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Increased freshwater input is making the ocean environment more acidic, faster. Photographer: Kjartan Mæstad / Institute of Marine Research
Coastal Waters Losing Acidity Buffer Due to Climate Change
NORWAY
Monday, May 19, 2025, 00:10 (GMT + 9)
Warmer, wetter winters lead to increased freshwater runoff, weakening the ocean's natural ability to neutralize carbon dioxide and causing faster acidification along coastlines, according to research from the Norwegian Institute of Marine Research.
Unusual weather patterns, characterized by warmer temperatures and increased precipitation, are impacting coastal marine environments. The sea's natural "buffer" against acidification is weakening due to these climate-driven changes, according to research reported by Vibeke Lund Opdal from the Havforskningsinstituttet (Norwegian Institute of Marine Research).
 The past winter has been described as warmer, wilder, and wetter, a trend particularly evident in the northern regions.
"This year, the winter has brought milder temperatures and more precipitation. There has been significant rainfall, interspersed with substantial snowfall during colder periods. This has resulted in multiple cycles of melting, occurring well before the typical arrival of spring", explains ocean researcher Elizabeth Jones.
Regardless of its form, whether rain or snow, the precipitation ultimately finds its way into the ocean.
“Rainwater and meltwater feed rivers, which then discharge into the ocean. When precipitation levels are higher than usual, the proportion of freshwater along the coast increases. This alteration affects the marine environment and ultimately contributes to a more acidic condition,” Jones elaborates.
The Impact of River Runoff
<-- Marine scientist Elizabeth Jones takes water samples from a CTD. This is a water sampling device that is lowered to the seabed and takes water samples from different depths. Photo: Institute of Marine Research
Elizabeth Jones, an oceanographer, analyzes ocean samples, monitors environmental shifts, and investigates the interplay between various factors, including terrestrial changes, and their effects on the marine environment.
“Increased rainfall and fluctuating temperatures lead to a greater volume of freshwater entering the ocean via rivers. Higher precipitation results in larger rivers and more frequent and intense flooding events,” Jones states.
This increased freshwater input accelerates the acidification of the ocean environment. The reason for this is that freshwater has a greater capacity to absorb CO₂ compared to saline seawater. Simultaneously, the influx of freshwater diminishes the ocean's natural ability to neutralize CO₂, creating a negative feedback loop.
“Measurements of salinity and acidity in the upper water layer reveal a clear correlation between freshwater inflows and a reduction in the ocean's buffering capacity. This phenomenon is particularly pronounced along coastlines where rivers discharge directly into the sea,” Jones observes.
Understanding the Ocean's "Buffer"
The ocean's capacity to absorb and process CO₂ hinges on the delicate balance between acids and bases.
In simplified terms, an acid is a substance that imparts a sour taste to water, while a base counteracts this sourness. In the ocean's case, dissolved CO₂ increases acidity, whereas the salts in seawater contain bases that neutralize this acidity, a mechanism scientists refer to as a buffer.
Freshwater disrupts the ocean's ability to absorb CO₂ on multiple levels and through various mechanisms. This leads to a faster rate of ocean acidification, and the impact of the increased acidity (lower pH) becomes more significant because:
- Cold freshwater, often forming a layer higher in the water column, absorbs more CO₂ than saltwater.
- Freshwater dilutes the concentration of bases in the ocean, weakening its buffering capacity, as freshwater does not neutralize CO₂ as effectively as saltwater.
A Year-Round Spring Trend?
The impact of freshwater on ocean acidity is currently most pronounced during the spring due to snowmelt. However, the increasing frequency of extreme and unstable weather patterns is leading to a greater influx of freshwater throughout the entire year.
"New data indicates that freshwater from rivers is extending far into fjords and along the coastline. This alters the seawater composition and elevates the risk of acidification. Last winter's multiple heavy snowfalls followed by periods of mild weather resulted in increased freshwater input even during the winter months. Strong winds and significant wave action further contribute by pulling the typically upper-layer freshwater downwards, causing it to mix with the saltwater", Jones explains.
Water from land also carries organic matter and nutrients like nitrate and phosphate, which contribute to increased algal blooms along the coast during the summer. The decomposition of this organic matter further releases CO₂ into the water.
The work is not over after the water samples have been collected. Now, meticulous work awaits Jones, in the lab and in the office, when the samples will be analyzed and the results will be compiled. Photo: Institute of Marine Research
Uncertain Future for Marine Life
The alteration of marine habitats towards more acidic conditions raises concerns about the future of marine life.
More acidic oceans create less favorable conditions for calcification, the process by which marine organisms build shells and skeletons, as acid dissolves calcium carbonate. Numerous species rely on calcium carbonate for essential biological functions. Snails build shells, shrimp and lobsters use it to strengthen their exoskeletons, and juvenile fish need it for skeletal development and growth.
“Unfortunately, our understanding of the long-term consequences of coastal ocean acidification remains limited. However, we are observing changes in marine life along the coast,” Jones notes.
The rich fish resources inhabiting coastal areas and fjords are vital to fisheries. If the ecosystem is significantly affected by acidification, it could have major repercussions for the fishing industry.
"Mussels, crabs, and corals depend on calcium to construct their skeletons. The same applies to young fish as they grow. When the ocean becomes more acidic, these animals expend more energy to produce calcium. While the adaptability of different species to a more acidic environment is still under investigation, their shells and skeletons are expected to weaken. In the most severe scenarios, some species could face extinction or be outcompeted by species more tolerant to acidification", Jones warns.
Northern Regions More Vulnerable
The oceans in the northern latitudes are particularly susceptible to acidification because colder Arctic waters have a greater capacity to absorb CO₂ than warmer oceans. The Barents Sea, especially its northern part, absorbs more CO₂ than other oceanic regions.
Climate change also exerts a more significant impact on Arctic coastal areas compared to land and open oceans. This heightened vulnerability stems from the dynamic nature of coastal zones, which are influenced by various localized processes in addition to broader climatic shifts.
“The human impact is more pronounced along the coast, where human populations and activities are concentrated. By conducting monthly monitoring of coastal waters over several years, consistently measuring the same parameters in the same locations, we can effectively document the changes occurring over time,” Jones concludes.
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