Hidden meltwater found deep in Antarctic coastal waters reveals stronger climate impacts

June 5, 2026 feature Hidden meltwater found deep in Antarctic coastal waters reveals stronger climate impacts Hannah Bird Author Gaby Clark Scientific Editor Robert Egan Associate Editor Freshwater from melting Antarctic glaciers may be influencing the Southern Ocean in ways scientists have largely overlooked. New research, published in Frontiers in Marine Science, has found that glacial meltwater is not confined to the ocean's surface, as previously assumed, but can also be detected much deeper in coastal waters along the Western Antarctic Peninsula. The findings suggest that meltwater from glaciers is being transported and stored tens of meters below the surface, where it could alter ocean circulation, affect the movement of heat and nutrients, and influence how the region responds to climate change. Beneath the surface The Western Antarctic Peninsula is one of the fastest-warming regions on Earth. As glaciers retreat and ice shelves melt, increasing amounts of freshwater are entering the surrounding ocean. Scientists have long known that this meltwater accumulates near the surface, where it can create a lighter layer of water that floats above denser seawater. However, much less is known about what happens below the upper ocean and whether glacial meltwater also reaches deeper layers. To investigate, Professor Aaron Micallef, of the Monterey Bay Aquarium Research Institute, U.S., and colleagues collected water samples from three locations along the peninsula: Cierva Cove, Paradise Bay and waters near Petermann Island. The team analyzed the samples for chemical and isotopic fingerprints that can reveal where the freshwater originated. In particular, they examined forms of oxygen and hydrogen that act like natural tracers (isotopes), allowing glacial meltwater to be distinguished from seawater and other potential freshwater sources. The results showed a consistent pattern. At all three sites, the scientists detected signs of freshwater more than 50 meters below the surface. In the more sheltered bays, evidence of glacial meltwater extended beyond 90 meters depth. Rather than being limited to a thin surface layer, some of the meltwater appeared to be stored within deeper parts of the water column. A hidden freshwater reservoir The researchers estimate that glacial meltwater comprised approximately 0.5% to 2% of the water found at these depths. While those percentages may sound small, they are significant enough to alter the density of seawater and influence how different layers of the ocean interact. The chemical evidence also helped the team rule out other explanations. Freshwater can potentially enter Antarctic coastal waters through several pathways, including groundwater flowing from land or the melting of sea ice. But the isotopic signatures and chemical ratios in the samples pointed overwhelmingly to glacial meltwater as the source of the deep freshening. According to the researchers, the freshwater is likely reaching this depth through a combination of processes. Meltwater released beneath glaciers can form buoyant underwater plumes that rise through the ocean before spreading sideways when they reach water of similar density. Ocean currents may then transport this glacially modified water along the coast, while mixing processes help distribute it through intermediate depths. The strongest subsurface signals were found in Cierva Cove and Paradise Bay, both relatively enclosed coastal embayments. By contrast, the waters around Petermann Island showed weaker meltwater fractions, which the authors suggest may reflect greater circulation and mixing with surrounding seawater. Why depth matters The discovery is important because freshwater affects how the ocean is layered, a property known as stratification. Freshwater is less dense than salty seawater, so adding it to the ocean can create distinct layers that are more resistant to mixing. This layering helps determine how heat moves through the water column. In Antarctica, that process is particularly significant because relatively warm deep water can accelerate melting when it reaches glacier fronts and the undersides of ice shelves. If meltwater is being stored deeper in the ocean than previously recognized, it could influence the exchange of heat between different water masses in ways that are not fully captured by current models. It may also affect how nutrients circulate, with potential consequences for marine ecosystems that depend on nutrient-rich waters reaching the surface. The findings add to a growing body of evidence that changes in Antarctic freshwater input can have far-reaching effects on ocean conditions. Recent studies have shown that freshwater layers can trap heat beneath the ocean surface, altering sea ice formation and influencing how warmth is redistributed through the Southern Ocean. Looking to the future Many ocean and climate models currently represent glacial runoff as freshwater entering mainly at the surface or in the upper ocean. The new study suggests that this simplified picture may miss an important part of the system. If a portion of Antarctic meltwater is routinely stored at intermediate depths, models may need to account for these hidden freshwater reservoirs to better simulate ocean circulation and future changes in the region. Understanding exactly where meltwater goes after it leaves glaciers is becoming increasingly important as warming temperatures drive continued ice loss around Antarctica. The authors caution that their study provides only a snapshot in time. More observations across different seasons and years will be needed to determine how persistent these subsurface meltwater layers are and how they vary under changing climate conditions. Nevertheless, the research highlights that the impacts of glacier melt extend beyond what can be seen at the ocean's surface. Beneath the waters of the Western Antarctic Peninsula, a hidden reservoir of freshwater appears to be reshaping the coastal ocean—offering new clues about how one of Earth's most rapidly changing regions is responding to a warming world. Written for you by our author Hannah Bird, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details Aaron Micallef et al, Glacial meltwater is the primary source of subsurface freshening off the Western Antarctic Peninsula, Frontiers in Marine Science (2026). DOI: 10.3389/fmars.2026.1779006. Journal information: Frontiers in Marine Science © 2026 Science X Network