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| Marine heatwaves are disrupting the ocean’s ability to store carbon Image Credit: Scientific Frontline / AI generated |
Heatwaves not only occur on land – they also occur in the oceans, causing ocean temperatures to stay warmer than normal for longer periods. Marine heatwaves can cover huge areas of the sea and have major effects on marine life, from plankton to reefs and whales.
Now, a new study shows that marine heatwaves may also affect how carbon is stored in the ocean.
The ocean is one of Earths biggest carbon sinks. It soaks up vast amounts of CO2 from the atmosphere, and in the surface water, algae and other photosynthetic microorganisms capture it and convert it to organic carbon. When these organisms die and sink to the bottom, the carbon sinks with them. In the deep ocean, the removed carbon can be locked away for hundreds, even thousands of years.
Back to the atmosphere
In a new study, published in Nature Communications, an international team of researchers finds that marine heatwaves may disrupt this conveyor belt. In stead of sinking, much of the carbon stays near the surface where it is much more likely to be respired back into CO2 and released to the atmosphere.
The study was led by Mariana B. Bif from Monterey Bay Aquarium Research Institute. From SDU, marine microbiologist Sachia Traving, contributed.
“Marine heatwaves are disrupting the ocean’s ability to store carbon”, she concludes.
Harmful effects of marine heat waves:
- Coral bleaching
- Toxic algae blooms
- Mass death of sea birds
- Fish species being forced to leave their habitats
“As marine heatwaves become more frequent and intense due to climate changes, these disruptions could weaken the oceans’ role as a long-term carbon sink. One of the big questions now is if the impact on the carbon pump is something we consistently see in response to marine heatwaves in other parts of the world”, Traving says.
According to the study, the change is caused by shifts in the oceans’ microscopic communities. The team saw this in their studies of two marine heatwaves in Gulf of Alaska. One observed change was an accumulation of particles so small they remained in the upper ocean instead of sinking down, giving the microbes in the water column more time to degrade the organic matter and respire it back as CO2.
In their work, the researchers used data from autonomous floats from the Global Ocean Biogeochemistry Array project and long-term plankton records in the Gulf of Alaska, which has experienced two notable marine heatwaves in recent years: the infamous “Blob” from 2013–2015, and another from 2019–2020.
More marine heatwaves in the future
“We see marine heatwaves around the globe and with these studies we can now show that not only larger marine animals are affected - even the microbes and biogeochemical cycles are being disrupted by these events”, says Traving.
The Intergovernmental Panel on Climate Change assesses that marine heatwaves will occur 20-50 times more often in the future than in pre-industrial times.
The report ”Marine heatwaves in Northern Sea Areas” from Roskilde University (2022) concludes that marine heatwaves pose a greater threat to marine environments than gradual global warming.
Title: Heatwaves at Sea May Force the Ocean to Release More CO2
Authors: Mariana B. Bif, Colleen T. E. Kellogg, Yibin Huang, Julia Anstett, Sachia Traving, M. Angelica Peña, Steven J. Hallam, and Kenneth S. Johnson
Research Material: Marine heatwaves in Northern Sea Areas (PDF)
Source/Credit: University of Southern Denmark | Birgitte Svennevig
Reference Number: env100825_01