Mangroves are often portrayed as climate champions: forests rooted in tidal mud, storing carbon in waterlogged soils and protecting coastlines from storms. Yet the carbon story at the surface of these ecosystems is far more dynamic than a simple balance sheet of trees absorbing carbon dioxide. A study by X. Ouyang, D. T. Maher, S. Y. Lee and colleagues, published in Nature Communications in 2026, examines how surface waters connected to mangrove forests exchange carbon with the atmosphere and how that exchange may respond to global warming. The research focuses attention on a critical but easily overlooked part of the coastal carbon cycle, where sunlight, tides, microbes, rainfall, plant respiration and ocean chemistry interact within a constantly shifting boundary between land and sea.
The surface of a mangrove creek, lagoon or flooded forest is not merely a passive layer of water. It is an active chemical interface through which carbon dioxide can either enter the atmosphere or be drawn down from it. When organic matter from leaves, roots and surrounding soils is broken down by microorganisms, carbon dioxide is released into the water. If the water becomes supersaturated with the gas, carbon dioxide can escape into the air. At other times, photosynthetic organisms in the water may consume carbon dioxide, while tidal transport carries dissolved carbon to coastal seas. The direction and intensity of this exchange can change over hours as tides rise and fall, making mangrove carbon accounting substantially more complicated than measuring the growth of trees alone.
The study’s title signals two central questions: how much carbon moves across the air-water boundary in mangrove environments, and how could that movement change as the planet warms. These questions matter because mangroves are frequently included in “blue carbon” strategies designed to protect ecosystems that capture and store atmospheric carbon. Their soils can retain substantial quantities of organic carbon for long periods, particularly where oxygen-poor sediments slow decomposition. But storage on the landscape scale does not necessarily mean that every part of the ecosystem is continuously removing carbon dioxide from the atmosphere. Surface waters may act as sources, sinks or conduits, and their role can vary across seasons, locations and tidal conditions.
Technically, air-water carbon exchange is governed by a combination of gas concentration and physical transport. The difference between the concentration of carbon dioxide in surface water and the concentration expected to be in equilibrium with the overlying atmosphere creates a driving force for exchange. Wind, current speed, turbulence and wave action determine how quickly gases cross the boundary. Warmer water generally holds less dissolved gas, while biological activity and chemical reactions can alter carbon dioxide concentrations independently of temperature. In mangrove systems, the water is also influenced by dissolved organic carbon, alkalinity, salinity and freshwater inputs. Together, these factors produce a highly variable carbon signal that may be missed by occasional sampling.
Global warming could modify nearly every part of this process. Higher temperatures accelerate many microbial reactions, potentially increasing the breakdown of organic matter and the release of carbon dioxide from mangrove-derived material. Warmer water can also reduce carbon dioxide solubility, making it easier for the gas to move into the atmosphere when concentrations are elevated. At the same time, warming may intensify evaporation, alter rainfall patterns and influence the timing and strength of freshwater flows. These changes can affect salinity, water residence time and the transport of carbon between mangrove channels and the open coast. The result is not a single predictable response but a network of linked physical, chemical and biological feedbacks.
Mangrove productivity could also respond in opposing ways. In some circumstances, additional carbon dioxide and warmth may stimulate plant growth, increasing the supply of organic material to soils and sediments. More vigorous vegetation could strengthen long-term carbon storage if the material is buried faster than it decomposes. However, heat stress, drought, rising salinity and extreme weather can damage mangrove trees and reduce their ability to absorb carbon. When roots and leaves die, the resulting organic matter can fuel microbial respiration. If warming also increases the rate at which this material is decomposed, some of the carbon previously retained in the ecosystem could be returned to the atmosphere or exported in dissolved form.
That distinction between storage and exchange is at the heart of the research. A mangrove forest may continue to accumulate carbon in its sediments while its surface waters release carbon dioxide at particular times or under particular conditions. These processes are not mutually exclusive. Carbon can be stored in buried soils over decades or centuries while another fraction is rapidly cycled through water and the atmosphere over hours or days. Understanding the difference is essential for reliable climate assessments, especially as governments, conservation groups and companies increasingly consider mangrove restoration and protection as tools for reducing greenhouse-gas emissions.
The research also has implications for how coastal ecosystems are represented in global carbon models. Many large-scale assessments rely on measurements from limited sites and then extrapolate across broad regions. Yet mangrove coastlines differ in tidal range, rainfall, vegetation structure, soil chemistry, connection to rivers and exposure to the sea. A carbon exchange rate observed in a sheltered tropical creek may not represent conditions in a drier, tide-dominated forest or a system receiving heavy river discharge. By focusing specifically on surface-water exchange and its response to warming, the study addresses a process that can introduce uncertainty into estimates of whether mangrove landscapes are net carbon sinks or sources.
For the public, the message is both cautionary and urgent. Mangroves remain extraordinarily valuable ecosystems, offering nursery habitat for fish, reducing coastal erosion and buffering communities from storms while storing carbon in biomass and sediment. But their climate benefits should not be reduced to a single number or treated as immune to a warming world. The new work draws attention to the invisible carbon traffic taking place across mangrove waters—traffic that can accelerate, reverse direction or intensify as environmental conditions change. Protecting these forests therefore requires more than planting trees. It demands preservation of natural tidal flows, reduction of pollution, protection from coastal development and long-term monitoring of the water chemistry that determines whether carbon stays put or escapes.
As climate change reshapes coastlines, the study provides a timely framework for viewing mangroves as living carbon networks rather than static carbon vaults. Their future climate role will depend on the balance among plant growth, sediment burial, microbial respiration, tidal export and atmospheric exchange. Clarifying that balance can help scientists improve emissions inventories and help policymakers design more credible nature-based climate strategies. The research does not diminish the importance of mangroves; instead, it reveals why their protection is even more consequential. The more rapidly the planet warms, the more important it becomes to understand not only how much carbon mangroves contain, but also how quickly carbon is moving through them—and where it ultimately ends up.
Subject of Research: Surface-water carbon exchange in mangrove ecosystems and its response to global warming.
Article Title: Surface-water carbon exchange from mangroves and responses to global warming
Article References: Ouyang, X., Maher, D. T., Lee, S. Y. et al. “Surface-water carbon exchange from mangroves and responses to global warming.” Nature Communications (2026). https://doi.org/10.1038/s41467-026-77058-2
Image Credits: AI Generated
DOI: 10.1038/s41467-026-77058-2
Keywords: mangroves, blue carbon, carbon dioxide, surface-water exchange, global warming, coastal ecosystems, climate change, carbon cycle, air-water gas exchange, ocean science
