How Marine Heatwaves Disrupt Ocean Food Webs and the Carbon Cycle: Key Insights for a Changing Planet

Marine heatwaves—those sudden surges of warm ocean water—are changing our oceans. They not only stress marine creatures but also affect how the ocean handles carbon, a key player in climate change.

A recent study by researchers from MBARI and other institutions explored the Gulf of Alaska. They found that these heatwaves disrupt the “biological carbon pump,” a process where tiny organisms help transport carbon down to the ocean’s depths.

Key Findings from the Study

During the notable heatwaves, especially the “Blob” from 2013 to 2015 and another from 2019 to 2020, researchers made some alarming discoveries. Typically, phytoplankton at the ocean’s surface absorb CO2 and create organic material. As larger marine life consumes them, this material would usually sink to deeper waters, effectively locking away carbon for long periods.

However, during the 2013-2015 heatwave, although carbon production was high, much of it stayed around 200 meters deep instead of sinking further. In the subsequent 2019-2020 event, scientists noted an unusual accumulation of carbon particles near the surface—more than phytoplankton could explain. They believe that this was due to carbon being recycled within marine life, causing a blockage in the carbon flow to deeper waters.

This stall in sinking carbon can be attributed to changes in plankton populations. Smaller grazers thrived, but their waste does not sink as rapidly, resulting in a build-up of carbon in upper ocean layers rather than belting down to the depths.

Global Implications: India in Focus

India’s oceans are also feeling the heat. Reports indicate that the Indian Ocean could face permanent marine heatwaves if greenhouse gas emissions aren’t controlled. The Bay of Bengal recorded six heatwave events in 2021 alone, with four occurring directly over the bay. This combination of heat and rising sea levels is harming coral reefs, particularly around the Lakshadweep Islands.

Moreover, marine heatwaves are linked to an increase in cyclones. If similar disruptions to the carbon pump occur in Indian waters as seen in Alaska, we risk more carbon lingering near the surface—potentially increasing atmospheric CO2 levels and contributing to global warming. This could have dire consequences for coastal ecosystems, fisheries, and weather patterns.

Why This Matters

Not every marine heatwave behaves the same way. Each event impacts plankton communities, which in turn affects carbon cycling. If the ocean’s carbon transport system becomes more frequently disrupted, more carbon may return to the atmosphere, amplifying climate change.

Experts stress the need for comprehensive ocean monitoring to grasp the long-term impacts of marine heatwaves. They suggest using varied technologies, including robotic floats and genetic analysis, to track how these warm episodes influence ecosystems, carbon capture, and climate dynamics.

Understanding these shifts is vital—not just for marine life but for the health of our planet overall. Keeping tabs on ocean changes can help us prepare for future challenges, mitigating risks for both our environment and society.

For detailed studies on this topic, consider exploring resources from Nature and other trusted scientific publications.

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Carbon pump, marine heatwaves, climate change, global warming, Alaska, Indian ocean, reefs