weathering. 

This study was executed within the framework of the DE-HEAT project, in collaboration with ULB and the Institutes of Natural Sciences

The green sand Papakōlea beach in Hawaii is 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. Today, the sand on the beach and in the water contains about 40% olivine. This makes the area ideal for studies of olivine weathering in a natural setting, as well as evaluation of long-term effects of the process. 

In the summer of 2022, we visited Papakōlea to measure the dissolution rate of olivine in these natural sediments. We used flow-through incubations in which 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 calculate how rapidly the olivine is weathering. 

The field work in Hawaii was conducted in collaboration with Vesta.