Unraveling the Deadly Trio: Ocean Acidification, Warming, and Deoxygenation
The world’s marine ecosystems are facing an unprecedented onslaught of climate-related challenges. Chief among these are the “deadly trio” – ocean acidification, warming, and deoxygenation – which are combining to devastating effect on aquatic biodiversity and ecosystem health.
Ocean acidification, primarily driven by rising carbon dioxide emissions, is reducing the availability of calcium carbonate that many marine organisms rely on to build their shells and skeletons. This makes it increasingly difficult for corals, mollusks, and certain plankton to thrive, with cascading impacts throughout the food web. Recent estimates indicate that pH levels in the North Atlantic have dropped by approximately 30% since the pre-industrial era.
Ocean warming is another major culprit, as rising temperatures alter the metabolic processes and distribution patterns of countless marine species. Warmer waters can increase oxygen demand, forcing mobile organisms to shift their ranges, often with disruptive consequences for ecosystems. Marine heatwaves in particular can devastate native species, opening the door for invasive newcomers to take over.
The third component of the “deadly trio” is deoxygenation – the loss of dissolved oxygen in seawater. This is exacerbated by both warming and increased nutrient runoff, leading to the expansion of hypoxic or anoxic “dead zones” that are lethal to many marine species, especially sessile organisms. Globally, the area affected by coastal hypoxia has increased four-fold since the 1950s.
“Multiple, high-intensity stressors are a common feature of past mass extinction events. These stressors include increased global warming, ocean acidification and increased deoxygenation – together commonly referred to as climate change’s ‘deadly trio’.” – Intergovernmental Panel on Climate Change
When these three factors converge, the synergistic effects can be catastrophic for marine life and ecosystem structure and function. Europe’s seas, for example, are already in a state of profound degradation, with most species groups faring poorly across the region.
Mapping Vulnerability and Targeting Resilience
To better understand and respond to these threats, scientists have developed new tools to assess the relative vulnerability of different marine regions and ecosystem components to climate change stressors. The European Marine Climate Change Index integrates a range of factors, from sea surface temperature and salinity to ocean acidification and oxygen content, to identify the areas most at risk.
Generally, semi-enclosed seas, shallower shelf areas, and coastal zones emerge as the most vulnerable, with particularly high-risk zones in parts of the Baltic Sea, Adriatic Sea, and North Sea. Benthic (bottom-dwelling) species tend to be the most impacted overall, though fish species account for a significant share of the climate-related effects in the Northeast Atlantic.
“Vulnerability is particularly high in parts of the Baltic Sea and the Adriatic Sea, and in parts of the North Sea. There are also vulnerable areas in the North-east Atlantic Ocean close to Svalbard, Norway.”
Understanding these spatial patterns of vulnerability is crucial for targeting management and conservation efforts to build ecosystem resilience. Expanding marine protected area (MPA) networks, for example, can help safeguard habitats and species, while improved integration of climate considerations into maritime spatial planning can guide more sustainable development of marine resources.
Policy Responses and the Path Forward
Addressing the impacts of climate change on aquatic ecosystems and biodiversity will require a multi-pronged approach, grounded in both emissions reduction and proactive adaptation strategies. The European Union has set ambitious targets through initiatives like the Marine Strategy Framework Directive (MSFD) and the Biodiversity Strategy for 2030, aiming to achieve “good environmental status” and protect 30% of its marine areas.
Key policy levers include:
- Greenhouse Gas Mitigation: Rapid and deep cuts in global greenhouse gas emissions to limit warming to 1.5-2°C are essential for slowing the pace of ocean acidification, warming, and deoxygenation.
- Ecosystem-Based Management: Integrating climate considerations into holistic, ecosystem-based approaches to managing human activities in the marine environment, including through maritime spatial planning.
- Habitat Protection and Restoration: Expanding marine protected area networks and investing in the restoration of critical coastal and marine habitats, such as mangroves, seagrasses, and coral reefs.
- Adaptive Fisheries Management: Adjusting fisheries management strategies to account for shifting species distributions and changes in productivity, ensuring the long-term sustainability of marine resources.
- Strengthening Monitoring and Research: Enhancing scientific understanding of climate impacts on aquatic ecosystems through improved monitoring, modeling, and targeted research.
“Even if we manage to stabilize global warming at a certain point in time, the warming, the acidification and the deoxygenation will continue to increase due to time lag of achieving a homeostasis between the global atmosphere and the ocean.”
By taking a comprehensive, science-driven approach that tackles both emissions and adaptation, we can work to build the resilience of aquatic ecosystems and the diverse life they support. This, in turn, will help safeguard the vital ecosystem services they provide – from food and livelihoods to coastal protection and carbon sequestration.
The stakes are high, but the path forward is clear. As the Joint Action for Water blog, we are committed to sharing the latest research, best practices, and policy innovations to help communities, governments, and stakeholders address the mounting challenges posed by climate change to our precious aquatic environments.
Empowering Communities and Catalyzing Action
While the impacts of climate change on aquatic ecosystems may seem daunting, there are many ways that individuals, communities, and organizations can get involved to drive positive change. Here are a few key ways to make a difference:
1. Advocate for Strong Climate and Environmental Policies
Stay informed about the latest policy developments related to marine conservation, emissions reduction, and climate adaptation. Engage with your elected representatives to ensure that aquatic ecosystems are prioritized in decision-making.
2. Support Sustainable Practices and Businesses
Make conscious choices as a consumer to support companies and industries that are committed to sustainable and eco-friendly practices. This could include choosing seafood from responsibly managed fisheries, or patronizing businesses that prioritize water conservation and pollution prevention.
3. Participate in Community-Based Monitoring and Restoration
Get involved with local initiatives to monitor the health of nearby waterways, wetlands, and coastal habitats. Volunteer for habitat restoration projects that help rebuild critical ecosystems. These hands-on efforts can provide valuable data and make a tangible difference.
4. Spread Awareness and Educate Others
Share what you’ve learned about the impacts of climate change on aquatic biodiversity with your friends, family, and community. Encourage others to adopt more sustainable behaviors and to advocate for policy solutions. The more people understand the urgency of this issue, the greater the momentum for change.
5. Support Organizations Driving Innovation and Impact
Consider donating or volunteering with nonprofits, research institutions, and other organizations that are at the forefront of addressing climate change and protecting aquatic ecosystems. Your support can help fund critical work and expand the reach of their efforts.
By taking action at the individual, community, and societal levels, we can all play a role in building a more resilient and sustainable future for our precious aquatic environments. The Joint Action for Water blog is here to empower and inspire you along the way.
Conclusion
The world’s marine and freshwater ecosystems are facing an unprecedented onslaught of climate-related challenges, from ocean acidification and warming to deoxygenation. This “deadly trio” of environmental stressors is driving widespread biodiversity loss, habitat degradation, and disruption to vital ecosystem services.
Yet even as the challenges seem daunting, there is hope. By leveraging the latest scientific insights, implementing comprehensive policy solutions, and empowering communities to take action, we can work to build the resilience of aquatic ecosystems and safeguard their irreplaceable value for generations to come.
The Joint Action for Water blog is dedicated to sharing the knowledge, strategies, and inspiration needed to address these critical issues. We invite you to join us in this vital mission, as we strive to protect the health and vitality of our blue planet.
