Marine Heatwaves Disrupt Ocean Food Webs, Carbon Cycle: Study Finds
Islamabad – Marine heatwaves are disrupting ocean food webs and hindering carbon transfer to the deep sea, undermining a critical natural defense against climate change, according to new research published Monday in Nature Communications.
An international team from the Monterey Bay Aquarium Research Institute, University of Miami, Hakai Institute and University of Washington found that prolonged ocean warming disrupts microscopic life at the base of marine ecosystems, exacerbating cascading effects on carbon storage and biodiversity.“The ocean’s biological carbon pump typically moves carbon from the surface to the deep sea,” explained lead author Mariana Bif.
“During marine heatwaves, this conveyor belt slows, increasing the risk that carbon returns to the atmosphere, worsening global warming.”The study analyzed over a decade of data from the Gulf of Alaska, which suffered two major heatwaves: “The Blob” (2013–2015) and another in 2019–2020. Using robotic floats from the Global Ocean Biogeochemical Array, satellite sensing, and Canada’s Line P plankton records, the scientists tracked temperature, oxygen, nutrients, and organic carbon through the water column. They found that each heatwave altered lower food web dynamics differently. During The Blob, surface carbon production increased, but accumulated about 200 meters deep instead of sinking further.
In the latter event, carbon-rich detritus built up at the surface and then stalled in the “twilight zone” (200–400 meters), disrupting carbon sequestration.“Our results show marine heatwaves impact plankton communities differently, complicating predictions of long-term carbon storage and ecosystem recovery,” said Bif. This highlights the need to improve climate models and sustain long-term ocean monitoring. “Robotic floats, pigment chemistry, satellites, and genetic sequencing together reveal how heatwaves impact the ocean and inform adaptation,” added co-author Dr. Thomas Weber.
Marine heatwaves, prolonged ocean temperature spikes lasting weeks to years, are becoming more frequent and intense due to climate change.
As oceans warm, their ability to absorb and store carbon dioxide diminishes, potentially accelerating global warming and threatening marine biodiversity and fisheries vital to millions. Currently, oceans absorb about a quarter of human-generated CO₂ annually, but intensifying heatwaves risk reducing this carbon sequestration, with broad climate and economic implications. Implications for Pakistan’s Coastal Ecosystems: Arabian Sea coastal waters face increased vulnerability to marine heatwaves, which threaten fisheries and biodiversity critical for coastal livelihoods.
Altered food webs may impact key commercial species such as shrimp, crab, and fish that sustain millions in Sindh and Balochistan fishing communities. Heatwaves also worsen coral bleaching in coastal reefs, jeopardizing habitats that serve as nurseries for important fish stocks.
This reduces ecosystem resilience to climate stress and weakens the carbon sequestration potential of Pakistan’s blue carbon sinks. Climate experts in Pakistan call for integrating marine heatwave monitoring into national marine and fisheries management plans, promoting sustainable practices and climate adaptation for vulnerable coastal populations. Expanding ocean observation aligned with global networks will help Pakistan prepare for ecological and socioeconomic challenges posed by marine heatwaves.
