Shallow coastal waters are critical areas for methane emissions, releasing large quantities of this powerful greenhouse gas into the atmosphere and contributing to climate change. Recent studies emphasize the significant role of tides, seasonal variations, and ocean currents in methane emissions, as well as how small microorganisms known as methanotrophs help mitigate their effects.
Shallow coastal waters are critical areas for methane emissions, releasing large quantities of this powerful greenhouse gas into the atmosphere and contributing to climate change. Recent studies emphasize the significant role of tides, seasonal variations, and ocean currents in methane emissions, as well as how small microorganisms known as methanotrophs help mitigate their effects. These insights are part of a dissertation by NIOZ PhD candidate Tim de Groot, which he will defend on January 31, 2025, at Utrecht University.
Coastal waters as methane hotspots
While the focus has typically been on human-generated methane, natural sources—especially coastal waters—are not as well understood. These shallow and dynamic ecosystems are abundant in methane. Due to the minimal water depth, there isn’t much time for methane-oxidizing microbes (methanotrophs) to convert it into less harmful substances before it escapes into the atmosphere.
The research examined three specific regions: the Doggerbank seep area in the North Sea, the Dutch Wadden Sea, and coastal areas near Svalbard in the Arctic. The results showed that methane emissions are significantly impacted by natural elements such as tidal movements and seasonal shifts, which also influence the activities of methane-absorbing microbes.
Insights from the Wadden Sea, North Sea, and Arctic
In the Wadden Sea, higher methane levels and emissions were noted during warmer seasons when microbial activity was more intense. Nevertheless, methane concentrations remained elevated during colder months, with windy weather contributing to substantial releases into the atmosphere. Additionally, tidal currents carried methane to nearby waters, allowing it to escape, thereby indicating the extensive implications of methane dynamics in coastal regions.
In the Doggerbank seep area, receding tides resulted in sudden releases of methane while also enhancing microbial activity in deeper layers of water. Conversely, in the cool autumn months, as water mixed, microbial activity waned, allowing greater volumes of methane to escape into the atmosphere compared to summer months.
In the Arctic region near Svalbard, the highest methane levels were found close to the ocean floor, where there were diverse and plentiful microbial communities. Ocean currents were crucial in distributing both methane and microbes, restricting the microbes’ capacity to fully break down the gas before it entered the atmosphere.
Microbial adaptability
The study also included laboratory trials revealing the exceptional adaptability of methanotrophic microbes. They flourish under varying environmental conditions, including changes in temperature, salinity, and methane concentrations. ‘As ecosystems transform, methane-eating microbes adjust. When one group faces challenges, another takes over, ensuring that nature’s methane filtration continues even as the world warms,’ notes Tim de Groot. ‘Coastal regions may comprise a small fraction of the ocean, yet they are key players in methane emissions. With climate change altering these systems, it is becoming crucial to comprehend how methane emissions will change and identify strategies to mitigate their impact.’
