Greenland’s Melting Glaciers Are Weakening Ocean’s Natural pH Buffering System

How Melting Glaciers Are Reshaping Greenland’s Coastal Ocean

When we think of melting glaciers, rising sea levels and retreating ice streams often come to mind. However, along Greenland’s coastline, a more subtle but critical transformation is unfolding—one that directly affects how the ocean regulates its chemistry and responds to environmental changes.

In Young Sound, a remote fjord on Greenland’s northeastern coast, researchers have spent decades documenting how glacial meltwater alters seawater composition. Their findings reveal that freshwater runoff doesn’t just dilute salt levels—it weakens the ocean’s natural resistance to acidity swings. This buffering capacity, which helps maintain stable pH levels in seawater, is being eroded by increased freshwater input, leaving coastal waters far more vulnerable to even minor biological and environmental disturbances.

The Arctic is warming faster than nearly any other region on Earth. Longer melt seasons and greater freshwater runoff are intensifying these changes, turning Greenland’s coastal ocean into both a frontline witness to climate change and a living laboratory for studying unexpected shifts in marine chemistry.

The Ocean’s Natural Chemical Defense System

Seawater relies on dissolved ions to act as a chemical safety net, absorbing excess acidity and stabilizing pH levels. Globally, the ocean absorbs about 25% of annual CO₂ emissions, helping slow climate change but at a cost: increased acidification. Fortunately, seawater contains negatively charged ions—carbonate, bicarbonate, and hydroxide—that neutralize hydrogen ions released when carbonic acid forms, keeping ocean pH relatively stable compared to freshwater systems.

Polar oceans play a disproportionate role in this balance and the global carbon cycle. Cold, high-latitude waters absorb atmospheric carbon dioxide faster than warmer tropical waters, yet these regions are also experiencing the most rapid environmental changes.

Two Decades of Research in Young Sound

For the past 20 years, a team from Aarhus University has tracked salinity, temperature, and carbon chemistry in Young Sound. Each August, researchers embark on a two-day journey to northeast Greenland, spending a month sailing the fjord’s 90-kilometer length to collect critical data (Figure 1).

Figure 1: The red line traces the 2023 research transect from the Greenland Ice Sheet to the Greenland Sea. Credit: Adapted from Henson et al., 2025, https://doi.org/10.1038/s43247-025-02685-4, CC BY-NC-ND 4.0

Over two decades of monitoring, the melt season in Young Sound has extended significantly. Sea ice–free conditions now last 8 days longer than they did 20 years ago. Glaciers feeding the fjord are thinning and retreating, discharging an additional 5.5 million cubic meters of freshwater into the fjord annually. These shifts have freshened the coastal ocean and subtly—but significantly—altered its chemistry.

Fjords as Critical CO₂ Sinks Under Threat

Fjords like Young Sound have long been recognized as major carbon sinks, with surface waters near glaciers often exhibiting very low CO₂ levels. However, the influx of meltwater is now disrupting this balance, reducing the ocean’s buffering capacity and increasing its sensitivity to further change.

As atmospheric warming accelerates Arctic ice loss, the consequences for coastal ocean chemistry—and the marine ecosystems that depend on it—are becoming increasingly urgent.