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Toxic algae and melting ice

High in the mountains of India and Pakistan summer heat melts glacial ice in the Karakoram, Hindu Kush and Himalayan ranges. These meltwaters then feed the Indus River at the start of its long journey to the ocean. On its journey, the water passes over the dry Indus plains where it provides life to 120 million people. Warmer global temperatures are shrinking this critical water supply. As the glacial ice disappears, it also alters marine ecosystems in the Arabian sea by creating blooms of toxic algae.

The connection between mountain glaciers and the Arabian sea is the winter monsoons that affect this region. Winter winds, chilled by the mountain ice, blow southward and pass over the Arabian sea, thus chilling the surface waters. The colder surface water becomes denser than the deeper waters and then sinks to the ocean bottom. This process allows for the upwelling of deep nutrient-rich waters, bringing nourishment to the surface plankton. The plankton then flourish and create the bottom level of the marine food chain.

The whole process depends on winter winds chilled by the mountain ice. However, higher average annual temperatures and disappearing mountain ice leave the winter monsoons warmer and moister than in the past. This change makes way for toxic algae blooms and spells trouble for the Arabian sea ecosystem. 

Noctiluca scintillans

Noctiluca scintillans is a millimeter-long marine dinoflagellate. This single-celled planktonic organism is also known as sea sparkle because of its bioluminescence. In the past, this particular planktonic organism was uncommon in the Arabian Sea. But changing ocean upwelling patterns now create conditions where it thrives. Where no Noctuluca existed before, now its massive blooms are visible from space.

These dinoflagellates possess characteristics that prove destructive for the existing marine food web. To start with, they feed on plankton, diatoms, and other dinoflagellates, thus eating the very food that supports the traditional ecosystem. Secondly, they thrive in hypoxic (oxygen-depleted) waters and low sunlight conditions. 

So warmer winter surface waters translate into no upwelling, nutrient depletion, and lower oxygen supply. These conditions stress other planktonic species, but the Noctilucase scintillans loves it.

Let them eat cake

If the creatures higher up the food chain don’t have their normal diet, then let them eat sea sparkle. Unfortunately, the Noctiluca possesses yet another undesirable trait. When they eat and grow, they then secrete ammonia. The progressive buildup of ammonia in the water is toxic to fish and other marine creatures. So, a Noctiluca scintillans algal bloom deprives the food chain of its usual base trophic level and leaves it with an uneatable substitute. 

Climate change demonstrates how the loss of ice in the Himalayan mountains and the demise of marine ecosystems in the Arabian sea are connected. The wintertime blooms of toxic algae will cause political headaches for countries bordering the Arabian sea if they damage fisheries that provide sustenance for local communities.


The world’s water towers (Source: ArcheanWeb) –  Also:

Heat, oxygen deprivation, and extinction (Source: ArcheanWeb) –  Also:

Heat affects the ocean’s food chain (Source: ArcheanWeb) – Also:


There’s a Surprising Connection Between Dangerous Algal Blooms And The Himalayas (By Carly Cassella; Science Alert) –

Feature Image: Arabian Sea Algal Bloom (Modified) – By NASA – , Public Domain,

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.