By Dr Mutshutshu Tsanwani and Onele Nyengule
Climate change is often discussed in terms of rising temperatures, droughts, floods and extreme weather. Yet one of the world’s most powerful climate regulators lies largely out of sight, quietly performing an indispensable service every day.
The ocean absorbs approximately a quarter of humanity’s carbon dioxide emissions, slowing the pace of global warming and buying valuable time for societies to transition to a low carbon future. This natural service, however, cannot be taken for granted.
Understanding how the ocean absorbs, stores and releases carbon has become one of the defining scientific challenges of our time. For South Africa, surrounded by three oceans and home to one of the world’s most dynamic marine environments, this challenge presents not only a scientific opportunity but also a national responsibility.
Our recent participation in the WHIRLS expedition aboard the SA Agulhas II Research Vessel offered a remarkable glimpse into the complexity of the ocean’s carbon cycle. The expedition focused on the Cape Basin and the Agulhas Bank, regions characterised by energetic ocean eddies that continually transport heat, nutrients and carbon.
While these swirling features may appear insignificant on the ocean’s surface, they play an outsized role in regulating the exchange of carbon dioxide between the atmosphere and the ocean.
For decades, scientists have understood that the ocean is a vital carbon sink. What is becoming increasingly clear is that the processes controlling this carbon sink operate at remarkably fine scales. Small ocean eddies, fronts and mixing processes influence where carbon enters the ocean, how deeply it is transported and how long it remains stored before returning to the atmosphere. These processes ultimately affect global climate, marine ecosystems and the health of our coastal waters.
During the expedition, our team continuously measured seawater carbon dioxide, pH, dissolved inorganic carbon, total alkalinity and chlorophyll underway while collecting water samples from surface to 1200 m depth across the anticyclonic and cyclonic eddies and measuring dissolved inorganic carbon and total alkalinity. This combination of high-resolution observations allowed us to examine carbon dynamics with unprecedented detail across contrasting ocean features.
Even the preliminary findings demonstrate why such observations matter. Cyclonic eddies appear to bring carbon rich deep water towards the surface, potentially increasing the release of carbon dioxide back into the atmosphere while simultaneously intensifying local ocean acidification. Conversely, anticyclonic eddies transport surface waters downward, helping redistribute carbon into deeper layers of the ocean. These dynamic processes remind us that the ocean is not a passive reservoir but a living, constantly changing system whose behaviour influences climate at regional and global scales.
Ocean acidification deserves particular attention. As more carbon dioxide dissolves into seawater, ocean chemistry changes in ways that reduce the availability of carbonate ions required by many marine organisms to build shells and skeletons. Corals, shellfish, pteropods and microscopic plankton form the foundation of marine ecosystems and fisheries that sustain livelihoods and food security. Understanding where and when acidification is likely to intensify is therefore essential for effective marine conservation and sustainable resource management.
South Africa occupies a strategically important position in the global ocean circulation system. The interaction between the Agulhas Current, the Southern Ocean and the South Atlantic influences weather patterns, biodiversity and carbon exchange far beyond our coastline. Scientific observations collected in our waters contribute not only to national environmental management but also to international efforts to improve climate models and predict future climate change.
This is why sustained investment in ocean observation is not a luxury reserved for scientists. It is an investment in better climate forecasting, stronger environmental policy, resilient coastal economies and evidence-based decision making. Reliable data enables governments to develop effective adaptation strategies, supports responsible fisheries management and strengthens South Africa’s contribution to international climate science.
The WHIRLS expedition also demonstrated another equally important reality: scientific progress depends on people. Behind every dataset are researchers working long hours under demanding conditions, maintaining sophisticated instruments, ensuring analytical precision and mentoring the next generation of scientists.
The collaboration between South African institutions and international partners illustrated how shared expertise can advance knowledge while building national scientific capacity.
As climate change accelerates, society will increasingly rely on science to navigate uncertainty. Yet science can only inform policy if it is supported by sustained observations, modern infrastructure and skilled researchers capable of interpreting increasingly complex environmental changes.
South Africa has already demonstrated that it possesses both the expertise and the institutional capability to contribute meaningfully to global ocean science. The challenge now is to ensure that this capability continues to grow. Long-term investment in marine research, observational programmes and scientific training will yield dividends far beyond academia. It will strengthen climate resilience, support the blue economy and safeguard the marine ecosystems upon which future generations depend.
The ocean has quietly protected humanity for decades by absorbing much of the carbon we have emitted. Understanding how long it can continue to do so, and under what conditions, may prove to be one of the most important scientific questions of this century.
South Africa is uniquely positioned to help answer that question, and the knowledge we generate today will shape the environmental decisions of tomorrow.
*Dr Tsanwani is a Carbon Dioxide and Carbonate Chemistry Research Scientist in the Department of Forestry, Fisheries and the Environment (DFFE) and Onele Nyengule is a Master’s Candidate in Marine Science in the DFFE