Ocean acidification, temperatures and salinity

Shifting oceans: Acidification, warming and the salinity spiral at the bottom of the world

“What happens in Antarctica doesn’t stay there.”
— Alessandro Silvano (2025)

Plain English explainer

What’s happening in the Southern Ocean — and why it matters

Scientists have discovered something surprising: the ocean around Antarctica is getting saltier, not fresher, just as the sea ice is disappearing at record speed. This was unexpected, because melting ice normally adds fresh water. But instead, it’s triggering a dangerous chain reaction.

Saltier water sinks, pulls heat from the deep ocean up to the surface and melts even more ice. That lost sea ice lets in more sunlight, warming the ocean even more. It’s a feedback loop — a cycle that feeds on itself.

This affects all of us. Increased ocean salinity speeds up climate change, disrupts weather patterns and endangers animals such as penguins and whales. It even threatens tiny sea creatures that feed the fish we eat.

Antarctica is no longer the frozen, stable place we once thought. The ocean is warning us that we’re running out of time — and we need to act now.

Full article

The Southern Ocean is speaking, and what it says may be one of the most urgent climate warnings yet. Recent data from the University of Southampton and European Space Agency satellites reveal that the Southern Ocean’s surface salt levels are rising dramatically, contrary to decades of expectations (Silvano, 2025). This increase coincides with a sharp, unprecedented collapse in Antarctic sea ice since 2015, an event now considered as potentially terminal.

Interlocking feedback loops

Ocean salinity, warming and acidification are not separate issues — they are deeply interconnected. When sea ice melts, we expect fresh water to enter the ocean, lowering salt levels. But what’s happening instead in the Southern Ocean is the opposite: salinity is rising. Why?

Denser, saltier water sinks, drawing warm water from the ocean depths up to the surface. This heat melts sea ice from below, which then increases solar absorption (less reflective ice means more heat is retained) and draws up even more salt, amplifying the feedback loop (Silvano, 2025).

Meanwhile, ocean acidification, which is driven by the absorption of excess atmospheric CO₂, weakens the ocean’s ability to buffer against further warming and chemical change. As Findlay et al. (2025) outline in their review, even the Southern Ocean — which once served as a vital carbon sink — is now nearing chemical tipping points that threaten small, calcifying organisms such pteropods and krill that play vital roles in marine food webs.

Why frozen water matters

This is not just about polar ice.

It’s about climate destabilisation:

• Less sea ice means more heat entering the planetary system.

• Warmer oceans mean stronger storms, more extreme heatwaves, and faster sea level rise.

• Acidified and warming waters disrupt krill populations, affecting entire food chains — from penguins and whales to global fisheries (Findlay et al., 2025).

• Salinity shifts may weaken global ocean currents, including the crucial Antarctic bottom water that helps regulate Earth's climate.

Has a tipping point passed?

The 2015 collapse in sea ice, coupled with the unexpected salinity spike, may indicate that we’ve already passed a threshold of irreversible change. The Southern Ocean appears to have entered a new state - one where sea ice continues to decline, regardless of seasonal recovery.

This kind of “state shift” is precisely what climate scientists fear. It marks a departure from linear change toward nonlinear, cascading disruption. Without urgent reductions in global emissions and major investment in ocean monitoring, we may be flying blind into deeper instability.

What can be done?

At MANA, we believe in action rooted in care, connection and complexity awareness.

Here’s how we hope to respond:

1. Raise ecological literacy
We are educating our community about ocean-climate links. Monthly Days of Mindfulness includes reflection on planetary systems, including our oceans.

2. Support Southern Ocean research
We encourage our members to support independent science organisations such as the Australian Antarctic Division, Commonwealth Scientific and Industrial Research Organisation, and the European Space Agency, who monitor sea ice and salinity.

3. Shift systems, not just habits
Personal change matters - but we also advocate for policy that reduces fossil fuel dependency, supports Indigenous land and sea care, and decouples economic growth from environmental harm.

4. Grow kinship with water
Our Natural Mindfulness practice may in future include a water-focused walk, observing seasonal creeks, rainfall, salt pans and coastal shifts. Understanding water’s movement helps us stay attuned to change.

References

• Findlay, H. S., Sabine, C. L., & Hauri, C. (2025). Emerging thresholds of ocean acidification in the Southern Hemisphere. Global Change Biology, 31(5), 1123–1139. https://doi.org/10.1111/gcb.17021

• Silvano, A. (2025, July 1). ‘Completely unexpected’: Antarctic sea ice may be in terminal decline due to rising Southern Ocean salinity. The Conversation. https://theconversation.com/completely-unexpected-antarctic-sea-ice-may-be-in-terminal-decline-due-to-rising-southern-ocean-salinity-234681