Climate scientists raise alarm to step up fisheries governance amid ocean warming and changing climates

20 Jul 2023 --- New climate model projections identifying the drivers for non-uniform Indian and Arabian ocean warming could facilitate better marine resource management. However, researchers warn that nutrient deficits could sweep across regions highly dependent on fish for daily survival.

Korean and Japanese researchers and scientists from Pusan National University used a large ensemble of simulations of the Community Earth System Model 2 (CESM2) and found distinct underlying mechanisms controlling the warming patterns. The model predicted non-uniform warming of the Indian Ocean with warming hotspots in the Arabian Sea and the southeastern Indian Ocean.

While changes in the ocean circulation patterns would amplify the warming in the Arabian Sea, reduced low cloud cover-induced heat fluctuations would lead to warming of the southeastern Indian Ocean.

Nutrition Insight speaks with Daniel Viana, a marine conservation scientist at the World Wildlife Fund and co-author of a recent study published in Scientific Reports titled “Nutrient Supply from Marine Small-Scale Fisheries,” who takes a stance on the consequences ocean warming pattern changes have on habitats and fishing practices.

“Ocean warming can lead to habitat degradation (for example, in coral reefs) and disrupt the natural reproductive and feeding patterns of fish species affecting their local abundance and distribution.”

“Geographical shifts of fish stocks can lead to a decline in catch and loss of livelihoods for fishing communities that depend on small-scale fisheries. Better governance over ocean resources decreases local stressors, thus allowing fish stocks a better chance to cope with the effects of ocean warming,” notes Viana.

Better governance involves adopting strategies that enable fish stocks and ecosystems to resist and recover from disturbances caused by warming oceans. Implementing sustainable Marine Protected Areas, Territorial Use Rights for Fisheries and Locally Managed Marine Areas help local fishing communities protect and manage critical habitats.

Unpredictable weather patterns circulating
The researchers caution there needs to be more understanding of the mechanisms that can lead to warming patterns found in their model and how they affect the weather in adjacent land areas. Hotspots have been identified in the Arabian Sea and southeastern Indian Ocean.

The authors investigated the Indian Ocean warming patterns using large ensemble simulations to bridge this knowledge gap. “Instead of running the climate model simulation only once, we performed one hundred simulations on CESM2, which represented the different realizations of the variability in the Indian Ocean’s climate system,” says Dr. Sahil Sharma, a Ph.D. student from Pusan National University.Map showing the locations of the deepest points in each of the world’s five oceans (Atlantic, Southern, Indian, Pacific and Arctic).

“This new modeling resource has been instrumental in identifying the complex ocean-atmosphere interactions responsible for modulating the IO circulation and warming patterns,” explains Sharma.

Atmospheric changes brewing
In the current study, authored by Sharma and published in Nature Communications, researchers performed an ocean-atmosphere-based analysis using the CESM2, identifying the physical mechanisms underlying the future non-uniform Indian Ocean warming.

Based on the results, the researchers conclude that these regional air-sea interactions can trigger large-scale variations in atmospheric circulations with widespread impacts even in regions outside the Indian Ocean.

“Unless carbon dioxide emissions are drastically reduced, global warming will continue to enhance the warming in the Arabian Sea with dire consequences for regional climate, marine biogeochemistry, and the African and Indian monsoon systems,” says Professor Kyung-Ja Ha from Pusan National University.

“This research could facilitate better marine resource management and information dissemination to fisheries and also guide future research on the effect of the projected non-uniform IO warming on regional rainfall patterns,” Ha adds.

This is corroborated by Viana’s study: “Our study highlighted the vulnerability coastal communities have to shocks in production because of their high nutritional dependence on fisheries.”

Declines in catch due to climate change, overfishing, pollution and habitat loss can have significant health consequences for communities due to increased nutrient deficiency.

“This highlights the need for policies that ensure the sustainability of fisheries. Coastal communities play a key role in this process. When local people actively manage coastal resources, this management is significantly more effective,” Viana explains.

Governments and civil society can support local fisheries management initiatives while improving livelihoods and access to sustainable alternative sources of nutrition, such as community-led aquaculture or sustainable farming.

Far-reaching consequences
Essentially, the projected warming in the southeastern Indian Ocean will be amplified by a reduction in the total low cloud cover over the region, resulting in more shortwave radiation hitting the ocean surface and causing it to warm.Habitat loss such as coral reef destruction occur as side effects of ocean warming. Changes in sea surface temperatures over IO could influence climate and rainfall trends across Asia, Africa and Australia.

Temperature variability, especially over oceans, has far-reaching consequences for the wind and weather systems, affecting societies and ecosystems across continents. The Arctic amplification patterns, for example, and the east-west temperature difference in the equatorial Pacific impacts regions far beyond the tropics.

Similarly, changes in sea surface temperatures over the Indian Ocean could influence climate and rainfall trends across Asia, Africa and Australia. The ocean’s warming variations can also impact North Atlantic temperature patterns and the Atlantic meridional overturning circulation, an essential component of the global climate system.

The researchers identified the air-sea interactions in the Eastern Indian Ocean – somewhere near western Indonesia – as a critical driver for the warming in the Arabian Sea. Colder deep water upwells to the surface, causing the Eastern Indian Ocean to be relatively cooler than other waters in the Indian Ocean with weak regional warming predicted.

This reduced regional warming is accompanied by enhanced sea-level pressure and strong winds blowing toward the Arabian Sea. Circulation is significantly altered which will cause the warmer tropical waters to move toward the Arabian Sea, resulting in its warming.

The process can induce wetter conditions in the region from increased rainfall and less evaporation, resulting in more stable near-surface-water stratification. In addition, it prevents the upwelling of more profound, cooler waters, further enhancing warming of the Arabian Sea.

By Inga de Jong

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