Marine cold waves, similar to their terrestrial counterparts, refer to sudden drops in sea temperatures that can have significant impacts on marine ecosystems, weather patterns, and local economies dependent on marine conditions. Read here to learn more.
The effects and causes of ocean warming are well documented. Still, events of marine cold waves are less frequently discussed than marine heatwaves but are equally important due to their potential ecological impacts.
When surface temperatures plummet rapidly by 10 degrees Celsius or more over a day or two and persist for several days to weeks- the area is said to be experiencing a cold wave, opposite to the more familiar marine heatwaves.
Marine cold waves
A marine cold wave occurs when sea temperatures drop sharply and remain significantly below the average for a prolonged period.
Various factors can trigger these events:
- Upwelling: Cold, deep ocean waters rise to the surface, usually driven by wind patterns that push surface waters away from the coast, allowing colder water from below to replace it. This is common along the western coasts of continents, such as the western coasts of North and South America.
- Changes in Ocean Currents: Shifts in ocean currents can bring colder water from higher latitudes or deeper ocean layers to typically warmer areas.
- Atmospheric Conditions: Prolonged periods of cloud cover, especially in tropical regions, can reduce solar heating of the surface water. Additionally, cold air outbreaks associated with polar or Arctic air masses moving over warmer ocean regions can also cool surface waters rapidly.
Impacts of Marine Cold Waves
- Ecological Effects: Sudden temperature drops can stress marine wildlife. Tropical species, which are typically less tolerant of temperature fluctuations, can experience high mortality rates during cold snaps. Coral bleaching events, often associated with high temperatures, can also occur due to cold stress.
- Fisheries: Cold waves can lead to shifts in fish distributions and behaviours, impacting commercial fisheries and local fishing communities. Some species may move to deeper waters or different regions seeking optimal temperatures, affecting catch rates and economic returns.
- Marine Vegetation: Seagrass beds and kelp forests might be adversely affected by cold temperatures. These ecosystems are crucial as they provide habitat, nursery grounds, and food for various marine species.
Research and Monitoring
In March 2021, the beaches of South Africa saw several large marine organisms washed up on the sands. Giant bat-winged manta rays, Hulking bull sharks, Pufferfish, and about 260 animals from 81 species died.
- To investigate the ramifications for marine fauna, the researchers tagged and studied bull sharks.
- Bull sharks are a highly migratory, tropical species that only tend to travel to upwelling regions during the warmer months. With the onset of winter, they migrate back to warm, tropical waters.
- Being mobile, they should have been able to avoid the local, cold temperatures, yet they perished.
- The study showed that bull sharks actively avoid areas of upwelling during their seasonal migrations up and down the coast, even when upwelling isn’t too intense.
- But if marine cold waves continue to become more sudden and intense, fleeing or hiding may no longer be enough even for these megafaunas.
- For example, in the event in South Africa that caused the death of manta rays and bull sharks water temperatures dropped from 21 degrees Celsius to 11.8 degrees Celsius in under 24 hours while the overall event lasted seven days.
Researchers now say that in some parts of the world, incidents like the 2021 cold spell appear to be getting more common as currents change, with potentially lethal consequences for marine life.
Why in the news?
A new study published in the journal, Nature Climate Change, has attempted to examine the effects of extreme marine cold waves in the oceans, which have not been very well researched before.
- Researchers from Australia, France, the UK and South Africa analysed the deaths of 260 marine organisms belonging to over 80 species affected in a single event off the South African coast in 2021, which, they discovered, was an extremely intense cold wave in the waters.
- The researchers further discovered that these extreme cold waves increased in intensity between 1981 and 2022.
- This is particularly dangerous for migratory marine megafauna species like bull sharks, which are operating dangerously close to their long-term thermal limits, the study explains, increasing their vulnerability to sudden and extreme temperature changes in the ocean.
How climate change will impact marine ecosystems?
As global temperatures rise, marine species migrate towards the poles, seeking water temperatures that match their historical living conditions.
However, these migrations make them vulnerable to atypical cold events caused by sudden shifts in ocean currents or atmospheric conditions.
- These cold snaps can be deadly for species not adapted to such fluctuations.
- Tropical and subtropical species are particularly at risk because they are physiologically less capable of coping with rapid decreases in temperature.
- For example, the bull sharks and whale sharks mentioned may face increased mortality or disruption in their migratory patterns when encountering these cold events.
- While the overarching trend is global warming, localized or short-term deviations such as marine cold waves highlight the nonlinear and unpredictable nature of climate change.
- These anomalies can lead to unexpected ecological consequences, making it difficult for species to adapt quickly.
The complexity of climate change impacts, as evidenced by the dual threats of warming and cold snaps, underscores the need for robust, adaptive environmental policies.
These policies should aim to reduce greenhouse gas emissions and also enhance the resilience of marine ecosystems to withstand both predictable and unexpected changes.
Way forward
The study of marine cold waves is crucial for understanding the full spectrum of climate variability and its impact on the marine environment.
- Improved monitoring through satellite technology, buoy networks, and oceanographic research helps predict and mitigate the effects of these temperature anomalies.
- This research is essential for developing strategies to manage fisheries and conserve marine ecosystems in the face of sudden climatic changes.
Conclusion
Marine cold waves are an important aspect of oceanic climatic phenomena that deserve more attention, especially in the context of global climate change.
While much focus has been on warming trends and heatwaves, understanding the occurrence and effects of cold spells is equally important for comprehensive climate models and effective marine resource management.
The research suggests that if cold upwellings become more frequent and intense, sub-tropical and tropical marine megafauna will be pushed to the edge of their thermal limits.
The authors surmise that such cold upwellings can lead to contracts in megafauna habitat among mobile marine animals resulting in large-scale ecosystem changes in the oceans.
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-Article by Swathi Satish
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