Often overlooked in climate discussions, the seabed contains a vast reservoir of carbon beneath our feet and beneath the ocean surface, storing vast amounts of carbon and a rich nutrient fabric.

What most people don’t know is that this quiet ocean floor contains a much larger reservoir of carbon than is found in our atmosphere as carbon dioxide. However, recent research shows that seafloor disturbances disrupt this balance, releasing stored carbon and nutrients and having significant consequences for the climate.

Degradation of seafloor and climate

In a recently published study in marine ecology, scientists carefully examined the effects of repeated disturbances on the dormancy state of the seabed.

Results? These failures have been found to release some of the stored carbon and nitrogen into the ocean, increasing sources of harmful greenhouse gases and carbon dioxide and increasing oxygen depletion on the seafloor. The resulting data highlight the vital role of the seafloor in maintaining climate stability.

Carbon’s journey to the ocean

The sea bed (or sediment, as marine researchers call it) stores vast reservoirs of carbon packaged into organic compounds from sources such as plankton, plants and animals. Much of this organic carbon has been sitting on the seafloor for hundreds of years and plays a critical role in stabilizing our climate.

Sediment also serves as a reservoir for nutrients such as nitrogen and phosphorus. Some of these nutrients are bound to organic compounds, while others exist as dissolved nutrient salts that are readily available to marine organisms and larger vegetation.

Observations in the laboratory

“Researchers have long assumed that physical disturbances to the seabed, such as fishing equipment such as trawls, increase the conversion of organic carbon to carbon dioxide,” said expert Christian Lønborg from the Institute of Environmental Sciences at Aarhus University.

“However, theoretical models lacked documentation in the form of measured values. With the help of laboratory experiments, we showed that this is indeed the case.”

The study focused on controlled experiments that spanned a period of about four months and involved repeated blasts to the seafloor. The researchers observed that carbon conversion and nitrogen release increased when the seabed turned into a sediment cloud, mimicking the effects of trawling.

Seabed carbon emissions

Human activities such as trawling and dredging move the seafloor into the water column, accelerating the decomposition of organic matter and releasing carbon dioxide and nutrients.

The additional production of carbon dioxide, the notorious greenhouse gas, further aggravates the climate and affects the global environment. Additionally, nutrient release can potentially trigger algal blooms in coastal waters.

Since algae produce organic carbon, this contributes to additional carbon leakage that must be recycled on the seafloor. Decomposition of organic matter in water requires oxygen. As a result, any scouring of the seafloor accelerates the depletion of oxygen in the water immediately above the seafloor.

Impact of the seabed on climate

Such disturbances of the sea bed can lead to large-scale oxygen loss, which is often seen in Danish waters in late summer.

“If we want to evaluate the impact of trawling equipment, dredging and seabed extraction, these impacts also need to be taken into account,” Lønborg said.

By shedding light on these hidden drivers of climate change, we can better understand our planet’s complex natural cycles and how we can prevent their disruption.

From ocean to coastal ecosystems

The ecological ripple effects of seabed disturbances go far beyond greenhouse gas emissions and climate change. As carbon and nutrients are released from the seafloor, they interact with surrounding marine ecosystems in complex ways. Excess of nutrients, especially nitrogen and phosphorus, can cause rapidly spreading algal blooms in coastal waters.

How do seabed disturbances affect climate?

Although blooms appear benign, they can have harmful effects for underwater plants by blocking sunlight and reducing oxygen levels, a phenomenon known as hypoxia. Lack of oxygen not only disrupts marine biodiversity, but also threatens populations of commercially valuable fish and shellfish, affecting both global food security and local economies.

Additionally, the influx of carbon and nutrients causes changes in the behavior of smaller marine organisms, including plankton, which play a crucial role in ocean food webs.

As these disturbances cascade throughout the marine ecosystem, they establish a delicate balance that depends on the stability of the seafloor. By studying this interdependence, scientists are gaining a clearer picture of how seafloor disturbances are exacerbating broader climate problems, from biodiversity loss to changes in the ocean’s carbon cycle.