Mangrove forests along the Amazon coast release significant amounts of trace elements such as neodymium and hafnium. These elements and their isotopic compositions can serve to understand the inputs of micronutrients which are vital for marine life.

Researchers at the GEOMAR Helmholtz Center for Ocean Research Kiel have investigated the processes behind these releases and their significance for the ocean. Their findings were published in Communications Earth & Environment.

Mangrove forests are not only critical carbon sinks and biodiversity hotspots but also play a key role as suppliers of trace elements to the ocean. This is shown by a study conducted by the GEOMAR Helmholtz Center for Ocean Research Kiel, Germany.

For example, mangrove systems along the Amazon coastline release about 8.4 million grams of dissolved neodymium into the ocean each year—64% of the total neodymium input in this region. Similar processes are likely for other essential trace elements, such as iron or manganese, which are crucial for marine ecosystems and the carbon cycle.

“Our research shows that mangroves play a central role in the global cycle of trace elements,” explains Dr. Antao Xu, first author of the study from GEOMAR.

“They act as biochemical reactors, releasing nutrients and metals into coastal waters through processes such as sediment dissolution and pore water exchange.”

Mangrove systems as ‘nutrient pumps’

The research team analyzed water samples from coastal waters, estuaries and mangrove sediments along the Amazonian coast. Distinct isotopic patterns of neodymium and hafnium were identified, revealing their origin and the interactions between sediments, pore water, and seawater.

“Mangroves are not only buffer zones that retain material from land; they are also key players that process and selectively release these substances and micronutrients into the ocean,” says Professor Martin Frank, co-author of the study and head of the research division Ocean Circulation and Climate Dynamics at GEOMAR. This exchange of substances supports coastal food chains.

Globally, mangrove systems contribute between six and nine percent of the total neodymium input to the ocean, according to the researchers. This contribution is comparable to the global input of neodymium from the atmosphere via dust.

The study’s findings underscore the urgent need to protect these threatened ecosystems.

Xu states, “Mangroves sit at the interface between land and sea and provide invaluable services for biodiversity and climate regulation. Their prominent role as a source of trace elements is another compelling reason to prioritize their conservation.”